• Neluwa-Liyanage Ruwan Indika Department of Biochemistry, Faculty of Medical Sciences, University of Sri Jayewardenepura, Nugegoda, Sri Lanka.
  • Nirmalie Gayathrie Fonseka National Blood Centre, Colombo 05, Sri Lanka


The addition of methylene blue to the standard treatment protocol has been shown to improve respiratory rate and oxygen saturation in COVID-19 patients, reducing morbidity and mortality. Evidence to date suggests that methylene blue inhibits protein-protein interactions between SARS-CoV-2 Spike protein and angiotensin-converting enzyme 2, which in turn inhibits the cell entry of SARS-CoV-2. However, the methylene blue dye-binding characteristics of sulfated glycosaminoglycans suggest additional inhibitory effects of the spike protein-heparan sulfate interaction. We hypothesize that the binding of cationic methylene blue neutralizes polyanionic heparan sulfate molecules on the host cell surface. As a consequence, electrostatic interactions between negatively charged heparan sulfate and the positively charged receptor binding domain of SARS-CoV-2 spike protein will be inhibited. Thus, methylene blue will exhibit a "shielding effect" on the heparan sulfate proteoglycans, inhibiting viral attachment to the cell surface. The proposed mechanism corroborates the possible broad-spectrum antiviral activity of methylene blue against multiple human coronaviruses that exploit the electrostatic interactions with sulfated glycosaminoglycans for virus entry. Methylene blue would exhibit the same anti-adhesive activity at the blood-brain-barrier and olfactory neuroepithelium, corroborating potential benefits in ameliorating post-COVID-19 neurological impairment. However, as cationic dyes can bind to both free glycosaminoglycans in circulation as well as proteoglycans attached to the cell surface, co-administration of intravenous heparin could possibly antagonize the proposed antiviral activity. This critical review focuses on empirical evidence to support the hypothesized heparan sulfate-dependent antiviral activity of MB.


Methylene blue, SARS-CoV-2, COVID-19, Heparan sulfate, Proteoglycans, Antiviral


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How to Cite

Neluwa-Liyanage Ruwan Indika, & Nirmalie Gayathrie Fonseka. (2021). METHYLENE BLUE INHIBITS THE INTERACTION BETWEEN HEPARAN SULFATE AND SARS-COV-2 SPIKE PROTEIN; A REVIEW OF EVIDENCE FOR A HYPOTHESIS. Malaysian Journal of Medical Research (MJMR), 5(4), 4-11. Retrieved from