Effects of complexing treatment administered with the onset of methyl mercury neurotoxic signs

Patients with homocystinuria: high metal concentrations in hair, blood and urine

Patients with homocystinuria excrete a large amount of metal in their urine. Homocysteine similar to penicillamine, administration to methylmercury treated rats resulted in a large amount of urinary methylmercury excretion. These results suggested that the total metal amounts in the whole body of patients with homocystinuria might be decreased. However, actually metal concentrations in hair and plasma of these patients were higher than those of normal controls. High plasma and hair metal levels are not accounted for in patients with homocystinuria. The physiological metal excretory mechanism in which small amounts of metals bind to the small, plasma molecular substances filter through the kidney and emerge in the urine is necessary for reconfirmation. Strongly perturbed metal metabolism exists in the patients with homocystinuria.

Treatment of acute methylmercury ingestion by hemodialysis with N-acetylcysteine (Mucomyst) infusion and 2,3-dimercaptopropane sulfonate

A case of acute methylmercury ingestion was treated sequentially with oral D-penicillamine, hemodialysis during N-acetylcysteine (NAC) infusion, and 2,3-dimercaptopropane sulfonate (DMPS) an experimental oral agent. Urinary organic mercury elimination rate increased almost 40-fold during and 84-fold after hemodialysis with NAC infusion, compared with elimination during initial D-penicillamine therapy. Mean clearance during hemodialysis was only 13 ml/min with an extraction rate of 3.7 mcg/min. Although whole blood mercury concentrations decreased from 568 to 265 ng/ml during dialysis, a rebound to 525 ng/ml occurred. A total of 1.6 mg mercury was renally eliminated during hemodialysis and in the following 24 hours. A total of 3.3 mg of predominantly organic mercury was renally eliminated during 18 days of combined therapies. Since renal elimination of inorganic mercury is seen with chronic methylmercury poisoning, the high ratio of organic to inorganic mercury in urine supports the acute nature of this exposure. DMPS was begun on day 4 and during the two weeks of administration whole blood concentrations fell by 15% to 355 ng/ml. An expected decrease in elimination half-life to 10 days was not observed during DMPS therapy, possibly due to concurrent administration of vitamins containing zinc and copper. The amount of methylmercury ingested was estimated as 45 mg, based on a post-distribution blood concentration of approximately 450 ng/ml. The patient developed no symptoms of methylmercury poisoning during the one year after the episode. We conclude that NAC may be useful to enhance renal elimination of methylmercury and merits further investigation as a potential binding agent to reduce the body burden of methylmercury.

The role of food consumption and amino acid uptake in the action of methylmercury on protein synthesis

The effect of methylmercury (MM) on protein synthesis was examined with respect to nutritional deficiency due to decreased food intake, method of amino acid administration, and amino acid uptake. Female rats were administered orally 40 mg MM hydroxide/kg and were compared with both ad libitum and pair-fed control groups. Synthesis of blood, liver, kidney, and cerebellar proteins of pair-fed controls was significantly lower than for ad libitum-fed controls. Relative to ad libitum-fed controls, MM transiently increased synthesis of blood proteins and then decreased it for blood and liver proteins. In contrast, using pair-fed controls, MM increased synthesis of blood and liver proteins. Comparison with either control showed MM to increase protein synthesis in the kidney and decrease it in the cerebellum. Intraperitoneal and intravenous administration of the [14C]amino acids showed similar results. The action of MM on protein synthesis seemed independent of its action on amino acid uptake, since MM did not affect aminoisobutyric acid uptake in the liver and cerebellum and decreased it in the kidney. In summary, we found that the effect of MM on food intake plays a significant role in the action of MM on protein synthesis and must be accounted for with pair-fed controls.

Early indices of methyl mercury toxicity and their use in treatment evaluation

Mercury distribution, food consumption, body weight, and in vivo protein synthesis were compared as criteria for evaluating the efficacy of D-penicillamine (DPA) in treating experimental methyl mercury (MM) intoxication. Female rats were orally administered MM hydroxide at 40 mg/kg and, after a 7- to 8-d latency period, displayed characteristic neurological signs of MM intoxication. Within 24 h of MM exposure food consumption decreased 75% causing a 12-g drop in body weight, and synthesis of whole blood and kidney protein increased. Protein synthesis in liver was increased 39% by MM after 3 d, and that in cerebellum was decreased 15% after 7 d. Treatment with DPA (1.2 g/kg.d sc on d 2, 3, and 4) prevented the appearance of neurological signs. DPA lowered the Hg content of all tissues; restored food consumption of control levels; increased the onset and amount of body weight gain; returned synthesis of blood, liver, and kidney proteins to control levels; and prevented the decrease in protein synthesis in cerebellum. By itself, DPA produced a transitory decrease in both food consumption and body weight, which could be prevented with vitamin B6. Vitamin B6 antagonized DPA's reversal of MM's action on protein synthesis. Furthermore, DPA and/or vitamin B6 had a variety of effects on protein synthesis in control rats. Thus it was not possible to use protein synthesis to predict the efficacy of the combination of DPA and vitamin B6 as found for the parameters of food consumption, body weight, and Hg distribution. Since changes in body weight and food consumption were the earliest and most pronounced and consistent responses to MM and effective DPA treatment, they were considered the best criteria for evaluating treatment efficacy in experimental MM poisoning in rats.