BACKGROUND AND PURPOSE:Diabetic nephropathy (DN) is a common complication of diabetes. Current treatments include renin-angiotensin-aldosterone system (RAAS) blockers and sodium-glucose co-transporter 2 (SGLT2) inhibitors. The cannabinoid CB1 receptor is a potential therapeutic target. We explored combining CB1 receptor inverse agonism and SGLT2 inhibition for treating DN, to offer better reno-protection. EXPERIMENTAL APPROACH:C57BLKS-Leprdb/db and control mice were fed a high-protein diet for 9 weeks. After 5 weeks, db/db mice were either exposed to placebo, empagliflozin (SGLT2 inhibitor), monlunabant (CB1 receptor inverse agonist) or a combination of both compounds (same dose) by daily oral gavage for 28 days. Diagnostic parameters for DN were analysed, along with markers of oxidative stress, inflammation and renal fibrosis. KEY RESULTS:Both single treatments improved albuminuria and albumin-to-creatinine ratios, but the combination was more effective. Similar results were seen for inflammatory oxidative stress markers. The combination showed additive protective effects on glomerular morphology, podocyte loss and proximal tubular cell injury. Dual treatment significantly reduced tubulointerstitial fibrosis compared to monotherapy and vehicle-treated mice. Transcriptomic analysis identified the STAT3 signalling pathway as a key mediator, with decreased STAT3 phosphorylation observed with both treatments. Key mediators involved included angiopoietin 1 and fibroblast growth factor 20, which modulated the STAT3 pathway via CB1 receptors and SGLT2, respectively. CONCLUSIONS AND IMPLICATIONS:Taken together, these data strongly suggest that a poly-pharmacological approach combining both SGLT2 inhibitors and CB1 receptor inverse agonism represents a promising therapeutic strategy for managing DN, with better reno-protection than mono-therapies.

To better understand diabetic nephropathy (DN), developing accurate animal models is crucial. Current models often fail to fully mimic human DN, showing only mild albuminuria, glomerular hypertrophy, and limited mesangial matrix expansion. Our study aims to develop a more robust model by combining streptozotocin (STZ)-induced diabetes with a high-protein diet (HPD). We divided C57Bl/6J mice into three groups: control, STZ with a standard diet (STZ-SD), and STZ with a HPD (45 kcal% protein) (STZ-HPD) for 12 weeks. Renal function was evaluated using the urinary albumin-to-creatinine ratio, and kidney tissues were analyzed for histological and molecular changes. The STZ-HPD group showed significantly higher albuminuria and more severe glomerular and tubular damage compared to the control and STZ-SD groups. These changes were accompanied by increased inflammatory and oxidative stress markers, highlighting the harmful effects of high-protein intake on renal injury. Our findings suggest that the STZ-HPD model could be a valuable tool for studying DN pathophysiology and evaluating therapeutic interventions, providing a new approach for preclinical research.

BACKGROUND AND AIMS:Although qualitative and quantitative alterations in liver Polyunsaturated Fatty Acids (PUFAs) are observed in MASH in humans, a causal relationship of PUFAs biosynthetic pathways is yet to be clarified. ELOVL5, an essential enzyme in PUFA elongation regulates hepatic triglyceride metabolism. Nonetheless, the long-term consequences of elongase disruption, particularly in murine models of MASH, have not been evaluated. APPROACH & RESULTS:In humans, transcriptomic data indicated that PUFAs biosynthesis enzymes and notably ELOVL5 were induced during MASH progression. Moreover, gene module association determination revealed that ELOVL5 expression was associated with mitochondrial function in both humans and mice. WT and Elovl5-deficient mice were fed a high-fat, high-sucrose (HF/HS) diet for four months. Elovl5 deficiency led to limited systemic metabolic alterations but significant hepatic phenotype was observed in Elovl5-/- mice after the HF/HS diet, including hepatomegaly, pronounced macrovesicular and microvesicular steatosis, hepatocyte ballooning, immune cell infiltration, and fibrosis. Lipid analysis confirmed hepatic triglyceride accumulation and a reshaping of FA profile. Transcriptomic analysis indicated significant upregulation of genes involved in immune cell recruitment and fibrosis, and downregulation of genes involved in oxidative phosphorylation in Elovl5-/- mice. Alterations of FA oxidation and energy metabolism were confirmed by non-targeted metabolomic approach. Analysis of mitochondrial function in Elovl5-/- mice showed morphological alterations, qualitative cardiolipin changes with an enrichment in species containing shorter unsaturated FAs, and decreased activity of I and III respiratory chain complexes. CONCLUSION:Enhanced susceptibility to diet-induced MASH and fibrosis in Elovl5-/- mice is intricately associated with disruptions in mitochondrial homeostasis, stemming from a profound reshaping of mitochondrial lipids, notably cardiolipins.

L’obésité et le diabète de type 2 affectent des millions de personnes dans le monde et entraînent de nombreuses complications graves telles que les maladies cardiovasculaires, la stéatose hépatique non alcoolique et les maladies rénales. Face à l’augmentation constante de leur prévalence et aux limites des traitements actuels, la recherche de nouvelles approches thérapeutiques est cruciale. Dans ce contexte, les antagonistes des récepteurs aux cannabinoïdes de type 1 (CB1) à action périphérique émergent comme une option prometteuse. Ces molécules innovantes exercent des effets bénéfiques sur le métabolisme en ciblant spécifiquement les récepteurs CB1 des organes périphériques, tels que le pancréas, le tissu adipeux, le foie et les reins, sans générer d’effets centraux indésirables. Cette revue fait le point sur l’état de l’art des études précliniques et cliniques passées portant sur l’utilisation des antagonistes des récepteurs CB1 à action périphérique de deuxième et troisième génération et sur les perspectives qu’ils ouvrent pour le traitement et la prévention des troubles métaboliques associés à l’obésité et au diabète de type 2.

Objective:This study assessed the efficacy of INV-202, a novel peripherally restricted cannabinoid type-1 receptor (CB1R) inverse agonist, in a streptozotocin-induced type-1 diabetes nephropathy mouse model.Methods:Diabetes was induced in 8-week-old C57BL6/J male mice via intraperitoneal injection of streptozotocin (45 mg/kg/day for 5 days); nondiabetic controls received citrate buffer. Diabetic mice were randomized to 3 groups based on blood glucose, polyuria, and albuminuria, and administered daily oral doses for 28-days of INV-202 at 0.3 or 3 mg/kg or vehicle.Results:INV-202 did not affect body weight but decreased kidney weight compared with the vehicle group. While polyuria was unaffected by INV-202 treatment, urinary urea (control 30.77 ± 14.93; vehicle 189.81 ± 31.49; INV-202 (0.3 mg/kg) 127.76 ± 20; INV-202 (3 mg/kg) 93.70 ± 24.97 mg/24h) and albumin (control 3.06 ± 0.38; vehicle 850.08 ± 170.50; INV-202 (0.3 mg/kg) 290.65 ± 88.70; INV-202 (3 mg/kg) 111.29 ± 33.47 µg/24h) excretion both decreased compared with vehicle-treated diabetic mice. Compared with the vehicle group, there was a significant improvement in the urinary albumin to creatinine ratio across INV-202 groups. Regardless of the dose, INV-202 significantly reduced angiotensin II excretion in diabetic mice. The treatment also decreased Agtr1a renal expression in a dose-dependent manner. Compared with nondiabetic controls, the glomerular filtration rate was increased in the vehicle group and significantly decreased by INV-202 at 3 mg/kg. While the vehicle group showed a significant loss in the mean number of podocytes per glomerulus, INV-202 treatment limited podocyte loss in a dose-dependent manner. Moreover, in both INV-202 groups, expression of genes coding for podocyte structural proteins nephrin (Nphs1), podocin (Nphs2), and podocalyxin (Pdxl) were restored to levels similar to nondiabetic controls. INV-202 partially limited the proximal tubular epithelial cell (PTEC) hyperplasia and normalized genetic markers for PTEC lesions. INV-202 also reduced expression of genes contributing to oxidative stress (Nox2, Nox4, and P47phox) and inflammation (Tnf). In addition, diabetes-induced renal fibrosis was significantly reduced by INV-202.Conclusions:INV-202 reduced glomerular injury, preserved podocyte structure and function, reduced injury to PTECs, and ultimately reduced renal fibrosis in a streptozotocin-induced diabetic nephropathy mouse model. These results suggest that INV-202 may represent a new therapeutic option in the treatment of diabetic kidney disease.

Pharmacological inhibition of mitochondrial fatty acid oxidation (FAO) has been clinically used to alleviate certain metabolic diseases by remodeling cellular metabolism. However, mitochondrial FAO inhibition also leads to mechanistic target of rapamycin complex 1 (mTORC1) activation-related protein synthesis and tissue hypertrophy, but the mechanism remains unclear. Here, by using a mitochondrial FAO inhibitor (mildronate or etomoxir) or knocking out carnitine palmitoyltransferase-1, we revealed that mitochondrial FAO inhibition activated the mTORC1 pathway through general control nondepressible 5-dependent Raptor acetylation. catabolism and increased intracellular acetyl-CoA levels. In response to the increased intracellular acetyl-CoA, acetyltransferase general control nondepressible 5 activated mTORC1 by catalyzing Raptor acetylation through direct interaction. Further investigation also screened Raptor deacetylase histone deacetylase class II and identified histone deacetylase 7 as a potential regulator of Raptor. These results provide a possible mechanistic explanation for the mTORC1 activation after mitochondrial FAO inhibition and also bring light to reveal the roles of nutrient metabolic remodeling in production.

Abstract BACKGROUND AND AIMS Renal diseases remain a burden for Public Health and chronic kidney disease (CKD) affects several millions of individuals worldwide. Diabetic Nephropathy (DN) is the most frequent consequence of diabetes and is characterized by an increase in urinary albumin excretion and progressive loss of renal function associated with glomerular basement membrane thickening, mesangial expansion, nodular glomerular sclerosis and tubulointerstitial fibrosis. To date, there are few treatments that can prevent its progression. Indeed, current therapeutic approaches including RAAS blockers, SGLT2 inhibitors or both approaches combined do not fully abrogate DN progression. A growing body of experimental evidence suggests that modulation of the endocannabinoid system, and in particular its type 1 receptor (CB1R), may be a therapeutic tool in the management of CKD and more particularly DN. CB1R blockade represents a potential therapeutic modality in the fight against obesity, diabetes and their metabolic sequelae. In kidney, CB1R inhibition promotes a reduction in albuminuria, renal fibrosis and preserves renal function in both obesity-induced and diabetic nephropathy in mice mainly through a direct action of CB1R in podocytes and/or proximal tubules. INV-202 is a peripherally acting Cannabinoid receptor-1 (CB1r) inverse agonist that is under clinical development for the treatment of diseases associated with diabetes and metabolic syndrome. Here we report the effects of INV-202 on renal function and associated parameters in a preclinical model of diabetic nephropathy. METHOD Twelve weeks after the initiation of diabetes using streptozotocin, C57BL6/J mice (8 per treatment group) were randomized to receive a daily oral dose of INV-202, 0.3 mg/kg and 3 mg/kg or vehicle for 4 weeks. Five mice not treated with STZ were used as a nondiabetic control. At the end of treatment, animals were sacrificed. Urinary albumin-to-creatinine ratio (ACR), renal matrix remodelling, glomerular filtration and interstitial fibrosis were assessed in addition to glucose levels, body weight and organ weights. RESULTS After 28 days of treatment, there was no significant effect on hyperglycemia or body weight with either dose of INV-202. Renal and hepatic weights were reduced while heart weight was unaffected. This remained true when normalizing for tibial length. Compared with vehicle-treated diabetic mice, INV-202-challenged mice displayed a marked decrease in many clinical features of DN such as albuminuria, albumin-to-creatinine ratio, urinary urea, loss of glomerular filtration rate and renal hypertrophy. Interestingly, we also found an improvement in both podocyte and proximal tubular cells morphology and health markers that were likely responsible for the improvement previously mentioned. In addition, INV-202 led to a downregulation of the angiotensin II receptor expression as well as a reduced urinary excretion, suggesting an inhibitory effect of this compound on the angiotensin II-mediated renal dysfunction in the context of DN. Furthermore, INV-202 also led to a drastic reduction in renal inflammation and oxidative stress markers that are known to be highly involved in the pathogenesis of DN. Finally, despite the limitation of our model in regard to interstitial fibrosis development, we could observe a marked anti-fibrotic effect of INV-202. CONCLUSION Treatment with INV-202 reduced the progression of nephropathy in STZ-induced diabetic mice. Improvements in kidney size, function and histology, with corresponding gene expression, were noted with both doses of INV-202. Further work to explore the effect of INV-202 in humans is warranted.

Targeting cannabinoid 1 receptors (CB1R) with peripherally restricted antagonists (or inverse agonists) shows promise to improve metabolic disorders associated with obesity. In this context, we designed and synthetized JM-00266, a new CB1R blocker with limited blood-brain barrier (BBB) permeability. Pharmacokinetics were tested with SwissADME and in vivo in rodents after oral and intraperitoneal administration of JM-00266 in comparison with Rimonabant. In silico predictions indicated JM-00266 is a non-brain penetrant compound and this was confirmed by brain/plasma ratios and brain uptake index values. JM-00266 had no impact on food intake, anxiety-related behavior and body temperature suggesting an absence of central activity. cAMP assays performed in CB1R-transfected HEK293T/17 cells showed that the drug exhibited inverse agonist activity on CB1R. In addition, JM-00266 counteracted anandamide-induced gastroparesis indicating substantial peripheral activity. Acute administration of JM-00266 also improved glucose tolerance and insulin sensitivity in wild-type mice, but not in CB1R(-/-) mice. Furthermore, the accumulation of JM-00266 in adipose tissue was associated with an increase in lipolysis. In conclusion, JM-00266 or derivatives can be predicted as a new candidate for modulating peripheral endocannabinoid activity and improving obesity-related metabolic disorders.

OBJECTIVE: Dyslipidemia observed in type 2 diabetes (T2DM) isatherogenic. Important features of diabetic dyslipidemia are increased levelsof triglyceride-rich lipoproteins and small dense LDL particles which, all haveapolipoprotein B100 (apoB100) as major apolipoprotein. This prompted us tostudy the effect of the GLP1 agonist, liraglutide, on the metabolism of apoB100containing lipoproteins.RESEARCH DESIGN AND METHODS: We performed an in vivo kinetic study with stable isotopes (L-[1-13C]leucine) in 10 T2DM patients before and after 6-month treatment withliraglutide (1.2 mg/day). We alsoevaluated, in mice, the effect of liraglutide on the expression of genesinvolved in apoB100 containing lipoprotein clearance.RESULTS: In T2DM patients, liraglutide treatment significantlyreduced plasma apoB100 (0.93±0.13 vs. 1.09±0.11 g/L,p=0.011) and fasting triglycerides (1.76±0.37 vs. 2.48±0.69 mmol/L, p=0.005). The kinetic study showed asignificant increase in indirect catabolism of VLDL1-apoB100(4.11±1.91 vs. 2.96±1.61 day-1,p=0.005), VLDL2-apoB100(5.17±2.53 vs. 2.84±1.65 day-1,p=0.008),IDL-apoB100 (5.27±2.77 vs. 3.74±1.85 day-1,p=0.017)and in catabolism of LDL-apoB100 (0.72±0.22 vs. 0.56±0.22 day-1,p=0.005). In mice, liraglutideincreased lipoprotein lipase (LPL) gene expression and reduced Proproteinconvertase subtilisin/kexin type 9 (PCSK9), Retinol Binding Protein 4 (RBP4)and Tumor Necrosis Factor alpha (TNF alpha) gene expression in adipose tissue,and decreased PCSK9 mRNA and increased LDL-receptor protein expression, inliver. In vitro, liraglutide directly reduced the expression of PCSK9 in theliver.CONCLUSIONS: Treatment with liraglutide induces a significantacceleration of the catabolism of triglyceride-rich lipoproteins (VLDL1,VLDL2, IDL) and LDL. Liraglutide modifies the expression of genesinvolved in apoB100 containing lipoprotein catabolism. These positive effectson lipoprotein metabolism may reduce cardiovascular risk in T2DM.

White adipose tissue (WAT) possesses the endocannabinoid system (ECS) machinery and produces the two major endocannabinoids (ECs), arachidonoylethanolamide (AEA) and 2-arachidonoylglycerol (2-AG). Accumulating evidence indicates that WAT cannabinoid 1 receptors (CB1R) are involved in the regulation of fat storage, tissue remodeling and secretory functions but their role in controlling lipid mobilization is unclear. In the present study, we used different strategies to acutely increase ECS activity in WAT and tested the consequences on glycerol production as a marker of lipolysis. Treating lean mice or rat WAT explants with JLZ195, which inhibits ECs degrading enzymes, induced an increase in 2-AG tissue contents that was associated with a CB1R-dependent decrease in lipolysis. Direct treatment of rat WAT explants with AEA also inhibited glycerol production while mechanistic studies revealed it could result from the stimulation of Akt-signaling pathway. Interestingly, AEA treatment decreased lipolysis both in visceral and subcutaneous WAT collected on lean subjects suggesting that ECS also reduces fat store mobilization in Human. In obese mice, WAT content and secretion rate of ECs were higher than in control while glycerol production was reduced suggesting that over-produced ECs may inhibit lipolysis activating local CB1R. Strikingly, our data also reveal that acute CB1R blockade with Rimonabant did not modify lipolysis in vitro in obese mice and human explants nor in vivo in obese mice. Taken together, these data provide physiological evidence that activation of ECS in WAT, by limiting fat mobilization, may participate in the progressive tissue remodeling that could finally lead to organ dysfunction. The present findings also indicate that acute CB1R blockade is inefficient in regulating lipolysis in obese WAT and raise the possibility of an alteration of CB1R signaling in conditions of obesity.

Endocannabinoids (eCBs) are endogenous lipid mediators that activate the cannabinoid-1 and -2 receptors (CB1R and CB2R, respectively), which mediate the effects of marijuana. The endocannabinoid system (ECS), consisting of eCBs, their receptors and the enzymes involved in their biosynthesis and degradation, is present in the central nervous system as well as in various peripheral tissues. The present chapter discusses accumulating evidence indicating that the ECS is involved in modulating energy homeostasis, adipose tissue metabolism, glucose and insulin balance as well as hepatic lipogenesis in health and metabolic diseases.

Diabeticdyslipidemia (DD), characterized by increased plasma triglycerides (TGs) anddecreased high-density lipoprotein cholesterol (HDL) levels, is a major factorcontributing to non-alcoholic steatohepatitis (NASH) and cardiovascular risk intype-2 diabetes. Activation of both the cannabinoid-1 receptor (CB1R) and induciblenitric oxide synthase (iNOS) are associated with NASH progression. Here, we testedwhether dual-targeting inhibition of hepatic CB1R andiNOS improvesDD in diet-induced obese (DIO) mice. DIO mice weretreated for 14 days with (S)-MRI-1867,a peripherally-restricted hybrid inhibitor of CB1R and iNOS. (R)-MRI-1867, the CB1R-inactive stereoisomerwhich retains iNOS inhibitory activity and JD-5037, a peripherally-restrictedCB1R antagonist were used to assess the relative contribution of the twotargets to the effects of (S)-MRI-1867.(S)-MRI-1867 reduced hepaticsteatosis, the rate of hepatic VLDL secretion, upregulated hepatic LDLRexpression and reduced the circulating levels of the proprotein convertasesubtilisin/kexin type 9 (PCSK9). The decrease in VLDL secretion could beattributed to CB1R blockade while the reduction of PCSK9 levels and the relatedincrease in LDLR resulted from iNOS inhibition via a mTORC1-dependent mechanism.In conclusion, this approach based on the concomitant inhibition of CB1R andiNOS represents a promising therapeutic strategy for the treatment ofdyslipidemia.

BACKGROUNDFish cannot use carbohydrate efficiently and instead utilize protein for energy supply, thus limiting dietary protein storage. Protein deposition is dependent on protein turnover balance, which correlates tightly with cellular energy homeostasis. Mitochondrial fatty acid β-oxidation (FAO) plays a crucial role in energy metabolism. However, the effect of remodeled energy homeostasis caused by inhibited mitochondrial FAO on protein deposition in fish has not been intensively studied.OBJECTIVESThis study aimed to identify the regulatory role of mitochondrial FAO in energy homeostasis maintenance and protein deposition by studying lipid, glucose, and protein metabolism in fish.METHODSCarnitine-depleted male Nile tilapia (initial weight: 4.29 ± 0.12 g; 3 mo old) were established by feeding them with mildronate diets (1000 mg/kg/d) for 6 wk. Zebrafish deficient in the carnitine palmitoyltransferase 1b gene (cpt1b) were produced by using CRISPR/Cas9 gene-editing technology, and their males (154 ± 3.52 mg; 3 mo old) were used for experiments. Normal Nile tilapia and wildtype zebrafish were used as controls. We assessed nutrient metabolism and energy homeostasis-related biochemical and molecular parameters, and performed 14C-labeled nutrient tracking and transcriptomic analyses.RESULTSThe mitochondrial FAO decreased by 33.1-88.9% (liver) and 55.6-68.8% (muscle) in carnitine-depleted Nile tilapia and cpt1b-deficient zebrafish compared with their controls (P < 0.05). Notably, glucose oxidation and muscle protein deposition increased by 20.5-24.4% and 6.40-8.54%, respectively, in the 2 fish models compared with their corresponding controls (P < 0.05). Accordingly, the adenosine 5'-monophosphate-activated protein kinase/protein kinase B-mechanistic target of rapamycin (AMPK/AKT-mTOR) signaling was significantly activated in the 2 fish models with inhibited mitochondrial FAO (P < 0.05).CONCLUSIONSThese data show that inhibited mitochondrial FAO in fish induces energy homeostasis remodeling and enhances glucose utilization and protein deposition. Therefore, fish with inhibited mitochondrial FAO could have high potential to utilize carbohydrate. Our results demonstrate a potentially new approach for increasing protein deposition through energy homeostasis regulation in cultured animals.

l-Carnitine is essential for mitochondrial β-oxidation and has been used as a lipid-lowering feed additive in humans and farmed animals. d-Carnitine is an optical isomer of l-carnitine and dl-carnitine has been widely used in animal feeds. However, the functional differences between l- and d-carnitine are difficult to study because of the endogenous l-carnitine background. In the present study, we developed a low-carnitine Nile tilapia model by treating fish with a carnitine synthesis inhibitor, and used this model to investigate the functional differences between l- and d-carnitine in nutrient metabolism in fish. l- or d-carnitine (0·4 g/kg diet) was fed to the low-carnitine tilapia for 6 weeks. l-Carnitine feeding increased the acyl-carnitine concentration from 3522 to 10 822 ng/g and alleviated the lipid deposition from 15·89 to 11·97 % in the liver of low-carnitine tilapia. However, as compared with l-carnitine group, d-carnitine feeding reduced the acyl-carnitine concentration from 10 822 to 5482 ng/g, and increased lipid deposition from 11·97 to 20·21 % and the mRNA expression of the genes involved in β-oxidation and detoxification in the liver. d-Carnitine feeding also induced hepatic inflammation, oxidative stress and apoptosis. A metabolomic investigation further showed that d-carnitine feeding increased glycolysis, protein metabolism and activity of the tricarboxylic acid cycle and oxidative phosphorylation. Thus, l-carnitine can be physiologically utilised in fish, whereas d-carnitine is metabolised as a xenobiotic and induces lipotoxicity. d-Carnitine-fed fish demonstrates increases in peroxisomal β-oxidation, glycolysis and amino acid degradation to maintain energy homeostasis. Therefore, d-carnitine is not recommended for use in farmed animals.

Obesity is one of the major public health issues, and its prevalence is steadily increasing all the world over. The endocannabinoid system (ECS) has been shown to be involved in the intake of palatable food via activation of cannabinoid 1 receptor (CB1R). However, the involvement of lingual CB1R in the orosensory perception of dietary fatty acids has never been investigated. In the present study, behavioral tests on CB1R−/− and wild type (WT) mice showed that the invalidation of Cb1r gene was associated with low preference for solutions containing rapeseed oil or a long-chain fatty acid (LCFA), such as linoleic acid (LA). Administration of rimonabant, a CB1R inverse agonist, in mice also brought about a low preference for dietary fat. No difference in CD36 and GPR120 protein expressions were observed in taste bud cells (TBC) from WT and CB1R−/− mice. However, LCFA induced a higher increase in [Ca2+]i in TBC from WT mice than that in TBC from CB1R−/− mice. TBC from CB1R−/− mice also exhibited decreased Proglucagon and Glp-1r mRNA and a low GLP-1 basal level. We report that CB1R is involved in fat taste perception via calcium signaling and GLP-1 secretion.

Objective— Treatment with liraglutide, a GLP-1 (glucagon-like peptide-1) agonist, has been shown to reduce postprandial lipidemia, an important feature of diabetic dyslipidemia. However, the underlying mechanisms for this effect remain unknown. This prompted us to study the effect of liraglutide on the metabolism of ApoB48 (apolipoprotein B48). Approach and Results— We performed an in vivo kinetic study with stable isotopes (D8-valine) in the fed state in 10 patients with type 2 diabetes mellitus before treatment and 6 months after the initiation of treatment with liraglutide (1.2 mg/d). We also evaluated, in mice, the effect of a 1-week liraglutide treatment on postload triglycerides and analysed in vitro on jejunum, the direct effect of liraglutide on the expression of genes involved in the biosynthesis of chylomicron. In diabetic patients, liraglutide treatment induced a dramatic reduction of ApoB48 pool (65±38 versus 162±87 mg; P=0.005) because of a significant decrease in ApoB48 production rate (3.02±1.33 versus 6.14±4.27 mg kg-1 d-1; P=0.009) and a significant increase in ApoB48 fractional catabolic rate (5.12±1.35 versus 3.69±0.75 pool d-1; P=0.005). One-week treatment with liraglutide significantly reduced postload plasma triglycerides in mice and liraglutide, in vitro, reduced the expression of ApoB48, DGAT1 (diacylglycerol O-acyltransferase 1), and MTP (microsomal transfer protein) genes. Conclusions— We show that treatment with liraglutide induces a significant reduction of the ApoB48 pool because of both a reduction of ApoB48 production and an increase in ApoB48 catabolism. In vitro, liraglutide reduces the expression of genes involved in chylomicron synthesis. These effects might benefit cardiovascular health. Clinical Trial Registration— URL: https://www.clinicaltrials.gov. Unique identifier: NCT02721888.

Impaired mitochondrial fatty acid β-oxidation has been correlated with many metabolic syndromes, and the metabolic characteristics of the mammalian models of mitochondrial dysfunction have also been intensively studied. However, the effects of the impaired mitochondrial fatty acid β-oxidation on systemic metabolism in teleost have never been investigated. In the present study, we established a low-carnitine zebrafish model by feeding fish with mildronate as a specific carnitine synthesis inhibitor [0.05% body weight (BW)/d] for 7 weeks, and the systemically changed nutrient metabolism, including carnitine and triglyceride (TG) concentrations, fatty acid (FA) β-oxidation capability, and other molecular and biochemical assays of lipid, glucose, and protein metabolism, were measured. The results indicated that mildronate markedly decreased hepatic carnitine concentrations while it had no effect in muscle. Liver TG concentrations increased by more than 50% in mildronate-treated fish. Mildronate decreased the efficiency of liver mitochondrial β-oxidation, increased the hepatic mRNA expression of genes related to FA β-oxidation and lipolysis, and decreased the expression of lipogenesis genes. Mildronate decreased whole body glycogen content, increased glucose metabolism rate, and upregulated the expression of glucose uptake and glycolysis genes. Mildronate also increased whole body protein content and hepatic mRNA expression of mechanistic target of rapamycin (mtor), and decreased the expression of a protein catabolism-related gene. Liver, rather than muscle, was the primary organ targeted by mildronate. In short, mildronate-induced hepatic inhibited carnitine synthesis in zebrafish caused decreased mitochondrial FA β-oxidation efficiency, greater lipid accumulation, and altered glucose and protein metabolism. This reveals the key roles of mitochondrial fatty acid β-oxidation in nutrient metabolism in fish, and this low-carnitine zebrafish model could also be used as a novel fish model for future metabolism studies.

Evidence has accumulated that obesity-related metabolic dysregulation is associated with overactivation of the endocannabinoid system (ECS), which involves cannabinoid receptor 1 (CB1R), in peripheral tissues, including adipose tissue (AT). The functional consequences of CB1R activation on AT metabolism remain unclear. Since excess fat mobilization is considered an important primary event contributing to the onset of insulin resistance, we combined in vivo and in vitro experiments to investigate whether activation of ECS could alter the lipolytic rate. For this purpose, the appearance of plasma glycerol was measured in wild-type and CB1R-/- mice after acute anandamide administration or inhibition of endocannabinoid degradation by JZL195. Additional experiments were conducted on rat AT explants to evaluate the direct consequences of ECS activation on glycerol release and signaling pathways. Treatments stimulated glycerol release in mice fasted for 6 h and injected with glucose but not in 24-h fasted mice or in CB1R-/-, suggesting that the effect was dependent on plasma insulin levels and mediated by CB1R. We concomitantly observed that Akt cascade activity was decreased, indicating an alteration of the antilipolytic action of insulin. Similar results were obtained with tissue explants exposed to anandamide, thus identifying CB1R of AT as a major target. This study indicates the existence of a functional interaction between CB1R and lipolysis regulation in AT. Further investigation is needed to test if the elevation of ECS tone encountered in obesity is associated with excess fat mobilization contributing to ectopic fat deposition and related metabolic disorders.