Plasma biomarkers to study mechanisms of liver injury in patients with hypoxic hepatitis

Abstract

Background and Aims Hypoxic hepatitis is a clinical condition precipitated by prolonged periods of oxygen deprivation to the liver. It can have several underlying causes. Despite its prevalence in critically ill patients, which can reach upwards of 10%, very little is known about the mechanisms of injury. Thus, we set out to measure previously identified circulating biomarkers in an attempt to describe mechanisms of injury following hypoxic hepatitis. Methods Plasma from patients diagnosed with hypoxic hepatitis was collected for this study. Biomarkers of hepatocellular injury, mitochondrial damage, and cell death were measured. These results were compared against results obtained from well characterized acetaminophen overdose patients. Results At peak injury, ALT measured 4082±606 U/L and gradually decreased over 5 days, corresponding to the clinically observed pattern of hypoxic hepatitis. Levels of GDH showed a similar pattern, but neither ALT nor GDH were significantly higher in these patients than in acetaminophen patients. Plasma levels of DNA fragments mimicked hepatocellular injury as measured by ALT and miRNA-122. Interestingly, we found a significant increase in caspase-cleaved cytokeratin-18; however, the full-length form greatly exceeded the cleaved form at the time of maximum injury (45837±12085 vs. 2528±1074 U/L). We also found an increase in acHMGB1 at later time points indicating a possible role of inflammation, but cytokine levels at these times were actually decreased relative to early time points. Conclusions The mechanism of injury following hypoxic hepatitis involves mitochondrial damage and DNA fragmentation. Importantly, necrosis, rather than apoptosis, is the main mode of cell death.

Cell Death and Prognosis of Mortality in Alcoholic Hepatitis Patients Using Plasma Keratin-18

“…8 ELISA tests have been developed for both K18 and cleaved K18 and are referred to as the M65 and M30 ELISA, respectively. Plasma or serum values of both M65 and M30 have been used extensively to better define cell death in many forms of liver disease, 10–15 as the liver expresses K18 in hepatocytes. 7 The ratio between M30 and M65 has been used as metric of cell death in both humans 10,12,15 and in animal models.…”

Mitochondrial dysfunction as a mechanism of drug-induced hepatotoxicity: current understanding and future perspectives

“…Other biomarkers such as miR-122 [244–247], full-length cytokeratin-18 [247–250], high mobility group box 1 (HMGB1) protein [247–249, 251], and argininosuccinate synthetase (ASS) [252] are generally considered indicators of mainly necrotic cell death [253]. On the other hand, increased plasma levels of the caspase-cleaved form of cytokeratin-18 [247, 248, 250, 254, 255] and activated caspases detected as enzyme activity and/or the protein by western blotting [164, 247, 249, 254], are markers of apoptotic cell death. However, due to the sensitivity of the assay, cleaved cytokeratin-18 levels should always be compared to the full-length version in order to assess the relative importance of apoptosis [247, 248, 254].…”

“…On the other hand, increased plasma levels of the caspase-cleaved form of cytokeratin-18 [247, 248, 250, 254, 255] and activated caspases detected as enzyme activity and/or the protein by western blotting [164, 247, 249, 254], are markers of apoptotic cell death. However, due to the sensitivity of the assay, cleaved cytokeratin-18 levels should always be compared to the full-length version in order to assess the relative importance of apoptosis [247, 248, 254]. The clinical utility of some of these biomarkers may be that they are highly specific for hepatocyte cell death, e.g.…”

“…Thus, nuclear DNA fragments in plasma can be considered indirect biomarkers of mitochondrial dysfunction at least for APAP overdose [164]. These mitochondrial damage biomarkers could be readily detected in plasma of patients with APAP overdose and hypoxic hepatitis and in APAP-treated mice in a time course that correlated with ALT increases [164, 247]. The only substantial difference was the fact that these biomarkers had a shorter half-life in plasma compared to ALT suggesting again that these types of biomarkers reflect more accurately the injury process.…”

“…Another hepatic mitochondrial matrix protein, carbamoyl phosphate synthetase-1 (CPS1), was detected during Fas-induced apoptosis and APAP-induced necrosis in cell culture supernatants, in mice in vivo and in plasma of human acute liver failure patients [261]. Similar to mtDNA, GLDH and nuclear DNA fragments [164, 247], CPS1 appears to be a general biomarker of cell death involving mitochondria, which means that it is detectable in acute liver failure patients with different etiology [261]. In addition, CPS1 has a half-life of 2 h [261].…”