Multidrug resistance proteins and the renal elimination of inorganic mercury mediated by 2,3-dimercaptopropane-1-sulfonic acid and meso-2,3-dimercaptosuccinic acid

Current therapies for inorganic mercury (Hg(2+)) intoxication include administration of a metal chelator, either 2,3-dimercaptopropane-1-sulfonic acid (DMPS) or meso-2,3-dimercaptosuccinic acid (DMSA). After exposure to either chelator, Hg(2+) is rapidly eliminated from the kidneys and excreted in the urine, presumably as an S-conjugate of DMPS or DMSA. The multidrug resistance protein 2 (Mrp2) has been implicated in this process. We hypothesize that Mrp2 mediates the secretion of DMPS- or DMSA-S-conjugates of Hg(2+) from proximal tubular cells. To test this hypothesis, the disposition of Hg(2+) was examined in control and Mrp2-deficient TR(-) rats. Rats were injected i.v. with 0.5 mumol/kg HgCl(2) containing (203)Hg(2+). Twenty-four and 28 h later, rats were injected with saline, DMPS, or DMSA. Tissues were harvested 48 h after HgCl(2) exposure. The renal and hepatic burden of Hg(2+) in the saline-injected TR(-) rats was greater than that of controls. In contrast, the amount of Hg(2+) excreted in urine and feces of TR(-) rats was less than that of controls. DMPS, but not DMSA, significantly reduced the renal and hepatic content of Hg(2+) in both groups of rats, with the greatest reduction in controls. A significant increase in urinary and fecal excretion of Hg(2+), which was greater in the controls, was also observed following DMPS treatment. Experiments utilizing inside-out membrane vesicles expressing MRP2 support these observations by demonstrating that DMPS- and DMSA-S-conjugates of Hg(2+) are transportable substrates of MRP2. Collectively, these data support a role for Mrp2 in the DMPS- and DMSA-mediated elimination of Hg(2+) from the kidney.     

Urinary excretion of argininosuccinic acid

A simplified algebraic proof is reported for the Alien correction equation and a new equation is derived which provides the theoretical justification for the application of the Alien equation in colorimetric analysis. The factors affecting the validity of the new equation in general and in particular with respect to the estimation of oestriol by the Kober reaction are analysed and discussed.     

Urinary albumin excretion in normal and diabetic subjects

Using an albumin radio-immuno-assay, urinary albumin concentration and excretion rate have been measured in diabetics and control subjects overnight, after several hours ordinary activity and during two successive one hour periods of recumbency. The urine albumin concentration was relatively constant throughout each of the four collection periods. Variations in albumin excretion rate were directly related to changes in urine flow. In assessing changes in urinary albumin, concentration and urine flow should be reported as well as the calculated albumin excretion rate.In the diabetics, selected for absence of clinical proteinuria, the mean concentration of albumin did not differ significantly from that of the controls. The overnight albumin excretion rate was higher in the diabetics, but this was due to the greater volume of urine.     

Determination and metabolism of dithiol chelating agents: X. In humans, meso-2,3-dimercaptosuccinic acid is bound to plasma proteins via mixed disulfide formation

meso-2,3-Dimercaptosuccinic acid (DMSA) is orally effective for the treatment of chronic lead intoxication in humans. Earlier studies have shown that the majority of DMSA, given p.o. to normal humans, is excreted in the urine as mixed disulfides with L-cysteine. We have developed an assay for the determination of DMSA that has made possible the determination of the form of DMSA in blood and plasma. After p.o. administration of 10 mg DMSA/kg to four normal young men, no unaltered DMSA (unaltered DMSA is the unbound, parent compound; total DMSA consists of unaltered DMSA plus oxidized (disulfide) DMSA and is determined after reduction with dithiothreitol) was found in the blood over an 8-hr period. Only after treatment of blood or plasma with the disulfide-reducing agent, dithiothreitol, was DMSA detected. This indicates that DMSA is in disulfide linkage with plasma proteins and/or non-protein sulfhydryl compounds. Most of the DMSA in the plasma (92-95%) was found to be bound to plasma proteins, mainly albumin. The remaining DMSA may be bound to small molecular weight (less than 10,000 MW) nonprotein sulfhydryl compounds such as cysteine. Plasma protein appears to serve as a depot and reservoir of DMSA, which can exchange for cysteine. The urinary excretion of unaltered DMSA and DMSA mixed disulfides with L-cysteine suggests that this exchange takes place at the kidney.(ABSTRACT TRUNCATED AT 250 WORDS)     

The pharmacology of 2,3-dimercaptosuccinic acid and its potential use in arsenic poisoning.

Arsenic (As2O3)-poisoned rats were treated with either 2,3-dimercaptosuccinic acid (DMS) or dimercaptopropanol (BAL) at doses of 30 mg/kg/day. A control group received no treatment. The total quantity of arsenic excreted was not significantly different in response to 4 days of treatment with either DMS or BAL. In addition, there was no difference between the two drug treatment groups in the residual arsenic content of brain, liver, kidney and spleen after treatment. Both drugs reduced the arsenic content of each tissue to approximately 40% of that of untreated controls. Previous studies have shown that DMS is orally effective for the treatment of lead poisoning. The LD50 of DMS was determined to be in excess of 3 g/kg in rats and mice, approximately 30 times the LD50 of BAL. No gross, histopathological or biochemical evidence of toxicity was observed in mice, rats or dogs which received DMS 5 days per week for 6 months. DMS did not affect the excretion of zinc, iron, calcium or magnesium. Urinary copper excretion was significantly elevated in response to 30 mg/kg of DMS, suggesting that the drug might also be useful for the treatment of Wilson's disease.     

Urinary excretion of beta-aminopropionitrile and cyanoacetic acid

Human serum did not convert beta-aminopropionitrile (BAPN) to the deaminated, nonlathyrogenic metabolite, cyanoacetic acid (CAA). Instead, its enzymic activity for oxidizing benzylamine was inhibited by BAPN (I50 = 2 X 10(-3) M). BAPN was found in the urine within one hour of oral administration. Oral 250 mg BAPN at 6-hr intervals each day for 21 days resulted in urinary BAPN recoveries approximating 16% of the total dose. BAPN was not detected in urine in specimens collected later than 7 hr after cessation of BAPN dosage. Urinary CAA appeared more slowly than BAPN and increased gradually to approximately three times that of urinary BAPN. After BAPN was discontinued, there was prolonged urinary excretion of BAPN-derived CAA. These along with earlier findings in experimental animals suggest that unexcreted BAPN is sequestered in tissues where it is metabolized to CAA before slowly released.     

Urinary excretion of morphine and its metabolites in morphine-dependent subjects.

Morphine, morphine glucuronide, morphine ethereal sulfate, normorphine and total normorphine in three consecutive 24-hour urines of four morphine-dependent subjects receiving morphine sulfate 60 mg s.c. q.i.d. have been determined with thin-layer chromatography and gas-liquid chromatography. With thin-layer chromatography the mean daily excretion of free morphine was 10% of the administered dose; morphine glucuronide, 65%; total (free and acid hydrolyzable conjugate) morphine 85%; and total normorphine, 3.5%. With gas-liquid chromatography, the percentage excretion for free morphine was 10%; total morphine, 74%; free normorphine, 1%; and total normorphine, 4%. The excretion of total drug was linearly related to the volume of the daily urine output.     

Urinary excretion of D-glucaric acid in porphyria cutanea tarda

Twenty patients with porphyria cutanea tarda who had ingested no alcohol for at least 10 days before sampling were found to possess urinary D-glucaric acid levels similar to those of 30 clinically healthy controls. Correlation between urinary excretion of D-glucaric acid on the one hand and plasma or urinary porphyrin concentrations on the other was not statistically significant. These results suggest that the high urinary concentrations of D-glucaric acid found in porphyria cutanea tarda patients by Budillon et al. (Acta Hepato-Gastroenterol. 25 (1978) 267) may have been due to recent consumption of alcohol rather than to the porphyrin pathology.     

Urinary excretion of 2-methyl-2,3-butanediol and 2,3-pentanediol in patients with disorders of propionate and methylmalonate metabolism

Urine samples from patients with propionic acidemia and from a patient with methylmalonic acidemia contained unknown non-acidic metabolites by gas chromatography/mass spectrometry after ethyl acetate extraction. It could be demonstrated by mass spectrometric studies and by synthesis of reference compounds that the major metabolite was 2-methyl-2,3-butanediol, while smaller amounts of 2,3-pentanediol were also present. These diols were present in abnormal amounts in these patients during attacks of metabolic decompensation.