Changes in extracellular pH and myocardial ischaemia alter the cardiac effects of diadenosine tetraphosphate and pentaphosphate

Silk Fibroin as a Bioink - A Thematic Review of Functionalization Strategies for Bioprinting Applications

Bioprinting is an emerging tissue engineering technique that has attracted the attention of researchers around the world, for its ability to create tissue constructs that recapitulate physiological function. While the technique has been receiving hype, there are still limitations to the use of bioprinting in practical applications, much of which is due to inappropriate bioink design that is unable to recapitulate complex tissue architecture. Silk fibroin (SF) is an exciting and promising bioink candidate that has been increasingly popular in bioprinting applications because of its processability, biodegradability, and biocompatibility properties. However, due to its lack of optimum gelation properties, functionalization strategies need to be employed so that SF can be effectively used in bioprinting applications. These functionalization strategies are processing methods which allow SF to be compatible with specific bioprinting techniques. Previous literature reviews of SF as a bioink mainly focus on discussing different methods to functionalize SF as a bioink, while a comprehensive review on categorizing SF functional methods according to their potential applications is missing. This paper seeks to discuss and compartmentalize the different strategies used to functionalize SF for bioprinting and categorize the strategies for each bioprinting method (namely, inkjet, extrusion, and light-based bioprinting). By compartmentalizing the various strategies for each printing method, the paper illustrates how each strategy is better suited for a target tissue application. The paper will also discuss applications of SF bioinks in regenerating various tissue types and the challenges and future trends that SF can take in its role as a bioink material.

Chemoresponsive polymer systems for selective molecular recognition of organic molecules in biological systems

Smart polymer materials that respond to a chemical stimulus are applied for the construction of biomedical devices and purification/separation systems. Small organic molecules are a particular type of stimulus. Their abnormal concentration indisputably indicates certain diseases. They are also hazardous environment contaminants. Polymer materials, which structure is selectively changed in the presence of a defined organic compound are promising in view of regulation of certain biomedical functions, as well as in view of chemical detectors construction. This review summarizes the state of the art in the self-assemblies of amphiphilic copolymers and polymer networks sensitive toward organic species, with an emphasis on the reports from the last decade. We focus on the relationship between the selectivity of introduced receptor moieties responsible for the change of material structure, the overall structure of material and its functionality.

Modulation of P2Y11-related purinergic signaling in inflammation and cardio-metabolic diseases

Chronic inflammation is the hallmark of cardiovascular pathologies with a major role in both disease progression and occurrence of long-term complications. The massive release of ATP during the inflammatory process activates various purinergic receptors, including P2Y11. This receptor is less studied but ubiquitously expressed in all cells relevant for cardiovascular pathology: cardiomyocytes, fibroblasts, endothelial and immune cells. While several studies suggested a potential pro-inflammatory role for P2Y11 receptors, recent literature data are supportive of an anti-inflammatory profile characterized by the immunosuppression of dendritic cells, inhibition of fibroblast proliferation and of cytokines and ATP secretion. Moreover, modulation of its activity appears to mediate the positive inotropic effect of ATP and mitigate endothelial dysfunction, thus rendering this receptor a promising therapeutic target in the cardiovascular disease armamentarium. The aim of the present review is to summarize the current available knowledge on P2Y11-related purinergic signaling in the setting of inflammation and cardio-metabolic diseases.

Fabrication and Characterization of Drug-Loaded Conductive Poly(glycerol sebacate)/Nanoparticle-Based Composite Patch for Myocardial Infarction Applications

Heart tissue engineering is critical in the treatment of myocardial infarction, which may benefit from drug-releasing smart materials. In this study, we load a small molecule (3i-1000) in new biodegradable and conductive patches for application in infarcted myocardium. The composite patches consist of a biocompatible elastomer, poly(glycerol sebacate) (PGS), coupled with collagen type I, used to promote cell attachment. In addition, polypyrrole is incorporated because of its electrical conductivity and to induce cell signaling. Results from the in vitro experiments indicate a high density of cardiac myoblast cells attached on the patches, which stay viable for at least 1 month. The degradation of the patches does not show any cytotoxic effect, while 3i-1000 delivery induces cell proliferation. Conductive patches show high blood wettability and drug release, correlating with the rate of degradation of the PGS matrix. Together with the electrical conductivity and elongation characteristics, the developed biomaterial fits the mechanical, conductive, and biological demands required for cardiac treatment.

Quantification of diadenosine polyphosphates in blood plasma using a tandem boronate affinity-ion exchange chromatography system

Endogenous diadenosine polyphosphates (Ap(n)As) have been associated with a variety of biological effects but quantifying their concentration in blood is difficult. We report on the development of a tandem affinity-ion exchange high-performance liquid chromatography (HPLC) system that employs boronate affinity upstream of ion exchange chromatography for automated rapid (45-min) resolution and extraction of Ap(n)As from human plasma. This system obviates previous requirements for multiple column separations and handling steps, so it is ideally set up for time- and cost-efficient screening of blood samples for Ap(n)A pharmacokinetic and biodistribution studies.

Coronary response to diadenosine pentaphosphate after ischaemia-reperfusion in the isolated rat heart

AIMS

Diadenosine polyphosphates are vasoactive mediators that may be released from platelet granules and which may be present at higher concentrations during coronary ischaemia-reperfusion. The objective of this study was to analyse their effects in such conditions.

METHODS AND RESULTS

Rat hearts were perfused in a Langendorff preparation and the response to diadenosine pentaphosphate (Ap5A, 10(-7)-10(-5) M) was recorded. In control hearts, Ap5A produced a small, transient coronary vasoconstriction followed by marked vasodilatation, as well as a reduction in the left ventricular developed pressure dP/dt and heart rate, both at the basal coronary resting tone or after pre-contracting coronary arteries with 9,11-dideoxy-11alpha, 9alpha-epoxymethanoprostaglandin F2alpha (U46619). After ischaemia-reperfusion, the vasoconstriction in response to Ap5A was augmented and vasodilatation diminished, both in hearts with basal or increased vascular tone. The pyridoxal derivative P(2) purinoceptor antagonist, pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS, 3 x 10(-6) M), inhibited this vasoconstriction, while the antagonist of purinergic P(2Y) receptors, Reactive Blue 2 (2 x 10(-6) M), inhibited the vasodilatation, both before and after ischaemia-reperfusion. The antagonist of nitric oxide synthesis N-omega-nitro-L- arginine methyl ester (L-NAME, 10(-4) M) did not modify the response to Ap5A, whereas the cyclooxygenase inhibitor, meclofenamate (2 x 10(-6) M), reduced contraction and increased the relaxation in response to Ap5A after ischaemia-reperfusion but not under control conditions.

CONCLUSION

Ischaemia-reperfusion reduces the vasodilatory response to Ap5A and increases the vasoconstriction provoked due to a reduced influence of purinergic P(2Y) receptors and/or to the production of vasoconstrictor prostanoids.

Positive inotropic and sustained anti-beta-adrenergic effect of diadenosine pentaphosphate in human and guinea pig hearts. Role of dinucleotide receptors and adenosine receptors

AIM

Diadenosine polyphosphates are present intracellularly and in extracellular fluid due to release from secretory vesicles in platelets, chromaffin cells and other cells. This study investigates effects of diadenosine pentaphosphate (AP5A) on heart muscle function.

METHODS

Contractile force amplitude and action potential duration at 90% repolarization (APD90) were measured after challenge with AP5A 50 microm or isoproterenol 50-70 nM in guinea pig papillary muscles. Isoproterenol was given immediately after AP5A-exposure or after 45 min washout. AP5A was combined with antagonists to the purinergic P2 receptor (suramin 100 microm), the dinucleotide receptor [diinosine pentaphosphate 30 microm (IP5I)] or adenosine receptors [8-(P-sulfophenyl) theophylline 50 microm (8-SPT)].

RESULTS

Results are %-change (mean +/- SEM) from value before exposure. AP5A increased contractile force by 22 +/- 3%* (*P <0.05), and IP5I abolished this. AP5A prolonged APD90 by 7 +/- 2%*. AP5A significantly reduced response to isoproterenol acutely from 31 +/- 4* (controls) to 9 +/- 4% and after 45 min washout from 61 +/- 14* (controls) to 16 +/- 5%. 8-SPT abolished the sustained effect. Increase in contractile force by AP5A was confirmed in human atria trabecula preparations.

CONCLUSION

AP5A increased contractile force and prolonged APD90. Contractile force increased by stimulation of the dinucleotide receptor in guinea pig myocardium. The sustained anti-beta-adrenergic effect of AP5A was due to adenosine receptor stimulation.

Diadenosine-5-phosphate exerts A1-receptor-mediated proarrhythmic effects in rabbit atrial myocardium

(1) Diadenosine polyphosphates have been described to be present in the myocardium and exert purinergic- and nonreceptor-mediated effects. Since the electrophysiological properties of atrial myocardium are effectively regulated by A(1) receptors, we investigated the effect of diadenosine pentaphosphate (Ap(5)A) in rabbit myocardium. (2) Parameters of supraventricular electrophysiology and atrial vulnerability were measured in Langendorff-perfused rabbit hearts. Muscarinic potassium current (I(K(ACh/Ado))) and ATP-sensitive potassium current (I(K(ATP))) were measured by using the whole-cell voltage clamp method. (3) Ap(5)A prolonged the cycle length of spontaneously beating Langendorff perfused hearts from 225+/-14 (control) to 1823+/-400 ms (Ap(5)A 50 micro M; n=6; P<0.05). This effect was paralleled by higher degree of atrio-ventricular block. Atrial effective refractory period (AERP) in control hearts was 84+/-14 ms (n=6). Ap(5)A>/=1 micro M reduced AERP (100 micro M, 58+/-11 ms; n=6). (4) Extrastimuli delivered to hearts perfused with Ap(5)A- or adenosine (>/= micro M)-induced atrial fibrillation, the incidence of which correlated to the concentration added to the perfusate. The selective A(1)-receptor antagonist CPX (20 micro M) inhibited the Ap(5)A- and adenosine-induced decrease of AERP. Atrial fibrillation was no longer observed in the presence of CPX. (5) The described Ap(5)A-induced effects in the multicellular preparation were enhanced by dipyridamole (10 micro M), which is a cellular adenosine uptake inhibitor. Dipyridamole-induced enhancement was inhibited by CPX. (6) Ap(5)A (</=1 mM) did neither induce I(K(Ado)) nor I(K(ATP)). No effect on activated I(K(Ado/ATP)) was observed in myocytes superfused with Ap(5)A. However, effluents from Langendorff hearts perfused with Ap(5)A 100 micro M activated I(K(Ado)) by using A(1) receptors. (7) Ap(5)A did not activate A(1) receptors in rabbit atrial myocytes. The Ap(5)A induced A(1)-receptor-mediated effects on supraventricular electrophysiology and vulnerability suggest that in the multicellular preparation Ap(5)A is hydrolyzed to yield adenosine, which acts via A(1) receptors. An influence on atrial electrophysiology or a facilitation of atrial fibrillation under conditions resulting in increased interstitial Ap(5)A concentrations might be of physiological/pathophysiological relevance.