Effect of estrogen replacement therapy on arthritis and bone mineral density in estrogen-replete rats with collagen-induced arthritis

The Use of Collagen-Induced Arthritis Animal Model on Studying Bone Metabolism

CIA is a well-studied animal model of autoimmune arthritis. It resembles rheumatoid arthritis as far as histopathological changes and molecular pathogenesis are concerned. CIA is induced by immunization with collagen type II in susceptible strains. The purpose of this review is to assess the use of CIA animal model on bone metabolism and the potential therapeutic agents that could reverse this effect. A database search from their inception to 2019 was conducted to identify experimental animal studies pertinent to CIA model and bone examination. Studies including ovariectomy or without a direct comparison between control and CIA groups were excluded. Forty-eight articles were considered suitable for inclusion. Imaging techniques, biomechanical analysis, histopathological studies, and molecular biology techniques were employed. A decrease in bone mineral density in CII arthritic animals was established. Bone loss was either periarticular, generalized or both. Although trabecular bone loss was clear, the effect on cortical bone is yet to be determined. The proposed mechanism is an imbalance between bone formation and resorption as a result of osteoclast activation. The signal pathways implicated appear to be the RANKL/RANK/OPG and the Wnt pathway. Many therapeutic targets were investigated with promising results.

Anti-Inflammatory Effects of the Essential Oils of Ginger (Zingiber officinale Roscoe) in Experimental Rheumatoid Arthritis

Ginger and its extracts have been used traditionally as anti-inflammatory remedies, with a particular focus on the medicinal properties of its phenolic secondary metabolites, the gingerols. Consistent with these uses, potent anti-arthritic effects of gingerol-containing extracts were previously demonstrated by our laboratory using an experimental model of rheumatoid arthritis, streptococcal cell wall (SCW)-induced arthritis. In this study, anti-inflammatory effects of ginger's other secondary metabolites, the essential oils (GEO), which contain terpenes with reported phytoestrogenic activity, were assessed in female Lewis rats with SCW-induced arthritis. GEO (28 mg/kg/d ip) prevented chronic joint inflammation, but altered neither the initial acute phase of joint swelling nor granuloma formation at sites of SCW deposition in liver. Pharmacologic doses of 17-β estradiol (200 or 600 μg/kg/d sc) elicited the same pattern of anti-inflammatory activity, suggesting that GEO could be acting as a phytoestrogen. However, contrary to this hypothesis, GEO had no in vivo effect on classic estrogen target organs, such as uterus or bone. En toto, these results suggest that ginger's anti-inflammatory properties are not limited to the frequently studied phenolics, but may be attributable to the combined effects of both secondary metabolites, the pungent-tasting gingerols and as well as its aromatic essential oils.

The pathogenesis of osteoarthritis involves bone, cartilage and synovial inflammation: may estrogen be a magic bullet?

The female predominance of polyarticular osteoarthritis (OA), and in particular the marked increase of OA in women after the menopause points to a likely involvement of female sex hormones in the maintenance of cartilage homeostasis. This perception has inspired many research groups to investigate the role of estrogens in the modulation of cartilage homeostasis with the ultimate aim to clarify whether estrogen replacement therapy (ERT) could provide benefits in preventing the rapid rise in the prevalence of OA in postmenopausal women. The effects of ERT and selective estrogen-receptor modulators on the joint in various experimental models have been investigated. Clinically, the effects of estrogens have been evaluated by post hoc analysis in clinical trials using biochemical markers of cartilage and bone degradation. Lastly, the Women's Health Initiative trial (WHI) investigated the effects of estrogens on the joint and joint replacements. Even though the exact mode of action still needs to be elucidated, the effect involves both direct and indirect mechanisms on the whole joint pathophysiology. Several animal models have demonstrated structural benefits of estrogens, as well as significant effects on joint inflammation. This is in complete alignment with clinical data using biochemical markers of joint degradation which demonstrated approximately 50% inhibition of cartilage destruction. These finding were recently validated in WHI, where women taking estrogens had significantly less joint replacement. In conclusion, the pleiotropic effect of estrogens on several different tissues may match the complicated aetiology of OA in some important aspects.