Assessment of DNA Methylation and Oxidative Changes in the Heart and Brain of Rats Receiving a High-Fat Diet Supplemented with Various Forms of Chromium

Is chromium(III) supplementation beneficial for dietary rodent models of prediabetes?

Chromium as the trivalent ion is believed to pharmaceutically active, increasing insulin sensitivity in high doses in genetic rodent models of diabetes. However, contradictory results have been obtained chemical rodent models of diabetes. The current review analyses the effects of dietary Cr supplementation of rodent models of prediabetes, where the condition is administered using a high-fat or high-sugar diet. Rat model studies display a range of quality, with studies utilizing basal diets of known Cr content suggesting Cr beneficially affects insulin sensitivity. Mouse model studies display too much heterogeneity in results for any firm conclusions to be drawn. Comparison of these results with those of clinical trials suggest that the effective dose of Cr may be proportionally lower for rodents than humans, if one exists for humans.

Chromium nanoparticles improve bone turnover regulation in rats fed a high-fat, low-fibre diet

The aim of the study was to investigate the effect of returning to a balanced diet combined with chromium picolinate (CrPic) or chromium nanoparticles (CrNPs) supplementation at a pharmacologically relevant dose of 0.3 mg/kg body weight on the expression level of selected genes and bone turnover markers in the blood and bones of rats fed an obese diet. The results of the study showed that chronic intake of a high-fat obesogenic diet negatively affects bone turnover by impairing processes of both synthesis and degradation of bones. The switch to a healthy diet proved insufficient to regulate bone metabolism disorders induced by an obesogenic diet, even when it was supplemented with chromium, irrespective of its form. Supplementation with CrPic with no change in diet stimulated bone metabolism only at the molecular level, towards increased osteoclastogenesis (bone resorption). In contrast, CrNPs added to the high-fat diet effectively regulated bone turnover by increasing both osteoblastogenesis and osteoclastogenesis, with these changes directed more towards bone formation. The results of the study suggest that unfavourable changes in bone metabolism induced by chronic intake of a high-fat diet can be mitigated by supplementation with CrNPs, whereas a change in eating habits fails to achieve a similar effect.

Chromium Nanoparticles Together with a Switch Away from High-Fat/Low-Fiber Dietary Habits Enhances the Pro-Healthy Regulation of Liver Lipid Metabolism and Inflammation in Obese Rats

The study on Wistar rats was conducted to investigate the effects of a pharmacologically relevant dose 0.3 mg/kg body weight of chromium supplementation (commonly used picolinate or novel form as nanoparticles) and switching away from obesogenic dietary habits on the parameters of lipid metabolism, inflammation, and oxidative stress in liver and plasma. Favorable effects related to dietary changes from the obesogenic diet were considerably enhanced when the diet was supplemented with chromium nanoparticles. This combination exerted the strongest fat content and cholesterol reduction in the liver. Moreover, in this group, a favorable antioxidative effect was observed through GSH/GSSG elevation in the liver as well as ALT activity reduction in the plasma and IL-6 levels in the liver. The molecular mechanisms associated with regulating lipid metabolism, oxidative stress and inflammation might be related to lower expression of HIF-1α, COX-2, and LOX-1 and upregulation of PPARα in the liver. Supplementation with chromium nanoparticles without changes in the obesogenic diet also favorably affected lipid metabolism and oxidative stress in the liver; however, the examined effects were moderate. In conclusion, the favorable effects of switching from an obesogenic to a balanced diet on hepatic lipid metabolism, oxidative stress, and inflammation induced by an obesogenic diet might be enhanced by supplementation with chromium nanoparticles.

Association of environmental exposure to chromium with differential DNA methylation: An epigenome-wide study

Introduction: Previous studies have reported that chromium (Cr)-induced epigenetic alterations and DNA methylation play a vital role in the pathogenesis of diseases induced by chromium exposure. Epigenomic analyses have been limited and mainly focused on occupational chromium exposure; their findings are not generalizable to populations with environmental Cr exposure. Methods: We identified the differential methylation of genes and regions to elucidate the mechanisms of toxicity related to environmental chromium exposure. DNA methylation was measured in blood samples collected from individuals in Cr-contaminated (n = 10) and unexposed areas (n = 10) by using the Illumina Infinium HumanMethylation850K array. To evaluate the relationship between chromium levels in urine and CpG methylation at 850 thousand sites, we investigated differentially methylated positions (DMPs) and differentially methylated regions (DMRs) by using linear models and DMRcate method, respectively. The model was adjusted for biologically relevant variables and estimated cell-type compositions. Results: At the epigenome-wide level, we identified five CpGs [cg20690919 (p _{FDR =}0.006), cg00704664 (p _{FDR =}0.024), cg10809143 (p _{FDR =}0.043), cg27057652 (p _{FDR =}0.047), cg05390480 (p _{FDR =}0.024)] and one DMR (chr17: 19,648,718-19,648,972), annotated to ALDH3A1 genes (p < 0.05) as being significantly associated with log₂ transformed urinary chromium levels. Discussion: Environmental chromium exposure is associated with DNA methylation, and the significant DMPs and DMR being annotated to cause DNA damage and genomic instability were found in this work. Research involving larger samples is required to further explore the epigenetic effect of environmental chromium exposure on health outcomes through DNA methylation.

Dietary Effects of Chromium Picolinate and Chromium Nanoparticles in Wistar Rats Fed with a High-Fat, Low-Fiber Diet: The Role of Fat Normalization

We aimed to evaluate how feeding a high-fat-low-fiber (F) diet to rats and dietary intervention with the implementation of a standard-fat-and-fiber (S) diet affects the response of the cardiovascular system to chromium (III) picolinate (Cr-Pic) and, alternatively, chromium nanoparticles (Cr-NPs). Young male Wistar Han rats (n/group = 12) from either the fatty group (18 weeks on F diet) or the intervention group (9 weeks on F diet + 9 weeks on S diet) received a pharmacologically relevant dose of 0.3 mg Cr/kg body weight in the form of Cr-Pic or Cr-NPs for 9 weeks. Our study on rats confirmed the pro-inflammatory effect of an F diet administered for 18 weeks. In the intervention group, both Cr-Pic and Cr-NPs decreased heart glutathione ratio (GSH+GSSG), enhanced participation of nitric oxide (NO) derived from inducible NO synthase (iNOS) in vascular relaxation to acetylcholine (ACh), increased the vasodilator net effect of cyclooxygenase-2 (COX-2)-derived prostanoids, and increased the production of superoxide anion (O₂^.-) in aortic rings. Meanwhile, in the fatty group, there was increased heart superoxide dismutase (SOD), decreased heart catalase (CAT), and reduced sensitivity in pre-incubated aortic rings to endogenous prostacyclin (PGI₂). The factors that significantly differentiated Cr-NPs from Cr-Pic were (i) decreased blood antioxidant capacity of water-soluble compounds (0.75-fold, p = 0.0205), (ii) increased hydrogen peroxide (H₂O₂) production (1.59-fold, p = 0.0332), and (iii) modified vasodilator response due to PGI₂ synthesis inhibition (in the intervention group) vs. modified ACh-induced vasodilator response due to (iv) COX inhibition and v) PGI₂ synthesis inhibition with thromboxane receptor blockage after 18 weeks on F diet (in the fatty group). Our results show that supplementation with Cr-Pic rather than with Cr-NPs is more beneficial in rats who regularly consumed an F diet (e.g., for 18 weeks). On the contrary, in the intervention group (9 weeks on F diet + 9 weeks of dietary fat normalization (the S diet)), Cr-Pic and Cr-NPs could function as pro-oxidant agents, initiating free-radical reactions that led to oxidative stress.

Oxidative, epigenetic changes and fermentation processes in the intestine of rats fed high-fat diets supplemented with various chromium forms

The aim of the study was to determine how feeding rats a high-fat diet (F) supplemented with various forms of chromium affects the responses of the immune and redox systems, as well as epigenetic changes in the ileal tissue and the course of fermentation processes in the caecum. The rats received a pharmacologically relevant dose 0.3 mg Cr/kg body weight in form of chromium(III) picolinate (Cr-Pic), chromium (III)-methionine (Cr-Met), or chromium nanoparticles (Cr-NPs). The F increased DNA oxidation and raised the level of interleukin IL-6. The F was shown to reduce the intensity of fermentation processes in the caecum while increasing the activity of potentially harmful enzymes in the faeces. The addition of Cr in the form of Cr-NPs and Cr-Met in rats fed F beneficially increased mobilization of enzymes of the DNA repair pathway. All forms of Cr, but especially Cr-NPs, beneficially decreased the activity of caecal bacterial β-glucuronidase, faecal β-glucosidase and β-glucuronidase. However, due to the increase in level of cytokine IL-2 in small intestinal wall, induced by all tested forms of chromium, it is difficult to state conclusively that this element can mitigate unfavourable pro-inflammatory and oxidative changes induced by a F in the small intestinal wall.

Effect of a high-fat diet and chromium on hormones level and Cr retention in rats

AIMS

The aim of the study was to determine how the administration of a high-fat diet supplemented with various forms of chromium to rats affects accumulation of this element in the tissues and levels of leptin, ghrelin, insulin, glucagon, serotonin, noradrenaline and histamine, as well as selected mineral elements.

METHODS

The experiment was conducted on 56 male Wistar rats, which were divided into 8 experimental groups. The rats received standard diet or high fat diet (HFD) with addition of 0.3 mg/kg body weight of chromium(III) picolinate (Cr-Pic), chromium(III)-methioninate (Cr-Met), or chromium nanoparticles (Cr-NP).

RESULTS

Chromium in organic forms was found to be better retained in the body of rats than Cr in nanoparticles form. However, Cr-Pic was the only form that increased the insulin level, which indicates its beneficial effect on carbohydrate metabolism. In blood plasma of rats fed a high-fat diet noted an increased level of serotonin and a reduced level of noradrenaline. The addition of Cr to the diet, irrespective of its form, also increased the serotonin level, which should be considered a beneficial effect. Rats fed a high-fat diet had an unfavourable reduction in the plasma concentrations of Ca, P, Mg and Zn. The reduction of P in the plasma induced by supplementation with Cr in the form of Cr-Pic or Cr-NP may exacerbate the adverse effect of a high-fat diet on the level of this element.

CONCLUSION

A high-fat diet was shown to negatively affect the level of hormones regulating carbohydrate metabolism (increasing leptin levels and decreasing levels of ghrelin and insulin).

Chromium induced neurotoxicity by altering metabolism in zebrafish larvae

BACKGROUND

Recently, both trivalent chromium Cr (III) and hexavalent chromium Cr (VI) have been reported to produce neurotoxicity. However, the underlying mechanisms of the neurotoxicity caused by different chemical valence of chromium remain unclear.

OBJECTIVE

The purpose of this study was to investigate the mechanism of neurotoxicity induced by exposure to chromium with different valence states based on metabolic disturbance in zebrafish larvae.

METHODS

Zebrafish embryos were exposed to 1 mg/L Cr (III) and 1 mg/L Cr (VI) for 120 hpf respectively. The related indexes of neural development were observed by stereoscope and behavior analysis system. 8OH-dG were detected using enzyme-linked immunosorbent assay. The generation of reactive oxygen species was detected using an oxidant-sensing probe 2',7'-dichlorodihydrofluorescein diacetate. AChE activity was determined by a colorimetric assay based on hydrolysis of acetylcholine. The expression levels of neurodevelopmental genes and methyltransferase genes in juvenile zebrafish was analyzed by real-time PCR. The methylation status of neurogenin1 and neurod1 genes was detected by bisulfite sequencing PCR. The binding of H3K27me3 was detected by chromatin immunoprecipitation-qPCR. Metabolic profiles and one carbon metabolic analysis were performed by UPLC-MS.

RESULTS

There were no significant differences in survival rate, hatching rate and spontaneous movement of zebrafish in both Cr-exposed groups compared to the control. The malformation rate in Cr (VI) -exposed group was obviously increased compared to the control and Cr (III) -exposed group. At 48hpf and 72hpf of exposure, the embryonic heart rate in Cr (III)-exposed group was significantly higher than that of Cr (VI)-exposed group and the control. At 120hpf, zebrafish in both Cr-exposed groups exhibited decreasing changes in swimming distance and disturbance of sensitivity to light and dark. 8OH-dG in Cr (VI)-exposed group were significantly higher than that in the control. The generation of ROS in both Cr -exposed groups was significantly higher than that in the control. The activity of AchE was significantly decreased in both Cr-exposed groups compared to the control. Most of early neurogenesis related genes, such as α-tubulin, elavl3, gap43, sox19b, neurogenin1 and neurod1 in Cr-exposed groups were significantly up-regulated compared to those in the control. The expression of dnmt1 and dnmt3 genes was significantly down-regulated in both Cr-exposed groups. BSP-PCR results showed that genic sequences in the neurogenin1 and neurod1 genes have lower levels of DNA methylation in both Cr-exposed groups, especial in Cr (VI)-exposed group. ChIP analysis showed that there was a decrease in H3K27me3 binding within the corresponding region of neurogenin1 in both Cr-exposed groups and that of neurod1 in Cr (III)-exposed group. Untargeted metabolomic analysis showed that significant changes in metabolites induced by Cr exposure were associated with differences in primary bile acid biosynthesis, phospholipid biosynthesis (phosphatidylcholine biosynthesis and phosphatidylethanolamine biosynthesis), linoleic acid metabolism, arachidonic acid metabolism, amino acid metabolism, purine metabolism, betaine metabolism, spermidine and spermine biosynthesis, and folate metabolism, the last four of which are related to one carbon metabolism. Targeted analysis of one carbon metabolites (5-MT, Gly, Met, SAH and Hcy) related with folate cycle and methionine metabolism were significantly decreased upon Cr exposure. The elevated SAM to SAH ratio in both Cr- exposed group indicated the decreasing capacity for methylation reaction.

CONCLUSION

Cr (III) and Cr (VI) can induce neurotoxicity by interfering with one carbon metabolism and affecting DNA methylation and histone methylation to regulate the expression of neuro-related genes. Cr exposure also influenced primary bile acid biosynthesis and phospholipid biosynthesis, which are associated with neuroprotective effects and need to be further validated.

Effects of Different Chromium Compounds on Hematology and Inflammatory Cytokines in Rats Fed High-Fat Diet

The aim of the study was to determine how a high-fat diet supplemented with various forms of chromium affects hematological and immune parameters of the blood of rats. The rats received a standard diet or a high-fat diet supplemented with chromium at 0.3 mg/kg body weight (BW) in the form of chromium(III) picolinate, chromium(III)-methionine or nano-sized chromium. Selected hematological parameters were determined in the blood of the rats, including total white blood cell (WBC) count, leukogram, red blood cell (RBC) count, hemoglobin level (HGB), hematocrit (HCT), platelet count (PLT) and platelet percentage (PCT), as well as immune parameters: levels of immunoglobulins A and E (IgA and IgE), interleukin-6 (IL-6), interleukin-2 (IL-2), and tumor necrosis factor α (TNF-α); activity of ceruloplasmin (Cp); and levels of caspase 3 and 8 (Casp3 and Casp8). Feeding rats a high-fat diet increased blood markers of induction of inflammation, ie pro-inflammatory cytokines IL-6 and TNF-α, and also significantly increased IgE. The diet had no effect on the blood count, except for an increase in the number of neutrophils. The chromium compounds tested, particularly Cr-Met and Cr-NPs, stimulated the immune system of the rats, as indicated by increased concentrations of IgA, IgE, IL-2, IL-6, TNF-α, and Cp. Given the increase in inflammatory mediators induced by chromium, it should not be used to mitigate the effects of a high-fat diet. Moreover, chromium picolinate and chromium nanoparticles were shown to increase the content of caspase 3 and 8 in the blood of rats, which indicates a pro-apoptotic effect. The effects of the use of chromium nanoparticles include reductions in the WBC count and in the thrombocyte count (leuko- and thrombopenia). Taking account these data the use of chromium as dietary supplement should be reconsidered.