Search

The topology of metabolic networks is recognisably modular with modules weakly connected apart from sharing a pool of currency metabolites. Here, we defined modules as sets of reversible reactions isolated from the rest of metabolism by irreversible reactions except for the exchange of currency metabolites. Our approach identifies topologically independent modules under specific conditions associated with different metabolic functions. As case studies, the E.coli iJO1366 and Human Recon 2.2 genome-scale metabolic models were split in 103 and 321 modules respectively, displaying significant correlation patterns in expression data. Finally, we addressed a fundamental question about the metabolic flexibility conferred by reversible reactions: “Of all Directed Topologies (DTs) defined by fixing directions to all reversible reactions, how many are capable of carrying flux through all reactions?”. Enumeration of the DTs for iJO1366 model was performed using an efficient depth-first search algorithm, rejecting infeasible DTs based on mass-imbalanced and loopy flux patterns. We found the direction of 79% of reversible reactions must be defined before all directions in the network can be fixed, granting a high degree of flexibility.

A hallmark of cancer cells is their ability to reprogram nutrient metabolism. Thus, disruption to this phenotype is a potential avenue for anti-cancer therapy. Herein we used a phenotypic chemical library screening approach to identify molecules that disrupted nutrient metabolism (by increasing cellular oxygen consumption rate) and were toxic to cancer cells. From this screen we discovered a 1,4-Naphthoquinone (referred to as BH10) that is toxic to a broad range of cancer cell types. BH10 has improved cancer-selective toxicity compared to doxorubicin, 17-AAG, vitamin K3, and other known anti-cancer quinones. BH10 increases glucose oxidation via both mitochondrial and pentose phosphate pathways, decreases glycolysis, lowers GSH:GSSG and NAPDH/NAPD(+) ratios exclusively in cancer cells, and induces necrosis. BH10 targets mitochondrial redox defence as evidenced by increased mitochondrial peroxiredoxin 3 oxidation and decreased mitochondrial aconitase activity, without changes in markers of cytosolic or nuclear damage. Over-expression of mitochondria-targeted catalase protects cells from BH10-mediated toxicity, while the thioredoxin reductase inhibitor auranofin synergistically enhances BH10-induced peroxiredoxin 3 oxidation and cytotoxicity. Overall, BH10 represents a 1,4-Naphthoquinone with an improved cancer-selective cytotoxicity profile via its mitochondrial specificity.

Nicotinamide adenine dinucleotide (NAD+) is an important cofactor and substrate for hundreds of cellular processes involved in redox homeostasis, DNA damage repair and the stress response. NAD+ declines with biological ageing and in age-related diseases such as diabetes and strategies to restore intracellular NAD+ levels are emerging as a promising strategy to protect against metabolic dysfunction, treat age-related conditions and promote healthspan and longevity. One of the most effective ways to increase NAD+ is through pharmacological supplementation with NAD+ precursors such as nicotinamide mononucleotide (NMN) which can be orally delivered. Long term administration of NMN in mice mitigates age-related physiological decline and alleviates the pathophysiologies associated with a high fat diet- and age-induced diabetes. Despite such efforts, there are certain aspects of NMN metabolism that are poorly understood. In this thesis, the mechanisms involved in the utilisation and transport of orally administered NMN were investigated using strategically labelled isotopes of NMN and mass spectrometry. A mass spectrometry method was developed to trace the incorporation of labelled NMN moieties in NAD+ metabolites following supplementation with labelled NMN compounds. This was validated in biologically relevant models such as mammalian cell lines (Chapter 3) and bacteria (Chapter 4), the latter serving as a proof-of-concept model to investigate NMN metabolism through bacterial routes before investigating its metabolic fate in vivo (Chapter 5). Following oral administration with labelled NMN compounds in mice, labelled NAD+ metabolites were detected in abundance in the peripheral tissues of mice treated with antibiotics but were largely absent in control mice. This suggests the majority of orally administered NMN is consumed by gut bacteria, limiting its availability to host peripheral tissues and insinuates host-microbe competition for NAD+ precursors. Interestingly, an ab

A hallmark of cancer cells is their ability to reprogram nutrient metabolism. Thus, disruption to this phenotype is a potential avenue for anti-cancer therapy. Herein we used a phenotypic chemical library screening approach to identify molecules that disrupted nutrient metabolism (by increasing cellular oxygen consumption rate) and were toxic to cancer cells. From this screen we discovered a 1,4-Naphthoquinone (referred to as BH10) that is toxic to a broad range of cancer cell types. BH10 has improved cancer-selective toxicity compared to doxorubicin, 17-AAG, vitamin K3, and other known anti-cancer quinones. BH10 increases glucose oxidation via both mitochondrial and pentose phosphate pathways, decreases glycolysis, lowers GSH:GSSG and NAPDH/NAPD(+) ratios exclusively in cancer cells, and induces necrosis. BH10 targets mitochondrial redox defence as evidenced by increased mitochondrial peroxiredoxin 3 oxidation and decreased mitochondrial aconitase activity, without changes in markers of cytosolic or nuclear damage. Over-expression of mitochondria-targeted catalase protects cells from BH10-mediated toxicity, while the thioredoxin reductase inhibitor auranofin synergistically enhances BH10-induced peroxiredoxin 3 oxidation and cytotoxicity. Overall, BH10 represents a 1,4-Naphthoquinone with an improved cancer-selective cytotoxicity profile via its mitochondrial specificity.