We present major, trace element, and Pb‐Sr‐Nd‐Hf isotope data for Quaternary basalt and basaltic andesite lavas from cross‐chain volcanoes in the northern Izu (N‐Izu) arc. Lavas from Izu‐Oshima, Toshima, Udonejima, and Niijima islands show consistent chemical changes with depth to the Wadati‐Benioff zone, from 120 km beneath Izu‐Oshima to 180 km beneath Niijima. Lavas from Izu‐Oshima at the volcanic front (VF) have elevated concentrations of large ion lithophile elements (LILEs), whereas rear‐arc (RA) lavas are rich in light rare earth elements (LREEs) and high field strength elements (HFSEs). VF lavas also have more radiogenic Pb, Nd, Sr, and Hf isotopic compositions. We have used the Arc Basalt Simulator version 3 (ABS3) to examine the mass balance of slab dehydration and melting and slab fluid/melt‐fluxed mantle melting and to quantitatively evaluate magma genesis beneath N‐Izu. The results suggest that the slab‐derived fluids/melts are derived from ∼20% sediment and ∼80% altered oceanic crust, the slab fluid is generated by slab dehydration for the VF magmas at 3.3–3.5 GPa/660°C–700°C, and slab melt for RA magmas is supplied at 3.4–4.4 GPa/830°C–890°C. The degree of fluxed melting of the mantle wedge varies between 17% and 28% (VF) and 6% and 22% (RA), with a slab flux fraction of 2%–4.5% (VF fluid) to 1%–1.5% (RA melt), and at melting depths 1–2.5 GPa (VF) and 2.4–2.8 GPa (RA). These conditions are consistent with a model whereby shallow, relatively low temperature slab fluids contribute to VF basalt genesis, whereas deeper and hotter slab melts control formation of RA basalts. The low‐temperature slab dehydration is the cause of elevated Ba/Th in VF basalt due mainly to breakdown of lawsonite, whereas deeper breakdown of phengite by slab melting is the cause of elevated K and Rb in RA basalts. Melting in the garnet stability field, and at lower degrees of partial melting, is required for the elevated LILEs, LREEs, and HFSEs observed in the RA basalts. Less radiogenic Sr, Nd, Hf, and Pb in RA basalts are all attributable to lesser slab flux additions. The low H2O predicted for RA basalt magmas (<1.5 wt %) relative to that in VF basalt magmas (5–8 wt %) is also due to melt addition rather than fluid. All these conclusions are broadly consistent with existing models; however, in this study they are quantitatively confirmed by the geochemical mass balance deduced from petrological ABS3 model. Overall, the P‐T‐X(H2O) structure of the slab and the mantle wedge exert the primary controls on arc basalt genesis.
Subarachnoid hemorrhage (SAH) by a rupture of cerebral aneurysms remains the most devastating cerebrovascular disease. Early brain injury (EBI) is increasingly recognized to be the primary determinant for poor outcomes, and also considered to cause delayed cerebral ischemia (DCI) after SAH. Both clinical and experimental literatures emphasize the impact of global cerebral edema in EBI as negative prognostic and direct pathological factors. The nature of the global cerebral edema is a mixture of cytotoxic and vasogenic edema, both of which may be caused by post‐SAH induction of tenascin‐C (TNC) that is an inducible, non‐structural, secreted and multifunctional matricellular protein. Experimental SAH induces TNC in brain parenchyma in rats and mice. TNC knockout suppressed EBI in terms of brain edema, blood‐brain barrier disruption, neuronal apoptosis and neuroinflammation, associated with the inhibition of post‐SAH activation of mitogen‐activated protein kinases and nuclear factor‐kappa B in mice. In a clinical setting, more severe SAH increases more TNC in cerebrospinal fluid and peripheral blood, which could be a surrogate marker of EBI and predict DCI development and outcomes. In addition, cilostazol, a selective inhibitor of phosphodiesterase type III that is a clinically available anti‐platelet agent and is known to suppress TNC induction, dose‐dependently inhibited delayed cerebral infarction and improved outcomes in a pilot clinical study. Thus, further studies may facilitate application of TNC as biomarkers for non‐invasive diagnosis or assessment of EBI and DCI, and lead to development of a molecular target drug against TNC, contributing to the improvement of post‐SAH outcomes.
Periostin may cause post-SAH early brain injury through activating downstream signaling pathways and interacting with tenascin-C, providing a novel approach for the treatment of early brain injury.
There are no direct evidences showing the linkage between Toll-like receptor 4 (TLR4) and blood-brain barrier (BBB) disruption after subarachnoid hemorrhage (SAH). The purpose of this study was to examine if selective blockage of TLR4 prevents BBB disruption after SAH in mice and if the TLR4 signaling involves mitogen-activated protein kinases (MAPKs). One hundred and fifty-one C57BL/6 male mice underwent sham or endovascular perforation SAH operation, randomly followed by an intracerebroventricular infusion of vehicle or two dosages (117 or 585 ng) of a selective TLR4 antagonist IAXO-102 at 30 min post-operation. The effects were evaluated by survival rates, neurological scores, and brain water content at 24-72 h and immunoglobulin G immunostaining and Western blotting at 24 h post-SAH. IAXO-102 significantly prevented post-SAH neurological impairments, brain edema, and BBB disruption, resulting in improved survival rates. IAXO-102 also significantly suppressed post-SAH activation of a major isoform of MAPK p46 c-Jun N-terminal kinase (JNK) and matrix metalloproteinase-9 as well as periostin induction and preserved tight junction protein zona occludens-1. Another selective TLR4 antagonist TAK-242, which has a different binding site from IAXO-102, also showed similar effects to IAXO-102. This study first provided the evidence that TLR4 signaling is involved in post-SAH acute BBB disruption and that the signaling is mediated at least partly by JNK activation. TLR4-targeted therapy may be promising to reduce post-SAH morbidities and mortalities.
Tenascin-C (TNC), a matricellular protein, is upregulated in brain parenchyma after experimental subarachnoid hemorrhage (SAH). Recent studies emphasize that early brain injury (EBI) should be overcome to improve post-SAH outcomes. The aim of this study was to investigate effects of TNC knockout (TNKO) on neuronal apoptosis and neuroinflammation, both of which are important constituents of EBI after SAH. C57BL/6 wild-type (WT) mice or TNKO mice underwent sham or filament perforation SAH modeling. Twenty-five WT mice and 25 TNKO mice were randomly divided into sham+WT (n = 10), sham+TNKO (n = 8), SAH+WT (n = 15), and SAH+TNKO (n = 17) groups. Beam balance test, neurological score, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining, immunostaining of Toll-like receptor 4 (TLR4), and Western blotting were performed to evaluate neurobehavioral impairments, neuronal apoptosis, and neuroinflammation at 24 h post-SAH. Deficiency of TNC significantly alleviated post-SAH neurobehavioral impairments and neuronal apoptosis. The protective effects of TNKO on neurons were associated with the inhibition of a caspase-dependent apoptotic pathway, which was at least partly mediated by TLR4/nuclear factor-κB/interleukin-1β and interleukin-6 signaling cascades. This study first provided the direct evidence that TNC causes post-SAH neuronal apoptosis and neuroinflammation, potentially leading to the development of a new molecular targeted therapy against EBI.
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