Erythrocytes study

The use of infrared is not limited to p structure detection, however. The erythrocyte study reported here clearly illustrates the information available when spectra are taken in D20. Optical changes permit one to estimate the extent and rapidity of proton exchange in proteins and hence to estimate the availability of peptide bonds to water protons as well as the contributions from random coil and a-helical conformations. The results with erythrocytes indicate that about two-thirds to three-fourths of the protein amide groups are freely accessible to water and that most of the protein exists in an open, mostly random, conformation. The fraction of non-exchangeable protons agrees reasonably well with the helical content determined by ORD. 

A. Gorchein, R. Weber (1987). (5-Aminolaevulinic acid in plasma, cerebrospinal fluid, saliva and erythrocytes studies in normal, uraemic and prophyric subjects. Clin. Sci., 72, 103-112. 

Effects of ascorbic acid on glucose-6-phosphate dehydrogenase-deficient erythrocytes studies in an aninial model. 

The L-leucine uniporter of human and rabbit erythrocytes studied by Win-... 

In summary, the presentation of patients with partial deficiency of HGPRT may be more varied than is usually described, and before absence or near absence of HGPRT activity is accepted, intact erythrocytes and/or nucleated cells must be examined. We suggest that intact erythrocyte studies, together with red cell GTP levels (see Simmonds et al, this volume) may provide a better guide to prognosis in affected subjects. 

Arkowitz R, Hoehn-Berlage M, Gersonde K (1987) The effect of cadmium ions on 2,3-bisphosphoglycerate in erythrocytes studied with NMR. FEES Lett 217 21-24. 

Jancik, J.M., Schauer, R., Andres, K.H., and von During, M. Sequestration of neuraminidase-treated erythrocytes. Studies on its topographic, morphologic and immunologic aspects. Cell Tissue Res. (1978) 186, 209-226. 

Nicotinic acid caused a quantitatively lesser reduction of PP-ribose-P in erythrocytes studied in vitro. Nicotinic acid has been shown by others to inhibit purine biosynthesis de novo in cultured fibro-... 

In vitro cytotoxicity assays using isolated cells have been applied intermittently to cyanobacterial toxicity testing over several years." Cells investigated for suitability in cyanobacterial toxin assays include primary liver cells (hepatocytes) isolated from rodents and fish, established permanent mammalian cell lines, including hepatocytes, fibroblasts and cancerous cells, and erythrocytes. Earlier work suggested that extracts from toxic cyanobacteria disrupted cells of established lines and erythrocytes," but studies with purified microcystins revealed no alterations in structure or ion transport in fibroblasts or erythrocytes,... 

Clinical studies, available only for entacapone and tolcapone, support preclinical findings. A dose-dependent (100-800 mg) inhibition of the COMT activity of the erythrocytes can be seen after nitrocatechols. However, effective and sufficient dose levels of both entacapone and tolcapone, given concomitantly with L-dopa and DDC inhibitors to patients with Parkinson s disease, appear to be 100-200 mg. However, the treatment strategies of entacapone and tolcapone differ entacapone is a short-acting compound that is given with each dose of L-dopa, and COMT activity may even... 

Hematological Effects. No information was found regarding hematological effects in humans following exposure to methyl parathion. Repeated oral exposure to methyl parathion resulted in decreased mean corpuseular volume in one study and decreased hematocrit and erythrocyte count in another study in rats. Chronic ingestion of methyl parathion induced reduction of mean hemoglobin, hematocrit, and erythrocyte eounts in rats. 

Neurologic signs did not occur over a 30-day period in male prisoner volunteers in California who ingested daily doses of methyl parathion ranging from 1.0 to 19 mg. There were no uniform changes in plasma or erythrocyte cholinesterase levels at any of these doses (Rider et al. 1969). By increasing concentrations of methyl parathion administered to the same experimental population and using the same protocol, a dose that inhibited cholinesterase values was established. These additional studies were published nearly 20 years ago in abstract form only therefore, they are not discussed in this section. 

Mice that were exposed dermally to residues of methyl parathion in emulsifiable concentrate on foliage, and were muzzled to prevent oral intake, developed inhibition of plasma cholinesterase and erythrocyte cholinesterase after two 10-hour exposures (Skinner and Kilgore 1982b). For the organophosphate pesticides tested in this study, cholinergic signs generally were seen in mice with cholinesterase inhibition >50% results for this end point were not broken down by pesticide. 

The only other information regarding the potential for age-related differences in susceptibility to methyl parathion came from a study by Garcia-Lopez and Monteoliva (1988). The investigators showed increasing mean erythrocyte acetylcholinesterase activity levels with increasing age range, starting at birth (in 10-year increments and >60 years of age) in both males and females. However, it is not known whether increased erythrocyte acetylcholinesterase activity indicates a decreased susceptibility to methyl parathion toxicity. 

Following exposure of humans to organophosphates, but not specifically methyl parathion, restoration of plasma cholinesterase occurs more rapidly than does restoration of erythrocyte cholinesterase (Grob et al. 1950 Midtling et al. 1985). These findings are supported by studies of methyl parathion in animals. Erythrocyte cholinesterase levels are representative of acetylcholinesterase levels in the nervous system, and, therefore, may be a more accurate biomarker of the neurological effects of chronic low level exposure of humans to methyl parathion (Midtling et al. 1985 NIOSH 1976). 

Several studies in animals suggest that age may affect susceptibility to methyl parathion toxicity, and that children may be more susceptible than adults, but the data are limited. (See Section 3.7 for more information on Children s susceptibility.) A study in humans showed that mean erythrocyte acetylcholinesterase activity levels increase with increasing age from birth through old age in both sexes (Garcia-Lopez ad Monteoliva 1988), but it is not known whether increased erythrocyte acetylcholinesterase activity indicates decreased susceptibility to methyl parathion. 

EPA has derived an RfD of. 00025 mg/kg/day, based on a NOAEL of 0.025 for reduced hematocrit, erythrocyte counts, and hemoglobin (cholinesterase inhibition was also listed as a critical effect but the reason for this was not explained). This NOAEL appears to be from the same study as for the ATSDR chronic-duration oral MRL, although the study is referenced differently (IRIS 2001). 

Effects noted in study and corresponding concentrations No adverse effects were observed in the low-dose male and female rats. Mean hemoglobin, hematocrit, and erythrocyte counts were significantly reduced in the high-dose females at 6-24 months of treatment mean hematocrit and erythrocyte counts were significantly reduced in the mid- and high-dose males at 24 months of treatment. 

Other additional studies or pertinent information that lend support to this MRL An intermediate-duration gavage study in rats found decreased hematocrit and erythrocyte counts relative to before-treatment values (Galal et al. 1977), but this study had some limitations, including lack of a control group and disparities between text and tables. Another intermediate duration gavage study in male rats demonstrated dose-related significant decreases in mean corpuscular volume (Undeger et al. 2000). An effect on the erythrocyte is plausible because erythrocyte cholinesterase has a function in the control of erythrocyte permeability (Wills 1972). 

In one study with common marmosets, the animals were dosed with diazinon (10, 90, or 130 mg/kg i.m.) and measnrements of erythrocyte cholinesterase inhibition... 

In the first group of studies, involving kinetic inhibition studies, comparisons of the uilibrium (K ), phosphorylation (IC), and inhibition constant (K.) for the inhibition of electric eel and human erythrocyte AChE by ANTX-A(S) and DFP were done (Table II). From Table II it is seen that ANTX- A(S) has a higher affinity for human erythrocyte AChE (K =0.253 fiM) than electric eel AChE (K j=3.67 aM). AN DC-A(S) also shows greater affinity for AChE than DFP (K =300 fiM). And finally the bimolecular rate constant, Kj, which indicates the overall rate of reaction, shows AChE is more sensitive toward inhibition by ANTX-A(S) (Kj=1.36 pM- min- ) than DFP (K, = 0.033 /iM- min ). These studies add information to the comparative activity of ANTX-A(S) and other irreversible AChE inhibitors but do not show the site of inhibition. 

In vitro studies on isolated cells including hepatocytes, erythrocytes, fibroblasts, and alveolar cells continue to demonstrate the specificity of action that these toxins have for liver cells (83,86,93). This specificity has led Aune and Berg (94) to use isolated rat hepatocytes as a screen for detecting hepatotoxic waterblooms of cyanobacteria. 

Many environmental toxins interact with specific cellular receptors, including enzymes, ion channels and ion pumps, and thus provide natural tools for the study of cellular signalling pathways. Palytoxin, a compound isolated from the coelen-terate of genus Palythoa, is one such useful and intriguing compound. The structure of palytoxin was first determined in 1981 independently by Hirata (7) and Moore (2). As one of the most potent marine toxins known, palytoxin has been studied in a variety of systems ranging from erythrocytes to neurons. As a tumor promoter of the non 12-O-tetradecanoylphorbol-13-acetate (TPA) type, palytoxin can also be studied in the context of a growth control system. 

Palytoxin (PTX) is one of the most potent marine toxins known and the lethal dose (LD q) of the toxin in mice is 0.5 Mg/kg when injected i.v. The molecular structure of the toxin has been determined fully (1,2). PTX causes contractions in smooth muscle (i) and has a positive inotropic action in cardiac muscle (4-6). PTX also induces membrane depolarization in intestinal smooth (i), skeletal (4), and heart muscles (5-7), myelinated fibers (8), spinal cord (9), and squid axons (10). PTX has been demonstrated to cause NE release from adrenergic neurons (11,12). Biochemical studies have indicated that PTX causes a release of K from erythrocytes, which is followed by hemolysis (13-15). The PTX-induced release of K from erythrocytes is depress by ouabain and that the binding of ouabain to the membrane fragments is inhibited by PTX (15). 

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