Catalase and superoxide dismutase secreted from Helicobacter pylori

Previously, we have reported that toxic oxidants produced by activated neutrophils play a pivotal role in the development of Helicobacter pylori-induced gastric mucosal damage. Microorganisms, however, are characterized by their ability to produce a variety of antioxidant enzymes. This study is designed to measure the oxygen radical scavenging enzymes, such as catalase and superoxide dismutase (SOD), and urease in the supernatant of H. pylori (NCTC11637) suspension.

H. pylori was inoculated on a sheep blood agar plate and harvested. Bacterial suspensions (10(9) cfu/ml phosphate buffer) were washed twice and incubated at 37 degrees C for 1, 2, 12, and 24 hours or were sonicated in ice. Their supernatants were obtained by centrifugation and filtration. SOD activity was measured spectrophotometrically by the cytochrome c method. Catalase activity was assayed by the fall in absorbance at 240 nm as H2O2 is degraded. Urease activity was determined by measuring the release of ammonia using Berthelot reaction.

Activities of both SOD and catalase were detected in the supernatants of 1-hour microaerophilic incubation. Their activities were almost constant in 4-, 12-, and 24-hour microaerobic incubation or sonication. Urease activity was increased dramatically in proportion to the period of microaerobic incubation.

Although H. pylori possesses antioxidant as a constitutive compartment, the magnitude of its secretion was below the detectable level. It is not likely that SOD and catalase play a significant role for scavenging the oxidants from injured gastric mucosa, such as infiltrated leukocytes.