Electron paramagnetic resonance imaging of oxidative stress in renal disease

Targeting oxidative stress, a crucial challenge in renal transplantation outcome

Disorders characterized by ischemia/reperfusion (I/R) are the most common causes of debilitating diseases and death in stroke, cardiovascular ischemia, acute kidney injury or organ transplantation. In the latter example the I/R step defines both the amplitude of the damages to the graft and the functional recovery outcome. During transplantation the kidney is subjected to blood flow arrest followed by a sudden increase in oxygen supply at the time of reperfusion. This essential clinical protocol causes massive oxidative stress which is at the basis of cell death and tissue damage. The involvement of both reactive oxygen species (ROS) and nitric oxides (NO) has been shown to be a major cause of these cellular damages. In fact, in non-physiological situations, these species escape endogenous antioxidant control and dangerously accumulate in cells. In recent years, the objective has been to find clinical and pharmacological treatments to reduce or prevent the appearance of oxidative stress in ischemic pathologies. This is very relevant because, due to the increasing success of organ transplantation, clinicians are required to use limit organs, the preservation of which against oxidative stress is crucial for a better outcome. This review highlights the key actors in oxidative stress which could represent new pharmacological targets.

Combination therapy with melatonin, stem cells and extracellular vesicles is effective in limiting renal ischemia-reperfusion injury in a rat model

OBJECTIVE

To evaluate the therapeutic value of melatonin, mesenchymal stem cells and their extracellular vesicles, exosomes, on renal ischemia-reperfusion.

METHODS

Female albino rats (n = 64) were divided into eight groups (n = 8 per group): control, sham (only laparotomy), renal ischemia-reperfusion (renal ischemia-reperfusion + phosphate-buffered saline), melatonin (renal ischemia-reperfusion + melatonin), mesenchymal stem cells (renal ischemia-reperfusion + mesenchymal stem cells), exosomes (renal ischemia-reperfusion + exosomes), melatonin + mesenchymal stem cells (renal ischemia-reperfusion + melatonin + mesenchymal stem cells) and melatonin + exosomes (renal ischemia-reperfusion + melatonin + exosomes). After the establishment of the renal ischemia-reperfusion model, rats in each group were bilaterally injected once with either mesenchymal stem cells or exosomes in both renal arteries during reperfusion.

RESULTS

Notable improvement of renal ischemia-reperfusion was obtained after different treatments, as evidenced by a lower histopathological score of kidney injury; decreased serum levels of urea, creatinine and retinol-binding protein; reduced lipid peroxidation marker malondialdehyde; increased superoxide dismutase and catalase activities; reduced apoptosis (lower DNA damage and B-cell lymphoma 2-associated X protein, and higher B-cell lymphoma 2 genes/proteins); and inhibition of kidney inflammatory and damage markers (tumor necrosis alpha, interleukin-1β, nuclear factor kappa B, kidney injury molecule-1, IL-18, matrix metalloproteinase 9, neutrophil gelatinase-associated lipocalin). The improvement order was (highest to lowest): melatonin + exosomes, melatonin + mesenchymal stem cells, exosomes, mesenchymal stem cells and melatonin group.

CONCLUSIONS

Our data suggest a potential therapeutic effect of combined therapy with melatonin, mesenchymal stem cells and their exosomes to minimize renal ischemia-reperfusion injury in rats.

ESR line width and line shape dependence of Overhauser-enhanced magnetic resonance imaging

Electron spin resonance and Overhauser-enhanced magnetic resonance imaging studies were carried out for various concentrations of ¹⁴ N-labeled 3-carbamoyl-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl in pure water. Overhauser-enhancement factor attains maxima in the range of 2.5-3 mm concentration. The leakage factor showed an asymptotic increase with increasing agent concentration. The coupling parameter showed the interaction between the electron and nuclear spins to be mainly dipolar in origin. The electron spin resonance parameters, such as the line width, line shape and g-factor, were determined. The line width analysis confirms that the line broadening is proportional to the agent concentration, and also the agent concentration is optimized in the range of 2.5-3 mm. The line shape analysis shows that the observed electron spin resonance line shape is a Voigt line shape, in which the Lorentzian component is dominant. The contribution of Lorentzian component was estimated using the winsim package. The Lorentzian component of the resonance line attains maxima in the range of 2.5-3 mm concentration. Therefore, this study reveals that the agent concentration, line width and Lorentzian component are the important factors in determining the Overhauser-enhancement factor. Hence, the agent concentration was optimized as 2.5-3 mm for in vivo/in vitro electron spin resonance imaging and Overhauser-enhanced magnetic resonance imaging phantom studies. Copyright © 2016 John Wiley & Sons, Ltd.

Kangen-karyu raises surface body temperature through oxidative stress modification

Kangen-karyu, a prescription containing six herbs, has been shown to achieve its pharmacological effect through oxidative stress-dependent pathways in animal models. The aim of this study is to investigate the relationship between the antioxidative effect and pharmacological mechanisms of Kangen-karyu, specifically its body temperature elevating effect in humans. Healthy human volunteers, age 35 ± 15 years old, were enrolled in this study. Surface body temperature, serum nitrite, reactive oxygen species (ROS) scavenging activities, and inflammatory cytokines were investigated before and 120 min after Kangen-karyu oral intake. Kangen-karyu significantly increased the surface-body temperature of the entire body; this effect was more remarkable in the upper body and continued for more than 120 min. Accompanying this therapeutic effect, serum nitrite levels were increased 120 min after oral administration. Serum ROS scavenging activities were enhanced against singlet oxygen and were concomitantly decreased against the alkoxyl radical. Serum nitrite levels and superoxide scavenging activities were positively correlated, suggesting that Kangen-karyu affects the O₂^•−-NO balance in vivo. Kangen-karyu had no effect on IL-6, TNF-α and adiponectin levels. These results indicate that the therapeutic effect of Kangen-karyu is achieved through NO- and ROS-dependent mechanisms. Further, this mechanism is not limited to ROS production, but includes ROS-ROS or ROS-NO interactions.

In vivo imaging of immuno-spin trapped radicals with molecular magnetic resonance imaging in a diabetic mouse model

Oxidative stress plays a major role in diabetes. In vivo levels of membrane-bound radicals (MBRs) in a streptozotocin-induced diabetic mouse model were uniquely detected by combining molecular magnetic resonance imaging (mMRI) and immunotrapping techniques. An anti-DMPO (5,5-dimethyl-1-pyrroline N-oxide) antibody (Ab) covalently bound to an albumin (BSA)-Gd (gadolinium)-DTPA (diethylene triamine penta acetic acid)-biotin MRI contrast agent (anti-DMPO probe), and mMRI, were used to detect in vivo levels of DMPO-MBR adducts in kidneys, livers, and lungs of diabetic mice, after DMPO administration. Magnetic resonance signal intensities, which increase in the presence of a Gd-based molecular probe, were significantly higher within the livers, kidneys, and lungs of diabetic animals administered the anti-DMPO probe compared with controls. Fluorescence images validated the location of the anti-DMPO probe in excised tissues via conjugation of streptavidin-Cy3, which targeted the probe biotin moiety, and immunohistochemistry was used to validate the presence of DMPO adducts in diabetic mouse livers. This is the first report of noninvasively imaging in vivo levels of MBRs within any disease model. This method can be specifically applied toward diabetes models for in vivo assessment of free radical levels, providing an avenue to more fully understand the role of free radicals in diabetes.

Bardoxolone methyl (BARD) ameliorates ischemic AKI and increases expression of protective genes Nrf2, PPARγ, and HO-1

Ischemic acute kidney injury (AKI) triggers expression of adaptive (protective) and maladaptive genes. Agents that increase expression of protective genes should provide a therapeutic benefit. We now report that bardoxolone methyl (BARD) ameliorates ischemic murine AKI as assessed by both renal function and pathology. BARD may exert its beneficial effect by increasing expression of genes previously shown to protect against ischemic AKI, NF-E2-related factor 2 (Nrf2), peroxisome proliferator-activated receptor-γ (PPARγ), and heme oxygenase 1 (HO-1). Although we found that BARD alone or ischemia-reperfusion alone increased expression of these genes, the greatest increase occurred after the combination of both ischemia-reperfusion and BARD. BARD had a different mode of action than other agents that regulate PPARγ and Nrf2. Thus we report that BARD regulates PPARγ, not by acting as a ligand but by increasing the amount of PPARγ mRNA and protein. This should increase ligand-independent effects of PPARγ. Similarly, BARD increased Nrf2 mRNA; this increased Nrf2 protein by mechanisms in addition to the prolongation of Nrf2 protein half-life previously reported. Finally, we localized expression of these protective genes after ischemia and BARD treatment. Using double-immunofluorescence staining for CD31 and Nrf2 or PPARγ, we found increased Nrf2 and PPARγ on glomerular endothelia in the cortex; Nrf2 was also present on cortical peritubular capillaries. In contrast, HO-1 was localized to different cells, i.e., tubules and interstitial leukocytes. Although Nrf2-dependent increases in HO-1 have been described, our data suggest that BARD's effects on tubular and leukocyte HO-1 during ischemic AKI may be Nrf2 independent. We also found that BARD ameliorated cisplatin nephrotoxicity.

Activation of the succinate receptor GPR91 in macula densa cells causes renin release

Macula densa (MD) cells of the juxtaglomerular apparatus (JGA) are salt sensors and generate paracrine signals that control renal blood flow, glomerular filtration, and release of the prohypertensive hormone renin. We hypothesized that the recently identified succinate receptor GPR91 is present in MD cells and regulates renin release. Using immunohistochemistry, we identified GPR91 in the apical plasma membrane of MD cells. Treatment of MD cells with succinate activated mitogen-activated protein kinases (MAPKs; p38 and extracellular signal-regulated kinases 1/2) and cyclooxygenase 2 (COX-2) and induced the synthesis and release of prostaglandin E(2), a potent vasodilator and classic paracrine mediator of renin release. Using microperfused JGA and real-time confocal fluorescence imaging of quinacrine-labeled renin granules, we detected significant renin release in response to tubular succinate (EC(50) 350 microM). Genetic deletion of GPR91 (GPR91(-/-) mice) or pharmacologic inhibition of MAPK or COX-2 blocked succinate-induced renin release. Streptozotocin-induced diabetes caused GPR91-dependent upregulation of renal cortical phospho-p38, extracellular signal-regulated kinases 1/2, COX-2, and renin content. Salt depletion for 1 wk increased plasma renin activity seven-fold in wild-type mice but only 3.4-fold in GPR91(-/-) mice. In summary, MD cells can sense alterations in local tissue metabolism via accumulation of tubular succinate and GPR91 signaling, which involves the activation of MAPKs, COX-2, and the release of prostaglandin E(2). This mechanism may be integral in the regulation of renin release and activation of the renin-angiotensin system in health and disease.

Dynamics of thromboxane level changes during early phase of allograft reperfusion

BACKGROUND

Thromboxane (Tx) is a metabolite of arachidonic acid, which exerts a significant influence on kidney homeostasis, and may be involved in the pathogenesis of allograft rejection. The aim of this study was to: examine the dynamics of TxB2 changes during early phase of kidney allograft reperfusion, and analyze whether the observed changes in the concentrations and direction of TxB2 changes, are associated with post-transplant graft function.

METHODS

Sixty-nine transplant recipients were divided into early, slow and delayed graft function group. Blood samples were collected directly before and during first the five minutes of allograft reperfusion. TxB2 concentrations were measured using ELISA. Creatinine and GFR levels were measured on the first, fifth, and 10th post-transplant day.

RESULTS

The results demonstrated that during reperfusion significant differences in TxB2 concentrations occur in all groups. Moreover, significant differences in the concentrations, as well as in the dynamics of TxB2 changes between patients with immediate graft function, and individuals with allograft activation problems, were noticed. These differences were associated with post-transplant graft function.

CONCLUSIONS

Human renal transplantations are accompanied by changes in TxB2 concentrations, and the dynamics of TxB2 changes is associated with early post-transplant graft function. Our results also highlight TxB2 as a potential pre-transplant marker of post-transplant allograft function.

Is it possible to predict the early post-transplant allograft function using 20-HETE measurements? A preliminary report

20-HydroxyEicosaTetraEnoic (20-HETE) acid is an arachidonic acid metabolite that is generated via cytochrome P450 enzymes, and according to the findings from recent studies, may be involved in the pathogenesis of ischemia-reperfusion injury. The aim of this study was to: examine the dynamics of 20-HETE changes during the first 5 min of allograft reperfusion, and analyze whether the observed changes are associated with post-transplant graft function. Sixty-nine renal transplant recipients were divided, according to their outcome, into early, slow and delayed graft function (EGF, SGF, DGF) group. Blood samples were collected directly before and during the first 5 min of allograft reperfusion. 20-HETE concentrations were measured using ELISA. The results demonstrated significant differences in the concentrations and in the dynamics of 20-HETE changes between patients with immediate graft function, and individuals with allograft activation problems. The sensitivity, specificity, positive and negative predictive value of 20-HETEDelta(5-0) parameter in discriminating EGF and SGF from DGF were 69%, 54%, 74% and 48% respectively. Therefore, our results demonstrated that the dynamics of 20-HETE changes, which occurs during early phase of allograft reperfusion, is associated with early post-transplant graft function and also highlighted 20-HETE as a novel clinical marker of post-transplant allograft function.

Effect of CV159-Ca(2+)/calmodulin blockade on redox status hepatic ischemia-reperfusion injury in mice evaluated by a newly developed in vivo EPR imaging technique

1,4-Dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinedicarboxylic acid methyl 6-(5-phenyl-3-pyrazolyloxy)hexyl ester (CV159) exhibits selective blocking of Ca(2+)/calmodulin and inhibits Ca(2+) overloading in living organisms. The effects of this antagonist in mice with hepatic ischemia-reperfusion injury were investigated using electron paramagnetic resonance imaging (EPRI) and ex vivo EPR (x-band EPR) techniques. The EPRI determined that the 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl half-life in CV159-treated mice was significantly shorter than that in untreated mice and was almost equal to that in the sham group. Both the cytosolic and the mitochondrial superoxide scavenging activities in CV-treated mice were significantly higher than that in untreated mice. Faint staining of the anti-superoxide dismutase antibody and strong staining of anti-inducible nitric oxide synthase antibody were observed in the liver of control group. In contrast to these findings, immunostaining of these antibodies in the liver of CV159-treated mice were reversed compared to control group. Western blotting showed that CV159 contributed to the high superoxide dismutase expression and low expression of inducible nitric oxide synthase. The alanine aminotransferase level in CV159-treated mice significantly decreased in comparison to that observed in the untreated mice. We conclude that CV159 retains its organ-reducing activity against radicals in hepatic reperfusion injury, which is mediated by the inhibition of Ca(2+) overloading.