**3. Relationship between diabetes and COVID 19**

### **3.1 Dipeptidyl peptidase-4**

Typically incretins, including the Glucagon peptide and gastric inhibitory peptide, are essential to increase insulin secretion. Nonetheless, these incretin values in type 2 diabetes are reduced due to degraded levels of dipeptidyl peptidase-4 in the small intestinal gut. The dipeptidyl peptidase-4 is a transmembrane glycoprotein that exists in the body as a dimer. The primary function of D dimer is to block the degrading enzyme and enhance the activity of incretins in insulin secretion [14].

This enzyme has been indicated as one of the components responsible for the entry receptors of the coronavirus. The place of the enzyme is at the entry of the bronchial tree.

#### **3.2 ACE2 receptors**

These receptors play a crucial role in facilitating the entry of SARS-CoV-2 into the human body cells. ACE2 receptors are mainly located on the cell membranes of the lungs, intestine, kidney, and vessels. ACE2 levels are known to be increased in diabetic patients, which is also associated with non-communicable diseases such as diabetes, hypertension, stroke predisposing to develop the SARS-CoV 2 infection [15, 16].

#### **3.3 ACEi and ARBs**

ACEi and ARBs are commonly used antihypertensive medications by patients with diabetes and hypertension. These medications are believed to increase the ACE2 levels within the body. However, clinical evidence is yet to be proved [17].
