One hallmark of Alzheimer's disease (AD) is the formation of neurofibrillary tangles, aggregated paired helical filaments composed of hyperphosphorylated tau. Amyloid-b (Ab) induces tau hyperphosphorylation, decreases microtubule (MT) stability and induces neuronal death. MT stabilizing agents have been proposed as potential therapeutics that may minimize Ab toxicity and here we report that paclitaxel (taxol) prevents cell death induced by Ab peptides, inhibits Abinduced activation of cyclin-dependent kinase 5 (cdk5) and decreases tau hyperphosphorylation. Taxol did not inhibit cdk5 directly but significantly blocked Ab-induced calpain activation and decreased formation of the cdk5 activator, p25, from p35. Taxol specifically inhibited the Ab-induced activation of the cytosolic cdk5-p25 complex, but not the membraneassociated cdk5-p35 complex. MT-stabilization was necessary for neuroprotection and inhibition of cdk5 but was not sufficient to prevent cell death induced by overexpression of p25. As taxol is not permeable to the blood-brain barrier, we assessed the potential of taxanes to attenuate Ab toxicity in adult animals using a succinylated taxol analog (TX67) permeable to the blood-brain barrier. TX67, but not taxol, attenuated the magnitude of both basal and Ab-induced cdk5 activation in acutely dissociated cortical cultures prepared from drug treated adult mice. These results suggest that MT-stabilizing agents may provide a therapeutic approach to decrease Ab toxicity and neurofibrillary pathology in AD and other tauopathies.

An on-line microdialysis microbore HPLC method is described for the determination of the bioreductive anti-tumor agent, tirapazamine (3-amino-1,2,4-benzotriazine-1,4-di-N-oxide, SR4233, WIN59075, Tirazone, TPZ) and its two major reduced metabolites, 3-amino-1,2,4-benzotriazine-1-N-oxide (SR4317) and 3-amino-1,2,4-benzotriazine (SR4330). Detection limits of 0.003 microM, 0.005 microM and 0.007 microM were obtained for tirapazamine, SR4317 and SR4330, respectively. Linear ranges of 0.011-20 microM, 0.017-20 microM and 0.025-20 microM for tirapazamine, SR4317 and SR4330 permitted quantitative analysis of all three compounds in microdialysis samples. Typical intra-day reproducibilities (n = 7) of 4.1% (tirapazamine), 6.6% (SR4317), 9.9% (SR4317), and 1.8% (tirapazamine), 2.4% (SR4317) and 2.6% (SR4330) were obtained at the 0.12 microM and 1.2 microM levels, respectively. Inter-day reproducibilities (n = 5) of 3.4% (tirapazamine), 1.8% (SR4317), 4.5% (SR4330) and 2.5% (tirapazamine), 2.5% (SR4317) and 1.7% (SR4330) were obtained at the 0.12 microM and 1.2 microM levels, respectively. The use of an on-line microdialysis HPLC system, permitted the determination of tirapazamine, SR4317 and SR4330 in blood and muscle tissue of rats with a high temporal resolution of sampling. The pharmacokinetics of tirapazamine and its metabolites were studied in the muscle and blood of rats previously administered an intraperitoneal dose of tirapazamine.

Capillary electrophoresis with end-column electrochemical detection (CEEC) was used to determine chlorite (ClO 2 À ) in drinking water. Two CE methods were developed. The ®rst method used a positive CE polarity with a 25 mM Borate buffer, pH 8.9. The second method used a negative CE polarity and a 25 mM phosphate buffer, pH 7.5 with 1 mM dodecyl trimethyl ammonium bromide (DTAB) added to reverse the EOF. The required detection potential was 1.0 V (vs. Ag/AgCl) in the positive polarity mode and 0.90 V (vs. Ag/AgCl) in the negative polarity mode. In both polarity modes, the analysis time for chlorite was less than 6 minutes. Calibration plots ClO 2 À in tap water and in deionized water were found to be linear between 0.1 and 10 mg L À1 (r 5 0.994) with detection limits of 5 mg L À1 (SaN 3) in both modes. The concentration of chlorite found in samples from a water treatment plant was 0.5 to 1.7 mg L À1 . The relative standard deviation (RSD) in peak height for injections of 1.0 mg L À1 chlorite standards were 5.4 % using the positive polarity mode and 2.7 % using the negative polarity mode. The RSD in peak height for injections of samples from the water treatment plant were 5.2 % and 6.6 % for positive and negative polarity, respectively (n 5).

A capillary electrophoretic (CE) method for the analysis of urinary extracts of the local anesthetic, bupivacaine, and its three main metabolites, desbutylbupivacaine, 3'-hydroxybupivacaine, and 4'-hydroxybupivacaine, in rat urine has been developed. The limits of detection were 0.22 microM for desbutylbupivacaine and bupivacaine, 0.15 microM for 3'-hydroxybupivacaine, and 0.16 microM for 4'-hydroxybupivacaine. The linear range was from 0.7 microM to 16.8 microM for all four compounds. Migration time and peak height reproducibilities, and extraction efficiencies were determined for all four compounds. Peak height reproducibilities (n = 5) for the overall method were improved through the use of prilocaine as an internal standard. Peak height reproducibilities were 5.6% RSD for desbutylbupivacaine and bupivacaine, and 9.9% RSD for 3'-hydroxybupivacaine and 4'-hydroxybupivacaine. Migration time reproducibilities (n = 5) were 2.4% for all compounds. Urine samples were collected from rats administered therapeutic doses of bupivacaine and extracted using a solid-phase extraction method (SPE). Separation of bupivacaine and its metabolites was achieved in 15 min.

Purpose-Incorporation of bupivacaine, a short acting local analgesic, into injectable microspheres provides a long acting formulation. Co-incorporation of dexamethasone into the microspheres results in extended activity. The purpose of this study is to compare tissue concentrations of bupivacaine resulting from the two types of microspheres and to determine if the observed sustained tissue concentration of bupivacaine is due to changes in its tissue clearance.Methods-Microdialysis probes were implanted into rat muscle. Following microsphere injection, bupivacaine tissue concentration was monitored (HPLC-UV), and the tissues histologically examined. The effect of vasoactive compounds on the tissue concentration of bupivacaine, not formulated in microspheres, was monitored.Results-Hind muscle histology showed significant granulomatous reactions around the probe and both types of microspheres. A higher, prolonged bupivacaine concentration was observed from microspheres. A higher, prolonged bupivacaine concentration was observed from microspheres with co-incorporated dexamethasone relative to those without dexamethasone. Addition of vasoconstrictors to the perfusate containing bupivacaine resulted in decreased bupivacaine delivery compared to bupivacaine alone, whereas the addition of a vasodilator increased bupivacaine delivery.Conclusions-The longer lasting effect of microspheres with co-incorporated dexamethasone results from higher, prolonged tissue concentrations of bupivacaine. Dexamethasone, a vasoconstrictor, decreases the clearance rate of bupivacaine from the tissue resulting in a higher, prolonged tissue concentration of bupivacaine.