Yolanda Gutiérrez-Martín

Fluorescence measurements of steady state peroxynitrite production upon SIN-1 decomposition: NADH versus dihydrodichlorofluorescein and dihydrorhodamine 123.

The production of peroxynitrite during 3-morpholinosydnonimine (SIN-1) decomposition can be continuously monitored, with a sensitivity ≤ 0.1 μM, from the kinetics of NADH fluorescence quenching in phosphate buffers, as well as in buffers commonly used with cell cultures, like Lockes buffer or Dulbeccos modified Eagles medium (DMEM-F12). The half-time for peroxynitrite production during SIN-1 decomposition ranged from 14–18 min in DMEM-F12 (plus and minus phenol red) to 21.5 min in Lockes buffer and 26 min in DMEM-F12 supplemented with apotransferrin (0.1 mg/mL). The concentration of peroxynitrite reached a peak that was linearly dependent upon SIN-1 concentration, and that for 100 μM SIN-1 amounted to 1.4 ± 0.2 μM in Lockes buffer, 3.2–3.6 μM in DMEM-F12 (plus and minus phenol red) and 1.8 μM in DMEM-F12 supplemented with apotransferrin. Thus, the maximum concentration of peroxynitrite ranged from 1.2 to 3.6% of added SIN-1. NADH was found to be less sensitive than dihydrorhodamine 123 and 2′,7′-dichlorodihydrofluorescein diacetate to oxidation by H2O2, which is produced during SIN-1 decomposition in common buffers. It is shown that peroxynitrite concentration can be controlled (±5%) during predetermined times by using sequential SIN-1 pulses, to simulate chronic exposure of cells or subcellular components to peroxynitrite.

Alteration of cytosolic free calcium homeostasis by SIN-1: high sensitivity of L-type Ca2+ channels to extracellular oxidative/ nitrosative stress in cerebellar granule cells

Exposure of cerebellar granule neurones in 25 mm KCl HEPES‐containing Lockes buffer (pH 7.4) to 50–100 µm SIN‐1 during 2 h decreased the steady‐state free cytosolic Ca2+ concentration ([Ca2+]i) from 168 ± 33 nm to 60 ± 10 nm, whereas exposure to ≥ 0.3 mm SIN‐1 produced biphasic kinetics: (i) decrease of [Ca2+]i during the first 30 min, reaching a limiting value of 75 ± 10 nm (due to inactivation of L‐type Ca2+ channels) and (ii) a delayed increase of [Ca2+]i at longer exposures, which correlated with SIN‐1‐induced necrotic cell death. Both effects of SIN‐1 on [Ca2+]i are blocked by superoxide dismutase plus catalase and by Mn(III)tetrakis(4‐benzoic acid)porphyrin chloride. Supplementation of Lockes buffer with catalase before addition of 0.5–1 mm SIN‐1 had no effect on the decrease of [Ca2+]i but further delayed and attenuated the increase of [Ca2+]i observed after 60–120 min exposure to SIN‐1 and also protected against SIN‐1‐induced necrotic cell death. α‐Tocopherol, the potent NMDA receptor antagonist (+)‐MK‐801 and the N‐ and P‐type Ca2+ channels blocker ω‐conotoxin MVIIC had no effect on the alterations of [Ca2+]i upon exposure to SIN‐1. However, inhibition of the plasma membrane Ca2+ ATPase can account for the increase of [Ca2+]i observed after 60–120 min exposure to 0.5–1 mm SIN‐1. It is concluded that L‐type Ca2+ channels are a primary target of SIN‐1‐induced extracellular nitrosative/oxidative stress, being inactivated by chronic exposure to fluxes of peroxynitrite of 0.5–1 μm/min, while higher concentrations of peroxynitrite and hydrogen peroxide are required for the inhibition of the plasma membrane Ca2+ ATPase and induction of necrotic cell death, respectively.

Acquired resistance to the anticancer drug paclitaxel is associated with induction of cytochrome P450 2C8

INTRODUCTION We have previously shown that human colorectal cancer tissue is able to inactivate the anticancer drug paclitaxel through cytochrome P450 (CYP)2C8 and CYP3A4 metabolisms. The aim of this study was to evaluate whether changes in the expression levels of genes coding for such enzymes are related to anticancer drug resistance after long-term exposure to the drug. METHODS Human colorectal cancer cells (Caco-2) that are sensitive to paclitaxel were exposed to increasing concentrations of the drug from 0-250 nM during one year, in order to select paclitaxel-resistant cells. Subsequently, we compared the sensitivity to paclitaxel and the extent of expression of the CYP2C8, CYP3A4 and CYP3A5 genes in original and resistant cells. RESULTS Resistant cancer cells displayed a 246-fold increased lethal dose (LD)50 to paclitaxel (p < 0.004) as compared with original cancer cells. A 4.4-fold (p = 0.005) enhancement of CYP2C8 expression and a 5.6-fold (p = 0.001) increase of multidrug resistance (MDR)1 expression was observed in resistant cells exposed to paclitaxel. When paclitaxel was removed from the culture medium, CYP2C8, but not MDR1 expression, reverted to basal levels and the resistance to paclitaxel decreased 3.2-fold (p = 0.005). No major changes in the expression levels of CYP3A4 and CYP3A5 were observed. CONCLUSIONS Caco-2 cells are capable of increasing the expression levels of CYP2C8 as a response to long-term exposure to paclitaxel. This study provides evidence for a mechanism of acquired resistance to anticancer therapy based on the induction of anticancer-metabolizing enzymes.

Synaptosomal plasma membrane Ca2+ pump activity inhibition by repetitive micromolar ONOO− pulses

A sustained increase of intracellular free [Ca(2+)] ([Ca(2+)](i)) has been shown to be an early event of neuronal cell death induced by peroxynitrite (ONOO(-)). In this paper, chronic exposure to ONOO(-) has been simulated by treatment of rat brain synaptosomes or plasma membrane vesicles with repetitive pulses of ONOO(-) during at most 50 min, which efficiently produced nitrotyrosine formation in several membrane proteins (including the Ca(2+)-ATPase). The plasma membrane Ca(2+)-ATPase activity at near-physiological conditions (pH 7, submicromolar Ca(2+), and millimolar Mg(2+)-ATP concentrations), which plays a major role in the control of synaptic [Ca(2+)](i), can be more than 75% inhibited by a sustained exposure to micromolar ONOO(-) (e.g., to 100 pulses of 10 microM ONOO(-)). This inhibition is irreversible and mostly due to a decreased V(max), and to the 2-fold increase of the K(0.5) for Ca(2+) stimulation and about 5-fold increase of the K(M) for Mg(2+)-ATP. [Ca(2+)](i) increases to >400 nM when synaptosomes are subjected to this treatment. Reduced glutathione can afford only partial protection against the inhibition produced by micromolar ONOO(-) pulses. Therefore, inhibition of the plasma membrane Ca(2+)-pump activity during chronic exposure to ONOO(-) may account by itself for a large and sustained increase of intracellular [Ca(2+)](i) in synaptic nerve terminals.

Mitochondrial impairment increases FL-PINK1 levels by calcium-dependent gene expression

Mutations of the PTEN-induced kinase 1 (PINK1) gene are a cause of autosomal recessive Parkinsons disease (PD). This gene encodes a mitochondrial serine/threonine kinase, which is partly localized to mitochondria, and has been shown to play a role in protecting neuronal cells from oxidative stress and cell death, perhaps related to its role in mitochondrial dynamics and mitophagy. In this study, we report that increased mitochondrial PINK1 levels observed in human neuroblastoma SH-SY5Y cells after carbonyl cyanide m-chlorophelyhydrazone (CCCP) treatment were due to de novo protein synthesis, and not just increased stabilization of full length PINK1 (FL-PINK1). PINK1 mRNA levels were significantly increased by 4-fold after 24 h. FL-PINK1 protein levels at this time point were significantly higher than vehicle-treated, or cells treated with CCCP for 3 h, despite mitochondrial content being decreased by 29%. We have also shown that CCCP dissipated the mitochondrial membrane potential (Δψm) and induced entry of extracellular calcium through L/N-type calcium channels. The calcium chelating agent BAPTA-AM impaired the CCCP-induced PINK1 mRNA and protein expression. Furthermore, CCCP treatment activated the transcription factor c-Fos in a calcium-dependent manner. These data indicate that PINK1 expression is significantly increased upon CCCP-induced mitophagy in a calcium-dependent manner. This increase in expression continues after peak Parkin mitochondrial translocation, suggesting a role for PINK1 in mitophagy that is downstream of ubiquitination of mitochondrial substrates. This sensitivity to intracellular calcium levels supports the hypothesis that PINK1 may also play a role in cellular calcium homeostasis and neuroprotection.

The NADH oxidase activity of the plasma membrane of synaptosomes is a major source of superoxide anion and is inhibited by peroxynitrite

Plasma membrane vesicles from adult rat brain synaptosomes (PMV) have an ascorbate‐dependent NADH oxidase activity of 35–40 nmol/min/(mg protein) at saturation by NADH. NADPH is a much less efficient substrate of this oxidase activity, with a Vmax 10‐fold lower than that measured for NADH. Ascorbate‐dependent NADH oxidase activity accounts for more than 90% of the total NADH oxidase activity of PMV and, in the absence of NADH and in the presence of 1 mm ascorbate, PMV produce ascorbate free radical (AFR) at a rate of 4.0 ± 0.5 nmol AFR/min/(mg protein). NADH‐dependent ·O2− production by PMV occurs with a rate of 35 ± 3 nmol/min/(mg protein), and is a coreaction product of the NADH oxidase activity, because: (i) it is inhibited by more than 90% by addition of ascorbate oxidase, (ii) it is inhibited by 1 µg/mL wheat germ agglutinin (a potent inhibitor of the plasma membrane AFR reductase activity), and (iii) the KM(NADH) of the plasma membrane NADH oxidase activity and of NADH‐dependent ·O2− production are identical. Treatment of PMV with repetitive micromolar ONOO– pulses produced almost complete inhibition of the ascorbate‐dependent NADH oxidase and ·O2− production, and at 50% inhibition addition of coenzyme Q10 almost completely reverts this inhibition. Cytochrome c stimulated 2.5‐fold the plasma membrane NADH oxidase, and pretreatment of PMV with repetitive 10 µm ONOO– pulses lowers the K0.5 for cytochrome c stimulation from 6 ± 1 (control) to 1.5 ± 0.5 µm. Thus, the ascorbate‐dependent plasma membrane NADH oxidase activity can act as a source of neuronal ·O2−, which is up‐regulated by cytosolic cytochrome c and down‐regulated under chronic oxidative stress conditions producing ONOO–.

Variability in ethanol biodisposition in whites is modulated by polymorphisms in the ADH1B and ADH1C genes.

Association between genetic variations in alcohol‐related enzymes and impaired ethanol biodisposition has not been unambiguously proven, and the effect of many newly described polymorphisms remains to be explored. The aims of this study are to elucidate the influence of genetic factors in alcohol biodisposition and effects. We analyzed alcohol pharmacokinetics and biodisposition after the administration of 0.5 g/kg ethanol; we measured ethanol effects on reaction time and motor time in response to visual and acoustic signals, and we analyzed 13 single nucleotide polymorphism (SNPs) in the genes coding for ADH1B, ADH1C, ALDH2, and CYP2E1 in 250 healthy white individuals. Variability in ethanol pharmacokinetics and biodisposition is related to sex, with women showing a higher area under the curve (AUC) (P = 0.002), maximum concentration (Cmax) (P < 0.001) and metabolic rate (P = 0.001). Four nonsynonymous SNPs are related to decreased alcohol metabolic rates: ADH1B rs6413413 (P = 0.012), ADH1C rs283413 (P < 0.001), rs1693482 (P < 0.001), and rs698 (P < 0.001). Individuals carrying diplotypes combining these mutations display statistically significant decrease in alcohol biodisposition as compared with individuals lacking these mutations. Alcohol effects displayed bimodal distribution independently of sex or pharmacokinetics. Most individuals had significant delays in reaction and motor times at alcohol blood concentrations under 500 mg/L, which are the driving limits for most countries. Conclusion: Besides the identification of new genetic factors related to alcohol biodisposition relevant to whites, this study provides unambiguous identification of diplotypes related to variability in alcohol biodisposition. (HEPATOLOGY 2010;51:491–500.)

Inhibition by 4-hydroxynonenal (HNE) of Ca2+ transport by SERCA1a: Low concentrations of HNE open protein-mediated leaks in the membrane

Exposure of sarcoplasmic reticulum membranes to 4-hydroxy-2-nonenal (HNE) resulted in inhibition of the maximal ATPase activity and Ca(2+) transport ability of SERCA1a, the Ca(2+) pump in these membranes. The concomitant presence of ATP significantly protected SERCA1a ATPase activity from inhibition. ATP binding and phosphoenzyme formation from ATP were reduced after treatment with HNE, whereas Ca(2+) binding to the high-affinity sites was altered to a lower extent. HNE reacted with SH groups, some of which were identified by MALDI-TOF mass spectrometry, and competition studies with FITC indicated that HNE also reacted with Lys(515) within the nucleotide binding pocket of SERCA1a. A remarkable fact was that both the steady-state ability of SR vesicles to sequester Ca(2+) and the ATPase activity of SR membranes in the absence of added ionophore or detergent were sensitive to concentrations of HNE much smaller than those that affected the maximal ATPase activity of SERCA1a. This was due to an increase in the passive permeability of HNE-treated SR vesicles to Ca(2+), an increase in permeability that did not arise from alteration of the lipid component of these vesicles. Judging from immunodetection with an anti-HNE antibody, this HNE-dependent increase in permeability probably arose from modification of proteins of about 150-160kDa, present in very low abundance in longitudinal SR membranes (and in slightly larger abundance in SR terminal cisternae). HNE-induced promotion, via these proteins, of Ca(2+) leakage pathways might be involved in the general toxic effects of HNE.