Laurel B. Deloria

EFFECTS OF INTERFERON-INDUCING AGENTS ON HEPATIC CYTOCHROME P-450 DRUG METABOLIZING SYSTEMS*

Duration and intensity of drug action are greatly influenced by the rates of which drugs are biotransformed by the cytochrome P-450-linked monooxygenase systems of the hepatic endoplasmic reticulum. Several interferon-inducing agents (poly rI.rC, tilorone, vaccines, viruses, endotoxin) are shown to markedly depress hepatic P-450 systems when administered to rodents. The interferon (IF) inducers that depress hepatic drug metabolism also modulate certain immune responses; it is therefore not known whether the depression of P-450 is due to IF per se or to the action of IF-inducing agents on one or more components of the immune system. The loss of cytochrome P-450 elicited by IF-inducing agents is accompanied by a perturbation of heme metabolism associated with the dissociation of heme from cytochrome P-450. The agents also cause losses of hepatic catalase and tryptophan 2,3-dioxygenase. These studies predict that viral infections, vaccinations, and treatment with IF-inducing agents will be shown to seriously impair the metabolism of drugs in humans.

Cell death after cartilage impact occurs around matrix cracks.

The damage from rapid high energy impacts to cartilage may contribute to the development of osteoarthritis (OA). Understanding how and when cells are damaged during and after the impact may provide insight into how these lesions progress. Mature bovine articular cartilage on the intact patella was impacted with a flat impacter to 53 MPa in 250 ms. Cell viability was determined by culturing the cartilage with nitroblue tetrazolium for 18 h or for 4 days in medium containing 5% serum before labeling (5‐day sample) and compared to adjacent, non‐impacted tissue as viable cells per area. There was a decrease in viable cell density only in specimens with macroscopic cracks and the loss was localized primarily near matrix cracks, which were in the upper 25% of the tissue. This was confirmed using confocal microscopy with a fluorescent live/dead assay, using 5′‐chloromethylfluorescein diacetate and propidium iodide. Cell viability in the impacted regions distant from visible cracks was no different than the non‐impacted control. At 5 days, viable cell density decreased in the surface layer in both the control and impacted tissue, but there was no additional impact‐related change. In summary, cell death after the impaction of cartilage on bone occurred around impact induced cracks, but not in impacted areas without cracks. If true in vivo, early stabilization of the damaged area may prevent late sequelae that lead to OA.

Induction of xanthine oxidase and depression of cytochrome P-450 by interferon inducers: Genetic difference in the responses of mice

Interferon and interferon inducing agents depress hepatic cytochrome P-450 systems. They also induce hepatic xanthine oxidase activity. It has been suggested that free radicals produced by xanthine oxidase may cause the loss of P-450. High titers of serum interferon are induced by poly IC (poly riboinosinic acid.polyribocytidylic acid) in both C57Bl/6J and C3H/HeJ mice; Newcastle disease virus (NDV) induces a high titer of interferon in C57Bl/6J mice but not in C3H/HeJ mice. The induction of xanthine oxidase activity by NDV in C3H/HeJ mice was less than half that seen in C57Bl/6J mice, thus demonstrating a relationship between the induction of xanthine oxidase, the depression of P-450 and a genetically determined difference in responsiveness of mice to interferon inducers.

Reversal of the inhibitory effect of lipid peroxides on the hepatic cytochrome P-450 monooxygenase system by a soluble factor from liver and a commercial isocitric dehydrogenase preparation from hog heart

Summary A factor (SF) contained in the 105,000 × g supernatant fraction of rat liver homogenate, previously described as a requirement for the maximal activity of the cytochrome P-450-dependent monooxygenase system of hepatic microsomes, was found to function by reversing the inhibitory effect of TPNH-supported microsomal lipid peroxidation. Commercial hog heart isocitric dehydrogenase preparations contain a large amount of SF or a substance like SF.

Analysis of Heparan Sulfate from the Engelbreth-Holm-Swarm (EHS) Tumor

The size of the heparan sulfate chains from the Engelbreth-Holm-Swarm (EHS) tumor heparan sulfate proteoglycan (PG) was measured by several techniques in order to resolve uncertainty about their size and the chains were chemically characterized for comparison with other basement membrane heparan sulfate PGs. Heparan sulfate size was determined by gel filtration (Mr = 5.5 - 6.0 x 10(4], by equilibrium sedimentation centrifugation (Mw = 6.8 x 10(4], and by end group analysis (Mn = 7.1 x 10(4]. A higher molecular weight (HMW) (Mw = 2.13 x 10(5] calculated from scattering measurements may reflect chain-chain interactions. Forty percent of newly synthesized chains eluted on gel filtration as a lower molecular weight (LMW) shoulder and in vivo turned over faster than the larger species. A large heparan sulfate PG was present after 4 hours of in vivo 35SO4 labeling in both a low density form and a high density, slightly smaller form with large heparan sulfate chains (Mr approximately 8.0 x 10(4]. Heparan sulfate PG of intermediate size (Kav = 0.3-0.65, Sepharose CL-4B) and of smaller size (Kav = 0.75, CL-4B) were found predominantly as high density species. These PGs contained chains (Mr = 3.5 x 10(4) and Mr = 1.2 x 10(4), respectively) which were partially sensitive to chondroitinase ABC (CABC) and may include a hybrid heparan sulfate/chondroitin sulfate PG. Heparan sulfate chains, possibly intracellular degradation products, were also found. Heparan sulfate chains were normal in N-sulfation (58% of hexosamine residues) and in iduronate content (approximately 30%). N-sulfation started within two disaccharides of the linkage region. The EHS heparan sulfate was unusually low in O-sulfation (10% of the total sulfation) and no 6-O sulfated, N-acetylated glucosamine residues adjacent to N-sulfated block regions were found.

Sequential administrations of polyriboinosinic acid and polyribocytidylic acid induce interferon and depress the hepatic cytochrome P-450-dependent monooxygenase system

Abstract Double-stranded polyriboinosinic acid·polyribocytidylic acid is a potent interferon inducing agent and depressant of hepatic cytochrome P-450 monooxygenase systems. Single-stranded polyriboinosinic acid or polyribocytidylic acid are not. However, it is known that interferon is induced in mice when the administration of polyriboinosinic acid is followed shortly thereafter by the administration of polyribocytidylic acid. The current study demonstrates that this sequential administration of single-stranded polynucleotides induces serum and hepatic interferon and depresses the cytochrome P-450 systems. Neither of these effects were seen when the order of administration of these polynucleotides was reversed.

LOSS AND RECOVERY OF HEPATIC MONOOXYGENASE ACTIVITIES AFTER THE ADMINISTRATION OF ALLYLISOPROPYLACETAMIDE (AIA) TO MICE

P-450-linked monooxygenase systems can be characterized by the losses, recoveries and inductions of activities that follow AIA administration to mice.