Franny Jongbloed

81 4 A PROTEIN-FREE DIET PROTECTS AGAINST RENAL IRI INTRODUCTION Dietary restriction (DR) is a reduction in food intake without malnutrition 1 . Long-term DR is known to extend lifespan, increase overall health and improve resistance to multiple stressors in a wide variety of organisms 1-5 . Although the effect of DR on human lifespan is unknown, studies demonstrate a favorable impact on metabolic parameters associated with long-term health 6-8 . In addition, DR has been shown to protect against acute stressors including toxic chemotherapy 9 , paracetamol intoxication 10 , and oxidative stress induced by ischemia-reperfusion injury (IRI) 1,11,12 . In clinical kidney transplantation, renal IRI is a major risk factor for organ damage which may result in acute kidney injury 13 , primary non-function 14 , delayed graft function 15 , and acute and chronic rejection 16 of the graft. After kidney retrieval, cessation of the blood flow (ischemia) leads to hypoxia, nutrient deprivation, and accumulation of metabolic waste products 15,16 . Reperfusion of the ischemic kidney promotes the generation of reactive oxygen species, triggers apoptotic cell death, and promotes the activation of an inflammatory response resulting in profound tissue injury 17 . Prevention or amelioration of renal IRI could increase graft quality, and prolong graft survival. Unfortunately, no effective treatment to reduce or prevent IRI is currently available. Using renal IRI as a model, we previously demonstrated that the benefits of DR on IRI are induced rapidly: two and four weeks of 30% preoperative DR as well as three days of fasting reduce renal injury and strongly improve survival and kidney function after renal IRI in mice 1,12 . Hence, DR is a potential intervention for living kidney donors to reduce IRI and improve the transplantation success rate. Whether the protective effect of short- and long-term DR is based on the reduction of calories per se, or specific nutrients, was first investigated in fruit flies, in which long-term protein restriction contributed more to lifespan extension than a reduction in carbohydrates 18 . In mice, glucose supplementation did not interfere with fasting-induced protection against renal IRI, which also points towards a role for specific (macro-) nutrients in inducing acute stress resistance 11 . In this study, we investigated the role of specific macronutrients in inducing resistance against renal IRI by unrestricted feeding of protein-, carbohydrate-, and fat-free diets. We showed that the absence of protein for three days is sufficient to induce resistance against renal IRI, and revealed common pathways and transcription factors that are implicated in the protective effect of calorie restriction induced by two weeks of 30% DR, three days of fasting, and protein restriction.