Biomedical subjects

G Bao

Publications and source records attributed to G Bao.

At least 19 recordsLinked to original sources

PubMed2004

Functionalization and peptide-based delivery of magnetic nanoparticles as an intracellular MRI contrast agent.

We report the development of functionalized superparamagnetic iron oxide nanoparticles with a PEG-modified, phospholipid micelle coating, and their delivery into living cells. The size of the coated particles, as determined by dynamic light scattering and electron microscopy, was found to be between 12 and 14 nm. The PEG-phospholipid coating resulted in high water solubility and stability, and the functional groups of modified PEG allowed for bioconjugation of various moieties, including a fluorescent dye and the Tat peptide. Efficient delivery of the functionalized nanoparticles into living cells was confirmed by fluorescence microscopy, relaxation time measurements, and magnetic resonance imaging (MRI). This demonstrates the feasibility of using functionalized magnetic nanoparticles with uniform (approximately 10 nm) sizes as an MRI contrast agent for intracellular molecular imaging in deep tissue. These micelle-coated iron oxide nanoparticles offer a versatile platform for conjugation of a variety of moieties, and their small size confers advantages for intracellular molecular imaging with minimal perturbation.

Animals↗

PubMed2003

Cell and molecular mechanics of biological materials.

Living cells can sense mechanical forces and convert them into biological responses. Similarly, biological and biochemical signals are known to influence the abilities of cells to sense, generate and bear mechanical forces. Studies into the mechanics of single cells, subcellular components and biological molecules have rapidly evolved during the past decade with significant implications for biotechnology and human health. This progress has been facilitated by new capabilities for measuring forces and displacements with piconewton and nanometre resolutions, respectively, and by improvements in bio-imaging. Details of mechanical, chemical and biological interactions in cells remain elusive. However, the mechanical deformation of proteins and nucleic acids may provide key insights for understanding the changes in cellular structure, response and function under force, and offer new opportunities for the diagnosis and treatment of disease. This review discusses some basic features of the deformation of single cells and biomolecules, and examines opportunities for further research.

Cytoskeleton↗

PubMed2003

Interactions between landscape changes and host communities can regulate Echinococcus multilocularis transmission.

An area close to the Qinghai-Tibet plateau region and subject to intensive deforestation contains a large focus of human alveolar echinococcosis while sporadic human cases occur in the Doubs region of eastern France. The current review analyses and compares epidemiological and ecological results obtained in both regions. Analysis of rodent species assemblages within quantified rural landscapes in central China and eastern France shows a significant association between host species for the pathogenic helminth Echinococcus multilocularis, with prevalences of human alveolar echinococcosis and with land area under shrubland or grassland. This suggests that at the regional scale landscape can affect human disease distribution through interaction with small mammal communities and their population dynamics. Lidicker's ROMPA hypothesis helps to explain this association and provides a novel explanation of how landscape changes may result in increased risk of a rodent-borne zoonotic disease.

Animals↗

PubMed2002

Two new species of Heligmoptera Nadtochiy, 1977 (Nematoda: Trichostrongylina: Heligmosomoidea) from myospalacine rodents in China (Gansu), with a redefinition of the genus.

Two species, Heligmoptera giraudouxi n. sp. and H. querei n. sp., are described. These are co-parasites of the small intestine of Myospalax fontanierii in China (Gansu). H. giraudouxi is closely related to the only existing species of the genus, H. myospalaxi (Nadtochiy, 1970), a parasite of Myospalax psilurus in the Primor'e Region of Russia. It is distinguished by the pattern of the left lateral lobe. H. querei differs from the two other species by possessing a long dorsal ray and from H. giraudouxi by the length of the left ala. From a phylogenetic point of view, these three species may form a small clade, adapted to Myospalax spp., derived from related forms in Insectivora, this capture resulting in the appearance of monodelphy.

Animals↗

PubMed2000

An epidemiological and ecological study of human alveolar echinococcosis transmission in south Gansu, China.

Human alveolar echinococcosis (AE) is usually a rare, highly pathogenic zoonotic disease, transmitted across the northern hemisphere between fox and rodent hosts. In China the first cases were described in 1965; however very few epidemiological studies have been undertaken since. Following identification in 1991 of a serious focus of human AE in south Gansu province, detailed village-based community and ecological studies were carried out between 1994 and 1997. Hepatic ultrasound mass screening with serological testing (five tests) identified 84/2482 new AE cases (3%). An overall prevalence of 4.1% (135/3331) was recorded for the area when previous cases were also included. Based on a seropositive result only, without an ultrasound scan indication, no additional AE cases were identified. Of the evolutive AE cases, 96% were seropositive in at least one test, while up 15-20% of individuals who exhibited hepatic calcified lesions and 12-15% exhibiting hepatic nodular lesions were seropositive for specific Em2 or Em18 antibodies. Village (n=31) human AE prevalence rates varied from 0 to 15.8%. Questionnaire analysis indicated that total number of dogs owned over a period was a risk factor (P<0.006), but not a history of red fox hunting (P>0.6). Rodent ecology studies revealed an association between density indices of voles (Microtus limnophilus) and village AE prevalence rates, on the one hand, and village landscape characterised by a ratio of scrub/grassland to total area above 50% (P<0.005). Long-term transmission of Echinococcus multilocularis and risk of zoonotic infection of south Gansu farmers may be related ultimately to a process of deforestation driven by agriculture. This in turn probably results in creation of optimal peri-domestic habitats for rodents that serve as intermediate host species (such as M. limnophilus) and subsequent development of a peri-domestic cycle involving dogs.

Adult↗

PubMed2000

Cell mechanics: mechanical response, cell adhesion, and molecular deformation.

As the basic unit of life, the cell is a biologically complex system, the understanding of which requires a combination of various approaches including biomechanics. With recent progress in cell and molecular biology, the field of cell mechanics has grown rapidly over the last few years. This review synthesizes some of these recent developments to foster new concepts and approaches, and it emphasizes molecular-level understanding. The focuses are on the common themes and interconnections in three related areas: (a) the responses of cells to mechanical forces, (b) the mechanics and kinetics of cell adhesion, and (c) the deformation of biomolecules. Specific examples are also given to illustrate the quantitative modeling used in analyzing biological processes and physiological functions.

Animals↗

PubMed2000

[Effects of stress level on the biomechanical behavior of the temporomandibular joint disc in domestic pigs].

This study aimed to examine the responses of the temporomandibular joint (TMJ) disc against compression, to clarify the property of viscoelasticity and permeability of the disc, and to provide experimental data for further analyzing the mechanism of stress dissipation within the TMJ disc. With the use of confined compression mechanics and biphasic theory, creep experiments on eight TMJ discs of four domestic pigs were performed under three stress levels(0.07 MPa, 0.13 MPa and 0.30 MPa). The results showed that at 0.07 stress level, the compressive stiffness at 2 seconds of the anterior band(AB), intermediate zone(IZ) and posterior band(PB) of the disc was 4.48 MPa, 3.93 MPa and 6.31 MPa, respectively; the coefficient K of permeability was 0.272 x 10(-12) m4/NS, 0.30 x 10(-12) m4/NS, and 0.042 x 10(-12) m4/NS. At 0.30 Mpa level, the compressive stiffness increased to 14.07 MPa, 13.68 Mpa and 14.00 MPa; the coefficient K lowered to 0.017 x 10(-12) m4/NS, 0.012 x 10(-12) m4/NS and 0.005 x 10(-12) m4/NS. In conclusion, the TMJ disc has viscoelastic and biobiphasic properties against compression. The stiffness of the disc increases with the increment of stress level but the coefficient of permeability decreases. These findings demonstrate that the modulation of stress and of permeability may be two important factors influencing stress dissipation and shock absorption behavior of the disc during compressive and impact loads.

Animals↗

PubMed2000

[Tensile mechanics of mandibular condylar cartilage].

OBJECTIVE: To study the biomechanical properties of the mandibular condyle cartilage and determine its functional importance. METHODS: Eight condyle specimens of the four pig temporomandibular joints were obtained by autopsy and stored in sealed plastic bags at -20 degrees C. These pigs were healthy, aged 1 year +/- 2 months. In the coronal direction, 300 microns wide, rectangular cartilage-bone specimens were prepared on the right condyles using specified knife. In the sagittal direction, rectangular cartilage-bone specimens with the same width were obtained on the left condyles. Standard rectangular testing specimens were prepared from cartilage-bone specimens in a microtome kept at -20 degrees C (300 microns wide and 250 microns thick). The specimens were inserted in a soft-tissue uniaxial tensile test machine and immersed in a bath of Ringer's solution at room temperature. Preconditioning of the specimens was carried out prior to the uniaxial tensile experiment and the specimens were elongated to failure with the constant strain rate (0.05 mm/s). The resulting mean values were curved fitted with Fung's two-parameter (A, B) exponential stress strain equation using a nonlinear regression program. RESULTS: The data obtained showed that a typical nonlinear biomechanical behavior of the condyle cartilage. Toe-region and quasi-linear zone were obvious on the experimental stress strain relation curve. Theoretically fitted parameter A and B were 0.47 and 4.13 (coronally) and 0.60 and 4.70 (sagittally). The sagittal specimens showed greater tensile stress (2.92 MPa), tensile stiffness (9.04 MPa), energy absorption (6.02 N.mm) but less tensile strain (37.34%) than that of the coronal specimens (2.15 MPa, 6.55 MPa, 4.91 N.mm, and 41.12%). The differences were statistically significant (P < 0.05). CONCLUSION: The mandibular condyle cartilage is a kind of biophasic material which shows nonlinear viscoelastic behavior, anistrophic characteristics in biomechanical function and high ability to resist tensile stress in the longitudinal direction.

Animals↗

PubMed2000

[A biomechanical study on the retrodiscal tissue of human temporomandibular joint].

In order to investigate the biomechanical properties and functional mechanism of the retrodiscal tissue (RT) of human temporomandibular joint (TMJ), we conducted a uniaxial tensile test on thirteen RT specimens taken from eight fresh TMJs of the human cadavers aged between 8-15 years (m = 11.8 yrs). The experimental data were analyzed in conjunction with the Quasi-Linear Viscoelastic Theory as proposed by Fung YC to characterize the time-dependent behaviour and the constitutive relationship of the RT. The results showed that the physiological biphasic zone of stress-strain curve lied within 20%-30% strain levels. The elastic modulus (MPa), tensile strength(MPa) and strain to failure(%) were high. There were significant differences in strain to yielding and energy resorption (N.mm) between lateral and medial RT. There was a good agreement between theoretical prediction value and experimental result within 6% strain level. These data suggest that there would be a higher passive deformation and lower safety storage of strength in the RT which could be related to anterior displacement of the TMJ disc and that Fung's Theory can adequately describe the stress-time behaviour and the constitutive relationship of the RT within lower strain rate.

Adolescent↗

PubMed2000

[Calcium activated non-selective cation channel in endothelial cell line ECV304 and inhibition of tumor necrosis factor-alpha].

OBJECTIVE: To study the character of non-selective cation channel in human umbilical cord vein endothelial cell line ECV304 and the effect of tumor necrosis factor-alpha (TNF-alpha) on channel activity. METHOD: Patch clamp technique was used to record single channel and whole cell currents. RESULTS: This channel can be activated by calcium, channel conductance was (19.74 +/- 2.35) pS and its Po was 0.260 +/- 0.006 (n = 5). 100 U/ml TNF-alpha inhibited channel activity, showing that conductance reduced to (10.69 +/- 4.68) pS and Po reduced to 0.230 +/- 0.051 (n = 5). Results in whole-cell configuration were consistent with that in cell-attached patches. Currents were obviously blocked by Cl- channel inhibitor anthracene-9-carboxylic acid (A9C). In order to testify the character of this channel further, KCl and NaCl were exchanged by K(+)-Aspartate in pipette solution. Under this condition, the single channel activities as before were recorded again. Its conductance was (18.33 +/- 2.98) pS(n = 8), and TNF-alpha as well as A9C could inhibit channel activity. But this channel activity could not be blocked by another Cl- channel blocker Zn2+. In the condition of K-Asparate replaced by CsCl in solution, identical channel activity as before could not be recorded. It seemed that Cs+ could not pass through this cation channel. CONCLUSION: It is inferred that calcium-activated non-selective-action channel recorded in endothelial cell ECV304, can be inhibited by TNF-alpha and A9C.

Anthracenes↗

PubMed2000

[G-protein modulates the inhibition of angiotensin II on BKCa in ECV304].

OBJECTIVE: To investigate the effect of angiotensin II (A II) on maxi-conductance calcium-activated potassium channel(BKCa) activity in ECV304 cell membrane, and the possible involvement of G-protein. METHODS: Cell-attached configuration of patch clamp technique was employed to record the current of BKCa in ECV304. RESULTS: 10(-7) mol/L angiotensin II inhibited the BKCa activity. Current amplitude and open probability were decreased, open time was shortened and close time was increased. G-protein activation could eliminate the inhibition of A II. CONCLUSIONS: A II significantly decreased the activity of BKCa in ECV304, which might depolarize the membrane, and the stability of membrane might change. Thus endothelial cell dysfunction might be induced. G-protein activation was involved in the regulation of the above A II inhibition process.

Angiotensin II↗

PubMed2000

[G-protein potentiates the activation of TNF-alpha on calcium-activated potassium channel in ECV304].

OBJECTIVE: Observe the effect of tumor necrosis factor-alpha (TNF-alpha) on calcium-activated potassium channel in ECV304 and the possible involvement of G-protein mediation in the action of TNF-alpha. METHOD: Using the cell-attached configuration of patch clamp technique. RESULTS: (1) the activity of high-conductance calcium-activated potassium channel (BKca) was recorded. Its conductance is (202.54 +/- 16.62) pS; (2) the activity of BKca was potentiated by 200 U/ml TNF-alpha; (3) G-protein would intensify this TNF-alpha activation. CONCLUSIONS: TNF-alpha acted on vascular endothelial cell ECV304 could rapidly activate the activity of BKca. Opening of BKca resulted in membrane hyper-polarization which could increase electro-chemical gradient for the resting Ca2+ influx and open leakage calcium channel, thus resting cytoplasmic free Ca2+ concentration could be elevated. G-protein may exert an important regulation in this process.

Calcium↗

PubMed2000

[Comparison of infrared spectroscopy between native and binding metals' phytoplankton].

Infrared spectroscopy of native and metalbinding duckweed was compared. After binding metals, the absorbance peak around 3,400 cm-1, which reflects OH group stretching vibration, had been moved about 83 cm-1, and its absorbance was decreased. The absorbance of the dominating bands near 1,650 and 1,540 cm-1, the characteristic IR absorption of protein, was decreased. Therefore, the peak absorbance at 620 cm-1 was increased significantly by exposure to high concentration of ZnSO4 solution. So we concluded that OH group play a important role in binding zinc cation and the structure of cell walls had changed due to zinc existing. Furthermore, the process of binding metals by duckweed is physical adsorption and chemical adsorption simultaneously.

Adsorption↗

PubMed1999

Dynamics of individual flexible polymers in a shear flow.

Polymer dynamics are of central importance in materials science, mechanical engineering, biology and medicine. The dynamics of macromolecular solutions and melts in shear flow are typically studied using bulk experimental methods such as light and neutron scattering and birefringence. But the effect of shear on the conformation and dynamics of individual polymers is still not well understood. Here we describe observations of the real-time dynamics of individual, flexible polymers (fluorescently labelled DNA molecules) under a shear flow. The sheared polymers exhibit many types of extended conformation with an overall orientation ranging from parallel to perpendicular with respect to the flow direction. For shear rates much smaller than the inverse of the relaxation time of the molecule, the relative populations of these two main types of conformation are controlled by the rate of the shear flow. These results question the adequacy of assumptions made in standard models of polymer dynamics.

Biopolymers↗

PubMed1999

Karyological and dental identification of Microtus limnophilus in a large focus of alveolar echinococcosis (Gansu, China).

A study of voles (Arvicolidae, Rodentia) from Gansu (China) designed to identify a potential host of Echinococcus multilocularis, responsible for human alveolar echinococcosis, leads to a general analysis of Microtus limnophilus population karyotypes, M1 of M. oeconomus populations from all of Eurasia and of M. limnophilus of Mongolia. The Microtus of Gansu belonging to the nominal subspecies M. limnophilus limnophilus (2n = 38; NF = 58) differs markedly in size and shape of M1 from the M. limnophilus of Mongolia, which must therefore be considered as a new subspecies M. limnophilus of malygini nov. ssp. (2n = 38; NF = 60) and the M. oeconomus of Mongolia should be ranked as M. oeconomus kharanurensis nov. ssp. (2n = 30; NF = 60).

Animals↗

PubMed1999

Acute and chronic blood pressure response to recurrent acoustic arousal in rats.

Repetitive episodic hypoxia every 30 sec administered chronically to Sprague-Dawley (SD) rats has been shown by previous studies to cause a sustained increase in daytime blood pressure (BP). Acoustic arousal in humans during wake or sleep produces an acute BP rise. The question then arises as to whether chronic episodic acoustic arousal applied with the same frequency and duration as episodic hypoxia induces elevated BP. We exposed 14-week-old (N = 10) SD rats in individual cages to recurrent buzzer noise (500 Hz, 100 dB) 6 out of every 30 sec, 7 h/day for 35 days. Ten other rats were placed in similar cages daily but not exposed to noise, to provide a sham condition. An infrared beam with a detector was positioned at the end of each cage. This allowed us to quantify motion by registering the number of times the rat broke the beam per 7 h period. Mean intraarterial BP was measured in unrestrained conscious animals at baseline and at the end of 35 days of their respective conditions. Acute episodic acoustic stimulation caused an immediate response in BP and heart rate. Habituation occurred in that the movement response to 120 noises per hour was 75% in hour one and 20% in hours two through seven on day one. The movement response was further reduced by day 35 but remained significantly higher than in animals not stimulated by noise. The cardiovascular response to noise also showed signs of habituation. Chronic noise stimulation produced no sustained increases in BP after 35 days of exposure.

Acoustic Stimulation↗

PubMed1999

Renin activity and blood pressure in response to chronic episodic hypoxia.

Previous studies in several strains of rats have demonstrated that 35 days of recurrent episodic hypoxia (EH) (7 hours per day), with a fractional concentration of inspired oxygen that produces desaturation equivalent to the recurrent hypoxemia of sleep apnea, results in an 8 to 13 mm Hg persistent increase in diurnal systemic blood pressure (BP). Carotid chemoreceptors and the sympathetic nervous system have been shown to be necessary for development of this BP increase. Both renal artery denervation and adrenal demedullation block the BP response to chronic EH. The present study was undertaken to define further the role of the kidneys and the renin-angiotensin system in this BP increase. Separate groups of male Sprague-Dawley rats had either (1) bilateral renal artery denervation with EH, (2) sham surgery with EH, (3) sham surgery with sham EH (compressed air), (4) EH with losartan, (5) unhandled with losartan, or (6) unhandled. The experimental period lasted 35 days. Both renal-artery denervated and losartan-treated animals showed no BP change or a lowering of BP in response to EH, whereas the sham-operated EH animals showed a progressive, sustained increase in resting room air BP. BP remained at basal levels or fell in unhandled and unhandled losartan-treated animals. Plasma renin activity was elevated 4-fold versus basal levels in EH animals with renal nerves intact but remained at baseline levels in denervated animals. At the end of the experiment, renal tissue catecholamines confirmed renal denervation in those animals. In conclusion, EH causes a progressive increase in BP, mediated in part through renal sympathetic nerve activity that acts to increase renin-angiotensin system activity through angiotensin II type 1 receptors.

Adrenal Medulla↗

PubMed1999

Pulmonary edema develops after recurrent obstructive apneas.

There are anecdotal reports of pulmonary edema after a night of recurrent obstructive apneas (OAs) in humans, but no data on lung water, gas exchange, filling pressure, or cardiac output (Q) exist in these patients. By clamping the endotracheal tube of eight intubated, anesthesized dogs, we created repetitive OAs of 45-s duration at 30-s intervals, for 8 h. Five additional dogs without apneas, but identically instrumented, were studied simultaneously, serving as nonapneic controls. Sa (O(2)) was measured by intraarterial catheter, pulmonary capillary wedge pressure (Pcw), continuous cardiac output (Q), and mixed venous oxygen saturation (Sv(O(2))) were measured by flotation catheter. Basal and hourly hemodynamics and blood gases (arterial and venous) under steady state respiration were measured. Venous admixture (Q S/Q T) was calculated by standard equations. Pa(O(2)) from the beginning to the end of the experiment fell from 89.6 to 82.8 mm Hg in apneic animals and from 92.2 to 85.5 mm Hg in controls. The Q S/Q T increased in both groups but more so in the apnea group (3.3 to 19.4%) than in nonapneic controls (3.1 to 7.9%). Neither Q nor Pcw changed significantly in either group. Lung wet/dry weight was 5.40 +/- 0.93 in apneic animals and 5.00 +/- 0.67 in controls. Light microscopy showed gross alveolar fluid in three apneic dogs, and electron microscopy showed interstitial fluid in two additional apneic dogs. One of the lung edema dogs expired of acute heart failure in the seventh hour of the experiment. Worsening of gas exchange and histology suggest that lung edema can result from recurrent OAs.

Animals↗