Controversias en la medición de 25 (OH) Vitamina D: comparación de dos metodologías / Controversies in measuring 25 (OH) Vitamin D: comparison of two methodologies

Introducción: Los métodos utilizados para la medición de Vitamina D tienen varios aspectos metodológicos sin definir: método de referencia, trazabilidad con estándar internacional, especificidad, etc.; situación que genera grandes controversias entre los resultados obtenidos. Objetivo: Comparar los resultados de la medición de Vitamina D con dos inmunoensayos de diferente especificidad y estandarización, y su impacto en la interpretación clínica de los mismos en individuos no tratados y tratados con Vitamina D2 o D3. Materiales y Métodos: Para la comparación de los métodos se consideraron dos grupos: G1 (95 muestras de suero de pacientes algunos de los cuales recibían Vitamina D2, otros Vitamina D3 y otros sin medicación) y G2 (40 muestras de suero luego de excluir a los 55 pacientes que recibían Vitamina D2). Resultados: Al analizar las medias de los resultados obtenidos por cada método, se hallaron diferencias altamente significativas (p<0.0001) en G1 y diferencias significativas (p< 0.0038) en G2. Cuando se compararon los resultados de EQLIA vs RIE, no se halló correlación (r:-0,00671; p=0,9483) en G1 pero sí en G2. (r=0.898, p<0.0000). Si bien en G1 se halló concordancia entre los resultados de los métodos se observa gran dispersión de los mismos (media 20,8 ng/ml). En cambio en el G2 se observa una mejor concordancia entre ellos (media 6.4 ng/ml). Conclusiones: Esta comparación de métodos nos permitió identificar las dos situaciones críticas que debemos considerar cuando nos solicitan la medición de Vitamina D: primero la condición del paciente en cuanto a si ha sido o no suplementado con Vitamina D y en ese caso si se le administró D2 o D3 y segundo: el método a emplear para su determinación. Las discrepancias entre los resultados de vitamina D obtenidos por diferentes metodologías impactarán en la utilidad clínica del informe emitido por el laboratorio y consecuentemente en la interpretación y decisión médica.

Introduction: The methods used for vitamin D measurement have several methodological aspects still not defined, such as reference method, traceability of international standard, specificity, etc, which generates great discrepancies between the results obtained. Objective: To compare the results of vitamin D measurements obtained with two different immunoassays of different specificity and standardization, and their impact on clinical interpretation in patients treated and not treated with vitamin D2 or D3. Materials and Methods: Two groups are considered for comparison of the methods: G1 (95 serum samples from patients who were receiving vitamin D2, vitamin D3 or no medication) and G2 (40 serum samples after excluding the 55 patients who received vitamin D2). Results: There are great differences between the samples measured by both assays. We found highly significant differences between means in G1 (p <0.0001) and significant differences in G2 (p < 0.0038). No correlation was observed between EQLIA vs. RIA in the G1 (r = -0.00671, p = 0.9483) but good correlation in G2. (r = 0.898, p < 0.0000). Although ECLIA was in agreement with RIA, in G1 the results of the methods shows a wide dispersion around the mean of the difference 20.8 ng / ml. In contrast, in G2 there is a better match between results (mean of the difference 6.4 ng/ml). Conclusions: This comparison of methods allowed us to identify two critical situations to consider when measuring vitamin D: first, whether the patient has been supplemented or not with Vitamin D, and in that case, if he/she has been given D2 or D3, and secondly, the method used for measurement. Discrepancies between the results of vitamin D measurements obtained by different methodologies will impact on the clinical usefulness of the report issued by the laboratory, and consequently in the interpretation and medical decision.

Binding of correolide to the K(v)1.3 potassium channel: characterization of the binding domain by site-directed mutagenesis.

Correolide is a novel immunosuppressant that inhibits the voltage-gated potassium channel K(v)1.3 [Felix et al. (1999) Biochemistry 38, 4922-4930]. [(3)H]Dihydrocorreolide (diTC) binds with high affinity to membranes expressing homotetrameric K(v)1.3 channels, and high affinity diTC binding can be conferred to the diTC-insensitive channel, K(v)3.2, after substitution of three nonconserved residues in S(5) and S(6) with the corresponding amino acids present in K(v)1.3 [Hanner et al. (1999) J. Biol. Chem. 274, 25237-25244]. Site-directed mutagenesis along S(5) and S(6) of K(v)1.3 was employed to identify those residues that contribute to high affinity binding of diTC. Binding of monoiodotyrosine-HgTX(1)A19Y/Y37F ([(125)I]HgTX(1)A19Y/Y37F) in the external vestibule of the channel was used to characterize each mutant for both tetrameric channel formation and levels of channel expression. Substitutions at Leu(346) and Leu(353) in S(5), and Ala(413), Val(417), Ala(421), Pro(423), and Val(424) in S(6), cause the most dramatic effect on diTC binding to K(v)1.3. Some of the critical residues in S(6) appear to be present in a region of the protein that alters its conformation during channel gating. Molecular modeling of the S(5)-S(6) region of K(v)1.3 using the X-ray coordinates of the KcsA channel, and other experimental constraints, yield a template that can be used to dock diTC in the channel. DiTC appears to bind in the water-filled cavity below the selectivity filter to a hydrophobic pocket contributed by the side chains of specific residues. High affinity binding is predicted to be determined by the complementary shape between the bowl-shape of the cavity and the shape of the ligand. The conformational change that occurs in this region of the protein during channel gating may explain the state-dependent interaction of diTC with K(v)1.3.

Increases in ornithine decarboxylase activity in the positive inotropism induced by androgens in isolated left atrium of the rat.

It is well established that the intracellular receptors of androgens act as transcription factors upon their activation by androgen binding. However, a growing number of studies have associated androgens with rapid biological responses independent of their classical action mechanism. In this sense, 5alpha- and 5beta-dihydrotestosterone elicited a rapid positive inotropism in the isolated left atrium of the rat via cAMP-dependent mechanisms that may involve genomic effects. In addition, polyamines are mediators of several biological actions including those acute and long-term effects induced by androgens in the heart. The present study analyzed the role of polyamine synthesis in the cardiotonic effect of androgens in the left atrium of male Wistar rats, electrically stimulated (0.5 Hz, 5 ms and supramaximal voltage) and placed in an organ bath in 10 ml of Tyrode's solution. Incubation in the organ bath with an inhibitor of ornithine decarboxylase activity, alpha-difluoromethylornithine 10 mM, significantly decreased the positive inotropism induced by 5alpha- and 5beta-dihydrotestosterone (0.1-100 microM). This suggests that ornithine decarboxylase seems to be involved in androgen-induced positive inotropism. Furthermore, 6-min exposure to 5alpha- or 5beta-dihydrotestosterone significantly increased the activity of ornithine decarboxylase from 61.81+/-7.53 (control) to 93.28+/-9.45 and 80.28+/-12 pmol/h/mg of protein, respectively. Northern blot analysis showed that 5alpha- and 5beta-dihydrotestosterone did not modify the level of expression of the ornithine decarboxylase gene. Therefore, our results suggest that polyamine synthesis might be involved in the positive inotropism elicited by androgens through the stimulation of ornithine decarboxylase activity without changes in the expression of the ornithine decarboxylase gene.

Positive inotropism induced by androgens in isolated left atrium of rat: evidence for a cAMP-dependent transcriptional mechanism.

Steroid hormones exert their biological actions via intracellular receptors modulation of transcription. In addition, a number of molecular interactions, and the existence of membrane receptors in several tissues, support the hypothesis of nongenomic action of steroids. The androgens, 5alpha- and 5beta-dihydrotestosterone (0.1 to 100 microM), induce a rapid positive inotropism in the isolated left atrium of male Wistar rats whose time course of response might suggest that it is a non-genomic effect. However, the fact that the facilitation of contractility was inhibited by actinomycin D (5 microg/ml) and cycloheximide (10 microg/ml) indicates that a transcriptional component might play a role. The existence of a rapid functional genomic role would be somewhat surprising. However, rapid transcriptional mechanisms were also observed in certain cAMP-dependent responses. In the left atrium of rat, Rp-cAMPS (10 microM), a cAMP-dependent protein kinase inhibitor, antagonized 5alpha- but not 5beta-dihydrotestosterone-induced positive inotropism. The inhibition by Rp-cAMPS of isoproterenol- and forskolin-induced positive inotropism, and the fact that these cAMP-dependent effects were also inhibited by actinomycin D and cycloheximide, suggest that a cAMP-dependent transcriptional component may be partly involved in the positive inotropism induced by 5alpha-dihydrotestosterone. In addition, 5alpha-dihydrotestosterone might increase the basal adenylyl cyclase activity by acting on unoccupied beta-adrenoceptor-G-protein-adenylyl cyclase complexes, since the elicited inotropism was inhibited by a beta-blocker, atenolol (1 microM), a G-protein inhibitor, pertussis toxin (2 microg/ml, 3 h), and an adenylyl cyclase inhibitor, dideoxy-adenosine (10 microM).

Binding of correolide to K(v)1 family potassium channels. Mapping the domains of high affinity interaction.

Correolide, a novel nortriterpene natural product, potently inhibits the voltage-gated potassium channel, K(v)1.3, and [(3)H]dihydrocorreolide (diTC) binds with high affinity (K(d) approximately 10 nM) to membranes from Chinese hamster ovary cells that express K(v)1.3 (Felix, J. P., Bugianesi, R. M., Schmalhofer, W. A., Borris, R., Goetz, M. A., Hensens, O. D., Bao, J.-M., Kayser, F. , Parsons, W. H., Rupprecht, K., Garcia, M. L., Kaczorowski, G. J., and Slaughter, R. S. (1999) Biochemistry 38, 4922-4930). Mutagenesis studies were used to localize the diTC binding site and to design a high affinity receptor in the diTC-insensitive channel, K(v)3.2. Transferring the pore from K(v)1.3 to K(v)3.2 produces a chimera that binds peptidyl inhibitors of K(v)1.3 with high affinity, but not diTC. Transfer of the S(5) region of K(v)1.3 to K(v)3.2 reconstitutes diTC binding at 4-fold lower affinity as compared with K(v)1.3, whereas transfer of the entire S(5)-S(6) domain results in a normal K(v)1.3 phenotype. Substitutions in S(5)-S(6) of K(v)1.3 with nonconserved residues from K(v)3.2 has identified two positions in S(5) and one in S(6) that cause significant alterations in diTC binding. High affinity diTC binding can be conferred to K(v)3.2 after substitution of these three residues with the corresponding amino acids found in K(v)1.3. These results suggest that lack of sensitivity of K(v)3.2 to diTC is a consequence of the presence of Phe(382) and Ile(387) in S(5), and Met(458) in S(6). Inspection of K(v)1.1-1.6 channels indicates that they all possess identical S(5) and S(6) domains. As expected, diTC binds with high affinity (K(d) values 7-21 nM) to each of these homotetrameric channels. However, the kinetics of binding are fastest with K(v)1.3 and K(v)1.4, suggesting that conformations associated with C-type inactivation will facilitate entry and exit of diTC at its binding site. Taken together, these findings identify K(v)1 channel regions necessary for high affinity diTC binding, as well as, reveal a channel conformation that markedly influences the rate of binding of this ligand.

Bactericidal effect of ADP and acetic acid on Bacillus subtilis.

Bacillus subtilis is a ubiquitous soil bacterium used for measuring the beta-lysin activity and in other bioassays. We observed a complete bactericidal effect of ADP on B. subtilis at concentrations of 50-100 microM at pH values <5.5, which disappeared at pH values above 6. The effect was also found for acetic acid at concentrations >17.4 microM and similar pH values. ATP, adenosine, and HCl were not bactericidal. We used BCECF-AM, a pH-sensitive probe, and found that the killing of B. subtilis was due to a change in the intracellular pH caused by the passage across the cell membrane of these weak organic acids when incubated with B. subtilis at pH values near the pK. More experiments are needed to determine the biological meaning of these in vitro findings.

Molecular cloning and sequencing of genomic DNA encoding yeast vacuolar carboxypeptidase yscS.

A Saccharomyces cerevisiae genomic DNA encoding vacuolar carboxypeptidase yscS was cloned from a yeast YEp13 library by complementation of the previously characterized mutation cps1-1 [(1981) J. Bacteriol. 147, 418-426], by means of staining carboxypeptidase activity in yeast colonies. The nucleotide sequence of the cloned gene was determined. The open reading frame of CPS1 consists of 576 codons and therefore encodes a protein of 64961 molecular weight. A stretch of 19 residues near the N-terminus of the deduced polypeptide sequence contains characteristics common to known hydrophobic leader sequences. CPS1 was determined by DNA blot analysis to be a single copy gene located on chromosome X. The cloned fragment was used to identify a 2.1 kb mRNA. A transcriptional activation of CPS1 occurs when cells grow on a substrate of carboxy-peptidase yscS as sole nitrogen source.

Expression of a class I MHC transgene: regulation by a tissue-specific negative regulatory DNA sequence element.

In vivo patterns of expression of a miniature swine class I major histocompatibility gene, PD7, were analyzed both in situ in the pig, and in transgenic mice. Structural analysis of PD7 DNA sequences revealed that PD7 is highly homologous to the pig gene PD1, which encodes a classical transplantation antigen. Despite the extensive homology, PD7 is expressed in situ at markedly lower levels than PD1 in nearly all tissues. Introduction of PD7 into mice results in a pattern of PD7 expression in the transgenic animals that parallels that observed in situ in the pig. Comparison of two lines of PD7 transgenic mice, which differ only in the extent of 5' flanking sequence, reveals the presence of a silencer element. The silencer activity is tissue specific: differences in PD7 expression are observed only in lymphoid tissues and skin. Skin from both lines of transgenics mediates graft rejection, but the rate of rejection correlates with the level of PD7 expression.

Biochemical and genetic analysis of an alpha-mannosidase mutant from Saccharomyces cerevisiae.

A yeast mutant lacking non-specific alpha-mannosidase activity was found as a background marker during our search for dap2 mutants (Suárez-Rendueles, P. and Wolf, D. H. (1987) J. Bacteriol. 169, 4041-4048). The mutant (DPS-15) is characterized in detail. The mutation called amd1 segregates 2:2 in meiotic tetrads, indicating a single chromosomal gene mutation which is recessive. Diploids heterozygous for amd1 show gene dosage. Thus, it appears that AMD1 might be the structural gene for alpha-mannosidase. Results obtained with this mutant show that alpha-mannosidase is not a vital component of the vegetative cell cycle. The differentiation process of sporulation is not disturbed in homozygous mutant diploids. Mannose turnover does not seem to be altered in mutant cells.

Localization of dipeptidyl aminopeptidase yscIV in the plasma membrane of Saccharomyces cerevisiae.

The subcellular distribution of dipeptidyl aminopeptidase activity was studied in protoplast lysates of Saccharomyces cerevisiae that were virtually free from vacuolar contamination. Dipeptidyl aminopeptidase yscIV, the STE13 gene product, was found to be associated with plasma membrane vesicles after sucrose gradient isopycnic centrifugation. Another dipeptidyl aminopeptidase activity, not yet fully characterized, was localized in a microvesicular population co-sedimenting with chitosomes.

Localization of the thermosensitive X-prolyl dipeptidyl aminopeptidase in the vacuolar membrane of Saccharomyces cerevisiae.

Most of the X-prolyl dipeptidyl aminopeptidase activity of Saccharomyces cerevisiae was found to be associated with purified vacuolar membranes (specific activity approx. 75-times higher than in the protoplast lysate). The tonoplast-bound enzyme is thermosensitive. Another heat-resistant enzyme was found in the protoplast lysate. The tonoplast-bound thermosensitive enzyme shows an apparent Km of 0.06 mM against L-alanyl-L-prolyl-p-nitroanilide while the heat-resistant enzyme shows an apparent Km of 0.4 mM against the same substrate.