Background: Several previous studies have suggested that sublethal doses of Escherichia coli lipopolysaccharide (endotoxin) and monophosphoryl lipid A Re595, a non-pyrogenic derivative of Salmonella minnesota lipopolysaccharide, exhibit antiarrhythmic effects in the rat model of ischemia–reperfusion arrhythmias.

Methods: In this study, the protective effect of lipopolysaccharide derivatives was also further investigated in drug (aconitine or ouabain)-induced arrhythmia models, and conclusions were drawn with particular emphasis on the molecular characteristics of different types of lipopolysaccharide.

Results: The importance of the molecular structure for the antiarrhythmic effect of mono-phosphoryl lipid A and E. coli lipopolysaccharide was tested in the ischemia–reperfusion arrhythmia model. In contrast to monophosphoryl lipid A from Salmonella typhimurium SL 684 which has only monophosphoryl residue in its structure, monophosphoryl lipid A Re595, obtained from S. minnesota, and E. coli lipopolysaccharide which have both mono and diphosphoryl residue reduced the duration of ventricular tachycardia (e.g., during reperfusion: vehicle: 176 ± 22.8; monophosphoryl lipid A Re595: 132.83 ± 12.1, as second, n = 8-10, P <.05) and the incidence of ventricular fibrillation. The antiarrhythmic effects of E. coli lipopolysaccharide and monophosphoryl lipid A Re595 in ischemia–reperfusion arrhythmia model were absent in either aconitine- (e.g., onset time for ventricular ectopic beats: saline 25.3 5.0, E. coli lipopolysaccharide 24.3 ± 7.1; vehicle: 24.0 ± 4.5, monophosphoryl lipid A SL684 23.8 ± 4.3, as second, n = 6, P >.05) or ouabain-induced arrhythmia models in mice.

Conclusion: Therefore, we conclude that lipopolysaccharide derivatives exhibit anti-arrhythmic effect only in ischemia–reperfusion arrhythmias, and lipopolysaccharide should possess diphosphoryl groups in its subcomponent composition for this antiar-rhythmic effect.