Low concentrations of formaldehyde induce DNA damage and delay DNA repair after UV irradiation in human skin cells

Abstract

Long-term occupational exposure to formaldehyde (FA) increases the risk for nasopharyngeal squamous cell carcinoma. As the skin is also in contact with FA by environmental exposure, we tested the genotoxic properties of appropriate low concentrations (<100 microM) of FA on cultured keratinocytes and fibroblasts of human skin. The initial DNA damage was assessed by comet assay. The induction of DNA protein crosslinks was measured by the ability of FA to reduce DNA migration induced by methyl-methane-sulfonate. Upon 4 h of exposure to FA, significant (P < 0.05) crosslink formations were observed in fibroblasts (50 microM FA) and in keratinocytes (25 microM FA). Upon 8 h of exposure to FA (25 microM FA), significant crosslink formations were observed in both the cell types. FA is known to inhibit different DNA repair pathways. Therefore, we studied the effect of FA on UV-induced repair. Human keratinocytes and fibroblasts exposed to 10 microM FA prior to UV irradiation showed disturbed repair kinetics after UVC and UVB, but not after UVA irradiation. Single-strand breaks (SSBs) derived from nucleotide excision repair disappeared 6 h after solely UVC (3 mJ/cm2) or 3 h solely UVB (30 mJ/cm2) exposure in both the cell types. In the presence of FA, SSBs were still present at these time points containing a reference to a delay in DNA resynthesis/ligation. FA at a concentration not inducing micronuclei (12.5 microM) caused significant increase of UVC-induced (4 mJ/cm2) chromosomal damage. Proliferation of keratinocytes and fibroblasts was in parallel to observed DNA damages. In conclusion, our data suggest that environmental exposure to FA may contribute to UV-induced skin carcinogenesis.

Comet assay: a reliable tool for the assessment of DNA damage in different models

“…White blood cells or lymphocytes are the most frequently used cell type for Comet assay in human biomonitoring studies (reviewed by Angerer et al 2007;Faust et al 2004a, b;Moller 2006b); however, other cells have also been used, e.g., buccal cells (Szeto et al 2005), nasal (Mussali-Galante et al 2005), sperm (Delbes et al 2007;Fraser 2004;Schmid et al 2007;Singh et al 2003), epithelial (Graham-Evans et al 2004Emri et al 2004;Rojas et al 2000), and placental cells (Augustowska et al 2007).…”

Nucleotide Excision Repair Eliminates Unique DNA-Protein Cross-links from Mammalian Cells

“…Some investigations suggest that DPCs kill cells based on the arrest of DNA and RNA synthesis at these "superbulky" adducts (8 -12). Therefore, the establishment of DPCs in an uncontrolled manner can prove lethal or perhaps mutagenic (13), whereas production of DPCs targeted to tumor cells can yield therapeutic benefit (14 -19).…”

Low-Dose Formaldehyde Delays DNA Damage Recognition and DNA Excision Repair in Human Cells

“…Previous studies suggested an interference of formaldehyde with the proper processing of various forms of DNA damage [22], [23]. In the case of global-genome NER activity, the detection of UV lesions depends on a specific accessory complex, known as UV-DDB (for UV-damaged DNA-binding), which consists of a damage sensor (DDB2) and a regulatory subunit (DDB1) [24].…”