ABSTRACT
Background and Aim Obesity and type 2 diabetes (T2D) show an increased risk for a severe COVID-19 disease. Treatment with DPP4 inhibitor (DPP4i) results in reduced mortality and better clinical outcome. Here, we aimed to identify potential mechanisms for the observed DPP4i effect in COVID-19. Methods We compared T2D subjects with (cases) and without (controls) DPP4i treatment (N=69), as well as patients hospitalised for severe COVID-19 and healthy controls (N=34) with regard to serum concentrations of soluble frizzle receptor protein 5 (sFRP5) using univariate statistics. Furthermore, we isolated pre-adipocytes, mature adipocytes and macrophages from adipose tissue biopsies (N=100) and performed western-blotting for sFRP5 and Wnt5a expression. Results In T2D patients, we identified a significant increase of the anti-inflammatory adipokine sFRP5 in relation to DPP4 inhibition. sFRP5 is a specific antagonist to Wnt5a, a glycopeptide secreted by adipose tissue macrophages acting proinflammatory in various diseases. We therefore examined sFRP5 levels in patients hospitalised for severe COVID-19 and found significant lower levels compared to healthy controls. Since sFRP5 might consequently be a molecular link for the beneficial effects of DPP4i in COVID-19, we further aimed to identify the exact source of sFRP5 in adipose tissue on cellular level. Results from western-blotting in adipose tissues showed a sFRP5 expression specifically in mature adipocytes of subcutaneous and omental adipose tissue. Conclusion In summary, our data suggest that DPP4i increase serum levels of anti-inflammatory sFRP5 which might be beneficial in COVID-19, reflecting a state of sFRP5 deficiency.
ABSTRACT
Aims Dipeptidylpeptidase is a key regulator of the incretin system. Initially, it's soluble form (sDPP-4) was described as an adipokine mediating metabolic inflammation. This is recently questioned in mechanistic rodent studies. To further clarify sDPP-4's role in physiology and metabolic diseases, we examined sDPP-4 in a large human cohort and during weight-loss interventions. Like ACE2, sDPP-4 serves as a binding partner for certain corona-like viruses enabling virus entry. As metabolic diseases are major risk factors for the COVID-19 pandemic, we additionally examined sDPP-4 in patients suffering severe Sars-CoV-2 infection. Methods sDPP-4 serum concentrations were measured using ELISA and related to various metabolic variables. Using a case-control-design, sDPP-4 was assessed in acute COVID-19 and sepsis infection. Results sDPP-4 increased with body weight, insulin resistance and hypertriglyceridemia but reduced in type 2 diabetes and arterial hypertension. Altered serum concentrations appeared with impaired liver and kidney but not cardiac function. No association to systemic inflammation was observed. Having found increased sDPP-4 in obesity, surgical (gastric bypass/sleeve gastrectomy) and non-surgical weight-loss interventions revealed a significant association of sDPP-4 with the improvement of liver function but neither with changes in body weight nor fat mass. Complementary, the case control study revealed reduced sDPP-4 concentrations specific for COVID-19 infection. Conclusions We suggest that sDPP-4 is rather related to hepatic abnormalities in obesity than primarily functioning as an adipokine. sDPP-4 is implicated in glucose and lipid metabolism, but not fundamentally in systemic inflammation. Additional to ACE-2, sDPP-4 might also have a regulatory role in COVID-19 infection.