Chloroquine effective in COVID-19: True or false?

Dr. Prashant R. Wankhade

Hypothesis:

It has been proposed that these viruses are internalized by receptor mediated endocytosis and delivered to lysosomes. At acidic pH, the membrane surrounding the virus fuses with the membrane of lysosome, allowing the nucleic acid of virus to cross lysosomal membrane and enter the cytoplasm where the virus replicates. Infection of tissue culture cells by these viruses can be prevented by chloroquine, an agent that blocks function of lysosome. Chloroquine is a weak base that diffuses in lysosome and raises the pH of lysosome causing impairment of function of lysosomal enzymes. Viruses that requires acidic pH to fuse with cell membrane can no longer do so in the presence of chloroquine and the cells are protected from infection.

Facts:

1. Aim of the virus is to reach the destination where it can replicate. This destination is cytoplasm for RNA viruses and nucleus for DNA viruses.

2. Normally viruses enter the cell by direct membrane fusion or endocytosis-based mechanism.

3. Exact mechanism of COVID-19 entry in cell isn’t clear (https://www.ncbi.nlm.nih.gov/books/NBK92477/). If its entry is via membrane fusion then there is no need for COVID-19 to cross Lysosome as the virus particles will get direct entry in cytoplasm. Even if the entry is endocytosis-based then also it is less likely to cross Lysosome.

4. Chloroquine and hydroxychloroquine are known to alter Lysosomal function. But there are discrepancies in the literature about whether or not chloroquine raises the lysosomal pH (Autophagy. 2018; 14(8): 1435–1455). Some studies do not support this fact whereas others state that the change in pH may not last longer than 1 to 4 hours. So, the fact that Chloroquine will cause alteration in viral cell cycle is not clear.

5. Viruses like polio virus and Hepatitis-C virus enters the cell via endocytosis; in that case Chloroquine would have helped in controlling these infections also, but no guidelines recommend its use.

6. This hypothesis related to Chloroquine and Viral infection is not new. One of the articles published in 2003 advocates its possible role in treatment of HIV infection but none of the guidelines has yet recommended (Lancet Infect Dis. 2003 Nov;3(11):722-7).

The same article advocates its possible role in clinical management of Corona related Middle East Respiratory syndrome (MERS) and Corona related severe acute respiratory syndrome (SARS) but no further data available on its definite role.

7. RNA viruses including COVID-19 can replicate in cytoplasm and need not require entry in the nucleus like DNA viruses. Chloroquine doesn’t have any effect on cytosolic pH to alter the replication of virus and in fact that will be hazardous for cell itself.

8. Thus, these facts put question mark on above hypothesis.

9. And finally, in this era of evidence-based medicine we need concrete evidence to support the hypothesis; as it’s not necessary for every hypothesis to reflect vis a vis in clinical applicability.

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