The Changes Of Sex Hormone Environment And Insulin Resistance After Menopause

Insulin resistance is defined as the peripheral tissues’decreased ability of utilizing glucose. As the common risk factor of coronary heart diseases, metabolic syndrome and type2diabetes, the increased incidence of insulin resistance after menopause is detrimental to the health of elderly women.During recent years many researches suggested that the changes of sex hormone environment after menopause were associated with insulin resistance, but the concrete mechanisms are still unknown. The most remarkable changes of sex hormone environment after menopause are the gradually reduced sex hormones originating from ovaries and the peripheral synthesis from dehydroepiandrosterone(DHEA) or dehydroepiandrosterone-sulfate (DHEA-S) originating from the adrenals.In these processes, sex hormone-binding globulin (SHBG) which is the key protein regulating sex hormones,free androgens,DHEA/DHEA-S and their peripheral transformation may mediated the key steps of insulin resistance.Our studies dicussed the relationships between the changes of sex hormone environment after menopause and insulin resistance according to population based investigation, animal experiment and cell experiment. To determine whether the changes of sex hormone environment after menopause mediate insulin resistance by modulating body fat distribution and blood lipids. We also analyzed whether hormone replacement therapy (HRT) in early postmenopausal women could improve insulin resistance and studied whether the changes of sex hormone receptors and peripheral transformation of DHEA/DHEA-S correlated with insulin resistance.Part Ⅰ The changes of sex hormone environment and insulin resistance after menopauseObjectives:To determine the relationships between insulin resistance and sex hormone environment which are different between early postmenopause and late postmenopause. To study whether the changes of sex hormone environment could improve insulin resistance by regulating body fat and blood lipids and whether hormone replacement therapy (HRT) in early postmenopausal women could improve insulin resistance.Methods:We enrolled postmenopausal women consisting of an early group years since menopause, n=105) and an elder group (≥10years since menopause, n=107). Each group was subdivided into normal weight (BMI<24kg/m2) group, overweight and obese (BMI≥24kg/m2) group. Body fat distribution was evaluated by dual-energy X-ray absorptiometry (DEXA). Fasting SHBG, T, E2, DHEA-S, Glu, Ins, TC, TG, HDL-c, LDL-c, apoA, apoB levels were measured and then calculated FAI and HOMA-IR. The relationships among sex hormone environment and body fat, blood lipids and insulin resistance were estimated by partial correlation, multiple linear regression and oneway ANOVA analyses. We also recruited25early postmenopausal women (≤5years since menopause) which accepted HRT (progynova+progesterone, cyclic combined therapy) for one year. Follow up visit were performed every3months. We measured sex hormones, body fat, blood lipids, insulin and glucose before and after therapy.The effects of HRT on body fat, blood lipids and insulin resistance were evaluated by matching t-test.Results:Compared to early postmenopausal women, late postmenopausal women had higher proportion of body fat, TG, Ins and HOMA-IR but they had lower DHEA-S,E2and apoA/apoB (all p<0.05).Both in early postmenopausal and late postmenopausal groups, overweight and obese women had higher T/L, the proportion of android fat, HOMA-IR and Ins, they had lower apoA/apoB and the proportion of gynoid fat than normal weight women (all p<0.05),but there were no significant differences in other blood lipids between normal weight women and overweight and obese women (p>0.05).In early postmenopausal group, overweight and obese women had lower SHBG and higher FAI than normal weight women (all p<0.05).In late postmenopausal group, overweight and obese women had higher DHEA-S and E2levels (all p<0.05). Partial correlation and multiple linear regression analyses suggested that:In early postmenopausal group, FAI correlated positively with abodominal fat accumulation, SHBG correlated positively with apoA/apoB and negatively with Ins and HOMA-IR, DHEA-S correlated positively with glucose (all p<0.05). In late postmenopausal group, DHEA-S correlated positively with abodominal fat accumulation and negatively with apoA, FAI correlated positively with glucose (all p<0.05).After one-year HRT, the quality of women’s life were significantly improved, their T/L, the proportion of android fat and HOMA-IR decreased significantly but the proportion of gynoid fat increased significantly (all p<0.05). There were no significant differences in blood lipids between before and after HRT (all p>0.05)Conclusions:The increased androgenic activities after menopause are associated with insulin resistance. These correlations are different during the different stages of posmenopause and mainly incarnate in:high FAI caused by low SHBG, compensatory high DHEA-S in obese postmenopausal women caused by gradual cesscation of ovary function. High FAI and DHEA-S and low SHBG may affect insulin resistance according to regulating body fat and apoA. HRT in early postmenopausal women could improve insulin resistance. Part II The effects of progynova on insulin resistance in ovariectomised rats and their nuclear receptor mechanismsObjectives:To determine the effects of progynova on sex hormones,body fat,blood lipids and insulin resistance in ovariectomised Sprague-Dawley rats.And then to discusss the effects of progynova on the expressions of SHBG、PPAR、AR、ERα、 ERβ、17β-HSD and aromatase.Methods:Twenty-seven female SD rats were divided into three groups:SHAM group (n=10), OVX group (n=8) and OVX+E2group (n=9).After ovariectomy OVX+E2group received800μg/kg progynova via gavage daily, SHAM and OVX groups received2ml water via gavage daily. Weight and food intake were recorded every two weeks. All of the animals were euthanized12weeks after ovariectomy, then we collected blood from abdominal aorta, after which their fasting SHBG,T,E2,DHEA,Glu,Ins,TC,TG,HDL-c,LDL-c,TNF-a,IL-6,adiponectin and leptin levels were measured. After euthanising the rats, we opened their abdominal cavities and accessed all of their intra-abdominal fat. We then weighed and calculated their visceral fat mass (VFM=visceral fat weight/body weight,%). Liver tissue slices were stained by hemotoxylin and eosin (HE).We also detected the expressions of SHBG、PPARγ、AR、ERα、ERβ、17β-HSD and aromatase in liver tissue using Western blot and Real-time PCR.Results:Compared to SHAM group, OVX group had lower E2and SHBG levels,higher FAI,DHEA,body weight,VFM,IL-6and HOMA-IR (all p<0.05),OVX group also had significantly higher fat accumulation in liver. Compared to OVX group,OVX+E2group had higher E2,SHBG and HDL-c levels,lower FAI,DHEA,body weight,VFM,LDL-c,IL-6,HOMA-IR and fat accumulation in liver (all p<0.05). In the meantime, the expressions of PPARy,AR,17β-HSD and aromatase in the liver of OVX group were higher than SHAM group.The expressions of SHBG and ERa in the liver of OVX group were lower than SHAM group (all p<0.05). After progynova therapy, these tendencies were reversed to some extent (all p<0.05)Conclusions:In animal experiment, progynova can reverse visceral fat accumaltion, high IL-6and HOMA-IR induced by surgical menopause (These changes correlated with low SHBG and E2, high FAI and DHEA-S). The increased incidence of insulin resistance after menopause correlated with high expressions of PPARy and AR, low expressions of SHBG and ERa, peripheral transformation of DHEA. PartⅢ The expressions of SHBG in the HepG2cell model of insulin resistance and the effects of peripheral transformation of DHEA on insulin receptor signal pathObjectives:To detect the expression of SHBG in cell model of insulin resistance and the effects of different concentrations of DHEA and their peripheral transformation on the key molecule(IR,IRS-2,GLUT-2) of insulin receptor signal path.Methods:We established cell model of insulin resistance in HepG2cell line induced by high dose of insulin and then detected the expression of SHBG in the condition of insulin resistance. After72h stimulation of E2,T and different concentrations of DHEA,then we detected the expressions of IR,IRS-2and GLUT-2. We used letrizole and trilostane to inhibit peripheral transformation of DHEA in HepG2cell line and then detected the expressions of IR, IRS-2and GLUT-2.Results:HepG2cells reached the extreme insulin resistance after the stimulation of insulin at a concentration of10-6M for36h. In the meantime, the expressions of SHBG protein and mRNA touched the bottom (p<0.05). High concentration of DHEA (10-5M) down-regulated the expressions of IR, IRS-2and GLUT-2, which was similar to T. As the concentration reduced, the effects of down-regulation were weakened.10-9M concentration of DHEA up-regulated the expressions of IRS-2and GLUT-2, which was similar to E2. Compared to the control group, E2significantly up-regulated the expressions of IR, IRS-2and GLUT-2. After inhibited by letrizole, the expressions of IR, IRS-2and GLUT-2were down-regulated compared with the effects of sole DHEA. The expressions of IR, IRS-2and GLUT-2were up-regulated after inhibited by trilostane than combination of DHEA and letrizole (p<0.05)Conclusions:There were two factors associated with insulin resistance in HepG2cell line:The expression of SHBG decreased and DHEA-S converted more readily to androgens than to estrogens. The effects of DHEA on insulin resistance correlated with its concentration:High concentration of DHEA down-regulated the expressions of IR, IRS-2and GLUT-2, which was similar to T. Low concentration of DHEA up-regulated the expressions of IRS-2and GLUT-2, which was similar to E2. 1、The changes of sex hormone environment after menopause (especially, the increased androgenic activities) increase the risk of insulin resistance and this correlation mainly incarnates in:In early postmenopause, low SHBG caused by low E2,high FAI caused by low SHBG, compensatory high DHEA induced by gradual cessation of ovarian function; In late postmenopause, the increased peripheral transformation of DHEA/DHEA-S induced by the cessation of ovarian function.2、Visceral fat accumulation, abnormal blood lipids and increased IL-6levels are the possible aspects of the effects of the changes of sex hormone environment after menopause on insulin resistance.Population based investigation and animal experiment suggested that HRT in early postmenopause could improve insulin resistance by regulating body fat distribution, blood lipids and IL-6levels.3、The decreased expression of SHBG induced by high PPARy,the decreased expression of ERa, the increased expression of AR are the possible receptor mechanisms which the changes of sex hormone environment mediated insulin resistance.4、DHEA-S converted more readily to androgens than to estrogens in liver, which correlates with insulin resistance. The effects of DHEA on insulin receptor signal path depending on its concentration:High concentration of DHEA promotes insulin resistance and low concentration of DHEA could improves insulin resistance.