Endocrine abnormalities in healthy first-degree relatives of type 2 diabetes patients--potential role of steroid hormones and leptin in the development of insulin resistance

Association between triglyceride glucose index and abnormal liver function in both urban and rural Chinese adult populations: Findings from two independent surveys

The purpose of this study was to investigate the association between triglyceride glucose (TyG) index and abnormal liver function both in urban and rural Chinese adult populations. The 5824 urban (Nanjing) and 20,269 rural (Hefei) Chinese adults, from random selected households provided clinical history, glucose, lipids, anthropometric, and blood pressure measurements. Liver functions were assessed using Alanine Aminotransferase (ALT). Linear regression was applied to examine the dose-response relationship between TyG index and ALT. Logistic regression was used to estimate the association between TyG index and abnormal liver and function. Cubic spline models were applied to investigate the dose-response association between TyG index and abnormal liver function. C-statistics was used to compare the discriminable capacity over triglyceride, glucose and TyG index. Linear dose-response relationship was identified between TyG index and ALT as 1.222 IU increase by 1 unit increase of TyG index (1.242 for urban population and 1.210 for rural population). The 6.0% of urban and 11.0% of rural Chinese adults were observed to have abnormal liver function. The linear association between TyG index and abnormal liver function was revealed as 2.044 (1.930 to 2.165) of odds ratio by in unit increase of TyG index (2.334 for urban population and 1.990 for rural population). Higher C-statistics was found for TyG index compared with fasting glucose and triglyceride both in Chinese urban and rural populations. This study suggested in both urban and rural Chinese adult populations, TyG index is associated with abnormal liver function. TyG index is a potential indicator to identify high-risk individuals with metabolic disorders, for example impaired liver function in Chinese population, especially in Chinese urban population.

The triglyceride glucose index can predict newly diagnosed biopsy-proven diabetic nephropathy in type 2 diabetes: A nested case control study

Insulin resistance is usually a key factor in the development of type 2 diabetes. The triglyceride glucose (TyG) index is a marker of insulin resistance which is also implicated in the risk of nephropathy among people with type 2 diabetes. This study aimed to examine associations and potential thresholds between TyG index and the risk of newly diagnosed biopsy-proven diabetic nephropathy in people with type 2 diabetes. A nested case-control study incorporating 950 incident biopsy-proven diabetic nephropathy cases and age, gender matched 4750 patients with treated type 2 diabetes as controls selected by risk-set sampling method was implemented. The dose-response association between TyG index with subsequent risk of newly diagnosed biopsy-proven diabetic nephropathy after adjustment for age, gender, blood pressure, and other major cardiovascular risk factors were examined by conditional logistic regression model. A non-linear relationship was identified between TyG index and the risk of newly diagnosed biopsy-proven diabetic nephropathy with a potential threshold of TyG at 9.05-9.09. Similar relationships with the same threshold were also found in the analyses by fasting glucose and triglyceride levels. TyG index might be a prognostic factor in predicting newly development of biopsy-proven diabetic nephropathy among patients with treated type 2 diabetes. In people with type 2 diabetes, TyG index above 9.05-9.09 could be a prognostic threshold to identify individuals at high risk of diabetic nephropathy. Further replication studies are warranted.

Liver fat and SHBG affect insulin resistance in midlife women: the Study of Women's Health Across the Nation (SWAN)

OBJECTIVE

The liver is an insulin-responsive organ that contributes significantly to both whole body insulin sensitivity and availability of sex steroids through the production of sex hormone binding globulin (SHBG). Our objective was to explore whether lower SHBG was associated with ectopic liver fat and mediated its effect on insulin resistance in The Study of Women's Health Across the Nation (SWAN).

DESIGN AND METHODS

A subset of midlife African American and Caucasian women from SWAN (n = 208; 50.9 ± 0.18 yrs; 71% Caucasian) had computed tomography scans to quantify visceral, subcutaneous and liver fat. Blood samples were collected and assayed for hormonal and metabolic markers.

RESULTS

The cohort, while overweight, was generally healthy, and both liver fat and SHBG were unaffected by menopausal stage or race. Both higher liver fat and lower SHBG levels were significantly associated with higher insulin concentrations after adjustment for adiposity (r = -0.25, P < 0.001 and r = -0.18, P = 0.01). SHBG and liver fat had additive effects on insulin concentrations such that women with the lowest SHBG and the highest fat levels had the highest values (interaction P = 0.09). The association between SHBG and insulin was more apparent among women with fattier livers. SHBG and liver fat appear to have independent effects on insulin levels as adjustment for each other did not diminish the strength of either association (P = 0.023 and 0.001 respectively).

CONCLUSION

These results confirmed the strong independent associations between increased liver fat and decreased SHBG with increased metabolic risk in midlife women. Further these data underscore the need for additional research into the role of liver fat in modifying SHBG's influence on insulin levels.

[Metabolic alteration in healthy men with first degree type 2 diabetic relatives]

INTRODUCTION

The recognition of prediabetic patients with the genetic risk of type 2 diabetes is very important as prediabetes is the last stage when manifestation of diabetes could be prevented by life style modification or drug intervention. This suggests the need for diagnostic processes to trace the risk of patients in time.

AIMS

The authors looked for metabolic differences between age and BMI in adjusted healthy men with or without first degree type 2 diabetic relatives.

METHODS

The study included 73 healthy men (21 with and 52 without) first-degree relatives with type 2 diabetes.

RESULTS

Total body and muscle tissue glucose utilization, glucose tolerance did not differ between the two groups, but free fatty acid levels were not suppressed by glucose load in subjects with diabetic relatives. In addition the body fat content, leptin and IL-6 levels were higher, while adiponectin and the free fatty acid/adiponectin ratio were significantly lover in healthy men with diabetic relatives. In this group HDL cholesterol, and the large buoyant LDL fraction were lower whereas the high density LDL - small molecular lipid fraction was higher than those measured in subjects without diabetic relatives.

CONCLUSIONS

These data suggest that deteriorations of insulin sensitivity and glucose tolerance is preceded by disturbances of fatty acid metabolism. The observed alteration in free fatty acid/adiponectin ratio, and/or the absence of free fatty acid suppression during glucose tolerance tests could be a screening tool for diabetes risk among men.

Skeletal muscle mitochondrial energetics in obesity and type 2 diabetes mellitus: endocrine aspects

During the development of type 2 diabetes mellitus, skeletal muscle is a major site of insulin resistance. The latter has been linked to mitochondrial dysfunction and impaired fatty acid oxidation. Some hormones like insulin, thyroid hormones and adipokines (e.g., leptin, adiponectin) have positive effects on muscle mitochondrial bioenergetics through their direct or indirect effects on mitochondrial biogenesis, mitochondrial protein expression, mitochondrial enzyme activities and/or AMPK pathway activation--all of which can improve fatty acid oxidation. It is therefore not surprising that treatment with these hormones has been proposed to improve muscle and whole body insulin sensitivity. However, treatment of diabetic patients with leptin and adiponectin has no effect on muscle mitochondrial bioenergetics showing resistance to these hormones during type 2 diabetes. Furthermore, treatment with most thyroid hormones has unexpectedly revealed negative effects on muscle insulin sensitivity. Future research should focus on development of agents that improve metabolic dysfunction downstream of hormone receptors.

Dysregulation of the Autonomic Nervous System Can Be a Link between Visceral Adiposity and Insulin Resistance

OBJECTIVE

To evaluate the interplay among abdominal adipose tissue distribution, the cortisol axis, the autonomic nervous system, and insulin resistance.

RESEARCH METHODS AND PROCEDURES

Two age-, sex-, and BMI-matched groups were studied. Fifteen subjects were first-degree relatives of patients with type 2 diabetes (R), and 15 had no family history of diabetes (controls, C). A hyperinsulinemic euglycemic clamp, cortisol measurements, and analysis of heart rate variability (HRV) were performed. Computed tomography was performed in a subgroup (n = 9 + 9) to determine abdominal adipose tissue distribution.

RESULTS

R tended to be less insulin-sensitive than C (M value 9.2 +/- 1.0 vs 10.3 +/- 0.7 mg/kg per minute, not significant). Stimulation with tetracosactin or corticotropin releasing hormone yielded lower peak serum cortisol levels in R (p = 0.03 and p = 0.06, respectively). The amount of visceral abdominal fat (VAT) tended to be greater in R. In all subjects, VAT was negatively correlated to insulin sensitivity (r = -0.93, p < 0.001). There was a positive association between VAT and resting heart rate (r = 0.70, p = 0.003) and sympathetic/parasympathetic ratio in HRV assessment after tilt (r = 0.53, p = 0.03). Subcutaneous abdominal tissue was not associated with insulin sensitivity or any of the hormonal or HRV assessments.

DISCUSSION

Subjects genetically predisposed for type 2 diabetes had a tendency toward a larger amount of VAT and to lower insulin sensitivity compared with control subjects. The amount of visceral fat was strongly associated with insulin resistance and signs of a high ratio of sympathetic vs. parasympathetic reactivity. A large amount of visceral fat may act in concert with sympathetic/parasympathetic imbalance to promote the development of insulin resistance, and this may be partly independent of genetic background.

Fasting hyperinsulinemia associates with increased sub-clinical inflammation in first-degree relatives normal glucose tolerant women independently of the metabolic syndrome

BACKGROUND

To evaluate the influence of gender on the relationship between inflammation and hyperinsulinemia in first-degree relatives of type 2 diabetic patients independently of metabolic syndrome.

METHODS

Study group consisted in 217 first-degree relatives with normal glucose tolerance after an oral glucose tolerance test. A logistic analysis, adjusted for age, sex and all the components of the metabolic syndrome, was used to determine the relationship between interleukin-6 (IL-6) and leptin and tertiles of fasting insulin, and to take into account the influence of gender.

RESULTS

In the whole cohort, IL-6 and leptin were significantly higher and adiponectin significantly lower in the III tertile when corrected for age, body mass index (BMI) and metabolic syndrome components. In women, but not in men, IL-6 and leptin remained significantly higher when corrected for metabolic syndrome. In the whole cohort and in women, univariate correlations between IL-6 concentrations and the parameters under evaluation showed that IL-6 and leptin were positively correlated with age, BMI, waist, systolic blood pressure (SBP), diastolic blood pressure (DBP), fasting glucose, fasting insulin, Delta AUC insulin area, triglyceride (TG), free fatty acids (FFA) and monocyte chemoattractant protein-1 (MCP-1) and inversely correlated with HDL cholesterol (HDL-C) and adiponectin. In women a forward stepwise linear regression analysis in a model including age, BMI, features of metabolic syndrome, fasting insulin, Delta AUC insulin and insulin sensitivity index (ISI) index revealed that only IL-6 and leptin were independently associated with fasting insulin levels.

CONCLUSIONS

In first-degree relatives normal glucose tolerant women, fasting hyperinsulinemia, independently of the presence of metabolic syndrome, is associated with elevated IL-6 and leptin levels, suggesting an increased cardiovascular risk.

Combined association of maternal and paternal family history of diabetes with plasma leptin and adiponectin in overweight Hispanic children

AIMS

To investigate the importance of a maternal and paternal family history of Type 2 diabetes and their combined association with plasma leptin and adiponectin levels in overweight Latino children with a family history of Type 2 diabetes (T2DM).

METHODS

This cross-sectional study investigated the combined association of a maternal and paternal family history of T2DM with leptin and adiponectin in 175 overweight Latino children (age 11.1 +/- 1.7 years). All subjects had a family history of T2DM. Plasma adiponectin and leptin levels, body fat measured by dual-energy X-ray absorptiometry, Tanner stage, age and insulin sensitivity were assessed.

RESULTS

After adjustment for age, gestational diabetes, insulin sensitivity and body fat, a combined maternal and paternal family history of T2DM was associated with higher leptin concentrations (P = 0.004) compared with a maternal or paternal family history alone. This association was most pronounced at Tanner stage 1 (P for interaction family history x tanner stage = 0.022). The presence of a combined maternal and paternal family history of T2DM accounted for 4% (P = 0.003) of the variation in leptin concentrations. No such combined association was observed for adiponectin levels.

CONCLUSIONS

Maternal and paternal family history of T2DM may have an additive impact on leptin, but not on adiponectin levels independent of adiposity and insulin sensitivity in overweight Latino children. This may contribute to a further clinically relevant deterioration of metabolic health in this population.

Fat cell enlargement is an independent marker of insulin resistance and 'hyperleptinaemia'

AIMS/HYPOTHESIS

The aim of this study was to explore whether fat cell size in human subcutaneous and omental adipose tissue is independently related to insulin action and adipokine levels.

MATERIALS AND METHODS

Fat cells were prepared from abdominal subcutaneous biopsies obtained from 49 type 2 diabetic and 83 non-diabetic subjects and from omental biopsies obtained from 37 non-diabetic subjects. Cell size and insulin action on glucose uptake capacity in vitro were assessed in isolated fat cells. Insulin sensitivity in vivo was assessed with euglycaemic-hyperinsulinaemic clamps. Fasting blood samples were collected and adipokines and NEFA were measured.

RESULTS

Negative correlations were found between subcutaneous fat cell size and insulin sensitivity assessed as M-value during clamp and as insulin action on glucose uptake in fat cells in vitro. This was seen in non-diabetic subjects after including age, sex and BMI in the analyses. No such relationship was found in type 2 diabetic subjects. In both groups, subcutaneous fat cell size correlated positively and independently with plasma levels of leptin but not to any of the other assessed adipokines. In non-diabetic subjects, omental fat cell size was independently and negatively correlated with insulin action in subcutaneous, but not omental, fat cells in vitro.

CONCLUSIONS/INTERPRETATION

Fat cell enlargement is associated with insulin resistance in non-diabetic individuals independently of BMI. This was not seen in type 2 diabetic subjects, suggesting that after development of type 2 diabetes other factors, not related to fat cell size, become more important for the modulation of insulin resistance.

Insulin resistance, endocrine function and adipokines in type 2 diabetes patients at different glycaemic levels: potential impact for glucotoxicity in vivo

OBJECTIVE

To evaluate the interplay between hyperglycaemia, insulin resistance, hormones and adipokines in patients with type 2 diabetes mellitus (T2DM).

DESIGN AND METHODS

Ten patients with T2DM with good glycaemic control (G), 10 with poor control (P) and 10 nondiabetic control subjects (C) were matched for sex (M/F 6/4), age and body mass index. A hyperinsulinaemic, euglycaemic clamp was performed and cytokines and endocrine functions, including cortisol axis activity were assessed.

RESULTS

Patients with diabetes were more insulin resistant than group C, and group P exhibited the highest degree of insulin resistance (P = 0.01, P vs C). Tumour necrosis factor (TNF)-alpha levels were elevated in patients with diabetes (P = 0.05) and group P had the highest levels of fasting serum cortisol (P = 0.05), nonesterified fatty acids (NEFA; P = 0.06) and C-reactive protein (CRP; P = 0.01). Adiponectin levels were lower in the P group. In partial correlation analyses, significant associations were found: glycaemic level (HbA1c) with insulin resistance, TNF-alpha, CRP and basal and ACTH-stimulated cortisol levels, insulin resistance with plasma NEFA, TNF-alpha and stimulated cortisol levels.

CONCLUSION

Poor glycaemic control in patients with T2DM was associated with insulin resistance and with elevated TNF-alpha, CRP and basal as well as stimulated cortisol levels. Inflammatory mediators, e.g. TNF-alpha, may contribute to insulin resistance in hyperglycaemic patients with T2DM and this might be a partial explanation for glucotoxicity.

Insulin resistance in diabetic nephropathy--cause or consequence?

Insulin resistance (IR) is associated with multiple risk factors for cardiovascular disease. Many studies have shown that IR is present in chronic renal failure (CRF), and recent evidence suggests that IR can also occur in the early stages of renal disease. Patients with diabetic nephropathy (DN) have an increase in cardiovascular mortality, and since IR may be a contributing factor, this emphasizes the importance of a detailed understanding of the mechanisms linking IR and renal dysfunction at different stages of DN. IR can be detected early on in DN, e.g. at the stage of microalbuminuria (MA) and this could indicate a common genetic trait for IR and DN. As DN progresses further, IR is aggravated and it may, in addition to other factors, possibly accelerate the decline in renal function toward end-stage renal disease (ESRD). Several potentially modifiable mechanisms including circulating hormones, neuroendocrine pathways and chronic inflammation, are said to contribute to the worsening of IR. In ESRD, uremic toxins are of major importance. In this review article, we address the association between different stages of DN and IR and attempt to summarize major findings on potential mechanisms linking DN and IR. We conclude that IR is a consequence, and potentially also a cause of DN. In addition, there are probably genetic and environmental background factors that predispose to both IR and DN.

Is insulin resistance caused by defects in insulin's target cells or by a stressed mind?

The importance of understanding insulin action is emphasized by the increasing prevalence of insulin resistance in various populations and by the fact that it plays an important pathophysiological role in many common disorders, for example, diabetes, obesity, hypertension and dyslipidemia. The primary factors responsible for the development of insulin resistance are so far unknown, although both genetic and environmental factors are involved. The genetic defects responsible for the common forms of insulin resistance, for example, in type 2 diabetes, are largely unidentified. Some studies from our group as well as by other investigators suggest that cellular insulin resistance is reversible and that it may be secondary to factors in the in vivo environment. These may include insulin-antagonistic action of hormones like catecholamines, glucocorticoids, sex steroids and adipokines as well as dysregulation of autonomic nervous activity and they could contribute to the early development of insulin resistance. Some of these factors can directly impair glucose uptake capacity and this might be due to alterations in key proteins involved in insulin's intracellular signaling pathways. This article briefly summarizes proposed mechanisms behind cellular and whole-body insulin resistance. In particular, we question the role of intrinsic defects in insulin's target cells as primary mechanisms in the development of insulin resistance in type 2 diabetes and we suggest that metabolic and neurohormonal factors instead are the main culprits.

Androgens, insulin resistance and vascular disease in men

Type 2 diabetes mellitus is increasing globally and is an established risk factor for the development of atherosclerotic vascular disease. Insulin resistance is the hallmark feature of type 2 diabetes and is also an important component of the metabolic syndrome. There is evidence to suggest that testosterone is an important regulator of insulin sensitivity in men. Observational studies have shown that testosterone levels are low in men with diabetes, visceral obesity (which is strongly associated with insulin resistance), coronary artery disease and metabolic syndrome. Short-term interventional studies have also demonstrated that testosterone replacement therapy produces an improvement in insulin sensitivity in men. Thus hypotestosteronaemia may have a role in the pathogenesis of insulin-resistant states and androgen replacement therapy could be a potential treatment that could be offered for improvements in glycaemic control and reduction in cardiovascular risk, particularly in diabetic men.

Short-term effects of repetitive arm work and dynamic exercise on glucose metabolism and insulin sensitivity

AIM

To determine whether repetitive arm work, with a large component of static muscle contraction alters glucose metabolism and insulin sensitivity.

METHOD

Euglycemic clamps (2 h) were started in ten healthy individuals 15 min after 37 min periods of: (1) repetitive arm work in a simulated occupational setting; (2) dynamic concentric exercise on a cycle ergometer at 60% of VO(2max) and (3) a resting regime as a control. During the experimental periods, blood samples were collected, blood pressure was measured repeatedly and electrocardiogram (ECG) was recorded continuously. During the clamps, euglycemia was maintained at 5 mmol l(-1) and insulin was infused at 56 mU m(-2) min(-1) for 120 min.

RESULTS

The insulin-mediated glucose disposal rate (M-value) for the steady-state period (60-120 min) of the clamp, tended to be lower following arm work than for both cycling and resting regimes. When dividing the steady-state period into 20-min intervals, the insulin sensitivity index (ISI) was significantly lower for arm work compared with the resting control situation between 60-80 min (P = 0.04) and 80-100 min (P = 0.01), respectively. Catecholamines increased significantly for arm work and cycling compared with resting regime. Data from heart rate variability (HRV) measurements indicated significant sympathetic activation during repetitive arm work.

CONCLUSION

The results indicate that repetitive arm work might acutely promote insulin resistance, whereas no such effect on insulin resistance was produced by dynamic concentric exercise.

In vitro reversal of hyperglycemia normalizes insulin action in fat cells from type 2 diabetes patients: is cellular insulin resistance caused by glucotoxicity in vivo?

Chronic hyperglycemia promotes the development of insulin resistance. The aim of this study was to investigate whether cellular insulin resistance is secondary to the diabetic state in human type 2 diabetes. Subcutaneous fat biopsies were taken from 3 age-, sex-, and body mass index (BMI)-matched groups with 10 subjects in each group: type 2 diabetes patients with either good (hemoglobin A(1c) [HbA(1c)] < 7%, G) or poor (HbA(1c) > 7.5%, P) metabolic control and healthy control subjects (C). Insulin action in vitro was studied by measurements of glucose uptake both directly after cell isolation and following a 24-hour incubation at a physiological glucose level (6 mmol/L). The relationship with insulin action in vivo was addressed by employing the euglycemic clamp technique. Freshly isolated fat cells from type 2 diabetes patients with poor metabolic control had approximately 55% lower maximal insulin response (1,000 microU/mL) on glucose uptake (P <.05) compared to C. Cells from P were more insulin-resistant (P <.05) than cells from G at a low (5 microU/mL) but not at a high (1,000 microU/mL) insulin concentration, suggesting insulin insensitivity. However, following 24 hours of incubation at physiological glucose levels, insulin resistance was completely reversed in the diabetes cells and no differences in insulin-stimulated glucose uptake were found among the 3 groups. Insulin sensitivity in vivo assessed with hyperinsulinemic, euglycemic clamp (M-value) was significantly associated with insulin action on glucose uptake in fresh adipocytes in vitro (r = 0.50, P <.01). Fasting blood glucose at the time of biopsy and HbA(1c), but not serum insulin, were negatively correlated to insulin's effect to stimulate glucose uptake in vitro (r = -0.36, P =.064 and r = - 0.41, P <.05, respectively) in all groups taken together. In the in vivo situation, fasting blood glucose, HbA(1c), and serum insulin were all negatively correlated to insulin sensitivity (M-value; r = -0.62, P<.001, r= -0.61, P<.001, and r = -0.56, p <.01, respectively). Cell size, waist-to-hip ration (WHR), and BMI correlated negatively with insulin's effect to stimulate glucose uptake both in vitro (r = -0.55, P <.01, r = -0.54, P <.01, and r = -0.43, P <.05, respectively) and in vivo (r = -0.43, P <.05, r = -0.50, P <.01, and r = -0.36, P <.05, respectively). Multiple regression analyses revealed that adipocyte cell size and WHR independently predicted insulin resistance in vitro. Furthermore, insulin sensitivity in vivo could be predicted by fasting blood glucose and serum insulin levels. We conclude that insulin resistance in fat cells from type 2 diabetes patients is fully reversible following incubation at physiological glucose concentrations. Thus, cellular insulin resistance may be mainly secondary to the hyperglycemic state in vivo.