Yukimi Kira

Mitochondrial generation of reactive oxygen species and its role in aerobic life.

Mitochondria are the major site for the generation of ATP at the expense of molecular oxygen. Significant fractions (approximately 2%) of oxygen are converted to the superoxide radical and its reactive metabolites (ROS) in and around mitochondria. Although ROS have been known to impair a wide variety of biological molecules including lipids, proteins and DNA, thereby causing various diseases, they also play critical roles in the maintenance of aerobic life. Because mitochondria are the major site of free radical generation, they are highly enriched with antioxidants including GSH and enzymes, such as superoxide dismutase (SOD) and glutathione peroxidase, on both sides of their membranes to minimize oxidative stress in and around this organelle. The present work reviews the sites and mechanism of ROS generation by mitochondria, mitochondrial localization of Mn-SOD and Cu,Zn-SOD which has been postulated for a long time to be a cytosolic enzyme. The present work also describes that a cross-talk of molecular oxygen, nitric oxide (NO) and superoxide radicals regulates the circulation, energy metabolism, apoptosis, and functions as a major defense system against pathogens. Pathophysiological significance of ROS generation by mitochondria in the etiology of aging, cancer and degenerative neuronal diseases is also described.

Tributyltin interacts with mitochondria and induces cytochrome c release.

Although triorganotins are potent inducers of apoptosis in various cell types, the critical targets of these compounds and the mechanisms by which they lead to cell death remain to be elucidated. There are two major pathways by which apoptotic cell death occurs: one is triggered by a cytokine mediator and the other is by a mitochondrion-dependent mechanism. To elucidate the mechanism of triorganotin-induced apoptosis, we studied the effect of tributyltin on mitochondrial function. We found that moderately low doses of tributyltin decrease mitochondrial membrane potential and induce cytochrome c release by a mechanism inhibited by cyclosporine A and bongkrekic acid. Tributyltin-induced cytochrome c release is also prevented by dithiols such as dithiothreitol and 2,3-dimercaptopropanol but not by monothiols such as GSH, N-acetyl-L-cysteine, L-cysteine and 2-mercaptoethanol. Further studies with phenylarsine oxide agarose revealed that tributyltin interacts with the adenine nucleotide translocator, a functional constituent of the mitochondrial permeability transition pore, which is selectively inhibited by dithiothreitol. These results suggest that, at low doses, tributyltin interacts selectively with critical thiol residues in the adenine nucleotide translocator and opens the permeability transition pore, thereby decreasing membrane potential and releasing cytochrome c from mitochondria, a series of events consistent with established mechanistic models of apoptosis.

Cross talk of nitric oxide, oxygen radicals, and superoxide dismutase regulates the energy metabolism and cell death and determines the fates of aerobic life.

Although oxygen is required for the energy metabolism in aerobic organisms, it generates reactive oxygen and nitrogen species that impair a wide variety of biological molecules, including lipids, proteins, and DNA, thereby causing various diseases. Because mitochondria are the major site of free radical generation, they are highly enriched with enzymes, such as Mn-type superoxide dismutase in matrix, and antioxidants including GSH on both sides of inner membranes, thus minimizing oxidative stress in and around this organelle. We recently showed that a cross talk of nitric oxide and oxygen radicals regulates the circulation, energy metabolism, reproduction, and remodeling of cells during embryonic development, and functions as a major defense system against pathogens. The present work shows that Cu/Zn-type superoxide dismutase, which has been postulated for a long time to be a cytosolic enzyme, also localizes bound to inner membranes of mitochondria, thereby minimizing oxidative stress in and around this organelle, while mitochondrial association decreases markedly with the variant types of the enzyme found in patients with familial amyotrophic lateral sclerosis. We also report that a cross talk of nitric oxide, superoxide, and molecular oxygen cooperatively regulates the fates of pathogens and their hosts and that oxidative stress in and around mitochondria also determines cell death in the development of animals and tissue injury caused by anticancer agents by some carnitine-inhibitable mechanism.

L-carnitine suppresses the onset of neuromuscular degeneration and increases the life span of mice with familial amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a fatal disease caused by progressive degeneration of motor neurons in the spinal cord and motor cortex. Although the etiology of ALS remains unknown, a mutation of the gene encoding Cu,Zn-superoxide dismutase (SOD1) has been reported in 20% of familial cases of ALS (FALS). Transgenic mice that overexpress a mutated human SOD1 exhibit a phenotype and pathology similar to those observed in patients with FALS. Mitochondrial abnormality has been reported in patients with ALS and in animal models of FALS. We recently reported that L-carnitine, an essential cofactor for the beta-oxidation of long-chain fatty acids, effectively inhibits various types of mitochondrial injury and apoptosis both in vitro and in vivo. The present study demonstrates that oral administration of L-carnitine prior to disease onset significantly delayed the onset of signs of disease (log-rank P=0.0008), delayed deterioration of motor activity, and extended life span (log-rank P=0.0001) in transgenic mice carrying a human SOD1 gene with a G93A mutation (Tg). More importantly, subcutaneous injection of L-carnitine increased the life span of Tg mice (46% increase in male, 60% increase in female) even when given after the appearance of signs of disease.

Plasma RANTES, IL-10, and IL-8 levels in non–small-cell lung cancer patients treated with EGFR-TKIs

BackgroundEpidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs), routinely used to treat advanced non-small-cell lung cancer (NSCLC) patients with activated EGFR mutations, are associated with excellent response and improved performance status. Recently, pro-inflammatory cytokines, such as regulated upon activation normal T cell expressed and secreted (RANTES), interleukin (IL)-10 and IL-8 have been proposed as mediators of cancer development. EGFR-TKIs have been found to affect this network of pro-inflammatory cytokines.MethodsEGFR-TKIs (erlotinib, 150 mg/day; and gefitinib, 250 mg/day) were administered once per day. Treatment was continued until disease progressed or the patient developed intolerable symptoms of toxicity, or withdrew his/her consent for study participation. The treatment was a part of standard care. We investigated the correlation between plasma pro-inflammatory cytokines (including plasma RANTES, IL-10, and IL-8) levels and clinical outcomes following EGFR-TKI treatment in lung cancer patients. Pro-inflammatory cytokine levels were evaluated at diagnosis and on treatment day 30 after the first administration of EGFR-TKIs.ResultsOverall, 33 patients were enrolled. Plasma pro-inflammatory cytokine levels were determined for all patients at diagnosis. Plasma samples from 26 patients were obtained on treatment day 30. High level of RANTES at diagnosis was associated with severe general fatigue (P = .026). Low level of RANTES at diagnosis was significantly associated with long-term survival (P = .0032). Percent decrease change of IL-10 was associated with severity of rash (P = .037). The plasma IL-8 level on treatment day 30 (median, 5.48 pg/mL; range, 0.49–26.13 pg/mL) was significantly lower than the level at diagnosis (median 10.45 pg/mL; 3.04–54.86 pg/mL; P = .021).ConclusionsThese results suggest that EGFR-TKIs may suppress systemic inflammation and promote tumor shrinkage. The network of pro-inflammatory cytokines was affected by EGFR-TKI treatment for NSCLC. In addition, the clinical outcomes of EGFR-TKI treatment were influenced by the status of the plasma pro-inflammatory cytokines at diagnosis.

Reduced CYP2D6 function is associated with gefitinib-induced rash in patients with non-small cell lung cancer

BackgroundRash, liver dysfunction, and diarrhea are known major adverse events associated with erlotinib and gefitinib. However, clinical trials with gefitinib have reported different proportions of adverse events compared to trials with erlotinib. In an in vitro study, cytochrome P450 (CYP) 2D6 was shown to be involved in the metabolism of gefitinib but not erlotinib. It has been hypothesized that CYP2D6 phenotypes may be implicated in different adverse events associated with gefitinib and erlotinib therapies.MethodsThe frequency of each adverse event was evaluated during the period in which the patients received gefitinib or erlotinib therapy. CYP2D6 phenotypes were determined by analysis of CYP2D6 genotypes using real-time polymerase chain reaction techniques, which can detect single-nucleotide polymorphisms. The CYP2D6 phenotypes were categorized into 2 groups according to functional or reduced metabolic levels. In addition, we evaluated the odds ratio (OR) of the adverse events associated with each factor, including CYP2D6 activities and treatment types.ResultsA total of 232 patients received gefitinib therapy, and 86 received erlotinib therapy. Reduced function of CYP2D6 was associated with an increased risk of rash of grade 2 or more (OR, 0.44; 95% confidence interval [CI], 0.21–0.94; *p = 0.03), but not diarrhea ≥ grade 2 (OR, 0.49; 95% CI, 0.17–1.51; *p = 0.20) or liver dysfunction ≥ grade 2 (OR, 1.08; 95% CI, 0.52–2.34; *p = 0.84) in the gefitinib cohort. No associations were observed between any adverse events in the erlotinib cohort and CYP2D6 phenotypes (rash: OR, 1.77; 95% CI, 0.54–6.41; *p = 0.35/diarrhea: OR, 1.08; 95% CI, 0.21–7.43; *p = 0.93/liver dysfunction: OR, 0.93; 95% CI, 0.20–5.07; *p = 0.93).ConclusionsThe frequency of rash was significantly higher in patients with reduced CYP2D6 activity who treated with gefitinib compared to patients with functional CYP2D6. CYP2D6 phenotypes are a risk factor for the development of rash in response to gefitinib therapy.

Prevention of venous thrombosis by preoperative glycyrrhizin infusion in a rat model

BackgroundGlycyrrhizin is an agent with the capacity to bind to selectin molecules expressed on vascular endothelial cells and potentially prevent the adherence of neutrophils to the vascular endothelial surface. It has been found to prevent intravenous thrombus formation.MethodsVenous thrombosis was induced in male rats by ligation of the inferior vena cava (IVC) for 6 h. Before the ligation, the study rats were given intravenous injections of glycyrrhizin through the IVC. After 6 h of venous ligation, the rats were sacrificed and the IVC segments were harvested. Thrombus within the IVC was collected to measure the wet weight. Gene expression of P-, L-, and E-selectin was detected by reverse transcriptase polymerase chain reaction using extracts of mRNA from the IVC vein wall. As baseline controls, IVC samples without ligation were harvested immediately after laparotomy. Neutrophil adhesion to the luminal surface of IVC was assessed on histological sections stained with hematoxylin and eosin. Blood samples were collected through the IVC proximal to the ligation after 6 h to estimate activated partial thromboplastin time (APTT) and prothrombin time (PT). To investigate the effect of glycyrrhizin on binding capacity of P-selectin to human neutrophils, real-time biospecific interaction analysis was performed with the Biacore 2000 system.ResultsThe mean weight of thrombus in the glycyrrhizintreated group was 12.9 ± 11.1 mg, which is significantly lower than that of the saline-treated control group (21.3 ± 12.5 mg). The expression level of P-and L-selectin mRNA in both saline-and glycyrrhizin-treated groups was significantly higher than that of the baseline control. Histological studies of cross sections of IVC showed significantly fewer neutrophils adhering to the luminal surface with glycyrrhizin treatment than in the saline-treated controls. There was no significant difference in the values of coagulation parameters with or without glycyrrhizin treatment. In vitro analysis showed that glycyrrhizin caused a dose-dependent reduction of neutrophils binding to immobilized recombinant P-selectin.ConclusionsPreoperative treatment with glycyrrhizin is potentially useful for preventing venous thrombosis by suppressing the adherence of neutrophils to the venous endothelium during the initial phase of thrombus formation without reducing coagulation capacity and the subsequent risk for increased bleeding.

C609T Polymorphism of NADPH Quinone Oxidoreductase 1 Correlates Clinical Hematological Toxicities in Lung Cancer Patients Treated with Amrubicin.

Background Amrubicin hydrochloride (AMR) is a key agent for lung cancer. NADPH quinone oxidoreductase 1 (NQO1) metabolizes the quinone structures contained in both amrubicin (AMR) and amrubicinol (AMR-OH). We hypothesized that NQO1 C609T polymorphism may affect AMR-related pharmacokinetics and clinical outcomes. Methods Patients received AMR doses of 30 or 40 mg/m2/day on days 1–3. Plasma sampling was performed 24 hours after the first and third AMR injections. Concentrations of AMR and AMR-OH were determined by HPLC and the NQO1 C609T polymorphism was assayed by RT-PCR. Results A total of 35 patients were enrolled. At a dose of 40 mg/m2, the T/T genotype exhibited a tendency toward a relationship with decrease concentrations of AMR-OH on days 2 and 4. The genotype also showed a significant decrease of hematological toxicities (P < 0.05). Conclusions NQO1 C609T polymorphism had a tendency of correlation with the plasma concentrations of AMR-OH, and thereby had significant correlations with hematologic toxicities.

The identification and characterization of a new GTP-binding protein [Gbp45] involved in cell proliferation and death related to mitochondrial function

We describe the identification and characterization of a GTP-binding protein with a molecular weight of 45 kD (Gbp45). Gbp45 cDNA was found to overlap with a hypothetical human protein, PTD004, the sequence of which was previously deposited in the databases. The gene for PTD004 was recently found to be one of the ATPases, hOLA1 (human Obg-like ATPase 1). The Gbp45 gene encodes a protein of 396 amino acid residues. Immunocytochemical analysis and examination with GFP-tagged protein revealed that Gbp45 is primarily located in the cytosolic compartment. Immunoblot analysis showed that the Gbp45 protein is strongly expressed in the neuronal tissues and pancreas. T43N and T56N mutations resulted in a loss of Gbp45’s ability to bind to GTP and a loss of GTPase activity. In cultured cells, the transfection of wild-type Gbp45 accelerated cell proliferation, though T43N and T56N mutations induced cell death. Down-regulating Gbp45 expression decreased the cell proliferation rate and increased the rate of cell death induced by the inhibition of mitochondrial electron transport. These findings indicate that Gbp45 plays important roles in cell proliferation and death related to mitochondrial function.

Effects of Preoperative Glycyrrhizin Infusion for the Prevention of Venous Thrombosis on the Tissue Expression of Antithrombin in a Rat Model

OBJECTIVE Using a thrombus model prepared by ligation of the inferior vena cava (IVC), the influences of the glycoside, glycyrrhizin, on plasma antithrombin levels and antithrombin mRNA expression levels in the liver and IVC with the inhibition of venous thrombosis were investigated. MATERIALS AND METHODS The rat IVC was exposed and ligated for 24 h immediately after the intravenous administration of 300 mg/kg glycyrrhizin. Among antithrombotic drugs, the Xa inhibitor, fondaparinux sodium, was used as a control drug. RESULTS The mean thrombus weight was significantly smaller in the glycyrrhizin-treated group (18.3 mg) than in the saline-treated group (34.3 mg). In contrast, the inhibition of thrombosis was not observed in the fondaparinux-treated group. Antithrombin mRNA expression levels in the liver were significantly higher in the ligated groups than in the baseline control group. The mean plasma antithrombin level was significantly lower in the glycyrrhizin group (96.6%) than in the saline group (114.4%), but was not significantly different from that in the baseline control group (102.4%). CONCLUSION The pretreatment with glycyrrhizin inhibited venous thrombosis, and antithrombin mRNA expression levels in the liver and IVC as well as plasma antithrombin levels were significantly lower than those in the saline group.