Interrelationships among insulin's antilipolytic and glucoregulatory effects and plasma triglycerides in nondiabetic and diabetic patients with endogenous hypertriglyceridemia

Interaction between adipocytes and high-density lipoprotein:new insights into the mechanism of obesity-induced dyslipidemia and atherosclerosis

Obesity is the most common nutritional disorder worldwide and is associated with dyslipidemia and atherosclerotic cardiovascular disease. The hallmark of dyslipidemia in obesity is low high density lipoprotein (HDL) cholesterol (HDL-C) levels. Moreover, the quality of HDL is also changed in the obese setting. However, there are still some disputes on the explanations for this phenomenon. There is increasing evidence that adipose tissue, as an energy storage tissue, participates in several metabolism activities, such as hormone secretion and cholesterol efflux. It can influence overall reverse cholesterol transport and plasma HDL-C level. In obesity individuals, the changes in morphology and function of adipose tissue affect plasma HDL-C levels and HDL function, thus, adipose tissue should be the main target for the treatment of HDL metabolism in obesity. In this review, we will summarize the cross-talk between adipocytes and HDL related to cardiovascular disease and focus on the new insights of the potential mechanism underlying obesity and HDL dysfunction.

Clinical Features of Nonobese, Apparently Healthy, Japanese Men With Reduced Adipose Tissue Insulin Sensitivity

CONTEXT

Adipose tissue insulin resistance has been observed in obese subjects and is considered an early metabolic defect that precedes insulin resistance in muscle and liver. Although Asians can readily develop metabolic disease without obesity, the clinical features of nonobese, apparently healthy, Asians with reduced adipose tissue insulin sensitivity (ATIS) have not been elucidated.

OBJECTIVE

To investigate the clinical parameters associated with reduced ATIS in nonobese, apparently healthy (body mass index <25 kg/m2), Japanese men.

METHODS

We studied 52 nonobese Japanese men without cardiometabolic risk factors. Using a two-step hyperinsulinemic euglycemic clamp with a glucose tracer, we evaluated the insulin sensitivity in muscle, liver, and adipose tissue. ATIS was calculated as the percentage of free fatty acid (FFA) suppression/insulin concentration during the first step of the glucose clamp.

RESULTS

Using the median ATIS value, the subjects were divided into low- and high-FFA suppression groups. The low-FFA suppression group had moderate fat accumulation in the abdominal subcutaneous adipose tissue and liver. Compared with the high-FFA group, they also had a lower fitness level, decreased insulin clearance, impaired insulin sensitivity in muscle, moderately elevated triglycerides, and lowered high-density lipoprotein cholesterol levels. All these factors correlated significantly with ATIS. Hepatic insulin sensitivity was comparable between the two groups.

CONCLUSIONS

In nonobese, apparently healthy, Japanese men, reduced ATIS was associated with moderate fat accumulation in subcutaneous fat and liver, lower insulin clearance, muscle insulin resistance, and moderate lipedema. These data suggest that reduced ATIS can occur early in the development of the metabolic syndrome, even in nonobese, apparently healthy, men.

The Role of Leptin in Maintaining Plasma Glucose During Starvation

For 20 years it has been known that concentrations of leptin, a hormone produced by the white adipose tissue (WAT) largely in proportion to body fat, drops precipitously with starvation, particularly in lean humans and animals. The role of leptin to suppress the thyroid and reproductive axes during a prolonged fast has been well defined; however, the impact of leptin on metabolic regulation has been incompletely understood. However emerging evidence suggests that, in starvation, hypoleptinemia increases activity of the hypothalamic-pituitary-adrenal axis, promoting WAT lipolysis, increasing hepatic acetyl-CoA concentrations, and maintaining euglycemia. In addition, leptin may be largely responsible for mediating a shift from a reliance upon glucose metabolism (absorption and glycogenolysis) to fat metabolism (lipolysis increasing gluconeogenesis) which preserves substrates for the brain, heart, and other critical organs. In this way a leptin-mediated glucose-fatty acid cycle appears to maintain glycemia and permit survival in starvation.

Subcutaneous Adipocyte Lipolysis Contributes to Circulating Lipid Levels

Supplemental Digital Content is available in the text.

Objective—

Fatty acids released via fat cell lipolysis can affect circulating lipid levels. However, the contribution of different lipolysis measures in adipose tissue is unknown and was presently examined in isolated subcutaneous adipocytes.

Approach and Results—

One thousand and sixty-six men and women were examined for lipolysis regulation in subcutaneous abdominal fat cells. Results were compared with fasting plasma levels of total cholesterol, high-density lipoprotein (HDL) cholesterol (HDL-C) and triglycerides. Spontaneous (basal) lipolysis and the effects of the major hormones stimulating (catecholamines and natriuretic peptides) and inhibiting lipolysis (insulin) were examined. Several statistically significant (P<0.0001) correlations between the different lipolysis parameters and plasma lipids were observed. However, physiologically relevant correlations (adjusted r²≥0.05) were only evident between basal or insulin-inhibited lipolysis and plasma triglycerides or HDL-C. Together, these lipolysis measures explained 14% of the variation in triglycerides or HDL-C, respectively. In comparison, a combination of established factors associated with variations in plasma lipids, that is, age; body mass index; waist circumference; waist-to-hip ratio; sex; nicotine use; fat cell volume; and pharmacotherapy against diabetes mellitus; hypertension; or hyperlipidemia explained 17% and 28%, respectively, of the variations in plasma triglycerides and HDL-C.

Conclusions—

Subcutaneous fat cell lipolysis is an important independent contributor to interindividual variations in plasma lipids. High spontaneous lipolysis activity and resistance to the antilipolytic effect of insulin associate with elevated triglyceride and low HDL-C concentrations. Thus, although several other factors also play a role, subcutaneous adipose tissue may have a causal influence on dyslipidemia.

Glucose uptake and lipid metabolism are impaired in epicardial adipose tissue from heart failure patients with or without diabetes

Type 2 diabetes mellitus is a complex metabolic disease, and cardiovascular disease is a leading complication of diabetes. Epicardial adipose tissue surrounding the heart displays biochemical, thermogenic, and cardioprotective properties. However, the metabolic cross-talk between epicardial fat and the myocardium is largely unknown. This study sought to understand epicardial adipose tissue metabolism from heart failure patients with or without diabetes. We aimed to unravel possible differences in glucose and lipid metabolism between human epicardial and subcutaneous adipocytes and elucidate the potential underlying mechanisms involved in heart failure. Insulin-stimulated [(14)C]glucose uptake and isoproterenol-stimulated lipolysis were measured in isolated epicardial and subcutaneous adipocytes. The expression of genes involved in glucose and lipid metabolism was analyzed by reverse transcription-polymerase chain reaction in adipocytes. In addition, epicardial and subcutaneous fatty acid composition was analyzed by high-resolution proton nuclear magnetic resonance spectroscopy. The difference between basal and insulin conditions in glucose uptake was significantly decreased (P= 0.006) in epicardial compared with subcutaneous adipocytes. Moreover, a significant (P< 0.001) decrease in the isoproterenol-stimulated lipolysis was also observed when the two fat depots were compared, and it was strongly correlated with lipolysis, lipid storage, and inflammation-related gene expression. Moreover, the fatty acid composition of these tissues was significantly altered by diabetes. These results emphasize potential metabolic differences between both fat depots in the presence of heart failure and highlight epicardial fat as a possible therapeutic target in situ in the cardiac microenvironment.

Association of demographic, lifestyle factors and serum biomarkers with hypertension in elderly Chinese people

Hypertension is a major cause of premature death in China. Understanding risk factors including behavioural and predisposing factors may help to prevent development of hypertension and control the extent of premature mortality. In this case-control design conducted in Hunan province, 416 hypertensive subjects were matched with an equal number of normotensive persons from nearly 9,000 volunteers. A self-report questionnaire was employed to collect demographic and lifestyle information, and fasting serum biomarkers related to lipid profile, renal function, glucose level and uric acid were assessed. When age and sex were stratified, serum biomarkers such as blood urea nitrogen and triglycerides showed a significant difference for hypertension, while lifestyle behaviours including university degree, alcohol use, Body Mass Index and psychological stress (job and married life) were also associated with hypertension. After adjusting for covariate confounding factors, only elevated triglyceride levels were strongly linked to high blood pressure, odds ratio = 1.55, 95 per cent confidence level = 1.16–2.06. To control high blood pressure, hypertriglyceridemia should be included in hypertension treatment and followed up to assess the substantial risk of cardiovascular diseases.

Fat depots, free fatty acids, and dyslipidemia

Body fat deposition and excess free fatty acid (FFA) metabolism contribute to dyslipidemia and the adverse health consequences of obesity. Individuals with upper body obesity have impaired functioning of adipocytes, the primary fatty acid storage site. Excess visceral fat is strongly associated with impaired suppression of FFA release in response to insulin, as well as with hypertriglyceridemia and low concentrations of high density lipoprotein (HDL) cholesterol. High FFA concentrations can induce insulin resistance in muscle and liver. Furthermore, failure of hyperinsulinemia to normally suppress FFA is associated with impaired carbohydrate oxidation and muscle glucose storage, reduced hepatic insulin clearance and elevated triglycerides. Understanding the impact of body fat distribution on FFA metabolism and dyslipidemia is critical for determining the link between overweight and obesity and cardiovascular disease risk. In the current review, we will explore the relationship between adipose tissue, body fat depots, and FFA metabolism.

Insulin-mediated FFA suppression is associated with triglyceridemia and insulin sensitivity independent of adiposity

CONTEXT

A central/visceral fat distribution and excess free fatty acid (FFA) availability are associated with dyslipidemia and insulin resistance. However, these two characteristics often coexist, making it difficult to detect the independent contributions of each. Whether FFA suppression is more closely linked to metabolic abnormalities is not clear.

OBJECTIVE

The aim of the study was to examine the relationship between FFA suppression, body fat distribution, and fitness as contributors toward insulin resistance and hypertriglyceridemia.

DESIGN

We measured systemic palmitate turnover using an iv infusion of [9,10-(3)H]palmitate; upper body sc adipose tissue (UBSQ) and visceral adipose tissue (VAT) with dual-energy x-ray absorptiometry and a single-slice abdominal computed tomography scan; fitness with a graded exercise treadmill test; and insulin sensitivity with both the iv glucose tolerance test (IVGTT) (SI(IVGTT)) and mixed meal tolerance test (SI(Meal)).

SETTING

The study was conducted at a General Clinical Research Center.

PARTICIPANTS

Baseline data were obtained from 140 elderly adults (age, 60-88 yr; 83 males) and 60 young adults (age, 18-31 yr; 31 males) who participated in a previously published trial assessing the effects of 2-yr supplementation of dehydroepiandrosterone or testosterone on body composition, glucose metabolism, and bone density.

INTERVENTIONS

There were no interventions.

MAIN OUTCOME MEASURES

We measured fasting plasma triglyceride (TG) concentrations, SI(IVGTT), and SI(Meal).

RESULTS

Using multivariate regression analysis, the strongest combined predictors of TG concentrations were VAT, postmeal nadir FFA concentrations, sex, and age. The best predictors of SI(IVGTT) were IVGTT nadir palmitate concentration, VAT, UBSQ fat, fitness, and age, whereas the best predictors of SI(Meal) were meal nadir palmitate concentration, UBSQ fat, fitness, and sex.

CONCLUSIONS

FFA suppression is associated with both fasting TG concentrations and insulin sensitivity, independent of measures of adiposity.

Determinants of insulin secretion and sensitivity in bangladeshi type 2 diabetic subjects

BACKGROUND

The relative contribution of insulin secretion and sensitivity in the development of type 2 diabetes mellitus (T2DM) vary from population to population due to the heterogeneous nature of the disease. The study was undertaken to evaluate the insulin secretory capacity and sensitivity in a Bangladeshi type 2 diabetic population and to explore the association of some of the anthropometric (BMI, WHR, MBP) and biochemical factors (glucose, lipids, HbA(1c)) known to modulate B-cell function and insulin action.

METHODS

Ninety three T2DM and 70 age-matched control subjects were studied for their fasting glucose, lipids, HbA(1c) (by HPLC) and C-peptide (by ELISA). Insulin secretion (HOMA B) and insulin sensitivity (HOMA S) were calculated by homeostasis model assessment (HOMA).

RESULTS

Both insulin secretion and sensitivity were significantly reduced in diabetic as compared to control subjects (HOMA B%, geometric M +/- SD, 34.67 +/- 1.73 vs 104.71 +/- 1.34, p < 0.001; HOMA S%, 67.60 +/- 1.69 vs 85.11 +/- 1.54, p < 0.01). However, the discriminant function coefficient for HOMA B (1.142) was about 1.5 times higher than that for HOMA S (0.731). In T2DM, HOMA B had positive correlation with BMI (r = 0.362, p < 0.001) and inverse correlation with plasma glucose (r = - 0.701, p < 0.001) and HbA1c (r = - 0.612, p < 0.001). HOMA S was inversely correlated to BMI (r = - 0.274, p < 0.01), WHR (r = - 0.252, p < 0.05), plasma total cholesterol (r = - 0.240, p < 0.05) and triglycerides (r = 0.301, p < 0.01).

CONCLUSIONS

Both insulin secretory dysfunction and insulin resistance are present in Bangladeshi T2DM subjects, but B-cell dysfunction seems to be the predominant defect. BMI, plasma glucose and insulin are the major determinants of insulin secretory capacity; and generalized as well as central obesity, plasma glucose, total cholesterol, triglycerides and insulin are among the major determinants of insulin sensitivity in this population.

A study of the antidiabetic activity of Barleria prionitisLinn

OBJECTIVES

To study the antidiabetic activity of Barleria prionitis Linn in normal and alloxan-induced diabetic rats.

MATERIALS AND METHODS

Alcoholic extract of leaf and root of B. prionitis was tested for their antidiabetic activity. Albino rats were divided into six groups of six animals each. In three groups, diabetes was induced using alloxan monohydrate (150 mg/kg b.w., i.p.) and all the rats were given different treatments consisting of vehicle, alcoholic extract of leaves, and alcoholic extract roots of B. prionitis Linn (200 mg/kg) for 14 days. The same treatment was given to the other three groups, comprising non-diabetic (normal) animals. Blood glucose level, glycosylated hemoglobin, liver glycogen, serum insulin, and body weight were estimated in normal and alloxan-induced diabetic rats, before and 2 weeks after administration of drugs.

RESULTS

Animals treated with the alcoholic extract of leaves of B. prionitis Linn showed a significant decrease in blood glucose level (P<0.01) and glycosylated hemoglobin (P<0.01). A significant increase was observed in serum insulin level (P<0.01) and liver glycogen level (P<0.05), whereas the decrease in the body weight was arrested by administration of leaf extract to the animals. The alcoholic extract of roots showed a moderate but non-significant antidiabetic activity in experimental animals.

CONCLUSION

The study reveals that the alcoholic leaf extract of B. prionitis could be added in the list of herbal preparations beneficial in diabetes mellitus.

Integrating siRNA and protein-protein interaction data to identify an expanded insulin signaling network

Insulin resistance is one of the dominant symptoms of type 2 diabetes (T2D). Although the molecular mechanisms leading to this resistance are largely unknown, experimental data support that the insulin signaling pathway is impaired in patients who are insulin resistant. To identify novel components/modulators of the insulin signaling pathway, we designed siRNAs targeting over 300 genes and tested the effects of knocking down these genes in an insulin-dependent, anti-lipolysis assay in 3T3-L1 adipocytes. For 126 genes, significant changes in free fatty acid release were observed. However, due to off-target effects (in addition to other limitations), high-throughput RNAi-based screens in cell-based systems generate significant amounts of noise. Therefore, to obtain a more reliable set of genes from the siRNA hits in our screen, we developed and applied a novel network-based approach that elucidates the mechanisms of action for the true positive siRNA hits. Our analysis results in the identification of a core network underlying the insulin signaling pathway that is more significantly enriched for genes previously associated with insulin resistance than the set of genes annotated in the KEGG database as belonging to the insulin signaling pathway. We experimentally validated one of the predictions, S1pr2, as a novel candidate gene for T2D.

Clinical and biochemical profile of patients with "pure" uric acid nephrolithiasis compared with "pure" calcium oxalate stone formers

The purpose of the present study was to compare the clinical characteristics of "pure" uric acid (UA) stone formers with that of "pure" calcium oxalate (CaOx) stone formers and to determine whether renal handling of UA, urinary pH, and urinary excretion of promoters and inhibitors of stone formation were different between the two groups. Study subjects comprised 59 patients identified by records of stone analysis: 30 of them had "pure" UA stones and 29 had "pure" CaOx nephrolithiasis. Both groups underwent full outpatient evaluation of stone risk analysis that included renal handling of UA and urinary pH. Compared to CaOx stone formers, UA stone formers were older (53.3 +/- 11.8 years vs. 44.5 +/- 10.0 years; P = 0.003); they had higher mean weight (88.6 +/- 12.5 kg vs. 78.0 +/- 11.0 kg; P = 0.001) and body mass index (29.5 +/- 4.2 kg/m(2) vs. 26.3 +/- 3.5 kg/m(2); P = 0.002) with a greater proportion of obese subjects (43.3% vs. 16.1%; P = 0.01). Patients with "pure" UA lithiasis had significantly lower UA clearance, UA fractional excretion, and UA/creatinine ratio, with significantly higher serum UA. The mean urinary pH was significantly lower in UA stone formers compared to CaOx stone formers (5.17 +/- 0.20 vs. 5.93 +/- 0.42; P < 0.0001). Patients with CaOx stones were a decade younger, having higher 24-h urinary calcium excretion (218.5 +/- 56.3 mg/24 h vs. 181.3 +/- 57.1 mg/24 h; P = 0.01) and a higher activity product index for CaOx [AP (CaOx) index]. Overweight/obesity and older age associated with low urine pH were the principal characteristic of "pure" UA stone formers. Impairment in urate excretion associated with increased serum UA was also another characteristic of UA stone formers that resembles patients with primary gout. Patients with pure CaOx stones were younger; they had a low proportion of obese subjects, a higher urinary calcium excretion, and a higher AP index for CaOx.

Marked Insulin Resistance in Obese Spontaneously Hypertensive Rat Adipocytes Is Ameliorated by in Vivo but Not in Vitro Treatment with Moxonidine

The obese spontaneously hypertensive rat (SHROB) is a model of marked insulin resistance with normoglycemia. We sought to determine whether insulin resistance extends to adipocytes and the impact of an insulin-sensitizing imidazoline, moxonidine (4 mg/kg/days for 21 days). Gonadal adipocytes were isolated from SHROB and lean spontaneously hypertensive rat (SHR) littermates. In lean SHR adipocytes, Akt activation by 100 nM insulin peaked at 3 min at 25-fold, whereas SHROB adipocytes showed only 4-fold activation. In dose-response experiments, the maximal response (E(max)) was markedly reduced 18.8 +/- 2.3 versus 3.7 +/- 0.8. Insulin sensitivity was also attenuated, with higher concentrations required for responses (EC(50) = 3.5 +/- 0.5 versus 29 +/- 3.8 nM). Glucose uptake as determined with [(3)H]2-deoxyglucose was also less responsive to insulin in SHROB relative to lean SHR. Moxonidine had little or no effect when applied acutely in vitro, but adipocytes isolated from SHROB treated with moxonidine in vivo showed significantly improved responses to insulin, both in terms of Akt activation and facilitation of glucose uptake. Chronic but not acute moxonidine treatment partially restores insulin sensitivity in SHROB adipocytes, suggesting an indirect action of this agent.

Lower plasma triglycerides are associated with increased need for insulin requirement in poorly controlled Type 2 diabetic patients

AIMS

To identify factors associated with insulin requirement in Type 2 diabetic patients, and to examine the significance of a normal plasma triglyceride level.

METHODS

One hundred and three poorly controlled (HbA1c = 9.4 +/- 1.9%) Type 2 diabetic patients initially not treated with insulin were followed up for 5 years. Insulin was administered if HbA1c > 8% despite maximal oral anti-diabetic treatment and bodyweight control. Variables were compared between insulin requiring and non-insulin-treated patients using unpaired t-tests. The outcomes of initially normotriglyceridaemic (< 1.7 mmol/l) and hypertriglyceridaemic patients were compared using unpaired t-tests, and a survival analysis (Cox proportional hazards model).

RESULTS

Sixty-three patients were transferred to insulin. They were 5 years older (P = 0.004), with a 3-year longer duration of their diabetes (P = 0.03), a 1.2% higher HbA1c (P = 0.002), and 50% lower triglyceride levels (P = 0.02) than the others. The survival analysis showed that a long duration of diabetes, a high HbA1c, and a normal triglyceride level were associated with the need for insulin; the effect of normotriglyceridaemia was significant in the most poorly controlled (HbA1c > 9.5%) patients (relative risk: 2.35, 95% confidence interval: 1.16-5.52, P = 0.016). The 46 normotriglyceridaemic patients were leaner (P = 0.0004) and had lower C-peptide levels (P = 0.0008) than the others. Despite similar diabetes duration and HBA1c, more were transferred to insulin (normotriglyceridaemic: 71%, hypertriglyceridaemic: 52%, P = 0.03).

CONCLUSION

A normal triglyceride level is associated with a need for insulin in poorly controlled Type 2 diabetes.

Effects of the PPARgamma agonist pioglitazone on lipoprotein metabolism in patients with type 2 diabetes mellitus

Elevated plasma levels of VLDL triglycerides (TGs) are characteristic of patients with type 2 diabetes mellitus (T2DM) and are associated with increased production rates (PRs) of VLDL TGs and apoB. Lipoprotein lipase-mediated (LPL-mediated) lipolysis of VLDL TGs may also be reduced in T2DM if the level of LPL is decreased and/or the level of plasma apoC-III, an inhibitor of LPL-mediated lipolysis, is increased. We studied the effects of pioglitazone (Pio), a PPARgamma agonist that improves insulin sensitivity, on lipoprotein metabolism in patients with T2DM. Pio treatment reduced TG levels by increasing the fractional clearance rate (FCR) of VLDL TGs from the circulation, without changing direct removal of VLDL particles. This indicated increased lipolysis of VLDL TGs during Pio treatment, a mechanism supported by our finding of increased plasma LPL mass and decreased levels of plasma apoC-III. Lower apoC-III levels were due to reduced apoC-III PRs. We saw no effects of Pio on the PR of either VLDL TG or VLDL apoB. Thus, Pio, a PPARgamma agonist, reduced VLDL TG levels by increasing LPL mass and inhibiting apoC-III PR. These 2 changes were associated with an increased FCR of VLDL TGs, almost certainly due to increased LPL-mediated lipolysis.

The epidemiology of central fat distribution in relation to disease

The effect of fat distribution on disease risk is a subject of great interest. Central fat has been measured anthropometrically, by computed tomography, and by magnetic resonance imaging. Both cross-sectional and longitudinal studies have related central fat to type 2 diabetes mellitus and cardiovascular disease, independent of body mass index. The mechanism may relate to increased lipolysis causing the liver to increase glucose and very low density lipoprotein output, while muscle uses less. This leads to a rise in blood glucose and triglycerides, a drop in HDL cholesterol, and an increase in small, dense LDL particles. There is also an increase in blood pressure and inflammatory markers. Certain populations put on excess fat more centrally than others. These include Asian populations. It is likely that with better differentiation of abdominal fat into visceral and subcutaneous depots, clearer data will accrue on their impact on disease risk.

Effect of eicosapentaenoic acid ethyl ester v. oleic acid-rich safflower oil on insulin resistance in type 2 diabetic model rats with hypertriacylglycerolaemia

The purpose of the present study was to test whether hyperlipidaemia and insulin resistance in type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats can be improved by dietary supplementation with purified eicosapentaenoic acid (EPA) or oleic acid (OA). Male OLETF rats were fed powdered chow (510 g fat/kg) alone (n 8) or chow supplemented with 10 g EPA- (n 8) or OA- (n 8) rich oil/kg per d from 5 weeks until 30 weeks of age. An oral glucose tolerance test and hyperinsulinaemic euglycaemic clamp was performed at 25 and 30 weeks of age. EPA supplementation resulted in significantly (P<0.05) reduced plasma lipids, hepatic triacylglycerols, and abdominal fat deposits, and more efficient in vivo glucose disposal compared with OA supplementation and no supplementation. OA supplementation was associated with significantly increased insulin response to oral glucose compared with EPA supplementation and no supplementation. Inverse correlation was noted between glucose uptake and plasma triacylglycerol levels (r -086, P<0.001) and abdominal fat volume (r -0.80, P<0.001). The result of oral glucose tolerance test study showed that the rats fed EPA tended to improve glucose intolerance, although this was not statistically significant. Levels of plasma insulin at 60 min after glucose was significantly increased in rats fed OA compared with the other two groups. The results indicate that long-term feeding of EPA might be effective in preventing insulin resistance in diabetes-prone rats, at least in part, due to improving hypertriacylglycerolaemia.

United States Cholesterol Guidelines 2001: expanded scope of intensive low-density lipoprotein-lowering therapy

The new clinical guidelines of the US National Cholesterol Education Program (NCEP) were released in May 2001. These guidelines were published as the NCEP's Adult Treatment Panel (ATP) III report. They are derived from an extensive review of the emerging literature so as to provide an evidence-based report. Thanks to recent clinical trials of cholesterol-lowering therapy, it is possible to expand the scope of clinical management for both dietary and drug therapies. This expansion derives from a conclusive demonstration of efficacy, safety, and cost-effectiveness of therapies. This article will review briefly the major features of ATP III.

Effect of a six month gemfibrozil treatment and dietary recommendations on the metabolic risk profile of visceral obese men

OBJECTIVE

The aim of the present study was to investigate the effects of a 6 month gemfibrozil treatment.

SUBJECTS

A sample of 64 visceral obese men (age 46+/-6 y; body mass index 31+/-3 kg/m(2); waist circumference 104+/-7 cm; mean+/-s.d.) who received dietary recommendations.

METHODS

Subjects were randomly assigned to receive a placebo (n=32) or gemfibrozil (1200 mg/day) (n=32).

RESULTS

In both placebo and gemfibrozil treated groups, significant reductions were noted in body weight, fat mass, waist circumference and visceral adipose tissue area measured by computed tomography (0.0001<P<0.05). Plasma cholesterol (CHOL) and apolipoprotein B (apo B) levels were also decreased in both groups (P<0.01) whereas plasma high density lipoprotein (HDL) and HDL-3-CHOL levels were only significantly (P<0.01) increased in the gemfibrozil-treated group. After the 6 month treatment period, gemfibrozil-treated men displayed significantly lower plasma triglycerides (TG) levels, compared to those who received the placebo (P<0.01). Finally, both fasting plasma insulin concentration and insulin area measured during an oral glucose load were significantly decreased only in the placebo group (P<0.05). Taken together, these results suggest that the improvement in plasma lipid/lipoprotein profile observed in gemfibrozil treated visceral obese men seems to be independent from changes in adipose tissue mass and in visceral fat accumulation. Furthermore, improvements in the plasma lipoprotein profile produced by gemfibrozil therapy appear to be independent from changes in indices of plasma glucose-insulin homeostasis.

Biochemical profile of idiopathic uric acid nephrolithiasis

BACKGROUND

The objective of this study was to elucidate a biochemical profile of patients with idiopathic uric acid nephrolithiasis, without secondary causes (such as dehydration or diarrhea). Study subjects comprised 56 patients with idiopathic uric acid nephrolithiasis (UA stone group) who underwent a full outpatient evaluation. The control group was composed of 54 with absorptive hypercalciuria and 2 normal subjects, matched with the UA stone group according to age, body mass index, and gender.

METHODS

Urinary pH and ammonium and serum and urinary uric acid were measured. The fractional excretion of urate was calculated.

RESULTS

Compared with the control group, the UA stone group had a significantly higher serum uric acid and significantly lower urinary uric acid, pH (5.34 +/- 0.23 vs. 6.17 +/- 0.36, P < 0.001), and fractional excretion of urate (0.052 +/- 0.028 vs. 0.080 +/- 0.029, P < 0.001), but individual values overlapped considerably between the two groups. Discriminant analysis of the relationship between urinary pH and fractional excretion of urate yielded a "discriminant score," which provided a much better separation between the two groups, with a correct classification in 95.5% of subjects. In contrast, urinary ammonium, citrate, sulfate, and potassium did not differ between two groups.

CONCLUSIONS

In idiopathic uric acid nephrolithiasis, urinary pH and fractional excretion of urate are significantly lower than in control subjects, suggestive of defects in urinary acidification and urate excretion. Since these impairments are believed to be associated with primary gout, the underlying disturbance in idiopathic uric acid nephrolithiasis may be primary gout.

Anti-lipolytic effects of insulin in African American and white prepubertal boys

OBJECTIVE

Relative to whites, African Americans have lower circulating triglycerides (TG) and greater highdensity lipoprotein cholesterol. The metabolic basis for this difference is not known. This study was conducted to test the hypothesis that insulin-induced suppression of free fatty acids (FFA) results in lower serum TG in African American versus white prepubertal children.

RESEARCH METHODS AND PROCEDURES

Insulin, FFA, and TG were determined at baseline and during a frequently sampled, intravenous glucose tolerance test in eight African American and eight white prepubertal males pair-matched for whole-body insulin sensitivity.

RESULTS

Baseline TG was lower in African Americans (0.43 +/- 0.10 vs. 0.79 +/- 0.37 mM/L; mean +/- SD; p < 0.01). African Americans had higher peak insulin (218 +/- 102 vs. 100 +/- 30 pM/L; mean +/- SD; p < 0.01) and a greater acute insulin response (9282 +/- 4272 vs. 4230 +/- 1326 pM/L x 10 minutes; mean +/- SD; p < 0.05). FFA and TG values determined at the FFA nadir were lower in African Americans (0.26 +/- 0.02 vs. 0.30 +/- 0.03 mEq/L; mean +/- SD; p < 0.01 for FFA nadir and 0.49 +/- 0.07 vs. 0.77 +/- 0.33 mM/L; mean +/- SD; p < 0.05 for TG). Among all subjects, FFA nadir was correlated with peak insulin (r = -0.54; p < 0.05). After adjusting for FFA nadir, neither baseline nor postchallenge TG differed with ethnicity (p = 0.073 and 0.192, respectively). The ethnic difference in FFA nadir disappeared after adjusting for peak insulin (p = 0.073).

DISCUSSION

These data suggest that hyperinsulinemiainduced suppression of FFA among African Americans is a determinant of lower TG in this group.

Endothelial dysfunction in men with small LDL particles

BACKGROUND

It is unknown whether LDL particle size is, independent of other lipids and lipoproteins, associated with endothelial dysfunction in vivo.

METHODS AND RESULTS

We determined in vivo endothelial function in 34 healthy men by measuring forearm blood flow responses to intrabrachial artery infusions of acetylcholine (ACh, an endothelium-dependent vasodilator) and sodium nitroprusside (an endothelium-independent vasodilator). LDL peak particle size was measured with gradient gel electrophoresis. Men with small LDL particles (LDL diameter </=25.5 nm, n=10) had a 39% lower blood flow response to ACh than men with large LDL particles (LDL diameter >25. 5 nm, n=24, blood flow 6.9+/-3.6 versus 11.4+/-5.1 mL/dL. min, P=0. 006). The groups had comparable LDL cholesterol concentrations (3. 9+/-0.6 versus 3.7+/-1.0 mmol/L, men with small versus large LDL particles), blood pressure, glucose concentrations, and body mass indexes. LDL size (r=0.45, P=0.01) but not HDL cholesterol (r=0.31, P=0.09) or triglycerides (r=-0.19, P=0.30) was significantly correlated with endothelium-dependent vasodilation. Serum triglyceride concentrations and LDL size were inversely correlated (r=-0.44, P=0.01). In multivariate regression analysis, LDL size was the only significant determinant of the ACh-induced increase in blood flow. Sodium nitroprusside-stimulated endothelium-independent vasodilation was similar in both groups.

CONCLUSIONS

Small LDL particles are associated with impaired in vivo endothelial function independent of HDL and LDL cholesterol and triglyceride concentrations. LDL size may therefore mediate adverse effects of hypertriglyceridemia on vascular function.

Cross-sectional but not longitudinal associations between non-esterified fatty acid levels and glucose intolerance and other features of the metabolic syndrome

AIMS

Cross-sectional studies have demonstrated an association between high non-esterified fatty acid (NEFA) concentrations and glucose intolerance. However, the direction of causality in these studies is uncertain. The aim of this study was to examine whether NEFA levels predicted the development of glucose intolerance in a prospective population-based cohort study.

METHOD

Four hundred and eighty-one women and 345 men participated in a prospective cohort study in which NEFA concentrations and glucose tolerance were measured at baseline and then repeated at follow-up 4.5 years later.

RESULTS

The data do not show longitudinal relationships between baseline NEFA levels and either glucose intolerance or other features of the metabolic syndrome at follow-up. In contrast, strong cross-sectional associations were observed between NEFA measures and glucose intolerance (and other features of the metabolic syndrome) in both baseline and follow-up studies. At follow-up, fasting NEFA levels and two measures of NEFA suppression were markedly different in subjects with features of the metabolic syndrome, compared to subjects with normal glucose tolerance (NGT) (NGT vs. metabolic syndrome for each NEFA value, P< 0.001).

CONCLUSIONS

These results support the hypothesis that plasma NEFA levels change as a consequence of the metabolic syndrome and do not support the notion that increased NEFA levels cause either the metabolic syndrome or diabetes.

Lipoprotein physiology

Lipoproteins are spherical macromolecular complexes in which hydrophobic molecules of triglyceride and cholesteryl ester are enveloped within a monolayer of amphipathic molecules of phospholipids, free cholesterol, and apoproteins. The major lipoprotein classes include intestinally derived chylomicrons that transport dietary fats and cholesterol, hepatic-derived VLDL, IDL, and LDL that can be atherogenic, and hepatic- and intestinally derived HDL that are anti-atherogenic. Apoprotein B is necessary for the secretion of chylomicrons (apo B48) and VLDL, IDL, and LDL (apo B100). Post-translational regulation of the assembly of apo B-containing lipoproteins by core lipid availability seems to be the major mechanism for variations in secretion. Plasma levels of VLDL triglycerides are determined mainly by rates of secretion and LPL lipolytic activity; plasma levels of LDL cholesterol are determined mainly by the secretion of apo B100 into plasma, the efficacy with which VLDL are converted to LDL and by LDL receptor-mediated clearance. Regulation of HDL cholesterol levels is complex and is affected by rates of synthesis of its apoproteins, rates of esterification of free cholesterol to cholesteryl ester by LCAT, levels of triglyceride-rich lipoproteins and CETP-mediated transfer of cholesteryl esters from HDL, and clearance from plasma of HDL lipids and apoproteins. Normal lipoprotein transport is associated with low levels of triglycerides and LDL cholesterol and high levels of HDL cholesterol. When lipoprotein transport is abnormal, lipoproteins levels can change in ways that predispose individuals to atherosclerosis.

Impaired myocardial vasodilation during hyperemic stress with dipyridamole in hypertriglyceridemia

OBJECTIVES

This study sought to investigate the specific role of hypertriglyceridemia in the myocardial hyperemic stress with dipyridamole/rest flow ratio (MDR).

BACKGROUND

Reduced MDR has been reported in hypercholesterolemic patients without evidence of ischemia. However, the specific role of hypertriglyceridemia in MDR has not been studied.

METHODS

Fifteen nondiabetic normocholesterolemic hypertriglyceridemic patients and 13 age-matched control subjects were studied. Myocardial blood flow (MBF) during dipyridamole administration and baseline MBF in hypertriglyceridemic patients and control subjects were measured using positron emission tomography and nitrogen-13 ammonia, after which the MDR was calculated.

RESULTS

Baseline MBF (ml/min per 100 g heart weight) in hypertriglyceridemic patients (mean +/- SD 73.6 +/- 24.1) did not differ significantly from that in control subjects (81.6 +/- 37.2). MBF during dipyridamole loading in hypertriglyceridemic patients (198 +/- 106) was significantly reduced compared with that in control subjects (313 +/- 176, p < 0.05), as was the MDR (2.71 +/- 1.07 vs. 3.73 +/- 1.14, respectively, p < 0.05). Spearman rank-order correlation analysis showed a significant relation between plasma triglyceride concentration and MDR (r = -0.466, asymptotic SE 0.157, p = 0.0125); however, no such significant relation was seen between total plasma cholesterol concentration and MDR (r = -0.369, asymptotic SE 0.130, p = 0.059).

CONCLUSIONS

Impaired myocardial vasodilation was suggested in hypertriglyceridemic patients without symptoms and signs of ischemia.

Abnormal metabolism of free fatty acids in hypertriglyceridaemic men: apparent insulin resistance of adipose tissue

OBJECTIVE

There is growing evidence that endogenous hypertriglyceridaemia is frequently accompanied by a state of insulin resistance. The present study was performed to determine whether patients with primary endogenous hypertriglyceridaemia commonly have abnormalities in plasma concentrations and turnover rates of free fatty acids (FFA), which could reflect a state of insulin resistance in adipose tissue and could account for raised plasma triglycerides.

DESIGN

Hypertriglyceridaemic and normotriglyceridemic control patients underwent measurements of plasma concentrations and turnover rates of FFA. Fat weights in both groups were determined by hydrodensitometry, and fat distribution was assessed by skin-folds and measurement of waist and hip circumferences. Other measurements included plasma glucose, insulin, lipids, and lipoproteins.

SUBJECTS

Fifteen men with normal plasma triglycerides and 21 men with primary endogenous hypertriglyceridaemia were studied. Men in both groups varied in body weights and total fat weights, but total fat weights were entirely overlapping for the two groups. Waist-to-hip ratios and waist circumferences also were similar for the two groups.

RESULTS

For any total body fat content or waist circumference, most hypertriglyceridaemia patients had higher mean plasma concentrations of FFA and higher turnover rates (flux) for FFA than did normotriglyceridemic patients. Hypertriglyceridaemic patients also had higher fasting insulin concentrations for a given body fat content. In general, both FFA flux and plasma insulin levels were positively correlated with plasma concentrations of triglyceride and inversely with high density lipoprotein (HDL) cholesterol.

CONCLUSIONS

These studies indicate that many patients with primary endogenous hypertriglyceridaemia have increased flux of FFA and hyperinsulinemia that cannot be explained either by increased total body fat content or by greater waist circumferences than observed in normotriglyceridemic patients.

A review on ethnic differences in plasma triglycerides and high-density-lipoprotein cholesterol: is the lipid pattern the key factor for the low coronary heart disease rate in people of African origin?

Black people in the UK, in the Caribbean, and to a lesser extent in the USA, experience coronary heart disease events at different rates than white people. Despite having higher prevalence of hypertension, cigarette smoking and diabetes, black males have significantly lower coronary heart disease rates than white males, whereas no significant differences have been detected in females. The only known risk factor differences that could account for the difference in CHD rates are higher HDL cholesterol and lower triglycerides that are seen in blacks compared with whites. Obesity and, in particular abdominal obesity, seems to determine TG and HDL cholesterol levels: black males are less centrally obese than whites, while total adiposity and central distribution of fat is more predominant in black females compared with white females. We propose that the less degree of abdominal adiposity observed in black males is related with an increased anti-lipolytic effect of insulin, which could account for low triglycerides and high HDL cholesterol levels, and consequently explain the higher protection from coronary heart disease experienced by black males compared with whites and black females.

Differences in insulin suppression of free fatty acid levels by gender and glucose tolerance status. Relation to plasma triglyceride and apolipoprotein B concentrations. Insulin Resistance Atherosclerosis Study (IRAS) Investigators

Most discussions of relations of insulin resistance to coronary heart disease risk factors have focused on insulin-stimulated glucose uptake, but insulin suppression of plasma free fatty acid (FFA) levels is also important in lipid and lipoprotein metabolism. To identify groups with impaired insulin suppression of FFAs, we studied a multiethnic cohort of 1521 women and men at four US centers that comprise the Insulin Resistance Atherosclerosis Study (IRAS): 682 with normal glucose tolerance, 352 with impaired glucose tolerance, and 487 with non-insulin-dependent diabetes. The FFA level 2 hours after a 75-gm oral glucose load adjusted for fasting FFAs was used as the measure of insulin suppression. After adjustment for age, center, ethnicity, body mass index, and fasting and 2-hour insulin levels, 2-hour FFA levels were significantly higher in men than women and in persons with impaired glucose tolerance and non-insulin-dependent diabetes mellitus versus normal glucose tolerance. The gender difference was largely accounted for by differences in central obesity as measured by waist-hip ratio; the difference by glucose tolerance status was not affected by central obesity, suggesting a different mechanism. In multivariate regression analyses, 2-hour FFA levels were strongly related to fasting triglyceride and apoB levels, respectively, after adjustment for age, fasting and 2-hour insulin concentrations, and fasting FFA concentrations. In summary, elevated plasma apoB and triglyceride concentrations associated with male gender and with glucose intolerance are partly accounted for by differences in the ability of insulin to suppress FFA concentrations.

Clara cell protein correlation with hyperlipidemia

Serum levels of protein 1 (P1), a Clara cell secretory protein, in 746 healthy subjects were measured and their correlations with different types of serum lipids and lipoproteins-that is, triglyceride (TG), total cholesterol (TCh), free cholesterol (FCh), high-density lipoprotein (HDL), low-density lipoprotein (LDL), and apoproteins (apo) A-I, A-II, and B-were examined. P1 serum levels were examined for their correlation with body mass index (BMI), and were compared for 47 obese, 70 normal, and 17 lean males. P1 serum levels in 69 patients with diabetes mellitus and 24 patients with atherosclerotic stenosis of the carotid artery or coronary artery were also compared to those in healthy control subjects. P1 showed a significant positive correlation with TG, TCh, FCh, apo A-I, apo A-II, apo B, and BMI (r = 0.93, 0.26, 0.42, 0.11, 0.35, 0.58, and 0.20, respectively; p < 0.0001 to 0.05), and an inverse correlation with HDL (r = -0.32; p < 0.01). P1 values in obese men (mean +/- SD: 139.2 +/- 98.2 micrograms/L) were significantly higher than those in normal (90.3 +/- 57.1) and lean ones (65.6 +/- 40.8) (p < 0.01). In both diabetic and atherosclerotic patients, P1 serum levels did not significantly differ from those in healthy subjects. From these results, we conclude the following: (1) the serum levels of P1 correlate significantly with those of lipids and lipoproteins; (2) P1 serum levels increase in the case of obesity.

Differential effects of acute hypertriglyceridemia on insulin action and insulin receptor autophosphorylation

Experimentally induced hypertriglyceridemia (HTG) and high plasma free fatty acid (FFA) levels impair in vivo insulin action. To determine if this is a consequence of impaired in vivo insulin receptor autophosphorylation and related to defective receptor signaling, hyperinsulinemic euglycemic clamps, indirect calorimetry, and skeletal muscle biopsies were performed in nine healthy subjects. In vivo insulin action was determined from the glucose infusion rate (GINF) and glucose oxidation (Glcox) during 40 and 120 mU/m2 /min clamps with (HTG clamp) and without (control clamp) a triglyceride emulsion infusion. The percentage of receptors autophosphorylated in vivo was determined by 125I-labeled insulin tracer binding in skeletal muscle immunoprecipitates of insulin receptors and phosphorylated receptors. Compared with the control clamps, plasma triglycerides and FFA increased four- and twofold, whereas GINF and Glcox decreased 15 and 35%, respectively, during the HTG clamps (all P<0.05). However, the percentages of receptors phosphorylated after the 40 and 120 mU/m2/min HTG clamps (9.2 +/- 1.5 and 21.1 +/- 2.6%, respectively) were similar to the control clamps (9.0 +/- 0.6 and 18.6 +/- 2.2%, respectively). These results indicate that, if impaired insulin signal transduction is a mechanism by which HTG and FFA impair insulin action, it occurs at a site downstream from insulin receptor autophosphorylation.

Metabolic consequences of obesity and body fat pattern: lessons from migrant studies

Prevalence of non-insulin-dependent diabetes mellitus and mortality from coronary heart disease are higher in people of South Asian (Indian, Pakistani and Bangladeshi) descent living in urban societies than in other ethnic groups. The high prevalence of diabetes is one manifestation of a pattern of metabolic disturbances related to central obesity and insulin resistance, which includes raised plasma very low density lipoprotein triglyceride and low plasma high density lipoprotein-cholesterol. Average waist/hip circumference ratios are higher in South Asians than in Europeans of similar body mass index: in this respect South Asians differ from other populations such as Pima Indians where high prevalence of non-insulin-dependent diabetes mellitus occurs in association with generalized obesity. The high rates of coronary heart disease in South Asians are most easily explained by the effects of this central obesity/insulin resistance syndrome, although ethnic differences in fasting lipids are unlikely to account fully for the excess risk. In Afro-Caribbean migrants, the prevalence of diabetes is almost as high as in South Asians but the lipid disturbances characteristic of the insulin resistance syndrome do not occur to the same extent. This may account for the low rates of coronary heart disease in this group.

Role of insulin resistance in the pathogenesis of NIDDM

The above discussion illustrating the multitude of variables which influence insulin sensitivity in normal subjects challenges the prevailing view that insulin sensitivity is genetically determined in patients with NIDDM. The lack of accurate quantitation of all determinants of insulin sensitivity in the cross-sectional studies, and the difficulty in distinguishing between insulin secretion and sensitivity in prospective studies implies that the inherited metabolic abnormality in NIDDM still remains to be defined. The methodological difficulties in assessing the fate of glucose in many insulin-resistant states raise the possibility that defects in glycogen synthesis may not be rate-limiting for insulin action. It seems more likely that defects in glucose transport or phosphorylation are rate-limiting for glucose disposal, and thus represent either the primary regulatory steps or the steps via which distal defects signal their influence on glucose uptake. The above considerations should not be interpreted to suggest that insulin resistance is unimportant in the pathogenesis of NIDDM. It clearly increases the risk of developing NIDDM, and more importantly, its early amelioration by lifestyle modification seems sufficient to prevent NIDDM.

Fetal growth and insulin resistance in adult life: role of plasma triglyceride and non-esterified fatty acids

Reduced fetal growth is associated with insulin resistance and a high prevalence of glucose intolerance in adult life. Because babies who are growth retarded have elevated levels of triglyceride and non-esterified fatty acids (NEFA), and because similar abnormalities are observed in subjects with the insulin resistance syndrome, impaired regulation of lipid metabolism could be one of the mechanisms explaining the link between reduced fetal growth and insulin resistance. We have, therefore, measured fasting plasma triglyceride and NEFA, and the insulin-mediated suppression of NEFA during an oral glucose tolerance test in 93 men and women aged 50, born in Preston, whose birthweight and body size at birth had been recorded. Elevated fasting plasma triglycerides and reduced NEFA suppression during the oral glucose tolerance test were associated with the male sex, glucose intolerance, central obesity as indicated by a high waist to hip ratio and insulin resistance as measured by a short insulin tolerance test. However there were no statistically significant relationships between the birth measurements and the circulating lipid levels. Moreover in regression analyses the relationships between thinness at birth and insulin resistance or glucose intolerance in adult life were unaffected by the addition of triglyceride or NEFA in the models. These results suggest that the link between reduced fetal growth and insulin resistance in the adult is not mediated by an abnormal regulation of lipid metabolism.

Modulation of in vivo insulin action by dietary protein during pregnancy

Rats were provided with a standard 20% protein diet or an isocaloric 8% protein diet from day 1 of gestation and were studied on day 19 of pregnancy. Fetal numbers per dam were unchanged, but total fetal weight at day 19 of gestation was reduced by 10% (P < 0.001) in the 8% protein group. In the basal state, endogenous glucose production (Ra) and muscle glucose uptake/phosphorylation were not significantly affected by dietary protein content. The glucose infusion rate required to maintain glycemia and Ra during euglycemic-hyperinsulinemic clamp (insulin infusion rate of 4.17 mU.kg-1.min-1) were reduced in the 8% protein group by 17% (P < 0.05) and 76% (P < 0.001), respectively. Suppression of Ra by insulin was not significant in the 20% protein group. Insulin-stimulated glucose disappearance (Rd) was 24% lower (P < 0.001) in the 8% protein group (25.0 +/- 0.8 mg.min-1.kg-1) than in the 20% protein group (32.7 +/- 0.5 mg.min-1.kg-1). The overall increment in muscle glucose utilization index (mean of 6 muscles) elicited by insulin was impaired by 38.1 +/- 4.0%. Insulin suppressed nonesterified fatty acid concentration (NEFA) by 83% (P < 0.001) and plasma triacylglycerol concentration (TAG) by 67% (P < 0.05) in the 20% protein group but evoked only a 43% (P < 0.01) decline in plasma NEFA and did not significantly suppress plasma TAG in the 8% protein group.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes of lipolytic enzymes cluster with insulin resistance syndrome. Botnia Study Group

The activities of hepatic and lipoprotein lipase and the levels of lipo- and apoproteins were compared in two groups of normoglycaemic men representing the highest (n = 18) and lowest (n = 15) fasting insulin quintiles of first degree male relatives of non-insulin-dependent diabetic patients. The high insulin group representing insulin-resistant individuals had significantly lower post-heparin plasma lipoprotein lipase activity than the low insulin group (14.2 +/- 4.0 vs 20 +/- 5.8 mumol NEFA.ml-1.h-1, p < 0.001); hepatic lipase activity did not differ between the two groups (24.2 +/- 11 vs 18.0 +/- 5.3 mumol NEFA.ml-1.h-1, NS). The lipoprotein lipase/hepatic lipase ratio in the high insulin group was decreased by 66% as compared to the low insulin group (0.75 +/- 0.57 vs 1.25 +/- 0.65, p < 0.01). In the high insulin group both total and VLDL triglycerides were higher than in the low insulin group (1.61 +/- 0.57 vs 0.86 +/- 0.26 mmol/l, p < 0.001 and 1.00 +/- 0.47 vs 0.36 +/- 0.16 mmol/l, p < 0.001, respectively) whereas HDL cholesterol and HDL2 cholesterol were lower (1.20 +/- 0.30 vs 1.43 +/- 0.22 mmol/l, p < 0.05 and 0.49 +/- 0.21 vs 0.71 +/- 0.17 mmol/l, p < 0.05, respectively). Total cholesterol, LDL cholesterol or HDL3 cholesterol did not differ between the two groups. The mean particle size of LDL was smaller in the high insulin group than in the low insulin group (258 +/- 7 vs 265 +/- 6 A, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Hypertriglyceridaemia in subjects with normal and abnormal glucose tolerance: relative contributions of insulin secretion, insulin resistance and suppression of plasma non-esterified fatty acids

Although plasma insulin and triglyceride concentrations are positively correlated in many studies, the relationships between insulin resistance, insulin secretion and hypertriglyceridaemia remain unclear. To study these associations, subjects between the ages of 40 and 64 were randomly selected from a general practice register and invited to attend for a standard oral glucose tolerance test for measurement of insulin, triglyceride and non-esterified fatty acid concentrations. The study comprised 1122 subjects who were not previously known to have diabetes and who completed the test. Using the World Health Organisation criteria, 51 subjects were classified to have non-insulin-dependent diabetes mellitus, 188 had impaired glucose tolerance and 883 subjects had normal glucose tolerance. Triglyceride concentrations in subjects with glucose intolerance were elevated compared to those in control subjects, even after adjustment for age, obesity and gender (p < 0.001 for subjects with diabetes and p < 0.01 for those with impaired glucose tolerance compared to normal subjects). In separate multiple regression analyses for males and females, the most important determinants of the plasma triglyceride concentration were the area under the non-esterified fatty acid suppression curve (p < 0.001 in both genders) and the waist-hip ratio (p < 0.001 for men and < 0.01 for women). The fasting insulin concentration was independently associated with triglyceride concentration in women only (p < 0.01). The most important determinant of the area under the non-esterified fatty acid suppression curve in men was the 30-min insulin increment, a measure of insulin secretion, (p < 0.001) whereas for women age (p < 0.001) and the body mass index (p < 0.01) were the most important.

Treatment of non-insulin-dependent diabetes mellitus and its complications. A state of the art review

Non-insulin-dependent diabetes mellitus (NIDDM) is a major health problem which occurs predominantly in the older population; 16.8% of persons over age 65 years have NIDDM. The total health costs of NIDDM are in excess of $US20 billion annually. The primary objective in the treatment of NIDDM is to achieve normoglycaemia, without aggravating coexisting abnormalities. Common abnormalities include obesity, hypertension, retinopathy, nephropathy and neuropathies. Diet, and consequent bodyweight reduction, is the cornerstone of therapy for NIDDM. Total calorie intake should be limited, while the percentage of calories from carbohydrates should be increased and that from fats and cholesterol should be decreased. Exercise may also help to reduce bodyweight. Sulphonylurea drugs stimulate insulin secretion from beta-cells, and may be a useful adjunct to nonpharmacological therapy. Failure to respond to sulphonylurea drugs may be primary (25 to 30% of initially treated patients) or secondary (5 to 10% per year). It is not clear which is the most effective pharmacological intervention in such cases. Options include switching to or combining therapy with insulin, a biguanide, or other insulin-sparing antihyperglycaemic agents, e.g. alpha-glucosidase inhibitors, thiazolidinediones, chloroquine or hydroxychloroquine, or fibric acid derivatives such as clofibrate. Other experimental agents include the fatty acid oxidation inhibitors and dichloroacetate. Specific agents, such as antihypertensives, lipid lowering agents and sorbitol inhibitors, may be needed to prevent the complications arising from the spectrum of clinical and metabolic abnormalities which arise from insulin resistance.

The effect of an antilipolytic agent (acipimox) on the insulin resistance of lipid and glucose metabolism in hypertriglyceridaemic patients

Hypertriglyceridaemia is associated with insulin resistance of both lipid and glucose metabolism. It is not known whether the insulin resistance affects both glucose oxidation and glycogen formation. To study the oxidative and non-oxidative pathways of non-esterified fatty acids (NEFA) and glucose metabolism, eight male hypertriglyceridaemic subjects were studied during insulin infusion (75 and 340 pmol/m2.min) in combination with indirect calorimetry and infusions of [3-3H]glucose and [1-14C]palmitate before and after 4 weeks of treatment with the antilipolytic agent acipimox (250 mg three times daily). Compared with eight healthy subjects the hypertriglyceridaemic subjects were resistant to the antilipolytic effect of insulin, both in the basal state (P < 0.05) and during insulin infusion (P < 0.05). This was associated with impaired insulin-stimulated glucose uptake (P < 0.05), predominantly in the non-oxidative pathway (P < 0.05). Acipimox decreased basal NEFA concentrations (P < 0.01) and reduced lipid oxidation during low-dose insulin infusion (P < 0.05). Glucose uptake, predominantly glycogen formation, was stimulated by acipimox (P < 0.05). In conclusion, the insulin resistance of glucose metabolism associated with hypertriglyceridaemia is largely due to a defect in non-oxidative glucose metabolism. Acipimox improves glucose metabolism both by affecting glucose oxidation (low-dose insulin) and non-oxidative glucose metabolism (high-dose insulin).

Relation of plasma triglyceride and apoB levels to insulin-mediated suppression of nonesterified fatty acids. Possible explanation for sex differences in lipoprotein pattern

To test whether a sex difference in insulin-mediated suppression of nonesterified fatty acids (NEFAs) could account for sex differences in plasma triglyceride levels, we studied 632 normoglycemic men and women of European and South Asian descent aged 40 to 69 years. Mean fasting NEFA levels were 19% higher in women than in men. Between fasting and 2 hours after a 75-g oral glucose load, NEFA levels fell by 69% in women and 55% in men, so that mean NEFA levels at 2 hours after loading were 19% lower in women than in men. Plasma triglyceride and apolipoprotein B levels were correlated with 2-hour NEFA levels in each sex and ethnic group, and these associations were independent of glucose, insulin, and central obesity. These results are consistent with experimental studies of the effects of insulin and NEFAs on hepatic production of triglycerides and apolipoprotein B. Suppression of NEFA levels in response to insulin is greater in women than in men, and this may account for some of the sex differences in lipoprotein pattern and coronary heart disease risk.

Adipocyte beta-adrenoceptor sensitivity influences plasma lipid levels

Catecholamine stimulation of lipolysis through adipocyte beta-adrenoceptors is of major importance for the regulation of lipid mobilization from adipose tissue. The influence of adipocyte beta-receptor sensitivity as assessed by an isoprenaline bioassay on circulating lipid levels was investigated in 46 healthy and drug-free subjects. beta-Receptor sensitivity was inversely related to total plasma triglycerides (r = -.62), very low density lipoprotein cholesterol (VLDL-C) (r = -.56), VLDL triglycerides (r = -.52), and apolipoprotein B (r = -.41). These relationships remained significant after adjustment for age, sex, body mass index, waist/hip ratio, fat cell volume, and circulating levels of insulin, noradrenaline, and adrenaline. beta-Receptor sensitivity accounted for 40% of the variance in total plasma triglycerides. beta-Receptor subtype sensitivity and binding capacity were also determined in fat cells using terbutaline (beta 2) and dobutamine (beta 1) bioassays and radioligand binding. Multiple regression analysis revealed that terbutaline sensitivity correlated inversely with total plasma triglycerides, apolipoprotein B, VLDL-C, and VLDL triglycerides (partial r from -.56 to -.42), but there was no correlation between dobutamine sensitivity and blood lipids (partial r from .05 to .18) or between receptor binding and blood lipids (partial r from .01 to .28). Thus, the lipolytic beta-receptor sensitivity in fat cells appears to play a hitherto-unrecognized role for lipoprotein metabolism, in particular that of VLDL. This relationship is receptor-subtype specific, particularly involving beta 2-receptors, and seems to be localized to a postreceptor step in lipolysis regulation. Low sensitivity may be of importance for the development of hypertriglyceridemia.

Insulin resistance and compensatory insulin secretion in middle-aged persons with hypertriglyceridemia

Insulin secretion and insulin sensitivity were measured in hypertriglyceridemic patients using the frequently sampled intravenous glucose tolerance test. Three groups of men who were matched for age and body mass index were studied: eight healthy control subjects (C), seven patients with mild hypertriglyceridemia and normal glucose tolerance (TG), and seven with well-controlled type 2 diabetes with hypertriglyceridemia (TG-DM). The first-phase insulin response was increased by 116% in the TG group and decreased by 59% in the TG-DM group. The second phase of insulin secretion was increased in both TG groups (TG by 310% and TG-DM by 250%). The mean insulin sensitivity index (SI) was reduced by 50% in the TG group and by 60% in the TG-DM group. Glucose effectiveness (SG) was reduced by 30% in the TG-DM group compared with the control subjects.