DOI: 10.1369/jhc.4A6456.2005 Volume 53 (1): 105-112, 2005 Copyright ©The Histochemical Society, Inc. Change in Renal Heme Oxygenase Expression in Cyclosporine A-induced Injury
Department of Biomedical Sciences and Biotechnology, University of Brescia, Brescia, Italy (RR,LR,BB,RB); Department of Pharmacology, New York Medical College, Valhalla, New York (AAG,NGA); and Department of Medicine, Robert Wood Johnson Medical School, New Brunswick, New Jersey (EAL) Correspondence to: Prof. Rita Rezzani, Department of Biomedical Sciences and Biotechnology, Division of Human Anatomy, University of Brescia, Viale Europa 11, 25123 Brescia, Italy. E-mail: rezzani{at}med.unibs.it
Cyclosporine A (CsA) is the first immunosuppressant used in allotransplantation. Its use is associated with side effects that include nephrotoxicity. This study explored the anatomic structures involved in CsA nephrotoxicity and the effect of heme oxygenase (HO) in preventing CsA injury. Rats were divided into four groups, which were treated with olive oil, CsA (15 mg/kg/day), CsA plus the HO inhibitor (SnMP; 30 µM/kg/day), and with the HO inducer (CoPP; 5 mg/100 g bw). Renal tissue was treated for morphological, biochemical, and immunohistochemical studies. CsA-treated rats showed degenerative changes with renal fibrosis localized mainly around proximal tubules. Collapsed vessels were sometimes seen in glomeruli. No HO-1 expression and increased expression of endothelin-1 (ET-1) were observed in CsA-treated rats compared with controls. In CsA plus SnMP-treated rats, HO-1 expression was further reduced and the morphology was not changed compared to the CsA group, whereas CsA plus CoPP-treated animals again showed normal morphology and with restoration and an increase in HO-1 levels. HO activity and immunohistochemical data showed similar alterations as HO expression. No changes were observed for HO-2 analysis. The observations indicate that HO-1 downregulation and ET-1 upregulation by CsA might be one mechanism underlying CsA-induced nephrotoxicity. Therefore, attempts to preserve HO levels attenuate CsA nephrotoxicity. (J Histochem Cytochem 53:105112, 2005)
Key Words: cyclosporine A heme oxygenase renal injury
THE USE OF CYCLOSPORINE A (CsA) as an immunosuppressant and anti-rejection drug has been related to nephrotoxicity. CsA causes a dose-related reversible renal vasoconstriction that mainly occurs in the afferent arterioles after prolonged treatment (Kahan 1989
The most common feature of CsA use is the development of interstitial fibrosis, which can be patchy or "striped" (Verpooten et al. 1986
It is unknown whether renal tissue possesses a defense mechanism against CsA-induced injury. Heme oxygenase (HO), the rate-limiting enzyme in heme catabolism, has been shown to attenuate the extent of various forms of renal injury, most notably injury due to ischemia and to inflammation (Wolf et al. 1994 The hypothesis tested is that HO expression is associated with the attenuation of CsA-induced nephrotoxicity. Moreover, we examined by electron microscopic analysis whether the negative CsA effects on intracellular structures might be related to their major susceptibility to drug metabolism and the anatomic structures that were considered to be the intrarenal target for CsA damage.
Animal Treatment Forty male Sprague-Dawley rats (average weight 200250 g) were used. The animals were divided into four groups and treated for 21 days. Group I (n=10) was injected SC with olive oil (the CsA vehicle) and served as control. Group II (n=10) was treated with CsA alone (15 mg/kg/day) for 21 days. Group III (n=10) was treated with CsA and the inhibitor of HO activity stannous mesoporphyrin (SnMP; 30 µmol/kg). Group IV (n=10) received one dose of the HO inducer cobalt protoporphyrin (CoPP; 5 mg/100 g bw) after 3 days of CsA treatment. All animals were sacrificed at the end of each treatment period. Kidney cortical sections from each rat were homogenized for Western blot analysis of HO-1 and HO-2 expression and for enzyme activity assay. A portion of the kidney tissue was fixed in formalin and was processed for sectioning (5-µm sections) and staining for identification of collagen using the Azan method and for HO and ET-1 immunohistochemistry (IHC). Another portion of kidney was fixed in 2.5% glutaraldehyde, dehydrated, and treated by standard procedures for electron microscopic analysis.
Renal Morphology
Western Blot Analyses
Statistical Analysis
Measurement of HO Enzyme Activity
Immunohistochemical Analysis for HO-1, HO-2, and ET-1 Proteins Specificities of antibody labeling were investigated using appropriate controls, incubating the tissue sections with Tris-buffered saline instead of the primary or secondary antibody.
Semiquantitative Analysis of HO-1, HO-2, and ET-1 Immunostaining
Morphological Findings in Control, CsA Alone, CsA plus SnMP-, and CsA plus CoPP-treated Rats Figure 1A shows that the kidneys had a normal morphology. The cortex showed a large number of glomeruli with proximal and distal tubules located around the latter. The electron microscopic analysis revealed that epithelial cells of proximal and distal tubules showed normal mitochondria near the nucleus. They were also randomly distributed in the cytoplasm or concentrated at the sites of high energy utilization (Figure 2A). The cristae and the membrane were clearly evident and were normal, as shown in the inset of Figure 2A. Renal injury was evident mainly in the cortex of kidneys from the CsA alone and CsA plus SnMP- treated animals. The injury consisted of tubulointerstitial changes visible as narrow stripes of fibrosis localized mainly around the proximal tubules, as well as lack or swelling of epithelial cell nuclei (Figures 1B and 1C). On our scoring system, a significant increase in fibrosis was observed in CsA-treated rats compared with controls (1.8 ± 0.2 vs 0.22 ± 0.04; p<0.01). The fibrosis increase in CsA-treated animals was similar to that observed in the CsA plus SnMP-treated rats (1.8 ± 0.2 vs 1.6 ± 0.3). These data are reported in Table 1. Moreover, glomerula showed changes in morphology. In particular, we sometimes observed a collapse of vessels in glomerula, as previously reported by other authors (Kim and Suh 1995
Effects of CsA Alone, CsA plus SnMP, and CsA plus CoPP Treatment on HO-1 and HO-2 Protein Expression Levels We studied the effect of CsA levels of HO-1 and HO-2 protein in cortical tissue homogenates by Western blot analysis. Basal levels of HO-1 protein were detectable in control (Figure3A, Lane 3) but not in CsA-treated rat kidneys (Figure 3A, Lane 1). In animals treated with CsA followed by administration of the HO inducer CoPP, renal HO-1 protein levels were restored and also increased (Figure 3A, Lane 4; compare with Lanes 1, 2, and 3). SnMP treatment induced a decrease in renal HO-1 protein levels (Figure 3A, Lane 2). In contrast, there was no significant difference in HO-2 levels among the different experimental groups (Figure 4A). The HO quantitative analyses are shown as histograms in Figures 3B and 4B.
Effects of CsA Alone, CsA plus SnMP, and CsA plus CoPP Treatment on HO Enzyme Activity In CsA-treated animals, renal cortical HO activity was reduced. To determine the extent of this reduction, a separate group of CsA-treated rats received the HO activity inhibitor SnMP. In these animals renal cortical HO activity was further reduced compared with levels in animals treated with CsA alone. The animals treated with CsA and CoPP showed HO activity levels similar to those of the control group (Table 2).
Effects of CsA Alone, CsA plus SnMP, and CsA plus CoPP Treatment on HO-1, HO-2 Protein Immunostaining We examined by IHC analysis the effect on the expression of HO-1 and HO-2 protein. In control rats, HO-1 protein showed weak positivity (+) in the epithelial cells of proximal tubules; glomerula and distal tubules were negative () (Figure 5A). Conversely, we observed that HO-1 expression decreased in renal parenchyma and was undetectable both in CsA alone and CsA plus SnMP-treated rats (Figures 5B and 5C). HO-1 expression was again similar to control in CsA plus CoPP-treated animals (Figure 5D).
HO-2 expression did not differ among the different experimental groups. In fact, HO-2 expression showed moderate positivity (++) in proximal tubules and very weak positivity (±) in distal tubules, whereas glomeruli were negative () (data not shown). All semiquantitative data are reported in Table 3.
Effects of CsA Alone, CsA plus SnMP, and CsA plus CoPP Treatment on ET-1 Protein Immunostaining In control rats, ET-1 protein showed very weak (±) positivity in proximal and distal tubules and in glomerula. Conversely, in CsA-treated rats we observed evident differences in the pattern of ET-1 positivity compared with controls. Proximal tubules were strongly (+++) positive, whereas ET-1 staining was very weak (±) in glomeruli and distal tubules. These results confirmed the data reported in our previous work (Rezzani et al. 2001a All semiquantitative data are reported in Table 3.
Nephrotoxicity is an important side effect of CsA treatment and constitutes the major detriment of this otherwise remarkable immunosuppressant and anti-rejection drug. CsA-induced renal vasoconstriction is due in part to alterations of arachidonic acid metabolism in favor of the vasoconstrictor TxA2 and to increases in ET-1 expression (Rezzani et al. 2001a
The vexing issue of CsA nephrotoxicity has prompted clinical and experimental strategies to attenuate this toxicity, particularly the vasoconstrictor component. Approaches such as low-dose dopamine infusion (Sabbatini et al. 1989 Our studies point to HO both as an underlying mechanism of CsA-induced nephrotoxicity and as a target for novel strategies to ameliorate this toxicity. In our model, 21 days of daily CsA treatment produced histopathological lesions, tubule interstitial fibrosis, and lack or swelling of epithelial cell nuclei resembling those seen in kidneys of organ recipients after long-term CsA treatment. In CsA-treated rats, renal HO-1 protein levels and HO renal enzyme activity were reduced. This observation, coupled with the well-established renoprotective effect of HO in various forms of renal injury, i.e., ischemia and inflammation, indicates that CsA depletes the kidney of an important defense system. The beneficial effects of HO activation in renal injury have been attributed to production of heme degradation products, mainly the vasodilator CO and bilirubinbiliverdin, which scavenge reactive oxygen radicals. With respect to CO, its cellular production is regulated by HO. Therefore, the depletion of HO caused by CsA might reduce CO production, thereby allowing action by unopposed vasoconstrictors, such as TxA2 and ET-1, according to the data reported in this work. On the other hand, a reduced production of biliverdinbilirubin may allow accumulation of reactive oxygen radicals. Our observations also show that the CsA-induced decrease in HO expression and activity is partial and that it can be restored by established HO inducers such as CoPP. This indicates that attempts to preserve or augment HO activity during administration of CsA treatment is a reasonable strategy to attenuate CsA-induced nephrotoxicity. To this end, augmentation of HO-1 activity would be beneficial by increasing production of CO and biliverdinbilirubin and by decreasing levels of heme. Reduction of cellular heme levels would reduce activity of heme-containing enzymes such as inducible NOS and TxA2 synthase. The byproduct of inducible NOS, high-output NO production, can be toxic, whereas the byproduct of TxA2 was shown to mediate the CsA-induced constriction of the renal microvasculature. In summary, our observations demonstrate that downregulation of HO is a putative mechanism of CsA-induced nephrotoxicity. This effect is partial and reversible. Strategies to preserve or augment HO activity during CsA treatment may attenuate its nephrotoxicity.
With regard to the structures considered targets for CsA nephrotoxicity, we showed that the proximal tubules were mainly involved in these negative effects. These data were confirmed by our previous works (Rezzani et al. 2001a
Received for publication June 24, 2004; accepted September 15, 2004
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