Hepatic encephalopathy and orotic aciduria associated with hepatocellular carcinoma in a noncirrhotic liver

Molecular Basis of Hyperammonemic Encephalopathy in Fibrolamellar Hepatocellular Carcinoma

Hyperammonemic encephalopathy is a potentially fatal condition associated with fibrolamellar hepatocellular carcinoma. The mechanism involved in hyperammonemia in patients with fibrolamellar carcinoma was unclear until a possible physiopathological pathway was recently proposed. An ornithine transcarboxylase dysfunction was suggested as a result of increased ornithine decarboxylase activity induced by c-Myc overexpression. This c-Myc overexpression resulted from Aurora kinase A overexpression derived from the activity of a chimeric kinase that is the final transcript of a deletion in chromosome 19, common to all fibrolamellar carcinomas. We performed the analysis of the expression of all enzymes involved and tested for the mutation in chromosome 19 in fresh frozen samples of fibrolamellar hepatocellular carcinoma, non-tumor liver, and hepatic adenomatosis. The specific DNAJB-PRKACA fusion protein that results from the recurrent mutation on chromosome 19 common to all fibrolamellar carcinoma was detected only in the fibrolamellar carcinoma sample. Fibrolamellar carcinoma and adenomyomatosis samples presented increased expression of Aurora kinase A, c-MYC, and ornithine decarboxylase when compared to normal liver, while ornithine transcarbamylase was decreased. The proposed physiopathological pathway is correct and that overexpression of c-Myc may also be responsible for hyperammonemia in patients with other types of rapidly growing hepatomas. This gives further evidence to apply new and adequate treatment to this severe complication.

Overview of organic anion transporters and organic anion transporter polypeptides and their roles in the liver

Organic anion transporters (OATs) and organic anion transporter polypeptides (OATPs) are classified within two SLC superfamilies, namely, the SLC22A superfamily and the SLCO superfamily (formerly the SLC21A family), respectively. They are expressed in many tissues, such as the liver and kidney, and mediate the absorption and excretion of many endogenous and exogenous substances, including various drugs. Most are composed of 12 transmembrane polypeptide chains with the C-terminus and the N-terminus located in the cell cytoplasm. OATs and OATPs are abundantly expressed in the liver, where they mainly promote the uptake of various endogenous substrates such as bile acids and various exogenous drugs such as antifibrotic and anticancer drugs. However, differences in the locations of glycosylation sites, phosphorylation sites, and amino acids in the OAT and OATP structures lead to different substrates being transported to the liver, which ultimately results in their different roles in the liver. To date, few articles have addressed these aspects of OAT and OATP structures, and we study further the similarities and differences in their structures, tissue distribution, substrates, and roles in liver diseases.

Encéphalopathie hyperammoniémique en Réanimation adulte : à propos de deux observations cliniques

L’hyperammoniémie est un trouble métabolique induit par un excès d’ammoniac plasmatique. La toxicité nerveuse de l’ammoniac peut entraîner une encéphalopathie d’aggravation rapide, avec risque de décès par oedème cérébral irréversible. En Réanimation adulte, lorsque l’hyperammoniémie n’est pas en lien avec une insuffisance hépatocellulaire aiguë, d’autres causes plus rares doivent être recherchées, incluant un déficit enzymatique du cycle de l’urée (urea cycle disorder [UCD]) de révélation tardive. C’est le bilan métabolique qui permettra de distinguer une hyperammoniémie primitive, par déficit enzymatique du cycle de l’urée, d’une hyperammoniémie secondaire. Nous rapportons les cas de deux patients pris en charge en Réanimation adulte pour encéphalopathie hyperammoniémique majeure révélatrice d’un déficit du cycle de l’urée dans un cas (acidurie argininosuccinique) et secondaire aux localisations hépatiques d’une tumeur dans l’autre cas. Nous souhaitons rappeler ici la démarche rigoureuse pour parvenir au diagnostic ainsi que la prise en charge thérapeutique spécifique de ces situations.

Acquired ornithine transcarbamylase deficiency in pediatric and adolescent patients with fibrolamellar hepatocellular carcinoma

Ornithine transcarbamylase deficiency (OTCD) disrupts the metabolic pathway responsible for converting nitrogenous waste to urea, allowing for excretion. When impaired, ammonia levels accumulate in the blood resulting in severe, sometimes life-threatening toxicities. Abnormalities of the urea cycle are often inherited, though there are some rarer acquired forms. We describe two cases of acquired OTCD in pediatric patients with fibrolamellar hepatocellular carcinoma (FL-HCC). We detail its presentation and management, explore potential underlying pathophysiology, and propose a practice change to optimize care of FL-HCC patients.

Liver involvement in urea cycle disorders: a review of the literature

Urea cycle disorders (UCDs) are inborn errors of metabolism of the nitrogen detoxification pathway and encompass six principal enzymatic deficiencies. The aging of UCD patients leads to a better knowledge of the long-term natural history of the condition and to the reporting of previously unnoticed manifestations. Despite historical evidence of liver involvement in UCDs, little attention has been paid to this organ until recently. Hence, we reviewed the available scientific evidence on acute and chronic liver dysfunction and liver carcinogenesis in UCDs and discuss their pathophysiology. Overall, liver involvement, such as acute liver failure or steatotic-like disease, which may evolve toward cirrhosis, has been reported in all six main UCDs. Excessive glycogen storage is also a prominent histologic feature, and hypoglycemia has been reported in citrin deficiency. Hepatocarcinomas seem frequent in some UCDs, such as in citrin deficiency, and can sometimes occur in non-cirrhotic patients. UCDs may differ in liver involvement according to the enzymatic deficiency. Ornithine transcarbamylase deficiency may be associated more with acute liver failure and argininosuccinic aciduria with chronic liver failure and cirrhosis. Direct toxicity of metabolites, downstream metabolic deficiencies, impaired tricarboxylic acid cycle, oxidative stress, mitochondrial dysfunction, energy deficit, and putative toxicity of therapies combine in various ways to cause the different liver diseases reported.

Efficacy of N-carbamoyl-L-glutamic acid for the treatment of inherited metabolic disorders

INTRODUCTION

N-carbamoyl-L-glutamic acid (NCG) is a synthetic analogue of N-acetyl glutamate (NAG) that works effectively as a cofactor for carbamoyl phosphate synthase 1 and enhances ureagenesis by activating the urea cycle. NCG (brand name, Carbaglu) was recently approved by the United States Food and Drug Administration (US FDA) for the management of NAGS deficiency and by the European Medicines Agency (EMA) for the treatment of NAGS deficiency as well as for the treatment of hyperammonenia in propionic, methylmalonic and isovaleric acidemias in Europe.

AREAS COVERED

The history, mechanism of action, and efficacy of this new drug are described. Moreover, clinical utility of NCG in a variety of inborn errors of metabolism with secondary NAGS deficiency is discussed.

EXPERT COMMENTARY

NCG has favorable pharmacological features including better bioavailability compared to NAG. The clinical use of NCG has proven to be so effective as to make dietary protein restriction unnecessary for patients with NAGS deficiency. It has been also demonstrated to be effective for hyperammonemia secondary to other types of inborn errors of metabolism. NCG may have additional therapeutic potential in conditions such as hepatic hyperammonemic encephalopathy secondary to chemotherapies or other liver pathology.

Hyperammonemic encephalopathy in an adenocarcinoma patient managed with carglumic acid

Hyperammonemic encephalopathy (he) is a rare complication of malignancy and chemotherapy. Although the cause of he is unclear, a functional arginine deficiency secondary to increased catabolism has been suggested as a possible mechanism. Either that deficiency or an undetermined metabolite could lead to inhibition of N-acetylglutamate synthase (nags), a urea cycle enzyme, resulting in hyperammonemia. We present a case of chemotherapy-induced he in a patient with no underlying primary urea cycle disorder. The patient had a successful trial of carglumic acid (a synthetic analog of the product of nags), which suggests that, at least in some cases, he can be treated by overcoming proximal inhibition of the urea cycle. Further, our case is the first in the literature to exclude genetic defects and disorders of the proximal urea cycle, suggesting that hyperammonemia in these patients is probably secondary to chemotherapy.

Fibrolamellar hepatocellular carcinoma mimicking ornithine transcarbamylase deficiency

We report an unusual case of recurrent non-hepatic hyperammonaemic encephalopathy in an adult patient. She had a previous history of treated fibrolamellar hepatocellular carcinoma (FLC). This posed a diagnostic challenge, as she had normal liver function tests and normal looking liver on imaging but with extra hepatic metastases. This case highlights the importance of measuring plasma ammonia levels in all patients presenting with unexplained acute confusion. Clinical awareness of non-hepatic hyperammonaemic encephalopathy can contribute to early diagnosis and timely initiation of life-saving treatment. Delay in treatment results in irreversible brain damage, deep coma and death. Treatment of hyperammonaemia must begin prior to confirmation of aetiology, for a favourable outcome. This case also highlights the need for further research to understand the exact mechanism of hyperammonaemia in hepatocellular carcinoma.

Mitochondrial metabolism in the noncancerous liver determine the occurrence of hepatocellular carcinoma: a prospective study

BACKGROUND

Recurrence determines the postoperative prognosis with hepatocellular carcinoma (HCC). It is unknown how the liver dysfunction involving organic anion transporter failure causes the occurrence of HCCs. This study was designed to elucidate the link between liver dysfunction and multicentric occurrence (MO) after radical hepatectomy.

METHODS

Forty-nine samples of noncancerous liver tissue from HCC patients within the Milan criteria who were treated at our institution between January 2004 and August 2008 were examined as a training set by using genome-wide gene expression analysis. Using the independent 2-institutional cohort of 134 patients between September 2008 and December 2009, we performed a validation study using tissue microarray analysis. Cox proportional hazard regression analyses for MFS were performed to estimate the risk factors.

RESULTS

In the Gene Ontology database (GO:0015711), SLC22A7 expression was the best predictor of MO-free survival [MFS] (Fold, 0.726; P = 0.001). High SLC22A7 gene expression prevented the occurrence of HCC after hepatectomy (odds ratio [OR], 0.2; P = 0.004). Multivariate analyses identified SLC22A7 expression as an independent risk factor (OR, 0.3; P = 0.043). In the validation study, multivariate analyses of MFS identified SLC22A7 expression as an independent risk factor (OR, 0.5; P = 0.012). As judged by gene set enrichment analysis, SLC22A7 down regulation was associated with mitochondrion (P = 0.008) and oxidoreductase activity (P = 0.006). Sirtuin 3 as a regulator of mitochondrial metabolism also determined MFS (P = 0.018).

CONCLUSIONS

The mitochondrial pathways may affect SLC 22A7 function to promote the occurrence of HCC. (Word count: 246).

Reduced organic anion transporter expression is a risk factor for hepatocellular carcinoma in chronic hepatitis C patients: a propensity score matching study

OBJECTIVES

Recent reports indicated that reduced SLC22A7 (a gene-encoding organic anion transporter 2) expression in noncancerous liver tissue predicts hepatocellular carcinoma (HCC) recurrence after curative resection. Our study aimed to elucidate the association between SLC22A7 expression and HCC development in chronic hepatitis C patients.

METHODS

HCC recurrence after local ablation therapy and SLC22A7 expression in noncancerous liver tissue were analyzed in 20 patients. Subsequently, the association between de novo HCC development and SLC22A7 expression was examined at baseline in 38 hepatitis C patients without HCC who subsequently developed HCC as well as in 76 hepatitis C patients who did not develop HCC and were matched for age, gender and stage of fibrosis.

RESULTS

In the patients whose HCC had been cured, reduced SLC22A7 expression in noncancerous liver tissue was significantly associated with a high incidence of multifocal HCC recurrence. In patients without HCC at baseline, cumulative incidence of de novo HCC development was significantly higher with a reduced SLC22A7 expression than with a normal expression (p = 0.01). This difference remained significant among patients without known risk factors for HCC like age and advanced fibrosis.

CONCLUSION

Reduced SLC22A7 expression in the liver indicates a significant risk for HCC development in chronic hepatitis C, independently of other risk factors.

Postchemotherapy hyperammonemic encephalopathy emulating ornithine transcarbamoylase (OTC) deficiency

A young patient with hepatocellular carcinoma receiving chemotherapy presented with encephalopathy. Evaluation of the patient revealed a metabolic profile consistent with ornithine transcarbamoylase (OTC) deficiency, an inherited disorder of the urea cycle. The evaluation yielded a plasma amino acid analysis consistent with OTC deficiency. However, genetic analysis did not reveal a somatic mutation of the OTC gene in this patient. The hyperammonemic encephalopathy was reversed by the infusion of arginine, a common treatment for hereditary OTC deficiency. This case may represent a distinct syndrome of reversible hyperammonemia in patients with hepatocellular carcinoma.

Diagnostic value of urinary orotic acid levels: applicable separation methods

Urinary orotic acid determination is a useful tool for screening hereditary orotic aciduria and for differentiating the hyperammonemia disorders which cannot be readily diagnosed by amino acid chromatography, thus reducing the need for enzyme determination in tissue biopsies. This review provides an overview of metabolic aberrations that may be related to increased orotic acid levels in urine, and summarises published methods for separation, identification and quantitative determination of orotic acid in urine samples. Applications of high-performance liquid chromatography, gas chromatography, and capillary electrophoresis to the analysis of urinary specimens are described. The advantages and limitations of these separation and identification methodologies as well as other less frequently employed techniques are assessed and discussed.

The effects of various inhibitors on the regulation of orotic acid excretion in sparse-fur mutant mice (spf/Y) deficient in ornithine transcarbamylase

Experiments were conducted to determine whether the excessive orotic aciduria, induced in sparse-fur male mice (spf/Y) deficient in ornithine transcarbamylase (OTC), may be regulated by some inhibitors, such as acivicin (0.014 mmol/100 g body weight, i.p.), N-(phosphonoacetyl)-L-aspartate (PALA, 2.5 mg/100 g body weight, i.p.), adenine (3 g/kg diet) and cycloheximide (0.35 mmol/kg body weight, i.p.). We also administered ornithine (1 mmol/100 g body weight, i.p.), a substrate of the urea cycle, to alleviate the metabolic deficiency of arginine in spf/Y mice which may also be responsible for excessive orotic aciduria. The orotic aciduria remained insensitive to acivicin, indicating mitochondria as the source of carbamyl phosphate. However, orotate excretion was significantly decreased by PALA (P < 0.01), due to its effect on the aspartate transcarbamylase activity. The ingestion of adenine resulted in an increase (P < 0.05) of urinary orotate, suggesting the blockage of the utilization of orotate for nucleotide biosynthesis. Ornithine administration led to a reduction (P < 0.01) of the excretion of orotate induced by the OTC deficiency in these mice, indicating that one of the regulatory steps in its synthesis may be the availability of ornithine. There were no changes in urinary orotate excretion in spf/Y mice when treated with cycloheximide. On the other hand, pretreatment with cycloheximide in an artificial model of OTC deficiency (Swiss-ICR normal mice on an arginine-deficient diet treated thereafter with norvaline, an inhibitor of OTC), caused a significant decrease in urinary orotate. These results suggest that spf/Y mice are unique in that the increased synthesis of orotate is not sensitive to cycloheximide. Perhaps this may reflect an adaptive phenomenon developed by the mutant mice to handle excess mitochondrial carbamyl phosphate and orotic acid.