A High-Protein Meal during a Night Shift Does Not Improve Postprandial Metabolic Response the Following Breakfast: A Randomized Crossover Study with Night Workers.

The aim of this study was to compare the acute effect of a high-protein/moderate carbohydrate (HP-MCHO) versus low-protein/high-carbohydrate (LP-HCHO) meal served at night on the postprandial metabolic response of male night workers the following breakfast. A randomized crossover study was performed with 14 male night workers (40.9 ± 8.9 years old; 29.1 ± 5.3 kg/m2). Participants underwent two different isocaloric dietary conditions at 1:00 h of the night shift: HP-MCHO (45 en% carbohydrate, 35 en% protein and 20 en% fat) and LP-HCHO (65 en% carbohydrate, 15 en% protein and 20 en% fat). Postprandial capillary glucose levels were determined immediately before the intake of the test meal and 30, 60, 90 and 120 min after the end of the meal. At the end of the work shift (6:30 h), participants received a standard breakfast and postprandial levels of glucose, insulin and triglycerides were determined immediately before and then every 30 min for 2 h (30, 60, 90 and 120 min). Higher values of capillary glucose were found after the LP-HCHO condition compared to the HP-MCHO condition (area under the curve (AUC) = 119.46 ± 1.49 mg/dL × min and 102.95 ± 1.28 mg/dL × min, respectively; p < 0.001). For the metabolic response to standard breakfast as the following meal, no significant differences in glucose, insulin, triglyceride, and HOMA-IR levels were found between interventions. A night meal with a higher percentage of protein and a lower percentage of carbohydrate led to minor postprandial glucose levels during the night shift but exerted no effect on the metabolic response of the following meal. This trial was registered at ClinicalTrials.gov as NCT03456219.

Insulin encapsulation in reinforced alginate microspheres prepared by internal gelation.

Insulin-loaded alginate microspheres prepared by emulsification/internal gelation were reinforced by blending with polyanionic additive polymers and/or chitosan-coating in order to increase the protection of insulin at simulated gastric pH and obtain a sustained release at simulated intestinal pH. Polyanionic additive polymers blended with alginate were cellulose acetate phtalate (CAP), Eudragit L100 (EL100), sodium carboxymethylcellulose (CMC), polyphosphate (PP), dextran sulfate (DS) and cellulose sulfate (CS). Chitosan-coating was applied by using a one-stage procedure. The influence of additive polymers and chitosan-coating on the size distribution of microspheres, encapsulation efficiency and release profile of insulin in simulated gastrointestinal pH conditions was studied. The mean diameter of blended microspheres ranged from 65 to 106 microm and encapsulation efficiency of insulin varied from 14 to 100%, reaching a maximum value when CS and DS were incorporated in the alginate matrix. Insulin release, at pH 1.2, was almost prevented by the incorporation of PP, DS and CS. When uncoated microspheres were transferred to pH 6.8, a fast dissolution occurred, independently of the additive polymer blended with alginate, and insulin was completely released. Increasing the additive polymer concentration in the alginate matrix and/or chitosan-coating the blended alginate microspheres did not promote a sustained release of insulin from microspheres at pH 6.8.

Alginate microspheres prepared by internal gelation: development and effect on insulin stability.

Recombinant human insulin was encapsulated within alginate microspheres by the emulsification/internal gelation technique with the objective of preserving protein stability during encapsulation procedure. The influence of process and formulation parameters was evaluated on the morphology and encapsulation efficiency of insulin. The in vitro release of insulin from microspheres was studied under simulated gastrointestinal conditions and the in vivo activity of protein after processing was assessed by subcutaneous administration of extracted insulin from microspheres to streptozotocin-induced diabetic rats. Microspheres mean diameter, ranging from 21 to 287 microm, decreased with the internal phase ratio, emulsifier concentration, mixer rotational speed and increased with alginate concentration. Insulin encapsulation efficiency, near 75%, was not affected by emulsifier concentration, mixer rotational speed and zinc/insulin hexamer molar ratio but decreased either by increasing internal phase ratio and calcium/alginate mass ratio or by decreasing acid/calcium molar ratio and alginate concentration. A high insulin release, above 75%, was obtained at pH 1.2 and under simulated intestinal pH a complete dissolution of microspheres occurred. Extracted insulin from microspheres decreased hyperglycemia of diabetic rats proving to be bioactive and showing that encapsulation in alginate microspheres using the emulsification/internal gelation is an appropriate method for protein encapsulation.

Microencapsulation of hemoglobin in chitosan-coated alginate microspheres prepared by emulsification/internal gelation.

Chitosan-coated alginate microspheres prepared by emulsification/internal gelation were chosen as carriers for a model protein, hemoglobin (Hb), owing to nontoxicity of the polymers and mild conditions of the method. The influence of process variables related to the emulsification step and microsphere recovering and formulation variables, such as alginate gelation and chitosan coating, on the size distribution and encapsulation efficiency was studied. The effect of microsphere coating as well its drying procedure on the Hb release profile was also evaluated. Chitosan coating was applied by either a continuous microencapsulation procedure or a 2-stage coating process. Microspheres with a mean diameter of less than 30 microm and an encapsulation efficiency above 90% were obtained. Calcium alginate cross-linking was optimized by using an acid/CaCO(3) molar ratio of 2.5, and microsphere-recovery with acetate buffer led to higher encapsulation efficiency. Hb release in gastric fluid was minimal for air-dried microspheres. Coating effect revealed a total release of 27% for 2-stage coated wet microspheres, while other formulations showed an Hb release above 50%. Lyophilized microspheres behaved similar to wet microspheres, although a higher total protein release was obtained with 2-stage coating. At pH 6.8, uncoated microspheres dissolved in less than 1 hour; however, Hb release from air-dried microspheres was incomplete. Chitosan coating decreased the release rate of Hb, but an incomplete release was obtained. The 2-stage coated microspheres showed no burst effect, whereas the 1-stage coated microspheres permitted a higher protein release.

Effect of chitosan-coated alginate microspheres on the permeability of Caco-2 cell monolayers.

Alginate microspheres were prepared by emulsification/internal gelation and coated with chitosan. The ability of chitosan-coated alginate microspheres to increase the paracellular transport across Caco-2 cell monolayers was evaluated in comparison to uncoated microspheres and chitosan solutions. Transport studies were performed by using a permeability marker, Lucifer Yellow (LY), and by measuring the transepithelial electric resistance (TEER) variations. Furthermore, the occurrence of cytotoxic effects was assessed by evaluating neutral red uptake in viable cells and lactate dehydrogenase (LDH) release from damaged cells. A 3-fold increase on LY permeability was obtained for coated microspheres when compared to chitosan solutions. TEER variations were in agreement with permeability results. Chitosan solutions exhibited a dose-dependent toxicity, but coated microspheres did not decrease the viability of cells. Chitosan-coated alginate microspheres have potential to be used as carriers of poorly absorbable hydrophilic drugs to the intestinal epithelia and possibly increase their oral bioavailability.