Silvia Sánchez

Adenosine receptors interacting proteins (ARIPs): Behind the biology of adenosine signaling

Adenosine is a well known neuromodulator in the central nervous system. As a consequence, adenosine can be beneficial in certain disorders and adenosine receptors will be potential targets for therapy in a variety of diseases. Adenosine receptors are G protein-coupled receptors, and are also expressed in a large variety of cells and tissues. Using these receptors as a paradigm of G protein-coupled receptors, the present review focus on how protein-protein interactions might contribute to neurotransmitter/neuromodulator regulation, based on the fact that accessory proteins impinge on the receptor/G protein interaction and therefore modulate receptor functioning. Besides affecting receptor signaling, these accessory components also play a key role in receptor trafficking, internalization and desensitization, as it will be reviewed here. In conclusion, the finding of an increasing number of adenosine receptors interacting proteins, and specially the molecular and functional integration of these accessory proteins into receptorsomes, will open new perspectives in the understanding of particular disorders where these receptors have been proved to be involved.

Pharmacological evidence for the involvement of the endogenous opioid system in the response to local inflammation in the rat paw.

&NA; We have investigated the role of the endogenous opioid system (EOS) on the inflammatory response induced by subplantar (s.p.) injection of saline (SS) and carrageenan (CA) in the hindpaw of the rat. The administration of intraperitoneal (i.p.) naloxone was used in order to unmask the effects of endogenous opiates released during peripheral inflammation. Three groups of rats received one of the following s.p. treatments: SS, CA, or no injection (NI). Pain pressure threshold (PPT), paw volume (edema) and local temperature were evaluated in baseline conditions and 3 h after treatment. In each group, the effects of i.p. vehicle, naloxone and (+)‐naloxone (0.1 mg/kg) were also investigated. Both SS and CA induced a significant inflammatory response with hyperalgesia, edema and local hyperthermia. The i.p. administration of naloxone but not that of (+)‐naloxone 15 min prior to testing, significantly increased edema in all groups of treatment (P<0.05), without altering PPT or local temperature. Two‐way ANOVA revealed that treatment and drugs, as well as their interaction, had a significant impact on edema which was related to the effects of CA and naloxone. Our findings illustrate the involvement of the EOS in the physiological response to local injury, regulating microvascular leakage in the inflamed tissues.

Interaction between metamizol and tramadol in a model of acute visceral pain in rats

Tramadol (TRM) and metamizol (MTZ) are drugs with complex mechanisms of action, extensively used in combination in pain management. In the present investigation we have evaluated the interaction between MTZ:TRM in the ethacrinic acid writhing test in rats. Dose—response curves (s.c.) were obtained for each drug individually, combined in fixed potency ratios (1:0.3, 1:1, 1:3), and for MTZ in presence of a fixed‐dose of TRM (3.5 mg/kg). Interactions were analysed using isobolograms, interaction indexes (INT‐I) and ANOVA. We used naloxone (1 mg/kg s.c.) to determine the opioid‐component of the effects (ED80).

Antinociceptive/Anti-Edema Effects of Liposomal Morphine during Acute Inflammation of the Rat Paw

We evaluated the anti-edema/antinociceptive effects of subcutaneous free and liposomal morphine in rats with carrageenan-induced inflammation of the paw. We assessed antinociception by the paw pressure test and edema by plethysmography. Unilamellar liposomes (150–200 nm) with 0.3% morphine hydrochloride were used; encapsulation signifcantly reduced the rate for release of morphine in vitro. During inflammation, the antinociceptive potency of free, but not liposomal morphine increased 2.5 times; moreover, duration of the effects was prolonged by encapsulation (p < 0.001). The anti-edema effects of liposomal morphine were more pronounced (p < 0.001) and of longer duration (p < 0.05). All the effects were reversed by naloxone. The results show that morphine encapsulation enhances the anti-edema effects and prolongs antinociception.

Adjuvant effect of caffeine on acetylsalicylic acid anti-nociception: Prostaglandin E2 synthesis determination in carrageenan-induced peripheral inflammation in rat

In the present study, we report a synergistic interaction between acetylsalicylic acid (ASA) and caffeine (CAF) on the inhibition of nociception in a model of peripheral inflammation in rat; on the contrary no interaction have been found on anti‐inflammatory effects and peripheral prostaglandin E2 (PGE‐2) synthesis inhibition. Acute inflammation was induced by the subplantar injection of carrageenan into the right hind paw, and the effects of the drugs were evaluated from 0 to 5h. Nociception was assessed using the Randall & Selitto test, and the inflammatory response by plethismometry. Oral administration of ASA (10–400mg/kg) induced dose‐related anti‐nociceptive and anti‐inflammatory effects. On the other hand, oral CAF administration (5–50mg/kg) did not show a dose‐related inhibitory effect, neither on the inhibition of nociception nor on the inflammatory response. To analyze a possible interaction between both drugs a dose—response curve to ASA plus a fixed dose of CAF (5mg/kg) was obtained 3h after the injection of carrageenan, when the inflammatory pain peaked. A fixed dose of CAF was able to improve the anti‐nociceptive, but not the anti‐inflammatory, effects of ASA. We also assessed, by enzyme immunoassay, the effects of the combination on peripheral PGE‐2 levels: CAF did not alter the inhibitory effect of ASA on PGE‐2 synthesis. Our results corroborate the well‐known clinical effects of combining ASA and CAF; on the other hand, we rule out that prostaglandin synthesis inhibition at peripheral sites would be the mechanism responsible of the adjuvant anti‐nociceptive effect of CAF.

G protein-coupled receptor oligomerization for what?

Although the G protein-coupled receptor (GPCR) oligomerization has been questioned during the last decade, under some premises the existence of a supramolecular organization of these receptors begins now to be widely accepted by the scientific community. Indeed, GPCR oligomers may enhance the diversity and performance by which extracellular signals are transferred to the G proteins in the process of receptor transduction, although the mechanism that underlie this phenomenon remains still unexplained. Recently, a trans-conformational switching model has been proposed as a mechanism allowing direct inhibition of receptor activation. Thus, heterotropic receptor–receptor allosteric regulations are behind the GPCR oligomeric function. Accordingly, we revise here how GPCR oligomerization impinge in several important receptor functions like biosynthesis, plasma membrane diffusion or velocity, pharmacology and signaling. Overall, the rationale of receptor oligomerization might lie in the cellular need of sensing complex extracellular signals and to translate into a simple computational mode.

G protein-coupled receptor oligomerization and brain integration: focus on adenosinergic transmission.

The control of glutamatergic corticostriatal transmission is essential for the induction and expression of plasticity mechanisms in the striatum, a phenomenon thickly regulated by G protein-coupled receptors (GPCRs). Interestingly, in addition to dopamine receptors, adenosine and metabotropic glutamate receptors also play a key role in striatal functioning. The existence of a supramolecular organization (i.e. oligomer) containing dopamine, adenosine and metabotropic glutamate receptors in the striatal neurons is now being widely accepted by the scientific community. Indeed, these oligomers may enhance the diversity and performance by which extracellular striatal signals are transferred to the G-proteins in the process of receptor transduction, and also may allow unpredictable receptor-receptor allosteric regulations. Overall, here we want to review how formations of adenosine, dopamine and metabotropic glutamate receptors-containing oligomers impinge into striatal functioning in both normal and pathological conditions. This article is part of a Special Issue entitled: Brain Integration.

Protective effect of fructose 1,6-bisphosphate against carrageenan-induced inflammation

Administration of carrageenan (0.5 mg) to the plantar tissue of rats resulted in reversible inflammatory injury. This damage was monitored as changes in foot volume, using a plethysmometer. Administration of fructose 1,6-bisphosphate at different doses, orally or intraperitoneally, prevented the inflammatory action induced by the simultaneous injection of carrageenan in the rat paw. The effect was dose and time dependent. In contrast, fructose or fructose 6-phosphate afforded no significant protection. In order to extend the average half-life of the drug, we prepared liposomes of fructose 1,6-bisphosphate which, administered orally or intraperitoneally, showed a greater and more prolonged antiinflammatory action. The significance of these findings with respect to the mechanism of the antiinflammatory action of fructose 1,6-bisphosphate is discussed.

Caffeine improves attention deficit in neonatal 6-OHDA lesioned rats, an animal model of attention deficit hyperactivity disorder (ADHD)

Nowadays the pharmacological treatment of the attention deficit hyperactivity disorder (ADHD) is based on amphetamine derivatives (i.e. methylphenidate). However, these drugs induce a large array of adverse side effects, thus less aggressive psychostimulant drugs (i.e. caffeine) are being proposed in the management of ADHD. Following this tendency, we decided to study the possible therapeutic use of caffeine in an animal model of ADHD, namely the neonatal 6-hydroxy-dopamine (6-OHDA)-lesioned rat. Therefore, at postnatal day 7 rats were lesioned at the left striatum with 6-OHDA or with saline. Thereafter, at postnatal day 25 their activity and attention were measured with the Olton maze before caffeine was administered ad libitum in the drinking water. Next, after 14 days of caffeine treatment, we repeated these measurements to assess the effect of caffeine on motor activity and attention deficit. Interestingly, while no changes in the motor activity measurements were observed before and after caffeine administration, a significant improvement in the attention deficit of the 6-OHDA lesioned rats was achieved after caffeine treatment. Thus, our results led us to hypothesize that caffeine might be useful to manage the attention deficit during the prepubertal period of ADHD.

Fentanyl–trazodone–paracetamol triple drug combination: Multimodal analgesia in a mouse model of visceral pain

Multimodal or balanced analgesia is commonly used in the management of acute and chronic pain in humans, in order to achieve the best analgesic/safety profile. Here, by using a model of visceral acute tonic pain, the acetic acid-induced writhing test of mice, we show a synergistic interaction between fentanyl, trazodone and paracetamol on the inhibition of nociception. First of all, once assessed that all drugs induced dose-related antinociceptive effects, they were mixed in fixed ratio (1:1) combinations and a synergistic drug-drug interaction was obtained in all circumstances. Thereafter, we assayed the effects of the triple combination of fentanyl-trazodone-paracetamol and it was demonstrated that they displayed a potent synergistic interaction on the inhibition of acetic acid-mediated nociception. Interestingly, drug dosage reduction permitted to reduce the incidence of possible adverse effects, namely exploratory activity and motor coordination, thus it was demonstrated that it improved the benefit/risk profile of such treatment. Afterwards, we attempted to elucidate the mechanism of action of such interaction, by means of the non-selective opioid receptor antagonist naloxone. Interestingly, naloxone completely antagonized the antinociceptive effects of fentanyl, and it also partially reversed paracetamol and trazodone mediated analgesia. Furthermore, when naloxone was co-administered with the triple-drug treatment it blocked the previously observed enhanced antinociceptive effects of the combination. Thus, these results indicated that the endogenous opioid system played a main role in the present drug-drug interaction. Overall, the triple combination of fentanyl-trazodone-paracetamol induced a potent synergistic antinociceptive effect, which could be of interest for optimal multimodal clinical analgesia.