Probing the hydrothermal system of the Chicxulub impact crater.

The ~180-km-diameter Chicxulub peak-ring crater and ~240-km multiring basin, produced by the impact that terminated the Cretaceous, is the largest remaining intact impact basin on Earth. International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Program (ICDP) Expedition 364 drilled to a depth of 1335 m below the sea floor into the peak ring, providing a unique opportunity to study the thermal and chemical modification of Earth's crust caused by the impact. The recovered core shows the crater hosted a spatially extensive hydrothermal system that chemically and mineralogically modified ~1.4 × 105 km3 of Earth's crust, a volume more than nine times that of the Yellowstone Caldera system. Initially, high temperatures of 300° to 400°C and an independent geomagnetic polarity clock indicate the hydrothermal system was long lived, in excess of 106 years.

The first day of the Cenozoic.

Highly expanded Cretaceous-Paleogene (K-Pg) boundary section from the Chicxulub peak ring, recovered by International Ocean Discovery Program (IODP)-International Continental Scientific Drilling Program (ICDP) Expedition 364, provides an unprecedented window into the immediate aftermath of the impact. Site M0077 includes ∼130 m of impact melt rock and suevite deposited the first day of the Cenozoic covered by <1 m of micrite-rich carbonate deposited over subsequent weeks to years. We present an interpreted series of events based on analyses of these drill cores. Within minutes of the impact, centrally uplifted basement rock collapsed outward to form a peak ring capped in melt rock. Within tens of minutes, the peak ring was covered in ∼40 m of brecciated impact melt rock and coarse-grained suevite, including clasts possibly generated by melt-water interactions during ocean resurge. Within an hour, resurge crested the peak ring, depositing a 10-m-thick layer of suevite with increased particle roundness and sorting. Within hours, the full resurge deposit formed through settling and seiches, resulting in an 80-m-thick fining-upward, sorted suevite in the flooded crater. Within a day, the reflected rim-wave tsunami reached the crater, depositing a cross-bedded sand-to-fine gravel layer enriched in polycyclic aromatic hydrocarbons overlain by charcoal fragments. Generation of a deep crater open to the ocean allowed rapid flooding and sediment accumulation rates among the highest known in the geologic record. The high-resolution section provides insight into the impact environmental effects, including charcoal as evidence for impact-induced wildfires and a paucity of sulfur-rich evaporites from the target supporting rapid global cooling and darkness as extinction mechanisms.

Author Correction: Rock fluidization during peak-ring formation of large impact structures.

In this Article, the middle initial of author Kosei E. Yamaguchi (of the IODP-ICDP Expedition 364 Science Party) was missing and his affiliation is to Toho University (not Tohu University). These errors have been corrected online.

Rock fluidization during peak-ring formation of large impact structures.

Large meteorite impact structures on the terrestrial bodies of the Solar System contain pronounced topographic rings, which emerged from uplifted target (crustal) rocks within minutes of impact. To flow rapidly over large distances, these target rocks must have weakened drastically, but they subsequently regained sufficient strength to build and sustain topographic rings. The mechanisms of rock deformation that accomplish such extreme change in mechanical behaviour during cratering are largely unknown and have been debated for decades. Recent drilling of the approximately 200-km-diameter Chicxulub impact structure in Mexico has produced a record of brittle and viscous deformation within its peak-ring rocks. Here we show how catastrophic rock weakening upon impact is followed by an increase in rock strength that culminated in the formation of the peak ring during cratering. The observations point to quasi-continuous rock flow and hence acoustic fluidization as the dominant physical process controlling initial cratering, followed by increasingly localized faulting.

Rapid recovery of life at ground zero of the end-Cretaceous mass extinction.

The Cretaceous/Palaeogene mass extinction eradicated 76% of species on Earth1,2. It was caused by the impact of an asteroid3,4 on the Yucatán carbonate platform in the southern Gulf of Mexico 66 million years ago 5 , forming the Chicxulub impact crater6,7. After the mass extinction, the recovery of the global marine ecosystem-measured as primary productivity-was geographically heterogeneous 8 ; export production in the Gulf of Mexico and North Atlantic-western Tethys was slower than in most other regions8-11, taking 300 thousand years (kyr) to return to levels similar to those of the Late Cretaceous period. Delayed recovery of marine productivity closer to the crater implies an impact-related environmental control, such as toxic metal poisoning 12 , on recovery times. If no such geographic pattern exists, the best explanation for the observed heterogeneity is a combination of ecological factors-trophic interactions 13 , species incumbency and competitive exclusion by opportunists 14 -and 'chance'8,15,16. The question of whether the post-impact recovery of marine productivity was delayed closer to the crater has a bearing on the predictability of future patterns of recovery in anthropogenically perturbed ecosystems. If there is a relationship between the distance from the impact and the recovery of marine productivity, we would expect recovery rates to be slowest in the crater itself. Here we present a record of foraminifera, calcareous nannoplankton, trace fossils and elemental abundance data from within the Chicxulub crater, dated to approximately the first 200 kyr of the Palaeocene. We show that life reappeared in the basin just years after the impact and a high-productivity ecosystem was established within 30 kyr, which indicates that proximity to the impact did not delay recovery and that there was therefore no impact-related environmental control on recovery. Ecological processes probably controlled the recovery of productivity after the Cretaceous/Palaeogene mass extinction and are therefore likely to be important for the response of the ocean ecosystem to other rapid extinction events.

[Recurrent bilateral anterior uveitis due to Leishmania infantum in a patient with immune deficiency related to HIV infection: a case report and literature review]. / Uvéite antérieure bilatérale récidivante à Leishmania infantum chez un patient présentant un déficit immunitaire lié à une infection à VIH : à propos d'un cas et revue de la littérature.

We report the case of a 56-year-old patient, presenting with bilateral hypertensive anterior uveitis due to Leishmania infantum, in the setting of immune deficiency related to HIV infection. The etiology of the uveitis was diagnosed following detection of L. infantum DNA on anterior chamber paracentesis. Initially, the patient received an intravitreal injection of liposomal amphotericin B, systemic antiparasitic treatment, topical steroid and ocular hypotensive treatment. Due to unfavourable disease progression in the right eye, we re-evaluated the anti-inflammatory, antiretroviral and antiparasitic medications (beginning meglumine antimoniate): the uveitis in the left eye was thus able to be controlled. We followed the efficacy of treatment with weekly quantification of Leishmania DNA in the aqueous humor. Uveitis secondary to leishmaniasis is rare and serious. Physicians must be aware of this cause of uveitis, particularly in immunodeficient patients. The quantitation of Leishmania DNA in the aqueous humor is an indispensible tool for monitoring the disease.

[Intravitreal bevacizumab pretreatment in vitrectomy for severe diabetic retinopathy: a series of six cases]. / Utilisation du bévacizumab (Avastin(®)) en injection intravitréenne avant vitrectomie pour rétinopathie diabétique sévère, à propos de six cas.

INTRODUCTION: Bevacizumab (Avastin(®), Roche) is a full-length humanized monoclonal antibody applicable to all subtypes of vascular endothelial growth factor (VEGF). The purpose of this study was to report the results of its use as a surgical additive in severe cases of proliferative diabetic retinopathy (PDR). PATIENTS AND METHOD: This retrospective study focused on six eyes of six patients with complicated diabetic retinopathy. A vitrectomy was performed within 13.6 days after an intravitreal bevacizumab injection of 0.1 mL (2.5mg), with dissection of the fibrovascular proliferation using a mono- or bimanual delamination technique. RESULTS: The mean follow-up after intravitreal injection was 13.3 months. The mean surgery time was 64 minutes. The bimanual technique was not necessary. Only one iatrogenic retinal tear was repaired. The intraoperative bleeding was negligible. No adverse events resulting from the drug nor recurrence were observed throughout the follow-up period. CONCLUSION: Intravitreal bevacizumab is useful as a surgical additive in severe cases of PDR, significantly improving surgical conditions. Nevertheless, its use beyond approved indications should be reserved for complex surgical cases.

[Sutureless transconjunctival 20-gauge vitrectomy]. / Évaluation de la vitrectomie transconjonctivale 20-gauge sans suture.

PURPOSE: To evaluate the safety and efficacy of 20-gauge transconjunctival sutureless vitrectomy for a variety of vitreoretinal conditions. PATIENTS AND METHODS: This study was a retrospective clinical case series examining 29 eyes of 29 patients treated with 20-gauge transconjunctival sutureless vitrectomy. The main outcome measures included intraocular pressure, visual acuity, surgical time, and intraoperative and postoperative complications. RESULTS: The mean follow-up duration was 5.7 months. There were only two cases of postoperative ocular hypotony (6.9%) and one suspect case of endophthalmitis. Mean overall acuity improved from 0.495 logMar at baseline to 0.29 logMar (p=0.002) and mean total operative time was 19 min. We observed no cases of retinal detachment. CONCLUSION: Twenty-gauge transconjunctival sutureless vitrectomy is an effective surgical technique, but other studies are needed to confirm its safety and its value in other indications.

[Characterization of the biometric eye profile of a high myopic population: does high myopia correspond to a homogenous phenotype?]. / Caractérisation du profil biométrique oculaire d'une population myope fort: la myopie forte correspond-elle à un phénotype homogène?

PURPOSE: High myopia is a public health problem because of its high prevalence and is a major cause of blindness. The physiopathology of myopia remains unknown and mechanisms causing the disease are most probably complex, combining acquired environmental and genetic factors. The most recent data suggest that genetic determinisms of high myopia could be highly dependent on subject phenotype. The aim of this study was to analyse the ocular components of a high myopic population to verify whether high myopia corresponds to a homogeneous phenotype. PATIENTS AND METHODS: We analysed the biometric characteristics of 718 myopic eyes with a spherical equivalent of less than -5 diopters. The biometric parameters (corneal radius, axial length, and intraocular pressure) were compared controlling for sex and the degree of myopia. RESULTS: We found a difference between the phenotype of males and females. For men, axial length was the only determinant of the myopic phenotype, whereas for women, the myopic phenotype was determined by axial length and corneal radius. This difference between the phenotypes was more evident for myopia with a spherical equivalent greater than -10 diopters (moderate myopia). This difference between males and females disappeared in myopia less than -15 diopters. CONCLUSION: There are intersex differences considering the high myopia phenotype at a spherical equivalent less than -5 diopters. However, this difference disappears for extremely high myopia with a spherical equivalence of less than -15 diopters.

[Pars plana vitrectomy, subretinal injection of recombinant tissue plasminogen activator and fluid-gas exchange in the management of massive submacular hemorrhages secondary to age-related macular degeneration]. / Traitement des hématomes maculaires compliquant la DMLA par vitrectomie, injection sous-rétinienne de rt-PA et tamponnement intraoculaire par gaz.

INTRODUCTION: The natural prognosis of eyes with subretinal hemorrhage resulting from age-related macular degeneration is generally poor. A variety of therapeutic approaches have been developed but no consensus was found. Therefore, we evaluated a technique consisting of pars plana vitrectomy and subretinal rt-PA injection followed by evacuation of the liquid blood using sulfur hexafluoride (SF6). PATIENTS AND METHODS: This study was a retrospective clinical case series examining 18 eyes of 16 patients with age-related macular degeneration and thick submacular hemorrhage treated with vitrectomy, subretinal injection of rt-PA (0.5mg), and fluid-gas exchange. RESULTS: The subretinal hemorrhage was displaced in all 18 cases, revealing a choroidal lesion in 17 eyes. A treatable lesion accountable for the bleeding was identified in ten eyes, which all received a secondary treatment (intravitreal injection or photodynamic therapy). After a mean follow-up of 6 months, the final visual acuity improved in ten eyes. Complications consisted of one case of retinal detachment and one case of hyphema. CONCLUSION: This surgical technique seems useful in displacing thick submacular hemorrhage secondary to age-related macular degeneration, allowing postoperative fluorescein angiography testing and, potentially, subsequent treatments. However, further controlled and multicentric studies will be required to assess its efficacy and safety in the management of this difficult clinical problem.

[Intravitreal bevacizumab for treatment of neovascular glaucoma. Report of 20 cases]. / Utilisation du bevacizumab en injection intravitréenne dans le traitement du glaucome néovasculaire. A propos de 20 cas.

INTRODUCTION: Bevacizumab is a recombinant humanised monoclonal antibody directed against the vascular endothelial growth factor (VEGF). We report the results of bevacizumab injections in the treatment of 20 cases of neovascular glaucoma. PATIENTS AND METHODS: Seven women and 13 men, of average age 73 years old, presented with neovascular glaucoma secondary to central retinal vein occlusion in 8 cases, proliferative diabetic retinopathy in 8 cases, central retinal artery occlusion in 2 cases, radiation retinopathy in 1 case and ocular ischemic syndrome in 1 case. Iris fluorescein angiography was performed before and two days after 2,5 mg intravitreal bevacizumab. Diode laser cyclophotocoagulation was realised in 12 cases of grade 4 neovascular glaucoma in the week following the injection. Panretinal photocoagulation was conducted in all cases. RESULTS: After a 4 months and a half follow up, iris angiography revealed dramatic regression of iris neovascularisation in a few days. In grade 2 and 3 neovascular glaucoma, the single injection is sufficient to control intraocular pressure. In grade 4 neovascular glaucoma, intraocular pressure was controlled in 87,5 % of cases with one injection and one or more diode laser cyclophotocoagulation. DISCUSSION: The antiangiogenic effect of bevacizumab leads to fast reduction of the iris neovascularization with control of intraocular pressure without any surgery in grade 2 or 3 neovascular glaucoma. Panretinal photocoagulation was facilitated by improvement of corneal swelling. Diode laser cyclophotocoagulation was necessary in grade 4. CONCLUSION: Intravitreal bevacizumab was effective in reversing iris neovascularization in association with panretinal photocoagulation and cyclophotocoagulation.

[Bilateral central retinal vein occlusion associated with moderate acute rejection of a cardiac graft]. / Oblitération bilatérale de la veine centrale de la rétine sur un rejet aigu léger de greffe cardiaque.

We report a case of bilateral central retinal vein occlusion following moderate acute rejection of a cardiac transplant. A 27-year-old man was admitted for sudden bilateral decreased vision due to bilateral central retinal vein occlusion. Visual acuity was 20/63 in the right eye and 20/25 in the left eye. This patient had undergone a heart transplant 6 months before and had presented with moderate acute rejection for a few days. The moderate acute rejection phenomenon includes inflammatory lymphocyte infiltrates, reflecting persistent immune response activation. Moderate acute rejection of a cardiac transplant graft might cause a bilateral central retinal vein occlusion.

Antioxidant and pro-oxidant actions of flavonoids: effects on DNA damage induced by nitric oxide, peroxynitrite and nitroxyl anion.

Antioxidant and pro-oxidant activities of flavonoids have been reported. We have studied the effects of 18 flavonoids and related phenolic compounds on DNA damage induced by nitric oxide (NO), peroxynitrite, and nitroxyl anion (NO-). Similarly to our previous findings with catecholamines and catechol-estrogens, DNA single-strand breakage was induced synergistically when pBR322 plasmid was incubated in the presence of an NO-releasing compound (diethylamine NONOate) and a flavonoid having an ortho-trihydroxyl group in either the B ring (e.g., epigallocatechin gallate) or the A ring (e.g., quercetagetin). Either NO or any of the above flavonoids alone did not induce strand breakage significantly. However, most of the tested flavonoids inhibited the peroxynitrite-mediated formation of 8-nitroguanine in calf-thymus DNA, measured by a new HPLC-electrochemical detection method, as well as the peroxynitrite-induced strand breakage. NO- generated from Angeli's salt caused DNA strand breakage, which was also inhibited by flavonoids but at only high concentrations. On the basis of these findings, we propose that NO- and/or peroxynitrite could be responsible for DNA strand breakage induced by NO and a flavonoid having an ortho-trihydroxyl group. Our results indicate that flavonoids have antioxidant properties, but some act as pro-oxidants in the presence of NO.