Effects of vanadium complexes with organic ligands on glucose metabolism: a comparison study in diabetic rats.

1. Vanadium compounds can mimic actions of insulin through alternative signalling pathways. The effects of three organic vanadium compounds were studied in non-ketotic, streptozotocin-diabetic rats: vanadyl acetylacetonate (VAc), vanadyl 3-ethylacetylacetonate (VEt), and bis(maltolato)oxovanadium (VM). A simple inorganic vanadium salt, vanadyl sulphate (VS) was also studied. 2. Oral administration of the three organic vanadium compounds (125 mg vanadium element 1(-1) in drinking fluids) for up to 3 months induced a faster and larger fall in glycemia (VAc being the most potent) than VS. Glucosuria and tolerance to a glucose load were improved accordingly. 3. Activities and mRNA levels of key glycolytic enzymes (glucokinase and L-type pyruvate kinase) which are suppressed in the diabetic liver, were restored by vanadium treatment. The organic forms showed greater efficacy than VS, especially VAc. 4. VAc rats exhibited the highest levels of plasma or tissue vanadium, most likely due to a greater intestinal absorption. However, VAc retained its potency when given as a single i.p. injection to diabetic rats. Moreover, there was no relationship between plasma or tissue vanadium levels and any parameters of glucose homeostasis and hepatic glucose metabolism. Thus, these data suggest that differences in potency between compounds are due to differences in their insulin-like properties. 5. There was no marked toxicity observed on hepatic or renal function. However, diarrhoea occurred in 50% of rats chronically treated with VS, but not in those receiving the organic compounds. 6. In conclusion, organic vanadium compounds, in particular VAc, correct the hyperglycemia and impaired hepatic glycolysis of diabetic rats more safely and potently than VS. This is not simply due to improved intestinal absorption, indicating more potent insulin-like properties.

Role of thiols in the in-vitro methylation of inorganic arsenic by rat liver cytosol.

Rat liver cytosol inactivates inorganic arsenic (Asi) through methylation; S-adenosylmethionine is the methyl group donor and reduced glutathione (GSH) is required for full activity. The study of the combined effects of Asi, GSH and other thiols in vitro and the results of our previous in-vivo studies in humans and rats are consistent with a pathway involving the formation of a monomethylated metabolite which is either rapidly further methylated into a dimethylated derivative or is spontaneously oxidized into monomethylarsonic acid (MMA). The dimethylated metabolite gives rise to dimethylarsinic acid. The first methylation reaction is rate limiting, can be stimulated by GSH and is catalyzed by an enzyme different from that which transfers the second methyl group. The latter is sensitive to inhibition by inorganic arsenic. The stimulation of the first methylation reaction by GSH can only be evidenced at high Asi concentration because under these conditions, the second methylating enzyme can be sufficiently inhibited by Asi to allow some accumulation of MMA. The latter may also slow down the first methylation reaction. A large excess of thiol groups may prevent the methylation reactions probably by decreasing the amount of free trivalent arsenic.

Investigations on the lung and kidney function in workers exposed to cadmium.

The kidney seems more sensitive to the chronic effect of cadmium than the lung. Only minor impairments of lung function (mild form of obstructive lung disease) were found after long-term occupational exposure (less than 20 yr) to moderate concentration of cadmium oxide dust and fume. This conclusion, cannot, however be extrapolated to acute or subacute inhalational exposure. The nephrotoxicity of cadmium consists in a tubular dysfunction characterized by an increased excretion of beta 2-microglobulin and giving rise to the classical tubular proteinuria and in a glomerular dysfunction evidenced by an increased excretion of high molecular weight proteins and increased levels of beta 2-microglobulin and creatinine in plasma and giving rise to a glomerular type proteinuria. These renal changes were mainly found in workers whose cadmium concentration at time of the survey exceeded 1 microgram Cd/100 ml in blood and 10 microgram Cd/g creatinine in urine. It should, however, be stressed that higher levels of Cd in blood and in urine are not necessarily associated with the presence of excessive proteinuria. In newly exposed workers, the Cd level in blood increases progressively to a plateau after several weeks. Cadmium level in urine fluctuates more. In workers exposed for several months to an airborne concentration exceeding 200 microgram/m3, Cd concentration in urine seems mainly influenced by recent exposure.

Characterization of cadmium proteinuria in man and rat.

In workers chronically exposed to cadmium and without signs of renal insufficiency, plasma proteins with molecular weight ranging from 11,800 to 450,000 are excreted in greater amount in urine. Increased urinary excretion of low and high molecular weight proteins can occur independently. Because of its greater stability in urine and provided a sensitive immunological technique is used, the determination of retinol-binding protein is a more practical and reliable test of proximal tubular function than beta 2-microglobulin. The evaluation of renal function of workers removed from cadmium exposure indicates that cadmium-induced renal lesions, albeit of slow progression, are not reversible when exposures ceases. In workers chronically exposed to cadmium or removed from cadmium exposure, metallothionein in urine is directly correlated with cadmium in urine but not with cadmium in blood or years of cadmium exposure. The association between cadmium in urine and metallothionein in urine is independent of the status of renal function and the intensity of current exposure to cadmium. Whereas the repeated IP injection of high doses of cadmium to rat gives rise to a mixed or tubular type proteinuria, the prolonged oral administration of cadmium results mainly in the development of a glomerular type proteinuria. The former is usually reversible after cessation of treatment whereas the latter is not. Circulating antiglomerular basement membrane antibodies have been found in man and in rat chronically exposed to cadmium. The pathogenic significance of this finding deserves further investigation.

Investigations of factors influencing exposure and response to lead, mercury, and cadmium in man and in animals.

The susceptibility of the heme biosynthetic pathway to lead, as reflected by increased free erythrocyte porphyrin (FEP) concentration, is in humans as well as in rats in the order of young greater than or equal to female greater than male. The difference between adult male and female rats can be explained at least partially by the interaction of estradiol and progesterone with the FEP response to lead; the hormonal influence on FEP does not seem to be mediated through changes in plasma iron. The classical "tubular type" proteinuria in workers chronically exposed to cadmium has two not necessarily concomitant components, namely, a tubular type and a glomerular type component characterized by increased excretion of low and high molecular weight proteins, respectivley. No synergistic effect of cadmium and lead on the proteinuria of workers simultaneously exposed to both metals was observed. Mercury (most likely methylmercury) is freely transferred from the mother to the fetus; there is only a slight placental barrier for lead and a rather strong one for cadmium. Compared to maternal blood, placenta does not accumulate lead or mercury but concentrates cadmium about 10-fold.

Determinants of serum zinc in a random population sample of four Belgian towns with different degrees of environmental exposure to cadmium.

This report investigated the distribution of serum zinc and the factors determining serum zinc concentration in a large random population sample. The 1977 participants (959 men and 1018 women), 20-80 years old, constituted a stratified random sample of the population of four Belgian districts, representing two areas with low and two with high environmental exposure to cadmium. For each exposure level, a rural and an urban area were selected. The serum concentration of zinc, frequently used as an index for zinc status in human subjects, was higher in men (13.1 mumole/L, range 6.5-23.0 mumole/L) than in women (12.6 mumole/L, range 6.3-23.2 mumole/L). In men, 20% of the variance of serum zinc was explained by age (linear and squared term, R = 0.29), diurnal variation (r = 0.29), and total cholesterol (r = 0.16). After adjustment for these covariates, a negative relationship was observed between serum zinc and both blood (r = -0.10) and urinary cadmium (r = -0.14). In women, 11% of the variance could be explained by age (linear and squared term, R = 0.15), diurnal variation in serum zinc (r = 0.27), creatinine clearance (r = -0.11), log gamma-glutamyltranspeptidase (r = 0.08), cholesterol (r = 0.07), contraceptive pill intake (r = -0.07), and log serum ferritin (r = 0.06). Before and after adjustment for significant covariates, serum zinc was, on average, lowest in the two districts where the body burden of cadmium, as assessed by urinary cadmium excretion, was highest. These results were not altered when subjects exposed to heavy metals at work were excluded from analysis.

Health effects of environmental exposure to cadmium: objectives, design and organization of the Cadmibel Study: a cross-sectional morbidity study carried out in Belgium from 1985 to 1989.

Cadmium is a cumulative environmental pollutant. For the general population mainly exposed by the oral route and through tobacco smoke inhalation, the kidney is the critical organ. Belgium is the principal producer of cadmium in Europe, and certain areas of the country are polluted by cadmium mainly because of past emissions from nonferrous industries. Preliminary studies carried out in one polluted area have suggested that environmental pollution might lead to an increased uptake of cadmium by the human body and possibly to health effects. Thus, a large-scale morbidity study has been initiated to assess the validity of this hypothesis. The present paper describes the protocol of this study. Its main objectives are to determine to what extent environmental exposure to cadmium resulting from industrial emissions may lead to accumulation of the metal in the human organism; to establish whether or not environmental exposure may induce renal changes and/or influence blood pressure; and to assess the acceptable internal dose of cadmium for the general population. The study design takes advantage of the fact that biological indicators of exposure, body burden, and early nephrotoxic effects of cadmium are available, which increase the likelihood of detecting a cause-effect relationship.

Absence of significant genotoxicity in lymphocytes and urine from workers exposed to moderate levels of cobalt-containing dust: a cross-sectional study.

Mortality studies have shown that, in the past, lung cancer occurred after exposure to mixtures of cobalt metal and metallic carbide particles, the main constituents of hard metals, but apparently not when exposure was to cobalt alone. The major objective of this biomonitoring study was to assess genotoxic effects as a measure for carcinogenic risk in workers from cobalt refineries and hard metal plants currently exposed to the threshold limit value/time-weighted average (TLV-TWA) for cobalt-containing dust. The study comprised three groups of workers: 35 workers exposed to cobalt dust from three refineries, 29 workers exposed to hard metal dust from two producing plants, and 35 matched control subjects recruited from the respective plants. The study design integrated complementary methodologies to assess biomarkers of effects that represent both initial DNA damage (8-hydroxydeoxyguanosine [8-OHdG] in urine and comet assay on lymphocytes) and definitive chromosome breakage/loss (micronuclei in lymphocytes). Cobalt and cotinine were determined in urine as a measure for cobalt exposure and recent smoking, respectively. No significant increase of genotoxic effects was detected in workers exposed to cobalt-containing dust as compared to controls. No difference in any genotoxicity biomarker was found between workers exposed to cobalt and hard metal dusts. Multiple regression analysis indicated that workers who smoked and were exposed to hard metal dusts had elevated 8-OHdG and micronuclei values. Because this observation is in line with a previous epidemiological study of an increased risk of dying from lung cancer in workers from the hard metal industry who smoked, it is concluded that this specific occupational group needs closer medical surveillance.

Determination of manganese in blood and urine by flameless atomic absorption spectrophotometry.

A method for the determination of manganese in blood and urine is described. A chelate fo manganese with cupferron is extracted with methylisobutylketone and determined by flameless atomic absorption spectrophotometry. The method is directly applicable to urine but the determination of manganese in blood required a preliminary digestion step. With the use of internal standards, this technique allows the determination of manganese concentrations of the order of 1 mug/1 of urine or 1 mug/100 ml whole blood.

Development of a method to monitor low molecular mass hydrocarbons in exhaled breath of man: preliminary evaluation of its interest for detecting a lipoperoxidation process in vivo.

Low molecular mass hydrocarbons, particularly ethane and pentane, have been measured in expired air of man. The air is collected into 5-10 l polyamide bags. After removal of water vapour and CO2, the hydrocarbons are concentrated on a silicagel column kept at 0 degree C. The column desorption is carried out at 290 degrees C, and the gases are analysed by gas chromatography. A slight but statistically significant increased pentane production was detected in cirrhotic patients.

Influence of 2,3-dimercaptopropane-1-sulfonate and dimercaptosuccinic acid on the mobilization of mercury from tissues of rats pretreated with mercuric chloride, phenylmercury acetate or mercury vapors.

The efficiency of the sodium salt of 2,3-dimercaptopropanesulfonic acid (DMPS) and meso-dimercaptosuccinic acid (DMSA) to mobilize mercury from tissues has been assessed in rats pretreated with different doses of HgCl2, phenylmercury acetate or exposed to different concentrations of mercury vapors. These pretreatments increase the mercury concentration in the kidney and to a lower extent in the liver. Only exposure to metallic mercury vapor leads to mercury accumulation in the brain. Both chelators mobilize mercury stored in the kidney and the amount of metal excreted in urine following a single administration of DMSA is a good indicator of the renal burden of mercury. The rate of removal is greater after DMPS administration than after DMSA but repeated administration of either agents eventually leads to the same total amount of mercury mobilized from the kidney. The loss of mercury from the liver can be slightly accelerated by repeated administration of the chelators. However, the chelators are inefficient in removing mercury from the brain.

Influence of sex hormones on free erythrocyte protoporphyrin response to lead in rats.

Following oral administration of lead a difference in free erythrocyte protoporphyrin (FEP) increase was found between adult male, adult female and suckling rats: young animals are more susceptible than adult female rats which in turn exhibit a greater FEP increase than adult male animals. This observation parallels that made previously in humans. Possible difference in iron metabolism does not appear to explain the sex-linked difference in FEP response to lead. Sex hormones mainly progesterone, seem to play a role but their interaction with lead on the FEP response is restricted to female rats and apparently is not mediated through changes in delta-aminolevulinic acid synthetase activity.

Study on in vivo and in vitro metabolism of dimethylformamide in male and female rats.

The study of dimethylformamide (DMF) metabolism by rat tissues in vitro indicates that formaldehyde is not a metabolic product as previously reported [1]. Furthermore, no other monocarbon derivative (CO, CH3OH, HCOOH, CH4) was detected when DMF was incubated with a fortified liver preparation. One metabolic product is methylhydroxymethylformamide (DMF-OH) measured as N-methylformamide (NMF) due to the breakdown of the hydroxymethyl group during gas chromatography. It was usually believed that the main metabolite excreted in urine following administration of DMF to male and female rats was NMF. The results of this study indicate that DMF-OH constitutes the main metabolite in vivo. A quantitatively less important urinary metabolite, hydroxymethylformamide (NMF-OH), is determined as formamide (F) by gas chromatography. In male and female rats, partial hepatectomy reduces markedly the in vivo biotransformation of DMF. Following administration of DMF or NMF, the total amount of metabolites (DMF-OH and/or NMF-OH) excreted in urine is identical in both sexes, but female rats excrete more unchanged parent compound than male rats. The rate of NMF-OH excretion in urine following high doses of DMF supports the hypothesis that DMF may inhibit its own biotransformation.

Effect of lead on some parameters of the heme biosynthetic pathway in rat tissues in vivo.

Lead was administered to male and female rats in drinking water for 3 and 6 weeks at the following doses: 0, 10, 100, 1000, 5000 ppm and for 6 months at 10 ppm only. Various parameters of blood - lead concentration (Pb-B), hematocrit (Htc), hemoglobin (Hb), free erythrocyte porphyrins (FEB), delta-aminolevulinate dehydratase (ALAD), reticulocytes - and tissue - ALAD, free tissue porphyrins (FTP), lead concentration (Pb-T) - were determined. Pb-B increases with dose but reaches rapidly a plateau despite continuous Pb administration. Concentration of Pb in kidney, liver and brain correlates with Pb-B. Pb does not accumulate in heart. Kidney is the main site of Pb deposition and kidney ALAD is the parameter most susceptible to lead, since reduction is observed in all treated groups after 3 weeks of exposure. However, kidney ALAD inhibition is transitory since after 6 weeks it is only observed in the 5000 ppm group. At 10 ppm lead prevents also the increase in blood ALAD activity normally associated with the reticulocytosis of repetitive bleeding. The next parameters affected by lead are: ALAD in blood which is inhibited after 6 weeks of treatment with 100 ppm lead, and FEP, delta-aminolevulinic acid plus other pyrrole-forming substances in urine (ALA-U), and FTP in kidney which are increased after 3 or 6 weeks of treatment with 1000 and 5000 ppm lead.

Effect of short-term administration of lead to pregnant rats.

Lead was administred to adult female rats in drinking water (0;0.1:1 and 10 ppm) for 3 weeks before mating, during pregnancy and during 3 weeks after delivery. On day 21 after delivery the mothers and their newborns were sacrified and various parameters of blood -- lead concentration on (Pb-B), hematocrit (Htc), hemoglobin (Hb), free erythrocyte porphyrins (FEP), delta0aminolevulinate dehydratase (ALAD) -- and tissue -- ALAD, free tissue porphyrins (FTP), lead concentration (Pb-T) -- were determined. In mothers a significant increase in Pb-B and Pb concentration in kidney was found in the 10 ppm group, but this increase in lead concentration was not associated with any statistically significant modification of the biochemical parameters. In newborns, lead concentration in blood and in kidney was also significantly increased in the 10 ppm group and this lead exposure was associated with a decrease of the ALAD activity in blood and an increase of FTP in kidney. On the basis of the biochemical parameters investigated one can therefore conclude that the developing organism is more susceptible to the biological action of lead than the organism of adult animals and that the "no-effect" level of lead administered during pregnancy and in the neonatal period is around 1 ppm.

Inorganic arsenic methylation by rat tissue slices.

Rat liver, kidney and lung slices methylate trivalent inorganic arsenic (AsIII) to monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA); the liver has the greatest methylating capacity. AsIII enters the liver cells by a diffusion process followed by extensive binding to intracellular components which favors its extensive accumulation inside the cells. Reduced glutathione regulates AsIII metabolism through several mechanisms: facilitation of AsIII diffusion into the cells, stimulation of the first methylation reaction and increase of DMA excretion by the cells. An excess of AsIII inhibits DMA production by liver cells but this inhibition is reversible; mercuric ions inhibit both MMA and DMA production probably by decreasing inorganic arsenic (Asi) uptake and the second methylation reaction. DMA can be produced from MMA by rat liver slices and this methylation step is stimulated by GSH. In contrast to AsIII, AsV is not extensively taken up by the hepatocyte and is thus poorly methylated.

Experimental confirmation in rats of the mixed type proteinuria observed in workers exposed to cadmium.

Recently we have reported that the proteinuria developed by workers exposed to cadmium was characterized by an increased excretion of high and low molecular weight proteins. These observations were confirmed experimentally. Female rats which were injected intraperitoneally with CdCl2 (1 mg Cd2+/kg) 5 times a week developed after 2 months of treatment a proteinuria qualitatively similar to that observed in workers exposed to cadmium. The analysis of this proteinuria by electrophoresis and gel filtration revealed an increased excretion of low and high molecular weight proteins. This animal study, which confirms previous observations on man, strengthens our hypothesis that the cadmium-induced proteinuria, classically considered as a tubular type proteinuria, is in fact a mixed type proteinuria, involving not only the tubule but also the glomerulus.

alpha 1-antitrypsin in cadmium toxicity: an evaluation of its suggested role.

Chowdhury and Louria [1] reported that cadmium could reduce in vitro the concentration and the trypsin inhibitory capacity of plasma alpha 1-antitrypsin. They suggested that this could explain the emphysema observed in some workers exposed to cadmium. Using the same experimental approach as these authors, we could not reproduce their observations. Furthermore, in vivo results obtained on workers excessively exposed to cadmium during more than 20 years and exhibiting obvious signs of chronic cadmium intoxication did not reveal a decrease in the concentration and the activity of plasma alpha 1-antitrypsin.

Comparison, by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, of urinary proteins excreted by workers exposed to cadmium, mercury or lead.

Urinary proteins from workers exposed to cadmium (Cd, n = 20), lead (Pb, n = 19) or mercury (Hg, n = 25) were analyzed by polyacrylamide gel electrophoresis (PAGE) in the presence of sodium dodecyl sulfate (SDS). The areas of the peaks with the relative mobilities of beta 2-microglobulin and retinol binding protein (low molecular weight proteins), albumins, transferrin and IgG (high molecular weight proteins) were measured and compared with those obtained in matched control groups. The concentrations (mean and range) of the metals in blood (B, micrograms/100 ml) and in urine (U, micrograms/g creatinine) of the exposed groups were as follows: Cd group, CD-B = 1.51 (0.18-4.31) and CD-U = 16.6 (2.08-59.3); Pb group, Pb-B = 44.5 (44.8-61.3) and Pb-U = 88.7 (15.2-298); Hg group, Hg-B = 3.74 (1.84-8.14) and Hg-U = 116 (51.8-206). The average duration of exposure to the metal was 30.5 (Cd), 12.5 (Pb) and 7.2 (Hg) years respectively. Under these exposure conditions, it was found that Cd increases the urinary excretion of low as well as high molecular weight proteins, Hg induces an increased urinary excretion of only high molecular weight proteins and lead has no significant effect on the renal excretion of either type of protein.

Potentiation of diabetic glomerulopathy in uninephrectomized rats subchronically exposed to cadmium.

The renal effects of diabetes mellitus and cadmium (Cd), separately or in combination, were investigated in unilaterally nephrectomized female Sprague-Dawley rats. Diabetes was induced by injection of streptozotocin and Cd was administered in drinking water at a concentration of 100 p.p.m. for 2.5 months. Cd did not affect the reduction in glomerular filtration rate or the rise in beta 2-microglobulinuria caused by diabetes. By contrast, the effect of diabetes on the urinary excretion of albumin, transferrin or IgG was greatly enhanced by concomitant exposure to Cd. This interaction occurred at Cd levels in the renal cortex which are very similar to those found in the general population of industrialized countries. These observations, in agreement with the results of a recent epidemiological study, suggest that Cd polluting the environment might potentiate the development of diabetic nephropathy.