Erythromycin-resistant Streptococcus pyogenes in Argentina

Erythromycin (ERY) resistance in Streptococcus pyogenes has recently emerged as a problem of growing concern all through the world. We are presenting the comparison of results of the continuous surveillance of erythromycin resistance in S. pyogenes performed since 1989 in the Hospital de Pediatría J.P.Garrahan of Buenos Aires City, with independently observed rates in other five centers of Buenos Aires and seven centers of six other Argentinian cities, obtained between 1999 and 2001. A significant increase of erythromycin resistance was observed among S. pyogenes isolated in the Hospital Garrahan (6.6% in 1998-1999 to 9.9% in 2000). Similar trends were also detected in other centers of other Argentinian cities when recent data were compared to results of a multicenter study performed in 1995. However, lower rates of resistance were recorded in Mendoza, Cipolletti and Neuquén in comparison with data of 1995, 1998 and 1998 respectively. The reason of such decreasing resistance rates deserves to be investigated. The average of ERY-resistance rates obtained in the surveyed centers was 6.7% (range 0.5-14.1%). Control of antimicrobial use should be performed to warrant the future effectiveness of macrolide antibiotics regarding the positive association between use and resistance. These results also suggest that susceptibility tests for macrolides should be performed whenever S. pyogenes is isolated in Argentina.

La resistencia a la eritromicina en Streptococcus pyogenes ha emergido en los últimos tiempos como un problema creciente en todo el mundo. En este trabajo se presenta la comparación de los resultados de la vigilancia continua de la resistencia a la eritromicina que se viene realizando en el Hospital de Pediatría J.P.Garrahan de Buenos Aires desde 1989, con resultados independientes de otros cinco centros de la ciudad de Buenos Aires y siete de otras seis ciudades argentinas, obtenidos entre 1999 y 2001. Se observó un aumento significativo en el Hospital Garrahan (6.6% en1998-1999 a 9.9% en el año 2000) y una tendencia similar en otros centros de diversas ciudades argentinas si secomparan estos datos con los de un estudio multicéntrico realizado en 1995. No obstante, se registraron menoresporcentajes de resistencia en Mendoza, Neuquén y Cipolletti, en relación a lo hallado en 1995, 1998 y 1998respectivamente. La razón de esta disminución merece ser investigada. El porcentaje promedio de resistencia aeritromicina obtenido en los distintos centros participantes de este estudio fue de 6.7% (rango 0.5-14.1%). Debeefectuarse un control en el uso de estos antibióticos para garantizar la efectividad futura de los macrólidos, teniendo en cuenta la asociación estrecha entre uso y resistencia. Estos resultados sugieren que deberían realizarse pruebas de sensibilidad a los macrólidos para todos los aislamientos de S. pyogenes en la Argentina.

Aldosterone impairs insulin responsiveness in U-937 human promonocytic cells via the downregulation of its own receptor.

In an earlier study, we have reported an inhibition of insulin receptor (IR) mRNA levels and insulin binding by aldosterone in U-937 human promonocytic cells. In the present extension of our studies, we demonstrate that this inhibition by aldosterone had no effects on basal glucose transport or on basal thymidine incorporation into DNA, while the cell responsiveness reflected by the maximal response to insulin was decreased by 23% for glucose transport and by 31% for DNA synthesis after the aldosterone treatment. We also prove that this inhibition of the insulin response by aldosterone is mediated by a downregulation of the levels of mineralocorticoid receptors (MRs) (50% decrease) and their mRNA (50% decrease). In addition, the mineralocorticoid antagonist spironolactone reversed the decrease in MR mRNA levels elicited by aldosterone, which suggests the involvement of this receptor in the process.

Inhibition by aldosterone of insulin receptor mRNA levels and insulin binding in U-937 human promonocytic cells.

The effect of aldosterone on insulin receptor (IR) expression was investigated in U-937 human promonocytic cells. The putative involvement of the mineralocorticoid receptor (MR) was also analysed. Aldosterone binding assays indicated the presence of MRs with high affinity and limited capacity in these cells. RNA blot assays showed that aldosterone treatment decreased the levels of the two major IR mRNAs (11 and 8.5 kb) present in these cells in a dose- and time-dependent manner. The partial reversal of such a decrease by the mineralocorticoid antagonist spironolactone suggested that MR was involved in the process. Experiments with the RNA synthesis inhibitor actinomycin D indicated that the decrease in IR mRNA content in aldosterone-treated cells was not the result of transcript destabilisation. The inhibitory action of aldosterone was not prevented by the simultaneous presence of the protein synthesis inhibitor cycloheximide, suggesting that the reduction of IR gene expression occurs as a direct response to the action of aldosterone. Furthermore, insulin binding assays showed that aldosterone decreased IR capacity but did not alter receptor affinity. In addition, the IR turnover resulted unaltered. These results provide the first evidence for an in vitro modulation of human IR expression by aldosterone.

In vivo tissue specific modulation of rat insulin receptor gene expression in an experimental model of mineralocorticoid excess.

Insulin receptor (IR) gene expression at the mRNA level was investigated in hindlimb skeletal muscle, epididymal adipose tissue and in the liver of rats exposed to prolonged in vivo administration of deoxycorticosterone acetate (DOCA). Following treatment, plasma insulin levels were reduced while glucose levels increased compared to values in control rats. DOCA-treated animals showed an increase in blood pressure and a reduction in body weight. This treatment also induced hypokalemia and decreased plasma protein levels. Sodium levels were unaffected. Moreover, no differences in DNA and protein content or in the indicator of cell size (protein/DNA) were observed in the skeletal muscle or adipose tissue of animals. In contrast, there was a clear increase in the protein and DNA contents of the liver with no change in the indicator of cell size. Northern blot assays revealed 2 major IR mRNA species of approximately 9.5 and 7.5 Kb in the 3 tissues from control animals. DOCA treatment induced no change in the levels of either RNA species in skeletal muscle. However, a decrease of approximately 22% was detected in the levels of both species in adipose tissue whereas the liver showed an increase of 64%. These results provide the first evidence for an in vivo tissue-specific modulation of IR mRNA levels under experimental conditions of mineralocorticoid excess.

Tissue-specific modulation of insulin receptor mRNA levels in adrenaline-treated rats.

Insulin receptor (IR) gene expression at the mRNA level was investigated in liver, hindlimb skeletal muscle, and epididymal adipose tissue of rats exposed to prolonged in vivo administration of adrenaline in relation to control rats. In the liver of adrenaline-treated rats, there were no differences in relation to controls when DNA and protein content were measured. In skeletal muscle, only a slight decrease in protein concentration was detected. By contrast, a clear increase in both protein and DNA content was observed in the adipose tissue of treated animals. Northern blot assays revealed two IR mRNA species of approximately 9.5 and 7.5 Kb in the three tissues from controls. Adrenaline treatment induced an increase of approximately 60% in the levels of both RNAs in adipose tissue but not in liver or skeletal muscle. These results provide evidence for an in vivo tissue-specific regulation of IR gene expression at the mRNA level in rats under an experimental condition of excess of catecholamines.

Tissue-specific changes in insulin receptor mRNA concentrations in dexamethasone-treated and adrenalectomized rats.

The relative concentrations of total insulin receptor (IR) mRNA were measured in the epididymal adipose tissue and liver of intact untreated rats, dexamethasone-treated rats, adrenalectomized rats and adrenalectomized rats treated with dexamethasone, using RNA blot assays and a specific IR cDNA probe. Northern blot assays revealed two IR mRNA species of approximately 9.5 and 7.5 kb, in both tissues. Dot-Blot assays followed by densitometry indicated that dexamethasone induced an approximately three-fold increase in IR mRNA in liver, but not in epididymal adipose tissue. By contrast, neither adrenalectomy alone nor the combination of adrenalectomy plus dexamethasone treatment altered the IR mRNA concentrations in liver nor in adipose tissue, which indicates that adrenalectomy was able to prevent the stimulation of IR gene expression caused by dexamethasone in rat liver. These results provide evidence for an "in vivo" tissue-specific regulation of IR gene expression, at the mRNA level, in rats under experimental conditions of an excess or insufficiency of glucocorticoids.

Identification of glucagon receptors in human adipocytes from a liposarcoma.

The presence of glucagon receptors on human adipocytes has not yet been described. In this work we present an exceptional case of glucagon binding to human adipocytes taken from a malignant tumor of adipose tissue of a patient with a liposarcoma. Binding analysis revealed that the total number of glucagon receptors on liposarcoma-cells was 99,000 and the apparent receptor affinity (ED:50) was 5 x 10(-9) M. Despite the presence of these specific receptors, glucagon was unable to induce a lipolytic response, or to activate the adenylate-cyclase system in these liposarcoma-cells. Whether the induction of glucagon receptors is a specific process of the tumor biology remains to be elucidated.

[Changes in the mechanism of action of insulin on fatty tissue accumulations in lipomas, Madelung's lipomatosis and liposarcoma]. / Alteraciones en el mecanismo de acción de la insulina en los acúmulos de tejido adiposo de lipomas, lipomatosis de Madelung y liposarcoma.

In this paper, the preliminary results regarding the alterations of the biological action mechanism of insulin in several types of pathological accumulations of fat, i.e. lipomas, Madelung's Lipomatosis and liposarcoma, are presented. The results indicate significant alterations both at the insulin receptor and post-receptor levels, with reduced biological activity of this hormone, which could have and inductive role in the pathogenesis of such entities.

Increased insulin receptor binding in erythrocytes from growth hormone-deficient children.

Erythrocytes from growth hormone-deficient children (GHd-children) (n = 10) showed a statistically significant increase in insulin binding at low unlabeled insulin concentrations, together with a threefold decrease in apparent receptor affinity, as compared to control children (C) (n = 11). Scatchard analysis of the binding data using the two-site model revealed that both the receptor concentration R1 [GHd-children 0.10 +/- 0.01 ng/ml and C 0.03 +/- 0.002 ng/ml] and the dissociation constant KD1 [GHd-children (0.48 +/- 0.05) x 10(-9) M and C (0.19 +/- 0.01) x 10(-9) M] for high affinity-low capacity sites were significantly increased in erythrocytes from GHd-children, while neither receptor concentrations (R2) nor the dissociation constant (KD2) for low affinity-high capacity sites proved to be altered. These events were accompanied by a normal sensitivity to insulin as well as glucose tolerance in the GHd-group. The meaning of the increased insulin binding with normal insulin sensitivity in GH-deficiency is discussed.

[Decreased insulin receptor number and affinity in subcutaneous adipose tissue in a patient with primary hyperaldosteronism]. / Disminución en el número y en la afinidad de los receptores de insulina en el tejido adiposo subcutáneo de un paciente con hiperaldosteronismo primario.

In the present work we study the binding of insulin to its receptors in adipocytes from subcutaneous adipose tissue of left hypochondria extracted during an adrenalectomy carried out in a patient with Conn's Syndrome (left adrenal adenoma), comparing it to insulin binding to its receptors in adipocytes from subcutaneous adipose tissue of right hypochondria, obtained during a cholecystectomy because of cholelithiasis (controls). According to our results, there is an evident decrease in insulin binding to its receptors in adipocytes of the patient with Conn's Syndrome in relation to control group. This decrease in binding would be based both in a decrease in insulin receptor number as in an affinity loss of these receptors for the hormone. These facts at the receptor level could be originating a decrease in tissue response to insulin and be the base for glucose intolerance observed in patients with this pathology.

Chronic and endogenous regulation of insulin receptors by catecholamines in adipocytes from patients with a phaeochromocytoma.

Insulin binding in adipocytes from patients with a phaeochromocytoma (PH) approached that of the controls (C) at low and higher concentrations of unlabeled insulin. The apparent receptor affinity was unchanged (ED50: PH 0.50 x 10(-9) M and C 0.60 x 10(-9) M). Scatchard analysis of the binding data using the negative cooperative model revealed a 46% decrease in the total number of receptors together with no changes in both K-e (PH 0.55 x 10(9) M-1 and C 0.36 x 10(9) M-1) and K-f (PH 0.13 x 10(9) M-1 and C 0.07 x 10(9) M-1). According to the two site model, an altered proportion in the two classes of insulin binding sites was detected. This was accompanied by a catecholamine-desensitization of the adipocytes to the antilipolytic action of insulin. These events could represent a final situation of a chronic and endogenous regulation by high levels of catecholamines of insulin receptors in human adipose tissue.

Binding and antilipolytic action of insulin in isolated adipocytes from cortisol-treated rats.

The effects of an in vivo cortisol-treatment to rats (2 X 2 mg/rat/day, for one week) on insulin plasma levels, insulin binding and antilipolytic activity in rat adipose tissue were investigated. Hyperinsulinemia together with an increase in insulin degradation in the serum of cortisol-treated rats were observed. The adipocytes from cortisol-treated animals showed a statistically significant decrease in insulin binding but no change in receptor numbers [cortisol-treated 103,000 +/- 8,000 (n = 8) receptors/cell and controls 138,000 +/- 15,000 (n = 16) receptors/cell], together with unchanged receptor affinity [ED50: cortisol-treated 3 X 10(-9) M and controls 3.2 X 10(-9) M], and a decreased sensitivity to the antilipolytic effect of insulin. The evidence presented for pre-receptor, receptor and post-receptor insulin defects on the action of cortisol in isolated rat adipocytes could represent a coordinated mechanism by which cortisol exerts "insulin resistance" in this tissue.

Decreased insulin binding and antilipolytic response in adipocytes from patients with Cushing's syndrome.

Human adipocytes from patients with chronic endogenous hypercortisolism (Cushing's syndrome) showed a statistically significant decrease in insulin binding at low unlabelled-insulin concentrations but no change in receptor numbers (Cushing's 180,000 +/- 48,000 (3) receptors/cell and controls 189,000 +/- 30,000 (7)) together with a fourfold decrease in apparent receptor affinity (ED50: Cushing's 2.25 x 10(-9) M and controls 0.57 x 10(-9) M) and a decreased sensitivity to the antilipolytic effect of insulin. These events could represent the final situation of a chronic and endogenous regulation by high levels of cortisol of insulin receptors in human adipose tissue.