Reply to: "Parkinson's Disease and COVID-19: Do We Need to Be More Patient?"

SARS-CoV-2 and Parkinson's Disease: A Review of Where We Are Now

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), which causes coronavirus disease 2019 (COVID-19), has been discussed in the context of Parkinson's disease (PD) over the last three years. Now that we are entering the long-term phase of this pandemic, we are intrigued to look back and see how and why the community of patients with PD was impacted and what knowledge we have collected so far. The relationship between COVID-19 and PD is likely multifactorial in nature. Similar to other systemic infections, a probable worsening of PD symptoms secondary to COVID-19, either transient or persistent (long COVID), has been demonstrated, while the COVID-19-related mortality of PD patients may be increased compared to the general population. These observations could be attributed to direct or indirect damage from SARS-CoV-2 in the central nervous system (CNS) or could result from general infection-related parameters (e.g., hospitalization or drugs) and the sequelae of the COVID-19 pandemic (e.g., quarantine). A growing number of cases of new-onset parkinsonism or PD following SARS-CoV-2 infection have been reported, either closely (post-infectious) or remotely (para-infectious) after a COVID-19 diagnosis, although such a link remains hypothetical. The pathophysiological substrate of these phenomena remains elusive; however, research studies, particularly pathology studies, have suggested various COVID-19-induced degenerative changes with potential associations with PD/parkinsonism. We review the literature to date for answers considering the relationship between SARS-CoV-2 infection and PD/parkinsonism, examining pathophysiology, clinical manifestations, vaccination, and future directions.

Coronavirus Disease 2019 and related Parkinsonism: the clinical evidence thus far

Background

The Coronavirus disease 2019 (Covid‐19) pandemic has fueled both research and speculation, as to whether it could be a “perfect storm” for a post‐Covid emergence of parkinsonism in some susceptible individuals, analogous to the post‐encephalitic parkinsonism reported after the 1918 influenza epidemic. This theory is further augmented by reports of a pathogenic effect of the Severe Acute Respiratory Syndrome Coronavirus‐2 (SARS‐CoV‐2) on the central nervous system with specific impact on the dopaminergic pathway, as well as the possibility of the virus to selectively bind to Angiotensin‐Converting Enzyme‐2 (ACE‐2); these molecules are expressed abundantly in the midbrain dopamine neurons and, are likely involved in several cellular mechanisms cited in Parkinson's Disease (PD) pathophysiology.

Objectives—Methods

Therefore, we performed a review of the literature up to February 2022 to explore the current landscape considering published cases of new‐onset parkinsonism after a SARS‐CoV‐2 infection in otherwise healthy individuals. We summarized their clinical features, diagnostic and treatment approaches, discussing potential underlying mechanisms in light of PD pathogenesis theories.

Results

Twenty cases that developed parkinsonian features simultaneously or shortly after a reported SARS‐CoV‐2 infection were reviewed. In 11 of them, parkinsonism appeared in the context of encephalopathy, while four patients developed post‐infectious parkinsonism without encephalopathy, and four bore similarities to idiopathic PD. Nine patients exhibited a good response to dopaminergic therapy, while four responded to immunomodulatory treatment.

Conclusions

Available data does not yet justify a clear association between the Covid‐19 pandemic and a parkinsonism wave. However, vigilance is necessary, as long‐term effects might have not been revealed.

Cascading from SARS-CoV-2 to Parkinson's Disease through Protein-Protein Interactions

Extensive extrapulmonary damages in a dozen of organs/systems, including the central nervous system (CNS), are reported in patients of the coronavirus disease 2019 (COVID-19). Three cases of Parkinson's disease (PD) have been reported as a direct consequence of COVID-19. In spite of the scarce data for establishing a definitive link between COVID-19 and PD, some hypotheses have been proposed to explain the cases reported. They, however, do not fit well with the clinical findings reported for COVID-19 patients, in general, and for the PD cases reported, in particular. Given the importance of this potential connection, we present here a molecular-level mechanistic hypothesis that explains well these findings and will serve to explore the potential CNS damage in COVID-19 patients. The model explaining the cascade effects from COVID-19 to CNS is developed by using bioinformatic tools. It includes the post-translational modification of host proteins in the lungs by viral proteins, the transport of modified host proteins via exosomes out the lungs, and the disruption of protein-protein interaction in the CNS by these modified host proteins. Our hypothesis is supported by finding 44 proteins significantly expressed in the CNS which are associated with PD and whose interactions can be perturbed by 24 host proteins significantly expressed in the lungs. These 24 perturbators are found to interact with viral proteins and to form part of the cargoes of exosomes in human tissues. The joint set of perturbators and PD-vulnerable proteins form a tightly connected network with significantly more connections than expected by selecting a random cluster of proteins of similar size from the human proteome. The molecular-level mechanistic hypothesis presented here provides several routes for the cascading of effects from the lungs of COVID-19 patients to PD. In particular, the disruption of autophagy/ubiquitination processes appears as an important mechanism that triggers the generation of large amounts of exosomes containing perturbators in their cargo, which would insult several PD-vulnerable proteins, potentially triggering Parkinsonism in COVID-19 patients.