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The present study was undertaken to explore whether retinoids, which are known to have immunomodulatory actions, could attenuate tumor necrosis factor-alpha (TNF)-stimulated inducible nitric oxide synthase (iNOS) expression in 3T3-L1 adipocytes. Adipocytes incubated with TNF induced dose- and time-dependent accumulation of nitrite in the culture medium through the iNOS induction as confirmed by Western blotting. Treatment of cells with TNF in the presence of all-trans-retinoic acid (RA) significantly decreased their ability to produce nitrite and iNOS induction. Both 13-cis- and all- trans-RA-induced suppression was dose-dependent, and all-trans-RA was somewhat potent than 13-cis-RA. The inhibitory effect of RA on TNF-induced iNOS induction was reversible, completely recovered after 2 days, and was exerted through the inhibition of NF-kappaB activation. TNF also suppressed the lipoprotein lipase (LPL) activity of 3T3-L1 adipocytes. RA could not reverse the TNF- induced LPL suppression at RA levels causing near complete inhibition of the TNF-induced NO production. These results indicate that RAs attenuate iNOS expression reversibly in TNF-stimulated 3T3-L1 adipocytes, and that the TNF-induced LPL suppression is not the result of NO overproduction.

Vibrio vulnificus infection has attracted special interest because of its high mortality rate. However, the identification of its major pathogenic determinant still remains obscure. In this study, a cytolysin-negative mutant strain of V. vulnificus CVD707 was used to determine the role of phospholipase A (PLA) in the pathogenesis of this bacterial infection. The mutant strain caused the lysis of erythrocytes in vitro and elevated plasma hemoglobin during the infection in mice. Both the hemolytic and PLA activities were dependent on calcium. Inhibition of hemolysis by PLA inhibitors including tetracyclin and the PLA substrate phosphatidylcholine also supports the possibility of membranous PLA as a major hemolytic factor in the cytolysin-deficient mutant. To identify the role of PLA in the pathogenesis of V. vulnificus infection, the effects of tetracycline on bacteriainduced macrophage cytotoxicity and lethality were compared with those of penicillin, an antibiotic with no inhibitory effect on PLA. Both the macrophage cytotoxicity and the lethality of V. vulnificus CVD707 to mice were significantly attenuated by tetracycline, but not by penicillin. However, bacterial counts in culture medium and mouse blood revealed that penicillin was more effective than tetracycline in killing bacteria under our experimental conditions. These results indicate that PLA activity is important in V. vulnificus-induced cytotoxicity and lethality, suggesting a crucial role for PLA in the pathogenesis of V. vulnificus infection.