*5.3. Anti-Inflammatory Pathway*

PTS possesses strong anti-inflammatory properties [27], with iNOS, COXs, leukotrienes, NF-κB, Tumor Necrosis Factor Alpha (TNF-α), and Interleukin-1 beta (IL-1β) reported as its primary targets [52]. Endoplasmic reticulum (ER) stress plays a vital role in inducing endothelial cell inflammation. In human umbilical vein endothelial cells (HUVECs) stimulated by TNF-α, PTS attenuated inflammatory cytokine production and inhibited monocyte adhesion. Importantly, PTS treatment also countered the ER-stress-related molecules stimulated by TNF-α [53]. In HT-29 colon cancer cell lines, PTS mediated the anti-inflammatory pathway through the inhibition of the protein kinase cascade activated by p38 mitogen and led to the suppression of pro-inflammatory cytokine production [54]. In canine chondrocytes, treatment with PTS decreased Matrix Metalloproteinase (MMP)-3, sGAG, and TNF-α, thereby exhibiting anti-inflammatory properties [8]. When combined with cyclodextrin, PTS treatment inhibited biofilm formation by *F. nucleatum* in periodontitis [55]. Importantly, PTS was identified to inhibit the NF-κB-induced inflammatory response by preventing its nuclear translocation. Indeed, PTS treatment in the TPA-induced mouse epidermis led to decreased IkappaB kinase (IKK) activity and improved the retention of IkappaBa (IKB-α),

which ultimately blocked the nuclear translocation of NF-κB [56]. Another significant pathway through which PTS inhibited inflammation was through the marked attenuation of the transcription factor activator protein-1 (AP-1) by affecting the binding of the c-JUN subunit to AP-1 response elements [56] (Figure 3).

**Figure 3. Anti-inflammatory pathway of pterostilbene**: PTS mediates its anti-inflammatory effect mainly through the inhibition of the transcription factors NFκB and AP-1, which leads to the attenuation of downstream pro-inflammatory mediators, including TNF-α. Further, PTS also inhibits P38 mitogen-activated protein kinase (MAPK) signaling and prevents the induction of iNOS and COX-2.

While studying the anti-inflammatory effects of PTS on ischemia/reperfusion injury in a middle cerebral artery occlusion (MCAO) rodent model, it was found that treatment with PTS suppressed the swelling and disintegration of cells, the infiltration of macrophages and monocytes, and the degranulation of polymorphonuclear leukocytes, thereby exhibiting a neuroprotective effect through an anti-inflammatory mechanism [57]. Moreover, PTS dampened the astrocyte-mediated inflammatory and oxidative damage caused by ischemia/reperfusion injury through the inhibition of NF-κB [58]. The effect of PTS on lipopolysaccharide-induced pulmonary fibrosis was identified to involve the activation of Keap-1/Nrf2, the inhibition of caspase-dependent A20/NF-κB and NLRP3 signaling pathways, and the suppression of inflammation [59]. Furthermore, PTS exhibited a protective role in arthritis induced by Freund's adjuvant (CFA) in rats by suppressing inflammatory mediators and cytokines [60].
