Berberine Inhibits Oxygen Consumption Rate Independent of Alteration in Cardiolipin Levels in H9c2 Cells

Abstract

Small clinical studies have shown that oral treatment with the plant alkaloid berberine (BBR) reduces blood glucose levels similar to that of metformin and have promoted its use as a novel anti-diabetic therapy. However, in vitro studies have shown that high concentrations of BBR potently inhibit cell proliferation through inhibition of mitochondrial function. Cardiolipin (Ptd2Gro) is a key phospholipid required for regulating mitochondrial bioenergetic function. We examined if BBR inhibited oxygen consumption rate in H9c2 cardiac myocytes through alteration in Ptd2Gro metabolism. Treatment of H9c2 cells with BBR resulted in a rapid (within minutes) concentration-dependent decrease in the oxygen consumption rate (OCR) as determined using a Seahorse XF24 analyzer. Concentrations of BBR as low as 1 µM were effective in inhibiting OCR. In addition, all concentrations of BBR inhibited the fatty acid-mediated increase in OCR that was observed in untreated cells. Treatment of H9c2 cells with up to 25 µM BBR for 24 h markedly reduced [3H]thymidine incorporation into cells but did not alter the pool size of Ptd2Gro. In contrast, 12.5 µM BBR increased [1-14C]palmitate incorporation into Ptd2Gro and 12.5 µM and 25 µM BBR reduced [1-14C]oleate incorporation into Ptd2Gro. Protein kinase C delta (PKCδ) activation through its increased membrane association is known to alter Ptd2Gro distribution within mitochondria. BBR treatment resulted in a decrease in membrane-associated PKCδ and attenuated the palmitate-mediated increase in PKCδ membrane-association. Thus, BBR treatment of H9c2 cardiac myocytes inhibits cellular OCR independent of alteration in Ptd2Gro levels.