This article is a brief multi-topic discussion of interesting and important Covid-19 news, including: vaccine candidates, new theories and treatments, molecular docking studies, in vitro studies, and the latest on clinical trials. This post will be updated repeatedly until the end of the week, when a new “week in review” will be posted. Unless I die of Covid, ironically.

Week of March 31 to June 6

* Vitamin D, Magnesium, B12 (“DMB”) cohort study
* What is an Inhibitor?
* Cialis may inhibit Covid-19
* Individual Spike Proteins Shed from Infected Cells
* Enantiomers of Chloroquine and Hydroxychloroquine
* Blood Types Study
* Terminology
* Endnotes

Vitamin D, Magnesium, B12 (“DMB”) cohort study

Tan, Chuen Wen, et al. “A cohort study to evaluate the effect of combination Vitamin D, Magnesium and Vitamin B12 (DMB) on progression to severe outcome in older COVID-19 patients.” medRxiv (2020).

“Cohort observational study of all consecutive hospitalized COVID-19 patients aged 50 and above in a tertiary academic hospital who received DMB compared to a recent cohort who did not.”

Result: Patients given DMB were 85% less likely to need oxygen therapy and/or intensive care support (multivariate analysis; p-value = 0.006).

Impressive result needs to be confirmed by RCT.

What is an Inhibitor?

An inhibitor is a smaller molecule which binds to a viral component, usually a protein, to prevent that viral component from working. Inhibitors usually target viral components, to slow down the progression of a disease. Inhibitors can also target normal human proteins to prevent them from being hijacked by the virus. The inhibitor must target the right site on the protein to prevent it from working, such as a the receptor binding domain. An analogy: if you “forget” to pay your parking tickets, the city will put an “inhibitor” on the “receptor binding domain” of your car, preventing it from working.

Cialis may inhibit Covid-19

A new study “Coagulation modifiers targeting SARS-CoV-2 main protease Mpro for COVID-19 treatment” [1] has a supplementary table listing the compounds which were effective inhibitors of Mpro. One of the top performing compounds was tadalafil, also known as Cialis. Yes, that Cialis®. It’s an erectile dysfunction medication. But it is also used for BPH (enlarge prostate). So more than a few older men take Cialis on a continuing basis. (No, it doesn’t directly cause an erection every time you take it.) (And, no, I’m not on it.)

The binding affinity (or “docking score”) for tadalafil (“Ta-da! La fil.) was -8.5, a very good score, indicating that, at the right concentration, the compound may inhibit the main protease needed by SARS-CoV-2 to replicate. And a quick look found several other molecular docking studies that also rated tadalafil as an effective inhibitor of multiple viral targets.

Qiao et al. [2] found that tadalafil inhibits the Main protease (Mpro) of SARS-CoV-2 with a docking score of -9.3 (higher than the score in the other study), and the Spike protein with a docking score of -7.5 (still pretty good).

Anwar et al. [3] found that tadalafil inhibits two non-structural proteins in SARS-CoV-2, Nsp1 and Nsp2, with docking scores of -8.5 and -11.2, respectively. A score of -11.2 indicates a particularly high binding affinity. So it looks like Cialis (tadalafil) inhibits four different Covid-19 proteins.

Then, Jian et al. [6] found that tadalafil inhibits Nsp16 (non-structural protein 16 of SARS-CoV-2). So that gives tadalafil a total of 5 viral targets across four different molecular docking studies. These results are very preliminary, but enough to propose further investigation.

The problem with tadalafil/Cialis is that the dosage is low, ranging from 2.5 mg/day (for ED) to 40 mg/day (for pulmonary hypertension) [per]. Inhibitors rely on concentration for their effectiveness. The effectiveness of the drug will be limited by that factor.

What is needed is a retrospective study comparing, among Covid-19 patients, men who were taking Cialis regularly to men who were not. Older men are the most common users of Cialis, and they are also more severely affected by Covid-19. So there might be a benefit. However, the low dosing and the possible severe side effects makes the drug unsuitable as a primary intervention for Covid-19.

Individual Spike Proteins Shed from Infected Cells

Horrific Hypothesis. Letarov et al. claim that Covid-19 may cause infected cells to release individual functional Spike proteins into the blood stream [4]. We know that a cell infected with SARS-CoV-2 makes copies of the virus and releases these viral progeny or “virions” into the bloodstream. But in this hypothesis, the infected cell also releases Spike proteins not attached to any virus:

“We hypothesize that the soluble SARS-CoV-2 spike protein S1 subunits shed from the infected cells and from the virions in vivo may bind to the ACE2 receptor and trigger ACE2 downregulation.” [4]

These Spikes float through the blood stream, attach to ACE2 receptors, and thereby deactivate may more ACE2 receptors. This throws the Renin-Angiotensin System out of balance, as there is much more activity in the system from ACE than from its counterbalance ACE2. If there are free floating Spikes as well as the Spikes on the virus itself, it increases the number of ACE2 receptors deactivated. And it makes it harder to put the system back in regulation. And it makes it becomes very difficult to inhibit the virus with inhibitors that target the Spikes. Bad news, if it turns out to be correct.

Enantiomers of Chloroquine and Hydroxychloroquine

Enantiomers are mirror images of the same chemical compound. When a molecule exists as two enantiomers, it is said to be “chiral”. Your hands are chiral. Enantiomers are pairs, and the two pairs are identical in formula and structure, except that one has the mirror image layout of its atoms in the molecule as compared to the other. We have known for a long time that enantiomers of drugs sometimes have very different effects in the body. They are chemically somewhat different, because, particularly in organic chemistry, the shape of the molecule is what matters.

This study [5] found that S-Hydroxychloroquine is a potentially superior drug for COVID-19. They say the S-enantiomer was 60% more effective than the R-enantiomer. The two enantiomers are designated “S” and “R”. I say: Yes, but “S” was only 17.6% more effective than the mix of R- and S-HCQ that is used as medicine. Usually a medicine is a mix of both enantiomers. Natural compounds, when they are chiral, often include only one enantiomer and not the other.

The result of the study is interesting, and there might be some benefit. But the study overstates its conclusion.

This is also one of very few in vitro studies of SARS-CoV-2. They tested Azithromycin in vitro, and they found its IC50 at 15.75 µM. That is a relatively low concentration, which might be achievable from the usual Covid-19 dosing of Azithromycin, 500 mg/day.

Note that azithromycin is not used as an antibiotic for Covid-19 patients. It is used as a viral inhibitor. The type of pneumonia in Covid-19 patients is not bacterial in origin; it is caused by an over-reaction of the immune system, which brings excessive fluid to the lungs.

Blood Types Study

One study found that persons with type “O” blood are less likely to contract Covid-19 [7].

“Our results demonstrated ABO histo-blood phenotypes are correlated with patients’ susceptibility to the infection. A higher rate of infection was observed among patients with the AB histo-blood group, while patients with the O histo-blood group have shown a lower rate of infection. The Rh blood group phenotype was not statistically significant in determining a patient’s vulnerability.” [7]

This result is similar to past studies finding a difference in infection rates for other viruses. However, several researchers, Gerard et al., proposed a modification to the theory.

“However, as already strongly suggested by others, this variable susceptibility to SARS-Covid-19 infection could be linked to circulating anti-A antibodies which could interfere or even inhibit the virus-to-cell adhesion process. We had the idea to analyze these important available data series from the anti-A or B antibodies viewpoint instead of ABO blood group antigens as the authors did.” [8]

The results of this second analysis show that “subjects with anti-A in serum (i.e. B+O blood groups) are significantly less represented in the COVID-19 group than those lacking anti-A whatever the group.” [8] But of the two, B and O, the safer blood type was O, which caused the authors to conclude that “anti-A from O is more protective than anti-A from B” [8].

Ronald L Conte Jr
Note: the author of this article is not a doctor, nurse, or healthcare provider.


Binding affinity — the extent to which an inhibitor latches on to its target of inhibition. Higher binding affinities indicate a more effective inhibition of the viral component. Binding affinities are usually expressed in negative numbers and in kcal/mol.

BPH — benign prostatic hyperplasic; enlarged prostate common in men over 50.

Coagulation modifiers — drugs that decrease or increase the ability of the blood to clot.

Docking score — a measurement of how well an inhibitor binds to its target. A good docking score means that the medication will effectively slow down the virus by interfering with one of its essential components, such as the Spike protein used to infect a cell, or the protease used to make working proteins, or the polymerase used to make copies of its RNA.

IC50 — the concentration sufficient to cause 50% inhibition against a particular protein or other target: Inhibition Concentration 50%.

Inhibitors — small molecules that bind to a viral component, usually a protein, in just the right place to deactivate the viral component. A set of inhibitors, targeting multiple viral components is needed to slow down the disease.

Mpro — an enzyme, specifically a protease, used by the virus to cut up long do-nothing proteins into working viral proteins. Mpro makes 11 cuts, while the lesser of the two proteases, PLpro, makes only 3 cuts. That’s what makes Mpro the “Main” protease.

SARS-CoV-2 — the virus that causes Covid-19, also called “the Coronavirus”.

µM is micromolar, one millionth of one mol per liter. A mol is 6.022 x 1023 molecules (or atoms or other small stuff).


1. Biembengut, Ísis Venturi, and Tatiana de Arruda Campos Brasil de Souza. “Coagulation modifiers targeting SARS-CoV-2 main protease Mpro for COVID-19 treatment.” (2020).

2. Qiao, Zhen, et al. “Computational View toward the Inhibition of SARS-CoV-2 Spike Glycoprotein and the 3CL Protease.” Computation 8.2 (2020): 53.

3. Anwar, Muhammad Umer, et al. “Combined Deep Learning and Molecular Docking Simulations Approach Identifies Potentially Effective FDA Approved Drugs for Repurposing Against SARS-CoV-2.” (2020).

4. Letarov, Andrey, and Vladislav Babenko. “Hypothesis: Free SARS-CoV-2 spike protein S1 particles may act as a factor of COVID-19 pathogenesis.” (2020).

5. Li, Guanguan, et al. “Enantiomers of Chloroquine and Hydroxychloroquine Exhibit Different Activities Against SARS-CoV-2 in vitro, Evidencing S-Hydroxychloroquine as a Potentially Superior Drug for COVID-19.” bioRxiv (2020).

6. Jiang, Yuanyuan, et al. “Repurposing therapeutics to identify novel inhibitors targeting 2′-O-ribose methyltransferase nsp16 of SARS-CoV-2.” (2020).

7. Abdollahi, Alireza, et al. “The Novel Coronavirus SARS-CoV-2 Vulnerability Association with ABO/Rh Blood Types.” Iranian Journal of Pathology (2020): 156-160.

8. Gérard, Christiane, Gianni Maggipinto, and Jean‐Marc Minon. “COVID‐19 & ABO blood group: another viewpoint.” British Journal of Haematology (2020).