Biomedical subjects

A J Cox

Publications and source records attributed to A J Cox.

At least 37 records · Page 2Linked to original sources

PubMed1999

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

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.

Animals↗

PubMed1999

Localization of secreted protein acidic and rich in cysteine (SPARC) expression in the rat eye.

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 Müller 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.

Animals↗

PubMed1998

Mutational analysis of the cystathionine beta-synthase gene: a splicing mutation, two missense mutations and an insertion in patients with homocystinuria. Mutations in brief no. 120. Online.

RT-PCR and direct sequence analyses were used to define mutations in the cystathionine beta-synthase (CBS) gene in two unrelated male patients with vitamin B6 nonresponsive homocystinuria. Both patients were compound heterozygotes for CBS alleles containing point mutations. One patient had a maternally derived G->A transition in the splice-donor site of intron 1, resulting in aberrant splicing of CBS mRNA. The other allele contained a missense mutation resulting in the previously reported E144K mutant CBS protein. The second patient had a maternally derived 4 bp insertion in exon 17, predicted to cause a CBS peptide of altered amino acid sequence. A 494G->A transition was found in exon 4 of the other allele, predicting a C165Y substitution. Expression of recombinant CBS protein, containing the C165Y mutation, had no detectable catalytic activity. Each mutation was confirmed in genomic DNA.

Alternative Splicing↗

PubMed1997

Clinical and histologic response of subcutaneous expanded polytetrafluoroethylene (Gore-Tex) and porous high-density polyethylene (Medpor) implants to acute and early infection.

OBJECTIVE: To examine the responses of subcutaneously implanted expanded polytetrafluoroethylene (e-PTFE, Gore-Tex) and porous high-density polyethylene (PHDPE, Medpor) to experimentally induced infection. DESIGN: Sprague-Dawley rats were implanted subcutaneously with either e-PTFE or PHDPE implants. Inocula of Staphylococcus aureus were injected directly over the implants and the wounds were observed for clinical signs of infection. After the animals were killed, the implants were harvested and underwent Histologic examination. SUBJECTS: Twenty-eight adult male Sprague-Dawley rats weighing 200 to 250 g. INTERVENTION: A 8-mm diameter, 1-mm-thick implant of either e-PTFE or PHDPE was placed in a subcutaneous pocket over each animal's dorsum. Either at the time of implantation or 14 days afterward, an inoculum of 10(9) colony-forming units of S aureus was injected transcutaneously directly over each implant. The animals were observed for 7 days before being killed. The implants were harvested and examined by both conventional light and scanning electron microscopy, and the degree of capsule reaction, infection, inflammation, and implant degradation was evaluated. RESULTS: Implants inoculated at the time of implantation were more likely to become clinically infected. Results for e-PTFE and PHDPE implants were similar in this group (5 of 5 e-PTFE and 5 of 5 PHDPE implants infected). The PHDPE implants inoculated 14 days after implantation were less likely to become infected (1 of 4 infected) than e-PTFE implants (3 of 4 infected), and were statistically less likely to become infected than PHDPE implants inoculated immediately after implantation (25% vs 100%; P < .02). Histologically, this resistance to infection correlated with increasing fibrovascular ingrowth into the PHDPE implants. The infected PHDPE implant had little to no ingrowth compared with PHDPE control implants. The uninfected e-PTFE implant had evidence of early fibrovascular ingrowth into the peripheral pores of the implant. CONCLUSIONS: Because of differences in pore size, PHDPE promotes faster fibrovascular ingrowth. The presence of vascularized host tissue in and around the implant lends stability and resistance to experimentally induced infection. Conservative management of clinical implant infections should be considered if bacterial seeding occurs after substantial fibrovascular ingrowth is present. Future alloplast designs should include pore sizes that will encourage invasion of the implant by host tissue.

Animals↗

PubMed1997

Sudden sensorineural hearing loss following nonotologic, noncardiopulmonary bypass surgery.

OBJECTIVES: To report 3 cases of sudden sensorineural hearing loss (SSHL) following nonotologic surgery in which cardiopulmonary bypass (CPB) surgery was not involved and to review reports in the literature of similar cases. DATA SOURCES: Clinical records and MEDLINE and Healthstar databases. STUDY SELECTION: Reports in the world literature of cases of SSHL following nonotologic, non-CPB surgery. DATA SYNTHESIS: While said to be more common after CPB surgery, fewer than 20 cases of SSHL following non-otologic, non-CPB surgery have been reported. A number of proposed causes of SSHL temporally related to non-otologic, non-CPB surgery have been theorized; however, the true cause is unknown. This report presents 3 cases of SSHL following nonotologic, non-CPB surgery. Two patients had profound unilateral loss; 1 had moderate bilateral loss. None of the patients demonstrated recovery despite diuretic and prednisone therapy; in approximately 30% of the cases reported to date, the patients experienced significant improvement. CONCLUSIONS: Sudden sensorineural hearing loss following nonotologic, non-CPB surgery is rare, and its cause remains unknown. The scarcity of reports of SSHL following nonotologic, non-CPB surgery raises the possibility that the apparent association may be spurious.

Aged↗

PubMed1997

Ingestion of caustic hair relaxer: is endoscopy necessary?

Hair relaxer, a commercially available alkaline product, is commonly the offending agent in caustic ingestion. These patients often experience oral cavity and facial burns; however, no clinically significant esophageal injuries have been reported. Therefore, we questioned the therapeutic and economic efficacy of the "standard treatment protocol" that includes hospitalization and endoscopic evaluation. Twenty-six patients over a 7-year period presented to our institution having ingested hair relaxer. Presenting signs and symptoms, esophageal findings, and cost of the standard treatment protocol were reviewed. Also, we analyzed the caustic potential and current packaging of hair relaxer. Our findings support modifications in the standard treatment protocol for hair relaxer ingestion including elimination of hospitalization and endoscopy in most patients. We also question compliance with childproof packaging laws and suggest avenues for prevention of hair relaxer ingestion.

Burns, Chemical↗

PubMed1996

Metabotropic glutamate receptors regulate APP processing in hippocampal neurons and cortical astrocytes derived from fetal rats.

It has previously been shown that stimulation of muscarinic m1 or m3 receptors can, by generating diacylglycerol (DAG) and activating protein kinase C (PKC), accelerate the breakdown of the amyloid precursor protein (APP) to form soluble, non-amyloidogenic peptides (APPs). This relationship has been demonstrated in human glioma and neuroblastoma cells as well as in transfected human embryonic kidney (HEK) cells and PC12 cells. We now provide evidence that stimulation of metabotropic glutamate receptors (mGluRs), which also are coupled to DAG and PKC, similarly accelerates processing of APP into non-amyloidogenic APPs in hippocampal neurons and cortical astrocytes derived from normal fetal rats. The mGluR antagonist, L(+)-2-amino-3-phosphonopropionic acid (L-AP3), and GF 109203X, an inhibitor of PKC, both blocked the release of APPs from hippocampal neurons and astrocytes evoked by glutamate receptor stimulation. Inasmuch as glutamatergic neurons in cortex and hippocampus are known to be damaged in Alzheimer's disease, our findings suggest that amyloid formation may be enhanced by the resulting glutamate deficiency and that selective mGluR agonists may be useful in facilitating synaptic efficacy and treating the disease.

Amyloid beta-Protein Precursor↗

PubMed1995

Amyloid precursor protein processing is stimulated by metabotropic glutamate receptors.

Stimulation of muscarinic m1 or m3 receptors can, by generating diacylglycerol and activating protein kinase C, accelerate the breakdown of the amyloid precursor protein (APP) to form soluble, nonamyloidogenic derivatives (APPs), as previously shown. This relationship has been demonstrated in human glioma and neuroblastoma cells, as well as in transfected human embryonic kidney 293 cells and PC-12 cells. We now provide evidence that stimulation of metabotropic glutamate receptors (mGluRs), which also are coupled to phosphatidylinositol 4,5-bisphosphate hydrolysis, similarly accelerates processing of APP into nonamyloidogenic APPs. This process is demonstrated both in hippocampal neurons derived from fetal rats and in human embryonic kidney 293 cells transfected with cDNA expression constructs encoding the mGluR 1 alpha subtype. In hippocampal neurons, both an mGluR antagonist, L-(+)-2-amino-3-phosphonopropionic acid, and an inhibitor of protein kinase C, GF 109203X, blocked the APPs release evoked by glutamate receptor stimulation. Ionotropic glutamate agonists, N-methyl-D-aspartate or S(-)-5-fluorowillardiine, failed to affect APPs release. These data show that selective mGluR agonists that initiate signal-transduction events can regulate APP processing in bona fide primary neurons and transfected cells. As glutamatergic neurons in the cortex and hippocampus are damaged in Alzheimer disease, amyloid production in these regions may be enhanced by deficits in glutamatergic neurotransmission.

Alanine↗

PubMed1993

The lux autoinducer regulates the production of exoenzyme virulence determinants in Erwinia carotovora and Pseudomonas aeruginosa.

Erwinia carotovora and Pseudomonas aeruginosa secrete exoenzymes that contribute to the pathogenesis of plant and mammalian infections respectively. E.carotovora mutants defective in synthesis of the pectinase, cellulase and protease exoenzymes were isolated and classified into two groups. Group 2 mutants were found to be defective in the production of a small freely diffusible molecule, N-3-(oxohexanoyl)-L-homoserine, lactone (HSL), and were avirulent. Addition of exogenous HSL to these group 2 mutants restores synthesis of the exoenzymes and virulence in planta. Of the exoenzymes of P.aeruginosa the metalloprotease, elastase, is an established virulence determinant. Mutants of P.aeruginosa that are defective in elastase production have been isolated and were again found to fall into two groups. Analogous to the group 2 mutants of E.carotovora, group 2 mutants of P. aeruginosa are defective in the synthesis of HSL and exogenous HSL restores elastase production. HSL has now been linked to the control of bioluminescence in Vibrio fischeri, carbapenem antibiotic production of E.carotovora and the above exoenzyme virulence determinants. This information significantly enhances our understanding of the extent and nature of pheromone mediated gene expression control in prokaryotes.

4-Butyrolactone↗

PubMed1992

Focal induction of IGF binding proteins in proximal tubules of diabetic rat kidney.

Diabetes-associated kidney enlargement is associated with increased kidney insulinlike growth factor I (IGF-I) binding. IGF-I binds to the type I IGF receptor, which mediates most of its actions, and to specific binding proteins (IGFBPs), which modulate its actions. To explore the nature and extent of IGF-I binding in the kidney, in vitro autoradiography was used to map the distribution of IGF binding in control and diabetic rat kidney. Specificity studies were performed with increasing concentrations of unlabeled IGF-I, IGF-II, des(1-3)IGF-I (an IGF-I derivative that binds to receptors normally but with decreased affinity to binding proteins), and insulin. In control rats, diffuse binding was found throughout the kidney with increased density in the papilla. Binding specificity in the cortex and outer medulla was typical of the type I IGF receptor (IGF-I = des[1-3]IGF-I greater than IGF-II much greater than insulin). Binding in the outer medulla of diabetic kidney was typical of the type I IGF receptor. A marked focal increase in proximal tubular binding occurred in 13 of 22 postpubertal diabetic rats. Binding specificity of the proximal tubular binding was consistent with the predominance of an IGF binding protein (IGF-I = IGF-II greater than des[1-3]IGF-I with minimal displacement by insulin). Northern-blot analysis revealed increased IGFBP-1 and IGFBP-3 mRNA in cortical tissue from diabetic rats displaying increased proximal tubular binding but not from diabetic rats not displaying this phenomenon. As cell surface association of IGFBPs is linked to potentiation of IGF activity, a possible mechanism for potentiation of local IGF-I action may be provided.

Animals↗

PubMed1991

Diabetes-related renal growth and IGF-I accumulation in castrated rats.

The effects of castration on diabetes-related renal growth and IGF-I regulation were studied. In the rat, prepubertal castration is associated with a normal or increased surge in plasma insulin-like growth factor I (IGF-I) at the time of 'puberty'. In order to determine the role of sex steroids in the development of diabetes-related kidney growth and IGF-I regulation, Sprague-Dawley rats were castrated at the age of 4 weeks and streptozotocin diabetes was induced at the age of 13 weeks. The development of renal enlargement and kidney IGF-I levels was studied over the following 7 days. Kidney weight in diabetic animals was significantly greater than in controls, and by day 7, had increased by 27% (1.20 +/- 0.03 vs 0.94 +/- 0.03 g, P less than 0.001). Kidney IGF-I content was significantly elevated in diabetic rats, peaking on day 1 (diabetic, 1159 +/- 302 ng/g vs control, 237 +/- 53 ng/g, P less than 0.001) and remaining higher than control levels throughout the 7 days of the experiment. The pattern of diabetes-related kidney growth and IGF-I regulation in castrated rats resembles that of age matched intact postpubertal controls, suggesting that sex steroids do not have a direct role in these phenomena.

Aging↗

PubMed1991

Insulin receptor sub-types in a human lymphoid-derived cell line (IM-9): differential regulation by insulin, dexamethasone and monensin.

The cells of the human IM-9 lymphocyte-derived line contain a subpopulation of insulin binding sites which differ from classical insulin binding sites in their higher binding affinity for insulin-like growth factor II (IGF-II) and insulin-like growth factor I (IGF-I). These atypical insulin binding sites are identified on IM-9 cells by [125I]IGF-II binding. To determine whether the atypical and classical insulin receptors of IM-9 cells were subject to different modes of in vivo regulation, we treated IM-9 cells with agents known to alter the surface expression of insulin receptors--insulin, dexamethasone and monensin. We then measured insulin and IGF-II binding to the surface of the washed cells. Pretreatment of IM-9 cells with 1 microM insulin for 20 h at 37 degrees C induced a 44-48% decrease in the number of high affinity insulin binding sites, but no change in the number of IGF-II binding sites. In contrast, the surface expression of both insulin and IGF-II binding sites (classical and atypical insulin receptors) increased 1.3 to 1.7-fold after treatment with dexamethasone (200 nM) and decreased 30 to 45% after monensin (1 microM). These results suggest that atypical and classical insulin receptors are differentially susceptible to down-regulation by insulin.

Binding, Competitive↗

PubMed1990

Insulin-like growth factor binding to the atypical insulin receptors of a human lymphoid-derived cell line (IM-9).

The cells of the IM-9 human lymphocyte-derived line contain a sub-population of insulin-binding sites whose immunological and hormone-binding characteristics closely resemble those of the atypical insulin-binding sites of human placenta. These binding sites, which have moderately high affinity for multiplication-stimulating activity [MSA, the rat homologue of insulin-like growth factor (IGF) II] and IGF-I, are identified on IM-9 cells by 125I-MSA binding. They account for approximately 30% of the total insulin-receptor population, and do not react with a monoclonal antibody to the type I IGF receptor (alpha IR-3). The relative concentrations of unlabelled insulin, MSA and IGF-I required to displace 50% of 125I-MSA from these binding sites (1:4.7:29 respectively) are maintained for cells, particulate membranes, Triton-solubilized membranes precipitated either by poly(ethylene glycol) or a polyclonal antibody (B-10) to the insulin receptor, and receptors purified by insulin affinity chromatography. Because the atypical insulin/MSA-binding sites outnumber the type I IGF receptors in IM-9 cells by approximately 10-fold, they also compete with the latter receptors for 125I-IGF-I binding. Thus 125I-IGF-I binding to IM-9 cells is inhibited by moderately low concentrations of insulin (relative potency ratios for insulin compared with IGF-I are approx. 1/14 to 1/4) and is partially displaced (65-80%) by alpha IR-3. When type I IGF receptors are blocked by alpha IR-3 or removed by B-10 immunoprecipitation or insulin affinity chromatography, the hormone-displacement patterns for 125I-IGF-I binding resemble those of the atypical insulin/MSA-binding sites.

Animals↗

PubMed1990

Neurochemical consequences following injection of the substance P analogue, DiMe-C7, into the rat ventral tegmental area.

The effect on forebrain catecholamine- and indoleamine-related neurochemical levels was investigated following stimulation of the rat ventral tegmental area with the substance P analogue, DiMe-C7. DiMe-C7 (6.0 micrograms) induced a marked hyperactivity in rats with maximal response between 15 and 30 min following the injection. Fifteen min following the DiMe-C7 injection levels of dopamine and/or its metabolites (3,4-dihydroxyphenylacetic acid, homovanillic acid) were significantly increased in the nucleus accumbens, amygdala, entorhinal cortex and striatum relative to vehicle-injected animals. Although the increase in dopamine metabolism in the nucleus accumbens is consistent with the behavioural hyperactivity, it is concluded that other forebrain nuclei may also be involved in the mediation of the hyperactivity response.

Animals↗

PubMed1990

Comparison of catheter surface morphologies.

The surface morphologies of different generic types of Foley catheter have been investigated using scanning electron microscopy (SEM). The characteristic features of each material are illustrated and it is shown that distinct differences exist between the inner and outer surfaces of latex-based catheters; these differences are attributed to the methods of manufacture. The possible relations between morphology and performance in situ are discussed.

Microscopy, Electron, Scanning↗

PubMed1990

Insulin-like growth factors and the developing and mature rat small intestine: receptors and biological actions.

To determine if insulin-like growth factor-I (IGF-I) or multiplication stimulating activity (MSA, rat IGF-II) might directly influence small intestinal epithelium, we studied the distribution of IGF binding sites during development of the rat intestine. Cell membranes from suckling rat mucosa bound 2-6 times as much 125I-IGF-I and 3-5 times as much 125I-MSA as did adult membranes. Isolated villus cells from suckling and adult rats specifically bound both IGFs. IGF-I binding tended to remain high during suckling, whereas MSA binding fell progressively from the early suckling period. Competitive displacement studies with insulin, IGF-I and MSA demonstrated the presence of type-I and type-II IGF receptors. In vitro autoradiography of 125I-IGF-I binding sites in adult and suckling rat jejunum showed highest binding in the submucosa with extensions up into the lamina propria. Immunocytochemical localization of type-II receptors showed highest density in villus epithelium and vessel walls. Administration of MSA by oral and IGF-I by oral and parenteral routes (1 microgram/day for 6 days) to suckling rats stimulated jejunal brush border enzymes, but not intestinal growth. Developmental changes in receptor density and effects on brush border enzymes suggest a specific role for IGFs in post-natal development of the rat intestine.

Animals↗

PubMed1990

Autocrine regulation of human tumor cell proliferation by insulin-like growth factor II: an in-vitro model.

We have shown that a pleomorphic cell line of abnormal human karyotype derived from a stomach carcinoma (LIM-1839) proliferates in serum-free medium, expresses insulin-like growth factor II (IGF-II) mRNA, and secretes IGF-II (up to 56 ng/ml in serum-free conditioned medium, as measured in a rat liver RRA. No detectable levels of IGF-I can be measured in serum-free conditioned medium by RIA. These cells also secrete IGF-binding proteins, detected by a charcoal adsorption assay. The release of IGF-II and IGF binding proteins into serum-free conditioned medium (1.7 pmol/10(6) cells.24 h and 0.8 pmol binding sites/10(6) cells.24 h for 3 days, respectively) is inhibited 80% by cycloheximide (10 micrograms/ml). The LIM-1839 cells have type I and type II IGF receptors, determined by affinity cross-linking and competition binding studies. These cells proliferated 1.6-fold over 4 days in serum-free medium, with fresh medium changes on days 0 and 2: their growth was inhibited 56% by 40 micrograms/ml Sm 1.2, a monoclonal antibody which recognizes IGF-I and IGF-II. The addition of 20 and 50 ng/ml multiplication stimulating activity (rat IGF-II) caused 1.8- and 1.7-fold increases in cell growth between days 0 and 4 compared to controls, while [Thr59]IGF-I, at 20 and 50 ng/ml, caused 1.6- and 2.0-fold increases. Insulin, at 2 and 10 micrograms/ml, had no significant effect. The stimulatory effects of endogenous and exogenous IGFs on LIM-1839 cell proliferation were inhibited by a monoclonal antibody to the type I IGF receptor, alpha IR-3. These results suggest that the LIM-1839 cells are biologically responsive to endogenously produced IGF-II, and may thereby provide an in vitro model for autocrine regulation of human tumor growth by IGF-II.

Antibodies, Monoclonal↗

PubMed1990

Comparison of structure, mechanical properties, and functions of lumbar spinal ligaments.

The organization of collagen in the supraspinous, interspinous, and longitudinal ligaments, as well as the ligamenta flava, in lumbar spines from human cadavers has been investigated by polarized light microscopy, scanning electron microscopy, and x-ray diffraction. These experiments were performed on ligaments in situ, with their bony attachments undisturbed, and on excised ligaments at a range of applied strains. Results were related to the composition (investigated by standard histologic techniques) and gross structures (investigated by light microscopy) of the ligaments. More importantly, the results were related to the mechanical properties of the ligaments, which include stiffness, failure conditions, stress relaxation, and hysteresis. Where necessary, results were supplemented by or compared with those obtained from pig ligaments. Mechanical properties were related to postural changes by ligament strains induced in cadaveric specimens, using results from the literature. Thus, ligament structures could be related to their physiologic functions.

Biomechanical Phenomena↗