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Hydrogen sulfide (H2S), is a gasotransmitter with several key roles in metabolism and vascular function. The effects of H2S are dependent on concentration and target organ. For example, increased H2S concentrations impair liver metabolic function but protect against vascular dysfunction and atherosclerosis. Thiosulfate sulfurtransferase (TST), a nuclear encoded mitochondrial matrix enzyme, is proposed to be a component of the sulfide oxidising unit (SOU) which metabolises H2S. Preliminary data has shown that Tst deletion in mice (Tst-/-) increases circulating H2S levels measured in whole blood. Therefore, it was hypothesised that Tst-/- mice would exhibit worsened metabolic function in the liver but also protection of vascular function under conditions of vascular stress e.g. atherosclerosis. Liver metabolism was assessed by extensive metabolic phenotyping of Tst-/-mice fed control diet and in conditions of metabolic dysfunction induced by a high fat diet (HFD). Tst deletion altered glucose metabolism in mice; gluconeogenesis was increased in liver from Tst-/-mice fed control diet. Glucose intolerance in HFD-fed Tst-/-mice was also more severe than HFDfed C57BL/6 controls. In vitro metabolic investigations in primary hepatocytes isolated from Tst-/-mice demonstrated that mitochondrial ATP-linked and leak respiration were increased compared to controls. The effect of Tst deletion on vascular function was investigated in Tst- /-mice fed control or HFD using myography. Tst deletion did not alter vessel function when mice were maintained on a normal diet. HFD feeding (20 weeks) reduced maximal vessel constriction in the presence of endothelial nitric oxide synthase and cyclooxygenase inhibitors in C57BL/6 aorta. However, in Tst-/-mice fed HFD there was no reduction in maximal constriction suggesting a protective action of Tst deletion. The effects of Tst deletion on atherosclerotic lesions was investigated by generating double knock-out (DKO) mice by deletion of the Tst gene in ApoE-/- mice and (ApoE-/-Tst-/-). Atherosclerotic lesion formation was accelerated by feeding mice a western diet. Within the brachiocephalic branch lesion volume and total vessel volume were reduced in DKO mice fed western diet for 12 weeks, indicating that Tst deletion reduced lesion formation. Plasma cholesterol was reduced in DKO mice compared to ApoE-/- controls and a trend towards reduced systolic blood pressure was also noted. Overall this work supported the hypothesis that Tst deletion engenders metabolic dysfunction but vascular protection. The findings are consistent with the reported effects of increased H2S signalling. Overall inhibition of TST represents a novel target for treatment of atherosclerosis, with the caveat that glycaemia may be worsened due to hepatic metabolic dysfunction.

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) techniques offer the opportunity to understand the physiological processes involved in the distribution of the contrast agent in vivo. This work utilises a liver specific contrast agent (gadoxetate) and demonstrates the potential use of these techniques to study transporter-mediated process in vivo. In vitro experiments investigated gadoxetate’s interaction with uptake and efflux transporters at the cellular level, ideally a prerequisite to understand the contribution of transporter proteins in in vivo pharmacokinetics. MRI was used to measure the accumulation of gadoxetate in fresh rat hepatocytes. Furthermore, LC-MS/MS methodology was optimised in conjunction with two in vitro systems to determine the role of transporters in gadoxetate uptake and efflux. HEK-OATP1B1 transfected cells were used to optimise the LC-MS/MS technique and Caco-2 cell monolayers were used to examine whether gadoxetate is a substrate of the efflux transporters, Pgp and BCRP. Subsequent studies demonstrated the use of DCE-MRI techniques to study transporter-mediated processes. Two pharmacokinetic models were proposed to quantify the uptake and efflux of gadoxetate in vivo. The suitability of the models in describing the liver concentration profiles of gadoxetate was assessed in pre-clinical and clinical reproducibility studies. Further pre-clinical experiments demonstrated the ability of the proposed DCE-MRI techniques to monitor changes in the uptake and efflux rate estimates of gadoxetate into hepatocytes, through co-administration of the transporter inhibitor, rifampicin, at two doses. The work presented demonstrates the potential use of DCE-MRI techniques as a diagnostic probe to assess transporter-mediated processes and drug-drug interactions (DDIs) in vivo.

A raised plasma fibrinogen is strongly associated with an increased risk of cardiovascular disease. 'Programming' in early life may influence cardiovascular disease in adult life. Poor growth in infancy has been linked to high plasma fibrinogen levels in adult life. This work hypothesises that reduced fetal growth is associated with high neonatal fibrinogen concentration. A cross-sectional study of neonates over a two-year period was undertaken in the Isle of Man. The subjects were primigravida mothers and their 4 day old babies. Measurements were taken of neonatal body size and plasma fibrinogen concentrations and maternal height. Data from maternal questionnaires and hospital records were collected. The main outcome measure was plasma fibrinogen. The results showed that low birthweight was associated with low neonatal plasma fibrinogen concentrations. The relationship was the opposite of that between adult plasma fibrinogen concentrations and early growth. Neonatal fibrinogen concentrations were also associated with the acute phase reaction and the sex of the neonate. The relation of larger size at birth with higher neonatal fibrinogen concentrations may indicate improved liver function in heavier babies.

Simple Summary For 657 cases of segment or less repeat liver resection with results of plasma albumin and bilirubin levels and platelet counts before and 3 months after surgery, the indicators were compared before and after surgery. There were 268 open repeat after open and 224 cases laparoscopic repeat after laparoscopic liver resection. The background factors and liver functional indicators before and after surgery, and the changes were compared between both groups. Plasma levels of albumin (p = 0.006) and total bilirubin (p = 0.01) were decreased, and ALBI score (p = 0.001) indicated worse liver function after surgery. Though laparoscopic group had poorer performance status and liver function, changes of the values and overall survivals were similar between both groups. Plasma levels of albumin and bilirubin and ALBI score could be the liver functional indicators for liver functional deterioration after liver resection. The laparoscopic group with poorer conditions showed a similar deterioration of liver function and overall survival to the open group. Whether albumin and bilirubin levels, platelet counts, ALBI, and ALPlat scores could be useful for the assessment of permanent liver functional deterioration after repeat liver resection was examined, and the deterioration after laparoscopic procedure was evaluated. For 657 patients with liver resection of segment or less in whom results of plasma albumin and bilirubin levels and platelet counts before and 3 months after surgery could be retrieved, liver functional indicators were compared before and after surgery. There were 268 patients who underwent open repeat after previous open liver resection, and 224 patients who underwent laparoscopic repeat after laparoscopic liver resection. The background factors, liver functional indicators before and after surgery and their changes were compared between both groups. Plasma levels of albumin (p = 0.006) and total bilirubin (p = 0.01) were decreased, and ALBI score (p = 0.001) indicated worse liver function after surgery. Laparoscopic group had poorer preoperative performance status and liver function. Changes of liver functional values before and after surgery and overall survivals were similar between laparoscopic and open groups. Plasma levels of albumin and bilirubin and ALBI score could be the indicators for permanent liver functional deterioration after liver resection. Laparoscopic group with poorer conditions showed the similar deterioration of liver function and overall survivals to open group.

Liver function is a dominant factor in the survival of patients with hepatocellular carcinoma (HCC). Measures of regional and global liver function are critical in guiding treatments for intrahepatic cancers. Regional and global liver function assessments important for defining the magnitude and spatial distribution of radiation dose to preserve functional liver parenchyma and reduce incidence of hepatotoxicity from radiation therapy (RT) for intrahepatic cancer treatment. This individualized liver function-guided RT strategy is critical for patients with heterogeneous and poor liver function, often observed in cirrhotic patients treated for HCC. Dynamic gadoxetic-acid enhanced (DGAE) magnetic resonance imaging (MRI) allows investigation of liver function through observation of the uptake of contrast agent into the hepatocytes. This work seeks to determine if gadoxetic uptake rate can be used as a reliable measure of liver function, and to develop robust methods for uptake estimation with an interest in the therapeutic application of this knowledge in the case of intrahepatic cancers. Since voxel-by voxel fitting of the preexisting nonlinear dual-input two-compartment model is highly susceptible to over fitting, and highly dependent on data that is both temporally very well characterized and low in noise, this work proposes and validates a new model for quantifying the voxel-wise uptake rate of gadoxetic acid as a measure of regional liver function. A linearized single-input two-compartment (LSITC) model is a linearization of the pre-existing dual-input model but is designed to perform uptake quantification in a more robust, computationally simpler, and much faster manner. The method is validated against the preexisting dual-input model for both real and simulated data. Simulations are used to investigate the effects of noise as well as issues related to the sampling of the arterial peak in the characteristic input functions of DGAE MRI. Further validation explores the relationship between gadoxetic acid uptake rate and two well established global measures of liver function, namely: Indocyanine Green retention (ICGR) and Albumin-Bilirubin (ALBI) score. This work also establishes the relationships between these scores and imaging derived measures of whole liver function using uptake rate. Additionally, the same comparisons are performed for portal venous perfusion, a pharmacokinetic parameter that has been observed to correlate with function in patients with relatively good liver function, and has been used as a guide for individualized liver function-guided RT. For the patients assessed, gadoxetic acid uptake rate performs significantly better as a predictor of whole liver function than portal venous perfusion. This work also investigates the possible gains that could be introduced through use of gadoxetic uptake rate maps in the creation of function-guided RT plans. To this end, plans were created using both perfusion and uptake, and both were compared to plans that did not use functional guidance. While the plans were generally broadly similar, significant differences were observed in patients with severely compromised uptake that did not correspond with compromised perfusion. This dissertation also deals with the problem of quantifying uptake rate in suboptimal very temporally sparse or short DGAE MRI acquisitions. In addition to testing the limits of the LSITC model for these limited datasets (both realistic and extreme), a neural network-based approach to quantification of uptake rate is developed, allowing for increased robustness over current models.

Under conditions of high self-regulatory effort, peripheral organ systems have been found to slow, potentially to rearrange energetic priorities in favor of the brain. The present study tested an expansion of this model by exploring the possibility that alcohol metabolism (i.e., liver function) may slow during self-regulation. We also anticipated that high trait self-control would attenuate the effect of condition on metabolism. Twelve males aged 21-25 completed two conditions in counterbalanced order. During each session, the participant received 0.33 ml/kg of absolute alcohol for a target peak blood alcohol concentration (BAC) of 0.03 g%. Participants then performed tasks (self-regulatory tasks in the high self-regulation condition and identical tasks without a self-regulatory component in the low self-regulation condition) and BAC was measured throughout. Although there was no main effect of condition, trait self-regulation moderated the effect of condition on alcohol metabolism such that only those with lower trait self-control had slower alcohol metabolism under high self-regulatory effort. These results provide support for the hypothesis that liver function may indeed be altered by self-regulatory effort. In addition to suggesting the liver as a target organ for psychophysiological research, these data provide further support for slowing of peripheral systems during high self-regulatory demand.

Phenytoin is a relatively old anticonvulsant, but it has been commonly prescribed for more than half a century. The variability of phenytoin pharmacokinetic characteristics presents a challenge in therapeutic drug monitoring; hence, in the past twenty years its pharmacokinetic characteristics have been studied extensively. Up to now the studies were done with either healthy individuals or patients with normal liver functions. In this study a multifactorial scale of liver function, Pugh-Modified CTC (Child-Turcotte Criteria), has been incorporated to develop and evaluate a population pharmacokinetic model for phenytoin to be used in patients with liver dysfunction. Nonlinear Mixed Effects Model (NONMEM), a regression computer program, was utilized to develop the population pharmacokinetic model on the data of this study. The predictive performance of this model was evaluated by means of bootstrapping of the prediction error (PE) with the improved prediction-error (PE imp ) serving as an estimate of internal validity. The developed and validated final population pharmacokinetic model for phenytoin in patients with liver dysfunction is presented as follows: [special characters omitted] where Vmax is the maximum metabolic rate (mg/h); &thetas; 1 , the intercept for Vmax, is 7.41 mg/h; WT is the body weight (Kg); LS indicates one of three liver statuses: normal (CTC ≤ 6), mild dysfunction (CTC scores of 7–9), and moderate dysfunction (CTC scores of 10–12); Vd, the apparent volume of distribution (L), is 184 L; &thetas; WT is 0.126 and &thetas; LS is 2.14 for moderate liver-dysfunction. The maximum metabolic rate increased in patients with liver dysfunction, and there was weak statistical evidence that Vmax might increase in patients with chronic alcohol abuse. Based on the aforementioned longitudinal (population) pharmacokinetic model, a dosing method was also developed. By utilizing the dosing method, it may be possible to improve phenytoin dosage regimens, initial doses, and Bayesian estimates of pharmacokinetic parameters. Improved initial doses and more accurate estimates of pharmacokinetic parameters may lead to fewer required measured phenytoin concentrations and fewer dose changes. A decrease in the number of dose changes should result in less time expended in the writing and processing prescriptions and orders, and there may also be fewer wasted doses. Additionally, the improved initial doses should result in concentrations more frequently in the therapeutic window; thereby, resulting in less toxicity, greater efficacy, and improved patient compliance. All of these effects should decrease the cost of therapy in patients receiving phenytoin, a factor which is an important consideration in this age of cost containment and managed care.

In situ perfusion of the rat liver, using Ficoll-70 in an acellular perfusate, proved an adequate technique for metabolic studies on the liver. Fasting animals for 24 hours, caused a marked decrease in the rates of lipid synthesis from glucose and acetate in the liver, but the rate of oxidation to C0₂ from these substrates remained approximately the same. A decrease in activity in the lipogenic pathways has occurred on fasting. The greater importance of the synthesis of phospholipids over the synthesis of triglycerides was shown by the maintenance of phospholipid synthesis in the livers from fasted animals with a decrease in the rate of triglyceride synthesis.