Immunohistochemical detection of 4-hydroxynonenal protein adducts in Parkinson disease.

TLDR

Oxidative stress and mitochondrial respiratory failure are implicated in nigral neuronal death in Parkinson disease, but it is unclear whether neurons or glial cells are the primary targets of oxygen‑mediated damage, and 4‑hydroxy‑2‑nonenal (HNE) protein adducts serve as stable markers of such oxidative injury. The study aimed to map oxidative damage in nigral neurons by immunostaining HNE‑protein conjugates in control subjects and Parkinson disease patients. Immunohistochemistry was performed on midbrain sections, with all nigral melanized neurons counted and categorized into no, weak, or intense HNE‑staining groups. In Parkinson disease, 58 % of nigral neurons were HNE‑positive versus 9 % in controls, a statistically significant difference, while oculomotor neurons showed minimal staining, indicating that oxidative stress in nigral neurons contributes to their degeneration.

Abstract

There is growing evidence that oxidative stress and mitochondrial respiratory failure with attendant decrease in energy output are implicated in nigral neuronal death in Parkinson disease (PD). It is not known, however, which cellular elements (neurons or glial cells) are major targets of oxygen-mediated damage. 4-Hydroxy-2-nonenal (HNE) was shown earlier to react with proteins to form stable adducts that can be used as markers of oxidative stress-induced cellular damage. We report here results of immunochemical studies using polyclonal antibodies directed against HNE-protein conjugates to label the site of oxidative damage in control subjects (ages 18-99 years) and seven patients that died of PD (ages 57-78 years). All the nigral melanized neurons in one of the midbrain sections were counted and classified into three groups according to the intensity of immunostaining for HNE-modified proteins--i.e., no staining, weak staining, and intensely positive staining. On average, 58% of nigral neurons were positively stained for HNE-modified proteins in PD; in contrast only 9% of nigral neurons were positive in the control subjects; the difference was statistically significant (Mann-Whitney U test; P < 0.01). In contrast to the substantia nigra, the oculomotor neurons in the same midbrain sections showed no or only weak staining for HNE-modified proteins in both PD and control subjects; young control subjects did not show any immunostaining; however, aged control subjects showed weak staining in the oculomotor nucleus, suggesting age-related accumulation of HNE-modified proteins in the neuron. Our results indicate the presence of oxidative stress within nigral neurons in PD, and this oxidative stress may contribute to nigral cell death.