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Biomedical subjects

J R Wright

Publications and source records attributed to J R Wright.

At least 55 records · Page 3Linked to original sources
PubMed2000

Metabolism of phosphatidylglycerol by alveolar macrophages in vitro.

In whole animal studies, it has been shown that turnover of surfactant dipalmitoylphosphatidylglycerol (DPPG) is faster than that of dipalmitoylphosphatidylcholine (DPPC). The goal of this investigation was to characterize the metabolism of DPPG by alveolar macrophages and to determine whether they contribute to the faster alveolar clearance of DPPG. Isolated rat alveolar macrophages were incubated with liposomes colabeled with [(3)H]DPPG and [(14)C]DPPC. Macrophages internalized both lipids in a time- and temperature-dependent manner. The uptake of both lipids was increased by surfactant protein (SP) A and by adherence of the macrophages to plastic slides. The isotope ratio of DPPC to DPPG internalized by macrophages in suspension in the absence of SP-A was significantly lower than the isotope ratio in liposomes, suggesting that macrophages preferentially internalize DPPG when SP-A is absent. Phospholipase activity in macrophage homogenate was higher toward sn-2-labeled DPPG than toward sn-2-labeled DPPC. These studies show that alveolar macrophages play an important role in catabolizing surfactant lipids and may be partially responsible for the relatively faster clearance of DPPG from the lung.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2000

Complement-mediated host defense in the lung.

Complement is a system of plasma proteins that aids in the elimination of pathogens from the body. We hypothesized that there is a functional complement system present in the lung that aids in the removal of pathogens. Western blot analysis revealed complement proteins of the alternative and classical pathways of complement in bronchoalveolar lavage fluids (BALF) from healthy volunteers. Functional classical pathway activity was detected in human BALF, but there was no significant alternative pathway activity in lavage fluid, a finding that correlates with the low level of the alternative pathway protein, factor B, in these samples. Although the classical pathway of complement was functional in lavage fluid, the level of the classical pathway activator C1q was very low. We tested the ability of the lung- specific surfactant proteins, surfactant protein A (SP-A) and surfactant protein D (SP-D), to substitute for C1q in classical pathway activation, since they have structural homology to C1q. However, neither SP-A nor SP-D restored classical pathway activity to C1q-depleted serum. These data suggest that the classical pathway of complement is functionally active in the lung where it may play a role in the recognition and clearance of bacteria.

Adult↗
PubMed2000

Effects of systemic arterial blood pressure on the contractile force of a human hand muscle.

The effect of physiological changes in systemic blood pressure on the force output of working abductor pollicis (AP) muscle was studied in six normal subjects. Supramaximal tetanic stimulation at the ulnar nerve produced repeated isometric contractions at 1-s intervals. Force output declined gradually with time. During the train of contractions, subjects voluntarily contracted the knee extensors for 1 min; this raised systemic blood pressure by 29%. Force output from AP rose in parallel with blood pressure so that 18% of the contraction force lost through fatigue was recovered for each 10% increase in blood pressure. When blood pressure in the hand was kept constant despite the increased systemic pressure, force output did not rise. The results show that muscle performance is strongly affected by physiological changes in central blood pressure and suggest that sensory input concerning the adequacy of muscle performance exerts a feedback control over the increase in systemic blood pressure during muscular activity.

Adult↗
PubMed2000

Surfactant protein A differentially regulates IFN-gamma- and LPS-induced nitrite production by rat alveolar macrophages.

Although several studies have demonstrated that the pulmonary collectins surfactant protein (SP)-A and SP-D contribute to innate immunity by enhancing pathogen phagocytosis, the role of SP-A and SP-D in regulating production of free radicals and cytokines is controversial. We hypothesized that the state and mechanism of activation of the immune cell influence its response to SP-A. The effects of SP-A and SP-D on production of nitric oxide (NO) and inducible nitric oxide synthase (iNOS) were assessed in isolated rat alveolar macrophages activated with lipopolysaccharide (LPS), interferon gamma (IFN-gamma), or both agonists. SP-A inhibited production of NO and iNOS in macrophages stimulated with smooth LPS, which did not significantly bind SP-A, or rough LPS, which avidly bound SP-A. In contrast, SP-A enhanced production of NO and iNOS in cells stimulated with IFN-gamma or INF-gamma plus LPS. Neither SP-A nor SP-D affected baseline NO production, and SP-D did not significantly affect production of NO in cells stimulated with either LPS or IFN-gamma. These results suggest that SP-A contributes to the lung inflammatory response by exerting differential effects on the responses of immune cells, depending on their state and mechanism of activation.

Animals↗
PubMed2000

Herd and state means for somatic cell count from dairy herd improvement.

To determine the impact of reducing the current legal limit of 750,000 cells/ml for somatic cell count (SCC) in US market milk, data were examined from 539,577 herd test days for Dairy Herd Improvement herds on test during 1996 and 1997. Somatic cell scores for individual cows were converted to SCC. The SCC for each cow was weighted by milk yield and used to compute herd mean on test day. The mean for each state was derived by weighting herd test-day SCC by herd test-day milk yield. State means were lowest in the West and highest in the Southeast. The percentage of herd test days with an SCC of >750,000 cells/ml ranged from 0 to 14% across states; the mean was 4%. Only 1% of the herd tests were >750,000 cells/ml on 2 consecutive test days. Mean SCC in the United States was 307,100 cells/ml for 1996 and 313,500 cells/ml for 1997. Mean SCC was lower during October through January (280,000 to 300,000 cells/ml) than during July and August (340,000 cells/ml). Herd size and SCC were negatively related; larger herds had lower SCC. Because records of some cows treated with antibiotics were included in the data, herd SCC means likely were higher than corresponding bulk tank SCC. Most herds had test-day SCC that were substantially below legal bulk tank limits and could have met lower limits (e.g., 500,000 cells/ml).

Animals↗
PubMed2000

Efficacy of ultraviolet light for reducing Escherichia coli O157:H7 in unpasteurized apple cider.

This study examined the efficacy of UV light for reducing Escherichia coli O157:H7 in unpasteurized cider. Cider containing a mixture of acid-resistant E. coli O157:H7 (6.3 log CFU/ml) was treated using a thin-film UV disinfection unit at 254 nm. Dosages ranged from 9,402 to 61,005 microW-s/cm2. Treatment significantly reduced E. coli O157:H7 (P < or = 0.0001). Mean reduction for all treated samples was 3.81 log CFU/ml. Reduction was also affected by the level of background microflora in cider. Results indicate that UV light is effective for reducing this pathogen in cider. However, with the dosages used in this experiment, additional reduction measures are necessary to achieve the required 5-log reduction.

Beverages↗
PubMed1999

Co-encapsulation of Sertoli enriched testicular cell fractions further prolongs fish-to-mouse islet xenograft survival.

BACKGROUND: We previously demonstrated that alginate microencapsulation can prolong fish (tilapia) islet xenograft survival in diabetic animals. However, at present, microencapsulation does not provide complete immune protection to discordant islet xenografts, and long-term graft survival requires supplemental low-dose systemic immunosuppression. In the present study, fish islets were co-encapsulated with Sertoli enriched testicular cell fractions to find out whether this would further prolong fish islet graft survival in diabetic mice. METHODS: Sertoli enriched testicular cell fractions were enzymatically harvested from adult Balb/c or Wistar-Furth rats. They were cultured and co-encapsulated with fragmented tilapia islets in alginate microcapsules. Encapsulated islets alone or islets co-encapsulated with Sertoli cells were then intraperitoneally transplanted into streptozotocin-diabetic Balb/c mice, and graft survival times were compared. Encapsulated and co-encapsulated islet function was also confirmed in streptozotocin-diabetic athymic nude mice. RESULTS: Co-encapsulation with Sertoli enriched testicular cell fractions further prolonged mean fish islet graft survival time from 21+/-6.7 days (encapsulated islet cells alone) to >46+/-6.3 days (co-encapsulated with syngeneic murine Sertoli cells), without additional systemic immunosuppression. Testicular cells harvested from xenogeneic Wistar-Furth rats produced similar protective results (>46+/-10.9 days). CONCLUSIONS: Our results support the theory that Sertoli cells produce local immunosuppressive factors. These factors supplement the immune protective feature of alginate microcapsules in our model. Testicular cell fractions may be an important naturally occurring facilitator in the development of new microencapsulation systems for islet xenotransplantation.

Animals↗
PubMed1999

Pulsed microwave induced light, sound, and electrical discharge enhanced by a biopolymer.

Intense flashes of light were observed in sodium bicarbonate and hydrogen peroxide solutions when they were exposed to pulsed microwave radiation, and the response was greatly enhanced by a microwave-absorbing, biosynthesized polymer, diazoluminomelanin. A FPS-7B radar transmitter, operating at 1.25 GHz provided pulses of 5.73 +/- 0.09 micros in duration at 10.00 +/- 0.03 pulses/s with 2.07 +/- 0.08 MW forward power (mean +/- standard deviation), induced the effect but only when the appropriate chemical interaction was present. This phenomenon involves acoustic wave generation, bubble formation, pulsed luminescence, ionized gas ejection, and electrical discharge. The use of pulsed microwave radiation to generate highly focused energy deposition opens up the possibility of a variety of biomedical applications, including targeting killing of microbes or eukaryotic cells. The full range of microwave intensities and frequencies that induce these effects has yet to be explored and, therefore, the health and safety implications of generating the phenomena in living tissues remain an open question.

Absorption↗
PubMed1999

Immunocytochemical characterization of the pancreatic islet cells of the Nile Tilapia (Oreochromis niloticus).

The cellular composition and topography of the pancreatic islet of Oreochromis niloticus, now known to be a donor source for islet xenotransplantation studies, were characterized. Whole tilapia islets were harvested using an enzymatic method and then further digested into single-cell preparations. Cell cytospin preparations of islet cells and paraffin sections of whole islets were stained using antisera against tilapia insulin, human glucagon, salmon somatostatin-25 (SST-25), human somatostatin-14 (SST-14), and salmon peptide tyrosine-tyrosine (PYY) using the immunoperoxidase method. Cell counts, performed on cytospin preparations using a Quantimet 570 computerized image analysis system, revealed that O. niloticus islets contained 78% endocrine cells and 22% immunonegative cells (i. e., mainly nucleated erythrocytes and rare tissue eosinophils). The proportions of immunopositive endocrine cell types were: 42.3% insulin immunopositive cells, 11.5% glucagon immunopositive cells, 23.1% SST-25 immunopositive cells, 21.8% SST-14 immunopositive cells, and 1.3% PYY immunopositive cells. Islet cell topography was evaluated using histologic sections of whole endocrine pancreata including large, medium, and small islets. Round to polygonal insulin immunopositive cells with round central nuclei were distributed in clusters throughout both the principal and the smaller islets. Elongate SST-14 immunopositive cells were closely associated with the clusters of insulin immunopositive cells; both were surrounded by SST-25 immunopositive cells, which were similar in shape to the insulin immunopositive cells. There were elongate glucagon immunopositive cells throughout the islets, whereas the PYY immunopositive cells were restricted to the periphery and to channels of fibrovascular connective tissue penetrating the islets.

Animals↗
PubMed1999

Streptozotocin dose-response curve in tilapia, a glucose-responsive teleost fish.

Streptozotocin (STZ) causes beta cell necrosis and insulin-dependent diabetes in many species. The specificity of this beta cell toxin relates to its structure as an alkylating agent with an attached glucose moiety. STZ uptake by rodent beta cells appears to be via the GLUT-2 glucose transporter. Teleost fish, in general, are severely glucose intolerant. The effects of STZ were examined in tilapia, a teleost fish with highly glucose-responsive islets. Fasted tilapia were given 0, 100, 150, 200, 250, 300, or 350 mg/kg STZ iv. Plasma glucose levels were followed for 72 h and the fish autopsied. Histological sections of islets were stained by immunoperoxidase for tilapia insulin. Severe hyperglycemia was seen in 20, 80, and 100% of fish receiving 250, 300, and 350 mg/kg doses; however, sections of islets showed only partial degranulation with no evidence of beta cell necrosis. Another group of fish receiving the highest dose were followed longer to determine whether beta cell necrosis and permanent hyperglycemia ensued. All fish died or were killed within 9 days because of severe hepatic failure characterized by hepatic necrosis, jaundice, and ascites; islet morphology was relatively normal suggesting, even in a glucose-sensitive species, that fish islets either do not take up STZ or are highly resistant to its "diabetogenic" effects. Tilapia may thus be a useful model to elucidate mechanisms of action of STZ. Furthermore, STZ may provide important insights into differences in glucose uptake and metabolism by mammalian and piscine beta cells.

Animals↗
PubMed1999

Heterotopic cardiac xenotransplantation: fish-to-rat.

The purpose of this study was to determine whether a vascularized organ transplanted from a teleost fish to a rodent would be hyperacutely rejected. Previous reports describing the results of discordant xenotransplantation are almost exclusively across orders within the class Mammalia. We chose a species combination that crosses many phylogenetic barriers (i.e. species, genus, family, order, and class) as well as several hundred million years on an evolutionary timescale. Because no published methodology existed, we developed a microvascular surgical method for fish (tilapia)-to-rat heterotopic cardiac xenotransplantation. To minimize the blood pressure to which the graft would be exposed, the tilapia heart was placed on the venous side of the rat circulation between the left kidney and the inferior vena cava by end-to-side anastomoses of the donor aorta to the recipient inferior vena cava and by end-to-end anastomosis of the donor sinus venosus to the recipient left renal vein. Tilapia hearts were rejected hyperacutely, based on both routine histopathological examination and immunofluorescent staining for immunoglobulin and complement, but rejection required hours rather than minutes.

Animals↗
PubMed1999

Regulation of protein phosphorylation and pathogen phagocytosis by surfactant protein A.

Surfactant protein A (SP-A), a pulmonary member of the collectin family of proteins, facilitates the rapid clearance of pathogens by upregulating immune cell functions in the lungs. SP-A binds to bacteria and targets them for rapid phagocytosis by alveolar macrophages, but the mechanism by which this stimulation occurs is not clear. To characterize the intracellular events that may be involved, we examined the roles of protein phosphorylation and cytoskeletal polymerization in SP-A-stimulated phagocytosis. In rat alveolar macrophages, SP-A stimulated rapid tyrosine phosphorylation of specific proteins in a dose- and time-dependent manner. The pattern of proteins that were phosphorylated in response to SP-A, as resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, was similar to that observed for immunoglobulin G (IgG)-stimulated macrophages. Both SP-A and IgG stimulated increases in phagocytosis of Streptococcus pneumoniae above levels in the absence of added protein by 394% +/- 81% and 200% +/- 25%, respectively. Phagocytosis in both cases was dependent on tyrosine kinases, protein kinase C, and actin polymerization but not on microtubule activity. These studies show that SP-A utilizes pathways similar to those used by IgG to increase macrophage phagocytosis of bacteria.

Animals↗
PubMed1999

Surfactant proteins A and D specifically stimulate directed actin-based responses in alveolar macrophages.

Surfactant protein (SP) A and SP-D are the pulmonary members of the collectin family, structurally related proteins involved in innate immune responses. Here, we have examined the abilities of SP-A, SP-D, mannose-binding protein (MBP), and the complement component C1q to stimulate actin-based cellular functions in rat alveolar macrophages and peripheral blood monocytes. Our goal in this study was to examine the cell specificity of the effects of the collectins to understand further the mechanisms by which SP-A and SP-D stimulate alveolar macrophages. We found that SP-A and SP-D have lung cell-specific effects at physiologically relevant concentrations; they stimulate directional actin polymerization and chemotaxis in alveolar macrophages but not in monocytes. Although C1q and MBP weakly stimulate the rearrangement of actin in both cell types, C1q is chemotactic only for peripheral blood monocytes and MBP does not stimulate chemotaxis of either cell type. Neither C1q nor MBP stimulates actin polymerization in alveolar macrophages. These results support the hypothesis that alveolar macrophages express receptors specific for the pulmonary collectins SP-A and SP-D and provide insight into the potential roles of collectins in the recruitment and maturation of mononuclear phagocytes in the lung.

Actins↗
PubMed1999

Surfactant protein A enhances the binding and deacylation of E. coli LPS by alveolar macrophages.

Surfactant protein (SP) A and SP-D are involved in multiple immunomodulatory functions of innate host defense partly via their interaction with alveolar macrophages (AMs). In addition, both SP-A and SP-D bind to bacterial lipopolysaccharide (LPS). To investigate the functional significance of this interaction, we first tested the ability of SP-A and SP-D to enhance the binding of tritium-labeled Escherichia coli LPS to AMs. In contrast to SP-D, SP-A enhanced the binding of LPS by AMs in a time-, temperature-, and concentration-dependent manner. Coincubation with surfactant-like lipids did not affect the SP-A-mediated enhancement of LPS binding. At SP-A-to-LPS molar ratios of 1:2-1:3, the LPS binding by AMs reached 270% of control values. Second, we investigated the role of SP-A in regulating the degradation of LPS by AMs. In the presence of SP-A, deacylation of LPS by AMs increased by approximately 2.3-fold. Pretreatment of AMs with phosphatidylinositol-specific phospholipase C had no effect on the SP-A-enhanced LPS binding but did reduce the amount of serum-enhanced LPS binding by 50%, suggesting that a cell surface molecule distinct from CD14 mediates the effect of SP-A. Together the results for the first time provide direct evidence that SP-A enhances LPS binding and degradation by AMs.

Acylation↗
PubMed1999

Effects of endotoxin on surfactant protein A and D stimulation of NO production by alveolar macrophages.

Surfactant protein (SP) A and SP-D affect numerous functions of immune cells including enhancing phagocytosis of bacteria and production of reactive species. Previous studies have shown that SP-A and SP-D bind to a variety of bacteria and to the lipopolysaccharide (LPS) components of their cell walls. In addition, purified preparations of SPs often contain endotoxin. The goals of this study were 1) to evaluate the effects of SP-A and SP-D and complexes of SPs and LPS on the production of nitric oxide metabolites by rat alveolar macrophages and 2) to evaluate methods for the removal of endotoxin with optimal recovery of SP. Incubation of SP-A or SP-D with polymyxin, 100 mM N-octyl-beta-D-glucopyranoside, and 2 mM EDTA followed by dialysis was the most effective method of those tested for reducing endotoxin levels. Commonly used storage buffers for SP-D, but not for SP-A, inhibited the detection of endotoxin. There was a correlation between the endotoxin content of the SP-A and SP-D preparations and their ability to stimulate production of nitrite by alveolar macrophages. SP-A and SP-D treated as described above to remove endotoxin did not stimulate nitrite production. These studies suggest that the functions of SP-A and SP-D are affected by endotoxin and illustrate the importance of monitoring SP preparations for endotoxin contamination.

Animals↗