De Novo Sphingolipid Biosynthesis in Atherosclerosis.

Atherosclerosis is the formation of fibrofatty lesions in the arterial wall, and this inflammatory state of the artery is the main cause of advanced pathological processes, including myocardial infarction and stroke. Dyslipidemic conditions with excess cholesterol accumulate within the arterial vessel wall and initiate atherogenic processes. Following vascular reaction and lipid accumulation, the vascular wall gradually thickens. Together with the occurrence of local inflammation, early atherosclerotic lesions lead to advanced pathophysiological events, plaque rupture, and thrombosis. Ceramide and sphingomyelin have emerged as major risk factors for atherosclerosis and coronary artery disease. Currently, the clinical association between de novo sphingolipid biosynthesis and coronary artery disease has been established. Furthermore, therapeutic strategies to modulate this pathway, especially those involving serine palmitoyltransferase and sphingomyelin synthase, against atherosclerosis, cancer, type 2 diabetes, and non-alcoholic fatty liver disease are actively under development. In this chapter, we focus on the relationship between de novo sphingolipid biosynthesis and coronary artery disease.

Annona muricata leaf extract attenuates hepatic lipogenesis and adipogenesis.

Annona muricata (graviola) is a medicinal plant that can be used to alleviate chronic human diseases by providing antioxidants and inducing immunomodulation. In this study, we found that treatment of AML12 hepatocytes with steam (SGE) and ethanol (EGE) extracts of graviola leaf downregulated the expression of fatty acid (FA) oxidation genes, including ACOX1, CPT1, and PPARα, with no change in the expression of FA synthesis genes. However, whereas EGE inhibited the differentiation and lipid accumulation of 3T3-L1 adipocytes and downregulated FA synthesis genes, no similar changes were observed in response to treatment with SGE. In an in vivo experiment using mice fed a high-fat diet (HFD), body weight was reduced in response to treatment with EGE, which also dose-dependently alleviated liver hepatocyte ballooning induced by the consumption of a HFD. However, genes involved in FA oxidation and the secretion of very low density lipoprotein (VLDL) were downregulated. We also found that the size of adipocytes was reduced in response to EGE treatment, and that there was a downregulated expression of genes involved in adipogenesis and FA synthesis. Furthermore, we detected increases in the levels of cholesterol in the plasma, whereas ALT activity was reduced. Collectively, these results indicates that EGE inhibits lipid influx into the liver and adipogenesis in adipose tissues. These bioactive properties of EGE indicate its potential as a natural ingredient that can be used to prevent obesity.

Hepatic Expression of the Serine Palmitoyltransferase Subunit Sptlc2 Reduces Lipid Droplets in the Liver by Activating VLDL Secretion.

OBJECTIVE: Ceramide is a signaling molecule that contributes to insulin resistance and hepatosteatosis. In the present study, we activated de novo ceramide synthesis by inducing the hepatic expression of Sptlc2 to investigate the role of ceramide in glucose and lipid metabolism. METHODS: We first constructed an adenovirus containing Sptlc2 (AdSptlc2), which encodes a major catalytic subunit of serine palmitoyltransferase (SPT). We then infected hepatocytes and mice fed a regular diet with AdSptlc2 to activate de novo ceramide biosynthesis. The liver-specific effects of ceramide biosynthesis on glucose and lipid metabolism were investigated by measuring changes in insulin signaling, lipid droplet formation, and very low-density lipoprotein (VLDL) secretion. RESULTS: In HepG2 hepatocytes, adenoviral Sptlc2 expression inhibited insulin signaling and increased ceramide levels via activation of c-Jun N-terminal kinase and serine phosphorylation of insulin receptor substrate 1. In contrast, in mice, AdSptlc2 infection decreased plasma glucose levels by downregulating gluconeogenic genes and increased plasma triglyceride levels by increasing VLDL secretion. In mice infected with AdSptlc2, glucose intolerance and insulin sensitivity improved, while pyruvate utilization via gluconeogenesis decreased. CONCLUSION: Hepatic ceramide was found to modulate hepatosteatosis and the insulin response via increased VLDL secretion and inhibition of gluconeogenesis in vivo. Although inhibition of the insulin response was observed in vitro, the compensatory mechanism of relieving ceramide-induced stress and reducing ceramide levels resulted in improvements of glucose and lipid metabolic profiles in vivo. This discrepancy between in vitro and in vivo regulation mechanisms suggests that ceramide plays a role in non-alcoholic fatty liver disease and insulin resistance.

Increased Intestinal Absorption of Vitamin U in Steamed Graviola Leaf Extract Activates Nicotine Detoxification.

Graviola leaves contain much vitamin U (vit U), but their sensory quality is not good enough for them to be developed as food ingredients. Addition of excipient natural ingredients formulated alongside vit U as active ingredients could enhance not only its sensory quality but also its bioavailability. The objectives of this study were to measure the bioaccessibility and intestinal cellular uptake of bioactive components, including rutin, kaempferol-rutinoside, and vit U, from steamed extract of graviola leaves (SGV) and SGV enriched with kale extract (SGK), and to examine how much they can detoxify nicotine in HepG2 cells. The bioaccessibility of vit U from SGV and SGK was 82.40% and 68.03%, respectively. The cellular uptake of vit U in SGK by Caco-2 cells was higher than that in SGV. Cotinine content converted from nicotine in HepG2 cells for 120 min was 0.22 and 0.25 µg/mg protein in 50 µg/mL of SGV and SGK, respectively, which were 2.86 and 3.57 times higher than the no-treatment control. SGK treatment of HepG2 cells upregulated CYP2A6 three times as much as did that of SGV. Our results suggest that graviola leaf extract enriched with excipient ingredients such as kale could improve vit U absorption and provide a natural therapy for detoxifying nicotine.

Fermented Cordyceps militaris Extract Prevents Hepatosteatosis and Adipocyte Hypertrophy in High Fat Diet-Fed Mice.

Nonalcoholic fatty liver diseases (NAFLD) is characterized by accumulation of lipid droplets in the liver. The objective of this study was to evaluate protective effects of fermented Cordyceps militaris extract by Pediococcus pentosaceus ON188 (ONE) against hepatosteatosis and obesity in mice fed a high-fat diet (HFD). Eight-week-old male C57BL/6J mice were fed HFD mixed with ONE for four weeks and its effects on hepatosteatosis and obesity were examined. Although ONE did not change food intake, it reduced body weights of mice at administration dose of 200 mg/kg/day. Activities of lactate dehydrogenase (LDH), aspartate transaminase (AST), and alanine transaminase (ALT) as plasma parameters were reduced by ONE in a dose-dependent manner. Hepatic lipid droplets and triglyceride (TG) levels were also reduced by ONE due to upregulation of fatty acid oxidizing genes such as carnithine palmitoyltransferase (CPT1) and peroxisomal proliferator activated receptor α(PPARα) mediated by induction of sphingosine kinase 2 (SPHK2). In epididymal fat tissue, sizes of adipocytes were significantly reduced by ONE in a dose-dependent manner. This is mainly due to suppression of lipogenesis and upregulation of adipocyte browning genes. Collectively, these results suggest that fermented ONE can activate fatty acid oxidation via SPHK2 in the liver. It can also suppress lipogenesis and activate browning in adipose tissue. Thus, ONE might have potential to be used for the development of functional foods against liver dysfunction and obesity.

Fermented Cordyceps militaris Extract Ameliorates Hepatosteatosis via Activation of Fatty Acid Oxidation.

Nonalcoholic fatty liver disease is a progressive disease involving the accumulation of lipid droplets in the liver. In this study, we investigated the anti-hepatosteatosis effects of fermented Cordyceps militaris extract (CME) in AML-12 hepatocytes. Although the levels of adenosine and cordycepin were reduced in the extracts of CM grown on germinated soybean (GSCE) and fermented CM grown on germinated soybean (GSC) by Pediococcus pentosaceus ON188 (ON188E), the expression of fatty acid oxidation (FAO) genes were upregulated only by GSC-ON188E treatment in a dose-dependent manner. In contrast, a lipogenic gene, stearoyl Coenzyme A desaturase 1, was downregulated by ON188E. Formation of intracellular lipid droplets by the addition of oleic acid was reduced by ON188E to levels observed in WY14643-treated cells. When cells were treated with ON188E, sphingosine kinase 2 mainly responsible for hepatic sphingosine 1-phosphate (S1P) synthesis was upregulated and S1P was elevated. Collectively, the fermented GSC extract activates FAO through elevation of S1P synthesis and has potential as a therapeutic for hepatosteatosis.

Inhibition of lactate dehydrogenase A suppresses inflammatory response in RAW 264.7 macrophages.

Lactate is an important metabolite in cellular metabolism and fluctuates in certain disease conditions including cancer and immune diseases. It was hypothesized that a decrease in lactate would modulate the inflammatory response elicited by lipopolysaccharides (LPS) in macrophages. When RAW 264.7 macrophages were treated with FX11, a specific lactate dehydrogenase (LDHA) inhibitor, the expression of the cytokines, inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX­2) was downregulated due to reduced cellular lactate levels. Genetic suppression of LDHA by small interfering RNA (siRNA) downregulated the LPS­activated expression of interleukin (IL)­6, iNOS, and COX­2, and reduced the production of IL­6 and nitrites. Pharmacological and genetic suppression of LDHA inhibited the phosphorylation of p38 mitogen­activated protein kinase. Microarray gene expression profile demonstrated that the genes involved in cell proliferation and inflammation were mainly altered by siRNA­mediated LDHA suppression. Collectively, the present observations suggest that lactate may be an important metabolite and implicated in regulation of inflammatory response.

Celecoxib-mediated activation of endoplasmic reticulum stress induces de novo ceramide biosynthesis and apoptosis in hepatoma HepG2 cells mobilization.

Ceramides are the major sphingolipid metabolites involved in cell survival and apoptosis. When HepG2 hepatoma cells were treated with celecoxib, the expression of the genes in de novo sphingolipid biosynthesis and sphingomyelinase pathway was upregulated and cellular ceramide was elevated. In addition, celecoxib induced endoplasmic reticulum (ER) stress in a time-dependent manner. SPTLC2, a subunit of serine palmitoyltransferase, was overexpressed by adenovirus. Adenoviral overexpression of SPTLC2 (AdSPTLC2) decreased cell viability of HEK293 and HepG2 cells. In addition, AdSPTLC2 induced apoptosis via the caspase-dependent apoptotic pathway and elevated cellular ceramide, sphingoid bases, and dihydroceramide. However, overexpression of SPTLC2 did not induce ER stress. Collectively, celecoxib activates de novo sphingolipid biosynthesis and the combined effects of elevated ceramide and transcriptional activation of ER stress induce apoptosis. However, activation of de novo sphingolipid biosynthesis does not activate ER stress in hepatoma cells and is distinct from the celecoxib-mediated activation of ER stress. [BMB Reports 2017; 50(3): 144-149].

Immunomodulatory Efficacy of Standardized Annona muricata (Graviola) Leaf Extract via Activation of Mitogen-Activated Protein Kinase Pathways in RAW 264.7 Macrophages.

Annona muricata, commonly known as Graviola, has been utilized as a traditional medicine to treat various human diseases. The aim of this study was to examine the immune-enhancing activity of Graviola leaf extracts in RAW 264.7 macrophage cells. Active ingredients in Graviola leaf extracts (GE) were identified as kaempferol-3-O-rutinoside and quercetin-3-O-rutinoside by LC-MS/MS. When treated with steam or 50% ethanol GE, cell morphology was altered due to initiation of cell differentiation. While the cell viability was not altered by the steam GE, it was reduced by the ethanol GE. Both steam and ethanol GE induced the transcriptional expression of cytokines, including tumor necrosis factor-α (TNF-α) and interleukin-1ß, but only the steam extract upregulated inducible nitric oxide synthase (iNOS). In consistence with mRNA expression, the production of TNF-α and nitrite was elevated by both steam and ethanol extracts of Graviola leaves. This is mainly due to activation of mitogen-activated protein (MAP) kinase signaling pathways. These results suggest that Graviola leaves enhance immunity by activation of the MAP kinase pathways. These bioactive properties of Graviola indicate its potential as a health-promoting ingredient to boost the immune system.

Bioefficacy of Graviola leaf extracts in scavenging free radicals and upregulating antioxidant genes.

The aims of this study were to determine bioactive components of Graviola leaf extracts and to examine the radical scavenging capacity, gene expression and transcription factors of antioxidant enzymes. Rutin, kaempferol-rutinoside, and vitamin U were identified from the steaming and 50% EtOH extracts of Graviola leaves. Graviola leaf extracts effectively scavenged peroxy and nitrogen radicals. 50% EtOH of Graviola leaves provided a 1-2.9 times higher trolox equivalent than the steaming extract. It also had a higher VCEAC. Graviola leaf extracts reduced the generation of reactive oxygen species (ROS) induced by H2O2 in a dose-dependent manner. The 50% EtOH extract of Graviola leaves upregulated SOD1 and Nrf2, but catalase and HMOX1 were not altered by the 50% EtOH extract of Graviola leaves.