Hexavalent chromium exposure induces lung injury via activation of NLRP3 and AIM2 inflammasomes in rats

Hexavalent chromium (Cr(VI)) has been identified as a Class I human carcinogen, but its carcinogenic mechanism is currently unclear. There is still a lack of understanding of its associations with early pulmonary inflammatory damages. Inflammation is an important stage before the occurrence of tumors, and under the long-term stimulation of inflammation, it can promote the development of tumors. In this study, the aim is to explore the effect of Cr(VI) exposure on pulmonary inflammation and its relationship with the mechanism of inflammation cancer transformation. We established a Cr(VI) exposure model in SD rats using tracheal instillation of potassium dichromate solution, and collected samples at the time of cessation of exposure and 14 days after cessation of exposure. Analyzing the experimental results, it was found that the lung index increased after exposure to Cr(VI), promoting the occurrence of apoptosis in lung tissue cells and exacerbating lung tissue damage. The damage situation improved after exposure termination; Inductively coupled plasma mass (ICPRQ) spectrometer detection found that the exposed group had significantly increased levels of blood chromium, blood manganese, blood copper, blood arsenic, urine chromium, urine copper, and urine lead; After two weeks of repair, blood chromium and blood manganese levels were significantly lower than those in the same dose group of the exposure group, while blood copper levels were significantly higher than those in the same dose group of the exposure group. There was no significant difference in blood arsenic levels between the exposure group and the exposure group. Urine chromium and urine lead levels were significantly lower than those in the same dose group of the exposure group, while urine copper levels only increased. At the same time, it was found that Cr(VI) exposure caused disruption of oxidative stress levels in rat lung tissues. After 14-day exposure, Cr(VI) significantly decreased and oxidative stress levels significantly decreased. Further investigation revealed that Cr(VI) induces activation of inflammasomes NLRP3, AIM2, and their signaling pathways in lung inflammatory injuries, but this condition persists even after cessation of exposure. The study suggested that in hexavalent chromium induced lung tissue injuries in rats, NLRP3 and AIM2 inflammasomes and their signaling pathways activation. Furthermore, the characteristic of sustained activation after cessation of exposure was also indicated. These results provide new ideas and references for further elucidating the mechanisms of Cr(VI), lung inflammation and inflammation cancer transformation.

Cellular senescence mediates hexavalent chromium-associated lung function decline: Insights from a structural equation Model

There is sufficient evidence suggesting that exposure to hexavalent chromium [Cr(VI)] can cause a decline in lung function and the onset of lung diseases. However, no studies have yet explored the underlying mechanisms of these effects from various perspectives such as systemic inflammation, oxidative stress, and cellular senescence, simultaneously. This cross-sectional study was conducted among 304 workers engaged in chromate production and processing in China. Urine was used for detection of 8-hydroxy-2'-deoxyguanosine (8-OHdG) and 8-iso-prostaglandin F2α (8-iso-PGF2α), while RNA and DNA extraction from peripheral blood cells was used for detection of mRNA, telomere length, and ribosomal DNA copy numbers (rDNA CNs). A 2.7-fold elevation in blood chromate (Cr) corresponded to a 7.86% (95% CI: 2.57%, 13.42%) rise in urinary 8-OHdG and a 4.14% (0.02%, 8.42%) increase in urinary 8-iso-PGF2α, indicating that exposure to chromates can cause oxidative stress. Furthermore, strong correlations emerged between blood Cr concentration and mRNA levels of P16, P21, TP53, and P15 in the cellular senescence pathway. Simultaneously, a 2.7-fold elevation in blood Cr associated with a -5.47% (-8.72%, -2.1%) change in telomere length, while rDNA CNs (5S, 5.8S, 18S, and 28S) changed by -3.91% (-7.99%, 0.34%), -9.4% (-15.73%, -2.6%), -8.06% (-14.01%, -1.69%), and -5.86% (-10.67%, -0.78%), respectively. Structural equation model highlighted that cellular senescence exerted significant indirect effects on Cr(VI)-associated lung function decline, with a mediation proportion of 23.3%. This study provided data supporting for 8-iso-PGF2α, telomere length, and rDNA CNs as novel biomarkers of chromate exposure, emphasizing the significant role of cellular senescence in the mechanism underlying chromate-induced lung function decline.

Potential mechanisms of lung injury and repair after hexavalent chromium [Cr(VI)] aerosol whole-body dynamic exposure

Hexavalent chromium [Cr(VI)], known as "Top Hazardous Substances", poses a significant threat to the respiratory system. Nevertheless, the potential mechanisms of toxicity and the lung's repair ability after injury remain incompletely understood. In this study, Cr(VI) aerosol whole-body dynamic exposure system simulating real exposure scenarios of chromate workers was constructed to evaluate the lung injury and repair effects. Subsequently, miRNA sequencing, mRNA sequencing and metabolomics analyses on lung tissue were performed to explore the underlying mechanisms. Our results revealed that Cr(VI) exposure led to an increase in lactic dehydrogenase activity and a time-dependent decline in lung function. Notably, after 13 w of Cr(VI) exposure, alveolar hemorrhage, thickening of alveolar walls, emphysema-like changes, mitochondrial damage of alveolar epithelial cells and macrophage polarization changes were observed. Remarkably, a two-week repair intervention effectively ameliorated lung function decline and pulmonary injury. Furthermore, significant disruptions in the expressions of miRNAs and mRNAs involved in oxidative phosphorylation, glycerophospholipid metabolism and inflammatory signaling pathways were found. The two-week repair period resulted in the reversal of expression of oxidative phosphorylation related genes, and inhibited the inflammatory signaling pathways. This study concluded that the inhibition of the mitochondrial oxidative phosphorylation pathway and the subsequent enhancement of inflammatory response might be key mechanisms underlying Cr(VI) pulmonary toxicity, and timely cessation of exposure could effectively alleviate the pulmonary injury. These findings shed light on the potential mechanisms of Cr(VI) toxicity and provide crucial insights into the health protection for occupational populations exposed to Cr(VI).

Hexavalent chromium caused DNA damage repair and apoptosis via the PI3K/AKT/FOXO1 pathway triggered by oxidative stress in the lung of rat

Hexavalent chromium [Cr(VI)] is an occupational carcinogen that accumulates in the lungs and causes lung injury and even lung cancer. 36 SD male rats received inhalable intratracheal instillation of Cr(VI) (0.05, 0.25 mg Cr/kg) or the same volume (3 ml/kg) of normal saline weekly for 28 days (total 5 times). After 28 days of exposure, half of the rats in each group were sacrificed for investigation, and the rest stopped exposure and began to be self-repaired for two weeks. Histopathology analyses revealed that Cr(VI) induced slight dilatation and hemorrhage of perialveolar capillaries, pulmonary bronchodilation, and congestion with peripheral flaky-like necrosis accompanied by inflammatory cell infiltration, especially the 0.25 mg Cr/kg group. Cr(VI) exposure caused the increase of blood Cr, urinary Cr, MDA, urinary 8-hydroxy-2' -deoxyguanosine (8-OHdG), and the decrease of GSH and MDA, while two-week repair only reduced urinary Cr. Exposure to Cr(VI) significantly upregulated FOXO1 and downregulated p-AKT and p-FOXO1 for two weeks. PI3K in the 0.25 mg Cr/kg group was inhibited after two weeks of repair. Cr(VI) exposure mainly promoted GADD45a and CHK2 in the exposure group, promoted Bim, Bax/Bcl-2, and suppressed Bcl-2 and Bcl-xL in the repair group. These results demonstrate that Cr(VI) may induce DNA damage repair and apoptosis in the lung by activating the PI3K/AKT/FOXO1 pathway. Two-week repair may alleviate oxidative stress and DNA damage induced by Cr(VI) exposure but couldn't eliminate its effects. This study provides a new perspective for exploring the Cr(VI) induced lung cancer mechanism.

Two-week repair alleviates hexavalent chromium-induced hepatotoxicity, hepatic metabolic and gut microbial changes: A dynamic inhalation exposure model in male mice

Hexavalent chromium [Cr(VI)] has been identified as a "Group I human carcinogen" with multisystem and multiorgan toxicity. A dynamic inhalation exposure model in male mice, coupled with the hepatic metabolome and gut microbiome, was used to explore hepatotoxicity, and hepatic metabolic and gut microbial changes under the exposure scenarios in the workspace and general environment. The present study set up an exposure group (EXP) that inhaled 150 μg Cr/m³ for 13 weeks, a control group (CONT) that inhaled purified air, as well as a two-week repair group (REXP) after 13 weeks of exposure and the corresponding control group (RCONT). Cr(VI) induced elevation of hepatic Cr accumulation, the ratio of ALT and AST, and folate in serum. Inflammatory infiltration in the liver and abnormal mitochondria in hepatocytes were also induced by Cr(VI). Glutathione, ascorbate, folic acid, pantetheine, 3'-dephospho-CoA and citraconic acid were the key metabolites affected by Cr(VI) that were associated with significant pathways such as pantothenate and CoA biosynthesis, hypoxia-inducible factor-1 signaling pathway, antifolate resistance, alpha-linolenic acid metabolism and one carbon pool by folate. g_Allobaculum was identified as a sensitive biomarker of Cr(VI) exposure because g_Allobaculum decreased under Cr(VI) exposure but increased after repair. The gut microbiota might be involved in the compensation of hepatotoxicity by increasing short-chain fatty acid-producing bacteria, including g_Lachnospiraceae_NK4A136_group, g_Blautia, and f_Muribaculaceae. After the two-week repair, the differential metabolites between the exposed and control groups were reduced from 73 to 29, and the KEGG enrichment pathways and differential microbiota also decreased. The mechanism for repair was associated with reversion of lipid peroxidation and energy metabolism, as well as activation of protective metabolic pathways, such as the AMPK signaling pathway, longevity regulating pathway, and oxidative phosphorylation. These findings might have theoretical and practical implications for better health risk assessment and management.

HBM4EU Chromates Study-Genotoxicity and Oxidative Stress Biomarkers in Workers Exposed to Hexavalent Chromium

A study was conducted within the European Human Biomonitoring Initiative (HBM4EU) to characterize occupational exposure to Cr(VI). Herein we present the results of biomarkers of genotoxicity and oxidative stress, including micronucleus analysis in lymphocytes and reticulocytes, the comet assay in whole blood, and malondialdehyde and 8-oxo-2′-deoxyguanosine in urine. Workers from several Cr(VI)-related industrial activities and controls from industrial (within company) and non-industrial (outwith company) environments were included. The significantly increased genotoxicity (p = 0.03 for MN in lymphocytes and reticulocytes; p < 0.001 for comet assay data) and oxidative stress levels (p = 0.007 and p < 0.001 for MDA and 8-OHdG levels in pre-shift urine samples, respectively) that were detected in the exposed workers over the outwith company controls suggest that Cr(VI) exposure might still represent a health risk, particularly, for chrome painters and electrolytic bath platers, despite the low Cr exposure. The within-company controls displayed DNA and chromosomal damage levels that were comparable to those of the exposed group, highlighting the relevance of considering all industry workers as potentially exposed. The use of effect biomarkers proved their capacity to detect the early biological effects from low Cr(VI) exposure, and to contribute to identifying subgroups that are at higher risk. Overall, this study reinforces the need for further re-evaluation of the occupational exposure limit and better application of protection measures. However, it also raised some additional questions and unexplained inconsistencies that need follow-up studies to be clarified.

Lung function assessment and its association with blood chromium in a chromate exposed population

Hexavalent chromium [Cr(VI)] and its compounds have been associated with various respiratory diseases, while few studies have attempted to determine its adverse effect on lung function. To explore the potential early indicators of health surveillance for respiratory diseases induced by chromate exposure, a longitudinal cohort study including 515 workers with 918 measurements across 2010-2017 was conducted to investigate the impact of individual internal exposure on lung function. Inductively coupled plasma mass spectrometry (ICP-MS) and spirometry were used to measure whole blood chromium (blood Cr) and lung function respectively. In the linear mixed-effects analysis, each 1- unit increase in Ln- transformed blood Cr was significantly associated with estimated effect percentage decreases of 1.80 (0.35, 3.15) % in FEV1, 0.77 (0.10, 1.43) % in FEV1/FVC, 2.78 (0.55, 4.98) % in PEF, and 2.73 (0.59, 4.71) % in FEF25-75% after adjusting for related covariates. Exposure- response curve depicted the reduction of lung function with blood Cr increase, and the reference value of blood Cr was proposed as 6 μg/L considering the lung function as health outcome. Based on the repeated-measure analysis, compared with the low frequency group, subjects with high frequency of high exposure across 2010-2017 had an additional reduction of 5.65 (0, 11.3) % in FVC. Subjects with medium frequency showed more obvious declines of 9.48 (4.16, 14.87) % in FVC, 8.63 (3.49, 13.97) % in FEV1, 12.94 (3.34, 22.53) % in PEF and 10.97 (3.63, 18.30) % in MVV. These findings suggested that short- term high exposure to Cr associated with obstructive ventilatory impairment, and long- term exposure further led to restrictive ventilatory impairment.

Systematic review of biomonitoring data on occupational exposure to hexavalent chromium

Occupational exposure to hexavalent chromium (Cr(VI)) can cause serious adverse health effects such as lung cancer and irritation of the skin and airways. Although assessment of chromium (Cr) in urine is not specific for Cr(VI) exposure, the total amount of Cr in urine is the most used marker of exposure for biomonitoring of Cr(VI). The purpose of this systematic review was fourfold: (1) to assess current and recent biomonitoring levels in subjects occupationally exposed to Cr(VI), with a focus on urinary Cr levels at the end of a working week, (2) to identify variables influencing these biomonitoring levels, (3) to identify how urinary Cr levels correlate with other Cr(VI) exposure markers and (4) to identify gaps in the current research. To address these purposes, unpublished and published biomonitoring data were consulted: (i) unpublished biomonitoring data comprised urinary Cr levels (n = 3799) of workers from different industries in Belgium collected during 1998-2018, in combination with expert scores indicating jobs with Cr exposure and (ii) published biomonitoring data was extracted by conducting a systematic literature review. A linear mixed effect model was applied on the unpublished biomonitoring data, showing a decreasing time trend of 30% in urinary Cr levels. Considering the observed decreasing time trend, only articles published between January 1, 2010 and September 30, 2020 were included in the systematic literature search to assess current and recent biomonitoring levels. Twenty-five studies focusing on human biomonitoring of exposure to Cr(VI) in occupational settings were included. Overall, the results showed a decreasing time trend in urinary Cr levels and the need for more specific Cr(VI) biomarkers. Furthermore, this review indicated the importance of improved working conditions, efficient use of personal protective equipment, better exposure control and increased risk awareness to reduce Cr levels in biological matrices. Further investigation of the contribution of the different exposure routes is needed, so that better guidance on the use of control measures can be provided. In addition, this review support the call for more harmonization of human biomonitoring.

Analysis of serum metabolome of workers occupationally exposed to hexavalent chromium: A preliminary study

Hexavalent chromium (Cr(VI)) compound is considered as a common environmental and occupational pollutant due to widespread application in industry and agriculture. Cr(VI) as a carcinogen poses a serious threat to human health and the underlying mechanisms need further investigation. Previous studies had demonstrated the characteristic expression profiling after Cr(VI) treatment in vitro and in vivo at the levels of gene and protein. The comprehensive metabolic signatures were also conducive to discover potential biomarkers for effects assessment of Cr(VI) toxicity. In the current study, Ultra-performance liquid chromatography coupled with mass spectrometry (UPLC-MS) non-targeted metabolomics was applied to analyze serum metabolic changes in 77 chromate exposure workers and 62 controls. Thirteen metabolites were found significantly decreased and 41 metabolites were increased, which were involved in arginine and proline metabolism, and glycerophospholipid metabolism by bioinformatic analysis. Furthermore, there were significant negative correlations between blood Cr level and Arginine, PC(18:2/24:4) and PC(14:0/16:0), subgroup analyses indicated that these correlations were observed in male-only subgroups, and were not found among chromate workers and controls separately. Diet could be a potential confounder which was not controlled rigorously in this study. These findings provided preliminary clues to investigate the underlying mechanisms of Cr(VI)-induced toxicity and were required to be further verified in future researches.

Hexavalent chromium: Regulation and health effects

Despite the knowledge about heavy metals toxicity on humans, its use is widely spread mainly for industrial processes. Chromium is an element that belongs to this group and although it is present in our daily diet, it can also be harmful for humans, causing skin allergies and increasing the risk of lung cancer, among other health effects reported. In this review, we highlight its nutritional role, its toxicokinetic and toxicodynamic in humans, its regulation in the industry and the biomonitoring proposal of this element in blood and urine samples with the aim to control the level of exposure of the workers in military industry and also of the general population.

Association of blood chromium and rare earth elements with the risk of DNA damage in chromate exposed population

Pollution of heavy metals often occurs in combination with multiple metal ions. Whether the genetic damage among chromate exposed population correlated with rare earth elements (REEs) was still not well elucidated. A total of 291 participants from a chromate production plant were recruited in the present study. The DNA oxidative damage was evaluated by urinary 8-hydroxydeoxyguanosine (8-OHdG) and the concentrations of chromium (Cr) and 15 REEs accumulated in the peripheral blood of participants were determined. The results showed that significant DNA oxidative damage was observed in chromate exposed workers. Blood REEs levels in the exposed group were significantly higher than the control group and blood REEs increased in a concentration dependent manner with Cr. Additionally, significant correlations were observed between blood Cr and 10 REEs concentrations. Blood Cr had a significant positive correlation with urinary 8-OHdG. Blood Cr and Yttrium had a positive interactive effect on urinary 8-OHdG. Collectively, the results suggested workers who had been working in the chromate plant were simultaneously exposed to chromate and a variety of REEs, which could have interactive effects on the DNA damage of workers.

Modulation of homologous recombination repair gene polymorphisms on genetic damage in chromate exposed workers

Hexavalent chromium [Cr(VI)] is one of the most common environmental carcinogens, which is associated with DNA damage, genetic instability and increase the risk of cancer development. However, the mechanisms of genetic damage induced by Cr(VI) remains to be thoroughly illustrated. A molecular epidemiological study was conducted on 120 chromate exposed workers and 97 controls. Results indicated that,the rs12432907 of XRCC3 carrying T allele, the rs144848 of BRCA2 with C allele and the rs1805800 of NBS1 with genotype(TT) of individuals were associated with lower genetic damage, while the rs2295152 of XRCC3 carrying T allele, the rs13312986 (CC and CT genotypes) and the rs2697679 of NBS1 with A allele were associated with higher genetic damage in workers exposed to chromate. The interaction of chromate exposure with rs2295152 of XRCC3 had a significant effect on micronuclei frequency (MNF). The gene polymorphisms in homologous recombination repair pathway could modulate chromate-induced genetic damage.

Cr(VI)-induced methylation and down-regulation of DNA repair genes and its association with markers of genetic damage in workers and 16HBE cells

To examine the mechanism of hexavalent chromium [Cr(VI)]-induced carcinogenesis, a cross-sectional study in workers with or without exposure to Cr(VI) as well as in vitro administration of Cr(VI) in 16HBE cells was conducted. We explored the associations between Cr(VI) exposure, methylation modification of DNA repair genes and their expression levels, and genetic damage. Results showed that hypermethylation of CpG sites were observed in both occupationally exposed workers and 16HBE cells administrated Cr(VI). DNA damage markers including 8-hydroxydeoxyguanosine (8-OHdG) and micronucleus frequency in Cr(VI)-exposed workers were significantly higher than the control group. Among workers, blood Cr concentration was positively correlaed with the methylation level of CpG sites in DNA repair genes including CpG6,7, CpG8, CpG9,10,11 of MGMT, CpG11 of HOGG1; CpG15,16,17, CpG19 of RAD51, and genetic damage markers including 8-OHdG and micronucleus frequency. Significant negative association between methylation levels of CpG sites in DNA repair genes and corresponding mRNA was also observed in 16HBE cells. This indicated that Cr(VI) exposure can down-regulate DNA repair gene expression by hypermethylation, which leads to enhanced genetic damage. The methylation level of these CpG sites of DNA repair genes can be potential epigenetic markers for Cr(VI)-induced DNA damage.