Biomedical subjects
Publications and source records attributed to J C White.
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Cells from cranial and spinal arachnoid membranes of humans were grown in culture. Their growth characteristics, morphology and details of their cytoskeletal composition are described. Arachnoid membranes, obtained at autopsy, were finely minced and incubated in tissue culture medium. Monolayers of cells of homogeneous morphology grew from these tissue fragments. The cells were flat and polygonal. They divided slowly to form nonoverlapping monolayers of low cell density. Electron microscopic examination of cultured arachnoid cells revealed numerous desmosome-like tight junctions and abundant intermediate filaments (tonofilaments). Both morphological features are characteristic of arachnoid cells in situ, but not of cells in the fibroblast-rich dura mater. Immunofluorescence microscopy with monoclonal antibodies demonstrated cytokeratin in the cytoplasm of primary cultures of arachnoid cells. Thus we demonstrated that these cultured cells retained certain of the specific differentiated properties of arachnoid cells in situ and that they are not fibroblasts (which lack tight junctions and cytokeratins). To our knowledge, there have been no previous reports of in vitro growth of arachnoid cells. This in vitro model should be useful in studying the response of arachnoid cells to a variety of substances thought to be involved in the chronic inflammatory condition of the meninges known as arachnoiditis.
Aberration in the physical structure or alignment of the eyes may produce pathologic neurocompensatory changes in the brain that, if left unattended, become irreversible. Two common examples of this abnormal state are accommodative esotropia and amblyopia. Both have a large optic component in their etiology and in most cases are correctable by optic methods. Generated retinal reflex photometry is a screening method that can detect, in the eyes of children, optic defects that tend to be the antecedents of more serious neurocompensatory processes. Detection at an early age permits more effective management and treatment of amblyopia. This technique is fast, safe, and inexpensive and provides a permanent record. It requires no response from the subject except a modicum of cooperation. It is attractive as an ocular screening method because it does not require highly trained personnel to administer the examination, yet appears to be accurate. The results lend themselves to mechanized processing.
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We carried out a statistically designed, multilaboratory study to evaluate a flame atomic emission spectroscopic (FAES) method for serum sodium as a Reference Method. definitive values for the serum pools for the study, with sodium in the 110-160 mmol/L range, were determined at the National Bureau of Standards by an ion-exchange/gravimetry method. The multilaboratory FAES results were judged against the preselected performance criteria for the Reference Method: maximum imprecision 1.5 mmol/L, maximum bias 2.0 mmol/L. The standard error of a single laboratory's performance of the method varied with concentration from 0.46 to 0.86 mmol/L with a maximum bias of 1.0 mmol/L; thus, the criteria were satisfied. The cooperating laboratories performed the method with either manual or semi-automated pipetting. Although both modes of pipetting satisfied our acceptability criteria, only the method with semi-automated pipetting is described here as the Reference Method. The statistical results indicate that the precision criterion can be fulfilled with fewer than four replicate analyses.
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Transport of methotrexate in mammalian cells is a complex process. Although the drug is pumped uphill into cells, metabolic poisons enhance influx and transmembrane gradients for this agent. Structurally unrelated inorganic and organic anions nonspecifically depress these parameters in a variety of tumor cells. It has been suggested that cell cyclic adenosine 3':5'-Monophosphate (cyclic AMP) plays a regulatory role in the transport of this agent. To evaluate this further, a number of different experimental approaches were used to analyze the relationship between methotrexate transport and cell cyclic AMP in the Ehrlich ascites tumor. The following results indicate that for the Ehrlich ascites tumor, at least, there is no evidence for a regulatory role for cyclic AMP in the transport of methotrexate. (a) A marked increase in cell cyclic AMP by cholera-toxin or reduction in cyclic AMP by ascorbate was unaccompanied by changes in methotrexate influx. (b) Instantaneous and constant inhibition of methotrexate influx by isobutylmethylxanthine was temporally dissociated from the slower rise in cell cyclic AMP that was induced by this agent. (c) Although isobutylmethylxanthine and dibutyryl cyclic AMP augment cell cyclic AMP and decrease methotrexate influx, they have different effects on efflux and net transport of methotrexate. Isobutylmethylxanthine stimulates net methotrexate uptake and slows methotrexate efflux but dibutyryl cyclic AMP depresses net methotrexate uptake without an effect on methotrexate efflux. (d) Azide markedly stimulates methotrexate influx and net transport without a change in cell cyclic AMP. (d) Dinitrophenol inhibits methotrexate influx and augments net methotrexate accumulation but does not alter cell cyclic AMP.
Influx of [3H]methotrexate into freshly isolated hepatocytes in suspension is mediated by two routes, one with a high affinity (Km = 5.9 microM) and another with a low affinity for methotrexate. Both transport routes are equally sensitive to the sulfhydryl group inhibitor, p-chloromercuriphenylsulfonic acid, alterations in temperature, substitution of extracellular Na+ with choline, and inhibition by ouabain or azide. The high-affinity pathway for methotrexate shows specificity for the 4-amino group of the pteridine moiety as methotrexate and aminopterin similarly inhibit influx of the labeled drug. On the other hand, 100 microM concentrations of the naturally occurring folates, folic acid, 5-methyltetrahydrofolate, and 5-formyltetrahydrofolate, are not inhibitory to influx of 1 microM methotrexate. Once in the cell, methotrexate rapidly reaches molar equivalence with dihydrofolate reductase following which both exchangeable and nonexchangeable intracellular methotrexate accumulates. The exchangeable component reaches steady state within 0.5 hr while the nonexchangeable component increases for at least 1 hr. The nonexchangeable component represents both bound methotrexate and methotrexate polyglutamates. Polyglutamates of methotrexate are a trivial component of total 3H within the cell until about 15 min, but thereafter, their rate of accumulation is constant so that by 1 hr they represent approximately 30% of total intracellular 3H. At steady state, there is a transmembrane chemical gradient for exchangeable methotrexate of 2.4:1; this is 24 times greater than the chemical gradient predicted for equilibrium when the transcellular membrane potential is considered. These results indicate that there are multiple routes for methotrexate transport in the rat hepatocyte that appear to be, at least in part, distinct from the routes for folic acid and the tetrahydrofolate cofactors. The data suggest that transport is energy and Na+ dependent and that the transport carrier requires intact sulfhydryl groups. Net association of methotrexate with the cells is a complex process determined by transport and binding to multiple sites within the cell and metabolism to polyglutamate derivatives that are retained within the cell.
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Interaction of positively charged liposomes with Ehrlich ascites tumor cells increases the bidirectional transmembrane fluxes of the anionic folic acid analog, methotrexate. Negative liposomes reduce methotrexate influx. Stimulation of methotrexate influx by positively charged liposomes is time and concentration dependent, requiring at least a 5-min incubation with 2.5 mM phosphatidylcholine containing 20% stearylamine for maximum effect. Stimulation is not appreciably reversed by washing the cells. Similar increases are observed for influx and efflux so that there is no change in the steady-state methotrexate electrochemical-potential difference across the cell membrane. The increase influx appears to be a stimulation of the carrier-mediated transport process for methotrexate since both control and stimulated influx are abolished by the competitive inhibitor, 5-formyltetrahydrofolate or the sulfhydryl group inhibitor, p-chloromercuriphenylsulfonic acid and the Q10 of the system remains unchanged. Influx of 5-methyltetrahydrofolate, which shares the same transport carrier as methotrexate, is also stimulated. However, the transport of folic acid, which is structurally similar to methotrexate but does not utilize the carrier, is unaffected. The kinetic change induced by positively charged liposomes is an increase in the Vma in, while the Kt in remains unchanged. Trans-stimulation of methotrexate influx by 5-formyltetrahydrofolate occurs to the same extent in the presence or absence of positively charged liposomes. The liposomes have no apparent effect on the intracellular water, the extracellular space, or the chloride distribution ratio. The data suggest that interaction of positively charged liposomes with Ehrlich ascites tumor cells accelerates the rate of transposition of the membrane carrier system for methotrexate, altering the kinetics of transport without a change in transport thermodynamics.
Serial EEGs with early and progressive bilateral periodic activity were recorded from a patient with clinically "atypical" but pathologically confirmed subcoritcal arteriosclerotic encephalopathy (Binswanger's type). This disease should be considered as a diagnostic possibility when periodic EEG activity is encountered, particularly when dementia, hypertension, and focal neurologic signs coexist. At times, white matter lesions may contribute to the production of periodic EEG activity.
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Polyglutamate derivatives of [3H]methotrexate (MTX) were detected in freshly isolated rat hepatocytes in suspension within 15 min after exposure to the folate analog. The rate of polyglutamate synthesis remained constant for at least one hr, and the polyglutamate derivatives accounted for an increasing proportion of the intracellular radiolabel with time. After initial exposure to 1 micron [3H]MTX, polyglutamate derivatives of Mtx continued to be synthesized even after the extracellular [3H]-MTX concentration had been reduced 20-fold. Prolonged exposure of hepatocytes in primary culture to 1 micron [3H]MTX resulted in the formation of longer-chain polyglutamate derivatives of MTX. The present studies demonstrate another important biosynthetic capacity of the freshly isolated hepatocyte and suggest the usefulness of this system for studying the mechanism of, and controlling factors in, the synthesis of polyglutamate derivatives of MTX. The ramifications of the formation of MTX polyglutamates on drug cytotoxicity in general and hepatotoxicity in particular are considered.
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