Effect of bedaquiline on the functions of rat liver mitochondria

The paper considers the effects of bedaquiline (BDQ), an antituberculous preparation of the new generation, on rat liver mitochondria. It was shown that 50?μM BDQ inhibited mitochondrial respiration measured with substrates of complexes I and II (glutamate/malate and succinate/rotenone systems respectively) in the states V₃ and V_DNP. At the same time, at concentrations below 50?μM, BDQ slightly stimulated respiration with substrates of complex I in the state V₂. BDQ was also found to suppress, in a dose-dependent manner, the activity of complex II and the total activity of complexes II?+?III of the mitochondrial transport chain. It was discovered that at concentrations up to 10?μM, BDQ inhibited H₂O₂ production in mitochondria. BDQ (10–50?μM) suppressed the opening of Ca²⁺-dependent CsA-sensitive mitochondrial permeability transition pore. The latter was revealed experimentally as the inhibition of Ca²⁺/P_i-dependent swelling of mitochondria, suppression of cytochrome c release, and an increase in the Ca²⁺ capacity of the organelles. BDQ also decreased the rate of mitochondrial energy-dependent K⁺ transport, which was evaluated by the energy-dependent swelling of mitochondria in a K⁺ buffer and DNP-induced K⁺ efflux from the organelles. The possible mechanisms of BDQ effect of rat liver mitochondria are discussed.     

TRPC1 and ORAI1 channels in colon cancer

Colon cancer cells, like other types of cancer cells, undergo the remodeling of the intracellular Ca²⁺ homeostasis that contributes to cancer cell hallmarks including enhanced cell proliferation, migration, and survival. Colon cancer cells display enhanced store-operated Ca²⁺ entry (SOCE) compared with their non-cancer counterparts. Colon cancer cells display an abnormal expression of SOCE molecular players including Orai1 and TRPC1 channels, and the stromal interacting molecule (STIM) 1 and 2. Interestingly, upregulation of Orai1 and TRPC1 channels and their contribution to SOCE are associated with cancer malignancy in colon cancer cells. In a specific cellular model of colon cancer, whereas in non-cancer colon cells SOCE is composed of the Ca²⁺ release activated (CRAC) currents, in colon cancer cells SOCE is composed of CRAC- and cationic, non-selective store operated (SOC) currents. Former SOCs are mediated by TRPC1 channels. Moreover, colon cancer cells also display dysregulation of the expression of 1,4,5-triphosphate receptors (IP₃R) that could contribute to the enhanced SOCE. Another important factor underlying the enhanced SOCE is the differential mitochondrial modulation of the CRAC and SOC currents in non-cancer and colon cancer cells. In colon cancer cells, mitochondria take up more Ca²⁺ that prevent the Ca²⁺-dependent inactivation of the SOCs, leading to sustained Ca²⁺ entry. Notably, the inhibition of SOCE in cancer colon cells abolishes their cancer hallmarks. Robust evidence has shown the efficiency of non-steroidal anti-inflammatory drugs (NSAIDs) and difluoromethylornithine (DFMO) to reverse the enhanced cell proliferation, migration, and apoptosis resistance of cancer cells. In colon cancer cells, both NSAIDs and DFMO decrease SOCE, but they target different molecular components of SOCE. NSAIDs decrease the Ca²⁺ uptake by mitochondria, limiting their ability to prevent the Ca²⁺-dependent inactivation of the SOCs that underlie SOCE. On the other hand, DFMO inhibits the expression of TRPC1 channels in colon cancer cells, eliminating their contribution to SOCE. The identification of players of SOCE in colon cancer cells may help to better understand the remodeling of the Ca²⁺ homeostasis in cancer. Importantly, the use of different pharmacological tools that target different SOCE molecular players in colon cancer cells may play a pivotal role in designing better chemoprevention strategies.     

The role of mitochondria in sepsis-induced cardiomyopathy

Sepsis is defined as a life-threatening organ dysfunction caused by a dysregulated host response to infection. Myocardial dysfunction, often termed sepsis-induced cardiomyopathy, is a frequent complication and is associated with worse outcomes. Numerous mechanisms contribute to sepsis-induced cardiomyopathy and a growing body of evidence suggests that bioenergetic and metabolic derangements play a central role in its development; however, there are significant discrepancies in the literature, perhaps reflecting variability in the experimental models employed or in the host response to sepsis. The condition is characterised by lack of significant cell death, normal tissue oxygen levels and, in survivors, reversibility of organ dysfunction. The functional changes observed in cardiac tissue may represent an adaptive response to prolonged stress that limits cell death, improving the potential for recovery. In this review, we describe our current understanding of the pathophysiology underlying myocardial dysfunction in sepsis, with a focus on disrupted mitochondrial processes.     

光周期和温度对布氏田鼠产热的影响

布氏田鼠（Ｍｉｃｒｏｔｕｓ ｂｒａｎｄｔｉ）分组驯化在：（１）长光照温暖环境（ＬＷ，１６Ｌ：８Ｄ，２５℃）；（２）长光照 低温环境（ＬＣ，１６Ｌ：８Ｄ，５℃）；（３）短光照温暖环境（ＳＷ，８Ｌ：１６Ｄ，２５℃）；（４）短光照低温环境（ＳＣ， ８Ｌ：１６Ｄ，５℃）。驯化四周后，长光照动物的体重比短光动物的体重有增加的趋势；四组动物的体温 没有明显差异；低温和短光照均促使静止代谢率（ＲＭＲ）增加；ＳＣ组动物的非颤抖性产热（ＮＳＴ）高 于ＬＷ组。低温诱导肝和褐色脂肪组织（ＢＡＴ）细胞线粒体蛋白增加，短光照再度地增强此作用。短 光照诱导肝细胞线粒体状态－４及状态－３呼吸活力增加，低温没有明显作用。低温和短光照均刺激肝 和ＢＡＴ线粒体细胞色素Ｃ氧化酶活力提高，但后者作用强度大于前者。低温明显激活ＢＡＴ线粒体 的ａ－磷酸甘油氧化酶的活力，短光照无明显影响、结果表明：低温和短光照均能提高布氏田鼠的产 热能力，短光照与低温因子两者的协同作用增强了对布氏四鼠热能代谢的调节。     

Actin Modulates the Gating of Neurospora crassa VDAC

VDAC forms the major pathway for metabolites across the mitochondrial outer membrane. The regulation of the gating of VDAC channels is an effective way to control the flow of metabolites into and out of mitochondria. Here we present evidence that actin can modulate the gating process of Neurospora crassa VDAC reconstituted into membranes made with phosphatidylcholine. An actin concentration as low as 50 nm caused the VDAC-mediated membrane conductance to drop by as much as 85% at elevated membrane potentials. Actin's effect could be quickly reversed by adding pronase to digest the protein. α-Actin, from mammalian muscle, has a stronger effect than β- and γ-actin from human platelets. The monomeric form of actin, G-actin, is effective. Stabilization of the fibrous form, F-actin, with the mushroom toxin, phalloidin, blocks the effect of actin on VDAC, indicating that F-actin might be ineffective. Cytochalasin B did not interfere with the ability of actin to favor VDAC closure. DNase-I did effectively block actin's effect on VDAC, and VDAC decreased actin's inhibitory effect on DNase-I activity, indicating that N. crassa VDAC competes with DNase-I for the same binding site on actin. The actin-VDAC interaction might be a mechanism by which actin regulates energy metabolism. Received: 28 August 2000/Revised: 1 December 2000     

Mitochondrial iron sequestration in dopamine-challenged astroglia: role of heme oxygenase-1 and the permeability transition pore

Little is currently known concerning the mechanisms responsible for the excessive deposition of redox-active iron in the substantia nigra of subjects with Parkinson's disease (PD). In the present study, we demonstrate that dopamine promotes the selective sequestration of non-transferrin-derived iron by the mitochondrial compartment of cultured rat astroglia and that the mechanism underlying this novel dopamine effect is oxidative in nature. We also provide evidence that up-regulation of the stress protein heme oxygenase-1 (HO-1) is both necessary and sufficient for mitochondrial iron trapping in dopamine-challenged astroglia. Finally, we show that opening of the mitochondrial transition pore (MTP) mediates the influx of non-transferrin-derived iron into mitochondria of dopamine-stimulated and HO-1-transfected astroglia. Our findings provide an explanation for the pathological iron sequestration, mitochondrial insufficiency, and amplification of oxidative injury reported in the brains of PD subjects. Pharmacological blockade of transition metal trapping by "stressed" astroglial mitochondria (e.g., using HO-1 inhibitors or modulators of the MTP) may afford effective neuroprotection in patients with PD and other neurological afflictions.     

Mitochondria at the Crossroad of Apoptotic Cell Death

In the past few years, it has become widely appreciated that apoptotic cell death generallyinvolves activation of a family of proteases, the caspases, which undermine the integrity ofthe cell by cleavage of critical intracellular substrates. Caspases, which are synthesized asinactive zymogens, are themselves caspase substrates and this cleavage leads to their activation.Hence, the potential exists for cascades of caspases leading to cell death. However, it has beenrecently recognized that another, perhaps more prominent route to caspase activation, involvesthe mitochondria. Upon receipt of apoptotic stimuli, either externally or internally generated,cells initiate signaling pathways which converge upon the mitochondria to promote release ofcytochrome C to the cytoplasm; cytochrome c, thus released, acts as a potent cofactor incaspase activation. Even cell surface death receptors such as Fas, which can trigger directcaspase activation (and potentially a caspase cascade), appear to utilize mitochondria as partof an amplification mechanism; it has been recently demonstrated that activated caspases cancleave key substrates to trigger mitochondrial release of cytochrome c, thereby inducing furthercaspase activation and amplifying the apoptotic signal. Therefore, mitochondria play a centralrole in apoptotic cell death, serving as a repository for cytochrome c.