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Background: Geant4 is a Monte Carlo code extensively used in medical physics for a wide range of applications, such as dosimetry, micro- and nanodosimetry, imaging, radiation protection, and nuclear medicine. Geant4 is continuously evolving, so it is crucial to have a system that benchmarks this Monte Carlo code for medical physics against reference data and to perform regression testing. Aims: To respond to these needs, we developed G4-Med, a benchmarking and regression testing system of Geant4 for medical physics. Materials and Methods: G4-Med currently includes 18 tests. They range from the benchmarking of fundamental physics quantities to the testing of Monte Carlo simulation setups typical of medical physics applications. Both electromagnetic and hadronic physics processes and models within the prebuilt Geant4 physics lists are tested. The tests included in G4-Med are executed on the CERN computing infrastructure via the use of the geant-val web application, developed at CERN for Geant4 testing. The physical observables can be compared to reference data for benchmarking and to results of previous Geant4 versions for regression testing purposes. Results: This paper describes the tests included in G4-Med and shows the results derived from the benchmarking of Geant4 10.5 against reference data. Discussion: Our results indicate that the Geant4 electromagnetic physics constructor G4EmStandardPhysics_option4 gives a good agreement with the reference data for all the tests. The QGSP_BIC_HP physics list provided an overall adequate description of the physics involved in hadron therapy, including proton and carbon ion therapy. New tests should be included in the next stage of the project to extend the benchmarking to other physical quantities and application scenarios of interest for medical physics. Conclusion: The results presented and discussed in this paper will aid users in tailoring physics lists to their particular application. Ministerio de Economía y Competitividad FPA2016-77689-C2-1-R National Institutes of Health U24CA215123 France-Greece PICS 8235 European Space Agency 4000126645/19/NL/BW Australian Research Council ARC DP170100967, DP170102423 Susan G Komen Foundation for the Cure IIR13262248

In X-ray imaging, photons are transmitted through and absorbed by the subject, but are also scattered in significant quantities. Previous attempts to use scattered photons for biological imaging used pencil or fan beam illumination. Here we present 3D X-ray Scatter Tomography using full-field illumination. Synchrotron imaging experiments were performed of a phantom and the chest of a juvenile rat. Transmitted and scattered photons were simultaneously imaged with separate cameras; a scientific camera directly downstream of the sample stage, and a pixelated detector with a pinhole imaging system placed at 45${}^\circ$ to the beam axis. We obtained scatter tomogram feature fidelity sufficient for segmentation of the lung and major airways in the rat. The image contrast in scatter tomogram slices approached that of transmission imaging, indicating robustness to the amount of multiple scattering present in our case. This opens the possibility of augmenting full-field 2D imaging systems with additional scatter detectors to obtain complementary modes or to improve the fidelity of existing images without additional dose, potentially leading to single-shot or reduced-angle tomography or overall dose reduction for live animal studies., Comment: 11 pages, 6 figures, Accepted for publication in IEEE Transactions on Medical Imaging

Low-cost muon detectors utilising cheap plastic scintillators and a limited number of individual silicon photomultipliers (SiPMs) offer a compelling approach to cheap experimental designs, provided the event localisation of a traversing particle can be accurately determined. In this theoretical work, we use Geant4 to simulate a diverse range of detector configurations, shapes and SiPM photosensors, predicting the light intensity received at a given SiPM. Testing a range of methods to localise muon events we determine that machine learning techniques outperform analytic models, and of these, a simple gradient boosted framework is the most reliably accurate localisation technique for our simulated scintillators. We find that a simple square scintillator outperforms other geometries and that AI performs, when applied to this shape, with a linear relationship between the positional accuracy of the event recovery and the average distance between photosensors around the detector perimeter.

Over the last decade one of the most significant technological advances made in the field of radiation detectors for nuclear medicine was the development of Silicon Photomultipler (SiPM) sensors. At present only a small number of SiPM based radiation detectors for Single Photon Emission Computed Tomography (SPECT) applications have been explored, and even fewer experimental prototypes developed. An in-silico investigation into the optimal design of a Philips DPC3200 SiPM photosensor-based thin monolithic scintillator detector for SPECT applications was undertaken using the Monte Carlo radiation transport modelling toolkit Geant4 version 10.5. The performance of the 20 different SPECT radiation detector configurations, 4 scintillator materials (NaI(Tl), GAGG(Ce), CsI(Tl) and LaBr3(Ce)) and 5 thicknesses (1–5 mm), were determined through the use of seven figures of merit. It was found that a crystal thickness range of 4–5 mm was required for all four materials to ensure acceptable energy resolution, sensitivity and spatial resolution performance with the Philips DPC3200 SiPM. Any thinner than this and the performance of all four materials was found to degrade rapidly due to a high probability of material specific fluorescence x-ray escape after incident gamma/x-ray photoelectric absorption. When factoring in each material's magnetic resonance imaging compatibility, hygroscopy, and cost, it was found that CsI(Tl) represents the most promising material to construct tileable Philips digital SiPM based thin monolithic scintillator detectors for SPECT applications.

A revised atomic deexcitation framework for the Geant4 general purpose Monte Carlo toolkit capable of simulating full Auger deexcitation cascades was implemented in June 2015 release (version 10.2 Beta). An overview of this refined framework and testing of its capabilities is presented for the irradiation of gold nanoparticles (NP) with keV photon and MeV proton beams. The resultant energy spectra of secondary particles created within and that escape the NP are analyzed and discussed. It is anticipated that this new functionality will improve and increase the use of Geant4 in the medical physics, radiobiology, nanomedicine research and other low energy physics fields.

A two-body fully relativistic three-dimensional scattering framework has been utilised to develop an alternative Compton scattering computational model to those adapted from Ribberfors’ work for Monte Carlo modelling of Compton scattering. Using a theoretical foundation that ensures the conservation of energy and momentum in the relativistic impulse approximation, this new model, the Monash University Compton scattering model, develops energy and directional algorithms for both the scattered photon and ejected Compton electron from first principles. The Monash University Compton scattering model was developed to address the limitation of the Compton electron directionality algorithms of other computational models adapted from Ribberfors’ work. Here the development of the Monash University Compton scattering model, including its implementation in a Geant4 low energy electromagnetic physics class, G4LowEPComptonModel, is outlined. Assessment of the performance of G4LowEPComptonModel was undertaken in two steps: (1) comparison with respect to the two standard Compton scattering classes of Geant4 version 9.5, G4LivermoreComptonModel and G4PenelopeComptonModel, and (2) experimental comparison with respect to Compton electron kinetic energy spectra obtained from the Compton scattering of 662 keV photons off the K-shell of gold. Both studies illustrate that the Monash University Compton scattering model, and in turn G4LowEPComptonModel, is a viable replacement for the majority of computational models that have been adapted from Ribberfors’ work. It was also shown that the Monash University Compton scattering model is able to reproduce the Compton scattering triply differential cross-section Compton electron kinetic energy spectra of 662 keV photons K-shell scattering off of gold to within experimental uncertainty.

Laplacian Erosion, an image deblurring technique for multi-plane Gamma-cameras, has been developed and tested for planar imaging using a GEANT4 Monte Carlo model of the Pixelated Emission Detector for RadioisOtopes (PEDRO) as a test platform. A contrast and Derenzo-like phantom composed of 125I were both employed to investigate the dependence of detection plane and pinhole geometry on the performance of Laplacian Erosion. Three different pinhole geometries were tested. It was found that, for the test system, the performance of Laplacian Erosion was inversely proportional to the detection plane offset, and directly proportional to the pinhole diameter. All tested pinhole geometries saw a reduction in the level of image blurring associated with the pinhole geometry. However, the reduction in image blurring came at the cost of signal to noise ratio in the image. The application of Laplacian Erosion was shown to reduce the level of image blurring associated with pinhole geometry and improve recovered image quality in multi-plane Gamma-cameras for the targeted radiotracer 125I.

International audience; At very low radiation dose rates, the effects of energy depositions in cells by ionizing radiation is best understood stochastically, as ionizing particles deposit energy along tracks separated by distances often much larger than the size of cells. We present a thorough analysis of the stochastic impact of the natural radiative background on cells, focusing our attention on E. coli grown as part of a long term evolution experiment in both underground and surface laboratories. The chance per day that a particle track interacts with a cell in the surface laboratory was found to be 6 × 10−5 day−1, 100 times less than the expected daily mutation rate for E. coli under our experimental conditions. In order for the chance cells are hit to approach the mutation rate, a gamma background dose rate of 20 μGy hr−1 is predicted to be required.

An energy discriminate CR-39 ® nuclear track etch dosimeter for use in a 220 Rn and 222 Rn gas monitor has been developed and experimentally assessed. It utilises a thin film of Mylar ® C to attenuate the alpha particle energies to allow only the damage tracks created by the 8.785 MeV alpha particles emitted from 212 Po of the 232 Th decay chain to be registered in the CR-39 ® plaque, allowing for the direct measurement of 220 Rn gas concentrations. The dosimeter was developed through a combination of experimental investigations and theoretical simulations using the Monte Carlo ion transport modelling program Stopping and Range of Ions in Materials (SRIM 2008). A film thickness of 54 μm has been shown to attenuate all alpha energies less then 7.7 MeV.

The Pixelated Emission Detector for RadiOisotopes (PEDRO) is a hybrid imaging system designed for the measurement of single photon emission from small animal models. The proof-of-principle device consists of a Compton-camera situated behind a mechanical collimator and is intended to provide optimal detection characteristics over a broad spectral range, from 30 to 511 keV. An automated routine has been developed for the optimization of large-area slits in the outer regions of a collimator which has a central region allocated for pinholes. The optimization was tested with a GEANT4 model of the experimental prototype. The data were blurred with the expected position and energy resolution parameters and a Bayesian interaction ordering algorithm was applied. Images were reconstructed using cone back-projection. The results show that the optimization technique allows the large-area slits to both sample fully and extend the primary field of view (FoV) determined by the pinholes. The slits were found to provide truncation of the back-projected cones of response and also an increase in the success rate of the interaction ordering algorithm. These factors resulted in an increase in the contrast and signal-to-noise ratio of the reconstructed image estimates. Of the two configurations tested, the cylindrical geometry outperformed the square geometry, primarily because of a decrease in artifacts. This was due to isotropic modulation of the cone surfaces, that can be achieved with a circular shape. Also, the cylindrical geometry provided increased sampling of the FoV due to more optimal positioning of the slits. The use of the cylindrical collimator and application of the transmission function in the reconstruction was found to improve the resolution of the system by a factor of 20, as compared to the uncollimated Compton camera. Although this system is designed for small animal imaging, the technique can be applied to any application of single photon imaging.

The Pixelated Emission Detector for RadiOisotopes (PEDRO) is a hybrid imager designed for the measurement of single photon emission from small animals. The proof-of-principle device currently under development consists of a Compton-camera situated behind a mechanical modulator. The combination of mechanical and electronic (hybrid) collimation should provide optimal detection characteristics over a broad spectral range ( 30 keV ≤ E γ ≤ 511 keV ) , through a reduction in the sensitivity-resolution trade-off, inherent in conventional mechanically collimated configurations. This paper presents GEANT4 simulation results from the PEDRO geometry operated only as a Compton camera in order to gauge its advantage when used in concert with mechanical collimation—regardless of the collimation pattern. The optimization of multiple detector spacing and resolution parameters is performed utilizing the Median Distance of Closest Approach (MDCA) and has been shown to result in an optimum distance, beyond which only a loss in sensitivity occurs.

Results are presented of a recent experiment at the Imaging and Medical beamline of the Australian Synchrotron intended to contribute to the implementation of low-dose high-sensitivity three-dimensional mammographic phase-contrast imaging, initially at synchrotrons and subsequently in hospitals and medical imaging clinics. The effect of such imaging parameters as X-ray energy, source size, detector resolution, sample-to-detector distance, scanning and data processing strategies in the case of propagation-based phase-contrast computed tomography (CT) have been tested, quantified, evaluated and optimized using a plastic phantom simulating relevant breast-tissue characteristics. Analysis of the data collected using a Hamamatsu CMOS Flat Panel Sensor, with a pixel size of 100 µm, revealed the presence of propagation-based phase contrast and demonstrated significant improvement of the quality of phase-contrast CT imaging compared with conventional (absorption-based) CT, at medically acceptable radiation doses.

BACKGROUND: A marked elevation of serum leptin is observed soon after the start of peritoneal dialysis (PD), suggesting that leptin production may be stimulated by this treatment. Glucose metabolism is the major factor regulating leptin. The current study was designed to test if glucose-based PD fluids might regulate leptin production in vitro. METHODS: 3T3-L1 adipocytes were exposed to a 50:50 mixture of dialysis solutions and medium M199 containing 10% serum for

AGeant4Monte Carlo simulation of the X-ray fluorescence microprobe (XFM) end-station at the Australian Synchrotron has been developed. The simulation is required for optimization of the scan configuration and reconstruction algorithms. As part of the simulation process, a Gaussian beam model was developed. Experimental validation of this simulation has tested the efficacy for use of the low-energy physics models inGeant4for this synchrotron-based technique. The observed spectral distributions calculated in the 384 pixel Maia detector, positioned in the standard back-scatter configuration, were compared with those obtained from experiments performed at three incident X-ray beam energies: 18.5, 11.0 and 6.8 keV. The reduced χ-squared (\chi^{2}_{\rm{red}}) was calculated for the scatter and fluorescence regions of the spectra and demonstrates that the simulations successfully reproduce the scatter distributions. Discrepancies were shown to occur in the multiple-scatter tail of the Compton continuum. The model was shown to be particularly sensitive to the impurities present in the beryllium window of the Maia detector and their concentrations were optimized to improve the \chi^{2}_{\rm{red}} parameterization in the low-energy fluorescence regions of the spectra.

Marked hyperleptinaemia and metabolic acidosis are common findings in patients with chronic renal failure. In animal models, both leptin administration and acidosis reduce food intake. However, leptin causes loss of body fat, while acidosis induces muscle wasting. Whether a low pH and leptin production are related has not been studied. Leptin secretion was measured in cultured 3T3-L1 adipocytes exposed to acid or control pH for up to 96 h. In addition, serum leptin was compared between acidotic and bicarbonate-treated uraemic Wistar rats using the remnant model. Leptin levels in the culture medium were decreased at an acid pH of 7.1 compared with a control pH of 7.5 at 96 h (562±78 and 831±103 pg·48 h-1·well-1 respectively; mean±S.E.M.; P = 0.037). Similarly, serum leptin in uraemic rats was found to be lower in the acidotic group than in the bicarbonate-treated group, although this observation fell just short of statistical significance (1273±171 compared with 2059±376 pg/ml; P = 0.07). In conclusion, acidosis decreases leptin secretion from cultured adipocytes. Accordingly, acidotic uraemic rats seem to exhibit lower serum leptin levels than their bicarbonate-supplemented counterparts. This study is the first report providing a link between acidosis and leptin levels.

BACKGROUND Glomerulosclerosis and interstitial fibrosis, which are cardinal features of the end-stage kidney, result from accumulation of extracellular matrix proteins, particularly collagen, in the glomerular mesangium and renal interstitium. This study examined the effect of D-penicillamine (DPC), which inhibits collagen deposition, on disease progression in the remnant kidney. METHODS Two groups of 10 rats underwent two-thirds nephrectomy and were pair-fed 20% casein paste (Gp 1) or the same paste supplemented with 90 mg/kg body wt per day of DPC (Gp 2). Two further groups of five non-nephrectomized animals also received 20% casein paste either alone (Gp 3) or supplemented with DPC (Gp 4). In a further experiment, systolic blood pressure was compared at 1 and 4 weeks after nephrectomy in eight DPC-treated remnants and eight untreated controls. RESULTS Gp 2 developed significantly less proteinuria than Gp 1 (41 +/- 9 vs 142 +/- 33 mg/24 h at 6 weeks, P < 0.005; 136 +/- 36 vs 282 +/- 59 mg/24 h at 12 weeks, P < 0.05). At sacrifice after 12 weeks, glomerular filtration rates were higher (1.34 +/- 0.08 vs 1.07 +/- 0.1 ml/min, P < 0.05), kidney total collagen content was lower (14.9 +/- 1.5 vs 26.9 +/- 5.4 mg/kidney, P < 0.05) and glomerular abnormalities, interstitial fibrosis and lymphocytic infiltration were less marked in Gp 2 compared with Gp 1. DPC had no effect on protein excretion, total kidney collagen or GFR in non-nephrectomized rats, and did not influence the early rise in blood pressure seen after two-thirds nephrectomy. CONCLUSIONS These findings demonstrate that DPC reduces renal injury in the remnant kidney, and raise the possibility of a therapeutic role for DPC in the treatment of patients with chronic renal failure.

Monte Carlo based radiation transport modelling is a useful tool in evaluating the interaction and effect of radiation in a defined environment. The process of simulating Compton scattering is of interest in a large number of different fields. Of the range of available Monte Carlo radiation transport programs, Geant4, one of the most popular, integrated the effects of Doppler broadening into their standard low energy Compton scattering package in 2008. However, there still exists a significant limitation within this standard Compton scattering package regarding the algorithms that determine the emission direction of Compton electrons. Here we outline the development of the Monash University Low Energy Compton Scattering (MULECS) package. The package addresses the current limitation of Compton electron directionality of Geant4 through the inclusion of additional directional information of the pre-collision momentum. MULECS is intended to replace the standard Compton scattering package of Geant4 to improve the accuracy of emission imaging simulations below 2 MeV.

Compton reconstruction requires the computationally intensive, yet highly parallelizable, task of Cone of Response (CoR) back-projection. The acceleration of CoR back-projection is of significant importance as a faster algorithm allows the user to increase either the size or resolution of the imaging volume. Such acceleration also lends itself to the realization of real-time reconstruction. The image estimate is formed by calculating and histogramming voxel-cone intersections in the imaging volume. As the level of computation increases with the cube of the length or resolution of the volume, the bottle-neck in processing the dataset is at the imaging-voxel level, as opposed to the event level. The reconstruction algorithm developed for the Pixelated Emission Detector for RadiOisotopes (PEDRO) system was optimized for threading at the voxel level and implemented in the C++ programming language. The benchmark C++ code was then extended with OpenCL to assess the acceleration that could be obtained by running the algorithm on a selection of commercially available Graphical Processing Units (GPUs). Increases of up to 102 times the bench-mark speed were achieved

The Pixelated Emission Detector for RadiOisotopes (PEDRO) is a hybrid imaging system designed for the measurement of single photon emission from small animal models. The proof-of-principle device consists of a Compton-camera situated behind a mechanical collimator and is intended to provide optimal detection characteristics over a broad spectral range, from 30 keV to 511 keV. An automated routine has been developed for the optimization of the mechanical collimator which consists of pinholes and open slits. The optimization was tested with a Geant4 model of the experimental prototype. The data were blurred with the expected position and energy resolution parameters and a Bayesian interaction ordering algorithm was applied. The results show that the optimization technique allows the large-area slits to sample fully the primary field of view (FoV). The slits were found to provide truncation of the back-projected cones of response and also an increase in the success rate of the interaction ordering algorithm. These factors resulted in an increase in the contrast and signal-to-noise ratios of the reconstructed image estimates.

Insulin resistance is a major cause of muscle wasting in patients with ESRD. Uremic metabolic acidosis impairs insulin signaling, which normally suppresses proteolysis. The low pH may inhibit the SNAT2 l-Glutamine (L-Gln) transporter, which controls protein synthesis via amino acid–dependent insulin signaling through mammalian target of rapamycin (mTOR). Whether SNAT2 also regulates signaling to pathways that control proteolysis is unknown. In this study, inhibition of SNAT2 with the selective competitive substrate methylaminoisobutyrate or metabolic acidosis (pH 7.1) depleted intracellular L-Gln and stimulated proteolysis in cultured L6 myotubes. At pH 7.1, inhibition of the proteasome led to greater depletion of L-Gln, indicating that amino acids liberated by proteolysis sustain L-Gln levels when SNAT2 is inhibited by acidosis. Acidosis shifted the dose-response curve for suppression of proteolysis by insulin to the right, confirming that acid increases proteolysis by inducing insulin resistance. Blocking mTOR or phosphatidylinositol-3-kinase (PI3K) increased proteolysis, indicating that both signaling pathways are involved in its regulation. When both mTOR and PI3K were inhibited, methylaminoisobutyrate or acidosis did not stimulate proteolysis further. Moreover, partial silencing of SNAT2 expression in myotubes and myoblasts with small interfering RNA stimulated proteolysis and impaired insulin signaling through PI3K. In conclusion, SNAT2 not only regulates mTOR but also regulates proteolysis through PI3K and provides a link among acidosis, insulin resistance, and protein wasting in skeletal muscle cells. There is now strong evidence that, even in patients without diabetes, insulin resistance in ESRD is a major cause of muscle wasting1,2 with its attendant morbidity and increased risk for mortality. An important contributor to this clinically serious problem is uremic metabolic acidosis,3 suggesting that low pH has a significant impact on insulin signaling in uremic muscle. The SNAT2 amino acid transporter in the plasma membrane of mammalian cells is strongly inhibited by low extracellular pH.4 We previously showed, using cultured skeletal muscle cells (L6 myotubes), that inhibition of SNAT2 rapidly depletes intracellular amino acids and thereby strongly impairs insulin signaling to protein synthesis through mammalian target of rapamycin (mTOR), which is a key sensor of amino acid availability.5 Although this provides a plausible explanation for the inhibition of muscle protein synthesis that occurs during acute metabolic acidosis in humans,6 the response of muscle to chronic uremic metabolic acidosis in renal patients usually involves increased proteolysis.7,8 A possible rationale for this chronic proteolysis is that it is an adaptation to the initial amino acid depletion, whereby amino acids are harvested from muscle protein to restore intracellular amino acid levels,9 thereby minimizing impairment of protein synthesis but at the expense of chronically elevated proteolysis. The stimulation of proteolysis by low pH in L6 myotubes has been attributed to a defect in insulin signaling through insulin receptor substrate 1 (IRS-1)-associated phosphatidylinositol-3-kinase (PI3K), leading to impaired activation of protein kinase B (PKB),10 and a similar defect has been demonstrated in acidotic and uremic rat skeletal muscle in vivo.11 Unlike mTOR signaling, type I PI3K signaling to PKB is not traditionally regarded as an amino acid–sensitive pathway, suggesting that inhibition of SNAT2 by acidosis is not responsible for this effect; however, a type III PI3K has been implicated in amino acid sensing by mTOR.12 There is also evidence from amino acid–starved L6 myotubes that extracellular amino acid concentration is sensed through SNAT2, which acts as a signaling protein in its own right—a so-called “transceptor”13 that signals to SNAT2 gene expression.13 This signal is blunted by inhibitors of PI3K,13 suggesting that coupling exists between SNAT2 and this enzyme. It is not known, however, whether such coupling influences PI3K signaling to PKB and proteolysis. The aims of this study were, first, to determine whether the effect of metabolic acidosis or SNAT2 inhibition on amino acid levels in L6 myotubes shows an adaptive response consistent with compensatory harvesting of amino acids by proteolysis; second, to determine whether metabolic acidosis or SNAT2 inhibition in the presence of insulin activates proteolysis by signaling through mTOR or PI3K; and, third, to determine whether coupling between SNAT2 and PI3K/PKB signaling is detectable when the activity or expression of SNAT2 is impaired

Wasting of lean tissue as a consequence of metabolic acidosis is a serious problem in patients with chronic renal failure. A possible contributor is inhibition by low pH of the System A (SNAT2) transporter, which carries the amino acid L-glutamine (L-Gln) into muscle cells. The aim of this study was to determine the effect of selective SNAT2 inhibition on intracellular amino acid profiles and amino acid-dependent signaling through mammalian target of rapamycin in L6 skeletal muscle cells. Inhibition of SNAT2 with the selective competitive substrate methylaminoisobutyrate, metabolic acidosis (pH 7.1), or silencing SNAT2 expression with small interfering RNA all depleted intracellular L-Gln. SNAT2 inhibition also indirectly depleted other amino acids whose intracellular concentrations are maintained by the L-Gln gradient across the plasma membrane, notably the anabolic amino acid L-leucine. Consequently, SNAT2 inhibition strongly impaired signaling through mammalian target of rapamycin to ribosomal protein S6 kinase, ribosomal protein S6, and 4E-BP1, leading to impairment of protein synthesis comparable with that induced by rapamycin. It is concluded that even though SNAT2 is only one of several L-Gln transporters in muscle, it may determine intracellular anabolic amino acid levels, regulating the amino acid signaling that affects protein mass, nucleotide/nucleic acid metabolism, and cell growth.

Metabolic acidosis, a common feature of uremia, has a well documented wasting effect on skeletal muscle. In contrast, the effect of metabolic acidosis on adipose tissue is unknown. Serum levels of the adipocyte hormone leptin have been shown to be lower in acidotic uremic rats when compared with uremic controls. This study investigated the effect of acidosis on leptin protein secretion and leptin gene expression. This was studied in vitro by means of 3T3-L1 cultured adipocytes. Leptin secretion was decreased at an acid pH of 7.1 compared with a control pH of 7.5 (1277 versus 1950 pg/well/48 h, P0.05). In contrast, acidosis did not affect leptin mRNA content. Glucose transport was reduced by 39% at pH 7.1 at 24 h, which was comparable in magnitude with the inhibition of leptin secretion at the same pH. The glucose transport inhibitors cytochalasin B (0.5 to 50 micro M) and phloretin (0.05 to 0.25 mM) mimicked the effect of acidosis and reduced leptin secretion in a dose-dependent fashion (P0.02). Dose-response curves for the inhibition of glucose uptake showed that decreasing glucose transport to the same extent as with acid was sufficient to drive down leptin secretion, independently of changes of leptin mRNA. Acid decreases leptin secretion from 3T3-L1 adipocytes through a post-transcriptional mechanism via changes in glucose transport. This starvation-like response may be physiologically important in conditions such as uremia to prevent excessive energy expenditure.

Background. Proteinuric renal disease is associated with accumulation of tubulointerstitial matrix proteins. Human proximal tubular cells (PTCs) produce fibronectin in response to serum proteins but not albumin alone. It has been suggested that renal toxicity of filtered albumin depends on its lipid moiety. We therefore investigated the functional consequences of different fatty acids (FAs) carried on human albumin after exposure to human PTCs in culture. Methods. Confluent human PTCs were exposed to recombinant human serum albumin (rHSA) or palmitate (P)-, stearate (S)-, oleate (O)-, and linoleate (L)-complexed rHSA. In all experimental conditions, test media contained 1 mg'ml rHSA alone or carrying 100 mmol FAs. Mitogenic response was assessed by [ 3 H]thymidine incorporation. Cell culture supernatants were assayed for fibronectin. Protein kinase C (PKC) activity was assessed in cell lysates. Results. Apical exposure to rHSA alone or the O-rHSA complex stimulated a significant increase in [ 3 H]thymidine incorporation, whereas the L-rHSA complex was markedly inhibitory to human PTC growth. The L-rHSA complex was associated with severe cytotoxicity as assessed by lactate dehydrogenase release. Among all conditions, O-rHSA was the only test media that significantly increased fibronectin levels over control conditions (150.1 ± 10.6% over control, P

In severe chronic renal failure (CRF) with associated metabolic acidosis, abnormalities in protein metabolism and amino acid (AA) profiles in the fed state are well described. To evaluate the effect of early uraemia and the influence of acid-base status on protein metabolism and AA profiles, three groups of pair-fed rats were studied: group I - rats with 1+ 1/2 nephrectomy; group II - rats with 1+ 1/2 nephrectomy receiving NaHCO3 supplementation, and group III - sham-operated rats with NaHCO3 supplementation. After 4 weeks, serum creatinine values were similar in groups I and II (111 +/- 5 and 119 +/- 4 mumol/l) and higher than in group III (51 +/- 5 mumol/l, p0.0001); HCO-3 was reduced only in group I (22.4 +/- 0.8 mmol/l) compared to group II (28.3 +/- 0.6 mmol/l, p0.001) and group III (28.2 +/- 1.3 mmol/l, p0.001). In the uraemic animals (groups I and II) arterial AA profiles showed increased levels of phenylalanine, glycine, glutamate, proline and alanine. The marked increase of threonine in group I was corrected by NaHCO3 supplementation in group II. The total nonessential AA were higher both in group I (1,832 +/- 53 mumol/l, p0.05) and group II (1,788 +/- 103 mumol/l, p0.05) than in group III (1,542 +/- 54 mumol/l). These results are similar to those described in the fed state of uraemic patients. Intracellular AA changes were detected, especially in group II namely increased glycine and a decrease in threonine and serine levels. No signs of malnutrition or changes in alkali-soluble protein (ASP) or ASP/DNA ratio in liver and muscle were observed. These results show that AA abnormalities in the fed state occur early in the course of CRF, and that the marked increase of threonine is corrected by NaHCO3 supplementation. These data suggest that either an impaired utilization of the ingested proteins might occur before the appearance of major alterations in endogenous protein metabolism or acid-base status might alter AA metabolic rate per se.