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Biomedical subjects

D E Smith

Publications and source records attributed to D E Smith.

At least 127 records · Page 7Linked to original sources
PubMed1996

In vivo biosynthesis of retinoic acid from beta-carotene involves and excentric cleavage pathway in ferret intestine.

This study was done to determine whether retinoic acid can be produced by excentric cleavage of beta-carotene in vivo. By using an inhibitor of retinaldehyde oxidation, citral, either retinaldehyde or beta-carotene was incorporated in a micellar solution and perfused through the upper portion of small intestine of ferrets. After 2 h perfusion of 1 microM retinaldehyde, retinoic acid rose in portal blood (+3.5 +/- 1.3 nmol/L) and was detected in the intestinal mucosa (30 +/- 2 pmol/g). When citral was added at 2 mM along with retinaldehyde, retinoic acid decreased in the portal blood and retinoic acid was not detected in the intestinal mucosa. With or without the presence of citral (2 mM), the perfusion of beta-carotene (10 microM) during 2 h caused a significant rise of retinoic acid in portal blood (+2.6 +/- 0.6 nmol/L and + 4.1 +/- 0.6 nmol/L, respectively) and in liver; moreover, significant amounts of retinoic acid were detected in the intestinal mucosa (19 +/- 3 pmol/g and 36 +/- pmol/g, respectively. This study demonstrates that after intestinal perfusion of beta-carotene in the ferret in vivo, a substantial amount of retinoic acid is formed via an excentric cleavage pathway.

Acyclic Monoterpenes↗
PubMed1996

Correlates and predictors of weight loss in young adults: the CARDIA study.

OBJECTIVE: To determine associations of sociodemographic characteristics, behaviors, attitudes and medical factors with weight loss in a population-based biracial cohort of young adults. DESIGN: Two-year longitudinal observation study. SUBJECTS: 4278 black and white men and women aged 18-30 years in 1985-1986. MEASUREMENTS: Weight, height, education, income, subscapular skinfold thickness, waist and hip circumferences, medical history, smoking, physical activity, dietary energy, fat and alcohol intake, physical fitness measured by treadmill testing, self-reported dieting, history of weight loss and regain, perception of body size and belief in health consequences of overweight. RESULTS: Weight loss, defined as reduction of 5% or more of baseline weight, occurred in 8.9% of the cohort, ranging from 4.9% among white men who were not overweight at baseline to 21.5% among white women who were overweight. Weight loss was more common in women than men and in overweight white women than overweight black women. Although findings differed among the four race-sex groups, weight loss was generally associated with greater baseline fatness, lower baseline physical fitness level, self-perception of being overweight, dieting and previous weight loss and regain. Greater baseline fatness, a perception of being overweight and dieting were also associated with weight gain. Among the overweight, low baseline fitness and an increase in physical activity were the factors most consistently associated with weight loss. CONCLUSION: Weight loss in young adults varies by race, sex and body weight and is associated with a variety of behaviors and attitudes, some of which are also associated with weight gain and, thus, may be associated with weight fluctuation.

Adolescent↗
PubMed1996

Exon-specific DNA hypomethylation of the p53 gene of rat colon induced by dimethylhydrazine. Modulation by dietary folate.

Folate deficiency enhances colorectal carcinogenesis in dimethylhydrazine-treated rats. Folate is an important mediator of DNA methylation, an epigenetic modification of DNA that is known to be dysregulated in the early stages of colorectal cancer. This study investigated the effect of dimethylhydrazine on DNA methylation of the colonic p53 gene and the modulation of this effect by dietary folate. Sprague-Dawley rats were fed diets containing 0, 2, 8, or 40 mg of folate/kg of diet. Five weeks after diet initiation, dimethylhydrazine was injected weekly for fifteen weeks. Folate-depleted and folate-replete control animals did not receive dimethylhydrazine and were fed the 0- and 8-mg folate diets, respectively. The extent of p53 methylation was determined by a quantitative HpaII-polymerase chain reaction. In exons 6 and 7, significant p53 hypomethylation was observed in all dimethylhydrazine-treated rats relative to controls (P < 0.01), independent of dietary folate. In exon 8, significant p53 hypomethylation was observed only in the dimethylhydrazine-treated folate-depleted rats compared with controls (P = 0.038) and was effectively overcome by increasing levels of dietary folate (P = 0.008). In this model, dimethylhydrazine induces exon-specific p53 hypomethylation. In some exons, this occurs independent of dietary folate, and in others, increasing levels of dietary folate effectively override the induction of hypomethylation in a dose-responsive manner. This may be a mechanism by which increasing levels of dietary folate inhibit colorectal carcinogenesis.

Animals↗
PubMed1995

Determination of quinapril and quinaprilat by high-performance liquid chromatography with radiochemical detection, coupled to liquid scintillation counting spectrometry.

Quinapril and quinaprilat concentrations were determined in perfusate, urine, and perfusate ultrafiltrate using a specific and sensitive reversed-phase high-performance liquid chromatographic procedure with radiochemical detection, coupled to liquid scintillation counting spectrometry. Quinapril and quinaprilat were measured in perfusate and urine after pretreatment with acetonitrile and subsequent centrifugation. Perfusate ultrafiltrate was used as collected. Two quinapril diketopiperazine metabolites, PD 109488 and PD 113413, were separated chromatographically from quinapril, quinaprilat, and from each other. Assay performance for quinapril and quinaprilat was assessed by examining precision and accuracy of the assay over four days. Using a 100-microliters sample volume, the limit of quantitation for both 3H-quinapril and 3H-quinaprilat (sp. act. approximately 2.0 muCi/micrograms) was 1 ng/ml.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1995

Stretching of a single tethered polymer in a uniform flow.

The stretching of single, tethered DNA molecules by a flow was directly visualized with fluorescence microscopy. Molecules ranging in length (L) from 22 to 84 micrometers were held stationary against the flow by the optical trapping of a latex microsphere attached to one end. The fractional extension x/L is a universal function of eta vL 0.54 +/- 0.05, where eta and v are the viscosity and velocity of the flow, respectively. This relation shows that the DNA is not "free-draining" (that is, hydrodynamic coupling within the chain is not negligible) even near full extension (approximately 80 percent). This function has the same form over a long range as the fractional extension versus force applied at the ends of a worm-like chain. For small deformations (< 30 percent of full extension), the extension increases with velocity as x approximately v0.70 +/- 0.08. The relative size of fluctuations in extension decreases as sigma x/x approximately equal to 0.42 exp (-4.9 x/L). Video images of the fluctuating chain have a cone-like envelope and show a sharp increase in intensity at the free end.

Biopolymers↗
PubMed1995

Reabsorption and metabolism of quinapril and quinaprilat in rat kidney: in vivo micropuncture studies.

The tubular uptake and esterolysis of quinapril and quinaprilat were studied in male Sprague-Dawley rats using an in vivo micropuncture technique. [3H]Quinapril or [3H]quinaprilat was injected with [14C]inulin into either proximal or distal segments of the renal tubules, and urine was collected over 30 min. Urine and perfusate were assayed for [14C]-inulin using dual label spectrometry. [3H]Quinapril and [3H]quinaprilat concentrations were determined in urine and perfusate using a reversed-phase HPLC procedure with radiochemical detection, coupled to liquid scintillation spectrometry. These studies demonstrated that quinapril could access the esterase enzyme from tubular fluid and be metabolized to quinaprilat in both proximal and to a lesser extent distal segments of the kidney tubule. Quinapril, but not quinaprilat, was extensively reabsorbed. Its reabsorption along the proximal tubule and/or the loop of Henle could account for as much as 45-50% of the available dose of quinapril. Further, the urinary recovery of quinapril and quinaprilat (after dosing quinapril into proximal segments) was urine flow rate dependent.

Absorption↗
PubMed1995

Disposition of quinapril and quinaprilat in the isolated perfused rat kidney.

An isolated perfused rat kidney model was used to probe the renal disposition of quinapril and quinaprilat after separate administration of each drug species. Control studies were performed with drug-free perfusate (n = 8) and perfusate containing quinapril (n = 9) or quinaprilat (n = 7) at initial drug concentrations of 1000 ng/ml (including corresponding tracer levels of tritiated drug). Physiologic parameters were within the normal range of values for this technique and were stable for the duration of each experiment. Quinapril and quinaprilat concentrations were determined in perfusate, urine, and perfusate ultrafiltrate using a specific and sensitive reversed-phase HPLC procedure with radiochemical detection, coupled to liquid scintillation spectrometry. Perfusate protein binding was determined using an ultrafiltration method at 37 degrees C. The total renal clearance of quinapril (CLr) was calculated as Dose/AUC(0-infinity), and is represented by the sum of its urinary and metabolic clearances. The urinary clearances (CLe) of quinapril and quinaprilat were calculated as urinary excretion rate divided by midpoint perfusate concentration for each respective species. Of the total renal clearance for quinapril (CLr = 4.49 ml/min), less than 0.1% was cleared as unchanged drug (CLe = 0.004 ml/min); over 99% of the drug was cleared as quinaprilat formed in the kidney. The clearance ratio of quinapril [CR = CLr/(fu.GFR)] was 41.0, a value representing extensive tubular secretion into the renal cells. Following quinaprilat administration, the clearance ratio of metabolite [CR = CLe/(fu.GFR)] was 3.85, indicating a net secretion process for renal elimination.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1995

Is late-life caloric restriction beneficial?

Caloric restriction initiated in young mice and rats results in increases in mean and median life span. When caloric restriction is implemented in older animals, an increase in life span is still observed; however, the magnitude of the increase is not as great as that observed in animals calorie restricted since they were young. Here we report the results of a pilot study in which caloric restriction was initiated in mature, older rats. Survival rates and terminal pathology were characterized and compared between a cohort of 17 continually ad libitum fed Long Evans rats and a cohort of 18 Long Evans rats, which were gradually introduced to 33% restriction in diet consumption at 18 months of age. No difference in the median life span was observed between the two groups. The data suggest there may be a level of maturity, or a stage in the aging process, after which caloric restriction no longer increases longevity.

Aging↗
PubMed1995

Responses to a nonpeptide angiotensin receptor agonist, L 163491, in the feline pulmonary vascular bed.

The mechanism by which a novel potent non-peptide angiotensin subtype 1 receptor (AT1) agonist, (5,7-dimethyl-2-ethyl-3-[[2'-[(butyloxycarbonyl) aminosulfonyl]-5'-(3-methoxybenzyl)-[1,1'-biphenyl]-4-yl] methyl]-3H-imidazo [4,5-b] pyridine) (L-163,491), increased pulmonary vascular resistance was investigated in the intact-chest anesthetized cat under conditions of controlled blood flow. Intralobar injections of L-163,491, in doses of 10-300 micrograms i.a., caused dose-related increases in lobar arterial pressure that were partially antagonized by an AT1 receptor antagonist, DuP 532, or by staurosporine, a protein kinase C inhibitor, in doses that antagonized pressor responses to Ang II, but not to the thromboxane A2 mimic, U46619. Responses to L 163491 were not altered by PD 123319, an AT2 receptor antagonist. These data provide support for the hypothesis that vasoconstrictor responses to L 163491 are mediated by the activation of AT1 receptors and the protein kinase C pathway in the pulmonary vascular bed of the intact-chest cat.

Alkaloids↗
PubMed1995

Gender differences in the development of hyperlipemia and atherosclerosis in hybrid hamsters.

In response to a diet enriched in saturated fat and cholesterol (CH), male Syrian hamsters develop hyperlipemia and changes of early atherosclerosis. However, it has not been determined if female hamsters are equally susceptible to an atherogenic diet. Male and female hamsters of the F1B hybrid strain (Bio Breeders, Fitchburg, MA) were fed either a chow diet or this diet (HiFat) with added saturated fat (10% coconut oil) and CH (0.05%) for up to 12 weeks. Female hamsters ate significantly more than males, and with the HiFat diet gained threefold more weight than males. However, with the HiFat diet, serum triglycerides (TGs) and CH were markedly increased only in male hamsters. Furthermore, only in males was there a significant increase in stainable fat in the aorta that corresponded to an increase in subintimal foam cells. In freely feeding males, the largest percentage increase in serum CH was in the TG-rich fraction of lipoproteins. After females were castrated, serum TG and CH levels increased to the same extent as in males. These studies demonstrate a profound gender difference in response to an atherogenic diet in these hamsters that has parallels to the lipid patterns of humans and their susceptibility to atherosclerosis.

Animals↗
PubMed1995

Dietary restriction delays cataract and reduces ascorbate levels in Emory mice.

Dietary restriction can effectively extend lifespan and retard many age-related debilities. One hypothesis to explain the beneficial effects of dietary restriction is that it prolongs maintenance of cellular homeostasis by limiting endogenous oxidative stress and preserves oxidative defense mechanisms during aging. Ascorbate, a primary antioxidant, may play a major role in preventing oxidative damage. Ascorbate levels were determined in dietary restricted (R) and control (C) Emory mice, a strain which develops age-related cataract due in part to oxidative damage to lens proteins. Mice which consumed a diet restricted by 40% in calories had lower ascorbate concentrations in plasma, liver and kidney. Nevertheless, R animals showed significantly delayed progression of cataract which extended over the entire second half of life. The R diet did not result in different ascorbate levels in this lens. Aging was associated with a decrease in ascorbate in all the examined tissues except lens of both the R and C groups. It is not clear from these data that ascorbate is a prominent factor in the delay of cataract formation or other debilities in R Emory mice. However, it also appears unlikely that lens ascorbate is cataractogenic.

Aging↗
PubMed1995

Cutaneous neuroendocrine (Merkel cell) carcinoma. A report of 35 cases.

Cutaneous neuroendocrine (Merkel cell) cancer (CNEC) is a rare skin tumor with a highly malignant nature. Initial treatment of this tumor has often been limited to a local excision. The medical records of 35 patients diagnosed with CNEC and treated at Southern California Kaiser Permanente Medical Group or UCLA Medical Center between 1980 and 1991 were reviewed. There were 26 male and 9 female patients were enrolled in this study. Minimum follow-up from date of diagnosis was 18 months, mean follow-up was 40 months; 25 patients presented with local disease (stage I) and 10 patients presented with regional disease (involved nodes, stage II). Patients who were treated initially with local therapy alone had a 65% recurrence rate and a 29% mortality rate, while those patients treated locoregionally at presentation had only a 27% recurrence rate and 14% mortality rate, although the majority presented with more advanced disease. Due to the high incidence of lymph node failure and death in patients treated locally versus locoregionally at presentation, we feel that planned locoregional treatment is indicated for all patients presenting with CNEC, regardless of stage.

Adult↗
PubMed1995

12-O-tetradecanoylphorbol-13-acetate activation of the MDR1 promoter is mediated by EGR1.

P-glycoprotein, the product of the MDR1 gene (multidrug resistance gene 1), is an energy-dependent efflux pump associated with treatment failure in some hematopoietic malignancies. Its expression is regulated during normal hematopoietic differentiation, although its function in normal hematopoietic cells is unknown. To identify cellular factors that regulate the expression of MDR1 in hematopoietic cells, we characterized the cis- and trans-acting factors mediating 12-O-tetradecanoylphorbol-13-acetate (TPA) activation of the MDR1 promoter in K562 cells. Transient-transfection assays demonstrated that an MDR1 promoter construct containing nucleotides -69 to +20 conferred a TPA response equal to that of a construct containing nucleotides -434 to +105. TPA induced EGR1 binding to the -69/+20 promoter sequences over a time course which correlated with increased MDR1 promoter activity and increased steady-state MDR1 RNA levels. The -69/+20 promoter region contains an overlapping SP1/EGR site. The TPA-responsive element was localized to the overlapping SP1/EGR site by using a synthetic reporter construct. A mutation in this site that inhibited EGR protein binding blocked the -69/+20 MDR1 promoter response to TPA. The expression of a dominant negative EGR protein also blocked the TPA response of the -69/+20 promoter construct. Finally, the expression of EGR1 was sufficient to activate a construct containing tandem MDR1 promoter SP1/EGR sites. These data suggest a role for EGR1 in modulating MDR1 promoter activity in hematopoietic cells.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1995

Vitamin A distribution among fat globule core, fat globule membrane, and serum fraction in milk.

In cream suspensions and partly skimmed milks obtained by successive centrifugation from whole milk, the concentration of vitamin A per gram of fat was inversely related to the mean size of fat globules. This result indicated that not all the vitamin A of milk was located in the fat globule core, which was further supported by studies of buttermilk and butter oil fractions obtained by churning of cream. These studies indicated that a portion of the vitamin A was associated with the fat globule membrane. The vitamin A content per gram of fat of purified fat globules was similar to vitamin A content per gram of fat of the whole milk from which they were isolated. This result indicated that the amount of vitamin A in the serum fraction was negligible and that vitamin A was localized in the fat globule and fat globule membrane.

Animals↗
PubMed1995

Gender and age variations in the self-image of Jamaican adolescents.

The purpose of the study was to investigate the relationships among gender, age, and self-image of adolescents attending three secondary schools in Jamaica. The relatively few studies that have been done regarding self-perceptions of these youth are not only dated but have utilized a unidimensional conceptualization of the self. The Offer Self-Image Questionnaire which employs a multidimensional construct of the self was administered to a sample of 174 Jamaican adolescents ranging in age from 14 to 18 years (M = 15.90 years, SD = 1.21). Results revealed statistically significant effects for both gender and age. Gender was found to be significant on one self-image dimension: Morals, while age differences were evident on six dimensions: Social Relationships, Morals, Sexual Attitudes, Mastery of the External World, Vocational and Educational Goals, and Emotional Health. The results in some instances were contrary to those of past research. Discussion focused on cultural socialization and other factors affecting youth in Jamaican society.

Adaptation, Psychological↗
PubMed1995

Gene expression as a target for new drug discovery.

Over the last 7 years we have carried out a major research effort focused on gene transcription as a novel approach to drug discovery. The goal is to identify small molecular weight compounds that modulate the expression of a target gene in a specific manner, thereby either increasing or decreasing the concentration of the corresponding protein product. Transcriptional modulation not only provides a potential means to replace recombinant proteins as drugs, but also provides a novel approach to manipulate key gene targets in many therapeutic areas. This article describes some of the features and advantages of transcription-based pharmaceuticals and illustrates how this approach can be applied to drug discovery with a program we are pursuing to identify new treatments for sickle cell disease and beta-thalassemia.

Anemia, Sickle Cell↗
PubMed1995

v-Raf activates transcription of growth-responsive promoters via GC-rich sequences that bind the transcription factor Sp1.

The serine/threonine kinase, Raf-1, is a component of intracellular signaling pathways that control responses to extracellular stimuli. Previously, we have shown that serum-induced transcription from the murine rep-3b and human mdr1 promoters is Raf-dependent and that the activated Raf kinase, v-Raf, induces transcription of mdr1 via a GC-rich element. We now demonstrate that GC-rich sequences in the rep-3b promoter are both necessary and sufficient for induction by v-Raf. The GC-rich, v-Raf-responsive elements of rep-3b and mdr1 bind the general transcription factor Sp1 in electromobility shift assays. Mutation of a minimal GC-rich element abolished inducibility by v-Raf and eliminated binding by the transcription factor Sp1. However, Sp1 binding activity following serum stimulation of quiescent NIH 3T3 cells was unchanged, suggesting that mitogenic signals may stimulate the transactivation potential of prebound Sp1.

3T3 Cells↗