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Biomedical subjects

H Cao

Publications and source records attributed to H Cao.

At least 181 records · Page 10Linked to original sources
PubMed1996

Accumulation of glucosylceramides in multidrug-resistant cancer cells.

Multidrug-resistant (MDR) tumors and cancer cell lines demonstrate a wide variety of biochemical changes. In this study we used drug-sensitive wild-type (wt) cancer cell lines and respective MDR subclones, and we demonstrate the accumulation of distinct lipids in MDR cells. These lipids were either absent or present at very low levels in drug-sensitive cells. The compounds, termed lipid-1 and lipid-2, migrated on thin-layer chromatography as a doublet. They could be radiolabeled by incubating MCF-7-AdrR (Adriamycin-resistant) breast cancer cells with [3H]serine, [3H]palmitic acid, or [3H]galactose. Utilization of these precursors by MCF-7-wt cells for synthesis of lipid-1 and -2 was minimal. Two inhibitors of sphingolipid biosynthesis, L-cycloserine and fumonisin B1, prevented the observed accumulation of the lipid compounds. An inhibitor of glucosylceramide synthesis, 1-phenyl-2-palmitoylamino-3-morpholino-1-propanol, completely abolished the formation of lipid-1 and -2 in MCF-7-AdrR cells and, to a lesser extent, inhibited the formation of lactosylceramides and gangliosides. Utilizing mass spectrometry, the multidrug resistance-associated lipids were further characterized as monoglycosylceramides of two major species that contained either 16-carbon (palmitic) or 24-carbon (lignoceric and nervonic) fatty acids. The carbohydrate head group of glycosylceramides was identified as glucose, not galactose, thus designating the accumulated lipids as glucosylceramides. Incorporation of [3H]palmitic acid into glucosylceramide was strikingly higher (8-10 times) in MCF-7-AdrR cells compared with MCF-7-wt cells. Since the rate of glucosylceramide degradation in MCF-7-AdrR cells was not attenuated, accelerated glycosphingolipid synthesis in MDR cells is suggested. Glucosylceramide also accumulated in KB-V-1, a vinblastine-resistant epidermoid carcinoma but not in KB-3-1, drug-sensitive wt cells. MDR ovarian adenocarcinoma cells (NIH:OVCAR-3) also contained elevated levels of glucosylceramide. Our results demonstrate a correlation between cellular drug resistance and alterations in glucosylceramide metabolism.

Chromatography, Thin Layer↗
PubMed1996

Evidence for essential arginine residues at the active sites of maize branching enzymes.

Alignment of 23 branching enzyme (BE) amino acid sequences from various species showed conservation of two arginine residues. Phenylglyoxal (PGO) was used to investigate the involvement of arginine residues of maize BEI and BEII in catalysis. BE was significantly inactivated by PGO in triethanolamine buffer at pH 8.5. The inactivation followed a time- and concentration-dependent manner and showed pseudo first-order kinetics. Slopes of 0.73 (BEI) and 1.05 (BEII) were obtained from double log plots of the observed rates of inactivation against the concentrations of PGO, suggesting that loss of BE activity results from as few as one arginine residue modified by PGO. BE inactivation was positively correlated with [14C]PGO incorporation into BE protein and was considerably protected by amylose and/or amylopectin, suggesting that the modified arginine residue may be involved in substrate binding or located near the substrate-binding sites of maize branching enzymes I and II.

1,4-alpha-Glucan Branching Enzyme↗
PubMed1996

Effect of repetitive impact on the mechanical strength of pyrolytic carbon.

Impact loading is experienced by mechanical heart valve components when the leaflet comes into contact with the housing orifice as the valve opens and closes during the cardiac cycle. Since the human heart beats approximately 40 million times per year, a large number of impact loading cycles are imposed on the carbon valve components. Contact loading can produce high mechanical stress at the contact area, leading to potential material damage and fracture. This paper describes a procedure for characterizing the effect of repetitive impact on the mechanical strength of pyrolytic carbon. The results shed light on the basic understanding of the damage formation and its strength degradation effect. In particular, fatigue crack growth was identified as the primary mechanism which causes the observed strength degradation. Design procedures based on fracture mechanics and contact mechanics are used in mechanical heart valve design to prevent structural failure associated with impact fatigue.

Biocompatible Materials↗
PubMed1996

Mechanical performance of pyrolytic carbon in prosthetic heart valve applications.

An experimental procedure has been developed for rigorous characterization of the fracture resistance and fatigue crack extension in pyrolytic carbon for prosthetic heart valve application. Experiments were conducted under sustained and cyclic loading in a simulated biological environment using Carbomedics Pyrolite carbon. While the material was shown to have modest fracture toughness, it exhibited excellent resistance to subcritical crack growth. The crack growth kinetics in pyrolytic carbon were formulated using a phenomenological description. A fatigue threshold was observed below which the crack growth rate diminishes. A damage tolerance concept based on fracture mechanics was used to develop an engineering design approach for mechanical heart valve prostheses. In particular, a new quantity, referred to as the safe-life index, was introduced to assess the design adequacy against subcritical crack growth in brittle materials. In addition, a weakest-link statistical description of the fracture strength is provided and used in the design of component proof-tests. It is shown that the structural reliability of mechanical heart valves can be assured by combining effective flaw detection and manufacturing quality control with adequate damage tolerance design.

Biocompatible Materials↗
PubMed1996

Structural failure of pyrolytic carbon heart valves.

Pyrolite carbon has been used for the manufacture of mechanical heart valve prostheses for the past 25 years. In general, pyrolytic carbon mechanical heart valves have provided adequate physiological function and satisfactory structural performance. Although rare in occurrence, incidents of valve failure due to fracture of one or more components have been reported. These reports of failure are reviewed and a few representative examples are examined in detail in order to determine the characteristic failure mechanism. Understanding the underlying factors responsible for causing these failures provides a solid basis for improved design and manufacture of future mechanical heart valve prostheses.

Biocompatible Materials↗
PubMed1996

Structural integrity assessment of heart valve prostheses: a damage tolerance analysis of the CarboMedics Prosthetic Heart Valve.

The design of mechanical heart valve prostheses must satisfy three basic requirements: biocompatibility, efficiency and durability. Over the past 25 years of clinical use, pyrolytic carbon has proven to be biocompatible and thromboresistant, and is therefore the material of choice for mechanical heart valve prostheses. However, in recent years the material has been questioned in this application because it is brittle and susceptible to subcritical crack growth. This has raised concerns regarding the structural reliability of prostheses constructed from this material. This paper describes the application of the damage tolerance methodology to assess the structural integrity of heart valve prostheses made of pyrolytic carbon. In particular, an analysis of the CarboMedics Prosthetic Heart Valve (CPHV) is presented. A new measure of fatigue lifetime, the fatigue safe-life index, is introduced. Additionally, the degradation of structural integrity from cavitation erosion is examined. It is shown that structural integrity, especially for brittle materials, is not just a function of design, but involves the entire manufacturing process. The damage tolerance method can be applied to assess and ensure the structural integrity of pyrolytic carbon prosthetic heart valve components.

Biocompatible Materials↗
PubMed1996

[Therapeutic effect of THAM on lactic acidosis of severe brain injury].

The presence of lactic acidosis in the cerebral spinal fluid of 50 patients with severe head injury was studied. The GCS scores of these patients were < or = 8. The patients were divided into two groups. We treated 25 patients with a dose of 4 to 5 ml/kg of THAM infused intravenously 2 to 3 times for daily administration. Other 25 patients who were not treated with THAM served as a control group. In each case, a ventricular pressure monitoring device was installed. The ICP was the contineously recorded. In addition, laboratory study, including lactate, pH, HCO-3 and BE in CSF was performed. THAM infusion was associated with improved survival, decreased ICP as compared to that in the control group. We believe that THAM treatment may significantly improve the prognosis of presence of lactic acidosis as a result of severe head injury.

Acidosis, Lactic↗
PubMed1996

Authentication of the Chinese drug "ku-di-dan" (herba elephantopi) and its substitutes using random-primed polymerase chain reaction (PCR).

DNA fingerprinting and polymorphism among the Chinese drug "Ku-Di-Dan" and its substitutes were demonstrated with arbitrarily primed polymerase chain reaction (AP-PCR) and random amplified polymorphic DNA (RAPD). Distinctive, reproducible genomic fingerprints from DNA of the Chinese drug Ku-Di-Dan and 9 species of Compositae were generated with six long (18-24 mer) and one short (10 mer) random-chosen primers with PCR. Ku-Di-Dan samples can be distinguished according to the banding patterns of their amplified DNA on agarose gels. Results showed that AP-PCR and RAPD fingerprints of the commercial samples of Ku-Di-Dan retailed in Fujian, Taiwan, Hong Kong and Macau markets are identical with that of Elephantopus scaber L. The relatedness of Ku-Di-Dan among 9 plants may also be estimated by the Similarity Indexes values of the genomic DNA fingerprints.

Asteraceae↗