Inhibition of arachidonic acid and iron-induced mitochondrial dysfunction and apoptosis by oltipraz and novel 1,2-dithiole-3-thione congeners

4-Methyl-5-(2-pyrazinyl)-1,2-dithiole-3-thione (oltipraz), a prototype drug candidate containing a 1,2-dithiole-3-thione moiety, has been widely studied as a cancer chemopreventive agent. Oltipraz and other novel 1,2-dithiole-3-thione congeners have the capability to prevent insulin resistance via AMP-activated protein kinase (AMPK) activation. Arachidonic acid (AA, a proinflammatory fatty acid) exerts a deleterious effect on mitochondria and promotes reactive oxygen species (ROS) production. This study investigated whether AA alone or in combination with iron (catalyst of autooxidation) causes ROS-mediated mitochondrial impairment, and if so, whether oltipraz and synthetic 1,2-dithiole-3-thiones protect mitochondria and cells against excess ROS produced by AA + iron. Oltipraz treatment effectively inhibited mitochondrial permeability transition promoted by AA + iron in HepG2 cells, thereby protecting cells from ROS-induced apoptosis. Oltipraz was found to attenuate apoptosis induced by rotenone (complex I inhibitor), but not that by antimycin A (complex III inhibitor), suggesting that the inhibition of AA-induced apoptosis by oltipraz might be associated with the electron transport system. AMPK activation by oltipraz contributed to cell survival, which was supported by the reversal of oltipraz's restoration of mitochondrial membrane potential by concomitant treatment of compound C. By the same token, an AMPK activator inhibited AA + iron-induced mitochondrial permeability transition with an increase in cell viability. Moreover, new 1,2-dithiole-3-thiones with the capability of AMPK activation protected cells from mitochondrial permeability transition and ROS overproduction induced by AA + iron. Our results demonstrate that oltipraz and new 1,2-dithiole-3-thiones are capable of protecting cells from AA + iron-induced ROS production and mitochondrial dysfunction, which may be associated with AMPK activation.     

New anthracene glycosides from <Emphasis Type="Italic">Rhodomyrtus tomentosa</Emphasis> stimulate osteoblastic differentiation of MC3T3-E1 cells

Two new anthracene glycosides (1, 2) were isolated from aerial parts of Rhodomyrtus tomentosa, along with three known compounds (3–5). The structures of two new compounds were established to be 4,8,9,10-tetrahydroxy-2,3,7-trimethoxyanthracene-6-O-β-D-glucopyranoside (1) and 2,4,7,8,9,10-hexahydroxy-3-methoxyanthracene-6-O-α-L-rhamnopyranoside (2) based on spectroscopic and chemical methods. Among them, compound 1, 2, and 5 significantly (P<0.05) increased the alkaline phosphatase activity, collagen synthesis, and mineralization of the nodules of MC3T3-E1 osteoblastic cells compared to those of the control, respectively.     

Synthesis and Evaluation of N-Nicotinoyl-2-{2-(2-Methyl-5-Nitroimidazol-1-yl)Ethyloxy}-D,L-Glycine as a Colon-Specific Prodrug of Metronidazole

Metronidazole (MTZ) is a drug of choice for protozoal infections such as luminal amoebiasis. We designed and synthesized N-nicotinoyl-2-{2-(2-methyl-5-nitroimidazol-1-yl)ethyloxy}-D,L-glycine (NMG) as a colon-specific prodrug of MTZ. The synthetic yield of NMG was about 34%. The apparent partition coefficient of MTZ was greatly reduced by the chemical modification. While (bio)chemically stable in the contents of the upper intestine, NMG was rapidly cleaved to liberate MTZ on incubation with the cecal contents of rats. MTZ metabolized quickly in the cecal contents at least partly by a microbial nitroreductase, suggesting that the metabolism of MTZ is relevant to its bioactivation leading to amoebicidal action. The systemic absorption, analyzed by the blood concentration and urinary recovery of NMG, was very low after oral administration of NMG. In parallel with this, whereas MTZ disappeared mostly during the transit of the proximal small intestine, a substantial amount of NMG remained in the small intestine moving down to the large intestine where it metabolized rapidly. Moreover, comparing systemic absorption of MTZ after oral administration of NMG or MTZ, NMG markedly reduced the systemic absorption. These results suggest that NMG is a potential colon-specific prodrug of MTZ which improves therapeutic and toxicological properties. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:4161–4169, 2009     

Mollugin induces apoptosis in human Jurkat T cells through endoplasmic reticulum stress-mediated activation of JNK and caspase-12 and subsequent activation of mitochondria-dependent caspase cascade regulated by Bcl-xL

Exposure of Jurkat T cells to mollugin (15–30 μM), purified from the roots of Rubia cordifolia L., caused cytotoxicity and apoptotic DNA fragmentation along with mitochondrial membrane potential disruption, mitochondrial cytochrome c release, phosphorylation of c-Jun N-terminal kinase (JNK), activation of caspase-12, -9, -7, -3, and -8, cleavage of FLIP and Bid, and PARP degradation, without accompanying necrosis. While these mollugin-induced cytotoxicity and apoptotic events including activation of caspase-8 and mitochondria-dependent activation of caspase cascade were completely prevented by overexpression of Bcl-xL, the activation of JNK and caspase-12 was prevented to much lesser extent. Pretreatment of the cells with the pan-caspase inhibitor (z-VAD-fmk), the caspase-9 inhibitor (z-LEHD-fmk), the caspase-3 inhibitor (z-DEVD-fmk) or the caspase-12 inhibitor (z-ATAD-fmk) at the minimal concentration to prevent mollugin-induced apoptosis appeared to completely block the activation of caspase-7 and -8, and PARP degradation, but failed to block the activation of caspase-9 and -3 with allowing a slight enhancement in the level of JNK phosphorylation. Both FADD-positive wild-type Jurkat clone A3 and FADD-deficient Jurkat clone I2.1 exhibited a similar susceptibility to the cytotoxicity of mollugin, excluding involvement of Fas/FasL system in triggering mollugin-induced apoptosis. Normal peripheral T cells were more refractory to the cytotoxicity of mollugin than were Jurkat T cells. These results demonstrated that mollugin-induced cytotoxicity in Jurkat T cells was mainly attributable to apoptosis provoked via endoplasmic reticulum (ER) stress-mediated activation of JNK and caspase-12, and subsequent mitochondria-dependent activation of caspase-9 and -3, leading to activation of caspase-7 and -8, which could be regulated by Bcl-xL.     

Regulation of renin secretion and expression in mice deficient in beta1- and beta2-adrenergic receptors

The present experiments were performed in beta1/beta2-adrenergic receptor-deficient mice (beta1/beta2ADR(-/-)) to assess the role of beta-adrenergic receptors in basal and regulated renin expression and release. On a control diet, plasma renin concentration (in ng angiotensin I per mL per hour), determined in tail vein blood, was significantly lower in beta1/beta2ADR(-/-) than in wild-type (WT) mice (222+/-65 versus 1456+/-335; P<0.01). Renin content and mRNA were 77% and 65+/-5% of WT. Plasma aldosterone (in picograms per mL) was also significantly reduced (420+/-36 in beta1/beta2ADR(-/-) versus 692+/-59 in WT). A low-salt diet (0.03%) for 1 week increased plasma renin concentration significantly in both beta1/beta2ADR(-/-) and WT mice (to 733+/-54 and 2789+/-555), whereas a high-salt diet (8%) suppressed it in both genotypes (to 85+/-24 in beta1/beta2ADR(-/-) and to 676+/-213 in WT). The absolute magnitude of salt-induced changes of plasma renin concentration was markedly greater in WT mice. Acute stimulation of renin release by furosemide, quinaprilat, captopril, or candesartan caused significant increases of plasma renin concentration in both beta1/beta2ADR(-/-) and WT mice, but again the absolute changes were greater in WT mice. We conclude that maintenance of normal levels of renin synthesis and release requires tonic beta-adrenergic receptor activation. In the chronic absence of beta-adrenergic receptor input, the size of the releasable renin pool decreases with a concomitant reduction in the magnitude of the plasma renin concentration changes caused by variations of salt intake or acute stimulation with furosemide, angiotensin-converting enzyme, or angiotensin type 1 receptor inhibition, but regulatory responsiveness is nonetheless maintained.