A first-in-human pharmacodynamic and pharmacokinetic study of a fully human anti-glucagon receptor monoclonal antibody in normal healthy volunteers

AIMS

Glucagon receptor (GCGR) blockers are being investigated as potential therapeutics for type 1 and type 2 diabetes. Here we report the safety, tolerability, pharmacokinetics (PK) and pharmacodynamics (PD) of REGN1193, a fully human glucagon receptor blocking monoclonal antibody from a first-in-human healthy volunteer randomized double-blinded trial.

METHODS

Healthy men and women received single ascending doses of REGN1193 ranging from 0.05 to 0.6 mg/kg (n = 42) or placebo (n = 14) intravenously. Safety, tolerability and PK were assessed over 106 days. The glucose-lowering effect of REGN1193 was assessed after induction of hyperglycaemia by serial glucagon challenges.

RESULTS

REGN1193 was generally well tolerated. There were small (<3× the upper limit of normal) and transient dose-dependent increases in hepatic aminotransferases. No increase in LDL-C was observed. Hypoglycaemia, assessed as laboratory blood glucose ≤70 mg/dL, occurred in 6/14 (43%) subjects on placebo and 27/42 (57%) on REGN1193 across all dose groups. All episodes of hypoglycaemia were asymptomatic, >50 mg/dL, and did not require treatment or medical assistance. Concentration-time profiles suggest a 2-compartment disposition and marked nonlinearity, consistent with target-mediated clearance. REGN1193 inhibited the glucagon-stimulated glucose increase in a dose-dependent manner. The 0.6 mg/kg dose inhibited the glucagon-induced glucose area under the curve for 0 to 90 minutes (AUC_{0-90 minutes} ) by 80% to 90% on days 3 and 15, while blunting the increase in C-peptide. REGN1193 dose-dependently increased total GLP-1, GLP-2 and glucagon, with plasma levels returning to baseline by day 29 in all dose groups.

CONCLUSION

REGN1193, a GCGR-blocking monoclonal antibody, produced a safety, tolerability and PK/PD profile suitable for further clinical development. The occurrence of transient elevations in serum hepatic aminotransferases observed here and reported with several small molecule glucagon receptor antagonists suggests an on-target effect of glucagon receptor blockade. The underlying mechanism is unknown.

Glucagon orchestrates stress-induced hyperglycaemia

Hyperglycaemia is commonly observed on admission and during hospitalization for medical illness, traumatic injury, burn and surgical intervention. This transient hyperglycaemia is referred to as stress-induced hyperglycaemia (SIH) and frequently occurs in individuals without a history of diabetes. SIH has many of the same underlying hormonal disturbances as diabetes mellitus, specifically absolute or relative insulin deficiency and glucagon excess. SIH has the added features of elevated blood levels of catecholamines and cortisol, which are not typically present in people with diabetes who are not acutely ill. The seriousness of SIH is highlighted by its greater morbidity and mortality rates compared with those of hospitalized patients with normal glucose levels, and this increased risk is particularly high in those without pre-existing diabetes. Insulin is the treatment standard for SIH, but new therapies that reduce glucose variability and hypoglycaemia are desired. In the present review, we focus on the key role of glucagon in SIH and discuss the potential use of glucagon receptor blockers and glucagon-like peptide-1 receptor agonists in SIH to achieve target glucose control.

Glycemic response and attainment of A1C goals following newly initiated insulin therapy for type 2 diabetes

OBJECTIVE

To identify the characteristics associated with glycemic response to newly initiated insulin therapy.

RESEARCH DESIGN AND METHODS

We identified 1,139 type 2 diabetic patients who initiated insulin therapy between 1 January 2009 and 30 June 2010. Outcomes of interest were the proportion of patients achieving A1C <7% and mean change in A1C within 3-9 months.

RESULTS

Mean A1C at insulin initiation was 8.2 vs. 9.2% among those who did and did not attain A1C <7% (P < 0.001). Within a mean of 5 months, 464 (40.7%) patients attained A1C <7%. In multivariable analyses controlling for insulin regimen, dose, and oral agent use, preinsulin A1C was responsible for nearly all the explained variance in A1C change. Each one percentage point of preinsulin A1C reduced the probability of attaining <7% by 26% (odds ratio 0.74 [95% CI 0.68-0.80]).

CONCLUSIONS

Insulin initiation at lower levels of A1C improves goal attainment and independently increases glycemic response.

A clinical trial assessing the safety and efficacy of the CB1R inverse agonist taranabant in obese and overweight patients: low-dose study

OBJECTIVE

To evaluate the weight loss efficacy, safety and tolerability of taranabant, a CB1R inverse agonist, in obese and overweight patients.

DESIGN

Multicenter, double-blind, randomized, placebo-controlled study.

SUBJECTS

Patients >or=18 years old, BMI 27-43 kg m(-2), were randomized to placebo (n=209) or taranabant 0.5 mg (n=207), 1 mg (n=208) or 2 mg given orally once daily (n=417) for 52 weeks.

MEASUREMENTS

Key efficacy measurements included body weight (BW), waist circumference (WC), lipid endpoints and glycemic endpoints.

RESULTS

Based on a last observation carried forward analysis of the all-patients-treated population, mean change in BW for taranabant 0.5, 1, and 2 mg and placebo was -5.4, -5.3, -6.7 and -1.7 kg, respectively (P<0.001 for all doses vs placebo). The proportions of patients who lost at least 5 and 10% of their baseline BW at week 52 were significantly higher for all taranabant doses vs placebo (P<0.001 for all doses). Reductions in WC, percentage of body fat, and triglycerides were significant for taranabant 2 mg and in triglycerides for taranabant 1 mg vs placebo. There was no effect of taranabant vs placebo on other lipid or glucose-related endpoints. Incidences of adverse experiences classified in the gastrointestinal (diarrhea and nausea), nervous system (dizziness/dizziness postural), psychiatric-related (irritability and anger/aggression) and vascular (flushing/hot flush) organ systems were higher and statistically significant in the taranabant 2-mg group compared with the placebo group. Irritability was higher and statistically significant in all taranabant groups compared with the placebo group.

CONCLUSION

All three doses of taranabant-induced clinically meaningful and statistically significant weight loss. Incidences of adverse experiences in organ systems known to express CB1R were higher in taranabant groups.

Early treatment-related changes in diabetes and cardiovascular disease risk markers in first episode psychosis subjects

OBJECTIVE

To examine prospective changes in cardiovascular disease (CVD) and type-2 diabetes risk factors in young adult first episode psychotic (FEP) patients treated with second generation antipsychotic medications.

METHODS

At baseline, fasting serum and anthropometric measures were obtained from 45 FEP patients and 41 healthy adults (controls) of similar age, ethnicity and sex; sixteen of the FEP patients remained on the same antipsychotic medication and were available for a second blood draw at 24 weeks of treatment. Serum was assayed for glucose, insulin, triglycerides, total cholesterol and high and low density lipoproteins (HDL, LDL), adiponectin, leptin, interleukin 6, E-selectin and VCAM-1. Wilcoxon nonparametric tests were used to compare risk markers between the FEP and control group at baseline and to evaluate pre-post treatment changes within the FEP group.

RESULTS

At baseline, the distributions of risk marker values were similar between the two groups and the percentages of FEP patients and healthy controls who were overweight/obese, dyslipidemic, hyperglycemic, and hyperinsulinemic did not differ. At 24 weeks, compared to baseline, FEP patients showed significant increases in BMI (p=0.0002), glucose (p=0.0449), insulin (p=0.0161), cholesterol (p=0.0129), leptin (p=0.0215), and E-selectin (p=0.0195), and a decrease in adiponectin (p=0.0371).

CONCLUSIONS

Among patients with first episode psychosis, 6-month treatment with second generation antipsychotics is associated with the exacerbation of pre-existing and emergence of new CVD and diabetes risk factors.

Adipose-specific disruption of signal transducer and activator of transcription 3 increases body weight and adiposity

To determine the role of STAT3 in adipose tissue, we used Cre-loxP DNA recombination to create mice with an adipocyte-specific disruption of the STAT3 gene (ASKO mice). aP2-Cre-driven disappearance of STAT3 expression occurred on d 6 of adipogenesis, a time point when preadipocytes have already undergone conversion to adipocytes. Thus, this knockout model examined the role of STAT3 in mature but not differentiating adipocytes. Beginning at 9 wk of age, ASKO mice weighed more than their littermate controls and had increased adipose tissue mass, associated with adipocyte hypertrophy, but not adipocyte hyperplasia, hyperphagia, or reduced energy expenditure. Leptin-induced, but not isoproterenol-induced, lipolysis was impaired in ASKO adipocytes, which may partially explain the increased cell size. Despite reduced adiponectin and increased liver triacylglycerol, ASKO mice displayed normal glucose tolerance. Overall, these findings demonstrate that adipocyte STAT3 regulates body weight homeostasis in part through direct effects of leptin on adipocytes.

Increased energy expenditure, dietary fat wasting, and resistance to diet-induced obesity in mice lacking renin

An overactive renin-angiotensin system is associated with obesity and the metabolic syndrome. However, the mechanisms behind it are unclear. Cleaving angiotensinogen to angiotensin I by renin is a rate-limiting step of angiotensin II production, but renin is suggested to have angiotensin-independent effects. We generated mice lacking renin (Ren1c) using embryonic stem cells from C57BL/6 mice, a strain prone to diet-induced obesity. Ren1c(-/-) mice are lean, insulin sensitive, and resistant to diet-induced obesity without changes in food intake and physical activity. The lean phenotype is likely due to a higher metabolic rate and gastrointestinal loss of dietary fat. Most of the metabolic changes in Ren1c(-/-) mice were reversed by angiotensin II administration. These results support a role for angiotensin II in the pathogenesis of diet-induced obesity and insulin resistance.

Diet-induced obese mice have increased mortality and altered immune responses when infected with influenza virus

Obesity is associated with an impaired immune response, an increased susceptibility to bacterial infection, and a chronic increase in proinflammatory cytokines such as IL-6 and TNFalpha. However, few studies have examined the effect of obesity on the immune response to viral infections. Because infection with influenza is a leading cause of morbidity and mortality worldwide, we investigated the effect of obesity on early immune responses to influenza virus exposure. Diet-induced obese and lean control C57BL/6 mice were infected with influenza A/PR8/34, and lung pathology and immune responses were examined at d 0 (uninfected), 3, and 6, postinfection. Following infection, diet-induced obese mice had a significantly higher mortality rate than the lean controls and elevated lung pathology. Antiviral and proinflammatory cytokine mRNA production in the lungs of the infected mice was markedly different between obese and lean mice. IFNalpha and beta were only minimally expressed in the infected lungs of obese mice and there was a notable delay in expression of the proinflammatory cytokines IL-6 and TNFalpha. Additionally, obese mice had a substantial reduction in NK cell cytotoxicity. These data indicate that obesity inhibits the ability of the immune system to appropriately respond to influenza infection and suggests that obesity may lead to increased morbidity and mortality from viral infections.

Midkine is an autocrine activator of signal transducer and activator of transcription 3 in 3T3-L1 cells

Mitotic clonal expansion is believed to be necessary for 3T3-L1 adipocyte formation. Signal transducer and activator of transcription 3 (STAT3), a mitogenic signaling protein, is activated through tyrosine phosphorylation during the proliferative phases of adipogenesis. We hypothesize that this signaling protein plays a key role in mitotic clonal expansion and differentiation. Here we determined that the adipocyte differentiation cocktail containing isobutylmethylxanthine, dexamethasone, and insulin (MDI) induced STAT3 tyrosine phosphorylation indirectly through the synthesis of an autocrine/paracrine factor. We further determined that the factor has heparin binding properties and identified the factor as midkine, a pleiotrophic growth factor previously associated with neuronal development and oncogenesis. Recombinant midkine induced STAT3 tyrosine phosphorylation in a time- and dose-dependent manner and stimulated the proliferation of postconfluent 3T3-L1 cells. Midkine neutralizing antibodies inhibited differentiation-induced STAT3 tyrosine phosphorylation as well as adipogenesis. These results show that MDI-induced synthesis and release of midkine explains the delayed activation of STAT3 during adipogenesis and that the midkine-STAT3 signaling pathway plays a necessary role in mitotic clonal expansion and differentiation.

Why do obese patients not lose more weight when treated with low-calorie diets? A mechanistic perspective

Maximal weight loss observed in low-calorie diet (LCD) studies tends to be small, and the mechanisms leading to this low treatment efficacy have not been clarified. Less-than-expected weight loss with LCDs can arise from an increase in fractional energy absorption (FEA), adaptations in energy expenditure, or incomplete patient diet adherence. We systematically reviewed studies of FEA and total energy expenditure (TEE) in obese patients undergoing weight loss with LCDs and in patients with reduced obesity (RO), respectively. This information was used to support an energy balance model that was then applied to examine patient adherence to prescribed LCD treatment programs. In the limited available literature, FEA was unchanged from baseline in short-term (<12 wk) treatment studies with LCDs; no long-term (>or=26 wk) studies were found. Review of doubly labeled water and respiratory chamber studies identified 10 reports of TEE in RO patients (n = 150) with long-term weight loss. These patients, who were weight stable, had a TEE almost identical to measured or predicted values in never-obese subjects (weighted mean difference: 1.3%; range: -1.7-8.5%). Modeling of energy balance, as supported by reviewed FEA and TEE studies, suggests that obese subjects participating in LCD programs have a weight loss less than half of that predicted. The small maximal weight loss observed with LCD treatments thus is likely not due to gastrointestinal adaptations but may be attributed, by deduction, to difficulties with patient adherence or, to a lesser degree, to metabolic adaptations induced by negative energy balance that are not captured by the current models.

How much may I eat? Calorie estimates based upon energy expenditure prediction equations

How much may I eat? Most healthcare workers, when asked this question, have insufficient knowledge to educate their patients on a healthy energy intake level. In this review we examine the available methods for estimating adult energy requirements with a focus on the newly developed National Academy of Sciences/Institute of Medicine (NAS/IOM) doubly-labelled water total energy expenditure (TEE) prediction equations. An overview is first provided of the traditional factorial method of estimating energy requirements. We then extend this overview by exploring the development of the NAS/IOM TEE prediction models and their role in estimating energy requirements as a function of sex, age, weight, height and physical activity level. The NAS/IOM prediction models were developed for evaluating group energy requirements, although the formulas can be applied in individual 'example' patients for educational purposes. Potential limitations and interpretation issues of both the factorial and NAS/IOM methods are examined. This information should provide healthcare professionals with the tools and understanding to appropriately answer the question, 'How much may I eat?'

Protein inhibitor of activated STAT3 inhibits adipogenic gene expression

Protein inhibitor of activated STAT3 (PIAS3), a cytokine-induced repressor of signal transducer and activator of transcription 3 (STAT3) and a modulator of a broad array of nuclear proteins, is expressed in white adipose tissue, but its role in adipogenesis is not known. Here, we determined that PIAS3 was constitutively expressed in 3T3-L1 cells at all stages of adipogenesis. However, it translocated from the nucleus to the cytoplasm 4 days after induction of differentiation by isobutylmethylxanthine, dexamethasone, and insulin (MDI). In ob/ob mice, PIAS3 expression was increased in white adipose tissue depots compared to lean mice and was found in the cytoplasm of adipocytes. Overexpression of PIAS3 in differentiating preadipocytes, which localized primarily to the nucleus, inhibited mRNA level gene expression of adipogenic transcription factors C/EBPalpha and PPARgamma, as well as their downstream target genes aP2 and adiponectin. PIAS3 also inhibited C/EBPalpha promoter activation mediated specifically by insulin, but not dexamethasone or isobutylmethylxanthine. Taken together, these data suggest that PIAS3 may play an inhibitory role in adipogenesis by modulating insulin-activated transcriptional activation events. Increased PIAS3 expression in adipose tissue may play a role in the metabolic disturbances of obesity.

Double-blind, placebo-controlled investigation of amantadine for weight loss in subjects who gained weight with olanzapine

OBJECTIVE

This study sought to determine if amantadine affects weight gain in psychiatric patients taking olanzapine.

METHOD

Twenty-one adults who had gained at least 5 lb with olanzapine were randomly assigned to receive amantadine (N=12) or placebo (N=9) in addition to olanzapine. The length of time taking olanzapine ranged from 1 to 44 months. Body mass index, psychiatric status, and fasting blood levels were assessed at baseline and 12 weeks.

RESULTS

Significantly fewer subjects taking amantadine gained weight, with a mean change in body mass index of -0.07 kg/m2 for the amantadine group and 1.24 kg/m2 for the placebo group. This effect remained significant when the authors controlled for baseline body mass index and length of olanzapine treatment. No changes in fasting glucose, insulin, leptin, prolactin, and lipid levels were seen. Positive and Negative Syndrome Scale scores remained stable.

CONCLUSIONS

Amantadine induced weight stabilization in subjects taking olanzapine and was well tolerated.

Effect of olanzapine on body composition and energy expenditure in adults with first-episode psychosis

OBJECTIVE

Weight gain is a commonly observed adverse effect of atypical antipsychotic medications, but associated changes in energy balance and body composition are not well defined. The authors report here the effect of olanzapine on body weight, body composition, resting energy expenditure, and substrate oxidation as well as leptin, insulin, glucose, and lipid levels in a group of outpatient volunteers with first-episode psychosis.

METHOD

Nine adults (six men and three women) experiencing their first psychotic episode who had no previous history of antipsychotic drug therapy began a regimen of olanzapine and were studied within 7 weeks and approximately 12 weeks after olanzapine initiation.

RESULTS

After approximately 12 weeks of olanzapine therapy, the median increase in body weight was 4.7 kg, a significant increase of 7.3% from first observation. Body fat, measured by dual-energy x-ray absorptiometry, increased significantly, with a propensity for central fat deposition. Lean body mass and bone mineral content did not change. Resting energy expenditure, measured by indirect calorimetry, did not change. Respiratory quotient significantly increased 0.12 with olanzapine and was greatest in those who gained >5% of their initial weight. Fasting insulin, C-peptide, and triglyceride levels significantly increased, but there were no changes in glucose levels; total, high density lipoprotein, or low density lipoprotein cholesterol levels; or leptin levels.

CONCLUSIONS

Olanzapine appears to have induced an increase in central body fat deposition, insulin, and triglyceride levels, suggesting the possible development of insulin resistance. The decrease in fat oxidation may be secondary or predispose patients to olanzapine-induced weight gain.

Interleukin-4 inhibits platelet-derived growth factor-induced preadipocyte proliferation

Interleukin-4 (IL-4) activates STAT6 in 3T3-L1 preadipocytes but its functional role is not known. In this report, we first assessed interleukin-4 receptor alpha (IL-4Ralpha) expression during adipogenesis. IL-4Ralpha was highly expressed in proliferating 3T3-L1 preadipocytes. Receptor expression was down-regulated in post-confluent growth arrested preadipocytes. Induction of differentiation led to a transient 36-h increase in expression, but then levels decreased to undetectable amounts 3-8 days after induction of differentiation. Depending on the cell type, IL-4 either increases or decreases cell proliferation. In growth arrested preconfluent 3T3-L1 preadipocytes, IL-4 alone had no effect on preadipocyte proliferation. In contrast, IL-4 inhibited platelet-derived growth factor (PDGF-BB) induced preadipocyte proliferation. PDGF-BB, but not IL-4, induced STAT3 tyrosine and AKT serine phosphorylation. Both PDGF-BB and IL-4 induced STAT6 tyrosine phosphorylation, but the bands showed distinct electrophoretic migration patterns. IL-4 alone and IL-4 added to the differentiation cocktail had no effect on adipocyte formation or PPARgamma expression. Collectively, these studies demonstrate that IL-4 inhibits PDGF-BB-induced preadipocyte proliferation, possibly through STAT6 activation. The pattern of IL-4 receptor expression suggests that the effects of IL-4 are targeted primarily towards preadipocytes.

New insights into inhibitors of adipogenesis

PURPOSE OF REVIEW

Adipose tissue is a dynamic organ that changes mass throughout life in response to the metabolic needs of the animal. In the past three decades, significant advances have been made in delineating key extracellular and intracellular stimulators of fat cell formation or adipogenesis. In this review, the author focuses on new findings of specific inhibitors of adipogenesis. Understanding the balance between positive and negative regulators of adipogenesis has important health-related implications for anti-obesity medical therapy and lipodystrophy.

RECENT FINDINGS

Adipogenesis is a highly regulated process requiring coordinated expression and activation of two main groups of adipogenic transcription factors, CCAAT/enhancer binding proteins and peroxisome proliferators activated receptor gamma. In response to hormonal and nutrient stimuli, the increased expression and activation of these transcription factors induce the expression of adipocyte-specific genes. More recently, several groups have identified extracellular inhibitors of adipocyte formation, including cytokines, lipid molecules, genistein, and protease inhibitors. Intracellular signaling molecules, which negatively regulate adipogenesis, include Pref-1, Foxo1, Foxa2, SMAD-3, WNT-10b, GATA-2 and GATA-3.

SUMMARY

The prevalence of obesity is increasing in the United States and in other westernized societies. Understanding the mechanisms of excessive energy storage in adipose tissue is necessary to develop a comprehensive strategy to prevent and treat obesity. One potential, but unrealized, approach to obesity treatment is to target excessive adipose tissue enlargement. A number of promising extra- and intracellular inhibitors of fat cell formation have been identified, but the modulation of adipose tissue mass may have both advantageous and deleterious health effects.

Rb regulates C/EBPβ-DNA-binding activity during 3T3-L1 adipogenesis

Two pathways are initiated upon 3T3-L1 preadipocyte differentiation: the reentry of cells into the cell cycle and the initiation of a cascade of transcriptional events that “prime” the cell for differentiation. The “priming” event involves the synthesis of members of the CCAAT/enhancer binding protein (C/EBP) family of transcription factors. However, the relationship between these two pathways is unknown. Here we report that in the 3T3-L1 preadipocytes induced to differentiate, cell cycle progression and the initiation of differentiation are linked by a cell cycle-dependent Rb-C/EBPβ interaction. Cell cycle arrest in G1 by l-mimosine inhibited differentiation-induced C/EBPβ-DNA-binding activity and Rb phosphorylation. However, cell cycle arrest after the G1/S transition by aphidicolin or nocodazole did not prevent C/EBPβ-DNA-binding activity or Rb phosphorylation. Furthermore, hypophosphorylated Rb and C/EBPβ coimmunoprecipitated, whereas phosphorylated Rb and C/EBPβ did not. Electrophoretic mobility shift assays demonstrated that recombinant hypophosphorylated Rb decreased C/EBPβ-DNA-binding activity and that Rb overexpression inhibited C/EBPβ-induced transcriptional activation of a C/EBPα-promoter-luciferase reporter gene. We conclude that C/EBPβ-DNA-binding activity is regulated by its interaction with hypophosphorylated Rb, thereby linking the progression of the cell cycle to the initiation of differentiation during 3T3-L1 adipogenesis.

Genistein inhibits CCAAT/enhancer-binding protein beta (C/EBPbeta) activity and 3T3-L1 adipogenesis by increasing C/EBP homologous protein expression

The tyrosine kinase inhibitor genistein inhibits 3T3-L1 adipogenesis when present during the first 72 h of differentiation. In this report, we investigated the underlying mechanisms involved in the anti-adipogenic effects of genistein. We found that genistein blocked the DNA binding and transcriptional activity of CCAAT/enhancer-binding protein beta (C/EBPbeta) during differentiation by promoting the expression of C/EBP homologous protein, a dominant-negative member of the C/EBP family. Loss of C/EBPbeta activity was manifested as a loss of differentiation-induced C/EBPalpha and peroxisome-proliferator-activated receptor gamma protein expression and a dramatic reduction in lipid accumulation. Further, we documented for the first time that C/EBPbeta was tyrosine-phosphorylated in vivo during differentiation and in vitro by activated epidermal growth factor receptor. Genistein inhibited both of these events. Collectively, these results indicate that genistein blocks adipogenesis and C/EBPbeta activity by increasing the level of C/EBP homologous protein and possibly by inhibiting the tyrosine phosphorylation of C/EBPbeta.

Dietary weight loss decreases serum angiotensin-converting enzyme activity in obese adults

OBJECTIVE

To study the effect of dietary weight loss, postural change, and an oral glucose load on serum angiotensin-converting enzyme (ACE) activity in obese adults.

RESEARCH METHODS AND PROCEDURES

Sixteen obese adult men and women with a mean body mass index of 35.7 +/- 4.3 kg/m(2) were studied after 1 week on a maintenance energy lead-in diet and after 5 weeks on an identical but 40% reduced-energy diet provided by the General Clinical Research Center (GCRC). ACE activity was measured spectrophotometrically. Plasma renin activity and serum aldosterone were measured by radioimmunoassay.

RESULTS

All subjects lost weight, with a mean decrease in body weight of 7.0 +/- 2.1 kg or 6 +/- 3% of initial body weight (p < 0.00001). Systolic and diastolic blood pressure, supine plasma renin activity, and serum aldosterone levels decreased with weight loss (p < 0.05). Supine ACE activity decreased 23 +/- 12% with weight loss (p < 0.00001). Standing ACE activity, which was significantly higher than supine ACE activity before and after weight loss (p < 0.05), also decreased 18 +/- 17% with weight loss (p = 0.0007). A 75-g oral glucose load had no effect on serum ACE activity over a 3-hour period.

DISCUSSION

In obese adults, serum ACE activity declines with modest weight loss, increases with postural change, and is unaffected by an oral glucose load.

Differential effects of flavonoids on 3T3-L1 adipogenesis and lipolysis

Flavonoids, polyphenolic compounds that exist widely in plants, inhibit cell proliferation and increase cell differentiation in many cancerous and noncancerous cell lines. Because terminal differentiation of preadipocytes to adipocytes depends on proliferation of both pre- and postconfluent preadipocytes, we predicted that flavonoids would inhibit adipogenesis in the 3T3-L1 preadipocyte cell line. The flavonoids genistein and naringenin inhibited proliferation of preconfluent preadipocytes in a time- and dose-dependent manner. When added to 2-day postconfluent preadipocytes at the induction of differentiation, genistein inhibited mitotic clonal expansion, triglyceride accumulation, and peroxisome proliferator-activated receptor-gamma expression, but naringenin had no effect. The antiadipogenic effect of genistein was not due to inhibition of insulin receptor subtrate-1 tyrosine phosphorylation. When added 3 days after induction of differentiation, neither flavonoid inhibited differentiation. In fully differentiated adipocytes, genistein increased basal and epinephrine-induced lipolysis, but naringenin had no significant effects. These data demonstrate that genistein and naringenin, despite structural similarity, have differential effects on adipogenesis and adipocyte lipid metabolism.

Differential expression of signal transducers and activators of transcription during human adipogenesis

Signal Transducers and Activators of Transcription (STATs) display unique expression patterns upon induction of differentiation of murine 3T3-L1 preadipocytes into adipocytes. During differentiation, expression of STAT1 and STAT5 increase, while STAT3 and STAT6 remain relatively unchanged. Here, we determined whether human subcutaneous preadipocytes expressed STATs and if the pattern of expression changed during adipogenesis. We found by Western blot analysis that freshly isolated preadipocytes expressed STAT1, STAT3, STAT5, and STAT6, but not STAT2 and STAT4. Induction of preadipocyte differentiation with 1-methyl-3-isobutylxanthine, dexamethasone, insulin, and BRL49653 decreased expression of STAT1, and increased expression of STAT3 and STAT5. STAT6 expression did not change during adipogenesis. Changes in expression of CCAAT/enhancer binding protein beta (C/EBPbeta), C/EBPdelta, C/EBPalpha, and peroxisome proliferator-activated receptor gamma were similar to murine cell lines. These results suggest that unlike the traditional adipogenic transcription factors, unique differences exist in STAT expression patterns between murine and human adipose cells.

Activation of signal transducer and activator of transcription-3 during proliferative phases of 3T3-L1 adipogenesis

Signal transducer and activator of transcription-3 (STAT3) is abundantly expressed in preadipocytes and adipocytes, but little is known about its activation status or functional role during adipogenesis. In this report we investigate STAT3 activation in 3T3-L1 preadipocytes before and after differentiation into adipocytes. STAT3 was highly tyrosine phosphorylated and bound to DNA in proliferating preadipocytes, but not in growth-arrested preadipocytes or adipocytes. In growth-arrested confluent preadipocytes, induction of differentiation with methylisobutylxanthine, dexamethasone, and high dose insulin led to a delayed, but prolonged (3-day), increase in STAT3 tyrosine phosphorylation. This increase in STAT3 phosphorylation coincided temporally with postconfluent preadipocyte mitotic clonal expansion. Insulin and methylisobutylxanthine alone, but not dexamethasone, induced STAT3 tyrosine phosphorylation in postconfluent cells. Diminution of endogenous STAT3 expression by antisense morpholino oligonucleotides significantly decreased preconfluent preadipocyte proliferation. Collectively, these findings suggest a regulatory role for STAT3 during the proliferative phases of adipogenesis.

Interleukin-4 mediates STAT6 activation in 3T3-L1 preadipocytes but not adipocytes

STAT6 is abundantly expressed in 3T3-L1 preadipocytes and adipocytes but activating ligands are not well defined. In this report, we provide evidence that interleukin 4 (IL-4) induced JAK2-mediated STAT6 tyrosine phosphorylation and DNA binding in 3T3-L1 preadipocytes but not in 3T3-L1 adipocytes. Loss of IL-4-mediated STAT6 tyrosine phosphorylation occurred 2 days after preadipocytes were induced to differentiate into adipocytes but when cells remained phenotypically preadipocytes. 3T3-L1 adipocytes were still responsive to IL-4 through tyrosine phosphorylation of other cellular proteins. We conclude that IL-4 signals through STAT6 in 3T3-L1 preadipocytes but not in 3T3-L1 adipocytes. This differentiation-dependent loss of STAT6 activation may be critical for distinct biological effects of IL-4 in 3T3-L1 preadipocytes and adipocytes.

Orlistat for the long-term treatment of obesity

Orlistat, a potent gastrointestinal lipase inhibitor, is a member of a new class of drugs designed for the long-term treatment of obesity. When given with a fat-containing meal, orlistat reduces dietary fat absorption by approximately 30%, which equates to a decrease in caloric absorption of approximately 200 kilocalories per day. A 2-year European study found a mean decrease in body weight of 10.2% (10.3 kg) in the orlistat group compared to 6.1% (6.1 kg) in the placebo group at 1 year. Additionally, 9.3% of the orlistat group versus 2.1% of the placebo group lost >20% of their initial weight. Serum lipids and diabetes control are also improved by orlistat. Related to orlistat's mechanism of action, side effects include oily spotting, flatulence and frequent loose stools, but not frank diarrhea or intestinal malabsorption. Vitamin D and beta-carotene levels decreased, but remained within the normal range. In summary, orlistat is the first example of a new class of antiobesity drugs that enhances weight loss and weight maintenance by interfering with dietary fat absorption. Orlistat has tolerable gastrointestinal side effects and no major drug toxicity. Orlistat is a viable adjunct to lifestyle interventions used in the long-term management of obesity.

Phosphorylation of p130Cas by angiotensin II is dependent on c-Src, intracellular Ca2+, and protein kinase C

p130Cas is a signaling molecule that was initially found to be tyrosine-phosphorylated in v-Crk and v-Src transformed cells. We characterized the regulation of p130Cas tyrosine phosphorylation in vascular smooth muscle cells by angiotensin II (Ang II). This ligand induced a transient increase in p130Cas tyrosine phosphorylation, which was sensitive to the actin polymerization inhibitor cytochalasin D and to the intracellular Ca2+ chelator BAPTA-AM but not the Ca2+ channel blocker verapamil. The Ang II-induced tyrosine phosphorylation of p130Cas was also dependent on an active Src family tyrosine kinase, since it could be blocked by the Src kinase inhibitors geldanamycin and PP1. Ang II treatment resulted in the ability of p130Cas to bind at least 11 different phosphate-containing proteins. Analysis of these proteins revealed that protein kinase Calpha and the cell adhesion signaling molecule pp120 formed temporal associations with p130Cas in response to Ang II. c-Src was found to associate with p130Cas in a manner that was independent of Ang II treatment. Inhibition of protein kinase C by either calphostin C or phorbol 12-myristate 13-acetate downregulation inhibited the Ang II-induced tyrosine phosphorylation of p130Cas. These results are the first to demonstrate that the tyrosine phosphorylation of p130Cas by Ang II is transduced by the Src, intracellular Ca2+, protein kinase C signaling pathway.

Angiotensin II-induced association of phospholipase Cgamma1 with the G-protein-coupled AT1 receptor

An early event in signaling by the G-protein-coupled angiotensin II (Ang II) AT1 receptor in vascular smooth muscle cells is the tyrosine phosphorylation and activation of phospholipase Cgamma1 (PLCgamma1). In the present study, we show that stimulation of this event by Ang II in vascular smooth muscle cells is accompanied by binding of PLCgamma1 to the AT1 receptor in an Ang II- and tyrosine phophorylation-dependent manner. The PLCgamma1-AT1 receptor interaction appears to depend on phosphorylation of tyrosine 319 in a YIPP motif in the C-terminal intracellular domain of the AT1 receptor and binding of the phosphorylated receptor by the most C-terminal of two Src homology 2 domains in PLCgamma1. PLCgamma1 thus binds to the same site in the receptor previously identified for binding by the SHP-2 phosphotyrosine phosphatase.JAK2 tyrosine kinase complex. A single site in the C-terminal tail of the AT1 receptor can, therefore, be bound in a ligand-dependent manner by two different downstream effector proteins. These data demonstrate that G-protein-coupled receptors can physically associate with intracellular proteins other than G proteins, creating membrane-delimited signal transduction complexes similar to those observed for classic growth factor receptors.

Role of Janus kinase/signal transducer and activator of transcription and mitogen-activated protein kinase cascades in angiotensin II- and platelet-derived growth factor-induced vascular smooth muscle cell proliferation

In vascular smooth muscle cells, the induction of early growth response genes involves the Janus kinase (JAK)/signal transducer and activators of transcription (STAT) and the Ras/Raf-1/mitogen-activated protein kinase cascades. In the present study, we found that electroporation of antibodies against MEK1 or ERK1 abolished vascular smooth muscle cell proliferation in response to either platelet-derived growth factor or angiotensin II. However, anti-STAT1 or -STAT3 antibody electroporation abolished proliferative responses only to angiotensin II and not to platelet-derived growth factor. AG-490, a specific inhibitor of the JAK2 tyrosine kinase, prevented proliferation of vascular smooth muscle cells, complex formation between JAK2 and Raf-1, the tyrosine phosphorylation of Raf-1, and the activation of ERK1 in response to either angiotensin II or platelet-derived growth factor. However, AG-490 had no effect on angiotensin II- or platelet-derived growth factor-induced Ras/Raf-1 complex formation. Our results indicate that: 1) STAT proteins play an essential role in angiotensin II-induced vascular smooth muscle cell proliferation, 2) JAK2 plays an essential role in the tyrosine phosphorylation of Raf-1, and 3) convergent mitogenic signaling cascades involving the cytosolic kinases JAK2, MEK1, and ERK1 mediate vascular smooth muscle cell proliferation in response to both growth factor and G protein-coupled receptors.

Role of intracellular calcium in the angiotensin II-mediated tyrosine phosphorylation and dephosphorylation of PLC-gamma 1

Angiotensin II induces the rapid temporal tyrosine phosphorylation and activation of phospholipase C-gamma 1 (PLC-gamma 1) and the elevation of intracellular calcium levels. To investigate the relationship of these intracellular signaling events, rat aortic smooth muscle cells were treated with the calcium chelator BAPTA-AM, the calcium channel blocker verapamil, the intracellular calcium antagonist TMB-8, and the calcium ionophore ionomycin. The effects of these agents on PLC-gamma 1 tyrosine phosphorylation were then measured. We found that treatment of these cells with the calcium inhibitors augmented the basal level of PLC-gamma 1 tyrosine phosphorylation, without changing the peak level of tyrosine phosphorylation induced by angiotensin II. The rapid dephosphorylation of PLC-gamma 1 that follows angiotensin II stimulation was prevented by these calcium antagonists. In contrast, angiotensin II-induced tyrosine phosphorylation of PLC-gamma 1 was inhibited by ionomycin. These results suggest that the angiotensin II-induced tyrosine phosphorylation of PLC-gamma 1 is calcium-independent, while the dephosphorylation is calcium-dependent.

Components of the renin-angiotensin system in adipose tissue: changes with maturation and adipose mass enlargement

White adipose tissue is a rich source of angiotensinogen protein and mRNA. Studies in clonal cells suggest that angiotensinogen, and its cleavage product, angiotensin II, are involved in preadipocyte differentiation into mature fat cells. No studies have determined whether angiotensinogen is also involved in adipose tissue development in vivo. In this report, we studied male Wistar rats at two stages of development to determine if angiotensinogen protein and mRNA are increased in retroperitoneal fat depots of rapidly growing young, lean, 8-week-old rats compared to 26-week-old rats that are fatter, but are undergoing less rapid adipose tissue growth. We also assessed renin mRNA and angiotensin I-generating activity, since it is less clear whether renin is locally produced in adipose tissue. We found that angiotensin I-generating activity was measurable in adipose tissue and adipocytes, but renin mRNA was undetectable by northern blot analysis. Angiotensinogen mRNA was abundant in adipocytes, but was absent in stromal-vascular cells of adipose tissue. Angiotensinogen content per 10 million fat cells was approximately threefold higher in 8-week-old rats compared to 26-week-old rats (p < .0002). Angiotensinogen mRNA was approximately twofold higher in adipocytes of 8-week-old rats compared to 26-week-old rats. The age-related decline in angiotensinogen protein and mRNA indicates that the local renin-angiotensin system may play an important role in adipose tissue growth, and possibly contribute to the changes in adipose mass and cellularity seen in old senescent rats.

Simplified enzymatic assay of angiotensin-converting enzyme in serum

We report a simple, enzymatic method for determining angiotensin-converting enzyme (ACE; EC 3.4.15.1) in serum. The proposed method features coupling an established reaction catalyzed by gamma-glutamyltransferase (GGT; EC 2.3.2.2) to the ACE reaction, which releases glycylglycine from the artificial substrate hippuryl-glycyl-glycine. The glycyl-glycine released by the ACE reaction becomes rate-limiting in the GGT reaction, in which it participates as a receptor substrate for a gamma-glutamyl group transferred from a donor substrate, L-gamma-glutamyl-3-carboxy-4-nitroanilide. The reaction releases 3-carboxy-4-nitroaniline, which is monitored spectrophotometrically at 410 nm. The resulting rate of change in absorbance is linearly related to the glycyl-glycine concentration and therefore to the activity of ACE. The linear range of the method extends from ACE values &lt; 50 to at least 1300 U/L of serum. Good precision is indicated by a low CV for replicate analyses (3.6% and 4.6% for within-run and day-to-day assays, respectively, for normal ACE activity, and 3.1% within-run for high ACE activity). Results also correlate well with those of an established colorimetric method (r = 0.978). The major advantages of the method are its procedural simplicity, limited cost, use of readily available reagents, applicability to isoenzyme studies, and adaptability to automation.

Simplified enzymatic assay of angiotensin-converting enzyme in serum

We report a simple, enzymatic method for determining angiotensin-converting enzyme (ACE; EC 3.4.15.1) in serum. The proposed method features coupling an established reaction catalyzed by gamma-glutamyltransferase (GGT; EC 2.3.2.2) to the ACE reaction, which releases glycylglycine from the artificial substrate hippuryl-glycyl-glycine. The glycyl-glycine released by the ACE reaction becomes rate-limiting in the GGT reaction, in which it participates as a receptor substrate for a gamma-glutamyl group transferred from a donor substrate, L-gamma-glutamyl-3-carboxy-4-nitroanilide. The reaction releases 3-carboxy-4-nitroaniline, which is monitored spectrophotometrically at 410 nm. The resulting rate of change in absorbance is linearly related to the glycyl-glycine concentration and therefore to the activity of ACE. The linear range of the method extends from ACE values < 50 to at least 1300 U/L of serum. Good precision is indicated by a low CV for replicate analyses (3.6% and 4.6% for within-run and day-to-day assays, respectively, for normal ACE activity, and 3.1% within-run for high ACE activity). Results also correlate well with those of an established colorimetric method (r = 0.978). The major advantages of the method are its procedural simplicity, limited cost, use of readily available reagents, applicability to isoenzyme studies, and adaptability to automation.

Nutrition and somatomedin. XXII: Molecular regulation of insulin-like growth factor-I during fasting and refeeding in rats

The liver is thought to be the locus of nutritional/hormonal regulation of circulating insulin-like growth factor-I (IGF-I). To probe the basis of nutritional regulation, we examined changes in serum IGF-I, hepatic content of extractable IGF-I immunoreactivity (a high Mr putative precursor) and hepatic IGF-I mRNA during fasting and refeeding in rats. Preliminary studies revealed that the hepatic level of IGF-I mRNA was consistently reduced only after food was withheld for 3 days, so the effects of refeeding were subsequently examined in such animals. After 3 days of fasting, animals lost 30% of their initial weight; weight regain was apparent within 3 h of refeeding ad libitum and, after 48 h, weight was comparable to initial fed levels. Fasting reduced levels of serum and extractable hepatic IGF-I to 19 and 26% of control (fed) values respectively (both P less than 0.005 vs control). There was no change in levels of serum IGF-I over the first 3 h of refeeding, but IGF-I rose above fasted levels at both 9 and 48 h (both P less than 0.005). Extractable hepatic IGF-I rose more slowly and was still below fasted levels after 9 h of refeeding, and modestly, but not significantly, greater than fasted levels after 48 h. The ratio of serum to hepatic IGF-I was decreased compared with control after 3 days of fasting, but increased after 3 and 9 h of refeeding (P less than 0.02 at 9 h). Northern blot analysis of total hepatic RNA revealed four species of IGF-I mRNA 0.8-1.1, 2.0, 4.0 and 7.5 kb in size. Each mRNA species fell to 15-28% of control levels after 3 days of fasting (all P less than 0.001). There was a prompt increase in each transcript after 3 h of refeeding, and all values were significantly (P less than 0.05) greater than fasted levels at 9 h but, at 48 h, most species were still below control levels. Levels of mRNA for the cytoskeletal proteins beta-actin and cyclophilin also fell with fasting, but were restored more rapidly than IGF-I mRNA, to or above control levels after 3 h of refeeding. The observation that IGF-I expression was decreased at 3 h when beta-actin and cyclophilin were normalized suggests specificity of regulation. Despite the temporal incongruity between IGF-I mRNA and serum and hepatic IGF-I, there were highly significant correlations (all P less than 0.002) between each pair of parameters.(ABSTRACT TRUNCATED AT 400 WORDS)

Nutrition and somatomedin. XXIII. Molecular regulation of IGF-I by amino acid availability in cultured hepatocytes

The poor growth associated with protein-calorie malnutrition occurs despite circulating growth hormone levels that are normal or elevated and is thought to be mediated partly by blunted generation of insulinlike growth factor I (IGF-I) in the liver. To explore underlying mechanisms, we asked whether altered availability of amino acids could regulate hepatic IGF-I release independent of the contributions of regulatory hormones. Normal rat hepatocytes were isolated by collagenase digestion and maintained in serum-free medium with fixed concentrations of insulin and dexamethasone. Levels of immunoassayable albumin and IGF-I accumulation in daily changes of medium were sustained for 3-5 days, and all studies were performed within this period. Cellular viability and content of DNA were unaffected by deprivation of the essential amino acids lysine or tryptophan and the nonessential amino acids cysteine and/or cystine. However, deletion of tryptophan or lysine from the culture medium led to 63 and 76% declines in IGF-I release, respectively (both P less than 0.001 vs. complete medium), although omission of cysteine or cysteine plus cystine produced no significant change. Over 5 days of culture, release of albumin was maintained in complete medium, but omission of tryptophan depressed albumin release over days 2-5 (P less than 0.001). In complete medium, IGF-I release rose for 3 days and then declined. In tryptophan-deficient medium, IGF-I levels were comparable to control values after 24 h but did not rise at 48 h and then fell rapidly after 72 h in culture, with values significantly below levels in complete medium (all P less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation and action of insulin-like growth factors at the cellular level

Present understanding of IGF-1 as a growth factor mediating integration of nutritional-hormonal interactions indicates that IGF-1 acts in both an endocrine mode on distant targets and an autocrine-paracrine mode on local targets. In the liver, the combined presence of GH, insulin, and critical metabolic fuels such as essential amino acids results in increased levels of IGF-1 messenger RNA, increased production of a high-MW IGF-1 precursor, and increased release of IGF-1 into the circulation, permitting action on distant target tissues bearing specific receptors for IGF-1. The net effect is distant amplification of anabolic hormone action via IGF-1 acting in an endocrine mode. In extrahepatic tissues, both 'general' anabolic hormones (insulin and GH) as well as 'specific' hormones (e.g. gonadotropins) acting on a wide variety of targets (including fibroblasts and chondrocytes as well as granulosa and Leydig cells) promote both local secretion of IGF-1 and an increase in IGF-1 receptors. Local actions of IGF-1 then result in a secondary increase in both hormone receptors and hormone responses. The net effect is local amplification of hormone action via IGF-1 acting as a growth factor in an autocrine-paracrine mode.