Ethanol-induced gastric damage in the rat: Lack of a correlation with oxygen-derived free radicals

The present study investigated the role of oxygen-derived free radicals as mediators of acute damage to rat gastric mucosae exposed to topically applied absolute ethanol. Although a hydroxyl radical scavenger, Dimethylthiourea, was noted to exhibit profound gastroprotective properties, other pretreatment regimens employing a host of known free radical scavengers, and enzyme inhibitors failed to confirm this hypothesis. Furthermore, no change in mucosal malondialdehyde, an indicator of free radical attack to cell membranes, could be detected in ethanol exposed tissues. Taken together, the present study fails to confirm that oxygen-derived free radicals mediate the gastric damaging effects of topically applied absolute ethanol. ^

Sulforaphane improves cognitive function administered following traumatic brain injury.

Recent studies have shown that sulforaphane, a naturally occurring compound that is found in cruciferous vegetables, offers cellular protection in several models of brain injury. When administered following traumatic brain injury (TBI), sulforaphane has been demonstrated to attenuate blood-brain barrier permeability and reduce cerebral edema. These beneficial effects of sulforaphane have been shown to involve induction of a group of cytoprotective, Nrf2-driven genes, whose protein products include free radical scavenging and detoxifying enzymes. However, the influence of sulforaphane on post-injury cognitive deficits has not been examined. In this study, we examined if sulforaphane, when administered following cortical impact injury, can improve the performance of rats tested in hippocampal- and prefrontal cortex-dependent tasks. Our results indicate that sulforaphane treatment improves performance in the Morris water maze task (as indicated by decreased latencies during learning and platform localization during a probe trial) and reduces working memory dysfunction (tested using the delayed match-to-place task). These behavioral improvements were only observed when the treatment was initiated 1h, but not 6h, post-injury. These studies support the use of sulforaphane in the treatment of TBI, and extend the previously observed protective effects to include enhanced cognition.

Studies of the mechanism of daunorubicin carcinogenesis: Modulation by vitamin E

Daunorubicin (DNR) is an anthracycline antibiotic used as a cancer chemotherapeutic agent. However, it causes mammary adenocarcinomas in female Sprague-Dawley (SD) rats. Vitamin E (E) has been found to reduce DNR carcinogenicity. I investigated the mechanism of DNR carcinogenicity and its interaction with E in SD rats by studying DNR-DNA adduct formation and the influence of E status on DNR clearance and free radical producing and detoxifying enzymes.^ The hypothesis was that DNR exerts its tumorigenic effect via free radicals generated during redox cycling and production of reactive intermediates capable of forming DNA adducts. E was postulated to act as a protective agent through a combination of its antioxidant property, modulation of drug clearance and levels of free radical producing and detoxifying enzymes.^ DNA adduct formation was measured by the nuclease P1 $\sp{32}$P-post labeling assay. In vitro, DNR was activated by rat liver microsomes and either NADPH or cumene hydrogen peroxide (CuOOH). Rat liver DNA incubated with this mixture formed two adducts when the cofactor was NADPH and three adducts when CuOOH was used. In vivo, SD rats were treated with i.v. doses of DNR. No detectable DNR-DNA adducts were formed in liver or mammary DNA in vivo, although there was an intensification of endogenous DNA adducts.^ Groups, 1, 2, 3 and 4 of weanling female SD rats were fed 0, 100, 1,000 and 10,000 mg $\alpha$-tocopheryl acetate/kg diet respectively. A comparison of Groups 1 and 4 showed no effect of E status on clearance of 10 mg tritiated DNR/kg body weight over 72 hours. However, liver cleared DNR at a faster rate than mammary epithelial cells (MEC).^ Xanthine oxidase, which catalyzes DNR redox cycling, was significantly decreased in liver and MEC of rats in group 4 compared to groups 1, 2, and 3. Detoxifying enzymes were not dramatically affected by E supplementation. Quinone reductase in MEC was significantly increased in group 4 compared to other groups. Overall, the liver had higher levels of free radical detoxifying enzymes compared to MEC.^ These data support a role of free radicals in DNR carcinogenicity because (1) endogenous DNA adducts formed due to free radical insult are further intensified by DNR treatment in vivo, (2) MEC, the specific target of DNR carcinogenicity, cannot rapidly clear DNR and have a lower free radical detoxifying capability than liver, (3) E supplementation caused lowering of free radical generating potential via xanthine oxidase, and increased DNR detoxification due to elevation of quinone reductase in MEC. ^

Structure and function study of prostaglandin H synthase

Prostaglandin H synthase (PGHS) is a key enzyme in biosynthesis of prostaglandins, thromboxane, and prostacyclin. It has two activities, cyclooxygenase and peroxidase. "PGHS" means PGHS-1. A current hypothesis considers the cyclooxygenase reaction to be a free radical chain reaction, initiated by interaction of the synthase peroxidase with hydroperoxides leading to the production of a tyrosyl free radical. According to this hypothesis, tyrosyl residue(s) may play a key role in the cyclooxygenase reaction. Tetranitromethane (TNM) can relatively selectively nitrate tyrosines at pH 8.0. The effect of TNM on both cyclooxygenase activity and peroxidase activity has been examined: reaction of the synthase holoenzyme with TNM at pH 8.0 led to inactivation of both activities, with the cyclooxygenase activity being lost rapidly and completely, while the peroxidase activity was lost more slowly. Indomethacin, a non-steroidal anti-inflammatory agent, can protect the synthase from the inactivation of TNM. Amino acid analyses indicated that a loss of tyrosine and formation of nitrotyrosine residues occurred during reaction with TNM, and that TNM-reacted holoenzyme with $<$10% residual cyclooxygenase activity had about 2.0 nitrotyrosine/subunit.^ PGH synthase is known to be an endoplasmic reticulum membrane-associated protein. Antibodies directed at particular PGHS peptide segments and indirect immunofluorescence have been used to characterize the membrane topology of crucial portions of PGHS. PGHS was expressed in COS-1 cells transfected with the appropriate cDNA. Stably-transfected human endothelial cells were also used for the topology study. The cells were treated with streptolysin-O, which selectively permeabilizes the plasma membrane, or with saponin to achieve general membrane disruption, before incubation with the antipeptide antibodies. Bound antipeptide antibody was stained by FITC-labelled secondary antibody and visualized by fluorescence microscopy. With the antipeptide antibodies against residues 51-66, 156-170 or 377-390, there was a significant reticular and perinuclear pattern of staining in cells permeabilized with saponin but not in cells permeabilized with SLO alone. Antibodies directed against the endogenous C-terminal peptide or against residues 271-284 produced staining in cells permeabilized with saponin, and also in a lower, but significant fraction of cells permeabilized with SLO. Similar results were obtained when COS-1 cells expressing recombinant PGHS with a viral reporter peptide inserted at the C-terminus were stained with antibody against the reporter epitope.^ The PGHS C-terminal sequence is similar to that of the consensus KDEL ER retention signal. The potential function of the PGHS C-terminus segment in ER retention was examined by mutating this segment and analyzing the subcellular distribution of the mutants expressed in COS-1 cells. None of the mutants had an altered subcellular distribution, although some had greatly diminished the enzyme activities. (Abstract shortened by UMI.) ^

ROLE OF GLUTATHIONE IN FORMALDEHYDE METABOLISM AND TOXICITY

Glutathione (GSH) is involved in the detoxication of numerous chemicals exogenously exposed or endogenously generated. Exposure to these agents cause depletion of cellular GSH rendering these cells more susceptible to the toxic action of these same agents. Formaldehyde (CH(,2)O) was found to deplete cellular GSH, presumably by the formation of the GSH-CH(,2)O complex, S-hydroxymethylglutathione, and its rapid extrusion into the extracellular medium.^ The metabolism and toxicity of CH(,2)O were determined to be dependent upon cellular GSH in vitro and in vivo. The rate of CH(,2)O oxidation decreased and the extent of toxicity increased when isolated rat hepatocytes or strain A/J mice were pretreated with the GSH-depleting agent, diethyl maleate (DEM). Additional experiments were designed to further study the role GSH plays in detoxication using isolated rat hepatocytes.^ L-Methionine protected against the extent of lipid peroxidation and leakage of the cytosolic enzyme, lactate dehydrogenase (LDH), caused by CH(,2)O in DEM-pretreated hepatocytes, further supporting the protective role of GSH against cellular toxicity. The antioxidants, ascorbate, butylated hydroxytoluene, and (alpha)-tocopherol, were all protective against the extent of lipid peroxidation and leakage of LDH in isolated rat hepatocytes. Whereas L-methionine may be protective by increasing the cellular concentration of GSH which is used to detoxify free radicals or by facilitating the rate of CH(,2)O oxidation, the antioxidant, ascorbate, was protective without altering the rate of CH(,2)O oxidation or increasing cellular GSH levels. These results suggest that the free radical-mediated toxicity caused by CH(,2)O in DEM-pretreated hepatocytes is due to the further depletion of GSH by CH(,2)O and not to increased CH(,2)O persistence. How this further depletion in GSH by CH(,2)O in DEM-pretreated hepatocytes results in lipid peroxidation and cell death was further investigated.^ The further decrease in GSH caused by CH(,2)O in DEM-pretreated hepatocytes, suspected of stimulating lipid peroxidation and cell death, was found not to be due to depletion of mitochondrial GSH but to depletion of protein sulfhydryl groups. In addition, cellular toxicity appears more closely correlated with depletion of protein sulfhydryl groups than with an increase in cytosolic free Ca('2+). The combination of CH(,2)O and DEM may be a useful tool in identifying these critical sulfhydryl-protein(s) and to further understand the role GSH plays in detoxication. ^

THE EFFECTS OF STREPTOZOTOCIN DIABETES AND DIETARY IRON INTAKE ON CATALASE, GLUTATHIONE PEROXIDASE, SUPEROXIDE DISMUTASE AND LIPID PEROXIDATION IN CARDIAC AND SKELETAL MUSCLES OF RATS

Catalase, glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) prevent oxygen free radical mediated tissue damage. Diabetes increases and a low dietary intake of iron decreases catalase activity in muscle. Therefore, the combined effects of diabetes and iron deficiency on the free radical scavenging enzyme system and lipid peroxidation were studied. Male, weanling rats were injected with streptozotocin (65 mg/kg, IV) and fed diets containing either 35 ppm iron (Db + Fe) or 8 ppm iron (Db $-$ Fe). Sham injected animals served as iron adequate (C + Fe) or iron deficient (C $-$ Fe) controls. Heart, gastrocnemius (GT), soleus and tibialis anterior (TA) muscles were dissected, weighted and analyzed for catalase, GSH-Px and SOD activities after 3, 6 or 9 weeks on the respective diets. The TBA assay was used to assess lipid peroxidation in the GT muscle. Diabetes elevated catalase activity in all muscles while it had a slight lowering effect on SOD and GSH-Px activities in the GT and TA muscles. In the C $-$ Fe rats, catalase activity declined and remained depressed in all muscles except the heart. There was an elevation in GSH-Px and SOD in the GT muscles of these animals after 6 weeks but not after 9 weeks of consuming the low iron diet. The Db $-$ Fe animals were unable to respond to the diabetic state with catalase activity as high as observed in the Db + Fe rats. Treatment with insulin or iron returned catalase to control levels. The C $-$ Fe animals had significantly lower levels of lipid peroxidation than the other groups at 6 and 9 weeks. Refeeding an iron adequate diet resulted in an increase in lipid peroxidation levels. These studies indicate that skeletal muscle free radical scavenging enzymes are sensitive to metabolic states and that dietary iron influences lipid peroxidation in this tissue. ^

INDUCTION OF DNA STRAND BREAKS AND CROSS-LINKS BY THE NEW ANTICANCER AGENT 3,6-DIAZIRIDINYL-2,5-BIS(CARBOETHOXYAMINO) -1,4-BENZOQUINONE

The DNA breakage effect of the anticancer agent 3,6-diaziridinyl-2,5-bis(carboethoxyamino)-1,4-benzoquinone (AZQ, NSC-182986) on bacteriophage PM2 DNA was investigated using agarose gel electrophoresis. AZQ caused both single-stranded and double-stranded breaks after reduction with NaBH(,4), but it was not active in the native state. At 120 (mu)M, it degraded 50% of the closed circular form I DNA into 40% form II DNA (single-stranded break) and 10% form III DNA (double-stranded break). It produced a dose-response breakage between 1 (mu)M and 320 (mu)M. The DNA breakage exhibited a marked pH dependency. At 320 (mu)M, AZQ degraded 80% and 60% of form I DNA at pH 4 and 10 respectively, but none between pH 6 to 8. The DNA breakage at physiologic pH was greatly enhanced when 10 (mu)M cupric sulfate was included in the incubation mixture. The DNA strand scission was inhibited by catalase, glutathione, KI, histidine, Tiron, and DABCO. These results suggest that the DNA breakage may be caused by active oxygen metabolites including hydroxyl free radical. The bifunctional cross-linking activity of reduced AZQ on isolated calf thymus DNA was investigated by ethidium fluorescence assay. The cross-linking activity exhibited a similar pH dependency; highest in acidic and alkaline pH, inactive under neutral conditions. Using the alkaline elution method, we found that AZQ induced DNA single-stranded breaks in Chinese hamster ovary cells treated with 50 (mu)M of AZQ for 2 hr. The single-stranded break frequencies in rad equivalents were 17 with 50 (mu)M and 140 with 100 (mu)M of AZQ. In comparison, DNA cross-links appeared in cells treated with only 1 to 25 (mu)M of AZQ for 2 hr. The cross-linking frequencies in rad equivalents were 39 and 90 for 1 and 5 (mu)M of AZQ, respectively. Both DNA-DNA and DNa-protein cross-links were induced by AZQ in CHO cells as revealed by the proteinas K digestion assay. DNA cross-links increased within the first 4 hr of incubation in drug-free medium and slightly decreased by 12 hr, and most of the cross-links disappeared after cells were allowed to recovered for 24 hr.^ By electrochemical analysis, we found that AZQ was more readily reduced at acidic pH. However, incubation of AZQ with NaBH(,4) at pH 7.8 or 10, but not at 4, produced superoxide anion. The opening of the aziridinyl rings of AZQ at pH 4 was faster in the presence of NaBH(,4) than in its absence; no ring-opening was detected at pH 7.8 regardless of the inclusion of NaBH(,4). . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI ^

Mitochondrial defects in primary leukemia cells: Biological consequences and therapeutic implications

Mitochondria are actively engaged in the production of cellular energy sources, generation of reactive oxygen species (ROS), and regulation of apoptosis. Mitochondrial DNA (mtDNA) mutations/deletions and other mitochondrial abnormalities have been implicated in many diseases, especially cancer. Despite this, the roles that these defects play in cancer development, drug sensitivity, and disease progression still remain to be elucidated. The major objective of this investigation was to evaluate the mechanistic relationship between mitochondrial defects and alterations in free radical generation and chemosensitivity in primary chronic lymphocytic leukemia (CLL) cells. This study revealed that the mtDNA mutation frequency and basal superoxide generation are both significantly higher in primary cells from CLL patients with a history of chemotherapy as compared to cells from their untreated counterparts. CLL cells from refractory patients tended to have high mutation frequencies. The data suggest that chemotherapy with DNA-damaging agents may cause mtDNA mutations, which are associated with increased ROS generation and reduced drug sensitivity. Subsequent analyses demonstrated that CLL cells contain significantly more mitochondria than normal lymphocytes. This abnormal accumulation of mitochondria was linked to increased expression of nuclear respiratory factor-1 and mitochondrial transcription factor A, two key free radical-regulated mitochondrial biogenesis factors. Further analysis showed that mitochondrial content may have therapeutic implications since patient cells with high mitochondrial mass display significantly reduced in vitro sensitivity to fludarabine, a frontline agent in CLL therapy. The reduced in vitro and in vivo sensitivity to fludarabine observed in CLL cells with mitochondrial defects highlights the need for novel therapeutic strategies for the treatment of refractory disease. Brefeldin A, an inhibitor of endoplasmic reticulum (ER) to Golgi protein transport that is being developed as an anticancer agent, effectively induces apoptosis in fludarabine-refractory CLL cells through a secretory stress-mediated mechanism involving intracellular sequestration of pro-survival secretory factors. Taken together, these data indicate that mitochondrial defects in CLL cells are associated with alterations in free radical generation, mitochondrial biogenesis activity, and chemosensitivity. Abrogation of survival signaling by blocking ER to Golgi protein transport may be a promising therapeutic strategy for the treatment of CLL patients that respond poorly to conventional chemotherapy. ^

Intrinsic oxidative stress in cancer cells: A biochemical basis for therapeutic selectivity using ROS -generating agents

A major goal of chemotherapy is to selectively kill cancer cells while minimizing toxicity to normal cells. Identifying biological differences between cancer and normal cells is essential in designing new strategies to improve therapeutic selectivity. Superoxide dismutases (SOD) are crucial antioxidant enzymes required for the elimination of superoxide (O2·− ), a free radical produced during normal cellular metabolism. Previous studies in our laboratory demonstrated that 2-methoxyestradiol (2-ME), an estradiol derivative, inhibits the function of SOD and selectively kills human leukemia cells without exhibiting significant cytotoxicity in normal lymphocytes. The present work was initiated to examine the biochemical basis for the selective anticancer activity of 2-ME. Investigations using two-parameter flow cytometric analyses and ROS scavengers established that O2·− is a primary and essential mediator of 2-ME-induced apoptosis in cancer cells. In addition, experiments using SOD overexpression vectors and SOD knockout cells found that SOD is a critical target of 2-ME. Importantly, the administration of 2-ME resulted in the selective accumulation of O 2·− and apoptosis in leukemia and ovarian cancer cells. The preferential activity of 2-ME was found to be due to increased intrinsic oxidative stress in these cancer cells versus their normal counterparts. This intrinsic oxidative stress was associated with the upregulation of the antioxidant enzymes SOD and catalase as a mechanism to cope with the increase in ROS. Furthermore, oxygen consumption experiments revealed that normal lymphocytes decrease their respiration rate in response to 2-ME-induced oxidative stress, while human leukemia cells seem to lack this regulatory mechanism. This leads to an uncontrolled production of O2·−, severe accumulation of ROS, and ultimately ROS-mediated apoptosis in leukemia cells treated with 2-ME. The biochemical differences between cancer and normal cells identified here provide a basis for the development of drug combination strategies using 2-ME with other ROS-generating agents to enhance anticancer activity. The effectiveness of such a combination strategy in killing cancer cells was demonstrated by the use of 2-ME with agents/modalities such as ionizing radiation and doxorubicin. Collectively, the data presented here strongly suggests that 2-ME may have important clinical implications for the selective killing of cancer cells. ^