Mercury and methylmercury differentially modulate hepatic cytochrome P450 1A1 and 1A2 in vivo and in vitro

Abstract

The cytochrome P450 1 A (CYP1A) subfamily enzymes are involved in the metabolic activation of several xenobiotics to toxic metabolites and reactive intermediates, resulting ultimately in carcinogenesis. Mercury and halogenated aromatic hydrocarbons (HAHs), typified by 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD), are persistent environmental pollutants involved in the modulation of aryl hydrocarbon receptor (AHR) gene battery, including cytochrome P450 (CYP) genes. We previously investigated the effect of coexposure to either inorganic or organic mercury (Hg+2 and MeHg) with TCDD on CYP1A1 in vitro. Thus, we examined the impact of coexposure to Hg+2 or MeHg and TCDD on AHR‐regulated genes (Cyp1a1/1a2) in vivo and in vitro. Therefore, male C57BL/6 mice were injected intraperitoneally with MeHg or Hg+2 (2.5 mg/kg) in the absence and presence of TCDD (15 μg/kg) for 6 or 24 h. The concentration‐dependent effect of MeHg was examined in murine hepatoma Hepa1c1c7 cells. In vivo, both MeHg and Hg2+ inhibited the TCDD‐mediated induction of Cyp1a1/1a2 mRNA levels. However, Only Hg2+ was able to inhibit the TCDD‐mediated induction at posttranscriptional levels of CYP1A1/1A2 protein and catalytic activity, suggesting differential modulation effects by Hg+2 and MeHg. In addition, the inhibitory role of HO‐1 (Heme oxygenase‐1) on CYP1A activity induced by TCDD was investigated using a HO‐1 competitive inhibitor, tin‐mesoporphyrin, that partially restored the MeHg‐mediated decrease in CYP1A1 activity. This study demonstrates that MeHg, alongside Hg2+, can differentially modulate the TCDD‐induced AHR‐regulated genes (Cyp1a1/1a2) at different expression levels in C57BL/6 mice liver and Hepa1c1c7 cells.

Methylmercury (MeHg) transcriptionally regulates NAD(P)H:quinone oxidoreductase 1 (NQO1) in Hepa-1c1c7 cells

“…This suggests that MeHg enhances the de novo synthesis of Nqo1 RNA, similar to the effect observed with TCDD, which induces this gene transcriptionally through XRE-ARE pathway. Third, MeHg was capable of increasing basal and inducible ARE-luciferase activity, however, we previously reported that MeHg did not alter XRE-luciferase activity using same cell line ( Alqahtani et al, 2023 ). Therefore, these findings imply that ARE (or NRF2) pathway, but not that of XRE (or AHR), may be solely involved in the NQO1 transcriptional regulation upon MeHg exposure.…”

“…All remaining materials are from Fisher Scientific (Waltham, MA, USA). Further details about the used materials not mentioned above can be found in our previously published paper ( Alqahtani et al, 2023 ).…”

“…To quantify a specific expression of a tested mRNA, real-time PCR was employed by amplifying the resulting single-stranded cDNA using the QuantStudio 5. More details about the real-time reaction and data calculation are described in our previous paper ( Alqahtani et al, 2023 ). For primers sequence see ( Table 1 ).…”

“…A previously described method was used to carry out the western blot analysis ( Alqahtani et al, 2023 ). Briefly, 100 μg of total cell lysates were electrophoresed on 10% SDS-PAGE gel, followed by transfer onto a PVDF membranes, then incubate them at 4 °C for at least 1 h in a blocking solution comprised 0.5% Tween-20, 3 mM potassium chloride, 0.15 M sodium chloride, 2% bovine serum albumin (BSA), 25 mM Tris-base (TBS), and skim milk (5%).…”

“…Mercury and other heavy metals have been linked with NRF2/ARE activation which is a crucial defense mechanism for cellular protection against oxidative stress and toxic xenobiotics. Also, they have been found to be capable of modulating the induced AHR-regulated genes expression in various cell lines ( Alqahtani et al, 2023 , El-Ghiaty et al, 2022 , El-Ghiaty et al, 2023 , Xu et al, 2019 , Zhou et al, 2019 ). Previously, we reported that Hg induced NQO1 expression in vivo ( Amara et al, 2012 ), and that finding was further demonstrated to be possibly through NRF2/ARE pathway in vitro ( Amara and El-Kadi, 2010 ).…”