Total adiponectin and adiponectin multimeric complexes in relation to weight loss-induced improvements in insulin sensitivity in obese women: the NUGENOB study

AIM

Adiponectin increases insulin sensitivity, protects arterial walls against atherosclerosis, and regulates glucose metabolism, and is decreased in obese, insulin resistant, and type 2 diabetic patients. Adiponectin circulates in plasma as high, medium, and low molecular weight forms (HMW, MMW, and LMW). The HMW form was suggested to be closely associated with insulin sensitivity. This study investigated whether diet-induced changes in insulin sensitivity were associated with changes in adiponectin multimeric complexes.

SUBJECTS

Twenty obese women with highest and twenty obese women with lowest diet induced changes in insulin sensitivity (responders and non-responders respectively), matched for weight loss (body mass index (BMI)=34.5 (s.d. 2.9) resp. 36.5 kg/m(2) (s.d. 4.0) for responders and non-responders), were selected from 292 women who underwent a 10-week low-caloric diet (LCD; 600 kcal/d less than energy requirements). Plasma HMW, MMW, and LMW forms of adiponectin were quantified using Western blot method.

RESULTS

LCD induced comparable weight reduction in responders and non-responders by 8.2 and 7.6 kg. Homeostasis model assessment insulin resistance index decreased by 48.1% in responders and remained unchanged in non-responders. Total plasma adiponectin and the quantity of HMW and MMW remained unchanged in both groups, while LMW increased by 16.3% in non-responders. No differences between both groups were observed at baseline and after the study. Total plasma adiponectin, MMW, and LMW were negatively associated with fasting insulin levels at baseline.

CONCLUSION

No differences in total plasma adiponectin, HMW, MMW, and LMW forms were observed between responders and non-responders following 10-week LCD, suggesting that adiponectin is not a major determinant of weight loss-induced improvements in insulin sensitivity.

Paraoxonase 1 phenotype distribution and activity differs in subjects with newly diagnosed Type 2 diabetes (the CODAM Study)

AIMS

Paraoxonase 1 (PON1) is an antioxidant high-density lipoprotein-bound enzyme, which was recently found to be expressed in the islets of Langerhans. A substitution (Q/R) at position 192 results in enzymes with different activity. Oxidation has been implicated in the onset of diabetes, and it can be hypothesized that PON1 may have a protective effect on diabetes. Our aim was to compare PON1 activities and PON1 Q/R phenotypes in subjects with different degrees of glucose intolerance.

METHODS

We examined 566 members of the Cohort study of Diabetes and Atherosclerosis Maastricht (CoDAM), including subjects with normal glucose tolerance (NGT, n = 298), impaired glucose regulation (IGR, n = 128), newly diagnosed Type 2 diabetes (nDM, n = 78) and treated, that is to say known, Type 2 diabetes (kDM, n = 64). PON1 activity was measured in serum using paraoxon and diazoxon as substrates. The PON1 phenotype was determined using two-dimensional enzyme analysis.

RESULTS

The RR-phenotype was significantly more frequent in nDM compared with NGT subjects (14.1 vs. 6.0%, P = 0.05). Adjusted for the PON1 phenotype, subjects with nDM had significant lower PON1 activity towards paraoxon and diazoxon than subjects with NGT. Adjusted odds ratios comparing the RR-variant with the QQ-variant were 2.17 [95% confidence interval (CI): 0.90-5.24] for impaired glucose tolerance, 2.84 (95% CI: 1.03-7.83) for nDM, 2.13 (95% CI; 0.61-7.42) for kDM and 2.65 (95% CI: 1.10-6.40) for total diabetes mellitus.

CONCLUSIONS

An aberrant PON1 phenotype distribution and PON1 activity were observed in early diabetes. In addition, the higher state of oxidative stress may affect the future development of complications.

Major differences in noradrenaline action on lipolysis and blood flow rates in skeletal muscle and adipose tissue in vivo

AIMS/HYPOTHESIS

The regulation of skeletal muscle lipolysis is not fully understood. In the present study, the effects of systemic and local noradrenaline administration on lipolysis and blood flow rates in skeletal muscle and adipose tissue were studied in vivo.

METHODS

First, circulating noradrenaline levels were raised tenfold by a continuous i.v. infusion (n=12). Glycerol levels (an index of lipolysis) were measured in m. gastrocnemius and in abdominal adipose tissue using microdialysis. Local blood flow was determined with the (133)Xe clearance technique and whole-body lipolysis rates assessed with a stable glycerol isotope technique ([(2)H(5)] glycerol). Second, interstitial glycerol levels in m. gastrocnemius, m. vastus and adipose tissue were measured by microdialysis during local perfusion with noradrenaline (10(-8)-10(-6) mol/l) (n=10). Local blood flow was monitored with the ethanol perfusion technique.

RESULTS

With regard to systemic noradrenergic stimulation, no change in fractional release of glycerol (difference between tissue and arterial glycerol) was seen in skeletal muscle. In adipose tissue it transiently increased twofold (p<0.0001), and the rate of appearance of glycerol in plasma showed the same kinetic pattern. Blood flow was reduced by 40% in skeletal muscle (p<0.005) and increased by 50% in adipose tissue (p<0.05). After noradrenaline stimulation in situ, a discrete elevation of skeletal muscle glycerol was registered only at the highest concentration of noradrenaline (10(-6) mol/l) (p<0.05). Adipose tissue glycerol doubled already at the lowest concentration (10(-8) mol/l) (p<0.05). In skeletal muscle a decrease in blood flow was seen at the highest noradrenaline concentrations (p<0.05).

CONCLUSIONS/INTERPRETATION

Lipolysis and blood flow rates are regulated differently in adipose tissue and skeletal muscle. Adipose tissue displays a high, but transient (tachyphylaxia) sensitivity to noradrenaline, leading to stimulation of both lipolysis and blood flow rates. In skeletal muscle, physiological concentrations of noradrenaline decrease blood flow but have no stimulatory effect on lipolysis rates.

Gender differences in fat metabolism

Women generally have a higher percentage of body fat than men. Also, women store more fat in the gluteal-femoral region, whereas men store more fat in the visceral (abdominal) depot. This review focuses on differences in regional fatty acid storage, mobilization and oxidation that may contribute to gender-related differences in body fat distribution. There are pronounced regional differences in the regulation of regional fatty acid metabolism between men and women. Firstly, there is evidence that in vivo, catecholamine mediated leg free fatty acid release is lower in women than in men, whereas free fatty acid release from the upper body depots is comparable. These data correspond to in-vitro adipose tissue biopsy data, which indicate a more pronounced difference in catecholamine mediated lipolysis between upper body and lower body fat depots in women than in men. Secondly, free fatty acid release by the upper body subcutaneous fat depots is higher in men than in women, indicating a higher resistance to the antilipolytic effect of meal ingestion in the upper body fat depots in men. Thirdly, there are indications that basal fat oxidation (adjusted for fat free mass) is lower in females as compared to males, thereby contributing to a higher fat storage in women. Finally, postprandial fat storage may be higher in subcutaneous adipose tissue in women than in men, whereas storage in visceral adipose tissue has been hypothesized to be higher in men. All the above differences may play a role in the variation in net regional fat storage between men and women, but the number of in-vivo studies on gender-related differences in fatty acid metabolism is very limited and most findings require confirmation. Furthermore, there is abundant evidence that the proportion of energy derived from fat during exercise is higher in women than in men. With respect to total body fat, this finding seems counterintuitive, as percentage body fat is increased in women. Further studies are necessary to investigate the significance of differences in exercise-induced fat oxidation on 24-h fat balance.

Functional food science and substrate metabolism

The present review addresses the role of food constituents in the aetiology of metabolic conditions and chronic diseases, mostly related to energy metabolism and substrate regulation, such as obesity and non-insulin-dependent diabetes mellitus. Second, attention is paid to malnutrition, a major cause of mortality and morbidity in developing countries, which may be a cause of concern in Europe because of the increasing number of elderly people in the population. Finally, the role of diet during exercise, a condition of enormous substrate demands, is evaluated. Based on a critical evaluation of the existing knowledge in the literature, implications for future research in relation to functional foods are discussed.

Forskolin potentiates isoprenaline-induced glycerol output and local blood flow in human adipose tissue in vivo

The synergistic action of forskolin on beta-adrenoceptor-mediated glycerol output and changes in local blood flow were investigated in situ, in human adipose tissue of healthy subjects, by the use of microdialysis. The addition of isoprenaline 0.1-1.0 microM or forskolin 10-100 microM to the perfusion solvent caused a concentration-dependent, marked and sustained increase in the levels of glycerol in the dialysate (lipolysis index) as compared to the solvent alone. On a molar basis, isoprenaline was almost one thousand times more potent than forskolin. Isoprenaline caused a rapid and concentration-dependent decrease in the ethanol clearance ratio (index of local blood flow, i.e. a decrease in ethanol ratio implies an increase in blood flow). Forskolin had no effect on the ethanol ratio at either 1.0 microM or 10 microM, while forskolin at 100 microM induced a significant decrease in the ethanol ratio. When adipose tissue was pre-treated with forskolin, the subsequent addition of isoprenaline to the microdialysate resulted in a significantly higher glycerol output and a significantly more prominent decrease in the ethanol ratio than with isoprenaline alone. In conclusion, the data demonstrate that forskolin and the (beta-adrenoceptor-agonist both stimulate lipolysis and local blood flow in human adipose tissue in vivo. Furthermore, forskolin, at concentrations that are ineffective alone, potentiates the actions of isoprenaline on lipolysis and blood flow.

Gender differences in adrenergic regulation of lipid mobilization during exercise

Gender differences in adrenergic regulation of glycerol levels in subcutaneous, abdominal adipose tissue were investigated during submaximal exercise in non-obese, healthy men and women, using microdialysis. During exercise, glycerol levels in venous plasma and venous serum concentrations of free fatty acids increased more in women and reached about two-fold higher values than in men (p < 0.005 or less). Plasma noradrenaline and insulin did not differ between the sexes, whereas plasma adrenaline was two-fold higher in men than in women during exercise (p < 0.01). The glycerol levels in adipose tissue increased during exercise and decreased in the post-exercise period in either sex. When the non-selective beta adrenoceptor blocking agent propranolol was added to the microdialysis perfusate before exercise was initiated, the subsequent increase in dialysate glycerol was significantly diminished in both sexes (p < 0.05). A similar addition of the alpha adrenoceptor blocking agent phentolamine, however, caused a significant further rise in tissue glycerol in men (p < 0.05), whereas the exercise induced increase in glycerol levels remained unaffected by phentolamine in women. Adipose tissue blood flow did not change during exercise in either men or women. In either sex, dialysate lactate levels increased during exercise. This increase was not altered if alpha- or beta-blocking agents were added to the perfusate. In summary, during short term submaximal work, women have a higher increase in circulating lipid than men. This appears, at least in part, to be due to a sex difference in the adrenergic regulation of lipid mobilization during exercise. In men exercise activates beta- as well as alpha-adrenergic receptors in adipose tissue, whereas only beta receptors are activated in adipose tissue of women. Finally, methodological investigations indicate that microdialysis is a valid method for short-term exercise experiments.

Effects of several putative beta 3-adrenoceptor agonists on lipolysis in human omental adipocytes

BACKGROUND

Atypical beta 3-adrenoceptor agonists have attained an increasing interest as potential drugs against obesity and diabetes. However, their pharmacological actions on the native, human beta 3-adrenoceptor are not well defined.

DESIGN

In the present study, the lipolytic effects of several putative beta 3-adrenoceptor agonists were investigated in human omental adipocytes.

RESULTS

CL 316 243 and CGP 12177 had selective partial beta 3-agonist effects (pD2 about 4 and 8, respectively); the latter drug is a beta 1-/beta 2-adrenoceptor blocker in addition to its beta 3-adrenoceptor agonist activity. BRL 37344 and SM 11044 were also partial agonists, but with significant beta 1- and/or beta 2-adrenoceptor agonist properties. Bucindolol, ZD 2079, ICI D7114 and SR 58611A were ineffective as lipolytic drugs. In addition, ICI D7114 was a non-selective beta 1-/beta 2-/beta 3-adrenoceptor antagonist in human adipocytes.

CONCLUSION

None of the beta 3-adrenoceptor agonists tested is an ideal drug for therapeutic use in man (i.e. regarded as a selective and full agonist with high receptor potency). Only CL 316 243 may have a potential therapeutic role, although the potency is very low. CGP 12177 is useful as a reference substance for human in vitro studies.

Quantifying intermediary metabolites in whole blood after a simple deproteinization step with sulfosalicylic acid

We assessed the reproducibility, recovery, and stability of several circulating metabolites--glucose, pyruvate, lactate, alanine, glutamate, glutamine, 3-hydroxybutyrate, acetoacetate, and glycerol--in the presence of sulfosalicylic acid (SSA), which was used to deproteinize blood. The assays, which involved reactions linked to NADH/NAD+, were carried out at 37 degrees C and measured at 355 nm with a Cobas-Bio centrifugal analyzer. The intra- and interbatch CVs were less than 2.1%, except for the interbatch CV for 3-hydroxybutyrate at low concentration (15-30 mumol/L), which was 5.4%. Analytical recovery of metabolites added to blood ranged from 96.4% to 103.0%. Of the metabolites studied, all were stable at -20 degrees C for 90 days in the SSA-blood extract, except for glutamine and acetoacetate, which progressively decreased with time. We conclude that these nine circulating metabolites can be satisfactorily measured after a single deproteinizing step with SSA. This single-step procedure has several advantages over many of the currently used methods.

Quantifying intermediary metabolites in whole blood after a simple deproteinization step with sulfosalicylic acid

We assessed the reproducibility, recovery, and stability of several circulating metabolites--glucose, pyruvate, lactate, alanine, glutamate, glutamine, 3-hydroxybutyrate, acetoacetate, and glycerol--in the presence of sulfosalicylic acid (SSA), which was used to deproteinize blood. The assays, which involved reactions linked to NADH/NAD+, were carried out at 37 degrees C and measured at 355 nm with a Cobas-Bio centrifugal analyzer. The intra- and interbatch CVs were less than 2.1%, except for the interbatch CV for 3-hydroxybutyrate at low concentration (15-30 mumol/L), which was 5.4%. Analytical recovery of metabolites added to blood ranged from 96.4% to 103.0%. Of the metabolites studied, all were stable at -20 degrees C for 90 days in the SSA-blood extract, except for glutamine and acetoacetate, which progressively decreased with time. We conclude that these nine circulating metabolites can be satisfactorily measured after a single deproteinizing step with SSA. This single-step procedure has several advantages over many of the currently used methods.

Effects of chronic and acute protein administration on renal function in patients with chronic renal insufficiency

In 6 volunteers with normal renal function, we investigated the effects of various kinds of protein (soy, lactoprotein and beef) and various amounts of an intravenously administered amino acid solution on glomerular filtration (GFR) and effective renal plasma flow (ERPF). As for the protein-induced changes in renal function, rises in GFR and ERPF were lowest with soy protein, and highest with beef (baseline GFR, 110 +/- 5; soy, 122 +/- 5; beef, 131 +/- 5 ml/min/1.73 m2; mean +/- SEM). High doses of intravenous amino acids induced a rise in GFR comparable to that after beef (132 +/- 5 ml/min/1.73 m2). In a combined test a liquid mixed meal together with intravenously administered amino acids induced a comparable increase of the GFR (baseline 114 +/- 5 versus 129 +/- 5 ml/min/1.73 m2). When investigating 9 patients with chronic renal insufficiency after 4 weeks of low protein intake (LP) and after 4 weeks of high protein intake (HP), GFR and ERPF rose significantly under baseline conditions (GFR-LP41 +/- 9 versus GFR-HP 45 +/- 9 ml/min/1.73 m2, p less than 0.02; ERPF-LP 169 +/- 39 versus ERPF-HP 180 +/- 40 ml/min/1.73 m2, p less than 0.02; paired Wilcoxon). At the end of both dietary periods a comparable rise in renal function could be induced through acute stimulation (GFR-LP 20 +/- 5, GFR-HP 16 +/- 4; ERPF-LP 23 +/- 7, ERPF-HP 22 +/- 3%).(ABSTRACT TRUNCATED AT 250 WORDS)