Investigation of mitigating effect of colon-specific prodrugs of boswellic acid on 2,4,6-trinitrobenzene sulfonic acid-induced colitis in Wistar rats: Design, kinetics and biological evaluation

Figure 1 Scheme of synthesis for the amide prodrugs.

Figure 2 In vitro release kinetics of β-boswellic acid from prodrugs in colon homogenates and fecal matter. FM: Fecal matter; C: Colon homogenates.

Figure 3 Proposed activation mechanism.

Figure 4 In vivo pharmacokinetics after oral administration of prodrug of β-boswellic acid with L-tryptophan (blood).

Figure 5 Colon-to-body weight ratio. Average of six readings is presented; One-way ANOVA followed by Dunnett’s multiple comparison Test, and statistical significance was considered at ^aP < 0.05, ^bP < 0.01, ^eP < 0.001 vs disease control. HC: Healthy control; DC: Disease control; BBA: β-boswellic acid; SLZ: Sulfasalazine; BH: Prodrug of BBA with L-histidine; BP: Prodrug of BBA with D-phenylalanine; BT: Prodrug of BBA with L-tryptophan; BTY: Prodrug of BBA with L-tyrosine; H: L-histidine; P: D-phenylalanine; T: L-tryptophan; TY: L-tyrosine; BBA + H: Physical mixture of BBA + L-histidine; BBA + P: Physical mixture of BBA + D-phenylalanine; BBA + T: Physical mixture of BBA + L-tryptophan; BBA + TY: Physical mixture of BBA + L-tyrosine.

Figure 6 MPO activity. Average of six readings is presented; One-way ANOVA followed by Dunnett’s multiple comparison test, and statistical significance was considered at ^aP < 0.05, ^bP < 0.01, ^eP < 0.001 vs disease control. HC: Healthy control; DC: Disease control; BBA: β-boswellic acid; SLZ: Sulfasalazine; BH: Prodrug of BBA with L-histidine; BP: Prodrug of BBA with D-phenylalanine; BT: Prodrug of BBA with L-tryptophan; BTY: Prodrug of BBA with L-tyrosine; H: L-histidine; P: D-phenylalanine; T: L-tryptophan; TY: L-tyrosine; BBA + H: Physical mixture of BBA + L-histidine; BBA + P: Physical mixture of BBA + D-phenylalanine; BBA + T: Physical mixture of BBA + L-tryptophan; BBA + TY: Physical mixture of BBA + L-tyrosine.

Figure 7 Histology of colon of rats subjected to 2,4,6-trinitrobenzene sulfonic acid. HC: Healthy control showing intact colonic cyto-architecture; DC: Disease control showing mucosal injury characterized by absence of epithelium, architectural distortion and a massive mucosal/submucosal infiltration of inflammatory cells; BBA: β-boswellic acid showing slight mucosal abscess and moderate protection against 2,4,6-trinitrobenzene sulfonic acid (TNBS); SLZ: Sulfasalazine showing corrected cyto-architecture of colon; BH: Prodrug of BBA with L-histidine; BP: Prodrug of BBA with D-phenylalanine; BT: Prodrug of BBA with L-tryptophan; BTY: Prodrug of BBA with L-tyrosine showing corrected morphology of colon; H: L-histidine; P: D-phenylalanine; T: L-tryptophan; TY: L-tyrosine; TY: Showing significant loss of epithelium without mucosal injury providing mild protection against TNBS; BBA + H: Physical mixture of BBA + L-histidine; BBA + P: Physical mixture of BBA + D-phenylalanine; BBA + T: Physical mixture of BBA + L-tryptophan; BBA + TY: Physical mixture of BBA + L-tyrosine showing some loss of epithelial layer while other layers seem reconstructed, indicating moderate protection of cyto-architecture.

Figure 8 Histology of liver of rats subjected to 2,4,6-trinitrobenzene sulfonic acid. All groups showing normal liver architecture with no significant pathological changes nor adverse effects on liver. HC: Healthy control; DC: Disease control; BBA: β-boswellic acid; SLZ: Sulfasalazine; BH: Prodrug of BBA with L-histidine; BP: Prodrug of BBA with D-phenylalanine; BT: Prodrug of BBA with L-tryptophan; BTY: Prodrug of BBA with L-tyrosine; H: L-histidine; P: D-phenylalanine; T: L-tryptophan; TY: L-tyrosine; BBA + H: Physical mixture of BBA + L-histidine; BBA + P: Physical mixture of BBA + D-phenylalanine; BBA + T: Physical mixture of BBA + L-tryptophan; BBA + TY: Physical mixture of BBA + L-tyrosine.

Figure 9 Histology of pancreas of rats subjected to 2,4,6-trinitrobenzene sulfonic acid. All groups showing normal pancreas architecture without any evidence of pancreatitis. HC: Healthy control; DC: Disease control; BBA: β-boswellic acid; SLZ: Sulfasalazine; BH: Prodrug of BBA with L-histidine; BP: Prodrug of BBA with D-phenylalanine; BT: Prodrug of BBA with L-tryptophan; BTY: Prodrug of BBA with L-tyrosine; H: L-histidine; P: D-phenylalanine; T: L-tryptophan; TY: L-tyrosine; BBA + H: Physical mixture of BBA + L-histidine; BBA + P: Physical mixture of BBA + D-phenylalanine; BBA + T: Physical mixture of BBA + L-tryptophan; BBA + TY: Physical mixture of BBA + L-tyrosine.