Purification of human gastric lipase by immunoaffinity and quantification of this enzyme in the duodenal contents using a new ELISA procedure

Lipase Supplementation before a High-Fat Meal Reduces Perceptions of Fullness in Healthy Subjects

Background/Aims

Postprandial symptoms of fullness and abdominal discomfort are common after fatty meals. Gastric lipases hydrolyze 10% to 20% of dietary triglycerides during the stomach trituration period of digestion. The aim of this study was to evaluate the effects of acid-resistant lipase on upper gastrointestinal symptoms, including fullness and bloating, as well as on gastric myoelectrical activity after healthy subjects ingested a high-fat, liquid meal.

Methods

This study utilized a double-blind, placebo-controlled, crossover design with 16 healthy volunteers who ingested either a capsule containing 280 mg of acid-resistant lipase or a placebo immediately before a fatty meal (355 calories, 55% fat). Participants rated their stomach fullness, bloating, and nausea before and at timed intervals for 60 minutes after the meal. Electrogastrograms were obtained to assess the gastric myoelectrical activity.

Results

Stomach fullness, bloating, and nausea increased significantly 10 minutes after ingestion of the fatty meal (p<0.01), whereas normal gastric myoelectrical activity decreased and tachygastria increased (p<0.05). With lipase, reports of stomach fullness were significantly lower compared with placebo (p<0.05), but no effect on gastric myoelectrical activity or other upper gastrointestinal symptoms was observed.

Conclusions

The high-fat meal induced transient fullness, bloating, nausea, and tachygastria in healthy individuals, consistent with post-prandial distress syndrome. Acid-resistant lipase supplementation significantly decreased stomach fullness.

Expression and characterization of the protein Rv1399c from Mycobacterium tuberculosis. A novel carboxyl esterase structurally related to the HSL family

The Mycobacterium tuberculosis genome contains an unusually high number of proteins involved in the metabolism of lipids belonging to the Lip family, including various nonlipolytic and lipolytic hydrolases. Driven by a structural genomic approach, we have biochemically characterized the Rv1399c gene product, LipH, previously annotated as a putative lipase. Rv1399c was overexpressed in E. coli as inclusion bodies and refolded. Rv1399c efficiently hydrolyzes soluble triacylglycerols and vinyl esters. It is inactive against emulsified substrate and its catalytic activity is strongly inhibited by the diethyl paranitrophenyl phosphate (E600). These kinetic behaviors unambiguously classify Rv1399c as a nonlipolytic rather than a lipolytic hydrolase. Sequence alignment reveals that this enzyme belongs to the alpha/beta hydrolase fold family and shares 30-40% amino acid sequence identity with members of the hormone-sensitive lipase subfamily. A model of Rv1399c derived from homologous three-dimensional structures reveals a canonical catalytic triad (Ser162, His290 and Asp260) located at the bottom of a solvent accessible pocket lined by neutral or charged residues. Based on this model, kinetic data of the Arg213Ala mutant partially explain the role of the guanidinium moiety, located close to His290, to confer an unusual low pH shift of the catalytic histidine in the wild type enzyme. Overall, these data identify Rv1399c as a new nonlipolytic hydrolase from M. tuberculosis and we thus propose to reannotate its gene product as NLH-H.

Cutinase binding and activity at the triolein-water interface monitored by oil drop tensiometry

Changes of the oil-water interfacial tension resulting from binding of Fusarium solani pisi cutinase and subsequent lipid hydrolysis were investigated using the oil drop technique. An ELISA was developed to determine the amount of cutinase bound to the triolein-water interface after biotinylation of the enzyme. Cutinase irreversibly adsorbs to a maximum value of about 2 mg/m2. A minimal specific activity of 110 mumol/min/mg was calculated for cutinase acting on a single oil droplet, which is close to the activity found for triglyceride emulsions. At a maximum surface load cutinase could generate one monolayer of fatty acid products per second at the interface. It was found that oleic acid rapidly dissolves into the oil phase under the conditions used. The interfacial tension measured reflects the adsorption of cutinase to the oil droplet and also responds to the fate of the hydrolysis products. A model is presented that describes the catalytic events at the oil-water interface during lipid hydrolysis.

An enzymatically active truncated form (-55 N-terminal residues) of rabbit gastric lipase. Correlation between the enzymatic activity and disulfide bond oxydo-reduction state

Rabbit gastric lipase (RGL) was subjected to proteolysis with trypsin and led to cleavage occurring at three defined sites (Lys-4, Arg-55 and Arg-229). The tryptic hydrolysate contained four fragments: Gly-230-Lys-379 (T1), Gly-56-Arg-229 (T2), Ser-5-Arg-55 (T3), as well as a 45 kDa molecular form consisting of peptides T1 and T2 linked by a disulfide bridge. The tryptic hydrolysate of RGL as well as the 55 N-terminal amino acid deleted forms conserved 30% of the initial enzymatic activity in a tributyrin assay. Two out of the three cysteine residues which are present in all the known gastric lipases were found to be involved in a disulfide bridge. Unlike HGL, RGL appears to have a heterogenous pattern of cysteine residues. The 30% enzymatic activity of RGL persisting after trypsin treatment may be attributable to the 45 kDa molecular form (with the Cys-227-Cys-236 or Cys-227-Cys-244 disulfide bridge). Trypsin-treated HGL, which was completely inactivated, showed that a single location of the disulfide bridge existed between cysteine residues 236 and 244. It can be concluded that the existence of one disulfide bridge is necessary to maintain the lipase activity of the 45 kDa form of RGL.

Purification and molecular characterization of lamb pregastric lipase

Lamb pregastric lipase (LPGL) was purified from pharyngeal tissues. The purification procedure was based on an aqueous extract containing 0.7% Tween 80 which was chromatographed on DEAE-cellulose anion-exchanger and adsorbed on HA-Ultrogel followed by gel filtration on Ultrogel AcA-54. The final enzymatic preparation, where the overall activity recovery was 3%, showed a single protein band on SDS-PAGE with a molecular mass of 50 kDa. LPGL is a glycoprotein containing approx. 14% (w/w) of carbohydrate. Extensive deglycosylation using peptide N-glycosidase F yielded a protein with an apparent molecular mass of 43 kDa. An uncontrolled proteolysis of LPGL during the purification lead to a 45 kDa form which was previously observed in human lysosomal acid lipase (HLAL) and rabbit gastric lipase (RGL). The labile bond X54-Leu55 was identified. Isoelectric focusing of LPGL reveals a major band corresponding to an isoelectric point of 4.8. The pure enzyme displayed specific activities of 950 U mg-1, 300 U mg-1 and 30 U mg-1 at pH 6.0, using tributyroylglycerol, trioctanoylglycerol and trioleoylglycerol as substrates, respectively. Using Western blot analysis, a cross-immunoreactivity of LPGL was observed with purified anti-human gastric lipase polyclonal antibodies. Determination of the amino-acid sequence of 62 residues revealed a high degree of homology with other known preduodenal lipases.

Human pancreatic lipase. Importance of the hinge region between the two domains, as revealed by monoclonal antibodies

Several monoclonal antibodies (mAbs) were prepared against human pancreatic lipase (HPL). Two enzyme-linked immunosorbent assay (ELISA) procedures were set up for screening hybridomas producing specific antibodies. Four mAbs (81-23, 146-40, 315-25, and 320-24) of the IgG1 isotype were found to react with HPL in both simple sandwich and double sandwich ELISAs, while mAb 248-31, of the IgG2b isotype, reacted only with HPL in a double sandwich ELISA. The results of Western blot analysis carried out with native and SDS-denatured HPLs indicated that mAb 248-31 recognized only native HPL, while all the other mAbs recognized both forms of HPL. Since mAb 248-31 did not recognize SDS-denatured HPL, it was not possible to localize its epitope. To carry out epitope mapping along the primary sequence of HPL, four fragments (14, 26, 30, and 36 kDa) resulting from a limited chymotryptic cleavage of HPL were characterized by Western blotting as well as N-terminal amino acid sequence analysis. Of the above five anti-HPL mAbs, four (81-23, 248-31, 315-25, and 320-24) were found to inhibit the lipolytic activity of HPL (in both the presence and absence of bile salts and colipase), while mAb 146-40 had no inhibitory effects. The epitope recognized by mAb 146-40 was found to be located in the N-terminal domain (Lys1-Phe335). Combined immunoinactivation and epitope mapping studies showed that three inhibitory mAbs (81-23, 315-25, and 320-24) recognize overlapping epitopes from the hinge region between the N- and C-terminal domains of HPL, belonging to the 26-kDa fragment. In the presence of lipids, a significant decrease has been observed in the bending angle between the N- and C-terminal domains of the HPL tertiary structure (van Tilbeurgh, H., Egloff, M. P., Martinez, C., Rugani, N., Verger, R. and Cambillau, C. (1993) Nature 362, 814-820). From the present immunochemical data, we further propose that locking the hinge movement with mAbs may induce lipase immunoinactivation.

Tryptic cleavage of gastric lipases: location of the single disulfide bridge

Human (HGL) and rabbit (RGL) gastric lipases were cleaved by trypsin and the resulting peptides were characterized. Exposure of HGL to trypsin led to the production of three identified fragments (H1, H2 and H3) resulting from cleavage sites at Lys-4 and Arg-229. Fragments H2 (Lys-4-Arg-229) and H3 (Glu-230-Lys-379) were derived from fragment H1 (Lys-4-Lys-379). The single disulfide bridge (Cys-236-Cys-244) of the molecule is localized in fragment H3. Out of the three cysteine residues conserved in all known gastric lipases, the free sulfhydryl group (Cys-227) was localized in fragment H2. Immunoblots, carried out with the tryptic fragments of HGL and anti-HGL mAbs, revealed that five inhibitory mAbs immunoreacted selectively with the N-terminal fragment H2, whereas two other non inhibitory mAbs immunoreacted exclusively with the C-terminal fragment H3. Trypsin also cleaved RGL at two sites (Arg-55 and Arg-229) leading to four identifiable fragments (R1, R2, R3 and R4). One cleavage site (Arg-229) was found to be identical in both RGL and HGL. We propose that this latter site is localized between the two domains of native gastric lipases.

Secretion and contribution to lipolysis of gastric and pancreatic lipases during a test meal in humans

BACKGROUND

The aim of this study was to quantitatively evaluate the relative contributions to in vivo lipolysis of gastric and pancreatic lipases.

METHODS

Gastric and pancreatic lipase secretions were measured, and their respective levels were determined in duodenal fluid during the digestion of a liquid test meal in healthy volunteers. Gastric lipase activity was clearly distinguished from that of pancreatic lipase by using both a specific enzymatic assay and an enzyme-linked immunosorbent assay. Lipolysis products were monitored throughout the digestion period.

RESULTS

On a weight basis, the ratio of pancreatic lipase to gastric lipase total secretory outputs was found to be around four after 3 hours of digestion. The level of gastric hydrolysis was calculated to be 10% +/- 1% of the acyl chains released from the meal triglycerides. Gastric lipase remained active in the duodenum where it might still hydrolyze 7.5% of the triglyceride acyl chains.

CONCLUSIONS

Globally during the whole digestion period, gastric lipase might hydrolyze 17.5% of the triglyceride acyl chains. In other words, gastric lipase might hydrolyze 1 acyl chain of 4, which need to be hydrolyzed for a complete intestinal absorption of monoglycerides and free fatty acids resulting from the degradation of two triglyceride molecules.