Effects of a 5-lipoxygenase inhibitor, AA861, on lipoxygenase metabolism and superoxide anion generation by human polymorphonuclear leukocytes--potentiation of superoxide anion generation by LTB4

Redox regulation of p53, redox effectors regulated by p53: a subtle balance

SIGNIFICANCE

Reactive oxygen species (ROS), generated by cells as side products of biological reactions, function as secondary messengers by impacting a host of cellular networks involved in maintaining normal homeostatic growth as well as pathological disease states. Redox-sensitive proteins, such as the tumor suppressor protein p53, are susceptible to ROS-dependent modifications, which could impact their activities and/or biological functions.

RECENT ADVANCES

p53 is a transcription factor that controls a wide variety of target genes and regulates numerous cellular functions in response to stresses that lead to genomic instability. Thus, redox modifications of p53 could impact cell fate signaling and could have profound effects on pathways fundamental to maintaining cell and tissue integrity.

CRITICAL ISSUES

Recent studies present evidence that ROS function upstream of p53 in some model systems, while in others ROS production could be a downstream effect of p53 activation.

FUTURE DIRECTIONS

In this review, we describe how ROS production regulates p53 activity and how p53 can, in turn, influence cellular ROS production.

A taurine-supplemented vegan diet may blunt the contribution of neutrophil activation to acute coronary events

Neutrophils are activated in the coronary circulation during acute coronary events (unstable angina and myocardial infarction), often prior to the onset of ischemic damage. Moreover, neutrophils infiltrate coronary plaque in these circumstances, and may contribute to the rupture or erosion of this plaque, triggering thrombosis. Activated neutrophils secrete proteolytic enzymes in latent forms which are activated by the hypochlorous acid (HOCl) generated by myeloperoxidase. These phenomena may help to explain why an elevated white cell count has been found to be an independent coronary risk factor. Low-fat vegan diets can decrease circulating leukocytes--neutrophils and monocytes--possibly owing to down-regulation of systemic IGF-I activity. Thus, a relative neutropenia may contribute to the coronary protection afforded by such diets. However, vegetarian diets are devoid of taurine - the physiological antagonist of HOCl--and tissue levels of this nutrient are relatively low in vegetarians. Taurine has anti-atherosclerotic activity in animal models, possibly reflecting a role for macrophage-derived myeloperoxidase in the atherogenic process. Taurine also has platelet-stabilizing and anti-hypertensive effects that presumably could reduce coronary risk. Thus, it is proposed that a taurine-supplemented low-fat vegan diet represents a rational strategy for diminishing the contribution of activated neutrophils to acute coronary events; moreover, such a regimen would work in a number of other complementary ways to promote cardiovascular health. Moderate alcohol consumption, the well-tolerated drug pentoxifylline, and 5-lipoxygenase inhibitors--zileuton, boswellic acids, fish oil--may also have potential in this regard.

Synergistic effects of pranlukast and leukotriene B4 receptor antagonist on antigen-induced pulmonary reaction

We now attempted to differentiate effects of cysteinyl-leukotrienes and leukotriene B4 on antigen-induced pulmonary reaction by using a selective leukotriene D4/E4 (CysLT1) receptor antagonist and a selective LTB4 (BLT) receptor antagonist in rats. An intratracheal challenge with ovalbumin to Brown-Norway rats actively sensitized with ovalbumin produced two phases of airway responses which were estimated based on airway resistance, the immediate-type airway response within 30 min, and the delayed-type airway response beginning from 4 to 6 h after the challenge. Pretreatment of the rats with a CysLT1 receptor antagonist (pranlukast) failed to reduce the elevation of airway resistance, and pretreatment with a BLT receptor antagonist (ONO-4057; 5-[2-(2-carboxyethyl)-3-[6-(4-methoxyphenyl)-5E-hexenyl]- oxyphenoxy] valeric acid) also produced no decrease. In contrast, combined pretreatment of the rats with pranlukast and ONO-4057 did not reduce the amplitude of the immediate-type airway response, but did allow the elevated airway resistance to return to its baseline level and also significantly inhibited the delayed-type airway response. Histological examination at 6 h after ovalbumin challenge showed infiltration of inflammatory cells with a predominance of neutrophils and scattered eosinophils in the bronchial submucosa. While pretreatment with neither pranlukast nor with ONO-4057 inhibited the infiltration of inflammatory cells in the bronchial submucosa, pretreatment with the two antagonists combined significantly inhibited the infiltration of granulocytes into the bronchial submucosa. On the contrary, intratracheal administration of either leukotriene D4 or leukotriene B4 up to 10 microg resulted in the infiltration of granulocytes into the bronchial submucosa, but no synergism for the infiltration of granulocytes was observed after combined administration. These results suggest that leukotriene B4 appears to play a significant role in the antigen-induced pulmonary reaction in association with cysteinyl-leukotrienes. Accordingly, the combined antagonism at the CysLT1 receptor and BLT receptor may be a useful intervention for the treatment of bronchial asthma.

Cancer cells isolated from malignant pleural and peritoneal effusions inhibit phospholipase A2 activity in human polymorphonuclear leukocytes

We studied the influence of cancer cells on the LTB4 production by human polymorphonuclear leukocytes (PMN). The cancer cells were isolated from malignant pleural effusion specimens taken from two patients or from a peritoneal effusion specimen of one patient. While human PMN produced LTB4 following stimulation with A23187, the addition of cancer cells inhibited LTB4, 5-HETE and 12-HETE production by PMN in a cell number-dependent manner, while the cancer cell lines also showed a similar inhibition. The addition of lysate of the breast cancer cells also inhibited in a dose-dependent manner the production of LTB4 by PMN following stimulation with A23187. The addition of arachidonic acid completely reversed the inhibition of PMN-LTB4 production by the addition of the breast cancer cell lysates, thus suggesting inhibition at the phospholipase A2 level. The addition of this lysate to the partially purified human cytosolic PLA2 also inhibited the PLA2 activity. In contrast, the addition of lymphoma cells isolated from metastatic lymphnodes did not inhibit the LTB4 production from PMN. Since LTB4 is one of the important chemotactic factors for PMN and monocytes, these findings suggest that the inhibition of the PLA2 activity by the cancer cells thus results in a reduced production of LTB4 from PMN and contributes to a predisposition to develop severe infection in patients with advanced cancer.