Detection, quantification, and investigation of the red blood cell partitioning of cryptolepine hydrochloride

Context: The fight against malaria is limited by the development of resistance of Plasmodium to medication. This has led to an urgent search for alternative medicinal agents. Aims: To determine the affinity of cryptolepine for the red blood cell. Methods: HPLC method for the identification and quantification of cryptolepine was developed. Lipid solubility for both quinine (control) and cryptolepine was determined. Partitioning and repartitioning of cryptolepine into RBCs were studied. Time, concentration, temperature and pH were varied to see their effect on the partitioning of cryptolepine. Plasma protein binding was determined by the red blood cell partitioning method. Results: An accurate, precise and robust HPLC method for cryptolepine hydrochloride was developed. Cryptolepine and quinine had lipophilicity of 0.91 ± 0.02 and 1.52 ± 0.27, respectively. The highest partitioning values of 2.02 ± 0.08 for cryptolepine and 0.93 ± 0.02 for quinine were obtained at 40 minutes. Concentration-dependent protein binding was observed for both compounds with cryptolepine having 0.43 and 0.38 for quinine. Partitioning was also found to be temperature dependent with the highest partitioning obtained at 370C for cryptolepine (1.56 ± 0.04) and quinine (0.78 ± 0.01). Partitioning of cryptolepine and quinine were inversely related to pH with R2 values of 0.94 and 0.96, respectively. P-values between partitioning and repartitioning for cryptolepine and quinine were 0.04 and 0.05, respectively. Conclusions: Partitioning was found to be time, temperature, concentration and pH dependent. Partitioning was irreversible for cryptolepine and reversible for quinine. Protein binding in both cases was moderate.