Digestion inhibition

Feeny (13) attempted to resolve this dilemma by proposing that forest trees may have developed a particularly recalcitrant defense, one which even insects could not overcome in hundreds of generations. His suggestion was that protein-complexing polyphenols, or tannins, could provide such protection. However, there are many insects which feed preferentially on high-tannin content tissues (14, ), and specific adaptations exist which can nullify or reduce the digestion inhibition effects of tannins (16). ... 

Folate is absorbed from dietary sources, such as those fisted above, mainly as reduced methyl- and formyl-tetrahy-dropteroylpolyglutamates. The bioavailabifity of folate from food sources is variable and dependent upon factors such as incomplete release firom plant cellular structure, entrapment in food matrix during digestion, inhibition of deglutamation by other dietary constituents, and possibly the degree of... 

Plasmin activity is eliminated from the blood by autocatalytic digestion, inhibition by antiplasmin agents, and elimination in the urine. 

Autocatalytic digestion Inhibition by antiplasmin. Excretion in urine... 

In 1990, appioximately 66,000 metric tons of alumina trihydiate [12252-70-9] AI2O2 3H20, the most widely used flame retardant, was used to inhibit the flammabihty of plastics processed at low temperatures. Alumina trihydrate is manufactured from either bauxite ore or recovered aluminum by either the Bayer or sinter processes (25). In the Bayer process, the bauxite ore is digested in a caustic solution, then filtered to remove siUcate, titanate, and iron impurities. The alumina trihydrate is recovered from the filtered solution by precipitation. In the sinter process the aluminum is leached from the ore using a solution of soda and lime from which pure alumina trihydrate is recovered (see Aluminum compounds). 

The nephrotoxic amino acid, lyskioalanine [18810-04-3] formed upon alkaline treatment of proteki, was reported ki 1964 (108). Its toxicity seems to be mitigated ki proteki ki that it is not released by normal digestion (109). Naturally occurring new amino acids, which can be classified as protekiaceous or non-protekiaceous, can, as ki the case of those from some legumes, show a remarkable toxicity (110). Eor the details of amino acid toxicity, see reference 6. Enzyme inhibition by amino acids and thek derivatives have been reviewed (111). 

Fiber components are the principal energy source for colonic bacteria with a further contribution from digestive tract mucosal polysaccharides. Rate of fermentation varies with the chemical nature of the fiber components. Short-chain fatty acids generated by bacterial action are partiaUy absorbed through the colon waU and provide a supplementary energy source to the host. Therefore, dietary fiber is partiaUy caloric. The short-chain fatty acids also promote reabsorption of sodium and water from the colon and stimulate colonic blood flow and pancreatic secretions. Butyrate has added health benefits. Butyric acid is the preferred energy source for the colonocytes and has been shown to promote normal colonic epitheUal ceU differentiation. Butyric acid may inhibit colonic polyps and tumors. The relationships of intestinal microflora to health and disease have been reviewed (10). 

Figure 2.14 shows examples of both cases, an isolated ribbon and a p sheet. The isolated ribbon is illustrated by the structure of bovine trypsin inhibitor (Figure 2.14a), a small, very stable polypeptide of 58 amino acids that inhibits the activity of the digestive protease trypsin. The structure has been determined to 1.0 A resolution in the laboratory of Robert Huber in Munich, Germany, and the folding pathway of this protein is discussed in Chapter 6. Hairpin motifs as parts of a p sheet are exemplified by the structure of a snake venom, erabutoxin (Figure 2.14b), which binds to and inhibits... 

Candidate protease inhibitor drugs must be relatively specific for the HIV-1 protease. Many other aspartic proteases exist in the human body and are essential to a variety of body functions, including digestion of food and processing of hormones. An ideal drug thus must strongly inhibit the HIV-1 protease, must be delivered effectively to the lymphocytes where the protease must be blocked, and should not adversely affect the activities of the essential human aspartic proteases. 

The first member of this class, acarbose, was introduced in the early 1990s. a-Glucosidase inhibitors slow the intestinal process of carbohydrate digestion by competitive inhibition of the activity of a-glucosidase enzymes located in the brush border of the enterocytes... 

When a-glucosidase activity is inhibited, carbohydrate digestion is prolonged and takes place further along the intestinal tract. This in turn delays and spreads the period of glucose absorption, which reduces the extent of the postprandial rise in blood glucose concentrations. The effectiveness of a-glucosidase inhibitors is dq en-dent on the consumption of a meal rich in complex carbohydrate. 

Sagir A, Schmitt M, Dilger K, Haussinger D (2003) Inhibition of cytochrome P450 3A relevant drug interactions in gastroenterology. Digestion 68 41 8... 

Fig. 2. A diagrammatic representation of the piasma kinin-forming cascade indicating the steps inhibitabie by Cl iNH. Aii functions of factor Xiia and kaiiikrein are affected. The iower figure indicates that further digestion of factor Xiia by kaiiikrein and piasmin generates factor Xii fragment (Xiif), which is an initiator of the compiement cascade. Both factor Xiif and Cl are inhibited by Cl iNH.

Inhibits platelet aggregation by increasing levels of cAMP Binds protein C, which is then cleaved by thrombin to yield activated protein C this in combination with protein S degrades factors Va and Villa, limiting their actions Activates plasminogen to plas-min, which digests fibrin the action of t-PA is opposed by plasminogen activator inhibitor- (PAI-1)... 

Diabetic patients have reduced antioxidant defences and suffer from an increased risk of free radical-mediated diseases such as coronary heart disease. EC has a pronounced insulin-like effect on erythrocyte membrane-bound acetylcholinesterase in type II diabetic patients (Rizvi and Zaid, 2001). Tea polyphenols were shown to possess anti-diabetic activity and to be effective both in the prevention and treatment of diabetes (Choi et al, 1998 Yang et al, 1999). The main mechanism by which tea polyphenols appear to lower serum glucose levels is via the inhibition of the activity of the starch digesting enzyme, amylase. Tea inhibits both salivary and intestinal amylase, so that starch is broken down more slowly and the rise in serum glucose is thus reduced. In addition, tea may affect the intestinal absorption of glucose. 

In addition to proteases, other inhibitors reduce the activity of amylase and other digestive enzymes (Ishimoto et al, 1999). Many varieties of beans produce a glycoprotein that complexes with and inhibits a-amylase (Mirkov et al, 1995). The amylase inhibitors are non-competitive and thermostable (Gallaher and Schneeman, 1986) and, unlike protease inhibitors, do not elicit heightened secretion of amylase (Toskes, 1986). Although over-expression... 

There is evidence that protease inhibitors selectively regulate the activity of specific digestive enzymes at the level of gene expression (Rosewicz et al., 1989). Specifically, soybean trypsin inhibitor increases secretion of proteases, including a form of trypsin that is resistant to inhibition but does not cause an increase in amylase secretion. Although the relationships between protease inhibitors and exocrine pancreatic secretion have received the most attention, pancreatic secretion is increased when potato fiber is added to the diet (Jacob et al., 2000), although the mechanism and signaling pathway have not been elucidated. 

CARMONA A (1996) Tannins thermostable pigments which complex dietary proteins and inhibit digestive enzymes. Latinoam Nutr. 44 31S-35S. 

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