Brain imaging for oxidative stress and mitochondrial dysfunction in neurodegenerative diseases.

Oxidative stress, one of the most probable molecular mechanisms for neuronal impairment, is reported to occur in the affected brain regions of various neurodegenerative diseases. Recently, many studies showed evidence of a link between oxidative stress or mitochondrial damage and neuronal degeneration. Basic in vitro experiments and postmortem studies demonstrated that biomarkers for oxidative damage can be observed in the pathogenic regions of the brain and the affected neurons. Model animal studies also showed oxidative damage associated with neuronal degeneration. The molecular imaging method with positron emission tomography (PET) is expected to delineate oxidatively stressed microenvironments to elucidate pathophysiological changes of the in vivo brain; however, only a few studies have successfully demonstrated enhanced stress in patients. Radioisotope copper labeled diacetyl-bis(N4-methylthiosemicarbazone) (Cu-ATSM) may be the most promising candidate for this oxidative stress imaging. The tracer is usually known as a hypoxic tissue imaging PET probe, but the accumulation mechanism is based on the electron rich environment induced by mitochondrial impairment and/or microsomal over-reduction, and thus it is considered to represent the oxidative stress state correlated with the degree of disease severity. In this review, Cu-ATSM PET is introduced in detail from the basics to practical methods in clinical studies, as well as recent clinical studies on cerebrovascular diseases and neurodegenerative diseases. Several other PET probes are also introduced from the point of view of neuronal oxidative stress imaging. These molecular imaging methods should be promising tools to reveal oxidative injuries in various brain diseases.