Preservation of cortical microcirculation after kidney ischemia-reperfusion: value of an iron chelator

An antioxidant system through conjugating superoxide dismutase onto metal-organic framework for cardiac repair

Acute myocardial infarction (AMI) remains a dominant origin of morbidity, mortality and disability worldwide. Increases in reactive oxygen species (ROS) are key contributor to excessive cardiac injury after AMI. Here we developed an immobilized enzyme with Superoxide Dismutase (SOD) activity cross-link with Zr-based metal-organic framework (ZrMOF) (SOD-ZrMOF) for mitigate ROS-caused injury. In vitro and in vivo evidence indicates that SOD-ZrMOF exhibits excellent biocompatibility. By efficiently scavenging ROS and suppressing oxidative stress, SOD-ZrMOF can protect the function of mitochondria, reduce cell death and alleviate inflammation. More excitingly, long-term study using an animal model of AMI demonstrated that SOD-ZrMOF can reduce the infarct area, protect cardiac function, promote angiogenesis and inhibit pathological myocardial remodeling. Therefore, SOD-ZrMOF holds great potential as an efficacious and safe nanomaterial treatment for AMI.

Myocardial reperfusion injury and oxidative stress: Therapeutic opportunities

Acute myocardial infarction (AMI) is the leading cause of death worldwide. Its associated mortality, morbidity and complications have significantly decreased with the development of interventional cardiology and percutaneous coronary angioplasty (PCA) treatment, which quickly and effectively restore the blood flow to the area previously subjected to ischemia. Paradoxically, the restoration of blood flow to the ischemic zone leads to a massive production of reactive oxygen species (ROS) which generate rapid and severe damage to biomolecules, generating a phenomenon called myocardial reperfusion injury (MRI). In the clinical setting, MRI is associated with multiple complications such as lethal reperfusion, no-reflow, myocardial stunning, and reperfusion arrhythmias. Despite significant advances in the understanding of the mechanisms accounting for the myocardial ischemia reperfusion injury, it remains an unsolved problem. Although promising results have been obtained in experimental studies (mainly in animal models), these benefits have not been translated into clinical settings. Thus, clinical trials have failed to find benefits from any therapy to prevent MRI. There is major evidence with respect to the contribution of oxidative stress to MRI in cardiovascular diseases. The lack of consistency between basic studies and clinical trials is not solely based on the diversity inherent in epidemiology but is also a result of the methodological weaknesses of some studies. It is quite possible that pharmacological issues, such as doses, active ingredients, bioavailability, routes of administration, co-therapies, startup time of the drug intervention, and its continuity may also have some responsibility for the lack of consistency between different studies. Furthermore, the administration of high ascorbate doses prior to reperfusion appears to be a safe and rational therapy against the development of oxidative damage associated with myocardial reperfusion. In addition, the association with N-acetylcysteine (a glutathione donor) and deferoxamine (an iron chelator) could improve the antioxidant cardioprotection by ascorbate, making it even more effective in preventing myocardial reperfusion damage associated with PCA following AMI.

TRPV4 activation mediates flow-induced nitric oxide production in the rat thick ascending limb

Nitric oxide (NO) regulates renal function. Luminal flow stimulates NO production in the thick ascending limb (TAL). Transient receptor potential vanilloid 4 (TRPV4) is a mechano-sensitive channel activated by luminal flow in different types of cells. We hypothesized that TRPV4 mediates flow-induced NO production in the rat TAL. We measured NO production in isolated, perfused rat TALs using the fluorescent dye DAF FM. Increasing luminal flow from 0 to 20 nl/min stimulated NO from 8 ± 3 to 45 ± 12 arbitrary units (AU)/min (n = 5; P < 0.05). The TRPV4 antagonists, ruthenium red (15 μmol/l) and RN 1734 (10 μmol/l), blocked flow-induced NO production. Also, luminal flow did not increase NO production in the absence of extracellular calcium. We also studied the effect of luminal flow on NO production in TALs transduced with a TRPV4shRNA. In nontransduced TALs luminal flow increased NO production by 47 ± 17 AU/min (P < 0.05; n = 5). Similar to nontransduced TALs, luminal flow increased NO production by 39 ± 11 AU/min (P < 0.03; n = 5) in TALs transduced with a control negative sequence-shRNA while in TRPV4shRNA-transduced TALs, luminal flow did not increase NO production (Δ10 ± 15 AU/min; n = 5). We then tested the effect of two different TRPV4 agonists on NO production in the absence of luminal flow. 4α-Phorbol 12,13-didecanoate (1 μmol/l) enhanced NO production by 60 ± 11 AU/min (P < 0.002; n = 7) and GSK1016790A (10 ηmol/l) increased NO production by 52 ± 15 AU/min (P < 0.03; n = 5). GSK1016790A (10 ηmol/l) did not stimulate NO production in TRPV4shRNA-transduced TALs. We conclude that activation of TRPV4 channels mediates flow-induced NO production in the rat TAL.

Comparative efficacy of renal preservation solutions to limit functional impairment after warm ischemic injury

In kidney transplantation, cold storage is the dominant modality used to prolong organ viability ex vivo, but is inevitably followed by a period of warm ischemia. Preservation fluids limit tissue damage during the ischemic period, but there is little information on the influence of preservation fluids on the physiologic consequences of warm ischemia alone, or on the comparative ability of such preservation fluids to limit warm ischemic injury. In this study, warm ischemia was induced in rat kidneys by crossclamping the left renal pedicle for 45 min with contralateral nephrectomy. The ischemic kidneys were flushed with Euro-Collins (EC), hyper osmolar citrate (HOC), University of Wisconsin (UW), or phosphate buffered sucrose (PBS)140 solution. Over a period of 2 h after reperfusion, urine and blood samples were collected and physiological parameters related to the function of the postischemic kidneys were assessed. The data show that postischemic renal function can be influenced by the choice of preservation fluid. Essentially, the continued use of EC as a renal preservation solution finds little support in these data, and, while HOC and UW solutions were better able to limit the decline in renal function after warm ischemia than EC, the solution most able to limit functional impairment after warm ischemia was PBS140. This analysis compares the efficacies of the commonly used preservation solutions and could form the basis for future solid-organ transplant studies that may ultimately allow us to propose best-practice guidelines and an optimum platform for improved preservation solutions.

An in vivo method for adenovirus-mediated transduction of thick ascending limbs

BACKGROUND

The thick ascending limb of the loop of Henle (THAL) plays an important role in the maintenance of salt, water, and acid-base balance. While techniques for gene transfer of renal vascular cells and some tubular segments have been described, in vivo transduction of THALs has not been successful. We hypothesized that in vivo injection of adenoviral vectors into the renal medulla would result in efficient transduction of THALs.

METHODS

We injected recombinant adenoviruses containing the reporter gene, green fluorescent protein (GFP), driven by either the cytomegalovirus promoter (Ad-CMVGFP) or the promoter for the Na/K/2 Cl cotransporter (Ad-NKCC2GFP), which is THAL-specific, into the outer medullary interstitium of Sprague-Dawley rat kidneys. Kidneys were removed at various times after viral injection and analyzed for GFP expression.

RESULTS

Western blots revealed strong GFP expression in the outer medulla (which is composed primarily of THALs) 5 days after Ad-CMVGFP injection. We quantified THAL transduction efficiency by scoring the number of fluorescent tubules in THALs suspensions, which showed that at least 77 +/- 3% of THAL expressed GFP. To specifically transduce THALs, we injected Ad-NKCC2GFP into the medullary interstitium. As determined by Western blot, GFP expression was only detected in the outer medulla. Immunohistochemistry and confocal microscopy showed that GFP was localized to tubular cells positive for Tamm-Horsfall protein. Thus, GFP fluorescence was only detected in THALs, not in cortical, inner medulla or vascular cells. Time-course studies showed that GFP expression in THALs was measurable from 4 to 14 days, peaked at 7 days, and had returned to background levels by 21 days.

CONCLUSION

This method facilitates highly efficient, THAL-specific transduction. While application of this technique for gene therapy in humans is unlikely due to the transient gene expression observed and the impossibility for repeated injections of adenoviral vectors, this method provides a valuable tool for investigators studying regulation and mechanisms of THAL ion transport and its relationship to whole-kidney physiology and pathophysiology.

Cold induces catalytic iron release of cytochrome P-450 origin: a critical step in cold storage-induced renal injury

Earlier experimental studies have suggested a role for iron in cold-storage-induced organ injury. Whether the cytochrome P-450 enzymes, shown to be a source for iron in several injury models, contribute to cold-induced iron release is not known. Storage of human proximal tubular epithelial (RPTE) cells at 4 degrees C in the University of Wisconsin (UW) solution caused a significant and time-dependent increase in bleomycin-detectable iron (BDI). To identify the cellular source of BDI, RPTE cells were subfractionated and stored at 4 degrees C for 4 h. Bleomycin-detectable iron release was highest in the microsomes, next in the cytosol and none in the mitochondria. As microsomes are rich in iron-containing cytochrome P-450 enzymes, microsomes were cold stored with P-450 inhibitors, cimetidine and piperonyl butoxide. P-450 inhibitors significantly reduced cold-induced BDI release. Furthermore, cimetidine and iron chelator deferoxamine (DFO) significantly reduced cold-induced cell injury, suggesting a role for P-450-derived iron in cold-induced cell injury. In rat kidney experiments, BDI and LDH release were significantly higher in cold-stored kidneys than in control kidneys. Inclusion of cimetidine and DFO in the cold-storage solution significantly suppressed the BDI and LDH release, and reduced the ultrastructural changes. Our data demonstrate for the first time that cold-induced catalytic iron release may be at least in part of microsomal cytochrome P-450 origin, and that it participates in cold-storage-induced renal injury. In the clinical setting, sequestering free iron released during cold storage is possible and may prove to be useful in limiting organ injury.

Diaspirin crosslinked hemoglobin (DCLHb): absence of increased free radical generation following administration in a rabbit model of renal ischemia and reperfusion

In control rabbits, a renal ischemia of 60 min followed by 10 min of reperfusion resulted in an enhanced free radical production in cortical tissue, as assessed by a significant decrease of free glutathione (42%), protein-bound GSH (17%), and vitamin E (49%). In contrast, catalase or glutathione peroxidase activities were not affected by these experimental conditions. Free radical production in this model was also measured directly using electron spin resonance (ESR) spectroscopy associated with a PBN (alpha-phenyl N-tert-butyl-nitrone) spin trap agent in the venous blood arising from the ischemic kidney. The signal consisted of a triplet of doublets. In contrast, no signal could be detected in control blood samples taken prior to inducing ischemia. The burst of free radical production occurred in the early phase after restoration of flow in the kidneys rendered ischemic, as evidenced by a signal of weak intensity which generally appeared within the third minute after reperfusion and progressively increased to form a well-defined asymmetric signal following 10 min of reperfusion. The precise nature of free radicals trapped by the PBN agent remains, however, to be elucidated, but analysis of the coupling constants (aN = 14.5-15 G; a beta H = 2.5-3 G) and asymmetry of the central doublets suggests that the ESR signal may arise from a nitorxy-radical adduct resulting from the spin trapping by PBN of both oxygen- or carbon-centered radicals of lipid origin. As evidenced by both direct and indirect measurements, exchange of rabbit blood immediately after inducing renal ischemia with 30 ml/kg of Diaspirin Crosslinked Hemoglobin (7.5 g/dl in lactated electrolyte) or human serum albumin (7.5 g/dl in lactated electrolyte) did not exacerbate free radical production mediated by an ischemia reperfusion phenomenon, a typical situation found in a resuscitation setting.