Isolation of the pyrrolizidine alkaloid 1-epialexine from Castanospermum australe

The Australian leguminous tree Castanospermum australe contains the anti-viral glucose analogue indolizidine alkaloid castanospermine. As the result of a search for new bioactive carbohydrate-like compounds we now report the isolation of the novel polyhydroxylated pyrrolizidine alkaloid, 1-epialexine, from the leaves and stems of C. australe. 1-Epialexine is a weak inhibitor of β-mannosidase from Cellullomonas fimi.     

Elevated Levels of Asymmetric Dimethylarginine (ADMA) in the Pericardial Fluid of Cardiac Patients Correlate with Cardiac Hypertrophy

Background

Pericardial fluid (PF) contains several biologically active substances, which may provide information regarding the cardiac conditions. Nitric oxide (NO) has been implicated in cardiac remodeling. We hypothesized that L-arginine (L-Arg) precursor of NO-synthase (NOS) and asymmetric dimethylarginine (ADMA), an inhibitor of NOS, are present in PF of cardiac patients and their altered levels may contribute to altered cardiac morphology.

Methods

L-Arg and ADMA concentrations in plasma and PF, and echocardiographic parameters of patients undergoing coronary artery bypass graft (CABG, n = 28) or valve replacement (VR, n = 25) were determined.

Results

We have found LV hypertrophy in 35.7% of CABG, and 80% of VR patients. In all groups, plasma and PF L-Arg levels were higher than that of ADMA. Plasma L-Arg level was higher in CABG than VR (75.7±4.6 μmol/L vs. 58.1±4.9 μmol/L, p = 0.011), whereas PF ADMA level was higher in VR than CABG (0.9±0.0 μmol/L vs. 0.7±0.0 μmol/L, p = 0.009). L-Arg/ADMA ratio was lower in the VR than CABG (VR_plasma: 76.1±6.6 vs. CABG_plasma: 125.4±10.7, p = 0.004; VR_PF: 81.7±4.8 vs. CABG_PF: 110.4±7.2, p = 0.009). There was a positive correlation between plasma L-Arg and ADMA in CABG (r = 0.539, p = 0.015); and plasma and PF L-Arg in CABG (r = 0.357, p = 0.031); and plasma and PF ADMA in VR (r = 0.529, p = 0.003); and PF L-Arg and ADMA in both CABG and VR (CABG: r = 0.468, p = 0.006; VR: r = 0.371, p = 0.034). The following echocardiographic parameters were higher in VR compared to CABG: interventricular septum (14.7±0.5 mm vs. 11.9±0.4 mm, p = 0.000); posterior wall thickness (12.6±0.3 mm vs. 11.5±0.2 mm, p = 0.000); left ventricular (LV) mass (318.6±23.5 g vs. 234.6±12.3 g, p = 0.007); right ventricular (RV) (33.9±0.9 cm² vs. 29.7±0.7 cm², p = 0.004); right atrial (18.6±1.0 cm² vs. 15.4±0.6 cm², p = 0.020); left atrial (19.8±1.0 cm² vs. 16.9±0.6 cm², p = 0.033) areas. There was a positive correlation between plasma ADMA and RV area (r = 0.453, p = 0.011); PF ADMA and end-diastolic (r = 0.434, p = 0.015) and systolic diameter of LV (r = 0.487, p = 0.007); and negative correlation between PF ADMA and LV ejection fraction (r = -0.445, p = 0.013) in VR.

Conclusion

We suggest that elevated levels of ADMA in the PF of patients indicate upregulated RAS and reduced bioavailability of NO, which can contribute to the development of cardiac hypertrophy and remodeling.     

Increases in endothelial Ca(2+) activate K(Ca) channels and elicit EDHF-type arteriolar dilation via gap junctions

In skeletal muscle arterioles, the pathway leading to non-nitric oxide (NO), non-prostaglandin-mediated endothelium-derived hyperpolarizing factor (EDHF)-type dilations is not well characterized. To elucidate some of the steps in this process, simultaneous changes in endothelial intracellular Ca(2+) concentration ([Ca(2+)](i)) and the diameter of rat gracilis muscle arterioles (approximately 60 microm) to acetylcholine (ACh) were measured by fura 2 microfluorimetry (in the absence of NO and prostaglandins). ACh elicited rapid increases in endothelial [Ca(2+)](i) (101 +/- 7%), followed by substantial dilations (73 +/- 2%, coupling time: 1.3 +/- 0.2 s) that were prevented by endothelial loading of an intracellular Ca(2+) chelator [1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid]. Arteriolar dilations to ACh were also inhibited by intraluminal administration of the Ca(2+)-activated K(+) (K(Ca)) channel blockers charybdotoxin plus apamin or by palmitoleic acid, an uncoupler of myoendothelial gap junctions without affecting changes in endothelial [Ca(2+)](i). The presence of large conductance K(Ca) channels on arteriolar endothelial cells was demonstrated with immunohistochemisty. We propose that in skeletal muscle arterioles, EDHF-type mediation is evoked by an increase in endothelial [Ca(2+)](i), which by activating endothelial K(Ca) channels elicits hyperpolarization that is conducted via myoendothelial gap junctions to the smooth muscle resulting in decreases in [Ca(2+)](i) and consequently dilation.     

Effect of Obesity on Growth‐related Oncogene Factor‐α, Thrombopoietin,and Tissue Inhibitor Metalloproteinase‐1 Serum Levels

We have recently identified several adipokines as oversecreted by omental adipose tissue (AT) of obese subjects: two chemokines (growth‐related oncogene factor‐α (GRO‐α), macrophage inflammatory protein‐1β (MIP‐1β)), a tissue inhibitor of metalloproteinases‐1 (TIMP‐1), an interleukin‐7 (IL‐7) and a megakaryocytic growth‐factor (thrombopoietin (TPO)). These adipokines are involved in insulin resistance and atherosclerosis. The objectives of this study were to determine whether the circulating levels of these adipokines were increased in obesity and to identify the responsible factors. A cross‐sectional study including 32 lean (BMI (kg/m²) <25), 15 overweight (BMI: 25–29.9), 11 obese (BMI: 30–39.9), and 17 severely obese (BMI >40) age‐matched women was carried out. Serum adipokine levels, insulin sensitivity, and substrate oxidation were measured by ELISA, euglycemic–hyperinsulinemic clamp, and indirect calorimetry, respectively. Circulating levels of GRO‐α, TPO, and TIMP‐1 were higher in obese and/or severely obese women than in lean ones (+30, 55, and 20%, respectively). Serum levels of these adipokines positively correlated with insulinemia or glycemia, and negatively with insulin sensitivity. TIMP‐1 also positively correlated with blood pressure, and TPO with triglyceride levels. Multiple regression analysis showed that fat mass per se was an independent determinant of GRO‐α, TPO, and TIMP‐1 levels, suggesting that hypertrophied adipocytes and recruited macrophages in expanded AT mainly contribute to this hyperadipokinemia. Insulinemia, glycemia and resistance of glucose oxidation to insulin were additional predictors for TPO. Circulating GRO‐α, TPO, and TIMP‐1 levels are increased in obesity. This may be partially due to augmented adiposity per se and to hyperinsulinemia/insulin resistance. These high systemic levels may in turn worsen/promote insulin resistance and cardiovascular disease.     

ABA Increases the Desiccation Tolerance of Photosynthesis in the Afromontane Understorey Moss Atrichum androgynum

The effect of pretreatment with abscisic acid (ABA) on the physiologyof the moss Atrichum androgynum during a desiccation–rehydrationcycle was examined. During rehydration following desiccationfor 16 h, net CO₂fixation recovered much more slowly than photosystemII (PSII) activity, conditions conducive to the formation ofreactive oxygen species (ROS) in the photosynthetic apparatus.Pretreatment with ABA increased the rate of recovery of photosynthesisand PSII activity, and also doubled non-photochemical quenching(NPQ). Increased NPQ activity will reduce ROS formation, andmay explain in part how ABA hardens the moss to desiccation.In ABA-pretreated, but not untreated mosses, desiccation significantlyincreased the concentration of soluble sugars. Sugar accumulationmay promote vitrification of the cytoplasm and protect membranesduring desiccation. Starch concentrations in freshly collectedA. androgynum were only approx. 40 mg g^-1dry mass; they roseslightly during desiccation but were only slightly affectedby ABA pretreatment. ABA did not reduce chlorophyll breakdownduring desiccation. Copyright 2001 Annals of Botany Company Moss, desiccation, abscisic acid, photosynthesis, chlorophyll fluorescence     

NMR-driven secondary and tertiary structure model of Ca2+-loaded calexcitin

Calexcitin (CE) is a Ca2+-binding protein which is expressed in neuronal cells and is a member of the sarcoplasmic Ca2+-binding protein subfamily. The peptide backbone of Ca2+-CE has been assigned by NMR and it shows that CE is composed of nine alpha-helices-forming four EF-hands and an additional helix near the C-terminus. A structural model of CE suggests the presence of a putative recessed hydrophobic pocket that may be involved in Ca2+-mediated protein-ligand interactions. This feature is unique to CE and is absent in other SCPs, such as those from Branchiostoma and Nereis, and from calerythrin.     

Phosphatidylglycerol Depletion Induces an Increase in Myxoxanthophyll Biosynthetic Activity in Synechocystis PCC6803 Cells

Phosphatidylglycerol (PG) depletion suppressed the oxygen-evolvingactivity of Synechocystis PCC6803 pgsA mutant cells. Shortageof PG led to decreased photosynthetic activity, which, similarto the effect of high light exposure, is likely to generatethe production of reactive oxygen species (ROS) or free radicals.Protection of the PG-depleted cells against light-induced damageincreased the echinenone and myxoxanthophyll content of thecells. The increased carotenoid content was localized in a solublefraction of the cells as well as in isolated thylakoid and cytoplasmicmembranes. The soluble carotenoid fraction contained carotenederivatives, which may bind to proteins. These carotene–proteincomplexes are similar to orange carotenoid protein that is involvedin yielding protection against free radicals and ROS. An increasein the content of myxoxanthophyll and echinenone upon PG depletionsuggests that PG depletion regulates the biosynthetic pathwayof specific carotenoids.