Long-acting exenatide does not prevent cognitive decline in mild cognitive impairment: a proof-of-concept clinical trial

PURPOSE

According to preclinical evidence, GLP-1 receptor may be an actionable target in neurodegenerative disorders, including Alzheimer's disease (AD). Previous clinical trials of GLP-1 receptor agonists were conducted in patients with early AD, yielding mixed results. The aim was to assess in a proof-of-concept study whether slow-release exenatide, a long-acting GLP-1 agonist, can benefit the cognitive performance of people with mild cognitive impairment (MCI).

METHODS

Thirty-two (16 females) patients were randomized to either slow-release exenatide (n = 17; 2 mg s.c. once a week) or no treatment (n = 15) for 32 weeks. The primary endpoint was the change in ADAS-Cog11 cognitive test score at 32 weeks vs baseline. Secondary endpoints herein reported included additional cognitive tests and plasma readouts of GLP-1 receptor engagement. Statistical analysis was conducted by intention to treat.

RESULTS

No significant between-group effects of exenatide on ADAS-Cog11 score (p = 0.17) were detected. A gender interaction with treatment was observed (p = 0.04), due to worsening of the ADAS-Cog11 score in women randomized to exenatide (p = 0.018), after correction for age, scholar level, dysglycemia, and ADAS-Cog score baseline value. Fasting plasma glucose (p = 0.02) and body weight (p = 0.03) decreased in patients randomized to exenatide.

CONCLUSION

In patients with MCI, a 32-week trial with slow-release exenatide had no beneficial effect on cognitive performance.

TRIAL REGISTRATION NUMBER

NCT03881371, registered on 21 July, 2016.

Haplotypes of the genes (GCK and G6PC2) underlying the glucose/glucose-6-phosphate cycle are associated with pancreatic beta cell glucose sensitivity in patients with newly diagnosed type 2 diabetes from the VNDS study (VNDS 11)

BACKGROUND

Elevated fasting plasma glucose has been associated with increased risk for development of type 2 diabetes (T2D). The balance between glucokinase (GCK) and glucose-6-phosphate catalytic subunit 2 (G6PC2) activity are involved in glucose homeostasis through glycolytic flux, and subsequent insulin secretion.

AIM

In this study, we evaluated the association between the genetic variability of G6PC2 and GCK genes and T2D-related quantitative traits.

METHODS

In 794 drug-naïve, GADA-negative, newly diagnosed T2D patients (VNDS; NTC01526720) we performed: genotyping of 6 independent tag-SNPs within GCK gene and 5 tag-SNPs within G6PC2 gene; euglycaemic insulin clamp to assess insulin sensitivity; OGTT to estimate beta-cell function (derivative and proportional control; DC, PC) by mathematical modeling. Genetic association analysis has been conducted using Plink software.

RESULTS

Two SNPs within GCK gene (rs882019 and rs1303722) were associated to DC in opposite way (both p < 0.004). Two G6PC2 variants (rs13387347 and rs560887) were associated to both parameters of insulin secretion (DC and PC) and to fasting C-peptide levels (all p < 0.038). Moreover, subjects carrying the A allele of rs560887 showed higher values of 2h-plasma glucose (2hPG) (p = 0.033). Haplotype analysis revealed that GCK (AACAAA) haplotype was associated to decreased fasting C-peptide levels, whereas, the most frequent haplotype of G6PC2 (GGAAG) was associated with higher fasting C-peptide levels (p = 0.001), higher PC (β = 6.87, p = 0.022) and the lower 2hPG (p = 0.012).

CONCLUSION

Our findings confirmed the role of GCK and G6PC2 in regulating the pulsatility in insulin secretion thereby influencing insulin-signaling and leading to a gradual modulation in glucose levels in Italian patients with newly diagnosed T2D.

Similar glycaemic control and risk of hypoglycaemia with patient- versus physician-managed titration of insulin glargine 300 U/mL across subgroups of patients with T2DM: a post hoc analysis of ITAS

AIMS

The Italian Titration Approach Study (ITAS) demonstrated comparable HbA_1c reductions and similarly low hypoglycaemia risk at 6 months in poorly controlled, insulin-naïve adults with T2DM who initiated self- or physician-titrated insulin glargine 300 U/mL (Gla-300) in the absence of sulphonylurea/glinide. The association of patient characteristics with glycaemic and hypoglycaemic outcomes was assessed.

METHODS

This post hoc analysis investigated whether baseline patient characteristics and previous antihyperglycaemic drugs were associated with HbA_1c change and hypoglycaemia risk in patient- versus physician-managed Gla-300 titration.

RESULTS

HbA_1c change, incidence of hypoglycaemia (any type) and nocturnal rates were comparable between patient- and physician-managed arms in all subgroups. Hypoglycaemia rates across subgroups (0.03 to 3.52 events per patient-year) were generally as low as observed in the full ITAS population. Small increases in rates of 00:00-pre-breakfast and anytime hypoglycaemia were observed in the ≤ 10-year diabetes duration subgroup in the patient- versus physician-managed arm (heterogeneity of effect; p < 0.05).

CONCLUSIONS

Comparably fair glycaemic control and similarly low hypoglycaemia risk were achieved in almost all patient subgroups with patient- versus physician-led Gla-300 titration. These results reinforce efficacy and safety of Gla-300 self-titration across a range of phenotypes of insulin-naïve people with T2DM.

CLINICAL TRIAL REGISTRATION

EudraCT 2015-001167-39.

Italian Titration Approach Study (ITAS) with insulin glargine 300 U/mL in insulin-naïve type 2 diabetes: Design and population

BACKGROUND AND AIMS

Fostering patient's self-managing of basal insulin therapy could improve glucose control, by removing patient's and physician's barriers to basal insulin initiation, titration and glucose monitoring. The Italian Titration Approaches Study (ITAS) aims at demonstrating non-inferiority (<0.3% margin) in efficacy of glucose control (change in glycated hemoglobin [HbA1c] after 24 weeks) by the same titration algorithm of insulin glargine 300 U/mL (Gla-300), managed by the (nurse assisted) patient versus the physician, in insulin naïve patients with Type 2 Diabetes Mellitus (T2DM), uncontrolled with previous treatments.

METHODS AND RESULTS

ITAS is a phase IV, 24-week, national, multicenter, open label, randomized (1:1) parallel group study. 458 patients were enrolled, 359 randomized, and 339 completed the study, in 46 Italian centers. Baseline characteristics and previous medications of the ITT population (N = 355) are reported. Mean ± SD age, T2DM duration, HbA1c, FPG and BMI were 64.0 ± 9.8 years, 11.6 ± 7.6 years, 8.79 ± 0.65%, 170.9 ± 42.3 mg/dL, and 30.3 ± 5.6 kg/m², respectively. Vascular and metabolic disorders were most frequent (73.8% and 58.3%, respectively). More than 90% of patients were on metformin.

CONCLUSION

ITAS is the first study to compare two different managers (nurse-assisted patient vs physician) of the same titration algorithm of Gla-300 in insulin naïve patients with T2DM in unsatisfactory glucose control. This study might provide novel evidence on the efficacy/effectiveness of patient-managed titration algorithm of Gla-300 in a pragmatic setting and may reduce barriers to basal insulin initiation and its titration.

Claimed effects, outcome variables and methods of measurement for health claims proposed under regulation (EC) 1924/2006 and related to cognitive function in adults

Some food/food components have been the object of request of authorization to the use of health claims related to cognitive function in adults and compliant with the Regulation (EC) 1924/2006. Most of the requests have received a negative opinion by the European Food Safety Authority (EFSA) also because of the choice of not appropriate outcome variables (OVs) and methods of measurement (MMs) selected in the trials used to substantiate the claim. This manuscript referes to the collection, collation and critical analysis of OVs and MMs related to cognitive function in adults. OVs and MMs were collected from the EFSA Guidance document and the applications for authorization of health claims pursuant to the Articles 13(5). The critical analysis of OVs and MMs, performed by a literature review, was aimed at defining their appropriateness in the context of a specific claimed effect. The results highlight the importance of an adequate choice of OVs and MMs for an effective substantiation of the claims related to cognitive functioning. The information provided in this document may serve to EFSA for updating the guidance on the scientific requirements for health claims related to cognitive functions, but also for a better design of randomized controlled trials aimed at substantiating such health claims.

Association of free-living physical activity measures with metabolic phenotypes in type 2 diabetes at the time of diagnosis. The Verona Newly Diagnosed Type 2 Diabetes Study (VNDS)

BACKGROUND AND AIM

Lifestyle is considered a major determinant of risk of type 2 diabetes (T2D). We investigated whether daily physical activity (DPA) is associated with beta-cell function (BF) and/or insulin sensitivity (IS) in patients with T2D at the time of diagnosis.

METHODS AND RESULTS

In 41 subjects enrolled in the Verona Newly-Diagnosed Type 2 Diabetes Study we assessed: (1) IS, by euglycaemic insulin clamp; (2) BF, estimated by prolonged-OGTT minimal modeling and expressed as derivative and proportional control; (3) DPA and energy expenditure (EE), assessed over 48-h monitoring by a validated wearable armband system. Study participants (median [IQR]; age: 62 [53-67] years, BMI: 30.8 [26.5-34.3] Kg m^-2, HbA1c: 6.7 [6.3-7.3]%; 49.7 [45.4-56.3] mmol/mol) were moderately active (footsteps/day: 7773 [5748-10,927]; DPA_≥3MET: 70 [38-125] min/day), but none of them exercised above 6 metabolic equivalents (MET). EE, expressed as EE_TOT (total daily-EE) and EE_≥3MET (EE due to DPA_≥3MET) were 2398 [2226-2801] and 364 [238-617] Kcal/day, respectively. IS (M-clamp 630 [371-878] μmol/min/m²) was positively associated with DPA and EE, independent of age, sex and BMI (p < 0.05). Among the DPA and EE parameters assessed, DPA_≥3MET and EE_TOT were independent predictors of IS in multivariable regression analyses, adjusted for age, sex, BMI (R² = 16%, R² = 19%, respectively; p < 0.01). None of model-derived components of BF was significantly associated with DPA or accompanying EE.

CONCLUSIONS

Our study highlighted moderate levels of DPA and total EE as potential determinants of IS, but not BF, in T2D at the time of diagnosis. Intervention studies are needed to conclusively elucidate the effect of DPA on these features.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov.

UNIQUE IDENTIFIER

NCT01526720.

Claimed effects, outcome variables and methods of measurement for health claims proposed under European Community Regulation 1924/2006 in the framework of protection against oxidative damage and cardiovascular health

BACKGROUND AND AIMS

The high number of negative opinions from the European Food Safety Authority (EFSA) to the requests for authorization of health claims is largely due to the design of human intervention studies, including the inappropriate choice of outcome variables (OVs) and of their methods of measurement (MMs). The present manuscript reports the results of an investigation aimed to collect, collate and critically analyse the information in relation to claimed effects, OVs and MMs, in the context of protection against oxidative damage and cardiovascular health compliant with Regulation 1924/2006.

METHODS AND RESULTS

Claimed effects, OVs and the related MMs were collected from EFSA Guidance documents and applications for authorization of health claims under Articles 13.5 and 14. The OVs and their MMs were evaluated only if the claimed effect was sufficiently defined and was considered beneficial by EFSA. The collection, collation and critical analysis of the relevant scientific literature consisted in the definition of the keywords, the PubMed search strategies and the creation of databases of references. The critical analysis of the OVs and their MMs was performed on the basis of the literature review and was aimed at defining the appropriateness of OVs and MMs in the context of the specific claimed effects.

CONCLUSIONS

The information provided in this document could serve to EFSA for the development of further guidance on the scientific requirements for health claims, as well as to the stakeholders for the proper design of human intervention studies aimed to substantiate such health claims.

The β-cell burden index of food: A proposal

The quantity and quality of dietary fat and/or carbohydrate may alter one or more of the basic components of the insulin-glucose system, which in turn affect the pathways leading to alterations in glucose homeostasis and, possibly, to cardiovascular disease. This viewpoint article, reviewing some of the currently available tools aiming at quantifying the impact of dietary carbohydrates on the glucose-insulin homeostatic loop, highlights the unmet need of a more thorough assessment of the complex interaction between dietary factors and the glucose-insulin system. A novel index, the "β-cell burden index", may turn out to be a valuable tool to quantify the role played by the diet in shaping the risk of type 2 diabetes, cardiovascular disease and other metabolic and degenerative disorders, ideally orienting their prevention with strategies based on dietary modifications.

Novel antidiabetic drugs and cardiovascular risk: Primum non nocere

AIMS

Diabetes treatments aim at preventing undesirable metabolic effects of hyperglycemia and at preventing/reducing tissue damage, including cardiovascular (CV) events. For approval, novel diabetes drugs undergo early systematic investigation to assess CV safety. This review provides an updated analysis of the results of recent studies examining novel diabetes medications and CV outcomes.

DATA SYNTHESIS

The new regulatory guidelines enforce adjudication of all CV events when testing novel diabetes drugs. Endpoints of CV mortality, myocardial infarction (MI), stroke and hospitalization for heart failure (HF) were included in the most recent clinical studies on novel antihyperglycemics. These are: the incretin mimetics glucagon-like peptide 1 (GLP-1) receptor agonists (GLP1-RA), the incretin enhancers dipeptidylpeptidase-4 (DPP-4) inhibitors (DPP4-I or gliptins), and the sodium-glucose cotransporter (SGLT2) inhibitors (SGLT2-I or gliflozins). The studies ELIXA and EXAMINE, testing lixisenatide and alogliptin, respectively, revealed non-inferiority versus placebo in terms of CV safety. The SAVOR-TIMI 53 results confirmed overall CV safety of saxagliptin, but raised a warning related to the increase in the risk of hospitalization for HF in the saxagliptin group. Recently, TECOS revealed a particularly favorable CV profile for sitagliptin while EMPA-REG showed a significant CV risk reduction in empagliflozin treated subjects. Ongoing studies will provide additional data on CV safety for other GLP1-RAs, DPP4-I and SGLT2-I.

CONCLUSIONS

Results of safety outcome studies focused on CV events, including HF and mortality for CV causes, are not homogeneous. A critical analysis of these studies may help cardiologists and diabetes specialists to adapt their therapeutic choices to individual patients.

Is common genetic variation at IRS1, ENPP1 and TRIB3 loci associated with cardiometabolic phenotypes in type 2 diabetes? An exploratory analysis of the Verona Newly Diagnosed Type 2 Diabetes Study (VNDS) 5

BACKGROUND AND AIMS

Insulin resistance is a hallmark of type 2 diabetes (T2DM), it is often accompanied by defective beta-cell function (BF) and is involved in the pathophysiology of cardiovascular disease (CVD). Commonalities among these traits may recognize a genetic background, possibly involving the genetic variation of insulin signaling pathway genes. We conducted an exploratory analysis by testing whether common genetic variability at IRS1, ENPP1 and TRIB3 loci is associated with cardiovascular risk traits and metabolic phenotypes in T2DM.

METHODS AND RESULTS

In 597 drug-naïve, GADA-negative, newly-diagnosed T2DM patients we performed: 1) genotyping of 10 independent single-nucleotide polymorphisms covering ∼ 90% of common variability at IRS1, ENPP1 and TRIB3 loci; 2) carotid artery ultrasound; 3) standard ECG (n = 450); 4) euglycaemic insulin clamp to assess insulin sensitivity; 5) 75 g-OGTT to estimate BF (derivative and proportional control) by mathematical modeling. False discovery rate of multiple comparisons was set at 0.20. After adjustment for age, sex and smoking status, rs4675095-T (IRS1) and rs4897549-A (ENPP1) were significantly associated with carotid atherosclerosis severity, whilst rs7265169-A (TRIB3) was associated with ECG abnormalities. Rs858340-G (ENPP1) was significantly associated with decreased insulin sensitivity, independently of age, sex and body-mass-index. No consistent relationships were found with BF.

CONCLUSION

Some associations were found between intermediate phenotypes of CVD and common genetic variation of gatekeepers along the insulin signaling pathway. These results need be replicated to support the concept that in T2DM the CVD genetic risk clock may start ticking long before hyperglycemia appears. ClinicalTrials.gov Identifier: NCT01526720.

PPARG2 Pro12Ala and ADAMTS9 rs4607103 as "insulin resistance loci" and "insulin secretion loci" in Italian individuals. The GENFIEV study and the Verona Newly Diagnosed Type 2 Diabetes Study (VNDS) 4

We investigated cross-sectionally whether the type 2 diabetes (T2DM) risk alleles of rs1801282 (PPARG2) and rs4607103 (ADAMTS9) were associated with T2DM and/or insulin sensitivity (IS) and beta cell function (βF) in Italians without and with newly diagnosed T2DM. In 676 nondiabetic subjects (336 NGR and 340 IGR) from the GENFIEV study and in 597 patients from the Verona Newly Diagnosed Type 2 Diabetes Study (VNDS), we (1) genotyped rs1801282 and rs4607103, (2) assessed βF by C-peptide/glucose modeling after OGTT, and (3) assessed IS by HOMA-IR in both studies and by euglycemic insulin clamp in VNDS only. Logistic, linear, and two-stage least squares regression analyses were used to test (a) genetic associations with T2DM and with pathophysiological phenotypes, (b) causal relationships of the latter ones with T2DM by a Mendelian randomization design. Both SNPs were associated with T2DM. The rs4607103 risk allele was associated to impaired βF (p < 0.01) in the GENFIEV study and in both cohorts combined. The rs1801282 genotype was associated with IS both in the GENFIEV study (p < 0.03) and in the VNDS (p < 0.03), whereas rs4607103 did so in the VNDS only (p = 0.01). In a Mendelian randomization design, both HOMA-IR (instrumental variables: rs1801282, rs4607103) and βF (instrumental variable: rs4607103) were related to T2DM (p < 0.03-0.01 and p < 0.03, respectively). PPARG2 and ADAMTS9 variants are both associated with T2DM and with insulin resistance, whereas only ADAMTS9 may be related to βF. Thus, at least in Italians, they may be considered bona fide "insulin resistance genes".

Type 2 diabetes mellitus: a disease of the governance of the glucose-insulin system: an experimental metabolic control analysis study

BACKGROUND AND AIMS

The relatives role of each component of the glucose-insulin system in determining hyperglycemia in type 2 diabetes is still under debate. Metabolic Control Analysis (MCA) quantifies the control exerted by each component of a system on a variable of interest, by computing the relevant coefficients of control (CCs), which are systemic properties. We applied MCA to the intravenous glucose tolerance test (IVGTT) to quantify the CCs of the main components of the glucose-insulin system on intravenous glucose tolerance.

METHODS AND RESULTS

We combined in vivo phenotyping (IVGTT/euglycaemic insulin clamp) and in silico modeling (GLUKINSLOOP.1) to compute the CCs of intravenous glucose tolerance in healthy insulin-sensitive (n = 9, NGR-IS), healthy insulin-resistant (n = 7, NGR-IR) and subdiabetic hyperglycemic (n = 8, PreT2DM) individuals and in patients with newly diagnosed type 2 diabetes (n = 7, T2DM). Altered insulin secretion and action were documented in NGR-IR and PreT2DM groups, but only 1st phase insulin secretion was significantly lower in T2DM than in PreT2DM (p < 0.05). The CCs changed little in the nondiabetic groups. However, several CCs were significantly altered in the patients (e.g. CCs of beta cell: -0.75 ± 0.10, -0.64 ± 0.15, -0.56 ± 0.09 and -0.19 ± 0.04 in NGR-IS, NGR-IR, PreT2DM and T2DM, respectively; p < 0.01 by MANOVA), and they could not be corrected by matching in silico nondiabetic and T2DM groups for 1st phase secretion.

CONCLUSIONS

Type 2 diabetes is characterized not only by loss of function of the elements of the glucose-insulin system, but also by changes in systemic properties (CCs). As such, it could be considered a disease of the governance of the glucose-insulin system.

Pancreatic diabetes manifests when beta cell area declines by approximately 65% in humans

AIMS/HYPOTHESIS

Diabetes frequently develops in patients with pancreatic disorders. We aimed to determine the lower threshold of beta cell area for diabetes manifestation as well as the impact of insulin sensitivity on glucose homoeostasis in patients with pancreatic diabetes.

METHODS

Eighty-two patients undergoing pancreatic surgery underwent pre-operative oral glucose challenge. Fractional pancreatic beta cell area was determined, and indices of insulin sensitivity and beta cell function were calculated.

RESULTS

HbA1c and glucose levels were similar in patients with high and intermediate beta cell area, but were significantly higher in those with the lowest beta cell area (p < 0.0001). Insulin secretion was reduced only in patients with the lowest beta cell area (p < 0.001). The relative beta cell deficits at the onset of diabetes and impaired glucose tolerance were 64% and 21%, respectively, based on 2 h glucose levels. Deteriorating insulin sensitivity was associated with a small increase in the incidence of diabetes.

CONCLUSIONS/INTERPRETATION

In conclusion, pancreatic diabetes probably develops after a reduction in beta cell area of ~65%. Post-challenge glucose excursions are much more closely related to pancreatic beta cell area than to fasting glycaemia, thereby underlining the usefulness of the OGTT in patients with pancreatic disorders.

Metabolic syndrome in subjects at high risk for type 2 diabetes: the genetic, physiopathology and evolution of type 2 diabetes (GENFIEV) study

BACKGROUND AND AIM

We evaluated the relationship between insulin resistance (IR) and insulin secretion with the metabolic syndrome (MS) in 885 subjects (377 men/508 women, age 49±11 years, BMI 29±5.2kgm(-2)) at risk of diabetes enrolled in the genetics, pathophysiology and evolution of type 2 diabetes (GENFIEV) study.

METHODS AND RESULTS

All subjects underwent a 75-g oral glucose tolerance test (OGTT) for the estimation of plasma levels of glucose and C-peptide, as well as fasting insulin and lipid profile. IR was arbitrarily defined as HOMA-IR value above the 75th centile of normal glucose tolerance (NGT) subjects. Overall MS prevalence (National Cholesterol Treatment Panel-Adult Treatment Panel (NCEP-ATPIII) criteria) was 33%, 19% in subjects with NGT, 42% in impaired fasting glucose (IFG), 34% in impaired glucose tolerance (IGT), 74% in IFG+IGT subjects, and 56% in newly diagnosed diabetic patients. Prevalence was slightly higher with IDF criteria. MS prevalence was >50% in subjects with 2h glucose >7.8mmoll(-1), independently of fasting plasma glucose. IR prevalence was higher in subjects with MS than in those without (63% vs. 23%; p<0.0001) and increased from 54% to 73% and 88% in the presence of three, four or five traits, respectively. IR occurred in 42% of subjects with non-diabetic alterations of glucose homeostasis, being the highest in those with IFG+IGT (IFG+IGT 53%, IFG 45%, IGT 38%; p<0.0001). Individuals with MS were more IR irrespective of glucose tolerance (p<0.0001) with no difference in insulinogenic index. Hypertriglyceridaemia (OR: 3.38; Confidence Interval, CI: 2.294.99), abdominal obesity (3.26; CI: 2.18-4.89), hyperglycaemia (3.02; CI: 1.80-5.07) and hypertension (1.69; CI: 1.12-2.55) were all associated with IR.

CONCLUSIONS

These results show that in subjects with altered glucose tolerance (in particular IFG+IGT) MS prevalence is high and is generally associated to IR. Some combinations of traits of MS may significantly contribute to identify subjects with IR.

Variants and haplotypes of TCF7L2 are associated with β-cell function in patients with newly diagnosed type 2 diabetes: the Verona Newly Diagnosed Type 2 Diabetes Study (VNDS) 1

CONTEXT

Intronic variants of TCF7L2 are confirmed genetic risk factors for type 2 diabetes and are associated to alterations in beta cell function in nondiabetic individuals.

OBJECTIVE

The objective of the study was to test whether TCF7L2 variability may affect β-cell function also in patients with type 2 diabetes.

DESIGN

This was a cross-sectional association study.

SETTING

The study was conducted at a university hospital referral center for diabetes.

PATIENTS

Patients included 464 (315 males and 149 females) glutamic acid decarboxylase-negative patients [age: median 59 yr (interquartile range: 52-65); body mass index: 29.3 kg/m(2) (26.5-32.9); fasting plasma glucose: 7.0 mmol/liter (6.1-8.0)] with newly diagnosed type 2 diabetes.

INTERVENTION(S)

Interventions included frequently sampled oral glucose tolerance test and euglycemic insulin clamp.

MAIN OUTCOME MEASURE(S)

β-Cell function (derivative control and proportional control); insulin sensitivity; genotypes of the following TCF7L2 single-nucleotide polymorphisms: rs7901695, rs7903146, rs11196205, and rs12255372.

RESULTS

Both rs7901695 and rs7903146 diabetes risk alleles were associated with reduced proportional control of β-cell function (P = 0.019 and P = 0.022, respectively). Two low-frequency haplotypes were associated with extreme (best and worst) phenotypes of β-cell function (P < 0.01). No associations between TCF7L2 genotypes and insulin sensitivity were detected.

CONCLUSIONS

TCF7L2 diabetes risk variants, either as single-nucleotide polymorphisms or as haplotypes, detrimentally influence β-cell function and might play a role in determining the metabolic phenotype of patients with newly diagnosed type 2 diabetes.

First Italian Consensus Statement on Diagnosis, Prevention and Treatment of Cardiovascular Complications in HIV-infected Patients in the HAART Era (2006)

The present document contains recommendations for assessment, prevention and treatment of cardiovascular risk for HIV-infected patients. All recommendations were graded according to the strength and quality of the evidence and were voted on by 73 members of the Italian Cardiovascular Risk Guidelines Working Group which includes both experts in HIV/AIDS care and in cardiovascular and metabolic medicine. Since antiretroviral drug exposure represents only one risk factor, continued emphasis on an integrated management is given. This should include prevention and treatment of known cardiovascular risk factors (such as dyslipidaemia, diabetes, insulin resistance, healthy diet, physical activity, avoidance of smoking), but also rational switch of antiretroviral drugs. A rational switch strategy should consider both metabolic and anthropometric disturbances and effectiveness of antiretroviral regimens.

Heritability of model-derived parameters of beta cell secretion during intravenous and oral glucose tolerance tests: a study of twins

AIMS/HYPOTHESIS

The genetic architecture of model-derived parameters of beta cell function has never been assessed. Therefore, we estimated heritability (h(2)) for model-derived phenotypes of insulin secretion in twins.

METHODS

Thirty-three monozygotic (MZ) and 23 dizygotic (DZ) twin pairs from the Finnish Twin Cohort Study underwent an OGTT (plasma glucose/C-peptide at 0, 30, 60, 90 and 120 min). A subset of the twin pairs (21 MZ/20 DZ) also underwent an IVGTT (frequent sampling of plasma glucose/insulin from 0 to 60 min) followed by a 160-min euglycaemic-hyperinsulinaemic clamp (45 mU.min(-1).m(-2)). Mathematical modelling was applied to the IVGTT and the OGTT to assess first-phase (readily releasable insulin [RRI]) and second-phase (sigma) secretion (IVGTT), and a global index of beta cell performance (OGTT beta index). Intraclass correlation coefficients and genetic and non-genetic components for trait variances were computed to assess the h(2) of model-derived parameters.

RESULTS

The intraclass correlation coefficients in MZ twins were 0.78 for RRI, 0.67 for sigma and 0.57 for OGTT beta index. In DZ twins the correlation coefficients were 0.23, 0.32 and 0.42, respectively. Using the most parsimonious model for each trait, the h(2)--the proportion of variance accounted for by genetic factors--was 76% (95% CI: 53-88%) for RRI, 28% (34-80%) for sigma and 53% (26-72%) for OGTT beta index.

CONCLUSIONS/INTERPRETATION

Our findings demonstrate that model-derived parameters of insulin secretion have a substantial genetic component and may be used in the search for genetic determinants of beta cell function in humans.

The Metabolic Syndrome is an independent predictor of cardiovascular disease in Type 2 diabetic subjects. Prospective data from the Verona Diabetes Complications Study

AIMS

To evaluate the cardiovascular risk associated with the presence of the Metabolic Syndrome in Type 2 diabetic subjects.

METHODS

Subjects with the Metabolic Syndrome, defined by WHO criteria, were identified in a large sample of non-insulin-treated Type 2 diabetic patients examined within the Verona Diabetes Complications Study (n = 946). At baseline and after a mean of 4.5 years follow-up, cardiovascular disease (CVD) was assessed by medical history, physical examination, electrocardiogram (ECG) and echo-duplex of carotid and lower limb arteries. Death certificates and medical records of subjects who died during the follow-up were scrutinized in order to identify CVD deaths. In statistical analyses, CVD was considered as an aggregate end-point, including fatal and non-fatal coronary, cerebrovascular and peripheral vascular disease as well as ischaemic ECG abnormalities and vascular lesions at the echo-duplex.

RESULTS

The proportion of subjects with the Metabolic Syndrome was very high (92.3%). At the baseline, 31.7% of subjects were coded positive for CVD, which was more prevalent in subjects with the Metabolic Syndrome (32.9 vs. 17.8%, P = 0.005). Among subjects free of CVD at the baseline (n = 559), CVD events during the follow-up were significantly increased in patients with the Metabolic Syndrome as compared with those without it (19.9% vs. 3.9%, P < 0.001). Multiple logistic regression analysis showed that, along with sex, age, smoking and HbA1c, the presence of the Metabolic Syndrome independently predicted prevalent (OR 2.01, P = 0.045) and incident CVD (OR 4.89, P = 0.031).

CONCLUSIONS

In Type 2 diabetes, the presence of the Metabolic Syndrome is associated with an almost 5-fold increase in CVD risk.

Metabolic Syndrome: epidemiology and more extensive phenotypic description. Cross-sectional data from the Bruneck Study

OBJECTIVES

The present study aimed at evaluating the prevalence of the Metabolic Syndrome and at identifying its additional clinical features.

RESEARCH DESIGN AND METHODS

Within a prospective population-based survey examining 888 subjects aged 40-79 y, subjects were identified fulfilling the WHO and the National Cholesterol Education Program-Adult Treatment Panel III (NCEP-ATPIII) criteria for diagnosing the Metabolic Syndrome. In these subjects and in the rest of the sample (controls), several metabolic and nonmetabolic biochemical parameters were compared.

RESULTS

The prevalence of the Metabolic Syndrome by WHO criteria was 34.1% (95% CI 31.0-37.2) and by NCEP-ATPIII criteria 17.8% (15.5-20.3). The prevalence was significantly higher in older subjects and in those less physically active. Subjects with the Metabolic Syndrome either by WHO or by NCEP-ATPIII criteria showed higher levels of oxidized low-density lipoprotein, apolipoprotein B, urate, leptin, fibrinogen, leukocytes, erythrocyte sedimentation rate, GOT, gamma-GT and soluble endothelial adhesion molecules (E-selectin, vascular adhesion molecule-1 and intercellular adhesion molecule-1) and lower apolipoprotein A concentrations. Insulin resistance, as assessed by the Homeostasis Model Assessment, increased with the increase in the number of traits composing the syndrome found within the single individual. Subjects with insulin resistance had more pronounced abnormalities in several parameters, including the additional features of the syndrome (eg fibrinogen and soluble adhesion molecules).

CONCLUSIONS

The Metabolic Syndrome occurs very frequently in the general population aged 40-79 y, and is associated with several additional metabolic and nonmetabolic abnormalities that likely contribute to an increased cardiovascular risk. Insulin resistance seems to play a major role in classic and additional abnormalities featuring the Metabolic Syndrome.

Predictors of insulin sensitivity in Type 2 diabetes mellitus

AIMS

To identify the independent predictors of insulin sensitivity in Type 2 diabetes, and to establish whether isolated Type 2 diabetes (i.e. diabetes without overweight, dyslipidaemia and hypertension) is a condition of insulin resistance.

METHODS

We examined 45 patients with non-insulin-treated Type 2 diabetes undergoing a 4-h euglycaemic hyperinsulinaemic clamp (20 mU/m2 per min) combined with 3H-3-D-glucose and 14C-U-glucose infusions and indirect calorimetry. We also examined 1366 patients with non-insulin-treated Type 2 diabetes randomly selected among those attending the Diabetes Clinic and in whom insulin resistance was estimated by Homeostasis Model Assessment (HOMA-IR).

RESULTS

In the 45 patients undergoing glucose clamp studies, insulin-mediated total glucose disposal (TGD) was independently and negatively associated with systolic blood pressure (standardized beta coefficient = -0.407, P = 0.003), plasma triglycerides (beta= -0.355, P = 0.007), and HbA1c (beta= -0.350, P = 0.008). The overall variability of TGD explained by these variables was 53%. Overweight diabetic subjects with central fat distribution, hypertension, hypertriglyceridaemia and poor glycometabolic control had insulin-mediated TGD values markedly lower than their lean counterparts without hypertension, with normal triglycerides, and with good glycometabolic control (16 +/- 5 vs. 31 +/- 10 micromol/min per kg lean body mass, P < 0.01). Nevertheless, the latter still were markedly insulin-resistant when compared with sex- and age-matched non-diabetic control subjects (31 +/- 10 vs. 54 +/- 13 micromol/min per kg lean body mass, P < 0.01). In the 1366 Type 2 diabetic patients of the epidemiological study, HOMA-IR value was independently associated with HbA1c (beta = 0.283, P < 0.0001), plasma triglycerides (beta = 0.246, P < 0.0001), body mass index (beta = 0.139, P < 0.001), waist girth (beta = 0.124, P < 0.001) and hypertension (beta = 0.066, P = 0.006).

CONCLUSION

Overweight, central fat distribution, dyslipidaemia, hypertension and poor glycometabolic control are strong independent predictors of insulin resistance in Type 2 diabetes. However, reduced insulin sensitivity can be found even when Type 2 diabetes is isolated and well controlled.

Plasma glucose levels throughout the day and HbA(1c) interrelationships in type 2 diabetes: implications for treatment and monitoring of metabolic control

OBJECTIVE

To evaluate the extent of plasma glucose excursions with meals, the relations between plasma glucose levels at different times of the day, and the relations between the latter and HbA(1c) in non-insulin-treated type 2 diabetic subjects.

RESEARCH DESIGN AND METHODS

Daily glucose profiles were assessed in non-insulin-treated type 2 diabetic patients. Outpatients at the diabetes clinic (n = 371; one daily plasma glucose profile) and at home (n = 30; five daily blood glucose profiles over 1 month) as well as inpatients (n = 455; profile of plasma glucose on the day of admission) were examined. Subjects had plasma/blood glucose assessment before and 2-3 h after breakfast, lunch, and dinner. HbA(1c) was also measured.

RESULTS

After the meals many subjects had glucose levels >8.9 mmol/l (160 mg/dl) and/or glucose excursions >2.2 mmol/l (40 mg/dl). This was also often found when HbA(1c) was satisfactory (<7%). The coefficients of simple correlation among plasma/blood glucose at different times of the day ranged from 0.52 to 0.88. Correlations between HbA(1c) and plasma/blood glucose at different times of the day ranged from 0.44 to 0.67. The strongest correlation was between HbA(1c) and mean daily glucose (r = 0.57-0.69). Multiple regression analyses showed that premeal but not postmeal plasma/blood glucose levels were independent predictors of HbA(1c).

CONCLUSIONS

These results suggest that 1) the majority of non-insulin-treated type 2 diabetic patients have exaggerated plasma/blood glucose excursions with meals, and many of them have higher-than-recommended glucose concentrations 2 h after the meals; 2) plasma/blood glucose levels throughout the day are not as strongly interrelated as one might believe; and 3) HbA(1c) is more related to preprandial than postprandial plasma/blood glucose levels. These findings have potential implications for treatment and monitoring of metabolic control in type 2 diabetes.

Relation between soluble adhesion molecules and insulin sensitivity in type 2 diabetic individuals: role of adipose tissue

OBJECTIVE

The purpose of this study was to explore the relation between insulin resistance and plasma levels of soluble adhesion molecules and to examine the effects of acute hyperinsulinemia on these molecules in type 2 diabetic individuals.

RESEARCH DESIGN AND METHODS

Intercellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, and E- and P-selectin plasma concentrations were measured in 36 nonobese type 2 diabetic patients without cardiovascular disease and in 7 healthy subjects. Insulin sensitivity was assessed by a 4-h euglycemic ( approximately 5 mmol/l)-hyperinsulinemic ( approximately 300 pmol/l) clamp performed in combination with [(3)H]3-D-glucose infusion.

RESULTS

Diabetic subjects were insulin resistant but did not show plasma concentrations of adhesion molecules that were significantly higher than control subjects. In diabetic subjects, plasma ICAM-1 and E-selectin were negatively correlated with total glucose disposal during the insulin clamp (r = -0.432, P < 0.01; and r = -0.375, P < 0.05, respectively), whereas plasma VCAM-1 and P-selectin were not. Plasma ICAM-1 as well as E- and P-selectin were positively correlated with BMI, total body fat (TBF), and waist girth (P < 0.05-0.001). In multiple regression analyses, the relation of plasma ICAM-1 and E-selectin with insulin sensitivity was lost after adjustment for potential confounders, including HbA(1c), blood pressure, and/or LDL cholesterol. In these analyses, BMI was the only independent predictor of plasma ICAM-1 (R(2) = 0.244, P < 0.002), whereas TBF was the only independent predictor of plasma E-selectin (R(2) = 0.202, P = 0.01). The 4-h insulin infusion during the glucose clamp did not significantly change plasma levels of adhesion molecules.

CONCLUSIONS

Overall adiposity, rather than insulin resistance, may be a determinant of plasma levels of ICAM-1 and E-selectin in type 2 diabetic individuals. In these patients, acute hyperinsulinemia does not exert any significant effect on plasma adhesion molecules. These findings support the possibility that adipose tissue releases one or more factors that may adversely affect endothelial function on one hand and insulin sensitivity on the other.

ACE genotype and endothelium-dependent vasodilation of conduit arteries and forearm microcirculation in humans

The ACE gene is a candidate gene for cardiovascular disease. Endothelial dysfunction is considered an intermediate phenotype in the pathogenesis of hypertension and atherosclerosis. We evaluated the role of ACE gene polymorphism in endothelial function of young healthy humans. We assessed ACE genotype (deletion [D]/insertion [I] polymorphism) in 92 young healthy individuals. In 88 of them, endothelium-dependent (flow-mediated) vasodilation and endothelium-independent (nitroglycerin-induced) vasodilation were measured in the common femoral artery and in the brachial (n=84) artery by echo Doppler technique. In 35 subjects, we also applied the forearm perfusion technique to quantify the responses of the forearm vascular bed to 3 increasing doses of 2 endothelium-dependent vasodilators (acetylcholine and bradykinin) and 1 endothelium-independent vasodilator (sodium nitroprusside). The D allele of the ACE gene was associated with a significant blunting (Delta approximately 26%) of endothelium-dependent vasodilation in the femoral artery (P=0.02) but not in the brachial artery (P=0.55) or in the forearm microcirculation (P=0.70 to 0.80). Endothelium-independent vasodilation was unaffected by the ACE genotype. In young healthy humans, the D allele of the ACE gene is associated with selective endothelial dysfunction of the femoral artery. It remains to be determined whether this association discloses a causal role in vascular, particularly peripheral artery, disease.

Intracellular partition of plasma glucose disposal in hypertensive and normotensive subjects with type 2 diabetes mellitus

The aim of this study was to ascertain whether the presence of hypertension conveys a more severe degree of insulin resistance in type 2 diabetes mellitus and, if so, which biochemical pathways are involved. We quantitated the rates of total glucose disposal, glycogen synthesis (GS), glycolysis, glucose oxidation, endogenous glucose production, and LOX in the basal state and during a 4-h euglycemic ( approximately 5 mM) hyperinsulinemic ( approximately 300 pM) clamp carried out in combination with a dual-tracer infusion ([(3)H]-3- and [(14)C]-U-D-glucose) and indirect calorimetry in 42 nonobese noninsulin-treated type 2 diabetic subjects (22 hypertensive and 20 normotensive) and 23 nonobese nondiabetic subjects (9 without and 14 with essential hypertension). Compared with normotensive controls, both groups of diabetic subjects were markedly insulin resistant. In the basal state, all glucose fluxes were similar in diabetic subjects with or without hypertension. During insulin infusion, total glucose disposal was significantly reduced in hypertensive diabetic subjects, compared with their normotensive counterparts (18.7 +/- 1.0 vs. 28.6 +/- 3.0 micromol/min.kg lean body mass; P < 0.01). This difference was almost entirely explained by a marked reduction in GS (4.5 +/- 2.0 vs. 12.5 +/- 3.3 micromol/min.kg lean body mass; P < 0.01). Endogenous glucose production was not different in the two diabetic groups during insulin infusion and was significantly higher than in normotensive controls. Lipid oxidation was less suppressed by hyperinsulinemia in hypertensive than in normotensive diabetic subjects (1.46 +/- 0.1 vs. 0.91 +/- 0.1 micromol/min.kg lean body mass; P < 0.01). Glucose fluxes were not significantly different in nondiabetic subjects with essential hypertension and in normotensive diabetic individuals. These results indicate that hypertension markedly aggravates insulin resistance featuring type 2 diabetes mellitus. The molecular defects underlying this phenomenon involve primarily GS.

Assessment of beta-cell function during the oral glucose tolerance test by a minimal model of insulin secretion

OBJECTIVE

To characterise the performance of beta-cell during a standard oral glucose tolerance test (OGTT).

DESIGN

Fifty-six subjects were studied. A minimal analogic model of beta-cell secretion during the OGTT was applied to all OGTTs (see below). The amount of insulin secreted over 120' in response to oral glucose (OGTT-ISR; Insulin Units 120'-1 m-2 BSA) and an index of beta-cell secretory 'force' (beta-Index; pmol.min-2.m-2 BSA) were computed with the aid of the model. In protocol A, 10 healthy subjects underwent two repeat 75 g OGTT with frequent (every 10'-15') blood sampling for glucose and C-peptide to test the reproducibility of OGTT-ISR and beta-Index with a complete or a reduced data set. In protocol B, 7 healthy subjects underwent three OGTTs (50, 100 or 150 g), to test the stability of the beta-Index under different glucose loads. In protocol C, 29 subjects (15 with normal glucose tolerance, 7 with impaired glucose tolerance and 7 with newly diagnosed type 2 diabetes) underwent two repeat 75 g OGTT with reduced (every 30' for 120') blood sampling to compare the reproducibility and the discriminant ratio (DR) of OGTT-ISR and beta-index with the insulinogenic index (IG-Index: Delta Insulin 30' - Basal/Delta Glucose 30' - Basal). In protocol D, 20 subjects (14 with normal glucose tolerance, 5 with impaired glucose tolerance and 1 with newly-diagnosed type 2 diabetes) underwent a 75 g OGTT and an intravenous glucose tolerance test (IVGTT) on separate days to explore the relationships between acute (0'-10') insulin response (AIR) during the IVGTT and beta-index and OGTT-ISR during the OGTT.

RESULTS

In all protocols, the minimal analogic model of C-peptide secretion achieved a reasonable fit of the experimental data. In protocol A, a good reproducibility of both beta-index and OGTT-ISR was observed with both complete and reduced (every 30') data sets. In protocol B, increasing the oral glucose load caused progressive increases in OGTT-ISR (from 2.63 +/- 0.70 to 5.11 +/- 0.91 Units.120'-1.m-2 BSA; P < 0.01), but the beta-index stayed the same (4.14 +/- 0.35 vs. 4.29 +/- 0.30 vs. 4.30 +/- 0.33 pmol.min-2.m-2 BSA). In protocol C, both OGTT-ISR and beta-index had lower day-to-day CVs (17.6 +/- 2.2 and 12.4 +/- 2.4%, respectively) and higher DRs (2.57 and 1.74, respectively) than the IG-index (CV: 35.5 +/- 6.3%; DR: 0.934). OGTT-ISR was positively correlated to BMI (P < 0.03), whereas beta-index was inversely related to both fasting and 2 h plasma glucose (P < 0.01 for both). In protocol D, beta-index, but not OGTT-ISR, was significantly correlated to AIR (r = 0.542, P < 0.02).

CONCLUSIONS

Analogically modelling beta-cell function during the OGTT provides a simple, useful tool for the physiological assessment of beta-cell function.

Effects of glucosamine infusion on insulin secretion and insulin action in humans

Glucose toxicity (i.e., glucose-induced reduction in insulin secretion and action) may be mediated by an increased flux through the hexosamine-phosphate pathway. Glucosamine (GlcN) is widely used to accelerate the hexosamine pathway flux, independently of glucose. We tested the hypothesis that GlcN can affect insulin secretion and/or action in humans. In 10 healthy subjects, we sequentially performed an intravenous glucose (plus [2-3H]glucose) tolerance test (IVGTT) and a euglycemic insulin clamp during either a saline infusion or a low (1.6 micromol x min(-1) x kg(-1)) or high (5 micromol x min(-1) x kg(-1) [n = 5]) GlcN infusion. Beta-cell secretion, insulin (SI*-IVGTT), and glucose (SG*) action on glucose utilization during the IVGTT were measured according to minimal models of insulin secretion and action. Infusion of GlcN did not affect readily releasable insulin levels, glucose-stimulated insulin secretion (GSIS), or the time constant of secretion, but it increased both the glucose threshold of GSIS (delta approximately 0.5-0.8 mmol/l, P < 0.03-0.01) and plasma fasting glucose levels (delta approximately 0.3-0.5 mmol/l, P < 0.05-0.02). GlcN did not change glucose utilization or intracellular metabolism (glucose oxidation and glucose storage were measured by indirect calorimetry) during the clamp. However, high levels of GlcN caused a decrease in SI*-IVGTT (delta approximately 30%, P < 0.02) and in SG* (delta approximately 40%, P < 0.05). Thus, in humans, acute GlcN infusion recapitulates some metabolic features of human diabetes. It remains to be determined whether acceleration of the hexosamine pathway can cause insulin resistance at euglycemia in humans.

Impaired glucose tolerance, Type II diabetes mellitus and carotid atherosclerosis: prospective results from the Bruneck Study

AIMS/HYPOTHESIS

Cardiovascular disease is a well-known severe complication of impaired glucose tolerance and Type II (non-insulin-dependent) diabetes mellitus. The independent contribution of glucose intolerance to cardiovascular disease and the underlying pathogenic mechanisms are still, however, not clear.

METHODS

In this prospective population-based study, 826 subjects aged 40-79 years underwent high resolution duplex ultrasound examinations of carotid arteries and extensive clinical and laboratory screenings for potential vascular risk factors at baseline and 5 years later. The ultrasound protocol involved measurements of maximum axial diameter of atherosclerotic plaques, if any, in common and internal carotid arteries on both sides and enable differentiation of two main stages in carotid artery disease, termed early non-stenotic and advanced stenotic atherosclerosis. Intima-media thickness was assessed at the follow-up examination.

RESULTS

Type II diabetes and, to a lesser extent, impaired glucose tolerance were found to be statistically significant risk predictors of 5-year changes in carotid atherosclerosis. These associations were in part independent of other vascular risk factors typically clustering with glucose intolerance. Both impaired glucose tolerance and Type II diabetes mellitus were not independently related to early non-stenotic atherosclerosis. In contrast, Type II diabetes mellitus was the strongest single risk predictor of advanced stenotic atherosclerosis [odds ratio 5.0 (95% confidence intervals 2.3-11.1)] and impaired glucose tolerance was of relevance as well [odds ratio 2.8 (1.2-6.4)] (p < 0.001).

CONCLUSION/INTERPRETATION

Impaired glucose tolerance and, to a greater extent, Type II diabetes were strong independent predictors of advanced carotid atherosclerosis in our prospective population-based study.

Fasting plasma glucose variability predicts 10-year survival of type 2 diabetic patients: the Verona Diabetes Study

OBJECTIVE

In the present study, we evaluated whether the coefficient of variation (CV) of fasting plasma glucose (FPG) over a 3-year period was a significant predictor of mortality in type 2 diabetic patients aged 56-74 years.

RESEARCH DESIGN AND METHODS

All type 2 diabetic patients (n = 1,409) aged 56-74 years attending the Verona Diabetes Clinic and having at least two FPG determinations in each of the years 1984-1986 were followed for 10 years (1987-1996) to assess total and cause-specific mortality Patients were grouped into tertiles of mean and CV of FPG during 1984-1986. These parameters as well as sex, age, diabetes duration, insulin treatment, smoking, hypertension, and hypercholesterolemia were included in multivariate survival analyses.

RESULTS

During the follow-up, 468 patients died. The CV of FPG was an independent predictor of total, cardiovascular, and cancer mortality. Mean FPG was a predictor of total mortality only when the CV of FPG was not included in the analyses.

CONCLUSIONS

Long-term variability of fasting glucose is an independent predictor of mortality in patients with type 2 diabetes. The CV of FPG might be considered a useful additional parameter in the management of these patients.

Homeostasis model assessment closely mirrors the glucose clamp technique in the assessment of insulin sensitivity: studies in subjects with various degrees of glucose tolerance and insulin sensitivity

OBJECTIVE

To evaluate whether the homeostasis model assessment (HOMA) is a reliable surrogate measure of in vivo insulin sensitivity in humans.

RESEARCH DESIGN AND METHODS

In the present study, we compared insulin sensitivity as assessed by a 4-h euglycemic (approximately 5 mmol/l) hyperinsulinemic (approximately 300 pmol/l) clamp with HOMA in 115 subjects with various degrees of glucose tolerance and insulin sensitivity.

RESULTS

We found a strong correlation between clamp-measured total glucose disposal and HOMA-estimated insulin sensitivity (r = -0.820, P<0.0001), with no substantial differences between men (r = -0.800) and women (r = -0.796), younger (aged <50 years, r = -0.832) and older (r = -0.800) subjects, nonobese (BMI <27 kg/m2, r = -0.800) and obese (r = -0.765) subjects, nondiabetic (r = -0.754) and diabetic (r = -0.695) subjects, and normotensive ( r = -0.786) and hypertensive (r = -0.762) subjects. Also, we found good agreement between the two methods in the categorization of subjects according to insulin sensitivity (weighted k = 0.63).

CONCLUSIONS

We conclude that the HOMA can be reliably used in large-scale or epidemiological studies in which only a fasting blood sample is available to assess insulin sensitivity

ACE inhibitors improve endothelial function in type 1 diabetic patients with normal arterial pressure and microalbuminuria

OBJECTIVE

The purpose of this study was to test whether a short-course treatment with ACE inhibitors may restore endothelium-dependent and/or -independent vasodilation in the femoral artery of microalbuminuric patients with type 1 diabetes and normal arterial pressure.

RESEARCH DESIGN AND METHODS

We studied nine normotensive microalbuminuric type 1 diabetic patients and two groups of control subjects matched for femoral artery diameter to type 1 diabetic patients after placebo (control group A, n = 17) and ACE inhibitor (control group B, n = 18) treatment, respectively. The patients were enrolled in a double-blind cross-over study with a 1-week trial of either placebo, captopril (25 mg t.i.d.), or enalapril (10 mg/day) in randomized order to ascertain whether short-term ACE inhibition obtained with (captopril) or without (enalapril) a sulfhydryl donor molecule ameliorates vessel wall function. Endothelium-mediated flow-dependent vasodilation and endothelium-independent vasodilation were evaluated in the right common femoral artery by echo Doppler.

RESULTS

Both captopril and enalapril normalized (control group B 22.9+/-3.2% per 8 min) endothelium-dependent response (19.6+/-7.5 and 18.0+/-5.3 vs. -10.4+/-4.1% per 8 min, P < 0.01, for both captopril and enalapril versus placebo, respectively) in the type 1 diabetic patients. Captopril (28.4+/-3.5 vs. 17.1+/-3.5% per 5 min during placebo, P < 0.05) but not enalapril (20.1+/-3.0 vs. 31.7+/-2.8% per 5 min, P < 0.05 for enalapril versus control group B, and NS for captopril vs. control group B) ameliorated endothelium-independent vasodilation in type 1 diabetic patients.

CONCLUSIONS

ACE inhibition improves endothelium-dependent vasodilation in the femoral artery of normotensive microalbuminuric type 1 diabetic patients. Captopril also ameliorates endothelium-independent vasodilation, possibly through its sulfhydryl donor properties. These results may be of pathophysiological relevance to prevent cardiovascular complications in these patients.

Effect of chronic treatment with lacidipine or lisinopril on intracellular partitioning of glucose metabolism in type 2 diabetes mellitus

Antihypertensive treatment is frequently needed in type 2 diabetes. In this study we measured the rates of total, oxidative, and nonoxidative glucose disposal, glycogen synthesis, glycolysis, endogenous glucose production, and lipid oxidation using a 4-h euglycemic (approximately 5 mmol/L) hyperinsulinemic (approximately 300 pmol/L) clamp in combination with a dual glucose tracer infusion ([3-(3)H]- and [U-14C] D-glucose) and indirect calorimetry in 40 nonobese subjects with type 2 diabetes. Subjects were studied twice: after a 4-week run-in period and after a 16-week period of double blind, randomized treatment with 4-6 mg/day lacidipine, a calcium channel blocker (n = 19), or 10-20 mg/day lisinopril, an angiotensin-converting enzyme inhibitor (n = 21). Antihypertensive treatment resulted in a significant increase in total glucose disposal during insulin clamp as well as in basal and insulin-stimulated nonoxidative glucose disposal rates. On the contrary, oxidative glucose disposal was significantly decreased by antihypertensive treatment, mainly in the basal state. The changes in glucose disposal rates were not significantly different in subjects treated with lacidipine and in those treated with lisinopril. The suppression of endogenous glucose production during insulin clamp was significantly greater after lacidipine than after lisinopril. These results suggest that treatment of subjects with type 2 diabetes with either lacidipine or lisinopril has no adverse effect on glucose metabolism. Conversely, both drugs seem to improve insulin sensitivity.

Prevalence of insulin resistance in metabolic disorders: the Bruneck Study

The prevalence of insulin resistance in the most common metabolic disorders is still an undefined issue. We assessed the prevalence rates of insulin resistance in subjects with impaired glucose tolerance (IGT), NIDDM, dyslipidemia, hyperuricemia, and hypertension as identified within the frame of the Bruneck Study. The study comprised an age- and sex-stratified random sample of the general population (n = 888; aged 40-79 years). Insulin resistance was estimated by homeostasis model assessment (HOMA(IR)), preliminarily validated against a euglycemic-hyperinsulinemic clamp in 85 subjects. The lower limit of the top quintile of HOMA(IR) distribution (i.e., 2.77) in nonobese subjects with no metabolic disorders (n = 225) was chosen as the threshold for insulin resistance. The prevalence of insulin resistance was 65.9% in IGT subjects, 83.9% in NIDDM subjects, 53.5% in hypercholesterolemia subjects, 84.2% in hypertriglyceridemia subjects, 88.1% in subjects with low HDL cholesterol, 62.8% in hyperuricemia subjects, and 58.0% in hypertension subjects. The prevalence of insulin resistance in subjects with the combination of glucose intolerance (IGT or NIDDM), dyslipidemia (hypercholesterolemia and/or hypertriglyceridemia and/or low HDL cholesterol), hyperuricemia, and hypertension (n = 21) was 95.2%. In isolated hypercholesterolemia, hypertension, or hyperuricemia, prevalence rates of insulin resistance were not higher than that in nonobese normal subjects. An appreciable number of subjects (n = 85, 9.6% of the whole population) was insulin resistant but free of IGT, NIDDM, dyslipidemia, hyperuricemia, and hypertension. These results from a population-based study documented that 1) in hypertriglyceridemia and a low HDL cholesterol state, insulin resistance is as common as in NIDDM, whereas it is less frequent in hypercholesterolemia, hyperuricemia, and hypertension; 2) the vast majority of subjects with multiple metabolic disorders are insulin resistant; 3) in isolated hypercholesterolemia, hyperuricemia, or hypertension, insulin resistance is not more frequent than can be expected by chance alone; and 4) in the general population, insulin resistance can be found even in the absence of any major metabolic disorders.

Estimation of blood flow heterogeneity in human skeletal muscle using intravascular tracer data: importance for modeling transcapillary exchange

Distributed models of blood-tissue exchange are widely used to measure kinetic events of various solutes from multiple tracer dilution experiments. Their use requires, however, a careful description of blood flow heterogeneity along the capillary bed. Since they have mostly been applied in animal studies, direct measurement of the heterogeneity distribution was possible, e.g., with the invasive microsphere method. Here we apply distributed modeling to a dual tracer experiment in humans, performed using an intravascular (indocyanine green dye, subject to distribution along the vascular tree and confined to the capillary bed) and an extracellular ([3H]-D-mannitol, tracing passive transcapillary transfer across the capillary membrane in the interstitial fluid) tracer. The goal is to measure relevant parameters of transcapillary exchange in human skeletal muscle. We show that assuming an accurate description of blood flow heterogeneity is crucial for modeling, and in particular that assuming for skeletal muscle the well-studied cardiac muscle blood flow heterogeneity is inappropriate. The same reason prevents the use of the common method of estimating the input function of the distributed model via deconvolution, which assumes a known blood flow heterogeneity, either defined from literature or measured, when possible. We present a novel approach for the estimation of blood flow heterogeneity in each individual from the intravascular tracer data. When this newly estimated blood flow heterogeneity is used, a more satisfactory model fit is obtained and it is possible to reliably measure parameters of capillary membrane permeability-surface product and interstitial fluid volume describing transcapillary transfer in vivo.

Role of tissue-specific blood flow and tissue recruitment in insulin-mediated glucose uptake of human skeletal muscle

BACKGROUND

Conflicting evidence exists concerning whether insulin-induced vasodilation plays a mechanistic role in the regulation of limb glucose uptake. It can be predicted that if insulin augments blood flow by causing tissue recruitment, this mechanism would enhance limb glucose uptake.

METHODS AND RESULTS

Twenty healthy subjects were studied with the forearm perfusion technique in combination with the euglycemic insulin clamp technique. Ten subjects were studied at physiological insulin concentrations (approximately 400 pmol/L) and the other 10 at supraphysiological insulin concentrations (approximately 5600 pmol/L). Four additional subjects underwent a saline control study. Pulse injections of a nonmetabolizable extracellular marker (1-[3H]-L-glucose) were administered into the brachial artery, and its washout curves were measured in one ipsilateral deep forearm vein and used to estimate the extracellular volume of distribution and hence the amount of muscle tissue drained by the deep forearm vein. Both during saline infusion and at physiological levels of hyperinsulinemia we observed no changes in blood flow and/or muscle tissue drained by the deep forearm vein. However, supraphysiological hyperinsulinemia accelerated total forearm blood flow (45.0+/-1.8 versus 36.5+/-1.3 mL x min(-1) x kg(-1), P<0.01) and increased the amount of muscle tissue drained by the deep forearm vein (305+/-46 versus 229+/-32 g, P<0.05). The amount of tissue newly recruited by insulin was strongly correlated to the concomitant increase in tissue glucose uptake (r=0.789, P<0.01).

CONCLUSIONS

Acceleration of forearm blood flow mediated by supraphysiological hyperinsulinemia is accompanied by tissue recruitment, which may be a relevant determinant of forearm (muscle) glucose uptake.

Cigarette smoking and insulin resistance in patients with noninsulin-dependent diabetes mellitus

To evaluate the effects of chronic cigarette smoking on insulin sensitivity in patients with noninsulin-dependent diabetes mellitus (NIDDM), we examined 28 smokers and 12 nonsmokers with NIDDM, of similar sex, age, body mass index, waist/hip ratio, alcohol consumption, physical activity level, glycometabolic control, diabetes duration, and treatment. Insulin and C-peptide responses to oral glucose load were significantly higher in smokers than nonsmokers, whereas glucose levels were not substantially different. During insulin clamp (20 mU/min.m2), carried out in combination with tritiated glucose infusion and indirect calorimetry, total glucose disposal was markedly reduced in smokers vs. nonsmokers [19 +/- 1.2 vs. 33 +/- 5 mumol/min.kg fat-free mass (FFM); P < 0.001], in a dose-dependent fashion (F = 6.8, P < 0.001 by ANOVA when subjects were categorized for number of cigarettes smoked per day). Oxidative (9 +/- 1 vs. 14 +/- 2 mumol/min.kg FFM; P < 0.01) and nonoxidative (10 +/- 1 vs. 19 +/- 4 mumol/min.kg FFM; P < 0.01) pathways of insulin-mediated intracellular glucose metabolism were similarly reduced in smokers vs. nonsmokers. Plasma free fatty acid levels (240 +/- 33 vs. 130 +/- 23 microEq/L; P < 0.05) and lipid oxidation rate (1.39 +/- 0.1 vs. 0.95 +/- 0.2 mumol/ min.kg FFM; P < 0.05) were less suppressed by hyperinsulinemia in smokers than nonsmokers. In conclusion, chronic cigarette smoking seems to markedly aggravate insulin resistance in patients with NIDDM.

Estimation of blood flow heterogeneity distribution in human skeletal muscle from positron emission tomography data

Regional blood flow distribution in animal skeletal muscle is markedly uneven at rest and during various physiological states (exercise and hyperemia). It has been hypothesized that the vasodilatory properties of insulin may concur with insulin action on the myocite in determining stimulation of muscle glucose metabolism in vivo. In this study, we developed a method to determine noninvasively both bulk flow and regional flow heterogeneity in human skeletal muscle. Positron emission tomography studies with [15O] water were performed in seven normal subjects, both in the basal state and after 1 hr of euglycemic hyperinsulinemia. Hyperinsulinemia almost doubled skeletal muscle blood flow, but apparently did not affect the relative dispersion, the skewness, or the kurtosis of the flow distribution. However, the regression line between basal and insulin-stimulated flow values showed a nonzero intercept, and the relationship between basal flow and its insulin-stimulated fractional change was hyperbolic. These findings suggest that insulin vasodilated proportionally more the areas with the lowest basal perfusion values. These are the first data to demonstrate that in human skeletal muscle: (i) blood flow is heterogeneous; and (ii) insulin, although doubling muscle bulk flow, does not affect the relative dispersion of its distribution. This result implies that regional redistribution of perfusion is not involved in determining the metabolic response of skeletal muscle to insulin. Yet, since insulin vasodilates proportionally more the less perfused areas, it still exerts an optimizing effect on flow distribution in human muscle.

Studies on the mass action effect of glucose in NIDDM and IDDM: evidence for glucose resistance

The ability of hyperglycaemia to enhance glucose uptake was evaluated in 9 non-insulin-dependent (NIDDM), 7 insulin-dependent (IDDM) diabetic subjects, and in 6 young and 9 older normal volunteers. Following overnight insulin-induced euglycaemia, a sequential three-step hyperglycaemic clamp (+ 2.8 + 5.6, and + 11.2 mmol/l above baseline) was performed with somatostatin plus replacing doses of basal insulin and glucagon, 3-3H-glucose infusion and indirect calorimetry. In the control subjects as a whole, glucose disposal increased at each hyperglycaemic step (13.1 +/- 0.6, 15.7 +/- 0.7, and 26.3 +/- 1.1 mumol/kg.min). In NIDDM (10.5 +/- 0.2, 12.1 +/- 1.0, and 17.5 +/- 1.1 mumol/kg.min), and IDDM (11.2 +/- 0.8, 12.9 +/- 1.0, and 15.6 +/- 1.1 mumol/kg.min) glucose disposal was lower during all three steps (p < 0.05-0.005). Hepatic glucose production declined proportionally to plasma glucose concentration to a similar extent in all four groups of patients. In control subjects, hyperglycaemia stimulated glucose oxidation (+4.4 +/- 0.7 mumol/kg.min) only at +11.2 mmol/l (p < 0.05), while non-oxidative glucose metabolism increased at each hyperglycaemic step (+3.1 +/- 0.7; +3.5 +/- 0.9, and +10.8 +/- 1.7 mumol/kg.min; all p < 0.05). In diabetic patients, no increment in glucose oxidation was elicited even at the highest hyperglycaemic plateau (IDDM = +0.5 +/- 1.5; NIDDM = +0.2 +/- 0.6 mumol/kg.min) and non-oxidative glucose metabolism was hampered (IDDM = +1.8 +/- 1.5, +3.1 +/- 1.7, and +4.3 +/- 1.8; NIDDM = +0.7 +/- 0.6, 2.1 +/- 0.9, and +7.0 +/- 0.8 mumol/kg.min; p < 0.05-0.005). Blood lactate concentration increased and plasma non-esterified fatty acid (NEFA) fell in control (p < 0.05) but not in diabetic subjects. The increments in blood lactate were correlated with the increase in non-oxidative glucose disposal and with the decrease in plasma NEFA.

IN CONCLUSION

1) the ability of hyperglycaemia to promote glucose disposal is impaired in NIDDM and IDDM; 2) stimulation of glucose oxidation and non-oxidative glucose metabolism accounts for glucose disposal; 3) both pathways of glucose metabolism are impaired in diabetic patients; 4) impaired ability of hyperglycaemia to suppress plasma NEFA is present in these patients. These results suggest that glucose resistance, that is the ability of glucose itself to promote glucose utilization, is impaired in both IDDM and NIDDM patients.

Roles of glucose transport and glucose phosphorylation in muscle insulin resistance of NIDDM

Insulin resistance for glucose metabolism in skeletal muscle is a key feature in NIDDM. The quantitative role of the cellular effectors of glucose metabolism in determining this insulin resistance is still imperfectly known. We assessed transmembrane glucose transport and intracellular glucose phosphorylation in vivo in skeletal muscle in nonobese NIDDM patients. We performed euglycemic insulin clamp studies in combination with the forearm balance technique (brachial artery and deep forearm vein catheterization) in five nonobese NIDDM patients and seven age- and weight-matched control subjects (study 1). D-Mannitol (a nontransportable molecule), 3-O-[14C]methyl-D-glucose (transportable, but not metabolizable) and D[3-3H]glucose (transportable and metabolizable) were simultaneously injected into the brachial artery, and the washout curves were measured in the deep venous effluent blood. In vivo rates of transmembrane transport and intracellular phosphorylation of D-glucose in forearm muscle were determined by analyzing the washout curves with the aid of a multicompartmental model of glucose kinetics in forearm tissues. At similar steady-state concentrations of plasma insulin (approximately 500 pmol/l) and glucose (approximately 5.0 mmol/l), the rates of transmembrane influx (34.3 +/- 9.1 vs. 58.5 +/- 6.5 micromol x min(-1) x kg(-1), P < 0.05) and intracellular phosphorylation (5.4 +/- 1.6 vs. 38.8 +/- 5.1 micromol x min(-1) x kg(-1), P < 0.01) in skeletal muscle were markedly lower in the NIDDM patients than in the control subjects. In the NIDDM patients (study 2), the insulin clamp was repeated at hyperglycemia, (approximately 13 mmol/l) trying to match the rates of transmembrane glucose influx measured during the clamp in the controls. The rate of transmembrane glucose influx (62 +/- 15 micromol x min(-1) x kg(-1)) in the NIDDM patients was similar to the control subjects, but the rate of intracellular glucose phosphorylation (16.6 +/- 7.5 micromol x min(-1) x kg(-1)), although threefold higher than in the patients during study 1 (P < 0.05), was still approximately 60% lower than in the control subjects (P < 0.05). These data suggest that when assessed in vivo, both transmembrane transport and intracellular phosphorylation of glucose are refractory to insulin action and add to each other in determining insulin resistance in skeletal muscle of NIDDM patients. It will be of interest to compare the present results with the in vivo quantitation of the initial rate of muscle glucose transport when methodology to perform this measurement becomes available.

A model to measure insulin effects on glucose transport and phosphorylation in muscle: a three-tracer study

We studied five healthy subjects with perfused forearm and euglycemic clamp techniques in combination with a three-tracer (D-[12C]mannitol, not transportable; 3-O-[14C]methyl-D-glucose, transportable but not metabolizable; D-[3-3H]glucose, transportable and metabolizable) intra-arterial pulse injection to assess transmembrane transport and intracellular phosphorylation of glucose in vivo in human muscle. The washout curves of the three tracers were analyzed with a multicompartmental model. A priori identifiability analysis of the tracer model shows that the rate constants of glucose transport into and out of the cells and of glucose phosphorylation are uniquely identifiable. Tracer model parameters were estimated by a nonlinear least-squares parameter estimation technique. We then solved for the tracee model and estimated bidirectional transmembrane transport glucose fluxes, glucose intracellular phosphorylation, extracellular and intracellular volumes of glucose distribution, and extracellular and intracellular glucose concentrations. Physiological hyperinsulinemia (473 +/- 22 pM) caused 2.7-fold (63.1 +/- 7.2 vs. 23.4 +/- 6.1 mumol.min-1.kg-1, P < 0.01) and 5.1-fold (42.5 +/- 5.8 vs. 8.4 +/- 2.2 mumol.min-1.kg-1, P < 0.01) increases in transmembrane influx and intracellular phosphorylation of glucose, respectively. Extracellular distribution volume and concentration of glucose were unchanged, whereas intracellular distribution volume of glucose was increased (approximately 2-fold) and intracellular glucose concentration was almost halved by hyperinsulinemia. In summary, 1) a multicompartment model of three-tracer kinetic data can quantify transmembrane glucose fluxes and intracellular glucose phosphorylation in human muscle; and 2) physiological hyperinsulinemia stimulates both transport and phosphorylation of glucose and, in doing so, amplifies the role of glucose transport as a rate-determining step of muscle glucose uptake.

Bicarbonate kinetics in humans: identification and validation of a three-compartment model

A model of bicarbonate kinetics is crucial to a correct interpretation of experiments for measuring oxidation in vivo of carbon-labeled compounds. The aim of this study is to develop a compartmental model of bicarbonate kinetics in humans from tracer data by devoting particular attention to model identification and validation. The data base consisted of impulse-dose studies of 14C-labeled bicarbonate in nine normal subjects. The decay curve of specific activity of CO2 in expired air (saRCO2) was frequently sampled for 4-7 h. In addition, endogenous production of CO2, VCO2, was measured by indirect calorimetry. A model of data, i.e., an exponential model, analysis of decay curves of saRCO2 showed first that three compartments are necessary and sufficient to describe bicarbonate tracer kinetics. Compartmental models were then used as models of system. To correctly describe the input-output configuration, labeled CO2 flux in the expired air, phi RCO2 (= saRCO2.VCO2), has been used as measurement variable in tracer model identification. A mammillary three-compartment model with a respiratory and a nonrespiratory loss has been studied. Whereas there is good evidence that respiratory loss takes place in the central compartment, whether nonrespiratory loss is taking place in the central compartment or in one of the two peripheral compartments is uncertain. Thus three competing tracer models were considered. Using a model-independent analysis of data, based on the body activity variable, to calculate mean residence time in the system, we have been able to validate a specific model structure, i.e., with the two irreversible losses taking place in the central compartment. This validated tracer model was then used to quantitate bicarbonate masses in the system. Because there is uncertainty about where endogenous production enters the system, lower and upper bounds of masses of bicarbonate in the body are derived.

In vivo effects of glucosamine on insulin secretion and insulin sensitivity in the rat: possible relevance to the maladaptive responses to chronic hyperglycaemia

We tested the hypothesis that glucosamine, a putative activator of glucose toxicity in vitro through acceleration of the hexosamine pathway, may determine in vivo the two key features of glucose toxicity in diabetes, namely, peripheral insulin resistance and decreased insulin secretion. Two groups of awake rats were studied either with intraarterial administration of glucosamine (5 mumol.kg-1.min-1) or saline. Insulin secretion was determined after arginine, glucose (hyperglycaemic clamp), and arginine/glucose infusions, while insulin-mediated glucose metabolism was assessed by the euglycaemic hyperinsulinaemic clamp in combination with [3-3H]-glucose infusion. Glucosamine had no effects on arginine-induced insulin secretion both at euglycaemia and hyperglycaemia, but significantly (40-50%) impaired glucose-induced insulin secretion (both first and second phases). During euglycaemic hyperinsulinaemic clamp studies, glucosamine decreased glucose uptake by approximately 30%, affecting glycolysis (estimated from 3H2O rate of appearance) and muscle glycogen synthesis (calculated from accumulation of [3H]-glucosyl units in muscle glycogen) to a similar extent. Muscle glucose 6-phosphate concentration was markedly reduced in the glucosamine-infused rats, suggesting an impairment in glucose transport/phosphorylation. Therefore, an increase in hexosamine metabolism in vivo: 1) inhibits glucose-induced insulin secretion, and 2) reduces insulin stimulation of both glycolysis and glycogen synthesis, thereby mimicking in normal rats the major alterations due to glucose toxicity in diabetes.

Free fatty acid and glucose metabolism in human aging: evidence for operation of the Randle cycle

We assessed insulin effects on plasma free fatty acid (FFA) and glucose metabolism in seven elderly (71 +/- 2 yr) and in seven younger (21 +/- 1 yr) subjects matched for body weight and body mass index but not for percent body fat (32.4 +/- 3.8% in elderly vs. 20.4 +/- 3.5% in young, P < 0.05), by performing sequential euglycemic clamps at five insulin doses (0.6, 1.5, 3, 6, and 15 pmol.min-1.kg-1) in combination with indirect calorimetry and [1-14C]palmitate plus [3-3H]glucose infusion. At baseline, plasma FFA concentration, turnover infusion. At baseline, plasma FFA concentration, turnover and oxidation, and total lipid oxidation were all increased in the elderly (897 +/- 107 vs. 412 +/- 50 mumol/l and 11.2 +/- 1.4 vs. 5.14 +/- 0.86, 3.45 +/- 0.65 vs. 1.37 +/- 0.25, and 4.63 +/- 0.72 vs. 3.01 +/- 0.33 mumol.min-1.kg-1 lean body mass, P < 0.05 for all comparisons), whereas glucose turnover was similar as a result of decreased glucose oxidation (8.2 +/- 1.4 vs. 13 +/- 1.9 mumol.min-1.kg-1 lean body mass, P < 0.05) and increased glucose storage (6.6 +/- 1.4 vs. 1.7 +/- 1.3 mmol.min-1.kg-1 lean body mass, P < 0.05). At all insulin infusions, plasma FFA concentration, turnover and oxidation, and total lipid oxidation were higher in the elderly than in the younger group (P < 0.05). However, if normalized per fat mass, all FFA and lipid metabolic fluxes, both in the postabsorptive state and during hyperinsulinemia, were comparable in the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of physiological hyperinsulinemia on the intracellular metabolic partition of plasma glucose

Methodology for assessing the glycolytic and oxidative fluxes from plasma glucose, by measuring 3H2O and 14CO2 rates of production during [3-3H]- and [U-14C]glucose infusion, was tested in healthy subjects. In study 1, during staircase 3H2O infusion in six subjects, calculated rates of 3H2O appearance agreed closely with 3H2O infusion rates. In study 2, when [2-3H]glucose and NaH14CO3 were infused in four subjects in the basal state and during a 4-h euglycemic insulin (approximately 70 microU/ml) clamp, accurate estimates of the rates of [2-3H]glucose detritiation were obtained (94-97% of the expected values), and the recovery factor of NaH14CO3 did not change during hyperinsulinemia. In study 3, 11 subjects underwent a 4-h euglycemic insulin (approximately 70 microU/ml) clamp with [3-3H]- and [U-14C]glucose infusion and measurement of gaseous exchanges by indirect calorimetry to estimate the rates of total glycolysis, glycogen synthesis, glucose oxidation, nonoxidative glycolysis, hepatic glucose production, glucose recycling, and glucose conversion to fat. Hyperinsulinemia stimulated glycogen synthesis above baseline more than glycolysis [increment of 4.78 +/- 0.37 vs. 2.0 +/- 0.17 mg.min-1 x kg-1 of lean body mass (LBM), respectively, P < 0.01] and incompletely suppressed (approximately 87%) hepatic glucose production. The major component of nonoxidative glycolysis shifted from glucose recycling in the postabsorptive state (approximately 57% of nonoxidative glycolysis) to glucose conversion to fat during hyperinsulinemia (approximately 59% of nonoxidative glycolysis). Lipid oxidation during the insulin clamp was negatively correlated with both isotopic glucose oxidation (r = -0.822, P < 0.002) and glycolysis (r = -0.582, P < 0.07). In conclusion, in healthy subjects, glycogen synthesis plays a greater role than glycolysis and glucose oxidation in determining insulin-mediated glucose disposal. Part of insulin-mediated increase in glycolysis/oxidation might be secondary to the relief of the competition between fat and glucose for oxidation.

Transmembrane glucose transport in skeletal muscle of patients with non-insulin-dependent diabetes

Insulin resistance for glucose metabolism in skeletal muscle is a key feature in non-insulin-dependent diabetes mellitus (NIDDM). Which cellular effectors of glucose metabolism are involved is still unknown. We investigated whether transmembrane glucose transport in vivo is impaired in skeletal muscle in nonobese NIDDM patients. We performed euglycemic insulin clamp studies in combination with the forearm balance technique (brachial artery and deep forearm vein catheterization) in six nonobese NIDDM patients and five age- and weight-matched controls. Unlabeled D-mannitol (a nontransportable molecule) and radioactive 3-O-methyl-D-glucose (the reference molecular probe to assess glucose transport activity) were simultaneously injected into the brachial artery, and the washout curves were measured in the deep venous effluent blood. In vivo transmembrane transport of 3-O-methyl-D-glucose in forearm muscle was determined by computerized analysis of the washout curves. At similar steady-state plasma concentrations of insulin (approximately 500 pmol/liter) and glucose (approximately 5.15 mmol/liter), transmembrane inward transport of 3-O-methyl-D-glucose in skeletal muscle was markedly reduced in the NIDDM patients (6.5 x 10(-2) +/- 0.56 x 10(-2).min-1) compared with controls (12.5 x 10(-2) +/- 1.5 x 10(-2).min-1, P < 0.005). Mean glucose uptake was also reduced in the diabetics both at the whole body level (9.25 +/- 1.84 vs. 28.3 +/- 2.44 mumol/min per kg, P < 0.02) and in the forearm tissues (5.84 +/- 1.51 vs. 37.5 +/- 7.95 mumol/min per kg, P < 0.02). When the latter rates were extrapolated to the whole body level, skeletal muscle accounted for approximately 80% of the defect in insulin action seen in NIDDM patients. We conclude that transmembrane glucose transport, when assessed in vivo in skeletal muscle, is insensitive to insulin in nonobese NIDDM patients, and plays a major role in determining whole body insulin resistance.

In vivo glucose metabolism in obese and type II diabetic subjects with or without hypertension

This study examined whether the presence of hypertension, an insulin-resistant condition, exacerbates the defect in insulin action observed in obesity and type II diabetes mellitus. Glucose metabolism in the basal state and in response to insulin was quantitated by using the euglycemic insulin (20 mU.min-1 x m-2) clamp in combination with 3-[3H]glucose infusion and indirect calorimetry in 20 obese nondiabetic subjects (10 hypertensive and 10 normotensive), 26 type II diabetic subjects (13 hypertensive and 13 normotensive), and 11 normal nondiabetic subjects. The two groups of obese subjects and the two groups of diabetic subjects were matched for sex, age, race, body mass index, and fat distribution. Both in the basal state and during insulin infusion, glucose disposal rates (total, oxidative, and nonoxidative) were similar in obese subjects with or without hypertension. Compared with control subjects, both groups of obese subjects were markedly insulin resistant. Similarly, type II diabetic individuals, whether normotensive or hypertensive, were equally insulin resistant. The severity of insulin resistance was nearly identical in obese and diabetic groups. In diabetic subjects, the inhibitory effect of insulin on hepatic glucose output, lipolysis, and lipid oxidation was blunted compared with normal subjects. In obese subjects the ability of insulin to inhibit lipolysis and lipid oxidation was impaired. However, hypertension did not alter the suppressive effects of insulin on hepatic glucose production, plasma free fatty acid levels, or lipid oxidation in either obese or type II diabetic subjects. These results indicate that hypertension does not confer a greater severity of insulin resistance than that already is present in obesity and type II diabetes mellitus.

Characterization of cellular defects of insulin action in type 2 (non-insulin-dependent) diabetes mellitus

Seven non-insulin-dependent diabetes mellitus (NIDDM) patients participated in three clamp studies performed with [3-3H]- and [U-14C]glucose and indirect calorimetry: study I, euglycemic (5.2 +/- 0.1 mM) insulin (269 +/- 39 pM) clamp; study II, hyperglycemic (14.9 +/- 1.2 mM) insulin (259 +/- 19 pM) clamp; study III, euglycemic (5.5 +/- 0.3 mM) hyperinsulinemic (1650 +/- 529 pM) clamp. Seven control subjects received a euglycemic (5.1 +/- 0.2 mM) insulin (258 +/- 24 pM) clamp. Glycolysis and glucose oxidation were quantitated from the rate of appearance of 3H2O and 14CO2; glycogen synthesis was calculated as the difference between body glucose disposal and glycolysis. In study I, glucose uptake was decreased by 54% in NIDDM vs. controls. Glycolysis, glycogen synthesis, and glucose oxidation were reduced in NIDDM patients (P < 0.05-0.001). Nonoxidative glycolysis and lipid oxidation were higher. In studies II and III, glucose uptake in NIDDM was equal to controls (40.7 +/- 2.1 and 40.7 +/- 1.7 mumol/min.kg fat-free mass, respectively). In study II, glycolysis, but not glucose oxidation, was normal (P < 0.01 vs. controls). Nonoxidative glycolysis remained higher (P < 0.05). Glycogen deposition increased (P < 0.05 vs. study I), and lipid oxidation remained higher (P < 0.01). In study III, hyperinsulinemia normalized glycogen formation, glycolysis, and lipid oxidation but did not normalize the elevated nonoxidative glycolysis or the decreased glucose oxidation. Lipid oxidation and glycolysis (r = -0.65; P < 0.01), and glucose oxidation (r = -0.75; P < 0.01) were inversely correlated. In conclusion, in NIDDM: (a) insulin resistance involves glycolysis, glycogen synthesis, and glucose oxidation; (b) hyperglycemia and hyperinsulinemia can normalize total body glucose uptake; (c) marked hyperinsulinemia normalizes glycogen synthesis and total flux through glycolysis, but does not restore a normal distribution between oxidation and nonoxidative glycolysis; (d) hyperglycemia cannot overcome the defects in glucose oxidation and nonoxidative glycolysis; (e) lipid oxidation is elevated and is suppressed only with hyperinsulinemia.

Effect of insulin on system A amino acid transport in human skeletal muscle

Transmembrane transport of neutral amino acids in skeletal muscle is mediated by at least four different systems (system A, ASC, L, and Nm), and may be an important target for insulin's effects on amino acid and protein metabolism. We have measured net amino acid exchanges and fractional rates of inward (k(in), min-1) and outward (kout, min-1) transmembrane transport of 2-methylaminoisobutyric acid (MeAIB, a nonmetabolizable amino acid analogue, specific for system A amino acid transport) in forearm deep tissues (skeletal muscle), by combining the forearm perfusion technique and a novel dual tracer ([1-H3]-D-mannitol and 2-[1-14C]-methylaminoisobutyric acid) approach for measuring in vivo the activity of system A amino acid transport. Seven healthy lean subjects were studied. After a baseline period, insulin was infused into the brachial artery to achieve local physiologic hyperinsulinemia (76 +/- 8 microU/ml vs 6.4 +/- 1.6 microU/ml in the basal period, P < 0.01) without affecting systemic hormone and substrate concentrations. Insulin switched forearm amino acid exchange from a net output (-2,630 +/- 1,100 nmol/min per kig of forearm tissue) to a net uptake (1,610 +/- 600 nmol/min per kg, P < 0.01 vs baseline). Phenylalanine and tyrosine balances simultaneously shifted from a net output (-146 +/- 47 and -173 +/- 34 nmol/min per kg, respectively) to a zero balance (16.3 +/- 51 for phenylalanine and 15.5 +/- 14.3 nmol/min per kg for tyrosine, P < 0.01 vs baseline for both), showing that protein synthesis and breakdown were in equilibrium during hyperinsulinemia. Net negative balances of alanine, methionine, glycine, threonine and asparagine (typical substrates for system A amino acid transport) also were decreased by insulin, whereas serine (another substrate for system A transport) shifted from a zero balance to net uptake. Insulin increased k(in) of MeAIB from a basal value of 11.8.10(-2) +/- 1.7.10(-2).min-1 to 13.7.10(-2) +/- 2.2.10(-2).min-1 (P < 0.02 vs the postabsorptive value), whereas kout was unchanged. We conclude that physiologic hyperinsulinemia stimulates the activity of system A amino acid transport in human skeletal muscle, and that this effect may play a role in determining the overall concomitant response of muscle amino acid/protein metabolism to insulin.