Plant Phenylpropanoids as Emerging Anti-Inflammatory Agents

Plant-derived phenylpropanoids (PPPs) compose the largest group of secondary metabolites produced by higher plants, mainly, for the protection against biotic or abiotic stresses such as infections, wounding, UV irradiation, exposure to ozone, pollutants, and herbivores. PPPs are parent molecules for biosynthesis of numerous structurally and functionally diverse plant polyphenols (simple phenolic acids and esters, glycosylated derivatives of primary PPPs, flavonoids, isoflavonoids, stilbenes, coumarins, curcuminoids, lignans, etc.), which play multiple essential roles in plant physiology. During the last few decades, extensive research has been dedicated to natural and biotechnologically produced PPPs for medicinal use as antioxidants, UV screens, anticancer, antiviral, anti-inflammatory, wound healing, and antibacterial agents. In the present review, the metabolic pathways of phenylpropanoid biosynthesis in plants and their re-construction in biotechnologically engineered systems are described. Chemical physical peculiarities of PPPs defining their antioxidant, metal chelating, and UV-protecting effects as a molecular basis for their anti-inflammatory properties are discussed as well. We focused also on the discovery of PPPs-based anti-inflammatory agents since distinct PPPs were found to modulate molecular pathways underlying inflammatory responses in human cells triggered by different pro-inflammatory stimuli in vitro and to inhibit inflammation in various tissues in vivo. The problem of low bioavailability, fast metabolism, and potential toxicity/sensitization as limiting factors for the development of PPPs-based anti-inflammatory drugs is also highlighted.