Receptor localization, native tissue binding and ex vivo occupancy for centrally penetrant P2X7 antagonists in the rat

BACKGROUND AND PURPOSE

The P2X7 receptor is implicated in inflammation and pain and is therefore a potential target for therapeutic intervention. Here, the development of a native tissue radioligand binding, localization and ex vivo occupancy assay for centrally penetrant P2X7 receptor antagonists is described.

EXPERIMENTAL APPROACH

Autoradiography studies using the P2X7 antagonist radioligand [³H]-A-804598 were carried out in rat brain and spinal cord. Subsequent in vitro binding and ex vivo occupancy assays were performed using rat cortex homogenate.

KEY RESULTS

P2X7 expression was shown to be widespread throughout the rat brain, and in the grey matter of the spinal cord. In binding assays in rat cortex homogenate, ∼60% specific binding was achieved at equilibrium. In kinetic binding assays, k_on and k_off values of 0.0021·min⁻¹·nM⁻¹ and 0.0070·min⁻¹ were determined, and the K_d derived from kinetic measurements was consistent with that derived from saturation analysis. Novel P2X7 antagonists inhibited the binding of [³H]-A-804598 to rat cortex P2X7 receptors with K_i values of <40 nM. In an ex vivo occupancy assay, a P2X7 antagonist dosed orally to rats caused a concentration-dependent inhibition of the specific binding of [³H]-A-804598 to rat cortex.

CONCLUSIONS AND IMPLICATIONS

The present study describes the development of an assay that allows localization of P2X7 receptors, the measurement of the binding affinity of P2X7 receptor antagonists in native tissue, and provides a means of determining central P2X7 receptor occupancy. These assays could form an important part of a P2X7 drug discovery programme.     

Antimycobacterial Evaluation of Fifteen Medicinal Plants in South Africa

Fifteen plant species were collected from the Nelspruit Botanical Garden based on a list of plants provided by Phytomedicine Programme at the University of Pretoria and their ethnopharmacological information. Hexane, dichloromethane (DCM), acetone and methanolic extracts were screened for antimycobacterial activity against Mycobacterium smegmatis. The acetone extract of Milletia stulhimannii was the most active, showing activity against Mycobacterium smegmatis with minimum inhibitory concentration (MIC) value of 0.13 mg/ml. Acetone extracts for all plants had lower MIC values ranging between 0.11–1.25 mg/ml against M. smegmatis. Milletia stulhimannii, Albizia gummifera, Xanthocercis zambesiaca and Barringtonia racemosa have shown great potential as anti-tuberculosis agents. They were active against M. smegmatis with average MIC values of acetone extracts of 0.13 mg/ml.     

5-取代-1-正丁基-3-吡唑烷酮类化合物的合成及抗惊作用的构效关系

1-正癸基-3-吡唑烷酮是一种新的抗惊活性物质。杜明慧、雷小平等相继合成了一系列3-吡唑烷酮类化合物,结果,1-正丙基-5-对氟苯基-3-吡唑烷酮的抗惊作用最强(EP_(50)=14.7 mg/kg)。为了继续研究1位和5位取代基对抗惊活性的影响,我们将前人合成的35个化合物(表1中化合物1～35)进行了Hansch分析得到以下方程:     

石斛类叶鞘的显微鉴定研究

商品石斛的植物来源复杂,规格繁多,外形鉴定较困难。为了准确鉴定石斛的品种,对常作为药用的16种石斛属(Dendrobium Sw)植物的叶鞘进行了显微观察,发现其表皮细胞的形状,大小,所含草酸钙结晶的形状、大小、分布等种间区别较明显,可作为鉴别石斛种类的科学依据之一。本文对金钗石斛D.nobile Lindl。等16种石斛的叶鞘表面特征加以描述,并附主要特征图和检索表。