Role of HO-1 in renoprotection: Location, location, location

The impact of heme oxygenase-2 on pharmacological research: A bibliometric analysis and beyond

Heme oxygenase (HO-2) is an enzyme mainly involved in the physiologic turnover of heme and intracellular gas sensing, and it is very abundant in the brain, testes, kidneys and vessels. Since 1990, when HO-2 was discovered, the scientific community has underestimated the role of this protein in health and disease, as attested by the small amount of articles published and citations received. One of the reason that have contributed to the lack of interest in HO-2 was the difficulty in upregulating or inhibiting this enzyme. However, over the last 10 years, novel HO-2 agonists and antagonists have been synthesized, and the availability of these pharmacological tools should increase the appeal of HO-2 as drug target. In particular, these agonists and antagonists could help explain some controversial aspects, such as the neuroprotective versus neurotoxic roles of HO-2 in cerebrovascular diseases. Furthermore, the discovery of HO-2 genetic variants and their involvement in Parkinson's disease, in particular in males, opens new avenues for pharmacogenetic studies in gender medicine.

Ethyl Pyruvate Directly Attenuates Active Secretion of HMGB1 in Proximal Tubular Cells via Induction of Heme Oxygenase-1

Renal ischemia reperfusion (IR) is a main cause of acute kidney injury leading to high morbidity and mortality during postoperative periods. This study investigated whether ethyl pyruvate (EP) protects the kidney against renal IR injury. Male C57BL/6 mice were treated with vehicle or EP (40 mg/kg) 1 h before ischemia and the plasma creatinine (Cr) levels and tubular damage were evaluated after reperfusion. EP attenuated the IR-induced plasma Cr levels, renal inflammation and apoptotic cell death, but the effect of EP was abolished by pretreating Zinc protoporphyrin (ZnPP), a heme oxygenase (HO)-1 inhibitor. HO-1 is a stress-induced protein and protects the kidney against IR injury. EP increased significantly HO-1 expression in the proximal tubular cells in vivo and HK-2 cells in vitro. Inhibition of PI3K/Akt pathway and knockdown of Nrf2 blocked HO-1 induction by EP. High mobility group box 1 (HMGB1) secretion was assessed as an early mediator of IR injury; plasma HMGB1 were significantly elevated as early as 2 h to 24 h after reperfusion and these were attenuated by EP, but the effect of EP was abolished by ZnPP. EP also reduced HMGB1 secretion stimulated by TNF-α in HK-2 cells, and the inhibition of PI3K/Akt and knockdown of HO-1 blocked the effect of EP. Conclusively, EP inhibits the active secretion of HMGB1 from proximal tubular cells during IR injury by inducing HO-1 via activation of PI3K/Akt and Nrf2 pathway.

High weight differences between donor and recipient affect early kidney graft function--a role for enhanced IL-6 signaling

The frequency of delayed function of kidney transplants varies greatly and is associated with quality of graft, donor age and the duration of cold ischemia time. Furthermore, body weight differences between donor and recipient can affect primary graft function, but the underlying mechanism is poorly understood. We transplanted kidney grafts from commensurate body weight (L-WD) or reduced body weight (H-WD) donor rats into syngeneic or allogeneic recipients. Twenty-four hours posttransplantation, serum creatinine levels in H-WD recipients were significantly higher compared to L-WD recipients indicating impaired primary graft function. This was accompanied by upregulation of IL-6 transcription and increased tubular destruction in grafts from H-WD recipients. Using DNA microarray analysis, we detected decreased expression of genes associated with kidney function and an upregulation of other genes such as Cyp3a13, FosL and Trib3. A single application of IL-6 into L-WD recipients is sufficient to impair primary graft function and cause tubular damage, whereas immediate neutralization of IL-6 receptor signaling in H-WD recipients rescued primary graft function with well-preserved kidney graft architecture and a normalized gene expression profile. These findings have strong clinical implication as anti-IL6R treatment of patients receiving grafts from lower-weight donors could be used to improve primary graft function.

Haem oxygenase-1 gene transfer protects retinal ganglion cells from ischaemia/reperfusion injury

RGC (retinal ganglion cell) death following ischaemic insult is the major cause of a number of vision-threatening diseases, including glaucoma. The aim of the present study was to evaluate the role of HO-1 (haem oxygenase-1) in the retina against IR (ischaemia/reperfusion) injury. Adenovirus-mediated HO-1 gene transfer (Adv-HO-1) was carried out by injection into the vitreous body to induce HO-1 overexpression. At 3 weeks after transfection, levels of HO-1 expression, as measured by Western blot analysis, immunohistochemical staining and activity assay, were drastically up-regulated. Transient retinal ischaemia was induced by raising the intraocular pressure to 150 mmHg for 60 min. Untreated IR caused a significant decrease in RGC numbers at 3 and 7 days after reperfusion (76.1 and 67.2% of control eyes with sham IR respectively; P<0.001). Eyes pretreated with Adv-HO-1 had less RGC loss on day 3 and 7 following reperfusion compared with control eyes injected with Adv-GFP (adenovirus containing a gene for green fluorescent protein; 94.3 and 88.2% respectively; P=0.007 and 0.001). SnP (tin protoporphyrin), an HO-1 inhibitor, counteracted the effects of Adv-HO-1. In conclusion, these findings provide evidence that augmentation of HO-1 enzyme overexpression by intravitreal injection is able to protect RGCs against IR-induced damage.

Heme oxygenase-1 protects against radiocontrast-induced acute kidney injury by regulating anti-apoptotic proteins

Radiocontrast agents are thought to induce acute kidney injury in part through increased production of reactive oxygen species and increased cellular apoptosis. In this study we determined whether heme oxygenase-1 could prevent or reduce radiocontrast-induced acute kidney injury and, if so, what were the mechanisms by which this can occur. Sodium iothalamate was administered to uninephrectomized, salt-depleted male Sabra rats to initiate acute kidney injury. Heme oxygenase-1 was induced with cobalt protoporphyrin or inhibited with stannous mesoporphyrin. Inhibition of heme oxygenase exacerbated kidney injury as measured by an increase in plasma creatinine and in superoxide production. Heme oxygenase-1 induction prevented the increase in plasma creatinine and in superoxide in both the cortex and medulla compared to untreated rats with acute kidney injury. This protective effect of heme oxygenase-1 was associated with increased anti-apoptotic proteins Bcl-2 and Bcl-xl and a decrease of pro-apoptotic caspase-3 and caspase-9 along with increased expression of inactive BAX. Our study suggests that increased levels of heme oxygenase-1 are protective against acute kidney injury due to radiocontrast exposure.

Effects of resveratrol on glycerol-induced renal injury

Glycerol-induced renal lesions can have many causes, including increased oxidative stress and inflammation. Resveratrol, a polyphenolic phytoalexin found in grapes and red wine, is an antioxidant agent with anti-inflammatory effects. In the present study, we investigated the possible protective effect of resveratrol on glycerol-induced nephrotoxicity. Male Wistar rats were injected intramuscularly with 8 ml/kg of either 50% glycerol (n=18), glycerol+resveratrol (n=22), 0.15 M saline (n=14), saline+carboxymethylcellulose (n=10) or saline+resveratrol (n=8). The rats were killed 3 days after the injections, at which time the kidneys were removed for histological and immunohistochemical studies and lipid peroxidation determination. Blood and urine samples were collected in order to quantify sodium and creatinine. The results of the histological and immunohistochemical studies were scored according to the extent of damage and immunostaining, respectively, in the cortical tubulointerstitium. Lipid peroxidation was estimated by measuring malondialdehyde in renal tissue samples collected from control rats and glycerol-injected rats. By postinjection day 3, glycerol-only treated rats presented increases in plasma creatinine levels, as well as in fractional excretion of sodium and potassium (P<0.001). These increases were less pronounced in glycerol+resveratrol-treated rats (P<0.05). Cortical expression of macrophages, lymphocytes, nuclear factor-kappa B, heme oxygenase-1 and nitrotyrosine was greater in glycerol-treated rats than in controls (P<0.001). In addition, the histological findings for glycerol-treated rats were characteristic of acute tubular necrosis. Resveratrol attenuated all of these alterations (P<0.001). We conclude that resveratrol ameliorates glycerol-induced renal injury by suppressing the inflammatory process and by inhibiting lipid peroxidation.

Albumin-bound fatty acids induce mitochondrial oxidant stress and impair antioxidant responses in proximal tubular cells

Albumin induces oxidative stress and cytokine production in proximal tubular cells (PTECs). Albumin-bound fatty acids (FAs) enhance tubulopathic effects of albumin in vivo. We proposed that FA aggravation of albumin-induced oxidative stress in PTECs might be involved. We hypothesized that mitochondria could be a source of such stress. Using a fluorescent probe, we compared reactive oxygen species (ROS) production after exposure of PTECs to bovine serum albumin (BSA) alone or loaded with oleic acid (OA-BSA) (3-30 g/l for 2 h). There was no difference in cellular albumin uptake, but OA-BSA dose-dependently induced more ROS than BSA alone (P<0.001). OA-BSA-induced ROS was significantly alleviated by mitochondrial inhibition, but not by inhibitors of nicotinamide adenine dinucleotide phosphate hydrogenase (NADPH) oxidase, xanthine oxidase, or nitric oxide synthase. Gene expression analysis showed that neither the NADPH oxidase component p22phox nor xanthine oxidase was induced by BSA or OA-BSA. OA-BSA, in contrast to BSA, failed to induce mitochondrial manganese superoxide dismutase 2 (SOD2) expression. OA-BSA showed a greater capacity than BSA to downregulate heme oxygenase-1 mRNA expression and accentuate inflammatory cytokine mRNA and protein. Supplementation of SOD activity with EUK-8 reduced ROS, and interleukin-6 protein expression was suppressed by both mitochondrial inhibition and SOD augmentation. Thus, in PTECs, FAs accentuate albumin-induced oxidative stress and inflammatory cytokine expression via increased mitochondrial ROS, while frustrating protective antioxidant responses.