Fatty-acid oxidation and calcium homeostasis are involved in the rescue of bupivacaine-induced cardiotoxicity by lipid emulsion in rats*

Objectives: Lipid emulsion has been shown to be effective in resuscitating bupivacaine-induced cardiac arrest but its mechanism of action is not clear. Here we investigated whether fatty-acid oxidation is required for rescue of bupivacaine-induced cardiotoxicity by lipid emulsion in rats. We also compared the mitochondrial function and calcium threshold for triggering of mitochondrial permeability transition pore opening in bupivacaine-induced cardiac arrest before and after resuscitation with lipid emulsion. Design: Prospective, randomized animal study. Setting: University research laboratory. Subjects: Adult male Sprague-Dawley rats. Interventions: Asystole was achieved with a single dose of bupivacaine (10 mg/kg over 20 secs, intravenously) and 20% lipid emulsion infusion (5 mL/kg bolus, and 0.5 mL/kg/min maintenance), and cardiac massage started immediately. The rats in CVT-4325 (CVT) group were pretreated with a single dose of fatty-acid oxidation inhibitor CVT (0.5, 0.25, 0.125, or 0.0625 mg/kg bolus intravenously) 5mins prior to inducing asystole by bupivacaine overdose. Heart rate, ejection fraction, fractional shortening, the threshold for opening of mitochondrial permeability transition pore, oxygen consumption, and membrane potential were measured. The values are mean ± SEM. Measurements and Main Results: Administration of bupivacaine resulted in asystole. Lipid Emulsion infusion improved the cardiac function gradually as the ejection fraction was fully recovered within 5 mins (ejection fraction = 64 ± 4% and fractional shortening = 36 ± 3%, n = 6) and heart rate increased to 239 ± 9 beats/min (71% recovery, n = 6) within 10 mins. Lipid emulsion was only able to rescue rats pretreated with low dose of CVT (0.0625 mg/kg; heart rate ~ 181 ± 11 beats/min at 10 mins, recovery of 56%; ejection fraction = 50 ± 1%; fractional shortening = 26 ± 0.6% at 5 mins, n = 3), but was unable to resuscitate rats pretreated with higher doses of CVT (0.5, 0.25, or 0.125 mg/kg). The calcium-retention capacity in response to Ca2+ overload was significantly higher in cardiac mitochondria isolated from rats resuscitated with 20% lipid emulsion compared to the group that did not receive Lipid Emulsion after bupivacaine overdose (330 ± 42 nmol/mg vs. 180 ± 8.2 nmol/mg of mitochondrial protein, p < .05, n = 3 in each group). The mitochondrial oxidative rate and membrane potential were similar in the bupivacaine group before and after resuscitation with lipid emulsion infusion. Conclusions: Fatty-acid oxidation is required for successful rescue of bupivacaine-induced cardiotoxicity by lipid emulsion. This rescue action is associated with inhibition of mitochondrial permeability transition pore opening.