Nitro Dihydrocapsaicin, a Non-Pungent Capsaicin Analogue, Inhibits Cellular Senescence of Lens Epithelial Cells via Upregulation of SIRT1

Diabetic cataracts are a common complication that can cause blindness among patients with diabetes mellitus. A novel nitro dihydrocapsaicin (NDHC), a capsaicin analog, was constructed to have a non-pungency effect. The objective of this research was to study the effect of NDHC on human lens epithelial (HLE) cells that lost function from hyperglycemia. HLE cells were pretreated with NDHC before an exposure to high glucose (HG) conditions. The results show that NDHC promoted a deacceleration of cellular senescence in HLE cells. This inhibition of cellular senescence was characterized by a delayed cell growth and lower production of reactive oxygen species (ROS) as well as decreased SA-β-galactosidase activity. Additionally, the expression of Sirt1 protein sharply increased, while the expression of p21 and phospho-p38 proteins decreased. These findings provide evidence that NDHC could exert a pharmacologically protective effect by inhibiting the senescence program of lens cells during diabetic cataracts.

Nitro Capsaicin Suppressed Microglial Activation and TNF-α-Induced Brain Microvascular Endothelial Cell Damage

Chronically activated microglia and brain vascular damage are major causes of neuroinflammation. The aim of this study was to determine the anti-inflammatory effects of nitro capsaicin, a newly modified capsaicin with less irritating characteristics, against microglial activation and brain microvascular endothelial cell damage. Using the SIMA9 microglia cell line, we found that nitro capsaicin reduced nitric oxide (NO) production in LPS-activated microglia better than its parent compound, capsaicin. Nitro capsaicin also decreased the expression of proinflammatory cytokines (TNF-α, IL-1β, and IL-6) and enhanced the levels of anti-inflammatory factors, IL-4 and IL-10, both at the mRNA and protein levels. In the TNF-α-induced vascular damage model, nitro capsaicin decreased expression and secretion of the proinflammatory cytokines IL-1β and IL-6. Phosphorylated NF-κB p65, a key transcription factor that stimulates the signaling of inflammatory pathways, was also reduced in the presence of nitro capsaicin, suggesting that the anti-inflammatory effects of nitro capsaicin were created through reducing NF-κB activation. Together, we concluded that nitro capsaicin has the potential to be further developed as an anti-neuroinflammatory agent.