No abstract

Cyclooxygenase (COX) exists in 2 related but unique isoforms: one is constitutive (COX-1) and functions in normal cell physiology, and the other is inducible (COX-2) and is expressed in response to inflammatory stimuli. Nonsteroidal antiinflammatory drugs (NSAIDs) cause renal toxicity following inhibition of renal cyclooxygenases. Humans and animals exhibit differences in susceptibility to NSAID-related renal toxicity, which may be associated with differences in expression of 1 or both isoforms of COX in the kidney. In this study, we evaluated COX-1 and COX-2 expression in the kidneys of mixed-breed dogs, Sprague-Dawley rats, cynomolgus monkeys, and humans. In addition, the effect of volume depletion on renal COX expression was investigated in rats, dogs, and monkeys. COX expression was evaluated using 1 or more of the following procedures: reverse transcriptase polymerase chain reaction, in situ hybridization, and immunohistochemistry. We demonstrated that both COX isoforms are expressed in the kidneys of all species examined, with differences in the localization and level of basal expression. COX-1 is expressed at high levels in the collecting ducts and renal vasculature of all species and in a small number of papillary interstitial cells in rats, monkeys, and humans. Basal levels of COX-2 are present in the maculae densa, thick ascending limbs, and papillary interstitial cells in rats and dogs and in glomerular podocytes and small blood vessels in monkeys and humans. COX-2 expression is markedly increased in volume-depleted rats and dogs but not monkeys. These results indicate that significant interspecies differences exist in the presence and distribution of COX isoforms, which may help explain the difference in species susceptibility to NSAID-related renal toxicity.

The discovery of a second isoform of cyclooxygenase (COX) led to the search for compounds that could selectively inhibit COX-2 in humans while sparing prostaglandin formation from COX-1. Celecoxib and rofecoxib were among the molecules developed from these efforts. We report here the pharmacological properties of a third selective COX-2 inhibitor, valdecoxib, which is the most potent and in vitro selective of the marketed COX-2 inhibitors that we have studied. Recombinant human COX-1 and COX-2 were used to screen for new highly potent and in vitro selective COX-2 inhibitors and compare kinetic mechanisms of binding and enzyme inhibition with other COX inhibitors. Valdecoxib potently inhibits recombinant COX-2, with an IC 50 of 0.005 M; this compares with IC 50 values of 0.05 M for celecoxib, 0.5 M for rofecoxib, and 5 M for etoricoxib. Unique binding interactions of valdecoxib with COX-2 translate into a fast rate of inactivation of COX-2 (110,000 M/s compared with 7000 M/s for rofecoxib and 80 M/s for etoricoxib). The overall saturation binding affinity for COX-2 of valdecoxib is 2.6 nM (compared with 1.6 nM for celecoxib, 51 nM for rofecoxib, and 260 nM for etoricoxib), with a slow off-rate (t 1/2 ϳ98 min). Valdecoxib inhibits COX-1 in a competitive fashion only at very high concentrations (IC 50 ϭ 150 M). Collectively, these data provide a mechanistic basis for the potency and in vitro selectivity of valdecoxib for COX-2. Valdecoxib showed similar activity in the human whole-blood COX assay (COX-2 IC 50 ϭ 0.24 M; COX-1 IC 50 ϭ 21.9 M). We also determined whether this in vitro potency and selectivity translated to significant potency in vivo. In rats, valdecoxib demonstrated marked potency in acute and chronic models of inflammation (air pouch ED 50 ϭ 0.06 mg/kg; paw edema ED 50 ϭ 5.9 mg/kg; adjuvant arthritis ED 50 ϭ 0.03 mg/kg). In these same animals, COX-1 was spared at doses greater than 200 mg/kg. These data provide a basis for the observed potent anti-inflammatory activity of valdecoxib in humans.

to support physiologic functions, including gastric muco-Cyclooxygenase (COX) exists as two unique isoforms (that is, sal defense and platelet aggregation. The COX-2 isoform COX-1 and COX-2) which are poorly understood with regard also is constitutive in some tissues, but unlike COX-1, to their roles in renal function. The renal effects of conventional this isozyme is markedly induced by bacterial endotoxnon-steroidal anti-inflammatory drugs (NSAIDs) are believed to ins, cytokines and growth factors, and catalyzes the synresult from the inhibition of one or both isoforms. Drugs that selectively inhibit COX-2 provide useful pharmacological tools thesis of pro-inflammatory PGs. for discerning the effects associated with the inhibition of the The antagonism of inflammation and pain by NSAIDs individual isoforms, and may help clarify the renal roles of COX-1 is believed to result from the inhibition of COX-2, while and COX-2. This review summarizes the current data on the the antagonism of gastric mucosal defense and platelet agrenal expression of COX isoforms and their potential roles in gregation are the results of COX-1 inhibition [5-7]. Clinirenal function, and reviews the studies that have attempted to correlate renal functional changes with selective isoform cal doses of NSAIDs non-selectively inhibit COX-1 and inhibition. Since there are significant differences in the expres-COX-2 [8-13]. Thus, therapeutic use of these rather usesion of COX isoforms in the kidneys of laboratory animals and ful drugs is limited by significant clinical toxicity, includhumans, this review also examines the correlation of the results ing gastrointestinal (GI) ulceration, perforation, obstrucof COX inhibition in experimental studies in laboratory anition, and bleeding. Drugs that selectively inhibit COX-2 mals with clinical data. Because of potential interspecies differences in the roles of COX isoforms in renal function, animal now are available, including celecoxib (Celebrex), valmodels may have limited predictive value for patients, particudecoxib (Bextra), and rofecoxib (Vioxx). These possess larly those with renal risk factors. Accordingly, any uncertainty anti-inflammatory properties similar to naproxen, ibuproconcerning the safety or therapeutic benefit of COX-2-specific fen, and diclofenac; but unlike conventional non-selective drugs in these patient populations will need to be resolved with NSAIDs, they spare COX-1 at clinical doses. This greatly clinical investigations.

Type I diabetes mellitus is an autoimmune disease characterized by the selective destruction of the insulinsecreting ␤-cell found in pancreatic islets of Langerhans. Cytokines such as interleukin-1 (IL-1), interferon-␥ (IFN-␥), and tumor necrosis factor-␣ (TNF-␣) mediate ␤-cell dysfunction and islet degeneration, in part, through the induction of the inducible isoform of nitric-oxide synthase and the production of nitric oxide by ␤-cells. Cytokines also stimulate the expression of the inducible isoform of cyclooxygenase, COX-2, and the production of prostaglandin E 2 (PGE 2 ) by rat and human islets; however, the role of increased COX-2 expression and PGE 2 production in mediating cytokine-induced inhibition of islet metabolic function and viability has been incompletely characterized. In this study, we have shown that treatment of rat islets with IL-1␤ or human islets with a cytokine mixture containing IL-1␤ ؉ IFN-␥ ؎ TNF-␣ stimulates COX-2 expression and PGE 2 formation in a time-dependent manner. Coincubation of rat and human islets with selective COX-2 inhibitors SC-58236 and Celecoxib, respectively, attenuated cytokine-induced PGE 2 formation. However, these inhibitors failed to prevent cytokine-mediated inhibition of insulin secretion or islet degeneration. These findings indicate that selective inhibition of COX-2 activity does not protect rat and human islets from cytokine-induced ␤-cell dysfunction and islet degeneration and, furthermore, that islet production of PGE 2 does not mediate these inhibitory and destructive effects.Type I diabetes mellitus is an autoimmune disease characterized by the selective destruction of insulin-secreting ␤-cells found in pancreatic islets of Langerhans. Although the initiation events leading to the development of disease are not well characterized, inflammatory cytokines and the free radical nitric oxide (NO) 1 appear to play an important role. We and others have shown that treatment of isolated rat and human islets with cytokines such as IL-1, IFN-␥, and TNF-␣ results in the inhibition of glucose-stimulated insulin secretion and islet degeneration. The inhibitory and destructive effects of cytokines on ␤-cell function and islet viability are mediated, in part, through the expression of the inducible form of nitric-oxide synthase (iNOS) and increased production of NO by ␤-cells (1-5). NO inhibits insulin secretion by targeting iron-sulfurcontaining enzymes such as aconitase and electron-transporting chain complexes I and II, resulting in decreased oxidative phosphorylation and ATP production (6 -9). Evidence in support of a role for NO in mediating cytokine-induced islet damage includes the protective actions of iNOS inhibitors aminoguanidine (AG) or N G -monomethyl L-arginine (L-NMMA) on cytokine-induced inhibition of insulin secretion and islet degeneration (2, 4, 10, 11), as well as the lack of an inhibitory action of cytokines on glucose-stimulated insulin secretion in islets isolated from iNOS-deficient mice (12). These results suggest that inflammatory cytokines m...