4,4,14 alpha-trimethyl 9 beta,19-cyclo-5 alpha-26-homocholesta-24,26-dien-3 beta-ol: a potent mechanism-based inactivator of delta 24(25)- to delta 25(27)-sterol methyl transferase

The title compound (4A) was synthesized and tested as a mechanism-based inactivator of the sterol methyl transferase (SMT) enzyme from Prototheca wickerhamii. Using cycloartenol as substrate, 4A was found to exhibit time-dependent inactivation kinetics, generating a Ki value of 30 microM and Kinact value of 0.30 min-1.     

Differential production of IL-10 by T cells and monocytes of HIV-infected individuals: association of IL-10 production with CD28-mediated immune responsiveness

The present study determines the proportions of unmyelinated cutaneous axons at the dermal-epidermal junction in glabrous skin and of myelinated and unmyelinated axons in the sural and medial plantar nerves that immunostain for subunits of the ionotropic glutamate receptors. Approximately 20% of the unmyelinated cutaneous axon profiles at the dermal-epidermal junction immunostain for either N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), or kainate receptor subunits. These findings are consistent with previous observations that NMDA and non-NMDA antagonists ameliorate nociceptive behaviors that result from noxious peripheral stimulation. In the sural nerve, where the large majority of myelinated fibers are sensory, approximately half of the myelinated axon profiles immunostain for the NMDA receptor 1 (R1) subunit, 28% immunostain for the glutamate receptor 1 (GluR1) AMPA subunit, and 11% for the GluR5,6,7 kainate subunits. Even higher proportions immunostain for these receptors in the medial plantar nerve, a mixed sensory and motor nerve. In the sural nerve, 20% of the unmyelinated axon profiles immunostain for NMDAR1 and only 7% label for GluR1 or GluR5,6,7. Because the sural nerve innervates hairy skin, these data suggest that glutamate will activate a higher proportion of unmyelinated axons in glabrous skin than in hairy skin. Measurements of fiber diameters indicate that all sizes of myelinated axon profiles, including Adelta and Abeta, are positively labeled for the ionotropic receptors. The presence of glutamate receptors on large-diameter myelinated axons suggests that these mechanosensitive receptors, presumably transducing touch and pressure, may also respond to local glutamate and thus be chemosensitive.     

Lipoxygenase products in human saliva: patients with oral cancer compared to controls

Porcine colipase, the protein cofactor of pancreatic lipase, was isolated from pancreas freshly collected on animals and from a side fraction from the production of insulin (Novo Nordisk A/S). Samples of purified colipase were analyzed for homogeneity by polyacrylamide gel electrophoresis, reverse-phase high-performance liquid chromatography (RPLC), quantitative N-terminal sequence determination and mass spectrometry. The activating properties of colipase preparations were assayed against tributyrin, triolein or the commercial Intralipid emulsion, in presence of bile salt. Two fractions of colipase with the same specific activity were purified from fresh pancreas. The major fraction (85%) contained one single protein corresponding to fragment 1-93 of the 95-residue form of colipase (procolipase) previously characterized in porcine pancreatic juice. The other fraction (15%) corresponded to fragment 1-91 of procolipase. Also, two fractions of colipase were purified from the side fraction supplied by Novo. These fractions consisted of the 95-residue proform of colipase and of fragment 1-93, respectively, both specifically cleaved at the Ile79-Thr80 peptide bond with partial removal of isoleucine at position 79 and serine at position 78. Procolipase split at the 79-80 bond retained full activity on tributyrin and triolein and on the Intralipid emulsion but the kinetics of hydrolysis of triacylglycerol substrates showed much longer lag periods than those observed with native procolipase. Also, all forms of procolipase split at the 79-80 bond showed one peak in RPLC but their retention time was markedly decreased as compared to that of native procolipase which indicated a weaker hydrophobic binding capacity. The value of the retention time was of the same order of magnitude as that of inactive reduced procolipase. Treatment of native procolipase by pancreatic endopeptidases showed that elastase is likely responsible for specific cleavage at the 79-80 bond of procolipase purified from the Novo extract. Limited proteolysis by trypsin of the proforms of colipase split at the 79-80 bond reduced the lag period. Results presented in this communication provide the first direct evidence showing that the finger-shaped peptide segment between half-cystine residues at positions 69 and 87 is involved in colipase-lipid interaction as previously hypothesized from the three-dimensional structure of the protein.     

The proteins synaptotagmin and syntaxin are not general targets of Lambert-Eaton myasthenic syndrome autoantibody

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune neuromuscular disease in which impairment of Ca2+ entry into the nerve ending and consequent impaired release of acetylcholine (ACh) results in muscle weakness. The identity of the primary antigenic target molecule(s) of the autoantibodies is uncertain. Electrophysiological studies and 45Ca2+ uptake studies implicate a direct effect on the Ca2+ channel complex at the motor nerve terminal. Some recent studies, however, suggest a more indirect interference caused by binding of autoantibodies to synaptotagmin or syntaxin, molecules presumed to be involved in docking and/or coupling the synaptic vesicles to the Ca2+ channels in the active zone for vesicle exocytosis and transmitter release. Western blot analyses of rat and human brain membrane proteins and pure recombinant synaptotagmin and syntaxin were used to examine directly the targets of LEMS autoantibodies and determine specifically whether or not synaptotagmin and/or syntaxin were general targets in LEMS. IgG from 14 patients with LEMS was used to probe western blots of gels containing synaptotagmin, syntaxin, rat synaptosomal proteins, and human brain membrane proteins. Several similar immunoreactive bands were observed using both rat and human brain membranes. These include high-molecular-weight protein bands whose size would be consistent with being components of Ca2+ channels. No reactive component was observed against either syntaxin or synaptotagmin in IgG of the 14 LEMS patients. However, both human and rat brain membranes contain proteins recognized by antibodies directed against synaptotagmin or syntaxin, indicating their immunologic relatedness and evolutionary conservation. These results suggest that large-molecular-weight proteins consistent with being Ca2+ channel subunits rather than syntaxin and synaptotagmin are general targets of LEMS autoantibodies.     

The interaction of DNA-targeted platinum phenanthridinium complexes with DNA

Cisplatin analogues were synthesised that consisted of platinum(II) diamine complexes tethered via a polymethylene chain ( n = 3, 5, 8 and 10) to a phenanthridinium cation. Both chloro and iodo leaving groups were examined. DNA adduct formation was quantitatively analysed using a linear amplification system with the plasmid pGEM-3Zf(+). This system utilised Taq DNA polymerase to extend from an oligonucleotide primer to the damage site. This damage site inhibited the extension of the DNA polymerase. The products were electrophoresed on a DNA sequencing gel enabling adduct formation to be determined at base pair resolution. The damage intensity at each site was determined by densitometry. The platinum phenanthridinium complexes were shown to damage DNA at shorter incubation times than cisplatin. To produce similar levels of damage, an 18 h incubation was required for cisplatin compared to 30 min for the n = 3 platinum phenanthridinium complexes; this indicates that the intercalating chromophore causes a large increase in the rate of platination. A reaction mechanism involving direct displacement of the chloride by the N-7 of guanine may account for the rate increase. These results indicate that further development of these compounds could lead to more effective cancer chemotherapeutic agents.     

Evidence of multiple ethanol pools in the brain: an in vivo proton magnetization transfer study

Studies of isolated cell membranes and animal brain extracts have shown that ethanol (EtOH) partitions into cell membranes. We tested the hypothesis that EtOH in the living brain after EtOH administration exists in two or more pools: a free, mobile pool of EtOH and one or more EtOH pools that are restricted in their molecular mobility, possibly because of association with membranes. In vivo brain proton magnetic resonance spectroscopy (1H MRS) routinely detects the methyl protons of the mobile EtOH pool but does not detect motionally restricted EtOH. We used in vivo brain 1H MRS in rat brain (n = 11) after intraperitoneal EtOH administration to measure the signal intensity of methyl EtOH protons in the presence and absence of off-resonance saturation. Off-resonance saturation resulted in a 33 +/- 4% decrease of the EtOH methyl proton signal. We interpret this signal reduction as a magnetization transfer effect. It is consistent with the existence of an MRS-invisible EtOH pool with restricted molecular mobility, which is in exchange with the free EtOH pool. Off-resonance saturation at the water frequency resulted in an even larger decrease of the EtOH methyl signal, consistent with water molecules being in close proximity to EtOH molecules at the restricted motion site(s). These results provide support for the hypothesis that partial MRS-invisibility of brain EtOH is at least to some extent caused by the presence of a (MRS-invisible) pool of motionally restricted EtOH. They also strongly suggest that water suppression, routinely used in in vivo 1H MRS, may reduce the observable EtOH methyl signal intensity through a magnetization transfer mechanism. These studies may provide both a mechanism of, and a means to investigate the alterations of EtOH MRS visibility observed in heavy drinkers.