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Biomedical subjects

H Yang

Publications and source records attributed to H Yang.

At least 1,063 records · Page 59Linked to original sources

In vitro culture and transplantation of encapsulated human fetal islets as an artificial endocrine pancreas.

There has been increasing evidence indicating that islet transplantation may offer an ideal endocrine replacement therapy for patients with Type I diabetes mellitus. However, allogenic islets are susceptible to immune rejection. In 1980, Lim and Sun first reported a novel technique of microencapsulation by which pancreatic islets used as transplants could be encapsulated and immunoisolated so as to survive and function for a period of 2-3 weeks. By further improving the biocompatibility of the capsular membrane, Sun's group demonstrated that islet allografts can be protected from rejection for up to 21 months in nonimmunosuppressed, streptozotocin-induced diabetic rats. The biocompatible polymer capsule membrane constitutes a physical barrier to the host's immune system. Permeability of the membrane can be controlled to allow free diffusion of small molecular nutrients, hormones, and metabolites, but exclude lymphocytes, leukocytes, and macromolecular immunoglobulins and complement. Darquy and Reach, in 1985, disclosed the role of the microcapsule membrane in protecting islets from cytotoxic antibodies. Sun's group further demonstrated that the microencapsulation technique effectively protected xenografts of rat islets transplanted into diabetic mice. In a previous report, we described the success of allotransplanted microencapsulated rat islets in treating streptozotocin-induced diabetes in Wistar rats. We now report the in vitro study of human fetal islets microencapsulated within an alginate-polylysine membrane. A preliminary clinical trial of allotransplants for the treatment of insulin-dependent diabetics is also presented.

Adult↗

Routine assessment of viability in split-thickness skin.

Effective quality control of allograft skin that is cryopreserved for transplantation requires a simple, reproducible technique for the assessment of cell viability. Tetrazolium reduction assays and an oxygen consumption technique have been the two methods of choice to determine the metabolic function of allograft skin after it has been thawed. In this study, we investigated the use of a novel tetrazolium salt, WST-1 (4-[3-(4-iodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzen e disulfonate), that is cleaved to a water-soluble formazan product. Porcine split-thickness skin in minimal essential medium without cryoprotectant was subjected to a graded freezing protocol to generate progressive amounts of cryoinjury. Recovery as determined with WST-1 was compared with measurements made with the use of the oxygen consumption technique. The similarity of the resulting recovery curves indicates that WST-1 is a simple, effective, and convenient technique for the assessment of metabolic function in porcine split-thickness skin. The WST-1 assay is applicable for the routine assessment of tissue viability in cryopreserved allograft skin.

Animals↗

Additional evidence of linkage between Crohn's disease and a putative locus on chromosome 12.

PURPOSE: The inflammatory bowel diseases (IBD), Crohn's disease (CD), and ulcerative colitis (UC) are chronic intestinal disorder of unknown etiology. Genetic factors play an important role in the pathogenesis of these diseases, but with a complex pattern of inheritance. A number of genome-wide scans have identified several putative susceptibility loci for both CD and UC, including a locus on chromosome 12 reported in a set of British families. We aim to evaluate the linkage between CD or UC and this chromosome 12 locus in an independent set of U.S. Caucasian families (36% being of Ashkenazi Jewish origin). METHODS: Microsatellite markers along chromosome 12 spaced at approximately 10 cm intervals were used to test the putative loci in CD only families (65 sib pairs from 46 families). Regions with positive linkage for CD were then tested in a panel of UC and mixed families (44 sib pairs from 29 families). Two point linkage analysis was performed with SIBPAL. Multipoint linkage analysis was carried out with MAPMAKER/SIBS. RESULTS: We observed evidence of linkage between the region on chromosome 12 and Crohn's disease, because there was a significant excess of allele sharing in CD sib pairs (pi = 0.62, p = 0.0004 from two-point linkage; and logarithm of the odds score (LOD) = 2.0 from multipoint linkage). However, we did not observe the same linkage in UC and mixed families (p = 0.48; not significant [ns]). CONCLUSION: Our data provided further evidence that the region on chromosome 12 is likely to contain a gene predisposing to CD.

Adolescent↗

Modifier locus for mitochondrial DNA disease: linkage and linkage disequilibrium mapping of a nuclear modifier gene for maternally inherited deafness.

PURPOSE: To examine the role of the nuclear genome in affecting the phenotypic expression of the simplest model of a mitochondrial DNA disease, maternally transmitted deafness. METHODS: Linkage analysis in families with maternally inherited deafness associated with the homoplasmic A1555G mutation. RESULTS: Significant linkage and linkage disequilibrium on chromosome 8 was identified. CONCLUSIONS: This finding represents the first identification of a modifier locus for a human mitochondrial DNA disease and supports the concept of mitochondrial DNA diseases having complex genetic inheritance. The eventual identification of this modifier gene will provide insights into the pathophysiological pathways determining the clinical expression of mitochondrial DNA diseases, an important step toward diagnostic and therapeutic interventions.

Cell Nucleus↗

Indicators nurses employ in deciding to test for hyperbilirubinemia.

OBJECTIVE: To identify the indicators nurses employ in deciding to test healthy full-term newborns for total serum bilirubin in the absence of a written protocol. DESIGN: Secondary analysis of data available on 130 mother-newborn pairs and informal interviews of 30 postpartum unit nurses. SETTING: Two university teaching hospitals. PARTICIPANTS: All tested newborns and a 33% random sample of remaining newborns from a control group data set created during a previous study and a convenience sample of postpartum nurses from all shifts. MEASUREMENT: Outcome data were obtained from a review of records. Background data were obtained from a review of records and questionnaires. Nurse data were obtained through a modified form of participant observation. RESULTS: Ninety-one percent of newborns tested for bilirubin were tested unnecessarily. In logistic regression analyses, variables predictive of nurse-driven total serum bilirubin testing were presence of jaundice, odds ratio (OR) = 31.95 (95% confidence interval, 6.71, 152.03), and feeding frequency, OR = 0.28 (0.11, 0.72). Identifying both presence and location of jaundice simultaneously did not significantly predict testing, OR = 1.82 (0.66, 5.04). Fifty-three percent of nurses who were interviewed identified both the presence of jaundice and feeding as indicators to consider for testing. CONCLUSION: Newborns are overtested for bilirubin. Indicators used by nurses in deciding to test a healthy newborn for total serum bilirubin are the presence of jaundice and feeding frequency. Nurses who assess feeding frequency are less likely to order bilirubin testing.

Attitude of Health Personnel↗

Plasticity of GAP-43 innervation of the spleen during immune response in the mouse. Evidence for axonal sprouting and redistribution of the nerve fibers.

The amount and distribution of growth-associated protein (GAP-43)-like immunoreactive nerve fibers in the spleen of normal and immunized BALB/c mice were studied using immunohistochemical methods. A significant increase in the amount, as well as redistribution and morphological changes, of the GAP-43-like immunoreactive nerve fibers occurred in PPD (purified protein derivative from tuberculin) immunized animals. In the control animals, the GAP-43-like immunoreactive nerve fibers were found mainly distributed in association with vascular plexuses, with minor extension into the parenchyma of the inner zone of the periarterial lymph sheath. In the immunized animals, in addition to denser vascular plexuses, more fibers appeared in the outer zone of the periarterial lymph sheath, the marginal zone, and the red pulp, all known to be the sites where immune responding lymphocytes are located. Furthermore, the nerve fibers tended to have more branches and bear richer varicosities. The results suggest that active nerve remolding takes place in the spleen during immune response, which may serve as a mechanism through which the nervous system regulates immune responses.

Animals↗

Evidence for hypothalamic paraventricular nucleus as an integrative center of neuroimmunomodulation.

It has been well documented that the medial parvocellular subnucleus of the hypothalamic paraventricular nucleus (PVN) participates in immune regulation by releasing corticotrophin-releasing hormone (CRH), which triggers the hypothalamus-pituitary-adrenal axis, leading to immunosuppression. Little is known about other possible influences of PVN on immunomodulation. Evidence, however, has been accumulating recently, indicating possible involvement of other subnuclei of this nucleus. By using the c-fos technique, the present study investigated the neuronal groups of the PVN that were activated in response to intracerebroventricularly administered IL-1 beta. In addition to strong Fos expression in the dorsal part of medial parvocellular subnucleus of the PVN, where CRH neurons are located, two more neuronal groups were found to express Fos protein. One of which was the oxytocin-immunoreactive magnocellular neurons, mainly concentrated in the anterior and medial magnocellular subnuclei of the PVN. The magnocellular PVN subnuclei are known to project to, and release their hormones, in the posterior pituitary. Another group of Fos-immunoreactive neurons were found in the brainstem and spinal cord projecting area of the PVN. By combining retrograde tracing technique and Fos immunohistochemistry, it was proved that many of the spinal cord projecting PVN neurons were activated following IL-1 beta administration, through which the spinal cord sympathetic outflow might be regulated. The present study indicates that the hypothalamic PVN may serve as an integrative center for immunomodulation via three channels, i.e., the CRH and oxytocin neuroendocrinological and the PVN-spinal cord sympathetic neural channels.

Animals↗

Does P-glycoprotein play a pivotal role in the drug resistance of an MDR variant, K562/Dox?

A multidrug-resistant (MDR) variant, K562/Dox, was selected from repeated exposure of human erythroleukemia cell line K562 to doxorubicin (Dox). K562/Dox displayed typical MDR features with respect to its cross-resistance to a variety of functionally and structurally unrelated compounds: vincristine (Vin), Dox, mitomycin C, reduced steady-state intracellular anthracycline accumulation, and elevated P-glycoprotein expression/mdr1 mRNA transcription/mdr1 gene amplification. Nevertheless, by incubation of cells with Dox/epirubicin (Epi)/daunorubicin (Dau) (5-80 micrograms/ml), the initial drug uptake was similar (p > 0.05) in K562/Dox and K562 cells, suggesting P-glycoprotein-mediated drug efflux would not occur unless a relatively high cellular drug concentration was reached. After 8 h incubation of cells with 50 ng/ml Dox (5 times higher than its IC50 to K562 cells), there were only slight differences (p > 0.05) in intracellular drug levels between K562/Dox and K562 cells, clearly indicating that K562/Dox, circumventing drug toxicity in this case, was irrelevant to reduced drug accumulation caused by P-glycoprotein. Similar results were obtained when Epi or Dau was applied. Despite complete restoration of anthracycline accumulation in K562/Dox cells in the presence of 6 mumol/l verapamil, the reversal of their drug resistance was incomplete. These results suggest that P-glycoprotein-mediated drug efflux possibly did not play a primary role in the drug resistance of K562/Dox cells.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

Tissue manganese concentrations and antioxidant enzyme activities in rats given total parenteral nutrition with and without supplemental manganese.

BACKGROUND: Manganese is an essential but potentially toxic mineral. Parenteral administration of manganese via total parenteral nutrition (TPN) bypasses homeostatic mechanisms (intestinal absorption and presystemic hepatic elimination). Our objective in this study was to determine the effect of supplemental manganese in TPN solutions on manganese status in a rat model. METHODS: Male Sprague-Dawley rats underwent jugular catheterization and were given 61.0 +/- 0.4 g/d TPN solution providing 0.5 +/- 0.2 nmol manganese/g (Mn-; n = 6) or 16 +/- 3 nmol manganese/g (Mn+; n = 7) for 7 days. Reference rats (RF; n = 8) were fed a purified diet containing 1.3 mmol manganese/g. RESULTS: Liver manganese decreased in both TPN groups, but tibia, spleen, and pancreas manganese concentrations were greater in Mn+ rats than in Mn- or RF rats. Although no treatment differences were seen in heart or liver manganese superoxide dismutase activity, heart copper-zinc superoxide dismutase activity was lower in the Mn+ rats than in Mn- or RF rats (p < .05). Glutathione peroxidase activity was depressed in livers of both Mn- and Mn+ rats relative to RF rats (p < .0001), which was not due to selenium deficiency. CONCLUSIONS: Supplemental parenteral manganese is taken up to a greater extent by peripheral tissues than the liver. In this first report of antioxidant enzyme activities in animals maintained with TPN, we found that TPN as well as supplemental manganese can influence antioxidant enzyme activities. We conclude that it is generally unnecessary and potentially toxic to supplement TPN solutions with manganese during short-term usage.

Animals↗

Insulin-like growth factor-I enhances immune response in dexamethasone-treated or surgically stressed rats maintained with total parenteral nutrition.

BACKGROUND: New evidence suggests that insulin-like growth factor-I (IGF-I) is an important regulator of immune response. Our objective was to determine the effects of IGF-I on immune response during total parenteral nutrition (TPN) using two stress models. METHODS: Male, Sprague-Dawley rats (230 to 250 g) were given TPN with or without coinfusion of recombinant human IGF-I (800 micrograms/d for 6 days) and subjected to either dexamethasone, a synthetic glucocorticoid, or surgical stress, in the form of a midline abdominal incision. In the dexamethasone model, immune response was assessed by total cellularity of the thymus and spleen, in vitro assays of lymphocyte proliferation, and interleukin 6 (IL-6) production, and concentrations of IL-6 and tumor necrosis factor alpha (TNF-alpha) in serum. In the surgical model, flow cytometry was used to identify and quantify splenic populations of T and B lymphocytes and macrophages. RESULTS: In rats immunosuppressed by dexamethasone, IGF-I infusion increased mitogen-induced proliferation of thymocytes, but did not alter cellularity in the thymus; enhanced proliferation and IL-6 production in peripheral blood mononuclear cells following treatment with concanavalin A or lipopolysaccharide; and reduced the serum concentration of IL-6, but not TNF-alpha. In surgically stressed rats, IGF-I infusion restored the splenic populations of immature and mature B lymphocytes, which were decreased by TPN. CONCLUSIONS: our data demonstrate that IGF-1 enhances immune response during TPN in rats.

Animals↗

Insulin-like growth factor-I but not growth hormone attenuates dexamethasone-induced catabolism in parenterally fed rats.

BACKGROUND: We demonstrated that recombinant human insulin-like growth factor-I (rhIGF-I) or growth hormone (rhGH) produces identical body weight gain during total parenteral nutrition (TPN) in surgically-stressed rats. Our current objective was to evaluate the relative anabolic and metabolic effects associated with administration of rhIGF-I and/or rhGH during hypocaloric TPN in rats with dexamethasone (DEX)-induced catabolism. METHODS: Male Sprague-Dawley rats (approximately 270 g) given TPN and DEX were treated with IGF-I and/or GH for 6 days. Two control groups, TPN and DEX, were included. Anabolic response was assessed by change in body protein content and nitrogen balance. Metabolic response was assessed by determination of serum concentrations of IGF-I, IGF binding proteins (IGFBPs), insulin, glucose, triacylglycerol, glycerol, and free fatty acids. RESULTS: Compared with GH, IGF-I attenuated DEX-induced loss of body protein and decreased serum concentrations of glucose, free fatty acids, glycerol, and triglycerol. Treatment with IGF-I plus GH showed an anabolic response similar to IGF-I alone. IGF-I and/or GH increased serum concentrations of IGF-I and IGFBP-3. IGF-I alone increased serum level of IGFBP-5. CONCLUSION: Administration of IGF-I, but not GH, attenuates DEX-induced protein catabolism in association with increased insulin sensitivity in rats. Glucocorticoid excess may limit the response to GH therapy during TPN.

Analysis of Variance↗

Whole-protein-based enteral formula stimulates intestinal ornithine decarboxylase activity more than single amino acids but does not affect mucosal adenosine triphosphate content in early postsurgical refeeding.

BACKGROUND: To restore intestinal integrity after starvation and trauma, luminal nutrients are essential. Specific nutrients such as glutamine support mucosal proliferation and energy metabolism. The aim of this study was to compare effects of enteral formula vs specific amino acids on ornithine decarboxylase (ODC) activity and adenine nucleotide metabolism in jejunal mucosa. METHODS: Male Wistar rats (240 to 280 g) were starved for 48 hours and subjected to intestinal transection, gastrotomy, and jejunal instillation of 5mL nutrient solution. In the first experiment, standard enteral formula (EF) was compared with isonitrogenous formula supplemented with the glutamine precursor, alpha-ketoglutarate (alpha-KG). In a second experiment, 2% glutamine was compared with isonitrogenous ornithine alpha-KG, arginine alpha-KG, glycine and diluted standard enteral formula (EF), or saline. The ODC activity, adenosine triphosphates (ATP), and RNA and protein in the jejunal mucosa were analyzed 2 hours after surgery. RESULTS: The ODC peak in jejunal mucosa in animals treated with EF was higher than when supplemented with alpha-KG (p < .05). Compared with specific amino compounds, EF resulted in a significantly higher ODC peak and no differences were seen between the different specific amino acids. Differences seen in ATP or energy charge between the groups were not significant. CONCLUSIONS: Immediate postoperative enteral feeding by standard EF results in rapid increase of ODC activity. This response was attenuated when the enteral nutrition was supplemented with alpha-KG and was absent when isonitrogenous single amino acids were administered. We found no significant effects on ATP content in the small bowel mucosa by supplementing the diet with alpha-KG.

Adenosine Triphosphate↗

Recyclable islet isografts: a biological insulin pump to facilitate surgery in diabetic rats.

A method is described to facilitate extensive abdominal surgery in diabetic rats using temporary renal subcapsular islet isografts. The procedure is performed in three stages--each separated by 2 wk. After each rat is made diabetic (Step 1), an isogenic islet transplant is performed beneath the left renal capsule (Step 2). Step 3 is the operative procedure, followed by a left nephrectomy. Finally, it is shown how the islet isograft can be excised from the nephrectomy specimen and "recycled" into another diabetic rat (Step 2). Using this three step process, it is possible to decrease the mortality rate following orthotropic liver transplantation in diabetic rats from 100% to about 30%. This procedure can also be used to facilitate other extensive surgical procedures in diabetic rats.

Animals↗

A method for mass harvesting islets (Brockmann bodies) from teleost fish.

In certain species of fish, the insulin-producing tissue is uniquely located in separate structures called Brockmann bodies (BBs). Tilapia BBs have been shown to be a simple and inexpensive source of islet cells for xenotransplantation research. Each donor tilapia contains roughly 12-15 BBs, measuring from 0.3 to 5.0 mm in maximum dimension, in a triangular region of adipose tissue bounded by the liver, stomach, and spleen/gallbladder. At present, the larger BBs (usually 2-4) are harvested by microdissecting these "BB regions" using jeweler's forceps and microvascular scissors while being visualized with the aid of a dissecting microscope. It is a simple but time-consuming task that would not be applicable for harvesting massive amounts of BB tissue for large animal studies. Therefore, we have developed an easier and more efficient method of harvesting BBs based on a standard enzymatic method for isolating human adipocytes. BB regions are harvested from donor fish and pooled into a 50 mL plastic tube containing collagenase Type II (3 mg/mL) in Hank's balanced salt solution (HBSS); the tube is then placed in a 37 degrees C waterbath/shaker for roughly 15 min. The exact length of the digestion interval is determined by visual inspection of the tube to determine whether the BBs have been liberated. The digestion is then stopped by adding excess cold HBSS. The adipocytes float while the BBs and residual connective tissue (i.e., a few blood vessels, nerves, and bile ducts) form a pellet. The pellet is washed several times in HBSS and then placed in a culture dish. The BBs are easily handpicked with a siliconized pipette. Based on functional data and DNA content, this new method roughly doubles or triples our yield of BB tissue per donor fish. To determine whether BBs harvested in this manner functioned in a manner similar to those harvested by microdissection, we performed a series of transplants using mass-harvested BBs. Long-term normoglycemia was achieved in streptozotocin-diabetic nude mice and mean graft survival time was not altered in streptozotocin-diabetic euthymic balb/c mice. However, the total weight of donor fish required per recipient was decreased by 50% in both strains.

Animals↗

Islet allograft rejection in rats: a time course study characterizing adhesion molecule expression, MHC expression, and infiltrate immunophenotypes.

Wistar Furth (RT1u) islets transplanted under the renal capsules of streptozotocin-diabetic Lewis (RT1l) rats reject after 5-6 days of normoglycemia. Hand-picked WF islets (1500-2000) were transplanted under the kidney capsules of diabetic Lew or WF rats. Rats bearing iso- or allografts were killed on posttransplant days 2, 4, and 6. Serial frozen sections of grafts and controls were stained by immunoperoxidase for rat MAC-1, class II MHC, CD2, CD4, CD8, B-cells, VLA-4, LFA-1, L-selectin, ICAM-1, and VCAM-1. Infiltrating cells, parenchymal cells, and endothelial cells in five distinct compartments (i.e., peritoneal reflection, subcapsular perivascular space, islet grafts, graft-kidney interface, and kidney) were evaluated for expression of the various markers at each interval. Significant infiltrates arrived in three distinct waves in both iso- and allografts. First, macrophages blanketed the peritoneal capsular reflection and infiltrated by day 2. Second, the first wave of lymphocytes arrived in the edematous subcapsular soft tissue via capsular vessels by day 2 (allo > iso). Third, the second wave of lymphocytes arrived from the renal parenchyma to form a dense band at the graft-kidney interface and around grafts by days 4 and 6 (allo >>> iso); CD4+ cells vastly outnumbered CD8+ cells, with CD4+ cells being mobilized first and from interstitial vessels throughout the entire kidney. CD8+ cells emigrated only from renal interstitial vessels adjacent to the graft. Large numbers of L-selectin+, VLA-4+, and LFA-1+ cells were seen in the infiltrates with the most intensely staining cells being intravascular. B-cells composed a very small proportion of infiltrating cells in both allo- and isografts. Endothelial staining for ICAM-1 and VCAM-1 was prominent throughout. Both class II MHC and ICAM-1 expression were induced on renal tubular epithelial cells, but neither was found on islet parenchymal cells. In conclusion, this study shows that islet allograft rejection is more complex than previously realized.

Animals↗

Tilapia--a source of hypoxia-resistant islet cells for encapsulation.

Encapsulation of pancreatic islets prevents graft revascularization after transplantation, resulting in graft hypoxia and attrition. Hypoxia-resistant islets would be ideal for encapsulation. Tilapia, a tropical teleost fish, have large, anatomically discrete islets that can be easily harvested without expensive, fickle islet isolation procedures and that provide mammalian-like glucose tolerance profiles when transplanted into diabetic recipients. Because tilapia can live in stagnant water, we speculated that tilapia islets might tolerate lower oxygen tensions than mammalian islets. Tilapia and rat islets (n = 30) were placed in paired 60-mm Petri dishes containing 10 mL of deoxygenated CMRL-1066 media and cultured together in sealed chambers gassed with 95% N2/5% CO2. Islet viability was determined by fluorscein diacetate/ethidium bromide staining at intervals varying from 2.5 h to 7 days; blood gas measurements were obtained on media samples at the end of selected incubation intervals. Rat islets underwent near-total necrosis and fragmentation in <24 h; occasional viable single cells could be identified until about 72 h. On the other hand, the fish islets showed no loss of viability until about 72 h when some showed mild central necrosis. Even at 7 days, all fish islets appeared roughly 50% viable. Fish islets cultured under hypoxic conditions for 72 h (media, pO2 = 27.8 mmHg) and then transplanted into streptozotocin-diabetic athymic nude mice were viable (6/6) but showed some diminished function (3/6) over a 25-day follow-up period. Our results suggest that tilapia islets will survive and function at lower oxygen tensions than mammalian islets.

Animals↗

In situ assessment of cell viability.

Cryobiological studies of tissues often require the simultaneous assessment of tissue structure and in situ cellular function. Localization of damage during cryopreservation occurs as a consequence of tissue structure and morphology and as a result of biophysical constraints imposed by diffusion and heat transfer. This study used five experimental model tissue systems: cells in suspension, cells attached to a substrate, a monolayer of cells attached to a substrate, porcine corneas, and intact porcine articular cartilage to examine the efficacy of assessing cell recovery using a novel fluorescent stain (SYTO-13). A graded freezing protocol was used to induce varying degrees of tissue damage. Recovery was assessed in the different tissue model systems using SYTO with ethidium bromide, fluorescein diacetate (FDA) with ethidium bromide, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT). In each of the tissue model systems, the SYTO/EB assessment technique was shown to be equally effective as the existing techniques for the determination of cell recovery. In addition, the properties of fluorescence intensity and rate of release for SYTO were significantly better than those obtained using FDA. Assessment of in situ cell viability was clearly demonstrated using porcine corneas and articular cartilage. The SYTO/EB assay is superior to the existing techniques used for the localization of cell damage in tissues after cryopreservation.

Animals↗