A Liver-Specific Defect of Acyl-CoA Degradation Produces Hyperammonemia, Hypoglycemia and a Distinct Hepatic Acyl-CoA Pattern

Nicolas Gauthier,Shu Pei Wang,Fernando Alvarez,Lawrence Sweetman,Yves Robitaille,Pierre Allard,Grant A Mitchell,Orval A Mamer,Lisa Kratz,Jiang Wei Wu,François Lépine,Ann B Moser

doi:10.1371/journal.pone.0060581

Abstract

Most conditions detected by expanded newborn screening result from deficiency of one of the enzymes that degrade acyl-coenzyme A (CoA) esters in mitochondria. The role of acyl-CoAs in the pathophysiology of these disorders is poorly understood, in part because CoA esters are intracellular and samples are not generally available from human patients. We created a mouse model of one such condition, deficiency of 3-hydroxy-3-methylglutaryl-CoA lyase (HL), in liver (HLLKO mice). HL catalyses a reaction of ketone body synthesis and of leucine degradation. Chronic HL deficiency and acute crises each produced distinct abnormal liver acyl-CoA patterns, which would not be predictable from levels of urine organic acids and plasma acylcarnitines. In HLLKO hepatocytes, ketogenesis was undetectable. Carboxylation of [2-14C] pyruvate diminished following incubation of HLLKO hepatocytes with the leucine metabolite 2-ketoisocaproate (KIC). HLLKO mice also had suppression of the normal hyperglycemic response to a systemic pyruvate load, a measure of gluconeogenesis. Hyperammonemia and hypoglycemia, cardinal features of many inborn errors of acyl-CoA metabolism, occurred spontaneously in some HLLKO mice and were inducible by administering KIC. KIC loading also increased levels of several leucine-related acyl-CoAs and reduced acetyl-CoA levels. Ultrastructurally, hepatocyte mitochondria of KIC-treated HLLKO mice show marked swelling. KIC-induced hyperammonemia improved following administration of carglumate (N-carbamyl-L-glutamic acid), which substitutes for the product of an acetyl-CoA-dependent reaction essential for urea cycle function, demonstrating an acyl-CoA-related mechanism for this complication.

Highlights

Much of the intermediary metabolism of proteins and fatty acids proceeds by the sequential oxidation of acyl-CoAs, and most of the conditions detected by expanded newborn blood screening are caused by deficiency of one of the many intramitochondrial enzymes that normally degrade acyl-CoAs
hydroxy-3-methylglutaryl-CoA lyase (HL) protein was undetectable in hepatocyte mitochondria from HL liver knockout (HLLKO) mice but was clearly present in control hepatocytes (Figure 2d)
HLLKO mice have many features of human inborn errors of acyl-CoA metabolism and show that liver is critical for the development of these signs

Summary

Introduction

Much of the intermediary metabolism of proteins and fatty acids proceeds by the sequential oxidation of acyl-CoAs, and most of the conditions detected by expanded newborn blood screening are caused by deficiency of one of the many intramitochondrial enzymes that normally degrade acyl-CoAs. Examples include methylmalonic, propionic, isovaleric and 3-hydroxy-3-methylglutaric acidemias. Each condition can present a complex and distinct array of manifestations. Many of these conditions have in common a state of chronic illness with acute and potentially fatal episodes of lethargy, coma, hypoglycemia and hyperammonemia. Key acyl-CoAs, acetyl-CoA, are critical for normal function of the urea cycle [1], the Krebs cycle [2] and for acetylation and regulation of many metabolites and proteins [3].

Methods

Results

Conclusion