Student Contributors: Arpan Bhattacharyya, Archita Sarkar.

Introduction

Following an outbreak of pneumonia without a clear cause in the city of Wuhan in China, a novel strain of coronavirus (SARS-CoV-2) was detected in December 2019.

Coronaviruses were identified in the mid-1960s and are known to infect humans and a variety of mammals. Since 2002, two coronaviruses infecting animals have evolved and caused outbreaks in humans: SARS-CoV (Severe Acute Respiratory Syndrome) identified in south China in 2003, and MERS-CoV (Middle East Respiratory Syndrome), identified in Saudi Arabia in 2012. The novel coronavirus has been identified as Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and the disease associated with it is called or coronavirus disease 19 (COVID-19), a type of respiratory illness. The World Health Organisation declared it a pandemic in March 2020 due to its effect worldwide.

SARS-CoV-2 is a positive-sense single-stranded RNA virus. A spillover event is likely to have initially introduced the virus into humans causing an outbreak through human to human transmission due to its highly contagious nature. The virus is primarily spread between people through close contact and via respiratory droplets produced from coughs or sneezes. It enters the human cells by binding to the receptor angiotensin-converting enzyme 2 (ACE2).

Symptoms of COVID-19

The symptoms of the disease can range from mild to severe. Also, people may be infected with the virus for 1 to 14 days before developing symptoms. Rarely the disease can be serious and fatal. Some of the common symptoms are as follows.

1. Fever
2. Tiredness
3. Dry cough
4. Shortness of breath
5. Loss of smell (also in some asymptomatic carriers of SARS-CoV-2)
6. Severe pneumonia (in severe cases)

Mechanism of action of SARS-CoV-2

It has established that  SARS-CoV-2 induces inflammation of the alveolar tissues in the lungs. This is confirmed by western blot which showed the presence of cytokines IL-1β, IL-6 from the cytosolic fraction. The inflammation of the lung tissues induces an immune response which leads to the accumulation of macrophages at the site of inflammation. This leads to activate of NADPH oxidase, (a macrophage membrane-bound enzyme)which in presence of oxygen catalyzes the conversion of NADPH to NADP⁺ and production of unstable superoxide anion radical (O₂^–) which finally converted to more powerful oxidant, hydrogen peroxide by the catalytic action of cytosolic and mitochondrial superoxide dismutase (Cu-Zn-SOD and Mn-SOD respectively). Accumulation of excess hydrogen peroxide resulted in the formation of highly stable hydroxyl radicals (^.OH) by an iron/copper (Fe²⁺/Cu⁺) driven Fenton reaction and superoxide anion mediated Haber-Weiss reaction. This hydroxyl radical causes lipid peroxidation, DNA damage and protein carbonylation (modify the pyrrolidone ring of the proline residue of alveolar fibrous proteins). All these eventually lead to deactivation of both type-I(involved in gaseous exchange during breathing) and type-II (responsible for the biosynthesis of lung surfactant for the maintenance of the capacitance of lung) pneumocytes of the alveoli. This causes the hypoxia-induced respiratory disorder, loss of the capacitance of lung, drowsiness and ultimately death.

To combat this situation, reduced glutathione (GSH) to oxidized glutathione (GSSG). So there is a chance of accumulation of free hydroxyl radical, due to the deficit of reduced glutathione, which occurs due to the loss of the counterbalance of glutathione peroxidase(GPX) and glutathione reductase(GR) activities.

A possible protective measure

To protect ourselves intake lots of antioxidants is a smart option in this condition. Some easily available medicinal plants such as tulsi, arjun, methi, vasaka and many more are good sources of antioxidants. These antioxidants present in aqueous extracts of different plant parts serve as potential scavengers of reactive oxygen species, which help to protect the alveoli from COVID-19 induced damage.

Table 1:Medicinal Plants along with their antioxidant ingredients and their protective mechanism:

So, from the detailing of the antioxidant profile from the above table, it may be concluded that a habit of intake at least one of these extracts helps to strengthen the existing physiological protective barrier. This may protect our system from fatal consequences during the SARS-CoV-2 infection. As, we are incapable to resist the invading of SARS-CoV-2 within our body, but still we can protect ourselves from these unwanted circumstances by taking at least those plant extract in our daily routine as the preventive measure. We have to remember —-“Prevention is better than cure”.