Modelling endocrine regulation of glycaemic control in animal models of diabetes

This thesis is concerned with mathematical modelling of the glucose-insulin homeostatic system, with the specific aim of mathematically modelling diabetes and diabetes-like conditions in animals. Existing models were examined and critiqued in this thesis. Additionally, structural identifiability analysis of the most widely-used model in the field, the Minimal Model, was performed using Taylor series and similarity transformation approaches. It was shown under certain assumptions that it was theoretically possible to obtain a unique set of parameters for the model from only measuring glucose. C-peptide deconvolution was performed using the WinNonLin algorithm and Maximum Entropy technique implemented in MATLAB. This was used to calculate insulin secretion, the percentage of insulin appearing in the periphery and insulin clearance rate. This was then further developed to model insulin appearance and clearance based on hepatic blood flow changes. A short-term model of the glucose-insulin and C-peptide system was initially formulated using a PID controller concept and later refined to reduce the number of model parameters. Structural identifiability analysis was performed using the Lie symmetries approach, followed by parameter estimation on rat and mice data from IVGTTs, OGTTs and hyperglycaemic clamps and sensitivity analysis. This short-term model was integrated into a long-term model to analyse Zucker and ZDF rat data to create a single model to cater for both short- and long-term dynamics. Finally, a software tool was developed to allow non-mathematical scientists to use and access the benefits of the model

Photonic Biosensors: Detection, Analysis and Medical Diagnostics

The role of nanotechnologies in personalized medicine is rising remarkably in the last decade because of the ability of these new sensing systems to diagnose diseases from early stages and the availability of continuous screenings to characterize the efficiency of drugs and therapies for each single patient. Recent technological advancements are allowing the development of biosensors in low-cost and user-friendly platforms, thereby overcoming the last obstacle for these systems, represented by limiting costs and low yield, until now. In this context, photonic biosensors represent one of the main emerging sensing modalities because of their ability to combine high sensitivity and selectivity together with real-time operation, integrability, and compatibility with microfluidics and electric circuitry for the readout, which is fundamental for the realization of lab-on-chip systems. This book, “Photonic Biosensors: Detection, Analysis and Medical Diagnostics”, has been published thanks to the contributions of the authors and collects research articles, the content of which is expected to assume an important role in the outbreak of biosensors in the biomedical field, considering the variety of the topics that it covers, from the improvement of sensors’ performance to new, emerging applications and strategies for on-chip integrability, aiming at providing a general overview for readers on the current advancements in the biosensing field

Stopping the progression towards type 2 diabetes mellitus : investigating the hypoglycaemic (glucose-lowering) potential of antioxidant-rich plant extracts : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Nutritional Science, Massey University, Albany, New Zealand

Chapter 4 was published under a Creative Commons Attribution 4.0 license (CC BY 4.0) as: Lim, W X J, Chepulis, L, von Hurst, P, Gammon, C S, & Page, R A. (2020). An acute, placebo-controlled, single-blind, crossover, dose-response, exploratory study to assess the effects of New Zealand pine bark extract (Enzogenol ®) on glycaemic responses in healthy participants. Nutrients,12(2):497. https://doi.org/10.3390/nu12020497Background: Prediabetes is a condition where the blood glucose levels are high but not high enough to be classified as having type 2 diabetes mellitus (T2DM). It is also considered a high risk for developing T2DM. There is increasing evidence that demonstrates antioxidant-rich plant extracts exhibiting hypoglycaemic effects in humans. Therefore the extracts may improve glycaemic control in individuals with prediabetes and help prevent or delay the progression of prediabetes towards T2DM. Overall Aim: To examine the acute hypoglycaemic potential of four antioxidant-rich plant extracts, namely the New Zealand pine bark, grape seed, rooibos tea and olive leaf extracts in humans. Methods/Design: The hypoglycaemic effects of the New Zealand pine bark was examined in healthy participants (n=25) in an acute, placebo-controlled, single-blind, crossover, dose-response (50 and 400 mg), exploratory study (Pine Bark study). Blood samples were collected via finger pricking using disposable lancet to measure glucose levels at -20, 0, 15, 30, 45, 60, 90 and 120 min during an oral glucose tolerance test (OGTT) with 75 g of glucose. The hypoglycaemic effects of grape seed, rooibos tea and olive leaf extracts matched for antioxidant capacity were examined in an acute, placebo-controlled, crossover study (GLARE study) in participants with prediabetes (n=19). Blood samples were collected via cannulating the antecubital fossa region of the arm at -10, 0, 15, 30, 45, 60, 90 and 120 min during the OGTT with 75 g of glucose. Outcome glycaemic measures were analysed in both clinical studies (Pine Bark study and GLARE study). An in vitro mechanistic study investigating the potential inhibitory action of all four plant extracts (grape seed, rooibos tea, olive leaf and New Zealand pine bark) on digestive enzyme α-amylase and the dipeptidyl peptidase-4 (DPP4) enzyme were carried out using appropriate enzymatic assays of inhibition. Results: Prior to secondary analysis in the Pine Bark study, a significant reduction in the primary outcome mean glucose incremental area under the curve (iAUC) was only observed for the 400 mg dose of pine bark (21.3% reduction, p=0.016) compared to control. After stratification in the monophasic glucose curve shape group (n=12), 50 and 400 mg of pine bark significantly reduced the mean glucose iAUC compared to control (28.1% reduction, p=0.034 and 29.5% reduction, p=0.012), respectively. In contrast, mean glucose iAUC was not significantly different in the complex glucose curve shape group (n=13). In the monophasic group, 400 mg dose further improved glycaemic indices by reducing mean percentage increment of postprandial glucose (%PG) (33.9% reduction, p=0.010), mean glucose peak (11.2% reduction, p=0.025), and mean 2h postprandial glucose (2hPG) (8.9% reduction, p=0.027) compared to control. Within the complex group, there were no other significant changes except for reductions in mean %PG after 50 mg and 400 mg dose (33.8% reduction, p=0.012 and 41.4% reduction, p=0.025) compared to control, respectively. There were no significant differences between treatments in both subgroups (p>0.05). In the GLARE study, there were no overall significant changes in glucose and insulin responses between the extracts and control, or amongst the plant extracts (p>0.05). After secondary analysis, the less healthy subgroup (n=9), grape seed consumption showed significant reduction in mean glucose iAUC (21.9% reduction, p=0.016), mean 2hPG (14.7% reduction, p=0.034) and mean 2h postprandial insulin (2hPI) (22.4% reduction, p=0.029), whilst there was significant improvement in mean overall insulin sensitivity (ISIoverall) (15.0% increase, p=0.028) and mean glucose metabolic clearance rate (MCR) (16.7% increase, p=0.016) compared to control. Rooibos tea extract was shown to improve β-cell function measured by the mean oral disposition index (DI) (32.4% increase, p=0.031) in the less healthy subgroup compared to control. This was coupled with a non-significant improvement in insulin sensitivity measured by mean insulin-secretion-sensitivity-index-2 (ISSI-2) (18.3% increase, p=0.074). Olive leaf exhibited improved mean insulin sensitivity indices of insulinogenic index (IGI₃₀) (27.8% increase, p=0.078), Stumvoll first phase insulin sensitivity (ISIfirst) (17.8% increase, p=0.075) and Stumvoll second phase insulin sensitivity (ISIsecond) (15.6% increase, p=0.062) in the less healthy subgroup compared to control, although significance was not reached. Olive leaf extract was also consistently shown to elevate insulin levels in the study, with a higher mean 2hPI in the healthier subgroup (49.5% increase, p=0.030) and an elevated mean insulin iAUC in the less healthy (16.7% increase, p=0.040) subgroups. There were no significant changes in glucose and insulin responses in the healthier subgroup (n=10) compared to control nor between treatments in both subgroups (p>0.05). The mechanistic study demonstrated that the New Zealand pine bark extract exhibited the greatest inhibitory effects against digestive enzyme α-amylase (IC₅₀ 3.98 ± 0.11 mg/mL) and DPP4 enzyme (IC₅₀ 2.51 ± 0.04 mg/mL) compared to the other extracts (p<0.001). Both grape seed and rooibos tea extracts showed good inhibition of both enzymes tested. Rooibos tea was able to inhibit DPP4 enzyme to a greater extent than grape seed (p=0.018). In contrast, olive leaf extract showed minimal inhibition on α-amylase and no inhibition action against DPP4 enzyme. Conclusions: All four plant extracts (New Zealand pine bark, grape seed, rooibos tea and olive leaf) have shown acute hypoglycaemic potential in the Pine Bark study and the GLARE study by improving various indices of glucose and insulin responses in humans. The inhibitory action of the New Zealand pine bark, grape seed and rooibos tea extracts on DPP4 enzyme might have contributed to the hypoglycaemic effects observed in the clinical studies conducted. Whereas for olive leaf extract other underlying mechanisms on glycaemia remain to be elucidated. Our acute studies have indicated the need to investigate the chronic impact of these plant extracts in longer-term studies. Future studies in the prediabetes cohort should also look to target different metabolic profiles of varying degrees of dysglycaemia, as this may provide more meaningful results

Physiological system modelling and clinical simulation for diagnosis

Chapter 0 Contains the thesis introduction thesis and concepts of NDIs, derivations and applications. It also summarizes the PNDIs that are derived in the subsequent chapters. Chapter 1 Introduces the concept of using Physiological Non-Dimensional Indexes (PNDI) for distinguishing or classifying patients who were diabetic from non-diabetic and those who are the risk of becoming diabetic. In the authors work, he has also demonstrated that those who were diabetic were actually at-risk and those who were normal were in fact at the rim of becoming diabetic. All the works were verified against with clinical data by parametric identification techniques. Chapter 2 Using the findings of the above chapter, the author conceptualized, and design and simulated a dynamic activity-based insulin infusion system. He has used the clinical data of diabetic patients in the above chapter for demonstrating the operations of the system. He has even demonstrated the stability of the system by having continual simulations till 4-hour. Chapter 3 In this chapter, the author has derived a series of system equations for identification of pulmonary diseases based in the inhale and exhale gas mixtures concentrations and volume space. Chapter 4 In this chapter, the author has derived a series of system equations for identification of diseased lungs based of the lungs’ pressurevolume graphs. He has even demonstrated the techniques of obtaining the Cardiac Output (CO) non-invasively. Chapter 5 The author has demonstrated how to obtain the relative urine outflow non-invasively for normal kidneys. Chapter 6 The author has described the significance and derivation background of PNDI

Exercise, glucose control and liver fat :providing the evidence for translation into clinical care

PhD ThesisNon-alcoholic fatty liver disease (NAFLD) has become the most common form of liver disease throughout much of the World. It affects between one in five and one in three adults in the general population. It is now believed to be the leading cause of liver cirrhosis and hepatocellular carcinoma. However, the majority of people with NAFLD do not go on to develop terminal liver disease but instead have an uncertain prognosis that can often include type 2 diabetes, cardiovascular disease, and/or non-hepatic cancers. Indeed, NAFLD is frequently accompanied impaired glucose control, and almost always suboptimal insulin sensitivity. This thesis explores the only currently recommended therapy – weight reduction by lifestyle modification. It reviews the published evidence supporting this recommendation by applying a systematic approach to review the literature, but examines the findings in the broader context of common NAFLD comorbidities and sequelae. It also examines interaction of age and physical activity with liver fat, specifically in women, using both primary and secondary research methods. Finally, it explores exercise, particularly high-intensity intermittent training as a means to reduce liver fat, improve body composition, and attenuate insulin resistance independent of weight change and dietary advice. The principle finding is that, although the literature supports the recommendation of weight reduction, exercise can be an effective therapy to reduce liver fat and improve glucose control/insulin independent of weight change in adults with NAFLD. High-intensity intermittent training is particularly ii effective for liver fat reduction, improves glucose control/insulin resistance, and results in positive changes to body composition

The Measurement and Modelling of Blood Glucose Dynamics in Man.

The aim of the work presented in this thesis is to establish a mathematical model for use in the study of blood glucose dynamics and their disorders in man. A large number of models have been developed that represent various aspects of blood glucose dynamics and of these the majority have been attempts to provide a mathematical description of glucose tolerance test curves. Most of these models have no immediate clinical application and have also failed to provide any real insight into the system that controls the flow of glucose into and from the blood glucose compartment. To do this a mathematical model must be formulated that approximates to an isomorphic description of the glucose regulatory system. Such a model must be based on sound biochemical and physiological knowledge. However, the complexity of the glucose system is such that complete simulation is not possible. In this study, a model has been developed and is described that places particular emphasis upon the role of the liver in controlling blood glucose dynamics. Compartments are provided for glucose, glucose-6-phosphate, and glycogen which are the dominant metabolic substrates. Mass balance equations have been written in terms of the enzymatic reactions that are involved in glucose transport and substrate kinetics. Insulin and glucagon hormonal controllers have also been incorporated. The model has been tested by inputs representing intravenous glucose infusion, intravenous glucose, insulin and glucagon injection. The model appears to simulate in general terms experimental data, and has yielded information about both the system structure and the enzyme dynamics involved. Of particular importance is the evidence that fine control of the glucose system is an intrinsic function of the enzyMe systems and that only coarse control of the system is provided by the hormonal environment.Little work has been done in this field, but the present model is unlike any previous model in that the inherent non-linearities of the metabolic system are developed from known enzymological data. The approach illustrates the possible value of using kinetic data obtained from -in -vitro, experiments in predicting physiological changes within the in vivo system. It is considered that mathematical models of this type can provide the biomedical scientist with insight into the functioning of metabolic systems and highlight areas of weak knowledge

Oral application of L-menthol in the heat: From pleasure to performance

When menthol is applied to the oral cavity it presents with a familiar refreshing sensation and cooling mint flavour. This may be deemed hedonic in some individuals, but may cause irritation in others. This variation in response is likely dependent upon trigeminal sensitivity toward cold stimuli, suggesting a need for a menthol solution that can be easily personalised. Menthol’s characteristics can also be enhanced by matching colour to qualitative outcomes; a factor which can easily be manipulated by practitioners working in athletic or occupational settings to potentially enhance intervention efficacy. This presentation will outline the efficacy of oral menthol application for improving time trial performance to date, either via swilling or via co-ingestion with other cooling strategies, with an emphasis upon how menthol can be applied in ecologically valid scenarios. Situations in which performance is not expected to be enhanced will also be discussed. An updated model by which menthol may prove hedonic, satiate thirst and affect ventilation will also be presented, with the potential performance implications of these findings discussed and modelled. Qualitative reflections from athletes that have implemented menthol mouth swilling in competition, training and maximal exercise will also be included