GPR109A mediates the effects of hippuric acid on regulating osteoclastogenesis and bone resorption in mice

The G protein-coupled receptor 109 A (GPR109A) is robustly expressed in osteoclastic precursor macrophages. Previous studies suggested that GPR109A mediates effects of diet-derived phenolic acids such as hippuric acid (HA) and 3-(3-hydroxyphenyl) propionic acid (3-3-PPA) on promoting bone formation. However, the role of GPR109A in metabolic bone homeostasis and osteoclast differentiation has not been investigated. Using densitometric, bone histologic and molecular signaling analytic methods, we uncovered that bone mass and strength were significantly higher in tibia and spine of standard rodent diet weaned 4-week-old and 6-month-old GPR109A gene deletion (GPR109A-/-) mice, compared to their wild type controls. Osteoclast numbers in bone and in ex vivo bone marrow cell cultures were significantly decreased in GPR109A-/- mice compared to wild type controls. In accordance with these data, CTX-1 in bone marrow plasma and gene expression of bone resorption markers (TNFα, TRAP, Cathepsin K) were significantly decreased in GPR109A-/- mice, while on the other hand, P1NP was increased in serum from both male and female GPR109A-/- mice compared to their respective controls. GPR109A deletion led to suppressed Wnt/β-catenin signaling in osteoclast precursors to inhibit osteoclast differentiation and activity. Indeed, HA and 3-3-PPA substantially inhibited RANKL-induced GPR109A expression and Wnt/β-catenin signaling in osteoclast precursors and osteoclast differentiation. Resultantly, HA significantly inhibited bone resorption and increased bone mass in wild type mice, but had no additional effects on bone in GPR109A-/- mice compared with their respective untreated control mice. These results suggest an important role for GPR109A during osteoclast differentiation and bone resorption mediating effects of HA and 3-3-PPA on inhibiting bone resorption during skeletal development.

Black Raspberries Suppress Colorectal Cancer by Enhancing Smad4 Expression in Colonic Epithelium and Natural Killer Cells

Innate immune cells in the tumor microenvironment have been proposed to control the transition from benign to malignant stages. In many cancers, increased infiltration of natural killer (NK) cells associates with good prognosis. Although the mechanisms that enable NK cells to restrain colorectal cancer (CRC) are unclear, the current study suggests the involvement of Smad4. We found suppressed Smad4 expression in circulating NK cells of untreated metastatic CRC patients. Moreover, NK cell-specific Smad4 deletion promoted colon adenomas in DSS-treated ApcMin/+ mice and adenocarcinomas in AOM/DSS-treated mice. Other studies have shown that Smad4 loss or weak expression in colonic epithelium associates with poor survival in CRC patients. Therefore, targeting Smad4 in both colonic epithelium and NK cells could provide an excellent opportunity to manage CRC. Toward this end, we showed that dietary intervention with black raspberries (BRBs) increased Smad4 expression in colonic epithelium in patients with FAP or CRC and in the two CRC mouse models. Also, benzoate metabolites of BRBs, such as hippurate, upregulated Smad4 and Gzmb expression that might enhance the cytotoxicity of primary human NK cells. Of note, increased levels of hippurate is a metabolomic marker of a healthy gut microbiota in humans, and hippurate also has antitumor effects. In conclusion, our study suggests a new mechanism for the action of benzoate metabolites derived from plant-based foods. This mechanism could be exploited clinically to upregulate Smad4 in colonic epithelium and NK cells, thereby delaying CRC progression.

Common gut microbial metabolites of dietary flavonoids exert potent protective activities in β-cells and skeletal muscle cells

Flavonoids are dietary compounds with potential anti-diabetes activities. Many flavonoids have poor bioavailability and thus low circulating concentrations. Unabsorbed flavonoids are metabolized by the gut microbiota to smaller metabolites, which are more bioavailable than their precursors. The activities of these metabolites may be partly responsible for associations between flavonoids and health. However, these activities remain poorly understood. We investigated bioactivities of flavonoid microbial metabolites [hippuric acid (HA), homovanillic acid (HVA), and 5-phenylvaleric acid (5PVA)] in primary skeletal muscle and β-cells compared to a native flavonoid [(-)-epicatechin, EC]. In muscle, EC was the most potent stimulator of glucose oxidation, while 5PVA and HA simulated glucose metabolism at 25 μM, and all compounds preserved mitochondrial function after insult. However, EC and the metabolites did not uncouple mitochonndrial respiration, with the exception of 5PVA at10 μM. In β-cells, all metabolites more potently enhanced glucose-stimulated insulin secretion (GSIS) compared to EC. Unlike EC, the metabolites appear to enhance GSIS without enhancing β-cell mitochondrial respiration or increasing expression of mitochondrial electron transport chain components, and with varying effects on β-cell insulin content. The present results demonstrate the activities of flavonoid microbial metabolites for preservation of β-cell function and glucose utilization. Additionally, our data suggest that metabolites and native compounds may act by distinct mechanisms, suggesting complementary and synergistic activities in vivo which warrant further investigation. This raises the intriguing prospect that bioavailability of native dietary flavonoids may not be as critical of a limiting factor to bioactivity as previously thought.

Synthesis and characterization of Mn(II), Au(III) and Zr(IV) hippurates complexes

Mn(II), Au(III) and Zr(III) complexes with N-benzoylglycine (hippuric acid) (abbreviation hipH) were synthesized and characterized by elemental analysis, molar conductivity, magnetic measurements, spectral methods (mid-infrared, 1H NMR, mass, X-ray powder diffraction and UV/vis spectra) and simultaneous thermal analysis (TG and DTG) techniques. The molar conductance measurements proved that all hippuric acid complexes are non-electrolytes. The electronic spectra and magnetic susceptibility measurements were used to infer the structures. The IR spectra of the ligand and its complexes are used to identify the type of bonding. The kinetic thermodynamic parameters such as: E*, DeltaH*, DeltaS* and DeltaG* are estimated from the DTG curves. The free ligand and its complexes have been studied for their possible biological antifungal activity.

Suppressive effect of post- or pre-treatment of aspirin metabolite on mitomycin C-induced genotoxicity using the somatic mutation and recombination test in Drosophila melanogaster

In our previous paper, we found that aspirin suppressed in a somatic mutation and recombination test (SMART) of mitomycin C (MMC) in Drosophila melanogaster. In order to reveal the mechanism of bio-antimutagenicity and/or preventive effect of aspirin, we evaluated the suppressive ability of each aspirin metabolite, such as salicylic acid (SA), salicyluric acid (SUA), gentisic acid (GA), gentisuric acid (GUA) and 2,3-dihydroxybenzoic acid (DHBA), in SMART in D. melanogaster using post- and pre-treatments. As for the post-treatment, SA reduced the numbers of large single and twin spots. GA reduced the small single and large single spots, and GUA reduced the single spots, large single and twin spots. The inhibition of GUA is slightly stronger than that of any other metabolites; the inhibition percentage is 49 at the dose of 5 mg/bottle. On the other hand, as for the pre-treatment, aspirin, SUA, GA and DHBA reduced the numbers of small single spots. SUA, GE and DHBA reduced the number of large single spots. Aspirin and its metabolites did not reduce the number of twin spots. The results of the present study suggest that SA, GA and GUA repair or replicate DNA-damage by MMC and SUA, GA, GUA and DHBA prevent DNA-damage by MMC. It is suggested that secondary cancer is prevented by aspirin post-treatment without losing the medicinal effectiveness (anti-tumor activity). Therefore, we consider there are effective doses and/or administration timing of aspirin and MMC to prevent secondary cancer.

Differential contributions of rOat1 (Slc22a6) and rOat3 (Slc22a8) to the in vivo renal uptake of uremic toxins in rats

PURPOSE

Evidence suggests that uremic toxins such as hippurate (HA), indoleacetate (IA), indoxyl sulfate (IS), and 3-carboxy-4-methyl-5-propyl-2-furanpropionate (CMPF) promote the progression of renal failure by damaging tubular cells via rat organic anion transporter 1 (rOat1) and rOat3 on the basolateral membrane of the proximal tubules. The purpose of the current study is to evaluate the in vivo transport mechanism responsible for their renal uptake.

METHODS

We investigated the uremic toxins transport mechanism using the abdominal aorta injection technique [i.e., kidney uptake index (KUI) method], assuming minimal mixing of the bolus with serum protein from circulating serum.

RESULTS

Maximum mixing was estimated to be 5.8% of rat serum by measuring estrone sulfate extraction after addition of 0-90% rat serum to the arterial injection solution. Saturable renal uptake of p-aminohippurate (PAH, K(m) = 408 microM) and benzylpenicillin (PCG, K(m) = 346 microM) was observed, respectively. The uptake of PAH and PCG was inhibited in a dose-dependent manner by unlabeled PCG (IC(50) = 47.3 mM) and PAH (IC(50) = 512 microM), respectively, suggesting that different transporters are responsible for their uptake. A number of uremic toxins inhibited the renal uptake of PAH and PCG. Excess PAH, which could inhibit rOat1 and rOat3, completely inhibited the saturable uptake of IA, IS, and CMPF by the kidney, and by 85% for HA uptake. PCG inhibited the total saturable uptake of HA, IA, IS, and CMPF by 10%, 10%, 45%, and 65%, respectively, at the concentration selective for rOat3.

CONCLUSIONS

rOat1 could be the primary mediator of the renal uptake of HA and IA, accounting for approximately 75% and 90% of their transport, respectively. rOat1 and rOat3 contributed equally to the renal uptake of IS. rOat3 could account for about 65% of the uptake of CMPF under in vivo physiologic conditions. These results suggest that rOat1 and rOat3 play an important role in the renal uptake of uremic toxins and the induction of their nephrotoxicity.

Effect of protein-bound uraemic toxins on the thermodynamic characteristics of human albumin

The ability of albumin to bind drugs and other lipophilic organic acids is decreased in chronic renal failure by the accumulation of albumin-bound uraemic toxins such as hippuric acid, indoxyl sulphate and 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF). This furan acid is the most highly bound and is not removed by haemodialysis. The inhibitory effects of these three uraemic toxins on the interaction of three marker ligands sodium octanoate (for medium chain fatty acids), salicylic acid and phenol red (bilirubin site/site I) with albumin have been investigated by differential scanning microcalorimetry and flow microcalorimetry. CMPF was the most potent inhibitor and its binding site coincided with that of bilirubin (site I). Indoxyl sulphate binds to the site for medium-chain fatty acids and tryptophan (site II) and hippuric acid, the weakest inhibitor, inhibited binding to the salicylic acid site.

Uremic sera contain inhibitors that block digitoxin-valproic acid interaction

BACKGROUND

Digitoxin and valproic acid show strong binding to serum albumin. Thus, when present simultaneously in serum, digitoxin and valproic acid compete for binding sites. We studied digitoxin-valproic acid interaction in normal and uremic sera.

METHODS

Fluorescence polarization immunoassays were used for measuring total digitoxin and total valproic acid concentrations. We used a modified protocol of improved sensitivity to measure free digitoxin concentrations. We supplemented 2 normal and 2 uremic pools with digitoxin and then aliquots of these pools were further supplemented with various concentrations of valproic acid. After incubation at 37 degrees C for 2 hours in a water bath, specimens were allowed to re-equilibrate at room temperature for 20 minutes. Free digitoxin concentrations were measured. We also investigated digoxin-valproic acid interaction using 1 normal and 1 uremic serum pool.

RESULTS

We observed significant increases in free digitoxin concentrations in normal sera in the presence of valproic acid. In contrast, we observed a slight decline in free digitoxin concentration in the presence of valproic acid in uremic sera. We speculated that uremic sera contained inhibitors that block digitoxin-valproic acid interaction and identified indoxyl sulfate as an inhibitor. However, another uremic compound, hippuric acid showed no inhibitory effect. Interestingly, we observed no significant interaction between digoxin and valproic acid in either normal or uremic serum pool. This is probably because of poor protein binding of digoxin.

CONCLUSION

We conclude that valproic acid significantly displaces digitoxin from protein binding sites in normal serum. However, uremic sera contain inhibitors that block digitoxin-valproic acid interaction.

Estrogenic activity and metabolism of n-butyl benzyl phthalate in vitro: identification of the active molecule(s)

Some phthalates are suspected to disrupt the endocrine system, especially by mimicking estrogens. N-butyl benzyl phthalate (BBP) has estrogenic effects in vitro but not in vivo. The aim of this study was to identify the active molecule(s) (parent compound and/or metabolite(s)) involved in the estrogenic activities of BBP. The estrogenic effects of BBP and its in vivo metabolites were assessed using the following tests: E-Screen, ER binding, and PR induction tests on the human breast cancer cell line MCF-7 (ER(+)). BBP, the parent compound, was a partial agonist. It stimulated MCF-7 proliferation in the E-Screen assay and increased cytosolic progesterone receptors (PR) levels in a concentration-dependent manner. No BBP metabolites were active except hippuric acid (HA), which had a weak effect at very high concentrations. BBP and HA stimulatory effects on MCF-7 proliferation were antagonized by tamoxifen. However, no competition was observed between BBP or HA and 17beta-estradiol for binding to the estrogen receptor (ER). BBP metabolism by MCF-7 cells was also investigated. After a 48-h incubation, only 10% of the initial BBP remained in the culture medium, demonstrating that BBP was extensively metabolized by the MCF-7 cells. The radioactivity recovered in the medium was represented by: mono-n-butyl phthalate (MBuP, 25%) and mono-n-benzyl phthalate (MBeP, 48%), phthalic acid (6%), and benzoic acid (3%). Since none of these metabolites had estrogenic activities, this study demonstrates that the parent compound was the active molecule involved in the in vitro estrogenic effects of BBP.

Synergistic potentiating effect of D(+)-mannose, orotic, and hippuric acid sodium salt on selective toxicity of a mixture of 13 substances of the circulatory system in culture for various tumor cell lines

Despite global immune system abnormalities in the autoimmune deficiency syndrome, the incidence of only a few tumor types increases, and the degree of immunosuppression does not seem to be critical in the development of these tumors, indicating that the immune system does not prevent tumor development. Consequently, because tumors do not develop in most individuals, other defense systems may exist. We demonstrated previously that 13 substances in the circulatory system acting synergistically induced apoptosis in vitro and in vivo in different tumor cell lines, but not in normal cells and animals. We investigated another 17 compounds and five ions in the circulatory system to determine their participation in the defense provided by the 13 substances. Three of the 17 substances but no ions had a potentiating effect on the mixture of substances used previously. The new 16-component mixture suppressed in vitro growth of six human and murine tumor cell lines, including multidrug-resistant tumor cells, without cytotoxic effects in two normal cell lines. The selectivity also was demonstrated by investigating the mixture's effect over time on tumor and normal cell growth.

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.

Hippuric Acid as a Modifier of Calcium Oxalate Crystallisation

Hippuric acid (HA) originating from the conjugation of benzoic acid with glycine is a physiological component of human urine. Findings suggest that HA inhibits calcium oxalate (CaOx) growth and considerably enhances the CaOx solubility in artificial urine. Thus, it is assumed that HA is a major modifier of CaOx formation. However, only a slight CaOx growth inhibition of 1-8% was also reported. These values were also derived from artificial urine. The key mechanism, which led HA to be of interest in urolithiasis research is the fact that in presence of Ca2+ ions HA can form a hippurate complex. By forming such a complex, Ca2+ concentration in urine decreases, and as a consequence, CaOx formation is inhibited. This study was performed in order to clarify the role of HA in native and artificial urine. Biochemical analyses to calculate the relative CaOx supersaturations and crystallisation experiments using an in-line laser probe were examined. BONN Risk Indices indicating the risk of CaOx crystallisation were calculated from the results of the crystallisation experiments. The results obtained from artificial as well as from native urines showed that HA has no significant effects on CaOx formation. We suggest that HA plays only a minor role as a crystallisation modifier in human urine.

Evaluation of potential disinfectants for preslaughter broiler crop decontamination

The broiler crop has recently been implicated as a major source of Salmonella contamination at commercial processing. Furthermore, feed withdrawal has been positively correlated with increased Salmonella incidence in the crop, probably due to coprophagy. In the present study, a rapid screening assay was developed to evaluate several potential disinfectants in the presence of large quantities of organic matter, simulating the crop environment. An apparent synergistic combination of d-Limonene (DL) and citric acid (CA) was observed when evaluating the potential to eliminate Salmonella in the presence of organic material. A method of encapsulation of DL and CA was developed for voluntary consumption by broilers during feed withdrawal. During an 8-h feed withdrawal individual 8-wk-old broilers voluntarily consumed an average of 21.5 capsules (total of 3.44 g material). When eight capsules were force-administered to Salmonella-challenged 8-wk-old broilers during an abbreviated 4 h feed withdrawal, Salmonella was not recovered using selective enrichment. To evaluate the effect of voluntary capsule consumption, 8-wk-old broilers were challenged with 1 x 108 cfu of Salmonella 5 d prior to an 8 h feed withdrawal. When these broilers were allowed unlimited continuous access to capsules containing DL/CA during an 8 h feed withdrawal, 24.8 capsules per broiler were ingested without affecting Salmonella recovery from crops. When access to capsules containing DL/CA was limited to the final 45 min of an 8 h feed withdrawal in a similar experiment, an average of 22.2 capsules were consumed by each broiler, resulting in a significant decrease in the number of Salmonella-positive crops. Although a number of practical questions and considerations remain, these data suggest that appropriate disinfectants could be administered during preslaughter feed withdrawal for the purpose of reducing foodborne pathogens in crops.

Disposition of 4-methylbenzoylglycine in rat isolated perfused kidney and effects of hippurates on renal mitochondrial metabolism

Hippurates tend to accumulate within proximal tubule cells during renal secretion. High intracellular concentrations can alter proximal tubular function or lead to tubular toxicity. In this study we examined the renal disposition of the hippurate 4-methylbenzoylglycine, a compound known for its high renal intrinsic clearance in-vivo. The effect of intracellular accumulation on mitochondrial respiration was also measured in-vitro and compared with that of the 2-methyl and 4-amino analogues. Experiments were performed with either 2.5% pluronic or a combination of 2.2% pluronic and 2% bovine serum albumin (BSA) as oncotic agents. Within the concentration range studied (1-200 microg mL(-1)) tubular secretion seemed to be a function of the amount of unbound drug in the perfusate. Renal excretion data were best fitted by a model in which a Michaelis-Menten term was used to describe active secretion. Parameters obtained after the analysis of renal excretion data were the maximum transport velocity (TM = 55+/-2 microg min(-1)) and the Michaelis-Menten constant for tubular transport (KT = 4.2+/-0.8 microg mL(-1)). The compound accumulated extensively in kidney tissue, ratios up to 600 times the perfusate concentration were reached. Accumulation could be explained by active tubular uptake and data were analysed best by a model similar to the model used to describe renal excretion. Calculated parameters were theoretical maximum capacity (RM =300+/-210 microg g(-1)) and affinity constant for renal accumulation (KA = 5.0+/-4.4 microg mL(-1)). The high intracellular concentrations of 4-methylbenzoylglycine had no effect on kidney function and mitochondrial oxygen consumption. The 2-methyl analogue reduced mitochondrial respiration slightly, but 4-aminobenzoylglycine (p-aminohippurate) caused a significant reduction. In conclusion, this study shows that renal accumulation of a hippurate is determined by the efficiency of its tubular secretion. Whether the high intracellular concentrations affect tubular cell functioning depends on the analogue involved.

Elevated free fosphenytoin concentrations in uremic sera: uremic toxins hippuric acid and indoxyl sulfate do not account for the impaired protein binding of fosphenytoin

Fosphenytoin is a new phosphate ester prodrug of phenytoin. Impaired protein binding of phenytoin in uremia has been extensively documented, which prompted us to investigate the protein binding of fosphenytoin in uremic sera. Also studied was the role of uremic toxins hippuric acid and indoxyl sulfate as potential inhibitor of the protein binding of fosphenytoin because these compounds impair protein binding of phenytoin in uremia. Five serum pools were prepared from normal volunteers and five pools from patients with uremia. None of them received phenytoin. The normal serum pools were diluted with saline to mimic the albumin concentration of uremic pool. Both the diluted normal pool and the uremic pool were supplemented with fosphenytoin; after incubation at room temperature for 30 minutes, total and free fosphenytoin concentrations as phenytoin equivalents were measured using fluorescence polarization immunoassay (Abbott Laboratories; Abbott Park, IL, U.S.A.). The authors observed significantly elevated free fosphenytoin concentration in uremic sera compared with that of normal sera in all cases. Because both normal and uremic sera had the same concentrations of albumin, the elevated free fosphenytoin concentration in uremic sera was not caused by hypoalbuminemia. Both indoxyl sulfate and hippuric acid cause significant displacement of phenytoin from protein binding. In contrast, none caused any displacement of fosphenytoin from protein binding.

Movement of carboxyfluorescein across retinal pigment epithelium-choroid

The movement of carboxyfluorescein (CF) across the isolated retinal pigment epithelium (RPE)-choroid of the albino rabbit was studied using an Ussing chamber under short-circuit conditions with CF concentrations ranging from 15 to 300 microM. The inward (from the choroid to vitreous side) permeability of the tissue to CF showed no significant change over the concentration range tested, averaging 2.2 x 10(-6) cm sec-1. Neither ouabain (1.0 microM), low external sodium concentration nor probenecid (100 microM) had significant effect on the inward movement of CF. The outward (from the vitreous to the choroid side) permeability of the tissue to CF gradually decreased as the concentration increased (ANOVA, P < 0.01: Scheffe's test, P < 0.05), averaging 3.7 x 10(-6) cm sec-1 at 75 microM. Further, it was always significantly greater than the inward permeability at the corresponding concentration (unpaired t-test, P < 0.05-0.01). The outward movement of CF was significantly inhibited by 2,4-dinitrophenol (10 microM), ouabain (1.0 microM), probenecid (100 microM), iodipamide (5.0 mM), hippurate (30 mM) or low external sodium concentration (25 mM). The net outward movement of CF became saturated as concentration was increased and a Lineweaver-Burk plot gave an apparent Km of 237 microM and Vmax of 1.8 nmol hr-1 cm-2. The results indicated that part of the outward movement of CF across the RPE-choroid depends on carrier mediated active transport, but to a much lesser extent than that of fluorescein. The inward movement of CF was thought to occur almost exclusively by passive diffusion through the paracellular spaces.

Influence of acetylsalicylic acid and metabolites on DU-145 prostatic cancer cell proliferation

Conflicting reports have been published on the anti-tumour activities of acetylsalicylic acid in various cancers. Therefore, the effect of acetylsalicylic acid and its major metabolites has been studied on human prostatic carcinoma DU-145 cells. Investigations concentrated on the influence of acetylsalicylic acid, salicylic acid and salicyluric acid, on cell proliferation, DNA- and protein synthesis of DU-145 cells. DNA and protein synthesis determinations were done in vitro by [3H]thymidine and [3H]glycine incorporation, respectively. No effect on cell plating efficiency was observed, however proliferation studies showed that acetylsalicylic acid and salicylic acid inhibited cell growth (10 mM, 100% inhibition). No significant effect on cell proliferation was ascertained with salicyluric acid. Both DNA and protein synthesis were 40% inhibited by 0.1 mM acetylsalicylic acid. This study demonstrates that acetylsalicylic acid exhibits a significant influence on cell growth of prostatic DU-145 cells. These preliminary results may contribute to a better understanding of the anti-tumour capabilities of acetylsalicylic acid.

Effect of substituted benzoylglycines (hippurates) and phenylacetylglycines on p-aminohippurate transport in dog renal membrane vesicles

The effect of substituted benzoylglycines (hippurates) and phenylacetylglycines on the transport of p-aminohippurate (PAH) was studied in basolateral (BLMV) and brush border membrane vesicles (BBMV) isolated from dog kidney cortex. The probenecid-sensitive part of 100 microM [3H]PAH uptake into BLMV and BBMV was measured in the presence and absence of 5 mM glycine conjugate. The benzoyl- and phenylacetylglycines studied were substituted in the 2-, 3-, or 4-position with an H, CH3, OCH3 or OH group. Benzoylglycines were stronger inhibitors of PAH transport than phenylacetylglycines and the inhibitory potency of the conjugates was in general lower against the transporter in BBMV than BLMV. The specificities of the transporters in both membranes appear to be very similar. The inhibitory potency of the benzoylglycines, expressed as the apparent inhibition constant (logKi), did not show a linear relationship with their lipophilicity as determined by reversed phase HPLC. Deviation from linearity was caused mainly by the 3-OH and 4-OH analogs, which showed a greater inhibitory potency than expected from their lipophilicity. Phenylacetylglycines only showed a small variation in logKi values, indicating that insertion of a CH2 group between the ring and the carbonyl practically abolishes the influence of the ring and its substituents. In conclusion, both hydrophobic and electronic properties are important determinants of affinity for the PAH transport system. An additional partially negative hydroxyl group in the ring, located preferably at the 3- or 4-position, increases the interaction with the transport system.

Improvement of aqueous solubility and rectal absorption of 6-mercaptopurine by addition of sodium benzoate

The solubility of 6-mercaptopurine (6-MP) in water increased as the concentration of sodium benzoate or sodium hippurate in the solution increased. The solubility of 6-MP in 20% (w/v) sodium benzoate or sodium hippurate solution was about 6-fold larger than that of 6-MP alone. The stability constant of the soluble complex of 6-MP with sodium benzoate was estimated to be 2-8 M-1 from (1) phase-solubility study and (2) analysis of chemical shifts observed in 1H-NMR. Partition of 6-MP from the saturated solution to n-octanol was also greatly increased by the addition of sodium benzoate or sodium hippurate, the degree being less in the latter. Administration of 6-MP with 20% (w/v) sodium benzoate to rat rectum resulted in enhanced absorption and the area under the plasma concentration-time curve was comparable to that obtained by intravenous administration (bioavailability = 100%), while the bioavailability after intrarectal administration of 6-MP with 20% (w/v) sodium hippurate was only 9%. The reason for the difference was discussed.

Mechanism and elimination of aspirin-induced interference in Emit II d.a.u. assays

The presence of salicylates in urine reduces the signal in Emit assays (Syva), potentially yielding false-negative drugs-of-abuse screening results. We demonstrate that the principal urinary metabolite of salicylate, salicyluric acid (SUA; 2-hydroxybenzoylaminoacetic acid), interferes with the measurement of NADH formed in the assay by reducing the molar absorptivity of NADH at 340 nm. Thus, for a given concentration of d.a.u. analyte the change in absorbance over the assay time interval is less in the presence of SUA. With the Emit cocaine assay on the Hitachi 704 analyzer, the rate of absorbance change (delta AR) monitored at 340 nm for a specimen containing approximately 270 micrograms/L benzoylecgonine (BE) was 57 +/- 1.9 mA/min without SUA and 29 +/- 2.7 mA/min with 5 g/L SUA (n = 20). In contrast, delta AR determined at 376 nm was 18.6 +/- 0.5 mA/min with and 17.9 +/- 0.8 mA/min without 5 g/L SUA (n = 20). Measuring the Emit assay signal at wavelengths where SUA has no absorbance (376 nm) eliminates the interference due to SUA while maintaining the precision of the assay near the cutoff concentration for BE (300 micrograms/L).

Lack of relationship between gamma-glutamyl transpeptidase and tyrosine transport in cultured bovine adrenal chromaffin cells

Effect of gamma-glutamyl transpeptidase (GGTP) inhibitor acivicin on tyrosine transport was investigated in cultured bovine adrenal chromaffin cells. Tyrosine transport into the cells was inhibited by acivicin at the low concentration range. This drug also caused the inhibition of GGTP in the cell lysates, but the concentration required for the inhibition of the enzyme was evidently different from that producing the inhibition of tyrosine transport into the cells. In addition, tyrosine transport was not affected by a GGTP activator hippurate even at the high concentration. These results seem to provide the evidence that GGTP may not be involved in the transport of tyrosine into the adrenal chromaffin cell.

Fast atom bombardment mass spectrometric determination of the molecular weight range of uremic compounds that displace phenytoin from protein binding: absence of midmolecular uremic toxins

Uremic compounds are known to displace phenytoin from protein binding, resulting in a higher concentration of the pharmacologically active free fraction of phenytoin. The true chemical identities and molecular weight range of all these compounds are still unknown. We demonstrated that indoxyl sulfate and hippuric acid, which are found at high concentrations in uremic patients, can only partially explain the elevated free phenytoin concentration. Other known uremic compounds, guanidine, methylguanidine, and guanidinosuccinic acid, do not displace phenytoin from the protein-binding sites. Uremic compounds from sera of patients on maintenance hemodialysis were removed using activated charcoal. These compounds were then backextracted from activated charcoal using methanol and analyzed by fast atom bombardment mass spectroscopy. Mass spectra of uremic sera showed no peak over m/z 450, indicating that midmolecular uremic toxins are not involved in displacing phenytoin from protein binding. We also observed additional peaks in the mass spectrum of uremic compounds when compared with the normal serum extract, indicating the presence of several endogenous compounds in uremic sera, as expected.

Ammoniagenesis in renal cell culture. Lack of extracellular ammoniagenesis at the apical surface of LLC-PK1 epithelia

In renal ammoniagenesis, two major pathways of glutamine metabolism have been described: (i) intracellular metabolism by phosphate-dependent glutaminase (PDG) and glutamate dehydrogenase and (ii) extracellular metabolism by phosphate-independent glutaminase. The latter has been identified as the hydrolytic activity of the apically membrane-bound gamma-glutamyl transpeptidase (gamma-GT). The growth properties of cultured renal epithelia enable the study of in vitro extracellular metabolic properties occurring at the apical epithelial surface in the culture dish. Therefore, confluent epithelia of the LLC-PK1 renal epithelial cell line were used to elucidate the role of extracellular (apical) hydrolysis of glutamine by gamma-GT in LLC-PK1 ammonia production. To distinguish between intra- and extracellular metabolism of glutamine, confluent LLC-PK1 epithelia were incubated with either D-glutamine as substrate, which cannot be metabolized intracellularly by PDG, or with L-glutamine and hippurate to stimulate, and AT-125 (acivicin) to inhibit gamma-GT activity, respectively. In addition, cellular uptake of the glutamate, extracellularly formed by gamma-GT, was inhibited by D-aspartate. D-Glutamine (2 mM) did not increase ammonia formation above endogenous production levels, indicating the negligible role of extracellular hydrolysis of glutamine by gamma-GT. After modulating gamma-GT activity by hippurate or AT-125, almost identical ammonia production rates were found within the various experimental protocols, further confirming that extracellular metabolism of glutamine does not significantly contribute to LLC-PK1 ammoniagenesis.

Solubility, inhibited growth and dissolution kinetics of calcium oxalate crystals in solutions, containing hippuric acid

An analysis of crystal growth and dissolution of slightly soluble salts in physiological solutions in the presence of complexing ions was carried out, simulating conditions typical in human urine. It was found that hippuric acid, a normal physiological constituent of urine, acts at increased concentrations as a dissolving agent with respect to calcium oxalate (CaOx) and CaOx calculi. The kinetics of dissolution of crystalline CaOx calculi in physiological solutions containing hippuric acid at different concentrations were studied, using the change in the Archimedean weight of samples immersed in the solution. Analysis of the experimental results enabled the determination of the increased solubility of CaOx in the presence of hippuric acid and the quantitative characterization of this substance as a new and promising agent for dissolving CaOx calculi in human urine. The possible effect of hippuric acid as a natural regulator of CaOx supersaturation and crystallization in human and mammalian urine is also discussed.

A furan fatty acid and indoxyl sulfate are the putative inhibitors of thyroxine hepatocyte transport in uremia

We studied the effects of 3-carboxy-4-methyl-5-propyl-2-furan-propanoic acid (CMPF), indoxyl sulfate, and hippuric acid on iodide production by rat hepatocytes in primary cultures. We questioned whether these substances could explain the alteration of serum thyroid hormone parameters observed in renal failure. Iodide production from [125I]T4 by rat hepatocytes was significantly inhibited in the presence of serum from uremic patients. Serum concentrations of CMPF, indoxyl sulfate, and hippuric acid were markedly elevated in uremic patients. The minimum concentration that inhibited iodide production, when expressed as a molar ratio of the inhibitor to BSA, was 0.13 for CMPF, 0.53 for indoxyl sulfate, and 1.33 for hippuric acid. This molar ratio was lower than the corresponding mean molar ratio in uremic sera for CMPF (0.38) and indoxyl sulfate (0.63), while it was higher than that found for hippuric acid (0.85). The inhibition was reproduced when the inhibitors were added to normal human serum. The decreased iodide production was not due to the inhibition of deiodinase activity. The deiodination of rT3 by rat liver microsomes was unaffected by these inhibitors. Charcoal adsorption of uremic serum normalized the iodide production by hepatocytes. This normalization coincided with almost complete removal of CMPF and indoxyl sulfate, with a concomitant reduction of the free T4 fraction. Dialysis of uremic serum only partially restored iodide production. Even though indoxyl sulfate and hippuric acid were no longer detectable, a high concentration of CMPF remained in the serum. The serum free T4 fraction remained elevated in uremic patients after dialysis. Our studies indicate that CMPF and indoxyl sulfate in concentrations normally present in the serum of uremic patients inhibit cellular transport and subsequent deiodination of T4. These substances may account for the low total T3 level in uremic patients.

Decrease of gastrointestinal mucosal damage by salicyluric acid compared with salicylic acid in rabbits

The gastrointestinal mucosal damage following the oral administration of salicylic acid or salicyluric acid was examined in rabbits using a scanning electron microscope. Six and 24 h after treatment with salicylic acid, morphological changes of gastric mucosa were recognized. In rabbits treated with salicyluric acid, however, severe damage in the gastric mucosa was not found after 24 h compared with the treatment with salicylic acid. Following the treatment with salicylic acid, some mucosal damage in the duodenum, jejunum and ileum was observed after 24 h. The surface character of the duodenal, jejunal, ileal, caecal and colonic mucosa were almost identical compared with the control following the treatment with salicyluric acid. It was reported that salicyluric acid is metabolized to salicylic acid by the intestinal microorganisms. From these results, it was suggested that prodrugs utilizing the metabolism of salicyluric acid to salicylic acid by intestinal microorganisms may be useful in reducing gastrointestinal mucosal damage.

Benzoate modulates renal and extrarenal nitrogen flow: metabolic mechanisms

The mechanism by which benzoate enhances total nitrogen excretion was investigated in-situ and in separated rat renal proximal tubules. Orally administered benzoate augmented NH4+, urea and hippurate excretion 2, 1.9 and 76 fold respectively, as compared to baseline for control. Hippurate had similar effects. Benzoate augmented renal blood flow, glutamine extraction and total NH4+ production. Arterio-venous concentration differences of glutamine, glutamate, and NH4+ across the kidney, liver and gut demonstrated an increase in glutamine uptake by the kidney despite reduced release and uptake by the liver and gut, respectively; glutamate release by the kidney and gut was increased; NH4+ handling was unchanged at these three organs. Studies in separated rat renal proximal tubules demonstrated that benzoate stimulated glutamine dependent ammonia-genesis by activation of gamma-glutamyltransferase, via the synthesis of hippurate. The results demonstrate that benzoate can modulate the interorgan partitioning of nitrogen metabolites across several organs, the net effect of which is physiologically expressed as enhanced NH4+ , urea and hippurate excretion.

Regulation of the hydrolytic and transfer activities of gamma-glutamyl transpeptidase

The activity of gamma-glutamyl transpeptidase was inhibited and stimulated by hippurate with and without acceptor molecules, respectively. Substrate activation was observed when acceptor molecules was not present but the activation was disappeared by the addition of hippurate. When glutamine was absent the inhibition degree of hippurate at pH 8.0 was greater than at pH 7.0, whereas in the presence of both hippurate and glutamine the results were opposed. These show a possibility that glutaminase is activated by hippurate under the condition of physiological pH. The activation of glutaminase by hippurate was also confirmed directly. The inhibition degree of transfer activity by glutamine was increased along the increase of acceptor concentration only in the presence of hippurate. Gamma-Glu-Phe-Gly satisfying prerequisites for donors doesn't act as a substrate, which shows that L-gamma-glutamyl-p-nitroanilide itself hardly acts as an acceptor. This contradicts to an idea that substrate activation caused by autotranspeptidation. The change of apparent Km and Vmax according to the change of pH in the presence of hippurate was different from that in the presence of acceptors. This shows a possibility that the active site on small subunit is inhibited and the latent active site in large subunit is exposed by the interaction of hippurate to the enzyme.

[Study on the uremic protein binding inhibitors as uremic toxin: toxic effect on erythroid colony formation, lymphocyte blast formation and renal function]

Certain uremic metabolites are recognized to have high affinity to serum protein and some of them have been identified as hippuric acid (HA), quinolinic acid (QA) and indoxyl sulfate (IS). Cell toxicity and effect on renal function of these substances were examined by means of erythroid colony formation, lymphocyte blast formation and isolated perfused rat kidney. These substances inhibited the binding of diphenylhydantoin to albumin, depending on the concentration of the substances. At the same concentration of 10 mg/dl, IS was most potent and QA was the second. QA and IS suppressed the erythroid colony formation, depending on the concentration of QA and IS. On the other hand, HA had no suppressive effect even at the higher concentration. The suppressive effect of QA and IS were attenuated by increasing erythropoietin concentration. QA and IS had strong suppressive effect of lymphocyte blast formation and interleukin 2 production at the concentration of uremic serum. However, they did not suppress the increase of intracellular calcium concentration of lymphocytes after stimulation by mitogen. This might indicate the possibility that these substances act not only on cell surface but on intracellular protein. HA and IS inhibited para-aminohippurate secretion and QA suppressed tubular reabsorption of sodium in isolated perfused rat kidney. These results show that the uremic protein binding inhibitors may influence renal regulation of fluid and electrolyte homeostasis. It is concluded that some of the protein binding inhibitors have toxic effects on cell function of various tissues and play a role in pathophysiology of uremia.

Sulfate homeostasis. I. Effect of salicylic acid and its metabolites on inorganic sulfate in rats

Homeostasis of inorganic sulfate, a physiologic anion necessary for both detoxification and biosynthetic reactions, involves predominantly capacity-limited renal clearance mechanisms. The objective of this investigation was to examine the effect of salicylic acid (SA) and its major metabolites, salicyluric acid and salicyl phenolic glucuronide, on the serum concentrations and renal clearance of inorganic sulfate in rats. Animals were studied using a crossover design in which they received a bolus i.v. injection (75 mg/kg) and infusion (approximately 0.26 mg/min/kg) of SA or the same volume of saline (the vehicle). Blood samples were collected at 2, 3 and 4 hr after administration and urine between 2 and 4 hr. The renal clearance of sulfate and creatinine were examined at mean steady-state SA serum concentrations of 249 micrograms/ml. Although no changes in the serum concentrations and renal clearance of creatinine were observed, the renal clearance of inorganic sulfate was increased significantly (2.13 +/- 0.74 vs. 1.09 +/- 0.54 ml/min/kg in controls, mean +/- S.D., n = 7) and its serum concentration decreased (0.55 +/- 0.12 vs. 1.04 +/- 0.23 mM in controls). These changes were not due to alterations in uric acid concentrations as uric acid serum concentrations and renal clearance were unchanged when examined at similar steady-state SA serum concentrations in a subsequent study. The effects on sulfate disposition also were probably not due to the major metabolites of SA: no changes in the serum concentrations or renal clearance of sulfate were observed at mean steady-state concentrations of 52 micrograms/ml of salicyluric acid or 73.7 micrograms/ml of salicyl phenolic glucuronide after their direct administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiologically based pharmacokinetic model for the renal clearance of phenolsulfonphthalein and the interaction with probenecid and salicyluric acid in the dog

Plasma kinetics and renal excretion of intravenous phenolsulfonphthalein (PSP, 1.0 g), with and without concomitant administration of probenecid or salicyluric acid (SUA), were studied in the Beagle dog. Pharmacokinetic analysis revealed that tubular secretion is the predominant route of excretion, and that secretion is inhibited by probenecid and SUA. A physiologically based kidney model was developed that incorporates the functional characteristics of the kidney that determine the excretion of PSP, i.e., renal plasma flow, urine flow, nonlinear protein binding, glomerular filtration, tubular secretion, and tubular accumulation. The model enabled an accurate description and analysis of the measured plasma levels and renal excretion rates. The interaction with probenecid and SUA could be adequately described with the model by inhibition of the carrier-mediated uptake of PSP into the proximal tubular cells. However, both compounds clearly differed in their inhibitory action. Whereas probenecid showed simple competitive inhibition, for SUA a considerably more complex interaction (two-site competitive system) had to be taken into consideration. Especially in the interaction experiments, only satisfactory fits to the model were obtained when secretion was assumed to be dependent on unbound PSP concentrations. Model calculations showed that in the control experiments tubular secretion was accompanied by a pronounced accumulation of PSP within the proximal tubular cells, which was clearly diminished in presence of probenecid or SUA. The predicted accumulation ratios were in good agreement with previous studies.

Brain uptake of tryptophan in urease-injected hyperammonemic rats after treatment with benzoate or hippurate

The tryptophan uptake into forebrain and brainstem was measured in urease-injected rats and in controls after prior application of sodium benzoate or hippurate. Benzoate led to an increased brain uptake index of tryptophan. This effect was additive to the increase in tryptophan uptake effected by the provoked hyperammonemia. In contrast, hippurate did not alter tryptophan uptake across the blood-brain barrier. We conclude that benzoate should be monitored especially when applied intravenously to patients with hyperammonemic coma.

Gamma glutamyltransferase ammonia production from glutamine: effect of physiological glutathione concentration

The formation of ammonia from physiological glutamine concentration catalyzed by gamma glutamyltransferase was studied in the presence of physiological glutathione concentration. The apparent Km for ammonia formation from glutamine was 1.6 mM some 2 fold greater than the actual plasma concentration. In the presence of 30 microM glutathione neither the apparent Km or Vmax were changed. At supraphysiological glutathione concentration, 1mM, the apparent Km was increased while the Vmax decreased to one third. Hippurate the physiological modulator of the enzyme's glutaminase activity reduced the Km to 0.9 mM, the physiological range, and elevated the Vmax 2.7 fold.

Ammoniagenesis catalyzed by hippurate-activated gamma-glutamyltransferase in the lumen of the proximal tubule. A microperfusion study in rat kidney in vivo

gamma-Glutamyltransferase (gamma-GT) is located in the brushborder membrane of the proximal tubule where the catalytic site of the enzyme faces the lumen. The (phosphate-independent) glutaminase activity of gamma-GT in vitro is activated by hippurate. In order to investigate glutamine deamidation in the tubule lumen in vivo, 14C-L-glutamine-containing solutions were continuously microperfused through sections of the proximal convoluted tubule in vivo and in situ. D-aspartate and L-phenylalanine (10 mmol/l, each) were added to the perfusate in order keep the reabsorption of L-glutamine as such low and to block reabsorption of any glutamate possibly formed, respectively. Intraluminal formation of glutamate from glutamine in the absence of hippurate is small. In presence of 10 mmol/l hippurate, 5%-70% of the recovered 14C-activity was 14C-glutamate at an initial 14C-L-glutamine concentration of 1 mmol/l. The respective absolute rate (+/- SEM) of glutamate formation, i.e., 36 +/- 5 pmol X s-1 X m-1, was increased 1.4-fold at an initial L-glutamine concentration of 3 mmol/l, but dropped to one third at initially 0.3 mmol/l. A rough estimate of the apparent kinetic constants resulted in a Km of 0.58 (0.19-0.97) mmol/l and a Vmax of 56 (40-93) pmol X s-1 X m-1. Deamidation of glutamine occurred also in the absence of L-phenylalanine. Acivicin (AT 125), a gamma-GT inhibitor, completely blocked glutamate formation. Endogenous hippurate concentrations determined by free flow micropuncture and HPLC were 0.16 mmol/l in the late proximal convolution, 0.6 mmol/l in the early distal convolution, and 4.9 mmol/l in the final urine.(ABSTRACT TRUNCATED AT 250 WORDS)

Aromatic amino acid metabolites as potential protein binding inhibitors in human uremic plasma

Decreased binding of aromatic acidic drugs and endogenous metabolites to plasma proteins of patients with severe renal failure appears to be due to accumulation of unknown solutes. Both the warfarin and indole binding sites of albumin, the principal binding protein for these ligands, are affected. We used a large number of endogenous aromatic acids and synthetic congeners as displacers (a) better to characterize the chemical requirements for binding to each site and (b) to derive clues to the chemical structure of the undefined binding inhibitors in uremic plasma. 14C-tryptophan, 14C-warfarin and 14C-salicylate were used as bound ligands. Numerous indoles, quinolines and phenyl derivatives were moderate to strong displacers with several structural correlates. Increasing apolar side chain length enhanced displacing potency. A hydroxyl group at the 5 position of indoles and at the para position of phenyl derivatives severely reduced activity. The two ends of amphophilic molecules showed opposite requirements for displacement of tryptophan: the greater the polarity at the hydrophilic end, the greater the tryptophan displacing potency. Conversely, the greater the total hydrophobic mass of the remainder of the molecule, the more potent the inhibition of binding. The dipeptides l-tryptophyl-l-tryptophan and l-tryptophyl-l-phenylalanine were potent displacers. Computer-assisted analysis of warfarin binding in the presence of xanthurenic acid revealed inhibition by a mechanism other than simple competition, probably via a third albumin binding locus. We conclude that decreased binding in uremic plasma is most likely the summation effect of a number of retained aromatic acids, peptides, or both types of ligands.

Uptake and metabolism of glutamine in cultured kidney cells

The metabolism of glutamine was investigated in cultured rat kidney cells. Glutamine utilization and product formation were followed as a function of time at either 10 microM or 1 mM initial glutamine concentration. At 1 mM glutamine, glutamate and gamma-glutamylglutamate were the major products formed at the end of a 5-min incubation period; glutamate accounted for 46% while gamma-glutamylglutamate accounted for 33% of the glutamine utilized. With time, glutamate continued to accumulate while gamma-glutamyl peptide formation leveled off. The role of gamma-glutamyl transpeptidase was assessed by using hippurate, a physiological activator of gamma-glutamyl transpeptidase and acivicin, L-(alpha S,5S)-alpha-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid, an inhibitor of gamma-glutamyl transpeptidase. Hippurate, 4 mM, increased the utilization of glutamine and the formation of glutamate, gamma-glutamyl peptides and ammonia. Exposure of cells to acivicin resulted in 98% inhibition of gamma-glutamyl transpeptidase without effecting phosphate-dependent glutaminase activity. Acivicin inhibition resulted in a decreased utilization of glutamine and product formation as compared to control; 5-oxoproline appearance fell 70%. The fractional distribution of glutamine carbon and nitrogen into its metabolic products in control, hippurate and acivicin-treated cells showed no change at the end of 60 min. The data provide evidence that gamma-glutamyl transpeptidase utilizes glutamine and forms gamma-glutamyl peptides in cultured kidney cells.

Evaluation of the dose response and in utero exposure to saccharin in the rat

A two-generation bioassay on sodium saccharin (NaS), involving 2500 second-generation male rats, was designed to determine the dose response for urinary bladder tumours in male rats and to evaluate other changes possibly related to the occurrence of the tumours. Six treatment groups (125-700 rats/group) were fed dietary levels of NaS ranging from 1.0 to 7.5%. To evaluate the role of in utero exposure, two additional groups were exposed to NaS either only during gestation via dams fed diet containing 5.0% NaS or for a single generation beginning at birth. In the latter group, the nursing dams were placed on an NaS diet immediately after giving birth and their offspring were weaned onto diets containing 5.0% NaS. A third additional group, included to evaluate the specificity of NaS and the role of excess sodium in the occurrence of urinary bladder tumours, was fed diet containing sodium hippurate (NaH) for two generations--5.0% NaH to the first generation and to the second until 8 wk old, and subsequently 3.0% because of unexpected toxicity. A clear dose response for urinary bladder tumours was observed in the second-generation NaS-treated male rats. The steep slope of the dose-response curve indicated a rapid decline in tumour incidence with decreasing dose. The 1.0% dietary level (fed to 700 rats) was considered to be a no-effect level for bladder tumours. The only other treatment-related pathological changes were an increase in urinary bladder weight in rats fed greater than or equal to 3.0% and an increase in mineralization of the kidneys with greater than or equal to 1.0%. Several physiological effects were seen in the NaS-treated groups showing an increase in bladder tumours (i.e. those fed greater than or equal to 3.0%). Some changes, e.g. depressed growth and increased water consumption, were indicative of a general disturbance of these rats, but analysis of body-weight, food-consumption, compound-consumption and water-consumption data revealed no correlations within any dose group between these quantitative data and the occurrence of bladder tumours. Other changes indicative of the compromised situations of the rats fed high dietary levels of NaS were anaemia in weanling rats fed 5.0 or 7.5% and a reduction in litter size at dietary levels greater than or equal to 3.0%. Changes in urine volume and urine osmolality were highly correlated with the occurrence of the urinary bladder tumours.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of high dietary levels of sodium saccharin on mineral and water balance and related parameters in rats

The effects of sodium saccharin (NaS) treatment on mineral and water balance and a number of related parameters were studied over a 10-day period in 7-month-old Charles River CD rats. Eight groups of 10 male and 10 female rats were studied. In four of the groups the rats were the F1 offspring of rats that had been exposed to NaS at 1, 3, 5 or 7.5% in the diet and the offspring were treated with the same dietary levels of NaS as their parents. Prior treatment in two other groups was modified in order to evaluate the role of in utero exposure to NaS on the study parameters: rats in one group were only exposed in utero via dams fed diets containing 5% NaS while treatment in the other group did not include in utero exposure, but was started at birth via dams fed diets containing NaS and continued at a dietary concentration of 5% NaS. Second-generation rats in another group were fed diets containing 5% sodium hippurate (NaH), a compound with a number of physical and chemical properties similar to those of NaS; this group was included in order to evaluate the specificity of NaS and/or the effect of sodium on the study parameters. A group of untreated rats served as controls. Treatment-related effects were observed in most study parameters. In addition, a number of differences between male and female rats in baseline values and/or in response to NaS administration were observed. With increasing dietary levels of NaS body weights decreased, but there were increases in water consumption, faecal water content, and caecal weights. NaS treatment resulted in increased urine volume and decreased urine osmolality, changes in urine mineral concentrations (increased sodium, decreased potassium and zinc) and increases in fresh and dry bladder weights, bladder-tissue hydration, and mineral concentrations (sodium, potassium, magnesium and zinc) in bladder tissue. The parameters in which clear sex-related differences in baseline values were observed were body weight, food and water consumption, urine volume, urine osmolality, fresh bladder mass, bladder-tissue hydration and the concentrations of sodium, potassium, magnesium and zinc in the bladder tissue. With the exception of urine osmolality, the values were higher in females. Differences between males and females in response to treatment were observed for NaS consumption (increased in females), caecal weight (increased in females), NaS concentration in the urine (increased in males), and the concentration of sodium, potassium, magnesium and zinc in the bladder tissue (increased in males).(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of methenamine-hippurate upon urinary risk factors for renal stone formation

Among the various treatments for renal calcium stone disease, none has been documented to reduce urinary oxalate. Methenamine-hippurate (Hiprex) has been used extensively in the treatment of urinary tract infections and from micropuncture studies in the rat, using para-aminohippurate, it could be expected to reduce the renal secretion of oxalate. A daily dose of 3 g was given orally to 15 healthy subjects for 2 weeks. However, there was no net decrease in the urinary excretion of oxalate, but a risk index based on the urinary content of calcium, magnesium, oxalate, citrate and urine became reduced during treatment. The urinary inhibition of calcium oxalate crystal growth was unaffected. It is concluded that there may be a potential in methenamine-hippurate for the treatment of calcium stone disease, which can only be evaluated, however, by a clinical trial in stone patients.

Effects of bile acids and their glycine conjugates on gamma-glutamyl transpeptidase

Glycine and taurine conjugates of bile acids modulate gamma-glutamyl transpeptidase by interacting with the cysteinylglycine binding site (acceptor site) of the enzyme. These compounds stimulate hydrolysis of glutamine and S-methylglutathione and the rate of the inactivation of the enzyme by the gamma-glutamyl site-directed reagent, AT-125 (L-(alpha S,5S)-alpha-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid). Transpeptidation between S-methylglutathione and methionine was inhibited by these compounds. These effects resemble those caused by hippurate; the glycine derivatives of bile acids, however, exhibit a much greater affinity for transpeptidase than hippurate. Cholate, as shown previously for benzoate, also seems to bind to a portion of the acceptor site as indicated by its effects on S-methylglutathione utilization and AT-125-dependent inactivation of the enzyme. The Kd values for cholate and benzoate are, however, at least one order of magnitude larger than those for their respective glycine derivatives. The acceptor site-directed modulators increase the affinity of the enzyme for AT-125 and kinetic and binding studies show that binding of gamma-glutamyl site-directed reagents increases the affinity of the enzyme for cholate. These results thus indicate cooperative interactions between the gamma-glutamyl donor and acceptor binding domains of the transpeptidase active center.

Isolation and chemical characterization of 2-hydroxybenzoylglycine as a drug binding inhibitor in uremia

An organic compound that inhibits drug binding in uremia has been isolated from the sera of chronic renal failure patients, and its chemical structure has been determined. Addition of the compound to normal human sera in vitro resulted in drug binding defects similar to those seen in uremia. The purification of this substance was accomplished by n-butyl chloride extraction of acidified (pH 3.0) uremic sera followed by column chromatography, thin-layer chromatography, and paper electrophoresis. From analytical studies including ultraviolet and fluorescence spectroscopy, gas chromatography, chemical ionization and electron impact mass spectrometry, and proton nuclear magnetic resonance spectroscopy, the chemical structure of the uremic binding inhibitor was deduced to be 2-hydroxybenzoylglycine. This confirms the hypothesis that the drug binding defect in uremia is due to the accumulation of endogenous metabolic products rather than an intrinsic structural defect in albumin.

Organic anion infusions exacerbate experimental acute renal failure

This investigation proposed to determine whether high organic anion (OA) loads per nephron increase renal susceptibility to acute ischemic and nephrotoxic injury. Anesthetized Sprague-Dawley rats were infused with a control infusate, Na2SO4, or an OA (hippurate, p-aminohippurate, cephalothin; 0.125-1.0 mg/min). After a 40-min control period, acute renal injury was induced by either bilateral renal pedicle cross-clamping (X25 min) or by HgCl2 administration (12 mg/kg i.v.). Glomerular filtration rate (clearance of [125I]iothalamate) was determined every 20 min before and after renal injury. Non-OA-infused rats lost 51 +/- 4% (ischemia) and 40 +/- 4% (HgCl2) of control GFR. OA infusion exacerbated this loss of renal function (ischemia, 89 +/- 2%; HgCl2, 84 +/- 4%). Renal histology demonstrated that OA-treated acute renal failure (ARF) rats had more vacuolar degeneration of proximal tubular cells (HgCl2, ischemia) and greater tubular dilatation (ischemia) than did non-OA-treated ARF rats. These functional and histologic responses to OA infusion were not OA dose dependent. Discontinuation of OA infusion did not cause a subsequent rise in GFR. Na2SO4 infusion had no detrimental effects on ischemic ARF. Control rats subjected to prolonged OA infusion (1 mg/min X 5 h) maintained stable GFR and had normal renal histology. ARF rats infused with low-dose cephalothin had terminal serum cephalothin concentrations within a range commonly seen in humans.

CONCLUSION

organic anion infusions can exacerbate early functional and histologic parameters of experimental ARF.

The antibacterial activity of hexamine (methenamine), hexamine hippurate and hexamine mandelate

The antibacterial activity of hexamine and two of its organic acid salts was compared by continuous turbidimetric monitoring of static cultures exposed to the drugs and in an in vitro model of the treatment of bacterial cystitis. At pH 5.5, concentrations of 32 to 125 mg hexamine per 1 caused some inhibition of bacterial growth, but 250 to 500 mg/l were needed to suppress growth overnight. Hexamine hippurate was found to be less active than hexamine itself, whereas hexamine mandelate was as active as the parent compound. The antibacterial effect was not inoculum dependent over the range 10(6) to 10(8) bacteria per ml, but the activity observed in pooled urine was rather less than that found in broth at the same pH. When a dense bacterial culture was exposed to changing concentrations of hexamine compounds in the bladder model, a 1 g dose infused over a 12-hour period suppressed bacterial growth for 16 to 20 hours. No systematic difference was found in the activity of the three hexamine compounds, but a similar effect was achieved by a very much lower concentration of ampicillin.

Metabolism of salicylic acid in the isolated perfused rat kidney. Interconversion of salicyluric and salicyclic acids

Renal metabolism of salicylic acid (SA) to salicyluric acid (SU), as well as the metabolism of SU to SA, was demonstrated in the isolated perfused rat kidney. SU formation was dependent upon the inclusion of a glycine pool and glycine concentration influenced the rate of SU excretion. The total conversion of SA to SU in 1 hr was 7.7% after the administration of 1 mg SA. Administration of increasing amounts of SA diminished this extent of SU formation. The addition of a competitive substrate, benzoic acid, produced a rapid formation and excretion of hippuric acid with a corresponding inhibition of SU formation and excretion. It is important to note that when isolated kidneys were perfused with 2.5 mg SU, 20--30% of the dose was metabolized to SA. Increasing the dose of SU to 10 mg decreased the amount of SA formed. In view of observed reversible SA/SU metabolism, a larger renal contribution to overall salicylate disposition is suggested.