Proton pump inhibitors exacerbate NSAID-induced small intestinal injury by inducing dysbiosis

BACKGROUND & AIMS

Proton pump inhibitors (PPIs) and nonsteroidal anti-inflammatory drugs (NSAIDs) are among the most commonly used classes of drugs, with the former frequently coprescribed to reduce gastroduodenal injury caused by the latter. However, suppression of gastric acid secretion by PPIs is unlikely to provide any protection against the damage caused by NSAIDs in the more distal small intestine.

METHODS

Rats were treated with antisecretory doses of omeprazole or lanzoprazole for 9 days, with concomitant treatment with anti-inflammatory doses of naproxen or celecoxib on the final 4 days. Small intestinal damage was blindly scored, and changes in hematocrit were measured. Changes in small intestinal microflora were evaluated by denaturing gradient gel electrophoresis and reverse-transcription polymerase chain reaction.

RESULTS

Both PPIs significantly exacerbated naproxen- and celecoxib-induced intestinal ulceration and bleeding in the rat. Omeprazole treatment did not result in mucosal injury or inflammation; however, there were marked shifts in numbers and types of enteric bacteria, including a significant reduction (∼80%) of jejunal Actinobacteria and Bifidobacteria spp. Restoration of small intestinal Actinobacteria numbers through administration of selected (Bifidobacteria enriched) commensal bacteria during treatment with omeprazole and naproxen prevented intestinal ulceration/bleeding. Colonization of germ-free mice with jejunal bacteria from PPI-treated rats increased the severity of NSAID-induced intestinal injury, as compared with mice colonized with bacteria from vehicle-treated rats.

CONCLUSIONS

PPIs exacerbate NSAID-induced intestinal damage at least in part because of significant shifts in enteric microbial populations. Prevention or reversal of this dysbiosis may be a viable option for reducing the incidence and severity of NSAID enteropathy.

Nordihydroguaiaretic acid and aspirin increase lifespan of genetically heterogeneous male mice

The National Institute on Aging's Interventions Testing Program was established to evaluate agents that are purported to increase lifespan and delay the appearance of age-related disease in genetically heterogeneous mice. Up to five compounds are added to the study each year and each compound is tested at three test sites (The Jackson Laboratory, University of Michigan, and University of Texas Health Science Center at San Antonio). Mice in the first cohort were exposed to one of four agents: aspirin, nitroflurbiprofen, 4-OH-alpha-phenyl-N-tert-butyl nitrone, or nordihydroguaiaretic acid (NDGA). Sample size was sufficient to detect a 10% difference in lifespan in either sex,with 80% power, using data from two of the three sites. Pooling data from all three sites, a log-rank test showed that both NDGA (p=0.0006) and aspirin (p=0.01) led to increased lifespan of male mice. Comparison of the proportion of live mice at the age of 90% mortality was used as a surrogate for measurement of maximum lifespan;neither NDGA (p=0.12) nor aspirin (p=0.16) had a significant effect in this test. Measures of blood levels of NDGA or aspirin and its salicylic acid metabolite suggest that the observed lack of effects of NDGA or aspirin on life span in females could be related to gender differences in drug disposition or metabolism. Further studies are warranted to find whether NDGA or aspirin, over a range of doses,might prove to postpone death and various age-related outcomes reproducibly in mice.

The role of the D(2) dopamine receptor (D(2)R) in A(2A) adenosine receptor (A(2A)R)-mediated behavioral and cellular responses as revealed by A(2A) and D(2) receptor knockout mice

The A(2A)R is largely coexpressed with D(2)Rs and enkephalin mRNA in the striatum where it modulates dopaminergic activity. Activation of the A(2A)R antagonizes D(2)R-mediated behavioral and neurochemical effects in the basal ganglia through a mechanism that may involve direct A(2A)R-D(2)R interaction. However, whether the D(2)R is required for the A(2A)R to exert its neural function is an open question. In this study, we examined the role of D(2)Rs in A(2A)R-induced behavioral and cellular responses, by using genetic knockout (KO) models (mice deficient in A(2A)Rs or D(2)Rs or both). Behavioral analysis shows that the A(2A)R agonist 2-4-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine reduced spontaneous as well as amphetamine-induced locomotion in both D(2) KO and wild-type mice. Conversely, the nonselective adenosine antagonist caffeine and the A(2A)R antagonist 8-(3-chlorostyryl)caffeine produced motor stimulation in mice lacking the D(2)R, although the stimulation was significantly attenuated. At the cellular level, A(2A)R inactivation counteracted the increase in enkephalin expression in striatopallidal neurons caused by D(2)R deficiency. Consistent with the D(2) KO phenotype, A(2A)R inactivation partially reversed both acute D(2)R antagonist (haloperidol)-induced catalepsy and chronic haloperidol-induced enkephalin mRNA expression. Together, these results demonstrate that A(2A)Rs elicit behavioral and cellular responses despite either the genetic deficiency or pharmacological blockade of D(2)Rs. Thus, A(2A)R-mediated neural functions are partially independent of D(2)Rs. Moreover, endogenous adenosine acting at striatal A(2A)Rs may be most accurately viewed as a facilitative modulator of striatal neuronal activity rather than simply as an inhibitory modulator of D(2)R neurotransmission.

Blockade of adenosine A2A receptors by SCH 58261 results in neuroprotective effects in cerebral ischaemia in rats

Blockade of adenosine receptors can reduce cerebral infarct size in the model of global ischaemia. Using the potent and selective A2A adenosine receptor antagonist, SCH 58261, we assessed whether A2A receptors are involved in the neuronal damage following focal cerebral ischaemia as induced by occluding the left middle cerebral artery. SCH 58261 (0.01 mg/kg either i.p. or i.v.) administered to normotensive rats 10 min after ischaemia markedly reduced cortical infarct volume as measured 24 h later (30% vs controls, p < 0.05). Similar effects were observed when SCH 58261 (0.01 mg/kg, i.p.) was administered to hypertensive rats (28% infarct volume reduction vs controls, p < 0.05). Neuroprotective properties of SCH 58261 administered after ischaemia indicate that blockade of A2A adenosine receptors is a potentially useful biological target for the reduction of brain injury.

An Aging Interventions Testing Program: study design and interim report

The National Institute on Aging's Interventions Testing Program (ITP) has developed a plan to evaluate agents that are considered plausible candidates for delaying rates of aging. Key features include: (i) use of genetically heterogeneous mice (a standardized four-way cross), (ii) replication at three test sites (the Jackson Laboratory, TJL; University of Michigan, UM; and University of Texas, UT), (iii) sufficient statistical power to detect 10% changes in lifespan, (iv) tests for age-dependent changes in T cell subsets and physical activity, and (v) an annual solicitation for collaborators who wish to suggest new interventions for evaluation. Mice in the first cohort were exposed to one of four agents: aspirin, nitroflurbiprofen (NFP), 4-OH-alpha-phenyl-N-tert-butyl nitrone (4-OH-PBN), or nordihydroguiaretic acid (NDGA). An interim analysis was conducted using survival data available on the date at which at least 50% of the male control mice had died at each test site. Survival of control males was significantly higher, at the interim time-point, at UM than at UT or TJL; all three sites had similar survival of control females. Males in the NDGA group had significantly improved survival (P = 0.0004), with significant effects noted at TJL (P < 0.01) and UT (P < 0.04). None of the other agents altered survival, although there was a suggestion (P = 0.07) of a beneficial effect of aspirin in males. More data will be needed to determine if any of these compounds can extend maximal lifespan, but the current data show that NDGA reduces early life mortality risks in genetically heterogeneous mice at multiple test sites.

Comparison of CGS 15943, ZM 241385 and SCH 58261 as antagonists at human adenosine receptors

Three structurally related non-xanthine compounds, CGS 15943, ZM 241385 and SCH 58261, are potent A2A adenosine receptor antagonists and have been used as tools in many pharmacological studies. We have now characterized their affinity and selectivity profile on human adenosine receptors stably transfected into either CHO cells (A1 and A2B receptors) or HEK-293 cells (A2A and A3 receptors). In binding studies using [3H]SCH 58261 as a radioligand, the three compounds were equally potent at A2A receptors, their K(i) value being less than 1 nM. Affinity for A1 and A3 receptors was measured using [3H]DPCPX and [125I]AB-MECA as radioligands. Given the lack of selective ligands, interaction with A2B receptors was assessed using the cAMP accumulation assay following stimulation by the adenosine receptor agonist N-ethylcarboxamidoadenosine (NECA). CGS 15943 was almost as potent at A1 receptors (K(i)3.5 nM) as at A2A receptors, showed moderate affinity for A3 receptors (K(i) 95 nM) and also interacted with A2B receptors (K(i) 44 nM; pA2 7.5). ZM 241385 showed little affinity for A1 receptors (K(i) 255 nM), and did not interact with A3 receptors (K(i)>10 microM); however, it displayed moderate affinity for A2B receptors (K(i) 50 nM; pA2 7.3). SCH 58261 had weak affinity for A1 receptors (K(i) 287 nM), no interaction with A3 receptors (K(i)>10 microM), and showed negligible interaction with A2B receptors (K(i) 5 microM; pA2 6.0). These data indicate that SCH 58261 is the most selective A2A antagonist currently available. Moreover, the different receptor selectivity of these three chemically related compounds provides useful information to progress with structure-activity relationship studies.

Non-steroidal anti-inflammatory drugs (NSAIDs) in Alzheimer's disease: old and new mechanisms of action

Alzheimer's disease (AD) is characterized by cerebral deposits of beta-amyloid (A beta) peptides and neurofibrillary tangles (NFT) which are surrounded by inflammatory cells. Epidemiological studies have shown that prolonged use of non-steroidal anti-inflammatory drugs (NSAIDs) reduces the risk of developing AD and delays the onset of the disease. It has been postulated that some NSAIDs target pathological hallmarks of AD by interacting with several pathways, including the inhibition of cyclooxygenases (COX) and activation of the peroxisome proliferator-activated receptor gamma. A variety of experimental studies indicate that a subset of NSAIDs such as ibuprofen, flurbiprofen, indomethacin and sulindac also possess A beta-lowering properties in both AD transgenic mice and cell cultures of peripheral, glial and neuronal origin. While COX inhibition occurs at low concentrations in vitro (nM-low microm range), the A beta-lowering activity is observed at high concentrations (< or = 50 microm). Nonetheless, studies with flurbiprofen or ibuprofen in AD transgenic mice show that the effects on A beta levels or deposition are attained at plasma levels similar to those achieved in humans at therapeutic dosage. Still, it remains to be assessed whether adequate concentrations are reached in the brain. This is a crucial aspect that will allow defining the dose-window and the length of treatment in future clinical trials. Here, we will discuss how the combination of anti-amyloidogenic and anti-inflammatory activities of certain NSAIDs may produce a profile potentially relevant to their clinical use as disease-modifying agents for the treatment of AD.

Interleukin-10 modulates neuronal threshold of vulnerability to ischaemic damage

Interleukin-10 (IL-10) is a powerful suppressor of cellular immune responses, with a postulated role in brain inflammation. First, we have evaluated the role of this cytokine in ischaemic brain damage using IL-10 knockout (IL-10-/-) mice. The middle cerebral artery (MCA) was occluded in either IL-10-/- or wild-type animals of corresponding strain (C57Bl/6) and age. Infarct volume was assessed 24 h later in serial brain sections. Brain infarct produced by MCA occlusion was 30% larger in the IL-10-/- than in wild-type mice (21. 8 +/- 1.2 vs. 16.9 +/- 1.0 mm3, respectively; P < 0.01; Student's t-test). To further characterize these findings, studies were extended to in vitro models. Primary neuronal cortical cultures derived from IL-10-/- animals were more susceptible to both excitotoxicity and combined oxygen-glucose deprivation compared with cell cultures from wild-type mice. Moreover, when added to the culture medium, recombinant murine IL-10 (0.1-100 ng/mL) exerted a concentration-dependent prevention of neuronal damage induced by excitotoxicity in both cortical and cerebellar granule cell cultures taken from either strain. The accordance of in vivo and in vitro data allows us to suggest a potential neuroprotective role of IL-10 against cerebral ischaemia when administered exogenously or made available from endogenous sources.

Adenosine A2A receptor antagonists are potential antidepressants: evidence based on pharmacology and A2A receptor knockout mice

1. Adenosine, an ubiquitous neuromodulator, and its analogues have been shown to produce 'depressant' effects in animal models believed to be relevant to depressive disorders, while adenosine receptor antagonists have been found to reverse adenosine-mediated 'depressant' effect. 2. We have designed studies to assess whether adenosine A2A receptor antagonists, or genetic inactivation of the receptor would be effective in established screening procedures, such as tail suspension and forced swim tests, which are predictive of clinical antidepressant activity. 3. Adenosine A2A receptor knockout mice were found to be less sensitive to 'depressant' challenges than their wildtype littermates. Consistently, the adenosine A2A receptor blockers SCH 58261 (1 - 10 mg kg(-1), i.p.) and KW 6002 (0.1 - 10 mg kg(-1), p.o.) reduced the total immobility time in the tail suspension test. 4. The efficacy of adenosine A2A receptor antagonists in reducing immobility time in the tail suspension test was confirmed and extended in two groups of mice. Specifically, SCH 58261 (1 - 10 mg kg(-1)) and ZM 241385 (15 - 60 mg kg(-1)) were effective in mice previously screened for having high immobility time, while SCH 58261 at 10 mg kg(-1) reduced immobility of mice that were selectively bred for their spontaneous 'helplessness' in this assay. 5. Additional experiments were carried out using the forced swim test. SCH 58261 at 10 mg kg(-1) reduced the immobility time by 61%, while KW 6002 decreased the total immobility time at the doses of 1 and 10 mg kg(-1) by 75 and 79%, respectively. 6. Administration of the dopamine D2 receptor antagonist haloperidol (50 - 200 microg kg(-1) i.p.) prevented the antidepressant-like effects elicited by SCH 58261 (10 mg kg(-1) i.p.) in forced swim test whereas it left unaltered its stimulant motor effects. 7. In conclusion, these data support the hypothesis that A2A receptor antagonists prolong escape-directed behaviour in two screening tests for antidepressants. Altogether the results support the hypothesis that blockade of the adenosine A2A receptor might be an interesting target for the development of effective antidepressant agents.

A2A-adenosine receptor reserve for coronary vasodilation

BACKGROUND

Adenosine is a potent coronary vasodilator and causes an increase of coronary blood flow by activation of A2A-adenosine receptors (A2A-AdoRs). The purpose of this study was to test the hypothesis that the high potency of adenosine and adenosine analogues to cause coronary vasodilation is explained by the presence of a large A2A-AdoR reserve ("spare receptors").

METHODS AND RESULTS

A novel, irreversible antagonist of A2A-AdoRs was used to inactivate receptors and reduce the response to agonist. Agonist-induced increases of coronary conductance before and after exposure of hearts to the irreversible antagonist were compared. Three agonists were studied: 2-p-(2-carboxyethyl)-phenethylamino-5'-N-ethylcarboxamidoadenosine (CGS21680), adenosine, and 2-chloro-N6-cyclopentyladenosine (CCPA). Data were analyzed to determine agonist KA (equilibrium dissociation constant) and EC50 values. Values of KA for activation of A2A-AdoRs by CGS21680, adenosine, and CCPA were 105, 1800, and 2630 nmol/L, respectively. In contrast, values of EC50 for CGS21680, adenosine, and CCPA to increase coronary conductance were 1.5, 85, and 243 nmol/L, respectively. By use of the law of mass action, it was calculated that half-maximal responses to CGS21680, adenosine, and CCPA occurred when only 1.3%, 5%, and 9%, respectively, of A2A-AdoRs were occupied by agonist.

CONCLUSIONS

Receptor reserves for 3 A2A-AdoR agonists were large. The receptor reserve for A2A-AdoRs to cause an increase of coronary conductance can explain both the high potency of adenosine to cause coronary vasodilation and the observation that an A2A-AdoR agonist can cause coronary vasodilation without systemic effects.

Nitric oxide release combined with nonsteroidal antiinflammatory activity prevents muscular dystrophy pathology and enhances stem cell therapy

Duchenne muscular dystrophy is a relatively common disease that affects skeletal muscle, leading to progressive paralysis and death. There is currently no resolutive therapy. We have developed a treatment in which we combined the effects of nitric oxide with nonsteroidal antiinflammatory activity by using HCT 1026, a nitric oxide-releasing derivative of flurbiprofen. Here, we report the results of long-term (1-year) oral treatment with HCT 1026 of two murine models for limb girdle and Duchenne muscular dystrophies (alpha-sarcoglycan-null and mdx mice). In both models, HCT 1026 significantly ameliorated the morphological, biochemical, and functional phenotype in the absence of secondary effects, efficiently slowing down disease progression. HCT 1026 acted by reducing inflammation, preventing muscle damage, and preserving the number and function of satellite cells. HCT 1026 was significantly more effective than the corticosteroid prednisolone, which was analyzed in parallel. As an additional beneficial effect, HCT 1026 enhanced the therapeutic efficacy of arterially delivered donor stem cells, by increasing 4-fold their ability to migrate and reconstitute muscle fibers. The therapeutic strategy we propose is not selective for a subset of mutations; it provides ground for immediate clinical experimentation with HCT 1026 alone, which is approved for use in humans; and it sets the stage for combined therapies with donor or autologous, genetically corrected stem cells.

Antagonism of adenosine A2A receptors underlies the behavioural activating effect of caffeine and is associated with reduced expression of messenger RNA for NGFI-A and NGFI-B in caudate-putamen and nucleus accumbens

Caffeine, the most widely consumed of all psychostimulant drugs, exerts its action by antagonizing adenosine receptors. To study the arousing properties of caffeine, we injected rats intraperitoneally with vehicle, caffeine (7.5, 15 or 30mg/kg), the selective adenosine A2A receptor antagonist, SCH 58261 (3.75 mg/kg) or the selective adenosine A1 receptor selective antagonist DPCPX (7.5 mg/kg). In a behavioural test it was found that administration of caffeine and SCH 58261 significantly increased locomotion and rearing, whereas DPCPX did not alter locomotion and reduced rearing. After the behavioural session the rats were killed, their brains were cut at several levels along a rostrocaudal axis and in situ hybridization against NGFI-A messenger RNA and NGFI-B messenger RNA was performed. A reduction of NGFI-A messenger RNA was found in several subregions of both caudate putamen and nucleus accumbens in caffeine-treated animals. Similarly, animals that had received SCH 58261 showed significant decreases of NGFI-A messenger RNA in the rostral part of caudate putamen and in the shell part of nucleus accumbens. By contrast, DPCPX treatment caused an increase in the expression of NGFI-A messenger RNA and a smaller increase in NGFI-B messenger RNA in the lateral parts of caudate putamen. In addition, it was found that caffeine, but not SCH 58261 or DPCPX, elevated the expression of NGFI-A and NGFI-B messenger RNA in the cerebral cortex, especially in its parietal part. Thus, these results provide evidence that endogenous adenosine, via adenosine A2A receptors, causes a tonic activation of striatopallidal neurons. By blocking this adenosine effect, caffeine causes behavioural activation.

Adenosine A2A receptor antagonism potentiates L-DOPA-induced turning behaviour and c-fos expression in 6-hydroxydopamine-lesioned rats

In order to investigate the role of adenosine A2A receptor blockade on dopamine-mediated motor responses, contralateral turning behaviour and expression of the early-gene c-fos was evaluated in rats with a unilateral 6-hydroxydopamine lesion of the dopaminergic nigrostriatal pathway. SCH 58261, (7-(2-phenylethyl)-5-amino-2-(2-furyl)-pyrazolo-[4,3-e]-1,2,4-triazolo[1 , 5-c]pyrimidine) a potent and selective antagonist of adenosine A2A receptors (5 mg/kg i.p.), induced a 70-fold increase in the contralateral turning behaviour induced by a low dose (2 mg/kg i.p.) of the dopamine precursor L-DOPA (L-3, 4-dihydroxyphenylalanine). Expression of c-fos as measured by Fos-like immunoreactivity after SCH 58261 plus L-DOPA was also potentiated as compared with L-DOPA alone, both in striatum and globus pallidus of the 6-hydroxydopamine-lesioned side of the brain. SCH 58261 induced a less marked potentiation (7-fold) of turning behaviour induced by dopamine D2 receptor stimulation with quinpirole, while Fos-like immunoreactivity in the striatum and globus pallidus was not affected. Previous studies have shown that SCH 58261 strongly potentiated dopamine D1 receptor-mediated responses. The results of the present study therefore indicate that the positive interaction between SCH 58261 and L-DOPA, in 6-hydroxydopamine-lesioned rats, is mainly due to an interaction with dopamine D1 receptors. The data also suggest that adenosine A2A receptor antagonists might be useful for potentiating the effects of L-DOPA in Parkinson's disease.

Potent, selective, and orally active adenosine A2A receptor antagonists: Arylpiperazine derivatives of pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidines

Antagonism of the adenosine A2A receptor offers great promise in the treatment of Parkinson's disease. Employing the known pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine A2A antagonist SCH 58261 as a starting point, we identified the potent and selective (vs. A1) antagonist 11h, orally active in the rat haloperidol-induced catalepsy model. We further optimized this lead to the methoxyethoxyethyl ether 12a (SCH 420814), which shows broad selectivity, good pharmacokinetic properties, and excellent in vivo activity.

Pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine derivatives: potent and selective A(2A) adenosine antagonists

A series of pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine derivatives (10a-o,q,r), bearing alkyl and aralkyl chains on positions 7 and 8, were synthesized in the attempt to obtain potent and selective antagonists for the A(2A) adenosine receptor subtype. The compounds were tested in binding and functional assays to evaluate their potency for the A(2A) compared with the A1 adenosine receptor subtype. In binding studies in rat brain membranes, most of the compounds showed affinity for A(2A) receptors in the low nanomolar range with a different degree of A(2A) versus A1 selectivity. Comparison of N(7) (10a-d,h-o)- and N(8) (10e-g)-substituted pyrazolo derivatives indicates that N(7) substitution decreases the A1 affinity with the concomitant increase of A(2A) selectivity. Specifically, the introduction of a 3-phenylpropyl group at pyrazolo nitrogen in position 7 (101) increased significantly the A(2A) selectivity, being 210-fold, while the A(2A) receptor affinity remained high (Ki=2.4 nM). With regards to the affinity for A(2A) receptors, also the compound 10n, bearing in the 7-position a beta-morpholin-4-ylethyl group, deserves attention (Ki=5.6 nM) even though the A2A selectivity (84-fold) was not as high as that of 101. Conversely, the compound 10m (N(7)-4-phenylbutyl derivative) showed a remarkable selectivity (A1/a(2A) ratio = 129) associated with lower A(2A) affinity (Ki = 21 nM). In functional studies, most of the compounds examined reversed 5'-(N-ethylcarbamoyl) adenosine-induced inhibition of rabbit platelet aggregation inhibition which is a biological response mediated by the A2A receptor subtype. The compounds are potent and selective A2A antagonists which can be useful to elucidate the pathophysiological role of this adenosine receptor subtype. These compounds deserve to be further developed to assess their potential for treatment of neurodegenerative disorders such as Parkinson's disease.

Adenosine A2A receptors and neuroprotection

The adenosine A2A receptor subtype is one of the four adenosine receptors that have been identified in the mammalian organism. In addition to being found in blood vessels, platelets and polymorphonuclear leukocytes, the A2A receptors are abundant in the central nervous system, especially in the striatum. The recent development of selective A2A receptor ligands, in particular of receptor antagonists, makes it possible to elucidate the function of A2A receptors in normal and altered conditions. Pharmacological studies have shown that A2A receptor antagonists are potentially effective for treatment of neurodegenerative processes such as Parkinson's disease. Their activity is attributed to the close anatomical and functional links between A2A receptors and dopaminergic pathways in the basal ganglia. More recently, A2A receptor antagonists have proved to be active in models of cerebral ischemia. While the mechanisms underlying the role of A2A receptors in the hypoxia/ ischemia processes remains to be clarified, it is recognized that A2A receptor antagonists counteract the effects of excitatory aminoacids, which are massively released after cerebral ischemia. Another function of A2A receptors is related to protection from seizures, but further studies are needed to elucidate their specific interaction, if any, with neuronal excitability. Altogether, the great advance recently made with the discovery of selective A2A receptor ligands provides increasing information on the function of A2A receptors and opens new perspectives for treatment of neurological disorders.

[3H]SCH 23390 binding sites increase after chronic blockade of D-1 dopamine receptors

Chronic treatment with SCH 23390, a selective D-1 dopamine receptor antagonist, increased (40%) the density of [3H]SCH 23390 binding sites in striatal membrane preparations but failed to change the apparent KD of the ligand for its binding sites. Haloperidol, which preferentially blocks D-2 receptors, induced only a slight, not significant increase in the total number of [3H]SCH 23390 binding sites. (-)Sulpiride, a selective D-2 receptor blocker, also failed to change either Bmax or KD of [3H]SCH 23390 binding. Thus, chronic blockade of D-1 receptor sites by SCH 23390 can lead to an increase in their total number.

3H-SCH 23390 binding sites in the rat substantia nigra: evidence for a presynaptic localization and innervation by dopamine

Chronic treatment with SCH 23390, a selective D-1 dopamine receptor antagonist, elicited a 32% increase in the density of 3H-SCH 23390 binding sites in nigral membrane preparations but failed to change the apparent KD of the ligand for its binding sites. Haloperidol, a D-2 dopamine receptor antagonist which blocks the dopamine-sensitive adenylate cyclase and (-) sulpiride, a selective D-2 dopamine receptor blocker, which does not block the dopamine-sensitive adenylate cyclase, failed to change both the Bmax and KD of 3H-SCH 23390 binding. Finally, the intrastriatal injection of kainic acid produced a marked decrease of both GAD activity and GABA content and 3H-SCH 23390 binding sites (65%) in the homolateral substantia nigra. The results show that in the rat substantia nigra most of the 3H-SCH 23390 binding sites have a presynaptic localization on the striato-nigral GABAergic afferent terminals and suggest that dopamine released from nigral dendrites exerts a tonic influence on these presynaptic D-1 dopamine receptors.

Up-regulation of ORL-1 receptors in spinal tissue of allodynic rats after sciatic nerve injury

Nociceptin, acting through the opioid receptor-like 1 (ORL1) receptor, produces anti-nociception in several models of neuropathy. We examined the involvement of the ORL1 receptor system in the allodynia developed after sciatic nerve ligation. Allodynic rats were selected by the von Frey hair and treated intrathecally with nociceptin or morphine. The peptide induced dose-dependent anti-allodynic activities, while morphine was effective at the higher dose only. By the semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) assay, the two described ORL1 receptor isoforms were up-regulated in the allodynic animals, but unmodified in non-allodynic rats. Both short and long ORL1 receptor mRNA isoforms increased in the ipsilateral lumbar enlargement (by 50% and 100%, respectively), while 50% and 60% increases were found in the ipsilateral L5-L6 dorsal root ganglia, respectively. No significant changes were observed for either the nociceptin precursor or mu-opioid receptor expression. Thus, the ORL1 receptor system seems to regulate the mechano-allodynia that developed after nerve damage, suggesting its potential role in the treatment of neuropathic pain.

Caffeine alters A2A adenosine receptors and their function in human platelets

BACKGROUND

Caffeine acts mainly via blockade of adenosine receptors, which have been classified into A1, A2A, A2B, and A3 subtypes. We determined whether repeated caffeine administration (750 mg/d for 1 week) upregulates the human platelet A2A adenosine receptor and is accompanied by sensitization of platelet responses (increase in cAMP accumulation and decrease in platelet aggregation) to selective stimulation of the A2A receptors.

METHODS AND RESULTS

Platelets were obtained from peripheral venous blood of 9 human volunteers at the end of 1 week of caffeine abstinence (control) and at 12 and 60 hours after the last dose of caffeine (withdrawal). The A2A receptor radioligand [3H]SCH 58261 (5-amino-7(phenylethyl)-2-(2-furyl)-pyrazolo[4,3-e]-1,2,4-triazolo[1, 5-c]-pyrimidine) bound to a single affinity class of sites in platelet membranes from controls with a Bmax of 98+/-2 fmol/mg protein and a KD of 1.29+/-0.05 nmol/L. At 12 and 60 hours after caffeine withdrawal, the radioligand bound with similar affinity (KD=1.36+/-0.06 and 1.21+/-0.05 nmol/L, respectively), but the Bmax was increased (P<0.01) to 128+/-3 and 132+/-2 fmol/mg protein. The A2A receptor agonist 2-hexynyl-5'-N-ethylcarboxamidoadenosine (HE-NECA) increased cAMP accumulation (EC50=59+/-3 nmol/L) and inhibited (IC50=90+/-6 nmol/L) aggregation of control platelets. The EC50 values for HE-NECA to increase cAMP accumulation of platelets were reduced (P<0.01) at 12 and 60 hours after caffeine withdrawal (31+/-3 and 21+/-2 nmol/L, respectively). The IC50 values for HE-NECA to inhibit ADP-induced platelet aggregation were 50+/-5 and 30+/-2 nmol/L at 12 and 60 hours after caffeine withdrawal, respectively.

CONCLUSIONS

Chronic caffeine intake leads to upregulation of A2A receptors and is accompanied by sensitization to the actions of the agonist HE-NECA.

Nitric oxide (NO)-releasing statin derivatives, a class of drugs showing enhanced antiproliferative and antiinflammatory properties

Inhibitors of 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase, namely statins, exert pleiotropic actions beyond lipid-lowering effects. Their pharmacological activity on atherosclerotic plaque stability and vascular inflammation appears to be mediated, at least in part, by nitric oxide (NO). With the aim of enhancing the nonlipid-lowering properties of selected statins, we introduced a NO-releasing moiety into the structure of pravastatin (NCX 6550) and fluvastatin (NCX 6553). NO release was evaluated as nitrosylhemoglobin adduct formation by using EPR spectroscopy in rat blood. Both compounds produced a linear time-dependent increase in nitrosylhemoglobin formation, which is consistent with slow NO release kinetics. In PC12 cells, unlike their native statins, both compounds stimulated cGMP formation (NCX 6550, EC(50) = 2.3 +/- 0.2 microM; NCX 6553, EC(50) = 2.7 +/- 0.2 microM). Moreover, NCX 6550 potently inhibited cell proliferation in rat aortic smooth muscle cells (IC(50) = 2.2 +/- 0.3 microM) with a mechanism that involved both the polyamine and HMG-CoA reductase signaling pathways. Hence, mevalonate or putrescine partially reverted the effects of NCX 6550 and their combination was fully effective. In RAW 264.7 murine macrophage cells stimulated with lipopolysaccharide (1 microg/ml), NCX 6550, but not pravastatin, significantly decreased inducible NO synthase and cyclooxygenase-2 protein expression as well as nitrite accumulation. All together, the data show that the previously undescribed NO-releasing statins retain HMG-CoA reductase inhibitory activity and release bioactive NO slowly. Among the additional properties, compared with native statins, the NO-releasing statins show enhanced antiinflammatory effects. Thus, NO-releasing statins represent an interesting class of drugs having potential in the therapy of disorders associated with endothelial dysfunction and vascular inflammation.

7-Substituted 5-amino-2-(2-furyl)pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidines as A2A adenosine receptor antagonists: a study on the importance of modifications at the side chain on the activity and solubility

It was demonstrated in the early 1990s that adenosine exerts many physiological functions through the interaction with four different receptors, named A1, A2A, A2B, and A3. In the past few years, our group has been involved in the development of A2A antagonists, which led to the synthesis of SCH 58261 (1), the first potent and selective adenosine A2A antagonist, which has been widely used as a reference compound. In this paper, we present an extended series of pyrazolotriazolopyrimidines synthesized with the aim to investigate the influence of the substitutions on the pyrazole ring. The choice of the substituents was based on their capability to improve water solubility while retaining high affinity and selectivity at the human A2A adenosine receptor subtype. In this series, some structural characteristics that are important for activity, i.e., tricyclic structure, free amino group at 5-position, furan ring, and substituent at 7-position on the pyrazole moiety, have been maintained. We focused our attention on the nature of the phenyl ring substituent to improve water solubility. Following this strategy, we developed new compounds with good affinity and selectivity for A2A adenosine receptors, such as 8d (K(i) 0.12 nM; hA1/hA2A ratio = 1025; R(m) = 2.8), 8h (K(i) 0.22; hA1/hA2A ratio = 9818; R(m) = 3.4), 8i (K(i) 0.18 nM; hA1/hA2A ratio = 994; R(m) = 2.8), 8k (K(i) 0.13 nM; hA1/hA2A ratio = 4430; R(m) = 3.6), and 14b (K(i) 0.19 nM; hA1/hA2A ratio = 2273; R(m) = 2.7). All the new synthesized compounds have no significant interaction with either A2B or A3 receptor subtypes. This new series of compounds deeply enlightens some structural requirements to display high affinity and selectivity for the A2A adenosine receptor subtype, although our goal of identifying new compounds with increased water solubility was not completely achieved. On this basis, other strategies will be devised to improve this class of compounds with a profile that appears to be promising for treatment of neurodegenerative disorders, such as Parkinson's disease.