Long-term decrease in body fat and in brown adipose tissue in capsaicin-desensitized rats

Evidence for acupoint catgut embedding treatment and TRPV1 gene deletion increasing weight control in murine model

Obesity is a global health problem affecting the general population. Acupoint catgut embedding (ACE) is an alternative treatment that involves the implantation of absorbable catgut suture at acupoints. The transient receptor vanilloid member 1 (TRPV1) is a calcium ion channel that responds to several chemical ligands and is identified in numerous locations throughout the body. The aim of the present study was to examine the effect of ACE treatment on obesity and its associated complications through various neural mechanisms in a murine model. A C57/BL6 wild type (WT) and TRPV1‑/‑ (KO) mouse model was utilized to exclude any psychological factors associated with obesity. The WT‑HFD‑ACE and WT‑HFD‑SHAM groups received weekly ACE or placebo treatments at the bilateral ST36 acupoint. The mice were fed with a normal mice chow diet (ND) or a high‑fat food diet (HFD; 45 kcal%), and their body weights were recorded once a week. After 8 weeks, the subjects were sacrificed and changes in the levels of a number of biomarkers were investigated using ELISA, immunoblotting and immunofluorescence. The results indicated a significant decrease in body weight variation for the WT‑HFD‑ACE group compared with the WT‑HFD and WT‑HFD‑SHAM groups, using the WT‑ND group as the body weight baseline. By contrast, KO mice fed with ND or HFD demonstrated notable body weight maintenance throughout the experimental period. Similar patterns were observed in adipose tissue mass, glucose, leptin and insulin plasma levels, and protein molecule density of TRPV1 and its associated molecules in the hypothalamus and nucleus tractus solitarii. In contrast, in the prefrontal cortex, significant decreases in the concentrations of MAPK pathway proteins in the WT‑HFD and WT‑HFD‑SHAM groups were observed. The levels of these proteins were significantly increased in the WT‑HFD‑ACE and KO‑HFD groups. These results suggested that TRPV1 and its associated pathways may be involved in body weight maintenance, and may be controlled through ACE treatment or genetic manipulation.

TRPV1 Antagonists as Novel Anti-Diabetic Agents: Regulation of Oral Glucose Tolerance and Insulin Secretion Through Reduction of Low-Grade Inflammation?

With a global prevalence among adults over 18 years of age approaching 9%, Type 2 diabetes mellitus (T2DM) has reached pandemic proportions and represents a major unmet medical need. To date, no disease modifying treatment is available for T2DM patients. Accumulating evidence suggest that the sensory nervous system is involved in the progression of T2DM by maintaining low-grade inflammation via the vanilloid (capsaicin) receptor, Transient Receptor Potential Vanilloid-1 (TRPV1). In this study, we tested the hypothesis that TRPV1 is directly involved in glucose homeostasis in rodents. TRPV1 receptor knockout mice (Trpv1^−/−) and their wild-type littermates were kept on high-fat diet for 15 weeks. Moreover, Zucker obese rats were given the small molecule TRPV1 antagonist, N-(4-Tertiarybutylphenyl)-4-(3-cholorphyridin-2-yl)tetrahydropyrazine-1(2H)-carbox-amide (BCTC), per os twice-a-day or vehicle for eight days. Oral glucose tolerance and glucose-stimulated insulin secretion was improved by both genetic inactivation (Trpv1^−/− mice) and pharmacological blockade (BCTC) of TRPV1. In the obese rat, the improved glucose tolerance was accompanied by a reduction in inflammatory markers in the mesenteric fat, suggesting that blockade of low-grade inflammation contributes to the positive effect of TRPV1 antagonism on glucose metabolism. We propose that TRPV1 could be a promising therapeutic target in T2DM by improving glucose intolerance and correcting dysfunctional insulin secretion.

Perivascular Adipose Tissue: the Sixth Man of the Cardiovascular System

Perivascular adipose tissue (PVAT) refers to the local aggregate of adipose tissue surrounding the vascular tree, exhibiting phenotypes from white to brown and beige adipocytes. Although PVAT has long been regarded as simply a structural unit providing mechanical support to vasculature, it is now gaining reputation as an integral endocrine/paracrine component, in addition to the well-established modulator endothelium, in regulating vascular tone. Since the discovery of anti-contractile effect of PVAT in 1991, the use of multiple rodent models of reduced amounts of PVAT has revealed its regulatory role in vascular remodeling and cardiovascular implications, including atherosclerosis. PVAT does not only release PVAT-derived relaxing factors (PVRFs) to activate multiple subsets of endothelial and vascular smooth muscle potassium channels and anti-inflammatory signals in the vasculature, but it does also provide an interface for neuron-adipocyte interactions in the vascular wall to regulate arterial vascular tone. In this review, we outline our current understanding towards PVAT and attempt to provide hints about future studies that can sharpen the therapeutic potential of PVAT against cardiovascular diseases and their complications.

Anti-obesity Effect of Capsaicin in Mice Fed with High-Fat Diet Is Associated with an Increase in Population of the Gut Bacterium Akkermansia muciniphila

Capsaicin (CAP) reduces body weight mainly through activation of transient receptor potential vanilloid 1 (TRPV1) cation channel. However, recent evidence indicates that the gut microbiota influences many physiological processes in host and might provoke obesity. This study determined whether the anti-obesity effect of CAP is related to the changes in gut microbiota. C57BL/6 mice were fed either with high-fat diet (HFD) or HFD with CAP (HFD-CAP) for 9 weeks. We observed a significantly reduced weight gain and improved glucose tolerance in HFD-CAP-fed mice compared with HFD-fed mice. 16S rRNA gene sequencing results showed a decrease of phylum Proteobacteria in HFD-CAP-fed mice. In addition, HFD-CAP-fed mice showed a higher abundance of Akkermansia muciniphila, a mucin-degrading bacterium with beneficial effects on host metabolism. Further studies found that CAP directly up-regulates the expression of Mucin 2 gene Muc2 and antimicrobial protein gene Reg3g in the intestine. These data suggest that the anti-obesity effect of CAP is associated with a modest modulation of the gut microbiota.

TRP Channels as Therapeutic Targets in Diabetes and Obesity

During the last three to four decades the prevalence of obesity and diabetes mellitus has greatly increased worldwide, including in the United States. Both the short- and long-term forecasts predict serious consequences for the near future, and encourage the development of solutions for the prevention and management of obesity and diabetes mellitus. Transient receptor potential (TRP) channels were identified in tissues and organs important for the control of whole body metabolism. A variety of TRP channels has been shown to play a role in the regulation of hormone release, energy expenditure, pancreatic function, and neurotransmitter release in control, obese and/or diabetic conditions. Moreover, dietary supplementation of natural ligands of TRP channels has been shown to have potential beneficial effects in obese and diabetic conditions. These findings raised the interest and likelihood for potential drug development. In this mini-review, we discuss possibilities for better management of obesity and diabetes mellitus based on TRP-dependent mechanisms.

Capsaicin induces browning of white adipose tissue and counters obesity by activating TRPV1 channel-dependent mechanisms

BACKGROUND AND PURPOSE

The growing epidemic of obesity and metabolic diseases necessitates the development of novel strategies to prevent and treat such diseases. Current research suggests that browning of white adipose tissue (WAT) promotes energy expenditure to counter obesity. Recent research suggests that activation of the TRPV1 channels counters obesity. However, the mechanism by which activation of TRPV1 channels counters obesity still remains unclear.

EXPERIMENTAL APPROACH

We evaluated the effect of dietary capsaicin to induce a browning program in WAT by activating TRPV1 channels to prevent diet-induced obesity using wild-type and TRPV1(-/-) mouse models. We performed experiments using preadipocytes and fat pads from these mice.

KEY RESULTS

Capsaicin stimulated the expression of brown fat-specific thermogenic uncoupling protein-1 and bone morphogenetic protein-8b in WAT. Capsaicin triggered browning of WAT by promoting sirtuin-1 expression and activity via TRPV1 channel-dependent elevation of intracellular Ca(2) (+) and phosphorylation of Ca(2) (+) /calmodulin-activated protein kinase II and AMP-activated kinase. Capsaicin increased the expression of PPARγ 1 coactivator α and enhanced metabolic and ambulatory activity. Further, capsaicin stimulated sirtuin-1-dependent deacetylation of PPARγ and the transcription factor PRDM-16 and facilitated PPARγ-PRDM-16 interaction to induce browning of WAT. Dietary capsaicin did not protect TRPV1(-/-) mice from obesity.

CONCLUSIONS AND INTERPRETATIONS

Our results show for the first time that activation of TRPV1 channels by dietary capsaicin triggers browning of WAT to counteract obesity. Our results suggest that activation of TRPV1 channels is a promising strategy to counter obesity.

Relations between metabolic homeostasis, diet, and peripheral afferent neuron biology

It is well established that food intake behavior and energy balance are regulated by crosstalk between peripheral organ systems and the central nervous system (CNS), for instance, through the actions of peripherally derived leptin on hindbrain and hypothalamic loci. Diet- or obesity-associated disturbances in metabolic and hormonal signals to the CNS can perturb metabolic homeostasis bodywide. Although interrelations between metabolic status and diet with CNS biology are well characterized, afferent networks (those sending information to the CNS from the periphery) have received far less attention. It is increasingly appreciated that afferent neurons in adipose tissue, the intestines, liver, and other tissues are important controllers of energy balance and feeding behavior. Disruption in their signaling may have consequences for cardiovascular, pancreatic, adipose, and immune function. This review discusses the diverse ways that afferent neurons participate in metabolic homeostasis and highlights how changes in their function associate with dysmetabolic states, such as obesity and insulin resistance.

Vanilloid receptors--do they have a role in whole body metabolism? Evidence from TRPV1

With increasing lifespan, therapeutic interventions for the treatment of disorders such as type 2 diabetes mellitus are in great demand. Despite billions of dollars invested to reduce the symptoms and complications due to diabetes mellitus, current treatments (e.g., insulin replacements, sensitization) remain inadequate, justifying the search for novel therapeutic approaches or alternative solutions, including dietary supplementation, for the treatment of diabetes mellitus in every age group. The involvement of the vanilloid system in the regulation of metabolism has been identified, and the emerging role of its receptors, the transient receptor potential vanilloid type 1 (TRPV1), in diabetes was recently demonstrated. Indeed, beneficial effects of dietary capsaicin, an agonist of TRPV1 receptors, were identified for improving glucose, insulin and glucagon-like peptide-1 levels. Recent findings regarding TRPV1 receptors in association with whole body metabolism including glucose homeostasis will be reviewed in this article.

Natural products and body weight control

The purpose of the review was to summarise the effect of some commonly available natural products used for body weight management. We collected data from PubMed and scientific journals. There are numerous publications on this topic, however we have summarized the most commonly available and potent natural products from recent 53 publications. The natural products analyzed in this paper include catechins, capsaicin, conjugated linoleic acid, fucoxanthin, soy isoflavone, glabridin, astaxanthin and cyaniding-3-glucoside. These natural products are effective and safe for body weight management. Further studies need to be conducted to investigate the mechanism of action, metabolism, long term safety and side effects of these natural products, as well as interactions between these natural products with dietary components.

Anterograde transneuronal viral tract tracing reveals central sensory circuits from brown fat and sensory denervation alters its thermogenic responses

Brown adipose tissue (BAT) thermogenic activity and growth are controlled by its sympathetic nervous system (SNS) innervation, but nerve fibers containing sensory-associated neuropeptides [substance P, calcitonin gene-related peptide (CGRP)] also suggest sensory innervation. The central nervous system (CNS) projections of BAT afferents are unknown. Therefore, we used the H129 strain of the herpes simplex virus-1 (HSV-1), an anterograde transneuronal viral tract tracer used to delineate sensory nerve circuits, to define these projections. HSV-1 was injected into interscapular BAT (IBAT) of Siberian hamsters and HSV-1 immunoreactivity (ir) was assessed 24, 48, 72, 96, and 114 h postinjection. The 96- and 114-h groups had the most HSV-1-ir neurons with marked infections in the hypothalamic paraventricular nucleus, periaqueductal gray, olivary areas, parabrachial nuclei, raphe nuclei, and reticular areas. These sites also are involved in sympathetic outflow to BAT suggesting possible BAT sensory-SNS thermogenesis feedback circuits. We tested the functional contribution of IBAT sensory innervation on thermogenic responses to an acute (24 h) cold exposure test by injecting the specific sensory nerve toxin capsaicin directly into IBAT pads and then measuring core (T(c)) and IBAT (T(IBAT)) temperature responses. CGRP content was significantly decreased in capsaicin-treated IBAT demonstrating successful sensory nerve destruction. T(IBAT) and T(c) were significantly decreased in capsaicin-treated hamsters compared with the saline controls at 2 h of cold exposure. Thus the central sensory circuits from IBAT have been delineated for the first time, and impairment of sensory feedback from BAT appears necessary for the appropriate, initial thermogenic response to acute cold exposure.

Sympathetic and sensory innervation of brown adipose tissue

The innervation of brown adipose tissue (BAT) by the sympathetic nervous system (SNS) is incontrovertible and, with its activation, functions as the principal, if not exclusive, stimulator of BAT thermogenesis. The parasympathetic innervation of BAT only appears in two minor BAT depots, but not in the major interscapular BAT (IBAT) depot. BAT thermogenesis is triggered by the release of norepinephrine from its sympathetic nerve terminals, stimulating β3-adrenoceptors that turns on a cascade of intracellular events ending in activation of uncoupling protein-1 (UCP-1). BAT also has sensory innervation that may function to monitor BAT lipolysis, a response necessary for activation of UCP-1 by fatty acids, or perhaps responding in a feedback manner to BAT temperature changes. The central sympathetic outflow circuits ultimately terminating in BAT have been revealed by injecting the retrograde viral transneuronal tract tracer, pseudorabies virus, into the tissue; moreover, there is a high degree of colocalization of melanocortin 4-receptor mRNA on these neurons across the neural axis. The necessary and sufficient central BAT SNS outflow sites that are activated by various thermogenic stimuli are not precisely known. In a chronic decerebration procedure, IBAT UCP-1 gene expression can be triggered by fourth ventricular injections of melanotan II, the melanocortin 3/4 receptor agonist, suggesting that there is sufficient hindbrain neural circuitry to generate thermogenic responses with this stimulation. The recent recognition of BAT in normal adult humans suggests a potential target for stimulation of energy expenditure by BAT to help mitigate increased body fat storage.

TRP channels and their implications in metabolic diseases

The transient receptor potential (TRP) channel superfamily is composed of 28 nonselective cation channels that are ubiquitously expressed in many cell types and have considerable functional diversity. Although changes in TRP channel expression and function have been reported in cardiovascular disease and renal disorders, the pathogenic roles of TRP channels in metabolic diseases have not been systemically reviewed. In this review, we summarised the distribution of TRP channels in several metabolic tissues and discussed their roles in mediating and regulating various physiological and pathophysiological metabolic processes and diseases including diabetes, obesity, dyslipidaemia, metabolic syndrome, atherosclerosis, metabolic bone diseases and electrolyte disturbances. This review provides new insight into the involvement of TRP channels in the pathogenesis of metabolic disorders and implicates these channels as potential therapeutic targets for the management of metabolic diseases.

Substance P promotes expansion of human mesenteric preadipocytes through proliferative and antiapoptotic pathways

White adipose tissue is intimately involved in the regulation of immunity and inflammation. We reported that human mesenteric preadipocytes express the substance P (SP)-mediated neurokinin-1 receptor (NK-1R), which signals proinflammatory responses. Here we tested the hypothesis that SP promotes proliferation and survival of human mesenteric preadipocytes and investigated responsible mechanism(s). Preadipocytes were isolated from mesenteric fat biopsies during gastric bypass surgery. Proliferative and antiapoptotic responses were delineated in 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS), bromodeoxyuridine (BrdU), caspase-3, and TUNEL assays, as well as Western immunoanalysis. SP (10(-7) M) increased MTS and proliferation (BrdU) and time dependently (15-30 min) induced Akt, EGF receptor, IGF receptor, integrin alphaVbeta3, phosphatidylinositol 3-kinase, and PKC-theta phosphorylation. Furthermore, pharmacological antagonism of Akt and PKC-theta activation significantly attenuated SP-induced preadipocyte proliferation. Exposure of preadipocytes to the proapoptotic Fas ligand (FasL, 100 microM) resulted in nuclear DNA fragmentation (TUNEL assay), as well as increased cleaved poly (ADP-ribose) polymerase, cleaved caspase-7, and caspase-3 expression. Cotreatment with SP almost completely abolished these responses in a NK-1R-dependent fashion. SP (10(-7) M) also time dependently stimulated expression 4E binding protein 1 and phosphorylation of p70 S6 kinase, which increased protein translation efficiency. SP increases preadipocyte viability, reduces apoptosis, and stimulates proliferation, possibly via cell cycle upregulation and increased protein translation efficiency. SP-induced proliferative and antiapoptotic pathways in fat depots may contribute to development of the creeping fat and inflammation characteristic of Crohn's disease.

Neuropeptides, mesenteric fat, and intestinal inflammation

The ability of fat tissue cells to produce proinflammatory cytokines and the concept that obesity represents a low-grade inflammatory response have been well documented during the past decade. The effects of fat-mediated inflammation on metabolic pathologies have also been drawing increasing interest. However, very little is known on the potential effects of adipose tissue in the pathophysiology of gastrointestinal diseases with an inflammatory component, such as inflammatory bowel disease (IBD). The development of large fat masses around the inflamed intestine during Crohn's disease makes this tissue a candidate for more intense investigation in studies aiming to gain insights into the pathogenesis and progress of the disease. Furthermore, neuropeptides act in many cases in a proinflammatory manner and are shown to participate in the pathogenesis of intestinal inflammation in animal models of IBD. However, the potential of these molecules to interact with fat cells in the context of IBD has not been investigated. In this review the authors' most recent data related to the effects of neuropeptides on noninflammatory fat tissue components are described. In addition, a discussion to associate neuropeptide-induced, adipose tissue-mediated responses with the generation of intestinal inflammatory conditions such as Crohn's disease is included.

Substance P, obesity, and gut inflammation

PURPOSE OF REVIEW

The purpose of this review is to present recent data on the effects of substance P on the development of two common pathological conditions, namely obesity and gut inflammation, and elucidate the role of this neuropeptide as a potential regulator between increased adiposity and exacerbated inflammatory responses during inflammatory bowel disease.

RECENT FINDINGS

We present data that demonstrate a role for substance P in both obesity and inflammatory bowel disease and investigate potential effects on fat tissue that may influence the progression of intestinal inflammation. More specifically, we discuss new evidence for direct effects of substance P on fat tissue that determine fat depot size and overall weight in mice and analyze some of the potential mechanisms. Furthermore, we present data that describe changes in the intestinal sensory innervation, in particular substance P-positive innervation, during gut inflammation and new direct evidence of the effects of preestablished obesity in the outcome of experimental inflammation of the colon in mice. In the end we propose a link between the role of substance P in the promotion of obesity and the potential consequences on inflammatory bowel disease.

SUMMARY

We propose that substance P may promote fat tissue expansion either centrally or peripherally and thus create a proinflammatory environment (as is the case with obesity) which may in turn affect the progression (exacerbate) of gut inflammation. Further studies are required on the effects of 'creeping fat' in inflammatory bowel disease in order to decipher the role of this type of fat-depot expansion in the development of the disease.

Noradrenergic parenchymal nerve fiber branching after cold acclimatisation correlates with brown adipocyte density in mouse adipose organ

The mammalian adipose organ is composed of subcutaneous and visceral depots containing white and brown adipocytes. Cold acclimatisation induces an increase in the brown component without affecting the overall number of adipocytes; this form of plasticity is associated to obesity and diabetes resistance in experimental models. Cold activates the drive of the sympathetic nervous system to the adipose organ, where the vast majority of nerve fibers are in fact noradrenergic. However, it is unclear whether and how such fibers are involved in the plastic changes of the adipose organ. We thus conducted a systematic study of the distribution and number of sympathetic noradrenergic nerve fibers in the adipose organ of mice kept at different environmental temperatures. Adult Sv129 female mice were kept at 28 degrees C or 6 degrees C for 10 days. The density of tyrosine hydroxylase (noradrenergic)-positive nerve fibers (no. of fibers per 100 adipocytes) was calculated in the subcutaneous and visceral depots of the adipose organ, and a correlation was sought between fiber density and proportion of brown adipocytes. Tyrosine hydroxylase-positive parenchymal fibers were detected in all subcutaneous and visceral depots among white as well as brown adipocytes, the mediastinal depot displaying the densest innervation. Cold acclimatisation induced a threefold increase in the total number of TH fibers in the whole organ. The proportion of brown adipocytes positively correlated with noradrenergic fiber density in the organ. Taken together, these data suggest that cold acclimatisation induces noradrenergic fiber branching in the adipose organ of adult mice, and that such changes may be a precondition for its plastic transformation into a brown phenotype.

TRPV1-null mice are protected from diet-induced obesity

We explored a role for the capsaicin receptor, transient receptor potential channel vanilloid type 1 (TRPV1), in the regulation of feeding and body mass. On a 4.5% fat diet, wild-type and TRPV1-null mice gained equivalent body mass. On an 11% fat diet, however, TRPV1-null mice gained significantly less mass and adiposity; at 44 weeks the mean body weights of wild-type and TRPV1-null mice were approximately 51 and 34g, respectively. Both groups of mice consumed equivalent energy and absorbed similar amounts of lipids. TRPV1-null mice, however, exhibited a significantly greater thermogenic capacity. Interestingly, we found that 3T3-L1 preadipocytes expressed functional calcitonin gene-related peptide receptors. Thus, these data support a potential neurogenic mechanism by which TRPV1-sensitive sensory nerves may regulate energy and fat metabolism.

Sensory or sympathetic white adipose tissue denervation differentially affects depot growth and cellularity

Functional and histological evidence for the sympathetic nervous system (SNS) innervation of white adipose tissue (WAT) exists for several species; however, its sensory innervation has only been shown in laboratory rats, and its function is unclear. We tested the effects of sensory and SNS innervation of Siberian hamster epididymal and inguinal WAT (EWAT and IWAT) by assessing calcitonin gene-related peptide (CGRP)- and tyrosine hydroxylase-immunoreactivity (ir), respectively. Next, we tested the role of the sensory innervation of WAT on growth and cellularity because WAT surgical denervation increases pad mass via selective increases in fat cell number, an effect ascribed to SNS denervation but that could be due to the accompanying surgical disruption of WAT sensory innervation. Sensory denervation was accomplished via multiple local microinjections of capsaicin into WAT, and its effects were compared with those of surgical denervation. Surgically denervated IWAT and EWAT showed significantly decreased tyrosine hydroxylase-ir and CGRP-ir, whereas capsaicin-treated WAT had only significantly decreased CGRP-ir. Surgically denervated pad masses were significantly increased; this was accompanied by increased total fat cell number in IWAT, with no change in fat cell size. EWAT only showed a significant increase in the number of small- to medium-sized adipocytes (75-125 mum diameter). By contrast, sensory-denervated pad masses were unchanged, but IWAT showed significantly increased average fat cell size. Collectively, these data provide immunohistochemical evidence for sensory and SNS innervation of WAT in Siberian hamsters and differential control of WAT cellularity by these innervations, as well as the ability of locally applied capsaicin to selectively reduce WAT sensory innervation.

Sympathetic innervation of white adipose tissue and its regulation of fat cell number

White adipose tissue (WAT) is innervated by the sympathetic nervous system (SNS), and the central origins of this innervation have been demonstrated for inguinal and epididymal WAT (iWAT and eWAT, respectively) using a viral transneuronal tract tracer, the pseudorabies virus (PRV). Although the more established role of this sympathetic innervation of WAT is as a major stimulator of lipid mobilization, this innervation also inhibits WAT fat cell number (FCN); thus, local denervation of WAT leads to marked increases in WAT mass and FCN. The purpose of this study was to extend our understanding of the SNS regulation of FCN using neuroanatomical and functional analyses. Therefore, we injected PRV into retroperitoneal WAT (rWAT) to compare the SNS outflow to this pad from what already is known for iWAT and eWAT. In addition, we tested the ability of local unilateral denervation of rWAT or iWAT to promote increases in WAT mass and FCN vs. their contralateral neurally intact counterparts. Although the overall pattern of innervation was more similar than different for rWAT vs. iWAT or eWAT, its SNS outflow appeared to involve more neurons in the suprachiasmatic and solitary tract nuclei. Denervation produced significant increases in WAT mass and FCN for both iWAT and rWAT, but FCN was increased significantly more in iWAT than in rWAT. These data suggest differences in origins of the sympathetic outflow to WAT and functional differences in the WAT SNS innervation that could contribute to the differential propensity for fat cell proliferation across WAT depots in vivo.