Alterations in hepatic heme and cytochrome P-450 metabolism in murphy-sturm lymphosarcoma-bearing rats implications for drug metabolism

Inflammatory response: an unrecognised source of variability in the pharmacokinetics and pharmacodynamics of cancer chemotherapy

An important limitation in the use of chemotherapy in cancer treatment is that cytotoxic agents have small margins of safety compared with other drugs. The largely unpredictable pharmacokinetics of cytotoxic agents contribute significantly to differences in toxicity and efficacy between individuals. Over the past few decades, evidence has accumulated that the inflammatory response to conditions such as infection, degenerative disease, and cancer can greatly affect the disposition of drugs. A more recent finding is that the presence of an inflammatory response identifies patients with more aggressive disease and may also compromise the pharmacodynamics of anticancer drugs. In this review, we discuss the changes in the pharmacokinetics of drugs caused by the presence of inflammation. Also, we discuss the modulating role of inflammatory mediators on the pharmacokinetics and pharmacodynamics of cytotoxic agents. We argue that, overall, these factors identify inflammatory response as a potentially important factor in the interindividual variability of response and toxic effects to cancer chemotherapy.

Chemistry and biology of heme. Effect of metal salts, organometals, and metalloporphyrins on heme synthesis and catabolism, with special reference to clinical implications and interactions with cytochrome P-450

Although free porphyrins occur in nature in small quantities, no known function has been assigned to them. In contrast, heme and cobalamin, which are Fe and Co chelates of porphyrins or porphyrin derivatives, respectively, carry out crucial biological functions. Heme is the prosthetic group for a number of hemoproteins. These include myoglobin and hemoglobin, which carry out oxygen binding or transport; mitochondrial cytochromes aa3, b, c, and c3, which are important in transferring electrons; microsomal cytochrome P-450, which catalyzes mixed-function oxidations; catalase, which decomposes H2O2; peroxidase, which activates H2O2; and tryptophan pyrrolase, which catalyzes the oxidation of tryptophan. Recently, heme has also been shown to be the prosthetic group of prostaglandin and peroxide synthetase and indoleamine dioxygenase. The elegant studies of the biochemical pathway for the formation of heme demonstrated the arrangement in the porphyrin macrocycle of the carbon and nitrogen atoms originating from the eight glycine and the succinic acid molecule that are the precursors of porphyrins. There are eight enzymes involved in the synthesis of heme. The first and last three of these enzymes are localized in mitochondria, while the intermediate enzymes are localized in cytosol. The catalytic site of HMOX recognizes metalloporphyrins with central metal atoms other than iron; it favors some of these metalloporphyrins over heme as a potential substrate, sometimes by a large factor, permitting the synthetic heme analogue to serve as a potent competitive inhibitor of HMOX reaction. Since these synthetic metalloporphyrins do not bind molecular oxygen, they are not metabolically degraded by ring rupture and do not add to the body pool of bile pigment. One possible consequence of this competitive inhibition of heme degradation is suppression of bile pigment formation to such a degree that excessive plasma levels of bilirubin may be diminished. The studies of Drummond and Kappas (1981) and later studies in rats, mice, monkeys, and man, and also our studies have proved the latter phenomenon. The compound does not appear to affect the metabolic disposition of preformed bilirubin but inhibits biliary bilirubin excretion derived from the metabolism of endogenous or exogenous heme. Whether some of the effect of Sn-PP on naturally occurring or experimentally induced jaundice in animals reflects diversion of heme to nonheme to oxygenase-dependent pathways of heme metabolism, or whether a pathway which is normally latent becomes activated concurrent with HMOX inhibition is not known.(ABSTRACT TRUNCATED AT 400 WORDS)

Protective effect of Sn-protoporphyrin against doxorubicin-induced perturbations of heme metabolism

The administration of doxorubicin, an anti-tumor antibiotic, to rodents resulted in an increase in heme oxygenase activity and a decrease in delta-aminolevulinate (ALA) synthase activity and in cellular heme and cytochrome P450 content in liver. Sn-protoporphyrin, a potent inhibitor of heme degradation both in vitro and in vivo, when administered to rodents prior to doxorubicin, mitigates the drug-induced toxic actions which are reflected by the drug-induced decreases of both cellular heme and cytochrome P450 content. Sn-protoporphyrin thus provides a pharmacological means of protecting against the toxic effects of doxorubicin and other drugs which enhance heme oxygenase activity and thus decrease cellular heme and cytochrome P450 content in vivo.

Tin-protoporphyrin inhibits heme oxygenase and prevents the decline in hepatic heme and cytochrome P-450 contents produced in nude mice by tumor transplantation

Heme and hemeprotein perturbations are present in nude mice bearing transplanted tumors. Hepatic microsomal heme oxygenase activity is increased 50-100% in tumor bearing nu/nu mice when compared with normal controls. This elevation in activity of the rate-limiting enzyme of heme degradation is associated with a 50% depletion of microsomal heme and cytochrome P-45 concentrations in liver. The synthetic heme analogue, Sn-protoporphyrin, a potent inhibitor of heme oxygenase, lowers the activity of heme oxygenase in tumor bearing animals to below control levels. This effect is associated with a normalization of hepatic heme and cytochrome P-450 contents. These findings might have implications for protecting normal cells during tumor growth and chemotherapy.

Interactions with glutathione S-transferases of porphyrins used in photodynamic therapy and naturally occurring porphyrins

Several naturally occurring porphyrins and porphyrins used in photodynamic therapy inhibit glutathione S-transferase isoenzymes either purified from rat liver or lung or in cytosol from normal and from cancerous (Morris 7288C hepatoma) liver. Although differences occur in the type and amount of transferases in normal and cancerous liver and in the liver of rats bearing an extrahepatic tumour, these enzymes are potential binding sites for porphyrins. Porphyrin structure is an important factor in determining the affinity of binding, as shown by the relative inhibitory effectiveness. Of the dicarboxylic porphyrins in the mixture used clinically, OO'-diacetylhaematoporphyrin and monohydroxyethylmonovinyldeuteroporphyrin are more effective inhibitors than haematoporphyrin and protoporphyrin IX. Of the naturally occurring porphyrins the order of effectiveness is protoporphyrin IX (dicarboxylic) greater than coproporphyrin (tetracarboxylic) greater than uroporphyrin (octacarboxylic) and type I greater than type III isomers of both uroporphyrin and coproporphyrin, and the synthetic tetra-meso-phenylporphinetetrasulphonate is a better inhibitor (apparent Ki = 250 nM) than coproporphyrin, which contains a comparable number of negative charges. In addition, iron-porphyrin chelates are more effective inhibitors of the transferases, with 25-fold decrease in Ki value, than the free porphyrins. These results indicate that one means whereby porphyrins accumulate in tissues is the occupation of intracellular binding sites, such as the transferases. Since porphyrins inhibit the activity of these important detoxifying enzymes, there will be metabolic consequences to the cell.