Diabetic cardiomyopathy is one of the causes of mortality and morbidity associated with diabetes. Diabetes is a disorder characterised by chronic hyperglycaemia and cardiovascular complications. The relationship between these integrally linked conditions has long been recognised, and for a significant portion of individuals the two conditions co-exist as part of metabolic syndrome. The presence of diabetes increases the risk of heart failure up to fivefold and three-fold in women and men, respectively, when compared to individuals without diabetes. While there has been a significant declining trend in cardiovascular mortality and morbidity in the general population over the past two decades, unfortunately such trends have not been seen among diabetic patients. As a result, this has persuaded many health professionals to re-evaluate their current treatment and pharmacological regimens. It is a well established fact that oxidative stress is a contributory mechanism in many agerelated disorders including T2DM, especially in those with poor glycaemic control. Thus far, clinical trials with antioxidant or carbonyl-trapping agents have produced mixed results, suggesting that the mechanisms underlying this disorder may be more complex than previously thought. Although altered systemic regulation of trace metals in diabetes has been previously investigated, it is still unclear whether changed trace metal metabolism would cause heart disease in common forms of diabetes and whether metal chelation can reverse this condition. Our hypothesis is that the accumulation of redox-active trace metals including Cu and Fe in cardiac muscle may, at least in part, result in cardiomyopathy through the generation of excess reactive oxygen species. We believed that the administration of a specific metal chelator should ameliorate this process by increasing the excretion of free systemic Cu and Fe, consequently limiting the production of superoxide oxygen free radicals and arresting the process of diabetic cardiomyopathy. Data from pre-clinical studies conducted in our laboratory using diabetic animal model with diabetes-induced abnormal Cu metabolism have been remarkably consistent in demonstrating that oral dosing with triethylenetetramine (TETA) can effectively remove systemic Cu via increased urinary Cu excretion, improve cardiomyocyte structure, reverse elevations in left ventricular collagen and β1-integrin, and alleviate heart failure, all in the presence of a consistently high circulating blood glucose profile. Taken together, these findings support the beneficial role of TETA in diabetic animal model and lay the foundation for its potential therapeutic effect in humans with diabetes. This thesis describes a series of randomised, placebo-controlled clinical trials that have investigated the metabolism of Cu and Fe and seven other trace metals in patients with chronic T2DM compared with non-diabetic control subjects. This thesis also examines the mechanism of action of TETA and addresses the hypothesis that a decrease in body systemic Cu pool through chelation therapy may improve cardiac complication in diabetic subjects. Trial 1 is a randomised, double-blind, placebo- and diet-controlled study which measured the 6d balance of Cu and Fe and seven other essential trace metals, in twenty male T2DM and twenty age-matched control subjects in whom we later probed systemic metal balance with oral TETA. Basal urinary output and balance of Cu and Fe was significantly elevated in diabetes, and the two output values correlated strongly (p<0.05). 6d treatment with 2400mg/d dose of TETA (maximum Wilson’s disease dose) has increased the urinary excretion of Cu, which was predicted by basal urinary Cu excretion, thereby causing a positive Cu balance to become negative in diabetes. Regulation of Cu metabolism was shown to be abnormal in diabetes and was selectively modified by TETA, which did not concomitantly modify Fe metabolism. Moreover, TETA did not cause a negative balance in any of the other seven trace metals monitored. These findings are consistent with TETA reversing the accumulation of free systemic Cu in diabetes, which may help to explain its potential therapeutic effects in some diabetic complications. Trial 2 investigated the acute response effect of a single 2400mg dose of TETA on urinary and serum trace metals in the first 10hr and 10~24hr post-dose. The results showed that TETA markedly increased the urinary Cu and Zn excretion in diabetes for the duration of 10hrs with the maximum excretion phase between 4~6hr post-drug (p<0.05). TETA did not change the metabolism of Mg and six other essential trace metals monitored. Trial 3 examined the dose-response effect of TETA, at and below the dose given to patients with the Wilson’s disease over a 7d period, on Cu and eight other trace metals in a subgroup of seven T2DM and seven control subjects who had completed trial 1. The results of this i i trial showed that there was a linear dose-response relationship over the dose range 300~2400 mg/d on urinary Cu excretion in both T2DM and control subjects. However, there was no significant difference between the two subject groups at any of the four doses tested. In addition, 300mg/d of TETA was effective in mobilizing Cu in both T2DM and healthy control subjects. Trial 4 described the full work-up of a sensitive LC-MS methodology to identify and quantify TETA and its metabolite(s) in human urine. Using the LC-MS, TETA metabolism and excretion was investigated by analysing the urine of seven T2DM and seven control subjects who received escalating doses of TETA (samples obtained from trial 3). I have successfully identified and characterised two major metabolites of TETA in the urine of both T2DM and control subjects, N1-monoacetytriethylenetetramine (MAT) and diacetytriethylenetetramine (DAT), the latter which has not been previously reported. The results from urinary TETA excretion analyses also showed that T2DM may metabolise TETA more extensively than control subjects, which in turn is associated with its higher uptake or bioavailability. Urinary Zn excretion was mainly linked with urinary TETA and MAT in T2DM and healthy controls, respectively, whereas urinary Cu excretion was associated with urinary TETA excretion in healthy controls and urinary TETA+MAT excretion in T2DM subjects. These results suggest that MAT may also be involved in the mechanism by which TETA extracts systemic free Cu in diabetes. The identification of the two major metabolites of TETA and the development of a robust analytical LC-MS methodology reported in this study is an important step to further investigate the pharmacological actions of TETA in diabetic individuals. Collectively, the results presented in this thesis and in association with previous animal and clinical studies from our laboratory have provided consistent supporting evidences for the use of TETA clinically as a safe and effective therapy to prevent the genesis of some diabetic complications, in conjunction with conventional complication modifying therapies.
| Identifer | oai:union.ndltd.org:ADTP/275229 |
| Date | January 2008 |
| Creators | Chan, Yih-Kai |
| Publisher | ResearchSpace@Auckland |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated., http://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm, Copyright: The author |
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