Proline-Specific Peptidase Activities in Plasma of Hospitalized COVID-19 Patients

These COVID-19 patients experience several features of dysregulated immune system observed in sepsis. The activity of proline-specific peptidases in plasma of COVID-19 hospitalized patients has been investigated. The peptidases studied were dipeptidyl peptidase 4 (DPP4), fibroblast activation protein alpha (FAP), prolyl oligopeptidase (PREP) and prolylcarboxpeptidase (PRCP).

Medical Biochemists at the University of Antwerp (Antwerp, Belgium) and their colleagues collected heparin plasma samples from 56 hospitalized patients with laboratory-confirmed (PCR test) COVID-19 shortly after hospital admission (=baseline, 1 to 5 days after hospital admission) and thereafter at irregular time points until discharge. Additionally, plasma was taken from a control group of 32 healthy volunteers.

The scientists measured DPP4 activity colorimetrically using the substrate Gly-Pro-pNA. FAP and PREP activity was measured fluorometrically using Z-Gly-Pro-AMC in a combined FAP/PREP assay. PRCP activity was determined by measuring the hydrolysis of Z-Pro-Phe by use of a reversed-phase high-performance liquid chromatography technique. The enzymatically formed Z-Pro was tracked by its UV absorbance at 210 nm after separation on a Shimadzu HPLC apparatus (Kyoto, Japan).

The investigators reported that compared to healthy controls, both DPP4 and FAP activities were significantly lower in COVID-19 patients at hospital admission and FAP activity further decreased significantly in the first week of hospitalization. While PRCP activity remained unchanged, PREP activity was significantly increased in COVID-19 patients at hospitalization and further increased during hospital stay and stayed elevated until the day of discharge.

The authors concluded that a similar pattern in the proline-specific peptidase activities in COVID-19 patients compared with patients experiencing septic shock: decreased DPP4 and FAP activity and elevated PREP activity. The study was published on March 10, 2022 in the journal Clinica Chimica Acta.