Investigation of the coordinated functional activities of cytochrome P450 3A4 and P-glycoprotein in limiting the absorption of xenobiotics in Caco-2 cells

The coordination of the functional activities of intestinal CYP3A4 and P-gp in limiting the absorption of xenobiotics in Caco-2 cells was investigated. Growing Caco-2 cells were exposed to increasing concentrations of doxorubicin (1-2 μM) in plastic flasks to encourage a subpopulation of cells, that displayed an intrinsically higher multidrug resistance (mdr) phenotype than the parent cells, to survive and grow. Doxorubicin-exposed (hereinafter referred to as type I cells) and nonexposed Caco-2 cells (parent cells) on collagen-coated inserts were also treated with either 0 (control) or 0.25 μM 1α,25-dihydroxyvitamin D3 to promote cellular CYP3A4 expression. Increased P-gp protein expression, as detected by Western blotting, was noted in type I cells (213±54.35%) compared to that of parent cells (100±6.05%). Furthermore, they retained significantly less [3H]vincristine sulphate (p<0.05), a P-gp substrate, after efflux (272.89±11.86 fmol/mg protein) than the parent cells (381.39±61.82 fmol/mg protein). The expression of CYP3A4 in parental cells after 1α,25-dihydroxyvitamin D3 treatment was quantified to be 76.2±7.6 pmol/mg protein and comparable with that found in human jejunal enterocytes (70.0±20.0 pmol/mg protein). Type I cells, however, expressed a very low quantity of CYP3A4 both before and after the treatment that was beyond the minimum detection limit of Western blotting. Functionally, the rates of 1-hydroxylation of midazolam by CYP3A for both cell types ranged from 257.0±20.0 to 1057.0±46.0 pmol/min/mg protein. Type I cells, although having a higher P-gp expression and activity comparatively, metabolized midazolam less extensively than the parent cells. The results suggested that there were noncoordinated functional activities of intestinal CYP3A4 and P-gp in Caco-2 cells, although they both functioned independently to minimize intestinal epithelial absorption of xenobiotics. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association.

Stable propagation of solitons with increased energy through the combined action of dispersion management and periodic saturable absorption

It is shown, through numerical simulations, that by using a combination of dispersion management and periodic saturable absorption it is possible to transmit solitonlike pulses with greatly increased energy near to the zero net dispersion wavelength. This system is shown to support the stable propagation of solitons over transoceanic distances for a wide range of input powers.

Characterization of nonlinear absorption in femtosecond laser inscription

Direct measurements of the absorbed energy in femtosecond laser inscription in a range of materials is performed. Key absorption parameters are characterized by fitting numerical modelling to measurements.

Cascaded nonlinear absorption of femtosecond laser pulses in dielectrics

We investigated the energy deposition process leading to the waveguide inscription in transparent dielectrics both experimentally and theoretically. Parameters of multiphoton absorption process and inscription thresholds were measured in a range of materials including YAG, ZnSe, RbPb2Cl5 crystals, and in fused silica and BK7 glasses.

A new strategy for selecting and evaluating physical solvents for gas absorption

This work describes how the physical properties of a solvent affect the design variables of a physical gas absorption process. The role of every property in determining the capital and the running cost of a process has been specified. Direct mathematical relationships have been formulated between every item of capital or running cost and the properties which are related to that item. The accuracy of the equations formulated has been checked by comparing their outcome with some actual design data. A good agreement has been found. The equations formulated may be used to evaluate on the basis of economics any suggested new solvents. A group of solvents were selected for evaluation. Their physical properties were estimated or collected as experimental data. The selected ones include three important solvents, the first is polyethylene glycol dimethyl ether (Selexol) which represents the currently most successful one, The other two solvents are acetonyl acetone (B2) and n-formyl morpholine which have been suggested previously as potential credible alternatives to the current ones. The important characteristics of: acetonyl acetone are its high solubility and its low viscosity, while the n-formyl morpholine is characterised by its low vapour pressure and its high selectivity. It was found that acetonyl acetone (B2) is the most attractive solvent for commercial applications particularly for process configurations that:include heat exchangers and strippers. The effect of the process configuration on the selected solvent was investigated in detail and it was found that there is no universal solvent which is the best for any process configuration, but that there is a best solvent for a given process configuration. In previous work, acetonyl acetone was suggested as a commercially promising physical solvent. That suggestion was not fully based on experimental measurement of all the physical properties. The viscosity of acetonyl acetone and its solubility at 1 atm were measured but the vapour pressure and the solubility of C02 and CH4 at high pressure were predicted. In this work, the solubilities of C02, CH4 and C3H8 in acetenyl acetone were measured for a partial pressure range of (2 ~ 22) bar at 25°C, The vapour pressure of this solvent was also measured, and the Antoine equation was formulated from tbe experimental data. The experimental data were found to be not In agreement with the predicted ones, so acetonyl acetone was re-evaluated according to the experimental data. It was found that this solvent can be recommended for further trials in a pilot plant study or for small scale commercial units.

The molecular design of a new solvent for the absorption of carbon dioxide

Gas absorption, the removal of one or more constitutents from a gas mixture, is widely used in chemical processes. In many gas absorption processes, the gas mixture is already at high pressure and in recent years organic solvents have been developed for the process of physical absorption at high pressure followed by low pressure regeneration of the solvent and recovery of the absorbed gases. Until now the discovery of new solvents has usually been by expensive and time consuming trial and error laboratory tests. This work describes a new approach, whereby a solvent is selected from considerations of its molecular structure by applying recently published methods of predicting gas solubility from the molecular groups which make up the solvent molecule. The removal of the acid gases of carbon dioxide and hydrogen sulfide from methane or hydrogen was used as a commercially important example. After a preliminary assessment to identify promising moecular groups, more than eighty new solvent molecules were designed and evaluated by predicting gas solubility. The other important physical properties were also predicted by appropriate theoretical procedures, and a commercially promising new solvent was chosen to have a high solubility for acid gases, a low solubility for methane and hydrogen, a low vapour pressure, and a low viscosity. The solvent chosen, of molecular structure Ch3-COCH2-CH2-CO-CH3, was tested in the laboratory and shown to have physical properties, except for vapour pressures, close to those predicted. That is gas solubilities were within 10% but lower than predicted. Viscosity within 10% but higher than predicted and a vapour pressure significantly lower than predicted. A computer program was written to predict gas solubility in the new solvent at the high pressures (25 bar) used in practice. This is based on the group contribution method of Skold Jorgensen (1984). Before using this with the new solvent, Acetonyl acetone, the method was show to be sufficiently accurate by comparing predicted values of gas solubility with experimental solubilities from the literature for 14 systems up to 50 bar. A test of the commercial potential of the new solvent was made by means of two design studies which compared the size of plant and approximate relative costs of absorbing acid gases by means of the new solvent with other commonly used solvents. These were refrigerated methanol(Rectisol process) and Dimethyl Ether or Polyethylene Glycol(Selexol process). Both studies showed in terms of capital and operating cost some significant advantage for plant designed for the new solvent process.