Showing papers by "Mark E. Cooper published in 1999"

Increased renal expression of vascular endothelial growth factor (VEGF) and its receptor VEGFR-2 in experimental diabetes.

Abstract: It has been suggested that the cytokine vascular endothelial growth factor (VEGF) has an important role in the pathogenesis of diabetic retinopathy, but its role in nephropathy has not been clearly demonstrated. Assessment of VEGF, 125I-VEGF binding, and vascular endothelial growth factor receptor-2 (VEGFR-2) in the kidney was performed after 3 and 32 weeks of streptozotocin-induced diabetes. Gene expression of both VEGF and VEGFR-2 was assessed by Northern blot analysis and the localization of the ligand and receptor was examined by in situ hybridization. VEGF and VEGFR-2 protein were also evaluated by immunohistochemistry. Binding of the radioligand 125I-VEGF was evaluated by in vitro and in vivo autoradiography. Diabetes was associated with increased renal VEGF gene expression. VEGF mRNA and protein were localized to the visceral epithelial cells of the glomerulus and to distal tubules and collecting ducts in both diabetic and nondiabetic rats. Renal VEGFR-2 mRNA was increased after 3 weeks of diabetes but not in long-term diabetes. In situ hybridization and immunohistochemical studies revealed that glomerular endothelial cells were the major site of VEGFR-2 expression. In addition, VEGFR-2 gene expression was detected in cortical and renomedullary interstitial cells and on endothelial cells of peritubular capillaries. There was an increase in 125I-VEGF binding sites after 3 but not 32 weeks of diabetes. The major VEGF binding sites were in the glomeruli. 125I-VEGF binding was also observed in medullary rays and in the renal papillae. These studies indicate an early and persistent increase in renal VEGF gene expression in association with experimental diabetes. In addition, an early and transient increase in renal VEGF receptors was also observed in diabetic rats. These findings are consistent with a role for VEGF in mediating some of the changes observed in the diabetic kidney.

Pathological expression of renin and angiotensin II in the renal tubule after subtotal nephrectomy. Implications for the pathogenesis of tubulointerstitial fibrosis.

Abstract: The finding that the systemic renin-angiotensin system (RAS) is not activated in most types of chronic renal disease has led to the suggestion that a local, intrarenal RAS may be an important determinant in the relentless progression of renal disease Therefore, cell specific changes in various components of the RAS in response to renal mass reduction and angiotensin converting enzyme (ACE) inhibition were examined Thirty Sprague-Dawley rats were randomly assigned to sham surgery, subtotal nephrectomy (STNx) alone or STNx treated with the ACE inhibitor, perindopril, and sacrificed after 12 weeks In sham rats, renin mRNA and protein were only present in the juxtaglomerular apparatus In contrast, in STNx kidneys, renin and angiotensin II expression were noted predominantly in renal tubular epithelial cells in association with overexpression of the prosclerotic cytokine, transforming growth factor-beta1 (TGF-beta1) In perindopril-treated STNx rats expression of renin and TGF-beta1 were similar to control animals These finding indicate that following renal mass reduction there is pathological tubular expression of various components of the RAS Furthermore, in contrast to the juxtaglomerular apparatus, tubular renin expression was reduced with ACE inhibition These changes within the intrarenal RAS may be pathogenetically linked to the development of tubulointerstitial injury

Role of angiotensin receptor subtypes in mesenteric vascular proliferation and hypertrophy.

Abstract: —The aim of this study was to explore the regulation of angiotensin receptors after chronic infusion with angiotensin II (Ang II) and to clarify the relative roles of the angiotensin type 1 (AT 1 ) and type 2 (AT 2 ) receptors in the mediation of Ang II–induced mesenteric vascular hypertrophy. In male Sprague-Dawley rats, Ang II infusion at a dose of 58.3 ng/min by subcutaneous osmotic minipumps for 14 days led to increased mesenteric weight and wall:lumen ratio of the vessels and proliferation of smooth muscle cells. These vascular changes were attenuated by either valsartan, an AT 1 receptor antagonist, at a dose of 30 mg · kg −1 · d −1 by gavage, or PD123319, an AT 2 receptor antagonist, at a dose of 830 ng/min by intraperitoneally implanted osmotic minipumps. Ang II infusion was associated with hypertension, which was prevented by valsartan, but not PD123319. 125 I-Sar 1 , Ile 8 Ang II binding to mesenteric vasculature was increased after Ang II infusion. Valsartan treatment was associated with reduced Ang II binding to both receptor subtypes, whereas PD123319 was associated with reduced Ang II binding to only the AT 2 receptor subtype. These findings suggest that the trophic and proliferative effects of Ang II on the mesenteric vasculature are mediated by both AT 1 and AT 2 receptors.

Computer simulation of a selection strategy to accommodate genotype environment interactions in a wheat recurrent selection programme

Abstract: Multi-environment trials (METs) are used in plant breeding programmes to evaluate genotypes (lines/families) as a basis for selection on expected performance (yield and/or quality) in a target population of environments (TPE). When a large component of the genotype-environment (G x E) interactions results from crossover interactions, samples of environments in METs that deviate From the TPE provide a suboptimal basis for selection of genotypes on performance expected in the TPE. To adjust for the negative effects of these deviations, a selection strategy that weights the data from the MET according to their expected frequency of occurrence in the TPE (i.e. a weighted selection strategy)was investigated. Computer simulation methodology was used to obtain preliminary information on the weighted selection strategy and compare it to the traditional unweighted selection strategy For a range of MET scenarios and G x E interaction models. The evaluation of the weighted selection strategy was conducted in context with the germplasm enhancement programme (GEP) of the Northern Wheat Improvement Programme in Australia. The results indicated that when the environments sampled in the MET matched those expected in the TPE, the unweighted and weighted selection strategies achieved a similar response to selection in the TPE. However. when the environments sampled in the MET did not match the expectations in the TPE and a large component of the G x E interactions resulted from crossover interactions, the weighted selection strategy achieved a greater response to selection in the TPE. The advantage of the weighted strategy increased as the amount of crossover G x E interaction increased or fewer environments were sampled in the METs.

The salt dependence of DNA recognition by NF-kappaB p50: a detailed kinetic analysis of the effects on affinityand specificity.

Abstract: The binding kinetics of NF-kappaB p50 to the Ig-kappaB site and to a DNA duplex with no specific binding site were determined under varying conditions of potassium chloride concentration using a surface plasmonresonance biosensor Association and dissociation rate constants were measured enabling calculation of the dissociation constants Under previously established high affinity buffer conditions, the k a for both sequences was in the order of 10(7) M-1s-1whilst the k d values varied 600-fold in a sequence-dependent manner between 10(-1) and 10(-4 )s-1, suggesting that the selectivity of p50 for different sequences is mediated primarily through sequence-dependent dissociation rates The calculated K D value for the Ig-kappaB sequence was 16 pM, whilst the K D for the non-specific sequence was 99 nM As the ionic strength increased to levels which are closer to that of the cellular environment, the binding of p50 to the non-specific sequence was abolished whilst the specific affinity dropped to nanomolar levels From these results, a mechanism is proposed in which p50 binds specific sequences with high affinity whilst binding non-specific sequences weakly enough to allow efficient searching of the DNA

Treatment of hypertension in diabetes.

Abstract: Patients with type I and II diabetes mellitus represent a population at high risk of the cardiovascular, cerebrovascular and renal effects of hypertension. Antihypertensive therapy should be considered for those with blood pressures above 130/85 mmHg with the aim to reduce levels below 125/75 especially for those with microalbummuria or diabetic nephropathy. Hypertension tends to occur on a background of multiple other risk factors. Life­style changes such as increased exercise and reduced salt intake, when combined with medication should improve the blood pressure response. On the currently available data, an Angiotensin Converting Enzyme (ACE) inhibitor, initially as mono-therapy, is the first choice antihypertensive agent in the absence of contraindications. Often dual or triple therapy is required to achieve target blood pressure levels.

A novel inhibitor of advanced glycation end-product formation inhibits mesenteric vascular hypertrophy in experimental diabetes

Abstract: Aims/hypothesis. Previous studies in our laboratory have shown that the vascular changes in diabetes include hypertrophy of the mesenteric vasculature and that this process can be attenuated by the inhibition of advanced glycation with aminoguanidine. Since aminoguanidine can also act as an inhibitor of nitric oxide synthase, the effect of a novel inhibitor of advanced glycation end-products, formation that does not inhibit nitric oxide synthase, known as 2,3 diaminophenazine (2,3 DAP) was evaluated. Methods. Initially, in vitro assessment of the ability of 2,3 diaminophenazine to inhibit formation of advanced glycation products was performed. Subsequently, in vivo studies evaluating 2,3 diaminophenazine and aminoguanidine were carried out. Animals were followed for 3 weeks after induction of diabetes and randomised to no treatment, aminoguanidine or 2,3 diaminophenazine. Mesenteric vessels were weighed and advanced glycation end-products were measured by radioimmunoassay in vessel and kidney homogenates. In addition, these products were assessed in mesenteric vessels by immunohistochemistry. Results. When compared with control animals, diabetes was associated with an increase in mesenteric vascular weight. Treatment of diabetic rats with aminoguanidine or 2,3 diaminophenazine resulted in attenuation of vascular hypertrophy. Both aminoguanidine and 2,3 diaminophenazine reduced the formation of advanced glycation end-products as measured by radioimmunoassay and as assessed immunohistochemically in these vessels. This reduction was also observed in the kidney. Conclusion/interpretation. These data support the concept that the effects of aminoguanidine in reducing diabetes associated vascular hypertrophy are via inhibition of advanced glycation end-products dependent pathways. [Diabetologia (1999) 42: 472–479]

Localization of Secreted Protein Acidic and Rich in Cysteine (SPARC) Expression in the Rat Eye

Abstract: Secreted protein acidic and rich in cysteine (SPARC) is a secreted glycoprotein protein which modulates cell shape and cell-matrix interactions and has been implicated in the regulation of angiogenesis, vascular permeability and cataract formation. In situ hybridization and immunohistochemical studies for SPARC were performed to determine the cell and tissue distribution of SPARC in rat eye. Studies demonstrated SPARC mRNA and protein co-localization at all sites. In the retina SPARC mRNA and protein were localized predominantly to the Muller and ganglion cells. Within the choroid, SPARC was found in vascular endothelial cells and fibroblasts; in the sclera SPARC was present in blood vessels and fibroblasts. SPARC was also present in the non-pigmented epithelial cells of the ciliary body, and in the epithelium of the lens capsule and cornea. The demonstrated anatomical distribution of SPARC in the rat eye is consistent with several of the biological functions ascribed to this matricellular protein and provides a rational basis for its examination in pathological conditions.

High Affinity Surface Binding of a Strongly Dimerizing Vancomycin-Group Antibiotic to a Model of Resistant Bacteria

Abstract: The factors that give rise to binding enhancements when a strongly dimerizing vancomycin-group antibiotic (chloroeremomycin) binds to a model cell surface of vancomycin-resistant enterococci (VRE) have been semiquantitated. The model cell surface is comprised of vesicles to which have been anchored cell wall precursor analogues of vancomycin-resistant bacteria (which terminate in -D-lactate) via a hydrophobic docosanoyl (C-22) chain. Using H-1 and F-19 NMR spectroscopy, a large binding enhancement at the model cell surface (compared to the binding of an analogous ligand in free solution) has been observed. This enhancement can be partitioned into two distinct factors: a simple concentrating factor arising from an-increase in local concentration of ligand when it is located at the vesicle surface and a factor arising from the cooperative interaction of species mutually bound to the membrane surface. The overall enhancement to binding at a surface compared to binding in free solution was found to be a factor of 10(2)-10(3). In contrast, no significant surface binding enhancement was observed for the weakly dimerizing antibiotic vancomycin.

Evaluation of white clover (Trifolium repens L.) populations for summer moisture stress adaptation in Australia

Abstract: Agenetic experiment was conducted using 80 full-sib families in irrigated and dryland treatments under the summer moisture stress conditions of the Northern Tablelands of New South Wales, over 3 years. This paper reports on the effects of climatic and soil moisture conditions, the genetic variation for stolon attributes and seasonal herbage yield, and the development of new recombinant genotypes in relation to the association between stolon attributes and herbage yield. Large components of variance were estimated for genotype-by-environment-by-year interactions for the attributes stolon density, number of branches, number of nodes, number of rooted nodes, stolon thickness, root diameter, internode length, and summer herbage yield. The combined analysis of variance across environments and years indicated the presence of genetic variation for the stolon attributes stolon density, number of branches, number of nodes, stolon thickness, internode length, and herbage yield. Crossing of the morphologically contrasting cultivars El Lucero x Tahora x Duron, and Barbian x El Lucero, resulted in generating genotypic recombinants with new associations between herbage yield and stolon density, number of branches, number of nodes, and number of rooted nodes. Evaluation of the full-sib families and check cultivars (cvv. Haifa and Huia) identified 5 full-sib families with relatively higher herbage yield, stolon density, number of branches, number of nodes, and number of rooted nodes than cultivars Haifa and Huia.

Grain nitrogen concentration differences among three sorghum hybrids with similar grain yield

Abstract: The differences in grain nitrogen (N) concentration among 3 sorghum (Sorghum bicolor (L.) Moench) hybrids with similar grain yield were examined under N-limiting conditions in relation to the availability of assimilate and N to grain. Several manipulation treatments [N fertiliser application, lower leaves shading, thinning (reduced plant population), whole canopy shading, canopy opening, spikelet removal] were imposed to alter the relative N and assimilate availability to grain under full irrigation supply. Grain N concentration increased by either increased grain N availability or yield reduction while maintaining N uptake. Grain N concentration, however, did not decrease in the treatments where relative abundance of N compared with assimilate was intended to be reduced. The minimum levels of grain N concentration differed from 0.95% (ATx623/RTx430) to 1.14% (DK55plus) in these treatments. Regardless of the extent of variation in assimilate and N supply to grain, the ranking of hybrids on grain N concentration was consistent across the manipulation treatments. For the 3 hybrids examined, higher grain N concentration was associated with higher N uptake during grain filling and, to a lesser extent, with higher N mobilisation. Hybrids with larger grain N accumulation had a larger number of grains. There was no tradeoff between grain N concentration and yield, suggesting that grain protein concentration can be improved without sacrificing yield potential.

Synthesis of extended bacterial cell-wall precursor analogues for ligand binding studies with glycopeptide antibiotics

Abstract: The synthesis of bacterial cell-wall precursor analogues, which resemble the naturally occurring precursor (lipid II) more closely than those hitherto used in NMR binding studies with glycopeptide antibiotics, is reported.