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.

Life-history traits of standard and autochthonous cladocerans: II. Acute and chronic effects of acetylsalicylic acid metabolites.

Metabolic products are often more toxic than their pharmacological parent compounds. Therefore, the acute and chronic effects of the main metabolites--salicylic acid (SAL), gentisic acid (GEN), and o-hydroxyhippuric acid (HDP)--of acetylsalicylic acid (ASA), the active ingredient in Aspirin and many other pharmaceuticals, were assessed using standard (Daphnia magna) and autochthonous (Daphnia longispina) cladocerans. The sequence of decreasing levels of acute and chronic toxicity of ASA metabolites to daphnids was GEN > SAL > HDP. HDP did not present acute toxicity, but chronic exposures enabled the production of abnormal neonates and, in particular, egg abortion. Thus, reproduction was the end point most susceptible to HDP. On the other hand, SAL and GEN induced changes in the normal patterns of reproduction and growth of both species. In general, D. longispina was more sensitive than was D. magna, although the population growth of the autochthonous species was superior under SAL exposures than that of the standard test species. Although the concentrations that were determined to have a toxic effect were above the levels detected in aquatic environmental samples, exposure to low levels of pharmacologically active substances for a duration longer than the test period may induce changes in nontarget organisms.

Oxidation of albumin is enhanced in the presence of uremic toxins.

Albumin has been considered a "sacrificial plasma antioxidant" due to the high reactivity of the protein sulfhydryl groups with oxidants such as hydrogen peroxide (H2O2) and hypochlorous acid (HOCl). Based on its large quantity and high turnover. It is considered as one of the most important plasma antioxidants for protecting key cellular and regulatory proteins. Since hemodialysis patients have lower overall levels of albumin and possible protein modifications due to uremic toxins, we investigated whether modifications by various uremic toxins would affect the susceptibility of albumin to an oxidative challenge. We incubated bovine serum albumin in the presence of carboxymethyllysine (CML) (10 micromol/L(-1) mmol/L), methyl glyoxal (50 micromol/L(-5) mmol/L), p-cresol (100 micromol/L-10 mmol/L) or hippuric acid (200 micromol/L-20 mmol/L) for 16 hours at 37 degrees C and then subsequently added 0.5 mmol/L(-1) mmol of H2O2/HOCl. We measured the extent of protein modification by the loss of protein sulfhydryl groups, dityrosine formation and the formation of advanced oxidation protein products (AOPP). Incubation of albumin with the uremic toxins caused a loss of protein sulfhydryl groups and an increase in dityrosines and AOPP. The presence of uremic toxins had no effect on the loss of protein sulfhydryl groups after addition of H2O2/HOCl; however, low levels of CML, p-cresol and methyl glyoxal inhibited the formation of AOPP and dityrosines. We suggest that uremic toxins may possibly play a role in mediating free radical initiated protein damage.

Valores de referência do ácido hipúrico urinário na regiäo metropolitana de Belo Horizonte / Urinary hippuric acid reference values in Belo Horizonte metropolitan area, Brazil

Objetivando estabelecer a faixa de valor referência para o ácido hipúrico na regiäo metropolitana de Belo Horizonte, urinas de indivíduos näo expostos ocupacionalmente ao tolueno foram analisadas por cromatografia em fase gasosa, utilizando-se detector de ionizaçäo de chama. Os valores encontrados experimentalmente (n=281) variaram de <0,1 a 2,79 g/L, mas a aplicaçäo de estudo estatístico delimita como faixa de referência,a nível de significância de 95 porcento, os valores de 0,361 a 0,481 g/L. Säo descritas, também, as condiçöes analíticas padronizadas para a determinaçäo cromatográfica do ácido hipúrico urinário

K1 and K3 capsular antigens of Klebsiella induce tumor necrosis factor activities.

Capsular polysaccharide antigens isolated from Klebsiella pneumoniae sero-type 1 (K1) and sero-type 3 (K3) could induce tumor necrosis factor-alpha in ICR mice. K1 and K3 capsular antigens were found to be non-toxic by brine shrimp bioassay. When injected into Ehrlich ascites tumor-bearing mice, both K1 and K3 capsular antigens exhibited significant suppression in the growth of tumor cells. The significance of these observations is discussed.

4-Maleimidohippuric acid--a tailor-made, direct, site-specific nephrotoxin: effects on renal function and ultrastructure in pentobarbital-anesthetized dogs.

A model has been proposed to explain at least one of the possible pathways through which a xenobiotic might produce proximal tubule necrosis. The model is formulated on the idea that a compound must possess two structural features: (i) a carboxyl or amino acid moiety that would allow for selective uptake into proximal tubule cells via the strategically located antiluminal membrane-bound organic anion transport system or the luminal membrane-bound amino acid transport system(s), respectively, and (ii) a highly reactive moiety that can directly alkylate proximal tubular components, or a moiety that can be biotransformed within proximal tubular cells to such a substance. In an attempt to validate the proposed structural features as prerequisites for xenobiotic induction of proximal tubular necrosis, a novel compound, 4-maleimidohippuric acid (4-MHA), was synthesized which possesses an anionic group and a reactive moiety. Following the administration of 4-MHA directly into the renal artery of pentobarbital-anesthetized dogs, specific unilateral ultrastructural damage was noted only in the S1 and S2 cell types of the proximal tubule; the most notable renal function changes included proteinuria and glucosuria. Anionic, but non-alkylating, relatives of 4-MHA failed to alter renal function or ultrastructure. The specific proximal tubular toxicity of 4-MHA validates the proposed structural requirements for induction of proximal tubular necrosis.

Roles of bladder distension, urinary pH and urinary sodium ion concentration in cell proliferation of urinary bladder epithelium in rats ingesting sodium salts.

The relative importance of bladder distension, urinary pH and sodium ion concentration for cell proliferation in the bladder epithelium of rats fed various sodium salts was investigated. When a diet containing 5% NaHCO3 was fed to male rats, the bladder epithelium showed an increase in replicating cells, together with distension, increased urine pH and high urine sodium ion concentration. Cell proliferation also occurred when bladders were subjected to distension in vivo by mechanical (female) or physiological (male) means. Inclusion of CaCO3 in the diet produced high urinary pH without alteration in the other factors and did not induce cell proliferation. Increased proliferation occurred when CaCO3 was combined with these mechanical or physiological treatments. Thus, high urinary pH was of secondary importance to bladder distension as a causative factor, but acted to enhance cell proliferation when distension occurred. Similar findings were obtained with regard to sodium ion concentration. In conclusion, this study demonstrated that bladder distension is one of the prerequisites for promoter-induced cell proliferation in the bladder epithelium, with high urinary pH and sodium ion concentration.

[Protein fractions in workers exposed to organic solvents]. / Zachowanie sie frakcji bialkowych u ludzi eksponowanych na rozpuszczalniki organiczne.

Industrial workers exposed to organic solvents were subject to examinations consisting in the assessment of the composition of serum proteins. The analysis revealed frequent shifts in protein fraction pattern. It was noted that the increased concentrations of organic solvents metabolites in urine have been usually accompanied by the increased gamma-globulins levels with a simultaneous decrease in albumin fraction and plasmatic index.

Similarities of toluene and o-cresol neuroexcitation in rats.

Exposure to high concentrations of toluene vapors, or to intravenous o-cresol (a toluene metabolite) at about 0.9 mg/min, caused excitation of the somatosensory evoked potential (SEP) and EEG of Fischer 344 rats. SEP excitation was characterized by a large increase in a positive waveform at about 20-50 msec. Prolonged exposure to either compound caused numerous oscillations to appear from 20 msec to the end of the recording (150 msec). Both substances induced an increase in EEG beta activity and caused a large increase in activity at 5 Hz. Toluene exposed rats were lightly anesthetized, while o-cresol rats were conscious but hyperreactive. If exposure was continued, both sets of rats had involuntary muscle movements and tremors. Benzoic acid and hippuric acid, also metabolites of toluene, were similarly tested. Neither caused neuroexcitation (about 2.4 mg/min IV, 144 mg total dose). It was concluded, therefore, that metabolically derived cresols are plausible candidates for the neuroexcitatory properties of toluene.

Mutagenicity testing of 5-(4-nitrophenyl)-2,4-pentadien-1-al (spy dust) and its metabolites in vitro and in vivo.

5-(4-Nitrophenyl)-2,4-pentadien-1-al (NPPD; spy dust) was tested for mutagenicity in Salmonella and for its ability to induce chromosome aberrations and sister chromatid exchanges (SCE) in cultured Chinese hamster ovary (CHO) cells and mouse bone marrow. Two metabolites of NPPD produced by the rat, 4-nitrobenzoic acid (NBA) and 4-nitrohippuric acid (NHA), were also tested in Salmonella and CHO cells. NPPD was mutagenic in Salmonella, and induced low-level increases in chromosome aberrations and SCE in bone marrow. It did not induce aberrations in CHO cells. NBA was positive in Salmonella and CHO cells, while NHA was negative. The mutagenicity of NPPD in Salmonella was partially, but not completely, eliminated in a strain lacking one of the bacterial nitroreductases.