Phenolic intestinal bacteria

Phenol is the main metabolite of benzene. It occurs mainly in foamed organic products, plastics, adhesives, tar and tarred roofing felt. Phenol is also a physiological metabolic product of intestinal bacteria. Entry into the human organism is analogous to that of benzene. The clinical picture corresponds to that of the BTX aromatics. 

Phenol and p-cresol noticeably accumulate in the serum of undialyzed and dialyzed uremic patients they play a role in the development of uremic coma and defective platelet aggregation. They are synthesized in the small intestine from phenylalanine and tyrosine through 4-hydroxybenzoic acid and 4-hydroxyphenylacetic acid, respectively, by intestinal bacteria, as shown in Fig. 9. Aerobic bacteria tend to produce phenol from tyrosine, whereas anaerobic bacteria produce p-cresol. These phenols are absorbed from intestine and normally excreted into urine, fri uremia, renal clearance of the phenols is impaired, leading to accumulation of the phenols in the blood. Compared to healthy controls, the serum p-cresol levels are 7-10 times higher in continuous ambulatory peritoneal dialysis patients, uremic outpatients, and hemodialysis patients. 

In that context, the present chapter gives insights into the relevance of phenolic compounds in human nutrition. We will primarily discuss bioavailability and biological properties of isoflavones and lignans in the context of human health and disease, our main focus being the metabolic activities of intestinal bacteria. 

Phenolic acids show greater antimicrobial potency than their corresponding flavonoids precursors such as the monomers (+)-catechin and (-)-epicatechin (Ganan et al. 2009 Cueva et al. 2010). Therefore, microbial transformations of dietary flavonoid compounds in the intestine conld lead to more potent microbial-inhibitory compounds (phenolic acids) and conld reach greater concentrations in the intestine. This may selectively inflnence intestinal bacteria species, and therefore conld affect the diversity and metabohc activity of the intestinal microbiota, inclnding the transformation of phenolics in the gnt (Cneva et al. 2010). 

Chung K-T, Lu Z, Chou MW (1998) Mechanism of inhibition of tarmic acid and related compounds on the growth of intestinal bacteria. Food Chem Toxicol 36 1053-1060 Deprez S, Brezillon C, Rabot S, PhUippe C, MUa 1, Lapierre C, Scalbert A (2000) Polymeric proanthocyanidins are cataboUzed by human colonic microflora into low-molecular-weight phenolic acids. J Nutr 130 2733-2738... 

The naturally occurring phenol which has most metabolic significance is tyrosine, an amino acid widely distributed in proteins. Many of the simpler phenols which are normally found in urine are believed to be derived from absorption of phenols formed by the bacterial decomposition of tyrosine and other aromatic amino acids in unabsorbed protein in the intestine. Between 1879 and 1886 Baumann (7,8) postulated the accompanying scheme for the degradation of tyrosine by intestinal bacteria. Full evi-... 

Saponins and phenolics also have anti-microbial properties (Chung et ah, 1998) and have been associated with reduced rumen functions (Klita et al., 1996 Reed, 1995), thereby limiting the nutrient quality of forages. Also, carbohydrate complexes with hgnins and other compounds reduce carbohydrate utilization by rumen bacteria (Cornu et al., 1994). The influence of such anti-microbials on rumen functions can affect small intestine characteristics by altering nutrient concentrations (Barry and McNabb, 1999). 

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