Showing papers by "Mark E. Cooper published in 2002"

Optical biosensors in drug discovery.

Abstract: Optical biosensors that exploit surface plasmon resonance, waveguides and resonant mirrors have been used widely over the past decade to analyse biomolecular interactions. These sensors allow the determination of the affinity and kinetics of a wide variety of molecular interactions in real time, without the need for a molecular tag or label. Advances in instrumentation and experimental design have led to the increasing application of optical biosensors in many areas of drug discovery, including target identification, ligand fishing, assay development, lead selection, early ADME and manufacturing quality control. This article reviews important advances in optical-biosensor instrumentation and applications, and also highlights some exciting developments, such as highly multiplexed optical-biosensor arrays.

Testing the Cretaceous greenhouse hypothesis using glassy foraminiferal calcite from the core of the Turonian tropics on Demerara Rise

Abstract: Glassy Turonian foraminifera preserved in clay-rich sediments from the western tropical Atlantic yield the warmest equivalent ?18O sea-surface temperatures (SSTs) yet reported for the entire Cretaceous-Cenozoic. We estimate Turonian SSTs that were at least as warm as (conservative mean ~30 °C) to significantly warmer (warm mean ~33 °C) than those in the region today. However, if independent evidence for high middle Cretaceous pCO2 is reliable and resulted in greater isotopic fractionation between seawater and calcite because of lower sea-surface pH, our conservative and warm SST estimates would be even higher (32 and 36 °C, respectively). Our new tropical SSTs help reconcile geologic data with the predictions of general circulation models that incorporate high Cretaceous pCO2 and lend support to the hypothesis of a Cretaceous greenhouse. Our data also strengthen the case for a Turonian age for the Cretaceous thermal maximum and highlight a 20–40 m.y. mismatch between peak Cretaceous-Cenozoic global warmth and peak inferred tectonic CO2 production. We infer that this mismatch is either an artifact of a hidden Turonian pulse in global ocean-crust cycling or real evidence of the influence of some other factor on atmospheric CO2 and/or SSTs. A hidden pulse in crust cycling would explain the timing of peak Cretaceous-Cenozoic sea level (also Turonian), but other factors are needed to explain high-frequency (~10–100 k.y.) instability in middle Cretaceous SSTs reported elsewhere.

Reduction of the Accumulation of Advanced Glycation End Products by ACE Inhibition in Experimental Diabetic Nephropathy

Abstract: The effect of ACE inhibition on the formation of advanced glycation end products (AGEs) and oxidative stress was explored. Streptozocin-induced diabetic animals were randomized to no treatment, the ACE inhibitor ramipril (3 mg/l), or the AGE formation inhibitor aminoguanidine (1 g/l) and followed for 12 weeks. Control groups were followed concurrently. Renal AGE accumulation, as determined by immunohistochemistry and both serum and renal fluorescence, were increased in diabetic animals. This was attenuated by both ramipril and aminoguanidine to a similar degree. Nitrotyrosine, a marker of protein oxidation, also followed a similar pattern. The receptor for AGEs, gene expression of the membrane-bound NADPH oxidase subunit gp91phox, and nuclear transcription factor-kappaB were all increased by diabetes but remained unaffected by either treatment regimen. Two other AGE receptors, AGE R2 and AGE R3, remained unchanged for the duration of the study. The present study has identified a relationship between the renin-angiotensin system and the accumulation of AGEs in experimental diabetic nephropathy that may be linked through oxidative stress

Prevention of Accelerated Atherosclerosis by Angiotensin-Converting Enzyme Inhibition in Diabetic Apolipoprotein E–Deficient Mice

Abstract: Background— Atherosclerosis is a major complication of diabetes, but the mechanisms by which diabetes promotes macrovascular disease have not been fully delineated. Although several animal studies have demonstrated that inhibition of ACE results in a decrease in the development of atherosclerotic lesions, information about the potential benefits of these agents on complex and advanced atherosclerotic lesions as observed in long-term diabetes is lacking. The aim of this study was to evaluate whether treatment with the ACE inhibitor perindopril affects diabetes-induced plaque formation in the apolipoprotein E (apoE)-deficient mouse. Methods and Results— Diabetes was induced by injection of streptozotocin in 6-week-old apoE-deficient mice. Diabetic animals received treatment with perindopril (4 mg · kg−1 · d−1) or no treatment for 20 weeks. Nondiabetic apoE-deficient mice were used as controls. Induction of diabetes was associated with a 4-fold increase in plaque area compared with nondiabetic animals. This ...

The relationship between shell size and Mg/Ca, Sr/Ca, δ18O, and δ13C of species of planktonic foraminifera

Abstract: The relationship between shell size and Mg/Ca, Sr/Ca, ?18O, and ?13C of planktonic foraminiferal calcite has been investigated using seventeen species in six different size fractions. Mg/Ca increases and Sr/Ca decreases with increasing size, except for two globorotaliid species which show the opposite trend. The changes in Mg/Ca broadly follow ?18O calcification temperatures except that surface and near-surface dwelling species show larger changes in Mg/Ca than can be accounted for by differences in calcification temperature derived from ?18O. The increases in Mg/Ca and decreases in Sr/Ca vary linearly with the well-established increase in ?13C with size. This is consistent with smaller individuals calcifying faster than larger individuals and larger individuals forming calcite that more closely reflects seawater temperature and composition. It appears that variations in calcification rate affect Mg and Sr shell chemistry. The observations may account for part of the temporal variability in foraminiferal Sr/Ca within a single size fraction that has been attributed to changes in seawater Sr/Ca.

Renal connective tissue growth factor induction in experimental diabetes is prevented by aminoguanidine.

Abstract: The aim of this study was to determine whether aminoguanidine (AG), an inhibitor of advanced glycation, prevents expression of the profibrotic cytokine, connective tissue growth factor (CTGF), as well as accumulation of the previously reported CTGF-dependent matrix protein, fibronectin, in a model of experimental diabetic nephropathy. Diabetic animals were randomly allocated into groups receiving 32 wk of AG or vehicle. Diabetic rats showed increases in CTGF mRNA and protein expression as well as in advanced glycation end-product (AGE) and fibronectin immunostaining, compared with nondiabetic rats. In the diabetic kidney, the increase in CTGF gene and protein expression as well as expression of the extracellular matrix protein fibronectin were prevented by AG. To further explore the relationship between AGEs and mesangial CTGF and fibronectin production, cultured human mesangial cells were exposed in vitro to soluble AGE-BSA and carboxymethyl lysine-BSA, and this led to induction of both CTGF and fibronectin. On the basis of our in vitro findings in mesangial cells linking AGEs to CTGF expression, the known prosclerotic effects of CTGF, and the ability of AG to attenuate mesangial expansion, it is postulated that the antifibrotic effects of AG in this animal model may be partially mediated by CTGF.

A Low-Sodium Diet Potentiates the Effects of Losartan in Type 2 Diabetes

Abstract: OBJECTIVE —Diabetic subjects have a high prevalence of hypertension, increased total body exchangeable sodium levels, and an impaired ability to excrete a sodium load. This study assessed the effect of dietary sodium restriction on the efficacy of losartan in hypertensive subjects with type 2 diabetes and albumin excretion rates of 10–200 μg/min. RESEARCH DESIGN AND METHODS —In this study, 20 subjects were randomized to losartan 50 mg/day ( n = 10) or placebo ( n = 10). Drug therapy was given in two 4-week phases separated by a washout period. In the last 2 weeks of each phase, patients were assigned to low- or regular-sodium diets, in random order. In each phase, 24-h ambulatory blood pressure, urinary albumin-to-creatinine ratio (ACR), and renal hemodynamics were measured. RESULTS —Achieved urinary sodium on a low-sodium diet was 85 ± 14 and 80 ± 22 mmol/day in the losartan and placebo groups, respectively. In the losartan group, the additional blood pressure-lowering effects of a low-sodium diet compared with a regular-sodium diet for 24-h systolic, diastolic, and mean arterial blood pressures were 9.7 mmHg (95% confidence interval [CI], 2.2−17.2; P = 0.002), 5.5 mmHg (2.6−8.4; P = 0.002), and 7.3 mmHg (3.3− 11.3; P = 0.003), respectively. In the losartan group, the ACR decreased significantly on a low-sodium diet versus on a regular-sodium diet (−29% [CI −50.0 to −8.5%] vs. + 14% [−19.4 to 47.9%], respectively; P = 0.02). There was a strong correlation between fall in blood pressure and percent reduction in the ACR ( r = 0.7, P = 0.02). In the placebo group, there were no significant changes in blood pressure or ACR between regular- and low-sodium diets. There were no significant changes in renal hemodynamics in either group. CONCLUSIONS —These data demonstrated that a low-sodium diet potentiates the antihypertensive and antiproteinuric effects of losartan in type 2 diabetes. The blood pressure reduction resulting from the addition of a low-sodium diet to losartan was of similar magnitude to that predicted from the addition of a second antihypertensive agent.

Angiotensin Type 2 Receptor Antagonism Confers Renal Protection in a Rat Model of Progressive Renal Injury

Abstract: The role of the angiotensin type 2 (AT2) receptor in the pathogenesis of progressive renal injury has not been previously elucidated. The renal expression of the AT1 and AT2 receptors in subtotally nephrectomized rats (STNx) and the effects of AT2 receptor blockade on renal injury were explored. Reduced renal expression of the AT1 but not the AT2 receptor was observed in STNx by reverse transcription-PCR, by in vitro autoradiography, and by immunohistochemical staining. The STNx rats were randomly assigned to AT1 re- ceptor antagonist valsartan, AT2 receptor antagonist PD123319, or the combination of both for 4 wk. Increased proteinuria in STNx rats was reduced by PD123319 but to a lesser degree when compared with valsartan. Reduced gene and protein expression of the slit diaphragm protein nephrin was prevented by either valsartan or PD123319. Expression of osteopontin, proliferating cell nuclear antigen, and monocyte/ macrophage infiltration was increased in STNx rats and was reduced by both AT1 and AT2 receptor antagonists. These effects of AT2 receptor antagonism were observed in the pres- ence of increased BP in STNx rats. These findings suggest that blockade of the AT2 receptor alone confers a degree of renal protection; in particular, it seems that the combination of the AT1 and AT2 receptor antagonists may confer additive renal effects than either receptor antagonist as monotherapy.

ALT-946 and Aminoguanidine, Inhibitors of Advanced Glycation, Improve Severe Nephropathy in the Diabetic Transgenic (mREN-2)27 Rat

Abstract: The severe diabetic nephropathy that develops in the hypertensive transgenic (mRen-2)27 rat with streptozotocin (STZ) diabetes has previously been considered angiotensin II-dependent. Because metabolic pathways are also activated in the diabetic kidney, the present study aimed to determine whether renoprotection could be afforded with inhibitors of advanced glycation end products (AGEs), ALT-946, and aminoguanidine (AG). At 6 weeks of age, nondiabetic control and STZ diabetic Ren-2 rats were randomized to receive vehicle, ALT-946 (1 g/l), or AG (1 g/l) and were studied for 12 weeks. Systolic blood pressure was unchanged with diabetes, ALT-946, or AG. Both kidney weight and glomerular filtration rate were increased with diabetes and unchanged with ALT-946 or AG. ALT-946 and AG equally ameliorated glomerulosclerosis and medullary pathology; however, ALT-946 did reduce cortical tubular degeneration to a greater extent than AG. Albumin excretion rate, which was elevated with diabetes, was reduced with ALT-946 but not AG. AGE immunolabeling was increased in glomeruli and reduced with ALT-946 and AG. These findings indicate that even in the context of renal injury presumed to be primarily blood pressure- and/or angiotensin II-dependent, approaches that interfere with metabolic pathways such as inhibitors of AGE formation can confer renal protection in experimental diabetes.

Hypertension and diabetes.

Abstract: Hypertension is often associated clinically with diabetes either as part of the insulin resistance syndrome or as a manifestation of renal disease. Elevated systemic blood pressure accelerates the progression of both microvascular and macrovascular complications in diabetes. Agents that interrupt the renin-angiotensin system confer renoprotection via a range of hemodynamic and nonhemodynamic mechanisms. Recent clinical trials confirm that these agents confer renoprotection in type 1 and type 2 diabetic patients with early or advanced renal disease. Hypertension also appears to accelerate vascular and cardiac abnormalities in diabetes, including increased atherosclerosis, arterial stiffness, left ventricular hypertrophy and diastolic dysfunction. A number of recently published and ongoing trials are exploring the role of aggressive antihypertensive treatment with a range of antihypertensive drugs in diabetic subjects at risk of or with macrovascular disease.

Using crop simulation to generate genotype by environment interaction effects for sorghum in water-limited environments

Abstract: Multi-environment trials (METs) used to evaluate breeding lines vary in the number of years that they sample. We used a cropping systems model to simulate the target population of environments (TPE) for 6 locations over 108 years for 54 'near-isolines' of sorghum in north-eastern Australia. For a single reference genotype, each of 547 trials was clustered into 1 of 3 'drought environment types' (DETs) based on a seasonal water stress index. Within sequential METs of 2 years duration, the frequencies of these drought patterns often differed substantially from those derived for the entire TPE. This was reflected in variation in the mean yield of the reference genotype. For the TPE and for 2-year METs, restricted maximum likelihood methods were used to estimate components of genotypic and genotype by environment variance. These also varied substantially, although not in direct correlation with frequency of occurrence of different DETs over a 2-year period. Combined analysis over different numbers of seasons demonstrated the expected improvement in the correlation between MET estimates of genotype performance and the overall genotype averages as the number of seasons in the MET was increased.

Modulation of nephrin in the diabetic kidney: association with systemic hypertension and increasing albuminuria.

Abstract: Objective: Nephrin, a cytoskeletal protein which localizes to the slit pore of podocytes, may play a role in proteinuria. This study examines the possible relationship between nephrin expression and albuminuria in normotensive and hypertensive diabetic rats. Methods: Streptozotocin diabetes was induced in both Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Diabetic and control animals were sacrificed and the kidneys obtained after 8, 16 and 24 weeks. The glomerular filtration rate (GFR) and albuminuria were also measured. Glycaemic control was assessed by measurement of plasma glucose and glycated haemoglobin (HbA1c). Nephrin gene expression was quantitated by real-time polymerase chain reaction (PCR) and localized by in situ hybridization. Nephrin protein expression was localized by immunohistochemistry and quantitated. Results: Following a transient rise at 8 weeks in the diabetic SHR (P < 0.05 versus control SHRs), nephrin gene expression, as determined by real-time PCR, was significantly decreased at 16 and 24 weeks (P < 0.05 versus control SHRs). In situ hybridization confirmed similar changes in nephrin gene expression, which were confined to the glomeruli. This reduction in glomerular nephrin gene expression was associated with increasing albuminuria at 16 and 24 weeks in diabetic SHRs. There were no significant changes in nephrin gene expression, either by real-time reverse transcription polymerase chain reaction or in situ hybridization, observed in normotensive diabetic WKY rats, in the context of much less albuminuria in this group. Immunohistochemistry for nephrin protein revealed a greater depletion in renal nephrin content in SHR than in WKY rats after 24 weeks of diabetes. Conclusion: Reduction in renal nephrin gene and protein expression is closely associated with the development of albuminuria, as observed in an experimental model of diabetes and hypertension.

Urinary Transforming Growth Factor-β Excretion in Patients With Hypertension, Type 2 Diabetes, and Elevated Albumin Excretion Rate: Effects of angiotensin receptor blockade and sodium restriction

Abstract: OBJECTIVE —Transforming growth factor-β (TGF-β) is a prosclerotic growth factor implicated in the pathogenesis of diabetic nephropathy. In addition to high glucose, other factors implicated in renal fibrosis and increased TGF-β synthesis include angiotensin II and high dietary sodium intake. The aim of this study was to examine the effect of angiotensin receptor blockade (ARB) and dietary sodium restriction on the plasma concentration and urinary excretion of TGF-β in hypertensive patients with type 2 diabetes and elevated albumin excretion rate (AER). RESEARCH DESIGN AND METHODS —Twenty-one subjects with hypertension and AER between 10 and 200 μg/min were randomized to receive either 50 mg losartan daily ( n = 11) or placebo ( n = 10). Drug therapy was given in two 4-week phases, separated by a 4-week washout period. In the last 2 weeks of each phase, patients were assigned to regular- or low-sodium diets in random order. Parameters measured at week 0 and 4 of each phase included plasma TGF-β concentration, TGF-β urinary excretion, AER, clinic mean arterial blood pressure, and urinary sodium excretion. RESULTS —Plasma TGF-β was unaffected by losartan treatment or sodium intake. In the losartan group, urinary TGF-β excretion decreased by 23.2% (−39.2 and 13.6) [median (interquartile range)] and 38.5% (−46.8 and −6.1) in the regular- and low-sodium phases, respectively ( P < 0.05 for drug effect). In the placebo group, median changes of 0.0% (−12.1 and 44.4) and 0.0% (−29.2 and 110.7) occurred in the regular- and low-sodium phases, respectively. Sodium restriction did not affect urinary TGF-β excretion in either losartan- or placebo-treated patients ( P = 0.54 for overall dietary effect), and there was no evidence of interaction between drug and diet ( P = 0.29). CONCLUSIONS —In hypertensive type 2 diabetic patients with elevated AER, the ARB losartan, but not sodium restriction, reduced urinary TGF-β excretion. These data suggest that the renoprotective effects of losartan in patients with type 2 diabetes and nephropathy may include a reduction in renal TGF-β production.

The GP problem: quantifying gene-to-phenotype relationships.

Abstract: In this paper we refer to the gene-to-phenotype modeling challenge as the GP problem. Integrating information across levels of organization within a genotype-environment system is a major challenge in computational biology. However, resolving the GP problem is a fundamental requirement if we are to understand and predict phenotypes given knowledge of the genome and model dynamic properties of biological systems. Organisms are consequences of this integration, and it is a major property of biological systems that underlies the responses we observe. We discuss the E(NK) model as a framework for investigation of the GP problem and the prediction of system properties at different levels of organization. We apply this quantitative framework to an investigation of the processes involved in genetic improvement of plants for agriculture. In our analysis, N genes determine the genetic variation for a set of traits that are responsible for plant adaptation to E environment-types within a target population of environments. The N genes can interact in epistatic NK gene-networks through the way that they influence plant growth and development processes within a dynamic crop growth model. We use a sorghum crop growth model, available within the APSIM agricultural production systems simulation model, to integrate the gene-environment interactions that occur during growth and development and to predict genotype-to-phenotype relationships for a given E(NK) model. Directional selection is then applied to the population of genotypes, based on their predicted phenotypes, to simulate the dynamic aspects of genetic improvement by a plant-breeding program. The outcomes of the simulated breeding are evaluated across cycles of selection in terms of the changes in allele frequencies for the N genes and the genotypic and phenotypic values of the populations of genotypes.

Identification of research to improve the efficiency of breeding strategies for white clover in Australia - a review

Abstract: A major challenge faced by today's white clover breeder is how to manage resources within a breeding program. It is essential to utilise these resources with sufficient flexibility to build on past progress from conventional breeding strategies, but also take advantage of emerging opportunities from molecular breeding tools such as molecular markers and transformation. It is timely to review white clover breeding strategies. This background can then be used as a foundation for considering how to continue conventional plant improvement activities and complement them with molecular breeding opportunities. In this review, conventional white clover breeding strategies relevant to the Australian dryland target population environments are considered. Attention is given to: (i) availability of genetic variation, (ii) characterisation of germplasm collections, (iii) quantitative models for estimation of heritability, (iv) the role of multi-environment trials to accommodate genotype-by-environment interactions, (v) interdisciplinary research to understand adaptation to dryland environments, (vi) breeding and selection strategies, and (vii) cultivar structure. Current achievements in biotechnology with specific reference to white clover breeding in Australia are considered, and computer modelling of breeding programs is discussed as a useful integrative tool for the joint evaluation of conventional and molecular breeding strategies and optimisation of resource use in breeding programs. Four areas are identified as future research priorities: (i) capturing the potential genetic diversity among introduced accessions and ecotypes that are adapted to key constraints such as summer moisture stress and the use of molecular markers to assess the genetic diversity, (ii) understanding the underlying physiological/morphological root and shoot mechanisms involved in water use efficiency of white clover, with the objective of identifying appropriate selection criteria, (iii) estimation of quantitative genetic parameters of important morphological/physiological attributes to enable prediction of response to selection in target environments, and (iv) modelling white clover breeding strategies to evaluate the opportunities for integration of molecular breeding strategies with conventional breeding programs.

Renal expression of angiotensin receptors in long-term diabetes and the effects of angiotensin type 1 receptor blockade.

Abstract: Objective The aims of this study were to assess the renal expression of angiotensin type 1 (AT1) and type 2 (AT2) receptors in diabetic spontaneously hypertensive rats (SHR) and the effect of AT1 receptor blockade on the expression of these receptors.Design Diabetes was induced by injection of strep

The E(NK) model: Extending the NK model to incorporate gene-by-environment interactions and epistasis for diploid genomes

Abstract: The haploid NK model developed by Kauffman can be extended to diploid genomes and to incorporate gene-by-environment interaction effects in combination with epistasis. To provide the flexibility to include a wide range of forms of gene-by-environment interactions, a target population of environment types (TPE) is defined. The TPE consists of a set of E different environment types, each with their own frequency of occurrence. Each environment type conditions a different NK gene network structure or series of gene effects for a given network structure, providing the framework for defining gene-by-environment interactions. Thus, different NK models can be partially or completely nested within the E environment types of a TPE, giving rise to the E(NK) model for a biological system. With this model it is possible to examine how populations of genotypes evolve in context with properties of the environment that influence the contributions of genes to the fitness values of genotypes. We are using the E(NK) model to investigate how both epistasis and gene-by-environment interactions influence the genetic improvement of quantitative traits by plant breeding strategies applied to agricultural systems. © 2002 Wiley Periodicals, Inc.

Combined inhibition of neutral endopeptidase with angiotensin converting enzyme or endothelin converting enzyme in experimental diabetes.

Abstract: OBJECTIVE The effects of combined inhibition of neutral endopeptidase (NEP) with either angiotensin-converting enzyme (ACE), or endothelin-converting enzyme (ECE) on blood pressure, urinary albumin excretion and heart weight were explored in experimental diabetes. DESIGN Streptozotocin-induced diabetic Sprague-Dawley rats were treated with vehicle, the NEP/ACE inhibitor S 21402, the NEP/ECE inhibitor CGS 26303, the NEP inhibitor SCH 42495, the ACE inhibitor captopril or the endothelin receptor antagonist bosentan for 4 weeks. METHODS Blood pressure was measured by tail-cuff method and radiotelemetry. Albuminuria, plasma renin activity and plasma atrial natriuretic peptide (ANP) were determined by radioimmunoassay. NEP binding was assessed by in vitro quantitative autoradiography. Metabolic and biochemistry parameters including food intake, 24-h urine volume, plasma glucose, glycated hemoglobin, glomerular filtration rate (GFR) and urinary sodium excretion were also determined. RESULTS Mean blood pressure over the 4-week study period after commencement of treatment was reduced to a similar extent by a range of treatments including the ACE inhibitor, NEP/ACE inhibitor, endothelin receptor antagonist, NEP/ECE inhibitor, but not the NEP inhibitor, compared with vehicle-treated diabetic rats. Heart to body weight ratio in diabetic rats was only reduced by the NEP/ACE and the NEP/ECE inhibitor. Increased albuminuria in diabetic rats (1.1 times/divided by 1.2 mg/day) was reduced by the NEP/ACE (0.6 times/divided by 1.2 mg/day) and the NEP/ECE inhibitors (0.4 times/divided by 1.2 mg/day). Renal NEP was reduced by the NEP/ACE inhibitor (35 +/- 4%) or NEP/ECE inhibitor (38 +/- 4%) as well as by the pure NEP inhibitor (27 +/- 4%) compared with the untreated diabetic group. Other abnormal metabolic and biochemical parameters in diabetic rats were not influenced by any drug treatment. CONCLUSIONS Combined inhibition of NEP/ACE or NEP/ECE confers beneficial effects on blood pressure, albuminuria and heart to body weight ratio in experimental diabetes.