5-Aminolevulinic Acid as a Novel Therapeutic for Inflammatory Bowel Disease

Abstract

5-Aminolevulinic acid (5-ALA) is a naturally occurring nonprotein amino acid licensed as an optical imaging agent for the treatment of gliomas. In recent years, 5-ALA has been shown to possess anti-inflammatory and immunoregulatory properties through upregulation of heme oxygenase-1 via enhancement of porphyrin, indicating that it may be beneficial for the treatment of inflammatory conditions. This study systematically examines 5-ALA for use in inflammatory bowel disease (IBD). Firstly, the ex vivo colonic stability and permeability of 5-ALA was assessed using human and mouse fluid and tissue. Secondly, the in vivo efficacy of 5-ALA, in the presence of sodium ferrous citrate, was investigated via the oral and intracolonic route in an acute DSS colitis mouse model of IBD. Results showed that 5-ALA was stable in mouse and human colon fluid, as well as in colon tissue. 5-ALA showed more tissue restricted pharmacokinetics when exposed to human colonic tissue. In vivo dosing demonstrated significantly improved colonic inflammation, increased local heme oxygenase-1 levels, and decreased concentrations of proinflammatory cytokines TNF-α, IL-6, and IL-1β in both plasma and colonic tissue. These effects were superior to that measured concurrently with established anti-inflammatory treatments, ciclosporin and 5-aminosalicylic acid (mesalazine). As such, 5-ALA represents a promising addition to the IBD armamentarium, with potential for targeted colonic delivery.

Keywords: 5 amino levulinic acid; Crohn’s disease; anti-inflammatory; colonic drug delivery; drug stability; inflammation; large intestine; microbiome; microbiota metabolism; ulcerative colitis.

Figure 1

Catabolism of heme, liberating carbon monoxide, iron, biliverdin, and bilirubin. The enzyme heme oxygenase-1 is induced by 5-ALA [44].

Figure 2

Overview of the study design. Mice were acclimatised for 7 days, then commenced group-specific treatment with concurrent colitis induction via DSS. All mice were sacrificed on day 10.

Figure 3

Stability profile of 5-ALA during, (A): incubation with faecal slurry (human (n = 3) and mouse (n = 10)); (B): incubation with colonic tissue enzymes (human (n = 1) and mouse (n = 3)); (C): percentage of 5-ALA in different compartments during Ussing experiment with human colonic tissue (1 donor); (D): percentage of 5-ALA in different compartments during Ussing experiment with mouse colonic tissue (n = 3). Permeation of 5-ALA occurs from the apical to basolateral side of tissue.

Figure 4

(A): Daily mean disease activity index (DAI) scores for PO treatment groups; (B): DAI scores for IR treatment groups; (C): mean colonic weight to length ratios per treatment group; (D): mean spleen weights per treatment group. n = 7 mice per treatment group. Error bars: standard deviation. The * marker indicates significant 5-ALA superiority where p < 0.05.

Figure 5

Plasma concentrations of inflammatory markers: TNF-α (A); IL-6 (B); IL-1β (C); and the anti-inflammatory marker, IL-10 (D), in mice following 10 days of treatment. n = 7 mice per treatment group. Error bars: SEM, the * marker indicates significant 5-ALA/SFC superiority where p < 0.05.

Figure 6

Colonic tissue concentrations of inflammatory markers: TNF-α (A); IL-6 (B); and IL-1β (C); and the anti-inflammatory marker, IL-10 (D), in mice following 10 days of treatment. n = 7 per treatment group. Error bars: SEM, the * marker indicates significant 5-ALA/SFC superiority where p < 0.05.

Figure 7

Heme oxygenase-1 (HO-1) concentrations in plasma and colonic tissue per group, after 10 days of treatment. n = 7 mice per treatment group. Error bars: SD.