Effects of chemoprotective agent HBB-2 on cell survival in SH-SY5Y neuroblastoma cells

MicroRNAs are endogenous non-coding RNAs which negatively regulate the expression of protein-coding genes in plants and animals. They are known to play an important role in several biological processes and, together with transcription factors, form a complex and highly interconnected regulatory network. Looking at the structure of this network it is possible to recognize a few overrepresented motifs which are expected to perform important elementary regulatory functions. Among them a special role is played by the microRNA-mediated feedforward loop in which a master transcription factor regulates a microRNA and, together with it, a set of target genes. In this paper we show analytically and through simulations that the incoherent version of this motif can couple the fine-tuning of a target protein level with an efficient noise control, thus conferring precision and stability to the overall gene expression program, especially in the presence of fluctuations in upstream regulators. Among the other results, a nontrivial prediction of our model is that the optimal attenuation of fluctuations coincides with a modest repression of the target expression. This feature is coherent with the expected fine-tuning function and in agreement with experimental observations of the actual impact of a wide class of microRNAs on the protein output of their targets. Finally we describe the impact on noise-buffering efficiency of the cross-talk between microRNA targets that can naturally arise if the microRNA-mediated circuit is not considered as isolated, but embedded in a larger network of regulations.Comment: 27 pages Main Paper (9 figures) + 36 pages of Supporting Information (15 figures). Revised version accepted for publicatio

Positron emission tomography studies on binding of central nervous system drugs and P-glycoprotein function in the rodent brain

The permeability of the blood-brain barrier (BBB) is one of the factors determining the bioavailability of drugs in the brain. The BBB only allows passage of lipophilic drugs by passive diffusion. However, some lipophilic drugs hardly enter the brain. The transmembrane protein P-glycoprotein (P-gp) is one of the carrier systems that is responsible for transportation of drugs out of the brain. P-Glycoprotein affects the pharmacokinetics of many drugs and can be inhibited by administration of modulators or competitive substrates. Identification and classification of central nervous system (CNS) drugs as P-gp substrates or inhibitors are of crucial importance in drug development. Positron emission tomography (PET) studies can play an important role in the screening process as a follow-up of high-throughput in vitro assays. Several rodent studies have shown the potential value of PET to measure the effect of P-gp on the pharmacokinetics and brain uptake of radiolabeled compounds. P-Glycoprotein-mediated effects were observed for two 5-HT1a receptor ligands, [F-18]MPPF vs. [carbonyl-C-11] WAY100635. Under control conditions, the specific brain uptake of [F-18]MPPF is five- to eightfold lower than that of [C-11]WAY100635. After cyclosporin A (CsA) modulation, [F-18]MPPF uptake in the rat brain increased five- to tenfold. Cerebral uptake of [carbonyl-C-11]WAY100635 was also increased by modulation, but in general the increase was lower than that observed for [F-18]MPPF (two- to threefold). Brain uptake of the P-adrenergic receptor ligands [C-11]carazolol and [F-18]fluorocarazolol was increased in P-gp knockout mice and CsA-treated rats. Both the specific and nonspecific binding of [F-18]fluorocarazolol were doubled by CsA. Cerebral uptake of [C-11]carazolol in rats was much lower than that of [18F]fluorocarazolol and no specific binding was measured. After CsA modulation, the uptake of [C-11]carazolol increased five- to sixfold, but this uptake was not receptor-mediated. Quantitative PET studies in rodents on P-gp functionality demonstrated a dose-dependent increase of radioligands after administration of CsA. Studies with [C-11]verapamil and [C-11]carvedilol showed that complete modulation was achieved at 50 mg/kg CsA. The distribution volume of [C-11]carvedilol increased from 0.25 in the control study to 1.0 after full modulation with CsA. By quantitative PET measurement of P-gp function, the dose of modulators required to increase the concentration of CNS drugs may be determined, which may result in improved drug therapy