Measuring Nitric Oxide/Peroxynitrite in Function/Dysfunction of Neuronal Nitric Oxide Synthase Using Metalloporphyrin Nanosensors – Implication for Neurodegenerative Diseases

Abstract

Nitric oxide (NO), an essential inorganic signaling molecule, plays a role in numerous physiological but also therapeutic applications. Its oxidation product, peroxynitrite ion (ONOO¯), is cytotoxic. Due to their short lifetimes, NO and ONOO¯ concentrations in biological environments are usually transient, at the sub–millimolar to millimolar level, and discriminately return to baseline levels. This work investigates the role of NO and ONOO¯ in neurological situations, with a focus on neurodegenerative diseases such as Alzheimer's disease (AD). To monitor NO and ONOO¯ concentrations in real time, electrochemical metalloporphyrin nanosensors (200–300 nm diameter) were applied and precisely positioned 4–5 ± 1 μm from human neural progenitor cell (hNPC) membranes. Healthy hNPCs produced an average of 107 ± 1 nmol/L of NO and 451 ± 7 nmol/L of ONOO¯, according to the data, resulting in a [NO]/[ONOO¯] ratio of 0.25 ± 0.005. While dysfunctional hNPCs treated to amyloid beta 42 (Aβ42) showed a significant imbalance, with ONOO¯ increasing to 843 ± 0.8 nmol/L and NO levels decreasing to 14 ± 0.1 nmol/L, the ratio was substantially reduced by 94% to 0.016 ± 0.0001. Accordingly, the hypothesis of the study validates the role of the [NO]/[ONOO¯] ratio as a potential biomarker for the neuronal nitric oxide synthase (nNOS) efficiency and the dysfunction of hNPCs, which may have relevance for other neurodegenerative disorders, such as AD. It also investigates pharmaceutical interventions targeting the NO/NOS pathway to restore the [NO]/[ONOO¯] balance in pathological conditions. The study proves the suitability of metalloporphyrin nanosensors for the detection of real-time molecular alterations in hNPCs and monitoring of nitroxidative stress that indicates their applicability for early diagnosis and therapeutic approaches of neurodegenerative diseases.