Retinol-binding protein 4 and peroxisome proliferator-activated receptor-γ in steatotic liver transplantation

Numerous steatotic livers are discarded for transplantation because of their poor tolerance of ischemia-reperfusion (I/R). The injurious effects of retinol-binding protein 4 (RBP4) in various pathologies are well documented. RBP4 levels are reduced by peroxisome proliferator-activated receptor-γ (PPARγ) agonists. Strategies aimed at increasing PPARγ protect steatotic livers under warm ischemia. Ischemic preconditioning (PC) based on brief periods of I/R protects steatotic liver grafts against I/R injury, but the responsible mechanism is poorly understood. We examined the roles of RBP4 and PPARγ in I/R injury associated with steatotic liver transplantation and the benefits of PC in such situations. We report that RBP4 and PPARγ expression levels in nonsteatotic livers were similar to those found in the sham group. However, reduced RBP4 and increased PPARγ levels were observed in steatotic livers. Treatment with either RBP4 or a PPARγ antagonist was effective only in steatotic livers. PC, which increased RBP4 levels, and RBP4 treatment both reduced PPARγ levels and hepatic injury in steatotic livers. When PPARγ was activated, neither RBP4 treatment nor PC (despite RBP4 induction) protected steatotic livers. In conclusion, steatotic liver grafts are more predisposed to down-regulate RBP4 and overexpress PPARγ. RBP4 treatment and PC, through RBP4 induction, reduced PPARγ levels in steatotic liver grafts, thus protecting them from the PPARγ detrimental effects.

Endoplasmic reticulum stress inhibition protects steatotic and non-steatotic livers in partial hepatectomy under ischemia-reperfusion

During partial hepatectomy, ischemia–reperfusion (I/R) is commonly applied in clinical practice to reduce blood flow. Steatotic livers show impaired regenerative response and reduced tolerance to hepatic injury. We examined the effects of tauroursodeoxycholic acid (TUDCA) and 4-phenyl butyric acid (PBA) in steatotic and non-steatotic livers during partial hepatectomy under I/R (PH+I/R). Their effects on the induction of unfolded protein response (UPR) and endoplasmic reticulum (ER) stress were also evaluated. We report that PBA, and especially TUDCA, reduced inflammation, apoptosis and necrosis, and improved liver regeneration in both liver types. Both compounds, especially TUDCA, protected both liver types against ER damage, as they reduced the activation of two of the three pathways of UPR (namely inositol-requiring enzyme and PKR-like ER kinase) and their target molecules caspase 12, c-Jun N-terminal kinase and C/EBP homologous protein-10. Only TUDCA, possibly mediated by extracellular signal-regulated kinase upregulation, inactivated glycogen synthase kinase-3β. This is turn, inactivated mitochondrial voltage-dependent anion channel, reduced cytochrome c release from the mitochondria and caspase 9 activation and protected both liver types against mitochondrial damage. These findings indicate that chemical chaperones, especially TUDCA, could protect steatotic and non-steatotic livers against injury and regeneration failure after PH+I/R.

Insulin-like growth factor and epidermal growth factor treatment: new approaches to protecting steatotic livers against ischemia-reperfusion injury

Hepatic steatosis is a major risk factor in ischemia-reperfusion (I/R). IGF-binding proteins (IGFBPs) modulate IGF-I action by transporting circulating IGF-I to its sites of action. Epidermal growth factor (EGF) stimulates IGF-I synthesis in vitro. We examined the effect of IGF-I and EGF treatment, separately or in combination, on the vulnerability of steatotic livers to I/R. Our results indicated that I/R impaired IGF-I synthesis only in steatotic livers. Only when a high dose of IGF-I (400 microg/kg) was given to obese animals did they show high circulating IGF-I:IGFBP levels, increased hepatic IGF-I levels, and protection against damage. In lean animals, a dose of 100 microg/kg IGF-I protected nonsteatotic livers. Our results indicated that the combined administration of IGF-I and EGF resulted in hepatic injury parameters in both liver types similar to that obtained by IGF-I and EGF separately. IGF-I increased egf expression in both liver types. The beneficial role of EGF on hepatic I/R injury may be attributable to p38 inhibition in nonsteatotic livers and to PPAR gamma overexpression in steatotic livers. In conclusion, IGF-I and EGF may constitute new pharmacological strategies to reduce the inherent susceptibility of steatotic livers to I/R injury.