Histopathological changes in relation to cadmium concentration in horse kidneys

Low-level exposure to lead, cadmium and mercury, and histopathological findings in kidney biopsies

BACKGROUND

Lead (Pb), cadmium (Cd) and mercury (Hg) are all nephrotoxic metals, and a large part of the body burden of Cd and Hg is found in the kidneys. There are, however, few studies on associations between exposure to these toxic metals and renal biopsy findings, and none at low-level exposure.

AIM

To examine the hypothesis that low-level concentration of Pb, Cd or Hg in the kidneys is associated with histopathological changes in the kidneys.

METHODS

We determined concentrations of Pb, Cd and Hg in kidney, blood and urine in 109 healthy kidney donors, aged 24-70 years. The renal biopsies were scored according to the Banff classification regarding tubular atrophy, interstitial fibrosis, glomerulosclerosis, arteriosclerosis, and arteriolohyalinosis. Kidney function was assessed based on glomerular filtration rate (GFR) as well as urinary excretion of albumin, low molecular weight proteins, kidney injury molecule 1 and N-acetylglucose aminidase. Associations between metal concentrations and histopathological changes, were assessed in models also including age, sex and smoking.

RESULTS

The median kidney concentrations of Pb, Cd and Hg were 0.08, 13 and 0.21 μg/g, respectively. There were signs of tubular atrophy in 63%, interstitial fibrosis in 21%, glomerulosclerosis in 71%, arteriosclerosis in 47%, and arteriolohyalinosis in 36% of the donors, but, as could be expected, the histopathological findings were limited, mostly Banff grade 1. In models adjusted for age, sex and smoking, kidney Cd was positively associated with tubular atrophy (p = 0.03) and possibly with arteriolohyalinosis (p = 0.06). Kidney Hg was associated with arteriosclerosis (p = 0.004).

DISCUSSION AND CONCLUSIONS

The results suggest that even low levels of Cd in the kidney can induce a mild degree of tubular atrophy. This is in line with previous findings at high-level Cd exposure. The association between kidney Hg and renal arteriosclerosis was unexpected, and may be a chance finding.

Concentrations of strontium, barium, cadmium, copper, zinc, manganese, chromium, antimony, selenium and lead in the equine liver and kidneys

The concentrations of specific elements in the equine liver and kidneys are of practical relevance since horses are not only food-producing animals, but also partially serve as an indicator for the environmental pollution, as the basic feed includes plants like grass, grain and fruits. In this study, the concentrations of strontium (Sr), barium (Ba), cadmium (Cd), copper (Cu), zinc (Zn), manganese (Mn), chromium (Cr), antimony (Sb), selenium (Se) and lead (Pb) were measured in the liver, renal cortex and renal medulla of 21 horses (8 male; 13 female; aged between 5 months-28 years), using inductively coupled plasma mass spectrometry. Comparable Cu and Zn concentrations were detected in the liver and renal cortex, while approximately 50% lower concentrations were measured in the renal medulla. The lowest Sr, Cd and Se, but the highest Mn, Sb and Pb concentrations were measured in the liver. The Ba concentrations were comparable in the renal cortex and medulla, but lower in the liver of the horses. Gender-related differences were observed for Cd, Mn and Cr, with higher Cd concentrations in the liver, but lower Mn concentrations in the renal cortex and lower Cr concentrations in the renal medulla of female horses. Age-related differences were detected for most measured elements, however, the animal number per age-group was only low. In conclusion, the present study provides important reference data for the storage of Sr, Ba, Cd, Cu, Zn, Mn, Cr, Sb, Se and Pb in the liver and kidneys of horses, which are of practical relevance for an evaluation of the exposure of horses to these elements, either via feed or the environment.

Accumulation and detoxification of metals and arsenic in tissues of cattle (Bos taurus), and the risks for human consumption

The aim of this study was to investigate metal accumulation and detoxification processes in cattle from polluted and unpolluted areas. Therefore dairy cows from farms and free ranging Galloway cows from nature reserves were used as study animals. The concentrations of Ag, Cd, Pb, Al, Cr, Mn, Fe, Co, Ni, Cu, Zn and As were determined in muscle, kidney, liver and lungs of cattle from polluted and reference areas in Belgium. In kidney and liver also the metallothionein concentrations were measured. For Ag, Mn, Co, Cu, Zn and As the concentrations in the different tissues were significantly higher in the sampled Galloways than in the sampled dairy cows. On the other hand Cd and Pb were significantly higher in tissues of both cattle breeds from polluted sites. Cadmium seemed to be the most important metal for metallothionein induction in kidneys whereas Zn seemed to be the most important metal for the induction of metallothionein in the liver. This study also suggested that only for Mn and Cd a significant part of the uptake occurs via the lungs. Although in muscle none of the Cd and Pb levels exceeded the European limits for human consumption, 40% of the livers and 85% of the kidneys of all examined cows were above the European limit for cadmium. Based on the existing minimum risk levels (MRLs) for chronic oral exposure, the present results suggested that a person of 70kg should not eat more than 150g cow meat per day because of the Cr levels in the muscles.

High cadmium accumulation among humans and primates: comparison across various mammalian species--a study from Japan

The majority of existing literature reports that cadmium (Cd) is toxic to humans and most living organisms. This paper reports the results of our study that measured Cd levels in the livers and kidneys of humans and other 50 mammalian species under normal conditions in Japan. The study tests the differences in the Cd concentrations across different mammalian species and sexes. Our results revealed that (1) there is a strong correlation between the Cd levels in the livers and kidneys across all examined species, (2) humans exhibit the highest Cd accumulation level in both organs, (3) primates also show a high Cd concentration at a level close to humans, (4) mice and rats show low Cd levels in both organs, indicating that humans accumulate about a few thousand times more Cd than mice and rats, and (5) the Cd concentration of female mammals is more than double of males for both organs. Our results indicate that these cross-sex as well as cross-species discrepancies cannot be explained by the difference in daily Cd intake. While further research is necessary to determine any potential role of Cd accumulation, we speculate that Cd plays some physiological function in the renal cortex of humans and primates.

Toxic and essential metal concentrations in four tissues of red deer (Cervus elaphus) from Baranja, Croatia

Kidney (n = 297), liver (n = 52), jawbone (n = 80) and muscle (n = 48) samples collected from red deer (Cervus elaphus) from north-eastern Croatia in the 2002--05 hunting season were analysed for cadmium (Cd), copper (Cu), iron (Fe), mercury (Hg), lead (Pb), selenium (Se) and zinc (Zn) using atomic absorption spectrometry. Statistical evaluation of results showed age-related accumulations of renal cortex Cd and Zn, bone Pb, and muscle Zn. Renal cortex Cd and Zn were significantly associated. In addition, concentrations of Cd and Pb in muscle tissue were significantly correlated with Fe content. Found levels of toxic metals were not likely to affect the health status of animals. A total of 49% of the muscle, 60% of the kidney and 6% of the liver samples were unsuitable for human consumption according to Croatian regulations for Cd in food. However, the calculated intake of Cd through deer meat consumption is small and represents no health risk when consumption is moderate.

A new index for evaluation of cadmium pollution in birds and mammals

The degree of cadmium (Cd) contamination in wildlife is often used as an indicator in the environmental monitoring of Cd poisoning. However, previous studies have not clarified the correlation between levels in wildlife and levels in the environment by comparing levels among different species of animals; therefore, assessing the level of pollution in this manner is not considered a reliably accurate indicator of levels in the environment. The aim of this study was to establish a new indicator for the non-polluted warm-blooded animals, one that is not species-dependent, which will facilitate using different species for Cd monitoring. First, the previous publications regarding Cd contents in wildlife, 27 reports in which Cd contents were represented as arithmetic means and described for both kidney and liver were selected. A regression line (CSRL) between Cd contents of kidney and that of liver was obtained in a high correlation coefficient (R (2) = 0.943, P < 0.01). The mean values from land and waterfowl, terrestrial mammals, seabirds, marine mammals, and non-polluted humans were located on the line and aligned in order. CSRL might allow an accurate determination of whether an animal is polluted by Cd. CSRL was confirmed using well-established and widely recognized pollution models such as Itai-itai patients and Cd-exposed experimental animals. The Cd contents from these models were located in different positions relative to CSRL depending on the level of contamination. Thus, this new indicator determining the Cd-pollution status of animals would be useful for environmental monitoring.

Environmental cadmium induces histopathological changes in kidneys of roe deer

Kidney samples of 224 roe deer (113 males, 111 females) aged three months to approximately nine years were collected in eastern Austria. Cadmium contents were examined and histological examinations were performed considering 11 different pathomorphological parameters. Cadmium burden was relatively high (range: 0.010-22.076 ppm) and increased with age. Females aged one to two years had higher contents than males of the same age. The culling site had no influence on cadmium load. The relation between the occurrence of histopathological changes and age, sex, origin, and cadmium concentration in 208 roe deer was tested. The frequency of vacuolic degeneration, pycnotic nuclei, caryolysis, and necrosis was related to increased cadmium levels. Increasing age correlated with lymphohistiocytic infiltration, interstitial fibrosis, and swelling of glomeruli. Pigment deposits and thickening of Bowman's capsule could be related to both cadmium and age. Furthermore, roe deer from an industrialized region showed alterations more frequently than animals from rural areas. We found no relation between morphological changes and sex. Though it remains to be established whether environmental cadmium exposure is the sole cause for the histopathological alterations observed, the results of this study indicate that chronic cadmium poisoning may be an important cofactor in the pathogenic mechanisms of renal damage in roe deer and that cadmium intoxication may be more widespread among wildlife than previously known.

Industrial chemicals and the horse

Poisoning resulting from exposure to a wide variety of industrial chemicals is not a common occurrence in horses, but it does happen on occasion. A wide range of toxicosis can occur from a wide range of industrial pollutants, such as dioxin, carbon tetrachloride, and tetrachloroethylene, to heavy metals, such as cadmium and zinc. The equine practitioner must consider industrial chemical toxicosis in differential diagnoses and work with a reputable veterinary diagnostic laboratory to confirm or rule out industrial chemical poisoning.

Cadmium in caribou and muskoxen from the Canadian Yukon and Northwest Territories

Cadmium, zinc, copper and metallothionein concentrations were measured in liver and kidney tissue of caribou and muskoxen collected from various sites in the Canadian Yukon and Northwest Territories. Cadmium concentrations in caribou tissues were substantially higher than in muskoxen for all age classes and were comparable to concentrations reported for caribou from northern Québec and Norway. No geographical site differences in cadmium concentration were observed. Cadmium concentrations were positively correlated with age for both caribou and muskoxen. The highest cadmium concentration observed (166 micrograms/g dry wt.) was in renal tissue of a 15-year-old caribou. Metal concentrations tended to be higher in spring than in fall for animals of comparable age. Renal cadmium concentrations were highly correlated with metallothionein concentrations, especially for cadmium concentrations exceeding 20 micrograms/g (dry wt.). It is estimated that the regular weekly consumption of kidney tissue from Arctic caribou of any age, and from muskoxen older than 1 year, will probably cause the WHO provisional weekly tolerable intake of cadmium to be exceeded.

Interactions of plant zinc and plant species on the bioavailability of plant cadmium to Japanese quail fed lettuce and spinach

Many cadmium-contaminated environments contain high levels of zinc. The effects of plant Zn and plant species on plant Cd bioavailability were tested in Japanese quail fed lettuce and spinach. Four groups of birds received 10% of their diets as lettuce or spinach leaves intrinsically labeled with 109Cd and containing low or high intrinsic Zn. Two other groups were fed control diets containing 109Cd as CdSO4 and low or high Zn as ZnCO3. Cadmium concentrations in diets ranged from 0.857 to 1.05 micrograms/g dry wt. Zinc concentrations in low-Zn diets ranged from 21.2 to 22.8, and in high-Zn diets from 56.0 to 63.3 micrograms/g dry wt. Increased lettuce and spinach Zn decreased plant Cd retention in kidney, liver, and jejunum-ileum of Japanese quail. Spinach Cd was less absorbed than lettuce Cd at both Zn levels. Inorganic Zn produced a lesser decrease in Cd retention in kidney, liver, and jejunum-ileum than did plant Zn. We conclude that (1) crops that transport Zn and Cd readily into edible tissues show lower Cd bioavailability when grown in Zn-Cd contaminated environments than in Cd-only polluted sites, (2) plant species differ in Cd bioavailability for identical concentrations of Zn and Cd in edible tissues, and (3) toxicological studies with animals exposed to Cd salts and Zn supplements do not assess Cd bioavailability of Zn-Cd contaminated crops.

Non-metallothionein-bound cadmium in the pathogenesis of cadmium nephrotoxicity in the rat

Male rats were injected SC with 0.6 mg Cd/kg/day for 5 days per week for 2, 4, 6, and 8 weeks. Liver and kidney were examined morphologically and analyzed for metallothionein, cadmium, zinc, and copper. Morphologic changes were found in kidney but not in liver. The earliest ultrastructural change consisted of myelin figures in vacuoles in cytoplasm of proximal tubular lining cells reflecting degeneration of membranes. This change occurred after 4 weeks with 801 +/- 25 nmol/g (89.9 micrograms/g) total kidney cadmium or 390 nmol/g (43.7 micrograms/g) of cadmium not bound to metallothionein. Similar changes were observed after 6 weeks but after 8 weeks pathological changes consisted of focal cellular necrosis and interstitial fibrosis. Other ultrastructural changes included altered mitochondria and increased numbers of microbodies. Renal cadmium after 8 weeks exposure was 1827 +/- 48 nmol/g (215.3 +/- 5.8 micrograms/g) or 628 nmol/g (70.2 micrograms/g) of cadmium not bound to metallothionein. Total cadmium was higher in liver than in kidney but partitioning between bound and nonbound cadmium differed in the two organs. The fraction not bound to metallothionein increased with time of exposure in both liver and kidney. However, total cadmium in the liver did not exceed potentially available binding sites of metallothionein, whereas total cadmium did exceed potentially available binding sites of metallothionein in the kidney where pathologic changes occurred. The results indicated that degeneration of cellular membranes is an early cellular effect of cadmium exposure followed later by toxicity to organelles, cellular necrosis, and interstitial fibrosis. Cadmium-induced cellular toxicity is more directly related to the fraction of cadmium in the kidney that is not bound to metallothionein than is total cadmium per se.

Renal kallikrein excretion as a distal nephrotoxicity marker during cadmium exposure in rats

Cadmium exposure is known to induce hypertension, but development of hypertension is not universal in exposed animals. However, the cellular uptake of cadmium could also exert renal cytotoxic effects which have been, until now, essentially only studied at the proximal tubule level. Kallikrein is an enzyme synthetized in renal cortex and excreted in the urine in the distal tubule. Therefore, to evaluate the distal renal effect of cadmium, we studied the daily urinary kallikrein excretion (UKE) in conscious unrestrained female Brown Norway rats during long-term chronic exposure to 2 dosages of cadmium given subcutaneously 3 times a week, a low dose (LD): 0.25 mg/kg and a high dose (HD): 1 mg/kg. Neither dose of cadmium was able to induce significant hypertension in the treated animals. HD administration for 24 weeks resulted in a decreased UKE associated with an increase in plasma renin activity and sodium and potassium excretions. LD administration had no significant effect on UKE. Twenty weeks after stopping cadmium administration, a persistent reduction in UKE was still observed; furthermore, the group which had been previously administered a LD of cadmium, now also exhibited a reduced UKE. During this re-examination period in both groups, the UKE reductions were associated with normal systolic blood pressure, glycosuria, natriuresis. Our data show that cadmium administration can influence UKE, plasma renin activity, plasma aldosterone concentration and electrolyte excretion without inducing any variation of blood pressure. This may reflect a nephrotoxic, non-hypertensive effect. Since this effect persisted after stopping cadmium administration, it may indicate a prolonged irreversible nephrotoxic effect at the distal nephron level. Thus, UKE may be a useful non-invasive index to evaluate distal nephrotoxicity.

Age dependent changes in metallothionein and accumulation of cadmium in horses

1. Analysis of livers and kidneys from 28 horses for cadmium, zinc and metallothionein showed low cadmium content in liver. There was a gradual increase in cadmium content in kidney with age. 2. Metallothionein values varied with zinc content in the liver and with cadmium content in the kidney; copper values did not vary in either tissue. 3. Metallothionein was localized mainly in the cytoplasms in liver and kidney of horses by immunohistochemistry.

Cadmium concentration in human kidney biopsies

This study reports the cadmium concentration and histopathology of kidney tissue from 29 patients with clinical findings that motivated a diagnostic percutaneous kidney biopsy and/or a history of possible exposure to cadmium. Cadmium was found in all specimens examined including those from controls. In the patients, the mean cadmium concentration was 12.9 (0.6-45.0) micrograms cadmium per g wet kidney tissue. The highest concentrations (30-45 micrograms/g) were found in three patients with morphological and clinical findings of tubulo-interstitial damage. Patients with signs of tubulo-interstitial disease had higher mean cadmium concentrations than those with glomerular changes, and patients with normal blood pressure had higher concentrations than those with diastolic hypertension. In a control group of 22 autopsies, the mean cadmium concentration was 8.7 (2.9-22.4) micrograms/g. The mean difference between the right and the left kidney was 2.3 (0.9-9.6) micrograms/g. Laboratory findings in patients with cadmium nephropathy were nonspecific. Thus, in patients with interstitial nephritis and cadmium exposure, a biopsy for the analysis of kidney cadmium concentration may be motivated. The combination of morphological and clinical findings of interstitial nephritis and a high concentration of cadmium in biopsied kidney tissue indicates cadmium nephropathy.

The critical level of cadmium in renal cortex: the concept and its limitations

Because renal cortex is a primary target organ of Cd the seriousness of human exposure is commonly assessed in terms of the extent to which it permits renal cortical Cd concentrations to approach a critical value. The critical value has been defined in terms of PCC-10, the population critical concentration at which 10% of exposed individuals may be expected to show abnormal renal function. In chronically exposed human populations, PCC-10 appears to lie in the range of 180 to 220 μg Cd/gram fresh weight of cortex. However, Cd accumulated in the kidney under these conditions is distributed between more than one compartment, in all likelihood differing greatly in their toxicological characteristics. For instance, a major fraction of this Cd is bound to metallothionein, and may as such be relatively inert. Compartmentation of tissue Cd, in turn, is strongly influenced by the nature of exposure, and the PCC-10 value of 200 μg/g may therefore have limited general significance. The problem of risk assessment is further complicated by the high variability of Cd absorption. Nevertheless, human renal Cd levels commonly reach values as high as 1/3 to 1/6 of the chronic PCC-10, and further increases in Cd intake should therefore be avoided.

Toxicity of cadmium chloride in vitro: indices of cytotoxicity with the pulmonary alveolar macrophage

Pulmonary alveolar macrophages were isolated from adult, male New Zealand white rabbits by bronchial lavage and exposed to cadmium chloride in vitro. The observed cell sensitivity to this metal was highly dependent upon the incubation conditions used as well as the cytotoxic index selected. An LC50 value, as measured by dye exclusion (erythrosin B), was determined to be 390 microM when these cells were exposed to cadmium in Ham's F12 culture medium for 8 hr at 35 degrees C. The presence of fetal calf serum in the medium (10%; v/v) enhanced this toxicity slightly, LC50 = 235 microM, as did raising the incubation temperature to 37 degrees C, LC50 = 201 microM. No effect on cadmium toxicity was observed when the culture medium was made deficient in Cu, Zn, and Fe, nor was there any effect observed when Hepes buffer was substituted for the bicarbonate/carbon dioxide buffering system. Measurements of cadmium-109 uptake by pulmonary alveolar macrophages were consistent with and could explain, at least in part, the above observations of cytotoxicity. In the standard culture system (an 8-hr exposure period at 35 degrees C in Ham's F12 culture medium plus serum), the appearance in the culture medium of two lysosomal enzyme activities, acid phosphatase and cathepsin D, paralleled cell death. In addition, an EC50 value of 102 microM was found for cadmium when cell respiration (O2 uptake) was measured; an EC50 value of 31 microM was found for cadmium when cell function (engulfment of killed yeast particles) was followed; and scanning electron microscopic studies showed cell membrane changes (loss of fine structure and blebbing) at cadmium concentrations as low as 30 microM. These findings suggest that loss of cell function and/or changes in cell morphology are more sensitive measurements of macrophage exposure to cadmium than is either cell death, lysosomal enzyme release, or cell respiration.

Cadmium/zinc relationships in kidney cortex and metallothionein of horse and red deer: histopathological observations on horse kidneys

Cadmium and zinc were determined in kidney cortex of 63 horses and 51 red deer (Cervus elaphus). Cadmium and zinc were also determined in protein fractions obtained by Sephadex chromatography of kidney cortex from 10 horses and 4 red deer. Histopathological parameters in kidney cortex of horses were compared to cadmium content. The metal contents (on wet weight basis) in kidney cortex of the horses were 0.31 +/- 0.22 mmole Cd/kg (range 0.03-1.21) and 0.63 +/- 0.17 mmole Zn/kg (range 0.36-1.23). The Zn content increased with the Cd content, the Zn increase being less at higher concentrations. No significant increase of the Cd content with age of the horses (range 2-19 years) was found. The metal contents in kidney cortex of the red deer were 0.030 +/- 0.031 mmole Cd/kg (range 0.002-0.13) and 0.51 +/- 0.37 mmole Zn/kg (range 0.30-2.82). Here the Zn content did not increase significantly with Cd content, and in this case a positive linear relation of Cd content with age of the deer (range 0-11 years) was observed. The molar Zn/Cd ratio in the metallothionein fractions of horse kidney cortex was less variable at higher Cd contents. All Cd and the increase of Zn above an average basal level of 0.36 mmole Zn/kg was recovered in the metallothionein fractions. No gross histopathological changes could be observed in kidney cortex of the horses. Nevertheless a slight increase of the thickness of the basement membrane of Bowman's Capsule and also of the diameter of Bowman's Capsule in relation to Cd content up to 0.3 mmole/kg could be observed.

Conceptual problems in establishing the critical concentration of cadmium in human kidney cortex

The definition of the "critical concentration" for cadmium is compared with the concepts used to establish this measure in some recent publications. The term has not been clearly defined on a population basis and this has given rise to certain confusion. Different groups of investigators therefore have arrived at different estimates of the "critical concentration" for cadmium in human kidney cortex. A new measure, the "population critical concentration" (PCC) with a clearly defined response rate, is suggested. A reanalysis of the published data indicates that the PCC-10 (10% response rate) for cadmium in kidney cortex is likely to be in the range 180-220 micrograms/g and the PCC-50 is likely to be about 25% higher.