**7. Resveratrol: a bioactive polyphenol with attractive medicinal properties**

Trans-resveratrol (trans-3,5,4′-trihydroxystilbene) (RES) is a polyphenol that can be sourced from various edible plants, which has demonstrated antioxidant, anti-inflammatory, antimicrobial, anticancer, and restorative properties [81–84]. Therefore, RES is positioned in alignment with the treatment principles for PD and the diseases with which it has been associated (**Figure 9**).

Even though RES is found in a breadth of plant-based foods (e.g., red wine, berries, peanuts, and dark chocolate), the naturally occurring concentrations of RES are not substantial enough (e.g., 0.1–0.7 mg/L in red wine) to reasonably attain the therapeutic values reported in the scientific literature (e.g., an oral dose of approximately 10 mg/kg body) [86–88].

Consequently, the purified and optimised extracts of RES are often used in research and some products have been made commercially available as wellness supplements (https://megaresveratrol.net; https://biotivia.com/pages/transmax-tr-1).

However, RES is a hydrophobic molecule and therefore, like other promising phytotherapeutics such as curcumin, has poor water solubility (<0.05 mg/mL). RES has also been found to rapidly metabolise *in vivo* and revert to its less stable isomer when exposed to light, demonstrating its instability and photosensitivity, respectively [85].

Additionally, the low oral bioavailability of RES has been considered a significant obstacle to its clinical translation, resulting in the development of drug carrier models. In fact, there is ample evidence indicating that nano-formulation may be a successful strategy to improve the pharmacological indices of RES under physiological conditions [89–91].

Interestingly, the design of functional foods also includes the application of nanotechnology, via the incorporation of liposomal nanocarriers or other nanoencapsulated systems. In this way, the therapeutic potential of customised, effective, and stable fortified foods with specific pharmacokinetic parameters, such as steady time-release, can be investigated [92].

Indeed, both oral and buccal delivery systems, such as those possible via functional food design, have plausible applications regarding PD therapeutics, especially since the primary target area for treatment is in the oral cavity. In fact, many nanoformulations also aim to enhance the delivery and efficacy of targeted therapeutics by engineering combinations of selected bioactive molecules that offer specific properties that promise to optimise the probability of the desired treatment outcome [93].

#### **Figure 9.**

*The molecular structures of trans-resveratrol (trans-3,5,4*′*-trihydroxystilbene) (RES) (see left), which is the more stable, and therefore bioactive form compared to its isomer, cis-resveratrol (see right) (Gambini et al. [85]).*

### **8. The attenuation of inflammatory processes by RES** *in vitro*

The modulation of deregulated inflammation, which has been consistently reported for RES in the *in vitro* reports within the literature, is a central treatment principle for a viable therapeutic for PD. Additionally, *in vitro* studies allow for a breadth of experiment parameter manipulation not afforded by *in vivo* studies. So, although such studies cannot probe disease development and treatment, they can support the elucidation of mechanisms of action, thus identifying potential molecular targets for therapeutic applications.

For example, studies that used LPS-stimulated human gingival fibroblasts (HGFs), found through ELISA, and MTT assays, that RES significantly decreased IL-6 and IL-8, but did not increase cell viability. Interestingly, once RES was combined with the polyphenol silymarin (SIL), the viability increased in combination with the decrease in IL-6, IL-8 as well as TNF-α, suggesting that RES- ± SIL have a more widespread modulatory effect on LPS-induced inflammation [94, 95].

Additionally, in 2014, Fordham et al. examined the effect of RES (plus antioxidants, phloretin, silymarin, hesperetin) on LPS-stimulated peripheral blood mononuclear cells (PBMCs) obtained from healthy human donors. ELISA showed that RES decreased the secretion of IL-1β, IL-6, and IFN-ɣ in the LPS-induced PBMCs. Further to this, TNF-α was attenuated at the level of mRNA, as determined by RT-PCR. The researchers concluded that hesperetin and RES significantly inhibited (p < 0.05) the inflammatory response in LPS-stimulated PBMCs [96].

### **9. The influence of RES on regenerative processes in periodontal cells**

RES has also shown promise regarding the restoration of periodontal tissue, which is a crucial part of the complete treatment of PD. For example, in a complex human *in vitro* and *in situ* study, Wang and colleagues reported that RES preserved cell aggregation and osteo-differentiation of normal human periodontal ligamental stem cells (HPLSCs) treated with TNF-α. In this study, histological analysis confirmed that RES treatment (even pre-implantation) improved regeneration in tissue originating from both healthy and pro-inflammatory microenvironments [97].

In accordance, Yuan and colleagues also found through histochemical analysis, RT-PCR, Western blot, and ELISA, that RES attenuated TNF-α – induced osteogenic suppression in HPLSCs *in vitro* [98].
