Malate transporters play a critical role in aluminum (Al) tolerance responses for some plant species, such as Arabidopsis (Arabidopsis thaliana). Here, we further characterize AtALMT1, an Arabidopsis aluminum-activated malate transporter, to clarify its specific role in malate release and Al stress responses. Malate excretion from the roots of accession Columbia was sharply induced by Al, which is concomitant with the induction of AtALMT1 gene expression. The malate release was specific for Al among rhizotoxic stressors, namely cadmium, copper, erbium, lanthanum, sodium, and low pH, which accounts for the specific sensitivity of a null mutant to Al stress. Al-specific malate excretion can be explained by a combined regulation of AtALMT1 expression and activation of AtALMT1 protein, which is specific for Al. Although low pH treatment slightly induced gene expression, other treatments did not. In addition, malate excretion in Al-activated seedlings was rapidly stopped by removing Al from the solution. Other rhizotoxic stressors were not effective in maintaining malate release. Protein kinase and phosphatase inhibitor studies indicated that reversible phosphorylation was important for the transcriptional and posttranslational regulation of AtALMT1. AtALMT1 promoter-β-glucuronidase fusion lines revealed that AtALMT1 has restricted expression within the root, such that unnecessary carbon loss is likely minimized. Lastly, a natural nonsense mutation allele of AtALMT1 was identified from the Al-hypersensitive natural accession Warschau-1.
Epidemiological studies suggest that the consumption of flavonoid-rich diets decreases the risk of cardiovascular diseases. However, the target sites of flavonoids underlying the protective mechanism in vivo are not known. Quercetin represents antioxidative/anti-inflammatory flavonoids widely distributed in the human diet. In this study, we raised a novel monoclonal antibody 14A2 targeting the quercetin-3-glucuronide (Q3GA), a major antioxidative quercetin metabolite in human plasma, and found that the activated macrophage might be a potential target of dietary flavonoids in the aorta. Immunohistochemical studies with monoclonal antibody 14A2 demonstrated that the positive staining specifically accumulates in human atherosclerotic lesions, but not in the normal aorta, and that the intense staining was primarily associated with the macrophage-derived foam cells. In vitro experiments with murine macrophage cell lines showed that the Q3GA was significantly taken up and deconjugated into the much more active aglycone, a part of which was further converted to the methylated form, in the activated macrophages. In addition, the mRNA expression of the class A scavenger receptor and CD36, which play an important role for the formation of foam cells, was suppressed by the treatment of Q3GA. These results suggest that injured/inflamed arteries with activated macrophages are the potential targets of the metabolites of dietary quercetin. Our data provide a new insight into the bioavailability of dietary flavonoids and the mechanism for the prevention of cardiovascular diseases.Flavonoids are widely distributed in plant foods and beverages and therefore are regularly ingested with the human diet. In 1936, Rusznyak and Szent-Gyoygi (1) found citrus flavonoids reduced capillary fragility and permeability in blood vessels. Thereafter, a large number of biological activities of flavonoids have been described which overall are believed to be beneficial for good health. Quercetin (3,3Ј,4Ј,5,7-pentahydroxyflavone) is a prime example of such a flavonoid and is bound to sugars in foods, mainly as -glycosides. The quercetin glycosides occur in broccoli, apples, and especially in onions, with an abundance as high as 0.25-0.5 g/kg (2). The average daily intake of the flavonoids subclasses in The Netherlands is 23 mg (calculated as aglycones) of which quercetin supplies 16 mg (3). Epidemiological evidence links diets rich in quercetin with decreased incidence of cardiovascular and neoplastic diseases (4 -9). Because oxidative stress has been implicated in the pathogenesis of these diseases, the bioavailability of quercetin and other flavonoids has been investigated in relation to their antioxidant activities in vivo. The antioxidant potential of quercetin is related to the number and position of the free hydroxyl groups in the molecule (10); therefore, the regioselectivity of conjugation of the hydroxyl groups can be expected to modulate the biological activity of quercetin. Upon ingestion with the diet, quercetin glycosides are rapidly ...
In recent years, depression has become recognized as a major public health problem. It is estimated that in the US approximately 20% of the population has some depressive symptoms, and around 2-5% are thought to suffer from severe forms of depression.1) Understanding how to prevent and treat depression is therefore an urgent subject. Although the mechanism provoking depression has not been clearly elucidated, the main trigger is known to be exposure to chronic stress.2,3) Many types of antidepressant drugs such as tricyclic antidepressants, and selective serotonin reuptake inhibitors (SSRI), as well as antidepressant herbal medicines like St. John's wort are used to treat depression. However, most of the synthetic drugs are not without side effects. 4)Furthermore disturbance of the drug metabolizing enzyme systems were revealed with St. John's wort, 5) and thus, the search for a new antidepressant herb without side effects is deemed important.The Ginkgo biloba tree has been used as a traditional Chinese herbal medicine for thousands of years.6) Several research groups have shown that extracts from the green leaves of the G. biloba tree (EGB) have diverse effects on improvement of mood and cognitive performance, protection of memory deficits and central nervous system (CNS) disorders, and alleviation of the symptoms of mild to moderate Alzheimer-type dementia.7-12) Until now, no antidepressant effect of EGB has yet been revealed. EGB is thought to possess anti-stress properties, 13) and is safe to use without distinct side effects. 8,14) EGB might be a useful option for the prevention and treatment for stress-induced disorders such as depression. In the present study, we evaluated the antidepressant effect of EGB using two behavioral models for screening antidepressants, the forced swimming test (FST) in rats and tail suspension test (TST) in mice. MATERIALS AND METHODS ChemicalsThe EGB used in the present study was Ginkgolon-24 from Tokiwa Phytochemical Co., Ltd. (Chiba, Japan), which was 75% ethanol extracts from the leaves of Japanese G. biloba tree. This product contains 25.5% of flavonoid glycosides, including more than 8.2% quercetin glycosides, more than 6.4% kaempferol glycosides, 1.6% methylmyricetin glycosides and 1.3% isorhamnetin glycosides, and 6.5% of terpenoids in the form of 2.98% bilobalide, 1.59% ginkgolide A, 1.16% ginkgolide B, and 0.75% ginkgolide C. The antidepressant drug imipramine (hydrochloride form) was purchased from Sigma-Aldrich Co. (St. Louis, MO, U.S.A.).Animals Male CD rats (240-260 g; Charles River Japan, Inc., Yokohama, Japan) and male C57BL/6J mice (22-26 g; SLC, Inc., Hamamatsu, Japan) were used in the FST and TST, respectively. All animals were housed in a controlled room (temperature, 25Ϯ1°C; humidity, 45-50%; light-dark cycle, 12 h each) with free access to laboratory chow (MF; Oriental Yeast Co., Ltd., Tokyo, Japan) and tap water. Rodents were divided randomly into control and experimental groups. This study was performed according to the guidelines for the care and use of...
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