Effect of chromium picolinate on histopathological alterations in STZ and neonatal STZ diabetic rats

Earlier studies from our laboratory have indicated insulin sensitizing action of chromium picolinate as the mechanism of its anti-diabetic activity in experimental models of type I and type II diabetes. In the present investigation, we have evaluated the effects of chronic administration of chromium picolinate on the functional and histological alterations of streptozotocin (STZ)-induced diabetes in rats. Type I diabetes was induced by intravenous injection of STZ (40 mg/kg) in adult rats, whereas, type II diabetes was induced by intraperitoneal injection of STZ (90 mg/kg) in 2-day old rat pups which in adulthood develop abnormalities resembling type II diabetes. Chromium picolinate was administered at 8 μg/ml in drinking water for 6 weeks and was found to improve glucose tolerance and increase insulin sensitivity of STZ-diabetic rats. This treatment decrease elevated serum creatinine and urea levels as well as elevated serum levels of hepatic enzymes of both groups of diabetic rats. Histopathological studies of kidney and liver show decrease in the intensity and incidence of vacuolations, cellular infiltration and hypertrophy of STZ and nSTZ (neonatal STZ) diabetic rats. Chronic treatment with chromium picolinate however, did not alter the normal function or morphology of control rats. Chronic chromium picolinate at the therapeutic doses that improved glucose tolerance, was observed to have no hepatotoxic or nephrotoxic potential. It was rather found to improve renal and hepatic function and to reduce abnormalities associated with STZ-diabetes. Chromium picolinate could play an important role in the long term management of diabetes mellitus.     

Effects of Aronia melanocarpa and Hypericum perforatum aqueous extracts on hexavalent chromium induced toxicity in rat’s thyrocytes

BackgroundHexavalent chromium known as oxidizing agent is able to form reactive oxygen species. Aronia melanocarpa and Hypericum perforatum are two plants known for their antioxidant effects. Our study aimed to establish if CrVI induces apoptosis and structural changes in thyrocytes and if its effect can be counteracted by the administration of both extracts.Materials and methodsWistar rats divided in five groups: C - distilled water (DW), Cr – 75 mg/L CrVI in DW for 3 months, Cr 2 – 75 mg/L CrVI in DW for 3 months followed by 1 month DW, CrA – 3 months 75 mg/L CrVI in DW and 1 month Aronia 2.5% extract, CrH – 3 months 75 mg/L CrVI in DW and 1 month Hypericum 2.5% extract. Histological assessment and qRT-PCR for evaluation of BAX and Bcl2 protein levels performed on thyroid samples.ResultsThe Cr and Cr2 groups were those with altered cytoarchitecture: increase in the diameter of many thyroid follicles, a decrease in their number, a decrease in the height of the follicular cells. The histological examination of the CrH group revealed almost recovery of structural architecture. The BAX gene levels were higher in the Cr and Cr2 groups indicating the apoptotic activity of chromium. In extract receiving groups the BAX gene expressions were significantly lower, but the lowest level presented the CrH group. Bcl2 gene expression levels indicate antiapoptotic activity being elevated in the Cr group, followed by CrA, Cr2, and CrH groups. The BAX/Bcl2 ratio which significantly increased in the case of the Cr and Cr2 group compared to the groups that were administered the two plant extracts.ConclusionThe results obtained in this study confirm that CrVI has toxic effects on thyroid endocrine cells and H. perforatum has stronger antioxidant properties against the action of hexavalent chromium in thyrocytes than A. melanocarpa.     

Phenotypic expression of Vogesella indigofera upon exposure to hexavalent chromium,Cr6+

A eubacterium producing a blue pigment was isolated from a drinking water filter, and subsequently identified as Vogesella indigofera. This bacterium was further investigated for its morphological and biochemical characteristics after exposure to hexavalent chromium, Cr⁶⁺. The threshold Cr⁶⁺ concentration inhibiting the pigment production by V. indigofera was 200–300 g ml^–1 in liquid cultures of nutrient broth and 100–150 g ml^–1 on nutrient agar plates. The Cr⁶⁺ concentration preventing V. indigofera growth was 300–400 g ml^–1 in liquid cultures, but greater than 150 g ml^–1 on agar plates. Moreover, rugose colonies without the blue pigmentation were observed on agar plates amended with 150 (g Cr⁶⁺) ml^–1. The biochemical utilization profiles of the colonies without pigmentation did not differ from the original pigment-producing ones, indicating phenotypic plasticity of this bacterium. The difference of phenotypic expression of V. indigofera under various Cr⁶⁺ concentrations might have potential application as a pollution bioindicator for heavy metals.     

Reduction of Cr(VI) by cysteine: Significance in human lymphocytes and formation of DNA damage in reactions with variable reduction rates

The induction of genotoxicity by Cr (VI) is dependent on its reductive activation inside the cell. Our recent studies have found that reduction of Cr (VI) by cysteine resulted in the formation of mutagenic Cr (III)-DNA adducts in the absence of oxidative DNA damage. In this work, we examined the formation of oxidative and Cr (III)-dependent types of DNA damage under a broader range of Cr (VI) and cysteine concentrations and investigated a potential role of this reducer in intracellular metabolism of Cr (VI). Peripheral lymphocytes from unexposed humans had 7.8-fold excess of glutathione over cysteine, whereas lymphocytes from stainless steel welders contained only 3 times higher amount of glutathione (p = 0.0009) which was entirely caused by the decrease in the concentration of glutathione. A strong correlation (r = 0.72) between the levels of both thiols was found in lymphocytes from controls. The number of DNA-protein crosslinks in lymphocytes from welders was 4.1 times higher than among controls, indicating the presence of Cr (VI)-dependent DNA damage. The average rate of Cr (VI) reduction by cysteine was approximately 5 times faster than that by glutathione. Higher reduction rate combined with the decrease in the intracellular concentration of glutathione should make cysteine a predominant Cr (VI)-reducing thiol in lymphocytes of welders. Analysis of the initial rates of Cr (VI) reduction by different concentrations of cysteine suggested the presence of one- and two-electron pathways, with one-electron mechanism dominating in the physiological range of concentrations. There was no detectable formation of DNA breaks or abasic sites under a broad range of Cr (VI) and cysteine concentrations, resulting in up to 68-fold differences in the rates of reduction and the production of as many as 3 Cr (III)-DNA adducts per 10 bp. The reactions with slow reduction rates (low concentrations of cysteine) led to the most extensive formation of Cr (III)DNA adducts. In summary, these results further establish Cr (III)-DNA adducts as the major form of DNA damage resulting from Cr (VI) metabolism by cysteine. The role of cysteine in reduction of Cr (VI) becomes more significant under conditions of occupational exposure to Cr (VI)-containing welding fumes.     

CR (VI) induces cell growth arrest through hydrogen peroxide‐mediated reactions

Cr (VI) compounds are widely used in industries and are recognized human carcinogens. The mechanism of carcinogenesis associated with these compounds is not well understood. The present study focused on Cr (VI)induced cell growth arrest in human lung epithelial A549 cells, using flow cytometric analysis of DNA content. Treatment of the cells with Cr (VI) at 1 M caused a growth arrest at G₂/M phase. An increase in Cr (VI) concentration enhanced the growth arrest. At a concentration of 25 M, Cr (VI)induced apoptosis became apparent. Superoxide dismutase (SOD) or sodium formate did not alter the Cr (VI)induced cell growth arrest. While catalase inhibited growth, indicating H₂O₂ is an important mediator in Cr (VI)induced G₂/M phase arrest. Electron spin resonance (ESR) spin trapping measurements showed that incubation of cells with Cr (VI) generated hydroxyl radical (OH). Catalase inhibited the OH radical generation, indicating that H₂O₂ was generated from cells stimulated by Cr (VI), and that H₂O₂ functioned as a precursor for OH radical generation. The formation of H₂O₂ from Cr (VI)stimulated cells was also measured by the change in fluorescence of scopoletin in the presence of horseradish peroxidase. The mechanism of reactive oxygen species generation involved the reduction of molecular oxygen as shown by oxygen consumption assay. These results support the following conclusions: (a) Reactive oxygen species are generated in Cr (VI)stimulated A549 cells through reduction of molecular oxygen, (b) Among the reactive oxygen species generated, H₂O₂ played a major role in causing G₂/M phase arrest in human lung epithelial cells.     

Hexavalent chromium reduction by an actinomycete, Arthrobacter crystallopoietes ES 32

Environmental contamination by hexavalent chromium, Cr(VI), presents a serious public health problem. This study assessed the reduction of Cr(VI) by intact cells and a cell-free extract (CFE) of an actinomycete, Arthrobacter crystallopoietes (strain ES 32), isolated from soil contaminated with dichromate. Both intact cells and CFE of A. crystallopoietes, displayed substantial reduction of Cr(VI). Intact cells reduced about 90% of the Cr(VI) added within 12 h and Cr(VI) was almost completely reduced after 24 h. The K _M and V _max of Cr(VI) bioreduction by intact cells were 2.61 μM and 0.0142 μmol/min/mg protein, respectively. Cell-free chromate reductase of the A. crystallopoietes (ES 32) reduced hexavalent chromium at a K _M of 1.78 μM and a V _max of 0.096 μmol/min/mg protein. The rate constant (k) of chromate reduction was inversely related to Cr(VI) concentration and the half-life (t _1/2) of Cr(VI) reduction increased with increasing concentration. A. crystallopoietes produced a periplasmic chromate reductase that was stimulated by NADH. Results indicate that A. crystallopoietes ES 32 can be used to detoxify Cr(VI) in polluted sites, particularly in stressed environments.     

A nearly symmetric trinuclear chromium(III) oxo carboxylate assembly: preparation, molecular and crystal structure, and magnetic properties of [Cr3O(O2CPh)6(MeOH)3](NO3) · 2MeOH

Complex [Cr₃O(O₂CPh)₆(MeOH)₃](NO₃) · 2MeOH (1 · 2MeOH) has been synthesized from the one-pot reaction between Cr(NO₃)₃ · 9H₂O and NaO₂CPh in MeOH. The structure of the complex has been solved by single-crystal X-ray crystallography. It crystallizes in the monoclinic space group P2₁/n with a=14.716(6) Å, b=22.569(8) Å, c=15.755(6) Å, β=95.02(1)°, V=5212.5(4) ų and Z=4. Although the cation does not possess any crystallographically imposed symmetry element, its {Cr₃(μ₃-O)} core is nearly symmetric. Each Cr^III…Cr^III vector is further bridged by two η¹:η¹:μ₂ benzoates, with a terminal MeOH molecule completing octahedral coordination at each metal ion. The crystal structure consists of layers that are parallel to (0 1 0) crystallographic plane and are formed through π-π stacking interactions and hydrogen bonds. Variable-temperature magnetic susceptibility and solid-state ¹H NMR studies indicate that the total spin value of the ground state is 1/2. EPR experiments reveal the existence of a distribution of trimers with axial anisotropy in the g tensor.     

Interactive effects of selenium and chromium on mammary tumor development and growth in MMTV-infected female mice and their relevance to human cancer

Evidence for interactive effects of chromium and selenium on the appearance of mammary tumors was obtained by exposing female virgin C₃H mice infected with the murine mammary tumorvirus (MMTV) to subtoxic levels of Cr [as Cr(III) nitrate] and Se (as sodium selenite) in the supply water. Cr counteracted the inhibitory effect of Se on tumor development in a dose-dependent manner, shortened the tumor latency period, and accelerated tumor growth rates. Exposure to Cr also altered the levels of Se in the liver and kidneys of the mice, indicating that Cr interacts with Se and affects its organ distribution. Chromium must be added to the list of Se-antagonistic elements that weaken or abolish the antitumorigenic effects of Se. These findings are relevant to human cancer as previous studies revealed the age-corrected mortalities from breast and other major forms of cancer in different countries to be inversely correlated with the dietary Se intakes, and directly correlated with the estimated intakes of Cr and of other Se-antagonistic elements. The presence of these elements in foods must be taken into account when estimating the optimal dose of supplemental Se for cancer risk reduction.     

Multiple biomarker response in rainbow trout during exposure to hexavalent chromium

This research investigated hexavalent chromium toxicity in rainbow trout using a panel of biomarkers at different levels of biological organization. A time-course experiment in which rainbow trout were exposed in hard water (63.5 mg/L CaCO3) to a sublethal concentration of hexavalent chromium (10 mg/L) for a period of 28 days was conducted. The responses of multiple biomarkers were measured in gill and liver tissues at varying time points. Significant differences in metallothionein induction, superoxide dismutase activity, lipid peroxidation, cellular morphology, and growth were observed. Results indicated that gill tissues were more sensitive than hepatic tissues to chromium toxicity, yet hepatic tissues appeared to play a larger role in the organism's adaptive response to chromium compared to gill tissues. This study highlights the importance of using a set of integrated biomarkers to assess contaminant exposure and effects.     

Removal of Cr(VI) from ground water by Saccharomyces cerevisiae

Chromium can be removed from ground water by the unicellular yeast, Saccharomyces cerevisiae. Local ground water maintains chromium as CrO₄ ^2- because of bicarbonate buffering and pH and E _h conditions (8.2 and +343 mV, respectively). In laboratory studies, we used commercially available, nonpathogenic S. cerevisiae to remove hexavalent chromium [Cr(VI)] from ground water. The influence of parameters such as temperature, pH, and glucose concentration on Cr(VI) removal by yeast were also examined. S. cerevisiae removed Cr(VI) under aerobic and anaerobic conditions, with a slightly greater rate occurring under anaerobic conditions. Our kinetic studies reveal a reaction rate (V_max) of 0.227 mg h^-1 (g dry wt biomass)^-1 and a Michaelis constant (Km) of 145 mg/l in natural ground water using mature S. cerevisiae cultures. We found a rapid (within 2 minutes) initial removal of Cr(VI) with freshly hydrated cells [55–67 mg h^-1 (g dry wt biomass)^-1] followed by a much slower uptake [0.6–1.1 mg h^-1 (g dry wt biomass)^-1] that diminished with time. A materials-balance for a batch reactor over 24 hours resulted in an overall shift in redox potential from +321 to +90 mV, an increase in the bicarbonate concentration (150–3400 mg/l) and a decrease in the Cr(VI) concentration in the effluent (1.9-0 mg/l).