Cadmium alters the formation of benzo[a]pyrene DNA adducts in the RPTEC/TERT1 human renal proximal tubule epithelial cell line

Abstract

Previously, we demonstrated the sensitivity of RPTEC/TERT1 cells, an immortalized human renal proximal tubule epithelial cell line, to two common environmental carcinogens, cadmium (Cd) and benzo[a]pyrene (B[a]P). Here, we measured BPDE-DNA adducts using a competitive ELISA method after cells were exposed to 0.01, 0.1, and 1 μM B[a]P to determine if these cells, which appear metabolically competent, produce BPDE metabolites that react with DNA. BPDE-DNA adducts were most significantly elevated at 1 μM B[a]P after 18 and 24 h with 36.34 ± 9.14 (n = 3) and 59.75 ± 17.03 (n = 3) adducts/108 nucleotides respectively. For mixture studies, cells were exposed to a non-cytotoxic concentration of Cd, 1 μM, for 24 h and subsequently exposed to concentrations of B[a]P for 24 h. Under these conditions, adducts detected at 1 μM B[a]P after 24 h were significantly reduced, 17.28 ± 1.30 (n = 3) adducts/108 nucleotides, in comparison to the same concentration at previous time points without Cd pre-treatment. We explored the NRF2 antioxidant pathway and total glutathione levels in cells as possible mechanisms reducing adduct formation under co-exposure. Results showed a significant increase in the expression of NRF2-responsive genes, GCLC, HMOX1, NQO1, after 1 μM Cd × 1 μM B[a]P co-exposure. Additionally, total glutathione levels were significantly increased in cells exposed to 1 μM Cd alone and 1 μM Cd × 1 μM B[a]P. Together, these results suggest that Cd may antagonize the formation of BPDE-DNA adducts in the RPTEC/TERT1 cell line under these conditions. We hypothesize that this occurs through priming of the antioxidant response pathway resulting in an increased capacity to detoxify BPDE prior to BPDE-DNA adduct formation.

Evaluation of interaction and combined toxicity of polyaromatic hydrocarbons (PAHs) and metals using human cell-based bioassays

“…The effects of metal mixtures on oxidative stress are supported by Wang and Fowler (2008) and Patra et al (2011). Combination of As and Cd with B [a]P also reported to increase oxidative stress , Simon et al 2014). …”

“…In addition, the Nrf2 (nuclear factor erythroid 2 - and also potentiate the genotoxicity of B[a]P (Maier et al 2002, Lewińska et al 2007. The available report for the mixture of B [a]P and Cd on the genotoxicity is inconsistent as both synergistic (Mukherjee et al 2004, Peng et al 2015 and antagonistic effect was reported by various authors (Lewińska et al 2007, Simon et al 2014. There is no detailed report available for the toxicity of these mixtures, especially for higher order mixtures (ternary and quaternary).…”

“…(Fowler et al 2004, Agrawal et al 2015, Ashok et al 2015. Cadmium in combination with B [a]P increased the activation of the Nrf2 antioxidant response pathway and total glutathione level compared to B[a]P alone (Simon et al 2014). Arsenic and Pb also showed a synergistic effect on the oxidative stress response in combination with B[a]P , Youbin et al 2013.…”

“…Arsenic was found to inhibit the DNA damage induced by B [a]P in rats (Tran et al 2002) and enhanced the DNA adduct formation by increasing the uptake of BPDE (Shen et al 2008). Cadmium has both synergistic (Mukherjee et al 2004) and antagonistic (Simon et al 2014 …”

“…Various epidemiological studies reported the increased incidences of lung cancer or genotoxic effects in humans followed by combined exposure to PAHs and metals (Hays et al 2006, Mielżyńska et al 2006. The data on the co-genotoxicity of metals and B [a]P have so far been limited to binary mixtures of B[a]P with As (Maier et al 2002, Tran et al 2002, Schwerdtle et al 2003, Evans et al 2004, Fischer et al 2005, Chiang and Tsou 2009 or Cd (Mukherjee et al 2004, Lewińska et al 2007, Simon et al 2014). …”