Tramadol is an analgesic that is used worldwide, but its mechanisms of action have not been elucidated. It has been speculated that tramadol acts primarily through the activation of μ-opioid receptors and the inhibition of monoamine reuptake. The majority of studies to date have focused on ion channels in the central nervous system as targets of anesthetics and analgesics. During the past decade, major advances have been made in our understanding of the physiology and pharmacology of G-protein coupled receptor (GPCR) signaling. Several studies have shown that GPCRs and ion channels are targets for analgesics and anesthetics. In particular, tramadol has been shown to affect GPCRs, including muscarinic acetylcholine receptors and 5-hydroxytryptamine receptors. Here, the effects of tramadol on monoamine transporters, GPCRs, and ion channels are presented, and recent research on the pharmacology of tramadol is discussed.
Lipid-laden foam cells were considered to be targets for therapeutic intervention in atherosclerosis. Several studies proposed new approaches to alter both lipid accumulation and inflammatory responses in macrophages. Finding anti-inflammatory signals during foam cell formation would provide new valid targets for anti-atherosclerotic treatment. The aim of the present study was to see whether oxidized low-density lipoprotein (ox-LDL) can active heme oxygenase (HO)-1 expression level in a human monocyte line, U937 cells, associated with the increase of cytokine secretion. We used hemin (HO-1 activator) and zinc protoporphyrin IX (ZnPP IX, HO-1 inhibitor) to determine the effect of HO-1 on the regulation of cytokine expressions. The results showed that hemin can significantly decrease pro-inflammatory cytokines interleukin (IL)-1β and tumor necrosis factor (TNF)-α levels, while enhancing IL-10 production in a dose-dependent manner in U937 foam cells. ZnPP IX did not significantly affect cytokine levels in foam cells. Our present results suggested that HO-1 is an important anti-inflammatory therapeutic target through inhibiting pro-inflammatory cytokines and enhancing anti-inflammatory cytokines for the management of atherogenesis.
In this study, we investigated hypolipidemic mechanisms of the ethanolic extract of Ananas comosus L. leaves (AC) in mice and then determined its activities in related enzymes. The results showed that AC (0.40 g/kg) significantly inhibited the increase in serum triglycerides by 40% in fructose-fed mice. In mice induced by alloxan and high-fat diets, serum total cholesterol remained at a high level (180 – 220 mg/dl) within 7 days of removing high-fat diets but reached normal level (120 – 140 mg/dl) after AC (0.40 g/kg per day) treatment. Also, AC (0.40 and 0.80 g/kg) significantly inhibited serum lipids from the increase in Triton WR-1339-induced hyperlipidemic mice. AC (0.01 – 100 μg/ml) selectively activated lipoprotein lipase (LPL) activity by 200% – 400% and significantly inhibited 3-hydroxyl-methyl glutaryl coenzyme A (HMGCoA) reductase activity by 20% – 49% in vitro. Furthermore, 2 months of fenofibrate (0.20 g/kg) administration particularly increased mice liver weights (0.0760 ± 0.0110 g/g) while AC (0.40 g/kg) had no effect (0.0403 ± 0.0047). Taken together, these results suggest that AC will be a new potential natural product for the treatment of hyperlipidemia that exerts its actions through mechanisms of inhibiting HMGCoA reductase and activating LPL activities. Its action mechanisms differentiate from those with fibrates but may be partly similar to those with statins. It is hopeful that AC may serve as the adjuvant for fibrates.
Cigarette smoking-induced oxidative stress plays a key role in the pathogenesis of atherosclerosis in smokers. Aqueous cigarette smoke extract (CSE) contains stable oxidants, peroxynitrite-like reactants, which have the ability to oxidize and nitrate low-density lipoprotein (LDL). We examined whether oxidants in CSE can penetrate into the blood through the lung alveolar wall and cause oxidative vascular injury. The oxidants in CSE and sodium peroxynitrite could easily pass through the reconstituted basement membrane. When CSE or sodium peroxynitrite solution was infused into the alveolar air space of an isolated rat lung mounted in tyrosine solution, CSE gradually increased the 3-nitrotyrosine levels in the external tyrosine solution while sodium peroxynitrite caused a rapid increase. CSE did not activate the rat alveolar macrophages. When rats were acutely exposed to the gas phase of cigarette smoke from which tar and nicotine had been removed, both serum levels of 3-nitrotyrosine and 8-hydroxy-2'-deoxyguanine, oxidative stress markers, rapidly increased. Our results demonstrate that relatively stable oxidants in CSE can pass through the pulmonary alveolar wall into the blood and induce systemic oxidative stress, which most likely facilitates oxidative modification of LDL and endothelial dysfunction, explaining early key events in the development of atherosclerosis.
Using the whole-cell voltage clamp, we examined the mechanism of activation of the Na+/Ca2+ exchanger (NCX) by hydrogen peroxide (H2O2) in isolated guinea-pig cardiac ventricular myocytes. Exposure to H2O2 increased the NCX current. The effect was inhibited by cariporide, an inhibitor of the Na+/H+ exchanger (NHE), suggesting that there are NHE-dependent and -independent pathways in the effect of H2O2 on NCX. In addition, both pathways were blocked by edaravone, a hydroxyl radical (•OH) scavenger; pertussis toxin, a Gαi/o protein inhibitor; and U0126, an inhibitor of mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK). On the other hand, wortmannin, a phosphatidylinositol 3-kinase (PI3K) inhibitor, inhibited only the NHE-dependent pathway, while PP2, a Src family protein tyrosine kinase inhibitor, inhibited only the NHE-independent pathway. Taken together, our data suggest that H2O2 increases the NCX current via two signal transduction pathways. The common pathway is the conversion of H2O2 to •OH, which activates Gαi/o protein and a mitogen-activated protein (MAP) kinase signaling pathway. Then, one pathway activates NHE with a PI3K-dependent mechanism and indirectly increases the NCX current. Another pathway involves activation of a Src family tyrosine kinase.
Recent findings have suggested that the N-methyl-D-aspartate (NMDA) receptor-dependent hydroxyl radical pathway in the hypothalamus of rabbit brain may mediate the fever induced by lipopolysaccharide (LPS). The aim of this study was to investigate whether aspirin exerts its antipyresis by suppressing hypothalamic glutamate and hydroxyl radicals in rabbits. The microdialysis probes were stereotaxically and chronically implanted into the preoptic anterior hypothalamus of rabbit brain for determination of both glutamate and hydroxyl radicals in situ. It was found that intravenous (i.v.) injection of LPS, in addition to inducing fever, caused increased levels of both glutamate and hydroxyl radicals in the hypothalamus. Pretreatment with aspirin (10 – 60 mg/kg, i.v.) one hour before an i.v. dose of LPS significantly reduced the febrile response and attenuated the LPS-induced increased levels of both glutamate and hydroxyl radicals in the hypothalamus. The increased levels of prostaglandin E2 (PGE2) in the hypothalamus induced by LPS could be suppressed by aspirin pretreatment. The data indicate that systemic administration of aspirin, in addition to suppressing PGE2 production, may exert its antipyresis by inhibiting the NMDA receptor-dependent hydroxyl radical pathways in the hypothalamus during LPS fever.
It has recently been suggested that neurogenesis in the dentate gyrus is decreased in schizophrenia and this phenomenon may contribute to the pathogenesis of the disorder. Since repeated administration of psychostimulants such as phencyclidine (PCP), MK-801, and methamphetamine (METH) induces schizophrenia-like behavioral changes in animals, we investigated whether repeated administration of these psychostimulants affects neurogenesis in the dentate gyrus of mice. Newborn cells were labeled by bromodeoxyuridine (BrdU) and detected by immunohistochemistry. Repeated administration of PCP and MK-801, but not METH, resulted in a decrease in the number of BrdU-labeled cells in the dentate gyrus. PCP-induced decrease in the number of BrdU-labeled cells was negated by co-administration of clozapine, but not haloperidol, although repeated antipsychotics treatment by themselves had no effect. Furthermore, co-administration of D-serine and glycine, but not L-serine, inhibited the PCP-induced decrease in the number of BrdU-labeled cells. These results suggest that chronic dysfunction of NMDA receptors causes a decrease in neurogenesis in the dentate gyrus.
Preliminary clinical studies of testosterone therapy in male patients with coronary artery disease obtained promising results. However, little is known about the in vitro effects of testosterone in human isolated arteries. We investigated the effect of testosterone on contractile tone of human isolated radial artery (RA). Testosterone was added (0.1 – 300 μM ) cumulatively to organ baths after precontraction with KCl (45 mM) and phenylephrine (PE, 10 μM). Testosterone-induced relaxations were tested in the presence of the cyclooxygenase inhibitor indomethacin (10 μM), nitric oxide synthase inhibitor Nω-nitro-L-arginine methyl ester (L-NAME, 100 μM), non-selective large conductance Ca2+-activated and voltage-sensitive K+ channel inhibitor tetraethylammonium (TEA, 1 mM), ATP-sensitive K+ channel inhibitor glibenclamide (GLI, 10 μM), and voltage-sensitive K+ channel inhibitor 4-aminopyridine (4-AP, 1 mM). Testosterone produced relaxation in human RA (Emax: 53.03 ± 2.76% and 66.83 ± 1.97% of KCl and PE-induced contraction, respectively). Except for GLI, the relaxation to testosterone is affected by neither K+ channel inhibitors (TEA, BaCl2, and 4-AP), L-NAME, nor indomethacin. We report for the first time that supraphysiological concentrations of testosterone induces relaxation in RA. This response may occur in part via ATP-sensitive K+ channel opening action.
We have reported that chronically administered pravastatin prevented coronary artery reperfusion-induced lethal ventricular fibrillation (VF) in anesthetized rats without lowering the serum cholesterol level. The present study was undertaken to evaluate whether pravastatin prevents ischemia-induced lethal VF, simultaneously examining myeloperoxidase (MPO) activity in ischemic myocardial tissues. Anesthetized rats were subjected to 30-min ischemia and 60-min reperfusion after chronic administration of pravastatin (0.02, 0.2, and 2 mg/kg), fluvastatin (2 and 4 mg/kg), or vehicle for 22 days, orally, once daily. ECG and blood pressure were continually recorded, and MPO was measured by a spectrophotometer. Pravastatin and fluvastatin significantly (P<0.05) decreased MPO activities, but only pravastatin decreased the incidence of ischemia-induced lethal VF. Both statins had no significant effects on body weight, blood pressure, heart rate, and QT interval as we reported earlier. Our results prove further that pravastatin has benefits to decrease cardiovascular mortality beyond its cholesterol-lowering effect. Pravastatin is more potent than fluvastatin in prevention of arrhythmias. A decrease in the neutrophil infiltration may be partly involved in the inhibitory effect of pravastatin on the ischemia-induced VF.
The aim of the present study was to elucidate the effects of indapamide on ischemic damage to the blood-brain barrier (BBB) in vitro. The ischemia/reperfusion conditions employed here significantly decreased the viability of mouse brain capillary endothelial (MBEC4) cells, an effect ameliorated by indapamide. Ischemia increased the permeability of MBEC4 cells to two cellular transport markers, sodium fluorescein and Evan’s blue-albumin. Indapamide reduced the ischemia-induced hyperpermeability of cells. These results suggest that indapamide may have a protective role against ischemia-induced injury and dysfunction of the BBB.
In this study, we examined the combination effects of L-DOPA and adenosine receptor antagonists on rotational behaviors in a hemi-Parkinsonian mouse model induced by unilateral 6-hydroxydopamine (6-OHDA) injection. The adenosine A2A antagonist SCH-58261, but not the A1-receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine or A2B-receptor antagonist alloxazine, synergistically potentiated the L-DOPA-induced rotational behaviors in the 6-OHDA-lesioned mice. In addtion, the 6-OHDA-induced lesions of the dopaminergic system did not affect the in vivo binding of an adenosine A2A-receptor tracer [11C]SCH-442416 in the striatatum. These findings suggest that adenosine A2A antagonists are extremely useful for pharmacotherapy of L-DOPA in Parkinson’s disease patients.