Kynurenine serves as useful biomarker in acute, Long- and Post-COVID-19 diagnostics.

Introduction: In patients with SARS-CoV-2, innate immunity is playing a central role, depicted by hyperinflammation and longer lasting inflammatory response. Reliable inflammatory markers that cover both acute and long-lasting COVID-19 monitoring are still lacking. Thus, we investigated one specific inflammatory marker involved as one key player of the immune system, kynurenine (Kyn), and its use for diagnosis/detection of the Long-/Post-COVID syndrome in comparison to currently used markers in both serum and saliva samples. Material and methods: The study compromised in total 151 inpatients with a SARS-CoV-2 infection hospitalized between 03/2020 and 09/2021. The group NC (normal controls) included blood bank donors (n=302, 144f/158m, mean age 47.1 ± 18.3 years (range 18-75)). Two further groups were generated based on Group A (n=85, 27f/58m, mean age 63.1 ± 18.3 years (range 19-90), acute admission to the hospital) and Group B (n=66, 22f/44m, mean age 66.6 ± 17.6 years (range 17-90), admitted either for weaning or for rehabilitation period due to Long-COVID symptoms/syndrome). Plasma concentrations of Kyn, C-Reactive Protein (CRP) and interleukin-6 (IL-6) were measured on admission. In Group B we determined Kyn 4 weeks after the negative PCR-test. In a subset of patients (n=11) concentrations of Kyn and CRP were measured in sera and saliva two, three and four months after dismission. We identified 12 patients with Post-COVID symptoms >20 weeks with still significant elevated Kyn-levels. Results: Mean values for NC used as reference were 2.79 ± 0.61 µM, range 1.2-4.1 µM. On admission, patients showed significantly higher concentrations of Kyn compared to NC (p-values < 0.001). Kyn significantly correlated with IL-6 peak-values (r=0.411; p-values <0.001) and CRP (r=0.488, p-values<0.001). Kyn values in Group B (Long-/Post-COVID) showed still significant higher values (8.77 ± 1.72 µM, range 5.5-16.6 µM), whereas CRP values in Group B were in the normal range. Conclusion: Serum and saliva Kyn are reflecting the acute and long-term pathophysiology of the SARS-CoV-2 disease concerning the innate immune response and thus may serve a useful biomarker for diagnosis and monitoring both Long- and Post-COVID syndrome and its therapy.

Attenuated early inflammatory response in solid organ recipients with COVID-19.

Immunosuppression leaves transplanted patients at particular risk for severe acute respiratory syndrome 2 (SARS-CoV-2) infection. The specific features of coronavirus disease 2019 (COVID-19) in immunosuppressed patients are largely unknown and therapeutic experience is lacking. Seven transplanted patients (two liver, three kidneys, one double lung, one heart) admitted to the Ludwig-Maximilians-University Munich because of COVID-19 and tested positive for SARS-CoV-2 were included. The clinical course and the clinical findings were extracted from the medical record. The two liver transplant patients and the heart transplant patient had an uncomplicated course and were discharged after 14, 18, and 12 days, respectively. Two kidney transplant recipients were intubated within 48 hours. One kidney and the lung transplant recipients were required to intubate after 10 and 15 days, respectively. Immunosuppression was adapted in five patients, but continued in all patients. Compared to non-transplanted patients at the ICU (n = 19) the inflammatory response was attenuated in transplanted patients, which was proven by decreased IL-6 blood values. This analysis might provide evidence that continuous immunosuppression is safe and probably beneficial since there was no hyperinflammation evident. Although transplanted patients might be more susceptible to an infection with SARS-CoV-2, their clinical course seems to be similar to immunocompetent patients.