Conjugation of Amisulpride, an Anti-Psychotic Agent, with 5-Aminosalicylic Acid via an Azo Bond Yields an Orally Active Mutual Prodrug against Rat Colitis

Abstract

Amisulpride (ASP), an anti-psychotic agent, is a pharmacologically equivalent to sulpiride (SP). Because SP demonstrates anti-ulcer and anti-colitic activities, ASP with an aniline moiety was azo-coupled to salicylic acid to generate 5-(aminoethanoylsulfamoyl)-N-[(1-ethylpyrrolidin-2-yl)methyl]-2-methoxybenzamide (ASP-azo-ASA), with the expectation that it would act as a colon-specific mutual prodrug against colitis. Following a 24 h incubation, approximately 80% of ASP-azo-ASA was cleaved to form ASP and 5-aminosalicylic acid (5-ASA) in the cecal contents, whereas it remained stable in the small intestinal contents. Oral gavage of ASP-azo-ASA (oral ASP-azo-ASA) delivered 5-ASA to the cecum to levels comparable with those observed for sulfasalazine (SSZ; clinical colon-specific prodrug of 5-ASA) and without detectable concentrations of ASP in the blood, indicating efficient colonic delivery. Oral ASP-azo-ASA ameliorated 2, 4-dinitrobenzenesulfonic acid hydrate (DNBS)-induced colitis in rats more effectively than oral SSZ. Additionally, oral ASP-azo-ASA lowered the levels of inflammatory mediators in the inflamed distal colon more effectively than oral SSZ. Combined treatment with 5-ASA and ASP via the rectal route more effectively reversed colonic damage and inflammation than treatment with 5-ASA or ASP alone, confirming the mutual anti-colitic actions of 5-ASA and ASP. In conclusion, ASP-azo-ASA is an orally active mutual prodrug against rat colitis with limited systemic absorption of ASP.

Keywords: 5-Aminosalicylic acid; amisulpride; colon-specific drug delivery; inflammatory bowel disease; mutual prodru.

Figure 1

Synthesis of 5-(aminoethanoylsulfamoyl)-N-[(1-ethylpyrrolidin-2-yl)methyl]-2-methoxybenzamide (ASP-azo-ASA). ASP: Amisulpride, 5-ASA: 5-aminosalicylic acid.

Figure 2

ASP-azo-ASA is a colon-specific prodrug activated to form ASP and 5-ASA. (A) Activation of ASP-azo-ASA by microbial azoreductase in large intestine. (B) ASP-azo-ASA (1 mM) or sulfasalazine (SSZ, 1 mM) was incubated in cecal contents and a mixture of small intestinal contents was suspended in pH 6.8 isotonic phosphate buffer (10%). At appropriate time intervals, the levels of 5-ASA in the samples were determined by high-performance liquid chromatography (HPLC). Data represent the percentage of 5-ASA released from ASP-azo-ASA or SSZ. (C) Male Sprague-Dawley rats (250–260 g) were starved for 24 h and allowed access to water. SSZ (30 mg/kg) or ASP-azo-ASA (39 mg/kg, equimolar to 30 mg of SSZ) suspended in PBS (1.0 mL) was administered to rats by oral gavage. The rats were sacrificed, and a midline incision was made to obtain the cecal contents. Drugs in the cecal contents were analyzed by HPLC. (D) ASP (28 mg/kg, equimolar to 39 mg of ASP-azo-ASA) or ASP-azo-ASA (39 mg/kg) suspended in PBS (1.0 mL) was administered orally to rats and blood was collected at predetermined intervals from the tail vein. Blood ASP levels were analyzed by HPLC. ND: Not detectable. The data in (B), (C) and (D) represent the mean ± standard deviation (n = 5).

Figure 3

ASP-azo-ASA is more effective than SSZ at ameliorating rat colitis. Three days after the induction of colitis by 2, 4-dinitrobenzenesulfonic acid hydrate (DNBS), ASP-azo-ASA (39 mg/kg), or SSZ (30 mg/kg) suspended in PBS (1.0 mL) was administered to rats by oral gavage once per day and the rats were sacrificed after 7 days of treatment. (A) Colonic damage score (CDS) was determined. *: α < 0.05 vs. the TNBS control (B). Myeloperoxidase (MPO) activity was measured using the inflamed distal colon (4 cm). The levels of the inflammatory mediators iNOS, COX-2 (C), and CINC-3 (D), were assessed in the inflamed colon. *P < 0.05 vs. control, NM: Not measurable. The data in (A), (B), and (D) represent the mean ± standard deviation (n = 5). * P < 0.05 vs. control, # P < 0.05.

Figure 4

Combined intracolonic treatment with 5-ASA and ASP alleviates rat colitis in an additive manner. Three days after the induction of colitis by DNBS, 5-ASA (30 mM) and/or ASP (30 mM) dissolved in PBS (0.5 mL) were/was administered rectally to rats once per day and the rats were sacrificed after 7 days of treatment. (A) CDSs were determined. *: α < 0.05 vs. the TNBS control (B). MPO activity was measured using the inflamed distal colon (4 cm). The levels of inflammatory mediators, iNOS, COX-2 (C), and CINC-3 (D), were assessed in the inflamed colon. * P < 0.05 vs. control. The data in (A), (B), and (D) represent the mean ± standard deviation (n = 5). * P < 0.05 vs. control, ^# P < 0.05.