Adipose Tissue Microdialysis Research Articles

Adipose tissue function and insulin sensitivity in syndromic obesity of Bardet-Biedl syndrome.

Bardet-Biedl syndrome (BBS) is a rare autosomal recessive syndromic obesity of childhood onset among many other features. To date, the excess risk of metabolic complications of severe early-onset obesity in BBS remains controversial. In-depth investigation of adipose tissue structure and function with detailed metabolic phenotype has not been investigated yet. To investigate adipose tissue function in BBS. A prospective cross-sectional study. To determine if there are differences in insulin resistance, metabolic profile, adipose tissue function and gene expression in patients with BBS compared to BMI-matched polygenic obese controls. 9 adults with BBS and 10 controls were recruited from the national centre for BBS, Birmingham, UK. An in-depth study of adipose tissue structure and function along with insulin sensitivity was performed using hyperinsulinemic-euglycemic clamp studies, adipose tissue microdialysis, histology and RNA sequencing, and measurement of circulating adipokines and inflammatory biomarkers. Adipose tissue structure, gene expression and in vivo functional analysis between BBS and polygenic obesity cohorts were similar. Using hyperinsulinemic-euglycemic clamp and surrogate markers of insulin resistance, we found no significant differences in insulin sensitivity between BBS and obese controls. Furthermore, no significant changes were noted in an array of adipokines, cytokines, pro-inflammatory markers and adipose tissue RNA transcriptomic. Although childhood-onset extreme obesity is a feature of BBS, detailed studies of insulin sensitivity and adipose tissue structure and function are similar to common polygenic obesity. This study adds to the literature by suggesting that it is the quality and quantity of adiposity not the duration that drives the metabolic phenotype.

Metabolic Response to Daytime Dry Fasting in Bahá’í Volunteers—Results of a Preliminary Study

Each year in March, adherents of the Bahá’í faith abstain from eating and drinking from sunrise to sunset for 19 days. Thus, Bahá’í fasting (BF) can be considered as a form of daytime dry fasting. We investigated whether BF decreased energy expenditure after a meal and whether it improved anthropometric measures and systemic and tissue-level metabolic parameters. This was a self-controlled cohort study with 11 healthy men. We measured anthropometric parameters, metabolic markers in venous blood and pre- and postprandial energy metabolism at systemic (indirect calorimetry) and tissue (adipose tissue and skeletal muscle microdialysis) level, both before and during BF. During BF, we found reduced body weight, body mass index, body fat and blood glucose. Postprandial increase in energy expenditure was lower and diet-induced thermogenesis tended to be lower as well. In adipose tissue, perfusion, glucose supply and lipolysis were increased. In skeletal muscle, tissue perfusion did not change. Glucose supply and lipolysis were decreased. Glucose oxidation was increased, indicating improved insulin sensitivity. BF may be a promising approach to losing weight and improving metabolism and health. However, outside the context of religiously motivated fasting, skipping a meal in the evening (dinner cancelling) might be recommended, as metabolism appeared to be reduced in the evening.

Obstructive sleep apnoea increases lipolysis and deteriorates glucose homeostasis in patients with type 2 diabetes mellitus

Obstructive sleep apnoea (OSA) is associated with type 2 diabetes mellitus (T2DM). However, mechanisms mediating association between these two conditions remain unclear. This study investigated, whether the OSA-associated changes in adipose tissue lipolysis might contribute to impaired glucose homeostasis in patient with T2DM. Thirty-five matched subjects were recruited into three groups: T2DM + severe OSA (T2DM + OSA, n = 11), T2DM with mild/no OSA (T2DM, n = 10) and healthy controls (n = 14). Subcutaneous abdominal adipose tissue microdialysis assessed spontaneous, epinephrine- and isoprenaline-stimulated lipolysis. Glucose metabolism was assessed by intravenous glucose tolerance test. Spontaneous lipolysis was higher in the T2DM + OSA compared with the T2DM (60.34 ± 23.40 vs. 42.53 ± 10.16 μmol/L, p = 0.013), as well as epinephrine-stimulated lipolysis (236.84 ± 103.90 vs. 167.39 ± 52.17 µmol/L, p < 0.001). Isoprenaline-stimulated lipolysis was unaffected by the presence of OSA (p = 0.750). The α2 anti-lipolytic effect was decreased in T2DM + OSA by 59% and 315% compared with T2DM and controls (p = 0.045 and p = 0.007, respectively). The severity of OSA (AHI) was positively associated with spontaneous (p = 0.037) and epinephrine-stimulated (p = 0.026) lipolysis. The α2-adrenergic anti-lipolytic effect (p = 0.043) decreased with increasing AHI. Spontaneous lipolysis was positively associated with Insulin resistance (r = 0.50, p = 0.002). Epinephrine-stimulated lipolysis was negatively associated with the Disposition index (r = − 0.34, p = 0.048). AHI was positively associated with Insulin resistance (p = 0.017) and negatively with the Disposition index (p = 0.038). Severe OSA in patients with T2DM increased adipose tissue lipolysis, probably due to inhibition of the α2-adrenergic anti-lipolytic effect. We suggest that dysregulated lipolysis might contribute to OSA-associated impairments in insulin secretion and sensitivity.

Relative Adipose Tissue Failure in Alström Syndrome Drives Obesity-Induced Insulin Resistance.

Obesity is a major risk factor for insulin resistance (IR) and its attendant complications. The pathogenic mechanisms linking them remain poorly understood, partly due to a lack of intermediary monogenic human phenotypes. Here, we report on a monogenic form of IR-prone obesity, Alström syndrome (ALMS). Twenty-three subjects with monogenic or polygenic obesity underwent hyperinsulinemic-euglycemic clamping with concomitant adipose tissue (AT) microdialysis and an in-depth analysis of subcutaneous AT histology. We have shown a relative AT failure in a monogenic obese cohort, a finding supported by observations in a novel conditional mouse model (Almsflin/flin) and ALMS1-silenced human primary adipocytes, whereas selective reactivation of ALMS1 gene in AT of an ALMS conditional knockdown mouse model (Almsflin/flin; Adipo-Cre+/−) restores systemic insulin sensitivity and glucose tolerance. Hence, we show for the first time the relative AT failure in human obese cohorts to be a major determinant of accelerated IR without evidence of lipodystrophy. These new insights into adipocyte-driven IR may assist development of AT-targeted therapeutic strategies for diabetes.

Co-administration of 5α-reductase Inhibitors Worsens the Adverse Metabolic Effects of Prescribed Glucocorticoids.

Glucocorticoids (GCs) are commonly prescribed, but their use is associated with adverse metabolic effects. 5α-reductase inhibitors (5α-RI) are also frequently prescribed, mainly to inhibit testosterone conversion to dihydrotestosterone. However, they also prevent the inactivation of GCs. We hypothesized that 5α-RI may worsen the adverse effects of GCs. Prospective, randomized study. A total of 19 healthy male volunteers (age 45 ± 2 years; body mass index 27.1 ± 0.7kg/m2). Participants underwent metabolic assessments; 2-step hyperinsulinemic, euglycemic clamp incorporating stable isotopes, adipose tissue microdialysis, and biopsy. Participants were then randomized to either prednisolone (10 mg daily) or prednisolone (10 mg daily) plus a 5α-RI (finasteride 5 mg daily or dutasteride 0.5 mg daily) for 7 days; metabolic assessments were then repeated. Ra glucose, glucose utilization (M-value), glucose oxidation, and nonesterified fatty acids (NEFA) levels. Co-administration of prednisolone with a 5α-RI increased circulating prednisolone levels (482 ± 96 vs 761 ± 57 nmol/L, P = 0.029). Prednisolone alone did not alter Ra glucose (2.55 ± 0.34 vs 2.62 ± 0.19 mg/kg/minute, P = 0.86), M-value (3.2 ± 0.5 vs 2.7 ± 0.7 mg/kg/minute, P = 0.37), or glucose oxidation (0.042 ± 0.007 vs 0.040 ± 0.004 mmol/hr/kg/minute, P = 0.79). However, co-administration with a 5α-RI increased Ra glucose (2.67 ± 0.16 vs 3.05 ± 0.18 mg/kg/minute, P < 0.05) and decreased M-value (4.0 ± 0.5 vs 2.6 ± 0.4 mg/kg/minute, P < 0.05), and oxidation (0.043 ± 0.003 vs 0.036 ± 0.002 mmol/hr/kg, P < 0.01). Similarly, prednisolone did not impair insulin-mediated suppression of circulating NEFA (43.1 ± 28.9 vs 36.8 ± 14.3 μmol/L, P = 0.81), unless co-administered with a 5α-RI (49.8 ± 8.6 vs 88.5 ± 13.5 μmol/L, P < 0.01). We have demonstrated that 5α-RIs exacerbate the adverse effects of prednisolone. This study has significant translational implications, including the need to consider GC dose adjustments, but also the necessity for increased vigilance for the development of adverse effects.

Hepatitis C virus infection is associated with hepatic and adipose tissue insulin resistance that improves after viral cure.

SummaryBackgroundChronic hepatitis C (CHC) is associated with systemic insulin resistance, yet there are limited data on the tissue‐specific contribution in vivo to this adverse metabolic phenotype, and the effect of HCV cure.MethodsWe examined tissue‐specific insulin sensitivity in a cohort study involving 13 patients with CHC compared to 12 BMI‐matched healthy control subjects. All subjects underwent a two‐step clamp incorporating the use of stable isotopes to measure carbohydrate and lipid flux (hepatic and global insulin sensitivity) with concomitant subcutaneous adipose tissue microdialysis and biopsy (subcutaneous adipose tissue insulin sensitivity). Investigations were repeated in seven patients with CHC following antiviral therapy with a documented sustained virological response.ResultsAdipose tissue was more insulin resistant in patients with CHC compared to healthy controls, as evidence by elevated glycerol production rate and impaired insulin‐mediated suppression of both circulating nonesterified fatty acids (NEFA) and adipose interstitial fluid glycerol release during the hyperinsulinaemic euglycaemic clamp. Hepatic and muscle insulin sensitivity were similar between patients with CHC and controls. Following viral eradication, hepatic insulin sensitivity improved as demonstrated by a reduction in endogenous glucose production rate. In addition, circulating NEFA decreased with sustained virological response (SVR) and insulin was more effective at suppressing adipose tissue interstitial glycerol release with a parallel increase in the expression of insulin signalling cascade genes in adipose tissue consistent with enhanced adipose tissue insulin sensitivity.ConclusionChronic hepatitis C patients have profound subcutaneous adipose tissue insulin resistance in comparison with BMI‐matched controls. For the first time, we have demonstrated that viral eradication improves global, hepatic and adipose tissue insulin sensitivity.

Treatment with PBI-4050 in patients with Alstr\xf6m syndrome: study protocol for a phase 2, single-Centre, single-arm, open-label trial

BackgroundAlström syndrome (ALMS) is a very rare autosomal recessive monogenic disorder caused by a mutation in the ALMS1 gene and characterised by childhood onset obesity, dyslipidaemia, advanced non-alcoholic fatty liver disease, diabetes and extreme insulin resistance. There is evidence of multi-organ fibrosis in ALMS and severity of the disease often leads to organ failure with associated morbidities, resulting in reduced life expectancy. There are no specific treatments for this disease, and current management consists of only symptomatic therapies. PBI-4050 is a new molecular entity with demonstrated anti-inflammatory and anti-fibrotic activities in preclinical models, including animal models of human diseases characterized by progressive fibrosis in the kidney, heart, liver and lungs. Moreover, completed Phase 2 studies in type 2 diabetes mellitus with metabolic syndrome and idiopathic pulmonary fibrosis further support the anti-inflammatory and anti-fibrotic activity of PBI-4050. Together, these data suggest that PBI-4050 has the potential to treat the pathological inflammatory and fibrotic features of ALMS. The aim of this study is to evaluate the safety and anti-inflammatory & anti-fibrotic activities of PBI-4050 in subjects with ALMS.MethodsThis is a Phase 2, single-centre, single-arm, open-label trial. A total of 18 patients with ALMS will be enrolled to receive PBI-4050 at a total daily oral dose of 800 mg for an initial 24 weeks with continuation for an additional 36 or 48 weeks. Standard assessments of safety include adverse events, clinical laboratory tests, vital signs, physical examination and electrocardiograms. Efficacy assessments include adipose tissue biopsy, hyperinsulinaemic-euglycaemic glucose clamp, adipose tissue microdialysis, liver transient elastography, liver and cardiac magnetic resonance imaging, and laboratory blood tests.DiscussionThis is the first clinical study of PBI-4050 in subjects with ALMS. Given the rarity and complexity of the disease, a single-centre, single-arm, open-label design has been chosen to maximise subject exposure and increase the likelihood of achieving our study endpoints. The results will provide valuable safety and preliminary evidence of the effects of PBI-4050 in ALMS, a rare heterogeneous disease associated with progressive fibrosis and premature mortality.Trial registrationThe trial is registered on ClinicalTrials.gov (Identifier; NCT02739217, February 2016) and European Union Drug Regulating Authorities Clinical Trials (EudraCT Number 2015–001625-16, Sept 2015).

Dual-5α-Reductase Inhibition Promotes Hepatic Lipid Accumulation in Man

Context:5α-Reductase 1 and 2 (SRD5A1, SRD5A2) inactivate cortisol to 5α-dihydrocortisol in addition to their role in the generation of DHT. Dutasteride (dual SRD5A1 and SRD5A2 inhibitor) and finasteride (selective SRD5A2 inhibitor) are commonly prescribed, but their potential metabolic effects have only recently been identified.Objective:Our objective was to provide a detailed assessment of the metabolic effects of SRD5A inhibition and in particular the impact on hepatic lipid metabolism.Design:We conducted a randomized study in 12 healthy male volunteers with detailed metabolic phenotyping performed before and after a 3-week treatment with finasteride (5 mg od) or dutasteride (0.5 mg od). Hepatic magnetic resonance spectroscopy (MRS) and two-step hyperinsulinemic euglycemic clamps incorporating stable isotopes with concomitant adipose tissue microdialysis were used to evaluate carbohydrate and lipid flux. Analysis of the serum metabolome was performed using ultra-HPLC-mass spectrometry.Setting:The study was performed in the Wellcome Trust Clinical Research Facility, Queen Elizabeth Hospital, Birmingham, United Kingdom.Main Outcome Measure:Incorporation of hepatic lipid was measured with MRS.Results:Dutasteride, not finasteride, increased hepatic insulin resistance. Intrahepatic lipid increased on MRS after dutasteride treatment and was associated with increased rates of de novo lipogenesis. Adipose tissue lipid mobilization was decreased by dutasteride. Analysis of the serum metabolome demonstrated that in the fasted state, dutasteride had a significant effect on lipid metabolism.Conclusions:Dual-SRD5A inhibition with dutasteride is associated with increased intrahepatic lipid accumulation.

PP66 - 7-keto-cholesterol: a free radical-derived oxysterol of human adipose tissue with anti-adipogenic activity

Aims Oxidative stress of adipose tissue (AT) emerges as an instigator of metabolic dysfunctions in obese insulin-resistant patients. Here we test the hypothesis whether free radical-derived cholesterol oxidation products (i.e., oxysterols) are: 1) generated in the dysfunctional “diabetic” AT, 2) secreted in AT interstitial fluid, 3) and active as modulators of AT stem cell (ASC) adipogenic differentiation. 7-ketocholesterol (7k-C) and 7β-hydroxycholesterol (7β OH-C) were assessed in AT microdialysis samples of healthy subjects as well as in subcutaneous abdominal AT of type 2 diabetic obese patients. Adipogenic differentiation and “canonical” Wnt and MAPK signaling were investigated in primary cultures of human ASCs treated with 7k-C or with the autoxidation-type II oxysterol 5,6-secosterol (5,6-S) for comparison. Results 7k-C and 7β OH-C were detected in human AT interstitial fluid (0.27±0.03 and 0.91±0.13 μM, respectively). When compared with non-diabetic individuals, diabetic obese patients showed increased levels of 7k-C and 7β OH-C, as well as of 4-HNE-protein adducts, in subcutaneous AT. Challenging ASCs with 7k-C at levels resembling those found in vivo (1 μM), resulted in a lowered adipogenic differentiation by the transient increase of cellular ROS and sequential activation of Wnt/β-catenin, ERK1/2, p38-MAPK and JNK signaling. Signaling data differentiated the anti-adipogenic response of 7k-C and 5,6-S. Innovation and Conclusion Free radical-derived oxysterols were identified in the human AT secretome and may act as novel adipokines with regulatory effects on ASC differentiation. Pathogenic effects of these molecules and particularly of 7k-C in the impaired de novo adipogenesis of insulin-resistant patients is worth of further investigation.

Mitochondrial dysfunction and ischemia in critical illness: an adipose tissue microdialysis study in 203 ICU patients

Ischemia and mitochondrial dysfunction have been implicated in critical illness. The potential of MD to diagnose and separate ischemia and mitochondrial dysfunction in ICU patients remains currently unknown.

Assessment of in situ adipose tissue inflammation by microdialysis

Inflammation, and specifically adipose tissue (AT) inflammation, is part of the pathophysiology of obesity and HIV-associated lipodystrophy. Local AT protein assessment methods are limited, and AT inflammation studies have therefore primarily examined inflammatory gene expression. We therefore investigated the utility of microdialysis to study in situ AT interstitial inflammatory protein levels. Abdominal subcutaneous AT microdialysis was performed in six healthy men, six HIV-infected men with lipodystrophy and six without lipodystrophy using the internal references (51) Cr-EDTA and (125) I-human serum albumin. We measured 41 inflammatory proteins in microdialysis samples by Luminex technology, as well as systemic levels in 14 subjects. Furthermore, in vitro studies of the internal reference technique for microdialysis recovery of inflammatory proteins were made. We detected in situ AT interstitial levels of 14 inflammatory proteins by microdialysis, while the 27 other inflammatory proteins assessed were only detected sporadically. Initial levels of IL-6 and IL-8 were undetectable. Insertion trauma affected IL-1α, IL-6, IL-8, monocyte chemotactic factor (MCP)-1, IP-10, G-CSF, growth-related oncogene (GRO), macrophage-derived chemokine (MDC) and macrophage inflammatory protein (MIP)-1β levels, while fibroblast growth factor (FGF)-2 was not affected. Systemic and AT interstitial levels were poorly correlated. The microdialysis recovery of smaller proteins was higher than for larger, and the internal references improved microdialysis by accounting for variation in perfusion across the membrane. Interstitial inflammatory proteins can be sampled in situ using microdialysis. Use of internal references improves the microdialysis technique. However, insertion trauma hampers the use of microdialysis to study AT inflammatory levels, except for FGF-2. Still, microdialysis gives unique insight to in situ AT interstitial concentrations.

Effect of liraglutide on adipose insulin resistance and hepatic de-novo lipogenesis in non-alcoholic steatohepatitis: substudy of a phase 2, randomised placebo-controlled trial

BackgroundAdipose tissue insulin resistance and lipotoxicity are key pathognomonic features in non-alcoholic steatohepatitis (NASH). Liraglutide is a once daily, glucagon-like peptide 1 (GLP-1) analogue that significantly improves glycaemic control, weight, and hepatic steatosis. The aim of this phase 2 study was to determine the effect of liraglutide on insulin sensitivity (hepatic, muscle, adipose), hepatic lipogenesis, and markers of adipose inflammation. Methods14 patients with biopsy-proven NASH were randomly assigned to either 1·8 mg liraglutide or placebo (once a day subcutaneously) for 12 weeks as part of the metabolic substudy of the double-blind, randomised placebo-controlled LEAN trial. At baseline and 12 weeks, patients underwent paired two-step hyperinsulinaemic euglycaemic clamps incorporating stable isotopes with concomitant adipose tissue microdialysis. Serum adipocytokines were measured with Fluorokine MAP multiplex kits (R&D Systems, UK). In-vitro isotope experiments were performed with Huh-7 and primary human hepatocytes. The LEAN trial is registered with ClinicalTrials.gov, number NCT01237119. FindingsLiraglutide significantly decreased weight, waist circumference, HbA1c, fasting glucose, LDL, and liver enzymes compared with placebo. Liraglutide significantly increased the suppression of hepatic glucose production with low-dose insulin. Liraglutide significantly decreased circulating non-esterified fatty acid (NEFA) in the fasting, low-dose, and high-dose insulin states. Liraglutide significantly reduced the insulin concentration required to half-maximally suppress circulating NEFA and significantly decreased adipose tissue lipolysis, as shown by a reduction in interstitial fluid glycerol concentrations. Furthermore, liraglutide significantly improved serum markers of adipose inflammation—namely, leptin, adiponectin, and chemokine ligand 2. In addition, liraglutide significantly decreased de-novo lipogenesis in vivo, as measured by incorporation of deuterated 2H20 into palmitate, compared with placebo. In support of our clinical observations, in-vitro experiments using both the Huh-7 cell line and primary cultures of human hepatocytes showed decreased de-novo lipogenesis, measured by incorporation of 14C-acetate into cellular lipid after treatment with GLP-1 (exendin-4). InterpretationLiraglutide significantly reduces metabolic dysfunction, hepatic lipogenesis, hepatic and adipose insulin resistance, and adipose inflammation in patients with NASH. GLP-1 analogue therapy might be a novel treatment for patients with this condition. FundingWellcome Trust, National Institute of Health Research, Novo Nordisk.

Improved Insulin Sensitivity during Pioglitazone Treatment Is Associated with Changes in IGF-I and Cortisol Secretion in Type 2 Diabetes and Impaired Glucose Tolerance

Background. Hypercortisolism and type 2 diabetes (T2D) share clinical characteristics. We examined pioglitazone's effects on the GH-IGF-I and HPA axes in men with varying glucose intolerance. Methods. 10 men with T2D and 10 with IGT received pioglitazone 30–45 mg for 12 weeks. OGTT with microdialysis in subcutaneous adipose tissue and 1 μg ACTH-stimulation test were performed before and after. Glucose, insulin, IGF-I, IGFBP1, and interstitial measurements were analyzed during the OGTT. Insulin sensitivity was estimated using HOMA-IR. Results. HOMA-IR improved in both groups. IGF-I was initially lower in T2D subjects (P = 0.004) and increased during treatment (−1.4 ± 0.5 to −0.5 ± 0.4 SD; P = 0.007); no change was seen in IGT (0.4 ± 39 SD before and during treatment). Fasting glycerol decreased in T2D (P = 0.038), indicating reduced lipolysis. Fasting cortisol decreased in T2D (400 ± 30 to 312 ± 25 nmol/L; P = 0.041) but increased in IGT (402 ± 21 to 461 ± 35 nmol/L; P = 0.044). Peak cortisol was lower in T2D during treatment (599 ± 32 to 511 ± 43, versus 643 ± 0.3 to 713 ± 37 nmol/L in IGT; P = 0.007). Conclusions. Pioglitazone improved adipose tissue and liver insulin sensitivity in both groups. This may explain increased IGF-I in T2D. Pioglitazone affected cortisol levels in both groups but differently, suggesting different mechanisms for improving insulin sensitivity between T2D and IGT.

Interrelationship between blood and tissue lactate in a general intensive care unit: A subcutaneous adipose tissue microdialysis study on 162 critically ill patients

PurposeThe aim of the study was to study the interrelationship between blood and tissue lactate in critically ill patients with or without shock admitted in a general intensive care unit. Materials and MethodsWe studied 162 mechanically ventilated patients: 106 with shock (septic shock, 97; cardiogenic shock, 9) and 56 without shock (severe sepsis, 38; systemic inflammatory response syndrome, 18). A microdialysis catheter was inserted in the subcutaneous adipose tissue of the upper thigh, and interstitial fluid was collected every 4 hours for a maximum of 6 days. We assessed the relationship between tissue and blood lactate using cross-approximate entropy and cross-correlation analysis. ResultsPatients with shock had higher area under the curve for blood (261 vs 175 mmol/L*hours, P < .0001) and tissue lactate (386 vs 281 mmol/L*hours, P < .0001) compared with patients without shock. The interrelationship of tissue-blood lactate, as assessed with cross-approximate entropy, was more regular in patients with shock compared with patients without shock. Cross-correlation of tissue vs blood lactate yielded higher correlation coefficients in patients with shock compared with those without shock, being higher when tissue lactate preceded blood lactate by 4 hours compared with tissue vs blood lactate with no lag time. ConclusionsIn critical illness, the detailed dynamics between blood and tissue lactate are affected by the presence of shock. In patients with shock, microdialysis-assessed tissue lactate is higher compared with those without shock and may detect metabolic disturbances before these become evident in the systemic circulation.

Catecholamine and insulin control of lipolysis in subcutaneous adipose tissue during long-term diet-induced weight loss in obese women

The aim of this study was to investigate the evolution of the adrenergic and insulin-mediated regulation of lipolysis during different phases of a 6-mo dietary intervention. Eight obese women underwent a 6-mo dietary intervention consisting of a 1-mo very low-calorie diet (VLCD) followed by a 2-mo low-calorie diet (LCD) and 3-mo weight maintenance (WM) diet. At each phase of the dietary intervention, microdialysis of subcutaneous adipose tissue (SCAT) was performed at rest and during a 3-h hyperinsulinemic euglycemic clamp. Responses of dialysate glycerol concentration (DGC) were determined at baseline and during local perfusions with adrenaline or adrenaline and phentolamine before and during the last 30 min of the clamp. Dietary intervention induced a body weight reduction and an improved insulin sensitivity. DGC progressively decreased during the clamp, and this decrease was similar during the different phases of the diet. The adrenaline-induced increase in DGC was higher at VLCD and LCD compared with baseline condition and returned to prediet levels at WM. In the probe with adrenaline and phentolamine, the increase in DGC was higher than that in the adrenaline probe at baseline and WM, but it was not different at VLCD and LCD. The results suggest that the responsiveness of SCAT to adrenaline-stimulated lipolysis increases during the calorie-restricted phases due to a reduction of the α(2)-adrenoceptor-mediated antilipolytic action of adrenaline. At WM, adrenaline-stimulated lipolysis returned to the prediet levels. Furthermore, no direct relationship between insulin sensitivity and the diet-induced changes in the regulation of lipolysis was found.

Intranasal application of the melanocortin 4 receptor agonist MSH/ACTH(4–10) in humans causes lipolysis in white adipose tissue

The melanocortin system has a highly significant role in the hypothalamic regulation of body weight and energy expenditure. In animals, intracerebroventricular infusion of melanocortin receptor 4 (MCR-4) agonists increases basal metabolic rate through activation of the sympathetic nervous system and subsequently reduces food intake. In humans, direct access of MCR-4 agonists to the central nervous system can be achieved by a transnasal route, which leads to weight loss with chronic administration. In the present study, we aimed at investigating the effects of intranasally administered MC4-R agonist MSH/ACTH(4-10) on lipolysis and sympathetic nervous system activity in healthy humans. Healthy normal weight, male volunteers (n=10) received either 10 mg MSH/ACTH(4-10) or placebo intranasally in a double-blinded randomized crossover design. Interstitial glycerol release was assessed by microdialysis in abdominal white adipose tissue (WAT) and in skeletal muscle (SM) of the forearm. Local blood flow, systemic blood pressure, heart rate and muscle sympathetic nerve activity (MSNA) within the superficial peroneal nerve were recorded at rest and after nitroprusside infusion. At 45 min after MSH/ACTH(4-10) administration WAT glycerol concentrations increased by 53.4±19.3% compared with baseline conditions (P<0.05) and remained significantly higher throughout the experiment when compared with placebo (P<0.05) while local glycerol release in SM was not significantly affected. Resting MSNA was not altered by MSH/ACTH(4-10) administration; however, sympathoexcitation by intravenous nitroprusside was markedly elevated (MSH/ACTH(4-10) 569±69% increase to baseline; placebo: 315±64%; P<0.01). Intranasally administered MCR-4 agonist MSH/ACTH 4-10 increases both subcutaneous WAT lipolysis and MSNA, which suggests a direct central nervous peptide effect in humans on key factors of human energy metabolism.

Interstitial cortisol levels obtained by adipose tissue microdialysis in mechanically ventilated septic patients: correlations with total and free serum cortisol

The aim of this study was to measure cortisol in the interstitial fluid of mechanically ventilated septic patients using MD and to examine the correlation between interstitial cortisol levels and total along with free serum cortisol.

Effect of the cannabinoid receptor-1 antagonist rimonabant on lipolysis in rats

The cannabinoid receptor 1 antagonist, rimonabant, reduces food intake and body weight, but contradictory findings have been reported as to whether the weight-reducing effect is fully accounted for by the reduced food intake or if rimonabant also mediates a lipolytic effect. In the present study, the effect on weight loss was studied in diet-induced obese rats after 3 days and 3 weeks of exposure to rimonabant, respectively. Induction of lipolysis was examined following acute administration and following 3 weeks of repeated dosing. Rimonabant-treated rats lost significantly more weight than their food-restricted controls. This effect was most pronounced in the beginning of the treatment period. No increase in lipolytic activity was found after 3 weeks of repeated dosing as measured by microdialysis in adipose tissue whereas acute administration of 10 mg/kg produced a significant increase in microdialysate levels of glycerol illustrating an acute stimulation of lipolysis. No equivalent increase in glycerol was, however, observed in vitro following incubation of isolated rat adipocytes with rimonabant. This finding excludes a direct lipolytic action of rimonabant on tissue level. Instead, administration of 10 mg/kg produced a significant increase in noradrenaline excretion in diet-induced obese rats, suggesting an increase in sympathoadrenal activity. In conclusion, the present study suggests an acute lipolytic effect of rimonabant mediated through activation of the sympathoadrenal system.

Adenosine Suppression of in-vivo Lipolysis in Obese Premenopausal Women

In obesity the endogenous inhibitor of lipolysis, adenosine, may be increased as a mechanism to increase blood flow and decrease intracellular lipolysis in order to limit the accumulation of fatty acids in the interstitium. Pharmacological and physiological stimulation of lipolysis via isoprenaline (ISO) and exercise, respectively, are commonly used means of studying lipolysis. However, the in-vivo effects of adenosine on these modes of stimulation are not well-known. PURPOSE: To determine the effects of adenosine on lipolysis under resting and exercise conditions. METHODS: We measured in-vivo lipolysis (interstitial glycerol levels) via microdialysis of subcutaneous abdominal adipose tissue (SCAAT) in 16 obese premenopausal women (29±4.7 yrs, BMI= 40.1±9.3kg/m2). Three microdialysis probes were perfused with: 1) control solution (Saline), 2) DPCPX (A1 adenosine receptor antagonist), or 3) 2-chloro-adenosine (2CA, adenosine receptor agonist) with and without local pharmacological stimulation by ISO. RESULTS: Local infusion of 2CA significantly reduced SCAAT glycerol concentrations (-11.5±4.9%, P = 0.013) compared to basal levels while local DPCPX infusion increased glycerol concentrations (11.8±4.7%, P = 0.055) compared to basal. The decreased glycerol concentration with 2CA at rest was abolished with inhibition of nitric oxide synthase using a co-infusion of 2CA and L-NMMA (5.3±4.6%, P = 0.51 vs basal and -11.5±4.9%, P = 0.015 vs 2CA alone). 2CA infusion also reduced the ISO stimulated increase in dialysate glycerol concentration (142.0±18.2% ISO alone vs. 74.7±12.5% ISO+ 2CA, P = 0.012). Exercise (30 min cycle ergometry at 60% VO2peak) resulted in a 64% increase in lipolysis above ISO alone with no differential effects of local infusions of 2CA or DPCPX (64.1±7.8% 2CA and 64.8±9.6% DPCPX, P = 0.920) on this increase. No differences in ethanol outflow/inflow ratio (index of local tissue blood flow) between probes or treatments during microdialysis were observed. CONCLUSION: Adenosine decreases resting and ISO-stimulated lipolysis in-vivo. However, adenosine does not inhibit maximally stimulated lipolysis via ISO and exercise combined. The endogenous lipolytic inhibitor, nitric oxide, may be a mechanism through which adenosine reduces lipolysis in-vivo. Supported by NIDDK 1R15DK074401.

Extracellular metabolic alterations in critically ill septic patients studied by adipose tissue microdialysis

Extracellular metabolic alterations in critically ill septic patients studied by adipose tissue microdialysis