Title:
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Liquid chromatography and mass spectrometry based metabolomic investigations of sulphur containing metabolites in human prostate cancer
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Low molecular weight thiols constitute a biologically important class of metabolites,
some of which play a principal role in cellular defence against oxidative stress. The
aetiology of cancer is generally linked with DNA mutation; often as a result of
oxidative damage when antioxidant defences are dysregulated. Accordingly, the
investigation of redox metabolites within cancer models is relevant to better
understand the initiation and development of the disease. Specifically, when
detected at an early stage, prostate cancer treatment by androgen ablation often
carries a high rate of success. After a period of 18-24 months however, the disease
is characterised by a shift to androgen insensitivity, and mortality increases
significantly in advanced states. Hence, early detection and improved understanding
of the changes in metabolism which accommodate a shift to androgen insensitivity
and increased rate of proliferation are also relevant.
Metabolomic profiling is a rapidly expanding field of systems biology which combines
sensitive, high resolution equipment with powerful chemometric data processing to
determine alterations in metabolic pathways in response to stress factors, including
internal and external stimuli; thus providing valuable insight into the mechanisms
involved in disease development. Whilst this approach has been applied to cancer
research in the past to discover new drug targets and putative biomarkers for early
detection, the complex metabolic pathways involved in cancer progression are not
fully understood. Moreover, recently reported dysregulation of redox status and
glutathione content in prostate cell models suggested significantly altered
metabolism in some cancers. In order to better understand the metabolic events
occurring, the aim of this study was to detect, and quantify where possible the
sulphur-containing metabolites in prostate cancer cell models.
Targeted metabolomic based methods using derivatisation with a specific reagent
(DTNB) were developed and validated to provide comprehensive quantitative
measurements of reduced thiols in cell models representing androgen sensitive
(LNCaP) and androgen insensitive (DU145) disease, in addition to control cells
representing healthy prostate epithelium (PZ-HPV-7). Furthermore, metabolomic
profiling was performed using these cell lines to identify up and down regulation of
key sulphur containing metabolites including disulphides and thioethers.
Measurements of glutathione and the oxidised form indicated increased oxidative
stress in LNCaP cells, whilst DU145 exhibited signs of adaptation to oxidative stress
by up-regulation of glutathione biosynthesis. Investigation of the metastatic,
androgen insensitive cell line, LNCaP, revealed a significant disparity in total thiol
content and glutathione, suggesting the presence of additional thiol metabolites.
Methods were developed and refined to determine the presence of cysteine,
cysteinylglycine and an additional previously unidentified thiol species in LNCaP
cells. Quantitative HPLC methods were validated and used to determine the
concentration of individual thiol components in each cell line, successfully accounting
for the total thiol content for the first time. The control cell contained 0.5 (± 0.03) and
6.3 (± 0.14) femtomoles per cell of cysteine and glutathione respectively, DU145
cells contained 0.3 (± 0.1) and 32.3 (± 2.3) femtomoles per cell of cysteine and
glutathione respectively, and LNCaP cells contained 2.7 (± 0.05), and 8.3 (± 0.73)
femtomoles per cell of cysteine and glutathione respectively. LNCaP cells
additionally contained 0.8 (± 0.1) femtomoles per cell of cysteinylglycine.
Further investigations proved that the unknown thiol (compound x) was a molecule of
cysteine and glycerate linked by a peptide bond. Through examination of metabolite
databases and chemical literature it was determined that the molecule had not
previously been reported. Profiling of the cells highlighted this metabolite as a key component of the LNCaP metabolic fingerprint, in addition to other metabolites with roles in cell energy production.
The developed methods stand as potentially useful tools for the sensitive detection
and quantitation of thiols and for metabolomic investigations in various cell lines.
Detection of a new thiol, cysteinyl-glycerate, in LNCaP cells warrants further
investigations into the biological role of this metabolite and the potential as a putative biomarker.
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