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PubMed2005

Nipecotic acid: systemic availability and brain delivery after nasal administration of nipecotic acid and n-butyl nipecotate to rats.

PURPOSE: The purpose of this research was to characterize nipecotic acid pharmacokinetics in blood and brain after intravenous (i.v.) and nasal administration of nipecotic acid and its n-butyl ester. METHODS: Nipecotic acid and its n-butyl ester were administered to rats i.v. and intranasally (n = 5 rats/drug per route), and nipecotic acid pharmacokinetics in blood were characterized. Nipecotic acid concentration-time profiles were determined in blood by noncompartmental and compartmental methods. Nipecotic acid was also dosed i.v. and its n-butyl ester was dosed by nasal and i.v. routes, and brain levels of nipecotic acid over the subsequent 4 h (n = 5 rats/time point per route) were assessed. RESULTS: The absolute systemic availability of nipecotic acid after nasal dosing was 14%. After i.v. and nasal dosing of the n-butyl ester, nipecotic acid systemic availability was 97% and 92%, respectively. Both i.v. and nasal administration of the n-butyl ester resulted in a significantly longer terminal half-life and larger mean resident time and volume of distribution for nipecotic acid than was observed after an i.v. nipecotic acid dose. Total brain exposure to nipecotic acid was not significantly different after nasal and i.v. dosing of the n-butyl ester. However, the brain/blood nipecotic acid ratio declined significantly with time after i.v. and nasal dosing of the ester prodrug. Nipecotic acid was not detectable in brain after i.v. dosing of nipecotic acid. CONCLUSIONS: The use of an ester formulation was crucial to delivering nipecotic acid to the brain. Preliminary evidence strongly suggests ester hydrolysis is rate limiting to nipecotic acid brain delivery. Once nipeoctic acid was formed, it displayed tissue trapping in brain. Parenteral dosing of nipecotic acid esters is unnecessary for systemic or brain delivery of nipecotic acid and possibly other CNS active zwitterion esters.

Administration, Intranasal↗

PubMed1986

An experimental study of bio-availability of fluoride from dietary sources in man.

After single, oral doses, 8 h profiles of fluoride (F) concentrations in plasma and saliva, and 24 h urinary excretions were determined in healthy adult volunteers. Bio-availability of F from dietary sources was evaluated in relation to that of NaF. Between 2 and 10 mg of F administered all 3 variables were dose-dependent. However, digestion, the chemical state of F, and interaction with accompanying foods may modify the kinetics of F passage through the human body. Low bio-availabilities were observed for most solid foods such as fish and algal flour and for mammalian and fish bones, when used as typical components of fluoride-rich foods such as meat- and fish-products. This data is important in the determination of optimum levels of F supplementation in human nutrition for caries-prevention programmes.

Adult↗

PubMed1981

An enzymatic assay for available zinc in plasma and serum.

A convenient enzymatic assay for available zinc in plasma and serum was developed. The assay is based upon the reactivation of the zinc metalloenzyme alkaline phosphatase which had been previously inactivated by nitrilotriacetic acid. The enzymatic assay was applied to serum samples from human subjects in a study of zinc utilization in pregnancy and to plasma samples from rats in a zinc deficiency study. Most plasma samples with low zinc levels (less than 70 microgram/dl) reactivated the enzyme to less than 30% of control activity. Most samples with normal zinc levels (70-120 microgram/dl) reactivated the enzyme 30-65%. Samples with elevated zinc levels (greater than 120 microgram/dl) reactivated the enzyme over 70%. The assay is quick, convenient, and in principle measures functionally available zinc.

Alkaline Phosphatase↗

PubMed1995

Effect of ingesta and of tablets of different strengths on the systemic availability of digoxin in normal dogs.

The plasma concentrations of digoxin were measured in eight normal dogs given digoxin on four occasions, using three different feeding regimens and tablets of two strengths. Although ingesta tended to slow the absorption of digoxin, the systemic availability of the drug, based on measurements of Cmax, tmax and AUC did not differ when digoxin tablets were given with canned food, with dry food, or without food. However, some of the pharmacokinetic characteristics and smaller individual variations with the dry food regimen would be considered advantageous for maintenance therapy. Tablets containing 62.5 micrograms or 250 micrograms of digoxin had a similar relative bioavailability. The peak plasma digoxin concentrations were higher in female dogs, and the trends in other data also suggested that the systemic availability of digoxin was better in female dogs.

Animals↗

PubMed1985

Mitochondrial iron not bound in heme and iron-sulfur centers and its availability for heme synthesis in vitro.

Rat liver mitochondrial fractions have previously been shown to contain a pool of iron which was bound neither in cytochromes nor in iron-sulfur centers (Tangerås, A., Flatmark, T., Bãckstrõm, D. and Ehrenberg, A. (1980) Biochim. Biophys. Acta 589, 162-175), and in the present study the availability of this iron pool for heme synthesis has been studied in isolated mitochondria. A minor fraction of this iron is here shown to originate from iron-rich lysosomes present as a contaminant in mitochondrial fractions isolated by differential centrifugation, and a method for the selective quantitation of this iron pool was developed. The availability of the mitochondrial iron pool for heme synthesis by mitochondria in vitro was studied using a recently developed HPLC method for the assay of ferrochelatase activity. When deuteroporphyrin was used as the substrate, 1.04 +/- 0.13 nmol/mg protein of deuteroheme was formed after 6 h incubation at 37 degrees C when a plateau was approached, and the initial rate of heme synthesis was 0.3 nmol/h per mg protein. Heme formation from the physiological substrate protoporphyrin was also seen. The heme synthesis increased with the amount of mitochondria used and was blocked by both Fe(II) and Fe(III) chelators. The heme synthesis was independent of mitochondrial oxidizable substrates and no difference was observed between pH 7.4 and 6.5. FMN slightly stimulated the formation of heme from endogenous iron, probably by mobilization of a small amount of contaminating lysosomal iron present in the preparations. The possibility that the mitochondrial iron pool functions as the proximate iron donor for heme synthesis by ferrochelatase in vivo is discussed.

Animals↗

PubMed2006

Evaluating the impacts of some environmentally relevant factors on the availability of bisphenol A with negligible-depletion SPME.

The effect of some environmentally relevant factors including salinity, pH, and humic acids on the availability of bisphenol A (BPA) was evaluated by using the negligible-depletion solid-phase microextraction (nd-SPME) biomimetic method. With the variation of salinity (0-500 mM NaCl) and pH (5.0-8.5) of aqueous solutions, the partition coefficients of BPA between the nd-SPME fiber and the aqueous solution varied in the range of logD=3.55-3.86, which indicates that the salinity and pH can influence the availability of BPA. By using Acros humic acid as model dissolved organic matter (DOM), it was also demonstrated that the environmental factors such as salinity and pH could affect the partitioning of BPA between DOM and aqueous solutions. The determined partition coefficients of BPA between dissolved organic carbon (DOC) and aqueous solutions were in the range of logD(DOC)=4.03-5.60 for Acros humic acid solutions with 1-50 mg l(-1) DOC. The influence of salinity and pH on logD(DOC) was more significant at low concentration (0-5 mg l(-1)) of DOC.

Benzhydryl Compounds↗

PubMed2004

Metal availability and soil toxicity after repeated croppings of Thlaspi caerulescens in metal contaminated soils.

Metal phytoextraction with hyperaccumulating plants could be a useful method to decontaminate soils, but it is not fully validated yet. In order to quantify the efficiency of Cd and Zn extraction from a calcareous soil with and without Fe amendment and an acidic soil, we performed a pot experiment with three successive croppings of Thlaspi caerulescens followed by 3 months without plant and 7 weeks with lettuce. We used a combined approach to assess total extraction efficiency (2 M HNO3-extractable metals), changes in metal bio/availability (0.1 M NaNO3-extractable metals and lettuce uptake) and toxicity (lettuce biomass and the BIOMET biosensor). The soil solution was monitored over the whole experiment. In the calcareous soil large Cu concentrations were probably responsible for chlorosis symptoms observed on T. caerulescens. When this soil was treated with Fe, the amount of extracted metal by T. caerulescens increased and metal availability and soil toxicity decreased when compared to the untreated soil. In the acidic soil, T. caerulescens was most efficient: Cd and Zn concentrations in plants were in the range of hyperaccumulation and HNO3-extractable Cd and Zn, metal bio/availability, soil toxicity, and Cd and Zn concentrations in the soil solution decreased significantly. However, a reduced Cd concentration measured in the third T. caerulescens cropping indicated a decrease in metal availability below a critical threshold, whereas the increase of dissolved Cd and Zn concentrations after the third cropping may be the early sign of soil re-equilibration. This indicates that phytoextraction efficiency must be assessed by different approaches in order not to overlook any potential hazard and that an efficient phytoextraction scheme will have to take into account the different dynamics of the soil-plant system.

Biodegradation, Environmental↗

PubMed2005

Can microbial mineralization be used to estimate microbial availability of organic contaminants in soil?

The aim of this study was to characterize the behaviour of a PAH-degrading bacterium to determine whether mineralization plateaus as a result of substrate removal, a decrease in microbial activity or nutrient availability in sterile soils over time. To investigate this, the mineralization of 14C-phenanthrene was measured until it plateaued; subsequently, additional 14C-phenanthrene, catabolic inocula or nutrients were introduced and mineralization was measured for a further 10 d. Cell numbers were also measured together with 14C-uptake into microbial biomass. Freshly added 14C-phenanthrene was rapidly metabolised by the microorganisms. Neither the addition of a catabolic inoculum nor nutrients affected the extent of 14C-phenanthrene mineralization. Cell numbers remained constant over time, with only a small amount of the 14C-activity incorporated into the microbial biomass. This study indicated that the termination of mineralization was due to the removal of available phenanthrene and not decreasing cellular activity or cell death. The mineralization values also correlated with 14C-phenanthrene extractability using beta-cyclodextrin.

Bacteria↗

PubMed2006

Determining algal-available phosphorus in pulp and paper mill effluents: algal assays vs routine phosphorus analyses.

We determined the potentially algal-available P (P(aa)) in pulp and paper mill effluents by two bioassay techniques (a dual-culture assay and a batch approach) and compared it with chemically analysed P (total P, total dissolved P, reactive P, dissolved reactive P and dissolved hydrolysable P). The mean P(aa) given by the dual-culture assay was within a 40% range of that given by the batch approach. The P(aa) obtained by both bioassays differed from total P. Dissolved reactive P appeared to be the most readily available chemical P fraction, but other P fractions also contributed to P(aa). The analysis of reactive P, which involves direct staining of an unfiltered sample, best approximated the P(aa) given by the dual-culture assay (relative error 9%). The results suggest that assessment of eutrophying effluent P can be improved by analysing simple chemical P fractions in wastewater. The fractions to be analysed, however, may be site specific.

Biological Assay↗

PubMed1999

Role of Ca2+ availability to myofilaments and their sensitivity to Ca2+ in myocyte contractile dysfunction in heart failure.

OBJECTIVE: Contractile function is depressed at the isolated myocyte level in heart failure (HF), which could result from the decreased availability of intracellular calcium ([Ca2+]i) to the myofibrils and/or the depressed sensitivity of myofilaments to [Ca2+]i. However, the cellular basis of contractile dysfunction remains unestablished. METHODS: We isolated left ventricular myocytes from dogs with rapid pacing-induced HF. Cell shortening and [Ca2+]i transients were measured by indo-1 fluorescence and the myofilament Ca2+ sensitivity was analyzed by the shortening-[Ca2+]i relation in intact myocytes as well as by the pCa tension relation in skinned cells. RESULTS: Peak cell shortening magnitude was depressed in HF, associated with a parallel decrease of [Ca2+]i transient amplitude. There was a significant positive correlation between these two variables (r = 0.71, P < 0.01). In contrast, myofibrillar sensitivity to Ca2+, determined by both intact and skinned myocytes, was comparable between control and HF. Further, there was no significant difference in Ca2+ sensitivity between control and HF even at shorter (1.8 microns) or longer (2.2 microns) sarcomere length. CONCLUSIONS: Using both intact and skinned cellular preparations, a potential defect in myocyte contractile function in HF was a reduction in Ca2+ availability to the myofilaments, rather than the inherent defects in myofilament sensitivity to Ca2+.

Actin Cytoskeleton↗

PubMed2002

Sustained release and biological availability of dalarelin from the biodegradable coacervate microcapsules.

A complex coacervation method was used to prepare microcapsules containing 74.8 +/- 1.5% of the 125I labelled dalarelin incorporated in the gelatine-algin coating. Microcapsules (62 +/- 1.7%) formed, did not exceed a size of 108 microm. The high content of the small size allowed this formulation to be administered by intramuscular injection to rats. It was found that the 125I labelled dalarelin in the form of microcapsules had better bioavailability and was active longer in the rat when compared with the 125I labelled dalarelin solution injections. Dalarelin administered in the microcapsular form was characterised by a higher biological availability. The degree of relative biological availability was calculated as 123% for the dalarelin in the microcapsular form.

Alginates↗

PubMedDate not supplied

Ricobendazole kinetics and availability following subcutaneous administration of a novel injectable formulation to calves.

The plasma and abomasal fluid disposition kinetics of ricobendazole (RBZ) after subcutaneous (s.c.) administration of a novel injectable formulation to calves, and the comparative plasma availability after s.c. injection of RBZ and that obtained after oral treatment with albendazole (ABZ), were characterised. Six parasite-free Holstein calves received RBZ (solution 150 mg ml(-1)) by s.c. injection at 3.75 mg kg(-1) (Experiment 1). Experiment 2 was conducted in two experimental phases; in phase I, five calves (Group A) received RBZ by s.c. injection and five animals (Group B) were orally treated with ABZ (suspension 100 mg ml(-1)), at 5 mg kg(-1). Drug treatments were reversed for each group in phase II and given at 7.5 mg kg(-1). Samples of abomasal fluid (via cannula) and jugular blood were collected over 72 hours post-treatment and analysed by HPLC. RBZ and its sulphone metabolite were detected in plasma following its s.c. administration. RBZ was rapidly absorbed, reaching the plasma Cmax at 4.5 hours post-dosing. The sulphone metabolite followed a similar kinetic pattern. Both molecules were rapidly and extensively distributed into the abomasum, being detected in abomasal fluid between 30 minutes and 36 hours post-administration. An extensive plasma/abomasum exchange process, with ionic-trapping in the abomasum, accounted for the higher AUC value (>200 per cent) obtained for RBZ in abomasum compared with plasma. The s.c. treatment with RBZ formulated as a solution resulted in a significantly greater plasma availability (measured as ABZ sulphoxide) than the oral treatment with ABZ (suspension) given at the same dose rates.

Administration, Oral↗

PubMed2001

137Cs availability for soil to understory transfer in different types of forest ecosystems.

A quantitative analysis of 137Cs bioavailability in forest soils in the long term after the Chernobyl NPP accident based on a 3-year (1996-1998) investigation is presented. Five forest sites with different trees, composition and properties of soil were studied to identify factors determining radiocaesium transfer to different understory species. The following parameters were investigated: 137Cs activity concentrations and its speciation in various horizons of forest soil, accumulation of this radionuclide by different species of understory vegetation and distribution of root biomass in the soil profile. It has been shown that one decade after the deposition maximum 137Cs activity in soil of the experimental sites considered is located in different soil layers dependent on moisture regime, characteristics of litter and soil properties. A linear dependence between aggregated transfer factors for different species and groups of species of understory vegetation and exchangeable and available fractions of radiocaesium in soil was found. The vertical distribution of 137Cs activity, percentage of exchangeable radiocaesium in each horizon of litter and soil, as well as distribution of root systems (mycelia) over the soil profile are key factors governing variations in the availability of 137Cs for transfer to all forest understory components.

Biological Availability↗

PubMed2001

Availability of cadmium and zinc from sewage sludge to the flounder, Platichthys flesus, via a marine food chain.

This paper examines the potential availability to a demersal fish of cadmium and zinc associated with digested sewage sludge, via a food chain as well as directly from the sludge, and the tissue distribution and possible excretion of any accumulated cadmium and zinc. Radioactive tracer techniques were used in order to follow the food chain transfer of the metals. Flounder (Platichthys flesus) accumulated cadmium both directly from sludge (delivered in newly ingested unassimilated gutfuls in the amphipods) and in assimilated form from the tissues of the amphipod crustacean Corophium volutator that had been feeding on a sludge-sediment mixture. Cadmium from both sources could be excreted by the fish. The concentration of cadmium within the whole fish increased as the input of cadmium in the diet increased. Zinc, similarly, is available to the flounder both directly from sludge and from zinc accumulated in C. volutator. Only a limited increase in net accumulation of zinc by the flounder was observed upon increased inputs of zinc through the diet, perhaps indicating some regulation of body zinc concentration by the flounder.

Animals↗

PubMed2001

Towards the characterisation of heavy metals in dredged canal sediments and an appreciation of 'availability': two examples from the UK.

Canal sediments can act as sinks for a wide range of contaminants including heavy metals from various sources (e.g. industrial and waste water discharges). Dredging of canals is required to maintain navigational depth and prevent flooding. The sediments removed from canals are often disposed of to land, being deposited either straight on to the banks of the canal or, in recent years, in licensed disposal sites. The aim of this work was to investigate the nature of dredged sediment-derived soils and the heavy metals present in them. Two disposal sites in the United Kingdom (UK) were investigated and soil samples taken. A variety of analytical techniques were used, including Aqua regia digestion and sequential extraction, in order to assess the concentrations and associations of metals present. Diethylene triaminepenta-acetic acid extracts, performed to illustrate plant-available metal concentrations, reveal that up to 40% of the total extracted metals were in an 'available' form. Variations in metal concentrations with depth in the soil cores show a significant correlation with total organic carbon content.

Biological Availability↗

PubMed1997

Ascorbate availability and neurodegeneration in amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis is a fatal neurodegenerative disease in which upper and lower motoneurons progressively deteriorate and die. Neuronal damage is most evident in the lower central nervous system, and death generally occurs following central respiratory failure. Proposed and demonstrated mechanisms for amyotrophic lateral sclerosis are diverse, and include altered superoxide dismutase and neurofilament proteins, autoimmune attack, and hyperglutamatergic activity. However, they do not account for the late onset of the disease, its earlier onset in males, and the differential vulnerability of neurons located in the brainstem and spinal cord. It is proposed here that, within the context of a specific defect such as altered superoxide dismutase, age-dependent decline in ascorbate availability triggers the disease. A role for ascorbate, which is found in millimolar levels in neurons, is suggested by a number of consistencies: 1) superoxide radicals being a common substrate for superoxide dismutase and ascorbate; 2) a close association between central nervous system ascorbate levels and injury tolerance; 3) a steady decline in ascorbate plasma levels and cellular availability with age; 4) plasma ascorbate levels being lower in males; 5) an association of ascorbate release with motor activity in central nervous system regions, in vivo; 6) the coupling of brain-cell ascorbate release with glutamate uptake; 7) possible roles for ascorbate modulation of N-methyl-D-aspartate receptor activity; 9) the ability of ascorbate to prevent peroxynitrite anion formation; and 10) evidence supporting the scorbutic guinea pig as a model for amyotrophic lateral sclerosis. Emphasis is placed on the probable competition between superoxide dismutase and ascorbate within the context of a primary defect of metal-binding or metal access in high-concentration proteins such as superoxide dismutase and human heavy neurofilaments. Finally, distinct features of alpha-motoneuronal physiology suggest that cell physiological characteristics such as high metabolic activity and extensive calcium dynamics may render neurons differentially vulnerable in amyotrophic lateral sclerosis.

Amyotrophic Lateral Sclerosis↗

PubMedDate not supplied

Phosphoenolpyruvate availability and the biosynthesis of shikimic acid.

The impact of increased availability of phosphoenolpyruvate during shikimic acid biosynthesis has been examined in Escherichia coli K-12 constructs carrying plasmid-localized aroF(FBR) and tktA inserts encoding, respectively, feedback-insensitive 3-deoxy-d-arabino-heptulosonic acid 7-phosphate synthase and transketolase. Strategies for increasing the availability of phosphoenolpyruvate were based on amplified expression of E. coli ppsA-encoded phosphoenolpyruvate synthase or heterologous expression of the Zymomonas mobilis glf-encoded glucose facilitator. The highest titers and yields of shikimic acid biosynthesized from glucose in 1 L fermentor runs were achieved using E. coli SP1.lpts/pSC6.090B, which expressed both Z. mobilis glf-encoded glucose facilitator protein and Z. mobilis glk-encoded glucose kinase in a host deficient in the phosphoenolpyruvate:carbohydrate phosphotransferase system. At 10 L scale with yeast extract supplementation, E. coli SP1.lpts/pSC6.090B synthesized 87 g/L of shikimic acid in 36% (mol/mol) yield with a maximum productivity of 5.2 g/L/h for shikimic acid synthesized during the exponential phase of growth.

3-Deoxy-7-Phosphoheptulonate Synthase↗

PubMed2001

Impacts of aging on in vivo and in vitro measurements of soil-bound polycyclic aromatic hydrocarbon availability.

Ingestion of contaminated soil is an exposure pathway at approximately one-half of the Superfund sites in the United States. This study was designed to evaluate the impacts of aging in soil on the availability of polycyclic aromatic hydrocarbons (PAHs). Two coal tar (CT)-amended soils were prepared. One was aged for 270 days and the other was not aged. Both of these treatments were incorporated into pellets and fed to male Fischer 344 rats. Excretion of 1-hydroxypyrene (1-OHP) in urine and PAH concentrations in the liver were monitored as end points. Additionally, soil:water partitioning and desorption were measured as comparisons to the in vivo results. After 5 days of ingesting their respective treatments, rats in the aged soil group excreted 4.41 +/- 1.67 ppm 1-OHP/mg of pyrene ingested while rats in the unaged soil group excreted 5.27 +/- 1.37 ppm/mg of pyrene ingested. Animals fed aged CT soil had 0.051 +/- 0.011 ppm carcinogenic PAHs in livers/mg ingested while rats fed unaged CT soil had 0.063 +/- 0.037 ppm carcinogenic PAHs in livers/mg ingested. Partitioning and desorption results revealed a similar results. These results indicate that, at high application rates, soil contact time may not play as significant a role in determining availability as simple dispersion and sorption on soil.

Animals↗