lysophosphatidylinositol and Obesity

Plasma lysophospholipids have emerged as signaling molecules with important effects on inflammation, insulin resistance, and fatty liver disease, each of which is linked closely to obesity. Dietary n-3 (ω-3) polyunsaturated fatty acids (PUFAs) may be able to improve these conditions.. The objective of this study was to assess the response of plasma lysophospholipids to obesity, n-3 PUFA consumption, and a high-fat meal challenge to better understand the role of lysophospholipid metabolism in the progression of obesity-related disorders.. We determined the concentrations of 8 lysophosphatidylcholines, 11 lysophosphatidylethanolamines, and 7 lysophosphatidylinositols in the plasma of 34 normal-weight and 38 obese subjects randomly assigned to consume corn oil (control) or n-3 PUFA-rich fish oil (3 g/d; n = 15-19/group) for 90 d. Blood samples were collected on the last day of the study under fasting conditions and 6 h after a high-fat meal (1135 kcal, 86 g fat) challenge. The profile of secreted lysophospholipids was studied in HepG2 cells under palmitate-induced steatosis.. Obese and normal-weight subjects had different profiles of plasma lysophospholipids. A multivariate combination of the 26 lysophospholipids could discriminate between normal-weight and obese subjects with an accuracy of 98%. The high-fat meal challenge altered the concentration of plasma lysophosphatidylcholines in an oil treatment-dependent manner in normal-weight but not obese subjects, suggesting that obesity impairs the sensitivity of lysophospholipid metabolism to n-3 PUFAs. Noncytotoxic steatosis in HepG2 cells affected the secretion pattern of lysophospholipids, partially resembling the changes observed in the plasma of obese subjects.. Obesity has a substantial impact on lysophospholipid metabolism, altering the plasma lysophospholipid profile and abolishing its sensitivity to dietary n-3 PUFAs. These effects could contribute to the onset or progression of alterations associated with obesity, such as inflammation, insulin resistance, and fatty liver disease. This trial was registered at www.controlled-trials.com as ISRCTN96712688.

Topics: Adult; Diet, High-Fat; Dietary Fats; Fatty Acids, Omega-3; Fatty Liver; Female; Hep G2 Cells; Humans; Inflammation; Insulin Resistance; Lysophospholipids; Male; Middle Aged; Obesity

G protein-coupled receptor (GPR) 55 is a putative cannabinoid receptor, and l-α-lysophosphatidylinositol (LPI) is its only known endogenous ligand. Although GPR55 has been linked to energy homeostasis in different organs, its specific role in lipid metabolism in the liver and its contribution to the pathophysiology of nonalcoholic fatty liver disease (NAFLD) remains unknown.. We measured (1) GPR55 expression in the liver of patients with NAFLD compared with individuals without obesity and without liver disease, as well as animal models with steatosis and nonalcoholic steatohepatitis (NASH), and (2) the effects of LPI and genetic disruption of GPR55 in mice, human hepatocytes, and human hepatic stellate cells. Notably, we found that circulating LPI and liver expression of GPR55 were up-regulated in patients with NASH. LPI induced adenosine monophosphate-activated protein kinase activation of acetyl-coenzyme A carboxylase (ACC) and increased lipid content in human hepatocytes and in the liver of treated mice by inducing de novo lipogenesis and decreasing β-oxidation. The inhibition of GPR55 and ACCα blocked the effects of LPI, and the in vivo knockdown of GPR55 was sufficient to improve liver damage in mice fed a high-fat diet and in mice fed a methionine-choline-deficient diet. Finally, LPI promoted the initiation of hepatic stellate cell activation by stimulating GPR55 and activation of ACC.. The LPI/GPR55 system plays a role in the development of NAFLD and NASH by activating ACC.

Topics: Acetyl-CoA Carboxylase; Adult; Aged; Animals; Biopsy; Cannabinoid Receptor Agonists; Cell Line; Cohort Studies; Diet, High-Fat; Disease Models, Animal; Female; Gene Knockdown Techniques; Hepatic Stellate Cells; Hepatocytes; Humans; Lipogenesis; Liver; Lysophospholipids; Male; Mice; Middle Aged; Non-alcoholic Fatty Liver Disease; Obesity; Receptors, Cannabinoid; Up-Regulation

GPR55 is a putative cannabinoid receptor, and l-α-lysophosphatidylinositol (LPI) is its only known endogenous ligand. We investigated 1) whether GPR55 is expressed in fat and liver; 2) the correlation of both GPR55 and LPI with several metabolic parameters; and 3) the actions of LPI on human adipocytes. We analyzed CB1, CB2, and GPR55 gene expression and circulating LPI levels in two independent cohorts of obese and lean subjects, with both normal or impaired glucose tolerance and type 2 diabetes. Ex vivo experiments were used to measure intracellular calcium and lipid accumulation. GPR55 levels were augmented in the adipose tissue of obese subjects and further so in obese patients with type 2 diabetes when compared with nonobese subjects. Visceral adipose tissue GPR55 correlated positively with weight, BMI, and percent fat mass, particularly in women. Hepatic GPR55 gene expression was similar in obese and type 2 diabetic subjects. Circulating LPI levels were increased in obese patients and correlated with fat percentage and BMI in women. LPI increased the expression of lipogenic genes in visceral adipose tissue explants and intracellular calcium in differentiated visceral adipocytes. These findings indicate that the LPI/GPR55 system is positively associated with obesity in humans.

Topics: 3T3-L1 Cells; Adipocytes; Adult; Animals; Body Mass Index; Calcium; Cell Differentiation; Female; Humans; Intra-Abdominal Fat; Linear Models; Liver; Lysophospholipids; Male; Mice; Obesity; Receptor, Cannabinoid, CB1; Receptor, Cannabinoid, CB2; Receptors, Cannabinoid; Receptors, G-Protein-Coupled; RNA, Messenger

The cannabinoid receptor 1 (CB(1)) and CB(2) cannabinoid receptors, associated with drugs of abuse, may provide a means to treat pain, mood, and addiction disorders affecting widespread segments of society. Whether the orphan G-protein coupled receptor GPR55 is also a cannabinoid receptor remains unclear as a result of conflicting pharmacological studies. GPR55 has been reported to be activated by exogenous and endogenous cannabinoid compounds but surprisingly also by the endogenous non-cannabinoid mediator lysophosphatidylinositol (LPI). We examined the effects of a representative panel of cannabinoid ligands and LPI on GPR55 using a beta-arrestin-green fluorescent protein biosensor as a direct readout of agonist-mediated receptor activation. Our data demonstrate that AM251 and SR141716A (rimonabant), which are cannabinoid antagonists, and the lipid LPI, which is not a cannabinoid receptor ligand, are GPR55 agonists. They possess comparable efficacy in inducing beta-arrestin trafficking and, moreover, activate the G-protein-dependent signaling of protein kinase CbetaII. Conversely, the potent synthetic cannabinoid agonist CP55,940 acts as a GPR55 antagonist/partial agonist. CP55,940 blocks GPR55 internalization, the formation of beta-arrestin GPR55 complexes, and the phosphorylation of ERK1/2; CP55,940 produces only a slight amount of protein kinase CbetaII membrane recruitment but does not stimulate membrane remodeling like LPI, AM251, or rimonabant. Our studies provide a paradigm for measuring the responsiveness of GPR55 to a variety of ligand scaffolds comprising cannabinoid and novel compounds and suggest that at best GPR55 is an atypical cannabinoid responder. The activation of GPR55 by rimonabant may be responsible for some of the off-target effects that led to its removal as a potential obesity therapy.

Topics: Analgesics; Arrestins; beta-Arrestins; Cannabinoid Receptor Agonists; Cannabinoids; Cell Line; Cyclohexanols; Humans; Ligands; Lysophospholipids; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Obesity; Phosphorylation; Piperidines; Protein Kinase C; Protein Kinase C beta; Pyrazoles; Receptors, Cannabinoid; Receptors, G-Protein-Coupled; Rimonabant