Effect of Tempol on Renal Cyclooxygenase Expression and Activity in Experimental Diabetes in the Rat

Abstract

Renal cyclooxygenase (COX)-2 expression is increased in the streptozotocin (STZ)-diabetic rat and is associated with enhanced renal prostaglandin release in response to arachidonic acid (AA). Endoperoxide-mediated vasoconstrictor responses to AA were also enhanced in the diabetic rat kidney. Because oxidative stress is increased in diabetes and has been shown to induce COX-2, we assessed its contribution to prostaglandin release by treating diabetic rats with tempol (120 mg/kg/day) for 28 days. Release of AA-stimulated prostaglandins PGE 2 and 6-ketoPGF 1␣ from the isolated perfused kidney was used as an index of COX activity, and Western analysis was used to determine COX-2 protein expression. In untreated diabetic rats, the release of prostaglandins in response to AA was markedly enhanced; the increase in release of both 6-ketoPGF 1␣ and PGE 2 after AA was twice that in control rats. Renal cortical COX-2 expression in diabetic rats was 3-fold that of control rats. Tempol treatment reduced the AA-stimulated release of prostaglandins to levels seen in control rats; this was associated with reduced expression of COX-2 protein to levels not different from that in control rats. However, the enhanced vasoconstrictor response to AA in diabetic rats was unaffected by tempol treatment but abolished by inhibition of COX-1 with SC58560 [5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-(trifluoromethyl)-1H-pyrazole]. The addition of tempol to the perfusate of kidneys from diabetic and control rats had only a slight effect on prostaglandin release. We conclude that oxidative stress is an integral component of the mechanism involved in the induction of renal COX-2 in diabetes.

Renal protective effect of chronic inhibition of COX-2 with SC-58236 in streptozotocin-diabetic rats

“…The increase in renal prostaglandins was linked to the characteristic hyperfiltration of diabetes by showing that the inhibition of COX with NSAIDs reduced GFR in human and experimental diabetes. Following the recognition of multiple COX isoforms, it was shown that the inducible form, COX-2, which is increased in inflammatory conditions, possibly in response to oxidative stress (18), was upregulated in kidneys of diabetic rats (17,24). Thus we have shown that Tempol treatment of diabetic rats prevented the induction of renal COX-2 (18).…”

“…We confirmed the increase in renal COX-2 in the diabetic rat and showed an association with enhanced prostaglandin release from the perfused kidney challenged with AA, which serves as an index of COX activity but does not distinguish the COX isoforms (24). Nonetheless, our studies have shown that interventions that prevent the upregulation of renal COX-2 in the diabetic rat are, for the most part, associated with a reduction of the exaggerated renal release of prostaglandins in response to AA, suggesting that increased COX-2 expression/activity contributes to the enhanced prostaglandin production in the diabetic rat (2,3,18). Subsequently, the upregulation of renal COX-2 was linked to elevated glomerular filtration rate (GFR) using inhibitors of COX-2 (17).…”

“…Following the recognition of multiple COX isoforms, it was shown that the inducible form, COX-2, which is increased in inflammatory conditions, possibly in response to oxidative stress (18), was upregulated in kidneys of diabetic rats (17,24). Thus we have shown that Tempol treatment of diabetic rats prevented the induction of renal COX-2 (18). Similarly, the inhibition of NO formation in diabetic rats prevented the upregulation of COX-2 (2), suggesting a possible role of peroxynitrite, and our recent study revealed that treatment of diabetic rats with a peroxynitrite decomposition catalyst also prevented the induction of renal COX-2 as well as the increase in creatinine clearance (4).…”

ROS dependence of cyclooxygenase-2 induction in rats subjected to unilateral ureteral obstruction

“…Nevertheless, a previous in vivo study (25) has demonstrated a similar effects of DPI in the attenuation of COX-2 induction during ischemiareperfusion damage in rat stomachs. In addition, Li et al (21) showed that chronic administration of the antioxidant tempol prevented increased renal expression of COX-2 in streptozotocin-induced diabetic rats, indicating that oxidative stress resulted in the induction of COX-2 in diabetes.…”

Effect of Cyclooxygenase-2 Blockade on Renal Hypertrophy Development during Early Diabetes Mellitus

“…Increased secretion of prostacyclin (PGI 2 ) and prostaglandin E 2 (PGE 2 ) at the initial DM stage followed by augmented production of prostaglandin F 2α (PGF 2α ) and thromboxane A 2 (TXA 2 ) in end-stage renal disease, have been demonstrated [18,19]. Studies in isolated perfused kidneys from diabetic rats have shown that the administration of inhibitors that prevent the upregulation of renal COX-2 reduces the exaggerated renal release of PGs in response to arachidonic acid, suggesting that increased COX-2 expression/activity contributes to the enhanced PGs production [19,20]. COX-2 is considered an inducible enzyme and it is upregulated in inflammatory conditions; however, it is also constitutively expressed at specific sites in the kidney and vasculature and there is evidence that COX-2 is the enzyme responsible for vascular prostacyclin synthesis [17].…”