Donepezil ameliorates fatigue and depression in PASC patients with HHV-6B SITH-1-induced acetylcholine deficiency, 2026, Oka et al.

[Chandelier]

Donepezil ameliorates fatigue and depression in PASC patients with HHV-6B SITH-1-induced acetylcholine deficiency

Spoiler: Authors

Oka, Naomi; Nakamura, Kensuke; Hirahata, Koichi; Ishii, Azusa; Yamakawa, Kazuma; Ie, Kenya; Goto, Tadahiro; Shimada, Kazuya; Fujitani, Shigeki; Kondo, Kazuhiro

Abstract​

Introduction: The pathogenesis of post-acute sequelae of SARS-CoV-2 infection (PASC) remains poorly understood, and no effective treatment has been established.
Reactivation of latent herpesviruses, particularly human herpesvirus 6B (HHV-6B), has been proposed as a possible contributor to the neuropsychiatric symptoms observed in PASC. SITH-1, a latency-associated protein expressed during HHV-6B reactivation in olfactory bulb astrocytes, induces specific antibody responses that can be detected in peripheral blood.
Importantly, SITH-1 has also been identified as a risk factor for depression, suggesting a mechanistic link between HHV-6B reactivation and the development of neuropsychiatric symptoms.

Methods: We measured serum anti-SITH-1 antibody titers in 156 PASC patients and compared them to healthy controls.
In this PASC cohort, neuropsychiatric symptoms were assessed using numerical rating scales.
In parallel, we developed a mouse model in which SITH-1 was transiently expressed in the olfactory bulb to assess its impact on brain function and behavior.
We also conducted a subgroup analysis of a previously reported randomized clinical trial (RCT) of donepezil, stratifying PASC patients by anti-SITH-1 antibody status.

Results: Anti-SITH-1 antibody positivity was observed in 62.8% of PASC patients, a significantly higher proportion than in controls.
Seropositive patients exhibited more severe fatigue and depressive symptoms. In the mouse model, SITH-1 expression led to reduced acetylcholine production and depression-like behavior, both of which were ameliorated by donepezil.
In the clinical trial subgroup of 73 PASC patients, 71.7% were seropositive for anti-SITH-1 antibodies.
Among these individuals, donepezil significantly improved fatigue and depression scores, as measured by the Chalder Fatigue Scale and the depression subscale of the Hospital Anxiety and Depression Scale (HADS).

Conclusion: These findings suggest that HHV-6B reactivation in the olfactory bulb, as indicated by anti-SITH-1 antibody titers, may contribute to fatigue and depression in a subset of PASC patients.
Donepezil may be effective in this subgroup, and these findings support the use of anti-SITH-1 antibody titers as a companion diagnostic marker for targeted treatment in PASC.


Web | DOI | PMC | PDF | Frontiers in Pharmacology

 

[Hutan]

Japanese team

Introduction

To explore one such mechanism, we focused on the disruption of acetylcholine signaling in the context of SARS-CoV-2 infection (Lysenkov et al., 2021; Lykhmus et al., 2022; Nadwa et al., 2023; Oka et al., 2023). In a previous study, we demonstrated that a COVID-19 model mouse expressing the SARS-CoV-2 spike (S1) protein in the nasal cavity exhibited fatigue- and depression-like behavioral symptoms resulting from brain inflammation. This inflammation was associated with dysfunction of the cholinergic anti-inflammatory pathway, driven by reduced levels of brain
acetylcholine. Administration of the acetylcholinesterase inhibitor like donepezil alleviated both the behavioral symptoms and brain inflammation, likely via restoration of cholinergic anti-inflammatory pathway (Oka et al., 2023).

Based on these findings, we conducted a randomized clinical trial (RCT) to investigate the efficacy of donepezil in treating post-COVID-19 fatigue and psychological symptoms (Kawabata et al., 2024; Nakamura et al., 2025). In that trial, however, donepezil did not show statistically significant efficacy, likely due to the inclusion of participants who either did not meet strict diagnostic criteria for PASC or had PASC arising from heterogeneous etiologies (Nakamura et al., 2025).

This led us to hypothesize that a subgroup of patients might benefit from donepezil when stratified using relevant biomarkers. In particular, anti-SITH-1 antibody titers, which reflect reactivation of HHV-6B through expression of the latency-associated protein SITH-1, emerged as a promising biomarker for identifying patients who are responsive to treatment (Kobayashi et al., 2020).

HHV-6B typically causes roseola infantum during primary infection and then establishes lifelong latency

The second site of latency is the brain, particularly astrocytes in the olfactory bulb (Donati et al., 2005). In this compartment, the SITH-1 protein is expressed during both latency establishment and reactivation (Kobayashi et al., 2020). Although olfactory bulb tissue is not readily accessible in humans, reactivation in this site can be inferred from elevated serum anti-SITH-1 antibody titers (Kobayashi et al., 2020). Because HHV-6B reactivation in the olfactory bulb can occur even in individuals with normal immune function, the reactivated virus remains localized near the olfactory bulb and does not lead to systemic HHV-6B infection.

 

[Hutan]

Method

The team had previously done a trial in PASC, 55 donepezil and 55 placebo completed the trial. They didn't get a positive result.

This study is a retrospective analysis, investigating the relationship between anti-SITH-1 antibody titers in the serum samples that were collected at the time of the trial and treatment efficacy.

The authors acknowledge this is an exploratory exercise.

Of the 110 participants, only 73 were used for the retrospective analysis.

Of the 110 participants, 73 patients (35 men and 38 women) were included in the subgroup analysis as PASC cases, based on the WHO concept of symptom persistence for at least 2 months. For this subgroup analysis, PASC was operationally defined as persistent fatigue lasting at least 60 days after SARS-CoV-2 infection. These 73 patients were analyzed according to their original randomized, double-blind treatment assignment to placebo (n = 35; 12 men, 23 women) or donepezil (n = 38; 16 men, 22 women).

I think the reason for the reduced number of participants is that the ones in this analysis had persistent fatigue for at least two months after Covid-19. That seems like a very low bar, and does suggest that there was an overly loose definition of PASC in their initial study.

Among the 73 patients included in the subgroup analysis, 52 participants (71.2%; 18 men and 34 women) were seropositive for anti-SITH-1 antibodies. Treatment efficacy was compared between seropositive and seronegative groups.

 

[Hutan]

The presence or absence of anti-SITH-1 antibodies had no relation to PASC symptoms. That is not necessarily death to the hypothesis I guess, maybe the herpes reactivation in the olfactory bulb doesn't result in anti-SITH-1 antibodies in the blood. Or maybe a range of antibodies or other things are causing much the same symptoms.

Here are the results they report for the treatment with donepezil.






Donepezil perhaps slightly improved depression and fatigue on average in the whole cohort, but there's not really a big enough difference to be convincing.

The donepezil group with SITH-1 positive ABs did much better than the placebo group. But, is it really ok to split out the SITH-1 positive people? The SITH-1 positive ABs groups accounted for about 72% of the PASC sample.

 

[Hutan]

The authors did a lot of work with mice - I haven't got it in me to look at that tonight.

I'm open to the idea of reactivation of a latent virus in a sensitive spot as a cause of ME/CFS. I'd want to read the paper more fully and think about it some more before deciding what I think about this paper.

I think perhaps the authors would benefit from looking at ME/CFS criteria and/or talking with clinicians who know what ME/CFS looks like. I think they might do better focusing on other symptoms and survey tools. HADS and the Chalder Fatigue Scale aren't the best, and symptoms like hair loss and the cough index might not be defining the group that they are after.