Is DPP4 inhibition a comrade or adversary in COVID-19 infection.

Hypertension and Diabetes are the most common comorbid conditions in patients with COVID-19 and has been shown to adversely impact prognosis globally. It has been shown that hyperglycemia is one of the factors that increases the risk of poor outcomes in these patients. These patients are usually on multiple medications and recently a series of discussion on how Dipeptidyl peptidase 4 inhibitors (DPP4i) may be beneficial in these patients has been presented. This commentary presents a nuanced debateon why the DPP4i may not bebeneficial in COVID-19 and that caution needs to be addressed in making any judgementsuntil real world data is available.

Hypertension and Diabetes are the most common comorbid conditions in patients with COVID-19 and has been shown to adversely impact prognosis globally [1]. It has been shown that hyperglycemia is one of the factors that increases the risk of poor outcomes in these patients [2]. It is worthwhile considering that these patients are on multiple oral hypoglycemic agents and these medications may also affect the response to infection. A series of discussion has been initiated on the possible effects of dipeptidyl peptidase 4 inhibitors (DPP4i) in diabetes patients with COVID-19 infection.

Firstly, bioinformatic approaches combining human-virus protein interaction prediction and protein docking based on crystal structures have been performed and it has been shown that although the SARS CoV interacts with DPP4 enzyme as a coreceptor, its interaction is not as strong as its interaction with angiotensin converting enzyme 2 (ACE-2) [3]. Furthermore, in the experimental model of human coronavirus-EMC, DPP4i did not inhibit the viral entry and viral receptor interaction was independent of peptidase activity of DPP4 [4]. Hence DDP4i may not play a significant role in reducing the transmission of infection.

Secondly, DPP4i is known to modulate inflammation and is known to suppress T cell proliferation and production of pro-inflammatory cytokine and population-based studies done in patients with diabetes show 30% lower autoimmune diseases like rheumatoid arthritis [5]. However, we need to be cautious in the extrapolation of these findings of a risk of suppression of T cell immunity to acute COVID-19 infection. In COVID-19 infection, SARS Co-V has been shown to infect T cells through S protein-mediated membrane fusion although it’s not clear whether the virus replicates inside the T cells or it leads to apoptosis [6]. Moreover, decreases in the counts of CD3 + T, CD4 + T, CD8 + T, NK cells, as well as increases in the CD4/CD8 ratio in COVID-19 patients compared to recovered patients have been reported. Lower levels have been reported to correlate with severity of infection. Regulatory T cells (Tregs) which have a very important role in autoimmune conditions did not have a significant role in COVID-19 [7]. It is possible that the baseline suppressed T cell immunity secondary to DPP4i may be a disadvantage in COVID-19 infection and lead to a more severe disease.

Thirdly, in a model of acute respiratory distress syndrome (ARDS), DPP4 inhibition by sitagliptin alleviated histological findings of lung injury by inhibiting proinflammatory cytokines IL-1β, TNFα, and IL-6 [8] and recently sitagliptin has been shown to have anti-fibroblastic activity in systemic sclerosis and to inhibit TGF-ß-induced lung fibroblasts activation in vitro study [9], [10]. Moreover, DPP4 inhibition by vidagliptin has been shown to reduce lung cancer growths through induction of macrophage mediated natural killer cell activity in mouse models [11] Again, there is very sparse evidence of translation of these findings to the human lung. Conversely, according to the Japanese Adverse Drug Event Report database, 63 cases of vildagliptin‐related Interstitial pneumonitis were reported between 2009 and 2018 [12]. Several case reports have been published of vildagliptin induced interstitial pneumonia and ground glass changes in lung postulated to mimic anti TNF-alpha treatment and is postulated to be secondary to reduced TNF-alpha. In one such case, these lesions had lymphocytosis with markedly increased CD4+/CD8+ ratio which is similar to what is seen in COVID-19 infection [13], [14]. Hence, it is possible that baseline DPP-4 inhibition may increase the risk of fibrotic lesions in the lungs in COVID-19 infection wherein T cell immunity is affected.

Fourthly, experimental mouse model studies have shown that CD26/DPP-4 inhibition recruits regenerative stem cells via stromal cell-derived factor-1 and beneficially influences ischaemia-reperfusion injury in mouse lung transplantation [15]. On the contrary, after critical limb ischemia in DDP4 deficient mice, paradoxical impairment of angiogenesis, endothelial function and circulating number of EPCs has been reported [16]. Consistent with this reduced post-operative DPP4 activity has been associated with worse patient outcome after cardiac surgery due to similar mechanism invoked during tissue ischemia [17].

Fifthly, loss of DPP4 activity is associated with a prothrombotic state in myocardial microvessels and human umbilical vein endothelial cells due to the upregulation of the pro-coagulant tissue factor [18]. Increasingly, more reports of increased arterial and venous thrombosis have been reported in patients with COVID-19 infections although the exact cause is not clear at this time [19], [20].

In summary, although DPP4 inhibitors have been reported to be beneficial and safe in the long term management of patients with diabetes wherein DPP4 enzyme is blocked at varying levels of 50–90%, there is no real world data published on the effect on the prognosis of COVID-19 infection. Until there is real world evidence and reports of observational evidence of impact of DPP4 inhibitors in patients with diabetes, no definite conclusions can be made with regards to the whether they are beneficial, neutral or harmful in the setting of COVID-19 infection.

Funding

The author is supported in part by Ministry of Health, Clinician Scientist Award [MOH-CSAINV17nov-0006]; and National Medical Research Council Centre Grant [NMRC/CG/017/2013].

Declaration of Competing Interest

The author declares no competing interests.