New quinoxaline 1,4-di-N-oxides for treatment of tuberculosis

Some quinoxaline 1,4-di-N-oxides derivatives with very different substituents in 2, 3, 6 and 7 positions have been synthesized in order to obtain new hypoxia selective agents. Some of these products have been tested as antituberculosis agents and very interesting results have been obtained from the first screening.     

Increased toxicity of cocaine on human hepatocytes induced by ethanol: role of GSH.

Increased toxicity of cocaine to human hepatocytes is observed when cells are simultaneously incubated with ethanol. Ethanol might exacerbate cocaine hepatocyte toxicity by three different pathways: a) by increasing the oxidative metabolism of cocaine and hence the oxidative damage; b) by the formation of a more toxic metabolite, namely cocaethylene; or c) by decreasing the defence mechanisms of the cell (i.e. GSH). In the present study, experiments were conducted to investigate the feasibility of these hypotheses. In hepatocytes preincubated for 48 hr with ethanol, neither significant changes in cocaine metabolism nor cytotoxicity were found despite differences in hepatocyte p-nitrophenol hydroxylase (largely CYP2E1 activity). Cocaethylene, the transesterification product of cocaine and ethanol, was found to be more toxic than cocaine for human hepatocytes (3x). However, the small amount formed when human hepatocytes were incubated with cocaine and ethanol would hardly explain the increased toxicity observed. On the other hand, the simultaneous presence of cocaine and ethanol caused a sustained decline in the intracellular GSH content that was larger than that observed in cocaine- or ethanol-treated cultures. Parallel to this phenomenon, a significant increase in lipid peroxidation was observed, as compared to cells treated with equimolar amounts of cocaine, ethanol, or cocaethylene. Finally, depletion of hepatocyte GSH with diethylmaleate down to levels similar to those found in ethanol-treated cells made hepatocytes more susceptible to cocaine. Taken together, the results of this research suggest that by decreasing GSH levels, ethanol makes human hepatocytes more sensitive to cocaine-induced oxidative damage.     

A new experimental approach in endothelium-dependent pharmacological investigations on isolated porcine coronary arteries mounted for impedance planimetry.

1. The aim of this study was to investigate whether the balloon-based impedance planimetry technique could be a useful tool in endothelium-dependent investigations. 2. Porcine large coronary arteries contracted with prostaglandin F2alpha (PGF2alpha, 10 microM) did not relax to bradykinin (0.1 nM - 0.1 microM), but did relax to sodium nitroprusside (SNP, 10 microM). However, after eversion of the segments, bradykinin induced relaxations with pD2 values and maximal responses of 8.78+/-0.09 and 75+/-2% (n=6), respectively. 3. Incubation with captopril (1 microM) did not reveal a relaxation to bradykinin in the normal vessel configuration and had no influence on the concentration-relaxation relationship in everted segments. 4. Lowering the luminal pressure in contracted segments from 131+/-5 mmHg (isometric, n=5) to 60 mmHg (isobaric, n=5) did not facilitate the action of bradykinin. 5. Eversion of segments did not influence the concentration-response relationship for K+ (4.7 - 125 mM), PGF2alpha (0.3 - 30 microM), and SNP (30 nM - 30 microM), although the time-courses of responses were faster when the agents were added from the intimal compared to the adventitial side of the preparation. 6. In the same everted segment contracted with PGF2alpha, the concentration-response relationship for bradykinin was not different under isometric and isobaric conditions. 7. These results indicate that, (1) reduced endothelium-dependent relaxations to adventitially administered substances can be ascribed to a diffusion barrier in the vessel wall, while enzymatic degradation, luminal pressure and precontractile responses seem not to play a role, (2) impedance planimetry applied to everted cylindrical segments could be a useful experimental approach in pharmacological studies of endothelium-dependent responses under isobaric and isometric conditions.     

Different receptors mediating the inhibitory action of exogenous ATP and endogenously released purines on guinea-pig intestinal peristalsis.

1 Adenosine 5'-triphosphate (ATP) is an enteric neurotransmitter which acts at purine receptors on intestinal nerve and muscle. This study set out to shed light on the receptor mechanisms by which exogenous and endogenous ATP influences intestinal peristalsis. 2 Peristalsis in isolated segments of the guinea-pig small intestine was triggered by a perfusion-induced rise of the intraluminal pressure. Motor changes were quantified by alterations of the peristaltic pressure threshold (PPT) at which propulsive muscle contractions were elicited. 3 ATP (>/= 3 microM) increased PPT and abolished peristalsis at concentrations of 100-300 microM. Adenosine 5'-O-2-thiodiphosphate (ADPbetaS, 3-100 microM) was more potent, whereas alpha,beta-methylene ATP (alpha,beta-meATP, 3-100 microM) was less potent, than ATP in depressing peristalsis. 4 8-Phenyltheophylline (10 microM) attenuated the anti-peristaltic effect of 10 and 30 microM ATP but not that of higher ATP concentrations. Apamin (0.5 microM) counteracted the ability of ATP, ADPbetaS and alpha,beta-meATP to enhance PPT. Suramin (300 microM) and pyridoxal phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS, 150 microM) antagonized the inhibitory effect of alpha,beta-meATP on peristalsis but did not alter the effect of ATP and ADPbetaS. 5 PPADS (50-150 microM) reduced PPT by as much as 50%. This stimulant effect on peristalsis was prevented by suramin (300 microM) but left unaltered by apamin (0.5 microM) and NG-nitro-L-arginine methyl ester (300 microM). 6 These data show that exogenous and endogenous ATP inhibits intestinal peristalsis via different apamin-sensitive purinoceptor mechanisms. Exogenous ATP depresses peristalsis mostly via suramin- and PPADS-insensitive P2 receptors, whereas endogenous purines act via P2 receptors sensitive to both suramin and PPADS.     

Pharmacological aspects of experimental headache models in relation to acute antimigraine therapy.

The last decade has witnessed a tremendous progress in the acute therapy of migraine, with sumatriptan, belonging to a new class of drugs, now known as 5-HT(1B/1D/1F) receptor agonists, leading the way. The undoubted success of sumatriptan stimulated the development of new triptans as well as other suitable pharmacological tools and experimental models to probe into complex migraine mechanisms. In this review, we discuss the main experimental models for migraine, against the background of the disease pathophysiology and 5-HT receptors considered most important for migraine therapy. We believe that the use of these migraine models will provide even better treatment for migraine patients in the next millennium.     

Impairment of neurogenic inflammatory and anti-inflammatory responses in diabetic rats

The effect was studied of a primary (preconditioning) neurogenic inflammatory challenge induced by electrical stimulation of the peripheral stump of the sciatic nerve (20 V, 0.5 ms, 5 Hz, for 5 min) on neurogenic oedema (5 min later) induced by stimulation of the contralateral sciatic nerve. Plasma extravasation due to the second stimulation was decreased by 52.7+/-3.1% (P<0.01) in normal animals and by 29.7+/-2.2 and 18.1+/-1.5% with 50 mg/kg streptozotocin pretreatment i.v. 4 and 8 weeks previously, respectively. Subsequently, bilateral sciatic nerve stimulation increased baseline plasma somatostatin levels from 6.4+/-0.3, 11. 7+/-1.4, and 16.8+/-3.8 to 28.3+/-2.9 (P<0.01), 17.9+/-3.7, and 25. 1+/-1.7 pmol/l in normal, and 4- and 8-week diabetic animals, respectively. We conclude that experimental diabetes impairs the capability of a preconditioning neurogenic inflammatory episode to elicit a systemic anti-inflammatory effect. This is accompanied by a deficiency in elevation of the plasma somatostatin level in response to nerve stimulation, although the baseline plasma somatostatin level increases proportionally to the duration of experimental diabetes.     

Bicyclic tripeptide mimetics with reverse turn inducing properties

Analogues of the hypertensive octapeptide angiotensin II, comprising novel constrained 5,8-bicyclic and 5,9-bicyclic tripeptide units adopting nonclassical beta-turn geometries, as deduced from theoretical conformational analysis, have been synthesized. Spontanous bicyclization upon acid-catalyzed deprotection of a model peptide, encompassing a protected omega-formyl alpha-amino acid in position 5 and cysteine residues in positions 3 and 7, revealed a strong preference for bicyclization toward the C-terminus. The bicyclic thiazolidine related angiotensin II analogues synthesized exhibited no affinity for the angiotensin II AT1 receptor.     

Angiotensin II analogues encompassing 5,9- and 5,10-fused thiazabicycloalkane tripeptide mimetics

A simple experimental procedure on solid phase for the construction of new tripeptidic 5,9- and 5,10-fused thiazabicycloalkane scaffolds that adopt beta-turns has been developed. This N-terminal-directed bicyclization, relying on masked aldehyde precursors derived from glutamic acid as key building blocks, provides a complement to the related bicyclization previously reported, where an aspartic acid-derived precursor was employed to induce cyclization toward the C-terminal end of the peptide. Thus, the regioselectivity of the bicyclization can be altered simply by varying the chain length of the incorporated aldehyde precursor. Four analogues of the hypertensive octapeptide angiotensin II, comprising the new scaffolds in the 3-5- and 5-7-positions, were synthesized. One of these conformationally constrained angiotensin II analogues exhibited AT(1) receptor affinity (K(i) = 750 nM). Results from theoretical conformational analysis of model compounds of the bicyclic tripeptide mimetics are presented, and they demonstrate that subtle differences in geometry have a strong impact on the affinity to the AT(1) receptor.     

5-(Tryptophyl)amino-1,3-dioxoperhydropyrido[1,2-c]pyrimidine-based potent and selective CCK(1) receptor antagonists: structural modifications at the tryptophan domain

Analogues of the previously reported potent and highly selective CCK(1) receptor antagonist (4aS, 5R)-2-benzyl-5-(N-Boc-tryptophyl)amino-1,3-dioxoperhydropyrido-[1, 2-c]pyrimidine (2a) were prepared to explore the structural requirements at the Boc-tryptophan domain for CCK(1) receptor affinity. Structural modifications of 2a involved the Trp side chain, its conformational freedom, the Boc group, and the carboxamide bond. Results of the CCK binding and in vitro functional activity evaluation showed three highly strict structural requirements: the type and orientation of the Trp side chain, the H-bonding acceptor carbonyl group of the carboxamide bond, and the presence of the Trp amino protection Boc. Replacement of this acid-labile group with 3, 3-dimethylbutyryl or tert-butylaminocarbonyl conferred acid stability to analogues 14a and 15a, which retained a high potency and selectivity in binding to CCK(1) receptors, as well as an in vivo antagonist activity against the acute pancreatitis induced by caerulein in rats. Oral administration of compounds 14a and 15a also produced a lasting antagonism to the hypomotility induced by CCK-8 in mice, suggesting a good bioavailability and metabolic stability.     

Combined effect of platination and intercalation upon DNA binding of novel cytotoxic Pt-bis(naphthalimide) complexes

The reaction of platinum salts with bis(naphthalimide), compound 1, yielded two Pt-bis(naphthalimide) complexes, compounds 2 and 3 which differ from each other in their leaving groups being 1,1-cyclobutane dicarboxylate or chloride, respectively. The testing of the cytotoxic activity of compounds 2 and 3 against several tumor cell lines indicated that both compounds may be endowed with important antineoplastic properties since they circumvent cisplatin resistance. At similar rates of DNA platination (r(b) = 0.025), compounds 2 and 3 unwind supercoiled pUC8 DNA by (48 +/- 2) degrees. Altogether, these data suggest (i) that the cytotoxic activity of compounds 2 and 3 may be due to a combined effect of platination and intercalation and (ii) that the bis(naphthalimide) ligand is a suitable "carrier" that favors DNA targeting by cis-Pt(II) centers.