The doses of raloxifene and oestradiol were chosen for their equipotent effects on BMD, and therefore it is possible that a higher dose of raloxifene could have activated the ERE to the same extent as oestradiol. The present study is the first to analyse the effects of CAIA on BMD and cartilage and bone remodelling. Sham-operated mice with CAIA, non-arthritic Ferroptosis phosphorylation OVX mice and OVX mice with CAIA displayed the same trabecular BMD. These results were unexpected, as

both OVX and CIA have been shown to induce bone loss separately and additively [9]. All mice had received an intraperitoneal injection of LPS 1 week prior to termination. LPS is well known to induce osteoporosis quickly [38,39]. Because we did not find any difference in BMD between the vehicle-treated mice that had received collagen-antibodies and the non-arthritic controls, osteoporosis may have been induced by the administration of LPS. Also, the duration of the experiment was 2 weeks after administration of antibodies, and this short observation time may conceal pro-osteoporotic properties of CAIA. This issue needs to be studied further. Interestingly, raloxifene treatment resulted in increased BMD, although it did not affect the severity of the arthritic disease, suggesting anti-osteoporotic properties by raloxifene during LPS-induced inflammation. In addition, raloxifene increased bone FK228 formation

as measured by serum levels of osteocalcin. This is in accordance with our previous results [6]. The histological Molecular motor destruction found in paw sections was not as severe as in some previous studies [10,12], and this was due most probably to the short experiment protocol (2 weeks of disease). Serum levels of COMP reflect the degree of cartilage destruction during arthritic disease [27–29]. To our knowledge, this has not been investigated previously in CAIA. The arthritic disease resulted in a significant increase in COMP levels in OVX mice compared to non-arthritic controls

(P < 0·001). As both groups had received an injection of LPS, administration of anti-CII antibodies contributed to the cartilage destruction. Indeed, it has been shown previously in vitro that anti-collagen II antibodies are pathogenic to chondrocytes, affecting both cartilage formation [40] and cartilage explants [41]. Administration of oestradiol and sham operation lowered the COMP levels compared to arthritic OVX controls, indicating protection of cartilage by both exogenous and endogenous oestradiol. In contrast, raloxifene did not influence the serum levels of COMP or the destruction of cartilage. It has been reported previously that raloxifene does not hamper granulocyte-mediated inflammation, whereas oestradiol does [19]. This could explain the difference between raloxifene and oestradiol treatment, as CII antibodies have been shown to mediate cartilage destruction even in the absence of inflammation [42,43].