Relationships between glycaemic abnormalities, obesity and insulin resistance in nondiabetic Polynesians of New Caledonia.

OBJECTIVE: Polynesians in New Caledonia have an increased risk for developing diabetes, compared to Melanesians or Europeans. They are also more prone to obesity. The aim of this study was to analyse differences in the pre-diabetic state that may explain the varying susceptibility to diabetes between these three ethnic groups, focusing on the balance between insulin resistance and capacity of pancreatic cells to secrete insulin. DESIGN AND SUBJECTS: The CALDIA Study is a population-based cross-sectional survey of diabetes prevalence conducted in New Caledonia. All participants who did not have diabetes, according to the results of a 0-2 h oral glucose tolerance test (n=392), were selected for analysis. RESULTS: Compared to Europeans, Polynesians and Melanesians had significantly higher body mass indices (BMI) and waist-to-hip ratios (WHRs). Polynesians had higher fasting plasma glucose values than Europeans or Melanesians (6.03 mmol/l, vs 5.78 and 5.46, respectively; P<0.0001). Fasting plasma insulin level and the estimate of insulin resistance by homeostasis model assessment were not significantly different between the three ethnic groups. Homeostasis model assessment estimate of beta-cell secretory capacity was lower in Polynesians compared to the two other ethnic groups (83.1 mU/mmol, vs 119.3 and 125.2, respectively; P<0.02). CONCLUSION: Despite a high prevalence of central obesity, as judged by high BMI and WHR, in Polynesians of New Caledonia, their high risk of diabetes may be more strongly related to a defect in insulin secretion capacity than to insulin resistance.

Relationships between physical activity, obesity and diabetes mellitus in a French elderly population: the POLA study. Pathologies Oculaires lieés á l' Age.

OBJECTIVE: To analyse the relationships between body mass index, waist circumference, waist-to-hip ratio, physical activity and the risk of type 2 diabetes in a French elderly population. DESIGN AND SUBJECTS: We conducted a cross-sectional study on 1113 men and 1419 women aged 60 y or more, participating in the POLA Study. RESULTS: The prevalence of diabetes was two-fold higher in men than in women (19.1% and 9.3%, respectively). The anthropometric variables studied-body mass index (BMI), waist circumference (WC) and the waist/hip ratio (WHR)-were all positively related to the prevalence of type 2 diabetes. The strongest relationships were found for BMI in men and WHR in women. In both genders, sport activity and diabetes were inversely linked whereas no relationship was shown between the amount of household activity and diabetes mellitus. CONCLUSION: In the elderly, overall obesity in men and abdominal fat accumulation in women appeared strongly related to diabetes. Sport activity was negatively and independently associated with the prevalence of diabetes mellitus.

Hormonal status and NIDDM in the European and Melanesian populations of New Caledonia: a case-control study. The CALedonia DIAbetes Mellitus (CALDIA) Study Group.

OBJECTIVE: To assess ethnic differences in androgenic status related to non insulin-dependent diabetes mellitus (NIDDM) in male and female Melanesians and Europeans of New Caledonia. DESIGN: This is a case-control study nested in a prevalence study for diabetes mellitus in the multiracial population of New Caledonia. SUBJECTS: 186 male subjects were included in the survey (77 Melanesians and 16 Europeans in each case and control group). Each case and control group included 104 female Melanesian subjects (69 premenopausal and 35 postmenopausal). METHODS: Diabetic subjects were matched for age, gender, ethnic group and location, with healthy normoglycaemic subjects. Testosterone levels in men and sex hormone-binding globulin (SHBG) levels in women (measured by radioimmunoassay, RIA) were compared between NIDDM and control subjects in relation to obesity, central adiposity and insulin levels. RESULTS: In both ethnic groups, NIDDM was associated with lower testosterone levels but there was a marked difference among Europeans. Testosterone was negatively associated with the body mass index (BMI) (r= -0.35, P <0.01) and fasting insulin (r= -0.37, P <0.001) in control Melanesians only. In Melanesian women, NIDDM was associated with lower SHBG levels in pre- and postmenopausal women (P <0.001). SHBG mean level was not associated with menopausal status. CONCLUSION: Our results confirm in a Pacific population that NIDDM is associated with low levels of testosterone in men and low levels in SHBG in women. In contrast to white populations, Melanesian women have a more androgenic profile, whatever their menopausal status.

[Physiopathology of androgen insensitivity syndromes. Contribution of molecular biology]. / Physiopathologie des syndromes d'insensibilité aux androgènes. Apport de la biologie moléculaire.

Molecular genetic study of androgen insensitivity syndrome is now easier by the development of powerful molecular tools. Complementary DNA of the androgen receptor gene has been recently cloned and sequenced. The development of cDNA probes gave the opportunity to study DNA restriction fragment length polymorphisms of patients with complete or partial androgen insensitivity syndrome. These studies demonstrated that deletions are rarely observed. Using PCR and sequencing of exons, several groups described point mutations within the androgen receptor gene. Enzymatic amplification along with denaturing gradient gel electrophoresis and single strand conformational polymorphism study allowed the description of new mutations. These powerful tools together with mRNA study, expression of muted gene, anti-receptor study had also permitted to analyze correlations between structure-function activity of the androgen receptor gene in patients with androgen insensitivity syndrome.

Rat liver cytosol oxysterol-binding protein. Characterization and comparison with the HTC cell protein.

A cytosol protein that specifically binds cholesterol derivatives oxygenated on the side chain has been demonstrated in rat liver and transformed HTC cells. This protein, of which the sedimentation coefficient is about 8 S, was saturable and showed a high binding affinity (Kd about 5 X 10(-9) M) for 25-hydroxycholesterol. Its molecular mass is about 160 kDa. The physicochemical characteristics of this protein were identical whether the model was normal or transformed. This oxysterol-binding protein differs from the well-known sterol carrier proteins.

Characterization of oxysterol-binding protein in rat embryo fibroblasts and variations as a function of the cell cycle.

A cell-free system assay involving cell freeze-thawing and protein fractionation by ammonium sulfate precipitation was developed to characterize a cytosol binding protein specific for oxysterols in rat embryo fibroblasts. This protein shared common characteristics with the oxysterol-binding protein described in L cells and in normal human lymphocytes: 8 S sedimentation coefficient, sterol-protein complex of Mr 160 600, saturability, high affinity (Kd in the range of 10(-9) M) and specificity for cholesterol derivatives oxidized on the side chain. These compounds were better inhibitors of DNA synthesis than the compounds oxidized on the nucleus, whereas no difference was found between sterols oxygenated either on the side chain or on the nucleus, as far as inhibition of hydroxymethylglutaryl-CoA reductase (HMG-CoA reductase) was concerned. Macromolecular components capable of specifically binding 25-hydroxycholesterol were also detected in the fibroblast nucleus. The cytosol oxysterol-binding protein showed a sharp increase (5-fold) in the G2M phase of the cell cycle and in exponentially growing cells (maximal binding site number/cell: 43 500, versus 8850 in confluent cells). Neither the affinity nor the sedimentation coefficient of the protein changed in either situation. The quantitative (but not qualitative) variations of oxysterol-binding protein could be related to the inhibitory effect of 25-hydroxycholesterol on DNA synthesis, which becomes critical when this sterol is added in the G2M phase of the cell cycle.

Physico-chemical properties of the hydroxysterol binding protein of human lymphocyte cytosol. Effects of high salt concentrations and molybdate.

Side chain-hydroxylated derivatives of cholesterol (OH sterol) inhibiting lymphoblastic transformation bind with high affinity and specificity to a hydroxysterol binding protein (OHSBP) in the cytosol of human lymphocytes. These binding properties of OHSBP suggested some analogies with that of steroid hormone receptors. The observation of a nuclear binding of 25-OH[3H]cholesterol prompted us to apply to the cytosolic OH sterol-OHSBP complex the physico-chemical treatments known to 'activate' the steroid hormone receptors. A change of sedimentation coefficient from 8.3 to 4.3 S was observed in hypertonic buffer (0.4 M KCl) but the resulting 4.3 S complex dissociates easily whereas the 'native' 8.3 S form does not. Moreover, molybdate did not prevent the 8.3----4.3 S transformation induced by KCl and neither ammonium sulfate precipitation nor increasing temperature had any effect on the sedimentation coefficient of the 8.3 S complex. Thus, several physico-chemical features differentiate the OH sterol-OHSBP complex from steroid hormone receptors.

DNA and cholesterol biosynthesis in synchronized embryonic rat fibroblasts. II. Effects of sterol biosynthesis inhibitors on cell division.

The relationships between cholesterogenesis and cell division were studied by using two inhibitors of hydroxymethylglutaryl-CoA reductase activity--25-hydroxycholesterol and compactin. The effects of both compounds on DNA synthesis were compared in synchronized rat fibroblasts cultured in a cholesterol-containing medium. Compactin did not inhibit DNA synthesis, except after a long time of contact and at high and almost cytotoxic concentrations. 25-Hydroxycholesterol inhibited DNA synthesis (without cytotoxic effects) after only 9-16 h of contact, depending on the phase of the cell cycle at which this compound was added to the culture medium. Sensitivity of cells to 25-hydroxycholesterol was maximal at the end of the S phase/beginning of the G2M phase. The rapid effect of 25-hydroxycholesterol on DNA synthesis appears to be separate from the inhibitory effect on sterol or non-sterol mevalonate-derived compound synthesis. Indeed, under our experimental conditions, the suppression of cholesterol biosynthesis is compensated by the presence of cholesterol in the culture medium, as demonstrated by the lack of effect of compactin on DNA synthesis; moreover, addition of mevalonolactone to the culture medium did not reverse the effect of 25-hydroxycholesterol. 25-Hydroxycholesterol could inhibit DNA synthesis by a direct action on the nucleus, after transfer by the intermediary of a specific hydroxysterol-binding protein.

DNA and cholesterol biosynthesis in synchronized embryonic rat fibroblasts. I. Temporal relationships between HMG-CoA reductase activity, sterol biosynthesis and thymidine incorporation into DNA.

Temporal relationships between hydroxymethylglutaryl-CoA reductase activity, biosynthesis of C27 sterols, and [3H]thymidine incorporation into DNA were studied in a rat embryo fibroblast cell line synchronized by double thymidine block and cultured in cholesterol-containing medium. Cyclic variations of HMG-CoA reductase activity and C27 sterols occurred, with two maxima in S and G2M phases; the relative shortness of the G1 phase (3 h) in these cells could be responsible for the shift of sterol synthesis in the S phase. No noticeable variation of the individual C27 sterols was observed during the entire cell cycle. In each experiment, there was a good linear correlation between HMG-CoA reductase activity and C27 sterol synthesis, but from one experiment to another, a given level of enzymatic activity led to varying levels of [2-14C]acetate incorporation into sterols. In our experimental conditions, total HMG-CoA reductase activity is measured, and the preceding observation could be explained by a varying degree of phosphorylation of the enzyme depending on the metabolic state of the cells at the start of the experiment. The cyclic variations of the enzyme activity seem to be due more to increased synthesis at given times of the cycle than to periodic dephosphorylation. We question the existence of a relationship between cell division and cyclic sterol synthesis occurring in cells cultured in cholesterol-containing medium.

A specific hydroxysterol binding protein in human lymphocyte cytosol.

A discriminating system capable of recognizing the oxygenated sterols was investigated in human lymphocytes. After labelling entire cells with 25-hydroxy [3H] cholesterol (10 nM) the cytosol was ultracentrifuged on a linear sucrose density gradient. Bound 25-hydroxy [3H] cholesterol was located in a single peak with a sedimentation coefficient of 8.3 S. Pronase treatment abolished the radioactive peak. This 8.3 S protein had a low binding capacity for 25-hydroxy [3H] cholesterol and probably a high affinity. This last parameter was not determined on account of some difficulties encountered in a cell-free system relating to the physico-chemical properties of 25-hydroxycholesterol. Only the hydroxylated sterols closely related to 25-hydroxycholesterol were capable of specifically binding to the 8.3 S protein, in contrast with cholesterol. This protein differed from the binding proteins of oxygenated derivatives of vitamin D3 and glucocorticoids. With the human lymphocyte as a model and under our experimental conditions, this hydroxylated sterol-binding protein seems to be involved rather in the cell division control than in the regulation of HMG-CoA reductase activity: indeed, the hydroxysterols able to inhibit thymidine [3H] incorporation into DNA are recognized by this protein whereas the hydroxysterols active on HMG-CoA reductase activity without affecting thymidine [3H] incorporation into DNA are not.