The invention relates to a method for the treatment or prevention of diseases or conditions associated with vascular endothelium dysfunction or liver injury comprising the administration to a patient in a need of such treatment or prevention of a therapeutically or prophylactically effective amount of a compound selected from the group consisting of: wherein R represents hydrogen atom, CH.sub.3, OH, pyridyl (C.sub.5H.sub.4N), 1-methylpyridyl (C.sub.5H.sub.4N--CH.sub.3) or pyridyl substituted with hydroxy group ((OH)C.sub.5H.sub.3N), and X represents a physiologically acceptable counterion.