Renal hemodynamic, inflammatory, and apoptotic responses to lipopolysaccharide in HO-1-/- mice

Arginase2 mediates contrast-induced acute kidney injury via facilitating nitrosative stress in tubular cells

Contrast-induced acute kidney injury(CI-AKI) is the third cause of AKI. Although tubular injury has been regarded as an important pathophysiology of CI-AKI, the underlying mechanism remains elusive. Here, we found arginase2(ARG2) accumulated in the tubules of CI-AKI mice, and was upregulated in iohexol treated kidney tubular cells and in blood samples of CI-AKI mice and patients, accompanied by increased nitrosative stress and apoptosis. However, all of the above were reversed in ARG2 knockout mice, as evidenced by the ameliorated kidney dysfunction and the tubular injury, and decreased nitrosative stress and apoptosis. Mechanistically, HO-1 upregulation could alleviate iohexol or ARG2 overexpression mediated nitrosative stress. Silencing and overexpressing ARG2 was able to upregulate and downregulate HO-1 expression, respectively, while HO-1 siRNA had no effect on ARG2 expression, indicating that ARG2 might inhibit HO-1 expression at the transcriptional level, which facilitated nitrosative stress during CI-AKI. Additionally, CREB1, a transcription factor, bound to the promoter region of ARG2 and stimulated its transcription. Similar findings were yielded in cisplatin- or vancomycin-induced AKI models. Taken together, ARG2 is a crucial target of CI-AKI, and activating CREB1/ARG2/HO-1 axis can mediate tubular injury by promoting nitrosative stress, highlighting potential therapeutic strategy for treating CI-AKI.

Oxypurinol protects renal ischemia/reperfusion injury via heme oxygenase-1 induction

Renal ischemia/reperfusion (I/R) injury is a major cause of acute kidney injury (AKI) by increasing oxidative stress, inflammatory responses, and tubular cell death. Oxypurinol, an active metabolite of allopurinol, is a potent anti-inflammatory and antioxidant agent. To investigate the therapeutic potential and underlying mechanism of oxypurinol in ischemic AKI, C57BL/6 male mice were intraperitoneally injected with oxypurinol and subjected to renal I/R or sham surgery. We found that oxypurinol-treated mice had lower plasma creatinine and blood urea nitrogen levels and tubular damage (hematoxylin-and-eosin staining) compared to vehicle-treated mice after renal I/R injury. Furthermore, oxypurinol treatment reduced kidney inflammation (i.e., neutrophil infiltration and MIP-2 mRNA induction), oxidative stress (i.e., 4-HNE, heme oxygenase-1 [HO-1], 8-OHdG expression, and Catalase mRNA induction), and apoptosis (i.e., TUNEL or cleaved caspase-3-positive renal tubular cells), compared to vehicle-treated mice. Mechanistically, oxypurinol induced protein expressions of HO-1, which is a critical cytoprotective enzyme during ischemic AKI, and oxypurinol-mediated protection against ischemic AKI was completely eliminated by pretreatment with tin protoporphyrin IX, an HO-1 inhibitor. In conclusion, oxypurinol protects against renal I/R injury by reducing oxidative stress, inflammation, and apoptosis via HO-1 induction, suggesting its preventive potential in ischemic AKI.

Heme oxygenase-1 as a predictor of sepsis-induced acute kidney injury: a cross-sectional study

BACKGROUND

Sepsis patients suffer from severe inflammation and poor prognosis. Oxidative stress and local inflammation that results from sepsis can trigger organ injury, including acute kidney injury (AKI). Previous studies have shown that heme oxygenase-1 (HO-1) is overexpressed in proximal tubular cells under oxidative stress and has significant cytoprotective and anti-inflammatory effects. Heme-induced inflammation in sepsis is antagonized by increased tissue expression of heme oxygenase-1 (HO-1), which impacts on AKI development. The investigators observed intrarenal HO-1 expression and corresponding potential increases in plasma and urinary HO-1 protein concentrations in four different AKI models. Since serum levels of HO-1 reflect HO-1 expression, we aimed to investigate whether serum HO-1 could predict the development of AKI in sepsis patient.

METHODS

A total of 83 sepsis patients were enrolled in this study including septic patients with AKI and sepsis patients without AKI. According to the definition of septic shock and the global kidney diagnostic criteria described in the Kidney Disease: Improving Global Outcomes (KDIGO), patients were allocated to the sepsis and septic shock groups with and without AKI, respectively. The serum levels of HO-1 were measured by enzyme-linked immunosorbent assays (ELISA). Statistical analyses were performed using SPSS software.

RESULTS

There were statistically significant differences between septic patients with AKI and sepsis patients without AKI in terms of Sequential Organ Failure Assessment (SOFA) score, hospitalization time, and laboratory indicators including serum HO-1, creatine kinase MB (CK-MB), troponin I (TnI), urea, myoglobin (MYO), serum creatinine (Scr), procalcitonin, and activated partial thromboplastin time. Serum levels of alkaline phosphatase (ALP), urea, MYO, Scr, procalcitonin, activated partial thromboplastin time, and prothrombin time exhibited significant differences among the four groups. The concentration of serum HO-1 was higher in sepsis-induced AKI compared with sepsis patients without AKI. Serum HO-1 levels were increased in patients with sepsis shock-induced AKI. The area under the receiver operating characteristic (ROC) curve for serum HO-1 combined with Scr was 0.885 [95% confidence interval (CI): 0.761-1.000].

CONCLUSIONS

Serum HO-1 is positively correlated with sepsis-induced AKI. These findings suggest that measurement of serum HO-1 may play a diagnostic and prediction role in sepsis-induced AKI.

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.

MicroRNA-122-5p regulates coagulation and inflammation through MASP1 and HO-1 genes

MiR-122-5p is a diagnostic and prognostic biomarker of sepsis and is correlated with coagulation abnormalities in sepsis. However, its functional aspects remain unknown. This study applied bioinformatics analysis to evaluate the coagulation-related target genes for miR-122-5p. THP-1, HUVEC, and LO-2 cell lines were used in this study. MiR-122-5p mimics were transfected into the three previously mentioned cell lines, which helped in detecting mRNA and protein levels by qRT-PCR and western blotting, respectively. Serum samples from 84 sepsis patients were collected to evaluate target gene code proteins. The protein and mRNA levels of Heme oxygenase1(HO-1), IL-1β, IL-6, monocyte chemoattractant protein 1(MCP-1), and TNF-α were also evaluated in three cell lines. Mannan binding lectin serine peptidase 1(MASP1) was a direct target gene of miR-122-5p, and levels of MASP1, C3, and C4 were all significantly lower in the sepsis with disseminated intravascular coagulopathy (DIC) group than in the sepsis without DIC group. MiR-122-5p mimics could down-regulate HO-1 in the three cell lines. HO-1, IL-1β, IL-6, MCP-1, and TNF-α gene and protein levels were decreased after miR-122-5p mimics were added. MiR-122-5p regulated coagulation and inflammation through MASP1 and HO-1, respectively.

Heme Oxygenase 1 in Vertebrates: Friend and Foe

HO-1 is the inducible form of the enzyme heme-oxygenase. HO-1 catalyzes heme breakdown, reducing the levels of this important oxidant molecule and generating antioxidant, anti-inflammatory, and anti-apoptotic byproducts. Thus, HO-1 has been described as an important stress response mechanism during both physiologic and pathological processes. Interestingly, some findings are demonstrating that uncontrolled levels of HO-1 byproducts can be associated with cell death and tissue destruction as well. Furthermore, HO-1 can be located in the nucleus, influencing gene transcription, cellular proliferation, and DNA repair. Here, we will discuss several studies that approach HO-1 effects as a protective or detrimental mechanism in different pathological conditions. In this sense, as the major organs of vertebrates will deal specifically with distinct types of stresses, we discuss the HO-1 role in each of them, exposing the contradictions associated with HO-1 expression after different insults and circumstances.

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.

Expression of ACE2 in the Intact and Acutely Injured Kidney

Background

The actions of angiotensin-converting enzyme 2 (ACE2) oppose those of the renin-angiotensin-aldosterone system. ACE2 may be a cytoprotectant in some tissues. This study examined ACE2 expression in models of AKI.

Methods

ACE2 mRNA and protein expression and ACE2 activity were assessed in murine ischemic AKI. Renal ACE2 mRNA expression was evaluated in LPS-induced AKI in wild-type (C57BL/6J) mice, in heme oxygenase-1+/+ and heme oxygenase-1-/- mice, and after unilateral ureteral obstruction (UUO) in wild-type mice. The effect of sex and age on renal ACE2 protein expression was also assessed.

Results

In ischemic AKI, ACE2 mRNA and protein expression and ACE2 activity were reduced as compared with such indices in the intact kidney. In ischemic AKI, ACE2, which, in health, is prominently expressed in the tubular epithelium, especially proximal tubules, is decreased in expression in these segments. Decreased ACE2 expression in AKI did not reflect reduced GFR, because ACE2 mRNA expression was unaltered after UUO. LPS induced renal ACE2 mRNA expression in wild-type mice, but this effect did not occur in heme oxygenase-1-deficient mice. In ischemic and LPS-induced AKI, renal expression of the Mas receptor was increased. In the intact kidney, renal ACE2 protein expression decreased in female mice as compared with male mice, but was unaltered with age.

Conclusion

We conclude that renal ACE2 expression is decreased in ischemic AKI, characterized by decreased GFR and abundant cell death, but is upregulated in LPS-induced AKI, an effect requiring heme oxygenase-1. Determining the significance of ACE2 expression in experimental AKI merits further study. We suggest that understanding the mechanism underlying ACE2 downregulation in AKI may offer insights relevant to COVID-19: ACE2 expression is downregulated after ACE2 mediates SARS-CoV-2 cellular entry; such downregulation is proinflammatory; and AKI commonly occurs and determines outcomes in COVID-19.

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).

Heme Oxygenase 1: A Defensive Mediator in Kidney Diseases

The incidence of kidney disease is rising, constituting a significant burden on the healthcare system and making identification of new therapeutic targets increasingly urgent. The heme oxygenase (HO) system performs an important function in the regulation of oxidative stress and inflammation and, via these mechanisms, is thought to play a role in the prevention of non-specific injuries following acute renal failure or resulting from chronic kidney disease. The expression of HO-1 is strongly inducible by a wide range of stimuli in the kidney, consequent to the kidney's filtration role which means HO-1 is exposed to a wide range of endogenous and exogenous molecules, and it has been shown to be protective in a variety of nephropathological animal models. Interestingly, the positive effect of HO-1 occurs in both hemolysis- and rhabdomyolysis-dominated diseases, where the kidney is extensively exposed to heme (a major HO-1 inducer), as well as in non-heme-dependent diseases such as hypertension, diabetic nephropathy or progression to end-stage renal disease. This highlights the complexity of HO-1's functions, which is also illustrated by the fact that, despite the abundance of preclinical data, no drug targeting HO-1 has so far been translated into clinical use. The objective of this review is to assess current knowledge relating HO-1's role in the kidney and its potential interest as a nephroprotection agent. The potential therapeutic openings will be presented, in particular through the identification of clinical trials targeting this enzyme or its products.

Integrating metabolomics and network pharmacology to explore Rhizoma Coptidis extracts against sepsis-associated acute kidney injury

Sepsis remains the most common cause of acute kidney injury (AKI) in critically ill patients, increasing the risk of in-hospital and long-term death. Rhizoma Coptidis (RC), a classical traditional Chinese herb, exhibits anti-inflammatory and antioxidant properties in various diseases including sepsis. This study aimed to investigate the protective effects of RC extracts (RCE) against sepsis-associated acute kidney injury (SA-AKI) and explore the underlying mechanisms with metabolomics-based network pharmacology. The results showed that RCE improved renal function and histological injury and decreased reactive oxygen species (ROS) production in SA-AKI. Using ultra-high-performance liquid chromatography coupled with quadrupole-time-of-flight mass spectrometry (UHPLC-Q-TOF/MS), 25 differential metabolites were identified that had a close connection with the pathological processes of SA-AKI and the effects of RCE. Afterward, a compound-metabolite-target-disease network was constructed and 17 overlapping target proteins of the components of RCE, the differential metabolites, and the disease-related genes were discovered. Among these overlapping target proteins, RCE increased the nuclear translocation of nuclear factor-erythroid 2-related factor-2 (Nrf2), the protein expression of heme oxygenase-1 (HO-1), the mRNA expression of peroxisome proliferator activated receptor α (PPARα) and reduced nitric oxide synthase 2 (NOS2) activity. In addition, molecular docking revealed that both berberine and quercetin could bond with NOS2 and PPARα, respectively. Therefore, RCE demonstrated protective effects for SA-AKI through the regulation of metabolism and different signaling pathways.

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.

Nicotine uncovers endotoxic-like cardiovascular manifestations in female rats: Estrogen and nitric oxide dependency

Endotoxic manifestations are diminished in female populations due to immune boosting actions of sex steroids. Considering that tobacco constituents including nicotine inhibit estrogen synthesis, we tested the hypothesis that nicotine exposure unveils cardiovascular anomalies of endotoxemia in female rats. Studies were undertaken in conscious female rats treated with i.v. lipopolysaccharide (LPS, 10 mg/kg) in absence and presence of nicotine. In contrast to no effects for LPS when used alone, dose-related decreases in blood pressure (BP) and serum estrogen were noted in endotoxic rats treated consequently with nicotine (25, 50, or 100 μg/kg i.v.). Signs of cardiac autonomic dysfunction appeared in LPS/nicotine-treated rats such as (i) decreased time-domain indices of heart rate variability (HRV), e.g. standard deviation of R-R intervals (SDNN) and root mean square of successive differences in R-R interval durations (rMSSD), and (ii) reduced total power of the frequency spectrum and shifted cardiac sympathovagal balance toward sympathetic dominance. Nicotine reversed the LPS-evoked modest rises in serum TNFα and IL-1β while had no effect on associated arterial baroreflex dysfunction, inferring no roles for inflammation or baroreflexes in LPS-nicotine interaction. Estrogen or aminoguanidine (iNOS inhibitor), but not pentoxifylline (TNFα inhibitor), abolished LPS/nicotine hypotension. Together, nicotine acts probably via reducing estrogen availability to uncover nitric oxide-dependent hypotension and autonomic dysregulation in endotoxic female rats.

Antioxidative, Antiapoptotic, and Anti-Inflammatory Effects of Apamin in a Murine Model of Lipopolysaccharide-Induced Acute Kidney Injury

Sepsis is the major cause of acute kidney injury (AKI) in severely ill patients, but only limited therapeutic options are available. During sepsis, lipopolysaccharide (LPS), an endotoxin derived from bacteria, activates signaling cascades involved in inflammatory responses and tissue injury. Apamin is a component of bee venom and has been shown to exert antioxidative, antiapoptotic, and anti-inflammatory activities. However, the effect of apamin on LPS-induced AKI has not been elucidated. Here, we show that apamin treatment significantly ameliorated renal dysfunction and histological injury, especially tubular injury, in LPS-injected mice. Apamin also suppressed LPS-induced oxidative stress through modulating the expression of nicotinamide adenine dinucleotide phosphate oxidase 4 and heme oxygenase-1. Moreover, tubular cell apoptosis with caspase-3 activation in LPS-injected mice was significantly attenuated by apamin. Apamin also inhibited cytokine production and immune cell accumulation, suppressed toll-like receptor 4 pathway, and downregulated vascular adhesion molecules. Taken together, these results suggest that apamin ameliorates LPS-induced renal injury through inhibiting oxidative stress, apoptosis of tubular epithelial cells, and inflammation. Apamin might be a potential therapeutic option for septic AKI.

6-Shogaol protects against ischemic acute kidney injury by modulating NF-κB and heme oxygenase-1 pathways

Acute kidney injury (AKI) due to renal ischemia-reperfusion (I/R) is a major clinical problem without effective therapy. Ginger is one of the most widely consumed spices in the world, and 6-shogaol, a major ginger metabolite, has anti-inflammatory effects in neuronal and epithelial cells. Here, we demonstrate our novel findings that 6-shogaol treatment protected against renal I/R injury with decreased plasma creatinine, blood urea nitrogen, and kidney neutrophil gelatinase-associated lipocalin mRNA synthesis compared with vehicle-treated mice subjected to renal I/R. Additionally, 6-shogaol treatment reduced kidney inflammation (decreased proinflammatory cytokine and chemokine synthesis as well as neutrophil infiltration) and apoptosis (decreased TUNEL-positive renal tubular cells) compared with vehicle-treated mice subjected to renal I/R. In cultured human and mouse kidney proximal tubule cells, 6-shogaol significantly attenuated TNF-α-induced inflammatory cytokine and chemokine mRNA synthesis. Mechanistically, 6-shogaol significantly attenuated TNF-α-induced NF-κB activation in human renal proximal tubule cells by reducing IKKαβ/IκBα phosphorylation. Furthermore, 6-shogaol induced a cytoprotective chaperone heme oxygenase (HO)-1 via p38 MAPK activation in vitro and in vivo. Consistent with these findings, pretreatment with the HO-1 inhibitor zinc protoporphyrin IX completely prevented 6-shogaol-mediated protection against ischemic AKI in mice. Taken together, our study showed that 6-shogaol protects against ischemic AKI by attenuating NF-κB activation and inducing HO-1 expression. 6-Shogaol may provide a potential therapy for ischemic AKI during the perioperative period.

Role of TLR4 signaling in the nephrotoxicity of heme and heme proteins

Destabilized heme proteins release heme, and free heme is toxic. Heme is now recognized as an agonist for the Toll-like receptor-4 (TLR4) receptor. This study examined whether the TLR4 receptor mediates the nephrotoxicity of heme, specifically, the effects of heme on renal blood flow and inflammatory responses. We blocked TLR4 signaling by the specific antagonist TAK-242. Intravenous administration of heme to mice promptly reduced renal blood flow, an effect attenuated by TAK-242. In vitro, TAK-242 reduced heme-elicited activation of NF-κB and its downstream gene monocyte chemoattractant protein-1(MCP-1); in contrast, TAK-242 failed to reduce heme-induced activation of the anti-inflammatory transcription factor Nrf2 and its downstream gene heme oxygenase-1 (HO-1). TAK-242 did not reduce heme-induced renal MCP-1 upregulation in vivo. TAK-242 did not reduce dysfunction and histological injury in the glycerol model of heme protein-induced acute kidney injury (AKI), findings corroborated by studies in TLR4+/+ and TLR4-/- mice. We conclude that 1) acute heme-mediated renal vasoconstriction occurs through TLR4 signaling; 2) proinflammatory effects of heme in renal epithelial cells involve TLR4 signaling, whereas the anti-inflammatory effects of heme do not; 3) TLR4 signaling does not mediate the proinflammatory effects of heme in the kidney; and 4) major mechanisms underlying glycerol-induced, heme protein-mediated AKI do not involve TLR4 signaling. These findings in the glycerol model are in stark contrast with findings in virtually all other AKI models studied to date and emphasize the importance of TLR4-independent pathways of heme protein-mediated injury in this model. Finally, these studies urge caution when using observations derived in vitro to predict what occurs in vivo.

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.

Length Polymorphisms in Heme Oxygenase-1 and AKI after Cardiac Surgery

Heme oxygenase-1 (HO-1) catalyzes the degradation of heme, which may be involved in the pathogenesis of AKI. Length polymorphisms in the number of GT dinucleotide repeats in the HO-1 gene (HMOX1) promoter inversely associate with HMOX1 mRNA expression. We analyzed the association between allelic frequencies of GT repeats in the HMOX1 gene promoter and postoperative AKI in 2377 white patients who underwent cardiac surgery with cardiopulmonary bypass. We categorized patients as having the short allele (S; <27 GT repeats) or long allele (L; ≥27 GT repeats), and defined AKI as an increase in serum creatinine ≥0.3 mg/dl within 48 hours or ≥50% within 5 days, or the need for RRT. Compared with patients with the SS genotype, patients with the LL genotype had 1.58-fold (95% confidence interval, 1.06 to 2.34; P=0.02) higher odds of AKI. After adjusting for baseline and operative characteristics, the odds ratio for AKI per L allele was 1.26 (95% confidence interval, 1.05 to 1.50; P=0.01). In conclusion, longer GT repeats in the HMOX1 gene promoter associate with increased risk of AKI after cardiac surgery, consistent with heme toxicity as a pathogenic feature of cardiac surgery-associated AKI, and with HO-1 as a potential therapeutic target.

Nitric oxide is an important regulator of heme oxygenase-1 expression in the lipopolysaccharide and interferon-γ-treated murine macrophage-like cell line J774.1/JA-4

Heme oxygenase-1 (HO-1) catabolizes the degradation of heme into bilirubin, carbon monoxide, and iron ions. The HO-1 products provide antioxidant cytoprotection in addition to having potent antiinflammatory and immunomodulatory functions. HO-1 is induced by its substrate heme and environmental factors including oxidative and heat stresses. Although previous studies reported that lipopolysaccharide (LPS) induced the expression of both the HO-1 gene and its protein in macrophages, the major regulators of HO-1 expression remain unknown. To identify these regulators, we used two types of cell, the murine macrophage-like cell line J774.1/JA-4 and its LPS-resistant mutant, LPS1916. Based on a comparison of the results obtained with these cells, we found that nitric oxide (NO) was closely linked to the induction of HO-1. Real-time polymerase chain reaction (PCR) showed that the time course for inducible HO-1 mRNA by LPS or LPS+interferon (IFN)-γ was similar to that for inducible NO synthase (iNOS) mRNA. Furthermore, the expression of iNOS mRNA and protein increased earlier than that of HO-1 mRNA and protein. N-Nitro-L-arginine methyl ester, an NO synthase inhibitor, reduced both HO-1 expression and NO production in LPS+IFN-γ-treated JA-4 cells. Furthermore, NOC-12, an NO donor, significantly induced HO-1 expression not only in JA-4 but also in LPS1916 cells. Reactive oxygen species (ROS) scavengers, such as superoxide dismutase and catalase, did not affect HO-1 protein expression in LPS+IFN-γ-treated JA-4 cells. These results suggest that, among ROS, NO plays an important role in HO-1 induction in activated macrophages treated with LPS+IFN-γ.

Spiranthes sinensis Suppresses Production of Pro-Inflammatory Mediators by Down-Regulating the NF-κB Signaling Pathway and Up-Regulating HO-1/Nrf2 Anti-Oxidant Protein

Spiranthes sinensis is an east Asian wild orchid used in Chinese folk medicine. In this study, an ethyl acetate fraction from S. sinensis(SSE) was found to suppress the production of LPS-stimulated inflammatory mediators in RAW264.7 cells and BALB/c mice. SSE inhibited the production of pro-inflammatory mediators such as nitric oxide (NO), prostaglandin E2 (PGE2), tumo necrosis factor-α (TNF-α), IL-1β, and IL-6 in LPS-stimulated RAW264.7 cells. SSE also significantly suppressed LPS-stimulated protein levels of iNOS and mPGES-1 by blocking IκB phosphorylation, NF-κB nuclear translocation, and MAPKs phosphorylation. In addition, SSE treatment also enhanced protein levels of HO-1 and anti-oxidant enzymes (SOD-1, CAT, and GPx-1) through the nuclear translocation of Nrf2 in LPS-stimulated RAW264.7 cells. In vivo, we demonstrated that SSE attenuated the levels of pro-inflammatory mediators (NO, TNF-α, IL-1β, and IL-6), ALT, and AST in the serum of LPS-stimulated BALB/c mice. Western blotting revealed that SSE enhanced HO-1 expression in lung and liver tissue after LPS injection in mice. These results suggest that the anti-inflammatory properties of SSE involve the suppression of iNOS, mPGES-1, and inflammatory mediators by inducing the HO-1 pathway in LPS-stimulated RAW264.7 cells and BALB/c mice.

The macrophage mediates the renoprotective effects of endotoxin preconditioning

Preconditioning is a preventative approach, whereby minimized insults generate protection against subsequent larger exposures to the same or even different insults. In immune cells, endotoxin preconditioning downregulates the inflammatory response and yet, preserves the ability to contain infections. However, the protective mechanisms of preconditioning at the tissue level in organs such as the kidney remain poorly understood. Here, we show that endotoxin preconditioning confers renal epithelial protection in various models of sepsis in vivo. We also tested the hypothesis that this protection results from direct interactions between the preconditioning dose of endotoxin and the renal tubules. This hypothesis is on the basis of our previous findings that endotoxin toxicity to nonpreconditioned renal tubules was direct and independent of immune cells. Notably, we found that tubular protection after preconditioning has an absolute requirement for CD14-expressing myeloid cells and particularly, macrophages. Additionally, an intact macrophage CD14-TRIF signaling pathway was essential for tubular protection. The preconditioned state was characterized by increased macrophage number and trafficking within the kidney as well as clustering of macrophages around S1 proximal tubules. These macrophages exhibited increased M2 polarization and upregulation of redox and iron-handling molecules. In renal tubules, preconditioning prevented peroxisomal damage and abolished oxidative stress and injury to S2 and S3 tubules. In summary, these data suggest that macrophages are essential mediators of endotoxin preconditioning and required for renal tissue protection. Preconditioning is, therefore, an attractive model to investigate novel protective pathways for the prevention and treatment of sepsis.

Epigallocatechin-3-Gallate Attenuates Oxidative Stress and Inflammation in Obstructive Nephropathy via NF-κB and Nrf2/HO-1 Signalling Pathway Regulation

Oxidative stress and inflammation contribute importantly to the pathogenesis of chronic kidney disease (CKD). Epigallocatechin-3-gallate (EGCG), which is the most abundant and most active catechin polyphenol extracted from green tea, has been proved to have many bioactivities. In this study, the renoprotective effect of EGCG was evaluated in a widely used kidney disease model, the unilateral ureteral obstruction (UUO) mice model. After 14 days of EGCG administration, mean arterial blood pressure, body-weight and obstructed kidney weight were measured. Levels of blood urea nitrogen (BUN) and creatinine (CR) and activities of glutamic-pyruvic transaminase (GPT) and lactate dehydrogenase (LDH) in serum were estimated as indicators of renal function. Periodic acid-Schiff (PAS) staining was performed to observe the pathological changes of the obstructed kidney. Antioxidant enzymes and pro-inflammatory cytokine production were estimated to reflect the oxidative stress and inflammatory state in the obstructed kidney. Finally, the main proteins in the NF-κB and Nrf2 signalling pathway and DNA binding activity of NF-κB and Nrf2 were measured to investigate the effect of EGCG on these two pathways. The results demonstrated that EGCG could restore UUO-induced kidney weight loss and renal dysfunction. In addition, UUO-induced oxidative stress and inflammatory responses in the obstructed kidney were also prevented by EGCG. Furthermore, EGCG could induce both NF-κB and Nrf2 nuclear translocation in the UUO kidney and promote heme oxygenase-1 (HO-1) production. These results indicated that the renoprotective effect of EGCG might be through its NF-κB and Nrf2 signalling pathway regulations.

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.

Synchronous recruitment of epigenetic modifiers to endotoxin synergistically activated Tnf-α gene in acute kidney injury

BACKGROUND

As a consequence of acute kidney injury (AKI), proximal tubular cells hyperrespond to endotoxin (lipopolysaccharide, LPS) by exaggerated renal Tnf-α Production. This LPS hyperresponsiveness is transcriptionally mediated. The epigenetic pathways that control these responses are unknown.

METHODS/FINDINGS

We applied multiplex chromatin immunoprecipitation platform (Matrix ChIP) to explore epigenetic pathways that underlie endotoxin hyperresponsiveness in the setting of preceding unilateral renal ischemia/reperfusion (I/R) in mouse AKI model. Endotoxin exposure after I/R resulted in enhanced transcription, manifested by hyperresponsive recruitment of RNA polymerase II (Pol II) at the Tnf-α gene. At this locus, LPS but not I/R increased levels of Pol II C-terminal domain (CTD) phosho-serine2 &5 and induced dephosphorylation of the transcription-repressive histone H4 phospho-serine-1. In contrast, I/R but not LPS increased the transcription-permissive histone phosphorylation (H3 phospho-serine-10, H3.3 phospho-serine-31) at the Tnf-α gene. In agreement with these observations, I/R but not LPS increased activity of cognate kinases (Erk1/2, Msk1/2 and Aurora A) at the Tnf-α locus. Cross-talk of histone phosphorylation and acetylation synergize to active gene expression. I/R and LPS increased histone acetylation. (H3K9/14Ac, H4K5/8/12/16Ac, H2KA5Ac, H2BK4/7Ac). Levels of some histone acetyltransferases at this gene (PCAF and MOF) were increased by I/R but not by LPS, while others were induced by either I/R or LPS and exhibited endotoxin hyperresponsive patterns (GCN5, CBP and p300). The adaptor protein 14-3-3 couples histone phosphorylation with acetylation, and tethers chromatin modifiers/transcription elongation factors to target genes. Both I/R and LPS increased levels of 14-3-3 and several chromatin/transcription modifiers (BRD4, BRG1, HP-1γ and IKKα) at the Tnf-α gene, all exhibiting endotoxin hyperresponsive recruitment patterns similar to Pol II.

CONCLUSIONS

Our results suggest that I/R and LPS differentially trigger phosphorylation (Pol II and histone) and acetylation (histone) epigenetic pathways that interact at the Tnf-α gene to generate endotoxin hyperresponse in AKI.

Age sensitizes the kidney to heme protein-induced acute kidney injury

Age increases the risk for ischemic acute kidney injury (AKI). We questioned whether a similar age-dependent injury occurs following exposure to hemoglobin, a known nephrotoxin. Old mice (~16 mo old), but not young mice (~6 mo old), when administered hemoglobin, exhibited marked elevation in blood urea nitrogen (BUN) and serum creatinine, and acute tubular necrosis with prominent tubular cast formation. The aged kidney exhibited induction of heme oxygenase-1 (HO-1) and other genes/proteins that may protect against heme-mediated renal injury, including ferritin, ferroportin, haptoglobin, and hemopexin. Old mice did not evince induction of HO-2 mRNA by hemoglobin, whereas a modest induction of HO-2 mRNA was observed in young mice. To determine the functional significance of HO-2 in heme protein-induced AKI, we administered hemoglobin to relatively young HO-2(+/+) and HO-2(-/-) mice: HO-2(-/-) mice, compared with HO-2(+/+) mice, exhibited greater renal dysfunction and histologic injury when administered hemoglobin. In addition to failing to elicit a protective system such as HO-2 in response to hemoglobin, old mice exhibited an exaggerated maladaptive response typified by markedly greater induction of the nephrotoxic cytokine IL-6 (130-fold increase vs. 10-fold increase in mRNA in young mice). We conclude that aged mice, unlike relatively younger mice, are exquisitely sensitive to the nephrotoxicity of hemoglobin, an effect attended by a failure to induce HO-2 mRNA and a fulminant upregulation of IL-6. Age thus markedly augments the sensitivity of the kidney to heme proteins, and HO-2 confers resistance to such insults.

Heme oxygenase-1 regulates the immune response to influenza virus infection and vaccination in aged mice

Underlying mechanisms of individual variation in severity of influenza infection and response to vaccination are poorly understood. We investigated the effect of reduced heme oxygenase-1 (HO-1) expression on vaccine response and outcome of influenza infection. HO-1-deficient and wild-type (WT) mice (kingdom, Animalia; phylum, Chordata; genus/species, Mus musculus) were infected with influenza virus A/PR/8/34 with or without prior vaccination with an adenoviral-based influenza vaccine. A genome-wide association study evaluated the expression of single-nucleotide polymorphisms (SNPs) in the HO-1 gene and the response to influenza vaccination in healthy humans. HO-1-deficient mice had decreased survival after influenza infection compared to WT mice (median survival 5.5 vs. 6.5 d, P=0.016). HO-1-deficient mice had impaired production of antibody following influenza vaccination compared to WT mice (mean antibody titer 869 vs. 1698, P=0.02). One SNP in HO-1 and one SNP in the constitutively expressed isoform HO-2 were independently associated with decreased antibody production after influenza vaccination in healthy human volunteers (P=0.017 and 0.014, respectively). HO-1 deficient mice were paired with sex- and age-matched WT controls. HO-1 affects the immune response to both influenza infection and vaccination, suggesting that therapeutic induction of HO-1 expression may represent a novel adjuvant to enhance influenza vaccine effectiveness.

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.

Plasma and urinary heme oxygenase-1 in AKI

AKI induces upregulation of heme oxygenase 1 (HO-1), which exerts cytoprotective effects and modulates the renal response to injury, suggesting that a biomarker of intrarenal HO-1 activity may be useful. Because HO-1 largely localizes to the endoplasmic reticulum and has no known secretory pathway, it is unclear whether plasma or urinary levels of HO-1 reflect intrarenal HO-1 expression. We measured plasma and urinary levels of HO-1 by ELISA during the induction and/or maintenance phases of four mouse models of AKI: ischemia/reperfusion, glycerol-induced rhabdomyolysis, cisplatin nephrotoxicity, and bilateral ureteral obstruction. In addition, we measured levels of HO-1 mRNA and protein in the renal cortex. Each AKI model increased renal HO-1 gene expression, which corresponded with release of HO-1 into plasma and urine by 4 hours. Over time, the magnitudes of plasma and urinary HO-1 paralleled renal cortical gene expression. AKI and the associated uremia did not seem to affect extrarenal HO-1 gene activity assessed in the liver, lung, and spleen. In iron-challenged, cultured proximal tubule cells, we observed a positive correlation between HO-1 mRNA level and HO-1 release. In humans, 10 patients with AKI demonstrated markedly higher levels of plasma and urine HO-1 levels than 10 critically ill patients without AKI or 20 patients with CKD or ESRD. In summary, these data suggest that plasma and urinary HO-1 levels may serve as biomarkers of AKI and intrarenal HO-1 gene activity.

Acute unilateral ischemic renal injury induces progressive renal inflammation, lipid accumulation, histone modification, and "end-stage" kidney disease

There is an emerging concept in clinical nephrology that acute kidney injury (AKI) can initiate chronic kidney disease (CKD). However, potential mechanisms by which this may occur remain elusive. Hence, this study tested the hypotheses that 1) AKI triggers progressive activation of selected proinflammatory genes, 2) there is a relative failure of compensatory anti-inflammatory gene expression, 3) proinflammatory lipid accumulation occurs, 4) these changes correspond with "gene-activating" histone acetylation, and 5) in concert, progressive renal disease results. CD-1 mice were subjected to 30 min of unilateral renal ischemia. Assessments were made 1 day, 1 wk, or 3 wk later. Results were contrasted to those observed in uninjured contralateral kidneys or in kidneys from normal mice. Progressive renal injury occurred throughout the 3-wk postischemic period, as denoted by stepwise increases in neutrophil gelatinase-associated lipocalin gene induction and ongoing histologic damage. By 3 wk postischemia, progressive renal disease was observed (massive tubular dropout; 2/3rds reduction in renal weight). These changes corresponded with progressive increases in proinflammatory cytokine/chemokine gene expression (MCP-1, TNF-α, TGF-β1), a relative failure of anti-inflammatory enzyme/cytokine (heme oxygenase-1; IL-10) upregulation, and progressive renal lipid (cholesterol/triglyceride) loading. Stepwise increases in collagen III mRNA and collagen deposition (Sirius red staining) indicated a progressive profibrotic response. Postischemic dexamethasone treatment significantly preserved renal mass, indicating functional significance of the observed proinflammatory state. Progressive gene-activating H3 acetylation was observed by ELISA, rising from 5% at baseline to 75% at 3 wk. This was confirmed by chromatin immunoprecipitation assay of target genes. In sum, these results provide experimental support for the clinical concept that AKI can trigger CKD, this is partially mediated by progressive postischemic inflammation, ongoing lipid accumulation results (potentially evoking "lipotoxicity"), and increasing histone acetylation at proinflammatory/profibrotic genes may contribute to this self-sustaining injury-promoting state.

The circadian deadenylase Nocturnin is necessary for stabilization of the iNOS mRNA in mice

Nocturnin is a member of the CCR4 deadenylase family, and its expression is under circadian control with peak levels at night. Because it can remove poly(A) tails from mRNAs, it is presumed to play a role in post-transcriptional control of circadian gene expression, but its target mRNAs are not known. Here we demonstrate that Nocturnin expression is acutely induced by the endotoxin lipopolysaccharide (LPS). Mouse embryo fibroblasts (MEFs) lacking Nocturnin exhibit normal patterns of acute induction of TNFα and iNOS mRNAs during the first three hours following LPS treatment, but by 24 hours, while TNFα mRNA levels are indistinguishable from WT cells, iNOS message is significantly reduced 20-fold. Accordingly, analysis of the stability of the mRNAs showed that loss of Nocturnin causes a significant decrease in the half-life of the iNOS mRNA (t(1/2) = 3.3 hours in Nocturnin knockout MEFs vs. 12.4 hours in wild type MEFs), while having no effect on the TNFα message. Furthermore, mice lacking Nocturnin lose the normal nighttime peak of hepatic iNOS mRNA, and have improved survival following LPS injection. These data suggest that Nocturnin has a novel stabilizing activity that plays an important role in the circadian response to inflammatory signals.

Haem oxygenase-1: non-canonical roles in physiology and pathology

HO-1 (haem oxygenase-1) is a ubiquitously expressed inducible enzyme degrading haem to CO, biliverdin and Fe2+. Its activation reduces oxidative stress in cells and inhibits inflammation, both due to removal of haem and because of the biological activity of HO-1 products. CO may act similarly to NO, activating soluble guanylate cyclase and elevating cGMP production. It inhibits platelet aggregation, reduces leucocyte adhesion, decreases apoptosis and lowers the production of some pro-inflammatory cytokines. Biliverdin is converted into bilirubin by biliverdin reductase, and both compounds are potent antioxidants, free radical scavengers and inhibitors of the complement cascade. Iron ions can be potentially toxic, increasing the generation of hydroxyl radicals, but simultaneous induction of ferritin and activation of the Fe-ATPase iron transporter protects cells from oxidative stress. Importantly, basal and induced expression of HO-1 is very variable in the human population because of the highly polymorphic (GT)n fragment in the promoter, which may have clinical relevance. The recognized roles of HO-1 are far beyond cytoprotection. The enzyme is important in the regulation of cell proliferation, differentiation and apoptosis. Its activity improves neovascularization, attenuates inflammation and modulates the immune response, thereby influencing carcinogenesis, wound healing, transplant survival and the progression of cardiovascular diseases. Recent results indicate that HO-1 may also act through the regulation of microRNAs, which suggests a much broader involvement of HO-1 in the modulation of cell functions and offers a potential explanation for some well-known activities whose mechanism has hitherto been unclear.

Genetic deficiency of Smad3 protects against murine ischemic acute kidney injury

TGF-β1 contributes to chronic kidney disease, at least in part, via Smad3. TGF-β1 is induced in the kidney following acute ischemia, and there is increasing evidence that TGF-β1 may protect against acute kidney injury. As there is a paucity of information regarding the functional significance of Smad3 in acute kidney injury, the present study explored this issue in a murine model of ischemic acute kidney injury in Smad3(+/+) and Smad3(-/-) mice. We demonstrate that, at 24 h after ischemia, Smad3 is significantly induced in Smad3(+/+) mice, whereas Smad3(-/-) mice fail to express this protein in the kidney in either the sham or postischemic groups. Compared with Smad3(+/+) mice, and 24 h following ischemia, Smad3(-/-) mice exhibited greater preservation of renal function as measured by blood urea nitrogen (BUN) and serum creatinine; less histological injury assessed by both semiquantitative and qualitative analyses; markedly suppressed renal expression of IL-6 and endothelin-1 mRNA (but comparable expression of MCP-1, TNF-α, and heme oxygenase-1 mRNA); and no increase in plasma IL-6 levels, the latter increasing approximately sixfold in postischemic Smad3(+/+) mice. We conclude that genetic deficiency of Smad3 confers structural and functional protection against acute ischemic injury to the kidney. We speculate that these effects may be mediated through suppression of IL-6 production. Finally, we suggest that upregulation of Smad3 after an ischemic insult may contribute to the increased risk for chronic kidney disease that occurs after acute renal ischemia.

Regional and systemic hemodynamic responses following the creation of a murine arteriovenous fistula

The study of hemodynamic alterations following the creation of an arteriovenous fistula (AVF) is relevant to vascular adaptive responses and hemodialysis access dysfunction. This study examined such alterations in a murine AVF created by anastomosing the carotid artery to the jugular vein. AVF blood flow was markedly increased due to reduced AVF vascular resistance. Despite such markedly increased basal blood flow, AVF blood flow further increased in response to acetylcholine. This AVF model exhibited increased cardiac output and decreased systemic vascular resistance; the kidney, in contrast, exhibited decreased blood flow and increased vascular resistance. Augmentation in AVF blood flow was attended by increased arterial heme oxygenase-1 (HO-1) mRNA and protein expression, the latter localized to smooth muscle cells of the AVF artery; AVF blood flow was substantially reduced in HO-1(-/-) mice compared with HO-1(+/+) mice. Finally, in a murine model of a representative disease known to exhibit impaired hemodynamic responses (sickle cell disease), the creation of an AVF was attended by decreased AVF flow and impaired AVF function. We conclude that this AVF model exhibits markedly increased AVF blood flow, a vasodilatory reserve capacity, increased cardiac output, decreased renal blood flow, and a dependency on intact hemodynamic responses, in general, and HO-1 expression, in particular, in achieving and maintaining AVF blood flow. We suggest that these findings support the utility of this model in investigating the basis for and the consequences of hemodynamic stress, including shear stress, and the pathobiology of hemodialysis AVF dysfunction.

Genipin up-regulates heme oxygenase-1 via PI3-kinase-JNK1/2-Nrf2 signaling pathway to enhance the anti-inflammatory capacity in RAW264.7 macrophages

Genipin, an aglycon of geniposide, has been reported to exhibit diverse pharmacological functions such as antitumor and anti-inflammatory effects. This study aimed to elucidate the anti-inflammatory mechanism of genipin, focusing particularly on the role of heme oxygenase-1 (HO-1), a potent anti-inflammatory enzyme. In RAW264.7 cells, genipin increased HO-1 expression and its enzyme activity via a NF-E2-related factor 2 (Nrf2)-antioxidant response element (ARE) pathway. These effects were significantly inhibited by exposure to the phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor, LY294002, or by expression of a dominant negative mutant of PI 3-kinase. Additional experiments showed that the activation of c-Jun NH(2)-terminal kinase 1/2 (JNK1/2) is required for genipin-induced phosphorylation and nuclear translocation of Nrf2 and antioxidant response element (ARE)-driven induction of HO-1, and acts as a downstream effector of PI 3-kinase. Furthermore, functional significance of HO-1 induction was revealed by genipin-mediated inhibition of lipopolysaccharide-stimulated inducible nitric oxide synthase expression or cyclooxygenase-2 promoter activity, the response was reversed by the blocking of HO-1 protein synthesis or HO-1 enzyme activity. Therefore, identification of PI 3-kinase-JNK1/2-Nrf2-linked signaling cascade in genipin-mediated HO-1 expression defines the signaling event that could participate in genipin-mediated anti-inflammatory response.

Characterization of a model of an arteriovenous fistula in the rat: the effect of L-NAME

Vascular access dysfunction contributes to the mortality of patients undergoing chronic hemodialysis. The present study analyzed the changes that evolve in a femoral arteriovenous fistula in the rat. The venous segment of this model exhibited, at 1 week, activation of pro-inflammatory transcription factors and up-regulation of pro-inflammatory, proliferative, procoagulant, and profibrotic genes; and at 4 weeks, the venous segment displayed neointimal hyperplasia, smooth muscle proliferation, and thrombus formation. These changes were accompanied by endothelial (e) nitric oxide synthase (NOS) and inducible (i) NOS up-regulation. The administration of NG-nitro-L-arginine methyl ester, an inhibitor of NOS activity, increased venous neointimal hyperplasia and pro-inflammatory gene expression (monocyte chemoattractant protein-1 and cytokine-induced neutrophil chemoattractant-1), increased systolic blood pressure, and decreased blood flow through the fistula. In another hypertensive model, the rat subtotal nephrectomy model, venous neointimal hyperplasia in the arteriovenous fistula was also exacerbated. We conclude that this arteriovenous fistula model recapitulates the salient features observed in dysfunctional, hemodialysis arteriovenous fistulas, and that venous neointimal hyperplasia is exacerbated when this model is superimposed in two different models of systemic hypertension. Since the uremic milieu contains increased amounts of asymmetric dimethylarginine, we speculate that such accumulation of this endogenous inhibitor of NOS, by virtue of its pressor or nitric oxide-depleting effects, or a combination thereof, may contribute to the limited longevity of arteriovenous fistulas used for hemodialysis.

Early and prominent alterations in hemodynamics, signaling, and gene expression following renal ischemia in sickle cell disease

Acute ischemic insults to the kidney are recognized complications of human sickle cell disease (SCD). The present study analyzed in a transgenic SCD murine model the early renal response to acute ischemia. Renal hemodynamics were profoundly impaired following ischemia in sickle mice compared with wild-type mice: glomerular filtration rate, along with renal plasma flow and blood flow rates, were markedly reduced, while renal vascular resistances were increased more than threefold in sickle mice following ischemia. In addition to these changes in renal hemodynamics, there were profound disturbances in renal signaling processes: phosphorylation of members of the MAPK and Akt signaling proteins occurred in the kidney in wild-type mice after ischemia, whereas such phosphorylation did not occur in the kidney in sickle mice after ischemia. ATP content in the postischemic kidney in sickle mice was less than half that observed in wild-type mice. Examination of the expression of candidate genes uncovered changes that may predispose to increased sensitivity of the kidney in sickle mice to ischemia: increased expression of inducible nitric oxide synthase and decreased expression of endothelial nitric oxide synthase, and increased expression of TNF-alpha. Inducibility of anti-inflammatory, cytoprotective genes, such as heme oxygenase-1 and IL-10, was not impaired in sickle mice after ischemia. We conclude that the kidney in SCD is remarkably vulnerable to acute ischemic insults. We speculate that such sensitivity of the kidney to ischemia in SCD may underlie the occurrence of acute kidney injury in patients with SCD and may set the stage for the emergence of chronic kidney disease in SCD.

The hepatic microcirculation: mechanistic contributions and therapeutic targets in liver injury and repair

The complex functions of the liver in biosynthesis, metabolism, clearance, and host defense are tightly dependent on an adequate microcirculation. To guarantee hepatic homeostasis, this requires not only a sufficient nutritive perfusion and oxygen supply, but also a balanced vasomotor control and an appropriate cell-cell communication. Deteriorations of the hepatic homeostasis, as observed in ischemia/reperfusion, cold preservation and transplantation, septic organ failure, and hepatic resection-induced hyperperfusion, are associated with a high morbidity and mortality. During the last two decades, experimental studies have demonstrated that microcirculatory disorders are determinants for organ failure in these disease states. Disorders include 1) a dysregulation of the vasomotor control with a deterioration of the endothelin-nitric oxide balance, an arterial and sinusoidal constriction, and a shutdown of the microcirculation as well as 2) an overwhelming inflammatory response with microvascular leukocyte accumulation, platelet adherence, and Kupffer cell activation. Within the sequelae of events, proinflammatory mediators, such as reactive oxygen species and tumor necrosis factor-alpha, are the key players, causing the microvascular dysfunction and perfusion failure. This review covers the morphological and functional characterization of the hepatic microcirculation, the mechanistic contributions in surgical disease states, and the therapeutic targets to attenuate tissue injury and organ dysfunction. It also indicates future directions to translate the knowledge achieved from experimental studies into clinical practice. By this, the use of the recently introduced techniques to monitor the hepatic microcirculation in humans, such as near-infrared spectroscopy or orthogonal polarized spectral imaging, may allow an early initiation of treatment, which should benefit the final outcome of these critically ill patients.

Lipopolysaccharides enhance the action of bradykinin in enteric neurons via secretion of interleukin-1beta from enteric glial cells

Functional changes of the enteric nervous system have been observed under inflammatory states of inflammatory bowel disease increasing the endotoxin level. The aim of the present study was to determine the effect of lipopolysaccharides (LPS) on myenteric neuron-glia interaction in vitro. We examined the increase of the intracellular Ca(2+) concentration ([Ca(2+)](i)) and the release of interleukin-1beta (IL-1beta) or prostaglandin E(2) (PGE(2)) and COX-2 expression in myenteric plexus cells from the rat intestine induced by LPS. LPS potentiated BK-induced [Ca(2+)](i) increases in both myenteric neurons and enteric glial cells, which were suppressed by a B1R antagonist. Only in enteric glial cells, a B1R agonist increased [Ca(2+)](i). The effects of LPS were blocked by pretreatment with an interleukin-1 receptor antagonist or by reducing the density of enteric glial cells in culture. LPS prompted the release of IL-1beta from enteric glial cells. The augmenting effects of IL-1beta on the BK-induced neural [Ca(2+)](i) increase and PGE(2) release from enteric glial cells were abolished by a phospholipase A(2) (PLA(2)) inhibitor and a COX inhibitor, and partly suppressed by a COX-2 inhibitor. IL-1beta up-regulated the COX-2 expression in enteric glial cells. LPS promotes IL-1beta secretion from enteric glial cells, resulting in augmentation of the neural response to BK through PGE(2) release via glial PLA(2) and COX-2. The alteration of the regulatory effect of glial cells may be the cause of the changes in neural function in the enteric nervous system in inflammatory bowel disease.

Inhibition and genetic deficiency of p38 MAPK up-regulates heme oxygenase-1 gene expression via Nrf2

Heme oxygenase (HO)-1 is the inducible isoform of the first and rate-limiting enzyme of heme degradation. The HO products carbon monoxide and bilirubin not only provide antioxidant cytoprotection, but also have potent anti-inflammatory and immunomodulatory functions. Although HO-1 has previously been shown to be induced by various stimuli via activation of the p38 MAPK signaling pathway, the role of this protein kinase for HO-1 gene regulation is largely unknown. In the present study, it is demonstrated that pharmacological inhibitors of p38 induced HO-1 expression in monocytic cells. Moreover, basal HO-1 gene expression levels were markedly higher in untreated murine embryonic fibroblasts (MEF) from p38alpha(-/-) mice compared with those from wild-type mice. Transfection studies with luciferase reporter gene constructs indicate that increased HO-1 gene expression via inhibition of p38 was mediated by the transcription factor Nrf2, which is a central regulator of the cellular oxidative stress response. Accordingly, inhibitors of p38 induced binding of nuclear proteins to a Nrf2 target sequence of the HO-1 promoter, but did not affect HO-1 protein expression and promoter activity in Nrf2(-/-) MEF. Genetic deficiency of p38 led to enhanced phosphorylation of ERK and increased cellular accumulation of reactive oxygen species. In addition, pharmacological blockage of ERK and scavenging of reactive oxygen species with N-acetylcysteine reduced HO-1 gene expression in p38(-/-) MEF, respectively. Taken together, it is demonstrated that pharmacological inhibition and genetic deficiency of p38 induce HO-1 gene expression via a Nrf2-dependent mechanism in monocytic cells and MEF.

Effect of heme oxygenase-1 on the kidney during septic shock in rats

The aim of this study was to clarify the effect of heme oxygenase (HO)-1 on the kidney during septic shock in rats. Eighty healthy and clean Sprague-Dawley rats were randomly divided into 4 groups: control group (group C) , septic shock group (group SS) , lipopolysaccharide plus ZnPP-IX group (group LZ) , and ZnPP-IX (group Z) . The plasma levels of COHb, Cr, and BUN; the urine levels of gamma-GTP, alpha1-MG, RBP, and NAG; and MDA content, SOD activity; HO-1mRNA; HO-2mRNA; HO-1 protein; and HO-2 protein from kidney were measured. The plasma levels of Cr and BUN; the urine levels of gamma-GTP, alpha1-MG, RBP, and NAG; and MDA content from kidney in group SS were obviously higher than in group C and Z (both P < 0.05), respectively, but lower than in group LZ (both P < 0.05), respectively. In contrast, the plasma levels of COHb and SOD activity from kidney in group SS were obviously lower than those in group C and Z (both P < 0.05), respectively, but higher than in group LZ (both P < 0.05), respectively. The HO-1mRNA and HO-1 protein of nephridial tissue in group LZ were obviously higher than in group C and Z, respectively (both P < 0.05), but lower than in group SS, respectively (both P < 0.05). There were no significant differences of HO-2mRNA and HO-2 protein among these 4 groups (both P > 0.05). It is concluded that upregulation of the HO-1 protein might contribute to the protection of kidney during septic shock in rats.

Heme oxygenase-1: its therapeutic roles in inflammatory diseases

Heme oxygenase (HO)-1 is an inducible enzyme that catalyzes the first and rate-limiting step in the oxidative degradation of free heme into ferrous iron, carbon monoxide (CO), and biliverdin (BV), the latter being subsequently converted into bilirubin (BR). HO-1, once expressed during inflammation, forms high concentrations of its enzymatic by-products that can influence various biological events, and this expression is proven to be associated with the resolution of inflammation. The degradation of heme by HO-1 itself, the signaling actions of CO, the antioxidant properties of BV/BR, and the sequestration of ferrous iron by ferritin all concertedly contribute to the anti-inflammatory effects of HO-1. This review focuses on the anti-inflammatory mechanisms of HO-1 actions and its roles in inflammatory diseases.