Growth Hormone and Obesity

Growth hormone (GH) exerts IGF-I dependent protein anabolic and direct lipolytic effects. Obesity reversibly suppresses GH secretion driven by elevated FFA levels, whereas serum IGF-I levels remain normal or elevated due to elevated portal insulin levels. Fasting in lean individuals suppresses hepatic IGF-I production and increases pituitary GH release, but this pattern is less pronounced in obesity. Fasting in obesity is associated with increased sensitivity to the insulin-antagonistic effects of GH. GH treatment in obesity induces a moderate reduction in fat mass and an increase in lean body mass but the therapeutic potential is uncertain.

Growth hormone signaling and action in obese versus lean human subjects

Growth hormone (GH) levels are blunted in obesity, but it is not known whether this relates to altered GH sensitivity and whether this influences the metabolic adaptation to fasting. Therefore, we investigated the effect of obesity on GH signal transduction and fasting-induced changes in GH action. Nine obese (BMI 35.7 kg/m²) and nine lean (BMI 21.5 kg/m²) men were studied in a randomized crossover design with 1) an intravenous GH bolus, 2) an intravenous saline bolus, and 3) 72 h of fasting. Insulin sensitivity (hyperinsulinemic, euglycemic clamp) and substrate metabolism (glucose tracer and indirect calorimetry) were measured in studies 1 and 2. In vivo GH signaling was assessed in muscle and fat biopsies. GH pharmacokinetics did not differ between obese and lean subjects, but endogenous GH levels were reduced in obesity. GH signaling (STAT5b phosphorylation and CISH mRNA transcription), and GH action (induction of lipolysis and peripheral insulin resistance) were similar in the two groups, but a GH-induced insulin antagonistic effect on endogenous glucose production only occurred in the obese. Fasting-induced IGF-I reduction was completely abrogated in obese subjects despite a comparable relative increase in GH levels (ΔIGF-I: lean, -66 ± 10 vs. obese, 27 ± 16 µg/l; P < 0.01; ΔGH: lean, 647 ± 280 vs. obese, 544 ± 220%; P = 0.76]. We conclude that 1) GH signaling is normal in obesity, 2) in the obese state, the preservation of IGF-I with fasting and the augmented GH-induced central insulin resistance indicate increased hepatic GH sensitivity, 3) blunted GH levels in obesity may protect against insulin resistance without compromising IGF-I status.

Prolonged fasting-induced metabolic signatures in human skeletal muscle of lean and obese men

Insulin resistance is a well-known physiological adaptation to prolonged fasting in healthy skeletal muscle. Obesity is associated with insulin resistance and metabolic inflexibility in skeletal muscle, and a pronounced increase in the risk of metabolic complications. Under the hypothesis that the metabolic traits of insulin resistance associated with prolonged fasting are different from insulin resistance associated with obesity, we examined nine obese and nine lean participants during 12 and 72h of fasting, respectively. Insulin resistance in obese participants was associated with impaired insulin signaling, and reduced levels of glucose-6-phosphate and TCA-cycle intermediates. 72h of fasting in lean participants reduced insulin-stimulated glucose uptake to levels similar to obese participants fasted for 12h. This was associated with increased lipid oxidation, but not accumulation of diacylglycerol or acylcarnitines and impairment of insulin signaling. Prolonged fasting was associated with pronounced increases in β-hydroxybutyrate and β- hydroxybutyrylcarnitine levels in skeletal muscle suggesting augmented ketone body metabolism. Fasting induced insulin resistance may be a consequence of substrate competition. The underlying mechanism behind insulin resistance in obesity is thus not comparable to the physiological adaptations in skeletal muscle induced by prolonged fasting in lean participants.

Differential regulation of lipid and protein metabolism in obese vs. lean subjects before and after a 72-h fast

Increased availability of lipids may conserve muscle protein during catabolic stress. Our study was designed to define 1) intracellular mechanisms leading to increased lipolysis and 2) whether this scenario is associated with decreased amino acid and urea fluxes, and decreased muscle amino acid release in obese subjects under basal and fasting conditions. We therefore studied nine lean and nine obese subjects twice, after 12 and 72 h of fasting, using measurements of mRNA and protein expression and phosphorylation of lipolytic and protein metabolic signaling molecules in fat and muscle together with whole body and forearm tracer techniques. Obese subjects displayed increased whole body lipolysis, decreased urea production rates, and decreased forearm muscle protein breakdown per 100 ml of forearm tissue, differences that persisted after 72 h of fasting. Lipolysis per fat mass unit was reduced in obese subjects and, correspondingly, adipose tissue hormone-sensitive lipase (HSL) phosphorylation and mRNA and protein levels of the adipose triglyceride lipase (ATGL) coactivator CGI58 were decreased. Fasting resulted in higher HSL phosphorylations and lower protein levels of the ATGL inhibitor G0S2. Muscle protein expressions of mammalian target of rapamycin (mTOR) and 4EBP1 were lower in obese subjects, and MuRf1 mRNA was higher with fasting in lean but not obese subjects. Phosphorylation and signaling of mTOR decreased with fasting in both groups, whereas ULK1 protein and mRNA levels increased. In summary, obese subjects exhibit increased lipolysis due to a large fat mass with blunted prolipolytic signaling, together with decreased urea and amino acid fluxes both in the basal and 72-h fasted state; this is compatible with preservation of muscle and whole body protein.

Physical exercise increases autophagic signaling through ULK1 in human skeletal muscle

Data from transgenic animal models suggest that exercise-induced autophagy is critical for adaptation to physical training, and that Unc-51 like kinase-1 (ULK1) serves as an important regulator of autophagy. Phosphorylation of ULK1 at Ser555 stimulates autophagy, whereas phosphorylation at Ser757 is inhibitory. To determine whether exercise regulates ULK1 phosphorylation in humans in vivo in a nutrient-dependent manner, we examined skeletal muscle biopsies from healthy humans after 1-h cycling exercise at 50% maximal O2 uptake on two occasions: 1) during a 36-h fast, and 2) during continuous glucose infusion at 0.2 kg/h. Physical exercise increased ULK1 phosphorylation at Ser555 and decreased lipidation of light chain 3B. ULK1 phosphorylation at Ser555 correlated positively with AMP-activated protein kinase-α Thr172 phosphorylation and negatively with light chain 3B lipidation. ULK1 phosphorylation at Ser757 was not affected by exercise. Fasting increased ULK1 and p62 protein expression, but did not affect exercise-induced ULK1 phosphorylation. These data demonstrate that autophagy signaling is activated in human skeletal muscle after 60 min of exercise, independently of nutritional status, and suggest that initiation of autophagy constitutes an important physiological response to exercise in humans.

Targeting amyloid-beta by glucagon-like peptide -1 (GLP-1) in Alzheimer's disease and diabetes

INTRODUCTION

Epidemiological evidence suggests an association between type 2 diabetes (T2DM) and Alzheimer's disease (AD), in that one disease increases the risk of the other. T2DM and AD share several molecular processes which underlie the tissue degeneration in either disease. Disturbances in insulin signaling may be the link between the two conditions. Drugs originally developed for T2DM are currently being considered as possible novel agents in the treatment of AD.

AREAS COVERED

This review discusses the potential role of glucagon-like peptide -1 (GLP-1) treatment in AD. GLP-1 receptors are expressed in areas of the brain important to memory and learning, and GLP-1 has growth-factor-like properties similar to insulin. A key neuropathological feature of AD is the accumulation of amyloid-beta (Aβ). In preclinical studies, GLP-1 and longer lasting analogues have been shown to have both neuroprotective and neurotrophic effects, and to protect synaptic activity in the brain from Aβ toxicity.

EXPERT OPINION

A convincing amount of evidence has shown a beneficial effect of GLP-1 agonist treatment on cognitive function, memory and learning in experimental models of AD. GLP-1 analogues may therefore be the new therapeutic agent of choice for intervention in AD.

[Vaginal oestrogen therapy in women with hormone-sensitive breast cancer]

Vaginal atrophy is a common problem in women who have previously been treated for breast cancer. Endocrine therapy plays an essential role in the treatment of breast cancer. Systemic hormonal treatment is contraindicated. Topical oestrogens are an effective treatment for vaginal atrophy, but are poorly studied in this group of patients. Physicians are reluctant to recommend it because of the potential increase in the risk of recurrence. The sparse data available suggest that vaginal oestrogen may be used relatively safely by women who are in tamoxifen treatment, but should not be used by women who receive aromatase inhibitor treatment.

Epidemiology of Cushing's syndrome

Overt Cushing's syndrome is a rare disorder with an annual incidence of 2-3/million of which benign adrenal adenomas account for 0.6/million. The female:male ratio is 3:1. Preliminary data indicate a high proportion of subclinical Cushing's syndrome in certain risk populations such as patients with type 2 diabetes or osteoporosis. The clinical implications of these observations are presently unclear. Surgery remains first line treatment for overt disease and initial cure or remission is obtained in 65-85% of patients with Cushing's disease. Late recurrences, however, occur in up to 20% and the risk does not seem to plateau even after 20 years of follow-up. A 2- to 3-fold increase in mortality is observed in most studies, and this excess mortality seems confined to patients in whom initial cure was not obtained. Cushing's syndrome continues to pose diagnostic and therapeutic challenges and life-long follow-up is mandatory.

[Counting of axillary lymph nodes during surgery of breast cancer. A comparison between radiographic examination and pathological assessment]

Proper breast cancer surgery should include removal of at least ten axillary lymph nodes according to recommendations given by DBCG (The Danish Breast Cancer Group). The present study evaluated the results of counting the lymph nodes peroperatively on radiographs of the axillary tissue compared to the final pathological examination, the latter being considered the "gold standard". Since agreement between the two methods was found in only 66 out of 90 patients (Kappa value 0.279), we consider the peroperative radiological examination of the axillary fat to be of no practical value.

[Dobutamine stress echocardiography. Use of dobutamine stress echocardiography in diagnosis and assessment of ischemic heart disease]

Dobutamine stress echocardiography (DSE) is a new diagnostic method for evaluation of patients with known or suspected coronary artery disease. We studied 30 consecutive patients referred for evaluation of chest pain. Coronary angiography was carried out in 28 patients. DSE was performed the following day. Readable echocardiographic recordings were obtained in all patients. Blinded wall motion analysis revealed a diagnostic sensitivity of 91% (95% confidence limits: 79-100%) for dobutamine stress echocardiography using coronary angiography as reference. No severe adverse events or arrhythmias occurred. It is concluded that DSE is well tolerated, feasible and has a high sensitivity for detecting coronary artery disease.

Effect of supine exercise on platelet aggregation and fibrinolytic activity

In 12 healthy young men, strenuous cycling exercise in the supine position, caused platelet aggregability to decrease and the ADP threshold to rise from 7.0 microM resting, to 9.5 exercising (P < 0.01). At the same time, fibrinolytic activity increased markedly: euglobulin clot lysis time shortened from 178 to 68 min, PAI-1 fell from 8.91 to 5.16 IU ml-1, and t-PA rose from 0.56 to 3.95 IU ml-1, all three values were significant to P < 0.01. When the erect posture was assumed after lying at ease for 1 h after exercise, it did not increase platelet activity as expected, but caused a modest increase of fibrinolytic activity. These results suggest that supine exercise will not affect the haemostatic system adversely.

[Occurrence of cardiovascular risk factors among working Danish men 20-59 years of age]

The prevalence of risk factors for ischaemic heart disease (IHD) was recorded in 1,365 men aged 20-59 years in active employment. The purpose was to evaluate the implications of a high-risk strategy based on the rather conservative Danish guidelines for treatment of hypercholesterolemia. The prevalence of various risk factors depends on age, but in all, 1% had diabetes mellitus, 5% had a family history of premature IHD, 50% were smokers, 21% were obese, 12% had systolic blood pressure greater than or equal to 160 mmHg, 8% had diastolic blood pressure greater than or equal to 100 mmHg and 14% had serum cholesterol greater than 7 mmol/l. Only 24% had none of these risk factors and there was a considerable clustering of risk factors in certain subgroups. Approximately 34%, varying from 17% of the younger to 49% of the older, required medical follow-up as part of the high risk strategy. We have estimated the required number of visits to a general practitioner, if all Danish men aged 20-59 years were screened within three years and approximately 30% required follow-up for five years, with three visits in the first year and one thereafter. The number of visits peaks at 450 visits per year during the third year, and a number of circumstances could reduce this figure considerably. Multifactorial models to estimate risk in connection with screening should be adopted to the Danish guidelines for treatment of hypercholesterolemia and hypertension, and future guidelines for intervention should probably be integrated in such a multifactorial model. To practice preventive medicine, many physicians will need greater knowledge of dietary counselling.

[Measurement of cholesterol in capillary blood using the Reflotron system. Results from approximately 1,000 comparisons with reference measurements of cholesterol in venous serum]

The results of 969 measurements of total cholesterol in capillary blood from fingerstick, performed with the Reflotron-system in the field, were compared with measurements of total cholesterol in venous serum. The comparison allows an evaluation of the combined effect of differences in sample material, working place, stability of methods and staff training. The mean values for all measurement were nearly identical with the two methods, and approximately 95% of the Reflotron-measurements were within an interval of +/- 0.7 mmol/l around the estimated true value. However, values below approximately 6 mmol/l were systematically underestimated, and values above approximately 7 mmol/l were overestimated with the Reflotron-system. The coefficient of variation of the system is below 5%, but both this precision and the accuracy appear to be unstable. Evaluated as a tool in screening for hypercholesterolemia, measurements with the system resulted in a modest extent of erroneous classification of subjects, but the positive diagnostic predictive value of the statement "cholesterol above 7 mmol/l" is only approximately 76%. Simulations of likely variations in the accuracy and precision of the method show a significant influence on the extent of errors. It is recommended that measurements with the system are routinely controlled by measuring an appropriate control material, at the start of each run and after every 30 samples.

[A comparison of results of simple evaluation of the risk of ischemic heart disease with calculations based on a multiplicative model]

A simple model for detection of subjects at risk of ischaemic heart disease, based on the addition of scores for different risk factors (Anggaard EE, Land JM, Lenihan J et al. Br Med J 1986; 293: 177-80), is at present widely applied in Denmark. The model could be tested in a prospective study, or a historical follow-up study, but we do not have the possibilities to do so. Instead we have compared the risk score of the model with the estimated five-year coronary mortality risk (ECR) in 742 men aged 40-44 years, calculated on the basis of data from the Seven Countries Study. There is a reasonable consistency in this comparison, in spite of the different principles of calculation, the consideration of different risk factors and/or weighting of risk factors. For example, the model has a sensitivity of 71%, a specificity of 89% and a positive predictive value of 68% in detecting 40-44 year old men in the upper quartile of ECR. The "false positives" are often men, who for other reasons may require preventive medical attention (obese heavy smokers), and the "false negatives" are often men with isolated hypertension.