The aloe ingredients responsible for physiological effects and the concentrations required to exert their biological activities are not fully understood. This study compares the anti-inflammatory effects of aloin and aloe-emodin with other polyphenols. Our results demonstrated that aloe-emodin dose-dependently inhibited inducible nitric oxide synthase (iNOS) mRNA expression and nitric oxide (NO) production at 5–40 μM. In addition, the levels of cyclooxygenase-2 (COX-2) mRNA and prostaglandin E₂ (PGE₂) production were suppressed by 40 μM aloe-emodin. Aloin also suppressed the production of NO at 5–40 μM, although it did not suppress PGE₂ production. The present results indicate that aloin and aloe-emodin possibly suppress the inflammatory responses by blocking iNOS and COX-2 mRNA expression. The anti-inflammatory effect of aloe-emodin was comparable to that of kaempferol and quercetin, indicating aloe-emodin as a possible key constituent responsible for the anti-inflammatory activity of aloe.

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