Although the precise mechanisms of Perilla treatment for allergy are not yet well elucidated, recent researches on the various phytochemicals and their pharmacological properties have also revealed some mechanisms of Perilla action in allergy. Kosuna () recently published a review on anti-inflammatory active compounds in Perilla.
Several active components contained in Perilla have been found to be linked with antiallergy and anti-inflammatory actions. These include elemicine, CX-pinene, caryophyllene, myristicin, β-sitosterol, apigenin, phenylpropanoids and also some flavonoids which act as anti-inflammatory agents (). From current knowledge, the mechanisms of allergy treatment by Perilla may involve the following aspects which are Linked to the regulation of the condition by the immune system.
Perilla Leaf Extract
Relevant to this section is the Perilla leaf extract which contains active components of molecular weight less than 10000. As mentioned above, Yamazaki reported that Perilla extract was shown to be active in inhibiting TNF production (). Kosuna proposed that more than ten active components contained in the Perilla leaf extract were active in inhibiting TNF production which plays an important role in controlling allergic reaction (). Sumimoto reported that plasma TNF-α concentration was increased in atopic dermatitis and the magnitude of the increase was correlated with the severity of the dermatitis. Also a significant correlation was found between plasma TNF-α and plasmahistamine concentrations in atopic dermatitis.Therefore, it seemed to be reasonable that Perilla was useful in treatment of atopic dermatitis and some other allergic reactions. However, TNF-α concentration was not or only slightly increased in plasma from bronchial asthma patients. This may explain why Perilla extract is less effective in asthma patients.
For the Perilla leaf extract which contains active components with a molecular weight more than 10000, Imaoka et al. () indicated that immunosuppressive effects of this kind of Perilla leaf extracts are preferentially on IgE production and that may be useful for the suppression of IgE antibodies in certain allergic disorders ().
As reported by Kosuna () and Fujita () and some other scientists, Perilla leaf extracts contain a lot of active constituents showing antioxidative activity such as flavonoids, anthocyanins, phenolics (rosmarinic acid, caffeic acid, caffeates, protocatechuic aldehyde etc.). Venge () reported that oxygen radicals may also play an important role in allergy. Studies indicated that the cells involved in the allergic inflammation are potent producers of various oxygen metabolites. These cells produced large amounts of oxygen radicals which related to the allergic symptoms. From this point of view, it could be suggested that some antioxidants present in Perilla leaves may be involved in its action in the treatment of allergy.
Perilla Essential Oil
Perilla seed, leaf and stem contain a total amount of essential oil about 0.5%. In addition to perillaldehyde, which was removed from the Perilla leaf extract products for its potential allergen property (), several other constituents contained in Perilla essential oil showed pharmacological activity. It was reported that in animal experiments, one of the constituent in the essential oil, β-caryophyllene, showed relaxing action to the windpipe of guinea pig. Also it showed significantly suppressing action to citric acid or acrylaldehyde induced cough. It may partially explain the action of Perilla on anticough and antiasthma. Another constituent, /-menthol showed antiitching action thus making Perilla helpful in the treatment of some allergic skin diseases ().
Martin et al. () have proved the anti-inflammatory activity of α-pinene and P-caryophyllene in the rat edema model induced by carrageenin or by PGE . Hashimoto and Fujita (1994) reported that elemicin was found to exhibit an inhibitory action on 5-lipoxygenase (5-LOX) which is the first enzyme in the conversion of arachidonic acid to leukotriene. Elemicin also had a suppressing action in the rat homologous PCA (passive cutaneous anaphylaxis) test which is the most commonly used bioassay to evaluate antiallergic effects on type I allergy.
Perilla Seed Oil
Earlier, it was proposed that the n-6 and n-3 polyunsaturated fatty acids in diets were importantly involved in allergy (). Recent studies have indicated that the dietary α-linolenate/linoleate balance affected on the development of some chronic diseases including allergy and that raising the (n-3) to (n-6) ratios of diets would be effective in reducing the severity of immediate-type allergic hypersensitivity (). It was hypothesized that if taking more n-3 fatty acid, resulted in a lowering of n-6 fatty acid uptake, this would lead to the inhibition of leukotriene production which is another important mediator causing allergy (). Therefore taking Perilla oil (contains mainly n-3 polyunsaturated fatty acid) might be beneficial for the prevention and treatment of allergy.
Ito et al. () reported a pilot study on atopic dermatitis patient treated with Perilla oil. In his study, patients treated with Perilla oil, in the phospholipid fraction in serum, the n-3:n-6 ratio and the EPA:AA ratio were significantly increased. Leukotriene C4 release from polymorphonuclea leukocytes by zymosan and fresh autologous serum was significantly decreased. This results might support the hypothesis that increasing α-linolenic acid could inhibit release of some chemical mediators (leukotrienes) linked with allergy.