Thiazolidine diones, specific ligands of the nuclear receptor retinoid Z receptor/retinoid acid receptor-related orphan receptor alpha with potent antiarthritic activity.

Rat adjuvant arthritis is a chronic T cell-dependent autoimmune disease with many similarities to rheumatoid arthritis. We have identified a class of thiazolidine diones with high potency in suppressing chronic inflammation and joint destruction in this experimental model. The lead compound CGP 52608 (1-(3-allyl-4-oxothiazolidine-2-ylidene)-4-methylthiosemicarbazone) exhibits antiarthritic activity at daily oral doses between 0.01 and 1 mg/kg and was shown to specifically activate the retinoid Z receptor/retinoid acid receptor-related orphan receptor alpha (RZR/RORalpha) in low nanomolar concentrations. This receptor is a novel member of the superfamily of ligand-inducible transcription factors, and we have recently identified the pineal gland hormone melatonin as a natural ligand. Structure-activity relationship studies with 13 closely related analogues of CGP 52608 revealed a striking correlation between RZR/RORalpha activation and antiarthritic activity. We therefore suggest that nuclear signaling via RZR/RORalpha is a key mechanism in mediating the antiarthritic effects of these thiazolidine diones and may open a novel therapeutic approach for the treatment of rheumatoid arthritis and other autoimmune diseases. The existence of a nuclear melatonin receptor may lead to a better understanding of the immunomodulatory actions of melatonin.

The analgesic drug buprenorphine inhibits osteoclastic bone resorption in vitro, but is proinflammatory in rat adjuvant arthritis.

We have examined the effect of the micro-opioid analgesic buprenorphine on osteoclastic bone resorption in vitro and in the rat adjuvant arthritis model. In the bone slice assay buprenorphine inhibited osteoclastic bone resorption with an IC50 of 1 microM. This effect was not mimicked by the micro-opioid agonist ([D-Ala, N-Me-Phe, Gly-ol]-enkephalin and was not prevented by the micro-opioid antagonist naloxone. Since other agents that inhibit osteoclastic bone resorption, such as bisphosphonates and calcitonin prevent bone erosion in the rat adjuvant arthritis model, we also examined the effect of buprenorphine in this model. Surprisingly, buprenorphine exacerbated inflammation measured by paw volume and increased joint destruction assessed by X-ray scores, in the injected paws and particularly in the non-injected paws. These studies also show that attempts to ameliorate animal suffering in this chronic model by using centrally acting analgesics such as buprenorphine may lead to complications in interpreting screening results obtained with novel, potential anti-arthritic compounds.

The influence of anti-rheumatic drugs on hepatic mRNA levels of acute-phase proteins in rats with adjuvant arthritis.

Using specific cDNA probes, we have investigated drug-induced changes in hepatic mRNA levels of the major acute-phase proteins (APP) fibrinogen, alpha 2-macroglobulin (alpha 2-MG), albumin and alpha 1-acid glycoprotein (alpha 1-AGP) in male Lewis rats with adjuvant arthritis. Test compounds were given orally from day 0 to 20 and hepatic mRNA analysis was performed at day 21. Prednisolone (1, 3, 10 mg/kg), Cyclosporine A (1, 3, 10 mg/kg) and cyclophosphamide (3 mg/kg) dose-dependently normalized hepatic mRNA levels of all four APP. Equipotent anti-inflammatory doses of indomethacin (0.3, 1 mg/kg) significantly downregulated alpha 2-MG mRNA levels but were much less effective in influencing albumin and alpha 1-AGP mRNA levels and even slightly increased hepatic fibrinogen mRNA levels. These results suggest that cytokine over-production, which is thought to be responsible for the acute-phase response in rats with adjuvant arthritis, can be effectively downregulated by immunosuppressive drugs, but is distinctly less affected by the cyclooxygenase inhibitor indomethacin.

Changes in hepatic mRNA levels of acute phase proteins during rat adjuvant arthritis.

Using specific cDNA probes, we have investigated changes in hepatic mRNA concentrations of the major acute phase proteins fibrinogen, alpha 2-macroglobulin (alpha 2-MG), albumin and alpha 1-acid glycoprotein (alpha 1-AGP) during developing adjuvant arthritis in Lewis rats. Continuously increasing levels in the mRNA of the positive reactants beta-fibrinogen, alpha 2-MG and alpha 1-AGP were found during developing disease with peak levels from day 15 to 21, whereas mRNA concentrations of the negative reactant albumin decreased, reaching their lowest levels on day 11 to 15. As early as 4 days after arthritis induction, the hepatic mRNA levels of beta-fibrinogen, alpha 1-AGP and albumin were distinctly different from control values. The most dramatic changes in the hepatic mRNA levels and plasma concentrations of acute phase reactants were seen between days 11 and 21. These results indicate that overproduction of the major inflammatory cytokines IL-1, TNF-alpha and IL-6, which are now felt to be largely responsible for the acute phase response in the rat, is an early event during adjuvant arthritis and that the highest amounts are produced during the inflammatory phase of the disease. mRNA changes in the acute phase proteins alpha 1-AGP and albumin, which are mainly regulated by IL-1/TNF alpha, were more pronounced than those of alpha 2-MG and beta-fibrinogen, which are predominantly controlled by IL-6.(ABSTRACT TRUNCATED AT 250 WORDS)