Ethnic variation in fat and lean body mass and the association with insulin resistance

CONTEXT

Body fat distribution varies among different ethnic groups, yet less is known regarding differences in lean mass and how this may affect insulin resistance.

OBJECTIVE

Our objective was to compare total body fat to lean mass ratio (F:LM) in Aboriginal, Chinese, European, and South Asian individuals with differences in insulin resistance.

PARTICIPANTS, DESIGN, AND SETTING

Aboriginal (196), Chinese (222), European (202), and South Asian (208) individuals were recruited across a range of body mass index to participate in this cross-sectional community study.

MAIN OUTCOME MEASURES

Total body fat, lean mass, and insulin resistance were assessed using homeostasis model assessment (HOMA).

RESULTS

After adjustment for confounders and at a given body fat, South Asian men had less lean mass than Aboriginal [3.42 kg less; 95% confidence interval (CI) = 1.55-5.29], Chinese (3.01 kg less; 95% CI = 1.33-4.70), and European (3.57 kg less; 95% CI = 1.82-5.33) men, whereas South Asian women had less lean mass than Aboriginal (1.98 kg less; 95% CI = 0.45-3.50), Chinese (2.24 kg less; 95% CI = 0.81-3.68), and European (2.97 kg less; 95% CI = 1.67-4.27) women. In adjusted models, F:LM was higher in South Asian compared with Chinese and European men and higher in South Asian compared with Aboriginal, Chinese, and European women (P < 0.01 for all). Insulin and HOMA were greatest in South Asians after adjustment; however, these differences were no longer apparent when F:LM was considered.

CONCLUSIONS

South Asians have a phenotype of high fat mass and low lean mass, which may account for greater levels of insulin and HOMA compared with other ethnic groups.

Diabetes, abdominal adiposity, and atherogenic dyslipoproteinemia in women compared with men

OBJECTIVE

To understand why atherogenic risk differs more between diabetic and nondiabetic women than between diabetic and nondiabetic men.

RESEARCH DESIGN AND METHODS AND RESULTS

Measures of cardiovascular risk, body composition, and serum hormones from the baseline examinations of the Insulin Resistance Atherosclerosis Study on 524 nondiabetic women, 258 diabetic women, 421 nondiabetic men, and 220 diabetic men were compared to detect greater adverse differences in women than in men. Systolic blood pressure; apolipoprotein B (apoB); total cholesterol; apoB-to-apoA-I ratio; non-HDL cholesterol; LDL particle count, small LDL, and intermediate-density lipoprotein by nuclear magnetic resonance; and C-reactive protein exhibited significant diabetes-sex interaction (P < 0.05). ApoB exhibited the most significant interaction (P = 0.0005). Age- and ethnicity-adjusted apoB means were lower in nondiabetic women than nondiabetic men (102.4 vs. 106.8 mg/dl, P < 0.05) but higher in diabetes (115.7 vs. 110.2 mg/dl, P < 0.01). Plotted against BMI, waist circumference was 6% higher and hip circumference 10% lower in diabetic than nondiabetic women (both P < 0.05), whereas the circumference measures did not differ conspicuously between diabetic and nondiabetic men.

CONCLUSIONS

In diabetic women, an elevated level of atherogenic particles, as manifested by apoB and LDL particle count, which may result from abdominal adiposity, represents a major treatable cardiovascular risk factor.

Non-HDL cholesterol and apoB in dyslipidaemia

On the basis of a high correlation, non-HDL-C (non-high-density lipoprotein cholesterol) and apoB (apolipoprotein B) have been suggested to be of equivalent value for clinical practice; however, the strength of this relationship has not been examined in detail in patients with dyslipidaemia. The present study examines the variance of non-HDL-C compared with apoB in 1771 consecutive patients evaluated in a lipid clinic. These patients were divided into normolipidaemic subjects (n=407), type I hyperlipoproteinaemia (n=16), type IIa (n=736) and IIb (n=231) hyperlipoproteinaemia, type III hyperlipoproteinaemia (n=38), type IV hyperlipoproteinaemia (n=509) and type V hyperlipoproteinaemia (n=101). The relationship between non-HDL-C and apoB was examined both in terms of correlation and concordance. Correlation was high, but concordance was only moderate in the normolipidaemic subjects and in those with type IIa and type IIb hyperlipoproteinaemia. Correlation and concordance were both low in the subgroups with type III and type V hyperlipoproteinaemia. In those with type IV hyper-lipoproteinaemia, correlation was moderately high (r=0.74), but concordance was only fair. In conclusion, our results indicate that there is substantial variance of apoB for given values of non-HDL-C in many dyslipidaemic subjects. It follows that correlation is not adequate as a sole judge of equivalence of laboratory parameters.

Apolipoprotein B, apolipoprotein A-I, insulin resistance and the metabolic syndrome

PURPOSE OF REVIEW

The goal of identifying subjects with metabolic syndrome is to detect those at higher risk of developing cardiovascular disease. Evidence continues to accumulate as to the superiority of apolipoprotein B and apolipoprotein A-I over the conventional lipoprotein lipids as markers of vascular risk. It would seem reasonable, therefore, to redefine the dyslipidemia of the metabolic syndrome incorporating apolipoproteins. Therefore, our objective is to elucidate how apolipoprotein B and apolipoprotein A-I amplify evidence of the interactions amongst metabolic syndrome, insulin resistance, abdominal obesity, and vascular risk.

RECENT FINDINGS

In several large epidemiological studies, including the NHANES III database, apolipoprotein B/apolipoprotein A-I ratio was tightly linked to the metabolic syndrome and each of its components, the descending order being: low HDL cholesterol, high triglyceride, high waist circumference, high glucose, and high blood pressure. Moreover, apolipoprotein B associates more closely with inflammatory markers and insulin resistance than triglyceride and all cholesterol markers. Yet despite close association of the apolipoprotein B/apolipoprotein A-I ratio to metabolic syndrome, both are independent predictors of future myocardial infarction.

SUMMARY

We believe that the dyslipidemia of the metabolic syndrome should be redefined to include apolipoprotein B and apolipoprotein A-I.

Hypertrophy and hyperplasia of abdominal adipose tissues in women

OBJECTIVE

To examine the expression of selected transcription factors involved in adipogenesis and genes related to lipid metabolism in abdominal subcutaneous and omental fat tissue.

RESEARCH DESIGN AND METHODS

We obtained subcutaneous and omental adipose tissue samples from 40 women undergoing abdominal hysterectomies (age: 47+/-5 years; BMI 27.9+/-5.3 kg/m(2)). We measured isolated adipocyte size and metabolism, and detailed measures of body fat accumulation and body fat distribution were obtained (dual-energy X-ray absorptiometry and computed tomography, respectively).

RESULTS

Adipocyte size of both subcutaneous and omental fat were increased with higher body fat mass values, with similar regression slopes in each compartment. In contrast, with higher body fat mass values, fat accumulation was progressively higher in the subcutaneous than in the visceral fat compartment, suggesting hyperplasia in the subcutaneous fat compartment. Messenger RNA levels of CEBPalpha, PPARgamma2, SREBP1c and genes related to lipid metabolism (LPL, FABP4, DGAT1, DGAT2, PLIN and HSL) were significantly higher in subcutaneous than in omental fat tissue (P< or =0.001 for all). Only subcutaneous expression of these genes tracked with obesity levels as reflected by significant positive associations between subcutaneous fat CEBPalpha, SREBP1c and DGAT2 expression and total body fat mass (r=0.37, r=0.41, r=0.57, respectively, P< or =0,05), fat percentage (r=0.40, r=0.39, r=058, respectively, P< or =0,05) and subcutaneous adipose tissue area (r=0.36, r=0.38, r=0.58, respectively, P< or =0,05). Omental adipose tissue expression levels of these genes were not significantly related to adiposity measures.

CONCLUSIONS

These results show that in obese women, hyperplasia is predominant in the subcutaneous fat depot, whereas fat cell hypertrophy is observed both in the omental and subcutaneous compartments.

Why might South Asians be so susceptible to central obesity and its atherogenic consequences? The adipose tissue overflow hypothesis

The rates of coronary disease have accelerated dramatically amongst South Asians, driven to an important extent by the atherogenic dyslipidemia and type 2 diabetes that have become so common amongst them. These precursors of vascular disease appear at lower absolute amounts of adipose tissue in South Asians than in whites. In this paper, we set out a new hypothesis--the adipose tissue overflow hypothesis--to account for these findings. The adipose tissue mass within our bodies can be divided into three different compartments: superficial subcutaneous adipose tissue, deep subcutaneous adipose tissue and visceral adipose tissue. The superficial subcutaneous adipose tissue compartment is the primary compartment, is present throughout the body, and constitutes the vast majority of the adipose tissue in the lower limb. With energy excess, the secondary adipose tissue compartments--the deep subcutaneous (mainly upper body) and the visceral adipose tissue compartments--become more prominent. Superficial subcutaneous adipose tissue is relatively inert metabolically, whereas the other two compartments are characterized by higher transmembrane fatty acid flux rates and thus are more closely linked to dyslipidemia and dysglycemia. We hypothesize that the superficial subcutaneous adipose tissue compartment is larger in whites than in South Asians. If so, as obesity develops, South Asians exhaust the storage capacity of their superficial subcutaneous adipose tissue compartment before whites do and that is why they develop the metabolic complications of upper body obesity at lower absolute masses of adipose tissue than white people.

Relation of age, the apolipoprotein B/apolipoprotein A-I ratio, and the risk of fatal myocardial infarction and implications for the primary prevention of cardiovascular disease

Age is by far the most powerful risk factor for cardiovascular disease. Moreover, the consequences of age are considered inevitable and irreversible. In this study, we examined whether age is, to a major degree, a modifiable risk factor. In the subjects in the Apolipoprotein-related Mortality Risk (AMORIS) study, we show that fatal myocardial infarction (MI) is uncommon in men before the sixth decade and in women before the seventh. In age-adjusted analyses, the risk of fatal MI increase successively with each decile of the apolipoprotein (apo) B/apoA-I ratio, confirming the importance of the balance of the atherogenic and antiatherogenic lipoproteins as a fundamental determinant of the likelihood of clinical events. We then determined the risk of fatal acute MI over time in the highest decile of the apoB/apoA-I ratio compared with the lowest decile. For the purposes of this analysis, we assume that all events in the lowest decile of the apoB/apoA-I ratio represent the nonmodifiable adverse effects of age. This assumption maximizes the irreversible effects of age. Because the change in age is identical for the subjects in both deciles, the difference in risk between the lowest and highest deciles of the apoB/apoA-I ratio represents the consequence of exposure over time to very high values of this ratio. Exposure is the modifiable element of risk, and it contributed to most of the risk. In conclusion, it appears that not all of the effects of age are irreversible. therefore, outcomes with early prevention might be much more favorable than usually assumed.

Low-density lipoprotein lowering in type 2 diabetes mellitus: how to know how low to go

PURPOSE OF REVIEW

Getting low-density lipoprotein to the right level in patients with type 2 diabetes should be relatively easy, given the potent pharmacological therapy that is available and the fact that low-density lipoprotein C is typically normal in these patients. Getting it right means getting the target for therapy right, however. The article examines the criteria that should be used to make this choice.

RECENT FINDINGS

In comparing different parameters, three criteria, in particular, need to be taken into account: the on-treatment predictive value of any parameter; the value relative to the population of one parameter compared with another, namely which is more deviant from the norm; and the concurrent level of high-density lipoprotein. The evidence from the low-density lipoprotein-lowering trials indicates that low-density lipoprotein C is not nearly as good as non-high-density lipoprotein C as a guide for the adequacy of low-density lipoprotein lowering, or, better still, apoB, with the apoB/apoA-I ratio being clearly the best of all.

SUMMARY

The evidence from the major clinical trials indicates the best single index of the adequacy of low-density lipoprotein lowering is the apoB/apoA-I ratio. Clinical practice should adapt to clinical evidence and, therefore, guidelines should be based on apolipoproteins rather than the conventional cholesterol indices.

Differential impact of plasma triglycerides on HDL-cholesterol and HDL-apo A-I in a large cohort

OBJECTIVES

To examine the relationship between plasma triglycerides (TG) to HDL-cholesterol (HDL-C) or HDL apo A-I.

DESIGN AND METHODS

Bivariate and multiple linear regression analyses in a large cohort of 1886 subjects.

RESULTS

Higher plasma TG levels were associated with lower concentrations of both HDL-C and HDL-apo A-I. However, the HDL-C/HDL-apo A-I ratio was inversely correlated with plasma TG indicating that the overall composition of the HDL changed as plasma TG changed. Plasma TG levels contributed to 15.9% of the variance of the HDL-C/HDL-apo A-I ratio, whereas gender, HDL-TG, LDL-TG, body mass index and plasma apo B levels represented between 0.15% and 2.21% of this variance.

CONCLUSIONS

These results indicate that increasing levels of plasma TG result in greater reduction in HDL-C levels than in HDL-apo A-I and this might explain, at least in part, the differences that have been observed in the magnitude of the association of HDL-C versus HDL-apo A-I with the risk of cardiovascular disease.

Effect of aging and obesity on the expression of dyslipidaemia in children from families with familial combined hyperlipidaemia

The aim of the present study was to delineate the mechanism(s) responsible for the increased secretion of VLDL (very-low-density lipoprotein) particles in patients with FCH (familial combined hyperlipidaemia). In 194 young adults (<25 years of age) recruited from families with FCH, we investigated how plasma lipids, (apo)lipoproteins and BMI (body mass index) varied with age. Furthermore, we performed a 5-year follow-up study of clinical and biochemical characteristics of a subset of this population (n=85) stratified by apoB (apolipoprotein B) levels (below or above the 75th percentile adjusted for age and gender). Plasma apoB concentration (r=0.45, P<0.0001), triacylglycerol (triglyceride) concentration (r=0.45, P<0.0001), LDL (low-density lipoprotein) subfraction profile (r=−0.46, P<0.0001) and BMI (r=0.51, P<0.0001) were significantly associated with age. Plasma apoB concentration in the hyperapoB group was already elevated at a young age, whereas other characteristics of FCH, as observed in adults, including triacylglycerol levels >1.5 mmol/l and/or small-dense LDL, were observed only sporadically. After the 5-year follow-up, BMI increased in both groups, and this increase was associated with changes in apoB (r=0.27, P<0.05), triacylglycerol (r=0.30, P<0.01), VLDL cholesterol (r=0.22, P<0.05), VLDL triacylglycerol (r=0.25, P<0.05) and high-density lipoprotein cholesterol (r=−0.27, P<0.05). In conclusion, we have found indirect evidence of a primary, presumably genetically determined, increase in plasma apoB concentration occurring early in life of offspring from families with FCH. However, aging-related post-maturation increases in adipose tissue mass also appear to contribute to an aggravation and/or modulation of this genetically determined apoB overproduction.

Apolipoprotein A1 and B

This article reviews the evidence showing that apolipoprotein (apo) B and A-1 are superior to the conventional cholesterol indices as analytes in laboratory practice, indices of the lipoprotein-related risk for vascular disease, and measures of the adequacy of low-density lipoprotein-lowering therapy.

Influence of hepatic steatosis (fatty liver) on severity and composition of dyslipidemia in type 2 diabetes

OBJECTIVE

The objective of this study was to examine the associations between the severity of hepatic steatosis and dyslipidemia in type 2 diabetes, including circulating apolipoprotein B100 (apoB) concentrations and lipoprotein particle size and numbers.

RESEARCH DESIGN AND METHODS

Computed tomography imaging was used to assess hepatic fat content and adipose tissue distribution in 67 men and women with type 2 diabetes, withdrawn from antidiabetic medications preceding the study. Fasting serum lipoprotein number and size was determined by nuclear magnetic resonance. Insulin sensitivity was measured with a glucose clamp and a [6,6-(2)H(2)]glucose isotope infusion.

RESULTS

Two-thirds of the cohort had fatty liver. Hepatic steatosis correlated with serum triglycerides (r = 0.40, P < 0.01) and lower HDL cholesterol (r = -0.31, P < 0.05). ApoB and LDL cholesterol did not, being virtually identical in those with or without steatosis. The association between serum triglycerides and hepatic steatosis was largely accounted for by greater triglyceride enrichment in VLDL particles, which were larger. Severe steatosis was also associated with 70% higher small, dense LDL concentrations. Visceral obesity did not fully explain these associations, and hepatic steatosis was better correlated with triglycerides than with hyperglycemia or hepatic insulin resistance (P > 0.05).

CONCLUSIONS

The presence of hepatic steatosis in type 2 diabetes does not appear to affect apoB levels, but potentially increases atherogenesis by increasing triglycerides, reducing HDL levels, and increasing small, dense LDL.

Identification of a Novel C5L2 Variant (S323I) in a French Canadian Family With Familial Combined Hyperlipemia

Objective— A functional acylation stimulating protein (ASP) receptor, C5L2, has been recently identified in ASP-responsive cells. Impaired ASP-mediated triglyceride synthesis has previously been described in a subset of hyperapolipoprotein B/familial combined hyperlipidemia subjects.

Methods and Results— DNA sequencing of C5L2 coding region in 61 unrelated probands identified a heterozygous variant (G968→T) in 1 subject, resulting in Ser323→Ile substitution in the carboxyl terminal region. This variant was not detected in 2176 additional chromosomes by restriction fragment length polymorphism or fluorescence polarization genotyping. Eight family members of the proband were identified with one altered (+/−)C5L2 allele. Nine other family members had the wild-type (+/+)C5L2 sequence. The abnormal allele was associated with increased plasma triglyceride, plasma cholesterol, low-density lipoprotein (LDL) cholesterol, apolipoprotein B and ASP. Of 23 subjects tested in cell-based ASP bioactivity assays, those with C5L2(+/−) variant (n=2) had a 50% reduction in ASP-stimulated triglyceride synthesis, glucose transport and marked reduction in maximal binding (B max ). By contrast, a C5L2(+/+) family member responded normally, as did hyperapolipoprotein B normal ASP subjects compared with C5L2(+/+) controls (n=6).

Conclusion— The S323I variant may alter C5L2 function and might be one molecular basis contributing to familial combined hyperlipidemia.

Errors that result from using the TC/HDL C ratio rather than the apoB/apoA-I ratio to identify the lipoprotein-related risk of vascular disease

The objective of this analysis was to demonstrate the frequency and extent of error that results from using the TC/HDL C ratio rather than the apoB/apoA-I ratio to estimate the lipoprotein-related risk of vascular disease within 94,667 men and 75,675 women in the Apoprotein-related Mortality Risk (AMORIS) cohort. The odds ratio (OR) for the risk of fatal myocardial infarction was determined for 1 SD change in the apoB/apoA-I ratio and all the conventional cholesterol ratios--TC/HDL C ratio, LDL C/HDL C ratio, non-HDL C/HDL C ratio. In both men and women, the apoB/apoA-I ratio was significantly greater than any of the cholesterol ratios, which, in fact, differed little. Therefore, the apoB/apoA-I ratio was taken as the most accurate index of the lipoprotein-related risk of vascular disease. Using Receiver Operating Characteristic analysis, it was demonstrated that the diagnostic accuracy of the apoB/apoA-I ratio was significantly greater than any cholesterol ratio in those with an LDL cholesterol <3.6 mmol L(-1) compared to those with an LDL cholesterol >3.6 mmol L(-1). Indeed, the difference between the apoB/apoA-I OR compared with the TC/HDL C OR progressively widened as risk increased. This suggests that the advantage of the apoB/apoA-I ratio is greatest in the population at highest risk. The distribution of subjects by quintiles showed in both genders that whilst agreement was greatest at the extremes, even at these points there was substantial discordance between the TC/HDL C and the apoB/apoA-I ratios. Within the middle of the distribution, less than 50% of the values were concordant. Finally, when comparing the ORs, the TC/HDL C ratio underestimated risk in 69.4% of male subjects and overestimated risk in 26.1% of male subjects, whereas in the female subjects, the TC/HDL C ratio underestimated risk in 84.9% of the subjects and overestimated risk in 12.0%. Thus, using the conventional cholesterol ratios rather than the apoB/apoA-I ratio results in frequent and substantial error in the estimation of the lipoprotein-related risk of vascular disease.

Does low-density lipoprotein size add to atherogenic particle number in predicting the risk of fatal myocardial infarction?

The lipoprotein-related risk of coronary artery disease is determined principally by the balance between atherogenic lipoprotein particles, i.e., the lipoprotein that contain apolipoprotein-B (apo-B), and the antiatherogenic particles, i.e., high-density lipoprotein particles that contain apo-A-I. However, there is also considerable evidence that patients with predominantly small dense low-density lipoprotein (LDL) have more adverse clinical outcomes than do those with large buoyant LDL. The AMORIS study prospectively examined the relative importance of lipoprotein lipids versus apolipoproteins on the risk of fatal myocardial infarction in a large Swedish cohort. This updated analysis includes 69,029 men and 57,167 women who were followed for a mean of 10.3 years. Our objective was to determine whether LDL size as reflected by the LDL cholesterol/apo-B ratio added significant predictive power to apo-B or the apo-B/apo-A-I ratio. Although apo-A-I added significantly to the predictive power of apo-B, categorical and continuous multivariate analyses showed that this is not the case for LDL size. The strongest single lipoprotein-related risk factor was the apo-B/apo-A-I ratio. In conclusion, these results provide further confirmation of the importance of determining apo-B and apo-A-I in routine clinical practice.

Apo B versus cholesterol in estimating cardiovascular risk and in guiding therapy: report of the thirty-person/ten-country panel

There is abundant evidence that the risk of atherosclerotic vascular disease is directly related to plasma cholesterol levels. Accordingly, all of the national and transnational screening and therapeutic guidelines are based on total or LDL cholesterol. This presumes that cholesterol is the most important lipoprotein-related proatherogenic risk variable. On the contrary, risk appears to be more directly related to the number of circulating atherogenic particles that contact and enter the arterial wall than to the measured concentration of cholesterol in these lipoprotein fractions. Each of the atherogenic lipoprotein particles contains a single molecule of apolipoprotein (apo) B and therefore the concentration of apo B provides a direct measure of the number of circulating atherogenic lipoproteins. Evidence from fundamental, epidemiological and clinical trial studies indicates that apo B is superior to any of the cholesterol indices to recognize those at increased risk of vascular disease and to judge the adequacy of lipid-lowering therapy. On the basis of this evidence, we believe that apo B should be included in all guidelines as an indicator of cardiovascular risk. In addition, the present target adopted by the Canadian guideline groups of an apo B <90 mg dL(-1) in high-risk patients should be reassessed in the light of the new clinical trial results and a new ultra-low target of <80 mg dL(-1) be considered. The evidence also indicates that the apo B/apo A-I ratio is superior to any of the conventional cholesterol ratios in patients without symptomatic vascular disease or diabetes to evaluate the lipoprotein-related risk of vascular disease.