Growth hormone acts along the PPARγ-FSP27 axis to stimulate lipolysis in human adipocytes

Application of PPAR Ligands and Nanoparticle Technology in Metabolic Steatohepatitis Treatment

Metabolic dysfunction-associated steatotic liver disease/steatohepatitis (MASLD/MASH) is a major disease worldwide whose effective treatment is challenging. Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear receptor superfamily and function as ligand-activated transcription factors. To date, three distinct subtypes of PPARs have been characterized: PPARα, PPARβ/δ, and PPARγ. PPARα and PPARγ are crucial regulators of lipid metabolism that modulate the transcription of genes involved in fatty acid (FA), bile acid, and cholesterol metabolism. Many PPAR agonists, including natural (FAs, eicosanoids, and phospholipids) and synthetic (fibrate, thiazolidinedione, glitazar, and elafibranor) agonists, have been developed. Furthermore, recent advancements in nanoparticles (NPs) have led to the development of new strategies for MASLD/MASH therapy. This review discusses the applications of specific cell-targeted NPs and highlights the potential of PPARα- and PPARγ-targeted NP drug delivery systems for MASLD/MASH treatment.

Adipocyte Subpopulations Mediate Growth Hormone-induced Lipolysis and Glucose Tolerance in Male Mice

In adipose tissue, growth hormone (GH) stimulates lipolysis, leading to an increase in plasma free fatty acid levels and a reduction in insulin sensitivity. In our previous studies, we have found that GH increases lipolysis by reducing peroxisome proliferator-activated receptor γ (PPARγ) transcription activity, leading to a reduction of tat-specific protein 27 (FSP27, also known as CIDEC) expression. In previous studies, our laboratory uncovered 3 developmentally distinct subpopulations of white adipocytes. In this manuscript, we show that one of the subpopulations, termed type 2 adipocytes, has increased GH-induced signaling and lipolysis compared to other adipocyte subtypes. To assess the physiological role of GH-mediated lipolysis mediated by this adipocyte subpopulation, we specifically expressed human FSP27 (hFSP27) transgene in type 2 adipocytes (type2Ad-hFSP27tg mice). Systemically, male type2Ad-hFSP27tg mice displayed reduced serum glycerol release and nonesterified fatty acids levels after acute GH treatment, and improvement in acute, but not chronic, GH-induced glucose intolerance. Furthermore, we demonstrate that type2Ad-hFSP27tg mice displayed improved hepatic insulin signaling. Taken together, these results indicate that this adipocyte subpopulation is a critical regulator of the GH-mediated lipolytic and metabolic response. Thus, further investigation of adipocyte subpopulations may provide novel treatment strategies to regulate GH-induced glucose intolerance in patients with growth and metabolic disorders.

Association of growth hormone deficiency with an increased number of preadipocytes in subcutaneous fat

The inhibitory effect of growth hormone (GH) on adipose tissue growth is well known, but the underlying mechanism is not fully understood. In this study, we determined the possibility that GH inhibits adipose tissue growth by inhibiting adipogenesis, the process of formation of adipocytes from stem cells, in the lit/lit mice. The lit/lit mice are GH deficient because of a spontaneous mutation to the GH releasing hormone receptor (ghrhr) gene, and they have more subcutaneous fat despite being smaller than the lit/+ mice at the same age. We found that cells of the stromal vascular fraction (SVF) of subcutaneous fat from the lit/lit mice had greater adipogenic potential than those from the lit/+ mice, as evidenced by forming greater numbers of lipid droplets-containing adipocytes and having greater expression of adipocyte marker genes during induced adipocyte differentiation in culture. However, addition of GH to the culture did not reverse the superior adipogenic potential of subcutaneous SVF from the lit/lit mice. Through florescence-activated cell sorting and quantification of mRNAs of preadipocyte markers, including CD34, CD29, Sca-1, CD24, Pref-1, and PPARγ, we found that subcutaneous SVF from the lit/lit mice contained more preadipocytes than that from the lit/+ mice. These results support the notion that GH inhibits adipose tissue growth in mice at least in part by inhibiting adipogenesis. Furthermore, these results suggest that GH inhibits adipogenesis in mice not by inhibiting the terminal differentiation of preadipocytes into adipocytes, rather by inhibiting the formation of preadipocytes from stem cells or the recruitment of stem cells to the fat depot.

Naringenin and β-carotene convert human white adipocytes to a beige phenotype and elevate hormone- stimulated lipolysis

Introduction

Naringenin, a peroxisome proliferator-activated receptor (PPAR) activator found in citrus fruits, upregulates markers of thermogenesis and insulin sensitivity in human adipose tissue. Our pharmacokinetics clinical trial demonstrated that naringenin is safe and bioavailable, and our case report showed that naringenin causes weight loss and improves insulin sensitivity. PPARs form heterodimers with retinoic-X-receptors (RXRs) at promoter elements of target genes. Retinoic acid is an RXR ligand metabolized from dietary carotenoids. The carotenoid β-carotene reduces adiposity and insulin resistance in clinical trials. Our goal was to examine if carotenoids strengthen the beneficial effects of naringenin on human adipocyte metabolism.

Methods

Human preadipocytes from donors with obesity were differentiated in culture and treated with 8µM naringenin + 2µM β-carotene (NRBC) for seven days. Candidate genes involved in thermogenesis and glucose metabolism were measured as well as hormone-stimulated lipolysis.

Results

We found that β-carotene acts synergistically with naringenin to boost UCP1 and glucose metabolism genes including GLUT4 and adiponectin, compared to naringenin alone. Protein levels of PPARα, PPARγ and PPARγ-coactivator-1α, key modulators of thermogenesis and insulin sensitivity, were also upregulated after treatment with NRBC. Transcriptome sequencing was conducted and the bioinformatics analyses of the data revealed that NRBC induced enzymes for several non-UCP1 pathways for energy expenditure including triglyceride cycling, creatine kinases, and Peptidase M20 Domain Containing 1 (PM20D1). A comprehensive analysis of changes in receptor expression showed that NRBC upregulated eight receptors that have been linked to lipolysis or thermogenesis including the β1-adrenergic receptor and the parathyroid hormone receptor. NRBC increased levels of triglyceride lipases and agonist-stimulated lipolysis in adipocytes. We observed that expression of RXRγ, an isoform of unknown function, was induced ten-fold after treatment with NRBC. We show that RXRγ is a coactivator bound to the immunoprecipitated PPARγ protein complex from white and beige human adipocytes.

Discussion

There is a need for obesity treatments that can be administered long-term without side effects. NRBC increases the abundance and lipolytic response of multiple receptors for hormones released after exercise and cold exposure. Lipolysis provides the fuel for thermogenesis, and these observations suggest that NRBC has therapeutic potential.

Growth hormone stimulates lipolysis in mice but not in adipose tissue or adipocyte culture

The inhibitory effect of growth hormone (GH) on adipose tissue growth and the stimulatory effect of GH on lipolysis are well known, but the mechanisms underlying these effects are not completely understood. In this study, we revisited the effects of GH on adipose tissue growth and lipolysis in the lit/lit mouse model. The lit/lit mice are GH deficient because of a mutation in the GH releasing hormone receptor gene. We found that the lit/lit mice had more subcutaneous fat and larger adipocytes than their heterozygous lit/+ littermates and that these differences were partially reversed by 4-week GH injection. We also found that GH injection to the lit/lit mice caused the mature adipose tissue and adipocytes to reduce in size. These results demonstrate that GH inhibits adipose tissue growth at least in part by stimulating lipolysis. To determine the mechanism by which GH stimulates lipolysis, we cultured adipose tissue explants and adipocytes derived from lit/lit mice with GH and/or isoproterenol, an agonist of the beta-adrenergic receptors. These experiments showed that whereas isoproterenol, expectedly, stimulated potent lipolysis, GH, surprisingly, had no effect on basal lipolysis or isoproterenol-induced lipolysis in adipose tissue explants or adipocytes. We also found that both isoproterenol-induced lipolysis and phosphorylation of hormone-sensitive lipase were not different between lit/lit and lit/+ mice. Taken together, these results support the conclusion that GH has lipolytic effect in mice but argue against the notion that GH stimulates lipolysis by directly acting on adipocytes or by enhancing β-adrenergic receptors-mediated lipolysis.

Endothelial-Specific Expression of CIDEC Improves High-Fat Diet-Induced Vascular and Metabolic Dysfunction

Cell death-inducing DNA fragmentation factor-α-like effector C (CIDEC), originally identified to be a lipid droplet-associated protein in adipocytes, positively associates with insulin sensitivity. Recently, we discovered that it is expressed abundantly in human endothelial cells and regulates vascular function. The current study was designed to characterize the physiological effects and molecular actions of endothelial CIDEC in the control of vascular phenotype and whole-body glucose homeostasis. To achieve this, we generated a humanized mouse model expressing endothelial-specific human CIDEC (E-CIDECtg). E-CIDECtg mice exhibited protection against high-fat diet-induced glucose intolerance, insulin resistance, and dyslipidemia. Moreover, these mice displayed improved insulin signaling and endothelial nitric oxide synthase activation, enhanced endothelium-dependent vascular relaxation, and improved vascularization of adipose tissue, skeletal muscle, and heart. Mechanistically, we identified a novel interplay of CIDEC-vascular endothelial growth factor A (VEGFA)-vascular endothelial growth factor receptor 2 (VEGFR2) that reduced VEGFA and VEGFR2 degradation, thereby increasing VEGFR2 activation. Overall, our results demonstrate a protective role of endothelial CIDEC against obesity-induced metabolic and vascular dysfunction, in part, by modulation of VEGF signaling. These data suggest that CIDEC may be investigated as a potential future therapeutic target for mitigating obesity-related cardiometabolic disease.

Deletion of Jazf1 gene causes early growth retardation and insulin resistance in mice

Single-nucleotide polymorphisms in the human juxtaposed with another zinc finger protein 1 (JAZF1) gene have repeatedly been associated with both type 2 diabetes (T2D) and height in multiple genome-wide association studies (GWAS); however, the mechanism by which JAZF1 causes these traits is not yet known. To investigate the possible functional role of JAZF1 in growth and glucose metabolism in vivo, we generated Jazf1 knockout (KO) mice and examined body composition and insulin sensitivity both in young and adult mice by using ¹H-nuclear magnetic resonance and hyperinsulinemic-euglycemic clamp techniques. Plasma concentrations of insulin-like growth factor 1 (IGF-1) were reduced in both young and adult Jazf1 KO mice, and young Jazf1 KO mice were shorter in stature than age-matched wild-type mice. Young Jazf1 KO mice manifested reduced fat mass, whereas adult Jazf1 KO mice manifested increased fat mass and reductions in lean body mass associated with increased plasma growth hormone (GH) concentrations. Adult Jazf1 KO manifested muscle insulin resistance that was further exacerbated by high-fat diet feeding. Gene set enrichment analysis in Jazf1 KO liver identified the hepatocyte hepatic nuclear factor 4 alpha (HNF4α), which was decreased in Jazf1 KO liver and in JAZF1 knockdown cells. Moreover, GH-induced IGF-1 expression was inhibited by JAZF1 knockdown in human hepatocytes. Taken together these results demonstrate that reduction of JAZF1 leads to early growth retardation and late onset insulin resistance in vivo which may be mediated through alterations in the GH-IGF-1 axis and HNF4α.

Important Hormones Regulating Lipid Metabolism

There is a wide variety of kinds of lipids, and complex structures which determine the diversity and complexity of their functions. With the basic characteristic of water insolubility, lipid molecules are independent of the genetic information composed by genes to proteins, which determine the particularity of lipids in the human body, with water as the basic environment and genes to proteins as the genetic system. In this review, we have summarized the current landscape on hormone regulation of lipid metabolism. After the well-studied PI3K-AKT pathway, insulin affects fat synthesis by controlling the activity and production of various transcription factors. New mechanisms of thyroid hormone regulation are discussed, receptor α and β may mediate different procedures, the effect of thyroid hormone on mitochondria provides a new insight for hormones regulating lipid metabolism. Physiological concentration of adrenaline induces the expression of extrapituitary prolactin in adipose tissue macrophages, which promotes fat weight loss. Manipulation of hormonal action has the potential to offer a new therapeutic horizon for the global burden of obesity and its associated complications such as morbidity and mortality.

Growth hormone inhibits adipogenic differentiation and induces browning in bovine subcutaneous adipocytes

OBJECTIVE

It is well established that growth hormone (GH) has the ability to stimulate lipolysis. The effects of GH on adipocyte differentiation and browning have not been clearly described. Therefore, the present study aimed to elucidate the role of GH in the differentiation and browning of bovine subcutaneous adipocytes as well as its underlying molecular mechanisms.

METHODS

We first treated bovine subcutaneous preadipocytes with different concentrations (0, 10, 100, and 500 ng/mL) of GH for 8 days and measured lipid accumulation and gene expression. Afterward, we treated preadipocytes and mature adipocytes with 500 ng/mL GH and determined differentiation and browning-related indicators. Finally, we investigated the expression of STAT5B in both preadipocytes and mature adipocytes after GH treatment.

RESULTS

We demonstrated that GH inhibited lipid accumulation and decreased the expression levels of adipogenic key genes (SCD1, SREBP1, PPARγ, and CEBPα) during adipocyte differentiation. Moreover, we observed that the inhibitory effect of GH on the early stage of adipocyte differentiation (0-2 days) was stronger than that on the later stage of adipocyte differentiation (2-8 days). We also found that GH promoted the expression levels of browning-related genes such as uncoupling protein 1 (UCP1) in mature adipocytes. Concurrently, GH promoted mitochondrial biogenesis and increased the expression levels of mitochondrial biogenesis-related genes. In addition, GH promoted phosphorylation of signal transducers and activator of transcription 5 b (STAT5B) and contributed to translocation of STAT5B to nucleus. After blocking the expression of STAT5B protein, GH weakened the inhibition of adipogenic key genes and reduced the promotion of browning-related genes in bovine subcutaneous adipocytes.

CONCLUSIONS

GH can inhibit adipocyte differentiation and promote adipocyte browning by regulating STAT5B in bovine subcutaneous adipocytes.

Growth Hormone and Counterregulation in the Pathogenesis of Diabetes

PURPOSE OF REVIEW

Canonical growth hormone (GH)-dependent signaling is essential for growth and counterregulatory responses to hypoglycemia, but also may contribute to glucose homeostasis (even in the absence of hypoglycemia) via its impact on metabolism of carbohydrates, lipids and proteins, body composition, and cardiovascular risk profile. The aim of this review is to summarize recent data implicating GH action in metabolic control, including both IGF-1-dependent and -independent pathways, and its potential role as target for T2D therapy.

RECENT FINDINGS

Experimental blockade of the GHR can modulate glucose metabolism. Moreover, the soluble form of the GH receptor (GHR, or GHBP) was recently identified as a mediator of improvement in glycemic control in patients with T2D randomized to bariatric surgery vs. medical therapy. Reductions in GHR were accompanied by increases in plasma GH, but unchanged levels of both total and free IGF-1. Likewise, hepatic GHR expression is reduced following both RYGB and VSG in rodents. Emerging data indicate that GH signaling is important for regulation of long-term glucose metabolism in T2D. Future studies will be required to dissect tissue-specific GH signaling and sensitivity and their contributions to systemic glucose metabolism.

The acromegaly lipodystrophy

Growth hormone (GH) and insulin-like growth factor 1 (IGF-1) are essential to normal growth, metabolism, and body composition, but in acromegaly, excesses of these hormones strikingly alter them. In recent years, the use of modern methodologies to assess body composition in patients with acromegaly has revealed novel aspects of the acromegaly phenotype. In particular, acromegaly presents a unique pattern of body composition changes in the setting of insulin resistance that we propose herein to be considered an acromegaly-specific lipodystrophy. The lipodystrophy, initiated by a distinctive GH-driven adipose tissue dysregulation, features insulin resistance in the setting of reduced visceral adipose tissue (VAT) mass and intra-hepatic lipid (IHL) but with lipid redistribution, resulting in ectopic lipid deposition in muscle. With recovery of the lipodystrophy, adipose tissue mass, especially that of VAT and IHL, rises, but insulin resistance is lessened. Abnormalities of adipose tissue adipokines may play a role in the disordered adipose tissue metabolism and insulin resistance of the lipodystrophy. The orexigenic hormone ghrelin and peptide Agouti-related peptide may also be affected by active acromegaly as well as variably by acromegaly therapies, which may contribute to the lipodystrophy. Understanding the pathophysiology of the lipodystrophy and how acromegaly therapies differentially reverse its features may be important to optimizing the long-term outcome for patients with this disease. This perspective describes evidence in support of this acromegaly lipodystrophy model and its relevance to acromegaly pathophysiology and the treatment of patients with acromegaly.

Covert actions of growth hormone: fibrosis, cardiovascular diseases and cancer

Since its discovery nearly a century ago, over 100,000 studies of growth hormone (GH) have investigated its structure, how it interacts with the GH receptor and its multiple actions. These include effects on growth, substrate metabolism, body composition, bone mineral density, the cardiovascular system and brain function, among many others. Recombinant human GH is approved for use to promote growth in children with GH deficiency (GHD), along with several additional clinical indications. Studies of humans and animals with altered levels of GH, from complete or partial GHD to GH excess, have revealed several covert or hidden actions of GH, such as effects on fibrosis, cardiovascular function and cancer. In this Review, we do not concentrate on the classic and controversial indications for GH therapy, nor do we cover all covert actions of GH. Instead, we stress the importance of the relationship between GH and fibrosis, and how fibrosis (or lack thereof) might be an emerging factor in both cardiovascular and cancer pathologies. We highlight clinical data from patients with acromegaly or GHD, alongside data from cellular and animal studies, to reveal novel phenotypes and molecular pathways responsible for these actions of GH in fibrosis, cardiovascular function and cancer.

Human CIDEC transgene improves lipid metabolism and protects against high-fat diet-induced glucose intolerance in mice

Cell death–inducing DNA fragmentation factor-like effector C (CIDEC) expression in adipose tissue positively correlates with insulin sensitivity in obese humans. Further, E186X, a single-nucleotide CIDEC variant is associated with lipodystrophy, hypertriglyceridemia, and insulin resistance. To establish the unknown mechanistic link between CIDEC and maintenance of systemic glucose homeostasis, we generated transgenic mouse models expressing CIDEC (Ad-CIDECtg) and CIDEC E186X variant (Ad-CIDECmut) transgene specifically in the adipose tissue. We found that Ad-CIDECtg but not Ad-CIDECmut mice were protected against high-fat diet-induced glucose intolerance. Furthermore, we revealed the role of CIDEC in lipid metabolism using transcriptomics and lipidomics. Serum triglycerides, cholesterol, and low-density lipoproteins were lower in high-fat diet-fed Ad-CIDECtg mice compared to their littermate controls. Mechanistically, we demonstrated that CIDEC regulates the enzymatic activity of adipose triglyceride lipase via interacting with its activator, CGI-58, to reduce free fatty acid release and lipotoxicity. In addition, we confirmed that CIDEC is indeed a vital regulator of lipolysis in adipose tissue of obese humans, and treatment with recombinant CIDEC decreased triglyceride breakdown in visceral human adipose tissue. Our study unravels a central pathway whereby adipocyte-specific CIDEC plays a pivotal role in regulating adipose lipid metabolism and whole-body glucose homeostasis. In summary, our findings identify human CIDEC as a potential ‘drug’ or a ‘druggable’ target to reverse obesity-induced lipotoxicity and glucose intolerance.

Growth Hormone and Insulin-Like Growth Factor 1 Regulation of Nonalcoholic Fatty Liver Disease

Patients with obesity have a high prevalence of nonalcoholic fatty liver disease (NAFLD), representing a spectrum of simple steatosis to nonalcoholic steatohepatitis (NASH), without and with fibrosis. Understanding the etiology of NAFLD is clinically relevant since NAFLD is an independent risk factor for diabetes and cardiovascular disease. In addition, NASH predisposes patients to the development of cirrhosis and hepatocellular carcinoma, and NASH cirrhosis represents the fastest growing indication for liver transplantation in the United States. It is appreciated that multiple factors are involved in the development and progression of NAFLD. Growth hormone (GH) and insulin-like growth factor 1 (IGF1) regulate metabolic, immune, and hepatic stellate cell function, and alterations in the production and function of GH is associated with obesity and NAFLD/NASH. Therefore, this review will focus on the potential role of GH and IGF1 in the regulation of hepatic steatosis, inflammation, and fibrosis.

Metformin Inhibits Lipid Droplets Fusion and Growth via Reduction in Cidec and Its Regulatory Factors in Rat Adipose-Derived Stem Cells

Metformin is still being investigated due to its potential use as a therapeutic agent for managing overweight or obesity. However, the underlying mechanisms are not fully understood. Inhibiting the adipogenesis of adipocyte precursors may be a new therapeutic opportunity for obesity treatments. It is still not fully elucidated whether adipogenesis is also involved in the weight loss mechanisms by metformin. We therefore used adipose-derived stem cells (ADSCs) from inguinal and epididymal fat pads to investigate the effects and mechanisms of metformin on adipogenesis in vitro. Our results demonstrate the similar effect of metformin inhibition on lipid accumulation, lipid droplets fusion, and growth in adipose-derived stem cells from epididymal fat pads (Epi-ADSCs) and adipose-derived stem cells from inguinal fat pads (Ing-ADSCs) cultures. We identified that cell death-inducing DFFA-like effector c (Cidec), Perilipin1, and ras-related protein 8a (Rab8a) expression increased ADSCs differentiation. In addition, we found that metformin inhibits lipid droplets fusion and growth by decreasing the expression of Cidec, Perilipin1, and Rab8a. Activation of AMPK pathway signaling in part involves metformin inhibition on Cidec, Perilipin1, and Rab8a expression. Collectively, our study reveals that metformin inhibits lipid storage, fusion, and growth of lipid droplets via reduction in Cidec and its regulatory factors in ADSCs cultures. Our study supports the development of clinical trials on metformin-based therapy for patients with overweight and obesity.

Fsp27 plays a crucial role in muscle performance

Fsp27 was previously identified as a lipid droplet-associated protein in adipocytes. Various studies have shown that it plays a role in the regulation of lipid homeostasis in adipose tissue and liver. However, its function in muscle, which also accumulate and metabolize fat, remains completely unknown. Our present study identifies a novel role of Fsp27 in muscle performance. Here, we demonstrate that Fsp27-/- and Fsp27+/- mice, both males and females, had severely impaired muscle endurance and exercise capacity compared with wild-type controls. Liver and muscle glycogen stores were similar among all groups fed or fasted, and before or after exercise. Reduced muscle performance in Fsp27-/- and Fsp27+/- mice was associated with severely decreased fat content in the muscle. Furthermore, results in heterozygous Fsp27+/- mice indicate that Fsp27 haploinsufficiency undermines muscle performance in both males and females. In summary, our physiological findings reveal that Fsp27 plays a critical role in muscular fat storage, muscle endurance, and muscle strength.NEW & NOTEWORTHY This is the first study identifying Fsp27 as a novel protein associated with muscle metabolism. The Fsp27-knockout model shows that Fsp27 plays a role in muscular-fat storage, muscle endurance, and muscle strength, which ultimately impacts limb movement. In addition, our study suggests a potential metabolic paradox in which FSP27-knockout mice presumed to be metabolically healthy based on glucose utilization and oxidative metabolism are unhealthy in terms of exercise capacity and muscular performance.

Loss of Adipocyte STAT5 Confers Increased Depot-Specific Adiposity in Male and Female Mice That Is Not Associated With Altered Adipose Tissue Lipolysis

STATs (Signal Transducers and Activators of Transcription) 5A and 5B are induced during adipocyte differentiation and are primarily activated by growth hormone (GH) and prolactin in fat cells. Previous studies in mice lacking adipocyte GH receptor or STAT5 support their roles in lipolysis-mediated reduction of adipose tissue mass. Male and female mice harboring adipocyte-specific deletion of both STAT5 genes (STAT5^AKO) exhibit increased subcutaneous or inguinal adipose tissue mass, but no changes in visceral or gonadal fat mass. Both depots display substantial increases in adipocyte size with no changes in lipolysis in adipose tissue explants. RNA sequencing analysis of subcutaneous adipose tissue and indirect calorimetry experiments reveal sex-dependent differences in adipose gene expression and whole-body energy expenditure, respectively, resulting from the loss of adipocyte STAT5.

Dispersion and utilization of lipid droplets mediates respiratory syncytial virus-induced airway hyperresponsiveness

BACKGROUND

Respiratory viral infections (RSV) can induce acute asthma attacks, thereby destroying lung function and accelerating the progression of the disease. However, medications in the stable phase of asthma are often not effective for acute attacks induced by viral infections. We aimed to clarify the possible mechanism of viral infection-induced asthma through fatty acid metabolism.

METHODS AND RESULTS

The airway resistances, inflammatory injuries, and oxidative stress in the RSV-induced animal models were significantly higher than those in the control group at acute phase (7 days) and chronic phase (28 days). Moreover, the concentrations of the medium- and long-chain fatty acids in lung tissue at (28 days) were significantly increased, including 14:0 (myristic acid), 16:0 (palmitic acid, PA), 18:1 (oleic acid, OA), and 18:2 (linoleic acid, LA) using non-targeted metabonomics. Airway epithelial cells treated with RSV showed the reduced expression of FSP27, RAB8A, and PLIN5, which caused the fusion and growth of lipid droplet (LD), and increased expression of the LD dispersion gene perilipin 2. There was also a decrease in PPARγ expression and an increase in the fatty acid catabolism gene PPARα, causing lipid oxidation, free fatty acid releases, and an upsurge in IL-1, IL-2, IL-4, and IL-6 expression, which could be abrogated by GPR40 inhibitor. Treated mice or epithelial cells with C18 fatty acid exhibited inhibition of epithelial proliferation, increases of inflammation, and oxidative damage.

CONCLUSIONS

RSV promoted lipid dispersion and utilization, causing enlarged oxidative injuries and an upsurge in the pro-inflammatory cytokines, leading to the progression of airway hyperresponsiveness (AHR).

Reversible insulin resistance in muscle and fat unrelated to the metabolic syndrome in patients with acromegaly

BACKGROUND

Patients with active acromegaly exhibit insulin resistance despite a lean phenotype whereas controlled disease improves insulin sensitivity and increases fat mass. The mechanisms underlying this paradox remain elusive, but growth hormone (GH)-induced lipolysis plays a central role. The aim of the study was to investigative the molecular mechanisms of insulin resistance dissociated from obesity in patients with acromegaly.

METHODS

In a prospective study, twenty-one patients with newly diagnosed acromegaly were studied at diagnosis and after disease control obtained by either surgery alone (n=10) or somatostatin analogue (SA) treatment (n=11) with assessment of body composition (DXA scan), whole body and tissue-specific insulin sensitivity and GH and insulin signalling in adipose tissue and skeletal muscle.

FINDINGS

Disease control of acromegaly significantly reduced lean body mass (p<0.001) and increased fat mass (p<0.001). At diagnosis, GH signalling (pSTAT5) was constitutively activated in fat and enhanced expression of GH-regulated genes (CISH and IGF-I) were detected in muscle and fat. Insulin sensitivity in skeletal muscle, liver and adipose tissue increased after disease control regardless of treatment modality. This was associated with enhanced insulin signalling in both muscle and fat including downregulation of phosphatase and tensin homolog (PTEN) together with reduced signalling of GH and lipolytic activators in fat.

INTERPRETATION

In conclusion, the study support that uncontrolled lipolysis is a major feature of insulin resistance in active acromegaly, and is characterized by upregulation of PTEN and suppression of insulin signalling in both muscle and fat.

FUNDING

This work was supported by a grant from the Independent Research Fund, Denmark (7016-00303A) and from the Alfred Benzon Foundation, Denmark.

The GH-IGF-1 Axis in Circadian Rhythm

Organisms have developed common behavioral and physiological adaptations to the influence of the day/night cycle. The CLOCK system forms an internal circadian rhythm in the suprachiasmatic nucleus (SCN) during light/dark input. The SCN may synchronize the growth hormone (GH) secretion rhythm with the dimming cycle through somatostatin neurons, and the change of the clock system may be related to the pulsatile release of GH. The GH-insulin-like growth factor 1 (IGF-1) axis and clock system may interact further on the metabolism through regulatory pathways in peripheral organs. We have summarized the current clinical and animal evidence on the interaction of clock systems with the GH-IGF-1 axis and discussed their effects on metabolism.

Towards Understanding the Direct and Indirect Actions of Growth Hormone in Controlling Hepatocyte Carbohydrate and Lipid Metabolism

Growth hormone (GH) is critical for achieving normal structural growth. In addition, GH plays an important role in regulating metabolic function. GH acts through its GH receptor (GHR) to modulate the production and function of insulin-like growth factor 1 (IGF1) and insulin. GH, IGF1, and insulin act on multiple tissues to coordinate metabolic control in a context-specific manner. This review will specifically focus on our current understanding of the direct and indirect actions of GH to control liver (hepatocyte) carbohydrate and lipid metabolism in the context of normal fasting (sleep) and feeding (wake) cycles and in response to prolonged nutrient deprivation and excess. Caveats and challenges related to the model systems used and areas that require further investigation towards a clearer understanding of the role GH plays in metabolic health and disease are discussed.

Loss of growth hormone signaling in the mouse germline or in adulthood reduces islet mass and alters islet function with notable sex differences

In the endocrine pancreas, growth hormone (GH) is known to promote pancreatic islet growth and insulin secretion. In this study, we show that GH receptor (GHR) loss in the germline and in adulthood impacts islet mass in general but more profoundly in male mice. GHR knockout (GHRKO) mice have enhanced insulin sensitivity and low circulating insulin. We show that the total cross-sectional area of isolated islets (estimated islet mass) was reduced by 72% in male but by only 29% in female GHRKO mice compared with wild-type controls. Also, islets from GHRKO mice secreted ∼50% less glucose-stimulated insulin compared with size-matched islets from wild-type mice. We next used mice with a floxed Ghr gene to knock down the GHR in adult mice at 6 mo of age (6mGHRKO) and examined the impact on glucose and islet metabolism. By 12 mo of age, female 6mGHRKO mice had increased body fat and reduced islet mass but had no change in glucose tolerance or insulin sensitivity. However, male 6mGHRKO mice had nearly twice as much body fat, substantially reduced islet mass, and enhanced insulin sensitivity, but no change in glucose tolerance. Despite large losses in islet mass, glucose-stimulated insulin secretion from isolated islets was not significantly different between male 6mGHRKO and controls, whereas isolated islets from female 6mGHRKO mice showed increased glucose-stimulated insulin release. Our findings demonstrate the importance of GH to islet mass throughout life and that unique sex-specific adaptations to the loss of GH signaling allow mice to maintain normal glucose metabolism.NEW & NOTEWORTHY Growth hormone (GH) is important for more than just growth. GH helps to maintain pancreatic islet mass and insulin secretion throughout life. Sex-specific adaptations to the loss of GH signaling allow mice to maintain normal glucose regulation despite losing islet mass.

Anacardic Acid Suppresses Adipogenesis Through Inhibition of the Hsp90/Akt Signaling Pathway in 3T3-L1 Preadipocytes

Anacardic acid (AA), a major component of cashew nut shell liquid, has extensive bioactivities. However, little is known about its antiadipogenic properties or the mechanism that underpins them. The aim of this study was to investigate the effect of AA on 3T3-L1 preadipocyte differentiation and its mechanisms of action. AA inhibits lipid accumulation during adipogenesis in 3T3-L1 preadipocyte (IC₅₀ = 25.45 μM). AA abrogates mRNA expressions of the genes implicated in lipogenesis and their transcription factors, especially Pparg and Cebpa. Furthermore, antibody microarray and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis results showed that the proteins implicated in the Akt signaling pathway were most likely altered by AA. Notably, upon AA treatment, heat shock protein 90 (Hsp90), a positive regulator of Akt, was decreased, resulting in Akt degradation. These findings indicate that AA, a natural product that acts as a Hsp90/Akt signaling inhibitor, may be a possible antiadipogenic agent.

The Relationship between Serum Insulin-Like Growth Factor-1 Levels and Body Composition Changes after Sleeve Gastrectomy

INTRODUCTION

We previously reported that preoperative serum insulin-like growth factor-1 (IGF-1) is a predictor of total weight loss percentage (%TWL) after laparoscopic sleeve gastrectomy (LSG). IGF-1 may suppress muscle loss after surgery. IGF-1 almost accurately reflects the growth hormone (GH) secretion status, and GH has lipolytic effects. Therefore, IGF-1 may influence both the maintenance of skeletal muscle and the reduction of adipose tissue after LSG. The identification of the relationship between preoperative serum IGF-1 and body composition changes after LSG can help in understanding the pathophysiology of obesity.

METHODS

We retrospectively reviewed 72 patients with obesity who underwent LSG and were followed up for 12 months. We analyzed the relationship between preoperative serum IGF-1 levels and body composition changes after LSG. A multiple regression model was used.

RESULTS

LSG led to a significant reduction in body weight. Both body fat mass and skeletal muscle mass decreased after LSG. Preoperative serum IGF-1 levels significantly correlated with %TWL, changes in skeletal muscle mass, and body fat mass after LSG. The multiple regression model showed that preoperative serum IGF-1 levels were related to decreased body fat mass and maintaining skeletal muscle mass after LSG.

DISCUSSION/CONCLUSION

Preoperative IGF-1 measurement helps predict not only successful weight loss but also decreases body fat mass and maintains skeletal muscle mass after LSG.

Effect of growth hormone on insulin signaling

Growth hormone (GH) is a pleiotropic hormone that coordinates an array of physiological processes, including effects on bone, muscle, and fat, ultimately resulting in growth. Metabolically, GH promotes anabolic action in most tissues except adipose, where its catabolic action causes the breakdown of stored triglycerides into free fatty acids (FFA). GH antagonizes insulin action via various molecular pathways. Chronic GH secretion suppresses the anti-lipolytic action of insulin and increases FFA flux into the systemic circulation; thus, promoting lipotoxicity, which causes pathophysiological problems, including insulin resistance. In this review, we will provide an update on GH-stimulated adipose lipolysis and its consequences on insulin signaling in liver, skeletal muscle, and adipose tissue. Furthermore, we will discuss the mechanisms that contribute to the diabetogenic action of GH.

Similar safety and efficacy in previously treated adults with growth hormone deficiency randomized to once-weekly somapacitan or daily growth hormone

OBJECTIVE

Somapacitan is a long-acting, reversible albumin-binding growth hormone (GH) derivative in development. This study aimed to evaluate the safety and efficacy of once-weekly somapacitan versus daily GH over 52 weeks in Japanese patients with adult growth hormone deficiency (AGHD).

DESIGN

Phase 3, multicentre, randomized, parallel-group, open-label, active-controlled trial (NCT03075644).

PATIENTS

Previously GH-treated Japanese patients with AGHD were randomized 3:1 to somapacitan (n = 46) or daily GH (n = 16) for 20 weeks' dose titration and 32 weeks' fixed-dose treatment.

MEASUREMENTS

Primary endpoint was the incidence of adverse events (AEs). Secondary endpoints included change from baseline to week 52 in visceral, subcutaneous and total adipose tissue (VAT, SAT and TAT).

RESULTS

Mean (SD) prescribed doses after titration were 1.780 (1.058) mg/week for somapacitan and 0.197 (0.083) mg/day for daily GH. Rate of AEs per 100 patient-years was similar between arms (somapacitan, 312.7; daily GH, 309.8). Four AEs in the somapacitan arm were serious; none were considered treatment-related. Mean insulin-like growth factor-I standard deviation score (IGF-I SDS) was maintained from baseline in both arms. No significant differences were observed between arms for change from baseline to week 52 in VAT, SAT or TAT (estimated difference, somapacitan - daily GH [95% CI]: -1.74 [-18.13; 14.66], -11.53 [-35.54; 12.48] and - 12.85 [-47.31; 21.62] cm² , respectively).

CONCLUSIONS

Treatment in both groups was well tolerated, with no unexpected safety findings. Impact on adipose tissue was similar to somapacitan and daily GH in patients with AGHD. A short visual summary of our work is available at https://bit.ly/3946YNF.

Disordered metabolism in mice lacking irisin

Irisin is a product of fibronectin type III domain-containing protein (Fndc5) and is involved in the regulation of adipokine secretion and the differentiation of osteoblasts and osteoclasts. In this study, we aimed to determine whether irisin lacking affects glucose/lipid and bone metabolism. We knocked out the Fndc5 gene to generate irisin-lacking mice. Remarkable, irisin lacking was related to poor 'browning response', with a bigger size of the intraperitoneal white adipose cell and decreased a number of brown adipose cells in brown adipose of interscapular tissue. The irisin lacking mice had hyperlipidemia and insulin resistance, reduced HDL-cholesterol level, increased LDL-cholesterol level, and decreased insulin sensitivity. The lacking of irisin was associated with reduced bone strength and bone mass in mice. The increased number of osteoclasts and higher expression of RANKL indicated increased bone resorption in irisin lacking mice. The level of IL-6 and TNF-α also increased in irisin lacking mice. The results showed that irisin lacking was related to decreased 'browning response', glucose/lipid metabolic derangement, and reduced bone mass with increased bone resorption. Further studies are needed to confirm these initial observations and explore the mechanisms underlying the effects of irisin on glucose/lipid and bone metabolism.

Insulin and Growth Hormone Balance: Implications for Obesity

Disruption of endocrine hormonal balance (i.e., increased levels of insulin, and reduced levels of growth hormone, GH) often occurs in pre-obesity and obesity. Using distinct intracellular signaling pathways to control cell and body metabolism, GH and insulin also regulate each other's secretion to maintain overall metabolic homeostasis. Therefore, a comprehensive understanding of insulin and GH balance is essential for understanding endocrine hormonal contributions to energy storage and utilization. In this review we summarize the actions of, and interactions between, insulin and GH at the cellular level, and highlight the association between the insulin/GH ratio and energy metabolism, as well as fat accumulation. Use of the [insulin]:[GH] ratio as a biomarker for predicting the development of obesity is proposed.

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.

The Lipolysome-A Highly Complex and Dynamic Protein Network Orchestrating Cytoplasmic Triacylglycerol Degradation

The catabolism of intracellular triacylglycerols (TAGs) involves the activity of cytoplasmic and lysosomal enzymes. Cytoplasmic TAG hydrolysis, commonly termed lipolysis, is catalyzed by the sequential action of three major hydrolases, namely adipose triglyceride lipase, hormone-sensitive lipase, and monoacylglycerol lipase. All three enzymes interact with numerous protein binding partners that modulate their activity, cellular localization, or stability. Deficiencies of these auxiliary proteins can lead to derangements in neutral lipid metabolism and energy homeostasis. In this review, we summarize the composition and the dynamics of the complex lipolytic machinery we like to call "lipolysome".

The effects of growth hormone on adipose tissue: old observations, new mechanisms

The ability of growth hormone (GH) to induce adipose tissue lipolysis has been known for over five decades; however, the molecular mechanisms that mediate this effect and the ability of GH to inhibit insulin-stimulated glucose uptake have scarcely been documented. In this same time frame, our understanding of adipose tissue has evolved to reveal a complex structure with distinct types of adipocyte, depot-specific differences, a biologically significant extracellular matrix and important endocrine properties mediated by adipokines. All these aforementioned features, in turn, can influence lipolysis. In this Review, we provide a historical and current overview of the lipolytic effect of GH in humans, mice and cultured cells. More globally, we explain lipolysis in terms of GH-induced intracellular signalling and its effect on obesity, insulin resistance and lipotoxicity. In this regard, findings that define molecular mechanisms by which GH induces lipolysis are described. Finally, data are presented for the differential effect of GH on specific adipose tissue depots and on distinct classes of metabolically active adipocytes. Together, these cellular, animal and human studies reveal novel cellular phenotypes and molecular pathways regulating the metabolic effects of GH on adipose tissue.

The acute effects of growth hormone in adipose tissue is associated with suppression of antilipolytic signals

AIM

Since GH stimulates lipolysis in vivo after a 2-hr lag phase, we studied whether this involves GH signaling and gene expression in adipose tissue (AT).

METHODS

Human subjects (n = 9) each underwent intravenous exposure to GH versus saline with measurement of serum FFA, and GH signaling, gene array, and protein in AT biopsies after 30-120 min. Human data were corroborated in adipose-specific GH receptor knockout (FaGHRKO) mice versus wild-type mice. Expression of candidate genes identified in the array were investigated in 3T3-L1 adipocytes.

RESULTS

GH increased serum FFA and AT phosphorylation of STAT5b in human subjects. This was replicated in wild-type mice, but not in FaGHRKO mice. The array identified 53 GH-regulated genes, and Ingenuity Pathway analysis showed downregulation of PDE3b, an insulin-dependent antilipolytic signal, upregulation of PTEN that inhibits insulin-dependent antilipolysis, and downregulation of G0S2 and RASD1, both encoding antilipolytic proteins. This was confirmed in 3T3-L1 adipocytes, except for PDE3B, including reciprocal effects of GH and insulin on mRNA expression of PTEN, RASD1, and G0S2.

CONCLUSION

(a) GH directly stimulates AT lipolysis in a GHR-dependent manner, (b) this involves suppression of antilipolytic signals at the level of gene expression, (c) the underlying GH signaling pathways remain to be defined.

Pgc1a is responsible for the sex differences in hepatic Cidec/Fsp27β mRNA expression in hepatic steatosis of mice fed a Western diet

Hepatic fat-specific protein 27 [cell death-inducing DNA fragmentation effector protein C (Cidec)/Fsp27] mRNA levels have been associated with hepatic lipid droplet extent under certain circumstances. To address its hepatic expression under different dietary conditions and in both sexes, apolipoprotein E (Apoe)-deficient mice were subjected to different experimental conditions for 11 wk to test the influence of cholesterol, Western diet, squalene, oleanolic acid, sex, and surgical castration on Cidec/Fsp27 mRNA expression. Dietary cholesterol increased hepatic Cidec/Fsp27β expression, an effect that was suppressed when cholesterol was combined with saturated fat as represented by Western diet feeding. Using the latter diet, neither oleanolic acid nor squalene modified its expression. Females showed lower levels of hepatic Cidec/Fsp27β expression than males when they were fed Western diets, a result that was translated into a lesser amount of CIDEC/FSP27 protein in lipid droplets and microsomes. This was also confirmed in low-density lipoprotein receptor (Ldlr)-deficient mice. Incubation with estradiol resulted in decreased Cidec/Fsp27β expression in AML12 cells. Whereas male surgical castration did not modify the expression, ovariectomized females did show increased levels compared with control females. Females also showed increased expression of peroxisome proliferator-activated receptor-γ coactivator 1-α (Pgc1a), suppressed by ovariectomy, and the values were significantly and inversely associated with those of Cidec/Fsp27β. When Pgc1a-deficient mice were used, the sex differences in Cidec/Fsp27β expression disappeared. Therefore, hepatic Cidec/Fsp27β expression has a complex regulation influenced by diet and sex hormonal milieu. The mRNA sex differences are controlled by Pgc1a.

FSP27 and Links to Obesity and Diabetes Mellitus

PURPOSE OF REVIEW

Obesity is a pandemic, yet preventable healthcare problem. Insulin resistance, diabetes mellitus, dyslipidemia, and cardiovascular complications are core manifestation of obesity. While adipose tissue is a primary site of energy storage, it is also an endocrine organ, secreting a large number of adipokines and cytokines. Nonetheless in obesity, the secretion of cytokines and free fatty acids increases significantly and is associated with the degree of adiposity and insulin resistance. Fat-specific protein 27 (FSP27) has emerged as one of the major proteins that promote physiological storage of fat in adipose tissue.

RECENT FINDINGS

Review of number of recent findings suggests that FSP27 plays a crucial role in physiological storage of fat within the adipose tissue especially in humans. However, in disease conditions such as obesity, FSP27 may contribute to ectopic fat accumulation in non-adipose tissue. More studies are required to highlight the tissue-specific role of FSP27, especially in humans.

Temporal patterns of lipolytic regulators in adipose tissue after acute growth hormone exposure in human subjects: A randomized controlled crossover trial

Objective

Growth hormone (GH) stimulates lipolysis, but the underlying mechanisms remain incompletely understood. We examined the effect of GH on the expression of lipolytic regulators in adipose tissue (AT).

Methods

In a randomized, placebo-controlled, cross-over study, nine men were examined after injection of 1) a GH bolus and 2) a GH-receptor antagonist (pegvisomant) followed by four AT biopsies. In a second study, eight men were examined in a 2 × 2 factorial design including GH infusion and 36-h fasting with AT biopsies obtained during a basal period and a hyperinsulinemic-euglycemic clamp. Expression of GH-signaling intermediates and lipolytic regulators were studied by PCR and western blotting. In addition, mechanistic experiments in mouse models and 3T3-L1 adipocytes were performed.

Results

The GH bolus increased circulating free fatty acids (p < 0.0001) together with phosphorylation of signal transducer and activator of transcription 5 (STAT5) (p < 0.0001) and mRNA expression of the STAT5-dependent genes cytokine-inducible SH2-containing protein (CISH) and IGF-1 in AT. This was accompanied by suppressed mRNA expression of G0/G1 switch gene 2 (G0S2) (p = 0.007) and fat specific protein 27 (FSP27) (p = 0.002) and upregulation of phosphatase and tensin homolog (PTEN) mRNA expression (p = 0.03). Suppression of G0S2 was also observed in humans after GH infusion and fasting, as well as in GH transgene mice, and in vitro studies suggested MEK-PPARγ signaling to be involved.

Conclusions

GH-induced lipolysis in human subjects in vivo is linked to downregulation of G0S2 and FSP27 and upregulation of PTEN in AT. Mechanistically, in vitro data suggest that GH acts via MEK to suppress PPARγ-dependent transcription of G0S2. ClinicalTrials.govNCT02782221 and NCT01209429.

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Acute GH exposure in human subjects in vivo stimulates lipolysis and release of FFA together with GH signaling in adipose tissue.

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GH-induced lipolysis is associated with suppression of G0S2 and FSP27 and upregulation of PTEN in human subjects in vivo.

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Inhibition of MEK and activation of PPARγ abrogate GH-induced suppression of G0S2 mRNA expression in vitro.

CIDE Proteins in Human Health and Disease

Cell death-Inducing DNA Fragmentation Factor Alpha (DFFA)-like Effector (CIDE) proteins have emerged as lipid droplet-associated proteins that regulate fat metabolism. There are three members in the CIDE protein family—CIDEA, CIDEB, and CIDEC (also known as fat-specific protein 27 (FSP27)). CIDEA and FSP27 are primarily expressed in adipose tissue, while CIDEB is expressed in the liver. Originally, based upon their homology with DNA fragmentation factors, these proteins were identified as apoptotic proteins. However, recent studies have changed the perception of these proteins, redefining them as regulators of lipid droplet dynamics and fat metabolism, which contribute to a healthy metabolic phenotype in humans. Despite various studies in humans and gene-targeting studies in mice, the physiological roles of CIDE proteins remains elusive. This review will summarize the known physiological role and metabolic pathways regulated by the CIDE proteins in human health and disease.

Insulin Resistance in Patients With Acromegaly

Acromegaly is characterized by chronic overproduction of growth hormone (GH) that leads to insulin resistance, glucose intolerance and, ultimately, diabetes. The GH-induced sustained stimulation of lipolysis plays a major role not only in the development of insulin resistance and prediabetes/diabetes, but also in the reduction of lipid accumulation, making acromegaly a unique case of severe insulin resistance in the presence of reduced body fat. In the present review, we elucidate the effects of GH hypersecretion on metabolic organs, describing the pathophysiology of impaired glucose tolerance in acromegaly, as well as the impact of acromegaly-specific therapies on glucose metabolism. In addition, we highlight the role of insulin resistance in the development of acromegaly-associated complications such as hypertension, cardiac disease, sleep apnea, polycystic ovaries, bone disease, and cancer. Taken together, insulin resistance is an important metabolic hallmark of acromegaly, which is strongly related to disease activity, the development of comorbidities, and might even impact the response to drugs used in the treatment of acromegaly.

Metabolic Effects of Testosterone Hormone Therapy in Normal and Orchiectomized Male Rats: From Indirect Calorimetry to Lipolytic Enzymes

BACKGROUND AND AIM

Changes in total energy expenditure (TEE) and substrate metabolism may help explain the metabolic actions of testosterone (T). This study measured respiratory quotient (RQ), TEE, ghrelin, insulin, and key lipolysis enzyme concentrations in relation to body weight (wt) and food intake (FI) in both normal and bilaterally orchiectomized rats with/without T treatment.

METHODS

In total, thirty-two male Wistar rats (300-400 g) were divided into four groups (n = 8/group), including (a) sham-operated and vehicle-injected group (Sham), (b) T-treated sham group (T-Sham) for which sham-operated rats were injected with IM testosterone undecanoate (100 mg/kg, for one week), (c) orchiectomy and vehicle-injected group (Orch), and (d) T-replaced orchiectomy group (T-Orch). After one week, FI and wt were automatically recorded, indirect calorimetry parameters were measured, and blood samples were collected to measure T, ghrelin, insulin, growth hormone (GH), glucose, hormone-sensitive lipase (HSL), adipocyte triglyceride lipase (ATGL), free fatty acids (FFA), and lipid profiles.

RESULTS

Orchiectomy decreased ghrelin, GH, and insulin levels, increased TEE and RQ, and lowered FI and wt. The T-Orch group exhibited increased levels of ghrelin (3-fold), insulin, GH, blood levels of lipolysis products, TEE, and FI in addition to reduced glucose levels (P < 0.05). This group demonstrated no significant changes in wt. In the T-Sham group, T increased ghrelin and insulin levels (P < 0.05) with strong positive correlations (r = 0.663 and 0.644, respectively, P < 0.05), increased ATGL levels, RQ toward carbohydrate utilization ranges, and TEE, and reduced HSL levels (P < 0.05) with insignificant changes in FI or wt.

CONCLUSIONS

T administration in orchiectomized rats significantly increased orexigenic mediators such as ghrelin and insulin without inducing any significant changes in wt. The mechanism for this finding might be the increased TEE and the stimulation of lipolysis through the ATGL enzyme. The associated rise of GH might help in interference with accumulation of lipid in adipose tissue. Apart from the effect on GH, T-Sham showed similar effects of T supplementation.