Decreased adiponectin links elevated adipose tissue autophagy with adipocyte endocrine dysfunction in obesity.

BACKGROUND/OBJECTIVES: Adipose tissue (AT) autophagy gene expression is elevated in human obesity, correlating with increased metabolic risk, but mechanistic links between the two remain unclear. Thus, the objective of this study was to assess whether elevated autophagy may cause AT endocrine dysfunction, emphasizing the putative role of adiponectin in fat-liver endocrine communication. SUBJECTS/METHODS: We utilized a large (N=186) human AT biobank to assess clinical associations between human visceral AT autophagy genes, adiponectin and leptin, by multivariate models. A broader view of adipocytokines association with elevated autophagy was assessed using adipocytokine array. Finally, to establish causality, ex vivo studies utilizing a murine AT-hepatocyte cell line co-culture system was used. RESULTS: Circulating high-molecular-weight adiponectin and leptin levels were associated with human omental-AT expression of ATG5 mRNA, associations that remained significant (ß=-0.197, P=0.011; ß=0.267, P<0.001, respectively) in a multivariate model adjusted for age, sex, body mass index and interleukin-6 (IL-6). A similar association was observed with omental-AT LC3A mRNA levels. Bafilomycin-A1 (Baf A) pretreatment of AT explants from high-fat-fed (HFF) mice had no effect on the secretion of some AT-derived endocrine factors, but partially or fully reversed obesity-related changes in secretion of a subset of adipocytokines by >30%, including the obesity-associated upregulation of IL-6, vascular endothelial growth factor, tumor necrosis factor alpha (TNFα) and certain insulin-like growth factor-binding proteins, and the HFF-induced downregulated secretion of IL-10 and adiponectin. Similarly, decreased adiponectin and increased leptin secretion from cultured adipocytes stimulated with TNFα+IL-1ß was partially reversed by small interfering RNA-mediated knockdown of ATG7. AT explants from HFF mice co-cultured with Hepa1c hepatoma cells impaired insulin-induced Akt and GSK3 phosphorylation. This effect was significantly reversed by pretreating explants with Baf A, but not if adiponectin was immunodepleted from the conditioned media. CONCLUSIONS: Reduced secretion of adiponectin may link obesity-associated elevated AT autophagy/lysosomal activity with adipose endocrine dysfunction.

Cystine transport is defective in isolated leukocyte lysosomes from patients with cystinosis.

The activity of a cystine transport system in lysosomes prepared from the leukocytes of patients with cystinosis was found to be deficient. In normal subjects, this system was resistant to N-ethylmaleimide and demonstrated saturation kinetics. Lysosomes from individuals heterozygous for cystinosis demonstrated a reduced maximum velocity for cystine egress from lysosomes. The rate of cystine escape from normal lysosomes was enhanced by adenosine triphosphate. The availability of normal and mutant lysosomes provides a means of investigating mechanisms of amino acid transport across lysosomal membranes.

Impaired carbohydrate metabolism of polymorphonuclear leukocytes in glycogen storage disease Ib.

This study measures hexose monophosphate (HMP) shunt activity, glycolytic rate, and glucose transport in PMN and lymphocytes of patients with glycogen storage disease (GSD) type Ib as compared with controls and with GSD Ia patients. HMP shunt activity and glycolysis were significantly lower in intact PMN cells of GSD Ib patients as compared with GSD Ia patients and with controls. These activities were above normal levels in disrupted GSD Ib PMN. HMP shunt activity and glycolytic rates in lymphocytes were similar in all three groups studied. The rate of 2-deoxyglucose transport into GSD Ib PMN was 30% of that into cells of normal controls. In GSD Ib lymphocytes or in GSD Ia PMN and lymphocytes transport was normal. The striking limitation of glucose transport across the cell membrane of the PMN of GSD Ib patients may account for the impairment of leukocyte function that is characteristic of GSD Ib, but not found in GSD Ia patients.

Effect of hydrocortisone and glucagon on glycogen metabolism in the fetal rat liver.

1. Hydrocortisone increases in vivo incorporation of [14C] glucose into fetal liver glycogen in the last days of gestation, whereas in glucagon-treated fetuses, a slight decrease in the incorporation rate was found. 2. Hydrocortisone increases total synthetase activity as that of synthetase a but was without effect on fetal liver glycogen phosphorylase. 3. Glucagon causes a slight increase in phosphorylase a activity on days 19-21, and was without effect on the activities of synthetase a and total synthetase. 4. Dibutyryl cyclic AMP had no effect on the key enzymes of glycogen metabolism 1 h after injection in utero, whereas after 6 h an increase in phosphorylase a activity was found without any change in synthetase a activity.

Rat liver glycogen metabolism in the perinatal period.

The correlation between blood glucose levels, the concentration of glycogen, the activities of glycogen synthase and phosphorylase and their respective kinases and phosphatases was examined in liver of rat fetuses between day 18 of gestation and one day after birth. Between day 18 and 21 there is a rapid increase in the concentration of glycogen and in the activity of synthase a and a much slower increase in the activity of phosphorylase a. The activity of the respective kinases increased rapidly during this period and reached maximum on day 21. The activity of synthase phosphatase and phosphorylase phosphatase increased after day 18, to reach a maximum on day 19 and 20, respectively, but decreased again towards day 21. The possibility that the changes in glycogen concentration and enzyme activities were related to an effect of glucose or AMP on the respective phosphatases was considered. It was found that the Km of phosphorylase phosphatase for glucose in the prenatal period was 5--7 mM, as in the adult. Since the level of blood glucose during this period was constant (2.8 mM), an effect of glucose on phosphatase activity seems unlikely. AMP concentration increased between day 18 and 21 from 6--15 nmol/g. In view of the low level of phosphorylase a activity during this period, the increase in AMP concentration is not considered to be important in the regulation of glycogen breakdown at this time. Immediately after birth blood glucose levels dropped to 5 mg/dl. This was accompanied by a rapid decrease in glycogen concentration and in the activity of glycogen synthase and a rise in phosphorylase activity. Blood glucose levels returned to the initial level within 1 h after birth, whereas the changes in glycogen concentration and enzyme activities continued for at least 3 h after birth. On day 22 all parameters examined had reached the level found in adult rat liver. It is suggested that the rapid changes observed immediately after birth are due to an effect of gypoglycemia mediated by hormones and cannot be ascribed to direct effects of metabolites on the enzyme systems involved.

The effect of ions and ionophores on cystine egress from human leucocyte lysosome-rich granular fraction.

This paper describes the stimulation of exodus of cystine from lysosome-rich granular fractions by potassium. Potassium permeability into lysosomes is low, but in the presence of an ionophore or permeable anion, the movement of K+ into lysosomes caused a large stimulation of cystine exodus. Lysosomal preparations from leucocytes of cystinotic patients, which lack carrier-mediated cystine transport, also manifested stimulation of cystine egress by valinomycin and K+. This suggests that potassium-dependent cystine egress involves a carrier different from that defective in cystinosis, or occurs through a non-carrier-mediated mechanism.

Prolonged oxidative stress impairs insulin-induced GLUT4 translocation in 3T3-L1 adipocytes.

Prolonged exposure of 3T3-L1 adipocytes to micromolar concentrations of H2O2 results in an impaired response to the acute metabolic effects of insulin. In this study, we further characterized the mechanisms by which oxidative stress impairs insulin stimulation of glucose transport activity. Although insulin induced a 2.5-fold increase in plasma membrane GLUT4 content and a 50% reduction in its abundance in the low-density microsomal (LDM) fraction in control cells, oxidation completely prevented these responses. The net effect of insulin on 2-deoxyglucose uptake activity was reduced in oxidized cells and could be attributed to GLUT1 translocation. Insulin stimulation of insulin receptor substrate (IRS) 1 tyrosine phosphorylation and the association of IRS-1 with phosphatidylinositol (PI) 3-kinase were not impaired by oxidative stress. However, a 1.9-fold increase in the LDM content of the p85 subunit of PI 3-kinase after insulin stimulation was observed in control, but not in oxidized, cells. Moreover, although insulin induced an increase in IRS-1-associated PI 3-kinase activity in the LDM in control cells, this effect was prevented by oxidation. These findings suggest that prolonged low-grade oxidative stress impairs insulin-stimulated GLUT4 translocation, potentially by interfering with compartment-specific activation of PI 3-kinase.

The HIV protease inhibitor nelfinavir induces insulin resistance and increases basal lipolysis in 3T3-L1 adipocytes.

HIV protease inhibitors (HPIs) are potent antiretroviral agents clinically used in the management of HIV infection. Recently, HPI therapy has been linked to the development of a metabolic syndrome in which adipocyte insulin resistance appears to play a major role. In this study, we assessed the effect of nelfinavir on glucose uptake and lipolysis in differentiated 3T3-L1 adipocytes. An 18-h exposure to nelfinavir resulted in an impaired insulin-stimulated glucose uptake and activation of basal lipolysis. Impaired insulin stimulation of glucose up take occurred at nelfinavir concentrations >10 micromol/l (EC(50) = 20 micromol/l) and could be attributed to impaired GLUT4 translocation. Basal glycerol and free fatty acid (FFA) release were significantly enhanced with as low as 5 micromol/l nelfinavir, displaying fivefold stimulation of FFA release at 10 micromol/l. Yet, the antilipolytic action of insulin was preserved at this concentration. Potential underlying mechanisms for these metabolic effects included both impaired insulin stimulation of protein kinase B Ser 473 phosphorylation with preserved insulin receptor substrate tyrosine phosphorylation and decreased expression of the lipolysis regulator perilipin. Troglitazone pre- and cotreatment with nelfinavir partly protected the cells from the increase in basal lipolysis, but it had no effect on the impairment in insulin-stimulated glucose uptake induced by this HPI. This study demonstrates that nelfinavir induces insulin resistance and activates basal lipolysis in differentiated 3T3-L1 adipocytes, providing potential cellular mechanisms that may contribute to altered adipocyte metabolism in treated HIV patients.

Reactive oxygen species activate glucose transport in L6 myotubes.

Under oxidative stress, increased energy requirements are needed To induce repair mechanisms. As glucose is a major energy source in L6 myotubes, we evaluated glucose metabolism and transport, following exposure to glucose oxidase (H2O2 generating system), or xanthine oxidase (O2. and H2O2 generating system), added to the medium. Exposure for 24 h to 5 mM glucose and 50 mU/ml glucose oxidase, or to 50 microM xanthine and 20 mU/ml xanthine oxidase resulted in significant oxidant stress indicated by increased DNA binding activity of NF-kappa B. Under these conditions, approximately 2-fold increase in glucose consumption, lactate production and CO2 release were observed. 2-deoxyglucose uptake into myotubes increased time and dose dependently, reaching a 2.6 +/- 0.4-fold and 2.2 +/- 0.7-fold after 24 h exposure to glucose oxidase and xanthine oxidase, respectively. Peroxidase prevented this effect, indicating the role of H2O2 in mediating glucose uptake activation. The elevation in glucose uptake under oxidative stress was associated with increased expression of GLUT1 mRNA and protein. The observed 2-deoxyglucose uptake activation by oxidants was not limited to the L6 cell line and was observed in 3T3-L1 adipocytes as well.

Metabolic effects of gamma-linolenic acid-alpha-lipoic acid conjugate in streptozotocin diabetic rats.

Data suggesting the involvement of increased oxidative stress in the pathophysiology of diabetes has raised interest in the potential therapeutic benefit of antioxidants. Although beneficial metabolic effects of antioxidant supplementation have been suggested, an antioxidant mode of action, particularly in skeletal muscle, has not been documented. In the present study, we evaluate the metabolic effects of a gamma-linolenic acid-alpha-lipoic acid conjugate (GLA-LA) in streptozotocin-induced diabetic rats, and assess its potential mode of action by comparing its effects with equimolar administration of LA and GLA alone. Ten days of oral supplementation of 20 mg/kg body weight GLA-LA, but not LA or GLA alone, caused a mild reduction in fasting blood glucose concentration as compared with vehicle-treated diabetic rats (375 +/- 11 vs. 416 +/- 16 mg/dl, p = 0.03), with no change in fasting plasma insulin levels. A peripheral insulin-sensitizing effect could be observed with GLA-LA, LA, and GLA treatments, as demonstrated by a significant (p < 0.04) 23%, 13%, and 10% reduction, respectively, in the area under the glucose curve following an intravenous insulin tolerance test. This effect was associated with a 67% and 50% increase in GLUT4 protein content in the membranes of gastrocnemius muscle of GLA-LA and LA-treated animals, respectively; however, no change was observed with GLA treatment alone. Interestingly, both GLA-LA and LA treatments corrected a diabetes-related decrease in the gastrocnemius muscle low-molecular-weight reduced thiols content. These data demonstrate insulin-sensitizing properties of the GLA-LA conjugate by distinct mechanisms attributable to each of its components, which are associated with antioxidant effects.

Adult muscle phosphorylase "b" kinase deficiency.

A 35-year-old man had severe exercise intolerance and cramps. Venous blood lactate did not rise after ischemic exercise, and electromyographically silent contracture of hand muscles appeared. Histochemistry and electronmicroscopy of a muscle biopsy revealed subsarcolemmal and intermyofibrillar accumulation of glycogen. Biochemical studies showed moderately increased amount of glycogen. Total phosphorylase activity was normal, but the active form "a" was 27% of normal. Phosphorylase kinase activity was 12% of the normal value and was normal in leukocytes and erythrocytes.

A lectin-like receptor on murine macrophage is involved in the recognition and phagocytosis of human red cells oxidized by phenylhydrazine.

Phenylhydrazine (Phz) is a powerful hemolytic agent which has several effects on both normal and G6PD deficient red blood cells (RBCs). We have studied the mechanism of removal of Phz-damaged human RBCs by murine macrophages. Phagocytosis of Phz-treated RBCs was found to be 50 RBCs/100 mac as compared to 2 RBCs/100 mac of the controls. EGTA and sodium azide inhibited the phagocytosis, indicating a requirement for both calcium ions and energy. Incubation of macrophages with sugars such as D-galactose or D-mannose reduced phagocytosis of Phz-treated RBCs by up to 60%, indicating the involvement of a macrophage lectin-like receptor in the recognition of Phz-treated RBCs. The presence of serum in the phagocytosis assay did not affect either phagocytosis of Phz-treated RBCs or inhibition by sugars. beta-Galactosidase, but not neuraminidase, treatment of RBCs caused a significant inhibition in phagocytosis of Phz-treated RBCs. These results suggest that galactosyl residues are exposed on RBC membrane during oxidation, probably not as a result of desialization. We conclude that Phz-treated RBCs are detected as damaged cells mainly due to sugar changes on their membrane, which are directly recognized by lectin-like receptors on the macrophages.

Enzymatic activity of glycogen metabolism in chorionic villi.

Glycogen content and six major enzymatic activities involved in glycogen metabolism were analysed in chorionic villi (CV). Glycogen levels were found to be lower than those known to exist in liver and muscle. Activities of alpha-glucosidase, amylo-1,6-glucosidase, phosphorylase b and phosphorylase kinase were detectable by standard methods. The enzymatic activities of glucose-6-phosphatase and phosphorylase a were undetectable. These findings suggest that CV biopsies can be useful for first-trimester diagnosis of glycogen storage disease types II, III and VI, but not for type I (glucose-6-phosphatase deficiency).

Duplication of distal 22q.

We report on three patients with duplication of distal 22q. One patient is a de novo carrier of the translocation t(21;22) (p13;q11), the other two are offspring of a translocation carrier t(10;22) (q26;q12). The clinical manifestations of these patients demonstrate the variability of the dup(22q) syndrome.

Glycogen storage disease type 1a in Israel: biochemical, clinical, and mutational studies.

Glycogen storage disease type 1a (von Gierke disease, GSD 1a) is caused by the deficiency of microsomal glucose-6-phosphatase (G6Pase) activity which catalyzes the final common step of glycogenolysis and gluconeogenesis. The recent cloning of the G6Pase cDNA and characterization of the human G6Pase gene enabled the characterization of the mutations causing GSD 1a. This, in turn, allows the introduction of a noninvasive DNA-based diagnosis that provides reliable carrier testing and prenatal diagnosis. In this study, we report the biochemical and clinical characteristics as well as mutational analyses of 12 Israeli GSD 1a patients of different families, who represent most GSD 1a patients in Israel. The mutations, G6Pase activity, and glycogen content of 7 of these patients were reported previously. The biochemical data and clinical findings of all patients were similar and compatible with those described in other reports. All 9 Jewish patients, as well as one Muslim Arab patient, presented the R83C mutation. Two Muslim Arab patients had the V166G mutation which was not found in other patients' populations. The V166G mutation, which was introduced into the G6Pase cDNA by site-directed mutagenesis following transient expression in COS-1 cells, was shown to cause complete inactivation of the G6Pase. The characterization of all GSD 1a mutations in the Israeli population lends itself to carrier testing in these families as well as to prenatal diagnosis, which was carried out in 2 families. Since all Ashkenzai Jewish patients harbor the same mutation, our study suggests that DNA-based diagnosis may be used as an initial diagnostic step in Ashkenazi Jews suspected of having GSD 1a, thereby avoiding liver biopsy.

Lipoic acid reduces glycemia and increases muscle GLUT4 content in streptozotocin-diabetic rats.

Alpha lipoic acid (lipoate [LA]), a cofactor of alpha-ketodehydrogenase, exhibits unique antioxidant properties. Recent studies suggest a direct effect of LA on glucose metabolism in both human and experimental diabetes. This study examines the possibility that LA positively affects glucose homeostasis in streptozotocin (STZ)-induced diabetic rats by altering skeletal muscle glucose utilization. Blood glucose concentration in STZ-diabetic rats following 10 days of intraperitoneal (i.p.) injection of LA 30 mg/kg was reduced compared with that in vehicle-treated diabetic rats (495 +/- 131 v 641 +/- 125 mg/dL in fed state, P = .003, and 189 +/- 48 v 341 +/- 36 mg/dL after 12-hour fast, P = .001). No effect of LA on plasma insulin was observed. Gastrocnemius muscle crude membrane GLUT4 protein was elevated both in control and in diabetic rats treated with LA by 1.5- and 2.8-fold, respectively, without significant changes in GLUT4 mRNA levels. Gastrocnemius lactic acid was increased in diabetic rats (19.9 +/- 5.5 v 10.4 +/- 2.8 mumol/g muscle, P < .05 v nondiabetic rats), and was normal in LA-treated diabetic rats (9.1 +/- 5.0 mumol/g muscle). Insulin-stimulated 2-deoxyglucose (2 DG) uptake into isolated soleus muscle was reduced in diabetic rats compared with the control group (474 +/- 15 v 568 +/- 52 pmol/mg muscle 30 min, respectively, P = .05). LA treatment prevented this reduction, resulting in insulin-stimulated glucose uptake comparable to that of nondiabetic animals. These results suggest that daily LA treatment may reduce blood glucose concentrations in STZ-diabetic rats by enhancing muscle GLUT4 protein content and by increasing muscle glucose utilization.

Lipoic acid acutely induces hypoglycemia in fasting nondiabetic and diabetic rats.

Lipoic acid (LA) is a unique antioxidant that increases peripheral glucose utilization in diabetic patients. This study was conducted to investigate whether the inhibition of glucose production could be an additional mechanism for the action of LA. Intravenous (i.v.) LA injection (100 or 60 mg/kg body weight) to fasting nondiabetic or streptozotocin (STZ)-induced diabetic rats caused a rapid reduction in blood glucose with no effect on circulating insulin levels. In vivo conversion of fructose to glucose was not inhibited by LA, whereas the gluconeogenesis flux from alanine was completely prevented. Reduced liver pyruvate carboxylase (PC) activity in vivo is suggested by the finding that LA induced a decrease in liver coenzyme A (CoA) content (44% and 28% reduction in nondiabetic and diabetic rats, respectively, compared with vehicle-treated animals) and liver acetyl CoA content (80% and 67% reduction in nondiabetic and diabetic rats, respectively). A reduction in plasma free carnitine (42% and 22% in nondiabetic and diabetic rats, respectively) was observed in LA-treated animals, and acylcarnitine levels were increased twofold. This could be attributed to elevated levels of C16 and C18 acylcarnitine, without a detectable accumulation of lipoylcarnitine. Under such conditions, a significant increase in the plasma free fatty acid (FFA) concentration (204% in nondiabetic and 151% in diabetic animals) with no elevation in beta-hydroxybutyrate levels was noted. In conclusion, this study suggests that short-term administration of LA at high dosage to normal and diabetic rats causes an inhibition of gluconeogenesis secondary to an interference with hepatic fatty acid oxidation. This may render LA an antihyperglycemic agent for the treatment of diabetic subjects, who display glucose overproduction as a major metabolic abnormality.

Amino acid disturbances in type III glycogenosis: differences from type I glycogenosis.

The plasma glucose, insulin, glucagon, lactate and amino acid response patterns to glucose and protein meals were examined in 11 patients with type III glycogen storage disease (GSD-III). The amino acid metabolism in GSD-III was shown to differ from that observed in normal subjects and in type I glycogen storage disease (GSD-I) patients. The outstanding findings involved the principal gluconeogenic amino acid, alanine. Postabsorptive levels of alanine in GSD-III were significantly below those of normal controls. Following glucose ingestion, alanine rose markedly in GSD-III, which differed from normal subjects in whom no change occurred, and from GSD-I patients in whom a sharp fall was observed. Following beef ingestion, the direction of change of alanine was similar in the three groups, but the circulating levels in GSD-III were significantly less than those observed in GSD-I and normal controls. The possibility that gluconeogenesis is enhanced in GSD-III was supported by the prompt rise in blood glucose observed following beef ingestion, which differed from GSD-I and normal subjects, in which no rise in glucose was observed.

Increased PLA2 activity is not related to increase GLUT1 expression in L6 myotubes under hypoxic conditions.

Incubation of L6 myotubes for 24 h under hypoxic conditions leads to a 5.8 +/- 1.2 fold increase in 2-deoxyglucose uptake. In those conditions phospholipase A2 is activated, leading to a 2.4 +/- 0.8 fold increased release of arachidonic acid (AA) to the medium, and to 95% increased synthesis of PGF2 alpha but not of PGE2 as compared to cells incubated in normoxic conditions. Under hypoxia, the PLA2 inhibitor bromophenacyl bromide (BPB) inhibited AA release and PGF2 alpha synthesis, yet it did not affect the increase in glucose uptake into L6 myotubes. The amount of GLUT1 immunoreactive proteins in total membranes of hypoxia treated cells was evaluated 5.1 +/- 1.2 fold compared to control cells. Neither 10 microM BPB nor 100 mM aspirin (ASA) prevented this increase in GLUT1 expression. Preincubation of myotubes for either 1 or 23 h with 50 microM exogenous AA, prevented insulin induced 2-deoxyglucose uptake stimulation, suggesting that although AA or one of its metabolites did not regulate the synthesis or stability of GLUT1, it may interfere with the signal transduction of insulin in muscle cells.

An interdisciplinary course in the basic sciences for senior medical and PhD students.

Integrating clinical and basic sciences throughout the medical school curriculum has become a major objective of various innovations in medical education. While early clinical exposure has evolved as an efficient means of introducing clinical studies in the preclinical years, interdisciplinary integration of basic sciences during the clinical years remains a challenge. The authors describe their three years of experience with an interdisciplinary course designed to demonstrate the continuum of medical information from the clinic to the basic sciences. In this course, sixth-year medical students are required to choose one of three to four different one-week programs, each of which requires them to conduct an in-depth investigation of a defined clinical topic. Program coordinators are encouraged to work in clinician-basic scientist teams and to use a variety of teaching methods, with an emphasis on tutored individual and group learning based on critical readings of original papers. Coordinators are also encouraged to enable graduate research students to participate. From 1998 to 2000, students participated in nine programs, seven of which were coordinated by interdisciplinary teams. Several clinical and basic science disciplines were represented in each program, and various teaching methods were used. Graduate students participated in two of the programs. Evaluation of the programs (a debriefing discussion as well as short written evaluations) indicated moderate to good achievement of the course objectives.