Steroids mediate resistance to the bactericidal effect of phosphatidylcholines againstHelicobacter pylori

Abstract

Helicobacter pylori assimilates various steroids as membrane lipid components, but it can also survive in the absence of steroids. It thus remains to be clarified as to why the organism relies on steroid physiologically. In this study, we have found that phosphatidylcholine carrying a linoleic acid molecule or arachidonic acid molecule has the potential to kill steroid-free H. pylori. The bactericidal action of phosphatidylcholines against H. pylori was due to the lytic activity of the phosphatidylcholines themselves and not due to the lytic activity of the unsaturated fatty acids or lyso-phosphatidylcholine resulting from the hydrolysis of the phosphatidylcholines. In contrast to the steroid-free H. pylori, the organism that absorbed and glucosylated free cholesterol was unaffected by the bactericidal action of the phosphatidylcholines. Similarly, H. pylori that absorbed estrone without glucosylating it also resisted the bactericidal action of the phosphatidylcholines. The steroids absorbed by H. pylori existed in both the outer and inner membranes, while the glucosyl-steroids produced via the steroid absorption were localized in the outer membrane rather than in the inner membrane. These results indicate that H. pylori absorbs the steroids to reinforce the membrane lipid barrier and thereby expresses resistance to the bacteriolytic action of hydrophobic compounds such as phosphatidylcholine.

Phosphatidylethanolamine of Helicobacter pylori Functions as a Steroid-Binding Lipid in the Assimilation of Free Cholesterol and 3 -Hydroxl Steroids into the Bacterial Cell Membrane

“…A study by our group in 2009 revealed that dM␤CD protects H. pylori cells from the bactericidal action of unsaturated fatty acids and LPC by inhibiting the absorption of those lipophilic compounds into the cell membranes (23). This suggests that the outer membrane of the H. pylori cell may incorporate dM␤CD by binding to PE and that the dM␤CD so incorporated may prevent the absorption of unsaturated fatty acids and LPC into the H. pylori cell by weakening the hydrophobic interaction between those lipophilic compounds and the outer membrane.…”

“…The glucosylation of FC also has been shown to play an important role in the colonization of H. pylori in the stomachs of mice and gerbils (17,28). Our group, meanwhile, has demonstrated that H. pylori retains steroids to reinforce the membrane lipid barrier, with or without glucosylation, and thereby acquires resistance against the bacteriolytic action of phosphatidylcholines (PCs) (23). A recent study by another group has shown that H. pylori expresses further resistance against bile salts (including ceragenins) by absorbing FC, even in the HP0421 (cgt) gene knockout mutant (26).…”

“…For H. pylori in serum-free medium, the medium is supplemented with 2,6-di-O-methyl-␤-cyclodextrin (dM␤CD) as a growth-supporting factor (4,15). While the mechanism by which dM␤CD supports H. pylori growth remains unclear, an earlier study by our group demonstrated that dM␤CD protects H. pylori from the antimicrobial actions of unsaturated fatty acids and lysophosphatidylcholine (LPC) by inhibiting the binding of those lipophilic compounds to the cells of the organism (23). In sum, one of the functions of dM␤CD is to somehow scavenge toxic compounds that affect the survival of H. pylori.…”

“…H. pylori cells aggressively ingest FC from FC-supplemented medium or extract FC from the lipid raft of the epithelial cell membrane. The FC absorbed into H. pylori membranes is glucosylated via enzymatic action (14), and the organism cells retain both FC itself and glucosylated FC as membrane lipid components (11,23). A previous study by our group identified three types of glucosylated FC (9): cholesteryl-␣-D-glucopyranoside (CGL), cholesteryl-6-O-tetradecanoyl-␣-D-glucopyranoside (CAG), and cholesteryl-6-Ophosphatidyl-␣-D-glucopyranoside (CPG).…”

Colonize, evade, flourish

“…80,81 It may also reinforce the bacterial membrane, promoting resistance to toxic host compounds. 82,83 Wunder et al 80 delivered a seminal set of data that helped define the role of membrane-incorporated cholesterol in promoting pathogenesis. They find that H. pylori can sense and move toward cholesterol in its environment at levels as low as 250 μM, extract it from the cholesterol-rich lipid rafts of epithelial cells, glucosylate it by the action of a cholesterol-α-glucosyltransferase, Hp0421, and integrate it into the membrane.…”