Characterization of cellular uptake and distribution of coenzyme Q₁₀ and vitamin E in PC12 cells

Coenzyme Q (CoQ) is a well-known electron transporter in the mitochondrial respiratory chain. Furthermore, ubiquinol (UQH₂) - a reduced form of ubiquinone (UQ) - has been shown to act as a radical-scavenging antioxidant. Some studies have reported the beneficial effect of CoQ addition to cultured cells; however, the cellular uptake and distribution of CoQ have not been elucidated. In the present study, we used rat pheochromocytoma PC12 cells to investigate and compare the cellular uptake and distribution of CoQ₁₀ and α-tocopherol (αT). UQ₁₀ or UQ₁₀H₂ treatment resulted in an increase in the cellular content of both CoQ₁₀ in a time- and concentration-dependent manner. A subcellular fractionation study revealed that the added UQ₁₀ as well as UQ₁₀H₂ mainly localized in the mitochondrial fraction, which is similar to the localization of endogenous CoQ but different from that of αT. The cellular distribution of αT directly corresponded to the lipid distribution, while the CoQ distribution did not show any relationship with the lipid distribution, particularly in the mitochondrial and microsomal fractions. These results indicate that the cellular distribution of CoQ is completely different from that of αT; moreover, a certain system which accumulates CoQ preferentially in mitochondria may be suggested.