COVID-19 Pandemic: current Challenges and future Perspectives


Sameh Saber1, Ahmed E. Khodir2, Abdalkareem Omar Maghmomeh3, Nehal A. Nouh4, Ahmed M. El-Baz5*

1Department of Pharmacology, Faculty of Pharmacy, Delta University for Science and Technology,

Gamasa, Egypt.

2Department of Pharmacology, Faculty of Pharmacy, Horus University, Egypt.

3Department of Biochemistry, Faculty of Pharmacy, Arab Private University for Science and Technology, Hama, Syria.

4Department of Microbiology, Albatterjee Medical College, Jeddah 6231, Saudi Arabia.
5Department of Microbiology and Biotechnology, Faculty of Pharmacy,

Delta University for Science and Technology, Gamasa, Egypt.

*Corresponding Author E-mail:,



The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) lead to the current pandemic of coronavirus disease 2019 (COVID-19) and more than one hundred million cases have been reported all over the world which resulted in millions of deaths and the outcome is increasing so far. It spreads certainly via contaminated droplets produced during breathing, coughing, sneezing and speaking. The mechanism of SARS-CoV-2 pathogenesis depends on the entry of the coronavirus into epithelial cells through ACE2 receptors. Previous studies have shown that increased proinflammatory cytokines (such as IL1β, IL6, IL12, INF-γ, IP10, and MCP1) in the serum of patients with SARS are associated with lung inflammation and extensive lung injury. Common symptoms include fever, cough, breathing difficulties, and loss of smell and taste. Complications may include pneumonia and acute respiratory distress syndrome (ARDS). There is no known specific antiviral medication, so primary treatment is currently symptomatic, while the current vaccines are still under testing and have not complete information's. Antiviral medications are under investigation for COVID-19, though none have yet been shown to be clearly effective on mortality. Herein, we discussed perspectives on pathophysiology, mechanisms underlying infection and some selected medications that are used in the challenge against COVID-19 pandemic.


KEYWORDS: COVID-19, Pathophysiology, Cytokine release syndrome, ACE2 receptor, Acute respiratory distress syndrome.




COVID-19 as a respiratory tract infection

Respiratory tract infections are considered one of the key players of pandemic diseases, such as the Spanish influenza and, recently, the coronavirus disease 2019 (COVID-19). A wide range of viruses contribute to the majority of respiratory tract infections. Viral respiratory tract infections can be transmitted by the inhalation of air that carries the virus in hanging droplets. This facilitates the spread of viruses among humans, causing difficult-to-control outbreaks of the disease 1. Moreover, viral respiratory tract infections are a leading cause of both morbidity and mortality worldwide, representing an enormous economic and disease burden.

The symptoms of viral respiratory diseases range from mild to fatal, the latter being especially prevalent among the elderly, children, and immunocompromised patients. Three major transmission routes allow the spread of viral respiratory tract infections: contact (direct or indirect), droplet, and aerosol transmission. The first transmission route is related to the direct transfer of the virus from an infected person to a liable individual or its indirect transfer via transitional objects, such as fomites. Conversely, viral transmission through the air can be achieved by the inhalation of droplets or aerosols that carry the virus 2.


The coronaviruses are a group of spherical or pleomorphic, single-stranded, enveloped, and positive-sense RNA viruses that belong to the Coronaviridae family, Orthocoronavirinae subfamily. Coronavirus infections are associated with respiratory illnesses and other conditions in humans and laboratory and domestic animals. The name coronavirus was adopted to describe the characteristic fringe of crown-like projections that surrounds the virus; these projections have a rounded (club-like) end, rather than the sharp or pointed ends that surround the myxoviruses. Similar to the myxoviruses, the coronaviruses are enveloped by a lipid layer with a diameter of 80-160 nm 3.


According to the World Health Organization (WHO), coronaviruses are a large family of viruses that infect the respiratory tract of birds, mammals, and humans. Coronaviruses were responsible for several worldwide epidemics, including the Severe Acute Respiratory Syndrome (SARS) pandemic of 2002-2003 and the Middle East Respiratory Syndrome (MERS) outbreak in Saudia Arabia in 2015. Recently, an outbreak of a novel coronavirus (SARS-CoV-2) occurred in China in December 2019, sparking international concern 4.


It was reported that sex hormones may affect the frequency of SARS-CoV-2 infection. It was found that adult males are more susceptible to SRAS-CoV-2 infection than are adult females with an average age of 34 to 59 years. The mechanism underlying the role of sex hormones in both the incidence and severity of the novel coronavirus remains under investigation. However, the first hypothesis focused on the genetic differences between males and females, as the female X chromosome carries a higher number of immune-related genes, resulting in a powerful immune response against SARS-CoV-2. The second hypothesis stated that the angiotensin-converting enzyme 2 (ACE2) receptors are more abundant in men, and it was demonstrated that these receptors are frequently located in men testes. ACE2 receptors are believed to be the portal of SARS-CoV-2 entry into host cells. The role of ACE2 in viral transmission represents a hot topic of recent COVID-19 research. The main entry of SARS-CoV-2 is achieved via ACE2 receptors located in the pulmonary endothelium. The relationship between the presence of this receptor and sex hormones has also been proven in animal studies. Diabetes and cardiovascular and cerebrovascular diseases represent crucial risk factors for SARS-CoV-2 infection. The majority of severe cases of COVID-19 were observed to be adults older than 60 years, especially those who had one or more of the previously mentioned risk factors 5.


The main symptoms of COVID-19 disease are almost flu-like symptoms that usually set in from 2 to 4 days after the infection. Symptoms vary from person to person, and some forms of the virus are believed to be fatal. The clinical manifestations of COVID-19 exhibit similarities with those of SARS-CoV, in which the most common symptoms include fever, dry cough, dyspnea, chest pain, fatigue, and myalgia. Conversely, other infrequent symptoms were detected in some cases of COVID-19, which include abdominal pain, diarrhea, nausea, vomiting, headache, and dizziness. Many biological samples from infected cases could be used for the detection of the novel coronavirus, such as bronchoalveolar lavage fluid and blood samples. To date, the prevalence of SARS-CoV-2 in feces and urine samples remains uncertain 6.


The mechanism of SARS-CoV-2 pathogenesis depends on the entry of the coronavirus into epithelial cells through ACE2 receptors, which are expressed at relatively high levels in the alveolar type 2 cells. This facilitates the entry of the virus into these cells and allows its multiplication to high levels. Furthermore, a high rate of viral multiplication leads to a massive production of several cytokines, including interferons (IFNs), interleukins (ILs), chemokines, colony-stimulating factors, and tumor necrosis factors (TNFs), in body fluids. In turn, these cytokines recruit immune cells and stimulate their accumulation at the sites of inflammation. This immune reaction is termed the cytokine storm. As a result of this immune response, nasal congestion, edema, fever, and lung tissue injury occur, potentially giving rise to acute respiratory distress syndrome (ARDS) and lung function failure. The wide distribution and expression of ACE2 receptors in many body organs, including the respiratory organs, duodenum, small intestines, testes, and kidneys, results in multiorgan dysfunctions after SARS-CoV-2 infection, such as intestinal dysfunction, renal insufficiency, and reduced fertility. Moreover, single-cell RNA sequencing showed that bile duct cells express the ACE2 receptor, which could explain the occurrence of bile duct dysfunction and liver function disturbances in some patients with COVID-19 7,8.



The derangement of several biochemical pathways has been reported in COVID-19, which can be attributed to the multiple interplaying levels of the viral attack. Despite the acknowledged role of immune-inflammation processes in the pathophysiology of this disease, hemoglobin alteration, hypoxemia, and iron dysmetabolism represent additional key factors to be investigated within the COVID-19 diagnostic-therapeutic approach. A viral interaction with the hemoglobin molecule, through ACE2, CD147, CD26, and other receptors located on erythrocytes, occurs in this disease. The hemoglobinopathy is derived from viral endocytosis through a link between the spike proteins and cell receptors. The viral ORF8 protein and surface glycoprotein bind to porphyrin and attack the heme group on the 1-beta chain of hemoglobin; consequently, SARS-CoV-2 induces hemolysis and forms a complex with the released heme, generating a dysfunctional hemoglobin and reduced oxygen and CO2 transport. A similar mechanism was demonstrated for Plasmodium malariae, which enters erythrocytes through the CD147 core receptor. CD147 plays a significant role in several metabolic pathways and diseases 9; it has been reported that there are about 3000 CD147 molecules per erythrocyte 10. Regardless of the limited evidence of the proposed molecular modeling, clinical-instrumental data account for a relevant loss of functioning hemoglobin, especially in the later stages of COVID-19 11. Other hemoglobin-associated markers, such as bilirubin and ferritin, increase progressively as the disease worsens. It is believed that SARS-CoV-2 attacks the bone marrow erythroblasts, leading to its replication and interaction with hemoglobin. Lactic acid dehydrogenase (LDH) is a reliable marker of hemolysis. Some studies have indicated that LDH levels are exceptionally accurate in screening for the severity of COVID-19. More interestingly, LDH levels are elevated by 2- or 3-fold in parallel with the hemoglobin decrease 12. Similarly, a relevant hypoferremia has been reported in patients admitted to intensive care unit (ICUs) with decreased serum iron levels, a condition that is associated with severe hypoxemia-related respiratory insufficiency 13.


A few case reports have described specific diagnostic or therapeutic features linked to myelodysplastic patterns in COVID-19, with the observation of atypical and relevant improvement in the COVID-19-associated blood alterations after erythropoietin administration. Other hematological findings have been reported for SARS-CoV-2-infected patients with thalassemia, who seem to exhibit a good prognosis 14 because of the reduction of hemoglobin beta-chains (which are potential targets of the virus); furthermore, the thalassemia-associated low hepcidin secretion may represent another “protective” mechanism in this context.


Together with the previously reported molecules, the GRP78 receptor has been considered as another SARS-CoV-2 entry facilitator. This endoplasmic reticulum heat-shock protein is also expressed in bone marrow stem cells. Putatively, this additional receptor would facilitate anti-hemoglobin viral action on hematopoietic stem cells. Moreover, the ascertained GRP78 downregulation in beta-thalassemia could be beneficial. Overall, the data available in the literature strengthen the hypothesis of erythrocyte or erythroblast involvement in COVID-19. Free circulating heme groups typically damage endothelial cells, and ferritin over deposition may contribute to vascular-wall remodeling and diffused endothelitis 15.


Regarding the lung consequences of SARS-CoV-2 infection, a systemic hypoxia state with normal pulmonary tissue compliance has been highlighted in up to 80% of ICU-admitted patients exhibiting respiratory distress, which led a few authors to question the ARDS diagnosis 16. Furthermore, a certain level of similarity between the computed tomography (CT), laboratory, and clinical features of high-altitude pulmonary edema (HAPE) and those of COVID-19 pneumonia has been highlighted. HAPE is a non-infectious, non-inflammatory interstitial pulmonary edema caused by the low inhaled oxygen and Starling’s law disequilibrium, with pulmonary vasoconstriction and hypertension. Interestingly, paCO2 is not significantly increased in most patients with critical-stage COVID-19. Furthermore, the PaO2/FiO2 ratio, which is usually high in patients with ARDS, is low in those with COVID-19 (HAPE-like), until critical respiratory insufficiency is achieved. Basically, the clinical and instrumental features of lung disease in COVID-19 seem to shift to typical ARDS features only when the alveolocapillary membrane becomes significantly deteriorated and/or the pulmonary circulation is impaired, possibly because of thromboembolic phenomena and ferroptosis. Similarly, the combination of hypoxia with relatively normal lung compliance and normocapnia could orientate the conventional pneumonia therapeutic approach differently. A kind of silent hypoxia was described in these patients, who showed a progressively worsened hypoxemia that was associated with normal CO2 levels. Normocapnia reflects normal pulmonary gas exchange, whereas CO2 elevation is the primary sensor of respiratory distress. For this reason, patients show relevant respiratory symptoms at later disease stages exclusively, when CO2 levels increase. Lastly, hyperferritinemia progressively affects the alveolar-capillary and cell membrane integrity and permeability. Moreover, inflammation, edema, and lung cell necrosis may complicate the pulmonary conditions ultimately.


Regarding the role of iron toxicity in COVID-19 pathophysiology, the putative hepcidin-mimetic action of SARS-CoV-2 may induce ferroportin internalization and blockage, which could explain the progressive anemia and hyperferritinemia associated with COVID-19. Hepcidin favors the iron entrance into cells and downregulates ferroportin, which is the key transporter of iron outside the cells. Basically, hepcidin is to iron as insulin is to glucose, and hepcidin excess may cause ferroptosis 17. Physiologically, hepcidin is respectively up- or downregulated depending on the serum levels of iron. Moreover, hepcidin is mimicked by the presence of inflammation (namely, IL-6), hyperoxemia, obesity, and diabetes. In contrast, hepcidin is antagonized, and ferroportin is upregulated, by hypoxemia, hypoxia-induced factors release, and anemia. Interestingly, the increased hepcidin levels in diabetics pair the higher levels of glycated dysfunctional hemoglobin. Concurrently, obese individuals and patients with diabetes overexpress the CD147 blood receptor, and this in addition to the biochemical imbalances raises their complication risk. Mimicking hepcidin action, SARS-CoV-2 might remarkably increase the circulating and tissue levels of ferritin (thus affecting the liver, spleen, bone marrow, and muscles), while inducing serum iron deficiency and a lack of hemoglobin. Hyperferritinemia gives rise to ferroptosis, accompanied by high oxidative stress and lipoperoxidation, ultimately increasing mitophagy with accelerated cell apoptosis and necrosis.


In fact, cell iron overload is tolerated up to a threshold, as is silent hypoxia (COVID-19 first phase). The increasing ferroptosis-linked multiorgan oxidative stress could precipitate the inflammatory and immune over-response (interleukin storm) in most patients with critical-stage COVID-19. Laboratory data showed significantly lower hemoglobin and higher ferritin levels in non-surviving patients compared with survivors. Tissue iron sequestration results in a unique increase in ferritin levels in the epithelium and immune cells of the lungs; these findings are probably linked to the physiological need to protect the pulmonary cells from air-oxygen-driven oxidative stress and pathogens. Hyperferritinemia may induce a series of direct and indirect injuries to most organs during COVID-19, such as coagulopathies, macrophage activation syndrome, hemochromatosis-like liver injury, and other ferroptosis-driven syndromes. The interaction of SARS-CoV-2 with the iron metabolism and oxygen supply could be linked to phylogenetic mechanisms that were developed in ancestral oxygen-free and iron-rich environments. In fact, viral RNA replication favors this hostile-to-humans ground, where the Fenton oxidative reaction is highly expressed 18.


Viruses generally increase iron deposition, to favor their diffusion in host cells; conversely, our immune system tends to control iron metabolism in case of infection, also via transferrin. This key factor of iron metabolism has ubiquitous (mainly in the lungs) receptors, which are used by many viruses to enter host cells. Possibly, future research could reveal the transferrin receptor as another target of SARS-CoV-2, which would further explain the iron dysmetabolism of this disease. Overall, the laboratory findings of COVID-19, such as hyperferritinemia, low hemoglobin, low serum iron, thrombocytopenia, and anisocytosis, with high figures of RDW, increased lactate, and LDH, are reasonably compatible with the hypothesized erythrocyte/bone marrow dysmetabolism and iron dysregulation 19.


Several organs are directly or indirectly targeted by SARS-CoV-2, and multiple pathomechanisms have been described for this virus, both of the immune and inflammatory type, and linked to hypoxia and ferroptosis. Thromboembolism also seems to play a relevant role in later stages of the disease. Overall, pathophysiological pathways seem to overlap in most cases; however, the hemoglobinopathy and iron dysmetabolism detected in this condition may induce a series of biological events, which objectively account for the clinical syndromes highlighted in COVID-19: i) decrease of functioning hemoglobin level; ii) iron increase in cells and tissues; iii) release of free toxic circulating heme; iv) hypoxemia and systemic hypoxia; v) reduction of NO levels; vi) coagulation activation; vii) ferroptosis with oxidative stress and lipoperoxidation; and viii) mitochondrial degeneration .


Clinical features:

The clinical symptoms and signs of COVID-19 are similar to those of many other acute respiratory infections, including SARS and MERS. The typical clinical symptoms of COVID-19 are fever (98%), fatigue (44%), and dry cough (76%). Atypical clinical symptoms include expectoration, headache (8%), hemoptysis, nausea, vomiting, and diarrhea (3%). Chemosensory dysfunctions, such as loss of smell and taste, are also closely associated with COVID-19 infection, but usually disappear within 2-4 weeks after infection. Some confirmed patients are asymptomatic or have low fever, mild fatigue, or other symptoms, without presenting with pneumonia, with most of them recovering within 1 week.


Some patients with COVID-19 have abnormal blood tests on admission, such as decreased albumin (75.8%), increased C-reactive protein (58.3%), increased lactate dehydrogenase (LDH) (57.0%), decreased lymphocytes (43.1%), increased erythrocyte sedimentation rate (ESR) (41.8%) , prolonged prothrombin time, increased D-dimer level, increased aspartate aminotransferase, increased creatinine, and increased creatine kinase, which indicate coagulation abnormalities and organ dysfunctions. In contrast, the serum level of procalcitonin, a blood marker of bacterial infections, was normal on admission of patients with COVID-19.


Moreover, cytokine storms are associated with the development of SARS-CoV-2 infection. First, cytokines such as IL1β, IL1RA, IL7, IL8, IL9, IL10, fibroblast growth factor, granulocyte colony-stimulating factor (GCSF), granulocyte macrophage colony-stimulating factor, interferon γ (INFγ), interferon gamma-induced protein 10 (IP10), monocyte chemoattractant protein 1 (MCP1), macrophage inflammation protein 1α (MIP1α), MIP1β, platelet-derived growth factor (PDGF), TNFα, and vascular endothelium growth factor were significantly increased in the plasma of patients with COVID-19 compared with the healthy control group. Second, several proinflammatory cytokines (IL2, IL7, IL10, GCSF, IP10, MCP1, MIP1α, and TNFα) were further increased in ICU-admitted patients compared with non-ICU-admitted patients, indicating that excessive acute inflammatory responses may lead to septic shock and death in patients with this disease. Furthermore, another common abnormality (i.e. bilateral multiple lobular and subsegmental areas of consolidation) was observed in chest CT images in 98% of patients with COVID-19.


In a recently published, single-center case series of 138 consecutive hospitalized patients with confirmed COVID-19, the investigators reported that approximately 10% of patients initially presented with GI symptoms prior to the subsequent development of respiratory symptoms. Common and often very subtle symptoms included diarrhea, nausea, and abdominal pain, with nonspecific GI illness being a less common symptom. New studies are expanding our understanding of the possible fecal transmission of COVID-19. Assessment by polymerase chain reaction (PCR) has provided evidence of the virus in the stool and the oropharynx, outside the nasopharynx and respiratory tract. The presence of the virus in the stool may be evident on presentation and persist even after the course of the illness (for up to 12 days after disappearance of evidence of the virus in the respiratory tract). In fact, in one of the most recent studies of evidence of the virus, which examined 73 patients, 24% of them retained a positive result for the virus in stool samples after showing a negative result in respiratory samples.


Cytokine release syndrome:

The pathophysiological mechanisms of SARS-CoV and MERS-CoV 20 are not completely clear and are related to cytokine abnormalities. Previous studies have shown that increased proinflammatory cytokines (such as IL1β, IL6, IL12, INF-γ, IP10, and MCP1) in the serum of patients with SARS are associated with lung inflammation and extensive lung injury. Infection with the MERS coronavirus could induce the release of proinflammatory cytokines (INF-γ, TNFα, IL15, and IL17). Similarly, patients infected with SARS-CoV-2 have high levels of IL1β, INF-γ, IP10, and MCP2; however, the secretion of anti-inflammatory cytokines, such as IL4 and IL10, by T-helper-2 (Th2) cells is also increased. A subsequent analysis found that plasma IL-2, IL-7, IL-10, GCSF, IP-10, MCP1, MIP1α, and TNF-α levels were higher in ICU-admitted patients than they were in non-ICU-admitted patients, suggesting that CRS may be associated with the severity of the disease. Different mechanisms may exist; moreover, the extent to which the disruption of the immune balance is responsible for the development and progression of novel coronavirus pneumonia is unknown. Based on 99 clinical cases of patients infected with SARS-CoV-2 in Wuhan, researchers found that viral particles spread through the respiratory mucosa and infect other cells, triggering CRS, generating a series of immune responses, and causing a decrease in immune cells, such as lymphocytes. Some cases progressed rapidly, developing ARDS, septic shock, and, eventually, multiple organ failure. Lymphopenia is common in patients with novel coronavirus pneumonia, especially for T and natural killer cells, whereas the number of B cells does not change significantly. However, lymphocytes do not have ACE2 receptors. Therefore, the virus does not infect lymphocytes, and there is no evidence of novel coronavirus infection of lymphocytes. The cause of the lymphopenia has not been determined. However, it is possible that SARS-CoV-2 acts as a superantigen that activates T cells in large numbers, resulting in apoptosis, which in turn causes lymphopenia. An alternative explanation is that the microenvironment that is necessary for lymphocyte development and differentiation is impaired because of multiple organ failure. The decrease in peripheral blood lymphocytes would cause immunosuppression and might lead to secondary microbial infections or tumors in critically ill patients. It is useful to speculate regarding whether lymphocyte dynamics could be used as a predictor of the progression to a critical state. At present, the mechanisms of the cytokine release syndrome and the connection with lymphocyte number in SARS-CoV-2 infection remain speculative. In conclusion, CRS might cause patients with SARS-CoV-2 infection to transition to a serious prognosis or even death; therefore, the pathogenesis of this virus requires further investigation. Severe COVID-19 cases may benefit from IL-6 pathway inhibition as a therapeutic target. Moreover, several reports have suggested that the cytokine receptors Fc-fusion proteins potentially serve as an antibody-like decoy to dampen the excessive cytokine levels, as a strategy for the treatment of SARS-CoV-2-infected patients 21.


The renin-angiotensin-aldosterone system (RAAS):

Severe acute respiratory syndrome coronavirus 1 (SARS-CoV-1) and SARS-CoV-2, which were responsible for the SARS epidemic of 2002 to 2004 and the more recent COVID-19 pandemic, respectively, interface with the RAAS through ACE2, an enzyme that physiologically counters RAAS activation but also functions as a receptor for the two SARS viruses . The interaction between the SARS viruses and ACE2 has been proposed as a potential factor in their infectivity. ACE2 acts as the receptor that allows the entry of emergent coronaviruses (SARS-CoV-2 and SARS-CoV) into human cells. Once bound to ACE2, the SARS-CoV-2 spike protein is activated by the type II transmembrane serine protease (TMPRSS2), to promote viral invasion and replication within the targets cells, including type II pneumocytes . RAAS inhibitors might increase the tissue expression of ACE2 22-30, thus raising theoretical concerns about increased infectivity of SARS-CoV-2. However, recent studies did not propose the presence of increased infectivity in patients with previous treatment with RAAS inhibitors. In fact, a population-based case-control study performed in Italy (Lombardy) that included more than 6000 patients did not find any evidence that RAAS inhibitors affected the risk of COVID-19 31. In addition, an observational study that included more than 12,500 patients tested for COVID-19 in New York did not find an association between previous treatment with RAAS inhibitors and a higher risk of testing positive for COVID-19. Moreover, these molecules could also have beneficial effects in patients with lung injury caused by SARS-CoV-2 infection. Preclinical data showed that mice infected with SARS-CoV and receiving losartan showed reduced lung injury compared with untreated mice 32. This protective effect was associated with an increased expression of ACE2 in response to losartan.


In humans, studies reported decreased mortality and lesser requirement of IMV in patients with viral pneumonia receiving RAAS blockers. RAAS blockers could have beneficial immunomodulatory effects at the systemic and pulmonary levels by decreasing cytokine levels. The benefit of maintaining treatment with RAAS blockers prescribed for chronic cardiovascular and/or chronic renal diseases might exceed their potential harm in patients with COVID-19, as RAAS inhibitors might protect against the organ injury, including myocardial injury that may be caused by SARS-CoV-2 infection. A recent Chinese study showed a lower risk of all-cause mortality in hospitalized patients with both COVID-19 and hypertension who received RAAS blockers compared with non-treated patients. Moreover, RAAS inhibitor administration was not associated with a higher risk of severe COVID-19 in Lombardy or in New York 31.


Some selected agents against COVID-19


Hydroxychloroquine (an analog of chloroquine) has been demonstrated to have anti-SARS-CoV activity in vitro; therefore, chloroquine and hydroxychloroquine were proposed as agents to fight COVID-19. Chloroquine and its hydroxyl analog, hydroxychloroquine, are weak bases that have been used as antimalarial agents for half a century. In addition to this antimalarial activity, chloroquine and hydroxychloroquine have gained interest in the treatment of infectious diseases. One of the most interesting mechanisms of action is that chloroquine leads to the alkalization of the acid vesicles that inhibit the growth of several intracellular bacteria, fungi, and viruses. This emphasizes the paradigm that activities mediated by lysosomotropic agents may offer an interesting weapon to face present and future infectious diseases worldwide. The clinical safety profile of hydroxychloroquine is better than that of chloroquine (during long-term use) and allows higher daily dose and has fewer concerns regarding drug-drug interactions. Treatment with hydroxychloroquine is significantly associated with viral load reduction or disappearance in patients with COVID-19, and its effect is reinforced by azithromycin 33.


Hydroxychloroquine inhibits endosome acidification and prevents the release of viral RNA into the cell, leading to a decrease in the damage that might be caused by the hyperactivation of the immune system. Regarding viruses, for reasons probably partly identical and involving the alkalization of the phagolysosome by chloroquine, several studies have shown the effectiveness of this molecule against coronaviruses. However, hydroxychloroquine retinopathy is a long-term side effect of hydroxychloroquine treatment that is associated with a secondary disruption of the retinal pigment epithelium of photoreceptors. The hydroxyl group in hydroxychloroquine reduces its capability of crossing the blood–retinal barrier, which explains the lower retinal toxicity of this drug compared with chloroquine. The monitoring of hydroxychloroquine blood levels is crucial in predicting the risk of retinopathy. Clinicians should consider decreasing the dosage of hydroxychloroquine in patients with high blood levels of the drug 34.



Azithromycin is used to treat a wide variety of bacterial infections. It is a macrolide-type antibiotic that acts via the inhibition of bacterial growth. It is used to prevent community-acquired pneumonia caused by C. pneumoniae, H. influenzae, M. pneumoniae, or S. pneumonia. Azithromycin appears to be effective in the treatment of chronic obstructive pulmonary disease through the suppression of inflammatory processes. Moreover, it is potentially useful in the treatment of asthma and sinusitis because of its anti-inflammatory effect. Azithromycin is believed to produce this effect by suppressing specific immune responses that may contribute to the inflammation of the airways. CD147, a receptor on host cells, is considered a novel route for SARS-CoV-2 invasion. Therefore, CD147 could be a target in COVID-19 treatment, and it is suggested that this protein is a possible pathway underlying the azithromycin-induced effects. Therefore, drugs that interfere with the interaction between the viral spike protein and CD147 or those that disrupt CD147 expression may inhibit viral invasion and dissemination among other cells, including progenitor or stem cells.


Azithromycin has been used for the treatment of infectious diseases with few side effects and can be rapidly produced in large scale. Moreover, progenitor and stem cells may participate extensively in the COVID-19-associated pulmonary fibrosis. Thus, in addition to the loss of airway epithelial cells, cellular regeneration is impaired. Certainly, further basic and clinical investigations of this issue are necessary for the development of effective therapeutic approaches. Combinations of pharmacological and MSC therapies for the successful treatment of COVID-19 and other viral diseases might be available in the future 35.



Famotidine is a histamine-2 receptor antagonist that suppresses gastric acid secretions. In vitro, it inhibits HIV replication. Recently, Wu et al. used computational methods to predict the structures of the proteins encoded by the SARS-CoV-2 genome and identified famotidine as one of the drugs that most likely inhibits the 3-chymotrypsin-like protease, which is supposed to be essential for viral replication 36.


Daniel et al. stated that, in hospitalized patients with COVID-19, the administration of famotidine was associated with a reduced risk of clinical deterioration. That study assumed that the usage of famotidine represented a continuation of home use; however, the documentation regarding why famotidine was prescribed was poor. The results were specific to famotidine (no protective association was observed for PPIs) and also specific for COVID-19 (no protective association was detected in patients without COVID-19). A lower peak ferritin value was observed in patients who received famotidine, supporting the hypothesis that the administration of famotidine decreases cytokine release in the setting of SARS-CoV-2 infection. A randomized controlled trial is currently under way to determine whether famotidine can improve the clinical outcomes of hospitalized patients with COVID-19 37.


ACE inhibitors and ARBs:

ACE2, an enzyme that physiologically counters RAAS activation, is the functional receptor of SARS-CoV-2. Several preclinical studies have suggested that RAAS inhibitors increase ACE2 expression, raising concerns regarding their safety in patients with COVID-19. Insufficient data are available to determine whether these observations readily translate to humans, and no studies have evaluated the effects of RAAS inhibitors in COVID-19. Clinical trials are under way to test the safety and efficacy of RAAS modulators, including recombinant human ACE2 and angiotensin II receptor blockers, such as losartan, in COVID-19. Abrupt withdrawal of RAAS inhibitors in high-risk patients, including those who have heart failure or post myocardial infarction, may result in clinical instability and adverse health outcomes. It was suggested that RAAS inhibitors should be continued in patients who are at risk for, are being evaluated for, or have COVID-19. Recombinant human ACE2 infusions or losartan both prevented severe lung injury and pulmonary edema in ACE2-knockout mice. The administration of recombinant human ACE2 improved lung injury in patients with SARS-CoV-2 infection 38.



Ivermectin is an FDA-approved broad-spectrum antiparasitic agent that was shown to have antiviral activity against a broad range of viruses in recent years. Recently, Caly et al. demonstrated the antiviral action of ivermectin against the SARS-CoV-2 clinical isolate in vitro; a single dose of the drug was able to control viral replication within 24 to 48 h. The authors hypothesized that such results were likely attributable to the inhibition of the importin-α/β11-mediated nuclear import of viral proteins, as shown for other RNA viruses. Hydroxychloroquine and ivermectin could act in a consequential and synergistic manner. In fact, hydroxychloroquine may behave as a first-level barrier by inhibiting the entry of the virus into the host cell, while ivermectin may reduce viral replication. No serious drug-related adverse events were detected between these drugs 39.



Digitoxin is a natural-occurring compound found in the leaves of foxglove (Digitalis purpurea). It was first extracted in the 18th century to be used for the management of heart conditions. It has also been used for the treatment of atrial fibrillation. Currently, its derivative, digoxin, is used for the same purpose. It was suggested that digitoxin suppresses the release of several cytokines and mediators, such as TNFα, GRO/KC, MIP2, MCP1, TGFβ, and INFγ. As the hyper-proinflammatory overproduction of cytokines is a host response, we suggest that digitoxin may have therapeutic potential not only for influenza, but also for coronavirus infections 40.


Kansuinine B:

Kansuinine B is a diterpenoid found in the Chinese herb Euphorbia kansui (also called Gan Sui locally). In Chinese herbal medicine, it has been used for a long time to treat edema, cough, pneumonia, dysuria, and constipation. A study showed that the usage of Euphorbia kansui suppresses the cytokine response by increasing the expression of the suppressor of cytokine signaling 3 (SOCS3) gene. A massive cytokine response, namely, the cytokine storm, is considered as the main factor for mortality in older patients with COVID-19. Hence, this is an additional factor that supports the usage of Euphorbia kansui for COVID-19 treatment 41.


Digitoxin and kansuinine B have promising attributes that render them good candidates for the treatment of COVID-19. Digitoxin and kansuinine B bind to the RdRp protein at different residue sites, covering a significant portion of the protein. This suggests that their combined use may inhibit the activity of RdRp significantly. The RdRp protein is responsible for the replication of the virus once it enters the cell. The inhibition of RdRp would impede the viral replication process. Moreover, kansuinine B exhibits a high binding affinity to the human ACE2 protein. This indicates that it also has a prophylactic effect 42.


Neuraminidase inhibitors:

Oseltamivir is a broad-spectrum anti-influenza drug that acts as a neuraminidase inhibitor by preventing the release of the virus from host cells. It could effectively treat MERS-CoV infection. Oseltamivir is used against COVID-19 only when influenza is present, because evidence of its efficacy against SARS-CoV-2 is lacking 43.


Janus kinase inhibitors:

Baricitinib is a Janus kinase inhibitor that not only interrupts the entry of the virus into cells, but also disrupts the assembly of viral particles in host cells. A bioinformatics analysis has proposed baricitinib as a potential treatment for COVID-19 44.


Glucocorticoid therapies:

Glucocorticoids have powerful anti-inflammatory and immunosuppressive effects; methylprednisolone is the main hormone used clinically. This hormone may have a powerful suppressive effect on the cytokine storm in patients with severe COVID-19. While glucocorticoids can reduce mortality among patients with severe pneumonia, they have serious adverse effects on patients with mild pneumonia. The WHO recommends the administration of glucocorticoids to patients with severe, but not mild, COVID-19. A prospective clinical trial evaluating the efficacy and safety of methylprednisolone in the treatment of patients with severe COVID-19 is ongoing 45.



Aprotinin, the basic trypsin inhibitor of the bovine pancreas, is a 58-amino-acid broad-spectrum serine protease inhibitor. Through the inhibition of kallikrein, thrombin, and plasmin, it attenuates the inflammatory, coagulation, and fibrinolytic pathways. Aprotinin inhibits the serine protease activity of TMPRSS2 in a dose-dependent manner and, when used in aerosolized form, reduces the rate of mortality of influenza and parainfluenza by more than 50% in infected mice. Moreover, aprotinin inhibits the implantation of SARS-CoV-2 in Clu-3 lung cells in a dose-dependent manner 46. Accordingly, further studies should evaluate the possible therapeutic effects of inhaled and injectable aprotinin on the course and outcomes of COVID-19.



Rimcazole is the top drug that modulates the binding affinity to the S protein of the virus, and the second in the modulation of the binding affinity to the ACE2 receptor, although its strongest affinity is to the inner part of the ACE2 receptor. Its potential is equal to that of other antiviral drugs, because it seems to be nonspecific and to strongly bind to few viral enzymes 47.



The severe acute respiratory syndrome coronavirus 2 (SARSCoV2) lead to the current pandemic of coronavirus disease 2019 (COVID19) and thirty million cases have been reported all over the world which resulted in about one million deaths. It spreads certainly via contaminated droplets produced during breathing, coughing, sneezing and speaking. Previous studies have shown that increased proinflammatory cytokines (such as IL1β, IL6, IL12, INF-γ, IP10, and MCP1) in the serum of patients with SARS are associated with lung inflammation and extensive lung injury. Until now, there is no known specific antiviral medication, so primary treatment is currently symptomatic. Antiviral medications are under investigation for COVID-19, though none have yet been shown to be clearly effective on mortality.



The authors declare no conflict of interest.



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Received on 05.02.2020            Modified on 25.07.2020

Accepted on 17.04.2021           © RJPT All right reserved

Research J. Pharm. and Tech 2022; 15(1):329-337.

DOI: 10.52711/0974-360X.2022.00054