No abstract

explored and provide evidence supporting this concept. This includes inactivation of hormone sensitive lipase (HSL) ( 5, 6 ) and A 1 -adenosine receptor agonists ( 7 ). In addition, several other G protein-coupled receptors (GPRs) are involved in controlling adipocyte FFA release, including GPR43, GPR81, and GPR109A ( 8-10 ).The GPR109A agonist nicotinic acid (NiAc) has been used clinically ever since its antidyslipidemic effects (HDL elevation and reductions of total cholesterol, LDL-cholesterol, and TG) were discovered more than 50 years ago ( 11-15 ). Although NiAc potently lowers FFA acutely, large-scale clinical studies, with repeated oral NiAc administration, often report increased levels of fasting glycemia ( 16-19 ). NiAc has not been optimized to achieve durable and therapeutically meaningful FFA lowering. By this, we specifi cally mean reducing around-the-clock FFA area under the curve (AUC). In theory, this might be achieved by sustained NiAc exposure; however, the FFA-lowering effect seen initially appears to be lost over time despite maintained NiAc exposure (tolerance development) ( 20 ). Time-dependent loss of both FFA lowering and glucose control improvement also occur in patients with type 2 diabetes, treated with the NiAc analog acipimox ( 21,22 ). To avoid tolerance development, drug holidays are needed. However, at the end of each NiAc exposure period, there is the risk of FFA rebound (here referring to the situation where FFA overshoots pretreatment levels in connection with NiAc decline) due to the short NiAc plasma half-life ( 23 ). FFA rebound is associated with impaired glucose control ( 24, 25 ). The question of whether there might be an optimal balance between periods of continuous exposure (which would minimize rebound) and drug holidays (which would minimize tolerance) in order to achieve maximal FFA lowering has not been addressed. Lipid overload in nonadipose tissues has been linked to the pathogenesis of insulin resistance and atherogenesis ( 1-4 ). A potential means for reversing peripheral lipid overload is to restrict the release of FFAs from adipose tissues. A number of independent mechanisms have been N.D. Oakes, P. Thalén, and A. Kjellstedt Abbreviations: ATGL, adipocyte triglyceride lipase; AUC, area under the curve; ER, extended release; GIR, glucose infusion rate; GPR, G protein-coupled receptor; HOMA-IR, homeostasis model assessment for insulin resistance; HSL, hormone sensitive lipase; NiAc, nicotinic acid; PDE-3B, phosphodiesterase-3B .

This study investigates the impact of disease on nicotinic acid (NiAc)-induced changes in plasma concentrations of non-esterified fatty acids (NEFA). NiAc was given by constant intravenous infusion to normal Sprague-Dawley and obese Zucker rats, and arterial blood samples were taken for analysis of NiAc, NEFA, insulin and glucose plasma concentrations. The intravenous route was intentionally selected to avoid confounding processes, such as absorption, following extravascular administration. Data were analyzed using nonlinear mixed effects modeling (NONMEM, version VI). The disposition of NiAc in the normal rats was described by a two-compartment model with endogenous synthesis of NiAc and two parallel capacity-limited elimination processes. In the obese rats disposition was described by a one-compartment model with endogenous synthesis of NiAc and one capacity-limited elimination process. The plasma concentration of NiAc drove NEFA (R) turnover via an inhibitory drug-mechanism function acting on the formation of NEFA. NEFA turnover was described by a feedback model with a moderator distributed over a series of transit compartments, where the first compartment (M 1 ) inhibited the formation of R and the last compartment (M N ) stimulated the loss of R. All processes regulating plasma NEFA concentrations were assumed to be captured by the moderator function. Differences in the pharmacodynamic response of the two strains included, in the obese animals, an increased NEFA baseline, diminished rebound and post-rebound oscillation, and a more pronounced slowly developing tolerance during the period of constant drug exposure. The feedback model captured the NiAc-induced changes in NEFA response in both the normal and obese rats. Differences in the parameter estimates between the obese and normal rats included, in the former group, increases in R 0 , k in and p by 44, 41 and 78 %, respectively, and decreases in k out and γ by 64 and 84 %, respectively. The estimates of k tol and IC 50 were similar in both groups. The NiAc-NEFA concentration-response relationship at equilibrium was substantially different in the two groups, being shifted upwards and to the right, and being shallower in the obese rats. The extent of such shifts is important, as they demonstrate the impact of disease at equilibrium and, if ignored, will lead to erroneous dose predictions and, in consequence, poorly designed studies. The proposed models are primarily aimed at screening and selecting candidates with the highest potential of becoming a viable drug in man.

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ObjectiveBone morphogenetic protein 4 (BMP4) adeno-associated viral vectors of serotype 8 (AAV8) gene therapy targeting the liver prevents the development of obesity in initially lean mice by browning the large subcutaneous white adipose tissue (WAT) and enhancing energy expenditure. Here, we examine whether this approach could also reduce established obesity.MethodsDietary-induced obese C57BL6/N mice received AAV8 BMP4 gene therapy at 17–18 weeks of age. They were kept on a high-fat diet and phenotypically characterized for an additional 10–12 weeks. Following termination, the mice underwent additional characterization in vitro.ResultsSurprisingly, we observed no effect on body weight, browning of WAT, or energy expenditure in these obese mice, but whole-body insulin sensitivity and glucose tolerance were robustly improved. Insulin signaling and insulin-stimulated glucose uptake were increased in both adipose cells and skeletal muscle. BMP4 also decreased hepatic glucose production and reduced gluconeogenic enzymes in the liver, but not in the kidney, in addition to enhancing insulin action in the liver.ConclusionsOur findings show that BMP4 prevents, but does not reverse, established obesity in adult mice, while it improves insulin sensitivity independent of weight reduction. The BMP antagonist Noggin was increased in WAT in obesity, which may account for the lack of browning.

No abstract

Nicotinic acid (NiAc) is a potent inhibitor of adipose tissue lipolysis. Acute administration results in a rapid reduction of plasma free fatty acid (FFA) concentrations. Sustained NiAc exposure is associated with tolerance development (drug resistance) and complete adaptation (FFA returning to pretreatment levels). We conducted a meta-analysis on a rich pre-clinical data set of the NiAc–FFA interaction to establish the acute and chronic exposure-response relations from a macro perspective. The data were analyzed using a nonlinear mixed-effects framework. We also developed a new turnover model that describes the adaptation seen in plasma FFA concentrations in lean Sprague–Dawley and obese Zucker rats following acute and chronic NiAc exposure. The adaptive mechanisms within the system were described using integral control systems and dynamic efficacies in the traditional model. Insulin was incorporated in parallel with NiAc as the main endogenous co-variate of FFA dynamics. The model captured profound insulin resistance and complete drug resistance in obese rats. The efficacy of NiAc as an inhibitor of FFA release went from 1 to approximately 0 during sustained exposure in obese rats. The potency of NiAc as an inhibitor of insulin and of FFA release was estimated to be 0.338 and 0.436 , respectively, in obese rats. A range of dosing regimens was analyzed and predictions made for optimizing NiAc delivery to minimize FFA exposure. Given the exposure levels of the experiments, the importance of washout periods in-between NiAc infusions was illustrated. The washout periods should be 2 h longer than the infusions in order to optimize 24 h lowering of FFA in rats. However, the predicted concentration-response relationships suggests that higher AUC reductions might be attained at lower NiAc exposures.

Macrophages are important regulators of obesity-associated inflammation and PPARα and -γ agonism in macrophages has anti-inflammatory effects. In this study, we tested the efficacy with which liposomal delivery could target the PPARα/γ dual agonist tesaglitazar to macrophages while reducing drug action in common sites of drug toxicity: the liver and kidney, and whether tesaglitazar had anti-inflammatory effects in an in vivo model of obesity-associated dysmetabolism.Methods: Male leptin-deficient (ob/ob) mice were administered tesaglitazar or vehicle for one week in a standard oral formulation or encapsulated in liposomes. Following the end of treatment, circulating metabolic parameters were measured and pro-inflammatory adipose tissue macrophage populations were quantified by flow cytometry. Cellular uptake of liposomes in tissues was assessed using immunofluorescence and a broad panel of cell subset markers by flow cytometry. Finally, PPARα/γ gene target expression levels in the liver, kidney, and sorted macrophages were quantified to determine levels of drug targeting to and drug action in these tissues and cells.Results: Administration of a standard oral formulation of tesaglitazar effectively treated symptoms of obesity-associated dysmetabolism and reduced the number of pro-inflammatory adipose tissue macrophages. Macrophages are the major cell type that took up liposomes with many other immune and stromal cell types taking up liposomes to a lesser extent. Liposome delivery of tesaglitazar did not have effects on inflammatory macrophages nor did it improve metabolic parameters to the extent of a standard oral formulation. Liposomal delivery did, however, attenuate effects on liver weight and liver and kidney expression of PPARα and -γ gene targets compared to oral delivery.Conclusions: These findings reveal for the first time that tesaglitazar has anti-inflammatory effects on adipose tissue macrophage populations in vivo. These data also suggest that while nanoparticle delivery reduced off-target effects, yet the lack of tesaglitazar actions in non-targeted cells such (as hepatocytes and adipocytes) and the uptake of drug-loaded liposomes in many other cell types, albeit to a lesser extent, may have impacted overall therapeutic efficacy. This fulsome analysis of cellular uptake of tesaglitazar-loaded liposomes provides important lessons for future studies of liposome drug delivery.