Insulin Signaling in Bupivacaine-induced Cardiac Toxicity Sensitization during Recovery and Potentiation by Lipid Emulsion

Background: The impact of local anesthetics on the regulation of glucose homeostasis by protein kinase B (Akt) and 5-adenosine monophosphate-activated protein kinase (AMPK) is unclear but important because of the implications for both local anesthetic toxicity and its reversal by IV lipid emulsion (ILE). Methods: Sprague-Dawley rats received 10 mg/kg bupivacaine over 20 s followed by nothing or 10 ml/kg ILE (or ILE without bupivacaine). At key time points, heart and kidney were excised. Glycogen content and phosphorylation levels of Akt, p70 s6 kinase, s6, insulin receptor substrate-1, glycogen synthase kinase-3, AMPK, acetyl-CoA carboxylase, and tuberous sclerosis 2 were quantified. Three animals received Wortmannin to irreversibly inhibit phosphoinositide-3-kinase (Pi3k) signaling. Isolated heart studies were conducted with bupivacaine and LY294002a reversible Pi3K inhibitor. Results: Bupivacaine cardiotoxicity rapidly dephosphorylated Akt at S473 to 63 5% of baseline and phosphorylated AMPK to 151 +/- 19%. AMPK activation inhibited targets downstream of mammalian target of rapamycin complex 1 via tuberous sclerosis 2. Feedback dephosphorylation of IRS1 to 31 +/- 8% of baseline sensitized Akt signaling in hearts resulting in hyperphosphorylation of Akt at T308 and glycogen synthase kinase-3 to 390 +/- 64% and 293 +/- 50% of baseline, respectively. Glycogen accumulated to 142 +/- 7% of baseline. Irreversible inhibition of Pi3k upstream of Akt exacerbated bupivacaine cardiotoxicity, whereas pretreating with a reversible inhibitor delayed the onset of toxicity. ILE rapidly phosphorylated Akt at S473 and T308 to 150 +/- 23% and 167 +/- 10% of baseline, respectively, but did not interfere with AMPK or targets of mammalian target of rapamycin complex 1. Conclusion: Glucose handling by Akt and AMPK is integral to recovery from bupivacaine cardiotoxicity and modulation of these pathways by ILE contributes to lipid resuscitation.