Lingual lipase in cystic fibrosis. Quantitation of enzyme activity in the upper small intestine of patients with exocrine pancreatic insufficiency

Staging exocrine pancreatic dysfunction

Digestive capacity of the gastrointestinal tract, largely but not wholly, depends on exocrine pancreatic function to achieve near complete digestion and absorption of ingested food. Coefficient of fat absorption (CFA), the proportion of ingested fat absorbed (normal >93%), reflects digestive capacity. Exocrine pancreatic insufficiency (EPI) is the state of insufficient digestive capacity (CFA <93%) caused by severe loss of pancreatic exocrine function despite variable compensation by upregulation of extra-pancreatic lipolysis. Fecal elastase 1 (FE1) level is the most widely used, though imperfect, non-invasive test of pancreatic enzyme output. Decline in pancreas enzyme output, or pancreatic exocrine dysfunction (EPD), has a variable correlation with measurable decline in CFA. EPI results in steatorrhea, weight loss and nutrient deficiency, which are mitigated by pancreatic enzyme replacement therapy (PERT). We propose a staging system for EPD, based on measurement of fecal elastase (FE1) and, if necessary, CFA and serum fat-soluble vitamin levels. In Stage I (Mild) EPD, FE1 is 100-200 mcg/gm; if steatorrhea is present, non-pancreatic causes are likely. In Stage II (Moderate) EPD), FE1 is < 100 mcg/gm without clinical and/or laboratory evidence of steatorrhea. In Stage III, there are marked reductions in FE1 and CFA, but vitamin levels remain normal (Severe EPD or EPI without nutritional deficiency). In Stage IV all parameters are abnormal (Severe EPD or EPI with nutritional deficiency). EPD stages I and II are pancreas sufficient and PERT may not be the best or first approach in management of early-stage disease; it needs further study to determine clinical utility. The term EPI refers strictly to EPD Stages III and IV which should be treated with PERT, with Stage IV requiring micronutrient supplementation as well.

Topical Pilocarpine Formulation for Diagnosis of Cystic Fibrosis

Cystic fibrosis is diagnosed in infants by estimating the levels of chloride ions present in the sweat induced by iontophoresis of pilocarpine solution. Elevated levels of chloride (≥60 mMol/L) in sweat are indicative of cystic fibrosis. However, the iontophoretic method of delivering pilocarpine is cumbersome and usually is associated with several side effects such as skin burn, skin rashes, erythema, and so forth. The objective of this study was therefore to develop a topical formulation that delivers adequate amount of pilocarpine. The drug delivery of formulation was compared with iontophoresis of aqueous solution of pilocarpine nitrate in vitro using porcine skin model. The pilocarpine levels in the skin exposed to topical pilocarpine solution under mild hyperthermia was 152.04 ± 52.23 μg/cm² after 10 min of application, whereas it was 97.05 ± 27.93 μg/cm² in the skin after 10 min of iontophoresis. The topical formulation was subjected to clinical evaluation to assess the efficacy of the product to induce sweat production. The average amount of the sweat secreted on application of topical formulation was found to be 77.28 ± 18.97 mg. Based on these results, it was found that the topical formulation was successful in delivering pilocarpine and to stimulate sweat secretion.

Variations in gastrointestinal lipases, pH and bile acid levels with food intake, age and diseases: Possible impact on oral lipid-based drug delivery systems

The lipids and some surfactants present in oral lipid-based drug delivery systems are potential substrates for the various lipases involved in gastrointestinal (GI) lipolysis. The levels of these enzymes, together with pH and biliairy secretion, are important parameters that condition the fate of lipid-based formulations (LBF) and the dispersion, solubilization and absorption of lipophilic drugs in the GI tract. Since in vitro methods of digestion are now combined with dissolution assays for a better assessment of LBF performance, it is essential to have a basic knowledge on lipase, pH and bile acid (BA) levels in vivo to develop relevant in vitro models. While these parameters and their variations in healthy subjects are today well documented, in vivo data on specific populations (age groups, patients with various diseases, patients with treatment affecting GI tract parameters, …) are scarce and obtaining them from clinical studies is sometimes difficult due to ethical limitations. Here we collected some in vivo data already available on the levels of digestive lipases, gastric and intestinal pH, and BAs at various ages and in patients with exocrine pancreatic insufficiency, a pathological situation that leads to drastic changes in GI tract parameters and impacts pharmacological treatments.

Salivary functions in mastication, taste and textural perception, swallowing and initial digestion

Saliva exerts multiple functions in relation to the initial digestive processes taking place in the upper parts of the gastrointestinal tract. Ingestion of food and beverages, in turn, is a strong stimulus for secretion of saliva with a differential composition depending on the neuronal stimulation pattern. This review paper provides insight into the mechanisms by which saliva acts in relation to taste, mastication, bolus formation, enzymatic digestion and swallowing. Also, the protective functions of saliva including maintenance of dental and mucosal integrity will be discussed as they indirectly influence the digestive process. The final part of this study focuses on the implications of xerostomia and salivary gland dysfunction on gastrointestinal functions.

Preliminary report of the (13)C-mixed triglyceride breath test to assess timing of pancreatic enzyme replacement therapy in children with cystic fibrosis

BACKGROUND

Despite guidelines suggesting pancreatic enzyme replacement therapy (PERT) should be taken before or during a meal, it is currently unknown whether this has benefits over administration after a meal in individuals with cystic fibrosis (CF).

METHODS

18 children with pancreatic insufficient CF were randomised to two (13)C-mixed triglyceride ((13)C-MTG) breath tests to assess lipase activity with PERT administered 10min before and 10min after a meal. Results were expressed as percentage cumulative dose recovered (PCDR) of (13)CO2 and were compared with established values in healthy subjects. Gastric half emptying time (T½) was also assessed by a (13)C-octanoate breath test.

RESULTS

There was no difference in mean PCDR of (13)CO2 between taking PERT before versus after the meal (p=0.68). Eleven subjects had a greater PCDR when PERT was taken before and 7 when PERT was taken after the meal. 6/8 subjects (75%) with a lower than normal PCDR at one time point normalised PCDR when PERT timing was changed. When PERT was taken after the meal, PCDR was higher in normal vs. fast T½ (p=0.04).

CONCLUSIONS

Changing PERT timing can result in normalised lipase activity. Gastric emptying rate may influence optimal timing of PERT. Clinical Trial Registration Number - This study was undertaken prior to the registration process being a commonly required practice.

Monitoring changes in plasma levels of pancreatic and intestinal enzymes in a model of pancreatic exocrine insufficiency--induced by pancreatic duct-ligation--in young pigs

PURPOSE

Plasma levels of pancreatic and intestinal enzymes were measured after pancreatic duct ligation (PDL) to monitor pancreatic exocrine insufficiency (PEI) in a model using young pigs.

MATERIAL/METHODS

Five, 6 week-old pigs (10.9±0.2kg), underwent PDL while age-matched, un-operated pigs were used as controls. Plasma levels of immunoreactive cationic trypsinogen (IRCT), amylase, lipase, and diamine oxidase (DAO) activities were analyzed for 48 days after PDL, including 1 week of oral pancreatic enzyme supplementation (PES) with Creon(®).

RESULTS

PDL resulted in an arrested body growth and a rapid surge of pancreatic enzymes (IRCT, amylase and lipase) into the plasma. Nine days after PDL, the plasma levels of these pancreatic enzymes had decreased. IRCT then remained below the level in un-operated pigs while amylase only fell below control at 25 days. The intestinally derived marker DAO and plasma protein levels were unaffected by PDL but DAO decreased slightly with time in PEI pigs. One-week of oral PES restored body growth, but had little effect on pancreatic enzyme plasma levels, except for a tendency towards increased DAO.

CONCLUSIONS

The study showed that PEI developed within 1-2 weeks after PDL and that only IRCT is a reliable plasma enzyme marker for this. The reduced plasma DAO indicated that PEI also affected the intestines, while PES therapy restored growth of the PDL pigs and slightly increased plasma DAO, suggesting an improved intestinal function.

Digestive system dysfunction in cystic fibrosis: challenges for nutrition therapy

Cystic fibrosis can affect food digestion and nutrient absorption. The underlying mutation of the cystic fibrosis trans-membrane regulator gene depletes functional cystic fibrosis trans-membrane regulator on the surface of epithelial cells lining the digestive tract and associated organs, where Cl(-) secretion and subsequently secretion of water and other ions are impaired. This alters pH and dehydrates secretions that precipitate and obstruct the lumen, causing inflammation and the eventual degradation of the pancreas, liver, gallbladder and intestine. Associated conditions include exocrine pancreatic insufficiency, impaired bicarbonate and bile acid secretion and aberrant mucus formation, commonly leading to maldigestion and malabsorption, particularly of fat and fat-soluble vitamins. Pancreatic enzyme replacement therapy is used to address this insufficiency. The susceptibility of pancreatic lipase to acidic and enzymatic inactivation and decreased bile availability often impedes its efficacy. Brush border digestive enzyme activity and intestinal uptake of certain disaccharides and amino acids await clarification. Other complications that may contribute to maldigestion/malabsorption include small intestine bacterial overgrowth, enteric circular muscle dysfunction, abnormal intestinal mucus, and intestinal inflammation. However, there is some evidence that gastric digestive enzymes, colonic microflora, correction of fatty acid abnormalities using dietary n-3 polyunsaturated fatty acid supplementation and emerging intestinal biomarkers can complement nutrition management in cystic fibrosis.

Characterising lipid lipolysis and its implication in lipid-based formulation development

Facing the increasing number of poorly water-soluble drugs, pharmaceutical scientists are required to break new grounds for the delivery of these pharmaceutically problematic drugs. Lipid-based drug delivery systems (LBDDS) have received increased interest as a novel drug delivery platform during the last decades and several successfully marketed products have shown the potential for LBDDS. However, there exists a discrepancy between the clear need for innovative delivery forms and their rational design. In the case of LBDDS, this can be attributed to the complexity of LBDDS after administration. Unlike conventional formulations, LBDDS are susceptible to digestion in the gastrointestinal tract, the interplay of delivery system, drug and physiology ultimately effecting drug disposition. In vitro lipolysis has become an important technique to mimic the enzymatic degradation. For the better understanding of how LBDDS promote drug delivery, in vitro lipolysis requires advanced characterisation methods. In this review, the physiological background of lipid digestion is followed by a thorough summary of the techniques that are currently used to characterise in vitro lipolysis. It would be desirable that the increasing knowledge about LBDDS will foster their rationale development thereby increasing their broader application.

Persistent fat malabsorption in cystic fibrosis; lessons from patients and mice

Fat malabsorption in pancreatic insufficient cystic fibrosis (CF) patients is classically treated with pancreatic enzyme replacement therapy (PERT). Despite PERT, intestinal fat absorption remains insufficient in most CF patients. Several factors have been suggested to contribute to the persistent fat malabsorption in CF (CFPFM). We reviewed the current insights concerning the proposed causes of CFPFM and the corresponding intervention studies. Most data are obtained from studies in CF patients and CF mice. Based on the reviewed literature, we conclude that alterations in intestinal pH and intestinal mucosal abnormalities are most likely to contribute to CFPFM. The presently available data indicate that acid suppressive drugs and broad spectrum antibiotics could be helpful in individual CF patients for optimizing fat absorption and/or nutritional status.

In vitro comparative study of three pancreatic enzyme preparations: dissolution profiles, active enzyme release and acid stability

BACKGROUND

Various pancreatic enzyme preparations are used for the treatment of pancreatic insufficiency but their bioequivalence is often unknown.

AIM

To determine in vitro the pH-dependent release and acid resistance of enzymes from three commercially available pancreatin capsules, two containing enteric-coated (Creon 25000; Eurobiol 25000) and one uncoated (Eurobiol 12500) microspheres.

METHODS

Dissolution experiments were performed at pH values ranging from 4.0 to 5.8. Lipase, chymotrypsin and amylase activities were measured in the solution as a function of time.

RESULTS

Eurobiol 25000 started to release its enzymes significantly at pH 5.0 (t(1/2) = 71 min), whereas the enzymes from Creon 25000 were only released at higher pH value (5.4; t(1/2) = 49.2 min). Unlike chymotrypsin, lipase and amylase were highly sensitive to acidic conditions at the lowest pH values tested. Both enzymes were also found to be sensitive to proteolytic inactivation at the highest pH values tested. Overall, Eurobiol 25000 released higher amounts of active amylase and lipase than Creon 25000 at the pH values usually found in duodenal contents. The uncoated Eurobiol 12500 preparation was, however, the only one that could immediately release rather high levels of active chymotrypsin and lipase at low pH (4.5).

CONCLUSION

These findings suggest that pH-sensitive enteric-coated pancreatin products containing similar amounts of enzymes might not be bioequivalent depending on the pH of duodenal contents.

Lipases and lipolysis in the human digestive tract: where do we stand?

PURPOSE OF REVIEW

The review evaluates current knowledge of the different lipases catalyzing triglyceride lipolysis in the human digestive tract, focusing on their mode of action - information useful for developing strategies to regulate the bioavailability of fatty acid.

RECENT FINDINGS

Optimal levels of digestive lipases promote efficient triglyceride lipolysis in healthy humans. Management of fatty acid bioavailability during pancreatic insufficiencies, however, requires enzyme replacement therapy. Such therapy entails gastro-protected porcine pancreatic powder, associated with antacid treatment when duodenal pH is too acidic; recently, enteric-coated high-buffered pancrelipase or recombinant gastric lipase have been used. Another promising strategy is to focus on lipid substrate to optimize lipid-water interface properties. Research on obesity treatment focuses on inhibitors. Orlistat is the first inhibitor to be used extensively. Others treatments are in development, including human pancreatic lipase C-terminal, polyphenols, specific proteins and peptides; however, their relevance has not yet been tested in humans.

SUMMARY

A better knowledge of lipase structure and mode of action will help the development of new natural inhibitors with fewer secondary effects. More intensive research in protein engineering for recombinant lipase production and in clinical nutrition, together with careful evaluation of patients' individual needs is necessary.

Human pancreatic digestive enzymes

A primary function of the pancreas is to produce digestive enzymes that are delivered to the small intestine for the hydrolysis of complex nutrients. Much of our understanding of digestive enzymes comes from studies in animals. New technologies and the availability of the sequence of the human genome allow for a critical review of older reports and assumptions based on animal studies. This report updates our understanding of human pancreatic digestive enzymes with a focus on new insights into the biology of human proteases, lipases and amylases.

Purification and biochemical characterization of the LIP2 lipase from Yarrowia lipolytica

The LIP2 lipase from the yeast Yarrowia lipolytica (YLLIP2) was obtained from two genetically modified strains with multi-copies of the lip2 gene and further purified using gel filtration and cation exchange chromatography. Four YLLIP2 isoforms were identified and subjected to N-terminal amino-acid sequencing and mass spectrometry analysis. These isoforms differed in their glycosylation patterns and their molecular masses ranged from 36,874 to 38,481 Da, whereas the polypeptide mass was 33,385 Da. YLLIP2 substrate specificity was investigated using short (tributyrin), medium (trioctanoin) and long (olive oil) chain triglyceride substrates at various pH and bile salt concentrations, and compared with those of human gastric and pancreatic lipases. YLLIP2 was not inhibited by bile salts at micellar concentrations with any of the substrates tested, and maximum specific activities were found to be 10,760+/-115 U/mg on tributyrin, 16,920+/-480 U/mg on trioctanoin and 12,260+/-700 U/mg on olive oil at pH 6.0. YLLIP2 was found to be fairly stable and still active on long chain triglycerides (1590+/-430 U/mg) at pH 4.0, in the presence of bile salts. It is therefore a good candidate for use in enzyme replacement therapy as a means of treating pancreatic exocrine insufficiency.

Mechanisms of lipid malabsorption in Cystic Fibrosis: the impact of essential fatty acids deficiency

Transport mechanisms, whereby alimentary lipids are digested and packaged into small emulsion particles that enter intestinal cells to be translocated to the plasma in the form of chylomicrons, are impaired in cystic fibrosis. The purpose of this paper is to focus on defects that are related to intraluminal and intracellular events in this life-limiting genetic disorder. Specific evidence is presented to highlight the relationship between fat malabsorption and essential fatty acid deficiency commonly found in patients with cystic fibrosis that are often related to the genotype. Given the interdependency of pulmonary disease, pancreatic insufficiency and nutritional status, greater attention should be paid to the optimal correction of fat malabsorption and essential fatty acid deficiency in order to improve the quality of life and extend the life span of patients with cystic fibrosis.

Quantitative study of digestive enzyme secretion and gastrointestinal lipolysis in chronic pancreatitis

BACKGROUND & AIMS

The contribution of human gastric lipase (HGL) to the overall lipolysis process in chronic pancreatitis (CP), as well as the relative pancreatic enzyme levels, rarely are addressed. This study was designed to quantify pancreatic and extrapancreatic enzyme output, activity, and stability in CP patients vs. healthy volunteers.

METHODS

Healthy volunteers (n = 6), mild CP patients (n = 5), and severe (n = 7) CP patients were intubated with gastric and duodenal tubes before the administration of a test meal. HGL, human pancreatic lipase (HPL), chymotrypsin, and amylase concentrations were assessed in gastric and duodenal samples by measuring the respective enzymatic activities. Intragastric and overall lipolysis levels at the angle of Treitz were estimated based on quantitative analysis of lipolysis products. Similar analyses were performed on duodenal contents incubated ex vivo for studying enzyme stability and evolution of lipolysis.

RESULTS

Although HPL, chymotrypsin, and amylase outputs all were extremely low, HGL outputs in patients with severe CP (46.8 +/- 31.0 mg) were 3-4-fold higher than in healthy controls (13.3 +/- 13.8 mg). Intragastric lipolysis did not increase, however, in patients with severe CP, probably because of the rapid decrease in the pH level of the gastric contents caused by a higher gastric acid secretion. HGL remains active and highly stable in the acidic duodenal contents of CP patients, and, overall, can achieve a significant lipolysis of the dietary triglycerides (30% of the control values) in the absence of HPL.

CONCLUSIONS

Although all pancreatic enzyme secretions are simultaneously reduced in severe CP, gastric lipase can compensate partly for the loss of pancreatic lipase but not normalize overall lipolytic activity.

Gastric function in children with cystic fibrosis: effect of diet on gastric lipase levels and fat digestion

The effect of diet, usual (44 +/- 4% energy as fat), high-fat (49 +/- 4% energy as fat), and moderate-fat (33 +/- 2% energy as fat), on gastric function (lipase and pepsin activities, pH, emptying rate) and intragastric digestion of fat were assessed in six children with cystic fibrosis. Fasting and postprandial activity of digestive enzymes, gastric pH, and gastric volume measured before, during, and after 120 min of feeding did not differ significantly as a function of fat intake. Postprandial gastric lipase output (units per kilogram of body weight) during usual, moderate-fat, and high-fat diets was close to or higher than (38.8 +/- 7.2, 44.9 +/- 8.6, and 54.8 +/- 5.5 U/kg per 20 min) gastric lipase output of premature infants (22.5 +/- 6.4 to 28.3 +/- 6.6 U/kg per 20 min) or of healthy adults (5.4 +/- 0.4 U/kg per 15 min) fed a high-fat diet. Postprandial pepsin output was higher (4749 +/- 797, 6117 +/- 925, and 5444 +/- 819 U/kg per 20 min) than in premature infants (597 +/- 77 to 743 +/- 97 U/kg per 20 min) or healthy adults (781 +/- 56 U/kg per 15 min). Eighty minutes after feeding gastric lipolysis reached 20 to 36%. This study shows that gastric lipase activity is high in cystic fibrosis patients maintained on diets providing 32% to 49% energy as fat, and that gastric lipase level did not increase over the ranges of dietary fat intake tested.

The enzyme levels in blood are not affected by oral administration of a pancreatic enzyme preparation (Creon 10,000) in pancreas-insufficient pigs

After oral intake, small amounts of intact protein may be absorbed into the blood circulation. The current study investigated whether orally administered pancreatic enzymes were absorbed from the intestine. The study included 28 pigs; 3 control pigs with intact pancreatic function and 25 pigs that were made exocrine pancreas insufficient by duct ligation (20 pigs) or total pancreatectomy (5 pigs). The pigs received a pancreatic enzyme preparation (0, 2, 4, or 8 g of Creon 10,000) together with the feed. The blood plasma was analyzed for pancreatic lipase activity with a [3H]-triolein substrate assay, while (pro)colipase and cationic trypsin(ogen) levels were measured with enzyme-linked immunosorbent assay (ELISA). Administration of Creon (0-8 g) caused no significant changes in plasma (pro)colipase or cationic trypsin(ogen) levels. Lipase activity peaks in plasma samples were found, but they did not correspond to the administration of Creon. The potential source of these plasma lipase activity peaks is discussed. The results showed no absorption into blood of pancreatic enzymes after oral administration (0, 2, 4, or 8 g of Creon mixed with 100 g of feed) to pancreas-insufficient pigs.

Importance of lipolysis in oral cavity for orosensory detection of fat

Lingual lipase is usually secreted from von Ebner's glands, although there is great variation between species. Lingual lipase is thought to be an auxiliary enzyme for fat digestion and absorption in mammals; however, the reason for lipolysis in the oral cavity is not known. We focused on the gustatory sense and investigated the significance of lingual lipase in the perception of a fat taste by using orlistat, a potent lipase inhibitor. Five-minute two-bottle preference tests demonstrated that the addition of orlistat diminished the preference for triacylglycerides but not for free fatty acids. Radioactive triolein applied on rats' circumvallate papilla revealed that lingual lipase was released continuously to generate significant amounts of fatty acids and other lipolytic products within 1-5 s, which was enough time to taste fat. These findings suggest that lingual lipase is released to perceive the taste of triacylglycerides and to find nutritive lipids in food.

Mechanisms of inhibition of triacylglycerol hydrolysis by human gastric lipase

In the human stomach, gastric lipase hydrolyzes only 10 to 30% of ingested triacylglycerols because of an inhibition process induced by the long chain free fatty acids generated, which are mostly protonated at gastric pH. The aim of this work was to elucidate the mechanisms by which free fatty acids inhibit further hydrolysis. In vitro experiments examined gastric lipolysis of differently sized phospholipid-triolein emulsions by human gastric juice or purified human gastric lipase, under close to physiological conditions. The lipolysis process was further investigated by scanning electron microscopy, and gastric lipase and free fatty acid movement during lipolysis were followed by fluorescence microscopy. The results demonstrate that: 1) free fatty acids generated during lipolysis partition between the surface and core of lipid droplets with a molar phase distribution coefficient of 7.4 at pH 5.40; 2) the long chain free fatty acids have an inhibitory effect only when generated during lipolysis; 3) inhibition of gastric lipolysis can be delayed by the use of lipid emulsions composed of small-size lipid droplets; 4) the release of free fatty acids during lipolysis induces a marked increase in droplet surface area, leading to the formation of novel particles at the lipid droplet surface; and 5) the gastric lipase is trapped in these free fatty acid-rich particles during their formation. In conclusion, we propose a model in which the sequential physicochemical events occurring during gastric lipolysis lead to the inhibition of further triacylglycerol lipolysis.

Saliva and gastrointestinal functions of taste, mastication, swallowing and digestion

Saliva has multiple essential functions in relation to the digestive process taking place in the upper parts of the gastrointestinal (GI) tract. This paper reviews the role of human saliva and its compositional elements in relation to the GI functions of taste, mastication, bolus formation, enzymatic digestion, and swallowing. The indirect function of saliva in the digestive process that includes maintenance of an intact dentition and mucosa is also reviewed. Finally, pathophysiological considerations of salivary dysfunction in relation to some GI functions are considered.

Digestion and absorption of 2 fat emulsions with different droplet sizes in the human digestive tract

BACKGROUND

The extent of fat emulsification affects the activity of digestive lipases in vitro and may govern digestion and absorption of dietary fat.

OBJECTIVE

We investigated the effect of the fat globule size of 2 enteral emulsions on fat digestion and assimilation in humans.

DESIGN

Healthy subjects received intragastrically a coarse (10 microm) and a fine (0.7 microm) lipid emulsion of identical composition in random order. Gastric and duodenal aspirates were collected throughout digestion to measure changes in fat droplet size, gastric and pancreatic lipase activities, and fat digestion. Blood lipids were measured postprandially for fat assimilation.

RESULTS

Despite an increase in droplet size in the stomach (2.75-6.20 microm), the fine emulsion retained droplets of smaller size and its lipolysis was greater than that of the coarse emulsion (36.5% compared with 15.8%; P < 0.05). In the duodenum, lipolysis of the fine emulsion was on the whole higher (73.3% compared with 46.3%). The overall 0-7-h plasma and chylomicron responses given by the areas under the curve were not significantly different between the emulsions, but the triacylglycerol peak was delayed with the fine emulsion (3 h 56 min compared with 2 h 50 min).

CONCLUSIONS

Fat emulsions behave differently in the digestive tract depending on their initial physicochemical properties. A lower initial fat droplet size facilitates fat digestion by gastric lipase in the stomach and duodenal lipolysis. Overall fat assimilation in healthy subjects is not affected by differences in initial droplet size because of efficient fat digestion by pancreatic lipase in the small intestine. Nevertheless, these new observations could be of interest in the enteral nutrition of subjects suffering from pancreatic insufficiency.

Fat malabsorption in cystic fibrosis patients receiving enzyme replacement therapy is due to impaired intestinal uptake of long-chain fatty acids

BACKGROUND

Pancreatic enzyme replacement therapy frequently fails to correct intestinal fat malabsorption completely in cystic fibrosis (CF) patients. The reason for this failure is unknown.

OBJECTIVE

We investigated whether fat malabsorption in CF patients treated with pancreatic enzymes is caused by insufficient lipolysis of triacylglycerols or by defective intestinal uptake of long-chain fatty acids.

DESIGN

Lipolysis was determined on the basis of breath 13CO2 recovery in 10 CF patients receiving pancreatic enzyme replacement therapy after they ingested 1.3-distearoyl,2[1-13C]octanoyl glycerol ([13C]MTG). Intestinal uptake of long-chain fatty acids was determined by analyzing plasma [13C]linoleic acid ([13C]LA) concentrations after patients ingested [13C]LA. For 3 d, dietary intakes were recorded and feces were collected.

RESULTS

Fecal fat excretion ranged from 5.1 to 27.8 g/d (mean+/-SD: 11.1+/-7.0 g/d) and fat absorption ranged from 79% to 93% (89+/-5%). There was no relation between breath 13CO2 recovery and dietary fat absorption (r = 0.04) after ingestion of [13C]MTG. In contrast, there was a strong relation between 8-h plasma [13C]LA concentrations and dietary fat absorption (r = 0.88, P < 0.001).

CONCLUSION

Our results suggest that continuing fat malabsorption in CF patients receiving enzyme replacement therapy is not likely due to insufficient lipolytic enzyme activity, but rather to incomplete intraluminal solubilization of long-chain fatty acids, reduced mucosal uptake of long-chain fatty acids, or both.

Uptake and metabolism of structured triglyceride by Caco-2 cells: reversal of essential fatty acid deficiency

Structured lipids have been proposed as efficient vehicles for the supplementation of essential fatty acids (EFA) to patients with malabsorption. We investigated how a novel structured triglyceride (STG), containing purely octanoic acid in the sn-1/sn-3 and [14C]linoleic acid in the sn-2 positions, was incorporated into different lipid classes in Caco-2 cells. We also evaluated the contribution of gastric lipase in the uptake and metabolism of [14C]linoleic acid from the STG. We furthermore determined the potential of the STG to correct EFA deficiency induced in Caco-2 cells. The absorption of STG by Caco-2 cells was significantly greater compared with that of triolein. The addition of human gastric lipase significantly enhanced cellular uptake of the labeled substrate, reflecting the stereoselectivity of gastric lipase to hydrolyze medium chain FA. Analysis of the intracellular lipids synthesized revealed a predominance of phospholipids-monoglycerides. Most of the radioactivity in the lipoproteins isolated from Caco-2 cells was recovered in TG-rich lipoproteins (45%) and to a lesser extent in the high-density lipoprotein (36%) and low-density lipoprotein (17%) fractions. The administration of STG to Caco-2 cells rendered EFA deficient produced a marked increase of the cellular level of linoleic and arachidonic acids. This resulted in a lower ratio of 20:3(n-9) to 20:4(n-6), reflecting the correction of EFA deficiency in Caco-2 cells. Our data demonstrate that STG, in the presence of gastric lipase, have beneficial effects on lipid incorporation, lipoprotein production, and EFA status, utilizing Caco-2 cells as a model of EFA deficiency.

Endogenous lipase activity in Caco-2 cells

Dietary triglycerides, the major precursors of long chain fatty acids (FA), require hydrolysis by pancreatic enzymes prior to their absorption by the small intestine. Although Caco-2 cells are frequently employed for the study of enterocyte lipid metabolism, the presence of an endogenous lipase activity has never been previously reported. The major goal of this investigation was to determine the presence of endogenous Caco-2 cell lipase activity, to examine its capacity to hydrolyze triglycerides, and to define its intracellular location. Caco-2 cells were found to have an endogenous lipase activity, capable of hydrolyzing [1-14C]triolein from the apical cell compartment. A time and concentration dependence of lipase activity was observed, with hydrolysis of triolein into free fatty acids and monoglyceride. The majority of the lipase activity was found in the cytosolic cell fraction and, to a lesser extent, in the apical brush border membrane and other organelles. Protamine sulfate markedly reduced the Caco-2 cell lipase activity, yet it remained relatively insensitive to high concentrations of NaCl, taurocholate, calcium, heparin and chloroquine. The addition of exogenous human gastric lipase to the medium of the apical compartment resulted in a significant increased rate of hydrolysis of triolein, followed by enhanced Caco-2 cell fatty acid uptake and basolateral lipid secretion. The major esterified intracellular lipids were triglycerides and phospholipids. We conclude that Caco-2 cells possess an endogenous lipase capable of hydrolyzing cytosolic triglycerides. Furthermore, activity present on the apical membrane and secreted into the apical medium, though quantitatively less important than the cytosolic lipase, may permit an additional route for energy uptake. The addition of gastric lipase to the Caco-2 cell cultures greatly enhanced FA uptake above that seen with the endogenous lipase alone.

The complete cDNA sequence encoding dog gastric lipase

Oligodeoxyribonucleotide ligation to single-stranded cDNA (SLIC) and polymerase chain reaction (PCR) techniques were used to clone an entire dog gastric lipase (DGL) cDNA. The size of the cDNA is confirmed by Northern blot analysis. The DGL is synthesized as a 379-amino acid mature polypeptide with a molecular mass of 43176 Da which is preceded by a 19-amino acid signal sequence located at the NH2-terminus. Comparison of the signal sequences reveals a high degree of similitude between the DGL, the human gastric lipase (HGL), the rabbit gastric lipase (RGL) and the rat lingual lipase (RLL).

Inhibition of lipid absorption as an approach to the treatment of obesity

A reduction in fat intake may be achieved by making educated choices to reduce total calorie intake, to consume a lower quantity of total fats, or to modify the ratio of saturated-to-polyunsaturated lipids. Leptin agonists or NPY or CCK antagonists may prove to be useful to diminish appetite and thereby reduce the total intake of food. But eating has such cultural, social, and hedonistic attributes that such a single-pronged approach is unlikely to be successful. The use of fat substitutes may prove to be popular to provide a wide range of snack food options, but these are likely to be of minimal use in weight reduction programs because of their distribution of additives in only a limited number of foods. The inhibitors of lipid digestion will be modestly successful in the short term; their long-term success will be influenced by gastrointestinal adverse effects and the need to consume fat-soluble vitamin supplements to prevent the development of fat-soluble vitamin deficiencies. The inhibition of lipid absorption is an attractive targeted approach for the treatment of obesity, since this would reduce the uptake of visible as well as invisible fats, which would potentially offer convenient dosing, and could also be a means to inhibit secondarily the uptake of carbohydrate calories.

Gastrointestinal pH, motility/transit and permeability in cystic fibrosis

I reviewed the literature (1966-1994) concerning gastrointestinal (GI) pH, motility/transit, and permeability in cystic fibrosis (CF). Most studies reported were performed with very small numbers of patients, but even when considered together the published data do not confirm some generally expressed views on these topics. The only clear findings were a high incidence of gastroesophageal reflux in CF; pre- and postprandial duodenal pH is 1-2 U lower in patients with CF than in healthy controls; and small intestinal paracellular permeability is 4-10 times greater than normal in CF. Some patients showed abnormalities of lower esophageal sphincter pressure and of esophageal motility, but apart from one case study other disturbances of GI motility have not been reported. The results of hydrogen breath tests strongly suggest that oro-cecal transit is slowed in CF, but these results must be confirmed by an alternative test. Measurements of colonic transit and colonic permeability have not been reported. The few studies of gastric emptying reported are controversial. Whether GI pH, apart from duodenal pH, is normal in CF or whether a subset of patients has exceptionally acid intestinal contents requiring specialized pancreatic enzyme supplementation to normalize digestion is not clear. Finally, I briefly discuss the findings in relation to their possible impact on the pathogenesis of fibrosing colonopathy.

Effect of human milk or formula on gastric function and fat digestion in the premature infant

The effect of diet, human milk or formula, on gastric function (lipase and pepsin activity, pH, and volume) and intragastric digestion of fat was assessed in 28 appropriate for gestational age preterm infants (gestational age, 28.9 +/- 1.4, 29.1 +/- 0.9, 29.5 +/- 0.6 wk; birth weight, 1.00 +/- 0.14 to 1.18 +/- 0.07 kg). The infants were fed either human milk (n = 11), SMA Super Preemie formula (n = 9), or Similac, Special Care formula (n = 8). Fasting and postprandial activity of digestive enzymes, pH, and gastric volume (measured before or during 50 min after gavage feeding) did not differ as a function of diet among the three groups of infants. Gastric lipase output, 23.1 +/- 5.1, 28.3 +/- 6.6, and 22.5 +/- 6.4 (U/kg of body weight) in human milk-, SMA SP-, or Similac SC-fed infants was comparable to the gastric lipase output of healthy adults fed a high fat diet (22.6 +/- 3.0). Pepsin output was, however, significantly lower (597 +/- 77, 743 +/- 97, and 639 +/- 142 U/kg of body weight) in human milk-, SMA SP-, and Similac SC-fed infants) than in healthy adults (3352 +/- 753 U/kg). The hydrolysis of dietary fat was 1.7-2.5-fold higher (p < 0.01) in human milk-fed infants than in infants fed either formula. We conclude that differences in type of feeding, i.e. different fatty acid profiles (long chain or medium chain triglycerides), different emulsions (natural or artificial), and different fat particle sizes do not affect the level of activity of gastric enzymes. However, the triglyceride within milk fat globules appears to be more accessible to gastric lipase than that within formula fat particles. We suggest that the contribution of gastric lipase to overall fat digestion might be greater in the newborn (a period of pancreatic insufficiency) than in the adult.

Production of human gastric lipase in the fission yeast Schizosaccharomyces pombe

A cDNA encoding human gastric lipase (hGL) has been expressed on multicopy plasmids in the fission yeast Schizosaccharomyces pombe (Sp). Active lipase is secreted from transformants containing the hGL cDNA under the control of either the Sp adh1 promoter (Padh1) or the plant cauliflower mosaic virus (CaMV) 35S promoter. Cell-wall-associated lipase activities are greatest in the early logarithmic growth phase and with Padh1. Western blot analysis indicates that a protein of identical molecular mass to natural hGL is secreted by Sp, although the major secreted product is of a higher molecular mass than either native hGL or recombinant hGL produced in the budding yeast Saccharomyces cerevisiae (Sc). Several distinct hGL are present within cells at all growth phases. Treatment of these proteins with endoglycosidase H gives rise to a single species equivalent in size to deglycosylated natural hGL, indicating that most of these are glycosylation intermediates. An hGL of similar molecular mass accumulates intracellularly in Sp when a modified version of cDNA is used which lacks the sequence encoding the natural secretory signal peptide. Production of hGL markedly slows the growth rate of Sp. The average copy number per cell of the plasmid expressing the hGL cDNA from the recombinant Padh1 is 2-3, as compared with 11-12 for the control plasmid.

Lipid metabolism in pediatric nutrition

The abrupt transition from carbohydrate to fat as the main energy source that occurs at birth is not matched by commensurate endogenous fat-digesting capacity in the newborn. Newborn infants are, however, able to digest fat efficiently through the activities of gastric lipase and the exogenous digestive lipase of human milk, which compensate for the low activity of pancreatic lipase. Fat absorption is well-developed at birth and is commensurate with the high fat intake of the infant. Tissue uptake of dietary fat is also adequate, based on sufficient lipoprotein lipase (above 26 to 27 weeks' gestation) and rapid postnatal increase of lecithin:cholesterol acyl transferase, the enzymes that regulate tissue uptake of circulatory lipoprotein triglyceride and cholesterol.

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.

Gastric and pancreatic lipase levels during a test meal in dogs

The levels of gastric and pancreatic lipases in the duodenum and the jejunum were measured during the digestion of a test meal in dogs. Using both a specific enzymatic titration and an enzyme-linked immunosorbent assay, it is shown for the first time that gastric lipase remains active in the duodenal and jejunal contents. An experimental device was set up for measuring the secretions and the intestinal flows of lipases during the digestion of a liquid test meal. In a dog equipped with gastric and duodenal cannulae, the secretion of gastric lipase was stimulated by food ingestion, reaching 3.0 +/- 0.3 mg/h (three times the basal secretion rate) during the 1st h of digestion. The total secretory outputs of gastric and pancreatic lipases recorded over a 3-h period of digestion were 7.2 +/- 1.2 mg and 18.7 +/- 1.2 mg, respectively.

Lipase and pepsin activity in the gastric mucosa of infants, children, and adults

The range of activity and the location of lipase and pepsin were determined in the stomach and duodenum of infants, children, and adults. The range of lipase activity in biopsy specimens from the gastric body, in 29 subjects aged from 3 months to 26 years, was 1.8-5.3 U/mg protein (1 U is 1 mumol [3H]oleic acid released from tri-[3H]olein per minute). There were no significant differences among age groups (5-19 months, 2-4 years, 6-10 years, 11-13 years, and 15-26 years). Lipase activity was low or undetectable in the gastric antrum of all subjects. Pepsin activity in specimens from the gastric body ranged from 180 to 780 pepsin units/mg protein (using hemoglobin as substrate). The antrum had significantly lower pepsin activity (P less than 0.001) than the gastric body. As with lipase activity, there were no statistically significant differences in pepsin activity among age groups. Lipase and pepsin activity was also quantified in pinch biopsy specimens from the duodenum and duodenal bulb in 13 subjects. Contrary to lipase activity, which was almost completely absent from the duodenum or duodenal bulb, these sites contained low pepsin activity (9-78 pepsin units/mg protein). The data show that in infants and children, as previously reported in adults, gastric lipase is localized primarily in the gastric body. Tissue pepsin levels and localization, reported here for the first time, are similar to those of lipase, although, contrary to lipase, the gastric antrum has considerable pepsin activity. The identical levels of lipase and pepsin activities in infants, children, and adults indicate that the gastric phase of nutrient digestion is well developed at birth.

Gastric lipase: evidence of an adaptive response to dietary fat in the rabbit

In the rabbit, the stomach is the only source of preduodenal lipase, and in humans, it is quantitatively the most important. Thus, the adaptive response of gastric and pancreatic lipases to dietary fat was studied in the adult rabbit. Effect of duration was studied by feeding rabbits 12% dietary fat for 1, 2, or 4 weeks or 2.7% for 2 weeks (control). To study the effects of the amount of fat, rabbits were fed the control diet (2.7% fat) or 6% and 12% dietary fat for 2 weeks. The influence of sunflower oil and butter was compared by feeding rabbits 12% dietary fat for 2 weeks. Approximately doubling (6% vs. 2.7%) the usual amount of dietary fat was sufficient to induce a maximum increase in gastric lipase activity in the fundus [+ 66.3% (units per gram tissue) or + 85.2% (units per milligram protein)] and the total stomach mucosa [+ 84.5% (units per mucosa)], whereas pancreatic lipase activity only significantly increased when rabbits were fed 12% dietary fat. A full adaptive response was observed for both gastric and pancreatic lipases after 2 weeks of diet. Triglyceride composition did not noticeably change the adaptive response of both lipolytic enzymes. The present results agree closely with those concerning lingual lipase in the rat and evidence that gastric lipase shows an adaptive response to moderate fat intake. The implications of these findings concerning humans are discussed.

Milk lipid digestion in the neonatal dog: the combined actions of gastric and bile salt stimulated lipases

Intragastric lipolysis may be particularly important for the digestion of milk lipid since milk fat globules are resistant to pancreatic lipase without prior disruption; milk bile salt stimulated lipase (BSSL) may supplement further intestinal hydrolysis. Previous information on gastric lipolysis has been based primarily on in vitro studies using artificial lipid emulsions containing a single component fatty acid and have focused on the preferential release of medium-chain fatty acids. The actual contribution of these enzymes to overall fat digestion in vivo on natural substrates has rarely been studied, however. The neonatal dog is an excellent model in the study of lipid digestion because, like the human, milk lipids are high in long-chain unsaturated fatty acids, milk contains BSSL and gastric lipase is the predominant lipolytic enzyme acting in the stomach. We used a combination of in vivo studies with in vitro incubations to investigate digestion of milk lipid by gastric and milk (BSSL) lipases in the suckling dog. In the first 4 weeks postpartum, 14-41% and 42-60% of milk triacylglycerol was hydrolyzed to primarily diacylglycerol and free fatty acid (FFA) in the first 30 and 60 min in the stomach, respectively. Milk lipid contained high levels (63%) of long-chain unsaturated fatty acids, which were preferentially released as FFA during in vivo gastric lipolysis, consistent with the actions and stereospecificity of gastric lipase. While levels of hydrolysis in gastric aspirates were significantly different (by age and time in stomach) at the start of in vitro studies, total hydrolysis in all incubation systems plateaued at about 65%, suggesting product inhibition by the long-chain FFA, but to a much lesser degree than previously expected from in vitro studies. The magnitude of in vivo intragastric lipolysis was 3- to 6-times greater than that predicted by in vitro assays using either milk lipid or labeled emulsion as substrate, respectively. Prior exposure to intragastric lipolysis resulted in 30% hydrolysis by BSSL compared to 5% hydrolysis without prior exposure. We suggest that previous in vitro studies have largely underestimated the actual degree of intragastric lipolysis that can occur and its activity on long-chain fatty acids; this study indicates the importance of the combined mechanisms of gastric lipase and BSSL to fat digestion in the suckling neonate.

Fatty acids generated by gastric lipase promote human milk triacylglycerol digestion by pancreatic colipase-dependent lipase

The concerted action of purified bovine gastric lipase and human pancreatic colipase-dependent lipase and colipase, or crude human pancreatic juice, in the digestion of human milk triacylglycerols was explored in vitro. Gastric lipase hydrolyzed milk triacylglycerol with an initially high rate but became severely inhibited already at low concentration of released fatty acid. In contrast, colipase-dependent lipase could not, by itself, hydrolyze milk triacylglycerol. However, a short preincubation of milk with gastric lipase, resulting in a limited lipolysis, made the milk fat triacylglycerol available for an immediate and rapid hydrolysis by pancreatic juice, and also for purified colipase-dependent lipase, provided colipase and bile salts were present. The same effect was obtained when incubation with gastric lipase was replaced by addition of long-chain fatty acid. Long-chain fatty acid increased the binding of colipase-dependent lipase to the milk fat globule. Binding was efficient only in the presence of both fatty acid and colipase. We conclude that a limited gastric lipolysis of human milk triacylglycerol, resulting in a release of a low concentration of long-chain fatty acids, is of major importance for the subsequent hydrolysis by colipase-dependent lipase in the duodenum.

Purification of lingual amylase from serous glands of rat tongue and characterization of rat lingual amylase and lingual lipase

Lingual amylase and lingual lipase, two digestive enzymes that are secreted from lingual serous glands (von Ebner's), were simultaneously purified from rat lingual serous glands with hydrophobic chromatography used as the final step. This method, previously developed for the purification of lingual lipase, includes homogenization of rat lingual serous glands, 100,000 g centrifugation, ammonium sulfate precipitation of proteins, and extraction of lipids with acetone at -20 degrees C, followed by hydrophobic chromatography on ethyl agarose or Agethane. Amylase was eluted after the elution of proteins that did not interact with the hydrophobic gel at pH 6.3. Lingual lipase was eluted with a solution containing micelles of taurodeoxycholate, monoolein, and oleic acid. Analysis of each of the purified enzymes by SDS-polyacrylamide gel electrophoresis revealed one band at Mr = 59,000 for amylase and one band at Mr = 51,000 for lingual lipase. Isoelectric focusing of amylase indicated a strong band at pI = 5.0 and two very faint bands at pI = 4.9 and 4.8, possibly isozymes or deamidated protein. Amino acid and hexosamine analyses were performed on the enzymes after electroelution from SDS-polyacrylamide gels. Both lingual lipase and lingual amylase had a high content of dicarboxylic (free and amide) amino acids. For lingual lipase and lingual amylase, the % molar ratios of aspartic acid/asparagine were 15.35 and 15.10, and the % molar ratios of glutamic acid/glutamine were 7.07 and 7.20, respectively. Lingual amylase was very similar to rat parotid, pancreatic, and mouse salivary amylases, except that it contained more proline (11.03% molar ratio).(ABSTRACT TRUNCATED AT 250 WORDS)

Gastric lipase: localization in the human stomach

The aim of this study was to determine the range of activity and the location of lipase in the human stomach. The range of lipase activity in gastric mucosa of surgical specimens from the fundic area of 22 subjects was 594 to 3350 mU [mean, 1598 +/- 144 mU tri[3H]olein, (1 mU-1 nmol [3H]oleic acid released from tri[3H]olein per minute per milligram protein)]. For localization of activity, pinch biopsy specimens of gastric mucosa from 6 subjects were taken from the greater and lesser curvatures within 2 cm of the gastroesophageal junction (upper greater curvature and upper lesser curvature) and within 2 cm of the pylorus (lower greater curvature and lower lesser curvature). Lipase activity was higher in the upper greater curvature (405 +/- 92 mU) than in the upper lesser curvature (32 +/- 13 mU) and lowest in the antral area (16 +/- 9 mU in the lower lesser curvature and 10 +/- 2 mU in the lower greater curvature). The data show that in the human, lipase activity is localized primarily in the fundic area of the stomach. Comparison of the lipase activity levels in the gastric mucosa with lingual lipase activity levels in specimens of lingual serous glands indicates that in humans, gastric lipase is the main lipase active in the stomach.

Hydrolysis of fluorescent pyrenetriacylglycerols by lipases from human stomach and gastric juice

Fluorescent triacylglycerols containing pyrenedecanoic (P10) and pyrenebutanoic (P4) acids were synthesized and their hydrolysis by lipases from human gastric juice and stomach homogenate was investigated. The existence in stomach homogenate of four different lipolytic enzymes hydrolyzing fluorescent triacylglycerols is suggested by the comparison of various enzymatic properties: acyl chain length specificity, heat inactivation and effect of detergents (Triton X-100 and taurocholate), serum albumin, diethyl-para-nitrophenyl phosphate (E600) and other inhibitors. (1) The acid pH4-lipase hydrolyzes P10-triacylglycerols but not P4-triacylglycerol and exhibited the characteristic properties of the lysosomal lipase: the maximal activating effect of detergents occurs at relatively high concentrations (the substrate/detergent optimal molar ratios were 1:5 and 1:25 for triacylglycerols/taurocholate and triacylglycerols/Triton X-100, respectively); its activity was strongly inhibited by para-chloromercuribenzoate (2.5 mmol/l), but was not significantly affected by serum albumin and E600 (10(-2) mmol/l). (2) The neutral pH7-lipase hydrolyzes P10-triacylglycerols but not P4-triacylglycerol. It is resistant to E600 and heat-stable, similarly to the acid pH4-lipase, but it is well discriminated from the acid enzyme by its substrate/detergent optimal molar ratios (1:2 and 1:3 for triacylglycerols/taurocholate and triacylglycerols/Triton X-100, respectively), whereas higher detergent concentrations, optimal for the acid lipase, are strongly inhibitory for the neutral enzyme. (3) The pH5-lipase present in gastric juice as well as in stomach homogenate exhibited properties obviously discriminating it from the other lipolytic enzymes from stomach homogenate: broad substrate specificity for P10- as well as P4-triacylglycerols, activation by low concentrations of amphiphiles (with optimal ratios triacylglycerols/taurocholate, triacylglycerols/taurocholate and triacylglycerols/phosphatidylcholine around 1:1, 1:3 and 1:0.1, respectively), heat-lability, strong activation by serum albumin and inhibition by E600 (10(-2) mmol/l). This pH5-lipase is the sole lipolytic enzyme present in gastric juice and is probably identical with the well-known 'gastric' lipase. (4) A pH7.5-enzyme is characterized by its specificity for P4-triacylglycerols, its heat-lability at 50 degrees C and its strong inhibition by E600 (10(-2) mmol/l).