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(Hypertension. 2002;40:273.)
© 2002 American Heart Association, Inc.
Scientific Contributions |
From the Max Delbrück Center for Molecular Medicine and Franz Volhard Clinic, HELIOS Kliniken-Berlin, Medical Faculty of the Charité, Humboldt University of Berlin, Germany.
Correspondence to Wolf-Hagen Schunck, Max Delbrück Center for Molecular Medicine, Robert-Rössle-Strasse 10, 13092 Berlin, Germany. E-mail schunck{at}mdc-berlin.de
| Abstract |
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Key Words: rats kidney cytochrome P450 arachidonic acid angiotensin II inflammation end-organ damage
| Introduction |
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B (NF-
B) and may thus prevent vascular inflammation at a very early stage. We have studied a double transgenic rat (dTGR) model, which harbors the human genes for renin and angiotensinogen.19,20 dTGR develop hypertension associated with impaired renal hemodynamics and tubular sodium reabsorption.21 They die of cardiac and renal failure at about the eighth week of age.20 In this model, end-organ damage is mainly caused by severe inflammation triggered by high angiotensin (Ang) II concentrations in the heart, kidney, and vasculature. Activation of the proinflammatory transcription factors NF-
B and activator protein (AP-1) plays a key role in the pathogenesis.20,2226 To what extent P450-dependent AA metabolites are involved as mediators in this model is unknown. We therefore addressed the question whether or not P450-dependent renal AA metabolism is altered in dTGR compared with the nontransgenic parental Sprague-Dawley (SD) strain. | Methods |
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Microsomal AA Metabolism
Microsomes were prepared from freshly dissected kidneys and livers of dTGR and SD rats. Homogenization was performed in 50 mmol/L Tris-HCl buffer (pH 7.4) containing (in mmol/L) sucrose 0.25, KCl 150, EDTA 2, dithiothreitol 2, and phenylmethylsulfonyl fluoride 0.25. Microsomes were isolated by differential centrifugation and resuspended in 50 mmol/L Tris-HCl (pH 7.7) containing 20% glycerol, 5 mmol/L EDTA, and 1 mmol/L dithiothreitol. [1-14C]AA (56 mCi/mmol) was purchased from Amersham Pharmacia-Biotech. The reaction mixtures contained (in a total volume of 0.1 mL) the following: 80 µg microsomal protein, 10 nmol AA (0.55x106 dpm), 50 nmol NADPH, 0.31 µmol glucose-6-phosphate, and 0.2 U glucose-6-phosphate dehydrogenase for regeneration of NADPH and (in µmol) Tris-HCl buffer 5 (pH 7.5), MgCl2 1, and KCl 15. Microsomes were preincubated for 10 minutes at 37°C with AA, and adding NADPH started the reactions. After shaking for 20 minutes at 37°C, the reactions were terminated by acidification to pH 3.5 to 4.0 with 0.4 mmol/L citric acid. The reaction products were extracted into ethyl acetate and resolved by reverse-phase high-performance liquid chromatography (RP-HPLC) (Shimadzu LC 10 Avp coupled with an online radioflow detector LB 509; Berthold). A Nucleosil 100-5C18 HD column (250x4 mm; Macherey-Nagel) was used with a linear solvent gradient ranging from acetonitrile (v)/water (v)/acetic acid (v) (50:50:0.1) to acetonitrile (v)/acetic acid (v) (100:0.1) over 40 minutes at a flow rate of 1 mL/min. AA hydroxylase activities were determined as the sum of 19- and 20-HETE (migrating unresolved at 16.1 minutes in RP-HPLC) formed per minute and milligrams of microsomal protein. Total AA epoxygenase activities were calculated from the sum of the following EETs and corresponding dihydroxyeicosatrienoic acids (DHETs): 8,9-EET/-DHET (retention times in RP-HPLC, 25.3 and 14.8 minutes, respectively), 11,12-EET/-DHET (retention times, 24.7 and 13.8 minutes), and 14,15-EET/-DHET (retention times, 23.4 and 12.7 minutes).
Immunoinhibition
Microsomes were preincubated for 30 minutes at 37°C with 100 µg/mL rabbit IgG (125 µg IgG/mg microsomal protein) before substrate and NADPH were added to constitute the complete reaction mixtures as described above for determining AA metabolism. The concentrations of anti-CYP2C23 IgG varied between 0 and 100 µg/mL, whereas the total amount of IgG was kept constant by appropriate additions of control rabbit IgG.
Western Blot Analysis
Microsomal protein (15 µg per lane) was separated on 10% SDS-PAGE and transferred to HybondECL nitrocellulose membranes (Amersham Life Sciences). Primary antibodies used were goat antisera against rat CYP4A1, rat CYP2C11, and rat CYP2E1 (Daiichi Pure Chemicals Co); rabbit antisera against human CYP2J2 (generated by D.C. Zeldin, National Institute of Environmental Health Sciences, NC4); and rabbit IgG against rat CYP2C23 (generated by J.H. Capdevila, Vanderbilt University, Nashville, Tenn3). The respective peroxidase conjugated secondary antibodies were from Sigma. Blots were developed with the chemiluminescence substrate from Roche and evaluated with the Image Reader LAS-1000 (Fujifilm).
Immunohistochemistry
Ice-cold acetone-fixed cryosections (6 µm) were stained for CYP2C11 by immunofluorescence and for CYP2C23 by alkaline phosphatase/antialkaline phosphatase technique as described earlier.24,25 We used the same primary antibodies as for Western blotting. Preparations were analyzed under a Zeiss Axioplan-2 microscope (Carl Zeiss) and were digital photographed by use of the AxioVision-2 multichannel image processing system (Carl Zeiss). For quantification of CYP2C23, 10 different cortical view fields per rat (n=5 per group) were analyzed. The sections were scored in the following categories: <60%, 60% to 80%, and 80% to 100% CYP2C23-positive tubules.
Statistical Analysis
All data are presented as mean±SEM and were analyzed by 1-way ANOVA followed by the Bonferroni multiple comparison test (InStat software; GraphPad Software Inc). A value of P<0.05 was considered statistically significant.
| Results |
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80 mm Hg compared with that in SD rats (199±2.9 versus 119±5.5 mm Hg; P<0.001) and the 24-hour albumin excretion reached 16.98±2.42 versus 0.16±0.02 mg/d (P<0.001). In contrast, the livers of dTGR appeared normal. No significant differences were found in the activities of alanine aminotransferase (79.7±11 versus 61±5.8 U/mL), aspartate aminotransferase (143.7±11.5 versus 149.8±20.6 U/mL), and glutamate dehydrogenase (10.2±2.3 versus 8.9±0.8 U/mL) in blood samples from dTGR and control rats.
P450-Dependent AA Metabolism
At week 7, renal microsomes of control rats showed an AA hydroxylase activity of 278±16 pmol · min-1· mg-1 and a total AA epoxygenase activity of 209±16 pmol · min-1· mg-1 (Figure 1). The epoxygenase product consisted of 14,15-, 11,12-, and 8,9-EET in a ratio of about 1:4:1. Renal microsomes from dTGR metabolized AA at significantly lower rates. The hydroxylase activities were 213±12 pmol · min-1· mg-1 (corresponding to 76% of the control value; P<0.01), and the epoxygenase activities reached only 132±10 pmol · min-1· mg-1 (63% of control; P<0.001). In contrast to these alterations in renal microsomal P450 activities, liver microsomes of dTGR and control rats hydroxylated and epoxygenated AA with almost identical rates (Figure 1).
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Immunoinhibition of AA Epoxygenase Activities
The antibody against CYP2C23 inhibited the AA epoxygenase activity of renal microsomes in a concentration-dependent manner without decreasing their ability to hydroxylate AA (Figure 2). Although slightly higher amounts of the antibody were required for 50% inhibition of EET formation with SD microsomes than with dTGR microsomes, the epoxygenase activities were almost completely abolished in both cases at higher antibody concentrations. The course of the inhibition curves and the epoxygenase activities remaining at the highest antibody concentration used were not significantly different in renal microsomes isolated from 5- and 7-week-old animals (Figures 2A and 2B).
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Alterations in P450 Protein Levels
The total P450 content of renal microsomes determined by carbon monoxide difference spectra averaged at 75 and 55 pmol/mg of protein for dTGR and SD rats and was not significantly different between the groups. Western blot analysis showed that the level of CYP2C11 protein was significantly decreased in renal microsomes of 7-week-old dTGR to
30% (29±4%) of control values (Figure 3). A similarly prominent decrease was observed for CYP2J proteins (32±6% of the control values) as detected with antibodies against human CYP2J2 (Figure 3). The levels of P450 proteins reacting with antibodies against rat CYP2C23 and rat CYP2E1 (Figure 3) were moderately decreased in dTGR to
70% of the control values (69±7% and 71±6%, respectively). No significant differences were found in the contents of CYP4A proteins when comparing renal dTGR and SD microsomes (Figure 3). Liver microsomes prepared from the same animals did not show significant changes in CYP2C11, CYP2C23, and CYP2J protein levels when comparing dTGR and SD control samples (data not shown).
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Comparisons at 5 and 7 Weeks
Further studies indicated that the alterations in renal P450-dependent AA metabolism described above for 7-week old dTGR were already apparent at week 5, before the development of albuminuria and severe end-organ damage (Figure 4A and 4B). Compared with SD rats of the same age, in dTGR the AA epoxgenase activity was reduced by 30% (Figure 4C). Western blot analysis demonstrated a significant downregulation of renal microsomal CYP2C11 protein. In addition, there was a tendency to reduced CYP2C23 levels (Figure 4D). In contrast to week 7, there was a significant reduction of CYP4A levels by 30%, comparing renal microsomes from 5-week-old dTGR and SD rats.
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Localization of CYP2C23 and CYP2C11
CYP2C23 protein was expressed in tubules in the renal cortex and outer renal medulla (Figures 5A and 5B). In contrast, CYP2C11 immunoreactivity was restricted to tubules of the outer medulla. Glomeruli and blood vessels showed no immunoreaction for either isoform. Semiquantification of kidney sections from 5- and 7-week-old dTGR and SD rats revealed progressive and significant changes in the cortical tubular CYP2C23 expression. At week 5, most of the transgenic and nontransgenic cortical tubules expressed CYP2C23. At week 7, >50% of analyzed dTGR tubules showed no CYP2C23 immunoreactivity, whereas >90% of SD tubules were positive for CYP2C23 (Figure 5C). Nevertheless, the few tubules remaining to express CYP2C23 in 7-week-old dTGR exhibited significantly increased labeling compared with SD tubules (Figure 5A). CYP2C11 was localized in tubules of the outer medulla (Figure 5D). No expression was observed in cortical tubules. The CYP2C11 immunostaining increased from weeks 5 to 7 in both groups. At all time points, CYP2C11 immunoreactivity was significantly increased in nontransgenic SD tubules compared with dTGR tubules (Figure 5D).
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| Discussion |
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CYP2C23 was localized in the tubules of the renal cortex and outer medulla. Untreated 7-week-old dTGR showed severe renal damage with a dramatic reduction of CYP2C23-positive tubules. Nevertheless, the remaining CYP2C23-positive tubules in dTGR showed an increased immunoreactivity. Thus, it appears that the availability of EETs was strongly reduced in most cortical tubular structures, whereas it may have even been enhanced in others. Unexpectedly, reduced AA epoxygenase activities were already apparent in 5-week-old dTGR before a significant decrease in CYP2C23 protein levels had occurred. This state of affairs was revealed both by immunohistochemistry and Western blot analysis. The reasons for this discrepancy are unclear. Possibly, a portion of the immunodetectable CYP2C23 was present in an enzymatically inactive form.
CYP2C11 was detected in tubular structures of the outer medulla but not in cortical regions expressing CYP2C23. The tubular expression of CYP2C11 was clearly reduced in both 5- and 7-week-old dTGR, a finding that substantiates the results of Western blot analysis. CYP2C11 is known for its high catalytic activity and represents the predominant AA epoxygenase in the liver of male rats.27 Thus, without contributing much to overall renal EET formation, changes in CYP2C11 expression may be important for EET availability in specific tubular segments. CYP2J enzymes are further candidates for renal AA epoxygenases. Moreover, an increase in both EET formation and CYP2J2 immunoreactive protein levels was reported in the spontaneously hypertensive rat.4 CYP2J2 was shown to be a potential source of EETs in human endothelial cells.18 Whether or not one of the different rat CYP2J isoforms plays this role in the rat renal vasculature is an important question for future studies.
In contrast to our findings in dTGR, hypertension induced by long-term infusion of Ang II in rat was not associated with reduced renal AA epoxygenase activities and decreased CYP2C23 and CYP2C11 levels.28 The main difference of our model, compared with Ang II infusion, may be related to the fact that uncontrolled inflammation triggered by high local Ang II concentrations is responsible for renal damage in dTGR.20 Downregulation during inflammation appears to be a general phenomenon for a number of different P450 isoforms.29 For example, the present finding that dTGR show strongly reduced renal CYP2C11 levels is directly paralleled by results of hepatic CYP2C11 expression in models of hepatic inflammation.29 In this case, a downregulation at the transcriptional level based on a NF-
Bbinding negative regulatory element was proposed.30 A NO-dependent mechanism was held responsible for decreased endothelial CYP2C expression and for downregulation of the endothelium-derived hyperpolarizing factor in response to proinflammatory mediators.31 Increased NO concentrations may be also responsible for inactivation of CYP4A enzymes.32 Because NF-
B is strongly activated and NO synthase II is induced in the kidney of dTGR, both mechanisms may be important in our model.20,23,24
The relationships between inflammation and P450 expression were previously studied mostly in terms of P450-dependent hepatic drug metabolism without investigating the possible consequences for the metabolism of endogenous P450 substrates such as AA. Whether or not the downregulation reflects a deleterious or protective mechanism is unclear.33,34 Treatment of rats with a general P450 inhibitor was reported to sensitize the animals to subsequent inflammatory stimuli.33 Although the actual cause-and-effect relationships remain open, our results point in a similar direction. They show that the expression and activity of AA epoxgenases was already significantly reduced in 5-week-old dTGR, before the animals developed severe hypertension and albuminuria. Proinflammatory cascades both in vascular endothelial cells and in tubular epithelial cells play a central role in triggering progressive inflammation and renal damage.35 For this reason, the exact intrarenal localization of the different EET-producing P450 isoforms is of special interest. Because EETs were shown to have anti-inflammatory properties in the vasculature,18 the question of whether or not this mechanism extends to the tubular system is important. Ang II and albumin can both trigger NF-
B activation in the renal tubules.36
Perspectives
Decreased EET levels are expected to have negative effects on the regulation of vascular tone, tubular function, and control of inflammation. All these effects may have contributed to the renal damage observed in our Ang IIbased model. In terms of future therapeutic interventions, both an induction of EET-generating CYP enzymes and an inhibition of systems involved in EET inactivation, such as soluble epoxide hydrolase, may represent interesting new targets to ameliorate hypertension and end-organ damage.
| Acknowledgments |
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Received May 31, 2002; first decision June 11, 2002; accepted June 28, 2002.
| References |
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-hydroxylase activity with ABT reduces blood pressure in the SHR. Am J Physiol. 1998; 275: R426R438.[Medline]
[Order article via Infotrieve]
B inhibition ameliorates angiotensin IIinduced inflammatory damage in rats. Hypertension. 2000; 35: 193201.
B and protects from angiotension IIinduced organ damage. FASEB J. 2001; 15: 18221824.
B, inflammation, and tissue factor in angiotensin IIinduced end-organ damage. Hypertension. 2000; 36: 282290.
B activation in angiotensin IIinduced cardiac injury. Hypertension. 2001; 37: 787793.
B binding at the transcription start site. Arch Biochem Biophys. 2000; 377: 187194.[CrossRef][Medline]
[Order article via Infotrieve]
-hydroxylase and epoxygenase activity are differentially modified by nitric oxide and sodium chloride. J Clin Invest. 1999; 104: 11311137.[Medline]
[Order article via Infotrieve]
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