Thread by @farid__jalali

🧵on serotonin, SSRIs, 5HT2 receptor antagonism, bromhexine, and niclosamide mechanisms of action in COVID as it pertains to our recently published RCT

This will be detailed. References in parentheses and listed in the last tweet.

https://x.com/farid__jalali/status/1768418776998158600?s=20

Clinical deterioration in COVID-19 typically occurs during the second week of illness, marked by a severe immune reaction and excessive production of pro-inflammatory cytokines such as IL-6, IL-8, TNF-α, and IL-1β. (2)

Elevations in these serum cytokines are not only predictive of and signify acute disease progression and mortality, but are also associated with a higher risk of developing post-acute sequelae of COVID-19 (PASC) #longcovid. (1, 2, 7)

Therefore, curtailing this immune dysregulation at an early stage using safe and affordable repurposed agents may reduce disease severity, improve clinical outcomes, and reduce the risk of #longcovid development.

That was the premise behind conducting our recently published RCT.

Now we can delve into the specific rationale for each agent we chose to include in this trial. First, fluvoxamine:

Previous clinical studies have shown that fluvoxamine, a selective serotonin reuptake inhibitor (SSRI), is associated with benefit in the treatment of acute COVID. (8, 9, 10)

Additionally, SSRI use during acute COVID-19 has also been associated with a 26% reduction in the risk of PASC development. (11)

The mechanism of this observed benefit remains unclear and is thought to be multifactorial.

Fluvoxamine may exert benefit by acting as an immunomodulator and a host-directed antiviral (as opposed to direct-acting antivirals such as Paxlovid) via its serotonin modulatory effects on platelets and immune cells.

These effects on platelets and immune cells are likely not unique to Fluvoxamine, but apply to SSRIs as a class.

Now how could the effect of SSRIs on platelets translate into possible clinical benefit?

COVID-19 disease progression is characterized by intense platelet activation, induced by afucosylated antibodies and mediated by the ​​FcγR receptor action on monocytes and platelets (12).

FcγR signaling via these afucosylated IgGs against the spike protein causes intense monocyte activation and destruction of platelets.

See this thread for details from our other work (submitted to a high-impact journal):

https://x.com/farid__jalali/status/1683707701866692608?s=20

Platelets contain the largest reservoir of serotonin in our bodies.

FcγR-mediated platelet activation and destruction by monocytes in COVID-19 leads to the release of a large amount of serotonin from platelets in COVID-19.

The amount of serotonin released from platelets in COVID-19 is demonstrated to be far beyond what occurs in other etiologies of acute lung injury including those caused by other infections (13).

Such FcγR-mediated platelet serotonin release has been shown to directly mediate acute lung injury and lung edema in other disorders (14).

In these animals studies, lung injury was markedly reduced by serotonin inhibition achieved by two means:

1⃣ by use of an SSRI to block platelet serotonin uptake and to deplete platelet serotonin, or

2⃣ by directly blocking the 5HT-2 serotonin receptor, which was shown to mediate the lung injury (14).

COVID-19 acute lung injury is similarly driven by FcγR-mediated platelet activation (12), making it plausible that ...

... platelet serotonin depletion by early SSRI use in COVID-19 may lower the risk of acute lung injury, lung edema, hypoxemia, and other pathogenic effects of FcγR-mediated platelet serotonin release such as shock (​14, 15).

That is, in other words, preventing "severe COVID"

Decreased platelet serotonin release by early SSRI use in COVID-19 may also diminish the endothelial injury and the immunopathology in this disease.

As serotonin released from activated platelets is shown to:

🔶 cause endothelial barrier disruption mediated by the 5HT2 receptor (16)

🔶 act as a potent mediator and propagator of platelet activation, platelet aggregation, and platelet-leukocyte aggregation (17, 18, 19)

and

🔶 modulate the release of pro-inflammatory cytokines including IL-6 and TNF-α from monocytes (19)

all of which are widely described as pivotal events in COVID-19 disease progression (20).

Now, how does serotonin modulation potentially lead to host-directed antiviral action? Is there any literature on this?

Decreased platelet serotonin release may indeed reduce the risk of viral persistence.

In a mouse model of LCMV infection (enveloped RNA virus, as is SARS-CoV-2), platelet serotonin release during the viral infection was shown to be responsible for

🔶 viral persistence, and
🔶 increased virus-induced immunopathology (21)

Once again, platelet serotonin depletion using an SSRI, or blocking the 5HT2 receptor reversed this effect and led to

🔶 faster viral clearance,
🔶 reduced viral persistence, and
🔶 reduced virus-induced immunopathology (21)

Other potential mechanisms of benefit of SSRIs, particularly fluvoxamine, include anti-inflammatory effects via the sigma-1 receptor action, and via the functional inhibition of acid sphingomyelinase (FIASMA) pathways (7).

Given (reviewed above) the central nature of the 5HT2 receptor in mediating pathogenic serotonin effects of:

🔶 endothelial barrier disruption (16),
🔶 platelet activation and
aggregation (17, 18, 19),
🔶 viral persistence (21), and
🔶 acute lung injury

and in light of recent data showing survival benefit in COVID-19 from the use of agents such as mirtazapine with potent 5HT2 receptor antagonism (22),

a generic 5HT2 receptor antagonist as in cyproheptadine was chosen to be used in combination with fluvoxamine.

Combining cyproheptadine with fluvoxamine had the added benefit of reducing the serotonergic side effects of SSRI initiation, a not uncommon practice safely employed in clinical psychiatry (23).

Reducing the serotonergic side effects of high-dose fluvoxamine by concurrent use of cyproheptadine can be crucial to its real-world applicability, as ...

such serotonergic side effects of fluvoxamine have been a source of medication intolerance among participants in prior trials (8, 9) ...

to the extent that these side effects have necessitated a reduction in the dose of fluvoxamine used in subsequent trials to allow better tolerability (24).

Other agents used in this trial include bromhexine hydrochloride and niclosamide.

Bromhexine hydrochloride is a potent inhibitor of transmembrane protease serine type 2 (TMPRSS2) which serves as one of the two key cell entry pathways for SARS-CoV-2 in humans (25).

TMPRSS2, expressed richly in human respiratory epithelial cells, has been shown to be essential for host cell viral entry and replication of SARS-CoV-2.

Therefore, inhibition of TMPRSS2 by bromhexine may reduce infectivity of host cells and facilitate faster viral clearance.

Early use of bromhexine in treatment of COVID-19 had demonstrated potential promise in smaller clinical trials (26, 27).

Lastly, niclosamide has been demonstrated to possess antiviral effects against SARS-CoV-2 by blocking spike-induced cell fusion and syncytia formation (28).

This effect by niclosamide is achieved via its inhibitory action on the calcium-activated chloride channel transmembrane protein TMEM16, which is found on the membrane of platelets and endothelial cells.

Niclosamide additionally blocks the procoagulant effect of SARS-CoV-2 Spike protein on platelets.

preventing externalization of phosphatidylserine, and thereby reducing thrombin-induced clot formation (28).

In a recent clinical trial, treatment with niclosamide among those with a higher initial respiratory SARS-CoV-2 viral load led to a faster viral clearance and a faster resolution of symptoms compared with placebo (29).

These four agents, though not known to act as direct-acting antiviral agents (e.g. Paxlovid) against SARS-CoV-2 ...

each employ different mechanisms to exert host-directed antiviral and immunomodulatory effects.

Therefore, it was plausible (to us at least) that combining these agents may provide synergistic action to achieve faster viral clearance and to attenuate the inflammatory and immunothrombotic pathways responsible for COVID-19 disease progression.

Hence, the arms in our RCT:

We hypothesized that combinations of these agents may potentiate the beneficial effects of each agent alone, and

early treatment with combination of these agents may reduce the risk of disease progression in COVID-19.

The aim of this trial was to investigate this hypothesis.

Below are the references for this thread. I encourage folks to read these references if possible.

We welcome questions and constructive feedback.

@dr_leshan

@dr_leshan Lastly, I forgot to mention:

We have animal data (submitted) showing SSRI use to deplete platelet serotonin significantly reduces thrombosis (clot) formation in an accurate model of acute COVID.

Hopefully we can release those results when completed peer review and published.