Pre-B-cell colony-enhancing factor as a potential novel biomarker in acute lung injury

Blood visfatin concentrations in normal full-term pregnancies

AIM

To prospectively investigate blood visfatin concentrations during the perinatal period in normal pregnancies.

METHODS

Visfatin concentrations were determined in maternal, umbilical cord (representing the foetal state) and neonatal blood on day 1 (N1) and 4 (N4).

RESULTS

Maternal and foetal visfatin concentrations were similar (18.83+/-4.27 and 19.35+/-4.90 ng/mL, respectively). There were significant correlations between maternal and foetal (r=0.742, p<0.001), as well as between N1 and N4 (r=0.487, p=0.029) visfatin concentrations. Foetal concentrations were significantly elevated compared to N1 (p=0.032). There was no difference between N1 and N4 concentrations. However, there was a correlation between birth weight and neonatal visfatin concentrations: there was a mean increase in N1 and N4 visfatin concentrations by 0.221 ng/mL and 0.292 ng/mL, respectively, for every unit increase in customized centile (adjusted birth weight) (p=0.021 and p=0.005, respectively). No association was found between serum visfatin concentrations and gender, parity or mode of delivery.

CONCLUSIONS

Expression in foetal membranes and placental transfer could be responsible for higher blood visfatin concentrations during intrauterine life. Customized centiles seem to be independent predictor variables for postnatal visfatin concentrations. This finding could be attributed to the production of visfatin in adipose tissue, a main contributor to birth weight and consequently to customized centiles.

Pre-B-cell Colony-enhancing Factor (PBEF/Visfatin) Gene Expression is Modulated by NF-κB and AP-1 in Human Amniotic Epithelial Cells

A localized intrauterine inflammatory response is often associated with the initiation of normal human parturition, whereas infection causes a similar but more florid response initiating preterm labor. Pre-B-cell colony-enhancing factor (PBEF) is expressed in the human fetal membranes and is up-regulated by labor, severe infection and inflammatory stimuli. The aim of this study was to determine the involvement of the transcription factors NF-kappaB and AP-1 in the response of PBEF to an inflammatory stimulus and compare it with IL-8. The results showed that this treatment of amniotic epithelial-like cells (WISH) and primary amniotic epithelial cells increased expression of PBEF and IL-8, but IL-8 responded 100-fold more than PBEF. IL-1beta treatment together with a panel of NF-kappaB and AP-1 inhibitors demonstrated the involvement of these transcription factors in the up-regulation of PBEF. These data show that an inflammatory stimulus in the fetal membranes inducing NF-kappaB and AP-1 would up-regulate PBEF as well as IL-8.

Plasma visfatin levels in patients with newly diagnosed and untreated type 2 diabetes mellitus and impaired glucose tolerance

Visfatin, a new adipokine, facilitates adipogenesis and has insulin-mimetic properties. We aimed to investigate the plasma visfatin levels in patients with newly diagnosed and untreated type 2 diabetes mellitus (T2DM) and impaired glucose tolerance (IGT), who had no obesity or hypertension. Twenty-two patients with T2DM, 18 subjects with IGT and 40 healthy controls were enrolled. Visfatin levels were measured along with the BMI, blood pressure, lipids, glucose, insulin, adiponectin and hsCRP levels, and HOMA-IR indexes. Age, sex and BMI were similar in all groups. Visfatin levels were higher in the diabetic group than the controls (p=0.01). There was no significant difference in the visfatin levels between the T2DM and IGT groups as well as IGT group and healthy controls. Plasma visfatin concentrations did not differ between men and women. Visfatin levels did not correlate with BMI, blood pressure, plasma adiponectin, insulin, hsCRP, glucose and lipid levels or HOMA-IR indexes in the three groups. These results indicate that hyperglycemia causes an increase in plasma visfatin levels and, as in people with T2DM but not with IGT, this increase gets more prominent as the glucose intolerance worsens.

Visfatin, an adipocytokine with proinflammatory and immunomodulating properties

Adipocytokines are mainly adipocyte-derived cytokines regulating metabolism and as such are key regulators of insulin resistance. Some adipocytokines such as adiponectin and leptin affect immune and inflammatory functions. Visfatin (pre-B cell colony-enhancing factor) has recently been identified as a new adipocytokine affecting insulin resistance by binding to the insulin receptor. In this study, we show that recombinant visfatin activates human leukocytes and induces cytokine production. In CD14(+) monocytes, visfatin induces the production of IL-1beta, TNF-alpha, and especially IL-6. Moreover, it increases the surface expression of costimulatory molecules CD54, CD40, and CD80. Visfatin-stimulated monocytes show augmented FITC-dextran uptake and an enhanced capacity to induce alloproliferative responses in human lymphocytes. Visfatin-induced effects involve p38 as well as MEK1 pathways as determined by inhibition with MAPK inhibitors and we observed activation of NF-kappaB. In vivo, visfatin induces circulating IL-6 in BALB/c mice. In patients with inflammatory bowel disease, plasma levels of visfatin are elevated and its mRNA expression is significantly increased in colonic tissue of Crohn's and ulcerative colitis patients compared with healthy controls. Macrophages, dendritic cells, and colonic epithelial cells might be additional sources of visfatin as determined by confocal microscopy. Visfatin can be considered a new proinflammatory adipocytokine.

Genomics and the cardiac surgeon

Until recently, genetics was a course relegated to Saturdays in medical school, and molecular biology was a subject you could only discuss while smoking a pipe. Now, some gene polymorphisms may predict perioperative trouble more precisely than a 10% ejection fraction. Gene chips will soon permit designer therapy and a micro-array "signature" will soon become fundamental to pre-operative risk stratification. It is time for the cardiac surgical community to come aboard.

Microarray-based analysis of ventilator-induced lung injury

Acute respiratory distress syndrome (ARDS) and acute lung injury (ALI) are a frequent cause of intensive care unit admission, affecting over 200,000 patients in the United States each year. Mechanical ventilation is a life-saving intervention in the setting of ARDS and ALI, but clinical trials have demonstrated that mechanical ventilation with excessive tidal volumes plays a role in promoting and perpetuating lung injury and leads to excess mortality. This process has been labeled ventilator-induced lung injury (VILI), but the molecular mechanisms driving this process and its interactions with predisposing risk factors such as sepsis and chemical injury remain incompletely understood. Genome-wide measurements of gene expression using microarray technology represent a powerful tool to examine the pathophysiology of VILI. Several recent studies have used this approach to study VILI in isolation and associated with endotoxin instillation or saline lavage. These studies and others examining gene expression profiles in epithelial cells subjected to cyclic stretch have provided novel insights on the molecular mechanisms underlying VILI. This review will summarize these findings and discuss implications for future studies.

The regulation of nicotinamide adenine dinucleotide biosynthesis by Nampt/PBEF/visfatin in mammals

PURPOSE OF REVIEW

Nicotinamide adenine dinucleotide (NAD) is a classic coenzyme in cellular redox reactions. Recently, NAD biochemistry has also been implicated in a broader range of biological functions in mammals, but the regulation of NAD biosynthesis has been poorly investigated. Recent progress in the field of NAD biochemistry has fueled new interest in the NAD biosynthetic pathways from its precursors and their physiological roles in metabolism. This review summarizes the latest knowledge on the NAD biosynthetic pathways and focuses on one of the key NAD biosynthetic enzymes, namely, nicotinamide phosphoribosyltransferase.

RECENT FINDINGS

Mammals predominantly use nicotinamide rather than nicotinic acid as a precursor for NAD biosynthesis. Nicotinamide phosphoribosyltransferase (Nampt) is the rate-limiting enzyme that converts nicotinamide to nicotinamide mononucleotide in the NAD biosynthetic pathway from nicotinamide in mammals. The same protein has also been identified as a cytokine (pre-B-cell colony-enhancing factor or PBEF) or an insulin-mimetic hormone (visfatin).

SUMMARY

We propose that the presumed multiple effects of Nampt/PBEF/visfatin may be entirely explained by its role as an intra and extracellular NAD biosynthetic enzyme. We also propose a new model of Namp/PBEF/visfatin-mediated systemic NAD biosynthesis and its possible physiological significance. Our model provides an important insight into developing preventive/therapeutic interventions for metabolic complications, such as obesity and diabetes.

Visfatin/pre-B-cell colony-enhancing factor: a protein with various suggested functions

Pre-B-cell colony-enhancing factor (PBEF) was recently found in high levels in visceral fat, and was therefore renamed visfatin. This new adipocytokine exerts insulin-mimetic effects in mice and in cultured cells by binding to and activating the insulin receptor. Despite some recent studies on this topic, the proposed role of visfatin in metabolism remains largely unknown. Initially, PBEF/visfatin was discovered as a cytokine for the differentiation of B-cells. Pre-B-cell colony-enhancing factor was also shown to inhibit apoptosis of neutrophils in sepsis and was discussed as a novel biomarker for acute lung injury (ALI). Although PBEF is missing a signal sequence, its secretion and function as a molecule involved in the regulation of inflammatory processes was reported in several studies. Investigations of PBEF/visfatin in gestational membranes suggest a function in the physiologic and pathologic pathways leading to labor. Furthermore, it was found upregulated in colorectal cancer and was brought into connection with the regulation of the cell cycle. Intra-cellular, PBEF/visfatin acts as a cytosolic enzyme involved in nicotinamide adenine dinucleotide (NAD) synthesis. This activity was shown to be important for vascular smooth muscle cell (SMC) maturation, indicating a possible involvement in vascular pathology. The important physiologic role of PBEF/visfatin is also underlined by its evolutionary highly conserved gene in different species. This review summarizes the current knowledge of the various functions of PBEF/visfatin towards involvements in pathophysiology of several diseases.

Peptidomic analysis of human peripheral monocytes persistently infected by Chlamydia trachomatis

Peptidomic analysis using Differential Peptide Display (DPD) of human peripheral blood mononuclear cells (PBMC) mock-infected or persistently infected by Chlamydia trachomatis (CT) revealed 10 peptides, expressed upon CT infection. Analysis of these 10 candidates by tandem mass spectrometry enabled the determination of seven candidates as fragments from the precursors (I) ferritin heavy chain subunit, (II) HLA class II histocompatibility antigen, (III) vimentin, (IV) indoleamine 2,3-dioxygenase, (V and VI) pre-B cell enhancing factor (PBEF), and (VII) Interleukin-8 (CXCL8). The identified candidates proved the presence of anti-bacterial and immunologically active monocytic proteins after CT infection.

Genetic epidemiology of acute respiratory distress syndrome: implications for future prevention and treatment

The genetic susceptibility to the development of and variable outcomes in acute lung injury/acute respiratory distress syndrome (ALI/ARDS) has become a topic of great interest in the pulmonary and critical care community. Published studies of variable genetic susceptibility to ALI/ARDS already have identified some important candidate genes and potential gene-environment interactions. This article reviews these recent studies, features of the current approach, and implications for future prevention and treatment in ALI. The challenges and potential contributions of genetic epidemiology to the future prevention and treatment in ALI are discussed.

Pathogenetic significance of biological markers of ventilator-associated lung injury in experimental and clinical studies

For patients with acute lung injury, positive pressure mechanical ventilation is life saving. However, considerable experimental and clinical data have demonstrated that how clinicians set the tidal volume, positive end-expiratory pressure, and plateau airway pressure influences lung injury severity and patient outcomes including mortality. In order to better identify ventilator-associated lung injury (VALI), clinical investigators have sought to measure blood-borne and airspace biological markers of VALI. At the same time, several laboratory-based studies have focused on biological markers of inflammation and organ injury in experimental models in order to clarify the mechanisms of ventilator-induced lung injury (VILI) and VALI. This review summarizes data on biological markers of VALI and VILI from both clinical and experimental studies with an emphasis on markers identified in patients and in the experimental setting. This analysis suggests that measurement of some of these biological markers may be of value in diagnosing VALI and in understanding its pathogenesis.

A visfatin promoter polymorphism is associated with low-grade inflammation and type 2 diabetes

Visfatin (also known as pre-B cell colony-enhancing factor, or PBEF) is a pro-inflammatory adipokine expressed predominantly in visceral fat. We investigated whether polymorphisms at the visfatin/PBEF locus influence the risk of type 2 diabetes (T2D). Linkage disequilibrium analysis of 52 single nucleotide polymorphisms spanning the entire gene (34.7 kb) plus 20.5 kb of the upstream region and 25.5 kb of the downstream region revealed a single haplotype block that could be tagged by seven single nucleotide polymorphisms. These seven tags were typed in a group of T2D patients (n = 814) and a group of non-diabetic controls (n = 320) of white origin. A significant association was observed at -948C>A, with minor allele frequencies of 0.157 in T2D cases and 0.119 in non-diabetic controls (p = 0.021). In a non-diabetic population (n = 630), the same -948 allele that conferred increased risk of T2D was significantly associated with higher plasma levels of fibrinogen and C-reactive protein (p = 0.0022 and 0.0038, respectively). However, no significant associations were observed with BMI, waist circumference, serum glucose levels, or fasting insulin levels. Our findings suggest that the visfatin/PBEF gene may play a role in determining T2D susceptibility, possibly by modulating chronic, low-grade inflammatory responses.

Genomic insights into acute inflammatory lung injury

Acute lung injury (ALI) is a devastating syndrome (usually associated with sepsis) that represents a major healthcare burden in the United States. We have focused our studies on unraveling the genetic underpinnings of this syndrome utilizing a candidate gene approach to identify novel genes for ALI susceptibility. Two novel genes identified by this approach include pre-B cell colony-enhancing factor (PBEF) and the gene for myosin light chain kinase (MLCK). PBEF protein levels were elevated in human bronchoalveolar lavage and serum samples from patients with ALI, and DNA sequencing identified two single nucleotide polymorphisms in the PBEF promoter (T-1001G, C-1543T) that were overrepresented in patients with sepsis-induced ALI. More recently, we found MLCK single polymorphisms and haplotypes to be associated with human ALI with unique variants observed in African-Americans with ALI. Thus genomic and genetic approaches represent powerful strategies in the identification of novel candidate genes and potential targets for ALI therapies.

Common polymorphisms in the promoter of the visfatin gene (PBEF1) influence plasma insulin levels in a French-Canadian population

The adipokine visfatin (PBEF1) exhibits insulin-mimetic effects and correlates strongly with visceral adiposity. We sequenced visfatin gene exons and 1,480 bp of the promoter in 23 individuals, including 18 individuals from the Quebec Family Study (QFS) with varying degrees of abdominal visceral fat, assessed by computed tomography, and 5 individuals from the Saguenay-Lac-Saint-Jean region of Québec. We identified a synonymous polymorphism in exon 7 (SER301SER) but no nonsynonymous mutations. We observed an additional 10 polymorphisms, including 5 intronic, 4 within the promoter, and 1 within the 3' untranslated region. Further promoter sequencing (816 bp) identified five additional single nucleotide polymorphisms (SNPs) in the QFS population. To investigate the role of visfatin gene variants in obesity-related phenotypes, we genotyped a total of 13 SNPs in the promoter region of the gene. From these, we analyzed the seven common SNPs in the QFS sample (918 participants from 208 families). A significant association was found between two SNPs (rs9770242 and rs1319501), in perfect linkage disequilibrium, and fasting insulin levels (P = 0.002). These SNPs were also associated with fasting glucose (P <or= 0.02). In addition, a more distal SNP (rs7789066) was significantly associated with the apolipoprotein B component of VLDL (P = 0.012).

Adipocytokines: mediators linking adipose tissue, inflammation and immunity

There has been much effort recently to define the role of adipocytokines, which are soluble mediators derived mainly from adipocytes (fat cells), in the interaction between adipose tissue, inflammation and immunity. The adipocytokines adiponectin and leptin have emerged as the most abundant adipocyte products, thereby redefining adipose tissue as a key component not only of the endocrine system, but also of the immune system. Indeed, as we discuss here, several adipocytokines have a central role in the regulation of insulin resistance, as well as many aspects of inflammation and immunity. Other adipocytokines, such as visfatin, have only recently been identified. Understanding this rapidly growing family of mainly adipocyte-derived mediators might be of importance in the development of new therapies for obesity-associated diseases.

Regulation of pre-B cell colony-enhancing factor by STAT-3-dependent interleukin-6 trans-signaling: implications in the pathogenesis of rheumatoid arthritis

OBJECTIVE

To determine whether interleukin-6 (IL-6) trans-signaling directs the expression of pre-B cell colony-enhancing factor (PBEF) in vitro and in vivo.

METHODS

Complementary DNA from rheumatoid arthritis (RA) synovial fibroblasts treated with IL-6 and soluble IL-6 receptor (sIL-6R) was used to probe a cytokine microarray. PBEF regulation by the IL-6-related cytokines, IL-6, sIL-6R, oncostatin M (OSM), IL-11, and leukemia inhibitory factor (LIF) was determined by reverse transcription-polymerase chain reaction analysis. IL-6-mediated STAT-3 regulation of PBEF was determined using a cell-permeable STAT-3 inhibitor peptide. Antigen-induced arthritis (AIA) was induced in wild-type (IL-6(+/+)) and IL-6-deficient (IL-6(-/-)) mice. PBEF and STAT were detected by immunohistochemistry, immunoblotting, and electrophoretic mobility shift assay. Synovial levels of PBEF were quantified by enzyme immunoassay.

RESULTS

IL-6 trans-signaling regulated PBEF in a STAT-3-dependent manner. In addition, PBEF was regulated by the IL-6-related cytokine OSM, but not IL-11 or LIF. Flow cytometric analysis of the IL-6-related cognate receptors suggested that OSM regulates PBEF via its OSM receptor beta and not its LIF receptor. The involvement of PBEF in arthritis progression was confirmed in vivo, where induction of AIA resulted in a 4-fold increase in the synovial expression of PBEF. In contrast, little or no change was observed in IL-6(-/-) mice, in which the inflammatory infiltrate was markedly reduced and synovial STAT-1/3 activity was also impaired. Analysis of human RA synovial tissue confirmed that PBEF immunolocalized in apical synovial membrane cells, endothelial cells, adipocytes, and lymphoid aggregates. Synovial fluid levels of PBEF were significantly higher in RA patients than in osteoarthritis patients.

CONCLUSION

Experiments presented herein demonstrate that PBEF is regulated via IL-6 trans-signaling and the IL-6-related cytokine OSM. PBEF is also actively expressed during arthritis. Although these data confirm an involvement of PBEF in disease progression, the consequence of its action remains to be determined.

Acute lung injury and the coagulation pathway: Potential role of gene polymorphisms in the protein C and fibrinolytic pathways

There is evidence that dysregulation of coagulation and fibrinolysis may participate in the pathogenesis of acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS). Altered concentrations of several proteins of the coagulation and fibrinolytic pathways in plasma and pulmonary edema fluid from patients with acute lung injury have been related to the severity of lung injury and clinical outcomes. Polymorphisms in the genes encoding for proteins of the protein C and fibrinolysis pathways are known to regulate the production of the respective proteins. It is plausible that these polymorphisms may be associated with the susceptibility to and severity of illness in ALI and ARDS. Well-designed studies that examine the association of these polymorphisms with susceptibility and severity of ALI and ARDS are needed to test the influence of both genetic and environmental factors on the clinical outcomes in patients with ALI and ARDS. There are several important considerations in the design of these genetic association studies, including selection of candidate genes with the most biological plausibility, definition of the phenotype, selection of appropriate controls, determination of the appropriate sample size and assessment of Hardy-Weinberg equilibrium among controls as a measure of internal validity.

Crystal structure of visfatin/pre-B cell colony-enhancing factor 1/nicotinamide phosphoribosyltransferase, free and in complex with the anti-cancer agent FK-866

Visfatin/pre-B cell colony-enhancing factor 1 (PBEF)/nicotinamide phosphoribosyltransferase (NAmPRTase) is a multifunctional protein having phosphoribosyltransferase, cytokine and adipokine activities. Originally isolated as a cytokine promoting the differentiation of B cell precursors, it was recently suggested to act as an insulin analog via the insulin receptor. Here, we describe the first crystal structure of visfatin in three different forms: apo and in complex with either nicotinamide mononucleotide (NMN) or the NAmPRTase inhibitor FK-866 which was developed as an anti-cancer agent, interferes with NAD biosynthesis, showing a particularly high specificity for NAmPRTase. The crystal structures of the complexes with either NMN or FK-866 show that the enzymatic active site of visfatin is optimized for nicotinamide binding and that the nicotinamide-binding site is important for inhibition by FK-866. Interestingly, visfatin mimics insulin signaling by binding to the insulin receptor with an affinity similar to that of insulin and does not share the binding site with insulin on the insulin receptor. To predict binding sites, the potential interaction patches of visfatin and the L1-CR-L2 domain of insulin receptor were generated and analyzed. Although the relationship between the insulin-mimetic property and the enzymatic function of visfatin has not been clearly established, our structures raise the intriguing possibility that the glucose metabolism and the NAD biosynthesis are linked by visfatin.

Visfatin in adipocytes is upregulated by hypoxia through HIF1alpha-dependent mechanism

Obesity is associated with metabolic disorders, such as insulin resistance. Visfatin is an adipose-derived secretory factor to exert insulin-mimetic effects. Plasma visfatin levels and mRNA levels of visfatin in adipose tissues are increased in obesity. However, the mechanism that mediates induction of visfatin mRNA in adipose tissue of obesity remains unknown. Recent studies have reported that fat tissue is hypoxia in obesity. In this study, we investigated the effects of hypoxia on mRNA expression of visfatin in adipocytes. Hypoxia increased visfatin mRNA expression. Desferoxamine and Cobaltous chloride, two hypoxia mimetic compounds, also increased visfatin mRNA levels. Dimethyloxallyl glycine, a stabilizer of hypoxia-inducible factor 1alpha (HIF1alpha), mimicked the hypoxia-mediated upregulation of visfatin, and YC1, an inhibitor of HIF1 cancelled the hypoxia-induced upregulation of visfatin mRNA. We identified two functional hypoxia responsive elements (HRE) in mouse visfatin promoter. Hypoxic treatment and overexpression of HIF1alpha increased the promoter activity, and mutation of the HRE blunted hypoxia-induced activation of visfatin promoter. Our results suggest that visfatin mRNA expression is upregulated in the fat tissue of obesity through the activation of HIF1alpha pathway due to hypoxia.

Hypoxic induction of human visfatin gene is directly mediated by hypoxia-inducible factor-1

Visfatin has been originally identified as a growth factor for early stage B cells and recently known as an adipokine. Here, we report that hypoxia induces the visfatin mRNA and protein levels in MCF7 breast cancer cells. We also demonstrate that induction of visfatin gene is regulated by hypoxia-inducible factor-1alpha (HIF-1alpha). Moreover, 5'-flanking promoter region of human visfatin gene contains two functional HIF responsive elements (HREs), activating the expression of visfatin. Mutation of these HREs in the visfatin promoter abrogates activation of a luciferase reporter gene driven by visfatin promoter under hypoxia. Taken together, our results demonstrate that visfatin is a new hypoxia-inducible gene of which expression is stimulated through the interaction of HIF-1 with HRE sites in its promoter region.

Microarray analysis of regional cellular responses to local mechanical stress in acute lung injury

Human acute lung injury is characterized by heterogeneous tissue involvement, leading to the potential for extremes of mechanical stress and tissue injury when mechanical ventilation, required to support critically ill patients, is employed. Our goal was to establish whether regional cellular responses to these disparate local mechanical conditions could be determined as a novel approach toward understanding the mechanism of development of ventilator-associated lung injury. We utilized cross-species genomic microarrays in a unilateral model of ventilator-associated lung injury in anesthetized dogs to assess regional cellular responses to local mechanical conditions that potentially contribute pathogenic mechanisms of injury. Highly significant regional differences in gene expression were observed between lung apex/base regions as well as between gravitationally dependent/nondependent regions of the base, with 367 and 1,544 genes differentially regulated between these regions, respectively. Major functional groupings of differentially regulated genes included inflammation and immune responses, cell proliferation, adhesion, signaling, and apoptosis. Expression of genes encoding both acute lung injury-associated inflammatory cytokines and protective acute response genes were markedly different in the nondependent compared with the dependent regions of the lung base. We conclude that there are significant differences in the local responses to stress within the lung, and consequently, insights into the cellular responses that contribute to ventilator-associated lung injury development must be sought in the context of the mechanical heterogeneity that characterizes this syndrome.

The contribution of biophysical lung injury to the development of biotrauma

Patients with severe acute respiratory distress syndrome who die usually succumb to multiorgan failure as opposed to hypoxia. Despite appropriate resuscitation, some patients' symptoms persist on a downward spiral, apparently propagated by an uncontained systemic inflammatory response. This phenomenon is not well understood. However, a novel hypothesis to explain this observation proposes that it is related to the life-saving ventilatory support used to treat the respiratory failure. According to this hypothesis, mechanical ventilation per se, by altering both the magnitude and the pattern of lung stretch, can cause changes in gene expression and/or cellular metabolism that ultimately can lead to the development of an overwhelming inflammatory response-even in the absence of overt structural damage. This mechanism of injury has been termed biotrauma. In this review we explore the biotrauma hypothesis, the causal relationship between biophysical injury and organ failure, and its implications for the future therapy and management of critically ill patients.

An update on visfatin/pre-B cell colony-enhancing factor, an ubiquitously expressed, illusive cytokine that is regulated in obesity

PURPOSE OF REVIEW

The aim of this article is to summarize all of the recent studies on pre-B cell colony-enhancing factor visfatin, a ubiquitously expressed secreted protein that has been implicated in obesity and insulin resistance. Although pre-B-cell colony-enhancing factor was discovered over 10 years ago, there are many remaining questions about the regulation and function of this protein.

RECENT FINDINGS

Studies in the last decade have revealed the endocrine properties of fat cells. One of the most recent proteins shown to be highly expressed in adipose tissue is visfatin, originally identified as pre-B-cell colony-enhancing factor. Visfatin/pre-B-cell colony-enhancing factor appears to be preferentially produced by the visceral adipose tissue and has insulin mimetic actions. Studies by many groups indicate that obesity-related diabetes and accompanying metabolic disorders in humans have been specifically linked to increased visceral adipose tissue mass. The different roles of various adipocyte depots, however, are still poorly understood. It has been hypothesized that understanding the differences in the biology of visceral and subcutaneous human adipose tissue may hold the key to therapeutic strategies aimed at reducing obesity-induced insulin resistance and alleviating symptoms of the metabolic syndrome. Interestingly, some observed actions of visfatin indicate that this secreted protein may be an interesting therapeutic target. Several recent studies, however, indicate that our understanding of visfatin is still speculative.

SUMMARY

This review summarizes all of the papers in the last year on the expression and function of visfatin/pre-B-cell colony-enhancing factor and highlights inconsistent observations from various investigators studying this protein. It also highlights previous observations on the role of pre-B-cell colony-enhancing factor. We suggest that the pathophysiologic role of visfatin/pre-B-cell colony-enhancing factor in humans remains largely unknown.

Gene expression profiling of acute liver stress during living donor liver transplantation

During liver transplantation, the donor graft is subjected to a number of acute stresses whose molecular basis is not well-understood. The effects of surgical stress, preservation and reperfusion injury were studied in 24 consecutive living donor liver transplant (LDLT) operations. Liver biopsies were taken early in the donor operation (OPENING), after transection of the donor liver (PRECLAMP) and following implantation of the graft (post hepatic artery, [PHA]); these were evaluated for histology, tissue glutathione content and gene expression using a 19K-human cDNA microarray. LDLT was associated with an ischemia/reperfusion injury, with accumulation of small numbers of neutrophils and decreased glutathione in the PHA biopsies. Following reperfusion, the expression of 129 genes increased and 106 genes decreased when compared to OPENING levels (> or <2-fold, p < 0.01). By real-time PCR a subset of 25 genes was verified (15 increased, 10 decreased). These genes were similarly altered in another condition of acute liver stress (the response to brain-death), but not in three chronic liver disease states (HCV, HBV and PBC). This study has identified a set of genes whose expression is altered in acute, but not chronic, liver stress, likely to play a central role in the pathogenesis of acute liver injury of liver transplantation.

Receptor for advanced glycation end-products is a marker of type I cell injury in acute lung injury

RATIONALE

Receptor for advanced glycation end-products (RAGE) is one of the alveolar type I cell-associated proteins in the lung.

OBJECTIVES

To test the hypothesis that RAGE is a marker of alveolar epithelial type I cell injury.

METHODS

Rats were instilled intratracheally with 10 mg/kg lipopolysaccharide or hydrochloric acid. RAGE levels were measured in the bronchoalveolar lavage (BAL) and serum in the rats and in the pulmonary edema fluid and plasma from patients with acute lung injury (ALI; n = 22) and hydrostatic pulmonary edema (n = 11).

MAIN RESULTS

In the rat lung injury studies, RAGE was released into the BAL and serum as a single soluble isoform sized approximately 48 kD. The elevated levels of RAGE in the BAL correlated well with the severity of experimentally induced lung injury. In the human studies, the RAGE level in the pulmonary edema fluid was significantly higher than the plasma level (p < 0.0001). The median edema fluid/plasma ratio of RAGE levels was 105 (interquartile range, 55-243). The RAGE levels in the pulmonary edema fluid from patients with ALI were higher than the levels from patients with hydrostatic pulmonary edema (p < 0.05), and the plasma RAGE level in patients with ALI were significantly higher than the healthy volunteers (p < 0.001) or patients with hydrostatic pulmonary edema (p < 0.05).

CONCLUSION

RAGE is a marker of type I alveolar epithelial cell injury based on experimental studies in rats and in patients with ALI.

Pre-B-cell-colony-enhancing factor is critically involved in thrombin-induced lung endothelial cell barrier dysregulation

Prior genomic and genetic studies identified pre-B-cell colony-enhancing factor (PBEF) as a novel candidate gene and biomarker in acute lung injury (ALI). As increased vascular permeability is a cardinal feature of ALI, we assessed the role of PBEF in in vitro vascular barrier regulation using confluent human pulmonary artery endothelial cell (HPAEC) monolayers. Reductions in PBEF protein expression (>70%) by siRNA significantly attenuated EC barrier dysfunction induced by the potent edemagenic agent, thrombin, reflected by reductions in transendothelial electric resistance (TER, approximately 60% reduction). Furthermore, PBEF siRNA blunted thrombin-mediated increases in Ca(2+) entry, polymerized actin formation, and myosin light chain phosphorylation, events critical to the thrombin-mediated permeability response. Finally, PBEF siRNA also significantly inhibited thrombin-stimulated increase of IL-8 secretion in HPAEC, a chemokine known to induce actin fiber formation and intercellular gap formation of endothelial cells. Taken together, these studies demonstrate that PBEF may be required for complete expression of the thrombin-induced inflammatory response and reveal potentially novel role for PBEF in the regulation of EC Ca(2+)-dependent cytoskeletal rearrangement and endothelial barrier dysfunction. Ongoing studies will continue to address the molecular mechanisms by which PBEF contributes to ALI susceptibility.

In vitro identification and in silico utilization of interspecies sequence similarities using GeneChip technology

Background

Genomic approaches in large animal models (canine, ovine etc) are challenging due to insufficient genomic information for these species and the lack of availability of corresponding microarray platforms. To address this problem, we speculated that conserved interspecies genetic sequences can be experimentally detected by cross-species hybridization. The Affymetrix platform probe redundancy offers flexibility in selecting individual probes with high sequence similarities between related species for gene expression analysis.

Results

Gene expression profiles of 40 canine samples were generated using the human HG-U133A GeneChip (U133A). Due to interspecies genetic differences, only 14 ± 2% of canine transcripts were detected by U133A probe sets whereas profiling of 40 human samples detected 49 ± 6% of human transcripts. However, when these probe sets were deconstructed into individual probes and examined performance of each probe, we found that 47% of human probes were able to find their targets in canine tissues and generate a detectable hybridization signal. Therefore, we restricted gene expression analysis to these probes and observed the 60% increase in the number of identified canine transcripts. These results were validated by comparison of transcripts identified by our restricted analysis of cross-species hybridization with transcripts identified by hybridization of total lung canine mRNA to new Affymetrix Canine GeneChip^®.

Conclusion

The experimental identification and restriction of gene expression analysis to probes with detectable hybridization signal drastically increases transcript detection of canine-human hybridization suggesting the possibility of broad utilization of cross-hybridizations of related species using GeneChip technology.

Molecular Cloning and Characterization of Canine Pre-B-Cell Colony-Enhancing Factor

During our previous attempt to search for the candidate genes to acute lung injury (ALI), we unexpectedly identified PBEF as the most highly upregulated gene in a canine model of ALI by crosshybridizing canine lung cRNA to the Affymetrix human gene chip HG-U133A. The result suggested that PBEF may be a potential biomarker in ALI. To extend and translate that finding, we have performed the molecular cloning and characterization of canine PBEF cDNA in this study. Deduced amino acid sequence alignment revealed that the PBEF gene is evolutionarily highly conserved, with the canine PBEF protein sequence 96% identical to human PBEF and 94% identical to both murine and rat PBEF counterparts. Canine PBEF protein was successfully expressed both by in vitro transcription coupled with translation in a cell-free system and by transfection of canine PBEF cDNA into the human lung type II alveolar adenocarcinoma cell line A549. The expressed canine PBEF protein was visualized by either an anti-V5 tag peptide polyclonal antibody or an anti-canine PBEF peptide polyclonal antibody. RT-PCR assay indicates that canine PBEF is expressed in canine lung, brain, heart, liver, spleen, kidney, pancreas, and muscle, with liver showing the highest expression,followed by muscle. Isolation of the canine PBEF cDNA and expression of its recombinant protein may provide molecular tools to study the molecular mechanism of ALI in the canine model and to elucidate the potential role of PBEF as an ALI biomarker.

Genetic determinants and ethnic disparities in sepsis-associated acute lung injury

Acute lung injury (ALI) is a common and devastating illness that occurs in the context of sepsis and other systemic inflammatory disorders. In systemic illnesses like sepsis, only a subset of patients develops ALI even when pathologic stimuli are apparently equivalent, suggesting that there are genetic features that may influence its onset. Considerable obstacles in defining the exact nature of the pathogenesis of ALI include substantial phenotypic variance, incomplete penetrance, complex gene-environment interactions and a strong potential for locus heterogeneity. Moreover, ALI arises in a critically ill population with diverse precipitating factors and appropriate controls that best match the reference population have not been agreed upon. The sporadic nature of ALI precludes conventional approaches such as linkage mapping for the elucidation of candidate genes, but tremendous progress has been made in combining robust, genomic tools such as high-throughput, expression profiling with case-control association studies in well characterized populations. Similar to trends observed in common, complex traits such as hypertension and diabetes, some of these studies have highlighted differences in allelic variant frequencies between European American and African American ALI patients for novel genes which may explain, in part, the complex interplay between ethnicity, sepsis and the development of ALI. In trying to understand the basis for contemporary differences in allelic frequency, which may lead to differences in susceptibility, the potential role of positive selection for genetic variants in ancestral populations is considered.