A 3D-printed multi-compartment device that enables dynamic PK/PD profiles of antibiotics.

Pathogens develop resistance to various drugs while under the selective pressure of antibiotics resulting in the emergence of bacterial strains that are resistant to multiple treatment options. Unfortunately, the resistance to antibiotics has also been accompanied by a reduction in the development of novel antibiotics to combat various pathogens. Current diagnostic tools, which are used in parts of the early developmental process of antibiotics, primarily consist of static susceptibility tests that do not resemble the pharmacokinetics of the therapy in vivo. Here, we designed and 3D-printed cubical inserts with membranes on two of the cube faces that allow diffusion of a molecule across two planes. These inserts are used with a 3D-printed device to create a two-compartment model to mimic the pharmacokinetics of a molecule in humans from multiple types of administration. Fluorescein was used to characterize the device and the diffusion of molecules from a flowing channel, through a membrane in the first plane (representing the primary compartment in vivo, or plasma), followed by measurement in the second compartment (that represents the interstitial fluid). The dynamic, two-compartment model was tested using both gram-positive and gram-negative bacterial strains in the secondary compartment. The ATP/OD600 (a measure of antibiotic activity) of a kanamycin-resistant E. coli strain challenged with the antibiotic levofloxacin increased after reaching an effective concentration of the antibiotic at 2 h, equating to a secondary compartment concentration of 3.5 ± 1.3 µM levofloxacin. The ATP/OD600 of a chloramphenicol-resistant B. subtilis strain challenged with the antibiotic levofloxacin remained steady or increased slightly after reaching an effective concentration of the antibiotic. The earliest statistical difference was detected 3 h after the start of the PK curve, which corresponds with a secondary compartment concentration of 4.8 ± 1.8 µM levofloxacin. Our results demonstrate that a fabricated 2-compartment model (1) provides realistic PK values to those published from in vivo studies and (2) can be used to determine antibiotic pharmacodynamics.

Albumin Glycation Affects the Delivery of C-Peptide to the Red Blood Cells.

Serum albumin is a prominent plasma protein that becomes modified in hyperglycemic conditions. In a process known as glycation, these modifications can change the structure and function of proteins, which decrease ligand binding capabilities and alter the bioavailability of ligands. C-peptide is a molecule that binds to the red blood cell (RBC) and stimulates the release of adenosine triphosphate (ATP), which is known to participate in the regulation of blood flow. C-peptide binding to the RBC only occurs in the presence of albumin, and downstream signaling cascades only occur when the albumin and C-peptide complex contains Zn2+. Here, we measure the binding of glycated bovine serum albumin (gBSA) to the RBC in conditions with or without C-peptide and Zn2+. Key to these studies is the analytical sample preparation involving separation of BSA fractions with boronate affinity chromatography and characterization of the varying glycation levels with mass spectrometry. Results from this study show an increase in binding for higher % glycation of gBSA to the RBCs, but a decrease in ability to deliver C-peptide (0.75 ± 0.11 nM for 22% gBSA) compared to samples with less glycation (1.22 ± 0.16 nM for 13% gBSA). A similar trend was measured for Zn2+ delivery to the RBC as a function of glycation percentage. When 15% gBSA or 18% gBSA was combined with C-peptide/Zn2+, the derived ATP release from the RBCs significantly increased to 113% or 36%, respectively. However, 26% gBSA with C-peptide/Zn2+ had no significant increase in ATP release from RBCs. These results indicate that glycation of BSA interferes in C-peptide and Zn2+ binding to the RBC and subsequent RBC ATP release, which may have implications in C-peptide therapy for people with type 1 diabetes.

A 3D-printed transfusion platform reveals beneficial effects of normoglycemic erythrocyte storage solutions and a novel rejuvenating solution.

A set of 3D-printed analytical devices were developed to investigate erythrocytes (ERYs) processed in conventional and modified storage solutions used in transfusion medicine. During storage, prior to transfusion into a patient recipient, ERYs undergo many chemical and physical changes that are not completely understood. However, these changes are thought to contribute to an increase in post-transfusion complications, and even an increase in mortality rates. Here, a reusable fluidic device (fabricated with additive manufacturing technologies) enabled the evaluation of ERYs prior to, and after, introduction into a stream of flowing fresh ERYs, thus representing components of an in vivo ERY transfusion on an in vitro platform. Specifically, ERYs stored in conventional and glucose-modified solutions were assayed by chemiluminescence for their ability to release flow-induced ATP. The ERY's deformability was also determined throughout the storage duration using a novel membrane transport approach housed in a 3D-printed scaffold. Results show that hyperglycemic conditions permanently alter ERY deformability, which may explain the reduced ATP release, as this phenomenon is related to cell deformability. Importantly, the reduced deformability and ATP release were reversible in an in vitro model of transfusion; specifically, when stored cells were introduced into a flowing stream of healthy cells, the ERY-derived release of ATP and cell deformability both returned to states similar to that of non-stored cells. However, after 1-2 weeks of storage, the deleterious effects of the storage were permanent. These results suggest that currently approved hyperglycemic storage solutions are having adverse effects on stored ERYs used in transfusion medicine and that normoglycemic storage may reduce the storage lesion, especially for cells stored for longer than 14 days.

Specific Binding of Leptin to Red Blood Cells Delivers a Pancreatic Hormone and Stimulates ATP Release.

Since its discovery in 1994, leptin continues to have new potential physiological roles uncovered, including a role in the regulation of blood flow. Leptin's role in regulating blood flow is not completely understood. Red blood cell (RBC)-derived ATP is a recognized stimulus of blood flow, and multiple studies suggest that C-peptide, a hormone secreted in equimolar amounts with insulin from the pancreatic ß-cells, can stimulate that release when delivered by albumin and in combination with Zn2+. Here, we report leptin delivers C-peptide and Zn2+ to RBCs in a saturable and specific manner. We labeled leptin with technetium-99 m (99mTc) to perform binding studies while using albumin to block the specific binding of 99mTc-leptin in the presence or absence of C-peptide. Our results suggest that leptin has a saturable and specific binding site on the RBC ((Kd = 1.79 ± 0.46) × 10-7 M) that is statistically equal to the binding affinity in the presence of 20 nM C-peptide ((Kd = 2.05 ± 0.20) × 10-7 M). While the binding affinity between leptin and the RBC did not change with C-peptide, the moles of bound leptin did increase with C-peptide, suggesting a separate binding site on the cell for a leptin/C-peptide complex. The RBC-derived ATP increased in the presence of a leptin/C-peptide/Zn2+ addition, in a concentration-dependent manner. Control RBCs ATP release increased (71 ± 5.6%) in the presence of C-peptide and Zn2+, which increased further to (94 ± 5.6%) in the presence of Zn2+, C-peptide, and leptin.