Impact of ischemia/reperfusion injury and early inflammatory responses in kidney transplantation

Renal-targeting triptolide-glucosamine conjugate exhibits lower toxicity and superior efficacy in attenuation of ischemia/reperfusion renal injury in rats

AIM

We previously reported a novel triptolide (TP)-glucosamine conjugate (TPG) that specifically accumulated in kidneys and protected renal function from acute ischemia/reperfusion (I/R) injury in rats. In this study we further examined the molecular mechanisms underlying the renoprotective action of TPG.

METHODS

The renal-targeting of TPG was investigated in a human proximal renal tubular epithelial cell line (HK-2) by measuring cell uptake of TP or TPG. The effects of TP or TPG on cell cycle distribution and apoptosis rate of HK-2 cells were assessed, and the activities of caspase-3 and caspase-9 were also measured. SD rats were subjected to bilateral renal ischemia by temporarily clamping both renal pedicles. The rats were administered TP (4.17 μmol·kg-1·d-1, iv) or TPG (4.17 μmol·kg-1·d-1, iv) for 3 d before the renal surgery. The kidneys were harvested after 24 h of recovery from the surgery. The levels of oxidative stress, proinflammatory cytokines, chemotactic cytokines and intracellular adhesion molecules in kidneys were examined.

RESULTS

The uptake of TPG in HK-2 cells was 2-3 times higher than that of TP at the concentrations tested. Furthermore, TPG targeting the proximal tubules was mediated through interactions with megalin receptors. TP (40-160 nmol/L) concentration-dependently increased G2/M arrest, apoptosis and caspase-3/caspase-9 activity in HK-2 cells, whereas the same concentrations of TPG did not show those features when compared with the control group. In I/R-treated rats, TPG administration caused more robust down-regulation of proinflammatory cytokines (TNF-α, IL-6, IL-1, TGF-β) and chemotactic cytokines (MCP-1) in the kidneys compared with TP administration, suggesting the inhibition of the proliferation and accumulation of lymphocytes. And TPG administration also caused more prominent inhibition on the levels of oxidative stress and intracellular adhesion molecules in the kidneys, compared with TP administration.

CONCLUSION

The renal-targeting TPG is more effective and less toxic than TP, in amelioration of I/R-induced rat renal injury, which may provide a new avenue for the treatment of acute kidney injury.

Mechanistic studies of a novel mycophenolic acid-glucosamine conjugate that attenuates renal ischemia/reperfusion injury in rat

Renal ischemia/reperfusion (I/R) injury causes high mortality and morbidity during renal procedures, yet current drugs should be used at high doses or for long periods due to lack of tissue specificity. In previous work we described a novel mycophenolic acid-glucosamine conjugate (MGC) that targets the proximal tubule epithelium, where it efficiently reduces renal I/R injury in rats and promotes recovery from reperfusion. Here we perform mechanistic studies of MGC in rats that suggest that the conjugate works by repressing the activation of renal inosine-5'-monophosphate dehydrogenase 2 (IMPDH2), thereby inhibiting the proliferation and accumulation of lympholeukocytes in the proximal tubules. In addition, MGC appears to inhibit inflammation through various pathways, including inhibition of free oxygen radical production, upregulation of bone morphogenetic protein-7, and downregulation of complement protein 3, TLR 4, intracellular adhesion molecules in the endothelium, proinflammatory cytokines (e.g., TNF-α, IL-6, IL-1, TGF-β), and chemotactic cytokines [e.g., monocyte chemoattractant protein-1 (MCP-1) and IL-8]. These findings suggest that MGC specifically targets the proximal tubules and acts through numerous mechanisms to substantially mitigate I/R injury in rats; this conjugate may provide a more effective alternative to current combination therapy.

Targeted drug delivery to renal proximal tubule epithelial cells mediated by 2-glucosamine

In order to develop a novel kidney-targeted drug delivery system, we synthesized prednisolone carbamate-glucosamine conjugate (PCG) using 2-glucosamine as a ligand, and investigated its potential targeting efficacy. In vitro studies demonstrated that PCG could remarkably improve the uptake of drug by kidney cells. And the specific uptake of PCG could be largely reduced by the inhibitors of megalin receptor. More importantly, PCG showed an excellent kidney targeting property in vivo, and the concentration of the conjugate in the kidney was 8.1-fold higher than that of prednisolone group at 60 min after intravenous injection. Besides, PCG could significantly reverse the disease progression in renal ischemia-reperfusion (I/R) injury animal models. Furthermore, PCG presented no adverse effect on bone density while prednisolone resulted in severe osteoporosis. Thus, it indicated that 2-glucosamine could be a potential ligand for kidney-targeted delivery of prednisolone.

Hypercoagulable state associated with kidney-pancreas transplantation. Thromboelastogram-directed anti-coagulation and implications for future therapy

BACKGROUND

The clinical consequences of type 1 diabetes mellitus (IDDM) include diabetic triopathy: retinopathy, nephropathy, and neuropathy, as well as microangiopathy, accelerated atherosclerotic disease, and hypercoagulability. The etiology of the hypercoagulability is multifactorial, involving various clotting factors or pathways (for example platelets, fibrinogen, individual components of the clotting system and/or fibrinolysis in different studies). The development of end-stage renal disease (ESRD), with the uremia-related platelet effect has the potential to protect from the existing hypercoagulable state. This has important implications for surgery, particularly simultaneous pancreas-kidney (SPK) transplantation, where the pancreas has historically been prone to thrombosis. This has led us to perform intra-operative thromboelastograms (TEG's) to evaluate the patient's current coagulation status.

METHODS

A TEG was performed in 85 SPK recipients along with a control group of 54 non-diabetic kidney transplant (KT) recipients.

RESULTS

For each of the 4 TEG coagulation parameters, the SPK recipients were significantly more hypercoagulable than the non-diabetic KT recipients. The use of intra-operative heparin is based on the degree of hypercoagulability by TEG and degree of operative hemostasis. There has been one PT lost to thrombosis (1%) in the first week following transplantation during this time.

CONCLUSION

The use of TEG is a helpful adjunct to SPK surgery, demonstrating the patient's current coagulation status. Nearly all SPK recipients (type 1 IDDM with ESRD) have been demonstrated to be hypercoagulable. The TEG allows the judicious use of anti-coagulation at the time of surgery, and beyond.

Cadaveric versus living-donor livers: differences in inflammatory markers after transplantation

BACKGROUND

Prolonged cold storage of organs for transplantation may lead to inflammatory damage upon reperfusion. The aim of this study was to investigate whether organs from living donors experience less damage upon reperfusion than those retrieved from cadaver donors, where cold ischemia times are significantly longer.

METHODS

Biopsies were obtained from cadaveric (n=23) and living-related donor (LRD) (n=10) liver transplants before and 2 hours after reperfusion. Cryosections were stained with antibodies against neutrophils, platelets, activated platelets, and endothelium.

RESULTS

LRD liver allografts showed minimal changes postreperfusion. In contrast, after reperfusion of cadaver allografts, neutrophil infiltration was detected in 22% and increased expression of von Willebrand factor (vWF), CD41, and P-selectin in 48%, 30%, and 13% of allografts, respectively. In cadaver allografts with deposition of activated platelets expressing either P-selectin or vWF, the cold ischemia time was significantly longer (885 +/- 123 min vs. 608 +/- 214 min, P=0.04; 776.8 +/- 171 min vs. 559.3 +/- 216 min, P=0.01, respectively). Increases in neutrophils and platelets after reperfusion were not significantly associated with clinical events posttransplant. However, in cadaver transplants that experienced early acute rejection, the mean cold ischemia time was significantly longer than in allografts with no rejection (732 +/- 174 min vs. 480 +/- 221 min, P=0.006).

CONCLUSIONS

This study demonstrates that in the clinical situation, cold ischemia causes platelet deposition and neutrophil infiltration after reperfusion of cadaveric liver allografts. These early inflammatory events may contribute to make the graft more susceptible to acute rejection.

Leukocyte infiltration and inflammatory antigen expression in cadaveric and living-donor livers before transplant

BACKGROUND

There is evidence to indicate that organs obtained from cadaveric donors may be injured as a result of inflammatory events occurring at around the time of brain death. The aim of this study was to investigate whether there are differences in the expression of proinflammatory molecules between cadaveric and living-donor livers before transplant and to determine whether there is any association with donor factors and posttransplant graft function.

METHODS

A comparison of biopsies obtained before implantation from cadaveric (n=22) and living-related donor (LRD) (n=10) livers was performed. Cryostat tissue sections were stained with antibodies to leukocyte subpopulations, adhesion molecules, and human leukocyte antigen class II antigens.

RESULTS

Significantly higher levels of CD3+ lymphocytes (1.5%+/-0.8% vs. 0.5%+/-0.3%; P=0.00004), CD68+ monocytes and macrophages (4.0%+/-1.2% vs. 2.7%+/-0.6%; P=0.0003), and Fas-ligand staining (4.2%+/-2.6% vs. 1.5%+/-1.1%; P=0.0003) were detected in cadaveric livers compared with LRD livers before transplantation. Furthermore, higher levels of intercellular adhesion molecule-1 expression were detected in cadaveric donor livers and found to be associated with longer periods of ventilation (P=0.01), infection in the donor (P=0.013), and administration of dopamine (P=0.03). Although there were no differences in neutrophil infiltration between cadaveric and LRD livers, significantly higher levels were found in cadaveric donors with infection (P=0.01).

CONCLUSION

This study demonstrates that inflammatory changes occur in cadaveric donor livers and are associated with events occurring during the period of intensive care. These proinflammatory changes did not seem to affect the short-term clinical outcome of cadaveric liver allografts but may contribute to alloimmune responses and impairment of graft function in the long term.

The regulation of ischemic acute renal failure by extrarenal organs

PURPOSE OF REVIEW

Recent work suggests that extrarenal organs, such as the liver, lung, spleen, brain, lymphoid tissues, and bone marrow, regulate acute renal failure. We now review several examples of such regulation.

RECENT FINDINGS

First, we demonstrate kidney-liver crosstalk during ischemic renal failure. Renal ischemia induces the renal production of interleukin 6 and the renal expression of interleukin 10 receptors; interleukin 6 stimulates the production of interleukin 10 by the liver; interleukin 10 ameliorates renal injury. The potential mechanisms of interleukin 6 and 10 are discussed. Second, we review the possible effects of the acute phase response on renal ischemic injury. We point out potential analogies between the recently reported association of increased interleukin 6 and C-reactive protein with myocardial ischemia, and renal ischemia. Third, we briefly review the salutary effects of hepatocyte growth factor, produced by the lung, spleen, and liver, on ischemic renal injury. Finally, we discuss how renal ischemia elicits an inflammatory response of neutrophils, macrophages, and T cells that may exacerbate the injury. Granulocyte-colony stimulating factor, produced by the kidney in response to ischemia, may participate in eliciting this inflammation. Such inflammation may be exacerbated by cytokines and growth factors released by the brain after traumatic injury.

SUMMARY

We discuss the existing evidence for extrarenal regulation of acute renal failure. This suggests that concurrent disease of those extrarenal organs might alter the course of acute renal failure.

Lecithinized superoxide dismutase reduces cold ischemia-induced chronic allograft dysfunction

BACKGROUND

Chronic renal allograft failure (CAF) is influenced by both allo-dependent and independent factors and is a major cause of graft loss in clinical renal transplantation. We evaluated a novel membrane-bound free radical scavenger, lecithinized superoxide dismutase (lec-SOD), to determine its potential in limiting the harmful effects of ischemia/reperfusion injury on CAF.

METHODS

Fisher rat kidneys were stored for either 1 hour or 18 hours in cold Marshall's preservation solution either with or without lec-SOD and transplanted into Lewis recipients.

RESULTS

Within 3 days of transplantation, an early inflammatory response involving granulocytes and macrophages was detected in renal allografts exposed to 18 hours cold ischemia that was significantly reduced by preservation with lec-SOD. By 24 weeks post-transplantation, elevated proteinuria and detection of apoptotic cells was observed in kidneys exposed to 18 hours of cold ischemia, that was attenuated by preservation with lec-SOD (P < 0.05). However, up-regulated expression of intracellular adhesion molecule-1 (ICAM-1) and major histocompatibility complex (MHC) Class II together with a T lymphocyte infiltration were observed at 24 weeks that was not prevented by preservation with lec-SOD.

CONCLUSIONS

These results demonstrate that ischemia/reperfusion injury, apoptotic cell death and allo-immune responses may be exacerbated by cold ischemia and accelerate the development of CAF. Preservation with lec-SOD may protect against the early damage induced by cold ischemia and reperfusion injury.

The role of mitochondria in ischemia/reperfusion injury

In organ transplantation, ischemia/reperfusion injury is a multifactorial process that leads to organ damage and primary graft dysfunction. Injury to the organ is mediated by a complex chain of events that involves depletion of energy substrates, alteration of ionic homeostasis, production of reactive oxygen species, and cell death by apoptosis and necrosis. There is increasing evidence that mitochondria play a role in this process because of the profound changes experienced during ischemia and reperfusion. Understanding the mechanisms that lead to mitochondrial damage may be important for developing strategies aimed at improving graft outcome. In this review, we examine the role of mitochondria in ischemia/reperfusion injury and the possible mechanisms that may contribute to organ dysfunction.

Endothelial cell protection against ischemia/reperfusion injury by lecithinized superoxide dismutase

BACKGROUND

Organs used for transplantation may experience long periods of cold ischemic preservation and consequently oxygen free radical-mediated damage following reperfusion. Lecithinized superoxide dismutase (lec-SOD) is a novel free radical scavenger that has been shown to bind with high affinity to cell membranes. The aim of this study was to determine whether lec-SOD bound to endothelial cells under organ preservation conditions to mediate direct antioxidant activity at the endothelial cell surface and thus offer protection against the harmful effects of ischemia/reperfusion injury.

METHODS

An in vitro study was performed on large vessel endothelial cells (HUVEC) and a human microvascular endothelial cell line HMEC-1, to investigate the potential therapeutic benefits of incorporating lec-SOD into organ preservation solution. A cold hypoxia/reoxygenation system was developed to examine lec-SOD binding affinity to endothelial cells, protection against hypoxia/reoxygenation-induced cell death, and neutrophil adhesion.

RESULTS

Lec-SOD bound to endothelial cells with higher affinity than unmodified recombinant human superoxide dismutase (rhSOD) and significantly protected both HUVEC and HMEC-1 from cell death following 27 hours of cold hypoxia (P < 0.01). Furthermore, neutrophil adhesion to the endothelium stimulated by hypoxia and reoxygenation was significantly inhibited by treatment with lec-SOD but not by lecithin or rhSOD (P < 0.01). Analysis by flow cytometry demonstrated that E-selectin and ICAM-1 were up-regulated by hypoxia/reoxygenation that was inhibited in part by lec-SOD.

CONCLUSIONS

The results from this study suggest that incorporation of lec-SOD into organ preservation solutions provides effective protection to endothelial cells against cold ischemia and reperfusion injury following transplantation.