Bioactive components in human milk are differentially associated with rates of lean and fat mass deposition in infants of mothers with normal vs. elevated BMI

OBJECTIVE

To model breastfed infant growth and body composition patterns over the first 4 months with multiple bioactive components of human milk (HM) and clinical factors (including maternal BMI status), which are related to growth.

METHODS

Longitudinal observation of infant growth and body composition from 0 to 4 months among 41 predominantly breastfed infants (25 mothers of Normal-weight and 16 mothers with overweight/obesity). Fasted morning HM samples were collected at 5 time-points. Macronutrients, leptin, adiponectin, ghrelin, insulin, cytokines and n-6:n-3 esterified fatty acid ratio were measured. Infant weight-for-length Z-score (WLZ) trajectory, fat-free mass (FFM) gain, fat mass gain and %fat gain were modelled controlling for clinical covariates.

RESULTS

HM insulin negatively associated with WLZ trajectory among infants of NW mothers (P = 0.028), but not associated with WLZ trajectory among infants of OW/Ob mothers. HM glucose (P < 0.001) was associated with slower rates of infant FFM gain. Infants of mothers with OW/Ob exhibited slower rates of FFM gain. HM protein, adiponectin and insulin concentrations, and n-6:n-3 ratio were all significant predictors in the model of infant fat mass gain (P < 0.03). Any amount of formula supplementation was associated with faster fat gain (P = 0.002). The model of %fat gain was similar to that of fat mass gain, excepting HM adiponectin was not a significant covariate, and a trend for maternal OW/Ob to correlate with faster %fat gain (P = 0.056).

CONCLUSIONS

Bioactive components in HM may contribute to regulation of partitioning of body composition, and these contributions may differ between mothers of normal-weight vs. with OW/Ob.

Human milk insulin is related to maternal plasma insulin and BMI: but other components of human milk do not differ by BMI

Background

The impact of maternal BMI and insulin sensitivity on bioactive components of human milk (HM) is not well understood. As the prevalence of obesity and diabetes rises, it is increasingly critical that we understand how maternal BMI and hormones associated with metabolic disease relate to concentrations of bioactive components in HM.

Methods

This longitudinal cohort design followed 48 breastfeeding mothers through the first four months of lactation, collecting fasting morning HM samples at 2-weeks and 1, 2, 3, and 4-months, and fasting maternal blood at 2-weeks and 4-months. Insulin, glucose, adipokines leptin and adiponectin, appetite regulating hormone ghrelin, marker of oxidative stress 8OHdG, and inflammatory cytokines (IL-6, IL-8, and TNF-a) were measured in HM and maternal plasma.

Results

26 normal weight (NW) (BMI=21.4±2.0 kg/m²), and 22 overweight/obese (OW/Ob) (BMI=30.4±4.2 kg/m²) were followed. Of all HM analytes measured, only insulin and leptin were different between groups - consistently higher in the OW/Ob group (leptin: p<0.001; insulin: p<0.03). HM insulin was 98% higher than maternal plasma insulin at 2-weeks and 32% higher at 4-months (p<0.001). Maternal fasting plasma insulin and HOMA-IR were positively related to HM insulin at 2-weeks (p<0.001, R²≥0.38, n=31), and 4-months (p≤0.005, R²≥0.20, n=38).

Conclusions

The concentrations of insulin in HM are higher than in maternal plasma and are related to maternal BMI and insulin sensitivity. With the exception of leptin, there were minimal other differences observed in HM composition across a wide range in maternal BMI.

Maternal diet quality in pregnancy and neonatal adiposity: the Healthy Start Study

BACKGROUND/OBJECTIVES

Poor maternal diet in pregnancy can influence fetal growth and development. We tested the hypothesis that poor maternal diet quality during pregnancy would increase neonatal adiposity (percent fat mass (%FM)) at birth by increasing the fat mass (FM) component of neonatal body composition.

METHODS

Our analysis was conducted using a prebirth observational cohort of 1079 mother-offspring pairs. Pregnancy diet was assessed via repeated Automated Self-Administered 24-h dietary recalls, from which Healthy Eating Index-2010 (HEI-2010) scores were calculated for each mother. HEI-2010 was dichotomized into scores of ⩽57 and >57, with low scores representing poorer diet quality. Neonatal %FM was assessed within 72 h after birth with air displacement plethysmography. Using univariate and multivariate linear models, we analyzed the relationship between maternal diet quality and neonatal %FM, FM, and fat-free mass (FFM) while adjusting for prepregnancy body mass index (BMI), physical activity, maternal age, smoking, energy intake, preeclampsia, hypertension, infant sex and gestational age.

RESULTS

Total HEI-2010 score ranged between 18.2 and 89.5 (mean: 54.2, s.d.: 13.6). An HEI-2010 score of ⩽57 was significantly associated with higher neonatal %FM (β=0.58, 95% confidence interval (CI) 0.07-1.1, P<0.05) and FM (β=20.74; 95% CI 1.49-40.0; P<0.05) but no difference in FFM.

CONCLUSIONS

Poor diet quality during pregnancy increases neonatal adiposity independent of maternal prepregnancy BMI and total caloric intake. This further implicates maternal diet as a potentially important exposure for fetal adiposity.

Associations of maternal weight status prior and during pregnancy with neonatal cardiometabolic markers at birth: the Healthy Start study

Background

Maternal obesity increases adult offspring risk for cardiovascular disease; however the role of offspring adiposity in mediating this association remains poorly characterized.

Objective

To investigate the associations of maternal pre-pregnant body mass index (maternal BMI) and gestational weight gain (GWG) with neonatal cardio-metabolic markers independent of fetal growth and neonatal adiposity.

Methods

A total of 753 maternal-infant pairs from the Healthy Start study, a large multi-ethnic pre-birth observational cohort were used. Neonatal cardio-metabolic markers included cord blood glucose, insulin, glucose-to-insulin ratio (Glu/Ins), total and high-density lipoprotein cholesterol (HDL-c), triglycerides, free fatty acids and leptin. Maternal BMI was abstracted from medical records or self-reported. GWG was calculated as the difference between the first pre-pregnant weight and the last weight measurement before delivery. Neonatal adiposity (percent fat mass) was measured within 72 hours of delivery using whole body air displacement plethysmography.

Results

In covariate adjusted models, maternal BMI was positively associated with cord blood insulin (p=0.01) and leptin (p<0.001) levels and inversely associated with cord blood HDL-c (p=0.05) and Glu/Ins (p=0.003). Adjustment for fetal growth or neonatal adiposity attenuated the effect of maternal BMI on neonatal insulin, rendering the association non-significant. However, maternal BMI remained associated with higher leptin (p<0.0011), lower HDL-c (p=0.02) and Glu/Ins (p=0.05), independent of neonatal adiposity. GWG was positively associated with neonatal insulin (p=0.02), glucose (p=0.03) and leptin levels (p<0.001) and negatively associated with Glu/Ins (p=0.006). After adjusting for neonatal adiposity, GWG remained associated with higher neonatal glucose (p=0.02) and leptin levels (p=0.02) and lower Glu/Ins (p=0.048).

Conclusions

Maternal weight prior and/or during pregnancy is associated with neonatal cardio-metabolic makers including leptin, glucose, and HDL-c at delivery, independent of neonatal adiposity. Our results suggest that intrauterine exposure to maternal obesity influences metabolic processes beyond fetal growth and fat accretion.

Maternal obesity alters feto-placental cytochrome P4501A1 activity

Cytochrome P4501A1 (CYP1A1), an important drug metabolizing enzyme, is expressed in human placenta throughout gestation as well as in fetal liver. Obesity, a chronic inflammatory condition, is known to alter CYP enzyme expression in non-placental tissues. In the present study, we test the hypothesis that maternal obesity alters the distribution of CYP1A1 activity in feto-placental unit. Placentas were collected from non-obese (BMI < 30) and obese (BMI > 30) women at term. Livers were collected from gestation day 130 fetuses of non-human primates fed either control diet or high-fat diet (HFD). Cytosol and microsomes were collected using differential centrifugation, and incubated with 7-ethoxyresorufin. The CYP1A1 specific activity (pmoles of resorufin formed/min/mg of protein) was measured at excitation/emission wavelength of 530/590 nm. Placentas of obese women had significantly reduced microsomal CYP1A1 activity compared to non-obese women (0.046 vs. 0.082; p < 0.05); however no such effect was observed on cytosolic activity. Similarly, fetal liver from HFD fed mothers had significantly reduced microsomal CYP1A1 activity (0.44 ± 0.04 vs. 0.20 ± 0.10; p < 0.05), with no significant difference in cytosolic CYP1A1 activity (control, 1.23 ± 0.20; HFD, 0.80 ± 0.40). Interestingly, multiple linear regression analyses of placental efficiency indicate cytosolic CYP1A1 activity is a main effect (5.67 ± 2.32 (β ± SEM); p = 0.022) along with BMI (-0.57 ± 0.26; p = 0.037), fetal gender (1.07 ± 0.26; p < 0.001), and maternal age (0.07 ± 0.03; p = 0.011). In summary, while maternal obesity affects microsomal CYP1A1 activity alone, cytosolic activity along with maternal BMI is an important determinant of placental efficiency. Together, these data suggest that maternal lifestyle could have a significant impact on CYP1A1 activity, and hints at a possible role for CYP1A1 in feto-placental growth and thereby well-being of fetus.

In vivo knockdown of p85alpha with an antisense oligonucleotide improves insulin sensitivity in Lep(ob/ob) and diet-induced obese mice

Phosphoinositide 3-kinase is a key signaling intermediate necessary for the metabolic actions of insulin. In this study, we assessed the effects of in vivo knockdown of the p85alpha subunit of phosphoinositide 3-kinase on insulin sensitivity, using an antisense oligonucleotide, in lean mice, diet-induced obese mice, and obese leptin-deficient Lep (ob/ob) mice. Mice were injected with either p85alpha-targeted antisense oligonucleotide or saline twice weekly for 4 weeks. Fasting levels of glycemia and insulinemia and insulin and glucose tolerance tests were used to determine insulin sensitivity. Western blot analysis and real-time polyacrylamide chain reaction were used to assess p85alpha protein and mRNA expression. IN VIVO administration of antisense oligonucleotide resulted in 50 and 60% knockdown of liver p85alpha protein and mRNA, respectively, in the lean, diet-induced obese and Lep (ob/ob) mice. This was associated with increased phosphoinositide 3-kinase activity and improved insulin sensitivity in diet-induced obese and Lep (ob/ob) mice. Thus, p85alpha could be an important therapeutic target to ameliorate insulin resistance.

A Novel Phospholipid Derivative of Indomethacin, DP-155 [Mixture of 1-Steroyl and 1-Palmitoyl-2-{6-[1-(p-chlorobenzoyl)-5-methoxy-2-methyl-3-indolyl acetamido]hexanoyl}-sn-glycero-3-phosophatidyl Choline], Shows Superior Safety and Similar Efficacy in Reducing Brain Amyloid β in an Alzheimer's Disease Model

Indomethacin has been suggested for the treatment of Alzheimer's disease (AD), but its use is limited by gastrointestinal and renal toxicity. To overcome this limitation, D-Pharm Ltd. (Rehovot, Israel) developed DP-155 (mixture of 1-steroyl and 1-palmitoyl-2-{6-[1-(p-chlorobenzoyl)-5-methoxy-2-methyl-3-indolyl acetamido] hexanoyl}-Sn-glycero-3-phosophatidyl [corrected] choline), a lecithin derivative of indomethacin. Safety was tested by daily oral administration of DP-155 or indomethacin to rats in a dose range of 0.007 to 0.28 mmol/kg. The prevalence of gastrointestinal ulceration was significantly lower (10-fold) for DP-155 than for indomethacin, and the ulcerations were delayed. Signs of renal toxicity, namely reduced urine output and increased urine N-acetyl glycosaminidase to creatinine ratio, were 5-fold lower for DP-155. Indomethacin, but not an equimolar dose of DP-155, reduced urine bicyclo-prostaglandin E(2). An equimolar oral dose of DP-155 or indomethacin, administered every 4 h for 3 days, was equally efficacious in reducing the levels of Abeta42 in the brains of Tg2576 mice. Indomethacin was the principal metabolite of DP-155 in the serum. After DP-155 oral administration, indomethacin's half-life in the serum and the brain was 22 and 93 h, respectively, compared with 10 and 24 h following indomethacin oral administration. The brain to serum ratio was 3.5 times higher for DP-155 than indomethacin. This finding explains the efficacy of DP-155 in reducing Abeta42 brain levels, despite the low systemic blood concentrations of indomethacin derived from DP-155. In conclusion, compared with indomethacin, DP-155 has significantly lower toxicity in the gut and kidney while maintaining similar efficacy to indomethacin in lowering Abeta42 in the brains of Tg2576 mice. This superior safety profile highlights DP-155's potential as an improved indomethacin-based therapy for AD.

A randomized clinical trial of valacyclovir in multiple sclerosis

OBJECTIVE

The human Herpesvirus type-6 (HHV-6) has been implicated in multiple sclerosis (MS). Valacyclovir is an antiviral agent with an excellent safety profile. A two-year placebo-controlled, double-blind study was conducted to (1) ascertain if high-dose, prolonged treatment with valacyclovir would be safe and (2) observe if valacyclovir would delay the progression of MS clinically or by magnetic resonance imaging (MRI).

DESIGN/METHODS

Fifty-eight patients were stratified as to severity and randomly assigned to receive valacyclovir (3000 mg/day) or placebo for a period of two years. Patients were followed clinically over the two-year period by means of the Expanded Disability Status Scale (EDSS), the Ambulation Index (AI) and brain MRI scans. Patients underwent routine lab studies every three months. Patients continued on the medication for two years unless they had a sustained progression or repeated exacerbations.

RESULTS

No patient discontinued the study due to side effects or toxicity. In Relative Ranking of Progression, time to first attack, attack rate, and time to withdrawal there were trends (but not statistically significant) toward drug effect over placebo in the Severe clinical category. MRI evaluation showed no significant drug effect.

CONCLUSIONS

Although not statistically significant, positive trends were detected for acyclovir by clinical measures, but not by MRI.

Fetoplacental transport and utilization of amino acids in IUGR — a review

Amino acids have multiple functions in fetoplacental development. The supply of amino acids to the fetus involves active transport across and metabolism within the trophoblast. Transport occurs through various amino acid transport systems located on both the maternal and fetal facing membranes, many of which have now been documented to be present in rat, sheep and human placentas. The capacity of the placenta to supply amino acids to the fetus develops during pregnancy through alterations in such factors as surface area and specific time-dependent transport system expression. In intrauterine growth restriction (IUGR), placental surface area and amino acid uptakes are decreased in human and experimental animal models. In an ovine model of IUGR, produced by hyperthermia-induced placental insufficiency (PI-IUGR), umbilical oxygen and essential amino acid uptake rates are significantly reduced in the most severe cases in concert with decreased fetal growth. These changes indicate that severe IUGR is likely associated with a shift in amino acid transport capacity and metabolic pathways within the fetoplacental unit. After transport across the trophoblast in normal conditions, amino acids are actively incorporated into tissue proteins or oxidized. In the sheep IUGR fetus, however, which is hypoxic, hypoglycemic and hypoinsulinemic, there appear to be net effluxes of amino acids from the liver and skeletal muscle, suggesting changes in amino acid metabolism. Potential changes may be occurring in the insulin/IGF-I signaling pathway that includes decreased production and/or activation of specific signaling proteins leading to a reduced protein synthesis in fetal tissues. Such observations in the placental insufficiency model of IUGR indicate that the combination of decreased fetoplacental amino acid uptake and disrupted insulin/IGF signaling in liver and muscle account for decreased fetal growth in IUGR.

Leptin administration prevents spontaneous gestational diabetes in heterozygous Lepr(db/+) mice: effects on placental leptin and fetal growth

Gestational diabetes mellitus (GDM) results from an interaction between susceptibility genes and the diabetogenic effects of pregnancy. During pregnancy, mice heterozygous for the lepin receptor (db/+) gain more weight, are glucose intolerant, and produce macrosomic fetuses compared with wild-type (+/+) mothers, suggesting that an alteration in leptin action may play a role in GDM and fetal overgrowth. To investigate whether leptin administration or pair-feeding can reduce adiposity and thereby prevent GDM and neonatal overgrowth, we examined energy balance, glucose and insulin tolerance, and fetal growth in pregnant db/+ and +/+ mice treated with recombinant human leptin-IgG during late pregnancy. Leptin reduced food intake and adiposity in pregnant db/+ mice to levels similar to pregnant +/+ mice and significantly reduced maternal weight gain. Maternal glucose levels were markedly lower during glucose and insulin challenge tests in leptin-treated db/+ mice relative to db/+ and pair-fed controls. Despite reduced energy intake and improved glucose tolerance, leptin administration did not reduce fetal overgrowth in offspring from db/+ mothers. Fetal and placental leptin levels were 1.3- to 1.5-fold higher in offspring from db/+ mothers and remained unchanged with leptin administration, whereas leptin treatment in +/+ mothers or pair-feeding decreased placental leptin concentration and reduced fetal birth weight. Our results provide evidence that leptin administration during late gestation can reduce adiposity and improve glucose tolerance in the db/+ mouse model of spontaneous GDM. However, fetal and placenta leptin levels are higher in db/+ mothers and are subject to reduced negative feedback in response to leptin treatment. These data suggest that alterations in placenta leptin may contribute to the regulation of fetal growth independently of maternal glucose levels.

Mice with a deletion in the gene for CCAAT/enhancer-binding protein beta have an attenuated response to cAMP and impaired carbohydrate metabolism

Fifty percent of the mice homozygous for a deletion in the gene for CCAAT/enhancer-binding protein beta (C/EBP beta-/- mice; B phenotype) die within 1 to 2 h after birth of hypoglycemia. They do not mobilize their hepatic glycogen or induce the cytosolic form of phosphoenolpyruvate carboxykinase (PEPCK). Administration of cAMP resulted in mobilization of glycogen, induction of PEPCK mRNA, and a normal blood glucose; these mice survived beyond 2 h postpartum. Adult C/EBP beta-/- mice (A phenotype) also had difficulty in maintaining blood glucose levels during starvation. Fasting these mice for 16 or 30 h resulted in lower levels of hepatic PEPCK mRNA, blood glucose, beta-hydroxybutyrate, blood urea nitrogen, and gluconeogenesis when compared with control mice. The concentration of hepatic cAMP in these mice was 50% of controls, but injection of theophylline, together with glucagon, resulted in a normal cAMP levels. Agonists (glucagon, epinephrine, and isoproterenol) and other effectors of activation of adenylyl cyclase were the same in liver membranes isolated from C/EBP beta-/- mice and littermates. The hepatic activity of cAMP-dependent protein kinase was 80% of wild type mice. There was a 79% increase in the concentration of RI alpha and 27% increase in RII alpha in the particulate fraction of the livers of C/EBP beta-/- mice relative to wild type mice, with no change in the catalytic subunit (C alpha). Thus, a 45% increase in hepatic cAMP (relative to the wild type) would be required in C/EBP beta-/- mice to activate protein kinase A by 50%. In addition, the total activity of phosphodiesterase in the livers of C/EBP beta-/- mice, as well as the concentration of mRNA for phosphodiesterase 3A (PDE3A) and PDE3B was approximately 25% higher than in control animals, suggesting accelerated degradation of cAMP. C/EBP beta influences the regulation of carbohydrate metabolism by altering the level of hepatic cAMP and the activity of protein kinase A.

Vanadate enhances but does not normalize glucose transport and insulin receptor phosphorylation in skeletal muscle from obese women with gestational diabetes mellitus

OBJECTIVE

We compared the insulin-mimetic effects of vanadate, a protein-tyrosine phosphatase inhibitor, with the effects of insulin on skeletal muscle glucose transport and insulin receptor and insulin receptor substrate 1 phosphorylation to test the hypothesis that protein-tyrosine phosphatases participate in pregnancy-induced insulin resistance.

STUDY DESIGN

Skeletal muscle fiber strips were obtained from the rectus abdominis during cesarean delivery in 7 patients with gestational diabetes mellitus, 11 pregnant women with normal glucose tolerance (pregnant control group), and 11 nonpregnant women undergoing elective surgery (nonpregnant control group). Muscle tissues were incubated in vitro for 15 to 60 minutes with or without maximal insulin (100 nmol/L) or sodium vanadate (6 micromol/L). Insulin receptor and insulin receptor substrate 1 tyrosine phosphorylation were measured, as was 2-deoxyglucose transport. The levels of protein-tyrosine phosphatase 1B were measured by Western blot analysis.

RESULTS

Vanadate stimulated maximal 2-deoxyglucose transport more than did insulin alone in all samples (P<.05), but the value was still less in muscle tissues from pregnant control subjects and patients with gestational diabetes mellitus (P<.05). In muscle tissues from pregnant control subjects vanadate increased tyrosine phosphorylation of the insulin receptor and insulin receptor substrate 1 to levels similar to those in muscle tissues from nonpregnant control subjects. In patients with gestational diabetes mellitus vanadate increased insulin receptor and insulin receptor substrate 1 tyrosine phosphorylation, but these values remained less than in muscle tissues from nonpregnant control subjects (P<.05). Protein-tyrosine phosphatase 1B levels were not significantly different in skeletal muscles from each group.

CONCLUSION

Vanadate did not restore normal glucose transport activity during pregnancy complicated by gestational diabetes mellitus, which indicates that decreased glucose uptake is probably not caused by impaired tyrosine phosphorylation events alone. Increased serine kinase activity and impaired glucose transporter 4 translocation probably contribute to insulin signaling abnormalities associated with pregnancy, especially in patients with gestational diabetes mellitus.

Decreased Akt kinase activity and insulin resistance in C57BL/KsJ-Leprdb/db mice

Recent studies suggest that the serine/threonine kinase protein kinase B (PKB or Akt) is involved in the pathway for insulin-stimulated glucose transporter 4 (GLUT4) translocation and glucose uptake. In this study we examined the components of the Akt signaling pathway in skeletal muscle and adipose tissue in vivo from C57BL/KsJ-Lepr(db/db) mice (db/db), a model of obesity, insulin resistance, and type II diabetes. There were no changes in the protein levels of GLUT4, p85alpha, or Akt in tissues from db/db mice compared with non-diabetic littermate controls (+/+). In response to acute insulin administration, GLUT4 recruitment to the plasma membrane increased twofold in muscle and adipose tissue from +/+ mice, but was significantly reduced by 42-43% (P<0.05) in both tissues from db/db mice. Insulin increased Akt-Ser(473) phosphorylation by two- to fivefold in muscle and adipose tissue from all mice. However, in db/db mice, maximal Akt-Ser(473) phosphorylation was decreased by 32% (P<0.05) and 69% (P<0.05) in muscle and adipose tissue respectively. This decreased phosphorylation in db/db mice corresponded with a significant decrease in maximal Akt kinase activity using a glycogen synthase kinase-3 fusion protein as a substrate (P<0.05). The level of insulin-stimulated tyrosine phosphorylation of p85alpha from phosphatidylinositol 3 (PI 3)-kinase, which is upstream of Akt, was also reduced in muscle and adipose tissue from db/db mice (P<0.05); however, there was no change in extracellular signal-regulated kinase-1 or -2 phosphorylation. These data implicate decreased insulin-stimulated Akt kinase activity as an important component underlying impaired GLUT4 translocation and insulin resistance in tissues from db/db mice. However, impaired insulin signal transduction appears to be specific for the PI 3-kinase pathway of insulin signaling, while the MAP kinase pathway remained intact.

The chicken B-cell receptor complex and its role in avian B-cell development

The bursa of Fabricius is critical to normal B-lymphocyte development in birds. During embryonic life, B-cell precursors migrate to the bursal rudiment and those which have undergone productive V(D)J recombination colonize lymphoid follicles and undergo immunoglobulin V gene diversification by gene conversion. The chicken surface IgM complex appears structurally and functionally equivalent to its mammalian counterpart, with homologs to CD79a and CD79b. Expression of a truncated Igmu chain is sufficient to drive the early stages of B-cell development in the embryo bursa. Bursal cells expressing the truncated mu receptor complex proliferate in bursal follicles, and those which contain V gene rearrangements undergo V gene diversification by gene conversion. The bursa is a gut-associated organ and antigen is focused to bursal lymphoid follicles after hatch. While expression of the truncated mu chain is sufficient to support B-cell development in the embryo, B cells expressing this receptor are rapidly eliminated after hatch. We suggest the possibility that B-cell development in the bursa after hatch is driven by encounter with antigen leading to redistribution of B cells within the lymphoid follicle, B-cell proliferation and V gene repertoire development by gene conversion.

Increased insulin receptor substrate-1 and enhanced skeletal muscle insulin sensitivity in mice lacking CCAAT/enhancer-binding protein beta

CCAAT/enhancer-binding protein beta (C/EBPbeta) controls gene transcription and metabolic processes in a variety of insulin-sensitive tissues; however, its role in regulating insulin responsiveness in vivo has not been investigated. We performed hyperinsulinemic-euglycemic clamps in awake, non-stressed, chronically catheterized adult mice homozygous for a deletion in the gene for C/EBPbeta (C/EBPbeta(-/-)). Fasting plasma insulin, glucose, and free fatty acid (FFA) levels were significantly lower in C/EBPbeta(-/-) mice compared with wild-type (WT) controls. Acute hyperinsulinemia (4 h) suppressed hepatic glucose production, phosphoenolpyruvate carboxykinase mRNA, and plasma FFA to a similar extent in WT and C/EBPbeta(-/-) mice, suggesting that C/EBPbeta deletion does not alter the metabolic and gene regulatory response to insulin in liver and adipose tissue. In contrast, using submaximal (5 milliunits/kg/min) and maximal (20 milliunits/kg/min) insulin infusions, whole-body glucose disposal was 77% (p < 0.01) and 33% (p < 0.05) higher in C/EBPbeta(-/-) mice, respectively, compared with WT mice. Maximal insulin-stimulated 3-O-methylglucose uptake in isolated soleus muscle was 54% greater in C/EBPbeta(-/-) mice (p < 0.05). Furthermore, insulin-stimulated insulin receptor and Akt Ser(473) phosphorylation and phosphatidylinositol 3-kinase activity were 1.6-2.5-fold greater in skeletal muscle from C/EBPbeta(-/-) mice compared with WT mice. The level of insulin receptor substrate-1 protein was increased 2-fold in skeletal muscle from C/EBPbeta(-/-) mice. These results demonstrate that C/EBPbeta deletion decreases plasma FFA levels and increases insulin signal transduction specifically in skeletal muscle, and both contribute to increased whole-body insulin sensitivity.

Decreased insulin receptor tyrosine kinase activity and plasma cell membrane glycoprotein-1 overexpression in skeletal muscle from obese women with gestational diabetes mellitus (GDM): evidence for increased serine/threonine phosphorylation in pregnancy and GDM

The cellular mechanisms for the insulin resistance of pregnancy and gestational diabetes mellitus (GDM) are unknown. The membrane protein plasma cell membrane glycoprotein-1 (PC-1) has been identified as an inhibitor of insulin receptor tyrosine kinase (IRTK) activity. We investigated insulin receptor function and PC-1 levels in muscle from three groups of obese subjects: women with GDM, pregnant women with normal glucose tolerance, and nonpregnant control subjects. Subjects (n = 6 for each group) were similar in age and degree of obesity (body fat >30%). IRTK activity, insulin receptor tyrosine phosphorylation, and protein levels of membrane glycoprotein PC-1 were determined in rectus abdominus muscle biopsies obtained at the time of either elective cesarean section or gynecological surgery. No significant differences were evident in basal insulin receptor tyrosine phosphorylation or IRTK activity in the three groups. After maximal insulin (10(-7) mol/l) stimulation, IRTK activity measured with the artificial substrate poly(Glu,Tyr) increased in all subjects but was lower in women with GDM by 25% (P < 0.05) and 39% (P < 0.001) compared with pregnant and nonpregnant control subjects, respectively. Similarly, insulin receptor tyrosine phosphorylation was significantly decreased in subjects with GDM (P < 0.05) compared with pregnant and nonpregnant control subjects. Treatment of the insulin receptors with alkaline phosphatase to dephosphorylate serine/threonine residues increased insulin-stimulated IRTK activity significantly in pregnant control and GDM subjects (P < 0.05), but these rates were still lower compared with nonpregnant control subjects (P < 0.05). PC-1 content in muscle from GDM subjects was increased by 63% compared with pregnant control subjects (P < 0.05) and by 206% compared with nonpregnant control subjects (P < 0.001). PC-1 content was negatively correlated with insulin receptor phosphorylation (r = -0.55, P < 0.05) and IRTK activity (r = -0.66, P < 0.05). These results indicate that pregnant control and GDM subjects had increased PC-1 content and suggest excessive phosphorylation of serine/threonine residues in muscle insulin receptors and that both may contribute to decreased IRTK activity. These changes worsen in women with GDM when controlling for obesity. These postreceptor defects in insulin signaling may contribute to the pathogenesis of GDM and the increased risk for type 2 diabetes later in life.

Physiologic and molecular alterations in carbohydrate metabolism during pregnancy and gestational diabetes mellitus

Recent progress suggests that postreceptor mechanisms that contribute to insulin resistance of pregnancy appear to be multifactorial, but are exerted at the beta-subunit of the insulin receptor and at the level of IRS-1. Gestational diabetes mellitus represents the combination of acquired and intrinsic abnormalities of insulin action. The resistance to insulin-mediated glucose transport appears to be greater in skeletal muscle from GDM subjects than from pregnancy alone. There is also a modest but significant decrease in maximal insulin receptor tyrosine phosphorylation in muscle from obese GDM subjects. Results also suggest that increased insulin receptor serine/threonine phosphorylation and PC-1 could underlie the insulin resistance of pregnancy and pathogenesis of GDM. Whether additional defects are exerted further downstream from IRS-1 remains to be investigated.

Molecular pathology in the obese spontaneous hypertensive Koletsky rat: a model of syndrome X

The SHROB rat is a unique strain with genetic obesity, hypertriglyceridemia, hyperinsulinemia, renal disease with proteinuria, and genetically determined hypertension, characteristics paralleling human Syndrome X. The obese phenotype results from a single homozygous recessive trait, designated faK, and is allelic with the Zucker fatty trait (fa), but of distinct origin. The faK mutation is a premature stop codon in the extracellular domain of the leptin receptor, resulting in a natural receptor knockout. The SHROB are glucose intolerant compared to heterozygous or wild-type SHR, but retain fasting euglycemia even on a high sucrose diet, suggesting that diabetes requires polygenic interaction with additional modifier genes. Insulin-stimulated phosphorylation of tyrosine residues on the insulin receptor and on the associated docking protein IRS-1 are reduced in skeletal muscle and liver compared to SHR, due mainly to diminished expression of insulin receptor and IRS-1 proteins. Despite multiple metabolic derangements and severe insulin resistance, hypertension is not exacerbated in SHROB compared to SHR. Thus, insulin resistance and hypertension are independent in this model. Increased activity of the sympathetic nervous system may be a common factor leading by separate pathways to hypertension and to insulin resistance. We studied the chronic effects of sympathetic inhibition with moxonidine on glucose metabolism in SHROB. Moxonidine (8 mg/kg/day), a selective I1-imidazoline receptor agonist, not only reduced blood pressure but also ameliorated glucose intolerance. Moxonidine reduced fasting insulin by 47% and plasma free fatty acids by 30%. Moxonidine enhanced expression and insulin-stimulated phosphorylation of IRS-1 in skeletal muscle by 74 and 27%, respectively. Thus, central sympatholytic therapy not only counters hypertension but also insulin resistance, glucose tolerance, and hyperlipidemia in the SHROB model of Syndrome X.

The association of the human herpesvirus-6 and MS

Given the clinical and pathological nature of Multiple Sclerosis (MS), a viral infection has long been hypothesized as part of the etiology. In this study we investigated the possibility that the human herpesvirus-6 (HHV-6) is present in a dormant or active phase in the tissue of MS patients, specifically oligodendrocytes. Using PCR assays of MS and non-MS brain sections with primers prepared against the HHV-6 structural protein 101, the results demonstrated that 36% of MS brains were positive for the virus, while 13.5% of non-MS brains were positive. Antibody to the HHV-6 structural protein was also used in immunohistochemical experiments in brain tissue. 47% (7/15) of MS brains were positive for HHV-6, whereas 0/16 controls were positive. In addition, MS patients demonstrated high immune reactivity to this virus, even when compared to auto-immune diseases, which might cause polyclonal activation. Sera obtained from MS and control patients revealed that the IgM response to the HHV-6 virus was significantly elevated in 80% patients compared to 16% non-MS controls, P<.001. The above experiments strongly suggest that a significant number of MS brain samples contain HHV-6 antigens and genomic fragments in a dormant or active phase compared to control specimens and that MS patients mount a brisk, early IgM response.

Impaired glucose transport and insulin receptor tyrosine phosphorylation in skeletal muscle from obese women with gestational diabetes

Women who develop gestational diabetes mellitus (GDM) have severe insulin resistance and markedly increased risk to develop subsequent type 2 diabetes. We investigated the effects of pregnancy and GDM on glucose transport activity and the expression and phosphorylation of the insulin receptor and insulin receptor substrate (IRS)-1 in human skeletal muscle fiber strips in vitro. Rectus abdominis muscle biopsies were obtained at the time of cesarean section from 11 pregnant women with normal glucose tolerance (pregnant control), 7 pregnant women with GDM, and 11 nonpregnant women undergoing elective surgery (nonpregnant control). Subjects were matched for age and similar degree of obesity. The rate of maximal insulin (10(-7) mol/l)-stimulated 2-deoxyglucose transport was reduced by 32% (P < 0.05) in muscle strips from the pregnant control group and even further in GDM subjects by 54% (P < 0.05 vs. pregnant control). The maximal effect of insulin on tyrosine phosphorylation of the insulin receptor was 37% lower (P < 0.05) in GDM subjects than in pregnant control subjects and was not related to changes in the abundance of the insulin receptor. Compared with nonpregnant control subjects, maximal insulin-stimulated IRS-1 tyrosine phosphorylation was significantly lower by 59 +/- 24% (mean +/- SD) (P < 0.05) and 62 +/- 28% (P < 0.05) in pregnant control and GDM subjects, respectively. This was reflected by a 23% (P < 0.05) and 44% (P < 0.002) reduction in IRS-1 protein levels in muscle from pregnant control and GDM subjects. Both pregnant control and GDM subjects exhibited a 1.5- to 2-fold increase in the levels of IRS-2 (P < 0.01) and p85alpha regulatory subunit of phosphatidylinositol (PI) 3-kinase (P < 0.05), despite reduced glucose transport activity. These data indicate that insulin resistance to glucose transport during pregnancy is uniquely associated with a decrease in IRS-1 tyrosine phosphorylation, primarily due to decreased expression of IRS-1 protein. However, in GDM subjects, a decrease in tyrosine phosphorylation of the insulin receptor beta-subunit is associated with further decreases in glucose transport activity. Thus, impaired insulin receptor autophosphorylation is an important early distinction underlying muscle insulin resistance in young women with GDM, and it may underlie future risk for the development of type 2 diabetes.

Anti-hyperglycemic activity of moxonidine: metabolic and molecular effects in obese spontaneously hypertensive rats

Hypertension and insulin resistance are often part of a complex set of abnormalities including obesity, hyperlipidemia, and glucose intolerance, described as syndrome X. Besides a common genetic basis, insulin resistance and hypertension might be linked by excessive activity of the sympathetic nervous system. We studied the effects of chronic inhibition of sympathetic activity with the antihypertensive agent moxonidine on glucose metabolism in the genetically obese SHR Koletsky rat (SHROB), a unique animal model which closely resembles human syndrome X, expressing genetic obesity, hypertension, and hyperlipidemia. Moxonidine, a selective I1-imidazoline receptor agonist, was administered to SHROB and SHR for 90 days in food at 8 mg/kg/day. Moxonidine not only lowered blood pressure, but also reduced fasting insulin levels by 49% in SHROB, and reduced plasma free fatty acids by 30%. In lean SHR, moxonidine treatment decreased circulating free fatty acids by 33% compared to controls. During oral glucose tolerance tests, blood glucose levels in moxonidine-treated SHROB were reduced from 60 min onwards, and there was a sharply higher insulin secretion post-challenge compared to control SHROB. Western blot analysis of insulin signaling proteins showed that IRS-1 was decreased 42% in control SHROB compared with SHR. Moxonidine treatment enhanced the expression of IRS-1 protein in skeletal muscle by 74% in SHROB and 40% in SHR. Moxonidine increased expression of IRS-1 protein in liver by 245% in SHROB and 268% in SHR. Long-term inhibition of sympathetic activity with moxonidine therapy lowered free fatty acids and significantly improved insulin secretion, glucose disposal, and expression of key insulin signaling intermediates. Thus, moxonidine should be considered for the treatment of multiple metabolic and cardiovascular abnormalities associated with syndrome X.

The transcription factor CCAAT/enhancer-binding protein beta regulates gluconeogenesis and phosphoenolpyruvate carboxykinase (GTP) gene transcription during diabetes

CCAAT/enhancer-binding protein (C/EBP) beta and C/EBPalpha are members of the c/ebp gene family and are highly expressed in mammalian liver and adipose tissue. C/EBPalpha is essential for adipogenesis and neonatal gluconeogenesis, as shown by the C/EBPalpha knockout mouse. C/EBPbeta binds to several sequences of the phosphoenolpyruvate carboxykinase (PEPCK) gene promoter with high affinity, and C/EBPbeta protein is increased 200% in the livers of streptozotocin-diabetic mice, concurrent with increased PEPCK mRNA. To elucidate the role of C/EBPbeta in the control of gluconeogenesis during diabetes, we studied the levels of plasma metabolites and hormones related to energy metabolism during diabetes in adult mice heterozygous and homozygous for a null mutation of the gene for C/EBPbeta. We also examined the expression of PEPCK and glucose 6-phosphatase mRNAs and regulation of blood glucose, including the contribution of gluconeogenesis to blood glucose in c/ebpbeta-/- mice. C/EBPbeta was not essential to basal PEPCK mRNA levels. However, C/EBPbeta deletion affected streptozotocin-diabetic response by: (a) delaying hyperglycemia, (b) preventing the increase of plasma free fatty acids, (c) limiting the full induction of PEPCK and glucose 6-phosphatase genes, and (d) preventing the increase in gluconeogenesis rate. Gel supershifts of transcription factor C/EBPalpha, bound to CRE, P3I, and AF-2 sites of the PEPCK promoter, was not increased in diabetic c/ebpbeta-/- mouse liver nuclei, suggesting that C/EBPalpha does not substitute for C/EBPbeta in the diabetic response of liver gene transcription. These results link C/EBPbeta to the metabolic and gene regulatory responses to diabetes and implicate C/EBPbeta as an essential factor underlying glucocorticoid-dependent activation of PEPCK gene transcription in the intact animal.

Effects of overexpression of human GLUT4 gene on maternal diabetes and fetal growth in spontaneous gestational diabetic C57BLKS/J Lepr(db/+) mice

During gestation, heterozygous C57BLKS/J-Lepr(db/+) mice develop spontaneous gestational diabetes mellitus (GDM), and the newborn fetuses are macrosomic compared with offspring from wild-type (+/+) mothers. To investigate the effects of the leptin receptor mutation on maternal metabolism and fetal growth during pregnancy, we studied +/+, db/+, and db/+ transgenic mice that overexpress the human GLUT4 gene two- to three-fold (db/+TG6). During pregnancy, fasting plasma glucose and hepatic glucose production were twofold greater in db/+ than +/+ mice, despite similar insulin levels. In skeletal muscle, insulin-stimulated tyrosine phosphorylation was decreased in pregnant +/+ mice, and even more so in db/+ mice: insulin receptor beta (IR-beta), +/+ 34%, db/+ 57% decrease, P<0.05; insulin receptor substrate 1 (IRS-1), +/+ 44%, db/+ 61% decrease, P<0.05; and phosphoinositol (PI) 3-kinase (p85alpha), +/+ 33%, db/+ 65% decrease, P<0.05. Overexpression of GLUT4 in db/+TG6 mice markedly improved glucose-stimulated insulin secretion, by 250%, and increased IRbeta, IRS-1, and p85alpha phosphorylation twofold, despite no change in concentration of these proteins. Plasma leptin concentration increased 40-fold during pregnancy, from 2.2+/-0.5 to 92+/-11 ng/ml and 3.6+/-0.1 to 178+/-34 ng/ml in +/+ and db/+ mice, respectively (P<0.01), but was increased to only 23+/-3 ng/ml in pregnant db/+TG6 mice (P<0.001). Maternal fat mass and energy intake were greater in db/+ mice, and fat mass was reduced by GLUT4 overexpression, independent of food intake. Fetal body weight was increased by 8.1 and 7.9% in db/+ and db/+TG6 mothers, respectively (P<0.05), regardless of fetal genotype, whereas fetuses from db/+TG8 mothers (four- to fivefold overexpression) weighed significantly less compared with pups from +/+ or db/+ mothers (P<0.05). These results suggest that the single mutant db allele effects susceptibility to GDM through abnormalities in insulin receptor signaling, defective insulin secretion, and greater nutrient availability. GLUT4 overexpression markedly improves insulin-signaling in GDM, resulting in increased insulin secretion and improved glycemic control. However, maternal hyperglycemia appears not to be the sole cause of fetal macrosomia. These data suggest that GDM is associated with defects in insulin receptor signaling in maternal skeletal muscle, and this may be an important factor provoking maternal and fetal perinatal complications.

Hypoglycemia and impaired hepatic glucose production in mice with a deletion of the C/EBPbeta gene

The transcription factor CCAAT/enhancer-binding protein beta (C/EBPbeta) is enriched in liver and adipose tissue and controls the expression of a wide variety of genes coding for important metabolic pathways, including gluconeogenesis and lipid synthesis. To investigate the role of C/EBPbeta on glucose homeostasis, we studied mice with a targeted deletion of the gene for C/EBPbeta-/- mice. Adult C/EBPbeta-/- mice have hypoglycemia after an 18-hour fast, accompanied by lower hepatic glucose production (40% of that of wild-type mice), with no change in plasma insulin and a lower concentration of plasma free fatty acids (FFA). Glucagon infusion during a pancreatic clamp acutely stimulated hepatic glucose production by 38% in wild-type animals, with no change detected in C/EBPbeta-/- mice. Unexpectedly, both the basal and glucagon-stimulated hepatic cyclic adenosine monophosphate (cAMP) levels were lower in C/EBPbeta-/- mice, indicating an essential role for C/EBPbeta in controlling proximal signal transduction. Fasting hypoglycemia was associated with normal levels of phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) gene expression, however net liver glycogenolysis was impaired in C/EBPbeta-/- mice. FFA release from isolated adipose tissue in response to epinephrine was 68% lower in C/EBPbeta-/- mice than in control animals; however, N6,O2'-dibutyryladenosine (Bt2) cAMP stimulated a twofold increase in FFA release in C/EBPbeta-/- compared with no further increase in wild-type mice. Because a deletion in the gene for C/EBPbeta reduces blood glucose and circulating FFA, it could be an important therapeutic target for the treatment of non-insulin-dependent diabetes and possibly obesity, based on designing antagonists that decrease C/EBPbeta activity.

Mechanisms of antihyperglycemic effects of moxonidine in the obese spontaneously hypertensive Koletsky rat (SHROB)

Increased activity of the sympathetic nervous system may be a critical factor in the development of impaired insulin secretion and insulin resistance. We studied the chronic effects of sympathetic inhibition with moxonidine on glucose metabolism in the spontaneously hypertensive genetically obese rat (SHROB). This unique animal model closely resembles human syndrome X, expressing insulin resistance, genetic obesity, spontaneous hypertension, and hyperlipoproteinemia. Moxonidine, a selective imidazoline receptor agonist, was administered to lean spontaneous hypertensive rats (SHR) and SHROBs for 90 days in food at 8 mg/kg/day and significantly reduced mean blood pressure. Moxonidine treatment reduced fasting insulin levels by 71% in SHROB and lowered plasma free fatty acids by 25%. In SHR, moxonidine treatment decreased free fatty acids by 17% compared with controls. During an oral glucose tolerance test, blood glucose levels in moxonidine-treated SHROB were reduced relative to untreated controls from 60 min onwards. Insulin secretion was facilitated at 30 min (83% greater) and 60 min (67% greater) postchallenge compared with control SHROB. In skeletal muscle, moxonidine treatment increased the expression of the insulin receptor beta subunit by 19% in SHROB but was without effect in SHR. The level of insulin receptor substrate-1 (IRS-1) protein was decreased by 60% in control SHROB compared with lean SHR. Moxonidine treatment enhanced the expression and insulin-stimulated phosphorylation of IRS-1 protein in skeletal muscle in SHROB by 74 and 27%, respectively, and in SHR by 40 and 56%, respectively. Moxonidine increased the levels of expression of IRS-1 protein in liver in SHR by 275% and in SHROB by 260%. These findings indicate that chronic inhibition of sympathetic activity with moxonidine therapy can lower free fatty acids and significantly improve insulin secretion, glucose disposal, and expression of key insulin signaling intermediates in an animal model of obese hypertension.

Phenotypic consequences of a nonsense mutation in the leptin receptor gene (fak) in obese spontaneously hypertensive Koletsky rats (SHROB)

The genetically obese Koletsky rat (SHROB, fak) has a novel point mutation of the leptin receptor at amino acid +763, resulting in a premature stop codon in the leptin receptor extracellular domain. This implies that all leptin receptor isoforms should be absent in this model. We examined the phenotypic consequences of this mutation on leptin and leptin receptor mRNA in hypothalamus and peripheral tissues from SHROB and their lean SHR littermates. Despite the mutation, mRNA for both the long (ObRa) and the short (ObRb) form were expressed at comparable levels in SHROB and SHR in brain and throughout peripheral tissues. Adipose tissue mRNA for leptin was two to three times greater in SHROB compared to SHR (P < 0.01), while circulating leptin concentration was 170 times greater than SHR littermates (P < 0.01), suggesting extreme leptin resistance in SHROB. Leptin was also detected in the cerebrospinal fluid (CSF) of SHR and SHROB (13.8 and 27.2 pmol/L, respectively); however, the CSF/plasma ratio for leptin was 32-fold greater in SHR than in SHROB. To assess the putative action of leptin and leptin receptors on insulin-mediated glucose transport, muscles from SHR and SHROB were incubated in vitro with recombinant human leptin. Leptin directly suppressed insulin-mediated glucose transport by 50% in skeletal muscle from SHR but not in obese SHROB rats lacking all forms of the leptin receptor. These results suggest that the natural leptin receptor knockout in the SHROB represents a unique rat model to define the functional role(s) of leptin in central and peripheral energy metabolism.

Longitudinal changes in maternal serum leptin concentrations, body composition, and resting metabolic rate in pregnancy

OBJECTIVE

We sought to evaluate the longitudinal changes in maternal serum leptin concentrations, body composition, and resting metabolic rate during pregnancy.

STUDY DESIGN

Ten women were evaluated before pregnancy, in early pregnancy (12 to 14 weeks), and in late pregnancy (34 to 36 weeks). Leptin concentrations were measured by radioimmunoassay, body composition with hydrodensitometry with adjustment for total body water, and resting metabolic rate by use of indirect calorimetry.

RESULTS

Using analysis of variance with repeated measures from pregravid to late pregnancy, a 66% increase (mean +/- SD) was found in leptin concentrations (in nanograms per milliliter) (before pregnancy, 25.4 +/- 19.9; in early pregnancy, 37.5 +/- 26.2; and in late pregnancy, 38.4 +/- 27.3, p = 0.003); a 9% increase in body fat (in kilograms) (before pregnancy, 29.4 +/- 15.7; in early pregnancy, 28.7 +/- 14.0; in late pregnancy, 31.4 +/- 14.6; p = 0.04); a 28% increase in oxygen consumption (in milliliters of oxygen per minute) (before pregnancy, 221.2 +/- 29.5; in early pregnancy, 230.4 +/- 42.9; in late pregnancy, 285.3 +/- 51.9; p < 0.0001); and a 9% increase in oxygen consumption (milliliters of oxygen per kilogram per minute) (before pregnancy, 3.02 +/- 0.43; in early pregnancy, 3.05 +/- 0.30; in late pregnancy, 3.31 +/- 0.37, p = 0.002) with advancing gestation. A significant positive correlation was present between leptin and body fat before pregnancy (r = 0.90, p < 0.0001), in early pregnancy (r = 0.91, p < 0.0001), and in late pregnancy (r = 0.87, p = 0.0005) and between leptin and oxygen consumption before pregnancy (r = 0.80, p = 0.004), in early pregnancy (r = 0.92, p < 0.0001), and in late pregnancy (r = 0.62, p = 0.06). When oxygen consumption was adjusted for maternal and fetal tissue mass, a significant negative correlation was found between leptin and oxygen consumption before pregnancy (r = -0.96, p < 0.0001), in early pregnancy (r = -0.80, p = 0.0034), and in late pregnancy (r = -0.70, p = 0.02).

CONCLUSION

We conclude that leptin increases significantly during early pregnancy before any major changes in body fat and resting metabolic rate. These data suggest that pregnancy represents a leptin-resistant state.

State of actin filaments is changed by anoxia in cultured rat neocortical neurons

Cultured neocortical neurons respond rapidly to oxygen deprivation. Within minutes they demonstrate an increase in intracellular calcium and pronounced changes in their morphology. These changes include swelling, bleb formations, process retraction and a change in shape of the soma from pyramidal or ellipsoidal to round. Since the cytoskeleton is responsible for the maintenance of cell shape, we investigated the changes in state of a major component of the neuronal cytoskeleton, the actin filaments. Actin exists in a dynamic equilibrium between the monomeric and filamentous states. This equilibrium is dependent, in part, upon intracellular ATP, which is reduced during anoxia. We differentially labelled monomeric actin with Texas Red-tagged DNase-1 and the polymeric form with Bodipy-phallicidin. Using confocal microscopy and image reconstruction, we have found that the ratio of filamentous to monomeric actin increases on average three-fold following 10 min of anoxia. In addition, filamentous actin redistributes within the soma and appears to have a more homogeneous distribution than in normoxic neurons. Our results show that, in cultured neocortical neurons, actin filaments are modulated by anoxia. We believe that, although the filamentous/monomeric ratio is modulated, at least in part, by the levels of ATP and ADP, the relative distribution and amount of the filamentous to monomeric form within neurons are likely regulated by other factors such as calcium-sensitive actin-binding and severing proteins.

Phosphoenolpyruvate carboxykinase (GTP) gene transcription and hyperglycemia are regulated by glucocorticoids in genetically obese db/db transgenic mice

The molecular mechanisms underlying increased hepatic phosphoenolpyruvate carboxykinase (PEPCK) gene transcription and gluconeogenesis in type II diabetes are largely unknown. To examine the involvement of glucocorticoids and the cis-acting insulin response sequence (IRS, -416/-407) in the genetically obese db/db mouse model, we generated crosses between C57BL/KsJ-db/+ mice and transgenic mice that express -460 or -2000 base pairs of the rat PEPCK gene promoter containing an intact or mutated IRS, linked to a reporter gene. Transgenic mice expressing the intact PEPCK(460)-CRP (C-reactive protein) transgene bred to near homozygosity at the db locus were obese, hyperinsulinemic, and developed fasting hyperglycemia (389 +/- 26 mg/100 ml) between 4 and 10 weeks of age. Levels of CRP reporter gene expression were increased 2-fold despite severe hyperinsulinemia compared with non-diabetic non-obese transgenic mice. Reporter gene expression was also increased 2-fold in transgenic obese diabetic db/db mice bearing a mutation in the IRS, -2000(IRS)-hGx, compared with non-obese non-diabetic transgenic 2000(IRS)-hGx mice. Treatment of obese diabetic db/db transgenic mice with the glucocorticoid receptor blocker RU 486 decreased plasma glucose by 50% and reduced PEPCK, GLUT2, glucose-6-phosphatase, tyrosine aminotransferase, CRP, and hGx reporter gene expression to levels similar to those of non-obese normoglycemic transgenic mice. Taken together, these results establish that -460 bp of 5'-flanking sequence is sufficient to mediate the induction of PEPCK gene transcription in genetically obese db/db mice during the development of hyperglycemia. The results further demonstrate that the mechanism underlying increased expression of gluconeogenic enzymes in the db/db mouse requires the action of glucocorticoids and occurs independently of factors acting through the PEPCK IRS (-416/-407) promoter binding site.

Reduced insulin receptor signaling in the obese spontaneously hypertensive Koletsky rat

Insulin resistance is associated with both obesity and hypertension. However, the cellular mechanisms of insulin resistance in genetic models of obese-hypertension have not been identified. The objective of the present study was to investigate the effects of genetic obesity on a background of inherited hypertension on initial components of the insulin signal transduction pathway and glucose transport in skeletal muscle and liver. Oral glucose tolerance testing in SHROB demonstrated a sustained postchallenge elevation in plasma glucose at 180 and 240 min compared with lean spontaneously hypertensive rat (SHR) littermates, which is suggestive of glucose intolerance. Fasting plasma insulin levels were elevated 18-fold in SHROB. The rate of insulin-stimulated 3-O-methylglucose transport was reduced 68% in isolated epitrochlearis muscles from the SHROB compared with SHR. Insulin-stimulated tyrosine phosphorylation of the insulin receptor beta-subunit and insulin receptor substrate-1 (IRS-1) in intact skeletal muscle of SHROB was reduced by 36 and 23%, respectively, compared with SHR, due primarily to 32 and 60% decreases in insulin receptor and IRS-1 protein expression, respectively. The amounts of p85 alpha regulatory subunit of phosphatidylinositol-3-kinase and GLUT-4 protein were reduced by 28 and 25% in SHROB muscle compared with SHR. In the liver of SHROB, the effect of insulin on tyrosine phosphorylation of IRS-1 was not changed, but insulin receptor phosphorylation was decreased by 41%, compared with SHR, due to a 30% reduction in insulin receptor levels. Our observations suggest that the leptin receptor mutation fak imposed on a hypertensive background results in extreme hyperinsulinemia, glucose intolerance, and decreased expression of postreceptor insulin signaling proteins in skeletal muscle. Despite these changes, hypertension is not exacerbated in SHROB compared with SHR, suggesting these metabolic abnormalities may not contribute to hypertension in this model of Syndrome X.

Anoxia-induced neuronal injury: role of Na+ entry and Na+-dependent transport

An important cause of anoxia-induced nerve injury involves the disruption of the ionic balance that exists across the neuronal membrane. This loss of ionic homeostasis results in an increase in intracellular calcium, sodium, and hydrogen and is correlated with cell injury and death. Using time-lapse confocal microscopy, we have previously reported that nerve cell injury is mediated largely by sodium and that removing extracellular sodium prevents the anoxia-induced morphological changes. In this study, we hypothesized that sodium enters neurons via specific mechanisms and that the pharmacologic blockade of sodium entry would prevent nerve damage. In cultured neocortical neurons we demonstrate that replacing extracellular sodium with NMDG+ prevents anoxia-induced morphological changes. With sodium in the extracellular fluid, various routes of sodium entry were examined, including voltage-sensitive sodium channels, glutamate receptor channels, and sodium-dependent chloride-bicarbonate exchange. Blockade of these routes had no effect. Amiloride, however, prevented the morphological changes induced by anoxia lasting 10, 15, or 20 min. At doses of 10 microM-1 mM, amiloride protected neurons in a dose-dependent fashion. We argue that amiloride acts on a Na+-dependent exchanger (e.g., Na+-Ca2+) and present a model to explain these findings in the context of the neuronal response to anoxia.

Exercise training down-regulates ob gene expression in the genetically obese SHHF/Mcc-fa(cp) rat

The recently cloned obesity gene (ob) encodes a protein, leptin, which is secreted from adipose tissue and interacts with hypothalamic receptors to decrease appetite, increase energy expenditure, and reduce body lipid stores. The levels of ob mRNA are increased in several models of obesity, consistent with the hypothesis that obese animals may be resistant to the actions of leptin. The present study examined the impact of increased energy expenditure through exercise training on ob mRNA gene expression and body composition in the SHHF/Mc-fa(cp) male rat, a rodent model of obesity, insulin resistance, and type II diabetes. Six week old lean and obese animals were trained 8-12 weeks by treadmill running at 70% peak oxygen uptake, 5 days/wk, for 1.5 hr/day. After endurance training, exercised rats had significantly lower total body fat compared to sedentary rats of the same age, despite maintaining the same body weight. In the obese SHHF/Mcc-fa(cp) rat, the level of ob mRNA expression was markedly increased by four fold in subcutaneous adipose tissue compared to lean controls (p<0.05). In response to exercise training, there was a significant 85 % decrease in ob mRNA in exercised-training lean rats (p < 0.05) compared with non-exercised controls, while in obese-exercised rats, ob gene expression was significantly reduced only by 50% relative to non-exercised obese rats (p < 0.05). These results demonstrate that exercise training reduces fat mass and ob mRNA in lean and obese rats, and supports the hypothesis of a feedback loop between the adipocyte and hypothalamus that attempts to maintain body weight at a constant level by reducing ob gene expression in response to increased energy expenditure.

Alterations in key gluconeogenic regulators with age and endurance training

The purpose of the present investigation was to examine changes in six potential regulators of hepatic gluconeogenesis with normal aging and endurance training: fructose 2,6-bisphosphate (F 2,6-P2), mitochondrial and cytosolic phosphoenolpyruvate carboxykinase (PEPCK) activity, PEPCK mRNA, and pyruvate carboxylase and malate dehydrogenase activity. Young (4 months), middle-aged (12 months), and old (22 months) male-Fischer 344 rats (N = 66) were divided into trained and sedentary groups. Trained animals were run 1 h/d, 5 d/wk for 10 weeks at treadmill speeds of 75% age-specific maximal running capacity. Animals were killed at rest, and the right main lobe of the liver was removed. F 2,6-P2 levels were significantly greater in old compared with young animals regardless of training condition (119% and 80% increase in old trained and untrained animals, respectively). No changes were found with training. Rates of cytosolic PEPCK activity declined significantly with age in both trained (1.3 +/- 0.1, 1.0 +/- 0.1, and 0.7 +/- 0.1 mumol/g/min in young, middle-aged, and old, respectively) and untrained (1.3 +/- 0.1, 1.1 +/- 0.1, and 0.8 +/- 0.2 mumol/g/min) groups. Training did not result in any significant differences between age groups. PEPCK gene expression (mRNA) determined by Northern blot analysis decreased 30% in trained and untrained old animals compared to the young counterparts; again, training had no effect in any age group. No significant differences were found in pyruvate carboxylase, mitochondrial PEPCK, or malate dehydrogenase activity with either age or training. These results suggest that previous age-related declines found in hepatic gluconeogenic capacity can be attributed, in part, to changes in F 2,6-P2, cytosolic PEPCK activity, and PEPCK mRNA, but not to alterations in the activities of mitochondrial PEPCK, malate dehydrogenase, or pyruvate carboxylase. Since training had no effect on any regulator studied, the factors responsible for attenuation in the age-related decline in gluconeogenesis with training remain to be determined.

The I1-imidazoline receptor: from binding site to therapeutic target in cardiovascular disease

OBJECTIVE

To review previous work and present additional evidence characterizing the I1-imidazoline receptor and its role in cellular signaling, central cardiovascular control, and the treatment of metabolic syndromes. Second-generation centrally-acting antihypertensives inhibit sympathetic activity mainly via imidazoline receptors, whereas first-generation agents act via alpha2-adrenergic receptors. The I1 subtype of imidazoline receptor resides in the plasma membrane and binds central antihypertensives with high affinity.

METHODS AND RESULTS

Radioligand binding assays have characterized I1-imidazoline sites in the brainstem site of action for these agents in the rostral ventrolateral medulla. Binding affinity at I1-imidazoline sites, but not at other classes of imidazoline binding sites, correlates closely with the potency of central antihypertensive agents in animals and in human clinical trials. The antihypertensive action of systemic moxonidine is eliminated by the I1/alpha2-antagonist efaroxan, but not by selective blockade of alpha2-adrenergic receptors. Until now, the cell signaling pathway coupled to I1-imidazoline receptors was unknown. Using a model system lacking alpha2-adrenergic receptors (PC12 pheochromocytoma cells) we have found that moxonidine acts as an agonist at the cell level and I1-imidazoline receptor activation leads to the production of the second messenger diacylglycerol, most likely through direct activation of phosphatidylcholine-selective phospholipase C. The obese spontaneously hypertensive rat (SHR; SHROB strain) shows many of the abnormalities that cluster in human syndrome X, including elevations in blood pressure, serum lipids and insulin. SHROB and their lean SHR littermates were treated with moxonidine at 8 mg/kg per day. SHROB and SHR treated with moxonidine showed not only lowered blood pressure but also improved glucose tolerance and facilitated insulin secretion in response to a glucose load. Because alpha2-adrenergic agonists impair glucose tolerance, I1-imidazoline receptors may contribute to the multiple beneficial effects of moxonidine treatment.

CONCLUSION

The I1-imidazoline receptor is a specific high-affinity binding site corresponding to a functional cell-surface receptor mediating the antihypertensive actions of moxonidine and other second-generation centrally-acting agents, and may play a role in countering insulin resistance in an animal model of metabolic syndrome X.

Vulnerability of CA1 neurons to glutamate is developmentally regulated

Although it is well documented that glutamate receptor subtypes are differentially expressed during central nervous system development postnatally, how glutamate affects neurons during postnatal development is unclear. We therefore examined the development of the intrinsic neuronal response to glutamate receptor activation by studying single, hippocampal CA1 neurons that had been acutely dissociated from newborn (P1-3), 1 week old (P6-8), and 3 week old (P21-25) rats. Using laser scanning confocal microscopy and the calcium dye Fluo-3, we made time-lapse studies of the effects of glutamate stimulation on free intracellular calcium ([Ca2+]i) and simultaneous changes in neuronal morphology. In P21-25 neurons, glutamate increased [Ca2+]i fluorescence, and caused marked somal swelling, blebbing, and retraction of dendrites into the soma. These major morphological changes were followed by sudden loss of intracellular fluorescence, indicative of a loss of membrane integrity and cell death. In P6-8 neurons, glutamate increased [Ca2+]i to the same extent, but this increase was not followed by either major morphological changes or loss of membrane integrity. In P1-3 neurons, glutamate increased [Ca2+]i minimally, and no morphologic changes were observed. P1-3 neurons dissociated without enzymatic digestion demonstrated glutamate responses identical to responses seen in neurons dissociated with enzymatic digestion. In the presence of MK-801 (15 microM), glutamate still increased [Ca2+]i and caused cell death in P21-25 neurons, but the latency to these effects more than tripled. This late, MK-801-resistant [Ca2+]i increase was not eliminated by DNQX or Ni2+/Cd2+, suggesting that this increase is mediated by metabotropic receptors. These findings demonstrate that (1) hippocampal neurons from newborns are intrinsically less vulnerable to glutamate toxicity than neurons from 3 weeks old animals, and (2) multiple glutamate receptor subtypes affect the magnitude of the [Ca2+]i increase in response to glutamate in the neuronal microenvironment.

Role of acetylated gangliosides on neurite extension

We have investigated the role of 9-O-acetylated gangliosides identified by the Jones monoclonal antibody (Jones mAb) in the elongation of neurites extended by neurons of embryonic rat dorsal root ganglia (DRG) explants grown on laminin substratum. The behavior of individual growth cones was recorded using a time-lapse video-enhanced imaging system before and after the addition of antibodies that recognize specific gangliosides known to be expressed on these growth cones. It was possible to demonstrate that the advance of growth cones on laminin was halted in the presence of Jones mAb. The onset of effects was rapid and signaled by an immediate cessation of elongation, a loss of lamellipodia and a retrieval of axoplasm. This effect was partially reverted by washing the explants for several minutes with culture medium. mAb A2B5 which also recognizes gangliosides expressed on these growth cones does not induce any change on the growth rate. Our findings show that 9-O-acetylated gangliosides may play an important role on the extension of growth cones and consequently influence navigation and pathway finding during development.

Involvement of transcription factor C/EBP-beta in stimulation of PEPCK gene expression during exercise

Prolonged exercise increases gluconeogenesis and activates transcription of the hepatic phosphoenol pyruvate carboxykinase (PEPCK) gene. The mechanisms that regulate the transcriptional control of gene expression depend on the interaction of nuclear proteins with distinct DNA sequences. To determine the involvement with the liver-enriched transcription factor CCAAT/enhancer binding protein beta (C/EMP-beta) in the induction of PEPCK gene transcription during prolonged exercise or adenosine 3',5'-cyclic monophosphate (cAMP) treatment, we examined C/EBP-beta mRNA and nuclear protein concentrations, as well as C/EBP-beta binding to the PEPCK promoter at the cAMP response element (CRE)(-87/-74) and P3I (-248/-230) binding sites. The requirement of these DNA elements for exercise-induced stimulation of PEPCK gene expression was established in transgenic mice carrying -460 +/- 73 of the PEPCK promoter with a mutation in either the CRE or P3I binding domain linked to a bovine growth hormone (bGH) reporter gene. In mice carrying the intact promoter, prolonged exercise increased the concentration of liver bGH mRNA by 510% compared with an increase of only 270% in mice with a mutation in either the CRE or P3I site. Exercise or cAMP injection induced a 7.5- and 13-fold increase in nuclear C/EBP-beta protein, respectively. In electrophoretic mobility shift assays (EMSA), the total quantity of nuclear proteins bound to either oligomer was not altered by treatment. However, addition of C/EBP-beta antisera in the EMSA in a supershift assay indicated that liver nuclear extracts from exercised or cAMP-treated mice demonstrated significantly greater DNA binding due to C/EBP-beta (CRE: control 44.4 +/- 2.3%, exercise 56.7% +/- 2.2%, cAMP 54.5 +/- 3.6% of total binding, P < 0.001; P3I: control 35.8 +/- 2.5%, exercise 64.9 +/- 1.9%, cAMP 57.3 +/- 2.5% of total binding, P < 0.001). Taken together, these results suggest that exercise and cAMP treatment induce a transient increase in C/EBP-beta that may contribute to the molecular mechanism for signaling PEPCK gene transcription and increasing gluconeogenesis during exercise.

Anoxia induces an increase in intracellular sodium in rat central neurons in vitro

Following our previous observations that anoxia induces a drop in extracellular Na+ in the brain slice and that removal of extracellular Na+ prevents the anoxia-induced morphological changes in dissociated hippocampal neurons, we hypothesized that intracellular Na+ increases during anoxia in isolated neurons. Using the fluorophore Sodium Green in freshly dissociated rat CA1 neurons, and SBFI in cultured cortical neurons, we found that 10 min of anoxia caused an increase in Nai+ in both types of cells, with a latency of about 2 min. In CA1 neurons, fluorescence increased by an average of 20.34% (n = 8). The mean baseline Nai+ level (determined using SBFI) was 25 +/- 2.5 mM, which increased to about an average of 52 +/- 3 mM after 3-4 min. These and our previous results strongly suggest that Na(+)-mediated events are involved in anoxia-induced nerve injury.

Glucose metabolism in incubated human muscle: effect of obesity and non-insulin-dependent diabetes mellitus

Skeletal muscle contributes significantly to reduced insulin-stimulated glucose disposal in patients with obesity and non-insulin-dependent (type II) diabetes mellitus (NIDDM). The biochemical basis for insulin resistance is not known but may involve reduced glucose transport and/or a defect in intracellular pathways for glucose disposal. To address this question, we measured basal and insulin-stimulated glucose oxidation, glycogen formation, and nonoxidative glycolysis (lactate and amino acid release) in an incubated muscle preparation from nonobese and morbidly obese patients with and without NIDDM. Pathways of glucose disposal were also determined in muscle of obese NIDDM patients incubated under hyperglycemic (20 mmol/L) conditions, which increases glucose uptake by mass action. Under basal conditions (no insulin present) there were no significant differences in glycogen formation or glucose oxidation between nonobese control, obese nondiabetic, or obese diabetics. Lactate release was significantly higher in obese controls compared to nonobese controls in the basal state at 5 mmol/L glucose (10.2 +/- 2.8 v 24.7 +/- 3.5 nmol/min/g, P < .05). Under maximal insulin-stimulated conditions, rates of glycogen formation, glucose oxidation, and nonoxidized glycolysis increased 1.9-, 2.3-, and 2.2-fold over basal (P < .05) in nonobese controls. By contrast, insulin was ineffective at stimulating significant increases in any metabolic pathway of glucose disposal in muscle of obese or obese NIDDM patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of glucocorticoids in activation of hepatic PEPCK gene transcription during exercise

The objective of these studies was to determine the molecular basis for the activation of phosphoenolpyruvate carboxykinase (PEPCK) gene transcription during prolonged submaximal exercise. Mice were fed a high-carbohydrate diet for 1 wk and exercised continuously by swimming for up to 120 min. The level of hepatic PEPCK mRNA increased progressively during exercise, reaching 510% above control, whereas transcription of the PEPCK gene increased 1,000%, before decreasing to control levels within 60 min of recovery. In transgenic mice carrying a chimeric gene consisting of the PEPCK promoter linked to a reporter gene for bovine growth hormone (bGH), PEPCK(-460)-bGH, the level of hepatic bGH mRNA increased by 490% in response to exercise, similar to the increase in the expression of the native PEPCK gene. However, in transgenic mice with a deletion of the glucocorticoid regulatory unit, PEPCK(-355)-bGH, bGH mRNA did not increase above control values. In transgenic mice with a block mutation in adenosine 3',5'-cyclic monophosphate (cAMP) regulatory regions -90/-82 and -250/-234, PEPCK cAMP response element 1 (CRE-1)/P3(1)-bGH, exercise increased bGH mRNA 260% above controls. Adrenalectomy (Adx) had no effect on PEPCK mRNA levels in nonexercised mice, whereas in adrenalectomized (Adx)-exercised mice, PEPCK mRNA increased only 80% above basal, and, in Adx mice injected with dexamethasone, PEPCK mRNA increased with exercise 570% above controls. Exercise was also associated with a large increase in transcription of the gene for the transcription factor CCAAT/enhancer-binding protein beta (C/EBP-beta) and a smaller rise in transcription of c-jun gene, both of which returned to control levels during recovery.(ABSTRACT TRUNCATED AT 250 WORDS)

Removal of extracellular sodium prevents anoxia-induced injury in freshly dissociated rat CA1 hippocampal neurons

Anoxia is believed to cause nerve injury and death in part, by inducing sustained, elevated levels of intracellular Ca2+. The increased concentration of intracellular Ca2+ is capable, by itself, of inducing nerve injury and death, even without the added stress of anoxia. However, we have recently shown that an increased level of intracellular Ca2+ is not necessary for anoxia-induced CA1 nerve injury. Since we have observed that extracellular Na+ decreases during anoxia, we studied the role of extracellular Na+ in anoxia-induced nerve injury. Removal of extracellular Na+ and its replacement with the impermeant cation N-methyl-D-glucamine (NMDG+) completely protected freshly dissociated CA1 neurons during and after severe anoxia, for up to 90 min. Intracellular Ca2+ decreased during anoxia, recovering during reoxygenation. Propidium iodide was excluded from the neurons for as long as Na+ was absent. Addition of Na+ (by replacing NMDG+) following anoxia resulted in rapid bleb formation, swelling and intracellular Ca2+ rise. Removal of Na+ before the rupture of blebs caused either shrinkage or pinching off of blebs so that the neuron apparently returned to its previous undisturbed state.(ABSTRACT TRUNCATED AT 250 WORDS)

The medical status of methadone maintenance patients in treatment for 11-18 years

To assess the safety and potential health consequences of long-term methadone maintenance treatment, we identified 111 male patients admitted to methadone maintenance treatment between 1965 and 1968, still enrolled in 1980 and in continuous treatment for at least 10 years. We were able, between 1980 and 1985, to examine patients or review records of 110 patients (99%). Most medical diagnoses, symptomatic complaints, physical examination findings and laboratory test results occurred with similar frequency in the long-term methadone maintenance patients and in a group of 56 long-term heroin addicts. These data suggest that prolonged methadone maintenance treatment is safe and is not associated with unexpected adverse effects.

Glucocorticoids regulate the induction of phosphoenolpyruvate carboxykinase (GTP) gene transcription during diabetes

The hormonal regulation of transcription of the phosphoenolpyruvate carboxykinase (GTP) (4.1.1.32) (PEPCK) gene during diabetes was studied using transgenic mice containing a chimeric gene consisting of segments of the PEPCK promoter (-2000/+73, -460/+73, -355/+73) linked to bovine growth hormone (bGH) reporter gene. The effect of diabetes and insulin on transgenic mice containing a mutation in cAMP regulatory sequences at -90/-82 and -250/-234 was also studied. In addition, we analyzed the transcriptional response of the PEPCK gene to adrenalectomy, the administration of glucocorticoids, and alterations in dietary protein and carbohydrate. Our results indicate that deletion of the insulin regulatory sequence of the PEPCK promoter did not affect dietary control of PEPCK gene expression. However, glucocorticoids and the glucocorticoid regulatory unit appear to be essential for induction of PEPCK gene transcription by diabetes. By contrast, mutation of cAMP regulatory elements of the PEPCK promoter did not limit induction of PEPCK transcription by diabetes, nor did it affect negative regulation of transcription by insulin. These results provide evidence for the interaction of insulin and glucocorticoid regulatory elements in the control of PEPCK gene transcription and suggest an important role of glucocorticoids as a gluconeogenic activator during diabetes.