Computational models to predict blood–brain barrier permeation and CNS activity

The blood-brain permeation of a structurally diverse set of 281 compounds was modeled using linear regression and a multivariate genetic partial least squares (G/PLS) approach. Key structural features affecting the logarithm of blood-brain partitioning (logBB) were captured through statistically significant quantitative structure-activity relationship (QSAR) models. These relationships reveal the importance of logP, polar surface area, and a variety of electrotopological indices for accurate predictions of logBB. The best models reveal an excellent correlation (r > 0.9) for a training set of 58 compounds. Likewise, the comparison of the average logBB values obtained from an ensemble of QSAR models with experimental values also verifies the statistical quality of the models (r > 0.9). The models provide good agreement (r approximately 0.7) between the predicted logBB values for 34 molecules in the external validation set and the experimental values. To further validate the models for use during the drug discovery process, a prediction set of 181 drugs with reported CNS penetration data was used. A >70% success rate is obtained by using any of the QSAR models in the qualitative prediction for CNS permeable (active) drugs. A lower success rate (approximately 60%) was obtained for the best model for CNS impermeable (inactive) drugs. Combining the predictions obtained from all the models (consensus) did not significantly improve the discrimination of CNS active and CNS inactive molecules. Finally, using the therapeutic classification as a guiding tool, the CNS penetration capability of over 2000 compounds in the Synthline database was estimated. The results were very similar to the smaller set of 181 compounds.     

Development of an analytical procedure for quantifying the underivatized neurotoxin β-N-methylamino-l-alanine in brain tissues

The cyanotoxin β-methylamino-l-alanine (BMAA) has received renewed attention as an environmental risk factor for sporadic cases of amyotrophic lateral sclerosis (ALS) (Nunn et al., Brain Res 410:375–379, 1987). The aim of the present study was to develop and to validate an analytical procedure that allows the quantification of native BMAA and of its natural isomer, 2,4 diaminobutyric acid (DAB), in brain tissues. An analytical procedure was previously reported by our group for the determination of underivatized BMAA in environmental samples. It included a step of sample clean-up by solid phase extraction (SPE) with a mixed-mode sorbent and the analyses were performed by LC/MS-MS using hydrophilic interaction chromatography and multiple reactions monitoring scan mode. As brain tissues have a higher lipid content, the crucial step of sample clean-up had been optimized by evaluating the efficiency of the addition of a liquid/liquid extraction step prior to the SPE procedure or alternatively, of washing steps to the SPE extraction procedure. The efficiency was checked by visualizing the complexity of the resulting chromatograms in LC/MS and their performance by using spiked brain samples. The optimized analytical procedure, including a washing step with cyclohexane to the SPE with a recovery yield close to 100 %, was validated using the total error approach and allowed the quantification of BMAA in a concentration level ranging from 20 to 1,500 ng/g in brain samples. Finally, the feasibility of implementation of this procedure was verified in human brain samples from two patients who died of ALS.     

Preparation of new technetium-99m NNS/X complexes and selection for brain imaging agent

Quantification of regional cerebral blood flow(rCBF) plays an important role in the diagnosis ofvarious cerebrovascular and neurological diseases. Innuclear medicine, brain perfusion imaging can providesituation of whole or regional cerebral blood flowperfusion (CBF or rCBF) to neurologists, help to findabnormality of cerebral blood flow before cere-brovascular and neurological diseases induce patho-logical changes in configuration or structure of brain.They offer important information for …     

BSA optimization and dosimetric assessment for an electron linac based BNCT of deep‐seated brain tumors

A study was conducted to investigate a photoneutron spectrum based on a 25 MeV electron linac for treatment of deep-seated brain tumors in the context of boron neutron capture therapy (BNCT). Based on a series of Mont Carlo N-Particle simulations, tungsten and uranium with optimized geometry were selected as the most appropriate converters for (e,γ) and (γ,n) reactions, respectively. The final optimized photoneutron source yield was 5.78 × 10¹³ n/s/mA, which is a high value for these kinds of sources. A beam shaping assembly (BSA) for the proposed neutron source containing optimal moderators, filter, reflector, and collimator was simulated. Results showed that using this BSA enables us to meet International atomic energy agency recommended figures of merit at the BSA beam port. Also, the calculated in-phantom figures of merit and dose evaluation results via a simulated head phantom confirmed that the designed neutron source and its related BSA configuration can potentially treat deep-seated brain tumors in BNCT framework. In the present study, some in-phantom figures of merit such as advantage depth, advantage depth dose rate, advantage ratio, and treatment time are 7.6 cm, 0.7 Gy/min, 4.2, and 17.8 min, respectively.     

Substituent,structural and positional isomerisation alter anti-oxidant activity of organochalcogen compounds in rats’ brain preparations

The objective of the present study was to elucidate the biochemical potencies of eighteen structurally related organoselenium and organosulfur compounds against Fe(II) induced thiobarbituric acid reactive species (TBARS) formation in rat’s brain homogenate. The efficacies of these compounds (only organosulfur) were further confirmed by radical scavenging and thiol peroxidase-like (TPx) activities. Our data revealed that electron-donating groups significantly improve, while an electron-withdrawing group decreases antioxidant activities. The effect of structural isomerisation proved that electron-donating groups attached to the benzyl moiety at ortho-, meta- or para-positions decreased antioxidant potential. The compound benzyl-p-tolyl selenide (C-6) showed the highest in vitro activity and was selected for the in vivo experiments. Treatment with C-6 at 0, 10, 25 or 50 mg/kg was not associated with mortality, body weight loss or oxidative stress as measured by TBARS production. Similarly it did not inhibit delta-aminolevulinate dehydratase (α-ALA-D) enzyme, in fact treatment with C-6 increased the non-protein thiol content. Exposure to the same compound did not affect plasma transaminase activities or levels of urea and creatinine, indicating negligible toxicity to hepatic and renal tissues. The present study gives useful information for the synthesis of organochalcogens with desired biological and pharmacological potential.     

Elemental analysis of the frontal lobe of “normal” brain tissue and that affected by Alzheimer's disease

Normal brain tissue and brain tissue affected by Alzheimer's disease has been taken from the frontal lobe of both hemispheres and their elemental compositions in terms of major, minor and trace elements compared. Brain samples were obtained from the MRC Alzheimer's Disease Brain Bank, London. 25 samples were taken from 18 individuals (5 males and 13 females) of mean age 79.9±7.3 years with pathologically confirmed Alzheimer'sdisease and 26 samples from 15 individuals (8 males and 7 females) of mean age 71.8±13.0 years with no pathological signs of Alzheimer's disease (normals). The elemental concentration of the samples were determined by the techniques of Rutherford backscattering (RBS) analysis, particle induced X-ray emission (PIXE) analysis and instrumental neutron activation analysis (INAA). Na, Mg, Al, Cl, K, Sc, Fe, Zn, Se, Br, Rb and Cs were detected by INAA and significant differences in concentrations were found between concentrations in normal and Alzheimer tissue for the elements. Na, Cl, K, Se, Br and Rb, P, S, Cl, K, Ca, Fe, Zn and Cd were detected by PIXE analysis and significant differences found for the elements P, S, Cl, K and Ca.     

Quantitative determination of β-hydroxymethylbutyrate and leucine in culture media and microdialysates from rat brain by UHPLC-tandem mass spectrometry

The main objective of the present work was to develop a method to determine β-hydroxymethylbutyrate (HMB) and leucine (Leu) in culture media and brain microdialysates. An accurate, selective, and cost-effective method, based on the use of ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS), was developed for the identification and quantification of both compounds. The method consisted of sample dilution, direct injection onto the chromatographic equipment, and quantification with a triple quadrupole mass spectrometer using an electrospray ionization interface in positive mode. The procedure and the UHPLC-MS/MS parameters were accurately optimized to achieve the highest recoveries and to enhance the analytical characteristics of the method. For chromatographic separation, an Acquity UPLC BEH Hilic column using acetonitrile–water gradient with formic acid as additive was employed. The total run time was 4 min. The limits of detection (LODs) obtained ranged from 0.01 to 0.04 μg mL^?1, and the limits of quantification (LOQs) ranged from 0.04 to 0.12 μg mL^?1. Precision (expressed as relative standard deviation) was lower than 15 %, and the determination coefficient (R ²) was higher than 99.0 % with a residual deviation for each calibration point lower than ±25 %. Mean recoveries were between 85 and 115 %. The method was successfully applied to the analysis of both compounds, HMB and Leu, in samples obtained from an experiment of blood–brain barrier (BBB) passage in vitro and to an experiment of brain microdialysis in rats in vivo after an oral challenge with HMB to detect its appearance in the brain.     

Mass spectrometry imaging of rat brain sections: nanomolar sensitivity with MALDI versus nanometer resolution by TOF–SIMS

Mass spectrometry imaging is becoming a more and more widely used method for chemical mapping of organic and inorganic compounds from various surfaces, especially tissue sections. Two main different techniques are now available: matrix-assisted laser desorption/ionizaton, where the sample, preliminary coated by an organic matrix, is analyzed by a UV laser beam; and secondary ion mass spectrometry, for which the target is directly submitted to a focused ion beam. Both techniques revealed excellent performances for lipid mapping of tissue surfaces. This article will discuss similarities, differences, and specificities of ion images generated by these two techniques in terms of sample preparation, sensitivity, ultimate spatial resolution, and structural analysis.     

Differences in trace element concentrations between Alzheimer and “normal” human brain tissue using instrumental neutron activation analysis (INAA)

Brain samples obtained from the Netherlands Brain Bank were taken fromthe superior frontal gyrus, superior parietal gyrus and medial temporal gyrusof 'normal' and Alzheimer's disease subjects in order todetermine elemental concentrations and compare elemental composition. Brainsamples from the cortex were taken from 18 subjects, eight 'normals'(6 males and 2 females) and eleven with Alzheimer's disease, (1 maleand 10 females) and the following elemental concentrations, Na, K, Fe, Zn,Se, Br, Rb, Ag, Cs, Ba, and Eu were determined by instrumental neutron activationanalysis (INAA). The element which showed the greatest difference was Br,which was found to be significantly elevated in the cortex of Alzheimer'sdisease brains as compared to the 'normals' at significance (p<0.001).     

Effects of trichlorfon on the contents of acetylcholine and choline in fish brain microdialysis samples by UPLC-MS/MS methodEI北大核心CSCD

A combination of microdialysis sampling with ultra-high performance liquid chromatography-tandem mass spectrometry（UPLC-MS/MS）was used to quantitatively analyze the effects of organophosphorus pesticides trichlorfon on acetylcholine （ACh） and choline （Ch） in the brain of crucian carp. The mechanism of organophosphorus pesticides poisoning was preliminarily discussed,showing that the ACh content in the brain of fish increased significantly with the increase of the exposure time to trichlorfon,while the Ch content decreased. It indicated that organophosphorus pesticides inhibited the activity of cholinesterase in organisms. © 2023, Youke Publishing Co.,Ltd. All rights reserved.     

Determination of melamine in rat plasma,liver, kidney,spleen, bladder and brain by liquid chromatography–tandem mass spectrometry

In this study, we describe a method for the analysis of melamine in rat plasma, liver, kidney, spleen, bladder, and brain using trichloroacetic acid precipitation with mixed-mode cation-exchange solid-phase extraction and hydrophilic interaction chromatography coupled to tandem mass spectrometry detection. Method validation was investigated completely, including linearity, precision, accuracy, matrix effect, extraction recovery, and carryover for the determination of melamine. The method exhibited a good linear range covering 20–500 ng/mL, and the overall precision ranged from 1.6 to 16.3%, with the accuracy varying from −7.9 to 15.1%. The mean matrix effects of melamine in rat plasma, liver, kidney, spleen, bladder, and brain ranged from 66.2 ± 6.7 to 95.5 ± 13.2%, and the mean recoveries for melamine varied from 79.8 ± 8.2 to 113.0 ± 9.6%. Rat kidney showed the highest level among the organs (192.5% of the plasma melamine level), and the average concentration of melamine in the brain was only 7.5% of the plasma melamine concentration. This work has pointed out that even with the application of two popular preparation procedures (acid precipitation and solid-phase extraction) of melamine, the matrix effect in analyzing biological samples still exists in certain kinds of matrices.     

Isoprenoid quantitation in human brain tissue: a validated HPLC–fluorescence detection method for endogenous farnesyl- (FPP) and geranylgeranylpyrophosphate (GGPP)

Farnesyl- and geranylgeranylpyrophosphate (FPP and GGPP) are isoprenoid intermediates in the mevalonate pathway. They play a crucial role in cell survival, growth and differentiation due to their attachment (isoprenylation) to small GTPases (Ras, Rho, etc.). Isoprenoid formation seems to be tightly regulated within the mevalonate pathway and its perturbation has been linked to certain diseases (e.g., cancer, Alzheimer's disease), but tissue levels are unknown. It is therefore of the utmost importance to quantify these isoprenoids in diseased tissue or in tissue after drug administration. The current work describes an isolation procedure utilizing a combination of Extrelut(R) liquid/liquid and reversed-phase solid-phase extraction (SPE) for homogenized human frontal cortex tissue. In addition, after a careful validation of an HPLC-fluorescence method, this assay allowed the determination of nanomolar concentrations of endogenous FPP and GGPP levels (4.5 and 10.6 ng/mg protein, respectively) in human brain tissue. The method is selective, precise (<15% RSD), accurate (<15% relative error) and sensitive over a linear range of 10-400 ng/mL for FPP and 50-1000 ng/mL for GGPP according to the current FDA criteria for bioanalytical method validation. Overall, this new method introduces the ability to simultaneously quantify FPP and GGPP in human brain tissue, and is potentially applicable to several other tissues and species.     

Expression of the plant viral protease NIa in the brain of a mouse model of Alzheimer's disease mitigates Aβ pathology and improves cognitive function

The plant viral protease, NIa, has a strict substrate specificity for the consensus sequence of Val-Xaa-His-Gln, with a scissoring property after Gln. We recently reported that NIa efficiently cleaved the amyloid-β (Aβ) peptide, which contains the sequence Val-His-His-Gln in the vicinity of the cleavage site by α-secretase, and that the expression of NIa using a lentiviral system in the brain of AD mouse model reduced plaque deposition levels. In the present study, we investigated whether exogenous expression of NIa in the brain of AD mouse model is beneficial to the improvement of cognitive deficits. To address this question, Lenti-NIa was intracerebrally injected into the brain of Tg-APPswe/PS1dE9 (Tg-APP/PS1) mice at 7 months of age and behavioral tests were performed 15-30 days afterwards. The results of the water maze test indicated that Tg-APP/PS1 mice which had been injected with Lenti-GFP showed an increased latency in finding the hidden-platform and markedly enhanced navigation near the maze-wall, and that such behavioral deficits were significantly reversed in Tg-APP/PS1 mice injected with Lenti-NIa. In the passive avoidance test, Tg-APP/PS1 mice exhibited a severe deficit in their contextual memory retention, which was reversed by NIa expression. In the marble burying test, Tg-APP/PS1 mice buried marbles fewer than non-transgenic mice, which was also significantly improved by NIa. After behavioral tests, it was verified that the Tg-APP/PS1 mice with Lenti-NIa injection had reduced Aβ levels and plaque deposition when compared to Tg-APP/PS1 mice. These results showed that the plant viral protease, NIa, not only reduces Aβ pathology, but also improves behavioral deficits.     

Two-photon dual-channel fluorogenic probe for in situ imaging the mitochondrial H2S/viscosity in the brain of drosophila Parkinson’s disease model

H₂S is an essential gas signal molecule in cells, and viscosity is a key internal environmental parameter. Recent studies have shown that H₂S acts as a cytoarchitecture agent and gas transmitter in many tissues, e.g., as a regulator of neuroendocrine in the brain for mediating vascular tone in blood vessels. Mitochondrial viscosity is an important parameter for judging whether mitochondrial function is normal. It has been reported that oxidative stress and mitochondrial dysfunction are connected with Parkinson’s disease (PD), and the protective role of H₂S in PD models has been extensively demonstrated. Herein, Mito-HS, a new two-photon fluorescent probe was demonstrated to detect cross-talk between the two channels of mitochondrial viscosity and H₂S content. Moreover, this probe could detect the relative amount of and changes in mitochondrial H₂S in situ due to the reduced mitochondrial targeting ability after reaction with H₂S. The results show that H₂S in mitochondria is inversely related to viscosity. The PD model has a lower H₂S in mitochondria and a higher mitochondrial viscosity than did the normal. This result is important for our deep understanding of PD and its causes.     

¹¹C-labeled analogs of indomethacin esters and amides for brain cyclooxygenase-2 imaging: radiosynthesis, in vitro evaluation and in vivo characteristics in mice

There is great potential in the use of positron emission tomography (PET) and suitable radiotracers for the study of cyclooxygenase type 2 (COX-2) enzyme in living subjects. In the present study, we prepared and evaluated five 11C-labeled ester and amide analogs derived from indomethacin as potential PET imaging agents for the in vivo visualization of the brain COX-2 enzyme. Five 11C-labeled COX-2 inhibitors, with different lipophilicities and moderate COX-2 inhibitory activity, were prepared by treatment of the corresponding O-desmethyl precursors with [11C]methyl triflate and purified by HPLC (radiochemical yields of 55-71%, radiochemical purity of >93%, and the specific activities of 22-331 GBq/μmol). In mice, radioactivity in the brain for all radiotracers was low, with very low brain-to-blood ratios. A clear inverse relationship was observed between brain uptake at 1 min postinjection and the lipophilicity (experimental log P?.?) of the studied 11C-radiotracers. Pretreatment of mice with cyclosporine A to block P-glycoproteins caused a significant increase in brain uptake of radioactivity following injection of the 11C-radiotracer compared to control. HPLC analysis showed that each radiotracer was rapidly metabolized, and a few metabolites, which were more polar than the original radiotracers, were found in both plasma and brain. No specific binding of the tracers towards the COX-2 enzyme in the brain was clearly revealed by in vivo blocking study. Further structural refinement of the tracer agent is necessary for better enhancement of brain uptake and for sufficient metabolic stability.