Biochemical and pharmacological characterization of periodate-oxidized adenosine analogues at adenosine A1 receptors

The exploration and utilization of functional substances in edible insects: a review

Edible insects as food have been considered as a core future protein source. Not only are edible insects abundant in nutrient value, but also have numbers of functional substances, which could provide a multiple valuable benefits for humans. This review examines and summarizes the functional substances in edible insects and their special effects for people, as well as the use and prospects for these functional substances. There are many functional substances in edible insects, such as antimicrobial peptides, interferon, sex attractant hormones, cordycepin, active polysaccharides, microelement, chitin/chitosan, steroidal material, vitamin, lecithin, etc., which could provide multiple benefits for human beings. These special functional substances could help people enhance immunity, inhibit tumor, regulate intestinal function, relieve fatigue, anti oxidation, protect against colds, improve sleeping, promote the growth and development, as well as reducing blood sugar and blood pressure, among others. According to these valuable efficacies, the functional substances extracted from edible insects can be exploited mainly in three ways: edible insects are used to discover new medicines or health care products for people; and edible insects are applied in chemical, agricultural, food technology, pollutant treatment and textile sectors; as well as being consumed as animal feedstuff for livestock and other animals, which indirectly meet the different requirements for humans. Currently, edible insects have generated global interest to be developed as different forms of products and has promoted more research and development. However, pupae and larvae are still the main consumption ways in the market, which is unacceptable to most people. It is expected that the edible insect industry would be prosperous and sustainable by integrating the power of beneficial policies and regulations, huge consumer demand and proper strategies of promotion and production.

Graphical Abstract

Ryanodine receptor modulation by diadenosine polyphosphates in synaptosomal and microsomal preparations of rat brain

Diadenosine polyphosphates (Ap(n)As) are transmitter-like substances that act intracellularly via unclear mechanisms. Here we tested hypotheses that diadenosine tetraphosphate (Ap(4)A) modulates ryanodine binding in microsomal and synaptosomal fractions of rat brain, and that Ap(4)A affects modulation of ryanodine binding by divalent cations and caffeine. Using [3H]ryanodine-binding assays, we showed that Ap(4)A produced significant and concentration-dependent increases in [3H]ryanodine binding in microsomes and these actions were reduced by Mg(2+) and potentiated by caffeine. In synaptosomal subfractions, effects of Ap(4)A on [3H]ryanodine binding were most profound in subfractions enriched in synaptic vesicle-associated protein synaptophysin. These results suggest that Ap(n)As and ryanodine receptors are well placed to modulate Ca(2+)-dependent synaptic processes.

Can thermodynamic measurements of receptor binding yield information on drug affinity and efficacy?

The present commentary surveys the methods for obtaining the thermodynamic parameters of the drug-receptor binding equilibrium, DeltaG degrees, DeltaH degrees, DeltaS degrees, and DeltaC degrees (p) (standard free energy, enthalpy, entropy, and heat capacity, respectively). Moreover, it reviews the available thermodynamic data for the binding of agonists and antagonists to several G-protein coupled receptors (GPCRs) and ligand-gated ion channel receptors (LGICRs). In particular, thermodynamic data for five GPCRs (beta-adrenergic, adenosine A(1), adenosine A(2A), dopamine D(2), and 5-HT(1A)) and four LGICRs (glycine, GABA(A), 5-HT(3), and nicotinic) have been collected and analyzed. Among these receptor systems, seven (three GPCRs and all LGICRs) show "thermodynamic agonist-antagonist discrimination": when the agonist binding to a given receptor is entropy-driven, the binding of its antagonist is enthalpy-driven, or vice versa. A scatter plot of all entropy versus enthalpy values of the database gives a regression line with the equation TDeltaS degrees (kJ mol(-1); T = 298.15 K) = 40.3 (+/- 0.7) + 1.00 (+/-0.01) DeltaH degrees (kJ mol(-1)); N = 184; r = 0.981; P < 0.0001 - which is of the form DeltaH degrees = beta. DeltaS degrees, revealing the presence of the "enthalpy-entropy compensation" phenomenon. This means that any decrease of binding enthalpy is compensated for by a parallel decrease of binding entropy, and vice versa, in such a manner that affinity constant values (K(A)) of drug-receptor equilibrium (DeltaG degrees = -RT ln K(A) = DeltaH degrees - TDeltaS degrees ) cannot be greater than 10(11) M(-1). According to the most recent hypotheses concerning drug-receptor interaction mechanisms, these thermodynamic phenomena appear to be a consequence of the rearrangement of solvent molecules that occurs during the binding.

Thermodynamic in vitro studies as a method to investigate the pharmacodynamic behavior of adenosine A1 receptor ligands

PURPOSE

A thermodynamic analysis of the binding to rat cortex adenosine A1 receptor of N6-substituted (full agonists) and N6-substituted-deoxyribose (partial agonists) adenosine derivatives was performed. The intrinsic activity of the compounds was evaluated by measurements of the inhibition of forskolin stimulated 3', 5'-cyclic adenosine monophosphate (c-AMP) levels in isolated epididymal rat adipocytes.

METHODS

The thermodynamic parameters deltaG(o) (standard free energy), deltaH(o) (standard enthalpy), and deltaS(o) (standard entropy) of the binding equilibrium were determined by means of affinity measurements carried out at different temperatures (0, 10, 20, 25, 30 degrees C). Levels of c-AMP were evaluated performing competitive protein binding assays.

RESULTS

The binding of the ligands increases with temperature enhancement and, as a consequence, is totally entropy driven. Standard entropy values correlate significantly with intrinsic activity ones.

CONCLUSIONS

It is proposed the data obtained by these in vitro experiments can be used to investigate the in vivo pharmacodynamic of A, full and partial agonists.

Thermodynamics of full agonist, partial agonist, and antagonist binding to wild-type and mutant adenosine A1 receptors

A thermodynamic analysis of the binding of a full agonist (N6-cyclopentyladenosine), a partial agonist (8-butylamino-N6-cyclopentyladenosine) and an antagonist (8-cyclopentyltheophylline) to human wild-type and mutant (mutation of a threonine (Thr) to an alanine (Ala) residue at position 277) adenosine A1 receptors expressed on Chinese hamster ovary (CHO) cells, and to rat brain adenosine A1 receptors was undertaken. The thermodynamic parameters deltaGo (standard free energy), deltaHo (standard enthalpy) and deltaSo (standard entropy) of the binding equilibrium to rat brain receptors were determined by means of affinity measurements carried out at four different temperatures (0, 10, 20 and 25 degrees) and van't Hoff plots. Two temperatures (0 and 25 degrees) were considered for human receptors. Affinity constants were obtained from inhibition assays on membrane preparations of rat brain and CHO cells by use of the antagonist [3H]1,3-dipropyl-8-cyclopentylxanthine ([3H]DPCPX) as selective adenosine A1 receptor radioligand. As for rat brain receptors, full agonist binding was totally entropy driven, whereas antagonist binding was essentially enthalpy driven. Partial agonist binding appeared both enthalpy and entropy driven. As for human receptors, full agonist affinity was highly dependent on the presence of Thr277. Moreover, affinity to both wild-type and mutant receptors was enhanced by temperature increase, suggesting a totally entropy-driven binding. Antagonist binding did not depend on the presence of Thr277. Antagonist affinity decreased with an increase in temperature, suggesting a mainly enthalpy-driven binding. Partial agonist binding was significantly dependent on the presence of Thr277 at 25 degrees, whereas such a dependence was not evident at 0 degrees. It is concluded that Thr277 contributes only to the binding of adenosine derivatives and that its role changes drastically with the receptor conformation and with the type of agonist (full or partial) interacting with the adenosine A1 receptors.

Binding thermodynamics at A1 and A2A adenosine receptors

Only recently the binding equilibrium of a number of ligands at adenosine A1 and A2a receptors has been analyzed from a thermodynamic point of view. This approach presents the advantage, with respect to usual affinity constant measurements, of a greater capability to give information about the molecular mechanisms underlying the binding process. All available data agree in indicating that, for both A1 and A2a receptors, agonist binding of adenosine derivatives was totally entropy-driven, while xanthine antagonist binding was essentially enthalpy-driven. The differences in thermodynamic behaviour of A1 and A2a agonists and antagonists could be interpreted in terms of a simplified general model of drug-receptor interaction, which accounted for the role played by the ribose moiety and N6-substituents of adenosinic drugs in determining both affinity and intrinsic activity properties. In the frame of this model, measurements of thermodynamic parameters of N6-monosubstituted agonists allowed to hypothesize, for the first time, the existence of partial agonists to adenosine A1 receptors, as now confirmed experimentally. All thermodynamic data concerning the interaction of all ligands studied with A1 and A2a receptors are briefly discussed in terms of the enthalpy-entropy compensation phenomenon which appears to be widely determined by the reorganization of solvent molecules in the binding process.