Paracetamol metabolism in postoperative patients

Introduction: Despite being available for more than 50 years, there is still much to learn about paracetamol. Postoperative analgesic regimens that maintain good pain control while minimising exposure to opiates are beneficial and paracetamol has had a resurgence in this role since an IV formulation came to market. However there is evidence to suggest currently licensed doses are sub-therapeutic, especially when administered orally or rectally. Higher, unlicensed doses are now being advocated but, prior to this study, there was little evidence of their safety in surgical patients. When assessing drug safety in surgical patients a number of surgery and patient related factors influence results, and these must be considered. Methods: Major and intermediate surgical patients were recruited from two hospitals in Ireland. They were administered IV paracetamol at either 9g or 4g daily doses. In addition they received daily sub therapeutic doses of four other medicines to indicate the activity of their CYP450 enzymes that are involved in paracetamol metabolism. Urine and blood samples were collected to determine paracetamol pharmacokinetics, CYP450 activity, inflammatory cytokine concentration and for evidence of hepatotoxicity. Results: There were 33 patients that participated in the study. There was no evidence of clinically significant hepatotoxicity occurring in any patient during the study period, but there could have been changes following this time. Paracetamol disposition was shown to change, however half-life remained relatively constant. There were a number of changes to the way paracetamol was metabolised following surgery that maintained this rate of elimination. Conclusion: Doses of up to 9g per day given to major surgical patients for up to five days postoperatively produced no evidence of hepatotoxicity. Further research is warranted to determine the clinical utility of these higher doses

An examination of the impact of dietary lipids on behaviour and neurochemistry

The molecular and cellular basis of stress pathology remains an important research question in biological science. A better understanding of this may enable the development of novel approaches for the treatment of stress-related disorders. There is a considerable body of scientific evidence suggesting that dietary lipids, phospholipids and omega-3 polyunsaturated fatty acids (n-3 PUFAs), have therapeutic potential for certain psychiatric disorders. Thus, we proposed n-3 PUFAs as a novel strategy for the prevention or amelioration of stress-related disorders. We hypothesised that these compounds would improve behavioural and neurobiological responses and alter gut microbial composition. Furthermore, we proposed a new mechanism of action exerted by n-3 PUFAs using an in vitro model of stress. Lastly, we explored the protective effects of both phospholipids and n-3 PUFAs against neuroinflammation, which has been shown to contribute to the development of stress-related disorders. We provide further evidence that glucocorticoids, inflammation and early-life stress induce vulnerability to psychopathologies. Specifically, we have demonstrated that corticosterone (CORT) alters cortical neuron and astrocyte percentage composition, reduces brain-derived-neuronal factor (BDNF) expression, and induces glucocorticoid receptor (GR) down-regulation in mixed cortical cultures. Interestingly, we found that lipopolysaccharide (LPS) treatment resulted in an over-expression of pro-inflammatory cytokines in cortical astrocyte cultures. Moreover, we demonstrate that early-life stress induces changes to the monoaminergic and immune systems as well as altered neuroendocrine response to stressors later in life. In addition, we found that early-life stress alters the gut microbiota in adulthood. These data demonstrate that n-3 PUFAs can attenuate CORT-induced cellular changes, but not those caused by LPS, within the cerebral cortex. Similarly, phospholipids were unable to reverse LPS-induced inflammation in cultured astrocytes. In addition, this thesis proposes that n-3 PUFAs may prevent the development or lessen the symptoms of mental illnesses, ameliorating anxiety- and depressive-like symptoms as well as cognitive effects, particularly when administered during neurodevelopment. Such effects may be mediated by GR activation as well as by modification of the gut microbiota composition. Taken together, our findings suggest that n-3 PUFAs have therapeutic potential for stress-related disorders and we provide evidence for the mechanisms by which they may exert these effects. These findings contribute to an exciting and growing body of research suggesting that nutritional interventions may have an important role to play in the treatment of stress-related psychiatric conditions.

Investigating metabolomic biomarkers of hypoxic ischaemic encephalopathy

Background An early objective biomarker to predict the severity of hypoxic-ischaemic encephalopathy (HIE) and identify infants suitable for intervention remains elusive. This thesis aims to progress metabolomic markers of HIE through a pipeline of biomarker discovery and validation by employing a novel untargeted mass spectrometry metabolomic method. Methodology Term infants with perinatal asphyxia were recruited, all having umbilical cord blood (UCB) drawn and biobanked within three hours of birth. HIE was defined by Sarnat score at 24hours and continuous multichannel-EEG. Infant neurodevelopment was assessed at 36-42 months using the Bayley Scales of Infant and Toddler Development Ed. III (BSID-III). Untargeted metabolomic analysis of UCB was performed using direct injection FT-ICR mass spectrometry (DI FT-ICR MS). Putative metabolite annotations and lipid classes were assigned and pathway analysis was performed. Results Untargeted metabolomic analysis: Thirty enrolled infants were diagnosed with HIE, including 17 mild, 8 moderate, and 5 severe cases. Pathway analysis revealed that ΔHIE was associated with a 50% and 75% perturbation of tryptophan and pyrimidine metabolism respectively, alongside alterations in amino acid pathways. Significant metabolite alterations were detected from six putatively identified lipid classes including fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterol lipids and prenol lipids. Outcome prediction: Metabolite model scores significantly correlated with outcome R=0.429 (model A) and R=0.549 (model B) respectively. Model B demonstrates the potential to predict both severe outcome (AUROC of 0.915) and intact survival (AUROC of 0.800). The effect of haemolysis: On average 5% of polar and 1.5% of non-polar features were altered between paired haemolysed and clean samples. However unsupervised multivariate analysis concluded that the preanalytical variability introduced by haemolysis was negligible compared with the inherent biological inter-individual variability. Conclusion This research has employed untargeted metabolomics to identify potential early cord blood biomarkers of HIE and has performed the technical validation of previously proposed markers.