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Biomedical subjects

S Guerrero

Publications and source records attributed to S Guerrero.

At least 19 recordsLinked to original sources
PubMed2000

K-ras codon 12 mutation induces higher level of resistance to apoptosis and predisposition to anchorage-independent growth than codon 13 mutation or proto-oncogene overexpression.

The position of the point mutation in the c-K-ras gene appears associated with different degrees of aggressiveness in human colorectal tumors. In addition, colon tumors carrying K-ras codon 12 mutations associate with lower levels of apoptosis than tumors lacking this mutation. To test the hypothesis of a distinct transforming capacity of different K-ras forms in an in vitro system, we generated stable transfectants of NIH3T3 cells expressing a plasmid containing K-ras mutated at codon 12 (K12) or at codon 13 (K13), or overexpressing the K-ras proto-oncogene (Kwt-oe). We evaluated changes in morphology, proliferative capacity, contact inhibition, and predisposition to apoptosis and anchorage-independent growth in K12, K13, and Kwt-oe transformants. In addition, we studied alterations in expression and/or activation of proteins that participate in signal transduction downstream of Ras or are involved in the regulation of apoptosis and cell-cell (E-cadherin and beta-catenin) and cell-substrate (focal adhesion kinase) interactions. We observed that K13 or Kwt-oe transformants died synchronically 24-48 h after reaching confluency. Their death was apoptotic. In contrast, K12 grew, forming bigger colonies with higher cell densities; and before reaching confluency, spontaneously formed spheroids and showed no sign of apoptosis. The enhanced resistance to apoptosis, loss of contact inhibition, and predisposition to anchorage-independent growth in the K12 transformants were associated with higher AKT/protein kinase B activation, bcl-2, E-cadherin, beta-catenin, and focal adhesion kinase overexpression, and RhoA underexpression, whereas the increased sensitivity of K13 or Kwt-oe transformants to apoptosis was associated with increased activation of the c-Jun-NH2-terminal kinase 1 pathway. All transformants showed a similar overactivation of mitogen-activated protein kinases and levels of bax expression similar to the endogenous level. Therefore, in our in vitro model, the localization of the mutation in the K-ras gene predisposes to a different level of aggressiveness in the transforming phenotype. K12 may increase aggressiveness not by altering proliferative pathways, but by the differential regulation of K-Ras downstream pathways that lead to inhibition of apoptosis, enhanced loss of contact inhibition, and increased predisposition to anchorage-independent growth. These results offer a molecular explanation for the increased aggressiveness of the tumors with K-ras codon 12 mutations observed in the clinical setting.

3T3 Cells↗
PubMed2000

Probabilistic modeling of Saccharomyces cerevisiae inhibition under the effects of water activity, pH, and potassium sorbate concentration.

Probabilistic microbial modeling using logistic regression was used to predict the boundary between growth and no growth of Saccharomyces cerevisiae at selected incubation periods (50 and 350 h) in the presence of growth-controlling factors such as water activity (a(w); 0.97, 0.95, and 0.93), pH (6.0, 5.0, 4.0, and 3.0), and potassium sorbate (0, 50, 100, 200, 500, and 1,000 ppm). The proposed model predicts the probability of growth under a set of conditions and calculates critical values of a(w), pH, and potassium sorbate concentration needed to inhibit yeast growth for different probabilities. The reduction of pH increased the number of combinations of a(w) and potassium sorbate concentration with probabilities to inhibit yeast growth higher than 0.95. With a probability of growth of 0.05 and using the logistic models, the critical pH values were higher for 50 h of incubation than those required for 350 h. With lower a(w) values and increasing potassium sorbate concentration the critical pH values increased. Logistic regression is a useful tool to evaluate the effects of the combined factors on microbial growth.

Food Microbiology↗
PubMed1999

[Milk fluoridation program in Codegua, Chile: evaluation after 3 years].

A study was done in 1994 to determine the effectiveness of the fluoridated dairy products that the Chilean National Program for Supplementary Feeding had been distributing to reduce the high prevalence of children's dental caries in rural areas of that country. For the study, the prevalence of caries was assessed in two rural communities of the Sixth Region of Chile. Children in the study community of Codegua had received fluoridated dairy products, while children in the control community of La Punta had received nonfluoridated dairy products. Three years after the program began in Codegua, the community showed a significant improvement in the indices of prevalence of caries. Over that time period, the prevalence of caries among children 3 to 6 years old declined between 40% and 60%. Among children 3 years old, the proportion of them without a history of caries increased by 74%, from 40.7% to 70.8%. Among 4-year-olds, that proportion rose by 71%, from 33.3% to 56.9%. Similar to results obtained elsewhere with programs to fluoridate drinking water, the outcomes in Codegua were achieved without any other steps by the National Program for Supplementary Feeding, such as motivational campaigns for mothers or educational efforts to encourage consumption of the program's food products.

Age Factors↗
PubMed1999

Saccharomyces cerevisiae thermal inactivation kinetics combined with ultrasound.

Inactivation kinetics of Saccharomyces cerevisiae during thermal treatments at moderate temperatures (45.0, 47.5, 50.0, 52.5, or 55.0 degrees C) combined with application of 20 kHz of ultrasound were evaluated. S. cerevisiae inactivation under the combined effects of heat and ultrasound followed first-order reaction kinetics, with decimal reduction times (D) that varied from 22.3 to 0.8 min. D values in treatments that combined heat and ultrasound were significantly smaller (P < 0.05) than D values obtained for thermal treatments and were more noticeable at temperatures below 50 degrees C. The dependence of the D value on temperature had a significantly (P < 0.05) greater z value for combined treatments. Yeast heat inactivation kinetics revealed decreased thermal resistance caused by ultrasound.

Animals↗
PubMed1998

Estimation of optimal concentration of fluoride in drinking water under conditions prevailing in Chile.

The purpose of this comparative study of caries and dental fluorosis experience in Chilean children was to estimate the optimal range of fluoride concentration in tap water under conditions currently prevailing in Chile. The sample included 2431 schoolchildren 7, 12 and 15 years old, life-long residents of five communities with fluoride concentrations in their tap water in the range 0.07-1.1 mg/L. The study population received an oral clinical examination including caries experience and an enamel fluorosis evaluation of the permanent dentition (Dean's scoring system). For 15-year-old children, the DMFT index changed from 5.06 to 2.60, and for 12-year-olds it changed from 3.10 to 1.36 when fluoride water concentration changed from 0.07 to 1.10 mg/L. For 7-year-old children the dmft index correspondingly changed from 3.67 to 1.59. The relationship between DMFT for 12-year-olds and water fluoride concentration was best fitted by a logarithmic function (r2=0.98). The Community Fluorosis Index (CFI) was used to assess enamel fluorosis in the study population, and it showed a linear relationship (r2=0.983) with increasing fluoride concentration of water for the 12-year-old group. Results obtained suggest that under current Chilean conditions, the optimal range of fluoride concentration in potable water should lie in the 0.5-0.6 mg/L range.

Adolescent↗
PubMed1998

Dental fluorosis in Chilean children: evaluation of risk factors.

The purpose of this case-control study was to determine the association between very-mild-to-moderate enamel fluorosis and exposure during early childhood to fluoridated water, mainly through ingestion of powdered milk. Analysis was performed on 136 residents of the optimally fluoridated community of San Felipe in the Chilean Fifth Region, who were categorised into one of three groups according to their age when water fluoridation was introduced in 1986: Group I was born after 1986; Group II was 16-24 months old in 1986; and Group III was >24 months of age. The case and control subjects were selected on the basis of a clinical examination given in July 1996. Dean's scoring system was used to determine fluorosis status. Risk factor exposure was ascertained by a questionnaire used in interviews with mothers of participating children. Logistic regression analysis, after adjustment for confounding variables, revealed that very-mild-to-moderate enamel fluorosis of permanent central maxillary incisors (CMI) was strongly associated both with the age of the subjects when water fluoridation began and with breast-feeding duration for children belonging to Group I. Subjects in Group I were 20.44 times more likely (95% CI: 5.00-93.48) to develop CMI fluorosis than children who were older than 24 months (Group III) when fluoridation began. Subjects who were between 16 and 24 months old when water fluoridation began were 4.15 times more likely (95% CI: 1.05-16.43) to have CMI fluorosis than children older than 24 months. An inverse association was found with breastfeeding duration (OR=0.86, 95% CI: 0.75-0.98) among Group I subjects but not in Groups II and III. Results obtained suggest that the current fluoride concentration in drinking water may be contributing to fluorosis. Further studies will be necessary to determine the relative competing risks of dental fluorosis and dental caries in Chilean children in order to establish the most appropriate water fluoridation level in Chile.

Analysis of Variance↗
PubMed1996

Caries experience and fluorosis prevalence in Chilean children from different socio-economic status.

Caries experience and enamel fluorosis prevalence in 8-year-old children belonging to different socio-economic classes were determined in two Chilean twin cities that are served by optimally fluoridated community water from the same waterworks facility. Low socio-economic status (LSES) children had a higher mean dmft and DMFT indices (P < 0.001) than high socioeconomic status (HSES) children. Prevalence of enamel fluorosis in the permanent teeth of LSES children was 0.79, significantly higher (chi 2 = 9.0; P < 0.003) than the value 0.59 found in HSES children. The proportion of Dean's scores 2, 3, 4 and 5 in first molars, mandibular and maxillary incisors in LSES children was higher than in HSES children (P < 0.001). Differences in prevalence and severity of enamel fluorosis between both groups are tentatively attributed to a different pattern of tap water and tea consumption at pre-school ages. Suggestions are advanced to minimize the undesirable prevalence and severity of enamel fluorosis.

Child↗
PubMed1994

[Dietary ingestion of fluoride and caries prevalence in preschool and school children in cities with different fluoride content in the drinking water and diet].

The consumption of dietary fluoride and its relationship with dental caries prevalence was determined in 780 preschool children and 802 school children from quique, Arica, Santiago and San Antonio, where drinking water has different fluoride concentration. Dietary fluoride was determined from dietary records and fluoride content of foods. The fluoride consumption from drinking water was calculated by Galagan and Vermillion formula. The total fluoride consumption was obtained. The dental caries prevalence was established by the evaluation of dental caries index in deciduous (dmft) and permanent (DMFT) dentition. Significantly lower DMFT values were founded in cities with lower fluoride levels in drinking water. The exception was San Antonio, where high dietary fluoride explained the lower DMFT values relative to Santiago. Our results suggest that not only fluoride in water but also the consumption of fluoride rich foods has a significant impact on the prevalence of caries.

Adolescent↗
PubMed1992

Prognostic value of echocardiography in hospitalized patients with pericardial effusion.

It is often difficult to predict outcome in hospitalized patients with pericardial effusion. To address this issue, the prognostic value of echocardiography was studied in 187 hospitalized patients diagnosed with pericardial effusions over a 1-year period. The index echocardiogram showed that 11 effusions were large (6%), 39 were moderate (21%), and 137 were small (73%). Right ventricular collapse was present in 7% of cases (13 of 178), right atrial collapse in 12% (21 of 168), and inferior vena cava (IVC) plethora with blunted response to respiration in 35% (46 of 132). During the course of hospitalization, 9 patients (5%) had cardiac tamponade and 16 (9%) had cardiac tamponade, pericardiocentesis and/or surgical drainage (combined end point). By univariate analysis, each echocardiographic sign was associated with both cardiac tamponade and the combined end point (p less than or equal to 0.01 for comparisons with size and right-sided chamber collapse; p less than or equal to 0.07 for comparisons with IVC plethora). When the data were analyzed with logistic regression modeling, effusion size was the most powerful predictor of outcome (cardiac tamponade: odds ratio 51, 95% confidence interval 3.5-729, p = 0.004; combined end point: odds ratio 78, 95% confidence interval 14-421, p = 0.0001), and neither right-sided chamber collapse nor IVC plethora with blunted response to respiration retained significant associations. It is concluded that echocardiographically determined effusion size is a powerful predictor of outcome in hospitalized patients with pericardial effusion, and that right-sided chamber collapse and IVC plethora with blunted response to respiration add little if any additional prognostic information.

Cardiac Tamponade↗
PubMed1990

[Effect of a participatory method on nutrition education in dentistry].

Based on results of a diagnostic test which measured the knowledge that University of Chile students of 5 different health careers have a food and nutrition (1982), the nutrition program of the school of Dentistry was modified from a traditional system of education (formal classes) to a participative methodology in 1984, a didactic material on nutritional recommendations. An increased level of knowledge as well as motivation was observed in those graduating in 1984, particularly the area of nutritional recommendation and diet, to which the students spent more extra time. We can conclude that the educational methodology that stresses participation and is centered around one person is very effective to teach nutrition in the school of Dentistry.

Community Participation↗
PubMed1990

[Caries prevention through a nutritional vehicle].

In order to evaluate the efficacy of fluoridated milk as a cariostatic nutritional product, the biological and technical possibilities of adding fluoride (F) as monofluorophosphate (MFP) to milk were studied, together with a preliminary cost estimation for this procedure. F ingestion by preschool children pertaining to the low and medium-low levels of population was estimated through polls and chemical analyses. The values of F ingestion obtained were in the range of 0.15-0.30 mg/day. The bioavailability of F in those dietary elements which have the highest F concentration was determined. Taking a value of 1.00 for F absorption from sodium fluoride (NaF) in water, relative values of 0.58 and 0.32 were obtained for tea ingestion on a fasting stomach, and together with solid food, respectively. The corresponding value for fish was 0.34. Through another bioavailability experiment it was shown that the absorption of F (from MFP) in milk, is as high as that of F (from NaF) in water. By means of a comparative cost estimation study, it was found that, for the Chilean situation, milk fluoridation is, at least, 1,000 times more economic than water fluoridation. It is concluded that milk fluoridation is an economical and viable alternative for some less developed countries.

Animals↗
PubMed1989

Fluoride bioavailability from disodium monofluorophosphate fluoridated milk in children and rats.

The aim of the present work was to study the usefulness of disodium monofluorophosphate (MFP) as a milk-fluoridating agent by measuring the bioavailability of F from MFP in milk relative to that of F from NaF in water. Long-term (multiple-dose) studies were performed on rats measuring F bone uptake. The relative F absorption from MFP in milk was also determined in preschool children by means of 24-hour F urinary excretion. In both studies F absorption was determined either under fasting conditions or when F ingestion occurred together with food intake. The results show that F absorption from MFP in milk is as high as that of NaF in water under fasting conditions and that the F bioavailability decrease from NaF in water is more important than that of MFP in milk when F ingestion occurs simultaneously with food intake.

Absorption↗
PubMed1988

Electrophysiological effects of verapamil on primary and transitional pacemaker cells of the frog heart.

1. In spontaneously beating preparations of sinus venosus of the frog Caudiverbera caudiverbera the electro-physiologic effects of verapamil on action potential parameters of both primary and transitional pacemaker cells were investigated. 2. Verapamil in concentrations ranging from 5 x 10(-8)M to 2 x 10(-6)M slowed the sinus rate and blocked impulse initiation. Action potential blockade was accompanied by oscillations of membrane potential and depolarization. 3. During blockade of primary pacemaker cells, pacemaker shift originated the activation of transitional or atrial contractile fibres. 4. Subthreshold concentrations of the drug to induce complete blockade (5 x 10(-8)M) allowed to observe a greater depression of bioelectric cell characteristics in primary than in transitional fibres. 5. Verapamil-induced blockade of transitional pacemaker action potentials was preceded by the appearance of a notch in their upstroke and the persistence of a fast depolarizing section that remained unblocked. This fast verapamil-resistant section of the upstroke was absent in preparations treated with tetrodotoxin (TTX). 6. The results confirmed most previously described actions of verapamil on mammalian sinoatrial preparations and provided a pharmacological dissection of the two slow and fast bio-electric components contributing to the upstroke of transitional pacemaker cells of the frog sinus venosus.

Action Potentials↗
PubMed1987

Electrophysiological characteristics of cardiac pacemaker cells of the frog Caudiverbera caudiverbera.

1. The cardiac pacemaker cells of the frog Caudiverbera caudiverbera are centrally located in the sinus venosus. These cells are rounded, smaller than contractile fibres and have large nuclei. 2. Intracellular recording confirmed the existence of primary and transitional pacemaker cells. 3. Action potentials from primary cells were resistant to blockade by tetrodotoxin (TTX), but were abolished by verapamil suggesting that their bioelectric activity is dependent on a slow inward current. 4. Transitional cells appeared to have two different inward currents contributing to the upstroke: a fast TTX-sensitive and a slow verapamil-sensitive current.

Action Potentials↗
PubMed1987

Electrophysiological effects of bupivacaine on transitional pacemaker cells of the frog heart.

The effects of bupivacaine, a long-acting local anesthetic, were studied on action potentials of spontaneously beating sinus venosus of the frog Caudiverbera caudiverbera. The study was accomplished by recording transmembrane potentials of pacemaker transitional cells. Action potentials of these cells are known to have both a fast and a slow ionic component. Bupivacaine (1 X 10(-5) M to 1 X 10(-4) M) caused a reversible negative chronotropic effect accompanied by decrease of diastolic depolarization rate and prolongation of sinus cycle length. This drug also markedly depressed rate of rise [(dV/dt)max] of action potentials. Tetrodotoxin (TTX) (1 X 10(-7) M) induced similar effects than bupivacaine. In atropine-treated sinus venosus the effect of bupivacaine on spontaneous rate of firing was less intense. However, in cells exposed to both drugs, a greater depression of (dV/dt)max and of other electrophysiological parameters such as action potential amplitude, overshoot and maximum diastolic potentials was observed. Depression of phase 4 depolarization seems difficult to be explained in view of the complex nature of the ionic currents underlying pacemaker depolarization. Reduction of (dV/dt)max caused by bupivacaine and mimicked by TTX was ascribed to blockade of sodium channels. It was concluded that bupivacaine by decreasing (dV/dt)max of transitional cells and by depressing diastolic depolarization slows down conduction of impulses arising from primary cells and that this action may contribute to its cardiac toxicity.

Action Potentials↗
PubMed1986

The effect of 4-aminoquinoline on frog atrial myocardium depolarized by potassium.

Intracellular recording was used to examine the effects of 4-aminoquinoline (4-AQ) on action potentials of frog atrial myocardium depolarized by potassium. Elevating [K+]0 to 12.5 mM resulted in decrease of resting membrane potential from 83 mV (normal Ringer) to 56 mV (P less than 0.001). Under these conditions, verapamil diminished amplitude, overshoot and duration of action potentials, whereas 4-AQ depressed overshoot and prolonged action potential duration (P less than 0.02). Action potentials recorded in 20 mM K+ (isoproterenol added) exhibited a mean resting potential of 38 mV and also a reduced amplitude and duration. Verapamil caused a rapid blockade of the electrophysiological response, suggesting that action potentials were mediated by a current carried by calcium ions. 4-AQ applied in two concentrations (0.25 and 0.5 mM) on atrial trabeculae exposed to 20 mM K+-isoproterenol partially restored resting membrane potential and significantly (P less than 0.001) increased amplitude, overshoot and duration of action potentials. These effects were attributed to an enhanced Ca2+ entrance induced either by a direct action upon voltage-sensitive calcium channels, or resulting from a prolonged action potential due to blockade of potassium conductance.

Action Potentials↗