Lack of protective effect by intermittent hypoxia on MPTP-induced neurotoxicity in mice

The Hypoxia Response Pathway: A Potential Intervention Target in Parkinson's Disease?

Parkinson's disease (PD) is a progressive neurodegenerative disorder for which only symptomatic treatments are available. Both preclinical and clinical studies suggest that moderate hypoxia induces evolutionarily conserved adaptive mechanisms that enhance neuronal viability and survival. Therefore, targeting the hypoxia response pathway might provide neuroprotection by ameliorating the deleterious effects of mitochondrial dysfunction and oxidative stress, which underlie neurodegeneration in PD. Here, we review experimental studies regarding the link between PD pathophysiology and neurophysiological adaptations to hypoxia. We highlight the mechanistic differences between the rescuing effects of chronic hypoxia in neurodegeneration and short-term moderate hypoxia to improve neuronal resilience, termed "hypoxic conditioning". Moreover, we interpret these preclinical observations regarding the pharmacological targeting of the hypoxia response pathway. Finally, we discuss controversies with respect to the differential effects of hypoxia response pathway activation across the PD spectrum, as well as intervention dosing in hypoxic conditioning and potential harmful effects of such interventions. We recommend that initial clinical studies in PD should focus on the safety, physiological responses, and mechanisms of hypoxic conditioning, as well as on repurposing of existing pharmacological compounds. © 2023 International Parkinson and Movement Disorder Society.

Chronic hypoxia attenuates ischemia-reperfusion-induced increase in pulmonary vascular resistance

This study explored the effect of chronic hypoxia on the elevation of pulmonary vascular resistance caused by ischemia-reperfusion (IR) in anesthetized rats. Experiments were separated into five parts. In Part 1, we examined the increase in left pulmonary vascular resistance (Rpl) after ischemia of the left lung and localized the major site for the increased resistance of the left pulmonary vasculature in both the normoxic and chronic hypoxia groups. Here, IR induced a significant increase in Rpl in the normoxic but not the chronic hypoxia group. This increased Rpl in the normoxic group was attributed to contraction of pulmonary arterial segments. Part 2 and Part 3 were focused on the changes in plasma nitrate/nitrite (NOx) and thromboxane B(2) (TxB(2)) levels. TxB(2) increased significantly in the normoxic group, whereas NOx increased significantly in the chronic hypoxia group, following ischemia. Indomethacin (Part 4) prevented IR-induced increase in Rpl in the normoxic group, whereas the IR-induced increase in Rpl appeared in the chronic hypoxia group after N(G)-nitro-L-arginine methyl ester treatment (Part 5). We conclude that IR elicited increases in the cyclooxygenase products such as TxB(2), which in turn caused an increase in Rpl. However, this increased Rpl was attenuated by elevated NOx in the chronic hypoxia group.