Dalton Transactions PAPER Cite this: Dalton Trans., 2013, 42, 6161 Received 3rd October 2012, Accepted 16th November 2012 DOI: 10.1039/c2dt32252h www.rsc.org/dalton Complex formation equilibria of Cu II and Zn II with triethylenetetramine and its mono- and di-acetyl metabolites† Valeria M. Nurchi,* a Guido Crisponi, a Miriam Crespo-Alonso, a Joanna I. Lachowicz, a Zbigniew Szewczuk b and Garth J. S. Cooper c,d Triethylenetetramine (TETA) dihydrochloride, or trientine, is a therapeutic molecule that has long been used as a copper-chelating agent for the second-line treatment of patients with Wilson’s disease. More recently, it has also been employed as an experimental therapeutic molecule in diabetes where it improves cardiac structure in patients with diabetic cardiomyopathy and left-ventricular hypertrophy. TETA is metabolized by acetylation, which leads to the formation of two main metabolites in humans and other mammals, monoacetyl-TETA (MAT) and diacetyl-TETA (DAT). These metabolites have been identified in the plasma and urine of healthy and diabetic subjects treated with TETA, and could them- selves play a role in TETA-mediated copper chelation and restoration of physiological copper regulation in diabetes. In this regard, a potentiometric and spectrophotometric study of Cu II -complex formation equilibria of TETA, MATand DAT is presented here, to provide a comprehensive evaluation of the stoichio- metries of the complexes formed and of their relative stability constants. A potentiometric study has also been conducted on the corresponding Zn II complexes, to evaluate any possible interference with TETA- mediated Cu II binding by this second physiological transition-metal ion, which is present in similar con- centrations in human plasma and which also binds to TETA. An ESI-MS study of these systems has both confirmed the complex formation mechanisms established from the potentiometric and spectrophoto- metric results, and in addition provided direct information on the stoichiometryof the complexes formed in solution. These data when taken together show that the 1 :1 complexes formed with Cu II and Zn II have different degrees of protonation. The stability of the Cu II and Zn II complexes with the three ligands, evaluated by the parameters pCu and pZn, decreases with the introduction of the acetyl groups. Never- theless the stability of Cu II complexes with MAT is sufficiently high to enable its participation in copper scavenging from the patient. A speciation study of the behavior of TETA and MATwith Cu II in the pres- ence of Zn II at peri-physiological plasma concentrations is also presented. While Zn II did not hinder copper binding, the possibility is raised that prolonged TETA treatment could possibly alter the homeo- static regulation of this essential metal ion. The lack of reliable literature stability constants concerning the Cu II and Zn II interaction with the major transport proteins in plasma is also briefly considered. Introduction Triethylenetetramine (TETA) dihydrochloride is a therapeutic molecule mainly used in the treatment of Wilson’s disease, a human disorder characterized by copper accumulation in certain organs including the liver, brain and eye. 1,2 In 1985 the U.S. Food and Drug Administration approved TETA as an orphan drug for treatment of penicillamine-intoler- ant patients with Wilson’s disease. In 1993 Kodama et al. found a TETA metabolite in the urine when TETA was orally administered to healthy volunteers. 3 The same authors successfully identified this metabolite as N 1 -acetyltriethylenetetramine (MAT). 4 † Electronic supplementary information (ESI) available. See DOI: 10.1039/c2dt32252h a Dipartimento di Scienze Chimiche e Geologiche, Cittadella Universitaria, 09042 Monserrato-Cagliari, Italy. E-mail: nurchi@unica.it; Fax: +39 070 6754478; Tel: +39 070 6754478 b Faculty of Chemistry, University of Wroclaw, F. Joliot Curie 14, 50-383 Wroclaw, Poland c Central Manchester NHS Hospitals Foundation Trust, and School of Biomedicine, The University of Manchester, and Manchester Academic Health Sciences Centre, Manchester, UK d School of Biological Sciences and Maurice Wilkins Centre for Molecular Biodiscovery, Faculty of Science, University of Auckland, Auckland 1010, New Zealand This journal is © The Royal Society of Chemistry 2013 Dalton Trans., 2013, 42, 6161–6170 | 6161 Downloaded by UNIV DEGLI STUDI DI CAGLIARI on 16/04/2013 14:01:45. Published on 19 November 2012 on http://pubs.rsc.org | doi:10.1039/C2DT32252H View Article Online View Journal | View Issue