Longitudinal Magnetic Resonance Imaging of Changes in Lung Morphology and Perfusion in Children with Cystic Fibrosis From Infancy through Adolescence.

RATIONALE: The progression of lung changes in cystic fibrosis (CF) from infancy through adolescence remains poorly understood due to limited longitudinal imaging data. OBJECTIVES: To assess changes in lung morphology and perfusion in children with CF through the pediatric age range by longitudinal chest magnetic resonance imaging (MRI). METHODS: 1112 annual chest MRI were performed in 226 patients with CF aged 0-18yr. MRI was assessed using a validated MRI scoring system. MEASUREMENTS AND MAIN RESULTS: The MRI global score continuously increased from 5.5±4.6 at infancy (0yr) to 17.9±8.4 at adolescence (range 12-18yr), and the MRI morphology score from 5.0±3.9 to 12.4±6.0 (P<0.001). Bronchiectasis/wall thickening prevalence increased from 89.1% at infancy to approx. 100% from preschool age (1-5yr), and the subscore increased from 3.1±1.9 at infancy to 6.6±2.1 at adolescence (P<0.001). Mucus plugging prevalence increased from 55.4% at infancy to 83.5% at adolescence, and the subscore increased from 1.2±1.6 to 3.7±2.5 in the same period (P<0.001). Perfusion abnormalities were found in 44.4% at infancy, and increased to approx. 90% from preschool age (P<0.001). The MRI perfusion score increased from 1.1±1.6 at infancy to 5.6±3.0 at adolescence (P<0.001). Chronic Pseudomonas aeruginosa infection was associated with higher MRI scores from school age (6-11yr, P<0.05-0.001). CONCLUSIONS: This is the first study assessing longitudinal changes in lung morphology and perfusion in CF throughout the pediatric age range, providing percentiles as age-specific reference for lung disease severity. Our data may facilitate the use of MRI as an endpoint in clinical trials in children with CF.

Navigator-based motion compensation for liver BOLD measurement with five-echo SAGE EPI and breath-hold task.

PURPOSE: The purpose of this work is to apply multi-echo spin- and gradient-echo (SAGE) echo-planar imaging (EPI) combined with a navigator-based (NAV) prospective motion compensation method for a quantitative liver blood oxygen level dependent (BOLD) measurement with a breath-hold (BH) task. METHODS: A five-echo SAGE sequence was developed to quantitatively measure T2 and T2* to depict function with sufficient signal-to-noise ratio, spatial resolution and sensitivity to BOLD changes induced by the BH task. To account for respiratory motion, a navigator was employed in the form of a single gradient-echo projection readout, located at the diaphragm along the inferior-superior direction. Prior to each transverse imaging slice of the spin-echo EPI-based readouts, navigator acquisition and fat suppression were incorporated. Motion data was obtained from the navigator and transmitted back to the sequence, allowing real-time adjustments to slice positioning. Six healthy volunteers and three patients with liver carcinoma were included in this study. Quantitative T2 and T2* were calculated at each time point of the BH task. Parameters of t value from first-level analysis using a general linear model and hepatovascular reactivity (HVR) of Echo1, T2 and T2* were calculated. RESULTS: The motion caused by respiratory activity was successfully compensated using the navigator signal. The average changes of T2 and T2* during breath-hold were about 1% and 0.7%, respectively. With the help of NAV prospective motion compensation whole liver t values could be obtained without motion artifacts. The quantified liver T2 (34.7 ± 0.7 ms) and T2* (29 ± 1.2 ms) values agreed with values from literature. In healthy volunteers, the distribution of statistical t value and HVR was homogeneous throughout the whole liver. In patients with liver carcinoma, the distribution of t value and HVR was inhomogeneous due to metastases or therapy. CONCLUSIONS: This study demonstrates the feasibility of using a NAV prospective motion compensation technique in conjunction with five-echo SAGE EPI for the quantitative measurement of liver BOLD with a BH task.

Magnetic Resonance Imaging of Lung Perfusion.

"Lung perfusion" in the context of imaging conventionally refers to the delivery of blood to the pulmonary capillary bed through the pulmonary arteries originating from the right ventricle required for oxygenation. The most important physiological mechanism in the context of imaging is the so-called hypoxic pulmonary vasoconstriction (HPV, also known as "Euler-Liljestrand-Reflex"), which couples lung perfusion to lung ventilation. In obstructive airway diseases such as asthma, chronic-obstructive pulmonary disease (COPD), cystic fibrosis (CF), and asthma, HPV downregulates pulmonary perfusion in order to redistribute blood flow to functional lung areas in order to conserve optimal oxygenation. Imaging of lung perfusion can be seen as a reflection of lung ventilation in obstructive airway diseases. Other conditions that primarily affect lung perfusion are pulmonary vascular diseases, pulmonary hypertension, or (chronic) pulmonary embolism, which also lead to inhomogeneity in pulmonary capillary blood distribution. Several magnetic resonance imaging (MRI) techniques either dependent on exogenous contrast materials, exploiting periodical lung signal variations with cardiac action, or relying on intrinsic lung voxel attributes have been demonstrated to visualize lung perfusion. Additional post-processing may add temporal information and provide quantitative information related to blood flow. The most widely used and robust technique, dynamic-contrast enhanced MRI, is available in clinical routine assessment of COPD, CF, and pulmonary vascular disease. Non-contrast techniques are important research tools currently requiring clinical validation and cross-correlation in the absence of a viable standard of reference. First data on many of these techniques in the context of observational studies assessing therapy effects have just become available. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 5.

Elexacaftor/Tezacaftor/Ivacaftor Improves Bronchial Artery Dilatation Detected by Magnetic Resonance Imaging in Patients with Cystic Fibrosis.

Rationale: Magnetic resonance imaging (MRI) detects improvements in mucus plugging and bronchial wall thickening, but not in lung perfusion in patients with cystic fibrosis (CF) treated with elexacaftor/tezacaftor/ivacaftor (ETI). Objectives: To determine whether bronchial artery dilatation (BAD), a key feature of advanced lung disease, indicates irreversibility of perfusion abnormalities and whether BAD could be reversed in CF patients treated with ETI. Methods: A total of 59 adults with CF underwent longitudinal chest MRI, including magnetic resonance angiography twice, comprising 35 patients with CF (mean age, 31 ± 7 yr) before (MRI1) and after (MRI2) at least 1 month (mean duration, 8 ± 4 mo) on ETI therapy and 24 control patients with CF (mean age, 31 ± 7 yr) without ETI. MRI was assessed using the validated chest MRI score, and the presence and total lumen area of BAD were assessed with commercial software. Results: The MRI global score was stable in the control group from MRI1 to MRI2 (mean difference, 1.1 [-0.3, 2.4]; P = 0.054), but it was reduced in the ETI group (-10.1 [-0.3, 2.4]; P < 0.001). In the control and ETI groups, BAD was present in almost all patients at baseline (95% and 94%, respectively), which did not change at MRI2. The BAD total lumen area did not change in the control group from MRI1 to MRI2 (1.0 mm2 [-0.2, 2.2]; P = 0.099) but decreased in the ETI group (-7.0 mm2 [-8.9, -5.0]; P < 0.001). This decrease correlated with improvements in the MRI global score (r = 0.540; P < 0.001). Conclusions: Our data show that BAD may be partially reversible under ETI therapy in adult patients with CF who have established disease.

Magnetic resonance imaging detects onset and association with lung disease severity of bronchial artery dilatation in cystic fibrosis.

Background: Bronchial artery dilatation (BAD) is associated with haemoptysis in advanced cystic fibrosis (CF) lung disease. Our aim was to evaluate BAD onset and its association with disease severity by magnetic resonance imaging (MRI). Methods: 188 CF patients (mean±sd age 13.8±10.6 years, range 1.1-55.2 years) underwent annual chest MRI (median three exams, range one to six exams), contributing a total of 485 MRI exams including perfusion MRI. Presence of BAD was evaluated by two radiologists in consensus. Disease severity was assessed using the validated MRI scoring system and spirometry (forced expiratory volume in 1 s (FEV1) % pred). Results: MRI demonstrated BAD in 71 (37.8%) CF patients consistently from the first available exam and a further 10 (5.3%) patients first developed BAD during surveillance. Mean MRI global score in patients with BAD was 24.5±8.3 compared with 11.8±7.0 in patients without BAD (p<0.001) and FEV1 % pred was lower in patients with BAD compared with patients without BAD (60.8% versus 82.0%; p<0.001). BAD was more prevalent in patients with chronic Pseudomonas aeruginosa infection versus in patients without infection (63.6% versus 28.0%; p<0.001). In the 10 patients who newly developed BAD, the MRI global score increased from 15.1±7.8 before to 22.0±5.4 at first detection of BAD (p<0.05). Youden indices for the presence of BAD were 0.57 for age (cut-off 11.2 years), 0.65 for FEV1 % pred (cut-off 74.2%) and 0.62 for MRI global score (cut-off 15.5) (p<0.001). Conclusions: MRI detects BAD in patients with CF without radiation exposure. Onset of BAD is associated with increased MRI scores, worse lung function and chronic P. aeruginosa infection, and may serve as a marker of disease severity.

Unsupervised clustering algorithms improve the reproducibility of dynamic contrast-enhanced magnetic resonance imaging pulmonary perfusion quantification in muco-obstructive lung diseases.

Background: Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) allows the assessment of pulmonary perfusion, which may play a key role in the development of muco-obstructive lung disease. One problem with quantifying pulmonary perfusion is the high variability of metrics. Quantifying the extent of abnormalities using unsupervised clustering algorithms in residue function maps leads to intrinsic normalization and could reduce variability. Purpose: We investigated the reproducibility of perfusion defects in percent (QDP) in clinically stable patients with cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD). Methods: 15 CF (29.3 ± 9.3y, FEV1%predicted = 66.6 ± 15.8%) and 20 COPD (66.5 ± 8.9y, FEV1%predicted = 42.0 ± 13.3%) patients underwent DCE-MRI twice 1 month apart. QDP, pulmonary blood flow (PBF), and pulmonary blood volume (PBV) were computed from residue function maps using an in-house quantification pipeline. A previously validated MRI perfusion score was visually assessed by an expert reader. Results: Overall, mean QDP, PBF, and PBV did not change within 1 month, except for QDP in COPD (p < 0.05). We observed smaller limits of agreement (± 1.96 SD) related to the median for QDP (CF: ± 38%, COPD: ± 37%) compared to PBF (CF: ± 89%, COPD: ± 55%) and PBV (CF: ± 55%, COPD: ± 51%). QDP correlated moderately with the MRI perfusion score in CF (r = 0.46, p < 0.05) and COPD (r = 0.66, p < 0.001). PBF and PBV correlated poorly with the MRI perfusion score in CF (r =-0.29, p = 0.132 and r =-0.35, p = 0.067, respectively) and moderately in COPD (r =-0.57 and r =-0.57, p < 0.001, respectively). Conclusion: In patients with muco-obstructive lung diseases, QDP was more robust and showed a higher correlation with the MRI perfusion score compared to the traditionally used perfusion metrics PBF and PBV.

Magnetic resonance imaging detects improvements of pulmonary and paranasal sinus abnormalities in response to elexacaftor/tezacaftor/ivacaftor therapy in adults with cystic fibrosis.

BACKGROUND: Therapy with Elexacaftor/Tezacaftor/Ivacaftor (ETI) was recently approved for adult cystic fibrosis (CF) patients with at least one F508del mutation. However, its effects on structural and functional lung abnormalities and chronic rhinosinusitis have not been studied by imaging. METHODS: 19 adults with CF (mean age 31±9y, range 19-55y) underwent standardized chest magnetic resonance imaging (MRI), and nine also same-session sinonasal MRI, before (MRI1) and after (MRI2) at least one month (mean duration 5 ± 3mon) on ETI. 24 control CF patients (30±7y, range 20-44y) without ETI underwent longitudinal chest MRI, and eleven also sinonasal MRI, twice (mean interval 40±15mon). MRI was assessed using the validated chest MRI score and chronic rhinosinusitis (CRS)-MRI score. Forced expiratory volume in 1 s percent predicted (FEV1%) was measured in all patients. RESULTS: In controls, the chest MRI global score and CRS-MRI sum score were stable from MRI1 to MRI2. In patients under ETI, the chest MRI global score improved (-11.4 ± 4.6, P<0.001), mainly due to reduction of bronchiectasis/wall thickening and mucus plugging subscores (-3.3 ± 2.2 and -5.2 ± 1.5, P<0.001, respectively). The improvement in chest MRI score correlated well with improved FEV1% (r=-0.703, P<0.001). The CRS-MRI sum score also improved in patients under ETI (-6.9 ± 3.0, P<0.001), mainly due to a reduction of mucopyoceles in the maxillary and ethmoid sinus (-50% and -39%, P<0.05, respectively). CONCLUSIONS: MRI detects improvements of chest MRI and CRS-MRI scores in adult CF patients who first received ETI, demonstrating reversibility of structural lung and paranasal sinus abnormalities in patients with established disease.

Echo Time-Dependence of Observed Lung T1 in Patients With Cystic Fibrosis and Correlation With Clinical Metrics.

BACKGROUND: Noninvasive monitoring of early abnormalities and therapeutic intervention in cystic fibrosis (CF) lung disease using MRI is important. Lung T1 mapping has shown potential for local functional imaging without contrast material. Recently, it was discovered that observed lung T1 depends on the measurement echo time (TE). PURPOSE: To examine TE-dependence of observed T1 in patients with CF and its correlation with clinical metrics. STUDY TYPE: Prospective. POPULATION: In all, 75 pediatric patients with CF (8.6 ± 6.1 years, range 0.1-23 years), with 32 reexamined after 1 year. FIELD STRENGTH/SEQUENCE: Patients were examined at 1.5T using an established MRI protocol and a multiecho inversion recovery 2D ultrashort echo time (UTE) sequence for T1 (TE) mapping at five TEs including TE1 = 70 µs. ASSESSMENT: Morphological and perfusion MRI were assessed by a radiologist (M.W.) with 11 years of experience using an established CF-MRI scoring system. T1 (TE) was quantified automatically. Clinical data including spirometry (FEV1pred%) and lung clearance index (LCI) were collected. STATISTICAL TESTS: T1 (TE) was correlated with the CF-MRI score, clinical data, and LCI. RESULTS: T1 (TE) showed a different curvature in CF than in healthy adults: T1 at TE1 was shorter in CF (1157 ms ± 73 ms vs. 1047 ms ± 70 ms, P < 0.001), but longer at TE3 (1214 ms ± 72 ms vs. 1314 ms ± 68 ms, P < 0.001) and later TEs. The correlations of T1 (TE) with patient age (ρTE1-TE5 = -0.55, -0.44, -0.24, -0.30, -0.22), and LCI (ρTE1-TE5 = -0.43, -0.42, -0.33, 0.27, -0.22) were moderate at ultra-short to short TE (P < 0.001) but decreased for longer TE. Moderate but similar correlations at all TE were found with MRI perfusion score (ρTE1-TE5 = -0.43, -0.51, -0.47, -0.46, -0.44) and FEV1pred% (ρTE1-TE5 = +0.44, +0.44, +0.43, +0.40, +0.39) (P < 0.05). DATA CONCLUSION: TE should be considered when measuring lung T1 , since observed differences between CF and healthy subjects strongly depend on TE. The different variation of correlation coefficients with TE for structural vs. functional metrics implies that TE-dependence holds additional information which may help to discern effects of tissue structural abnormalities and abnormal perfusion. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY STAGE: 1 J. MAGN. RESON. IMAGING 2020;52:1645-1654.

Vessel architecture imaging using multiband gradient-echo/spin-echo EPI.

OBJECTIVES: To apply the MB (multiband) excitation and blipped-CAIPI (blipped-controlled aliasing in parallel imaging) techniques in a spin and gradient-echo (SAGE) EPI sequence to improve the slice coverage for vessel architecture imaging (VAI). MATERIALS AND METHODS: Both MB excitation and blipped-CAIPI with in-plane parallel imaging were incorporated into a gradient-echo (GE)/spin-echo (SE) EPI sequence for simultaneous tracking of the dynamic MR signal changes in both GE and SE contrasts after the injection of contrast agent. MB and singleband (SB) excitation were compared using a 20-channel head coil at 3 Tesla, and high-resolution MB VAI could be performed in 32 glioma patients. RESULTS: Whole-brain covered high resolution VAI can be achieved after applying multiband excitation with a factor of 2 and in-plane parallel imaging with a factor of 3. The quality of the images resulting from MB acceleration was comparable to those from the SB method: images were reconstructed without any loss of spatial resolution or severe distortions. In addition, MB and SB signal-to-noise ratios (SNR) were similar. A relative low g-factor induced from the MB acceleration method was achieved after using a blipped-CAIPI technique (1.35 for GE and 1.33 for SE imaging). Performing quantitative VAI, we found that, among all VAI parametric maps, microvessel type indicator (MTI), distance map (I) and vascular-induced bolus peak-time shift (VIPS) were highly correlated. Likewise, VAI parametric maps of slope, slope length and short axis were highly correlated. CONCLUSIONS: Multiband accelerated SAGE successfully doubles the number of readout slices in the same measurement time when compared to conventional readout sequences. The corresponding VAI parametric maps provide insights into the complexity and heterogeneity of vascular changes in glioma.

Outracing Lung Signal Decay - Potential of Ultrashort Echo Time MRI.

BACKGROUND: Magnetic resonance imaging (MRI) of the pulmonary parenchyma is generally hampered by multiple challenges related to patient respiratory- and circulation-related motion, low proton density and extremely fast signal decay due to the structure of the lungs evolved for gas exchange. METHODS: Systematic literature database research as well as annual participation in conferences dedicated to pulmonary MRI for more than the past 20 years by at least one member of the author team. RESULTS AND CONCLUSION: The problem of motion has been addressed in the past by developments such as triggering, gating and parallel imaging. The second problem has, in part, turned out to be an advantage in those diseases that lead to an increase in lung substance and thus an increase in signal relative to the background. To reduce signal decay, ultrashort echo time (UTE) methods were developed to minimize the time between excitation and readout. Having been postulated a while ago, improved hardware and software now open up the possibility of achieving echo times shorter than 200 µs, increasing lung signal significantly by forestalling signal decay and more effectively using the few protons available. Such UTE techniques may not only improve structural imaging of the lung but also enhance functional imaging, including ventilation and perfusion imaging as well as quantitative parameter mapping. Because of accelerating progress in this field of lung MRI, the review at hand seeks to introduce some technical properties as well as to summarize the growing data from applications in humans and disease, which promise that UTE MRI will play an important role in the morphological and functional assessment of the lung in the near future. KEY POINTS: · Ultrashort echo time MRI is technically feasible with state-of-the-art scanner hardware.. · UTE MRI allows for CT-like image quality for structural lung imaging.. · Preliminary studies show improvements over conventional morphological imaging in lung cancer and airways diseases.. · UTE may improve sensitivity for functional processes like perfusion and tissue characterization.. CITATION FORMAT: · Wielpütz MO, Triphan SM, Ohno Y et al. Outracing Lung Signal Decay - Potential of Ultrashort Echo Time MRI. Fortschr Röntgenstr 2019; 191: 415 - 423.

Non-contrast enhanced magnetic resonance imaging detects mosaic signal intensity in early cystic fibrosis lung disease.

OBJECTIVES: To determine if morphological non-contrast enhanced magnetic resonance imaging (MRI) of the lung is sensitive to detect mosaic signal intensity in infants and preschool children with cystic fibrosis (CF). MATERIALS AND METHODS: 50 infant and preschool CF patients (mean age 3.5 ±â€¯1.4y, range 0-6y) routinely underwent morphological (T2-weighted turbo-spin echo sequence with half-Fourier acquisition, HASTE) and contrast-enhanced 4D perfusion MRI (gradient echo sequence with parallel imaging and echo sharing, TWIST). MRI studies were independently scored by two readers blinded for patient age and clinical data (experienced Reader 1 = R1, inexperienced Reader 2 = R2). The extent of lung parenchyma signal abnormalities on HASTE was rated for each lobe from 0 (normal), 1 (<50% of lobe affected) to 2 (≥50% of lobe affected). Perfusion MRI was rated according to the previously established MRI score, and served as the standard of reference. RESULTS: Inter-method agreement between MRI mosaic score and perfusion score was moderate with κ = 0.58 (confidence interval 0.45-0.71) for R1, and with κ = 0.59 (0.46-0.72) for R2. Bland-Altman analysis revealed a slight tendency of the mosaic score to underestimate perfusion abnormalities with a score bias of 0.48 for R1 and 0.46 for R2. Inter-reader agreement for mosaic score was substantial with κ = 0.71 (0.62-0.79), and a low bias of 0.02. CONCLUSIONS: This study demonstrates that non-contrast enhanced MRI reliably detects mosaic signal intensity in infants and preschool children with CF, reflecting pulmonary blood volume distribution. It may thus be used as a surrogate for perfusion MRI if contrast material is contra-indicated or alternative techniques are not available.

Morpho-Functional 1H-MRI of the Lung in COPD: Short-Term Test-Retest Reliability.

PURPOSE: Non-invasive end-points for interventional trials and tailored treatment regimes in chronic obstructive pulmonary disease (COPD) for monitoring regionally different manifestations of lung disease instead of global assessment of lung function with spirometry would be valuable. Proton nuclear magnetic resonance imaging (1H-MRI) allows for a radiation-free assessment of regional structure and function. The aim of this study was to evaluate the short-term reproducibility of a comprehensive morpho-functional lung MRI protocol in COPD. MATERIALS AND METHODS: 20 prospectively enrolled COPD patients (GOLD I-IV) underwent 1H-MRI of the lung at 1.5T on two consecutive days, including sequences for morphology, 4D contrast-enhanced perfusion, and respiratory mechanics. Image quality and COPD-related morphological and functional changes were evaluated in consensus by three chest radiologists using a dedicated MRI-based visual scoring system. Test-retest reliability was calculated per each individual lung lobe for the extent of large airway (bronchiectasis, wall thickening, mucus plugging) and small airway abnormalities (tree in bud, peripheral bronchiectasis, mucus plugging), consolidations, nodules, parenchymal defects and perfusion defects. The presence of tracheal narrowing, dystelectasis, pleural effusion, pulmonary trunk ectasia, right ventricular enlargement and, finally, motion patterns of diaphragma and chest wall were addressed. RESULTS: Median global scores [10(Q1:8.00;Q3:16.00) vs.11(Q1:6.00;Q3:15.00)] as well as category subscores were similar between both timepoints, and kappa statistics indicated "almost perfect" global agreement (ĸ = 0.86, 95%CI = 0.81-0.91). Most subscores showed at least "substantial" agreement of MRI1 and MRI2 (ĸ = 0.64-1.00), whereas the agreement for the diagnosis of dystelectasis/effusion (ĸ = 0.42, 95%CI = 0.00-0.93) was "moderate" and of tracheal abnormalities (ĸ = 0.21, 95%CI = 0.00-0.75) "fair". Most MRI acquisitions showed at least diagnostic quality at MRI1 (276 of 278) and MRI2 (259 of 264). CONCLUSION: Morpho-functional 1H-MRI can be obtained with reproducible image quality and high short-term test-retest reliability for COPD-related morphological and functional changes of the lung. This underlines its potential value for the monitoring of regional lung characteristics in COPD trials.

Potential involvement of adipocyte insulin resistance in obesity-associated up-regulation of adipocyte lysophospholipase D/autotaxin expression.

AIMS/HYPOTHESIS: Autotaxin is a lysophospholipase D that is secreted by adipocytes and whose expression is substantially up-regulated in obese, diabetic db/db mice. The aim of the present study was to depict the physiopathological and cellular mechanisms involved in regulation of adipocyte autotaxin expression. METHODS: Autotaxin mRNAs were quantified in adipose tissue from db/db mice (obese and highly diabetic type 2), gold-thioglucose-treated (GTG) mice (highly obese and moderately diabetic type 2), high-fat diet-fed (HFD) mice (obese and moderately diabetic type 2), streptozotocin-treated mice (thin and diabetic type 1), and massively obese humans with glucose intolerance. RESULTS: When compared to non-obese controls, autotaxin expression in db/db mice was significantly increased, but not in GTG, HFD, or streptozotocin-treated mice. During db/db mice development, up-regulation of autotaxin occurred only 3 weeks after the emergence of hyperinsulinaemia, and simultaneously with the emergence of hyperglycaaemia. Adipocytes from db/db mice exhibited a stronger impairment of insulin-stimulated glucose uptake than non-obese and HFD-induced obese mice. Autotaxin expression was up-regulated by treatment with TNFalpha (insulin resistance-promoting cytokine), and down-regulated by rosiglitazone treatment (insulin-sensitising compound) in 3T3F442A adipocytes. Finally, adipose tissue autotaxin expression was significantly up-regulated in patients exhibiting both insulin resistance and impaired glucose tolerance. CONCLUSIONS/INTERPRETATION: The present work demonstrates the existence of a db/db-specific up-regulation of adipocyte autotaxin expression, which could be related to the severe type 2 diabetes phenotype and adipocyte insulin resistance, rather than excess adiposity in itself. It also showed that type 2 diabetes in humans is also associated with up-regulation of adipocyte autotaxin expression.

Lysophosphatidic acid synthesis and release.

Lysophosphatidic acid (LPA) is a bioactive phospholipid controlling numerous cellular responses through the activation of specific G-protein coupled transmembrane receptors. LPA is present in several biological fluids (serum, plasma, aqueous humor) and can be secreted by several cell types (platelets, fibroblasts, adipocytes, cancer cells). Whereas, multiple pathways of synthesis and degradation of LPA have been described, their relative contribution in extracellular secretion and biodisponibility is still a matter of debate. The first part of the present review is devoted to the description of the different enzymes involved in LPA synthesis (acyltransferases, phospholipases, kinases) and degradation (lysophospholipases, lipid-phosphatases), as well as to the molecules involved in LPA transport (albumin, fatty acid binding proteins, gelsolin, lipoproteins). In a second part, the different physio-pathological situations (aggregation, cancer, injuries) associated with LPA production, as well as the potential role played by LPA in genesis of certain diseases (cancer, obesity, arteriosclerosis) are listed and analyzed.

Identification of pancreatic type I secreted phospholipase A2 in human epidermis and its determination by tape stripping.

Phospholipases A2 (PLA2) catalyse the release of fatty acids from the sn-2 position of phospholipids and have been suggested to play a key part in permeability barrier homeostasis. Using a sensitive and versatile fluorometric method, significant PLA2 activity has been detected in both human skin homogenates and tape strippings of stratum corneum. Based on various properties (resistance to heat and sulphuric acid treatment, neutral optimal pH, absolute requirement for millimolar calcium concentrations, inhibition by dithiothreitol and p-bromophenacyl bromide, and resistance to a trifluoromethyl ketone derivative of arachidonic acid, AACOCF3, a specific inhibitor of cytosolic PLA2), this enzyme was characterized as a secretory PLA2 (sPLA2). Immunohistochemistry revealed strong labelling of type I pancreatic sPLA2 at the stratum corneum-stratum granulosum junction, type II sPLA2 being undetectable. An increase in PLA2 activity in tape-stripped material from the deepest level of the stratum corneum was correlated with partial morphological disappearance of type I sPLA2 immunolabelling. Our data thus provide the first convincing evidence that pancreatic sPLA2 is significantly expressed in human epidermis, where it might participate in the accumulation of free fatty acids contributing to the permeability barrier. In addition, our method for determining PLA2 activity in easily available tape strippings should allow further clinical studies aimed to explore possible PLA2 abnormalities in various dermatoses.

New developments in phospholipase A2.

Some of the most recent data concerning various phospholipases A2, with special emphasis on secretory, cytosolic, and calcium-independent phospholipases A2 are summarized. Besides their contribution to the production of proinflammatory lipid mediators, the involvement of these enzymes in key cell responses such as apoptosis or tumor cell metastatic potential is also discussed, taking advantage of transgenic models based on gene invalidation by homologous recombination. The possible role of secretory and cytosolic platelet-activating factor acetyl hydrolases is also briefly mentioned. Finally, the ectopic expression in epididymis of an intestinal phospholipase B opens some novel issues as to the possible function of phospholipases in reproduction.

Lysophosphatidic acid-induced Ca2+ mobilization in human A431 cells: structure-activity analysis.

Lysophosphatidic acid (LPA; 1-acyl-sn-glycero-3-phosphate) is a platelet-derived lipid mediator that activates its own G-protein-coupled receptor to trigger phospholipase C-mediated Ca2+ mobilization and other effector pathways in numerous cell types. In this study we have examined the structural features of LPA that are important for activation of the Ca(2+)-mobilizing receptor in human A431 carcinoma cells, which show an EC50 for oleoyl-LPA as low as 0.2 nM. When the acyl chain at the sn-1 position is altered, the rank order of potency is oleoyl-LPA > arachidonoyl-LPA > linolenoyl-LPA > linoleoyl-LPA > stearoyl-LPA = palmitoyl-LPA > myristoyl-LPA. The shorter-chain species, lauroyl- and decanoyl-LPA, show little or no activity. Ether-linked LPA (1-O-hexadecyl-sn-glycero-3-phosphate) is somewhat less potent than the corresponding ester-linked LPA; its stereoisomer is about equally active. Deletion of the glycerol backbone causes a 1000-fold decrease in potency. Replacement of the phosphate group in palmitoyl-LPA by a hydrogen- or methyl-phosphonate moiety results in complete loss of activity. A phosphonate analogue with a methylene group replacing the oxygen at sn-3 has strongly decreased activity. All three phosphonate analogues induce cell lysis at doses > 15 microM. Similarly, the methyl and ethyl esters of palmitoyl-LPA are virtually inactive and become cytotoxic at micromolar doses. None of the LPA analogues tested has antagonist activity. Sphingosine 1-phosphate, a putative messenger with some structural similarities to LPA, elicits a transient rise in intracellular [Ca2+] only at micromolar doses; however, cross-desensitization experiments indicate that sphingosine 1-phosphate does not act through the LPA receptor. The results indicate that, although many features of the LPA structure are important for optimal activity, the phosphate group is most critical, suggesting that this moiety is directly involved in receptor activation.

Effect of PCR 4099 on ADP-induced calcium movements and phosphatidic acid production in rat platelets.

Antiplatelet activity of PCR 4099, an analogue of ticlopidine, resides in its specific effect against exogenous as well as released ADP. This study investigated in rat platelets the effects of the drug on ADP-induced shape change, elevation of cytosolic free Ca2+ concentration ([Ca2+]i) and hydrolysis of inositol phospholipids, monitored as [32P]phosphatidic acid formation. Shape change and influx of Ca2+ ions across the plasma membrane were not modified after PCR 4099 administration using aspirin-treated platelets. On the other hand, phosphatidic acid formation and calcium mobilization from internal stores were strongly inhibited. These results suggest that PCR 4099 leaves intact the machinery involved in ADP-induced platelet shape change and influx of calcium ions, but inhibits an early step in the ADP-response coupling leading to inositol phospholipid hydrolysis and aggregation.

Broad spectrum anti-platelet activity of ticlopidine and PCR 4099 involves the suppression of the effects of released ADP.

Aggregation and serotonin secretion were studied in washed rat platelets after oral administration of ticlopidine or its more potent analog PCR 4099. Besides a complete suppression of the ADP-induced aggregation, the two drugs significantly inhibited aggregation and secretion induced by three protein kinase C activators (1-oleoyl-2-acetyl-sn-glycerol, OAG; 12-0-tetradecanoyl phorbol-13-acetate, TPA; phospholipase C), by the calcium ionophore A 23187 and by thrombin. The highest inhibition was observed at low stimuli concentrations but could be partly or almost completely overcome by increasing their concentrations. The combination of aspirin (ASA) with the ADP scavenging system, creatine phosphate/creatine phosphokinase (CP/CPK) in vitro resulted in an inhibition similar to that observed ex vivo after ticlopidine or PCR 4099 treatment. Moreover, these in vitro and ex vivo treatments were not additive. As identical results were obtained with CP/CPK alone but not with ASA, it is concluded that ticlopidine and PCR 4099 do not interfere with protein kinase C or calcium movements but specifically inhibit the effects of released ADP, which might explain the broad spectrum anti-platelet activity of these drugs.

Activation of phospholipase C in thrombin-stimulated platelets does not depend on cytoplasmic free calcium concentration.

Human platelets loaded with the fluorescent Ca2+ indicator quin2 and with different radioactive compounds including [3H]serotonin, [14C]arachidonic acid (AA) and [32P]orthophosphate were stimulated by thrombin under conditions producing secretion. In the absence of external Ca2+ (Ca2+e), cytoplasmic free [Ca2+], [Ca2+]i, increased to 340 nM, against 1685 nM at 1 mM [Ca2+]e. In both cases, diglyceride and phosphatidic acid production proceeded at the same rate, whereas AA release was inhibited at low [Ca2+]i. It is concluded that, at variance with phospholipase A2, phospholipase C activation does not depend on [Ca2+]i. These results give further support to the hypothesis of a Ca2+-independent pathway of cell activation involving phospholipase C and protein kinase C.