Exploratory Data Analysis of Cell and Mitochondrial High-Fat, High-Sugar Toxicity on Human HepG2 Cells

Comparison of HepaRG and HepG2 cell lines to model mitochondrial respiratory adaptations in non‑alcoholic fatty liver disease

Although some clinical studies have reported increased mitochondrial respiration in patients with fatty liver and early non‑alcoholic steatohepatitis (NASH), there is a lack of in vitro models of non‑alcoholic fatty liver disease (NAFLD) with similar findings. Despite being the most commonly used immortalized cell line for in vitro models of NAFLD, HepG2 cells exposed to free fatty acids (FFAs) exhibit a decreased mitochondrial respiration. On the other hand, the use of HepaRG cells to study mitochondrial respiratory changes following exposure to FFAs has not yet been fully explored. Therefore, the present study aimed to assess cellular energy metabolism, particularly mitochondrial respiration, and lipotoxicity in FFA‑treated HepaRG and HepG2 cells. HepaRG and HepG2 cells were exposed to FFAs, followed by comparative analyses that examained cellular metabolism, mitochondrial respiratory enzyme activities, mitochondrial morphology, lipotoxicity, the mRNA expression of selected genes and triacylglycerol (TAG) accumulation. FFAs stimulated mitochondrial respiration and glycolysis in HepaRG cells, but not in HepG2 cells. Stimulated complex I, II‑driven respiration and β‑oxidation were linked to increased complex I and II activities in FFA‑treated HepaRG cells, but not in FFA‑treated HepG2 cells. Exposure to FFAs disrupted mitochondrial morphology in both HepaRG and HepG2 cells. Lipotoxicity was induced to a greater extent in FFA‑treated HepaRG cells than in FFA‑treated HepG2 cells. TAG accumulation was less prominent in HepaRG cells than in HepG2 cells. On the whole, the present study demonstrates that stimulated mitochondrial respiration is associated with lipotoxicity in FFA‑treated HepaRG cells, but not in FFA‑treated HepG2 cells. These findings suggest that HepaRG cells are more suitable for assessing mitochondrial respiratory adaptations in the developed in vitro model of early‑stage NASH.

From Non-Alcoholic Fatty Liver to Hepatocellular Carcinoma: A Story of (Mal)Adapted Mitochondria

Non-alcoholic fatty liver disease (NAFLD) is a global pandemic affecting 25% of the world's population and is a serious health and economic concern worldwide. NAFLD is mainly the result of unhealthy dietary habits combined with sedentary lifestyle, although some genetic contributions to NAFLD have been documented. NAFLD is characterized by the excessive accumulation of triglycerides (TGs) in hepatocytes and encompasses a spectrum of chronic liver abnormalities, ranging from simple steatosis (NAFL) to steatohepatitis (NASH), significant liver fibrosis, cirrhosis, and hepatocellular carcinoma. Although the molecular mechanisms that cause the progression of steatosis to severe liver damage are not fully understood, metabolic-dysfunction-associated fatty liver disease is strong evidence that mitochondrial dysfunction plays a significant role in the development and progression of NAFLD. Mitochondria are highly dynamic organelles that undergo functional and structural adaptations to meet the metabolic requirements of the cell. Alterations in nutrient availability or cellular energy needs can modify mitochondria formation through biogenesis or the opposite processes of fission and fusion and fragmentation. In NAFL, simple steatosis can be seen as an adaptive response to storing lipotoxic free fatty acids (FFAs) as inert TGs due to chronic perturbation in lipid metabolism and lipotoxic insults. However, when liver hepatocytes' adaptive mechanisms are overburdened, lipotoxicity occurs, contributing to reactive oxygen species (ROS) formation, mitochondrial dysfunction, and endoplasmic reticulum (ER) stress. Impaired mitochondrial fatty acid oxidation, reduction in mitochondrial quality, and disrupted mitochondrial function are associated with a decrease in the energy levels and impaired redox balance and negatively affect mitochondria hepatocyte tolerance towards damaging hits. However, the sequence of events underlying mitochondrial failure from steatosis to hepatocarcinoma is still yet to be fully clarified. This review provides an overview of our understanding of mitochondrial adaptation in initial NAFLD stages and highlights how hepatic mitochondrial dysfunction and heterogeneity contribute to disease pathophysiology progression, from steatosis to hepatocellular carcinoma. Improving our understanding of different aspects of hepatocytes' mitochondrial physiology in the context of disease development and progression is crucial to improving diagnosis, management, and therapy of NAFLD/NASH.

Brassica oleracea Var italica by-Products Prevent Lipid Accumulation and Cell Death in a Liver Cell Model of Lipid Toxicity

Obesity, a rising concern in the Eastern world, encompasses several co-morbidities, namely non-alcoholic fatty liver disease (NAFLD). Potential natural-based interventions to decrease the burden of obesity complications are being investigated. Many of the edible parts of plants are not sold for consumption and end up as massive waste, losing nutritional potential. In fact, a sizeable amount of waste is generated within the different steps of the food supply chain, representing a massive loss of both plant material and natural resources. A good example is Brassica by-products (BBPs). The objective of this work was to investigate the effect of three different extracts from broccoli (Brassica oleracea var italica) by-products in an in vitro model of free fatty acid (FFA)-induced lipotoxicity using human hepatoma HepG2 cells. Broccoli leaf, stalk, and inflorescence extracts induced a dose-dependent decrease in the cell viability of HepG2 cells. However, the maximal non-lethal concentrations of leaves, stalks, and inflorescences (10 μg/mL) did not compromise mitochondrial function or neutral lipid accumulation in HepG2 cells. The extracts significantly decreased FFA-induced lipid accumulation in HepG2 cells either in a co-incubation or pre-incubation strategy. The broccoli extracts' capacity to prevent the FFA-induced decrease in catalase activity in HepG2 may explain the observed effects.

Preparation, physicochemical characterization, and bioactivity evaluation of berberine-entrapped albumin nanoparticles

Berberine (BBR) is an isoquinoline alkaloid with several clinical therapeutic applications. Its low water solubility, absorption, and cellular bioavailability diminish BBR's therapeutic efficacy. In this study, BBR was encapsulated into bovine serum albumin nanoparticles (BSA NPs) core to reduce BBR limitations and enhance its clinical therapeutic properties. Several physicochemical characterization tools, such as Dynamic Light Scattering and Ultraviolet-Visible spectroscopic measurements, field emission transmission electron microscopy surface morphology, Fourier transforms infrared spectroscopy, thermal stability analysis, and releasing studies, were used to evaluate the BBR-BSA NPs. Compared to BBR, BBR-BSA nanoparticles demonstrated superior free radical scavenging and antioxidant capacities, anti-hemolytic and anticoagulant efficacies, and antimicrobial activities, as demonstrated by the findings of the in vitro studies. Furthermore, a stressed pancreatic rat model was induced using a high-fat, high-sucrose diet plus carbon tetrachloride injection. The in vivo results revealed that BBR-BSA NPs substantially restored peripheral glucose metabolism and insulin sensitivity. Oral administration of BBR-BSA NPs also improved pancreatic β-cells homeostasis, upregulated pancreatic antioxidant mechanisms, inhibited oxidants generation, and attenuated oxidative injury in the stressed pancreatic tissues. In conclusion, our in vitro and in vivo results confirmed that BBR-BSA NPs demonstrated more potent antioxidant properties and restored pancreatic homeostasis compared to BBR.

Mitochondria-targeted anti-oxidant AntiOxCIN4 improved liver steatosis in Western diet-fed mice by preventing lipid accumulation due to upregulation of fatty acid oxidation, quality control mechanism and antioxidant defense systems

Non-alcoholic fatty liver disease (NAFLD) is a health concern affecting 24% of the population worldwide. Although the pathophysiologic mechanisms underlying disease are not fully clarified, mitochondrial dysfunction and oxidative stress are key players in disease progression. Consequently, efforts to develop more efficient pharmacologic strategies targeting mitochondria for NAFLD prevention/treatment are underway. The conjugation of caffeic acid anti-oxidant moiety with an alkyl linker and a triphenylphosphonium cation (TPP+), guided by structure-activity relationships, led to the development of a mitochondria-targeted anti-oxidant (AntiOxCIN4) with remarkable anti-oxidant properties. Recently, we described that AntiOxCIN4 improved mitochondrial function, upregulated anti-oxidant defense systems, and cellular quality control mechanisms (mitophagy/autophagy) via activation of the Nrf2/Keap1 pathway, preventing fatty acid-induced cell damage. Despite the data obtained, AntiOxCIN4 effects on cellular and mitochondrial energy metabolism in vivo were not studied. In the present work, we proposed that AntiOxCIN4 (2.5 mg/day/animal) may prevent non-alcoholic fatty liver (NAFL) phenotype development in a C57BL/6J mice fed with 30% high-fat, 30% high-sucrose diet for 16 weeks. HepG2 cells treated with AntiOxCIN4 (100 μM, 48 h) before the exposure to supraphysiologic free fatty acids (FFAs) (250 μM, 24 h) were used for complementary studies. AntiOxCIN4 decreased body (by 43%), liver weight (by 39%), and plasma hepatocyte damage markers in WD-fed mice. Hepatic-related parameters associated with a reduction of fat liver accumulation (by 600%) and the remodeling of fatty acyl chain composition compared with the WD-fed group were improved. Data from human HepG2 cells confirmed that a reduction of lipid droplets size and number can be a result from AntiOxCIN4-induced stimulation of fatty acid oxidation and mitochondrial OXPHOS remodeling. In WD-fed mice, AntiOxCIN4 also induced a hepatic metabolism remodeling by upregulating mitochondrial OXPHOS, anti-oxidant defense system and phospholipid membrane composition, which is mediated by the PGC-1α-SIRT3 axis. AntiOxCIN4 prevented lipid accumulation-driven autophagic flux impairment, by increasing lysosomal proteolytic capacity. AntiOxCIN4 improved NAFL phenotype of WD-fed mice, via three main mechanisms: a) increase mitochondrial function (fatty acid oxidation); b) stimulation anti-oxidant defense system (enzymatic and non-enzymatic) and; c) prevent the impairment in autophagy. Together, the findings support the potential use of AntiOxCIN4 in the prevention/treatment of NAFLD.

Mitochondriotropic antioxidant based on caffeic acid AntiOxCIN4 activates Nrf2-dependent antioxidant defenses and quality control mechanisms to antagonize oxidative stress-induced cell damage

Mitochondria are key organelles involved in cellular survival, differentiation, and death induction. In this regard, mitochondrial morphology and/or function alterations are involved in stress-induced adaptive pathways, priming mitochondria for mitophagy or apoptosis induction. We have previously shown that the mitochondriotropic antioxidant AntiOxCIN₄ (100 μM; 48 h) presented significant cytoprotective effect without affecting the viability of human hepatoma-derived (HepG2) cells. Moreover, AntiOxCIN₄ (12.5 μM; 72 h) caused a mild increase of reactive oxygen species (ROS) levels without toxicity to primary human skin fibroblasts (PHSF). As Nrf2 is a master regulator of the oxidative stress response inducing antioxidant-encoding gene expression, we hypothesized that AntiOxCIN₄ could increase the resistance of human hepatoma-derived HepG2 to oxidative stress by Nrf2-dependent mechanisms, in a process mediated by mitochondrial ROS (mtROS). Here we showed that after an initial decrease in oxygen consumption paralleled by a moderate increase in superoxide anion levels, AntiOxCIN₄ led to a time-dependent Nrf2 translocation to the nucleus. This was followed later by a 1.5-fold increase in basal respiration and a 1.2-fold increase in extracellular acidification. AntiOxCIN₄ treatment enhanced mitochondrial quality by triggering the clearance of defective organelles by autophagy and/or mitophagy, coupled with increased mitochondrial biogenesis. AntiOxCIN₄ also up-regulated the cellular antioxidant defense system. AntiOxCIN₄ seems to have the ability to maintain hepatocyte redox homeostasis, regulating the electrophilic/nucleophilic tone, and preserve cellular physiological functions. The obtained data open a new avenue to explore the effects of AntiOxCIN₄ in the context of preserving hepatic mitochondrial function in disorders, such as NASH/NAFLD and type II diabetes.