Interactions between sex steroid hormones and leptin in women. Studies in vivo and in vitro

Influence of aerobic exercise training on cardiovascular and endocrine-inflammatory biomarkers in hypertensive postmenopausal women

Given that few studies have examined the interaction between endocrine-inflammatory mediators and aerobic exercise training in hypertensive postmenopausal women, the aim of this study was to investigate whether aerobic exercise training (AET) for twenty-four sessions would alter cortisol, leptin and interleukin-1β (IL-1β) levels. To further analyze endothelium function in response to AET, we also examined redox state as well as NO/cGMP pathway in this population. Eighteen hypertensive postmenopausal women finished this study. AET program consisted of 24 sessions in treadmill, 3 times per week, duration of 30 up to 40 min for each session, for 8 weeks at intensity of 100% of the MLSS according to previous incremental test. Heart rate was monitored in all studied time (resting and during exercise sessions). After 48 h of the last exercise session, blood samples were collected for biochemical analyses (levels of cortisol, leptin, IL-1β, nitrite/nitrate (NOx⁻), cGMP, malondialdehyde (MDA) and asymmetric dimethylarginine (ADMA); superoxide and catalase activity). We also measured systolic and diastolic blood pressure. A significant reduction in body mass was observed. As expected, systolic and diastolic blood pressure values were significantly reduced after AET in hypertensive women. We also found a marked increase in NOx⁻ levels as well as cGMP concentration in trained women, approximately 37.7 and 30.8%, respectively. No changes in cortisol, leptin, ADMA and IL-1β levels were observed after AET. Similarly, MDA levels and catalase activity were not affected by AET. In contrast, a marked increase in SOD activity was found (86.6%). In conclusion, our findings show that aerobic exercise training for twenty-four sessions promoted a significant reduction in blood pressure by activating NO/cGMP pathway as well as by promoting an up-regulation of SOD activity without changing in cortisol/leptin levels in postmenopausal hypertensive women.

Plasma leptin levels are related to body composition, sex, insulin levels and the A55V polymorphism of the UCP2 gene

OBJECTIVE

Circulating leptin levels show a high degree of individual variability even after the main effect of body fatness is accounted for. We therefore wanted to determine the roles of variation in body composition, age, sex and polymorphisms of the UCP2 gene and promoter region on levels of circulating leptin.

SUBJECTS

One hundred and fifty Caucasian subjects, which represented a cross-section of the population from NE, Scotland, were recruited.

MEASUREMENTS

Body composition was measured using dual X-ray absorptiometry. Fasted circulating leptin, insulin, T3 and T4 levels were measured, and all individuals were genotyped for the UCP2 polymorphisms A55V, -866G>A and exon-8 ins/del.

RESULTS

The results indicate that circulating leptin was significantly related to sex and principle component (PC) scores representing overall adipose tissue mass and a second representing the contrast of central to peripheral bone mineral content. Residual leptin was associated with the A55V polymorphism (P< 0.001) explaining 11.3% of the residual variance. There was a marginal effect associated with exon-8 ins/del (P=0.045) explaining 4.4% of the residual variance in leptin. Log(e) transformed circulating fasting insulin was related to PC scores representing general adiposity and sex. Residual Log(e) insulin was associated with the A55V and exon-8 ins/del polymorphisms explaining 5.7% (P=0.015) and 5% (P=0.026) of the residual variation, respectively. The -866G>A polymorphism was not significantly associated with residual leptin or insulin. Leptin and insulin were significantly (P=0.007) correlated. Statistically removing the effect of insulin on leptin still showed association between leptin and A55V (P=0.002). Removing the effect of leptin on insulin, the A55V polymorphism was no longer significant (P=0.120). After accounting for the correlation between insulin and leptin, the exon-8 ins/del was no longer significant for residual leptin (P=0.119) or Log(e) insulin (P=0.252).

CONCLUSION

These data suggest that the A55V polymorphism directly affected the levels of leptin but not via an effect on insulin.

Plasma levels of leptin and mammographic density among postmenopausal women: a cross-sectional study

Introduction

Obesity has been linked to increased risk of breast cancer in postmenopausal women. Increased peripheral production of estrogens has been regarded as the main cause for this association, but other features of increased body fat mass may also play a part. Leptin is a protein produced mainly by adipose tissue and may represent a growth factor in cancer. We examined the association between leptin plasma levels and mammographic density, a biomarker for breast cancer risk.

Methods

We included data from postmenopausal women aged 55 and older, who participated in a cross-sectional mammography study in Tromsø, Norway. Mammograms, plasma leptin measurements as well as information on anthropometric and hormonal/reproductive factors were available from 967 women. We assessed mammographic density using a previously validated computer-assisted method. Multiple linear regression analysis was applied to investigate the association between mammographic density and quartiles of plasma leptin concentration. Because we hypothesized that the effect of leptin on mammographic density could vary depending on the amount of nondense or fat tissue in the breast, we also performed analyses on plasma leptin levels and mammographic density within tertiles of mammographic nondense area.

Results

After adjusting for age, postmenopausal hormone use, number of full-term pregnancies and age of first birth, there was an inverse association between leptin and absolute mammographic density (P_trend = 0.001). When we additionally adjusted for body mass index and mammographic nondense area, no statistically significant association between plasma leptin and mammographic density was found (P_trend = 0.16). Stratified analyses suggested that the association between plasma leptin and mammographic density could differ with the amount of nondense area of the mammogram, with the strongest association between leptin and mammographic absolute density in the stratum with the medium breast fat content (P_trend = 0.003, P for interaction = 0.05).

Conclusion

We found no overall consistent association between the plasma concentration of leptin and absolute mammographic density. Although weak, there was some suggestion that the association between leptin and mammographic density could differ with the amount of fat tissue in the breast.

Direct effects of sex steroid hormones on adipose tissues and obesity

Sex steroid hormones are involved in the metabolism, accumulation and distribution of adipose tissues. It is now known that oestrogen receptor, progesterone receptor and androgen receptor exist in adipose tissues, so their actions could be direct. Sex steroid hormones carry out their function in adipose tissues by both genomic and nongenomic mechanisms. In the genomic mechanism, the sex steroid hormone binds to its receptor and the steroid-receptor complex regulates the transcription of given genes. Leptin and lipoprotein lipase are two key proteins in adipose tissues that are regulated by transcriptional control with sex steroid hormones. In the nongenomic mechanism, the sex steroid hormone binds to its receptor in the plasma membrane, and second messengers are formed. This involves both the cAMP cascade and the phosphoinositide cascade. Activation of the cAMP cascade by sex steroid hormones would activate hormone-sensitive lipase leading to lipolysis in adipose tissues. In the phosphoinositide cascade, diacylglycerol and inositol 1,4,5-trisphosphate are formed as second messengers ultimately causing the activation of protein kinase C. Their activation appears to be involved in the control of preadipocyte proliferation and differentiation. In the presence of sex steroid hormones, a normal distribution of body fat exists, but with a decrease in sex steroid hormones, as occurs with ageing or gonadectomy, there is a tendency to increase central obesity, a major risk for cardiovascular disease, type 2 diabetes and certain cancers. Because sex steroid hormones regulate the amount and distribution of adipose tissues, they or adipose tissue-specific selective receptor modulators might be used to ameliorate obesity. In fact, hormone replacement therapy in postmenopausal women and testosterone replacement therapy in older men appear to reduce the degree of central obesity. However, these therapies have numerous side effects limiting their use, and selective receptor modulators of sex steroid hormones are needed that are more specific for adipose tissues with fewer side effects.

Is Leptin Associated with Serum Lipid Profile or Any other Parameters of Blood Biochemistry in Post-Menopausal Women with Osteoporosis?

We investigated the relationship between serum leptin concentration, serum lipid profile and other blood biochemistry parameters in healthy post-menopausal women. Blood samples for analysis of serum leptin concentration, blood biochemistry and hormonal status, and urine samples for calcium measurement were taken from 122 women. No significant correlation was found between serum leptin concentration and serum lipid profile. The concentration of serum leptin was significantly associated with body mass index (BMI), luteinizing hormone (LH) and alanine transaminase (ALT). BMI was found to be a statistically significant independent factor for serum leptin concentration. We conclude that leptin was not associated with serum lipids and lipoproteins in post-menopausal women. Leptin was associated with BMI, ALT and LH, however, with BMI being an independent predictor of leptin concentration. There was a relationship between LH and serum leptin concentration even after menopause, and ALT correlated with serum leptin concentration through BMI.

Effects of obesity on the relationship of leptin mRNA expression and adipocyte size in anatomically distinct fat depots in mice

In support of leptin's physiological role as humoral signal of fat mass, we have shown that adipocyte volume is a predominant determinant of leptin mRNA levels in anatomically distinct fat depots in lean young mice in the postabsorptive state. In this report, we investigated how obesity may affect the relationship between leptin mRNA levels and adipocyte volume in anatomically distinct fat depots in mice with genetic ( Lepob/ Lepoband Ay/+), diet-induced, and aging-related obesity. In all of the obese mice examined, tissue leptin mRNA levels relative to the average adipocyte volume were lower in the perigonadal and/or retroperitoneal than in the inguinal fat depots and were lower than those of the lean young mice in the perigonadal fat depot. A close, positive correlation between leptin mRNA level and adipocyte volume was present from small to hypertrophic adipocytes within each perigonadal and inguinal fat pad in the obese mice, but the slopes of the regression lines relating leptin mRNA level to adipocyte volume were significantly lower in the perigonadal than in the inguinal fat pads of the same mice. These results suggest that obesity per se is associated with a decreased leptin gene expression per unit of fat mass in mice and that the positive correlation between leptin mRNA level and adipocyte volume is an intrinsic property of adipocytes that is not disrupted by adipocyte hypertrophy in obese mice.

Effect of hormone replacement therapy and tibolone on serum leptin levels in postmenopausal women

OBJECTIVE

To evaluate the effect of estrogen replacement therapy (ERT), continuous combined hormone replacement therapy (HRT) and tibolone on serum leptin levels in healthy postmenopausal women.

METHODS

Eighty-four healthy postmenopausal women aged 43-63 years were studied prospectively. Hysterectomized women (n = 16) received conjugated equine estrogens (CEE) 0.625 mg. Women with an intact uterus were randomly allocated either to CEE+medroxyprogesterone acetate (CEE/MPA) 5 mg or tibolone 2.5 mg. Serum leptin levels were assessed at baseline and after 6 months of treatment.

RESULTS

The three groups did not differ with respect to age, body mass index (BMI) or baseline serum leptin levels. Overweight women (BMI > 25 kg/m2) had higher baseline leptin levels (27.0 +/- 11.4 ng/ml) compared to their lean counterparts (BMI < or = 25 kg/m2; leptin: 16.5 +/- 8.1 ng/ml, P = 0.0001). Neither CEE nor CEE/MPA had any effect on serum leptin levels at the end of 6 months either in overweight or in lean women (overweight: CEE baseline 34.4 +/- 13.3 ng/ml, 6 months 36.9 +/- 15.8, P = 0.89, CEE/MPA baseline 22.4 +/- 9.8 ng/ml, 6 months 26.8 +/- 8.7 ng/ml, P = 0.1; lean: CEE baseline 12.6 +/- 4.4 ng/ml, 6 months 13.2 +/- 5.8 ng/ml, P = 0.36, CEE/MPA baseline 17.2 +/- 10.6 ng/ml, 6 months 18.8 +/- 8.8 ng/ml, P = 0.31). Similarly serum leptin remained unchanged at the end of the study in both lean and overweight women on tibolone (overweight: baseline 22.9 +/- 8.1 ng/ml, 6 months 18.5 +/- 12 ng/ml, P = 0.37; lean: baseline 13.2 +/- 5.6 ng/ml, 6 months 17.3 +/- 8.4 ng/ml).

CONCLUSION

BMI is a strong determinant of serum leptin levels in healthy postmenopausal women. Neither ERT/HRT nor tibolone exert any effect on serum leptin after 6 months in lean or overweight postmenopausal women. Further studies are required to verify the exact role of estrogen and tibolone on leptin production and function in postmenopausal women.

The relationship between plasma levels of leptin and androgen in healthy and preeclamptic pregnant women

BACKGROUND

To clarify the role of leptin and androgens in the pathogenesis of preeclampsia, we wanted to assess role of maternal leptin in women with severe and mild preeclampsia and the effects of sex steroid hormones on leptin production.

METHODS

The groups consisted of 40 healthy pregnant women (HPW) as well as 55 pregnant women with severe preeclampsia (SPE) and 41 pregnant women with mild preeclampsia (MPE). No significant differences were observed between the three groups regarding age, gestational age and body mass index (BMI). Plasma leptin, total testosterone (T), estradiol (E(2)), dehydroepiandrosterone sulfate (DHEAS) and androstenedione (A) levels were measured. Statistical analysis was achieved with one-way analysis of variance (anova) followed by post hoc multiple comparisons with the Tukey honestly significant difference (HSD) test by using SPSS for Windows statistical computer program, and the Pearson's coefficient of correlation was calculated.

RESULTS

The plasma level of leptin was significantly increased in the SPE and MPE groups (p < 0.001), whereas the plasma level of T was significantly increased only in the SPE group (p < 0.001). However, there was no significant difference in plasma levels of DHEAS among the three groups (p < 0.05). The plasma level of A was significantly decreased in the MPE group (p < 0.05). There was no significant difference in the plasma level of E(2) in the MPE and SPE groups (p < 0.05). There was a significant positive correlation between the plasma levels of leptin and E(2) in the MPE group (r = 0.41, p < 0.001).

CONCLUSION

We concluded that the elevated plasma levels of leptin and testosterone could contribute to the endothelial dysfunction involved in the pathogenesis of preeclampsia, and that estradiol might lead to an increase in the plasma levels of leptin.

Determinants of serum leptin levels in healthy postmenopausal women

The aim of this study was to evaluate factors that influence leptin levels in postmenopausal women. One hundred and forty-four postmenopausal women were evaluated cross-sectionally. In every woman a complete medical history was obtained, body mass index (BMI) was recorded and morning fasting blood was obtained for the determination of serum leptin, follicle stimulating hormone (FSH), estradiol, testosterone, delta4androstendione, dehydroepiandrosterone sulphate (DHEAS) and insulin. In univariate analysis, age, BMI and insulin were positively correlated with serum leptin, while DHEAS showed a negative association with leptin concentrations (age r=0.21, p=0.005, BMI r=0.41, p=0.0001, insulin r=0.20, p=0.008, DHEAS r=-0.28, p=0.0001). In stepwise multivariate regression analysis serum leptin could be best predicted from BMI, serum insulin and serum DHEAS [leptin= (1.41 * BMI) - (0.01 * DHEAS) + (3.26 * insulin) - 26.3; model r2=0.24, p=0.001]. In conclusion, BMI and serum insulin have a positive while serum DHEAS has a negative impact on serum leptin. Neither endogenous estradiol, nor endogenous testosterone are associated with leptin levels. Further studies are needed to elucidate the role of leptin in determining body weight and composition in postmenopausal women.

Effect of two modes of antiandrogen treatment on insulin sensitivity and serum leptin in women with PCOS

Androgens are suggested to interact with leptin production and with insulin sensitivity in both polycystic ovary syndrome (PCOS) and obesity. The aim of the study was to follow these interactions along with two forms of antiandrogen treatment. Twenty women with PCOS were treated with ethinylestradiol and high dose of cyproteroneacetate (EE-CA) and 8 with the gonadotrophin-releasing hormone (GnRH) analogue goserelin for 6 months. The patients were divided into a low and a high body weight group and compared with a group of overweight women without PCOS. Both treatments resulted in a significant reduction of free testosterone but the concentration of leptin remained unchanged. EECA treatment resulted in deterioration and GnRH in improvement of insulin sensitivity. Serum leptin correlated only with body weight and body fat. It is concluded that leptin levels do not adequately reflect changes in insulin sensitivity or androgen levels after short-term antiandrogen or antigonadotropin treatment.

Changes in serum leptin levels during GnRH agonist therapy

The purpose of the present study was to investigate changes in serum leptin levels during GnRH agonist therapy. Twenty regularly menstruating women with uterine leiomyomas were enrolled. These subjects were given GnRH agonist (leuprorelin acetate, 3.75 mg) monthly for 4 months. Serum leptin and estradiol (E2) levels were measured at the two time points of day 1 or 2 of the menstrual cycle and the end of GnRH agonist therapy. Weight, total body fat mass, percentage of body fat, and total body lean mass were measured by whole body scanning with dual-energy X-ray absorptiometry. The ratio of serum leptin levels to total body fat mass (leptin-fat mass ratio), and the ratio of serum leptin levels to total body lean mass (leptin-lean mass ratio) were calculated. All subjects became amenorrheic after the initial administration of GnRH agonist. Baseline E2 levels were 45.4 +/- 21.0 pg/mL, which significantly decreased after GnRH agonist therapy (13.3 +/- 4.2 pg/mL, p<0.01). Baseline leptin levels were 8.7 +/- 8.1 ng/mL, which did not differ from the values after 4 months of GnRH agonist administration (8.9 +/- 6.8 ng/mL). Total body fat mass significantly increased from 20.0 +/- 10.4 to 21.0 +/- 9.4 kg (p<0.05), while total body lean mass significantly decreased (34.5 +/- 4.2 kg to 33.3 +/- 3.9 kg, p<0.01). However, leptin-fat mass ratio after GnRH agonist therapy did not differ from the baseline values (0.39 +/- 0.16 ng/mL/kg vs 0.38 +/- 0.16 ng/mL/kg). Hypogonadism does not have a major impact on circulating leptin levels.

Blood leptin homeostasis: sex-associated differences in circulating leptin levels in rats are independent of tissue leptin expression

Circulating leptin levels are higher in women than in men. The aim of the study has been to determine in rats the putative existence of sex-associated differences in leptin expression in different adipose tissue depots (gonadal, retroperitoneal, mesenteric and inguinal white adipose tissue and interscapular brown adipose tissue) and the relationship with circulating leptin levels. Adult male and female Wistar rats acclimated to 22 degrees C or to 28 degrees C were used. Leptin mRNA expression was assessed by northern blot and serum leptin levels by enzyme-linked immunosorbent assay (ELISA). Contrary to what happens in humans, we report here that male rats acclimated to standard animal house conditions (22 degrees C) have a higher leptin concentration in blood than female rats. This situation cannot be explained by a greater size of the fat depots in males, because the adiposity index is similar in both genders, but are rather associated to higher leptin specific mRNA expression by the white adipose tissue. Around thermoneutral conditions (28 degrees C), sex related differences in leptin mRNA expression disappear, but the gender difference in circulating leptin levels remains. In addition, leptin mRNA expression is higher in both genders in thermoneutral conditions but this is not reflected in changes in the circulating leptin levels. In conclusion, this study shows that rat circulating leptin levels are finely regulated, and not exclusively dependent on leptin mRNA expression, but other mechanisms are also involved, possibly regarding leptin rate of degradation.

Leptin production in pre- and postmenopausal women

OBJECTIVES

To investigate the differences in leptin production between pre- and postmenopausal women.

METHODS

Subjects were 75 pre- and 75 postmenopausal women. Age, height, weight, and body mass index (BMI, wt/ht(2)) were recorded. Serum leptin levels were measured by RIA. Total body fat mass and percentage of body fat mass were measured by whole-body scanning with dual-energy X-ray absorptiometry. Serum leptin levels, the ratio of serum leptin levels to total body fat mass (leptin-fat mass ratio), baseline characteristics, and anthropometric variables were compared between the two groups. In all subjects (n=150), relationship of serum leptin levels with menopausal status (pre- and postmenopause) was investigated by univariate and multiple regression analysis.

RESULTS

Serum leptin levels in premenopausal women 8.4+/-4.8 ng/ml, which did not differ from that in postmenopausal women (9.2+/-7.1 ng/ml). Total body fat mass, percentage of body fat mass, and BMI did not differ between the two groups. Leptin-fat mass ratio in premenopausal women was 0.43+/-0.17 ng/ml/kg, which did not differ from that in postmenopausal women (0.44+/-0.24 ng/ml/kg). On both univariate and multiple regression analysis, serum leptin levels were not correlated with menopausal status.

CONCLUSIONS

Menopausal status does not have a significant impact on leptin production.

Effects of breed, parity, and folic acid supplement on the expression of leptin and its receptors' genes in embryonic and endometrial tissues from pigs at day 25 of gestation

Recent evidence has pointed toward a possible role of leptin (Lep) and its receptor (Lepr) in early gestation materno-fetal cross-talk. However, in gestating sows, exhaustive characterization of leptin mRNA expression in backfat and leptin-receptor mRNA expression in endometrial and embryonic tissues is still pending. The objectives of this study were to characterize the Lep, Lepr, and long Lepr-L isoform mRNA expression according to the breed and parity of gestating sows or to specific folic acid (B(9)) + glycine dietary treatments. To this end, nulliparous (GT) and multiparous occidental Yorkshire-Landrace (YL) sows as well as multiparous Chinese Meishan-Landrace (ML) sows were used. These sows were randomly assigned to two different dietary treatments: 0 or 15 ppm of B(9) + 0.6% glycine, given from the estrous preceding mating until slaughter on Day 25 of gestation. Jugular blood samples were collected at mating and on Day 25 of gestation and assayed for circulating leptin concentrations. Expression levels of Lep in backfat and of Lepr and Lepr-L in endometrial and embryonic tissues were performed using semiquantitative reverse transcription-polymerase chain reaction. Results demonstrated that on Day 25 of pregnancy, the ML sows showed higher concentrations of circulating leptin along with higher backfat thickness and higher expression of Lep in backfat tissue. Moreover, in embryonic tissues, the mRNA expression levels of Lepr and Lepr-L genes were higher in ML than in YL sows. Parity effects were observed for mRNA expression of Lepr in both endometrial and embryonic tissues, whereas mRNA levels were higher in YL than in GT sows. In addition, embryonic Lepr-L mRNA levels were higher in GT than in YL sows, and B(9) + glycine dietary supplement decreased the mRNA expression levels of Lep in backfat and of Lepr in embryonic tissues. These decreases were independent of breed or parity of the sows. The effect of B(9) + glycine on Lepr-L mRNA expression levels was only seen in YL sows, whereas the treatment lowered Lepr-L expression levels in both endometrial and embryonic tissues. These results indicate that leptin and its receptor may play a role during early stages of development of the pig embryo-fetus, and that these roles could be modulated according to the breed and parity of the sows. Moreover, the effects of B(9) + glycine on expression levels of embryonic and endometrial Lepr-L mRNA in YL sows may explain the previously reported effects of B(9) on embryo survival rate and litter size observed in occidental multiparous sows.