Adamandia D. Kriketos

Beyond insulin resistance in NASH: TNF-α or adiponectin?

Adiponectin has antilipogenic and anti‐inflammatory effects, while tumor necrosis factor α (TNF‐α) reduces insulin sensitivity and has proinflammatory effects. We examined (1) the extent to which hypoadiponectinemia and TNF‐α activation are features of nonalcoholic steatohepatitis (NASH) and (2) whether serum levels of these markers correlate with the severity of histological changes in 109 subjects with nonalcoholic fatty liver disease (NAFLD), including 80 with NASH and 29 with simple steatosis. By multivariate analysis, subjects with NASH had reduced adiponectin level and increased TNF‐α and soluble TNF receptor 2 (sTNFR2)—but not leptin levels, compared with controls matched by age, sex, and body mass index; these differences were independent of the increased insulin resistance (by homeostasis model [HOMA‐IR]) in NASH. When compared with simple steatosis, NASH was associated with lower adiponectin levels and higher HOMA‐IR, but there were no significant differences in the levels of TNF‐α and sTNFR2. The majority of subjects with steatohepatitis (77%) had adiponectin levels less than 10 μg/mL and HOMA‐IR greater than 3 units, but only 33% of those with pure steatosis had these findings. HOMA‐IR and low serum adiponectin were also independently associated with increased grades of hepatic necroinflammation. In conclusion, hypoadiponectinemia is a feature of NASH independent of insulin resistance. Reduced adiponectin level is associated with more extensive necroinflammation and may contribute to the development of necroinflammatory forms of NAFLD. (HEPATOLOGY 2004;40:46–54.)

Nicotinic acid-induced insulin resistance is related to increased circulating fatty acids and fat oxidation but not muscle lipid content.

Insulin resistance is associated with increased circulating lipids and skeletal muscle lipid content. Chronic nicotinic acid (NA) treatment reduces insulin sensitivity and provides a model of insulin resistance. We hypothesized that the reduction in insulin sensitivity occurs via elevation of circulating nonesterified fatty acids (NEFAs) and an increase in intramyocellular lipid (IMCL). A total of 15 nondiabetic males (mean age 27.4 +/- 1.6 years) were treated with NA (500 mg daily for 1 week, 1 g daily for 1 week). Insulin sensitivity (glucose infusion rate [GIR]) was determined pre- and post-NA by euglycemic-hyperinsulinemic clamp. Substrate oxidation was determined by indirect calorimetry. Skeletal muscle lipid was assessed by estimation of long-chain acyl-CoA (LCACoA) and triglyceride (TG) content and by (1)H-magnetic resonance spectroscopy quantification of IMCL (n = 11). NA reduced GIR (P =.03) and nonoxidative glucose disposal (P <.01) and increased fasting NEFAs (P =.01). The decrease in GIR related significantly to the increase in fasting NEFAs (r(2) =.30, P =.03). The intrasubject increase in basal and clamp fat oxidation correlated with the decrease in GIR (r(2) =.45, P <.01 and r(2) =.63, P <.01). There were no significant changes in muscle LCACoA, TG, or IMCL content. Therefore, induction of insulin resistance by NA occurs with increased availability of circulating fatty acids to muscle rather than with increased muscle lipid content.

The postprandial response of adiponectin to a high-fat meal in normal and insulin-resistant subjects

OBJECTIVE: Adiponectin is an adipose-specific protein with short-term effects in vivo on glucose and fatty acid levels. We studied the plasma concentration and the proteolytic activation status of adiponectin following the consumption of a high-fat, low-carbohydrate meal.DESIGN: Analysis of adiponectin concentration and polypeptide structure after consumption of a fat meal.SUBJECTS: Normal subjects (n=24) and first-degree relatives of patients with type II diabetes (n=20).MEASUREMENTS: All subjects had a normal fasting plasma glucose and glucose tolerance. Blood was collected for the determination of plasma insulin, adiponectin, triglyceride, and free fatty acids. Body composition was assessed with dual-energy X-ray absorptiometry and whole-body insulin sensitivity with a euglycaemic, hyperinsulinaemic clamp. Postprandial response over 6 h was determined for plasma adiponectin, glucose, insulin, triglyceride, and free fatty acids. Adiponectin was measured by commercial RIA and its polypeptide structure examined by Western blotting.RESULTS: The relatives were more insulin resistant and had increased adiposity compared with control subjects. There was no significant difference in postprandial response in fatty acids, triglyceride, or insulin between the groups. Postprandial levels of adiponectin measured by radioimmunoassay were not significantly different from fasting levels, and no breakdown products of adiponectin were detectable in postprandial samples by Western blotting.CONCLUSIONS: Levels of circulating adiponectin do not alter in response to a fat meal, despite evidence in mice that acute changes in adiponectin significantly affect postprandial fatty acid flux. Moreover, a fat meal challenge did not lead to significant activation of adiponectin by proteolytic conversion.

Muscle fibre type composition in infant and adult populations and relationships with obesity.

OBJECTIVES: To investigate the fibre type composition of skeletal muscle in infants and young children and to compare the findings to an adult population. To relate the fibre type profile of skeletal muscle in adults to measures of adiposity. DESIGN: Cross-sectional studies of skeletal muscle fibre composition in infants and adults with measures of adiposity in the adults. SUBJECTS: 21 healthy infants and young children (age: 3–21 months) and 40 healthy adult Australian Caucasians (age: 26–62 y; BMI: 18–48 kg/m2). MEASUREMENTS: Skeletal muscle fibre type composition (by myosin ATPase method) and relative body fatness (BMI, waist circumference and waist/hip ratio (WHR)). RESULTS: Infants and young children had significantly lesser proportions of glycolytic Type 2b fibres (6.2±1.1%; range 0.3–18.9%) compared with adults (20.5±1.6%; range 4.9–36.0%) (p<0.0001). The percentage of Type 2b fibres was directly related to BMI (r=0.44, p=0.02), waist circumference (r=0.49, p=0.009) and WHR (r=0.44, p=0.02) in adults. A significant, direct relationship was also found between the proportion of glycolytic Type 2b fibres and age in the adults (r=0.45, p=0.01). CONCLUSION: Skeletal muscle fibre type composition is different in infants and adults and there is an age-dependent increase in Type 2b fibres over the lifespan. An increased proportion of glycolytic Type 2b fibres is associated with obesity in adults. Results support a gene-environment interaction on fibre type composition in human skeletal muscle.

Low serum PYY is linked to insulin resistance in first-degree relatives of subjects with type 2 diabetes

Low circulating peptide YY (PYY) levels are reported in obese and type II diabetic subjects and results from PYY knockout animals suggests that PYY deficiency may have a causative role in the etiology of obesity and type 2 diabetes. Here, our aims were to determine whether people with a genetic predisposition to developing type 2 diabetes and obesity differ from otherwise similar subjects without such family history, in fasting or meal-related PYY levels, fasting insulin, insulin secretion (HOMA-B) and insulin sensitivity. We also investigated whether PYY ablation affects the intrinsic ability of islets to secrete insulin, which may be a contributing factor to the hyperinsulinemia observed in PYY knockout mice. Healthy female first-degree relatives of people with type 2 diabetes were matched for age, gender and BMI to control subjects but had significantly lower insulin sensitivity (p<0.05). Relatives also had significantly lower fasting serum PYY levels than controls (p<0.05), but their PYY response to a high fat meal (4250 kJ, 73% fat) was not significantly different. Fasting PYY level correlated positively with glucose infusion rate (r=0.713, p=0.002) and fasting adiponectin (r=0.5, p=0.02). Islets of Langerhans from PYY knockout mice were found to hypersecrete insulin in response to 25 mM glucose (p<0.05). These data demonstrate that lack of PYY enhances insulin secretion from the Islets of Langerhans and that low fasting PYY levels are associated with insulin resistance in humans. Together, these findings suggest that low circulating levels of PYY could contribute to hyperinsulinemia and insulin resistance, and possibly contribute to subsequent development of obesity and type 2 diabetes.

Ketosis and appetite-mediating nutrients and hormones after weight loss

Background/Objectives:Diet-induced weight loss is accompanied by compensatory changes, which increase appetite and encourage weight regain. There is some evidence that ketogenic diets suppress appetite. The objective is to examine the effect of ketosis on a number of circulating factors involved in appetite regulation, following diet-induced weight loss.Subjects/Methods:Of 50 non-diabetic overweight or obese subjects who began the study, 39 completed an 8-week ketogenic very-low-energy diet (VLED), followed by 2 weeks of reintroduction of foods. Following weight loss, circulating concentrations of glucose, insulin, non-esterified fatty acids (NEFA), β-hydroxybutyrate (BHB), leptin, gastrointestinal hormones and subjective ratings of appetite were compared when subjects were ketotic, and after refeeding.Results:During the ketogenic VLED, subjects lost 13% of initial weight and fasting BHB increased from (mean±s.e.m.) 0.07±0.00 to 0.48±0.07 mmol/l (P<0.001). BHB fell to 0.19±0.03 mmol/l after 2 weeks of refeeding (P<0.001 compared with week 8). When participants were ketotic, the weight loss induced increase in ghrelin was suppressed. Glucose and NEFA were higher, and amylin, leptin and subjective ratings of appetite were lower at week 8 than after refeeding.Conclusions:The circulating concentrations of several hormones and nutrients which influence appetite were altered after weight loss induced by a ketogenic diet, compared with after refeeding. The increase in circulating ghrelin and subjective appetite which accompany dietary weight reduction were mitigated when weight-reduced participants were ketotic.

Relationship of adiponectin with insulin sensitivity in humans, independent of lipid availability

Objective: To test in humans the hypothesis that part of the association of adiponectin with insulin sensitivity is independent of lipid availability.

Serum Adiponectin Levels in Normal and Hypertensive Pregnancy

Objective: The aim of this study was to quantify adiponectin levels in women with normal and hypertensive pregnancies to determine whether there is an independent association, while controlling for body fat and insulin sensitivity. Methods: A cross-sectional study was conducted in the following categories: 12 normotensive non-pregnant women, 10 normotensive, 12 gestational hypertensive, 13 essential hypertensive, and 12 preeclamptic women. All subjects underwent measurements of body fat by bio-impedance analysis and blood sampling. Results: Percentage of body fat and insulin resistance were greater in all pregnant groups compared with non-pregnant women. Adiponectin concentrations were significantly lower in women with normal pregnancies (18.6 ± 1.4 μg/mL, p = 0.02) compared with non-pregnant women (24.0 ± 1.5 μg/mL). However, adiponectin levels were not significantly different among normal pregnancy, gestational hypertension (19.0 ± 3.1 μg/mL), essential hypertension (24.0 ± 3.7 μg/mL) and pre-eclampsia (22.4 ± 2.5 μg/mL) groups. Adiponectin levels were inversely related to percent body fat and insulin resistance. When adiponectin levels were corrected for percent body fat and insulin resistance, no significant differences were seen among the study groups. Conclusions: Adiponectin levels are decreased in normal pregnancy, however this difference disappears when adiponectin levels are corrected for the pregnancy-related increases in body fat and insulin resistance. Adiponectin levels are not altered significantly in states of hypertension in pregnancy compared with normal pregnancy.

Central fat predicts deterioration of insulin secretion index and fasting glycaemia: 6‐year follow‐up of subjects at varying risk of Type 2 diabetes mellitus

Aims To examine the relationships between body composition and changes in fasting glycaemia, and in indices of insulin secretion and insulin action over 6 years in females with a family history of Type 2 diabetes with or without prior gestational diabetes (‘at risk’ group, AR) and control females (control group, C).

Response of the alternative complement pathway to an oral fat load in first-degree relatives of subjects with type II diabetes

OBJECTIVE:To investigate levels of components of the alternative pathway of complement, and of two activation products, ASP and Bb, in persons ranging in insulin resistance both fasting and following the consumption of a high-fat, low-carbohydrate meal.SUBJECTS:Healthy controls (n=17) and normoglycaemic first-degree relatives of patients with type II diabetes (n=15).MEASUREMENTS:All subjects had normal glucose tolerance. Blood was collected for the measurement of plasma glucose, insulin, triglycerides and free fatty acids. Body composition was assessed with dual energy X-ray absorptiometry (DEXA) and whole-body insulin sensitivity with a euglycaemic, hyperinsulinaemic clamp. Basal and postprandial values over 6 h were determined for plasma C3, B, D, Bb and ASP. Basal levels of C1q, C4 and CRP were also determined.RESULTS:Controls did not differ significantly from the relatives of patients with type II diabetes for any metabolic parameter except in their degree of insulin resistance and central fat (kg). Across all subjects, basal levels of C3, but no other complement protein, were correlated with insulin resistance. Native complement proteins, but not ASP or Bb, were correlated with body mass index and the amount (kg) of central fat. Basal levels of C3 and factor B were significantly higher in the relatives group, whereas factor D and the classical pathway proteins C1q and C4 did not differ between the two groups. Postprandially, levels of factor D were significantly reduced in both groups. ASP levels also fell postprandially, the decline achieving significance in the relatives group.CONCLUSIONS:Elevated levels of C3 and factor B in the diabetic relatives group may have resulted from increased synthesis by adipose tissue. There was no evidence of alternative pathway activation in response to a fat meal in terms of ASP or Bb production, or significant consumption of C3 and factor B. These data do not support an essential requirement of the hypothesis that ASP is produced in response to the intake of fat.