P: 79 Central Inhibition of IGFBP3 Attenuates Symptoms of Hepatic Encephalopathy in a Mouse Model of Acute Liver Failure

Abstract

BACKGROUND: Insulin-like growth factor binding protein 3 (IGFBP3) has a strong binding affinity for IGF proteins and can inhibit the function of IGF by preventing interaction with its receptor. In addition, IGFBP3 can exert IGF-independent effects via direct interaction with a putative IGFBP3 receptor. Little is known about the function of IGFBP3 in the brain, outside of a role in brain cancer development. We have recently demonstrated that IGF1 expression is suppressed in the frontal cortex in a number of rodent models of hepatic encephalopathy (HE) and central administration of recombinant IGF1 attenuates the neurological complications. However, the role of IGFBP3 in the pathogenesis of HE is unknown and is the aim of this study. METHODS: C57Bl/6 mice were injected with azoxymethane (AOM) to induce acute liver failure and HE. In parallel, mice were given an intracerebroventricular infusion of the IGFBP inhibitor, NBI31772 for 3 days prior to AOM injection. Cognitive impairment was monitored by reflex response assessment at various time points and neuromuscular deficits were assessed using a grip strength meter. Liver damage was determined by H&E staining and serum chemistry. The expression of IGFBP3 and IGF1 was assessed in the cortex by qPCR, EIA and immunofluorescence using NeuN (neuronal), GFAP (astrocytic) or Iba1 (microglial) antibodies as a counterstain. Microglia activation was evaluated by assessment of field Iba1 staining and microglia cell morphology. Neuroinflammation was also measured by the expression of key proinflammatory cytokines. RESULTS: IGFBP3 was predominantly expressed in neurons of the cortex and increased once significant neurological deficits were observed after AOM injection. Pretreatment of mice with the IGFBP inhibitor had no effect on the underlying liver damage, but delayed the onset of neurological symptoms, attenuated the neuromuscular deficits, inhibited neuroinflammation and increased the bioavailability of the neuroprotective IGF1 after AOM injection, suggesting that IGFBP3 may be contributing to the pathogenesis of HE. CONCLUSIONS: Elevated cortical IGFBP3 expression contributes to the pathogenesis of HE in AOM-treated mice via a mechanism that may involve increasing IGF1 bioavailability, although IGF1-independent effects can not be ruled out. Targeting IGFBP3 in the cortex may prove promising for the development of adjunct therapies to manage the neurological complications of acute liver failure.