Involvement of prostaglandins and histamine in nickel wire-induced acute inflammation in mice

Microbial colony sequencing combined with metabolomics revealed the effects of chronic hexavalent chromium and nickel combined exposure on intestinal inflammation in mice

The pollution and toxic effects of hexavalent chromium [Cr(VI)] and divalent nickel [Ni(II)] have become worldwide public health issues. However, the potential detailed effects of chronic combined Cr(VI) and Ni exposure on colonic inflammation in mice have not been reported. In this study, 16S rDNA sequencing, metabolomics data analysis, qPCR and other related experimental techniques were used to comprehensively explore the mechanism of toxic damage and the inflammatory response of the colon in mice under the co-toxicity of chronic hexavalent chromium and nickel. The results showed that long-term exposure to Cr(VI) and/or Ni resulted in an imbalance of trace elements in the colon of mice with significant inflammatory infiltration of tissues. Moreover, Cr(VI) and/or Ni poisoning upregulated the expression levels of IL-6, IL-18, IL-1β, TNF-α, IFN-γ, JAK2 and STAT3 mRNA, and downregulated IL-10 mRNA, which was highly consistent with the trend in protein expression. Combined with multiomics analysis, Cr(VI) and/or Ni could change the α diversity and β diversity of the gut microbiota and induce significant differential changes in metabolites such as Pyroglu-Glu-Lys, Val-Asp-Arg, stearidonic acid, and 20-hydroxyarachidonic acid. They are also associated with disorders of important metabolic pathways such as lipid metabolism and amino acid metabolism. Correlation analysis revealed that there was a significant correlation between gut microbes and metabolites (P < 0.05). In summary, based on the advantages of comprehensive analysis of high-throughput sequencing sets, these results suggest that chronic exposure to Cr(VI) and Ni in combination can cause microbial flora imbalances, induce metabolic disorders, and subsequently cause colonic damage in mice. These data provide new insights into the toxicology and molecular mechanisms of Cr(VI) and Ni.

Expression of Histidine Decarboxylase and Its Roles in Inflammation

Histamine is a well-known mediator of inflammation that is released from mast cells and basophils. To date, many studies using histamine receptor antagonists have shown that histamine acts through four types of receptors: H1, H2, H3, and H4. Thus, histamine plays more roles in various diseases than had been predicted. However, our knowledge about histamine-producing cells and the molecular mechanisms underlying histamine production at inflammatory sites is still incomplete. The histamine producing enzyme, histidine decarboxylase (HDC), is commonly induced at inflammatory sites during the late and chronic phases of both allergic and non-allergic inflammation. Thus, histamine levels in tissues are maintained at effective concentrations for hours, enabling the regulation of various functions through the production of cytokines/chemokines/growth factors. Understanding the regulation of histamine production will allow the development of a new strategy of using histamine antagonists to treat inflammatory diseases.

Zinc ions have a potential to attenuate both Ni ion uptake and Ni ion-induced inflammation

Nickel ions (Ni²⁺) are eluted from various metallic materials, such as medical devices implanted in human tissues. Previous studies have shown that Ni²⁺ enters inflammatory cells inducing inflammation. However, the regulation of Ni²⁺ uptake in cells has not yet been reported in detail. In the present study, we investigated the effects of various divalent cations on Ni²⁺ uptake and Ni²⁺-induced interleukin (IL)-8 production in the human monocytic cell line, THP-1. We demonstrated that ZnCl_2, MnCl₂, and CoCl₂ inhibited the Ni²⁺ uptake, while CuCl₂, FeCl₂, MgCl₂, and divalent metal transporter (DMT)-1 inhibitor, Chlorazol Black, did not. Furthermore, ZnCl₂ inhibited Ni²⁺-induced IL-8 production, correlating with the inhibition of Ni²⁺ uptake. These results suggested that Ni²⁺ uptake occurred through Zn²⁺, Mn²⁺, and Co²⁺-sensitive transporters and that the inhibition of Ni²⁺ uptake resulted in the inhibition of IL-8 production. Furthermore, using an Ni wire-implanted mouse model, we found that Ni wire-induced expression of mouse macrophage inflammatory protein-2 (MIP-2) and cyclooxygenase-2 (COX-2) mRNA in the skin tissue surrounding the wire were enhanced by low Zn conditions. These results suggested that the physiological concentration of Zn²⁺ modulates Ni²⁺ uptake by inflammatory cells, and a Zn deficient state might increase sensitivity to Ni.