ABT-089 [2-methyl-3-(2-(S)-pyrrolidinylmethoxy)pyridine]: I. A potent and selective cholinergic channel modulator with neuroprotective properties.

Accumulating preclinical and clinical evidence data suggests that compounds that selectively activate neuronal nicotinic acetylcholine receptor (nAChR) subtypes may have therapeutic utility for the treatment of several neurological disorders. In the present study, the in vitro pharmacological properties of the novel cholinergic channel modulator ABT-089 [2-methyl-3-(2-(S)-pyrrolidinylmethoxy)pyridine], are described. In radioligand binding studies, ABT-089 was shown to display selectivity toward the high-affinity (-)-cytisine binding site present on the alpha4beta2 nAChR subtype (Ki = 16 nM) relative to the [125I]alpha-bungarotoxin binding site present on the alpha7 (Ki > or = 10,000 nM) and alpha1beta1deltagamma (Ki > 1000 nM) nAChR subtypes. In cation flux and channel current studies, ABT-089 displayed a more complex profile than (-)-nicotine having agonist, partial agonist and inhibitory activities depending on the nAChR subtype with which it interacts. ABT-089 differentially stimulated neurotransmitter release. The compound displayed a similar potency and efficacy to (-)-nicotine to facilitate ACh release (ABT-089, EC50 = 3 microM; (-)-nicotine, EC50 = 1 microM), but was markedly less potent and less efficacious than (-)-nicotine to stimulate dopamine release (ABT-089, EC50 = 1.1 microM; (-)-nicotine, EC50 = 0.04 microM). Additionally, ABT-089 was neuroprotective against the excitotoxic insults elicited by exposure to glutamate in both rat cortical cell cultures (EC50 = 10 +/- 3 microM) and differentiated human IMR32 cells (EC50 = 3 +/- 2 microM). The differential full agonist/partial agonist profile of ABT-089, as compared with (-)-nicotine and ABT-418, illustrates the complexity of nAChR activation and the potential to target responses at subclasses of the neuronal and peripheral receptors.

Variation in postantibiotic effect of clindamycin against clinical isolates of Staphylococcus aureus and implications for dosing of patients with osteomyelitis.

Initial measurements of postantibiotic effect (PAE) were made by a standard laboratory method (exposure to 1 mg of clindamycin per liter for 1 h). The range of PAE for 21 strains of Staphylococcus aureus isolated from osteomyelitis patients was 0.4 to 3.9 h, which markedly exceeded the coefficient of variation for the method (6 to 19%). Exposure of S. aureus to three doses of clindamycin at 8-h intervals had no consistent effect on either PAE or MIC. The PAE was dependent on both concentration and duration of exposure to clindamycin: for example, the PAEs for one strain were 1.7 h after exposure to 1 mg/liter for 1 h, 2.4 h after exposure to 4 mg/liter for 1 h, and 5.9 h after exposure to 4 mg/liter for 3 h. Pharmacokinetic simulations showed that the dose required to maintain free serum clindamycin concentrations above the MIC was 300 mg 6 hourly after oral administration (95% confidence interval, 243 to 301 mg) and 1.2 g 6 hourly (95% confidence interval, 305 to 1,145 mg) after intravenous (i.v.) administration. The duration of PAE would have to be at least 2.4 h to allow an increase in the oral dose interval to 8 h or to allow i.v. administration of 300 mg 6 hourly. Additional PAE experiments were performed with the three strains for which PAEs are the shortest after exposure to 1 mg/liter for 1 h (0.4 to 1.2 h). The PAE for these three strains increased markedly to 4.4 to 6.7 h following exposure to 2 mg/liter for 6 h (to mimic the area under the concentration-time curve from 0 to 6 h after a 300-mg dose). These data suggest that oral clindamycin could be administered at 300 mg 8 hourly in the treatment of S. aureus infection, whereas the i.v. dose interval should be 6 h. These suggestions should be confirmed by performing clinical trials.

In vitro neuroprotective properties of the novel cholinergic channel activator (ChCA), ABT-418.

Recent literature has shown that compounds interacting with neuronal nicotinic acetylcholine receptors (nAChRs) have the potential to be neuroprotective both in vitro and in vivo. ABT-418 is a novel ChCA that selectively stimulates discrete subtypes of the nAChRs and exhibits cognitive enhancing activity. In the present study, the neuroprotective effects of ABT-418 and (-)-nicotine, as measured by the release of lactate dehydrogenase (LDH) into the media, were investigated in a glutamate (Glu)-induced cytotoxicity assay using either primary rat cortical neurons or a human differentiated cell line, IMR 32. The neuroprotection elicited by ABT-418 and (-)-nicotine is both time and concentration dependent with an optimal concentration of 10 microM and an optimal pretreatment time of 2 h. ABT-418 remained neuroprotective and not cytotoxic to rat cortical cells following subacute exposure for 7 days. Protection appears to be mediated via an interaction with nAChRs, possibly the alpha 7 subtype, since the neuroprotection was prevented by alpha-bungaratoxin (alpha-Bgt) and methyllycaconitine (MLA), both selective alpha 7 antagonists. Removal of extracellular Ca2+ prevented the neuroprotective effects of ABT-418 and (-)-nicotine, consistent with the known ability of alpha 7 nAChRs to modulate calcium dynamics. These data support the idea that ABT-418 not only enhances cognition, but may possibly slow the progression of the neurodegenerative process.

AUUUA-specific mRNA binding proteins in astrocytes.

Binding of ribonucleoproteins to specific regions of mRNA can alter mRNA stability. This level of posttranscriptional regulation has been shown to play a major role in gene expression of eukaryotic cells. This process involves the binding of ribonucleoproteins to specific region(s) of unstable, rapidly degrading mRNAs such as those found in various cytokines, lymphokines, and oncogenes, thereby increasing the mRNA's stability. In many instances the instability of the mRNA has been mapped to an AU-rich motif in the 3' untranslated region. We transcribed RNA molecules containing four reiterations of an AUUUA motif, and demonstrated with RNA- band shift experiments that the AUUUA motif complexes with phosphorylated AUUUA-specific 43-47 kDa mRNA binding protein(s) found in the cytosol of both rat brain and cultured rat astrocytes.

Preprotachykinin gene expression in the human basal ganglia: characterization of mRNAs and pre-mRNAs produced by alternate RNA splicing.

The nature and distribution of preprotachykinin (PPT, i.e. substance P/neurokinin A-encoding) gene expression in human basal ganglia was determined. Northern blot analysis visualized a single band of approximately 1300 bases, confirming the postmortem stability of PPT mRNA. Gross anatomical analysis indicated that PPT gene expression was relatively evenly distributed throughout the human caudate and putamen, but absent in the globus pallidus and substantia nigra. Nuclease protection analysis of these tissues established that human PPT mRNA consisted of approximately 80-85% beta-PPT (exon 1-7 derived) mRNA and 15-20% gamma-PPT (minus exon 4), with no alpha-PPT (minus exon 6) mRNA detected; these data contrast with the proportions of PPT mRNAs seen in non-human species. The incompletely spliced PPT RNA species detected in basal ganglia accounted for approximately 8% of total human PPT RNA and suggested a fixed order of exon splicing. Since various PPT mRNAs encode different combinations of tachykinin peptides with distinct biological activities, the markedly different proportions of PPT mRNAs seen in human basal ganglia compared to non-human tissues may be of physiological significance.