The Potential Role of Leptin Antagonist in Assisted Reproduction

Abstract

<p>Leptin is a 16- kDa cytokine protein hormone secreted mainly by the adipose tissues with an essential role in the regulation of body weight by controlling food intake and energy expenditure. Recently Leptin has been considered an important signalling molecule of the reproductive system, and it is considered to play a role in regulating gonadotrophin production. Leptin acts as a reproductive hormone, regulating the puberty onset. Leptin has been demonstrated to produce inhibitory actions on steroidogenesis and spermatogenesis. It has been demonstrated that leptin regulates energy balance and female reproductive function, primarily by action on the hypothalamic-pituitary-ovarian axis (HPO) function. Leptin improves ovarian folliculogenesis by regulation of ovarian angiogenesis via direct effects on the ovary and via an effect on the hypothalamo- pituitary ovarian axis (HPO- axis), leading to participation in GnRH, LH, and FSH secretion. </p> <p>We conducted a series of works examining the effects of raised or reduced leptin levels on pregnancy outcomes in female humans and female and male mice. First, we conducted a systematic review of the effects of serum and follicular fluid leptin levels on pregnancy outcomes in women undergoing IVF. Then we conducted a series of animal (mice) experiments on the effects of administration of a leptin-antagonist in mice.</p> <p>Our first work was a systematic review (Chapter 2). Outcomes were: BMI, serum leptin level at hCG injection, serum and follicular fluid leptin level at the oocyte pick up, and serum 17βestradiol level at oocyte pick up time, oocytes retrieved and embryo transfer number. Results indicated that follicular fluid leptin concentrations at the oocyte pick up were significantly lower in women who became pregnant compared with those who did not (MD= -5.13(ng/ml); 95%CI: -8.52, 1.75; p-value<0.003). The results of this work show that elevated leptin concentration in the follicular fluid at oocyte pick up time is significantly associated with an adverse pregnancy outcome in women undergoing an IVF program. This work informed our subsequent experiments.</p> <p>Our first experimental study (Chapter 3) was to investigate the effect of leptin antagonist administration on reproductive function in normal immature and mature female mice. Female mice were administered anti-leptin antibody subcutaneously (sc), with or without gonadotropins, and ovaries and uteruses were weighed and collected for hormonal measurement. Control animals were treated with non-immune serum. Our results showed that the body weights of the three treatment groups were not significantly (P>0.05) different from the control and from each other in both immature and mature female mice. In immature female mice, ovary weights of mice administered gonadotropins and anti-leptin plus gonadotropins groups were significantly (P<0.05) higher compared to the anti-leptin treated group and control, whereas uterus weights of mice treated with anti-leptin plus gonadotropins were significantly higher from control. In mature female mice, the ovary weights of the three treatment groups were significantly (P<0.05) higher of the control, whereas uterus weights of the three treatment groups were not significantly (P>0.05) different from the control and each other. Serum ovarian and uterine progesterone concentrations were significantly increased in mice administrated with anti-leptin and anti-leptin plus gonadotropins compared to control. This data shows that the reduction of leptin improves ovarian function and increases serum, ovarian and uterine progesterone concentrations, leading to an increased chance of successful embryonic implantation.</p> <p>Our second experiment (Chapter 4) investigated the effect of leptin antagonist administration on reproductive function in normal immature male mice, who were administered an anti-leptin antibody subcutaneously on six occasions, testes and seminal vesicles were weighed and collected for hormonal measurements. Control animals were treated with non-immune serum. The administration of the anti-leptin antibody resulted in a significant (p˂0.05) increase in seminal vesicle weight compared with control seminal vesicles. When immature male mice were administered an anti-leptin antibody on three occasions, with or without gonadotropins, seminal vesicle weights were significantly (p˂0.05) increased in both groups administrated anti-leptin antibodies. Seminal vesicle weights were significantly (p˂0.05) increased in mice administrated anti-leptin antibodies, with or without gonadotropins, compared to control. Serum testosterone concentrations significantly (p˂0.05) decreased only in mice administrated anti-leptin antibodies compared to the other groups, whereas androstenedione concentrations were not significantly different between treatments and control groups. Testosterone and androstenedione concentrations in seminal vesicle were not significantly (p>0.05) different between treatment and control groups. These results indicate that peripheral leptin may act as an inhibitor of seminal vesicle and testis development, and therefore reduction of leptin concentrations in the circulation promotes seminal vesicle and testis development in immature male mice.</p> <p>Our third experiment (Chapter 5), mature male mice, results showed a significant (p<0.05) increase in seminal vesicle weight of administrated mice by gonadotropins and anti-leptin plus gonadotropins groups compared to control group. Testicular weight was not significantly (p>0.05) different between the three treatment groups compared to control. Testosterone concentrations in serum were significantly (p<0.05) higher in mice administrated by anti-leptin antibody compared to control, but serum androstenedione concentrations were not significantly affected. Testicular testosterone and androstenedione concentrations were not affected by antileptin antibody treatment. Androstenedione concentrations in seminal vesicle were significantly (p<0.05) higher in mice administrated by anti-leptin antibody compared to control but testosterone concentrations were not affected. This study shows that anti-leptin antibody administration to mature male mice increased circulating testosterone and increased androstenedione hormone concentrations in seminal vesicle but has no actual effect on testicular and seminal vesicle weight.</p> <p>Our fourth experiment (Chapter 6), investigated the effect of reducing peripheral leptin concentrations on ovarian follicular development in immature female, mice who were given two subcutaneous (sc) injections anti-leptin antibody two days, with or without gonadotropins, and ovaries and uteruses were weighed, and ovaries collected for follicle counting. Control animals were treated with non-immune serum. The administration of anti-leptin antibody, with or without gonadotropins, resulted in a significant increase in the ovarian weight of mice treated with anti-leptin plus eCG compared with other treatment and control groups (P<0.05). Uterine weight of mice treated with anti-leptin plus eCG was the highest and significantly greater than that from anti-leptin treated mice and control groups. Furthermore, the ovaries of mice treated with anti-leptin plus eCG showed the highest increase of ovulated eggs collected from the ampulla and were significantly higher than that from anti-leptin treated mice and control groups (P<0.05) (Experiment 1), whereas mice that given (sc) injection of anti-leptin antibody, with or without half eCG and hCG (half dose of the standard protocol), showed a significant decrees in the numbers of ovulated eggs of mice treated with half eCG and hCG, whereas other treatment groups showed no significant difference compared to control (P<0.05) (Experiment 2). Our results showed that synergies of anti-leptin and eCG have a positive effect on folliculogenesis. We conclude that reducing concentrations of leptin in circulation promotes ovarian follicle development in female mice, suggesting that leptin may act as an inhibitor of ovarian follicle development. </p> <p>The overall conclusion is showing that The data supports that leptin has adverse reproductive outcomes in women and adverse reproductive organ development and function in both female and male, mature and immature mice. Bloking leptin could improve reproductive outcomes.</p>