Beneficial effect of ursodeoxycholic acid in patients with acyl‐CoA oxidase 2 (ACOX2) deficiency–associated hypertransaminasemia

Abstract

Background and Aims: A variant (p.Arg225Trp) of peroxisomal acyl-CoA oxidase 2 (ACOX2), involved in bile acid (BA) side-chain shortening, has been associated with unexplained persistent hypertransaminasemia and accumulation of C27-BAs, mainly 3α,7α,12α-trihydroxy-5β-cholestanoic acid (THCA).We aimed to investigate the prevalence of ACOX2 deficiency-associated hypertransaminasemia (ADAH), its response to ursodeoxycholic acid (UDCA), elucidate its pathophysiological mechanism and identify other inborn errors that could cause this alteration.Methods and Results: Among 33 patients with unexplained hypertransaminasemia from 11 hospitals and 13 of their relatives, seven individuals with abnormally high C27-BA levels (>50% of total BAs) were identified by highperformance liquid chromatography-mass spectrometry. The p.Arg225Trp variant was found in homozygosity (exon amplification/sequencing) in two patients and three family members. Two additional nonrelated patients were heterozygous carriers of different alleles: c.673C>T (p.Arg225Trp) and c.456_459del (p.Thr154fs). In patients with ADAH, impaired liver expression of ACOX2, but not ACOX3, was found (immunohistochemistry). Treatment with UDCA normalized aminotransferase levels. Incubation of HuH-7 hepatoma cells with THCA, which was efficiently taken up, but not through BA transporters, increased reactive oxygen species production (flow cytometry), endoplasmic reticulum stress biomarkers (GRP78, CHOP, and XBP1-S/XBP1-U ratio), and BAXα expression (reverse transcription followed by quantitative polymerase chain reaction and immunoblot), whereas cell viability was decreased (tetrazolium salt-based cell viability test). THCA-induced cell toxicity was higher than that of major C24-BAs and was not prevented by UDCA.Fourteen predicted ACOX2 variants were generated (site-directed mutagenesis) and expressed in HuH-7 cells. Functional tests to determine their ability to metabolize THCA identified six with the potential to cause ADAH.Conclusions: Dysfunctional ACOX2 has been found in several patients with unexplained hypertransaminasemia. This condition can be accurately identified by a noninvasive diagnostic strategy based on plasma BA profiling and ACOX2 sequencing. Moreover, UDCA treatment can efficiently attenuate liver damage in these patients.

Cholestasis associated to inborn errors in bile acid synthesis

“…A more recent study has detected a new mutation and identified several mutations with a potential dysfunctional impact on ACOX2 activity. Moreover, in two patients, the coexistence of two different mutations in heterozygosis but on different alleles also resulted in metabolic disorder leading to C27-BA accumulation [72]. Interestingly, this study revealed that patients with ACOX2 deficiency-associated hypertransaminasemia (ADAH) could benefit from treatment with UDCA, which normalizes serum levels of aminotransferases [72].…”

“…Moreover, in two patients, the coexistence of two different mutations in heterozygosis but on different alleles also resulted in metabolic disorder leading to C27-BA accumulation [72]. Interestingly, this study revealed that patients with ACOX2 deficiency-associated hypertransaminasemia (ADAH) could benefit from treatment with UDCA, which normalizes serum levels of aminotransferases [72]. Two Acox2 knockout mice models have recently been reported.…”

Etiopathogenesis and pathophysiology of cholestasis

“…Thus, the existence of inborn errors in bile acid metabolism leading to the generation of molecular species with unsaturated steroid ring and non-shortened sidechain (C27-bile acids) able to impair hepatocyte function has been described. Inhibition of de novo synthesis with endogenous C24-bile acids together with the hepatoprotective activity of ursodeoxycholic acid (UDCA) could be beneficial in these patients (Figure 2) [118].…”

“…In the case of impaired bile secretion due to the accumulation of cholestatic bile acid species, since the secretory machinery is not constitutively impaired but only inhibited, the pharmacological correction of the altered metabolic pathway restores the function. Moreover, intestinal sequestering of endogenous bile acids using resin cholestyramine [119] or dilution of the secreted by treatment with exogenous UDCA [118] have been reported as strategies to reduce the signs of liver damage. Next-generation sequencing has allowed identifying several very infrequent forms of PFIC.…”

Impact of Liver Inflammation on Bile Acid Side Chain Shortening and Amidation

“…This condition can be accurately identified by a noninvasive diagnostic strategy based on plasma BA profiling, characterized by the predominance of C27-BA intermediates, and ACOX2 sequencing. Ursodeoxycholic acid (UDCA) treatment seems to efficiently attenuate liver damage in these patients [ 29 ]. Whether there is a link between ACOX2 expression and liver inflammation is unknown.…”