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Biomedical subjects

Hazel Y Stevens

Publications and source records attributed to Hazel Y Stevens.

9 recordsLinked to original sources
PubMed2004

Extracellular signal-regulated kinase activation and endothelin-1 production in human endothelial cells exposed to vibration.

Hand-arm vibration syndrome is a vascular disease of occupational origin and a form of secondary Raynaud's phenomenon. Chronic exposure to hand-held vibrating tools may cause endothelial injury. This study investigates the biomechanical forces involved in the transduction of fluid vibration in the endothelium. Human endothelial cells were exposed to direct vibration and rapid low-volume fluid oscillation. Rapid low-volume fluid oscillation was used to simulate the effects of vibration by generating defined temporal gradients in fluid shear stress across an endothelial monolayer. Extracellular signal-regulated kinase (ERK1/2) phosphorylation and endothelin-1 (ET-1) release were monitored as specific biochemical markers for temporal gradients and endothelial response, respectively. Both vibrational methods were found to phosphorylate ERK1/2 in a similar pattern. At a fixed frequency of fluid oscillation where the duration of each pulse cycle remained constant, ERK1/2 phosphorylation increased with the increasing magnitude of the applied temporal gradient. However, when the frequency of flow oscillation was increased (thus decreasing the duration of each pulse cycle), ERK1/2 phosphorylation was attenuated across all temporal gradient flow profiles. Fluid oscillation significantly stimulated ET-1 release compared to steady flow, and endothelin-1 was also attenuated with the increase in oscillation frequency. Taken together, these results show that both the absolute magnitude of the temporal gradient and the frequency/duration of each pulse cycle play a role in the biomechanical transduction of fluid vibrational forces in endothelial cells. Furthermore, this study reports for the first time a link between the ERK1/2 signal transduction pathway and transmission of vibrational forces in the endothelium.

Blotting, Western↗
PubMed2004

Computerized methods for X-ray-based small bone densitometry.

Animal models have been widely used to correlate in vivo changes in bone mineral density (BMD) with changes in disease state of bone. In small animal models, e.g. the hindlimb suspension model of bone loss, a non-invasive assessment of BMD is required. X-ray radiography has been surpassed in some cases by quantitative computed tomography (QCT) and dual X-ray absorptiometry (DEXA) quantitation. However, there are drawbacks in using the computerized methods, especially for small animals. In this paper, we present image-processing algorithms to quantitatively determine bone area and mineral density in digitized radiographs. Image calibration is based on a calibration step wedge, and the algorithm automatically detects the steps and computes the calibration data. In addition, we demonstrate how the algorithm can accurately determine the cortical outline of the bone and provide reliable data and statistics for small animal studies. A downloadable implementation example for the popular NIH Image package is provided.

Absorptiometry, Photon↗
PubMed2004

Cell membrane fluidity changes and membrane undulations observed using a laser scattering technique.

Local transversal micromotions of cell membranes have been reported. These may provide the physical basis for changes in membrane fluidity. In this study, tissue scattering properties are used to measure the magnitude of transversal micromotions under varying stimuli. Laser light is directed at the cell surface at a low incident angle of 12 degrees so that reflected or refracted light does not enter the microscope objective. Scattered light showed strong low-frequency intensity fluctuations with random-walk behavior. Fluctuations were quantified by the median coefficient of variation over the entire observed cell area. Incubation of the cells with protein crosslinkers (paraformaldehyde) and metabolic suppressors (sodium azide) suppressed these fluctuations by 62 and 44%, respectively. The application of hypoosmotic media caused an increase of fluctuation magnitude by 23% (p < 0.005). Agents that increase membrane fluidity (2% ethanol and xenon) increased fluctuation magnitude by 15 and 31%, respectively (p < 0.05). Cessation of the ethanol and xenon exposure led to partial recovery of the fluctuation magnitude, which was nonsignificant for ethanol. This study shows a strong link between membrane fluidity and transversal membrane undulations and provides an important step in the understanding of the mechanosensing function of the cell membrane.

Cell Line, Tumor↗
PubMed2002

Mechanical loading: biphasic osteocyte survival and targeting of osteoclasts for bone destruction in rat cortical bone.

Bone is removed or replaced in defined locations by targeting osteoclasts and osteoblasts in response to its local history of mechanical loading. There is increasing evidence that osteocytes modulate this targeting by their apoptosis, which is associated with locally increased bone resorption. To investigate the role of osteocytes in the control of loading-related modeling or remodeling, we studied the effects on osteocyte viability of short periods of mechanical loading applied to the ulnae of rats. Loading, which produced peak compressive strains of -0.003 or -0.004, was associated with a 78% reduction in the resorption surface at the midshaft. The same loading regimen resulted in a 40% relative reduction in osteocyte apoptosis at the same site 3 days after loading compared with the contralateral side (P = 0.01). The proportion of osteocytes that were apoptotic was inversely related to the estimated local strain (P < 0.02). In contrast, a single short period of loading resulting in strains of -0.008 engendered both tissue microdamage and subsequent bone remodeling and was associated with an eightfold increase in the proportion of apoptotic osteocytes (P = 0.02) at 7 days. This increase in osteocyte apoptosis was transient and preceded both intracortical remodeling and death of half of the osteocytes (P < 0.01). The data suggest that osteocytes might use their U-shaped survival response to strain as a mechanism to influence bone remodeling. We hypothesize that this relationship reflects a causal mechanism by which osteocyte apoptosis regulates bone's structural architecture.

Animals↗
PubMed2002

Phospholipid-bound molecular rotors: synthesis and characterization.

Molecular rotors are fluorescent molecules with a viscosity-sensitive quantum yield that are often used to measure viscosity changes in cell membranes and liposomes. However, commercially available molecular rotors, such as DCVJ (1) do not localize in cell membranes but rapidly migrate into the cytoplasm leading to unreliable measurements of cell membrane viscosity. To overcome this problem, we synthesized molecular rotors covalently attached to a phospholipid scaffold. Attaching the rotor group to the hydrophobic end of phosphatidylcholine (PC) did not affect the rotor's viscosity sensitivity and allowed adequate integration into artificial bilayers as well as complete localization in the plasma membrane of an endothelial cell line. Moreover, these new rotors enabled the monitoring of phospholipid transition temperature. However, attachment of the rotor groups to the hydrophilic head of the phospholipid led to a partial loss of viscosity sensitivity. The improved sensitivity and exclusive localization in the cell plasma membrane exhibited by the phospholipid-bound molecular rotors suggest that these probes can be used for the study of membrane microviscosity.

Cell Line↗
PubMed2002

Temporal gradients in shear stimulate osteoblastic proliferation via ERK1/2 and retinoblastoma protein.

Bone cells are subject to interstitial fluid flow (IFF) driven by venous pressure and mechanical loading. Rapid dynamic changes in mechanical loading cause transient gradients in IFF. The effects of pulsatile flow (temporal gradients in fluid shear) on rat UMR106 cells and rat primary osteoblastic cells were studied. Pulsatile flow induced a 95% increase in S-phase UMR106 cells compared with static controls. In contrast, ramped steady flow stimulated only a 3% increase. Similar patterns of S-phase induction were also observed in rat primary osteoblastic cells. Pulsatile flow significantly increased relative UMR106 cell number by 37 and 62% at 1.5 and 24 h, respectively. Pulsatile flow also significantly increased extracellular signal-regulated kinase (ERK1/2) phosphorylation by 418%, whereas ramped steady flow reduced ERK1/2 activation to 17% of control. Correspondingly, retinoblastoma protein was significantly phosphorylated by pulsatile fluid flow. Inhibition of mitogen-activated protein (MAP)/ERK kinase (MEK)1/2 by U0126 (a specific MEK1/2 inhibitor) reduced shear-induced ERK1/2 phosphorylation and cell proliferation. These findings suggest that temporal gradients in fluid shear stress are potent stimuli of bone cell proliferation.

Animals↗
PubMed2002

A novel approach to blood plasma viscosity measurement using fluorescent molecular rotors.

Molecular rotors, a group of fluorescent molecules with viscosity-dependent quantum yield, were tested for their suitability to act as fluorescence-based plasma viscometers. The viscosity of samples of human plasma was modified by the addition of pentastarch (molecular mass 260 kDa, 10% solution in saline) and measured with a Brookfield viscometer. Plasma viscosity was 1.6 mPa x s, and the mixtures ranged up to 4.5 mPa x s (21 degrees C). The stimulated light emission of the molecular rotors mixed in the plasma samples yielded light intensity that was nonoverlapping and of significantly different intensity for viscosity steps down to 0.3 mPa x s (n = 5, P < 0.0001). The mathematical relationship between intensity (I) and viscosity (eta) was found to be eta = (kappaI)(nu). After calibration and scaling the fluorescence based measurement had an average deviation versus the conventional viscometric measurements that was <1.8%. These results show the suitability of molecular rotors for fast, low-volume biofluid viscosity measurements achieving accuracy and precision comparable to mechanical viscometers.

Blood Viscosity↗