Free radical stimulation of tyrosine kinase and phosphatase activity in human peripheral blood mononuclear cells

Oxidative and modulatory effects of trace metals on metabolism of polycyclic aromatic hydrocarbons in the Antarctic fish Trematomus bernacchii

Biological interactions between various classes of pollutants are of great relevance for the Antarctic marine environment, where the naturally elevated bioavailability of metals like cadmium might indirectly influence sensitivity of endemic organisms toward other environmental pollutants, e.g. polycyclic aromatic hydrocarbons (PAHs). To further investigate reciprocal effects of different chemicals, the fish Trematomus bernacchii was exposed to trace metals (Cd, Cu, Hg, Ni, Pb) and benzo[a]pyrene (BaP, as a model PAH), dosed alone and in combinations. Co-exposures revealed that BaP did not influence the accumulation of metals, while these elements caused significant changes on tissue levels of the PAH. The marked EROD induction caused by BaP was completely suppressed by co-exposure with Cd and Cu, but no effects were observed with Ni, Hg and Pb. Similar results were confirmed at the protein level by Western blot analyses while CYP1A1 mRNA levels were reduced only during Cd co-exposures. Clear evidence of oxidative perturbations was observed in fish co-treated with Cd and BaP and the reduced capability to absorb peroxyl and hydroxyl radicals suggested some oxidative pathways by which this element might indirectly modulate the biotransformation efficiency of Cytochrome P450. Partly different and post-transcriptional mechanisms of action could be hypothesized for Cu, while moderate oxidative effects of Hg, Ni and Pb during co-exposures would confirm their limited influence on metabolism of PAHs. In general, the overall results revealed a complex pathway of interactions between different chemicals during co-exposures and the importance of oxidative status in modulating induction and expression of CYP1A1.

p40phox: The last NADPH oxidase subunit

The phagocytic NADPH-oxidase is a multiprotein system activated during the inflammatory response to produce superoxide anion (O2-), which is the substrate for formation of additional reactive oxygen species (ROS). The importance of this system for innate immunity is established by chronic granulomatous disease (CGD), a primary immunodeficiency caused by defects in the NADPH oxidase. In this review, we present and discuss recent knowledge about p40phox, the last NADPH oxidase component to be identified. Furthermore, its interaction with cellular pathways outside of the NADPH oxidase is discussed. Described in this review is evidence that p40phox participates in NADPH oxidase dynamics within cells, what is known about its role in the oxidase, the possibility that p40phox participates in non-NADPH oxidase processes in phagocytic and non-phagocytic cells and whether p40phox could mediate a similar function in other NADPH oxidases. An improved understanding of p40phox should provide new insights about NADPH oxidase, the physiology of phagocytic cells and the innate immune system.

Effects of renal diseases on the regulation and expression of renal and hepatic drug-metabolizing enzymes: a review

1. The activity of drug-metabolizing enzymes (DMEs) in extrahepatic organs is highest in the kidneys. Generally, the kidneys contain most, if not all, of the DMEs found in the liver. Surprisingly, some of these DMEs show higher activity in the kidneys than in the liver. 2. Most of the renal DMEs are localized in the cortex of the kidneys, especially in the proximal tubules. DMEs are also found in the distal tubules and collecting ducts. 3. Renal diseases such as acute and chronic renal failure and renal cell carcinoma alter the regulation of both hepatic and extrahepatic phase I and II DMEs. Changes in the expression of these DMEs seem to be tissue and species specific. 4. Generally, there is significant down-regulation of most of the phase I and a few of phase II DMEs at the protein, mRNA and activity levels. Unfortunately, the mechanisms leading to the alteration in DMEs in renal diseases remain unclear, although many theories have been made. 5. The presence of some circulating factors such as cytokines, nitric oxide, parathyroid hormones and increased intracellular calcium play a role in the regulation of DMEs in renal diseases.

Garlic's ability to prevent in vitro Cu2+-induced lipoprotein oxidation in human serum is preserved in heated garlic: effect unrelated to Cu2+-chelation

Background

It has been shown that several extracts and compounds derived from garlic are able to inhibit Cu²⁺-induced low density lipoprotein oxidation. In this work we explored if the ability of aqueous garlic extract to prevent in vitro Cu²⁺-induced lipoprotein oxidation in human serum is affected by heating (a) aqueous garlic extracts or (b) garlic cloves. In the first case, aqueous extract of raw garlic and garlic powder were studied. In the second case, aqueous extract of boiled garlic cloves, microwave-treated garlic cloves, and pickled garlic were studied. It was also studied if the above mentioned preparations were able to chelate Cu²⁺.

Methods

Cu²⁺-induced lipoprotein oxidation in human serum was followed by the formation of conjugated dienes at 234 nm and 37°C by 240 min in a phosphate buffer 20 mM, pH 7.4. Blood serum and CuSO₄ were added to a final concentration of 0.67% and 0.0125 mM, respectively. The lag time and the area under the curve from the oxidation curves were obtained. The Cu²⁺-chelating properties of garlic extracts were assessed using an approach based upon restoring the activity of xanthine oxidase inhibited in the presence of 0.050 mM Cu²⁺. The activity of xanthine oxidase was assessed by monitoring the production of superoxide anion at 560 nm and the formation of uric acid at 295 nm. Data were compared by parametric or non-parametric analysis of variance followed by a post hoc test.

Results

Extracts from garlic powder and raw garlic inhibited in a dose-dependent way Cu²⁺-induced lipoprotein oxidation. The heating of garlic extracts or garlic cloves was unable to alter significantly the increase in lag time and the decrease in the area under the curve observed with the unheated garlic extracts or raw garlic. In addition, it was found that the garlic extracts were unable to chelate Cu²⁺.

Conclusions

(a) the heating of aqueous extracts of raw garlic or garlic powder or the heating of garlic cloves by boiling, microwave or pickling do not affect garlic's ability to inhibit Cu²⁺-induced lipoprotein oxidation in human serum, and (b) this ability is not secondary to Cu²⁺-chelation.

Functional role of NADPH oxidase in activation of platelets

Involvement of phagocyte NADPH oxidase in host defense response is well established. In contrast, little is known about the functional role of NADPH oxidase in platelets. In this study, we analyzed involvement of platelet NADPH oxidase in aggregation of human platelets and in amplification of production of reactive oxygen species (ROS) by activated human neutrophils. Apocynin, a known NADPH oxidase inhibitor, as well as superoxide dismutase mimetic Mn(III)tetrakis(1-methyl-1-pyridyl)porphyrin, inhibited ROS generation by collagen-activated platelets, collagen-induced aggregation of platelets, as well as collagen-induced release of thromboxane B2. These data suggest the key role of intracellular ROS derived from NADPH oxidase in the control of thromboxane A2 (TXA2) production in platelets stimulated by collagen. Apocynin also inhibited thrombin-induced ROS production and thrombin-induced platelet aggregation. Activation of neutrophils with latex resulted in an outburst of ROS that was inhibited by apocynin. ROS production by latex-stimulated platelets was modest and also inhibited by apocynin. However, when a mixture of platelets and neutrophils was stimulated with latex, ROS production was three to six times higher in comparison with activation of neutrophils alone. Platelet-dependent augmentation of neutrophil ROS production was abrogated by TXA2 synthase inhibitor (furegrelate, 1 microM) or by aspirin (300 microM). In summary, NADPH oxidase in platelets seems to play a major role as an intracellular signaling mechanism in the activation of platelets. However, in host defense response involving neutrophils and platelets, platelets enhance ROS production by neutrophils and possibly their cytotoxic potential via the release of TXA2, which in turn in platelets is not affected by the extracellular release of free radicals.

Prevention of macrophage adhesion molecule-1 (Mac-1)-dependent neutrophil firm adhesion by taxifolin through impairment of protein kinase-dependent NADPH oxidase activation and antagonism of G protein-mediated calcium influx

Taxifolin has been reported to down-regulate the expression of intercellular adhesion molecule-1 (ICAM-1), a receptor-mediating firm adhesion with beta2 integrin (e.g., Mac-1) expressed on leukocytes. To evaluate whether taxifolin could modulate Mac-1-dependent firm adhesion by neutrophils, and the possible mechanism(s) underlying its anti-inflammatory action, its effects on N-formyl-methionyl-leucyl-phenylalanine (fMLP) or phorbol-12-myristate-13-acetate (PMA)-activated peripheral human neutrophils were studied. Pretreatment with taxifolin (1-100 microM) concentration-dependently diminished fMLP- or (PMA)-induced Mac-1-dependent firm adhesion and upexpression of surface Mac-1. Mobilisation of intracellular calcium and production of reactive oxygen species (ROS) signal the upexpression of Mac-1 and firm adhesion by neutrophils. Taxifolin impeded the calcium influx induced by fMLP (a receptor-mediated activator) or AlF(4)(-) (a G protein-mediated activator). Taxifolin also effectively inhibited the fMLP- or PMA-induced ROS production with 50% inhibitory concentration (IC(50)) less than 10microM, possibly through impairing the activation of NADPH oxidase, a major ROS-generating enzyme in neutrophils, by restricting the activation of p38 mitogen-activated protein kinase (p38 MAPK) and protein kinase C (PKC). In conclusion, we propose that impairment of ROS production by NADPH oxidase through interfering with p38 MAPK- and/or PKC-dependent signals, and antagonism of G protein-mediated calcium influx may account for the inhibition of Mac-1-dependent neutrophil firm adhesion that confers taxifolin the anti-inflammatory activity.

Antioxidant properties of aged garlic extract: an in vitro study incorporating human low density lipoprotein

Oxidation of low-density lipoprotein (LDL) has been recognized as playing an important role in the development and progression of atherosclerotic heart disease. Human LDL was isolated and challenged with a range of oxidants either in the presence or absence of AGE or its diethyl ether extract. Oxidative modification of the LDL fraction using CuSO(4), 5-lipoxygenase and xanthine/xanthine oxidase was monitored by both the appearance of thiobarbituric-acid substances (TBA-RS) and an increase in electrophoretic mobility. This study indicates that AGE is an effective antioxidant as it scavenged superoxide ions and reduced lipid peroxide formation in cell free assays. Superoxide production was completely inhibited in the presence of a 10% (v/v) aqueous preparation of AGE and reduced by 34% in the presence of a 10% (v/v) diethyl ether extract of AGE. The presence of 10% (v/v) diethyl ether extract of AGE significantly reduced Cu(2+) and 15-lipoxygenase-mediated lipid peroxidation of isolated LDL by 81% and 37%, respectively. In addition, it was found that AGE also had the capacity to chelate copper ions. In contrast, the diethyl ether extract of AGE displayed no copper binding capacity, but demonstrated distinct antioxidant properties. These results support the view that AGE inhibits the in vitro oxidation of isolated LDL by scavenging superoxide and inhibiting the formation of lipid peroxides. AGE was also shown to reduce LDL oxidation by the chelation of Cu(2+). Thus, AGE may have a role to play in preventing the development and progression of atherosclerotic disease.

Chromium(III)-induced apoptosis of lymphocytes: death decision by ROS and Src-family tyrosine kinases

Apoptosis is an active process induced by a variety of physiological and external stimuli, in which elimination of damaged cells are effected through a genetically controlled process. In this study, we have examined the mechanism of chromium(III) [Cr(III)]-induced cytotoxicity with respect to its relationship to oxidative stress. Morphology, flow cytometry, and DNA fragmentation studies show that tris-(1,10-phenanthroline)chromium(III) [Cr(III)-phen], tris-(2,2'-bipyridyl)chromium(III) [Cr(III)-bpy], trans-diaqua[1,2-bis(salicylideneamino)ethanechromium(III)] [Cr(III)-salen], and trans-diaqua[1,3-bis(salicylideneamino)propanechromium(III)] [Cr(III)-salprn] induced apoptosis of lymphocytes. Pentaammineaquachromium(III) [Cr(III)-hpa] does not induce apoptosis. Apoptosis induced by these complexes involves the generation of reactive oxygen species (ROS) as seen by increased fluorescence of dichloroflourescein (DCF) observed through flow cytometry. Pretreatment of lymphocytes with antioxidants completely abrogate apoptosis. Cr(III) treatment also increased the expression and activation of Src-family tyrosine kinases viz. p56lck, p59fyn, and p53/56lyn, as seen by immunoblotting and immune complex kinase assay. PP2, a selective Src-family tyrosine kinase inhibitor, abolishes apoptosis, indicating that Src-family tyrosine kinases are directly involved in eliciting apoptosis. Interestingly, a one-to-one correlation between the expression of Src-family tyrosine kinases and ROS is observed, since antioxidants pretreatment inhibits the expression and the activation of these kinases. These results further indicate that Cr(III)-induced apoptosis is mediated through production of ROS, which in turn activates the Src-family tyrosine kinases. The increased activation of Src-family tyrosine kinases may be a mechanism involved in apoptosis of lymphocytes elicited by various other physiological stimuli that exploit ROS as a second messenger.

Oxidant-dependent phosphorylation of p40phox in B lymphocytes

As with the neutrophil NADPH oxidase, the B lymphocyte NADPH oxidase consists of a membrane-bound flavocytochrome b and regulatory factors including Rac and the cytosolic phox protein triad p67phox, p47phox, and p40phox. Here we demonstrate by phosphoamino acid analysis and the use of the potent PKC inhibitor GFX that, in response to stimulation of B lymphocytes with sodium orthovanadate and H(2)O(2), the p40phox component of the cytosolic phox triad is selectively phosphorylated on serine and threonine residues by a PKC-type protein kinase. The pattern of p40phox phosphorylation was closely related to the kinetics of tyrosine phosphorylation of PKC-delta, the main PKC isotype of B lymphocytes. Blocking H(2)O(2)-dependent tyrosine phosphorylation of PKC by genistein resulted in inhibition of p40phox phosphorylation. The correlation between the tyrosine phosphorylation of PKC-delta and the serine/threonine phosphorylation of p40phox, together with the inhibition of p40phox phosphorylation by rottlerin, a selective inhibitor of PKC-delta, makes the activated PKC-delta a likely candidate in the process of the oxidant-dependent phosphorylation of p40phox in B cells.

Effect of overexpression of human Cu/Zn-SOD on activation-induced lymphocyte proliferation and apoptosis

The process of lymphocyte proliferation and apoptosis is known to be linked to oxidative stress. In the present study, we have used a new transgenic mouse model to investigate the effect of human Cu/Zn superoxide dismutase (Cu/Zn-SOD) overexpression on activation-induced lymphocytes proliferation and apoptosis. Cu/Zn-SOD activity was 3.5-fold higher in the spleen of the transgenic mice overexpressing Cu/Zn-SOD (Tg-Cu/Zn-SOD) compared to the wild-type littermates. Proliferative response of lymphocytes to lipopolysaccharide (LPS), Concanavalin A (Con A), and anti-CD3 was measured by [3H]-thymidine incorporation. Activation-induced apoptosis was determined by incubating the T cells with anti-CD3 (primary stimulus) for 72 h, followed by restimulation with Con A (secondary stimulus) for various times. Apoptosis was assessed by measuring DNA fragmentation using a spectrofluorimetric assay and monitoring the expression of the specific apoptotic markers (Fas/CD95 receptor and Fas/CD95 ligand (Fas-L) using flow cytometry. There was no significant difference in proliferative response of lymphocytes to LPS, Con A, or anti-CD3 in transgenic mice overexpressing human Cu/Zn superoxide dismutase (Tg-Cu/Zn-SOD) compared to wild-type littermates. In addition, no significant difference was observed in lymphocyte populations and subsets between Tg-Cu/Zn-SOD mice and wild-type littermates. However, splenic T cells from Tg-Cu/Zn-SOD mice exhibited a significantly (p <.05) higher level of activation-induced DNA fragmentation than T cells from wild-type littermates. The increase in DNA fragmentation was paralleled with an increase in the proportion of T cells expressing Fas and Fas-L molecules. The possible consequences of Cu/Zn-SOD overproduction on activation-induced apoptosis are discussed.

The phagocytosis-associated respiratory burst in human monocytes is associated with increased uptake of glutathione

During the phagocytic respiratory burst, oxygen is converted to potent cytotoxic oxidants. Monocytes and macrophages are potentially long-lived, and we have hypothesized that protective mechanisms against oxidant stress are varied and fully expressed in these cells. We report here that the respiratory burst in monocytes is accompanied by an increase in the uptake of [35S]glutathione ([35S]GSH) after 20-30 min to levels up to 10-fold greater than those at baseline. By 30 min, 49% of the cell-associated radioactivity was in the cytosol, 41% was in membrane, and 10% was associated with the nuclear fraction. GSH uptake was inhibited by catalase, which removes hydrogen peroxide (H2O2), and micromolar H2O2 stimulated GSH uptake effectively in monocytes and also lymphocytes. Oxidation of GSH to glutathione disulfide with H2O2 and glutathione peroxidase prevented uptake. Acivicin, which inhibits GSH breakdown by gamma-glutamyl transpeptidase (GGT), had no effect on the enhanced uptake seen during the respiratory burst. Uptake of cysteine or cystine, possible products of GGT activity, stayed the same or decreased during the respiratory burst. These results suggest that a GGT-independent mechanism is responsible for the enhanced GSH uptake seen during the respiratory burst. We describe here a sodium-independent, methionine-inhibitable transport system with a Km (8.5 microM) for GSH approximating the plasma GSH concentration. These results suggest that monocytes have a specific GSH transporter that is triggered by the release of H2O2 during the respiratory burst and that induces the uptake of GSH into the cell. Such a mechanism has the potential to protect the phagocyte against oxidant damage.

Tyrosine and calcium/calmodulin kinases are common signaling components in the generation of reactive oxygen species in human lymphocytes

This study examined the signaling mechanism involved in the generation of reactive oxygen species (ROS) in human lymphocytes activated by formyl-Met-Leu-Phenylalanine (fMLP; 200 nmol/L) or phorbol-myristate-acetate (PMA; 100 nmol/L). ROS were monitored spectrophotometrically using dichlorofluorescin diacetate. fMLP and PMA significantly increased ROS above the control levels (p<0.05 and 0.001, respectively). These increases were significantly inhibited by catalase, sodium azide, and dimethylsulfoxide but not by superoxide dismutase, suggesting that the ROS apparently included hydrogen peroxide, singlet oxygen and hydroxyl ion but not superoxide anion. PMA-induced responses were reduced by tyrphostin (p<0.01), ST-638 (p<0.05), KN-62 (p<0.001), bisindolylmaleimide (p<0.001), RO-31-8220 (p<0.001), and by LY-83583 (p<0.001), suggesting significant involvement of tyrosine kinase, calcium/calmodulin kinase II, protein kinase C and guanylyl cyclase. fMLP-induced responses were significantly reduced by only tyrphostin (p<0.001), ST-638 (p<0.05), and KN-62 (p<0.01). The results show that tyrosine kinase and calcium/calmodulin kinase II are common signalling components in the production of reactive oxygen species in activated lymphocytes.

Lycopene and beta-carotene protect against oxidative damage in HT29 cells at low concentrations but rapidly lose this capacity at higher doses

Epidemiological studies have clearly demonstrated a link between dietary carotenoids and the reduced incidence of certain diseases, including some cancers. However recent intervention studies (e.g. ATBC, CARET and others) have shown that beta-carotene supplementation has little or no beneficial effect and may, in fact, increase the incidence of lung cancers in smokers. This presents a serious dilemma for the scientific community - are carotenoids at high concentrations actually harmful in certain circumstances? Currently, a significant number of intervention studies are on-going throughout the world involving carotenoids (of both natural and synthetic origin). Our approach has been to study the ability of supplementary carotenoids in protecting cells against oxidatively-induced DNA damage (as measured by the comet assay), and membrane integrity (as measured by ethidium bromide uptake). Both lycopene and beta-carotene only afforded protection against DNA damage (induced by xanthine/xanthine oxidase) at relatively low concentrations (1-3 microM). These levels are comparable with those seen in the plasma of individuals who consume a carotenoid-rich diet. However, at higher concentrations (4-10 microM), the ability to protect the cell against such oxidative damage was rapidly lost and, indeed, the presence of carotenoids may actually serve to increase the extent of DNA damage. Similar data were obtained when protection against membrane damage was studied. This would suggest that supplementation with individual carotenoids to significantly elevate blood and tissue levels is of little benefit and, may, in fact, be deleterious. This in vitro data presented maybe significant in the light of recent intervention trials.