Localization of pyruvate:NADP+ oxidoreductase in sporozoites of Cryptosporidium parvum

Cryptosporidium parvum contains a unique fusion protein pyruvate:NADP+ oxidoreductase (CpPNO) that is composed of two distinct, conserved domains, an N-terminal pyruvate:ferredoxin oxidoreductase (PFO) and a C-terminal cytochrome P450 reductase (CPR). Unlike a similar fusion protein that localizes to the mitochondrion of the photosynthetic protist Euglena gracilis, CpPNO lacks an N-terminal mitochondrial targeting sequence. Using two distinct polyclonal antibodies raised against CpPFO and one polyclonal antibody against CpCPR, Western blot analysis has shown that sporozoites of C. parvum express the entire CpPNO fusion protein. Furthermore, confocal immunofluorescence and transmission electron microscopy confirm that CpPNO is localized within the cytosol rather than the relict mitochondrion of C. parvum. The distribution of this protein is not, however, strictly confined to the cytosol. CpPNO also appears to localize posteriorly within the crystalloid body.

Defensive nature of Sargassum polycystum (Brown alga) against acetaminophen-induced toxic hepatitis in rats: role of drug metabolizing microsomal enzyme system, tumor necrosis factor-alpha and fate of liver cell structural integrity

AIM

To assess the defensive nature of Sargassum polycystum (S. polycystum) (Brown alga) against acetaminophen (AAP)-induced changes in drug metabolizing microsomal enzyme system, tumor necrosis factor (TNF-alpha) and fine structural features of the liver during toxic hepatitis in rats.

METHODS

Male albino Wistar strain rats used for the study were randomly categorized into 4 groups. Group I consisted of normal control rats fed with standard diet. Group II rats were administered with acetaminophen (800 mg/kg body weight, intraperitoneally). Group III rats were pre-treated with S. polycystum extract alone. Group IV rats were orally pre-treated with S. polycystum extract (200 mg/kg body weight for 21 d) prior to acetaminophen induction (800 mg/kg body weight, intraperitoneally). Serum separated and liver was excised and microsomal fraction was isolated for assaying cytochrome P450, NADPH Cyt P450 reductase and b(5). Serum TNF-alpha was detected using ELISA. Fine structural features of liver were examined by transmission electron microscopy.

RESULTS

Rats intoxicated with acetaminophen showed considerable impairment in the activities of drug metabolizing microsomal enzymes, such as cytochrome P450, NADPH Cyt P450 reductase and b(5) when compared with the control rats. The rats intoxicated with acetaminophen also significantly triggered serum TNF-alpha when compared with the control rats. These severe alterations in the drug metabolizing enzymes were appreciably prevented in the rats pretreated with S. polycystum. The rats pretreated with S. polycystum showed considerable inhibition in the elevation of TNF-alpha compared to the rats intoxicated with acetaminophen. The electron microscopic observation showed considerable loss of structural integrity of the endoplasmic reticulum, lipid infiltration and ballooning of mitochondria in the acetaminophen-intoxicated rats, whereas the rats treated with S. polycystum showed considerable protection against acetaminophen-induced alterations in structural integrity.

CONCLUSION

These observations suggest that the animals treated with S. polycystum extract may have the ability to protect the drug metabolizing enzyme system and mitochondrial functional status from free radical attack, thereby showing its defense mechanism in protecting hepatic cells from acetaminophen toxic metabolite N-acetyl-para-benzoquinone-imine (NAPQI).

Cytochrome P4501A is induced in endothelial cell lines from the kidney and lung of the bottlenose dolphin, Tursiops truncatus

Marine mammals respond to the presence of polycyclic and planar halogenated aromatic hydrocarbons (PAH or PHAH) with the induced expression in endothelium of cytochrome P4501A1, regulated through the aryl hydrocarbon receptor (AHR) transcription factor. Physiological responses in other animals, such as edema and inflammation indicate that the endothelium may be compromised by exposure to AHR agonists, which are ubiquitous in the marine environment. In other mammals and fish the cellular and molecular consequences of exposure to AHR agonists have been elucidated in cultured endothelial cells. We have cultured and characterized cetacean endothelial cells (EC) and used them in induction studies. Endothelial cells were cultured from the lung and kidney of the bottlenose dolphin, Tursiops truncates, and exposed to the AHR agonists beta-naphthoflavone (betaNF) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). betaNF (1-3 microM) induced significant increases in CYP1A1 (O-deethylation of 7-ethoxyresorufin to resorufin; EROD) activity to 3.6 and 0.92 pmol/mg/min in lung and kidney EC, respectively. TCDD was more potent than betaNF, and more efficacious, with maximum induction of CYP1A1 activity of 10.1 and 15.2 pmol/mg/min in lung and kidney EC at 3-10 nM TCDD. The differential response indicates that the lung and kidney endothelial cells in culture retain the ability to respond in a selective manner to specific stimuli. Both the molecular mechanisms of induction and the physiological consequences, especially in the vasculature, of toxicant exposure can be studied in this system.

Cytochrome P450 epoxygenases provide a novel mechanism for penile erection

Erectile dysfunction (ED) is estimated to affect more than 30 million American men and 152 million men worldwide. Therapeutic agents targeting the nitric oxide/cyclic GMP signaling pathway have successfully treated patients with ED; however, the efficacies of these treatments are significantly lower in specific populations such as patients with diabetes. The goal of this study was to discover and identify new endothelium-derived relaxing factors involved in the regulation of erectile function, providing alternative therapeutic targets for treatment of ED. Immunoblotting results showed that protein expressions of epoxygenases from cytochrome P450 (CYP)2B, 2C and 2J subfamilies, as well as NADPH CYP reductase were present in rat corpora cavernosa, which was confirmed by immunohistochemical analysis. Furthermore, CYP2C was localized in cavernosal endothelial cells using double immunolabeling. CYP epoxygenase activity was analyzed by reverse-phase high-pressure liquid chromatography; and the results showed that 11,12- epoxyeicosatrienoic acid (EET) was the major product metabolized by CYP epoxygenases in rat corpora cavernosa. Inhibition of EETs function by injection of an EETs antagonist into rat penis significantly decreased intracavernosal pressure-induced by electrical stimulation of the major pelvic ganglion in vivo. In conclusion, our results suggest that EETs, produced by CYP epoxygenases, in penile endothelial cells serve as vasodilators. Inhibition of this pathway attenuated erectile function, suggesting that EETs are required for normal erection.

Quantifying immunohistochemical staining of phospho-eIF2alpha, heme oxygenase-2 and NADPH cytochrome P450 reductase in oligodendrocytes during experimental autoimmune encephalomyelitis

As a consequence of inflammation associated with multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE), stress responses are induced in many cells within the CNS, however, those that occur within the primary pathological target, the oligodendrocyte, are not fully established. Recently, we found that phosphorylated eukaryotic initiation factor-2alpha (eIF2alpha), an inhibitor of protein translation associated with the stress response, is expressed in a greater number of oligodendrocytes in EAE animals compared to controls. However, since numerous oligodendrocytes in control animals also expressed phospho-eIF2alpha, a method was developed to detect expression levels within oligodendrocytes that did not rely on the number of oligodendrocytes that were stained. This method utilized a high dilution of the primary antibody so that the staining density was kept below a maximum plateau which could eliminate expression differences. Furthermore, the staining density within oligodendrocytes, as determined by image analysis, was corrected by the background density or that within neurons. In either case, the density of staining was greater in oligodendrocytes from EAE animals versus controls. The expression of heme oxygenase-2 and NADPH cytochrome P450 reductase also were examined, but unlike phospho-eIF2alpha, neither was increased in oligodendrocytes from EAE animals compared to controls. In summary, a protocol involving a high dilution of primary antibody and image analysis revealed that the expression of phospho-eIF2alpha within oligodendrocytes was increased in EAE animals compared to control animals.

The occurrence of NADPH-ferrihemoprotein reductase in Corbula caribea, from a natural oil seep at La Brea, Trinidad

Corbula caribea is the most common non-polychaete macrofaunal organism identified at a large natural oil seep at La Brea in south Trinidad. It is hypothesized that these animals may possess (NADPH-ferrihemoprotein reductase) a component of the Mixed Function Oxygenase system (MFO), which may allow them to ameliorate the potentially deleterious effects resulting from exposure to the high levels of petroleum hydrocarbons within this environment. This study was designed to determine whether organisms from the seep site showed greater enzyme activity when compared to organisms from a non-seep reference site. NADPH-ferrihemoprotein reductase activity was determined by incubating 10 microm cryostat sections with nitro-blue tetrazolium. The reaction product was determined by visual assessment and quantified by measuring the relative mean stain intensity. The intense staining, indicative of enzyme activity was evident in the digestive epithelia of seep animals. Observations indicated that organisms from the seep showed more intense staining, indicating greater enzyme activity, when compared to animals from a non-seep reference site. The relative stain intensity of NADPH-ferrihemoprotein reductase determined for organisms from the seep was 61.30. This was significantly higher than the stain intensity determined for organisms from the non-seep reference site (7.11). This supported visual assessments, which suggested that the seep organisms showed higher enzyme activity than organisms from the non-seep site. The results suggest that NADPH-ferrihemoprotein reductase may be present in Corbula caribea from the seep site and not in those from the non-seep site. It is possible that this enzyme may contribute to these animals ability to tolerate chronic exposure to petroleum hydrocarbons and offer then a selective advantage for survival the seep environment.

R25 is an intracellular membrane receptor for a snake venom secretory phospholipase A(2)

Ammodytoxin is a presynaptically neurotoxic (beta-neurotoxic) snake venom secretory phospholipase A(2) (sPLA(2)). We detected a 25 kDa protein which binds the toxin with very high affinity (R25) in porcine cerebral cortex. Here we show that R25 is an integral membrane protein with intracellular localisation. It is the first sPLA(2) receptor known to date that localises to intracellular membranes. Centrifugation on sucrose gradients was used to fractionate porcine cerebral cortex. The subcellular composition of the fractions was determined by following the distribution of organelle-specific markers. The distribution of R25 in the fractions matched the distribution of the mitochondrial marker succinate dehydrogenase, but not the markers for plasma membrane, lysosomes, endoplasmic reticulum, synaptic and secretory vesicles. R25 most likely resides in mitochondria, which are known to be targets for sPLA(2) neurotoxins in the nerve ending and are potentially implicated in the process of beta-neurotoxicity.

Automatic identification of proteins with a MALDI-quadrupole ion trap mass spectrometer

A matrix-assisted laser desorption/ionization (MALDI) ion trap mass spectrometer of new design is described. The instrument is based on a commercial Finnegan LCQ ion trap mass spectrometer to which we have added a MALDI ion source that incorporates a sample stage constructed from a compact disk and a new ion transmission interface. The ion interface contains a quadrupole ion guide installed between the skimmer and the octapoles of the original instrument configuration, allowing for operation in both MALDI and electrospray ionization modes. The instrument has femtomole sensitivity for peptides and is capable of collecting a large number of MALDI MS and MALDI MS/MS spectra within a short period of time. The MALDI source produces reproducible signals for 10(4)-10(5) laser pulses, enabling us to collect MS/MS spectra from all the discernible singly charged ions detected in a MS peptide map. We describe the different modes of the instrument operation and algorithms for data processing as applied to challenging protein identification problems.

[Cytochrome P-450 content and activity of NADPH-cytochrome P-450 c-reductase in experimental subarachnoid hemorrhage]

The condition was studied of the brain monooxigenase system (MOS) in experimental subarachnoidal hemorrhage in rats. The results show that the above hemorrhage leads to a significant depression of activity of brain MOS enzymes (cytochrome P-450, NADPN-cytochrome C-reductase). Depression of activity of the enzymic system is manifest from day 1 and has a tendency toward reduction but at day 14 and 21 the indices are still below the control values. Under the exposure to phenobarbital the reduction of activity of the enzyme system in subarachnoidal hemorrhage gets accelerated, with normalization of the indices occurring by day 7 after the hemorrhage.

Ca-ATPase of human myometrium plasma membranes

We determined and characterized the Mg2+-dependent, Ca2+-stimulated ATPase (Ca-ATPase) activity in cell plasma membranes from the myometrium of pregnant women, and compared these characteristics to those of the active Ca2+-transport already demonstrated in this tissue. Similarly to the Ca2+-transport system, the Ca2+-ATPase is Mg2+-dependent, stimulated by calmodulin, and inhibited by vanadate. The Km for Ca2+ activation is 0.40 microM, very similar to that found for active calcium transport, i.e. 0.25 microM. Consequently, this Ca2+-ATPase can be responsible for the active calcium transport across the plasma membranes of smooth muscle cells.

Developmental changes in steroidogenic enzymes in human postnatal adrenal cortex: immunohistochemical studies

Adrenarche is considered to occur as a result of intra-adrenal changes in steroidogenic enzymes involved in C19 steroid production. The present study was conducted because developmental changes in steroidogenic enzymes have not been examined well in human postnatal adrenal. Twenty-four specimens of nonpathological human adrenals from 7 months to 62 years retrieved from autopsy files. Immunohistochemistry for P450 side-chain cleavage (P450scc), 17alpha hydroxylase (P450c17), dehydroepiandrosterone sulfotransferase (DHEA-ST), P450 oxidoreductase, cytochrome b5, and 3beta-hydroxysteroid dehydrogenase (3betaHSD) was per-formed in these specimens, and the immuno-intensity was evaluated using CAS 200 computed image analysis system. Immunoreactivity of P450scc was marked in the zona glomerulosa, fasciculata and reticularis in the adrenal glands of all the cases examined. P450c17 and DHEA-ST immunoreactivity was weak in the zona fasciculata and reticularis in the adrenals of age 7 months to 5 years, but thereafter became prominent in the zona reticularis. Immunoreactivity of P450 oxidoreductase and cytochrome b5, components of the electron transfer system hypothesized to regulate the 17-20 lyase activity of P450c17, was weak in all three zones of adrenal cortex from 7 months to 5 years, and became more marked in the zona reticularis after age 5 years. 3betaHSD immunoreactivity was marked in all three zones of the adrenal cortex from 7 months to 8 years but thereafter decreased in the zona reticularis. These data suggest that the human adrenal zona reticularis markedly begins to develop morphologically and functionally at around 5 years of age. The increased level of P450c17, DHEA-ST, P450 oxidoreductase, and cytochrome b5, and the decreased level of 3betaHSD in the reticularis is likely to contribute to increased C19 steroid production during adrenarche.

Lanosterol 14alpha-demethylase (CYP51), NADPH-cytochrome P450 reductase and squalene synthase in spermatogenesis: late spermatids of the rat express proteins needed to synthesize follicular fluid meiosis activating sterol

Lanosterol 14alpha-demethylase (CYP51) is a cytochrome P450 enzyme involved primarily in cholesterol biosynthesis. CYP51 in the presence of NADPH-cytochrome P450 reductase converts lanosterol to follicular fluid meiosis activating sterol (FF-MAS), an intermediate of cholesterol biosynthesis which accumulates in gonads and has an additional function as oocyte meiosis-activating substance. This work shows for the first time that cholesterogenic enzymes are highly expressed only in distinct stages of spermatogenesis. CYP51, NADPH-P450 reductase (the electron transferring enzyme needed for CYP51 activity) and squalene synthase (an enzyme preceding CYP51 in the pathway) proteins have been studied. CYP51 was detected in step 3-19 spermatids, with large amounts in the cytoplasm/residual bodies of step 19 spermatids, where P450 reductase was also observed. Squalene synthase was immunodetected in step 2-15 spermatids of the rat, indicating that squalene synthase and CYP51 proteins are not equally expressed in same stages of spermatogenesis. Discordant expression of cholesterogenic genes may be a more general mechanism leading to transient accumulation of pathway intermediates in spermatogenesis. This study provides the first evidence that step 19 spermatids and residual bodies of the rat testis have the capacity to produce MAS sterols in situ.

A comparative study of the isolation of type II epithelial cells from rat, hamster, pig and human lung tissue

Data is reported on the reproducibility and purity of alveolar type II cell isolations from 4 species. Human and pig type II cells were isolated using a tissue slice method to remove blood and contaminating cells, whilst rat and hamster cells were isolated using the method of protease instillation. All cells were purified on Percoll gradients and by differential attachment. Cell type purity was assessed by phase contrast microscopy, electron microscopy (EM), percentage of cells alkaline phosphatase (AP) positive and percentage of cells staining strongly for NADPH dependent nitro blue tetrazolium reductase (NBT). These enzymes are considered as markers for type II and Clara cells respectively. The purity of all cell preparations was enhanced following 24 h culture on a biomatrix and whilst plating efficiency was similar for all species, the human tissue consistently yielded the highest purity of type II cells. All cells with lamellar bodies did not contain AP, and activity was variable between species. Further studies are needed to determine if NBT is equally nonspecific as a cell marker enzyme. In summary, sufficient type II cells of high purity can be isolated thus permitting interspecies comparative studies to investigate the effects of selective and non-specific pulmonary toxins, but more specific marker enzymes are required to identify Type II and Clara cells.

NADPH-cytochrome P-450 reductase, cytochrome P-450 2C11 and P-450 1A1, and the aryl hydrocarbon receptor in livers of rats fed methyl-folate-deficient diets

We investigated three hepatic cytochrome P-450 isozymes and the aryl hydrocarbon (Ah) receptor in rats fed one of the following three diets for 15 months: a diet containing the AIN vitamin mixture (control), the control diet devoid of choline and folate (CFD), or the CFD diet devoid of niacin (CFND). Hepatic tumors developed in all CFD- and CFND-fed rats. Western blot analyses of nontumor hepatic tissue showed that NADPH-cytochrome P-450 reductase (P-450 reductase) increased significantly in the CFD and CFND groups compared with the control group. Hepatic cytochrome P-450 2C11 (CYP2C11) was not detectable in the CFD and CFND groups compared with the control group. Ah receptor and cytochrome P-450 1A1 (CYP1A1) were detected in higher amounts in livers of both deficient groups. CYP1A1 is an enzyme associated with bioactivation of exogenous genotoxins. To our knowledge, this is the first time it has been shown that CYP1A1 and the Ah receptor are induced by dietary deficiencies.

Dietary oxidized linoleic acid modifies lipid composition of rat liver microsomes and increases their fluidity

The effect of dietary oxidized oil on the lipid composition, fluidity and function of rat liver microsomes was studied. Male growing rats were fed diets containing 10 g/100 g of a fresh (control) or oxidized (experimental) linoleic acid-rich preparation for 4 wk. High levels of fluorescent compounds and of thiobarbituric acid reactive substances indicated the occurrence of substantial lipid peroxidation in the microsomes of the experimental rats. The fluidity of the liver microsomes derived from rats fed the experimental diet was significantly higher than that of the membranes of the controls. This was due to profound differences in lipid composition of the liver microsomes, namely, a lower cholesterol to phospholipid molar ratio and a greater arachidonic acid content in the phospholipids of the rats fed the experimental diet. The fluidity differences were accompanied by greater activity of the microsomal enzymes, aldehyde dehydrogenase and NADPH cytochrome C reductase. The study demonstrated that ingestion of oxidized lipids caused profound alterations in membrane composition, fluidity and function. These alterations are likely to be associated with an enhanced cholesterol turnover, as indicated by the greater cholesterol excretion observed for the experimental rats.

Characterization of Saccharomyces cerevisiae CYP51 and a CYP51 fusion protein with NADPH cytochrome P-450 oxidoreductase expressed in Escherichia coli

Saccharomyces cerevisiae CYP51, target of azole antifungal agents, and CYP51 fused with S. cerevisiae cytochrome P-450 oxidoreductase (FUS protein) were expressed in active forms in Escherichia coli by cloning into pET15b. The expression was monitored immunologically, catalytically, and by using reduced carbon monoxide difference and type II binding spectra. CYP51 and FUS enzymes were located in membranes and produced a Soret peak at 448 nm in the reduced CO difference spectrum. The cytochrome P-450 contents in the membrane fractions containing CYP51 and FUS proteins were 12.8 +/- 2.6 and 17.4 +/- 3.7 pmol/mg of protein, respectively. The NADPH cytochrome P-450 oxidoreductase (CPR) content was estimated to be 15.7 +/- 1.1 pmol/mg of protein in FUS membrane fractions. FUS protein catalyzed the demethylation of substrate at the 14alpha position, with a turnover number of 1.96 +/- 0.37 min(-1) in the presence of NADPH. No reductase activity was observed in membrane fractions containing CYP51, and therefore, CYP51 did not function catalytically in the presence of NADPH, but in the presence of an artificial electron donor, cumene hydroperoxide, activity was comparable to that of the FUS enzyme. Further support for a normal structure for the hemoproteins was obtained from type II binding spectra, in which the spectral response was saturated with an equimolar concentration of ketoconazole.

Selective localisation of P450 enzymes and NADPH-P450 oxidoreductase in rat basal ganglia using anti-peptide antisera

Environmental or endogenous toxins may cause nigral cell death in Parkinson's disease (PD) due to altered expression of P450 enzymes. In rat brain, immunohistochemistry using anti-peptide antisera showed NADPH-P450 oxidoreductase and CYP2B1/2 in various hypothalamic nuclei and CYP1A1 in the globus pallidus, but neither enzyme was expressed in substantia nigra. No specific immunoreactivity to CYP2D1 or CYP3A1 was found in any brain region examined. In contrast, CYP2E1 was expressed in substantia nigra and in striatal blood vessels. Since CYP2E1 is associated with free radical production, it may contribute to the oxidative stress believed to underlie nigral degeneration.

Tritrichomonas foetus: isolation and characterization of the Golgi complex

An effective methodology to isolate and characterize the Golgi complex of Tritrichomonas foetus is described in this work. Using sucrose density gradient centrifugation, two highly enriched Golgi fractions (GF1 and GF2) were obtained. Enzymatic assays of GF1 and GF2 showed a strong enrichment in galactosyltransferase activity (20- and 7-fold, respectively), with minimal contamination with other organelles. The GF fraction was further subfractionated by alkaline treatment, which resulted in the production of Golgi content and membrane subfractions. Electron microscopic observations of intact cells or Golgi fractions fixed in solutions containing glutaraldehyde and tannic acid, as well as of deep-etched replicas of isolated fractions, revealed the presence of discrete bridges only between closely apposed cisternae.

Peri- and postnatal changes in reduced nicotinamide adenine dinucleotide phosphate-cytochrome P-450 reductase content in hepatocytes of rats

To study the process of the expression of reduced nicotinamide adenine dinucleotide phosphate-cytochrome P-450 reductase (EC 1.6.2.4) in the liver during development, the amount of enzyme in the cytoplasm of periportal and perivenular hepatocytes in sections cut from livers of male rats was measured during peri- and postnatal growth by quantitative immunohistochemistry with a video image processor. In livers of 19-day-old foetuses, the reductase content in the cytoplasm of periportal and perivenular hepatocytes was 0.16 microM and 0.20 microM, respectively. From the 19th day of gestation to 5 days after birth, the enzyme content increased markedly in the cytoplasm of periportal (288%) and perivenular hepatocytes (301%). Subsequently, the content in the cytoplasm of periportal hepatocytes increased slightly (46%) from 5 to 20 days of age, remained unchanged from 20 to 45 days of age, and increased slightly (15%) from 45 to 90 days of age. However, the content in the cytoplasm of perivenular hepatocytes increased progressively (125%) between 5 and 90 days of age. Thus, the amount of cytochrome P-450 reductase increases markedly in periportal and perivenular hepatocytes during the perinatal period, and subsequently the enzyme content increases gradually in periportal hepatocytes and progressively in perivenular hepatocytes. The present results also suggest that the divergence between cytochrome P-450 expression and the cytochrome P-450-dependent drug metabolic activity in hepatocytes during the perinatal period, found in previous studies, can be attributed to a low cytochrome P-450 reductase density in the membrane of endoplasmic reticulum of periportal and perivenular hepatocytes.

Effects of cold preservation and reperfusion on microsomal cytochrome P-450-linked monooxygenase system of the rat liver

The effects of cold preservation and reperfusion of the liver on the hepatic microsomal cytochrome P-450-linked monooxygenase system (P-450 system) were investigated. Rat livers were preserved with cold University of Wisconsin solution for 0, 12, 24, 36, and 48 hr. Half of them in 0-, 24-, and 48-hr groups were reperfused for 1 hr at 37 degrees C with oxygenated Krebs-Henseleit buffer. After preservation or reperfusion, the liver microsomes were prepared and the concentration of each component of the P-450 system [NADPH-cytochrome b5 reductase (b5 reductase), cytochrome b5 (b5), NADPH-cytochrome P-450 reductase (P-450 reductase) and cytochrome P-450 (P-450)] and their drug metabolizing activities and concentration of apo-cytochrome P-450 2E1 (apo-P-450 2E1) were measured. After 48-hr preservation, b5 concentration did not decrease, whereas the concentration of P-450, P-450 reductase, and b5 reductase decreased from 0.865 to 0.676 nmole/mg protein, from 0.262 to 0.233 micromole/mg protein/min and from 5.34 to 4.86 micromole/mg protein/min, respectively. During cold preservation, the activities of p-nitroanisole O-demethylase and aniline p-hydroxylase did not change. Aminopyrine N-demethylase activity was inhibited from 4.45 to 3.34 nmole/mg protein/min after 48-hr cold preservation. Apo-P-450 2E1 was gradually decreased during cold preservation. Reperfusion caused a further decrease in the activities and concentration of the components of the P-450 system and concentration of apo-P-450 2E1 to 80-90% after 1-hr reperfusion. It was suggested that the prolonged preservation caused deterioration of the P-450 system and the loss of the abilities of metabolism and detoxication of xenobiotics.

Induction of hepatic cytochrome P450 by phenobarbitone in rhesus monkey (Macaca mulatta)

An intraperitoneal administration of PB at a daily dose of 50 mg Kg-1 body wt for 4 days increased the specific content of hepatic microsomal heme, cytochrome P450 and the activity of aminopyrine N-demethylase by 1.8, 2.8 and 3.5 fold respectively. These results were substantiated by the intensification of the 52.5 KDa polypeptide in the electrophoretogram of sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the hepatic microsomes obtained from PB-pretreated versus control macaques. PB did not affect the hepatic content of cytochrome b5 and the activity of NADPH cytochrome c reductase, whereas it decreased the activity of NADH cytochrome c reductase in the rhesus monkeys. To the best of our knowledge this is a first report on the induction of hepatic cytochrome P450 and related enzymes by PB in rhesus monkeys.

Alterations in expression of CYP1A1 and NADPH-cytochrome P450 reductase during lung tumor development in SWR/J mice

We investigated the expression of the cytochrome P450 isozyme, CYP1A1, during the course of tumor development and examined the distribution of the CYP1A1 protein in hyperplastic foci, adenomas and carcinomas. The expression of NADPH-cytochrome P450 reductase, a flavoprotein that mediates the reduction of cytochrome P450, was also determined. Mice were administered urethane (1 mg/g body wt) and were killed at 10, 22 and 52 weeks to coincide with the time at which hyperplastic foci, adenomas and carcinomas were established, respectively. Protein immunoblotting revealed that the antibody for CYP1A1 detected a protein band of approximately M(r) 56,000 in microsomes from mice treated with beta-naphthoflavone. The antibody for NADPH-cytochrome P450 reductase detected a protein band of approximately M(r) 79,000 in microsomes from control mice and mice treated with beta-naphthoflavone. Immunohistochemical studies showed that CYP1A1 was not detected constitutively in the lungs of both non-tumor- and tumor-bearing mice. Treatment with beta-naphthoflavone evoked high induction of CYP1A1 in morphologically normal tissues of all mice, with localization of the protein mainly in endothelial and alveolar type II cells. In contrast, inducibility of CYP1A1 by beta-naphthoflavone was markedly reduced in early hyperplastic foci seen 10 weeks after urethane exposure. At 22 weeks, CYP1A1 was found at low levels in both solid and papillary tumors, whereas at 52 weeks, lung carcinomas were devoid of expression of this protein. However, CYP1A1 inducibility was highly expressed in late hyperplastic foci manifested at 52 weeks. NADPH-cytochrome P450 reductase was expressed in morphologically normal lung tissue of all mice under control conditions and after treatment with beta-naphthoflavone, and was localized mainly in Clara and alveolar type II cells. In contrast, reductase expression in all tumor sites was diminished and closely paralleled that of CYP1A1. These results demonstrated progressive depression of induced CYP1A1 and reductase expression in early hyperplasias, adenomas and carcinomas, suggesting that the co-ordinate regulation of both enzymes is highly conserved during tumor development. Furthermore, these findings suggested diminished capabilities for metabolic activation of potential toxicants and/or carcinogens after neoplastic transformation.

In vivo reconstitution of highly active Candida maltosa cytochrome P450 monooxygenase systems in inducible membranes of Saccharomyces cerevisiae

To establish a system for functional characterization of individual Candida maltosa cytochrome P450 monooxygenases, the NADPH-cytochrome P450 reductase from this yeast species was co-expressed in Saccharomyces cerevisiae with each of the following cytochrome P450 forms; P450Cm1 (CYP52 A3), P450Cm2 (CYP52 A4), and P450AlK2A (CYP52 A5). For this purpose, a multicopy plasmid was constructed that contained two independent expression units controlled by the galactose-inducible GAL10 promoter. As shown by spectral and immunological methods, large amounts of the desired monooxygenase components could be simultaneously produced in the respective S. cerevisiae transformants. It was important, however, to adjust semi-anaerobic cultivation conditions during induction by galactose to minimize a mutual impairment of cytochrome P450 and NADPH-cytochrome P450 reductase formation. Compared to the specific cellular content of the host-own enzyme, a 75- to 100-fold overproduction of the reductase component was obtained resulting in P450/reductase molar ratios of about 1:3 in the microsomal fractions prepared from the co-expression strains. At the same time, the rates of cytochrome P450-dependent lauric acid hydroxylation increased more than 10-fold, showing a proper reconstitution of the C. maltosa monooxygenase systems in S. cerevisiae. Using intact cells, an efficient biotransformation of lauric acid to omega-hydroxylauric acid and dodecanedioic acid was found. S. cerevisiae cells coexpressing cytochrome P450 and NADPH-cytochrome P450 reductase were characterized by a marked proliferation of the endoplasmic reticulum. Immunoelectron microscopy revealed a colocalization of the monooxygenase components produced to these newly formed membrane structures.

Effect of quinolinic acid administered during pregnancy on the brain of offspring

The brains of rat offspring were histologically and histochemically examined after quinolinic acid administration to mothers during the gestation period. Quinolinic acid was administered intraperitoneally in a dose of 30 or 60 mmol, once daily, throughout the entire gestation period. Brain specimens were taken on days 1, 5, and 21 after birth from experimental and control animals. The neuronal cell body injury was detected in the selected brain formations. More profound alterations were seen in the substantia nigra and cerebral cortex, especially within the entorhinal area, whereas much less damage was noted in the striatum and hippocampus. Strongly pronounced symptoms of cerebral edema were seen. Histochemically, an increased activity of NADPH-reductase within neuronal cell bodies of the pyramidal layer in the hippocampus, striatum and cerebral cortex was demonstrated. The decrease of activity of succinic and alpha-glycerophosphate dehydrogenases within areas of tissue spongiosis was noted. The weak overall activity of MAO made it impossible to register changes in its intensity. No changes in the Ca-ATP-ase activity in brain formations after quinolinic acid treatment were observed. It has been reported that excitotoxic brain injury caused by quinolinic acid displays a selective pattern of neuronal degeneration that affects neuronal cell bodies but spares axons at the site of intracerebral injections (Schwarcz et al. 1983; Lehmann et al. 1985; Vezzani et al. 1986), as well as following systemic administration (Beskid and Markiewicz 1988; Beskid and Finiewicz-Murawiejska 1992). The excitotoxic activity of this compound can be detected by making use of the properties of the N-methyl-D-aspartate (NMDA) receptor agonist (Stone et al. 1987).(ABSTRACT TRUNCATED AT 250 WORDS)

Glutathione-S-transferase and NADPH cytochrome P450 reductase activities in rat placenta during pregnancy

Mammalian gestation depends on the continuous synthesis of steroid hormones such as progesterone, estrogens and gonadotrophic hormones. Placental microsomes are involved in the metabolism of steroid hormones via NADPH cytochrome P450 reductase; this last enzyme is involved in the generation of O2 and H2O2. These partially reduced oxygen forms are scavenged by endogenous antioxidants such as GSH and the related GSH-S-transferase enzyme. The present study has the aim of evaluating whether placental hormonal modification occurring during gestation influences NADPH cytochrome P450 reductase and GSH-S-transferase activities. The results demonstrate a gradual increase of both enzymatic activities which suggests a defense ability of the placenta.

Measurement of NADPH-cytochrome P-450 reductase content in rat liver sections by quantitative immunohistochemistry with a video image processor

We have a quantitative light microscopic immunohistochemical method using video image processing. First, an antigen (NADPH-cytochrome P-450 reductase) content in homogenates of livers of rats was measured by enzyme immunoassay. Then frozen sections from rat livers were incubated with the anti-NADPH-cytochrome P-450 reductase antibody under saturation conditions by the indirect immunoperoxidase method. Subsequently, relative staining intensities in small portions and those in wide areas in the sections were measured with a video image processor. Finally, the resulting relative values obtained from the small portions were converted into absolute NADPH-cytochrome P-450 reductase contents using the results of enzyme immunoassay and the average relative staining intensity obtained from the wide areas in the sections. The reductase content in sections from rat livers measured by the image processing method coincided with the content measured by the microphotometric method using a nitrocellulose model system. The present image processing method is applicable to measurement of contents of antigens that can not be immobilized in model systems.

Expression of cytochrome P450 in rat pleural mesothelial cells in secondary cultures

Cultured rat pleural mesothelial cells (RPMC) isolated from male Sprague-Dawley rats have been shown to metabolize polycyclic aromatic hydrocarbons to more oxygenated metabolites. This capacity, which is maintained with passages, suggested the presence of monooxygenase enzymes. In order to clarify the enzymatic pathway, we investigated the expression of cytochromes P450 (CYP) in cultured RPMC by Western and Northern blot analyses. Cells were cultured in Ham's F10 medium supplemented with 10% fetal calf serum. The CYP expression was studied from passage 9 to 16 on different cell strains treated for 48 hours with P450 inducers. CYP1A1 apoprotein expression was very low in untreated cells, but was markedly induced after treatment with 1 microM 3-methylcholanthrene or 22 microM beta-naphthoflavone. CYP1A1 mRNA was not detected in untreated cells and appeared after 3-methylcholanthrene treatment. CYP2E1 apoprotein was constitutively expressed in cultured RPMC, and markedly increased by 170 mM ethanol, and 0.1 microM or 1 microM dexamethasone treatments. Unexpectedly, whereas the amount CYP2E1 mRNA was not modified by ethanol treatment, dexamethasone has a marked inductive effect on CYP2E1 mRNA level. The CYP expression pattern was found similar in RPMC issued from different rats, and not dependent on passage number. The CYP expression and the detection of NADPH-P450 reductase, and of epoxide hydrolase, ascertained that RPMC contain the overall enzymatic pathway required for the biotransformation and activation of procarcinogen compounds, such as polycyclic aromatic hydrocarbons and nitrosamines. Both expression and regulation properties are maintained in long-term cultures of RPMC.

Localization of NADPH cytochrome P450 oxidoreductase in rat brain by immunohistochemistry and in situ hybridization and a comparison with the distribution of neuronal NADPH-diaphorase staining

An antibody to cytochrome P450 oxidoreductase, purified from rat liver, has been used for the immunohistochemical localization of cytochrome P450 oxidoreductase-like immunoreactivity in the rat central nervous system. The distribution of this immunoreactivity has been confirmed using in situ hybridization with specific cytochrome P450 oxidoreductase antisense DNA probes. Cytochrome P450 oxidoreductase immunoreactivity was detected in neurons and was found in some glial populations. Immunoreactivity and in situ messenger RNA signals were present in many forebrain areas including the olfactory bulb, in the cerebral cortex, caudate-putamen, globus pallidus, hypothalamus, thalamus and hippocampus. Cytochrome P450 oxidoreductase was also detected in the nucleus of the posterior commissure, superior colliculus, intermediate gray layer, periaqueductal gray and in the molecular, Purkinje and granular layers of the cerebellum. In the brain stem, cytochrome P450 oxidoreductase was detected in the substantia nigra, nucleus locus coeruleus and raphe nucleus. Western blotting studies revealed the brain immunoreactive protein has a mol. wt of approximately 72,000, as reported for cytochrome P450 oxidoreductase purified from rat brain microsomes. The distribution of cytochrome P450 oxidoreductase immunoreactivity was compared with the distribution of cells exhibiting NADPH diaphorase activity, which has been established as a histochemical marker for neuronal nitric oxide synthase, an enzyme which has a C-terminus with some structural similarity with cytochrome P450 oxidoreductase and catalyses a complex reaction resulting in the synthesis of nitric oxide from arginine. In general, cytochrome P450 oxidoreductase immunoreactivity and nitric oxide synthase diaphorase activity did not co-localize; however, some neuronal populations did express nitric oxide synthase and exhibit cytochrome P450 oxidoreductase immunoreactivity. Results of immunohistochemistry and in situ hybridization experiments suggest cytochrome P450 oxidoreductase is widespread in the rat central nervous system. The distribution pattern of cytochrome P450 oxidoreductase did not match with those of any one neurotransmitter; however, it did coincide with some brain regions known to harbour central catecholaminergic neurons. The general distribution of cytochrome P450 oxidoreductase was similar to the distribution reported for haeme oxygenase 2 and several cytochrome P450 enzymes. It is possible that malfunctions in cytochrome P450 enzyme systems and/or the haeme oxygenase 2 pathways, both of which involve cytochrome P450 oxidoreductase, may have implications in neurodegenerative diseases.

Several compartments of Saccharomyces cerevisiae are equipped with Ca(2+)-ATPase(s)

Sucrose density fractionation of yeast membranes revealed two major and two minor peaks of 45Ca2+ transport activity which all co-migrate with marker enzymes of the endoplasmic reticulum, Golgi and membranes associated with these compartments as well as with ATPase activity measured when all other known ATPase are inhibited. Co-migration of 45Ca2+ transport and ATPase activities was also found after removal of plasma membranes by concanavalin A treatment. SDS-PAGE at pH 6.3 shows the Ca(2+)-dependent formation of acyl phosphate polypeptides of about 110 and 200 kDa. It is concluded that several compartments or sub-compartments of yeast are equipped with Ca(2+)-ATPase(s). It is proposed that these compartments are derived from the protein secretory apparatus of yeast.

Inhibition of thyroid NADPH-oxidase by 2-iodohexadecanal in a cell-free system

The major nonpolar iodolipid formed in horse thyroid cells has recently been identified as 2-iodohexadecanal (2-IHDA). We have investigated in vitro the effect of 2-IHDA on the NADPH-oxidase, NADPH-cytochrome c reductase, and thyroid peroxidase (TPO) activities of a porcine thyroid plasma membrane preparation. 2-IHDA inhibited NADPH-oxidase activity, with half-inhibition at 3-5 microM, but it had no effect on NADPH-cytochrome c reductase. It inhibited the TPO-catalyzed iodination of protein, but not iodide oxidation. Hexadecanal also inhibited NADPH-oxidase. Inhibition by the non-iodinated lipid aldehydes depended on the length of their aliphatic chain: dodecanal and tridecanal gave maximal inhibition. Free iodide, 2-iodohexadecanol and palmitic acid all had no inhibitory effect. Washing treated membranes showed that the inhibition of NADPH-oxidase by hexadecanal was fully reversible, whereas that of 2-IHDA and other iodinated or brominated alkanals was irreversible. Thus the interaction between some residues of the thyroid NADPH-oxidase and the lipid aldehyde groups was favored or stabilized by the iodine atom. Modification of primary amine and thiol groups of NADPH-oxidase inhibited its activity. These groups could also be the target of lipid aldehydes. We suggest that 2-IHDA, because it inhibits TPO and more profoundly the H2O2-generating system in thyroid plasma membrane, modulates iodide metabolism in the thyrocyte and may mediate the Wolff-Chaikoff effect.

Stability of microsomal monooxygenases in murine liver S9 fractions derived from phenobarbital and beta-naphthoflavone induced animals under various long-term conditions of storage

The aim of this study was to define the long-term stability of metabolizing enzymes in activating preparations for short-term genotoxicity bioassays under various storage conditions. Expressions of cytochrome P450 content, NADPH-cytochrome (P450) c-reductase activity, and of the several monooxygenases, such as aminopyrine N-demethylase (class IIIA P450), p-nitroanisole O-demethylase (mixed), dinemorphan N-demethylase (IIB1), ethoxyresorufin O-deethylase (IA1), ethoxycoumarin O-deethylase (mixed), and pentoxyresorufin O-dealkylase (IIB1), were examined in S9 fractions derived from Na-phenobarbital (PB) plus beta-naphthoflavone (beta-NF) induced male and female mice, stored at -80 degrees C, or lyophilized and stored at -20 degrees C. Lipid peroxidation was also determined. Cytochrome P450 and the associated activities were decreased by 30-82% within 9 months of storage. The pattern and degree of relative stabilities were different for the various isoforms. The IA1-like activity, for example, was much more stable (approximately 49% loss) than IIB1-like activities (up to 82% loss). In general, lyophilized enzymes were less stable than directly frozen preparations. In addition, immediately after freeze-drying (lyophilization), a marked decrease in activity of up to 35% was observed. On the contrary, demethylation of aminopyrine and p-nitroanisole remains almost constant over 6 months storage at -196 degrees C. The results obtained indicate that either fresh, daily made S9 fractions or, alternatively, fractions stored in liquid nitrogen (up to 6 months) are recommended for mutagenesis studies.

Rate of alteration of hepatic mixed-function oxidase system in rats fed different dietary fats

Studies were carried out to evaluate and relate the rate of alteration in mixed-function oxidase system with the changes of the fatty acid composition of rat microsomes induced by different dietary lipids. Male weanling rats were fed from day 21 to 120 with a commercial rat diet or a semisynthetic diet containing no fat or 10% fat consisting of peanut-rapeseed oil, sunflower oil, or salmon oil. In rats fed a fat-free diet, the cytochrome P-450 concentration and aniline hydroxylase, aminopyrine N-demethylase, and NADPH-cytochrome-c reductase activities of liver microsomes at 120 days were, respectively, 26, 16, 10, and 24% lesser than those of rats fed the control diet. However, cytochrome b5 concentration and NADH-cytochrome-b5 reductase activity were, respectively, 33 and 43% higher than those of the control group at the same time. When rats were fed the sunflower oil diet, the cytochrome P-450 concentration and NADH-cytochrome-b5 reductase activity at 120 days were, respectively, 11 and 23% lesser than those of control group. But the cytochrome b5 concentration was 10% higher than that of the control group. In rats fed the fish oil diet, the cytochrome P-450 concentration and NADPH-cytochrome-c reductase, aniline hydroxylase, and aminopyrine N-demethylase activities at 120 days were, respectively, 30, 48, 41, and 31% higher than those of rats fed the control diet. These enzymes were correlated very well (0.84 < r < 0.93), P < 0.05 with dietary sigma polyunsaturated fatty acids (n-3).(ABSTRACT TRUNCATED AT 250 WORDS)

Tissue distribution of microsomal cytochrome P-450 monooxygenases and their inducibility by phenobarbital in the insecticide resistant LPR strain of house fly, Musca domestica L

Cytochrome P-450s, cytochrome b5, P-450 reductase, and four P-450 monooxygenase activities were abundant in proximal intestine (PI), Malpighian tubules (MT), and fat bodies (FB) in the insecticide resistant (LPR) strain of house fly. Insecticide resistance in LPR flies was associated with increases in P-450 monooxygenase activities in nearly all of these tissues relative to an insecticide susceptible strain. Cytochrome P-450lpr was present in all tissues and at higher levels in LPR than in susceptible flies suggesting that the role of P-450lpr in monooxygenase-mediated insecticide resistance is not due to its higher levels in a single tissue. However, it appears that fat bodies may have a major role in resistance due to their relatively large size and the abundance of P-450lpr in this tissue. Total cytochrome P-450s, cytochrome P-450lpr and P-450 monooxygenase activities were generally refractory to phenobarbital (PB) induction in LPR. This contrasts with a previous report in susceptible house flies showing that P-450 monooxygenases were induced by PB. It appears that total P-450s, cytochrome P-450lpr and monooxygenase activities were expressed at constitutive high levels in several tissues of LPR house flies.

Calcium transport by basolateral membranes of diabetic rats

The current study was designed to examine calcium transport across the basolateral membrane of the enterocyte of control and diabetic rats. The slope of initial rate of ATP-dependent calcium uptake was significantly greater in controls than in diabetic rats (P < 0.001). Kinetic analysis of ATP-dependent calcium uptake showed a maximum velocity (Vmax) of 0.19 +/- 0.02 and 0.37 +/- 0.01 mumol.g protein-1.-s-1 in diabetic and control rats, respectively (P < 0.01). Km values were similar. Insulin therapy and calmodulin added to freeze-thawed basolateral membranes vesicles stimulated Vmax of ATP-dependent calcium uptake in diabetic membranes to values close to those of controls without a change in Km values. In contrast, the C(++)-Na+ exchange process was similar in both control and diabetic rats. These results suggest that the ATP-dependent calcium uptake process is decreased in diabetic animals. This decrease is stimulated by calmodulin or insulin therapy, implying a causal relationship between insulin deficiency and calmodulin activity in diabetes.

Effects of aging on cholinephosphotransferase activity on guinea pig lung mitochondria and microsomes

It is known that the composition of phospholipids in lung changes with age. The final step in the de novo synthesis of phosphatidylcholine, a major component of lung surfactant, by the CDP-choline pathway, requires the enzyme cholinephosphotransferase (CPT). Even though CPT has earlier been proposed to be located exclusively in the endoplasmic reticulum, we have recently demonstrated its presence also in the mitochondria. We have earlier reported a gestational variation of CPT activity in fetal mitochondria and microsomes. In the present study we examined the subcellular distribution of CPT activity in lung as a function of age. After birth, the microsomal CPT activity continued to increase until adulthood (24 wks of age), thereafter it gradually decreased. On the otherhand, the CPT activity of mitochondria continued to increase with the advancement of age and beyond 72 wks of age, it was approximately 2-fold higher than that of the microsomal fraction.

Carbon monoxide: a putative neural messenger

Carbon monoxide, an activator of guanylyl cyclase, is formed by the action of the enzyme heme oxygenase. By in situ hybridization in brain slices, discrete neuronal localization of messenger RNA for the constitutive form of heme oxygenase throughout the brain has been demonstrated. This localization is essentially the same as that for soluble guanylyl cyclase messenger RNA. In primary cultures of olfactory neurons, zinc protoporphyrin-9, a potent selective inhibitor of heme oxygenase, depletes endogenous guanosine 3',5'-monophosphate (cGMP). Thus, carbon monoxide, like nitric oxide, may be a physiologic regulator of cGMP. These findings, together with the neuronal localizations of heme oxygenase, suggest that carbon monoxide may function as a neurotransmitter.

Densities of NADPH-ferrihemoprotein reductase and cytochrome P-450 molecules in the endoplasmic reticulum membrane of rat hepatocytes

In hepatocytes, NADPH-ferrihemoprotein reductase (reductase) has been hypothesized to exist as aggregates or micelles in endoplasmic reticulum (ER) membrane. However, if the number of reductase molecules per unit area of ER is low, this hypothesis cannot explain how a few reductase molecules efficiently reduce many P-450 molecules. To test this hypothesis, we estimated the numbers of reductase and P-450 molecules per unit ER area (reductase and P-450 densities) by microphotometry of the two enzymes in conjunction with morphometry of ER in periportal, midzonal, and perivenular rat hepatocytes. The reductase density in periportal, midzonal, and perivenular hepatocytes (107-179 molecules/microns 2 of ER) was high enough to efficiently reduce all P-450 molecules in the ER, although the value in perivenular hepatocytes was lowest owing to the relatively greater amount of ER in this region. The pattern of sublobular gradient in the reductase density was similar to that in the P-450 density. Consequently, the molar ratio of P-450 to reductase in ER was similar (about 40:1) in hepatocytes regardless of their positions within the liver lobule.

Stable expression of guinea pig NADPH-cytochrome P450 reductase and monkey P4501A1 cDNAs in Chinese hamster cells: establishment of cell lines highly sensitive to aflatoxin B [corrected]

To the cell line (A-15) expressing monkey P4501A1, which was developed from a Chinese hamster fibroblast cell line (CHL), a guinea pig [corrected] cDNA encoding NADPH-cytochrome P450 reductase was introduced and the transformants (designated AR-10, AR-13, and AR-18) stably expressing the reductase of increased level were established. The high-level expression of the reductase was confirmed by Northern and Western blot analyses and by measurement of the reductase activity in microsomes. The transfected clones showed 4- to 11-fold higher activity of the reductase than the parental cells. These cells showed about 9-fold higher sensitivity toward aflatoxin B1 (AFB1) cytotoxicity than A-15 cells and about 330-fold more than parental CHL cells. No difference in sensitivity was observed between CHL and the CHL-derived clones (CR-50, CR-52, and CR-68) expressing high levels of the reductase alone. Increased sensitivity of AR-10 cells was also observed with respect to sterigmatocystin cytotoxicity. Furthermore, in the assay for the induction of chromosomal aberrations, these clones were highly sensitive to AFB1. These results indicate that the level of the P450 reductase existing in parental CHL cells is not sufficient for maximal activity of monkey P4501A1.

Investigation of the mechanism by which cyclophosphamide alters cytochrome P450 in male rats

The effects of administration of the cytotoxic agent cyclophosphamide on cytochrome P450 have been examined in the liver microsomes of male rats. Microsomes were prepared after cyclophosphamide administration 1, 4 or 7 days prior to killing. The coadministration of cyclophosphamide with N-acetylcysteine has also been investigated. The microsomes were assayed for NADPH cytochrome P450 reductase, aminopyrine demethylase, erythromycin demethylase and androstenedione hydroxylase activities. Activities were generally unchanged 1 and 4 days after cyclophosphamide administration and were significantly decreased at 7 days. N-Acetylcysteine did not alter the effects of cyclophosphamide at 7 days. The effect of cyclophosphamide in vitro has also been examined. Microsomes from untreated animals were subjected to the above assays following in vitro metabolic activation of cyclophosphamide in a reconstituted system in the presence and absence of N-acetylcysteine. All enzyme activities were significantly reduced by the cyclophosphamide metabolites. The presence of N-acetylcysteine prevented this inactivation. The results of these investigations suggest that cyclophosphamide inactivates hepatic cytochrome P450 in vitro and in vivo via different mechanisms.

Purification of an inositol 1,4,5-trisphosphate-binding calreticulin-containing intracellular compartment of HL-60 cells

To investigate the identity of Ins(1,4,5)P3-sensitive intracellular Ca2+ stores in myeloid cells, we have developed a method that yields subcellular fractions highly enriched in Ins(1,4,5)P3 binding. HL-60 cells were disrupted by nitrogen cavitation, and subcellular fractions were obtained by differential centrifugation, followed by Percoll- and sucrose-density-gradient separations. A subcellular fraction enriched 26-fold in Ins(1,4,5)P3-binding sites was obtained. This fraction showed no enrichment in plasma-membrane markers and only a comparatively moderate enrichment (7-fold) in endoplasmic-reticulum markers. The ratio between specific enrichment of Ins(1,4,5)P3 binding and endoplasmic-reticulum markers in the different fractions varied over 50-fold, from less than 0.1 to greater than 5. The purified Ins(1,4,5)P3-binding fraction was enriched to a similar extent (27-fold) in the putative intravesicular Ca(2+)-storage protein calreticulin. Our results favour the concept of a distinct Ins(1,4,5)P3-binding, calreticulin-containing compartment (i.e. the calciosome) in HL-60 cells.

Subcellular distribution of (+)-[3H]SKF 10,047 binding sites in rat liver

The distribution of (+)-[3H]SKF 10,047 binding sites and the distribution of the established plasma membrane, nuclear, mitochondrial and endoplasmic reticulum markers in subcellular fractions of rat liver have been studied. The distribution profile of (+)-[3H]SKF 10,047 binding sites coincided with that of NADPH-cytochrome c reductase, the endoplasmic reticulum marker. (+)-[3H]SKF 10,047 binding sites in rat liver are therefore suggested to be located on the endoplasmic reticulum membrane and to represent a membrane-bound enzyme.

Superoxide anion production and toxicity in V79 cells of six hydroxy-anthraquinones

This study investigates the cytotoxic and genotoxic effects of various carboxy AQ, 1,4-dihydroxy 6-carboxy AQ, 1,8-dihydroxy 3-carboxy AQ, 1,4-dihydroxy AQ, 1,5-dihydroxy AQ, 1,8-dihydroxy AQ and 2,6-dihydroxy AQ in V79 Chinese hamster cells. The V79 cells were used since, as they contain flavoproteins but not cytochrome P-450, they can bioactive xenobiotics only through the reductive pathway excluding the oxidative one. In addition, the abilities of AQs to stimulate O2-production using both purified flavoproteins (NADH-dehydrogenase, NADPH-cytochrome P-450 reductase) and V79 subcellular fractions (homogenate and microsomes) were assayed. The NADH and NADPH consumption stimulated by AQs in V79 microsomes was also determined. The results showed that the carboxylic-containing drugs and the 1,4-dihydroxy AQ were weak sister chromatid exchange inducers and the most toxic among the six anthraquinones examined. Dicumarol, a potent inhibitor of DT-diaphorase, reduced, rather than potentiated, both the cytotoxicity and genotoxicity caused by these AQs. Thus, the higher superoxide formation rates stimulated by the carboxylic-containing AQs compared to those of the other quinones with all the in vitro systems used, suggested, except for the 1,4-dihydroxy AQ, a possible relationship between cytotoxicity and O2-production. For the 1,4-dihydroxy AQ toxicity, a specific bioactivation route was hypothesized.

Differences in lipid characteristics of undifferentiated and enterocytic-differentiated HT29 human colonic cells

In this paper we compared several lipid characteristics of the homogenate and the corresponding plasma membrane in undifferentiated and differentiated HT29 human colon cancer cells, using normal human colonic cells as a reference. Electron microscopy showed that HT29 cells were morphologically undifferentiated when cultured in the presence of either glucose or inosine without glucose at early confluency. On the contrary, HT29 cells cultured at late confluency in a glucose-free medium containing inosine or grown in nude mice exhibited an enterocytic differentiation with the presence of tight junctions and an apical brush border. The cell homogenate and the plasma membrane were prepared from each cell type. The study of specific marker enzymes showed the same degree of purity in all plasma membranes, with a highly marked increase of brush border-associated hydrolases (N-aminopeptidase and alkaline phosphatase) only in the organelles isolated from differentiated HT29 and colonic cells. Respective similar increases in the amount of free cholesterol and phospholipid and in the free cholesterol:phospholipid molar ratio were found in the plasma membrane as compared with the homogenate in all HT29 cell types. This ratio, due to an increased phospholipid content in both homogenate and plasma membrane, was lowered in colonic cells. No differences in the phospholipid profile were found between the homogenates of all cell types and the plasma membrane of undifferentiated HT29 cells, with the exception of a decrease of cardiolipin in this organelle. On the contrary, the plasma membrane phospholipid composition was different from that of the corresponding homogenate in differentiated HT29 and colonic cells. The most striking changes were a highly increased sphingomyelin amount and concomitant decreases in phosphatidylethanolamine, phosphatidylserine, and cardiolipin. Moreover, differences in the percentage of phosphatidylcholine plus sphingomyelin as well as in phosphatidylcholine:sphingomyelin, phosphatidylethanolamine, and/or phosphatidylcholine molar ratios were also found. The monounsaturated:polyunsaturated fatty acid ratio in phosphatidylethanolamine was similar in differentiated HT29 and colonic cells and lower than in undifferentiated HT29 cells. A decrease in this latter ratio in phosphatidylcholine was also observed in colonic cells and HT29 cells grown in nude mice. These changes were essentially due to opposite variations in the percentage of palmitoleic acid and those of linoleic and/or arachidonic acids in both phospholipids. Thus, these data indicate that undifferentiated HT29 cells were characterized by the absence of a specific phospholipid composition in their plasma membrane, which is suggested to be related to altered phospholipid sorting. The plasma membrane phospholipid profile reversed essentially to the normal pattern when HT29 cells recovered the ability to differentiate.

Microsomal enzymes in lambs and adult sheep, and their possible relationship to alveld

The difference in susceptibility to alveld between lambs and adult sheep may be caused by differences in the microsomal enzyme activities in their livers. There was no difference in NADPH-cytochrome c reductase or 7-ethoxyresorufin-O-deethylase (EROD) activity between ewes, control lambs and phenobarbitone-dosed lambs 3 weeks after dosing ceased. However, aldrin epoxidase activity was at that time significantly highest in the phenobarbitone-dosed lambs and significantly lowest in the ewes. The liver cytosolic glutathione transferase activity was significantly highest in the ewes and significantly lowest in the control lambs at the same time.

Caloric restriction affects liver microsomal monooxygenases differentially in aging male rats

Caloric restriction (CR) extends life span and retards the onset of physiological changes and pathologies associated with aging, but the underlying mechanisms remain unresolved. This study demonstrates that CR postpones the documented age-related declines in and/or enhances the activity and microsomal concentration of several liver monooxygenases in male rats, i.e., NADPH cytochrome P-450 reductase, total cytochromes P-450. However, the relative concentration of cytochrome P-450b+C did not exhibit statistically significant changes, whereas another isozyme, the male specific P-450h, declined significantly in both ad libitum-fed and CR rats as a function of increasing age. While CR appears to retard age-associated changes in certain liver enzymes, this effect is by no means universal. The hepatic monooxygenases constitute a well-characterized enzyme system in which to examine the perturbation of the aging process by CR.

Mechanisms of cyclophosphamide action on hepatic P-450 expression

Cyclophosphamide was administered to adult male rats (130 mg/kg, single i.p. injection) and its effects on the P-450 enzymes that contribute to the activation of this drug in rat liver were then assessed. P-450-mediated cyclophosphamide 4-hydroxylase activity in isolated rat liver microsomes decreased by approximately 70% over a 9-day period following drug treatment. This decrease was due to the loss of cytochrome P-450 form 2c (IIC11), a major contributor to cyclophosphamide 4-hydroxylation in untreated male rat liver, while the other major hepatic cyclophosphamide 4-hydroxylase, P-450 PB-1 (IIC6), was largely unaffected. The loss of P-450 2c activity did not result from a decrease in P-450 reductase or from direct inactivation of the P-450 protein by cyclophosphamide or its metabolites, but rather was due to a reduction in hepatic P-450 2c protein and mRNA levels. Hepatic P-450 2a (IIIA2) and P-450 RLM2 (IIA2) were also suppressed by cyclophosphamide treatment. Serum testosterone, which contributes to the expression of P-450s 2c, 2a, and RLM2, was severely depleted in the cyclophosphamide-treated rats; however, this loss was not the direct cause of the decreases in these hepatic P-450s, since the decreases were not reversed upon restoration of normal testosterone levels by human chorionic gonadotropin stimulation of testicular androgen production. In contrast to the suppression of these testosterone-dependent P-450s, P-450 3 (IIA1), P-450j (IIE1), and the P-450-independent microsomal enzyme steroid 5 alpha-reductase were each elevated in rat liver following cyclophosphamide administration. In contrast to P-450 3 and steroid 5 alpha-reductase, however, the elevation of P-450j protein was transient and was not accompanied by an increase in P-450j-associated hepatic microsomal aniline hydroxylase activity. In vitro experiments revealed that P-450j was severalfold more susceptible to inactivation by the cyclophosphamide metabolite acrolein as compared with P-450 3. These observations suggest that P-450j protein is induced by cyclophosphamide treatment but that the protein is inactivated by the cyclophosphamide metabolite acrolein. These findings establish that cyclophosphamide treatment can modulate hepatic P-450 activities through multiple mechanisms and in a manner that may alter P-450 metabolism of cyclophosphamide and perhaps other anticancer drugs that undergo bioactivation in the liver.

Reductive metabolism of 3-amino-1,2,4-benzotriazine-1,4-dioxide (SR 4233) and the induction of unscheduled DNA synthesis in rat and human derived cell lines

The cellular and microsomal reductive metabolism of 3-amino-1,2,4-benzotriazine-1,4-dioxide (SR 4233) was studied aerobically and anaerobically in rat (JB1, BL8, Walker) mouse (3T3) and human (HepG2) derived cell lines. In all cases rates or reduction to the mono-N-oxide (SR 4317) were greater under anaerobic than aerobic conditions when determined using HPLC with UV and fluorescence detection. Of the rat derived cells, a transformed liver epithelial line (JB1) showed the greatest cellular and microsomal rates of reduction while Walker 256 carcinoma cells showed the lowest. Microsomal reduction of SR 4233 was the highest in preparations from rat liver but carbon monoxide did not inhibit the reaction, suggesting cytochrome P450 was not involved. Purified cytochrome P450 reductase could carry out the reduction of SR4233. Rates of reduction of SR4233 in microsomal preparations from the cell lines and in rat liver nuclei correlated with activities of cytochrome P450 reductase. Activation of SR 4233 to cause cellular DNA damage was measured using unscheduled DNA synthesis as an index. Under anaerobic conditions, SR 4233 caused a dose-dependent increase in unscheduled DNA synthesis. Only a slight increase occurred following aerobic incubation. No increase was seen using the reduced metabolites SR 4317 or SR 4330. Of the cell lines studied, Walker cells showed the highest induction of unscheduled DNA synthesis. It was concluded that rates of reduction of SR 4233 did not necessarily reflect the potential DNA-damaging effects of this compound.

Cytochrome P450 reductase, antioxidant enzymes and cellular resistance to doxorubicin

Our data suggest that DOX resistance in P388/R-84 cells may result, at least in part, from reduced free radical formation by both suppression of flavin reductase(s) and overexpression of certain antioxidant enzymes such as GSH peroxidase and catalase. In addition, our results, in conjunction with other studies, indicate that flavin reductase(s) and antioxidant enzymes are differentially altered in cancer cells with acquired or de novo resistance to DOX. Further studies are needed, however, to elucidate the mechanism(s) by which the gene expression of these enzymes is regulated in drug-sensitive and -resistant cells.