Gloria López

Late Cenozoic transpressional ductile deformation north of the Nazca–South America–Antarctica triple junction

Abstract The southern Andes plate boundary zone records a protracted history of bulk transpressional deformation during the Cenozoic, which has been causally related to either oblique subduction or ridge collision. However, few structural and chronological studies of regional deformation are available to support one hypothesis or the other. We address along- and across-strike variations in the nature and timing of plate boundary deformation to better understand the Cenozoic tectonics of the southern Andes. Two east–west structural transects were mapped at Puyuhuapi and Aysen, immediately north of the Nazca–South America–Antarctica triple junction. At Puyuhuapi (44°S), north–south striking, high-angle contractional and strike-slip ductile shear zones developed from plutons coexist with moderately dipping dextral-oblique shear zones in the wallrocks. In Aysen (45–46°), top to the southwest, oblique thrusting predominates to the west of the Cenozoic magmatic arc, whereas dextral strike-slip shear zones develop within it. New 40Ar–39Ar data from mylonites and undeformed rocks from the two transects suggest that dextral strike-slip, oblique-slip and contractional deformation occurred at nearly the same time but within different structural domains along and across the orogen. Similar ages were obtained on both high strain pelitic schists with dextral strike-slip kinematics (4.4±0.3 Ma, laser on muscovite–biotite aggregates, Aysen transect, 45°S) and on mylonitic plutonic rocks with contractional deformation (3.8±0.2 to 4.2±0.2 Ma, fine-grained, recrystallized biotite, Puyuhuapi transect). Oblique-slip, dextral reverse kinematics of uncertain age is documented at the Canal Costa shear zone (45°S) and at the Queulat shear zone at 44°S. Published dates for the undeformed protholiths suggest both shear zones are likely Late Miocene or Pliocene, coeval with contractional and strike-slip shear zones farther north. Coeval strike-slip, oblique-slip and contractional deformation on ductile shear zones of the southern Andes suggest different degrees of along- and across-strike deformation partitioning of bulk transpressional deformation. The long-term dextral transpressional regime appears to be driven by oblique subduction. The short-term deformation is in turn controlled by ridge collision from 6 Ma to present day. This is indicated by most deformation ages and by a southward increase in the contractional component of deformation. Oblique-slip to contractional shear zones at both western and eastern margins of the Miocene belt of the Patagonian batholith define a large-scale pop-up structure by which deeper levels of the crust have been differentially exhumed since the Pliocene at a rate in excess of 1.7 mm/year.

Genetic predisposition and environmental factors leading to the development of insulin-dependent diabetes mellitus in Chilean children

This study was designed to examine the hypothesis that some environmental factors increase the risk for insulin-dependent diabetes mellitus. Data on dietary history was collected from 80 diabetic children from the Santiago de Chile Registry and from 85 nondiabetic control subjects who were comparable in terms of age, sex, and ethnic characteristics. Early exposure was defined as the ingestion of food sources other than maternal milk before 3 months of age. To define genetic susceptibility to insulin-dependent diabetes mellitus each subject was typed in terms of HLA DQA1 and DQB1, and the possible conformation of susceptible heterodimers was considered as a risk marker. Fewer children were exclusively breast fed in the diabetic group than in the control group (21.55±15.05 vs. 33.95±20.40 weeks, P<0.01). In addition, exposure to cows milk and solid foods occurred earlier in the diabetic group than in the control group (15.90±10.95 vs. 21.15 13.65 and 16.85±10.25 vs. 21.20±12.35 weeks, P<0.05). Our data show that a short duration of breast-feeding and early exposure to cows milk and solid foods may be important factors in the development of insulin-dependent diabetes mellitus. The high relative risk observed in individuals genetically predisposed indicates an interaction effect between genetic and environmental components.

Zinc as a Potential Coadjuvant in Therapy for Type 2 Diabetes

Background Type 2 diabetes is highly prevalent in populations having high rates of overweight and obesity. It is a chronic condition responsible for long-term severe dysfunction of several organs, including the kidneys, heart, blood vessels, and eyes. Although there are a number of pharmacologic products in the market to treat insulin resistance and impaired insulin secretion—the most prominent features of this disease—interventions directed at preserving the integrity and function of β-cells in the long term are less available. The use of some nutrients with important cellular protective roles that may lead to a preservation of β-cells has not been fully tested; among these, zinc may be an interesting candidate. Objective To assess the potential of zinc supplementation as coadjuvant to diabetes therapy. Methods This article reviews the available information on the use of zinc as part of diabetes therapy. Results Cellular and animal models provide information on the insulin mimetic action of zinc, as well as its role as a regulator of oxidative stress, inflammation, apoptosis, and insulin secretion. Zinc supplementation studies in humans are limited, although some positive effects have been reported; mainly, a modest but significant reduction in fasting glucose and a trend to decreased glycated hemoglobin (HbA1c). Conclusions Zinc supplementation may have beneficial effects on glycemic control. Nevertheless, among the studies considered, the vast majority lasted for 6 months or less, suggesting the importance of conducting long-duration studies given the characteristics of type 2 diabetes as a chronic disease.

II Consenso de la Sociedad Chilena de Endocrinología y Diabetes sobre resistencia a la insulina

Insulin resistance is a prevalent condition commonly associated with unhealthy lifestyles. It affects several metabolic pathways, increasing risk of abnormalities at different organ levels. Thus, diverse medical specialties should be involved in its diagnosis and treatment. With the purpose of unifying criteria about this condition, a scientific-based consensus was elaborated. A questionnaire including the most important topics such as cardio-metabolic risk, non-alcoholic fatty liver disease and polycystic ovary syndrome, was designed and sent to national experts. When no agreement among them was achieved, the Delphi methodology was applied. The main conclusions reached are that clinical findings are critical for the diagnosis of insulin resistance, not being necessary blood testing. Acquisition of a healthy lifestyle is the most important therapeutic tool. Insulin-sensitizing drugs should be prescribed to individuals at high risk of disease according to clinically validated outcomes. There are specific recommendations for pregnant women, children, adolescents and older people.Insulin resistance is a prevalent condition commonly associated with unhealthy lifestyles. It affects several metabolic pathways, increasing risk of abnormalities at different organ levels. Thus, diverse medical specialties should be involved in its diagnosis and treatment. With the purpose of unifying criteria about this condition, a scientific-based consensus was elaborated. A questionnaire including the most important topics such as cardio-metabolic risk, non-alcoholic fatty liver disease and polycystic ovary syndrome, was designed and sent to national experts. When no agreement among them was achieved, the Delphi methodology was applied. The main conclusions reached are that clinical findings are critical for the diagnosis of insulin resistance, not being necessary blood testing. Acquisition of a healthy lifestyle is the most important therapeutic tool. Insulin-sensitizing drugs should be prescribed to individuals at high risk of disease according to clinically validated outcomes. There are specific recommendations for pregnant women, children, adolescents and older people.

Genetics of Endothelial Damage Associated to Diabetes Mellitus Type 2

Diabetes mellitus (DM) is a serious worldwide public health problem due to its frequency, chronic complications and their high associated costs. This disease is considered a multifactorial pathology that involves insulin resistance and is associated to obesity, dyslipidemia, endothelial dysfunction, inflammation and hypertension (Petersen & Shulman, 2006). Type 2 diabetes (DM2) is one of the most common diseases in the developed world and is recognized now as a global burden (van Dieren et al., 2010). Released in 2000, the initial edition of the Diabetes Atlas estimated the global prevalence of this disease at 4.6%, representing 151 million people, and projected an increase to 333 million people by 2025. On the basis of the most recent evidence, the current Diabetes Atlas has predicted that the number of people with diabetes will have risen to a staggering 438 million or 7.8% of the world`s population in 2030 (Colagiuri, 2010; www.diabetesatlas.org). The development of DM2 requires the involvement of genetic and environmental factors such as android obesity and sedentary lifestyle that determine hyposecretion of insulin in response to glucose stimulation and a decreased insulin action in peripheral tissues. Most of the complications associated to DM2 are related to pathophysiological alterations of the vascular endothelium, and are the main cause of morbidity and mortality among DM patients. Endothelial dysfunction is the initial event that predisposes the vascular wall to diverse alterations leading to the establishment of so-called cardiovascular complications of diabetes. Known risk factors of diabetic complications such as hyperglycemia, hypertension and dyslipidemia stimulate the production of reactive oxygen species (ROS) in the vascular wall. Hyperglycemia is now considered a key causal factor in the development of chronic complications of diabetes (Giuliano et al., 2008). The vascular endothelium consists of endothelial cells and is a type of monostratified squamous epithelium that lines the inner surface of all blood vessels including the heart. Its crucial role is to regulate the vascular tone and it also has a structural function. In addition, the vascular endothelium normally inhibits platelet and leukocyte adhesion to the vascular surface and maintains a balance between profibrinolytic and prothrombotic activities