The p38 MAP kinase signal transduction pathway is an important regulator of proinflammatory cytokine production and inflammation. Defining the roles of the various p38 family members, specifically p38␣ and p38, in these processes has been difficult. Here we use a chemical genetics approach using knock-in mice in which either p38␣ or p38 kinase has been rendered resistant to the effects of specific inhibitors along with p38 knock-out mice to dissect the biological function of these specific kinase isoforms. Mice harboring a T106M mutation in p38␣ are resistant to pharmacological inhibition of LPS-induced TNF production and collagen antibody-induced arthritis, indicating that p38 activity is not required for acute or chronic inflammatory responses. LPS-induced TNF production, however, is still completely sensitive to p38 inhibitors in mice with a T106M point mutation in p38. Similarly, p38 knock-out mice respond normally to inflammatory stimuli. These results demonstrate conclusively that specific inhibition of the p38␣ isoform is necessary and sufficient for anti-inflammatory efficacy in vivo.
The incidence and severity of rheumatoid arthritis (RA) are reduced during pregnancy. Estradiol-17 and relaxin (RLX), hormones of pregnancy, are implicated in decreased immune responsiveness. The aim of this study was to determine the effects of estrogen and RLX, alone or in combination, on the development of adjuvant-induced arthritis (AIA) in ovariectomized (OVX) Lewis rats. Arthritis was induced on day 0 by adjuvant injection in the left hind paw. Rats were treated with estradiol valerate (E), porcine RLX, E ϩ RLX, or vehicle. Healthy OVX control animals were used for comparison. Treatment with RLX or E alone decreased adjuvant-induced inflammation in both the injected (primary) and noninjected (secondary) hind paws. Combined treatment with E and RLX was more effective than either hormone alone in blocking secondary paw inflammation. Furthermore, E plus RLX reduced changes to spleen and thymus weights induced by adjuvant injection. Both E and RLX alone decreased circulating tumor necrosis factor (TNF) ␣. The combination of E and RLX resulted in a greater decline in TNF␣ than treatment with either hormone alone. There was no effect of hormones on the proinflammatory cytokine, interleukin (IL)-1. The anti-inflammatory cytokine IL-10 increased in response to E and E plus RLX. In conclusion, combined therapy with E and RLX was more effective than either hormone alone in reducing chronic inflammation, joint changes, and high circulating TNF␣ associated with AIA in rats. Accordingly, these hormones could play a role in reducing RA-induced inflammation during pregnancy by an effect on the immune system.
The renal outer medullary potassium (ROMK) channel, located at the apical surface of epithelial cells in the thick ascending loop of Henle and cortical collecting duct, contributes to salt reabsorption and potassium secretion, and represents a target for the development of new mechanism of action diuretics. This idea is supported by the phenotype of antenatal Bartter's syndrome type II associated with loss-of-function mutations in the human ROMK channel, as well as, by cardiovascular studies of heterozygous carriers of channel mutations associated with type II Bartter's syndrome. Although the pharmacology of ROMK channels is still being developed, channel inhibitors have been identified and shown to cause natriuresis and diuresis, in the absence of any significant kaliuresis, on acute oral dosing to rats or dogs. Improvements in potency and selectivity have led to the discovery of MK-7145 [5,5'-((1R,1'R)-piperazine-1,4-diylbis(1-hydroxyethane-2,1-diyl))bis(4-methylisobenzofuran-1(3H)-one)], a potential clinical development candidate. In spontaneously hypertensive rats, oral dosing of MK-7145 causes dose-dependent lowering of blood pressure that is maintained during the entire treatment period, and that displays additive/synergistic effects when administered in combination with hydrochlorothiazide or candesartan, respectively. Acute or chronic oral administration of MK-7145 to normotensive dogs led to dose-dependent diuresis and natriuresis, without any significant urinary potassium losses or changes in plasma electrolyte levels. Elevations in bicarbonate and aldosterone were found after 6 days of dosing. These data indicate that pharmacological inhibition of ROMK has potential as a new mechanism for the treatment of hypertension and/or congestive heart failure. In addition, Bartter's syndrome type II features are manifested on exposure to ROMK inhibitors.
A reduction in the incidence and severity of rheumatoid arthritis is seen in pregnant women. Relaxin, a hormone of pregnancy, has been implicated in decreased immune responsiveness. Consequently, the effects of relaxin and estradiol valerate, alone or in combination, were assessed in the development of adjuvant-induced arthritis in the rat. Combination hormone therapy reduced adjuvant-induced paw inflammation. Radiographic analysis of the tarsal joints showed that estradiol valerate plus relaxin treatment minimized soft tissue damage and bone changes when compared to vehicle-treated arthritic controls. These results indicate that relaxin may be a factor in reducing inflammation during pregnancy.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.