CuII(atsm) as a potential therapeutic for neurodegenerative diseases

Abstract

Neurodegenerative disease is caused by a progressive deterioration of cells in the central nervous system. Commonly known neurodegenerative diseases include Alzheimer's disease (AD), Parkinson's disease (PD), frontotemporal lobar degeneration (FTLD), Huntington's disease (HD) and amyotrophic lateral sclerosis (ALS). These diseases are all fatal and do not have effective therapeutics. Through the use of various models of neurodegenerative disease, metallocomplexes of bis(thiosemicarbazones) have been identified with a strong therapeutic potential. Of these compounds, diacetylbis(N(4)-methylthiosemicarbazonato) copper(II) (CuII(atsm)) has demonstrated the best potential as a treatment for a broad range of neurodegenerative diseases. Treating with CuII(atsm) has thus far shown to attenuate disease symptoms in multiple mouse models of PD and a mouse model of ALS. This project therefore aimed to determine the broader therapeutic activity of CuII(atsm), by examining its therapeutic effects in additional mouse models of neurodegenerative disease.

Treatment with CuII(atsm) at a daily dose of 30mg per kg of body weight to the SOD1G37R mouse model of ALS, the TDP-43A315T mouse model of FTLD/ALS and the R6/1 mouse model of HD, showed CuII(atsm) was only able to improve the disease phenotype of the SOD1G37R mice. Treatment with CuII(atsm) improved the survival of the SOD1G37R mice by 16% and their locomotor deficit, however there was no phenotypic change of symptoms with CuII(atsm) treatment in the TDP-43A315T or R6/1 mice. Biochemically, treating with CuII(atsm) decreased markers of inflammation and/or oxidative damage in all of the mouse models analysed. Given that CuII(atsm) treatment only improved the phenotype of one of the animal models analysed, suggest the suppression of the inflammatory and oxidative damage pathways in isolation in these animal models of disease are insufficient for CuII(atsm) to mediate its therapeutic effects.

Although treatment with CuII(atsm) in the SOD1G37R mice attenuated disease symptoms and improved survival, the treatment also paradoxically increased levels of the ALS-causing mutant form of the copper/zinc containing superoxide dismutase 1 (SOD1). To investigate this paradox, mass spectrometry was utilised to analyse how increasing levels of the putative pathogenic mutant SOD1 could decrease disease symptoms in the SOD1G37R mice. For its normal function, SOD1 requires one copper and one zinc ion per subunit, but analysis of the ALS model mice spinal cord showed a majority of the SOD1 was copper-deficient. Treatment with CuII(atsm) increased the copper content of the mutant SOD1 and consequently, increased the fully-metallated, non-toxic and stable form of mutant SOD1. Thus, increasing the bioavailability of metals and improving the aberrant metallation states of pathogenic metalloproteins may be a part of the therapeutic activity of CuII(atsm).

Overall, outcomes from this thesis indicate treatment with CuII(atsm) suppresses markers of oxidative stress and/or inflammation in distinct animal models of ALS, FTLS/ALS and HD. However, the inability of CuII(atsm) to alter the phenotype of the TDP-43A315T and R6/1 mice suggest the alteration of these pathogenic pathways alone is insufficient for CuII(atsm) to have therapeutic efficacy. If the protective activity of CuII(atsm) observed in the SOD1G37R mice is related to the ability of the compound to improve the metal state of mutant SOD1, this may indicate the therapeutic potential for CuII(atsm) is best suited to diseases in which pathogenesis is related to disrupted metal homeostasis.