Synthesis and biological characterization of novel 2-quinolinecarboxamide ligands of the peripheral benzodiazepine receptors bearing technetium-99m or rhenium

Potential receptor imaging agents based on Tc-99m for the in vivo visualization of the peripheral benzodiazepine receptor (PBR) have been designed on the basis of the information provided by the previously published structure-affinity relationship studies, which suggested the existence of tolerance to voluminous substituents in the receptor area interacting with 3-position of the quinoline nucleus of 2-quinolinecarboxamides 5. In the first step of the investigation, the stereoelectronic features of the above-indicated receptor area were also probed by means of 4-phenyl-3-[(1-piperazinyl)methyl]-2-quinolinecarboxamide derivatives bearing different substituents on the terminal piperazine nitrogen atom (compounds 6a-f). The structure-affinity relationship data confirmed the existence of a tolerance to bulky lipophilic substituents and stimulated the design of bifunctional ligands based on the 4-phenyl-3-[(1-piperazinyl)methyl]-2-quinolinecarboxamide moiety (compounds 6h,j,k,m). The submicromolar PBR affinity of rhenium complexes 6j,m suggests that the presence of their metal-ligand moieties with encaged rhenium is fairly compatible with the interaction with the PBR binding site. Thus, in order to obtain information on the in vivo behavior of these bifunctional ligands, (99m)Tc-labeled compounds 6h,k were synthesized and evaluated in preliminary biodistribution and single photon emission tomography (SPET) studies. The results suggest that both tracers do not present a clear preferential distribution in tissues rich in PBR, probably because of their molecular dimensions, which may hamper both the intracellular diffusion toward PBR and the interaction with the binding site.     

In vitro Antioxidant Activity of <Emphasis Type="Italic">Valeriana officinalis</Emphasis> Against Different Neurotoxic Agents

Valeriana officinalis L. (Valerian) is widely used as a traditional medicine to improve the quality of sleep. Although V. officinalis have been well documented as promising pharmacological agent; the exact mechanisms by which this plant act is still unknown. Limited literature data have indicated that V. officinalis extracts can exhibit antioxidant properties against iron in hippocampal neurons in vitro. However, there is no data available about the possible antioxidant effect of V. officinalis against other pro-oxidants in brain. In the present study, the protective effect of V. officinalis on lipid peroxidation (LPO) induced by different pro-oxidant agents with neuropathological importance was examined. Ethanolic extract of valerian (0–60 μg/ml) was tested against quinolinic acid (QA); 3-nitropropionic acid; sodium nitroprusside; iron sulfate (FeSO₄) and Fe²⁺/EDTA induced LPO in rat brain homogenates. The effect of V. officinalis in deoxyribose degradation and reactive oxygen species (ROS) production was also investigated. In brain homogenates, V. officinalis inhibited thiobarbituric acid reactive substances induced by all pro-oxidants tested in a concentration dependent manner. Similarly, V. officinalis caused a significant decrease on the LPO in cerebral cortex and in deoxyribose degradation. QA-induced ROS production in cortical slices was also significantly reduced by V. officinalis. Our results suggest that V. officinalis extract was effective in modulating LPO induced by different pro-oxidant agents. These data may imply that V. officinalis extract, functioning as antioxidant agent, can be beneficial for reducing insomnia complications linked to oxidative stress.     

In vivo and in vitro inhibition of mice thioredoxin reductase by methylmercury

The thioredoxin (Trx) system, involving redox active Trxs and thioredoxin reductases (TrxRs), sustain a number of important Trx-dependent pathways. These redox active proteins support several processes crucial for cell function, cell proliferation, antioxidant defense, and redox-regulated signaling cascades. Methylmercury (MeHg) is an important environmental toxicant that has a high affinity for thiol groups and can cause oxidative stress. The Trx system is the major system responsible for maintaining the redox state of cells and this function involves thiol reduction mediated by selenol groups in TrxRs. MeHg has a great affinity to thiols and selenols, thus the potential toxic effects of MeHg on TrxR inhibition were determined in the current study. A single administration of MeHg (1, 5, and 10 mg/Kg) caused a marked inhibition of kidney TrxR activity, while significant inhibition was observed in the liver after exposure to 5 and 10 mg/Kg of MeHg. TrxR activity was determined 24 h after MeHg. In the brain, MeHg did not inhibit TrxR activity. In vitro exposure to MeHg indicated that MeHg inhibits cerebral (IC₅₀, 0.158 μM), hepatic (IC₅₀, 0.071 μM), and renal TrxR activity (IC₅₀, 0.078 μM). The results presented herein demonstrated for the first time that renal and hepatic TrxRs can serve as an in vivo target for MeHg. This study suggests that MeHg can bind to selenocysteine residues present in the catalytic site of TrxR, in turn causing enzyme inhibition that can compromise the redox state of cells.     

Harpagophytum Procumbens Ethyl Acetate Fraction Reduces Fluphenazine-Induced Vacuous Chewing Movements and Oxidative Stress in Rat Brain

Neurochemical Research - Long-term treatment with fluphenazine is associated with manifestation of extrapyramidal side effects, such as tardive dyskinesia. The molecular mechanisms related to the...     

Asymmetric synthesis and preliminary evaluation of (R)- and (S)-[11C]bisoprolol, a putative beta1-selective adrenoceptor radioligand

(+/-)-1-[4-(2-Isopropoxyethoxymethyl)-phenoxy]-3-isopropylamino-2-propanol (bisoprolol) is a potent, clinically used beta(1)-adrenergic agent. (R)-(+) and (S)-(-) enantiomers of bisoprolol were labelled with carbon-11 (t(1/2)=20.4 min) as putative tracers for the non-invasive assessment of the beta(1)-adrenoceptor subtype in the human heart and brain with positron emission tomography (PET). The radiosynthesis consisted of reductive alkylation of des-iso-propyl precursor with [2-11C]acetone in the presence of sodium cyanoborohydride and acetic acid. The stereo-conservative synthesis of (R)-(+) and (S)-(-)-1-[4-(2-isopropoxyethoxymethyl)-phenoxy]-3-amino-2-propanol to be used as the precursors for the radiosynthesis of [11C]bisoprolol enantiomers was readily accomplished by the use of the corresponding chiral epoxide in three steps starting from the commercially available hydroxybenzyl alcohol. The final labelled product (either (+) or (-)-1-[4-(-isopropoxyethoxymethyl)-phenoxy]-3- [11C]isopropylamino-2-propanol) was obtained in 99% radiochemical purity in 30 min with 15+/-5% (EOS, non-decay corrected) radiochemical yield and 3.5+/-1 Ci/micromol specific radioactivity. Preliminary biological evaluation of the tracer in rats showed that about 30% of heart uptake of [11C](S)-bisoprolol is due to specific binding. The high non-specific uptake in lung might mask the heart uptake, thus precluding the use of [11C](S)-bisoprolol for heart and lung studies by PET. The remarkably high uptake of the tracer in rat brain areas rich of beta-adrenergic receptors such as pituitary (1.8+/-0.3% I.D. at 30 min) was blocked by pre-treatment with the beta-adrenergic antagonists propranolol (45%) and bisoprolol (51%, p<0.05). [11C](S)-bisoprolol deserves further evaluation in other animal models as a putative beta(1) selective radioligand for in vivo investigation of central adrenoceptors.     

Radiolocalization of 99mTc-labeled fragments in a melanoma xenografted model

A xenograft model of human malignant melanoma was used to compare, in terms of tumor localization, the specific antimelanoma monoclonal antibody (MoAb) 225.28S with an irrelevant antibody (4C4). Both specific and non-specific 99mTc-labeled fragments were injected in 12 nude mice bearing subcutaneous tumor. The animals were then sacrificed at 6 and 24 hours post-injection and immediately dissected. Radioactivity of the tumor and normal tissues was measured in a well scintillation counter and autoradiography of tumor, liver and kidneys was also obtained. Tumor localization of 99mTc-labeled MoAb 225.28S fragments was highly specific compared with 99mTc-labeled irrelevant antibody 4C4. With the exception of the kidneys, already at six hours there was a satisfactory tumor-to-normal tissue ratio, which improved at 24 hours. However, the percentage of injected dose per gram of tumor decreased with time, probably due to the weaker bond of radiolabeled Fab' fragments to tumor cells. These results would indicate 99mTc-fragments of the antimelanoma MoAb 225.28S as a suitable radiotracer in clinical nuclear medicine.