<Emphasis Type="Italic">In vitro</Emphasis> effects of fat,FA, and cholesterol on sphingomyelin hydrolysis induced by rat intestinal alkaline sphingomyelinase |
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Authors: | Jian-Jun?Liu ?ke?Nilsson Email author" target="_blank">Rui-Dong?DuanEmail author |
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Affiliation: | (1) Cell Biology B, Biomedical Center B11, Lund University, S-221 84 Lund, Sweden;(2) Institute of medicine, Lund University Hospital, S-221 85 Lund, Sweden |
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Abstract: | Dietary sphingomyelin (SM) may have regulatory effects on cell proliferation and tumorigenesis in the colon. Alkaline sphingomyelinase
(SMase) is the major enzyme responsible for hydrolysis of SM in the gut. Previously we purified the enzyme and showed that
the presence of glycerophospholipids inhibited SM hydrolysis induced by alkaline SMase in vitro. In the present work, we studied the effects of TG, DG, FA, ceramide, and cholesterol on SM hydrolysis catalyzed by purified
alkaline SMase. The results showed that both TG (triolein and tristearin) and DG (1,2-dioleoyl-sn-glycerol and 1,2-distearoyl-rac-glycerol) inhibited the activity of alkaline SMase. 1-Mono-oleoyl-rac-glycerol, 1-monostearoyl-rac-glycerol, stearic acid, oleic acid, linoleic acid, linolenic acid, and arachidonic acid stimulated the activity of alkaline
SMase at 0.4–0.8 mM concentrations but inhibited the enzyme at higher concentrations. There was no difference between the
effects induced by saturated and unsaturated FA. A short-chain FA such as lauric acid had a stronger stimulatory effect at
low concentrations and weaker inhibitory effect at high concentrations than long-chain FA. Choosing linoleic acid as an example,
we found that FA had similar effects on both alkaline SMase and neutral SMase. Cholesterol and ceramide when mixed with FA
to increase its solubility in bile salt micelles inhibited SMase activity. In conclusion, glycerides, FA, ceramide, and cholesterol
influence SM hydrolysis catalyzed by intestinal alkaline SMase. The presence of lipids in the diet may thus influence the
course of SM digestion in the gut and thereby the exposure of colon to SM metabolites. |
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