Deep slab seismicity limited by rate of deformation in the transition zone.

Deep earthquakes within subducting tectonic plates (slabs) are enigmatic because they appear similar to shallow earthquakes but must occur by a different mechanism. Previous attempts to explain the depth distribution of deep earthquakes in terms of the temperature at which possible triggering mechanisms are viable, fail to explain the spatial variability in seismicity. In addition to thermal constraints, proposed failure mechanisms for deep earthquakes all require that sufficient strain accumulates in the slab at a relatively high stress. Here, I show that simulations of subduction with nonlinear rheology and compositionally dependent phase transitions exhibit strongly variable strain rates in space and time, which is similar to observed seismicity. Therefore, in addition to temperature, variations in strain rate may explain why there are large gaps in deep seismicity (low strain rate), and variable peaks in seismicity (bending regions), and, possibly, why there is an abrupt cessation of seismicity below 660 km.

In vitro evaluation of traditionally used Surinamese medicinal plants for their potential anti-leishmanial efficacy.

ETHNOPHARMACOLOGICAL RELEVANCE: Plant-based preparations are extensively used in Surinamese folk medicine for treating leishmaniasis, but often without a scientific rationale. AIM OF THE STUDY: To evaluate 25 Surinamese medicinal plants for their potential efficacy against leishmaniasis. MATERIALS AND METHODS: Concentrated plant extracts were evaluated for their effect on the viability of L. (V.) guyanensis AMC, L. (L.) major NADIM5, and L. (L.) donovani GEDII promastigotes, as well as intracellular amastigotes of L. (L.) donovani BHU814 in infected THP-1 cells. Selectivity was assessed by cytotoxicity against THP-1 cells. RESULTS: The only plant extract that showed potentially meaningful anti-leishmanial activity was that from Solanum lycocarpum that displayed mean IC50 values of about 51, 61, and <16 µg/mL against L. (V) guyanensis, L. (L) major, and L. (L) donovani promastigotes, respectively; about 374 µg/mL against L. (L) donovani amastigotes; and >500 µg/mL against THP-1 cells. The Bryophyllum pinnatum, Inga alba, and Quassia amara extracts displayed moderate to high IC50 values against promastigotes (about 51 to >500 µg/mL) and/or amastigotes (about 224 to >500 µg/mL) but were relatively toxic to THP-1 cells (IC50 values <16 to about 42 µg/mL). The remaining plant extracts exhibited in many cases IC50 values close to, around, or above 500µg/mL against promastigotes, amastigotes, and THP-1 cells. CONCLUSIONS: The S. lycocarpum preparation may be useful against leishmaniasis and may have a good safety index, warranting further investigations into its active constituents and mechanism(s) of action.

Effects of nutraceuticals on sprouting of cultured human umbilical vein endothelial cells and growth of sub-intestinal vessels in zebra fish embryos

OBJECTIVE: Nutraceuticals such as resveratrol, catechins, and curcumin have been reported to interfere, among others, with angiogenesis. Based on these reports, we evaluated a number of Surinamese nutraceuticals for their effects on angiogenesis in a cell culture and zebra fish model. DESIGN AND METHODS: Parts from Cecropia peltata, Luffa acutangula, Momordica charantia, Morinda citrifolia, Oenocarpus bacaba, Psidium guajava, and Spondias mombin were extracted with distilled water, freeze-dried, and evaluated for their cytotoxicity in cultured human umbilical vein endothelial cells (HUVEC) using a sulforhodamine B assay, as well as the sprouting of these cells in a scratch-wound assay. In parallel, the plant extracts were assessed for their effects on sub-intestinal vessel length in embryos of the zebra fish Danio rerio. RESULTS: At lowly cytotoxic concentrations (< IC50 values), the C. peltata, L. acutangula, M. charantia, and M. citrifolia extracts yielded 20 to 100% larger wound gap areas when compared to those in untreated cell cultures, while the O. bacaba extract produced a roughly 20% smaller wound gap area. Furthermore, the L. acutangula, M. charantia, and P. guajava extracts inhibited sub-intestinal vessel growth in zebra fish embryos by 30 to 50%, while the O. bacaba preparation stimulated this phenomenon by about 50%. CONCLUSIONS: The inhibitory effects of the L. acutangula, M. charantia, and P. guajava extracts, and the stimulatory effect of the O. bacaba sample on HUVEC sprouting and zebra fish sub-intestinal vessel growth, suggest that these nutraceuticals are able to interfere with angiogenesis.

Evaluation of Surinamese medicinal plants for their effects on the contractility of hypoxic guinea pig myocardial tissue

OBJECTIVE: Cardiac stunning occurs after a transient hypoxic or ischemic insult. Preparations from Anona muricata L., Bixa orelana L., Cecropia palmata Willd., Erythrina fusca Lour., Hibiscus esculentus L., Psidium guajava L., and Terminalia catappa L. were evaluated for their possible positive-inotropic effects in a laboratory model of cardiac stunning. DESIGN AND METHOD: Thus, isolated guinea pig atria perfused in oxygenated Ringer-Locke buffer, were exposed to 5-min periods of hypoxic stress and then allowed to recover for 2 x 3 min in oxygenated buffer alone or supplemented with norepinephrine (10-5 M) or a plant extract (0.001 – 1 mg/mL). Atrial contraction force (F) was measured with a force transducer and contractility was derived by calculation of dF/dt. Troponin C - a highly specific marker for heart muscle cell death - was measured in the perfusion solution in the absence or presence of the plant extracts. RESULTS: Reoxygenation led to a gradual recovery of the atria, but they remained in a state of depressed contractility for at least 4 min. However, exposure to the A. muricata, B. orellana, C. palmata, and T. catappa extracts increased the contractility by 50 to 250%. Notably, troponin C release was 3- to 6-fold higher in incubations with the two latter preparations. CONCLUSION: Preparations from A. muricata, B. orellana, C. palmata, and T. catappa may possess positive-inotropic properties that may be useful in cardiac stunning. However, those from C. palmata and T. catappa may cause myocardial damage that may limit their usefulness in this condition.

Cytotoxic and genotoxic effects of commonly used surinamese medicinal plants in cultured Chinese hamster ovary cells

OBJECTIVE: Medicinal plants are popularly used in Suriname for treating a wide variety of conditions. However, there are often no records about their possible adverse maternal and perinatal effects. For this reason, we assessed a number of commonly used plant-derived folk medicines for their potential genotoxic effects in a cell culture model. DESIGN AND METHODS: Parts from Aloe vera, Apium graveolens, Azaradichta indica, Carica papaya, Cocos nucifera, Dioscorea villosa, Eryngium foetidum, Gossypium barbadense, Momordica charantia, Musa x paradisiaca, and Senna reticulata were extracted with distilled water, freeze-dried, and stored at -20oC. Next, they were evaluated at serial dilutions for their effects on the proliferation of, and DNA damage formation in cultured Chinese hamster ovary (CHO) cells using a sulforhodamine B and a single cell gel electrophoresis (comet) assay, respectively. The latter studies were validated by assessing the DNA strand-breakage induced by etoposide. RESULTS: The extracts from A. vera, G. barbadense, M. charantia, M. paradisiaca, and S. reticulata inhibited cell growth at IC50 values of 100 to 400 μg/mL, whereas the remaining samples were hardly cytotoxic (IC50 values > 1,000 μg/mL). However, only the extracts from G. barbadense and M. paradisiaca caused appreciable DNA damage, viz. 40 and 30%, respectively. CONCLUSIONS: Preparations from G. barbadense and M. paradisiaca should be used with caution, particularly by pregnant women. These samples are now further evaluated in more comprehensive models of genotoxicity.

Reconciling surface plate motions with rapid three-dimensional mantle flow around a slab edge.

The direction of tectonic plate motion at the Earth's surface and the flow field of the mantle inferred from seismic anisotropy are well correlated globally, suggesting large-scale coupling between the mantle and the surface plates. The fit is typically poor at subduction zones, however, where regional observations of seismic anisotropy suggest that the direction of mantle flow is not parallel to and may be several times faster than plate motions. Here we present three-dimensional numerical models of buoyancy-driven deformation with realistic slab geometry for the Alaska subduction-transform system and use them to determine the origin of this regional decoupling of flow. We find that near a subduction zone edge, mantle flow velocities can have magnitudes of more than ten times the surface plate motions, whereas surface plate velocities are consistent with plate motions and the complex mantle flow field is consistent with observations from seismic anisotropy. The seismic anisotropy observations constrain the shape of the eastern slab edge and require non-Newtonian mantle rheology. The incorporation of the non-Newtonian viscosity results in mantle viscosities of 10(17) to 10(18) Pa s in regions of high strain rate (10(-12) s(-1)), and this low viscosity enables the mantle flow field to decouple partially from the motion of the surface plates. These results imply local rapid transport of geochemical signatures through subduction zones and that the internal deformation of slabs decreases the slab-pull force available to drive subducting plates.