COVID-19: Melatonin as a potential adjuvant treatment
https://doi.org/10.1016/j.lfs.2020.117583

Excessive inflammation, oxidation, and exaggerated immune response very likely contribute to COVID-19 pathology.

This leads to cytokine storm and acute lung injury (ALI)/acute respiratory distress syndrome (ARDS).

Melatonin is anti-inflammatory and anti-oxidative and protective against acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) caused by virus.

Melatonin reduce vessel permeability

Melatonin may be beneficial for better clinical outcomes for COVID-19 patients. Additional studies are required to confirm this speculation.

Melatonin has a high safety profile.

Melatonin limits virus-related diseases

There is no specific treatment for COVID-19. (Antiviral therapy, corticosteroid therapy and mechanical respiratory support have been applied).

Melatonin (N-acetyl-5-methoxytryptamine) is a bioactive molecule with an health-promoting properties;

Melatonin alleviate acute respiratory stress induced by virus, bacteria, radiation, etc.

Lungs from mild COVID-19 patients showed edema, proteinaceous exudate with globules, patchy inflammatory cellular infiltration and moderate formation of hyaline membranes

These findings resemble the pathological features found in SARS- and MERS-induced pneumonia.

Covid19-coronavirus (SARS-CoV-2) shares 79.0% nucleotide identity to SARS (SARS-CoV) and 51.8% nucleotide identity to MERS (MERS-CoV)

SARS-CoV and MERS-CoV may activate a “cytokine storm”, and apoptosis of epithelial cells and endothelial cells; vascular leakage, abnormal T cell and macrophages responses

It has been predicted that a cytokine storm also prevails in patients with COVID-19.

Compared to that of SARS patients the blood of patients with COVID-19 has marked increase in interleukin 1β (IL-1β), interferon γ (IFN-γ), interferon-inducible protein 10 (IP-10), monocyte chemoattractant protein 1 (MCP-1), IL-4 and IL-10.

This suggests some difference from SARS and MERS in the pathogenesis of coronavirus.

There may be repressed immune function in COVID-19 patients with hypo-albuminemia, lymphopenia, neutropenia, and decreased percentage of CD8+ T cell.

Some COVID-19 patients, although negative for the viral nucleic acid test, still sometimes present high inflammation.

TNF blocker (certolizumab pegol) along with other anti-virus therapies may have beneficial effects in COVID-19 patients.

Inflammation is a major feature in COVID-19 patients.

Excessive inflammation, depressed immune system, and cytokine storm may contribute to the pathogenesis of COVID-19.

In early stages of coronaviruses infection, dendritic cells and epithelial cells express pro-inflammatory cytokines and chemokines including IL-1β, IL-2, IL-6, IL-8, both IFN-α/β, tumor necrosis factor (TNF), CC motif chemokine 3 (CCL3), CCL5, CCL2, and IP-10, etc.

Overproduction of these cytokines and chemokines contributes to the disease.

IL-10, produced by T-helper-2 (Th2), is antiviral. Coronavirus is leading to a decrease in this agent.

Interestingly, COVID-19 patients sometimes have elevated level of IL-10 (this could be a feature of the COVID-19 infection or the result of medical treatment).

The amplification of the inflammatory response would promote cellular apoptosis/necrosis of affected cells, which would further fuel inflammation, followed by increasing permeability of blood vessels and accumulation of inflammatory monocytes, macrophages and neutrophils in the lung alveoli.

This vicious circle would intensify the situation as the regulation of immune response is lost and cytokine storm is further activated, resulting in bad consequences.

This putative “cytokine storm” pathology associated with coronaviruses is supported by experimental models of SARS (SARS-CoV), one of which showed that the severity of ALI was accompanied by an elevated expression of inflammation-related genes rather than increased viral titers.

In another case, ablation of IFN-α/β receptor or depletion of inflammatory monocytes/macrophages caused rise in the survival rate of coronaviruses host without change in viral load.

Both situations suggest potential amplifying mechanism in CoV-induced ALI/ARDS regardless of viral load.

If similar pathology exists in COVID-19, attenuation of cytokine storm could improve outcomes.

Melatonin has indirect anti-viral actions due to anti-inflammation, anti-oxidation and immune enhancing features.

In mice infected by virus (encephalitis), melatonin reduced paralysis and decreased virus load.

In respiratory syncytial virus models, melatonin caused down-regulation of acute lung oxidative injury and down-regulation of cytokine release.

Melatonin's anti-inflammation, anti-oxidation, immune enhancing actions supports its potential attenuation of COVID-19 infection.

We postulate that lungs infected by SARS-CoV-2, and suppressed immune response, elevated inflammation and excessive oxidation stress results in activation of cytokine storm.

Melatonin may play a role of adjuvant medication in the regulation of immune system, inflammation and oxidation stress.

ALI: Acute lung injury;
ARDS: Acute respiratory distress syndrome.

3. Melatonin & anti-inflammation
Melatonin exerts anti-inflammatory effects through various pathways.

Sirtuin-1 (SIRT1) may mediate the anti-inflammatory actions of melatonin by inhibiting high mobility group boxechromosomal protein 1 (HMGB1), and thus down-regulating the polarization of macrophages towards the pro-inflammatory type.

In sepsis-induced ALI, the proper regulation of SIRT1 attenuates lung injury and inflammation, in which the application of melatonin might be beneficial.

Nuclear factor kappa-B (NF-κB) is associated with pro-inflammatory and pro-oxidative responses while being an inflammatory mediator in ALI.

The anti-inflammatory effect of melatonin involves suppression of NF-κB activation in ARDS.

Melatonin down-regulate NF-κB activation in T cells and lung tissue.

Stimulation of NF-E2-related factor 2 (Nrf2) is crucial in protecting lung from injury.

Melatonin induces up-regulation of Nrf2 with therapeutic effects in hepatoprotection, cardioprotection, etc.

The close interaction of SIRT1, NF-κB and Nrf2 suggests their participation in the CoV-induced ALI/ARDS.

Inflammation is associated with elevated production of cytokines and chemokines

Melatonin causes a reduction in the pro-inflammatory cytokines.

TNF-α, IL-1β, IL-6, and IL-8, and an elevation in the level of anti-inflammatory cytokine IL-10.

There may be, however, some concerns about the potential pro-inflammatory actions of melatonin when used in very high doses or under suppressed immune conditions where it may induce an increase production of pro-inflammatory cytokines, IL-1β, IL-2, IL-6, IL-12, TNF-α, and IFN-γ.

Conversely, in ALI infection models, melatonin presents with anti-inflammatory and protective action.

4. Melatonin & anti-oxidation
The anti-oxidative effect of melatonin cooperates with its anti-inflammatory actions by up-regulating anti-oxidative enzymes (e.g. superoxide dismutase), down-regulating pro-oxidative enzymes (e.g. nitric oxide synthase), and it may also interact directly with free radicals, functioning as free radical scavenger.

Viral infections generate oxidized products.

In a SARS-induced ALI model, the production of oxidized low density lipoprotein activates innate immune response by overproduction of IL-6 alveolar macrophages via Toll-like receptor 4 (TLR4)/NF-kB signaling, thereby leading to ALI.

TLR4 is a receptor for the innate immune system, and it is also a therapeutic target for melatonin.

In brain ischemia, gastritis and periodontitis disease models, melatonin has documented anti-inflammation actions via TLR4 signaling.

Anti-oxidative effect of melatonin has been confirmed in ALI caused by radiation, sepsis and ischemia-reperfusion.

In ALI/ARDS patients, especially when the disease is advanced and in patients treated in intense care units (ICUs), severe inflammation, hypoxemia and mechanical ventilation with high oxygen concentrations increases oxidant generation locally and systematically.

We speculate that excessive oxidation is likely involved in COVID-19.

Melatonin to treat newborn infants with respiratory distress has anti-oxidant and anti-inflammatory actions (of melatonin) in the lung.

It is likely that application of melatonin would be beneficial in controlling inflammation and oxidation in COVID-19.

5. Melatonin & immunomodulation
When virus is inhaled and infects respiratory epithelial cells, dendritic cells phagocytose the virus and present antigens to T cells.

Effector T cell function by killing infected epithelial cells, and cytotoxic CD8+ T cells produce and release pro-inflammatory cytokines which induce cell apoptosis.

Both the coronavirus and the cell apoptosis trigger and amplify the immune response.

The cytokine production, recruitment of immune cells and uncontrollable epithelial damage generates a vicious circle for infection related ALI/ARDS.

The clinical characteristics of COVID-19 suggest a reduced level of neutrophils, lymphocytes and CD8+ T cells in peripheral blood.

Melatonin exerts regulatory actions on the immune system and enhances the immune response by improving proliferation and maturation of natural killing cells, T and B lymphocytes, granulocytes and monocytes in both bone marrow and other tissues.

In macrophages, antigen presentation is augmented after the application of melatonin, where up-regulation of complement receptor 3, MHC class I and class II, and CD4 antigens were detected.

NOD-like receptor 3 (NLRP3) inflammasome is part of the innate immune response during lung infection.

There is probably a balance of the protective and damaging actions of NLRP3 in the lung.

In a mouse experiment inhibition of NLRP3 in early phase of infection increased mortality, whereas suppression of NLRP3 at peak of infection gave protective effect.

This supports the use of melatonin in ALI/ARDS when inflammation is most severe.

Inflammasome NLRP3 is correlated to lung diseases caused by infection, including influenza A virus, syncytial virus, and bacteria.

The efficacy of melatonin in regulating NLRP3 has been proven in radiation-induced lung injury, allergic airway inflammation and oxygen-induced ALI and LPS-induced ALI models (in which melatonin reduced the infiltration of macrophages and neutrophils into the lung in ALI due to the inhibition of NLRP3 inflammasome).

6. Melatonin effects in cytokine levels in human
There is no report of use of melatonin in COVID-19 patients

In subjects with other diseases and increased level of inflammation, melatonin showed promising results (regarding the attenuation of circulating cytokines levels).

In patients with diabetes mellitus and periodontitis oral intake of 6 mg/d melatonin decreased serum levels of IL-6, TNF-α and hs-C-reactive protein (hs-CRP).

In patients suffering with severe multiple sclerosis, orally 25 mg/d of melatonin for 6 months promoted a reduction in serum concentrations of TNF-α, IL-6, IL-1β and lipoperoxides.

In the acute phase of inflammation (during surgical stress, brain reperfusion, and coronary artery reperfusion), melatonin intake of 10 mg/d, 6 mg/d and 5 mg/d for less than 5 days reduced levels of pro-inflammatory cytokines.

22 trials suggested that melatonin is associated with reduction of TNF-α and IL-6 level.

This suggests that use of melatonin reduce the levels of circulating cytokines, and may also lower pro-inflammatory cytokine levels in COVID-19 patients.

7. Melatonin & other supportive adjuvant effects
The integrity of the vascular endothelial barrier is crucial in the immunoregulation within alveoli.

Severe inflammation and immune responses induce epithelial and endothelial cell apoptosis, and increase production of VEGF, which aggravates edema and extravasation of immune cells from blood vessels.

Melatonin may mediate suppression of VEGF in vascular endothelial cells.

COVID-19 patients with severe ALI/ARDS may have increased risk of sepsis and cardiac arrest.

Application of melatonin may ameliorate septic shock via the NLRP3 pathway.

Melatonin may have preventive effect against sepsis-induced renal injury, septic cardiomyopathy and liver injury.

Melatonin benefit patients with myocardial infarction, cardiomyopathy, hypertensive heart diseases and pulmonary hypertension, and probably functions via the TLR4/survivor activating factor enhancement pathway.

Melatonin exerts neurological protection by reducing the cerebral inflammatory response, cerebral edema and brain-blood barrier permeability.

In the ICU, deep sedation is associated with increased long-term mortality, and application of melatonin reduces sedation use and the frequency of pain, agitation, anxiety.

Melatonin improves sleep quality in patients in the ICU.

The rationale for use of melatonin in COVID-19 patients not only focus on attenuation of infection-induced respiratory disorders, but also patients' wellbeing.

8. Melatonin & safety
Short-term use of melatonin is safe, even in those given high doses, and the adverse effects are limited to occasional dizziness, headache, nausea and sleepiness.

Doses of 3 mg, 6 mg and 10 mg of melatonin oral intake by patients in ICU showed safe.

Even when melatonin was given at 1 g/d for a month, there were no adverse reports.

There were no adverse effects after use of melatonin in ALI/ARDS animal studies.

Safety of melatonin has been verified in many human studies, but its effect when given to COVID-19 patients should be monitored despite the very high safety profile of melatonin.

9. Conclusion
Possible beneficial effects of melatonin in COVID-19 anti-inflammation, anti-oxidation, immune response regulation has been demonstrated in respiratory disorder models.

Melatonin use by COVID-19 patients predictably would be beneficial.