Calcium Supplementation Increases Bone Mass in GH-Deficient Prepubertal Children during GH Replacement

Leptin and its potential interest in assisted reproduction cycles

BACKGROUND

Leptin, an adipose hormone, has been shown to control energy homeostasis and food intake, and exert many actions on female reproductive function. Consequently, this adipokine is a pivotal factor in studies conducted on animal models and humans to decipher the mechanisms behind the infertility often observed in obese women.

METHODS

A systematic PubMed search was conducted on all articles, published up to January 2015 and related to leptin and its actions on energy balance and reproduction, using the following key words: leptin, reproduction, infertility, IVF and controlled ovarian stimulation. The available literature was reviewed in order to provide an overview of the current knowledge on the physiological roles of leptin, its involvement in female reproductive function and its potential interest as a prognostic marker in IVF cycles.

RESULTS

Animal and human studies show that leptin communicates nutritional status to the central nervous system and emerging evidence has demonstrated that leptin is involved in the control of reproductive functions by acting both directly on the ovaries and indirectly on the central nervous system. With respect to the clinical use of leptin as a biomarker in IVF cycles, a systematic review of the literature suggested its potential interest as a predictor of IVF outcome, as high serum and/or follicular fluid leptin concentrations have correlated negatively with cycle outcome. However, these preliminary results remain to be confirmed.

CONCLUSION

Leptin regulates energy balance and female reproductive function, mainly through its action on hypothalamic-pituitary-ovarian function, whose molecular and cellular aspects are progressively being deciphered. Preliminary studies evaluating leptin as a biomarker in human IVF seem promising but need further confirmation.

Regulation of the ovarian oxidative status by leptin during the ovulatory process in rats

Leptin exerts both stimulatory and inhibitory effects on the ovulatory process. In this study, we investigated whether these opposite effects involve changes in the oxidative status in response to different levels of leptin. To this end, we performed bothin vivoandin vitroassays using ovaries of immature rats primed with gonadotropins to induce ovulation. Superoxide dismutase (SOD) and catalase (CAT) activity, lipid peroxidation, glutathione (GSH) content, and reactive oxygen species (ROS) were studied as oxidative damage-related parameters. The expression of BCL2, BAX, and caspase 3 were measured by western blot as apoptosis-related biomarkers. The acute treatment with leptin, which inhibits ovulation, decreased SOD activity and increased active caspase 3 expression. No differences were found in CAT activity, lipid peroxidation, or total GSH. In contrast, the daily administration of leptin, which induces ovulation, decreased GSH content, ROS levels, and Bax and active caspase 3 expression, but caused no changes in other parameters. In addition, the daily administration of leptin induced follicular growth, measured by the number of antral follicles in ovarian sections. Using ovarian explant cultures, we found increased BCL2 expression and decreased SOD activity at low and high concentrations of leptin respectively. Thus, leptin can modulate the oxidative status of the ovarian tissue, during the ovulatory process, by acting on different targets according to its circulating levels. At low concentration, leptin seems to play a protective role against the oxidative stress, whereas at high concentrations, this protein seems to be involved in cell death.

Leptin fails to blunt the lipopolysaccharide-induced activation of the hypothalamic-pituitary-adrenal axis in rats

Obesity is a risk factor for sepsis morbidity and mortality, whereas the hypothalamic-pituitary-adrenal (HPA) axis plays a protective role in the body's defence against sepsis. Sepsis induces a profound systemic immune response and cytokines serve as excellent markers for sepsis as they act as mediators of the immune response. Evidence suggests that the adipokine leptin may play a pathogenic role in sepsis. Mouse endotoxaemic models present with elevated leptin levels and exogenously added leptin increased mortality whereas human septic patients have elevated circulating levels of the soluble leptin receptor (Ob-Re). Evidence suggests that leptin can inhibit the regulation of the HPA axis. Thus, leptin may suppress the HPA axis, impairing its protective role in sepsis. We hypothesised that leptin would attenuate the HPA axis response to sepsis. We investigated the direct effects of an i.p. injection of 2 mg/kg leptin on the HPA axis response to intraperitoneally injected 25 μg/kg lipopolysaccharide (LPS) in the male Wistar rat. We found that LPS potently activated the HPA axis, as shown by significantly increased plasma stress hormones, ACTH and corticosterone, and increased plasma interleukin 1β (IL1β) levels, 2 h after administration. Pre-treatment with leptin, 2 h before LPS administration, did not influence the HPA axis response to LPS. In turn, LPS did not affect plasma leptin levels. Our findings suggest that leptin does not influence HPA function or IL1β secretion in a rat model of LPS-induced sepsis, and thus that leptin is unlikely to be involved in the acute-phase endocrine response to bacterial infection in rats.

Enhanced effect of zinc and calcium supplementation on bone status in growth hormone-deficient children treated with growth hormone: a pilot randomized controlled trial

Reduced bone mineral content in growth hormone-deficient children (GHD) has been reported. Calcium, zinc, and vitamin D play an important role in bone formation. Hence, the aim of this pilot randomized controlled study was to evaluate the effect of calcium, vitamin D, and zinc supplementation in prepubertal GHD children treated with GH on bone health parameters. After 1 year of treatment with GH (20 mg/m(2)/week), 31 GHD (mean age 8.7 ± 2.8 years, 18 boys) prepubertal children were randomised to receive calcium (500 mg/day) and vitamin D (60,000 IU/3 months) [Group A] or a similar supplement of calcium, vitamin D, and zinc (as per Indian Recommended Allowance) [Group B] along with GH therapy for the next 12 months. The two groups were similar in anthropometric and body composition parameters at baseline (p > 0.1). After 1 year of GH therapy, height-adjusted % gain was similar in both groups, 48 % in bone mineral content (BMC) and 45 % in bone area (BA). Height-adjusted % increase in BMC was significantly (p < 0.05) higher in the second year than in the first in both the groups. This % increase in BMC and BA was greater in Group B (51 and 36 % respectively) than in Group A (49 and 34 %), although marginally (p < 0.05). Supplementation of calcium and vitamin D along with GH therapy in GHD Indian children has the potential for enhancing bone mass accrual; this effect was further enhanced through the addition of zinc supplement.

Increase of fecundity by probiotic administration in zebrafish (Danio rerio)

It is well known established that reproduction is sensitive to the state of energy reserves, and that there is a balance between energy homeostasis and fertility. In this view, this study examined the effects of the probiotic Lactobacillus rhamnosus, as a feed additive, on zebrafish (Danio rerio) fecundity. Ten days of probiotic treatment modulate the gene expression of neuropeptide hormones and metabolic signals, such as kiss1, kiss2 and leptin both at the CNS level and at the peripheral level. The increase in fecundity brought about by the probiotic was demonstrated by the higher number of ovulated eggs in vivo and by the higher germinal vesicle breakdown rate obtained with the in vitro maturation assay. The increase in oocyte maturation was associated with increased transcription of genes coding for signals which induce the maturation phase, such as lhcgr, cbr1l, and paqr8 genes, concomitant with a decreased transcription of genes coding for local factors which prevent oocyte maturation, such as tgfb1, gdf9, and bmp15. In conclusion, all these findings highlight the action of L. rhamnosus both on the endocrine system and at the local level by inducing oocyte maturation. The significance of the results herein obtained underlined the importance of diet in the reproductive process, supporting the hypothesis that feed additives can improve fecundity. Considering that the zebrafish has been clearly established as a vertebrate model for biomedical research, these results support the potentiality of feed additives such as probiotics, frequently used in the human diet, as a new technology to improve reproduction in all vertebrates, including humans.

The adverse effects of obesity on conception and implantation

Whilst many multiparous women are obese (body mass index >30 kg/m(2)), obesity has been associated with impaired fecundity; however, the mechanism which links obesity to reduced fertility remains to be fully elucidated. Obese women, particularly those with central obesity, are less likely to conceive per cycle. Obese women suffer perturbations to the hypothalamic-pituitary-ovarian axis, menstrual cycle disturbance and are up to three times more likely to suffer oligo-/anovulation. A fine hormonal balance regulates follicular development and oocyte maturation, and it has been observed that obesity can alter the hormonal milieu. Leptin, a hormone produced by adipocytes, is elevated in obese women, and raised leptin has been associated with impaired fecundity. Obesity impairs ovulation but has also been observed to detrimentally affect endometrial development and implantation. The expression of polycystic ovary syndrome (PCOS) is regulated, in part, by weight, and so obese women with PCOS often have a more severe phenotype and experience more subfertility. Obesity also impairs the response of women to assisted conception treatments. Weight loss through lifestyle modification or bariatric surgery has been demonstrated to restore menstrual cyclicity and ovulation and improve the likelihood of conception. In this article, we will discuss the effect of obesity upon key reproductive mechanisms and its relation to fertility treatments.

Influence of leptin on in vitro maturation and steroidogenic secretion of cumulus–oocyte complexes through JAK2/STAT3 and MEK 1/2 pathways in the rabbit model

Extreme body mass indexes may impair reproductive outcome in assisted reproductive technologies. Leptin reflects the amount of body fat and could act as a modulator of oocyte quality through activation of specific transcription factors. The aim of this work was to establish whether: 1) leptin influences meiotic and cytoplasmic oocyte maturation; 2) STAT3 and MAPK mediate the effects of leptin and 3) leptin modulates steroid secretion by cumulus–oocyte complexes (COC) duringin vitromaturation (IVM). We confirmed immunolocalisation of leptin receptor in oocytes, cumulus/granulosa cells during the peri-ovulatory period. The confocal study showed that COC supplemented with 1, 10 and 100 ng/ml leptin had a significantly higher metaphase II (MII) percentage than those IVM without leptin (P<0.05) and a similar MII index compared to the group supplemented with 10% FCS. Leptin did not increase the percentage of cytoplasmically matured oocytes in terms of cortical granule migration rate, whereas a significantly higher index was found in the FCS group (P<0.001). Oestradiol concentrations in spent media were higher in the FCS group compared to other treatments (P<0.001). Leptin-stimulated nuclear oocyte maturation was significantly impaired when leptin-induced JAK2/STAT3 and MEK 1/2 activation was suppressed by the inhibitors (P<0.001). Steroid secretion of COC was not affected by leptin activation of JAK2/STAT3 or MEK 1/2 pathways. In conclusion, JAK2/STAT3 and MEK 1/2 pathways mediate the enhancement of nuclear oocyte maturation by leptin; however, neither cytoplasmic oocyte maturation nor steroidogenic response of COC were improved in the present rabbit model.

Inhibitory effect of leptin on the rat ovary during the ovulatory process

The aims of this study were to investigate the negative action of leptin on some intraovarian ovulatory mediators during the ovulatory process and to assess whether leptin is able to alter the expression of its ovarian receptors. Immature rats primed with gonadotrophins were used to induce ovulation. Serum leptin concentration was diminished 4 h after human chorionic gonadotrophin (hCG) administration, whereas the ovarian expression of leptin receptors, measured by western blot, was increased by the gonadotrophin treatment. Serum progesterone level, ovulation rate and ovarian prostaglandin E (PGE) content were reduced in rats primed with equine chorionic gonadotrophin (eCG)/hCG and treated with acute doses of leptin (five doses of 5 mug each). These inhibitory effects were confirmed by in vitro studies, where the presence of leptin reduced the concentrations of progesterone, PGE and nitrites in the media of both ovarian explants and preovulatory follicle cultures. We also investigated whether these negative effects were mediated by changes in the expression of the ovarian leptin receptors. Since leptin treatment did not alter the expression of ovarian leptin receptor, the inhibitory effect of leptin on the ovulatory process may not be mediated by changes in the expression of its receptors at ovarian level, at least at the concentrations assayed. In summary, the ovulatory process was significantly inhibited in response to an acute treatment with leptin, and this effect may be due, at least in part, to the direct or indirect impairment of some ovarian factors, such as prostaglandins and nitric oxide.

The ovarian expression of mRNAs for aromatase, IGF-I receptor, IGF-binding protein-2, -4 and -5, leptin and leptin receptor in cycling ewes after three days of leptin infusion

An experiment was carried out to determine the pattern of follicular expression of mRNAs for aromatase, IGF-I receptor (IGF-IR), IGF-binding protein (IGFBP)-2, -4 and -5, leptin and the long form of the leptin receptor (Ob-Rb) in ten ewes infused with human recombinant leptin (n = 5; 1 microg/h) or saline (n = 5) for 72 h in the luteal phase of the oestrous cycle. At the end of infusion a follicular phase was induced with a luteolytic dose of a prostaglandin F2alpha analogue and the ovaries were collected 32 h later. One ovary from each ewe was serially sectioned at 10 microm using a cryostat at -20 degrees C. All follicles >1 mm in diameter were counted and probed with specific oligoprobes for aromatase, IGF-IR and IGFBP-2, -4 and -5 and specific riboprobes for leptin and Ob-Rb. Leptin mRNA was detected in theca and granulosa cells and Ob-Rb mRNA was detected only in granulosa cells, of some, but not all antral follicles. Leptin doubled the number of follicles with a diameter >/=3.5 mm (1.0 +/- 0.36 (s.e.m.) vs 2.4 +/- 0.24; control vs leptin; P < 0.02) but had no effect on the number of >/=1 < 3.5 mm follicles. Leptin had no effect on the number of follicles expressing aromatase mRNA but it decreased significantly the number of follicles expressing mRNA for IGF-IR (10.7 +/- 0.79 vs 7.4 +/- 0.81; control vs leptin; P < 0.05), IGFBP-2 (10.0 +/- 0.82 vs 5.2 +/- 0.87; control vs leptin; P < 0.05) and IGFBP-5 (5.2 +/- 1.60 vs 1.2 +/- 0.30; control vs leptin; P < 0.05). Leptin increased the diameter of IGFBP-2 mRNA-positive follicles (1.5 +/- 0.15 vs 2.2 +/- 0.31 mm; control vs leptin; P < 0.05) and increased follicular mRNA expression for IGFBP-2 (0.30 +/- 0.021 vs 0.39 +/- 0.027 arbitrary units; control vs leptin; P < 0.05) and IGFBP-5 (0.46 +/- 0.019 vs 0.25 +/- 0.053 arbitary units; control vs leptin; P < 0.05). The mRNA for IGFBP-4 was detected in the theca of only two follicles from the control group. Leptin increased the number of follicles expressing Ob-Rb mRNA (0.25 +/- 0.25 vs 1.40 +/- 1.17; control vs leptin; P < 0.05) but had no effect on the number expressing leptin mRNA. Leptin decreased plasma concentrations of oestradiol (P < 0.05) and increased concentrations of FSH (P < 0.001) and insulin (P < 0.001), with no effect on glucose concentrations. These data show that: (i) ovine granulosa cells express mRNA for Ob-Rb and leptin and (ii) leptin increased the number of follicles >/=3.5 mm. Furthermore, the data suggest that suppression of oestradiol production by leptin is not mediated by inhibition of aromatase gene expression. Finally, the data indicate that the action of leptin in ovarian follicles is mediated by the IGF system, because leptin increased mRNA expression of IGFBP-2 and -5. Leptin also decreased the number of follicles expressing IGF-IR and IGFBP-2 and -5. We suggest that these actions of leptin on the IGF system decrease the bioavailability of IGF-I, resulting in decreased oestradiol production.

Gender difference in diet-induced obesity hypertension: implication of renal alpha2-adrenergic receptors

Although the pathogenesis of the obesity-related hypertension is not fully understood, prevalence of the cardiovascular complications is much higher in obese men than obese women. In a recent study, we reported that male rats fed a cafeteria diet, while becoming obese, developed hypertension and important changes in their renal alpha2-adrenergic receptor subtypes distributions. The aim of the present study was to investigate whether these alterations are sex dependent. After 10 weeks of the cafeteria diet, male and female rats had the same increase in fat pad weight and in plasma leptin levels. However, in contrast to males, females had normal blood pressure (BP). On the basis of radioligand-binding studies using [3H]-RX821002 and confirming our recent observation, an increase in alpha2-adrenergic receptor densities occurred in kidneys of cafeteria-fed male but not female rats. Moreover, in contrast with the situation observed in males, ligand competition studies failed to reveal any change in the renal alpha2A- and alpha2B-adrenergic receptors subtypes distribution in females. Finally, in the cafeteria-fed females reverse transcription-polymerase chain reaction experiments showed unaltered expression of these two alpha2-adrenergic receptor subtypes. These data thus suggest a strong relationship between the sexual dimorphism in the cafeteria diet-induced hypertension and altered expression of the alpha2-adrenergic receptor subtypes in the kidney.