Effects of chronic pulmonary overcirculation on pulmonary vasomotor tone

BACKGROUND

A model of shunt-induced pulmonary hypertension was used to study the effects of pulmonary overcirculation on endothelial nitric oxide synthase (eNOS) and cytochrome P450-4A (cP450-4A) vasodilatory mechanisms and related hemodynamic responses.

METHODS

An aortopulmonary shunt was constructed in 6-week-old piglets (n = 7, sham-operated controls n = 8). Hemodynamic measurements were made 4 weeks later under serial experimental conditions: baseline (fractional concentration of oxygen, 0.4); inhaled nitric oxide, 25 ppm (INO); hypoxia (fractional concentration of oxygen, 0.14); hypoxia + INO; N(omega)-nitro-L-arginine methylester (L-NAME 30 mg/kg intravenously, competitive NOS inhibitor); and L-NAME + INO. Lung protein levels of eNOS and cP450-4A and NOS activity were compared between groups.

RESULTS

Shunted animals had a higher baseline pulmonary artery pressure (p < 0.05). L-NAME resulted in a greater increase in pulmonary vascular resistance in shunted animals (150% +/- 26% shunt versus 69% +/- 14% control; p = 0.01). The INO administered during baseline conditions decreased pulmonary vascular resistance only in control animals (p < 0.05). Protein levels of eNOS and NOS activity were similar in both groups; however, cP450-4A protein levels were decreased in the shunted group (p = 0.02).

CONCLUSIONS

The NO production was preserved in shunted animals but they demonstrated greater vasodilatory dependence on NO, evidenced by an exaggerated increase in pulmonary vascular resistance after NOS inhibition. Loss of the cP450-4A vasodilatory system may be the driving force for NO dependency in the shunted pulmonary circulation.

Cytochrome P450 1B1 mRNA measured in blood mononuclear cells by quantitative reverse transcription-PCR

Cytochrome P450 (CYP) 1B1 activates polycyclic aromatic hydrocarbons and aryl aromatic hydrocarbons to carcinogens. We describe a competitive reverse transcription-PCR (RT-PCR) assay for the quantification of CYP1B1 mRNA in blood mononuclear cells (BMCs) by simultaneous RT and PCR amplification of cellular RNA with decreasing amounts of an internal standard. The concentration of CYP1B1 mRNA is derived from the ratio between the intensities of the bands corresponding to the amplified products. To reduce the variability of mRNA extraction efficiency, the measured amount of CYP1B1 has been calculated in relation to the beta-actin gene products. We measured CYP1B1 expression in the BMCs of 75 human subjects; no significant differences in the CYP1B1:beta-actin ratio were detected between women (range, 0.47-4.35; median, 2.0) and men (range, 0.72-3.85; median, 2.09). The analytical imprecision (CV) of duplicates was 14% (n = 25 pairs), and the intraindividual CV for two samples, 1 month apart, was 22% (n = 20). No significant differences were detected in smokers (n = 25; range, 0.77-3.55; median, 2.14) compared with nonsmokers (n = 50; range, 0.47-4.35; median, 2.0). The method has a wide range of linearity, good sensitivity and precision, and is suitable for studies of individual susceptibility as indicated by CYP1B1 expression in BMCs.

Fatty acid omega- and (omega-1)-hydroxylation in experimental alcoholic liver disease: relationship to different dietary fatty acids

Arachidonic acid concentrations in liver are decreased in response to ethanol administration. In addition, the oxygenated products of arachidonic acid metabolites could affect the severity of alcoholic liver injury. Selective utilization of arachidonic acid by the cytochrome P-450 system could, in part, account for the decrease in arachidonic acid. To evaluate this pathway further, male Wistar rats were fed different dietary fats: medium chain triglycerides, palm oil, and corn oil or fish oil with either ethanol or isocaloric amounts of dextrose. Histopathology, cytochrome P-4502E1 (CYP2E1) and cytochrome P-4504A (CYP4A), and omega- and (omega-1)-hydroxylation products of lauric and arachidonic acids were evaluated. Ethanol induction of CYP2E1 was related to the concentration of polyunsaturated fatty acids in the diet; induction of CYP4A by ethanol was seen in all groups. The highest levels of 11-hydroxy-lauric acid and 19-hydroxyarachidonic acid (omega-1) were seen in rats fed ethanol with palm oil and corn oil. Highly significant correlations were seen between the (omega-1)-hydroxylation products and CYP2E1 activity. No correlation was seen between the omega-hydroxylation products and CYP2E1 activity. In contrast, the levels of omega-hydroxylation products correlated with CYP4A. The overall results showed a significant increase in (omega-1)-hydroxylation products in rats fed diets containing significant amounts of linoleic acid (i.e., palm oil and corn oil).

Analysis of midazolam and metabolites in plasma by high-performance liquid chromatography: probe of CYP3A

Hydroxylation of midazolam (MDZ) is mediated almost exclusively by CYP3A isoforms. The authors describe a high-performance liquid chromatography assay involving MDZ, 1'-hydroxymidazolam, and 4-hydroxymidazolam in plasma. The compounds were eluted on an Ultrasphere ODS, 3-microm particle size, 7.5 cm x 4.6 mm reversed-phase column and monitored by ultraviolet absorbance at 254 nm. The composition of the mobile phase was 35.2% acetonitrile:4.8% methanol:60% buffer acetate (vol/vol/vol), 0.1 M, pH 4.7; the flow rate was 1 ml/minute. Calibration curves were linear (coefficients of correlation > 0.99) within the range of concentrations established (20 to 640 nM). Within- and between-day coefficients of variation were consistently better than 8%. The overall recovery was >90% and the lowest detectable concentration was 8 nM. This approach provides a simple, rapid, and sensitive assessment of MDZ and metabolites in plasma, with a very good accuracy and precision, which enables it as an in vivo marker of CYP3A activity in humans.

Effect of dietary lipids on hepatic and extrahepatic sterol 27-hydroxylase activity in high- and low-responding baboons

Our previous studies found that low low-density lipoprotein (LDL)-responding baboons compared with high LDL-responding baboons have higher hepatic sterol 27-hydroxylase activity when consuming a high-cholesterol and high-fat (HCHF) diet. The present studies were conducted to determine whether the extrahepatic activity of sterol 27-hydroxylase is also higher in low-responding baboons and to assess whether the enzyme is regulated at the protein level. We measured the hepatic sterol 27-hydroxylase activity and protein level and plasma 27-hydroxycholesterol concentration in six low- and six high-responding baboons on both the basal and the HCHF diet. We also compared the sterol 27-hydroxylase activity in the adrenal gland and 27-hydroxycholesterol concentration in blood lymphocytes from high- and low-responding baboons consuming the HCHF diet. With the HCHF diet, the plasma 27-hydroxycholesterol concentration and hepatic sterol 27-hydroxylase activity and protein level increased rapidly in low responders, but not in high responders. Blood lymphocytes of low-responding baboons cultured in the presence of lipoprotein-deficient serum (LPDS) had lower cholesterol concentrations than those from high-responding baboons. Addition of exogenous 27-hydroxycholesterol to the culture medium of blood lymphocytes decreased the cellular cholesterol concentration. Plasma 27-hydroxycholesterol and hepatic sterol 27-hydroxylase activity and protein levels were negatively correlated with the plasma VLDL + LDL cholesterol concentration and VLDL + LDL/HDL cholesterol ratio after 6 weeks on the HCHF diet, but not on the chow diet. The results suggest that sterol 27-hydroxylase activity in both hepatic and extrahepatic tissues attenuates the dietary responsiveness in baboons, and the enzyme activity is not regulated by the specific activity of the protein.

Expression of CYP2M1, CYP2K1, and CYP3A27 in brain, blood, small intestine, and other tissues of rainbow trout

Expression of five constitutive forms of cytochrome P450 [(LMC1 (CYP2M1), LMC2 (CYP2K1), LMC3, LMC4, and LMC5 (CYP3A27)] in selected tissues from sexually immature 2-year old female and male rainbow trout (Oncorhynchus mykiss) were examined at the translational level by Western blot using polyclonal antibodies raised in rabbits against those purified trout hepatic P450s. Tissues examined were from brain, liver, muscle, blood, head kidney, trunk kidney, upper intestine, stomach, heart, and gonad (ovary or testis). The results showed that the liver was the major organ for expression of all the trout P450s studied. Trunk kidney was the secondary expression site except for LMC5. Selective translational expression of these P450 isoforms or similar proteins was observed for LCM1 and LMC5 in brain; for LMC2 and LMC5 in female upper intestine; and for LMC2 in blood plasma of the fish studied under the experimental and sampling conditions.

Effects of horminone on liver mixed function mono-oxygenases and glutathione enzyme activities of Wistar rat

The present study reports on the effects of horminone on serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels, on hepatic cytochrome P450 (P450) and cytochrome b5 (cyt b5) contents and on the activities of NADPH-cytochrome P450 reductase (NR), mixed function mono-oxygenases (MFO), glutathione-S-transferase (GST) and glutathione reductase (GR) of Wistar male rat. Horminone is a diterpenoid quinone (7,12-dihydroxyabiet-8,12-diene-11,14-dione) present in several species of the Labiatae family and used as medicinal plants in folk medicine. In this study, horminone was administered by the intraperitoneal route (i.p.) at a concentration of 1 or 10 mg/kg to each group of six mice, using water as a vehicle. On the one hand, results showed that horminone increased serum ALT and AST levels and cyt b5 content and induced the activities of ethylmorphine N-demethylase (EMD). On the other hand, horminone decreased P450 content and inhibited the activities of 7-ethoxyresorufin O-deethylase (ERD), 7-ethoxycoumarin O-deethylase (ECD), aniline 4-hydroxylase (AH) and NR. Based on these results, the possibility of toxic effects occurring after administration of plant extracts containing horminone must be considered.

Role of intestinal P-glycoprotein (mdr1) in interpatient variation in the oral bioavailability of cyclosporine

Interpatient differences in the oral clearance of cyclosporine (INN, ciclosporin) have been partially attributed to variation in the activity of a single liver enzyme termed CYP3A4. Recently it has been shown that small bowel also contains CYP3A4, as well as P-glycoprotein, a protein able to transport cyclosporine. To assess the importance of these intestinal proteins, the oral pharmacokinetics of cyclosporine were measured in 25 kidney transplant recipients who each had their liver CYP3A4 activity quantitated by the intravenous [14C-N-methyl]-erythromycin breath test and who underwent small bowel biopsy for measurement of CYP3A4 and P-glycoprotein. Forward multiple regression revealed that 56% (i.e., r2 = 0.56) and 17% of the variability in apparent oral clearance [log (dose/area under the curve)] were accounted for by variation in liver CYP3A4 activity (p < 0.0001) and intestinal P-glycoprotein concentration (p = 0.0059), respectively. For peak blood concentration, liver CYP3A4 activity accounted for 32% (p = 0.0002) and P-glycoprotein accounted for an additional 30% (p = 0.0024) of the variability. Intestinal levels of CYP3A4, which varied tenfold, did not appear to influence any cyclosporine pharmacokinetic parameter examined. We conclude that intestinal P-glycoprotein plays a significant role in the first-pass elimination of cyclosporine, presumably by being a rate-limiting step in absorption. Drug interactions with cyclosporine previously ascribed to intestinal CYP3A4 may instead be mediated by interactions with intestinal P-glycoprotein.

In vivo function tests of hepatic drug-oxidizing capacity in patients with liver disease

Aminopyrine, antipyrine and trimethadione have been widely used for some time as probe drugs to assess non-selective P450 liver function. They have proved useful in evaluating pre- and post-operative liver function when performing surgery, transplantations, etc., in addition to a general evaluation of liver function and drug interactions. Progress has recently been made both in these non-selective P450 function tests and in the analysis of drug-metabolizing enzymes at a molecular level, which has resulted in more selective P450 function tests. The caffeine (CYP1 A2), chlorzoxazone (CYP2E1), lidocaine (CYP3 A) and midazolam (CYP3 A) function tests and the erythromycin breath test (CYP3 A) are currently being used as specific probes. The future use of these tests needs to be discussed in terms of potential clinical implications.

Three-fold induction of renal 25-hydroxyvitamin D3-24-hydroxylase activity and increased serum 24,25-dihydroxyvitamin D3 levels are correlated with the healing process after chick tibial fracture

To investigate the possible biological actions of 24,25-dihydroxyvitamin D3 (24,25(OH)2D3), a tibial fracture-healing model was established in White Leghorn chicks. Three-week-old White Leghorn chicks fed a vitamin D3-replete diet were divided into four groups (control, anesthetized, sham, and fractured). On varying days after tibial fracture (F) or sham manipulation (S), renal 25(OH)D3-1 alpha-hydroxylase and 25(OH)D3-24-hydroxylase (24-hydroxylase) activities and serum Ca2+ concentrations were measured. Metofane anesthesia was found to have no effect on the activity of either of the hydroxylases; the activities of the hydroxylases in the control, anesthetized, and sham-operated birds were similar. By 10 days after tibial fracture, the renal 24-hydroxylase activity increased more than 3-fold in F (1.33 +/- 0.07 pmol/mg of protein) as compared with S (0.42 +/- 0.03 pmol/mg of protein) (p < 0.0001). A time-dependent study of the renal 24-hydroxylase activity during the fracture repair process revealed a slow increase from the first day after fracture, a higher activity at 8 days, which peaked at 10-11 days, which is consistent with the formation of the callus. The 24-hydroxylase activity then returned to the same level as the sham group 14 days after fracture. There was no significant difference in serum Ca2+ levels between the F and S groups over the 3-week postfracture period. Serum levels of vitamin D3 metabolites were also measured during the fracture healing process: a 3.4x increase of the 24,25(OH)2D3 level in the fractured group (3.64 +/- 1.16 nM) was observed as compared with the control groups (1.08 +/- 0.49 nM) at 10 days after fracture (p = 0.068). No significant differences were observed in the plasma levels of 25(OH)D3 or 1 alpha, 25(OH)2D3 between the group with a fracture and the controls. Exposure of primary chick kidney cells in culture to serum obtained from chicks with a tibial fracture for 20 h resulted in an approximately 40% increase in the activity of the 24-hydroxylase as compared with cells exposed to serum from control birds. These results suggest that 24,25(OH)2D3 is involved in the early process of fracture repair and that there is some form of physiological communication between the fractured bone and the kidney so as to increase the renal 24-hydroxylase and the circulating concentration of this metabolite.

Nitric oxide differentially affects constitutive cytochrome P450 isoforms in rat liver

Recently nitric oxide (NO) was suggested as a final mediator of down-regulation of cytochrome P450 by bacterial lipopolysaccaride (LPS). One proposed mechanism is based on the ability of NO to effectively bind to cytochrome P450 heme iron. However, other evidences exist demonstrating down-regulation of P450 proteins by LPS as well as by different cytokines. Therefore, it is the purpose of our study to investigate the relationship between NO and different P450 proteins in rat liver. One group of Sprague-Dowley rats was treated with LPS for 24 hr and another group was given NO synthase inhibitors, N(G)-nitro L-arginine methyl ester or aminoguanidine at 0, 3, 6, 10 and 20 hr after LPS. LPS treatment caused a 20-fold increase in plasma nitrates, which was almost completely abolished by NO synthase inhibitors. LPS caused a substantial inhibition of the activities of 16alpha- and 6beta-androstenedione hydroxylation, 7-ethoxyresorufin- and 7-pentoxyresorufin-O-dealkylation (EROD, PROD) that was fully prevented by cotreatment with N(G)-nitro L-arginine methyl ester and aminoguanidine. Western blotting showed that the apoproteins of 3A2, 2C11, 1A2 and 2B1/2 were suppressed and NOS inhibitors showed from 29% (3A2) to 100% (2C11) protection of corresponding apoprotein from suppression by LPS. The changes in apoprotein were largely due to changes in corresponding mRNA levels, as demonstrated by Northern blotting. Thus, NO appears to be one of the mediators of the inhibition of 2C11, 3A2, 1A2 and 2B1/2 isozymes by LPS in rat liver.

Selective expression of CYP3A5 and not CYP3A4 in human blood

There is a marked variation between people in the activity of CYP3A4 in liver and intestine. We reasoned that if CYP3A4 was expressed in peripheral blood cells, a simple blood based test of CYP3A4 phenotype might be feasible. We prepared peripheral blood smears from healthy volunteers and performed immunostaining with a rabbit polyclonal antibody that selectively reacts with enzymes within the CYP3A subfamily. Staining was observed only within the cytoplasm of neutrophils (PMNs). cDNA prepared from isolated PMNs and mononuclear cells was subjected the polymerase chain reaction using as primers synthetic oligonucleotides that selectively amplify fragments of each known CYP3A cDNAs (CYP3A3, CYP3A4, CYP3A5, and CYP3A7). Amplification was only obtained with the CYP3A5 specific oligonucleotides, predominantly in PMNs, and the identity of the amplified fragment was confirmed by sequencing. Next, whole white cell homogenate prepared from human blood was reacted on immunoblots with a monoclonal antibody that recognizes all CYP3A proteins or an absorbed polyclonal antibody that recognizes only CYP3A5. Both antibodies recognized a protein in the white cells that comigrated with purified CYP3A5. However, metabolism of midazolam, a substrate of CYP3A, could not be detected in homogenates of isolated granulocytes, in homogenates of the whole WBC fractions, or in incubations with unlysed WBC preparations. We conclude that CYP3A4 is not expressed in peripheral blood and hence a blood phenotyping test for this enzyme will not be feasible. Our discovery that CYP3A5 is present may be important since this enzyme is also present in the liver intestine and kidney of many people.

[Role of myoglobin in supplying oxygen to tissues]

The functional properties and role of myoglobin in oxygen-supplying system of tissues are discussed on the basis of literature data. The mechanisms of myoglobin participation in conservation and intracellular transport of oxygen, as well as its antioxidase, monooxygenase and peroxidase activity are considered.

In vivo induction of cytochrome P450 CYP3A expression in rat leukocytes using various inducers

Although the induction of cytochromes P450 3A (CYP3A) is relatively well characterized in liver, its inducibility in an easily available tissue such as the peripheral leukocytes is not known. The purpose of this study was, therefore, to determine if CYP3A is inducible in vivo in peripheral leukocytes. Microsomes from rat leukocytes and liver were examined for CYP3A protein expression using Western blotting with a rabbit polyclonal antibody against rat CYP3A. Although CYP3A was not detected in control leukocytes, in vivo treatment with known CYP3A inducers (dexamethasone, clotrimazole, phenobarbital, pregnenolone-16 alpha-carbonitrile) resulted in CYP3A leukocyte levels of 0.2-0.8 pmol/mg protein. This leukocyte induction was approximately 1000-fold lower than in induced liver. Interestingly, there was an apparent linear relationship between leukocyte and liver CYP3A contents (r2 = 0.748, n = 29). These results not only demonstrate for the first time that CYP3A is inducible in rat leukocytes after in vivo treatment with various CYP3A inducers, but also suggest that peripheral leukocytes could be used to assess induction in vivo.

CB pattern in the harbour porpoise: bioaccumulation, metabolism and evidence for cytochrome P450 IIB activity

Metabolism of chlorobiphenyls (CBs) was studied in harbour porpoise by comparing patterns of CB-X/CB-153 ratios in blood, brain, liver and blubber with the patterns in herring, the main food source. The CBs were classified in five groups, based on the presence/absence of vicinal H-atoms (vic. Hs) in meta,para (m,p) and/or ortho,meta (o,m) positions and the number of ortho-Cl-atoms (ortho-Cls). Plots of CB-X/CB-153 ratios in porpoise tissue vs the ratios in herring appeared to be linear for each CB group in all tissues. Slopes of these plots (metabolic slopes) were used as quantitative indicators of metabolic activity. In this way, activity of PB-type isozymes of the P450 monooxygenase system was apparent: in contrast to existing literature data, harbour porpoise appears to be able to metabolize congeners with m,p vic. Hs, even in the presence of more than 2 ortho-Cls. The presence of 3-MC-type (MC-type) isozymes was also detected. The metabolic slopes were also used as basis for risk assessment. Due to their metabolism the most toxic non-ortho CBs were not present in the tissues at detectable levels. We suggest a risk assessment approach which takes this into account. It is considered to be an alternative and more reliable basis for risk assessment than the use of toxic equivalent factors. The results support the model of equilibrium distribution of CBs in harbour porpoise and the role of blood as central transport medium. The model has been developed for persistent compounds; it appears to hold for metabolizable CB congeners as well.

Toxic effects of butylated triphenyl phosphate-based hydraulic fluid and tricresyl phosphate in female F344 rats

Triaryl phosphates, including tricresyl phosphate (TCP and butylated triphenyl phosphates (BTP), are used in the commercial manufacture of plastics, lubricants, and hydraulic fluids. Recent reports implicate these compounds as endocrine and reproductive toxicants that can cause cholesteryl lipidosis in adrenocortical (AC) and ovarian interstitial (OI) cells, suggesting altered metabolism of steroid hormones or cholesterol or of both. We investigated potential mechanisms of BTP and TCP toxicity to determine if there were functional abnormalities of the adrenal cortex or ovary. Groups of intact (nine or 12) and ovariectomized (six) female F344 rats, 10-12 weeks of age, received 0, 0.4 g/kg TCP, or 1.7 g/kg BTP in sesame oil vehicle or 1.7 g/kg neat BTP for 20, 40, or 60 days. All rats administered BTP and TCP developed cholesteryl lipidosis in AC and OI cells; the TCP-treated group was most severely affected. Serum concentrations of androstenedione and corticosterone were unchanged, but estradiol levels were significantly (P < or = 0.05) elevated in BTP- and TCP-treated groups (14.5 times and 37.5 times greater than controls, respectively). Vaginal cytology revealed that BTP- but not TCP-treated females had abnormal reproductive cycles that were significantly prolonged in diestrus (3 times greater than control). There were significant elevations in serum total cholesterol (TCP-treated group was 1.3 times greater than controls), low-density lipoprotein (TCP-treated group was 1.8 times greater than controls), alanine transaminase (BTP-treated group was 2 times greater than controls), and albumin (a major serum estradiol-binding protein; BTP-treated group was 4.6 g/dl vs. 3.6 g/dl for controls).(ABSTRACT TRUNCATED AT 250 WORDS)

TCDD reduces rat hepatic epidermal growth factor receptor: comparison of binding, immunodetection, and autophosphorylation

Administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a potent tumor promoter, to rats resulted in a dose-dependent decrease in hepatic plasma membrane epidermal growth factor receptor (EGFR). The present study is the first to quantify and compare alterations in hepatic EGFR levels in female Sprague-Dawley rats 7 days after a single oral gavage dose of TCDD (0, 1, 5, 25, and 50 micrograms/kg) using three different techniques: (1) equilibrium receptor binding, (2) EGF induced receptor autophosphorylation, and (3) Western blot detection with a rabbit anti-rat EGFR polyclonal antibody. All three methods similarly demonstrated that the level of hepatic EGFR is significantly decreased at a dose of TCDD as low as 1 micrograms/kg. We showed that the immunoblot technique is a sensitive and quantitative alternative to radioligand binding assays. It is concluded that TCDD decreased total EGFR protein and maximum binding capacity without altering ligand binding affinity (Kd). The results demonstrated that ligand-induced autophosphorylation capacity and basal phosphotyrosine residues of plasma membrane EGFR were both decreased parallel with the decrease in EGFR protein, suggesting no TCDD-related alteration in the inherent functional ability of the receptor to undergo activation. Furthermore, it was found that the dose-response curve for EGFR protein level determined by Western blot analysis was similar for both male and female Sprague-Dawley rats.

2-Butanol metabolism by rat hepatic and pulmonary cytochromes P450

Three microsomal enzyme inducers, ethanol, phenobarbital (PB), and beta-naphthoflavone (beta NF), were compared for their effects on butanol oxidase activity in rat hepatic and pulmonary microsomes. Four concentrations of 2-butanol (1.0, 5.0, 10, and 33 mM) were used to determine if the effects of induction on 2-butanol metabolism were substrate concentration dependent. Ethanol induced at all substrate concentrations in the liver while PB induced at only the high substrate concentrations (5.0, 10, and 33 mM). beta NF did not induce at any substrate concentration. 2-Butanol oxidation in the lung was not induced by any of the treatments. Thus, both ethanol and phenobarbital induce hepatic enzymes capable of 2-butanol oxidation, and the isozyme(s) induced by the latter has a somewhat lesser affinity for this alcohol.