André Tchernof

Small, Dense Low-Density Lipoprotein Particles as a Predictor of the Risk of Ischemic Heart Disease in Men Prospective Results From the Que´bec Cardiovascular Study

BACKGROUND Case-control studies have reported that patients with ischemic heart disease (IHD) have a higher proportion of small, dense LDL particles than do healthy control subjects. The extent to which the risk attributed to small LDL particles may be independent of concomitant variations in plasma lipoprotein-lipid concentrations remains to be clearly determined, however, particularly through prospective studies. METHODS AND RESULTS Baseline characteristics were obtained in 2103 men initially free of IHD, among whom 114 developed IHD during a 5-year follow-up period. These 114 case patients were matched with healthy control subjects for age, body mass index, smoking habits, and alcohol intake. LDL peak particle diameter (PPD) was measured a posteriori in 103 case-control pairs by nondenaturing gradient gel electrophoresis of whole plasma. Conditional logistic regression analysis of the case-control status revealed that men in the first tertile of the control LDL-PPD distribution (LDL-PPD < or = 25.64 nm) had a 3.6-fold increase in the risk of IHD (95% CI, 1.5 to 8.8) compared with those in the third tertile (LDL-PPD > 26.05 nm). Statistical adjustment for concomitant variations in LDL cholesterol, triglycerides, HDL cholesterol, and apolipoprotein B concentrations had virtually no impact on the relationship between small LDL particles and the risk of IHD. CONCLUSIONS These results represent the first prospective evidence suggesting that the presence of small, dense LDL particles may be associated with an increased risk of subsequently developing IHD in men. Results also suggest that the risk attributed to small LDL particles may be partly independent of the concomitant variation in plasma lipoprotein-lipid concentrations.

Pathophysiology of Human Visceral Obesity: An Update

Excess intra-abdominal adipose tissue accumulation, often termed visceral obesity, is part of a phenotype including dysfunctional subcutaneous adipose tissue expansion and ectopic triglyceride storage closely related to clustering cardiometabolic risk factors. Hypertriglyceridemia; increased free fatty acid availability; adipose tissue release of proinflammatory cytokines; liver insulin resistance and inflammation; increased liver VLDL synthesis and secretion; reduced clearance of triglyceride-rich lipoproteins; presence of small, dense LDL particles; and reduced HDL cholesterol levels are among the many metabolic alterations closely related to this condition. Age, gender, genetics, and ethnicity are broad etiological factors contributing to variation in visceral adipose tissue accumulation. Specific mechanisms responsible for proportionally increased visceral fat storage when facing positive energy balance and weight gain may involve sex hormones, local cortisol production in abdominal adipose tissues, endocannabinoids, growth hormone, and dietary fructose. Physiological characteristics of abdominal adipose tissues such as adipocyte size and number, lipolytic responsiveness, lipid storage capacity, and inflammatory cytokine production are significant correlates and even possible determinants of the increased cardiometabolic risk associated with visceral obesity. Thiazolidinediones, estrogen replacement in postmenopausal women, and testosterone replacement in androgen-deficient men have been shown to favorably modulate body fat distribution and cardiometabolic risk to various degrees. However, some of these therapies must now be considered in the context of their serious side effects. Lifestyle interventions leading to weight loss generally induce preferential mobilization of visceral fat. In clinical practice, measuring waist circumference in addition to the body mass index could be helpful for the identification and management of a subgroup of overweight or obese patients at high cardiometabolic risk.

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.

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.

Androgens and body fat distribution.

An important sex difference in body fat distribution is generally observed. Men are usually characterized by the android type of obesity, with accumulation of fat in the abdominal region, whereas women often display the gynoid type of obesity, with a greater proportion of their body fat in the gluteal-femoral region. Accordingly, the amount of fat located inside the abdominal cavity (intra-abdominal or visceral adipose tissue) is twice as high in men compared to women. This sex difference has been shown to explain a major portion of the differing metabolic profiles and cardiovascular disease risk in men and women. Association studies have shown that circulating androgens are negatively associated with intra-abdominal fat accumulation in men, which explains an important portion of the link between low androgens and features of the metabolic syndrome. In women, the low circulating sex hormone-binding globulin (SHBG) levels found in abdominal obesity may indirectly indicate that elevated free androgens are related to increased visceral fat accumulation. However, data on non SHBG-bound and total androgens are not unanimous and difficult to interpret for total androgens. These studies focusing on plasma levels of sex hormones indirectly suggest that androgens may alter adipose tissue mass in a depot-specific manner. This could occur through site-specific modulation of preadipocyte proliferation and/or differentiation as well as lipid synthesis and/or lipolysis in mature adipocytes. Recent results on the effects of androgens in cultured adipocytes and adipose tissue have been inconsistent, but may indicate decreased adipogenesis and increased lipolysis upon androgen treatment. Finally, adipose tissue has been shown to express several steroidogenic and steroid-inactivating enzymes. Their mere presence in fat indirectly supports the notion of a highly complex enzymatic system modulating steroid action on a local basis. Recent data obtained in both men and women suggest that enzymes from the aldoketoreductase 1C family are very active and may be important modulators of androgen action in adipose tissue.

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/m2). 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 CEBPα, PPARγ2, 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⩽0.001 for all). Only subcutaneous expression of these genes tracked with obesity levels as reflected by significant positive associations between subcutaneous fat CEBPα, SREBP1c and DGAT2 expression and total body fat mass (r=0.37, r=0.41, r=0.57, respectively, P⩽0,05), fat percentage (r=0.40, r=0.39, r=058, respectively, P⩽0,05) and subcutaneous adipose tissue area (r=0.36, r=0.38, r=0.58, respectively, P⩽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.

Regional differences in adipose tissue metabolism in women : Minor effect of obesity and body fat distribution

Studies comparing adipose tissue metabolism in central versus peripheral fat depots have generated equivocal data. We examined whether regional differences in abdominal subcutaneous and omental adipose tissue metabolism in women exist and whether they persist across the spectrum of body fatness and abdominal adiposity values. We measured adipocyte size; lipoprotein lipase (LPL) activity; and basal, isoproterenol-, forskolin-, and dibutyryl cAMP–stimulated lipolysis in adipose tissue or mature adipocytes isolated from the omental and subcutaneous fat depots in a sample of 55 healthy women undergoing elective gynecological surgery. Measures of body fat mass and body fat distribution were also obtained by dual-energy X-ray absorptiometry and computed tomography. Subcutaneous adipocytes were significantly larger than omental adipocytes (P < 0.0001). LPL activity expressed as a function of cell number was significantly higher in subcutaneous versus omental adipose tissue (P < 0.0001). Basal, isoproterenol-stimulated, dibutyryl cAMP–stimulated (10−3 mol/l) and forskolin-stimulated (10−5 mol/l) lipolysis (expressed as a function of cell number) were all significantly higher in subcutaneous versus omental adipocytes (P < 0.05 to P < 0.0001). However, the response of omental adipocytes to lipolytic stimuli tested (fold increase over basal level) was significantly greater in magnitude compared with subcutaneous adipocytes (P < 0.01). These differences were relatively constant across total body fat mass and visceral adipose tissue area tertiles. In conclusion, compared with adipocytes from the omental fat compartment, subcutaneous adipocytes are larger, have higher LPL activity, and are more lipolytic on an absolute basis, which may reflect a higher fat storage capacity in this depot in women. In contrast, omental adipocytes display greater relative responsiveness to both adrenergic receptor–and postreceptor-acting agents compared with subcutaneous adipocytes. Overall and visceral obesity have only minor effects on regional differences in adipose tissue metabolism.

Plasma free fatty acid levels and the risk of ischemic heart disease in men: prospective results from the Québec Cardiovascular Study.

Insulin resistance, through numerous related disturbances in glucose and lipoprotein-lipid metabolism, is associated with an increased risk of ischemic heart disease (IHD). The purpose of the present study was to examine the relationship between increased plasma free fatty acid (FFA) concentrations, as a feature of the insulin resistance syndrome, and the risk of IHD in men. Analyses were carried out in a nested, case-control sample of men selected from a population of 2103 individuals without IHD at baseline among whom 114 developed IHD during a 5-year follow-up period. Incident IHD cases were matched with controls for age, body mass index, smoking habits and alcohol intake. Analyses were performed while excluding (88 cases and 98 controls) and including (103 cases and 99 controls) patients with type 2 diabetes. Among non-diabetic individuals, elevated plasma FFA concentrations (3rd tertile of the distribution) yielded a twofold increase in the risk of IHD (odds ratio [OR] 2.1, P=0.05) compared with lower plasma FFA levels (lowest tertile) after adjusting for non-lipid risk factors. Further adjustment for insulin, triglycerides, apolipoprotein B, HDL cholesterol and small dense LDL attenuated significantly the relationship between plasma FFA concentrations and the risk of IHD. High plasma FFA levels showed no synergism with selected features of the insulin resistance syndrome in determining the risk of IHD. Inclusion of diabetic subjects in the study did not improve FFA independent prognostic value to the risk of IHD. These results suggest that elevated plasma FFA concentrations are associated with an increased risk of IHD. However, a single fasting measurement of plasma FFA levels does not appear to improve our ability to predict IHD onset in men when information on other risk factors is considered.

Menopause-related differences in inflammation markers and their relationship to body fat distribution and insulin-stimulated glucose disposal☆

OBJECTIVE To determine whether postmenopausal status is associated with elevated plasma inflammation markers compared to premenopausal status, and how this explains differences in fat distribution and insulin-stimulated glucose disposal. DESIGN Cross-sectional. SETTING Clinical research center. PATIENT(S) Forty-five premenopausal women and 44 postmenopausal women. INTERVENTION(S) None. MAIN OUTCOME MEASURE(S) C-reactive protein (CRP), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha) were measured by ELISA. Intraabdominal, subcutaneous abdominal, and total fat were measured by computed tomographic scan and dual-photon x-ray absorptiometry. Insulin-stimulated glucose disposal was measured by euglycemic clamp. RESULT(S) The TNF-alpha was higher in postmenopausal compared to premenopausal women (4.81 +/- 1.99 vs. 3.54 +/- 0.85 pg/mL). Interleukin-6 and CRP did not differ by menopausal status. In both premenopausal and postmenopausal women, CRP was related positively to total fat. The CRP was related to intraabdominal fat only in postmenopausal women and was negatively related to insulin-stimulated glucose disposal in both premenopausal and postmenopausal women. CONCLUSION(S) Postmenopausal status is characterized by higher TNF-alpha. The CRP may be associated with increased cardiovascular risk in postmenopausal women by its association with higher intraabdominal fat. Higher CRP is associated with lower insulin-stimulated glucose disposal in both premenopausal and postmenopausal women.

Characterization of UDP-glucuronosyltransferases active on steroid hormones ☆

In recent years, the enzymes which are involved in the formation of DHT in steroid target tissues have been well investigated, however, enzymes responsible for the catabolism and elimination of steroids in these tissues, in particular the uridine diphospho-glucuronosyltransferase (UGT) family of enzymes, have received much less attention. We have recently demonstrated that human and monkey are unique in having high plasma levels of C19 steroid glucuronides. These circulating conjugates have been proposed to reflect the peripheral conversion of adrenal and gonadal C19 steroids to potent androgens, especially DHT. In humans, the presence of steroid UGT activities is found in the liver and several extrahepatic tissues including the prostate, mammary gland and ovary. In addition, UGT activities were observed in breast and prostate tumor cell lines such as MCF-7 and LNCaP, respectively. In agreement with the presence of steroid conjugating enzymes in extrahepatic tissues, UGT cDNA clones, which encode steroid conjugating proteins, have been isolated from libraries constructed from human and monkey prostate mRNA. The presence of UGT transcripts and proteins in extrahepatic tissues in both species, as determined by Northern blot, ribonuclease protection, specific RT-PCR, in situ hybridization, Western blot and immunocytochemistry analysis, indicate the relevance of steroid glucuronidation in tissues other than the liver. Knowing that both the human prostate and the human prostate cancer LNCaP cell line express steroid metabolizing proteins, including UGT enzymes, regulation of UGT mRNA and protein levels, as well as promoter activity was studied in these cells. The results demonstrate a differential regulation between the two highly related isoforms UGT2B15 and UGT2B17, where only the expression of UGT2B17 was affected following treatments of LNCaP cells with androgens, growth factors or cytokines. Steroid conjugation by UGT enzymes is potentially involved in hormone inactivation in steroid target tissues, thus modifications in UGT expression levels may influence hormonal responses.