Prevention of cell damage in ischaemia: novel molecular targets in mitochondria

The Effects of Difumarate Salt S-15176 after Spinal Cord Injury in Rats

Objective

In the present study we analyzed neuroprotective and antiapoptotic effect of the difumarate salt S-15176, as an anti-ischemic, an antioxidant and a stabilizer of mitochondrial membrane in secondary damage following spinal cord injury (SCI) in a rat model.

Methods

Three groups were performed with 30 Wistar rats; control (1), trauma (2), and a trauma+S-15176 (10 mg/kg i.p., dimethyl sulfoxide) treatment (3). SCI was performed at the thoracic level using the weight-drop technique. Spinal cord tissues were collected following intracardiac perfusion in 3rd and 7th days of posttrauma. Hematoxylin and eosin staining for histopatology, terminal deoxynucleotidyl transferase dUTP nick end labeling assay for apoptotic cells and immunohistochemistry for proapoptotic cytochrome-c, Bax and caspase 9 were performed to all groups. Functional recovery test were applied to each group in 3rd and 7th days following SCI.

Results

In trauma group, edematous regions, diffuse hemorrhage, necrosis, leukocyte infiltration and severe degeneration in motor neurons were observed prominently in gray matter. The number of apoptotic cells was significantly higher (p<0.05) than control group. In the S-15176-treated groups, apoptotic cell number in 3rd and 7th days (p<0.001), also cytochrome-c (p<0.001), Bax (p<0.001) and caspase 9 immunoreactive cells (p<0.001) were significantly decreased in number compared to trauma groups. Hemorrhage and edema in the focal areas were also noticed in gray matter of treatment groups. Results of the locomotor test were significantly increased in treatment group (p<0.05) when compared to trauma groups.

Conclusion

We suggest that difumarate salt S-15176 prevents mitochondrial pathways of apoptosis and protects spinal cord from secondary injury and helps to preserve motor function following SCI in rats.

Mitochondrial injury underlies hyporeactivity of arterial smooth muscle in severe shock

BACKGROUND

Our previous data showed membrane hyperpolarization of arteriolar smooth muscle cells (ASMCs) caused by adenosine triphosphate (ATP)-sensitive potassium channels (K(ATP)) activation contributed to vascular hyporeactivity in shock. Despite supply of oxygen and nutrients, vascular hyporeactivity to vasoconstrictor agents still remains, which may result from low ATP level. The study was designed to investigate shock-induced mitochondrial changes of rat ASMCs in the genesis and treatment of hypotension in severe shock.

METHODS

The animals were divided into four groups: controls, hemorrhagic shock, CsA+shock (preadministration of cyclosporin A before bleeding), and ATR+CsA+shock (preadministration of atractyloside, followed by CsA and bleeding). ASMCs were isolated and the ultrastructure and function of ASMC mitochondria and the vasoresponsiveness to norepinephrine (NE) was measured on microcirculatory preparations.

RESULTS

Ultrastructurally, the hemorrhagic shock group showed swollen mitochondria with poorly defined cristae. In this group, the number of ASMCs with low mitochondrial membrane potential (Δψ(m)) was increased by 49.7%, and the intracellular ATP level was reduced by 82.1%, which led to activation of K(ATP) plasma membrane channels with resultant ASMC hyperpolarization and low vasoreactivity. These changes were reduced in the CsA+shock group. When mitochondrial damage was aggravated by ATR in the ATR+CsA+shock group, the CsA did not protect. Compared to the shock group, vasoresponsiveness to NE was much improved in the CsA+shock group.

CONCLUSIONS

Mitochondrial ASMC dysfunction is involved in the genesis of reduced vasoreactivity in severe shock. Mitochondrial protection may therefore be a new approach in the treatment of shock-induced hypotension.

Peripheral-type benzodiazepine receptor overexpression and knockdown in human breast cancer cells indicate its prominent role in tumor cell proliferation

The peripheral-type benzodiazepine receptor (PBR), an 18-kDa high affinity drug and cholesterol binding protein, is expressed at high levels in various cancers. Its expression is positively correlated with aggressive metastatic behavior in human breast cancer cells. To determine the role of PBR in tumor progression, two human mammary carcinoma cell lines were utilized: the non-aggressive MCF-7 cell line, which expresses extremely low PBR levels, and the highly aggressive MDA-MB-231 cell line, which has much higher PBR levels. We have generated stably transfected lines of the tetracycline-repressible MCF-7 cell line (MCF-7 Tet-Off) with inducible human PBR cDNA. Induction of PBR expression in MCF-7 Tet-Off cells increased PBR ligand binding and cell proliferation. Transfection of MDA-MB-231 cells with multiple siRNAs complementary to PBR (PBR-siRNAs) led to different levels of PBR mRNA knockdown. Lentiviral-mediated PBR RNA interference in MDA-MB-231 cells decreased PBR levels by 50%. Decreased PBR expression was associated with cell cycle arrest at G2 phase, decreased cell proliferation, and significant increases in the protein levels of the cyclin-dependent kinase inhibitor p21(WAF/CIP1). These changes were accompanied by p53 activation seen as increased p53 phosphorylation (Ser15). In parallel, increased proteolytic activation of caspase-3 was also observed. Taken together these results suggest that PBR protein expression is directly involved in regulating cell survival and proliferation in human breast cancer cells by influencing signaling mechanisms involved in cell cycle control and apoptosis.

Effect of the mitochondrial transition pore inhibitor, S-15176, on rat liver mitochondria: ATP synthase modulation and mitochondrial uncoupling induction

S-15176 is a new inhibitor of the permeability transition pore (PTP) which has been shown to display anti-ischemic properties. We show here that S-15176 prevented PTP, cytochrome c release and maintained mitochondrial membrane potential when low concentrations of S-15176 were used (not exceeding 50 nmol/mg protein). For higher concentrations S-15176 is able to collapse mitochondrial potential. This effect was reversed by the recoupling agent 6-ketocholestanol (6-KCh) suggesting that S-15176 has uncoupling properties. In addition, S-15176 is able to inhibit ATP synthase activity and to stimulate the hydrolytic activity of the enzyme but none of these effects appears to be related to its PTP inhibiting property. These data demonstrate that S-15176 interacts with several targets in mitochondria and these pharmacological properties should be considered in the examination of its health benefits as well as its potential cytotoxicity.

Mechanism underlying mitochondrial protection of asiatic acid against hepatotoxicity in mice

Asiatic acid (AA) is one of the triterpenoid components of Terminalia catappa L., which has antioxidative, anti-inflammatory and hepatoprotective activity. This research focused on the mitochondrial protection of AA against acute liver injury induced by lipopolysaccharide (LPS) and D-galactosamine (D-GalN) in mice. It was found that pretreatment with 25, 50 or 100 mg kg(-1) AA significantly blocked the LPS + D-GalN-induced increase in both serum aspartate aminotransferase (sAST) and serum alanine aminotransferase (sALT) levels, which was confirmed by ultrastructural observation under an electron microscope, showing improved nuclear condensation, ameliorated mitochondrion proliferation and less lipid deposition. Meanwhile, different doses of AA could decrease both the transcription and the translation level of voltage-dependent anion channels (VDACs), the most important mitochondrial PTP component protein, and block the translocation of cytochrome c from mitochondria to cytosol. On the other hand, pre-incubation with 25, 50 and 100 microg mL(-1) AA inhibited the Ca(2+)-induced mitochondrial permeability transition (MPT), including mitochondrial swelling, membrane potential dissipation and releasing of matrix Ca(2+) in liver mitochondria separated from normal mice, indicating the direct role of AA on mitochondria. Collectively, the above data suggest that AA could protect liver from damage and the mechanism might be related to up-regulating mitochondrial VDACs and inhibiting the process of MPT.

Inhibition by [corrected] ursolic acid of [corrected] calcium-induced mitochondrial permeability transition and release of two proapoptotic proteins

The possible inhibition by [corrected] ursolic acid (UA) of [corrected] mitochondrial permeability transition (MPT) in mouse liver was investigated to identify the mechanisms underlying the hepatoprotective effect of UA. The effect of UA on liver MPT induced by Ca2+ was assessed by measuring changes in mitochondrial volume, mitochondrial membrane potential (MMP), release of matrix Ca2+, and transfer of cytochrome c (Cyt c) and apoptosis-inducing factor (AIF) from the intermembrane space to the cytoplasm. The results showed that obvious mitochondrial swelling, loss of MMP, and release of matrix Ca2+ occurred after the addition of 50 microM Ca2+. However, preincubation with 20, 50 or 100 microg ml(-1) UA significantly blocked the above changes. Addition of 100 microg ml(-1) UA inhibited on mitochondrial swelling by 73.2% after 5 min, while the MMP dissipating and Ca2+ releasing were, respectively, suppressed by 59.3% and 54.1% after 3 min. In addition, Western blot analysis showed Cyt c and AIF transferred from mitochondrial pellet to the supernatant after the addition of 50 microM Ca2+, but the process was significantly inhibited by various concentrations of UA. The results suggest that the mechanisms underlying the hepatoprotection of UA may be related to its direct inhibitory action on MPT.

Peripheral-type benzodiazepine receptor: structure and function of a cholesterol-binding protein in steroid and bile acid biosynthesis

Cholesterol transport from the outer to the inner mitochondrial membrane is the rate-determining step in steroid and bile acid biosyntheses. Biochemical, pharmacological and molecular studies have demonstrated that the peripheral-type benzodiazepine receptor (PBR) is a five transmembrane domain mitochondrial protein involved in the regulation of cholesterol transport. PBR gene disruption in Leydig cells completely blocked cholesterol transport into mitochondria and steroid formation, while PBR expression in bacteria, devoid of endogenous PBR and cholesterol, induced cholesterol uptake and transport. Molecular modeling of PBR suggested that cholesterol might cross the membrane through the five helices of the receptor and that synthetic and endogenous ligands might bind to common sites in the cytoplasmic loops. A cholesterol recognition/interaction amino acid consensus (CRAC) sequence in the cytoplasmic carboxy-terminus of the PBR was identified by mutagenesis studies. In vitro reconstitution of PBR into proteoliposomes demonstrated that PBR binds both drug ligands and cholesterol with high affinity. In vivo polymeric forms of PBR were observed and polymer formation was reproduced in vitro, using recombinant PBR protein reconstituted into proteoliposomes, associated with an increase in drug ligand binding and reduction of cholesterol-binding capacity. This suggests that the various polymeric states of PBR might be part of a cycle mediating cholesterol uptake and release into the mitochondria, with PBR functioning as a cholesterol exchanger against steroid product(s) arising from cytochrome P450 action. Taking into account the widespread presence of PBR in many tissues, a more general role of PBR in intracellular cholesterol transport and compartmentalization might be considered.

S-15176 inhibits mitochondrial permeability transition via a mechanism independent of its antioxidant properties

Mitochondrial Ca(2+) accumulation can induce a sudden increase in the permeability of the inner membrane. This phenomenon is due to the generation of a large nonselective ion channel, termed the permeability transition pore (PTP), which contributes to cellular injury during ischemia and reperfusion. Inhibition of PTP generation constitutes a relevant pharmacological target to protect a cell from death. In this study, we examined the effect of S-15176 ((N-[(3,5-di-tertiobutyl-4-hydroxy-1-thiophenyl)]-3-propyl-N'-(2,3,4-trimethoxybenzyl)piperazine), a novel anti-ischemic agent, on PTP in rat liver mitochondria. S-15176 prevented PTP opening generated by various triggering agents, as attested by the concentration-dependent inhibition of mitochondrial swelling, of mitochondrial membrane potential dissipation and of NADPH oxidation. These effects were associated with an increase in the Ca(2+) loading capacity of mitochondria. S-15176 was a strong inhibitor of lipid peroxidation, but experiments with another trimetazidine derivative devoid of antioxidant activity indicated that this activity was not essential to the inhibitory effect. Binding studies demonstrated that [3H]S-15176 bound to mitochondrial binding sites, especially those localized in the inner membrane. These sites were shared by several well-known inhibitors of PTP opening. These results demonstrate that the mechanism by which S-15176 protects mitochondria against the deleterious effects of ischemia-reperfusion involves inhibition of PTP opening and provide evidence that the drug operates through low structural specificity binding sites located in the inner mitochondrial membrane.