[Serum levels of retinol-binding protein-4 and its association with metabolic syndrome in first-degree relatives of type 2 diabetes mellitus].

OBJECTIVE: To evaluate serum levels of retinol-binding protein-4 (RBP-4) in first-degree relatives (FDR) of type 2 diabetes mellitus (T2DM) with different glucose tolerance status and to observe its correlation to metabolic syndrome (MS). METHODS: Subjects from FDR of T2DM, including 174 with NGT, 55 with IGT/IFG, and 71 patients with newly diagnosed of T2DM and 114 subjects without diabetic family history as control group [(18 +/- 7) microg/ml vs (22 +/- 8) microg/ml, (NC) [(18 +/- 7) microg/ml vs (22 +/- 8) microg/ml, were recruited. Serum RBP-4 level was measured by radioimmunoassay. Insulin resistance was evaluated by the homeostasis model assessment (HOMA-IR). MS was diagnosed according to 2005 IDF consensus. RESULTS: (1) Serum RBP-4 levels in NC, NGT, IFG/IGT and T2DM groups were (18 +/- 7), (22 +/- 8), (24 +/- 9) and (26 +/- 9) microg/ml respectively. Serum RBP-4 was significantly elevated in NGT group of diabetic FDR as compared with NC group [(26 +/- 9) microg/ml vs (24 +/- 9) microg/ml], and increased with the severity of glucose intolerance. However, no difference was found between serum RBP-4 in the IFG/IGT and T2DM groups. (2) When the distribution of RBP-4 was stratified into quartiles (Q1-Q4), subjects in the top quartile (Q4) was not only associated with greater risk for impaired glucose regulation as compared with Q1 OR = 5.26) , but also significantly with risk for hypertension (OR = 1.96), dyslipidemia (OR = 4.14), obesity (OR = 2.18) and MS (OR = 4.30). CONCLUSION: (1) Serum RBP-4 levels in FDR of T2DM were elevated significantly even before the development of impaired glucose regulation and were further increased with severity of glucose tolerance, suggesting a possible role of RBP-4 in the early pathogenesis of T2DM. (2) Serum RBP-4 level was closely related to MS.

[A highly sensitive enzyme-linked immunosorbent assay for measurement of leptin secretion in human adipocytes].

OBJECTIVE: To establish a highly sensitive and specific ELISA method for measurement of leptin and further to study the secretion of leptin during human preadipocytes differentiation and effects of troglitazone. METHODS: Rabbits Balb/c mice were immunized by recombinant human leptin and Balb/c mice were immunized by human leptin so as to produce rabbit anti-human leptin polyclonal antibodies (PAb) and mouse anti-human leptin monoclonal antibodies (MAb). Combination of the PAb as coating antibody, with a carefully paired biotinylated MAb as detector, and the avidin-horseradish peroxidase as the amplifier of detecting signals, a sandwich method, biotin-avidin ELISA (BA-ELISA) was established. Human omental preadipocytes were cultured, introduced to differentiate, and treated with 10 micromol/L troglitazone; the leptin secretion in the supernatant was detected by BA-ELISA. Peripheral blood samples were collected from 114 healthy persons and the serum leptin was detected by BA-ELISA. RESULTS: The sensitivity of BA-ELISA was 0.03 ng/ml with a working range of 0.05 - 5 ng/ml and a exogenous leptin recovery rate of 97.8%, and the intra- and interassay coefficients of variation (CVs) were less than 7.4% and 9.3% respectively. The assay detected only a single free leptin peak in gel chromatographic fractions from the mixed human sera or adipocytes culture media. The leptin secretion level detected by BA-ELISA showed that the leptin secretion of the preadipocytes increased strongly when the cells differentiated into mature adipocytes. The peak leptin secretion level of the troglitazone treated group was 2 times as that of the control group. The leptin concentration of women was than 7.6 ng/ml, significantly higher than that of the men (3.2 ng/ml, P < 0.001), and the serum leptin level was significantly correlated with body mass index both for men (r = 0.67, P < 0.001) and for women (r = 0.61, P < 0.001). CONCLUSION: A highly sensitive BA-ELISA specific for free leptin has been developed that is especially suited for the accurate measurement of the rather low leptin levels of clinical blood specimens and for basic research use.

[Primary culture of human omental preadipocytes and study of their biological properties].

OBJECTIVE: To develop a primary culture method of human omental preadipocytes and to study their biological properties, such as hyperplasia, hypertrophy and endocrine secretion of human visceral adipose tissue. METHODS: Using enzyme-digesting method, fibroblast-like cells from the human omental adipose tissues were cultured. The morphological changes of the cultured cells were observed and the growth curve was drawn by MTT method. The intracytoplasmic lipid of the cultured cells was determined by oil red O staining. The leptin and adiponectin levels in the culture supernatants were measured by ELISA. RESULTS: The cultured fibroblast-like cells were homogeneous. Proliferation of cells began at the 3 rd day and the cell numbers increased in indicial way from the 3 rd day to the 9 th day. The doubling time of cells was about 60 hours. During the process of induction by conditional medium, the cells became round and larger, and more adipose droplets were aggregated. On the 21 st day, more than 90% of the cells became adipocytes. Leptin secretion was detected at low level in the preadipocytes and continuously increased during differentiation, with a peak on day 17. It remained constant from day 17 onward. Unlike leptin, adiponectin secretion was not detected until day 7 after induction, when differentiated adipocytes had already been observed. Its secretion increased dramatically between days 7 and 17, and reached a maximum level on day 17, but had a significant reduction on day 21. Extraction of intracytoplasmic lipid stained with oil red O and detection of leptin and adiponectin both verified the isolated cells were preadipocytes functioning actively. CONCLUSION: A human omental preadipocytes model has been established and different secretion patterns of leptin and adiponectin secretion related to preadipocyte differentiation has been characterized. Adiponectin may be proposed as a specific marker for preadipocyte differentiation.

[Leptin and clustering of the components of risk factors for metabolic syndrome].

OBJECTIVES: To evaluate relationship between serum level of leptin and the components of risk factors for metabolic syndrome and to analyze the characteristics and laws of clustering of the risk factors. METHODS: Totally, 795 non-diabetic adult Chinese subjects (691 men and 104 women, aged 40 - 75 years) from a diabetes prevalence survey in 2000 were involved in this study. Measurements included serum levels of true insulin (TI), leptin, fasting lipids, fasting glucose (FBG) and 2 h postchallenge glucose, as well as seated blood pressure (BP), body mass index (BMI), ratio of waist circumference to hip circumference (WHR), calculated quantitative insulin sensitivity check index (QUICKI), etc. Relationship between serum level of leptin and all the variables mentioned above was studied by statistical methods such as factor analysis, etc. RESULTS: Serum level of leptin in the study subjects increased with the number of components of abnormal metabolism they had. Detection rates of obesity, hypertension, dyslipidemia and metabolic syndrome were significantly higher in those with the upper tertile of serum leptin level than in those with the lower tertile. Factor analysis revealed that variation of the 11 variables including serum level of leptin was affected by the three factors, i.e., the central factor associated with BMI, WHR, FTI, QUICKI and higher serum level of triglyceride (TG) and lower serum level of high-density lipoprotein-cholesterol (HDL-C), the glucose intolerance factor loaded with blood glucose level, FTI, QUICKI and higher serum level of TG (in women only) and the hypertension factor loaded with blood pressure and BMI (in men only), which could explain 62.0% and 66.7% of total variance in men and women, respectively, and higher serum level of TI and insulin resistance also loaded with both the central factor and glucose tolerance factor. CONCLUSIONS: Serum level of leptin was significantly associated with the key markers of metabolic syndrome. Hyperleptinaemia could be a new component of metabolic syndrome. Clustering of the risk factors for metabolic syndrome could be affected by many factors, and although insulin resistance played an important role in it, insulin resistance alone could not explain its etiology.

[Reduced resistin levels in patients with type 2 diabetes mellitus].

OBJECTIVE: To measure the serum resistin level of patients with type 2 diabetes mellitus so as to examine whether there exists a relationship between resistin, obesity and diabetes. METHODS: ELISA was used to examine the fasting serum resistin, leptin, and true insulin and those 2-hours after taking 75-g glucose in 51 untreated type 2 diabetic patients, 30 males and 21 females, and 52 sex and age-matched normal control subjects. Blood glucose, blood pressure, height, weight, waist circumstance, hip girth were measured. Body mass index (BMI), waist to hip ratio (WHR), and quantitative insulin sensitivity check index (QUICKI) were calculated. RESULTS: In comparison with the control, the diabetic group had higher waist-to-hip ratio (WHR) and serum insulin levels (P < 0.05), but significantly lower resistin levels both in the fasting status (23 ng/ml +/- 15 ng/ml vs 30 ng/ml +/- 18 ng/ml, P < 0.05) and 2 hours after glucose loading (22 ng/ml +/- 11 ng/ml vs 31 ng/ml +/- 15 ng/ml, P < 0.001). The leptin level was not statistically different between the two groups (P > 0.05). The resistin level 2 hours after glucose loading was not significantly different between these 2 groups. Correlation analysis demonstrated that fasting resistin level was not correlated with sex, BMI, leptin, and blood pressure, but positively correlated with QUICKI (r = 0.30, P < 0.01) and negatively correlated with blood glucose (r = -0.21, P < 0.05). CONCLUSION: The serum resistin level of patients with type 2 diabetes is reduced rather than increased in fasting status and 2 hours after glucose taking. Resistin may not be the major link between obesity and diabetes in human beings. Since human resistin level is positively correlated with insulin sensitivity, the use of term "resistin", originally for its resistance to insulin, may be somewhat premature.

[Role of leptin in the pathogenesis of obesity-related hypertension].

OBJECTIVE: To assess the role of leptin in the pathogenesis of obesity-related hypertension and the relationship between blood pressure (BP), and body mass index (BMI), insulin resistance and leptin were examined. METHODS: 560 non-diabetic men, aged 35 - 75, selected from volunteers of health screening test during 2 000 were divided into hypertension group (n = 321, BP >or= 140/90 mm Hg without antihypertensive medication). and normal blood pressure group (n = 239). The body weight, waist hip ratio,BP, plasma glucose, serum lipids, true insulin (TI) and leptin were measured after overnight fast. Insulin sensitivity was assessed by the HOMA insulin resistance index (HOMA-R). RESULTS: Fasting leptin level showed good correlation with BMI, fasting TI, HOMA-R, BP and also triglycerides (all P < 0.01). After adjustment for age, BMI and HOMA-R, serum leptin was still positively correlated to SBP (r = 0.11, P < 0.05), and was significantly higher in hypertensive subjects than in normotensive subjects (geometric mean 6.4 vs 4.7 micro g/L, P < 0.001). Logistic regression analysis demonstrated that leptin remained significantly associated with hypertension after adjustment for potentially confounding factors. CONCLUSION: Leptin may play an important role in the pathogenesis of obesity related hypertension.

[The relationship between serum leptin, proinsulin, true insulin levels and insulin resistance in non-diabetic subjects: a population-based study].

OBJECTIVE: Leptin is involved in the regulation of body weight and metabolism. Previous data have suggested that leptin levels are related to insulin resistance and in a few reports with impaired insulin secretion. Some even revealed the existence of adipoinsular axis. However, little is known of these relations in Chinese population. With the availability of measurements of true insulin (TI), proinsulin (PI) and leptin, we examined the possible correlation of leptin with TI, PI and with insulin resistance (the HOMA model) in non-diabetic subjects of north China. We also evaluated whether leptin levels were associated with impaired insulin secretion, as evaluated by the fasting PI/TI ratio. METHODS: 902 non-diabetic subjects (670 with normal and 232 impaired glucose tolerance, aged 30 - 80 y) from a population of Beijing residents who underwent a diabetes survey in 2000 were studied. Fasting serum leptin, PI and TI levels were detected by sensitive and specific enzyme-linked immunosorbent assays (ELISA) which were all developed in our laboratory. RESULTS: Serum leptin values were higher in women. Correlation analysis showed that leptin levels were significantly correlated with fasting TI, PI and insulin resistance (HOMA-IR) (in men, n = 794, r = 0.345, 0.236 and 0.364 respectively; in women, n = 110, r = 0.574, 0.375 and 0.576 respectively, P < 0.001), but not with PI/TI ratio (r = -0.09, P < 0.01) in both sex. After adjustment for age, body mass index (BMI) and waist-to-hip ratio (WHR), leptin levels remained significantly correlated with TI, PI and HOMA-IR, although the magnitude of the association was considerably attenuated. CONCLUSIONS: TI and PI levels were positively related to leptin levels independent of obesity and body fat distribution. Thus, subjects with increased insulin levels and/or insulin resistance may be relatively resistant to the effects of leptin, suggesting a dysfunction of leptin-insulin axis. However, leptin levels are not significantly associated with the fasting PI/TI ratio suggesting that leptin levels are not associated with an impairment in insulin secretion. The role of association between hyperinsulinemia/insulin resistance and hyperleptinemia/leptin resistance in the pathogenesis of insulin resistance-related diseases needs further study.