High chronic fructose consumption is linked to a nonalcoholic steatohepatitis (NASH) type of hepatotoxicity. Oxalate is the major endpoint of fructose metabolism, which accumulates in the kidney causing renal stone disease. Both diseases are life-threatening if not treated. Our objective was to study the molecular cytotoxicity mechanisms of fructose and some of its metabolites in the liver. Fructose metabolites were incubated with primary rat hepatocytes, but cytotoxicity only occurred if the hepatocytes were exposed to non-toxic amounts of hydrogen peroxide such as those released by activated immune cells. Glyoxal was most likely the endogenous toxin responsible for fructose induced toxicity formed via autoxidation of the fructose metabolite glycolaldehyde catalyzed by superoxide radicals, or oxidation by Fenton’s hydroxyl radicals. As for hyperoxaluria, glyoxylate was more cytotoxic than oxalate presumably because of the formation of condensation product oxalomalate causing mitochondrial toxicity and oxidative stress. Oxalate toxicity likely involved pro-oxidant iron complex formation.

High chronic fructose consumption is linked to a nonalcoholic steatohepatitis (NASH) type of hepatotoxicity. Oxalate is the major endpoint of fructose metabolism, which accumulates in the kidney causing renal stone disease. Both diseases are life-threatening if not treated. Our objective was to study the molecular cytotoxicity mechanisms of fructose and some of its metabolites in the liver. Fructose metabolites were incubated with primary rat hepatocytes, but cytotoxicity only occurred if the hepatocytes were exposed to non-toxic amounts of hydrogen peroxide such as those released by activated immune cells. Glyoxal was most likely the endogenous toxin responsible for fructose induced toxicity formed via autoxidation of the fructose metabolite glycolaldehyde catalyzed by superoxide radicals, or oxidation by Fenton’s hydroxyl radicals. As for hyperoxaluria, glyoxylate was more cytotoxic than oxalate presumably because of the formation of condensation product oxalomalate causing mitochondrial toxicity and oxidative stress. Oxalate toxicity likely involved pro-oxidant iron complex formation.

L’hyperoxalurie primitive de type 1 (ou HP1) est une maladie héréditaire du métabolisme liée à un déficit en enzyme hépatocytaire AGT (alanine:glyoxylate aminotransférase), codée par le gène AGXT. Ce déficit entraîne, chez les patients atteints d’HP1, une excrétion hépatique accrue d’oxalate ; celui-ci est ensuite éliminé dans les urines où il se complexe avec le calcium pour former des néphrolithiases oxalo-calciques massives, pouvant conduire à une insuffisance rénale chronique. Le seul traitement curatif disponible pour cette pathologie est la greffe allogénique combinée hépatorénale, actuellement limitée par la disponibilité des donneurs de greffons, une morbi-mortalité significative et la nécessité d’un traitement immunosuppresseur au long cours. L’objectif du projet de recherche est de développer une thérapie génique de l’HP1 par greffe de cellules hépatiques autologues génétiquement corrigées. La faible disponibilité et la difficulté d’amplification in vitro des hépatocytes adultes nous a conduit à explorer la piste des cellules souches pluripotentes induites (iPSCs) pour produire des cellules hépatiques humaines utilisables en médecine régénérative. Nous avons dérivé et caractérisé des lignées de cellules iPSCs à partir de fibroblastes de patients atteints d’HP1, après expression transitoire des facteurs de reprogrammation par des vecteurs Sendai. Nous avons développé deux stratégies de thérapie génique additive par insertion d’un minigène codant une séquence optimisée de l’ADNc AGXT au moyen (1) d’un vecteur lentiviral à expression hépato-spécifique et (2) d’un processus de recombinaison homologue au locus AAVS1 facilité par le système de clivage ciblé de l’ADN « CRISPR/Cas9 ». Enfin, nous avons mis en évidence l’expression de la cassette thérapeutique après différenciation hépatocytaire des iPSCs génétiquement corrigées. Ces résultats ouvrent de nouvelles perspectives de médecine régénérative pour l’HP1 par transplantation de cellules hépatocytaires autologues génétiquement corrigées dérivées d’iPSCs de patients. / Primary hyperoxaluria type 1 (or PH1) is an inherited metabolic disorder related to the deficiency of the hepatic AGT enzyme (alanine:glyoxylate aminotransferase), which is encoded by the AGXT gene. In PH1 patients, this deficiency leads to oxalate overexcretion by liver, followed by urine filtration and complexation with calcium to form massive calcium-oxalate nephrolithiasis potentially leading to chronic renal failure. The only available curative treatment is combined hepatorenal allogeneic engraftment, which is currently limited by the availability of transplant donors, significant morbidity and mortality, and the need for long-term immunosuppressive treatment. The aim of our research project is to develop gene therapy for PH1, consisting in engraftment of genetically corrected autologous liver cells. Considering that adult hepatocytes are hardly available and expandable in vitro, we chose to explore the use of induced pluripotent stem cells (iPSCs) to produce human liver cells for application in regenerative medicine. We derived and characterized iPSC lines from PH1 patient fibroblasts after transient expression of reprogramming factors delivered by Sendai virus vectors. We developed two additive gene therapy strategies by inserting a minigene encoding an optimized AGXT cDNA sequence using (1) a lentiviral vector designed for liver-specific expression and (2) homologous recombination process at the AAVS1 locus favoured by the targeted DNA cutting system “CRISPR/Cas9”. Finally, we highlighted therapeutic cassette expression after hepatic differentiation of genetically corrected iPSCs. These results pave the way for regenerative medicine for PH1 by transplantation of genetically modified autologous hepatocyte-like cells derived from patient-specific iPSCs.

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