Melatonin attenuates estradiol-induced oxidative damage to DNA: relevance for cancer prevention

Estrogens exert pro-oxidative effects and have been shown to damage DNA, potentially leading to cancer. Melatonin is a well-known antioxidant, free radical scavenger, and oncostatic agent. Changes in the levels of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo), an index of DNA damage, and the levels of malondialdehyde + 4-hydroxyalkenals, an index of lipid peroxidation, were measured in kidneys, liver, and testes from hamsters treated with E2 (75 mg/kg body wt) and were collected 3 or 5 hr later. Other animals were treated with melatonin (15 mg/kg body wt, 30 min before and 120 min after E2 treatment) or were given both compounds. Additionally, lipid peroxidation was measured in liver homogenates exposed to ferrous sulfate (15 microM) in vitro. E2 treatment caused an increase in 8-oxodGuo levels in kidneys collected 5 hr after E2 administration, and in liver 3 hr after estrogen treatment. Melatonin completely prevented E2-induced DNA damage in both organs. Melatonin alone or when given with E2 and examined 3 hr later decreased the base level of 8-oxodGuo in testes. A tendency for a reduction in in vivo lipid peroxidation was observed after treatment of hamsters with either melatonin, E2, or both compounds, with a statistically significant decrease being measured in the liver following E2 administration. In vitro exposure to iron significantly enhanced lipid peroxidation in hepatic homogenates from untreated, melatonin-treated, or E2-injected hamsters; in the hepatic homogenates of hamsters given both E2 and melatonin, ferrous sulfate failed to augment lipid peroxidation. Our results confirm the dual actions of estrogens relative to oxidative damage, i.e., estrogen increases oxidative destruction of DNA while reducing lipid peroxidation. Melatonin had antioxidative actions in reducing oxidative damage to both DNA and to membrane lipids. Melatonin completely prevented the damaging action of E2 on DNA and synergized with the steroid to reduce lipid peroxidation.

Relative efficacies of indole antioxidants in reducing autoxidation and iron-induced lipid peroxidation in hamster testes

Increased iron stores are associated with free radical generation and carcinogenesis. Lipid peroxidation is involved in DNA damage, thus indirectly participating in the early steps of tumor initiation. Melatonin and structurally related indoles are effective in protecting against oxidative stress. The aim of the study was to compare the relative efficacies of melatonin, N-acetylserotonin (NAS), indole-3-propionic acid (IPA), and 5-hydroxy-indole-3-acetic acid (5HIAA) in altering basal and iron-induced lipid peroxidation in homogenates of hamster testes. To determine the effect of the indoles on the autoxidation of lipids, homogenates were incubated in the presence of each agent in concentrations of 0.0, 0.01, 0.05, 0.1, 0.25, 0.5, 0.75, 1.0, 2.0, 2.5, or 5.0 mM. To study their effects on induced lipid peroxidation, homogenates were incubated with FeSO(4) (30 microM + H(2)O(2) (0.1 mM) + each of the indoles in the same concentrations as above. The degree of lipid peroxidation was expressed as concentrations of malondialdehyde + 4-hydroxyalkenals (MDA + 4-HDA) per mg protein. The indoles decreased both basal and iron-related lipid peroxidation in a concentration-dependent manner. Melatonin reduced basal MDA + 4-HDA levels when used at the concentrations of 0.25 mM or higher, and prevented iron-induced lipid peroxidation at concentrations of 1.0, 2.0, 2.5, or 5.0 mM. The lowest effective concentrations of NAS required to lower basal and iron-related lipid peroxidation were 0.05 mM and 0.25 mM, respectively. IPA, only when used in the highest concentrations of 2.5 mM or 5 mM inhibited basal lipid peroxidation levels and it was ineffective on the levels of MDA + 4-HDA due to iron damage. 5HIAA reduced basal lipid peroxidation when used at concentrations of 0.25 mM or higher, and it prevented iron-induced lipid peroxidation only at the highest applied concentration (5 mM). In conclusion, melatonin and related indoles at pharmacological concentrations protect against both the autoxidation of lipids as well as induced peroxidation of lipids in testes. In doing so, these agents would be expected to reduce testicular cancer that is initiated by products of lipid peroxidation.