Hypertriglyceridemic waist: A marker of the atherogenic metabolic triad (hyperinsulinemia; hyperapolipoprotein B; small, dense LDL) in men?

BACKGROUND

The present study tested the hypothesis that simple variables, such as waist circumference and fasting plasma triglyceride (TG) concentrations, could be used as screening tools for the identification of men characterized by a metabolic triad of nontraditional risk factors (elevated insulin and apolipoprotein [apo] B and small, dense LDL particles).

METHODS AND RESULTS

Results of the metabolic study (study 1) conducted on 185 healthy men indicate that a large proportion (>80%) of men with waist circumference values >/=90 cm and with elevated TG levels (>/=2.0 mmol/L) were characterized by the atherogenic metabolic triad. Validation of the model in an angiographic study (study 2) on a sample of 287 men with and without coronary artery disease (CAD) revealed that only men with both elevated waist and TG levels were at increased risk of CAD (odds ratio of 3.6, P<0.03) compared with men with low waist and TG levels.

CONCLUSIONS

It is suggested that the simultaneous measurement and interpretation of waist circumference and fasting TG could be used as inexpensive screening tools to identify men characterized by the atherogenic metabolic triad (hyperinsulinemia, elevated apo B, small, dense LDL) and at high risk for CAD.

Subcutaneous adipose tissue metabolism at menopause: importance of body fatness and regional fat distribution

The aim of this study was to examine the contribution of menopause per se on sc adipose tissue (AT) metabolism in 16 women classified on the basis of their menopausal status: 8 postmenopausal (mean +/- SD age, 57 +/- 6 yr) vs. 8 premenopausal individuals (37 +/- 5 yr). These 2 groups were matched for sc abdominal adipose cell size (within 0.02 microg lipid/cell) and visceral AT accumulation (within 15 cm2), measured by computed tomography. Fasting plasma glucose and insulin levels as well as their responses to an oral glucose load were similar regardless of the women's hormonal status. Subcutaneous abdominal and femoral AT lipoprotein lipase activities as well as fat cell lipolysis were determined in both groups. Epinephrine induced antilipolysis at low concentrations and lipolysis at higher doses in both adipose sites and groups. The maximal lipolytic response to epinephrine or to isoproterenol (beta-adrenergic agonist) as well as the maximal antilipolytic effect of either the catecholamine or UK-14304 (alpha2-adrenergic agonist) assessed in sc adipocytes were similar in pre- and postmenopausal women. In addition, neither the beta- nor the alpha2-adrenoceptor sensitivity of sc adipose cells differed according to subjects' age. Finally, maximal lipolysis promoted by postadrenoceptor agents and AT-lipoprotein lipase activity did not vary among adipose regions or between groups. Taken together, these results suggest that menopause per se does not influence sc AT metabolism once the variation related to adipose cell size and total body fatness is taken into account.

Hyperleptinemia is more closely associated with adipose cell hypertrophy than with adipose tissue hyperplasia

OBJECTIVES

To investigate the relationships of fat cell weight (FCW) as well as of estimated total adipose cell number to fasting plasma leptin concentration.

DESIGN

Cross-sectional correlational study.

SUBJECTS

A sample of 63 men (mean age+/-s.d.: 36+/-4 y) and 42 premenopausal women (35+/-5 y).

MEASUREMENTS

Adipose tissue (AT) biopsies were obtained in order to determine FCW as well as estimated adipose cell number. Fasting plasma leptin and insulin concentrations as well as various fatness and body fat distribution variables (underwater weighing and computed tomography) were also measured.

RESULTS

In both genders, mean FCW as well as the estimated adipose cell number were significantly correlated with body fatness and AT distribution variables (0.41</=r</=0.84). Larger abdominal (P<0.005) and femoral (P<0.0001) FCW were found in women than in men. This gender difference in adipose cell size was associated with increased leptin concentrations in women compared with men. In both genders, increased abdominal FCW was associated with higher plasma leptin concentrations (men: r=0.38, P<0.005 and women: r=0.55, P<0.0001). However, the association between femoral FCW and leptinemia was only significant in women (r=0.45, P<0.005). Contrary to women, plasma leptin concentrations were associated with estimated adipose cell number in men (r=0.59, P<0.0001). Multiple regression analyses revealed that gender (43.3%), mean FCW (16.2%) and the estimated adipose cell number (10.1%) were significant predictors of fasting leptinemia.

CONCLUSIONS

Results of the present study indicate that in men and women, adipose cell hypertrophy is associated with increased plasma leptin concentrations. This finding provides further support to the observation that adipose tissue leptin secretion may be regulated, at least to a certain extent, by adipocyte size. Thus, the present study suggests that the higher plasma leptin concentrations found in women than in men could be partly explained by the well documented gender difference in adipose cell size and number.

Effect of metformin on the vascular and glucose metabolic actions of insulin in hypertensive rats

We investigated the long-term effect of metformin treatment on blood pressure, insulin sensitivity, and vascular responses to insulin in conscious spontaneously hypertensive rats (SHR). The rats were instrumented with intravascular catheters and pulsed Doppler flow probes to measure blood pressure, heart rate, and blood flow. Insulin sensitivity was assessed by the euglycemic hyperinsulinemic clamp technique. Two groups of SHR received metformin (100 or 300 mg x kg(-1) x day(-1)) for 3 wk while another group of SHR and a group of Wistar Kyoto (WKY) rats were left untreated. We found that vasodilation of skeletal muscle and renal vasculatures by insulin is impaired in SHR. Moreover, a reduced insulin sensitivity was detected in vivo and in vitro in isolated soleus and extensor digitorum longus muscles from SHR compared with WKY rats. Three weeks of treatment with metformin improves the whole-body insulin-mediated glucose disposal in SHR but has no blood pressure-lowering effect and no influence on vascular responses to insulin (4 mU x kg(-1) x min(-1)). An improvement in insulin-mediated glucose transport activity was detected in isolated muscles from metformin-treated SHR, but in the absence of insulin no changes in basal glucose transport activity were observed. It is suggested that part of the beneficial effect of metformin on insulin resistance results from a potentiation of the hormone-stimulating effect on glucose transport in peripheral tissues (mainly skeletal muscle). The results argue against a significant antihypertensive or vascular effect of metformin in SHR.

Evidence of pleiotropic loci for fasting insulin, total fat mass, and abdominal visceral fat in a sedentary population: the HERITAGE family study

OBJECTIVE

To examine whether there is a major gene effect on fasting insulin and pleiotropic loci for fasting insulin, total fat mass (FM), and abdominal visceral fat (AVF).

RESEARCH METHODS AND PROCEDURES

A major gene hypothesis for fasting plasma insulin levels was assessed using segregation analyses of data on 495 members in 98 normolipidemic sedentary families of white descent who participated in the HERITAGE Family Study.

RESULTS

Segregation analyses were performed on insulin adjusted for age, on insulin adjusted for age and FM, and on insulin adjusted for age and AVF. Before adjustment for AVF and FM, a major gene effect on fasting insulin levels was indicated. The putative locus accounted for 54% of the variance under a recessive inheritance pattern, affecting 11% of the sample (i.e., allele frequency = 0.33). However, after adjusting for the effects of AVF or FM, neither a major effect alone nor a multifactorial component alone could be rejected, and support for a major gene was equivocal, i.e., neither the hypothesis of Mendelian tau values or that of the equal tau(s) were rejected and the equal tau model fit the data better than the Mendelian tau model. This pattern (i.e., major gene evidence for insulin before but not after adjustment for AVF or FM) suggests that there is a putative locus with pleiotropic effects on both insulin and FM and another pleiotropic locus for both insulin and AVF.

DISCUSSION

Although these data do not directly support an additional major gene for insulin independent of AVF and FM, such support cannot be ruled out because there is still a significant major effect on FM- or AVF-adjusted insulin (albeit the Mendelian nature of this effect is ambiguous).

Impact of left ventricular diastolic dysfunction on maximal treadmill performance in normotensive subjects with well-controlled type 2 diabetes mellitus

Patients with type 2 diabetes often have impaired exercise capacity compared with nondiabetic subjects. Left ventricular (LV) diastolic dysfunction has been shown to limit exercise performance in nondiabetic subjects. Men with well-controlled type 2 diabetes were divided into 2 groups: normal LV diastolic function (group 1, n = 9) or LV diastolic dysfunction (group 2, n = 10) based on standard echocardiographic criteria using pulmonary veins and transmitral flow recordings. They were matched for age and had no evidence of systemic hypertension, macroalbuminuria, coronary artery disease, congestive heart failure, clinical diabetic complications, and thyroid disease. Good metabolic control was demonstrated by glycated hemoglobin levels of 6.7+/-1.6% and 6.6+/-2.5% (means +/- SD) in patients with LV diastolic dysfunction and in controls, respectively. Each subject performed a symptom-limited modified Bruce protocol treadmill exercise test. Maximal treadmill performance was higher in subjects with normal diastolic function compared with subjects with LV diastolic dysfunction when expressed in time (803+/-29 vs. 662+/-44 seconds, respectively, p<0.02) or in METs (11.4+/-1.2 vs. 9.5+/-1.9 METs, respectively, p<0.02). Moreover, there was a correlation between E/A ratio and exercise duration (r = 0.64, p = 0.004) or E/A ratio and METs (r = 0.658, p = 0.003). There were no significant differences in maximal heart rate, maximal systolic and diastolic blood pressure, or maximal rate-pressure product attained during the exercise test. In conclusion, this study demonstrated that LV diastolic dysfunction influences maximal treadmill performance and could explain lower maximal performance observed in patients with type 2 diabetes.

Plasma adrenal, gonadal, and conjugated steroids following long-term exercise-induced negative energy balance in identical twins

There are few reports of the change in sex hormone levels accompanying a weight change in men, although an excessive decline in testosterone (TESTO) has been described as an associate of stress-induced weight loss. Plasma levels of cortisol, TESTO, dihydrotestosterone (DHT), dehydroepiandrosterone sulfate (DHEA-S), androsterone glucuronide (ADT-G), and androstane-3alpha, 17beta-diol glucuronide (3alphaDIOL-G) were measured in seven pairs of sedentary male monozygotic twins (age, 21.0 +/- 0.8 years; body mass index [BMI], 26.2 +/- 5.5 kg/m2) before and after 93 days of standardized submaximal (50% to 55% maximum oxygen consumption) cycle-ergometer exercise. A total energy deficit of 244 +/- 9.7 MJ induced significant changes (P < .0001) in body weight ([BW] -5.0 +/- 2.2 kg) and body fatness measures. Plasma TESTO and DHEA-S increased and 3alphaDIOL-G decreased. The increase in TESTO was a significant inverse correlate of loss in all measures of body fat, particularly central adiposity (r = -.58 to -.86, P < .001, fat loss-adjusted). Lower postexercise levels of 3alphaDIOL-G correlated positively with decreased body composition measures (r = .65 to .68, P < .01). The increase in plasma TESTO accompanying the loss of abdominal visceral fat (AVF) was greater in men with lower fasting insulin levels (P < .0001). The baseline within-twin-pair resemblance in TESTO and 3alphaDIOL-G (intraclass correlation coefficients [ICC] = .83 and .78, respectively, P < .01) was lost with intervention. Cortisol, DHEA-S, and ADT-G developed within-twin-pair similarity (ICC adjusted for fat loss: cortisol, .72; ADT-G, .62, P < .05; DHEA-S, .85, P < .002). We conclude that a steroid profile characterized by high TESTO and low androgen metabolite levels accompanied the changes in body composition and body fat distribution generated by the exercise-induced negative energy balance. Furthermore, these changes were characterized by a significant resemblance within identical-twin pairs.

Contribution of the cholesteryl ester transfer protein gene TaqIB polymorphism to the reduced plasma HDL-cholesterol levels found in abdominal obese men with the features of the insulin resistance syndrome

OBJECTIVE

The aim of this study was to examine the relation between the CETP-TaqIB polymorphism and reduced plasma HDL-cholesterol levels commonly observed among men characterized by abdominal obesity and features of the insulin resistance syndrome.

SUBJECTS

A total of 187 sedentary men, non-smokers and free from metabolic disorders were classified on the basis of their CETP-TaqIB genotype.

RESULTS

Plasma HDL and HDL3-cholesterol concentrations as well as the CETP activity were significantly different between the three genotypes, B1B1 men having significantly lower HDL and HDL3-cholesterol levels and higher CETP activity than B2B2 homozygotes. A 2x3 ANOVA was used to determine the source of variation of plasma HDL and HDL2-cholesterol levels among the three genotypic groups of men divided on the basis of either a high (>/=27 kg/m2) or a low (<27 kg/m2) BMI, a high (>/=130 cm2) or a low (<130 cm2) accumulation of visceral adipose tissue assessed by computed tomography, or a low versus a high fasting plasma insulin concentration (using the median value as a cut-off point). The effect of the CETP genotype observed on plasma HDL-cholesterol concentrations was attenuated among men with features of the insulin resistance syndrome. It seems that the expected raising effect of the B2 allele on plasma HDL-cholesterol concentrations was blunted in the presence of a BMI>/=27 kg/m2, a high accumulation of visceral adipose tissue or hyperinsulinaemia.

CONCLUSION

Our data indicate that the CETP gene TaqIB polymorphism influences plasma CETP activity on one hand and plasma HDL-cholesterol concentrations on the other hand among men. The association between the TaqIB polymorphism and plasma HDL-cholesterol concentrations is altered by the presence of abdominal obesity and some features of the insulin resistance syndrome.

Age-related increase in visceral adipose tissue and body fat and the metabolic risk profile of premenopausal women

OBJECTIVE

Age-related differences in body fat and, more specifically, in the accumulation of abdominal visceral adipose tissue (AT) were examined as potential covariates of the age-related difference in the metabolic profile predictive of cardiovascular disease (CVD) risk observed in young, as compared with middle-aged, premenopausal women.

RESEARCH DESIGN AND METHODS

Body composition, AT distribution, plasma lipoprotein-lipid levels, glucose tolerance, and plasma insulin concentrations were assessed in a sample of 122 young women (27.4+/-7.5 years, mean +/- SD) and compared with a sample of 52 middle-aged premenopausal women (49.5+/-5.3 years) who still had a normal menstrual cycle.

RESULTS

Middle-aged women were characterized by elevated levels of total abdominal and visceral AT and greater body fat mass and waist circumference, as well as by higher plasma levels of total cholesterol, LDL cholesterol, apolipoprotein (apo)B, and LDL-apoB compared with younger women. Furthermore, middle-aged women showed a greater glycemic response to a 75-g oral glucose load than young women (P < 0.01). In both young and middle-aged subjects, visceral AT accumulation was significantly correlated with plasma triglyceride, apoB, and LDL-apoB levels and with the cholesterol/HDL cholesterol ratio, as well as with plasma glucose, insulin, and C-peptide levels measured in the fasting state and after the oral glucose load, and negatively correlated with HDL cholesterol levels (-0.41 < or = r < or = 0.65, P < 0.05). When variables were adjusted for levels of visceral AT and fat mass, age-related differences that were initially found in plasma apoB and LDL-apoB levels, as well as in fasting glycemia and glucose tolerance, were eliminated.

CONCLUSIONS

Results of the present study suggest that even before the onset of menopause there is an age-related deterioration in the metabolic risk profile and an increase in visceral AT deposition in middle-aged women compared with young control subjects. Furthermore, our results provide support for the notion that the age-related increase in visceral AT accumulation is a significant factor involved in the deterioration of the CVD risk profile noted in premenopausal women with age.

Isradipine and insulin sensitivity in hypertensive rats

The present study was designed to investigate the effect of a reduction in blood pressure, by using the calcium channel antagonist isradipine, on insulin sensitivity and vascular responses to insulin in conscious spontaneously hypertensive male rats (SHR). The rats were instrumented with intravascular catheters and pulsed Doppler flow probes to measure blood pressure, heart rate, and blood flows. Insulin sensitivity was assessed by the euglycemic-hyperinsulinemic clamp technique. Two groups of rats received isradipine at a dose of 0.05 or 0.15 mg. kg-1. h-1, whereas a third group received a continuous infusion of vehicle (15% DMSO). Both doses of isradipine were found to decrease mean blood pressure (-25 +/- 4 mmHg at the dose of 0.05 mg. kg-1. h-1 and -20 +/- 2 mmHg at the dose of 0.15 mg. kg-1. h-1) and to improve insulin sensitivity. Moreover, in the rats treated with the low dose of isradipine, we observed vasodilations in renal, superior mesenteric, and hindquarter vascular beds. In the untreated group, the euglycemic infusion of insulin (4 mU. kg-1. min-1) was found to cause vasoconstrictions in superior mesenteric and hindquarter vascular beds, but no changes in mean blood pressure, heart rate, or renal vascular conductance were found. In contrast, in the isradipine-treated groups, the same dose of insulin was found to produce vasodilations in the renal vascular bed and to abolish the vasoconstrictor responses previously observed. We concluded that short-term treatment with isradipine in SHR can lower blood pressure and improve insulin sensitivity, mainly through hemodynamic factors, as supported by experiments with hydralazine as a positive vasodilator control.

Evidence of a major locus for lipoprotein lipase (LPL) activity in addition to a pleiotropic locus for both LPL and fasting insulin: results from the HERITAGE Family Study

A major gene hypothesis for heparin releasable plasma lipoprotein lipase (PH-LPL) activity was assessed using segregation analyses of data on 495 members in 98 normolipidemic sedentary families of Caucasian descent who participated in the HERITAGE Family Study. Segregation analyses were performed on PH-LPL adjusted for age, and on PH-LPL activity adjusted for age and fasting insulin. Prior to adjustment for insulin, neither a major gene effect nor a multifactorial component could be rejected, and support for a major gene was equivocal i.e. neither the Mendelian transmission nor the no transmission (equal tau s) models were rejected. However, after adjusting for the effects of insulin, a major gene effect on PH-LPL activity was unambiguous. The putative locus accounted for 60% of the total phenotypic variance, and the homozygous recessive form affected 10% (q2) of the sample (i.e. gene frequency (q) = 0.31), and led to a low PH-LPL value. The lack of a significant multifactorial effect suggested that the familial etiology of PH-LPL activity adjusted for insulin was likely to be primarily a function of the major locus. In conclusion, the present study is the first to report segregation analyses on PH-LPL activity prior to and after adjusting for insulin, and suggests that there is an indication of a pleiotropic genetic effect on PH-LPL activity and insulin, in addition to a major gene effect on PH-LPL activity alone.

Apolipoprotein E polymorphism and the relationships of physical fitness to plasma lipoprotein-lipid levels in men and women

PURPOSE

A high level of cardiovascular fitness is generally associated with a plasma lipoprotein-lipid profile predictive of a low cardiovascular disease risk. We have investigated whether apolipoprotein (apo) E polymorphism could alter the relationships of physical fitness to plasma lipoprotein-lipid levels in a sample of healthy untrained subjects (64 premenopausal women and 65 men).

METHODS

Subjects were grouped according to gender and apo E phenotype determined by isoelectric focusing electrophoresis.

RESULTS

In both genders, VO2max expressed in mL x kg(-1) x min(-1) was negatively correlated with plasma triglyceride levels in apo E2 carriers and apo E3 homozygotes (-0.55< or =r< or =0.31; P<0.05), whereas these associations were not found in apo E4 groups. Plasma low-density lipoprotein (LDL)-C levels were negatively associated with VO2max (r = -0.39; P<0.05) only in women homozygotes for apo E3 whereas VO2max was positively correlated with plasma high-density lipoprotein (HDL)2-C levels only in men (r = 0.51; P<0.001) and women (r = 0.65; P<0.001) who were apo E3 homozygotes. A control for concomitant association with body fat mass and glucose intolerance performed by partial correlation analyses revealed that, with the exception of the plasma HDL2-C levels in the apo E3 homozygotes, most of the significant associations between VO2max (mL x kg(-1) x min(-1)) and plasma lipoprotein-lipid levels were mediated by concomitant variation in body fatness and glucose tolerance.

CONCLUSIONS

These results suggest that the magnitude of the relationships between VO2max and plasma lipoprotein-lipid levels is influenced by the apo E polymorphism. Thus, apo E2 carriers may be particularly responsive to improved fitness, thereby preventing the development of hypertriglyceridemia and type III dyslipoproteinemia.

Relationship of visceral adipose tissue to metabolic risk factors for coronary heart disease: is there a contribution of subcutaneous fat cell hypertrophy?

Visceral adipose tissue (VAT) accumulation is an important correlate of the metabolic complications found in obese patients. The aim of this study was to evaluate the respective contribution of VAT deposition versus subcutaneous abdominal or femoral fat cell hypertrophy as correlates of the metabolic risk profile in 69 men and 65 premenopausal women (aged 35+/-5 years) with a wide range of fatness (body mass index, 18 to 57 kg/m2). In both genders, VAT accumulation was positively correlated with fasting plasma insulin, triglyceride (TG), and low-density lipoprotein (LDL)-apolipoprotein B (apo B) levels and the cholesterol (CHOL)/high-density lipoprotein (HDL)-CHOL ratio (.24 < or = r < or = .71, P < .05). A similar pattern of positive relationships was found between subcutaneous abdominal fat cell weight and metabolic risk variables in men and women (.33 < or = r < or = .60, P < .01). Positive associations were also observed in women between femoral fat cell weight and fasting plasma insulin, TG, and CHOL levels and the CHOL/HDL-CHOL ratio (.29 < or = r < or = .42, P < .05). However, only plasma TG concentrations and the CHOL/HDL-CHOL ratio were positively correlated with femoral fat cell weight in men (r = .30, P < .05). To better investigate the relationships between the metabolic risk profile and hypertrophic subcutaneous obesity, individuals with small versus large subcutaneous abdominal adipocytes were matched according to VAT accumulation. Men with large abdominal fat cells displayed higher plasma TG and LDL-apo B levels compared with men characterized by small abdominal adipocytes (P < .05). Stepwise multiple regression analyses showed that subcutaneous abdominal fat cell weight was the best independent variable predicting plasma TG and LDL-apo B levels in men. No significant difference was found in the metabolic profile of subjects displaying small versus large femoral adipocytes. Taken together, these results suggest that for a given VAT deposition, the presence of hypertrophied subcutaneous abdominal adipocytes in men appears to be associated with further deterioration in the metabolic risk profile. On the other hand, the hypertrophy of femoral adipocytes does not further alter the metabolic complications generally related to obesity in both men and women.

Linkage of the Na,K-ATPase alpha 2 and beta 1 genes with resting and exercise heart rate and blood pressure: cross-sectional and longitudinal observations from the Quebec Family Study

OBJECTIVE

To investigate whether genetic variations in the genes encoding the alpha and beta subunits of the Na,K-ATPase are linked with hemodynamic phenotypes.

DESIGN AND PARTICIPANTS

Cross-sectional data based on 533 subjects (no antihypertensive medication) were obtained from 150 families of phase 2 of the Quebec Family Study, together with longitudinal data from 338 subjects (105 families) who had been measured 12 years earlier in phase 1 of the Quebec Family Study.

MAIN OUTCOME MEASURES

Restriction fragment length polymorphisms were examined at the alpha 2 (exon 1 and exon 21-22 with BglII) and beta 1 (Msp I and Pvu II) loci of Na,K-ATPase. Hemodynamic phenotypes measured included systolic and diastolic blood pressure, heart rate and rate-pressure product at rest and during low-intensity exercise.

RESULTS

Sib-pair analysis revealed relatively strong linkages (P = 0.0003-0.002) between the resting heart rate and rate-pressure product and the alpha 2 exon 21-22 marker and alpha 2 haplotype. Moreover, the alpha 2 exon 21-22 marker showed suggestive linkages (P = 0.01 to 0.043) with resting systolic blood pressure and exercise diastolic blood pressure, heart rate and rate-pressure product, and the alpha 2 haplotype with exercise diastolic blood pressure and rate-pressure product and the 12-year change in resting systolic blood pressure (P = 0.03 to 0.05). Both the beta 1 Msp I marker and the beta 1 haplotype were linked with the resting rate-pressure product (P = 0.007 and 0.003, respectively), and all beta 1 markers showed linkage with the change in resting systolic blood pressure (P = 0.00005 to 0.024). In men, there was a significant (P = 0.01) interaction between the alpha 2 exon 21-22 genotype and the postglucose plasma insulin level with regard to resting systolic blood pressure.

CONCLUSIONS

These data suggest that the alpha 2 and beta 1 genes of Na,K-ATPase contribute to the regulation of hemodynamic phenotypes in healthy subjects.

Is visceral adiposity a significant correlate of subcutaneous adipose cell lipolysis in men?

The aim of the present study was to examine whether site differences in s.c. adipose tissue (AT) lipolysis may be considered a contributing factor to the altered metabolic risk profile of visceral compared to peripheral obese men once the concomitant variation in adipose cell size is taken into account. For this purpose, sc abdominal and femoral fat cell lipolytic responses were investigated in two groups of men (body mass index, 28 +/- 2 kg/m2), aged 36 +/- 3 yr, who were matched for both s.c. abdominal AT area (256 +/- 64 cm2) and s.c. abdominal adipose cell weight (0.55 +/- 0.08 microg lipid/cell) but were characterized by either a high (162 +/- 29 cm2; n = 18) or a low (101 +/- 21 cm2; n = 18) visceral AT deposition. The maximal lipolytic response to epinephrine or to isoproterenol (beta-adrenergic agonist) as well as the maximal antilipolytic effect of either epinephrine or clonidine (alpha2-adrenergic agonist) assessed in s.c. adipocytes were similar among men with low vs. high levels of visceral AT. However, the beta-adrenoceptor sensitivity was increased in s.c. abdominal adipose cells of individuals with a high visceral AT accumulation compared to those with a low intraabdominal fat deposition. Positive relationships were also found between the lipolytic sensitivity of s.c. abdominal adipocytes and plasma insulin concentrations measured in the fasting state and after an oral glucose load. These results suggest that variation in the degree of visceral adiposity in men does not seem to be associated with differences in regional adipose cell maximal lipolytic capacity once fat cell size is taken into account. However, the greater beta-adrenoceptor lipolytic sensitivity of s.c. abdominal adipocytes could be considered a significant correlate of the increased insulinemia observed among men characterized by high levels of visceral AT.

Familial clustering of insulin and abdominal visceral fat: the HERITAGE Family Study

Abdominal visceral fat (AVF) is an obesity-related phenotype thought to be associated with insulin resistance, diabetes mellitus, and atherosclerosis. Significant genetic influences on both AVF and insulin levels have been reported. However, information is lacking as to whether common genetic influences on AVF and insulin levels exist. AVF was assessed by computed tomography scan, and fasting insulin was measured by RIA in 512 members of 98 sedentary Caucasian families participating in the HERITAGE Family Study. Baseline data, collected before exercise training, were used in the present investigation. A bivariate familial correlation model was applied to evaluate whether there are familial influences that are common to insulin and AVF before and after adjustment for total fat mass (FM), and to assess the overall heritability of insulin and AVF. The maximal heritability for AVF, before and after adjustment for total FM, was 42% and 50%, respectively; and for insulin, it was 21%. Interestingly, 29% of the familial influences on insulin were also common to AVF, whereas 14% of the familial influences on AVF were shared by insulin. Furthermore, after AVF was adjusted for total FM, these common familial influences were increased to 48% and 20%. Genes and/or familial nongenetic factors with pleiotropic effects seem to influence both AVF and plasma insulin levels to a certain degree. Genes involved in the regulation of lipid storage and mobilization in the abdominal fat depot are potential candidates for these genetic pleiotropic effects.

Plasma adrenal, gonadal, and conjugated steroids before and after long-term overfeeding in identical twins

An analysis of the data collected in the Quebec Overfeeding Study of identical twins was undertaken to determine any evidence of a genotype effect on plasma levels of adrenal and gonadal steroids arising from long term positive energy balance. Plasma levels of sex hormone-binding globulin (SHBG), testosterone, dihydrotestosterone (DHT), dehydroepiandrosterone sulfate (DHEA-S), androsterone glucuronide, androstane-3 alpha, 17 beta-diol glucuronide (3 alpha-DIOL-G), and cortisol were measured in 12 pairs of young, sedentary, male monozygotic twins before and after 100 days of overfeeding. The dietary energy excess of 4.2 MJ/day (1000 Cal), 6 days a week, resulted in a total positive energy balance of 353 MJ (84,000 Cal). Overfeeding induced significant changes (P < 0.0001) in body weight and other measures of body composition. Within-twin pair resemblance was observed at baseline in all steroids, except cortisol [intraclass correlation range: DHEA-S, 0.50 (P < 0.05); DHT, 0.77 (P < 0.001)] and was lost with overfeeding, except for DHT and SHBG (P < 0.05). SHBG levels fell and 3 alpha-DIOL-G rose with the gain in body fatness. The change in testosterone was a significant correlate of the change in upper body fat (r = -0.48; P < 0.05). The change in 3 alpha-DIOL-G correlated positively with increases in all measures of central adiposity (r = 0.52; P < 0.01). A decrease in DHEA-S occurred with a higher, but not with a lower, gain in abdominal visceral fat (P < 0.05). Thus, analysis of adrenal and gonadal steroids and of conjugated metabolites before and after overfeeding in monozygous twins supports the idea that there is a genotype effect on steroid circulating steroid levels and that these blood levels are correlated with the pattern of body fat distribution. Moreover, the baseline within-twin pairs similarity in steroid levels was attenuated by prolonged positive energy balance and body fat gain.

Hyperinsulinemia and abdominal obesity affect the expression of hypertriglyceridemia in heterozygous familial lipoprotein lipase deficiency

We have reported three missense mutations (G188E, P207L, and D250N) in the lipoprotein lipase (LPL) gene among French-Canadians, resulting in the absence of measurable postheparin plasma LPL activity in homozygotes. Presence of triglyceride- and cholesterol-rich VLDL, as well as cholesterol-poor HDL particles, has been shown in heterozygotes affected by partial reduction in postheparin LPL activity. However, significant heterogeneity in their plasma triglyceride levels has been found, even among individuals carrying the same LPL gene mutation, indicating that factors other than LPL deficiency could affect the phenotypic expression of hypertriglyceridemia in the heterozygous state. The aim of the present study was to examine the combined effects of abdominal fat accumulation and hyperinsulinemia on plasma triglyceride levels among heterozygous patients for familial LPL deficiency. Based on sex and BMI, 43 heterozygotes (25 women and 18 men) were matched with noncarrier control subjects. Our data indicate that heterozygotes with higher abdominal fat deposition, as defined as waist girth values above the 50th percentile, had higher plasma triglyceride levels than nonobese heterozygotes. However, an important proportion of male heterozygote subjects were hypertriglyceridemic, even in absence of abdominal obesity, suggesting that another factor(s) was involved in the modulation of hypertriglyceridemia in these subjects. Indeed, multivariate analyses revealed that fasting hyperinsulinemia was a significant correlate of hypertriglyceridemia among these heterozygotes. Results of the present study indicate that abdominal obesity and hyperinsulinemia both have deleterious effects on plasma triglyceride levels in familial LPL deficiency. It is suggested that heterozygotes with moderate obesity and/or insulin resistance may be at higher risk of coronary artery disease because of the expression of an atherogenic lipoprotein phenotype among these patients.

Linkage and association studies between the melanocortin receptors 4 and 5 genes and obesity-related phenotypes in the Québec Family Study

BACKGROUND

The agouti yellow mouse shows adult onset of moderate obesity and diabetes. A depressed basal lipolytic rate in adipocytes or a decreased adrenergic tone arising from antagonizing alpha-melanocyte-stimulating hormone (MSH) activation of melanocortin receptors (MCR) could be at the origin of the obesity phenotype.

MATERIAL AND METHODS

MCR 4 and 5 (MC4R, MC5R) genes were studied in the Québec Family Study. Sequence variations were detected by Southern blot probing of restricted genomic DNA, and mRNA tissue expression was detected by RT-PCR. Subjects with a wide range of weight were used for single-point sib-pair linkage studies (maximum of 289 sibships from 124 nuclear families). Analysis of variance across genotypes in unrelated males (n = 143) and females (n = 156) was also undertaken. Body mass index (BMI), sum of six skin-folds (SF6), fat mass (FM), percent body fat (%FAT), respiratory quotient (RQ), resting metabolic rate (RMR), fasting glucose and insulin, and glucose and insulin area during an oral glucose tolerance test were analyzed.

RESULTS

MC4R showed polymorphism with NcoI, and MC5R, with PstI and PvuII, with a heterozygosity of 0.38, 0.10, and 0.20, respectively. Linkages were observed between MC5R and BMI (p = 0.001), SF6 (p = 0.005), FM (p = 0.001), and RMR (p = 0.002), whereas associations were observed in females between MC5R and BMI (p = 0.003), and between MC4R and FM (p = 0.002) and %FAT (p = 0.004). After correction for multiple tests, these p values are lowered by one tenth. MC4R and MC5R mRNAs have been detected in brain, adipose tissue, and skeletal muscle.

CONCLUSIONS

MC4R and MC5R exhibit evidence of linkage or association with obesity phenotypes, but this evidence is strongest for MC5R.

Plasma leptin concentrations: gender differences and associations with metabolic risk factors for cardiovascular disease

The cloning of the obese gene and the characterization of its protein product, leptin, has permitted the study of a new hormone potentially involved in the regulation of adipose tissue mass. The present study examined the gender differences in fasting plasma leptin concentration and its relationship to body fatness, adipose tissue distribution and the metabolic profile in samples of 91 men (mean age +/- SD: 37.3 +/- 4.8 years) and 48 women (38.5 +/- 6.8 years). Plasma leptin concentrations were strongly associated with body fat mass measured by underwater weighing [men: r = 0.80, p < 0.0001; women: r = 0.85, p < 0.0001]. In both genders, plasma leptin levels were also strongly correlated with waist girth as well as cross-sectional areas of abdominal subcutaneous and visceral adipose tissue measured by computed tomography. Women had, on average, plasma leptin concentrations that were three times higher than men. Furthermore, this gender difference remained significant when comparing men and women matched for similar levels of body fat mass. The associations between plasma leptin and lipoprotein concentrations were dependent of adiposity. In both men and women, elevated fasting plasma leptin levels were associated with higher plasma insulin concentrations, but only in women was the association maintained after correction for fat mass. Thus, results of the present study show that women have higher plasma leptin levels compared to men, independent of the concomitant variation in total body fat mass. Furthermore, our results also suggest that, in women, the association between plasma leptin and insulin concentrations is independent of adiposity, a finding which provides further support to the observation that adipose tissue leptin secretion may be upregulated by insulin.

Relationships between endogenous steroid hormone, sex hormone-binding globulin and lipoprotein levels in men: contribution of visceral obesity, insulin levels and other metabolic variables

Excess visceral adipose tissue (AT) and hyperinsulinemia are important correlates of an altered lipoprotein profile. It has also been reported that testosterone, adrenal C19 steroids and sex hormone-binding globulin (SHBG) concentrations are associated with plasma lipoprotein levels. The aim of the present study was to investigate the relative contributions of endogenous steroid hormone and SHBG levels, of visceral AT accumulation measured by computed tomography, and of fasting insulin and free fatty acid (FFA) concentrations to the variation of plasma lipoprotein levels in men. For this purpose, plasma concentrations of testosterone, dehydroepiandrosterone (DHEA), androstene-3beta,17beta-diol (delta5-DIOL), androstenedione (delta4-DIONE), estrone and estradiol, as well as SHBG levels were determined in a sample of 76 men covering a wide range of body fatness values. Higher testosterone levels were associated with a more favorable lipoprotein profile as it showed significant correlations with triglyceride (TG), total cholesterol and LDL-cholesterol (LDL-C) concentrations (r= -0.25, -0.25 and -0.27, respectively; P < 0.05). Higher plasma adrenal C19 steroid levels were also associated with a favorable lipoprotein profile as DHEA, delta4-DIONE and delta5-DIOL levels were negatively correlated with total cholesterol (r = -0.24, -0.33 and -0.24, respectively; P < 0.05) and LDL-C (r = -0.23, -0.31 and -0.28, respectively; P < 0.05). SHBG levels were negatively correlated with TG concentrations (r = -0.33; P < 0.005) whereas delta5-DIOL, testosterone and SHBG were negatively correlated with apolipoprotein B levels (-0.32 < or = r < or = -0.43; P < 0.005). Statistical adjustment for visceral AT area, fasting insulin, fasting free fatty acid (FFA) levels and total body fat mass eliminated most of the correlations between steroid and lipoprotein levels, while SHBG remained significantly correlated with lipoprotein concentrations after such adjustments. Multivariate analyses revealed that SHBG, delta4-DIONE, delta5-DIOL and metabolic variables all contributed to the variance in plasma lipoprotein concentrations (from 10 to 29% of explained variance). Visceral AT, fasting FFA and insulin levels as well as SHBG concentrations appeared to be independent correlates of lipoprotein concentrations. Thus, metabolic and anthropometric variables examined in the present study could have represented important confounding factors in previous studies which have examined the relationship of steroid hormones to plasma lipoprotein concentrations.

Identification of an obesity quantitative trait locus on mouse chromosome 2 and evidence of linkage to body fat and insulin on the human homologous region 20q

Chromosomal synteny between the mouse model and humans was used to map a gene for the complex trait of obesity. Analysis of NZB/BINJ x SM/J intercross mice located a quantitative trait locus (QTL) for obesity on distal mouse chromosome 2, in a region syntenic with a large region of human chromosome 20, showing linkage to percent body fat (likelihood of the odds [LOD] score 3.6) and fat mass (LOD score 4.3). The QTL was confirmed in a congenic mouse strain. To test whether the QTL contributes to human obesity, we studied linkage between markers located within a 52-cM region extending from 20p12 to 20q13.3 and measures of obesity in 650 French Canadian subjects from 152 pedigrees participating in the Quebec Family Study. Sib-pair analysis based on a maximum of 258 sib pairs revealed suggestive linkages between the percentage of body fat (P < 0.004), body mass index (P < 0.008), and fasting insulin (P < 0.0005) and a locus extending approximately from ADA (the adenosine deaminase gene) to MC3R (the melanocortin 3 receptor gene). These data provide evidence that a locus on human chromosome 20q contributes to body fat and insulin in a human population, and demonstrate the utility of using interspecies syntenic relationships to find relevant disease loci in humans.

Acute and chronic effects of exercise on leptin levels in humans

The acute (single bout of exercise) and chronic (exercise training) effects of exercise on plasma leptin were investigated in 97 sedentary adult men (n = 51) and women (n = 46) participating in the HERITAGE Family Study. Exercise training consisted of a standardized 20-wk endurance training program performed in the laboratory on a computer-controlled cycle ergometer. Maximal oxygen uptake, body composition assessed by hydrostatic weighing, and fasting insulin level were also measured before and after training. Pre- and posttraining blood samples were obtained before and after completion of a maximal exercise test on the cycle ergometer. Exercise training resulted in significant changes in maximal oxygen uptake (increase in both genders) and body composition (reduction of fat mass in men and increase in fat-free mass in women). There were considerable interindividual differences in the leptin response to acute and chronic effects of exercise, some individuals showing either increase or reduction in leptin, others showing almost no change. On average, leptin levels were not acutely affected by exercise. After endurance training was completed, leptin levels decreased significantly in men (from 4.6 to 3.9 ng/ml; P = 0.004) but not in women. However, after the training-induced changes in body fat mass were accounted for, the effects of exercise training were no longer significant. Most of the variation observed in leptin levels after acute exercise or endurance training appears to be within the confidence intervals of the leptin assay. We conclude that there are no meaningful acute or chronic effects of exercise, independent of the amount of body fat, on leptin levels in humans.

Regional variation in adipose tissue insulin action and GLUT4 glucose transporter expression in severely obese premenopausal women

Insulin action and GLUT4 expression were examined in adipose tissue of severely obese premenopausal women undergoing gastrointestinal surgery. Fat samples were taken from three different anatomical regions: the subcutaneous abdominal site, the round ligament (deep abdominal properitoneal fat), and the greater omentum (deep abdominal intraperitoneal fat). The stimulatory effect of insulin on glucose transport and the ability of the hormone to inhibit lipolysis were determined in adipocytes isolated from these three adipose depots. Insulin stimulated glucose transport 2-3 times over basal rates in all adipocytes. However, round ligament adipose cells showed a significantly greater responsiveness to insulin when compared to subcutaneous and omental adipocytes. Round ligament fat cells also displayed the greatest sensitivity and maximal antilipolytic response to insulin. We also investigated whether regional differences in fat cell insulin-stimulated glucose transport were linked to a differential expression of the GLUT4 glucose transporter. GLUT4 protein content in total membranes was 5 and 2.2 times greater in round ligament adipose tissue than in subcutaneous and omental fat depots, respectively. Moreover, GLUT4 mRNA levels were 2.1 and 3 times higher in round ligament than in subcutaneous or omental adipose tissues, respectively. Adipose tissue GLUT4 protein content was strongly and negatively associated (r = -0.79 to -0.89, p < 0.01) with the waist-to-hip ratio but not with total adiposity. In conclusion, these results demonstrate the existence of site differences in adipose tissue insulin action in morbidly obese women. The greater insulin effect on glucose transport in round ligament adipocytes was associated with a higher expression of GLUT4 when compared to subcutaneous abdominal and omental fat cells. Moreover, despite the regional variation in GLUT4 expression, an increased proportion of abdominal fat was found to be associated with lower levels of GLUT4 in all adipose regions investigated.

Androstane-3alpha,17beta-diol glucuronide as a steroid correlate of visceral obesity in men

Plasma levels of androstane-3alpha,17beta-diol glucuronide (3alpha-DIOL-G) and androsterone glucuronide (ADT-G) as well as testosterone and adrenal C19 steroid concentrations were measured in a sample of 80 men in whom visceral adipose tissue (AT) accumulation was also determined by computed tomography. Plasma 3alpha-DIOL-G concentrations showed significant positive correlations with total body fat mass (r = 0.31; P < 0.05) and percent body fat (r = 0.28; P < 0.05). Furthermore, plasma 3alpha-DIOL-G levels were significantly associated with visceral adipose tissue accumulation (r = 0.41; P < 0.0005) as well as fasting plasma insulin (r = 0.35; P < 0.005) and glycemic and insulinemic responses to an oral glucose load (r = 0.39; P < 0.0005 and r = 0.32; P < 0.005, respectively). However, associations between 3alpha-DIOL-G and plasma glucose-insulin homeostasis indexes were no longer significant after adjustment for visceral AT area. ADT-G levels were not significantly associated with any of the adiposity variables. Subjects matched for abdominal sc AT area but with either low or high levels of visceral AT area showed significant differences in 3alpha-DIOL-G concentrations (P < 0.05), whereas subjects with low or high levels of abdominal sc AT but similar levels of visceral AT had similar 3alpha-DIOL-G concentrations. Among men with high testosterone levels, subjects with reduced 3alpha-DIOL-G concentrations had lower visceral adipose tissue accumulation than subjects with increased 3alpha-DIOL-G levels. The present results indicate that plasma 3alpha-DIOL-G, but not ADT-G, is a steroid correlate of visceral obesity. Excess visceral adipose tissue and/or concomitant alterations in insulin levels or in vivo insulin action could be responsible for the increased 3alpha-DIOL-G formation observed in this condition.

Abdominal visceral fat is associated with a BclI restriction fragment length polymorphism at the glucocorticoid receptor gene locus

Several investigations have suggested that body fat distribution is influenced by nonpathologic variations in the responsiveness to cortisol. Genetic variations in the glucocorticoid receptor (GRL) could therefore potentially have an impact on the level of abdominal fat. A restriction fragment length polymorphism (RFLP) has previously been detected with the BclI restriction enzyme in the GRL gene identifying two alleles with fragment lengths of 4.5 and 2.3 kb. This study investigates whether abdominal fat areas measured by computerized tomography (CT) are associated with this polymorphism in 152 middle-aged men and women. The less frequent 4.5-kb allele was found to be associated with a higher abdominal visceral fat (AVF) area independently of total body fat mass (4.5/4.5 vs. 2.3/2.3 kb genotype; men: 190.7 +/- 30.1 vs. 150.7 +/- 33.3 cm2, p = 0.04; women: 132.7 +/- 37.3 vs. 101.3 +/- 34.5 cm2, p = 0.06). However, the association with AVF was seen only in subjects of the lower tertile of the percent body fat level. In these subjects, the polymorphism was found to account for 41% (p = 0.003) and 35% (p = 0.007), in men and women, respectively, of the total variance in AVF area. The consistent association between the GRL polymorphism detected with BclI and AVF area suggests that this gene or a locus in linkage disequilibrium with the BclI restriction site may contribute to the accumulation of AVF.

Suggestive linkages between markers on human 1p32-p22 and body fat and insulin levels in the Quebec Family Study

A single-gene rodent mutation (diabetes) and a quantitative trait locus (dietary obese 1) mapped to the mid portion of mouse chromosome 4 have been related to obesity and/or insulin levels. Synteny relationships place their putative human homologs on 1p31 and 1p35-p31, respectively. In 137 sibships of adult brothers and sisters from the Québec Family Study, genetic linkages between seven microsatellite markers from 1p32-p22 and various obesity- and diabetes-related quantitative phenotypes were examined using single locus sibpair linkage analysis. Suggestive linkages were observed between markers D1S476 and body mass index (p = 0.05), fat mass (p = 0.02), the sum of six skinfolds (p = 0.02), the insulin area after an oral glucose tolerance test (p = 0.02), and between the neighboring marker D1S200 and body mass index (p = 0.03), and fat mass (p = 0.009). Suggestive linkages were also observed between the more telomeric markers D1S193 and body mass index (p = 0.03), and between the neighboring marker D1S197 and fasting insulin level (p = 0.05). No linkage was observed with the trunk to extremity skinfolds ratio. These linkages suggest that human homologs of the mouse diabetes or dietary obese 1 and/or other genes in this interval on chromosome 1 play a role in the regulation of body mass, body composition, and insulin levels, but not of subcutaneous fat distribution.

The MspI polymorphism of the apolipoprotein A-II gene as a modulator of the dyslipidemic state found in visceral obesity

The aim of the present study was to examine the effect of variation at the apolipoprotein (apo) A-II gene locus on lipoprotein levels in visceral obesity. A total of 145 sedentary men, free from metabolic disorders requiring pharmacotherapy, were classified into two groups on the basis of their apo A-II-MspI genotype determined by the polymerase chain reaction: 1) 43 M1 carriers or M1M2, including two M1M1 homozygotes and 41 M1M2 heterozygotes, and 2) 102 M2M2 homozygotes for the presence of a MspI restriction site. The two genotypic groups did not differ for body mass index (BMI, expressed in kg/m2), body fat mass, visceral adipose tissue (AT) accumulation, as well as for insulin, glucose and free fatty acids levels measured in the fasting state and in response to an oral glucose tolerance test. In addition, 65 and 63% of M1 carriers had plasma HDL2 cholesterol levels and a HDL2/HDL3 cholesterol ratio below the 50th percentile of their distributions compared with 45%(P < 0.05) and 46%(P = 0.06), respectively, in M2M2 homozygotes. When subjects were further divided on the basis of visceral AT accumulation (below and above a value of 130 cm2), M1 carriers with low levels of visceral AT were characterized by high plasma HDL cholesterol and HDL2 cholesterol concentrations as well as by a higher HDL2/HDL3 ratio, compared with M1 carriers with high levels of visceral AT (> 130 cm2), or with M2M2 homozygotes with either a high or a low accumulation of visceral AT. Furthermore, M1 carriers with high levels of visceral AT showed a trend for lower plasma HDL2 cholesterol levels and were characterized by a significantly lower HDL2/HDL3 cholesterol ratio compared with the other three groups. No difference in HDL and HDL2 cholesterol levels and in the HDL2/HDL3 cholesterol ratio was noted when M2 homozygotes with lower versus higher levels of visceral AT were compared. The contribution of hyperinsulinemia was also examined by dividing subjects on the basis of the 50th percentile of the integrated insulin response to an oral glucose challenge. Significantly lower plasma HDL2 cholesterol levels and a reduced HDL2/HDL3 cholesterol ratio were noted among M1 carriers with high plasma insulin responses compared with M1 carriers with low insulin responses. Among M2M2 homozygotes, no difference was noted in plasma HDL cholesterol and in HDL2 cholesterol concentrations between men with low versus high insulin responses to the oral glucose load. These results suggest that the apo A-II-MspI polymorphism could modulate plasma HDL cholesterol levels among visceral obese, insulin-resistant men.

Negative energy balance with exercise in identical twins: plasma glucose and insulin responses

The effects of long-term (93 days) negative energy balance on plasma glucose and insulin were investigated by means of exercise with constant energy intake in seven pairs of young sedentary male identical twins. Results showed a significant decrease in fasting (-24%, P < 0.02) and postprandial insulin (-16%, P < 0.05). Fasting and postprandial plasma glucose and glucagon were not modified. Mean glucose disposal rate measured during a euglycemic-hyperinsulinemic clamp performed in five twin pairs was increased by 34% (P = 0.13). No significant intrapair similarity was found for the responses of fasting and postprandial insulin levels and of glucose disposal rate. Changes in glucose disposal rate were significantly greater in high compared with low losers for computerized tomography-measured abdominal visceral fat (3.0 +/- 1.1 vs. 0.3 +/- 0.5 mg x kg(-1) x min(-1), P < 0.05) despite similar losses in total body fat. We conclude that 1) a long-term negative energy balance generated by exercise training significantly reduces plasma insulin levels, whereas insulin sensitivity tends to be improved; 2) training-induced changes in insulin sensitivity are associated with changes in abdominal visceral fat; and 3) data from this experiment conducted with a small number of twin pairs suggest that the genotype does not seem to be a major determinant of the changes in insulin levels and sensitivity brought about by negative energy balance with exercise.

In situ hybridization analysis of ZPK gene expression during murine embryogenesis

ZPK is a recently described protein serine/threonine kinase that has been originally identified from a human teratocarcinoma cell line by the polymerase chain reaction and whose function in signal transduction has not yet been elucidated. To investigate the potential role of this protein kinase in developmental processes, we have analyzed the spatial and temporal patterns of expression of the ZPK gene in mouse embryos of different gestational ages. Northern blot analysis revealed a single mRNA species of about 3.5 KB from Day 11 of gestation onwards. In situ hybridization studies demonstrated strong expression of ZPK mRNA in brain and in a variety of embryonic organs that rely on epitheliomesenchymal interactions for their development, including skin, intestine, pancreas, and kidney. In these tissues, the ZPK mRNA was localized primarily in areas composed of specific types of differentiating cells, and this expression appeared to be upregulated at a time concomitant with the onset of terminal differentiation. Taken together, these observations raise the possibility that the ZPK gene product is involved in the establishment and/or maintenance of a fully cytodifferentiated state in a variety of cell lineages.

Familial correlations in the Québec family study: cross-trait familial resemblance for body fat with plasma glucose and insulin

This study represents one component in our investigation of the familial factors underlying the insulin resistance (or metabolic) syndrome involving obesity, hyperinsulinaemia, glucose intolerance, dyslipidaemia, and hypertension. Here we examine the cross-trait familial resemblance between four measures of body size (two assessing total fat [body mass index and sum of six skinfolds] and two assessing fat patterning [ratio of trunk skinfold sum to extremity skinfold sum, adjusted and unadjusted for total subcutaneous fat]) with fasting plasma levels of glucose, insulin, and the ratio of insulin to glucose (IGR) in non-diabetic families participating in phase 1 of the Québec Family Study. A bivariate familial correlation model assessed both intraindividual (e.g. father's body size with father's insulin) and interindividual (e.g. father's body size with son's insulin) cross-trait associations. Intraindividual correlations suggested a greater degree of cross-trait associations for body fat (rather than fat distribution) measures with insulin and the IGR (rather than with glucose) levels. While the intraindividual correlations were significant for most cross-trait comparisons, only the sum of six skinfolds evidenced any familial association (i.e. interindividual resemblance) with insulin and the IGR. Specifically, cross-trait parent-offspring (but not sibling or spouse) correlations were significant, with a bivariate familiality estimate (i.e. polygenic and/or common familial environment) of about 8%. While the lack of sibling correlations does not suggest a simple familial hypothesis, a more complex genetic effect underlying the common covariation between total body fat with insulin and IGR cannot be ruled out.

Role of body fat loss in the exercise-induced improvement of the plasma lipid profile in non-insulin-dependent diabetes mellitus

The study was designed to examine the impact of exercise training on the plasma lipid profile in non-insulin-dependent diabetes mellitus (NIDDM) and, more particularly, to determine the relationship between changes in body fat mass and changes in the lipid profile. Eleven men with NIDDM exercised for 1 hour thrice per week on an ergocycle over a 6-month period at 60% maximal oxygen uptake (Vo2max). Diet and hypoglycemic agents were kept constant throughout this period. Vo2max, body composition, fasting plasma glucose and insulin levels, glycosylated hemoglobin, and the lipid profile were determined at baseline, in the middle (3 months), and at the end (6 months) of the training program. When the subjects were considered as a group, the only significant effect of training was on Vo2max, which increased from 32.2 +/- 1.2 mL/kg/min at baseline to 38.0 +/- 1.7 mL/kg/min at 6 months (P < .001). When the data were analyzed on an individual basis, significant associations were observed between changes in body fat mass and changes in the low-density lipoprotein (LDL) cholesterol/high-density lipoprotein (HDL) cholesterol ratio (r = .62,P = .04) or triglyceride (TG) levels (r = .64,P = .03). These data indicate that fat loss, not training per se, favorably alters the lipid profile of subjects with NIDDM who participate in an aerobic physical-conditioning program.

The apoB-100 gene EcoRI polymorphism influences the relationship between features of the insulin resistance syndrome and the hyper-apoB and dense LDL phenotype in men

The aim of this study was to investigate whether the EcoRI polymorphism of the apolipoprotein B (apoB) gene influences the relationships between features of the insulin resistance syndrome and the dense LDL phenotype and apoB concentrations. A sample of 65 men was divided into two groups on the basis of the EcoRI genotype. Forty-four subjects were (+/+) homozygotes for the presence of the EcoRI restriction site that is associated with a glutamic acid at codon 4154. Twenty-one men were (+/-) heterozygotes for the absence of the restriction site resulting from a glutamic acid to a lysine substitution at codon 4154. In the (+/-) group, fasting plasma FFA levels were positively correlated with plasma apoB, LDL-apoB, and the LDL particle score that was calculated from the migration distances of LDL subspecies and their relative band intensities, reflecting the proportion of small dense LDL particles. However, these associations were not found among (+/+) subjects. The two genotypic groups were further divided into two subgroups on the basis of fasting FFA concentrations, and the LDL particle score and the LDL-apoB levels were compared. High FFA levels were associated with a higher proportion of small dense LDL particles, as reflected by a higher mean LDL particle score, irrespective of the genotype. However, the apoB-EcoRI polymorphism appeared to influence the association between high FFA levels and LDL-apoB concentrations because (+/-) heterozygotes with high FFA levels had higher LDL-apoB concentrations than (+/-) heterozygotes with low FFA levels. In addition, the integrated area under the curve of plasma insulin concentrations, measured in response to a 75-g oral glucose challenge, and the amount of visceral adipose tissue, measured by computed tomography, were positively associated with the LDL particle score only in (+/-) heterozygotes. When subjects were divided on the basis of insulin area (low vs. high) or visceral adipose tissue (low vs. high), (+/-) heterozygotes with high insulin area or with high levels of visceral adipose tissue had a higher mean LDL particle score than (+/-) heterozygotes with low insulin area or low visceral adipose tissue. However, among (+/+) homozygotes, low or high levels of insulin or visceral adipose tissue could not discriminate between men with large or small LDL particles. Therefore, (+/-) heterozygotes may be more susceptible to develop the dense LDL phenotype in presence of hyperinsulinemia and visceral obesity. Results of the present study suggest that the apoB-EcoRI polymorphism may exacerbate the alterations in the LDL particle (size and concentration) found among visceral obese-hyperinsulinemic men.

Insulin sensitivity and hemodynamic responses to insulin in Wistar-Kyoto and spontaneously hypertensive rats

The insulin-mediated vasodilator effect has been proposed as an important physiological determinant of insulin action on glucose disposal in normotensive humans. The present study was designed to further examine the acute regional hemodynamic effects of insulin in different vascular beds and to explore the relationships between insulin vascular effects and insulin sensitivity during euglycemic hyperinsulinemic clamps in conscious normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). The rats were instrumented with intravascular catheters and pulsed Doppler flow probes to measure blood pressure, heart rate, and regional blood flows. In WKY rats, the euglycemic infusion of insulin (4 and 16 mU.kg-1.min-1) causes vasodilations in renal and hindquarter vascular beds but no changes in mean blood pressure, heart rate, or superior mesenteric vascular conductance. In contrast, in SHR, the same doses of insulin produce vasoconstrictions in superior mesenteric and hindquarter vascular beds and, at high doses, increase blood pressure. Moreover, at the lower dose of insulin tested, we found a reduction in the insulin sensitivity index in the SHR compared with the WKY rats. The present findings provide further evidence for an association between insulin sensitivity and insulin-mediated hemodynamic responses.

Seven-year changes in body fat and visceral adipose tissue in women. Association with indexes of plasma glucose-insulin homeostasis

OBJECTIVE

To study the associations between changes in body fatness, visceral adipose tissue (AT), and indexes of plasma glucose-insulin homeostasis over a 7-year follow-up period.

RESEARCH DESIGN AND METHODS

A sample of 30 nondiabetic women aged 35.2 +/- 5.6 (SD) years at baseline was studied.

RESULTS

Changes in visceral AT and in subcutaneous AT (measured by computed tomography) as well as changes in body fat mass (obtained by hydrostatic weighting) were significantly related to changes in fasting plasma insulin levels and in plasma insulin area measured after a 75-g oral glucose load (0.47 < or = r < or = 0.62; P < 0.01). Changes in visceral AT but not in body fat mass or in subcutaneous AT area were significantly associated with changes in plasma glucose area (r = 0.37; P < 0.05). When two subgroups of women with similar mean increases in body fat mass but with either small or large increases in visceral AT were compared, the subgroup with the largest gain in visceral AT showed the greatest deterioration in indexes of plasma glucose-insulin homeostasis. On the other hand, when two subgroups with similar mean increases in visceral AT but with different changes in body fat mass were compared, both subgroups showed similar changes in plasma glucose and insulin concentrations.

CONCLUSIONS

Results of this 7-year follow-up study in women suggest that changes in indexes of plasma glucose-insulin homeostasis are significantly associated with changes in visceral AT, even after control for changes in body fat mass.

Cell-specific expression of the ZPK gene in adult mouse tissues

ZPK is a recently identified human putative protein kinase gene that encodes an unusual serine/threonine kinase containing two potential leucine zipper motifs similar to those found in transcription factors as well as in members of the newly discovered mixed-lineage family of protein kinases. To study the normal biological function of ZPK, we have isolated a mouse ZPK cDNA and examined the pattern of ZPK mRNA expression in adult mouse tissues by Northern blot and in situ hybridization analyses. The predicted open reading frame of this cDNA encodes an 888-amino-acid protein that shares 95% overall identity with its human counterpart. By Northern blot analysis, we detected expression of ZPK mRNA in the brain of adult mice, but not in any other tissue tested. In situ hybridization analysis of mouse brain sections revealed specific association of ZPK mRNA with neuronal cell populations, primarily in the hippocampus, the cerebral cortex, and the Purkinje cell layer of the cerebellum. Interestingly, a remarkable pattern of cell-type-specific expression was also found in the epithelial compartment of various organ systems, including stomach, small intestine, liver, and pancreas, as well as in the seminiferous tubules of mature testes. Taken together, these observations suggest that ZPK could play a role in development, function, and maintenance of a variety of specialized cells.

Overfeeding in identical twins: 5-year postoverfeeding results

From a total of 12 pairs of young male identical twins who were overfed by an estimated 84,000 kcal over a period of 100 days, several pairs (eight to 11, depending on variables) were remeasured for body weight, body composition with the underwater weighing technique, regional fat distribution from skinfolds, girths, computed tomography (CT) fat areas in the abdominal region, and fasting plasma glucose, insulin, total cholesterol, high-density lipoprotein (HDL) cholesterol, and triglycerides 4 months and 5 years after completion of the overfeeding protocol. At 4 months, the twins had lost approximately 7 of 8 kg that they had gained with overfeeding. However, 5 years later, body weight had increased by 5 kg over the preoverfeeding level. Fluctuations in fat mass were greater than those in fat-free mass. The younger twins gained approximately twice as much as the older twins in the late recovery period, a difference attributed to the late phase of growth in body mass in the former. Upper-body fat was reduced at 4 months of follow-up study, but was increased in the late recovery phase. All blood values were normalized in the postoverfeeding periods. A within-pair resemblance was generally observed for the changes noted in the recovery periods, but it was more striking when variations between preoverfeeding and 4-month or 5-year values were considered. We conclude from these observations that there were no persistent effects of exposure to the overfeeding protocol over the expected age-associated increases in body mass, body fat, upper-body fat, abdominal visceral fat (AVF), and metabolic variables predictive of risk for common diseases in individuals of normal body weight and with no family history of obesity. The intrapair resemblance suggests that the genotype contributes to the alterations observed in the recovery from overfeeding and in the age-associated changes.

Postprandial glucose, insulin, and lipid responses to four meals containing unpurified dietary fiber in non-insulin-dependent diabetes mellitus (NIDDM), hypertriglyceridemic subjects

OBJECTIVE

To evaluate the effects of two levels of total dietary fiber (10 g vs. 20 g) and two soluble:insoluble fiber ratios (1:4 vs. 2:3) on postprandial glucose and lipid metabolism in hypertriglyceridemic subjects with non-insulin-dependent diabetes mellitus (NIDDM).

METHODS

Eight NIDDM, mildly hypertriglyceridemic subjects consumed four test breakfasts, each containing variable proportions of the same cereal and fruit fiber sources. Blood samples were obtained during the 4 hours following the test meals and analyzed for glucose, insulin, triglyceride, total cholesterol and high density lipoprotein cholesterol.

RESULTS

The incremental area under the curve for glucose and insulin was lowered after consuming 20 g as compared to 10 g of dietary fiber (p < 0.05), but was not affected by the soluble insoluble fiber ratio. The postprandial lipemia was similar after all test meals.

CONCLUSION

The proportion of soluble to insoluble fiber in cereal and fruit does not necessarily predict the effect of fiber on the glycemic response, while the overall quantity of fiber does appear to affect postprandial glucose metabolism in NIDDM.

Effect of physical training on mitochondrial function in skeletal muscle of normal and diabetic rats

The study was designed to assess the impact of physical training on the oxidative phosphorylation rate (OPR) in mitochondria isolated from two different skeletal muscles of rats with or without chronic diabetes mellitus. Diabetes was induced by an intravenous injection of streptozotocin (50 mg/kg), and only animals with a blood glucose level between 14 and 22 mmol/L 1 week later were kept in the protocol. Exercise training was performed on a treadmill with a progressive 10-week program. Rats were killed by decapitation at the end of the training program, and mitochondria were isolated from the gastrocnemius and the red vastus lateralis muscles. When the data were expressed as per milligrams of protein, OPR was significantly depressed by diabetes mellitus in the mitochondria from each muscle; a similar negative impact also appeared to be produced by physical training in mitochondria isolated from the red vastus lateralis muscle. However, due to changes in mitochondrial protein yield between groups, the capacity to oxidize pyruvate and malate was also calculated per gram of muscle. Adenosine triphosphate (ATP) production rate appeared to be unaffected by diabetes but significantly increased by training in both muscles of diabetic and nondiabetic rats. This effect of training was not associated with any improvement in plasma glucose or insulin levels in diabetic animals. However, the large increase in plasma levels of beta-hydroxybutyric acid in sedentary diabetic rats was partly reversed by training (1,079 +/- 472 v 3,424 +/- 618 micromol, P < .001). These results suggest that the training-induced increase in the capacity of skeletal muscles to oxidize substrates and generate energy may also contribute to reduce the elevated plasma beta-hydroxybutyric acid levels observed in a state of insulin deficiency. This may have clinical relevance, since ketoacidosis remains a life-threatening event in insulin-dependent diabetic subjects.

Plasma high-density lipoprotein cholesterol but not apolipoprotein A-I is a good correlate of the visceral obesity-insulin resistance dyslipidemic syndrome

Apolipoprotein (apo) A-I is a major component of high-density lipoproteins (HDLs), and it has been suggested that measurement of apo A-I may provide additional information in the assessment of coronary heart disease (CHD) risk. In the present study in a sample of 111 men (age [mean +/- SD], 35.3 +/- 6.6 years), we determined whether a low apo A-I concentration is associated with the cluster of metabolic abnormalities that characterize the visceral obesity-insulin resistance dyslipidemic syndrome. For this purpose, the first and fourth quartiles of apo A-I and HDL cholesterol (HDL-C) concentrations were compared in relation to body fat distribution, glucose tolerance, and plasma insulin and lipoprotein levels. Men in the first quartile (< the 25th percentile) of HDL-C, as compared with men in the fourth quartile (> the 75th percentile), were characterized by an elevated visceral adipose tissue (AT) accumulation (P < .05), as well as by increased plasma levels of triglycerides ([TGs] P < .0001), apo B (P < .0005), and insulin (P < .01). These differences were not found when the first and fourth quartiles of plasma apo A-I concentrations were compared. These results suggest that plasma levels of HDL-C are more closely associated with the various features of the visceral obesity-insulin resistance syndrome than plasma apo A-I.

Insulin and glucagon responses to adrenaline infusion in abdominal obese men

OBJECTIVE

To investigate the hormonal, cardiovascular and metabolic responses of visceral vs subcutaneous obese men to infused adrenaline.

DESIGN

Intervention study of an hour adrenaline infusion (0.01 micrograms/kg fat-free mass/min).

SUBJECTS

Eighteen moderately obese men (age: 30-40 y, BMI: 28-34 kg/m2) divided according to their degree (low vs high) of visceral adipose tissue (AT) accumulation.

MEASUREMENTS

Various fatness and fat distribution variables (computed tomography and anthropometry), heart rate and blood pressure, plasma concentrations of gluco-regulatory hormones, glucose, glycerol and free fatty acids (FFA).

RESULTS

Similar increases were noted in heart rate, plasma adrenaline, FFA and glycerol levels in both low and high visceral AT groups after hormonal infusion. There was a tendency for plasma glucagon responses to be higher in men with high amounts of visceral fat (p = 0.07). Plasma glucose levels increased in both groups, but significantly more in men with low levels of visceral AT (p < 0.05), whereas plasma insulin concentrations increased significantly only in men with high amounts of visceral AT in response to adrenaline infusion (p < 0.01). In the overall sample of obese men, visceral AT accumulation (but not the fat mass) was positively correlated with plasma insulin (r = 0.70) and glucagon responses (r = 0.63) to the hormone infusion (p < 0.01). These metabolic responses were not related to the achieved catecholamine concentration.

CONCLUSION

These results suggest that some of the impairments in plasma glucose-insulin homeostasis noted in visceral obesity may be related to an abnormal metabolic response to an adrenaline challenge.

Early insulin and glucagon responses to different food items

An early postprandial insulin release has previously been described when high carbohydrate meals are fed. The present investigation on humans shows that this response takes place not only with high carbohydrate (sugar pie) but also with high lipid (whipped cream) and protein (beef steak or fish fillet) meals, suggesting that it is caused by the palatability of the food rather than to its composition. This increment takes place at the very beginning of the meal and even if the period of feeding lasted 10 min, the response has disappeared at that time. Thirty min later due to plasma glucose elevation, a significant increase in insulin was observed with the sugar pie. At that time a similar increase was observed with the fish filet or the beef steak but not with the whipped cream. A cephalic glucagon response was not observed with any of the meals but 30 min after feeding the plasma level of this hormone increased with both beef and fish feeding and decreased significantly with the sugar pie meal. The usefulness of these responses is discussed with relation to the metabolic responses associated with feeding.

The dense LDL phenotype. Association with plasma lipoprotein levels, visceral obesity, and hyperinsulinemia in men

OBJECTIVE

To investigate the potential relationship between the cluster of metabolic abnormalities found in visceral obesity and the small dense LDL phenotype.

RESEARCH DESIGN AND METHODS

We have estimated LDL peak particle size by nondenaturing 2-16% gradient gel electrophoresis in a sample of 79 men. Glucose tolerance and fasting plasma insulin and lipoprotein levels were also measured.

RESULTS

The LDL particle score, calculated from migration, distances and relative band intensities and reflecting the proportion of small dense LDL particles, was positively correlated with plasma triglyceride (TG) (r = 0.60, P < 0.0001) and negatively correlated with HDL cholesterol (r = -0.56, P < 0.0001) levels. Although the LDL particle score was not associated with variations in plasma LDL cholesterol or LDL apolipoprotein (apo) B concentrations, it was significantly correlated with the LDL apo B-to-LDL cholesterol ratio (r = 0.60, P < 0.0001). Fasting plasma insulin and visceral adipose tissue (AT) areas measured by computed tomography were weakly but significantly correlated with the LDL particle score (r = 0.23 and 0.29, respectively, P < 0.05). LDL peak particle size showed similar but inverse correlations with anthropometric and metabolic variables. Subjects classified as having small dense LDL particles (by comparing subjects in the highest tertile versus those in the lowest tertile of the LDL particle score distribution) were characterized by increased plasma TG, reduced HDL cholesterol, higher fasting insulin levels, and elevated visceral AT accumulation. However, multiple regression analyses revealed that visceral AT accumulation was not an independent predictor of the dense LDL phenotype after inclusion of TG and HDL cholesterol levels and lipoprotein ratios in the model.

CONCLUSIONS

It thus appears that the high TG-low HDL cholesterol dyslipidemia frequently found in visceral obesity and in a hyperinsulinemic state is a strong correlate of the small dense LDL phenotype. Although associated with the dense LDL phenotype, visceral obesity and hyperinsulinemia were not independent predictors of an increased proportion of small dense LDL particles after controlling for TG and HDL cholesterol levels.

The lipoprotein lipase HindIII polymorphism modulates plasma triglyceride levels in visceral obesity

The aim of this study was to investigate the potential interaction between the lipoprotein lipase (LPL) HindIII polymorphism and visceral adipose tissue (AT) accumulation in the modulation of triglyceride levels in visceral obesity. The LPL-HindIII genotype was determined by polymerase chain reaction in 52 min. Twenty-three subjects were heterozygous (+/-) and 28 were homozygous (+/+) for the presence of the restriction site. One subject who was homozygous for the--allele was excluded from analysis. Body mass index (BMI), fasting insulin level, and visceral AT area as measured by computed tomography were positively correlated with triglyceride levels only in subjects homozygous for the + allele. Furthermore, whereas these variables were negatively correlated with plasma HDL2 cholesterol concentrations in the +/+ group, these associations were not found in +/- heterozygotes, with the exception of BMI. To further investigate the interaction of the LPL-HindIII polymorphism with visceral obesity and hyperinsulinemia, the two genotype groups were further subdivided on the basis of BMI (low versus high), fasting insulin level (low versus high), and visceral AT area (low versus high), and their lipoprotein profiles were compared. Elevated levels of abdominal visceral AT were significantly associated with increased triglyceride concentrations in +/+ homozygous men, suggesting that visceral obesity may lead to hypertriglyceridemia in the presence of the +/+ genotype. In the +/- group, variation in the amount of visceral AT was not associated with differences in triglyceride concentration. However, hypertriglyceridemia and an increased cholesterol-to-HDL cholesterol ratio were observed in the hyperinsulinemic state irrespective of LPL-HindIII genotype status.(ABSTRACT TRUNCATED AT 250 WORDS)