Effect of a trypsin inhibitor from soybeans (Bowman-Birk) on the secretory activity of the human pancreas

Investigation of the nutritional quality of raw and processed Canadian faba bean (Vicia faba L.) flours in comparison to pea and soy using a human in vitro gastrointestinal digestion model

Faba bean is an ancient legume that is regaining interest due to its environmental and nutritional benefits. Very little is known on the protein quality of the new faba bean varieties. In this study, the digestibility and the Digestible Indispensable Amino Acid Score (DIAAS) of the protein quality of three Canadian faba bean varieties (Fabelle, Malik and Snowbird) were compared to pea and soy using the harmonized in vitro digestion procedure developed by the International Network of Excellence on the Fate of Food in the Gastrointestinal Tract (INFOGEST). The impact of boiling on the nutritional quality of faba bean flours was also ascertained. Protein content in faba bean (28.7-32.5%) was lower than defatted soy (56.6%) but higher than pea (24.2%). Total phenolics and phytate content were higher (p < 0.05) in faba bean (2.1-2.4 mg/g and 11.5-16.4 mg/g respectively) and soy (2.4 mg/g and 19.8 mg/g respectively) comparatively to pea (1.3 mg/g and 8.9 mg/g). Trypsin inhibitor activity was significantly higher (p < 0.05) in soy (15.4 mg/g) comparatively to pea (0.7 mg/g) and faba bean (0.8-1.1 mg/g). The digestibility of free amino acids of raw faba bean flours ranged from 31 to 39% while the digestibility of total amino acids ranged from 38 to 39%. The in vitro Digestible Indispensable Amino Acid Score (IV-DIAAS) of raw faba bean flours ranged from 13 to 16 (when calculated based on free amino acid digestibility) to 32-38 (when calculated based on total amino acid digestibility) and was in a similar range to pea (13-31) and soy (11-40). Boiling modified the protein electrophoretic profile and decreased trypsin inhibitor activity (30-86% reduction), while total phenolics and phytate content were unaffected. The IV-DIAAS significantly decreased in all boiled legumes, possibly due to an increased protein aggregation leading into a lower protein digestibility (18-32% reduction). After boiling, the nutritional quality of faba bean was significantly lower (p < 0.05) than soy, but higher than pea. Our results demonstrate that faba bean has a comparable protein quality than other legumes and could be used in similar food applications.

The soymilk diet: A previously unknown etiology of acute pancreatitis

We present a case of daily, large ingestions of soymilk that likely led to acute pancreatitis. Soybean contains trypsin inhibitor that when ingested will reduce the activity of trypsin in the intestine. A decrease in intestinal proteolytic activity removes the negative feedback on the pancreatic acinar cells, leading to an inappropriate increase in intrapancreatic trypsin secretion. When trypsin activation exceeds the capacity of pancreatic secretory trypsin inhibitor, the subsequent cascade of events can lead to acute pancreatitis.

A Novel, Orally Delivered Antibody Therapy and Its Potential to Prevent Clostridioides difficile Infection in Pre-clinical Models

Clostridioides difficile infection (CDI) is a toxin-mediated infection in the gut and a major burden on healthcare facilities worldwide. We rationalized that it would be beneficial to design an antibody therapy that is delivered to, and is active at the site of toxin production, rather than neutralizing the circulating and luminal toxins after significant damage of the layers of the intestines has occurred. Here we describe a highly potent therapeutic, OraCAb, with high antibody titers and a formulation that protects the antibodies from digestion/inactivation in the gastrointestinal tract. The potential of OraCAb to prevent CDI in an in vivo hamster model and an in vitro human colon model was assessed. In the hamster model we optimized the ratio of the antibodies against each of the toxins produced by C. difficile (Toxins A and B). The concentration of immunoglobulins that is effective in a hamster model of CDI was determined. A highly significant difference in animal survival for those given an optimized OraCAb formulation versus an untreated control group was observed. This is the first study testing the effect of oral antibodies for treatment of CDI in an in vitro gut model seeded with a human fecal inoculum. Treatment with OraCAb successfully neutralized toxin production and did not interfere with the colonic microbiota in this model. Also, treatment with a combination of vancomycin and OraCAb prevented simulated CDI recurrence, unlike vancomycin therapy alone. These data demonstrate the efficacy of OraCAb formulation for the treatment of CDI in pre-clinical models.

Anabolic Properties of Mixed Wheat-Legume Pasta Products in Old Rats: Impact on Whole-Body Protein Retention and Skeletal Muscle Protein Synthesis

The mechanisms that are responsible for sarcopenia are numerous, but the altered muscle protein anabolic response to food intake that appears with advancing age plays an important role. Dietary protein quality needs to be optimized to counter this phenomenon. Blending different plant proteins is expected to compensate for the lower anabolic capacity of plant-based when compared to animal-based protein sources. The objective of this work was to evaluate the nutritional value of pasta products that were made from a mix of wheat semolina and faba bean, lentil, or split pea flour, and to assess their effect on protein metabolism as compared to dietary milk proteins in old rats. Forty-three old rats have consumed for six weeks isoproteic and isocaloric diets containing wheat pasta enriched with 62% to 79% legume protein (depending on the type) or milk proteins, i.e., casein or soluble milk proteins (SMP). The protein digestibility of casein and SMP was 5% to 14% higher than legume-enriched pasta. The net protein utilization and skeletal muscle protein synthesis rate were equivalent either in rats fed legume-enriched pasta diets or those fed casein diet, but lower than in rats fed SMP diet. After legume-enriched pasta intake, muscle mass, and protein accretion were in the same range as in the casein and SMP groups. Mixed wheat-legume pasta could be a nutritional strategy for enhancing the protein content and improving the protein quality, i.e., amino acid profile, of this staple food that is more adequate for maintaining muscle mass, especially for older individuals.

Rational Use of Pancreatic Enzymes for Pancreatic Insufficiency and Pancreatic Pain

We describe the rational use of enteric coated and unprotected replacement pancreatic enzymes for treatment of malabsorption due to pancreatic insufficiency and for pancreatic pain. Enteric coated formulations mix poorly with food allowing separation of enzymes and nutrients when emptying from the stomach. The site of dissolution of the enteric coating in the intestine is also unpredictable and enzymes may not be released until the distal intestine. Together, these barriers result in the lack of dose-response such that the strategy of increasing the dosage following a suboptimal effect is often ineffective. The ability to maintain the intragastric pH ≥4 with the combination of proton pump inhibitors and antacids suggests that it should be possible to reliably obtain a good response with uncoated enzymes. We also discuss the recognition, treatment and prevention of nutritional deficiencies associated with pancreatic insufficiency and recommend a test and treat strategy to identify and resolve nutritional deficits. Finally, we focus on mechanisms causing pain that may be amenable to therapy with pancreatic enzymes. Pain due to malabsorbed digestive contents can be prevented by successful therapy of malabsorption. Feedback inhibition of endogenous pancreatic secretion can prevent pain associated with pancreatic secretion but requires use of non-enteric coated formulations.

Cholecystokinin (CCK) Regulation of Pancreatic Acinar Cells: Physiological Actions and Signal Transduction Mechanisms

Pancreatic acinar cells synthesize and secrete about 20 digestive enzymes and ancillary proteins with the processes that match the supply of these enzymes to their need in digestion being regulated by a number of hormones (CCK, secretin and insulin), neurotransmitters (acetylcholine and VIP) and growth factors (EGF and IGF). Of these regulators, one of the most important and best studied is the gastrointestinal hormone, cholecystokinin (CCK). Furthermore, the acinar cell has become a model for seven transmembrane, heterotrimeric G protein coupled receptors to regulate multiple processes by distinct signal transduction cascades. In this review, we briefly describe the chemistry and physiology of CCK and then consider the major physiological effects of CCK on pancreatic acinar cells. The majority of the review is devoted to the physiologic signaling pathways activated by CCK receptors and heterotrimeric G proteins and the functions they affect. The pathways covered include the traditional second messenger pathways PLC-IP3-Ca²⁺ , DAG-PKC, and AC-cAMP-PKA/EPAC that primarily relate to secretion. Then there are the protein-protein interaction pathways Akt-mTOR-S6K, the three major MAPK pathways (ERK, JNK, and p38 MAPK), and Ca²⁺ -calcineurin-NFAT pathways that primarily regulate non-secretory processes including biosynthesis and growth, and several miscellaneous pathways that include the Rho family small G proteins, PKD, FAK, and Src that may regulate both secretory and nonsecretory processes but are not as well understood. © 2019 American Physiological Society. Compr Physiol 9:535-564, 2019.

Bowman-Birk inhibitor affects pathways associated with energy metabolism in Drosophila melanogaster

Bowman-Birk inhibitor (BBI) is toxic when fed to certain insects, including the fruit fly, Drosophila melanogaster. Dietary BBI has been demonstrated to slow growth and increase insect mortality by inhibiting the digestive enzymes trypsin and chymotrypsin, resulting in a reduced supply of amino acids. In mammals, BBI influences cellular energy metabolism. Therefore, we tested the hypothesis that dietary BBI affects energy-associated pathways in the D. melanogaster midgut. Through microarray and metabolomic analyses, we show that dietary BBI affects energy utilization pathways in the midgut cells of D. melanogaster. In addition, ultrastructure studies indicate that microvilli are significantly shortened in BBI-fed larvae. These data provide further insights into the complex cellular response of insects to dietary protease inhibitors.

Negative control of human pancreatic secretion: physiological mechanisms and factors

The negative control of pancreatic exocrine secretion in man occurs during the interdigestive and postprandial periods of the digestive cycle. The physiological mechanisms involved include negative feedback mechanisms, well described and accepted in animals, and controlled by the cholecystokinin- and secretin-releasing factors of pancreatic and duodenal origin, along with the active pancreatic proteases present in the upper gut. The presence of these factors and their efficacy in humans, however, have their supporters and detractors, with a possibility for reconciliation among opponents. Besides these releasing factors, hormones, mostly from the intestine, are also involved in this inhibitory process of pancreatic secretion. Somatostatin, peptide YY, pancreatic polypeptide, glucagon, ghrelin, and leptin were described as potentially involved from studies mostly performed on animals. Finally, bile and bile salts have mixed responses on this inhibition, and their effects seem to be at the intestine level with gastrointestinal hormones involved. Future studies will have to be performed in humans to determine the presence of cholecystokinin- and secretin-releasing factors and their role. Finally, the demonstrated modulatory action of hormones and bile acids in other species needs to be confirmed in humans.

The biochemical and functional food properties of the bowman-birk inhibitor

The Bowman-Birk inhibitor (BBI) is a small water-soluble protein present in soybean and almost all monocotyledonous and dicotyledonous seeds. The molecular size of BBI ranges from 1,513 Da to about 20,000 Da. BBI is to seeds what alpha(1)-antitrypsin is to humans. Soy-based food products rich in BBI include soybean grits, soymilk, oilcake, soybean isolate, and soybean protein concentrate. BBI is stable within the pH range encountered in most foods, can withstand boiling water temperature for 10 min, resistant to the pH range and proteolytic enzymes of the gastrointestinal tract, bioavailable, and not allergenic. BBI reduces the proteolytic activities of trypsin, chymotrypsin, elastase, cathepsin G, and chymase, serine protease-dependent matrix metalloproteinases, urokinase protein activator, mitogen activated protein kinase, and PI3 kinase, and upregulates connexin 43 (Cx43) expression. Several studies have demonstrated the efficacy of BBI against tumor cells in vitro, animal models, and human phase IIa clinical trials. FDA considers BBI as a drug. In 1999, FDA allowed a health claim on food labels stating that a daily diet containing 25 grams of soy protein, also low in saturated fat and cholesterol, may reduce the risk of heart disease [corrected] This review highlights the biochemical and functional food properties of the Bowman-Birk inhibitor.

Lack of trophic pancreatic effects in humans with long-term administration of ximelagatran

OBJECTIVES

Negative feedback regulation of pancreatic proteases controls pancreatic secretion in most species and pancreatic growth in rodents. Its mechanism involves the inhibition of intraluminal proteases, resulting in sustained elevation of plasma cholecystokinin (CCK) concentrations, producing a chronic trophic stimulus to the pancreas that leads to the formation of pancreatic nodules and adenomas. Ximelagatran, whose active form, melagatran, inhibits both thrombin and the serine protease trypsin, is under clinical development as an oral anticoagulant. Recent data indicate species differences in the expression of CCK receptor subtypes in the pancreas. CCK1 receptors are abundant in rat pancreas but are either absent or present at very low levels in human pancreas. As part of the clinical studies, we examined whether long-term ximelagatran administration causes CCK release and exerts possible trophic effects on the pancreas in humans.

METHODS

One hundred thirty patients requiring anticoagulation treatment for atrial fibrillation randomly received, in a double-blind fashion, either 36 mg oral ximelagatran twice daily or warfarin dose adjusted to an international normalized ratio of 2.0 to 3.0. Before enrollment and after 12 months of treatment, computed tomography scans of the pancreas were performed, and pancreas volumes were quantified using the summation-of-areas technique. Three months after the initiation of drug treatment, plasma CCK concentrations were measured by radioimmunoassay 120 minutes after the patients drank 240 mL of a mixed liquid meal (Ensure).

RESULTS

After 3 months of treatment, plasma CCK concentrations did not differ between the ximelagatran and warfarin groups, 15 +/- 18 and 11 +/- 17 pmol/L (X +/- SD; P = 0.22), respectively. The initial average pancreas volumes were 82 +/- 31 and 88 +/- 28 mL in the ximelagatran and warfarin groups, respectively, and decreased to 70 +/- 25 and 75 +/- 28 mL, respectively, after 12 months of treatment. Although the decrease in pancreas volume with time was significant in each group (P = 0.0001), the magnitude of the volume reduction was similar in the 2 groups.

CONCLUSION

In contrast to rats, in which long-term oral administration of ximelagatran stimulates pancreatic growth and adenoma formation, in humans, ximelagatran does not increase plasma CCK concentrations and has no demonstrable trophic effect on the human pancreas.

In vitro inhibition of the activation of Pro-matrix Metalloproteinase 1 (Pro-MMP-1) and Pro-matrix metalloproteinase 9 (Pro-MMP-9) by rice and soybean Bowman-Birk inhibitors

The in vitro inhibitory activity of the rice Bowman-Birk inhibitor (rBBI) or soybean Bowman-Birk inhibitor (sBBI) against trypsin-catalyzed activation of pro-matrix metalloproteinase 1 or 9 (pro-MMP-1 or pro-MMP-9), respectively, was investigated using electrophoresis with silver staining, heparin-enhanced zymography, biotinylated gelatin, Biotrak assay, and fluorescence quenched substrate hydrolysis. rBBI at concentrations of 0.08-0.352 mg/mL dose-dependently inhibited the in vitro activation of 45 microg/mL pro-MMP-1 by trypsin. Heparin-enhanced zymography analysis of pro-MMP-1, trypsin-activated MMP-1, and a mixture of pro-MMP-1-trypsin-rBBI showed clear zones associated with trypsin-activated MMP-1 and the absence of clear zones in lanes containing pro-MMP-1 or a mixture of pro-MMP-1, trypsin, and rBBI. The results of the Biotrak assay also indicated that rBBI dose-dependently suppressed the activation of pro-MMP-1 by trypsin. sBBI dose-dependently inhibited the activation of 100 microg/mL of pro-MMP-9 by trypsin. Biotinylated gelatin assays demonstrated that pro-MMP-9 or pro-MMP-9 in the presence of trypsin and BBI did not hydrolyze gelatin, whereas p-aminophenylmercury acetate (APMA)-activated MMP-9 and trypsin-activated MMP-9 caused significant hydrolysis of gelatin. Quenched fluorescence substrate hydrolysis for total MMP activity showed that pro-MMP-1 or pro-MMP-9 did not hydrolyze the substrate Mca-Pro-Leu-Gly-Leu-Dpa-Ala-Arg-NH2; active MMP-1 or MMP-9 hydrolyzed the substrate, but lower substrate hydrolysis was obtained when pro-MMP-1 or pro-MMP-9 was incubated with trypsin in the presence of increasing concentrations of rBBI. The results are discussed in light of the role of MMP-1 and MMP-9 in the process of angiogenesis and the potential of rBBI or sBBI as a functional food ingredient.

Persistent decreased plasma cholecystokinin levels in celiac patients under gluten-free diet: respective roles of histological changes and nutrient hydrolysis

Celiac disease is associated with impaired cholecystokinin (CCK) release. The mechanism by which CCK release is impaired is poorly understood and seems to be related to the mucosal atrophy or to decreased stimulation due to reduced intraduodenal nutrient hydrolysis. The aims of our study were to evaluate basal and postprandial CCK in celiac patients presenting with distinctive types of mucosal lesions (normal, infiltrative and atrophic), and to study the role of protein hydrolysis on CCK release. Plasma CCK was measured in 20 celiac patients (normal mucosa: n=6; infiltrative type: n=6; atrophic type=8) and 9 controls, before and after ingestion of a polymeric or a semi-elemental meal. Significant decreases in basal CCK plasma (B 0.6 [95% CI, 0.3-1.3] pmol/l; p<0.003) and postprandial CCK area under curve (AUC 34 [19-61] pmol/l x 120 min, p<0.0001) were observed in patients with an atrophic mucosa compared with treated patients (B 1.6 [1.0-2.4] pmol/l, AUC 267 [172-414] pmol/l x 120 min) or healthy volunteers (B 1.0 [0.7-1.4] pmol/l, AUC 186 [131-264] pmol/l x 120 min). A significant defective CCK release was also observed in patients with an infiltrative type: B 0.4 [0.2-0.7] pmol/l and AUC 56 [31-101] pmol/l x 120 min; p<0.0001. Administration of a semi-elemental diet did not correct the defective CCK release. In conclusion, the decreased CCK levels observed in celiac patients are not strictly related to the mucosal atrophy but rather to the lymphocytic infiltrate. Administration of a predigested meal did not correct the impaired CCK release. Some inhibitory mechanism could be involved in the CCK cell dysfunction observed in celiac patients presenting with lesser degrees of disease activity.

A trail of research revisted

The author describes how his interest in the nutritional value of soybeans led to a trail of research that had many ramifications. In an attempt to account for the poor nutritional value of raw soybeans and the beneficial effect of heat treatment, a protein displaying hemagglutinating activity and capable of inhibiting the growth of rats was isolated and characterized. This protein subsequently proved to be an example of a class of proteins that were later referred to as "lectins". Lectins were also isolated from kidney beans and shown to be even more toxic than the soybean lectin. Concurrent studies with the soybean trypsin inhibitors revealed that these proteins inhibited growth by stimulating the secretory activity of the pancreas and could in the long term cause acinar cell adenoma of the pancreas. Acute experiments with human subjects showed that the human pancreas also responded to the stimulatory effects of the so-called Bowman-Birk soybean inhibitor. The studies on soybean trypsin inhibitors were expanded to include a protease inhibitor present in blood, alpha-1-antitrypsin, a deficiency of which leads to emphysema in humans. The mechanism whereby this protein inhibits leucocyte elastase was investigated. On the basis of these results the intratracheal administration of a synthetic peptide inhibitor of elastase attached to albumin microspheres was found to prevent elastase-induced emphysema in hamsters.

Pathological evaluation, clinical chemistry and plasma cholecystokinin in neonatal and young miniature swine fed soy trypsin inhibitor from 1 to 39 weeks of age

The potential toxicity of dietary soy trypsin inhibitor (TI) was evaluated in neonatal miniature swine. From 1 to 6 weeks of age, two groups of male piglets were artificially reared in an Autosow and automatically fed either TI or control liquid diet. From 6 to 39 weeks of age, these two groups were fed either TI or control chow diet. A third group, sow control (SC), suckled from birth to 6 weeks of age, were also weaned to control chow from 6 to 39 weeks of age. Clinical chemistry and plasma cholecystokinin (CCK) determined at 6, 18, 30 and 39 weeks of age, and serum amylase activity with gross and histopathological analyses of major organs at 6 and 39 weeks of age are reported. TI had no effect on plasma CCK, serum amylase activity, or numerous clinical chemistry values. TI-fed piglets had a larger relative liver weight at 6 weeks of age. Relative pancreas weight decreased with age but was not affected by TI. Gross and histopathological analyses of major organs, except the spleen, were within normal limits. Increased incidence of extramedullary hematopoiesis was noted in the spleen of the TI group at 6 but not at 39 weeks of age. There was no consistent pattern in immunohistochemical foci for secretin, gastrin releasing polypeptide or CCK, and no change in DNA, RNA, mitotic index or nuclear density of pancreatic cells. At 6 weeks of age, TI increased pancreatic protein and amylase activity but not trypsin or chymotrypsin activity. None of the effects suggested that this dose of TI was toxic to either the neonatal or sexually mature miniature male swine.

Luminal CCK-releasing factor stimulates CCK release from human intestinal endocrine and STC-1 cells

CCK is secreted into the blood from intestinal endocrine cells following ingestion of a meal. Recently, it has been demonstrated that the ability of certain foods to stimulate CCK release is mediated by endogenously produced CCK-releasing factors. A newly discovered luminal CCK-releasing factor (LCRF) is secreted into the intestine, where it stimulates CCK secretion. However, the mechanism whereby LCRF affects intestinal epithelial cells is unknown. The current study was designed to determine whether LCRF has a direct effect on CCK cells to stimulate hormone secretion. In dispersed human intestinal mucosal cells, LCRF (5-200 nM) significantly stimulated CCK release in a concentration-dependent manner. This stimulatory effect was absent in calcium-free media and was inhibited by the L-type calcium-channel blockers diltiazem and nifedipine. To examine direct cellular effects of LCRF on CCK cells, further studies were conducted in the CCK-containing enteroendocrine cell line STC-1. As in native cells, LCRF significantly stimulated CCK release from STC-1 cells in a calcium-dependent manner. In cells loaded with a calcium-sensitive dye, LCRF stimulation produced a rapid increase in intracellular calcium. To examine the electrophysiological basis for this stimulation, whole cell recordings were made from STC-1 cells. Whole cell calcium currents were identified under basal conditions; moreover, calcium-channel activity was increased by LCRF. These studies demonstrate that 1) LCRF has a direct effect on human intestinal cells to stimulate CCK secretion, 2) stimulated hormone release is calcium dependent, and 3) LCRF activates calcium currents in CCK cells, which leads to CCK secretion.

The influence of the albumin fraction on the bioavailability and postprandial utilization of pea protein given selectively to humans

Pulse seed proteins such as those found in peas (Pisum sativum) contain fractions of very dissimilar composition and properties, which may therefore be differently utilized by the human body. To analyze the nutritional value of the soluble protein fractions of pea seed, human volunteers ingested a mixed meal of 30 g of raw purified pea protein either as [15N]-globulins (G, n = 9) or as a mix of [15N]-globulins and [15N]-albumins (GA, n = 7) in their natural proportions (22:8). Dietary and endogenous nitrogen fluxes at the terminal ileum were assessed using a tube perfusion technique with an isotopic dilution method. Systemic dietary amino acid availability and the retention of dietary amino acids were determined using 15N enrichment in plasma amino acids and deamination products in blood and urine for 8 h postprandially. The results showed that the pea albumin fraction had the following effects: 1) significantly lowered the real ileal digestibility of pea protein (94 +/- 2.5% for G vs. 89.9 +/- 4% for GA), probably because of a direct effect of trypsin inhibitors; 2) did not promote acute intestinal losses of endogenous nitrogen; and 3) did not significantly improve the postprandial biological value of pea protein (76.5 +/- 3.9% for G vs. 78.7 +/- 3.6% for GA), despite the fact that it corrected the globulin deficiency in sulfur amino acids. We conclude that both G and GA are of good nutritional value for humans and show that cysteine-rich albumins have a far more modest effect on the efficiency of postprandial dietary protein utilization than would be expected from the amino acid scores.

Nutritional and health benefits of soy proteins

Soy protein is a major component of the diet of food-producing animals and is increasingly important in the human diet. However, soy protein is not an ideal protein because it is deficient in the essential amino acid methionine. Methionine supplementation benefits soy infant formulas, but apparently not food intended for adults with an adequate nitrogen intake. Soy protein content of another essential amino acid, lysine, although higher than that of wheat proteins, is still lower than that of the milk protein casein. Adverse nutritional and other effects following consumption of raw soybean meal have been attributed to the presence of endogenous inhibitors of digestive enzymes and lectins and to poor digestibility. To improve the nutritional quality of soy foods, inhibitors and lectins are generally inactivated by heat treatment or eliminated by fractionation during food processing. Although lectins are heat-labile, the inhibitors are more heat-stable than the lectins. Most commercially heated meals retain up to 20% of the Bowman-Birk (BBI) inhibitor of chymotrypsin and trypsin and the Kunitz inhibitor of trypsin (KTI). To enhance the value of soybeans in human nutrition and health, a better understanding is needed of the factors that impact the nutrition and health-promoting aspects of soy proteins. This paper discusses the composition in relation to properties of soy proteins. Also described are possible beneficial and adverse effects of soy-containing diets. The former include soy-induced lowering of cholesterol, anticarcinogenic effects of BBI, and protective effects against obesity, diabetes, irritants of the digestive tract, bone, and kidney diseases, whereas the latter include poor digestibility and allergy to soy proteins. Approaches to reduce the concentration of soybean inhibitors by rearrangement of protein disulfide bonds, immunoassays of inhibitors in processed soy foods and soybean germplasm, the roles of phytoestrogenic isoflavones and lectins, and research needs in all of these areas are also discussed. This integrated overview of the widely scattered literature emphasizes general concepts based on our own studies as well as recent studies by others. It is intended to stimulate interest in further research to optimize beneficial effects of soy proteins. The payoff will be healthier humans and improved animal feeds.

Fatores antinutricionais: inibidores de proteases e lectinas

Os fatores antinutricionais presentes em alimentos podem provocar efeitos fisiológicos adversos ou diminuir a biodisponibilidade de nutrientes. A maior questão sobre os riscos à saúde provocados por antinutrientes é o desconhecimento dos níveis de tolerância, do grau de variação do risco individual e da influência de fatores ambientais sobre a capacidade de detoxificação do organismo humano. Dentre os fatores antinutricionais os inibidores de proteases e as lectinas são considerados instáveis ao tratamento térmico. A hipertrofia pancreática causada pelos inibidores de tripsina tem sido relatada em alguns estudos com animais. As alterações da função fisiológica em animais causadas por ação de lectinas no intestino parecem estar relacionadas à especificidade destas substâncias com as células da mucosa intestinal. Os possíveis efeitos adversos dos inibidores de proteases e das lectinas na maioria das vezes são inferidos somente de experimentos com animais de laboratório.

Pathophysiological role of cholecystokinin in humans

Cholecystokinin (CCK) is a major gastrointestinal hormone that plays an important role in stimulation of pancreatic secretion and gall-bladder contraction, regulation of gastrointestinal motility and induction of satiety. Ingestion of fat and protein induces significant increases in plasma CCK. Intraluminal mediators of CCK secretion, luminal CCK releasing factor and diazepam-binding inhibitor, were purified from rat intestinal secretion. These CCK-releasing factors (RF) are secreted tonically by the small intestine and stimulate CCK release. Another kind of CCK-RF named 'monitor peptide' was purified from the rat pancreatic juice that stimulates CCK secretion when introduced into rat intestine. Bile exclusion from the duodenum causes an increase in basal CCK and enhances stimulated plasma CCK release, and bile salt replacement reverses these effects. Thus, the CCK-RF are spontaneously secreted into the intestinal lumen in humans, while the CCK-producing cells are under constant suppression by intraduodenal bile acids. In acute pancreatitis, plasma CCK levels are high in patients with gallstone pancreatitis, but not in patients with pancreatitis from other causes, such as alcoholic and idiopathic pancreatitis. A transient disturbance of bile flow into the duodenum by stones or oedema of the pancreas together with impairment of pancreatic exocrine function might cause the increase in plasma CCK release in gallstone pancreatitis. Patients with chronic pancreatitis with mild to moderate impairment of exocrine function and abdominal pain, had significantly higher plasma CCK concentrations, whereas patients with pancreatic insufficiency had a significantly lower plasma CCK response to a test meal than the healthy subjects. The increased CCK may further aggravate pancreatitis and worsen the prognosis of pancreatitis by stimulating the injured pancreas, resulting in the vicious circle via endogenous CCK release. The CCK-A receptor antagonist might be therapeutically useful in acute pancreatitis by stopping the vicious circle.

Enzymatic therapy in patients with chronic pancreatitis

Pancreatic enzyme replacement therapy has proved useful in the treatment of malabsorption and persistent pain in patients with chronic pancreatitis. The formulation of pancreatic enzyme preparation varies considerably. Treatment of chronic pain is facilitated by the use of a high-protease enzyme preparation, preferably non-microsphere encoated. Treatment of steatorrhea is optimized by use of high-lipase-containing preparations.

Palliation of pain in chronic pancreatitis. Use of enzymes

According to the concept of negative feedback regulation of pancreatic enzyme secretion by proteases, treatment with pancreatic extracts has been proposed to lower pain in chronic pancreatitis by decreasing pancreatic duct pressure. The author, however, has demonstrated in healthy volunteers that intraduodenal application of porcine pancreatic extracts does not inhibit but rather stimulates pancreatic enzyme secretion. This is probably because of the high-protein content of porcine pancreatic extracts that may overwhelm a potential inhibitory effect of proteases. In a prospective placebo-controlled, double-blind multicenter study to investigate the effect of acid-protected porcine pancreatic extracts on pain in 43 patients with chronic pancreatitis, pain improved in most patients regardless of whether they started with placebo or verum. There was no significant difference between both treatment arms. In a meta-analysis, which included the author's study, six randomized, double-blind, placebo-controlled studies were evaluated. Statistical analysis demonstrated no benefit of the application of porcine pancreatic extracts to relieve pain in chronic pancreatitis. The author concluded that pancreatic extracts neither inhibit pancreatic enzyme secretion nor are they efficient in lowering pain in chronic pancreatitis.

Adaptation of the human pancreas to inhibition of luminal proteolytic activity

BACKGROUND & AIMS

Feedback regulation of pancreatic enzyme secretion is well established in animals, and their pancreases are able to adapt to intraduodenal inhibition of pancreatic enzymes by proteinase inhibitors such as Camostate (FOY-305; Schwarz GmbH, Monheim, Germany). In this study, we addressed whether similar adaptive changes occur in the human pancreas after 4 weeks of 2 g/day Camostate application.

METHODS

Before, at the end of, and 2 weeks after 4-week Camostate treatment (four times 500 mg daily), pancreatic changes were analyzed with the use of a secretin-cerulein test, a test-meal stimulation, cholecystokinin plasma measurement, and standardized ultrasonographic investigations of the pancreas.

RESULTS

Duodenal trypsin output after secretion stimulation was significantly increased (+44%; P < 0.01) and duodenal bicarbonate output decreased 22% (P < 0.05) after 4 weeks of Camostate application. The size of the pancreatic head (vertical) increased 8% (P < 0.05) at week 4 and decreased to pretreatment values 2 weeks after treatment (week 6). The other three diameters measured (head oblique, body, and tail) showed a similar pattern. Stimulated cholecystokinin plasma levels 15 minutes after application of a standard test meal increased 62% (P < 0.05).

CONCLUSIONS

The human pancreas adapts to oral application of the proteinase inhibitor Camostate. These findings support the theory that feedback control of the exocrine pancreas operates in humans.

Chemopreventive agents: protease inhibitors

Certain protease inhibitors, called the anticarcinogenic protease inhibitors in this review, are capable of preventing carcinogenesis in a wide variety of in vivo and in vitro model systems. The anticarcinogenic protease inhibitors are extremely potent agents with the ability to prevent cancer, with some unique characteristics as anticarcinogenic agents. The anticarcinogenic protease inhibitors have the ability to irreversibly suppress the carcinogenic process. They do not have to be continuously present to suppress carcinogenesis. They can be effective when applied in both in vivo and in vitro carcinogenesis assay systems at long time periods after carcinogen exposure, and are effective as anticarcinogenic agents at extremely low molar concentrations. While several different types of protease inhibitors can prevent the carcinogenic process, the most potent of the anticarcinogenic protease inhibitors on a molar basis are those with the ability to inhibit chymotrypsin or chymotrypsin-like proteases. The soybean-derived protease inhibitor, Bowman-Birk inhibitor (BBI), is a potent chymotrypsin inhibitor that has been extensively studied for its ability to prevent carcinogenesis in many different model systems. Much of this review is focused on the characteristics of BBI as the anticarcinogenic protease inhibitor, as this is the protease inhibitor that has risen to the human trial stage as a human cancer chemopreventive agent. Part of this review hypothesizes that the Bowman-Birk family of protease inhibitors plays a role in plants similar to that of alpha1-antichymotrypsin in people. Both BBI and alpha1-antichymotrypsin are potent inhibitors of chymotrypsin and chymotrypsin-like enzymes, are highly anti-inflammatory, and are thought to play important roles in the defense of their respective organisms. It is believed that BBI will be shown to play a major role in the prevention and/or treatment of several different diseases, in addition to cancer.

Influence of high-dose pancreatic enzyme treatment on pancreatic function in healthy volunteers

CONCLUSIONS

Adaptive changes in exocrine and endocrine pancreatic function, as well as changes in pancreas size and morphology, were not observed after 4-wk of oral pancreatic enzyme application. These findings suggest that the normal pancreas does not significantly adapt--either morphologically or functionally--to a 4-wk oral application of high-dose pancreatic enzymes.

BACKGROUND

The control of exocrine pancreatic enzyme secretion is not completely understood. Although it has been established that exocrine pancreatic secretion is mainly regulated in the short-term by the amount of pancreatic enzymes in the proximal small intestine, it is not known whether long-term application of pancreatic enzymes causes changes in exocrine pancreatic secretion in humans.

METHODS

Twelve healthy male volunteers (median age 27 yr) participated in a prospective, randomized, placebo-controlled, double-blind study. Six were placed in the treatment group and six in the placebo group. Over a 4-wk period, the six subjects in the treatment group took 18 capsules of Panzytrat (20,000 units of lipase, 18,000 units of amylase, and 1000 units of protease per capsule) daily. Before (wk 0), 4 wk following pancreatic enzyme application and 2 wk afterward, a secretin-cerulein test was carried out in all subjects to study exocrine pancreatic function (trypsin, chymotrypsin, bicarbonate content, and total pancreatic fluid secretion in the duodenum). One day following the secretin-cerulein test, a standard test meal was given to all subjects to analyze endocrine pancreatic function. Additionally, before starting the treatment, once per week during treatment and 2 wk afterward, an ultrasound examination of the pancreas was carried out to see whether there was any change in pancreas size and morphology.

RESULTS

Trypsin content in the duodenal aspirates following simultaneous stimulation with secretin and cerulein after 4 wk of high-dose pancreatic enzyme application was 92% in the treatment group and 82% in the placebo group compared with the wk 0 test results (100%). Two weeks after enzyme application, the secretin/cerulein-stimulated trypsin content was 88% in the treatment group and 107% in the placebo group. None of these changes was statistically significant. The same results were seen for chymotrypsin content, amylase, and bicarbonate content as well as for total pancreatic fluid secretion. Additionally, no change in the endocrine pancreatic function could be observed after 4 wk of pancreatic enzyme treatment. Pancreas ultrasonography revealed no alteration in pancreas size or parenchymal structure during the 4 wk of treatment and the following 2 wk.

CCK-, secretin-, and cholinergic-independent pancreatic fluid hypersecretion in protease inhibitor-treated rats

Plasma cholecystokinin (CCK) levels in fed rats increased from 2.59 +/- 0.13 pmol/l to the peak of 27.6 +/- 4.1 pmol/l at 1 h after a single oral administration of synthetic protease inhibitor (PI; ethyl N-allyl-N-[(E)-2-methyl-3-[4-(4-amidino-phenoxycarbonyl)phenyl] propenoyl] amino acetate methansulfonate; 20 mg/kg body wt), but then returned to the preloading value at 12 h after administration. The pancreatic fluid secretion, rich in chloride but poor in bicarbonate, was significantly elevated at 6-12 h postfeeding (100.9 +/- 8.2 vs. 27.3 +/- 2.3 microliters/30 min in control rats, P < 0.01). Loxiglumide (50 mg.kg body wt-1.h-1), atropine (100 micrograms.kg body wt-1.h-1), or antisecretin serum (100 microliters/rat) at 12 h postfeeding did not modify the fluid hypersecretion. Loxiglumide, when given together with PI, completely abolished fluid hypersecretion, but it could not inhibit hypersecretion when applied 3 h after PI treatment. Labeling with 5-bromo-2'-deoxyuridine showed active proliferation of acinar cells at 3 h after PI treatment (3.56 +/- 0.29% vs. 0.46 +/- 0.08% in control, P < 0.001), but not in rats given loxiglumide together with PI. In rats that fasted from 12 h before to 12 h after PI feeding, neither pancreatic fluid hypersecretion nor active proliferation of acinar cells was observed. These results suggest that pancreatic fluid hypersecretion in fed rats at 6-12 h after PI treatment is caused not by CCK-, secretin-, or cholinergic-dependent mechanisms but probably by acinar cell proliferation.

Distribution and localization of a novel cholecystokinin-releasing factor in the rat gastrointestinal tract

The purpose of this study was to examine the distribution and localization of an intestinal cholecystokinin (CCK)-releasing factor, called luminal CCK-releasing factor (LCRF), in the gastrointestinal tract and pancreas of the rat. RIA analysis indicates that LCRF immunoreactivity is found throughout the gut including the pancreas, stomach, duodenum, jejunum, ileum, and colon with the highest levels in the small intestine. Immunohistochemistry analysis shows LCRF immunoreactivity staining in intestinal villi, Brunner's glands of the duodenum, the duodenal myenteric plexus, gastric pits, pancreatic ductules, and pancreatic islets. These results indicate potential sources for secretagogue-stimulated release of luminal LCRF and support the hypothesis that LCRF is secreted into the intestinal lumen to stimulate CCK release from mucosal CCK cells.

Protease inhibitors and carcinogenesis: a review

This brief review article deals with the subject of anticarcinogenic activity of protease inhibitors (PI). Three basic premises are made: (1) Although PI are prevalent constituents of dietary staples such as soy products, which have been epidemiologically associated with reduced cancer incidences at multiple target sites, they are unlikely to be the active anticarcinogenic entities. Cooked soy products, which are devoid of PI activity, are equally as effective at reducing cancer development as raw soy products. Isoflavones are likely to represent major chemopreventive agents in soy, although other constituents may well contribute. (2) Although supplementation of diets with PI (natural or synthetic), or direct topical administration, results in lower cancer incidences in many experimental models in vivo, this effect appears to be indirect. Dietary PI are, in general, poorly absorbed from the GI tract, and never reach target organs in any measurable quantity. The most attractive hypothesis is that dietary PI could induce synthesis and distribution of endogenous PI (acute-phase reactants), which have widespread effects on cell growth and behavior. Effects of topical administration of PI also encompass prominent anti-inflammatory effects. (3) A spectrum of PI inhibit in vitro transformation induced by a variety of carcinogenic agents. Their effects can be grouped into three basic categories, affecting: (a) signal transduction pathways; (b) DNA repair processes; and (c) nuclear proteases. I suggest that the nuclear multicatalytic protease activity, in particular the chymotrypsin-like activity, represents an important cellular target for which considerable anecdotal support can be garnered.

Bile-pancreatic juice replacement not cholinergic- and cholecystokinin-receptor blockade reverses acinar cell hyperstimulation after bile-pancreatic duct ligation

BACKGROUND

Acinar cell inhibitors (eg, atropine) fail to ameliorate clinical and experimental acute pancreatitis. We hypothesized that amelioration of pancreatic acinar cell hyperstimulation after bile and pancreatic duct ligation is better with gut replacement of bile and pancreatic juice than with cholinergic- and cholecystokinin (CCK)-receptor blockade.

METHODS

Using acinar cell amylase activity as an index of hyperstimulation, we studied 63 rats in two sets of experiments. Bile-pancreatic juice exclusion from gut--without (set one) and with (set two) bile and pancreatic duct obstruction--was treated with atropine and CCK-receptor antagonist L-364,718, or with enteral replacement of bile-pancreatic juice.

RESULTS

In the set one experiment, acinar cell hyperstimulation after bile-pancreatic juice exclusion was reversed by combined L-364,718 and atropine pretreatment. In set two, acinar cell hyperstimulation after bile and pancreatic duct ligation was reversed by enteral bile and pancreatic juice replacement, but not by combined L-364,718 and atropine pretreatment.

CONCLUSIONS

According to this experimental corollary of early gallstone impaction, prevention of acinar cell hyperstimulation after duct occlusion should be aimed at the source of the response to bile-pancreatic juice exclusion, namely, the gut, rather than at the target of the response, the pancreatic acinar cell.

Development and regulation of porcine pancreatic function

A surgical and experimental procedure was developed to enable the collection of pure and inactivated pancreatic juice during the growth of the pig. Studies have shown that, during the suckling period, both the basal and the secretory responses to suckling are low, if present at all. After weaning, basal levels of the total exocrine secretion, total protein, amylase, and trypsin, respectively, increase slightly, while the postprandial levels of total protein, amylase, trypsin, lipase, colipase, and carboxylester lipase, respectively, increase markedly. The pancreatic juice enzyme composition changes qualitatively and the antibacterial activity of the pancreatic juice also significantly increases. Piglet age appeared to be of minor importance, since weaning at either 4 or 6 wk of age gave the same results. Secretin and CCK administered together in supraphysiological doses only significantly affect exocrine function from 3-4 wk of age. However, CCK may also affect the exocrine pancreas indirectly via reflexes initiated intraduodenally. Milk consumption in the suckling pig leads to a postprandial increase in glucose levels but not insulin. Milk appears to be able to regulate the exocrine pancreas to produce only the amount and type of enzymes required for digestion. Thus, milk components or digestive products may affect pancreas function regulation. Studies show that enterostatin, the procolipase activation peptide, may inhibit pancreatic secretion mediated indirectly through the GI tract. Pancreastatin, an endocrine peptide, inhibits both insulin secretion and protein and trypsin secretion to pancreatic juice. In hypoinsulinemic (alloxan+streptozotocin diabetes) pigs (15-20 kg), no postprandial pancreatic juice response is seen, although CCK 33 + secretin can stimulate pancreatic secretion. Hypoinsulinemic pigs have a reduced capacity for glucose tissue utilization, suggesting that tissue metabolism and exocrine pancreas secretion are related.

No effect of long-term treatment with pancreatic extract on recurrent abdominal pain in patients with chronic pancreatitis

BACKGROUND

This study was aimed to investigate the effect of long-term treatment with high-protease pancreatic extract on the recurrent abdominal pain of patients with chronic pancreatitis.

METHODS

Twenty-six patients with a firm diagnosis of chronic pancreatitis and a pattern of recurrent pain were recruited and randomly assigned to treatment with pancreatic extract (Pancrex-Duo capsules, each containing 34,375 USP units of protease in enteric-coated microspheres) or placebo, at a dose of four capsules four times daily, for 4 months. At the end of the first period patients were switched to the other medication for the next 4 months. Four patients did not complete the study because of unbearable recurring pain or inadequate compliance with treatment. The other 22 patients daily recorded the presence, intensity, and duration of pain and the consumption of analgesics, for 8 months.

RESULTS

No difference was found when intraindividual records during placebo and extract treatment periods were compared. Conversely, in the second 4 months of follow-up, regardless of the treatment given in the first period, there was a significant reduction in the cumulative pain score (median, 95; range, 0-1005, versus 134; 0-972; p < 0.05), in the number of days (8; 0-132, versus 13; 0-126; p < 0.02) and hours (54; 0-680, versus 80; 0-602; p < 0.05) of pain, and in the analgesic consumption score (0; 0-22, versus 12; 0-44; p = 0.02).

CONCLUSIONS

Chronic supplementation with pancreatic extract is not beneficial in the management of recurrent pain in patients with chronic pancreatitis.

Inhibitor-stimulated non-parallel pancreatic secretion in man: hormonal and neural regulation?

BACKGROUND

We wanted to study whether a total inhibition of tryptic activity in the duodenum would induce a cholecystokinin (CCK)-dependent increase in pancreatic exocrine proteinase secretion.

METHODS

Concentrations of CCK and activities and concentrations of pancreatic enzymes were measured in human plasma and duodenal juices, respectively, collected during continuous intraduodenal instillations of proteinase inhibitors, with and without intravenous atropine administration.

RESULTS

Inhibitor instillation totally abolished tryptic activity and reduced the chymotryptic and elastase (1 and 2) activities by 95-100%. The inhibitors caused a rapid increase in the concentrations of trypsin, chymotrypsin, and pancreatic secretory trypsin inhibitor (PSTI) but had only a slight or no effect on amylase and elastase 1 secretion. An enhanced secretion of PSTI lends support to a possible connection between PSTI (resembling the monitor peptide causing CCK release in rats) and the enzyme secretion in man. CCK increased from 7 to 12-13 pmol/l. Intravenous atropine almost completely blocked the inhibitor-stimulated enzyme and PSTI secretion and reduced amylase activity by 50%. A further significant (P = 0.002) increase in the inhibitor-induced CCK output was found during atropine administration, as compared with the test situation without atropine.

CONCLUSION

The inhibitor-induced pancreatic secretion during total inhibition of tryptic activity shows a non-parallel secretion requiring different signals for different enzymes. The increase in plasma CCK levels indicates that CCK is feedback-regulated by both an inhibitor-mediated decrease in duodenal enzyme activity and a further decrease in pancreatic enzyme secretion by atropine.

Roles of gut hormones in negative-feedback regulation of pancreatic exocrine secretion in humans

BACKGROUND/AIMS

Secretin has been shown to mediate feedback control of pancreatic secretion of fluid and bicarbonate in rats, guinea pigs, and dogs. However, little is known about secretin in the feedback regulation in humans. We investigated the roles of secretin, cholecystokinin, neurotensin, and pancreatic polypeptide on feedback regulation of pancreatic secretion in 10 human volunteers.

METHODS

A 5-lumen tube was positioned in the proximal jejunum of fasting subjects under fluoroscopy so that gastric juice via lumen 1 and duodenal contents via lumen 3 were collected separately in 15-minute samples while polyethylene glycol solution was infused into duodenum via lumen 2. An acidified (pH 2.0) 4.25% amino acid mixed with phenol red was infused into proximal jejunum via lumen 4, which was alternated with NaHCO3 (control solution) or trypsin (test solution) via lumen 5 intermittently every 15 minutes during separate test periods.

RESULTS

Infusion of control solution significantly increased both bicarbonate (total change [delta], 7799 +/- 1400 mumol/h) and chymotrypsin (delta 5500 +/- 762 mumol/h) outputs and levels of all four plasma hormones. The test solution significantly inhibited both bicarbonate (delta 2999 +/- 700 mumol/h; P < 0.01) and chymotrypsin output (delta 1000 +/- 120 U/h, P < 0.01), which coincided with a significant suppression of plasma concentration of secretin and cholecystokinin but not pancreatic peptide and neurotensin.

CONCLUSIONS

A negative-feedback regulation of pancreatic secretion of bicarbonate and enzyme occurs in humans and is mediated via both secretin and cholecystokinin.

Effect of bile salt binding or protease inactivation on plasma cholecystokinin and gallbladder responses to bombesin

BACKGROUND/AIMS

Bombesin-stimulated plasma cholecystokinin levels decrease after an initial increase despite continuous infusion of bombesin. The aim of this study was to determine if a feedback mechanism, mediated by bile salts or proteolytic enzymes, is responsible for this decline.

METHODS

Bombesin (1.0 ng.kg-1.min-1) was infused into volunteers for 180 minutes on separate occasions. Cholestyramine, colestipol, camostate, or saline were perfused intraduodenally during the second hour of the tests. Cholestyramine was also administered without infusion of bombesin.

RESULTS

Colestipol and cholestyramine, dependent on their bile salt-binding capacity, markedly enhanced (P < 0.05) bombesin-stimulated plasma cholecystokinin from 2.1 +/- 0.5 pmol/L to 6.4 +/- 2.2 pmol/L and 12.1 +/- 3.3 pmol/L (P < 0.05 vs. colestipol), respectively, and further decreased gallbladder volume (P < 0.05) from 9.4 +/- 1.6 mL to 2.0 +/- 0.4 mL and 2.2 +/- 0.5 mL, respectively. The protease inhibitor camostate had no effect. Bile salt precipitation also enhanced plasma pancreatic polypeptide responses (P < 0.01) but did not alter gastrin responses. Plasma cholecystokinin responses to cholestyramine without bombesin infusion varied considerably, but increments were highly correlated to decreases in gallbladder volume (r = 0.91; P < 0.005).

CONCLUSIONS

Bile salt sequestration but not protease inactivation enhances plasma cholecystokinin and gallbladder responses to bombesin infusion in humans.

Gastro-jejunal digestion of soya-bean-milk protein in humans

In order to determine how soya-bean proteins are digested and metabolized in the human intestine before colonic bacterial fermentation and to estimate their true digestibility, the gastro-jejunal behaviour of soya-bean proteins in water and in two other forms (a concentrated soya-bean-protein solution (isolate) and a drink composed of crude soya-bean proteins (soymilk)) was studied in humans. Experiments were carried out in eight healthy volunteers using a double-lumen steady-state intestinal perfusion method with polyethyleneglycol (PEG) as a non-absorbable volume marker. Gastric emptying and N and electrolyte contents of the jejunal digesta were analysed. Gastric half-emptying time (min) of the liquid phase after water ingestion (12.59 (SE 0.12)) was shorter (P < 0.05) than those for soymilk (37.74 (SE 11.57)) and isolate (36.52 (SE 11.23)). Electrolytic balances showed that for all meals, Na+, Cl- and K+ were secreted when Ca2+ was efficiently absorbed from the jejunal lumen. Gastro-jejunal N absorption for isolate and soymilk were 63 and 49% respectively, and were not significantly different from one another; after water ingestion, endogenous N was estimated to be 21 mmol. An estimate of the exogenous:endogenous values for the effluents was obtained from the amino acid compositions of soymilk and effluents after water or soymilk ingestion, indicating that 70% of the total N was exogenous and 30% endogenous. Under these conditions the endogenous fraction represented 31 mmol after soymilk ingestion and the gastro-jejunal N balance indicated that 54% of the soymilk was absorbed. This finding indicates that the true gastrojejunal digestibility of soya-bean proteins is similar to that of milk proteins.

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.

Implications of antinutritional components in soybean foods

There are a number of components present in soybeans that exert a negative impact on the nutritional quality of the protein. Among those factors that are destroyed by heat treatment are the protease inhibitors and lectins. Protease inhibitors exert their antinutritional effect by causing pancreatic hypertrophy/hyperplasia, which ultimately results in an inhibition of growth. The lectin, by virtue of its ability to bind to glycoprotein receptors on the epithelial cells lining the intestinal mucosa, inhibits growth by interfering with the absorption of nutrients. Of lesser significance are the antinutritional effects produced by relatively heat stable factors, such as goitrogens, tannins, phytoestrogens, flatus-producing oligosaccharides, phytate, and saponins. Other diverse but ill-defined factors appear to increase the requirements for vitamins A, B12, D, and E. The processing of soybeans under severe alkaline conditions leads to the formation of lysinoalanine, which has been shown to damage the kidneys of rats. This is not generally true, however, for edible soy protein that has been produced under milder alkaline conditions. Also meriting consideration is the allergenic response that may sometimes occur in humans, as well as calves and piglets, on dietary exposure to soybeans.

Effect of duodenal juice on bombesin-stimulated cholecystokinin release during loxiglumide administration in man

Stimulation of cholecystokinin release by bombesin in augmented by cholecystokinin receptor blockade with loxiglumide. We hypothesize that this augmented cholecystokinin release results from inhibition of the pancreatico-biliary response to bombesin during cholecystokinin receptor blockade. To test this hypothesis, we infused bombesin for 180 min in six healthy subjects Three bombesin-infusion experiments were performed in each subject in random order on different days. In two of these experiments loxiglumide was co-infused with bombesin, while in the third experiment saline was co-infused with bombesin. In one of the loxiglumide experiments, duodenal juice, collected on the previous day during infusion of cholecystokinin-GIH, was reperfused intraduodenally during the second hour of bombesin infusion. In the saline experiment, the integrated cholecystokinin response during the first hour of bombesin-infusion (262 +/- 63 pmol 60 min-1) was significantly (P < 0.01) higher than during the second (88 +/- 26 pmol 60 min-1) and third (87 +/- 31 pmol 60 min-1) hour of bombesin-infusion. Loxiglumide augmented bombesin-stimulated cholecystokinin secretion from 262 +/- 63 pmol 60 min-1 to 453 +/- 63 pmol 60 min-1 in the first hour of bombesin infusion (P < 0.01). Integrated cholecystokinin values in the second (489 +/- 90 pmol 60 min-1) and third (450 +/- 74 pmol 60 min-1) hour of the loxiglumide experiment, were significantly (P < 0.01) higher than in the saline experiment.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Raw soybeans stimulate human pancreatic proteinase secretion

Intraduodenal instillation of raw soybeans stimulated pancreatic proteinase secretion in humans. Raw soybeans almost abolished the activity of chymotrypsin and severely reduced (50%) the tryptic activity. Immunoreactive tryptic and chymotryptic material simultaneously appeared in amounts 2 to 4 times basal concentrations. This increase, demonstrated with rocket immunoelectrophoresis, was begun within the first 10 min of soybean instillation. The enhanced secretion also persisted throughout the succeeding saline instillation, and it is suggested that the presence of Kunitz trypsin inhibitor contributed to this postprandial stimulation. An amidase that hydrolyzes low-molecular-weight substrates (i.e., benzoyl-arginine p-nitroanilide) was found in raw soybeans. Its low activity was not assumed to substantially bias standard trypsin assays. The increased proteinase secretion was, as previously published, not preceded by an elevated plasma cholecystokinin concentration. The raw soybeans also caused a nonparallel secretion of amylase and proteinases. Nervous, perhaps cholinergic, regulation mediates the inhibitor-stimulated proteinase secretion in humans. This stimulation yields both a general increase of proteinases and also a specific inhibitor-resistant trypsin. This is consistent with the physiologic need for proenzyme-activation in the presence of inhibitors and for restoration of the proteolytic capacity of the duodenal juice.

Changes in plasma and duodenal cholecystokinin concentrations after pancreatic duct occlusion in rats

The changes in plasma and duodenal cholecystokinin (CCK) concentrations after pancreatic duct occlusion were examined in rats. The rats were sacrificed 1, 3, 7, 10, 14, and 30 days after occlusion of the duct. Histological examination showed acute inflammation on days 1 and 3 after duct occlusion, interstitial fibrosis and regenerative changes on days 7, 10, and 14, and pancreatic atrophy on day 30. The plasma CCK concentration increased from 0.45 pM to 2.0 pM after the occlusion and then remained high throughout the observation period. In contrast to the stable increase in plasma CCK concentration, the CCK content in the duodenum increased on days 1 and 3, decreased on day 7, increased on day 10, reaching over the control level on day 14, and then returned to the control level on day 30. Administration of boiled and 10-fold concentrated rat pancreatic juice or human pancreatic secretory trypsin inhibitor for seven days after pancreatic duct occlusion reversed the decrease in duodenal CCK content. The major molecular forms of duodenal CCK were CCK-8, -33, and -58. These results indicate that (1) basal plasma CCK concentration did not reflect the duodenal CCK content, (2) duodenal CCK content was well correlated with a decrease in inflammation in the pancreas, and (3) a nonenzymatic component in the pancreatic juice reversed the decrease in duodenal CCK content and body weight caused by pancreatic duct occlusion.

Early indicators of exocrine pancreas carcinogenesis produced by non-genotoxic agents

In the past 40 years the incidence of pancreatic cancer in many Western countries had increased. Since no single factor responsible for the development of pancreatic cancer has been identified, it is believed that non-genotoxic factors may play an important role in the pathogenesis of this highly fatal form of cancer. Focal abnormalities of acinar cells, referred to as atypical acinar cell foci or nodules, occur spontaneously in rats and some other species. Their incidence increases with age from zero at birth to about 75% in 2-year-old rats. These spontaneous lesions have a phenotype that cannot be distinguished from the putative, atypical preneoplastic, acinar cell foci induced in rat pancreas by the carcinogen azaserine. Unsaturated fat (corn oil) has been found to increase the incidence of atypical acinar cell nodules and adenomas in the pancreas of non-carcinogen-treated rats without influencing the weight of the pancreas. Furthermore, unsaturated fat has a specific promoting effect on the growth potential of atypical acinar cell foci and nodules induced in rat pancreas by azaserine, resulting in an increase in the number and size of these lesions. Rats fed raw soya flour or trypsin inhibitors develop an enlarged pancreas as a result of hypertrophy and hyperplasia. They also develop acidophilic atypical acinar cell foci and nodules, adenomas and adenocarcinomas after being fed full-fat raw soya flour for 2 years. It may be concluded from the observations in rat pancreas that non-genotoxic compounds or conditions that enhance pancreatic growth may be classified as non-genotoxic pancreatic tumour promoters. The observations with corn oil, however, indicate that there may be non-genotoxic compounds that specifically enhance growth of spontaneous initiated atypical acinar cell foci without causing hyperplasia of the pancreas. The possible mechanisms whereby unsaturated fat and trypsin inhibitors exert their effects on exocrine pancreatic carcinogenesis are discussed.

Characterization of a human trypsin resistant to Kunitz soybean trypsin inhibitor. Studies of duodenal juices after tube instillation of raw soybean extract

Human duodenal juices collected during tube instillation of raw soybean extract into the duodenum contained free trypsin and free Kuntiz soybean trypsin inhibitor (KTI) in the simultaneous presence of trypsin-KTI complexes. It has previously been suggested that this KTI-non-inhibitable trypsin has a general resistance to serine protease inhibitors. Four different trypsin forms have been found and partly characterized by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and isoelectric focusing followed by Western immunoblotting or enzyme staining. In addition, crossed immunoelectrophoresis and affinity chromatography with antibody-coupled gels have been used for identification of free and inhibitor-complexed trypsin.