Serum levels of osteopontin predict diabetes remission after bariatric surgery

AIM

Bariatric surgery has been shown to effectively improve glycaemic control in morbidly obese subjects. However, the molecular bases of this association are still elusive and may act independently of weight loss. Here, our retrospective study has investigated the inflammatory molecule osteopontin (OPN) as a potential predictor of type 2 diabetes mellitus (T2DM) remission.

METHODS

Baseline serum levels of OPN were analyzed in 41 T2DM patients who underwent bariatric surgery. Anthropometric measures and biochemical variables, including insulin sensitivity indices (HOMA2), were assessed at baseline and at 1 and 3 years after surgery.

RESULTS

At baseline, patients who experienced T2DM remission had increased waist circumference, body weight and BMI, and higher serum OPN, compared with non-remitters. Patients with and without T2DM remission improved their lipid and glucose profiles, although insulin resistance indices were only improved in the T2DM remission group. In the overall cohort of both T2DM remission and non-remission patients, baseline circulating levels of OPN significantly correlated with reductions of body weight and BMI over time, and insulin sensitivity improved as well. However, only the HOMA2-%S remained independently associated with serum OPN on multivariate linear regression analysis (B: 0.227, 95% CI: 0.067-0.387, β = 0.831; P = 0.010). Baseline values of OPN predicted 3-year T2DM remission independently of body weight loss, lower BMI and duration of diabetes (OR: 1.046, 95% CI: 1.004-1.090; P = 0.033).

CONCLUSION

Although larger studies are still needed to confirm our preliminary results, pre-operative OPN serum levels might be useful for predicting 3-year T2DM remission independently of weight loss in patients undergoing bariatric surgery.

High baseline C-reactive protein levels predict partial type 2 diabetes mellitus remission after biliopancreatic diversion

BACKGROUND AND AIMS

Several studies demonstrated that surgery can improve inflammation parameters, such as C-reactive protein (CRP). Few biomarkers have been investigated to potentially predict type 2 diabetes mellitus (T2DM) remission. We aimed at determining whether pre-surgery serum CRP levels could predict T2DM remission after 3 years in patients undergoing bariatric surgery, especially biliopancreatic diversion (BPD).

METHODS AND RESULTS

This study was conducted from 2007 to 2009 at the Surgical Department of the University of Genoa, Italy. Forty-four patients with T2DM undergoing BPD (n = 38) or Roux-en-Y gastric bypass (n = 6) were enrolled. The primary endpoint was to evaluate whether pre-surgery CRP levels could predict T2DM partial remission at 3-year follow-up. Secondary endpoints were to assess whether glycaemic, lipid, and inflammatory parameters modified during the follow-up. At baseline, patients with T2DM ranged from overweight to morbid obesity, had mild dyslipidaemia, and a low-grade inflammation. Bariatric surgery improved body weight, lipid and glycaemic profile both at 1- and 3-year follow-up. Pre-surgery CRP levels progressively decreased at 1- and 3-year follow-up. Among inflammatory pre-surgery parameters, only high CRP levels were shown to predict T2DM partial remission after 3 years. Multivariate analysis confirmed the predictive value of pre-surgery CRP levels independently of age, gender, type of surgery, and body mass index.

CONCLUSION

Bariatric surgery, in particular BPD, improved both metabolic and inflammatory biomarkers at 1- and 3-year follow-up. Pre-surgery high CRP levels predicted 3-year T2DM partial remission, indicating a promising target population to be especially treated with BPD.

Caveolin-1 and polymerase I and transcript release factor: new players in insulin-like growth factor-I receptor signaling

Caveolae are plasma membrane regions enriched in Caveolin proteins which regulate vesicular transport, endocytosis, and cell signaling. IGF-I receptor (IGF-IR) localizes in caveolae and tyrosine phosphorylates Caveolin-1 (Cav-1), the most represented caveolar protein. Cav-1 participates to IGF-IR internalization and signaling directly interacting with IGF-IR and its substrates. Recently, polymerase I and transcript release factor (PTRF) or Cavin-1, has been identified in the caveolar backbone. PTRF does not play a Cav-1 ancillary role and emerging data support a direct role of PTRF in IGF-IR signaling. PTRF and Cav-1 can bind IGF-IR and regulate IGF-IR internalization and plasma membrane replacement, mechanisms frequently deregulated in cancer cells. Although the exact roles of Cav-1 and IGF-IR in human cancer continue to be a matter of some debate, there is a strong evidence for an association between Cav-1 and IGF-IR in cancer development. With the discovery of IGF-IR interaction with PTRF in caveolae, new insight emerged to understand the growing functions of these domains in IGF-I action.

Changes in adiponectin and leptin concentrations during glucocorticoid treatment: a pilot study in patients with polymyalgia rheumatica

This study is concerned with an evaluation of the effects of glucocorticoids (GC) on adiponectin and leptin concentrations in patients with polymyalgia rheumatica (PMR). Seven patients diagnosed with PMR were studied at baseline and after one and three months of prednisone treatment. Serum leptin and adiponectin, serum glucose and insulin, erythrocyte sedimentation rate, C-reactive protein, and IL-6 were all measured by commercial assays. The treatment with GC normalized inflammation markers and significantly increased adiponectin and leptin concentrations without any impairment of insulin sensitivity measured by HOMA-IR. Adiponectin significantly increased only between baseline and 1 month (P= 0.013). A significant correlation was found between adiponectin and leptin concentrations both at baseline and after 3 months of treatment (both rho = 0.89, P= 0.03). In addition, adiponectin correlated also with serum glucose at baseline (rho = 0.81, P= 0.047). According to our results, adiponectin concentrations seem to be driven by inflammation, whereas leptin seems to be increased directly by the use of steroids.

Lower fasting blood glucose, glucose variability and nocturnal hypoglycaemia with glargine vs NPH basal insulin in subjects with Type 1 diabetes

BACKGROUND AND AIMS

To compare switching from NPH insulin (NPH) to insulin glargine (glargine) with continuing NPH for changes in fasting blood glucose (FBG) in patients with Type 1 diabetes on basal-bolus therapy with insulin lispro as bolus insulin. Secondary objectives included self-monitoring blood glucose, mean daily blood glucose (MDBG) and mean amplitude glucose excursion (MAGE) values alongside changes in HbA(1c) and safety profiles.

METHODS AND RESULTS

This was a 30-week, parallel, open-label, multicentre study. Seven-point profiles were used to calculate MDBG and MAGE. Hypoglycaemia and adverse events were recorded by participants. FBG improved significantly with both glargine (baseline-endpoint change: -28.0 mg/dL; 95% CI: -37.3, -18.7 mg/dL; p<0.001) and NPH (-9.8 mg/dL; 95% CI: -19.1, -0.5 mg/dL; p=0.0374). The improvement was significantly greater with glargine than NPH (mean difference: -18.2 mg/dL; 95% CI: -31.3, -5.2 mg/dL; p=0.0064). MDBG (-10.1 mg/dL; 95% CI: -18.1, -2.1 mg/dL; p=0.0126) and MAGE (-20.0 mg/dL; 95% CI: -34.5, -5.9 mg/dL; p=0.0056) decreased significantly with glargine, but not NPH although endpoint values were no different with the two insulins. Baseline to endpoint change in HbA(1c) was similar (-0.56 vs -0.56%) with no differences at endpoint. Overall hypoglycaemia was no different, but glargine reduced nocturnal hypoglycaemia ("serious episodes" with BG < 42 mg/dl, p=0.006) whereas NPH did not (p=0.123), although endpoint values were no different.

CONCLUSION

Switching from NPH to glargine is well tolerated and results into lower FBG, and lower glucose variability while reducing nocturnal hypoglycaemia. These data provide a rationale for more aggressive titration to target with glargine in Type 1 diabetes.

Hypoadiponectinemia in lipodystrophic HIV individuals: a metabolic marker of subclinical cardiac damage

BACKGROUND AND AIM

To evaluate cardiovascular abnormalities in highly active antiretroviral therapy (HAART) treated HIV patients with no signs or symptoms of cardiovascular impairment, and to assess the relative role of multiple concomitant risk factors.

METHODS AND RESULTS

Forty-four consecutive HIV subjects (mean age 41+/-6 yrs) were enrolled. Inclusion criteria were HIV infection, CD4+cell count>150/ml, HAART treatment for at least 4 years. Metabolic serum levels, morphological and functional echocardiographic parameters were assessed in all subjects. Sixteen healthy age and sex matched subjects with no cardiovascular risk factors were recruited as controls. HIV patients showed increased left ventricular mass index with reduced mid-wall fractional shortening (mFS) when compared to controls (50.2+/-10.5 vs. 38.6+/-14.4, p=0.05 and 18.3+/-0.6 vs. 21.9+/-0.7, p<0.05, respectively). Twenty-nine patients were lipodystrophic (LD) and showed a longer HAART period (p=0.0004) and greater use of protease inhibitors (PI) (p=0.001). Coronary flow reserve (CFR) was significantly reduced in HIV patients as compared to controls (p<0.0001), as it was in LD subjects when compared to non-lipodystrophic ones (NLD) (p<0.001). Adiponectin concentrations were found to be significantly lower in LD subjects than in NLD ones (7.8+/-0.8 vs. 13.8+/-1.2 microg/ml, p=0.01), and showed a direct correlation with CFR. In multiple regression analysis, insulin, HDL and adiponectin accounted for 63% of CFR variations.

CONCLUSIONS

Left ventricular hypertrophy, depressed mFS and reduced CFR represent the main signs of subclinical cardiac damage in HIV subjects treated with HAART. Hypoadiponectinemia in these subjects seems to be a metabolic risk factor of cardiovascular impairment.

Alterations in the autonomic control of heart rate variability in patients with anorexia or bulimia nervosa: correlations between sympathovagal activity, clinical features, and leptin levels

Changes in body composition, hormone secretions, and heart function with increased risk of sudden death occur in eating disorders. In this observational clinical study, we evaluated sympathovagal modulation of heart rate variability (HRV) and cardiovascular changes in response to lying-to-standing in patients with anorexia (AN) or bulimia nervosa (BN) to analyze: a) differences in autonomic activity between AN, BN, and healthy subjects; b) relationships between autonomic and cardiovascular parameters, clinical data and leptin levels in patients with eating disorders. HRV, assessed by power spectral analysis of R-R intervals, blood pressure (BP) and heart rate (HR) were studied by tilt-table test in 34 patients with AN, 16 with BN and 30 healthy controls. Autonomic and cardiovascular findings were correlated with clinical data, and serum leptin levels. Leptin levels were lowered in AN vs BN and healthy subjects (p<0.0001), but both AN and BN patients showed unbalanced sympathovagal control of HRV due to relative sympathetic failure, prevalent vagal activity, impaired sympathetic activation after tilting, independently from their actual body weight and leptin levels. No significant correlations were obtained between HRV data vs clinical data, BP and HR findings, and leptin levels in eating disorders. Body mass indices (BMI) (p<0.02), and leptin levels (p<0.04) correlated directly with BP values. Our data showed alterations of sympathovagal control of HRV in eating disorders. These changes were unrelated to body weight and BMI, diagnosis of AN or BN, and leptin levels despite the reported effects of leptin on the sympathetic activity.

Reduction of cardiovascular morbidity and mortality in type 2 diabetes. A rational approach to hypoglycemic therapy

Type 2 diabetes mellitus is the single most important risk factor for the development of coronary artery disease. Unfortunately, the traditional therapeutic strategies for the treatment of hyperglycemia have proven to be ineffective in preventing cardiovascular complications. In recent years the number of available hypoglycemic agents has increased and considerable progress has been made regarding the comprehension of the pathophysiology of diabetes and its vascular complications. In the present article we firstly present benefits and risks of intensive vs standard hypoglycemic intervention, and the pros and cons of therapy targeted to postprandial hyperglycemia. Secondly, we discuss the cardiovascular effects of sulfonylurea agents and insulin, focusing on the role of intensive insulin treatment in the context of acute coronary syndromes. Thirdly, we review the epidemiological, clinical and experimental evidence linking insulin resistance and cardiovascular disease. Finally, we present the rationale and the role of metformin and thiazolidinedionetherapy in the prevention of cardiovascular complications. We conclude that the optimal use of the full spectrum of hypoglycemic agents has the potential to play a key role in the prevention of diabetes-related macrovascular complications.

Long-term normalization of insulin sensitivity following biliopancreatic diversion for obesity

OBJECTIVE

Assess insulin sensitivity and metabolic status of obese patients with stable weight loss at long term following biliopancreatic diversion (BPD).

MATERIAL AND METHODS

The study was carried out in 36 nondiabetic severely obese patients undergoing BPD. Serum concentration of glucose, insulin and leptin were determined prior to and at 2 y following the operation. Insulin sensitivity was calculated according to the homeostatic model assessment (HOMA IR).

RESULTS

At 2 y following BPD, weight loss in all subjects corresponded to a marked drop in serum leptin concentration and improvement of insulin sensitivity within physiological range. Following the operation, HOMA IR values were positively correlated with serum leptin concentration independently of body mass index values.

DISCUSSION

The stable weight loss following BPD at long term is accompanied by a complete reversal of the preoperative insulin resistance. Serum leptin concentration and HOMA IR data were positively related only postoperatively, suggesting that the action of factors that could influence the relation between leptin and insulin action in the obese status can be reverted.

The extracellular portion of the insulin receptor beta-subunit regulates the cellular trafficking of the insulin-insulin receptor complex. Studies on Chinese hamster ovary cells carrying the Cys 860-->Ser insulin receptor mutation

OBJECTIVE

Chinese hamster ovary (CHO) cells transfected with human engineered insulin receptor (IR) cDNA to mutate Cys 860 to Ser (CHO-IR(C860S)) showed a defective insulin internalization without affecting insulin binding and IR autophosphorylation. Moreover, this mutation reduces insulin receptor substrate (IRS)-1 tyrosine phosphorylation and insulin-induced metabolic and mitogenic effects. Altogether, these observations support a role of the extracellular domain of IR beta-subunit in insulin and receptor intracellular targeting as well as in insulin signaling.

DESIGN AND METHODS

This study assesses in more details the effect of IR(C860S) mutation on the trafficking of the insulin-IR complex. In particular, IR internalization, phosphorylation, dissociation and recycling, as well as insulin degradation and retroendocytosis have been investigated in CHO cells overexpressing either wild type (CHO-IR(WT)) or mutated IRs.

RESULTS

the C860S mutation significantly decreases IR internalization both insulin stimulated and constitutive. In spite of a similar dissociation of internalized insulin-IR complex, recycling of internalized IR was significantly faster (half life (t(1/2)): 21 min vs 40 min, P<0.001) and more extensive (P<0.01) for IR(C860S) than for IR(WT). On the other hand, insulin degradation and retroendocytosis were superimposable in both cell lines. As expected, insulin-induced phosphorylation was similar in both IRs, however dephosphorylation was much more rapid and was greater (P<0.01) in CHO-IR(WT) as compared with CHO-IR(C860S) cells.

CONCLUSIONS

Transmembrane and intracellular domain of IR seem to be determinants for IR internalization. Now we report that Cys 860 in the IR beta-subunit ectodomain may be of relevance in ensuring a proper internalization and intracellular trafficking of the insulin-IR complex.

Phenotypic expression of familial hypobetalipoproteinemia in three kindreds with mutations of apolipoprotein B gene

We report the clinical phenotype in three kindreds with familial heterozygous hypobetalipoproteinemia (FHBL) carrying novel truncated apolipoprotein Bs (apoBs) of different sizes (apoB-8.15, apoB-33.4 and apoB-75.7). In D.A. kindred, we found three carriers of a C-deletion in exon 10 leading to the synthesis of apoB-8.15 not detectable in plasma. They showed steatorrhea and fatty liver. In N.L. kindred, the proband is heterozygous for a nonsense mutation in exon 26, leading to the formation of apoB-33.4. He had premature cerebrovascular disease and fatty liver; two apoB-33.4 carriers in this kindred showed only fatty liver. In B.E. kindred, the proband is heterozygous for a T-deletion in exon 26, which converts tyrosine at codon 3435 into a stop codon, resulting in apoB-75.7. The proband, a heavy alcohol drinker, had steatohepatitis, whereas his teetotaller daughter, an apoB-75.7 carrier, had no detectable fatty liver. This study suggests that: i) fatty liver invariably develops in FHBL carriers of short and medium-size truncated apoBs (< apoB-48), but its occurrence needs additional environmental factors in carriers of longer apoB forms; ii) intestinal lipid malabsorption develops only in carriers of short truncated apoBs, which are not secreted into the plasma; and iii) cerebrovascular disease due to premature atherosclerosis may occur even in FHBL subjects.

Sulfonylurea treatment of type 2 diabetic patients does not reduce the vasodilator response to ischemia

OBJECTIVE

Sulfonylureas block the activation of vascular potassium-dependent ATP channels and impair the vasodilating response to ischcmia in nondiabetic individuals, but it is not know whether this occurs in type 2 diabetic patients under chronic treatment with these drugs. Glimepiride, a new sulfonylurea, apparently has no cardiovascular interactions. The aim of our study was to compare the effect of the widely used compound glibenclamide, the pancreas-specific glimepiride, and diet treatment alone on brachial artery response to acute forearm ischemia.

RESEARCH DESIGN AND METHODS

Brachial artery examination was performed by a high-resolution ultrasound technique on 20 type 2 diabetic patients aged mean +/- SD) 67 +/- 2 years and on 18 nondiabetic patients matched for age, hypertension, and dislipidemia. Diabetic subjects underwent three separate evaluations at the end of each 8-week treatment period, during which they received glibenclamide, glimepiride, or diet alone according to crossover design. Scans were obtained before and after 4.5 min of forearm ischemia. Postischemic vasodilation and hyperemia were expressed as percent variations in vessel diameter and blood flow.

RESULTS

Postischemic vasodilation and hyperemia were, respectively, 5.42 +/- 0.90 and 331 +/- 38% during glibenclamide, 5.46 +/- 0.69 and 326 +/- 28% during glimepiride, and 5.17 +/- 0.64 and 357 +/- 35% during diet treatment (NS). These results were similar to those found in the nondiabetic patients (6.44 +/- 0.68 and 406 +/- 42%, NS).

CONCLUSIONS

In type 2 diabetic patients, the vasodilating response to forearm ischemia was the same whether patients were treated with diet treatment alone or with glibenclamide or glimepiride at blood glucose-lowering equipotent closes.

Cys 786 and Cys 776 in the posttranslational processing of the insulin and IGF-I receptors

The extracellular regions of insulin and IGF-I receptors (IR and IGF-IR) contain fibronectin type III repeats with cysteine residues potentially involved in S==S bond. In this report we show that Cys 786 in the IR and the corresponding Cys 776 in the IGF-IR regulate proreceptor dimerization with high specificity. Both C786S insulin and C776S IGF-I proreceptors reach the monomeric 210-kDa step, but do not proceed further. Mature IR(C786S) and IGF-IR(C776S) expression on plasmamembrane is abolished. No retention of C786S IR precursor was detected in the endoplasmic reticulum, which is degraded by a nonlysosomal mechanism. The rearrangement of the remaining cysteines in the insulin receptor beta subunit ectodomain does not rescue dimerization of C786S insulin proreceptor. As observed in other transmembrane receptors, iuxtamembrane cysteines, specifically Cys 786 in the IR and Cys 776 in the IGF-IR, are critical for correct processing of proreceptors.

Three novel missense mutations in the glucokinase gene (G80S; E221K; G227C) in Italian subjects with maturity-onset diabetes of the young (MODY). Mutations in brief no. 162. Online

The maturity-onset diabetes of the young (MODY), an autosomal dominant form of non-insulin dependent diabetes mellitus (NIDDM), is caused by mutations in the glucokinase (GK, MODY 2) and in the hepatocyte nuclear factor 1a (MODY 3) and 4a (MODY 1) genes. We have screened the glucokinase gene by the polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) in fifteen subjects with clinical characteristics of MODY and one parent with NIDDM, impaired glucose tolerance or gestational diabetes. PCR products with abnormal mobility in DGGE were directly sequenced. We have identified four mutant alleles, three of them (G80S, E221K, G227C) are new missense mutations located in or near the region of the active site cleft of the enzyme. The mutations co-segregate with hyperglycemia in the families of the three probands, whose biochemical and clinical phenotype is similar to other individuals with MODY 2 mutations.

Serum leptin concentrations during the menstrual cycle in normal-weight women: effects of an oral triphasic estrogen-progestin medication

OBJECTIVE

To investigate in normal-weight premenopausal women the relationship between circulating leptin and serum gonadotropins and gonadal steroids, during both spontaneous and pharmacologically induced menstrual cycles.

DESIGN

Clinical longitudinal study.

METHODS

Two groups of age-matched, normal-weight premenopausal volunteer women (groups I and II) were enrolled in this study. Women in group I were free of any hormonal treatment, while women in group II were taking a triphasic estrogen--progestin contraceptive preparation. Blood samples were collected daily in both groups after an overnight fast throughout a complete menstrual cycle.

RESULTS

In the spontaneously cycling women, serum leptin concentration positively correlated with estradiol (P<0.03) and progesterone (P<0. 05) and was higher in the luteal than in the follicular phase (P<0. 05). However, a significant (P<0.03) short-lasting increase in circulating leptin was present in the late follicular phase of all subjects. In the women using hormonal contraception serum leptin remained unchanged throughout the cycle, along with constantly low values of circulating luteinizing hormone and follicle-stimulating hormone.

CONCLUSIONS

In normal-weight premenopausal women serum leptin concentrations differ during the menstrual cycle in line with changes in gonadotropin and gonadal steroid concentrations, increasing in the luteal phase of the cycle after a peri-ovulatory peak. These findings suggest a permissive role for leptin with regard to the functioning of the corpus luteum.

Evaluation of growth hormone administration in patients with chronic heart failure secondary to coronary artery disease

We have examined the effects of 6 months of treatment with growth hormone (GH) (0.02 U/kg/day) in 10 patients with chronic postischemic cardiac failure. Ten patients matched for age, body mass index, functional class, and ejection fraction served as a control group. In the GH group, 1 patient died and 2 were withdrawn from the study because of arrhythmia or worsening of heart failure. In the control group, 1 patient died and 1 patient was withdrawn from the study because of progressive heart failure. Among GH patients, those with an unfavorable outcome had a greater left ventricular end-diastolic diameter (79, 82, and 88 mm) on entry to the study than patients without adverse events (range 62 to 72 mm). At the end of the study, the seven GH patients reported a feeling of well-being and had a significant increase in their exercise test duration (462 +/- 121 vs 591 +/- 105 seconds, p <0.05). Low baseline insulin-like growth factor-I values were increased with GH treatment (189 +/- 52 vs 100 +/- 22 ng/ml, p <0.01). GH did not change left ventricular diameters or wall thickness. A trend toward decreased serum triglyceride levels and adipose body tissue associated with an increase in high-density lipoproteins was observed in the GH group. In conclusion, our present data support previous suggestions that GH treatment exerts some beneficial effects in patients with chronic, stabilized, moderately severe heart failure, but may have deleterious effects in patients with more severe heart failure.

Effects of dietary restriction on serum leptin concentration in obese women

OBJECTIVE

To investigate the short- and long-term effects of dietary restriction on serum leptin in obese women and the role of the gastrointestinal system in the short-term regulation of leptin production.

DESIGN

Clinical longitudinal study of anthropometric and serum leptin changes induced in obese women by a balanced 300 kcal/d very low calorie diet (VLCD), administered either orally or parenterally for 5 d, and by a balanced 900 kcal/d low calorie diet (LCD) lasting six months.

SUBJECTS

20 obese women (age: 38.1 +/- 12.7 y; body mass index (BMI): 40.2 +/- 8.3 kg/m2).

RESULTS

Five days following VLCD, a modest, even if significant (P < 0.0001), fall of both body weight (BW) and BMI was observed, along with a dramatic (> 50%) highly significant (P < 0.0001) reduction of circulating serum leptin. Baseline and five-day anthropometric and biochemical findings were closely similar in the group of orally fed subjects, when compared with those of their parenterally fed counterparts. The baseline positive correlation between serum leptin and BMI (p = 0.533) increased (P < 0.05) at the end of the five day VLCD (p = 0.849). A further fall of BW and BMI was observed at day 30 (P < 0.001) and day 180 (P < 0.01) during the 900 kcal/d LCD, while the serum leptin concentration gradually increased until day 180 when it was only slightly but non significantly lower than at baseline. At the end of the study, the correlation between serum leptin and BMI was similar to the baseline (p = 0.562).

CONCLUSIONS

Energy restriction causes a fall of serum leptin apparently not mediated by gastrointestinal signals and it seems not to affect the long-term regulatory pathways of circulating leptin.

Role of proline 193 in the insulin receptor post-translational processing

AIMS/HYPOTHESIS

A point mutation, P193L, in the insulin receptor alpha subunit, has been previously identified in a patient affected by an extreme form of insulin resistance due to reduced insulin binding. In our study we investigated the cellular mechanisms by which P193L substitution causes a reduction of insulin receptor numbers on the cell surface.

METHODS

Mutated insulin receptors have been generated and expressed in COS1 cells. Transcription as well as translation of P193L insulin receptor have been measured and compared with wild type insulin receptor.

RESULTS

P193L insulin receptor is normally transcribed and progresses to the step of insulin proreceptor, which does not proceed to dimerization, resulting in the accumulation of the 210 kDa form. These findings suggest that the P193L insulin proreceptor is retained in the endoplasmic reticulum, where several molecular chaperones drive the folding of protein precursors. Therefore the interaction between mutated insulin receptor precursor and two endoplasmic reticulum resident chaperones (GRP78 and calnexin) were investigated. P193L insulin proreceptor co-immunoprecipitates with greater amounts of GRP78 and its interaction with calnexin is greatly delayed compared with wild type insulin receptor precursor. Co-transfection of wild type and mutated insulin receptors causes a considerable reduction of cell surface wild type insulin receptors.

CONCLUSION/INTERPRETATION

P193 is critical for insulin proreceptor folding. The monomeric form of P193L insulin proreceptor is retained in the endoplasmic reticulum by a calnexin and GRP78 mediated mechanism that reduces mature insulin receptor expression on the cell surface.

Role of IRS-1 and SHC activation in 3T3-L1 fibroblasts differentiation

The early steps of 3T3-L1 fibroblasts differentiation to adipocytes are characterized by a proliferation phase, termed clonal expansion, that ends after the first 48 h of exposure of confluent cells to high doses of insulin, dexamethasone, 3-methyl-isobutylxanthine and FCS (differentiation mix). Since insulin is a key hormone for adipocyte conversion, and IRS-1 (insulin receptor substrate -1) and Shc (Src homology collagen)-proximal intracellular substrates of the insulin receptor-control cell proliferation, the aim of this study was to investigate the role of IRS-1 and Shc in the early steps of differentiation. At the end of clonal expansion, 48 h after induction of differentiation with differentiation mix, p66 Shc phosphorylation and IRS-1 amounts were reduced in those cells committed to fully differentiate. Conversely, in cells treated with insulin alone or dexamethasone alone (unable to be differentiated), p66 Shc and IRS-1 activities were maintained unaltered, compared to basal values. These observations suggest that the modifications of p66 Shc and IRS-1 in the first 48 h of 3T3-L1 conversion into adipocytes could play a role on this process, or alternatively they could represent an early cellular marker of differentiation.

Serum leptin and weight loss in severely obese patients undergoing biliopancreatic diversion

OBJECTIVE

To evaluate the influence of body fat and food intake on serum leptin concentration.

DESIGN

Longitudinal study of a group of obese patients prior to and at, long term follow-up, after biliopancreatic diversion (BPD), when body weight was steadily reduced and food consumption was similar to or greater than preoperatively.

RESULTS

In obese patients, very high serum leptin concentrations were found. Following the operation, with the body weight stable and normalized, a sharp fall of serum leptin concentration had occurred, with values returned to normal range.

CONCLUSION

The changes in serum leptin concentration observed in the long term after weight loss are substantially accounted for by the loss of body fat and appear unrelated to the reduction of oral food intake.

Cys860 in the extracellular domain of insulin receptor beta-subunit is critical for internalization and signal transduction

The C860S mutation (IRC860S) in the extracellular domain of the insulin receptor beta-subunit has previously been shown to result in an inhibition of insulin receptor internalization. The present work aims at further dissecting the consequences of this mutation not only on insulin receptor internalization, but also on the signaling of the receptor. Following transfection of Chinese hamster ovary (CHO) cells with insulin receptors with the C860S mutation (CHO-IRC860S) and quantitative electron microscopic analysis of [125I]insulin localization in these cells, the inhibition of receptor internalization appears to be due to an inhibition of the lateral translocation of the receptor from microvilli to nonvillous domains of the cell surface. At 37 C, insulin-stimulated insulin receptor substrate-1 (IRS-1) phosphorylation is inhibited by 50% in CHO-IRC860S, whereas Shc phosphorylation remains unaffected. The inhibition of IRS-1 phosphorylation is still present when experiments are conducted at 4 C, a temperature at which insulin receptor internalization is prevented, suggesting that the defect in IRS-1 phosphorylation is not due to the reduced internalization of the receptor. In terms of biological effects, the mutation has negative consequences on insulin-stimulated c-fos expression and DNA synthesis as well as on glycogen synthase activity. Eventually, the events observed are specific for Cys860, as individual substitution of the two more proximal Cys residues (795 and 872) to Ser is not accompanied by any change in either insulin-induced insulin receptor internalization or IRS-1 phosphorylation. Thus, the present analysis of CHO-IRC860S 1) reveals that insulin receptor surface redistribution is not solely dependent on receptor autophosphorylation, 2) emphasizes that IRS-1 phosphorylation is not dependent on receptor internalization and can be triggered from microvilli, and 3) stresses divergent aspects between two of the major signaling pathways of the insulin receptor.

Toxic thyroid adenoma: absence of DNA mutations of the TSH receptor and Gs alpha

DNA point mutations of the TSH receptor and of the alpha subunit of the stimulatory GTP-binding protein (Gs alpha) have been suggested as major causes of hyperfunctioning thyroid adenomas. However, significant differences in the prevalence of these mutations (from 0.3 to 84%) have been found in different populations. The present study was designed to evaluate further the presence of mutations in discrete fragments of cDNA encoding critical regions of the TSH receptor and of the Gs alpha involved in signal transduction and cAMP production. Genomic DNA extracted from 15 thyroid adenomas and surrounding quiescent thyroid tissues was used as a template to amplify four DNA fragments of TSH receptor and one DNA fragment of Gs alpha. TSH receptor and Gs alpha DNAs were analyzed by a number of techniques. We did not detect any mutations (new or previously described) in our patients. These results confirm that the causes of solitary toxic adenomas are protean, and only some of them may be somatic DNA point mutations. Since the clinical features of solitary toxic adenoma are homogeneous, it could be important to establish the specific molecular defect underlying each case, in order to follow up the patients and to assess their clinical evolution.

The human skeletal muscle glycogenin gene: cDNA, tissue expression and chromosomal localization

Glycogen synthesis is impaired in first degree relatives of subjects with non-insulin-dependent diabetes mellitus and genes relevant to this metabolic pathway are considered reasonable candidates in the pathogenesis of the disease. In skeletal muscle the de novo synthesis of glycogen in primed by an enzyme named glycogenin. We have cloned the glycogenin cDNA from human skeletal muscle mRNA: human glucogenin is a 333 amino acid protein exhibiting 93% identity with rabbit glycogenin. A single transcript of about 2.4 kb, prominent in skeletal muscle, was detected by Northern blot analysis. In situ hybridization unequivocally located the human glycogenin gene to chromosome 3q25.1. Furthermore, we mapped two intronless glycogenin-related sequences to human chromosomes 12 and 13.

Insulin-like growth factor-I and angiographically documented coronary artery disease

In conclusion, we have reported an association between low IGF-I concentrations and CAD in relatively young men. This observation raises the possibility that IGF-I deficiency could be part of the polymetabolic syndrome. Whether a subnormal IGF-I production is due to growth hormone secretory abnormalities or to other metabolic reasons (e.g., insulin resistance or fat distribution, or both) is still unknown.

A ser for Cys mutation in the extracellular portion of insulin receptor beta subunit impairs the insulin-insulin receptor complex internalization in CHO cells

We investigated the effects of a ser for cys 860 mutation, located in the extracellular portion of insulin receptor beta subunit, on several receptor functions. CHO cells, stably transfected with the mutated cDNA, were used for this study. In the present paper, we show that the ser 860 mutation does not affect the 125I-insulin binding, but severely impairs the insulin-insulin receptor complex internalization. The kinetic analysis of internalization indicates that this process is inhibited at steps preceding the coated pit endocytosis. The beta subunit autophosphorylation of the mutated receptor is higher both in the basal and insulin stimulated states, compared with autophosphorylation measured in wild type insulin receptors. The ser 860 mutation impairs also the insulin receptor down regulation, thus suggesting an effect on the intracellular sorting of insulin-insulin receptor complex. On the basis of these results we suggest that the cys 860 plays an important role in insulin receptor lateral moving on cell surface, after insulin binding, and on the intracellular sorting to degradation pathways.

[Hyperinsulinemia and cardiovascular risk]

A large body of evidence has been accumulating that insulin plays a role in coronary heart disease (CHD). Hyperinsulinemia has been considered a risk factor for CHD according to prospective studies. Cross-sectional studies found an association between hyperinsulinemia and prevalence of CHD, while population studies have shown that populations at increased risk for CHD are hyperinsulinemic. Strong relations between hyperinsulinemia and atherosclerotic coronary lesions have been demonstrated by angiographic studies. It has recently been observed that also patients with microvascular angina are hyperinsulinemic. Several mechanisms have been proposed to explain the role of hyperinsulinemia in the development of atherothrombosis. Hyperinsulinemia is the consequence of insulin resistance, a defect in insulin-mediated glucose uptake. Experimental evidence suggests that insulin has actions that may promote atherosclerosis, which clinical studies suggest the existence of a metabolic syndrome characterized by the presence of major coronary risk factors in which insulin resistance is the common link.

The overexpression of insulin receptor makes CHO cells resistant to the action of IGF-1: role of IRS-1

We investigated the influence of the relative abundance of insulin and IGF-1 receptors on cellular growth, by measuring the stimulation of c-fos expression and of H3-thymidine incorporation into DNA by insulin and IGF-1 in CHO cells overexpressing insulin Receptor (CHO-IR). We found that CHO-IR cells were resistant to the action of IGF-1, but were more responsive to insulin, compared to parental clone. This result suggest the presence of a limiting step, distal to the IGF-1 receptor, in the transduction pathway. To address this question we measured the IGF-1 effect on c-fos expression in CHO-IR cells, transiently transfected with the cDNA for IRS-1, the common intracellular substrate for both insulin and IGF-1 receptors (CHO-IR/IRS-1 cells). In these cells IGF-1 stimulated a 10 fold higher c-fos expression compared to CHO-IR cells. These results suggest that the abundance of IRS-1, relative to the number of insulin and IGF-1 receptors, represents a limiting step for the intracellular transduction of insulin and IGF-1 biological messages.

Linkage analysis does not support a role for glucokinase gene in the aetiology of type 2 diabetes mellitus among north western Italians

The contribution of a 3' glucokinase gene polymorphism to the aetiology of type 2 diabetes mellitus was studied in 17 diabetic pedigrees from North-Western Italy; linkage methodology was used. A CA repeat sequence was employed as a marker and amplified by PCR. Three alleles were found: Z (195 bp), Z + 4 (199 bp) and Z + 10 (205 bp). Since in diabetic families linkage analysis gave values of LOD score between -0.000438 and 0.026, the association between GK polymorphism and type 2 diabetes could not be either excluded or accepted. Based on these data, we conclude that glucokinase polymorphism is not a major determinant of type 2 diabetes mellitus, at least in our population, but, consistent with LOD score obtained, in some pedigrees it could assume a minor role in the aetiology of this disease.

Substitution of Leu for Pro-193 in the insulin receptor in a patient with a genetic form of severe insulin resistance

Mutations have been identified in the insulin receptor (IR) gene in patients who are insensitive to insulin action. We studied an extremely insulin resistant patient whose insulin binding to Epstein-Barr virus (EBV) transformed lymphocytes was severely reduced. Transmembrane signalling, evaluated as insulin receptor autophosphorylation, was normal. The patient's IR was immunoprecipitated normally by AbP6, a polyclonal antibody directed to the beta subunit. However, there was an approximately 50% decrease in the affinity of IR immunoprecipitation by a monoclonal antibody (MA-10) directed against the alpha subunit. These observations suggested that there were likely to be a mutation in the patient's insulin receptor that caused misfolding of the IR alpha subunit. Analysis of gene structure by Southern blotting experiments did not reveal any major deletion in the IR gene of the proband. Northern blot analysis showed a normal level of expression of IR gene. We applied denaturing gradient gel electrophoresis (DGGE) as well as direct sequence analysis to study the 22 exons of IR gene amplified by polymerase chain reaction (PCR) using the proband's genomic DNA as a template. We identified a new missense mutation substituting leucine (CTG) for proline (CCG) in homozygous state at codon 193 in exon 3. Both parents are heterozygous for the Leu193 mutation. The Leu193 mutation was not detected in any of 75 normal subjects (150 chromosomes), indicating that it is not a common sequence variant of the insulin receptor. In addition, during the course of screening the patient's DNA with perpendicular DGGE, we identified two previously unreported silent substitutions in exon 9.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional cerebral blood flow and cerebrovascular reactivity in IDDM

OBJECTIVE

To investigate both rCBF and cerebrovascular reactivity, evaluated as pre- and post-ACZ rCBF differences in a group of IDDM patients with differences in duration of disease and severity of complications.

RESEARCH DESIGN AND METHODS

rCBF was measured by the 133Xenon inhalation method in 20 IDDM patients and in 15 healthy control subjects before and after an intravenous injection of ACZ, a carbonic anhydrase inhibitor commonly used to assess cerebrovascular reactivity.

RESULTS

Basal global CBF (the mean of 32 regional values) was within the normal range in all patients but 1, who showed slight hyperperfusion; moreover, in 3 patients with long-lasting disease, some hypoperfused regions were found. ANOVA showed an inverse correlation between basal global CBF (P < 0.01) and duration of diabetes, but no correlation with Hb, MABP, serum glucose concentration, or GHb. Compared with control subjects, the percentage of global CBF increment after ACZ administration was significantly impaired in 4 patients and gave a borderline response in 2 patients; 4 of these poor ACZ responders had retinopathy, and 1 had suffered from a TIA. Duration of diabetes, Hb, MABP, serum glucose concentration, and GHb did not correlate with the percentage of post-ACZ global CBF changes, and did not differ among the 6 poor ACZ responders and the other diabetic patients or control subjects.

CONCLUSIONS

These results confirm that global CBF is within the normal range in most IDDM patients, although it is significantly influenced by the duration of diabetes; pathophysiological correlates of the altered cerebrovascular reactivity need to be further investigated. rCBF measurements, before and after ACZ administration, seem to represent a safe and reliable tool for assessing cerebrovascular function in IDDM.

Effect of in vivo vanadate treatment on insulin receptor tyrosine kinase activity in partially pancreatectomized diabetic rats

Liver-purified insulin receptor tyrosine kinase (IRTK) activity was examined in partially pancreatectomized rats following normalization of blood glucose concentration by either phlorizin or vanadate treatment. Chronic moderate hyperglycemia did not modify the IRTK activity, despite the presence of in vivo and in vitro insulin resistance. Oral vanadate administration for 3 weeks normalized glucose tolerance and caused a 2.5-fold increase in basal IRTK activity. In contrast, correction of hyperglycemia with phlorizin, an inhibitor of renal glucose reabsorption, did not change the IRTK activity, although glucose tolerance was returned to normal. The vanadate-induced effect on basal IRTK was due to an increase in Vmax of the enzyme; the Km remained unchanged. The insulin-stimulated IRTK activity was not affected by either vanadate or phlorizin treatment. These results suggest that: 1) partial (90%) pancreatectomy in rats causes insulin resistance in the absence of in vitro alterations in IRTK and 2) correction of chronic hyperglycemia with vanadate, but not with phlorizin, is associated with an increased basal activation of the protein tyrosine kinase in liver insulin receptors.

Effect of metformin treatment on insulin action in diabetic rats: in vivo and in vitro correlations

The mechanism (both at the whole body and cellular level) by which metformin improves insulin sensitivity has yet to be defined. In the present study, we examined in vivo insulin-mediated whole-body glucose disposal, glycogen synthesis, hepatic glucose production, and insulin secretion, as well as in vitro muscle insulin receptor tyrosine kinase activity in eight control, eight neonatal streptozotocin diabetic rats, and eight diabetic rats before and after treatment with metformin. Ten weeks after birth diabetic rats had higher fasting (132 + 5 v 101 + 2 mg/dL) and postmeal (231 + 10 v 133 + 3) plasma glucose levels compared with controls (P less than .001). Metformin treatment was followed by a significant decrease in the growth rate and normalized glucose tolerance without enhancing the deficient insulin response. Insulin-mediated glucose uptake in diabetic versus control rats was reduced (P less than .01) during the high-dose (15.4 + 0.6 v 18.3 + 1.0 mg/kg.min) insulin clamp study and was increased to values greater (P less than .05) than controls following metformin treatment. Muscle glycogen synthetic rate in vivo, measured by incorporation of 3H-3-glucose radioactivity, was diminished by 25% (P less than .01) in diabetic rats, restored to normal values with metformin, and correlated closely (r = .82, P less than .002) with total-body glucose uptake during the insulin clamp in all three groups. Insulin receptor tyrosine kinase activity, measured in partially purified insulin receptors, was reduced in diabetic rats and increased to supernormal levels after metformin. The decrease in muscle tyrosine kinase activity in diabetic versus control animals was entirely accounted for by a reduction in maximal velocity (Vmax) (32 v 45 pmol/mg.min, P less than .01) and increased to supernormal levels following metformin (91 pmol/mg.min, P less than .001) without any change in affinity (Km). Muscle tyrosine kinase activity was closely correlated with both the muscle glycogen synthetic rate (r = .82, P less than .002) and total-body insulin-mediated glucose disposal (r = .64, P less than .01) in vivo. The close correlation between in vivo insulin action, muscle glycogen synthesis, and muscle insulin receptor tyrosine kinase activity is consistent with an important role of the enzyme in the insulin resistance of diabetes and its improvement following metformin treatment.

Antipeptide antibodies toward the extracellular domain of insulin receptor beta-subunit

In order to investigate structure and function of beta-subunit extracellular portion, four polyclonal antibodies (AP1, AP2, AP3 and AP4) toward peptides comprised in this region were generated. None of them recognizes native human and rat insulin receptor both in vitro and in whole cells. Two antibodies, AP1 and AP2, immunoprecipitate isolated (DTT-reduced) human beta-subunits and bind to human IM-9 cell after alpha-subunit tryptic cleavage. Only AP1 recognizes rat beta-subunit both in vitro and in trypsin treated rat FAD cells. These findings suggest that: (i) the extracellular portion of the insulin receptor beta-subunit is partially covered by the alpha-subunit in human and rat native insulin receptors; (ii) human and rat beta-subunit extracellular domains are different, at least in the amino acid sequence corresponding to residues 785-796 of the human insulin receptor.

An extracellular domain of the insulin receptor beta-subunit with regulatory function on protein-tyrosine kinase

Anti-insulin receptor monoclonal antibody MA-10 inhibits insulin receptor autophosphorylation of purified rat liver insulin receptors without affecting insulin binding (Cordera, R., Andraghetti, G., Gherzi, R., Adezati, L., Montemurro, A., Lauro, R., Goldfine, I. D., and De Pirro, R. (1987) Endocrinology 121, 2007-2010). The effect of MA-10 on insulin receptor autophosphorylation and on two insulin actions (thymidine incorporation into DNA and receptor down-regulation) was investigated in rat hepatoma Fao cells. MA-10 inhibits insulin-stimulated receptor autophosphorylation, thymidine incorporation into DNA, and insulin-induced receptor down-regulation without affecting insulin receptor binding. We show that MA-10 binds to a site of rat insulin receptors different from the insulin binding site in intact Fao cells. Insulin does not inhibit MA-10 binding, and MA-10 does not inhibit insulin binding to rat Fao cells. Moreover, MA-10 binding to down-regulated cells is reduced to the same extent as insulin binding. In rat insulin receptors the MA-10 binding site has been tentatively localized in the extracellular part of the insulin receptor beta-subunit based on the following evidence: (i) MA-10 binds to insulin receptor in intact rat cells; (ii) MA-10 immunoprecipitates isolated insulin receptor beta-subunits labeled with both [35S]methionine and 32P; (iii) MA-10 reacts with rat insulin receptor beta-subunits by the method of immunoblotting, similar to an antipeptide antibody directed against the carboxyl terminus of the insulin receptor beta-subunit. Moreover, MA-10 inhibits autophosphorylation and protein-tyrosine kinase activity of reduced and purified insulin receptor beta-subunits. The finding that MA-10 inhibits insulin-stimulated receptor autophosphorylation and reduces insulin-stimulated thymidine incorporation into DNA and receptor down-regulation suggests that the extracellular part of the insulin receptor beta-subunit plays a role in the regulation of insulin receptor protein-tyrosine kinase activity.

Effect of two different glucose concentrations on insulin receptor mRNA levels in human hepatoma HepG2 cells

Glucose is known to affect mRNA levels of several genes. In order to investigate possible effects of glucose on insulin receptor mRNA levels, we cultured human hepatoma cells (HepG2) in two different culture media: DMEM containing 100 mg/dl glucose and DMEM containing 450 mg/dl glucose. Insulin receptor mRNA levels and insulin binding activity were reduced in HepG2 cultured at lower glucose concentrations. These data suggest that glucose affects insulin receptor gene expression.

Direct modulation of insulin receptor protein tyrosine kinase by vanadate and anti-insulin receptor monoclonal antibodies

Sodium vanadate activates "in vitro" insulin receptor autophosphorylation and protein tyrosine kinase in a dose-dependent manner. Insulin receptor protein tyrosine kinase is directly activated also by the anti-insulin receptor beta subunit monoclonal antibody 18-44. We previously demonstrated that the anti-insulin receptor monoclonal antibody MA-10 decreases insulin-stimulated receptor protein tyrosine kinase activity "in vitro", without inhibiting insulin receptor binding. In this report we show that insulin receptor protein tyrosine kinase, activated by sodium vanadate or by monoclonal antibody 18-44, is inhibited by MA-10 antibody. These data suggest that insulin receptor protein tyrosine kinase activity can be either activated and inhibited through mechanisms different from insulin binding.

Species specificity of insulin binding and insulin receptor protein tyrosine kinase activity

The effect of monoclonal anti-insulin receptor antibody MA 10 on [125I]insulin binding and on insulin receptor protein tyrosine kinase activity was investigated in human and rat tissues. It was observed that MA 10 inhibits insulin binding to human, but not rat, tissues while inhibiting insulin-stimulated receptor autophosphorylation and protein tyrosine kinase activity in both human and rat tissues. These data suggest that MA 10 is directed against a region of the insulin receptor that is in between the insulin-binding domain and the beta-subunit and that in human, but not rat, tissues, this region is involved in insulin binding.

Regulation of insulin receptor-associated tyrosine kinase by a polyclonal IgG

The effect of a polyclonal anti-insulin receptor antibody (pIgG) on the insulin receptor tyrosine kinase (IRTK) activity toward poly-(Glu-Tyr) was examined using wheat germ agglutinin agarose-purified insulin receptors from rat liver membranes. The main effect of pIgG was a reduction of Vmax (from 60.8 to 31.8 pmol/min/mg), without changes of Km, when IRTK was activated by insulin. In contrast, when IRTK was activated by ATP preincubation, pIgG was unable to affect the reaction, suggesting that IRTK possesses at least two regulatory mechanisms, one of which can be affected by pIgG.

Effects of three low-dose oral contraceptive formulations on lipid metabolism

Three oral contraceptive preparations were studied in 60 healthy women. This randomized, comparative, baseline controlled study was designed to investigate the effects of the preparations on plasma lipids and lipoproteins. The following formulations were studied: a monophasic preparation containing ethinylestradiol and desogestrel (M-DSG) and two triphasic formulations containing ethinylestradiol and gestodene or levonorgestrel respectively (T-GSD and T-LNG). These preparations were studied for six treatment cycles. Total cholesterol and apoprotein B did not change in any group. Low density lipoprotein (LDL) cholesterol was significantly decreased in the groups of women treated with M-DSG and T-GSD respectively. No changes were observed in the T-LNG group. With M-DSG, significant increases were observed in high-density lipoprotein (HDL) cholesterol and HDL3 cholesterol, whilst HDL2 cholesterol did not change. With both T-GSD and T-LNG, no changes were observed in HDL cholesterol, whilst a significant increase in HDL3 cholesterol together with a trend to decrease in HDL2 cholesterol were observed. Apolipoprotein AI increased with the following ranking M-DSG greater than T-GSD greater than T-LNG. The LDL/HDL cholesterol ratio significantly decreased with both M-DSG and T-GSD. In the T-LNG group there was no change in this ratio. Triglycerides increased to the same extent in all treatment groups. As far as concerns the risk of arterial diseases, these three oral contraceptive formulations mostly induced negligible and/or partly favorable changes in plasma lipids and lipoproteins; however, the lipoprotein pattern during M-DSG treatment resulted better than during T-GSD, and the latter turned out to be better than during T-LNG.

Insulin receptor autophosphorylation and kinase activity in streptozotocin diabetic rats. Effect of a short fast

Insulin receptor associated kinase activity and its relationships with the insulin resistance of streptozotocin-induced diabetes were investigated in rats, using solubilized, partially purified insulin receptors from liver membranes. Insulin receptor kinase activity was measured by means of both autophosphorylation and phosphorylation of the exogenous substrate Glu4:Tyr1. Diabetes was associated with a 45% reduction in kinase activity, in the same number of insulin receptors, with no change in insulin binding affinity. To investigate the independent roles of hyperglycemia and hypoinsulinemia on the observed impairment of receptor kinase activity, diabetic rats were fasted for 24 h in order to normalize blood glucose levels only. After this short fast, no change in kinase activity, from the values measured in fed diabetic animals, was observed. Our findings suggest that streptozotocin diabetes is associated with a reduction of insulin receptor kinase activity, which a short fast is not able to reverse.

Insulin-like growth factor I (IGF I) receptor autophosphorylation and kinase activity. Effect of a human polyclonal antibody (pIgG)

IGF I receptor is a tyrosine kinase capable of phosphorylating the receptor itself and other substrates. A high degree of homology does exist in tyrosine kinase domain among receptors for several polypeptide growth factor receptors and this enzymic activity has been indicated as a possible mediator of biological action. Nevertheless growth factor receptors possess peculiar specificities both in their functions and tissue distribution. A human polyclonal IgG (pIgG), previously characterized as anti insulin receptor antibody, able to inhibit insulin receptor kinase activity, was used to further investigate subunit homologies and differences in antigenicity and functional regulation between IGF I and insulin receptors, IGF I receptor tyrosine kinase was stimulated by a IGF I analog (aIGF I), produced by DNA recombinant technology, pIgG was able to inhibit IGF I receptor kinase activity, thus revealing antigenic homologies between the kinase domains of insulin and IGF I receptors. However the more pronounced inhibition of IGF I receptor-compared with insulin receptor kinase activity by pIgG suggests the existence of different regulatory mechanisms.