The antimicrobial activity of zinc against group B Streptococcus is strain-dependent across diverse sequence types, capsular serotypes, and invasive versus colonizing isolates

BACKGROUND

Streptococcus agalactiae or Group B Streptococcus (GBS) is an encapsulated gram-positive bacterial pathobiont that commonly colonizes the lower gastrointestinal tract and reproductive tract of human hosts. This bacterium can infect the gravid reproductive tract and cause invasive infections of pregnant patients and neonates. Upon colonizing the reproductive tract, the bacterial cell is presented with numerous nutritional challenges imposed by the host. One strategy employed by the host innate immune system is intoxication of bacterial invaders with certain transition metals such as zinc.

METHODOLOGY

Previous work has demonstrated that GBS must employ elegant strategies to circumnavigate zinc stress in order to survive in the vertebrate host. We assessed 30 strains of GBS from diverse isolation sources, capsular serotypes, and sequence types for susceptibility or resistance to zinc intoxication.

RESULTS

Invasive strains, such as those isolated from early onset disease manifestations of GBS infection were significantly less susceptible to zinc toxicity than colonizing strains isolated from rectovaginal swabs of pregnant patients. Additionally, capsular type III (cpsIII) strains and the ST-17 and ST-19 strains exhibited the greatest resilience to zinc stress, whereas ST-1 and ST-12 strains as well as those possessing capsular type Ib (cpsIb) were more sensitive to zinc intoxication. Thus, this study demonstrates that the transition metal zinc possesses antimicrobial properties against a wide range of GBS strains, with isolation source, capsular serotype, and sequence type contributing to susceptibility or resistance to zinc stress.

Long-lasting antidepressant-like activity of the GPR39 zinc receptor agonist TC-G 1008

BACKGROUND

The discovery of the zinc-sensing receptor, has provided new possibilities for explaining the neurobiology of zinc. Recent studies indicate that the GPR39 zinc receptor may play an important role in the pathogenesis of depression as well as in the antidepressant mechanism of action.

METHODS

In this study we evaluated the time-course of the antidepressant response of the GPR39 agonist (TC-G 1008), imipramine, ZnCl₂ and MK-801 in the forced swim test in mice 30 min, 3 h, 6 h and 24 h after acute drug administration as well as after 14-day treatment. Zinc level was measured in serum of mice. BDNF protein level was evaluated in hippocampus following both acute and chronic TC-G 1008 treatment.

RESULTS

A single administration of the GPR39 agonist caused an antidepressant-like effect lasting up to 24 h following the injection, which is longer than the effect of imipramine, ZnCl₂ and MK-801. Chronic treatment with these compounds caused a decrease in immobility time in the FST. Serum zinc concentrations showed an increased level following chronic ZnCl₂ administration, but not following administration of TC-G 1008, imipramine or MK-801. We also observed some tendencies for increased BDNF following acute TC-G 1008 treatment.

LIMITATIONS

TC-G 1008 is new drug designed to study GPR39 therefore additional pharmacodynamic and pharmacokinetic properties in preclinical studies are required.

CONCLUSION

This study shows for the first time the long-lasting antidepressant effect of the GPR39 agonist in comparison with imipramine, ZnCl2 and MK-801. Our findings suggest that GPR39 should be considered as a target in efforts to develop new antidepressant drugs.

Different dynamic accumulation and toxicity of ZnO nanoparticles and ionic Zn in the soil sentinel organism Enchytraeus crypticus

There is still no consensus over the specific effects of metal-based nanoparticles when compared with the conventional metal salts. Here, the accumulation and toxicity of ZnO-NPs and ZnCl₂ in Enchytraeus crypticus over time (1-14 d) were investigated using a sand-solution exposure medium and applying a toxicokinetics and toxicodynamics approach. For both Zn forms, body Zn concentration in the organisms was dependent on both the exposure concentration and exposure time, with equilibrium being reached after 7-14 days of exposure. Generally, the uptake and elimination rate constants (K_u and K_e1) were smaller for ZnO-NPs (5.74-12.6 mg kg^-1d^-1 and 0.17-0.39 d^-1) than for ZnCl₂ (8.32-40.1 mg kg^-1d^-1 and 0.31-2.05 d^-1), suggesting that ionic Zn was more accessible for E. crypticus than nanoparticulate Zn. Based on external exposure concentrations, LC50s for ZnO-NPs and ZnCl₂ decreased with time from 123 to 67 Zn mg L^-1 and from 86 to 62 Zn mg L^-1, reaching an almost similar ultimate value within 14 d. LC50s based on body Zn concentrations were almost constant over time (except for 1 d) for both ZnO-NPs and ZnCl₂, with overall LC50_body of Zn being 1720 and 1306 mg kg^-1 dry body weight, respectively. Body Zn concentration, which considers all available pathways, was a good predictor of dynamic toxicity of ZnCl₂, but not for ZnO-NPs. This may be attributed to the specific internal distribution and detoxification mechanisms of ZnO-NPs. The particles from ZnO-NPs dominated the accumulation (>75%) and toxicity (∼100%). Our results suggest that dynamic aspects should be taken into account when assessing and comparing NPs and metals uptake and consequent patterns of toxicity.

Pharmacokinetics and bioavailability of chromium malate and its influence on trace metals absorption after oral or intravenous administration

OBJECTIVES

In our preliminary study, chromium malate could decrease the blood glucose level in mice with diabetes and exhibits good benefits in treating glycometabolism and adipose metabolization obstacle in rats with type 2 diabetes. This study was aimed at assessing the pharmacokinetics and bioavailability of chromium malate and influence on trace metals absorption in rats.

METHODS

BAPP 2.3 pharmacokinetic calculating program (China Pharmaceutical University Medicine Center) was used to calculate the pharmacokinetic parameters. Models of type 2 diabetic mellitus rats were applied to analyzed Ca, Mg, Fe, Cu, and Zn contents.

RESULTS

The results showed that mean retention time (MRT) in chromium malate group was significantly prolonged and the area under the curve (AUC) and relative bioavailability of chromium malate (male) group were significant increase compared to chromium picolinate group. The serum Ca, Mg, Fe, Cu, and Zn contents in chromium malate (at doses of 15 and 20 μg Cr/kg bw) groups were significantly increased compared to control group, chromium trichloride group, and chromium picolinate group in type 2 diabetes mellitus rats.

CONCLUSIONS

Those results indicated that chromium malate can significantly prolong MRT and increase AUC (male). Moreover, chromium malate is more effective at treating increased serum Ca, Mg, Fe, Cu, and Zn contents compared to chromium trichloride and chromium picolinate.

Hematological, biochemical, and histopathological impacts of barium chloride and barium carbonate accumulation in soft tissues of male Sprague-Dawley rats

The present study was designed to investigate the hematotoxicity, sero-biochemical and histological changes due to the accumulation of BaCl₂ and BaCO₃, the most important barium salts in our daily lives, in different soft tissues including the liver, kidney, heart, and spleen of adult rats after an oral exposure for 30 consecutive days, and to explain the different mechanisms by which this metal can exert these impacts. For this purpose, adult male rats were divided into three main groups of 15 animals each: group I, serving as controls, group II, receiving BaCl₂ orally in a dose of 179 mg barium/kg b.wt, and group III, receiving BaCO₃ orally in a dose of 418 mg barium/kg b.wt. for 30 consecutive days. Obviously, normocytic normochromic anemia was evident in both barium groups. Serum biochemical analysis revealed significant declines in glutathione peroxidase, catalase, superoxide dismutase, and urea with significant elevations in malondialdehyde, lactate dehydrogenase, and creatine kinase levels. Hyperphosphatemia, hypokalemia, hypocalcemia, and hypochloremia were also evident in both barium groups. Besides, residual analysis of both barium salts in different body organs revealed significantly abundant barium residues in the liver, spleen, heart, and kidney, respectively in both barium salts groups. Moreover, splenic tissue showed hemosiderosis, peritubular congestion, and necrotic glomeruli with intratubular hemorrhage. Sever subepicardial congestion with intramuscular edema was evident in the heart. In conclusion, BaCl₂ and BaCO₃ were able to deliver mortalities, antioxidant enzymes exhaustion, and a sort of normocytic normochromic anemia, as well as marked disturbances in cardiac, hepatic, and renal functions due to the accumulation of these two salts in the soft tissues. Therefore, these results demonstrate the unrecognized toxicity of those two barium salts due to their accumulation in various soft tissues of the body and so, this needs to reconsider about barium exposure.

Effects of Zinc and N-Acetylcysteine in Damage Caused by Lead Exposure in Young Rats

This study investigated the toxicity of rats exposed to lead acetate (AcPb) during the second phase of brain development (8-12 days postnatal) in hematological and cerebral parameters. Moreover, the preventive effect of zinc chloride (ZnCl₂) and N-acetylcysteine (NAC) was investigated. Pups were injected subcutaneously with saline (0.9% NaCl solution), ZnCl₂ (27 mg/kg/day), NAC (5 mg/kg/day) or ZnCl₂ plus NAC for 5 days (3rd-7th postnatal days), and with saline (0.9% NaCl solution) or AcPb (7 mg/kg/day) in the five subsequent days (8th-12th postnatal days). Animals were sacrificed 21 days after the last AcPb exposure. Pups exposed to AcPb presented inhibition of blood porphobilinogen-synthase (PBG-synthase) activity without changes in hemoglobin content. ZnCl₂ pre-exposure partially prevented PBG-synthase inhibition. Regarding neurotoxicity biomarkers, animals exposed to AcPb presented a decrease in cerebrum acetylcholinesterase (AChE) activity and an increase in Pb accumulation in blood and cerebrum. These changes were prevented by pre-treatment with ZnCl₂, NAC, and ZnCl₂ plus NAC. AcPb exposure caused no alteration in behavioral tasks. In short, results show that AcPb inhibited the activity of two important enzymatic biomarkers up to 21 days after the end of the exposure. Moreover, ZnCl₂ and NAC prevented the alterations induced by AcPb.

Study of potential transfer of aluminum to the brain via the olfactory pathway

Many employees in the aluminum industry are exposed to a range of aluminum compounds by inhalation, and the presence of ultrafine particles in the workplace has become a concern to occupational health professionals. Some metal salts and metal oxides have been shown to enter the brain through the olfactory route, bypassing the blood-brain barrier, but few studies have examined whether aluminum compounds also use this pathway. In this context, we sought to determine whether aluminum was found in rat olfactory bulbs and whether its transfer depended on physicochemical characteristics such as solubility and granulometry. Aluminum salts (chloride and fluoride) and various nanometric aluminum oxides (13nm, 20nm and 40-50nm) were administered to rats by intranasal instillation through one nostril (10μg Al/30μL for 10days). Olfactory bulbs (ipsilateral and contralateral relative to instilled nostril) were harvested and the aluminum content was determined by graphite furnace atomic absorption spectrometry after tissue mineralization. Some transfer of aluminum salts to the central nervous system via the olfactory route was observed, with the more soluble aluminum chloride being transferred at higher levels than aluminum fluoride. No cerebral translocation of any of the aluminas studied was detected.

Toxicokinetics of zinc-oxide nanoparticles and zinc ions in the earthworm Eisenia andrei

The toxicokinetics of zinc in the earthworm Eisenia andrei was investigated following exposure for 21 days to ionic zinc (ZnCl₂) or zinc oxide nanoparticles (ZnO-NPs) in Lufa 2.2 soil, followed by 21 days elimination in clean soil. Two concentrations were tested for both ZnCl₂ (250 and 500μg Zn g^-1) and ZnO-NPs (500 and 1000μg Zn g^-1), corresponding to EC₂₅ and EC₅₀ for effects on reproduction. Based on the measured internal Zn concentrations in the earthworms over time of exposure, the kinetics parameters k_a - assimilation rate constant (g_soil g^-1_{body weight} day^-1) and k_e - elimination rate constant (day^-1) were estimated using a one-compartment model for either total Zn concentrations in the soil or porewater Zn concentrations. In the ZnCl₂ treatments, k_a was higher for total Zn concentrations in soil, whereas in the ZnO-NP treatments, k_a was higher for porewater Zn concentrations. The value of k_e did not differ between the two Zn forms (ZnCl₂ vs ZnO-NPs) for either EC₅₀ or EC₂₅ when related to total Zn concentrations in soil, but for EC₅₀, k_e related to porewater Zn concentrations was significantly higher for ZnCl₂ than for ZnO-NPs. It is concluded that differences in kinetic parameters between treatments were connected with exposure concentrations rather than with the form of Zn. Zinc was efficiently regulated by the earthworms in all treatments: a 2-fold increase in exposure concentration resulted in a less than 2-fold increase in internal concentration, and after transfer to uncontaminated soil the internal Zn concentrations in the earthworms returned to ca 111μgg^-1 dw in all treatments.

Inhibitory effect of divalent metal cations on zinc uptake via mouse Zrt-/Irt-like protein 8 (ZIP8)

AIMS

There is controversy regarding the substrate specificity of ZIP8, a ZIP isoform, involved in regulation of extra- and intracellular zinc levels. Here, we investigated the inhibitory effects of divalent metal cations on zinc uptake via mouse ZIP8 (mZIP8).

MAIN METHODS

mZIP8 cDNA was transfected into HEK293T cells by a lipofection method, and its functional expression was evaluated by immunocytochemistry, Western blotting and ⁶⁵Zn (⁶⁵ZnCl₂) uptake measurement.

KEY FINDINGS

Transfection of mZIP8 cDNA into HEK293T cells induced expression of mZIP8 in the cells, and increased zinc uptake. mZIP8-mediated zinc uptake depended on extracellular bicarbonate, and the Michaelis constant for the uptake was estimated to be 8.48±2.46μM. In the inhibition study, iron and cadmium competitively, and cobalt, nickel and copper non-competitively inhibited the mZIP8-mediated zinc uptake, the inhibition constants being calculated to be 3.37, 55.5, 80.6, 198 and 48.3μM, respectively. In contrast, magnesium and manganese at concentrations of up to 1500 and 200μM, respectively, had no inhibitory effect on the zinc uptake via mZIP8.

SIGNIFICANCE

In this study, we reveal that the inhibition profiles of divalent metal cations as to zinc uptake via mZIP8 apparently differ from those for mZIP1, especially in the affinity and inhibition manner of nickel. These findings should contribute to identification of ZIP isoforms involved in total cellular zinc transport.

NMR relaxation studies with MnDPDP

Purpose: Our studies were designed to compare the efficacy of mangafodipir triso-dium (MnDPDP, Teslascan) as a tissue-specific MR agent with that of manganese chloride (MnCl2), to compare the efficacy of different doses and rates of administration of MnDPDP, and to collect the data needed for predicting optimum pulse sequences.

Material and Methods: The dose response for the relaxation rates R1 and R2 at 0.47 T, and the manganese (Mn) concentrations in rat liver and in the liver, pancreas, heart and adrenals of pigs was determined for both MnDPDP and MnCl2 administered i.v. Computer simulations were carried out to model the effects of different tissue Mn concentrations and TR on signal intensities and contrast-to-noise ratios.

Results: In rat liver and pig organs both compounds produced a positive dose-response in R1 and tissue Mn concentration, and only small or no response in R2. The Mn concentration in rat liver was positively correlated with R1, regardless of the form in which Mn was given, or the rate of administration. Optimal imaging parameters are therefore expected to be different pre- and post-MnDPDP administration.

Conclusion: The added cardiovascular safety of MnDPDP compared with MnCl2 does not result in loss of efficacy in increasing R1 at the intended clinical dose of 5 μmol/kg MnDPDP. The changes in R2 were too small to affect T2-weighted images. The data give the basis for choosing the appropriate pulse sequences for MnDPDP-en-hanced MR imaging.

Comparison of manganese biodistribution and MR contrast enhancement in rats after intravenous injection of MnDPDP and MnCl2

Purpose: To compare the time course of the MR enhancing properties and biodistri-bution of manganese (Mn) in rats given i.v. Mn dipyridoxyl diphosphate (MnDPDP) or Mn chloride (MnCl2).

Material and Methods: Twenty-four adult rats were injected i.v. with 5 μmol/kg MnDPDP or MnCl2, or with 0.5 ml/kg saline. High resolution T1-weighted MR imaging was performed during early (10 min), mid (2 h) and late (24 h) phases after injection. Mn concentrations in major organs were measured by using an ICP-AES technique, and correlated with MR findings.

Results: Variable degrees of signal enhancement of major organs observed in MR images corresponded with the amount of Mn uptake after injection of MnDPDP or MnCl2. A prominently lower cardiac, pancreatic and hepatic uptake of Mn was seen at 10 min in rats injected with MnDPDP compared with those given MnCl2 and this was reflected in a difference in signal intensity (SI) in the MR images. At 2 h, the Mn content and SI in the major organs were similar with both MnDPDP and MnCl2. An overall Mn clearance was achieved at 24 h without any important organ retention, with kidney excretion of Mn seen only with MnDPDP.

Conclusion: With both MnDPDP and MnCl2, the Mn uptake correlates with the SI enhancement in tissues. The reduced initial cardiac uptake of Mn after MnDPDP treatment compared to MnCl2 may account for the favourable cardiovascular safety of the contrast agent. These data contribute to an understanding of SI enhancement by MnDPDP, and are consistent with other studies showing that at a dose of 5 μmol/kg, MnDPDP can be safely used as a potent MR organ-specific contrast agent.

The distribution of Mn2+ in rabbit eyes after topical administration for manganese-enhanced MRI

PURPOSE

To analyze the distribution of Mn(2+) in rabbit eyes after topical administration of Mncl2 for manganese-enhanced MRI.

METHODS

Forty-eight Chinese white rabbits were divided into three groups. In group 1 (n = 4), the baseline concentration of Mn(2+) in aqueous, vitreous and serum samples were analyzed. In group 2 and 3, the rabbits received one topical instillation (20 μL) of Mncl2 (1 mol • L(-1)). In group 2 (n = 40), aqueous, vitreous and serum samples were collected and analyzed at predetermined time points (0.5, 1, 2, 4, 6, 12, 24, 48, 72 and 168 hours postdose). Assays were performed using inductively coupled plasma-mass spectrometer (ICP-MS). In group 3 (n = 4), after topical administration of Mncl2, dynamic manganese-enhanced MRI (MEMRI) was performed at predetermined time points. The signal-to-noise ratio (SNR) was calculated to evaluate the enhancements of eyes.

RESULTS

After topical administration, the maximum concentrations of Mn(2+) in the aqueous and vitreous samples were 11.1641 ± 0.7202 (2 hours) and 1.5622 ± 0.1567 (12 hours). In group 3, the maximum enhancement of aqueous humor (SNR = 108.81 ± 10.65) appeared at 2 hours postdose, whereas, no significant changes were detected in vitreous.

CONCLUSION

Mn(2+) could distribute into aqueous humor rapidly after topical administration of Mncl2, whereas, the concentration of Mn(2+) in vitreous body fluctuated in a narrow range over the course. The uptake of Mn(2+) in retina may involve several different pathways.

Stable oligomeric clusters of gold nanoparticles: preparation, size distribution, derivatization, and physical and biological properties

Reducing dilute aqueous HAuCl4 with NaSCN under alkaline conditions produces 2-3 nm diameter yellow nanoparticles without the addition of extraneous capping agents. We here describe two very simple methods for producing highly stable oligomeric grape-like clusters (oligoclusters) of these small nanoparticles. The oligoclusters have well-controlled diameters ranging from ∼5 to ∼30 nm, depending mainly on the number of subunits in the cluster. Our first ["delay-time"] method controls the size of the oligoclusters by varying from seconds to hours the delay time between making the HAuCl4 alkaline and adding the reducing agent, NaSCN. Our second ["add-on"] method controls size by using yellow nanoparticles as seeds onto which varying amounts of gold derived from "hydroxylated gold", Na(+)[Au(OH4-x)Clx](-), are added-on catalytically in the presence of NaSCN. Possible reaction mechanisms and a simple kinetic model fitting the data are discussed. The crude oligocluster preparations have narrow size distributions, and for most purposes do not require fractionation. The oligoclusters do not aggregate after ∼300-fold centrifugal-filter concentration, and at this high concentration are easily derivatized with a variety of thiol-containing reagents. This allows rare or expensive derivatizing reagents to be used economically. Unlike conventional glutathione-capped nanoparticles of comparable gold content, large oligoclusters derivatized with glutathione do not aggregate at high concentrations in phosphate-buffered saline (PBS) or in the circulation when injected into mice. Mice receiving them intravenously show no visible signs of distress. Their sizes can be made small enough to allow their excretion in the urine or large enough to prevent them from crossing capillary basement membranes. They are directly visible in electron micrographs without enhancement, and can model the biological fate of protein-like macromolecules with controlled sizes and charges. The ease of derivatizing the oligoclusters makes them potentially useful for presenting pharmacological agents to different tissues while controlling escape of the reagents from the circulation.

Anti-tumour and pharmacokinetics study of 2-Formyl-8-hydroxy-quinolinium chloride as Galipea longiflora alkaloid analogue

The quinolinium chloride salt of 8-hydroxyqinolinecarbaldehyde (2-Formyl-8-hydroxy-quinolinium chloride) was prepared as Galipea longiflora alkaloid analogue and its anticancer activity was evaluated both in vitro and in vivo. This chloride salt was found to show certain degree of selectivity between hepatoma cells and normal hepatocytes in vitro. Athymic nude mice Hep3B xenograft model further demonstrated that this 2-Formyl-8-hydroxy-quinolinium chloride could execute strong anti-tumour activity with the identification of extensive necrotic feature from the tumour xenograft and limited adverse toxicological effect.

Regional specificity of manganese accumulation and clearance in the mouse brain: implications for manganese-enhanced MRI

Manganese-enhanced MRI has recently become a valuable tool for the assessment of in vivo functional cerebral activity in animal models. As a result of the toxicity of manganese at higher dosages, fractionated application schemes have been proposed to reduce the toxic side effects by using lower concentrations per injection. Here, we present data on regional-specific manganese accumulation during a fractionated application scheme over 8 days of 30 mg/kg MnCl2 , as well as on the clearance of manganese chloride over the course of several weeks after the termination of the whole application protocol supplying an accumulative dose of 240 mg/kg MnCl2 . Our data show most rapid accumulation in the superior and inferior colliculi, amygdala, bed nucleus of the stria terminalis, cornu ammonis of the hippocampus and globus pallidus. The data suggest that no ceiling effects occur in any region using the proposed application protocol. Therefore, a comparison of basal neuronal activity differences in different animal groups based on locally specific manganese accumulation is possible using fractionated application. Half-life times of manganese clearance varied between 5 and 7 days, and were longest in the periaqueductal gray, amygdala and entorhinal cortex. As the hippocampal formation shows one of the highest T1 -weighted signal intensities after manganese application, and manganese-induced memory impairment has been suggested, we assessed hippocampus-dependent learning as well as possible manganese-induced atrophy of the hippocampal volume. No interference of manganese application on learning was detected after 4 days of Mn(2+) application or 2 weeks after the application protocol. In addition, no volumetric changes induced by manganese application were found for the hippocampus at any of the measured time points. For longitudinal measurements (i.e. repeated manganese applications), a minimum of at least 8 weeks should be considered using the proposed protocol to allow for sufficient clearance of the paramagnetic ion from cerebral tissue.

Intravenous application of HI-6 salts (dichloride and dimethansulphonate) in pigs: comparison with pharmacokinetics profile after intramuscular administration

OBJECTIVES

Oxime HI-6 is an acetylcholinesterase reactivator therapeutically efficient against nerve agents. Because of their physico-chemical properties, oximes are typically applied intramuscularly (i.m.). This route of administration has also some disadvantages, and alternative strategies ought to be examined. We evaluated the pharmacokinetic profiles of two HI-6 salts after their intravenous (i.v.) administration, and compare the results with the known pharmacokinetics after i.m. administration.

METHODS

Pigs were administered with HI-6 salts (i.v), either HI-6 dichloride (10.71 mg/kg) or molar equivalent HI-6 dimethansulphonate (13.59 mg/kg). Doses of the HI-6 salts corresponded with a standard HI-6 dichloride dose in one autoinjector (500 mg) and were recalculated for one kilogram of body weight.

RESULTS

The main pharmacokinetic parameters are comparable after i.v. and i.m. HI-6 administration. The compared pharmacokinetic parameters were half-life, terminal rate constant, mean residence time of the molecule in the body, clearance, and the apparent volume in the terminal phase. The bioavailability after i.m. administration was comparable with that of i.v.; these results suggest that the oxime is well released from the muscle depot. Significant differences were found in parameters Cmax and Tmax which are important in cases of emergency when rapidity and bioavailability are paramount for the success of treatment.

CONCLUSIONS

I.v. administration should solve the problem of rapid clearance. Infusion or bolus administration may be considered as a logical subsequent step in oxime treatment strategy. The main advantage is in maintenance of an effective therapeutic plasma concentration, a more easily achievable effective therapeutic concentration, and fewer local adverse reactions.

Manganese alters rat brain amino acids levels

Manganese (Mn) is an essential element and it acts as a cofactor for a number of enzymatic reactions, including those involved in amino acid, lipid, protein, and carbohydrate metabolism. Excessive exposure to Mn can lead to poisoning, characterized by psychiatric disturbances and an extrapyramidal disorder. Mn-induced neuronal degeneration is associated with alterations in amino acids metabolism. In the present study, we analyzed whole rat brain amino acid content subsequent to four or eight intraperitoneal injections, with 25 mg MnCl₂/kg/day, at 48-h intervals. We noted a significant increase in glycine brain levels after four or eight Mn injections (p < 0.05 and p < 0.01, respectively) and arginine also after four or eight injections (p < 0.001). Significant increases were also noted in brain proline (p < 0.01), cysteine (p < 0.05), phenylalanine (p < 0.01), and tyrosine (p < 0.01) levels after eight Mn injections vs. the control group. These findings suggest that Mn-induced alterations in amino acid levels secondary to Mn affect the neurochemical milieu.

Empirical mathematical model for dynamic manganese-enhanced MRI of the murine pancreas for assessment of β-cell function

Autoimmune ablation of pancreatic β-cells and alteration of its microvasculature may be a predictor of Type I diabetes development. A dynamic manganese-enhanced MRI (MEMRI) approach and an empirical mathematical model were developed to monitor whole pancreatic β-cell function and vasculature modifications in mice. Normal and streptozotocin-induced diabetic FVB/N mice were imaged on a 9.4T MRI system using a 3D magnetization prepared rapid acquisition gradient echo pulse sequence to characterize low dose manganese kinetics in the pancreas head, body and tail. Average signal enhancement in the pancreas (head, body, and tail) as a function of time was fit by a novel empirical mathematical model characterizing contrast uptake/washout rates and yielding parameters describing peak signal, initial slope, and initial area under the curve. Signal enhancement from glucose-induced manganese uptake was fit by a linear function. The results demonstrated that the diabetic pancreatic tail had a significantly lower contrast uptake rate, smaller initial slope/initial area under the curve, and a smaller rate of Mn uptake following glucose activation (p<0.05) compared to the normal pancreatic tail. These observations parallel known patterns of β-cell loss and alteration in supportive vasculature associated with diabetes. Dynamic MEMRI is a promising technique for assessing β-cell functionality and vascular perfusion with potential applications for monitoring diabetes progression and/or therapy.

The effects of glutamate and citrate on absorption and distribution of aluminum in rats

The objective of this study was to evaluate the effect of glutamate (Glu) and citrate (Cit) on the absorption and distribution of aluminum in rats. In the in vitro experiment, 18 adult male Sprague-Dawley rats (average weight of 250 ± 15 g) were randomly divided into three groups. The entire intestine was rapidly removed and cultured in prediction samples of 20 mmol AlCl(3), 20 mmol AlCl(3)+20 mmol Cit, and 20 mmol AlCl(3)+20 mmol Glu, respectively. Liquid in different intestines and the intestines were obtained for Al determination. In the in vivo chronic study, 24 adult male Sprague-Dawley rats (average weight of 127 ± 10 g) were divided into four groups fed with the following diets: no Al and Glu added (control), AlCl(3) (1.2 mmol), AlCl(3) (1.2 mmol) + Cit (1.2 mmol), and AlCl(3) (1.2 mmol) + Glu (1.2 mmol) daily for 50 days, respectively. After rat sacrifice, blood samples were obtained for biochemical analyses, and organ samples like the brain, kidney, liver, and bone were rapidly taken for Al determination. The results showed that the absorption rate of Al with the following order: duodenum > jejunum > ileum in the in vitro study and the administration of AlCl(3)+Cit or AlCl(3)+Glu resulted in significant increases in Al absorption in the three parts of the gut (duodenum, jejunum, and ileum) compared to the AlCl(3) alone group based on wet weight (P < 0.05). There were no differences between the AlCl(3)+Cit and AlCl(3)+Glu groups. In the in vivo chronic study, supplementing either AlCl(3) alone or AlCl(3)+Glu decreased food consumption significantly (P < 0.05) compared with the control group. Compared with the control group, animals fed with the AlCl(3) diet monitored for red blood cell, kidney, and liver showed a higher level (P < 0.05), but did not significantly increase Al retention in the brain and bone (P > 0.05); animals fed with AlCl(3)+Cit diets were monitored for higher Al retention in the brain, kidney, bone, and liver (P < 0.05), while animals fed with AlCl(3)+Glu diets were monitored for red blood cell, brain, and kidney (P < 0.05). Compared with the AlCl(3) group, simultaneous administration of AlCl(3) and Glu led to a significant increase in Al retention in red blood cell, brain, and kidney (P < 0.01) while AlCl(3) and Cit in the kidney and bone (P < 0.01). Simultaneous administration of AlCl(3) and Cit significantly increases plasma malondialdehyde level (P < 0.05); both simultaneous administration of AlCl(3) and Glu or AlCl(3) and Cit led to significant decreases in superoxide dismutase level in the plasma (P < 0.05), while AlCl3 alone did not. The results indicated that both Cit and Glu enhanced Al absorption in the intestine in vitro, and Glu increased Al deposition in red blood cell, brain, and kidney in vivo.

Comparative toxicity of nanoparticulate/bulk Yb₂O₃ and YbCl₃ to cucumber (Cucumis sativus)

With the increasing utilization of nanomaterials, there is a growing concern for the potential environmental and health effects of them. To assess the environmental risks of nanomaterials, better knowledge about their fate and toxicity in plants are required. In this work, we compared the phytotoxicity of nanoparticulate Yb(2)O(3), bulk Yb(2)O(3), and YbCl(3)·6H(2)O to cucumber plants. The distribution and biotransformation of the three materials in plant roots were investigated in situ by TEM, EDS, as well as synchrotron radiation based methods: STXM and NEXAFS. The decrease of biomass was evident at the lowest concentration (0.32 mg/L) when exposed to nano-Yb(2)O(3), while at the highest concentration, the most severe inhibition was from YbCl(3). The inhibition was dependent on the actual amount of toxic Yb uptake by the cucumber plants. In the intercellular regions of the roots, Yb(2)O(3) particles and YbCl(3) were all transformed to YbPO(4). We speculate that the dissolution of Yb(2)O(3) particles induced by the organic acids exuded from roots played an important role in the phytotoxicity. Only under the nano-Yb(2)O(3) treatment, YbPO(4) deposits were found in the cytoplasm of root cells, so the phytotoxicity might also be attributed to the Yb internalized into the cells.

Proposed revision to the radiation dosimetry of 82Rb

Three models for the biodistribution and dosimetry of 82Rb-chloride were reviewed and a proposal is made for the best dosimetry for this agent to be adopted. Data from three proposed biokinetic models for 82Rb-chloride were used to calculate dose estimates for the compound, and the results were compared. The blood content-based model was found to produce dose estimates that were considered to be overly conservative, and a blood flow-based model, which showed good agreement with available measured data, was considered to be more reasonable. A new set of dose estimates for 82Rb-chloride, based on the blood flow-based kinetic model are suggested for general use.

Influence of pH on transungual passive and iontophoretic transport

The present study investigated the effects of pH on nail permeability and the transport of ions such as sodium (Na) and chloride (Cl) ions endogenous to nail and hydronium and hydroxide ions present at low and high pH, which might compete with drug transport across hydrated nail plate during iontophoresis. Nail hydration and passive transport of water across the nail at pH 1-13 were assessed. Subsequently, passive and iontophoretic transport experiments were conducted using (22)Na and (36)Cl ions under various pH conditions. Nail hydration was independent of pH under moderate pH conditions and increased significantly under extreme pH conditions (pH >11). Likewise, nail permeability for water was pH independent at pH 1-10 and an order of magnitude higher at pH 13. The results of passive and iontophoretic transport of Na and Cl ions are consistent with the permselective property of nail. Interestingly, extremely acidic conditions (e.g., pH 1) altered nail permselectivity with the effect lasting several days at the higher pH conditions. Hydronium and hydroxide ion competition in iontophoretic transport was generally negligible at pH 3-11 was significant at the extreme pH conditions studied.

INVOLVEMENT OF Na+-K+-2Cl−COTRANSPORTERS IN HYPERTONICITY-INDUCED RISE IN INTRACELLULAR CALCIUM CONCENTRATION

A hypertonic saline containing propylene glycol facilitates calcium (Ca(2+)) influx through voltage-dependent Ca(2+) channels. The present study performed experiments to elucidate the mechanism by which Na(+)-K(+)-2Cl(-) cotransporters participate in the rise in the intracellular calcium concentration ([Ca(2+)]i) under the hypertonic condition. Both furosemide and ethacryonic acid significantly decreased the [Ca(2+)]i raised by hypertonicity. Similarly, Na(+)-, K(+)-, or Cl(-)-free saline also reduced it. Both norepinephrine and dopamine significantly enhanced the rise in [Ca(2+)]i. In conclusion, the findings obtained indicate that the Na+-K+-2Cl- cotransporters evoke cell depolarization and that this depolarization raises the [Ca(2+)]i by activating voltage-dependent Ca(2+) channels.

High net calcium uptake explains the hypersensitivity of the freshwater pulmonate snail, Lymnaea stagnalis, to chronic lead exposure

Previous studies have shown that freshwater pulmonate snails of the genus Lymnaea are exceedingly sensitive to chronic Pb exposure. An EC20 of <4microgl(-1)Pb for juvenile snail growth has recently been determined for Lymnaea stagnalis, which is at or below the current USEPA water quality criterion for Pb. We characterized ionoregulation and acid-base balance in Pb-exposed L. stagnalis (young adults approximately 1g) to investigate the mechanisms underlying this hypersensitivity. After 21-day exposure to 18.9microgl(-1)Pb, Ca(2+) influx was significantly inhibited (39%) and corresponding net Ca(2+) flux was significantly reduced from 224 to -23nmolg(-1)h(-1). An 85% increase in Cl(-) influx was also observed, while Na(+) ion transport appeared unaffected. Finally, a marked alkalosis of extracellular fluid was observed with pH increasing from 8.35 in the control to 8.65 in the 18.9microgl(-1) Pb-exposed group. Results based on direct measurement of Ca(2+) influx in 1g snails gave an influx nearly an order of magnitude higher (750nmolg(-1)h(-1)) than in comparably sized fish in similar water chemistry. Under control conditions, specific growth rate in newly hatched snails was estimated at 16.7% per day over the first 38-day post-hatch and whole body Ca(2+) concentrations were relatively constant at approximately 1100nmolg(-1) over this period. Based on these data, it is estimated that newly hatched snails have net Ca(2+) uptake rates on the order of 7600nmolg(-1)h(-1). A model was developed integrating these data and measured inhibition of Ca(2+) influx rates of 13.4% and 38.7% in snails exposed to 2.7 and 18.9microgl(-1)Pb, respectively. The model estimates 45% and 83% reductions in newly hatched snail growth after 30-day exposure in these two Pb-exposed groups. These results compare well with previous direct measurements of 47% and 90% reductions in growth at similar Pb concentrations, indicating the high net Ca(2+) uptake is the controlling factor in observed Pb hypersensitivity.

Fractionated manganese-enhanced MRI

We investigated the use of manganese-enhanced MRI (MEMRI) with fractionated doses as a way to retain the unique properties of manganese as a neuronal contrast agent while lessening its toxic effects in animals. First, we followed the signal enhancement on T1-weighted images of the brains of rats receiving 30 mg/kg fractions of MnCl2 . 4H2O every 48 h and found that the signal increased in regions with consecutive fractionated doses and ultimately saturated. Second, we used T1 mapping to test whether the amount of MRI-visible manganese that accumulated depended on the concentration of manganese in the fractions. For a fixed cumulative dose of 180 mg/kg MnCl2 . 4H2O, increasing fraction doses of 6 x 30 mg/kg, 3 x 60 mg/kg, 2 x 90 mg/kg and 1 x 180 mg/kg produced progressively shorter T1 values. The adverse systemic health effects, including complications at the injection site and poor animal well-being, also rose with the fraction dose. Thus, fractionated MEMRI can be used to balance the properties of manganese as a contrast agent in animals against its toxic effects.

Analysis of laminar activity in normal and injured rat spinal cord by manganese enhanced MRI

The present study provides an account of a sensitive and rapid experimental approach for MRI visualization and analysis of spinal cord (SC) laminar activity in normal and injured animals. This approach is based upon neuronal activity-dependant manganese (Mn) uptake after focal SC injection of MnCl(2), and subsequent ex-vivo magnetic resonance imaging (MRI) of activated SC pathways. The method was designed as an alternative to time-intensive histochemical and behavioral approaches typically used for analysis of spinal cord injury (SCI) and our results provide both anatomical and functional insights. We show that ex vivo imaging can determine layer-specific activity over an extended region of the rat SC. In addition, we demonstrate that the Mn concentration profile along the SC axis accurately reflects the type of SC injury. The approach is flexible since MRI analysis can be done immediately after animal sacrifice, or alternatively several days later, without a loss of sensitivity. Moreover, the integrity and functional state of SC circuitry can be analyzed in less than 1 h whereas several days and weeks are necessary to perform classical histochemical and behavioral analysis. Thus our method can be used for precise assessment of the extent of dysfunction or change in SC disorders and may facilitate the screening of molecules with therapeutic potential after SC injury.

Dynamic water changes in excised rat myocardium assessed by continuous distribution of T1 and T2

Ischemic changes in excised rat myocardium were followed by series of T1 or T2 measurements from 1 to 60 min after isolated perfusion cessation, and the influence of manganese enhancement was investigated. An inverse Laplace transformation (ILT) of T1 or T2 data was used to resolve the number, time constants, and fractions of tissue water components in a continuous distribution. For T1 distributions, one single tissue component approximately 900 ms was significantly shortened and dispersed by manganese enhancement (25 and 200 microM MnCl2). For T2 distributions, three tissue components (approximately 30, approximately 100, and approximately 350 ms) were obtained initially. The two shortest components merged after approximately 10 min to one component (approximately 40 ms). Both T1 and T2 tissue components became shorter with time. In particular, the T2 distribution dynamics might be compatible with complex sequential changes in tissue water fractions during ischemia.

Steroid regulation of the GABAA receptor: ligand binding, chloride transport and behaviour

Certain endogenous steroids are modulators of GABAA receptors. Tetrahydroprogesterone (THP, 5 alpha-pregnan-3 alpha-ol-20-one) and tetrahydrodeoxy-corticosterone (THDOC, 5 alpha-pregnane-3 alpha, 21-diol-20-one) behave as allosteric agonists of GABAA receptors whereas pregnenolone sulphate acts as an antagonist. THP and THDOC modulate ligand binding to GABAA receptors like barbiturates; they potentiate binding of the GABAA receptor agonist muscimol and the benzodiazepine flunitrazepam and they allosterically inhibit binding of the convulsant t-butylbicyclophosphorothionate. THP and THDOC also stimulate chloride uptake and currents in synaptoneurosomes and neurons. Pregnenolone sulphate acts principally as an allosteric GABAA receptor antagonist; it competitively inhibits binding of [35S] TBPS and blocks GABA agonist-activated Cl- uptake and currents in synaptoneurosomes and neurons. In behavioural experiments the GABA-agonistic steroid THDOC shows anxiolytic actions whereas the GABA-antagonistic steroid pregnenolone sulphate antagonizes barbiturate-induced hypnosis. Changes in physiological levels of GABAergic steroids may alter GABAA receptor function, influencing neuronal excitability and CNS arousal. For example, pregnancy and the puerperium are associated with alterations in GABAA receptor binding which might be attributable to steroid actions.

Manganese-enhanced MRI studies of alterations of intraretinal ion demand in models of ocular injury

PURPOSE

To provide proof-of-concept that the extent of intraretinal manganese uptake after systemic MnCl(2) injection, detected with manganese-enhanced MRI (MEMRI), assesses alterations in intraretinal ion demand in models of ocular insult.

METHODS

In Sprague-Dawley rats, retinal ion demand and thickness were measured from MEMRI data collected before, 4 hours after, or 1, 3, and 7 days after intraperitoneal injection of MnCl(2). Choroidal contribution or blood-retinal barrier permeability surface area product (BRB PS') was determined using MRI after Gd-DTPA injection. Ocular injury was evaluated 24 hours after intravitreal injection of phosphate-buffered saline (PBS, vehicle) or PBS + ouabain, or after intraperitoneal injection of sodium iodate. Manganese retinal toxicity was assessed by comparing full-field, white-flash electroretinographic (ERG) data obtained before and after systemic MnCl(2) administration. Rat choroidal thickness was measured from cross-sections prepared from paraformaldehyde-perfused adult rats.

RESULTS

Comparing pre- and post-Gd-DTPA images demonstrated minimal choroidal contribution to intraretinal analysis. Intraretinal signal intensity returned to baseline by 7 days after MnCl(2) injection. After ouabain injection, receptor and postreceptor uptake of manganese were subnormal (P < 0.05). After sodium iodate exposure, intraretinal manganese uptake was supernormal (P < 0.05) and did not increase with increasing BRB PS'. ERG data did not show any effect of MnCl(2) on photoreceptor a-wave and postreceptor b-wave relative to baseline at either observation time.

CONCLUSIONS

MEMRI measurements of uptake of systemically administered and nontoxic doses of manganese appear to be a powerful approach for measuring alteration in intraretinal ion demand in models of ocular injury.

A high molecular weight soluble fraction of tempeh protects against fluid losses in Escherichia coli-infected piglet small intestine

Enterotoxigenic Escherichia coli (ETEC) is an important cause of diarrhoea in children and piglets. Infection of ETEC results in fluid secretion and electrolyte losses in the small intestine. In this study the effects of tempeh, a traditional fungal fermented soyabean product, on fluid losses induced by ETEC infection in piglets was investigated. Pairs of ETEC-infected and non-infected small intestinal segments of piglets were perfused simultaneously for 8 h with pre-digested tempeh, its supernatant and saline as an internal control. In saline perfused segments, ETEC infection reduced net fluid absorption by more than 500 μl/cm2, whereas this reduction was significantly less for pre-digested tempeh and its supernatant (75 and 282 μl/cm2, respectively). The supernatant of pre-digested tempeh was also compared with its permeate and retentate fractions. These fractions were created by ultra-filtration and contained respectively low and high molecular weight (>5 kDa) compounds. Again ETEC infection caused a significant reduction of net fluid absorption when perfused with saline (386 μl/cm2) and also with the permeate fraction (300 μl/cm2), but much less with the supernatant and the retentate fraction (125 and 140 μl/cm2, respectively). The reduction in net fluid absorption upon ETEC infection when perfused with supernatant of either undigested or pre-digested tempeh was not different. Therefore from this study it can be concluded that a high molecular weight soluble fraction of tempeh is able to protect against fluid losses induced by ETEC, suggesting that this could play a potential role in controlling ETEC-induced diarrhoea.

Aluminum Induces Tau Aggregation in vitro but not in vivo

Etiological studies suggest that aluminum (Al) intake might increase an individual's risk of developing Alzheimer's disease (AD). Biochemical analysis data on the effects of Al, however, are inconsistent. Hence, the pathological involvement of Al in AD remains unclear. If Al is involved in AD, then it is reasonable to hypothesize that Al might be involved in the formation of either amyloid plaques or neurofibrillary tangles (NFTs). Here, we investigated whether Al might be involved in NFT formation by using an in vitro tau aggregation paradigm, a tau-overexpressing neuronal cell line (N2a), and a tau-overexpressing mouse model. Although Al induced tau aggregation in a heparin-induced tau assembly assay, these aggregates were neither thioflavin T positive nor did they resemble tau fibrils seen in human AD brains. With cell lysates from stable cell lines overexpressing tau, the accumulation of SDS-insoluble tau increased when the lysates were treated with at least 100 muM Al-maltolate. Yet Al-maltolate caused illness or death in transgenic mice overexpressing human tau and in non-transgenic littermates well before the Al concentration in the brain reached 100 muM. These results indicate that Al has no direct link to AD pathology.

Effect of zinc supplementation on bone metabolism in male rats chronically exposed to cadmium

The aim of the present study is to investigate, based on the rat model of moderate and relatively high human exposure to cadmium (Cd), whether zinc (Zn) supplementation may prevent Cd-induced disorders in bone metabolism. For this purpose, male Wistar rats received Cd (5 and 50mg/l) or/and Zn (30 and 60mg/l) in drinking water for 6 and 12 months. Bone densitometry and biochemical markers of bone turnover were used to assess the effects of Cd or/and Zn. Bone mineral content (BMC) and density (BMD) were measured in the femur. Serum osteocalcin (OC) and alkaline phosphatase in trabecular (bT-ALP) and cortical (bC-ALP) bone were determined as bone formation markers, and carboxy-terminal cross-linking telopeptides of type I collagen (CTX) in serum were measured as bone resorption marker. Serum concentration of calcium (Ca) and its renal handling, as well as Zn and Cd concentrations in the serum/blood, urine and femur were evaluated as well. The exposure to 5 and 50mg Cd/l (0.340+/-0.026 and 2.498+/-0.093mg Cd/kg body wt/24h, respectively), in a dose and duration dependent manner, affected bone turnover (inhibited bone formation and stimulated its resorption) and disturbed bone mineralization (decreased BMC, BMD and Zn concentration). Zn supply at the concentration of 30 and 60mg/l (1.904+/-0.123 and 3.699+/-0.213mg/kg body wt/24h, respectively) during Cd exposure influenced the Cd-induced disorders in bone metabolism. Zn administration to the Cd-exposed rats enhanced the bone ALP activity and prevented Cd-induced bone resorption, but had no statistically significant effect on BMC and BMD; however, mean values of the densitometric parameters in the rats receiving both Cd and Zn were higher than in those treated with Cd alone. Moreover, Zn supplementation at both levels of Cd exposure was found to prevent Cd accumulation in the femur and the Cd-induced decrease in bone Zn concentration. The results of the present study allow the conclusion that Zn supplementation during Cd exposure may partly protect from disorders in bone metabolism. The influence of Zn may be accompanied by its ability to prevent Cd-induced Zn deficiency and to decrease Cd accumulation in bone tissue. The findings seem to indicate that enhanced dietary intake of Zn in subjects chronically exposed to moderate and relatively high Cd levels may have a protective influence on the skeleton.

Ncx (Enx, Hox11L.1) is required for neuronal cell death in enteric ganglia of mice

BACKGROUND/PURPOSE

Ncx (Enx, Hox11L.1)-deficient (Ncx-/-) mice develop mega-ileo-ceco-colon with a larger number of neuronal cells in the enteric ganglia. We investigated mechanisms related to this abnormality and directed our attention to the effects on gastrointestinal tract functions.

METHODS

The number of NADPH diaphorase or cuprolinic blue-positive neuronal cells in the enteric ganglia was examined during growth of the mice. Neuronal cell death of enteric ganglia was assayed by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling. Function of the gastrointestinal tract was determined by measuring excretion time of the barium chloride given into the stomach.

RESULTS

The number of neuronal cells decreased in control mice older than 2 weeks, and neuronal cell death was evident in the ganglia. However, the number of neuronal cells did not decrease in Ncx-/- mice, and cell death was rare. Excretion time of barium chloride was prolonged in all Ncx-/- mice examined and was improved by the administration of an inhibitor of nitric oxide synthase.

CONCLUSIONS

Ncx participates in cell death of enteric neurons. Motor abnormality of the gastrointestinal tract in Ncx-/- mice may be attributed to the large number of neuronal cells.

Mechanisms of dietary Cu uptake in freshwater rainbow trout: evidence for Na-assisted Cu transport and a specific metal carrier in the intestine

Copper (Cu) is both a vital nutrient and a potent toxicant. The objective of this study was to analyze the mechanistic nature of intestinal Cu transport in rainbow trout using radiolabeled Cu (64Cu) and an in vitro gut sac technique. Reduction of mucosal NaCl levels inhibited Cu transport while increase caused stimulation; Na(2)SO(4) had an identical effect, implicating Na(+) rather than the anion. These responses were unrelated to solvent drag, osmotic pressure or changes in transepithelial potential. The presence of elevated luminal Ag stimulated Cu and Na(+) uptake. Phenamil caused a partial inhibition of both Cu and Na(+) uptake while hypercapnia stimulated Na(+) and Cu transport. Cu uptake was sensitive to luminal pH and inhibited by a tenfold excess of Fe and Zn. These factors had no effect on Na(+ )uptake. On the basis of these results we propose a novel Na(+)-assisted mechanism of Cu uptake wherein the Na(+) gradient stimulates an increase in the H(+) concentration of the brushborder creating a suitable microenvironment for the effective transport of Cu via either DMT1 or Ctr1.

Manganese-enhanced magnetic resonance imaging (MEMRI) of rat brain after systemic administration of MnCl2: Changes in T1 relaxation times during postnatal development

PURPOSE

To measure regional T(1) changes in the postnatal rat brain following systemic administration of the contrast agent manganese chloride (MnCl(2)).

MATERIALS AND METHODS

MnCl(2) (120 mM) was administered intravenously (i.v.) at 1.25 mL/hour to a dose of 175 mg/kg body weight. MRI experiments were performed on anaesthetized animals (32 male Wistar rats, postnatal days (PDs) 11, 16, 21, and 31) at 2.0 T. Regions of interest (ROIs) were drawn in sagittal slices and placed over five brain regions: olfactory bulb, cerebellum, cortex, thalamus, and hypothalamus. The signal intensities of each ROI were measured and fitted to a three-parameter function to estimate T(1) values.

RESULTS

In the brains of animals who did not receive the contrast agent (control group), we observed a consistent age-dependent decrease in T(1) values. In the brains of manganese-infused animals (manganese group), however, T(1) values were significantly lower than in the control group, indicating the uptake of manganese, but no dependence of T(1) on age was found.

CONCLUSION

Our T(1) measurements indicate that the relative Mn(2+) concentrations are higher in neonates and decrease with brain development. An estimate of the relative cortical concentration of manganese shows a two-fold drop from PD 11 to PD 31.

Luminal oxidants selectively modulate electrogenic ion transport in rat colon

AIM: To investigate the effects of luminal exposure to H₂O₂ and two related thiol oxidizing agents on basal and stimulated chloride secretion in native colon using electrophysiological and pharmacological approaches.

METHODS: Unstripped rat distal colon segments were mounted in Ussing chambers. Potential difference, calculated resistance and short-circuit current across unstripped colon segments were monitored with a dual voltage/current clamp. Paracellular permeability was assessed by measuring the mucosa-to-serosa flux of a fluorescent probe (FITC).

RESULTS: Luminal exposure to hydrogen peroxide transitorily stimulated chloride secretion without altering barrier function. This stimulatory effect could be blocked by basolateral atropine but not indomethacin. The cysteine and methionine oxidizing compounds, phenylarsine oxide and chloramine T respectively, mimicked the effect of H₂O₂, except for a drop in transcolonic resistance after 30 min. In contrast to the observed stimulatory effect on basal secretion, cAMP-stimulated electrogenic ion transport was blunted by luminal H₂O₂. However, the Ca²⁺-activated response remained unchanged.

CONCLUSION: H₂O₂ may be an important selective modulator of intestinal ion and water secretion in certain pathologic conditions such as inflammation or ischemia-reperfusion by multiple mechanisms.

The SloR/Dlg metalloregulator modulates Streptococcus mutans virulence gene expression

Metal ion availability in the human oral cavity plays a putative role in Streptococcus mutans virulence gene expression and in appropriate formation of the plaque biofilm. In this report, we present evidence that supports such a role for the DtxR-like SloR metalloregulator (called Dlg in our previous publications) in this oral pathogen. Specifically, the results of gel mobility shift assays revealed the sloABC, sloR, comDE, ropA, sod, and spaP promoters as targets of SloR binding. We confirmed differential expression of these genes in a GMS584 SloR-deficient mutant versus the UA159 wild-type progenitor by real-time semiquantitative reverse transcriptase PCR experiments. The results of additional expression studies support a role for SloR in S. mutans control of glucosyltransferases, glucan binding proteins, and genes relevant to antibiotic resistance. Phenotypic analysis of GMS584 revealed that it forms aberrant biofilms on an abiotic surface, is compromised for genetic competence, and demonstrates heightened incorporation of iron and manganese as well as resistance to oxidative stress compared to the wild type. Taken together, these findings support a role for SloR in S. mutans adherence, biofilm formation, genetic competence, metal ion homeostasis, oxidative stress tolerance, and antibiotic gene regulation, all of which contribute to S. mutans-induced disease.

Superoxide stimulates NaCl absorption in the thick ascending limb via activation of protein kinase C

Abnormal production of superoxide (O(2)(-)) contributes to hypertension, in part because of its effects on the kidney. The thick ascending limb absorbs 20% to 30% of the filtered load of NaCl. O(2)(-) stimulates NaCl absorption by the thick ascending limb by enhancing Na(+)/K(+)/2Cl(-) cotransporter activity; however, the signaling mechanism is unknown. We hypothesized that O(2)(-) stimulates NaCl absorption by activating protein kinase C (PKC). To test this, we measured the effect of O(2)(-) on: (1) Cl(-) absorption in the presence and absence of PKC inhibitors, (2) total PKC activity, and (3) activation of specific PKC isoforms. Isolated perfused medullary thick ascending limbs were exposed to O(2)(-) generated by xanthine oxidase (1 mU/mL) and hypoxanthine (0.5 mmol/L). O(2)(-) increased Cl(-) absorption by 42% (from 76.2+/-3.6 to 108.2+/-11.9 pmol/min per millimeter; n=5; P<0.05). After treatment with the general PKC inhibitor staurosporine (10 nmol/L), O(2)(-) did not stimulate Cl(-) absorption (Delta-5.7+/-8.6%; n=6). In thick ascending limb suspensions, O(2)(-) increased total PKC activity by 33% (from 66+/-11 to 88+/-12 mU/mg protein; n=5; P<0.05) and increased PKC-alpha and PKC-delta activity by 1.75- and 0.37-fold, respectively. The PKC-alpha/beta-selective inhibitor Gö976 (100 nmol/L) blocked the ability of O(2)(-) to stimulate Cl(-) absorption by isolated perfused medullary thick ascending limbs (Delta4.5+/-15.0%; n=5). The role of PKC-delta could not be studied because of cell necrosis caused by the selective inhibitor rottlerin. We conclude that PKC-alpha is required for O(2)(-)-stimulated NaCl absorption in the thick ascending limb.

Translocation of inhaled ultrafine manganese oxide particles to the central nervous system

BACKGROUND

Studies in monkeys with intranasally instilled gold ultrafine particles (UFPs; <100 nm) and in rats with inhaled carbon UFPs suggested that solid UFPs deposited in the nose travel along the olfactory nerve to the olfactory bulb.

METHODS

To determine if olfactory translocation occurs for other solid metal UFPs and assess potential health effects, we exposed groups of rats to manganese (Mn) oxide UFPs (30 nm; approximately 500 microg/m(superscript)3(/superscript)) with either both nostrils patent or the right nostril occluded. We analyzed Mn in lung, liver, olfactory bulb, and other brain regions, and we performed gene and protein analyses.

RESULTS

After 12 days of exposure with both nostrils patent, Mn concentrations in the olfactory bulb increased 3.5-fold, whereas lung Mn concentrations doubled; there were also increases in striatum, frontal cortex, and cerebellum. Lung lavage analysis showed no indications of lung inflammation, whereas increases in olfactory bulb tumor necrosis factor-alpha mRNA (approximately 8-fold) and protein (approximately 30-fold) were found after 11 days of exposure and, to a lesser degree, in other brain regions with increased Mn levels. Macrophage inflammatory protein-2, glial fibrillary acidic protein, and neuronal cell adhesion molecule mRNA were also increased in olfactory bulb. With the right nostril occluded for a 2-day exposure, Mn accumulated only in the left olfactory bulb. Solubilization of the Mn oxide UFPs was <1.5% per day.

CONCLUSIONS

We conclude that the olfactory neuronal pathway is efficient for translocating inhaled Mn oxide as solid UFPs to the central nervous system and that this can result in inflammatory changes. We suggest that despite differences between human and rodent olfactory systems, this pathway is relevant in humans.

The potential and short-circuit current across isolated rumen epithelium of the sheep

1. A technique is described for working with isolated sheets of rumen epithelium. Epithelium was obtained at operations for rumen fistulation or in acute experiments and was rapidly mounted between two cone-shaped chambers each of which held 40 ml. of bathing fluid. The fluids were gassed with 95% O2/5% CO2 and 20 cm2 of epithelium was exposed to the fluids. 2. Electrical measurements were made of (a) the potential generated across the epithelium, (b) the short-circuit current which flowed and (c) the resistance of the epithelium. 3. The results are grouped according to the composition of the sheep Ringer solution used to bathe the epithelium. The most stable preparation was obtained when the solutions contained 5 mM each of glucose, acetate, propionate and butyrate as well as bicarbonate and phosphate buffers. 4. In Cl- media, the average initial p.d., short-circuit current (s.-c.c.) and resistance were 9.3 mV, 11.6 microA/cm2 and 1156 omega x cm2 respectively. Higher values of 17.6 mV, 17.3 microA/cm2 and 1501omega x cm2 were recorded in SO4(2-) media. In both media, the s.-c.c. declined at approximately 1.5 microA/cm2. hr and preparations were suitable for study over periods from 4 to 6 hr. 5. When the concentration of potassium was varied on either side of the epithelium at constant [Na+], the potential showed a linear relation with log [K+] for both sides of the epithelium. 6. Changing the sodium concentrations at constant [K+] on either side of the epithelium caused negligible alterations in the potential. 7. Exclusion of sodium from the media bathing both sides of the epithelium abolished the potential and s.-c.c. 8. The addition of ouabain to the blood side of the preparation abolished the potential and s.-c.c. whereas on the rumen side these parameters were unaffected.

Observations on the potential across the rumen of the sheep

1. The electric potential difference between rumen contents and jugular venous blood was measured in anaesthetized sheep. In order to investigate the effect on the potential of changing the ionic concentrations within the rumen, the digesta were removed from the rumen and various salt solutions were substituted. The reticulo-rumen sac was isolated before the experiment by ligation of the oesophagus and the reticulo-omasal junction. 2. The observation of Dobson & Phillipson (1958) that the rumen contents are normally of the order of 30 mV negative to the blood was confirmed. 3. For potassium concentrations between 25 and 100 mM the potential at constant [Na+] varied linearly with log [K+]. With sulphate as the anion, the slope for a 10-fold concentration change was 39.7 +/- 3.0 mV when [Na+] was around 50 mM. The slope showed a tendency to increase when [Na+] was lowered, and to decrease when [Na+] was raised. 4. When chloride was substituted for sulphate, both the slope and the absolute size of the potential were slightly reduced. 5. When the sodium concentration was varied at constant [K+], the potential increased as an approximately linear function of [Na+]. At around 10 mM-K the mean slope was 0-32 +/- 0.07 mV/mM; at the highest potassium concentrations it fell to 0-13 +/- 0 05 mV/mM. 6. In most of these experiments isotonicity was maintained with sucrose. The results of a few tests in which Li+ was substituted for Na+ or K+ suggested that the rumen epithelium behaves in a relatively inert fashion towards this ion.

Quantitative elemental analysis on aluminum accumulation by HVTEM-EDX in liver tissues of mice orally administered with aluminum chloride

Quantitative elemental analysis on Al was carried out by high-accelerating voltage transmission electron microscopy (HVTEM) equipped with energy-dispersive X-ray microanalysis (EDX) using an accelerating voltage at 300 kV with high permeability in 1-mum-thick samples obtained from mice administered with aluminum chloride solution for 3, 9, and 17 weeks. By light microscopic observation, no morphological changes were observed in the hepatocytes and macrophages in the liver tissues of mice that were administered with excess Al as compared with the normal control mice. In contrast, by electron microscopic observation, ultrastructural changes were observed in the lysosomes in the hepatocytes as well as the pinocytotic vesicles in the macrophages in the experimental animals. Therefore, the concentrations of Al detected in lysosomes in hepatocytes and pinocytotic vesicles in macrophages of livers of mice administered with Al were measured in relationship to those administration periods. Moreover, transitional changes of hepatocyte lysosome ratios by image analysis and the macrophage counts in the unit area increased in liver tissues of mice administered with Al as compared with normal control mice. From the results, it was demonstrated that hepatocyte lysosome ratio and macrophage count increased in liver tissues of treated mice during those short-term excessive Al administration periods. It was also clarified that the concentrations of Al in both hepatocytes and macrophages increased as observed by HVTEM-EDX. In conclusion, Al accumulated in hepatocytes and macrophages at 3 and 9 weeks administration, while the ultrastructural changes remained in the hepatocytes and macrophages. In contrast, Al concentration did not increase in the liver at 17 weeks administration.

Removal of molybdate from water by adsorption onto ZnCl2 activated coir pith carbon

Removal and recovery of molybdate from aqueous solution was investigated using ZnCl2 activated carbon developed from coir pith. Studies were conducted to delineate the effects of contact time, adsorbent dose, molybdate concentration, pH and temperature. Two theoretical adsorption isotherms, namely, Langmuir and Freundlich were used to describe the experimental results. The Langmuir adsorption capacity (Q0) was found to be 18.9 mg molybdate/g of the adsorbent. Adsorption followed second order kinetics. Studies were performed at different pH values to find out the pH at which maximum adsorption occurred. The pH effect and desorption studies showed that ion exchange and chemisorption mechanism were involved in the adsorption process. Thermodynamic parameters such as DeltaG0, DeltaH0 and DeltaS0 for the adsorption were evaluated. Effect of foreign ions on adsorption of molybdate has been examined. The results showed that ZnCl2 activated coir pith carbon was effective for the removal and recovery of molybdate from water.

Desiccation responses and survival of Sinorhizobium meliloti USDA 1021 in relation to growth phase, temperature, chloride and sulfate availability

AIMS

To identify physical and physiological conditions that affect the survival of Sinorhizobium meliloti USDA 1021 during desiccation.

METHODS AND RESULTS

An assay was developed to study desiccation response of S. meliloti USDA 1021 over a range of environmental conditions. We determined the survival during desiccation in relation to (i) matrices and media, (ii) growth phase, (iii) temperature, and (iv) chloride and sulfate availability.

CONCLUSIONS

This study indicates that survival of S. meliloti USDA 1021 during desiccation is enhanced: (i) when cells were dried in the stationary phase, (ii) with increasing drying temperature at an optimum of 37 degrees C, and (iii) during an increase of chloride and sulfate, but not sodium or potassium availability. In addition, we resolved that the best matrix to test survival was nitrocellulose filters.

SIGNIFICANCE AND IMPACT OF THE STUDY

The identification of physical and physiological factors that determine the survival during desiccation of S. meliloti USDA 1021 may aid in (i) the strategic development of improved seed inocula, (ii) the isolation, and (iii) the development of rhizobial strains with improved ability to survive desiccation. Furthermore, this work may provide insights into the survival of rhizobia under drought conditions.

Cl- channels of the distal nephron

Cl- currents were observed under whole cell clamp conditions in cells of the rat cortical collecting duct (CCD), connecting tubule (CNT), and thick ascending limb of Henle's loop (TALH). These currents were much larger in intercalated cells compared with principal cells of the CCD and were also larger in the TALH and in the CNT compared with the CCD. The conductance had no strong voltage dependence, and steady-state currents were similar in inward and outward directions with similar Cl- concentrations on both sides of the membrane. Current transients were observed, particularly at low Cl- concentrations, which could be explained by solute depletion and concentration in fluid layers next to the membrane. The currents had a remarkable selectivity among anions. Among halides, Br- and F- conductances were only 15% of that of Cl-, and I- conductance was immeasurably small. SCN- and OCN- conductances were approximately 50%, and aspartate, glutamate, and methanesulfonate conductance was approximately 5% that of Cl-. No conductance could be measured for any other anion tested, including NO3-, HCO3-, formate, acetate, or isethionate; NO3- and I- appeared to block the channels weakly. Conductances were diminished by lowering the extracellular pH to 6.4. The properties of the conductance fit best with those of the cloned renal anion channel ClC-K2 and likely reflect the basolateral Cl- conductances of the cells of these nephron segments.

Tissue distribution and subcellular localization of trace metals in the pond snail Lymnaea stagnalis with special reference to the role of lysosomal granules in metal sequestration

The present study was undertaken to elucidate the cellular mechanisms, which govern metal sequestration and detoxification in gastropods. For this purpose the pond snail, Lymnaea stagnalis was exposed to environmentally relevant concentrations of three species of metals (Al, Zn and Cd) for 30 days and the localization and fate of these metals were followed in different tissues of the snails. The measurement of relative distribution of metals between tissues revealed that the digestive gland and kidney account for most of the accumulated metals. Al and Cd (non-essential metals) were redistributed to the digestive gland, possibly because of the presence of specific binding entities in the digestive glands of the herein species. This study focuses on the role of intracellular metal-containing granules on metal sequestration. Three main types of granules were identified in the digestive gland cells namely small, green and yellow granules. The morphological examination and the progressive accumulation of elements within these granules revealed that they are developmental stages with the yellow granule being the mature one. The total number of these granules was found to be significantly increased upon exposure of the snails to Al only. This increase may be a response to the large amount of Al that is accumulated through feeding route of this grazing snail. X-ray microanalysis (XRMA) revealed that metals were localized in all three types of digestive gland granules. The increased amount of ligands (P and S) in the granules may give evidence for their role in metal sequestration. Levels of Al and P were positively correlated in the digestive gland granules. It is possible that aluminium is bound to phosphorus to render it insoluble and so to both immobilize it within the lysosome and to be excreted in a highly insoluble form. On the other hand, both Zn and Cd induced marked upregulation of S in mature (yellow) granules by 26- and 11-folds, respectively. The lysosomal codeposition of S and either Cd or Zn in the lysosomal granules in addition to the increase in RER cisternae may indicate that the exposure to these metals could induce metallothionein synthesis in the cells. The microscopical examinations in the present study revealed that metal detoxification from the digestive gland cells may occur via faeces or via basal exocytosis towards hemocytes dispersed by the connective tissue in the visceral mass. In the kidney, one type of granules, the excretory concretions, was identified in the nephrocytes. The significant increase in the number of these concretions in the snail L. stagnalis upon exposure to metals may give further evidence for their role in metal excretion.

Postnatal manganese exposure attenuates cocaine-induced locomotor activity and reduces dopamine transporters in adult male rats

In the present study, we examined whether exposing rats to manganese (Mn) during the preweanling period would affect basal or cocaine-induced locomotor activity in adulthood and reduce the number of striatal dopamine transporter binding sites. On postnatal day (PD) 1-21, rats were given oral supplements of vehicle or Mn chloride (250 or 750 microg/day). Striatal Mn and iron (Fe) accumulation as well as serum Fe levels were measured on PD 14, PD 21, and PD 90. Throughout the dosing period, rats were evaluated on standard measures of sensory and motor development. During adulthood, the basal and cocaine-induced locomotor activity of vehicle- and Mn-exposed rats was assessed using automated testing chambers. After completion of behavioral testing, striatal dopamine transporter binding sites were measured using [(3)H]GBR 12935. Results showed that early Mn exposure enhanced striatal Mn accumulation on PD 14 and PD 21, while depressing serum Fe levels on PD 21. Exposure to Mn on PD 1-21 did not affect striatal or serum Mn or Fe levels on PD 90. During the second postnatal week, Mn-exposed rat pups performed more poorly than controls on a negative geotaxis task, however basal motor activity of preweanling rat pups was not affected by Mn treatment. When tested in adulthood, basal locomotor activity of vehicle- and Mn-exposed rats also did not differ. In contrast, adult rats previously exposed to 750 microg/day Mn showed an enhanced locomotor response when challenged with 10 mg/kg cocaine. A different pattern of results occurred after treatment with a higher dose of the psychostimulant, because Mn-exposed rats showed an attenuated locomotor response when given 20 mg/kg cocaine. Importantly, Mn-exposed rats exhibited long-term reductions in striatal dopamine transporter binding sites. Considered together, these results indicate that postnatal Mn exposure has long-term behavioral and neurochemical effects that can persist into adulthood.

Postprandial augmentation of absorption of water and electrolytes in jejunum is neurally modulated: implications for segmental small bowel transplantation

Postprandial augmentation of absorption of water and electrolytes is believed to occur in the jejunum. Neural mechanisms of control, however, have not been studied in the in situ jejunum or in the transplanted bowel. The aim of this study was to determine if postprandial augmentation of absorption occurs in the in situ jejunum and to evaluate neural mechanisms controlling postprandial jejunal absorption. Based on our previous work, we hypothesized that postprandial augmentation of absorption does not occur in the jejunum in situ and that extrinsic denervation of the jejunum is associated with decreased postprandial absorption. Absorption was studied in an 80 cm, in situ jejunal segment in six dogs by using an isosmolar electrolyte solution alone, or with 80 mmol/L glucose before and after jejunal transection to disrupt intrinsic neural continuity of the study segment with the remaining gut. Net absorptive fluxes of water and electrolytes were measured in the fasted state and after a 400-kcal meal. Another six dogs were studied 3 weeks after our validated model of extrinsic denervation of jejunoileum; identical fasting and postprandial absorptive states were evaluated. Postprandial augmentation of absorption of water and electrolytes did occur in the jejunum (P < 0.03) both in the absence and in the presence of intraluminal glucose. After intrinsic neural transection or extrinsic denervation, no postprandial augmentation of absorption occurred, with or without glucose. Postprandial augmentation of absorption of water and electrolytes occurs in the in situ jejunum. Disrupting intrinsic neural continuity or extrinsic denervation (as after intestinal transplantation) abolishes postprandial augmentation.

Basal Ganglia accumulation and motor assessment following manganese chloride exposure in the C57BL/6 mouse

Equivocal clinical evidence for involvement of manganese in development of Parkinson's disease necessitates experimental studies on this issue. The aged, 1-methyl-4-phenyl-1,2,3,6-tetrahyropyridine-treated C57BL/6 mouse is one of the most common models for Parkinson's disease. However, there is little information on brain bioaccumulation of manganese, and little or no information on clinical/behavioral manifestations of manganese neurotoxicity, in this strain. Male C57BL/6 retired breeder mice were given a single subcutaneous injection of either 0, 50, or 100 mg/kg of MnCl(2) (single-dose regimen) or three injections of either of these doses over 7 days (multiple-dose regimen). Behavioral assessment was performed 24 h after final injection, followed by sacrifice, and body weight was recorded each day. There was a 105% increase in striatal manganese concentration 1 day after a single 100 mg/kg injection, and 421% and 647% increases, respectively, 1 day after multiple doses of 50 or 100 mg/kg of MnCl(2). One day after a single injection, there were respective 30.9% and 38.9% decreases in horizontal movement (grid crossing) for the 50 and 100 mg/kg doses and a 43.2% decrease for the multiple dose of 100 mg/kg. There was no significant main effect of dose level on rearing, swimming, grip strength, or grip fatigue. Unlike previous work with the C57BL/6 strain using smaller intraperitoneal doses, this study established dosing regimens that produced significant increases in basal ganglia manganese concentration reminiscent of brain increases in the CD-1 mouse following subcutaneous doses close to our lowest. A decrease in locomotor behavior, significant but not severe in this study, has been reported following manganese exposure in other mouse strains. These data, particularly the significant increase in basal ganglia manganese concentration, provide guidance for designing studies of the potential role of manganese in Parkinson's disease using the most common animal model for the disorder.