Gene transfer-induced local heme oxygenase-1 overexpression protects rat kidney transplants from ischemia/reperfusion injury

Oxidative stress and the role of redox signalling in chronic kidney disease

Chronic kidney disease (CKD) is a major public health concern, underscoring a need to identify pathogenic mechanisms and potential therapeutic targets. Reactive oxygen species (ROS) are derivatives of oxygen molecules that are generated during aerobic metabolism and are involved in a variety of cellular functions that are governed by redox conditions. Low levels of ROS are required for diverse processes, including intracellular signal transduction, metabolism, immune and hypoxic responses, and transcriptional regulation. However, excess ROS can be pathological, and contribute to the development and progression of chronic diseases. Despite evidence linking elevated levels of ROS to CKD development and progression, the use of low-molecular-weight antioxidants to remove ROS has not been successful in preventing or slowing disease progression. More recent advances have enabled evaluation of the molecular interactions between specific ROS and their targets in redox signalling pathways. Such studies may pave the way for the development of sophisticated treatments that allow the selective control of specific ROS-mediated signalling pathways.

Free heme and hemopexin in acute kidney injury after cardiopulmonary bypass and transient renal ischemia

Free heme is released from hemoproteins during hemolysis or ischemia reperfusion injury and can be pro-inflammatory. Most studies on nephrotoxicity of hemolysis-derived proteins focus on free hemoglobin (fHb) with heme as a prosthetic group. Measurement of heme in its free, non-protein bound, form is challenging and not commonly used in clinical routine diagnostics. In contrast to fHb, the role of free heme in acute kidney injury (AKI) after cardiopulmonary bypass (CPB) surgery is unknown. Using an apo-horseradish peroxidase-based assay, we identified free heme during CPB surgery as predictor of AKI in patients undergoing cardiac valve replacement (n = 37). Free heme levels during CPB surgery correlated with depletion of hemopexin (Hx), a heme scavenger-protein. In mice, the impact of high levels of circulating free heme on the development of AKI following transient renal ischemia and the therapeutic potential of Hx were investigated. C57BL/6 mice were subjected to bilateral renal ischemia/reperfusion injury for 15 min which did not cause AKI. However, additional administration of free heme in this model promoted overt AKI with reduced renal function, increased renal inflammation, and reduced renal perfusion on functional magnetic resonance imaging. Hx treatment attenuated AKI. Free heme administration to sham operated control mice did not cause AKI. In conclusion, free heme is a predictor of AKI in CPB surgery patients and promotes AKI in transient renal ischemia. Depletion of Hx in CPB surgery patients and attenuation of AKI by Hx in the in vivo model encourage further research on Hx therapy in patients with increased free heme levels during CPB surgery.

Head-to-head comparison of two SGLT-2 inhibitors on AKI outcomes in a rat ischemia-reperfusion model

The CREDENCE trial testing canagliflozin and the EMPA-REG OUTCOME trial testing empagliflozin suggest different effects on acute kidney injury (AKI). AKI diagnosis was mainly made based on changes of serum creatinine (sCr) although this also reflect mode of action of SGLT-2 inhibitors. We analyzed both compounds in a rat AKI model. The renal ischemia-reperfusion injury (I/R) model was used. Four groups were analyzed: sham, I/R+placebo, I/R+canagliflozin (30 mg/kg/day), I/R+ empagliflozin (10 mg/kg/day). Glucose excretion was comparable in both treatment groups indicating comparable SGLT-2 inhibition. Comparing GFR surrogate markers after I/R (sCr and blood urea nitrogen (BUN)), sCr peaked 24 h after I/R, BUN after 48 h, respectively, in the placebo treated I/R group. At all investigated time points after I/R sCr and BUN was higher in the I/R + canagliflozin group as compared to placebo treated rats, whereas the empagliflozin group did not differ from the placebo group. I/R led to tubular dilatation and necrosis. Empagliflozin was able to reduce that finding whereas canagliflozin had no effect. Treatment with empagliflozin also resulted in a significant reduction in an improved inflammatory score (p = 0.006). Renal expression of kidney injury molecule-1 (KIM-1) increased after I/R and empagliflozin but not canagliflozin significantly alleviated KIM-1 expression. I/R reduced urinary miR-26a excretion. Empagliflozin but not canagliflozin was able to restore normal levels of urinary miR-26a. This study in an AKI model confirmed safety data in the EMPA-REG OUTCOME trial suggesting that empagliflozin might reduce AKI risk. The empagliflozin effects on KIM-1 and miR-26a might indicate beneficial regulation of inflammation. These data should stimulate clinical studies with AKI risk as primary endpoint.

Does G Protein-Coupled Estrogen Receptor 1 Contribute to Cisplatin-Induced Acute Kidney Injury in Male Mice?

Nephrotoxicity is the dose-limiting side-effect of the chemotherapeutic agent cisplatin (Cp). Recent evidence points to renal protective actions of G protein-coupled estrogen receptor 1 (GPER1). In addition, it has been shown that GPER1 signaling elicits protective actions against acute ischemic injuries that involve multiple organ systems; however, the involvement of GPER1 signaling in Cp-induced acute kidney injury (AKI) remains unclear. This study tested whether genetic deletion of GPER1 exacerbates Cp-induced AKI in male mice. We subjected male mice, homozygous (homo) and heterozygous (het) knockout for the GPER1 gene, and wild-type (WT) littermates to Cp or saline injections and assessed markers for renal injury on the third day after injections. We also determined serum levels of proinflammatory markers in saline and Cp-treated mice. Given the protective role of heme oxygenase-1 (HO-1) in Cp-mediated apoptosis, we also investigated genotypic differences in renal HO-1 abundance, cell death, and proliferation by Western blotting, the TUNEL assay, and Ki67 immunostaining, respectively. Cp increased serum creatinine, urea, and neutrophil gelatinase-associated lipocalin (NGAL) levels, the renal abundance of kidney injury molecule-1, and NGAL in all groups. Cp-induced AKI resulted in comparable histological evidence of injury in all genotypes. WT and homo mice showed greater renal HO-1 abundance in response to Cp. Renal HO-1 abundance was lower in Cp-treated homo, compared to Cp-treated WT mice. Of note, GPER1 deletion elicited a remarkable increase in renal apoptosis; however, no genotypic differences in cell proliferation were observed. Cp augmented kidney Ki67-positive counts, regardless of the genotype. Overall, our data do not support a role for GPER1 in mediating Cp-induced renal injury. GPER1 deletion promotes renal apoptosis and diminishes HO-1 induction in response to Cp, suggesting that GPER1 may play cytoprotective and anti-apoptotic actions in AKI. GPER1-induced regulation of HO-1 and apoptosis may offer novel therapeutic targets for the treatment of AKI.

Carbon Monoxide in Renal Physiology, Pathogenesis and Treatment of Renal Disease

Carbon monoxide (CO) is one of the endogenous gaseous messengers or gasotransmitters, and is a paramount mediator in physiological and disease conditions. In this review, we focus on the functions of CO in normal and pathological renal physiology. We discuss endogenous renal CO production and signaling in the normal kidney, the characteristic of CO-releasing molecules (CORMs) modalities, and outline its regulatory functions in renal physiology. This article summarizes the mechanisms as well as the effect of CO in the evolving field of renal diseases. We predict numerous innovative CO applications forevolvingcutting-edge scholarly work in the future.

Application of carbon monoxide in kidney and heart transplantation: A novel pharmacological strategy for a broader use of suboptimal renal and cardiac grafts

Carbon monoxide (CO) was historically regarded solely as a poisonous gas that binds to hemoglobin and reduces oxygen-carrying capacity of blood at high concentrations. However, recent findings show that it is endogenously produced in mammalian cells as a by-product of heme degradation by heme oxygenase, and has received a significant attention as a medical gas that influences a myriad of physiological and pathological processes. At low physiological concentrations, CO exhibits several therapeutic properties including antioxidant, anti-inflammatory, anti-apoptotic, anti-fibrotic, anti-thrombotic, anti-proliferative and vasodilatory properties, making it a candidate molecule that could protect organs in various pathological conditions including cold ischemia-reperfusion injury (IRI) in kidney and heart transplantation. Cold IRI is a well-recognized and complicated cascade of interconnected pathological pathways that poses a significant barrier to successful outcomes after kidney and heart transplantation. A substantial body of preclinical evidence demonstrates that CO gas and CO-releasing molecules (CO-RMs) prevent cold IRI in renal and cardiac grafts through several molecular and cellular mechanisms. In this review, we discuss recent advances in research involving the use of CO as a novel pharmacological strategy to attenuate cold IRI in preclinical models of kidney and heart transplantation through its administration to the organ donor prior to organ procurement or delivery into organ preservation solution during cold storage and to the organ recipient during reperfusion and after transplantation. We also discuss the underlying molecular mechanisms of cyto- and organ protection by CO during transplantation, and suggest its clinical use in the near future to improve long-term transplantation outcomes.

Adapting decarbonylation chemistry for the development of prodrugs capable of in vivo delivery of carbon monoxide utilizing sweeteners as carrier molecules

Carbon monoxide as an endogenous signaling molecule exhibits pharmacological efficacy in various animal models of organ injury. To address the difficulty in using CO gas as a therapeutic agent for widespread applications, we are interested in developing CO prodrugs through bioreversible caging of CO in an organic compound. Specifically, we have explored the decarboxylation-decarbonylation chemistry of 1,2-dicarbonyl compounds. Examination and optimization of factors favorable for maximal CO release under physiological conditions led to organic CO prodrugs using non-calorific sweeteners as leaving groups attached to the 1,2-dicarbonyl core. Attaching a leaving group with appropriate properties promotes the desired hydrolysis-decarboxylation-decarbonylation sequence of reactions that leads to CO generation. One such CO prodrug was selected to recapitulate the anti-inflammatory effects of CO against LPS-induced TNF-α production in cell culture studies. Oral administration in mice elevated COHb levels to the safe and efficacious levels established in various preclinical and clinical studies. Furthermore, its pharmacological efficacy was demonstrated in mouse models of acute kidney injury. These studies demonstrate the potential of these prodrugs with benign carriers as orally active CO-based therapeutics. This represents the very first example of orally active organic CO prodrugs with a benign carrier that is an FDA-approved sweetener with demonstrated safety profiles in vivo.

Expression of HO1 and PER2 can predict the incidence of delirium in trauma patients with concomitant brain injury

Intensive care unit (ICU)-acquired delirium is associated with adverse outcome in trauma patients with concomitant traumatic brain injury (TBI), but diagnosis remains challenging. Quantifying circadian disruption by analyzing expression of the circadian gene period circadian regulator 2 (PER2) and heme oxygenase 1 (HO1), which determines heme turnover, may prove to be potential diagnostic tools. Expression of PER2 and HO1 was quantified using qPCR from blood samples 1 day and 7 days after trauma. Association analysis was performed comparing mRNA expression levels with parameters of trauma (ISS—injury severity score), delirium, acute kidney injury (AKI) and length of ICU stay. 48 polytraumatized patients were included (equal distribution of TBI versus non-TBI) corrected for ISS, age and gender using a matched pairs approach. Expression levels of PER2 and HO1 were independent of age (PER2: P = 0.935; HO1: P = 0.988), while expression levels were significantly correlated with trauma severity (PER2: P = 0.009; HO1: P < 0.001) and longer ICU length of stay (PER2: P = 0.018; HO1: P < 0.001). High expression levels increased the odds of delirium occurrence (PER2: OR = 4.32 [1.14–13.87]; HO1: OR = 4.50 [1.23–14.42]). Patients with TBI showed a trend towards elevated PER2 (OR = 3.00 [0.84–9.33], P = 0.125), but not towards delirium occurrence (P = 0.556). TBI patients were less likely to develop AKI compared to non-TBI (P = 0.022). Expression levels of PER2 and HO1 correlate with the incidence of delirium in an age-independent manner and may potentially improve diagnostic algorithms when used as delirium biomarkers.

Trial registration: German Clinical Trials Register (Trial-ID DRKS00008981; Universal Trial Number U1111-1172-6077; Jan. 18, 2018).

New insights into the role of heme oxygenase-1 in acute kidney injury

Acute kidney injury (AKI) is attended by injury-related biomarkers appearing in the urine and serum, decreased urine output, and impaired glomerular filtration rate. AKI causes increased morbidity and mortality and can progress to chronic kidney disease and end-stage kidney failure. AKI is without specific therapies and is managed by supported care. Heme oxygenase-1 (HO-1) is a cytoprotective, inducible enzyme that degrades toxic free heme released from destabilized heme proteins and, during this process, releases beneficial by-products such as carbon monoxide and biliverdin/bilirubin and promotes ferritin synthesis. HO-1 induction protects against assorted renal insults as demonstrated by in vitro and preclinical models. This review summarizes the advances in understanding of the protection conferred by HO-1 in AKI, how HO-1 can be induced including via its transcription factor Nrf2, and HO-1 induction as a therapeutic strategy.

Adaptive Potential of the Heme Oxygenase/Carbon Monoxide Pathway During Hypoxia

Heme oxygenase (HO) enzymes catalyze heme into biliverdin, releasing carbon monoxide (CO) and iron into circulation. These byproducts of heme degradation can have potent cytoprotective effects in the face of stressors such as hypoxia and ischemia-reperfusion events. The potential for exogenous use of CO as a therapeutic agent has received increasing attention throughout the past few decades. Further, HO and CO are noted as putatively adaptive in diving mammals and certain high-altitude human populations that are frequently exposed to hypoxia and/or ischemia-reperfusion events, suggesting that HO and endogenous CO afford an evolutionary advantage for hypoxia tolerance and are critical in cell survival and injury avoidance. Our goal is to describe the importance of examining HO and CO in several systems, the physiological links, and the genetic factors that underlie variation in the HO/CO pathway. Finally, we emphasize the ways in which evolutionary perspectives may enhance our understanding of the HO/CO pathway in the context of diverse clinical settings.

HO-1 concentrations 24 hours after cardiac surgery are associated with the incidence of acute kidney injury: a prospective cohort study

Background

Acute kidney injury (AKI) is a serious complication after cardiac surgery that is associated with increased mortality and morbidity. Heme oxygenase-1 (HO-1) is an enzyme synthesized in renal tubular cells as one of the most intense responses to oxidant stress linked with protective, anti-inflammatory properties. Yet, it is unknown if serum HO-1 induction following cardiac surgical procedure involving cardiopulmonary bypass (CPB) is associated with incidence and severity of AKI.

Patients and methods

In the present study, we used data from a prospective cohort study of 150 adult cardiac surgical patients. HO-1 measurements were performed before, immediately after and 24 hours post-CPB. In univariate and multivariate analyses, the association between HO-1 and AKI was investigated.

Results

AKI with an incidence of 23.3% (35 patients) was not associated with an early elevation of HO-1 after CPB in all patients (P=0.88), whereas patients suffering from AKI developed a second burst of HO-1 24 hours after CBP. In patients without AKI, the HO-1 concentrations dropped to baseline values (P=0.031). Furthermore, early HO-1 induction was associated with CPB time (P=0.046), while the ones 24 hours later lost this association (P=0.219).

Conclusion

The association of the second HO-1 burst 24 hours after CBP might help to distinguish between the causality of AKI in patients undergoing CBP, thus helping to adapt patient stratification and management.

Head-to-head comparison of structurally unrelated dipeptidyl peptidase 4 inhibitors in the setting of renal ischemia reperfusion injury

Background and Purpose

Results regarding protective effects of dipeptidyl peptidase 4 (DPP4) inhibitors in renal ischaemia–reperfusion injury (IRI) are conflicting. Here we have compared structurally unrelated DPP4 inhibitors in a model of renal IRI.

Experimental Approach

IRI was induced in uninephrectomized male rats by renal artery clamping for 30 min. The sham group was uninephrectomized but not subjected to IRI. DPP4 inhibitors or vehicle were given p.o. once daily on three consecutive days prior to IRI: linagliptin (1.5 mg·kg⁻¹·day⁻¹), vildagliptin (8 mg·kg⁻¹·day⁻¹) and sitagliptin (30 mg·kg⁻¹·day⁻¹). An additional group received sitagliptin until study end (before IRI: 30 mg·kg⁻¹·day⁻¹; after IRI: 15 mg·kg⁻¹·day⁻¹).

Key Results

Plasma‐active glucagon‐like peptide type 1 (GLP‐1) increased threefold to fourfold in all DPP4 inhibitor groups 24 h after IRI. Plasma cystatin C, a marker of GFR, peaked 48 h after IRI. Compared with the placebo group, DPP4 inhibition did not reduce increased plasma cystatin C levels. DPP4 inhibitors ameliorated histopathologically assessed tubular damage with varying degrees of drug‐specific efficacies. Renal osteopontin expression was uniformly reduced by all DPP4 inhibitors. IRI‐related increased renal cytokine expression was not decreased by DPP4 inhibition. Renal DPP4 activity at study end was significantly inhibited in the linagliptin group, but only numerically reduced in the prolonged/dose‐adjusted sitagliptin group. Active GLP‐1 plasma levels at study end were increased only in the prolonged/dose‐adjusted sitagliptin treatment group.

Conclusions and Implications

In rats with renal IRI, DPP4 inhibition did not alter plasma cystatin C, a marker of glomerular function, but may protect against tubular damage.

Heme Oxygenase 1 as a Therapeutic Target in Acute Kidney Injury

A common clinical condition, acute kidney injury (AKI) significantly influences morbidity and mortality, particularly in critically ill patients. The pathophysiology of AKI is complex and involves multiple pathways, including inflammation, autophagy, cell-cycle progression, and oxidative stress. Recent evidence suggests that a single insult to the kidney significantly enhances the propensity to develop chronic kidney disease. Therefore, the generation of effective therapies against AKI is timely. In this context, the cytoprotective effects of heme oxygenase 1 (HO-1) in animal models of AKI are well documented. HO-1 modulates oxidative stress, autophagy, and inflammation and regulates the progression of cell cycle via direct and indirect mechanisms. These beneficial effects of HO-1 induction during AKI are mediated in part by the by-products of the HO reaction (iron, carbon monoxide, and bile pigments). This review highlights recent advances in the molecular mechanisms of HO-1-mediated cytoprotection and discusses the translational potential of HO-1 induction in AKI.

Recent early clinical drug development for acute kidney injury

INTRODUCTION

Despite significant need and historical trials, there are no effective drugs in use for the prevention or treatment of acute kidney injury (AKI). There are several promising agents in early clinical development for AKI and two trials have recently been terminated. There are also exciting new findings in pre-clinical AKI research. There is a need to take stock of current progress in the field to guide future drug development for AKI. Areas covered: The main clinical trial registries, PubMed and pharmaceutical company website searches were used to extract the most recent clinical trials for sterile, transplant and sepsis-associated AKI. We summarise the development of the agents recently in clinical trial, update on their trial progress, consider reasons for failed efficacy of two agents, and discuss new paradigms in pre-clinical targets for AKI. Agents covered include- QPI-1002, THR-184, BB-3, heme arginate, human recombinant alkaline phosphatase (recAP), ciclosporin A, AB103, levosimendan, AC607 and ABT-719. Expert opinion: Due to the heterogenous nature of AKI, agents with the widest pleiotropic effects on multiple pathophysiological pathways are likely to be most effective. Linking preclinical models to clinical indication and improving AKI definition and diagnosis are key areas for improvement in future clinical trials.

Paternal High Fat Diet in Rats Leads to Renal Accumulation of Lipid and Tubular Changes in Adult Offspring

Along with diabetes and obesity, chronic kidney disease (CKD) is increasing across the globe. Although some data support an effect of maternal obesity on offspring kidney, the impact of paternal obesity is unknown; thus, we have studied the effect of paternal obesity prior to conception. Male Sprague Dawley rats were fed chow diet or high fat diet (HFD) for 13-14 weeks before mating with chow-fed females. Male offspring were weaned onto chow and killed at 27 weeks for renal gene expression and histology. Fathers on HFD were 30% heavier than Controls at mating. At 27 weeks of age offspring of obese fathers weighed 10% less; kidney triglyceride content was significantly increased (5.35 ± 0.84 vs. 2.99 ± 0.47 μg/mg, p < 0.05, n = 8 litters per group. Histological analysis of the kidney demonstrated signs of tubule damage, with significantly greater loss of brush border, and increased cell sloughing in offspring of obese compared to Control fathers. Acat1, involved in entry of fatty acid for beta-oxidation, was significantly upregulated, possibly to counteract increased triglyceride storage. However other genes involved in lipid metabolism, inflammation and kidney injury showed no changes. Paternal obesity was associated with renal triglyceride accumulation and histological changes in tubules, suggesting a mild renal insult in offspring, who may be at risk of developing CKD.

Hemin Preconditioning Upregulates Heme Oxygenase-1 in Deceased Donor Renal Transplant Recipients: A Randomized, Controlled, Phase IIB Trial

BACKGROUND

The enzyme heme oxygenase-1 (HO-1) degrades heme and protects against ischemia-reperfusion injury. Monocytes/macrophages are the major source of HO-1 and higher levels improve renal transplant outcomes. Heme arginate (HA) safely induces HO-1 in humans.

METHODS

The Heme Oxygenase-1 in renal Transplantation study was a randomized, placebo-controlled, IIb trial to evaluate HA effect on HO-1 upregulation after deceased donor kidney transplantation. 40 recipients were randomized to either 3 mg kg HA or placebo (0.9% NaCl), given preoperatively (day 0) and again on day 2. Recipient blood and urine were collected daily. Graft biopsies were taken preoperatively and on day 5. Primary outcome was HO-1 upregulation in peripheral blood mononuclear cells (PBMCs). Secondary outcomes were graft HO-1 upregulation and injury, urinary biomarkers, and renal function.

RESULTS

The HA upregulated PBMC HO-1 protein more than placebo at 24 hours: HA 11.1 ng/mL versus placebo 0.14 ng/mL (P = < 0.0001). The PBMC HO-1 messenger RNA also increased: HA 2.73-fold versus placebo 1.41-fold (P = 0.02). Heme arginate increased day 5 tissue HO-1 protein immunopositivity compared with placebo: HA 0.21 versus placebo -0.03 (P = 0.02) and % HO-1-positive renal macrophage also increased: HA 50.8 cells per high power field versus placebo 22.3 (P = 0.012). Urinary biomarkers were reduced after HA but not significantly. Histological injury and renal function were similar but the study was not powered for this. Adverse events were equivalent between groups.

CONCLUSIONS

The primary outcome was achieved and demonstrated for the first time that HA safely induces HO-1 in transplant recipients. Planned larger studies will determine the impact of HO-1 upregulation on clinical outcomes and evaluate the benefit to patients at risk of ischemia-reperfusion injury.

Molecular mechanisms of ischemic preconditioning in the kidney

More effective therapeutic strategies for the prevention and treatment of acute kidney injury (AKI) are needed to improve the high morbidity and mortality associated with this frequently encountered clinical condition. Ischemic and/or hypoxic preconditioning attenuates susceptibility to ischemic injury, which results from both oxygen and nutrient deprivation and accounts for most cases of AKI. While multiple signaling pathways have been implicated in renoprotection, this review will focus on oxygen-regulated cellular and molecular responses that enhance the kidney's tolerance to ischemia and promote renal repair. Central mediators of cellular adaptation to hypoxia are hypoxia-inducible factors (HIFs). HIFs play a crucial role in ischemic/hypoxic preconditioning through the reprogramming of cellular energy metabolism, and by coordinating adenosine and nitric oxide signaling with antiapoptotic, oxidative stress, and immune responses. The therapeutic potential of HIF activation for the treatment and prevention of ischemic injuries will be critically examined in this review.

Anti-inflammatory and anti-osteoclastogenic effects of zinc finger protein A20 overexpression in human periodontal ligament cells

BACKGROUND AND OBJECTIVE

Although overexpression of the nuclear factor κB inhibitory and ubiquitin-editing enzyme A20 is thought to be involved in the pathogenesis of inflammatory diseases, its function in periodontal disease remains unknown. The aims of the present study were to evaluate A20 expression in patients with periodontitis and to study the effects of A20 overexpression, using a recombinant adenovirus encoding A20 (Ad-A20), on the inflammatory response and on osteoclastic differentiation in lipopolysaccharide (LPS)- and nicotine-stimulated human periodontal ligament cells (hPDLCs).

MATERIAL AND METHODS

The concentration of prostaglandin E2 was measured by radioimmunoassay. Reverse transcription-polymerase chain reactions and western blot analyses were used to measure mRNA and protein levels, respectively. Osteoclastic differentiation was assessed in mouse bone marrow-derived macrophages using conditioned medium from LPS- and nicotine-treated hPDLCs.

RESULTS

A20 was upregulated in the gingival tissues and neutrophils from patients with periodontitis and in LPS- and nicotine-exposed hPDLCs. Pretreatment with A20 overexpression by Ad-A20 markedly attenuated LPS- and nicotine-induced production of prostaglandin E2 , as well as expression of cyclooxygenase-2 and proinflammatory cytokines. Moreover, A20 overexpression inhibited the number and size of tartrate-resistant acid phosphatase-stained osteoclasts, and downregulated osteoclast-specific gene expression. LPS- and nicotine-induced p38 phosphorylation and nuclear factor κB activation were blocked by Ad-A20. Ad-A20 inhibited the effects of nicotine and LPS on the activation of pan-protein kinase C, Akt, GSK-3β and protein kinase Cα.

CONCLUSIONS

This study is the first to demonstrate that A20 overexpression has anti-inflammatory effects and blocks osteoclastic differentiation in a nicotine- and LPS-stimulated hPDLC model. Thus, A20 overexpression may be a potential therapeutic target in inflammatory bone loss diseases, such as periodontal disease.

Heme oxygenase-1 ameliorates kidney ischemia-reperfusion injury in mice through extracellular signal-regulated kinase 1/2-enhanced tubular epithelium proliferation

Heme oxygenase (HO)-1 confers transient resistance against oxidative damage, including renal ischemia-reperfusion injury (IRI). We investigated the potential protective effect of HO-1 induction in a mouse model of renal IRI induced by bilateral clamping of the kidney arteries. The mice were randomly assigned to five groups to receive an intraperitoneal injection of PBS, hemin (an HO-1 inducer, 100μmol/kg), hemin+ZnPP (an HO-1 inhibitor, 5mg/kg), hemin+PD98059 (a MEK-ERK inhibitor, 10mg/kg) or a sham operation. All of the groups except for the sham-operated group underwent 25min of ischemia and 24 to 72h of reperfusion. Renal function and tubular damage were assessed in the mice that received hemin or the vehicle treatment prior to IRI. The renal injury score and HO-1 protein levels were evaluated via H&E and immunohistochemistry staining. Hemin-preconditioned mice exhibited preserved renal cell function (BUN: 40±2mg/dl, creatinine: 0.53±0.06mg/dl), and the tubular injury score at 72h (1.65±0.12) indicated that tubular damage was prevented. Induction of HO-1 induced the phosphorylation of extracellular signal-regulated kinases (ERK) 1/2. However, these effects were abolished with ZnPP treatment. Kidney function (BUN: 176±49mg/dl, creatinine: 1.54±0.39mg/dl) increased, and the tubular injury score (3.73±0.09) indicated that tubular damage also increased with ZnPP treatment. HO-1-induced tubular epithelial proliferation was attenuated by PD98059. Our findings suggest that HO-1 preconditioning promotes ERK1/2 phosphorylation and enhances tubular recovery, which subsequently prevents further renal injury.

Xenon Treatment Protects against Remote Lung Injury after Kidney Transplantation in Rats

BACKGROUND

Ischemia-reperfusion injury (IRI) of renal grafts may cause remote organ injury including lungs. The authors aimed to evaluate the protective effect of xenon exposure against remote lung injury due to renal graft IRI in a rat renal transplantation model.

METHODS

For in vitro studies, human lung epithelial cell A549 was challenged with H2O2, tumor necrosis factor-α, or conditioned medium from human kidney proximal tubular cells (HK-2) after hypothermia-hypoxia insults. For in vivo studies, the Lewis renal graft was stored in 4°C Soltran preserving solution for 24 h and transplanted into the Lewis recipient, and the lungs were harvested 24 h after grafting. Cultured lung cells or the recipient after engraftment was exposed to 70% Xe or N2. Phospho (p)-mammalian target of rapamycin (mTOR), hypoxia-inducible factor-1α (HIF-1α), Bcl-2, high-mobility group protein-1 (HMGB-1), TLR-4, and nuclear factor κB (NF-κB) expression, lung inflammation, and cell injuries were assessed.

RESULTS

Recipients receiving ischemic renal grafts developed pulmonary injury. Xenon treatment enhanced HIF-1α, which attenuated HMGB-1 translocation and NF-κB activation in A549 cells with oxidative and inflammatory stress. Xenon treatment enhanced p-mTOR, HIF-1α, and Bcl-2 expression and, in turn, promoted cell proliferation in the lung. Upon grafting, HMGB-1 translocation from lung epithelial nuclei was reduced; the TLR-4/NF-κB pathway was suppressed by xenon treatment; and subsequent tissue injury score (nitrogen vs. xenon: 26 ± 1.8 vs. 10.7 ± 2.6; n = 6) was significantly reduced.

CONCLUSION

Xenon treatment confers protection against distant lung injury triggered by renal graft IRI, which is likely through the activation of mTOR-HIF-1α pathway and suppression of the HMGB-1 translocation from nuclei to cytoplasm.

Transduced PEP-1-heme oxygenase-1 fusion protein reduces remote organ injury induced by intestinal ischemia/reperfusion

Background

A fusion protein composed of heme oxygenase-1 (HO-1) and cell-penetrating peptide PEP-1 has been shown to reduce local intestinal injury after intestinal ischemia/reperfusion (I/R). In this study, we investigated the effects of PEP-1-HO-1 fusion protein on remote organ injury induced by intestinal I/R in rats.

Material/methods

We randomly assigned 24 male Sprague-Dawley rats to 3 groups: Sham, I/R, and I/R plus PEP-1-HO-1 treatment (HO). The model of intestinal I/R was established by occluding the superior mesenteric artery for 45 min followed by 120-min reperfusion. In HO group, PEP-1-HO-1 was administered intravenously 30 min before ischemia, while animals in the Sham and I/R groups received the equal volume of physiological saline. At the end of the experiment, lung, liver, and blood samples were collected and analyzed.

Results

Malondialdehyde levels and histological injury scores were increased, and superoxide dismutase activities were decreased in the lung and liver tissues in the I/R group compared with the Sham group (P<0.05). Serum levels of alanine aminotransferase, aspartate aminotransferase, tumor necrosis factor-α, interleukin-6, and lung tissue wet weight to dry weight ratio were increased in the I/R group compared with the Sham group (P<0.05). NF-κB expression in intestinal tissues was significantly higher in the I/R group than in the Sham group. These changes were significantly reversed by treatment with PEP-1-HO-1.

Conclusions

This study demonstrates that administration of PEP-1-HO-1 has a protective role against lung and liver injury after intestinal I/R, attributable to the reduction of released proinflammatory cytokines regulated by NF-κB.

Heme oxygenase-1 and acute kidney injury

PURPOSE OF REVIEW

Heme oxygenase activity, possessed by an inducible heme oxygenase-1 (HO-1) and a constitutive isoform (HO-2), catalyzes the conversion of heme to biliverdin, liberates iron, and generates carbon monoxide. First shown in acute kidney injury (AKI), HO-1 is now recognized as a protectant against diverse insults in assorted tissues. This review summarizes recent contributions to the field of HO-1 and AKI.

RECENT FINDINGS

Recent findings elucidate the following: the transcriptional regulation and significance of human HO-1 in AKI; the protective effects of HO-1 in age-dependent and sepsis-related AKI, cardiorenal syndromes, and acute vascular rejection in renal xenografts; the role of heme oxygenase in tubuloglomerular feedback and renal resistance to injury; the basis for cytoprotection by HO-1; the protective properties of ferritin and carbon monoxide; HO-1 and the AKI-chronic kidney disease transition; HO-1 as a biomarker in AKI; the role of HO-1 in mediating the protective effects of specific cytokines, stem cells, and therapeutic agents in AKI; and HO-2 as a protectant in AKI.

SUMMARY

Recent contributions support, and elucidate the basis for, the induction of HO-1 as a protectant against AKI. Translating such therapeutic potential into a therapeutic reality requires well tolerated and effective modalities for upregulating HO-1 and/or administering its products, which, optimally, should be salutary even when AKI is already established.

Homocysteine in renovascular complications: hydrogen sulfide is a modulator and plausible anaerobic ATP generator

Homocysteine (Hcy) is a non-protein amino acid derived from dietary methionine. High levels of Hcy, known as hyperhomocysteinemia (HHcy) is known to cause vascular complications. In the mammalian tissue, Hcy is metabolized by transsulfuration enzymes to produce hydrogen sulfide (H2S). H2S, a pungent smelling gas was previously known for its toxic effects in the central nervous system, recent studies however has revealed protective effects in a variety of diseases including hypertension, diabetes, inflammation, atherosclerosis, and renal disease progression and failure. Interestingly, under stress conditions including hypoxia, H2S can reduce metabolic demand and also act as a substrate for ATP production. This review highlights some of the recent advances in H2S research as a potential therapeutic agent targeting renovascular diseases associated with HHcy.

MicroRNA-24 antagonism prevents renal ischemia reperfusion injury

Ischemia-reperfusion (I/R) injury of the kidney is a major cause of AKI. MicroRNAs (miRs) are powerful regulators of various diseases. We investigated the role of apoptosis-associated miR-24 in renal I/R injury. miR-24 was upregulated in the kidney after I/R injury of mice and in patients after kidney transplantation. Cell-sorting experiments revealed a specific miR-24 enrichment in renal endothelial and tubular epithelial cells after I/R induction. In vitro, anoxia/hypoxia induced an enrichment of miR-24 in endothelial and tubular epithelial cells. Transient overexpression of miR-24 alone induced apoptosis and altered functional parameters in these cells, whereas silencing of miR-24 ameliorated apoptotic responses and rescued functional parameters in hypoxic conditions. miR-24 effects were mediated through regulation of H2A histone family, member X, and heme oxygenase 1, which were experimentally validated as direct miR-24 targets through luciferase reporter assays. In vitro, adenoviral overexpression of miR-24 targets lacking miR-24 binding sites along with miR-24 precursors rescued various functional parameters in endothelial and tubular epithelial cells. In vivo, silencing of miR-24 in mice before I/R injury resulted in a significant improvement in survival and kidney function, a reduction of apoptosis, improved histologic tubular epithelial injury, and less infiltration of inflammatory cells. miR-24 also regulated heme oxygenase 1 and H2A histone family, member X, in vivo. Overall, these results indicate miR-24 promotes renal ischemic injury by stimulating apoptosis in endothelial and tubular epithelial cell. Therefore, miR-24 inhibition may be a promising future therapeutic option in the treatment of patients with ischemic AKI.

Genomics of liver transplant injury and regeneration

While improved surgical techniques, post-operative care, and immunosuppression regimens have reduced morbidity and mortality associated with orthotopic liver transplantation (OLT), further improvement of outcomes requires personalized treatment and a better understanding of genomic mechanisms involved. Gene expression profiles of ischemia/reperfusion (I/R) injury, regeneration, and rejection, may suggest mechanisms for development of better predictive tools and treatments. The liver is unique in its regenerative potential, recovering lost mass and function after injury from ischemia, resection, and rejection. I/R injury, an inevitable consequence of perfusion cessation, cold storage, and reperfusion, is regulated by the interaction of the immune system, inflammatory cytokines, and reduced microcirculatory blood flow in the liver. Rejection, a common post-operative complication, is mediated by the recipient's immune system through T-cell-dependent responses activating proinflammatory and apoptotic pathways. Characterizing distinctive gene expression signatures for these events can identify therapies to reduce injury, promote regeneration, and improve outcomes. While certain markers of liver injury and regeneration have been observed in animals, many of these are unverified in human studies. Further investigation of these genomic signatures and mechanisms through new technology offers promise, but continues to pose a significant challenge. An overview of the current fund of knowledge in this area is reviewed.

Emerging role of gasotransmitters in renal transplantation

Once patients with kidney disease progress to end-stage renal failure, transplantation is the preferred option of treatment resulting in improved quality of life and reduced mortality compared to dialysis. Although 1-year survival has improved considerably, graft and patient survival in the long term have not been concurrent, and therefore new tools to improve long-term graft and patient survival are warranted. Over the past decades, the gasotransmitters nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S) have emerged as potent cytoprotective mediators in various diseases. All three gasotransmitters are endogenously produced messenger molecules that possess vasodilatory, anti-apoptotic, anti-inflammatory and anti-oxidant properties by influencing an array of intracellular signaling processes. Although many regulatory functions of gasotransmitters have overlapping actions, differences have also been reported. In addition, crosstalk between NO, CO and H2S results in synergistic regulatory effects. Endogenous and exogenous manipulation of gasotransmitter levels modulates several processes involved in renal transplantation. This review focuses on mechanisms of gas-mediated cytoprotection and complex interactions between gasotransmitters in renal transplantation.

Alternative 5' untranslated regions are involved in expression regulation of human heme oxygenase-1

The single nucleotide polymorphism rs2071746 and a (GT)_n microsatellite within the human gene encoding heme oxygenase-1 (HMOX1) are associated with incidence or outcome in a variety of diseases. Most of these associations involve either release of heme or oxidative stress. Both polymorphisms are localized in the promoter region, but previously reported correlations with heme oxygenase-1 expression remain not coherent. This ambiguity suggests a more complex organization of the 5’ gene region which we sought to investigate more fully.

We evaluated the 5‘ end of HMOX1 and found a novel first exon 1a placing the two previously reported polymorphisms in intronic or exonic positions within the 5’ untranslated region respectively. Expression of exon 1a can be induced in HepG2 hepatoma cells by hemin and is a repressor of heme oxygenase-1 translation as shown by luciferase reporter assays. Moreover, minigene approaches revealed that the quantitative outcome of alternative splicing within the 5’ untranslated region is affected by the (GT)_n microsatellite.

This data supporting an extended HMOX1 gene model and provide further insights into expression regulation of heme oxygenase-1. Alternative splicing within the HMOX1 5' untranslated region contributes to translational regulation and is a mechanistic feature involved in the interplay between genetic variations, heme oxygenase-1 expression and disease outcome.

Transduced PEP-1-heme oxygenase-1 fusion protein protects against intestinal ischemia/reperfusion injury

BACKGROUND

Heme oxygenase-1 (HO-1) has been shown to have antioxidant and anti-apoptotic properties. The present study transduced HO-1 protein into intestinal tissues using PEP-1, a cell-penetrating peptide, and investigated its potentiality in prevention against intestinal ischemia/reperfusion (I/R) injury.

MATERIALS AND METHODS

PEP-1-HO-1 fusion protein was administered intravenously to explore the time and dose characteristics through measuring serum HO-1 levels. Twenty-four male Sprague-Dawley rats were randomly divided into three groups: sham, intestinal I/R (II/R), II/R + PEP-1-HO-1 fusion protein (HO). The model was established by occluding the superior mesenteric artery for 45 min followed by 120 min reperfusion. In HO group, PEP-1-HO-1 was administered intravenously 30 min before ischemia, whereas animals in sham and II/R groups received the equal volume of physiological saline. After the experiment, the intestines were harvested for determination of histologic injury, wet/dry ratio, enzyme activity, apoptosis, and His-probe protein (one part of PEP-1-HO-1).

RESULTS

Levels of serum HO-1 were dose- and time-dependent manner after intravenous injection of PEP-1-HO-1. I/R caused deterioration of histologic characteristics and increases in histologic injury scoring, wet/dry ratio, myeloperoxidase activity, malondialdehyde, and intestinal apoptosis. These changes were also accompanied by a decrease in superoxide dismutase activity (P < 0.05). PEP-1-HO-1 treatment significantly reversed these changes (P < 0.05). Furthermore, His-probe protein expression was only detected in PEP-1-HO-1-treated animals.

CONCLUSION

Treatment of PEP-1-HO-1 attenuates intestinal I/R injury, which might be attributable to its antioxidant and anti-apoptotic roles of HO-1.

Donor simvastatin treatment prevents ischemia-reperfusion and acute kidney injury by preserving microvascular barrier function

Ischemia-reperfusion injury (IRI) after kidney transplantation may result in delayed graft function. We used rat renal artery clamping and transplantation models to investigate cholesterol-independent effects of clinically relevant single-dose peroral simvastatin treatment 2 h before renal ischemia on microvascular injury. The expression of HMG-CoA reductase was abundant in glomerular and peritubular microvasculature of normal kidneys. In renal artery clamping model with 30-min warm ischemia, simvastatin treatment prevented peritubular microvascular permeability and perfusion disturbances, glomerular barrier disruption, tubular dysfunction and acute kidney injury. In fully MHC-mismatched kidney allografts with 16-h cold and 1-h warm ischemia, donor simvastatin treatment increased the expression of flow-regulated transcription factor KLF2 and vasculoprotective eNOS and HO-1, and preserved glomerular and peritubular capillary barrier integrity during preservation. In vitro EC Weibel-Palade body exocytosis assays showed that simvastatin inhibited ischemia-induced release of vasoactive angiopoietin-2 and endothelin-1. After reperfusion, donor simvastatin treatment prevented microvascular permeability, danger-associated ligand hyaluronan induction, tubulointerstitial injury marker Kim-1 immunoreactivity and serum creatinine and NGAL levels, and activation of innate and adaptive immune responses. In conclusion, donor simvastatin treatment prevented renal microvascular dysfunction and IRI with beneficial effects on adaptive immune and early fibroproliferative responses. Further studies may determine potential benefits in clinical cadaveric kidney transplantation.

Xenon treatment protects against cold ischemia associated delayed graft function and prolongs graft survival in rats

Prolonged hypothermic storage causes ischemia-reperfusion injury (IRI) in the renal graft, which is considered to contribute to the occurrence of the delayed graft function (DGF) and chronic graft failure. Strategies are required to protect the graft and to prolong renal graft survival. We demonstrated that xenon exposure to human proximal tubular cells (HK-2) led to activation of range of protective proteins. Xenon treatment prior to or after hypothermia-hypoxia challenge stabilized the HK-2 cellular structure, diminished cytoplasmic translocation of high-mobility group box (HMGB) 1 and suppressed NF-κB activation. In the syngeneic Lewis-to-Lewis rat model of kidney transplantation, xenon exposure to donors before graft retrieval or to recipients after engraftment decreased caspase-3 expression, localized HMGB-1 within nuclei and prevented TLR-4/NF-κB activation in tubular cells; serum pro-inflammatory cytokines IL-1β, IL-6 and TNF-α were reduced and renal function was preserved. Xenon treatment of graft donors or of recipients prolonged renal graft survival following IRI in both Lewis-to-Lewis isografts and Fischer-to-Lewis allografts. Xenon induced cell survival or graft functional recovery was abolished by HIF-1α siRNA. Our data suggest that xenon treatment attenuates DGF and enhances graft survival. This approach could be translated into clinical practice leading to a considerable improvement in long-term graft survival.

Xenon treatment attenuates early renal allograft injury associated with prolonged hypothermic storage in rats

Prolonged hypothermic storage elicits severe ischemia-reperfusion injury (IRI) to renal grafts, contributing to delayed graft function (DGF) and episodes of acute immune rejection and shortened graft survival. Organoprotective strategies are therefore needed for improving long-term transplant outcome. The aim of this study is to investigate the renoprotective effect of xenon on early allograft injury associated with prolonged hypothermic storage. Xenon exposure enhanced the expression of heat-shock protein 70 (HSP-70) and heme oxygenase 1 (HO-1) and promoted cell survival after hypothermia-hypoxia insult in human proximal tubular (HK-2) cells, which was abolished by HSP-70 or HO-1 siRNA. In the brown Norway to Lewis rat renal transplantation, xenon administered to donor or recipient decreased the renal tubular cell death, inflammation, and MHC II expression, while delayed graft function (DGF) was therefore reduced. Pathological changes associated with acute rejection, including T-cell, macrophage, and fibroblast infiltration, were also decreased with xenon treatment. Donors or recipients treated with xenon in combination with cyclosporin A had prolonged renal allograft survival. Xenon protects allografts against delayed graft function, attenuates acute immune rejection, and enhances graft survival after prolonged hypothermic storage. Furthermore, xenon works additively with cyclosporin A to preserve post-transplant renal function.

Generation and characterization of human heme oxygenase-1 transgenic pigs

Xenotransplantation using transgenic pigs as an organ source is a promising strategy to overcome shortage of human organ for transplantation. Various genetic modifications have been tried to ameliorate xenograft rejection. In the present study we assessed effect of transgenic expression of human heme oxygenase-1 (hHO-1), an inducible protein capable of cytoprotection by scavenging reactive oxygen species and preventing apoptosis caused by cellular stress during inflammatory processes, in neonatal porcine islet-like cluster cells (NPCCs). Transduction of NPCCs with adenovirus containing hHO-1 gene significantly reduced apoptosis compared with the GFP-expressing adenovirus control after treatment with either hydrogen peroxide or hTNF-α and cycloheximide. These protective effects were diminished by co-treatment of hHO-1 antagonist, Zinc protoporphyrin IX. We also generated transgenic pigs expressing hHO-1 and analyzed expression and function of the transgene. Human HO-1 was expressed in most tissues, including the heart, kidney, lung, pancreas, spleen and skin, however, expression levels and patterns of the hHO-1 gene are not consistent in each organ. We isolate fibroblast from transgenic pigs to analyze protective effect of the hHO-1. As expected, fibroblasts derived from the hHO-1 transgenic pigs were significantly resistant to both hydrogen peroxide damage and hTNF-α and cycloheximide-mediated apoptosis when compared with wild-type fibroblasts. Furthermore, induction of RANTES in response to hTNF-α or LPS was significantly decreased in fibroblasts obtained from the hHO-1 transgenic pigs. These findings suggest that transgenic expression of hHO-1 can protect xenografts when exposed to oxidative stresses, especially from ischemia/reperfusion injury, and/or acute rejection mediated by cytokines. Accordingly, hHO-1 could be an important candidate molecule in a multi-transgenic pig strategy for xenotransplantation.

Pathophysiology of acute kidney injury

Acute kidney injury (AKI) is the leading cause of nephrology consultation and is associated with high mortality rates. The primary causes of AKI include ischemia, hypoxia, or nephrotoxicity. An underlying feature is a rapid decline in glomerular filtration rate (GFR) usually associated with decreases in renal blood flow. Inflammation represents an important additional component of AKI leading to the extension phase of injury, which may be associated with insensitivity to vasodilator therapy. It is suggested that targeting the extension phase represents an area potential of treatment with the greatest possible impact. The underlying basis of renal injury appears to be impaired energetics of the highly metabolically active nephron segments (i.e., proximal tubules and thick ascending limb) in the renal outer medulla, which can trigger conversion from transient hypoxia to intrinsic renal failure. Injury to kidney cells can be lethal or sublethal. Sublethal injury represents an important component in AKI, as it may profoundly influence GFR and renal blood flow. The nature of the recovery response is mediated by the degree to which sublethal cells can restore normal function and promote regeneration. The successful recovery from AKI depends on the degree to which these repair processes ensue and these may be compromised in elderly or chronic kidney disease (CKD) patients. Recent data suggest that AKI represents a potential link to CKD in surviving patients. Finally, earlier diagnosis of AKI represents an important area in treating patients with AKI that has spawned increased awareness of the potential that biomarkers of AKI may play in the future.

Protective effect of heme oxygenase-1 induction against hepatic injury in alcoholic steatotic liver exposed to cold ischemia/reperfusion

AIMS

The purpose of this study was to investigate the cytoprotective role of heme oxygenase-1 (HO-1) induction in hepatic injury in alcoholic steatotic liver exposed to cold ischemia/reperfusion (I/R).

MAIN METHODS

Animals were fed an ethanol liquid diet or isocaloric control diet for 5 weeks. Isolated perfused rat livers were preserved in Histidine-Tryptophan-Ketoglutarate at 4 °C. After 24 h of storage, livers were subjected to 120 min of reperfusion with Krebs-Henseleit bicarbonate buffer at 37 °C. Animals were pretreated with cobalt protoporphyrin (CoPP, 5 mg/kg, i.p.) or zinc protoporphyrin (ZnPP, 25 mg/kg, i.p.), HO-1 inducer and antagonist, respectively.

KEY FINDINGS

In the model of ischemia/isolated perfusion, endogenous HO-1 was downregulated in the livers fed with ethanol diet (ED I/R). In ED I/R group, portal pressure and lactate dehydrogenase release were significantly increased, while bile output and hyaluronic acid clearance decreased compared to rats fed on control diet (CD I/R). Furthermore, hepatic glutathione content decreased and lipid peroxidation increased in the ED I/R group compared to the CD I/R group. These alterations were attenuated by upregulation of HO-1 with CoPP pretreatment.

SIGNIFICANCE

Our results suggest that chronic ethanol consumption aggravates hepatic injury during cold I/R and it is likely due to downregulation of endogenous HO-1. Prior induction of HO-1 expression may provide a new strategy to protect livers against hepatic I/R injury or to increase the donor transplant pool through modulation of marginal alcoholic steatotic livers.

Preservation strategies to reduce ischemic injury in kidney transplantation: pharmacological and genetic approaches

PURPOSE OF REVIEW

In the current graft shortage, it is paramount to improve the quality of transplanted organs. Organ preservation represents an underused therapeutic window with great potential to reduce ischaemia-reperfusion injury (IRI) and improve graft quality. Herein, we review strategies using this window as well as other promising work targeting IRI pathways using pharmacological treatments and gene therapy.

RECENT FINDINGS

We highlight studies using molecules administered during kidney preservation to target key components of IRI such as inflammation, oxidative stress, mitochondrial activity and the coagulation pathway. We further expose recent studies of gene therapy directed against inflammation or apoptosis during cold storage. Other pathways with potential therapeutic molecules are cited.

SUMMARY

The use of cold preservation as a therapeutic window to deliver pharmacological or gene therapy treatments can significantly improve both short-term and long-term graft outcomes. Even if human gene therapy remains hampered by the quantity of agent needed and the potential harmfulness of the vector, it clearly offers a wide array of possibilities for the future. Although gene therapy is still too immature, we expose pharmacological strategies which can readily be applied to the clinic and improve both transplantation success rates and the patients' quality of life.

Sulforaphane prevents microcystin-LR-induced oxidative damage and apoptosis in BALB/c mice

Microcystins (MCs), the products of blooming algae Microcystis, are waterborne environmental toxins that have been implicated in the development of liver cancer, necrosis, and even fatal intrahepatic bleeding. Alternative protective approaches in addition to complete removal of MCs in drinking water are urgently needed. In our previous work, we found that sulforaphane (SFN) protects against microcystin-LR (MC-LR)-induced cytotoxicity by activating the NF-E2-related factor 2 (Nrf2)-mediated defensive response in human hepatoma (HepG2) and NIH 3T3 cells. The purpose of this study was to investigate and confirm efficacy the SFN-induced multi-mechanistic defense system against MC-induced hepatotoxicity in an animal model. We report that SFN protected against MC-LR-induced liver damage and animal death at a nontoxic and physiologically relevant dose in BALB/c mice. The protection by SFN included activities of anti-cytochrome P450 induction, anti-oxidation, anti-inflammation, and anti-apoptosis. Our results suggest that SFN may protect mice against MC-induced hepatotoxicity. This raises the possibility of a similar protective effect in human populations, particularly in developing countries where freshwaters are polluted by blooming algae.

Association between the heme oxygenase-1 promoter polymorphism and renal transplantation outcome in Greece

BACKGROUND

Heme oxygenase-1 (HO-1) is the enzyme that catabolizes heme into carbon monoxide, biliverdin, and free iron. The induction of this enzyme is an important cytoprotective mechanism, which occurs as an adaptive and beneficial response to a wide variety of oxidant stimuli. HO-1 has recently been suggested to protect transplants from ischemia/reperfusion and immunologic injury. HO-1 inducibility is mainly modulated by a (GT)(n) repeat polymorphism in the promoter region, and has been shown that short repeats (S) are associated with greater upregulation of HO-1, compared with long repeats (L). In the present study we investigated the influence of this HO-1 gene polymorphism on clinical outcome after transplantation and on renal transplant function.

METHODS

DNA from 175 donor/recipient pairs who underwent transplantation between October 2002 and June 2007 was genotyped. We divided the HO-1 alleles into 2 subclasses, the S ≤ 27 repeats and L > 27 repeats.

RESULTS

There has been significant relevance between the genotype of the donor and the outcome of the graft, as far as recipients with normal graft function and recipients with deteriorated graft function are concerned (P = .021). In patients with normal graft function, grafts from L-homozygotes were found in 24%, whereas in patients with deteriorated function, grafts from L-homozygotes exhibited in higher rate (50%). Neither the donor's nor the recipient's polymorphism influenced the graft survival (log-rank test P = .228 for the donors and log-rank test P = 0.844 for the recipients). There was no evidence of a gene-dose effect on graft survival (P = .469). Recipients of allografts from S-carriers donors had significantly lower serum creatinine levels at 24 months compared with recipients of allografts from L-homozygotes donors (P = .016).

A new role for myeloid HO-1 in the innate to adaptive crosstalk and immune homeostasis

Increasing evidence supports the presence of a dynamic crosstalk between innate and adaptive immunity with a pivotal role played by pathways governing innate immune responses. TLRs (Toll-like receptors) and RLHs (retinoic acid-inducible gene I [RIG-I]-like helicases) are known to play a key role in these processes. A molecule of high significance in the protection against innate and adaptive immune aberrations is heme oxygenase 1 (HO-1). HO-1 is a microsomal enzyme that catalyses the degradation of heme to iron, carbon monoxide and bilirubin. These by-products appear to be the key mediators of its anti--inflammatory and cytoprotective action, mainly through the downregulation of pro-inflammatory and upregulation of anti-inflammatory molecules. Recent data from our lab support the presence of an additional direct effect of myeloid HO-1 on innate immune conditioning, and more specifically on the TLR3/TLR4/RIG-I pathway. In myeloid cells, HO-1 forms a complex with the transcription factor IRF3 (Interferon regulating factor 3) and is required for IRF3 phosphorylation and consequent type-I interferon and chemokine gene induction. Myeloid HO-1-deficient mice show reduced expression of IRF3 target genes and altered responses to infectious and organ-specific auto-immune diseases. This new frame of understanding HO-1 function should also be important for the future design of novel interventions differentially targeting the enzymatic versus the IRF3 modulating properties of HO-1.

Exogenous biliverdin improves the function of lung grafts from brain dead donors in rats

BACKGROUND

Biliverdin, a product of heme oxygenase-1 (HO-1), ameliorates the posttransplant functions of heart, kidney, and liver. In this study, we investigated the effects of biliverdin on lung grafts from brain dead (BD) rat donors.

METHODS

Male Wistar rats were randomly divided into 3 groups. The sham group (n = 7), did not undergo BD. Both donor and recipient rats in the BD biliverdin group (n = 8) were injected with biliverdin (35 mg/kg in 1 mL) intraperitoneally after confirmed BD and transplantation. In the BD group (n = 8), both donor and recipient rats received the same volume of saline (35 mg/kg in 1 mL) as the BD biliverdin group. All donor rats were observed for 1.5 hours before undergoing lung transplantation. Two hours after transplantation, we obtained blood and lung graft samples.

RESULTS

Biliverdin reversed the aggravation of Pa(O(2)) in recipients, reduced the grafts wet/dry ratio, decreased the severity of lung injury measured by histologic examination, reduced serum tumor necrosis factor-alpha and interleukin-8 levels and inhibited myeloperoxidase activity (MPO) in the grafts. Furthermore, it significantly decreased malonaldehyde levels and increased superoxide dismutase levels. Biliverdin reduced cell apoptosis, activated protein expression of biliverdin reductase, and inhibited expression of HO-1 and nuclear factor (NF)-kappaB in lung grafts.

CONCLUSION

Biliverdin exerts protective effects on lung grafts from BD donors through anti-inflammatory, antioxidant, and anti-apoptotic mechanisms.

Role of heme oxygenase-1 in transplantation

Heme oxygenase-1 (HO-1) is the rate-limiting enzyme in heme catabolism that converts heme to Fe++, carbon monoxide and biliverdin. HO-1 acts anti-inflammatory and modulates apoptosis in many pathological conditions. In transplantation, HO-1 is overexpressed in organs during brain death, when undergoing ischemic damage and rejection. However, intentionally induced, it ameliorates pathological processes like ischemia reperfusion injury, allograft, xenograft or islet rejection, facilitates donor specific tolerance and alleviates chronic allograft changes. We herein consistently summarize the huge amount of data on HO-1 and transplantation that have been generated in multiple laboratories during the last 15years and suggest possible clinical implications and applications for the near future.

In vitro and in vivo immunomodulatory effects of cobalt protoporphyrin administered in combination with immunosuppressive drugs

BACKGROUND

Immunosuppressive strategies are designed to take advantage of potential synergies between drugs to possibly decrease the risk of side-effects. In the present study, the ability of Cobalt protoporphyrin (CoPP) to potentiate the effect of the immunosuppressive drugs mycophenolate sodium (MPS) or cyclosporin A (CsA) was explored in vitro and in vivo.

METHODS

In vitro analyses of proliferation and apoptosis were performed on primate T cell cultures, following incubation with the immunosuppressive drugs MPS or CsA, alone or in combination with CoPP. In vivo the effect of CoPP and CsA combination therapy was assessed in a rat heterotopic cardiac allotransplantation model.

RESULTS

In vitro results suggest that co-administration of CoPP with CsA or MPS increases immunosuppressive effects of these drugs when combined with CoPP. In particular, the co-administration of CoPP with CsA resulted in the synergistic induction of lymphocyte apoptosis. In vivo, animals immunosuppressed with CsA (1.5 mg/kg) or CoPP (20 mg/kg) alone, had a median survival of 7 or 8 days, respectively. In contrast, animals immunosuppressed with CsA (1.5 mg/kg) combined with CoPP (20 mg/kg) had significantly prolonged median survival (12 days), compared to recipients treated with CsA or CoPP alone (p<0.05).

CONCLUSION

Our in vitro and in vivo studies demonstrate that CoPP can potentiate the immunomodulatory effects of CsA, ultimately extending allograft survival.

Anti-inflammatory treatment strategies for ischemia/reperfusion injury in transplantation

Inflammatory reactions in the graft have a pivotal influence on acute as well as long-term graft function. The main reasons for an inflammatory reaction of the graft tissue are rejection episodes, infections as well as ischemia/reperfusion (I/R) injury. The latter is of particular interest as it affects every solid organ during the process of transplantation. I/R injury impairs acute as well as long-term graft function and is associated with an increased number of acute rejection episodes that again affect long-term graft outcome.

I/R injury is the result of ATP depletion during prolonged hypoxia. Further tissue damage results from the reperfusion of the tissue after the ischemic insult. Adaptive cellular responses activate the innate immune system with its Toll-like receptors and the complement system as well as the adaptive immune system. This results in a profound inflammatory tissue reaction with immune cells infiltrating the tissue. The damage is mediated by various cytokines, chemokines, adhesion molecules, and compounds of the extracellular matrix. The expression of these factors is regulated by specific transcription factors with NF-κB being one of the key modulators of inflammation.

Strategies to prevent or treat I/R injury include blockade of cytokines/chemokines, adhesion molecules, NF-κB, specific MAP kinases, metalloproteinases, induction of protective genes, and modulation of the innate immune system. Furthermore, preconditioning of the donor is an area of intense research. Here pharmacological treatment as well as new additives to conventional cold storage solutions have been analyzed together with new techniques for the perfusion of grafts, or methods of normothermic storage that would avoid the problem of cold damage and graft ischemia.

However, the number of clinical trials in the field of I/R injury is limited as compared to the large body of experimental knowledge that accumulated during recent years in the field of I/R injury. Future activities in the treatment of I/R injury should focus on the translation of experimental protocols into clinical trials in order to reduce I/R injury and, thus, improve short- as well as long-term graft outcome.

Epoetin delta reduces oxidative stress in primary human renal tubular cells

Erythropoietin (EPO) exerts (renal) tissue protective effects. Since it is unclear whether this is a direct effect of EPO on the kidney or not, we investigated whether EPO is able to protect human renal tubular epithelial cells (hTECs) from oxidative stress and if so which pathways are involved. EPO (epoetin delta) could protect hTECs against oxidative stress by a dose-dependent inhibition of reactive oxygen species formation. This protective effect is possibly related to the membranous expression of the EPO receptor (EPOR) since our data point to the membranous EPOR expression as a prerequisite for this protective effect. Oxidative stress reduction went along with the upregulation of renoprotective genes. Whilst three of these, heme oxygenase-1 (HO-1), aquaporin-1 (AQP-1), and B-cell CLL/lymphoma 2 (Bcl-2) have already been associated with EPO-induced renoprotection, this study for the first time suggests carboxypeptidase M (CPM), dipeptidyl peptidase IV (DPPIV), and cytoglobin (Cygb) to play a role in this process.

Genetic ablation of transcription repressor Bach1 reduces neural tissue damage and improves locomotor function after spinal cord injury in mice

Heme oxygenase (HO)-1 is an inducible cytoprotective enzyme that degrades heme to iron, carbon monoxide (CO), and biliverdin, the latter two of which are thought to mediate the anti-inflammatory and antioxidant actions of HO-1. Bach1 is a transcriptional repressor of the HO-1 gene (Hmox-1). Previous reports have demonstrated that the genetic ablation of Bach1 engenders an increased HO-1 expression and a marked reduction in the degree of oxidative tissue damage in vivo. However, the function of Bach1 in spinal cord injury is still not understood. In the present study, we examined whether Bach1 deficiency increases HO-1 expression and reduces neural tissue damage in a spinal cord injury model using Bach1 knock-out (KO) mice and wild-type (WT) mice. The expression of HO-1 protein in the spinal cord was significantly higher in the Bach1 KO mice than in the WT mice before and after injury. The KO mice also had significantly higher Basso mouse scale scores for locomotor function and larger areas of spared white matter than the WT mice at 6 weeks after injury. Neuronal loss and apoptotic cell death in the injured spinal cord was significantly reduced in the KO mice in comparison to the WT mice. These results suggest that Bach1 deficiency engenders a constitutively higher expression of HO-1 and a dramatic increase in cytoprotection against spinal cord injury.

Heme oxygenase-1, a critical arbitrator of cell death pathways in lung injury and disease

Increases in cell death by programmed (i.e., apoptosis, autophagy) or nonprogrammed mechanisms (i.e., necrosis) occur during tissue injury and may contribute to the etiology of several pulmonary or vascular disease states. The low-molecular-weight stress protein heme oxygenase-1 (HO-1) confers cytoprotection against cell death in various models of lung and vascular injury by inhibiting apoptosis, inflammation, and cell proliferation. HO-1 serves a vital metabolic function as the rate-limiting step in the heme degradation pathway and in the maintenance of iron homeostasis. The transcriptional induction of HO-1 occurs in response to multiple forms of chemical and physical cellular stress. The cytoprotective functions of HO-1 may be attributed to heme turnover, as well as to beneficial properties of its enzymatic reaction products: biliverdin-IXalpha, iron, and carbon monoxide (CO). Recent studies have demonstrated that HO-1 or CO inhibits stress-induced extrinsic and intrinsic apoptotic pathways in vitro. A variety of signaling molecules have been implicated in the cytoprotection conferred by HO-1/CO, including autophagic proteins, p38 mitogen-activated protein kinase, signal transducer and activator of transcription proteins, nuclear factor-kappaB, phosphatidylinositol 3-kinase/Akt, and others. Enhanced HO-1 expression or the pharmacological application of HO end-products affords protection in preclinical models of tissue injury, including experimental and transplant-associated ischemia/reperfusion injury, promising potential future therapeutic applications.

Melatonin protects kidney grafts from ischemia/reperfusion injury through inhibition of NF-kB and apoptosis after experimental kidney transplantation

Free radicals are involved in pathophysiology of ischemia/reperfusion injury (IRI). Melatonin is a potent scavenger of reactive oxygen and nitrogen species. Thus, this study was designed to elucidate its effects in a model of rat kidney transplantation. Twenty Lewis rats were randomly divided into 2 groups (n = 10 animals each). Melatonin (50 mg/kg BW) dissolved in 5 mL milk was given to one group via gavage 2 hr before left donor nephrectomy. Controls were given the same volume of milk only. Kidney grafts were then transplanted into bilaterally nephrectomized syngeneic recipients after 24 hr of cold storage in Histidine-Tryptophan-Ketoglutarate solution. Both graft function and injury were assessed after transplantation through serum levels of blood urea nitrogen (BUN), creatinine, transaminases, and lactate dehydrogenase (LDH). Biopsies were taken to evaluate tubular damage, the enzymatic activity of superoxide dismutase (SOD) and lipid hydroperoxide (LPO), and the expression of NF-kBp65, inducible nitric oxide synthase (iNOS), caspase-3 as indices of oxidative stress, necrosis, and apoptosis, respectively. Melatonin improved survival (P < 0.01) while decreasing BUN, creatinine, transaminases, and LDH values up to 39-71% (P < 0.05). Melatonin significantly reduced the histological index for tubular damage, induced tissue enzymatic activity of SOD while reducing LPO. At the same time, melatonin down-regulated the expression of NF-kBp65, iNOS, and caspase-3. In conclusion, donor preconditioning with melatonin protected kidney donor grafts from IRI-induced renal dysfunction and tubular injury most likely through its anti-oxidative, anti-apoptotic and NF-kB inhibitory capacity.

Antioxidant enzyme gene transfer for ischemic diseases

The balance of redox is pivotal for normal function and integrity of tissues. Ischemic insults occur as results of a variety of conditions, leading to an accumulation of reactive oxygen species (ROS) and an imbalanced redox status in the tissues. The oxidant stress may activate signaling mechanisms provoking more toxic events, and eventually cause tissue damage. Therefore, treatments with antioxidants, free radical scavengers and their mimetics, as well as gene transfer approaches to overexpress antioxidant genes represent potential therapeutic options to correct the redox imbalance. Among them, antioxidant gene transfer may enhance the production of antioxidant scavengers, and has been employed to experimentally prevent or treat ischemic injury in cardiovascular, pulmonary, hepatic, intestinal, central nervous or other systems in animal models. With improvements in vector systems and delivery approaches, innovative antioxidant gene therapy has conferred better outcomes for myocardial infarction, reduced restenosis after coronary angioplasty, improved the quality and function of liver grafts, as well as outcome of intestinal and cerebral ischemic attacks. However, it is crucial to be mindful that like other therapeutic armentarium, the efficacy of antioxidant gene transfer requires extensive preclinical investigation before it can be used in patients, and that it may have unanticipated short- or long-term adverse effects. Thus, it is critical to balance between the therapeutic benefits and potential risks, to develop disease-specific antioxidant gene transfer strategies, to deliver the therapy with an optimal time window and in a safe manner. This review attempts to provide the rationale, the most effective approaches and the potential hurdles of available antioxidant gene transfer approaches for ischemic injury in various organs, as well as the possible directions of future preclinical and clinical investigations of this highly promising therapeutic modality.