Body fat distribution, insulin mediated suppression of non-esterified fatty acids and plasma triglycerides in obese subjects

Serum lipoprotein lipase mass: clinical significance of its measurement

Lipoprotein lipase (LPL) is a lipolytic enzyme involved in catalyzing hydrolysis of triglycerides (TG) in chylomicrons and very low-density lipoprotein (VLDL) particles. Over the last decade, increasing attention has been paid to the clinical significance of measuring serum LPL protein mass without heparin injection to the study subjects. In earlier studies, this marker was utilized to classify LPL deficient subjects, which is an extremely rare metabolic disorder with a frequency of one in one million. Later, researchers paid more attention to the clinical significance of measuring this parameter in more common metabolic disorders. Studies have shown that pre-heparin plasma or serum LPL mass has significant relationships with serum lipids and lipoproteins, visceral fat area, insulin resistance, and even the development of coronary atherosclerosis in cross-sectional studies, although this might be a metabolic surrogate marker with almost no catalytic activities, which does not appear to be involved in catalyzing hydrolysis of TG in TG-rich lipoproteins. Recently, a prospective study has demonstrated that low serum LPL concentration predicts future coronary events. Taken together, we suggest that pre-heparin LPL mass in plasma or sera provide us with useful and important information on the development of metabolic disorders leading to atherosclerotic disease.

Pre-heparin Lipoprotein Lipase Mass

Lipoprotein lipase (LPL) is a lipolytic enzyme involved in catalyzing the hydrolysis of triglycerides (TG) in chylomicrons and very low-density lipoprotein (VLDL) particles. Over the last decade, the clinical significance of measuring LPL mass without heparin injection has been increasingly studied. In earlier studies, it was shown that this marker was utilized to classify type 1 hyperlipoproteinemia, which is an extremely rare metabolic disorder. Later, researchers paid more attention to the clinical significance of measuring this parameter in more common metabolic disorders. Studies have shown that pre-heparin plasma LPL mass has significant relationships with serum lipid and lipoproteins, visceral fat area, and even a marker for acute inflammation, although this might be a metabolic surrogate marker which does not appear to be involved in catalyzing the hydrolysis of TG in TG-rich lipoproteins. We suggest that pre-heparin LPL mass in plasma or sera provides us with useful and important information on the pathophysiology of metabolic disorders or acute inflammation despite its simplicity from a practical point of view.

Lack of association between central adiposity and lipaemia in UK Sikh men

OBJECTIVE

To determine whether the positive statistical associations between measures of total and regional adiposity and measures of glucose, insulin and triacylglycerol (TAG) metabolism reported in Caucasian men, are also observed in UK Sikhs.

DESIGN

A matched cross-sectional study in which each volunteer provided a blood sample after a 12-h overnight fast and had anthropometric measurements taken.

SUBJECTS

A total of 55 healthy Caucasian and 55 healthy UK Sikh men were recruited. The Caucasian and Sikh men were matched for age (48.7+/-10.9 and 48.3+/-10.0 y, respectively) and body mass index (BMI) (26.1+/-2.8 and 26.3+/-3.2 kg/m(2), respectively).

MEASUREMENTS

Anthropometric measurements were performed to assess total and regional fat depots. The concentrations of plasma total cholesterol, high-density cholesterol (HDL-C), low-density cholesterol (LDL-C) and small dense LDL (LDL3), TAG, glucose, fasting insulin (ins) and nonesterified fatty acids (NEFA) were analysed in fasted plasma. Surrogate measures of insulin resistance (HOMA-IR) and insulin sensitivity (RQUICKI) were calculated from insulin and glucose (HOMA-IR) and insulin, glucose and NEFA (RQUICKI) measurements.

RESULTS

The Sikh men had significantly higher body fat, with the sum of the four skinfold measurements (Ssk) (P=0.0001) and subscapular skinfold value (P=0.009) higher compared with the Caucasian men. The Sikh volunteers also had characteristics of the metabolic syndrome: lower HDL-C (P=0.07), higher TAG (P=0.004), higher % LDL3 (P=0.0001) and insulin resistance (P=0.05). Both ethnic groups demonstrated positive correlations between insulin and waist circumference (Caucasian: r=0.661, P=0.0001; Sikh: r=0.477, P=0.0001). The Caucasian men also demonstrated significant positive correlations between central adiposity (r=0.275, P=0.04), other measures of adiposity (BMI and suprailiac skinfold) and plasma TAG, whereas the Sikh men showed no correlation for central adiposity (r=0.019, ns) and TAG with a trend to a negative relationship between other measures (Ssk and suprailiac) which reached near significance for subscapular skinfold and TAG (r=-0.246, P=0.007). The expected positive association between insulin and TAG was observed in the Caucasian men (r=0.318, P=0.04) but not in the Sikh men (r=0.011, ns).

CONCLUSIONS

In the Caucasian men, the expected positive association between plasma TAG and centralized body fat was observed. However, a lack of association between centralized, or any other measure of adiposity, and plasma TAG was observed in the matched Sikh men, although both ethnic groups showed the positive association between centralized body fat and insulin resistance, which was less strong for Sikhs. These findings in the Sikh men were not consistent with the hypothesis that there is a clear causal relationship between body fat and its distribution, insulin resistance, and lipid abnormalities associated with the metabolic syndrome, in this ethnic group.

Adiposity, insulin and lipid metabolism in post-menopausal women

OBJECTIVE

To investigate relationships between body fat and its distribution and carbohydrate and lipid tolerance using statistical comparisons in post-menopausal women.

DESIGN

Sequential meal, postprandial study (600 min) which included a mixed standard breakfast (30 g fat) and lunch (44 g fat) given at 0 and 270 min, respectively, after an overnight fast.

SUBJECTS

Twenty-eight post-menopausal women with a diverse range of body weight (body mass index (BMI), mean 27.2, range 20.5-38.8 kg/m2) and abdominal fat deposition (waist, mean 86.4, range 63.5-124.0 cm). Women with BMI < 18 or > 37 kg/m2, age > 80 y and taking hormone replacement therapy (HRT) were excluded.

MEASUREMENTS

Anthropometric measurements were performed to assess total and regional fat deposits. The concentrations of plasma total cholesterol, high density lipoprotein (HDL) cholesterol, triacylglycerol (TAG), glucose, insulin (ins), non-esterified fatty acids (NEFA) and apolipoprotein (apo) B-48 were analysed in plasma collected at baseline (fasted state) and at 13 postprandial time points for a 600 min period.

RESULTS

Insulin concentrations in the fasted and fed state were significantly correlated with all measures of adiposity (BMI, waist, waist-hip ratio (W/H), waist-height ratio (W/Ht) and sum of skinfold thickness (SSk)). After controlling for BMI, waist remained significantly and positively associated with fasted insulin (r=0.559) with waist contributing 53% to the variability after multiple regression analysis. After controlling for waist, BMI remained significantly correlated with postprandial (IAUC) insulin (r=0.535) contributing 66% of the variability of this measurement. No association was found between any measures of adiposity and glucose concentrations, although insulin concentration in relation to glucose concentration (glucose-insulin ratio) was significantly negatively correlated with all measures of adiposity. A significant positive correlation was found between fasted TAG and BMI (r=0.416), waist (r=0.393) and Ssk (r=0.457) and postprandial (AUC) TAG with BMI (r=0.385) and Ssk (r=0.406). A significantly higher postprandial apolipoprotein (apo) B-48 response was observed in those women with high BMI (> 27 kg/m2). Fasting levels of NEFA were significantly and positively correlated with all measures of adiposity (except W/H). No association was found between cholesterol containing particles and any measure of adiposity.

CONCLUSION

Hyperinsulinaemia associated with increasing body fat and central fat distribution is associated with normal glucose but not TAG or NEFA concentrations in postmenopausal women.

Cross-sectional and prospective associations between abdominal adiposity and proinsulin concentration

The objective of this study was to investigate the associations of total and abdominal obesity with variation in proinsulin concentration in a Native Canadian population experiencing an epidemic of type 2 diabetes mellitus (DM). Between 1993 and 1995, 728 members of a Native Canadian community participated in a population-based survey to determine the prevalence and risk factors for type 2 DM. Samples for glucose, C-peptide, and proinsulin were drawn after an overnight fast, and a 75-g oral glucose tolerance test was administered. Type 2 DM and impaired glucose tolerance (IGT) were diagnosed using World Health Organization criteria. Height, weight, waist circumference, and percent body fat were measured. In 1998, 95 individuals who, at baseline, had IGT or normal glucose tolerance with an elevated 2-h glucose level (> or = 7.0 mM) participated in a follow-up evaluation using the same protocol. After adjustment for age, sex, C-peptide concentration, per cent body fat, and waist circumference, proinsulin was found to be significantly elevated in diabetic subjects, relative to subjects with both impaired and normal glucose tolerance (both P < 0.0001); and the concentration in those with IGT was higher, compared with normals (P < 0.0001). Among nondiabetic subjects, proinsulin showed significant univariate associations with percent body fat, body mass index, and waist circumference (r = 0.34, 0.45, 0.41, respectively, all P < 0.0001). After adjustment for body fat and other covariates, waist circumference remained significantly associated with proinsulin concentration in nondiabetic subjects (r = 0.20, P < 0.0001). In prospective analysis, adjusted for covariates (including baseline IGT and follow-up glucose tolerance status), baseline waist circumference was positively associated with both follow-up and change in proinsulin concentration (r = 0.27, P = 0.01; r = 0.24, P = 0.03, respectively). These data highlight the detrimental effects of abdominal obesity on beta-cell function, and support the hypothesis that beta-cell dysfunction occurs early in the natural history of glucose intolerance.

Lack of association between lipaemia and central adiposity in subjects with an atherogenic lipoprotein phenotype (ALP)

OBJECTIVE

To investigate the associations between indices of adiposity and cardiovascular risk factors in individuals with an atherogenic lipoprotein phenotype (ALP).

SUBJECTS

Fifty-five men, aged 34-69 y, body mass index (BMI) 22-35 kg/m2, with an ALP lipid profile (triglycerides (TG) 1.5-4.0 mmol/l, HDL<1.1 mmol/l; %LDL-3>40% total LDL).

DESIGN

Each participant provided a fasting blood sample and underwent an 8 h postprandial assessment and had anthropometric measurements taken.

OUTCOME MEASURES

BMI, waist circumference (W), waist-to-hip ratio (W/H), sum of skinfolds (SSK), fasting and postprandial concentrations of glucose, insulin and plasma lipids, post-heparin lipase activity, and apoE genotype.

RESULTS

The expected positive associations between BMI, W and SSK and fasting and postprandial insulin were observed (r=0.42-0.65). Little association between glucose responses and any measures of adiposity was evident. Unexpectedly, there were no positive associations between measures of central adiposity (W and W/H) and fasting and postprandial TG responses, with a trend towards negative associations in this study group (TG AUC vs W, r=-0.23, P=0.097; TG IAUC vs W/H, r=-0.26, P=0.068). Subgroup analysis indicated that lack of a positive association between central adiposity and postprandial TG values was more evident in those with one E4 allele (r=-0.42, P=0.077) relative to non-E4 carriers (r=-0.16, P=0.430). The expected positive associations between insulin and TG responses were not observed (r=-0.03 to -0.36).

CONCLUSION

In this ALP group the expected positive association between TG responses and a centralized distribution of body fat was not observed, particularly in individuals with an apoE4 genotype. Our findings are not in line with the view that there is a clear causal relationship between insulin resistance and the lipid abnormalities associated with ALP.

Type II diabetes abrogates sex differences in endothelial function in premenopausal women

BACKGROUND

Obesity is a more potent cardiovascular risk factor (CVRF) in men than in women. Because traditional CVRFs cannot fully account for this sex difference, we tested the hypothesis that compared with men, women exhibit more robust endothelial function independent of obesity and that this sex difference is abrogated by diabetes.

METHODS AND RESULTS

We studied leg blood flow (LBF) responses to graded intrafemoral artery infusions of the endothelium-dependent vasodilator methacholine chloride (Mch) and the endothelium-independent vasodilator sodium nitroprusside (SNP) in groups of lean, obese (OB), and type II diabetic (DM) premenopausal women and age- and body mass index-matched men. LBF response to intrafemoral administration of L-NMMA, an inhibitor of nitric oxide synthase, was also assessed in normal men and women. Maximum LBF increments in response to Mch were 347+/-57% versus 231+/-22% in lean women versus men (P<0.05) and 203+/-25% versus 111+/-17% in OB women versus men (P<0.01), respectively. In DM, maximum LBF increments in response to Mch were 104+/-24% and 138+/-33% in women and men, respectively, (P=NS). LBF decrements in response to L-NMMA were 34.9+/-4.1% and 17.1+/-4.2% in women and men, respectively (P<0.01). The response to SNP was not different between sexes and groups.

CONCLUSIONS

Premenopausal nondiabetic women exhibit more robust endothelium-dependent vasodilation owing to higher rates of nitric oxide release than men. Given the protective vascular action of nitric oxide, this difference may partially explain the lower incidence of macrovascular disease in women. In premenopausal women, DM causes impairment of endothelial function beyond that observed with obesity alone and leads to endothelial dysfunction similar to that observed in DM men. These findings may help explain the similar rates of coronary artery disease and mortality in diabetic men and women.