Androgens are well known for their many functions in promoting sexual differentiation and the induction of the male phenotype. In the male, the two endogenous androgens most active in promoting these effects are testosterone and nonaromatizable 5a-dihydrotestosterone (DHT). They also play important roles in the regulation of bone metabolism. The direct effects of androgen on bone cells is suggested by the presence of androgen receptors (AR) on several human and rat established osteoblast cell lines as well as normal human osteoblast cells (HOB).1) Androgens increase rates of cellular proliferation and differentiation of osteoblasts, increase TGF-b levels, increase production of matrix proteins and inhibit osteoclast function.2,3) A role of androgens in skeletal regulation is substantiated by numerous studies in human and rodents, demonstrating that chemical or surgical castration, as well as untreated hypogonadism in men and androgen deficiency in women with hypopituitarism, lead to accelerated bone loss.2,4-7) Importantly, the deleterious effects of these conditions on bone can be reversed by treatment with androgens.One apparently unique effect of androgens is to increase periosteal bone formation in cortical bone, while estrogens depress it.8) This reflects a major gender difference in bone size, which is one of important factors determining the bone strength. A number of studies provide the proof of principle that androgens are osteoanabolic in rodents, women and men. Nonaromatizable DHT increased cortical bone volume and periosteal bone formation rates when administrated to ovariectomized rats.9) The synthetic anabolic steroids, such as nandrolone decanoate or stanozolol, have been shown to increase bone mass in postmenopausal women, possibly via stimulation of bone formation.10,11) Beneficial anabolic effects of androgens on bone in postmenopausal osteoporosis are well-documented in recent studies using combined testosterone and estrogen administration.12,13) On the other hand, bone resorption inhibitors such as estrogens, bisphosphonates, selective estrogen receptor modulators (SERMs) and calcitonin, which are still first line of treatment/prevention of osteoporosis, are not sufficient to restore bone mass for patients who have already lost a significant amount of bone. In addition, bone turnover rate differs from site to site; higher in the cancellous bone of vertebrae than in the cortical bone of the long bones. Therefore, osteoanabolic agents, which increase cortical/periosteal bone formation and bone mass of long bones, would address unmet need in the treatment of osteoporosis especially for patients with high risk of fractures. The osteoanabolic agents also complement the bone resorption inhibitors that target the cancellous bones, leading to a biomechanically favorable bone structure. 14)Despite the beneficial effects of androgens in therapies for osteoporosis, hypogonadism and other androgen deficient diseases, clinical use of them has been limited because of the undesirable virilizing (acne, hirsu...

Bone diseases such as osteoporosis and osteoarthritis are regarded as age-associated diseases, and occur in a significantly increasing number of patients, but the underlying mechanisms of these age-associated bone diseases are not yet clear. We have established a transgenic mouse line by an insertion mutation. These mice exhibit many features related to precocious aging. Homozygote mutant mice, which lack expression of the newly identified targeted gene, klotho (kl), exhibit atherosclerosis, emphysema, hypogonadism and calcification of soft tissues, and die within 3-4 months. We describe here the radiological and histological characteristics of the skeletal abnormalities in the bones of the mice with a mutation in the kl gene locus. In heterozygous mice (+/kl), the skeletal patterns and structures remain normal and most features are similar to those in the wild-type, whereas histological examinations of homozygous mice (kl/kl) show abnormal elongation of the trabecular bone(s) in the epiphyses of long bones. As with their long bones, on radiographic examination the mid parts of the vertebral bones of these mice show less radiopacity compared with the wild-type, again resembling human vertebrae of osteoporotic patients. The elongation of the trabecular bones results in high radiopacity on both ends of each of the vertebrae, and in the epiphyses of the long bones. Cancellous bone volume in the epiphyses of the homozygote mice is three times that of the wild-type mice. The kl/kl mice are smaller than the wild-type litter mates and hence the size of their long bones is less than that of the wild-type litter mates. These observations, and the osteopenia in the vertebrae and long bones in these mice, suggest the presence of abnormality in bone metabolism, the elongation of the trabecular bone apparently resulting from the relatively low levels of bone resorption. Therefore, the kl/kl mutant mice could serve as an interesting tool to study the effects of the lack of the product of the new gene, klotho, on bone metabolism.

We have studied non-steroidal selective androgen receptor modulators (SARMs) to develop anti-osteoporosis drugs for males and females. Many SARMs have been studied for their anabolic effects on bone or muscle with reduced virilizing effects in male animals. However, the tissue selectivities of these agents in female animals have not been fully evaluated. We evaluated the novel SARM S-101479 from tetrahydroquinoline libraries in ovariectomized (OVX) rats. S-101479 preferentially bound to the androgen receptor with nanomolar affinity among nuclear receptors. It increased the bone mineral density (BMD) of femurs and diminished the effects on the uterus and clitoral gland in OVX rats. We then compared the effect of S-101479 on bone with those of commercial anti-osteoporosis drugs such as alendronate, raloxifene, and teriparatide. Furthermore, we evaluated the effects of combination treatments with these agents in OVX rats. After 16-week treatment, all agents significantly increased BMD, but the magnitude of bone mineral content (BMC) and/or bone size (projected bone area) were different. Alendronate, raloxifene, and teriparatide maintained BMC and bone size in this experimental dose. Only S-101479 increased BMC with bone size on single treatments. In combination treatment, S-101479 significantly increased BMC and bone size compared with single treatments of other agents. S-101479, like natural androgen, may have showed periosteal bone formation of the cortical area and indicated additive effects with commercial anti-osteoporosis drugs. These results indicate that S-101479 may be a useful anti-osteoporosis drug, particularly for patients with established severe osteoporosis.Key words selective androgen receptor modulator; bone anabolic; additive effect Androgens are known to have beneficial anabolic effects on various tissues such as bone, muscle, and red blood cells (RBCs).1-4) However, the clinical use of androgens has been limited because of their undesirable virilizing and metabolic actions. Their effect on the prostate gland is an extremely serious side effect because the risk of prostate cancer or benign prostate hyperplasia may increase. 5,6) The side effects of androgens are not lethal in women, but many virilizing effects (e.g., hirsutism, voice change, and acne) have been observed. 7,8) Anabolic steroids were developed to reduce the side effects of androgens and treat osteoporosis. However, their actions were not sufficient to reduce virilizing effects, and they exhibited hepatotoxic actions. [9][10][11][12] Recently, the actions of non-steroidal selective androgen receptor modulators (SARMs) have been investigated in many laboratories. [13][14][15][16][17] Typically, they were observed to be more tissue-selective than anabolic steroids and were orally available in preclinical models. We have focused on bone anabolic SARMs to develop anti-osteoporosis agents without serious virilizing effects.