Membrane-Immobilized Liver Microsome Drug Detoxifier

Abstract

The common occurrence of poisoning due to drug overdose has led to an increasing need for a safe, simple, effective, and inexpensive means of removing such drugs from the blood in the emergency treatment of drug-overdose victims. Various devices and techniques based on extracorporeal blood processing have been investigated. Physical techniques include hemodialysis (Kennedy et al., 1969), charcoal adsorption (Widdop et al.,1975; Chang et al., 1973), and ion-exchange adsorption (Rosenbaum et al., 1971; Medd et al., 1974). Biological techniques include liver perfusion (McDermott and Norman, 1971), liver slice perfusion (Koshino et al., 1975), perfusion over hepatic cell suspensions in direct contact with the blood (Eisman and Soyer, 1971; Soyer et al., 1973), and perfusion through hollow fibers containing cultured hepatic cells on the outer surface of the fibers (Wolf and Munkelt, 1975). It is well accepted that the biological system responsible for detoxification of a variety of drugs is located in the smooth endoplasmic reticulum of hepatic cells which can be isolated as microsomes by cell fractionation. The microsomes contain a complex mixture of enzymes, including cytochrome P-450, which requires the coenzyme NADPH and molecular oxygen for drug detoxification. In general these detoxification enzymes modify toxins by increasing their polarity and consequently their aqueous solubility, thus decreasing their permeation into tissues (Mandel, 1971) and promoting excretion. The chemical modifications catalyzed by the microsomal drug detoxification enzymes include, among others, hydroxylation, demethylation, and conjugation reactions. Several of the microsomal detoxification enzymes have been purified (Lu and Levin, 1974; Brunner, 1975; Ziegler and Mitchell, 1972) and at least two have been immobilized by covalent bonding to insoluble particles (Brunner, 1975; Parikh et al., 1976; Sofer et al.,1975). One approach for utilization of these enzymes in an extracorporeal drug detoxification system is to purify the individual enzymes and then reconstitute the multienzyme complex by binding to insoluble particles. An alternative approach, the one we have chosen, is to utilize the isolated microsomes themselves. This method has the advantage of simplicity and lower cost. More importantly, in contrast to the former approach, it assures that all the microsomal enzymes are present in proportions and molecular arrangement closely resembling the in vivo state. We have used an extracorporeal hollow fiber-based enzyme reactor in an attempt to develop a therapeutic technique suitable for treatment of drug and poison detoxification. Since all the protein components of the system are impermeable to the hollow fiber membranes, adverse immunological reactions will be avoided. In addition, the safety of blood processing using hollow fiber devices has been well established in recent years by extensive use in hemodialysis.