Article · Physiopathology & COVID-19 · March 2020 · Episode 3/3
30 March 2020 · ~20 pages · English · Also available in French
Historical note. This article was written on 30 March 2020 and represents the state of scientific knowledge available to the author at that date. The therapeutic options discussed (hydroxychloroquine, lopinavir/ritonavir, remdesivir) were subsequently evaluated in large-scale clinical trials with mixed or negative results. The pathophysiological mechanisms described (ACE2 binding, cytokine storm, ARDS progression) have been largely confirmed by subsequent research.
1 · ACE2 and TMPRSS2: the entry mechanism
SARS-COV2 binds ACE2 (angiotensin-converting enzyme 2) with 10–20× greater affinity than SARS-COV1. TMPRSS2 serine protease primes the spike protein for membrane fusion. ACE2 distribution explains tissue tropism: lungs (type II pneumocytes), heart, kidneys, intestinal epithelium. Critical insight: patients on ACE inhibitors or ARBs may overexpress ACE2, partially explaining hypertensive comorbidity.
2 · Clinical phases
Five-stage progression model: (1) incubation (2–14 days, median 5); (2) viral multiplication with flu-like symptoms; (3) pulmonary phase with bilateral ground-glass opacities; (4) hyperinflammatory phase — cytokine storm (IL-6, TNF-α, IL-1β), ARDS, coagulopathy; (5) sepsis and multi-organ failure (mortality 30–50%). Key temporal marker: clinical deterioration can occur in under 3 hours.
3 · Predictive biomarkers
Laboratory markers of severe progression: lymphopenia (CD4/CD8 counts), elevated IL-6, elevated ferritin, D-dimer elevation (coagulopathy marker), viral RNAaemia (presence of viral RNA in blood — indicator of systemic dissemination). The author argues for early biomarker monitoring to identify patients at risk of rapid deterioration before the cytokine storm becomes irreversible.
4 · Therapeutic targets
Survey of candidate therapies by mechanism: (a) viral entry inhibitors (chloroquine/hydroxychloroquine — ACE2 glycosylation interference); (b) protease inhibitors (lopinavir/ritonavir); (c) RNA polymerase inhibitors (remdesivir); (d) immunomodulators (tocilizumab — anti-IL-6); (e) convalescent plasma (passive immunisation). Each mechanism is analysed from first principles with appropriate caveats about clinical evidence available at the time.
This is the most technically dense article in the series, drawing directly on the author's PhD training in biotechnology (ENS Ulm / AgroParisTech). The ACE2-centred analysis of comorbidity — explaining why hypertension, diabetes and cardiovascular disease are risk factors, rather than merely observing that they are — was sophisticated for a public-facing publication in late March 2020.
The emphasis on predictive biomarkers for early identification of severe progression directly prefigures the author's subsequent work on biomarker-driven digital twins in the TweenMe platform and the Programme Sentinelle IA for metabolic syndrome management.