Attenuation of ischemia-reperfusion injury by ascorbic acid in the canine renal transplantation

Vitamin C in Health and Disease: A Companion Animal Focus

Vitamin C is synthesized in the liver in most species, including dogs and cats, and is widely distributed through body tissues. Vitamin C has an important physiologic role in numerous metabolic functions including tissue growth and maintenance, amelioration of oxidative stress, and immune regulation. It is also a co-factor in the production of important substances such as catecholamines and vasopressin. Decreased vitamin C levels have been documented in a wide variety of diseases, and in critically ill human patients may be associated with increased severity of disease and decreased survival. Intravenous supplementation with vitamin C has been proposed as a potential life-saving treatment in conditions such as septic shock, and results of small some human trials are promising. Data in companion in animals is very limited, but the possible benefits and , seemingly low risk of adverse effects , and the low cost of this treatment make vitamin C therapy a promising area of future investigation in critically ill dogs and cats.

Protective Role for Antioxidants in Acute Kidney Disease

Acute kidney injury causes significant morbidity and mortality in the community and clinic. Various pathologies, including renal and cardiovascular disease, traumatic injury/rhabdomyolysis, sepsis, and nephrotoxicity, that cause acute kidney injury (AKI), induce general or regional decreases in renal blood flow. The ensuing renal hypoxia and ischemia promotes the formation of reactive oxygen species (ROS) such as superoxide radical anions, peroxides, and hydroxyl radicals, that can oxidatively damage biomolecules and membranes, and affect organelle function and induce renal tubule cell injury, inflammation, and vascular dysfunction. Acute kidney injury is associated with increased oxidative damage, and various endogenous and synthetic antioxidants that mitigate source and derived oxidants are beneficial in cell-based and animal studies. However, the benefit of synthetic antioxidant supplementation in human acute kidney injury and renal disease remains to be realized. The endogenous low-molecular weight, non-proteinaceous antioxidant, ascorbate (vitamin C), is a promising therapeutic in human renal injury in critical illness and nephrotoxicity. Ascorbate may exert significant protection by reducing reactive oxygen species and renal oxidative damage via its antioxidant activity, and/or by its non-antioxidant functions in maintaining hydroxylase and monooxygenase enzymes, and endothelium and vascular function. Ascorbate supplementation may be particularly important in renal injury patients with low vitamin C status.

Ascorbic acid prolongs the viability and stability of isolated perfused lungs: A mechanistic study using 31P and hyperpolarized 13C nuclear magnetic resonance

Ex vivo lung perfusion (EVLP) has recently shown promise as a means of more accurately gauging the health of lung grafts and improving graft performance post-transplant. However, reperfusion of ischemic lung promotes the depletion of high-energy compounds and a progressive loss of normal mitochondrial function, and it remains unclear how and to what extent the EVLP approach contributes to this metabolic decline. Although ascorbate has been used to mitigate the effects of ischemia-reperfusion injury, the nature of its effects during EVLP are also not clear. To address these uncertainties, this study monitored the energy status of lungs during EVLP and after the administration of ascorbate using (31)P and hyperpolarized (13)C NMR (nuclear magnetic resonance). Our experiments demonstrated that the oxidative phosphorylation capacity and pyruvate dehydrogenase flux of lungs decline during ex vivo perfusion. The addition of ascorbate to the perfusate prolonged lung viability by 80% and increased the hyperpolarized (13)C bicarbonate signal by a factor of 2.7. The effect of ascorbate is apparently due not to its antioxidant quality but rather to its ability to energize cellular respiration given that it increased the lung's energy charge significantly, whereas other antioxidants (glutathione and α-lipoic acid) did not alter energy metabolism. During ascorbate administration, inhibition of mitochondrial complex I with rotenone depressed energy charge and shifted the metabolic state of the lung toward glycolysis; reenergizing the electron transport chain with TMPD (N,N,N',N'-tetramethyl-p-phenylenediamine) recovered metabolic activity. This indicates that ascorbate slows the decline of the ex vivo perfused lung's mitochondrial activity through an independent interaction with the electron transport chain complexes.

Different from renal artery only clamping, artery and vein clamping causes a significant reduction in number of rat glomeruli during warm ischemia

PURPOSE

To evaluate glomerular injury in the rat model during renal warm ischemia (WI), comparing artery and vein (AV) clamping with artery only (AO) clamping.

MATERIALS AND METHODS

Twenty-four adult male rats underwent 60 minutes of renal WI in the left kidney. The animals were divided into three groups: AV clamping, AO clamping, and Sham surgery. After 30 days, the animals were euthanized, and both kidneys were processed for paraffin embedding and stained with hematoxylin and eosin. Glomerular volume density (Vv[glom]), mean glomerular volume (MGV), and number of glomeruli per mm(3) (Nv[glom]) were evaluated in the renal cortex.

RESULTS

The Vv[glom] was reduced in the left kidney (ischemic) when compared with the right kidney in both AV and AO groups by 11.1% and 35.4%, respectively; however, the difference was significant only in the AV group. The Nv[glom] was reduced in the left kidney when compared with the right kidney in both AV and AO groups by 11.6% and 31.4%, respectively; nevertheless, the difference was significant only in the AV group. The MGV of left and right kidneys was the same in both Sham and AO groups and was diminished by 6.7% in the AV group-not significant.

CONCLUSION

AV clamping causes a significant decrease in the number of glomeruli in the rat model, while AO clamping reduces the glomerular number, but not significantly. To minimize renal injury, AO clamping may be preferred over AV clamping when WI is necessary in patients with previously compromised renal function.

Role of combination of L-arginine and α-tocopherol in renal transplantation ischaemia/reperfusion injury: a randomized controlled experimental study in a rat model

What's known on the subject? and What does the study add? Renal ischaemia/reperfusion (I/R) injury is an inevitable consequence of kidney transplantation. It contributes to delayed graft function (DGF), acute renal failure and graft rejection. The present study investigates for the first time the impact of a combination of L-arginine and alpha tocopherol on the renal ischemia/reperfusion injury in a rodent model of kidney transplantation. We found that concomitant administration of L-arginine and α-tocopherol has a more protective effect and synergistic antioxidant effect on ischaemia/reperfusion injury in transplanted rat kidneys.

OBJECTIVES

To investigate the role of L-arginine and α-tocopherol in ischaemia/reperfusion injury in a kidney transplanted rat model.

MATERIALS AND METHODS

In total, 40 male Sprague-Dawley rats subjected to renal transplantation received FK506 (tacrolimus) to overcome early acute rejection episodes. Animals were divided randomly into four groups (ten rats each). Group I were treated with FK506 (2 mg/kg/bw/day) and served as the control group. Group II were treated with L-arginine 300 mg/kg/bw. Group III were treated with α-tocopherol 30 mg/kg/bw. Group IV were treated with L-arginine and α-tocopherol. Urine and blood samples were taken at 0 (before operation), 2, 7 and 14 days post-transplantation for estimation of urine sodium, creatinine, fractional excretion of sodium, serum creatinine, sodium and blood urea nitrogen. Histological examination and measurement of malondialdehyde in kidney tissues were also performed.

RESULTS

Serum creatinine and blood urea nitrogen significantly decreased in L-arginine and α-tocopherol, as well as combination groups, compared to the control group. Malondialdehyde was significantly decreased in the combination group compared to L-arginine and α-tocopherol alone. Histological examination of the control group showed that acute tubular necrosis was markedly decreased in transplanted kidneys treated with a combination of both L-arginine and α-tocopherol.

CONCLUSIONS

Concomitant administration of l-arginine and α-tocopherol has a more protective effect and synergistic antioxidant effect on ischaemia/reperfusion injury in transplanted rat kidneys.

Prevenção do estresse oxidativo na síndrome de isquemia e reperfusão renal em ratos com suplementação nutricional com antioxidantes

OBJETIVO: Verificar o potencial efeito protetor de suplementação com vitaminas antioxidantes em um modelo de síndrome de isquemia-reperfusão renal em ratos. MÉTODOS: Foram utilizados 29 ratos Wistar, divididos em três grupos: Grupo I e II (n=10 cada), submetidos a indução do estresse oxidativo pela aplicação de 60 minutos de isquemia renal, seguidos de 10 minutos de reperfusão; adicionalmente, os animais do Grupo II foram pré-tratados por doze dias com vitaminas antioxidantes (vitamina C 11,43mg/kg e vitamina E 28,57mg/kg) antes da submissão à isquemia; Grupo III (n=9), correspondendo aos animais Sham, que foram manipulados de forma equivalente aos outros grupos, porém sem indução do estresse oxidativo e sem suplementação antioxidante. Findo isso, as amostras de sangue e os rins foram colhidos para avaliação dos níveis do malondialdeído, do ácido úrico e da capacidade antioxidante total. RESULTADOS: Para o malondialdeído e ácido úrico do Grupo I foi observado um aumento estatisticamente significante (p<0,01) em relação ao Grupo III, o qual não apresentou diferença em relação ao Grupo II. Para os níveis de capacidade antioxidante total, foi encontrada uma diminuição nos animais do Grupo I em relação aos Grupos II e III (p<0,01). CONCLUSÃO: Esses dados confirmam não apenas a efetiva participação do estresse oxidativo neste modelo de síndrome de isquemia e reperfusão renal em ratos, como também que o uso de vitaminas antioxidantes, associadas à dieta, pode proteger os animais das alterações oxidativas.

The protective effects of ascorbic acid against renal ischemia-reperfusion injury in male rats

There is increasing evidence to suggest that toxic oxygen radicals play an essential role in the pathogenesis of ischemia/reperfusion (I/R) injury in the kidney. This study was designed to investigate the effects of ascorbic acid (AA) in I/R-induced renal injury in rats. Thirty two male Sprague-Dawley rats were divided equally into four groups: group 1 (control; dissection of the right renal pedicle without nephrectomy), group 2 (sham operated; unilateral nephrectomy), group 3 (I/R; unilateral nephrectomy + I/R); and group 4 (AA+I/R; unilateral nephrectomy and I/R treated with ascorbic acid, 250mg kg(-1) i.p., for one hour prior to ischemia). On the 15th day following nephrectomy, groups 3 and 4 were subjected to 45 min of renal pedicle occlusion followed by 3 h of reperfusion. At the end of the treatment period, kidney samples were taken for histological examination or determination of the renal malondialdehyde (MDA) and glutathione (GSH) levels. Serum creatinine, blood urea nitrogen (BUN), and lactate dehydrogenase (LDH) concentrations were measured for the evaluation of renal function. I/R caused a significant decrease in GSH level, which was accompanied with a significant increase in MDA level of kidney tissues. Similarly, serum BUN and creatinine levels, as well as LDH, were elevated in the I/R group as compared to the control group. In group four, AA treatment reversed all the changes in these biochemical indices, as well as histopathological alterations normally induced by I/R. The findings imply that reactive oxygen species play a causal role in I/R-induced renal injury, and that AA exerts renoprotective effects, probably by radical scavenging and antioxidant activities.

The role of nutrients in modulating disease

The role of nutrition in the management of diseases has often centred on correcting apparent nutrient deficiencies or meeting estimated nutritional requirements of patients. Nutrition has traditionally been considered a supportive measure akin to fluid therapy and rarely it has been considered a primary means of ameliorating diseases. Recently, however, further understanding of the underlying mechanisms of various disease processes and how certain nutrients possess pharmacological properties have fuelled an interest in exploring how nutritional therapies themselves could modify the behaviour of various conditions. Nutrients such as omega-3 fatty acids, antioxidants and certain amino acids such as arginine and glutamine have all been demonstrated to have at least the potential to modulate diseases. Developments in the area of critical care nutrition have been particularly exciting as nutritional therapies utilising a combination of approaches have been shown to positively impact outcome beyond simply proving substrate for synthesis and energy. Application of certain nutrients for the modulation of diseases in veterinary patients is still in early stages, but apparent successes have already been demonstrated, and future studies are warranted to establish optimal approaches. This review describes the rationale of many of these approaches and discusses findings both in human beings and in animals, which may guide future therapy.

Novel pharmacological approaches to the treatment of renal ischemia-reperfusion injury: a comprehensive review

Renal ischemia-reperfusion (I-R) contributes to the development of ischemic acute renal failure (ARF). Multi-factorial processes are involved in the development and progression of renal I-R injury with the generation of reactive oxygen species, nitric oxide and peroxynitrite, and the decline of antioxidant protection playing major roles, leading to dysfunction, injury, and death of the cells of the kidney. Renal inflammation, involving cytokine/adhesion molecule cascades with recruitment, activation, and diapedesis of circulating leukocytes is also implicated. Clinically, renal I-R occurs in a variety of medical and surgical settings and is responsible for the development of acute tubular necrosis (a characteristic feature of ischemic ARF), e.g., in renal transplantation where I-R of the kidney directly influences graft and patient survival. The cellular mechanisms involved in the development of renal I-R injury have been targeted by several pharmacological interventions. However, although showing promise in experimental models of renal I-R injury and ischemic ARF, they have not proved successful in the clinical setting (e.g., atrial natriuretic peptide, low-dose dopamine). This review highlights recent pharmacological developments, which have shown particular promise against experimental renal I-R injury and ischemic ARF, including novel antioxidants and antioxidant enzyme mimetics, nitric oxide and nitric oxide synthase inhibitors, erythropoietin, peroxisome-proliferator-activated receptor agonists, inhibitors of poly(ADP-ribose) polymerase, carbon monoxide-releasing molecules, statins, and adenosine. Novel approaches such as recent research involving combination therapies and the potential of non-pharmacological strategies are also considered.