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PubMed1996

Efficiency of lysine or threonine retention in growing rats fed diets limiting in either lysine or threonine.

Over a 21-d experiment, the efficiency of lysine and threonine retention was determined in 80 male Sprague-Dawley rats (65.9 +/- 0.3 g, means +/- SE) fed purified diets containing an amino acid mix limiting in either lysine or threonine. With additional increments of the first limiting amino acid, lysine concentration in total body protein (g/16 g N) increased (P < 0.01) in rats fed lysine-limiting diets but, when fed threonine-limiting diets, lysine concentration in body protein first increased and then decreased (P < 0.01). As increments of the first limiting amino acid were added, the threonine concentration in total body protein increased then decreased when both lysine- (P < 0.01) and threonine- (P < 0.06) limiting diets were fed. Lysine and threonine retention were calculated based on comparative slaughter. Sixteen rats were killed on d 0 to estimate the grams of amino acid in the body. Retention responses were analyzed using a logistic equation in which lysine or threonine intake was used to predict retention. The maximum marginal efficiency (dr/dI, retention/intake) was observed at <40% of maximum retention. For lysine retention, it was 81% when lysine was limiting and 70% when threonine was limiting. For threonine retention, it was 58% when threonine was limiting and 49% when lysine was limiting. The maximum cumulative efficiency (retention adjusted for maintenance relative to cumulative intake) for lysine retention was 62% when lysine was limiting or 58% when threonine was limiting. For threonine retention, it was 51% when threonine was limiting and 35% when lysine was limiting. Thus, amino acid concentration in body protein is not constant, and amino acids are used with higher efficiency when first limiting.

Amino Acids↗

PubMed2001

An analysis of multifactorial influences on the transcriptional control of ompF and ompC porin expression under nutrient limitation.

Expression of the major outer-membrane porins in Escherichia coli is transcriptionally controlled during nutrient limitation. Expression of ompF was more than 40-fold higher under glucose limitation than under nitrogen (ammonia) limitation in chemostat cultures at the same growth rate. In contrast, ompC expression was higher under N limitation. The basis of regulation by nutrient limitation was investigated using mutations affecting expression of porin genes. The influence of cyaA, rpoS, ackA and pta, as well as the two-component envZ-ompR system, was studied under glucose and N limitation in chemostat cultures. A major contributor to low ompF expression under N limitation was negative control by the RpoS sigma factor. RpoS levels were high under N limitation and loss of RpoS resulted in a 19-fold increase in ompF transcription, but little change was observed with ompC. Lack of RpoS under glucose limitation had a lesser stimulatory effect on ompF expression. Porin production was minimally dependent on EnvZ under N limitation due to OmpR phosphorylation by acetyl phosphate. Evidence obtained with pta and ackA mutants suggested that the acetyl phosphate level also regulates porins independently and indirectly via RpoS and other pathways. pta-envZ double mutants had a residual level of porin transcription, implicating alternative means of OmpR phosphorylation under nutrient limitation. Another critical factor in regulation was the level of cAMP, as a cyaA mutant hardly expressed ompF under glucose limitation but boosted ompC. In addition, the role of DNA-binding proteins encoded by hns and himA was tested under glucose limitation: the hns mutation reduced the glucose-limitation peak, but the himA mutation suppressed the hns effect, suggesting a complex web of interrelationships between the DNA-binding proteins. Indeed, multiple inputs and no single regulator were responsible for the high peak of ompF expression under glucose limitation.

Adenylyl Cyclases↗

PubMedDate not supplied

The widow(er)'s limit provision of Social Security.

Widow benefits have been a part of the Social Security program since the 1939 amendments to the Social Security Act (widower benefits were added later). For many years, the Social Security law called for paying a widow(er) a fraction of the deceased worker's primary insurance amount (PIA). However, the worker--while alive--may have received the full PIA as his or her retirement benefit. Over time, arguments were made that a widow(er) should be treated as generously as his or her spouse was. The 1972 amendments to the Social Security Act allowed for a widow(er) to receive a full PIA, subject to actuarial reductions if the widow(er) benefit was claimed before the normal retirement age (NRA) and subject to a new provision of the law commonly referred to as the widow(er)'s limit. Generally, the widow(er)'s limit specifies that if a worker received reduced retirement benefits (because the worker claimed benefits before the NRA), then the worker's widow(er) cannot receive a monthly benefit equal to the full PIA. Rather, the widow(er)'s benefit is generally limited to the amount the worker would receive if he or she was still alive. The limit provision appears to be motivated by the overall intent of the 1972 Congress to pay a benefit to a widow(er) that was comparable with what the worker received. A number of changes to the limit provision have been discussed. This article looks at the following options: Abolishing the limit, Raising the limit by requiring that it never be set below the average PIA among all retired-worker beneficiaries. Adjusting the limit for some widow(er)s--that is, only persons who are widowed before the NRA (the ARLA option), Making a simpler adjustment to the limit by abolishing it for persons who are widowed before age 62 (the SARLA option), and A proposal by Robert J. Myers that would make modest adjustments to the limit for cases in which the worker died before the NRA. The most fundamental change--abolishing the limit--would increase benefits for about 2.8 million widow(er)s and would cost about $3.1 billion a year. Most of the additional government expenditures would not go to the poor and the near poor. Another change would be more successful in aiding low-income widow(er)s: requiring that the limit amount never be set below the average PIA among all retired-worker beneficiaries. About 58 percent of the government expenditures from that option would be received by the poor and the near poor. Overall, 1.2 million widow(er)s would be helped, and the cost would be about $816 million a year. Although the limit provision is consistent with the overall intent of the 1972 Congress, it can have effects that may have been unintended and that some policymakers might consider unusual. Persons who delay receipt of Social Security benefits usually receive higher monthly benefit amounts, but a widow(er) who faces a limit cannot increase his or her monthly benefit through delayed receipt of benefits. Thus, many persons who are widowed before the NRA face strong incentives to claim benefits early. That is somewhat unusual because the actuarial adjustments under Social Security are approximately fair, so there are no cost savings to the Social Security program from "forcing" a widow(er) to claim early benefits as opposed to allowing him or her to delay receipt of benefits in exchange for a higher monthly amount. And many widow(er)s would be better off if they could use the Social Security program to, in effect, save (that is, delay receipt of benefits in exchange for a higher amount later). This article analyzes two other options that would provide widow(er)s with additional filing options under Social Security. The ARLA option would ultimately help about 229,000 widow(er)s, and the cost would be small (about $69 million a year). The SARLA option would help about 117,000 widow(er)s, and the cost would be about $41 million a year. Robert J. Myers, a former Chief Actuary of Social Security, has offered a proposal that would provide relief from the widow(er)'s limit in cases in which the worker dies shortly after retirement. That proposal would help about 115,000 widow(er)s, and the cost would be low (about $57 million a year).

Aged↗

PubMed2005

Geometric mean ratio-dependent scaled bioequivalence limits with leveling-off properties.

In this study, novel approaches for the design of bioequivalence (BE) limits are developed. The new BE limits scale with intrasubject variability but only until a geometric mean ratio (GMR)-dependent plateau value and combine the classic (0.80-1.25) and expanded (0.70-1.43) BE limits into a single criterion. Plots of the extreme GMR values accepted as a function of coefficient of variation (CV) have a convex shape, similar to the classic unscaled 0.80-1.25 limits. The performance of the novel approaches in comparison to the classic unscaled 0.80-1.25 limits as well as the two expanded BE limits, i.e., 0.70-1.43 and 0.75-1.33 was assessed using simulated data. Two-period crossover BE investigations with 12, 24 or 36 subjects were simulated with assumptions of CV 10%, 20%, 30% or 40%. At low CV values, the performance of the novel BE limits is almost identical to the 0.80-1.25 criterion. On the contrary, the expanded BE limits are very permissive even at high GMR values. For high CV% values (30% and 40%), the new BE limits show a much greater probability of declaring BE when GMR = 1 in comparison to the classic 0.80-1.25 limits. In addition, when the drug products differ more than 25%, the new BE limits show much lower percentage of acceptance than the expanded 0.70-1.43 limits. One of the major advantages of the new BE limits is their gradual expansion with variability until a GMR-dependent plateau value. Finally, the continuity and leveling-off properties of the new BE limits make them suitable for the assessment of BE studies, irrespective of the level of variability encountered.

Analysis of Variance↗

PubMed1967

Effect of growth rate and substrate limitation on the composition and structure of the cell wall of Saccharomyces cerevisiae.

1. A study was made of the composition and structure of walls isolated from yeast grown in continuous culture at different rates, under three conditions of glucose limitation in which the concentrations of glucose and ammonium sulphate in the medium and the oxygen-transfer rate in the culture were varied, and one condition of NH(4) (+) limitation. 2. The contents of total glucan and total mannan in the walls were relatively little affected by the growth rate under any of the four sets of conditions. The phosphorus and protein contents of walls from yeast grown under each of the four conditions increased as the growth rate was decreased. Walls from yeast grown under NH(4) (+) limitation contained only half as much protein as walls from cells grown under glucose limitation. The proportion of lipid was greatest in walls from yeast grown under NH(4) (+) limitation. 3. A procedure was devised for fractionating isolated walls, based on the ease with which the glucan and mannan were extracted with water and with hot and cold 6% (w/v) potassium hydroxide solution. The percentage of glucan, mannan, protein and phosphorus in each of the fractions was affected by the rate of growth and by the nature of the substrate limitation. 4. The beta-fructofuranosidase activities of yeast grown under glucose limitation increased as the growth rate was lowered, but decreased at very low growth rates. The effects at low growth rates were probably due to repression of enzyme synthesis by residual glucose in the culture filtrate. The beta-fructofuranosidase activities of yeast grown under NH(4) (+) limitation were much lower than those from yeast grown under any of the conditions of glucose limitation. 5. Yeast cells grown at any of the rates under NH(4) (+) limitation were longer and thinner than those grown at the same rate under any of the conditions of glucose limitation. Mean cell volumes were dependent on growth rate but not on the nature of the substrate limitation. 6. Electron micrographs of thin sections of isolated walls showed that cells grown under NH(4) (+) limitation had a more porous structure than those from cells grown under any of the conditions of glucose limitation.

Cell Wall↗

PubMed2003

[Formation of polyhydroxyalkanoates during the dual-nutrient-limited zone by Ralstonia eutropha].

Polyhydroxyalkanoates (PHAs) are a class of polyesters biosynthesized by microorganisms (esp. Ralstonia eutropha) under an unbalanced growth condition, and which are supposed to partly take the place of traditional plastics made from petroleum in the near future since they are harmless to the environment and biodegradable. Organic acids (mainly butyrate, lactate, propionate and acetate) produced from anaerobic digested food wastes, industrial wastes and sewage may be used as cheap carbon sources since the large amounts of the above wastes disposed by industry and family each year. In order to better understand the process of PHAs formation with acids as carbon sources, so as to increase the yields of PHAs. Biosynthesis of PHAs by R. eutropha during the dual nutrient-limitation-zone was investigated with mixed organic acids (the mass ratio of the four component acids was butyrate: propionate: acetate: lactate = 3: 3: 1: 1, which was simulated as once the result of anaerobic digestion of food wastes) as carbon sources and (NH4)2 SO4 as nitrogen source. Two different manners of maintaining the dual-nutrient-limitation zone were adopted by feeding mixed acids and (NH4 )2SO4 at determined rates to the fermentation culture which were free of carbon sources (manner A) or nitrogen sources (manner B) firstly. The results suggest that, first of all, the meaning of the limitation of mixed acids or (NH4)2 SO4 does not mean to limit the supply of them, but mean to feed as more as possible of carbon and nitrogen sources in order to meet the cell growth and PHAs formation of R. eutropha by the largest extent. However, it's indispensable to make the residual concentration of carbon and nitrogen sources as low as possible since organic acids are inhibitive to the cell growth, and most importantly, only under the presence of nitrogen during the PHAS formation period of the fermentation could R. eutropha produce more PHAs than any other unbalanced growth condition. Secondly, with the increase of the width of the dual-nutrient-limitation zone, the yield of PHAs would also increase, it suggest that most of the PHAs were biosynthesized during the dual-nutrient-limitation zone. Finally, in contrast with the dual-nutrient-limitation manner of limiting the nitrogen source at first (manner B), the dual-nutrient-limitation manner of limiting the carbon source at first (manner A) was more favorable for the production of PHAs, and the maximum production of PHAs of these two manners are 3.72 g/L and 2.55 g/L, respectively. It may be because that PHAs formation required enzymes could not be well developed when R. eutropha grow under the state of nitrogen limitation from the beginning of fermentation. Besides, yield of PHAs produced by the dual-nutrient-limitation fermentation is larger than that of the single-nutrient-limitation batch culture. Therefore, it seems that to increase the output of PHAs production, the strategy of maintaining as wide as possible the width of dual-nutrient (C, N)-limitation zone may be effective.

Acetates↗

PubMed1995

Value of high-resolution intraoperative ultrasonography in the determination of limits of horizontal tumor spread during surgery for gastric malignancy.

Determination of the resection margins during surgery for gastric malignancy is a subject of controversy because accurate detection of horizontal limits of tumor spread is difficult by current methods. In this study, we investigated the value of intraoperative-ultrasonography (IUS) in the detection of proximal and distal limits of horizontal tumor spread (HTS) in 19 gastric adenocarcinoma (Group I) and five gastric lymphoma (Group II) patients. After sonographic and clinical limits of HTS were marked, resections were carried out 2 cm away from the IUS limits, and biopsies from IUS limits and resection margins were obtained. Then, the gap between IUS and clinical limits were recorded and compared with results of pathology. In both groups, the distance from clinical to IUS limits ranged from 0 cm to 3 cm and IUS limits were never inside the clinical limits. In Group I, results of sonographic proximal limit detection were satisfactory in all patients excluding recurrent cases (n:2) and a patient with early gastric cancer. Sonographic accuracy of distal limit detection was 68%. In Group I, only one resection margin (distal) was found to be infiltrated with cancer. In Group II, the success rate of IUS-guided HTS detection was 40%. IUS seems to be a valuable method for determining the extent of HTS during operation for gastric adenocarcinomas, especially so for the most problematic proximal limits. In recurrent cancers and lymphomas, however, results of IUS may be frequently misleading. IUS can be advocated as a routine procedure to determine the tumor limits and thus the resection margins during surgery for primary gastric adenocarcinomas.

Adenocarcinoma↗

PubMed2002

Low back pain in individuals with chronic airflow limitation and their partners--a preliminary prevalence study.

BACKGROUND AND PURPOSE: The prevalence of low back pain in individuals with chronic airflow limitation, and their partners, is unknown. Individuals with chronic airflow limitation, and their respective partners, are likely to have several risk factors that may increase the predisposition for low back pain. The aim of the present study was to provide preliminary data on the prevalence of low back pain in individuals with chronic airflow limitation, and their partners. METHOD: A cross-sectional observational study design was used. Individuals with chronic airflow limitation, and their partners, were approached at South Australian metropolitan Lung Support Group meetings and invited to participate in the study. Three commonly used questionnaires: the Medical Outcomes Survey Short-Form 36 (MOS SF-36); the St George's Respiratory Questionnaire (SGRQ); and the Nordic Low Back Pain Questionnaire (NLBPQ) were used to collect data on general health, respiratory health and low back pain prevalence, respectively. Odds ratios and independent Student's t-tests were used to analyse data by use of Epi Info Version 6.0 software. RESULTS: Sixty subjects participated in the study: 41 individuals with chronic airflow limitation and 19 partners of individuals with chronic airflow limitation. The lifetime, 12-month and seven-day prevalence of low back pain in individuals with chronic airflow limitation was 69%, 58% and 31%, respectively. The prevalence of low back pain in the partners of individuals with chronic airflow limitation was found to be higher, at 74%, 68% and 58%, respectively. Four significant relationships between general and respiratory health, and low back pain were demonstrated for individuals with chronic airflow limitation. CONCLUSIONS: The prevalence of low back pain in individuals with chronic airflow limitation was comparable to the lifetime prevalence for the general and older population, and greater than the 12-month prevalence reported for the older population. The prevalence of low back pain for the partners of individuals with chronic airflow limitation was consistently higher than the lifetime and 12-month prevalence reported for individuals with chronic airflow limitation, the older population and family care workers. These findings suggest a larger prevalence study of low back pain in individuals with chronic airflow limitation, and their partners, is warranted.

Activities of Daily Living↗

PubMed2005

Comparison of volume- and pressure-limited NPPV at night: a prospective randomized cross-over trial.

Both pressure- and volume-limited non-invasive positive pressure ventilation (NPPV) have been used in patients with chronic respiratory failure. The aim of the present study was to compare the efficacy of ventilation during nocturnal volume- and pressure-limited NPPV. Fifteen patients (nine COPD, six non-COPD) were randomly assigned to receive either volume-limited or pressure-limited NPPV and were switched to the complementary mode after 6 weeks. Ten patients (five COPD, five non-COPD) completed the study. PaCO2 during sleep comparably decreased from 54.6+/-8.0 to 46.2+/-6.1 mmHg during volume-limited NPPV (P<0.05), and to 46.5+/-6.4 mmHg during pressure-limited NPPV (P<0.05). Improvements in sleep quality assessed by polysomnography were comparable, but less gastrointestinal side effects were reported for pressure-limited NPPV (P<0.05). Using a pneumotachograph the variance of inspiratory volumes was lower, but the variance of peak inspiratory pressures was higher during volume-limited NPPV compared to pressure-limited NPPV. Substantial leak volumes which accounted for 57% (volume-limited NPPV) and for 58% (pressure-limited NPPV) of the applied inspiratory volume were independent from the mode of ventilation. In conclusion, nocturnal volume- and pressure-limited NPPV have similar effects on gas exchange and sleep quality in patients with hypercapnic chronic respiratory failure, but volume-limited NPPV is associated with more gastrointestinal side effects.

Adult↗

PubMed1972

The role of oxygen limitation in the formation of poly- -hydroxybutyrate during batch and continuous culture of Azotobacter beijerinckii.

Azotobacter beijerinckii was grown in ammonia-free glucose-mineral salts media in batch culture and in chemostat cultures limited by the supply of glucose, oxygen or molecular nitrogen. In batch culture poly-beta-hydroxybutyrate was formed towards the end of exponential growth and accumulated to about 74% of the cell dry weight. In chemostat cultures little poly-beta-hydroxybutyrate accumulated in organisms that were nitrogen-limited, but when oxygen limited a much increased yield of cells per mol of glucose was observed, and the organisms contained up to 50% of their dry weight of poly-beta-hydroxybutyrate. In carbon-limited cultures (D, the dilution rate,=0.035-0.240h(-1)), the growth yield ranged from 13.1 to 19.8g/mol of glucose and the poly-beta-hydroxybutyrate content did not exceed 3.0% of the dry weight. In oxygen-limited cultures (D=0.049-0.252h(-1)) the growth yield ranged from 48.4 to 70.1g/mol of glucose and the poly-beta-hydroxybutyrate content was between 19.6 and 44.6% of dry weight. In nitrogen-limited cultures (D=0.053-0.255h(-1)) the growth yield ranged from 7.45 to 19.9g/mol of glucose and the poly-beta-hydroxybutyrate content was less than 1.5% of dry weight. The sudden imposition of oxygen limitation on a nitrogen-limited chemostat culture produced a rapid increase in poly-beta-hydroxybutyrate content and cell yield. Determinations on chemostat cultures revealed that during oxygen-limited steady states (D=0.1h(-1)) the oxygen uptake decreased to 100mul h(-1) per mg dry wt. compared with 675 for a glucose-limited culture (D=0.1h(-1)). Nitrogen-limited cultures had CO(2) production values in situ ranging from 660 to 1055mul h(-1) per mg dry wt. at growth rates of 0.053-0.234h(-1) and carbon-limited cultures exhibited a variation of CO(2) production between 185 and 1328mul h(-1) per mg dry wt. at growth rates between 0.035 and 0.240h(-1). These findings are discussed in relation to poly-beta-hydroxybutyrate formation, growth efficiency and growth yield during growth on glucose. We suggest that poly-beta-hydroxybutyrate is produced in response to oxygen limitation and represents not only a store of carbon and energy but also an electron sink into which excess of reducing power can be channelled.

Anaerobiosis↗

PubMed1994

Effect of amino acid limitation on the expression of 19 genes in rat hepatoma cells.

We showed previously that the abundance of serum albumin mRNA is decreased in H4-II-E rat hepatoma cells limited for a single essential amino acid (phenylalanine, methionine, leucine, or tryptophan). To define the specificity of this phenomenon, we examined the effect of amino acid limitation on the abundance of mRNAs for 19 genes in the H4-II-E cells. These genes included six genes whose expression is either completely liver-specific or highly enriched in the liver compared with other tissues [albumin, transthyretin (TTR), transferrin, carbamyl phosphate synthetase-I, urate oxidase, class I alcohol dehydrogenase], as well as a number of ubiquitously expressed "housekeeping" genes. The results indicated that the 19 genes could be divided into three classes based on their response to amino acid limitation. Class I genes (the six liver-specific genes and alpha-tubulin) exhibit decreased expression in response to amino acid limitation. The expression of class II genes [beta 2-microglobulin, hypoxanthine-guanine phosphoribosyl transferase (HPRT), H-ferritin, ubiquitin (UbB), insulin-like growth factor binding protein-4, HNF-1 alpha] is not significantly affected by amino acid limitation. Class III genes [gadd153, beta-actin, ubiquitin (UbC), phosphoglycerate kinase-1, C/EBP alpha, C/EBP beta] exhibit increased expression in response to amino acid limitation. Thus, specific inductive as well as repressive effects on gene expression are quite common in amino acid-limited cells. The observation that all six genes whose expression is liver-specific exhibited decreased expression in amino acid-limited cells suggests a common mode of regulation of these genes by amino acid availability. The strong induction by amino acid limitation of the C/EBP inhibitor gadd153 is of interest in this regard, as increased levels of gadd153 could interfere with C/EBP, which is required for high expression of most liver-specific genes. To investigate further the molecular mechanism for the decrease in albumin mRNA abundance, albumin nuclear transcript levels were quantified in control and tryptophan-limited cells. Tryptophan limitation caused a decrease in albumin nuclear transcript abundance, and this decrease preceded the decrease in albumin mRNA, suggesting that the decrease in albumin mRNA was caused at least partly by a decrease in albumin gene transcription. Additional experiments with actinomycin D indicated that albumin mRNA was also destabilized in the tryptophan-limited cells. Thus, the overall results indicate that the decrease in albumin mRNA in the tryptophan-limited cells is caused by a specific decrease in albumin nuclear transcript abundance and destabilization of albumin mRNA.

Amino Acids↗

PubMed2006

The choice of threshold limits for pediatric ambulatory blood pressure monitoring influences clinical decisions.

OBJECTIVES: Hypertension in children may be defined by blood pressure elevated above the 95th percentile according to sex and age. Population data for ambulatory blood pressure provide different age-related and sex-related threshold limits to office-derived data. We sought to determine whether, when using ambulatory blood pressure monitoring in a clinical setting, changing 95th percentile threshold limit sets from office-derived to ambulatory blood pressure-derived would lead to different diagnostic decisions. METHODS: Three nephrologists who were blinded as to patient identity and limit setting method reported on 42 ambulatory blood pressure records from a mixed group of patients aged 5-18 years by using both office-derived threshold limits for the 95th centile of blood pressure and ambulatory blood pressure-derived limits. Decisions regarding the presence or absence of hypertension were compared for each patient according to the limit set. RESULTS: Thirty-five (83%) patients were considered to be hypertensive when office-derived threshold limits were used and 20% (P=0.005) fewer records were reported as showing hypertension when ambulatory blood pressure-derived threshold limits were used. When ambulatory blood pressure limits were applied, there were fewer records with an awake systolic blood pressure load >50% (P=0.004) and the average awake systolic blood pressure load was significantly lower (P<0.001). CONCLUSION: Ambulatory blood pressure normative data tend to provide higher blood pressure limits for age and sex. Consequently, when ambulatory blood pressure data are used to set threshold limits, clinical decisions based on ambulatory blood pressure may be different than when office limits are used. These findings demonstrate the importance of using the most appropriate limit sets to analyze ambulatory blood pressure and when interpreting ambulatory blood pressure-based research.

Adolescent↗

PubMed1989

Influence of iron-limited and replete continuous culture on the physiology and virulence of Neisseria gonorrhoeae.

Neisseria gonorrhoeae strains P9-2 (PenS) and KW2 (PenR) were grown in chemostats of nonferrous design at constant growth rate, pH and dissolved oxygen tension. Iron limitation (micromax 0.1 h-1) was imposed by omitting iron salts from the defined medium and titrating increasing concentrations of the non-metabolizable iron chelators ovotransferrin and Desferal, to progressively decrease the growth yield. Metabolic activity during iron limitation was very high, with a qGlc which was 2- or 11-fold greater than during cystine- or glucose-limited growth, respectively. More aspartate and isoleucine were metabolized during cystine-limited growth, while more glutamate, proline and serine were metabolized during glucose- or iron-limited growth. Significant concentrations of alanine or valine were excreted during cystine- or glucose-limited growth, respectively. Iron-limited growth of an initial inoculum of non-piliated, transparent colony-forming (P-O-) gonococci resulted in the selection of 100% piliated bacteria. Initial inocula of P+O- gonococci retained this phenotype for over 100 generations. Iron-limited gonococci were extremely virulent in the guinea-pig subcutaneous chamber model and inocula of even 12 bacteria grew rapidly and persisted. By contrast, cystine-limited (iron-replete) gonococci retained piliation but did not survive in the chambers. Transition from iron-limited to glucose-limited growth resulted in marked loss of piliation but the bacteria remained virulent. Loss of virulence did not correlate with susceptibility to killing by normal human serum, nor with changes in the content or composition of lipooligosaccharide, which contained 2.9, 3.7, 4.3 and 4.8 kDa moieties. Additional proteins were detectable in Sarkosyl-purified outer membranes of iron-limited gonococci but several proteins with molecular masses similar to those described in the literature for iron-restricted gonococci were detectable in cystine- or glucose-limited bacteria.

Bacterial Outer Membrane Proteins↗

PubMed2005

Easy-to-use, accurate and flexible individualized Bayesian limited sampling method without fixed time points for ciclosporin monitoring after liver transplantation.

BACKGROUND: New methods to estimate the systemic exposure to ciclosporin such as the level 2 h after dosing and limited sampling formulas may lead to improved clinical outcome after orthotopic liver transplantation. However, most strategies are characterized by rigid sampling times. AIM: To develop and validate a flexible individualized population-pharmacokinetic model for ciclosporin monitoring in orthotopic liver transplantation. METHODS: A total of 62 curves obtained from 31 patients at least 0.5 year after orthotopic liver transplantation were divided into two equal groups. From 31 curves, relatively simple limited sampling formulas were derived using multiple regression analysis, while using pharmacokinetic software a two-compartment population-pharmacokinetic model was derived from these same data. We then tested the ability to estimate the AUC by the limited sampling formulas and a different approach using several limited sampling strategies on the other 31 curves. The new approach consists of individualizing the mean a priori population-pharmacokinetic parameters of the two-compartment population-pharmacokinetic model by means of maximum a posteriori Bayesian fitting with individual data leading to an individualized population-pharmacokinetic limited sampling model. From the individualized pharmacokinetic parameters, AUC(0-12h) was calculated for each combination of measured blood concentrations. The calculated AUC(0-12h) both from the limited-sampling formulas and the limited-sampling model were compared with the gold standard AUC(0-12h) (trapezoidal rule) by Pearson's correlation coefficient and prediction precision and bias were calculated. RESULTS: The AUC(0-12h) value calculated by individualizing the population-pharmacokinetic model using several combinations of measured blood concentrations: 0 + 2 h (r(2) = 0.94), 0 + 1 + 2 h (r(2) = 0.94), 0 + 1 + 3 h (r(2) = 0.92), 0 + 2 + 3 h (r(2) = 0.92) and 0 + 1 + 2 + 3 h (r(2) = 0.96) had excellent correlation with AUC(0-12h), better than limited sampling formulas with less than three sampling time points. Even trough level with limited sampling method (r(2) = 0.86) correlated better than the level after 2 h of dosing (r(2) = 0.75) or trough level (r(2) = 0.64) as single values without limited sampling method. Moreover, the individualized population-pharmacokinetic model had a low prediction bias and excellent precision. CONCLUSION: Multiple rigid sampling time points limit the use of limited sampling formulas. The major advantage of the Bayesian estimation approach presented here, is that blood sampling time points are not fixed, as long as sampling time is known. The predictive performance of this new approach is superior to trough level and that after 2 h of dosing and at least as good as limited sampling formulas. It is of clear advantage in busy out-patient clinics.

Adult↗

PubMed2006

Differences in plant function in phosphorus- and nitrogen-limited mangrove ecosystems.

Mangrove ecosystems can be either nitrogen (N) or phosphorus (P) limited and are therefore vulnerable to nutrient pollution. Nutrient enrichment with either N or P may have differing effects on ecosystems because of underlying differences in plant physiological responses to these nutrients in either N- or P-limited settings. Using a common mangrove species, Avicennia germinans, in sites where growth was either N or P limited, we investigated differing physiological responses to N and P limitation and fertilization. We tested the hypothesis that water uptake and transport, and hydraulic architecture, were the main processes limiting productivity at the P-limited site, but that this was not the case at the N-limited site. We found that plants at the P-deficient site had lower leaf water potential, stomatal conductance and photosynthetic carbon-assimilation rates, and less conductive xylem, than those at the N-limited site. These differences were greatly reduced with P fertilization at the P-limited site. By contrast, fertilization with N at the N-limited site had little effect on either photosynthetic or hydraulic traits. We conclude that growth in N- and P-limited sites differentially affect the hydraulic pathways of mangroves. Plants experiencing P limitation appear to be water deficient and undergo more pronounced changes in structure and function with relief of nutrient deficiency than those in N-limited ecosystems.

Belize↗

PubMed1994

Upper limit of vulnerability reliably predicts the defibrillation threshold in humans.

BACKGROUND: The upper limit of vulnerability is the stimulus strength above which electrical stimulation cannot induce ventricular fibrillation even when the stimulus occurs during the vulnerable period of the cardiac cycle. The purpose of this study was to test the hypothesis that the upper limit of vulnerability can accurately predict the defibrillation threshold in patients undergoing implantable cardioverter-defibrillator (ICD) implantation using nonthoracotomy lead systems. METHODS AND RESULTS: We studied 77 patients at the time of ICD implantation. Multiple endocardial-endocardial and endocardial-subcutaneous shock pathways were used. Two different protocols were used to test the upper limit of vulnerability. In protocol 1 (n = 17), the upper limit of vulnerability was tested with two shocks on the peak or the up-slope of the T wave of paced rhythm. The shocks were given randomly either at the peak and 20 milliseconds before the peak of T wave (n = 7) or at 20 and 40 milliseconds before the peak of T wave (n = 10). In protocol 2 (n = 60), the upper limit of vulnerability was tested with three shocks delivered at 0, 20, and 40 milliseconds before the peak of the T wave. The weakest shock that failed to induce ventricular fibrillation by a 5-J step-down or step-up method was defined as the upper limit of vulnerability. The defibrillation threshold was also determined by a 5-J step-down or step-up method. In protocol 1, the upper limit of vulnerability (9 +/- 6 J) was significantly lower than the defibrillation threshold (13 +/- 7 J) with a correlation coefficient of .87 and P < .001. In protocol 2, the upper limit of vulnerability (13 +/- 6 J) was not significantly different from the defibrillation threshold (13 +/- 6 J) with a correlation coefficient of .85 and P < .001. In 45 of the 60 patients, the upper limit of vulnerability was < or = 15 J; all had a defibrillation threshold of < or = 20 J. In 51 of the 60 patients, the upper limit of vulnerability was within 5 J of the defibrillation threshold. The upper limit of vulnerability overestimated the defibrillation threshold by > 10 J in 8 patients and underestimated the defibrillation threshold by > 10 J in only 1 patient. The overestimation and underestimation occurred only in patients with the upper limit of vulnerability > 15 J. CONCLUSIONS: When tested with three shocks on and before the peak of the T wave, the upper limit of vulnerability accurately predicted the defibrillation threshold in patients undergoing ICD implantation using nonthoracotomy lead systems. This method required either one or no episodes of ventricular fibrillation in most patients.

Aged↗

PubMed2004

Impairments, activity limitations and participation restrictions: prevalence and associations among persons living with HIV/AIDS in British Columbia.

BACKGROUND: To measure the prevalence of and associations among impairments, activity limitations and participation restrictions in persons living with HIV in British Columbia to inform support and care programs, policy and research. METHODS: A cross-sectional population-based sample of persons living with HIV in British Columbia was obtained through an anonymous survey sent to members of the British Columbia Persons With AIDS Society. The survey addressed the experience of physical and mental impairments, and the experience and level of activity limitations and participation restrictions. Associations were measured in three ways: 1) impact of types of impairment on social restriction; 2) impact of specific limitations on social restriction; and 3) independent association of overall impairments and limitations on restriction levels. Logistic regression was used to measure associations with social restriction, while ordinal logistic regression was used to measure associations with a three-category measure of restriction level. RESULTS: The survey was returned by 762 (50.5%) of the BCPWA participants. Over ninety percent of the population experienced one or more impairments, with one-third reporting over ten. Prevalence of activity limitations and participation restrictions was 80.4% and 93.2%, respectively. The presence of social restrictions was most closely associated with mental function impairments (OR: 7.0 for impairment vs. no impairment; 95% CI: 4.7 - 10.4). All limitations were associated with social restriction. Among those with 5 vs. no limitation, 95%CI: 4.9-125.0). Among those with > 200 CD4 cells/mm3, the odds of higher restriction were increased with higher limitation (OR: 2.7 for limitation score of 1-5 vs. no limitation, 95%CI: 1.4-5.1; OR: 8.6 for limitation score > 5 vs. no limitation, 95%CI: 3.9-18.8), as well as by additional number of impairments (OR:1.2 for every additional impairment; 95% CI:1.1-1.3). CONCLUSIONS: This population-based sample of people living with HIV has been experiencing extremely high rates of impairments, activity limitations and participation restrictions. Furthermore, the complex inter-relationships identified amongst the levels reveal lessons for programming, policy and research in terms of the factors that contribute most to a higher quality of life.

Acquired Immunodeficiency Syndrome↗

PubMed2006

Transcriptome analysis of a shikimic acid producing strain of Escherichia coli W3110 grown under carbon- and phosphate-limited conditions.

Shikimic acid, which is produced in the aromatic amino acid pathway in plants and microorganisms, is an industrially interesting chiral starting material for the synthesis of many chemical substances, e.g. the influenza medicine Tamiflu. When produced by genetically modified Escherichia coli it has previously been found that carbon-rich conditions (e.g. phosphate-limitation) favors production of shikimic acid over shikimate pathway by-products, whereas the situation is the opposite at carbon-(glucose-) limited conditions. In the present study, gene expression patterns of the shikimate producing strain W3110.shik1 (W3110 with aroL deletion and plasmid-overexpressed aroF) and the wild type strain W3110 grown under carbon- and phosphate-limited (carbon-rich) chemostat conditions (D=0.23h(-1)) were analyzed. The study suggests that the by-product formation under carbon-limitation is explained by a set of upregulated genes coupled to the shikimate pathway. The genes, ydiB, aroD and ydiN, were strongly induced only in carbon-limited W3110.shik1. Compared to W3110 the lg(2)-fold changes were: 6.25 (ydiB); 3.93 (aroD) and 8.18 (ydiN). In addition, the transcriptome analysis revealed a large change in the gene expression when comparing phosphate- to carbon-limitation, which to a large part could be explained by anabolic-catabolic uncoupling, which is present under phosphate-limitation but not under carbon-limitation. Interestingly, there was also a larger difference between the two strains under carbon-limitation than under phosphate-limitation. The reason for this difference is interpreted in terms of starvation for aromatic amino acids under carbon-limitation which is relieved under phosphate-limitation due to an upregulation of aroK and aroA.

Bioreactors↗