SUPEROXIDE DISMUTASE-DEPENDENT, CATALASE-SENSITIVE PEROXIDES IN HUMANENDOTHELIAL-CELLS INFECTED BY RICKETTSIA-RICKETTSII

The generation and intracellular accumulation of reactive oxygen speci es have been shown to be associated with the infection of human umbili cal vein endothelial cells (HUVEC) by Rickettsia rickettsii. In respon se to the oxidant superoxide, the activity of the enzyme superoxide di smutase (SOD) increases following infection by this obligate intracell ular bacterium, Other oxidants which are capable of oxidizing the fluo rescent probe 2',7'-dichlorofluorescin (DCFH) also accumulate intracel lularly within infected cells, In the study reported here, we show tha t (i) an inhibitor of SOD, diethyldithiocarbamic acid, reduces the obs erved rise in SOD activity in infected cells by 40 to 60% and at the s ame time reduces the degree of intracellular oxidation of DCFH; (ii) c atalase-sensitive peroxides can be detected in supernatants of R. rick ettsii-infected cells shortly after rickettsial exposure; and (iii) fl uorescence-activated cell sorter analysis demonstrates significant int racellular oxidant activity in infected cells within 5 h after exposur e to R. rickettsii, The results of these experiments indicate that hyd rogen peroxide is a major oxidant associated with infection of HUVEC b y R. rickettsii and that intracellular oxidant activity sensitive to S OD inhibition is detectable early and prior to significant rickettsial multiplication and much earlier than the ultrastructural manifestatio ns of cell injury seen by electron microscopy.