Metabolic profiling analysis upon acylcarnitines in tissues of hepatocellular carcinoma revealed the inhibited carnitine shuttle system caused by the downregulated carnitine palmitoyltransferase 2

Abstract

The carnitine shuttle system (CSS) plays a crucial role in the transportation of fatty acyls during fatty acid β‐oxidation for energy supplementation, especially in cases of high energy demand, such as in cancer. In this study, to systematically characterize alterations of the CSS in hepatocellular carcinoma (HCC), acylcarnitine metabolic profiling was carried out on 80 pairs of HCC tissues and adjacent noncancerous tissues (ANTs) by using ultra‐performance liquid chromatography coupled to mass spectrometry. Twenty‐four acylcarnitines classified into five categories were identified and characterized between HCCs and ANTs. Notably, increased saturated long‐chain acylcarnitines (LCACs) and decreased short‐ and medium‐chain acylcarnitines (S/MCACs) were simultaneously observed in HCC samples. Subsequent correlation network and heatmap analysis indicated low correlations between LCACs and S/MCACs. The mRNA and protein expressions of carnitine palmitoyltransferase 2 (CPT2) was significantly downregulated in HCC samples, whereas CPT1A expression was not significantly changed. Correspondingly, the relative levels of S/MCACs were reduced and those of LCACs were increased in BEL‐7402/CPT2‐knockdown cells compared to negative controls. Both results suggested that decreased shuttling efficiency in HCC might be associated with downregulation of CPT2. In addition, decreases in the mRNA expression of acetyl‐CoA acyltransferase 2 were also observed in HCC tissues and BEL‐7402/CPT2‐knockdown cells, suggesting potential low β‐oxidation efficiency, which was consistent with the increased expression of stearoyl‐CoA desaturase 1 in both samples. The systematic strategy applied in our study illustrated decreased shuttling efficiency of the carnitine shuttle system in HCC and can provide biologists with an in‐depth understanding of β‐oxidation in HCC.

Altered serum acylcarnitine profile is associated with the status of nonalcoholic fatty liver disease (NAFLD) and NAFLD-related hepatocellular carcinoma

“…Second, although carnitine homeostasis is maintained by dietary intake (mainly meat products) as well as endogenous synthesis and renal reabsorption 34 , we did not have data on dietary habits in this cohort. Third, although we and another group previously identified downregulation of CPT2 as a critical factor for acylcarnitine accumulation in HCC tissues 10,22 , the mechanism underlying the changes in serum acylcarnitine profiles during the progression of NAFLD remains unclear. One possibility is that FAO in patients with advanced-stage NASH may be impaired in the process of acyl-CoA dehydrogenation that is catalyzed by acyl-CoA dehydrogenases including very long-chain acyl-CoA dehydrogenase (VLCAD), long-chain acyl-CoA dehydrogenase (LCAD), and medium-chain acyl-CoA dehydrogenase (MCAD).…”

“…Consistent with our results, Lu et al . recently reported that the serum and tissue levels of long-chain acylcarnitine species increased but those of short- and middle-chain acylcarnitine species decreased in patients with hepatitis virus-related HCC, and such changes in acylcarnitine profiles were caused by downregulation of CPT2 22 . In contrast, Zhou et al .…”

“…Especially, AC18:1 was significantly positively correlated with serum levels of inflammatory cytokines and significantly increased in NAFLD patients with HCC, which were consistent with our previous mouse experiments 10 . To date, several studies have reported associations between acylcarnitine profiles and liver disease 19–22 . However, those studies included relatively small numbers of NAFLD patients, and, to the best of our knowledge, this is the largest study to assess the relationships between acylcarnitine species and the status of NAFLD.…”

Comprehensive Metabolomic Search for Biomarkers to Differentiate Early Stage Hepatocellular Carcinoma from Cirrhosis

“…However, acylcarnitines with medium-chain fatty acids can freely pass through the mitochondrial membranes and are utilized to produce fuel for energy [29,33]. Previous studies demonstrated that carnitine palmitoyltransferase 2 (CPT 2) expression is downregulated, thereby reducing hepatic beta-oxidation of fatty acids in patients with HCC [34,35]. A lack of CPT 2 expression ultimately leads to an increased level of long-chain acylcarnitines and reduced level of short- and medium-chain acylcarnitines in circulation [34,35].…”

“…Previous studies demonstrated that carnitine palmitoyltransferase 2 (CPT 2) expression is downregulated, thereby reducing hepatic beta-oxidation of fatty acids in patients with HCC [34,35]. A lack of CPT 2 expression ultimately leads to an increased level of long-chain acylcarnitines and reduced level of short- and medium-chain acylcarnitines in circulation [34,35]. Therefore, we speculate that due to the rapid transport of medium-chain acylcarnitines into the liver, the cancer cells may utilize this energy source to proliferate.…”