Pre-treatment with simvastatin prevents LPS-induced hyporesponsiveness of porcine isolated coronary artery

Introduction

Several retrospective studies suggest that prior use of statins can reduce hospital mortality in patients diagnosed with either bacteraemia or sepsis. Simvastatin has been shown to modify the proinflammatory effect of lipopolysaccharide (LPS) on neutrophils and endothelial cells. However, it is not clear whether these effects are also manifest on vascular smooth muscle, which becomes hyporesponsive to vasoconstrictor agents due to the induction of nitric oxide synthase. We have investigated the effect of pre-treatment with simvastatin on LPS-induced changes in contractions of porcine isolated coronary artery (PCA).

Methods

Segments (5 mm) of the PCA were dissected from hearts and incubated in Krebs-Henseleit (K-H) solution at 37°C in the presence of an antibiotic mixture (60 μg/ml benzylpenicillin and 20 μg/ml streptomycin sulphate), with or without 1 μg/ml LPS, 3 μM simvastatin or a combination of the two (simvastatin added 60 minutes before LPS). After 16 to 18 hours, segments were prepared for isometric tension recording in K-H solution. The segments were then exposed to cumulatively increasing concentrations of KCl and then U46619. In some experiments, some segments were exposed to 10 μM 1400 W, a selective inhibitor of inducible nitric oxide synthase prior to the addition of the agonists. Responses are shown as gram weight or calculated as the concentration causing 50% of the maximum effect (-log EC₅₀). Differences between mean values were assessed by ANOVA (post-hoc Dunnett test).

Results

KCl and U46619 caused concentration-dependent contraction of the PCA. Table 1 shows that treatment with 1 μg/ml LPS overnight (and subsequent removal) significantly reduced the maximum response to KCl and U46619 in the PCA by 32.0 ± 4.5% (n = 12) and 28.9 ± 12.3% (n = 12), without changing the potency of either agent. These effects of LPS on vasoconstrictor responses were not observed when 10 μM 1400 W was added to the organ bath, after removal of the endotoxin (Table 1). LPS also failed to impair constrictor responses if 3 μM simvastatin was present during the incubation period and was subsequently removed (Table 1).

Table 1 Effect of LPS, 1400 W and simvastatin on maximum response and potency of vasoconstrictor agent on the PCA

Conclusion

Prolonged exposure to LPS caused hyporesponsive-ness of the PCA by a mechanism that appears to involve the induction of nitric oxide synthase. Since pre-treatment of the PCA with simvastatin reduced LPS-induced changes in vasoconstrictor responses, it unlikely that the effect of the statin involves direct inhibition of NOS (compare 1400 W). These findings are consistent with clinical studies suggesting that prior use of statins may afford protection against bacterial sepsis.