Biomedical subjects
Publications and source records attributed to F Svec.
Dendritic macromolecules substituted with various numbers of trimethylsilyl and dodecyl groups have been separated by reversed-phase HPLC. While size-exclusion chromatography only provides a rough picture of the composition of the mixture, reversed-phase chromatography allows the separation of individual components and estimation of the distribution of each component.
Dehydroepiandrosterone (DHEA) reduces food intake in obese Zucker rats. To study the role of taste aversion on this process, we used two approaches. First, we presented increasing concentrations of DHEA in chow to lean and obese Zucker rats, either in competition with unadulterated chow, or alone. Second, we examined energy intake following parenteral DHEA administration. Both lean and obese rats always preferred nonadulterated chow to DHEA-supplemented chow. However, lean rats required a higher DHEA concentration (0.06%) than obese rats (0.015%) to achieve the same degree of aversion. When DHEA-supplemented chow was presented alone, only high concentrations (0.3 and 0.6% DHEA) decreased food intake. Rats given DHEA by IP injection (200 mg/kg/day) also decreased their energy intakes. The results demonstrate that although DHEA can cause taste aversion at low concentrations in Zucker rats, it does not alter energy intake until high concentrations are given. In addition, nonoral DHEA also decreases energy intake in these animals. These results suggest that DHEA's antiobesity effect is not mediated by taste aversion.
Cyclo(His-Pro) (CHP) is a gut-neuropeptide that influences both appetite and carbohydrate metabolism. This study was undertaken to determine whether concentrations of CHP correlated with various clinical markers of nutritional status and progression of HIV infection. Serum concentrations of CHP were analyzed in a clinical sample of 100 HIV-positive patients whose HIV clinical status ranged from asymptomatic to advanced disease with weight loss. We found a relationship between CHP concentrations and serum albumin and hemoglobin levels, markers of chronic nutrition and disease. However, no correlation was seen between CHP and cortisol concentrations, a marker of acute stress. To analyze the relationship of HIV clinical stage and CHP, patients were divided into three subgroups: asymptomatic, mildly symptomatic, and clear-cut AIDS. CHP concentrations were significantly correlated with HIV clinical stage. These data lead to the hypothesis that CHP is a marker of disease progression and that it potentially plays a role in modulating the nutrition of HIV-infected patients.
A macroporous poly(styrene-co-divinylbenzene) rod has been prepared by a free-radical polymerization of a mixture containing monomers, initiator, and porogenic solvent in the confines of a chromatographic column and used for the first time in the very fast reversed-phase HPLC of proteins. Characterization of the pore structure of the continuous rod by mercury intrusion porosimetry revealed a large volume of pores with a diameter of about 1 micron to pores below 100 nm. Size exclusion chromatography and scanning electron microscopy confirmed the unusual pore size distribution. The presence of large pores make the rod easily permeable to eluents, and therefore, the back pressure of the rod column is modest even at high flow rates. The efficiency of the polymerized column is almost independent of the flow rate. The slope of the line showing capacity factor vs composition of the mobile phase was determined for several proteins, and a gradient for the separation of their mixtures was developed. Excellent separation was achieved even at a high flow rate of 25 mL/min as documented by the resolution data. Tripling the length of the column did not improve the column resolution in protein separation.
The application of superselective endovascular occlusion in vascular radiology has broadened the scope of possible radical surgery of giant angiodysplasias by reducing considerably the risk of severe haemorrhage during the surgery. Occlusion was performed on 229 patients using spherical and cylindrical particles of porous poly(2-hydroxyethyl methacrylate). The treatment of a patient suffering from angiodysplasia of the pelvis is described as an example. The first day following endovascular occlusion a hypercoagulation reaction developed, with a decrease of both the level of fibrinolysis and of anticoagulant factors. This was mainly due to a decrease of the level of antithrombin III and activation of the factor XIII indicating a strong tendency of intravascular thrombosis. During the third day, the hypercoagulation reaction increased. However, on the fifteenth day, parameters of the haemostasis system were close to normal values. Only the activity of the factor XIII remained high suggesting the stabilization and the organization of fibrin clot in the embolized blood vessel territory.
Oral dehydroepiandrosterone (DHEA) causes weight loss in the obese Zucker rat. To study this process, we fed lean and obese female Zucker rats either control chow diets alone or diets containing 0.6% DHEA for 4 weeks. DHEA treatment led to a significant increase in the caloric intake of lean-treatment rats and a significant decrease in obese-treatment rats compared to their respective controls. These phenotype-specific divergent effects began acutely and were sustained. The energy intake changes with DHEA treatment were significant after correcting for body weight. Divergent effects of DHEA were also observed in body weight changes and in the food efficiency ratios of the animals; DHEA affected obese rats but not lean ones. The results of the present study suggest that the appetite component of DHEA's antiobesity effect in the Zucker fatty rat cannot be discounted.
Dehydroepiandrosterone (DHEA) decreases the activity of hepatic tyrosine aminotransferase (TAT), a glucocorticoid-inducible enzyme, in the obese, hypercorticosteronemic Zucker rat. To investigate the mechanism of this antiglucocorticoid action, the effect of exogenous DHEA on hepatic glucocorticoid receptor (GC) number and affinity was quantitated. Food supplementation with DHEA (0.6% w/w) for 1 or 7 days had no effect on either receptor number or affinity in obese Zucker rats. After 28 days, however, DHEA treatment resulted in a nearly 40% decrease in cytosolic hepatic receptor content (Bmax; fmol/mg cytosolic protein) without any change in affinity (Kd) in both lean and obese rats. DHEA treatment for 28 days also resulted in an increased liver size and cytosolic protein content. When the hepatic GC receptor content was normalized based on the change in liver size and protein content, the apparent number of GC binding sites per liver was not affected by DHEA treatment. This observation suggests that DHEA's effect on GC receptor content may not be a specific action and that downregulation of the GC receptor is not the mechanism of DHEA action on GC induced TAT activity. This is supported by the effect of DHEA on obese rat TAT activity in the same experiment where the greatest inhibition occurred after only 1 day of treatment. From these experiments it is concluded that although long-term DHEA treatment may decrease the relative concentration of GC receptors in rat liver, this change is not the mechanism through which DHEA mediates its acute antiglucocorticoid action.
Human immunodeficiency virus (HIV) is a major cause of immunoincompetence. Whether the virus, itself, accounts for all the deficiency remains in question. Steroids can also influence immune function; glucocorticoids cause immunoincompetence while dehydroepiandrosterone (DHEA) enhances immune function. Changes in the levels of such hormones during the course of HIV illness might result in significant changes in immune competence. The purpose of this study is to investigate whether dehydroepiandrosterone-sulphate (DHEA-S) or cortisol levels correlate with absolute CD4 lymphocyte levels. Plasma for cortisol and DHEA-S was drawn from 98 adults with HIV. Of these, 67 had simultaneous CD4 levels. Cortisol levels were 12.4 +/- 4.6 micrograms/dl, DHEA-S 262 +/- 142 micrograms/dl, and CD4 levels were 308 +/- 217/mm3 (mean +/- SD). Correlational analysis revealed a significant relationship between DHEA-S and CD4 levels (r = 0.30; p = 0.01) but not between CD4 levels and cortisol (r = 0.11; p = 0.36) or cortisol/DHEA-S ratios (r = 0.17; p = 0.16). When analyzed by clinical subgroups, significant differences were also found with a decrease in DHEA-S levels seen in persons with more advanced illness. The data exhibit a positive relationship between the immune status of patients with HIV-related illness and DHEA, leading to the hypothesis that DHEA deficiency may worsen immune status.
The obese Zucker rat is a model of youth-onset obesity associated with hyperphagia. In this study, dehydroepiandrosterone's effect at decreasing food intake and body weight in the obese Zucker rat was investigated. Rats were treated with a dehydroepiandrosterone-supplemented diet (0.0, 0.06, 0.15, 0.3, or 0.6%) for 7 days. The 0.3 and 0.6% treatment groups showed a dramatic decrease in daily food intake, which was evident the 1st day. In addition to the reduction in food intake, body weight changes also were affected significantly in the high-dose treatment groups. The possibility that these dehydroepiandrosterone-induced changes were correlated to perturbations in central neurotransmitter levels associated with appetite control was investigated. The hypothalamus, frontal cortex, striatum, and hippocampus of dehydroepiandrosterone-treated animals were assayed for neurotransmitters known to have inhibitory or stimulatory effects on feeding behavior (serotonin, dopamine, norepinephrine, and epinephrine). Significant differences from steroid-free controls were noted only in the levels of hypothalamic serotonin in animals treated with dehydroepiandrosterone. Serotonin in the hypothalamus has been shown to decrease feeding behavior. The magnitude of dehydroepiandrosterone's effect on hypothalamic serotonin correlated with its effect on feeding behavior. Thus, dehydroepiandrosterone may reduce hyperphagia by altering hypothalamic levels of serotonin.
A novel approach to monosized macroporous polymeric separation media with vastly enhanced pore size distributions and chromatographic properties has been developed. Key to this approach is the combined use of monodispersed polymeric particles and suitable solvents as porogens in the copolymerization of styrene and divinylbenzene. Following polymerization, the polymeric porogen is dissolved, leaving behind the monosized beads with a controlled pore structure. The exact pore size and pore size distribution of the final beads are largely controlled by the amount of soluble polymer in the polymerizing mixture: the larger the proportion of soluble polymer in the system, the larger the pores. The uniformly sized macroporous beads prepared with an optimized ratio of polymeric and low molecular weight porogens proved to be very efficient even in short columns for the separation of polystyrene standards in the SEC mode and the separation of proteins in the reversed-phase mode. The relationship between pore size and specific surface area, on one hand, and chromatographic properties of the stationary phase, on the other, have been clearly documented.
The aminohexyl derivative of the copolymer of 2-hydroxyethyl methacrylate and ethylene dimethacrylate (p(HEMA)-Hex) in the form of regular spherical particles was used as a polymeric carrier for chemically sorbed methotrexate (MTX). The effect of the washed p(HEMA)-Hex-MTX carrier on the morphological structure of donor blood, on blood coagulation indicators and on responses of the living tissue surrounding the material which has been in the blood vessel of the rabbit for various periods of time was evaluated. MTX is capable of diffusion for several days from the embolic material.
A haemostatic material suitable for embolization was prepared by the adsorption of haemostatics--ethamsylate and aminocaproic acid in the spherical particles of porous poly(2-hydroxyethyl methacrylate) (p(HEMA)). The degree of purification of ethamsylate-treated particles was tested by an analysis of donor blood in contact with the material. An evaluation of the haemostatic properties of these materials was obtained by the determination of the indicators of blood clotting: activated partial thromboplastin time, thrombin time, and prothrombin time. Ethamsylate or aminocaproic acid-containing p(HEMA) has a distinct haemostatic effect on pathological blood of patients suffering from focal alterations of the liver. These haemostatic emboli materials show promise for the immediate control of various haemorrhages; when introduced into a zone with increased haemorrhage, they may help to correct disturbed haemostasis.
Embolization using poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogel particles, of cylindrical spherical form, was successfully achieved in 42 children treated for non-operable haemangiomas of the liver, and angiodysplasias. Spherical PHEMA hydrogels appeared to be the only possibility for the treatment of 26 children suffering from extensive cavernous haemangiomas of face and neck. Particles were able to cover the tumour, stop its growth and allow the use of local hyperthermia with the electromagnetic field. A partial two-stage embolization using beaded PHEMA was also used as part of the multistage treatment for curing the spleen in 28 children suffering from haemolytic spherocytic anaemia, thrombocytopenic purpura and portal hypertension.
The acute effect of dehydroepiandrosterone (DHEA) and its conjugate, DHEA-sulfate (DHEA-S) on glucocorticoid action was tested in vivo using male Swiss-Webster mice. The authors found that DHEA and DHEA-S significantly inhibited induction of hepatic tyrosine aminotransferase activity, although the former was more potent. This inhibition was dose- and time-dependent and was not demonstrable with other steroids. The same inhibitory effect of DHEA was seen with kidney tyrosine aminotransferase induction, as well as with liver and kidney ornithine decarboxylase enzyme activity, another glucocorticoid-induced enzyme. The conclusion is that DHEA acts acutely as an antiglucocorticoid and exerts its effect in different glucocorticoid-sensitive systems.
A large biracial cross-section of 1038 healthy children aged 6-18 yr with 519 blacks, 519 whites, 678 males, and 360 females was evaluated for Tanner stage and serum levels of androstenedione, dehydroepiandrosterone-sulfate, estradiol, progesterone, and testosterone. The anthropometric values of the blacks and whites were very similar at each Tanner stage with only minor differences in age, height, and weight related to an earlier onset of puberty in blacks. The hormones dehydroepiandrosterone-sulfate, progesterone, and testosterone did not exhibit any racial differences. Estradiol showed a significantly higher level among black males compared to white males (P less than or equal to 0.05) whereas androstenedione was significantly higher in both white males (P = 0.0001) and females (P less than or equal to 0.01) compared with blacks. Many hormones are known to effect insulin resistance and others have reported a correlation between insulin levels and androstenedione. Blacks suffer disproportionately from diabetes. Since puberty is a time of dramatic changes in insulin resistance, racial (black-white) differences in steroid hormone changes were explored. This study shows that a racial difference in androstenedione levels exist during puberty, at a time when racial differences in insulin resistance are becoming manifest.
Three hundred and seventy-seven children and adolescents aged 5-17 yr from the biracial (black-white) community of Bogalusa, Louisiana, were evaluated for Tanner stage of sexual development, plasma glucose, and insulin levels during an oral glucose tolerance test. Children of the two races were of similar age, weight, and height at each Tanner stage. Overall insulin response was compared by measuring the area under the insulin curve from the glucose tolerance test. Blacks, especially black females, had significantly higher insulin responses than their white counterparts. The insulin-glucose ratio at the initial t = 0 min baseline did not vary with race or sex throughout the Tanner stages. However, the 30 min postglucose data revealed clear differences between the races with blacks showing a higher insulin-glucose ratio. Ratios increased throughout puberty for both blacks and whites, boys and girls. The trends of racial contrasts seemed to be discernible even at the earliest stage of development. It is concluded that there is a clear difference between blacks and whites in insulin response to a glucose load early in childhood. These findings lead to the hypothesis that the greater prevalence of non-insulin-dependent diabetes mellitus seen in adult blacks, especially females, may be an expression of a difference in insulin secretion and related insulin resistance in early childhood.
Dehydroepiandrosterone (DHEA) reduces weight gain in the hypercorticosteronemic Zucker fatty rat, an animal model of genetic obesity. However, the mechanism of action of DHEA is still unclear. We propose that DHEA acts as an antiglucocorticoid in the Zucker fatty rat. To test this hypothesis we examined DHEA's ability to block the activation of the glucocorticoid-inducible enzymes tyrosine aminotransferase (TAT) and ornithine decarboxylase (ODC) by dexamethasone (i.p. 5 micrograms/100 g body weight) in hepatic tissue of 6-10 week old Zucker rats. Injections of DMSO, the vehicle, served as a control. DHEA alone did not affect TAT, but when DHEA (500 micrograms/100 g b.w.) was administered simultaneously with dexamethasone, activation did not occur. Similar results were seen using a second tissue (kidney). We conclude that DHEA can act acutely as an antiglucocorticoid in the young obese Zucker rat and hypothesize that its chronic anti-obesity effect may reflect, at least in part, a chronic antiglucocorticoid activity.
Cyclic dipeptides or diketopiperazines are readily generated during in vitro hydrolysis of proteins and polypeptides. This led us to examine whether cyclo(His-Pro) (CHP), a diketopiperazine containing histidine and proline, could be formed in vivo from dietary proteins. The data presented here show that at least in rat, neither urinary nor plasma concentration of CHP is elevated by consumption of a diet rich in proteins. Several dietary supplements derived from casein and/or soy protein hydrolysates, however, contain high levels of CHP-LI. Oral intake of one such supplement led to a sharp increase in the plasma level of CHP-LI.