Metabolic endotoxemia and saturated fat contribute to circulating NGAL concentrations in subjects with insulin resistance

The relevance of intestinal barrier dysfunction, antimicrobial proteins and bacterial endotoxin in metabolic dysfunction-associated steatotic liver disease

BACKGROUND

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a leading cause of end-stage liver disease associated with increased mortality and cardiovascular disease. Obesity and diabetes are the most important risk factors of MASLD. It is well-established that obesity-associated insulin resistance leads to a situation of tissue lipotoxicity characterized by an accumulation of excess fat in non-fat tissues such as the liver, promoting the development of MASLD, and its progression into metabolic dysfunction-associated steatohepatitis.

METHODS

Here, we aimed to review the impact of disrupted intestinal permeability, antimicrobial proteins and bacterial endotoxin in the development and progression of MASLD.

RESULTS AND CONCLUSION

Recent studies demonstrated that obesity- and obesogenic diets-associated alterations of intestinal microbiota along with the disruption of intestinal barrier integrity, the alteration in antimicrobial proteins and, in consequence, an enhanced translocation of bacterial endotoxin into bloodstream might contribute to this pathological process through to impacting liver metabolism and inflammation.

The Influence of Gut Microbial Species on Diabetes Mellitus

Diabetes mellitus (DM) is a metabolic disorder with an alarming incidence rate and a considerable burden on the patient's life and health care providers. An increase in blood glucose level and insulin resistance characterizes it. Internal and external factors such as urbanization, obesity, and genetic mutations could increase the risk of DM. Microbes in the gut influence overall health through immunity and nutrition. Recently, more studies have been conducted to evaluate and estimate the role of the gut microbiome in diabetes development, progression, and management. This review summarizes the current knowledge addressing three main bacterial species: Bifidobacterium adolescentis, Bifidobacterium bifidum, and Lactobacillus rhamnosus and their influence on diabetes and its underlying molecular mechanisms. Most studies illustrate that using those bacterial species positively reduces blood glucose levels and activates inflammatory markers. Additionally, we reported the relationship between those bacterial species and metformin, one of the commonly used antidiabetic drugs. Overall, more research is needed to understand the influence of the gut microbiome on the development of diabetes. Furthermore, more efforts are required to standardize the model used, concentration ranges, and interpretation tools to advance the field further.

The role of iron in host-microbiota crosstalk and its effects on systemic glucose metabolism

Iron is critical for the appearance and maintenance of life on Earth. Almost all organisms compete or cooperate for iron acquisition, demonstrating the importance of this essential element for the biological and physiological processes that are key for the preservation of metabolic homeostasis. In humans and other mammals, the bidirectional interactions between the bacterial component of the gut microbiota and the host for iron acquisition shape both host and microbiota metabolism. Bacterial functions influence host iron absorption, whereas the intake of iron, iron deficiency and iron excess in the host affect bacterial biodiversity, taxonomy and function, resulting in changes in bacterial virulence. These consequences of the host-microbial crosstalk affect systemic levels of iron, its storage in different tissues and host glucose metabolism. At the interface between the host and the microbiota, alterations in the host innate immune system and in circulating soluble factors that regulate iron (that is, hepcidin, lipocalin 2 and lactoferrin) are associated with metabolic disease. In fact, patients with obesity-associated metabolic dysfunction and insulin resistance exhibit dysregulation in iron homeostasis and alterations in their gut microbiota profile. From an evolutionary point of view, the pursuit of two important nutrients - glucose and iron - has probably driven human evolution towards the most efficient pathways and genes for human survival and health.

Association Of Blood Lipocalin-2 Levels with Gestational Diabetes Mellitus: A Systematic Review and Meta-Analysis

Lipocalin-2 (LCN2) is becoming recognized as a pleiotropic mediator of metabolic disorders. However, the relationship between LCN2 and gestational diabetes mellitus (GDM) is not well understood. We performed a systematic review and meta-analysis to explore it. A systematic search of Cochrane Library, PubMed, Embase, Scopus, Web of Science, Chinese National Knowledge Infrastructure, and Wan-fang Database was done for relevant articles published up to September 29, 2021. Standardized mean difference (SMD) with 95% confidence intervals (CI) was calculated to explore the association of LCN2 levels with GDM using Revman 5.3 and Stata 15.1. Fifteen case-control studies were included in this meta-analysis. The patients with GDM had significantly higher levels of blood LCN2 than parturients with normal glucose tolerance (SMD=3.41, 95% CI=2.24 to 4.58). Meta-regression and subgroup analysis were conducted to investigate the source of heterogeneity. Likely sources of heterogeneity were age and testing methods. This study found that GDM showed higher blood LCN2 levels than controls. However, caution is warranted on the interpretation of these findings. Standardized LCN2 measurement methods and longitudinal studies are required to disentangle and better understand the relationships observed.

Concentrations of Neutrophil Gelatinase-Associated Lipocalin are increased in serum and peritoneal fluid from horses with inflammatory abdominal disease and non-strangulating intestinal infarctions

BACKGROUND

Neutrophil gelatinase-associated lipocalin (NGAL) is produced in response to inflammation in horses, but it has not yet been investigated as a biomarker in horses with abdominal disease.

OBJECTIVES

To investigate NGAL in serum and peritoneal fluid in horses with abdominal disease.

STUDY DESIGN

Retrospective clinical study.

METHODS

Data from medical records of 270 horses admitted with acute abdominal disease (simple obstructions [n=43], strangulating obstructions [n=104], inflammatory abdominal disease [n=99], non-strangulating intestinal infarction [NSII, n=24]) and 9 healthy control horses were reviewed, and serum and peritoneal fluid samples were retrieved from a biobank. NGAL was measured in serum and peritoneal fluid by ELISA. Differences in NGAL concentrations between groups were assessed.

RESULTS

Healthy horses had low serum and peritoneal fluid concentrations of NGAL (median = 21.0 and 9.5 μg/L, respectively). Neither serum nor peritoneal fluid NGAL concentrations (median serum, peritoneal fluid) differed between healthy horses and horses with simple (28.1 μg/L, 13.0 μg/L) and strangulating intestinal obstructions (34.7 μg/L, 38.4 μg/L). Horses with NSII (308.0 μg/L, 2163.0 μg/L) and inflammatory abdominal disease (171.1 μg/L, 314.1 μg/L) had higher serum and peritoneal fluid concentrations of NGAL than the other groups (P<0.001). Peritoneal fluid NGAL concentrations in horses with NSII were higher than in horses with inflammatory abdominal disease (P=0.03).

MAIN LIMITATIONS

Retrospective study design; small group of control horses.

CONCLUSIONS

NGAL is a marker of inflammation in horses with abdominal disease. The high peritoneal fluid concentration of NGAL in horses with NSII compared to all other groups may render NGAL useful for identifying this condition, which is otherwise difficult to differentiate from other types of peritonitis. Thereby, NGAL may potentially facilitate timely surgical intervention in this group of patients. The results of this study must be evaluated in larger, and preferably prospective, studies to obtain a more comprehensive evaluation of the diagnostic utility of NGAL. This article is protected by copyright. All rights reserved.

The Gut Microbiome: Connecting Diet, Glucose Homeostasis, and Disease

Type 2 diabetes rates continue to rise unabated, underscoring the need to better understand the etiology and potential therapeutic options available for this disease. The gut microbiome plays a role in glucose homeostasis, and diabetes is associated with alterations in the gut microbiome. Given that consumption of a Western diet is associated with increased metabolic disease, and that a Western diet alters the gut microbiome, it is plausible that changes in the gut microbiota mediate the dysregulation in glucose homeostasis. In this review, we highlight a few of the most significant mechanisms by which the gut microbiome can influence glucose regulation, including changes in gut permeability, gut-brain signaling, and production of bacteria-derived metabolites like short-chain fatty acids and bile acids. A better understanding of these pathways could lead to the development of novel therapeutics to target the gut microbiome in order to restore glucose homeostasis in metabolic disease. Expected final online publication date for the Annual Review of Medicine, Volume 73 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Lipocalin-2: Structure, function, distribution and role in metabolic disorders

Lipocalin-2 (LCN-2) is a novel, 198 amino acid adipocytokine also referred to as neutrophil gelatinase-associated lipocalin (NGAL). LCN-2 is a circulatory protein responsible for the transportation of small and hydrophobic molecules (steroid, free fatty acids, prostaglandins and hormones) to target organs after binding to megalin/glycoprotein and GP330 SLC22A17 or 24p3R LCN-2 receptors. LCN-2 has been used as a biomarker for acute and chronic renal injury. It is present in a large variety of cells including neutrophil, hepatocytes, lung, bone marrow, adipose tissue, macrophages, thymus, non-neoplastic breast duct, prostate, and renal cells. Different functions have been associated with LCN-2. These functions include antibacterial, anti-inflammatory, and protection against cell and tissue stress. Moreover, LCN-2 can increase the pool of matrix metalloproteinase 9 in human neutrophil granulocytes. Other reported functions of LCN-2 include its ability to destroy the extracellular matrix, which could enable cancer progression and spread of metastasis. Recent reports show that the tissue level of LCN-2 is increased in metabolic disorders such as obesity and type 2 diabetes, suggesting an association between LCN-2 and insulin sensitivity and glucose homeostasis. The precise role of LCN-2 in the modulation of insulin sensitivity, glucose and lipid metabolism is still unclear. This review explores the structure of LCN-2, tissue distribution, and its interaction with important metabolic pathways.

Lipocalin 2 as a link between ageing, risk factor conditions and age-related brain diseases

Chronic (neuro)inflammation plays an important role in many age-related central nervous system (CNS) diseases, including Alzheimer's disease, Parkinson's disease and vascular dementia. Inflammation also characterizes many conditions that form a risk factor for these CNS disorders, such as physical inactivity, obesity and cardiovascular disease. Lipocalin 2 (Lcn2) is an inflammatory protein shown to be involved in different age-related CNS diseases, as well as risk factor conditions thereof. Lcn2 expression is increased in the periphery and the brain in different age-related CNS diseases and also their risk factor conditions. Experimental studies indicate that Lcn2 contributes to various neuropathophysiological processes of age-related CNS diseases, including exacerbated neuroinflammation, cell death and iron dysregulation, which may negatively impact cognitive function. We hypothesize that increased Lcn2 levels as a result of age-related risk factor conditions may sensitize the brain and increase the risk to develop age-related CNS diseases. In this review we first provide a comprehensive overview of the known functions of Lcn2, and its effects in the CNS. Subsequently, this review explores Lcn2 as a potential (neuro)inflammatory link between different risk factor conditions and the development of age-related CNS disorders. Altogether, evidence convincingly indicates Lcn2 as a key constituent in ageing and age-related brain diseases.

Mesenchymal stem cells protect renal tubular cells via TSG-6 regulating macrophage function and phenotype switching

Tumor necrosis factor (TNF)-α-induced gene/protein (TSG)-6 regulates the immunomodulatory properties of mesenchymal stem cells (MSCs), but its ability to protect the ischemic kidney is unknown. In a swine model of renal artery stenosis (RAS) and metabolic syndrome (MetS), we assessed the contribution of TSG-6 produced by MSCs to their immunomodulatory properties. Pigs were studied after 16 wk of diet-induced MetS and unilateral RAS and were either untreated or treated 4 wk earlier with intrarenal autologous adipose tissue-derived MSCs (n = 6 each). Lean, MetS, and RAS sham animals served as controls. We studied renal function in vivo (using computed tomography) and kidney histopathology and macrophage phenotype ex vivo. In vitro, TSG-6 levels were also measured in conditioned media of human MSCs incubated with TNF-α and levels of the tubular injury marker lactate dehydrogenase in conditioned media after coculturing macrophages with injured human kidney 2 (HK-2) cells with or without TSG-6. The effects of TSG-6 on macrophage phenotype (M1/M2), adhesion, and migration were also determined. MetS + RAS showed increased M1 macrophages and renal vein TNF-α levels. After MSC delivery, renal vein TSG-6 increased and TNF-α decreased, the M1-to-M2 ratio decreased, renal function improved, and fibrosis was alleviated. In vitro, TNF-α increased TSG-6 secretion by human MSCs. TSG-6 decreased lactate dehydrogenase release from injured HK-2 cells, increased expression of macrophage M2 markers, and reduced M1 macrophage adhesion and migration. Therefore, TSG-6 released from MSCs may decrease renal tubular cell injury, which is associated with regulating macrophage function and phenotype. These observations suggest that TSG-6 is endowed with renoprotective properties.NEW & NOTEWORTHY Tumor necrosis factor-α-induced gene/protein (TSG)-6 regulates the immunomodulatory properties of MSCs, but its ability to protect the ischemic kidney is unknown. In pigs with renal artery stenosis, we show that MSC delivery increased renal vein TSG-6, decreased kidney inflammatory macrophages, and improved renal function. In vitro, TSG-6 decreased inflammatory macrophages and tubular cell injury. Therefore, TSG-6 released from MSCs may decrease renal tubular cell injury, which is associated with regulating macrophage function and phenotype.

Oxidative Stress and Low-Grade Inflammation in Polycystic Ovary Syndrome: Controversies and New Insights

The pathophysiology of Polycystic Ovary Syndrome (PCOS) is quite complex and different mechanisms could contribute to hyperandrogenism and anovulation, which are the main features of the syndrome. Obesity and insulin-resistance are claimed as the principal factors contributing to the clinical presentation; in normal weight PCOS either, increased visceral adipose tissue has been described. However, their role is still debated, as debated are the biochemical markers linked to obesity per se. Oxidative stress (OS) and low-grade inflammation (LGI) have recently been a matter of researcher attention; they can influence each other in a reciprocal vicious cycle. In this review, we summarize the main mechanism of radical generation and the link with LGI. Furthermore, we discuss papers in favor or against the role of obesity as the first pathogenetic factor, and show how OS itself, on the contrary, can induce obesity and insulin resistance; in particular, the role of GH-IGF-1 axis is highlighted. Finally, the possible consequences on vitamin D synthesis and activation on the immune system are briefly discussed. This review intends to underline the key role of oxidative stress and low-grade inflammation in the physiopathology of PCOS, they can cause or worsen obesity, insulin-resistance, vitamin D deficiency, and immune dyscrasia, suggesting an inverse interaction to what is usually considered.

Lipocalin 2 deficiency-induced gut microbiota dysbiosis evokes metabolic syndrome in aged mice

Lipocalin 2 (Lcn2) is a multifunctional innate immune protein that limits microbial overgrowth. Our previous study demonstrated that the gut microbiota directly induces intestinal Lcn2 production, and Lcn2-deficient (Lcn2^-/-) mice exhibit gut dysbiosis. Coincidentally, gut dysbiosis is associated with metabolic syndrome pathogenesis, and elevated Lcn2 levels has been considered a potential clinical biomarker of metabolic syndrome. Yet whether Lcn2 mitigates or exacerbates metabolic syndrome remains inconclusive. Our objective was to determine whether Lcn2 deficiency-induced compositional changes in gut microbiota contribute to gain in adiposity in aged mice. Utilizing Lcn2^-/- mice and their wild-type (WT) littermates, we measured metabolic markers, including fasting blood glucose, serum lipids, fat pad weight, and insulin resistance at ages 3, 6, and 9 mo old. Relative to WT mice, aged Lcn2^-/- mice exhibited a gain in adiposity associated with numerous features of metabolic syndrome, including insulin resistance and dyslipidemia. Surprisingly, supplementation with a high-fat diet did not further aggravate metabolic syndrome that spontaneously occurs in Lcn2^-/- mice by 6 mo of age. Interestingly, chow-fed Lcn2^-/- mice displayed marked differences in the bacterial abundance and metabolomic profile of the gut microbiota compared with WT mice. Overall, our results demonstrate that Lcn2 is essential to maintain metabolic and gut microbiotal homeostasis, where deficiency induces spontaneous delayed onset of metabolic syndrome.

Plasmatic lipocalin-2 levels in chronic low-grade inflammation syndromes: Comparison between metabolic syndrome, total and partial adult growth hormone deficiency

Lipocalin-2 (LCN2) is a secreted glycoprotein involved in several chronic inflammatory processes. Metabolic syndrome (MetS) and adult growth hormone deficiency (GHD) are known as chronic inflammatory conditions. The primary objective of this observational cross-sectional study was to compare LCN2 plasmatic levels in these clinical settings, whereas the secondary objective was to investigate any possible correlation between LCN2 and BMI and/or indexes of insulin sensitivity/resistance. Seventy-four patients were divided as follows: Group A, MetS (18 patients, 13 females and 5 males, mean ± SEM age 45.1 ± 4.11 years, BMI 31.22 ± 1.73 kg/m² ); Group B, total GHD (18 patients, 8 females and 10 males, age 52.44 ± 2.61 years, BMI 30.49 ± 1.87 kg/m² ); Group C, Partial GHD (pGHD; 19 patients, 13 females and 6 males, age 48.63 ± 2.19 years, BMI 29.11 ± 1.85 kg/m² ); Group D, Controls (19 patients, 13 females and 6males, age 40.26 ± 2.87 years, BMI 23.25 ± 0.95 kg/m² ). They were evaluated for glucose and insulin, HOMA-index, QUICKI-index, Total/low-density lipoprotein/high-density lipoprotein cholesterol, triglycerides, uric acid, IGF-1, and LCN2. LCN2 plasmatic levels were significantly increased in MetS, while no significant differences with controls were found in total and pGHD. LCN2 levels did not correlate with BMI. A significant positive correlation between LCN2 and HOMA-index was found in controls, while a trend-like, yet not significant, a positive correlation was observed in pGHD. Our data show an increase in LCN2 plasmatic levels in MetS. Different inflammatory patterns characterize MetS and GHD. The correlation between HOMA index and LCN2 in normal subjects and possibly in pGHD ones suggests a modulatory action of LCN2 on insulin resistance.

IRW and IQW Reduce Colitis-Associated Cancer Risk by Alleviating DSS-Induced Colonic Inflammation

Background and Objective

Bioactive peptides exert great influence in animals and human health by targeting gastrointestinal tracts. The colitis model of mice was induced by dextran sulfate sodium (DSS). Thirty-two 8-week-old mice weighing 23 g on average were randomly assigned to four groups of 8 each: mice fed basal diet (CON), mice fed basal diet with 5% DSS (DSS), mice fed 0.03% IRW with 5% DSS (IRW-DSS), and mice fed 0.03% IRW with 5% DSS (IQW-DSS). After an adaptation period of 3 days, on day 8, all mice were slaughtered. Serum samples were collected to determine the level of amino acids; colonic tissue was quick-frozen for the determination of gene expression.

Methods

The aim of this study was to assess the ability of two kinds of peptides (IRW and IQW) to repair intestinal inflammatory in the DSS-induced model in accordance with serum amino acids and intestinal inflammatory factors.

Results

The results demonstrated that the addition of IRW and IQW had a mitigating effect on DSS-induced intestinal inflammation. The level of Asp decreased in the serum of mice supplemented with IRW-DSS (P < 0.05), and IQW enhanced the level of Leu, but lowered the level of Ser (P < 0.05). IQW and IRW addition reduced the level of TNF-α and IL-17 (P < 0.05). No other significant effects were observed.

Conclusions

The present study demonstrated that intracolic administration of IRW and IQW might be a novel option for preventing inflammatory bowel disease via regulating the level of serum amino acid and enhancing the intestinal immune defense.

Estrogen interacts with glucocorticoids in the regulation of lipocalin 2 expression in human adipose tissue. Reciprocal roles of estrogen receptor α and β in insulin resistance?

The adipokine lipocalin 2 (LCN2) is linked to insulin resistance. Its expression in human adipose tissue (AT) can be regulated in a sex-specific manner by a synthetic glucocorticoid, dexamethasone, suggesting an underlying role of sex steroids. We show that 17-β-estradiol (E2) dose-dependently increased LCN2 gene expression in subcutaneous AT from postmenopausal women. This was also seen in the presence of estrogen receptor (ER) α antagonist alone but not with ERβ antagonist, suggesting that E2 effects on LCN2 are mediated via ERβ pathway. Dexamethasone alone or E2+dexamethasone had no significant effect on LCN2. However, E2+dexamethasone increased LCN2 expression with ERα-blockade. Dexamethasone reduced ERα but increased ERβ expression. Dexamethasone can regulate LCN2 expression via inhibition of ERα and stimulation of ERβ and may contribute to the development of glucocorticoid-induced insulin resistance in human AT. In conclusion, ERβ and ERα pathways have opposite effects on LCN2 expression and they interact with glucocorticoid action.

Obesity-Induced TNFα and IL-6 Signaling: The Missing Link between Obesity and Inflammation-Driven Liver and Colorectal Cancers

Obesity promotes the development of numerous cancers, such as liver and colorectal cancers, which is at least partly due to obesity-induced, chronic, low-grade inflammation. In particular, the recruitment and activation of immune cell subsets in the white adipose tissue systemically increase proinflammatory cytokines, such as tumor necrosis factor α (TNFα) and interleukin-6 (IL-6). These proinflammatory cytokines not only impair insulin action in metabolic tissues, but also favor cancer development. Here, we review the current state of knowledge on how obesity affects inflammatory TNFα and IL-6 signaling in hepatocellular carcinoma and colorectal cancers.

Correlations between serum concentration of three bone-derived factors and obesity and visceral fat accumulation in a cohort of middle aged men and women

BACKGROUND

The aim of this study was to investigate the interrelationships between three bone-derived factors [serum osteocalcin (OCN), fibroblast growth factor (FGF) 23, and neutrophil gelatinase-associated lipocalin (NGAL) levels] and body fat content and distribution, in order to reveal the potential endocrine function of bone in the development of obesity.

METHODS

We recruited 1179 people (aged 59.5 ± 6.2 years) from communities in Shanghai. Serum OCN levels were determined using an electrochemiluminescence immunoassay. Serum FGF23 and NGAL levels were determined using a sandwich enzyme-linked immunosorbent assay. The abdominal fat distribution, including visceral fat area (VFA), was assessed by magnetic resonance imaging. Visceral obesity was defined as a VFA ≥ 80 cm².

RESULTS

Serum OCN levels were inversely correlated with body fat parameters, while FGF23 and NGAL were positively correlated (P < 0.05). After adjusting for confounders, waist circumference (W) and VFA had a closer relationship with serum OCN, FGF23, and NGAL levels than body mass index (BMI) and body fat percentage (fat%, all P < 0.05). The risk of visceral obesity significantly increased with higher FGF23 and/or NGAL levels, as well as with reduced OCN levels (all P < 0.05). In addition, serum OCN, FGF23, and NGAL levels were independently associated with visceral obesity (all P < 0.01). The relationships persisted among subjects with normal glucose tolerance or subjects with hyperglycaemia (both P < 0.05).

CONCLUSIONS

Compared to the indicators of overall adiposity such as BMI or fat%, visceral adiposity indicators (W or VFA) were more closely related to serum OCN, FGF23 and NGAL levels. There was no interaction among the relationship of three bone-derived factors with visceral obesity, which revealed the independent relationship of endocrine function of skeleton with body fat.

Biomechanics, obesity, and osteoarthritis. The role of adipokines: When the levee breaks

Osteoarthritis is a high-incidence painful and debilitating disease characterized by progressive degeneration of articular joints, which indicates a breakdown in joint homeostasis favoring catabolic processes. Biomechanical loading, associated with inflammatory and metabolic imbalances of joint, strongly contributes to the initiation and progression of the disease. Obesity is a primary risk factor for disease onset, and mechanical factors increased the risk for disease progression. Moreover, inflammatory mediators, in particular, adipose tissue-derived cytokines (better known as adipokines) play a critical role linking obesity and osteoarthritis. The present article summarizes the knowledge about the role of adipokines in cartilage and bone function, highlighting their contribution to the imbalance of joint homeostasis and, consequently, pathogenesis of osteoarthritis. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:594-604, 2018.

Lipocalin-2: A Master Mediator of Intestinal and Metabolic Inflammation

Lipocalin-2 (LCN2), also known as neutrophil gelatinase-associated lipocalin (NGAL), is released by various cell types and is an attractive biomarker of inflammation, ischemia, infection, and kidney damage. Both intestinal and metabolic inflammation, as observed in obesity and related disorders, are associated with increased LCN2 synthesis. While LCN2 in the intestinal tract regulates the composition of the gut microbiota and shows anti-inflammatory activities, it also exhibits proinflammatory activities in other experimental settings. In animal models of metabolic inflammation, type 2 diabetes mellitus (T2DM), or nonalcoholic steatohepatitis (NASH), increased LCN2 expression favors inflammation via the recruitment of inflammatory cells, such as neutrophils, and the induction of proinflammatory cytokines. A better understanding of this crucial marker of innate immunity might pave the way for targeting this pathway in future therapies.

The relationship between circulating neutrophil gelatinase-associated lipocalin and early alteration of metabolic parameters is associated with dietary saturated fat intake in non-diabetic Korean women

Circulating neutrophil gelatinase-associated lipocalin (NGAL) is associated with obesity-related metabolic disorders. This study investigated the relationship between serum NGAL and early alteration of metabolic parameters in non-diabetic Korean women, particularly with respect to saturated fat (SFA) intake. Anthropometric parameters, fasting glycemic status, and levels of lipids, oxidative stress/inflammatory markers, and NGAL were measured in 82 non-diabetic Korean women [Super-healthy group (n=57) with 0 metabolic syndrome risk factor (MetS RF) and MetS-risk group (n=25) with MetS RF≥1]. Age, weight, waist circumference, blood pressure, fasting glucose, HbA1C, triglyceride, LDL and total-cholesterol, and NGAL levels were higher, and HDL-cholesterol was lower in the MetS-risk group than in the Super-healthy group. Age-adjusted serum NGAL levels were higher in the MetS-risk group than in the Super-healthy group. NGAL increased proportionally with increase in MetS RFs (p=0.038) and correlated positively with BMI, triglycerides, LDL- and total-cholesterol, interleukin-6, white blood cell count, and neutrophil%, and negatively with HDL-cholesterol and superoxide dismutase activity. Serum NGAL levels positively correlated with SFA intake before and after adjustment (age and BMI). Serum NGAL levels were higher in high-SFA consumers [≥7g/day, ≥7% of total calorie intake (TCI)] than in low-SFA consumers (<7g/day, <7% of TCI). Serum NGAL levels were highest in the MetS-risk group consuming higher SFA and lowest in the Super-healthy group consuming lower SFA. However, serum NGAL did not significantly differ between the low-SFA consuming MetS-risk and Super-healthy groups. The relationship between circulating NGAL and early alteration of metabolic parameters is associated with dietary SFA intake in non-diabetic Korean women.

Acute low-dose endotoxin treatment results in improved whole-body glucose homeostasis in mice

BACKGROUND

Obese individuals present with an increased inflammatory tone as compared to healthy, normal-weight individuals, which is associated with insulin resistance. One factor hypothesized to contribute to increased inflammation in obese and diabetic states is elevated blood endotoxin levels, a condition known as metabolic endotoxemia. In non-obese and insulin sensitive individuals, circulating endotoxin concentrations fluctuate over the course of the day with elevations in the post-prandial state that return to baseline levels in the post-absorptive state. Evidence suggests that high-fat feeding alters these fluctuations causing endotoxin levels to remain high throughout the day. The effects of alterations in endotoxin levels on glucose metabolism are not clearly understood.

PURPOSE/PROCEDURES

The goal of this study was to determine the effects of both short-term and long-term increases in endotoxin (lipopolysaccharide, LPS) of a low magnitude on the glucose tolerance and insulin signaling in a human primary cell line as well as the effects of short-term endotoxin treatments on glucose homeostasis in a C57/Bl6 mouse model. First, we tested the hypothesis that short-term low-dose endotoxin treatments would augment insulin signaling and glycogen synthesis while long-term treatments would be disruptive in the cell culture model. Second, we examined if these short-term low dose treatments of endotoxin would contribute to similar improvements in whole-body glucose homeostasis in a mouse model.

MAIN FINDINGS

Contrary to our initial hypothesis, short-term endotoxin treatment had no effect on insulin signaling or glycogen synthesis, however long-term treatment indeed decreased glycogen synthesis (P<.05). Interestingly, short-term endotoxin treatment resulted in significant improvements in glucose homeostasis in the mouse model (P<.01); which is believed to be at least partly attributed to an inhibitory action of LPS on liver glucose production.

CONCLUSIONS

This research shows that low-magnitude, short-term changes in LPS can have significant effects on whole body glucose metabolism and this likely occurs through its direct actions on the liver. Additional studies are necessary to understand the mechanisms responsible for altered glucose metabolism in response to low magnitude changes in LPS levels.

The Usefulness of Determining Neutrophil Gelatinase-Associated Lipocalin Concentration Excreted in the Urine in the Evaluation of Cyclosporine A Nephrotoxicity in Children with Nephrotic Syndrome

Introduction. The use of cyclosporine (CsA) in the treatment of nephrotic syndrome (NS) contributed to a significant reduction in the amount of corticosteroids used in therapy and its cumulative side effects. One of the major drawbacks of CsA therapy is its nephrotoxicity. Prolonged CsA treatment protocols require sensitive, easily available, and simple to measure biomarkers of nephrotoxicity. NGAL is an antibacterial peptide, excreted by cells of renal tubules in response to their toxic or inflammatory damage. Aim of the Study. The aim of this study was to assess the suitability of the NGAL concentration in the urine as a potential biomarker of the CsA nephrotoxicity. Material and Methods. The study was performed on a group of 31 children with NS treated with CsA. The control group consisted of 23 children diagnosed with monosyptomatic enuresis. The relationship between NGAL excreted in urine and the time of CsA treatment, concentration of CsA in blood serum, and other biochemical parameters was assessed. Results. The study showed a statistically significant positive correlation between urine NGAL concentration and serum triglycerides concentration and no correlation between C0 CsA concentration and other observed parameters of NS. The duration of treatment had a statistically significant influence on the NGAL to creatinine ratio. Conclusions. NGAL cannot be used alone as a simple CsA nephrotoxicity marker during NS therapy. Statistically significant correlation between NGAL urine concentration and the time of CsA therapy indicates potential benefits of using this biomarker in the monitoring of nephrotoxicity in case of prolonged CsA therapy.

Chronic Sleep Disruption Alters Gut Microbiota, Induces Systemic and Adipose Tissue Inflammation and Insulin Resistance in Mice

Chronic sleep fragmentation (SF) commonly occurs in human populations, and although it does not involve circadian shifts or sleep deprivation, it markedly alters feeding behaviors ultimately promoting obesity and insulin resistance. These symptoms are known to be related to the host gut microbiota. Mice were exposed to SF for 4 weeks and then allowed to recover for 2 weeks. Taxonomic profiles of fecal microbiota were obtained prospectively, and conventionalization experiments were performed in germ-free mice. Adipose tissue insulin sensitivity and inflammation, as well as circulating measures of inflammation, were assayed. Effect of fecal water on colonic epithelial permeability was also examined. Chronic SF-induced increased food intake and reversible gut microbiota changes characterized by the preferential growth of highly fermentative members of Lachnospiraceae and Ruminococcaceae and a decrease of Lactobacillaceae families. These lead to systemic and visceral white adipose tissue inflammation in addition to altered insulin sensitivity in mice, most likely via enhanced colonic epithelium barrier disruption. Conventionalization of germ-free mice with SF-derived microbiota confirmed these findings. Thus, SF-induced metabolic alterations may be mediated, in part, by concurrent changes in gut microbiota, thereby opening the way for gut microbiome-targeted therapeutics aimed at reducing the major end-organ morbidities of chronic SF.

Lipopolysaccharide-binding protein is a negative regulator of adipose tissue browning in mice and humans

AIMS/HYPOTHESIS

Adipocyte lipopolysaccharide-binding protein (LBP) biosynthesis is associated with obesity-induced adipose tissue dysfunction. Our purpose was to study the role of LBP in regulating the browning of adipose tissue.

METHODS

Adult mice were maintained at 4°C for 3 weeks or treated with the β3-adrenergic agonist, CL316,243, for 1 week to induce the browning of white fat. Precursor cells from brown and white adipose tissues were cultured under differentiation-inducing conditions to yield brown and beige/brite adipocytes, respectively. In vitro, Lbp was knocked down in 3T3-L1 adipocytes, and cells were treated with recombinant LBP or co-cultured in transwells with control 3T3-L1 adipocytes. Wild-type and Lbp-null mice, fed a standard or high fat diet (HFD) for 15 weeks, were also used in investigations. In humans, subcutaneous and visceral adipose tissue samples were obtained from a cohort of morbidly obese participants.

RESULTS

The induction of white fat browning by exposure of mice to cold or CL316,243 treatment was strongly associated with decreased Lbp mRNA expression in white adipose tissue. The acquisition of the beige/brite phenotype in cultured cells was associated with downregulation of Lbp. Moreover, silencing of Lbp induced the expression of brown fat-related genes in adipocytes, whereas LBP treatment reversed this effect. Lbp-null mice exhibited the spontaneous induction of subcutaneous adipose tissue browning, as evidenced by a remarkable increase in Ucp1 and Dio2 gene expression and the appearance of multivacuolar adipocyte clusters. The amount of brown adipose tissue, and brown adipose tissue activity were also increased in Lbp-null mice. These changes were associated with decreased weight gain in Lbp-null mice and protection against HFD-induced inflammatory responses, as shown by reduced IL-6 levels. However, rather than improving glucose homeostasis, these effects led to glucose intolerance and insulin resistance.

CONCLUSIONS/INTERPRETATION

LBP is identified as a negative regulator of the browning process, which is likely to contribute to the obesity-promoting action of LBP. The deleterious metabolic effects of LBP deletion are compatible with the concept that the appropriate regulation of inflammatory pathways is necessary for a healthy systemic metabolic profile, regardless of body weight regulation.

Lipocalin-2 inhibits autophagy and induces insulin resistance in H9c2 cells

Lipocalin-2 (Lcn2; also known as neutrophil gelatinase associated lipocalin, NGAL) levels are increased in obesity and diabetes and associate with insulin resistance. Correlations exist between Lcn2 levels and various forms or stages of heart failure. Insulin resistance and autophagy both play well-established roles in cardiomyopathy. However, little is known about the impact of Lcn2 on insulin signaling in cardiomyocytes. In this study, we treated H9c2 cells with recombinant Lcn2 for 1 h followed by dose- and time-dependent insulin treatment and found that Lcn2 attenuated insulin signaling assessed via phosphorylation of Akt and p70S6K. We used multiple assays to demonstrate that Lcn2 reduced autophagic flux. First, Lcn2 reduced pULK1 S555, increased pULK1 S757 and reduced LC3-II levels determined by Western blotting. We validated the use of DQ-BSA to assess autolysosomal protein degradation and this together with MagicRed cathepsin B assay indicated that Lcn2 reduced lysosomal degradative activity. Furthermore, we generated H9c2 cells stably expressing tandem fluorescent RFP/GFP-LC3 and this approach verified that Lcn2 decreased autophagic flux. We also created an autophagy-deficient H9c2 cell model by overexpressing a dominant-negative Atg5 mutant and found that reduced autophagy levels also induced insulin resistance. Adding rapamycin after Lcn2 could stimulate autophagy and recover insulin sensitivity. In conclusion, our study indicated that acute Lcn2 treatment caused insulin resistance and use of gain and loss of function approaches elucidated a causative link between autophagy inhibition and regulation of insulin sensitivity by Lcn2.

Serum lipocalin-2 levels are positively associated with not only total body fat but also visceral fat area in Chinese men

Serum lipocalin-2 (LCN2) plays an important role in the regulation of the obesity-associated dysmetabolic state and cardiovascular disease. However, relatively little is known about the relationship between serum LCN2 levels and body fat content and distribution. We examined the associations of total body fat content and abdominal fat distribution with serum LCN2 levels in Chinese men.The study was based on a cross-sectional analysis of data for 1203 Chinese men aged 22 to 78 years from the Shanghai Obesity Study. Body fat percentage (fat%) was assessed by bioelectrical impedance analysis, and magnetic resonance imaging was adopted to quantify the visceral fat area (VFA) and subcutaneous fat area (SFA). Serum levels of LCN2 were measured with a standard enzyme-linked immunosorbent assay method.Subjects with a high fat% had higher serum LCN2 levels than those with a normal fat% regardless of their body mass index category (<25 and ≥25 kg/m). The frequency of isolated high VFA was increased with increasing quintiles of serum LCN2 levels (P < 0.001), but the frequency of isolated high SFA did not differ between quintiles of serum LCN2 levels. A trend of increasing VFA was observed with increasing serum LCN2 levels (P < 0.001). Multiple stepwise regression analysis showed that VFA was positively associated with serum LCN2 levels, independent of overall obesity and other confounding factors (standardized β = 0.082, P = 0.008).Serum LCN2 levels are positively correlated with body fat content and independently associated with VFA in Chinese men.

Low-grade inflammatory polarization of monocytes impairs wound healing

Impaired wound healing often accompanies low-grade inflammatory conditions, during which circulating levels of subclinical super-low-dose endotoxin may persist. Low-grade inflammatory monocyte polarization may occur during chronic inflammation and deter effective wound repair. However, little is understood about the potential mechanisms of monocyte polarization by sustained insult of subclinical super-low-dose endotoxin. We observed that super-low-dose endotoxin preferentially programmes a low-grade inflammatory monocyte state in vitro and in vivo, as represented by the elevated population of CD11b(+) Ly6C(high) monocytes and sustained expression of CCR5. Mechanistically, super-low-dose endotoxin caused cellular stress, altered lysosome function and increased the transcription factor IRF5. TUDCA, a potent inhibitor of cellular stress, effectively blocked monocyte polarization and improved wound healing in mice injected with super-low-dose endotoxin. Our data revealed the polarization of low-grade inflammatory monocytes by sustained endotoxin challenge, its underlying mechanisms and a potential intervention strategy. Copyright © 2015 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

The potential of lipocalin-2/NGAL as biomarker for inflammatory and metabolic diseases

Lipocalin-2 (LCN2), also known as neutrophil gelatinase-associated lipocalin (NGAL), is a secreted glycoprotein that belongs to a group of transporters of small lipophilic molecules in circulation. LCN2 has been recently characterized as an adipose-derived cytokine. This adipokine is believed to bind small substances, such as steroids and lipopolysaccharides, and has been reported to have roles in the induction of apoptosis in hematopoietic cells, transport of fatty acids and iron, modulation of inflammation, and metabolic homeostasis. Recently, LCN2 has emerged as a useful biomarker and rheumatic diseases. This review provides an overview of LCN2 in inflammation, immunity, and metabolism.

The Ligands of Neutrophil Gelatinase-Associated Lipocalin

Neutrophil gelatinase associated lipocalin (NGAL), was originally identified in neutrophil granules as a heterodimer complex with gelatinase B (matrix metalloproteinase 9, MMP9), but more recently has been found to be secreted by damaged epithelial cells. Ngal is a member of the lipocalin family and subsequently named as lipocalin 2 on the basis of structural similarity with other members of the lipocalin family and its potential association with hydrophobic retinol and cholesterol oleate more strongly than their hydrophilic counterparts. In 2002, a landmark paper suggested that Ngal is a bacteriostatic agent which blocks iron acquisition by interacting with a number of bacterial siderophores, especially enterobactin. Since then, more siderophore-carrying functions have been reported than the possibility of hydrophobic ligand transport. In this setting, Ngal was renamed Siderocalin. Functions of siderocalin include not only bacteriostatic activity but potentially as a mediator of cell growth and differentiation; some of these functions appear to be referable to the holo siderocalin:siderophore:iron complex and recent work suggests that metabolic products may act as mammalian siderophores bound by Ngal. While still speculative, it may be that the mammalian siderophores can establish the missing link between Ngal and a number of its functions in vivo. This review provides an overview of the discoveries of the different ligands of Ngal and consequently related functions. Hydrophobic ligands, bacterial siderophores as well as their modified structures (synthetic siderophores), and mammalian siderophores are summarized.

Mechanisms Linking Glucose Homeostasis and Iron Metabolism Toward the Onset and Progression of Type 2 Diabetes

OBJECTIVE

The bidirectional relationship between iron metabolism and glucose homeostasis is increasingly recognized. Several pathways of iron metabolism are modified according to systemic glucose levels, whereas insulin action and secretion are influenced by changes in relative iron excess. We aimed to update the possible influence of iron on insulin action and secretion and vice versa.

RESEARCH DESIGN AND METHODS

The mechanisms that link iron metabolism and glucose homeostasis in the main insulin-sensitive tissues and insulin-producing β-cells were revised according to their possible influence on the development of type 2 diabetes (T2D).

RESULTS

The mechanisms leading to dysmetabolic hyperferritinemia and hepatic overload syndrome were diverse, including diet-induced alterations in iron absorption, modulation of gluconeogenesis, heme-mediated disruption of circadian glucose rhythm, impaired hepcidin secretion and action, and reduced copper availability. Glucose metabolism in adipose tissue seems to be affected by both iron deficiency and excess through interaction with adipocyte differentiation, tissue hyperplasia and hypertrophy, release of adipokines, lipid synthesis, and lipolysis. Reduced heme synthesis and dysregulated iron uptake or export could also be contributing factors affecting glucose metabolism in the senescent muscle, whereas exercise is known to affect iron and glucose status. Finally, iron also seems to modulate β-cells and insulin secretion, although this has been scarcely studied.

CONCLUSIONS

Iron is increasingly recognized to influence glucose metabolism at multiple levels. Body iron stores should be considered as a potential target for therapy in subjects with T2D or those at risk for developing T2D. Further research is warranted.

Revisiting the adipocyte: a model for integration of cytokine signaling in the regulation of energy metabolism

Adipose tissue constitutes an extremely active endocrine organ with a network of signaling pathways enabling the organism to adapt to a wide range of different metabolic challenges, such as starvation, stress, infection, and short periods of gross energy excess. The functional pleiotropism of adipose tissue relies on its ability to synthesize and release a huge variety of hormones, cytokines, complement and growth factors, extracellular matrix proteins, and vasoactive factors, collectively termed adipokines. Obesity is associated with adipose tissue dysfunction leading to the onset of several pathologies including type 2 diabetes, dyslipidemia, nonalcoholic fatty liver, or hypertension, among others. The mechanisms underlying the development of obesity and its associated comorbidities include the hypertrophy and/or hyperplasia of adipocytes, adipose tissue inflammation, impaired extracellular matrix remodeling, and fibrosis together with an altered secretion of adipokines. Recently, the potential role of brown and beige adipose tissue in the protection against obesity has been also recognized. In contrast to white adipocytes, which store energy in the form of fat, brown and beige fat cells display energy-dissipating capacity through the promotion of triacylglycerol clearance, glucose disposal, and generation of heat for thermogenesis. Identification of the morphological and molecular changes in white, beige, and brown adipose tissue during weight gain is of utmost relevance for the identification of pharmacological targets for the treatment of obesity and its associated metabolic diseases.

Iron status in obesity: An independent association with metabolic parameters and effect of weight loss

BACKGROUND AND AIMS

Growing evidence has shown that ferritin concentrations are associated with obesity and insulin resistance, and with nonalcoholic fatty liver disease. However, it is unclear whether ferritin is simply an inflammatory marker, or it may directly contribute to the pathogenesis of obesity-related metabolic alterations. The aim of our study was to investigate the independent associations of ferritin levels with metabolic parameters in overweight/obese subjects before and after hypocaloric diet-induced weight changes.

METHODS AND RESULTS

A sample study of 48 premenopausal, 39 postmenopausal women and 50 men was retrospectively analyzed. Clinical, bioimpedentiometry and biochemical data from baseline evaluations and after 3, 6 and 12 months of hypocaloric diet were collected. In the whole sample study, the baseline values of ferritin concentrations were positively correlated with body mass index (BMI) (r = 0.21, p < 0.05) and mass body fat (MBF) (r = 0.26, p < 0.05), whereas the serum iron level was negatively correlated with MBF (r = -0.29, p < 0.05). In premenopausal women, BMI-adjusted ferritin concentrations were negatively associated with high-density lipoprotein-cholesterol and positively related with triglycerides and aspartate aminotransferase. Moreover, the quantitative ferritin reduction at 12 months was positively associated with the relative reduction of BMI (r = 0.34, p < 0.05). Finally, the association between changes of alanine aminotransferase and ferritin levels at 12 months from baseline turned out to be independent of respective BMI changes (β = 0.31, p < 0.05).

CONCLUSION

In obesity, ferritin, putatively entailing increased iron storage, is independently associated with lipid derangements and transaminase levels, and the association with the latter persists after weight changes.

Stress induces endotoxemia and low-grade inflammation by increasing barrier permeability

Chronic non-communicable diseases (NCDs) are the leading causes of work absence, disability, and mortality worldwide. Most of these diseases are associated with low-grade inflammation. Here, we hypothesize that stresses (defined as homeostatic disturbances) can induce low-grade inflammation by increasing the availability of water, sodium, and energy-rich substances to meet the increased metabolic demand induced by the stressor. One way of triggering low-grade inflammation is by increasing intestinal barrier permeability through activation of various components of the stress system. Although beneficial to meet the demands necessary during stress, increased intestinal barrier permeability also raises the possibility of the translocation of bacteria and their toxins across the intestinal lumen into the blood circulation. In combination with modern life-style factors, the increase in bacteria/bacterial toxin translocation arising from a more permeable intestinal wall causes a low-grade inflammatory state. We support this hypothesis with numerous studies finding associations with NCDs and markers of endotoxemia, suggesting that this process plays a pivotal and perhaps even a causal role in the development of low-grade inflammation and its related diseases.

Plasma neutrophil gelatinase-associated lipocalin and kidney function decline and kidney disease-related clinical events in older women

BACKGROUND

It is still unclear whether serum neutrophil gelatinase-associated lipocalin (NGAL), a biomarker of renal tubular injury, is a prognostic marker for the progression of chronic kidney disease (CKD) in the general population.

METHODS

A prospective-cohort study of 1,245 women aged ≥70 from the general population. Associations between plasma NGAL and change in 5-year estimated glomerular filtration rate (eGFR), rapid renal decline and 10-year risk of acute or chronic renal disease-related hospitalisations and/or mortality were examined.

RESULTS

Compared to women with above-median plasma NGAL of 76.5 ng/l, women with below-median plasma NGAL had a 9.3% reduction in eGFR over a 5-year period. Among women with above-median plasma NGAL, there was over a 1.7-fold increased risk of rapid renal decline (eGFR decline of >3 ml/min/year) (adjusted odds ratio 1.76, 95% CI 1.003, 3.102, p = 0.049). Compared to women with baseline eGFR of <60 ml/min/1.73 m(2), women with above-median plasma NGAL experienced over a 2.5-fold increased risk of renal disease events at 10 years (hazard ratio 2.55, 95% CI 1.13, 5.78, p = 0.025) after adjustment of age, hypertension and diabetes. Addition of plasma NGAL in participants with eGFR of <60 ml/min/1.73 m(2) significantly improved the accuracy in predicting the 10-year risk of renal disease events (adjusted area-under-curve receiver operator characteristics without and with NGAL 0.64 and 0.71, respectively; p = 0.027) and reclassified 13% of women who experienced renal disease events into the higher risk categories (p = 0.03).

CONCLUSION

Plasma NGAL is of modest clinical utility in predicting the renal function decline and risk of renal disease-related clinical events, particularly those with mild to moderate CKD.

Innate immune programing by endotoxin and its pathological consequences

Monocytes and macrophages play pivotal roles in inflammation and homeostasis. Recent studies suggest that dynamic programing of macrophages and monocytes may give rise to distinct "memory" states. Lipopolysaccharide (LPS), a classical pattern recognition molecule, dynamically programs innate immune responses. Emerging studies have revealed complex dynamics of cellular responses to LPS, with high doses causing acute, resolving inflammation, while lower doses are associated with low-grade and chronic non-resolving inflammation. These phenomena hint at dynamic complexities of intra-cellular signaling circuits downstream of the Toll-like receptor 4 (TLR4). In this review, we examine pathological effects of varying LPS doses with respect to the dynamics of innate immune responses and key molecular regulatory circuits responsible for these effects.

Mechanism and clinical evidence of lipocalin-2 and adipocyte fatty acid-binding protein linking obesity and atherosclerosis

Obesity is considered to be a chronic inflammatory state in which the dysfunction of adipose tissue plays a central role. The adipokines, which are cytokines secreted by adipose tissue, are key links between obesity and related diseases such as metabolic syndrome and atherosclerosis. LCN2 and A-FABP, both of which are major adipokines predominantly produced in adipose tissue, have recently been shown to be pivotal modulators of vascular function. However, different adipokines modulate the development of atherosclerosis in distinctive manners, which are partly attributable to their unique regulatory mechanisms and functions. This review highlights recent advances in the understanding of the role of two adipokines in mediating chronic inflammation and the pathogenesis of atherosclerosis.

The different molecular forms of urine neutrophil gelatinase-associated lipocalin present in dogs with urinary diseases

Background

Neutrophil gelatinase-associated lipocalin (NGAL) is a useful biomarker for the early prediction of renal diseases. NGAL may exist as monomer, dimer and/or NGAL/MMP-9 complex forms in humans. In this study, the existence of various forms of NGAL in urine (uNGAL) was determined and whether these forms are related to the different urinary diseases found in dogs is further discussed.

Results

Eighty-one urine samples from dogs with different forms of renal disease (41), pyuria (19) and a number of non-renal related diseases (10), as well as healthy dogs (11), were collected. uNGAL concentrations and their molecular forms in dogs were measured by ELISA and Western blot analysis, respectively. The uNGAL concentrations of dogs with pyuria (median: 15.35 ng/mL) were significantly higher than those of the healthy control animals (median: 3.92 ng/mL) (p < 0.01), but lower than those of dogs with renal diseases (median: 23.77 ng/mL). Each NGAL molecular form could be detected in dog urine. In particular, monomer was detected more frequently in patients with renal disease than those with non-renal diseases; while the dimer form appeared in a significantly higher percentage of cases with pyuria compared to those without pyuria. The NGAL/MMP-9 complex was found to exist not only in the patients with cystitis, but also in the cases with renal injury.

Conclusion

Different molecular forms of uNGAL can indicate different origins of the urinary abnormalities. Determining the molecular forms of uNGAL present in diseased dogs may provide clinical workers with a tool that will help the early and more precise detection of different urinary diseases.

Molecular and cellular mechanisms responsible for cellular stress and low-grade inflammation induced by a super-low dose of endotoxin

Super-low-dose endotoxemia in experimental animals and humans is linked to low-grade chronic inflammatory diseases. However, the underlying molecular and cellular mechanisms are not well understood. In this study, we examined the effects of a super-low dose of LPS on low-grade inflammation in macrophages as well as underlying mechanisms. We observed that a super-low dose of LPS induces mitochondrial fission and cell necroptosis in primary murine macrophages, dependent upon interleukin 1 receptor-associated kinase (IRAK-1). Mechanistically, our study reveals that a super-low dose of LPS causes protein ubiquitination and degradation of mitofusin 1 (Mfn1), a molecule required for maintaining proper mitochondrial fusion. A super-low dose of LPS also leads to dephosphorylation and activation of Drp1, a molecule responsible for mitochondrial fission and cell necroptosis. Furthermore, we demonstrated that a super-low dose of LPS activates receptor interacting protein 3 kinase (RIP3), a key molecule critical for the assembly of the necrosome complex, the initiation of Drp1 dephosphorylation, and necroptosis. The effects of a super-low dose of LPS are abolished in macrophages harvested from IRAK-1-deficient mice. Taken together, our study identified a novel molecular pathway that leads to cellular stress and necroptosis in macrophages challenged with a super-low dose of endotoxin. This may reconcile low-grade inflammation often associated with low-grade endotoxemia.

Effects of iron overload on chronic metabolic diseases

Iron can affect the clinical course of several chronic metabolic diseases such as type 2 diabetes, obesity, non-alcoholic fatty liver disease, and atherosclerosis. Iron overload can affect major tissues involved in glucose and lipid metabolism (pancreatic β cells, liver, muscle, and adipose tissue) and organs affected by chronic diabetic complications. Because iron is a potent pro-oxidant, fine-tuned control mechanisms have evolved to regulate entry, recycling, and loss of body iron. These mechanisms include the interplay of iron with transferrin, ferritin, insulin, and hepcidin, as well as with adipokines and proinflammatory molecules. An imbalance of these homoeostatic mechanisms results in systemic and parenchymal siderosis that contributes to organ damage (such as β-cell dysfunction, fibrosis in liver diseases, and atherosclerotic plaque growth and instability). Conversely, iron depletion can exert beneficial effects in patients with iron overload and even in healthy frequent blood donors. Regular assessment of iron balance should be recommended for patients with chronic metabolic diseases, and further research is needed to produce guidelines for the identification of patients who would benefit from iron depletion.

The changes of neutrophil gelatinase-associated lipocalin in plasma and its expression in adipose tissue in pregnant women with gestational diabetes

AIMS

To investigate plasma levels and the expression of neutrophil gelatinase-associated lipocalin (NGAL) in subcutaneous adipose tissue (SAT) in patients with gestational diabetes mellitus (GDM).

METHODS

The study recruited 260 Chinese women divided into three groups: 96 were healthy pregnant women with pre-pregnancy body mass index (pre-pregnancy BMI) below 25kg/m(2) (GROUP 1), 84 were women with GDM with pre-pregnancy BMI below 25kg/m(2) (GROUP 2) and 80 were women with GDM with pre-pregnancy BMI over 25kg/m(2) (GROUP 3). Laboratory and anthropometric measurements were recorded and NGAL plasma levels were determined by ELISA for subjects in all groups. Real-time RT-PCR and Western blotting were used to assess the relative mRNA and protein expression of NGAL and tumor necrosis factor-α (TNF-α) in SAT (30 cases in each group).

RESULTS

Our results demonstrated statistically significant elevation in plasma NGAL concentrations in GROUP 2 and GROUP 3 compared with GROUP 1 (p<0.001 for both group comparisons). Moreover, SAT NGAL mRNA (p<0.001 and p<0.001, respectively) and protein (p<0.001 and p<0.001, respectively) expression levels were higher in GROUP 3 than in both GROUP 1 and GROUP 2. Correlations were noted between the plasma NGAL concentration and various parameters of insulin resistance.

CONCLUSIONS

Plasma NGAL may play a role in the development of insulin resistance in GDM, and the high levels of NGAL expression in SAT in overweight women with GDM suggests that NGAL in SAT is associated with obesity in women with GDM.

Adipokines, metabolic syndrome and rheumatic diseases

The metabolic syndrome (MetS) is a cluster of cardiometabolic disorders that result from the increasing prevalence of obesity. The major components of MetS include insulin resistance, central obesity, dyslipidemia, and hypertension. MetS identifies the central obesity with increased risk for cardiovascular diseases (CVDs) and type-2 diabetes mellitus (T2DM). Patients with rheumatic diseases, such as rheumatoid arthritis, osteoarthritis, systemic lupus erythematosus, and ankylosing spondylitis, have increased prevalence of CVDs. Moreover, CVD risk is increased when obesity is present in these patients. However, traditional cardiovascular risk factors do not completely explain the enhanced cardiovascular risk in this population. Thus, MetS and the altered secretion patterns of proinflammatory adipokines present in obesity could be the link between CVDs and rheumatic diseases. Furthermore, adipokines have been linked to the pathogenesis of MetS and its comorbidities through their effects on vascular function and inflammation. In the present paper, we review recent evidence of the role played by adipokines in the modulation of MetS in the general population, and in patients with rheumatic diseases.

Lipopolysaccharide-binding protein plasma levels in children: effects of obstructive sleep apnea and obesity

BACKGROUND

Obstructive sleep apnea (OSA) has been linked to obesity, inflammation, and metabolic syndrome. The gut microbiota, which serves as reservoir for bacterial lipopolysaccharides (LPS), could be altered by OSA and trigger inflammation. LPS-binding protein (LBP) serves as a surrogate marker of underlying low-grade endotoxemia by LPS from the gut. We hypothesized that systemic LBP levels would be higher in obese children and in those with OSA.

METHODS

Consecutive snoring and nonsnoring children (mean age 6.8 ± 1.3 y) were included after overnight polysomnography, and fasting levels of lipids, insulin glucose, and high-sensitivity C-reactive protein were obtained. Children were subdivided into four subgroups based on the presence of obesity or OSA. Plasma LBP levels were assayed using ELISA.

RESULTS

Of 219 participants, nonobese controls had the lowest levels of LBP, and the presence of obesity without OSA was associated with significant LBP increases. Nonobese children with OSA exhibited increased LBP levels, with obese children with OSA demonstrating the highest LBP levels of all four groups. Furthermore, LBP was independently associated with body mass index and with measures of OSA severity as well as with metabolic dysfunction, particularly insulin resistance as indicated by the homeostasis model assessment of insulin resistance.

CONCLUSIONS

Systemic low-level endotoxemia and resultant systemic inflammation is present in children who are either obese or suffer from OSA and is particularly prominent when both conditions are present. We postulate that disrupted sleep and other factors facilitating obesity such as a high-fat diet may disrupt the gut microbiome and lead to increased systemic LPS levels with resultant inflammation, promoting downstream metabolic dysfunction.

Metagenome and metabolism: the tissue microbiota hypothesis

Over the last decade, the research community has revealed the role of a new organ: the intestinal microbiota. It is considered as a symbiont that is part of our organism since, at birth, it educates the immune system and contributes to the development of the intestinal vasculature and most probably the nervous system. With the advent of new generation sequencing techniques, a catalogue of genes that belong to this microbiome has been established that lists more than 5 million non-redundant genes called the metagenome. Using germ free mice colonized with the microbiota from different origins, it has been formally demonstrated that the intestinal microbiota causes the onset of metabolic diseases. Further to the role of point mutations in our genome, the microbiota can explain the on-going worldwide pandemic of obesity and diabetes, its dissemination and family inheritance, as well as the diversity of the associated metabolic phenotypes. More recently, the discovery of bacterial DNA within host tissues, such as the liver, the adipose tissue and the blood, which establishes a tissue microbiota, introduces new opportunities to identify targets and predictive biomarkers based on the host to microbiota interaction, as well as to define new strategies for pharmacological, immunomodulatory vaccines and nutritional applications.

A physical interaction between the adaptor proteins DOK3 and DAP12 is required to inhibit lipopolysaccharide signaling in macrophages

DNAX-activating protein of 12 kD (DAP12) is an immunoreceptor tyrosine-based activation motif (ITAM)-containing adaptor protein found in myeloid cells and natural killer cells, and it couples to various receptors that mediate either cellular activation or inhibition. DAP12 inhibits Toll-like receptor (TLR) signaling, such as that of TLR4 in response to its ligand lipopolysaccharide (LPS), as well as cytokine responses by coupling to TREM2 (triggering receptor expressed on myeloid cells 2) at the plasma membrane. Understanding the mechanisms that inhibit inflammatory responses in macrophages is important for the development of therapies to treat inflammatory diseases. We show that inhibition of LPS responses by DAP12 is mediated by the adaptor protein DOK3 (downstream of kinase 3). DOK3 physically associated with the ITAM of DAP12 through its phosphotyrosine-binding domain. In response to LPS, DOK3 was phosphorylated in a DAP12- and Src-dependent manner, which led to translocation of phosphorylated DOK3 to the plasma membrane. DOK3-deficient cells exhibited increased production of proinflammatory cytokines and activation of extracellular signal-regulated kinase (ERK). Compared to wild-type mice, DOK3-deficient mice had increased susceptibility to challenge with a sublethal dose of LPS and produced increased serum concentrations of the inflammatory cytokine tumor necrosis factor-α (TNF-α). Together, these data suggest the mechanism by which DAP12 and TREM2 inhibit LPS signaling in macrophages to prevent inflammation.

Supplemental naringenin prevents intestinal barrier defects and inflammation in colitic mice

Intestinal barrier defects are involved in the pathogenesis of inflammatory bowel disease. The present study investigated the ameliorative effects of naringenin, a citrus polyphenol, on intestinal tight junction (TJ) barrier defects and inflammation in a murine model of colitis. In Expt. 1, using a 2 × 2 fractional design, the mice were administered water or 2% dextran sulfate sodium (DSS) in combination with feeding control or naringenin-containing diets for 9 d (severe disease stage). DSS administration caused severe colon damage and inflammation, as indicated by body weight loss, increased clinical sores, colon shortening, and gene expressions of inflammatory cytokines [interferon-γ, interleukin (IL)-6, macrophage inflammatory protein-2, and IL-17A). DSS administration also impaired TJ barrier integrity in the colon, as indicated by increased colon permeability and plasma LPS-binding protein levels, resulting from the impaired colonic expression of TJ proteins, occludin, junctional adhesion molecule-A, and claudin-3. Supplemental feeding with naringenin totally or partially attenuated these symptoms, suggesting that naringenin ameliorates the DSS-induced colitis at least partially through protection of the TJ barrier. In Expt. 2, analyses were performed at different disease stages (d 3, 6, and 9) to more widely examine the ameliorative role of naringenin on the initiation and development of colitis. DSS administration moderately induced colon shortening at d 3 and 6 and increased the disease activity index (DAI) and inflammatory cytokine (IL-6 and IL-17A) expression without any significant increases in colonic permeability. Feeding naringenin attenuated the increased DAI and colon shortening and tended to suppress the increased cytokine expression. These findings suggest that the presence of an additional mechanism underlying the naringenin-mediated, anticolitic effect along with barrier protection.

Sex dimorphism and depot differences in adipose tissue function

Obesity, characterized by excessive adiposity, is a risk factor for many metabolic pathologies, such as type 2 diabetes mellitus (T2DM). Numerous studies have shown that adipose tissue distribution may be a greater predictor of metabolic health. Upper-body fat (visceral and subcutaneous abdominal) is commonly associated with the unfavorable complications of obesity, while lower-body fat (gluteal-femoral) may be protective. Current research investigations are focused on analyzing the metabolic properties of adipose tissue, in order to better understand the mechanisms that regulate fat distribution in both men and women. This review will highlight the adipose tissue depot- and sex-dependent differences in white adipose tissue function, including adipogenesis, adipose tissue developmental patterning, the storage and release of fatty acids, and secretory function. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.