Marked accumulation of arachidonic acid (AA) and intracellular Ca2+ and Na+ overloads are seen during brain ischemia. In this study, we show that, in neurons, AA induces cytosolic Na+ ([Na+]cyt) and Ca2+ ([Ca2+]cyt) overload via a non‐selective cation conductance (NSCC), resulting in mitochondrial [Na+]m and [Ca2+]m overload. Another two types of free fatty acids, including oleic acid and eicosapentaenoic acid, induced a smaller increase in the [Ca2+]i and [Na+]i. RU360, a selective inhibitor of the mitochondrial Ca2+ uniporter, inhibited the AA‐induced [Ca2+]m and [Na+]m overload, but not the [Ca2+]cyt and [Na+]cyt overload. The [Na+]m overload was also markedly inhibited by either Ca2+‐free medium or CGP3715, a selective inhibitor of the mitochondrial Na+cyt‐Ca2+m exchanger. Moreover, RU360, Ca2+‐free medium, Na+‐free medium, or cyclosporin A (CsA) largely prevented AA‐induced opening of the mitochondrial permeability transition pore, cytochrome c release, and caspase 3‐dependent neuronal apoptosis. Importantly, Na+‐ionophore/Ca2+‐free medium, which induced [Na+]m overload, but not [Ca2+]m overload, also caused cyclosporin A‐sensitive mitochondrial permeability transition pore opening, resulting in caspase 3‐dependent apoptosis, indicating that [Na+]m overload per se induced apoptosis. Our results therefore suggest that AA‐induced [Na+]m overload, acting via activation of the NSCC, is an important upstream signal in the mitochondrial‐mediated apoptotic pathway. The NSCC may therefore act as a potential neuronal death pore which is activated by AA accumulation under pathological conditions.

Arachidonic acid (AA) exerts multiple physiological and pathophysiological effects in the brain. By continuously measuring the intracellular pH (pHi) and Ca2+ levels ([Ca2+]i) in primary cultured rat cerebellar granule cells, we have found, for the first time, that 20 min treatment with 10 μm AA resulted in marked increases in Ca2+ and H+ levels in both the cytosol and nucleus. A much higher concentration (40 mm) of another weak acid, propionic acid, was needed to induce a similar change in pHi. The [Ca2+]i increase was probably caused by AA‐induced activation of Ni2+‐sensitive cationic channels, but did not involve NMDA channels or the Na+‐Ca2+ exchanger. AA‐induced acidosis occurs by a different mechanism involving predominantly the passive diffusion of the un‐ionized form of AA, rather than a protein carrier, as proposed by Kamp & Hamilton for fatty acids (FAs) in artificial phospholipid bilayers (the ‘flip‐flop’ model). The following results, which are similar to those observed in lipid bilayers, support this conclusion: (1) FAs containing a ‐COOH group (AA, linoleic acid, α‐linolenic acid, and docosahexaenoic acid) induced intracellular acidosis, whereas a FA with a ‐COOCH3 group (AA methyl ester) had little effect on pHi, (2) a FA amine, tetradecylamine, induced intracellular alkalosis, and (3) the AA‐/FA‐induced pHi changes were reversed by bovine serum albumin. Further evidence in support of a passive diffusion model, rather than a membrane protein carrier, is that: (1) there was a linear relationship between the initial rate of acid flux and the concentration of AA (2‐100 μm), (2) acidosis was not inhibited by 4,4′‐diisothiocyanatostilbene‐2,2′‐disulphonic acid, a potent inhibitor of the plasma membrane FA carrier protein, and (3) the involvement of most known H+‐related membrane carriers and H+ conductance has been ruled out. Since AA can be released under both physiological and pathophysiological conditions, the possible significance of the AA‐evoked increases in H+ and Ca2+ in both the cytoplasm and nucleoplasm is discussed.

Pretreatment with thaliporphine before ischemia affords cardioprotective effects against reperfusion injury via antioxidant activity. This study evaluated whether thaliporphine administered at a certain period after myocardial ischemia conferred the same cardioprotection and assessed its possible new mechanism. The left main coronary artery of anaesthetized rats was occluded for 1 h and then reperfused for 2 h. Thaliporphine was administered at 10 min before reperfusion. Controls received saline only. Morphine, a nonselective opioid receptor agonist, was used as reference compound at 0.3 mg/kg. Thaliporphine at 0.05 and 0.5 mg/kg were found to reduce the infarct size. Recovery of cardiac function was higher in thaliporphine (0.5 mg/kg) group, as assessed by a significant improvement in the rates of pressure development (+dp/dt (max)). This compound also reduced plasma creatine kinase and cardiac MPO activity. These protective effects afforded by thaliporphine were diminished by the opioid receptor antagonists (naloxone or naltrexone) and by the mitochondrial K(ATP) blocker 5HD. In comparison, morphine reduced infarct size and MPO activity in the myocardium but produced slightly improvement in cardiac function after ischemia-reperfusion. These results demonstrate that reperfusion therapy with thaliporphine protect cardiac injury through further mechanism via activation of opioid receptor and opening of mitochondrial K(ATP) channels as morphine but with stronger activity.

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Hepatocellular carcinoma (HCC) has become one of most common malignancies and a leading cause of cancer mortality worldwide. Previous study has shown that 4-acetylantroquinonol B (4AAQB) isolated from Antrodia cinnamomea (or niu-chang-chih) was observed to inhibit HepG2 cell proliferation via affecting cell cycle. However, the in vivo effects and antimetastatic activity of 4AAQB have not yet been addressed. This study found that 4AAQB inhibited HepG2 and HuH-7 hepatoma cell growth in both in vitro and in vivo models and exhibited pronounced inhibitory effects on HuH-7 tumor growth in xenograft and orthotopic models. 4AAQB efficiently inhibited the phosphorylation of mTOR and its upstream kinases and the downstream effectors and decreased the production of VEGF and activity of Rho GTPases in HuH-7 cells. Furthermore, 4AAQB inhibited in vitro HuH-7 cell migration and in vivo pulmonary metastasis. The results suggested that 4AAQB is a potential candidate for HCC therapy.