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Biomedical subjects

T M Chang

Publications and source records attributed to T M Chang.

At least 145 records · Page 8Linked to original sources
PubMed1992

Bovine hemoglobin anaerobically reacted with divinyl sulfone: a potential source for hypothermic oxygen carriers.

The bifunctional reagent divinyl sulfone was anaerobically reacted with bovine hemoglobin to give a noncrosslinked intramolecularly-modified new derivative (HbBv-DVS). By employing a high molar ratio of divinyl sulfone to HbBv-DVS, it was possible to effect anaerobic intermolecular crosslinkage. The polymerized material (Poly HbBv-DVS) was shown to consist of a mixture of modified intermolecularly-crosslinked hemoglobins characterized by molecular masses ranging from 130 to -500 kDa. Some functional properties of HbBv-DVS and Poly HbBv-DVS have been evaluated in vitro and in vivo. Viscosities of HbBv-DVS solutions at temperatures as low as 15 degrees C and concentrations up to 14.0 g/dl were proved to be much lower than that of normal human blood at 37 degrees C (-4 cp). Poly HbBv-DVS (14.0 g/dl) was iso-oncotic (COP = 23 mm Hg) with plasma, and had viscosities of 3.37 and 4.57 cp at 37 and 15 degrees C, respectively. The clearance of Poly HbBv-DVS from the circulation was significantly delayed (T1/2 = 270 min), compared with those of HbBv and HbBv-DVS (T1/2 = 80 and 100 min, respectively. The P50 values were substantially increased (P50 = 52 and 61 mm Hg at 37 degrees C, 0.15 M Cl- and pH 7.4 for HbBv-DVS and Poly HbBv-DVS, respectively). Due to their right-shifted oxygen equilibrium curves, these derivatives still yielded P50 values of about 20 mm Hg at the low temperature of 15 degrees C, as compared with only 7 mm Hg for native bovine hemoglobin. These properties make HbBv-DVS and Poly HbBv-DVS potential new candidates for low-temperature organ perfusion.

Animals↗
PubMed1992

Purification and quantitative determination of carboxymethylchitin incorporation into submicron bilayer-lipid membrane artificial cells (liposomes) encapsulating hemoglobin.

The separation of carboxymethylchitin-coated hemoglobin-loaded liposomes (CMC-LEHb)s from the non-adsorbed CMC has been achieved by gel chromatography. This purification takes place at the physiological pH of 7.4 favoring HbO2 preservation. A comparative study between experimental techniques for the quantitative determination of the absorption of carboxymethylchitin (CMC) onto liposomes encapsulating hemoglobin (LEHb)s has been conducted. Results suggest that FT-IR spectroscopy gives a more accurate quantitative absorption index while the chitinase-based enzymatic assay should be used as a qualitative detection tool. Quantitative bilayer and surface characterization show that the RBC membrane composition has been closely simulated by that of CMC-LEHbs in terms of total lipids and carbohydrates at 87.8% (phospholipids and cholesterol) and 12.2% CMC respectively.

Animals↗
PubMed1992

Endotoxin removed from hemoglobin solution using polymyxin-B immobilized fibre (PMX-F) followed by a new turbidometric endotoxin assay.

Endotoxin contamination in modified hemoglobin can result in side effects. Accurate measurement and effective elimination of endotoxin are important in producing safe hemoglobin preparation. A new turbidometric endotoxin assay (Toxinometer) was studied, in which absorbance of wavelength was applied at 660 nm. This method is not affected by the presence of hemoglobin in solution. This way, toxinometer can accurately measure endotoxin concentration in hemoglobin solution. For the elimination of endotoxin, polymyxin-B immobilized fiber (PMX-F) was studied in-vitro and compared with commercial materials. The PMX-F was found to be a convenient and less expensive approach.

Animals↗
PubMed1992

Effect of a single replacement of one of Ringer lactate, hypertonic saline/dextran, 7g% albumin, stroma-free hemoglobin, o-raffinose polyhemoglobin or whole blood on the long term survival of unanesthetized rats with lethal hemorrhagic shock after 67% acute blood loss.

This study is based on an unanesthetized lethal hemorrhagic shock rat model (67% blood volume bled in 2 stages). The 8 groups studied were as follows. 1. Control--no resuscitation fluid. 2. Reinfusion of rat's own shed whole blood. 3. Ringer lactate solution--3 times shed blood volume. The following 4 fluids were each given as equal to the shed blood volume. 4. 7.5g% NaCl hypertonic saline/6% Dextran 70, followed by 3 volumes Ringer lactate dextran. 5. Ringer lactate solution. 6. Human albumin 7g% in Ringer lactate. 7. Stroma-free hemoglobin in Ringer lactate 8. o-raffinose polyhemoglobin in Ringer Lactate. Blood pressure and other vital signs were recorded continuously during the control period, bleeding periods, infusion period and 60 minutes after infusion. After this all surviving animals were followed for 14 days with no other special treatments. Group 4 had transient (10 minutes) returned of blood pressure to control levels. The 3 groups with sustained blood pressure at control level when followed for 1 hour were groups 2, 6 and 7. The 2 groups with 100% survival on days 14 were group 2 and group 7.

Animals↗
PubMed1992

A preclinical screening test for modified hemoglobin to bridge the gap between animal safety studies and use in human.

The infusion of large amount of modified hemoglobin as blood substitute can potentially result in hypersensitivity and anaphylactic reactions, antibody-antigen reactions and others. Animal safety studies are important. However, response in animals may not be the same as in human. Before injecting into human, we may need to use an in-vitro screening procedure. One approach is based on testing the effects of modified Hb on complement activation (C3a) of human plasma. This paper describes this screening test. It also discusses how this may potentially be used. For instance using this to test for contamination from trace membrane fragments with blood group antigen or lipids, antibody-antigen complexes, endotoxin, trace fragments of microorganisms, residual amounts of some polymers, emulsifying agents, and organic solvents. There is also the possibility of obtaining plasma from a very large human population and analyse each of these to study the epidemiology of adverse reactions in different groups and types of patients.

Anaphylaxis↗
PubMed1992

Immunological effects of hemoglobin, encapsulated hemoglobin, polyhemoglobin and conjugated hemoglobin using different immunization schedules.

Repeated subcutaneous immunizing injections into rats of Freund's adjuvant containing rat hemoglobin or o-raffinose rat polyhemoglobin did not result in increase in IgG antibody titers. However, heterologous hemoglobin injected as above is antigenic (49.50 + 6.70 % CPM). Crosslinking heterologous hemoglobin into o-raffinose polyhemoglobin further increased its antigenicity (75.60 + 4.08). Thus, unlike homologous hemoglobin, cross-linking of heterologous hemoglobin increased its antigenicity. Liposome encapsulated homologous hemoglobin injected subcutaneously with or without Freund's adjuvant did not show antigenicity. Encapsulated heterologous hemoglobin resulted in a minimal increase in antibody titers (10.73 + 4.64) only with Freund's adjuvant, but no increase when injected without Freund's adjuvant. Conjugated heterologous hemoglobin (PEG-Hb) injected intravenously by itself at weekly intervals did not result in significant increase in antibody titers on the 5th week.

Animals↗
PubMed1991

The secretin gene: evolutionary history, alternative splicing, and developmental regulation.

The gene encoding the hormone secretin has been isolated and structurally characterized. The transcriptional unit is divided into four exons spanning 813 nucleotides. Comparison of the rat secretin gene to the other members of the glucagon-secretin gene family reveals that similarities are restricted to the exons encoding the biologically active peptides. Analysis of RNA from porcine intestine indicates that at least two transcripts are generated from the porcine secretin gene as a result of differential splicing. The longer and more abundant transcript appears to be identical to a previously isolated cDNA, which encodes a precursor that includes a 72-amino acid C-terminal extension peptide. The shorter transcript does not contain the third exon and, as a result, encodes only 44 residues beyond the C terminus of secretin. The amino acid sequence deduced from the shorter transcript is identical to a precursor form of secretin recently isolated from porcine duodenum [Gafvelin, G., Jornvall, H. & Mutt, V. (1990) Proc. Natl. Acad. Sci. USA 87, 6781-6785]. Developmental studies reveal that both secretin mRNA and peptide levels in the intestine are highest just before birth, prior to the onset of gastric acid secretion and feeding. This observation implies that secretin biosynthesis in developing animals is controlled independently of the principal factors known to regulate secretin release in adult animals.

Amino Acid Sequence↗
PubMed1991

Effects of mass transfer and reaction kinetics on serum cholesterol depletion rates of free and immobilized Pseudomonas pictorum.

Pseudomonas pictorum in free or immobilized form can deplete serum cholesterol. The reaction kinetics control the global rate of cholesterol depletion during the initial part of free P. pictorum fermentation. Then, mass transfer takes control of the global rate. In this part of the fermentation, the global rate is first order with respect to the cholesterol concentration. The halftime was 330 min. The global rate is zero order with respect to the bacterial concentration. The activation energy was 83 kJ/mol. These results are consistent with the aqueous cholesterol diffusion model. The open pore agar microcapsule experimental effective diffusivity for lipoproteins at 37 degrees C was 6.7 x 10(-11) m2/s. Mass transfer across the microcapsule was not the limiting factor for the global rate.

Agar↗
PubMed1991

Role of cholecystokinin in pancreatic bicarbonate secretion in dogs.

We investigated the effects of endogenous and exogenous cholecystokinin (CCK) on pancreatic exocrine secretion, in particular that of bicarbonate. In six dogs prepared with gastric cannulas and Thomas duodenal cannulas, intraduodenal administration of corn oil (Lipomul) incubated with hog pancreatic enzymes significantly increased pancreatic secretion of both bicarbonate and protein. Increase in pancreatic secretion of both bicarbonate and protein was accompanied by the increase in plasma CCK concentration. However, the increase in bicarbonate as well as protein secretion was blocked by proglumide, a CCK antagonist, given intravenously. In contrast, intraduodenal infusion of undigested Lipomul failed to stimulate the pancreatic exocrine secretion or release of endogenous CCK. These observations indicate that endogenous CCK plays an important role in secretion of both bicarbonate and protein stimulated by digested corn oil. In a group of four dogs with pancreatic fistulas, intravenous infusion of CCK potentiated the stimulatory effect of secretin on pancreatic bicarbonate secretion. The stimulatory effect as well as potentiating effect of CCK on pancreatic bicarbonate secretion was blocked by infusion of proglumide. We conclude that endogenous CCK plays a significant role in fat-stimulated pancreatic secretion, and it is apparent that both endogenous CCK and secretin are equally important for stimulation of pancreatic bicarbonate secretion, which results from potentiation of the action of the two hormones.

Animals↗
PubMed1991

Mechanism of oleic acid-induced inhibition on gastric acid secretion in rats.

We investigated the existence of an enterogastrone in rats induced by duodenal administration of oleic acid. Acid secretion by the luminally perfused stomach was stimulated in anesthetized rats by intravenous infusion of 0.3 micrograms.kg-1.h-1 pentagastrin. Intraduodenal administration of 3 mmol of oleic acid produced a profound inhibition (94%) of pentagastrin-stimulated acid output in 10 rats (P less than 0.01). Of several peptides in plasma including secretin, neurotensin, somatostatin, and peptide YY, only secretin was found to increase significantly (P less than 0.001). A similar degree of inhibition of acid output (93%) was caused by porcine secretin, 5.6 pmol.kg-1.h-1, given intravenously to mimic the plasma level of secretin produced by oleic acid infusion. The inhibitory effect of oleic acid on the acid secretion was completely reversed by intravenous injection of a rabbit antisecretin serum but not by a normal rabbit serum. These observations strongly suggest that the inhibition was mediated via circulating secretin. The inhibition produced by either oleic acid or secretin was completely blocked by indomethacin. The blocking action was completely reversed by intravenous administration of 48 micrograms.kg-1.h-1 prostaglandin E2. We conclude that endogenous secretin is a major enterogastrone released by oleic acid in anesthetized rats and that the inhibitory action of secretin requires endogenous prostaglandins.

Animals↗
PubMed1991

Effects of hepatic stimulatory factor released from free or microencapsulated hepatocytes on galactosamine induced fulminant hepatic failure animal model.

This paper describes the presence of a cell free hepatocyte stimulating factor secreted by hepatocyte cultures. Hepatocytes were isolated from 70-90 grams Wistar-Lewis rats. Free or microencapsulated hepatocytes in alginate matrix were cultured separately. Cell free supernatant was collected from the culture medium in which was cultured free hepatocytes; microencapsulated hepatocytes or control microcapsules containing no microcapsules. This was tested in the galactosamine rats. A galactosamine dose of 2.7 g/Kg of body weight given intraperitoneally to Wistar-Lewis rats resulted in reproducible hepatic necrosis with 90% mortality. Cell free supernatant from one day old free hepatocyte cultures was able to increase survival time and incorporation of 3H-thymidine in liver of galactosamine induced fulminant hepatic failure rats at the time of maximal liver damage. The cell free supernatant of one day old microencapsulated hepatocyte cultures did not have the same stimulatory effect either on survival time or incorporation of thymidine. Another study was carried out as follows. The microcapsules containing hepatocytes were ruptured. The supernatant of the microcapsule contents was collected. This was found to have hepatic stimulatory effect as shown by survival time and incorporation of thymidine. This suggests that hepatocytes are a source of a factor(s) which is capable of stimulating liver regeneration in the galactosamine induced fulminant hepatic failure rats at the time of maximal liver damage. Since the molecular weight cut off of this particular preparation of microcapsule is molecular larger than albumin, this suggests that the molecular weight of this factor is in the macromolecular range.

Animals↗
PubMed1991

Physicochemical characteristics of hepatic stimulatory factor prepared from cell free supernatant of hepatocyte cultures.

We previously reported that the cell free supernatant of hepatocyte cultures contained a hepatic stimulatory factor, which increases survival time and stimulates liver regeneration in the galactosamine induced fulminant hepatic failure animal model. When hepatocytes were microencapsulated in an alginate matrix, the cell free supernatant outside the microcapsuled lacked the above stimulatory effects. However, the cell free content of microcapsules was able to increase both survival time and incorporation of 3H-thymidine in our animal model. This hepatic stimulatory factor has a molecular weight greater than albumin because alginate microcapsules allow the penetration of albumin but not the hepatic stimulatory factor. In this paper we report the molecular weight study and some other physiochemical characteristics of this factor. Using Sephacryl gel chromatography we showed that this factor has a molecular weight of over 110,000 D. This factor loses its hepatic stimulatory effect after heat or trypsin treatment. Although its elution profile on Sephacryl gel does not change after such treatments.

Acrylic Resins↗
PubMed1991

The microencapsulation of cells within alginate poly-L-lysine microcapsules prepared with the standard single step drop technique: histologically identified membrane imperfections and the associated graft rejection.

Standard alginate-polylysine microcapsules containing isolated rat hepatocytes were prepared. These capsules were intraperitoneally implanted into mice, and retrieved after seven days. Histological sections of the recovered microcapsules showed peritoneal lymphocyte and macrophage infiltration. Additional microscopic observations at various stages of the microencapsulation procedure, and histological observations of control non-implanted microcapsules; illustrate that encapsulated cells became embedded within the microcapsular membrane matrix. The microcapsular membrane at these sites appeared thin and often poorly formed. The cellular infiltration into the implanted microcapsules can occur through holes developed in these thin and poorly formed areas found in the microcapsular membrane. Similar observations were seen in microcapsules prepared with 20 x 10(6) and at a lower cell concentration of 10 x 10(6) suspended cells per millilitre of sodium alginate.

Alginates↗
PubMed1991

A novel two step procedure for immobilizing living cells in microcapsules for improving xenograft survival.

Histologically identified surface irregularities caused by the physical entrapment of encapsulated cells in the microcapsular membrane matrix of standard alginate-polylysine microcapsules potentiated graft rejection in mice. We have therefore devised a novel two step procedure to prevent the entrapment of cells in the capsular membrane matrix. With the new method the capsular membrane appeared uniform and without the physical entrapment of cells in the capsular membrane matrix. Furthermore, after 7 days of intraperitoneal implantation of encapsulated rat hepatocytes in mice, microcapsular membrane perforations and leukocyte infiltrations were not observed. Also a greater percentage of the modified capsules, free from fibrous encapsulation, were recovered after 7 and 11 days of intraperitoneal implantation compared to the standard microcapsule preparations.

Alginates↗
PubMed1991

Preparation and surface characterization of carboxymethylchitin-incorporated submicron bilayer-lipid membrane artificial cells (liposomes) encapsulating hemoglobin.

In view of the desirability to increase the survival time of the lipsome-based artificial red blood cells in vivo, bovine hemoglobin-loaded liposomes (LEHb) are incorporated with a polyanionic polymer, a highly substituted type of carboxymethylchitin (CMC). The liposomes are prepared by a modified Reverse Phase Evaporation technique and then purified using a Sepharose 4B column. A comparative study between experimental techniques for the determination of adsorption efficiency suggests that FT-IR spectroscopy gives a more accurate quantitative adsorption index while the chitinase-based enzymatic assay should be used as a qualitative detection tool. The overall composition of the bilayer(s) can be approximated by that of the natural (RBC) membrane in terms of total lipids and carbohydrates at 87.8% (phospholipids and cholesterol) and 12.2% CMC respectively.

Biocompatible Materials↗
PubMed1991

Encapsulated hepatocytes for controlling hyperbilirubinemia in Gunn rats.

Hepatocytes encapsulated in an alginate-polylysine-membrane were used to lower bilirubin levels in hyperbilirubinemia. The animal model was the Gunn rat. The microencapsulated hepatocytes were implanted intraperitoneally. 15 x 16(6) microencapsulated hepatocytes from Wistar rats lowered the bilirubin from 14 mg/100 ml to 6 mg/100 ml after 20 days. 15 x 10(6) microencapsulated hepatocytes from Sprague-Dawley rats lowered the bilirubin levels from 8 mg/100 ml to 5 mg/100 ml. They were as effective as free Sprague-Dawley hepatocytes. 12 x 10(6) Guinea pig hepatocytes, whether encapsulated or free, lowered the bilirubin from 9.36 mg/100 ml to 4.37 mg/100 ml.

Alginates↗