**3. Discussion**

Considering the global health threat posed by kidney disease burden, a search for new nephroprotective drugs from our local flora could prove a powerful strategy to respond to this health threat. Potential of plant-derived triterpenes as new nephroprotective agents has been demonstrated using various animal models [13,19].

This study investigated the antihyperuricemic and nephroprotective potential of RA-3, a lanosteryl triterpene from *P. longifolia*. The increased serum levels of these biomarkers along with a robust display of glomerular congestion and epithelial degeneration in the kidney samples from the MC group confirmed the induction of hyperuricemia and nephrotoxicity in the rats. It was interesting to observe the significant decrease in serum levels of these biomarkers (UA, BUN, Cr) with improved histomorphology of the kidney tissues from the rats treated with RA-3 at both concentrations. The results served as an indication of the hypouricemic and nephroprotective potential of the triterpene. Substantial experimental evidence has also demonstrated the significant nephroprotective properties of some other plant-derived triterpenes [13,19,20].

While renal toxicity of gentamicin is strongly linked to oxidative stress [3], adenine's toxicity is associated with renal tubular obstruction and hyperuricemic e ffect [21]. Hyperuricemia is considered an independent risk factor of kidney disease [5]. Blood UA levels are physiologically regulated by XO activity, an enzyme that catalyzes the formation of UA from xanthine. The XO catalyzed reaction also generates reactive oxygen species (ROS) which can trigger inflammatory reactions and consequent tissue damage [22]. The reduced serum levels of UA along with decreased XO activity in the triterpene treated groups supported the antihyperuricemic e ffect of RA-3. These observations were also similar to those of the group treated with allopurinol, a standard hyporuricemic drug. Experimental evidence has shown that antihyperuricemic compounds do possess nephroprotective e ffect [19,23].

Hyperuricemia is known to cause, among others, vascular smooth muscle cell proliferation, endothelial dysfunction, and increased IL-6 synthesis, all of which may contribute to the progression of chronic kidney disease [9]. Though there was no significant di fference between the model control and the treated nephrotoxic groups, the relatively lower serum levels of IL-6 in the RA-3 and allopurinol treated groups were observed. This could further be correlated with the suppressed XO activity in these groups. Since XO activity is known to trigger inflammatory reactions and consequent tissue damage [22], the observed results further indicated the tissue protective potential of the triterpene.

It has further been demonstrated that even mild elevations in serum UA can cause hypertension and renal microvascular disease without causing urate crystal deposition in kidneys [24]. The hypertensive effect of elevated serum UA has been associated with activation of the renin-angiotensin system (RAS) [7]. The vasoconstrictive e ffect of RAS is mediated by ACE, an enzyme that catalyzes conversion of angiotensin I to a bioactive angiotensin II. The observed lower ACE activity in the lanosteryl triterpene treated groups further suggests the potential role of RA-3 in managemen<sup>t</sup> of hypertension, another important risk factor of nephropathy [25]. The role of ACE inhibitors in prevention of renal function deterioration is well-established [26,27]. The hypouricemic e ffect exhibited by RA-3 may also be vital in the prevention of other ailments known to be associated with hyperuricemia [28–30].

Furthermore, despite the ROS-mediated renal toxicity of gentamicin and adenine, the improved serum total antioxidant status, GSH and SOD along with reduced MDA content in the rats treated with RA-3 indicated its tissue protective potential against oxidative damage. It is interesting to note from these results that the ability of RA-3 to enhance endogenous antioxidant defense while inhibiting lipid peroxidation has previously been demonstrated in streptozotocin (STZ)-induced diabetes and isoproterenol (ISO)-induced myocardial injury in rat models [15,16]. It is also worth noting that similar to gentamicin induced renal tubular toxicity, the necrotic toxicity of STZ and ISO are also associated with oxidative stress [31,32]. Since inflammation and oxidative tissue damage are common culprits in various pathophysiologies including nephropathy, nephroprotective drugs with both anti-inflammatory and antioxidant properties are highly desired. The nephroprotective potential of most medicinal plant extracts and their derived compounds has been associated with their antioxidant and anti-inflammatory activities [11,33].
