The impact of obesity-associated glycine deficiency on the elimination of endogenous and exogenous metabolites via the glycine conjugation pathway

Background

Glycine is an integral component of the human detoxification system as it reacts with potentially toxic exogenous and endogenously produced compounds and metabolites via the glycine conjugation pathway for urinary excretion. Because individuals with obesity have reduced glycine availability, this detoxification pathway may be compromised. However, it should be restored after bariatric surgery because of increased glycine production.

Objective

To examine the impact of obesity-associated glycine deficiency on the glycine conjugation pathway. We hypothesize that the synthesis rates of acylglycines from endogenous and exogenous sources are significantly reduced in individuals with obesity but increase after bariatric surgery.

Methods

We recruited 21 participants with class III obesity and 21 with healthy weight as controls. At baseline, [1,2-13C2] glycine was infused to study the glycine conjugation pathway by quantifying the synthesis rates of several acylglycines. The same measurements were repeated in participants with obesity six months after bariatric surgery. Data are presented as mean ± standard deviation, and p-value< 0.05 is considered statistically significant.

Results

Baseline data of 20 participants with obesity were first compared to controls. Participants with obesity were significantly heavier than controls (mean BMI 40.5 ± 7.1 vs. 20.8 ± 2.1 kg/m2). They had significantly lower plasma glycine concentration (168 ± 30 vs. 209 ± 50 μmol/L) and slower absolute synthesis rates of acetylglycine, isobutyrylglycine, tigylglycine, isovalerylglycine, and hexanoylglycine. Pre- and post-surgery data were available for 16 participants with obesity. Post-surgery BMI decreased from 40.9 ± 7.3 to 31.6 ± 6.0 kg/m2. Plasma glycine concentration increased from 164 ± 26 to 212 ± 38 μmol/L) and was associated with significantly higher rates of excretion of acetylglycine, isobutyrylglycine, tigylglycine, isovalerylglycine, and hexanoylglycine. Benzoic acid (a xenobiotic dicarboxylic acid) is excreted as benzoylglycine; its synthesis rate was significantly slower in participants with obesity but increased after bariatric surgery.

Conclusion

Obesity-associated glycine deficiency impairs the human body's ability to eliminate endogenous and exogenous metabolites/compounds via the glycine conjugation pathway. This impairment is ameliorated when glycine supply is restored after bariatric surgery. These findings imply that dietary glycine supplementation could treat obesity-associated metabolic complications due to the accumulation of intramitochondrial toxic metabolites.

Clinical trial registration

https://clinicaltrials.gov/study/NCT04660513, identifier NCT04660513.

Rats with Long-Term Cholestasis Have a Decreased Cytosolic but Maintained Mitochondrial Hepatic CoA Pool

Previous studies showed that rats with long-term bile duct ligation have reduced coenzyme A stores per g of liver but maintained mitochondrial CoA stores. Based on these observations, we determined the CoA pool in the liver homogenate, liver mitochondria, and liver cytosol of rats with bile duct ligation for 4 weeks (BDL rats, n = 9) and sham-operated control rats (CON rats, n = 5). In addition, we tested the cytosolic and mitochondrial CoA pools by assessing the metabolism of sulfamethoxazole and benzoate in vivo and of palmitate in vitro. The hepatic total CoA content was lower in BDL than CON rats (mean ± SEM; 128 ± 5 vs. 210 ± 9 nmol/g), affecting all subfractions equally (free CoA (CoASH), short- and long-chain acyl-CoA). In BDL rats, the hepatic mitochondrial CoA pool was maintained, and the cytosolic pool was reduced (23.0 ± 0.9 vs. 84.6 ± 3.7 nmol/g liver; CoA subfractions were affected equally). The urinary excretion of hippurate after i.p. benzoate administration (measuring mitochondrial benzoate activation) was reduced in BDL rats (23.0 ± 0.9 vs. 48.6 ± 3.7% of dose/24 h), whereas the urinary elimination of N-acetylsulfamethoxazole after i.p. sulfamethoxazole administration (measuring the cytosolic acetyl-CoA pool) was maintained (36.6 ± 3.0 vs. 35.1 ± 2.5% of dose/24 h BDL vs. CON rats). Palmitate activation was impaired in the liver homogenate of BDL rats but the cytosolic CoASH concentration was not limiting. In conclusion, BDL rats have reduced hepatocellular cytosolic CoA stores, but this reduction does not limit sulfamethoxazole N-acetylation or palmitate activation. The hepatocellular mitochondrial CoA pool is maintained in BDL rats. Impaired hippurate formation in BDL rats is explained best by mitochondrial dysfunction.

Impaired Tubular Secretion of Organic Solutes in Advanced Chronic Kidney Disease

BACKGROUND

The clearance of solutes removed by tubular secretion may be altered out of proportion to the GFR in CKD. Recent studies have described considerable variability in the secretory clearance of waste solutes relative to the GFR in patients with CKD.

METHODS

To test the hypothesis that secretory clearance relative to GFR is reduced in patients approaching dialysis, we used metabolomic analysis to identify solutes in simultaneous urine and plasma samples from 16 patients with CKD and an eGFR of 7±2 ml/min per 1.73 m2 and 16 control participants. Fractional clearances were calculated as the ratios of urine to plasma levels of each solute relative to those of creatinine and urea in patients with CKD and to those of creatinine in controls.

RESULTS

Metabolomic analysis identified 39 secreted solutes with fractional clearance >3.0 in control participants. Fractional clearance values in patients with CKD were reduced on average to 65%±27% of those in controls. These values were significantly lower for 18 of 39 individual solutes and significantly higher for only one. Assays of the secreted anions phenylacetyl glutamine, p-cresol sulfate, indoxyl sulfate, and hippurate confirmed variable impairment of secretory clearances in advanced CKD. Fractional clearances were markedly reduced for phenylacetylglutamine (4.2±0.6 for controls versus 2.3±0.6 for patients with CKD; P<0.001), p-cresol sulfate (8.6±2.6 for controls versus 4.1±1.5 for patients with CKD; P<0.001), and indoxyl sulfate (23.0±7.3 versus 7.5±2.8; P<0.001) but not for hippurate (10.2±3.8 versus 8.4±2.6; P=0.13).

CONCLUSIONS

Secretory clearances for many solutes are reduced more than the GFR in advanced CKD. Impaired secretion of these solutes might contribute to uremic symptoms as patients approach dialysis.

Molecular Typing of Campylobacter jejuni and Campylobacter coli of Human Strains Isolated in Turkey Over an Eight-Year Period

BACKGROUND

Campylobacter spp. is one of the leading causes of bacterial foodborne infections worldwide. In this study, we aimed to investigate the genetic diversity of 341 Campylobacter strains isolated in Turkey.

METHODS

Campylobacter spp. was identified by phenotypical methods and PCR. Species level identification was carried out by the hippurate hydrolysis test and PCR. C. jejuni and C. coli strains were typed by using flaA-RFLP and PFGE.

RESULTS

Of 341 strains, 300 (88%), 37 (10.8%), and four were identified as C. jejuni, C. coli, and non-jejuni/non-coli, respectively. The hippurate hydrolysis test misidentified 12% of 341 strains. The typeabilities of flaA-RFLP and PFGE were 100% for C. coli, whereas those of flaA-RFLP and PFGE for C. jejuni were 99.3% and 99%, respectively. The discriminatory power of the combination of PFGE and flaA-RFLP was determined to be higher than either method alone for both C. jejuni and C. coli. Both of the strains were so diverse that 80% and 64% of C. jejuni and C. coli genotypes included only one strain, respectively. In two patients, Campylobacter strains that were isolated from the first stool samples were C. jejuni where as those isolated from the second samples, collected eight and 20 days after the collection of the first samples, were C. coli. C. jejuni strains that were recovered from two different stool samples of two patients, collected 1 - 2 days apart, were found to be genetically different.

CONCLUSIONS

Species identification of Campylobacter strains should be done using molecular methods. Combination of two methods is prerequisite for increasing the accuracy of molecular typing. Mixed or subsequent infection by different Campylobacter species and C. jejuni of different genotypes should not be underestimated.

Small-molecules that covalently react with a human prolyl hydroxylase - towards activity modulation and substrate capture

We describe covalently binding modulators of the activity of human prolyl hydroxylase domain 2 (PHD2) and studies towards a strategy for photocapture of PHD2 substrates. Reversible active site binding of electrophile bearing compounds enables susbsequent covalent reaction with a lysine residue (K408) in the flexible C-terminal region of PHD2 to give a modified protein that retains catalytic activity.

Renal energy excretion of horses depends on renal hippuric acid and nitrogen excretion

The prediction of renal energy excretion is crucial in a metabolizable energy system for horses. Phenolic acids from forage cell walls may affect renal energy losses by increasing hippuric acid excretion. Therefore, the relationships were investigated between renal energy, nitrogen (N) and hippuric acid excretion of four adult ponies (230-384 kg body weight (BW)) consuming diets based on fresh grass, grass silage, grass cobs (heat-dried, finely chopped, pressed grass), alfalfa hay, straw, extruded straw and soybean meal. Feed intake was measured; urine and faeces were quantitatively collected for three days. Feed was analysed for crude nutrients, gross energy, amino acids and neutral-detergent-insoluble crude protein (CP); faeces were analysed for crude nutrients and cross energy; urine was analysed for N, hippuric acid, creatinine and gross energy. Renal energy excretion (y; kJ/kg BW0.75 ) correlated with renal N excretion (x1 ; g/kg BW0.75 ) and renal hippuric acid excretion (x2 ; g/kg BW0.75 ): y = 14.4 + 30.2x1 +20.7x2 (r = .95; n = 30; p < .05). Renal hippuric acid excretion was highest after intake of fresh grass and lowest after intake of soybean meal. The ratio of hippuric acid to creatinine in urine and the excretion of hippuric acid per gram of dry matter intake was significantly higher for fresh grass than for all other rations. There was no relationship between aromatic amino acid intake and renal hippuric acid excretion. The results of the present study and literature data suggest that feed can be categorized into four groups with regard to the energy losses per gram CP intake: (i) protein supplements (e.g., soybean meal): 4.2-4.9 kJ/g CP intake (ii) alfalfa hay, grains, dried sugar beet pulp: 6.4 kJ/g CP intake, (iii) hay, preserved grass products, straw: 5.2-12.3 kJ/g CP intake (mean 8) and (iv) fresh grass. For group (iii) a negative relationship was observed between renal energy losses per gram of CP and the content of CP or neutral-detergent-insoluble CP in dry matter.

Probiotics Blunt the Anti-Hypertensive Effect of Blueberry Feeding in Hypertensive Rats without Altering Hippuric Acid Production

Previously we showed that feeding polyphenol-rich wild blueberries to hypertensive rats lowered systolic blood pressure. Since probiotic bacteria produce bioactive metabolites from berry polyphenols that enhance the health benefits of berry consumption, we hypothesized that adding probiotics to a blueberry-enriched diet would augment the anti-hypertensive effects of blueberry consumption. Groups (n = 8) of male spontaneously hypertensive rats were fed one of four AIN '93G-based diets for 8 weeks: Control (CON); 3% freeze-dried wild blueberry (BB); 1% probiotic bacteria (PRO); or 3% BB + 1% PRO (BB+PRO). Blood pressure was measured at weeks 0, 2, 4, 6, and 8 by the tail-cuff method, and urine was collected at weeks 4 and 8 to determine markers of oxidative stress (F2-isoprostanes), nitric oxide synthesis (nitrites), and polyphenol metabolism (hippuric acid). Data were analyzed using mixed models ANOVA with repeated measures. Diet had a significant main effect on diastolic blood pressure (p = 0.046), with significantly lower measurements in the BB- vs. CON-fed rats (p = 0.035). Systolic blood pressure showed a similar but less pronounced response to diet (p = 0.220), again with the largest difference between the BB and CON groups. Absolute increase in blood pressure between weeks 0 and 8 tended to be smaller in the BB and PRO vs. CON and BB+PRO groups (systolic increase, p = 0.074; diastolic increase, p = 0.185). Diet had a significant main effect on hippuric acid excretion (p<0.0001), with 2- and ~1.5-fold higher levels at weeks 4 and 8, respectively, in the BB and BB+PRO vs. PRO and CON groups. Diet did not have a significant main effect on F2-isoprostane (p = 0.159) or nitrite excretion (p = 0.670). Our findings show that adding probiotics to a blueberry-enriched diet does not enhance and actually may impair the anti-hypertensive effect of blueberry consumption. However, probiotic bacteria are not interfering with blueberry polyphenol metabolism into hippuric acid.

Determination of renal plasma flow by endogenous hippuric acid clearance in the conscious rat

(1) The endogenous hippuric acid can be fluorometrically determined down to a minimum of 0.6 micrograms/ml in 10 microliters of rat serum. This enables the determination of the effective renal plasma flow (ERPF) by measurement of the renal clearance of the endogenous hippuric acid in the conscious rat. (2) Endogenous hippuric acid clearance (128 ml/min . m2 or 2.48 ml/min/100 g body weight) corresponds in its extent with the clearance after a single injection of unlabelled hippuric acid and is higher (20%) than the clearance after a single injection of 131I-hippuran. (3) Exogenous hippuric acid has a short biological half-time of 12-20 min and a distribution space of about 50%; therefore, alteration of its intermediary supply can disturb the estimate of the renal clearance of endogenous hippuric acid. (4) The daily rhythm of the renal excretion of endogenous hippuric acid shows a constant low excretion between 0800 and 1200 hours; this period is the best suited for clearance measurements.

The finite dose technique as a valid in vitro model for the study of percutaneous absorption in man

An in vitro model of percutaneous absorption has been developed which permits close stimulation of conditions commonly associated with topical drug use in living man. Quantitative comparison of the absorption of selected compounds in the model and in living man was made to test the validity of the model. Excellent agreement has been found between the two sets of data, both with respect to the total amount absorbed and the kinetics of absorption.

[Antimicrobial sensitivity of hippurate-negative Campylobacter and Helicobacter pullorum strains isolated from patients with diarrhea]

C. jejuni as well as some hippurate-negative Campylobacter species and related diarrheagenic organisms, are the leading cause of gastroenteritis in our environment all throughout the year. The aim of the present study was to determine the sensitivity of hippurate-negative Campylobacter and Helicobacter pullorum strains isolated from the stools of patients with diarrhea. We tested 39 Campylobacter coli, two C. lari and five Helicobacter pullorum strains identified by mass spectrometry analysis. The sensitivity to amoxicillin-clavulanic acid, erytrhomycin, azithromycin, gentamicin, ciprofloxacin, levofloxacin, tetracycline, tigecycline and chloramphenicol was tested by E-test. Most hippurate-negative Campylobacter and H. pullorum isolates studied showed high resistance to tetracycline and to the two fluorquinolones tested. On the other side, all strains were sensitive to amoxicillin-clavulanic acid, tigecycline and chloramphenicol, while most of them were sensitive to both macrolides tested and to gentamicin.

Targeted projection NMR spectroscopy for unambiguous metabolic profiling of complex mixtures

Unambiguous identification of individual metabolites present in complex mixtures such as biofluids constitutes a crucial prerequisite for quantitative metabolomics, toward better understanding of biochemical processes in living systems. Increasing the dimensionality of a given NMR correlation experiment is the natural solution for resolving spectral overlap. However, in the context of metabolites, natural abundance acquisition of (1)H and (13)C NMR data virtually excludes the use of higher dimensional NMR experiments (3D, 4D, etc.) that would require unrealistically long acquisition times. Here, we introduce projection NMR techniques for studies of complex mixtures, and we show how discrete sets of projection spectra from higher dimensional NMR experiments are obtained in a reasonable time frame, in order to capture essential information necessary to resolve assignment ambiguities caused by signal overlap in conventional 2D NMR spectra. We determine optimal projection angles where given metabolite resonances will have the least overlap, to obtain distinct metabolite assignment in complex mixtures. The method is demonstrated for a model mixture composition made of ornithine, putrescine and arginine for which acquisition of a single 2D projection of a 3D (1)H-(13)C TOCSY-HSQC spectrum allows to disentangle the metabolite signals and to access to complete profiling of this model mixture in the targeted 2D projection plane.

In-vitro study on the competitive binding of diflunisal and uraemic toxins to serum albumin and human plasma using a potentiometric ion-probe technique

The competitive binding of diflunisal and three well-known uraemic toxins (3-indoxyl sulfate, indole-3-acetic acid and hippuric acid) to bovine serum albumin (BSA), human serum albumin (HSA) and human plasma was studied by direct potentiometry. The method used the potentiometric drug ion-probe technique with a home-made ion sensor (electrode) selective to the drug anion. The site-oriented Scatchard model was used to describe the binding of diflunisal to BSA, HSA and human plasma, while the general competitive binding model was used to calculate the binding parameters of the three uraemic toxins to BSA. Diflunisal binding parameters, number of binding sites, ni and association constants for each class of binding site, Ki, were calculated in the absence and presence of uraemic toxins. Although diflunisal exhibits high binding affinity for site I of HSA and the three uraemic toxins bind primarily to site II, strong interaction was observed between the drug and the three toxins, which were found to affect the binding of diflunisal on its primary class of binding sites on both BSA and HSA molecules and on human plasma. These results are strong evidence that the decreased binding of diflunisal that occurs in uraemic plasma may not be solely attributed to the lower albumin concentration observed in many patients with renal failure. The uraemic toxins that accumulate in uraemic plasma may displace the drug from its specific binding sites on plasma proteins, resulting in increased free drug plasma concentration in uraemic patients.

Evolution of protein-bound uraemic solutes during predilution haemofiltration

BACKGROUND

Protein-bound uraemic toxins provoke multiple biological changes involved in uraemia. Few if any dialytic strategies remove these compounds.

METHODS

In this post hoc analysis of remnant samples from a randomised controlled trial, we evaluate whether predilution haemofiltration (HF) decreases the pretreatment concentration of protein- bound uraemic solutes. Patients treated with low-flux haemodialysis (HD) were enrolled into a group continuing this strategy (group A, n=8) over 6 months, whereas group B (n=12) was switched to predilution online HF. Blood was sampled at baseline and after 6 months to determine total and free concentration and percentage binding of indoxyl sulfate (IS), indole-3-acetic acid (IAA), hippuric acid (HA), p-cresol (PC) and 3-carboxy- 4-methyl-5-propyl-2-furanpropionic acid (CMPF).

RESULTS

Comparing concentrations at start versus 6 months of treatment by paired analysis, HD had no impact. In contrast, at the end of the HF period, we found a decrease in total and free PC, free IAA and total CMPF. In addition, the percentage protein binding of IAA increased significantly. However, unpaired analysis revealed no statistical difference between HD and HF, both at baseline and after 6 months of treatment for all compounds.

CONCLUSIONS

Paired analysis showed a beneficial impact of predilution online HF for several proteinbound uraemic solutes. Unpaired analysis, however, showed no statistical difference.

Ototoxicity of the three xylene isomers in the rat

Numerous experiments have shown that the aromatic solvents can affect the auditory system in the rat, the cochlea being targeted first. Solvents differ in cochleotoxic potency: for example, styrene is more ototoxic than toluene or xylenes. The goal of this study was to determine the relative ototoxicity of the three isomers of xylene (o-, m- or p-xylene). Moreover, by dosing with the two urinary metabolites of xylene, methylhippuric (MHAs) and mercapturic acids (MBAs), this study points toward a causal relationship between the cochleotoxic effects and potential reactive intermediates arising from the biotransformation of the parent molecules. Separate groups of rats were exposed by inhalation to one isomer following this schedule: 1800 ppm, 6 h/d, 5 d/wk for 3 wk. Auditory thresholds were determined with brainstem-auditory evoked potentials. Morphological analysis of the organ of Corti was performed by counting both sensory and spiral ganglion cells. Among the three isomers, only p-xylene was cochleotoxic. A 39-dB permanent threshold shift was obtained over the tested frequencies range from 8 to 20 kHz. Whereas outer hair cells were largely injured, no significant morphological change was observed within spiral ganglia. The concentrations of urinary p-, o- or m-MHA were greater (p-MHA: 33.2 g/g; o-MHA: 7.8 g/g; m-MHA: 20.4 g/g) than those obtained for MBAs (p-MBA: 0.04 g/g; o-MBA: 6.2 g/g; m-MBA: 0.03 g/g). Besides, there is a large difference between o-MBA (6.2 g/g) and p-MBA (0.04 g/g). As a result, since the cysteine conjugates are not determinant in the ototoxic process of xylenes, the location of the methyl groups around the benzene nucleus could play a key role.

Neither hippurate-negative Brachyspira pilosicoli nor Brachyspira pilosicoli type strain caused diarrhoea in early-weaned pigs by experimental infection

A hippurate-negative biovariant of Brachyspira pilosicoli (B. pilosicoli^hipp-) is occasionally isolated in diarrhoeic pigs in Finland, often concomitantly with hippurate-positive B. pilosicoli or Lawsonia intracellularis. We studied pathogenicity of B. pilosicoli^hipp- with special attention paid to avoiding co-infection with other enteric pathogens. Pigs were weaned and moved to barrier facilities at the age of 11 days. At 46 days, 8 pigs were inoculated with B. pilosicoli^hipp- strain Br1622, 8 pigs were inoculated with B. pilosicoli type strain P43/6/78 and 7 pigs were sham-inoculated. No signs of spirochaetal diarrhoea were detected; only one pig, inoculated with P43/6/78, had soft faeces from day 9 to 10 post inoculation. The pigs were necropsied between days 7 and 23 after inoculation. Live pigs were culture-negative for Brachyspira spp., but B. pilosicoli^hipp- was reisolated from necropsy samples of two pigs. The lesions on large colons were minor and did not significantly differ between the three trial groups. In silver-stained sections, invasive spirochaetes were detected in colonic mucosae of several pigs in all groups. Fluorescent in situ hybridisation for genus Brachyspira, B. pilosicoli and strain Br1622 was negative. However, in situ detection for members of the genus Leptospira was positive for spirochaete-like bacteria in the colonic epithelium of several pigs in both infected groups as well as in the control group. L. intracellularis, Salmonella spp., Yersinia spp. and intestinal parasites were not detected. The failure of B. pilosicoli strains to cause diarrhoea is discussed with respect to infectivity of the challenge strains, absence of certain intestinal pathogens and feed and management factors.

Metabonomic identification of two distinct phenotypes in Sprague-Dawley (Crl:CD(SD)) rats

Genetic drift in animal populations has been a recognized concern for many years. Less understood is the potential for phenotypic "drift" or variation that is not related to any genetic change. Recently, stock Sprague-Dawley (Crl:CD(SD)) rats obtained from the Charles River Raleigh facility demonstrated a distinct endogenous urinary metabonomic profile that differed from historical control SD urine spectral profiles obtained over the past several years in our laboratory. In follow-up studies, the origin of the variant phenotype was narrowed down to animals of both sexes that were housed in one specific room (Room 9) in the Raleigh facility. It is likely that the two phenotypes are related to distinct populations of gut flora that particularly impact the metabolism of aromatic molecules. The most pronounced difference between the two phenotypes is the relative amounts of hippuric acid versus other aromatic acid metabolites of chlorogenic acid. Though both molecular species are present in either phenotype, the marked variation in levels of these molecules between the two phenotypes has led to the designation of high hippuric acid (HIP) and high chlorogenic acid metabolites (CA) phenotypes. Specific urinary components that distinguish the phenotypes have been thoroughly characterized by NMR spectroscopy with additional, limited characterization by LC-MS (high performance liquid chromatography coupled with mass spectrometry). Co-habitation of rats from the two phenotypes rapidly facilitated a switch of the CA phenotype to the historical Sprague-Dawley phenotype (HIP). The impact of these variant phenotypes on drug metabolism and long-term safety assessment studies (e.g., carcinogenicity bioassays) is unknown.

Increased tubular organic ion clearance following chronic ACE inhibition in patients with type 1 diabetes

BACKGROUND

The tubular excretion of creatinine significantly contributes to its clearance. Administration of an angtiotensin-converting enzyme (ACE) inhibitor is associated with increased organic ion clearance in experimental diabetes. This study examines the effect and implications of chronic ACE inhibition on renal organic ion excretion in patients with type 1 diabetes.

METHODS

Samples were obtained from the Melbourne Diabetic Nephropathy Study Group (MDNSG) that randomized patients to receive perindopril (N= 11), nifedipine (N= 11), or placebo (N= 8). Albumin excretion rate, creatinine clearance, and isotopic glomerular filtration rate (GFR) were assessed at baseline and after 24 months. In addition, the clearance of the endogenous cations N-methylynicotinamide (NMN), creatinine, and the anion hippurate were determined by high-performance liquid chromatography (HPLC).

RESULTS

Following treatment with the ACE inhibitor, perindopril, renal clearance of NMN was increased (+96%) (P < 0.05). There was no difference in patients treated with nifedipine (P= 0.25) and NMN clearance fell in the placebo-treated patients (-26%) (P < 0.05). Changes in NMN clearance were unaffected after adjusting for the effects of perindopril on GFR. However, they were attenuated after adjusting for hippurate clearance, a marker of renal blood flow. This effect of perindopril on NMN clearance was seen in both men and women, regardless of baseline clearance and was correlated with reduced albuminuria following perindopril treatment.

CONCLUSION

Organic ion clearance is increased in patients with diabetes following chronic ACE inhibition. This is consistent with experimental models showing increased ion transporter expression and improved tubular blood flow, following blockade of the renin-angiotensin system (RAS). These findings may have implications for the interpretation of creatinine-based indices in patients with diabetes.

High-performance liquid chromatographic determination of enalapril in human plasma by enzyme kinetic analytical method

A high-performance liquid chromatographic method for indirect determination of enalapril in human plasma, was developed and validated. An exogenous angiotensin converting enzyme after drug inhibition was determined by reacting with hippuryl-histidyl-leucine to produce hippuric acid (HA) which was inversely proportional to the amount of enalaprilat in plasma. The HPLC was carried out on a Lichrosphere 60RP-select B, C18, 5 microm (125 mm x 4.0 mm i.d.) column at flow rate of 1.0 ml/min. The analysis time per injection was within 6.5 min. The lowest concentration of enalaprilat to be quantitated was 3.0 ng/ml with the acceptable accuracy and precision. This successfully developed method was practically and accurately used for pharmacokinetics and bioequivalent study of enalapril.

Statistical total correlation spectroscopy: an exploratory approach for latent biomarker identification from metabolic 1H NMR data sets

We describe here the implementation of the statistical total correlation spectroscopy (STOCSY) analysis method for aiding the identification of potential biomarker molecules in metabonomic studies based on NMR spectroscopic data. STOCSY takes advantage of the multicollinearity of the intensity variables in a set of spectra (in this case 1H NMR spectra) to generate a pseudo-two-dimensional NMR spectrum that displays the correlation among the intensities of the various peaks across the whole sample. This method is not limited to the usual connectivities that are deducible from more standard two-dimensional NMR spectroscopic methods, such as TOCSY. Moreover, two or more molecules involved in the same pathway can also present high intermolecular correlations because of biological covariance or can even be anticorrelated. This combination of STOCSY with supervised pattern recognition and particularly orthogonal projection on latent structure-discriminant analysis (O-PLS-DA) offers a new powerful framework for analysis of metabonomic data. In a first step O-PLS-DA extracts the part of NMR spectra related to discrimination. This information is then cross-combined with the STOCSY results to help identify the molecules responsible for the metabolic variation. To illustrate the applicability of the method, it has been applied to 1H NMR spectra of urine from a metabonomic study of a model of insulin resistance based on the administration of a carbohydrate diet to three different mice strains (C57BL/6Oxjr, BALB/cOxjr, and 129S6/SvEvOxjr) in which a series of metabolites of biological importance can be conclusively assigned and identified by use of the STOCSY approach.

Comparative pharmacokinetics of acetyl salicylic acid and its metabolites in children suffering from autoimmune diseases

The aim of the present study was to compare the effect produced by juvenile rheumatoid arthritis (JRA) or rheumatic fever (RF) on the pharmacokinetics of acetyl salicylic acid (ASA) and its metabolites in children with autoimmune diseases (AD).

METHODS

A prospective, open labelled study was performed in 17 children with JRA and 17 with RF who received a single dose of 25 mg ASA/kg orally. The pharmacokinetics of ASA and its metabolites were determined. The blood and urine levels of each salicylate collected during 24 h were measured by HPLC. A group of 15 healthy teenage volunteers was included as a control group.

RESULTS

The maximum plasma concentration, half-life time, area under the curve and the amount of salicylates excreted were statistically different between the JRA and the RF groups, as well as between the RF group and the controls, however, there were no significant differences between the JRA group and the controls.

CONCLUSIONS

Dosage schemes must be adjusted for JRA patients, since the half life in these patients is longer than in RF patients. However, due to ample variability of pharmacokinetic parameters it is recommended that dose schemes are individualized on the type of autoimmune disease considered.

Model complexes with naturally occurring ligands (salicylglycine and imidazol) and the biometals copper and cobalt

Two new complexes [Cu(Imz)(4)Cl(2)][Cu(Imz)(4)Cl] (2)(2-OH-Hip)(2) (1) and [Co(2-OH-Hip)(Imz)(3)].H(2)O (2) (with Imz=Imidazol and 2-OH-Hip=2-hydroxyhippuric acid) were prepared and characterized. The molecular structures and the solution and solid state behavior of the complexes were investigated. Complex 1 crystallizes in the monoclinic space group P2(1)/c with a=16.880(1), b=8.046(1), c=24.683(1) A, beta=107.88(1) degrees, and Z=2, while complex 2 crystallizes in the orthorhombic space group Pbca with a=11.712(2), b=15.741(4), c=22.254(4) A, and Z=8. The [Cu(Imz)(4)Cl(2)][Cu(Imz)(4)Cl](2)(2-OH-Hip)(2) solid consists in two distinct monomeric Cu(II) complexes: one of them is neutral octahedral [Cu(Imz)(4)Cl(2)] and the other, charged square basis pyramida [Cu(Imz)(4)Cl](+). The 2-hydroxyhippuric acid, which here acts as a counter ion, is deprotonated at its carboxylic group. Cobalt(III) ion in [Co(2-OH-Hip)(Imz)(3)].H(2)O is at the center of an octahedral environment, coordinated to three Imidazol ligands and to a triply deprotonated 2-hydroxyhippuric acid molecule acting as a tridentate ligand. Aqueous solution equilibrium of the quaternary system Cu(2+)/2-OH-Hip/Imz/H(+) was studied by potentiometric titrations.

Identification of campylobacteria isolated from Danish broilers by phenotypic tests and species-specific PCR assays

AIMS

To validate a phenotypic Campylobacter species identification method employed to identify campylobacters in broilers by comparison with campylobacterial species identification using various species-specific PCR analyses.

METHODS AND RESULTS

From a collection of 2733 phenotypically identified campylobacterial cultures, 108 Campylobacter jejuni cultures and 351 campylobacterial cultures other than Camp. jejuni were subjected to various species-specific PCR assays. On the basis of the genotypic tests, it was demonstrated that Camp. jejuni and Camp. coli constituted approx. 99% of all cultures, while other species identified were Helicobacter pullorum, Camp. lari and Camp. upsaliensis. However, 29% of the 309 Camp. coli cultures identified by phenotypic tests were hippurate-variable or negative Camp. jejuni cultures, whereas some Camp. lari cultures and unspeciated campylobacter cultures belonged to H. pullorum. It was also notable that 2-6% of the cultures were, in fact, mixed cultures.

CONCLUSIONS

The phenotypic identification scheme employed failed to appropriately differentiate Campylobacter species and particularly to identify the closely related species, H. pullorum.

SIGNIFICANCE AND IMPACT OF THE STUDY

Future phenotypic test schemes should be designed to allow a more accurate differentiation of Campylobacter and related species. Preferably, the phenotypic tests should be supplemented with a genotypic strategy to disclose the true campylobacterial species diversity in broilers.

Comparison of the BAX® System with a multiplex PCR method for simultaneous detection and identification of Campylobacter jejuni and Campylobacter coli in environmental samples

The Campylobacter detection is performed by conventional culture methods and the identification of Campylobacter jejuni and Campylobacter coli is principally based on the hippurate hydrolysis test. The two major drawbacks of this biochemical test for species identification include the inconsistency of the results and the presence of atypical strains, which can lead to the misidentification of an isolate. As an alternative, multiplex polymerase chain reaction (mPCR) protocols for the simultaneous detection and identification of different Campylobacter species have been developed. This study examined the performances of an experimental BAX System assay for the C. jejuni and C. coli identification in comparison to a multiplex PCR protocol recently published. The samples tested were represented by 106 environmental swabs collected on Teflon strips and tables, stainless steel saws, hooks and trays, ceramic floors and walls, as well as equipment surfaces, located in a swine (N=50) and a poultry (N=56) slaughterhouse. The highest Campylobacter detection rate was obtained after 48 h of enrichment by using both the PCR procedures. After 24 h, the BAX System provides a more rapid and accurate Campylobacter detection and identification assay than the multiplex PCR. Except for two samples, all the broths where Campylobacter cells were detected after 24 or 48 h of enrichment, with at least one of the PCR protocols, gave Campylobacter colonies using the culture method.

Protein-bound uremic retention solutes

Protein-bound uremic retention solutes are molecules with low molecular weight (MW) but should be considered middle or high MW substances. This article describes the best known substances of this group, which include p-cresol, indoxyl sulfate, hippuric acid, 3-carboxy-4-methyl-5-propyl-2-furan-propionic acid (CMPF), and homocysteine. At concentrations encountered during uremia, p-cresol inhibits phagocyte function and decreases leukocyte adhesion to cytokine-stimulated endothelial cells. CMPF has been implicated in anemia and neurologic abnormalities of uremia. CMPF could alter the metabolism of drugs of inhibiting their binding to albumin and their tubular excretion. Indoxyl sulfate administrated to uremic rats increases the rate of progression of renal failure. Hippuric acid inhibits glucose utilization in the muscle, and its serum concentration is correlated with neurologic symptoms of uremia. Homocysteine predisposes uremic patients to cardiovascular disease through impairment of endothelial and smooth muscle cell functions. The removal of protein-bound compounds by conventional hemodialysis is low. Other strategies to decrease their concentrations include increase in dialyze pore size, daily hemodialysis, peritoneal dialysis, reduction of production or acceleration of degradation, and preservation of residual renal function.

Urinary excretion of salicyluric and salicylic acids by non-vegetarians, vegetarians, and patients taking low dose aspirin

AIM

To compare amounts of salicyluric acid (SU) and salicylic acid (SA) excreted daily in the urine of non-vegetarians and vegetarians not taking salicylate drugs, and patients taking 75 or 150 mg aspirin/day.

METHODS

Urine excreted over 24 hours was collected from volunteers in the four groups. The volumes were recorded and the concentrations of SU and SA were determined electrochemically after separation by high performance liquid chromatography.

RESULTS

Significantly more SU was excreted daily by vegetarians (median, 11.01; range, 4.98-26.60 micro mol/24 hours) than by non-vegetarians (median, 3.91; range, 0.87-12.23 micro mol/24 hours), although amounts were significantly lower than those excreted by patients taking aspirin. Median amounts of SU excreted by patients taking 75 and 150 mg/day of low dose aspirin were 170.69 (range, 13.15-377.18) micro mol/24 hours and 165.17 (range, 5.61-429.12) micro mol/24 hours, respectively. The amount of SU excreted by patients taking either 75 or 150 mg of aspirin/day was not significantly different. Significantly more SA was excreted by vegetarians (median, 1.19; range, 0.02-3.55 micro mol/24 hours) than by non-vegetarians (median, 0.31; range, 0.01-2.01 micro mol/24 hours). The median amounts of SA excreted by vegetarians and the patients taking aspirin were not significantly different.

CONCLUSIONS

More SU and SA is excreted in the urine of vegetarians than in non-vegetarians, consistent with the observation that fruits and vegetables are important sources of dietary salicylates. However, significantly less SU was excreted by vegetarians than patients taking aspirin, indicating that the daily intake of bioavailable salicylates by vegetarians is considerably lower than that supplied by a single 75 or 150 mg dose of aspirin.

Chlorogenic acid, quercetin-3-rutinoside and black tea phenols are extensively metabolized in humans

Dietary phenols are antioxidants, and their consumption might contribute to the prevention of cardiovascular disease. Coffee and tea are major dietary sources of phenols. Dietary phenols are metabolized extensively in the body. Lack of quantitative data on their metabolites hinders a proper evaluation of the potential biological effects of dietary phenols in vivo. The aim of this study was to identify and quantify the phenolic acid metabolites of chlorogenic acid (major phenol in coffee), quercetin-3-rutinoside (major flavonol in tea) and black tea phenols in humans, and determine the site of metabolism. Healthy humans (n = 20) with an intact colon participated in a dietary controlled crossover study, and we identified and quantified approximately 60 potential phenolic acid metabolites in urine. Half of the ingested chlorogenic acid and 43% of the tea phenols were metabolized to hippuric acid. Quercetin-3-rutinoside was metabolized mainly to phenylacetic acids, i.e., 3-hydroxyphenylacetic acid (36%), 3-methoxy-4-hydroxyphenylacetic acid (8%) and 3,4-dihydroxyphenylacetic acid (5%). In contrast, in seven humans without a colon, we found only traces of phenolic acid metabolites in urine after they had ingested chlorogenic acid and quercetin-3-rutinoside. This implies that the colonic microflora convert most of these dietary phenols into metabolites that then reach the circulation. Metabolites of dietary phenols have lower antioxidant activity than their parent compounds; therefore, the contribution of dietary phenols to antioxidant activity in vivo might be lower than expected from in vitro tests.

Moment analysis of metabolic heterogeneity: conjugation of benzoate with glycine in rat liver studied by multiple indicator dilution technique

Metabolic zonation was assessed with the multiple indicator dilution (MID) technique in the single-pass perfused rat liver with use of moment analysis of the formed metabolite (M) data. During single-pass, retrograde rat liver perfusion with 17 Awake M benzoate, a bolus containing tracer preformed metabolite (PM) [(3)H]hippurate was injected rapidly into the hepatic vein at 20 min postperfusion, followed by injection of a second bolus containing [(14)C]benzoate at 30 min. Both doses also contained noneliminated reference indicators ((51)Cr-labeled RBCs, (125)I-labeled albumin, [(14)C]- or [(3)H]sucrose, and (2)H(2)O). The steady-state extraction ratio of benzoate, the area under the curve (AUC) and its mean transit time (MTT) during retrograde flow were identical to those previously observed for prograde flow. Values of AUC(PM) and MTT(PM) and AUC(M) were also similar to previously published prograde data, but the MTT(M) with retrograde perfusion was smaller than that for prograde perfusion. This, according to theory based on the tubes-in-series model, was consistent with perivenous enrichment of glycination activity when transport of drug was even and when the ratio of drug influx/efflux coefficient exceeded that for metabolite. Similar benzoate transport in periportal, homogeneous and perivenous isolated rat hepatocytes existed, and the influx/efflux coefficients (partition ratio) of benzoate from MID indeed exceeded that of hippurate. However, metabolism by zonal hepatocytes failed to reveal the anticipated metabolic zonation, and this is likely due to the shallow gradient of metabolic activity. The study demonstrates that moment theory is useful in delineating the perivenous enrichment of glycine conjugation activity.

Analysis method of the angiotensin-I converting enzyme inhibitory activity based on micellar electrokinetic chromatography

A micellar electrokinetic chromatography (MEKC) method was developed for estimating the angiotensin-I converting enzyme (ACE) inhibitory activity by separating the hippuric acid liberated in the ACE reaction mixture in the presence of an inhibitor, captopril. The hippuric acid was successfully separated and detected by MEKC with a 25 mM sodium dodecyl sulfate solution in a 25 mM phosphate-50 mM borate buffer at pH 7.0; the total analysis took about 5 min. A good linear relationship was observed between the inhibitor and the peak area of hippuric acid release. No significant difference in the ACE inhibitory activity (IC50) of captopril (an antihypertensive medicine) or autolyzed-mushrooms (functional foods) was observed between the conventional method and the MEKC method. The MEKC method was found to be a useful technique for a rapid assay of the ACE inhibitory activity.

Peptides with angiotensin I-converting enzyme (ACE) inhibitory activity from defibrinated, hydrolyzed bovine plasma

Defibrinated bovine plasma (DBP) was treated with the microbial protease Flavourzyme to obtain protein hydrolysates with various degrees of hydrolysis (DH). The angiotensin I-converting enzyme (ACE) inhibiting activity of the hydrolyzed protein was assessed with hippuryl-His-Leu as the substrate. The amount of hippuric acid released, due to uninhibited ACE activity, was determined by high-performance liquid chromatography. ACE inhibiting (ACEI) activity was found to increase with increasing DH; the 43% DH hydrolysate exhibited the highest activity and had an IC(50) of 1.08 mg/mL. Peptide fractions with high ACEI activity were isolated using size exclusion chromatography. The fraction that possessed the highest ACEI activity contained peptides with GYP, HL(I), HPY, HPGH, L(I)F, SPY, and YPH sequence motifs, as determined by reversed-phase liquid chromatography-tandem mass spectrometry using a novel immonium precursor-ion scanning technique. Some of these motifs correspond to sequences found in bovine serum albumin, a potential source of ACEI peptides in bovine plasma.

Simultaneous determination of metabolites of trimethylbenzenes, dimethylbenzylmercapturicacid and dimethylhippuric acid, in human urine by solid-phase extraction followed by liquid chromatography tandem mass spectrometry

We describe a novel method for the determination of three kinds of dimethylbenzylmercapturic acids (DMM) and six kinds of dimethylhippuric acids (DMH), found in urine as metabolites of trimethylbenzenes, based on liquid chromatography/electrospray ionization tandem mass spectrometry. A solid-phase extraction procedure was used for the extractions of DMM and DMH from a urine sample, and the separation was performed on a reversed-phase C(30) column. The analytes were ionized by electrospray in the positive-ion mode. Operating in the multiple reaction monitoring mode, the linearity of the relative mass spectrometric responses to the internal standard versus analyte concentrations were established in the range 0.1-100 ng ml(-1). The extraction procedure was rapid and the relative standard deviations were below 5%. The detection limits of DMM and DMH in the urine by the proposed method were in the ranges 0.26-0.41 and 0.42-2.0 ng l(-1), respectively. Furthermore, DMM and DMH were detected in a urine sample from an individual who did not suffer from occupational exposure to trimethylbenzenes, by using this method.

Simultaneous detection of hippuric acid and methylhippuric acid in urine by Empore disk and gas chromatography-mass spectrometry

A method is described for the determination of hippuric acid (HA) and o-, m-, and p-methylhippuric acids (o-, m-, p-MHAs) in urine using solid-phase extraction and gas chromatography-mass spectrometry (GC-MS). The extraction procedure uses an Empore disk, derivatized into the respective trimethyl silyl derivatives. All metabolites including the internal standard (I.S.) were clearly able to be analyzed by the DB-17 column. The calibration curves for the four acids show linearity in the range of 5-70 microg/ml. The detection limit of each acid was 1.0-2.5 microg/ml.

The effect of cigarette smoking on urinary hippuric acid concentration in Thai workers with occupational exposure to toluene

Urine hippuric acid determination is helpful for monitoring of group of workers at risk for exposure to toluene. However, some problems about the external source of variation are mentioned. Some studies have indicated that smoking is an important external source of variation for determination of urine hippuric acid level while the others stated the opposite findings. This study was conducted in an attempt to study the difference of urine hippuric acid between smoking and non smoking subjects in a press workers group. Urine samples were obtained from 46 workers (all male) who worked as press workers in the same press factory in Bangkok. The individuals were classified as control (non smoking, N = 26) and experimental (smoking, N = 20) according to their smoking. All samples were analyzed for hippuric acid level. The average urine hippuric acid level for the control were (0.35 +/- 0.31 mg/gCr) and experimental group (0.40 + 0.45 mg/gCr) were respectively. No significant difference was found between urine hippuric acid level between both groups. The data from the current study indicates that smoking does not influence the urinary hippuric acid levels in this study group.

Toluene metabolites as biological indicators of exposure

The measurement of exhaled and excreted xenobiotics and their metabolites can provide accurate, non-invasive, and time-flexible measurements of internal dose. We analyzed rates of exhaled (2)H(8)-toluene and excreted urinary metabolites from 33 exposures of men to 50 ppm of (2)H(8)-toluene for 2 h at rest. The total dose was distributed as follows: exhaled (2)H(8)-toluene, 13 +/- 6.2%; (2)H(5)-hippuric acid, 75 +/- 6.4%; (2)H(7)-o-cresol, 0.31 +/- 0.22%; (2)H(7)-m-cresol, 0.53 +/- 0.44%; and (2)H(7)-p-cresol, 11 +/- 3.8%. Interindividual variability was assessed using the coefficients of variation for peak exhalation or excretion rates, and fractions of dose excreted: (2)H(8)-toluene, c.v.=60, 47%; (2)H(5)-hippuric acid, 29, 8.6%; (2)H(7)-o-cresol, 80, 73%; (2)H(7)-m-cresol, 37, 83%; and (2)H(7)-p-cresol, 38, 34%. Excretion rates of the cresols were stable over the first 5 h post-exposure, and o-cresol was determined to be the best urinary indicator of exposure, given the lower background levels of this isomer. The hippuric acid/cresol rate ratios for the first 5 h post-exposure could be described by single exponential terms, and thus provided a means for estimating time since exposure for any finite toluene duration/exposure combination.

Hippurate metabolism as a hydroxyl radical trapping mechanism in the rat kidney

Hippurate (Hip) is considered to be the end product of benzoate (BA) metabolism. However, the kidney is able to metabolize Hip. Although only Hip but no BA is present in the blood, rat urine contains under normal conditions less Hip (about 0.4 mM) than BA (about 4.5 mM) and of hydroxylated derivatives of BA (hydroxy-BAs = HB and dihydroxy-BAs = DHB). Generation of HBs and DHBs is the result of radical substitution by free OH radicals (*OH). Thus, rate of synthesis of HBs and DHBs may reflect the production rate of *OH in the kidney *OH generation is elevated following ischemic stress. Therefore, production of HBs and DHBs can be expected to be elevated in postischemic injury. The validity of this assumption was tested in vitro on isolated tubular segments and in vivo in the rat. Metabolism of Hip at 0.1 mmol x l(-1 ) (0.1 mM) as well as of BA resulted in enlarged production of both HBs (especially 3-HB and 4-HB) and of DHBs (especially 2,6-DHB). Production of 2,3- and especially of 2,5-DHB was elevated in the presence of high concentration (1.0 mM) of salicylate (2-HB) only. In vivo both in acute (120 min) and in chronic (5 days) experiments ligation of one renal artery for 30 respectively 60 min resulted in enlarged excretion of HBs and DHBs, especially of 2,6- and 3,5-DHB. This finding is noteworthy since (a) formation of 2,6-DHB necessitates as precursor salicylate which could not be detected in our experiments and (b) the spontaneous attack of *OH upon the benzol ring would prefer the positions 2,3- 2,5- and 3,4-. Therefore, the existence of regulating factor(s) guiding OH groups to definite positions is a distinct possibility. These results indicate that metabolism of Hip leading to hydroxylated BAs may be a renoprotective mechanism against attack of *OH in reoxygenated renal tissue.

Detoxification in relation to toxin tolerance in desert woodrats eating creosote bush

We studied the relationship between the use of three detoxification pathways and urine pH and the tolerance of desert woodrats from two populations to a mixture of naturally occurring plant secondary metabolites (mostly phenolics) in resin from creosote bush (Larrea tridentata). The two populations of desert woodrats came from the Mojave desert (Mojave woodrats), where woodrats consume creosote bush, and from the Great Basin desert (Great Basin woodrats), where the plant species is absent. We fed woodrats alfalfa pellets containing increasing levels of the phenolic resin and measured three detoxification pathways and urine pH that are related to detoxification of allelochemicals. We found that the excretion rate of two phase II detoxification conjugates, glucuronides and sulfides. increased with increasing resin intake, whereas excretion of hippuric acid was independent of resin intake, although it differed between populations. Urine pH declined with increasing resin ingestion. The molar proportion of glucuronides in urine was three times that of the other conjugates combined. Based on an evaluation of variation in the three detoxification pathways and urine pH in relation to resin intake, we rejected the hypotheses that woodrats' tolerance to resin intake is related to capacity for amination, sulfation, or pH regulation. However, Mojave woodrats had higher maximum glucuronide excretion rates, and we accepted the hypothesis that within and between populations woodrats tolerate more resin because they have a greater capacity for glucuronide excretion.

Fast homogeneous assay for plasma procarboxypeptidase U

Carboxypeptidase U (EC 3.4.17.20, CPU, TAFIa) is a novel determinant of the fibrinolytic rate. It circulates as an inactive zymogen, procarboxypeptidase U, which becomes active during the process of coagulation. We developed a high throughput method on microtiter plates for the determination of the procarboxypeptidase U concentration in human plasma samples. Following activation of procarboxypeptidase U by thrombin-thrombomodulin, the resulting enzyme activity cleaves p-OH-Hip-Arg and the generated p-OH-hippuric acid is converted by hippuricase to p-hydroxybenzoic acid and glycine. Finally, oxidative coupling of p-hydroxybenzoic acid with 4-aminoantipyrine by NaIO4 forms the quinoneimine dye. The absorbance of the latter dye is determined at 506 nm in a microtiter plate reader. A mean value of 620 U/l was found, with a CV of 3.0% within-run and 4.3% between-run. The assay showed a good correlation with the activities observed using a HPLC assay as reference method (n = 25, r = 0.979). The presented method enables the routine analysis of large sample pools in clinical setting.

Growth of the purple bacterium Rhodobacter capsulatus on the aromatic compound hippurate

The purple nonsulfur bacterium Rhodobacter capsulatus strain B10 grew phototrophically on the aromatic compound hippurate (N-benzoyl-L-glycine) and related benzoyl amino acids. Absorption spectra, extraction, and GC/MS analysis of culture supernatants showed that hippurate was stoichiometrically converted to benzoate and glycine, with the latter used as a carbon or nitrogen source for growth. This conclusion was supported by detection of the enzyme hippuricase in permeabilized intact cells. Chemotrophic growth on hippurate by Rba. capsulatus, either at full or reduced oxygen tensions, was not observed. The type strain of Rhodobacter sphaeroides as well as four strains of Rhodopseudomonas palustris also grew phototrophically on hippurate, while several other aromatic-degrading species of purple bacteria did not.

Interactions of d(10) metal ions with hippuric acid and cytosine. X-ray structure of the first cadmium (II)-amino acid derivative-nucleobase ternary compound

The interactions of Zn(II), Cd(II) and Hg(II) with hippuric acid (hipH) were studied and several novel compounds were synthesized and studied by NMR. Some new metal-hippuric-cytosine ternary compounds were formed and the structure of the [Cd(hip)(2)(cyt)(H(2)O)](2) ternary complex resolved. Each cadmium (II) atom has a distorted trigonal bipyramid coordination which is linked to a water molecule, a cytosine via N(3), a carboxylic oxygen atom of a hippurate moiety and two bridging dicoordinated hippurates bound through the carboxylic oxygen atoms. To these five main bonds, two longer ancillary interactions can be observed: the second oxygen of the monocoordinated hippurate group and the carboxylic oxygen of the cytosine ligand. The compound is stabilized by an intramolecular stacking between the benzene and cytosine rings and by the hydrogen bonds between the coordinated water molecules and the ligands. This is, to our knowledge, the first structure of a cadmium-amino acid derivative-natural nucleobase compound described so far.

Hepatic uptake and metabolism of benzoate: a multiple indicator dilution, perfused rat liver study

Multiple, noneliminated references ((51)Cr-labeled erythrocytes, (125)I-albumin, [(14)C]- or [(3)H]sucrose, and [(2)H](2)O), together with [(3)H]hippurate or [(14)C]benzoate, were injected simultaneously into the portal vein of the perfused rat liver during single-pass delivery of benzoate (5-1,000 microM) and hippurate (5 microM) to investigate hippurate formation kinetics and transport. The outflow dilution data best fit a space-distributed model comprising vascular and cellular pools for benzoate and hippurate; there was further need to segregate the cellular pool of benzoate into shallow (cytosolic) and deep (mitochondrial) pools. Fitted values of the membrane permeability-surface area products for sinusoidal entry of unbound benzoate were fast and concentration independent (0.89 +/- 0.17 ml. s(-1). g(-1)) and greatly exceeded the plasma flow rate (0.0169 +/- 0.0018 ml. s(-1). g(-1)), whereas both the influx of benzoate into the deep pool and the formation of hippurate occurring therein appeared to be saturable. Results of the fit to the dilution data suggest rapid uptake of benzoate, with glycination occurring within the deep and not the shallow pool as the rate-determining step.

Directly coupled high-performance liquid chromatography and nuclear magnetic resonance spectroscopic with chemometric studies on metabolic variation in Sprague--Dawley rats

We report here the first combined use of NMR-PR (pattern recognition) analysis and directly coupled HPLC--NMR analysis to identify metabolic subpopulations in normal laboratory animals and their discriminating endogenous urinary biomarkers. Urine samples obtained from control Sprague-Dawley rats (n = 68) were analyzed using (1)H NMR spectroscopy and principal components (PC) analysis to investigate physiological variability. Two distinct subpopulations of animals were classified based on metabolite excretion profiles. Analysis of the PC loadings established the spectral regions that were responsible for classification of the subpopulations and was used to direct the identification of biomarkers using a directly coupled HPLC--NMR analysis. One population had low urinary hippurate levels together with an increased concentration of 3-(3-hydroxyphenyl)propionic acid (3-HPPA)and 3-hydroxycinnamic acid (3-HCA). The other subpopulation excreted high levels of hippurate. Thus, we report the bimodal occurrence of hippuric acid and chlorogenic acid metabolites in a genetically homogeneous population of rats maintained under identical conditions, which may have significance in relation to the understanding of the consequences of biochemical variation in animals used for drug toxicity testing.

Characterization of p-hydroxy-hippuric acid as an inhibitor of Ca2+-ATPase in end-stage renal failure

Characterization of p-hydroxy-hippuric acid as an inhibitor of Ca2+-ATPase in end-stage renal failure. In patients with end-stage renal failure (ESRF), disturbances of Ca2+ metabolism are common. Besides hormonal changes, inhibition of cellular Ca2+-ATPase was postulated to contribute to uremic toxicity. We purified a potent inhibitor of the Ca2+-ATPase from the ultrafiltrate of patients with ESRF by multiple steps of high-performance liquid chromatography to homogeneity, and identified the isolated inhibitor by mass spectrometric methods as p-hydroxy-hippuric acid. The enzyme used for the Ca2+-ATPase assay system was isolated from red blood cells by cross-flow filtration. The activity of the Ca2+-ATPase was measured spectrophotometrically as the difference in hydrolysis of adenosine 5'-triphosphate (ATP) in the presence and absence of Ca2+ with different concentrations of ATP and p-hydroxyhippuric acid. The Ca2+-ATPase was found to be inhibited by p-hydroxy-hippuric acid at a concentration above 11.7 micromol/L. p-Hydroxyhippuric acid inhibited the erythrocyte Ca2+-ATPase by reducing Vmax and increasing the Km value. The EC50 (log mol/L; mean +/- SEM) for p-hydroxy-hippuric acid was calculated as 4.82 +/- 0.14. In conclusion, p-hydroxy-hippuric acid may play a role in disturbed Ca2+ metabolism in end-stage renal failure.

Protein-bound uremic solutes: the forgotten toxins

The present concept of dialysis focuses mainly on the removal of small water-soluble compounds, and also, the currently applied kinetic parameters of dialysis adequacy are based on the behavior of water-soluble compounds. Nevertheless, many of the currently known biological effects in uremia are attributable to compounds with different physicochemical characteristics, and among these, protein-bound solutes play an important role. In this article, we review the characteristics and consequences of changes in protein binding in uremia, as well as the toxicity of the protein-bound uremic solutes 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid (CMPF), indoxyl sulfate, hippuric acid, homocysteine, and p-cresol. Starting from the example of p-cresol, we then summarize the impact of protein-binding on dialytic removal, whereby it is concluded that this removal is largely hampered by this protein-binding compared with that of classic markers such as urea and creatinine. Alternative removal strategies, such as strategies to modify intestinal generation or absorption, are considered.

Hippurate participates in the correction of metabolic acidosis

Hippurate (Hip), an endogenous conjugate, belongs to the group of uremic toxins. Hip stimulates P-independent glutaminase (PIG) localized at the proximal luminal membrane, desamidating glutamine with the formation of ammonia, a dominant and adaptive elimination product of H+. This appears to be important because metabolic acidosis (MAC) does not stimulate PIG. Moreover, Hip inhibits ammonia production by P-dependent mitochondrial glutaminase (PDG) that is primarily stimulated by MAC. By this mechanism, it shifts the ammonia production from mitochondria to proximal tubular lumen. MAC stimulates Hip synthesis in the liver and kidney and increases Hip plasma concentration and even fractional excretion by the kidney, which creates an effective regulatory loop of ammoniagenesis. Thus, it appears that Hip by its participation in the correction of MAC possesses the modulatory function.

Hippuric Acid Test Using 13C-Labelling and NMR Spectroscopy

This article describes a 13C-labelling and nuclear magnetic resonance approach for hippuric acid test which is potentially useful for evaluating liver reserve. In this approach, urine samples collected after ingestion of 13C-labelled benzoic acid were directly analysed by 13C nuclear magnetic resonance spectroscopy, and the excreted 13C-labelled hippuric acid formed from the administered benzoic acid was quantitated. The amount of labelled hippuric acid excreted in a specified time can be a useful index of liver reserve. In this study, the feasibility of the nuclear magnetic resonance approach has been investigated in several healthy subjects. This approach is simple and convenient compared with conventional analytical procedures, because no chromatographic separation is required. The approach could give new insights into the liver reserve, because the benzoic acid conversion to hippuric acid intimately relates to the hepatic energy metabolism. This measurement can be conducted at a wide range of dosages without interference from endogenous hippuric acid.

Amidation of salicyluric acid and gentisuric acid: a possible role for peptidylglycine alpha-amidating monooxygenase in the metabolism of aspirin

Bifunctional peptidylglycine alpha-amidating monooxygenase (PAM) catalyzes the copper-, ascorbate-, and O2-dependent cleavage of C-terminal glycine-extended peptides, N-acylglycines, and the bile acid glycine conjugates to the corresponding amides and glyoxylate. Two known metabolites of aspirin, salicyluric acid and gentisuric acid, are also substrates for PAM, leading to the formation of salicylamide and gentisamide. The time course for O2 consumption and glyoxylate production indicates that salicylurate amidation is a two-step reaction. Salicylurate is first converted to N-salicyl-alpha-hydroxyglycine, which is ultimately dealkylated to salicylamide and glyoxylate. The enzymatically generated salicylamide and N-salicyl-alpha-hydroxyglycine were characterized by mass spectrometry and two-dimensional 1H-13C heteronuclear multiple quantum coherence NMR.