Effect of oligomer procyanidins on reperfusion arrhythmias and lactate dehydrogenase release in the isolated rat heart.

The antiarrhythmic effect of an oral 3-week-pretreatment with oligomer procyanidins derived from Vitis vinifera was investigated on the isolated perfused heart after global no-flow ischemia (procyanidin-treated group: n = 9, control group: n = 13). Hearts were perfused with a modified Krebs-Henseleit solution in which the K+ content was reduced to 3.0 mmol/l in order to lower the fibrillation threshold. Monophasic action potentials in addition to ECG were recorded. The durations of ischemia and reperfusion were 20 and 30 min, respectively. Arrhythmias including ventricular fibrillation (VF), ventricular tachycardia (VT), flutter (Fl) and bradycardia were evaluated. During the reperfusion, irreversible VF occurred in most of control hearts. The incidence of VF (percentage of the hearts in which VF occurred) was lowered by oligomer procyanidins from 84.6 to 55.6 %, and the duration of the episodes of VF (expressed as percentage relative to the total duration) was significantly shortened from 76.1 +/- 27.9 % to 36.6 +/- 40.6 % (p = 0.036). Simultaneously, the percentage of duration of normal sinus rhythm (NSR) increased from 19.5 +/- 30.3 % to 46.2 +/- 35.9 % (n.s.). VF occuring in the procyanidin-treated hearts could be reversed in two hearts within few minutes to a stage of "reversible arrhythmias" consisting of short episodes (1 to 60 s) of either Fl or VT or bradycardia or NSR alternating with each other. LDH (lactate dehydrogenase) release in the first drops appearing from the reperfused heart was significantly reduced in the procyanidin-treated rats (66.7 +/- 36.2 mU/min, n = 8) in comparison to controls (159.7 +/- 79.0 mU/min, n = 10; p = 0.010). These results demonstrate an antiarrhythmic and cytoprotective effect of oral pretreatment with oligomer procyanidins under the given experimental conditions.

Relevance and mechanism of oxysterol stereospecifity in coronary artery disease.

Cholesterol oxidation products (oxysterols) are markers for in vitro LDL oxidation. They are potent inducers of programmed cell death and are also found in high concentrations inside atherosclerotic lesions. Among physiologically occurring oxysterols, 7beta-OH-cholesterol suggests an increase of lipid peroxidation in vivo. In the underlying study, we quantified free plasma oxysterols by means of gas chromatography in patients with stable coronary artery disease (CAD). Total free plasma oxysterols were elevated more than 2-fold in patients with stable CAD (233 +/- 49 vs 108 +/- 19 ng/ml, n = 22, P < 0.05) compared to a control group (n = 20) with similar atherogenic risk profile and angiographically normal coronary arteries. We found that 7-ketocholesterol, as well as the beta-isomers of epoxide (25.7 +/- 10.0 vs 7.3 +/- 1.4 ng/ml, P = 0.07) and 7beta-OH-cholesterol (65.1 +/- 15.7 vs 19.4 +/- 8.9 ng/ml, P < 0.01), was mainly responsible for this increase. To elucidate a potential relevance of oxysterol stereospecificity in regard to endothelial damage, we further conducted in vitro experiments using human arterial endothelial cells (HAECs). Surprisingly, beta-isomers exerted an up to 10-fold higher amount of cell death in equivalent doses when compared to alpha-isomers. The greater cytotoxic potential of beta-isomers was due to increased apoptosis, preceded by mitochondrial release of cytochrome c with subsequent caspase-3 activation. Stereospecific release of cytochrome c depended on the presence of an intact cytoplasmic membrane, hinting at the existence of a putative oxysterol receptor or a direct stereospecific effect on membrane biology. Finally, both isoforms of oxysterols directly released cytochrome c only in conjunction with protein containing cytosol and endoplasmatic reticulum. Free plasma oxysterol levels, particularly 7-ketocholesterol, beta-epoxide and 7beta-OH-cholesterol, are elevated in patients with stable CAD, independent of their LDL cholesterol levels. Due to the highly increased cytotoxicity of oxysterol beta-isomers in vitro, they may represent important atherogenic risk factors.