Inhibition of insect glutathione S-transferase (GST) by conifer extracts.

Insecticide synergists biochemically inhibit insect metabolic enzyme activity and are used both to increase the effectiveness of insecticides and as a diagnostic tool for resistance mechanisms. Considerable attention has been focused on identifying new synergists from phytochemicals with recognized biological activities, specifically enzyme inhibition. Jack pine (Pinus banksiana Lamb.), black spruce (Picea mariana (Mill.) BSP.), balsam fir (Abies balsamea (L.) Mill.), and tamarack larch (Larix laricina (Du Roi) Koch) have been used by native Canadians as traditional medicine, specifically for the anti-inflammatory and antioxidant properties based on enzyme inhibitory activity. To identify the potential allelochemicals with synergistic activity, ethanol crude extracts and methanol/water fractions were separated by Sephadex LH-20 chromatographic column and tested for in vitro glutathione S-transferase (GST) inhibition activity using insecticide-resistant Colorado potato beetle, Leptinotarsa decemlineata (Say) midgut and fat-body homogenate. The fractions showing similar activity were combined and analyzed by ultra pressure liquid chromatography-mass spectrometry. A lignan, (+)-lariciresinol 9'-p-coumarate, was identified from P. mariana cone extracts, and L. laricina and A. balsamea bark extracts. A flavonoid, taxifolin, was identified from P. mariana and P. banksiana cone extracts and L. laricina bark extracts. Both compounds inhibit GST activity with taxifolin showing greater activity compared to (+)-lariciresinol 9'-p-coumarate and the standard GST inhibitor, diethyl maleate. The results suggested that these compounds can be considered as potential new insecticide synergists.

[Effects of Tagetes erecta extracts on glutathione S-transferase and protease activities and protein content in Tetranychus viennensis].

With in vivo and in vitro Tagetes erecta roots under light and dark as test materials, this paper studied the effects of their extracts on the glutathione S-transferase and protease activities and protein content in Tetranychus viennensis. The results showed that the chloroform extract of T. erecta roots had the highest light-activated activity, followed by water extract, and methanol extract. After treated with chloroform extract, the glutathione S-transferase and protease activities in T. viennensis increased markedly, while its protein content decreased obviously. The variation degree of T. viennensis protease activity and protein content was significantly higher when the chloroform extract came from the T. erecta roots under light, suggesting that there existed active matters in the extract, which could promote the activation of protease, and thus, the decomposition of protein in T. viennensis. The bioactivity of T. erecta metabolites was mainly of light-activated one.