Effects of individual and multiple fatty acids (palmitate, oleate and docosahaexenoic acid) on cell viability and lipid metabolism in LO2 human liver cells

Determining the temporal, dose, and composition effects of nutritional substrates in an in vitro model of intrahepatocellular triglyceride accumulation

Pathological accumulation of intrahepatic triglyceride underpins the early stages of nonalcoholic fatty liver disease (NAFLD) and can progress to fibrosis, cirrhosis, and cancer of the liver. Studies in humans suggest that consumption of a diet enriched in saturated compared to unsaturated fatty acids (FAs), is more detrimental to liver fat accumulation and metabolism. However, the reasons for the divergence remain unclear and physiologically-relevant cellular models are required. Therefore, the aims of this study were to investigate the effect of modifying media composition, concentration, and treatment frequency of sugars, FAs and insulin on intrahepatocellular triglyceride content and intracellular glucose, FA and circadian function. Huh7 cells were treated with 2% human serum and a combination of sugars and FAs (low fat low sugar [LFLS], high fat low sugar [HFLS], or high fat high sugar [HFHS]) enriched in either unsaturated (OPLA) or saturated (POLA) FAs for 2, 4, or 7 days with a daily or alternating treatment regime. Stable isotope tracers were utilized to investigate basal and/or insulin-responsive changes in hepatocyte metabolism in response to different treatment regimes. Cell viability, media biochemistry, intracellular metabolism, and circadian biology were quantified. The FA composition of the media (OPLA vs. POLA) did not influence cell viability or intracellular triglyceride content in hepatocytes. In contrast, POLA-treated cells had lower FA oxidation and media acetate, and with higher FA concentrations, displayed lower intracellular glycogen content and diminished insulin stimulation of glycogenesis, compared to OPLA-treated cells. The addition of HFHS also had profound effects on circadian oscillation and gene expression. Cells treated daily with HFHS for at least 4 days resulted in a cellular model displaying characteristics of early stage NAFLD seen in humans. Repeated treatment for longer durations (≥7 days) may provide opportunities to investigate lipid and glucose metabolism in more severe stages of NAFLD.

Metabolic and antioxidant status during transition is associated with changes in the granulosa cell transcriptome in the preovulatory follicle in high-producing dairy cows at the time of breeding

In this study, we hypothesized that early postpartum (pp) metabolic and oxidative stress conditions in dairy cows (particularly those with severe negative energy balance, NEB) are associated with long-term changes in granulosa cell (GC) functions in the preovulatory follicle at the time of breeding. Blood samples were collected at wk 2 and wk 8 pp from 47 healthy multiparous cows. Follicular fluid (FF) and GC were collected from the preovulatory follicle after estrous synchronization at wk 8. Several metabolic and antioxidant parameters were measured in blood and FF, and their correlations were studied. Subsequently, 27 representative GC samples were selected for RNA sequencing analysis. The GC gene expression data of LH-responsive genes and the estradiol:progesterone ratio in FF were used to identify pre- and post-LH surge cohorts. We compared the transcriptomic profile of subgroups of cows within the highest and lowest quartiles (Q4 vs. Q1) of each parameter, focusing on the pre-LH surge cohort (n = 16, at least 3 in each subgroup). Differentially expressed genes (DEG: adjusted P-value < 0.05, 5% false discovery rate) were determined using DESeq2 analysis and were functionally annotated. Blood and FF β-carotene and vitamin E concentrations at wk 2, but not at wk 8, were associated with the most pronounced transcriptomic differences in the GC, with up to 341 DEG indicative for lower catabolism, increased oxidoreductase activity and signaling cascades that are known to enhance oocyte developmental competence, increased responsiveness to LH, and a higher steroidogenic activity. In contrast, elevated blood NEFA concentrations at wk 2 (and not at wk 8) were associated with a long-term carryover effect detectable in the GC transcriptome at wk 8 (64 DEG). These genes are related to response to lipids and ketones, oxidative stress, and immune responses, which suggests persistent cellular stress and oxidative damage. This effect was more pronounced in cows with antioxidant deficiencies at wk 8 (up to 148 DEG), with more genes involved in oxidative stress-dependent responses, apoptosis, autophagy and catabolic processes, and mitochondrial damage. Interestingly, within the severe NEB cows (high blood NEFA at wk 2), blood antioxidant concentrations (high vs. low) at wk 8 were associated with up to 194 DEG involved in activation of meiosis and other signaling pathways, indicating a better oocyte supportive capacity. This suggests that the cow antioxidant profile at the time of breeding might alleviate, at least in part, the effect of NEB on GC functions. In conclusion, these results provide further evidence that the metabolic and oxidative stress in dairy cows early postpartum can have long-term effects on GC functions in preovulatory follicles at the time of breeding. The interplay between the effects of antioxidants and NEFA illustrated here might be useful to develop intervention strategies to minimize the effect of severe NEB on fertility.

Camellia oil Enhances Plasma Antioxidant Metabolism and Improves Plasma Lipid Metabolism in High-fat Diet-fed Rats

Living on a high-fat, high-calorie, and high-protein diet for a long period may compromise human immunity due to the long-term accumulation of free radicals and plasma lipids. The antioxidant and lipid-lowering compounds (ie polyphenols and vitamin E) in Camellia oil help to decrease the risk of numerous ailments, including cardiovascular disease (CVD), and obesity.

The aims of this study were to study the hypolipidemic and antioxidant effects of Camellia oil in high-fat-fed rats and to promote the high-value use of camellia resources. The high-fat-fed rats were administrated with 2.5, 7.5, and 15 mL/kg BW Camellia oil (Camellia oil group), and 10 mg/kg BW atorvastatin (atorvastatin group), respectively, and compared with a model group (only fed with high fat) and a control group (fed with basal diet). Several parameters were measured, including (1) body weight (BW), liver-to-BW ratio; (2) plasma total cholesterol (TC), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C); and (3) alanine aminotransferase (ALT), alanine aminotransferase (AST), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) activity, model driven architecture (MDA) content, lipid metabolism-related genes, and antioxidant-related genes in liver tissue.

Compared with the model group, the high-fat-fed rats in the Camellia oil and atorvastatin group had significantly lower BW and liver-to-BW ratio ( P < .01), plasma TC, TG, and LDL-C levels and ALT and AST activities, but higher HDL-C levels. The relative expressions of ACAT1, DGAT2, FAS, and SREBP genes were significantly reduced in the Camellia oil and atorvastatin groups, while the relative expressions of LCAT, UCP2, MCD, and CPT-1 genes were significantly increased. The rats in the Camellia oil group showed significantly higher SOD and GSH-Px activities, significantly lower MDA content, and significantly higher relative expression of antioxidant genes (eg SOD1, GPx1, CAT, and Gclm). Thus, atorvastatin and Camellia oil exhibited significant hypolipidemic and antioxidant effects, which were better at a dose of 7.5 mL/kg (BW) of Camellia oil. Therefore, Camellia oil becomes a potential new natural resource for future research and development of antioxidant and hypolipidemic drugs, nutraceuticals, and additives.

DHA Protects Hepatocytes from Oxidative Injury through GPR120/ERK-Mediated Mitophagy

Oxidative stress occurs in a variety of clinical liver diseases and causes cellular damage and mitochondrial dysfunction. The clearance of damaged mitochondria by mitophagy may facilitate mitochondrial biogenesis and enhance cell survival. Although the supplementation of docosahexaenoic acid (DHA) has been recognized to relieve the symptoms of various liver diseases, the antioxidant effect of DHA in liver disease is still unclear. The purpose of our research was to investigate the antioxidant effect of DHA in the liver and the possible role of mitophagy in this. In vitro, H₂O₂-induced injury was caused in AML12 cells. The results showed that DHA repressed the level of reactive oxygen species (ROS) induced by H₂O₂ and stimulated the cellular antioxidation response. Most notably, DHA restored oxidative stress-impaired autophagic flux and promoted protective autophagy. In addition, PINK/Parkin-mediated mitophagy was activated by DHA in AML12 cells and alleviated mitochondrial dysfunction. The ERK1/2 signaling pathway was inhibited during oxidative stress but reactivated by DHA treatment. It was proven that the expression of ERK1/2 was involved in the regulation of mitophagy by the ERK1/2 inhibitor. We further proved these results in vivo. DHA effectively alleviated the liver oxidative damage caused by CCl₄ and enhanced antioxidation capacity; intriguingly, autophagy was also activated. In summary, our data demonstrated that DHA protected hepatocytes from oxidative damage through GPR120/ERK-mediated mitophagy.

Co-Administration of Propionate or Protocatechuic Acid Does Not Affect DHA-Specific Transcriptional Effects on Lipid Metabolism in Cultured Hepatic Cells

Long-chain n-3 polyunsaturated fatty acids (n-3 LC-PUFAs) are collectively recognized triglyceride-lowering agents, and their preventive action is likely mediated by changes in gene expression. However, as most studies employ fish oil, which contains a mixture of n-3 LC-PUFAs, the docosahexaenoic acid (DHA)-specific transcriptional effects on lipid metabolism are still unclear. The aim of the present study was to further elucidate the DHA-induced transcriptional effects on lipid metabolism in the liver, and to investigate the effects of co-administration with other bioactive compounds having effects on lipid metabolism. To this purpose, HepG2 cells were treated for 6 or 24 h with DHA, the short-chain fatty acid propionate (PRO), and protocatechuic acid (PCA), the main human metabolite of cyanidin-glucosides. Following supplementation, we mapped the global transcriptional changes. PRO and PCA alone had a very slight effect on the transcriptome; on the contrary, supplementation of DHA highly repressed the steroid and fatty acid biosynthesis pathways, this transcriptional modulation being not affected by co-supplementation. Our results confirm that DHA effect on lipid metabolism are mediated at least in part by modulation of the expression of specific genes. PRO and PCA could contribute to counteracting dyslipidemia through other mechanisms.

Micheliolide alleviates hepatic steatosis in db/db mice by inhibiting inflammation and promoting autophagy via PPAR-γ-mediated NF-кB and AMPK/mTOR signaling

The anti-inflammatory, immunomodulatory, and anticancer effects of micheliolide (MCL) isolated from Michelia champaca were previously reported, but its role and underlying mechanisms in relieving liver steatosis remain unclear. Herein, we investigated the effects of MCL on hepatic steatosis using a db/db mouse model and lipid mixture (LM)-induced AML12 and LO2 cells. The body and liver weights, food consumption, lipid content and liver aminotransferase levels in serum, the lipid content and inflammatory cytokine levels in liver tissue, and the extent of hepatic steatosis in db/db mice were increased compared with those in db/m mice, and these increases were reversed by MCL treatment. Similarly, MCL also attenuated the inflammatory responses and lipid accumulation in LM-treated AML12 and L02 cells by upregulating PPAR-γ and decreasing p-IкBα and p-NF-κB/p65, thereby inhibiting the NF-κB pathway and reducing lipotoxicity. Furthermore, MCL administration increased LC3B, Atg7 and Beclin-1 expression and the LC3B-II/I ratio in db/db mouse livers and LM-treated AML12 and L02 cells, and these MCL-induced increases were mediated by the activation of PPAR-γ and p-AMPK and inhibition of p-mTOR and induce autophagy. These effects were blocked by PPAR-γ and AMPK inhibitors. Our findings suggest that MCL ameliorates liver steatosis by upregulating PPAR-γ expression, thereby inhibiting NF-κB-mediated inflammation and activating AMPK/mTOR-dependent autophagy.

Evidence of a DHA Signature in the Lipidome and Metabolome of Human Hepatocytes

Cell supplementation with bioactive molecules often causes a perturbation in the whole intracellular environment. Omics techniques can be applied for the assessment of this perturbation. In this study, the overall effect of docosahexaenoic acid (DHA) supplementation on cultured human hepatocyte lipidome and metabolome has been investigated using nuclear magnetic resonance (NMR) in combination with traditional techniques. The effect of two additional bioactives sharing with DHA the lipid-lowering effect—propionic acid (PRO) and protocatechuic acid (PCA)—has also been evaluated in the context of possible synergism. NMR analysis of the cell lipid extracts showed that DHA supplementation, alone or in combination with PCA or PRO, strongly altered the cell lipid profile. The perfect discrimination between cells receiving DHA (alone or in combination) and the other cells reinforced the idea of a global rearrangement of the lipid environment induced by DHA. Notably, gas chromatography and fluorimetric analyses confirmed the strong discrimination obtained by NMR. The DHA signature was evidenced not only in the cell lipidome, but also in the metabolome. Results reported herein indicate that NMR, combined with other techniques, represents a fundamental approach to studying the effect of bioactive supplementation, particularly in the case of molecules with a broad spectrum of mechanisms of action.

Hepatic PPARγ Is Not Essential for the Rapid Development of Steatosis After Loss of Hepatic GH Signaling, in Adult Male Mice

Our group has previously reported de novo lipogenesis (DNL) and hepatic triglyceride content increases in chow-fed male mice within 7 days of hepatocyte-specific GH receptor knockdown (aLivGHRkd). Here, we report that these changes are associated with an increase in hepatic expression of peroxisome proliferator-activated receptor γ (PPARγ), consistent with previous reports showing steatosis is associated with an increase in PPARγ expression in mice with congenital loss of hepatic GH signaling. PPARγ is thought to be an important driver of steatosis by enhancing DNL, as well as increasing the uptake and esterification of extrahepatic fatty acids (FAs). In order to determine whether hepatic PPARγ is critical for the rapid development of steatosis in the aLivGHRkd mouse model, we have generated aLivGHRkd mice, with or without PPARγ (ie, adult-onset, hepatocyte-specific double knockout of GHR and PPARγ). Hepatic PPARγ was not required for the rapid increase in liver triglyceride content or FA indexes of DNL (16:0/18:2 and 16:1/16:0). However, loss of hepatic PPARγ blunted the rise in fatty acid translocase/CD36 and monoacylglycerol acyltransferase 1 expression induced by aLivGHRkd, and this was associated with a reduction in the hepatic content of 18:2. These results suggest that the major role of PPARγ is to enhance pathways critical in uptake and reesterification of extrahepatic FA. Because FAs have been reported to directly increase PPARγ expression, we speculate that in the aLivGHRkd mouse, the FA produced by DNL enhances the expression of PPARγ, which in turn increases extrahepatic FA uptake, thereby further enhancing PPARγ activity and exacerbating steatosis overtime.