Indigo naturalis is effective in treating nail psoriasis coexisting with microorganism infections. This study examines the antimicrobial effects of indigo naturalis prepared from Strobilanthes formosanus Moore. Eight bacterial and seven fungal strains were assayed using the agar diffusion method to examine the effects of indigo naturalis and its bioactive compounds. The bioactive compounds of indigo naturalis were purified sequentially using GFC, TLC, and HPLC. Their structures were identified using mass spectrometry and NMR spectroscopy. UPLC-MS/MS was applied to compare the metabolome profiles of indigo naturalis ethyl-acetate (EA) extract and its source plant, Strobilanthes formosanus Moore. The results of in vitro antimicrobial assays showed that indigo naturalis EA-extract significantly (≥1 mg/disc) inhibits Gram-positive bacteria (Staphylococcus aureus, S. epidermis and methicillin-resistant S. aureus (MRSA)) and mildly inhibits non-dermatophytic onychomycosis pathogens (Aspergillus fumigates and Candida albicans), but has little effect on dermatophyes. Isatin and tryptanthrin were identified as the bioactive compounds of indigo naturalis using S. aureus and S. epidermis as the bioassay model. Both bioactive ingredients had no effect on all tested fungi. In summary, indigo naturalis prepared from Strobilanthes formosanus Moore exhibits antimicrobial effects on Staphylococcus and non-dermatophytic onychomycosis pathogens. Tryptanthrin and isatin may be its major bioactive ingredients against Staphylococcus and the inhibitory effect on MRSA may be due to other unidentified ingredients.

Letter from JAMA Dermatology — Comparison of Refined and Crude Indigo Naturalis Ointment in Treating Psoriasis — Randomized, Observer-Blind, Controlled, Intrapatient Trial

The use of indigo naturalis to treat psoriasis has proved effective in our previous clinical studies. The present study was designed to examine the anti-inflammatory effect of indigo naturalis in primary cultured human umbilical vein endothelial cells (HUVECs). Pretreatment of cells with indigo naturalis extract attenuated TNF-α-induced increase in Jurkat T cell adhesion to HUVECs as well as decreased the protein and messenger (m)RNA expression levels of vascular cell adhesion molecule-1 (VCAM-1) on HUVECs. Indigo naturalis extract also inhibited the protein expression of activator protein-1 (AP-1)/c-Jun, a critical transcription factor for the activation of VCAM-1 gene expression. Since the reduction of lymphocyte adhesion to vascular cells by indigo naturalis extract could subsequently reduce the inflammatory reactions caused by lymphocyte infiltration in the epidermal layer and help to improve psoriasis, this study provides a potential mechanism for the anti-inflammatory therapeutic effect of indigo naturalis extract in psoriasis.

Background: In the treatment of nail psoriasis, standardized therapeutic regimens are currently lacking. Objective: To evaluate the therapeutic efficacy of indigo naturalis oil extract in patients with nail psoriasis. Methods: Patients with nail psoriasis applied indigo naturalis oil extract on affected nails twice daily for 24 weeks. Efficacy was evaluated using the Nail Psoriasis Severity Index (NAPSI) and modified target NAPSI for the single most severely affected nail. Results: Twenty-eight out of 32 patients completed the study. The mean NAPSI was 36.1 ± 14.7 at baseline and decreased to 14.9 ± 11.1 at week 24 while the mean modified target NAPSI was 11.7 ± 3.9 at baseline and decreased to 3.6 ± 3.2 at week 24. Conclusions: Indigo naturalis oil extract appeared to improve nail psoriasis. Although preliminary, these results indicate that it could provide a novel therapeutic option for nail psoriasis, a disease notoriously difficult to treat.