A combined metabolomics and molecular biology approach to reveal hepatic injury and underlying mechanisms after chronic l-lactate exposure in mice

Comput Struct Biotechnol J. 2022 Jul 25:20:3935-3945. doi: 10.1016/j.csbj.2022.07.034. eCollection 2022.

Abstract

This study aimed to explore whether chronic l-lactate exposure could affect the peripheral tissues of mice and to determine the underlying pathogenesis. Herein, male C57BL/6 mice were divided into control and l-lactate groups. After l-lactate treatment for eight weeks (1 g/kg), metabolic changes in liver, kidney, muscle, and serum samples were determined by 1H nuclear magnetic resonance (1H NMR)-based metabolomics. Additionally, organ function was evaluated by serum biochemical and histopathological examinations. Reactive oxygen species (ROS) levels were measured using dihydroethidium staining; levels of signals involved in lactate metabolism and ROS-related pathways were detected using western blotting or polymerase chain reaction. Apoptosis was detected by TUNEL-fluorescence staining. Metabolomic analysis revealed that l-lactate mice showed decreased levels of glutathione (GSH), taurine, ATP, and increased glucose content, compared to control mice. Furthermore, l-lactate mice presented significantly higher serum levels of alanine aminotransferase and aspartate aminotransferase and increased glycogen content in hepatic tissues, compared to control mice. l-lactate mice also had a greater number of apoptotic nuclei in the livers than controls. Moreover, l-lactate exposure reduced mRNA and protein levels of superoxide dismutase-2 and c-glutamylcysteine ligase, elevated levels of cytochrome P450 2E1 and NADPH oxidase-2, and increased the protein expressions of LDHB, Bax/Bcl-2, cleaved caspase-3, and sirtuin-1 in hepatic tissues. Together, these results indicate that chronic l-lactate exposure increases oxidative stress and apoptosis in hepatocytes via upregulation of Bax/Bcl-2 expression and the consequent mitochondrial cytochrome-C release and caspase-3 activation, which contributes to the pathogenesis of hepatic dysfunction.

Keywords: AD, Alzheimer's disease; ALT, alanine aminotransferase; AST, aspartate aminotransferase; BDNF, brain-derived neurotrophic factor; BUN, blood urea nitrogen; CREB, cyclic AMP-responsive element binding protein; Cyp2e1, cytochrome P450 2E1; DHE, dihydroethidium; GSH, glutathione; Gclc, c-glutamylcysteine ligase catalytic subunit; H&E, hematoxylin and eosin; Hepatic injury; LDH, lactate dehydrogenase; MCT, monocarboxylate transporter; MDA, malondialdehyde; Metabolomics; NMR, nuclear magnetic resonance; Nox2, NADPH oxidase-2; Nuclear magnetic resonance; OPLS-DA, orthogonal projection to latent structures discriminant analysis; PAS, periodic acid-Schiff; ROS, reactive oxygen species; SCR, serum creatinine; Sirt1, silent information regulator 1; Sod2, superoxide dismutase-2; TCA, tricarboxylic acid; TSP, trimethylsilyl propionate; VIP, variable importance in projection; VLDL/LDL, very low-density lipoproteins/low-density lipoproteins; l-lactate.