Comparative analysis of pharmacologic and/or genetic disruption of cyclooxygenase-1 and cyclooxygenase-2 function in female reproduction in mice.

Cyclooxygenase (COX)-derived prostaglandins are critical in female reproduction. Gene targeting studies show that ovulation, fertilization, implantation, and decidualization are defective in COX-2 deficient mice. We used genetic and pharmacologic approaches to perturb COX function and examine the differential and synergistic effects of inhibition of COX-1, COX-2, or of both isoforms on reproductive outcomes during early pregnancy in mice. The results demonstrate that simultaneous inhibition of COX-1 and COX-2 produces more severe effects on early pregnancy events than inhibition of either isoform alone. The effects of pharmacological inhibition of COX-2 on female reproductive functions were less severe than the null mutation of the COX-2 gene. A combined approach showed that COX-2 inhibition in COX-1(-/-) mice induced complete reproductive failure, suggesting a lack of alternative sources of prostaglandin synthesis. This investigation raises caution regarding the indiscriminate use of COX inhibitors and shows for the first time the distinct and overlapping pathways of the cyclooxygenase systems in female reproduction.

Cox-2-specific inhibitors: definition of a new therapeutic concept.

Nonsteroidal anti-inflammatory drugs have been a mainstay in the treatment of inflammatory diseases such as rheumatoid arthritis. However, these agents can result in severe and occasionally life-threatening adverse effects that can limit therapeutic benefit. Progress toward safer anti-inflammatory therapy was aided by the discovery that cyclooxygenase (COX) exists as two isozymes, COX-1 and COX-2. Both isozymes form prostaglandins that support physiologic functions; however, the formation of proinflammatory prostaglandins is catalyzed by COX-2. Inhibition of COX-2 accounts for the anti-inflammatory and analgesic action of NSAIDs; however, concurrent inhibition of COX-1 inhibits prostaglandin-dependent mechanisms such as gastroduodenal mucosal defense and platelet aggregation. This inhibition is the basis of the gastrointestinal toxicity and bleeding characteristic of these drugs. These findings led to the hypothesis that agents that selectively inhibit COX-2 would possess anti-inflammatory and analgesic action but would spare COX-1, thereby avoiding adverse effects in the gastrointestinal tract and platelets. Selective COX-2 inhibitors are now available. The novelty of these agents has raised questions in the medical community as to what constitutes selectivity for COX-2. This review outlines the criteria that must be met to characterize a compound as COX-2-specific. Clinical evidence of clear improvement in gastrointestinal tolerability and safety must be demonstrated in addition to complementary evidence of COX-2 selectivity obtained from enzyme, biochemical, and clinical pharmacology evaluations.

Pharmacokinetics of celecoxib after oral administration in dogs and humans: effect of food and site of absorption.

Celecoxib pharmacokinetics was evaluated after single and multiple oral dosing; after dosing in a solution and as a solid; with and without food; and after administration into different sites of the GI tract using dog. After oral dosing in a solution, celecoxib was rapidly absorbed and reached maximum concentrations by 1 h; absorption was delayed another 1 to 2 h when administered as a solid. The absolute bioavailability of celecoxib was higher when given as a solution (64--88%) compared with capsule (22--40%). The absorption of celecoxib given in a capsule was delayed by food, although systemic exposure increased by 3- to 5-fold. The systemic availability of celecoxib given intragastrically in solution was similar to that obtained following direct instillation into the duodenum, jejunum, or colon through a chronic intestinal access port. Collectively, these data suggest that celecoxib is a highly permeable drug that can be absorbed throughout the GI tract and that dissolution may be a rate-limiting factor for absorption from solid dosage forms. Unlike dogs, celecoxib given to humans with a high fat meal exhibits only a slight increase in AUC(0--infinity) (11%) that is not clinically significant with regard to safety or efficacy. In humans, a lower dose and a longer GI residence time may promote the opportunity for absorption of a poorly soluble drug such as celecoxib that can be absorbed throughout the GI tract. This would minimize the effect of food on absorption; as such, patients with arthritis can be given celecoxib with or without food.

Pharmacokinetics, tissue distribution, metabolism, and excretion of celecoxib in rats.

The pharmacokinetics, tissue distribution, metabolism, and excretion of celecoxib, 4-[5-(4-methylphenyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl] benzenesulfonamide, a cyclooxygenase-2 inhibitor, were investigated in rats. Celecoxib was metabolized extensively after i.v. administration of [(14)C]celecoxib, and elimination of unchanged compound was minor (less than 2%) in male and female rats. The only metabolism of celecoxib observed in rats was via a single oxidative pathway. The methyl group of celecoxib is first oxidized to a hydroxymethyl metabolite, followed by additional oxidation of the hydroxymethyl group to a carboxylic acid metabolite. Glucuronide conjugates of both the hydroxymethyl and carboxylic acid metabolites are formed. Total mean percent recovery of the radioactive dose was about 100% for both the male rat (9.6% in urine; 91.7% in feces) and the female rat (10.6% in urine; 91.3% in feces). After oral administration of [(14)C]celecoxib at doses of 20, 80, and 400 mg/kg, the majority of the radioactivity was excreted in the feces (88-94%) with the remainder of the dose excreted in the urine (7-10%). Both unchanged drug and the carboxylic acid metabolite of celecoxib were the major radioactive components excreted with the amount of celecoxib excreted in the feces increasing with dose. When administered orally, celecoxib was well distributed to the tissues examined with the highest concentrations of radioactivity found in the gastrointestinal tract. Maximal concentration of radioactivity was reached in most all tissues between 1 and 3 h postdose with the half-life paralleling that of plasma, with the exception of the gastrointestinal tract tissues.

Evidence for polymorphism in the canine metabolism of the cyclooxygenase 2 inhibitor, celecoxib.

The pharmacokinetics of celecoxib, a cyclooxygenase-2 inhibitor, was characterized in beagle dogs. Celecoxib is extensively metabolized by dogs to a hydroxymethyl metabolite with subsequent oxidization to the carboxylic acid analog. There are at least two populations of dogs, distinguished by their capacity to eliminate celecoxib from plasma at either a fast or a slow rate after i.v. administration. Within a population of 242 animals, 45.0% were of the EM phenotype, 53.5% were of the PM phenotype, and 1.65% could not be adequately characterized. The mean (+/-S.D.) plasma elimination half-life and clearance of celecoxib were 1.72 +/- 0.79 h and 18.2 +/- 6.4 ml/min/kg for EM dogs and 5.18 +/- 1.29 h and 7.15 +/- 1.41 ml/min/kg for PM dogs. Hepatic microsomes from EM dogs metabolized celecoxib at a higher rate than microsomes from PM dogs. The cDNA for canine cytochrome P-450 (CYP) enzymes, CYP2B11, CYP2C21, CYP2D15, and CYP3A12 were cloned and expressed in sf 9 insect cells. Three new variants of CYP2D15 as well as a novel variant of CYP3A12 were identified. Canine rCYP2D15 and its variants, but not CYP2B11, CYP2C21, and CYP3A12, readily metabolized celecoxib. Quinidine (a specific CYP2D inhibitor) prevented celecoxib metabolism in dog hepatic microsomes, providing evidence of a predominant role for the CYP2D subfamily in canine celecoxib metabolism. However, the lack of a correlation between celecoxib and bufuralol metabolism in hepatic EM or PM microsomes indicates that other CYP subfamilies besides CYP2D may contribute to the polymorphism in canine celecoxib metabolism.

Interspecies differences in renal localization of cyclooxygenase isoforms: implications in nonsteroidal antiinflammatory drug-related nephrotoxicity.

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.

Effect of papillotoxic agents on expression of cyclooxygenase isoforms in the rat kidney.

Inhibition of renal vasodilatory prostaglandins (PGs) and secondary ischemia due to inhibition of cyclooxygenase (COX) activity has been suggested as a possible mechanism for development of analgesic-related renal papillary necrosis (RPN) in rats. Recently, it has been shown that COX exists in two related but unique isoforms, COX-1 and COX-2. It is unclear what potential roles these isoforms play in the maintenance of blood flow in the renal papilla or genesis of RPN. We evaluated the effect of 2 papillotoxic agents, including a nonsteroidal anti-inflammatory drug, indomethacin, and a chemical agent, 2-bromoethanamine hydrobromide (2-BEA), on COX-1 and COX-2 in the renal papilla as a means of assessing what changes occur in the expression of these isoforms during the development of RPN. Female Wistar rats approximately 10-17 wk old were treated with either indomethacin (75 mg/kg, single dose, or 10 mg/kg/day for 5 days) or 2-BEA (100 mg/kg/day for 4 days) to create lesions of RPN. In this study, a single 75-mg/kg dose of indomethacin did not cause light microscopic changes of RPN. However, RPN was observed in animals administered indomethacin at 10 mg/kg/day for 1 wk or 2-BEA for 5 days. The immunohistochemical analyses of kidneys showed that both COX-1 and COX-2 were present in the renal papilla of control rats. In animals treated with indomethacin (75 mg/kg), a slight to moderate decrease in both isoforms was observed in essentially normal renal papillary cells within 2 hr, that was followed by an increase in COX-2 immunoreactivity in the renal papilla, macula densa, and thick ascending limbs (both 10- and 75-mg/kg animals). This COX-2 immunoreactivity was greatest in animals with concomitant indomethacin-induced gastrointestinal injury, suggesting a possible role of inflammatory cytokines in COX-2 induction. No changes in the expression of COX isoforms in the intact papilla occurred as a result of 2-BEA; however, cells undergoing degeneration and necrosis lost immunoreactivity to both COX isoforms. The possible mechanism that leads to an initial decrease in COX immunoreactivity in indomethacin-treated animals is not known; however, a reversible ultrastructural change in the papillary cells cannot be ruled out. This decrease in COX isoforms in the renal papilla may contribute to the development of RPN through the loss of vasodilatory PGs.

The differential effects of hepatotoxicants on the sulfation pathway in rats.

This study characterized the effects of liver damage produced by a variety of hepatotoxicants on several components of the sulfation pathway in rats. Specifically, the concentration of cosubstrate, adenosine 3'-phosphate 5'-phosphosulfate (PAPS), and the hepatic capacity for PAPS synthesis were measured in livers of rats treated with carbon tetrachloride (CCl4), 1,1-dichloroethylene (DCE), alpha-naphthylisothiocyanate (ANIT), aflatoxin B1 (ATX), allyl alcohol (AA), bromobenzene (BB), cadmium chloride (Cd), or thioacetamide (TA). Liver damage was assessed by measuring serum sorbitol dehydrogenase (SDH) and alanine aminotransferase (ALT) activities as well as by histopathological examination. Hepatic PAPS concentration was generally decreased as a result of treatment with hepatotoxicants (35-80% of control), although BB, AA, and ANIT were without effect. Maximal hepatic capacity for PAPS synthesis, determined as the activities of PAPS synthetic enzymes, ATP sulfurylase, and APS kinase, was selectively decreased by the hepatotoxicants. ATP sulfurylase activity was decreased by Cd and TA (55 and 62% of control, respectively), whereas APS kinase activity was decreased by Cd, TA, BB, and DCE (60-77% of control, respectively). In addition, phenol sulfotransferase (PST) activity was measured toward 1- and 2-naphthol in order to determine whether apparent changes in PST activity in damaged livers are substrate-dependent. Treatment with hepatotoxicants generally decreased 1-naphthol-directed PST activity but not PST activity directed toward 2-naphthol. In conclusion, (1) not all xenobiotic-induced liver injury results in decreased hepatic PAPS concentration, (2) some hepatotoxicants decrease PAPS concentration by a mechanism other than decreased cosubstrate synthesis, and (3) the effect of hepatotoxicants on PST activity is dependent upon the choice of substrate used in the enzymatic assay.

Diphenylthiazole-induced changes in renal ultrastructure and enzymology: toxicologic mechanisms in polycystic kidney disease?

The mechanism by which various chemicals induce renal cystic disease is unknown. To examine the early events in cystogenesis the ultrastructure and biochemistry of liver and kidney were analyzed after the administration of a chemical that induces renal cyst formation. Special emphasis was placed on examining potential mechanisms that would account for the observed loss of extracellular proteoglycans. Renal cystic disease was chemically induced in rats by feeding 2-amino-4,5-diphenylthiazole (DPT) for up to 4 weeks. After 4 days of feeding, DPT had induced a 4-fold increase in total urine output relative to diet-restricted control groups. Both groups maintained, but did not gain, weight during the feeding schedule. Cyst formation was localized to the medullary collecting tubules. Relative to diet-restricted controls, rats fed DPT exhibited diminished renal and hepatic catalase activity, but elevated activity for UDP-glucuronosyltransferase. Medulla showed an increase in the specific activities of the enzymes galactosyltransferase and sulfatase B. These enzymological findings correlated with ultrastructural observations of a loss of peroxisomes, proliferation of endoplasmic reticulum and enlargement of the golgi apparatus. Serum and urinary levels of inorganic sulfate were significantly increased in DPT-fed rats relative to controls. Tissue levels of UDP-glucuronic acid and adenosine 3'-phosphate 5'-phosphosulfate were not depressed by DPT feeding. Thus, DPT-induced cyst formation and loss of staining for glycosaminoglycans does not involve gross depletions of UDP-glucuronic acid and adenosine 3'-phosphate 5'-phosphosulfate, mutual cosubstrates for Phase II drug conjugation reactions and glycosaminoglycan synthesis.