The host response to poly(lactide-co-glycolide) scaffolds protects mice from diet induced obesity and glucose intolerance

Recent advances in drug delivery systems based on natural and synthetic polymes for treating obesity

Obesity stands as a pervasive global public health issue, posing a formidable threat to human well-being as its prevalence continues to surge year by year. Presently, pharmacological treatment remains the favored adjunct strategy for addressing obesity. However, conventional delivery methods suffer from low bioavailability and the potential for side effects, underscoring the pressing need for more efficient and targeted delivery approaches. Recent research has delved extensively into emerging drug delivery systems employing polymers as carriers, with numerous preclinical studies contributing to the growing body of knowledge. This review concentrates on the utilization of natural polymers as drug delivery systems for the treatment of obesity, encompassing recent advancements in both natural and synthetic polymers. The comprehensive exploration includes an analysis of the advantages and disadvantages associated with these polymer carriers. The examination of these characteristics provides valuable insights into potential future developments in the field of drug delivery for obesity treatment.

Biomaterial-Based Therapeutic Strategies for Obesity and Its Comorbidities

Obesity is a global public health issue that results in many health complications or comorbidities, including type 2 diabetes mellitus, cardiovascular disease, and fatty liver. Pharmacotherapy alone or combined with either lifestyle alteration or surgery represents the main modality to combat obesity and its complications. However, most anti-obesity drugs are limited by their bioavailability, target specificity, and potential toxic effects. Only a handful of drugs, including orlistat, liraglutide, and semaglutide, are currently approved for clinical obesity treatment. Thus, there is an urgent need for alternative treatment strategies. Based on the new revelation of the pathogenesis of obesity and the efforts toward the multi-disciplinary integration of materials, chemistry, biotechnology, and pharmacy, some emerging obesity treatment strategies are gradually entering the field of preclinical and clinical research. Herein, by analyzing the current situation and challenges of various new obesity treatment strategies such as small-molecule drugs, natural drugs, and biotechnology drugs, the advanced functions and prospects of biomaterials in obesity-targeted delivery, as well as their biological activities and applications in obesity treatment, are systematically summarized. Finally, based on the systematic analysis of biomaterial-based obesity therapeutic strategies, the future prospects and challenges in this field are proposed.

Effect of fabrication parameters on morphology and drug loading of polymer particles for rosiglitazone delivery

For the past several decades, drug-encapsulated polymer particles have been investigated as locally-delivered, long-acting therapies. The most common method of producing such particles is the oil in water solvent extraction technique. Using this technique, we produced poly(lactide-co-glycolide) (PLG) microparticles encapsulating rosiglitazone, a small molecule anti-diabetic drug. We investigated the impact of modulating fabrication parameters, including choice of organic solvent, concentration of polymer, and speed of homogenization and centrifugation on particle morphology and drug loading. Additionally, we studied the ratio of air-water-interface area to the extraction bath volume, a previously unstudied fabrication parameter, and its impact on rosiglitazone loading when using dichloromethane as the organic solvent. Under the conditions tested, drug loading can be increased 5-fold by increasing this ratio, which may be achieved by simply selecting a larger extraction vessel. By changing the organic solvent from dichloromethane to ethyl acetate, we produced particles with 60% higher rosiglitazone loading. Interestingly, the particles made with ethyl acetate appeared phase dark under light microscopy suggesting the presence of internal pores. By increasing the proportion of organic phase in the emulsion we eliminated the aberrant morphology but did not alter drug loading. As a final step in the development of the particles, we established that rosiglitazone remained stable throughout the encapsulation process and its subsequent release from particles by demonstrating that rosiglitazone loaded particles enhanced adipocyte lipid storage and adiponectin secretion. Taken together, for this system, air-water-interface area to volume ratio of the extraction bath and organic solvent both arose as key parameters in maximizing rosiglitazone loading in PLG microparticles. This study of how fabrication parameters impact drug loading and particle morphology may be useful in other investigations to encapsulate small molecules in polymer particles for controlled release applications.

Fibroblasts upregulate expression of adhesion molecules and promote lymphocyte retention in 3D fibroin/gelatin scaffolds

Bioengineered scaffolds are crucial components in artificial tissue construction. In general, these scaffolds provide inert three-dimensional (3D) surfaces supporting cell growth. However, some scaffolds can affect the phenotype of cultured cells, especially, adherent stromal cells, such as fibroblasts. Here we report on unique properties of 3D fibroin/gelatin materials, which may rapidly induce expression of adhesion molecules, such as ICAM-1 and VCAM-1, in cultured primary murine embryonic fibroblasts (MEFs). In contrast, two-dimensional (2D) fibroin/gelatin films did not show significant effects on gene expression profiles in fibroblasts as compared to 3D culture conditions. Interestingly, TNF expression was induced in MEFs cultured in 3D fibroin/gelatin scaffolds, while genetic or pharmacological TNF ablation resulted in diminished ICAM-1 and VCAM-1 expression by these cells. Using selective MAPK inhibitors, we uncovered critical contribution of JNK to 3D-induced upregulation of these adhesion molecules. Moreover, we observed ICAM-1/VCAM-1-dependent adhesion of lymphocytes to fibroblasts cultured in 3D fibroin/gelatin scaffolds, but not on 2D fibroin/gelatin films, suggesting functional reprogramming in stromal cells, when exposed to 3D environment. Finally, we observed significant infiltration of lymphocytes into 3D fibroin/gelatin, but not into collagen scaffolds in vivo upon subcapsular kidney implantation in mice. Together our data highlight the important features of fibroin/gelatin scaffolds, when they are produced as 3D sponges rather than 2D films, which should be considered when using these materials for tissue engineering.

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3D, but not 2D fibroin-based scaffolds promote expression of adhesion molecules in murine fibroblasts.

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Overexpression of adhesion molecules in 3D fibroin/gelatin-cultured fibroblasts is TNF- and JNK-dependent.

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Culturing of fibroblasts in 3D fibroin/gelatin scaffolds promotes adhesion of T-lymphocytes.

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Implantation of 3D fibroin/gelatin scaffolds in vivo induces infiltration and clustering of T- and B-lymphocytes.

Regulation of adipose tissue inflammation and systemic metabolism in murine obesity by polymer implants loaded with lentiviral vectors encoding human interleukin-4

Dysfunctional adipose tissue plays a central role in the pathogenesis of the obesity-related metabolic disease, including type 2 diabetes. Targeting adipose tissue using biopolymer implants is a novel therapeutic approach for metabolic disease. We transplanted porous poly(lactide-co-glycolide) (PLG) implants coated with human interleukin-4 (hIL-4)-expressing lentivirus into epididymal white adipose tissue (eWAT) of mice fed a high-fat diet. Tissue and systemic inflammation and metabolism were studied with flow cytometry, immunohistochemistry, quantitative real-time polymerase chain reaction, adipose tissue histology, and in vivo glucose tolerance testing at 2 and 10 weeks of a high-fat diet. PLG implants carrying hIL-4-expressing lentivirus implanted into epididymal white adipose tissue of mice-regulated adipose tissue inflammation, including increased CD3+ CD4+ T-cell frequency, increased eWAT adipocyte hypertrophy, and decreased FASN and ATGL expression, along with reduced fasting blood glucose levels. These effects were observed in early obesity but were not maintained in established obesity. Local delivery of bioimplants loaded with cytokine-expressing lentivirus vectors to adipose tissue influences tissue inflammation and systemic metabolism in early obesity. Further study will be required to show more durable metabolic effects. These data demonstrate that polymer biomaterials implanted into adipose tissue have the potential to modulate local tissue and systemic inflammation and metabolism.

Modulation of adipocyte size and fat pad weight via resveratrol releasing scaffolds implanted into the epididymal adipose tissue

Lipid overload of the adipose tissue, which can be caused by overnutrition, underlies metabolic disease. We hypothesized that increasing the energy demand of adipose tissue is a promising strategy to combat excessive lipid accumulation. Resveratrol, a natural polyphenol, activates lipid catabolism in fat tissue; however, its clinical success is hindered by poor bioavailability. Here, we implanted resveratrol releasing poly(lactide-co-glycolide) scaffolds into epididymal fat to overcome its poor bioavailability with the goal of enhancing local lipid catabolism. In lean mice, resveratrol scaffolds decreased adipocyte size relative to scaffolds with no drug, a response that correlated with AMP kinase activation. Immunohistochemistry indicated that macrophages and multinucleated giant cells within the scaffold expressed carnitine palmitoyltransferase 1 (CPT1) at higher levels than other cells in the adipose tissue. Furthermore, resveratrol increased CPT1 levels in cultured macrophages. Taken together, we propose that resveratrol scaffolds decrease adipocyte size because resveratrol increases lipid utilization in scaffold-infiltrating immune cells, possibly through elevating CPT1 levels or activity. In a follow-up study, mice that received resveratrol scaffolds 28-day prior to a high-fat diet exhibited decreased weight gain, adipose tissue expansion, and adipocyte hypertrophy compared to mice with control scaffolds. Notably, this scaffold-based strategy required a single resveratrol administration compared to the daily regiment generally needed for oral administration. These results indicate that localized delivery of metabolism modulating agents to the adipose tissue may overcome issues with bioavailability and that the role of biomaterials should be further investigated in this therapeutic strategy for metabolic disease.

Scaffold Implant Into the Epididymal Adipose Tissue Protects Mice From High Fat Diet Induced Ectopic Lipid Accumulation and Hyperinsulinemia

Ectopic lipid accumulation, the deposition of lipids in lean tissue, is linked to type 2 diabetes through an association with insulin resistance. It occurs when adipose tissue fails to meet lipid storage needs and there is lipid spillover into tissues not equipped to store them. Ectopic lipid contributes to organ dysfunction because lipids can interfere with insulin signaling and other signaling pathways. Clinical studies indicate that decreasing ectopic lipids through diet and exercise is effective in treating type 2 diabetes; however, its prevalence continues to rise. We propose that strategies to improve lipid handling in the adipose tissue would be adjunctive to healthy lifestyle modification and may address difficulties in treating type 2 diabetes and other syndromes spurred by ectopic lipid. Herein, we investigate biomaterial implants as a means to increase lipid utilization in adipose tissue through the recruitment of highly metabolic cells. Poly(lactide-co-glycolide) scaffolds were implanted into the epididymal fat of mice fed a high fat diet that overwhelms the adipose tissue and promotes ectopic lipid accumulation. Over 5 weeks, mice with scaffolds gained less weight compared to mice without scaffolds and were protected from hyperinsulinemia. These effects correlated with a 53% decrease in triglyceride in the gastrocnemius and a 25% decrease in the liver. Scaffolds increased CPT1A protein levels in the epididymal fat and histology revealed high expression of CTP1A in the cells infiltrating the scaffold relative to the rest of the fat pad. In addition, lacing the scaffold with resveratrol increased CPT1A expression in the epididymal fat over scaffolds with no drug; however, this did not result in further decreases in weight gain or ectopic lipid. Mechanistically, we propose that the cellular activity caused by scaffold implant mitigates the lipid load imposed by the high fat diet and leads to a substantial decrease in lipid accumulation in the muscle and liver. In conclusion, this study establishes that a tissue engineering approach to modulate lipid utilization in the epididymal fat tissue can mitigate ectopic lipid accumulation in mice fed a high fat diet with positive effects on weight gain and whole-body insulin resistance.

Amino acid-based compound activates atypical PKC and leptin receptor pathways to improve glycemia and anxiety like behavior in diabetic mice

Differences in glucose uptake in peripheral and neural tissues account for the reduced efficacy of insulin in nervous tissues. Herein, we report the design of short peptides, referred as amino acid compounds (AAC) with and without a modified side chain moiety. At nanomolar concentrations, a candidate therapeutic molecule, AAC2, containing a 7-(diethylamino) coumarin-3-carboxamide side-chain improved glucose control in human peripheral adipocytes and the endothelial brain barrier cells by activation of insulin-insensitive glucose transporter 1 (GLUT1). AAC2 interacted specifically with the leptin receptor (LepR) and activated atypical protein kinase C zeta (PKCς) to increase glucose uptake. The effects induced by AAC2 were absent in leptin receptor-deficient predipocytes and in Lepr^db mice. In contrast, AAC2 established glycemic control altering food intake in leptin-deficient Lep^ob mice. Therefore, AAC2 activated the LepR and acted in a cytokine-like manner distinct from leptin. In a monogenic Ins2^Akita mouse model for the phenotypes associated with type 1 diabetes, AAC2 rescued systemic glucose uptake in these mice without an increase in insulin levels and adiposity, as seen in insulin-treated Ins2^Akita mice. In contrast to insulin, AAC2 treatment increased brain mass and reduced anxiety-related behavior in Ins2^Akita mice. Our data suggests that the unique mechanism of action for AAC2, activating LepR/PKCς/GLUT1 axis, offers an effective strategy to broaden glycemic control for the prevention of diabetic complications of the nervous system and, possibly, other insulin insensitive or resistant tissues.