Adipose Tissue Hypoxia Research Articles

Abstract 14057: IL-19 Preserves the Metabolic Activity of Adipocytes in Obesity

Lack of compensatory vascularization causes hypoxia with adipose tissue dysfunction in obesity. Dysfunctional adipocytes instigate systemic low-grade inflammation which is associated with increased morbidity and mortality of metabolic disorders and related cardiovascular disease. A remaining challenge in the field is how to preserve adipocyte metabolic function by suppressing the negative aspect of inflammation, without blocking its angiogenic function. We investigated the role of IL-19, a uniquely immuno-modulatory, pro-angiogenic interleukin expressed also in adipose tissue. We hypothesize that IL-19 acts as a novel adipokine whose expression in expanding adipose depots is essential for maintaining glucose homeostasis. We report that IL-19 is expressed in adipose tissue at both the transcript and protein level and its expression is increased in inflamed visceral adipose tissue but not subcutaneous adipose tissue (p<0.05). Utilizing Il19 -/- knockout mice, we found the loss of IL-19 leads to a metabolic phenotype characterized by reduced glucose and insulin tolerance, increased adipose tissue hypoxia and fibrosis, decreased adipose tissue vessel density and increased adipocyte hypertrophy both in response to standard chow diet and chronic high fat diet (p<0.05). Acute treatment with IL-19 reduced glucose and insulin intolerance in obese wild-type mice (p<0.05). In primary murine epididymal adipocytes the addition of IL-19 leads to increased glucose uptake (p<0.05). These metabolic actions of IL-19 were linked to upregulation of the insulin type-2 receptor and subsequent increased expression/phosphorylation of the protein kinase B (Akt) in adipocytes. Overall, these data propose that IL-19 has novel therapeutic potential in that it can effectively allow adipose tissue expansion without concomitant inflammation and insulin insensitivity.

Hypoxia induces stress fiber formation in adipocytes in the early stage of obesity

In obese adipose tissue (AT), hypertrophic expansion of adipocytes is not matched by new vessel formation, leading to AT hypoxia. As a result, hypoxia inducible factor-1⍺ (HIF-1⍺) accumulates in adipocytes inducing a transcriptional program that upregulates profibrotic genes and biosynthetic enzymes such as lysyl oxidase (LOX) synthesis. This excess synthesis and crosslinking of extracellular matrix (ECM) components cause AT fibrosis. Although fibrosis is a hallmark of obese AT, the role of fibroblasts, cells known to regulate fibrosis in other fibrosis-prone tissues, is not well studied. Here we have developed an in vitro model of AT to study adipocyte-fibroblast crosstalk in a hypoxic environment. Further, this in vitro model was used to investigate the effect of hypoxia on adipocyte mechanical properties via ras homolog gene family member A (RhoA)/Rho-associated coiled-coil kinases (ROCK) signaling pathways. We confirmed that hypoxia creates a diseased phenotype by inhibiting adipocyte maturation and inducing actin stress fiber formation facilitated by myocardin-related transcription factor A (MRTF-A/MKL1) nuclear translocation. This work presents new potential therapeutic targets for obesity by improving adipocyte maturation and limiting mechanical stress in obese AT.

Adipose Tissue Hypoxia Correlates with Adipokine Hypomethylation and Vascular Dysfunction.

Obesity is characterized by the accumulation of dysfunctional adipose tissues, which predisposes to cardiometabolic diseases. Our previous in vitro studies demonstrated a role of hypoxia in inducing adipokine hypomethylation in adipocytes. We sought to examine this mechanism in visceral adipose tissues (VATs) from obese individuals and its correlation with cardiometabolic risk factors. We propose an involvement of the hypoxia-inducible factor, HIF1α, and the DNA hydroxymethylase, TET1. Blood samples and VAT biopsies were obtained from obese and non-obese subjects (n = 60 each) having bariatric and elective surgeries, respectively. The analyses of VAT showed lower vascularity, and higher levels of HIF1α and TET1 proteins in the obese subjects than controls. Global hypomethylation and hydroxymethylation were observed in VAT from obese subjects along with promoter hypomethylation of several pro-inflammatory adipokines. TET1 protein was enriched near the promotor of the hypomethylated adipokines. The average levels of adipokine methylation correlated positively with vascularity and arteriolar vasoreactivity and negatively with protein levels of HIF1α and TET1 in corresponding VAT samples, serum and tissue inflammatory markers, and other cardiometabolic risk factors. These findings suggest a role for adipose tissue hypoxia in causing epigenetic alterations, which could explain the increased production of adipocytokines and ultimately, vascular dysfunction in obesity.

Chronic Intermittent Hypoxia Induces Early-Stage Metabolic Dysfunction Independently of Adipose Tissue Deregulation.

Several studies demonstrated a link between obstructive sleep apnea (OSA) and the development of insulin resistance. However, the main event triggering insulin resistance in OSA remains to be clarified. Herein, we investigated the effect of mild and severe chronic intermittent hypoxia (CIH) on whole-body metabolic deregulation and visceral adipose tissue dysfunction. Moreover, we studied the contribution of obesity to CIH-induced dysmetabolic states. Experiments were performed in male Wistar rats submitted to a control and high-fat (HF) diet. Two CIH protocols were tested: A mild CIH paradigm (5/6 hypoxic (5% O2) cycles/h, 10.5 h/day) during 35 days and a severe CIH paradigm (30 hypoxic (5% O2) cycles, 8 h/day) during 15 days. Fasting glycemia, insulinemia, insulin sensitivity, weight, and fat mass were assessed. Adipose tissue hypoxia, inflammation, angiogenesis, oxidative stress, and metabolism were investigated. Mild and severe CIH increased insulin levels and induced whole-body insulin resistance in control animals, effects not associated with weight gain. In control animals, CIH did not modify adipocytes perimeter as well as adipose tissue hypoxia, angiogenesis, inflammation or oxidative stress. In HF animals, severe CIH attenuated the increase in adipocytes perimeter, adipose tissue hypoxia, angiogenesis, and dysmetabolism. In conclusion, adipose tissue dysfunction is not the main trigger for initial dysmetabolism in CIH. CIH in an early stage might have a protective role against the deleterious effects of HF diet on adipose tissue metabolism.

Contribution of Adipose Tissue Oxidative Stress to Obesity-Associated Diabetes Risk and Ethnic Differences: Focus on Women of African Ancestry

Adipose tissue (AT) storage capacity is central in the maintenance of whole-body homeostasis, especially in obesity states. However, sustained nutrients overflow may dysregulate this function resulting in adipocytes hypertrophy, AT hypoxia, inflammation and oxidative stress. Systemic inflammation may also contribute to the disruption of AT redox equilibrium. AT and systemic oxidative stress have been involved in the development of obesity-associated insulin resistance (IR) and type 2 diabetes (T2D) through several mechanisms. Interestingly, fat accumulation, body fat distribution and the degree of how adiposity translates into cardio-metabolic diseases differ between ethnicities. Populations of African ancestry have a higher prevalence of obesity and higher T2D risk than populations of European ancestry, mainly driven by higher rates among African women. Considering the reported ethnic-specific differences in AT distribution and function and higher levels of systemic oxidative stress markers, oxidative stress is a potential contributor to the higher susceptibility for metabolic diseases in African women. This review summarizes existing evidence supporting this hypothesis while acknowledging a lack of data on AT oxidative stress in relation to IR in Africans, and the potential influence of other ethnicity-related modulators (e.g., genetic-environment interplay, socioeconomic factors) for consideration in future studies with different ethnicities.

Markers of adipose tissue hypoxia are elevated in subcutaneous adipose tissue of severely obese patients with obesity hypoventilation syndrome but not in the moderately obese

It has been suggested that metabolic dysfunction in obesity is at least in part driven by adipose tissue (AT) hypoxia. However, studies on AT hypoxia in humans have shown conflicting data. Therefore we aimed to investigate if markers of AT hypoxia were present in the subcutaneous AT of severly obese individuals (class III obesity) with and without hypoventilation syndrome (OHS) in comparison to moderately obese (class I obesity) and lean controls. To provide a proof-of-concept study, we quantified AT hypoxia by hypoxia inducible factor 1 A (HIF1A) protein abundance in human participants ranging from lean to severly obese (class III obesity). On top of that nightly arterial O2 saturation in individuals with obesity OHS was assessed. Subjects with class III obesity (BMI > 40 kg/m2) and OHS exhibited significantly higher adipose HIF1A protein levels versus those with class I obesity (BMI 30–34.9 kg/m2) and lean controls whereas those with class III obesity without OHS showed an intermediate response. HIF1A gene expression was not well correlated with protein abundance. Although these data demonstrate genuine AT hypoxia in the expected pathophysiological context of OHS, we did not observe a hypoxia signal in lesser degrees of obesity suggesting that adipose dysfunction may not be driven by hypoxia in moderate obesity.

Chronic tissue inflammation and metabolic disease.

Obesity is the most common cause of insulin resistance, and the current obesity epidemic is driving a parallel rise in the incidence of T2DM. It is now widely recognized that chronic, subacute tissue inflammation is a major etiologic component of the pathogenesis of insulin resistance and metabolic dysfunction in obesity. Here, we summarize recent advances in our understanding of immunometabolism. We discuss the characteristics of chronic inflammation in the major metabolic tissues and how obesity triggers these events, including a focus on the role of adipose tissue hypoxia and macrophage-derived exosomes. Last, we also review current and potential new therapeutic strategies based on immunomodulation.

Hypoxia-inducible factor (HIF): The link between obesity and COVID-19.

The COVID-19 death toll has involved to date more than 1 million confirmed deaths. The death rate is even higher in the obese COVID-19 patients, as a result of hypoxia, due to the interplay between adipose tissue hypoxia and obstructive sleep apnea. The discrepancy of manifestations seen in COVID-19 seems to be mediated by a differential immune response rather than a differential viral load. One of the key players of the immune response is HIF. HIF-1β is a stable constitutively expressed protein in the nucleus; and under hypoxic changes, its activity is unaffected, whereas the HIF-α subunit has a short half-life and because of its degradation by an enzyme known as propyl hydroxylase; under hypoxic conditions, propyl hydroxylase gets deactivated thus leading to the stabilization of HIF-1α. As mentioned before, HIF-1α expression is triggered by hypoxic states, this crippling condition will aggravate the pro-inflammatory characteristics of HIF-1α. The vast majority of decompensated COVID19 cases manifest with drastic lung injury and severe viral pneumonia, the infection-induced hypoxia will the existing hypoxia in obesity. This will additionally augment HIF-1α levels that will provoke the already existing cytokines' storm to fulminant. Consequently, this will directly correlate the effect of a hypoxic environment with the increase of HIF-1α level. HIFɑ exists in two main isoforms HIF-1α and HIF-2α. HIF-1α and HIF-2α act in distinct ways in how they work on different target genes. For example, HIF-2α may act on hemopoietin genes (heme-regulating genes); while HIF-1α acts on EPO. HIF-1α release seems to be markedly augmented in obesity due to adipose tissue hypoxia and obstructive sleep apnea resulting in cyclic hypoxia. HIF-1α can also be secreted by direct viral proteolytic effects. Whereas, HIF-2α is stimulated by chronic hypoxia. HIF-1α exerts detrimental effects on the immune system, characterized by unopposed pro-inflammation at the macrophages, dendritic cells, T cells, and complement levels resulting in cytokines’ storm, which is linked to the poor outcomes of COVID-19. On the other hand, HIF-2α role is regulatory and largely opposes the actions mediated by HIF-1α. In view of this, inhibiting HIF-1α release or switching its production to HIF-2α by natural products such as resveratrol or by synthetic drugs, offer a good therapeutic strategy that can prevent COVID-19 worst outcome in infected patients. The approach of breaking the vicious circle between lung damage-induced hypoxia and HIF-1α pro-inflammatory stimulant through drugs is considered to be extremely promising as a therapeutic manner to combat further deterioration of COVID19 cases.

HIF-1α-Dependent Induction of Carboxypeptidase A4 and Carboxypeptidase E in Hypoxic Human Adipose-Derived Stem Cells.

Hypoxia induces the expression of several genes through the activation of a master transcription factor, hypoxia-inducible factor (HIF)-1α. This study shows that hypoxia strongly induced the expression of two carboxypeptidases (CP), CPA4 and CPE, in an HIF-1α-dependent manner. The hypoxic induction of CPA4 and CPE gene was accompanied by the recruitment of HIF-1α and upregulation in the active histone modification, H3K4me3, at their promoter regions. The hypoxic responsiveness of CPA4 and CPE genes was observed in human adipocytes, human adipose-derived stem cells, and human primary fibroblasts but not mouse primary adipocyte progenitor cells. CPA4 and CPE have been identified as secreted exopeptidases that degrade and process other secreted proteins and matrix proteins. This finding suggests that hypoxia changes the microenvironment of the obese hypoxic adipose tissue by inducing the expression of not only adipokines but also peptidases such as CPA4 and CPE.

Characterization and Treatment of Inflammation and Insulin Resistance in Obese Adipose Tissue.

Adipose tissue is the largest energy storage and protection organ. It is distributed subcutaneously and around the internal organs. It regulates metabolism by storing and releasing fatty acids and secreting adipokines. Excessive nutritional intake results in adipocyte hypertrophy and proliferation, leading to local hypoxia in adipose tissue and changes in the release of adipokines. These lead to recruit of more immune cells into adipose tissue and release of inflammatory signaling factors. Excess free fatty acids and inflammatory factors interfere with intracellular insulin signaling. In this review, we summarize the characteristics of obese adipose tissue and analyze how its inflammation causes insulin resistance. We further discuss the latest clinical research progress on the control of insulin resistance and inflammation resulting from obesity through anti-inflammatory therapy and bariatric surgery. Our review shows that targeted anti-inflammatory therapy is of great significance for obese patients with insulin resistance.

Obesity, Insulin Resistance, and Type 2 Diabetes: Associations and Therapeutic Implications.

Obesity is a triggering factor for diabetes associated with insulin resistance. In individuals who are obese, higher amounts of non-esterified fatty acids, glycerol, hormones, and pro-inflammatory cytokines that could participate in the development of insulin resistance are released by adipose tissue. Besides, endoplasmic reticulum stress, adipose tissue hypoxia, oxidative stress, lipodystrophy, and genetic background have a role in insulin resistance. However, no effective drug therapy was developed for type 2 diabetes mellitus targeting these physiological factors. This is might be due to a lack of agreement on the comprehensive mechanism of insulin resistance. Therefore, this review assesses the cellular components of each physiologic and pathophysiologic factors that are involved in obesity associated insulin resistance, and may encourage further drug development in this field.

245-LB: Aberrant DNA Methylation as a Contributor to Obesity-Associated Vascular Dysfunction

Obesity is a major risk factor for cardiovascular disease. We previously demonstrated an impaired vascular function in obese adults (OB). We now hypothesize a role of obesity-associated hypoxia in disturbing the methylation of genes involved in inflammation and vascular dysfunction and propose a mediating role of the hypoxia-inducible factor, HIF1α and the DNA hydroxymethylase, TET1. Methods: We obtained subcutaneous and visceral adipose tissue (AT) biopsies from bariatric patients (n=60; age: 36±7 yrs; BMI: 50.7±8.7 kg/m2) and non-obese (NOB) adults having elective surgeries (n=36; age: 36±2 yrs; BMI: 25.8±1 kg/m2). AT-isolated arterioles were tested for vasoreactivity in response to increasing pressure gradients. Arteriolar nitric oxide (NO) and reactive oxygen species (ROS) were measured. Protein expression of HIF1α and TET1 and promoter methylation/gene expression of leptin, IL1β, IL6, IL8, IL17, CXCL5, TNF-α, and IFNɣ were measured in the AT biopsy. Brachial artery flow-mediated dilation (FMD) was measured via doppler ultrasound. Results: Flow-induced dilation (FID) was 40-50% higher in NOB than OB adults across all pressure gradients (p<0.05). NO production was higher, and ROS generation was lower in the OB arterioles compared to NOB. HIF1α and TET1 proteins were 2 to 4-fold higher in OB compared to NOB adults and correlated negatively with arteriolar FID and NO and brachial artery FMD (r=0.82, 0.64, 0.91, respectively; p<0.001) and positively with arteriolar ROS production (r=-0.71, p<0.01). Global hydroxymethylation was observed in OB compared to NOB as well as DNA promoter hypomethylation and increased gene expression of the targeted adipocytokines. Conclusion: Our results suggest that vascular dysfunction in OB adults may be attributed to aberrant DNA methylation and increased expression of adipocytokines in the hypoxic AT. A downstream target for this pathway could reside in endothelial cells of nearby arterioles and remote arteries resulting in vascular dysfunction. Disclosure M.M. Ali: None. C. Hassan: None. M. Masrur: None. F. Bianco: Consultant; Self; Intuitive, Medtronic. S.A. Phillips: None. A.M. Mahmoud: None. Funding National Institutes of Health (4R00HL140049, 031K99, HL14004901)

SAT-618 Nattokinase to Improve Insulin Sensitivity and Weight Loss in Women with Obesity +/- Diabetes

Background: Diabetes (DM) and obesity are related health issues which are increasing in prevalence. But not all obesity is related to DM. Women suffering from Lipedema are categorized as gynoid obese. Nattokinase (Natto) is an enzyme supplement that has been shown to degrade fibrin. Patients with obesity tend to have elevated clotting factors which can lead to adipose tissue hypoxia, impaired insulin signaling, and lead to insulin resistance. Research in fat disorders noted that fat biopsies from women with Lipedema likely had micro-clots, and patients with Lipedema treated with Natto reported a decrease in clothing size and fat distribution. Objective: Determine the effect of Natto on participants with Obesity and DM and in patients with Lipedema without DM. Materials and Methods: Group 1: Involved subjects with Obesity and DM. This was a double blinded, randomized controlled clinical trial over 3 months. A total of 17 female patients were recruited from a rural clinic. Nine received Natto 2,000 FU daily and eight received an identical placebo capsule daily. Fasting labs, questionnaires, bioimpedance, and anthropometric measurements were completed at Baseline and 3 months. Group 2: 42 women with Lipedema seen at a Fat Disorder Clinic. 21 received Natto and 21 did not. We compared for weight only from the day Nattokinase was started until follow-up, which varied from 4 months to 1 year 8 months. Results: Group 1: After 3 months, there was no difference in weight loss in both groups. Per Bioimpedance, more subjects lost water weight in the Natto group (63%) compared to Placebo (33%). More subjects in the Natto group had a decrease in HbA1c (43%) compared to Placebo (22%), with average decrease in the Natto group of 0.9%. Also, more subjects in the Natto group had lower fasting insulin levels (75% vs 22%), lower fasting glucose level (50% vs 22%) and lower HOMA index (63% vs 22%). Group 2: 57% of patients in the Natto group lost weight compared to only 33% of patients not on Natto. Conclusions: In participants with obesity and DM, regardless of weight loss, metabolic health improved after taking Natto for 3 months. Higher percentage of subjects in the treated group had improved HbA1c, fasting Insulin, glucose, and HOMA score. We hypothesize that if treatment time was beyond 3 months, further metabolic improvement would be noted, indicating that Natto could have potential as an adjunct to DM care. The difference in weight loss between Metabolic Obesity and Lipedema reflects the difference in adipose tissue, likely differing in etiology and pathophysiology. Further studies are needed to evaluate long term benefits of Natto, including larger and longer randomized controlled trials, and assessment of clotting factors.

Hypoxia increases endothelin‐1 production via Hif1α in adipocytes

Severe obesity causes a state of adipose tissue hypoxia and low blood flow. Both human and rodent visceral adipose tissue have been shown to have low oxygen tension (~15mmHg PO2) and increased levels of hypoxia inducible factor alpha (Hif1α), a prominent transcription factor in response to hypoxic conditions. Hif1α has been shown to increase endothelin‐1 (ET‐1) levels at the transcriptional level in endothelial cells. Obesity is associated with high circulating levels of ET‐1, which plays an important role in energy metabolism and insulin signaling when acting on the ET‐1 type A and B receptors on adipocytes. Therefore, the goal of this study was to determine whether hypoxia increases ET‐1 expression in adipocytes via Hif1α and inhibits insulin signaling. We utilized 3T3‐L1 murine fibroblast (passage 3–4) differentiated into adipocyte like cells. Exposure of 3T3‐L1 adipocytes to hypoxia (5% O2) for 24 hours led to a significant 3‐fold increase in ET‐1 mRNA compared to normoxic control cells (21% O2). Associated with increased ET‐1, hypoxia reduced insulin mediated glucose uptake and glycerol release compared to normoxic cells (148.8±16.4 vs. 237.6±24.4 glucose, 83.17±0.6 vs. 93.22±2.8 glycerol percent of control). In a separate experiment, 6‐hour exposure of 3T3‐L1 adipocytes caused a significant increase in ET‐1 and Hif1α mRNA (25.5±2.5 vs. 77.5±7.09 ET‐1, 2117±235.5 vs. 5015±370.2 Hif1α copies/50ng of RNA). Inhibition of Hif1a with either IDF‐11774 (1,25, and 50uM) or GN 44028 (1,10,20 uM) resulted in a significant attenuation in ET‐1 mRNA in response to hypoxia (77.5±7.09 vs. 22.35±3.7 ET‐1, 5015±370.2 vs. 3569±223.5 Hif1α Copies/50ng of cDNA) in a dose dependent manner. These data suggest that a hypoxia promotes ET‐1 production in adipocytes via Hif1α and is associated with diminished insulin sensitivity, suggesting a potential mechanism by which adipose tissue hypoxia promotes insulin resistance in obese individuals.Support or Funding InformationR00HL127178, P206M104357

Cardiac Autonomic Neuropathy and Hemodynamic Dysfunction as a Consequence of Mild Hypercaloric Intake: Modification by Phosphate Supplementation

Cardiac autonomic neuropathy (CAN) has been linked to negative outcomes in diabetic patients, where it is associated with a high risk of cardiac arrhythmia and sudden death. Our previous research showed that prediabetic rats develop CAN in absence of overt signs of metabolic derangement or change in body weight. This was associated with vascular dysfunction and perivascular adipose tissue (PVAT) inflammation, which preceded inflammatory changes in other adipose pools, possibly linked to increased Uncoupling protein 1 (UCP1) and hypoxia‐inducible factor (HIF1‐a) expression. In parallel, phosphate supplementation is a simple intervention to improve body weight, energy metabolism, and glucose tolerance. Moreover, inorganic phosphate acts as a UCP1 inhibitor. Here, we examined the role of phosphate supplementation in ameliorating the early signs of cardiovascular dysfunction in metabolically challenged rats. Male SD rats (5–6 weeks) were randomly allocated into four groups fed either control diet (group 1) or high‐calorie (HC) diet for 12 weeks with three different levels of dietary phosphate; group 2: low phosphate (LP)‐ 0.37 mg/KCal, group 3: intermediate phosphate (IP)‐0.7 mg/KCal, group 4: high phosphate (HP)‐ 1.5 mg/KCal. Daily food intake, body weight, and body composition were recorded. Serum insulin was measured by ELISA. Invasive hemodynamic measurements were done and baroreceptor sensitivity (BRS) was assessed by the vasoactive method. After sacrifice, organs were collected for immunohistochemistry and western blotting. No changes in caloric intake, body weight, blood pressure, and blood glucose levels were observed. However, rats on HC diet showed an increase in serum insulin level and fat/lean ratio. Consistent with our previous work, HC‐feeding was associated with significant reduction in parasympathetic BRS in both the LP and IP groups. This was also accompanied by a reduced left ventricular systolic function. On the cellular level, Oil Red O stain showed a significant increase in the diameter of PVAT adipocytes in LP condition, together with increased expression of HIF‐1α, IL‐1β and UCP‐1. Of note, inflammatory changes observed in the PVAT were not detected in neither white nor brown adipose tissue. Furthermore, higher macrophage infiltration and total ROS score in the PVAT, heart mid‐section and brainstem were observed in LP when compared to control. Our present results highlight a role of phosphate supplementation in the amelioration of the HC induced parasympathetic dysfunction. This could be due to the reported ability of dietary phosphate to improve the assimilation of fat and reduce adipose tissue hypoxia possibly via UCP1 inhibition.Support or Funding InformationFunded by an AUB CRS grantIL1‐UCP1 for perivascular adipose tissue (PVAT), white adipose tissue (WAT), and brown adipose tissue (BAT)Figure 1

Toward noninvasive quantification of adipose tissue oxygenation with MRI.

Molecular oxygen (O2) plays a key role in normal and pathological adipose tissue function, yet technologies to measure its role in adipose tissue function are limited. O2 is paramagnetic and, in principle, directly influences the magnetic resonance (MR) 1H longitudinal relaxation rate constant of lipids, R1; thus, we hypothesize that MR imaging (MRI) can directly measure adipose O2 via a simple measure of R1. R1 was measured in a 4.7T preclinical MRI system at discrete oxygen partial pressure (pO2) levels. These measures were made in vitro in an idealized system and in vivo in subcutaneous and visceral white adipose of rodents. pO2 was determined using an invasive fiber-optic oxygen monitor. From the MRI and fiber optic data we determined the "relaxivity" of O2 in lipid, a critical parameter in converting the MRI-based R1 measurement into pO2. We used breathing gas challenge to estimate the changes in lipid pO2 (ΔpO2). The relaxivity of O2 in lipid was determined to be 1.7·10-3 ± 4·10-4 mmHg-1s-1 at 4.7T and 37 °C, and was consistent between in vitro and in vivo adipose tissue. There was a strong, significant correlation between MRI- and gold standard OxyLite-based measurements of lipid ΔpO2 for in vivo visceral and subcutaneous fat depots in rodents. This study lays the foundation for a direct, noninvasive measure of adipose pO2 using MRI and will allow for noninvasive measurement of O2 flux in adipose tissue. The proposed approach would be of particular importance in the interrogation of the pathogenesis of type 2 diabetes, where it has been suggested that adipose tissue hypoxia is an independent driver of insulin resistance pathway.

CXCL13 is a differentiation- and hypoxia-induced adipocytokine that exacerbates the inflammatory phenotype of adipocytes through PHLPP1 induction.

Hypoxia in adipose tissue is regarded as a trigger that induces dysregulation of the secretory profile in adipocytes. Similarly, local dysregulation of adipocytokine secretion is an initial event in the deleterious effects of obesity on metabolism. We previously reported that CXCL13 is highly produced during adipogenesis, however little is known about the roles of CXCL13 in adipocytes. Here, we found that hypoxia, as modeled by 1% O2 or exposure to the hypoxia-mimetic reagent desferrioxamine (DFO) has strong inductive effects on the expression of CXCL13 and CXCR5, a CXCL13 receptor, in both undifferentiated and differentiated adipocytes and in organ-cultured white adipose tissue (WAT). CXCL13 was also highly expressed in WAT from high fat diet-fed mice. Hypoxic profile, typified by increased expression of interleukin-6 (IL-6) and plasminogen activator inhibitor-1 (PAI-1) and decreased expression of adiponectin, was significantly induced by CXCL13 treatment during adipogenic differentiation. Conversely, the treatment of adipocytes with a neutralizing-antibody against CXCL13 as well as CXCR5 knockdown by specific siRNA effectively inhibited DFO-induced inflammation. The phosphorylation of Akt2, a protective factor of adipose inflammation, was significantly inhibited by CXCL13 treatment during adipogenic differentiation. Mechanistically, CXCL13 induces the expression of PHLPP1, an Akt2 phosphatase, through focal adhesion kinase (FAK) signaling; and correspondingly we show that CXCL13 and DFO-induced IL-6 and PAI-1 expression was blocked by Phlpp1 knockdown. Furthermore, we revealed the functional binding sites of PPARγ2 and HIF1-α within the Cxcl13 promoter. Taken together, these results indicate that CXCL13 is an adipocytokine that facilitates hypoxia-induced inflammation in adipocytes through FAK-mediated induction of PHLPP1 in autocrine and/or paracrine manner.

Hypoxic adipocytes induce macrophages to release inflammatory cytokines that render skeletal muscle cells insulin resistant

Adipose tissue hypoxia occurs early in obesity and is associated with increased tissue macrophages and systemic inflammation that impacts muscle insulin responsiveness. We investigated how hypoxia interacted with adipocyte-macrophage crosstalk and inflammatory cytokine release, using co-culture and conditioned media (CM). Murine primary adipocytes from lean or obese mice were cultured under normoxic (21% O2) or hypoxic (1% O2) conditions. RAW264.7 macrophages were incubated under normoxic or hypoxic conditions with or without adipocyte conditioned media. Macrophage and adipocyte-macrophage co-culture CM were also collected. We found hypoxia did not elicit direct cytokine release from macrophages. However, adipocyte CM or adipocyte co-culture, synergistically stimulated TNFα and MCP-1 release from macrophages that was not further impacted by hypoxia. Exposure of muscle cells to elevated cytokines led to reduced insulin and muscle stress/inflammatory signaling. We conclude hypoxia or obesity induces release of inflammatory TNFα and MCP-1 from mice primary adipocytes but the two environmental conditions do not synergize to worsen macrophage signal transduction or insulin responsiveness.

Vitamin C Physiology: The Known and the Unknown in Obesity

Vitamin C is effective in strengthening the immune system, capillary blood vessels and protecting the dental health, as well as in the convenient use of iron, calcium, thiamine, riboflavin, folic acid, vitamin A and E in the body. Vitamin C also acts as a cofactor for 15 different enzymes, and shows antioxidant activity as a electron donor reducing agent. It acts as a powerful free radical scavenger by protecting tissues against oxidative stress and reduces inflammation. Obesity is defined as “mild inflammatory disease” due to the increase in inflammatory markers such as C reactive protein (CRP), tumor necrosis factor alpha (TNF) and IL-6. Since antioxidant enzyme activity and serum antioxidant levels decrease in obese individuals, the effect of antioxidant vitamins on weight loss is further investigated. In studies investigating the effectiveness of vitamin C in the treatment of obesity; vitamin C was found to reduce systemic inflammation by inhibiting CRP and TNF alpha pathways, shown to inhibit the hypoxia in adipose tissue with potential for protection against free radicals and decreasing lipid peroxidation. On the other hand, it was shown that vitamin C inhibits mature adipocyte formation and cell growth, inhibits lipolysis, and can be considered as a treatment model for obesity to offer solutions for abnormal fat accumulation. In this review, the action mechanism of vitamin C and its role in dietary treatment were investigated in order to prevent obesity complications and to provide weight loss.

Exenatide mitigates inflammation and hypoxia along with improved angiogenesis in obese fat tissue

Obesity-associated chronic inflammation in adipose tissue is partly attributed to hypoxia with insufficient microcirculation. Previous studies have shown that exenatide, a glucagon-like peptide 1 (GLP-1) receptor agonist, plays an anti-inflammatory role. Here, we investigate its effects on inflammation, hypoxia and microcirculation in white adipose tissue of diet-induced obese (DIO) mice. DIO mice were injected intraperitoneally with exenatide or normal saline for 4 weeks, while mice on chow diet were used as normal controls. The mRNA and protein levels of pro-inflammatory cytokines, hypoxia-induced genes and angiogenic factors were detected. Capillary density was measured by laser confocal microscopy and immunochemistry staining. After 4-week exenatide administration, the dramatically elevated pro-inflammatory cytokines in serum and adipose tissue and macrophage infiltration in adipose tissue of DIO mice were significantly reduced. Exenatide also ameliorated expressions of hypoxia-related genes in obese fat tissue. Protein levels of endothelial markers and pro-angiogenic factors including vascular endothelial growth factor and its receptor 2 were augmented in accordance with increased capillary density by exenatide in DIO mice. Our results indicate that inflammation and hypoxia in adipose tissue can be mitigated by GLP-1 receptor agonist potentially via improved angiogenesis and microcirculation in obesity.