Showing papers by "National University of La Plata published in 1992"

Dietary intake of fiber and decreased risk of cancers of the colon and rectum: Evidence from the combined analysis of 13 case-control studies

Abstract: BACKGROUND Colorectal cancer is a major public health problem in both North America and western Europe, and incidence and mortality rates are rapidly increasing in many previously low-risk countries. It has been hypothesized that increased intakes of fiber, vitamin C, and beta carotene could decrease the risk of colorectal cancer. PURPOSE The objective of this study was to examine the effects of fiber, vitamin C, and beta-carotene intakes on colorectal cancer risk in a combined analysis of data from 13 case-control studies previously conducted in populations with differing colorectal cancer rates and dietary practices. The study was designed to estimate risks in the pooled data, to test the consistency of the associations across the studies, and to examine interactions of the effects of the nutrients with cancer site, sex, and age. METHODS Original data records for 5287 case subjects with colorectal cancer and 10,470 control subjects without disease were combined. Logistic regression analysis was used to estimate relative risks and confidence intervals for intakes of fiber, vitamin C, and beta carotene, with the effects of study, sex, and age group being adjusted by stratification. RESULTS Risk decreased as fiber intake increased; relative risks were 0.79, 0.69, 0.63, and 0.53 for the four highest quintiles of intake compared with the lowest quintile (trend, P < .0001). The inverse association with fiber is seen in 12 of the 13 studies and is similar in magnitude for left- and right-sided colon and rectal cancers, for men and for women, and for different age groups. In contrast, after adjustment for fiber intake, only weak inverse associations are seen for the intakes of vitamin C and beta carotene. CONCLUSION This analysis provides substantive evidence that intake of fiber-rich foods is inversely related to risk of cancers of both the colon and rectum. IMPLICATIONS If causality is assumed, we estimate that risk of colorectal cancer in the U.S. population could be reduced about 31% (50,000 cases annually) by an average increase in fiber intake from food sources of about 13 g/d, corresponding to an average increase of about 70%.

Early Paleozoic orogenic belt of the Andes in southwestern South America: Result of Laurentia-Gondwana collision?

Abstract: The late Precambrian to early Paleozoic age rock units of the Pampean ranges, the Puna, and the North Patagonian massif of southwestern South America constitute the Famatinian orogenic belt. They are interpreted as an Ordovician collisional belt between the Occidentalia terrane and the Gondwana craton. They include mafic and ultramafic belts of Neoproterozoic to early Paleozoic age. An intense tectonothermal event resulted from the collision; syntectonic granitoids represent crustal melting. In that collision syntectonic to late-tectonic foreland basins developed. The recently proposed juxtaposition of Laurentia and East Antarctica-Australia in the Neoproterozoic raises the possibility that Laurentia and western South America were close together in the early Paleozoic, and therefore that the Famatinian belt resulted from Laurentia-Gondwana collision. Occidentalia, which is bordered by a Cambrian carbonate platform similar to that of eastern North America, may be a sliver detached from Laurentia during Late Ordovician time.

Inhibition of Stearoyl-CoA Desaturase 1 expression in human lung adenocarcinoma cells impairs tumorigenesis.

Abstract: Saturated (SFA) and monounsaturated (MUFA) fatty acids, the most abundant fatty acid species, have many divergent biological effects including the regulation of cell proliferation, programmed cell death and lipid-mediated cytotoxicity. Their distribution is regulated by Stearoyl-CoA Desaturases (SCD), the enzymes that convert SFA into MUFA. A positive correlation between high levels of tissue MUFA and several types of cancer has been reported, but a causal relationship between the function of SCD1, the main human SCD isoform, and cancer development has not yet been firmly established. Here we report that the stable knockdown of SCD1 gene expression in A549 human lung adenocarcinoma cells decreased the ratio MUFA/SFA in total lipids and inhibited the incorporation of glucose into cell lipids. Cell proliferation and anchorage-independent growth were considerably decreased in SCD1-depleted cells, whereas the rate of apoptosis was elevated, with respect to control A549 cells. In addition, phosphorylation of Akt-Ser473 and GSK-3beta-Ser9 was found notably impaired in SCD1-ablated A549 cells. Interestingly, the effects of SCD1 blockade on Akt activation, cancer cell growth and apoptosis could not be reversed by exogenously added oleic acid. Remarkably, the reduction of SCD1 expression in lung cancer cells significantly delayed the formation of tumors and reduced the growth rate of tumor xenografts in mice. Our study demonstrates that SCD1 activity regulates Akt activation and determines the rate of cell proliferation, survival and invasiveness in A549 cancer cells and shows, for the first time, that SCD1 is a key factor in the regulation of tumorigenesis in vivo.

Did the Taconic Appalachians continue into southern South America

Abstract: The Appalachian Mountains, now terminating abruptly at the Gulf of Mexico coastal plain, may have formerly continued into southern South America. Rocks forming the basement of the Argentine Andes can be interpreted as remnants of an early Paleozoic orogen, the Famatinian belt, not unlike the Taconic Appalachians. Both orogens are bordered to the west (present coordinates) by lower Paleozoic carbonate platforms bearing the Olenellid trilobite fauna that is characteristic of Laurentia. Paleomagnetic and geologic data indicate that they could have formed as one continuous mountain chain, possibly extending into Antarctica, during Ordovician closure of an ocean basin ("southern" Iapetus) between Laurentia and Gondwana. The Taconic and Famatinian segments of the chain may have been truncated during Late Ordovician separation of Laurentia and Gondwana along the preexisting (late Neoproterozoic to Cambrian) rift system that initiated formation of the Ouachita embayment and the southern margin of North America.

First discovery of monotremes in South America

Abstract: UNTIL now, the egg-laying monotremes were only known from the Australian continent, where they have lived since the early Cretaceous period to the present1. Here we report the first monotreme from outside the Australian continent, an ornithorhyn-chid, from sediments of late early Palaeocene age in Patagonia, southern Argentina. This discovery demonstrates the Gondwanan nature of monotremes and supports the hypothesis that the Patagonian Terrane of southern South America had a biotic history distinct from that of the rest of the continent.

Colon cancer in Argentina. I: Risk from intake of dietary items.

Abstract: A case-control study has been conducted to investigate the relationship between dietary components and risk of colon cancer in the La Plata area of Argentina. Cases are 110 patients newly diagnosed with colon cancer in 10 major hospitals between 1985 and 1986. Two neighbourhood controls per case were individually matched by age, sex and place of residence. Personal interviews elicited information on frequency of consumption of 140 food items during the 5-year period up to 6 months prior to interview. Risk is analyzed by quartiles of individual food items and groups of items. Multivariate conditional logistic regression modelling indicates that consumption of eggs is associated with increased risk for colon cancer (odds ratios by quartile: 1.0, 1.58, 2.02, 4.66), as are some dairy products (ORs of 1.93 for the highest quartile of consumption of cheese). Intake of vegetables, fish and poultry is associated with statistically significant decreasing risk (ORs of 0.075, 0.39 and 0.39, for the highest categories of consumption of vegetables, fish and poultry, respectively). The risk for red meat does not consistently increase as consumption increases. Risks are not altered by the inclusion of potential confounders such as education or body mass index. These findings confirm those of several previous studies and are of particular interest, since the Argentinean diet typically includes a high intake of red meat.

Earliest hunters and gatherers of South America

Abstract: Traditional syntheses of the archaeology of the late Pleistocene period in South America have focused primarily on the peopling of the continent by North American cultural groups and on identifying associations among regional sites. This focus has tended to ignore the widespread culture diversity of the period and the possible effects of different paleolandscapes on human migration and colonization, such as the presence of unglaciated tropical and temperate environments in the northern lowlands, the gateway to the interior. The earliest known cultural assemblages are characterized by various unifacial and bifacial lithic industries that may represent regional processes reminiscent of an Archaic lifeway. The major archaeological sites and associated artifact assemblages are examined in terms of regional and continental patterns of environmental and cultural change. Results suggest that the Pleistocene archaeological record of South America must be explained in its own terms and that the events and processes producing this record either occurred earlier than previously thought or are very different from those in North America.

A Rhizobium meliloti lipopolysaccharide mutant altered in competitiveness for nodulation of alfalfa.

Abstract: A transposon Tn5-induced mutant of Rhizobium meliloti Rm2011, designated Rm6963, showed a rough colony morphology on rich and minimal media and an altered lipopolysaccharide (LPS). Major differences from the wild-type LPS were observed in (i) hexose and 2-keto-3-deoxyoctonate elution profiles of crude phenol extracts chromatographed in Sepharose CL-4B, (ii) silver-stained sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis patterns of crude and purified LPS fractions, and (iii) immunoreactivities otherwise present in purified LPS of the parental strain Rm2011. In addition, Rm6963 lost the ability to grow in Luria-Bertani medium containing the hydrophobic compounds sodium deoxycholate or SDS and showed a decrease in survival in TY medium supplemented with high calcium concentrations. The mutant also had altered symbiotic properties. Rm6963 formed nodules that fixed nitrogen but showed a delayed or even reduced ability to nodulate the primary root of alfalfa without showing changes in the position of nodule distribution profiles along the roots. Furthermore, 2 to 3 weeks after inoculation, plants nodulated by Rm6963 were smaller than control plants inoculated with wild-type bacteria in correlation with a transient decrease in nitrogen fixation. In most experiments, the plants recovered later by expressing a full nitrogen-fixing phenotype and developing an abnormally high number of small nodules in lateral roots after 1 month. Rm6963 was also deficient in the ability to compete for nodulation. In coinoculation experiments with equal bacterial numbers of both mutant and wild-type rhizobia, only the parent was recovered from the uppermost root nodules. A strain ratio of approximately 100 to 1 favoring the mutant was necessary to obtain an equal ratio (1:1) of nodule occupancy. These results show that alterations in Rm6963 which include LPS changes lead to an altered symbiotic phenotype during the association with alfalfa that affects the timing of nodule emergence, the progress of nitrogen fixation, and the strain competitiveness for nodulation.

Bacillus thuringiensis growth, sporulation and δ-endotoxin production in oxygen limited and non-limited cultures.

Abstract: The production of crystals and spores ofBacillus thuringiensis var.israelensis was studied under different aeration conditions. The results with 4 l batch cultures showed that for O2 non-limited, cultures cell yield, toxin production and spore count were constant for all oxygen transfer rates (OTR). Under O2 limitation, °-endotoxin concentrations and spore counts were lower than those obtained in non-limited cultures. In addition, δ-endotoxin yields diminished under O2 limitation, suggesting that the toxin synthesis mechanism could have been affected.

Triassic Gondwana' granites of the Gastre district, North Patagonian Massif

Abstract: Granites of the Batholith of Central Patagonia were emplaced into late Precambrian metamorphic basement rocks and Palaeozoic orthogneisses (here dated by Rb-Sr whole-rock errorchrons at 346 ± 35 Ma and 267 ± 27 Ma), and are in fault-contact with younger volcanic rocks, mostly andesites. Two main suites of granites are recognised: both are much younger than their previously-supposed Late Palaeozoic age. The Gastre Suite is composed predominantly of hornblende-biotite granodiorite and monzogranite, often slightly foliated, and has yielded a Rb-Sr whole-rock isochron age of 220 ± 3 Ma

Zinc-Rich Paints on Steels in Artificial Seawater by Electrochemical Impedance Spectroscopy

Abstract: Electrochemical impedance spectroscopy (EIS) was applied over a wide frequency range to characterize the corrosion protection behavior by two types of zinc-rich paints (ZRP) (zinc-rich epo...

On the analytical solution of the Ornstein-Zernike equation with Yukawa closure

Abstract: We discuss the solution of the Ornstein-Zernike equation for most general closure consisting of a sum ofM Yukawa-type exponentials. A formal solution for the factored case is bound for an arbitrary mixture of hard spheres introducing a general scaling matrix Γ of dimensions M×M. A sufficient number of equations for this matrix is obtained from symmetry considerations and the boundary condition. We discuss also restricted and semirestricted case, for which explicit solutions in terms of the scaling parameters and input parameters are found.

On the asymptotic exactness of Bank-Weiser's estimator

Abstract: In this paper we analyze an error estimator introduced by Bank and Weiser. We prove that this estimator is asymptotically exact in the energy norm for regular solutions and parallel meshes. By considering a simple example we show that this is not true for general meshes.

Critical exponents for the irreversible surface reaction A + B → AB with B desorption on homogeneous and fractal media

Abstract: A model for the surface reaction A+B\ensuremath{\rightarrow}AB with B desorption exhibits a continuous irreversible phase transition from an A-poisoned state to a reactive regime. At criticality, an empty patch embedded in the poisoned state spreads on the sample following a random-walk diffusion behavior. So, a relationship between dynamic exponents of the reaction process, the random-walk exponent, and the fractal dimension of the substrate is conjectured and tested.

Nucleation of strange matter in dense stellar cores

Abstract: We investigate the nucleation of strange quark matter inside hot, dense nuclear matter. Applying Zel'dovich's kinetic theory of nucleation we find a lower limit of the temperature {ital T} for strange-matter bubbles to appear, which happens to be satisfied inside the Kelvin-Helmholtz cooling era of a compact star life but not much after it. Our bounds thus suggest that a prompt conversion could be achieved, giving support to earlier expectations for nonstandard type-II supernova scenarios.

Colon cancer in argentina. II: Risk from fibre, fat and nutrients

Abstract: A case-control study has been conducted to investigate the relationship between total energy intake, fibre and nutrients and colon cancer in Argentina. Cases are 110 newly diagnosed patients from 10 hospitals between 1985 and 1986. Two neighbourhood controls per case were matched on age, sex and place of residence. The intake of calories, fibre and nutrients was estimated from the information collected on food consumption during the 5-year period up to 6 months prior to interview of subjects, based on a pilot study and standard portion sizes in Argentina. In conditional regression models, dietary fibre is highly protective (odds ratio (OR) = 0.07 per 19.02 g/day; 95% confidence interval (CI): 0.02 to 0.25) and total energy intake increases risk (RR = 1.82 per 1000 kcal/day; 95% CI: 1.20 to 2.77), each with adjustment for the other. Analysis of caloric components (fat, protein and carbohydrates) reveals that carbohydrates are the most important factor driving the total energy effect. Other nutrients make little apparent contribution to risk.