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T M Chang

Publications and source records attributed to T M Chang.

At least 199 records · Page 11Linked to original sources
PubMed1988

Syntheses and properties of circular dichroism active phospholipids.

A group of circular dichroism (CD) active phospholipids has been synthesised, in which one or both acyl chains has been replaced with a cinnamoyl or azobenzene chromophore-containing acid. Studies on the structure, CD activity and thermodynamic property of liposome membranes composed of CD active phospholipids were carried out. CD active liposomes were found to be stable, normal liposomes of approximately 550 A diameter based on the electron micrograph and dynamic light scattering, and to have thermodynamic property similar to the conventional phospholipid membranes without serious perturbation by aromatic bulk groups based on DSC. Liposomes composed of phospholipid having two trans-azobenzene chromophores showed an extremely large CD enhancement even well above Tc. This CD enhancement was drastically changed by the presence of cis-azobenzene chromophore and cis-cis isomer content after irradiation was higher than the theoretical value, suggesting the importance of interchromophore interaction in the liposome membranes.

Circular Dichroism↗
PubMed1988

Circular dichroism study of membrane dynamics focused on effect of monosialogangliosides.

Monosialogangliosides (GM) purified from bovine brain were incorporated into circular dichroism (CD)-active liposomes and the effects of GM on the membrane dynamics were studied by CD spectroscopy. In the presence of 7 mol% of GM, the phase transition temperature (Tc) of the membrane increased by ca. 10 degrees C compared with the membrane without GM and characteristic CD spectra were observed for CD-active liposomes incorporating GM at low temperature. Asialogangliosides had no effect on the CD spectra or Tc. We have also studied the role of GM in reducing leakage of [3H]sucrose from liposomes composed of egg phosphatidylcholine, dipalmitoyl phosphatidic acid, cholesterol and alpha-tocopherol with a molar ratio of 4 : 1 : 5 : 0.1 in the presence of human plasma at 25 degrees C. The half-life of [3H]-sucrose leakage was 173 h for liposomes incorporating 7 mol% of GM. On the other hand, the half-lives for liposomes incorporating 7 mol% of asialogangliosides and liposomes without glycolipids were 45 and 42 h, respectively. These results indicate that sialic acid on the membrane surface contributes to the increase of Tc, to the change of the aggregation state of phospholipids and to the stabilization of liposomes in plasma.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1988

Acid-independent release of secretin and cholecystokinin by intraduodenal infusion of fat in humans.

In order to clarify a possible role of fat content in the release of secretin and cholecystokinin by liquid nutritional supplements in humans, duodenal pH and plasma concentrations of secretin and cholecystokinin were studied during the intraduodenal infusion of Ensure, Vivonex, 10% Intralipid, and sodium oleate. Significant release of secretin was observed with Intralipid and sodium oleate, while significant release of cholecystokinin was observed with all four testing solutions. Duodenal pH was rarely below 4.5 during the infusion of Ensure, Intralipid, and sodium oleate. Duodenal pH was high, greater than 6.0, when plasma secretin and cholecystokinin levels were elevated during the administration of Ensure, Intralipid, and sodium oleate. We conclude that both secretin and cholecystokinin are released in response to fat solutions in the duodenum and that low duodenal pH was not responsible for either secretin or cholecystokinin release during intraduodenal infusions of Ensure, Intralipid, or sodium oleate.

Adult↗
PubMed1988

Role of pancreatic enzymes on release of cholecystokinin-pancreozymin in response to fat.

In dogs prepared with either pancreatic duct ligation (PDL) or chronic pancreatic fistula (PF), we investigated the effect of pancreatic enzymes on release of cholecystokinin (CCK) in response to corn oil in the upper small intestine. In control dogs without PDL, intraduodenal administration of corn oil (Lipomul containing 15 mmol of triglyceride) resulted in a marked and sharp increase in plasma CCK concentration during the 1st h, which then decreased during the following 1.5 h. In PDL dogs, on the other hand, no immediate increase occurred during the 1st 45 min after which a modest but gradual increase occurred in plasma CCK concentration during the following 2 h. Likewise, plasma CCK concentration increased significantly when Lipomul predigested with pancreatic enzymes or oleic acid was administered to PDL dogs. The increase was comparable to the response to Lipomul alone in control dogs. The infusion of Lipomul resulted in similar responses of plasma CCK in PF dogs as were found in PDL dogs when pancreatic juice was diverted to the exterior from the duodenum. The increases in plasma CCK paralleled the pancreatic protein secretion, and a significant correlation was found between plasma CCK concentration and the protein output. The present observations indicate that release of endogenous CCK by fat from the upper small intestine depends on an adequate digestion of neutral fat by pancreatic enzymes. Thus pancreatic enzymes play an important role on release of CCK in response to a neutral fat.

Animals↗
PubMed1988

Role of pancreatic polypeptide in the regulation of pancreatic exocrine secretion in dogs.

The effect of intravenous infusion of synthetic human pancreatic polypeptide (HPP) or a rabbit anti-PP serum on pancreatic exocrine secretion was studied in 10 dogs with gastric and Thomas duodenal cannulas. The infusion of HPP, at a dose of 1 microgram.kg-1.h-1, achieved a plasma PP concentration that mimicked the peak plasma concentration of PP in both interdigestive and postprandial states. This dose of HPP significantly inhibited pancreatic secretion in the interdigestive state. By contrast, immunoneutralization of circulating PP by a rabbit anti-PP serum resulted in significant increases (P less than 0.05) in both interdigestive and postprandial pancreatic secretion, including water, bicarbonate, and protein. The increase in the pancreatic secretion paralleled a decrease in circulating PP level, which lasted for as long as 5 days. Furthermore, the anti-PP serum blocked the inhibitory action of exogenous HPP on pancreatic exocrine secretion. The present study indicates that endogenous PP plays a significant role in the regulation of the pancreatic exocrine secretion in both interdigestive and digestive states. Thus we conclude that PP is another hormone regulating pancreatic exocrine secretion in dogs.

Animals↗
PubMed1988

Artificial cells as bioreactive biomaterials.

Artificial cells can have the same dimensions as biological cells. They can enclose and retain a large variety of bioreactants. Artificial cell membranes can have the required permeability characteristics to allow the rapid equilibration of external molecules to be acted on by the enclosed bioreactants. Polymer, protein, protein-lipid, polymer-lipid, lipid or other materials can form artificial cell membranes. It is possible to vary the membrane thickness and permeability characteristics over a wide range. Many different forms of bioreactive artificial cells are available. This article contains only a few examples. This includes its applications in (1) red blood cell substitutes; (2) immobilisation of enzymes, multienzymes with cofactor recycling, cell cultures and other biotechnological applications; (3) hemoperfusion in kidney failure, poisoning, removal of aluminum and iron; (4) use in liver failure; (5) other applications in microencapsulation.

Adsorption↗
PubMed1988

The viability and regeneration of artificial cell microencapsulated rat hepatocyte xenograft transplants in mice.

Viable hepatocytes were microencapsulated within artificial cells to form a bio-artificial liver. Trypan blue stain exclusion testing generally showed that 60% of the encapsulated hepatocytes remained viable immediately after encapsulation. To determine if xenogeneic hepatocytes can be successfully transplanted, encapsulated rat hepatocytes were implanted intra-peritoneally into mice and galactosamine induced liver failure mice. After 29 days of implantation in mice and 8 days of implantation in liver failure induced mice there was no significant change observed in the number of hepatocytes within the free floating microcapsules recovered from the peritoneal cavity. The percentage viability of the hepatocytes inside the recovered microcapsules increased from 62% to nearly 100% after 29 days of implantation in mice. The percentage viability of the encapsulated hepatocytes implanted in the liver failure induced mice was followed for 8 days. The percentage viability of the hepatocytes inside the microcapsule also increased from 42% to nearly 100%. In mice implanted with free rat hepatocytes, no viable hepatocytes were observed as early as 4 and 5 days after implantation. Instead a larger number of lymphoid cells and remnants of hepatocytes were recovered from the peritoneal cavity. In all cases the viability of the rat hepatocytes were determined with trypan blue stain.

Animals↗
PubMed1988

Release of hepatic stimulatory substance from cultures of free and microencapsulated hepatocytes: preliminary report.

The galactosamine induced liver failure animal model was used to study the release of hepatic stimulatory substance (HSS) from free and microencapsulated hepatocytes in culture. Free hepatocyte cultures released HSS which significantly increased DNA synthesis in hepatocyte and the survival time of this animal model. The release HSS was not observed when hepatocytes were microencapsulated in an alginate matrix. The alginate matrix has a pore size which does not allow molecules larger than albumin (64,000 M.W.) to pass through the matrix. This suggests that of the two different ranges of molecular weights suggested for the hepatic stimulatory substance, those in the higher molecular range are important for liver regeneration.

Animals↗
PubMed1988

Pyridoxylated-polyhemoglobin solution: a low viscosity oxygen-delivering blood replacement fluid with normal oncotic pressure and long-term storage feasibility.

Stroma-free hemoglobin (P50 = 14 torr, T1/2 = 3 hr, COP = 60 torr @ 15 g%) was pyridoxylated (PP-SFHb P50 = 28 torr) and then cross-linked with glutaraldehyde to yield pyridoxylated-polyhemoglobin (PP-PolyHb). Sephadex G-200 gel chromatography showed 33% to be in the 470-750,000 dalton range, 60% 470,000 MW, and 10% remaining unmodified. PP-PolyHb (14 g%), was iso-oncotic (COP = 25 torr) with plasma, and had a viscosity at 37 degrees C = 3.8 cP. Despite glutaraldehyde crosslinking PP-PolyHb retained some cooperative oxygen binding (Hill coefficient n = 1.88), with a P50 of 20 torr. MetHb levels ranged from 3.1-4.8% in fresh PP-PolyHb solutions. Storage in liquid form was possible at 4 degrees C for up to 12 months, with MetHb forming at 0.6%/month. At 25 degrees C storage was possible for 6 months if lyophilized with 3.0% glucose, after which MetHb levels rose at 9.4%/year. At -20 degrees C, the lyophilized PP-PolyHb could be stored for up to 3 years, with MetHb levels remaining below 6.0%.

Blood Substitutes↗