Emerging evidence suggests an important role of nutritional factors (e.g. biological active peptides or amino acids) in prevention of cardiovascular diseases such as atherosclerosis, heart attack or stroke. The present study investigates the involvement of heme oxygenase-1 (HO-1) and ferritin in mediating cytoprotective and antioxidant actions of sulphur-containing amino acids and ACE-inhibitory oligopeptides. Incubation of human endothelial cells with L-methionine, L-cysteine, S-adenosylmethionine (SAM) and the ACE-inhibitory dipeptide methionine-tyrosine (Met-Tyr) led to an increased expression of HO-1 protein in a concentration- and time-dependent fashion. In contrast, the single amino acids L-methionine and L-tyrosine at micromolar concentrations as well as other ACE-inhibitory agents (captopril, methionine-phenylalanine) or methionine-containing dipeptides (methionine-methionine) left HO-1 protein expression unaltered. L-Methionine- and L-cysteine-induced HO-1 protein expression was accompanied by an increased catalytic activity of the enzyme. L-Cysteine and SAM significantly elevated HO-1 mRNA levels in a concentration- and time-dependent manner. HO-1 gene expression was regulated at the level of transcription via increased promoter activity. L-Methionine and Met-Tyr did not influence HO-1 mRNA expression directly. However, there is strong evidence that these substances stabilize HO-1 mRNA. Treatment of endothelial cells with L-methionine or Met-Tyr markedly prolonged the half-life of HO-1 mRNA after exposure to the potent HO-1 inducer CdCl2. Furthermore, L-methionine, L-cysteine and Met-Tyr produced increases in ferritin protein expression. L-Methionine, SAM and Met-Tyr reduced NADPH-dependent production of oxygen radicals at concentrations that were also effective in HO-1 induction. This effect was observed only after several hours of pretreatment and sustained after washing out either agent, pointing to an indirect antioxidant action of the tested substances rather than direct radical scavenging. The cytoprotective action of Met-Tyr occurred independently of its ACE-inhibitory properties and was specific for this dipeptide. The role of HO-1 as a mediator of antioxidant activities of the tested substances under these conditions was demonstrated by the direct radical scavenging effect of the HO-1 product bilirubin. In agreement with this, endothelial cell protection by L-methionine, SAM and Met-Tyr was abrogated in the presence of the HO-inhibitor zinc deuteroporphyrin IX 2,4-bis-ethylene glycol, suggesting that HO-1 and its enzymatic products are indeed of functional relevance and responsible for the observed antioxidant actions. These findings demonstrate that several sulphur-containing amino acids and the ACE-inhibitory dipeptide Met-Tyr are potent activators of antioxidant and anti-inflammatory pathways. This novel, potentially antiatherogenic mechanism of the tested nutritional factors underlines the importance of dietary measures in prevention of atherosclerosis and other inflammatory processes.