Summary
Ischemia-reperfusion injury is inevitable to transplantation. During ischemia adenosine triphosphate (ATP) is depleted coincided with the formation of free radicals. Thiamine pyrophosphate is the ‘active’ thiamine co-enzyme for at least three enzymes involved in glucose metabolism. These enzymes play a role in both the regeneration of reduced glutathione (GSH) as substrate for anti-oxidant enzymes and the regeneration of ATP for maintenance of energy-requiring metabolic processes. Thereby thiamine is crucial for optimal amounts of GSH and for regeneration of ATP in cells.
In chapter 2 the hypothesis why thiamine deficiency could be detrimental in kidney transplantation is described. Thiamine is a B-vitamin (vitamin B1) and an essential micronutrient for mammalians. It is difficult to maintain thiamine stores without continuous supplementation with thiamine from food or other resources. Subclinical thiamine deficiency is very common in patients at admission to intensive care units. Intensive care patients are the typical kidney donors. A further cause of thiamine deficiency may be related to the preservation procedure of the organ prior to transplantation. Thiamine is water-soluble, and may diffuse from the organ into the preservation solution during cold flushing and during storage. Thiamine is required for optimal regeneration of GSH and ATP in cells. In the reperfusion phase tissue demands of GSH and ATP are high in order to counterbalance events as production of reactive oxygen species and acute cell swelling. Several studies have shown that thiamine supplementation was beneficial in ischaemia-reperfusion models of different organs. This leads to the hypothesis that thiamine deficiency is an important determinant of the occurrence of acute tubule necrosis and delayed graft function in kidney transplantation.
In chapter 3 we describe the development of thiamine deficiency in different tissues. This study showed that brain and heart tissue are relatively protected by thiamine deficiency.
However clinical signs of thiamine deficiency appear first in these tissues. This indicates that when signs of thiamine deficiency are clinically present such as Wernicke’s encephalopathy and wet beriberi also other tissues then brain and heart are affected. Subclinical thiamine deficiency of certain tissues could thereby well exist. Moreover this study gives a rationale for the period of thiamine deficient diet as used in chapter 4. It showed that kidney tissue is already deficient after two weeks of feeding a thiamine deficient diet. This deficient state is prior to weight loss of the animals and before they decrease their dietary food intake.
In chapter 4 the influence of thiamine deficiency on ischaemia-reperfusion injury in the kidney was tested. In contrast to our hypothesis, we could not show that thiamine deficiency aggravated ischaemia-reperfusion injury. Moreover when thiamine deficiency
135 was complicated by a decreased food intake and weight loss this prevented ischaemia-reperfusion injury. However there was no effect of thiamine deficiency when it was not complicated by decreased food intake and weight loss. Thereby we surmised that the weight loss and reduced food may explain the unexpected protective effect.
In chapter 5 we describe a double-blind, randomized, placebo-controlled clinical trial, in which we tested the hypothesis whether benfotiamine could decrease albuminuria in diabetic nephropathy. In this study there was no effect of benfotiamine treatment on albuminuria and other markers of kidney damage. However thiamine status improved in the study period, indicating proper adherence to the study treatment. In studies that showed an effect of thiamine supplementation on albuminuria in diabetic nephropathy there were less patients on angiotensin-converting-enzyme inhibitor and angiotensin receptor blocker treatment. This indicates that patients who are optimally treated for diabetic nephropathy do not benefit from (benfo)thiamine supplementation as much as suboptimal treated patients do.
In chapter 6 we did not show an effect of peri-operative fasting on ischaemia-reperfusion injury. However, this could be due to timeframe and experimental design. The duration of fasting was 48 h prior to ischaemia-reperfusion procedure, and it could be that to induce a protective effect in rats longer period of fasting is necessary. However, longer period of fasting prior to ischaemia-reperfusion procedure would not be applicable in the clinical setting. Instead of fasting also other forms of dietary restriction could be used, such as caloric restriction. As fasting is known to play a role in ischaemia-reperfusion injury and kidney disease we proceeded to study the correlation of non-esterified fatty acids and malondialdehyde in renal transplant recipients. In chapter 7 we describe the protective effects of non-esterified fatty acids on graft failure in stable renal transplant recipients. In experimental studies it has been described that non-esterified fatty acids carried by albumin are detrimental for kidney function. However the effect of non-esterified fatty acids had not been measured in stable renal transplant recipients. In this chapter we showed that non-esterified fatty acids protect against graft loss. Recent in vitro studies suggest that type of non-esterified fatty acids is important in protective or detrimental effects. Malondialdehyde has, as described in chapter 8, been shown to be correlated with lower change of graft failure in stable renal transplant recipients. Malondialdehyde is historically seen as a marker of oxidative stress. However malondialdehyde excretion will also rise when salmon is consumed or after exercise. Thereby it could be rather a marker of lifestyle than of oxidative stress in stable renal transplant recipients.
In chapter 9 we tested the hypothesis whether caloric restriction in combination with ketogenic diet protects against nephropathy in a proteinuric rat model. We introduced
caloric restriction with or without the combination of a ketogenic diet in a proteinuric rat model when proteinuria had already developed. Thereby we attempted to mimick the clinical situation in which a patient is treated when proteinuria is already established. We showed that caloric restriction lowers proteinuria and decreases renal damage. This was irrespective of ketogenesis since a ketogenic diet did not shown any changes. This suggests that other mechanisms rather than ketogenesis underlie the beneficial effects of caloric restriction. One mechanism could be the effect of caloric restriction on lowering the blood pressure.