Franny Jongbloed

251 9 SUMMARY AND DISCUSSION FUTURE PERSPECTIVES The cornerstone of the studies described in this thesis is the effects of dietary restriction (DR) on acute stress-related injury. We demonstrated the beneficial effects of three days of fasting, a 3-day protein-free diet as well as a 3-day essential amino acid-free diet on renal and hepatic ischemia-reperfusion injury (IRI) as well as on chemotherapy induced toxicity, and linked the phenotypical protective response to a differentiated network of pathways and transcription factors on a transcriptional level. We successfully translated the preclinical data to a safe, feasible and effective diet in living kidney donors and their kidney transplant recipients, and showed that it improves graft outcome and function. These data show a unique comprehensive picture of the effects of nutritional preconditioning from a phenotypical, transcriptional and clinical point of view, and has brought us a step further to develop the optimal preoperative DR strategy in an elective clinical setting. We showed that the beneficial effects of three days of fasting on IRI can be reproduced in an animal model that represents human aging and obesity. The effects of DR were more pronounced in young-lean mice and female mice were able to resist longer periods of renal IRI, indicating that the intensity of stress resistance is dependent on factors as age, body weight and gender. Future studies including a large cohort of female and male mice of different ages and body weights, could point us further towards understand the extent of which these factors play a role in the protection. As a result, factors including age, body weight and gender should be held into account when applying DR in the clinic, and future studies should include a sufficient number of patients to correct for and investigate the exact role of these factors. As described, the protective effects of a short-term fasting regimen could also be applied to reduce the adverse effects of chemotherapy 56 . Since fasting did not affect the antitumor efficacy of chemotherapy treatment, the concept of differential stress sensitization (DSS) was confirmed in our studies 42 . Huisman et al. proposed the role of phase II proteins in the increased stress resistance in normal cells, including NRF2 and upregulation of xenobiotic metabolism 41 . We could partially verify this hypothesis with the activation of the NRF2 stress response in healthy liver cells, whereas the transcriptional changes as seen in the liver did not occur in tumor tissue. The role of NRF2 as sole contributor to the beneficial effects of fasting on stress resistance has not yet been demonstrated 26 . Extending the experimental setup to different chemotherapeutics, larger groups and various time points of analysis could further elucidate the mechanisms responsible for this DSS. As a consequence, higher dosages of chemotherapeutics might be applied in the near future, thereby increasing the chance of an effective treatment for cancer and survival benefits in cancer patients.