*6.3. Therapeutic Effect of PTS in Liver Diseases*

Liver fibrosis results from the overt and chronic accumulation of extracellular matrix proteins, resulting in the scarring of hepatic tissue and the marked disruption of hepatic vasculature, which can ultimately lead to cirrhosis [103]. Along with an increased risk of mortality, cirrhosis is also a risk factor for developing hepatocellular carcinoma [103]. Studies employing both acute and chronic liver injury models have identified the alleviation of liver injury post-PTS administration (Table 2). Of note, PTS treatment administered to a dimethylnitrosamine (DMN)-induced liver fibrosis model in Sprague-Dawley rats reduced DMN-induced changes and attenuated pro-fibrogenic hepatic stellate cell activation. PTS also exhibited hepatoprotective activity through the inhibition of TGF-b1/Smad signaling [75].

NAFLD is a chronic progressive liver disorder in metabolic syndromes such as obesity and insulin resistance caused by excessive fat accumulation (hepatic steatosis). PTS administration in Zucker rats showed reduced insulin resistance and attenuated hepatic triacylglycerol levels, thus reducing liver steatosis. Importantly, treatment with PTS reduced hepatic steatosis from grade 2 to grade 1. Of note, PTS was observed to reduce the triacylglycerol synthesis capacity of the liver through a reduction in fatty acid disposal and through the inhibition of triacylglycerol synthesis enzymes such as DGAT2. The PTS-treated rats had improved fatty acid profiles, attributed to its delipidating effect [76]. Furthermore, PTS and its derivative 3 -Hydroxy-pterostilbene reduced NAFLD pathogenesis induced by free fatty acids and a fat-rich diet through the upregulation of SIRT1/AMPK and insulin signaling pathways and the downregulation of the protein expression of SREBP-1, which results in the activation of the β-oxidation of fatty acids and the consequent reduction in fatty acid synthesis. Moreover, PTS was also observed to promote the growth of vital beneficial microbiota, such as Oscillospira, while down-regulating the population of potentially pathogenic bacteria, such as Allobaculum, Phascolarctobacterium, and Staphylococcus [104].

Zhang et al. employed an IUGR-induced liver injury model and demonstrated increased circulating alanine transaminase activity, an elevated hepatocyte apoptosis rate, and ROS generation and accumulation. PTS administration reduced these pathogenic processes by preventing the accumulation of hepatic superoxide anions, 8-hydroxy-2 deoxyguanosine, and 4-hydroxynonenal-modified protein by stimulating the translocation of Nrf2 to the nucleus and inducing the antioxidant enzyme SOD2 [39]. Further, in a study investigating the efficacy of PTS against obesity, it was found that PTS formed three hydrogen bonds with the amino acids of PPAR-α, thereby inducing its expression in the livers of BBPX hamsters and lowering the plasma LDL concentration. Furthermore, PTS was also observed to regulate fatty acid oxidation by dose-dependently elevating the phosphorylation of 5 -AMPK [77].

#### *6.4. Effects of PTS on Diseases of the Central Nervous System*

The antioxidant and anti-inflammatory properties of PTS have been reported to be therapeutic for the aging brain. Evidence from experimental studies indicates that PTS confers protective benefits against Alzheimer's disease (AD) and vascular dementia [105] (Table 2). PTS treatment potently modulated cognitive impairment and cellular stress. This effect was closely linked to the presence of methoxy groups, which increases lipophilicity. It also positively modulates cellular stress markers by upregulating PPAR-α expression [82].

Joseph et al. administered PTS to rats at various doses and measured its concentration in blood plasma and brain tissue (hippocampus). The amount of PTS in the hippocampus was directly related to the intake of PTS and alleviated cognitive function through the modulation of neural plasticity and motor activity. When administered at high doses, the compound was detected in the serum and brain tissue; however, low doses were only found in the serum and not detected in brain tissue [105]. Dose studies are warranted to further understand the threshold dosage for PTS to cross the BBB.

The induction of the NF-kB signaling pathway is a vital pathogenic component in neurodegenerative diseases. Through the downregulation of NF-kB, PTS limited the inflammatory response in the CNS [82]. Cerebral ischemia/reperfusion injury is a period of impaired blood supply to the brain during an ischemic stroke. Five days of PTS treatment (10 mg/kg) in a common carotid artery occlusion model markedly elevated the membrane potential of mitochondria and induced cytochrome c expression, as well as complex I and IV activity. PTS attenuated the ROS generated by mitochondria and reduced the cytochrome c levels in the cytosol. Considering that HO-1 signaling exhibits protection in Parkinson's, Alzheimer's, and other neurodegenerative diseases, the upregulation of HO-1 expression by PTS exhibited cerebral protective effects [81].

PTS confers neuroprotection to neuronal Sh-SY5Y cells by reviving estrogen-receptor-αinduced signaling [106]. A reduction in high-glucose-induced CNS injury and mitochondrialdysfunction-derived oxidative stress was observed upon PTS administration due to the activation of Nrf2 in hippocampal neuronal cells [107]. However, high doses of PTS or resveratrol inhibited the physiological immune response to pathogens [108–110]. Further dose-dependent studies are required to identify the appropriate PTS dose to achieve the therapeutic effect.

#### *6.5. Effects of PTS on Cardiovascular Diseases*

Hypercholesterolemia is associated with an increased risk of cardiovascular diseases. PTS treatment was demonstrated to reduce atherosclerosis and myocardial infarction in animal models of cardiovascular diseases (Table 2). PTS treatment lowered plasma lipoproteins and cholesterol, protecting vascular endothelial cells from oxidation and promoting cytoprotective macroautophagy [7]. pTeroPure, a highly purified trans-PTS patented by Chromadex, Irvine, CA, has been proven to significantly reduce blood pressure in adults [2]. The combination of PTS and hydroxypropyl-β-cyclodextrin improved cardiac function in an experimental monocrotaline (MCT)-induced/arterial-hypertension-provoked rightheart-failure model through the induction of the antioxidative response. In particular, PTS enabled the rehabilitation of glutathione metabolism and restored redox homeostasis in the right ventricle of MCT-treated rats. At higher doses, PTS attenuated lipoperoxidation and total phospholamban while increasing the levels of sarcoplasmic reticulum calcium ATPase (SERCA) in the right ventricles of diseased rodents [83].

An elevation of mechanical stress in the endothelium puts the heart at risk of injury to its vasculature and thrombogenesis, which is worsened by oxidative stress. The endogenous antioxidative response of the vascular system is responsible for exerting a protective effect by attenuating oxidative damage; however, the antioxidant capacity may become exhausted due to increased and chronic exposure to ROS, creating an imbalance between oxidant and antioxidant activities. In an ischemia/reperfusion-induced myocardial damage experimental model, PTS showed a cardioprotective effect by reducing myocardial peroxynitrite, superoxide production, malondialdehyde content, and NADPH oxidase enzyme expression and by increasing the antioxidant SOD activity to protect against oxidative stress [111].

The unchecked proliferation of vascular smooth muscle cells leads to atherosclerosis and the consequent development of vascular stenosis [112]. In atherosclerosis, PTS has been reported to exhibit protective effects through the modulation of vascular smooth muscle cells (VSMCs) and VECs through the blocking of an Akt (a serine/threonine kinase) dependent pathway. In a platelet-derived growth factor (PDGF)-BB-induced VSMC proliferation model, PTS treatment downregulated the promoters of DNA synthesis and VSMC proliferation, including cyclin-dependent kinase (CDK)-2, CDK-4, cyclin E, cyclin D1, retinoblastoma (Rb), and proliferative cell nuclear antigen (PCNA) [113].

#### *6.6. Effects of PTS on Aging*

Polyphenols have been extensively documented to protect against aging and agerelated diseases such as atherosclerosis, arthritis, cataracts, osteoporosis, diabetes, and neurodegenerative and cardiovascular disorders. Studies indicate that PTS acts as an anti-aging agent by regulating hallmark features, including oxidative damage, inflammation, telomere attrition, and cell senescence [43] (Table 2). Owing to its ability to cross the BBB, PTS can localize within the brain and provide potential therapeutic benefits against age-related neurodegenerative disorders [108]. Indeed, PTS countered lipopolysaccharide-induced microglial activation in rodents and ameliorated learning and memory impairments [114]. PTS was also demonstrated to effectively reverse aging-associated behavioral deficits in rats. Indeed, the concentration of PTS in the rat hippocampus was directly correlated with dopamine release and working memory [105].

Employing the SAMP8 mouse, which is increasingly being recognized as an effective model of accelerated aging in the background of sporadic and age-related AD, Chang et al. demonstrated that dietary doses of PTS exhibited more potency when compared to resveratrol in modulating cognitive behavior and cellular stress [82]. Notably, the study attributed the anti-aging effect to the activation of PPAR-α. Moreover, PTS was also reported to extend the lifespan of SAMP8 mice, an effect attributed to c-Jun N-terminal protein kinase inhibition [115].

Ocular surface inflammation is a multifactorial disease that is particularly prevalent among the elderly. PTS has been reported to restore the imbalance between oxygenases and antioxidative enzymes through the attenuation of COX-2 and the upregulation of SOD1 and peroxiredoxin-4 (PRDX4) activities in the background of hyperosmotic stress [116]. PTS treatment is associated with a reduction in oxidative damage mediators, including malondialdehyde (MDA), 4-hydroxynonenal (4-HNE), aconitase-2, and 8-hydroxydeoxyguanosine (8-OHdG) levels, in a human corneal epithelial cell model induced by hyperosmotic medium stress [116]. Blueberry consumption has been reported to prolong the lifespan and improve thermo-tolerance in C. elegans [117]. In D. melanogaster, blueberry extracts upregulated the expression of the antioxidant enzymes SOD and catalase, which were mainly attributed to lifespan extension [118]. Dietary supplementation with blueberries, which contain polyphenols such as PTS, alleviated the damaging effect of aging on motor behavior and neuronal signaling and lowered the amyloid-beta content in a transgenic AD rodent model [119]. In an open-label, single-arm, monocentric study investigating the efficacy of Pon skin brightening and PTS anti-aging, a cream formulation containing 0.4% PTS was highly effective in reducing aging markers and brightening the skin tone of study participants. Furthermore, employing an in vitro experiment, PTS was reported to exhibit anti-tyrosinase activity and inhibit melanogenesis, which could have contributed to the reduction in the markers of skin aging [120].

Arthritis is characterized by the painful swelling of joints, which worsens with age. In a Freund's adjuvant (CFA)-induced arthritis model in rats, PTS significantly reduced paw swelling, the arthritic score, and body weight. Interestingly, it also helped restore the healthy gut microbiota ecosystem by reducing the relative abundance of Helicobacter, Desulfovibrio, Lachnospiraceae, and Mucispirillum. Considering the evidence of PTS in suppressing inflammation through intestinal bacteria alterations, studies investigating its therapeutic potential against inflammatory bowel disorders could be of clinical value [60].
