Direct inhibition of the hexose transporter GLUT1 by tyrosine kinase inhibitors

The facilitative hexose transporter GLUT1 is a multifunctional protein that transports hexoses and dehydroascorbic acid, the oxidized form of vitamin C, and interacts with several molecules structurally unrelated to the transported substrates. Here we analyzed in detail the interaction of GLUT1 with a group of tyrosine kinase inhibitors that include natural products of the family of flavones and isoflavones and synthetic compounds such as the tyrphostins. These compounds inhibited, in a dose-dependent manner, the transport of hexoses and dehydroascorbic acid in human myeloid HL-60 cells, in transfected Chinese hamster ovary cells overexpressing GLUT1, and in normal human erythrocytes, and blocked the glucose-displaceable binding of cytochalasin B to GLUT1 in erythrocyte ghosts. Kinetic analysis of transport data indicated that only tyrosine kinase inhibitors with specificity for ATP binding sites inhibited the transport activity of GLUT1 in a competitive manner. In contrast, those inhibitors that are competitive with tyrosine but not with ATP failed to inhibit hexose uptake or did so in a noncompetitive manner. These results, together with recent evidence demonstrating that GLUT1 is a nucleotide binding protein, support the concept that the inhibitory effect on transport is related to the direct interaction of the inhibitors with GLUT1. We conclude that predicted nucleotide-binding motifs present in GLUT1 are important for the interaction of the tyrosine kinase inhibitors with the transporter and may participate directly in the binding transport of substrates by GLUT1.     

Covariance and decoupling of floral and vegetative traits in nine Neotropical plants: a re-evaluation of Berg's correlation-pleiades concept

Nearly forty years ago R. L. Berg proposed that plants with specialized pollination ecology evolve genetic and developmental systems that decouple floral morphology from phenotypic variation in vegetative traits. These species evolve separate floral and vegetative trait clusters, or as she termed them, "correlation pleiades." The predictions of this hypothesis have been generally supported, but only a small sample of temperate-zone herb and grass species has been tested. To further evaluate this hypothesis, especially its applicability to plants of other growth forms, we examined the patterns of phenotypic variation and covariation of floral and vegetative traits in nine species of Neotropical plants. We recognized seven specific predictions of Berg's hypothesis. Our results supported some predictions but not others. Species with specialized pollination systems usually had floral traits decoupled (weak correlation; Canna and Eichornia) or buffered (relationship with shallow proportional slope; Calathea and Canna) from variation in vegetative traits. However, the same trend was also observed in three species with unspecialized pollination systems (Echinodorus, Muntingia, and Wedelia). One species with unspecialized pollination (Croton) and one wind-pollinated species (Cyperus) showed no decoupling or buffering, as predicted. While species with specialized pollination usually showed lower coefficients of variation for floral traits than vegetative traits (as predicted), the same was also true of species with unspecialized or wind pollination (unlike our prediction). Species with specialized pollination showed less variation in floral traits than did species with unspecialized or wind pollination, as predicted. However, the same was true of the corresponding vegetative traits, which was unexpected. Also in contrast to our prediction, plants with specialized pollination systems did not exhibit tighter phenotypic integration of floral characters than did species with generalized pollination systems. We conclude that the patterns of morphological integration among floral traits and between floral and vegetative traits tend to be species specific, not easily predicted from pollination ecology, and generally more complicated than R. L. Berg envisaged.     

Derivatives of 1,4-dihydropyridines as modulators of ascorbate-induced lipid peroxidation and high-amplitude swelling of mitochondria, caused by ascorbate, sodium linoleate and sodium pyrophosphate

A group of 26 2,6-dimethyl-3,5-disubstituted and 2,6-dimethyl-3,4, 5-trisubstituted-1,4-dihydropyridines (1,4-H(2)Py=1,4-DHPs) and five related pyridines were studied as inhibitors of rat liver mitochondrial swelling and O(2) uptake by ascorbic acid-dependent lipid peroxidation (LP) and as modulators of mitochondrial swelling induced by Na(+)-linoleate or Na(+)-pyrophosphate. 1,4-DHPs studied include 4-unsubstituted and 4-methyl- and 4-phenyl-substituted 3, 5-dialkoxycarbonylderivatives of 2,6-dimethyl-1,4-DHP with variations in alkoxy chain length and composition, 4-unsubstituted and 4-methyl-, 4-aryl- and 4-pyridyl-substituted 3, 5-dianilidocarbonylderivatives, and a structurally related group of 3,5-dipyridylamidocarbonylderivatives. Many 1,4-DHPs possess marked antioxidant (AO) and membrane stabilizing activity, expressed as the mitochondrial swelling (deltaA(520)/t) and/or O(2) uptake rate decrease (V(0)/V) as well as prolongation of the induction period (tau/tau(0)) of mitochondrial swelling and/or O(2) uptake at ascorbic acid-dependent LP of rat liver mitochondria. 4-Unsubstituted 3,5-dialkoxycarbonyl-2,6-dimethyl-1,4-DHPs, as well as 4-unsubstituted or those possessing lipophylic 4-aryl- groups 3, 5-diamido-2,6-dimethyl-1,4-DHPs, reveal marked AO and membrane stabilizing properties. Oxidized (heteroaromatized) derivatives have minimal activity. Perhaps 1,4-DHPs preferably act as antioxidants on stages of initiation and prolongation of LP chain reactions at low concentrations: IC(50) (when V(0)/V or tau/tau(0)=2) are 0.1 microM to 100 microM. At 100 microM 3,5-di-p-hydroxyphenoxycarbonyl- and 3, 5-di-p-tolyloxycarbonyl-2,6-dimethyl-1,4-DHPs, as well as 3, 5-diethoxycarbonyl-2,6-dimethylpyridine (oxidized form of Hantzsch ester) and 3,5-diamyloxycarbonyl-2,6-dimethylpyridine, alter the mitochondrial swelling rate in the presence of natural protonophore Na(+)-linoleate (0.063 mM and 0.125 mM). 3,5-Di-n-butyloxycarbonyl-2, 6-dimethyl-1,4-DHP at 100 microM completely stops mitochondrial swelling in the presence of 0.8 mM Na(+)-pyrophosphate. In the presence of many of the 1,4-DHPs, the lipid peroxidation process was inhibited. However, the swelling process could be prolonged, promoted, accelerated or inhibited-depending on 1,4-DHPs structure, concentration, the type of initiators of the swelling process and the medium composition.     

Presence of non-suppressive, M2-related dsRNAs molecules in Saccharomyces cerevisiae strains isolated from spontaneous fermentations

Total dsRNA extractions in five killer K2 strains of Saccharomyces cerevisiae isolated from spontaneous fermentations revealed the presence of a novel dsRNA fragment (which we named NS dsRNA) of approximately 1.30 kb, together with L and M2 dsRNAs. NS dsRNA appeared to be encapsidated in the same kind of viral particles as L and M2 dsRNA. Northern blot hybridization experiments indicated that NS dsRNA was derived from M2 dsRNA, likely by deletion of the internal A+U-rich region. However, unlike S dsRNAs (suppressive forms derived from M1 dsRNA in K1 killers), NS dsRNA did not induce exclusion of the parental M2 dsRNA when the host strain was maintained for up to 180 generations of growth.     

The effect of new lipophilic chelators on the activities of cytosolic reductases and P450 cytochromes involved in the metabolism of anthracycline antibiotics: studies in vitro

A major obstacle to the therapeutic use of anthracyclines, highly effective anticancer agents, is the fact that their administration results in dose-dependent cardiomyopathy. According to the currently accepted hypothesis, anthracyclines injure the heart by generating oxygen free radicals. The ability of pyridoxal isonicotinoyl hydrazone (PIH) and salicylaldehyde isonicotinoyl hydrazone (SIH) -- new iron chelators -- to protect against peroxidation as well as their suitable biological, physical and chemical properties make the compounds promising candidates for pre-clinical and clinical studies. Activities of carbonyl reductase CR (1.1.1.184), dihydrodiol dehydrogenase DD2 (1.3.1.20), aldehyde reductase ALR1 (1.1.1.2) and P450 isoenzymes (CYP1A1, CYP1A2, CYP2B, CYP3A) involved in the metabolism of daunorubicin, doxorubicin and other drugs or xenobiotics were studied. Various concentrations of the chelators were used either alone or together with daunorubicin or doxorubicin for in vitro studies in isolated hepatocytes. A significant decrease of activity was observed for all enzymes only at PIH and SIH concentrations higher than those presumed to be used for therapy. The results show that PIH and SIH have no effect on the activities of the enzymes studied in vitro and allow us to believe that they will not interfere with the metabolism of co-administered drugs and other xenobiotics. Daunorubicin (Da) and doxorubicin (Dx) significantly reduce cytochrome P450 activity, but the addition of SIH and PIH chelators (50 microM) reverses the reduction and restores the activity to 70-90 % of the activity of relevant controls.     

A new heptasubstituted (E)-aurone glucoside and other aromatic compounds of Gomphrena agrestis with biological activity

A new aurone 1 and two known substances, aurantiamide acetate (2) and tiliroside (3), were isolated from the ethanolic extract of Gomphrena agrestis. The structural determination of 1 was based on spectroscopic and spectrometric data. The substance was defined as (E)-3'-O-beta-D-glucopyranosyl-4,5,6,4'-tetrahydroxy-7,2'-dimethoxyaurone. Biological activity of the ethanolic crude extract and isolated compounds against bacteria, fungi and Leishmania amazonensis amastigotes was evaluated. This appears to be the first report documenting aurone and aurantiamide compounds in the Amaranthaceae family. In the evaluation of biological activity the ethanolic extract of G. agrestis and compounds 1, 2, and 3 were shown to be active mainly against Staphylococcus aureus, Staphylococcus epidermidis and Pseudomonas aeruginosa.