Submitted to: Life Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2004
Publication Date: 3/5/2004
Citation: Zhou, Q., Band, M.R., Hernandez, A., Liu, Z., Kummerow, F.A. 2004. 27-Hydroxycholesterol inhibits neutral sphingomyelinase in cultured human endothelial cells. Life Sciences. 75:1567-1577. Interpretive Summary: Oxysterol:cholesterol ratio in human plasma and lesions from atherosclerotic patients is significantly higher than those from normal persons. 27-Hydroxycholesterol is one of major oxysterol in human plasma and lesions. The plasma from coronary artery bypass grafting patients also has higher concentrations of 27-hydroxycholesterol than that from the controls of the same age and sex. The high levels of 27-hydroxycholesterol further increase concentrations of sphingomyelin, a lipid, in blood and vessels. The enhanced lipid then causes a cellular calcium accumulation. However, there is no knowledge available for the effect of the 27-hydroxycholesterol on the lipid catabolism. This paper examined a special enzyme gene expression in the initial step of the lipid catabolic pathway and suggested that the inhibition to the enzyme might be attributed from an alteration of cell membrane fluidity by 27-hydroxycholesterol, as a consequence of changes in cell membrane lipid composition. This research impacts basic studies for human health in cellular regulation and the pathological events leading to atherosclerosis. This is a collaborated research with Dr. F. A. Kummerow at the University of Illinois at Urbana-Champaign, IL.
Technical Abstract: To study the effect of 27-hydroxycholesterol (27OHC) on the catabolism of sphingomyelin, we cultured endothelial cells (ECs) from human umbilical veins with 27OHC, then measured activities of acid sphingomyelinase (ASMase) and neutral sphingomyelinase (NSMase) and sphingomyelin consumption by using [14C]sphingomyelin, and determined NSMase mRNA expressions by RT-PCR method. The results indicated that [14C]sphingomyelin accumulated in cells treated with 27OHC, and that the activities of both NSMase and ASMase were inhibited in ECs cultured with 27OHC. To further study the effect of 27OHC on NSMase, we used desipramine, an inhibitor of ASMase, to exclude the possible interference of ASMase's residual activity at neutral condition. Also, we observed the significant inhibition of NSMase activity by using glutathione, an inhibitor of NSMase, but found no further impact when 27OHC was added later. To determine whether the inhibition of NSMase activity was directly due to the effect of 27OHC, we exposed cell homogenate to 27OHC, and found no inhibitive effect of 27OHC on the activity of NSMase. All of our data confirmed that 27OHC had only an indirect inhibitive effect on NSMase. Our finding that no change of the NSMase mRNA expression by 27OHC indicated that the inhibitive effect of 27OHC on NSMase activity occurred at a post-transcriptional level. We suggest that an altered membrane fluidity caused by 27OHC could be involved in the inhibited activity of NSMase.