Acid lipase in rat intestinal mucosa: physiological parameters

Area of Science:

• Gastroenterology
• Biochemistry
• Cell Biology

Background:

• Up to 50% of dietary triacylglycerol bypasses lymphatic absorption in the intestine.
• This suggests an alternative pathway for fatty acid transport, potentially involving mucosal lipases and portal vein circulation.

Purpose of the Study:

• To characterize a novel acid-active lipase identified in rat intestinal mucosa.
• To investigate the enzyme's cellular localization, activity, and potential role in triacylglycerol metabolism.

Main Methods:

• Assay of acid lipase activity using a radiolabeled triolein emulsion at pH 5.8.
• Differential centrifugation of mucosal homogenates to isolate cellular organelles.
• Sequential release of cells from villi using citrate and EDTA.
• Enzyme activity assessment across intestinal segments and villus height.
• Chromatographic analysis using Sepharose 6B and assessment of detergent effects.

Main Results:

• The acid-active lipase exhibited peak activity in the proximal intestinal quarter and the upper villus regions.
• The enzyme was predominantly localized within the lysosomal fraction.
• Lingual lipase was excluded as the precursor via esophageal diversion.
• Bile salts significantly stimulated lipase activity (3-5 fold), while other detergents were mostly inhibitory.
• Chromatography indicated the enzyme forms mixed micelles with SDS and taurocholate.

Conclusions:

• A distinct, intrinsic mucosal acid lipase exists in the rat intestine, primarily of lysosomal origin.
• Its localization suggests a significant role in the disposal and processing of mucosal triacylglycerol.
• This enzyme may contribute to the alternative portal vein transport of fatty acids.