Mevastatin induces degeneration and decreases viability of cAMP-induced differentiated neuroblastoma cells in culture by inhibiting proteasome activity, and mevalonic acid lactone prevents these effects

Abstract

Statins with a closed-ring structure (mevastatin, lovastatin, and simvastatin) and with an open-ring structure (pravastatin and fluvastatin) are widely used in the human population to manage hypercholesterolemia. These statins may have neuroprotective or neurotoxic effects, but these effects remain controversial. We have utilized adenosine 3',5'-cyclic monophosphate-induced terminally differentiated murine neuroblastoma (NB) cells in culture as an experimental model to study the effect of statins. Results showed that mevastatin induced degenerative changes and reduced the viability of differentiated NB cells by inhibiting proteasome activity. Lactacystin, an established inhibitor of proteasome, also produced similar degenerative changes in these cells. In contrast, pravastatin neither affected the degeneration and viability of differentiated NB cells nor the proteasome activity. High-performance liquid chromatography (HPLC) analysis of the extract obtained from mevastatin-treated growth medium and differentiated cells revealed that about 50% of mevastatin is converted to an open-ring structure in the growth medium; however, differentiated cells did not convert any portion of mevastatin into an open-ring structure and accumulated only mevastatin with a closed-ring structure. Mevalonic acid lactone by itself did not affect the viability of differentiated NB cells or the proteasome activity, but it completely prevented mevastatin-induced degeneration and decreased viability by reducing the uptake of mevastatin and by blocking its action on proteasome activity. Mevalonic acid failed to prevent lactacystin-induced degeneration and inhibition of proteasome activity. Our results suggest that mevastatin could act as a neurotoxic agent or neuroprotective agent, depending upon the extent of its hydrolysis to an open-ring structure and the level of mevalonic acid.