Investigation of Dissolution Behavior HPMC/Eudragit<Superscript>®</Superscript>/Magnesium Aluminometasilicate Oral Matrices Based on NMR Solid-State Spectroscopy and Dynamic Characteristics of Gel Layer

Burst drug release is often considered a negative phenomenon resulting in unexpected toxicity or tissue irritation. Optimal release of a highly soluble active pharmaceutical ingredient (API) from hypromellose (HPMC) matrices is technologically impossible; therefore, a combination of polymers is required for burst effect reduction. Promising variant could be seen in combination of HPMC and insoluble Eudragits^® as water dispersions. These can be applied only on API/insoluble filler mixture as over-wetting prevention. The main hurdle is a limited water absorption capacity (WAC) of filler. Therefore, the object of this study was to investigate the dissolution behavior of levetiracetam from HPMC/Eudragit^®NE matrices using magnesium aluminometasilicate (Neusilin^® US2) as filler with excellent WAC. Part of this study was also to assess influence of thermal treatment on quality parameters of matrices. The use of Neusilin^® allowed the application of Eudragit^® dispersion to API/Neusilin^® mixture in one step during high-shear wet granulation. HPMC was added extragranularly. Obtained matrices were investigated for qualitative characteristics, NMR solid-state spectroscopy (ssNMR), gel layer dynamic parameters, SEM, and principal component analysis (PCA). Decrease in burst effect (max. of 33.6%) and dissolution rate, increase in fitting to zero-order kinetics, and paradoxical reduction in gel layer thickness were observed with rising Eudragit^® NE concentration. The explanation was done by ssNMR, which clearly showed a significant reduction of the API particle size (150–500 nm) in granules as effect of surfactant present in dispersion in dependence on Eudragit^®NE amount. This change in API particle size resulted in a significantly larger interface between these two entities. Based on ANOVA and PCA, thermal treatment was not revealed as a useful procedure for this system.     

A review of the off-label use of selamectin (Stronghold<Superscript>®</Superscript>/Revolution<Superscript>®</Superscript>) in dogs and cats

Since its introduction approximately seven years ago, selamectin (Stronghold^®/Revolution^®, Pfizer Inc.) has been used off-label to treat a number of ecto- and endoparasite conditions in dogs and cats. It has been used as a successful prophylactic against Dirofilaria repens and as a treatment for Aelurostrongylus abstrusus in cats. It has also been used to treat notoedric mange, infestation with the nasal mite Pneumonyssoides caninum, Cheyletiella spp. and Neotrombicula autumnalis infestations and larval Cordylobia anthropophaga infection. However, to date attempts to treat generalised canine demodicosis have not been successful. In all cases, treatment was apparently well tolerated by the host.     

Prolonged Intragastric Drug Delivery Mediated by Eudragit<Superscript>®</Superscript><Emphasis Type="Bold">E-Carrageenan Polyelectrolyte Matrix Tablets</Emphasis>

Interpolyelectrolyte (IPE) complexation between carrageenan (CG) and Eudragit E (EE) was studied in 0.1 M HCl and was used to develop floating matrix tablets aimed to prolong gastric-residence time and sustain delivery of the loaded drug. The optimum EE/CG IPE complexation weight ratio (0.6) was determined in 0.1 M HCl using apparent viscosity measurements. The IPE complex was characterized by Fourier transform infrared spectroscopy and differential scanning calorimetry. Metronidazole matrix tablets were prepared by direct compression using EE, CG, or hybrid EE/CG with ratio optimal for IPE complexation. Corresponding effervescent tablets were prepared by including Na bicarbonate as an effervescent agent. Tablets were evaluated for in vitro buoyancy and drug release in 0.1 M HCl. Both CG and EE–CG effervescent matrices (1:2 drug to polymer weight ratio, 60 mg Na bicarbonate) achieved fast and prolonged floating with floating lag times less than 30 s and floating duration of more than 10 h. The corresponding EE effervescent matrices showed delayed floating and rapid drug release, and completely dissolved after 3 h of dissolution. CG matrices showed an initial burst drug release (48.3 ± 5.0% at 1 h) followed by slow drug release over 8 h. EE–CG matrices exhibited sustained drug release in almost zero-order manner for 10 h (68.2 ± 6.6%). The dissolution data of these matrices were fitted to different dissolution models. It was found that drug release followed zero-order kinetics and was controlled by the superposition of the diffusion and erosion.     

The Effect of Contrast Medium SonoVue<Superscript>®</Superscript> on the Electric Charge Density of Blood Cells

The effect of contrast medium SonoVue® on the electric charge density of blood cells (erythrocytes and thrombocytes) was measured using a microelectrophoretic method. We examined the effect of adsorbed H⁺ and OH^? ions on the surface charge of erythrocytes or thrombocytes. Surface charge density values were determined from electrophoretic mobility measurements of blood cells performed at various pH levels. The interaction between solution ions and the erythrocyte’s or thrombocyte’s surface was described by a four-component equilibrium model. The agreement between the experimental and theoretical charge variation curves of the erythrocytes and thrombocytes was good at pH 2–9. The deviation observed at a higher pH may be caused by disregarding interactions between the functional groups of blood cells.     

Comparison of Alexa Fluor<Superscript>®</Superscript> and CyDye<Superscript>™</Superscript> for practical DNA microarray use

Microarrays are a powerful tool for comparison and understanding of gene expression levels in healthy and diseased states. The method relies upon the assumption that signals from microarray features are a reflection of relative gene expression levels of the cell types under investigation. It has previously been reported that the classical fluorescent dyes used for microarray technology, Cy3 and Cy5, are not ideal due to the decreased stability and fluorescence intensity of the Cy5 dye relative to the Cy3, such that dye bias is an accepted phenomena necessitating dye swap experimental protocols and analysis of differential dye affects. The incentive to find new fluorophores is based on alleviating the problem of dye bias through synonymous performance between counterpart dyes. Alexa Fluor 555 and Alexa Fluor 647 are increasingly promoted as replacements for CyDye in microarray experiments. Performance relates to the molecular and steric similarities, which will vary for each new pair of dyes as well as the spectral integrity for the specific application required. Comparative analysis of the performance of these two competitive dye pairs in practical microarray applications is warranted towards this end. The findings of our study showed that both dye pairs were comparable but that conventional CyDye resulted in significantly higher signal intensities (P < 0.05) and signal minus background levels (P < 0.05) with no significant difference in background values (P > 0.05). This translated to greater levels of differential gene expression with CyDye than with the Alexa Fluor counterparts. However, CyDye fluorophores and in particular Cy5, were found to be less photostable over time and following repeated scans in microarray experiments. These results suggest that precautions against potential dye affects will continue to be necessary and that no one dye pair negates this need.     

The Antioxidant and Antigenotoxic Effects of Pycnogenol<Superscript>®</Superscript> on Rats Treated With Cisplatin

Oxidative stress and inflammation are implicated in the pathogenesis of cisplatin-induced toxicity. Pycnogenol® is known for its strong antioxidant and anti-inflammatory effects. In this study, the possible protective effects of pycnogenol on kidney, bone marrow, and red blood cells in rats treated with cisplatin were investigated. The rats were divided into four groups. Group 1 was the control and groups 2, 3, and 4 were orally treated with pycnogenol (200 mg/kg bw, o.p) for 5 days, treated with cisplatin (7 mg/kg bw, i.p.) on the fifth day and treated with cisplatin plus pycnogenol, respectively. Antioxidative parameters in kidney and red blood cells were measured. Chromosome anomalies in bone marrow and renal histopathology were also investigated. Activities of pro-oxidant enzymes (myeloperoxidase and xanthine oxidase), malondialdehyde, and nitric oxide levels significantly increased but antioxidant enzymes activities decreased in the kidneys and red blood cells after cisplatin treatment. Pycnogenol treatment prior to the administration of cisplatin significantly decreased cisplatin-induced injury, as evidenced by its normalizing these parameters. Chromosomal aberrations decreased and mitotic index frequencies increased in bone marrow treated with cisplatin plus pycnogenol. These findings suggest that pycnogenol may be a useful protective agent against the toxicity associated with cisplatin therapy.     

Effect of different methods of Ca<Superscript>2+</Superscript> extraction from PSII oxygen-evolving complex on the Q<Subscript>A</Subscript><Superscript>−</Superscript> oxidation kinetics

Lumenal extrinsic proteins PsbO, PsbP, and PsbQ of photosystem II (PSII) protect the catalytic cluster Mn₄CaO₅ of oxygen-evolving complex (OEC) from the bulk solution and from soluble compounds in the surrounding medium. Extraction of PsbP and PsbQ proteins by NaCl-washing together with chelator EGTA is followed also by the depletion of Ca²⁺ cation from OEC. In this study, the effects of PsbP and PsbQ proteins, as well as Ca²⁺ extraction from OEC on the kinetics of the reduced primary electron acceptor (Q_A ^?) oxidation, have been studied by fluorescence decay kinetics measurements in PSII membrane fragments. We found that in addition to the impairment of OEC, removal of PsbP and PsbQ significantly slows the rate of electron transfer from Q_A ^? to the secondary quinone acceptor Q_B. Electron transfer from Q_A ^? to Q_B in photosystem II membranes with an occupied Q_B site was slowed down by a factor of 8. However, addition of EGTA or CaCl₂ to NaCl-washed PSII did not change the kinetics of fluorescence decay. Moreover, the kinetics of Q_A ^? oxidation by Q_B in Ca-depleted PSII membranes obtained by treatment with citrate buffer at pH 3.0 (such treatment keeps all extrinsic proteins in PSII but extracts Ca²⁺ from OEC) was not changed. The results obtained indicate that the effect of NaCl-washing on the Q_A ^? to Q_B electron transport is due to PsbP and PsbQ extrinsic proteins extraction, but not due to Ca²⁺ depletion.     

Flow of Deposited Inorganic N in Two Gleysol-dominated Mountain Catchments Traced with <Superscript>15</Superscript>NO<Subscript>3</Subscript><Superscript>−</Superscript> and <Superscript>15</Superscript>NH<Subscript>4</Subscript><Superscript>+</Superscript>

In two mountain ecosystems at the Alptal research site in central Switzerland, pulses of ¹⁵NO₃ and ¹⁵NH₄ were separately applied to trace deposited inorganic N. One forested and one litter meadow catchment, each approximately 1600 m², were delimited by trenches in the Gleysols. K¹⁵NO₃ was applied weekly or fortnightly over one year with a backpack sprayer, thus labelling the atmospheric nitrate deposition. After the sampling and a one-year break, ¹⁵NH₄Cl was applied as a second one-year pulse, followed by a second sampling campaign. Trees (needles, branches and bole wood), ground vegetation, litter layer and soil (LF, A and B horizon) were sampled at the end of each labelling period. Extractable inorganic N, microbial N, and immobilised soil N were analysed in the LF and A horizons. During the whole labelling period, the runoff water was sampled as well. Most of the added tracer remained in both ecosystems. More NO₃⁻ than NH₄⁺ tracer was retained, especially in the forest. The highest recovery was in the soil, mainly in the organic horizon, and in the ground vegetation, especially in the mosses. Event-based runoff analyses showed an immediate response of ¹⁵NO₃⁻ in runoff, with sharp ¹⁵N peaks corresponding to discharge peaks. NO₃⁻ leaching showed a clear seasonal pattern, being highest in spring during snowmelt. The high capacity of N retention in these ecosystems leads to the assumption that deposited N accumulates in the soil organic matter, causing a progressive decline of its C:N ratio.     

Improved accuracy of <Superscript>15</Superscript>N–<Superscript>1</Superscript>H scalar and residual dipolar couplings from gradient-enhanced IPAP-HSQC experiments on protonated proteins

The presence of dipole-dipole cross-correlated relaxation as well as unresolved E.COSY effects adversely impacts the accuracy of ¹ J _NH splittings measured from gradient-enhanced IPAP-HSQC spectra. For isotropic samples, the size of the systematic errors caused by these effects depends on the values of ² J _NHα , ³ J _NHβ and ³ J _HNHα . Insertion of band-selective ¹H decoupling pulses in the IPAP-HSQC experiment eliminates these systematic errors and for the protein GB3 yields ¹ J _NH splittings that agree to within a root-mean-square difference of 0.04 Hz with values measured for perdeuterated GB3. Accuracy of the method is also highlighted by a good fit to the GB3 structure of the ¹H-¹⁵N RDCs extracted from the minute differences in ¹J_NH splitting measured at 500 and 750 MHz ¹H frequencies, resulting from magnetic susceptibility anisotropy. A nearly complete set of ² J _NHα couplings was measured in GB3 in order to evaluate whether the impact of cross-correlated relaxation is dominated by the ¹⁵N–¹H ^α or ¹⁵N–¹H ^β dipolar interaction. As expected, we find that ² J _NHα  ≤ 2 Hz, with values in the α-helix (0.86 ± 0.52 Hz) slightly larger than in β-sheet (0.66 ± 0.26 Hz). Results indicate that under isotropic conditions, N–H^N/N–H ^β cross-correlated relaxation often dominates. Unresolved E.COSY effects under isotropic conditions involve ³ J _HNHα and J _NHα , but when weakly aligned any aliphatic proton proximate to both N and H^N can contribute. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Tolerability and efficacy of the intestinal phosphate binder Lantharenol<Superscript>®</Superscript> in cats

Background

Tolerability and efficacy of the intestinal phosphate binder Lantharenol^® (lanthanum carbonate octahydrate) were tested in two prospective, randomized and negative controlled laboratory studies with healthy adult cats fed commercial maintenance diets non-restricted in phosphorus. In the first study, the maximal tolerated dose was determined. Starting from a dose of 0.125 g/kg body weight mixed with the daily feed ration, the dose of Lantharenol^® was doubled every other week until signs of intolerability were observed (N = 10 cats compared to 5 untreated controls). In the second study, the effects of feed supplementation for two weeks with approximately 2, 6, and 20% of the maximal tolerated dose on phosphorus excretion patterns and balance were assessed (N = 8 cats per group).

Results

Lantharenol^® was found to be safe and well tolerated up to the dose of 1 g/kg bodyweight, corresponding to a concentration of 84 g Lantharenol^®/kg complete feed, defined as dry matter with a standard moisture content of 12%. Feed supplementation for two weeks with approximately 2-20% of this dosage (i.e., 1.6, 4.8, and 16 g/kg complete feed) resulted in a shift from urinary to faecal phosphorus excretion. Apparent phosphorus digestibility was dose-dependently reduced compared to the control group fed with diet only (N = 8).

Conclusions

The feed additive was well accepted and tolerated by all cats. Therefore, Lantharenol^® presents a well tolerated and efficacious option to individually tailor restriction of dietary phosphorus as indicated, for instance, in feline chronic kidney disease.

     

Molecular Weight and Subunit Composition of the Sensitive to GABA-Ergic Ligands Cl<Superscript>−</Superscript>/HCO<Stack><Subscript>3</Subscript><Superscript>−</Superscript></Stack>-Stimulated Mg<Superscript>2+</Superscript>-ATPase from Plasma Membrane of Rat Brain

The molecular weight and subunit composition of Cl-,HCO3(-)- and picrotoxin-stimulated Mg2+-ATPase from rat brain plasma membrane solubilized in sodium deoxycholate were studied by gel filtration chromatography. The enzyme activity eluted from a Sephacryl S-300 column in a single peak associated with a protein of molecular weight approximately 300 kD and a Stokes radius of 5.4 nm. The enzyme-enriched fraction, concentrated and denatured by SDS, migrated through a Sephacryl S-200 column as three peaks with molecular weights of approximately 57, 53, and 45 kD. SDS-PAGE also showed three major protein bands with molecular weights of about 57, 53, and 48 kD. The molecular weight and subunit composition of the Cl- and HCO3(-)-stimulated Mg2+-ATPase from neuronal membrane of rat brain are similar with the molecular properties of GABA(A)-benzodiazepine receptor complex from mammalian brain but are different from those of P-type transport ATPases.     

The Effect of Acid pH Modifiers on the Release Characteristics of Weakly Basic Drug from Hydrophlilic–Lipophilic Matrices

The solubility of weakly basic drugs within passage though GI tract leads to pH-dependent or even incomplete release of these drugs from extended release formulations and consequently to lower drug absorption and bioavailability. The aim of the study was to prepare and evaluate hydrophilic–lipophilic (hypromellose–montanglycol wax) matrix tablets ensuring the pH-independent delivery of the weakly basic drug verapamil-hydrochloride by an incorporation of three organic acidifiers (citric, fumaric, and itaconic acids) differing in their concentrations, pK_a, and solubility. The dissolution studies were performed by the method of changing pH values, which better corresponded to the real conditions in the GI tract (2 h at pH 1.2 and then 10 h at pH 6.8). Within the same conditions, pH of matrix microenvironment was measured. To determine relationships between the above mentioned properties of acidifiers and the monitored effects (the amount of released drug and surface pH of gel layer in selected time intervals—360 and 480 min), the full factorial design method and partial least squares PLS-2 regression were used. The incorporation of the tested pH modifiers significantly increased the drug release rate from matrices. PLS-components explained 75% and 73% variation in the X- and Y-data, respectively. The obtained results indicated that the main crucial points (p < 0.01) were the concentration and strength of acidifier incorporated into the matrix. Contrary, the acid solubility surprisingly did not influence the selected effects except for the surface pH of gel layer in time 480 min.Key words: gel layer, matrix tablets, pH-independent drug release, pH modifiers, statistical evaluation     

Effect of culture container and carbohydrate content on in vitro slow growth storage of the cherry rootstock ‘Gisela<Superscript>®</Superscript>5’

The present study investigated the effects of gas-tight and gas-permeable culture containers and different sucrose concentrations, as well as sucrose and mannitol combinations on the development of an effective in vitro slow growth storage protocol (at 4 °C, in darkness) for ‘Gisela^®5’ shoot cultures. ‘Gisela^®5’ is the most widely used cherry rootstock in Europe. This dwarf triploid hybrid has many advantages over the conventional cherry rootstocks. Optimizations for the cold storage of ‘Gisela^®5’ in vitro shoot cultures included use of storage medium supplemented with 10, 20, 30, 45, and 60 g L^?1 sucrose and sucrose (15, 30 g L^?1) and mannitol (15 g L^?1) combinations, contained in gas-tight glass jars and gas-permeable ‘Star Pac?’ bags. Cold storage was prolonged to 12 months, during which in every 3 months, cultures were evaluated. Possibility of 16 month-cold storage in gas-tight glass jars was also explored, during which gas chromatographic analysis was performed for the detection of CO₂ and ethylene accumulation for the first 5 months of cold storage. Our results showed that both the 12- and 16-month conservations were possible, especially when 45 or 60 g L^?1 sucrose was supplemented to storage medium, contained in glass jars. Mannitol inclusion to the storage medium was also effective to reduce the metabolic activity of the shoot cultures during storage; however, it did not have a significant positive influence on shoot quality in post-conservation.     

Toxicological evaluation of genetically modified cotton (Bollgard<Superscript>®</Superscript>) and Dipel<Superscript>®</Superscript> WP on the non-target soil mite <Emphasis Type="Italic">Scheloribates praeincisus</Emphasis> (Acari: Oribatida)

Insecticides derived from the bacterium Bacillus thuringiensis (Bt) and plants genetically modified (GM) to express B. thuringiensis toxins are important alternatives for insect pest control worldwide. Risk assessment of B. thuringiensis toxins to non-target organisms has been extensively studied but few toxicological tests have considered soil invertebrates. Oribatid mites are one of the most diverse and abundant arthropod groups in the upper layers of soil and litter in natural and agricultural systems. These mites are exposed to the toxic compounds of GM crops or pesticides mainly when they feed on vegetal products incorporated in the soil. Although some effects of B. thuringiensis products on Acari have been reported, effects on oribatid mites are still unknown. This study investigated the effects of the ingestion of Bt cotton Bollgard and of the B. thuringiensis commercial product Dipel WP on the pantropical species Scheloribates praeincisus (Scheloribatidae). Ingestion of Bollgard and Dipel did not affect adult and immature survivorship and food consumption (estimated by number of fecal pellets produced daily) or developmental time of immature stages of S. praeincisus. These results indicate the safety of Bollgard and Dipel to S. praeincisus under field conditions where exposition is lower and other food sources besides leaves of Bt plants are available. The method for toxicological tests described here can be adapted to other species of Oribatida, consisting on a new option to risk assessment studies.     

Genotoxic and cytotoxic effects of <Superscript>60</Superscript>Co γ-rays and <Superscript>90</Superscript>Sr/<Superscript>90</Superscript>Y β-rays on Chinese hamster ovary cells (CHO-K1)

Among various types of ionizing radiation, the beta emitter radionuclides are involved in many sectors of human activity, such as nuclear medicine, nuclear industries and biomedicine, with a consequently increased risk of accidental, occupational or therapeutic exposure. Despite their recognized importance, there is little information about the effect of beta particles at the cellular level when compared to other types of ionizing radiation. Thus, the objective of the present study was to evaluate the genotoxic and cytotoxic effects of ⁹⁰Sr/⁹⁰Y—a pure, highly energetic beta source—on Chinese hamster ovary (CHO) cells and to compare them with data obtained with ⁶⁰Co. CHO cells irradiated with different doses of ⁶⁰Co (0.34 Gy min^–1) and ⁹⁰Sr/⁹⁰Y (0.23 Gy min^–1) were processed for analysis of clonogenic death, induction of micronuclei (MN) and interphase death. The survival curves obtained for both types of radiation were fitted by the exponential quadratic model and were found to be similar. Also, the cytogenetic results showed similar frequencies of radio-induced MN between gamma and beta radiations and the MN distribution pattern among cells did not follow the expected Poisson probability pattern. The relative variance values were significantly higher in cells irradiated with ⁹⁰Sr/⁹⁰Y than with ⁶⁰Co in all exposure doses. The irradiated cells showed more necrotic cells 72 h and 96 h after exposure to beta than to gamma radiation. In general, the ⁹⁰Sr/⁹⁰Y -radiation was more damaging than ⁶⁰Co -rays. The data obtained also demonstrated the need to use several parameters for a better estimate of cellular sensitivity to the action of genotoxic agents, which would be important in terms of radiobiology, oncology and therapeutics.     

Distribution of Several Activating and Inhibitory Receptors on CD3<Superscript>−</Superscript>CD16<Superscript>+</Superscript> NK Cells and Their Correlation with NK Cell Function in Healthy Individuals

The aim of this study was to estimate the distribution and density of a representative set of activating and inhibitory receptors on gated natural killer (NK) cells, as well as on their bright and dim subsets, and to correlate the receptor expression with NK cell activity for healthy individuals on CD3⁻CD16⁺ NK cells. We show that in 43 healthy controls NK cell activity against K562 target cells was 37.34% (E:T, 80:1) by standard chromium release assay. The expression of receptors on NK cells and their subsets was analyzed by flow cytometry. The cytotoxic CD3⁻CD16^bright NK subset constituted 78.97%, while the regulatory CD3⁻CD16^dim NK subset constituted 21.03% of NK cells. We show the distribution of NKG2D, CD161, CD158a, and CD158b receptors on CD3⁻CD16⁺ NK cells in peripheral blood lymphocytes (PBLs), on gated NK cells, and on the CD3⁻CD16^bright and CD3⁻CD16^dim subsets. Contrary to CD158a and CD158b killer immunoglobulin-like receptors (KIRs), there is a significant positive correlation of NKG2D and CD161 expression with NK cytotoxicity. We show the kinetics of change in CD3⁻CD16⁺NK/K562 conjugate composition, together with the stronger target binding capacity of CD16^bright NK cells. Furthermore, we show that after coculture of PBLs with K562 the expression of CD107a, a degranulation marker, on CD3⁻CD16⁺NK cells and subsets is time dependent and significantly higher on the cytotoxic CD3⁻CD16^bright NK subset. The novel data obtained regarding expression of NK cell activating and inhibitory receptors for healthy individuals may aid in detecting changes that are associated with various diseases.     

Effect of NO<Subscript>3</Subscript><Superscript>−</Superscript>:NH<Subscript>4</Subscript><Superscript>+</Superscript> ratios on growth,root morphology and leaf metabolism of oilseed rape (<Emphasis Type="Italic">Brassica napus</Emphasis> L.) seedlings

The effect of NO₃ ^?:NH₄ ⁺ ratio (14:1, 9:6, 7.5:7.5, 1:14, total 15 mmol/L N) in the nutrient solution on biomass, root morphology, and C and N metabolism parameter in hydroponically grown oilseed rape (Brassica napus L.) was evaluated. The dry weights of leaves and roots were significantly largest at the equal NO₃ ^?:NH₄ ⁺ ratio (7.5:7.5) compared with those of high NO₃ ^?:NH₄ ⁺ ratio (14:1) or low NO₃ ^?:NH₄ ⁺ ratio (1:14). Additionally, low NO₃ ^?:NH₄ ⁺ ratio (1:14) reduced total root length and root surface area compared with the equal NO₃ ^?:NH₄ ⁺ ratio (7.5:7.5), while high NO₃ ^?:NH₄ ⁺ ratio (14:1) did not show any significant effect on root morphology except average diameter. The maximum of chlorophyll a, chlorophyll b and carotenoid were obtained under 7.5:7.5 treatment, whereas the maximum of the leaf net photosynthetic (P _n), stomatal conductance (G _s) and transpiration rate (T _r) were increased with increase in NH₄ ⁺ concentration in the nutrient solution. The activity of nitrate reductase (NR) showed a significant difference at different NO₃ ^?:NH₄ ⁺ ratios and ranged 9:6 > 7.5:7.5 > 14:1 > 1:14, whereas the range of soluble sugar and soluble protein was 7.5:7.5 > 1:14 > 9:6 > 14:1. Our study reveals that oilseed rape growth is greater under 7.5:7.5 treatment than that under three other treatments. Oilseed rape growth at high or low NO₃ ^?:NH₄ ⁺ ratios was inhibited by decreased pigments, NR activity, soluble sugar, and soluble protein, whereas subdued root growth should be apprehended considerate under high NH₄ ⁺ condition.     

Comparative Studies on Dicholesteroyl Diselenide and Diphenyl Diselenide as Antioxidant Agents and their Effect on the Activities of Na<Superscript>+</Superscript>/K<Superscript>+</Superscript> ATPase and <Emphasis Type="Italic">δ</Emphasis>-Aminolevulinic acid Dehydratase in the Rat Brain

The present study sought to evaluate the effect of a newly synthesized selenium compound, dicholesteroyl diselenide (DCDS) and diphenyl diselenide (DPDS) on the activities of delta-aminolevulinate dehydratase and Na⁺/K⁺-ATPase in the rat brain. The glutathione peroxidase mimetic activity of the two compounds as well as their ability to oxidize mono- and di- thiols were also evaluated. The antioxidant effects were tested by measuring the ability of the compounds to inhibit the formation of thiobarbituric acid reactive species and also their ability to inhibit the formation of protein carbonyls. The results show that DPDS exhibited a higher glutathione peroxidase mimetic activity as well as increased ability to oxidize di-thiols than DCDS. In addition, while DPDS inhibited the formation of thiobarbituric acid reactive species and protein carbonyls, DCDS exhibited a prooxidant effect in all the concentration range (20–167 μM) tested. Also the activities of cerebral delta-aminolevulinate dehydratase and Na⁺/K⁺ ATPase were significantly inhibited by DPDS but not by DCDS. In addition, the present results suggested that the inhibition of Na⁺/K⁺ ATPase by organodiselenides, possibly involves the modification of the thiol group at the ATP binding site of the enzyme. In conclusion, the results of the present investigation indicated that the non-selenium moiety of the organochalcogens can have a profound effect on their antioxidant activity and also in their reactivity towards SH groups from low-molecular weight molecules and from brain proteins.