Effect of a Single-dose Denosumab on Semen Quality in Infertile Men (FITMI): A Randomized Controlled Trial

Background and rationale Infertility is a common problem globally and impaired semen quality is responsible for up to 40% of all cases. Despite the high prevalence there are currently only very limited treatment options to improve semen quality for infertile men. Instead, almost all infertile couples are treated with inseminations or assisted reproductive techniques (ARTs) independently of the etiology of infertility. ARTs are very successful but expensive and associated with a significant treatment burden of the female partner due to the invasive methodology and the need for hormonal treatment often for several months.

RANKL is a ligand for the receptor activator of nuclear factor κB (RANK), and their pathway plays a prominent role in the regulation of bone metabolism. The binding of RANKL to RANK on osteoclast precursors induces osteoclast maturation and activation, thereby stimulating bone resorption, and regulates cell cycle i.e., proliferation, differentiation, and apoptosis. Osteoprotegerin (OPG) is a secreted decoy receptor that controls RANKL-RANK interaction by binding RANKL and inhibits activation of RANK and preventing osteoclast differentiation and activation.

Denosumab, a drug used in millions of patients worldwide under trade names Prolia® and Xgeva®, inhibits the RANKL pathway and is used to treat osteoporosis and bone metastases. The drug's mechanism of action inhibits RANKL and thus inhibits bone resorption through reduced osteoclast activation. This reduces the loss of bone mineral density (BMD), which reduces the risk of bone loss and thereby the risk of fracture and osteoporosis. Denosumab has been shown in several clinical studies to be a safe and effective drug in both women and men and has been in clinical use in both sexes for many years. As Denosumab has a teratogenic effect, pharmacokinetic studies in both monkeys and healthy men were performed before approval of the drug as a treatment for osteoporosis in men. These studies showed that Denosumab concentration in semen does not pose a risk to the fetus during sexual intercourse with the pregnant woman and therefore is safe to use for the suggested infertility indication as there is no risk of fetal transmission.

Our research Recently, the research group has demonstrated the role of vitamin D in male reproduction by using functional animal studies supported by a randomized clinical trial. These investigations revealed that several bone factors such as Runx2, Osterix, FGF23, and in particular RANKL are expressed in the testis. The investigators found expression of RANKL in Sertoli cells, the receptor RANK in the testicular germ cells, and OPG in the peritubular cells in mice and human tissue. The presence of the RANKL system in these distinct testicular cell types indicates a possible direct effect on spermatogenesis.

The investigators therefore examined the effect of Denosumab in human testicular germ cell lines as well as in human testicular tissue ex vivo "hanging drop" cultures. Denosumab treatment in both cases increased the proliferation of the germinal cells. These studies confirmed that Denosumab treatment in vitro has a possibly beneficial effect on sperm production by reducing apoptosis in the germ cells. To further investigate this in vivo, the investigators injected the natural RANKL inhibitor OPG into mice daily for 14 days and compared them with their controls. Here, a a significantly increased testicular weight, increased thickness of germinal cell epithelium, and markedly higher sperm production was found. This prompted a human pilot study of 12 infertile men who besides infertility were healthy young men under 40 years of age. The men were treated with one 60 mg dosage of Denosumab subcutaneous (s.c.). The pilot study showed that as a group, the men's sperm production had increased 80 days after treatment. However, there was a large variation and 60% of men experienced an increase between 100-600% in sperm counts. The rest of the participants did not appear to benefit from the treatment. To validate putative biomarkers, a placebo controlled RCT was conducted in 100 infertile men with severe male infertility (Denosumab and Male Infertility: a RCT. ClinicalTrials.gov Identifier: NCT03030196). In this study, active treatment with 60 mg Denosumab s.c. was compared to placebo treatment. Importantly, there were no serious adverse reactions reported, nor severe hypocalcemia, nor abortions in the female partners of the patients. Data from this study has not been published yet.