The biological variation of insulin resistance in polycystic ovarian syndrome

Increased insulin resistance (IR) is a cardinal feature of overweight patients with polycystic ovarian syndrome (PCOS). However, there are no data on the variability of IR for subjects with PCOS. The biological variation of IR (homeostasis model assessment model) was assessed by measuring IR at 4-d intervals on 10 consecutive occasions in 12 overweight PCOS patients (median age, 28 yr; range, 18-31 yr) and 11 weight-matched control women having regular menses and without PCOS (median age, 30 yr; range, 19-33 yr). The distribution of IR was log Gaussian in PCOS and Gaussian distribution in the control group. The IR in PCOS subjects was significantly greater than in the controls [mean (range), 5.85 U (1-42.1) vs. 1.67 U (0.48-3.49); P = 0.001]. After accounting for analytical variation, the mean intraindividual variance was also substantially greater in PCOS patients than in controls (mean, 1.19 vs. 0.23). As a consequence, at any level of IR, a subsequent sample must rise by more than 322% or fall by more than 31% to be considered significantly different from the first. IR, measured using the homeostasis model assessment model, is significantly greater and more variable for overweight patients with PCOS. Therefore, this inherent variability needs to be accounted for in studies of IR in PCOS.     

High serum sex hormone-binding globulin (SHBG) in premature thelarche

OBJECTIVE: We determined serum sex hormone-binding globulin (SHBG), serum dehydroepiandrosterone sulphate, serum oestradiol and serum testosterone and its fractions in girls with premature thelarche. DESIGN: Blood was drawn from girls with recently diagnosed (3-12 weeks) premature thelarche. Serum was kept frozen for at least one year before hormonal determination to exclude precocious puberty by clinical evaluation. PATIENTS: Seventeen girls with premature thelarche aged 0.83-7.16 years were studied, and compared with a group of 22 normal prepubertal girls. MEASUREMENTS: SHBG was measured by saturation analysis and serum dehydroepiandrosterone sulphate, serum total oestradiol and serum total testosterone were determined by radioimmunoassay. Non-SHBG-bound testosterone and free testosterone were calculated from an equation derived from the law of mass action. RESULTS: Median serum SHBG in premature thelarche was 137 nmol/l (range 64-221), significantly higher than in normal controls, 93.7 (32-172) (P < 0.05) non-parametric test of medians. Serum SHBG decreased significantly with age in controls but not in premature thelarche. No difference was found in serum dehydroepiandrosterone sulphate. Median serum total testosterone (0.34 nmol/l, 0.17-0.97), median serum non-SHBG-bound testosterone (0.04 nmol/l, 0.02-0.10) and median free testosterone (2.2 pmol/l, 1.0-4.5) were significantly lower in premature thelarche than in control (P < 0.001). CONCLUSIONS: Serum SHBG is high and bioavailable T is low in girls with premature thelarche. This might alter the oestrogen/androgen ratio in the breast.     

多囊卵巢综合征患者性激素结合球蛋白和总睾酮与胰岛素抵抗的相关性

目的 了解性激素结合球蛋白(SHBG)和总睾酮在预测多囊卵巢综合征(PCOS)患者胰岛素抵抗和生殖内分泌以及糖脂代谢紊乱中的作用.方法 选择2004年6月至2006年5月在复旦大学附属妇产科医院就诊的344例PCOS患者为病例组,年龄12～35岁,平均年龄(23±5)岁.选择同期月经规律、基础体温双相的100名妇女作为对照组,比较PCOS患者SHBG和总睾酮与对照组的差异,并用Spearman相关分析法分别分析SHBG和总睾酮与其他指标的相关性,Logistic回归分析胰岛素抵抗的风险因子并做SHBG对胰岛素抵抗的受试者操作特征(ROC)曲线,获得预测胰岛素抵抗的风险值,比较不同水平SHBG患者的糖脂代谢紊乱的程度.结果 PCOS患者SHBG为(114±88)mmol/L,与对照组[(201±106)mmol/L]比较差异有统计学意义(t=-5.60,P<0.01),总睾酮为(2.8±1.0)nmol/L,与对照组[(1.7±0.6)nmol/L]比较差异有统计学意义(t=7.73,P<0.01);SHBG与空腹胰岛素、胰岛素释放试验曲线下面积、口服葡萄糖耐量试验(OGTT)的葡萄糖曲线下面积、胰岛素抵抗指数、甘油三酯和腰围/臀围比呈负相关(r值分别为:-0.30、-0.26、-0.29、-0.19、-0.20、-0.29、-0.22,均P<0.01);总睾酮与空腹胰岛素(r=0.14,P<0.01)、胰岛素释放试验(1、2、3 h的r值分别为0.15、0.12、0.11,均P<0.05)以及相应的曲线下面积(r=0.15,P<0.05)、胰岛素抵抗指数(r=0.11,P<0.05)呈正相关.Logistic回归分析发现SHBG是PCOS患者胰岛素抵抗的独立危险因素(OR=3.741).由ROC曲线得到SHBG预测胰岛素抵抗的大致风险值为88 mmol/L(95%CI为0.668～0.774).在低SHBG(<88 mmol/L)患者中,空腹胰岛素、胰岛素释放试验相应的曲线下面积、胰岛素抵抗指数、空腹血糖、OGTT的葡萄糖曲线下面积与高SHBG(≥88 mmoL/L)患者比较差异有统计学意义(t值分别为-6.45、-5.08、-6.19、-3.16、-3.66,均P<0.01),甘油三酯也高于高SHBG患者(t=-2.06,P<0.05).结论 PCOS患者总睾酮水平高于对照组,SHBG低?     

Plasma sex hormone-binding globulin rather than corticosteroid-binding globulin is a marker of insulin resistance in obese adult males

Aim:  Plasma levels of corticosteroid-binding globulin (CBG) and sex hormone-binding globulin (SHBG) may be regulated by insulin. The aim of this study was to test the hypothesis that these steroid-binding proteins are markers of insulin resistance and obesity in adult patients with the metabolic syndrome.
Methods:  Fasting blood samples were obtained from 108 male and 88 female overweight adult patients who had varying degrees of dyslipidaemia, adiposity and insulin resistance. We measured plasma levels of SHBG and CBG and investigated their correlation with insulin resistance [homeostasis model assessment (HOMA) % sensitivity] and anthropometric markers of adiposity.
Results:  In male patients, plasma SHBG correlated positively with HOMA (% sensitivity) and negatively with anthropometric measurements, including body mass index, waist circumference (cm) and percentage body fat. There was no correlation with CBG and any other parameter in the male patients. The female patients were treated as two groups, those not using oral contraceptives or hormone replacement therapy (n = 67) and those taking steroid medications (n = 21). Female patients using steroid medications had significantly higher SHBG levels but neither group showed any correlation between SHBG, insulin resistance and adiposity. Correlation studies of CBG with other parameters in the female subgroups did not reach statistical significance.
Conclusions:  We conclude that plasma SHBG is another surrogate marker for insulin resistance in obese males but not in obese females. It also appears that plasma CBG is not a useful marker of insulin resistance in patients with the metabolic syndrome.     

Sex hormone-binding globulin as a marker for hyperinsulinemia and/or insulin resistance in obese children

OBJECTIVE: A relationship between hyperinsulinemia and decreased serum sex hormone-binding globulin (SHBG) has been described in adults. We evaluated the usefulness of SHBG as an index of hyperinsulinemia and/or insulin resistance in obese children (aged 6-9 years) of both sexes and its possible influence on the androgenic status. DESIGN: We carried out a cross-sectional study of cases and controls. We studied 61 obese children (22 males, 39 females) with body mass index (BMI) superior to the 90(th) percentile and a control group of age- and sex-matched non-obese children. We measured serum glucose, insulin, TSH, free thyroxine, 17beta-estradiol, testosterone and SHBG. Also, we correlated these parameters with anthropometric measures. RESULTS: The obese group presented significantly elevated levels of insulin (P=0.001) and insulin/glucose ratio (P=0.0012) compared with the control group. SHBG (P=0.0001) and testosterone (P=0.0169) levels were significantly lower than those in the non-obese group. We did not find any difference in the free androgen index (FAI). Fasting insulin (r=-0.4512; P<0.001), BMI (r=-0.3185; P<0.05) and testosterone (r=-0.3705; P<0.01) were inversely correlated with SHBG concentration. According to multivariate analyses, insulin was the only independent predictor factor for serum SHBG concentration in the obese group (r partial=0.1280; P=0.0171). CONCLUSIONS: In summary, at this age there is a strong relationship between insulin and SHBG. The changes in SHBG levels of the obese group did not affect FAI and, therefore, they did not cause changes in the androgenic status. Our data support the role of insulin in the regulation of serum SHBG levels.     

Association of sex hormone-binding globulin and insulin resistance among Japanese-American subjects

An association between sex hormone-binding globulin (SHBG) and insulin resistance expressed by the homeostasis model (HOMA-R), and the significance of both variables as risk factors for the development of type 2 diabetes were investigated in 483 Japanese-American subjects. The serum SHBG level was significantly higher in women (68.7 nmol/l) than in men (45.1 nmol/l). This difference was also significant independently of age, body mass index (BMI), waist to hip ratio (WHR), and HOMA-R. When multiple regression analysis was performed after adjustment for age and BMI, SHBG was not correlated with HOMA-R in men. In women, SHBG was not significantly correlated with HOMA-R after adjustment for age, BMI, and WHR. In a 3-year prospective analysis, HOMA-R was significantly higher in converters to type 2 diabetes than non-converters in both men and women which was independent of age, BMI and WHR. However, after adjusting these variables, SHBG was not a significant risk factor either in men or women. These results indicate that SHBG might be related to insulin resistance secondarily via BMI and/or WHR in both men and women among Japanese-Americans. HOMA-R is a useful index for both men and women as a risk factor of type 2 diabetes when only fasting blood samples can be obtained.     

Post-heparin lipolytic enzyme activities, sex hormones and sex hormone-binding globulin (SHBG) in men and women: The HERITAGE Family Study

We tested the hypothesis that androgen, estrogen, and sex hormone-binding globulin (SHBG) levels would be significantly related to post-heparin hepatic lipase (HL) and lipoprotein lipase (LPL) activities in a sample of Caucasian men (n = 233) and women (n = 235) aged 17-64 years from the HERITAGE Family Study. Body composition (hydrostatic weighing), abdominal adipose tissue distribution (computed tomography), plasma lipid-lipoprotein and hormone levels, and post-heparin lipases activities were measured. HL activity was significantly higher in males, whereas LPL activity was higher in women (P < 0.005). In women only, HL activity was positively associated with body fat mass (r = 0.17, P < 0.05) and intra-abdominal adipose tissue area (r = 0.18, P < 0.05). Significant associations were also found between fasting insulin and LPL activity (r = -0.16, P < 0.05 and r = -0.18, P < 0.005) as well as HL activity (r = 0.22, P < 0.005, and r = 0.27, P < 0.0001) in men and women, respectively. A positive association between total testosterone and HL activity was noted in men (r = 0.13, P = 0.05). In women, plasma SHBG levels were negatively associated with HL activity (r = -0.48, P < 0.0001), and statistical adjustment for body fat mass, visceral adipose tissue area, and fasting insulin did not attenuate this correlation. In multivariate analyses with models including adiposity variables and measurements of the hormonal profile, insulin, and testosterone levels were both independent positive predictors of HL activity in men. In women, hormone use was a significant positive predictor, and SHBG level a strong negative predictor of HL activity, independent of plasma estradiol and testosterone concentrations. Fasting insulin was the only significant predictor of LPL activity in men (negative association), whereas menstrual status, fasting insulin (negative associations), and plasma SHBG levels (positive association) were all independent predictors of LPL activity in women. These results suggest that the postulated sensitivity of lipolytic enzymes to androgens and estrogens is reflected by a strong negative association between SHBG levels and HL, and a lower magnitude positive association of this hormonal parameter to LPL activity in women. These associations appear to be independent from concomitant variation in total adiposity or body fat distribution.     

Biological variation of total testosterone, free androgen index and bioavailable testosterone in polycystic ovarian syndrome: implications for identifying hyperandrogenaemia

Objective Hyperandrogenaemia is one of the three Rotterdam consensus diagnostic criteria for polycystic ovarian syndrome (PCOS) and may be measured by estimation of total testosterone, free androgen index (FAI) or bioavailable testosterone (BioT). The aim of this study was to compare the biological variability of total testosterone with that of the biological variability of both the FAI and BioT, to determine the least variable measurement for clinical practice. Design Comparative study. Patients Blood samples were collected after an overnight fast at 4‐day intervals on 10 consecutive occasions from 12 PCOS patients and 11 weight‐ and age‐matched control women. Measurements Duplicate samples of stored serum were analysed for total testosterone, SHBG and BioT in a single batch. Results The PCOS group had a significantly higher median BioT, FAI and total testosterone than controls. In both the PCOS and control groups, the intraindividual variance was small and similar for BioT and FAI. There was no significant difference between the within‐subject biological coefficient of variation (CV_I) for BioT, FAI and total testosterone. The maximum and minimum critical differences were +58% and –37% for BioT and +70% and –40% for FAI, respectively. Conclusion FAI appears to be the better diagnostic marker to distinguish hyperandrogenism in patients with PCOS, but once diagnosis has been made, all three methods should be equally good in monitoring further changes in the androgen status.     

Common genetic variation in the sex steroid hormone-binding globulin (SHBG) gene and circulating shbg levels among postmenopausal women: the Multiethnic Cohort

SHBG transports sex steroid hormones in the blood, and levels in humans are thought to partially be genetically determined. Recently, studies have found a pentanucleotide (TAAAA)n repeat polymorphism in the promoter of the SHBG gene and a missense polymorphism in exon 6 (Asp327Asn) to predict circulating SHBG levels. Based on the potential role of common genetic variation in SHBG to serve as a marker of SHBG levels in the general population, we evaluated the association between the (TAAAA)n repeat polymorphism, Asp327Asn polymorphism, and SHBG levels in a population of African-American, Native Hawaiian, Japanese, Latina, and white healthy postmenopausal women from the Multiethnic Cohort Study (n = 372). Mean SHBG levels were not significantly different between carriers and noncarriers of the Asn327 allele [minor allele frequency range across ethnic groups, 0.02-0.14; Asp/Asn and Asn/Asn genotypes, 33.6 mol/liter; 95% confidence interval (CI), 28.2-40.0; n = 49; Asp/Asp genotype, 30.8 mol/liter (95% CI, 28.7-33.1; n = 296); P = 0.37]. For the repeat polymorphism, we observed six different SHBG repeat alleles segregating in the population (TAAAA6-11), and the distribution of these alleles varied widely across populations. We found suggestive evidence of linkage disequilibrium between the Asn327 allele and the eight-repeat allele in all populations except African-Americans (P > or = 0.08). In analysis of the repeat polymorphism, SHBG levels among carriers of two short alleles (seven or fewer repeats; 31.2 nmol/liter; 95% CI, 27.3-35.6; n = 82) were not statistically different from those of carriers of two long alleles (more than seven repeats; 32.7 nmol/liter; 95% CI, 29.4-36.3; n = 124; P = 0.59). We did, however, observe individual genotypic classes (n = 16) to contribute modestly to the overall prediction of SHBG levels (by analysis of covariance, P = 0.03). Carriers of the six-repeat allele (27.9 nmol/liter; 95% CI, 25.2-30.8; n = 147) were found to have nominally significantly lower SHBG levels than noncarriers (32.4 nmol/liter; 95% CI, 29.7-35.2; n = 202; P = 0.03). This effect was stronger among the subset of women who also carried the Asn327 allele (interaction, P = 0.006). In summary, these results suggest that genetic variation at the SHBG locus may contribute to modest differences in SHBG levels among healthy postmenopausal women, and that much larger studies will be needed to better comprehend the effects of common variations at this locus in predicting circulating SHBG levels.     

Glucose-to-insulin ratio rather than sex hormone-binding globulin and adiponectin levels is the best predictor of insulin resistance in nonobese women with polycystic ovary syndrome

Polycystic ovary syndrome (PCOS), the main androgen disorder in women, has been suggested to be associated with a high risk of developing cardiovascular disease and type 2 diabetes. In many PCOS patients, overweight or central obesity is generally associated with increases in fasting insulin levels, insulin resistance, and glucose intolerance, and has been identified as a target for new therapeutic strategy, including early change in lifestyle. Early biochemical marker(s) for identifying at-risk patients will be useful for prevention studies. The main goal of the present study was to search for such tool(s). We investigated 16 nonobese PCOS women by performing euglycemic hyperinsulinemic clamp and measuring insulin levels during fasting and oral glucose tolerance test, as well as the serum concentrations of SHBG, leptin, and adiponectin, the newly identified adipose factors. Eight of the 16 patients had a steady-state glucose disposal rate less than 8.5 mg/kg.min, the lowest normal value for nonobese control women. These insulin-resistant patients had significant higher body mass index (BMI) and waist-to-hip ratio (WHR), and lower high-density lipoprotein cholesterol and SHBG levels. As expected, glucose disposal correlated negatively with BMI (P = 0.01), WHR (P = 0.01), and fasting insulin level (P = 0.003). On stepwise regression analysis, however, the glucose-to-insulin ratio (GIR) emerged as the strongest independent parameter to appraise insulin resistance (R(2) = 0.61). SHBG level correlated positively with GIR (P < 0.001) and negatively with BMI (P = 0.003) but did not correlate with either insulin response during the glucose tolerance test or plasma leptin and/or adiponectin levels. In contrast, BMI was the only independent predictive parameter of SHBG (P = 0.003, R(2) = 0.73). Interestingly, plasma adiponectin levels were positively associated with glucose disposal rate (P = 0.043) and negatively with WHR (P = 0.024), waist circumference being the best predictor of adiponectin level (P < 0.01). Leptin level correlated only with BMI (r = 0.62, P = 0.01). This study confirmed that insulin resistance, despite the lack of obesity as such, is clearly present in many PCOS women, and demonstrated that GIR is the best predictor for insulin resistance. It was also shown that adiponectin level is a good indicator of abdominal fat mass and is associated to insulin resistance. Finally, low SHBG levels in PCOS are intimately associated with BMI, suggesting that some signal(s) from the adipose tissue, independent of adiponectin and leptin, may regulate liver production of SHBG.     

High serum sex hormone-binding globulin (SHBG) and low serum non-SHBG-bound testosterone in boys with idiopathic hypopituitarism: effect of recombinant human growth hormone treatment

We measured serum sex hormone-binding globulin (SHBG), total testosterone (T), non-SHBG-bound T, albumin-bound T, free T, and SHBG-bound T in 19 prepubertal boys with hypopituitarism. Serum SHBG decreased with age with a slope similar to that in 91 normal prepubertal boys at higher level, and therefore, it reached similar values at a later age. Serum SHBG was significantly higher in hypopituitary prepubertal boys [mean, 123 +/- 12 (+/- SE) nmol/L] than in normal prepubertal boys (76 +/- 4; P less than 0.001) despite the fact that their mean age was also higher (10.0 +/- 4 vs. 7.1 +/- 4.1 yr; P less than 0.001). In 4 boys with isolated hypogonadotropic hypogonadism (Kallman's syndrome), aged 15.6 +/- 1.5 yr, serum SHBG was 21 +/- 14 nmol/L, a value below the 95% confidence limit of the regression line in GH-deficient boys. The affinity constants of association of the SHBG-DHT complex were similar in hypopituitary and normal boys. Eleven of the 19 hypopituitary boys (mean chronological age, 8.3 +/- 2.5 yr; mean bone age, 4.1 +/- 2.1 yr) were treated with recombinant hGH (0.5 U/kg BW.week) for 1 yr. Their mean serum SHBG level before treatment was 154 +/- 14 nmol/L, and it decreased gradually to 106 +/- 5 nmol/L (P less than 0.01) after 12 months of treatment. The tendency toward normalization of serum SHBG during treatment suggested that GH deficiency was responsible for the high serum SHBG levels. Serum SHBG correlated negatively with age in both treated hypopituitary and normal boys, but the slope of the regression line was significantly steeper in treated hypopituitary boys (P less than 0.01). On the other hand, the mean serum non-SHBG-bound T level was 0.10 +/- 0.02 (+/- SE) nmol/L in hypopituitary boys, significantly lower than that in normal boys (0.21 +/- 0.02 nmol/L; P less than 0.02). Since serum total T concentrations were similar in the two groups, the higher serum SHBG concentration resulted in lower serum bioavailable T levels in the hypopituitary boys. These changes might explain the poor response to T treatment reported in GH-deficient patients. The lower serum non-SHBG-bound T concentrations in the GH-deficient boys suggest there may be delayed exposure of central nervous system structures to increased levels of sex hormones, which, in turn, may slow body maturation. This mechanism might play a role in the delay of puberty that occurs in patients with isolated GH deficiency.     

Serum levels of sex hormone-binding globulin (SHBG) are not associated with lower levels of non-SHBG-bound testosterone in male newborns and healthy adult men

OBJECTIVE: It is generally accepted that SHBG decreases the bioavailability and activity of testosterone (T). In in vitro experiments increased levels of SHBG will be associated with decreased levels of non-SHBG bound testosterone (non-SHBG-T). However, in vivo SHBG can alter both production and clearance rates and thus plasma levels of T. DESIGN AND PATIENTS: In order to study the effect of SHBG on the levels of non-SHBG-T in vivo in the presence of an active hypothalamo-pituitary-gonadal (HPG) axis we conducted a cross sectional study in 400 healthy adult men with an age range of 40-80 years and in 106 newborn boys. MEASUREMENTS: In both groups, regression coefficients (beta) and partial correlation coefficients (r) were calculated for the relationship between SHBG and T or non-SHBG-T. Adult men were divided into age groups per decade (40-50 years, 51-60 years, 61-70 years and 71-80 years) to study possible differences in the impact of SHBG on the level of non-SHBG-T throughout ageing. RESULTS: Higher levels of SHBG were associated with higher levels of total testosterone in neonates (beta = 0.02 +/- 0.004, r = 0.44, P < 0.001) but not with non-SHBG-T (beta = -0.001 +/- 0.001, r = 0.05, P = 0.52). In adult men there was a significant age related increase in levels of SHBG and an age-related decrease of both total and non-SHBG-T. Higher SHBG was strongly associated with higher total testosterone in all age groups (beta = 0.26, 0.26, 0.26 and 0.23 for 40-50 years, 51-60 years, 61-70 years and 71-80 years, respectively, P < 0.001 for all age groups). Higher SHBG was not or only slightly associated with higher non-SHBG-T beta = 0.02 (P = 0.32), beta = 0.04 (P = 0.03), beta = 0.04 (P = 0.02) and beta = 0.02 (P = 0.16) for 40-50 years, 51-60 years, 61-70 years and 71-80 years, respectively. CONCLUSIONS: In contrast to general belief, SHBG levels barely influence levels of non-SHBG-bound testosterone both in male newborns and healthy adult men: the influence, if any, is positive. Consequently the age related increase of SHBG does not account for the age related decline in non-SHBG-T in healthy adult men.