Influence of Dairy Products on Bioavailability of Zinc from Other Food Products: A Review of Complementarity at a Meal Level

In this paper, we reviewed the role of dairy products in dietary zinc absorption. Dairy products can have a reasonable contribution for dietary zinc intake in Western diets, where dairy consumption is high. However, the co-ingestion of dairy products can also improve zinc absorption from other food products. Such improvements have been observed when dairy products (e.g., milk or yoghurt) were ingested together with food such as rice, tortillas or bread products, all of which are considered to be high-phytate foods with low inherent zinc absorption. For foods low in phytate, the co-ingestion of dairy products did not improve zinc absorption. Improved zinc absorption of zinc from high-phytate foods following co-ingestion with dairy products may be related to the beneficial effects of the citrate and phosphopeptides present in dairy products. Considering that the main dietary zinc sources in areas in the world where zinc deficiency is most prevalent are typically high in phytate, the inclusion of dairy products in meals may be a viable dietary strategy to improve zinc absorption.

Physiology-based toxicokinetic modelling of aluminium in rat and man

A sufficient quantitative understanding of aluminium (Al) toxicokinetics (TK) in man is still lacking, although highly desirable for risk assessment of Al exposure. Baseline exposure and the risk of contamination severely limit the feasibility of TK studies administering the naturally occurring isotope 27Al, both in animals and man. These limitations are absent in studies with 26Al as a tracer, but tissue data are limited to animal studies. A TK model capable of inter-species translation to make valid predictions of Al levels in humans-especially in toxicological relevant tissues like bone and brain-is urgently needed. Here, we present: (i) a curated dataset which comprises all eligible studies with single doses of 26Al tracer administered as citrate or chloride salts orally and/or intravenously to rats and humans, including ultra-long-term kinetic profiles for plasma, blood, liver, spleen, muscle, bone, brain, kidney, and urine up to 150 weeks; and (ii) the development of a physiology-based (PB) model for Al TK after intravenous and oral administration of aqueous Al citrate and Al chloride solutions in rats and humans. Based on the comprehensive curated 26Al dataset, we estimated substance-dependent parameters within a non-linear mixed-effect modelling context. The model fitted the heterogeneous 26Al data very well and was successfully validated against datasets in rats and humans. The presented PBTK model for Al, based on the most extensive and diverse dataset of Al exposure to date, constitutes a major advancement in the field, thereby paving the way towards a more quantitative risk assessment in humans.

Regional citrate anticoagulation "non-shock" protocol with pre-calculated flow settings for patients with at least 6 L/hour liver citrate clearance

BACKGROUND

Regional citrate anticoagulation (RCA) for the prevention of clotting of the extracorporeal blood circuit during continuous kidney replacement therapy (CKRT) has been employed in limited fashion because of the complexity and complications associated with certain protocols. Hypertonic citrate infusion to achieve circuit anticoagulation results in variable systemic citrate- and sodium load and increases the risk of citrate accumulation and hypernatremia. The practice of "single starting calcium infusion rate for all patients" puts patients at risk for clinically significant hypocalcemia if filter effluent calcium losses exceed replacement. A fixed citrate to blood flow ratio, personalized effluent and pre-calculated calcium infusion dosing based on tables derived through kinetic analysis enable providers to use continuous veno-venous hemo-diafiltration (CVVHDF)-RCA in patients with liver citrate clearance of at least 6 L/h.

METHODS

This was a single-center prospective observational study conducted in intensive care unit patients triaged to be treated with the novel pre-calculated CVVHDF-RCA "Non-shock" protocol. RCA efficacy outcomes were time to first hemofilter loss and circuit ionized calcium (iCa) levels. Safety outcomes were surrogate of citrate accumulation (TCa/iCa ratio) and the incidence of acid-base and electrolyte complications.

RESULTS

Of 53 patients included in the study, 31 (59%) had acute kidney injury and 12 (22.6%) had the diagnosis of cirrhosis at the start of CVVHDF-RCA. The median first hemofilter life censored for causes other than clotting exceeded 70 h. The cumulative incidence of hypernatremia (Na > 148 mM), metabolic alkalosis (HCO3- > 30 mM), hypocalcemia (iCa < 0.9 mM) and hypercalcemia (iCa > 1.5 mM) were 1/47 (1%), 0/50 (0%), 1/53 (2%), 1/53 (2%) respectively and were not clinically significant. The median (25th-75th percentile) of the highest TCa/iCa ratio for every 24-h interval on CKRT was 1.99 (1.91-2.13).

CONCLUSIONS

The fixed citrate to blood flow ratio, as opposed to a titration approach, achieves adequate circuit iCa (< 0.4 mm/L) for any hematocrit level and plasma flow. The personalized dosing approach for calcium supplementation based on pre-calculated effluent calcium losses as opposed to the practice of "one starting dose for all" reduces the risk of clinically significant hypocalcemia. The fixed flow settings achieve clinically desirable steady state systemic electrolyte levels.

Regional citrate anticoagulation with a substitute containing calcium for continuous hemofiltration in children

Regional citrate anticoagulation (RCA) was recommended as the first treatment option for adults by the Kidney Disease Improving Global Outcomes Kidney Foundation in 2012, for the characteristic of sufficient anticoagulation in vitro, but almost no anticoagulation in vivo. Traditionally, the substitute for RCA is calcium-free. This study investigated a simplified protocol of RCA for continuous hemofiltration (CHF) in children using a commercially available substitute containing calcium.An analytical, observational, retrospective study assessed 59 pediatric patients with 106 sessions and 3580 hours of CHF. Values before and after treatment were compared, including Na, ionic calcium (iCa) and HCO3 concentrations, pH, and the ratio of total calcium to iCa (T/iCa). In addition, in vivo and in vitro iCa, treatment time, sessions with continuous transmembrane pressure >200 mm Hg, and sessions with clotting and bleeding were recorded.The average treatment time was 33.8 ± 10.1 hours. In vitro, 88.5% of iCa achieved the target (0.25-0.35 mmol/L), and in vivo, 95.4% of iCa achieved the target (1.0-1.35 mmol/L). There were 8 sessions with a transmembrane pressure >200 mm Hg and 3 sessions with filters clotted. After treatment, there were 2, 1, and 2 sessions with T/iCa > 2.5 (implying citrate accumulation), iCa < 0.9 mmol/L, and iCa > 1.35 mmol/L. No sodium disorders were recorded. There were fewer cases of acidemia and more cases of alkalemia after treatment compared to before.RCA-CHF with a substitute containing calcium and close monitoring could be a safe and effective treatment for children. In addition, the calcium test site in vitro and the adjustment of citrate should be given strict attention.

Time-course assessment of the aggregation and metabolization of magnetic nanoparticles

To successfully develop biomedical applications for magnetic nanoparticles, it is imperative that these nanoreagents maintain their magnetic properties in vivo and that their by-products are safely metabolized. When placed in biological milieu or internalized into cells, nanoparticle aggregation degree can increase which could affect magnetic properties and metabolization. To evaluate these aggregation effects, we synthesized citric acid-coated iron oxide nanoparticles whose magnetic susceptibility can be modified by aggregation in agar dilutions and dextran-layered counterparts that maintain their magnetic properties unchanged. Macrophage models were used for in vitro uptake and metabolization studies, as these cells control iron homeostasis in the organism. Electron microscopy and magnetic susceptibility studies revealed a cellular mechanism of nanoparticle degradation, in which a small fraction of the particles is rapidly degraded while the remaining ones maintain their size. Both nanoparticle types produced similar iron metabolic profiles but these profiles differed in each macrophage model. Thus, nanoparticles induced iron responses that depended on macrophage programming. In vivo studies showed that nanoparticles susceptible to changes in magnetic properties through aggregation effects had different behavior in lungs, liver and spleen. Liver ferritin levels increased in these animals showing that nanoparticles are degraded and their by-products incorporated into normal metabolic routes. These data show that nanoparticle iron metabolization depends on cell type and highlight the necessity to assess nanoparticle aggregation in complex biological systems to develop effective in vivo biomedical applications.

STATEMENT OF SIGNIFICANCE

Magnetic iron oxide nanoparticles have great potential for biomedical applications. It is however imperative that these nanoreagents preserve their magnetic properties once inoculated, and that their degradation products can be eliminated. When placed in a biological milieu nanoparticles can aggregate and this can affect their magnetic properties and their degradation. In this work, we showed that iron oxide nanoparticles trigger the iron metabolism in macrophages, the main cell type involved in iron homeostasis in the organism. We also show that aggregation can affect nanoparticle magnetic properties when inoculated in animal models. This work confirms iron oxide nanoparticle biocompatibility and highlights the necessity to assess in vivo nanoparticle aggregation to successfully develop biomedical applications.

[DIAGNOSIS OF METABOLIC DISORDERS AND METAPHYLAXIS OF RECURRENT CALCIUM OXALATE UROLITHIASIS]

The paper presents the results of the 1-year screening of biochemical parameters of urine in female patient with recurrent calcium urate urolithiasis. Based on the data of quantitative X-ray phase analysis of the composition of stone and a complex of clinical and laboratory examination, reasons for recurrent stone formation were determined. The main reasons included hypocitraturia, hyperosmolarity of urine and uric acid diathesis. Therapy with citrate mixtures and adequate water schedule (daily urine--2-2.5 liters) for 10 weeks allowed to increase the urinary pH, led to 2.5-fold increase in daily urinary citrate excretion and getting rid of residual stones in both kidneys. The effect of citrate therapy lasted for a further six months after drug withdrawal. Subsequently, the daily urinary citrate excretion and pH decreased, but even after 8 months remained still above baseline values. Obviously, for high risk patients it is necessary to define the daily excretion of citrate, and diagnosis of hypocitraturia requires long course therapy with citrate mixtures, with a break ofnot more than six months and obligate maintenance of adequate diuresis.

Dual radiolabeling as a technique to track nanocarriers: the case of gold nanoparticles

Gold nanoparticles (AuNPs) have shown great potential for use in nanomedicine and nanotechnologies due to their ease of synthesis and functionalization. However, their apparent biocompatibility and biodistribution is still a matter of intense debate due to the lack of clear safety data. To investigate the biodistribution of AuNPs, monodisperse 14-nm dual-radiolabeled [¹⁴C]citrate-coated [¹⁹⁸Au]AuNPs were synthesized and their physico-chemical characteristics compared to those of non-radiolabeled AuNPs synthesized by the same method. The dual-radiolabeled AuNPs were administered to rats by oral or intravenous routes. After 24 h, the amounts of Au core and citrate surface coating were quantified using gamma spectroscopy for ¹⁹⁸Au and liquid scintillation for the ¹⁴C. The Au core and citrate surface coating had different biodistribution profiles in the organs/tissues analyzed, and no oral absorption was observed. We conclude that the different components of the AuNPs system, in this case the Au core and citrate surface coating, did not remain intact, resulting in the different distribution profiles observed. A better understanding of the biodistribution profiles of other surface attachments or cargo of AuNPs in relation to the Au core is required to successfully use AuNPs as drug delivery vehicles.

Alternating magnetic field-induced hyperthermia increases iron oxide nanoparticle cell association/uptake and flux in blood-brain barrier models

PURPOSE

Superparamagnetic iron oxide nanoparticles (IONPs) are being investigated for brain cancer therapy because alternating magnetic field (AMF) activates them to produce hyperthermia. For central nervous system applications, brain entry of diagnostic and therapeutic agents is usually essential. We hypothesized that AMF-induced hyperthermia significantly increases IONP blood-brain barrier (BBB) association/uptake and flux.

METHODS

Cross-linked nanoassemblies loaded with IONPs (CNA-IONPs) and conventional citrate-coated IONPs (citrate-IONPs) were synthesized and characterized in house. CNA-IONP and citrate-IONP BBB cell association/uptake and flux were studied using two BBB Transwell(®) models (bEnd.3 and MDCKII cells) after conventional and AMF-induced hyperthermia exposure.

RESULTS

AMF-induced hyperthermia for 0.5 h did not alter CNA-IONP size but accelerated citrate-IONP agglomeration. AMF-induced hyperthermia for 0.5 h enhanced CNA-IONP and citrate-IONP BBB cell association/uptake. It also enhanced the flux of CNA-IONPs across the two in vitro BBB models compared to conventional hyperthermia and normothermia, in the absence of cell death. Citrate-IONP flux was not observed under these conditions. AMF-induced hyperthermia also significantly enhanced paracellular pathway flux. The mechanism appears to involve more than the increased temperature surrounding the CNA-IONPs.

CONCLUSIONS

Hyperthermia induced by AMF activation of CNA-IONPs has potential to increase the BBB permeability of therapeutics for the diagnosis and therapy of various brain diseases.

Toxicity, bioaccumulation, and biotransformation of silver nanoparticles in marine organisms

The toxicity, bioaccumulation, and biotransformation of citrate and polyvinylpyrrolidone (PVP) coated silver nanoparticles (NPs) (AgNP-citrate and AgNP-PVP) in marine organisms via marine sediment exposure was investigated. Results from 7-d sediment toxicity tests indicate that AgNP-citrate and AgNP-PVP did not exhibit toxicity to the amphipod (Ampelisca abdita) and mysid (Americamysis bahia) at ≤75 mg/kg dry wt. A 28-d bioaccumulation study showed that Ag was significantly accumulated in the marine polychaete Nereis virens (N. virens) in the AgNP-citrate, AgNP-PVP and a conventional salt (AgNO3) treatments. Synchrotron X-ray absorption spectroscopy (XAS) results showed the distribution of Ag species in marine sediments amended with AgNP-citrate, AgNP-PVP, and AgNO3 was AgCl (50–65%) > Ag2S (32–42%) > Ag metal (Ag0) (3–11%). In N virens, AgCl (25–59%) and Ag2S (10–31%) generally decreased and, Ag metal (32–44%) increased, relative to the sediments. The patterns of speciation in the worm were different depending upon the coating of the AgNP and both types of AgNPs were different than the AgNO3 salt. These results show that the AgNP surface capping agents influenced Ag uptake, biotransformation, and/or excretion. To our knowledge, this is the first demonstration of the bioaccumulation and speciation of AgNPs in a marine organism (N. virens).

[Hepatoduodenal circulation and excretion of the new GABA derivative citrocard]

Pharmacokinetic investigation of a new gamma-aminobutyric acid (GABA) derivative cirtocard showed that, upon the intravenous introduction, the drug is determined in high concentrations in organs of elimination--the liver and kidneys. The tissue accessibility amounts to 1.341 for the liver and 4.053 for the kidneys and the separation factor is 1.041 for the liver and 4.486 for the kidneys. The study of drug excretion showed that cirtocard is determined in the urine for 48 h, its nephritic clearance being 0.047 L/h and extra-nephritic clearance, 0.33 L/h. For the unchanged substance, a large significance ofhepatoduodenal circulation is low probable, since no more than 1 - 2% of the introduced dose was isolated with bile over entire experiment. It is established that the removal of the unchanged substance does not exceed 10% of the introduced dose. There is high probability of hepatoduodenal circulation and excretion of the preparation in the form of metabolites.

Comparative in vitro study of the intestinal absorption of titanium and iron in rats

Rat Everted Gut Sac (EGS) model was employed to study the intestinal uptake of titanium and iron. Incubation of freshly prepared rat EGS in Earle's medium pH = 7.4 containing titanium showed that the absorption of titanium as well as iron was a dose dependent process. Ascorbic acid enhanced the absorption of both metal ions, while NaF (1 mM) as an inhibitor of glycolytic energy supply, decreased their absorption. The Na+-K+ ATPase inhibitor, ouabain (1 mM) reduced intestinal absorption of Titanium. This suggests that titanium uptake is an active transport process as is iron uptake. Iron absorption was reduced approximate by 17% when titanium was presented to incubation medium EGS whereas, the absorption of titanium was decreased by 35% when iron was added to the reaction mixture.

Calcium flux in continuous venovenous haemodiafiltration with heparin and citrate anticoagulation

BACKGROUND

Calcium chelation with citrate is an effective alternative to heparin for anticoagulation of the extracorporeal circuit during continuous venovenous haemodiafiltration (CVVHD-F). Calcium release occurs upon citrate metabolism; however, ultrafiltration of citrate-bound and free ions also occurs.

OBJECTIVE

To quantify calcium loss and improve understanding of calcium homeostasis in CVVHD-F.

METHODS

Calcium loss was prospectively quantified from heparinised and citrated circuits in consecutive intensive care patients requiring CVVHD-F. CVVHD-F prescription and anticoagulation choice was by the treating intensivist using commercial solutions (Gambro, Lundia, Sweden). Sample sets comprising arterial, prefilter and postfilter blood and an effluent sample were analysed for ionised total calcium (iCa(2+)) and magnesium levels. Flow rates were then used to calculate calcium flux. Citrate dose (predilution rate) and calcium replacement followed unit protocols to maintain a circuit iCa(2+) concentration of 0.3-0.5 mmol/L and an arterial iCa(2+) concentration of 0.8-1.1 mmol/L.

RESULTS

26 heparinised circuits and 22 citrated circuits in 13 patients were included; 334 sample sets were tested. For target extracorporeal blood flows of 200 mL/min, mean predilution Prismocitrate 10/2 flows were 1660 mL/h, delivering 2.42 mmol citrate per litre of blood. For heparin, mean predilution flows of Hemosol B0 were 2058mL/h. Mean calcium loss was 4.01 mmol/h from citrate anticoagulated circuits versus a gain of 0.24mmol/h from heparinised circuits (P < 0.001). Despite calcium replacement, citrate patients experienced a mean calcium loss of 1.12 mmol/h (SD, 0.70; 95% CI 1.0-1.22mmol/h; P < 0.001). Calculated effective diffusion volume (Q(E)) for calcium was closer to total blood water volume in heparin circuits and closer to plasma water volume in citrate circuits.

CONCLUSIONS

Despite supplementation to maintain arterial iCa(2+) levels, citrate anticoagulation results in a net calcium deficit. An equation for estimating required citrate dose may allow revision of citrate dosing protocols.

Effect of dentin treatment time with tetraclean on its residual antibacterial activity

The goal of this study was to evaluate the effect of dentin treatment duration (10 minutes, 24 hours, and seven days) with Tetraclean on its residual antibacterial activity in bovine root dentin. Results showed that the number of colony-forming units in all three experimental groups was zero at the first culture. Furthermore, the 10-minute group and seven-day group demonstrated the highest and the lowest number of colony-forming units, respectively.

[Bioequivalence evaluation of orally disintegrating tablet of pentoxyverine citrate]

OBJECTIVE

To evaluate the bioequivalence of orally disintegrating tablets of pentoxyverine citrate (tested preparation) in healthy male volunteers.

METHODS

A single oral dose of the tested and reference preparations at 25 mg were given to 20 healthy volunteers in a randomized two-period cross-over design. Plasma pentoxyverine citrate concentrations were determined by HPLC-MS/ESI+ method. The pharmacokinetic parameters were calculated and the bioequivalence of the two preparations were evaluated using DAS program.

RESULTS

The Tmax, Cmax, AUC0 15 and AUC0infinity of tested and reference preparations were 1.62-/+0.75 h and 2.52-/+1.21 h, 62.28-/+33.06 microg/L and 59.72-/+33.25 microg/L, 234.44-/+130.01 microg.h.L(-1) and 228.77-/+129.24 microg.h.L(-1), 246.80-/+136.19 microg.h.L(-1) and 244.11-/+140.73 microg.h.L(-1), respectively. The 90% confidence interval of C(max), AUC0 15 and AUC0infinity of tested preparations were 81.4%-138.4%, 86.0%-123.3% and 86.5%-121.2%, respectively.

CONCLUSION

The tested and reference preparations are bioequivalent.

Comparative tissue uptake and cellular deposition of three different plutonium chemical forms in rats

PURPOSE

To evaluate the influence of the chemical form of plutonium (Pu) on its distribution in tissues and within liver cells populations.

MATERIALS AND METHODS

Groups of male Sprague-Dawley rats were contaminated by intravenous injection of either Pu citrate, Pu nitrate or Pu phytate. Pu content was determined in various tissues at different times after injection. Pu liver distribution was analysed by autoradiography and after cellular separation.

RESULTS

Biokinetic studies indicate that Pu citrate and Pu nitrate predominantly retained in the skeleton within the first hours after injection, whereas most of the Pu was in the liver after injection of Pu phytate. Autoradiographs showed that Pu citrate was homogeneously distributed in the liver, while Pu nitrate accumulated into 'hot points'. Pu phytate showed an intermediate distribution pattern. Hepatic cell separation revealed a difference of uptake between the two cell types depending on the chemical form of injected Pu, and on the time after contamination.

CONCLUSIONS

Distinct Pu behaviour was observed for biokinetics, retention and liver distribution. The large differences noted between citrate, nitrate and phytate might be explained by differences in systemic and hepatic transport.

Topical application of acidified nitrite to the nail renders it antifungal and causes nitrosation of cysteine groups in the nail plate

BACKGROUND

Topical treatment of nail diseases is hampered by the nail plate barrier, consisting of dense cross-linked keratin fibres held together by cysteine-rich proteins and disulphide bonds, which prevents penetration of antifungal agents to the focus of fungal infection. Acidified nitrite is an effective treatment for tinea pedis. It releases nitric oxide (NO) and other NO-related species. NO can react with thiol (-SH) groups to form nitrosothiols (-SNO).

OBJECTIVES

To determine whether acidified nitrite can penetrate the nail barrier and cure onychomycosis, and to determine whether nitrosospecies can bind to the nail plate.

METHODS

Nails were treated with a mixture of citric acid and sodium nitrite in a molar ratio of 0.54 at either low dose (0.75%/0.5%) or high dose (13.5%/9%). Immunohistochemistry, ultraviolet-visible absorbance spectroscopy and serial chemical reduction of nitrosospecies followed by chemiluminescent detection of NO were used to measure nitrosospecies. Acidified nitrite-treated nails and the nitrosothiols S-nitrosopenicillamine (SNAP) and S-nitrosoglutathione (GSNO) were added to Trichophyton rubrum and T. mentagrophytes cultures in liquid Sabouraud medium and growth measured 3 days later. Thirteen patients with positive mycological cultures for Trichophyton or Fusarium species were treated with topical acidified nitrite for 16 weeks. Repeat mycological examination was performed during this treatment time.

RESULTS

S-nitrothiols were formed in the nail following a single treatment of low- or high-dose sodium nitrite and citric acid. Repeated exposure to high-dose acidified nitrite led to additional formation of N-nitrosated species. S-nitrosothiol formation caused the nail to become antifungal to T. rubrum and T. mentagrophytes. Antifungal activity was Cu(2+) sensitive. The nitrosothiols SNAP and GSNO were also found to be antifungal. Topical acidified nitrite treatment of patients with onychomycosis resulted in > 90% becoming culture negative for T. rubrum.

CONCLUSIONS

Acidified nitrite cream results in the formation of S-nitrosocysteine throughout the treated nail. Acidified nitrite treatment makes a nail antifungal. S-nitrosothiols, formed by nitrosation of nail sulphur residues, are the active component. Acidified nitrite exploits the nature of the nail barrier and utilizes it as a means of delivery of NO/nitrosothiol-mediated antifungal activity. Thus the principal obstacle to therapy in the nail becomes an effective delivery mechanism.

A method for evaluating the fluctuations in the intensity of substance transport between blood and bones in the predominant direction

The dynamics of fluctuations in the intensity of the blood-bone flow of substances in the predominant and opposite directions was evaluated using the percent radioactivity difference coefficient and its graphic presentation. The technology of calculating this coefficient is described.

Tolerable infusion rate of citrate based on clinical signs and the electrocardiogram in conscious dogs

BACKGROUND & AIMS

The possible clinical significance of the toxic effects of citrate has not yet been fully clarified. This study was therefore conducted to confirm the toxicity and determine the tolerable infusion rate of citrate administered by rapid intravenous infusion to conscious dogs.

METHODS

Citrate solutions were infused via the cephalic vein of 4 conscious dogs at 0.33, 0.67, or 1.33mmol/kg/h up to 1.33mmol/kg. Clinical signs and the electrocardiogram were observed during and after infusion. Serum citrate and ionized calcium levels were also measured.

RESULTS

Although the mean citrate level increased in accordance with the infusion rate, the calcium level decreased. No significant changes in clinical signs or the electrocardiogram were observed during infusion at 0.33mmol/kg/h despite an increase in the serum citrate level to 1.22+/-0.11mmol/l (pre-infusion value: 0.38+/-0.01mmol/l) and a decrease in the serum calcium level to 1.28+/-0.03mmol/l (pre-infusion value: 1.50+/-0.05mmol/l). Vomiting and QTc prolongation were observed at 0.67mmol/kg/h or higher. Salivation and tachycardia were observed at 1.33mmol/kg/h.

CONCLUSIONS

Based on clinical signs and the electrocardiogram, the tolerable infusion rate of citrate in conscious dogs is concluded to be 0.33mmol/kg/h.

Characterization of OpdH, a Pseudomonas aeruginosa porin involved in the uptake of tricarboxylates

The Pseudomonas aeruginosa outer membrane is intrinsically impermeable to many classes of antibiotics, due in part to its relative lack of general uptake pathways. Instead, this organism relies on a large number of substrate-specific uptake porins. Included in this group are the 19 members of the OprD family, which are involved in the uptake of a diverse array of metabolites. One of these porins, OpdH, has been implicated in the uptake of cis-aconitate. Here we demonstrate that this porin may also enable P. aeruginosa to take up other tricarboxylates. Isocitrate and citrate strongly and specifically induced the opdH gene via a mechanism involving derepression by the putative two-component regulatory system PA0756-PA0757. Planar bilayer analysis of purified OpdH demonstrated that it was a channel-forming protein with a large single-channel conductance (230 pS in 1 M KCl; 10-fold higher than that of OprD); however, we were unable to demonstrate the presence of a tricarboxylate binding site within the channel. Thus, these data suggest that the requirement for OpdH for efficient growth on tricarboxylates was likely due to the specific expression of this large-channel porin under particular growth conditions.

Maximum acceptable infusion rate of citrate: relationship between blood ionized calcium levels and cardiovascular effects in anesthetized rats

BACKGROUND & AIMS

Citrate is a useful chemical as a stabilizer for infusion solutions. However, cardiovascular depression associated with ionized hypocalcemia has been observed during massive transfusion of citrated blood products. The goal of the present study was to determine the maximum acceptable infusion rate of citrate and safe blood ionized calcium (Ca(2+)) levels.

METHODS

Citrate was administered intravenously to anesthetized rats at infusion rates between 0.5 and 2.0 mmol/kg/h for 4 h. Changes in heart rate (HR), arterial blood pressure, and the concentrations of plasma citrate and blood Ca(2+) were measured.

RESULTS

Infusion of citrate caused decreases in arterial blood pressure and HR, but no severe cardiovascular depression was observed at infusion rates up to 1.0 mmol/kg/h. Plasma citrate levels reached a steady state within 1 h after the start of infusion at up to 1.0 mmol/kg/h. The concentrations of plasma citrate and blood Ca(2+) were 1.35 and 0.89 mmol/l, respectively, 4h after the start of infusion at 1.0 mmol/kg/h.

CONCLUSIONS

The maximum acceptable infusion rate of citrate was 1.0 mmol/kg/h in anesthetized rats, and no severe cardiovascular effects were observed when the blood Ca(2+) level was 0.89 mmol/l or above.

Functional characterization of Na+-coupled citrate transporter NaC2/NaCT expressed in primary cultures of neurons from mouse cerebral cortex

Neurons are known to express a high-affinity Na+ -coupled dicarboxylate transporter(s) for uptake of tricarboxylic acid cycle intermediates, such as alpha-ketoglutarate and malate, which are precursors for neurotransmitters including glutamate and gamma-aminobutyric acid. There is, however, little information available on the molecular identity of the transporters responsible for this uptake process in neurons. In the present study, we investigated the characteristics of Na+ -dependent citrate transport in primary cultures of neurons from mouse cerebral cortex and established the molecular identity of this transport system as the Na+ -coupled citrate transporter (NaC2/NaCT). Reverse transcriptase (RT)-PCR and immunocytochemical analyses revealed that only NaC2/NaCT was expressed in mouse cerebrocortical neurons but not in astrocytes. Uptake of citrate in neurons was Na+ -dependent, Li+ -sensitive, and saturable with the Kt value of 12.3 microM. This Kt value was comparable with that in the case of Na+ -dependent succinate transport (Kt = 9.2 microM). Na+ -activation kinetics revealed that the Na+ -to-citrate stoichiometry was 3.4:1 and concentration of Na+ necessary for half-maximal activation (K0.5(Na)) was 45.7 mM. Na+ -dependent uptake of [14C]citrate (18 microM) was significantly inhibited by unlabeled citrate as well as dicarboxylates such as succinate, malate, fumarate, and alpha-ketoglutarate. This is the first report demonstrating the molecular identity of the Na+ -coupled di/tricarboxylate transport system expressed in neurons as NaC2/NaCT, which can transport the tricarboxylate citrate as well as dicarboxylates such as succinate, alpha-ketoglutarate, and malate.

Biodistribution of 225Ra citrate in mice: retention of daughter radioisotopes in bone

Alpha-particle-emitting radionuclides have potential for therapy of localized disease due to their high linear energy transformation and short pathlengths. Radiometals that home naturally to bone can be exploited for this purpose, and 223Ra (t(1/2)=11.4 days) recently has been studied for therapy of bone tumors in mice and rats. Actinium-225 (t(1/2)=10 days) is also an attractive radioisotope for endoradiotherapy. In a single decay of a 225Ac nucleus and its subsequent decay daughters, over 27 MeV ( approximately 90% of total energy) is released by sequential emission of four alpha particles, ranging in energy from 5.7 to 8.4 MeV. Although Ac3+ does not home naturally to bone, its parent radioisotope 225Ra (beta(-), t(1/2)=15 days) can be used as an in vivo source for 225Ac. Thus, injection of 225Ra takes advantage of the bone-homing properties of radium coupled with the significant amount of energy released from the 225Ac decay chain. Our data confirm that a large fraction of radium citrate injected intravenously into mice localizes rapidly in bone. Injected doses per gram (ID/g) for 225Ra range from 25% in skull to about 10% in sternum. Once deposited, the 225Ra remains in the bone with a biological half life of >40 days. Furthermore, >95% of the daughter radioisotope, 225Ac, is retained in the bone. However, a significant fraction of one of the daughter radioisotopes, 213Bi, is found in kidney. The biodistribution data indicate that 225Ra injection should be a powerful agent for killing cells associated with bone; however, the toxicity of this radioisotope which is similar to that of other alpha emitters limits the dose that can be tolerated.

Placebo-controlled study of intravenous magnesium supplementation during large-volume leukapheresis in healthy allogeneic donors

BACKGROUND

Marked decreases in ionized magnesium (iMg) levels occur during large-volume leukapheresis (LVL); however, the effect of intravenous (IV) magnesium supplementation in this setting has not been carefully studied.

STUDY DESIGN AND METHODS

Thirty healthy allogeneic peripheral blood progenitor cell donors receiving citrate anticoagulant with IV calcium prophylaxis were randomized to receive either IV magnesium (0.2 mg Mg per mL acid citrate dextrose-A) or placebo during LVL, with a double-blind design.

RESULTS

Thirty subjects underwent 75 LVL pro- cedures, 37 with magnesium and 38 with placebo. Group characteristics were similar for sex, weight, citrate infusion rate (1.36 mg/kg/min vs. 1.37 mg/kg/min), and volume processed (16 L vs. 17 L). Serum iMg levels remained within the reference range with magnesium supplementation, but decreased 39+/-11 percent below baseline (p<10(-10)) after placebo, with greater decreases after consecutive procedures. Subjects receiving magnesium had more vigorous parathyroid hormone responses and higher glucose levels and also tended to have higher serum potassium and ionized calcium levels. Mild paresthesias, coldness, and nausea occurred in 28, 20, and 7 percent of donors, respectively, with no significant differences between groups. Severe symptoms (chest tightness) occurred in only one subject receiving placebo.

CONCLUSION

IV magnesium supplementation exerts a significant impact on serum magnesium levels, but does not reduce the frequency or severity of the relatively mild citrate-related effects observed in LVL performed with continuous IV calcium prophylaxis.

Hypocitraturia as a risk factor for nephrocalcinosis after kidney transplantation

Calcium-oxalate crystal deposition in kidney transplant biopsy specimen led us to investigate the impact of calcineurin inhibitor treatment on urinary excretion of lithogenic and stone inhibitory substances in 53 children after successful kidney transplantation (KTx) receiving cyclosporine A (CsA) or tacrolimus. We compared the values obtained with those of 12 patients with recurrent nephrotic syndrome under CsA and of 6 patients with Rasmussen encephalitis (RE) under tacrolimus therapy. Renal ultrasound examinations were repeatedly performed. Hypocitraturia was found in 69% of patients, with KTx patients having a significantly lower urinary citrate excretion than those receiving calcineurin inhibitors for other reasons. Secondly, we found hyperoxaluria in 35% of patients, again especially in those after KTx. No significant difference in urinary substances was seen comparing CsA with tacrolimus treatment. Urolithiasis was found in one and calcium-oxalate crystal deposition in biopsy specimen of three KTx patients. Calcineurin inhibitor treatment can lead to significant hypocitraturia, especially in patients after KTx receiving the highest dose of medication. Hyperoxaluria is primarily the result of a removal of significant body oxalate stores, deposited during dialysis, but may not be suspected as a specific side effect of calcineurin inhibitor therapy. Both findings can increase the risk for urolithiasis or nephrocalcinosis.

Transport mechanism for aluminum citrate at the blood–brain barrier: kinetic evidence implies involvement of system Xc− in immortalized rat brain endothelial cells

Although accumulation of aluminum (Al) in the brain is known to cause neurodegenerative disorders and to be regulated mainly by the blood-brain barrier (BBB), the mechanism responsible for Al transport at the BBB has not been clarified yet. In this study, we investigated what kind of transporter is involved in the transport of Al citrate, which is the major species of Al in the brain, at the BBB using a rat immortalized brain endothelial cell line (RBEC1), focusing on the glutamate transporter family. The uptake of Al citrate showed temperature- and concentration-dependency, and did not require an inwardly directed Na+-gradient as a driving force, ruling out the involvement of Na+-dependent glutamate transporters in its transport. By RT-PCR, in RBEC1, there were mRNAs for the components of a Na+-independent glutamate transporter, system Xc-. L-Glutamate and L-cystine, representative ligands for system Xc-, significantly inhibited the uptake of Al citrate, and loading of them into the cells resulted in stimulation of its uptake in RBEC1. These results demonstrated that Al citrate is taken up into RBEC1 via system Xc-, and that this system might play an important role in Al citrate transport at the BBB.

Improving the delivery of continuous renal replacement therapy using regional citrate anticoagulation

AIMS

Regional citrate anticoagulation during acute renal replacement therapy (RRT) effectively prevents extracorporeal thrombosis and avoids bleeding risk. There have been a number of citrate anticoagulation protocols published; but a simple and predictable scheme with standardized components and procedures, as well as clearly defined citrate pharmacokinetics, is needed for continuous RRT (CRRT) that is now used frequently in the critical care setting. The present study sets forth methodology with standardized blood flow and dialysate composition, and with citrate and calcium infusions that are quantitatively linked to extracorporeal blood flow rate--a predictable and easily replicated CRRT paradigm.

MATERIALS AND METHODS

CRRT using continuous venovenous hemofiltration with dialysis (CVVHD) was standardized using 150-200 ml/min blood flow, calcium-free dialysate with only moderate sodium (135 mEq/l) and bicarbonate (28 mEq/l) concentrations, and ultrafiltration limited to that needed for overall fluid balance in the intensive care unit. Citrate infusion (ACD-A solution) into the extracorporeal blood and calcium repletion in blood returned to the patient were proportional to blood flow. Anticoagulation was accomplished by keeping extracorporeal ionized calcium below 0.4 mM/l. Filter performance, citrate removal and changes in calcium, sodium and alkali were evaluated longitudinally.

RESULTS

CVVHD using this protocol delivered urea clearance exceeding 2 l/h (48 l/d) when filter function was sustained. Filter longevity was markedly improved using citrate when compared with standard heparin anticoagulation, and nursing time spent on initiating and troubleshooting CRRT was approximately halved using this protocol. Sieving coefficients for urea, creatinine and citrate were approximately 0.9 and were sustained through nearly 3 days of filter use. Citrate clearance and removal were quantitatively linked to dialysate and ultrafiltration flow, resulting in 35-50% direct removal of the citrate-calcium chelate and reduced systemic citrate load. Serum tonicity and acid-base status were not problematic. The only notable side effect was modest calcium accumulation that necessitated reduction in calcium repletion rate.

CONCLUSIONS

CVVHD is well suited to regional citrate anticoagulation. The present protocol is straightforward and predictable, with minor metabolic consequences that can be anticipated and adjusted. These results commend regional citrate anticoagulation to wider application.

Differing effects of two iron compounds on experimental arthritis, TNF-α levels and immune response in mice

The effects of ferric-sorbitol-citrate and ferric-citrate on the severity of experimental arthritis, TNF-alpha secretion and the immune status were examined in mice. Arthritis was induced by footpad injection of methylated BSA and intraperitoneal injection of Bordetella pertussis. Joint and footpad swelling were measured weekly by a caliper. TNF-alpha serum levels were measured by ELISA. The immune status was determined by the response of mouse lymphocytes to ConA in vitro and by the antigen-presenting cell assay. Experimental arthritis was aggravated by ferric-citrate, whereas ferric-sorbitol-citrate did not promote it. If applied to normal (non-arthritic) mice three times a week for 4 weeks, ferric-sorbitol-citrate stimulated isolated splenocytes to increase production of TNF-alpha, the function of antigen-presenting cells and lymphocyte proliferation in response to ConA in vitro. TNF-alpha production by cultured splenocytes was also stimulated. In mice with antigen-induced arthritis, iron compounds did not additionally stimulate TNF-alpha production. Thus, we have shown that ferric-sorbitol-citrate stimulated TNF-alpha production, antigen-presenting cell activity and cellular immune response. Development of antigen-induced arthritis and TNF-alpha production in arthritic mice were not stimulated.

Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study

Published data on the bioavailability of various Mg preparations is too fragmented and scanty to inform proper choice of Mg preparation for clinical studies. In this study, the relative bioavailability of three preparations of Mg (amino-acid chelate, citrate and oxide) were compared at a daily dose of 300 mg of elemental Mg in 46 healthy individuals. The study was a randomised, double-blind, placebo-controlled, parallel intervention, of 60 days duration. Urine, blood and saliva samples were taken at baseline, 24 h after the first Mg supplement was taken ('acute' supplementation) and after 60 days of daily Mg consumption ('chronic' supplementation). Results showed that supplementation of the organic forms of Mg (citrate and amino-acid chelate) showed greater absorption (P = 0.033) at 60 days than MgO, as assessed by the 24-h urinary Mg excretion. Mg citrate led to the greatest mean serum Mg concentration compared with other treatments following both acute (P = 0.026) and chronic (P = 0.006) supplementation. Furthermore, although mean erythrocyte Mg concentration showed no differences among groups, chronic Mg citrate supplementation resulted in the greatest (P = 0.027) mean salivary Mg concentration compared with all other treatments. Mg oxide supplementation resulted in no differences compared to placebo. We conclude that a daily supplementation with Mg citrate shows superior bioavailability after 60 days of treatment when compared with other treatments studied.

Influence of enteric citric acid on the release profile of 4-aminopyridine from HPMC matrix tablets

A weakly basic experimental drug, 4-aminopyridine (4-AP), was taken as a model to study the influence of enteric citric acid (ECA) on the release profile from hydroxypropyl methylcellulose (HPMC) matrices, to set up a system bringing about gradual release of the drug. For this purpose, powder mixtures were wet granulated with water and compressed with a hydraulic press at 55 MPa. Dissolution studies were made using first 900 ml HCl 0.1 N, and then phosphate buffer pH 7.4. Dissolution curves were described by M(t)/M(inf)=kt(n). As physically expected, increasing proportions (2-9%) of the in acid insoluble ECA decreased the release rate. In an acid medium, ECA acts as a physical barrier obstructing the diffusion path, dissolving after the pH change to 7.4. Both circumstances flattening the release profile. Apparent zero order release was observed at ECA concentrations of about 10%. The presence of ECA compensates the effect of decreased solubility of 4-AP at pH 7.4. Unexpectedly, higher ECA proportions (10-50%) act increasing the dissolution rate. This is attributed to a void space formation around the insoluble ECA, after HPMC hydration, which percolates after a critical ECA proportion of approximately 10%. Moreover, decreasing release constant values (k) show a logarithmic relationship with increasing values of the exponent (n). This indicates that an apparent zero-order release can be obtained at a given release constant.

Urine stone risk factors in nephrolithiasis patients with and without bowel disease

BACKGROUND

The prevalence of nephrolithiasis among patients with bowel disease is higher than in the general population. We examined urine stone risk factors and clinical characteristics of these patients, contrasted with a large group of stone forming patients without systemic disease.

METHODS

A total of 180 patients with bowel disease were compared with a group of 2048 nephrolithiasis patients with calcium or uric acid stones and without systemic diseases. Bowel diseases included inflammatory bowel disease with and without bowel resections, bowel resections from cancer or trauma, and bypass procedures for obesity or hypercholesterolemia. Urine stone risk factors, stone rates, stone compositions, and creatinine clearance were measured.

RESULTS

Compared to ordinary stone forming patients, bowel patients formed stones higher in rate of recurrence and in uric acid content. Uric acid content was highest when colon surgery had occurred. Urine volumes were low among all bowel patients except those with a bypass. Average creatinine clearance values were low among all bowel patients. Urine oxalate excretion was modestly elevated after small bowel resection, but very high with bypass. Supersaturations were increased mainly by low urine volume and-for uric acid-low pH. Patients with no surgery were indistinguishable from routine stone formers.

CONCLUSIONS

Low urine volume and pH are the main stone-forming abnormalities in bowel disease patients. Hyperoxaluria is extreme after bypass, but only modest after small bowel surgery. In the absence of surgery, bowel disease patients with stones cannot be distinguished from common stone formers by comprehensive stone risk measurements.

Manganese distribution across the blood-brain barrier. I. Evidence for carrier-mediated influx of managanese citrate as well as manganese and manganese transferrin

Manganese (Mn) is an essential element and a neurotoxicant. Regulation of Mn movement across the blood-brain barrier (BBB) contributes to whether the brain Mn concentration is functional or toxic. In plasma, Mn associates with water, small molecular weight ligands and proteins. Mn speciation may influence the kinetics of its movement through the BBB. In the present work, the brain influx rates of 54Mn2+, 54Mn citrate and 54Mn transferrin (54Mn Tf) were determined using the in situ brain perfusion technique. The influx rates were compared to their predicted diffusion rates, which were determined from their octanol/aqueous partitioning coefficients and molecular weights. The in situ brain perfusion fluid contained 54Mn2+, 54Mn citrate or 54Mn Tf and a vascular volume/extracellular space marker, 14C-sucrose, which did not appreciably cross the BBB during these short experiments (15-180 s). The influx transfer coefficient (Kin) was determined from four perfusion durations for each Mn species in nine brain regions and the lateral ventricular choroid plexus. The brain Kin was (5-13) x 10(-5), (3-51) x 10(-5), and (2-13) x 10(-5) ml/s/g for 54Mn2+, 54Mn citrate, and 54Mn Tf, respectively. Brain Kin values for any one of the three Mn species generally did not significantly differ among the nine brain regions and the choroid plexus. However, the brain Kin for Mn citrate was greater than Mn2+ and Mn Tf Kin values in a number of brain regions. When compared to calculated diffusion rates, brain Kin values suggest carrier-mediated brain influx of 54Mn2+, 54Mn citrate and 54Mn Tf. 55Mn citrate inhibited 54Mn citrate uptake, and 55Mn2+ inhibited 54Mn2+ uptake, supporting the conclusion of carrier-mediated brain Mn influx. The greater Kin values for Mn citrate than Mn2+ and its presence as a major non-protein-bound Mn species in blood plasma suggest Mn citrate may be a major Mn species entering the brain.

Manganese distribution across the blood-brain barrier. II. Manganese efflux from the brain does not appear to be carrier mediated

There is concern about manganese (Mn) neurotoxicity. Mn can enter the brain by carrier-mediated influx. There have been no previous reports of investigation of Mn efflux from the brain. We used an established method that determines the rate of efflux out of the brain across the blood-brain barrier (BBB) from the product of the brain distribution volume (Vbrain) and the apparent elimination rate constant (Kel). Vbrain is determined as 54Mn uptake into rat parietal brain slices versus time. Kel is determined from the percentage of 54Mn remaining in the brain at various times after its discrete injection into the parietal cortex, compared to a reference compound which is expected to very slowly diffuse out of the brain. The Mn ion, Mn citrate and Mn transferrin (Mn Tf) were studied. 14C-sucrose and 14C-dextran were used as reference compounds. The volume of distribution of the Mn species in brain slices was approximately 3-5 ml/g, indicating concentrative uptake. Mn, as the Mn ion or Mn citrate, was injected into the brain with sucrose or dextran to determine Kel. Based on the rapid exchange rate of Mn with ligands and on thermodynamic calculations, injection of Mn ion or Mn citrate into the brain would be expected to result in rapid formation of the same Mn species, predominantly the Mn ion, Mn citrates and Mn phosphate, in brain extracellular fluid. After injection into the brain Mn did not efflux from the brain more rapidly than sucrose or dextran, which diffuse across the BBB. Brain capillary diffusion of the Mn ion and Mn citrate would be expected to be slower than sucrose or dextran. The rate of Mn efflux from the brain is consistent with diffusion.

Penetration and distribution of three lipophilic probes in vitro in human skin focusing on the hair follicle

Fluorescent model substances of increasing lipophilicity (Oregon Green) 488, Bodipy, FL C5 and Bodipy 564/570 C5) were selected to enable the visualization in the skin using confocal laser scanning microscopy. After measuring the penetration for 18 h, the nonfixed human scalp skin was imaged from the bottom parallel to the stratum corneum and in a cross-section view perpendicular to the skin surface. The images were evaluated by calculating relative accumulation values for different penetrants. The studies indicate that the penetrated amount is highest for Bodipy FL C5 (medium lipophilicity) and lowest for Bodipy 564/570 C5 (high lipophilicity) whereas Bodipy 564/570 C5 (high lipophilicity) reveals the highest relative accumulation in parts of the hair follicle compared to Oregon Green 488 (low lipophilicity). The addition of 30% (v/v) ethanol to the donor phase of substance with a low lipophilicity increases the follicular delivery. From our results we conclude that delivery to the hair follicle can be improved by increasing the drugs lipophilicity and optimizing the composition of the donor phase. However, no conclusion can be drawn about the actual route of transport to the hair follicle.

Direct effect of vanadium on citrate uptake by rat renal brush border membrane vesicles (BBMV)

Vanadium pentoxide is used as a catalyst and a ferrovanadium alloy ingredient in automotive steels and in jet engines and airframes. In addition, vanadium is found in fuel oils. Thus, occupational exposures to vanadium pentoxide and trioxide may occur during the cleaning of oil-fired ship boilers, and from oil-fired power station boilers. Occupational exposure to vanadium pentoxide induces green tongue, asthmatic symptoms and albuminuria with cast. Urinary citrate is freely filtered at the glomerulus, and its reabsorption in the proximal tubule is the major determinant of the rate of renal excretion. In this study, we exposed rat renal brush border membrane vesicles (BBMV) to vanadium pentoxide and examined their citrate uptake characteristics. The preincubation of BBMV with 1 mM V2O5 for 8 hours significantly inhibited citrate uptake compared with that of BBMV without V2O5, preincubation. These findings indicate that the preincubation of BBMV with vanadium pentoxide results in a time-dependent inhibition of citrate uptake by BBMV. These findings might contribute to nephrotoxicity in vanadium exposure.

Controlled study of citrate effects and response to i.v. calcium administration during allogeneic peripheral blood progenitor cell donation

BACKGROUND

Leukapheresis procedures are generally performed at citrate anticoagulation rates extrapolated from shorter plateletpheresis procedures. However, neither the metabolic effects nor the management of associated symptoms have been critically evaluated during leukapheresis in healthy donors.

STUDY DESIGN AND METHODS

Symptom assessments (n = 315) and laboratory analyses (n = 49) were performed during 244 procedures performed with and 71 without prophylactic calcium (Ca) chloride or Ca gluconate given at a dose linked to the citrate infusion rate (1.0-2.2 mg/kg/min).

RESULTS

During leukapheresis of 12 to 25 L processed, ionized Ca and ionized magnesium (Mg) decreased as much as 35 and 56 percent, respectively, each exhibiting a tight negative correlation with marked increases in serum citrate levels. Significant increases in urinary Ca and Mg excretion accompanied the renal excretion of a large citrate load. Serum divalent cation levels remained depressed 24 hours after leukapheresis. Symptoms were more frequent in donors who were women, had low initial total Mg levels, and underwent procedures in which larger volumes were processed at higher citrate infusion rates. Ca infusions reduced clinically significant paresthesias by 96 percent and also attenuated decreases in serum potassium. Ca chloride maintained higher Ca levels than Ca gluconate.

CONCLUSIONS

Prophylactic Ca infusions safely attenuate the marked metabolic effects of citrate administration and promote faster, more comfortable, leukapheresis procedures.

Behavior of alginate gel beads containing chitosan salt prepared with water-soluble vitamins

Alginate gel beads were prepared which contained weak acid salts of chitosan (Alg-CS) and water-soluble vitamins (e.g. ascorbic acid (AS)) and the behavior of the beads, uptake of bile acids was investigated in vitro. The Alg-CS beads rapidly took up bile acid and this phenomenon was observed for both hydrogel beads and dried beads. About 120 micromol of taurocholic acid was taken up into Alg-CS (1 g) prepared with orotic acid. Dried Alg-CS is the granule which can be made easily, and keeps the ability of CS salt, and all elements can be taken as a food. Therefore, Alg-CS could serve as a useful dietary agent for the prevention of hyperlipidemia.

Functional characterization of CitM, the Mg2+-citrate transporter

The CitM transporter from Bacillus subtilis transports citrate as a complex with Mg2+. In this study, CitM was functionally expressed and characterized in E. coli DH5a cells. In the presence of saturating Mg2+ concentrations, the Km for citrate in CitM was 274 mM, similar to previous studies using whole cells of B. subtilis. CitM has a high substrate specificity for citrate. Other di- and tricarboxylic acids including succinate, isocitrate, cis-aconitate and tricarballylic acid did not significantly inhibit the uptake of citrate in the presence of Mg2+. However, CitM accepts complexes of citrate with metal ions other than Mg2+. The highest rate of citrate transport was seen in the presence of Mg2+, followed in order of preference by Mn2+, Ba2+, Ni2+, Co2+ and Ca2+. Citrate transport by CitM appears to be proton coupled. The transport was inhibited in transport buffers more alkaline than pH 7.5 and not affected by pH at acidic values. Transport was also inhibited by ionophores that affect the transmembrane proton gradient, including FCCP, TCC and nigericin. Valinomycin did not affect the uptake by CitM, suggesting that transport is electroneutral. In conclusion, the cloned CitM transporter from B. subtilis expressed in E. coli has properties similar to the transporter in intact B. subtilis cells. The results support a transport model with a coupling stoichiometry of one proton coupled to the uptake of one complex of (Mg2+-citrate)1-.

The placebo response to citric acid-induced cough: pharmacodynamics and gender differences

Characteristics of the response to placebo in a citric acid-induced cough challenge were investigated as part of a randomized, double-blind crossover trial to assess the antitussive effect of dextromethorphan. Baseline cough responses were established on two occasions in 22 healthy subjects. They received 60 ml placebo antitussive syrup and cough frequency following five inhalations of 10% citric acid over 5 min was measured at regular intervals up to 12 h. Response-time models of varying complexity were used to describe the placebo cough suppression data. The cough response to placebo was also compared to that of the untreated state. The placebo cough response was best characterized by a non-linear increase in cough suppression up to a maximum reduction of 1.6 coughs from baseline at 4-4.5 h, followed by a non-linear return to baseline. The cough response in the untreated state was not different from that of placebo (P=0.99). Females coughed more frequently than males (median number of coughs=10.5 vs. 9.0, respectively P<0.001; Mann-Whitney U test), and adaptation to the cough stimulus was significantly more rapid in females (P<0.025). Accordingly, in trials that use citric acid-induced cough, gender should be considered in study design, particularly in relation to the timing of measurements.

Buffering action of human dentin in vitro

PURPOSE

The purpose of this study was to determine the relative contributions of the mineral and organic phases of dentin to its total buffering capacity and to compare the buffering abilities of normal and caries-affected dentin for acids used in adhesive dentistry.

MATERIALS AND METHODS

Disks of normal and caries-affected human coronal dentin 0.6 mm thick were prepared. Fifty microL of various acids were applied to the surface of mineralized or completely demineralized dentin for varying lengths of time. They were collected from the surface and combined with water rinses to permit titration of the total amount of acid applied, the amount recovered, the total amount that was taken up by the dentin, and the amount that diffused across dentin into 1 mL of water. Equal volumes of acids were applied to mineralized or demineralized dentin powder or hydroxyapatite powder.

RESULTS

About 88% to 90% of applied acid was recovered from the surface; only 10% to 12% of the acid was taken up by dentin. Of the H+ that was taken up, only 1% to 2% actually diffused across 0.6 mm of dentin. Increasing the application time of 37% phosphoric acid did not increase the amount of H+ that diffused across dentin. Increasing the concentration of phosphoric acid from 10% to 65% produced only slight increases in H+ diffusion across dentin. There was no difference in the buffering capacity of normal vs caries-affected dentin disks. Almost all of the buffering capacity of dentin is due to its mineral phase.

CONCLUSION

The high buffering capacity of dentin and the high reactivity of H+ insure that little H+ diffuses through dentin more than 0.6 mm thick.

Transferrin-mediated uptake of aluminium by human parathyroid cells results in reduced parathyroid hormone secretion

BACKGROUND

The present study investigates whether aluminium-transferrin (Al-Tf) uptake by Tf receptor-mediated endocytosis induces hypoparathyroidism and thus might contribute to the increasing prevalence of adynamic bone disease (ABD) in the current dialysis population.

METHODS AND RESULTS

Human parathyroid glands as well as in vitro cultured human parathyroid cells were shown to express Tf receptors. Five-day-old cultures of parathyroid cells were incubated for 48 h in serum-free DMEM/F12 supplemented with 12 microM apo-Tf: 12 microM Tf to which 150 microg/l Al or 150 microg/l Al-citrate (Al-ci) was bound. The amount of Al taken up by the parathyroid cells either as Al-Tf or Al-ci did not differ. However, incubation of cell cultures with Al-Tf showed a significant proportional decrease (mean+/-SEM, -23.1+/-4.5%) in iPTH secretion as compared to the reference apo-Tf cultures. Al-ci did not suppress PTH secretion (+3.4+/-6.5%). The Al uptake after incubation with Al-Tf was found to be dose-dependent. With regard to iPTH secretion, a tendency toward a dose response relationship was observed. Northern blot analysis of parathyroid cells incubated in 12 microM apo-Tf or 12 microM Al-Tf demonstrated that the PTH mRNA synthesis was unaffected by the Tf-mediated uptake of Al. These observations suggest an effect of Al on PTH release rather than on PTH synthesis. Since the cytoskeleton can play an important role in the release of secretory vesicles, the influence of Al on the structure of actin, beta-tubulin and vimentin was investigated by confocal microscopy. Comparison of cultures incubated with apo-Tf and Al-Tf revealed no difference in the organization of these cytoskeletal proteins in relation to the inhibitory effect of Al-Tf on PTH secretion.

CONCLUSION

In summary, data in the present paper demonstrate that the (i) human parathyroid gland/parathyroid cells exhibit Tf receptors; (ii) Al-Tf complex is taken up by the parathyroid gland in a dose-dependent manner; and (iii) uptake of Al by Tf receptor-mediated endocytosis reduces the secretion of PTH but not its synthesis. These in vitro findings allow us to suggest that Tf receptor-mediated uptake of Al might, besides other factors such as vitamin D, high calcium dialysate or CaCO(3) intake, play a role in the development of hypoparathyroidism associated with ABD. The exact mechanism by which Al-Tf suppresses iPTH secretion remains to be elucidated.

Bioavailability and intestinal absorption of aluminum in rats: effects of aluminum compounds and some dietary constituents

In the present investigation, the deposition of aluminum in intestinal fragment and the appearance in blood were studied in a perfused rat intestine in situ for 1 h with several aluminum forms (16 mM). We observed that aluminum absorption was positively correlated with the theoretic affinity of aluminum and the functional groups of the chelating agent. The absorption of aluminum after ingestion of organic compounds is more important than after ingestion of mineral compounds, with the following order: Al citrate > Al tartrate, Al gluconate, Al lactate > Al glutamate, Al chloride, Al sulfate, Al nitrate. Absorption depends on the nature of the ligands associated with the Al3+ ion in the gastrointestinal fluid. The higher the aluminum retention in intestinal fragment, the lower the absorption and appearance in blood. However, the higher aluminum concentration is always in the jejunal fragment because of the influence of pH variation on this fragment. Another objective of the present study was to determine the influence of several parameters on aluminum citrate absorption: with or without 0.1 mmol dinitrophenol/L, with aluminum concentration from 3.2, 16, 32, and 48, to 64 mmol/L, media containing 0, 3, or 6 mmol Ca/L, with or without phosphorus or glucose. It is concluded that aluminum is absorbed from the gastrointestinal tract by (1) a paracellular energy independent and nonsaturable route, mainly used for high aluminum concentration, which is modified by extracellular calcium, and (2) a transcellular and saturable route, the aluminum level was not modified with enhancement of aluminum quantity in intestinal lumen. This pathway can be similar with calcium transfer through the intestine and is energy dependent because of a decrease of aluminum absorption that follows the removal of glucose and phosphorus.

Citrate and succinate transport in proximal tubule cells

Urinary citrate, which inhibits calcium nephrolithiasis, is determined by proximal reabsorption via an apical dicarboxylate transporter. Citrate is predominantly trivalent at physiological pH, but citrate(-2) is transported at the apical membrane. We now demonstrate that low-Ca solutions induce transport of citrate(-2) and succinate in opossum kidney cells. With 1.2 mM extracellular Ca, citrate uptake was pH insensitive and not competed by succinate(-2). In contrast, with low extracellular Ca, citrate uptake increased twofold, was inhibited by succinate (and other dicarboxylates), was stimulated by lowering extracellular pH (consistent with citrate(-2) transport), and increased further by lowering extracellular Mg. The effect of Ca was incrementally concentration dependent, between 0 and 1.2 mM. The effect of Ca was not simply complexation with citrate because succinate (which is complexed significantly less) was affected by Ca similarly. Incubation of cells for 48 h in a low-pH media increased citrate transport (studied at control pH) more than twofold, suggesting induction of transporters.

Kinetic modeling of 52Fe/52mMn-citrate at the blood-brain barrier by positron emission tomography

The kinetics of iron at the blood-brain barrier of the monkey were studied in vivo using positron emission tomography (PET) and the tracer 52Fe/52mMn-citrate. 52mMn is the beta(+)-emitting daughter nuclide of 52Fe and therefore contributes to the observed signal and background in the PET images and may influence the quantification of physiological relevant iron parameters. The kinetics of pure (52m)Mn-citrate at the blood-brain barrier of the monkey were studied experimentally, and the analysis of the data with a reasonable compartment model led to equal efflux and influx parameters for Mn (1.35 +/- 0.3 x 10(-2) min(-1)). By using complexes between Mn and diethylenetriaminepentaacetic acid, the validity of the proposed model could be confirmed. To describe the observed kinetics of 52Fe/(52m)Mn-citrate, the manganese model was coupled to an iron model, which finally allowed the quantification of two iron-specific parameters: an input rate into global brain tissue of 7.15 +/- 2.6 x 10(-4) min(-1) and a time delay of roughly 24 min to account for the observed activities. The simpler linearization procedure has been proposed and could be applied to all our data sets and is able to replace the complicated nonlinear iron/manganese tracer kinetic model neglecting any influence of manganese on the analysis.

Comparative absorption of calcium sources and calcium citrate malate for the prevention of osteoporosis

Anthropologically speaking, humans were high consumers of calcium until the onset of the Agricultural Age, 10,000 years ago. Current calcium intake is one-quarter to one-third that of our evolutionary diet and, if we are genetically identical to the Late Paleolithic Homo sapiens, we may be consuming a calcium-deficient diet our bodies cannot adjust to by physiologic mechanisms. Meta-analyses of calcium and bone mass studies demonstrate supplementation of 500 to 1500 mg calcium daily improves bone mass in adolescents, young adults, older men, and postmenopausal women. Calcium citrate malate has high bioavailability and thus has been the subject of calcium studies in these populations. Positive effects have been seen in prepubertal girls, adolescents, and postmenopausal women. The addition of trace minerals and vitamin D in separate trials has improved the effect of calcium citrate malate on bone density and shown a reduction of fracture risk.

Citrate transport by the kidney and intestine

Citrate is an important metabolite that is transported in the kidney and intestine. Low urinary citrate concentrations, which may be determined in part by transport processes in the kidney, are associated with the development of kidney stones. Citrate is reabsorbed from the tubular filtrate in the renal proximal tubule on a sodium-coupled transporter, the Na+/dicarboxylate cotransporter, with a broad substrate specificity for Krebs cycle intermediates. The same transporter is found on the brush-border membrane of enterocytes. In contrast to the well-characterized apical pathway for citrate, there is relatively little information about citrate transport across the basolateral membrane. Recently, the complementary DNAs coding for the Na+/citrate transporters from the apical membranes of rabbit and human kidney, NaDC-1 and hNaDC-1, have been cloned and sequenced. These transporters belong to a separate gene family that includes the renal Na+/sulfate cotransporter, NaSi-1.

Characterisation of citrate and iron citrate uptake by cultured rat hepatocytes

BACKGROUND/AIMS

The endogenous low molecular weight iron chelator, citrate, is considered to be an important contributor to iron transport and the liver the main site of uptake of iron citrate in subjects suffering from diseases of iron overload. Moreover, the citrate-metabolising enzyme, aconitase, is implicated in the regulation of cellular iron metabolism. This study was undertaken to determine the role of citrate and ferric citrate in the uptake of iron by rat hepatocytes.

METHODS

Cultured rat hepatocytes were incubated (37 degrees C, 15 min) with 100 microM [14C]-citrate in the presence or absence of 1.0 microM 55Fe. Membrane-bound and intracellular radiolabel were separated by incubation with the general protease, Pronase.

RESULTS

Our results suggest that ferric citrate uptake is mediated by a specific citrate binding site which exhibits a higher affinity for citrate in the presence of iron than in its absence. Citrate was internalised by hepatocytes, with at least 70% being oxidised to CO2 within 15 min. Citrate uptake was pH-dependent, did not require the presence of sodium and increased with increasing iron concentration. Metabolic energy, anion channels, the Na+, K+-ATPase and vesicle acidification do not appear to play a role in uptake of ferric citrate, but functional sulphydryl groups may be involved.

CONCLUSIONS

The data suggest either that ferric citrate complexes with higher molar ratios of iron to citrate relative to the incubation medium are bound preferentially to the membrane, or that once citrate has delivered its iron to the membrane, the complex dissociates and the components are internalised separately.

Gastrointestinal absorption of aluminium and citrate in man

Aluminium (Al) is an abundant terrestrial element, but toxic to tissues, including brain. The body is largely protected because systemic Al absorption is very low and in normal individuals almost all absorbed Al is excreted from the body. However gastrointestinal (Gl) absorption is enhanced by organic acids, including citrate. Aluminium and citrate Gl absorption was measured in three healthy males, aged 40-46. After overnight fast, subjects drank a 100 ml fruit drink containing 280 mg Al and 3.2 g citrate (104 and 167 mM, respectively). Al was measured in timed blood and urine samples by GFAAS and serum citrate by enzymatic assay. Blood Al peaked by an increase of 13 +/- 2.1 micrograms/l after 87 +/- 19 min then fell slowly over 24 h. Plasma citrate peaked after 32 min, returning to baseline by 90 min. Al was excreted at a constant rate for the first 24 h, 0.4% of the dose being excreted in urine by this time. It is unlikely that Al is absorbed as Al citrate because the blood citrate peak preceded the Al peak by 45-60 min.

Aluminum citrate is transported from brain into blood via the monocarboxylic acid transporter located at the blood-brain barrier

Aluminum citrate transport across the blood-brain barrier was assessed in rats by in vivo microdialysis. Microdialysis probes were implanted in the jugular vein as well as the left and right frontal cortex. It was demonstrated previously (Allen et al., 1995), in this study, that the steady-state aluminum citrate brain-to-blood-ratio (BBr) is less than 1, suggesting the presence of a process other than diffusion. The addition of 2,4-dinitrophenol (10 microM) to the dialysate perfusing a microdialysis probe in the brain increased the steady-state aluminum citrate brain-to-blood-ratio to a value (1.14) not significantly different from 1, suggesting the presence of an active transporter that is blocked by the metabolic inhibitor. The addition of valproic and pyruvic acid, as putative and known substrates for the monocarboxylic acid transporter, respectively, to brain dialysate (10 and 100 mM) had different outcomes. Valproic acid was ineffective at either concentration, whereas pyruvic acid (100 mM) significantly increased the aluminum citrate brain-to-blood-ratio from 0.19 to 0.31. Pyruvic acid (1 M in the dialysate) increased the aluminum citrate brain-to-blood-ratio to a value not different from unity, suggesting competition between aluminum citrate and pyruvic acid for transport. The only energy-dependent, pyruvic acid-inhibitable transporter is the monocarboxylic acid transporter. Theoretical, pharmacokinetic modeling suggests that the transporter producing an aluminum citrate brain-to-blood-ratio less than 1 is predominantly located at the blood-brain barrier, rather than at neuronal or glial cell membranes. We propose that the monocarboxylic acid transporter at the blood-brain barrier maintains a steady-state aluminum citrate brain-to-blood-ratio much less than 1.

Impairment of citrate metabolism in acute hepatic failure

AIMS

To compare the utilization of citrate employed as anticoagulant in patients with acute hepatic failure and subjects with normal liver function.

PATIENTS AND METHODS

Three patients in acute hepatic failure and normal renal function were studied during therapeutic plasma exchange with citrate containing fresh frozen plasma. Six patients receiving immunapheresis or LDL-apheresis anticoagulated with citrate served as controls. Determinations of serum citrate concentrations, of ionized calcium and blood pH were performed before, during, and after the extracorporeal treatment. Total body clearance and elimination half life were calculated in a two compartment model.

RESULTS

Preinfusion citrate levels were higher in the patients with acute hepatic failure than in the controls (n.s.). The citrate level rose to 1.73 +/- 0.2 mmol/l in the liver patients versus 0.99 +/- 0.1 mmol/l in the healthy subjects (p < 0.03). Total body clearance was markedly reduced in patients with acute hepatic failure (3.31 +/- 0.03 ml/kg/min) as compared with the controls (6.34 +/- 0.16 ml/kg/min) (p < 0.02), the elimination half life (t/2 k1e) was prolonged (49.7 +/- 5.4 vs. 32.9 +/- 1.02 min, p < 0.05). In the controls blood pH rose from 7.4 +/- 0.01 to 7.45 +/- 0.01 (p < 0.05) after citrate infusion, whereas in the liver patients no rise in pH was observed, again reflecting the impairment of citrate metabolism. Ionized calcium was lower in the patients with acute hepatic failure at the beginning (1.01 +/- 0.05 vs. 1.21 +/- 0.04 mmol/l, p < 0.05) and the end (0.68 +/- 0.02 vs. 0.93 +/- 0.04 mmol/l, p < 0.05) of the citrate infusion.

CONCLUSIONS

Citrate metabolism is severely impaired and the plasmatic calcium stores are reduced in acute hepatic failure and, thus, the risk of adverse effects is high. Therapeutic infusions of citrate should be restricted in patients with acute hepatic failure and, if necessary, therapy should be closely monitored by repeated measurements of ionized calcium to avoid the development of potentially hazardous hypocalcemia.