Figure 1.

Mechanisms of the action of phytochemicals in the common cold. (A) The oral administration of plant products leads to their intestinal transformation, absorption, and conversion by the liver to degradation products, exhibiting different effects on common colds. (B) A number of phytochemicals such as flavonoids, phenylethanoloids, iridoids, and alkamides, and constituents of essential oils such as monoterpenoids, and phenolic glycosides inhibit the synthesis and the activity of different pro-inflammatory mediators. This effect includes the inhibition of the activities of cyclooxygenase-1, and -2 (COX-1, COX-2), lipoxygenase 5 and 15 (5-LOX, 15-LOX), transcription factors as NF-kB, interleukins 1β, 2, 6, and 8 (IL-1β, IL-2, Il-6, Il-8), tumor necrosis factor α (TNF-α), phospholipase A₂ (PLA₂), leukotriene B4 (LTB4), and prostaglandin E₂ (PGE₂). Other phytochemicals such as as coumarins and proanthocyanidins exhibit anti-oxidant activities, while compounds such as isovitexin and ferulic acid present direct antiviral activities against respiratory syncytial virus (RSV) and adenovirus (ADV), respectively. Mucilages and monoterpenoids can also exert bronchospasmolytic activities by calcium influx blockage through the inhibition of transient receptor potential ankyrin 1 (TRPA1) and transient receptor potential vanilloid 1 (TRPV1), or by blocking the L-type calcium channels, respectively.