Chymotrypsinogen in the intestine of rats fed soybean trypsin inhibitor and its inability to suppress pancreatic enzyme secretions

Factors Influencing Proteolysis and Protein Utilization in the Intestine of Pigs: A Review

Pigs are among the most important farm animals for meat production worldwide. In order to meet the amino acid requirements of the animals, pigs rely on the regular intake of proteins and amino acids with their feed. Unfortunately, pigs excrete about two thirds of the used protein, and production of pork is currently associated with a high emission of nitrogen compounds resulting in negative impacts on the environment. Thus, improving protein efficiency in pigs is a central aim to decrease the usage of protein carriers in feed and to lower nitrogen emissions. This is necessary as the supply of plant protein sources is limited by the yield and the cultivable acreage for protein plants. Strategies to increase protein efficiency that go beyond the known feeding options have to be investigated considering the characteristics of the individual animals. This requires a deep understanding of the intestinal processes including enzymatic activities, capacities of amino acid transporters and the microbiome. This review provides an overview of these physiological factors and the respective analyses methods.

Protein Corona Liposomes Achieve Efficient Oral Insulin Delivery by Overcoming Mucus and Epithelial Barriers

Oral delivery of peptide/protein drugs has attracted worldwide attention due to its good patient compliance and convenience of administration. Orally administered nanocarriers always encounter the rigorous defenses of the gastrointestinal tract, which mainly consist of mucus and epithelium barriers. However, diametrically opposite surface properties of nanocarriers are required for good mucus penetration and high epithelial uptake. Here, bovine serum albumin (BSA) is adsorbed to cationic liposomes (CLs) to form protein corona liposomes (PcCLs). The aim of using PcCLs is to conquer the mucus and epithelium barriers, eventually improving the oral bioavailability of insulin. Investigations using in vitro and in vivo experiments show that the uptake amounts and transepithelial permeability of PcCLs are 3.24- and 7.91-fold higher than that of free insulin, respectively. Further study of the behavior of PcCLs implies that BSA corona can be shed from PcCLs as they cross the mucus layer, which results in the exposure of CLs to improve the transepithelial transport. Intrajejunal administration of PcCLs in type I diabetic rats produces a remarkable hypoglycemic effect and increases the oral bioavailability up to 11.9%. All of these results imply that PcCLs may provide a new insight into the method for oral insulin delivery by overcoming the multiple barriers.

Dietary levels of protein and free amino acids affect pancreatic proteases activities, amino acids transporters expression and serum amino acid concentrations in starter pigs

The dietary contents of crude protein and free amino acids (AA) may affect the protein digestion and AA absorption in pigs. Trypsin and chymotrypsin activities, AA serum concentrations and expression of AA transporters in the small intestine of pigs fed a low protein, AA-supplemented (19.2%, LPAA) or a high protein (28.1%, HP), wheat-soybean meal diet were measured in two 14-d trials. The LPAA diet contained free L-Lys, L-Thr, DL-Met, L-Leu, L-Ile, L-Val, L-His, L-Trp and L-Phe. All pigs were fed the same amount of feed (890 and 800 g/d for trial 1 and 2 respectively). In trial 1, samples of mucosa (duodenum, jejunum and ileum) and digesta (duodenum and jejunum) were collected from 14 pigs (17.2 ± 0.4 kg); in trial 2, blood samples were collected from 12 pigs (12.7 ± 0.3 kg). The trypsin and chymotrypsin activities in both intestinal segments were higher in pigs fed the HP diet (p < 0.01). Trypsin activity was higher in jejunum than in duodenum regardless the dietary treatment (p < 0.05). Pigs fed the LPAA diet expressed more b^0,+ AT in duodenum, B⁰ AT1 in ileum (p < 0.05), and tended to express more y⁺ LAT1 in duodenum (p = 0.10). In pigs fed the LPAA diet, the expression of b^0,+ AT was higher in duodenum than in jejunum and ileum (p < 0.01), but no difference was observed in pigs fed the HP diet. Ileum had the lowest b^0,+ AT expression regardless the diet. The serum concentrations of Lys, Thr and Met were higher in LPAA pigs while serum Arg was higher in HP pigs (p < 0.05). Serum concentrations of AA appear to reflect the AA absorption. In conclusion, these data indicate that the dietary protein contents affect the extent of protein digestion and that supplemental free AA may influence the intestinal site of AA release and absorption, which may impact their availability for growth of young pigs.

Aflatoxin B1 misregulates the activity of serine proteases: possible implications in the toxicity of some mycotoxin

Aflatoxins are highly hazardous contaminants of common food and feed. Aflatoxin B1 in particular, the most predominant among aflatoxins, was thoroughly demonstrated to be highly toxic, mutagenic, teratogenic and carcinogenic in many animal species. Besides its established targets and effects, this work investigates on the possible direct interaction between aflatoxin B1 and three major serine proteases, namely elastase, thrombin and trypsin. These proteases belongs to a class of structurally and functionally related proteins pivotal in both direct and indirect regulation of a number of cellular events. Additionally, several pathological processes, including cancer, inflammatory processes and thrombosis, rely upon the subtle equilibrium between these enzymes and their potential modulators: in fact, their misregulation, caused by foreign molecules, could facilitate (or be the cause for) the occurrence of these pathologies. Our results provide the evidence for a reversible binding between AFB1 and these enzymes, likely to have profound implications in the manifestation of aflatoxicosis. Precisely, the toxin behaved as a moderate competitive inhibitor toward the enzymatic activity of the serine proteases in the low micromolar range.

Feedback inhibition of cholecystokinin secretion by bile acids and pancreatic proteases

Feedback inhibition of CCK release by bile acids and pancreatic proteases is well established in the rat. The question of whether these mechanisms are important in humans has not been completely resolved, but current evidence strongly suggests that feedback regulation of CCK release by bile acids is present in humans and is physiologically significant, whereas the existence and importance of feedback regulation of CCK release by pancreatic proteases in humans are still highly controversial.

Effect of chymotrypsin on human cholecystokinin release: use of clostripain in the validation of a new radioimmunoassay

We have developed and validated a new radioimmunoassay for cholecystokinin. In order to establish that the antiserum binds large and small forms of CCK to an equal extent, we used the microbial enzyme clostripain, which cleaves large forms of CCK yielding CCK 8. Cleavage by clostripain of synthetic and purified forms of CCK, and CCK extracted at from human jejunum and CCK in human plasma was found not to affect immunoactivity, indicating that the antiserum reacts similarly with all forms of CCK. There is controversy over whether intraduodenal trypsin inhibits release of CCK in man. We used our radioimmunoassay to investigate whether chymotrypsin, rather than trypsin, could be the major mediator of negative feedback control of CCK release. Six normal subjects received an intraduodenal infusion of L-phenylalanine and L-tryptophan on two occasions, with the addition of either 1 g/l bovine chymotrypsin or 1 g/l albumin. Plasma CCK concentrations rose in response to the amino acid infusion, but were not affected by the addition of chymotrypsin, indicating that this enzyme is not a mediator of CCK feedback regulation in man.

Mechanism of increased exocrine pancreatic secretion in pancreatic juice-diverted rats

We investigated a possible role of endogenous cholecystokinin-pancreozymin (CCK-PZ) in the mechanism of exocrine pancreatic secretion after excluding pancreatic juice from the intestine in rats. Fasting plasma immunoreactive CCK-PZ was determined in normal rats, in rats with pancreatic duct ligation, and in sham-operated rats. The mean fasting plasma CCK-PZ concentration of rats with pancreatic duct ligation, 25.1 +/- 2.0 pM, was significantly greater (p less than 0.001) than those of normal and sham-operated rats, 14.3 +/- 1.7 and 11.5 +/- 2.2 pM, respectively. Whereas mean postprandial plasma CCK-PZ concentrations of normal and sham-operated rats were significantly greater (p less than 0.001) than their fasting levels, no significant increase occurred in the rats with pancreatic duct ligation after a meal. The mean fasting plasma CCK-PZ concentration of rats with pancreatic duct ligation was comparable to the mean postprandial CCK-PZ level of normal and sham-operated rats. To determine a possible role of circulating endogenous CCK-PZ on the pancreatic secretion, anesthetized rats were prepared with ligation of pylorus and cannulation of pancreatic duct. After diversion of pancreatic juice began, pancreatic secretion including protein significantly increased, which coincided with a significant increase in plasma CCK-PZ concentration. The increases in both pancreatic secretion and plasma CCK-PZ were reversed by intraduodenal administration of bovine trypsin or rat pancreatic juice. Furthermore, the increase in pancreatic secretion was abolished by intravenous infusion of proglumide or an intravenous bolus injection of a rabbit anti-CCK-PZ serum, which also blocked clearly the increase in the pancreatic secretion stimulated by exogenous CCK-PZ8 (0.125 micrograms X kg-1 X h-1) in rats. Thus we conclude that the increase in pancreatic secretion resulting from elimination of pancreatic juice from the intestine is attributable, in part, to increased release of CCK-PZ, and thus it is suggested that trypsin in the intestinal lumen plays a significant role in release of CCK-PZ.

Negative feedback inhibition of pancreatic exocrine secretion in humans

The evidence is quite solid that a feedback inhibition system of the pancreatic exocrine secretion exists in a number of animal species. Whether or not such a regulatory system is operative in man remains controversial. Studies in normal human subjects which have been interpreted as evidence that such a regulatory system is not present in man suffer from serious flaws in experimental design, such as the inability to completely divert pancreatic enzymes (chymotrypsin, elastase) as important principles in this control mechanism. Studies in both normal human subjects and patients with chronic pancreatitis will be reviewed.

Effect of obstructive jaundice on amylase secretion in rat pancreatic acini

The effect of obstructive jaundice on pancreatic amylase secretion was studied in isolated pancreatic acini prepared from bile duct ligated rats (7 days postoperatively), sham operated rats being used as control. Obstructive jaundice caused increase in pancreatic wet weight, pancreatic protein content and pancreatic amylase content by 27.9%, 40.1% and 33.2%, respectively. In acini prepared from obstructive jaundice group, compared with acini from sham operation group, responsiveness to cholecystokinin (CCK) and carbachol was decreased when amylase release was expressed as the percentage of total amylase activity initially present in acini. However, sensitivity to both secretagogues was unchanged when expressed as the percentage of maximally stimulated amylase release. The dose-response curves to Ca2+ ionophore for amylase release were similarly shaped in both groups. These results suggested that a pancreatico-trophic effect, compared with altered responsiveness of pancreatic acini, should play a major role in hypersecretion in obstructive jaundice.

Exocrine pancreatic function in rats after acute trypsin inhibitor treatment

A single oral dose of synthetic trypsin inhibitor (TI, 20 mg/100 g) was given to rats by orogastric tube 6, 12, 18, or 24 hr before the removal of the pancreas and the preparation of isolated perfused pancreas. TI treatment induced no significant changes in body weight and total amount of DNA content in the pancreas, but pancreatic wet weight, total pancreatic protein and amylase, and the concentration of total protein and amylase relative to DNA were significantly decreased at 6 or 12 hr posttreatment, with a partial return toward control values at 18-24 hr after TI treatment. In isolated perfused pancreas, basal amylase output was similar in the control and in all 4 groups of TI-pretreated rats, while basal rate of flow of pancreatic juice was significantly increased at 12-24 hr posttreatment. Caerulein (0.1 ng/ml; 64 pM) stimulated pancreatic juice flow was greatly increased in rats pretreated with TI 12-24 hr earlier. In contrast, caerulein-stimulated amylase output was significantly lower in TI-pretreated groups compared with the control. However, when amylase output was related to the total content in the pancreas, the secretory responsiveness for amylase release was significantly higher in rats at 6-18 hr posttreatment compared with the control. The present study indicates that a single oral administration of TI modulates biological response to caerulein in the isolated perfused pancreas. The enhanced responsiveness of amylase release to subsequent stimulation is seen in early periods, while that of pancreatic juice flow is observed in late periods.

Kinetics of native and modified Bowman-Birk soya-bean trypsin inhibitor on growth and enzymes activities of the chick pancreas

1. The Bowman-Birk soya-bean trypsin inhibitor (BBTI) begins to cause pancreatic enlargement and increased enzymic activity in the pancreas of chicks after a minimum of 7 d of feeding. 2. The active inhibitory site of BBTI against trypsin is the factor involved in the pancreatic enlargement and increase of pancreatic enzyme activity in chicks.

Significance for humans of biologically active factors in soybeans and other food legumes

Among the many biologically active factors present in the soybean, only protease inhibitors (PI) have been shown to exert significant adverse effects on animals consuming diets containing soybean protein. Evidence is presented to suggest that (a) PI are only partially responsible for the poor nutritive value of inadequately processed soybeans, (b) low levels of PI are relatively harmless to animals, (c) human trypsin is only weakly inhibited by PI, and (d) the human pancreas is probably insensitive to the hypertrophic effects of PI. Parelleling the wide spread distribution of PI in the plant kingdom are the so called phytohemagglutinins or lectins. Unlike the lectin present in soybeans which appears to have only a marginal effect on the nutritional quality of the protein, the lectin of the common bean (Phaseolus vulgaris) is quite toxic. Moreover, the major storage protein of such beans is quite resistant to digestion unless denatured by heat, thus emphasizing the importance of adequate processing of those legumes when used in the human diet. Although goiter‐inducing compounds are present in most cruciferous plants and cyanide‐producing substances may be found in cassava and lima beans, traditional methods of preparation and present technology have served to minimize any harmful effects that may accompany the ingestion of these foods by man. Brief mention will also be made of two human diseases, lathyrism and favism, associated with the consumption ofLathyrus sativus andVicia faba, respectively, their causative agents and mechanism of action. Although there are numerous examples of so called toxic constituents in legumes, they nevertheless have provided a valuable source of protein to man over the centuries. This can be attributed, in part, to the fact that man has learned how to detoxify them by suitable preparative measures. The varied nature of our diet also minimizes the contribution of a toxicant from any one foodstuff. Nevertheless, there is the ever present possibility that the prolonged consumption of a particular legume that may be improperly processed could bring to the surface toxic effects that otherwise would not be apparent. As the shortage of protein becomes more acute, it is not unlikely that much of the population of the world will be faced, in the future, with a more limited selection of protein‐foods, most of which will be of plant origin and, hence, potential carriers of toxic constituents. The food scientist should at least be cognizant of such a possibility and be prepared to apply his knowledge and skill to meeting this challenge.

Changes in rat pancreatic protein synthesis after a single feeding with diets containing raw or heated soybeans

The patterns of protein synthesis following the administration of a single meal containing defatted ground soybeans (RSD) or heated defatted ground soybeans (HSD) were compared. A double label method was used so that the determination of the relative rate of synthesis of an enzyme could not be obscured by a possible alteration of the activity or quantity of the enzyme. Rats were given one meal of RSD or HSD and were subsequently killed at different times after the meal. Eight hours after the meal, the relative rate of synthesis of one of the three trypsinogens was substantially increased with RSD feeding, whereas that of the amylases and one chymotrypsinogen were somewhat lower. The synthetic rate of lipase, ribonclease, proelastase, another chymotrypsinogen and of two trypsinogens was unaffected when feeding RSD is compared to feeding HSD. The relative rate of synthesis of one of the trypsinogens was unaffected 8 hours after RSD feeding, but was increased 16 hours after RSD feeding. Actinomycin D could suppress the effects of RSD feeding on the protein synthetic rate of some, but not of all, secretory proteins.

Effect of bile duct obstruction on pancreatic enzyme secretion and intestinal proteolytic enzyme activity in the rat

The role of bile in regulation of intestinal proteolytic activity in rats was investigated by studying the effects of bile diversion and bile duct obstruction on pancreatic protease secretion and on recovery of protease from the intestine. Diversion of bile and pancreatic juice from the intestine caused a large increase in pancreatic enzyme secretion; replacement of bile partially suppressed this response. Bile duct obstruction resulted (3-4 days postobstruction) in a threefold increase in pancreatic juice chymotrypsin but caused a large decreases in intestinal trypsin and chymotrypsin activities and total proteolytic activity. Recovery of pancreatic juice protein (labeled with 14C) from intestinal contents was markedly decreased in bile duct obstruction, indicating a more rapid rate of degradation and absorption of pancreatic jucie protein. The evidence suggests that interruption of bile flow results in an accelerated rate of degradation of pancreatic proteolytic enzymes, and that the increase in pancreatic enzyme secretion is an adaptation to decreased intestinal proteolytic activity.

Adaptation of the domestic chicken, Gallus domesticus, to continuous feeding of albumin amylase inhibitors from wheat flour as gastro-resistant microgranules

Albumin amylase inhibitors were extracted from wheat flour, precipitated by salting out the extract with ammonium sulphate, and enclosed in cellulose-coated microgranules resistant to the peptic action in the chicken gizzard. Continuous intake of gastro-resistant wheat albumins significantly (P less than 0.01) depressed chicken growth rate, whereas native wheat albumins did not show such an effect. After 4 weeks of treatment, treated chickens showed a growth rate identical to that of control chickens thus showing that an adaptation to the presence of wheat albumins in the diet had occurred. Treated chickens also showed pancreas hypertrophy and a number of histological changes in the pancreas indicating degenerative processes in progress. Moreover, in treated chickens the production of pancreatic amylase was markedly increased (P less than 0.02), whereas pancreatic protease activity was less affected. The data obtained suggest that the synthesis of pancreatic amylase in chicken is under some homeostatic control of alpha-amylase in the intestine.

Effect of dietary raw soybean and soybean trypsin inhibitor on trypsin and chymotrypsin activities in the pancreas and in small intestinal juice of growing swine

Sixty-eight growing gilts with a 12 kg average initial weight were used in seven trials to study the effect of dietary raw soybean (Harosov) and SBTI (Kunitz soybean trypsin inhibitor) on pancreatic and small intestinal trypsin and chymotrypsin activities. A solvent-extracted, heated soybean meal (SBM) was used, cause reduced growth. Both a single-meal and continuous feeding of the raw soybean diet caused a decrease in the pancreatic trypsin and chymotrypsin activities. In contrast, to the rat and the chick, the pancreas of the pigs did not enlarge subsequent to consumption of the raw soybean or SBTI diets. Raw soybean feeding also resulted in an inhibition of the intestinal trypsin and chymotrypsin activities. This inhibiting effect was greater than that of the SBTI, especially the chymotrypsin-inhibiting effect. This suggested that soybean constituents other than the SBTI, such as the Bowman-Birk inhibitor, caused inhibition. In the pig the inhibition of the intestinal proteolysis may be a major cause of reduced growth when raw soybean is fed.

Enteropancreatic circulation of digestive enzymes

Intact digestive enzymes can be absorbed by the intestine and resecreted by the pancreas. The pancreas, therefore, appears to be able to recycle proteins much as the liver recycles bile salts, although the magnitude of this process remains uncertain.