Treatment-refractory ulcerative colitis responsive to indigo naturalis

Abstract

Background: Indigo naturalis (IN) is an herbal medicine that has been used for ulcerative colitis with an unclear mechanism of action. Indigo and indirubin, its main constituents, are ligands of the aryl hydrocarbon receptor (AhR). We assessed the safety, efficacy, and colon AhR activity of IN given orally to patients with treatment-refractory ulcerative colitis. The role of AhR in IN benefit was further evaluated with an AhR antagonist in a murine colitis model.

Methods: This open-label, dose-escalation study sequentially treated 11 patients with ulcerative colitis with either IN 500 mg/day or 1.5 g/day for 8 weeks, followed by a 4-week non-treatment period. The primary efficacy endpoint was clinical response at week 8, assessed by total Mayo score. Secondary endpoints included clinical remission, Ulcerative Colitis Endoscopic Index of Severity, quality of life, and colon AhR activity measured by cytochrome P450 1A1 (CYP1A1) RNA expression.

Results: Ten of 11 (91%) patients, including 8/9 (89%) with moderate-to-severe disease, achieved a clinical response. Among these 10 patients, all had failed treatment with 5-aminosalicylic acid, 8 patients with a tumour necrosis factor (TNF)-alpha inhibitor, and 6 patients with TNF-alpha inhibitor and vedolizumab. Five patients were corticosteroid dependent. Clinical response was observed in all five patients who had been recommended for colectomy. Three patients achieved clinical remission. All patients experienced improved endoscopic severity and quality of life. Four weeks after treatment completion, six patients had worsened partial Mayo scores. Four patients progressed to colectomy after study completion. Colon CYP1A1 RNA expression increased 12 557-fold at week 8 among six patients evaluated. No patient discontinued IN due to an adverse event. Concomitant administration of 3-methoxy-4-nitroflavone, an AhR antagonist, in a murine colitis model abrogated the benefit of IN.

Conclusion: IN is a potentially effective therapy for patients with treatment-refractory ulcerative colitis. This benefit is likely through AhR activation.

Trial registration number: NCT02442960.

Keywords: clinical trials; inflammatory bowel disease; ulcerative colitis.

Figure 1

Individual patient efficacy outcomes. (A) Total Mayo score at baseline and week 8. (B) Partial Mayo score at weeks 0, 2, 4, 6, and 12. (C) Ulcerative Colitis Endoscopic Index of Severity (UCEIS) score at baseline and week 8. (D) Short Inflammatory Bowel Disease Questionnaire (SIBDQ) scores for all visits.

Figure 2

Representative endoscopic images at baseline and week 8 for four patients.

Figure 3

Calprotectin levels at weeks 0, 4, 8, and 12 for six patients. Normal levels are ≤50 µg/g, 200 µg/g is commonly considered positive for inflammatory bowel disease, and the upper quantifiable limit was 1000 µg/g.

Figure 4

CYP1A1 expression in one to two colon tissues each from seven patients, measured by quantitative real-time PCR. The black line indicates average normalised baseline expression and the red line marks the average normalised increase (12 557-fold). Error bars represent propagated errors from CYP1A1 (n=4) and 18S (n=4) levels measured simultaneously for sample normalisation. CYP1A1, cytochrome P450 1A1.

Figure 5

Disease Activity Index for mice with dextran sodium sulfate-induced colitis treated with vehicle or indigo naturalis (IN) through 9 days, with or without the aryl hydrocarbon receptor antagonist 3-methoxy-4-nitroflavone (MNF). Error bars represent SEM (n=8). The scoring method is outlined in table 3. Maximum score is 12.