Ceramide induces cytochrome c release from isolated mitochondria

This chapter addresses the role of mitochondria in apoptosis. Emphasis is put on the recently observed influence of ceramides on mitochondrial functions. We report here that N-acetylsphingosine (C²-ceramide), N-hexanoylsphingosine (C⁶-ceramide) and, to a much lesser extent, C²-dihydroceramide, induce cytochrome c (cyt c) release from isolated rat liver mitochondria. Ceramide-induced cyt c release is prevented by a low concentration of Bcl-2. The release takes place when cyt c is oxidized, but not when it is reduced. Upon cyt c release mitochondrial oxygen consumption, mitochondrial transmembrane potential (ΔΨ^m) and Ca²⁺ retention are diminished. Bcl-2 prevents, and addition of cyt c reverses, the alteration of these mitochondrial functions. In ATP-energized mitochondria ceramides do not alter ΔΨ^m, neither when cyt c is oxidized nor when it is reduced. This rules out a non-specific disturbance by ceramides of mitochondrial-membrane integrity. It is concluded that some of the apoptogenic properties of ceramides are mediated via their interaction with mitochondrial cyt c followed by its release.