New glutathione conjugate of pyrrolizidine alkaloids produced by human cytosolic enzyme-dependent reactions in vitro

The effect of infusion time on Echium amoenum extract -induced hepatotoxicity in vitro

Echium amoenum is an annual herb native to the northern mountains of Iran which has medicinal application. Petals of Echium amoenum (Gole-Gavzaban) is one of the most valuable medicinal plants in Iranian folk medicine. The dry petals of E. amoenum have long been used as a sedative, tonic, anxiolytic and as a treatment for sore throat, cough and inflammation. Previous studies have shown that petals of E. amoenum contain four toxic pyrrolizidine alkaloids but conflicting results have been acquired in experimental studies investigating the hepatotoxicy of E. amoenum. However, the direct effect of E. amoenum on liver cells and the complete mechanisms of its possible cytotoxic effects toward these cells remain to be defined. The main aim of this study was to assay the mechanisms underlying the toxic effects of E. amoenum toward hepG2 cells. E. amoenum extract was obtained by infusion of dried petals in hot water (90 centigrade) for 15 or 30 min. Cell viability and mechanistic parameters were determined following 12 h incubation of hepG2 with E. amoenum extract that was obtained after 15 or 30 min infusion. The results indicated that E. amoenum extract exerts cytotoxic effects on hepG2 cells, probably through mitochondrial and lysosomal damage induced by glutathione depletion and oxidative stress.

In vitro metabolism of pyrrolizidine alkaloids - Metabolic degradation and GSH conjugate formation of different structure types

Pyrrolizidine alkaloid (PA) forming plants are found worldwide and may contaminate food products at levels being of concern for human health. Due to the high biodiversity of PA producing plants many different types of PA structures are formed. PAs themselves are not toxic but require metabolic activation to exert toxicity. To investigate if the structure of the PAs affects their in vitro metabolism, we incubated a set of 22 PAs and compared the degradation rates and the amount of formed glutathione (GSH) conjugates. With human liver microsomes, no metabolic degradation of monoesters was found. Degradation rates of diester PAs tended to correlate with their hydrophilicity, whereby the more polar and branched-chained PAs exhibited lower degradation. There was a trend towards higher degradation rates in the presence of rat liver microsomes, but the GSH conjugate levels were similar. Although an effective degradation seems to be related with high GSH conjugate levels, no clear correlation between both parameters could be deduced. For both species no GSH conjugates, or only trace amounts, were formed from monoesters. However, for both open-chained as well as cyclic diesters GSH conjugates were detected and determined levels were comparable for both ester types without major structure-dependent differences.