An hCG antagonist reduces ovulation and diminishes OHSS in a rat model through down-regulation of VEGF

Abstract

OHSS is a complication of IVF, attributable to changes following hCG treatment to induce final oocyte maturation. These changes increase vascular endothelial growth factor (VEGF) resulting in increased vascular permeability (VP). We have shown that a modified hCG (hCG-Ant) binds competitively to the LH receptor, blocking LH activity in vitro. In a rat OHSS model, hCG-Ant reduces ovulation and significantly diminishes OHSS by reducing VP. We quantified the effect of hCG-Ant on ovulation and OHSS by measuring hormone levels and determining VEGF and VEGF receptor 2 (VEGFR-2) protein localization and mRNA expression in tissue, as well as changes in ovarian weight between treatment groups. In vivo studies used standard rat models for ovulation and OHSS. For ovulation studies, immature female Wistar rats were randomized to 2 groups. 11 rats received 10 IU pregnant mare serum gonadotropin (PMSG) ip for 1d, followed by 10 IU hCG or hCG-Ant 48h later. Rats were sacrificed 24h post-hCG and serum was obtained for E2, P4, and inhibin assays. For OHSS studies, 12 rats were randomized to receive 10 IU PMSG for 4d, followed by 0.1 mL saline (control, n = 4), 30 IU hCG to induce OHSS (n = 4), or 30 IU hCG followed by 30 IU hCG-Ant 24 h later (treatment group, n = 4). After 48 h, tissue was prepared for Western blotting and RT-PCR using standard methods. Ovarian weight was higher in the hCG group vs. hCG-Ant (0.0361 ± 0.014 g vs. 0.019 ± 0.007 g, P<.05). E2 and P4 levels were higher in the hCG vs. hCG-Ant group (91.45 ± 30.84 pg/mL and 6.48 ± 4.13 ng/mL vs. 53.12 ± 18.55 pg/mL and 3.43 ± 2.03 ng/mL, P<.05). Inhibin A increased linearly as luteal E2 and P4 rose. Average inhibin A was higher in the hCG vs. hCG-Ant group (553.63 ± 107.18 pg/mL vs. 247.2 ± 74.19 pg/mL, P<.05). Western blot showed VEGF was present in ovaries treated with hCG and saline and absent in ovaries treated with hCG-Ant following hCG. VEGFR-2 was present in the ovary by Western blot for all groups. RT-PCR confirmed increased ovarian mRNA expression of VEGF in the hCG and saline groups vs. hCG-Ant following hCG. HCG-Ant linearly decreases luteal E2, P4, and inhibin A, reflecting a reduction in ovulation, suggesting a dose-dependent effect. Controlling ovulation may diminish OHSS risk. Ovarian VEGF expression is abolished by giving hCG-Ant after hCG in an OHSS model. Clinically, during an IVF cycle, hCG-Ant may be given following hCG treatment and oocyte retrieval to reduce OHSS while preserving IVF cycle outcome.