Glutathione S-transferase Mu (GST Mu) deficiency and DNA adducts in lymphocytes of smokers

Abstract

The effect of smoking on DNA adduct formation in lymphocytes was analysed in individuals with low (deficient) and high (non-deficient) glutathione S-transferase (class Mu) activity. DNA adduct levels in lymphocytes were determined by the highly sensitive nuclease P1-enhanced ³²P-postlabeling assay. The lymphocyte DNA adducts/10⁸ nucleotides of smokers deficient in glutathione S-transferase Mu activity (n=12) were significantly higher than those of smokers non-deficient (n=9) in glutathione S-transferase Mu activity. The DNA adduct levels of the lymphocytes inversely correlated with glutathione S-transferase Mu activity. A correlation was found between DNA adduct levels and daily cigarette consumption. Results of the present study suggest that individuals deficient in glutathione S-transferase Mu activity may be at greater risk of DNA damage.

Introduction

In humans there are three distinct classes of GST isozymes based on isoelectric point: the acidic or Pi form (Guthenberg et al., 1979), the near neutral or Mu form (Warholm et al., 1980), and the basic or alpha form (Kamisaka et al., 1975). These isozymes have different and overlapping substrate specificities and are variably expressed in different tissues. For example, the alpha form is found in adult livers of all individuals but the GST Mu isozyme also referred to as GSTM1 is detected in about half of the Caucasian population (Hussey et al., 1987). A large concentration of the Mu form is found in the liver, adrenal gland and leukocytes, and is highly active towards benzo(a)pyrene-4,5-oxide and styrene-7,8-oxide (Warholm et al., 1981, Warholm et al., 1983). In humans, the GST activity towards trans-stilbene oxide, is identical with the hepatic Mu form (Seidegard et al., 1987). There is a hereditary polymorphism of this isozyme in the Caucasian population (Seidegard and Pero, 1985) and the gene expression of Mu has been proposed to be a host determinant of susceptibility to smoking-related cancer (Seidegard et al., 1990, Lafuente et al., 1993, Nakajima et al., 1995).

Recently, ³²P-postlabeling studies demonstrated the presence of smoking-associated aromatic DNA adducts in tissues that are targets for tobacco smoke-related carcinogenesis (Reddy and Randerath, 1986Phillips et al., 1988Savela et al., 1989Phillips et al., 1990). Lung and/or bronchial tissues were used in order to evaluate adduct concentration in smokers and non-smokers and interesting results were reported. Gallagher et al. (1993)succeeded in showing a specific smokers-associated DNA, not co-migrating with the major benzo(a)pyrene adduct in lymphocytes and concluded that smoking-related DNA adduct levels are elevated, when compared to non-smokers.

The present studies were designed to determine whether the human GST Mu polymorphism influences in vivo DNA adduct formation in smokers. In the present study lymphocytes of smokers with low or high GST Mu activity towards trans-stilbene oxide were compared for the presence of DNA adducts.