We have examined the role of cyclooxygenase 2 (COX-2) in a model of inflammaion in vivo. Carrageenan administration to the subcutaneous rat air pouch induces a rapid inflammatory response characterized by hih levels of prostaglandins (PGs) and leukotrienes in the fluid exudate. The time course of the induction of COX-2 mRNA and protein coincided with the production of PGs in the pouch tissue and cellular infiltrate. Carrageenan-induced COX-2 immunoreactivity was localized to macrophages obtained from the fluid exudate as well as to the inner surface layer of cells within the pouch lining. Dexamethasone inhibited both COX-2 expression and PG synthesis in the fluid exudate but failed to inhibit PG synthesis in the stomach. Furthermore, NS-398, a selective COX-2 inhibitor, and indomethacin, a nonselective COX-1/COX-2 inhibitor, blocked proinflammatory PG synthesis in the air pouch. In contrast, only indomethacin blocked gastric PG and, additionally, produced gastric lesions. These results suggest that inhibitors of COX-2 are potent antiinflammatory agents which do not produce the typical side effects (e.g., gastric ulcers) associated with the nonselective, COX-1-direc antiinfla tory drugs.Nonsteroidal antiinflammatory drugs (NSAIDs) are used to treat acute and chronic inflammatory disorders such as rheumatoid arthritis. The antiinflammatory mechanism of NSAIDs is due to a reduction ofprostaglandin (PG) synthesis by the direct inhibition of cyclooxygenase (COX; prostaglandin-endoperoxide synthase, EC 1.14.99.1) (1). Unfortunately, inhibition of PG production in organs such as stomach and kidney can result in gastric lesions, nephrotoxicity, and increased bleeding.COX exists in two forms. COX-1 is in most tissues and is involved in the physiological production of PGs. COX-2 is cytokine-inducible and is expressed in inflammatory cells (2-9). The identification of constitutive and inducible COX enzymes led to the hypothesis that COX-2 is primarily responsible for PGs produced in inflammation and COX-1 for PGs involved in normal homeostasis (4-6, 10, 11).The rat air pouch is a convenient model to study acute inflammation (12). It is formed by the subcutaneous injection of air over several days and is composed of a lining of cells that consists primarily of macrophages and fibroblasts. Injection of carrageenan into the fully formed air pouch produces an inflammatory granulomatous reaction characterized by a marked production of biochemical mediators in the fluid exudate, including PGs and leukotrienes, as well as a significant influx of polymorphonuclear leukocytes (PMNs) and macrophages (13). Using molecular and pharmacological reagents, we studied the role of COX-2 in this model of inflammation by specific examination of the induction of COX-2 mRNA and protein as well as the production of PGs in the pouch exudate. The results indicate that induction of COX-2 is responsible for the production of PGs at the site of inflammation, whereas the normal synthesis of PGs in the stomach appears to depend on constitutive...

Leukotriene B(4) (LTB(4)) is a pro-inflammatory mediator that has been implicated in the pathogenesis of a number of diseases including inflammatory bowel disease (IBD) and psoriasis. Since the action of LTA(4) hydrolase is the rate-limiting step for LTB(4) production, this enzyme represents an attractive pharmacological target for the suppression of LTB(4) production. From an in-house screening program, SC-22716 (1, 1-[2-(4-phenylphenoxy)ethyl]pyrrolidine) was identified as a potent inhibitor of LTA(4) hydrolase. Structure-activity relationship (SAR) studies around this structural class resulted in the identification of a number of novel, potent inhibitors of LTA(4) hydrolase, several of which demonstrated good oral activity in a mouse ex vivo whole blood assay.

Prostaglandin E 2 (PGE 2 ) is the major prostaglandin produced both centrally and in the periphery in models of acute and chronic inflammation, and its formation in both locations is blocked by cyclooxygenase-2 (COX-2) inhibitors such as celecoxib. In animal models of inflammation, PGE 2 inhibition in the brain may occur secondarily to a peripheral action by inhibiting local PG formation that elicits increased firing of pain fibers and consequent activation of PG synthesis in the central nervous system (CNS). Celecoxib was studied in the kainate-induced seizure model in the rat, a model of direct central prostaglandin induction, to determine whether it can act directly in the CNS. In the kainate-treated rat brain there was increased PGE 2 , PGF 2␣ , and PGD 2 production, with COX activity and PGE 2 formation increased about 7-fold over normal. We quantitated mRNA levels for enzymes involved in the prostaglandin biosynthetic pathways and found that both COX-2 and PGE synthase (PGEs) mRNA levels were increased in the brain; no changes were found for expression of COX-1 or PGD synthase mRNA. By Western blot analysis, COX-2 and PGEs were induced in total brain, hippocampus, and cortex, but not in the spinal cord. Immunohistological studies showed that COX-2 protein expression was enhanced in neurons. Dexamethasone treatment reduced the expression of both COX-2 and PGEs in kainatetreated animals. Celecoxib reduced the elevated PGE 2 levels in brain of kainate-treated rats and inhibited induced COX activity, demonstrating the ability of this compound to act on COX-2 in CNS. Doses of celecoxib that inhibited brain COX-2 were lower than those needed for anti-inflammatory activity in adjuvant arthritis, demonstrating a potent direct central action of the compound.

Myelopoietins (MPOs) constitute a family of engineered, chimeric molecules that bind and activate the IL-3 and G-CSF receptors on hematopoietic cells. This study investigated the in vivo hematopoietic response of rhesus monkeys administered MPO after radiation-induced myelosuppression. Animals were total body irradiated (TBI) in 2 series, with biologically equivalent doses consisting of either a 700 cGy dose of Cobalt-60 (60Co) γ-radiation or 600 cGy, 250 kVp x-irradiation. First series: On day 1 after 700 cGy irradiation, cohorts of animals were subcutaneously (SC) administered MPO at 200 μg/kg/d (n = 4), or 50 μg/kg/d (n = 2), twice daily, or human serum albumin (HSA) (n = 10). Second series: The 600 cGy x-irradiated cohorts of animals were administered either MPO at 200 μg/kg/d, in a daily schedule (n = 4) or 0.1% autologous serum (AS) , daily, SC (n = 11) for 23 days. MPO regardless of administration schedule (twice a day or every day) significantly reduced the mean durations of neutropenia (absolute neutrophil count [ANC] < 500/μL) and thrombocytopenia (platelet < 20 000/μL) versus respective control-treated cohorts. Mean neutrophil and platelet nadirs were significantly improved and time to recovery for neutrophils (ANC to < 500/μL) and platelets (PLT < 20 000/μL) were significantly enhanced in the MPO-treated cohorts versus controls. Red cell recovery was further improved relative to control-treated cohorts that received whole blood transfusions. Significant increases in bone marrow-derived clonogenic activity was observed by day 14 after TBI in MPO-treated cohorts versus respective time-matched controls. Thus, MPO, administered daily was as effective as a twice daily schedule for multilineage recovery in nonhuman primates after high-dose, radiation-induced myelosuppression.