The adenosine receptor agonist, APNEA, increases calcium influx into rat cortical synaptosomes through N-type channels associated with A2a receptors

Amino acid-based supramolecular chiral hydrogels promote osteogenesis of human dental pulp stem cells via the MAPK pathway

Critical-size defects (CSDs) of the craniofacial bones cause aesthetic and functional complications that seriously impact the quality of life. The transplantation of human dental pulp stem cells (hDPSCs) is a promising strategy for bone tissue engineering. Chirality is commonly observed in natural biomolecules, yet its effect on stem cell differentiation is seldom studied, and little is known about the underlying mechanism. In this study, supramolecular chiral hydrogels were constructed using L/d-phenylalanine (L/D-Phe) derivatives. The results of alkaline phosphatase expression analysis, alizarin red S assay, as well as quantitative real-time polymerase chain reaction and western blot analyses suggest that right-handed D-Phe hydrogel fibers significantly promoted osteogenic differentiation of hDPSCs. A rat model of calvarial defects was created to investigate the regulation of chiral nanofibers on the osteogenic differentiation of hDPSCs in vivo. The results of the animal experiment demonstrated that the D-Phe group exhibited greater and faster bone formation on hDPSCs. The results of RNA sequencing, vinculin immunofluorescence staining, a calcium fluorescence probe assay, and western blot analysis indicated that L-Phe significantly promoted adhesion of hDPSCs, while D-Phe nanofibers enhanced osteogenic differentiation of hDPSCs by facilitating calcium entry into cells and activate the MAPK pathway. These results of chirality-dependent osteogenic differentiation offer a novel therapeutic strategy for the treatment of CSDs by optimising the differentiation of hDPSCs into chiral nanofibers.

Purinergic Receptors in Neurological Diseases With Motor Symptoms: Targets for Therapy

Since proving adenosine triphosphate (ATP) functions as a neurotransmitter in neuron/glia interactions, the purinergic system has been more intensely studied within the scope of the central nervous system. In neurological disorders with associated motor symptoms, including Parkinson's disease (PD), motor neuron diseases (MND), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), Huntington's Disease (HD), restless leg syndrome (RLS), and ataxias, alterations in purinergic receptor expression and activity have been noted, indicating a potential role for this system in disease etiology and progression. In neurodegenerative conditions, neural cell death provokes extensive ATP release and alters calcium signaling through purinergic receptor modulation. Consequently, neuroinflammatory responses, excitotoxicity and apoptosis are directly or indirectly induced. This review analyzes currently available data, which suggests involvement of the purinergic system in neuro-associated motor dysfunctions and underlying mechanisms. Possible targets for pharmacological interventions are also discussed.

A Novel Method for Screening Adenosine Receptor Specific Agonists for Use in Adenosine Drug Development

Agonists that target the A1, A2A, A2B and A3 adenosine receptors have potential to be potent treatment options for a number of diseases, including autoimmune diseases, cardiovascular disease and cancer. Because each of these adenosine receptors plays a distinct role throughout the body, obtaining highly specific receptor agonists is essential. Of these receptors, the adenosine A2AR and A2BR share many sequence and structural similarities but highly differ in their responses to inflammatory stimuli. Our laboratory, using a combination of specially developed cell lines and calcium release analysis hardware, has created a new and faster method for determining specificity of synthetic adenosine agonist compounds for the A2A and A2B receptors in human cells. A2A receptor expression was effectively removed from K562 cells, resulting in the development of a distinct null line. Using HIV-lentivector and plasmid DNA transfection, we also developed A2A and A2B receptor over-expressing lines. As adenosine is known to cause changes in intracellular calcium levels upon addition to cell culture, calcium release can be determined in these cell lines upon compound addition, providing a functional readout of receptor activation and allowing us to isolate the most specific adenosine agonist compounds.

Photomodulation of G protein-coupled adenosine receptors by a novel light-switchable ligand

The adenosinergic system operates through G protein-coupled adenosine receptors, which have become promising therapeutic targets for a wide range of pathological conditions. However, the ubiquity of adenosine receptors and the eventual lack of selectivity of adenosine-based drugs have frequently diminished their therapeutic potential. Accordingly, here we aimed to develop a new generation of light-switchable adenosine receptor ligands that change their intrinsic activity upon irradiation, thus allowing the spatiotemporal control of receptor functioning (i.e., receptor activation/inactivation dependent on location and timing). Therefore, we synthesized an orthosteric, photoisomerizable, and nonselective adenosine receptor agonist, nucleoside derivative MRS5543 containing an aryl diazo linkage on the N⁶ substituent, which in the dark (relaxed isomer) behaved as a full adenosine A₃ receptor (A₃R) and partial adenosine A_2A receptor (A_2AR) agonist. Conversely, upon photoisomerization with blue light (460 nm), it remained a full A₃R agonist but became an A_2AR antagonist. Interestingly, molecular modeling suggested that structural differences encountered within the third extracellular loop of each receptor could modulate the intrinsic, receptor subtype-dependent, activity. Overall, the development of adenosine receptor ligands with photoswitchable activity expands the pharmacological toolbox in support of research and possibly opens new pharmacotherapeutic opportunities.

The pathophysiology of retinopathy of prematurity: an update of previous and recent knowledge

Retinopathy of prematurity (ROP) is a disease that can cause blindness in very low birthweight infants. The incidence of ROP is closely correlated with the weight and the gestational age at birth. Despite current therapies, ROP continues to be a highly debilitating disease. Our advancing knowledge of the pathogenesis of ROP has encouraged investigations into new antivasculogenic therapies. The purpose of this article is to review the findings on the pathophysiological mechanisms that contribute to the transition between the first and second phases of ROP and to investigate new potential therapies. Oxygen has been well characterized for the key role that it plays in retinal neoangiogenesis. Low or high levels of pO2 regulate the normal or abnormal production of hypoxia-inducible factor 1 and vascular endothelial growth factors (VEGF), which are the predominant regulators of retinal angiogenesis. Although low oxygen saturation appears to reduce the risk of severe ROP when carefully controlled within the first few weeks of life, the optimal level of saturation still remains uncertain. IGF-1 and Epo are fundamentally required during both phases of ROP, as alterations in their protein levels can modulate disease progression. Therefore, rhIGF-1 and rhEpo were tested for their abilities to prevent the loss of vasculature during the first phase of ROP, whereas anti-VEGF drugs were tested during the second phase. At present, previous hypotheses concerning ROP should be amended with new pathogenetic theories. Studies on the role of genetic components, nitric oxide, adenosine, apelin and β-adrenergic receptor have revealed new possibilities for the treatment of ROP. The genetic hypothesis that single-nucleotide polymorphisms within the β-ARs play an active role in the pathogenesis of ROP suggests the concept of disease prevention using β-blockers. In conclusion, all factors that can mediate the progression from the avascular to the proliferative phase might have significant implications for the further understanding and treatment of ROP.

Effect of uridine of presynaptic NMDA and kainate receptor of rat brain cortex

It was demonstrated that uridine affects presynaptic NMDA and kainite receptors of rat brain cortex. Uridine considerably inhibited (45)Ca2+ uptake into synaptoneurosomes (IC50 = 7.1 x 10(-12) M) under conditions NMDA stimulation and increased it under conditions AMPA stimulation (157.8%).

Protecting motor neurons from toxic insult by antagonism of adenosine A2a and Trk receptors

The death of motor neurons in amyotrophic lateral sclerosis (ALS) is thought to result from the interaction of a variety of factors including excitotoxicity, accumulation of toxic proteins, and abnormal axonal transport. Previously, we found that the susceptibility of motor neurons to excitotoxic insults can be limited by inhibiting signals evoked by brain-derived neurotrophic factor (BDNF) activation of the receptor tyrosine kinase B (TrkB). Here we show that this can be achieved by direct kinase inhibition or by blockade of a transactivation pathway that uses adenosine A2a receptors and src-family kinases (SFKs). Downstream signaling cascades (such as mitogen-activated protein kinase and phosphatidylinositol-3 kinase) are inhibited by these blockers. In addition to protecting motor neurons from excitotoxic insult, these agents also prevent toxicity that follows from the expression of mutant proteins (G85R superoxide dismutase 1; G59S p150(glued)) that cause familial motor neuron disease. TrkB, adenosine A2a receptors, and SFKs associate into complexes in lipid raft and nonlipid raft membranes and the signaling from lipids rafts may be particularly important because their disruption by cholesterol depletion blocks the ability of BDNF to render motor neurons vulnerable to insult. The neuroprotective versatility of Trk antagonism suggests that it may have broad utility in the treatment of ALS patients.

Endothelial and Microvascular Function

The endothelium is more than just a passive vessel lining. New advances have revealed and expanded the multifactorial role of the endothelium in the homeostatic regulation of the microvasculature, including control of primary hemostasis, blood coagulation and fibrinolysis, platelet and leukocyte interactions with the vessel wall, lipoprotein metabolism, presentation of histocompatibility antigens, regulation of vascular tone and growth, and regulation of blood pressure. It possesses numerous receptors and releases compounds that affect the regulation of vascular tone and contribute to vascular permeability. Many crucial vasoactive endogenous compounds are formed in the endothelial cells to control the functions of vascular smooth muscle cells and circulating blood cells. Gap junctions facilitate the exchange of metabolites, ions, and other messenger molecules among endothelial cells and smooth muscle cells, and regulate cell growth. Among the numerous regulatory systems affecting microvascular function are the cholinergic and adrenergic (α1, α2, and β) systems. Flow-metabolism coupling is affected by a variety of signaling systems, including adenosine, oxygen, carbon dioxide, lactate, nitric oxide, and others. Agents such as the angiotensin system and endothelin, as well as others, play a role in autoregulation (maintenance of constant flow in the face of changing pressure). All of these are discussed in detail.

Characterisation of an uridine-specific binding site in rat cerebrocortical homogenates

Parameters of [3H]uridine binding to synaptic membranes isolated from rat brain cortex (K(D)=71+/-4 nM, B(max)=1.37+/-0.13 pmol/mg protein) were obtained. Pyrimidine and purine analogues displayed different rank order of potency in displacement of specifically bound [3H]uridine (uridine>5-F-uridine>5-Br-uridine approximately adenosine>>5-ethyl-uridine approximately suramin>theophylline) and in the inhibition of [14C]uridine uptake (adenosine>uridine>5-Br-uridine approximately 5-F-uridine approximately 5-ethyl-uridine) into purified cerebrocortical synaptosomes. Furthermore, the effective ligand concentration for the inhibition of [14C]uridine uptake was about two order of magnitude higher than that for the displacement of specifically bound [3H]uridine. Adenosine evoked the transmembrane Na(+) ion influx, whereas uridine the transmembrane Ca(2+) ion influx much more effectively. Also, uridine was shown to increase free intracellular Ca(2+) ion levels in hippocampal slices by measuring Calcium-Green fluorescence. Uridine analogues were found to be ineffective in displacing radioligands that were bound to various glutamate and adenosine-recognition and modulatory-binding sites, however, increased [35S]GTPgammaS binding to membranes isolated from the rat cerebral cortex. These findings provide evidence for a rather specific, G-protein-coupled site of excitatory action for uridine in the brain.

Pharmacology of adenosine receptors in the vasculature

Adenosine is widely distributed in mammals. One of the primary roles of adenosine within the cardiovascular system is to directly control the functions of both cardiac and vascular tissues. Recently, there has been considerable interest in the subclassification of adenosine receptors. Characterization of a heterogeneous population of receptors for adenosine could provide an opportunity for the development of novel compounds of therapeutic value. Adenosine is released from cells as a result of metabolism, and its release can be increased dramatically from cells that are metabolically stressed. This implies that adenosine can be released from a variety of cells throughout the body, as a result of increased metabolic rates, in concentrations that can have a profound impact on blood vessel function and, consequently, blood flow. It is recognized that the actions of this nucleoside on the vasculature are most prominent when oxygen demand is high and there is a reduction in oxygen tension at the site in question. Therefore, it is not surprising that adenosine has been shown to be an important regulator of blood vessel tone under hypoxic conditions. Furthermore, the activation of adenosine receptors on blood vessels can result in relaxation and/or contractions. The nature of the response subsequent to the activation of adenosine receptors is primarily dependent on the type of blood vessel involved and basal tone. This review will focus on the characterization of subtypes of adenosine receptors in blood vessels, as well as the effect of the stimulation of adenosine receptors on the peripheral circulation.