Differential cytoprotective effect of copper- and iron-containing chlorophyllins against oxidative stress-mediated cell death.

Chlorophyllin (CHL), a copper-containing chlorophyll derivative, was previously reported to possess reactive oxygen species (ROS) scavenging activity. However, the antioxidant property of iron-containing chlorophyllin, iron chlorin e6 (FeCe6), has not been explored in detail. This study systematically investigated the antioxidant capacity of two chlorophyllins, CHL and FeCe6, and their cytoprotective effects against ROS toxicity in human Jurkat T-cells. Both CHL and FeCe6 exhibited a wide range of antioxidant activities to ABTS radical, singlet oxygen, peroxynitrite, and peroxyl radical. Notably, FeCe6 exerted a significant suppressive effect on hydrogen peroxide-dependent cytotoxicity and apoptosis in Jurkat T-cells, while negligible or much weaker inhibition was observed by CHL. This differential cytoprotective effect is likely due to the different hydrogen peroxide scavenging capacity of two chlorophyllins. Moreover, FeCe6 attenuated menadione-induced cell death and tumour necrosis factor (TNF)-alpha-induced IkappaB phosphorylation via scavenging of intracellular ROS. Taken together, the results suggest that FeCe6 is a promising cytoprotective antioxidant against oxidative stress-mediated cellular toxicity.

Peroxynitrite scavenging activity of indole derivatives: interaction of indoles with peroxynitrite.

One of the products of nitrogen-derived free radicals, peroxynitrite (ONOO(-)), is formed by the reaction of superoxide anion (O(2)(*-)) with nitric oxide (NO). ONOO(-) can cause damage to proteins and DNA through nitration. In particular, proteins and their constituent amino acids have been proven to be extremely sensitive to ONOO(-). However, the lack of specific endogenous defense enzymes to protect against ONOO(-) has prompted many researchers to search for endogenous scavengers. We previously found 5-hydroxytryptamine (HT), which is an indole derivative (ID), to be an efficient ONOO(-) scavenger. In the present study, the interaction of several other indoles was further investigated: tryptophan (TRP), 5-hydroxyL-tryptophan (HLT), HT, N-acetyl-5-hydroxytryptamine (AHT), 5-methoxyindole-3-acetate (MIA), 5-methoxytryptamine (MT), and melatonin. The ONOO(-) scavenging activity of ID was assayed by measuring the formation of oxidized dihydrorhodamine-123 (DHR-123). The scavenging efficacy was expressed as the IC(50), denoting the concentration of each indole required to cause 50% inhibition of DHR-123 formation. In a separate in vitro study, the protective effect of IDs against ONOO(-)-induced nitration of bovine serum albumin was investigated. Nitration was quantified using an immunoassay with a monoclonal anti-nitrotyrosine antibody, and a horseradish peroxidase-conjugated anti-mouse secondary antibody from sheep. The results revealed that the inhibitory activities of indoles were as follows: HLT, IC(50) = 0.73 microM; HT, IC(50) = 1.03 microM; and AHT, IC(50) = 0.98 microM), showing relatively strong activities against ONOO(-). Interestingly, TRP, MIA, MT, and melatonin were less effective. Regarding the protection of albumin by IDs, the data showed that the formation of ONOO(-) was inhibited in a dose-dependent manner. Further probing of the mode of the interaction of indoles revealed that the hydroxyl groups in IDs are required for the enhanced scavenging action. It was concluded that several indole derivatives with hydroxyl groups are effective scavengers against ONOO(-), and that the scavenging efficacy depends on the presence of hydroxyl groups located within the indole ring structure.