Evidence and potential mechanism of action of indigo naturalis and its active components in the treatment of psoriasis.

Background: Indigo naturalis is effective against psoriasis. Indigo, indirubin and tryptanthrin, the main active components of indigo naturalis, have anti-inflammatory properties.

Objective: To evaluate the efficacy and safety of indigo naturalis and its active components in the treatment of psoriasis.

Methods: Seven databases were searched for studies of indigo naturalis and its active components for the treatment of psoriasis.

Results: The findings demonstrated a higher response rate in the Chinese herbal medicine (CHM) formula groups than in the control group for Psoriasis Area and Severity Index 60 (PASI60) (Rate difference [RD] = 0.22,  < .0001). Among all adverse events, only the incidence of gastrointestinal adverse reactions was higher in the CHM formula group than in the control group (RD = 0.09,  < .0001). In preclinical studies, indirubin showed better performance in improving the phenotype of psoriasis-like mice compared to that in controls, including the PASI score (mean difference [MD] = -3.58,  < .0001), epidermal thickness (MD = -29.13,  < .0001), interleukin-(IL) 17 A mRNA expression (MD = -2.27,  = .0066) and IL-23 mRNA (MD = -5.36,  = .01).

Conclusion: Indigo naturalis combined with conventional treatments is useful for treating psoriasis. Indigo naturalis display anti-proliferative, anti-inflammatory and anti-angiogenic effects by regulating the TAK1, JAK3/STAT3, Wnt/β-catenin, Akt/PKB, FAK and AP-1/c-Jun pathway.