Urinary Excretion Of P-cresol Research Articles

Modulation of protein fermentation does not affect fecal water toxicity: a randomized cross-over study in healthy subjects.

ObjectiveProtein fermentation results in production of metabolites such as ammonia, amines and indolic, phenolic and sulfur-containing compounds. In vitro studies suggest that these metabolites might be toxic. However, human and animal studies do not consistently support these findings. We modified protein fermentation in healthy subjects to assess the effects on colonic metabolism and parameters of gut health, and to identify metabolites associated with toxicity.DesignAfter a 2-week run-in period with normal protein intake (NP), 20 healthy subjects followed an isocaloric high protein (HP) and low protein (LP) diet for 2 weeks in a cross-over design. Protein fermentation was estimated from urinary p-cresol excretion. Fecal metabolite profiles were analyzed using GC-MS and compared using cluster analysis. DGGE was used to analyze microbiota composition. Fecal water genotoxicity and cytotoxicity were determined using the Comet assay and the WST-1-assay, respectively, and were related to the metabolite profiles.ResultsDietary protein intake was significantly higher during the HP diet compared to the NP and LP diet. Urinary p-cresol excretion correlated positively with protein intake. Fecal water cytotoxicity correlated negatively with protein fermentation, while fecal water genotoxicity was not correlated with protein fermentation. Heptanal, 3-methyl-2-butanone, dimethyl disulfide and 2-propenyl ester of acetic acid are associated with genotoxicity and indole, 1-octanol, heptanal, 2,4-dithiapentane, allyl-isothiocyanate, 1-methyl-4-(1-methylethenyl)-benzene, propionic acid, octanoic acid, nonanoic acid and decanoic acid with cytotoxicity.ConclusionThis study does not support a role of protein fermentation in gut toxicity. The identified metabolites can provide new insight into colonic health.Trial RegistrationClinicalTrial.gov NCT01280513

Effects of a wheat bran extract containing arabinoxylan oligosaccharides on gastrointestinal health parameters in healthy adult human volunteers: a double-blind, randomised, placebo-controlled, cross-over trial

Wheat bran extract (WBE) is a food-grade soluble fibre preparation that is highly enriched in arabinoxylan oligosaccharides. In this placebo-controlled cross-over human intervention trial, tolerance and effects on colonic protein and carbohydrate fermentation were studied. After a 1-week run-in period, sixty-three healthy adult volunteers consumed 3, 10 and 0g WBE/d for 3 weeks in a random order, with 2 weeks' washout between each treatment period. Fasting blood samples were collected at the end of the run-in period and at the end of each treatment period for analysis of haematological and clinical chemistry parameters. Additionally, subjects collected a stool sample for analysis of microbiota, SCFA and pH. A urine sample, collected over 48h, was used for analysis of p-cresol and phenol content. Finally, the subjects completed questionnaires scoring occurrence frequency and distress severity of eighteen gastrointestinal symptoms. Urinary p-cresol excretion was significantly decreased after WBE consumption at 10g/d. Faecal bifidobacteria levels were significantly increased after daily intake of 10g WBE. Additionally, WBE intake at 10g/d increased faecal SCFA concentrations and lowered faecal pH, indicating increased colonic fermentation of WBE into desired metabolites. At 10g/d, WBE caused a mild increase in flatulence occurrence frequency and distress severity and a tendency for a mild decrease in constipation occurrence frequency. In conclusion, WBE is well tolerated at doses up to 10g/d in healthy adults volunteers. Intake of 10g WBE/d exerts beneficial effects on gut health parameters.

Dose-Response Effect of Arabinoxylooligosaccharides on Gastrointestinal Motility and on Colonic Bacterial Metabolism in Healthy Volunteers

Objective: Arabinoxylooligosaccharides (AXOS) are non-digestible in the upper gastrointestinal tract and have been shown to exert prebiotic effects in animals. The aim of this study was to characterize the influence of AXOS with an average degree of polymerization of 15 and an average degree of arabinose substitution of 0.26 (AXOS-15-0.26) on gastrointestinal motility and colonic bacterial metabolism in healthy human volunteers.Methods: Twelve healthy volunteers received five test meals, containing different amounts of AXOS-15-0.26, with one week intervals between each test meal. Breath tests were used to measure gastric emptying rate, oro-cecal transit time (OCTT) and hydrogen excretion. Colonic bacterial metabolism was estimated using the biomarkers lactose-[15N, 15N′]-ureide (15N-LU) and p-cresol.Results: Gastric emptying and OCTT were not influenced by addition of varying amounts of AXOS-15-0.26. Administration of 2.2g or 4.9g AXOS-15-0.26 significantly decreased the urinary 15N-excretion (respectively p = 0.008 and p = 0.035) as compared to the baseline, whereas fecal 15N-excretion was significantly increased (respectively p = 0.034 and p = 0.019). This shift from urinary to fecal 15N-excretion suggests a higher uptake or incorporation by bacteria due to the stimulation of colonic bacterial growth and/or metabolic activity. Furthermore, a significant increase in hydrogen excretion after administration of 2.2g (p = 0.002) and 4.9g (p = 0.004) AXOS-15-0.26 was observed. No influence on urinary p-cresol excretion was observed.Conclusion: These findings suggest that a minimal dose of 2.2g AXOS-15-0.26 favorably modulates the colonic bacterial metabolism in healthy humans. However, long term studies are required to confirm a possible prebiotic effect.

Baseline microbiota activity and initial bifidobacteria counts influence responses to prebiotic dosing in healthy subjects

Dietary intervention with prebiotics can cause changes in the colonic microbiota and their metabolic activities. To investigate whether the response to prebiotic dosing is influenced by the baseline metabolic activity of the colonic flora and bifidobacteria counts. The 4-week effect of lactulose (10 g bid.; n = 29) and oligofructose-enriched inulin (10 g bid.; n = 19) was evaluated in healthy human volunteers. Lactose-[(15)N, (15)N]-ureide was used to study the colonic NH(3)-metabolism. Urine (48 h) and faeces (72 h) were collected and analysed for p-cresol and (15)N-content by gas chromatography-mass spectrometry and isotope ratio mass spectrometer, respectively. Faecal bifidobacteria were quantified by real-time polymerase chain reaction. After the 4-week prebiotic administration period, the urinary excretion of p-cresol and (15)N was significantly decreased in both groups (P < 0.05) corresponding to a significantly higher faecal excretion of (15)N (P < 0.05). The decrease in urinary (15)N and p-cresol excretion significantly correlated with baseline (15)N and p-cresol levels (P < 0.05), indicating that subjects with higher baseline levels showed a higher response to prebiotic dosing. Furthermore, a significant correlation was seen between baseline bifidobacteria counts and the effect of prebiotic intake (P < 0.05). The response to prebiotic dosing, as indicated by the fate of NH(3), p-cresol and bifidobacteria, is determined by the initial colonic conditions.

Influence of Long-Term Administration of Lactulose and Saccharomyces Boulardii on the Colonic Generation of Phenolic Compounds in Healthy Human Subjects

Objective: Proteins are degraded in the colon by bacterial fermentation into potentially toxic metabolites such as phenolic compounds. The aim of the present study was to investigate whether long-term administration of lactulose or Saccharomyces boulardii cells would result in a lower protein degradation. In addition, the influence of a long-term dietary intake on different gastrointestinal parameters was investigated.Methods: The effect of long-term intervention of the substrates was evaluated in a randomized, cross-over study in 43 healthy volunteers. At the start of the study and at the end of each 4-week treatment period, urine was collected during 48 h in different fractions and faeces during 72 h. Breath test samples and blood samples were taken to study gastrointestinal parameters.Results: No influence of long-term administration of both substrates was found on GE, OCTT and serum lipids. A significant decrease in small intestinal permeability was found after long-term dietary intervention with lactulose. Long-term administration of lactulose significantly decreased urinary p-cresol excretion, but did not lower fecal p-cresol excretion. No significant effects were observed after S. boulardii intake.Conclusion: The results obtained in present study have indicated that colonic amino acid fermentation can be reduced by the administration of lactulose as a fermentable carbohydrate.

Acarbose treatment lowers generation and serum concentrations of the protein-bound solute p-cresol: A pilot study

Several protein-bound uremic retention solutes (including p-cresol) originate from colonic bacterial fermentation of protein. Higher colonic availability of carbohydrates drives this process towards lower production of toxic metabolites. Small intestinal alpha-glucosidase inhibitors like Acarbose (Glucobay) enhance the amount of undigested carbohydrates reaching the colon. We studied the effect of Acarbose on generation and serum concentrations of p-cresol. Nine healthy volunteers (age 25 (22-36) years) with a creatinine clearance of 89.6 ml/min/1.73 m(2) (85.5-116.4) were treated with Acarbose for 3 weeks. Dose was gradually increased to reach 300 mg/day after 1 week. Blood sampling, 24-h urine and stool collections on 3 consecutive days were performed before and during the last days of the treatment period. p-Cresol generation was estimated from mean 24-h urinary elimination. Gastrointestinal side effects, if present, were mild to moderate. Serum concentrations of p-cresol declined significantly after Acarbose treatment (before: 1.14 mg/l (0.93-3.03); after: 1.11 mg/l (0.31-1.82); P=0.047). Urinary excretion of p-cresol, reflecting its colonic generation rate, was significantly lower after treatment (before: 29.93 mg/day (6.79-75.19); after: 10.54 mg/day (1.08-30.85); P=0.031). The fecal excretion of nitrogen increased after treatment (before: 1.04 g/day (0.47-2.29); after: 1.99 g/day (0.76-3.08); P=0.047). This pilot study suggests that Acarbose treatment lowers generation and serum concentrations of the protein-bound uremic solute p-cresol. Although further confirmation is warranted, the data may point to a novel treatment option for chronic kidney disease patients in view of the potential toxic effects of p-cresol and related substances.

Comparative kinetics of the uremic toxin p-cresol versus creatinine in rats with and without renal failure

p-cresol, which is extensively metabolized into p-cresylglucuronide in the rat, is related to several biochemical and physiologic alterations in uremia and is not removed adequately by current hemodialysis strategies. The knowledge of its in vivo kinetic behavior could be helpful to improve the current removal strategies. We investigated the kinetic behavior of intravenously injected p-cresol (10 mg/kg) in rats with normal and decreased renal function, and compared the results with those obtained for creatinine (60 mg/kg) under similar conditions. Renal failure was obtained by 5/6 nephrectomy. Both p-cresol and p-cresylglucuronide were analyzed using reversed-phase high-performance liquid chromatography (RP-HPLC). The relation between the p-cresylglucuronide peak height and the underlying amount of p-cresol was determined after hydrolysis of the glucuronide with beta-glucuronidase. We calculated urinary excretion of p-cresol with and without taking p-cresylglucuronide into account. In addition, total, renal, and non-renal clearance, half-life, and volume of distribution were calculated for p-cresol. Over a 4-hour period, p-cresol serum concentration showed only a minimal decline in rats with decreased renal function (t1/2 = 11.7 +/- 0.4 hours), compared to rats with normal renal function (t1/2 = 1.4 +/- 0.7 hours). A similar observation was made for p-cresylglucuronide. In rats with normal renal function, 21.0 +/- 10.0% of the injected p-cresol was excreted in urine as p-cresol and 60.7 +/- 25.0% as p-cresylglucuronide; in rats with renal failure, the respective amounts were 6.7 +/- 7.5% and 32.0 +/- 25.3% (P < 0.05 vs. normal renal function) (total recovery 81.81 +/- 31.07% vs. 38.50 +/- 32.09%, P < 0.05). The volume of distribution of p-cresol was approximately 4 times larger than that of creatinine, but was not significantly affected by renal failure. Not only renal, but also non-renal and total clearance, were much lower in rats with decreased renal function. The present data sheds a light on the kinetic behavior of p-cresol in uremic patients; the large volume of distribution, especially, might explain the inadequate dialytic removal of p-cresol. In addition, a substantial amount of p-cresol is removed by metabolism, and both renal and non-renal clearance are disturbed in uremia.

Urinary excretion of the uraemic toxin p-cresol in the rat: contribution of glucuronidation to its metabolization.

Increasing evidence indicates that lipophilic and/or protein-bound substances such as p-cresol are responsible for adverse physiological alterations in uraemic patients. To better understand the evolution of p-cresol disposition in renal failure and dialysis patients, it is necessary to determine its kinetic characteristics and biotransformation pathways. We studied the biotransformation of p-cresol after intravenous injection of the compound in eight rats with normal renal function. Urine was collected in four 1 h intervals. To evaluate the presence of p-cresol metabolites, beta-glucuronidase was added to urine samples and the isolated unidentified chromatographic peak observed in previous experiments was submitted to tandem mass spectrometry (MS/MS) analysis. Administration of p-cresol produced a p-cresol peak and an unknown peak, suggesting biotransformation of the compound. Addition of beta-glucuronidase to urine samples and incubation at 37 degrees C resulted in a marked decrease in the unidentified peak height (P<0.001) together with an increase in p-cresol peak height (P<0.001), suggesting that the unidentified peak was composed, at least in part, of p-cresylglucuronide. Mass spectrometry (MS) and MS/MS analysis of the isolated unidentified peak confirmed the presence of p-cresylglucuronide. Linear regression between the peak height of p-cresylglucuronide before enzyme treatment and the increase in p-cresol peak height after enzyme treatment in samples incubated with beta-glucuronidase allowed us to calculate the amount of p-cresylglucuronide as its p-cresol equivalents. This revealed that 64% of the injected p-cresol was excreted as glucuronide. There was no change in peak heights when sulphatase was added to the urine. When p-cresol and p-cresylglucuronide levels were combined, approximately 85% of all administered p-cresol was recovered in the urine. In addition, the combined urinary excretion of p-cresol and p-cresylglucuronide was more than four times greater than excretion of p-cresol by itself (P<0.01). In rats with normal renal function, intravenous administration of p-cresol results in immediate and extensive metabolization of the compound into p-cresylglucuronide. The elimination of p-cresol from the body depends largely on the urinary excretion of this metabolite.

Lactobacillus Strain GG Supplementation Decreases Colonic Hydrolytic and Reductive Enzyme Activities in Healthy Female Adults

The effects of yogurt containing viable Lactobacillus strain GG (L. GG) and/or fiber supplements on fecal enzyme activities (beta-glucuronidase, nitroreductase, beta-glucosidase, glycocholic acid hydrolase, urease) and on bacterial metabolites in urine (phenol, p-cresol) were studied in 64 females, 20-41 y old. The subjects were randomly divided into three groups: the first group received L. GG yogurt (2 x 150 mL/d, containing 10(11) colony-forming units (cfu)/L of L. GG), the second group received L. GG yogurt and a rye fiber product (30 g/d, equivalent to 9 g fiber/d), and the third group received placebo yogurt (pasteurized) and fiber. The supplementation period lasted 4 wk, with a preceding 2-wk baseline period and a 2-wk follow-up period. The mean fecal count of L. GG was approximately 10(6) cfu/g feces during the supplementation, and L. GG persisted in the fecal samples of 28% of the subjects for 2 wk after supplementation. L. GG yogurt alone or with fiber significantly decreased fecal beta-glucuronidase, nitroreductase and glycocholic acid hydrolase activities. These enzyme activities returned to baseline levels during the follow-up period. beta-Glucosidase and urease activities were not altered significantly during the study. The addition of fiber to L. GG and placebo yogurt had no effect on the enzymic activities. Urinary excretion of p-cresol decreased significantly in groups receiving L. GG. These data demonstrate that L. GG can modify the colonic environment with possible health effects.

Suppressive effect of an oral sorbent on the accumulation of p-cresol in the serum of experimental uremic rats.

Serum p-cresol and phenol are markedly accumulated in uremic patients. To determine if an oral sorbent (AST-120) can decrease their serum concentrations in the uremic state, an oral sorbent was administered to experimental nephrectomized uremic rats. In uremic rats fed with oral sorbent, the serum concentration and the urinary excretion of p-cresol were markedly and significantly lower than those in control uremic rats, while those of phenol tended to be low in the uremic rats with oral sorbent as compared with control uremic rats. The concentrations of serum creatinine and blood urea nitrogen were significantly decreased in the uremic rats with oral sorbent. These findings demonstrate that oral sorbent adsorbs especially p-cresol in the intestine and prevents the accumulation of p-cresol in the serum of uremic rats.

The effect of saccharin ingestion on the excretion of microbial amino acid metabolites in rat and man

Low dietary levels of sodium saccharin (0–2%) fed to male rats for 6 weeks produced a dose-related increase in the urinary excretion of p-cresol, a major microbial metabolite of tyrosine. Some animals fed higher levels of saccharin (5–7.5%) for 6 weeks excreted increased amounts of p-cresol, but many excreted negligible amounts so that the overall dose-response relationship was bell shaped. After 20 weeks of exposure, all rats in the higher dose groups showed increased p-cresol excretion and by 26 weeks the 7.5% saccharin group showed a 36-fold increase over animals fed the 0% saccharin diet. The urinary excretion of phenol, another microbial amino acid metabolite, was constant in animals fed dietary levels of saccharin below 2% for 6 weeks, but was virtually abolished at higher levels. The excretion of indican (formed from indole, a microbial metabolite of tryptophan) was increased by saccharin in a dose-related fashion at all time points, but showed only a 3-fold increase at 7.5% compared with the 0% group. p-Cresol may therefore prove more sensitive than indican as an indicator of altered microbial metabolism due to saccharin. In a separate study the effect of 7.5% saccharin on p-cresol and indican excretion was shown to be largely reversible and the excretion of phenol increased rapidly when saccharin was withdrawn from the diet. Chronic saccharin administration to man at high doses (1 g/day for 4 weeks) had no perceptible effect on the excretion of these three metabolites.

The effects of antibiotics in the weanling pig diet on growth and the excretion of volatile phenolic and aromatic bacterial metabolites

The purpose of this study was to investigate the effects of dietary antibiotic supplementation on the fecal urinary excretion of volatile phenolic and aromatic bacterial metabolites by the weanling pig, and to determine if a relationship exists between an exposure to these metabolites and growth performance. Wealing pigs were fed a basal diet, supplemented with either 110 ppm chlortetracycline, 110 ppm sulfamethazine and 55 ppm penicillin, 40 ppm lincomycin sulfate, or no antibiotics, for 30 days. Pigs on the chlortetracycline-sulfamethazine-penicillin diet on the average tended to grow at a faster rate, attained a higher percentage weight gain, and weighed slightly more than pigs on either the lincomycin sulfate or no antibiotic diets. Under all treatments, p-cresol was the predominant metabolite of the volatile phenolic and aromatic metabolites detected in feces and urine, with the urine accounting for 88% of its total daily excretion. Pigs on the chlortetracycline-sulfamethazine-penicillin diet excreted less urinary p-cresol than pigs on either the lincomycin sulfate or no antibiotic diets. Total p-cresol excretion expressed on the metabolic body size, resulted in significant treatment differences. Regression analysis of percentage body weight gain on urinary p-cresol excretion gave a negative correlation coefficient (r = -0.73). The results suggest that intestinal p-cresol production may be responsible for depressing the growth of the weanling pig.