SARS-CoV-2 Infection and Valproic Acid: Comparison
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Please note this is a comparison between Version 1 by Donatas Stakišaitis and Version 2 by Catherine Yang.

The histone deacetylase inhibitor valproic acid (VPA) is a potential drug that could be adapted to prevent the progression and complications of SARS-CoV-2 infection. VPA has a history of research in the treatment of various viral infections. VPA inhibits SARS-CoV-2 virus entry, suppresses the pro-inflammatory immune cell and cytokine response to infection, and reduces inflammatory tissue and organ damage by mechanisms that may appear to be sex-related. The antithrombotic, antiplatelet, anti-inflammatory, immunomodulatory, glucose- and testosterone-lowering in blood serum effects of VPA suggest that the drug could be promising for therapy of COVID-19. Sex-related differences in the efficacy of VPA treatment may be significant in developing a personalised treatment strategy for COVID-19.

  • valproic acid
  • COVID-19

1. SARS-CoV-2 Virus and VPA

The docking, binding energy calculation determines that VPA metabolite 4-ene-VPA-CoA creates a stable interaction with nsP12 of SARS-CoV2 RNA polymerase and VPA-CoA could specifically inhibit the target. SARS-CoV-2 RNA polymerase is an enzyme playing in viral RNA replication and the virus’s survival in a host [1][2][51,52]. The SARS-CoV-2 virus x-ray crystal structure of a critical protein in the virus’s life cycle is the central protease (Mpro, 3CLpro) [3][4][5][53,54,55]. The Mpro importance recognises Mpro as a target for antiviral drugs, designed as a virus 3CLpro inhibitor, for COVID-19 therapy [6][7][56,57]. HDACs’ inhibitors are tightly bound into the active site of the crystallographic virus Mpro structure [8][58]. The SARS-CoV-2 protease NSP5 interacts with the HDAC2. Researchers predict that NSP5 may inhibit the transportation of HDAC2 into a nucleus, and could affect the HDAC2 strength to interfere with the interferon response and inflammation [9][10][59,60]. Experimental studies show that the binding of HDAC2 to the promoters was lower in females than in males [11][61]. The HDAC2 activity can not only be modulated by VPA binding to the catalytic center, but the HDAC2 protein level is susceptible to selective regulation by VPA [12][62]. VPA blocks the zinc-containing catalytic domain of HDACs [13][63]. VPA treatment reduced HDAC2 level in male rats’ brain frontal cortex tissue, but no VPA effect was for HDAC2 protein in females [14][64].

2. Sex-Related COVID-19 Infection Progression Mechanisms and VPA

Due to the high viral infection load, membrane ACE2 and its mRNA expression are significantly diminished in COVID-19 patients [15][16][17][18][69,94,95,96]. At a later COVID-19 infection stage, down-regulated ACE2 in tissues may worsen the imbalance in the renin-angiotensin system (RAS). ACE2 has a protective effect through RAS regulation [19][97], and protects against RAS-mediated activations of harmful effects [15][20][69,98]. Depleting ACE2 in tissue cells leads to an increase in angiotensin II (Ang II) blood serum level and the activation of the AT1 receptors, which would activate ADAM17 more. The ACE2 expression is transcriptionally suppressed due to AT1 activation [21][99]. Increased Ang II levels act as a vasoconstrictor and a pro-inflammatory molecule through AT1 [22][100]. ACE2 knockout results in pathology similar to the acute respiratory distress syndrome in mice [23][101]. The ACE2 molecule reduces RAS activity by converting Ang II into Ang 1–7 [24][25][26][102,103,104], decreasing Ang II level and the AT1 activation, which manages reduced pathological inflammation effects in tissues [15][27][28][69,105,106]. Sex distinctions of the RAS in response to stimulation and inhibition of the system have been reviewed [29][30][31][81,107,108]. Higher levels of ANG (1–7) in women may inhibit the harmful effects of ANG II and its activation [32][109]. Compared with female rats, males have higher AT1 receptor RNA, higher AT1 protein levels, higher receptor density in kidneys and ∼40% higher specific AT1 binding in the glomeruli than females. These differences are 17β-estradiol (E2) dependent [29][31][33][81,108,110]. Activation of AT1 mediates ANG II’s biological functions, such as sodium reabsorption, vasoconstriction, increased oxidative stress and inflammation [34][35][111,112]. VPA, inhibiting HDAC1 and HDAC2, down-regulates Ang II and AT1 activity [36][37][113,114]. VPA reverses the ANG II-induced increment of HDAC2 RNA and protein levels in cardiomyocytes [38][115]. Anti-hypertensive action of VPA is mediated by the inhibition of HDAC1 via acetylation processes [36][39][113,116].

3. COVID-19 Thrombotic Complications and VPA

3.1. SARS-CoV-2 and Sex-Related Thrombotic Complications

The pathophysiology of COVID-19 complications is characterised by clinical features of thrombosis and disseminated intravascular coagulopathy in the airways, myocardium, kidneys, brain and other organs [40][179]. Thrombosis is found in approximately 30% of COVID-19 hospitalised patients [41][180]. The incidence of thrombosis in COVID-19 is higher in men than in women and explains the higher mortality in men [42][181]. In an analysis of 29 studies, 70% of all thromboembolic events occurred in men and 30% in women [43][182]. Viral invasion due to severe vascular endothelial damage triggers the coagulation cascade, impairs fibrinolytic activity, releases von-Willebrand factor [44][13], increases total cytokine release, activates platelets and the complement system and generates thromboxane [45][46][183,184]. SARS-CoV-2 can directly activate coagulation via the viral Mpro; the active site of Mpro is structurally similar to the active site of FXa and thrombin and can therefore activate coagulation [47][185]. The development of thrombosis has been attributed to the direct effects of the virus by increasing the levels of pro-inflammatory cytokines and pro-inflammatory M1 macrophages, by activation of the complement system and by endothelial dysfunction, leading to disseminated intravascular coagulopathy [48][49][50][51][186,187,188,189]. Endothelial dysfunction and its association with thrombosis have been implicated in SARS-CoV-2-induced target organ damage [52][190]. VPA binding to SARS-CoV-2 Mpro is expected to inhibit Mpro pathways [53][191]. Older men with hypertension, chronic kidney disease, coronary disease, diabetes mellitus and obesity are at increased risk of thrombotic complications [54][55][56][192,193,194]. Changes in plasma levels of D-dimer, von Willibrand factor (vWF), fibrinogen, tissue-type plasminogen activator (t-PA), plasminogen activator inhibitor-1 antigen (PAI-1) antigen are associated with poorer outcomes in COVID-19 patients [57][58][59][60][195,196,197,198].

3.2. VPA Effect on Thrombosis Mechanisms, COVID-19

The VPA effects on thrombogenesis have been explored in pre-clinical studies and during the treatment of patients with VPA (Table 12). HDAC inhibitors have reduced platelet counts and inhibit platelet function [61][62][199,200], while other VPA experimental and clinical trials did not find such effects [63][64][201,202]. The baseline platelet count was similar in women and men. A causal relationship between prolonged use and rising plasma VPA levels and reduced platelet counts, with reversal of thrombocytopenia after reduction of VPA dosage, was reported: that of thrombocytopenia substantially increased at VPA levels above 100 ug/mL in women and above 130 ug/mL in men; women were significantly more likely to develop thrombocytopenia [65][203]. There is a significantly higher female overrepresentation in heparin-induced thrombocytopenia, with females at approximately twice the risk of thrombocytopenia than males. However, the underlying mechanism for this sex difference is unclear [66][204]. VPA may affect several different coagulation factors: decrease in von Willebrand factor:antigen (vWF:Ag) concentration [67][68][205,206]; protein C level [67][69][205,207], protein S level [69][70][207,208], antithrombin III level, decrease prothrombin time [67][68][205,206] and increase activated partial thromboplastin time [67][68][69][205,206,207].
Table 12. VPA treatment effect on thrombogenesis.
# Thrombogenesis Related Factor Cells/Animals/Human Sex VPA Treatment Effect Ref.
1. Complement C3 HepG2 cells unknown ↓ C3 gene expression [71][209]
2. t-PA Human umbilical vein endothelial cells unknown ↑ t-PA production [72][210]
3. ICAM-1 expression Human umbilical vein ECs and

human coronary artery EC		 unknown ↓ ICAM-1 expression [73][83]
4. Platelets number C57BL/6 mice unknown ↓ platelets count [62][200]
5. Vascular t-PA C57BL/6 mice males ↑ endothelial vascular t-PA production;

↓ fibrin accumulation in response to vascular injury		 [63][201]
6. E-selectin and ICAM-1 Sprague–Dawley rats with subarachnoid hemorrhage induced vasospasm males ↓ the E-selectin and ICAM-1 level [74][211]
7. Platelets number Epileptic adult patients

and

healthy control		 men

and

women		 relationship between rising plasma VPA level and reduced platelet counts, with female sex additional risk factor [65][203]
8. Arachidonate cascade thromboxane A2 in platelets Epileptic adult patients

and

healthy control		 men ↓ activity of the arachidonate cascade in platelets;

↓ the cyclooxygenase pathway;

↓ synthesis thromboxane A2		 [61][199]
9. Von Willebrand factor:antigen Epileptic children patients

and healthy control		 male + female

(combined)		 ↓ concentration in blood serum [67][68][205,206]
10. Protein C Epileptic children patients

and healthy control		 male + female

(combined)		 ↓ concentration in blood serum [67][69][205,207]
11. Protein S Epileptic children patients

and healthy control		 male + female

(combined)		 ↓ concentration in blood serum [69][70][207,208]
12. Antithrombin III Epileptic children patients

and healthy control		 male + female

(combined)		 ↓ concentration in blood serum [67][68][205,206]
13. Prothrombin time Epileptic children patients

and healthy control		 male + female

(combined)		 ↓ concentration in blood serum [67][68][205,206]
14. Activated partial thromboplastin time Epileptic children patients

and healthy control		 male + female

(combined)		 ↓ concentration in blood serum [67][68][69][205,206,207]
↓ decreased; ↑ increased.
SARS-CoV-2 activates the complement system, either directly or through an immune response. Activated complement promotes inflammation [75][212]. Complement activation is increased and constant in severely ill COVID-19 patients, and complement activation is via the alternative pathway (AP) [76][213]. The anaphylatoxins C3a and C5a are significant contributors to the cytokine storm syndrome [77][214]. The healthy adult population is characterised by substantial sex-related differences in complement levels and function: significantly lower AP activity was in females than males. AP revealed lower C3 levels in women [78][215]. In experimental intestinal ischemia with an acute inflammatory response, complement activity was sex-dependent: female MBL-/- and P-/- mice had significantly less C5a in their serum than males [79][216]. Experimental results indicate that lysine acetylation by VPA is associated with attenuated C3 gene expression. VPA-associated reductions in circulating complement and clotting factors result from changes in liver-specific gene expression [71][209]. VPA inhibits intercellular adhesion molecule-1 (ICAM-1) and E-selectin [73][74][83,211]. Analysis from patients hospitalised with COVID-19 showed higher circulating VCAM-1 and E-selectin levels in men than women [80][217]. The endothelial cell adhesion molecules elevated levels promote tissue infiltration of circulating leukocytes and are associated with inflammation and thrombosis, which occur at a higher frequency in males [81][218]. VPA reduced endothelial cell dysfunction through the mechanisms of action of transforming growth factor-β (TGF-β) and vascular endothelial growth factor (VEGF) in a porcine model of ischemia-reperfusion of hemorrhagic shock [82][219]. Inhibiting TGF-β activity, VPA alleviates pulmonary fibrosis through epithelial-mesenchymal transition inhibition in vitro and in vivo [83][132]. Estradiol has been shown to decrease TGF-β1 synthesis [84][220]. VPA inhibiting IL-12 and TNF-α, reversing macrophage polarisation from pro-inflammatory to the anti-inflammatory type, and reducing macrophage infiltration reduces the risk of thrombosis [85][86][117,137].

3.3. VPA and Fibrinolysis

Treatment with VPA in a rat thrombosis model reduced thrombus formation and did not increase bleeding tendency [63][201]. VPA can selectively manipulate the fibrinolytic system to reduce thrombus formation in blood vessels in vivo. In a murine model of thrombosis induced by intravascular injury, VPA treatment increased t-PA production in blood vessels [63][72][87][88][89][201,210,221,222,223] was associated with less fibrin accumulation and fewer thrombi [63][90][201,224]. Impaired fibrinolysis, due to reduced t-PA production and depleted storage or increased expression of a significant inhibitor of fibrinolysis PAI-1 [91][92][225,226], has been reported in coronary heart disease patients with cardiovascular risk factors, such as hypertension and obesity [93][94][95][96][97][227,228,229,230,231]. A clinical trial of VPA treatment showed a significant reduction in PAI-1 and signs of improvement in fibrinolysis, favourably altered the balance between t-PA and PAI-1, and the dose of VPA treatment was significantly lower than the usual dose of VPA for epilepsy [64][89][90][202,223,224]. Thus, VPA could be a potential alternative for preventing thrombotic events based on improved endogenous fibrinolysis [64][202].
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