Effects of certain natural products in adjuvant-induced arthritis

ABSTRACT

The effects of curcumin [80 mg/kg; p.o.] and quercetin [50 mg/kg; p.o.],alone or combined, with diclofenac [2 mg/kg; i.p.] on adjuvant-induced arthritis in rats were studied and compared with diclofenac monotherapy. Experimental arthritis was induced by s.c. injection of 0.4 ml Freund's complete adjuvant [FCA] into the subplanter tissue of the right hind paw of all rats except the normal group [1% tween 80; p.o.]. The test agents were administered daily for 28 days starting from the 1[st] day of adjuvant inoculation. The control arthritic group received the vehicle [1% tween 80; p.o.] daily for the whole experiment period. Assessment of the anti-inflammatory effects of different treatments was done by measurement of paw volume before FCA injection and at different time intervals, for 28 days, thereafter using water plethysmometer. Collection of blood samples was carried out after the last paw measurement [day 28]. They were used for determination of serum lactate dehydrogenase [LDH] activity and levels of serum total antioxidants, tumor necrosis factor-alpha [TNF-alpha], interleukin-1 beta [IL-1 beta], calcium [Ca[2+]] and nitrite, a stable metabolite of nitric oxide [NO] which reflects its level. In addition, the level of thiobarbituric acid reactive substances [TBARS], as an index of lipid peroxidation was also determined. Histopathological examination of paw tissues was also carried out. Injection of FCA into the hind paw of rats induced marked arthritis manifested by paw edema during the 28-day experiment period. Treatment with diclofenac alone markedly inhibited adjuvant-induced arthritis at all the studied time intervals. Curcumin, alone, reduced FCA induced edema at day 19 only and its combination with diclofenac antagonized the anti-inflammatory effect of the latter at all the studied time intervals. Quercetin, on the other hand, reduced edema during the chronic phase of arthritis at days 19 and 28 and its combination with diclofenac antagonized the anti-inflammatory effect of the latter at day 11 only. FCA resulted in increased levels of serum TBARS, TNF-alpha, IL-1beta and nitrite as well as increased serum LDH activity. Whereas, no significant changes on serum total antioxidants or Ca[2+] levels were noted. Treatments with curcumin or quercetin alone or combined with diclofenac attenuated most of the biochemical changes elicited by FCA. Histopathological examination of paw tissues showed marked vacuolar degeneration and degradation of articular surfaces by FCA injection. Diclofenac and curcumin, alone or combined together, markedly attenuated FCA-induced histopathological changes. On the other hand, quercetin alone or in combination with diclofenac was less protective. In conclusion, the effect of diclofenac monotherapy was still superior compared to curcumin and quercetin. Effects of curcumin and quercetin seem to be mediated through influences on production of pro-inflammatory cytokines, NO level as well as lipid peroxidation