Effect of lithium maintenance therapy on thyroid and parathyroid function.
(33/1952)
OBJECTIVES: To assess changes induced by lithium maintenance therapy on the incidence of thyroid, parathyroid and ion alterations. These were evaluated with respect to the duration of lithium therapy, age, sex, and family history (whether or not the patient had a first-degree relative with thyroid disease). DESIGN: Prospective study. SETTING: Affective Disorders Clinic at St. Mary's Hospital, Montreal. PATIENTS: One hundred and one patients (28 men and 73 women) with bipolar disorder receiving lithium maintenance therapy ranging from 1 year's to 32 years' duration. The control group consisted of 82 patients with no psychiatric or endocrinological diagnoses from the hospital's out-patient clinics. OUTCOME MEASURES: Laboratory analyses of calcium, magnesium and thyroid-stimulating hormone levels performed before beginning lithium therapy and at biannual follow-up. RESULTS: Hypothyroidism developed in 40 patients, excluding 8 patients who were hypothyroid at baseline. All patients having first-degree relatives affected by thyroid illness had accelerated onset of hypothyroidism (3.7 years after onset of lithium therapy) compared with patients without a family history (8.6 years after onset of lithium therapy). Women over 60 years of age were more often affected by hypothyroidism than women under 60 years of age (34.6% versus 31.9%). Magnesium levels in patients on lithium treatment were unchanged from baseline levels. After lithium treatment, calcium levels were higher than either baseline levels or control levels. Thus, lithium treatment counteracted the decrease in plasma calcium levels associated with aging. CONCLUSIONS: Familial thyroid illness is a risk factor for hypothyroidism and hypercalcemia during lithium therapy. (+info)
The role of glycogen synthase kinase 3beta in insulin-stimulated glucose metabolism.
(34/1952)
To characterize the contribution of glycogen synthase kinase 3beta (GSK3beta) inactivation to insulin-stimulated glucose metabolism, wild-type (WT-GSK), catalytically inactive (KM-GSK), and uninhibitable (S9A-GSK) forms of GSK3beta were expressed in insulin-responsive 3T3-L1 adipocytes using adenovirus technology. WT-GSK, but not KM-GSK, reduced basal and insulin-stimulated glycogen synthase activity without affecting the -fold stimulation of the enzyme by insulin. S9A-GSK similarly decreased cellular glycogen synthase activity, but also partially blocked insulin stimulation of the enzyme. S9A-GSK expression also markedly inhibited insulin stimulation of IRS-1-associated phosphatidylinositol 3-kinase activity, but only weakly inhibited insulin-stimulated Akt/PKB phosphorylation and glucose uptake, with no effect on GLUT4 translocation. To further evaluate the role of GSK3beta in insulin signaling, the GSK3beta inhibitor lithium was used to mimic the consequences of insulin-stimulated GSK3beta inactivation. Although lithium stimulated the incorporation of glucose into glycogen and glycogen synthase enzyme activity, the inhibitor was without effect on GLUT4 translocation and pp70 S6 kinase. Lithium stimulation of glycogen synthesis was insensitive to wortmannin, which is consistent with its acting directly on GSK3beta downstream of phosphatidylinositol 3-kinase. These data support the hypothesis that GSK3beta contributes to insulin regulation of glycogen synthesis, but is not responsible for the increase in glucose transport. (+info)
Dynamic regulation of expression and phosphorylation of tau by fibroblast growth factor-2 in neural progenitor cells from adult rat hippocampus.
(35/1952)
The nature of the extracellular signals that regulate the expression and the phosphorylation of the microtubule-associated protein tau, which is aberrantly hyperphosphorylated in Alzheimer disease and other adult-onset neurodegenerative diseases, is not known. We have found that neural progenitor cells from adult rat hippocampus express adult isoforms of tau and that the expression and the phosphorylation of tau are regulated by fibroblast growth factor-2 (FGF-2). Astrocytes that are differentiated from these cells by stimulation with ciliary neurotrophic factor express phosphorylated tau similarly when cultured in the presence of FGF-2. In fetal progenitor cells that express only the fetal tau isoform, expression, but not the phosphorylation, of this protein is regulated by FGF-2 in cultures of higher passages. The FGF-2-mediated tau hyperphosphorylation is inhibited by lithium, an inhibitor of glycogen synthase kinase-3 (GSK-3), but not by inhibitors of mitogen-activated protein kinase or the cyclin-dependent kinases. Furthermore, both GSK-3 activity and the phosphorylation of tau increase when the concentration of FGF-2 is increased up to 40 ng/ml. These results demonstrate that proliferating adult rat hippocampal progenitor cells express adult isoforms of tau stably and that FGF-2 upregulates the expression and, by upregulating GSK-3 activity, the phosphorylation of tau. (+info)
The expression and function of cadherin-mediated cell-to-cell adhesion in human embryonal carcinoma cells.
(36/1952)
Human embryonal carcinoma (EC) cells typically require high cell densities to maintain their characteristic phenotype; they are generally subject to differentiation when cultured at low cell densities, marked by changes in morphology and expression of the surface antigen, SSEA-1. To test whether cadherin mediated cell-to-cell adhesion may be responsible for maintaining an EC phenotype we ascertained that human EC cells generally express E- and P-cadherins, and are subject to cadherin mediated, Ca2+ dependent aggregation. However, in the NTERA2 human EC cell line, inhibition of cadherin mediated adhesion by culture in low levels of Ca2+ did not result in the changes typically seen under low cell density conditions. Low Ca2+ levels also did not affect the pattern of differentiation in these cells following induction with retinoic acid. Therefore, cadherin-mediated cell adhesion does not appear to play a role in maintaining an EC phenotype. On the other hand, culture at both low cell density and in the absence of Ca2+ did result in changes in the patterns of cadherin expression suggesting a feedback regulatory effect of cell-to-cell adhesion. Further, lithium which inhibits the cytoplasmic kinase GSK3beta and hence influences beta-catenin levels did cause differentiation of NTERA2 cells. However, consideration of the phenotype of the resultant cells suggested that this effect may be because of lithium mimicking activation of a Wnt signalling pathway, rather than an effect on signalling consequent upon cadherin mediated cell to cell adhesion. (+info)
Structural characterization of triacylglycerols as lithiated adducts by electrospray ionization mass spectrometry using low-energy collisionally activated dissociation on a triple stage quadrupole instrument.
(37/1952)
We describe features of tandem mass spectra of lithiated adducts of triacylglycerol (TAG) species obtained by electrospray ionization mass spectrometry (ms) with low-energy collisionally activated dissociation (CAD) on a triple stage quadrupole instrument. The spectra distinguish isomeric triacylglycerol species and permit assignment of the mass of each fatty acid substituent and positions on the glycerol backbone to which substituents are esterified. Source CAD-MS2 experiments permit assignment of double bond locations in polyunsaturated fatty acid substituents. The ESI/MS/MS spectra contain [M + Li - (RnCO2H)]+, [M + Li - (RnCO2Li)]+, and RnCO+ ions, among others, that permit assignment of the masses of fatty acid substituents. Relative abundances of these ions reflect positions on the glycerol backbone to which substituents are esterified. The tandem spectra also contain ions reflecting combined elimination of two adjacent fatty acid residues, one of which is eliminated as a free fatty acid and the other as an alpha, beta-unsaturated fatty acid. Such combined losses always involve the sn-2 substituent, and this feature provides a robust means to identify that substituent. Fragment ions reflecting combined losses of both sn-1 and sn-3 substituents without loss of the sn-2 substituent are not observed. Schemes are proposed to rationalize formation of major fragment ions in tandem mass spectra of lithiated TAG that are supported by studies with deuterium-labeled TAG and by source CAD-MS2 experiments. These schemes involve initial elimination of a free fatty acid in concert with a hydrogen atom abstracted from the alpha-methylene group of an adjacent fatty acid, followed by formation of a cyclic intermediate that decomposes to yield other characteristic fragment ions. Determination of double bond location in polyunsaturated fatty acid substituents of TAG is achieved by source CAD experiments in which dilithiated adducts of fatty acid substituents are produced in the ion source and subjected to CAD in the collision cell. Product ions are analyzed in the final quadrupole to yield information on double bond location. (+info)
Distinction among isomeric unsaturated fatty acids as lithiated adducts by electrospray ionization mass spectrometry using low energy collisionally activated dissociation on a triple stage quadrupole instrument.
(38/1952)
Features of tandem mass spectra of dilithiated adduct ions of unsaturated fatty acids obtained by electrospray ionization mass spectrometry with low-energy collisionally activated dissociation (CAD) on a triple stage quadrupole instrument are described. These spectra distinguish among isomeric unsaturated fatty acids and permit assignment of double-bond location. Informative fragment ions reflect cleavage of bonds remote from the charge site on the dilithiated carboxylate moiety. The spectra contain radical cations reflecting cleavage of bonds between the first and second and between the second and third carbon atoms in the fatty acid chain. These ions are followed by a closed-shell ion series with members separated by 14 m/z units that reflect cleavage of bonds between the third and fourth and then between subsequent adjacent pairs of carbon atoms. This ion series terminates at the member reflecting cleavage of the carbon-carbon single bond vinylic to the first carbon-carbon double bond. Ions reflecting cleavages of bonds distal to the double bond are rarely observed for monounsaturated fatty acids and are not abundant when they occur. For polyunsaturated fatty acids that contain double bonds separated by a single methylene group, ions reflecting cleavage of carbon-carbon single bonds between double bonds are abundant, but ions reflecting cleavages distal to the final double bond are not. Cleavages between double bonds observed in these spectra can be rationalized by a scheme involving a six-membered transition state and subsequent rearrangement of a bis-allylic hydrogen atom to yield a terminally unsaturated charge-carrying fragment and elimination of a neutral alkene. The location of the beta-hydroxy-alkene moiety in ricinoleic acid can be demonstrated by similar methods. These observations offer the opportunity for laboratories that have tandem quadrupole instruments but do not have instruments with high energy CAD capabilities to assign double bond location in unsaturated free fatty acids by mass spectrometric methods without derivatization. (+info)
Increased Na+/Li+ countertransport activity may help to identify type 1 diabetic adolescents and young adults at risk for developing persistent microalbuminuria.
(39/1952)
OBJECTIVE: To evaluate whether erythrocyte sodium-lithium countertransport (Na+/Li+ CT) activity may identify adolescents and young adults with childhood-onset of type 1 diabetes to be at greater risk to develop persistent microalbuminuria and incipient diabetic nephropathy. RESEARCH DESIGN AND METHODS: In January 1989, Na+/Li+ CT was measured in 170 normoalbuminuric diabetic adolescents and young adults (age 12-23 years; onset of diabetes before age 18 years; duration of diabetes longer than 7 years). Participants were clinically examined at baseline and biennially thereafter. Na+/Li+ CT activity was measured every 2 years during the 8-year follow-up period. Na+/Li+ CT activity was measured also in parents of diabetic offspring. RESULTS: Over 8 years, 18 (10 male, 8 female) out of 170 patients (10.5%) developed persistent microalbuminuria; no patient developed overt nephropathy. The risk of developing microalbuminuria was higher in children with increased Na+/Li+ CT (using 300 mumol.1 erythrocytes-1.h-1 as the arbitrary cutoff point) (group 1) compared with those with normal Na+/Li+ CT at the beginning of the study (group 2) (18.98 vs. 3.29%, P < 0.01; sensitivity 96.7%; specificity 57.9%). Sex did not influence predictive value, sensitivity, or specificity. Na+/Li+ CT was not significantly correlated with HbA1c or duration of type 1 diabetes. The percentage of offspring with both parents having Na+/Li+ CT activity above the median values was significantly higher in patients in group 1 than in group 2. The odds ratio for the occurrence of microalbuminuria after adjustment for confounding variables (albumin excretion rate [AER], sex, HbA1c, mean blood pressure, cholesterol, triglycerides) in type 1 diabetic adolescents with elevated baseline erythrocyte Na+/Li+ CT was 4.5 (95% CI of 2.1-11.4). CONCLUSIONS: These results confirm those of previous studies and suggest that Na+/Li+ CT may be one of the predictors and risk factors for incipient diabetic nephropathy in adolescents and young adults with onset of diabetes during childhood. Persistently increased Na+/Li+ CT activity may help to identify normotensive, normoalbuminuric patients with type 1 diabetes who are predisposed to develop microalbuminuria and incipient diabetic nephropathy. (+info)
On the molecular basis of ion permeation in the epithelial Na+ channel.
(40/1952)
The epithelial Na+ channel (ENaC) is highly selective for Na+ and Li+ over K+ and is blocked by the diuretic amiloride. ENaC is a heterotetramer made of two alpha, one beta, and one gamma homologous subunits, each subunit comprising two transmembrane segments. Amino acid residues involved in binding of the pore blocker amiloride are located in the pre-M2 segment of beta and gamma subunits, which precedes the second putative transmembrane alpha helix (M2). A residue in the alpha subunit (alphaS589) at the NH2 terminus of M2 is critical for the molecular sieving properties of ENaC. ENaC is more permeable to Li+ than Na+ ions. The concentration of half-maximal unitary conductance is 38 mM for Na+ and 118 mM for Li+, a kinetic property that can account for the differences in Li+ and Na+ permeability. We show here that mutation of amino acid residues at homologous positions in the pre-M2 segment of alpha, beta, and gamma subunits (alphaG587, betaG529, gammaS541) decreases the Li+/Na+ selectivity by changing the apparent channel affinity for Li+ and Na+. Fitting single-channel data of the Li+ permeation to a discrete-state model including three barriers and two binding sites revealed that these mutations increased the energy needed for the translocation of Li+ from an outer ion binding site through the selectivity filter. Mutation of betaG529 to Ser, Cys, or Asp made ENaC partially permeable to K+ and larger ions, similar to the previously reported alphaS589 mutations. We conclude that the residues alphaG587 to alphaS589 and homologous residues in the beta and gamma subunits form the selectivity filter, which tightly accommodates Na+ and Li+ ions and excludes larger ions like K+. (+info)