Biomedical subjects

A Avignon

Publications and source records attributed to A Avignon.

29 records · Page 2Linked to original sources

PubMed1997

Activation of protein kinase C (alpha, beta, and zeta) by insulin in 3T3/L1 cells. Transfection studies suggest a role for PKC-zeta in glucose transport.

We presently studied (a) insulin effects on protein kinase C (PKC) and (b) effects of transfection-induced, stable expression of PKC isoforms on glucose transport in 3T3/L1 cells. In both fibroblasts and adipocytes, insulin provoked increases in membrane PKC enzyme activity and membrane levels of PKC-alpha and PKC-beta. However, insulin-induced increases in PKC enzyme activity were apparent in both non-down-regulated adipocytes and adipocytes that were down-regulated by overnight treatment with 5 microM phorbol ester, which largely depletes PKC-alpha, PKC-beta, and PKC-epsilon, but not PKC-zeta. Moreover, insulin provoked increases in the enzyme activity of immunoprecipitable PKC-zeta. In transfection studies, stable overexpression of wild-type or constitutively active forms of PKC-alpha, PKC-beta1, and PKC-beta2 failed to influence basal or insulin-stimulated glucose transport (2-deoxyglucose uptake) in fibroblasts and adipocytes, despite inhibiting insulin effects on glycogen synthesis. In contrast, stable overexpression of wild-type PKC-zeta increased, and a dominant-negative mutant form of PKC-zeta decreased, basal and insulin-stimulated glucose transport in fibroblasts and adipocytes. These findings suggested that: (a) insulin activates PKC-zeta, as well as PKC-alpha and beta; and (b) PKC-zeta is required for, and may contribute to, insulin effects on glucose transport in 3T3/L1 cells.

3T3 Cells↗

PubMed1997

Nonfasting plasma glucose is a better marker of diabetic control than fasting plasma glucose in type 2 diabetes.

OBJECTIVE: To evaluate the relative value of plasma glucose (PG) at different time points in assessing glucose control of type 2 diabetic patients. RESEARCH DESIGN AND METHODS: Glycemic profiles, i.e., PG at prebreakfast (8:00 A.M.), prelunch (11:00 A.M.), postlunch (2:00 P.M.), and extended postlunch (5:00 P.M.) times over the same day, were obtained in 66 type 2 diabetic patients on an ambulatory basis. The different time points of PG were compared with a measurement of HbA1c made in a reference laboratory. RESULTS: Extended postlunch PG was lower than prebreakfast PG (104 +/- 21 vs. 133 +/- 35 mg/dl, P < 0.02) in patients demonstrating good diabetic control (HbA1c < or = 7.0%), was not different from prebreakfast PG (149 +/- 47 vs. 166 +/- 26 mg/dl, NS) in patients demonstrating fair diabetic control (7.0% < HbA1c < or = 8.5%), and was higher than prebreakfast PG (221 +/- 62 vs. 199 +/- 49 mg/dl, P < or = 0.01) in those demonstrating poor diabetic control (HbA1c < or = 8.5%). Prebreakfast, prelunch, postlunch, and extended postlunch PG values were all significantly correlated with HbA1c. Multiple linear regression analysis demonstrated that postlunch PG and extended postlunch PG correlated significantly and independently with HbA1c, but that prebreakfast PG and prelunch PG did not. Moreover, postlunch PG and extended postlunch PG demonstrated better sensitivity, specificity, and positive predictive value in predicting poor glycemic control than did prebreakfast PG or prelunch PG. CONCLUSIONS: In type 2 diabetes, postlunch PG and extended postlunch PG are better predictors of glycemic control than fasting plasma glucose (FPG). We therefore suggest that they be more widely used to supplement, or substitute for, FPG in evaluating the metabolic control of type 2 diabetic patients.

Adult↗

PubMed1997

[Determinants of the left ventricular mass in obese patients. Influence of lean body mass].

Systolic blood pressure and body mass index (BMI) are the main determinants of the left ventricular mass (LVM). The mechanism of this cardiac hypertrophy in the obese individual is multifactorial and involves hemodynamic as well as metabolic factors. The association of LVM with the morphologic features of the individual are well known. The aim of this study was to assess the influence of the morphologic and metabolic features of obese women on LVM. 2D echocardiography evaluation of LVM was done in 24 normotensive, normoglycemic obese women (BMI [27.5-52.2 Kg/m2). Lean and fat body mass were determined by bio-impedancemetry, insulin sensitivity (Si) by the minimal model (Bergman), and basal metabolism by using indirect calorimetry. There was a positive correlation between LVM and BMI (r = 0.61; p = 0.001), waist to hip ratio (r = 0.45; p = 0.03), basal metabolism (r = 0.61, p = 0.001), lean (r = 0.74, p = 0.0002) and fat (r = 0.49; p = 0.01) body mass. Fasting glycemia was positively correlated with LVM (r = 0.62; p = 0.001), but not Si. LVM was also positively correlated to the triglyceride level. No relations were found with systolic or diastolic blood pressure. Multivariate regression analysis was performed to determine the relative contribution of lean body mass (the morphologic variable with the best association to LVM in univariate analysis), blood glucose, waist to hip ratio, age and triglycerides. The multiple r for the model was 0.87 (p < 0.001). Lean body mass and blood glucose were found to be the only significant and independent predictors of LVM (p = 0.001 and p = 0.03 respectively). We conclude that: 1) lean body mass is an important determinant of LVM in obese normotensive individuals. Hence, in obese women, correcting LVM for lean body mass might be more accurate than correcting it for body surface area or height. 2) There is no relationship between LVM and insulin sensitivity. The link between blood glucose and LVM needs to be studied further.

Adult↗

PubMed1996

The phosphatidylinositol 3-kinase inhibitor, wortmannin, inhibits insulin-induced activation of phosphatidylcholine hydrolysis and associated protein kinase C translocation in rat adipocytes.

We questioned whether phosphatidylinositol 3-kinase (PI 3-kinase) and protein kinase C (PKC) function as interrelated signalling mechanisms during insulin action in rat adipocytes. Insulin rapidly activated a phospholipase D that hydrolyses phosphatidylcholine (PC), and this activation was accompanied by increases in diacylglycerol and translocative activation of PKC-alpha and PKC-beta in the plasma membrane. Wortmannin, an apparently specific PI 3-kinase inhibitor, inhibited insulin-stimulated, phospholipase D-dependent PC hydrolysis and subsequent translocation of PKC-alpha and PKC-beta to the plasma membrane. Wortmannin did not inhibit PKC directly in vitro, or the PKC-dependent effects of phorbol esters on glucose transport in intact adipocytes. The PKC inhibitor RO 31-8220 did not inhibit PI 3-kinase directly or its activation in situ by insulin, but inhibited both insulin-stimulated and phorbol ester-stimulated glucose transport. Our findings suggest that insulin acts through PI 3-kinase to activate a PC-specific phospholipase D and causes the translocative activation of PKC-alpha and PKC-beta in plasma membranes of rat adipocytes.

Adipose Tissue↗

PubMed1996

Insulin translocates PKC-epsilon and phorbol esters induce and persistently translocate PKC-beta 2 in BC3H-1 myocytes.

Initial studies suggested that insulin increases diacylglycerol and activates protein kinase C (PKC) in BC3H-1 myocytes. In these earlier studies, insulin was found to translocate PKC-beta, but the presence of PKC-epsilon was not appreciated. More recently, the presence of PKC-epsilon was documented, but PKC-beta was not detected, and it was questioned whether insulin activates PKC in BC3H-1 myocytes [Stumpo, D.J., Haupt, D.M. and Blackshear, P.J. (1994) J. Biol. Chem. 269:21184-21190]. We questioned whether insulin translocates PKC-epsilon in BC3H-1 myocytes, and re-evaluated the question of whether myocytes truly contain a PKC-beta isoform whose existence can be verified by its response to phorbol ester treatment. We found that PKC-epsilon was acutely translocated by insulin and phorbol esters from the cytosol to the membrane fraction in BC3H-1 myocytes; in addition, PKC-epsilon, like PKC-alpha, was depleted by chronic phorbol ester treatment. We also found that BC3H-1 myocytes containing a 76,000 Mr PKC-beta isoform that is acutely translocated and subsequently depleted by phorbol esters. Moreover, chronic phorbol ester treatment induced an 84,000 Mr PKC-beta 2 isoform that appeared to be persistently translocated and activated, as suggested by studies of myristoylated arginic-rich C kinase substrate (MARCKS) phosphorylation. We conclude that: (1) insulin acutely translocates PKC-epsilon, as well as PKC-beta, in BC3H-1 myocytes; and (2) PKC-beta is not truly downregulated by phorbol esters in BC3H-1 myocytes.

Amino Acid Sequence↗

PubMed1996

Chronic activation of protein kinase C in soleus muscles and other tissues of insulin-resistant type II diabetic Goto-Kakizaki (GK), obese/aged, and obese/Zucker rats. A mechanism for inhibiting glycogen synthesis.

We examined the possibility that protein kinase C (PKC) is chronically activated and may contribute to impaired glycogen synthesis and insulin resistance in soleus muscles of hyperinsulinemic type II diabetic Goto-Kakizaki (GK) rats. Relative to nondiabetic controls, PKC enzyme activity and levels of immunoreactive PKC-alpha, beta, epsilon, and delta were increased in membrane fractions and decreased cytosolic fractions of GK soleus muscles. In addition, PKC-theta levels were decreased in both membrane and cytosol fractios, whereas PKC-zeta levels were not changed in either fraction in GK soleus muscles. These increases in membrane PKC (alpha, beta, epsilon, and delta) could not be accounted for by alterations in PKC mRNA or total PKC levels but were associated with increases in membrane diacylglycerol (DAG) and therefore appeared to reflect translocative activation of PKC. In evaluation of potential causes for persistent PKC activation, membrane PKC levels were decreased in soleus muscles of hyperglycemic streptozotocin (STZ)-induced diabetic rats; thus, a role for simple hyperglycemia as a cause of PKC activation in GK rats was not evident in the STZ model. In support of the possibility that hyperinsulinemia contributed to PKC activation in GK soleus muscles, we found that DAG levels were increased, and PKC was translocated, in soleus muscles of both (1) normoglycemic hyperinsulinemic obese/aged rats and (2) mildly hyperglycemic hyperinsulinemic obese/Zucker rats. In keeping with the possibility that PKC activation may contribute to impaired glycogen synthase activation in GK muscles, phorbol esters inhibited, and a PKC inhibitor, RO 31-8220, increased insulin effects on glycogen synthesis in soleus muscles incubated in vitro. Our findings suggested that: (1) hyperinsulinemia, as observed in type II diabetic GK rats and certain genetic and nongenetic forms of obesity in rats, is associated with persistent translocation and activation of PKC in soleus muscles, and (2) this persistent PKC activation may contribute to impaired glycogen synthesis and insulin resistance.

Adipocytes↗

PubMed1995

Effects of insulin on the translocation of protein kinase C-theta and other protein kinase C isoforms in rat skeletal muscles.

Protein kinase C (PKC)-theta is a newly recognized major PKC isoform in skeletal muscle. In this study we found that insulin provoked rapid biphasic increases in membrane-associated immunoreactive PKC-theta, as well as PKC-alpha, PKC-beta and PKC-epsilon, in rat soleus muscles incubated in vitro. Effects of insulin on PKC isoforms in the soleus were comparable in magnitude with those of phorbol esters. Increases in membrane-associated PKC-theta, PKC-alpha, PKC-beta and PKC-epsilon were also observed in rat gastrocnemius muscles after insulin treatment in vivo. Our findings suggest that PKC-theta, like other diacylglycerol-sensitive PKC isoforms (alpha, beta and epsilon), may play a role in insulin action in skeletal muscles.

Animals↗

PubMed1995

Insulin increases mRNA levels of protein kinase C-alpha and -beta in rat adipocytes and protein kinase C-alpha, -beta and -theta in rat skeletal muscle.

Effects of insulin of levels of mRNA encoding protein kinase C (PKC)-alpha, PKC-beta, PKC-epsilon and PKC-theta were examined by ribonuclease protection assay in primary cultures of rat adipocytes in vitro, and in rat adipose tissue and gastrocnemius muscle in vivo. In all cases, insulin increased the levels of PKC-alpha mRNA and PKC-beta mRNA, and, in muscle, insulin also increased the level of PKC-theta mRNA. PKC-epsilon mRNA levels, on the other hand, were not altered significantly. Insulin also stimulated the apparent translocation of PKC-alpha, -beta, -epsilon and -theta, to the membrane fractions of adipocytes, adipose tissue and gastrocnemius muscles, and, in some instances, total PKC levels were diminished, e.g. PKC-alpha and PKC-beta in cultured adipocytes in vitro and/or whole adipose tissue in vivo, and PKC-alpha and PKC-theta in the gastrocnemius muscle. Thus, insulin-induced increases in PKC mRNA may have been partly compensatory in nature to restore PKC levels following translocation and proteolytic losses. However, much more severe depletion of PKC-alpha and PKC-beta by phorbol ester treatment in cultured rat adipocytes in vitro resulted in, if anything, smaller increases in PKC-alpha mRNA and PKC-beta mRNA, and it therefore appears that insulin effects on PKC mRNA levels were not simply due to decreases in respective PKC levels. In addition, effects of insulin, particularly on PKC-beta mRNA, could not be attributed to increased glucose metabolism, which alone decreased PKC-beta mRNA in cultured adipocytes in vitro. We conclude that insulin-induced translocation and degradation of PKC-alpha, PKC-beta and PKC-theta are attended by selective increases in their mRNAs. This mechanism of increasing mRNA may be important in maintaining PKC levels during the continued action of insulin.

Adipocytes↗

PubMed1994

Effects of insulin on protein kinase-C (PKC) in HIRC-B cells: specific activation of PKC epsilon and its resistance to phorbol ester-induced down-regulation.

We evaluated the role of protein kinase-C (PKC) during insulin action in HIRC-B cells. Insulin provoked rapid increases in 1) diacylglycerol; 2) translocation of PKC epsilon, but not PKC alpha, PKC delta, or PKC zeta, from the cytosol to the membrane fraction; 3) membrane PKC enzyme activity; and 4) phosphorylation of immunoprecipitable 80-kilodalton (kDa) myristylated alanine-rich C-kinase substrate (MARCKS) protein and heat-stable 80-kDa protein (also probably MARCKS). Phorbol esters stimulated the translocation of PKC alpha and PKC delta as well as PKC epsilon, but not PKC zeta. The effects of phorbol esters on 80-kDa MARCKS phosphorylation were approximately 4 times as strong as those of insulin. Treatment of HIRC-B cells with phorbol esters for 20-24 h resulted in complete loss of immunoreactive PKC alpha and PKC delta in cytosol and membrane fractions, but substantial amounts of PKC epsilon were persistently translocated to the membrane fraction of down-regulated cells. This persistently translocated, residual PKC epsilon in down-regulated cells was associated with increased basal hexose uptake, but this was not due to PKC activation, as it was not inhibited by the PKC inhibitor, RO 31-8220. Acute insulin treatment, on the other hand, increased hexose uptake in down-regulated cells, and this insulin-stimulated uptake was inhibited by RO 31-8220 in down-regulated cells as well as in nondown-regulated cells. Insulin also stimulated the phosphorylation of the heat-stable 80-kDa protein in down-regulated cells, suggesting that the residual PKC epsilon in these cells can be activated by insulin.

Animals↗

PubMed1990

[Left ventricular mass and glomerular hyperfiltration in essential hypertension].

OBJECTIVE: to assess the early involvement to target organs in never treated essential hypertensives (HT). METHODS: effective renal plasma flow (ERPF, 131I-Hippurate) and glomerular filtration rate (GFR, 99mTc-DTPA) were estimated in 80 mild HT. Left ventricular mass (LVM, M-mode echocardiography), sodium intake (24h UNaV) and urinary kallikrein (Kall) were also measured. Hyperfiltering patients (HF, GFR = 155 +/- 3 ml/min: 1.73 m2, n = 21) were defined by comparison with age-matched normotensive. HF patients were pair-matched for age, sex and blood pressure level with normofiltering hypertensives (NF, GFR = 112 +/- 3, n = 21). RESULTS: are expressed as mean +/- sem [table: see text] CONCLUSION: These results suggest that a high Na intake is associated with hyperfiltration and higher LVMI in subjects with never treated essential hypertension of short duration.

Adult↗

PubMedDate not supplied

[Hyperparathyroidism diagnosed during pregnancy].

BACKGROUND: Diagnosis of hyperparathyroidism during pregnancy is rare because symptoms are often moderate and similar to signs observed during normal pregnancy. The gravity of such an association is probably underscored. CASE REPORT: The diagnosis of hyperparathyroidism was made at 9 weeks gestation in a young woman who declined surgery. She was seen again at 32 weeks gestation for in utero fetal death. Nine months later she accepted surgery and a parathyroid adenoma was removed. DISCUSSION: Hyperparathyroidism during pregnancy is associated with significant morbidity with major maternal or fetal complications in 50% of the cases. Surgery during the second trimester of pregnancy is the treatment of choice. If hyperparathyroidism is diagnosed in young women who desire pregnancy, surgery should be performed before advising pregnancy.

Adenoma↗