Measurement of lysophospholipase D/autotaxin activity in human serum samples

Autotaxin is a potential predictive marker for the development of veno-occlusive disease/sinusoidal obstruction syndrome after allogeneic hematopoietic cell transplantation

Veno-occlusive disease/sinusoidal obstruction syndrome (VOD/SOS) is a life-threatening complication after allogeneic hematopoietic cell transplantation (allo-HCT), and stratification of the high-risk group before transplantation is significant. Serum autotaxin (ATX) levels have been reported to increase in patients with liver fibrosis caused by metabolic inhibition from liver sinusoidal endothelial cells. Considering that the pathophysiology of VOD/SOS begins with liver sinusoidal endothelial cell injury, an increase in serum ATX levels may precede the onset of VOD/SOS. A retrospective study with 252 patients, including 12 patients with VOD/SOS, who had received allo-HCT was performed. The cumulative incidence of VOD/SOS was higher in the group with serum ATX levels before conditioning (baseline ATX) above the upper reference limit (high ATX group, p < 0.001), and 1-year cumulative incidences were 22.7% (95% confidence interval [95%CI], 3.1-42.4%) and 3.5% (95%CI, 1.1-5.8%), respectively. In the multivariate analysis, elevated baseline ATX was identified as an independent risk factor for VOD/SOS development and showed an additive effect on the predictive ability of known risk factors. Furthermore, the incidence of VOD/SOS-related mortality was greater in the high ATX group (16.7% vs. 1.3%; p = 0.005). Serum ATX is a potential predictive marker for the development of VOD/SOS.

An Autotaxin-Induced Ocular Hypertension Mouse Model Reflecting Physiological Aqueous Biomarker

Purpose

Animal models of ocular hypertension (OH) have been developed to understand the pathogenesis of glaucoma and facilitate drug discovery. However, many of these models are fraught with issues, including severe intraocular inflammation and technical challenges. Lysophosphatidic acid (LPA) is implicated in trabecular meshwork fibrosis and increased resistance of aqueous outflow, factors that contribute to high intraocular pressure (IOP) in human open-angle glaucoma. We aimed to elevate IOP by increasing expression of the LPA-producing enzyme autotaxin (ATX) in mouse eyes.

Methods

Tamoxifen-inducible ATX transgenic mice were developed. Tamoxifen was administered to six- to eight-week-old mice via eye drops to achieve ATX overexpression in the eye. IOP and retinal thickness were measured over time, and retinal flat-mount were evaluated to count retinal ganglion cells (RGCs) loss after three months.

Results

Persistent elevation of ATX expression in mouse eyes was confirmed through immunohistochemistry and LysoPLD activity measurement. ATX Tg mice exhibited significantly increased IOP for nearly two months following tamoxifen treatment, with no anterior segment changes or inflammation. Immunohistochemical analysis revealed enhanced expression of extracellular matrix near the angle after two weeks and three months of ATX induction. This correlated with reduced outflow facility, indicating that sustained ATX overexpression induces angle fibrosis, elevating IOP. Although inner retinal layer thickness remained stable, peripheral retina showed a notable reduction in RGC cell count.

Conclusions

These findings confirm the successful creation of an open-angle OH mouse model, in which ATX expression in the eye prompts fibrosis near the angle and maintains elevated IOP over extended periods.

Lipoprotein(a) As a Potential Predictive Factor for Earlier Aortic Valve Replacement in Patients with Bicuspid Aortic Valve

Bicuspid aortic valve (BAV) affects 0.5-2% of the general population and constitutes the major cause of severe aortic valve stenosis (AVS) in individuals ≤70 years. The aim of the present study was to evaluate the parameters that may provide information about the risk of AVS developing in BAV patients, with particular emphasis on lipoprotein(a) (Lp(a)), which is a well-recognized risk factor for stenosis in the general population. We also analyzed the impact of autotaxin (ATX) and interleukin-6 (IL-6) as parameters potentially related to the pathomechanism of Lp(a) action. We found that high Lp(a) levels (>50 mg/dL) occurred significantly more frequently in patients with AVS than in patients without AVS, both in the group below and above 45 years of age (p = 0.036 and p = 0.033, respectively). Elevated Lp(a) levels were also strictly associated with the need for aortic valve replacement (AVR) at a younger age (p = 0.016). However, the Lp(a) concentration did not differ significantly between patients with and without AVS. Similarly, we observed no differences in ATX between the analyzed patient groups, and both ATX activity and concentration correlated significantly with Lp(a) level (R = 0.465, p < 0.001 and R = 0.599, p < 0.001, respectively). We revealed a significantly higher concentration of IL-6 in young patients with AVS. However, this observation was not confirmed in the group of patients over 45 years of age. We also did not observe a significant correlation between IL-6 and Lp(a) or between CRP and Lp(a) in any of the analyzed groups of BAV patients. Our results demonstrate that a high level of Lp(a), greater than 50 mg/dL, may be a significant predictive factor for earlier AVR. Lp(a)-related parameters, such as ATX and IL-6, may be valuable in providing information about the additional cardiovascular risks associated with developing AVS.

Role of Autotaxin in High Glucose-Induced Human ARPE-19 Cells

Autotaxin (ATX) is an enzymatic with lysophospholipase D (lysoPLD) activity. We investigated the role of ATX in high glucose (HG)-induced human retinal pigment epithelial (ARPE-19) cells to explore the pathogenesis of diabetic retinopathy (DR). We performed a quantitative real-time polymerase chain reaction, Western blotting, immunocytochemistry, enzyme-linked immunosorbent assay, cell permeability assay, and transepithelial electrical resistance measurement in HG-induced ARPE-19 cells and compared their results with those of normal glucose and osmotic pressure controls. ATX expression and its lysoPLD activity, barrier function, and expression of vascular endothelial growth factor receptors VEGFR-1 and VEGFR-2 were downregulated, while fibrotic responses, cytoskeletal reorganization, and transforming growth factor-β expression were upregulated, in the HG group. Our results suggest that HG induces intracellular ATX downregulation, barrier dysfunction, and fibrosis, which are involved in early DR and can be targeted for DR treatment.

Autotaxin Activity in Chronic Subdural Hematoma: A Prospective Clinical Study

Autotaxin (ATX) is the ectoenzyme producing the bulk of lysophosphatidic acid (LPA) in circulation. ATX and LPA-mediated signaling (the ATX-LPA axis) play critical roles in the vascular and nervous system development. In adults, this axis contributes to diverse processes, including coagulation, inflammation, fibroproliferation and angiogenesis under physiological and/or pathophysiological conditions. Given evidence implicating several of these processes in chronic subdural hematoma (CSDH) pathogenesis and development, we assessed ATX activity in CSDH patients. Twenty-eight patients were recruited. Blood and hematoma fluid were collected. Enzymatic assays were used to establish serum and hematoma ATX activity. Enzyme-linked immunosorbent assays were used to establish hematoma beta trace (BT) levels, a cerebrospinal fluid (CSF) marker, in a hematoma. ATX activity was nearly three folds higher in hematoma compared to serum (P < 0.001). There was no significant correlation between BT levels and ATX activity in a hematoma. The present results show, for the first time, that ATX is catalytically active in the hematoma fluid of CSDH patients. Moreover, our findings of significantly elevated ATX activity in hematoma compared to serum, implicate the ATX-LPA axis in CSDH pathophysiology. The CSF origin of ATX could not be inferred with the present results. Additional research is warranted to establish the significance of the ATX-LPA axis in CSDH and its potential as a biomarker and/or therapeutic target.

Serum autotaxin levels in chronic disease and acute exacerbation of fibrosing interstitial lung disease

Background

Autotaxin (ATX) is an ecto-enzyme that catalyses the hydrolysis of lysophospholipids to the lipid mediator lysophosphatidic acid (LPA). LPA/ATX signalling has emerged as a new therapeutic target for pulmonary fibrosis; however, the serum levels and dynamics of ATX during the clinical course of fibrosing interstitial lung disease (ILD) remain unknown. This study sought to examine the serum ATX levels in fibrosing ILD in the chronic phase and in acute exacerbation of idiopathic pulmonary fibrosis (AE-IPF). We aimed to elucidate the association between serum ATX level and clinical characteristics including disease progression and prognosis.

Methods

In total, 119 patients with fibrosing ILD and 38 healthy volunteers as controls were enrolled in the study and their serum ATX activity was analysed. We also included six male patients with AE-IPF in order to analyse the changes in serum ATX at the onset of AE-IPF.

Results

Patients with fibrosing ILD showed significantly higher serum ATX levels compared with healthy controls in both sexes. Per cent change in forced vital capacity after 1 year correlated with serum ATX levels in female patients. High serum ATX levels (>0.721 mg· L⁻¹) were associated with worse outcome in survival curve and multivariate analysis of male patients. Serum ATX activity decreased after the onset of AE-IPF.

Conclusion

Serum ATX levels were significantly higher in patients with fibrosing ILD compared with healthy controls, and this was associated with disease progression and outcome. This suggests the potential of serum ATX as a promising biomarker for the treatment of fibrosing ILD.

Serum ATX levels are higher in fibrosing ILD than in healthy controls; this is associated with disease progression and outcome. Serum ATX levels decrease at the onset of AE-IPF.https://bit.ly/3hLR9jN

Serum autotaxin as a novel prognostic marker in patients with non-ischaemic dilated cardiomyopathy

Aims

Autotaxin (ATX) promotes myocardial inflammation, fibrosis, and the subsequent cardiac remodelling through lysophosphatidic acid production. However, the prognostic impact of serum ATX in non‐ischaemic dilated cardiomyopathy (NIDCM) has not been clarified. We investigated the prognostic impact of serum ATX in patients with NIDCM.

Methods and results

We enrolled 104 patients with NIDCM (49.8 ± 13.4 years, 76 men). We divided the patients into two groups using different cutoffs of median serum ATX levels for men and women: high‐ATX group and low‐ATX group. Cardiac events were defined as a composite of cardiac death and heart failure resulting in hospitalization. Median ATX level was 203.5 ng/mL for men and 257.0 ng/mL for women. Brain natriuretic peptide levels [224.0 (59.6–689.5) pg/mL vs. 96.5 (40.8–191.5) pg/mL, P = 0.010] were higher in the high‐ATX group than low‐ATX group, whereas high‐sensitivity C‐reactive protein and collagen volume fraction levels in endomyocardial biopsy samples were not significantly different between the two groups. Kaplan–Meier survival analysis revealed that the event‐free survival rate was significantly lower in the high‐ATX group than low‐ATX group (log‐rank; P = 0.007). Cox proportional hazard analysis revealed that high‐ATX was an independent determinant of composite cardiac events. In both sexes, serum ATX levels did not correlate with high‐sensitivity C‐reactive protein levels and collagen volume fraction but had a weak correlation with brain natriuretic peptide levels (men; spearman's rank: 0.274, P = 0.017, women; spearman's rank: 0.378, P = 0.048).

Conclusion

High serum ATX levels can be associated with increasing adverse clinical outcomes in patients with NIDCM. These results indicate serum ATX may be a novel biomarker or therapeutic target in NIDCM.

Suppressing postcollection lysophosphatidic acid metabolism improves the precision of plasma LPA quantification

Lysophosphatidic acid (LPA) is a potent signaling lipid, and state-dependent alterations in plasma LPA make it a promising diagnostic marker for various diseases. However, plasma LPA concentrations vary widely among reports, even under normal conditions. These variations can be attributed, at least in part, to the artificial metabolism of LPA after blood collection. Here, we aimed to develop an optimized plasma preparation method that reflects the concentration of LPA in the circulating blood. The main features of the devised method were suppression of both LPA production and degradation after blood collection by keeping whole blood samples at low temperature followed by the addition of an autotaxin inhibitor to plasma samples. Using this devised method, the LPA level did not change for 30 min after blood collection. Also, human and mouse LPA levels were found to be much lower than those previously reported, ranging from 40 to 50 nM with minimal variation across the individual. Finally, the increased accuracy made it possible to detect circadian rhythms in the levels of certain LPA species in mouse plasma. These results demonstrate the usefulness of the devised plasma preparation method to determine accurate plasma LPA concentrations.

Development of Tandem Mass Tag Labeling Method for Lipid Molecules Containing Carboxy and Phosphate Groups, and Their Stability in Human Serum

In clinical lipidomics, it is a challenge to measure a large number of samples and to reproduce the quantitative results. We expanded the range of application of the tandem mass tag (TMT) method, which is widely used in proteomics, to lipidomic fields. There are various types of lipid molecule, for example, eicosanoids have a carboxyl group and phosphatidic acid has a phosphate group. We modified these functional groups simultaneously with TMT. This approach allows for a single analysis by mixing six samples and using one of the six samples as a bridging sample; the quantitative data can be easily normalized even if the number of measurements increases. To accommodate a large number of samples, we utilize a pooled serum sample of 300 individuals as a bridging sample. The stability of these lipid molecules in serum was examined as an analytical validation for the simultaneous TMT labeling. It was found that the stability of these lipid molecules in serum differs greatly depending on the lipid species. These findings reaffirmed the importance of proper sample preparation and storage to obtain reliable data. The TMT labeling method is expected to be a useful method for lipidomics with high-throughput and reliable reproducibility.

The impact of achieving a sustained virological response with direct-acting antivirals on serum autotaxin levels in chronic hepatitis C patients

Background

Autotaxin (ATX) is an emerging biomarker for liver fibrosis. Achievement of sustained virological response (SVR) by direct-acting antivirals (DAAs) results in hepatic fibrosis regression in chronic hepatitis C (CHC) patients. In this context, the clinical implications of ATX have not yet been well-defined. In this study, we aimed to assess the impact of achieving SVR with DAA therapy on serum ATX levels and whether these levels can reflect the regression of hepatic fibrosis in CHC patients. We evaluated serum ATX levels at baseline and 12 weeks post-DAA therapy in 48 CHC patients. We compared ATX with FIB4 score and AST-to-Platelet Ratio Index (APRI) as regards the detection of grade F3–4 fibrosis.

Results

Serum ATX levels were significantly declined in 47 patients after the achievement of SVR12 (p < 0.001). The diagnostic ability of ATX for the detection of grade F3–4 fibrosis was inferior to FIB4 and APRI scores at baseline and SVR12.

Conclusion

Achievement of SVR with DAA therapy causes a significant decline in serum autotaxin concentrations, suggesting early regression of hepatic fibrosis in CHC patients. However, its diagnostic capability for routine patient monitoring and follow-up is still under debate.

Urinary autotaxin concentrations are associated with kidney injury

BACKGROUND

While basic researches have shown the involvement of the autotaxin-lysophosphatidic acid (ATX-LPA) axis in the pathogenesis of kidney diseases, no clinical studies have revealed the association between urinary ATX concentrations and kidney disease yet. We investigate the clinical characteristics in relation to the urinary ATX concentrations and the potential association between urinary ATX concentrations and various kidney diseases.

METHODS

We measured the urinary ATX concentrations in residual urine samples after routine clinical testing from a total of 326 subjects with various kidney diseases and healthy subjects. We compared the urinary ATX concentrations in relation to clinical parameters and urinary biomarkers, and investigated their association with various kidney diseases.

RESULTS

The urinary ATX concentrations were associated with the gender, eGFR, presence/absence of hematuria, serum ATX, urinary concentrations of total protein (TP), microalbumin, N-acetyl-β-D-glucosaminidase (NAG), α1-microglobulin (α1-MG), and transforming growth factor-β. Multiple regression analyses identified urinary α1-MG, age, urinary TP, NAG, and hematuria as being significantly associated with the urinary ATX concentrations. Urinary ATX concentrations were higher in subjects with membranous nephropathy and systemic lupus erythematosus than in the control subjects.

CONCLUSIONS

Urinary ATX might be associated with pathological conditions of the kidney associated with kidney injury.

Usefulness of autotaxin for the complications of liver cirrhosis

BACKGROUND

Autotaxin (ATX) has been reported as a direct biomarker for estimating the evaluation of liver fibrosis. But available data on ATX as a useful biomarker for the complications of liver cirrhosis (LC) are scant.

AIM

To assess the clinical usefulness of ATX for assessing the complications of LC.

METHODS

This multicenter, retrospective study was conducted at six locations in Japan. We include patients with LC, n = 400. The ATX level was evaluated separately in men and women because of its high level in female patients. To assess the clinical usefulness of ATX for the complications of LC, the area under the curve (AUC) of ATX assessing for the severe complications was analyzed in comparison with the model for end-stage liver disease score, albumin-bilirubin (ALBI) score, fibrosis-4 index, and aspartate aminotransferase-to-platelet ratio index.

RESULTS

The mean age was 68.4 ± 11.4 years, 240 patients (60.0%) were male. A total of 213 (53.3%) and 187 (46.8%) patients were compensated and decompensated, respectively. The numbers of patients with varix rupture, hepatic ascites, and hepatic encephalopathy were 35 (8.8%), 131 (32.8%), and 103 (25.8%), respectively. The AUCs of ATX in men for hepatic encephalopathy, hepatic ascites, and varix ruptures were 0.853, 0.816, and 0.706, respectively. The AUCs of ATX in women for hepatic encephalopathy, hepatic ascites, and varix rupture were 0.759, 0.717, and 0.697, respectively. The AUCs of ATX in men were higher than those in women, as were all the other biomarkers used to detect encephalopathy and varix ruptures. However, for detecting ascites, the AUC of ALBI in men was more effective than using ATX.

CONCLUSION

ATX in men was more effective than any other biomarkers for detecting hepatic encephalopathy and varix ruptures.

Elevated Autotaxin and LPA Levels During Chronic Viral Hepatitis and Hepatocellular Carcinoma Associate with Systemic Immune Activation

Circulating autotaxin (ATX) is elevated in persons with liver disease, particularly in the setting of chronic hepatitis C virus (HCV) and HCV/HIV infection. It is thought that plasma ATX levels are, in part, attributable to impaired liver clearance that is secondary to fibrotic liver disease. In a discovery data set, we identified plasma ATX to be associated with parameters of systemic immune activation during chronic HCV and HCV/HIV infection. We and others have observed a partial normalization of ATX levels within months of starting interferon-free direct-acting antiviral (DAA) HCV therapy, consistent with a non-fibrotic liver disease contribution to elevated ATX levels, or HCV-mediated hepatocyte activation. Relationships between ATX, lysophosphatidic acid (LPA) and parameters of systemic immune activation will be discussed in the context of HCV infection, age, immune health, liver health, and hepatocellular carcinoma (HCC).

Lysophosphatidic acids and their substrate lysophospholipids in cerebrospinal fluid as objective biomarkers for evaluating the severity of lumbar spinal stenosis

Lysophospholipids (LPLs) are known to have potentially important roles in the initiation and maintenance of neuropathic pain in animal models. This study investigated the association between the clinical severity of lumbar spinal stenosis (LSS) and the cerebrospinal fluid (CSF) levels of LPLs, using human samples. We prospectively identified twenty-eight patients with LSS and fifteen controls with idiopathic scoliosis or bladder cancer without neurological symptoms. We quantified LPLs from CSF using liquid chromatography-tandem mass spectrometry. We assessed clinical outcome measures of LSS (Neuropathic Pain Symptom Inventory (NPSI) and Zurich Claudication Questionnaire (ZCQ)) and categorized patients into two groups according to their severity. Five species of lysophosphatidic acid (LPA), nine species of lysophosphatidylcholine (LPC), and one species of lysophosphatidylinositol (LPI) were detected. The CSF levels of all species of LPLs were significantly higher in LSS patients than controls. Patients in the severe NPSI group had significantly higher LPL levels (three species of LPA and nine species of LPC) than the mild group. Patients in the severe ZCQ group also had significantly higher LPL levels (four species of LPA and nine species of LPC). This investigation demonstrates a positive correlation between the CSF levels of LPLs and the clinical severity of LSS. LPLs are potential biomarkers for evaluating the severity of LSS.

Autotaxin, bile acid profile and effect of ileal bile acid transporter inhibition in primary biliary cholangitis patients with pruritus

BACKGROUND AND AIMS

Pruritus is a common symptom in patients with primary biliary cholangitis (PBC) for which ileal bile acid transporter (IBAT) inhibition is emerging as a potential therapy. We explored the serum metabonome and gut microbiota profile in PBC patients with pruritus and investigated the effect of GSK2330672, an IBAT inhibitor.

METHODS

We studied fasting serum bile acids (BAs), autotaxin and faecal microbiota in 22 PBC patients with pruritus at baseline and after 2 weeks of GSK2330672 treatment. Control group included 31 asymptomatic PBC patients and 18 healthy volunteers. BA profiling was done by ultra performance liquid chromatography coupled to a mass spectrometry (UPLC-MS). Faecal microbiomes were analysed by 16S ribosomal RNA gene sequencing.

RESULTS

In PBC patients with pruritus, serum levels of total and glyco-conjugated primary BAs and autotaxin were significantly elevated. Autotaxin activity correlated significantly with tauro- and glyco-conjugated cholic acid (CA) and chenodeoxycholic acid (CDCA), both at baseline and after GSK2330672. GSK2330672 significantly reduced autotaxin and all tauro- and glyco- conjugated BAs and increased faecal levels of CA (P = 0.048) and CDCA (P = 0.027). Gut microbiota of PBC patients with pruritus was similar to control groups. GSK2330672 increased the relative abundance of Firmicutes (P = 0.033) and Clostridia (P = 0.04) and decreased Bacteroidetes (P = 0.033) and Bacteroidia (P = 0.04).

CONCLUSIONS

Pruritus in PBC does not show a distinct gut bacterial profile but is associated with elevated serum bile acid and autotaxin levels which decrease after IBAT inhibition. In cholestatic pruritus, a complex interplay between BAs and autotaxin is likely and may be modified by IBAT inhibition.

Measurement of plasma choline in acute coronary syndrome: importance of suitable sampling conditions for this assay

Blood choline has been proposed as a predictor of acute coronary syndrome (ACS), however different testing procedures might affect the choline concentration because the lysophospholipase D activity of autotaxin (ATX) can convert lysophosphatidylcholine to lysophosphatidic acid (LPA) and choline in human blood. Although the influences of ATX on LPA levels are well known in vivo and in vitro, those on choline have not been elucidated. Therefore, we established suitable sampling conditions and evaluated the usefulness of plasma choline concentrations as a biomarker for ACS. Serum LPA and choline concentrations dramatically increased after incubation depending on the presence of ATX, while their concentrations in plasma under several conditions were differently modulated. Plasma choline levels in genetically modified mice and healthy human subjects, however, were not influenced by the ATX level in vivo, while the plasma LPA concentrations were associated with ATX. With strict sample preparation, the plasma choline levels did not increase, but actually decreased in ACS patients. Our study revealed that ATX increased the choline concentrations after blood sampling but was not correlated with the choline concentrations in vivo; therefore, strict sample preparation will be necessary to investigate the possible use of choline as a biomarker.

Lysophospholipids in laboratory medicine

Lysophospholipids (LPLs), such as lysophosphatidic acid (LPA), sphingosine 1-phosphate (S1P), and lysophosphatidylserine (LysoPS), are attracting attention as second-generation lipid mediators. In our laboratory, the functional roles of these lipid mediators and the mechanisms by which the levels of these mediators are regulated in vivo have been studied. Based on these studies, the clinical introduction of assays for LPLs and related proteins has been pursued and will be described in this review. Although assays of these lipids themselves are possible, autotaxin (ATX), apolipoprotein M (ApoM), and phosphatidylserine-specific phospholipase A₁ (PS-PLA₁) are more promising as alternate biomarkers for LPA, S1P, and LysoPS, respectively. Presently, ATX, which produces LPA through its lysophospholipase D activity, has been shown to be a useful laboratory test for the diagnosis and staging of liver fibrosis, whereas PS-PLA₁ and ApoM are considered to be promising clinical markers reflecting the in vivo actions induced by LysoPS and S1P.

Performance of autotaxin as a serum marker for liver fibrosis

Background Because autotaxin reportedly has a better performance than hyaluronic acid as a marker for liver fibrosis for the prediction of cirrhosis caused by hepatitis C, we aimed to further evaluate the role of autotaxin in liver fibrosis of other aetiologies. Methods Autotaxin antigen was measured in serum samples from 108 patients with chronic hepatitis B and 128 patients with non-alcoholic fatty liver disease who had undergone a liver biopsy as well as healthy subjects and patients with chronic kidney disease, diabetes mellitus, rheumatoid arthritis and cardiac dysfunction. Results When evaluated using receiver operator characteristics curves, the performance of autotaxin for the prediction of significant fibrosis (F2-F4) in chronic hepatitis B patients was better than that of hyaluronic acid or type IV collagen 7S. In non-alcoholic fatty liver disease patients, however, the performance of autotaxin for the prediction of significant fibrosis was poorer than that of hyaluronic acid or type IV collagen 7S. The increase in the serum autotaxin concentrations was less notable than that of hyaluronic acid or type IV collagen in patients with chronic kidney disease, diabetes mellitus, rheumatoid arthritis or cardiac dysfunction. Food intake did not affect the serum autotaxin concentrations. Conclusions Autotaxin is useful as a serum marker for liver fibrosis caused by not only chronic viral hepatitis C but also by hepatitis B, although it was less useful in patients with non-alcoholic fatty liver disease. The increase in serum autotaxin concentrations is fairly specific for liver fibrosis, and the serum autotaxin concentrations can be analysed without consideration of food intake before blood collection.

Lysophosphatidic acid plasma concentrations in healthy subjects: circadian rhythm and associations with demographic, anthropometric and biochemical parameters

Background

Lysophosphatidic acid (LPA) is a bioactive lipid with a wide biological activity. Previous studies have shown its potential usefulness as a diagnostic marker for ovarian cancer. The aim of the study was to investigate which factors may influence plasma LPA concentrations in healthy subjects and to propose reference values.

Methods

The study group consisted of 100 healthy subjects. From all of them the blood samples were taken at 7 a.m. (fasting state). From 40 volunteers additional blood samples were taken at 2 p.m., at 8 p.m. and at 2 a.m. next morning. Concentrations of LPA were measured in plasma samples using enzyme-linked immunosorbent assay.

Results

Analysis of samples from 100 healthy volunteers showed significant influence of sex and age on plasma LPA. The reference range for the plasma LPA concentration corrected for age and sex, determined at 2.5–97.5 percentile interval is 0.14–1.64 μM. LPA correlates positively with BMI, serum total cholesterol, triacylglycerols, uric acid and negatively with estimated glomerular filtration rate and serum albumin. Concentration of LPA at 2 a.m. was lower than at 2 p.m. There were not any significant differences between plasma LPA at 7 a.m. and any other time of the day.

Conclusions

Plasma LPA is associated with demographic, anthropometric and biochemical parameters. It seems that LPA concentrations have no specific circadian rhythm and the time of donation and fasting state have marginal effect on plasma LPA. These findings may be helpful in future incorporation of LPA as a diagnostic marker.

An Autotaxin/Lysophosphatidic Acid/Interleukin-6 Amplification Loop Drives Scleroderma Fibrosis

OBJECTIVE

We previously implicated the lipid mediator lysophosphatidic acid (LPA) as having a role in dermal fibrosis in systemic sclerosis (SSc). The aim of this study was to identify the role of the LPA-producing enzyme autotaxin (ATX), and to connect the ATX/LPA and interleukin-6 (IL-6) pathways in SSc.

METHODS

We evaluated the effect of a novel ATX inhibitor, PAT-048, on fibrosis and IL-6 expression in the mouse model of bleomycin-induced dermal fibrosis. We used dermal fibroblasts from SSc patients and control subjects to evaluate LPA-induced expression of IL-6, and IL-6-induced expression of ATX. We next evaluated whether LPA-induced ATX expression is dependent on IL-6, and whether baseline IL-6 expression in fibroblasts from SSc patients is dependent on ATX. Finally, we compared ATX and IL-6 expression in the skin of patients with SSc and healthy control subjects.

RESULTS

PAT-048 markedly attenuated bleomycin-induced dermal fibrosis when treatment was initiated before or after the development of fibrosis. LPA stimulated expression of IL-6 in human dermal fibroblasts, and IL-6 stimulated fibroblast expression of ATX, connecting the ATX/LPA and IL-6 pathways in an amplification loop. IL-6 knockdown abrogated LPA-induced ATX expression in fibroblasts, and ATX inhibition attenuated IL-6 expression in fibroblasts and the skin of bleomycin-challenged mice. Expression of both ATX and IL-6 was increased in SSc skin, and LPA-induced IL-6 levels and IL-6-induced ATX levels were increased in fibroblasts from SSc patients compared with controls.

CONCLUSION

ATX is required for the development and maintenance of dermal fibrosis in a mouse model of bleomycin-induced SSc and enables 2 major mediators of SSc fibrogenesis, LPA and IL-6, to amplify the production of each other. Our results suggest that concurrent inhibition of these 2 pathways may be an effective therapeutic strategy for dermal fibrosis in SSc.

Analysis of glycero-lysophospholipids in gastric cancerous ascites

Lysophosphatidic acid (LysoPA) has been proposed to be involved in the pathogenesis of various cancers. Moreover, glycero-lysophospholipids (glycero-LysoPLs) other than LysoPA are now emerging as novel lipid mediators. Therefore, we aimed to elucidate the possible involvement of glycero-LysoPLs in the pathogenesis of gastric cancer by measuring glycero-LysoPLs, autotaxin (ATX), and phosphatidylserine-specific phospholipase A1 (PS-PLA₁) in ascites obtained from patients with gastric cancer and those with cirrhosis (as a control). We observed that after adjustments according to the albumin levels, the lysophosphatidylserine (LysoPS) and lysophosphatidylglycerol (LysoPG) levels were significantly higher, while the LysoPA and ATX levels were lower, in the ascites from patients with gastric cancer. We also found that multiple regression analyses revealed that ATX was selected as a significant explanatory factor for all the detectable LysoPA species only in the cirrhosis group and that a significant positive correlation was observed between LysoPS and PS-PLA₁ only in the gastric cancer group. In conclusion, the LysoPA levels might be determined largely by LysoPC and LysoPI (possible precursors) and the PS-PLA₁-mediated pathway might be involved in the production of LysoPS in gastric cancer. Glycero-LysoPLs other than LysoPA might also be involved in the pathogenesis of cancer directly or through being converted into LysoPA.

Higher LPA2 and LPA6 mRNA Levels in Hepatocellular Carcinoma Are Associated with Poorer Differentiation, Microvascular Invasion and Earlier Recurrence with Higher Serum Autotaxin Levels

Hepatocellular carcinoma (HCC) commonly develops in patients with liver fibrosis; in these patients, the blood levels of lysophosphatidic acid (LPA) and its generating enzyme autotaxin (ATX) increase with the liver fibrosis stage. We aimed to examine the potential relevance of ATX and LPA in HCC. Fifty-eight HCC patients who underwent surgical treatment were consecutively enrolled in the study. Among the LPA receptors in HCC, higher LPA2 mRNA levels correlated with poorer differentiation, and higher LPA6 mRNA levels correlated with microvascular invasion, which suggested a higher malignant potential of HCC with increased LPA2 and LPA6 expression. In patients with primary HCC, neither LPA2 nor LPA6 mRNA levels were associated with recurrence. However, when serum ATX levels were combined for analysis as a surrogate for plasma LPA levels, the cumulative intra-hepatic recurrence rate was higher in patients in whom both serum ATX levels and LPA2 or LPA6 mRNA levels were higher than the median. However, the mRNA level of phosphatidic acid-selective phospholipase A1ɑ, another LPA-generating enzyme, in HCC patients was not associated with pathological findings or recurrence, even in combination with the expression of LPA receptors. Higher LPA2 mRNA levels were associated with poorer differentiation, and higher LPA6 levels were associated with microvascular invasion in HCC; both became a risk factor for recurrence after surgical treatment when combined with increased serum ATX levels. ATX and LPA receptors merit consideration as therapeutic targets of HCC.

Serum Autotaxin Activity Correlates With Pruritus in Pediatric Cholestatic Disorders

OBJECTIVE

Pruritus is a common symptom of cholestatic liver disorders. The present study aimed at evaluating autotaxin (ATX), a lysophospholipase recently identified as potential cause for cholestatic pruritus, in pediatric cholestatic diseases presenting with or without itching.

METHODS

A cohort of 45 children consisting of 14 patients experiencing itching (Alagille syndrome [n = 10], complete extrahepatic biliary atresia [n = 2], neonatal sclerosing cholangitis (n = 1), progressive familial intrahepatic cholestasis type 2 [n = 1]), 9 patients with bile acid synthesis defects (3β-hydroxy-C27-steroid-oxidoreductase [n = 7] and Δ-3-oxosteroid-5β-reductase deficiency [n = 2]), and 22 healthy children were studied. Serum ATX activity and total serum bile salt were determined enzymatically, ATX protein content was semiquantified by Western blotting. Using real-time polymerase chain reaction, ATX mRNA expression was studied in HepG2 cells treated with farnesoid-X-receptor agonists or vehicle.

RESULTS

Serum ATX activity was increased in pruritic children with Alagille and other cholestatic syndromes (mean ± standard deviation: 16.1 ± 4.3 nmol · mL · min) compared with children with nonpruritic cholestatic diseases with bile acid synthesis defects (10.4 ± 4.7 nmol · mL · min; P < 0.01) and healthy controls (7.6 ± 2.3 nmol · mL · min; P < 0.001). ATX protein levels closely correlated with serum ATX activity. Serum ATX activity and total serum bile salt showed a linear correlation with itch intensity (r = 0.66, P < 0.001 and r = 0.80, P < 0.001, respectively). No correlation was observed between ATX activity and bilirubin. ATX mRNA expression in HepG2 cells was not induced by farnesoid-X-receptor ligands.

CONCLUSIONS

Serum ATX activity correlated with itch intensity in children with cholestatic diseases. Bile salts did not increase ATX expression in vitro. ATX inhibitors may be useful antipruritic agents in pediatric cholestatic disorders.

Autotaxin activity increases locally following lung injury, but is not required for pulmonary lysophosphatidic acid production or fibrosis

Lysophosphatidic acid (LPA) is an important mediator of pulmonary fibrosis. In blood and multiple tumor types, autotaxin produces LPA from lysophosphatidylcholine (LPC) via lysophospholipase D activity, but alternative enzymatic pathways also exist for LPA production. We examined the role of autotaxin (ATX) in pulmonary LPA production during fibrogenesis in a bleomycin mouse model. We found that bleomycin injury increases the bronchoalveolar lavage (BAL) fluid levels of ATX protein 17-fold. However, the LPA and LPC species that increase in BAL of bleomycin-injured mice were discordant, inconsistent with a substrate-product relationship between LPC and LPA in pulmonary fibrosis. LPA species with longer chain polyunsaturated acyl groups predominated in BAL fluid after bleomycin injury, with 22:5 and 22:6 species accounting for 55 and 16% of the total, whereas the predominant BAL LPC species contained shorter chain, saturated acyl groups, with 16:0 and 18:0 species accounting for 56 and 14% of the total. Further, administration of the potent ATX inhibitor PAT-048 to bleomycin-challenged mice markedly decreased ATX activity systemically and in the lung, without effect on pulmonary LPA or fibrosis. Therefore, alternative ATX-independent pathways are likely responsible for local generation of LPA in the injured lung. These pathways will require identification to therapeutically target LPA production in pulmonary fibrosis.-Black, K. E., Berdyshev, E., Bain, G., Castelino, F. V., Shea, B. S., Probst, C. K., Fontaine, B. A., Bronova, I., Goulet, L., Lagares, D., Ahluwalia, N., Knipe, R. S., Natarajan, V., Tager, A. M. Autotaxin activity increases locally following lung injury, but is not required for pulmonary lysophosphatidic acid production or fibrosis.

Serum Autotaxin Levels Are Associated with Proteinuria and Kidney Lesions in Japanese Type 2 Diabetic Patients with Biopsy-proven Diabetic Nephropathy

Objective We evaluated the relationships between the serum autotaxin (ATX) levels and the clinical and pathological parameters, as well as the long-term renal outcome, in type 2 diabetic patients with biopsy-proven diabetic nephropathy. Methods In this retrospective single-center cohort study, serum samples were collected from 38 Japanese type 2 diabetic patients with biopsy-proven diabetic nephropathy at the time of renal biopsy. The serum ATX levels were measured using a specific sandwich enzyme immunoassay. Results A multivariate linear regression analysis revealed the urinary protein excretion to be independently associated with the serum ATX levels. In addition, patients with serum ATX levels above the median showed more advanced diffuse lesions, nodular lesions and arteriolar hyalinosis compared to those with serum ATX levels below the median. However, high serum ATX levels were not associated with any increase in the number of renal composite events [a need for dialysis or a 50% decline in the estimated glomerular filtration rate (eGFR) from baseline]. Conclusion The serum ATX levels in type 2 diabetic patients with diabetic nephropathy were associated with proteinuria and diabetic kidney lesions, although the serum ATX levels were not identified to be a predictive indicator for the renal outcome.

Serum Autotaxin/ENPP2 correlates with insulin resistance in older humans with obesity

OBJECTIVE

Autotaxin (ATX) is an adipocyte-derived lysophospholipase D that generates the lipid signaling molecule lysophosphatidic acid (LPA). The ATX/LPA pathway in adipose tissue has recently been implicated in obesity and insulin resistance in animal models, but the role of circulating ATX in humans remains unclear. The aim of the present study was to determine the relationship between serum ATX and insulin resistance.

METHODS

Older (60-75 years), nondiabetic human participants with overweight or obesity (BMI 25-37 kg m(-2) ) were characterized for metabolic phenotype including measures of energy, glucose, and lipid homeostasis. The relationship between serum ATX and metabolic parameters was then determined using correlative and predictive statistics.

RESULTS

Serum ATX was higher in females than in males. After controlling for sex, serum ATX correlated with multiple measures of adiposity and glucose homeostasis/insulin action. Serum ATX and BMI also independently predicted glucose infusion rate during a hyperinsulinemic euglycemic clamp and homeostatic model assessment of insulin resistance after controlling for sex and medication use.

CONCLUSIONS

Serum ATX correlates with and predicts measures of glucose homeostasis and insulin sensitivity in older humans, suggesting that it may be a potential pathogenic factor and/or diagnostic/therapeutic target for insulin resistance in this population.

Autotaxin activity has a high accuracy to diagnose intrahepatic cholestasis of pregnancy

BACKGROUND & AIMS

Intrahepatic cholestasis of pregnancy (ICP) is defined by pruritus, elevated total fasting serum bile salts (TBS) and transaminases, and an increased risk of adverse fetal outcome. An accurate diagnostic marker is needed. Increased serum autotaxin correlates with cholestasis-associated pruritus. We aimed at unraveling the diagnostic accuracy of autotaxin in ICP.

METHODS

Serum samples and placental tissue were collected from 44 women with uncomplicated pregnancies and 105 with pruritus and/or elevated serum transaminases. Autotaxin serum levels were quantified enzymatically and by Western blotting, autotaxin gene expression by quantitative PCR.

RESULTS

Serum autotaxin was increased in ICP (mean ± SD: 43.5 ± 18.2 nmol ml(-1)min(-1), n=55, p<0.0001) compared to other pruritic disorders of pregnancy (16.8 ± 6.7 nmol ml(-1)min(-1), n=33), pre-eclampsia complicated by HELLP-syndrome (16.8 ± 8.9 nmol ml(-1)min(-1), n=17), and pregnant controls (19.6 ± 5.7 nmol ml(-1)min(-1), n=44). Longitudinal analysis during pregnancy revealed a marked rise in serum autotaxin with onset of ICP-related pruritus. Serum autotaxin was increased in women taking oral contraceptives. Increased serum autotaxin during ICP was not associated with increased autotaxin mRNA in placenta. With a cut-off value of 27.0 nmol ml(-1)min(-1), autotaxin had an excellent sensitivity and specificity in distinguishing ICP from other pruritic disorders or pre-eclampsia/HELLP-syndrome. Serum autotaxin displayed no circadian rhythm and was not influenced by food intake.

CONCLUSIONS

Increased serum autotaxin activity represents a highly sensitive, specific and robust diagnostic marker of ICP, distinguishing ICP from other pruritic disorders of pregnancy and pregnancy-related liver diseases. Pregnancy and oral contraception increase serum autotaxin to a much lesser extent than ICP.

Challenges in accurate quantitation of lysophosphatidic acids in human biofluids

Lysophosphatidic acids (LPAs) are biologically active signaling molecules involved in the regulation of many cellular processes and have been implicated as potential mediators of fibroblast recruitment to the pulmonary airspace, pointing to possible involvement of LPA in the pathology of pulmonary fibrosis. LPAs have been measured in various biological matrices and many challenges involved with their analyses have been documented. However, little published information is available describing LPA levels in human bronchoalveolar lavage fluid (BALF). We therefore conducted detailed investigations into the effects of extensive sample handling and sample preparation conditions on LPA levels in human BALF. Further, targeted lipid profiling of human BALF and plasma identified the most abundant lysophospholipids likely to interfere with LPA measurements. We present the findings from these investigations, highlighting the importance of well-controlled sample handling for the accurate quantitation of LPA. Further, we show that chromatographic separation of individual LPA species from their corresponding lysophospholipid species is critical to avoid reporting artificially elevated levels. The optimized sample preparation and LC/MS/MS method was qualified using a stable isotope-labeled LPA as a surrogate calibrant and used to determine LPA levels in human BALF and plasma from a Phase 0 clinical study comparing idiopathic pulmonary fibrosis patients to healthy controls.

Increased serum autotaxin levels in hepatocellular carcinoma patients were caused by background liver fibrosis but not by carcinoma

BACKGROUND

Controversy exists as to whether autotaxin (ATX) may be importantly associated with pathophysiology of hepatocellular carcinoma (HCC).

METHODS

We evaluated serum ATX levels and its mRNA expression in consecutive 148 HCC patients treated with radiofrequency ablation (RFA) and 30 patients with hepatic resection.

RESULTS

Although increased serum ATX levels were observed in almost all the patients treated with RFA, they were not reduced after RFA. Furthermore, serum ATX levels were associated not with tumor burden but with the parameters predicting for liver fibrosis, such as liver stiffness values. Then, in surgically-treated patients, there was no significant correlation between serum ATX levels and ATX mRNA expression levels in HCC tissues. Notably, ATX mRNA expression levels in HCC tissues were not higher than those in peri-tumorous tissues. Finally, serum ATX levels in surgically-treated HCC patients were rather correlated with ATX mRNA expression levels in peri-tumorous tissues as well as with liver fibrosis stage.

CONCLUSION

The increase in serum ATX levels in HCC patients may not be caused by abundant ATX production in HCC tissues but by fibrosis in the background livers.

Cross-sectional and dynamic change of serum metabolite profiling for Hepatitis B-related acute-on-chronic liver failure by UPLC/MS

Summary Acute-on-chronic liver failure(ACLF) is an increasingly recognized entity encompassing an acute deterioration of liver function and results in the failure of one or more organs with high short-term mortality. The focus of this study was to discover noninvasive and reliable biomarkers for the diagnosis and prognosis of hepatitis B-related ACLF. Ultra-performance liquid chromatography-mass spectrometry (UPLC/MS) was used to analyse serum metabolites of 28 patients with hepatitis B-related ACLF, 35 patients with Child-Pugh A cirrhosis, 30 patients with chronic hepatitis B and 35 healthy volunteers (HS). Characteristic metabolites were screened, identified and dynamically tracked to investigate their value for diagnosis and prognosis. After comparing serum metabolic profile of hepatitis B-related ACLF and Child-Pugh A cirrhosis, 99 characteristic metabolites were selected, and 38 of them were identified. Dynamic tracking model demonstrated that 17 metabolites were related to prognosis of hepatitis B-related ACLF, and there were also 11 metabolites which improved with treatment in the survival group. The correlations between these characteristic metabolites and the model for end-stage liver disease score were strong. These observations contributed to the investigation of the mechanisms of hepatitis B-related ACLF manifestation and progression on the metabolic level, and they provided information for the identification of biomarkers for the diagnosis and prognosis of hepatitis B-related ACLF.

Validity of Autotaxin as a Novel Diagnostic Marker for Liver Fibrosis in Egyptian Chronic HCV Patients

We aimed to detect the validity of serum ATX as a diagnostic marker for liver fibrosis. Forty-eight males and 16 females were enrolled in the current study. Their ages ranged from 29-57 years with mean of 45.09, all were chronically HCV infected. Laboratory assessment was done for all subjects in form of complete blood picture; liver function test; lipid profile and serum detection of ATX. Patients were grouped according to the stage of fibrosis into group 1: fibrosis score 0, 1, 2, 3; group 2: fibrosis score: 4, 5, 6.The mean values of ATX in all studied patients with chronic HCV infection was 63.02 ± 36.29 while that of healthy controls was 65.31 ± 12.24 without any significant difference. Surprisingly, mean values of ATX were higher among patients with group 1 but it did not reach the significant level. In each group of them, the differences between mean values of ATX among different grades of liver fibrosis were insignificant. It was also noticed that the mean values of ATX were higher among men than in women .It was concluded that Autotoxin might not be used as a useful diagnostic marker for liver fibrosis in Egyptian chronic HCV patients.

Blood cytokine, chemokine and gene expression in cholestasis patients with intractable pruritis treated with a molecular adsorbent recirculating system: a case series

BACKGROUND

The molecular adsorbent recirculating system (MARS) is an albumin-dialysis modality that has been investigated predominantly in patients with acute and acute-on-chronic liver failure.

OBJECTIVES

To report the clinical efficacy and safety of MARS therapy for intractable pruritus in cholestasis patients with stable chronic liver disease, characterizing the impact of MARS on cytokine levels and on the transcriptome in the blood compartment.

METHODS

MARS therapy was performed on three patients with cholestatic liver disease using 8 h runs for two consecutive days. The expression levels of 65 cytokines⁄chemokines and 24,000 genes were profiled by Luminex (Luminex Corporation, USA) and microarray, respectively.

RESULTS

A quality-of-life assessment demonstrated a marked improvement during therapy, which was sustained in two of three patients. No bleeding or infectious complications were observed. Bile acid levels were markedly reduced following MARS (mean [± SD] pretreatment 478.9±112.2 µmol⁄L versus post-treatment 89.7±68.8 µmol⁄L). Concordant decreases in cytokine⁄chemokine levels were noted for interleukin (IL)-1beta, IL-2, IL-6, IL-8, IL-12 (p40), RANTES, tranforming growth factor-alpha, tumour necrosis factor-alpha and thrombopoietin following MARS. On microarray profiling, biologically relevant concordant changes among all patients were evident for 20 different genes (10 upregulated and 10 downregulated). The upregulation of several potentially immune suppressive⁄regulatory genes (eg, early growth response 3 [EGR-3], ephrin-A2 [EFNA2] and serum amyloid A1 [SAA1]), concurrent with downregulation of genes involved in innate immunity (eg, toll-like receptor 4 interactor with leucine-rich repeats [TRIL]) and inflammation (eg, ephrin receptor B1 [EPHB1]), was observed.

CONCLUSIONS

This investigative approach offers new insights into intractable pruritus and suggests future therapeutic targets. The clinical benefit of MARS in cholestasis patients with intractable pruritus may not exclusively result from filtration of pruritogens, but also from systemic changes in cytokine⁄chemokine levels and changes in gene expression of blood cells.

Serum autotaxin is increased in pruritus of cholestasis, but not of other origin, and responds to therapeutic interventions

Pruritus is a seriously disabling symptom accompanying many cholestatic liver disorders. Recent experimental evidence implicated the lysophospholipase, autotaxin (ATX), and its product, lysophosphatidic acid (LPA), as potential mediators of cholestatic pruritus. In this study, we highlight that increased serum ATX levels are specific for pruritus of cholestasis, but not pruritus of uremia, Hodgkin's disease, or atopic dermatitis. Treatment of patients with cholestasis with the bile salt sequestrant, colesevelam, but not placebo, effectively reduced total serum bile salts and fibroblast growth factor 19 levels, but only marginally altered pruritus intensity and ATX activity. Rifampicin (RMP) significantly reduced itch intensity and ATX activity in patients with pruritus not responding to bile salt sequestrants. In vitro, RMP inhibited ATX expression in human HepG2 hepatoma cells and hepatoma cells overexpressing the pregnane X receptor (PXR), but not in hepatoma cells in which PXR was knocked down. Treatment of severe, refractory pruritus by the molecular adsorbents recirculation system or nasobiliary drainage improved itch intensity, which, again, correlated with the reduction of ATX levels. Upon reoccurrence of pruritus, ATX activity returned to pretreatment values.

CONCLUSION

Serum ATX activity is specifically increased in patients with cholestatic, but not other forms of, systemic pruritus and closely correlates with the effectiveness of therapeutic interventions. The beneficial antipruritic action of RMP may be explained, at least partly, by the PXR-dependent transcriptional inhibition of ATX expression. Thus, ATX likely represents a novel therapeutic target for pruritus of cholestasis.

Autotaxin in liver fibrosis

Autotaxin (ATX) hydrolyzes lysophosphatidylcholine to produce lysophosphatidic acid (LPA), a multi-functional bioactive lipid mediator. ATX is a major determinant of LPA levels in the blood, and the pathophysiological functions of ATX are thought to be largely attributed to its ability to produce LPA. Liver fibrosis is one of the rare disorders exhibiting the increased ATX and LPA levels in the blood. This review summarizes the recent findings on the relation between ATX or LPA and liver fibrosis, the usefulness of serum ATX levels to predict the stages of liver fibrosis, and speculated roles of increased serum ATX and plasma LPA levels in liver fibrosis.

Specific increase in serum autotaxin activity in patients with pancreatic cancer

OBJECTIVES

To evaluate the potential clinical significance of serum autotaxin (ATX) level in patients with cancers of the digestive system.

DESIGN AND METHODS

Serum ATX activity was measured as the lysophospholipase D activity in patients with cancer of the esophagus (n=8), stomach (n=18), colorectum (n=21), biliary tract (n=19), or pancreas (n=103) and in patients with benign pancreatic diseases (n=73).

RESULTS

Among patients with various cancers of digestive system, increased serum ATX activity was predominantly observed among pancreatic cancer patients. Serum ATX activity was not increased in patients with chronic pancreatitis or pancreatic cysts. In the diagnosis of pancreatic cancer, the area under the receiver operating curve for serum ATX activity was 0.541 (95% CI, 0.435-0.648) for men and 0.772 (95% CI, 0.659-0.885) for women. No significant correlation was observed between serum ATX activity and CEA, CA19-9 or Dupan2 levels.

CONCLUSION

Serum ATX activity may be useful for identifying pancreatic cancer when used together with other serum markers of pancreatic cancer.

Autotaxin as a novel serum marker of liver fibrosis

BACKGROUND

The clinical significance of autotaxin (ATX), a key enzyme for the production of the bioactive lysophospholipid lysophosphatidic acid remains unknown. Serum ATX enzymatic activity reportedly increases in parallel with liver fibrosis and exhibits a gender difference.

METHODS

Serum ATX antigen level, measured easier than the activity, was evaluated as a marker of liver fibrosis in 2 cohorts of chronic liver disease caused by hepatitis C virus.

RESULTS

In the first cohort, serum ATX level correlated significantly with liver fibrosis stage and was the best parameter for prediction of cirrhosis with an area under the receiver operating characteristic curve (AUROC) of 0.756 in male and 0.760 in female, when compared with serum hyaluronic acid and aminotransferase-to-platelet ratio index, an established marker of liver fibrosis. In another cohort, serum ATX level correlated significantly with liver stiffness, a novel reliable marker of liver fibrosis, being the second-best parameter in male (AUROC, 0.799) and in female (AUROC, 0.876) for prediction of significant fibrosis, and the best parameter in male (AUROC, 0.863) and the third-best parameter in female (AUROC, 0.872) for prediction of cirrhosis, both of which were judged by liver stiffness.

CONCLUSIONS

Serum ATX level may be a novel marker of liver fibrosis.

Lysophosphatidic acid is a potential mediator of cholestatic pruritus

BACKGROUND & AIMS

Pruritus is a common and disabling symptom in cholestatic disorders. However, its causes remain unknown. We hypothesized that potential pruritogens accumulate in the circulation of cholestatic patients and activate sensory neurons.

METHODS

Cytosolic free calcium ([Ca(2+)](i)) was measured in neuronal cell lines by ratiometric fluorometry upon exposure to serum samples from pruritic patients with intrahepatic cholestasis of pregnancy (ICP), primary biliary cirrhosis (PBC), other cholestatic disorders, and pregnant, healthy, and nonpruritic disease controls. Putative [Ca(2+)](i)-inducing factors in pruritic serum were explored by analytical techniques, including quantification by high-performance liquid chromatography/mass spectroscopy. In mice, scratch activity after intradermal pruritogen injection was quantified using a magnetic device.

RESULTS

Transient increases in neuronal [Ca(2+)](i) induced by pruritic PBC and ICP sera were higher than corresponding controls. Lysophosphatidic acid (LPA) could be identified as a major [Ca(2+)](i) agonist in pruritic sera, and LPA concentrations were increased in cholestatic patients with pruritus. LPA injected intradermally into mice induced scratch responses. Autotaxin, the serum enzyme converting lysophosphatidylcholine into LPA, was markedly increased in patients with ICP versus pregnant controls (P < .0001) and cholestatic patients with versus without pruritus (P < .0001). Autotaxin activity correlated with intensity of pruritus (P < .0001), which was not the case for serum bile salts, histamine, tryptase, substance P, or mu-opioids. In patients with PBC who underwent temporary nasobiliary drainage, both itch intensity and autotaxin activity markedly decreased during drainage and returned to preexistent levels after drain removal.

CONCLUSIONS

We suggest that LPA and autotaxin play a critical role in cholestatic pruritus and may serve as potential targets for future therapeutic interventions.

Autotaxin

Autotaxin is a protein of approximately 900 amino acids discovered in the early 1990s. Over the past 15 years, a strong association between cancer cells and autotaxin production has been observed. Recent publications indicate that autotaxin and the capacity of cancer to metastasise are intimately linked. The discovery of new molecular targets in pharmacology is a mixture of pure luck, hard work and industrial strategy. Despite a crucial and desperate need for new therapeutic tools, many targets are approached in oncology, but only a few are validated and end up at the patient bed. Outside the busy domain of kinases, few targets have been discovered that can be useful in treating cancer, particularly metastatic processes. The fortuitous relationship between autotaxin and lysophosphatidic acid renders the results of observations made in the diabetes/obesity context considerably important. The literature provides observations that may aid in redesigning experiments to validate autotaxin as a potential oncology target.

Lipopolysaccharide induces autotaxin expression in human monocytic THP-1 cells

Autotaxin (ATX) is a secreted enzyme with lysophospholipase D (lysoPLD) activity, which converts lysophosphatidylcholine (LPC) into lysophosphatidic acid (LPA), a bioactive phospholipid involved in numerous biological activities, including cell proliferation, differentiation, and migration. In the present study, we found that bacterial lipopolysaccharide (LPS), a well-known initiator of the inflammatory response, induced ATX expression in monocytic THP-1 cells. The activation of PKR, JNK, and p38 MAPK was required for the ATX induction. The LPS-induced ATX in THP-1 cells was characterized as the beta isoform. In the presence of LPC, ATX could promote the migrations of THP-1 and Jurkat cells, which was inhibited by pertussis toxin (PTX), an inhibitor of Gi-mediated LPA receptor signaling. In summary, LPS induces ATX expression in THP-1 cells via a PKR, JNK and p38 MAPK-mediated mechanism, and the ATX induction is likely to enhance immune cell migration in proinflammatory response by regulating LPA levels in the microenvironment.

Measurement of plasma lysophosphatidic acid concentration in healthy subjects: strong correlation with lysophospholipase D activity

BACKGROUND

Lysophosphatidic acid (LPA) plays important roles in a variety of biological responses, especially in the area of vascular biology, and the determination of its plasma concentration is believed to be important. Several mechanisms are known to be involved in the metabolism of LPA.

METHODS

To identify factors that may determine the plasma concentrations of this important bioactive lipid, we examined its concentrations using an enzymatic cycling assay and related parameters in 146 healthy subjects.

RESULTS

The LPA concentration was significantly higher in women (mean +/- SD, 0.103 +/- 0.032 micromol/L; n = 47) than in men (0.077 +/- 0.026 micromol/L; n = 99). A multiple regression analysis showed a strong positive correlation between the plasma LPA concentration and serum lysophospholipase D (lysoPLD) activity, while the LPA concentration was correlated with the plasma lysophosphatidylcholine (LPC) concentration only in men. Other lipid-related parameters were only slightly correlated or were not correlated with the LPA concentration.

CONCLUSIONS

Our findings suggested that conversion from LPC by lysoPLD might be the major route for LPA production in plasma.

Serum autotaxin measurement in haematological malignancies: a promising marker for follicular lymphoma

Autotaxin (ATX) is a tumour cell motility-stimulating factor originally isolated from melanoma cell supernatants. ATX is identical to lysophospholipase D, which produces a bioactive lipid mediator, lysophosphatidic acid (LPA), from lysophosphatidylcholine. ATX is overexpressed in various malignancies, including Hodgkin lymphoma, and ATX may stimulate tumour progression via LPA production. The present study measured the serum ATX antigen levels in patients with haematological malignancies using a recently developed automated enzyme immunoassay. The serum ATX antigen levels in patients with B-cell neoplasms, especially follicular lymphoma (FL), were higher than those in healthy subjects. Serum ATX antigen levels in FL patients were associated with tumour burden and changed in parallel with the patients' clinical courses. The serum ATX antigen levels were little affected by inflammation, unlike the soluble interleukin-2 receptor and beta2-microglobulin levels. As expected, the plasma LPA levels in FL patients were correlated with the serum ATX antigen levels. Given that leukaemic tumour cells from FL patients expressed ATX, the shedding of ATX from lymphoma cells probably leads to the elevation of serum ATX antigen levels. Our results suggest that the serum ATX antigen level may be a promising and novel marker for FL.

Measurement of autotaxin/lysophospholipase D activity

Lysophosphatidic acid (LPA) is a bioactive lipid mediator present in the blood and other biological fluids at physiologically relevant concentrations. In the cardiovascular system, studies using in vitro and in vivo experimental models indicate that LPA stimulates platelet activation, differentiation and migration of vascular smooth muscle cells, and changes in vascular tone. A growing body of evidence suggests that aberrant production and actions of LPA could play an important role in atherothrombotic disease. Hydrolysis of lysophospholipids by the secreted plasma protein autotaxin/lysophospholipase D (lysoPLD) is a major mechanism for generation of LPA in the blood. This chapter describes methods for determining the activity of recombinant autotaxin/lysoPLD using radiolabeled and fluorogenic substrates.

Targeting the lipids LPA and S1P and their signalling pathways to inhibit tumour progression

The bioactive lipids lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P), the enzymes that generate and degrade them, and the receptors that receive their signals are all potential therapeutic targets in cancer. LPA and S1P signalling pathways can modulate a range of cellular processes that contribute to tumourigenesis, such as proliferation and motility, and components of the signalling pathways often show aberrant expression and altered activity upon malignant transformation. This article reviews LPA- and S1P-mediated activities that might contribute to the aetiology of cancer, and examines the potential of the many antagonists that have been developed to inhibit LPA and S1P signalling pathways. In addition, the outcomes of various clinical trials using LPA- and S1P-associated targets in cancer and other diseases are described, and future directions are discussed.

Validation of an autotaxin enzyme immunoassay in human serum samples and its application to hypoalbuminemia differentiation

BACKGROUND

Autotaxin (ATX), a tumor cell motility-stimulating factor, regulates the blood concentrations of lysophosphatidic acid (LPA), an important and multi-functional bioactive lipid, through its lysophospholipase D activity (lysoPLD). The introduction of ATX measurements into clinical laboratory testing is urgently needed.

METHODS

Anti-human ATX monoclonal antibodies were produced by immunization of recombinant human ATX expressed in a baculovirus system. An immunoassay for the quantitative determination of ATX was established, and human serum samples were assayed.

RESULTS

The within-run and between-run precision, interference, detection limit, and linearity studies were satisfactory. The central 95 percentile reference interval for the serum ATX antigen concentration in healthy subjects was 0.468-1.134 mg/l (n=120) and was strongly correlated with the serum lysoPLD activity. The ATX concentration was significantly (p<0.001) higher in women (0.625-1.323 mg/l) than in men (0.438-0.914 mg/l). The serum ATX concentrations were increased in patients with chronic liver diseases and decreased in postoperative prostate cancer patients but were not altered in nephrosis patients. Thus, serum ATX antigen concentrations could be used to discriminate these hypoalbuminemia conditions.

CONCLUSIONS

The present ATX antigen assay may be useful for clinical laboratory testing.