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K C Lewis

Publications and source records attributed to K C Lewis.

18 recordsLinked to original sources
PubMed2005

Transposable elements donate lineage-specific regulatory sequences to host genomes.

The evolutionary implications of transposable element (TE) influences on gene regulation are explored here. An historical perspective is presented to underscore the importance of TE influences on gene regulation with respect to both the discovery of TEs and the early conceptualization of their potential impact on host genome evolution. Evidence that points to a role for TEs in host gene regulation is reviewed, and comparisons between genome sequences are used to demonstrate the fact that TEs are particularly lineage-specific components of their host genomes. Consistent with these two properties of TEs, regulatory effects and evolutionary specificity, human-mouse genome wide sequence comparisons reveal that the regulatory sequences that are contributed by TEs are exceptionally lineage specific. This suggests a particular mechanism by which TEs may drive the diversification of gene regulation between evolutionary lineages.

Animals↗
PubMed1999

Retinoid metabolism in the prostate: effects of administration of the synthetic retinoid N-(4-hydroxyphenyl)retinamide.

We have carried out a series of complementary in vivo and in vitro studies to better understand the metabolism of vitamin A by the prostate gland. Male Sprague-Dawley rats were fed either a control diet sufficient in vitamin A [CON group; 0.8 microg retinol equivalents (RE)/g diet] or a CON diet supplemented with the synthetic retinoid N-(4-hydroxyphenyl)retinamide (4-HPR; CON+/-4HPR group; 1,173 )microg of 4-HPR/g diet). After an i.v. injection of a physiological radiolabeled dose of retinol, the vitamin A content and radioactivity of plasma and a number of tissues, including the prostate glands, were monitored for time periods ranging between 30 min and 41 days. On the basis of the results of these vitamin A turnover studies, we developed tissue subsystem models to describe vitamin A dynamics in the prostates of both the CON and CON+4HPR groups. There was a gradual decrease in the vitamin A content of the prostates of the 4-HPR-treated group as compared with the control, such that by the end of the study period, the CON+4HPR group averaged 0.166 +/- 0.0827 (mean +/- SD) REs, whereas the CON group was 0.732 +/- 0.190 REs. The fraction of vitamin A exiting the prostate each day was not significantly different in the CON as compared with the CON+4HPR group [0.149 +/- 0.103 versus 0.155 +/- 0.191 h(-1) (mean +/- FSD), respectively]; however, the average amount of vitamin A turning over from the CON+4HPR group prostates (0.0885 /microg/day) was nearly three times less than that of the CON group (0.243 microg/day). To obtain more detailed information on the mechanisms that might be involved in the changes in vitamin A kinetics observed in our in vivo studies, we used both a normal human prostate cell line (PrEC) and a human prostate adenocarcinoma cell line (LNCaP) to monitor in vitro retinol and 4-HPR dynamics. Cells were treated with 4-HPR for different time periods up to 48 h (PrEC) or 96 h (LNCaP). Retinol in the media was taken up readily by both PrEC and LNCaP cells, and there was conversion of retinol to the major storage esters of vitamin A, retinyl palmitate and retinyl stearate, as well as several minor retinyl esters, in a pattern indicative of normal retinoid esterification activity. Although 4-HPR was taken up readily and over time accumulated in both cell lines, conversion of 4-HPR to its major metabolite, N-[4-methoxyphenyl]retinamide, as well as several other metabolites of 4-HPR was apparent only in the LNCaP cells. Our findings would suggest that a study design that includes appropriately designed complementary in vivo and in vitro experimental systems represents a useful approach to better understanding possible mechanisms involved in basic retinoid functioning and interactions in the prostate as well as in other organs and related tissue culture systems.

Animals↗
PubMed1997

Comprehensive on-line LC/LC/MS of proteins.

This is a description of a comprehensive two-dimensional liquid chromatography (LC) system for the separation of protein mixtures. This system uses cation-exchange chromatography followed by reversed-phase chromatography (RPLC). The two LC systems are coupled by an eight-port valve equipped with two storage loops and under computer control. The RPLC effluent is sampled by both a UV detector and an electrospray mass spectrometer. In this way, complex mixtures of large biomolecules can be rapidly separated, desalted, and analyzed for molecular weight in less than 2 h. The system's utility is demonstrated with a mixture of standards and an Escherichia coli cell lysate.

Chromatography, Ion Exchange↗
PubMed1997

Ultrahigh-pressure reversed-phase liquid chromatography in packed capillary columns.

The use of extremely high pressures in liquid chromatography can improve the efficiency and reduce analysis time for columns packed with small particles. In this work, fused-silica capillaries with inner diameters of 30 microns are slurry packed with 1.5 microns nonporous octadecylsilane-modified silica particles. These columns are prepared in lengths up to 66 cm with packing pressures as high as 4100 bar (60,000 psi). Near the optimum flow rate, columns generate as many as 300,000 theoretical plates for lightly retained compounds (k' < 0.5) and over 200,000 plates for more retained compounds (k' approximately 2). These translate to plate heights (Hmin) as low as 2.1 microns. The pressures required to run at optimum flow rates are on the order of 1400 bar (20,000 psi). Analysis times at these pressures are on the order of 30 min (k' approximately 2) and can be reduced to less than 10 min at higher than optimum flow rates. Capacity factors are observed to increase linearly with applied pressure.

Chromatography, High Pressure Liquid↗
PubMed1996

Effects of chronic administration of N-(4-hydroxyphenyl)retinamide (4-HPR) in rats on vitamin A metabolism in the eye.

The retinoid N-(4-hydroxyphenyl)retinamide (4-HPR) effectively inhibits cancer in a variety of tissues. In contrast to many other retinoids, the toxicity problems associated with administration of 4-HPR have been found to be minimal or absent. However, the effects of 4-HPR upon normal metabolism of native physiological forms of vitamin A in vivo have not been adequately investigated. To understand better the interaction between 4-HPR and the native physiological forms of vitamin A, the present study examines the effects of long-term administration of 4-HPR upon normal vitamin A metabolism in the eyes. Male Sprague-Dawley rats were fed either a control diet sufficient in vitamin A (CON group; 0.8 retinol equivalents [RE]/g diet; n = 28) or a CON diet supplemented with 4-HPR (CON + 4-HPR group; 1173 micrograms 4-HPR/g diet; n = 28). Following an i.v. dose of physiologically radiolabelled retinol, associated with its normal plasma transport complex, the vitamin A content and radioactivity of the plasma and eyes were examined at different times over a 41 day period. Mean plasma retinol levels measured during the study period were significantly reduced in the CON + 4-HPR group as compared with the CON group (23.5 +/- 7.0 and 50.3 +/- 5.3 [mean +/- S.D.] micrograms/dl, respectively). From approximately 7 days post-dosing, vitamin A levels in the eyes of the 4-HPR-treated group steadily decreased such that by the end of the study, they were only approximately one-fifth those of the CON group (0.098 +/- 0.075 and 0.50 +/- 0.053 RE, respectively). Kinetic analysis of vitamin A turnover in the eyes indicated that there was no apparent down-regulation of the fraction of vitamin A leaving this tissue on a daily basis; these values were found to be similar in both groups, averaging 0.104 +/- 0.0393 and 0.113 +/- 0.0373 per day (mean +/- fractional standard deviation [F.S.D.]) for the CON and CON + 4-HPR groups, respectively. At the same time, the flow of vitamin A through the eyes was significantly decreased in the CON + 4-HPR group eyes (0.0162 +/- 0.101 microgram/day) as compared with the CON group (0.0604 +/- 0.0672 micrograms/day). Our results suggest that compensatory mechanisms that would normally function to conserve depleting ocular vitamin A stores may be blocked in the 4-HPR-treated animals and further, that the 4-HPR itself appears to be interfering with the normal uptake and/or metabolism of vitamin A in the eye. These findings may help to provide at least a partial explanation for the visual impairment problems that have been reported in human trials that include long-term administration of 4-HPR.

Animals↗
PubMed1994

Effects of N-(4-hydroxyphenyl)retinamide supplementation on vitamin A metabolism.

The efficacy of the retinoid N-(4-hydroxyphenyl)retinamide (4-HPR) has been demonstrated in the inhibition of cancers in a variety of tissues. Moreover, toxicity effects following administration of 4-HPR have been found to be reduced or absent when compared to other retinoids. Pharmacokinetic studies in both animals and humans have focused on the metabolism of 4-HPR and its metabolites, and relatively little information has been published detailing the effects of long-term administration of 4-HPR upon normal endogenous vitamin A metabolism. Thus, the present study was carried out to examine the effects of long-term administration of 4-HPR upon plasma and tissue vitamin A kinetics. Male Sprague-Dawley rats were fed either a control diet sufficient in vitamin A [CON group; 1.0 retinol (ROH) equivalents/g diet] or a CON diet supplemented with 4-HPR (CON+4HPR group; 1173 micrograms 4-HPR/g diet). Following i.v. injection of a physiologically radiolabeled dose of ROH, ROH tracer and tracee kinetics were monitored in plasma and tissues over a 41-day period. Kinetic parameters were determined using the SAAM/CONSAM computer modeling programs to carry out graphical analysis of the tracer concentration curves. Mean plasma ROH levels measured for the CON+4HPR group were reduced to one-third of those of the CON group. Most of the kinetic parameters calculated were found to be significantly altered by the inclusion of 4-HPR in the diet. The fraction of the plasma ROH being catabolized per day (fractional catabolic rate) was nearly twice as high in the CON+4HPR treated group (3.61 +/- 0.49 day-1; mean +/- SD) as compared to the CON group (2.00 +/- 0.68 day-1). The amount of time that vitamin A molecules spent in the body before being lost irreversibly from the system (system residence time) was decreased by half in the CON+4HPR group (19.20 +/- 7.13 days) versus the CON group (38.63 +/- 9.62 days). Despite the increased catabolic rates and decreased system residence times measured for the CON+4HPR group, the estimated vitamin A use in these animals (11.01 +/- 3.10 micrograms/day) was 33% less than that used by the CON group (16.31 +/- 2.47 micrograms/day). Studies investigating the mechanisms by which 4-HPR alters vitamin A kinetics are presently under way in our laboratory. Nevertheless, these results suggest that long-term administration of 4-HPR markedly perturbs normal vitamin A metabolism in rats. Whether 4-HPR similarly alters human vitamin A metabolism with untoward clinical consequences deserves careful evaluation.

Animals↗
PubMed1994

Electrospray-condensation particle counter: a molecule-counting LC detector for macromolecules.

A new detector for macromolecular separations is described. The detector counts individual macromolecules (molecular weights greater than about 10,000) and reports counts per second. The chromatographic effluent is electrosprayed, neutralized, and swept to the detector by a stream of air. The detector is a condensation particle counter that detects individual particles by light scattering from droplets condensed on the particles. When used as the detector for a size exclusion separation of proteins, the detector has a linear range of 4 orders of magnitude with detection limits as low as 0.1 microgram/mL. The detector can be directly interfaced (no makeup flow) with effluent flows as low as 10 nL/min. A Monte Carlo model based on size measurements of the electrosprayed droplets correctly predicts the observed detector behavior.

Biopolymers↗
PubMed1993

Production of human plasma retinol-binding protein in Escherichia coli.

We designed a polymerase chain reaction (PCR) primer pair which allowed us to clone the cDNA coding for the human plasma retinol-binding protein (hRBP) into an Escherichia coli expression vector. Production of hRBP was confirmed by probing Western blots with antisera against plasma hRBP. Purification and characterization of the E. coli-produced plasma hRBP are also described. The availability of this expression system makes it possible to obtain large quantities of hRBP to facilitate our continuing studies of retinol and RBP metabolism.

Amino Acid Sequence↗
PubMed1990

Relationship between age and serum vitamin A in children aged 4-11 y.

The association between age and serum vitamin A concentrations in children was examined by using total serum vitamin A values from the second National Health and Nutrition Examination Survey (NHANES II) and serum retinol values for Mexican Americans from the Hispanic HANES. Analyses included multivariate strategies to identify confounders of serum vitamin A. After the effect of the use of vitamin-mineral supplements on total serum vitamin A values was controlled for, the data indicated that younger children (aged 4-5 y) have lower serum vitamin A concentrations than do older children (aged 9-11 y) regardless of whether the measure was total serum vitamin A or serum retinol. This relationship was systematic across the distribution of values and suggested that the difference may be due to normal physiological events. A different interpretive criterion may be needed for younger and older children when serum vitamin A is used to indicate vitamin A status.

Aging↗
PubMed1990

Retinol metabolism in rats with low vitamin A status: a compartmental model.

A compartmental model was developed to describe the metabolism of vitamin A in rats with low vitamin A status maintained by a low dietary intake of vitamin A (approximately 2 micrograms retinol equivalents/day). After the IV bolus injection of [3H]retinol in its physiological transport complex, tracer and trace data were obtained from plasma, organs (liver, kidneys, small intestine, eyes, adrenals, testes, lungs, carcass), and tracer data were obtained from urine and feces. The dietary protocol developed for this study resulted in animals having plasma vitamin A levels less than 10 micrograms retinol/dl and total liver vitamin A levels of approximately 1 microgram retinol equivalent. Four compartments were used to model the plasma: one to describe retinol, one to describe the nonphysiological portion of the dose, and two to simulate polar metabolites derived from retinol. The liver required two compartments and a delay, the carcass (small intestine, eyes, adrenals, testes, and lungs, plus remaining carcass) required three compartments, and the kidneys required two. The model predicted a vitamin A utilization rate of 1.65 micrograms retinol equivalents/day with the urine and feces accounting for most of the output. The plasma retinol turnover rate was approximately 20 micrograms retinol equivalents/day; this was 12 times greater than the utilization rate. This indicated that, of the large amount of retinol moving through the plasma each day, less than 10% of this was actually being irreversibly utilized. Similarly, as compared to the whole-body utilization rate, there was a relatively high turnover rate of retinol in the kidneys, carcass, and liver (9.0, 8.2, and 5.8 micrograms retinol equivalents/day, respectively), coupled with a high degree of recycling of vitamin A through these tissues. Of the total vitamin A that entered the liver from all sources including the diet, approximately 86% was mobilized into the plasma. Similarly, of the vitamin A that entered the carcass, approximately 76% was returned to the plasma. All of the retinol that entered the kidneys was modeled as recycling to the plasma. The present studies provide quantitative and descriptive evidence of an efficient metabolism of vitamin A from absorption through turnover and utilization in rats with very low vitamin A status. Furthermore, although their body stores of vitamin A were extremely low, these rats maintained a high level of recycling of vitamin A throughout the body.

Animals↗
PubMed1987

Variation in retinol utilization rate with vitamin A status in the rat.

The relationship of vitamin A status to retinol (ROH) utilization rate (disposal rate, DR) and other kinetic parameters was studied in rats with low (LO), marginal (MAR) or high (HI) mean liver vitamin A levels (2.2, 43 and 985 micrograms, respectively) and low or normal plasma ROH concentrations (6.8, 46 and 42 micrograms/dL). Kinetic parameters were calculated by input-output analysis of plasma [3H]ROH turnover monitored for 35 (LO and MAR) or 115 d (HI) after injection of [3H]ROH in its plasma transport complex. There was a highly significant negative correlation between fraction of dose in plasma 5 d after injection of [3H]ROH and the natural log of liver total vitamin A. The total time an average ROH molecule spent in plasma (residence time), as well as the time spent during each pass (transit time), was significantly lower in HI (0.77 d and 1.9 h) than in LO (0.98 d and 2.7 h) and MAR (0.92 d and 2.8 h) rats; however, the total time in the system (mean sojourn time) increased markedly with vitamin A status (5, 18 and 77 d). The number of times an average ROH molecule recycled through plasma before irreversible loss (7-9 times) was similar in all groups. Most of the ROH molecules (approximately 90%) that left the plasma were recycled, not irreversibly metabolized, in all groups. Among groups, ROH DR increased significantly from 1.2 (LO) to 8.0 (MAR) to 11.8 micrograms/d (HI). For LO versus MAR and LO versus HI, differences in DR were positively related to differences in the plasma ROH pool size. These results suggest that low plasma ROH concentrations are associated not only with low liver vitamin A levels, but also with a decreased ROH DR. This decreased DR may or may not reflect a compromised functioning of ROH-dependent systems.

Animals↗
PubMed1981

Vitamin A turnover in rats as influenced by vitamin A status.

Vitamin A turnover was studied in rats fed vitamin A-sufficient (+A) or vitamin A-deficient (--A) diets for 24--25 days. Hepatic vitamin A stores of the +A group (543 microgram) were significantly larger than those of the --A group (11 microgram) and similarly, the plasma vitamin A concentration of the +A group (56 microgram/dl) was significantly higher than that of the --A group (26 microgram/dl). Rats were injected intravenously with plasma containing tritium-labeled retinol (3H-ROH) obtained from vitamin A-deficient donor rats previously fed 3H-ROH. Plasma samples from injected recipients were collected over a 48-hour period. Kinetic analysis of plasma tracer concentration versus time curves indicated that the data fit a three-pool model. The plasma vitamin A turnover rate of the +A group was significantly more rapid than that of the --A group (5.19 versus 1.98 microgram/hour). Plasma fractional turnover rates for the +A group (1.31 hour--1) were not significantly different from those of the --A group (0.90 hour--1). The data suggest that for both dietary groups, the metabolism of retinol associated with the prealbumin and retinol-binding protein complex involved extensive recycling among the liver, plasma, interstitial fluid and peripheral tissues.

Animals↗
PubMed1979

Response of plasma levels of vitamin A to a dose of vitamin A as an indicator of hepatic vitamin A reserves in rats.

Rats were fed diets deficient [-A] or sufficient [+A] (3 mg retinol equivalents/kg) in vitamin A, and without [-RA] or with [+RA] (12 mg/kg) retinoic acid supplementation for up to 33 days. Rats with plasma vitamin A levels ranging from 7 to 62 micrograms/dl were studied at intervals during progressive depletion of liver stores of vitamin A (expt. 2) and when liver stores were nearly exhausted (less than 10 micrograms/g) or replete (up to 100 micrograms/g) with vitamin A (expt. 1). A dose of retinyl acetate in corn oil (20 micrograms retinol equivalents) was administered by intubation directly into the stomach. The relative dose response (RDR), expressed as a percentage and defined as the absolute magnitude of the rise in plasma vitamin A levels 5 hours after the dose of retinyl acetate, divided by the plasma level of vitamin A attained after 5 hours, was determined for each rat and correlated over a wide range of vitamin A plasma and liver levels. An RDR above 50% invariably was associated with low plasma levels (10 to 30 micrograms/dl) and low liver stores (less than 10 micrograms/g) of vitamin A, whereas an RDR of less than 40% was associated with plasma levels above 30 micrograms/dl and liver stores ranging from 3 to 100 micrograms/g.

Animals↗
PubMed1979

Effects of dietary vitamin A deficiency, retinoic acid and protein quantity and quality on serially obtained plasma and liver levels of vitamin A in rats.

Rats were fed vitamin A-deficient diets either alone, supplemented with retinoic acid (RA), or of limited protein quality or quantity (7%rice or 7% casein protein); one group was fed 7% rice protein supplemented with vitamin A. Plasma and liver levels of vitamin A were determined serially. Plasma levels in rats fed otherwise adequate vitamin A-deficient diets remained above 30 micrograms/dl until liver reserves were below 10 micrograms/g tissue, at which point plasma levels decreased in some but not all rats while liver levels continued to decline (at a slower rate) to levels as low as 3 micrograms/g. Supplementation with RA caused an immediate and sustained reduction of 15 to 20 micrograms/dl in circulating vitamin A. At 7% dietary protein, plasma levels of vitamin A remained above 30 micrograms/dl when casein protein was fed or when the rice protein diet was supplemented with dietary vitamin A, but not when the rice protein diet was fed without an exogenous source of the vitamin. A scheme is proposed suggesting possible regulatory mechanisms that might control homeostatic levels of plasma vitamin A.

Animals↗
PubMedDate not supplied

Capillary zone electrophoresis with electrospray condensation particle counting detection.

A new sheath flow microelectrospray interface combines capillary electrophoretic separation of protein standards with condensation particle counting detection. Protein separations are performed in both coated and uncoated fused-silica columns. The electrospray needle utilizes a sheath flow rate between 0 and a few microL/min. Typically, the makeup flow is equal to or less than the electroosmotic flow from the separation capillary; thus there is minimal dilution while still providing pH adjustment and solid electrical contact with the separation capillary. While there are some inherent restrictions to a condensation particle counting detector, the microelectrospray needle performs well and has direct application to electrospray mass spectrometry.

Aerosols↗