A new formulation to estimate the variance of model prediction. Application to near infrared spectroscopy calibration.

Evaluation of uncertainty affecting predictions is a major trend in analytical chemistry and chemometrics. Several approximate expressions and resampling methods have been proposed for the estimation of prediction uncertainty when using multivariate calibration. This article proposes a new expression for the variance of prediction, adapted to near infrared spectroscopy specificities and particularly to the spectral error structure, induced by the high colinearity of the variables. The proposed analytical expression enables a detailed evaluation of the different contributions and components of uncertainty affecting the model. An application to real data of feedstuff near infrared spectra related to protein content has shown its advantages.

Low-level subchronic arsenic exposure from prenatal developmental stages to adult life results in an impaired glucose homeostasis.

We evaluated how low-level (3 ppm) subchronic inorganic arsenic (iAs) exposure from prenatal developmental stages until adult life affects glucose homeostasis. Biochemical parameters of glucose and lipid metabolism, pancreatic insulin and glycosylated haemoglobin were determined in 4-month-old female offspring of adult Wistar rats. Pancreatic histology was also performed. Statistical comparisons between control and iAs-treated groups were performed by unpaired two-tailed Student's t-test. Statistical significance was set at p<0.05. We found that iAs treatment resulted in an impaired glucose tolerance test, suggestive of impaired glucose metabolism. This group was found to have hyperglycaemia and high levels of HOMA-IR, glycosylated haemoglobin, cholesterol and pancreatic insulin compared to control rats. However, plasma insulin, triglycerides and high-density lipoprotein cholesterol were not different from control rats. Moreover, ß-cell damage found in iAs-treated rats consisted of cells with a nucleus with dense chromatin and predominance of eosinophilic cytoplasm, as well as changes in the pancreatic vasculature. The current study provided evidence that subchronic iAs exposure at 3 ppm from prenatal developmental stages to adult life resulted in damage to pancreatic ß cells, affected insulin secretion and demonstrated altered glucose homeostasis, thus supporting a causal association between iAs exposure and diabetes.

Multivariate near-infrared reflection spectroscopy strategies for ensuring correct labeling at feed bagging in the animal feed industry.

A key concern in animal feed factories is guaranteeing the correct labeling of compound feeds. Therefore, due to incorrect labeling, there is an urgent need for new control methods on the claims that can be made. In this study, this question has been tackled with different multivariate classification algorithms based on the near-infrared spectral fingerprint obtained from a given compound feed analyzed in its original physical market presentation form (i.e., cubes, coarse meals, pellets). The objective of this paper is the evaluation of different methods for establishing a separation among 24 feed types. Two linear methods, soft independent modeling of class analogy (SIMCA) and partial least squares (PLS) with two approaches to classification (PLSD and PLS-LDA); and one nonlinear method, support vector machines (SVM), were studied. The database used had the following structure: a first division was made between granules and meals; within these two groups, there was a second division according to three animal species to which the feed was marketed (bovine, ovine, and porcine); within each species there was a third division according to the age or physiological status of the animal (i.e., lactating dairy cattle, starters, etc.). Given the database structure, all the methods were evaluated following two strategies: (1) development of a model composed of the nine classification models corresponding to the structure of the data; and (2) development of a unique model that discriminates among the 24 classes of different feeds. With both strategies the lowest percentage of misclassified samples was achieved with the SVM method (3.96% with strategy 1 and 2.31% with strategy 2). Among the linear methods evaluated, SIMCA yielded the best results, with a percentage of 8.47% misclassified samples with strategy 1 and 4.05% misclassified samples with strategy 2. The results in this study show the ability of near-infrared spectroscopy to make acceptable classifications of feed types based only on spectral information, with differences in performance depending on the multivariate algorithm used.

Application of the critical molar concentration concept to heat-mediated antigen retrieval in immunohistochemistry.

Previously we have applied Scott's critical molar concentration concept to show that divalent cations, especially Mg2+ may be used to measure the affinity of a known monoclonal antibody for its antigen. In this paper we report the application of this same procedure to a study of a series of antigens (three globular proteins and three intermediate filaments). The concept was applied to samples without any previous treatment or after the application of heat-mediated antigen retrieval (using a pressure cooker). Our findings suggest that heat-mediated antigen retrieval sets free protein side-chain(s) that have been masked by formaldehyde fixation. This is reflected in a higher affinity of the antibody for the antigen in question.

[Gallstone dissolution in an adult female population: trial with lovastatin therapy]. / Disolución de cálculos vesiculares en una población de mujeres adultas: ensayo de terapia con lovastatina.

BACKGROUND: There are no chilean reports on gallstone dissolution using oral medications. AIM: To measure the proportion of asymptomatic adult women eligible for gallstone dissolution therapy and to test the effectiveness and tolerance of lovastatin for this purpose. SUBJECTS AND METHODS: Three hundred fifty six women working at health care institutions were subjected to a gallbladder ultrasound examination. Non pregnant women with radiolucent gallstones of less than 2 cm phi were invited to receive lovastatin 20 mg od and were followed during six months. RESULTS: Twenty two women had gallstones and eight eligible women received lovastatin therapy. No reduction in stone size was observed in these women. CONCLUSIONS: Less than half of asymptomatic women with gallstones are eligible for oral dissolution therapy. Lovastatin did not reduce gallstone size after six months of therapy.

[Cholecystectomy in young women from the south-oriental area of Santiago: comparison between 2 periods]. / Colecistectomía en mujeres jovenes del area suroriente de Santiago: comparación entre dos períodos.

The aim of this study was to know if cholecystectomy rates have decreased in young women, considering that these rates have decreased in the last years in the general chilean population. The frequency of previous cholecystectomy was compared in 1582 women aged 23.9 +/- 5.8 years admitted to a maternity for delivery between 1985 and 1986 and 4943 women aged 24.6 +/- 5.9 years admitted between 1989 and 1990 for the same reason. There was a reduction in cholecystectomy frequency from 4.7 to 2.5% specially among women 21 to 35 years old. Cholecystectomy was performed at a mean age of 23 years in both groups and 42.6% of the procedures were done before the first pregnancy. An unexpected finding was a lower body weight among women studied in the second period (62.5 +/- 9.1 vs 67.7 +/- 8.4 k).

Effect of a milk-based food supplement on maternal nutritional status and fetal growth in underweight Chilean women.

The effects on pregnancy outcome and maternal iron status of powdered milk (PUR) and a milk-based fortified product (V-N) were compared in a group of underweight gravidas. These take-home products were distributed during regular prenatal visits. Women in the V-N group had greater weight gain (12.29 vs 11.31 kg, p less than 0.05) and mean birth weights (3178 vs 3105 g, p less than 0.05) than those in the PUR group. Values for various indicators of maternal Fe status were also higher in the V-N group. Compared with self-selected noncompliers, similar in all control variables to compliers, children of women who consumed powdered milk or the milk-based fortified product had mean birth weights that were higher by 258 and 335 g, respectively. Data indicate a beneficial effect of the fortified product on both maternal nutritional status and fetal growth.

PIP: The effects on maternal and infant weight gain and maternal iron status of powdered milk (PUR) and a milk-based fortified product (V-N) were compared in underweight women attending prenatal clinics in Santiago, Chile. All pregnant women attending 9 prenatal clinics of the Southeast Health Area, over 18 years old, parity 0-5, nonsmoking, nonalcohol-consuming and underweight (95% of standard) joined the study. They were given either the PUR, powdered milk with 26% milkfat, or V-N, (Vita-Nova Mother-food, Melkunie Holland, Woerden) which contained micronutrients and added vegetable fat, as mandated by law. Those who failed to consume supplements were relegated to the control group. The V-N group had greater weight gain (12.29 vs 11.31 kg, p0.05), mean birth weights (3178 vs 3105 g, p0.05) than the PUR group. Iron status, shown by significantly higher mean hematocrit, hemoglobin, mean corpuscular volume, transferrin saturation and plasma ferritin levels near term, was also better in the V-N group than in the PUR. Other significant differences in favor of the V-N supplement were number of intrauterine growth retarded infants and birth weights under 3001 g. The V-N group had greater fluid retention: the import of this is unknown. The infants of non-compliers had birthweights 258 and 335 g lower than the women consuming PUR and V-N, respectively. The babies of V-N mothers gained 74 g/kg maternal weight gain, higher than many previously reported increments, perhaps due to the micronutrients in the supplement.