Copyright ©The Author(s) 2018. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Hepatol. Feb 27, 2018; 10(2): 246-253
Published online Feb 27, 2018. doi: 10.4254/wjh.v10.i2.246
Alkaline sphingomyelinase (NPP7) in hepatobiliary diseases: A field that needs to be closely studied
Rui-Dong Duan
Rui-Dong Duan, Gastroenterology and Nutrition Lab, Department of Clinical Sciences, Lund University, Lund S-22184, Sweden
Author contributions: Duan RD wrote this review.
Conflict-of-interest statement: No conflict-of-interest to be disclosed.
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See:
Correspondence to: Rui-Dong Duan, MD, PhD, Professor, Director, Gastroenterology and Nutrition Lab, Department of Clinical Sciences, University of Lund, Biomedical Center B11, Lund S-22184, Sweden.
Telephone: +46-46-2220708
Received: November 26, 2017
Peer-review started: November 26, 2017
First decision: December 18, 2017
Revised: January 13, 2018
Accepted: January 23, 2018
Article in press: January 23, 2018
Published online: February 27, 2018

Alkaline sphingomyelinase cleaves phosphocholine from sphingomyelin, platelet-activating factor, lysophosphatidylcholine, and less effectively phosphatidylcholine. The enzyme shares no structure similarities with acid or neutral sphingomyelinase but belongs to ecto-nucleotide pyrophosphatase/phosphodiesterase (NPP) family and therefore is also called NPP7 nowadays. The enzyme is expressed in the intestinal mucosa in many species and additionally in human liver. The enzyme in the intestinal tract has been extensively studied but not that in human liver. Studies on intestinal alkaline sphingomyelinase show that it inhibits colonic tumorigenesis and inflammation, hydrolyses dietary sphingomyelin, and stimulates cholesterol absorption. The review aims to summarize the current knowledge on liver alkaline sphingomyelinase in human and strengthen the necessity for close study on this unique human enzyme in hepatobiliary diseases.

Keywords: Sphingomyelin, Alkaline sphingomyelinase, Nucleotide pyrophosphatase/phosphodiesterase 7, Autotaxin, Platelet-activating factor, Cholangiocarcinoma, Liver diseases, Gallstone

Core tip: Alkaline sphingomyelinase is an enzyme expressing in the intestinal tract and additionally human liver. It hydrolyzes sphingomyelin, platelet activating factor and lysophospholipase. In the intestinal tract, it digests dietary sphingomyelin, stimulates cholesterol absorption, and inhibits development of colon cancer. Less is known about the implications of the enzyme in liver diseases. The review summarizes the current knowledge of its roles in hepatobiliary disease and raised special topics for future investigations.