Lack of association between the cyclooxygenase 2 -765G>C polymorphism and prostate cancer risk: a meta-analysis.

The aim of this study was to investigate the association between the cyclooxygenase 2 (COX2) -765G>C (rs20417) polymorphism and prostate cancer (PC) risk using meta-analysis. A systematic literature search was performed using the PubMed, Embase, Cochrane Library, and Google Scholar databases by using the terms "cyclooxygenase-2/COX-2/PTGs2", "polymorphism" or "variation", and "prostate" and "cancer" or "carcinoma" to identify relevant articles up to June 14, 2014. Crude odds ratios (ORs) with 95% confidence intervals (CIs) were assessed for PC risk associated with COX2 -765G>C polymorphism using fixed- and random-effect models. We identified a total of nine publications, including 5952 cases and 5078 controls, to investigate the effect of COX2 -765G>C on PC risk, and found no significant association in any genetic model tested (CC vs GG: OR = 0.993, 95%CI = 0.923-1.068; GC+CC vs GG: OR = 1.041, 95%CI = 0.931-1.103; CC vs GC+GG: OR = 0.858, 95%CI = 0.689-1.067; CC vs GG: OR = 0.871, 95%CI = 0.689-1.086; GC vs GG: OR = 1.032, 95%CI = 0.945-1.127). Power analysis and tests for publication bias ensured the reliability of our results. This meta-analysis suggested that the functional COX2 -765G>C polymorphism, located in the COX2 gene promoter, is unlikely to be associated with PC risk. However, additional larger, well-designed studies are still required to reach a conclusive result on this issue.

Molecular basis for the stereoselective interactions of catecholamines with alpha-adrenoceptors.

The catecholamines were found to inhibit the binding of the alpha 2-adrenoceptor agonist, [3H]-clonidine, to the recombinant wild type alpha 2a-adrenoceptor (Table 1) with potencies that are consistent with their functional activity in alpha 2-adrenoceptor test systems [6,7]. Mutation of Ser165 to alanine had no significant effect (less than 2-fold) on the affinity of any of the catecholamines for the alpha 2a-adrenoceptor, and in particular, the ratios of affinities between the corresponding (-)- and (+)-enantiomers of the catecholamines were not altered by the point mutation at Ser165. These findings indicate clearly that Ser165, in contrast to predictions made by molecular modeling, plays little if any role in the binding of the catecholamines in general, and cannot be involved in the attachment of the beta-hydroxyl group to the alpha 2a-adrenoceptor. Mutation of either Ser90 on transmembrane helix II or Ser419 on transmembrane helix VII to alanine produced dramatic and selective reductions in the affinity of the (-)-enantiomers of the catecholamines for the alpha 2a-adrenoceptor, with no changes occurring in affinities of the (+)-enantiomers. Thus, the affinities of (-)-norepinephrine and (-)-epinephrine for the Ser90 and Ser419 mutants of the alpha 2a-adrenoceptor were 35-75 fold lower than their affinities for the wild type receptor (Table 1), suggesting that Ser90 and/or Ser419 are involved in the attachment of the beta-hydroxyl groups of the catecholamines to the receptor. Similarly, the affinity of (+/-)-6-fluoronorepinephrine was reduced by 100-fold for the Ser90 mutant receptor (Table 1). Importantly, the affinities of the (+)-enantiomers of the catecholamines, as well as dopamine and epinine, which are the corresponding analogs of norepinephrine and epinephrine which lack the beta-hydroxyl group, were not affected by mutation of Ser90 or Ser419 to alanine (Table 1). Asn293 in transmembrane helix VI has also been proposed to be involved in the interaction of the beta-hydroxyl group of isoproterenol with the beta 2-adrenoceptor [4]. The alpha 2a-adrenoceptor contains three hydroxyl bearing amino acids at a position corresponding to this site (Thr393-Tyr394-Thr395). These amino acids could theoretically form a hydrogen bond with the beta-hydroxyl group of a catecholamine, and therefore could serve as a potential point of attachment. Simultaneous mutation of all three of these amino acids to Ala-Phe-Ala reduced the affinity of the (-)-enantiomers of the catecholamines by 12-20 fold, which is somewhat less than what was observed for mutation of either Ser90 or Ser419 (Table 1). However, in contrast to mutation of Ser90 or Ser419, which had no effect on the affinity of the (+)-enantiomers, mutation of the three residues in transmembrane helix VI did significantly reduce the affinities of the (+)-enantiomers of the catecholamines by approximately 5- to 9-fold, indicating that mutations at these points of the receptor are not selective for the (-)-enantiomers, and are therefore not likely to be involved in the attachment of the beta-hydroxyl group of the catecholamines.

Ser165 of transmembrane helix IV is not involved in the interaction of catecholamines with the alpha-2a-adrenoceptor.

Molecular modeling studies have predicted that the beta-hydroxyl group of the catecholamines interacts with the beta 2-adrenoceptor at the serine residue at position 165 (Ser165) located on transmembrane helix IV; however, this has not been confirmed by site-directed mutagenesis. It has been inferred that this site, which is conserved in all of the nine known alpha- and beta-adrenoceptor subtypes, is also involved in the interaction of catecholamines with the alpha 2a-adrenoceptor. To test the hypothesis that the beta-hydroxyl group of the catecholamines interacts with Ser165 of the alpha 2a-adrenoceptor, we prepared a mutant alpha 2a-adrenoceptor where Ser165 was mutated to alanine. Mutation of Ser165 of the alpha 2a-adrenoceptor to alanine had no effect on the affinity of dopamine (which lacks the beta-hydroxyl group) or either enantiomer of norepinephrine or epinephrine (both of which possess the beta-hydroxyl group), indicating that Ser165 is not involved in the interaction of the catecholamines with the alpha 2a-adrenoceptor. We have previously shown that mutation of Ser90, located in transmembrane helix II, to either alanine or cysteine produces a selective reduction in the affinity of the (-)-enantiomers of the catecholamines for the alpha 2a-adrenoceptor, with no effect on the (+)-enantiomers or the corresponding beta-desoxy analogs. This is consistent with the known stereoselectivity involved in the interactions of catecholamines with the alpha 2a-adrenoceptor. The results of the present investigation indicate that Ser165 is not involved in the interaction of catecholamines with the alpha 2a-adrenoceptor. Because all known alpha-adrenoceptor subtypes have a serine residue at a position corresponding to Ser90 of the alpha 2a-adrenoceptor, it would appear that this site represents an important point for attachment of the beta-hydroxyl group of catecholamines.

Evidence that a novel 8-phenyl-substituted xanthine derivative is a cardioselective adenosine receptor antagonist in vivo.

The ability of caffeine, enprofylline (3-propylxanthine), 8-phenyltheophylline, 8-p-sulphophenyl-theophylline, 8-(4'-carboxymethyloxyphenyl)-1,3-dipropylxanthine, and 8-(4'-carboxymethyloxyphenyl)-1,3-dipropylxanthine-2-aminoethyl amide (XAC) to antagonize the effects of an adenosine analogue, N-5'-ethylcarboxamidoadenosine, on heart rate and blood pressure in anesthetized rats was examined. The first five xanthine derivatives were equally active in antagonizing the two responses. By contrast, XAC was approximately 20 times more potent in antagonizing the heart rate response than the blood pressure response. Measurements of the concentration of XAC in plasma and brain indicate that it penetrates the central nervous system poorly. It is concluded that XAC is a cardioselective adenosine antagonist, and since adenosine is supposed to reduce heart rate via an effect on A1-receptors, and the blood pressure via A2-receptors, XAC may be a selective A1-adenosine receptor antagonist in vivo.

Effects of adenosine and two stable adenosine analogues on blood pressure, heart rate and colonic temperature in the rat.

Adenosine exerts effects via receptors of the AI- and A2-subtype. L-phenylisopropyl adenosine (L-PIA) is more potent than N-5'-ethylcarboxamido adenosine (NECA) at the A1-subtype receptor whereas the potency order is reversed at the A2-subtype receptor. Adenosine analogues have been shown to decrease blood pressure and heart rate and to induce a marked hypothermia. In the present series of experiments adenosine, L-PIA and NECA were given i.p. or i.v. to rats, and blood pressure, ECG and colonic temperature were recorded. The NECA was the most potent of the compounds in reducing blood pressure (EC50 2 micrograms kg-1 i.v.), followed by L-PIA (EC50 approximately 30 micrograms kg-1 i.v.) and adenosine (EC50 approximately 300 micrograms kg-1 i.v.). In contrast, L-PIA and NECA were equally active in reducing heart rate (EC50 approximately 6 micrograms kg-1 i.v.). and considerably more potent than adenosine (EC50 approximately 300 micrograms kg-1 i.v.). It is suggested that simultaneous measurement of blood pressure and heart rate could be a simple in vivo model for comparison of A1- and A2-receptor subtype mediated effects. Colonic temperature was markedly reduced after i.p. administration of the adenosine analogues. Thus, 100 micrograms NECA kg-1 reduced colonic temperature from 37.8 to 26 degrees C. A 5 degrees C temperature drop was obtained by 10 micrograms kg-1 NECA, by 200 micrograms kg-1 L-PIA and by 200 mg kg-1 adenosine. The fall in colonic temperature was associated with a loss of muscular activity, as determined by needle electrodes or by palpation, indicating an inhibition of shivering.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine analogues stimulate cyclic AMP formation in rabbit cerebral microvessels via adenosine A2-receptors.

This study has examined the accumulation of cyclic AMP in microvessels from rabbit and feline cerebral cortex induced by a series of adenosine analogues to determine the type of receptor involved. The conversion of tritium labelled adenine nucleotides to [3H]cyclic AMP was determined in [3H]adenine labelled microvessels in the presence of an inhibitor of cyclic AMP hydrolysis, rolipram (30 microM). In microvessels from both cats and rabbits two adenosine analogues, N-5'-ethylcarboxamido adenosine (NECA) and L (S)-phenylisopropyladenosine (PIA), stimulated cyclic AMP accumulation. The response was larger and more reproducible in rabbits than in cats. In rabbit cerebral microvessels the order of potency as stimulator of cyclic AMP accumulation was NECA greater than 2-chloroadenosine greater than L-PIA greater than cyclohexyladenosine (CHA) greater than D-PIA. This order of potency defines the receptor involved as being of the A2 subtype. Although the maximal response to CHA appeared to be lower than that to NECA, CHA did not inhibit the response to NECA, suggesting that it is not a classical partial agonist. In the presence of the adenylate cyclase stimulating compound forskolin (I microM) NECA was more active than in its absence (close to 30-fold increase in EC50) and also produced a maximal effect six times higher. The maximal responses to PIA and CHA increased proportionally in the presence of forskolin. These results show that rabbit cerebral microvessels possess adenosine receptors of the A2 subtype capable of stimulating the formation of cyclic AMP. The functional significance of such receptors is not known, but may be related to regulation of vascular permeability.