Human MC4R variants affect endocytosis, trafficking and dimerization revealing multiple cellular mechanisms involved in weight regulation.

The Melanocortin-4 Receptor (MC4R) plays a pivotal role in energy homeostasis. We used human MC4R mutations associated with an increased or decreased risk of obesity to dissect mechanisms that regulate MC4R function. Most obesity-associated mutations impair trafficking to the plasma membrane (PM), whereas obesity-protecting mutations either accelerate recycling to the PM or decrease internalization, resulting in enhanced signaling. MC4R mutations that do not affect canonical Gαs protein-mediated signaling, previously considered to be non-pathogenic, nonetheless disrupt agonist-induced internalization, ß-arrestin recruitment, and/or coupling to Gαs, establishing their causal role in severe obesity. Structural mapping reveals ligand-accessible sites by which MC4R couples to effectors and residues involved in the homodimerization of MC4R, which is disrupted by multiple obesity-associated mutations. Human genetic studies reveal that endocytosis, intracellular trafficking, and homodimerization regulate MC4R function to a level that is physiologically relevant, supporting the development of chaperones, agonists, and allosteric modulators of MC4R for weight loss therapy.

Mechanism of action of camphoryl-benzene sulfonamide derivative on glucose uptake in adipose tissue.

The aim of the present study was to investigate the mechanism of action of a sulfonamide derivative on glucose uptake in adipose tissue, as well as to characterize the effects of this compound on intestinal disaccharidases and advanced glycation end-products (AGEs) formation. Camphoryl-benzene sulfonamide (CS) was able to stimulate glucose uptake in isolated adipocytes, adipose tissue, and in soleus muscle. The stimulatory effect of the compound (10 µM) on glucose uptake on adipose tissue was blocked by diazoxide, wortmannin, U73122, colchicine, and N-ethylmaleimide. On the other hand, the effects of CS were not blocked by glibenclamide, an inhibitor of the K+ -ATP channel, or even by the inhibitor of protein p38 MAPK, SB 203580. In vivo, this compound reduced intestinal disaccharidase activity, while, in vitro, CS reduced the formation of AGEs at 7, 14, and 28 days of incubation. The stimulatory effect of CS on glucose uptake requires the activation of the K+ -ATP channel, translocation, and fusion of GLUT4 vesicles to the plasma membrane on adipocytes for glucose homeostasis. In addition, the inhibition of disaccharidase activity contributes to the glucose homeostasis in a short-term as well as the remarkable reduction in AGE formation indicates that the CS may prevent of complications of late diabetes.

Hypericin encapsulated in solid lipid nanoparticles: phototoxicity and photodynamic efficiency.

The hydrophobicity of some photosensitizers can induce aggregation in biological systems, which consequently reduces photodynamic activity. The conjugation of photosensitizers with nanocarrier systems can potentially be used to overcome this problem. The objective of this study was to prepare and characterise hypericin-loaded solid lipid nanoparticles (Hy-SLN) for use in photodynamic therapy (PDT). SLN were prepared using the ultrasonication technique, and their physicochemical properties were characterised. The mean particle size was found to be 153 nm, with a low polydispersity index of 0.28. One of the major advantages of the SLN formulation is its high entrapment efficiency (EE%). Hy-SLN showed greater than 80% EE and a drug loading capacity of 5.22% (w/w). To determine the photodynamic efficiency of Hy before and after encapsulation in SLN, the rate constants for the photodecomposition of two (1)O2 trapping reagents, DPBF and AU, were determined. These rate constants exhibited an increase of 60% and 50% for each method, respectively, which is most likely due to an increase in the lifetime of the triplet state caused by the increase in solubility. Hy-SLN presented a 30% increase in cell uptake and a correlated improvement of 26% in cytotoxicity. Thus, all these advantages suggest that Hy-loaded SLN has potential for use in PDT.