Impact of Glucose, Inflammation and Phytochemicals on ACE2, TMPRSS2 and Glucose Transporter Gene Expression in Human Intestinal Cells.

Inflammation is associated with the pathophysiology of type 2 diabetes and COVID-19. Phytochemicals have the potential to modulate inflammation, expression of SARS-CoV-2 viral entry receptors (angiotensin-converting enzyme 2 (ACE2) and transmembrane protease, serine 2 (TMPRSS2)) and glucose transport in the gut. This study assessed the impact of phytochemicals on these processes. We screened 12 phytochemicals alongside 10 pharmaceuticals and three plant extracts, selected for known or hypothesised effects on the SARS-CoV-2 receptors and COVID-19 risk, for their effects on the expression of ACE2 or TMPRSS2 in differentiated Caco-2/TC7 human intestinal epithelial cells. Genistein, apigenin, artemisinin and sulforaphane were the most promising ones, as assessed by the downregulation of TMPRSS2, and thus they were used in subsequent experiments. The cells were then co-stimulated with pro-inflammatory cytokines interleukin-1 beta (IL-1β) and tumour necrosis factor-alpha (TNF-α) for ≤168 h to induce inflammation, which are known to induce multiple pathways, including the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway. Target gene expression (ACE2, TMPRSS2, SGLT1 (sodium-dependent glucose transporter 1) and GLUT2 (glucose transporter 2)) was measured by droplet digital PCR, while interleukin-1 (IL-6), interleukin-1 (IL-8) and ACE2 proteins were assessed using ELISA in both normal and inflamed cells. IL-1β and TNF-α treatment upregulated ACE2, TMPRSS2 and SGLT1 gene expression. ACE2 increased with the duration of cytokine exposure, coupled with a significant decrease in IL-8, SGLT1 and TMPRSS2 over time. Pearson correlation analysis revealed that the increase in ACE2 was strongly associated with a decrease in IL-8 (r = -0.77, p < 0.01). The regulation of SGLT1 gene expression followed the same pattern as TMPRSS2, implying a common mechanism. Although none of the phytochemicals decreased inflammation-induced IL-8 secretion, genistein normalised inflammation-induced increases in SGLT1 and TMPRSS2. The association between TMPRSS2 and SGLT1 gene expression, which is particularly evident in inflammatory conditions, suggests a common regulatory pathway. Genistein downregulated the inflammation-induced increase in SGLT1 and TMPRSS2, which may help lower the postprandial glycaemic response and COVID-19 risk or severity in healthy individuals and those with metabolic disorders.