Inhibition of triglyceride synthesis as a treatment strategy for obesity: lessons from DGAT1-deficient mice

Obesity-Facilitated Colon Cancer Progression Is Mediated by Increased Diacylglycerol O-Acyltransferases 1 and 2 Levels

BACKGROUND & AIMS

The obesity epidemic is associated with increased colon cancer progression. As lipid droplets (LDs) fuel tumor growth, we aimed to determine the significance of diacyltransferases (diacylglycerol o-acyltransferases 1 and 2 [DGAT1/2]), responsible for LDs biogenesis, in obesity-mediated colonic tumorigenesis.

METHODS

Human colon cancer samples, colon cancer cells, colonospheres, and ApcMin/+ colon cancer mouse model on a high-fat diet were employed. For DGAT1/2 inhibition, enzymatic inhibitors and small interfering RNA were used. Expression, pathways, cell cycle, and growth were assessed. Bioinformatic analyses of CUT&RUN and RNA sequencing data were performed.

RESULTS

DGAT1/2 levels in human colon cancer tissue are significantly elevated with disease severity and obesity (vs normal). Their levels are increased in human colon cancer cells (vs nontransformed) and further enhanced by fatty acids prevalent in obesity; augmented DGAT2 expression is MYC-dependent. Inhibition of DGAT1/2 improves FOXO3 activity by attenuating PI3K, resulting in reduced MYC-dependent DGAT2 expression and accumulation of LDs, suggesting feedback. This inhibition attenuated growth in colon cancer cells and colonospheres via FOXO3/p27kip1 cell cycle arrest and reduced colonic tumors in ApcMin/+ mice on a high-fat diet. Transcriptomic analysis revealed that DGAT1/2 inhibition targeted metabolic and tumorigenic pathways in human colon cancer and colon cancer crypts, stratifying human colon cancer samples from normal. Further analysis revealed that this inhibition is predictive of advanced disease-free state and survival in patients with colon cancer.

CONCLUSIONS

This is a novel mechanism of DGAT1/2-dependent metabolic and tumorigenic remodeling in obesity-facilitated colon cancer, providing a platform for future development of effective treatments for patients with colon cancer.

Transcription factor ETV4 plays a critical role in the development of non-alcoholic fatty liver disease

The Angiopoietin-like 4 (ANGPTL4) and ETS Variant Transcription Factor 4 (ETV4) are involved in the metabolic transition and carcinogenesis in the liver. However, the role of ETV4 in the development of non-alcoholic fatty liver disease (NAFLD) is currently unknown. Our study reveals that ETV4 expression was upregulated in the diet-induced non-alcoholic fatty liver disease, and plays a critical role in the dysregulated lipid metabolism. We demonstrate a mechanism by which ANGPTL4 regulates lipid homeostasis via involving the AMPK/ETV4 axis. Transient knockdown of ETV4 abolished the ANGPTL4-induced expression of Srebp1c, Acc and Fasn. Insulin treatment potentially increased the physical association of ETV4 with SREBP1, and promotes nuclear translocation and transcriptional activity of SREBP1. In addition, we show that combined therapy with omega-3 fatty acids and diacylglycerol O-acyltransferase inhibitor 1 (DGAT1) inhibitor (A-922500) counteracted the ANGPTL4-ETV4 axis-induced lipogenesis in vitro, and in vivo in obese mice via activation of GPR120-βarrestin2-AMPK pathway. Finally, we demonstrate that targeted pharmacologic therapy using GalNac-ETV4 siRNA that specifically inhibits ETV4 gene expression in the liver protects against diet-induced NAFLD, obesity and dyslipidemia. Hence, our study reveal previously unrecognized role of ETV4 in the NAFLD, and provides rationale targeting ETV4 to treat NAFLD.

Role of diacylglycerol O-acyltransferase 1 (DGAT1) in lipolysis and autophagy of adipose tissue from ketotic dairy cows

High-yielding dairy cows in early lactation often encounter difficulties in meeting the energy requirements essential for maintaining milk production. This is primarily attributed to insufficient dry matter intake, which consequently leads to sustained lipolysis of adipose tissue. Fatty acids released by lipolysis can disrupt metabolic homeostasis. Autophagy, an adaptive response to intracellular environmental changes, is considered a crucial mechanism for regulating lipid metabolism and maintaining a proper cellular energy status. Despite its close relationship with aberrant lipid metabolism and cytolipotoxicity in animal models of metabolic disorders, the precise function of diacylglycerol o-acyltransferase 1 (DGAT1) in bovine adipose tissue during periods of negative energy balance is not fully understood, particularly regarding its involvement in lipolysis and autophagy. The objective of the present study was to assess the effect of DGAT1 on both lipolysis and autophagy in bovine adipose tissue and isolated adipocytes. Adipose tissue and blood samples were collected from cows diagnosed as clinically ketotic (n = 15) or healthy (n = 15) following a veterinary evaluation based on clinical symptoms and serum concentrations of BHB, which were 3.19 mM (interquartile range = 0.20) and 0.50 mM (interquartile range = 0.06), respectively. Protein abundance of DGAT1 and phosphorylation levels of unc-51-like kinase 1 (ULK1), were greater in adipose tissue from cows with ketosis, whereas phosphorylation levels of phosphoinositide 3-kinase (PI3K), protein kinase B (AKT), and mammalian target of rapamycin (mTOR) were lower. Furthermore, when adipocytes isolated from the harvested adipose tissue of 15 healthy cows were transfected with DGAT1 overexpression adenovirus or DGAT1 small interfering RNA followed by exposure to epinephrine (EPI), it led to greater ratios and protein abundance of phosphorylated hormone-sensitive triglyceride lipase (LIPE) to total LIPE and adipose triglyceride lipase (ATGL), while inhibiting the protein phosphorylation levels of ULK1, PI3K, AKT, and mTOR. Overexpression of DGAT1 in EPI-treated adipocytes reduced lipolysis and autophagy, whereas silencing DGAT1 further exacerbated EPI-induced lipolysis and autophagy. Taken together, these findings indicate that upregulation of DGAT1 may function as an adaptive response to suppress adipocytes lipolysis, highlighting the significance of maintaining metabolic homeostasis in dairy cows during periods of negative energy balance.

Modeling the cell biology of monogenetic intestinal epithelial disorders

Monogenetic variants are responsible for a range of congenital human diseases. Variants in genes that are important for intestinal epithelial function cause a group of disorders characterized by severe diarrhea and loss of nutrient absorption called congenital diarrheas and enteropathies (CODEs). CODE-causing genes include nutrient transporters, enzymes, structural proteins, and vesicular trafficking proteins in intestinal epithelial cells. Several severe CODE disorders result from the loss-of-function in key regulators of polarized endocytic trafficking such as the motor protein, Myosin VB (MYO5B), as well as STX3, STXBP2, and UNC45A. Investigations of the cell biology and pathophysiology following loss-of-function in these genes have led to an increased understanding of both homeostatic and pathological vesicular trafficking in intestinal epithelial cells. Modeling different CODEs through investigation of changes in patient tissues, coupled with the development of animal models and patient-derived enteroids, has provided critical insights into the enterocyte differentiation and function. Linking basic knowledge of cell biology with the phenotype of specific patient variants is a key step in developing effective treatments for rare monogenetic diseases. This knowledge can also be applied more broadly to our understanding of common epithelial disorders.

Novel DGAT1 Mutations Identified in Congenital Diarrheal Disorder 7: A Case Report with Therapeutic Experience

Congenital diarrheal disorders (CDD) are a group of rare inherited intestinal disorders, among which CDD7 was recently identified to be associated with only 24 mutations in gene coding for diacylglycerol-acyltransferase 1 (DGAT1). We report on a female patient who presented with diarrhea, vomiting, hypoalbuminemia, and failure to thrive after birth. Two novel variants of c.1215_1216delAG and c.838C>T were found in the DGAT1 gene by whole exome sequencing, which was confirmed to be compound heterozygous by Sanger sequencing. Her symptoms and nutritional status improved significantly after 1 year of a fat-restricted enteral diet. Weight for age and weight for length increased from -5.0 SDS and -4.0 SDS at 3 months to +0.08 SDS and +1.75 SDS at 15 months, respectively. This report expanded the mutation spectrum of DGAT1-related CDD7 and enriched our knowledge of the clinical features. Moreover, early fat-restricted enteral diet intervention was suggested for the treatment of such patients.

Lipidomic Assessment of the Inhibitory Effect of Standardized Water Extract of Hydrangea serrata (Thunb.) Ser. Leaves during Adipogenesis

Obesity is primarily exacerbated by excessive lipid accumulation during adipogenesis, with triacylglycerol (TG) as a major lipid marker. However, as the association between numerous lipid markers and various health conditions has recently been revealed, investigating the lipid metabolism in detail has become necessary. This study investigates the lipid metabolic effects of Hydrangea serrata (Thunb.) Ser. hot water leaf extract (WHS) on adipogenesis using LC-MS-based lipidomics analysis of undifferentiated, differentiated, and WHS-treated differentiated 3T3-L1 cells. WHS treatment effectively suppressed the elevation of glycerolipids, including TG and DG, and prevented a molecular shift in fatty acyl composition towards long-chain unsaturated fatty acids. This shift also impacted glycerophospholipid metabolism. Additionally, WHS stabilized significant lipid markers such as the PC/PE and LPC/PE ratios, SM, and Cer, which are associated with obesity and related comorbidities. This study suggests that WHS could reduce obesity-related risk factors by regulating lipid markers during adipogenesis. This study is the first to assess the underlying lipidomic mechanisms of the adipogenesis-inhibitory effect of WHS, highlighting its potential in developing natural products for treating obesity and related conditions. Our study provides a new strategy for the development of natural products for the treatment of obesity and related diseases.

DGAT inhibition at the post-absorptive phase reduces plasma FA by increasing FA oxidation

In this Correspondence, A. Sharma & C. Wolfrum report that DGAT1/2 pharmacological inhibition at post-absorptive phase in mice leads to increased fatty acid oxidation and reduced plasma fatty acid levels, which could open new therapeutic avenues to avoid GI complications observed in clinical trials.

The roles of DGAT1 and DGAT2 in human myotubes are dependent on donor patho-physiological background

The roles of DGAT1 and DGAT2 in lipid metabolism and insulin responsiveness of human skeletal muscle were studied using cryosections and myotubes prepared from muscle biopsies from control, athlete, and impaired glucose regulation (IGR) cohorts of men. The previously observed increases in intramuscular triacylglycerol (IMTG) in athletes and IGR were shown to be related to an increase in lipid droplet (LD) area in type I fibers in athletes but, conversely, in type II fibers in IGR subjects. Specific inhibition of both diacylglycerol acyltransferase (DGAT) 1 and 2 decreased fatty acid (FA) uptake by myotubes, whereas only DGAT2 inhibition also decreased fatty acid oxidation. Fatty acid uptake in myotubes was negatively correlated with the lactate thresholds of the respective donors. DGAT2 inhibition lowered acetate uptake and oxidation in myotubes from all cohorts whereas DGAT1 inhibition had no effect. A positive correlation between acetate oxidation in myotubes and resting metabolic rate (RMR) from fatty acid oxidation in vivo was observed. Myotubes from athletes and IGR had higher rates of de novo lipogenesis from acetate that were normalized by DGAT2 inhibition. Moreover, DGAT2 inhibition in myotubes also resulted in increased insulin-induced Akt phosphorylation. The differential effects of DGAT1 and DGAT2 inhibition suggest that the specialized role of DGAT2 in esterifying nascent diacylglycerols and de novo synthesized FA is associated with synthesis of a pool of triacylglycerol, which upon hydrolysis results in effectors that promote mitochondrial fatty acid oxidation but decrease insulin signaling in skeletal muscle cells.

Preferential lipolysis of DGAT1 over DGAT2 generated triacylglycerol in Huh7 hepatocytes

Two distinct diacylglycerol acyltransferases (DGAT1 and DGAT2) catalyze the final committed step of triacylglycerol (TG) synthesis in hepatocytes. After its synthesis in the endoplasmic reticulum (ER) TG is either stored in cytosolic lipid droplets (LDs) or is assembled into very low-density lipoproteins in the ER lumen. TG stored in cytosolic LDs is hydrolyzed by adipose triglyceride lipase (ATGL) and the released fatty acids are converted to energy by oxidation in mitochondria. We hypothesized that targeting/association of ATGL to LDs would differ depending on whether the TG stores were generated through DGAT1 or DGAT2 activities. Individual inhibition of DGAT1 or DGAT2 in Huh7 hepatocytes incubated with oleic acid did not yield differences in TG accretion while combined inhibition of both DGATs completely prevented TG synthesis suggesting that either DGAT can efficiently esterify exogenously supplied fatty acid. DGAT2-made TG was stored in larger LDs, whereas TG formed by DGAT1 accumulated in smaller LDs. Inactivation of DGAT1 or DGAT2 did not alter expression (mRNA or protein) of ATGL, the ATGL activator ABHD5/CGI-58, or LD coat proteins PLIN2 or PLIN5, but inactivation of both DGATs increased PLIN2 abundance despite a dramatic reduction in the number of LDs. ATGL was found to preferentially target to LDs generated by DGAT1 and fatty acids released from TG in these LDs were also preferentially used for fatty acid oxidation. Combined inhibition of DGAT2 and ATGL resulted in larger LDs, suggesting that the smaller size of DGAT1-generated LDs is the result of increased lipolysis of TG in these LDs.

Garcinia mangostana Suppresses Triacylglycerol Synthesis in Hepatocytes and Enterocytes

Regulation of diacylglycerol acyltransferase (DGAT) and pancreatic lipase (PL) activities is important in the treatment of triacylglycerol (TG)-related metabolic diseases. Garcinia mangostana, also known as mangosteen, is a traditional medicine ingredient used in the treatment of inflammation in Southeast Asia. In this study, The ethanolic extract of G. mangostana peel inhibited human recombinant DGAT1 and DGAT2, and PL enzyme activities in vitro. The inhibitory activity of DGAT1 and DGAT2 enzymes of four representative bioactive substances in mangosteen was confirmed. In addition, G. mangostana was confirmed to suppress the serum TG levels in C57 mice by inhibiting the absorption and synthesis of TG in the gastrointestinal tract. Through this study, it was revealed that G. mangostana extract could be useful for the prevention and amelioration of TG-related metabolic diseases such as obesity and fatty liver.

Uncoupling Lipid Synthesis from Adipocyte Development

Obesity results from the expansion of adipose tissue, a versatile tissue regulating energy homeostasis, adipokine secretion, thermogenesis, and inflammation. The primary function of adipocytes is thought to be lipid storage through lipid synthesis, which is presumably intertwined with adipogenesis. However, during prolonged fasting, adipocytes are depleted of lipid droplets yet retain endocrine function and an instant response to nutrients. This observation led us to question whether lipid synthesis and storage can be uncoupled from adipogenesis and adipocyte function. By inhibiting key enzymes in the lipid synthesis pathway during adipocyte development, we demonstrated that a basal level of lipid synthesis is essential for adipogenesis initiation but not for maturation and maintenance of adipocyte identity. Furthermore, inducing dedifferentiation of mature adipocytes abrogated adipocyte identity but not lipid storage. These findings suggest that lipid synthesis and storage are not the defining features of adipocytes and raise the possibility of uncoupling lipid synthesis from adipocyte development to achieve smaller and healthier adipocytes for the treatment of obesity and related disorders.

Basal re-esterification finetunes mitochondrial fatty acid utilization

OBJECTIVE

Emerging evidence suggest the existence of constant basal lipolysis and re-esterification of a substantial fraction of thus liberated fatty acids. In stimulated lipolysis, the re-esterification is proposed to be a protective mechanism against lipotoxicity; however, the role of the lipolysis coupled to re-esterification under basal conditions has not been deciphered.

METHODS

We used adipocytes (in vitro differentiated brown and white adipocytes derived from a cell line or primary SVF culture) to study the effect of inhibition of re-esterification by pharmacological DGAT1 and DGAT2 inhibitors alone or in combination. We then evaluated cellular energetics, lipolysis flux, and lipidomic parameters along with mitochondrial properties and fuel utilization.

RESULTS

In adipocytes, DGAT1 and 2 mediated re-esterification is a moderator of fatty acid oxidation. Combined inhibition of both DGATs (D1+2i) increases oxygen consumption, which is largely due to enhanced mitochondrial respiration by lipolysis-derived fatty acids (FAs). Acute D1+2i selectively affects mitochondrial respiration without affecting the transcriptional homeostasis of genes relevant to mitochondrial health and lipid metabolism. D1+2i enhances the mitochondrial import of pyruvate and activates AMP Kinase to counteract CPT1 antagonism, thus facilitating the mitochondrial import of fatty acyl-CoA.

CONCLUSIONS

These data implicate the process of re-esterification in the regulation of mitochondrial FA usage and uncover a mechanism of FAO regulation via crosstalk with FA re-esterification.

AgRP Neuron-Specific Ablation Represses Appetite, Energy Intake, and Somatic Growth in Larval Zebrafish

Neuronal circuits regulating appetite are dominated by arcuate nucleus neurons, which include appetite-promoting and -suppressing neurons that release the orexigenic neuropeptide agouti-related protein (AgRP) and anorexigenic neuropeptide pro-opiomelanocortin, respectively, to compete for melanocortin receptors to modulate feeding behavior. In this study, we expressed novel agrp promoters, including different lengths of the 5' flanking regions of the agrp gene (4749 bp) in the zebrafish genome. We used the agrp promoter to derive the enhanced green fluorescent protein (EGFP)-nitroreductase (NTR) fusion protein, allowing expression of the green fluorescence signal in the AgRP neurons. Then, we treated the transgenic zebrafish AgRP4.7^NTR (Tg [agrp-EGFP-NTR]) with metronidazole to ablate the AgRP neurons in the larvae stage and observed a decline in their appetite and growth. The expression of most orexigenic and growth hormone/insulin-like growth factor axis genes decreased, whereas that of several anorexigenic genes increased. Our findings demonstrate that AgRP is a critical regulator of neuronal signaling for zebrafish appetite and energy intake control. Thus, AgRP4.7^NTR can be used as a drug-screening platform for therapeutic targets to treat human appetite disorders, including obesity. Furthermore, the unique agrp promoter we identified can be a powerful tool for research on AgRP neurons, especially AgRP neuron-mediated pathways in the hypothalamus, and appetite.

Dietary additive octyl and decyl glycerate modulates metabolism and inflammation under different dietary patterns with the contribution of the gut microbiota

Octyl and decyl glycerate (ODG), a medium-chain triglyceride (MCT), is widely used as a food additive. Medium-chain monoglycerides, such as glycerol monolaurate and glycerol monocaprylate, were found to change the composition of the gut microbiota and influence glucose and lipid metabolism and inflammation. However, whether ODG influences the gut microbiota and whether the alteration in the gut microbiota contributes to the metabolic phenotype remain unknown. Under a normal-chow diet, mice were treated with or without different dosages of ODG (150, 800, 1600 mg kg^-1) for 22 weeks. All doses of ODG significantly decreased the ratio of HDL to LDL cholesterol, improved the inflammation and insulin resistance, and increased the α-diversity of the gut microbiota and the abundance of Bifidobacterium and Turicibacter. Under a high-fat diet, mice were treated with or without 1600 mg kg^-1 ODG for 16 weeks. The results demonstrated that ODG significantly alleviated the increase in the ratio of HDL to LDL cholesterol, insulin resistance, and inflammation caused by HFD. The expression of related genes was consistent with the above observations. ODG also altered the composition of the gut microbiota and increased the Bifidobacterium abundance under HFD. Our findings indicated that ODG similarly improved glucose metabolism and inflammation but exhibited differential effects on lipid metabolism under different dietary patterns. Furthermore, changes in the gut microbiota caused by ODG supplementation might contribute to the alteration in glucose and lipid metabolism and inflammation, which might be influenced by dietary patterns.

A novel regulatory facet for hypertriglyceridemia: The role of microRNAs in the regulation of triglyceride-rich lipoprotein biosynthesis

Atherosclerotic cardiovascular disease (ASCVD) is one of the major leading global causes of death. Genetic and epidemiological studies strongly support the causal association between triacylglycerol-rich lipoproteins (TAGRL) and atherogenesis, even in statin-treated patients. Recent genetic evidence has clarified that variants in several key genes implicated in TAGRL metabolism are strongly linked to the increased ASCVD risk. There are several triacylglycerol-lowering agents; however, new therapeutic options are in development, among which are miRNA-based therapeutic approaches. MicroRNAs (miRNAs) are small non-coding RNAs (18-25 nucleotides) that negatively modulate gene expression through translational repression or degradation of target mRNAs, thereby reducing the levels of functional genes. MiRNAs play a crucial role in the development of hypertriglyceridemia as several miRNAs are dysregulated in both synthesis and clearance of TAGRL particles. MiRNA-based therapies in ASCVD have not yet been applied in human trials but are attractive. This review provides a concise overview of current interventions for hypertriglyceridemia and the development of novel miRNA and siRNA-based drugs. We summarize the miRNAs involved in the regulation of key genes in the TAGRLs synthesis pathway, which has gained attention as a novel target for therapeutic applications in CVD.

Supplementation of Enriched Polyunsaturated Fatty Acids and CLA Cheese on High Fat Diet: Effects on Lipid Metabolism and Fat Profile

Epidemiological studies have demonstrated a positive relationship between dietary fat intake and the onset of several metabolic diseases. This association is particularly evident in a diet rich in saturated fatty acids, typical of animal foods, such as dairy products. However, these foods are the main source of fatty acids with a proven nutraceutical effect, such as the ω-3 fatty acid α-linolenic acid (ALA) and the conjugated linoleic acid (CLA), which have demonstrated important roles in the prevention of various diseases. In the present study, the effect of a supplementation with cheese enriched with ω-3 fatty acids and CLA on the metabolism and lipid profiles of C57bl/6 mice was evaluated. In particular, the analyses were conducted on different tissues, such as liver, muscle, adipose tissue and brain, known for their susceptibility to the effects of dietary fats. Supplementing cheese enriched in CLA and ω-3 fats reduced the level of saturated fat and increased the content of CLA and ALA in all tissues considered, except for the brain. Furthermore, the consumption of this cheese resulted in a tissue-specific response in the expression levels of genes involved in lipid and mitochondrial metabolism. As regards genes involved in the inflammatory response, the consumption of enriched cheese resulted in a reduction in the expression of inflammatory genes in all tissues analyzed. Considering the effects that chronic inflammation associated with a high-calorie and high-fat diet (meta-inflammation) or aging (inflammaging) has on the onset of chronic degenerative diseases, these data could be of great interest as they indicate the feasibility of modulating inflammation (thus avoiding/delaying these pathologies) with a nutritional and non-pharmacological intervention.

KRAS Affects Adipogenic Differentiation by Regulating Autophagy and MAPK Activation in 3T3-L1 and C2C12 Cells

Kirsten rat sarcoma 2 viral oncogene homolog (Kras) is a proto-oncogene that encodes the small GTPase transductor protein KRAS, which has previously been found to promote cytokine secretion, cell survival, and chemotaxis. However, its effects on preadipocyte differentiation and lipid accumulation are unclear. In this study, the effects of KRAS inhibition on proliferation, autophagy, and adipogenic differentiation as well as its potential mechanisms were analyzed in the 3T3-L1 and C2C12 cell lines. The results showed that KRAS was localized mainly in the nuclei of 3T3-L1 and C2C12 cells. Inhibition of KRAS altered mammalian target of rapamycin (Mtor), proliferating cell nuclear antigen (Pcna), Myc, peroxisome proliferator-activated receptor γ (PPARγ), CCAAT/enhancer binding protein beta (C/ebp-β), diacylglycerol O-acyltransferase 1 (Dgat1), and stearoyl-coenzyme A desaturase 1 (Scd1) expression, thereby reducing cell proliferation capacity while inducing autophagy, enhancing differentiation of 3T3-L1 and C2C12 cells into mature adipocytes, and increasing adipogenesis and the capacity to store lipids. Moreover, during differentiation, KRAS inhibition reduced the levels of extracellular regulated protein kinases (ERK), c-Jun N-terminal kinase (JNK), p38, and phosphatidylinositol 3 kinase (PI3K) activation. These results show that KRAS has unique regulatory effects on cell proliferation, autophagy, adipogenic differentiation, and lipid accumulation.

Identifying disease-critical cell types and cellular processes across the human body by integration of single-cell profiles and human genetics

Genome-wide association studies (GWAS) provide a powerful means to identify loci and genes contributing to disease, but in many cases the related cell types/states through which genes confer disease risk remain unknown. Deciphering such relationships is important for identifying pathogenic processes and developing therapeutics. Here, we introduce sc-linker, a framework for integrating single-cell RNA-seq (scRNA-seq), epigenomic maps and GWAS summary statistics to infer the underlying cell types and processes by which genetic variants influence disease. We analyzed 1.6 million scRNA-seq profiles from 209 individuals spanning 11 tissue types and 6 disease conditions, and constructed gene programs capturing cell types, disease progression, and cellular processes both within and across cell types. We evaluated these gene programs for disease enrichment by transforming them to SNP annotations with tissue-specific epigenomic maps and computing enrichment scores across 60 diseases and complex traits (average N= 297K). Cell type, disease progression, and cellular process programs captured distinct heritability signals even within the same cell type, as we show in multiple complex diseases that affect the brain (Alzheimer’s disease, multiple sclerosis), colon (ulcerative colitis) and lung (asthma, idiopathic pulmonary fibrosis, severe COVID-19). The inferred disease enrichments recapitulated known biology and highlighted novel cell-disease relationships, including GABAergic neurons in major depressive disorder (MDD), a disease progression M cell program in ulcerative colitis, and a disease-specific complement cascade process in multiple sclerosis. In autoimmune disease, both healthy and disease progression immune cell type programs were associated, whereas for epithelial cells, disease progression programs were most prominent, perhaps suggesting a role in disease progression over initiation. Our framework provides a powerful approach for identifying the cell types and cellular processes by which genetic variants influence disease.

Short-term changes in the serum metabolome after laparoscopic sleeve gastrectomy and Roux-en-Y gastric bypass

INTRODUCTION

Bariatric surgery is known to be the most effective treatment for weight loss in obese patients and for the rapid remission of obesity-related comorbidities. These short-term improvements result from not only limited digestion or absorption but also dynamic changes in metabolism throughout the whole body. However, short-term metabolism studies associated with bariatric surgery in Asian individuals have not been reported.

OBJECTIVES

The aim of this study was to investigate the short-term metabolome changes in the serum promoted by laparoscopic sleeve gastrectomy (SG) and Roux-en-Y gastric bypass (RYGB) and to determine the underlying mechanisms that affect obesity-related comorbidities.

METHODS

Serum samples were collected from Korean patients who underwent RYGB or SG before and 4 weeks after the surgery. Metabolomic and lipidomic profiling was performed using UPLC-Orbitrap-MS, and data were analyzed using statistical analysis.

RESULTS

Metabolites mainly related to amino acids, lipids (fatty acids, glycerophospholipids, sphingolipids, glycerolipids) and bile acids changed after surgery, and these changes were associated with the lowering of risk factors for obesity-related diseases such as nonalcoholic fatty liver disease (NAFLD), type 2 diabetes (T2D) and atherosclerosis. Interestingly, the number of significantly altered metabolites related to the lipid metabolism were greater in SG than in RYGB. Furthermore, the metabolites related to amino acid metabolism were significantly changed only after SG, whereas bile acid changed significantly only following RYGB.

CONCLUSION

These differences could result from anatomical differences between the two surgeries and could be related to the gut microbiota. This study provides crucial information to expand the knowledge of the common but different molecular mechanisms involved in obesity and obesity-related comorbidities affected by each bariatric procedure.

Microtubule affinity regulating kinase 4: A promising target in the pathogenesis of atherosclerosis

Microtubule affinity regulating kinase 4 (MARK4), an important member of the serine/threonine kinase family, regulates the phosphorylation of microtubule-associated proteins and thus modulates microtubule dynamics. In human atherosclerotic lesions, the expression of MARK4 is significantly increased. Recently, accumulating evidence suggests that MARK4 exerts a proatherogenic effect via regulation of lipid metabolism (cholesterol, fatty acid, and triglyceride), inflammation, cell cycle progression and proliferation, insulin signaling, and glucose homeostasis, white adipocyte browning, and oxidative stress. In this review, we summarize the latest findings regarding the role of MARK4 in the pathogenesis of atherosclerosis to provide a rationale for future investigation and therapeutic intervention.

Comparison of Cell-Free Extracts from Three Newly Identified Lactobacillus plantarum Strains on the Inhibitory Effect of Adipogenic Differentiation and Insulin Resistance in 3T3-L1 Adipocytes

Obesity and associated metabolic disorders, including cardiovascular disease and diabetes, are rapidly becoming serious global health problems. It has been reported that Lactobacillus plantarum (L. plantarum) extracts have the beneficial activities of antiobesity and antidiabetes, although few studies have compared the beneficial effects among various L. plantarum extracts. In this study, three new L. plantarum (named LP, LS, and L14) strains were identified, and the antiobesogenic and diabetic effects of their extracts were investigated and compared using 3T3-L1 cells in vitro. Lipid accumulation in maturing 3T3-L1 cells was significantly decreased by the addition of LS and L14 extracts. The mRNA expression levels of Pparγ, C/ebpα, Fabp4, Fas, and Dgat1 were significantly decreased by the addition of LP, LS, and L14 extracts. Interestingly, the protein expression levels of PPARγ, C/EBPα, FABP4, and FAS were downregulated in mature 3T3-L1 cells with the addition of the L14 extract. Moreover, the LS and L14 extract treatments stimulated glucose uptake in maturing adipocytes. The L14 extract treatments exhibited a significant reduction in TNF-α protein expression, which is a key factor of insulin resistance in adipocytes. Of the three extracts, L14 extract markedly reduced adipogenic differentiation and insulin resistance in vitro, suggesting that the L14 extract may be used as a therapeutic agent for obesity-associated metabolic disorders.

ROS Modulating Effects of Lingonberry (Vaccinium vitis-idaea L.) Polyphenols on Obese Adipocyte Hypertrophy and Vascular Endothelial Dysfunction

Oxidative stress and dysregulated adipocytokine secretion accompanying hypertrophied adipose tissue induce chronic inflammation, which leads to vascular endothelial dysfunction. The present study investigated the ability of anthocyanin (ACN) and non-anthocyanin polyphenol (PP) fractions from lingonberry fruit to mitigate adipose tissue hypertrophy and endothelial dysfunction using 3T3-L1 adipocytes and human umbilical vein endothelial cells (HUVECs). This study showed that the PP fraction decreased intracellular ROS generation in hypertrophied adipocytes by enhancing antioxidant enzyme expression (SOD2) and inhibiting oxidant enzyme expression (NOX4, iNOS). Moreover, PP and ACN fractions reduced triglyceride content in adipocytes accompanied by downregulation of the expression of lipogenic genes such as aP2, FAS, and DAGT1. Treatment with both fractions modulated the mRNA expression and protein secretion of key adipokines in hypertrophied adipocytes. Expression and secretion of leptin and adiponectin were, respectively, down- and upregulated. Furthermore, PP and ACN fractions alleviated the inflammatory response in TNF-α-induced HUVECs by inhibiting the expression of pro-inflammatory genes (IL-6, IL-1β) and adhesion molecules (VCAM-1, ICAM-1, SELE). The obtained results suggest that consuming polyphenol-rich lingonberry fruit may help prevent and treat obesity and endothelial dysfunction due to their antioxidant and anti-inflammatory actions.

The Race to Bash NASH: Emerging Targets and Drug Development in a Complex Liver Disease

Nonalcoholic steatohepatitis (NASH) is a severe form of nonalcoholic fatty liver disease (NAFLD) characterized by liver steatosis, inflammation, and hepatocellular damage. NASH is a serious condition that can progress to cirrhosis, liver failure, and hepatocellular carcinoma. The association of NASH with obesity, type 2 diabetes mellitus, and dyslipidemia has led to an emerging picture of NASH as the liver manifestation of metabolic syndrome. Although diet and exercise can dramatically improve NASH outcomes, significant lifestyle changes can be challenging to sustain. Pharmaceutical therapies could be an important addition to care, but currently none are approved for NASH. Here, we review the most promising targets for NASH treatment, along with the most advanced therapeutics in development. These include targets involved in metabolism (e.g., sugar, lipid, and cholesterol metabolism), inflammation, and fibrosis. Ultimately, combination therapies addressing multiple aspects of NASH pathogenesis are expected to provide benefit for patients.

Rewiring Neuronal Glycerolipid Metabolism Determines the Extent of Axon Regeneration

How adult neurons coordinate lipid metabolism to regenerate axons remains elusive. We found that depleting neuronal lipin1, a key enzyme controlling the balanced synthesis of glycerolipids through the glycerol phosphate pathway, enhanced axon regeneration after optic nerve injury. Axotomy elevated lipin1 in retinal ganglion cells, which contributed to regeneration failure in the CNS by favorably producing triglyceride (TG) storage lipids rather than phospholipid (PL) membrane lipids in neurons. Regrowth induced by lipin1 depletion required TG hydrolysis and PL synthesis. Decreasing TG synthesis by deleting neuronal diglyceride acyltransferases (DGATs) and enhancing PL synthesis through the Kennedy pathway promoted axon regeneration. In addition, peripheral neurons adopted this mechanism for their spontaneous axon regeneration. Our study reveals a critical role of lipin1 and DGATs as intrinsic regulators of glycerolipid metabolism in neurons and indicates that directing neuronal lipid synthesis away from TG synthesis and toward PL synthesis may promote axon regeneration.

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Injury-elevated Lipin1 and DGAT in retinal ganglion cells suppress regeneration

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Neuronal lipin1 and DGATs increase triglyceride and decrease phospholipids

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Redirecting triacylglyceride to phospholipid synthesis promotes axon regeneration

Wheat Flour, Enriched with γ-Oryzanol, Phytosterol, and Ferulic Acid, Alleviates Lipid and Glucose Metabolism in High-Fat-Fructose-Fed Rats

(1) Background: Modern dietary patterns with a high intake of fat and fructose, as well as refined carbohydrates, closely relate to lipid/glucose metabolic disorders. The main objective of this study is to provide new thoughts in designing functional food with some lipid/glucose metabolism regulating effects for obese people. (2) Methods: The alleviating abilities of γ-oryzanol, phytosterol or ferulic acid-enriched wheat flour on lipid/glucose metabolic dysfunction were evaluated in male SD rats induced by a high-fat-fructose diet. The underlying mechanisms were clarified using western blot. (3) Results: In an in vitro cell model, γ-oryzanol, phytosterol and ferulic acid regulate lipid/glucose metabolism by increasing the phosphorylation of AMPK and Akt, and PI3K expression, as well as decreasing expressions of DGAT1 and SCD. The in vivo study shows that ferulic acid and γ-oryzanol-enriched flours are beneficial for managing body weight, improving glucose metabolism, hyperlipidemia and hepatic lipid accumulation. Phytosterol-enriched flour exerted remarkable effects in regulating hyperinsulinemia, insulin resistance and hyperuricemia. Western blot analysis of proteins from liver samples reveals that these enriched flours alleviated hepatic lipid accumulation and insulin resistance through their elevation in the phosphorylation of AMPK and Akt. (4) Conclusions: Our study indicates that these enriched flours can serve as a health-promoting functional food to regulate obesity-related lipid/glucose metabolic dysfunction in rats.

Potential Anti-obesity and Lipid Lowering Natural Products: A Review

Obesity has reached epidemic proportions globally, with more than 1 billion adults overweight - at least 300 million of them clinically obese. In Ayurveda, obesity is called ‘medoroga’. The detailed features and treatments of the disease have been described in an old Ayurvedic text, Charak and Sushrut Samhita. There are some native plants that are commonly used for the treatment of obesity in Ayurveda. Unfortunately, only few medications are available in the market, with side effects and unacceptable efficacy. With the current view that botanical drugs can be developed faster and more cheaply than conventional single entity pharmaceuticals, the review mainly focuses on the rationality of their use with appropriate literature data support.

DGAT1 Inhibitor Suppresses Prostate Tumor Growth and Migration by Regulating Intracellular Lipids and Non-Centrosomal MTOC Protein GM130

Acyl-CoA:diacylglycerol acyltransferase I (DGAT1) is a key enzyme in lipogenesis which is increased in metabolically active cells to meet nutrient requirements. DGAT1 has been recognized as an anti-obesity target; however, its role in the tumor microenvironment remains unclear. We postulated that, in prostate cancer (PCa) cells, augmented lipogenesis and growth are due to increased DGAT1 expression leading to microtubule-organizing center (MTOC) amplification. Thus, therapeutic targeting of DGAT1 potentially has tumor suppressive activity. We tested whether blocking DGAT1 in PCa cells altered MTOC and lipid signaling. Western blot and immunofluorescence were performed for MTOC and triglyceride mediators. Treatment with a DGAT1 inhibitor was evaluated. We found a stepwise increase in DGAT1 protein levels when comparing normal prostate epithelial cells to PCa cells, LNCaP and PC-3. Lipid droplets, MTOCs, and microtubule-regulating proteins were reduced in tumor cells treated with a DGAT1 inhibitor. Depletion of the non-centrosomal MTOC protein GM130 reduced PCa cell proliferation and migration. Inhibition of DGAT1 reduced tumor growth both in vitro and in vivo, and a negative feedback loop was discovered between DGAT1, PEDF, and GM130. These data identify DGAT1 as a promising new target for suppressing PCa growth by regulating GM130, MTOC number and disrupting microtubule integrity.

The mechanism through which dietary supplementation with heated linseed grain increases n-3 long-chain polyunsaturated fatty acid concentration in subcutaneous adipose tissue of cashmere kids

The aim of this study was to investigate the effects of dietary supplementation with heated linseed on the fatty acid (FA) composition of the plasma, liver, and subcutaneous adipose tissue (SADT) of Albas white cashmere kids, particularly the effect on n-3 long-chain polyunsaturated FA profiles and the mRNA expression of genes related to lipid metabolism in SADT. Sixty 4-month-old castrated male kids (average BW 18.6 ± 0.1 kg) were selected and randomly allocated into three groups in a randomized block design. Three dietary treatments were used: (1) basal diet without supplementation (Control), (2) basal diet supplemented with linseed oil (LSO), and (3) basal diet supplemented with heated linseed grain (HLS). The diets were fed for 104 d, consisting of 14 d for adaptation followed by 90 d of measurement. Different FA profiles were found in SADT between LSO and HLS. Kids fed HLS had more C18:3n3 (P < 0.0001), C22:6n3 (P = 0.007), and n-3 PUFA (P < 0.0001) and a less (P < 0.0001) n-6/n-3 ratio than LSO kids. These FA differences between LSO and HLS kids were due to the increased expression of elongation of very long chain FA protein 5 (P < 0.0001), delta-6 desaturase (P < 0.0001), and peroxisome proliferator-activated receptor α (P = 0.003) in SADT of HLS kids and was also associated with liver fat metabolism. Together, these results suggest that the consumption of HLS leads to more C22:6n3 than LSO in SADT by increasing liver C22:6n3 content and by increasing SADT mRNA expression of ELOVL5 and FADS2 through promoting PPARα expression.

Chokeberry Extract and Its Active Polyphenols Suppress Adipogenesis in 3T3-L1 Adipocytes and Modulates Fat Accumulation and Insulin Resistance in Diet-Induced Obese Mice

Berries of Aronia melanocarpa (chokeberry) are known to be a rich source of biologically active polyphenols. In the present study, the effects of seven anti-adipogenic polyphenolic phytochemicals isolated from A. melanocarpa methanol extract on adipogenic transcription factors were investigated. Amygdalin and prunasin were found to inhibit 3T3-L1 adipocyte differentiation by suppressing the expressions of PPARγ (peroxisome proliferator-activated receptor γ), C/EBPα (CCAAT/enhancer binding protein α), SREBP1c (sterol regulatory element binding protein 1c), FAS (fatty acid synthase), and aP2 (adipocyte fatty-acid⁻binding protein). A. melanocarpa extract-treated (100 or 200 mg/kg/day on body weight) high fat diet (HFD)-induced obese mice showed significant decreases in body weight, serum triglyceride (TG), and low-density lipoprotein cholesterol (LDLC) levels and improved insulin sensitivity as compared with HFD controls. This research shows A. melanocarpa extract is potentially beneficial for the suppression of HFD-induced obesity.

Mixture of Two Lactobacillus plantarum Strains Modulates the Gut Microbiota Structure and Regulatory T Cell Response in Diet-Induced Obese Mice

SCOPE

The gut microbiota has been linked to diet-induced obesity, and microorganisms that influence obesity have important health implications. In this study, the anti-obesity effects of two Lactobacillus plantarum strains (DSR M2 and DSR 920) isolated from kimchi are investigated.

METHODS AND RESULTS

Mice are fed a normal or high-fat diet with or without DSR M2 and DSR 920 (DSR, 1 × 10⁹ CFU d^-1 ) for 12 weeks. DSR improves the obesity state, as evidenced by the i) suppressed obesity-related markers, e.g., gains in body weight and fat mass, ii) reduced serum and liver triglyceride levels, iii) upregulated β-oxidation and downregulated lipogenesis-related genes in the liver, iv) reduced serum leptin levels, v) altered microbial communities, vi) increased regulatory T cell immunity, and vii) suppressed inflammatory response. In addition, correlation analysis shows that Akkermansia muciniphila and the genus Anaerostipes, which are increased in the DSR group, are negatively correlated with obesity-related markers, but Mucispirillum schaedleri, which is increased in the high-fat-diet (HFD) group, is positively correlated with serum leptin level.

CONCLUSION

Lactobacillus plantarum DSR M2 and DSR 920 are candidate probiotics for the prevention and amelioration of obesity.

Reversible deficits in apical transporter trafficking associated with deficiency in diacylglycerol acyltransferase

Deficiency in diacylglycerol acyltransferase (DGAT1) is a rare cause of neonatal diarrhea, without a known mechanism or in vitro model. A patient presenting at our institution at 7 weeks of life with failure to thrive and diarrhea was found by whole-exome sequencing to have a homozygous DGAT1 truncation mutation. Duodenal biopsies showed loss of DGAT1 and deficits in apical membrane transporters and junctional proteins in enterocytes. When placed on a very low-fat diet, the patient's diarrhea resolved with normalization of brush border transporter localization in endoscopic biopsies. DGAT1 knockdown in Caco2-BBe cells modeled the deficits in apical trafficking, with loss of apical DPPIV and junctional occludin. Elevation in cellular lipid levels, including diacylglycerol (DAG) and phospholipid metabolites of DAG, was documented by lipid analysis in DGAT1 knockdown cells. Culture of the DGAT1 knockdown cells in lipid-depleted media led to re-establishment of occludin and return of apical DPPIV. DGAT1 loss appears to elicit global changes in enterocyte polarized trafficking that could account for deficits in absorption seen in the patient. The in vitro modeling of this disease should allow for investigation of possible therapeutic targets.

Polyacetylene From Dendropanax morbifera Alleviates Diet-Induced Obesity and Hepatic Steatosis by Activating AMPK Signaling Pathway

The extract tea of Dendropanax morbifera is popular beverages in Korea, and their preventive and therapeutic roles in metabolic disorders have been reported. However, the molecular mechanism has not been studied despite the known efficacy of D. morbifera. Eleven fractions (fr.1–fr.11) were divided by MPLC to find the active compound. Among them, Fr.5 was superior to others in that the inhibitory efficacy of de novo triglyceride (TG) biosynthesis. NMR analysis revealed that Fr.5 is composed 98% or more (9Z,16S)-16-hydroxy-9,17-octadecadiene-12,14-diynoic acid (HOD). Treatment of HOD diminished oleic acid (OA)-induced TG accumulation in HepG2 hepatocytes and differentiation of 3T3-L1 preadipocytes by activating LKB1/AMPK. In addition, we determined the effect of the oral administration of the extract of D. morbifera on obesity and hepatic steatosis in high-fat diet (HFD)-induced obese mice. This study proved that D. morbifera containing HOD, the active substance, can show preventive or therapeutic efficacy on obesity and hepatic steatosis through the targeting LKB1/AMPK axis.

DS-7250, a Diacylglycerol Acyltransferase 1 Inhibitor, Enhances Hepatic Steatosis in Zucker Fatty Rats via Upregulation of Fatty Acid Synthesis

Diacylglycerol acyltransferase 1 (DGAT1) catalyzes the final step in triglyceride synthesis. Since Dgat1^-/- mice fed a high-fat diet (HFD) are resistant to hepatic steatosis, DGAT1 inhibitors are expected to have antifatty liver effects. To evaluate the hepatic effects of DS-7250, a selective DGAT1 inhibitor, vehicle or 10 mg/kg of DS-7250 was administered orally to male Fisher 344 (F344) and Zucker fatty (ZF) rats fed a standard diet or HFD for 14 or 28 days. ZF rats showed slight hepatic steatosis regardless of feeding conditions. DS-7250 exacerbated hepatic steatosis in ZF rats fed an HFD compared with the vehicle control. Hepatic steatosis did not occur in F344 rats fed an HFD, in which systemic exposures of DS-7250 were comparable to those in ZF rats. There was a higher expression of genes involved in lipid uptake and fatty acid synthesis in ZF rats compared to F344 rats under HFD conditions. DS-7250 upregulated key genes involved in de novo lipogenesis, which causes hepatic steatosis independently of DGAT1, in ZF rats fed an HFD compared with the vehicle control. These data suggest that ZF rats were more susceptible to hepatic steatosis due to their genetic characteristics and DS-7250 exacerbated hepatic steatosis independently of DGAT1.

Maternal High-Fat and High-Salt Diets Have Differential Programming Effects on Metabolism in Adult Male Rat Offspring

Maternal high-fat or high-salt diets can independently program adverse cardiometabolic outcomes in offspring. However, there is a paucity of evidence examining their effects in combination on metabolic function in adult offspring. Female Sprague Dawley rats were randomly assigned to either: control (CD; 10% kcal from fat, 1% NaCl), high-salt (SD; 10% kcal from fat, 4% NaCl), high-fat (HF; 45% kcal from fat, 1% NaCl) or high-fat and salt (HFSD; 45% kcal from fat, 4% NaCl) diets 21 days prior to mating and throughout pregnancy and lactation. Male offspring were weaned onto a standard chow diet and were culled on postnatal day 130 for plasma and tissue collection. Adipocyte histology and adipose tissue, liver, and gut gene expression were examined in adult male offspring. HF offspring had significantly greater body weight, impaired insulin sensitivity and hyperleptinemia compared to CD offspring, but these increases were blunted in HFSD offspring. HF offspring had moderate adipocyte hypertrophy and increased expression of the pre-adipocyte marker Dlk1. There was a significant effect of maternal salt with increased hepatic expression of Dgat1 and Igfb2. Gut expression of inflammatory (Il1r1, Tnfα, Il6, and Il6r) and renin-angiotensin system (Agtr1a, Agtr1b) markers was significantly reduced in HFSD offspring compared to HF offspring. Therefore, salt mitigates some adverse offspring outcomes associated with a maternal HF diet, which may be mediated by altered adipose tissue morphology and gut inflammatory and renin-angiotensin regulation.

Discovery of Tetralones as Potent and Selective Inhibitors of Acyl-CoA:Diacylglycerol Acyltransferase 1

Acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1) plays an important role in triglyceride synthesis and is a target of interest for the treatment of metabolic disorders. Herein we describe the structure-activity relationship of a novel tetralone series of DGAT1 inhibitors and our strategies for overcoming genotoxic liability of the anilines embedded in the chemical structures, leading to the discovery of a candidate compound, (S)-2-(6-(5-(3-(3,4-difluorophenyl)ureido)pyrazin-2-yl)-1-oxo-2-(2,2,2-trifluoroethyl)-1,2,3,4-tetrahydronaphthalen-2-yl)acetic acid (GSK2973980A, 26d). Compound 26d is a potent and selective DGAT1 inhibitor with excellent DMPK profiles and in vivo efficacy in a postprandial lipid excursion model in mice. Based on the overall biological and developability profiles and acceptable safety profiles in the 7-day toxicity studies in rats and dogs, compound 26d was selected as a candidate compound for further development in the treatment of metabolic disorders.

Pharmacological inhibition of diacylglycerol acyltransferase-1 and insights into postprandial gut peptide secretion

AIM

To examine the role that enzyme Acyl-CoA:diacylglycerol acyltransferase-1 (DGAT1) plays in postprandial gut peptide secretion and signaling.

METHODS

The standard experimental paradigm utilized to evaluate the incretin response was a lipid challenge. Following a lipid challenge, plasma was collected via cardiac puncture at each time point from a cohort of 5-8 mice per group from baseline at time zero to 10 h. Incretin hormones [glucagon like peptide-1 (GLP-1), peptide tyrosine-tyrosine (PYY) and glucose dependent insulinotropic polypeptide (GIP)] were then quantitated. The impact of pharmacological inhibition of DGAT1 on the incretin effect was evaluated in WT mice. Additionally, a comparison of loss of DGAT1 function either by genetic ablation or pharmacological inhibition. To further elucidate the pathways and mechanisms involved in the incretin response to DGAT1 inhibition, other interventions [inhibitors of dipeptidyl peptidase-IV (sitagliptin), pancreatic lipase (Orlistat), GPR119 knockout mice] were evaluated.

RESULTS

DGAT1 deficient mice and wildtype C57/BL6J mice were lipid challenged and levels of both active and total GLP-1 in the plasma were increased. This response was further augmented with DGAT1 inhibitor PF-04620110 treated wildtype mice. Furthermore, PF-04620110 was able to dose responsively increase GLP-1 and PYY, but blunt GIP at all doses of PF-04620110 during lipid challenge. Combination treatment of PF-04620110 and Sitagliptin in wildtype mice during a lipid challenge synergistically enhanced postprandial levels of active GLP-1. In contrast, in a combination study with Orlistat, the ability of PF-04620110 to elicit an enhanced incretin response was abrogated. To further explore this observation, GPR119 knockout mice were evaluated. In response to a lipid challenge, GPR119 knockout mice exhibited no increase in active or total GLP-1 and PYY. However, PF-04620110 was able to increase total GLP-1 and PYY in GPR119 knockout mice as compared to vehicle treated wildtype mice.

CONCLUSION

Collectively, these data provide some insight into the mechanism by which inhibition of DGAT1 enhances intestinal hormone release.

The role of lipids in the pathogenesis and treatment of type 2 diabetes and associated co-morbidities

In the past decade, the incidence of type 2 diabetes (T2D) has rapidly increased, along with the associated cardiovascular complications. Therefore, understanding the pathophysiology underlying T2D, the associated complications and the impact of therapeutics on the T2D development has critical importance for current and future therapeutics. The prevailing feature of T2D is hyperglycemia due to excessive hepatic glucose production, insulin resistance, and insufficient secretion of insulin by the pancreas. These contribute to increased fatty acid influx into the liver and muscle causing accumulation of lipid metabolites. These lipid metabolites cause dyslipidemia and non-alcoholic fatty liver disease, which ultimately contributes to the increased cardiovascular risk in T2D. Therefore, understanding the mechanisms of hepatic insulin resistance and the specific role of liver lipids is critical in selecting and designing the most effective therapeutics for T2D and the associated co-morbidities, including dyslipidemia and cardiovascular disease. Herein, we review the effects and molecular mechanisms of conventional anti-hyperglycemic and lipid-lowering drugs on glucose and lipid metabolism. [BMB Reports 2016; 49(3): 139-148].

Triglycerides Revisited to the Serial

This review discusses the role of triglycerides (TGs) in the normal cardiovascular system as well as in the development and clinical manifestation of cardiovascular diseases. Regulation of TGs at the enzymatic and genetic level, in addition to their possible relevance as preclinical and clinical biomarkers, is discussed, culminating with a description of available and emerging treatments. Due to the high complexity of the subject and the vast amount of material in the literature, the objective of this review was not to exhaust the subject, but rather to compile the information to facilitate and improve the understanding of those interested in this topic. The main publications on the topic were sought out, especially those from the last 5 years. The data in the literature still give reason to believe that there is room for doubt regarding the use of TG as disease biomarkers; however, there is increasing evidence for the role of hypertriglyceridemia on the atherosclerotic inflammatory process, cardiovascular outcomes, and mortality.

Long-term fructose consumption prolongs hepatic stearoyl-CoA desaturase 1 activity independent of upstream regulation in rats

Dietary fructose is considered a risk factor for metabolic disorders, such as fatty liver disease. However, the mechanism underlying the effects of fructose is not well characterized. We investigated the hepatic expression of key regulatory genes related to lipid metabolism following fructose feeding under well-defined conditions. Rats were fed standard chow supplemented with 10% w/v fructose solution for 5 weeks, and killed after chow-fasting and fructose withdrawal (fasting) or chow-fasting and continued fructose (fructose alone) for 14 h. Hepatic deposition of triglycerides was found in rats from both groups. As expected, fructose alone increased mRNA levels of lipogenesis-related genes and correspondingly decreased mRNA levels of lipid oxidative genes in the liver. Interesting, hepatic levels of stearoyl-CoA desaturase (SCD)1 mRNA remained elevated under fructose withdrawn conditions, although expression levels of other genes, including two key transcription factors (carbohydrate response element binding protein (ChREBP) and sterol regulatory element-binding protein (SREBP)-1c) fell to normal levels, indicating that long-term fructose intake increased SCD1 activity, independent of upstream regulatory genes, such as ChREBP and SREBP-1c. In conclusion, SCD1 overexpression in fatty liver disease is not affected by fasting after long-term fructose consumption in rats. Regulation of SCD1 plays an important role in fructose-induced hepatic steatosis.

An LC-MRM method for measuring intestinal triglyceride assembly using an oral stable isotope-labeled fat challenge

Aim: A traditional oral fatty acid challenge assesses absorption of triacylglycerol (TG) into the periphery through the intestines, but cannot distinguish the composition or source of fatty acid in the TG. Stable isotope-labeled tracers combined with LC-MRM can be used to identify and distinguish TG synthesized with dietary and stored fatty acids. Results: Concentrations of three abundant TGs (52:2, 54:3 and 54:4) were monitored for incorporation of one or two 2H11-oleate molecules per TG. This method was subjected to routine assay validation and meets typical requirements for an assay to be used to support clinical studies. Conclusion: Calculations for the fractional appearance rate of TG in plasma are presented along with the intracellular enterocyte precursor pool for 12 study participants.

Camphene, a Plant Derived Monoterpene, Exerts Its Hypolipidemic Action by Affecting SREBP-1 and MTP Expression

The control of hyperlipidemia plays a central role in cardiovascular disease. Previously, we have shown that camphene, a constituent of mastic gum oil, lowers cholesterol and triglycerides (TG) in the plasma of hyperlipidemic rats without affecting HMG-CoA reductase activity, suggesting that its hypocholesterolemic and hypotriglyceridemic effects are associated with a mechanism of action different than that of statins. In the present study, we examine the mechanism by which camphene exerts its hypolipidemic action. We evaluated the effect of camphene on the de novo synthesis of cholesterol and TG from [14C]-acetate in HepG2 cells, along with the statin mevinolin. Camphene inhibited the biosynthesis of cholesterol in a concentration-dependent manner, and a maximal inhibition of 39% was observed at 100 μM while mevinolin nearly abolished cholesterol biosynthesis. Moreover, treatment with camphene reduced TG by 34% and increased apolipoprotein AI expression. In contrast, mevinolin increased TG by 26% and had a modest effect on apolipoprotein AI expression. To evaluate the mode of action of camphene, we examined its effects on the expression of SREBP-1, which affects TG biosynthesis and SREBP-2, which mostly affects sterol synthesis. Interestingly, camphene increased the nuclear translocation of the mature form of SREBP-1 while mevinolin was found to increase the amount of the mature form of SREBP-2. The effect of camphene is most likely regulated through SREBP-1 by affecting MTP levels in response to a decrease in the intracellular cholesterol. We propose that camphene upregulates SREBP-1 expression and MTP inhibition is likely to be a probable mechanism whereby camphene exerts its hypolipidemic effect.

Prolonged silencing of diacylglycerol acyltransferase-1 induces a dedifferentiated phenotype in human liver cells

Diacylglycerol acyltransferase‐1 (DGAT1), a key enzyme in triglyceride (TG) biogenesis, is highly associated with metabolic abnormalities, such as obesity and type 2 diabetes. However, the effects of DGAT1 silencing in the human liver have not been elucidated. To investigate the effects of DGAT1 silencing in human liver cells, we compared the cellular behaviours of DGAT1‐deficient Huh‐7.5 cell lines with those of control Huh‐7.5 cells. DGAT1‐deficient cells acquired dedifferentiated and stem cell‐like characteristics, such as formation of aggregates in the presence of high levels of growth factors, high proliferation rates and loss of albumin secretion. In relation to aggregate formation, the expression level of various adhesion molecules was significantly altered in DGAT1‐deficient cells. Microarray data analysis and immunostaining of patient tissue samples clearly showed decreased expression levels of DGAT1 and integrin β1 in patients who have nodular cirrhosis without fatty degeneration.

Pharmacokinetics, pharmacodynamics, safety, and tolerability of pradigastat, a novel diacylglycerol acyltransferase 1 inhibitor in overweight or obese, but otherwise healthy human subjects

Pradigastat is a potent and selective inhibitor of diacylglycerol acyltransferase 1, an enzyme highly expressed in the small intestine that plays a key role in postprandial triglyceride synthesis. This first-in-human study evaluated the pharmacokinetics, pharmacodynamics, safety, and tolerability of pradigastat administered at single and multiple doses in overweight or obese healthy subjects. In single-dose cohorts (n = 72), subjects were randomized sequentially to receive single doses of pradigastat (1, 3, 10, 30, 100, or 300 mg) or placebo under fasted condition and prior to breakfast. In multiple-dose cohorts (n = 106), subjects were randomized to receive pradigastat (1, 5, 10, or 25 mg) or placebo prior to breakfast for 14 days. Following a single oral dosing, pradigastat was absorbed slowly, with a median tmax of ∼10 hours and eliminated slowly with a long half-life. With multiple oral doses, a 10- to 17-fold higher systemic exposure was observed. Pradigastat treatment (single and multiple doses) led to dose-dependent suppression of postprandial triglyceride excursions over 9 hours following a high-fat meal test. In addition, pradigastat suppressed postprandial glucose and insulin and increased plasma glucagon-like peptide-1 levels. Overall, pradigastat was safe and tolerated at single and multiple doses in healthy subjects.

Roles of Acyl-CoA:Diacylglycerol Acyltransferases 1 and 2 in Triacylglycerol Synthesis and Secretion in Primary Hepatocytes

OBJECTIVE

Very low-density lipoprotein assembly and secretion are regulated by the availability of triacylglycerol. Although compelling evidence indicates that the majority of triacylglycerol in very low-density lipoprotein is derived from re-esterification of lipolytic products released by endoplasmic reticulum-associated lipases, little is known about roles of acyl-CoA:diacylglycerol acyltransferases (DGATs) in this process. We aimed to investigate the contribution of DGAT1 and DGAT2 in lipid metabolism and lipoprotein secretion in primary mouse and human hepatocytes.

APPROACH AND RESULTS

We used highly selective small-molecule inhibitors of DGAT1 and DGAT2, and we tracked storage and secretion of lipids synthesized de novo from [(3)H]acetic acid and from exogenously supplied [(3)H]oleic acid. Inactivation of individual DGAT activity did not affect incorporation of either radiolabeled precursor into intracellular triacylglycerol, whereas combined inactivation of both DGATs severely attenuated triacylglycerol synthesis. However, inhibition of DGAT2 augmented fatty acid oxidation, whereas inhibition of DGAT1 increased triacylglycerol secretion, suggesting preferential channeling of separate DGAT-derived triacylglycerol pools to distinct metabolic pathways. Inactivation of DGAT2 impaired cytosolic lipid droplet expansion, whereas DGAT1 inactivation promoted large lipid droplet formation. Moreover, inactivation of DGAT2 attenuated expression of lipogenic genes. Finally, triacylglycerol secretion was significantly reduced on DGAT2 inhibition without altering extracellular apolipoprotein B levels.

CONCLUSIONS

Our data suggest that DGAT1 and DGAT2 can compensate for each other to synthesize triacylglycerol, but triacylglycerol synthesized by DGAT1 is preferentially channeled to oxidation, whereas DGAT2 synthesizes triacylglycerol destined for very low-density lipoprotein assembly.

Obesity and cancer progression: is there a role of fatty acid metabolism?

Currently, there is renewed interest in elucidating the metabolic characteristics of cancer and how these characteristics may be exploited as therapeutic targets. Much attention has centered on glucose, glutamine and de novo lipogenesis, yet the metabolism of fatty acids that arise from extracellular, as well as intracellular, stores as triacylglycerol has received much less attention. This review focuses on the key pathways of fatty acid metabolism, including uptake, esterification, lipolysis, and mitochondrial oxidation, and how the regulators of these pathways are altered in cancer. Additionally, we discuss the potential link that fatty acid metabolism may serve between obesity and changes in cancer progression.

Potential approaches to ameliorate hepatic fat accumulation seen with MTP inhibition

Microsomal triglyceride transfer protein (MTP) is one of the promising targets for the therapy of dyslipidemia and MTP inhibition can lead to robust plasma low-density lipoprotein cholesterol (LDL-C) reduction. Lomitapide, a small-molecule MTP inhibitor, was recently approved by the US FDA as an additional treatment for homozygous familial hypercholesterolemia (hoFH). However, liver-related side effects, including hepatic fat accumulation and transaminase elevations, are the main safety concerns associated with MTP inhibitors. Here, we review recent knowledge on the mechanisms underlying liver toxicity of MTP inhibitors. The contribution of altered levels of intracellular triglycerides, cholesteryl esters, and free cholesterols toward cellular dysfunction is specifically addressed. On this basis, therapies targeted to attenuate cellular lipid accumulation, to reduce risk factors for non-alcoholic fatty liver disease (NAFLD) (i.e., insulin resistance and oxidative stress) and to specifically inhibit intestinal MTP may be useful for ameliorating liver damage induced by MTP inhibitors. In particular, weight loss through lifestyle interventions is expected to be the most effective and safest way to minimize the undesirable side effects. Specific dietary supplementation might also have protective effects against hepatosteatosis. Despite that, to date, few clinical data support these therapeutic options in MTP inhibition-related liver damage, such proposed approaches may be further explored in the future for their use in preventing unwanted effects of MTP inhibitors.