Baylis-Hillman reaction assisted parallel synthesis of 3,5-disubstituted isoxazoles and their in vivo bioevaluation as antithrombotic agents.

The solution-phase parallel synthesis involving reactions of Baylis-Hillman products of 3-substituted-5-isoxazolecarbaldehydes with nucleophiles and their in vivo antithrombotic evaluations are described along with the results of in vitro platelet aggregation inhibition assay of a few compounds. Results of the detailed evaluation of one of the compounds as an inhibitor of platelet aggregation are also presented.

Neutrophil-free radical generation and enzymatic antioxidants in migraine patients.

The present study was undertaken to elucidate the role of circulating neutrophils if any in oxidative stress in migraine by evaluating free radical generation and activities of enzymatic antioxidants in the blood in 55 patients with migraine and 60 healthy controls. Free radical generation was assessed by flow cytometry, while activity of catalase, superoxide dismutase (SOD) and glutathione peroxidase (GPx) was estimated in blood polymorphonuclear neutrophils (PMNs) by standard procedures. Platelet SOD was also measured. No significant change was found in free radical generation and in the activity of catalase, SOD and GPx in migraine patients. Univariate analysis of PMN catalase level revealed that migraineurs with a positive family history had significantly lower catalase activity compared with those with a negative family history. No correlation was found in the activity of antioxidant enzymes with age, duration of disease, time since last attack and headache index. The platelet SOD also did not show any significant change in patients of migraine without aura. Platelet aggregation in the presence or absence of PMNs was also not altered significantly. Thus the findings of the present study suggest that neutrophils are not the cause of oxidative stress observed in migraine patients.

Role of ascorbic acid in the modulation of inhibition of platelet aggregation by polymorphonuclear leukocytes.

OBJECTIVES: We investigated the modulatory effect of ascorbate on the inhibition of platelet aggregation response by polymorphonuclear leukocytes (PMNs) and characterized the mechanism of the inhibitory response. BACKGROUND: PMNs have been reported to play a significant role in vascular homeostasis by releasing various factors including short-lived reactive oxygen species (ROS) and nitric oxide (NO). NO prevents the activation of circulating platelets and plays a significant role in hemostasis. In addition, PMNs also have the capacity to store very high concentrations of ascorbate. The physiological implications of storing such high concentrations of an antioxidant by a cell-releasing free radicals is unknown, viz. a viz. hemostatic regulation. METHODS: ADP-induced aggregation in human, monkey and rat platelet-rich plasma (PRP) was monitored in the presence of PMNs treated with varying concentrations of ascorbate/dehydroascorbate. NO generation from rat and human PMNs treated with ascorbate was monitored on a FACS Calibur flow cytometer and intraplatelet cyclic guanosine 3',5'-monophosphate (cGMP) levels was also measured. RESULTS: PMNs induced a cell number and time-dependent inhibition of ADP-induced aggregation. The PMNs dependent inhibition was enhanced significantly at 30 min by ascorbate (300 microM). Ascorbate seemed to exert its effects through its oxidized product, dehydroascorbate, as the effects was prevented in the presence of D-glucose (10 mM). Dehydroascorbate elicited significant potentiation of the PMNs induced inhibitory responses and these effects were mediated by the release of NO and subsequent activation of platelet guanylyl cyclase. Flow cytometry experiments with human and rat PMNs confirmed the release of NO and the elevated platelet cGMP levels confirmed NO-mediated activation of guanylyl cyclase. CONCLUSIONS: Ascorbate in circulation seems to prevent the activation of platelets by enhancing the release of antiaggregatory NO, from neighbouring or cohabitant PMNs. The ascorbate effect is mediated through its conversion to dehydroascorbate, subsequently, gets taken up by the cell and converted back to ascorbate. Intracellular ascorbate potentiates the release of NO from the PMNs and subsequently activates guanylyl cyclase in the platelets.

Role of endogenous reactive oxygen derived species and cyclooxygenase mediators in 5-hydroxytryptamine-induced contractions in rat aorta: relationship to nitric oxide.

Endogenous reactive oxygen species (superoxide anion, hydroxyl radical and hydrogen peroxide), endothelium-derived nitric oxide and cyclooxygenase mediators are involved in the regulation of vascular smooth muscle tone. An imbalance of these mediators can have profound implications in various cardiovascular disorders. Involvement of endogenous reactive oxygen species, endothelium-derived nitric oxide (NO) and cyclooxygenase mediators in 5-hydroxytryptamine- (5-HT-) induced contractions of endothelium intact rat aortic rings have been investigated in the present study. The contribution of each of the endogenous reactive oxygen species in mediating 5-HT-induced contractions was studied by pretreating the rings with their respective scavengers. Pretreatment of the rings with superoxide dismutase (superoxide radical scavenger), catalase (H (2)O (2)inactivator), mannitol (extracellular OH. scavenger), or thiourea (intracellular OH. radical scavenger) significantly depressed the 5-HT-induced contractions in the aortic rings. The responses to 5-HT in the presence of SOD or catalase were augmented byL -NAME pretreatment. Though aminotriazole partially inhibited the catalase activity, it inhibited 5-HT-induced contractions significantly. The results obtained thus suggest that endogenous generation of ROS (O(2).(-), H (2)O (2)and OH.) modulates 5-HT-induced rat aortic ring contractions. In addition, H (2)O (2)generated in the endothelium seems to regulate the vascular response and also act as a mediator to release other vasoactive substances. Basal production of NO by the endothelium seems to affect the vascular response due to its interaction with ROS mediators.