Regulation of insulin-like growth factor-binding protein-1 and progesterone secretion from human granulosa-luteal cells: effects of octreotide and insulin

Visfatin and SREBP-1c mRNA Expressions and Serum Levels Among Egyptian Women with Polycystic Ovary Syndrome

Background: Obesity and insulin resistance are common features accompanying polycystic ovary syndrome (PCOS). Aim: To analyze the impact of obesity on the expression of the visfatin and sterol regulatory element-binding protein (SREBP)-1c genes among a group of Egyptian women with PCOS, and to assess their suitability as PCOS biomarkers. Subject and methods: Seventy healthy women (control group) (35 nonobese and 35 obese) and 140 women with PCOS (70 nonobese and 70 obese) were enrolled in this study. The visfatin and SREBP-1c genes' expression analyses were performed via real-time polymerase chain reaction. Serum visfatin and SREBP-1c protein levels were measured with ELISA kits. Results: Among PCOS patients, upregulation of visfatin and SREBP-1c expression was observed. We did not identify significant differences between the obese and nonobese PCOS patients nor between obese and non-obese controls. The mRNA expression levels of both genes were significantly positively correlated with their serum protein levels, as well as with fasting serum insulin levels, homeostatic model assessments of insulin resistance (HOMA-IR), luteinizing hormone (LH) ratios, LH/follicular stimulating hormone ratios, total testosterone, and free androgens. We observed significant negative correlations between visfatin and SREBP-1c expression levels and sex hormone binding globulin levels in all studied groups. Receiver operating characteristic curve analyses revealed that combining the visfatin and SREBP-1c expression data increased the sensitivity (95.92%) and specificity (93.2%) for PCOS diagnoses. Conclusion: Upregulation of visfatin and SREBP-1c was observed among PCOS patients. These genes may play a role in the pathogenesis of PCOS independent of obesity. Combined visfatin and SREBP-1c analyses could be used as a noninvasive biomarker for PCOS.

Diabetes and the female reproductive system

The insulin/insulin-like growth factor (IGF) pathways and glucose metabolism act as mediators of human ovarian function and female fertility. In normal insulin action, insulin binds to its own receptors in the ovary to mediate steroidogenesis and act as a co-gonadotropin. Insulin with other factors may influence ovarian growth and cyst formation. The IGF pathway also seems to influence normal ovarian function. Insulin signaling affects reproductive function. Dysregulation of this pathway leads to altered puberty, ovulation, and fertility. Better understanding of the normal physiology and pathophysiology of insulin, IGF, and glucose effects on the human reproductive system will allow for better outcomes.

Kit ligand and the somatostatin receptor antagonist, BIM-23627, stimulate in vitro resting follicle growth in the neonatal mouse ovary

In the mammalian ovary, kit ligand (KL), coded by a cAMP-stimulatable gene, is a protein that promotes initiation of follicle growth. The neuropeptide somatostatin (SST) is a small peptide that inhibits cAMP generation in many cell types. Consequently, SST receptor agonists might alter KL production and subsequent follicle growth. The present study was undertaken to look for the existence of a functional SST system in the mouse ovary, to test the effects of the SST receptor 2 (SSTR-2) antagonist BIM-23627 on in vitro folliculogenesis, and to compare them with those of KL, which was demonstrated to stimulate follicle growth in the neonatal rat ovary. Pairs of ovaries from 5-d-old mice were incubated in vitro during 15 d in the presence of either KL or BIM-23627. For every mouse, one ovary was cultured in culture medium (control), and the other ovary was cultured in the presence of either KL or BIM-23627. After 5, 10, and 15 d culture, the ovaries were histologically assessed for the content of primordial, primary, and secondary follicles. The SSTR-2 and -5, but not SST, were identified at the transcriptional and translational (mainly in granulosa cells) levels. Both KL and BIM-23627 triggered a reduction of the percentages of primordial follicles and an increase of the percentages of primary and secondary follicles when compared with control ovaries from the same animal. In conclusion, extraovarian SST, acting through its receptors 2 and 5 present on granulosa cells, may be involved in mouse folliculogenesis by reducing recruitment of resting follicles.

Insulin and human chorionic gonadotropin cause a shift in the balance of sterol regulatory element-binding protein (SREBP) isoforms toward the SREBP-1c isoform in cultures of human granulosa cells

The isoforms of sterol regulatory element-binding proteins (SREBP) (1a, 1c, and 2) are key transcriptional regulators of lipid biosynthesis. We examined their regulation by gonadotropin and insulin in human granulosa cells. After removal of leukocytes, granulosa cells were exposed to hormonal additions for 16 h starting on d 2 of culture. Progesterone, lactate, and IGF binding protein-1 were measured in culture medium and cellular mRNA measured by competitive RT-PCR. Addition of human chorionic gonadotropin (hCG) (100 ng/ml) stimulated progesterone production (7.0-fold, P < 0.001 vs. control), whereas lactate was increased by hCG (1.6-fold, P < 0.001) and insulin (1.4-fold, P < 0.001; 1000 ng/ml). Insulin decreased IGF binding protein-1 production by 85% (P < 0.001). There were no significant effects on the expression of SREBP-1a but significant increases in mRNA for SREBP-1c with insulin (6.3-fold), hCG (10.4-fold) and in combination (15.2-fold; P < 0.01 for all comparisons). No consistent effects on SREBP-2 were observed. The expression of mRNA for fatty acid synthase, a target gene for SREBP-1c, was increased by hCG (24-fold, P = 0.006) and insulin (19-fold, P = 0.024), which also increased the level of cellular, total fatty acid (1.34-fold; P = 0.03). Thus, hCG and insulin cause a switch toward expression of the SREBP-1c isoform with consequent effects on fatty acid synthesis. We suggest that high circulating insulin, associated with clinically defined insulin resistance, may up-regulate SREBP-1c expression in the ovary.

Glycodelin responses to hyperinsulinaemic clamp vary according to basal serum glycodelin concentration

OBJECTIVE

Treatment with metformin, an insulin-lowering agent, increases serum glycodelin, a progesterone-regulated lipocalin protein of the reproductive axis that may play a role in foeto-maternal defence mechanisms. This finding led to the hypothesis that insulin might decrease serum glycodelin concentration.

DESIGN, PATIENTS AND MEASUREMENTS

Euglycaemic hyperinsulinaemic clamp experiments (n = 50) were carried out on 28 women of reproductive age (range 25-47 years; mean +/- SEM 39 +/- 1.0 years), and the results were analysed with respect to their baseline serum progesterone (< 10 or > or = 10 nmol/l) and glycodelin (< 10 or > or = 10 microg/l, equivalent to < 357 or > or = 357 pmol/l) concentrations at the onset of the clamp. Ten clamp experiments were performed on five women wearing a levonorgestrel-releasing intrauterine device (IUD), and these were analysed as a separate group.

RESULTS

Contrary to the hypothesis, no acute glycodelin-lowering effect of insulin was found in any of the groups studied. All the small rises in glycodelin levels detected during acute hyperinsulinaemia occurred in the comparisons of medians and not means, and all such changes took place within the limits seen in the women with no progesterone exposure. In the group with low progesterone/low glycodelin (n = 21), glycodelin showed a small but significant increase at 30 and 90 min of the clamp (P < 0.01). In the group with elevated progesterone/low glycodelin (n = 11), there was a slight glycodelin increase at 30 min (P < 0.05), whereas no increase was found in the group with elevated glycodelin levels (n = 8). In the clamp experiments on women with levonorgestrel-releasing IUD, the basal glycodelin level was low in all cases and, as in the other women with low glycodelin levels, glycodelin was slightly increased at 30, 60 and 90 min of hyperinsulinaemia (P < 0.01).

CONCLUSIONS

The results rule out any acute glycodelin-reducing effects of insulin, although indirect long-term effects mediated by insulin on glycodelin secretion cannot be excluded.

Chronic somatostatin treatment affects pituitary gonadotrophs, ovaries and onset of puberty in rats

The effects of chronic somatostatin (SRIH-14) treatment on the pituitary gonadotrophs (FSH and LH cells) and ovaries of female Wistar rats were examined. Females were given 20 microg/100 g b.w. twice per day from the immature (23rd day) till the adult period of life (71st day). The onset of puberty was determined by daily examination for vaginal opening. The peroxidase-antiperoxidase immunocytochemical procedure was used to study the gonadotrophs. Changes in the number per unit area (mm2), cell volume and volume densities of LH- and FSH-immunoreactive cells were evaluated by morphometry and stereology. Ovaries were analysed by simple point counting of follicles and corpora lutea (CL). Follicles were divided by size according to the classification of Gaytán and Osman. The mitotic indexes of granulosa and theca cells in the follicles were estimated at all stages of folliculogenesis. The number, volume and the volume density of FSH- and LH-immunoreactive cells decreased after chronic SRIH-14 treatment, particularly the latter. In the ovary, SRIH-14 treatment decreased the number of healthy follicles at all phases of folliculogenesis, lowered the mitotic indexes of granulosa and theca cells but increased the number of atretic follicles. Healthy CL were fewer in number, while regressive CL were increased. Vaginal opening occurred at a later age in treated females. It can be concluded that chronic SRIH-14 treatment markedly inhibited LH cells and to a lesser extent FSH cells. In the ovary SRIH-14 inhibited folliculogenesis, enhanced atretic processes and lowered proliferative activity of granulosa and theca cells. It also delayed puberty onset.

Regulation of insulin-like growth factor binding protein secretion by human granulosa luteal cells in a polycystic ovary-like environment

OBJECTIVE

To determine the effect of androstenedione (A), insulin, and LH on secretion of insulin-like growth factor binding proteins (IGFBPs) from human granulosa luteal cells.

DESIGN

Human granulosa cells were cultured for a total of 4 days in serum-free medium containing A (10(-6) mol/L), with or without insulin (100 microU/mL-800 microU/mL), LH (1 microU/mL-10 microg/L), and A (10(-5) mol/L).

SETTING

Granulosa cells were obtained from IVF procedures.

PATIENT(S)

Women undergoing IVF for tubal disease.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Immunoassay and autoradiographs of Western ligand blotting detected IGFBP accumulations in the medium.

RESULT(S)

Cultured granulosa cells secreted IGFBP-1 through IGFBP-4. Insulin (100 microU/mL-800 microU/mL), LH (1 microg/L-10 microg/L), and A (10(-5) mol/L) caused a significant decrease in IGFBP-1 accumulation in the medium both alone and when added in combination. The release of IGFBP-2 and IGFBP-4 was significantly stimulated by insulin, whereas LH had no effect. Elevated levels of androgen (10(-5) mol/L) significantly stimulated the secretion of IGFBP-2, whereas the release of IGFBP-4 was reduced.

CONCLUSION(S)

These results demonstrate that androgen and insulin are important regulators of IGFBP release and that elevated levels of the two hormones may contribute to the altered IGFBP profile found in PCOS follicles, compared with the case of estrogen-dominant follicles.

Inhibition of the UCI-107 human ovarian carcinoma cell line by a targeted cytotoxic analog of somatostatin, AN-238

BACKGROUND

Cytotoxic analogs of somatostatin (SST), such as AN-238, which consists of 2-pyrrolinodoxorubicin (AN-201) linked to the SST carrier RC-121, can be targeted to tumors that express SST receptors. Because SST receptors are present in ovarian carcinoma cells, the authors evaluated the effect of AN-238 on the UCI-107 ovarian carcinoma cell line.

METHODS

An analysis of microsatellite alleles in cocultured SST receptor positive and receptor negative cells was used for the demonstration of in vitro targeting. The toxicity and antitumor effects of AN-238 in nude mice bearing UCI-107 human ovarian tumors were investigated with or without pharmacologic inhibition of serum carboxylesterases (CE). The expression of SST receptor subtypes was determined by reverse transcriptase-polymerase chain reaction analysis, and the binding affinity of AN-238 to SST receptors was determined by radioligand assays.

RESULTS

The proliferation of SST receptor positive UCI-107 cells in vitro was inhibited preferentially by AN-238. AN-238 showed high-affinity binding to UCI-107 tumor membranes at a 50% inhibition concentration of 3.39 nM +/- 0.74 nM. In vivo, the volume and weights of UCI-107 tumors treated with AN-238 were decreased by more than 60% (P < 0.05) compared with controls. Cytotoxic radical AN-201 or the unconjugated mixture of AN-201 with carrier RC-121 had no significant effects on tumors and were toxic. In mice with inhibited serum CE activity, AN-201 at 400 nmol/kg was lethal, whereas AN-238 at a total dose of 800 nmol/kg caused only 22% mortality and reduced tumor weight by 69% and volume by 70% (P < 0.05 vs. control).

CONCLUSIONS

Targeted chemotherapy with the SST conjugate AN-238 inhibits SST receptor positive experimental ovarian tumors. AN-238 may provide a new treatment modality for patients with advanced ovarian carcinoma.

Impaired insulin action on granulosa-lutein cells in women with polycystic ovary syndrome and insulin resistance

We studied the in vitro response to insulin of granulosa-lutein cells derived from patients with polycystic ovary syndrome (PCOS) and clinically defined insulin resistance. Insulin sensitivity was assessed by continuous infusion of glucose with model assessment test (CIGMA). Insulin resistant (PCOS-IR; n = 8), noninsulin resistant (PCOS-NIR; n = 9) patients with PCOS, and women with tubal factor infertility (TF; n = 8) underwent controlled ovarian stimulation with long-term gonadotropin-releasing hormone (GnRH) agonist, recombinant follicle stimulating hormone (FSH), and in vitro fertilization. Primary cultures of granulosa-lutein cells were incubated with insulin (10, 100, 500 ng/ml) and/or luteinizing hormone (LH) (10, 100 ng/ml) in the presence of low density lipoprotein (100 micrograms/ml). The progesterone and lactate accumulation were measured in the culture medium. LH potently stimulated the progesterone secretion in all groups. Insulin alone had no effect on progesterone release in any of the groups, but stimulated lactate formation in the PCOS-NIR and TF groups. Insulin augmented the effect of LH on progesterone secretion selectively in the PCOS-NIR group. The expression of the insulin receptor was determined by Western blotting in separate cultures of granulosa-lutein cells, and showed receptor down-regulation in the PCOS-IR patients. We infer that the in vitro effect of insulin on progesterone and lactate release by granulosa-lutein cells is impaired in insulin resistant PCOS patients.

Placental growth hormone (GH), GH-binding protein, and insulin-like growth factor axis in normal, growth-retarded, and diabetic pregnancies: correlations with fetal growth

We previously described significant changes in GH-binding protein (GHBP) in pathological human pregnancy. There was a substantial elevation of GHBP in cases ofnoninsulin-dependent diabetes mellitus and a reduction in insulin-dependent diabetes mellitus. GHBP has the potential to modulate the proportion of free placental GH (PGH) and hence the impact on the maternal GH/insulin-like growth factor I (IGF-I) axis, fetal growth, and maternal glycemic status. The present study was undertaken to investigate the relationship among glycemia, GHBP, and PGH during pregnancy and to assess the impact of GHBP on the concentration of free PGH. We have extended the analysis of specimens to include measurements of GHBP, PGH, IGF-I, IGF-II, IGF-binding protein-1 (IGFBP-1), IGFBP-2, and IGFBP-3 and have related these to maternal characteristics, fetal growth, and glycemia. The simultaneous measurement of GHBP and PGH has for the first time allowed calculation of the free component of PGH and correlation of the free component to indexes of fetal growth and other endocrine markers. PGH, free PGH, IGF-I, and IGF-II were substantially decreased in IUGR at 28-30 weeks gestation (K28) and 36-38 weeks gestation (K36). The mean concentration (+/-SEM) of total PGH increased significantly from K28 to K36 (30.0 +/- 2.2 to 50.7 +/- 6.2 ng/mL; n = 40), as did the concentration of free PGH (23.4 +/- 2.3 to 43.7 +/- 6.0 ng/mL; n = 38). The mean percentage of free PGH was significantly less in IUGR than in normal subjects (67% vs. 79%; P < 0.01). Macrosomia was associated with an increase in these parameters that did not reach statistical significance. Multiple regression analysis revealed that PGH/IGF-I and IGFBP-3 account for 40% of the variance in birth weight. IGFBP-3 showed a significant correlation with IGF-I, IGF-II, and free and total PGH at K28 and K36. Noninsulin-dependent diabetes mellitus patients had a lower mean percentage of free PGH (65%; P < 0.01), and insulin-dependent diabetics had a higher mean percentage of free PGH (87%; P < 0.01) than normal subjects. Mean postprandial glucose at K28 correlated positively with PGH and free PGH (consistent with the hyperglycemic action of GH). GHBP correlated negatively with both postprandial and fasting glucose. Although GHBP correlated negatively with PGH (r = -0.52; P < .001), free PGH and total PGH correlated very closely (r = 0.98). The results are consistent with an inhibitory function for GHBP in vivo and support a critical role for placental GH and IGF-I in driving normal fetal growth.