Ubiquinone status in neurons and astrocytes : the effects of nitrosative stress and lovastatin
An HPLC method has been established for the determination of ubiquinone (C0Q9 and C0Q10) levels in biological samples. This necessitated the synthesis of a novel internal standard for C0Q9 and C0Q10 measurement in rodent tissue. Rat glial cell lines contained C0Q9 as the predominant ubiquinone isoform this was C0Q10 in human tissue. Comparison with primary cultures of rat astrocytes showed that these human and rat glial cancer cell lines had relatively less CoQ9+i0 than primary glial cultures, possibly reflecting a lower dependence of transformed cells upon OXPHOS for ATP generation. Lovastatin decreased C0Q9 (but not C0Q10) in primary astrocytes and glial cell lines. Moreover, glial cell lines displayed an approximately 10-fold higher sensitivity to lovastatin or its P-hydroxy acid isoform than primary rat astrocyte cultures. Cellular C0Q9 levels did not appear to be limiting for mitochondrial complex II+III activity, thus it is possible that C0Q10 is more intimately involved in OXPHOS than C0Q9. Primary cultures of rat astrocytes and neurons contained approximately equal levels of C0Q9. However C0Q10 levels were significantly higher in neuronal cultures. In contrast to transformed cell lines, the neuron's reliance on mitochondrial OXPHOS to synthesise ATP may manifest as higher cellular availability of C0Q10 Activation of iNOS in rat primary astrocytes to generate nitric oxide (NO) for 24h did not alter C0Q9 or C0Q10 levels. Following 36h exposure, activation of iNOS significantly decreased C0Q9 and C0Q10. An NO-donor decreased astrocyte C0Q9 and C0Q10 after 24h exposure, while in neurons, both CoQ isoforms were maintained. Additionally 36h exposure of astrocytes to DETA-NO appeared to cause a recovery in the amount of C0Q9 and C0Q10, possibly representing a protective effect in response to RNS exposure. Additionally, preliminary data demonstrated that small interfering RNA (siRNA) may decrease C0Q9 but not C0Q10 in rat primary astrocytes although not HEK293T cells.