Matrix metalloproteinase-9 in fulminant hepatic failure

Abstract

We read with interest the article by Chen et al.,1 who found altered expression of several tight junction (TJ) proteins in cultured brain endothelial cells and brain from mice with acute liver failure (ALF) and relate these abnormalities to the activation of matrix metalloproteinase-9 (MMP-9). The results are in accordance to prior data in the same animal model of toxic liver injury (azoxymethane).2 Their findings led to the proposal that MMP-9 released by the necrotic liver could alter the expression of TJ proteins and cause blood-brain barrier (BBB) leakage and brain swelling.3 The hypothesis is interesting because it could result in new treatments for this severe complication of fulminant hepatic failure (FHF). To further explore the relevance of this hypothesis, we determined the plasmatic levels of MMP-9 (via enzyme-linked immunosorbent assay) in 32 patients with FHF and compared the values to those obtained in 11 patients with acute hepatitis A and 20 patients with advanced (Child class B/C) hepatic cirrhosis with or without hepatic encephalopathy. During the follow-up of patients with FHF, intracranial hypertension was diagnosed in 14 patients (confirmed by intracranial pressure monitor in 13). We found high levels of MMP-9 compared to normal reference values in all group of patients (Fig. 1). Patients with acute liver injury (FHF or acute hepatitis A) showed higher values than those with chronic liver failure (cirrhosis). There was no association between MMP-9 and intracranial hypertension. Plasmatic levels of MMP-9 as determined by an enzyme-linked immunosorbent assay. FHF, fulminant hepatic failure; HC, hepatic cirrhosis; HE, hepatic encephalopathy; ICH, intracranial hypertension. *Compared to controls. #Compared to HC with or without HE. The presence of high levels of MMP-9 in our patients can be explained by remodeling liver parenchyma during acute and chronic liver injury.4 The lack of relationship with intracranial hypertension does not invalidate that MMP-9 can cause disturbances of TJ proteins. However, our results are in accordance with a series of data indicating that brain edema in FHF is mostly secondary to cytotoxic mechanisms. In vasogenic edema, brain swelling relates to leakage of the BBB and develops in the extracellular compartment. In comparison, cytotoxic edema develops secondary to osmotic differences across the BBB or energy failure and causes accumulation of water in the intracellular compartment. Most available data indicate that the BBB is grossly intact in FHF.5 Magnetic resonance shows a decrease in the apparent diffusion coefficient in humans6 and in rats,7 which is in accordance with an increase of water in the intracellular compartment. Our findings indicate that MMP-9 is increased in the plasma of patients with FHF, but does not participate in the pathogenesis of brain edema. MMPs are big molecules that must cross the BBB to exert their function in brain tissue. In patients and experimental models of stroke, the effects of MMPs are associated with neutrophil infiltration that may carry some of those MMPs in their tertiary granules.8 In previous neuropathological studies, no signs of neutrophil infiltration were detected in patients with FHF.5 Recently, Bémeur et al.9 performed a study in mice with azoxymethane-induced ALF, where they strictly controlled the temperature (a factor that affects the outcome of this model) and could not detect immunoglobulin G extravasation, in accordance with BBB integrity. Lluis Palenzuela Ph.D.* , Antoni Mas M.D. §, Joan Montaner M.D. , Juan Cordoba M.D.* §, * Liver Unit and Institut de Recerca, Hospital Universitari Vall d'Hebron, Barcelona, Spain, Neurovascular Research Laboratory, Hospital Universitari Vall d'Hebron, Barcelona, Spain, Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas (CIBEREHD), Instituto de Salud Carlos III, Madrid, Spain, § Liver Unit and Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Hospital Clinic i Provincial, Barcelona, Spain.