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Heme oxygenase-1 in renal injury: Conclusions of studies in humans and animal models
Kidney International, Vol. 59 (2001), pp. 378–379
EDITORIAL
Heme oxygenase-1 in renal injury: Conclusions of studies in humans and animal models Heme, a ferroprotoporphyrin, derived from various hemoproteins, is catabolized by the enzyme heme oxygenase [1–4]. It degrades heme to biliverdin, which is metabolized by biliverdin reductase to bilirubin. The catabolism of heme to biliverdin by heme oxygenase requires oxygen and the reduced form of nicotinamideadenine dinucleotide phosphate (NADPH). During this reaction iron is released from the heme ring and carbon monoxide is produced. Heme oxygenase activity is confined to its three isoenzymes: HO-1, HO-2, and HO-3. HO-1 is the isoenzyme induced in tissues by various stimuli, a large number of which are pro-oxidant. During the last decade, there has been a tremendous interest in the biology of HO-1, in part because it serves as a fortuitous protective agent as opposed to the deleterious effects exerted by the degradation products of its substrate, heme, in various forms of tissue injury [2, 3]. The mechanisms relevant to the protective effects of HO-1 in human renal disease, reinforced in animal studies, are highlighted in this issue of Kidney International by Nath et al [5]. The studies described herein [5] represent a continuum of intense efforts launched in Dr. Nath’s laboratory a decade ago to delineate the mechanism(s) of renal injury and responses to such injury in the kidney exposed to heme proteins [5–13]. In 1992, he and his colleagues demonstrated that exposure to heme proteins produces a rapid increase in the expression of HO-1 and ferritin, and such an induction provides a protective response to renal tubular injury [6]. These studies represent a landmark contribution because they provide the first demonstration—in any tissue and for any insult and in either in vitro or in vivo settings—for a protective role of HO-1, a role only previously theorized for this enzyme [1]. Further strides were made to delineate the mechanism(s) by which induced HO-1 provided protection against the oxidant injury to the kidney. The authors explored the mechanisms by which heme proteins induced renal vasoconstriction [7, 8] and also identified the renal intracellular targets vulnerable to the deleterious effects of such toxic proteins [7, 9]. In addition, they Key words: nuclear factor-B (NF-B) heme proteins, tubulointerstitial injury, fibrogenic cytokines inflammatory response, monocyte chemoattractant peptide (MCP-1).
2001 by the International Society of Nephrology
378
demonstrated that cytoprotection against heme protein– induced toxicity can occur even when HO-1 is induced by agents such as an endotoxin [10] or by the administration of heterologous antibody as in nephrotoxic serum nephritis [11]. More recently, they confirmed the role of this enzyme in HO-1–deficient mice stressed with heme proteins. These mice exhibited severe renal insufficiency and increased mortality [12]. Nath et al extended the above studies to explore whether HO-1 protected against the inflammatory assault by heme proteins in the HO-1–deficient mice in a clinical setting. The impetus for the studies described in the accompanying article was a patient with paroxysmal nocturnal hemoglobinuria who developed progressive chronic tubulointerstitial disease with up-regulation of HO-1 in the kidney and in renal tubular cells exposed to patient’s urine. In previous studies in rats, Nath and colleagues had demonstrated a triphasic response in the kidney exposed to heme proteins. Initially, kidneys exhibit acute sensitivity to hemoproteins, followed by acquisition of resistance to them, and finally a progressive tubulointerstitial disease with up-regulation of inflammatory and fibrogenic cytokines [13]. Based on this information, they explored the status of HO-1 in various phases and devised a regimen that used sufficiently low doses of murine hemoglobin so that its repeated administration caused minimal mortality in HO-1–deficient mice. An acute sensitivity was noted both in wild-type and HO-1–deficient mice with the initial doses of hemoglobin, and eventually both the strains developed resistance as well to heme proteins. Remarkably, the response differed in the third phase. HO-1–deficient mice had marked exacerbation of tubulointerstitial disease, suggesting that the capacity to recruit HO-1, as it occurs in wild-type mice, provides a mechanism that holds in check the inflammatory response induced by heme proteins. To delineate the mechanism involved, they focused on the monocyte chemoattractant peptide (MCP-1), since the latter contributes to progressive tubulointerstitial injury [14] as a redox-sensitive gene. Novel data emerged from the experiments. A relatively very high up-regulation of MCP-1 in the kidney was observed in HO-deficient mice with repeated chronic administration of hemoglobin. Concomitantly, nuclear factor-kappa B (NF-B), a transcription factor that induces the expression of
Editorial
MCP-1, was avidly activated in the HO-1–deficient mice. This implied that HO-1 down-regulates MCP-1 by inhibiting the activation of NF-B. These findings clearly demonstrate that the induction of HO-1 serves as an adaptive response in the kidney subjected to repeated chronic exposure of heme proteins. The response thus restrains inflammation, which otherwise, in the absence of HO-1, would be markedly enhanced in addition to uncontrolled induction of NF-B and MCP-1. These studies suggest that HO-1 acts as a protectant not only during the acute phase of nephrotoxicity but also in the chronic inflammatory damage induced by heme proteins. The novel role HO-1 as a suppressor of inflammatory responses, mediated in part by in vivo down-regulating the expression of MCP-1, is further underscored in several other disease settings as well, for example, in acute pleurisy [15], xenotransplant rejection [16], transplant vasculopathy [17], and hyperoxic lung injury [18]. The present study also raises the question, What other cytokines and pro-inflammatory species are influenced by HO-1? Equally important is the molecular basis for the anti-inflammatory effect of HO-1 in the described model. Each of the products of HO-1—ferritin, bilirubin, and carbon monoxide—may exert cytoprotective and/or anti-inflammatory effects, and it would be interesting to determine which of these products are involved in exerting such anti-inflammatory effects in these settings. Nath and his colleagues previously speculated that heme proteins contributed to the progressive tubulointerstitial disease in hematuric glomerulonephritides. In such a scenario, the heme proteins are brought into tubular epithelial cells as a consequence of the incorporation and degradation of erythrocytes by the renal tubular epithelium, which then lead to a tubulointerstitial injury [19]. These findings, that there was an intense up-regulation of MCP-1 in heme-induced renal injury, point toward the molecular basis by which such an inflammatory damage ensues. In conclusion, the studies by Nath and his colleagues provide novel concepts regarding the understanding of the pathogenesis of tubulointerstitial injury, where HO-1 acts as a suppressor of an inflammatory response in the kidney repetitively exposed to heme proteins. This suppressive effect of HO-1 on inflammatory responses may relate to the capacity of HO-1 to suppress the chemokine, MCP-1, possibly through the antioxidant effect of HO-1 retarding the activation of the redox-sensitive transcription factor, NF-B. Importantly, heme proteins strongly up-regulate the chemokine, MCP-1, thereby uncovering such a stimulus for this chemokine. Moreover, the upregulated renal HO-1/ferritin expression in the patient repeatedly exposed to heme proteins during the course of paroxysmal nocturnal hemoglobinuria attests to the original contention enunciated by Nath and colleagues, that is, that HO-1 and ferritin are induced in the kidney in response to the stress by hemoproteins [6]. Finally, this study, representing a combination of clinical and
379
experimental observations, demonstrates how the exploration of a human disease process can provide important insights and engender important questions that can be analyzed using genetically engineered mice. Yashpal S. Kanwar Chicago, Illinois, USA Correspondence to Yashpal S. Kanwar, M.D., Ph.D., Department of Pathology, Northwestern University Medical School, 303 East Chicago Avenue, Chicago, Illinois 60611, USA. E-mail: [email protected]
REFERENCES 1. Stocker R: Induction of heme oxygenase as a defense against oxidative stress. Free Rad Res Commun 9:101–112, 1990 2. Nath KA: Heme oxygenase-1: A redoubtable response that limits reperfusion injury in the transplanted adipose liver. J Clin Invest 104:1485–1486, 1999 3. Dong Z, Lavrovsky Y, Venkatachalam MA, Roy AK: Heme oxygenase-1 in tissue pathology. Am J Pathol 156:1485–1488, 2000 4. Agarwal A, Nick HS: Renal response to tissue injury: Lessons from heme oxygenase-1 gene ablation and expression. J Am Soc Nephrol 11:965–973, 2000 5. Nath KA, Vercellotti GM, Grande JP, et al: Heme proteininduced chronic renal inflammation: Suppressive effect of induced heme oxygenase-1. Kidney Int 59:106–117, 2001 6. Nath KA, Balla G, Vercellotti GM, et al: Induction of heme oxygenase is a rapid, protective response in rhabdomyolysis in the rat. J Clin Invest 90:267–270, 1992 7. Nath KA, Balla J, Croatt A, Vercellotti GM: Heme proteinmediated renal injury: A protective role for 21-aminosteroids in vitro and in vivo. Kidney Int 47:592–602, 1995 8. Warden DH, Croatt AJ, Katusic ZS, Nath KA: Physiologic characterization of acute reversible systemic hypertension in a model of heme protein-induced renal injury. Am J Physiol 277 (Renal Physiol 46):F58–F65, 1999 9. Nath KA, Grande JP, Croatt AJ, et al: Intracellular targets in heme protein-induced renal injury. Kidney Int 53:100–111, 1998 10. Vogt BA, Alam J, Croatt AJ, et al: Acquired resistance to acute oxidative stress: Possible role of heme oxygenase and ferritin. Lab Invest 72:474–483, 1995 11. Vogt BA, Shanley TP, Croatt AJ, et al: Glomerular inflammation induces resistance to tubular injury in the rat: A novel form of acquired heme oxygenase-dependent resistance to renal injury. J Clin Invest 98:2139–2145, 1996 12. Nath KA, Haggard JJ, Croatt AJ, et al: The indispensability of heme oxygenase-1 (HO-1) in protecting against heme proteininduced toxicity in vivo. Am J Pathol 156:1527–1535, 2000 13. Nath KA, Croatt AJ, Haggard JJ, Grande JP: Renal response to repetitive exposure to heme proteins: Chronic injury induced by an acute insult. Kidney Int 57:2423–2433, 2000 14. Wenzel UO, Abboud HE: Chemokines and renal disease. Am J Kid Dis 26:982–994, 1995 15. Willis D, Moore AR, Frederick R, Willoughy DA: Heme oxygenase: A novel target for the modulation of the inflammatory response. Nature Med 2:87–90, 1996 16. Soares MP, Lin Y, Anrather J, Cxizmadia E, et al: Expression of heme oxygenase-1 can determine cardiac xenograft survival. Nature Med 4:1073–1077, 1998 17. Hancock WW, Buelow R, Sayegh MH, Turka LA: Antibodyinduced transplant arteriosclerosis is prevented by graft expression of anti-oxidant and anti-apoptotic genes. Nature Med 4:1392–1396, 1998 18. Otterbein LE, Kolls JK, Mantell LL, et al: Exogenous administration of heme oxygenase-1 by gene transfer provide protection against hyperoxia-induced lung injury. J Clin Invest 103:1047– 1054, 1999 19. Nath KA: Tubulointerstitial changes as a major determinant in the progression of renal damage. Am J Kid Dis 20:1–17, 1992
EDITORIAL
Heme oxygenase-1 in renal injury: Conclusions of studies in humans and animal models Heme, a ferroprotoporphyrin, derived from various hemoproteins, is catabolized by the enzyme heme oxygenase [1–4]. It degrades heme to biliverdin, which is metabolized by biliverdin reductase to bilirubin. The catabolism of heme to biliverdin by heme oxygenase requires oxygen and the reduced form of nicotinamideadenine dinucleotide phosphate (NADPH). During this reaction iron is released from the heme ring and carbon monoxide is produced. Heme oxygenase activity is confined to its three isoenzymes: HO-1, HO-2, and HO-3. HO-1 is the isoenzyme induced in tissues by various stimuli, a large number of which are pro-oxidant. During the last decade, there has been a tremendous interest in the biology of HO-1, in part because it serves as a fortuitous protective agent as opposed to the deleterious effects exerted by the degradation products of its substrate, heme, in various forms of tissue injury [2, 3]. The mechanisms relevant to the protective effects of HO-1 in human renal disease, reinforced in animal studies, are highlighted in this issue of Kidney International by Nath et al [5]. The studies described herein [5] represent a continuum of intense efforts launched in Dr. Nath’s laboratory a decade ago to delineate the mechanism(s) of renal injury and responses to such injury in the kidney exposed to heme proteins [5–13]. In 1992, he and his colleagues demonstrated that exposure to heme proteins produces a rapid increase in the expression of HO-1 and ferritin, and such an induction provides a protective response to renal tubular injury [6]. These studies represent a landmark contribution because they provide the first demonstration—in any tissue and for any insult and in either in vitro or in vivo settings—for a protective role of HO-1, a role only previously theorized for this enzyme [1]. Further strides were made to delineate the mechanism(s) by which induced HO-1 provided protection against the oxidant injury to the kidney. The authors explored the mechanisms by which heme proteins induced renal vasoconstriction [7, 8] and also identified the renal intracellular targets vulnerable to the deleterious effects of such toxic proteins [7, 9]. In addition, they Key words: nuclear factor-B (NF-B) heme proteins, tubulointerstitial injury, fibrogenic cytokines inflammatory response, monocyte chemoattractant peptide (MCP-1).
2001 by the International Society of Nephrology
378
demonstrated that cytoprotection against heme protein– induced toxicity can occur even when HO-1 is induced by agents such as an endotoxin [10] or by the administration of heterologous antibody as in nephrotoxic serum nephritis [11]. More recently, they confirmed the role of this enzyme in HO-1–deficient mice stressed with heme proteins. These mice exhibited severe renal insufficiency and increased mortality [12]. Nath et al extended the above studies to explore whether HO-1 protected against the inflammatory assault by heme proteins in the HO-1–deficient mice in a clinical setting. The impetus for the studies described in the accompanying article was a patient with paroxysmal nocturnal hemoglobinuria who developed progressive chronic tubulointerstitial disease with up-regulation of HO-1 in the kidney and in renal tubular cells exposed to patient’s urine. In previous studies in rats, Nath and colleagues had demonstrated a triphasic response in the kidney exposed to heme proteins. Initially, kidneys exhibit acute sensitivity to hemoproteins, followed by acquisition of resistance to them, and finally a progressive tubulointerstitial disease with up-regulation of inflammatory and fibrogenic cytokines [13]. Based on this information, they explored the status of HO-1 in various phases and devised a regimen that used sufficiently low doses of murine hemoglobin so that its repeated administration caused minimal mortality in HO-1–deficient mice. An acute sensitivity was noted both in wild-type and HO-1–deficient mice with the initial doses of hemoglobin, and eventually both the strains developed resistance as well to heme proteins. Remarkably, the response differed in the third phase. HO-1–deficient mice had marked exacerbation of tubulointerstitial disease, suggesting that the capacity to recruit HO-1, as it occurs in wild-type mice, provides a mechanism that holds in check the inflammatory response induced by heme proteins. To delineate the mechanism involved, they focused on the monocyte chemoattractant peptide (MCP-1), since the latter contributes to progressive tubulointerstitial injury [14] as a redox-sensitive gene. Novel data emerged from the experiments. A relatively very high up-regulation of MCP-1 in the kidney was observed in HO-deficient mice with repeated chronic administration of hemoglobin. Concomitantly, nuclear factor-kappa B (NF-B), a transcription factor that induces the expression of
Editorial
MCP-1, was avidly activated in the HO-1–deficient mice. This implied that HO-1 down-regulates MCP-1 by inhibiting the activation of NF-B. These findings clearly demonstrate that the induction of HO-1 serves as an adaptive response in the kidney subjected to repeated chronic exposure of heme proteins. The response thus restrains inflammation, which otherwise, in the absence of HO-1, would be markedly enhanced in addition to uncontrolled induction of NF-B and MCP-1. These studies suggest that HO-1 acts as a protectant not only during the acute phase of nephrotoxicity but also in the chronic inflammatory damage induced by heme proteins. The novel role HO-1 as a suppressor of inflammatory responses, mediated in part by in vivo down-regulating the expression of MCP-1, is further underscored in several other disease settings as well, for example, in acute pleurisy [15], xenotransplant rejection [16], transplant vasculopathy [17], and hyperoxic lung injury [18]. The present study also raises the question, What other cytokines and pro-inflammatory species are influenced by HO-1? Equally important is the molecular basis for the anti-inflammatory effect of HO-1 in the described model. Each of the products of HO-1—ferritin, bilirubin, and carbon monoxide—may exert cytoprotective and/or anti-inflammatory effects, and it would be interesting to determine which of these products are involved in exerting such anti-inflammatory effects in these settings. Nath and his colleagues previously speculated that heme proteins contributed to the progressive tubulointerstitial disease in hematuric glomerulonephritides. In such a scenario, the heme proteins are brought into tubular epithelial cells as a consequence of the incorporation and degradation of erythrocytes by the renal tubular epithelium, which then lead to a tubulointerstitial injury [19]. These findings, that there was an intense up-regulation of MCP-1 in heme-induced renal injury, point toward the molecular basis by which such an inflammatory damage ensues. In conclusion, the studies by Nath and his colleagues provide novel concepts regarding the understanding of the pathogenesis of tubulointerstitial injury, where HO-1 acts as a suppressor of an inflammatory response in the kidney repetitively exposed to heme proteins. This suppressive effect of HO-1 on inflammatory responses may relate to the capacity of HO-1 to suppress the chemokine, MCP-1, possibly through the antioxidant effect of HO-1 retarding the activation of the redox-sensitive transcription factor, NF-B. Importantly, heme proteins strongly up-regulate the chemokine, MCP-1, thereby uncovering such a stimulus for this chemokine. Moreover, the upregulated renal HO-1/ferritin expression in the patient repeatedly exposed to heme proteins during the course of paroxysmal nocturnal hemoglobinuria attests to the original contention enunciated by Nath and colleagues, that is, that HO-1 and ferritin are induced in the kidney in response to the stress by hemoproteins [6]. Finally, this study, representing a combination of clinical and
379
experimental observations, demonstrates how the exploration of a human disease process can provide important insights and engender important questions that can be analyzed using genetically engineered mice. Yashpal S. Kanwar Chicago, Illinois, USA Correspondence to Yashpal S. Kanwar, M.D., Ph.D., Department of Pathology, Northwestern University Medical School, 303 East Chicago Avenue, Chicago, Illinois 60611, USA. E-mail: [email protected]
REFERENCES 1. Stocker R: Induction of heme oxygenase as a defense against oxidative stress. Free Rad Res Commun 9:101–112, 1990 2. Nath KA: Heme oxygenase-1: A redoubtable response that limits reperfusion injury in the transplanted adipose liver. J Clin Invest 104:1485–1486, 1999 3. Dong Z, Lavrovsky Y, Venkatachalam MA, Roy AK: Heme oxygenase-1 in tissue pathology. Am J Pathol 156:1485–1488, 2000 4. Agarwal A, Nick HS: Renal response to tissue injury: Lessons from heme oxygenase-1 gene ablation and expression. J Am Soc Nephrol 11:965–973, 2000 5. Nath KA, Vercellotti GM, Grande JP, et al: Heme proteininduced chronic renal inflammation: Suppressive effect of induced heme oxygenase-1. Kidney Int 59:106–117, 2001 6. Nath KA, Balla G, Vercellotti GM, et al: Induction of heme oxygenase is a rapid, protective response in rhabdomyolysis in the rat. J Clin Invest 90:267–270, 1992 7. Nath KA, Balla J, Croatt A, Vercellotti GM: Heme proteinmediated renal injury: A protective role for 21-aminosteroids in vitro and in vivo. Kidney Int 47:592–602, 1995 8. Warden DH, Croatt AJ, Katusic ZS, Nath KA: Physiologic characterization of acute reversible systemic hypertension in a model of heme protein-induced renal injury. Am J Physiol 277 (Renal Physiol 46):F58–F65, 1999 9. Nath KA, Grande JP, Croatt AJ, et al: Intracellular targets in heme protein-induced renal injury. Kidney Int 53:100–111, 1998 10. Vogt BA, Alam J, Croatt AJ, et al: Acquired resistance to acute oxidative stress: Possible role of heme oxygenase and ferritin. Lab Invest 72:474–483, 1995 11. Vogt BA, Shanley TP, Croatt AJ, et al: Glomerular inflammation induces resistance to tubular injury in the rat: A novel form of acquired heme oxygenase-dependent resistance to renal injury. J Clin Invest 98:2139–2145, 1996 12. Nath KA, Haggard JJ, Croatt AJ, et al: The indispensability of heme oxygenase-1 (HO-1) in protecting against heme proteininduced toxicity in vivo. Am J Pathol 156:1527–1535, 2000 13. Nath KA, Croatt AJ, Haggard JJ, Grande JP: Renal response to repetitive exposure to heme proteins: Chronic injury induced by an acute insult. Kidney Int 57:2423–2433, 2000 14. Wenzel UO, Abboud HE: Chemokines and renal disease. Am J Kid Dis 26:982–994, 1995 15. Willis D, Moore AR, Frederick R, Willoughy DA: Heme oxygenase: A novel target for the modulation of the inflammatory response. Nature Med 2:87–90, 1996 16. Soares MP, Lin Y, Anrather J, Cxizmadia E, et al: Expression of heme oxygenase-1 can determine cardiac xenograft survival. Nature Med 4:1073–1077, 1998 17. Hancock WW, Buelow R, Sayegh MH, Turka LA: Antibodyinduced transplant arteriosclerosis is prevented by graft expression of anti-oxidant and anti-apoptotic genes. Nature Med 4:1392–1396, 1998 18. Otterbein LE, Kolls JK, Mantell LL, et al: Exogenous administration of heme oxygenase-1 by gene transfer provide protection against hyperoxia-induced lung injury. J Clin Invest 103:1047– 1054, 1999 19. Nath KA: Tubulointerstitial changes as a major determinant in the progression of renal damage. Am J Kid Dis 20:1–17, 1992