Brush border digestion : development of a physiologically relevant in vitro model : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Physiology at Massey University, Manawatū, New Zealand

Chapter Two has, in part, been published in the Springer publication, Reviews of Physiology, Biochemistry and Pharmacology, but the Author retains the right to publish the material in any collection consisting of the Author's own works: Hooton, D., Lentle, R., Monro, J., Wickham, M., & Simpson, R. (2015). The secretion and action of brush border enzymes in the mammalian small intestine. In: B. Nilius, T. Gudermann, R. Jahn, R. Lill, O. Petersen, & P. de Tombe (Eds.), Reviews of Physiology, Biochemistry and Pharmacology (vol 168, pp. 59-118). Cham: Springer. doi: 10.1007/112_2015_24The majority of current in vitro digestion methods either exclude the small intestinal brush border (BB) phase of digestion or do not incorporate the entire array of BB enzymes that are required to achieve terminal endogenous digestion in vivo. Accordingly, the digestate, and its derivitives, may not be representative of the digestive process in vivo. In order to improve the fidelity of the in vitro digestion process this thesis developed a physiologically relevant small intestinal BB phase using enzymes isolated from rat small intestinal mucosal tissue. The activities of BB enzymes were assessed and compared with known values, and under conditions physiologically representative of the small intestine. Although there were significant differences in BB enzyme activities depending on pH, enzyme solubilisation, and upon prolonged exposure to biliopancreatic secretions the BB preparation was deemed suitable for use in an in vitro digestion method. A rationale for the composition of the BB digestive phase was developed based on published physiological data, and was validated using glycosylated polyphenolic compounds as substrates. Liquid chromatography mass spectrometry (LC-MS) was used to assess the derivatisation products of BB digestion. In the absence of biliopancreatic secretions the onion flesh polyphenolic compounds quercetin-4ʹ-glucoside and isorhamnetin-4ʹ-glucoside, but not quercetin-3-glucoside or quercetin-34ʹ-diglucoside were hydrolysed. The positive control quercetin-3-glucoside was hydrolysed, and the negative control quercetin-3-rutinoside was not hydrolysed. The deglycosylation of quercetin-3-glucoside was monitored under conditions representative of the small intestine, i.e. incorporating bile and pancreatin, while at the appropriate pH. Quercetin-3-glucoside was significantly deglycosylated in BB treatments (no treatment or pancreatin alone) compared to BB treatments with bile (bile alone or pancreatin and bile). The mammalian digestive system is equipped to hydrolyse macronutrients from their polymeric form through to monomers and oligomers suitable for absorption across the epithelial layer. As such the inactivation or degradation of some BB enzymes during the BB digestive phase by bile or pancreatin was not unexpected, and does not preclude its use as an in vitro tool in the future

Using Long-Term Outdoor Exposure Data to Benchmark Accelerated Durability Test Methods

Many performance-based durability test methods adopted in various national and international standards were developed decades ago based on short-term evaluations. Most durability tests use various methods to accelerate reactions in order to obtain results in a reasonably short period of time. Then pass/fail criteria are set for these tests in standard specifications. However, the acceleration techniques used maybe overly severe, and preclude the use of concrete materials and mix designs that perform perfectly well in the field. The inclusion of long-term field tests or outdoor exposure tests can be used to verify the appropriateness of both the test methods and the test limits. This provides more confidence that the results from the test methods are meaningful and that the adopted specification limits are appropriate. This approach has been used to verify or modify ASTM and CSA test methods for sulfate resistance, mitigation of alkali-silica reaction, de-icer salt scaling resistance, and for resistance to chloride ingress for marine and deicer exposures. However, in addition to the time and costs for such programs, another limiting factor can be that the materials and mix designs used in the long-term tests may no longer be representative of those currently in use. As another issue, the precision of all test methods needs to be evaluated by inter-laboratory test programs to provide confidence in the reproducibility of test results obtained. This contribution describes results from several long-term test programs and inter-laboratory studies focused on verifying specific standard test methods for durability

Defect Energies And Entropies From Computer Simulation And Ionic Conductivity Measurements

Ionic conductivity measurements have been made on pure and strontium- and sulphide-doped sodium chloride and the data analysed by means of a non-linear least squares fitting routine. The purpose of this investigation was two-fold. First, the question as to what types of defects occur in NaCl needed to be resolved. Recent work on KCl indicated that a small concentration of Frenkel defects was present on both sub-lattices in addition to Schottky defects, which have been assumed to predominate in alkali halides. Secondly, a wide variety of values for the anion vacancy migration energy have been given in the literature and it was hoped that the present investigation would help to resolve the correct value of this defect energy. The analysis of the data indicated that Schottky defects do indeed predominate in NaCl. A value of 0.744 eV was determined for the anion migration enthalpy.;In addition to this, calculations were carried out with new potentials for SrCl{dollar}\sb2{dollar} and Na{dollar}\sb2{dollar}S using the HADES code. The main purpose of these calculations was to develop potentials to be used in defect calculations of NaCl containing Sr{dollar}\sp{lcub}2+{rcub}{dollar} and S{dollar}\sp{lcub}2-{rcub}{dollar} impurities; however the availability of these potentials made it possible to carry out additional calculations on SrCl{dollar}\sb2{dollar} and Na{dollar}\sb2{dollar}S. Although the problem of low defect migration energies commonly found in defect calculations of fluorites still persisted, some improvements were made with SrCl{dollar}\sb2{dollar}. No defect calculations on Na{dollar}\sb2{dollar}S had been done previously.;An investigation of the quasi-harmonic approximation was carried out with a set of temperature dependent potentials for NaCl, KCl, and KBr. In the past, quasi-harmonic calculations have been undertaken only with potentials developed at 0 K. However, a lattice which is strain-free at 0 K is no longer at equilibrium at higher temperatures. The temperature dependent potentials were developed over a wide temperature range by fitting to the physical properties of the crystal at 50 K intervals and minimizing the bulk lattice strain. The resulting defect energies were compared to values calculated using the potentials of Catlow, Diller, and Norgett developed at 0 K, and additional thermodynamic properties were calculated in the quasi-harmonic approximation