Immunologists conducted research into the HPA axis¹ and discovered that on average the post-Covid patient only produces half of the cortisol. Other immunologists investigated the kynurenine pathway (KP) ² and discovered that the KP is working overtime and produces many toxic KP metabolites. And an article in Cell ³ recently stated that on average serotonin levels have halved in post-Covid patients. All three studies underlying these interesting articles lie in the field of neurology and neuropsychiatry. For example, it has been known for a long time that the HPA axis is disturbed in depression.⁴Articles have also been published since 2014 about disturbances in the KP in, for example, MS ⁵ and in many neuro-psychiatric disorders.  It is therefore clear that post-Covid immunologists are partly entering the field in which neuropsychiatrists have already done a lot of research and who have already found medicines for many diseases. These can now be partly used post-Covid. Immunologists should therefore step outside their comfort zone and learn from their fellow psychiatrists.

After their discovery that serotonin levels have halved, the authors of the Cell article have already taken a step forward, because they recommend conducting research with SSRIs: antidepressants. But they also describe in their article that research with tryptophan is appropriate. In my view, that is better not to happen, because tryptophan is indeed the building block of serotonin, but also the building block of the kynurenine pathway that works overtime in post-Covid. So it makes more sense to take a direct precursor of serotonin, namely 5-http, and do research with it.

In our exploratory study of 95 post-Covid patients whom we treated with an SSRI ⁶ ,in our hypothesis formation about the use of SSRIs in post-Covid, we examined both the disrupted KP, HPA axis and serotonin metabolism involved. Because SSRIs affect all three. And our first study on this seems to confirm our hypotheses. So, as physician-researchers, let us work together from now on to achieve better results faster for the large group of post-Covid patients who have sometimes been suffering for years.
1.

https://www.nature.com/articles/s41586-023-06651-y

2.

https://www.nature.com/articles/s41590-022-01396-8

3.

https://doi.org/10.1016/j.cell.2023.09.013

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5313380/

5.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9680557/

https://www.nature.com/articles/s41598-023-45072-9

Carla Rus, MD, neuropsychiatrist in The Hague, the Netherlands.