Biomedical subjects

C J Holloway

Publications and source records attributed to C J Holloway.

7 recordsLinked to original sources

PubMed1979

Thiols and hepatic coma.

The plasma concentrations of methane and ethane thiols have been determined during the course of acute liver failure by a gas-chromatographic technique, and a prognostic evaluation is possible using this analysis. Further, the effects of some therapeutic measures, notably hemoperfusion, on the thiol levels have been investigated. It is concluded that these toxins, which are to a large extent covalently protein-bound, are extremely difficult to remove in an extracorporeal liver support system. Since the cause of the pathological thiol concentrations is probably the elevated plasma methionine levels associated with severe liver disease, it is suggested that the most hopeful course of action against the accumulation of thiols in the body might be a preventative therapy involving the normalization of methionine at an early stage of the disease.

Charcoal↗

PubMed1979

The application of immobilized enzymes in an artificial liver support system.

A novel method of extracorporeal support for fulminant liver failure is reported whereby the most important detoxification processes of the liver are reproduced in an enzyme reactor. Most of the endogenous toxins involved in hepatic coma can be deactivated directly by conjugation with a hydrophilic residue such as glucuronic acid or glutathione, or by the neutralization of active groups through structural modification by methyl transfer. The enzymes responsible for these processes have been isolated and purified from rabbit liver, and covalently bound onto a hemocompatible form of agarose matrix. This system has been shown to be capable of catalyzing the desired reactions with endogenous toxins such as phenols and mercaptans in vitro, and phenols in rabbits in vivo.

Acetaminophen↗

PubMed1979

Enzymatic methylation of alkane thiols.

A membrane-bound enzymatic activity has been found in rabbit liver microsomes, which catalyses the transmethylation from S-adenosylmethionine to a series of C1-C3 alkane thiols. Methane and ethane thiols are known to be endogenous toxins, which may play an important role in the pathogenesis of hepatic coma, and methylation could provide an important pathway for the metabolic 'detoxification' of this class of compounds through neutralisation of the highly reactive sulph-hydryl group.

Animals↗

PubMed1979

Large agarose beads for extracorporeal detoxification systems. Preparation and enzymatic properties of agarose-bound UDP-glucuronyltransferase.

UDP-glucuronlytransferase, E.C. 2.4.1.17, has been solubilised from the microsomal fraction of liver homogenate from phenobarbital pretreated rabbits by lipase or detergent treatments. A 110-fold purification of the enzyme with respect to the crude homogenate was achieved by precipitation and column separations. The cholate-detergent solubilised enzyme was far more stable than that prepared by the lipase method. The partially purified UDP-glucuronyltransferase has been covalently bound to cyanogen bromide-activated agarose in the form of large haemocompatible beads to the extent of 0.22 mg protein per mg agarose dryweight, equivalent to about 25 mg of swollen gel. The acceptors for glucuronidation employed were the non-physiological phenolic compounds p-nitrophenol and 1-naphthol, and an exogenous and endogenous substance of physiological importance, namely paracetamol and phenol respectively. The immobilised enzyme exhibited at least 80% of the original activity of the solubilised enzyme, and the catalytic function was preserved for a much longer period of time in the carrier-bound form. The system described in this publication could well be applied in an extracorporeal liver assist device for the replacement of glucuronidation function.

Animals↗

PubMed1979

The removal of hypnotic drugs from human serum. A comparative investigation of the adsorptive properties of native and agarose-encapsulated resins and charcoal.

The adsorptive capacities of some ion-exchange resins and activated charcoal towards the hypnotic drugs, phenobarbital, glutethimide, carbromal, and methaqualone, have been investigated. Furthermore, the properties of some of these resins and charcoal, encapsulated in an agarose matrix in the form of beads, have been compared with those of the adsorbent phases in their native states. In general, the adsorptive capacities of charcoal were at least as good as, and frequently better than those of the resins. Amberlite XAD-type resins had a higher affinity than Dowex-type resins for all the drugs tested, except for phenobarbital, which was not adsorbed to a satisfactory extent onto Amberlite XAD-4. The encapsulation of adsorbent phases into agarose beads of diameter 5-10 mm results in a reduction of the adsorbtion of the drugs. Nonetheless, the remaining adsorptive capacity is sufficient for application in an extracorporeal detoxification system. Moreover, the overwhelming advantage of good haemocompatibility is provided by the agarose-encapsulated adsorbents.

Adsorption↗

PubMed1979

Agarose-encapsulated adsorbents.

A method is described for the encapsulation of ion-exchange and adsorbent resins of native particle diameter 0.2-1.0 mm into agarose spheres of diameter 5-10 mm. Plasma components diffuse rapidly through the agarose coating, but blood corpuscles have no direct access to the resins. At least 0.3 g of resin can be incorporated into 1 g of the agarose beads, so that the effective surface area with regard to erythrocytes, thrombocytes, and leucocytes is reduced by a factor of at least 5, and up to 20, depending on the native resin particle size. Pulverised active charcoal, or resins in powder form can also be encapsulated in this manner. The haemocompatibility of the agarose coating seems to be considerably more acceptable than that of the adsorbents in their native state.

Adsorption↗

PubMed1978

Large agarose beads for extracorporeal detoxification systems.

A method is reported by which agarose beads of diameter 1000 to 10000 microns can be prepared from Sepharose (R) 4B (native bead diameter 40 to 190 microns). Haemoperfusion experiments indicate that the enlarged beads are relatively haemocompatible; platelet loss is considerably less than that reported for many other bio-materials employed in haemoperfusion, and haemolysis is slight even after perfusion for several hours at flow-rates in excess of 25 ml/min. The beads can be activated by cyanogen bromide for the immobilisation of proteins. The sites for protein fixation are not restricted to the outside surface of the beads; small water soluble molecules, and serum proteins diffuse quite rapidly through the enlarged beads. A possible medical application of the large beads is in extracorporeal detoxification by chromatographic extraction or enzymatic modification, particularly of lipophilic toxins, using the enlarged beads as a carrier-matrix. The results described in this publication prove the viability of this concept. Such methods should be especially useful as artificial supports in fulminant hepatic failure.

Acetaminophen↗