Molybdenum cofactor biosynthesis in humans. Identification of two complementation groups of cofactor-deficient patients and preliminary characterization of a diffusible molybdopterin precursor.

Molybdenum cofactor deficiency is a devastating disease with affected patients displaying the symptoms of a combined deficiency of sulfite oxidase and xanthine dehydrogenase. Because of the extreme lability of the isolated, functional molybdenum cofactor, direct cofactor replacement therapy is not feasible, and a search for stable biosynthetic intermediates was undertaken. From studies of cocultured fibroblasts from affected individuals, two complementation groups were identified. Coculture of group A and group B cells, without heterokaryon formation, led to the appearance of active sulfite oxidase. Use of conditioned media indicated that a relatively stable, diffusible precursor produced by group B cells could be used to repair sulfite oxidase in group A recipient cells. Although the extremely low levels of precursor produced by group B cells preclude its direct characterization, studies with a heterologous, in vitro reconstitution system suggest that the precursor that accumulates in group B cells is the same as a molybdopterin precursor identified in the Neurospora crassa molybdopterin mutant nit-1, and that a converting enzyme is present in group A cells which catalyzes an activation reaction analogous to that of a converting enzyme identified in the Escherichia coli molybdopterin mutant ChlA1.

Urinary metallothionein as a new index of renal dysfunction in "Itai-Itai" disease patients and other Japanese women environmentally exposed to cadmium.

The significance of elevated excretion of metallothionein in urine of women living in cadmium-polluted areas of Japan was studied with respect to renal dysfunction. The relationships between the concentrations of metallothionein in urine and those of other non-specific urinary indices of renal dysfunction, i.e., total protein, glucose, beta 2-microglobulin, retinol-binding protein, alpha-amino nitrogen and proline were examined. In addition, the relationships between urinary metallothionein and urinary cadmium and copper were also evaluated. It was found that the logarithm of the metallothionein concentration in urine was significantly correlated with the logarithm of the concentrations of each of the above parameters. When subjects with signs of renal dysfunction, including "itai'itai" disease patients and patients suspected of the disease, were compared with subjects with normal renal functions, as a group, the former excreted significantly higher concentrations of metallothionein in their urine than the latter. The results suggest that the elevated excretion of metallothionein is not only an index of excessive cadmium exposure, but also of renal dysfunction caused by chronic exposure to this metal.

Cadmium, copper, and zinc excretion and their binding to metallothionein in urine of cadmium exposed rats.

The urinary excretion of Cd, Cu, and Zn was measured in rats injected with 0.5 mg/kg Cd, sc, 6 d/wk for u to 25 wk. Gel chromatographic analysis for these urinary metals were also carried out. The Cd excretion slightly increased at first, followed by a rapid increase with concurrent appearance of proteinuria around 6 wk. During these early weeks, excretion of Cu in the urine showed a more pronounced increase and reached a plateau level (three to four times the control value). Zn excretion showed a sharp increase accompanied by proteinuria, following a slight increase, and reached about 10 times the control value. A linear relation was obtained between Cd and both Cu and Zn in the urine before proteinuria appeared. Metallothionein (MT) in the urine was associated only with Cu before the appearance of proteinuria. Cu-MT increased with increasing excretion of urinary Cu. Cd-containing MT first appeared in the urine after on onset of proteinuria, but it was still rich in Cu at first. Fron 10 wk, urinary MT showed an excess increase and contained much Cd than Cu. Zn-MT was not observed in the urine. Most of the urinary Zn was recovered from the lower-molecular-weight fractions. The results suggest that MT is directly involved in urinary excretion of Cu in the absence of renal damage and in the excretion of Cd as well as Cu after the appearance of toxicity in Cd-exposed rats.

Elevated urinary excretion of metallothionein due to environmental cadmium exposure.

Metallothionein, a low molecular weight cadmium-binding protein, has been determined for the first time in urine of "itai-itai" disease patients and other Japanese women environmentally exposed to cadmium. On a group basis, the urinary metallothionein levels of "itai-itai" disease patients and suspected patients were significantly higher than that of women living in a cadmium-polluted area. Women living in a non-polluted area excreted significantly less metallothionein than women living in a cadmium-polluted area. A similar trend was observed for urinary beta 2-microglobulin, a nonspecific index of renal tubular dysfunction. However, mean levels of urinary cadmium in the "itai-itai" disease patients, suspected patients and women living in the cadmium-polluted area were similar. It is suggested that if, in addition to beta 2-microglobulin and cadmium, metallothionein is used as another index of cadmium exposure, monitoring of renal tubular dysfunction caused by cadmium may be more effectively carried out.

Metallothionein excretion in urine upon cadmium exposure: its relationship with liver and kidney cadmium.

The relationships between quantities of accumulated cadmium in the liver and kidney and those of metallothionein in urine was studied in occupationally exposed workers and experimentally exposed rats. Cadmium-exposed workers who had been employed at a cadmium production plant for periods of 8-29 years had significantly higher levels of cadmium in both liver and kidney and excreted significantly larger amounts of metallothionein in urine when compared with workers who had been employed for less than 1 year, with office workers at the plant or with control subjects having no known occupational exposure to cadmium. The excretion of metallothionein in urine of the cadmium-exposed workers appeared to be related to the levels of cadmium in both liver and kidney. A similar dose-effect relationship was also observed among rats given repeated subcutaneous injections of 5 mumol CdCl2/kg. However, in the rats the metallothionein excretion increased markedly when the liver and renal cortex Cd levels exceeded approximately 300 microgram/g and 200 microgram/g, respectively. It appears tht urinary metallothionein may be a useful biological indicator of liver and kidney cadmium levels.