Effect of lipopolysaccharide on the physical conformation of the erythrocyte cytoskeletal proteins

Desensitization of nicotinic acetylcholine receptors as a strategy for drug development

The specific pharmacological response evoked by a nicotinic acetylcholine receptor (nAChR) agonist is governed by the anatomical distribution and expression of each receptor subtype and by the stoichiometry of subunits comprising each subtype. Contributing to this complexity is the ability of agonists that bind to the orthosteric site of the receptor to alter the affinity state of the receptor and induce desensitization and the observation that, at low doses, some nAChR antagonists evoke agonist-like nicotinic responses. Brain concentrations of nicotine rarely increase to the low-mid micromolar concentrations that have been reported to evoke direct agonist-like responses, such as calcium influx or neurotransmitter release. Low microgram per kilogram doses of nicotine administered to humans or to nonhuman primates to improve cognition and working memory probably result only in low nanomolar brain concentrations--more in line with the ability of nicotine to induce receptor desensitization. Here we review data illustrating that nicotine, its major metabolite cotinine, and two novel analogs of choline, JWB1-84-1 [2-(4-(pyridin-3-ylmethyl)piperazin-1-yl)ethanol] and JAY2-22-33, JWB1-84-1 [2-(methyl(pyridine-3-ylmethyl)amino)-ethanol], improve working memory in macaques. The effectiveness of these four compounds in the task was linearly related to their effectiveness in producing desensitization of the pressor response to ganglionic stimulation evoked by a nAChR agonist in rats. Only nicotine evoked an agonist-like action (increased resting blood pressure). Therefore, it is possible to develop new chemical entities that have the ability to desensitize nAChRs without an antecedent agonist action. Because these "silent desensitizers" are probably acting allosterically, an additional degree of subtype specificity could be attained.

Effect of beta-amyloid peptide 1-42 on the cytoprotective action mediated by alpha7 nicotinic acetylcholine receptors in growth factor-deprived differentiated PC-12 cells

Brain deposition of beta-amyloid peptide (Abeta1-42)-containing senile plaques is a consistent finding in Alzheimer's disease (AD). However, the link between Abeta1-42 and neuronal degeneration remains unclear. It has been reported that Abeta peptides bind with selectivity to alpha7 nicotinic acetylcholine receptors (alpha7nAChRs) and that the two proteins are associated in human AD brain tissue. A potential functional interaction between alpha7nAChRs and Abeta1-42 also has been suggested through the ability of nicotine to inhibit Abeta1-42-induced cytotoxicity. Differentiated PC-12 cells share several features in common with cholinergic basal forebrain neurons. The cells express alpha7nAChRs, they require growth factor stimulation for their maintenance and survival, and nicotine protects against cytotoxicity subsequent to growth factor withdrawal. Using these cells as a model system, we designed experiments to more directly determine whether Abeta peptides (Abeta1-42 and Abeta1-40) interfere with a potential nicotinic cytoprotective action and with the ability of nicotine to increase intracellular Ca2+. Differentiated PC-12 cells were preloaded with fura 2/acetoxymethyl ester and intracellular free Ca2+ levels were determined by fluorescent imaging. Nicotine-induced Ca2+ signals were inhibited by pretreatment with the alpha7nAChR-selective antagonists alpha-bungarotoxin and methyllycaconitine, and they were completely absent in cells maintained in Ca2+-free medium. The nicotine response also was blocked by pretreatment with 100 nM Abeta1-42. Nicotine (1-1000 muM) produced a concentration-dependent increase in cell viability in differentiated PC-12 cells that underwent nerve growth factor withdrawal for 24 h. Cell viability was maintained near 100% by 100 muM nicotine. The cytoprotective action of nicotine was efficiently antagonized by cotreatment with alpha7nAChR antagonists. A concentration-dependent inhibition of the cytoprotective action of nicotine also was produced by cotreatment with Abeta1-42 (1-100 nM), but not with Abeta40 -1. It is possible, therefore, that in AD, as growth factor support to basal forebrain cholinergic neurons declines, the interaction of Abeta peptides with alpha7nAChRs may enhance toxicity by interfering with an important nicotinic signal for neuronal viability.

The effect of glutathione and N-acetylcysteine on lipoperoxidative damage in patients with early septic shock

Both the hyperproduction of oxygen free radicals (OFR) and the weakening of natural scavenging mechanisms have been implicated as contributors to multiple organ failure in septic shock. This study examined whether the antioxidants glutathione (GSH) and N-acetyl-L-cysteine (NAC) play a protective role against damage by OFR in early septic shock. We randomly entered 30 patients with septic shock into one of three groups within 24 h of diagnosis. All of the patients received septic shock therapy, including parenteral nutrition, antibiotics, and volume-expanding and inotropic agents. One group (Group B) also received 70 mg/kg/d of intravenous GSH, and a second group (Group C), 70 mg/kg/d of intravenous GSH and 75 mg/kg/d of intravenous NAC. The protection against OFR damage was evaluated by measuring expired ethane, plasma malondialdehyde, erythrocyte deformability, complement activation, and clinical scores at admission and on Days 3 and 5 of treatment. A significant decrease in peroxidative indexes was observed at Day 5 in Group B as compared with both the control group and basal values. The decrease in peroxidative indexes was even more marked in Group C. Clinical scores in this group were also significantly improved. In conclusion, the administration of high doses of NAC added to GSH significantly decreased the peroxidative stress of patients with septic shock.

Predictive markers in the late gestation period for retained placenta in black-pied dairy cows under field conditions in France

A prospective ecopathogical survey was conducted in French commercial dairy herds located in Brittany. Previous production and reproduction data and blood parameters were used to identify predictive indicators of risk for retained placenta (RP) in Black-Pied cows. All the cows had delivered a single calf after a dry period of at least 30 d and had produced milk for at least 30 d. The cows with and without retained placenta were allocated to groups according to herd and interval between antepartum blood sampling and calving. Two groups of cows with (RP-positive group, n = 45) and without (RP-negative group, n = 184) retained placenta were compared. Univariate analysis indicated lower plasma glucose concentration, lower monocyte count and higher red blood cell count in the RP-positive group. A multiple logistic regression was run, with herd and blood sampling to calving interval as the fixed effects. It showed that a high red cell count and a low monocyte count were predictive indicators for retained placenta risk, which was found to be lower at third calving. Relationships of circulating indicators with placental retention etiology are discussed in terms of polyunsaturated fatty acid imbalance, its consequences on monocyte and erythrocyte functions, uterine motility and circulatory disturbances.

Free radical oxidation of brain proteins in accelerated senescence and its modulation by N-tert-butyl-alpha-phenylnitrone

According to the free radical theory of aging, reactive oxygen species cause oxidative damage, proposed to be an underlying factor of the aging process. In the current study, we have used electron paramagnetic resonance spin labeling, measurements of protein carbonyl content, an index of protein oxidation, and determination of the activity of glutamine synthetase (an oxidatively sensitive enzyme) to report that cortical synaptosomal membranes from the senescence accelerated-prone (SAMP8) mouse showed structural characteristics of free radical oxidative stress relative to the senescence accelerated-resistant (SAMR1) mouse. The SAMP8 mouse exhibited a decrease in the relevant EPR parameter consistent with oxidative stress (P < 0.002), a decreased glutamine synthetase activity (P < 0.05), and an increased protein carbonyl content (P < 0.01) compared with these parameters in the SAMR1 mouse. Further, because free radical trapping compounds have been demonstrated to extend maximum life span and improve cognition in SAMP8 mice, we investigated the protective nature of the known free radical scavenger, N-tert-butyl-alpha-phenylnitrone (PBN), on the physical state of cortical synaptosomal membrane proteins. For 14 days, SAMR1 and SAMP8 mice were injected with 30 mg/kg PBN while the controls were injected with the corresponding volume of saline. Characteristic of less oxidized systems, cortical synaptosomal membranes from the PBN-injected SAMP8 mouse exhibited a return toward normal values of the relevant EPR parameter [the M1 = +1 low-field weakly immobilized line/M1 = +1 low-field strongly immobilized line (W/S) ratio of a protein-specific spin label] (P < 0.001) compared with that from saline-injected SAMP8 mice. In SAMR1 mice, in contrast to SAMP8, there was no significant change in the conformation of membrane proteins or protein carbonyl content of cortical synaptosomal membranes from the PBN-injected and saline-injected SAMR1 mice, showing that PBN itself did not induce conformational changes in cortical synaptosomal membrane proteins. The results are discussed with reference to the use of free radical scavengers as potential anti-aging agents.