Effects of gossypol on DNA replication in mammalian cells

Gossypol, a binaphthalene compound, possesses male infertility effects. However, its mechanism of action and effects on somatic cells are not yet understood. The purpose of this study was to examine the effects of gossypol on mammalian cell growth and DNA replication, using tissue culture cells (HeLa) as an in vivo model.^ Gossypol inhibited DNA synthesis in HeLa cells at low doses, without affecting RNA or protein synthesis. This caused cells to accumulate in S phase without affecting cells in other phases of the cell cycle. The inhibition of DNA synthesis was both dose- and time-dependent. This irreversible block was associated with a decrease in HeLa plating efficiency. Gossypol did bind to DNA but did not measurably affect its ability to serve as a template for DNA polymerase $\alpha$, the major replicative enzyme. Only in the absence of serum could gossypol induce single-strand DNA breaks in HeLa cells; no DNA-DNA or DNA-protein crosslinks were formed.^ Gossypol exhibited dose-dependent inhibition of a number of eukaryotic and prokaryotic replicative DNA polymerases both in vitro and in vivo. This inhibition was kinetically non-competitive with respect to the DNA template and dNTP substrates. Both a filter binding assay and polyacrylamide gel electrophoresis were used to study gossypol binding to DNA polymerase. Inhibition resulted from drug binding to two adjacent amino acid residues on the enzyme. Binding was found to be irreversible and mediated through either non-covalent interactions or by Schiff's base formation between the aldehyde groups of gossypol and the $\varepsilon$-NH$\sb2$ groups of amino acid residues on the polymerase. Structure-function studies using eleven gossypol derivatives revealed that both aldehyde and hydroxyl groups function independently to effect inhibition of DNA polymerase and DNA replication. The activities of DNA polymerase $\beta$ and ribonucleotide reductase were also inhibited by increasing gossypol concentrations.^ These studies demonstrate that the gossypol-mediated inhibition of DNA replication is due in part to inhibition of key replicative enzymes, such as DNA polymerase $\alpha$. The study of DNA polymerase may serve as a model for the interaction of enzymes with gossypol, a drug which may prove useful as a chemotherapeutic agent. ^

Ethnic differences in adolescents' mental distress

Objectives. The aims of this cross-sectional study were to (1) examine differences among four ethnic groups of middle school students (Anglos, African Americans [AAs], Hispanics, and Asians) on (a) three indicators of mental distress (depression, somatic symptoms, suicidal ideation) (b) social stress (general social stress, process-oriented stress, discrimination) and resources (family relationships, coping, self-esteem) and (2) identify significant risk factors and resources for each ethnic group by examining the moderating effects of ethnicity. ^ Methods. Respondents included 316 students from three schools (144 Anglos, 66 AAs, 77 Hispanics, 29 Asians/Others) who completed self-administered questionnaires. Social stress and somatic symptoms were measured by using the SAFE-C and Somatic Symptom Scale, respectively. The DSD was used to assess depression and suicidal ideation. Resources were measured by using the FES, age-appropriate adaptations of two existing coping scales, and Rosenberg's Self-Esteem Scale. For specific aims, descriptive statistics, ANOVA, ANCOVA, and logistic regression analysis were used. ^ Findings. No statistically significant ethnic group or gender differences were observed in depression and somatic symptoms, but the odds of experiencing depression symptoms were about 9.7 times greater for Hispanic females than for the referent group, Anglo males. Hispanics were also 2.04 times more likely to have suicidal ideation than Anglos ( P < 0.05). AAs and Hispanics reported significantly higher levels of stress than Anglos (OR: 2.2–4.3, 0.00 ≤ P ≤ 0.03). These findings imply that adolescents in these ethnic groups may be exposed to considerable amounts of stress even if they do not exhibit significant symptoms of mental distress yet. Negative moderating effects for ethnicity were found by the significant interaction between ethnicity and social stress in somatic symptoms among AAs and Hispanics. This finding indicates that AA and Hispanic adolescents may require higher levels of social stress to exhibit the same amount of somatic symptoms as Anglo adolescents. Observed ethnic differences in social stress and interaction between social stress and ethnicity in relation to somatic symptoms demonstrated a need for subsequent longitudinal studies, and provided a rationale for incorporating social stress as a critical component not only in research but also in culturally sensitive prevention programs. ^