Brain Leukocytes as the Potential Therapeutic Target for Post-COVID-19 Brain Fog.

After recovering from the acute phase of coronavirus disease 2019 (COVID-19), many patients struggle with additional symptoms of long COVID during the chronic phase. Among them, the neuropsychiatric manifestations characterized by a short-term memory loss and inability to concentrate are called "brain fog". Recent studies have revealed the involvement of "chronic neuro-inflammation" in the pathogenesis of brain fog following COVID-19 infection. In the COVID-related brain fog, similarly to neurodegenerative disorders caused by neuro-inflammation, brain leukocytes, such as microglia and lymphocytes, are hyperactivated, suggesting the overexpression of delayed rectifier K+-channels (Kv1.3) within the cells. In our previous patch-clamp studies, drugs, such as antihistamines, statins, nonsteroidal anti-inflammatory drugs, antibiotics and anti-hypertensive drugs, suppressed the Kv1.3-channel activity and reduced the production of pro-inflammatory cytokines. Additionally, newer generation antihistamines, antibiotics and corticosteroids strongly stabilize mast cells that directly activate microglia in the brain. Taking such pharmacological properties of these commonly used drugs into account, they may be useful in the treatment of COVID-related brain fog, in which the enhanced innate and adaptive immune responses are responsible for the pathogenesis.

Targeting ACE2 as a potential prophylactic strategy against COVID-19-induced exacerbation of chronic kidney disease.

Patients with chronic kidney disease (CKD) are at higher risk for severe coronavirus disease 2019 (COVID-19). Such patients are more likely to develop "COVID-19-induced acute kidney injury (AKI)", which exacerbates the pre-existing CKD and increases the mortality rate of the patients. COVID-19-induced AKI is pathologically characterized by acute tubular necrosis and the interstitial infiltration of proinflammatory leukocytes. In our rat model with advanced CKD, immunohistochemistry for angiotensin-converting enzyme 2 (ACE2) and transmembrane protease serine 2 (TMPRSS2) demonstrated their strong expression in the cytoplasm of damaged proximal tubular cells and the infiltrating leukocytes within the cortical interstitium, which overlapped with the lesions of COVID-19-induced AKI. Since ACE2 and TMPRSS2 are enzymes that facilitate the viral entry into the cells and trigger the onset of cytokine storm, the renal distribution of these proteins in advanced CKD was thought to be responsible for the development of COVID-19-induced AKI. Concerning such mechanisms, the pharmacological blockade of ACE2 or the use of soluble forms of the ACE2 protein may halt the entry of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) into host cells. This would protect against the COVID-19-induced exacerbation of pre-existing CKD by preventing the development of AKI.

Potential prophylactic efficacy of mast cell stabilizers against COVID-19 vaccine-induced anaphylaxis.

To fight against coronavirus disease 2019 (COVID-19), the vaccination is currently the most effective approach. However, in addition to common systemic side effects, the vaccines can cause serious allergic reactions or anaphylaxis. In anaphylaxis, the exposure to the allergen causes a sudden release of chemical mediators from mast cells, for which adrenaline is the drug of first choice. In our previous basic studies, in addition to adrenaline, anti-allergic drugs (olopatadine, loratadine, tranilast and ketotifen), antibiotics (clarithromycin), corticosteroids (hydrocortisone and dexamethasone) and certain food constituents (caffeine and catechin) inhibited the process of exocytosis and showed their effectiveness as highly potent mast cell stabilizers. In these studies, since mast cells were pre-incubated with these drugs or the food constituents before exocytosis was induced, the findings strongly indicated their prophylactic efficacy in stabilizing mast cells. Considering such pharmacological properties of these commonly prescribed medications or the food constituents, their prophylactic use may potentially be beneficial in preventing anaphylaxis caused by COVID-19 vaccination.

Does immunosuppressive property of non-steroidal anti-inflammatory drugs (NSAIDs) reduce COVID-19 vaccine-induced systemic side effects?

To help stop the coronavirus disease 2019 (COVID-19) pandemic, vaccines are currently the most critical tool. However, the COVID-19 mRNA vaccines frequently cause systemic side effects shortly after the injection, such as fever, headache and generalized fatigue. In our survey, after receiving the second dose of the COVID-19 vaccine, 80% developed fever, 62% headache and 69% generalized fatigue. Among people who required antipyretics, the average durations of fever and headache were significantly shorter in those who took non-steroidal anti-inflammatory drugs (NSAIDs), such as aspirin, loxoprofen and ibuprofen, than those who took acetaminophen. In our patch-clamp studies, NSAIDs effectively suppressed the delayed rectifier K+-channel (Kv1.3) currents in T-lymphocytes and thus exerted immunosuppressive effects. Because of this pharmacological property, the use of NSAIDs should be more effective in reducing the vaccine-induced systemic side effects that are caused primarily by the enhanced cellular immunity.

Stabilizing mast cells by commonly used drugs: a novel therapeutic target to relieve post-COVID syndrome?

Regardless of the severity of coronavirus disease 2019 (COVID-19), a high proportion of patients struggle with persistent respiratory or systemic symptoms after recovery. This is called "postCOVID syndrome", for which pulmonary fibrosis is one of the pathogenesis. Besides T-lymphocytes and macrophages, mast cells also contribute to the development of cytokine storm and thus stimulate the activity of fibroblasts. Additionally, by the exocytotic release of fibroblast-activating factors, mast cells directly facilitate the progression of pulmonary fibrosis. In our previous basic studies, anti-allergic drugs (olopatadine, ketotifen), antibiotics (clarithromycin) and corticosteroids (hydrocortisone, dexamethasone) inhibited the process of exocytosis and showed their potency as highly effective mast cell stabilizers. Given such pharmacological properties of these commonly used drugs, they may be useful in the treatment of post-COVID-19 pulmonary fibrosis and in relieving the symptoms of post-COVID syndrome.

Targeting lymphocyte Kv1.3-channels to suppress cytokine storm in severe COVID-19: Can it be a novel therapeutic strategy?

In the midst of a pandemic, finding effective treatments for coronavirus disease 2019 (COVID-19) is the urgent issue. In "chronic inflammatory diseases", the overexpression of delayed rectifier K+-channels (Kv1.3) in leukocytes is responsible for the overactivation of cellular immunity and the subsequent cytokine storm. In our previous basic studies, drugs including chloroquine and azithromycin strongly suppressed the channel activity and pro-inflammatory cytokine production from lymphocytes. These findings suggest a novel pharmacological mechanism by which chloroquine, with or without azithromycin, is effective for severe cases of COVID-19, in which the overactivation of cellular immunity and the subsequent cytokine storm are responsible for the pathogenesis.