*6.2. In Vivo Animal Studies*

VCE-004.8, a synthetic agonist for PPAR-γ and CB2 receptors, demonstrated antiinflammatory properties in an in vivo study on mice with bleomycin-induced scleroderma performed by del Río et al. [177]. The non-thiophilic, fully substituted CBD quinol derivative labeled VCE-004.8 decreased the expression of IL-1β and IL-13, and prevented macrophage infiltration and mast cells degranulation, thus indirectly reducing the concentration of Transforming Growth Factor-beta (TGF-β), a key factor in fibrosis development. Another study on the same experimental model, performed by Balistreri et al., showed the similar properties of another synthetic cannabinoid labeled WIN55,212-2, a full CB1 agonist that prevents dermal fibrosis by inhibiting TGF-β as well as connective tissue growth factor and platelet-derived growth factor [178]. Mast cell downregulation, alongside a decrease in IL-4 levels, was also reported in an in vivo model for ACD induced with oxazolone on Balb/c and hairless mice that were treated with a topical synthetic CB1 agonist named α-oleoyl oleylamine serinol (α-OOS) [179].

Topically applied cannabidiol has also demonstrated anti-inflammatory and analgesic effects by inhibiting cyclooxygenase and lipoxygenase, properties that were observed by Formukong et al. in an experimental model of the tetradecanoylphorbol acetate-induced erythema of mouse skin performed decades ago, a study which represented a basis for more advanced research and unlocked the potential for the application of cannabinoids in acne, ACD, dermatomyositis, and other inflammatory skin disorders [180].

A suspected yet unconfirmed consequence of the anti-inflammatory roles of cannabinoids is the decrease of tumor viability, proliferation and growth in cutaneous melanoma. Armstrong et al. studied a combination of THC and CBD in a cutaneous melanoma model on mice bearing BRAF wild-type melanoma xenografts and found that the product caused a reduction of reactive oxygen species production and caspase activation, effects that may be triggered by the anti-inflammatory effects of CBD [181]. Skin tumorigenesis is an intricate process that depends on molecules common to the inflammatory signaling pathways, entailing complex interferences induced by substances such as matrix metalloproteinases, TNF-α and IL-1 that are implicated in inflammation as well as a wide array of malignancies, including skin cancer [182–186].

The decreased expression of TNF-α and NF-κB triggered by cannabinoids noted in in vitro studies was also demonstrated in an in vivo study on the CB receptors in the inflammatory milieu of skin cancer. Zheng et al. showed that CB receptors play a role in the resistance to ultraviolet (UV) B inflammation in an in vivo model of UV-induced skin carcinogenesis, and that CB receptor deficiency correlates with an increase in the expression of TNF-α, and the activation of NF-κB and mitogen-activated protein MAP kinases [187].
