Studies of binding by 2-imidazolines to human serum albumin and alpha1-acid glycoprotein by high-performance affinity chromatography

• Published in: Journal of pharmaceutical and biomedical analysis 2021-08, Vol.202, p.114135-114135, Article 114135
• Main Authors: Woolfork, Ashley G., Suh, Kyungah, Weigand, Miranda, Hage, David S.
• Format: Article
• Language: English
• Subjects: 2-Imidazolines; Affinity microcolumn; Alpha1-acid glycoprotein; Drug-protein binding; High-performance affinity chromatography; Human serum albumin
• ISSN: 0731-7085; 1873-264X
• DOI: 10.1016/j.jpba.2021.114135

•Affinity HPLC was used to study binding to serum transport proteins by various common 2-imidazoline drugs.•Microcolumns were used that contained the proteins human serum albumin (HSA) or alpha1-acid glycoprotein (AGP).•HSA had weak-to-moderate strength binding for the group of tested imidazolines.•AGP had stronger binding than HSA for these compounds and was stereoselective for lofexidine and its metabolite LADP.•The methods and tools in this work can be extended to binding studies for other 2-imidazolines and drugs with HSA or AGP. 2-Imidazoline drugs are used in a variety of applications, such as the treatment of hypertension and opioid withdrawal. It is known these drugs bind to serum proteins and have significant variations within this class of compounds in the overall level of this binding. However, little specific information is available on the interactions of these compounds with the two major transport proteins for many drugs, human serum albumin (HSA) and alpha1-acid glycoprotein (AGP). This study examined binding by 2-imidazolines to these proteins by using 25 mm × 2.1 mm i.d. high-performance affinity microcolumns that contained HSA or AGP. The drugs that were examined were antazoline, clonidine, dexmedetomidine, lofexidine, moxonidine, phentolamine, and tizanidine, which represented a wide range of structures and pharmaceutical applications. The major metabolite of lofexidine, N-(2-aminoethyl)-2-(2,6-dichlorophenoxy) propenamide (LADP), was also examined. All these 2-imidazolines were found to have weak-to-moderate binding to HSA, with global affinities that ranged from 1.62 × 102 to 1.07 × 104 M−1 at pH 7.4 and 37 °C. These compounds had stronger binding with AGP, with global affinities constants ranging from 3.80 × 102 to 1.85 × 104 M−1. No stereoselectivity was observed by HSA for the enantiomers of dexmedetomidine, lofexidine, or LADP. However, AGP did show some stereoselectivity for lofexidine and LADP but not for dexmedetomidine. These results provide a better understanding of interactions of 2-imidazoline with HSA vs AGP in the circulation and of how this binding can change between drugs within this class of compounds.