Differential Effects of MitoVitE, α-Tocopherol and Trolox on Oxidative Stress, Mitochondrial Function and Inflammatory Signalling Pathways in Endothelial Cells Cultured under Conditions Mimicking Sepsis

Sepsis is a life-threatening response to infection associated with inflammation, oxidative stress and mitochondrial dysfunction. We investigated differential effects of three forms of vitamin E, which accumulate in different cellular compartments, on oxidative stress, mitochondrial function, mRNA and protein expression profiles associated with the human Toll-like receptor (TLR) -2 and -4 pathways. Human endothelial cells were exposed to lipopolysaccharide (LPS)/peptidoglycan G (PepG) to mimic sepsis, MitoVitE, α-tocopherol, or Trolox. Oxidative stress, mitochondrial function, mitochondrial membrane potential and metabolic activity were measured. NFκB-P65, total and phosphorylated inhibitor of NFκB alpha (NFκBIA), and STAT-3 in nuclear extracts, interleukin (IL)-6 and IL-8 production in culture supernatants and cellular mRNA expression of 32 genes involved in Toll-like receptor-2 and -4 pathways were measured. Exposure to LPS/PepG caused increased total radical production (p = 0.022), decreased glutathione ratio (p = 0.016), reduced membrane potential and metabolic activity (both p < 0.0001), increased nuclear NFκB-P65 expression (p = 0.016) and increased IL-6/8 secretion (both p < 0.0001). MitoVitE, α- tocopherol and Trolox were similar in reducing oxidative stress, NFκB activation and interleukin secretion. MitoVitE had widespread downregulatory effects on gene expression. Despite differences in site of actions, all forms of vitamin E were protective under conditions mimicking sepsis. These results challenge the concept that protection inside mitochondria provides better protection.

MitoVitE, a mitochondria-targeted antioxidant, limits paclitaxel-induced oxidative stress and mitochondrial damage in vitro, and paclitaxel-induced mechanical hypersensitivity in a rat pain model

BACKGROUND

Neuropathic pain is a common side-effect of chemotherapy. Although precise mechanisms are unclear, oxidative stress and mitochondrial damage are involved. We investigated whether the mitochondria targeted antioxidant, MitoVitE, provided better protection against paclitaxel-induced mitochondrial damage in rat dorsal root ganglion (DRG) cells, than a non-targeted form of vitamin E, Trolox. We also determined whether MitoVitE, compared with duloxetine, could limit paclitaxel-induced mechanical hypersensitivity in rats.

METHODS

Mitochondrial function was measured in DRG cells exposed to paclitaxel with and without MitoVitE or Trolox. The effect of MitoVitE or Trolox on paclitaxel-induced cell killing in cancer cell lines was also determined. Rats received a cumulative dose of 8 mg kg^-1 paclitaxel plus either MitoVitE (2 mg^-1 kg day^-1), duloxetine (10 mg kg^-1 day^-1) or vehicle control daily. Mechanical hind paw withdrawal thresholds were measured every two days.

RESULTS

Paclitaxel caused loss of membrane potential in DRG cells. At 100 µM paclitaxel median [range] change was 61[44-78]%, P < 0.0001, which was ameliorated by MitoVitE (86[62-104]%) but not Trolox (46[46-57]%). Similarly, loss of metabolic activity and glutathione induced by paclitaxel (both P < 0.0001) were reduced by MitoVitE but not Trolox. Cytotoxicity of paclitaxel was not affected by co-exposure of ovarian cancer cells to either MitoVitE or Trolox, but was slightly reduced against breast cancer cells, in the presence of Trolox. Mean (SD) areas under the curve of withdrawal thresholds at 6 h after injection in rats given paclitaxel + control, or + MitoVitE (P < 0.0001) or + duloxetine (P < 0.0001) were 110 (5), 145 (10) and 156 (13) respectively.

CONCLUSIONS

Paclitaxel affected mitochondrial function and glutathione in DRG cells, which was abrogated by MitoVitE but not Trolox, without decreasing cancer cell cytotoxicity. In rats, paclitaxel-induced mechanical hypersensitivity was ameliorated by MitoVitE treatment to an extent similar to duloxetine. These data confirm mitochondria as a mechanistic target for paclitaxel-induced damage and suggest mitochondria targeted antioxidants as future therapeutic strategies.

Melatonin limits paclitaxel-induced mitochondrial dysfunction in vitro and protects against paclitaxel-induced neuropathic pain in the rat

Chemotherapy-induced neuropathic pain is a debilitating and common side effect of cancer treatment. Mitochondrial dysfunction associated with oxidative stress in peripheral nerves has been implicated in the underlying mechanism. We investigated the potential of melatonin, a potent antioxidant that preferentially acts within mitochondria, to reduce mitochondrial damage and neuropathic pain resulting from the chemotherapeutic drug paclitaxel. In vitro, paclitaxel caused a 50% reduction in mitochondrial membrane potential and metabolic rate, independent of concentration (20-100 μmol/L). Mitochondrial volume was increased dose-dependently by paclitaxel (200% increase at 100 μmol/L). These effects were prevented by co-treatment with 1 μmol/L melatonin. Paclitaxel cytotoxicity against cancer cells was not affected by co-exposure to 1 μmol/L melatonin of either the breast cancer cell line MCF-7 or the ovarian carcinoma cell line A2780. In a rat model of paclitaxel-induced painful peripheral neuropathy, pretreatment with oral melatonin (5/10/50 mg/kg), given as a daily bolus dose, was protective, dose-dependently limiting development of mechanical hypersensitivity (19/43/47% difference from paclitaxel control, respectively). Melatonin (10 mg/kg/day) was similarly effective when administered continuously in drinking water (39% difference). Melatonin also reduced paclitaxel-induced elevated 8-isoprostane F₂ α levels in peripheral nerves (by 22% in sciatic; 41% in saphenous) and limited paclitaxel-induced reduction in C-fibre activity-dependent slowing (by 64%). Notably, melatonin limited the development of mechanical hypersensitivity in both male and female animals (by 50/41%, respectively), and an additive effect was found when melatonin was given with the current treatment, duloxetine (75/62% difference, respectively). Melatonin is therefore a potential treatment to limit the development of painful neuropathy resulting from chemotherapy treatment.

Pharmacological activation of endogenous protective pathways against oxidative stress under conditions of sepsis

BACKGROUND

Mitochondrial oxidative stress has a role in sepsis-induced organ dysfunction. The endogenous mechanisms to initiate protective pathways are controlled by peroxisome proliferator-activated receptor gamma co-activator 1-alpha (PGC1α) and nuclear factor erythroid 2-like 2 (NFE2L2). Activation of these pathways are potential therapeutic targets in sepsis. We used pharmacological activators to determine the effects on markers of mitochondrial damage and inflammation in human endothelial cells under conditions of sepsis.

METHODS

Human endothelial cells were exposed to lipopolysaccharide plus peptidoglycan G to mimic a sepsis environment, with a range of concentrations of a selective synthetic agonist of silent information regulator-1 (SIRT-1) which activates PGC1α, or bis(2-hydroxy-benzylidene) acetone (2HBA) which activates NFE2L2, with and without inhibitors of these pathways. Cells were cultured for up to seven days and we measured mitochondrial membrane potential, metabolic activity, and density (as a marker of biogenesis), interkeukin-6 (to reflect inflammation) and glutathione (as a measure of antioxidant status).

RESULTS

Under conditions mimicking sepsis, activation of the PGC1α and NFE2L2 pathways protected cells from LPS/PepG-induced loss of mitochondrial membrane potential (P=0.0002 and P=0.0009, respectively) and metabolic activity (P=0.05 and P<0.0001, respectively), and dampened interleukin-6 responses (P=0.003 and P=0.0001, respectively). Mitochondrial biogenesis (both P=0.0001) and glutathione (both P<0.0001) were also increased. These effects were blunted by the respective inhibitors.

CONCLUSIONS

The development of organ dysfunction during human sepsis is linked to mitochondrial dysfunction, and so activation of PGC1α/NFE2L2 is likely to be beneficial. These pathways are attractive therapeutic targets for sepsis.

Low zinc and selenium concentrations in sepsis are associated with oxidative damage and inflammation

BACKGROUND

Oxidative stress with dysregulated inflammation are hallmarks of sepsis. Zinc and selenium have important antioxidant functions, such that they could be important in patients with sepsis. We used an in vitro approach to assess the effect of zinc and selenium on oxidative stress, mitochondrial function, and inflammatory responses in conditions mimicking sepsis and related the findings to plasma concentrations and biomarkers in patients with and without sepsis.

METHODS

Human endothelial cells were exposed to a range of zinc and selenium concentrations in conditions mimicking sepsis. Zinc, selenium, and a series of biomarkers of oxidative stress and inflammation were measured in plasma from critically ill patients with and without sepsis.

RESULTS

Culturing cells with different concentrations of zinc caused altered zinc transporter protein expression and cellular zinc content, and selenium affected glutathione peroxidase 3 activity. Although zinc or selenium at physiological concentrations had no effect on interleukin-6 release in vitro, higher concentrations of the trace elements were associated with improved mitochondrial function. Plasma zinc and selenium concentrations were low in patients [zinc: median (range) 4.6 (2.1-6.5) μM in control patients without sepsis and 3.1 (1.5-5.4) μM in patients with sepsis, P=0.002; and selenium: 0.78 (0.19-1.32) μM in control patients and 0.42 (0.22-0.91) μM in sepsis patients, P=0.0009]. Plasma concentrations of interleukin-6, other biomarkers of inflammation, and markers of oxidative damage to proteins and lipids were elevated, particularly in patients with sepsis, and were inversely related to plasma zinc and selenium concentrations.

CONCLUSIONS

Zinc and selenium concentrations were reduced in critically ill patients, with increased oxidative stress and inflammatory biomarkers, particularly in patients with sepsis. Oxidative stress as a result of suboptimal selenium and zinc concentrations might contribute to damage of key proteins.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov: registration number NCT01328509.

Melatonin as a potential therapy for sepsis: a phase I dose escalation study and an ex vivo whole blood model under conditions of sepsis

Sepsis is a massive inflammatory response mediated by infection, characterized by oxidative stress, release of cytokines, and mitochondrial dysfunction. Melatonin accumulates in mitochondria, and both it and its metabolites have potent antioxidant and anti-inflammatory activities and may be useful in sepsis. We undertook a phase I dose escalation study in healthy volunteers to assess the tolerability and pharmacokinetics of 20, 30, 50, and 100 mg oral doses of melatonin. In addition, we developed an ex vivo whole blood model under conditions mimicking sepsis to determine the bioactivity of melatonin and the major metabolite 6-hydroxymelatonin at relevant concentrations. For the phase I trial, oral melatonin was given to five subjects in each dose cohort (n = 20). Blood and urine were collected for measurement of melatonin and 6-hydroxymelatonin, and symptoms and physiological measures were assessed. Validated sleep scales were completed. No adverse effects after oral melatonin, other than mild transient drowsiness with no effects on sleeping patterns, were seen, and no symptoms were reported. Melatonin was rapidly cleared at all doses with a median [range] elimination half-life of 51.7 [29.5-63.2] min across all doses. There was considerable variability in maximum melatonin levels within each dose cohort, but 6-hydoxymelatonin sulfate levels were less variable and remained stable for several hours. For the ex vivo study, blood from 20 volunteers was treated with lipopolysaccharide and peptidoglycan plus a range of concentrations of melatonin/6-hydroxymelatonin. Both melatonin and 6-hydroxymelatonin had beneficial effects on sepsis-induced mitochondrial dysfunction, oxidative stress, and cytokine responses at concentrations similar to those achieved in vivo.

Antioxidants that protect mitochondria reduce interleukin-6 and oxidative stress, improve mitochondrial function, and reduce biochemical markers of organ dysfunction in a rat model of acute sepsis

Background

Sepsis-induced organ failure is the major cause of death in critical care units, and is characterized by a massive dysregulated inflammatory response and oxidative stress. We investigated the effects of treatment with antioxidants that protect mitochondria (MitoQ, MitoE, or melatonin) in a rat model of lipopolysaccharide (LPS) plus peptidoglycan (PepG)-induced acute sepsis, characterized by inflammation, mitochondrial dysfunction and early organ damage.

Methods

Anaesthetized and ventilated rats received an i.v. bolus of LPS and PepG followed by an i.v. infusion of MitoQ, MitoE, melatonin, or saline for 5 h. Organs and blood were then removed for determination of mitochondrial and organ function, oxidative stress, and key cytokines.

Results

MitoQ, MitoE, or melatonin had broadly similar protective effects with improved mitochondrial respiration (P<0.002), reduced oxidative stress (P<0.02), and decreased interleukin-6 levels (P=0.0001). Compared with control rats, antioxidant-treated rats had lower levels of biochemical markers of organ dysfunction, including plasma alanine amino-transferase activity (P=0.02) and creatinine concentrations (P<0.0001).

Conclusions

Antioxidants that act preferentially in mitochondria reduce mitochondrial damage and organ dysfunction and decrease inflammatory responses in a rat model of acute sepsis.

Dehydroascorbic acid as pre-conditioner: protection from lipopolysaccharide induced mitochondrial damage

Oxidative stress-induced mitochondrial dysfunction is a common consequence of severe sepsis. However, oxidative stress also activates signalling cascades which enable protection of cells against subsequent oxidative damage. This study hypothesized that cellular uptake of vitamin C as dehydroascorbic acid rather than ascorbic acid would up-regulate antioxidant enzyme systems and impart a protective effect to mitochondria in cells subsequently exposed to lipopolysaccharide (LPS) in an iron free environment. Treatment of monocytes with dehydroascorbic acid, but not ascorbic acid, caused oxidative stress (p< 0.001). Dehydroascorbic acid exposure also resulted in increased manganese superoxide dismutase (p= 0.018) and catalase (p= 0.003) expression. Pre-treatment of monocytes with dehydroascorbic acid followed by LPS resulted in higher mitochondrial membrane potentials than cells without pre-treatment (p< 0.0001). Lower cytochrome c in cytosol (p< 0.05) and higher mitochondrial expression of the anti-apoptotic Bcl-2 protein (p= 0.029) was also found in monocytes pre-treated before subsequent LPS exposure, compared to cells without pre-treatment. In conclusion, acute exposure of monocytes to dehydroascorbic acid in an iron free environment induces cytoprotective antioxidant enzymes and protected mitochondria from the harmful effects of oxidative stress prior to a septic insult, which was abrogated when cells were pre-incubated with the DHA uptake inhibitor cytocholasin B.

Regulation of pentraxin-3 by antioxidants

BACKGROUND

Pentraxin-3 (PTX3) may be a useful biomarker in sepsis, but its regulatory mechanisms are still unclear. Oxidative stress is well defined in patients with sepsis and has a role in regulation of inflammatory pathways which may include PTX3. We undertook an in vitro study of the effect of antioxidants on regulation of PTX3 in endothelial cells combined with a prospective observational pilot study of PTX3 in relation to markers of antioxidant capacity and oxidative stress in patients with sepsis.

METHODS

Human endothelial cells were cultured with lipopolysaccharide 2 microg ml(-1), peptidoglycan G 20 microg ml(-1), tumour necrosis factor (TNF) alpha 10 ng ml(-1), interleukin-1 (IL-1) beta 20 ng ml(-1), or killed Candida albicans yeast cells plus either N-acetylcysteine (NAC) 25 mM, trolox 100 mM, or idebenone 1 microM. Plasma samples were obtained from 15 patients with sepsis and 11 healthy volunteers.

RESULTS

PTX3 levels in plasma were higher in patients with sepsis than in healthy people [26 (1-202) ng ml(-1) compared with 6 (1-12) ng ml(-1), P=0.01]. Antioxidant capacity was lower in patients with sepsis than healthy controls [0.99 (0.1-1.7) mM compared with 2.2 (1.3-3.3) mM, P=0.01]. In patients with sepsis, lipid hydroperoxide levels were 3.32 (0.3-10.6) nM and undetectable in controls. We found no relationship between PTX3 and antioxidant capacity or lipid hydroperoxides. Cell expression of PTX3 increased with all inflammatory stimulants but was highest in cells treated with TNFalpha plus IL-1beta. PTX3 concentrations were lower in cells co-treated with antioxidants (all P<0.05), associated with lower nuclear factor kappaB expression for NAC and trolox (P<0.05).

CONCLUSIONS

PTX3 expression is down-regulated in vitro by antioxidants. Plasma levels of PTX3 are elevated in sepsis but seem to be unrelated to markers of oxidant stress or antioxidant capacity.

The mitochondria targeted antioxidant MitoQ protects against fluoroquinolone-induced oxidative stress and mitochondrial membrane damage in human Achilles tendon cells

Tendinitis and tendon rupture during treatment with fluoroquinolone antibiotics is thought to be mediated via oxidative stress. This study investigated whether ciprofloxacin and moxifloxacin cause oxidative stress and mitochondrial damage in cultured normal human Achilles' tendon cells and whether an antioxidant targeted to mitochondria (MitoQ) would protect against such damage better than a non-mitochondria targeted antioxidant. Human tendon cells from normal Achilles' tendons were exposed to 0-0.3 mM antibiotic for 24 h and 7 days in the presence of 1 microM MitoQ or an untargeted form, idebenone. Both moxifloxacin and ciprofloxacin resulted in up to a 3-fold increase in the rate of oxidation of dichlorodihydrofluorescein, a marker of general oxidative stress in tenocytes (p<0.0001) and loss of mitochondrial membrane permeability (p<0.001). In cells treated with MitoQ the oxidative stress was less and mitochondrial membrane potential was maintained. Mitochondrial damage to tenocytes during fluoroquinolone treatment may be involved in tendinitis and tendon rupture.

The mitochondria-targeted antioxidant MitoQ protects against organ damage in a lipopolysaccharide-peptidoglycan model of sepsis

Sepsis is characterised by a systemic dysregulated inflammatory response and oxidative stress, often leading to organ failure and death. Development of organ dysfunction associated with sepsis is now accepted to be due at least in part to oxidative damage to mitochondria. MitoQ is an antioxidant selectively targeted to mitochondria that protects mitochondria from oxidative damage and which has been shown to decrease mitochondrial damage in animal models of oxidative stress. We hypothesised that if oxidative damage to mitochondria does play a significant role in sepsis-induced organ failure, then MitoQ should modulate inflammatory responses, reduce mitochondrial oxidative damage, and thereby ameliorate organ damage. To assess this, we investigated the effects of MitoQ in vitro in an endothelial cell model of sepsis and in vivo in a rat model of sepsis. In vitro MitoQ decreased oxidative stress and protected mitochondria from damage as indicated by a lower rate of reactive oxygen species formation (P=0.01) and by maintenance of the mitochondrial membrane potential (P<0.005). MitoQ also suppressed proinflammatory cytokine release from the cells (P<0.05) while the production of the anti-inflammatory cytokine interleukin-10 was increased by MitoQ (P<0.001). In a lipopolysaccharide-peptidoglycan rat model of the organ dysfunction that occurs during sepsis, MitoQ treatment resulted in lower levels of biochemical markers of acute liver and renal dysfunction (P<0.05), and mitochondrial membrane potential was augmented (P<0.01) in most organs. These findings suggest that the use of mitochondria-targeted antioxidants such as MitoQ may be beneficial in sepsis.

Antiserum detection of reactive carbonyl species-modified DNA in human colonocytes

Polyunsaturated fats have been linked to occurrences of sporadic colon cancer. One possible cause may be degradation of polyunsaturated fats during cooking, resulting in multiple reactive carbonyl species (RCS) that can damage nuclear DNA and proteins, particularly in rapidly dividing colon crypt cells. This study describes a novel antiserum against RCS-modified DNA, with apparent order of reactivity to DNA modified with 4-hydroxy-trans-2-nonenal > glyoxal > acrolein > crotonaldehyde > malondialdehyde; some reactivity was also observed against conjugated Schiff base-type structures. Anti-(RCS-DNA) antiserum was successfully utilised to demonstrate formation of RCS-DNA in a human colon cell model, exposed to RCS insult derived from endogenous and exogenous lipid peroxidation sources. Further utilisation of the antiserum for immunohistochemical analysis confirmed RCS-modified DNA in crypt areas of 'normal' colon tissue. These results fully support a potential role for dietary lipid peroxidation products in the development of sporadic colon cancer.

Production of soluble triggering receptor expressed on myeloid cells by lipopolysaccharide-stimulated human neutrophils involves de novo protein synthesis

The triggering receptor expressed on myeloid cells (TREM-1) is a recently identified receptor expressed on neutrophils and monocytes. Activation of the receptor induces neutrophils to release the enzyme myeloperoxidase and inflammatory cytokines such as interleukin-8. TREM-1 has an alternatively spliced variant that lacks the transmembrane region, resulting in the receptor being secreted in a soluble form (sTREM-1). Soluble TREM-1 has been detected in plasma during experimental and clinical sepsis and has been advocated as a diagnostic marker of infection for pneumonia and as a prognostic marker for patients with septic shock. We studied TREM-1 surface expression, using flow cytometry, and simultaneously measured sTREM-1 concentrations in culture supernatants of lipopolysaccharide (LPS)-stimulated neutrophils. TREM-1 surface expression was constitutive and was not upregulated upon LPS stimulation. However, sTREM-1 release from neutrophils was significantly upregulated by LPS stimulation (P < 0.0001), an effect that was abrogated by cycloheximide. Soluble TREM-1 is therefore secreted by human neutrophils in response to LPS challenge in a process involving de novo protein synthesis that is not accompanied by an upregulation of the TREM-1 receptor on the surfaces of the cells.

Pharmacogenetics and anesthesiologists

Genetic variation contributes to an individual’s sensitivity and response to a variety of drugs important to anesthetic practice. Early insights into the clinical impact of pharmacogenetics were provided by anesthesiology – investigations into prolonged apnea after succinylcholine administration, thiopental-induced porphyria and malignant hyperthermia contributed to the novel science of pharmacogenetics in the early 1960s. Genetic polymorphisms involved in pharmacokinetics (absorption, distribution, metabolism, and excretion of drugs) and pharmacodynamics (receptors, ion channels and enzymes) can affect an individual’s response to the drugs used in anesthetic practice. In addition, genetic variation in proteins directly unrelated to drug action or metabolism can influence responses to environmental changes that occur during anesthesia. This review will summarize the current knowledge of genetic variation in response to drugs relevant to anesthesia, and how this impacts upon clinical practice.

A Microarray Analysis of Potential Genes Underlying the Neurosensitivity of Mice to Propofol

Establishing the mechanism of action of general anesthetics at the molecular level is difficult because of the multiple targets with which these drugs are associated. Inbred short sleep (ISS) and long sleep (ILS) mice are differentially sensitive in response to ethanol and other sedative hypnotics and contain a single quantitative trait locus (Lorp1) that accounts for the genetic variance of loss-of-righting reflex in response to propofol (LORP). In this study, we used high-density oligonucleotide microarrays to identify global gene expression and candidate genes differentially expressed within the Lorp1 region that may give insight into the molecular mechanism underlying LORP. Microarray analysis was performed using Affymetrix MG-U74Av2 Genechips and a selection of differentially expressed genes was confirmed by semiquantitative reverse transcription-polymerase chain reaction. Global expression in the brains of ILS and ISS mice revealed 3423 genes that were significantly expressed, of which 139 (4%) were differentially expressed. Analysis of genes located within the Lorp1 region showed that 26 genes were significantly expressed and that just 2 genes (7%) were differentially expressed. These genes encoded for the proteins AWP1 (associated with protein kinase 1) and "BTB (POZ) domain containing 1," whose functions are largely uncharacterized. Genes differentially expressed outside Lorp1 included seven genes with previously characterized neuronal functions and thus stand out as additional candidate genes that may be involved in mediating the neurosensitivity differences between ISS and ILS.

Estrogenic alkylphenols induce cell death by inhibiting testis endoplasmic reticulum Ca(2+) pumps

Industrial alkylphenols in the environment may act as "xenoestrogens" to disrupt testicular development and decrease male fertility. Amongst possible targets for these compounds are testicular Sertoli cells, which nurture the developing sperm cells. We demonstrate that SERCA 2 and 3 Ca(2+) pumps are relatively abundant in rat testis microsomal membranes, and also in Sertoli, myoid, and TM4 cells (a Sertoli cell line). A number of estrogenic alkylphenols such as nonylphenol, octylphenol, bisphenol A, and butylated hydroxytoluene all inhibit testicular Ca(2+) ATPase in the low micromolar concentration range. These agents also mobilize intracellular Ca(2+) in intact TM4 cells in a manner consistent with the inhibition of ER Ca(2+) pumps. Alkylphenols dramatically decrease the viability of TM4 cells, an effect that is reversed by either a caspase inhibitor or by BAPTA, and is therefore consistent with Ca(2+)-dependent cell death via apoptosis. We postulate that alkylphenols disrupt testicular development by inhibiting ER Ca(2+) pumps, thus disturbing testicular Ca(2+) homeostasis.

Site-specific tamoxifen-DNA adduct formation: lack of correlation with mutational ability in Escherichia coli

We have mapped sites of tamoxifen adduct formation, in the lacI gene using the polymerase STOP assay, following reaction in vitro with alpha-acetoxytamoxifen and horseradish peroxidase (HRP)/H(2)O(2) activated 4-hydroxytamoxifen. For both compounds, most adduct formation occurred on guanines. However, one adenine, within a run of guanines, generated a strong polymerase STOP site with activated 4-hydroxytamoxifen, and a weaker STOP site with alpha-acetoxytamoxifen at the same location. In Escherichia coli the lac I gene reacted with 4-hydroxytamoxifen was more likely to be mutated (2 orders of magnitude) than when reacted with alpha-acetoxytamoxifen, despite the greater DNA adduct formation by alpha-acetoxytamoxifen. This correlates with the greater predicted ability of activated 4-hydroxytamoxifen adducts to disrupt DNA structure than alpha-acetoxytamoxifen adducts. For lac I reacted with activated 4-hydroxytamoxifen, a hot spot of base mutation was located in the region of the only adenosine adduct. No mutational hot spots were observed with alpha-acetoxytamoxifen. Our data clearly shows a lack of correlation between gross adduct number, as assayed by (32)P-postlabeling and mutagenic potential. These data indicate the importance of minor adduct formation in mutagenic potential and further that conclusions regarding the mutagenicity of a chemical may not be reliably derived from the gross determination of adduct formation.