Pro-2-PAM therapy for central and peripheral cholinesterases

Novel therapeutics to overcome the toxic effects of organophosphorus (OP) chemical agents are needed due to the documented use of OPs in warfare (e.g. 1980-1988 Iran/Iraq war) and terrorism (e.g. 1995 Tokyo subway attacks). Standard OP exposure therapy in the United States consists of atropine sulfate (to block muscarinic receptors), the acetylcholinesterase (AChE) reactivator (oxime) pralidoxime chloride (2-PAM), and a benzodiazepine anticonvulsant to ameliorate seizures. A major disadvantage is that quaternary nitrogen charged oximes, including 2-PAM, do not cross the blood brain barrier (BBB) to treat brain AChE. Therefore, we have synthesized and evaluated pro-2-PAM (a lipid permeable 2-PAM derivative) that can enter the brain and reactivate CNS AChE, preventing seizures in guinea pigs after exposure to OPs. The protective effects of the pro-2-PAM after OP exposure were shown using (a) surgically implanted radiotelemetry probes for electroencephalogram (EEG), (b) neurohistopathology of brain, (c) cholinesterase activities in the PNS and CNS, and (d) survivability. The PNS oxime 2-PAM was ineffective at reducing seizures/status epilepticus (SE) in diisopropylfluorophosphate (DFP)-exposed animals. In contrast, pro-2-PAM significantly suppressed and then eliminated seizure activity. In OP-exposed guinea pigs, there was a significant reduction in neurological damage with pro-2-PAM but not 2-PAM. Distinct regional areas of the brains showed significantly higher AChE activity 1.5h after OP exposure in pro-2-PAM treated animals compared to the 2-PAM treated ones. However, blood and diaphragm showed similar AChE activities in animals treated with either oxime, as both 2-PAM and pro-2-PAM are PNS active oximes. In conclusion, pro-2-PAM can cross the BBB, is rapidly metabolized inside the brain to 2-PAM, and protects against OP-induced SE through restoration of brain AChE activity. Pro-2-PAM represents the first non-invasive means of administering a CNS therapeutic for the deleterious effects of OP poisoning by reactivating CNS AChE.

α-Linolenic acid does not contribute appreciably to docosahexaenoic acid within brain phospholipids of adult rats fed a diet enriched in docosahexaenoic acid

Adult male unanesthetized rats, reared on a diet enriched in both alpha-linolenic acid (alpha-LNA) and docosahexaenoic acid (DHA), were infused intravenously for 5 min with [1-(14)C]alpha-LNA. Timed arterial samples were collected until the animals were killed at 5 min and the brain was removed after microwaving. Plasma and brain lipid concentrations and radioactivities were measured. Within plasma lipids, > 99% of radioactivity was in the form of unchanged [1-(14)C]alpha-LNA. Eighty-six per cent of brain radioactivity at 5 min was present as beta-oxidation products, whereas the remainder was mainly in 'stable' phospholipid or triglyceride as alpha-LNA or DHA. Equations derived from kinetic modeling demonstrated that unesterified unlabeled alpha-LNA rapidly enters brain from plasma, but that its incorporation into brain phospholipid and triglyceride, as in the form of synthesized DHA, is < or = 0.2% of the amount that enters the brain. Thus, in rats fed a diet containing large amounts of both alpha-LNA and DHA, the alpha-LNA that enters brain from plasma largely undergoes beta-oxidation, and is not an appreciable source of DHA within brain phospholipids.

Non-selenium glutathione peroxidase without glutathione S-transferase activity from bovine ciliary body

A glutathione peroxidase was purified from bovine ciliary body by ammonium sulfate fractionation. Sephacryl S-300 gel filtration, diethylaminoethyl (DEAE)-cellulose chromatography and hydroxyapatite chromatography. The purified enzyme has an apparent mw of 112 kDa by gel filtration and 29 kDa by SDS-polyacrylamide gel electrophoresis. The enzyme therefore is composed of four identical subunits. The ciliary enzyme is active with H2O2 (25), cumene hydroperoxide (170), t-butyl hydroperoxide (22), triphenylcarbinyl hydroperoxide (12), linoleic hydroperoxide (34) and 5-phenylpentenyl hydroperoxide (22): the numbers after substrates are K'm in microM. Glutathione is essential for the reaction; L-cysteine, dithiothreitol and 2-mercaptoethanol are inactive. Mercaptosuccinate (10 microM) inhibits the enzyme competitively (Ki = 7 microM) when cumene hydroperoxide is substrate, and uncompetitively (Ki = 10 microM) when H2O2 is substrate. No selenium was found in the enzyme by the fluorometric assay with 2.3-diaminonaphthalene. The enzyme demonstrates no glutathione S-transferase activity when tested with 1-chloro-2,4-dinitrobenzene, and several other compounds. A partial sequence of the enzyme shows some similarities both to Se-glutathione peroxidases and a glutathione S-transferase isozyme.