Stability and degradation profiles of Spantide II in aqueous solutions

Abstract

Spantide II is an 11 amino acid peptide that has been shown to be a potential anti-inflammatory agent. The stability and degradation profiles of Spantide II in aqueous solutions were evaluated with the long-term objective of developing topical formulations of this compound for various skin disorders. The stability profile of Spantide II at various temperature and pH conditions was monitored by high performance liquid chromatography (HPLC) and the resulting degradation products were identified by liquid chromatography-mass spectroscopy (LC-MS). Forced degradation of Spantide II was performed at extreme acidic (pH <2.0) and alkaline (pH >10.0) conditions and by addition of hydrogen peroxide (oxidizing agent). The degradation pattern of Spantide II followed pseudo first-order kinetics. The shelf life ( T 90%) of Spantide II in aqueous ethanol (50%) was determined to be 230 days at 25 °C. Spantide II was susceptible to degradation at pH <2 and pH >5 and showed maximum stability at pH 3–5. The stability under various pH conditions indicates that Spantide II was most stable at pH 3.0 with a half-life of 95 days at 60 °C. Spantide II degradation was attributed to hydrolysis of peptide bonds [Pro 2-(pyridyl)Ala 3, (nicotinoyl)Lys 1-Pro 2, Pro 4-PheCl 2 5, Trp 7-Phe 8, Phe 8-Trp 9, Nle 11-NH 2), racemization of the peptide fragments that resulted from hydrolysis, cleavage and formation of (nicotinoyl)Lys 1-Pro 2 diketopiperazine. In the presence of an oxidizing agent, Pro 2,4 residues degraded by ring opening to form glutamyl-semialdehyde and by bond cleavage at Pro 4 to form 2-pyrrolidone, while Phe 5,8 degraded to form 2-hydroxyphenylalanine. Spantide II was found to be stable in aqueous medium with T 90% of 230 days. The major degradation pathways of Spantide II were identified as hydrolysis, racemization, cleavage and formation of diketopiperazine.