Gastric lipase in alcoholic pancreatitis. Comparison of secretive profiles following pentagastrin stimulation in normal adults and patients with pancreatic insufficiency

Relevant pH and lipase for in vitro models of gastric digestion

The development of in vitro digestion models relies on the availability of in vivo data such as digestive enzyme levels and pH values recorded in the course of meal digestion. The variations of these parameters along the GI tract are important for designing dynamic digestion models but also static models for which the choice of representative conditions of the gastric and intestinal conditions is critical. Simulating gastric digestion with a static model and a single set of parameters is particularly challenging because the variations in pH and enzyme concentration occurring in the stomach are much broader than those occurring in the small intestine. A review of the literature on this topic reveals that most models of gastric digestion use very low pH values that are not representative of the fed conditions. This is illustrated here by showing the variations in gastric pH as a function of meal gastric emptying instead of time. This representation highlights those pH values that are the most relevant for testing meal digestion in the stomach. Gastric lipolysis is still largely ignored or is performed with microbial lipases. In vivo data on gastric lipase and lipolysis have however been collected in humans and dogs during test meals. The biochemical characterization of gastric lipase has shown that this enzyme is rather unique among lipases: (i) stability and activity in the pH range 2 to 7 with an optimum at pH 4-5.4; (ii) high tensioactivity that allows resistance to bile salts and penetration into phospholipid layers covering TAG droplets; (iii) sn-3 stereospecificity for TAG hydrolysis; and (iv) resistance to pepsin. Most of these properties have been known for more than two decades and should provide a rational basis for the replacement of gastric lipase by other lipases when gastric lipase is not available.

Understanding the lipid-digestion processes in the GI tract before designing lipid-based drug-delivery systems

Many of the compounds present in lipid-based drug-delivery systems are esters, such as acylglycerols, phospholipids, polyethyleneglycol mono- and di-esters and polysorbate, which can be hydrolyzed by the various lipolytic enzymes present in the GI tract. Lipolysis of these compounds, along with dietary fats, affects the solubility, dispersion and bioavailibity of poorly water-soluble drugs. Pharmaceutical scientists have been taking a new interest in fat digestion in this context, and several studies presenting in vitro gastrointestinal lipolysis models have been published. In most models, it is generally assumed that pancreatic lipase is the main enzyme involved in the gastrointestinal lipolysis of lipid formulations. It was established, however, that gastric lipase, pancreatic carboxyl ester hydrolaze and pancreatic lipase-related protein 2 are the major players involved in the lipolysis of lipid excipients containing acylglycerols and polyethyleneglycol esters. These findings have shown that the lipolysis of lipid excipients may actually start in the stomach and involve several lipolytic enzymes. These findings should therefore be taken into account when testing in vitro the dispersion and bioavailability of poorly water-soluble drugs formulated with lipids. In this review, we present the latest data available about the lipolytic enzymes involved in gastrointestinal lipolysis and suggest tracks for designing physiologically relevant in vitro digestion models.

Dietary counseling versus dietary supplements for malnutrition in chronic pancreatitis: a randomized controlled trial

BACKGROUND & AIMS

Up to 50% of patients with chronic pancreatitis (CP) are malnourished. There are limited data on the role of dietary intervention in improving the nutritional status of such patients. The aim was to compare the efficacy of medium chain triglyceride (MCT)-enriched commercial dietary supplements with dietary counseling for homemade food in the management of malnutrition in patients with CP.

METHODS

In a randomized controlled trial, consecutive undernourished patients with CP (body mass index [BMI] <18.5 kg/m(2)) at a tertiary care hospital were randomized to receive either dietary counseling for regular homemade food or commercial MCT-enriched dietary supplements for a period of 3 months to compensate for the dietary calorie deficit. All patients received standard management for CP including pancreatic enzyme supplements. Primary outcome measure was improvement in BMI.

RESULTS

Sixty malnourished patients with CP were randomized to counseling group (n = 29; mean age, 32 +/- 10 years; male, 83%) and supplementation group (n = 31; mean age, 28 +/- 10 years; male, 84%). BMI increased in both the counseling group and supplementation group (17.2 +/- 1.7 vs 18.1 +/- 1.8 kg/m(2), P = .001; 16.7 +/- 1.6 vs 18.2 +/- 1.6 kg/m(2), P = .001). There were similar improvements in triceps skinfold thickness, dietary intake, fecal fat, and pain score during a period of 3 months in both groups. There was, however, no significant difference between the counseling and supplementation groups with regard to any of the outcome measures.

CONCLUSIONS

Dietary counseling for a balanced homemade diet is as good as commercial food supplements in improving malnutrition in patients with CP.

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.

Quantitative and qualitative study of gastric lipolysis in premature infants: do MCT-enriched infant formulas improve fat digestion?

Intragastric fat digestion was investigated by analyzing the products of lipolysis and the gastric lipase (HGL) levels of premature infants fed with a formula enriched with medium chain triglycerides (MCT) and those of infants fed with human milk. Infants were fed using a gastric tube and the gastric contents were aspirated twice a day for 5 d, before and at various times after gavage feeding. HGL levels were measured using the pHstat technique. After extraction, lipids were separated and quantified using thin-layer chromatography coupled to a flame ionization detector. Fatty acid methyl esters were analyzed by gas chromatography. HGL concentration increased during digestion, reaching 77.4 +/- 43.1 microg/mL (around 75% of those recorded in adults). Mean HGL output was 115 +/- 43 microg for 3 h and the overall intragastric lipolysis was 6.1 +/- 2.6%. Although the formula was enriched with octanoic and decanoic acid, the main fatty acids released in the stomach were palmitic (C16:0, 17.03 +/- 0.23% wt/wt) and oleic (C18:1 n-9, 28.23 +/- 1.26% wt/wt) acid. Similar results were obtained with infants fed with human milk. MCT supplementation has no quantitative or qualitative effects on the intragastric lipolysis, which is not higher in premature infant than in adults.

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.

Treatment of alcoholic pancreatitis

Chronic pancreatitis is characterized by progressive and irreversible loss of pancreatic exocrine and endocrine function. The majority of cases in the Western world are related to alcohol consumption. Treatment of alcoholic chronic pancreatitis has been difficult, since the mechanisms of disease progression and the causes of pain are poorly understood. The conservative management of chronic pancreatitis focuses on (a) avoidance of precipitating factors such as alcohol and smoking; (b) treatment of pain, and (c) replacement of exocrine and endocrine function. There is a lack of good controlled, randomized treatment trials in alcoholic pancreatitis. However, there is good evidence that lifestyle changes, such as alcohol cessation, hamper progression of the disease. Conservative treatment of pain should be based on a stepwise approach; however, underlying causes such as pseudocysts may require endoscopic or surgical therapy. Treatment of exocrine insufficiency requires pancreatic enzyme supplementation and adjustment to several smaller meals per day, while treatment of endocrine insufficiency requires insulin treatment.

Cephalic phase of lipolysis is impaired in pancreatic insufficiency: role of gastric lipase

BACKGROUND

Gastric lipase contributes significantly to overall lipolysis and is regulated by interacting neuro-hormonal mechanisms. Patients with alcoholic chronic pancreatitis (ACP) have low, or even absent, activity of pancreatic lipases. In that state the secretion of gastric lipase could be essential and compensate for the pancreatic defect. However, conflicting studies have not resolved the order of magnitude of gastric lipase secretion in these patients. This could be explained by differences in regulatory mechanisms, gastric mucosal changes, and abdominal vagal tone.

METHODS

Nasogastric intubation with modified sham feeding and upper endoscopy including biopsies for histologic classification and Helicobacter pylori infection status were performed in eight ACP patients, and eight healthy volunteers were studied on separate occasions. Vagal nerve function was assessed by calculation of heart rate variability in ACP patients. Gastric lipase was measured in aspirates by means of enzyme-linked immunosorbent assay and an enzyme kinetic assay. Plasma concentrations of gastrin, secretin, cholecystokinin, and pancreatic polypeptide were measured throughout the study.

RESULTS

Sham feeding rapidly and significantly increased gastric lipase secretion in healthy volunteers, whereas ACP patients did not respond to sham feeding. Two of eight patients were infected with H. pylori and had mucosal changes accordingly. The lack of lipase response could not be ascribed to dysfunction of the abdominal vagus.

CONCLUSIONS

The cephalic phase of gastric lipase secretion is impaired in ACP patients. Although their fundic cells continue to secrete gastric lipase, they are not subject to normal neuro-hormonal regulation.

Effect of medium- and long-chain triglycerides on lower esophageal sphincter pressure: role of CCK

Fat meals are known to decrease lower esophageal sphincter (LES) pressure, possibly through postprandial CCK release. Dietary fat consists mainly of long-chain triglycerides (LCT), which potently stimulate CCK secretion. This effect contrasts with that of medium-chain triglycerides (MCT), which do not induce CCK release. We recorded LES pressure and gallbladder volume in six healthy subjects on five separate occasions during intraduodenal administration of 1) saline control, 2) LCT, 3) MCT, 4) LCT during intravenous infusion of the CCK receptor antagonist loxiglumide, and 5) MCT together with loxiglumide. LES pressure decreased significantly during administration of both LCT and MCT. Loxiglumide completely prevented the reduction in LES pressure during intraduodenal LCT, but not during intraduodenal MCT. Gallbladder volume decreased during LCT, but not during MCT. It is concluded that intraduodenal administration of equimolar amounts of both LCT and MCT significantly reduces LES pressure. The effect of LCT on LES pressure is mediated by CCK. The effect of MCT is not dependent on CCK, since MCT does not release CCK and loxiglumide does not prevent the MCT-induced reduction in LES pressure.

Deficient gastric lipase secretion in pancreatic insufficiency

BACKGROUND

Gastrin is an important stimulator of gastric lipase secretion in man. In advanced pancreatic insufficiency gastric lipases might compensate for the lack of pancreatic lipases, but the role of gastrin in such compensation remains to be evaluated. The aim of this study was to examine the effect of gastrin on the gastric lipase secretion in patients with pancreatic insufficiency.

METHODS

Eight patients with pancreatic insufficiency secondary to alcohol abuse were studied, and six healthy subjects volunteered as controls for the study. All volunteers received identical doses of intravenous gastrin-17 (10, 30, and 60 pmol/kg/h). The gastric content was measured, using a nasogastric tube for aspiration, and the amount and activity of gastric lipase output were determined. Plasma concentrations of gastrin, secretin, and cholecystokinin were measured by radioimmunoassays.

RESULTS

The increased plasma levels of gastrin were accompanied by a dose-dependent increase in the amount and activity of gastric lipase in controls, but in the patients the response was almost abolished.

CONCLUSIONS

Gastrin in postprandial concentrations does not influence the secretion of gastric lipase in patients with pancreatic insufficiency due to chronic pancreatitis.

Low doses of pentagastrin stimulate gastric lipase secretion in man

BACKGROUND

Gastric lipase is an important enzyme for dietary triglyceride digestion in normal subjects. Its regulation is unknown, as is the relation between the quantity and activity of the enzyme.

METHODS

In a dose-response study we investigated the effect of low doses of pentagastrin (less than 1000 ng/kg/h) on the output of gastric lipase measured by a kinetic assay and an enzyme-linked immunosorbent assay (ELISA).

RESULTS

In five healthy volunteers stepwise intravenous pentagastrin infusions of 0, 50, 100, 500, and 1000 ng/kg/h resulted in a stepwise increase in the lipase output, as measured with ELISA. However, the lipolytic activity, measured with a kinetic assay, decreased as the pH of the gastric contents decreased.

CONCLUSION

We conclude that secretion of the gastric lipase is stimulated by pentagastrin, but the simultaneous secretion of acid counteracts the lipolytic activity of the enzyme when food is not present.

Effect of equimolar amounts of long-chain triglycerides and medium-chain triglycerides on small-bowel transit time in humans

BACKGROUND

The use of medium-chain triglycerides in diets is limited by the frequent occurrence of diarrhea or crampy abdominal pain. Because these symptoms may result from an accelerated transit time induced by medium-chain triglycerides, we investigated the effect of equimolar amounts of long-chain triglycerides and medium-chain triglycerides on small-bowel transit time in 10 healthy subjects.

METHODS

Small-bowel transit time was measured by the lactulose hydrogen breath test after intraduodenal administration of lactulose.

RESULTS

Intraduodenal administration of 20 mmol of long-chain triglycerides per hour for 90 minutes did not alter small-bowel transit time compared with control (77 +/- 11 minutes vs 77 +/- 10 minutes, respectively), whereas intraduodenal infusion of an equimolar dose of medium-chain triglycerides significantly accelerated small-bowel transit time (59 +/- 6 minutes) compared with long-chain triglycerides and control (p < .05). In six individuals, small-bowel transit time was shorter during the administration of medium-chain triglycerides compared with control, and three of these subjects experienced abdominal symptoms. Plasma cholecystokinin levels increased significantly (p < .05) during the administration of long-chain triglycerides, from 2.6 +/- 0.3 pmol/L to a maximum of 4.3 +/- 0.6 pmol/L. No significant alterations were observed in plasma cholecystokinin levels during administration of medium-chain triglycerides or in the control experiment.

CONCLUSIONS

Although it significantly increases cholecystokinin secretion, the intraduodenal infusion of long-chain triglycerides does not affect small-bowel transit time, whereas the infusion of medium-chain triglycerides accelerates small-bowel transit time, independent of cholecystokinin.

Comparative effects of adjuvant cimetidine and omeprazole during pancreatic enzyme replacement therapy

In a double-blind, randomized crossover study, the hypotheses were tested that more powerful inhibition of gastric acid secretion by adjuvant omeprazole further improves the efficacy of pancreatic enzyme replacement therapy compared to adjuvant cimetidine and that excluding the influence of pH-related factors, by virtually complete inhibition of gastric acid secretion with 60 mg omeprazole daily, does not lead to total elimination of steatorrhea. During both adjuvant cimetidine and omeprazole treatment, fecal fat excretion was significantly lower compared to pancreatin monotherapy (P < 0.01). Omeprazole showed a trend towards a more favorable decrease of fecal fat excretion compared to cimetidine but no statistically significant difference. Steatorrhea was almost never abolished, even during 60 mg omeprazole daily. Generally, pH-related factors are considered to explain an inadequate therapeutic response during pancreatic enzyme replacement therapy. However, this study indicates that in vivo other factors also play a significant role.

Variation of gastric lipase secretion in the Heidenhain pouch of the cat

In the cat, gastric lipase secretion was equally but weakly stimulated by pentagastrin, a major stimulant of acid secretion, and by carbamylcholine, a major stimulant of pepsin secretion. Lipase was also stimulated by fresh liver, which induces a large blood gastrin release and not by canned food, which is a poor gastrin releaser. Lipase output always preceded that of acid an pepsin. Lipase was not correlated with acid and pepsin secretion while acid and pepsin were well correlated during all stimulations but not in basal state. Lipase is co-localized with pepsin in the chief cells but is also present in pepsin-free cells, the mucus surface cells of the fundus and the antrum. The distribution of lipase explains the lack of correlation between pepsin and lipase as already mentioned. However, our data show that lipase secretion is under the control of gastric stimulants and might play a role in the gastric initiation of pancreatic meal lipolysis.

Cholinergic and pentagastrin stimulation of the gastric secretions of acid, pepsin and lipase in the awake rabbit

Acid, pepsin and lipase secretions were simultaneously studied in awake rabbits with a Heidenhain pouch during cholinergic (carbamylcholine 20 micrograms.kg-1 x h-1) or maximal pentagastrin stimulation (64 mu.kg-1 x h-1). To avoid lipase inactivation by low pH, the pouch was perfused at a constant pH, with a solution irrigating the pouch without inducing any pressure. Acid and pepsin outputs were equally activated by both stimulants. Lipase output was stimulated much more by pentagastrin (x26) than by carbamylcholine (x6). The maximal lipase output preceded that of acid output. Lipase concentration increased in the gastric juice whereas pepsin concentration remained constant. A negative correlation was calculated between acid and lipase or pepsin and lipase output. A positive correlation was obtained between acid and pepsin. Our data show that pepsin and lipase secretions which come from distinct chief cells, in the rabbit, responded to the same stimulants but with quantitative and timing differences.

Dog gastric lipase: stimulation of its secretion in vivo and cytolocalization in mucous pit cells

Dog gastric lipase (DGL) secretion is stimulated in vivo by urecholine, pentagastrin, histamine, 16,16-dimethyl prostaglandin E2, and secretin. Under fasting conditions, DGL is irreversibly inactivated by gastric acid below pH 1.5; consequently, DGL output can be underestimated. This problem has been resolved by buffering the acid or by using an antisecretory drug such as omeprazole during stimulation. There is a clear parallelism between the secretion of DGL and of gastric mucus. This observation led to the present investigation of the cellular localization of DGL using immunofluorescence techniques. Results showed that DGL is cytolocalized in mucous pit cells of gastric glands. Pepsinogen is found in chief cells. To the authors' knowledge, this is the first description of an enzyme (gastric lipase) secreted by mucous-type gastric cells. In contrast to other species, gastric lipase of the dog is located in cardiac, fundic, and antral mucosae.