Cells In Flow System Research Articles

Mechanisms of cellular retention of melanin bound drugs: Experiments and computational modeling.

Melanin binding of drugs is known to increase drug concentrations and retention in pigmented eye tissues. Even though the correlation between melanin binding in vitro and exposure to pigmented eye in vivo has been shown, there is a discrepancy between rapid drug release from melanin particles in vitro and the long in vivo retention in the pigmented tissues. We investigated mechanisms and kinetics of pigment-related drug retention experimentally using isolated melanin particles from porcine retinal pigment epithelium and choroid, isolated porcine eye melanosomes, and re-pigmented ARPE-19 cells in a dynamic flow system. The experimental studies were supplemented with kinetic simulations. Affinity and capacity of levofloxacin, terazosin, papaverine, and timolol binding to melanin revealed Kd values of ≈ 50-150μM and Bmax≈40-112nmol.mg-1. The drugs were released from melanin in <1h (timolol) or in 6-12h (other drugs). The drugs were released slower from the melanosomes than from melanin; the experimental differences ranged from 1.2-fold (papaverine) to 7.4-fold (timolol). Kinetic simulations supported the role of the melanosomal membrane in slowing down the release of melanin binders. In release studies from the pigmented ARPE-19 cells, drugs were released from the cellular melanin to the extracellular space in ≈ 1day (timolol) and ≈ 11days (levofloxacin), i.e., much slower than the release from melanin or melanosomes. Simulations of drug release from pigmented cells in the flow system matched the experimental data and enabled further sensitivity analyses. The simulations demonstrated a significant prolongation of drug retention in the cells as a function of decreasing drug permeability in the melanosomal membranes and increasing melanin content in the cells. Overall, we report the impact of cellular factors in prolonging drug retention and release from melanin-containing cells. These data and simulations will facilitate the design of melanin binding drugs with prolonged ocular actions.

Mechanism of the adhesion and migration of neutrophils on sinusoidal endothelial cells in flow system

Mechanism of the adhesion and migration of neutrophils on sinusoidal endothelial cells in flow system

Paraxial analysis of light scattering by biological cells in a flow system

A special mathematical model is developed to find the scattered light pattern of biological cells in a fluid flow system. A paraxial approximation to the diffraction integral is used to accommodate nonspherical and asymmetrical cells. The paraxial approximation results are in good agreement with Mie calculations for homogeneous spheres of comparable size and refractive index. A 2-D fast Fourier transform program is used to simulate variable cell morphology and experimental conditions. Distinct signature differences for two types of cells resembling normal and abnormal malignant human cervical cells are found useful as discriminant features. The ability to handle a variety of model cell shapes and distortions by these methods is demonstrated, and use of signature features for cell discrimination is shown experimentally.

A means for orienting flat cells in flow systems

Flattened cells, such as red blood cells, epithelial cells, and sperm of many species, cause problems for fluorescence-activated cell analysis and sorting machines because the flow systems of such devices are unable to control the orientation of these cells as they flow past the detectors. For this reason, the fluorescence or scattered light measurements for identical cells may vary greatly. A flow geometry is here described that orients flat cells in a coaxial flow system so that each cell presents the same aspect to the observation device. A wedge-shaped exit on the sample injection tube in a coaxial flow system is sufficient to produce the desired orientation effect when used with low sample flow rates. Data is presented showing the effect of orientation of fixed chicken erythrocytes on histograms of small forward-angle light-scattering measurements.