Increased B-lymphopoiesis by interleukin 7 induces bone loss in mice with intact ovarian function: Similarity to estrogen deficiency

Estrogen deficiency caused by ovariectomy (OVX) results in a marked bone loss due to stimulated bone resorption by osteoclasts. During our investigations of the pathogenesis of bone loss in estrogen deficiency, we found that OVX selectively stimulates B-lymphopoiesis which results in marked accumulation of B220-positive pre-B cells in mouse bone marrow. To examine the possible correlation between stimulated B-lymphopoiesis and bone loss, 8-week-old female mice were treated with interleukin (IL) 7, which stimulates B-lymphopoiesis in bone marrow. We also examined bone mass in IL-7 receptor-knockout mice that exhibit marked suppression of B-lymphopoiesis in the bone marrow. The increased B-lymphopoiesis induced by IL-7 administration resulted in marked bone loss by stimulation of osteoclastic bone resorption in mice with intact ovarian function. The changes in both B-lymphopoiesis and bone mass in IL-7-treated female mice were similar to those in age-matched OVX mice. In contrast, the trabecular bone volume of the femur was greatly increased in both female and male IL-7 receptor-knockout mice when compared with the respective wild-type and heterozygous littermates. These results show that the perturbation of B-lymphopoiesis in the bone marrow is closely linked to the change in bone mass. We propose here that the increased B-lymphopoiesis due to estrogen deficiency is involved in the mechanism of stimulated bone resorption.

Loss of ovarian function promotes angiogenesis in human ovarian carcinoma

We show here that elevated levels of gonadotropins (luteinizing hormone and follicle stimulating hormone), as found in menopause or after ovariectomy, promote growth of human ovarian carcinoma by induction of tumor angiogenesis. Human epithelial ovarian cancer tumors progressed faster in ovariectomized mice. This induced growth could be attributed to the elevated levels of gonadotropins associated with loss of ovarian function because direct administration of gonadotropins also was effective in promoting tumor progression in vivo. On the other hand, gonadotropins had no direct effect on the proliferation of human ovarian cancer cells in vitro. Using MRI, we demonstrated that ovariectomy significantly (P < 0.02) induces neovascularization of human ovarian carcinoma spheroids implanted in nude mice. Moreover, conditioned medium of gonadotropin-treated human ovarian carcinoma cells showed increased mitogenic activity to bovine endothelial cells, and this activity could be blocked by neutralizing antibodies against luteinizing hormone and against vascular endothelial growth factor. Accordingly, gonadotropin stimulation resulted in a dose-dependent-induced expression of vascular endothelial growth factor in monolayer culture as well as in the outer proliferating cells of human ovarian cancer spheroids. These results demonstrate the significance of the elevated levels of gonadotropins, as found in menopause and in all ovarian cancer patients, on the progression of ovarian cancer and could explain the protective effect of estrogen replacement therapy. Based on these results, we suggest that hormonal therapy aimed at lowering the circulating levels of gonadotropins may possibly prolong remission in ovarian cancer by extending tumor dormancy.

Luteinizing hormone-releasing hormone (LH-RH) antagonist Cetrorelix down-regulates the mRNA expression of pituitary receptors for LH-RH by counteracting the stimulatory effect of endogenous LH-RH

The mechanisms through which LH-RH antagonists suppress gonadotroph functions and LH-RH receptor (LH-RH-R) production are incompletely understood. To elucidate these mechanisms, we investigated the effects of Cetrorelix on the mRNA expression of pituitary LH-RH-R and luteinizing hormone (LH) secretion in three experimental systems with different pituitary LH-RH environments. Ovariectomy induced 3.61-fold and 6.34-fold increases in the mRNA expression of pituitary LH-RH-R in rats after 11 and 21 days, respectively. After (5 h) a single injection of 100 μg Cetrorelix, no significant decrease occurred in the mRNA levels of pituitary LH-RH-R in ovariectomized (OVX) rats with high pituitary exposure to LH-RH, but there was a significant 23.2% reduction in cycling rats with normal hypophysial LH-RH environment. Prolonged treatment for 10 days with a Cetrorelix depot formulation releasing 100 μg/day decreased the concentration of mRNA for pituitary LH-RH-R by 72.6% in OVX rats, but only by 32.9% in normal rats. The decline in serum LH was 98.7% in OVX rats and 63.2% in normal rats, resulting in a minimal 0.1–0.2 ng/ml LH concentration in both groups. A continuous exposure of pituitary cells to 100 nM Cetrorelix in the superfusion system, which is devoid of LH-RH, did not cause any significant changes in LH-RH-R mRNA level. These studies demonstrate that prolonged exposure to Cetrorelix in vivo, but not in vitro, down-regulates the mRNA expression of the pituitary receptors for LH-RH. Our findings indicate that LH-RH antagonists exert their inhibitory effects on the gene expression of pituitary LH-RH-R by counteracting the stimulatory effect of endogenous LH-RH.