Assessment of cell-specific cytotoxic responses in the kidney to aromatic hydrocarbons : a focus on the deregulation of glomerular mesangial cell proliferation by benzo(a)pyrene

Abstract

The present studies were conducted to assess cell-specific cytotoxic responses of the kidney to selected aromatic hydrocarbons (AHs) using in vitro culture systems of glomerular mesangial (GMCs) and cortical tubular epithelial cells (TECs). Experiments were also conducted to evaluate the ability of BaP to modulate GMC proliferation in vitro and define the role of oxidative metabolism in the cytotoxic response. Primary cultures of GMCs or TECs were treated for 24 hr with naphthalene (NAPH), 2-methylnaphthalene (2-MNAPH), benzo(a)pyrene (BaP), pentachlorophenol (PCP), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 2,3,7,8-tetrachlorodibenzofuran (TCDF). Cellular potassium content, lactate dehydrogenase (LDH) leakage, cellular glutathione (GSH) content, mitochondrial membrane fragility and $rmlbracksp3Hrbrack$-thymidine incorporation into DNA were used as indices of functional and/or structural integrity. The results of cytotoxicity measurements in vitro suggested that GMCs are most sensitive to the cytotoxic effects of BaP, while TECs exhibited enhanced susceptibility to NAPH and 2-MNAPH. In view of the enhanced susceptibility of GMCs to BaP, subsequent studies were conducted to further evaluate the growth inhibitory effects of BaP in GMCs and determine if sequential treatment of GMCs with BaP followed by methoxamine (MeoA) or TCDD upregulated GMC proliferation. The findings of these studies demonstrated that acute treatment of GMCs with BaP resulted in a growth inhibitory response which was cell cycle-related. Repeated exposure of GMCs to BaP and agents which modulate growth-related gene expression results in the acquisition of a more proliferative phenotype associated with enhanced c-jun expression. In studies to evaluate the role of cytochrome P-450IA1 (CYPIA1) in the toxic responses of GMCs to BaP we found that BaP and TCDD induced CYPIA1 mRNA and AHH activity without increasing EROD activity. Metabolism of BaP by AHH mediated the formation of DNA adducts. The unique profile of CYPIA1 expression in GMCs suggests that regulation of CYP genes in these cells is inherently different from that of hepatocytes and other cell systems. Collectively, these studies demonstrate that GMCs are sensitive to BaP-induced cytotoxic effects, a response which may be related to metabolism.