William B. Melchior

Arylamine–DNA adduct conformation in relation to mutagenesis

A considerable body of evidence has indicated that local conformational alterations induced by DNA adducts may provide the molecular basis for differences in mutational specificities exhibited by structurally similar adducts. To elucidate the relationships between adduct structure and mutation induction, the ability of several single-ring arylamines present in tobacco smoke (i.e., methylanilines, dimethylanilines, and ethylanilines) to form DNA adducts was investigated. In all cases, the major adducts were C8-substituted deoxyguanosine derivatives, which is consistent with what has been observed with more carcinogenic arylamines, such as 2-aminofluorene and 4-aminobiphenyl. Spectroscopic and theoretical data on the adducts indicated conformational differences depending upon the location of the alkyl substituents. Adducts containing alkyl groups ortho to the amino function (e.g., 2-methylaniline) had a greater percentage of syn conformers about the glycosyl bond than those not bearing such groups. Arylamines with ortho alkyl substituents tend to be more mutagenic and tumorigenic than analogues not containing an ortho alkyl substituent. This increase in biological activity may be due in part to the greater propensity of ortho alkylated adducts to adopt a syn conformation.

Thermal inactivation reaction rates for ricin are influenced by pH and carbohydrates.

Ricin is a lethal protein toxin produced by the castor bean plant. Ricin is known to possess significant heat resistance. Therefore, we placed it in a variety of foods to study the influence of the food matrix on behavior of a thermally stable protein toxin. First order rate constants for the thermal inactivation of ricin in foods and simple buffers were measured using cytotoxicity assays. We observed greater thermal stability at 75 °C for the cytotoxic activity of ricin when it was placed in a yogurt-containing fruit drink compared to its stability when placed in the other foods tested. We found that galactose and high molecular weight exopolysaccharides present in various dairy products contributed to the thermal stability of ricin. Differential scanning calorimetry also showed enhanced thermal stability for ricin at pH 4.5. Our results demonstrate the importance of considering pH and the presence of stabilizing ligands in the thermal inactivation of protein toxins in foods.

Prolactin and Dehydroepiandrosterone Levels in Women with Systemic Lupus Erythematosus: The Role of the Extrapituitary Prolactin Promoter Polymorphism at −1149G/T

Systemic lupus erythematosus (SLE) has shown an association with high levels of prolactin, low levels of dehydroepiandrosterone (DHEA), and induction of inflammatory cytokines in the serum of patients with the disease. This preliminary study examined the relevance of a −1149G/T functional single-nucleotide polymorphism (SNP) (rs1341239) in the promoter of the extrapituitary prolactin gene in a cohort of African American and European American women with lupus. Examination of this SNP revealed that the −1149TT genotype was correlated with higher levels of prolactin in serum and prolactin gene expression (p = 0.0001) in peripheral blood mononuclear cells (PBMCs). Lower levels of DHEA in serum were demonstrated in lupus patients (p = 0.001); those with the −1149TT genotype had the lowest levels of DHEA. Furthermore, a small subset of women who were on DHEA therapy and had a TT genotype showed a significant decrease in prolactin gene expression and lower disease activity scores (SLEDAI). Lupus patients, particularly African Americans, had significantly higher levels of IL-6 (p = 0.0001) and TNF-α (p = 0.042). This study suggests that the −1149TT genotype may be a risk factor for lupus and may predict who could possibly benefit from DHEA therapy; therefore, these results should be validated in a larger cohort with all ethnic groups.

Autophagy in drug-induced liver toxicity

Liver injury resulting from exposure to drugs and chemicals is a major health problem. Autophagy is an important factor in a wide range of diseases, such as cancer, liver disease, muscular disorder, neurodegeneration, pathogen infection, and aging, and emerging evidence indicates that autophagy makes a substantial contribution to the pathogenesis of drug- and chemical-induced liver toxicity. In this review, we summarize current knowledge on autophagy triggered by toxicants/toxins, the protective role of autophagy in liver toxicity, and the underlying molecular mechanisms. We also highlight experimental approaches for studying autophagy.