Optimization and impact of sensitivity mode on abbreviated scan protocols with population-based input function for parametric imaging of [18F]-FDG for a long axial FOV PET scanner

BACKGROUND

The long axial field of view, combined with the high sensitivity of the Biograph Vision Quadra PET/CT scanner enables the precise deviation of an image derived input function (IDIF) required for parametric imaging. Traditionally, this requires an hour-long dynamic PET scan for [18F]-FDG, which can be significantly reduced by using a population-based input function (PBIF). In this study, we expand these examinations and include the scanner's ultra-high sensitivity (UHS) mode in comparison to the high sensitivity (HS) mode and evaluate the potential for further shortening of the scan time.

METHODS

Patlak Ki and DV estimates were determined by the indirect and direct Patlak methods using dynamic [18F]-FDG data of 6 oncological patients with 26 lesions (0-65 min p.i.). Both sensitivity modes for different number/duration of PET data frames were compared, together with the potential of using abbreviated scan durations of 20, 15 and 10 min by using a PBIF. The differences in parametric images and tumour-to-background ratio (TBR) due to the shorter scans using the PBIF method and between the sensitivity modes were assessed.

RESULTS

A difference of 3.4 ± 7.0% (Ki) and 1.2 ± 2.6% (DV) was found between both sensitivity modes using indirect Patlak and the full IDIF (0-65 min). For the abbreviated protocols and indirect Patlak, the UHS mode resulted in a lower bias and higher precision, e.g., 45-65 min p.i. 3.8 ± 4.4% (UHS) and 6.4 ± 8.9% (HS), allowing shorter scan protocols, e.g. 50-65 min p.i. 4.4 ± 11.2% (UHS) instead of 7.3 ± 20.0% (HS). The variation of Ki and DV estimates for both Patlak methods was comparable, e.g., UHS mode 3.8 ± 4.4% and 2.7 ± 3.4% (Ki) and 14.4 ± 2.7% and 18.1 ± 7.5% (DV) for indirect and direct Patlak, respectively. Only a minor impact of the number of Patlak frames was observed for both sensitivity modes and Patlak methods. The TBR obtained with direct Patlak and PBIF was not affected by the sensitivity mode, was higher than that derived from the SUV image (6.2 ± 3.1) and degraded from 20.2 ± 12.0 (20 min) to 10.6 ± 5.4 (15 min). Ki and DV estimate images showed good agreement (UHS mode, RC: 6.9 ± 2.3% (Ki), 0.1 ± 3.1% (DV), peak signal-to-noise ratio (PSNR): 64.5 ± 3.3 dB (Ki), 61.2 ± 10.6 dB (DV)) even for abbreviated scan protocols of 50-65 min p.i.

CONCLUSIONS

Both sensitivity modes provide comparable results for the full 65 min dynamic scans and abbreviated scans using the direct Patlak reconstruction method, with good Ki and DV estimates for 15 min short scans. For the indirect Patlak approach the UHS mode improved the Ki estimates for the abbreviated scans.

Spin-Orbit and Zeeman Effects on the Electronic Properties of Single Quantum Rings: Applied Magnetic Field and Topological Defects

Within the framework of effective mass theory, we investigate the effects of spin-orbit interaction (SOI) and Zeeman splitting on the electronic properties of an electron confined in GaAs single quantum rings. Energies and envelope wavefunctions in the system are determined by solving the Schrödinger equation via the finite element method. First, we consider an inversely quadratic model potential to describe electron confining profiles in a single quantum ring. The study also analyzes the influence of applied electric and magnetic fields. Solutions for eigenstates are then used to evaluate the linear inter-state light absorption coefficient through the corresponding resonant transition energies and electric dipole matrix moment elements, assuming circular polarization for the incident radiation. Results show that both SOI effects and Zeeman splitting reduce the absorption intensity for the considered transitions compared to the case when these interactions are absent. In addition, the magnitude and position of the resonant peaks have non-monotonic behavior with external magnetic fields. Secondly, we investigate the electronic and optical properties of the electron confined in the quantum ring with a topological defect in the structure; the results show that the crossings in the energy curves as a function of the magnetic field are eliminated, and, therefore, an improvement in transition energies occurs. In addition, the dipole matrix moments present a non-oscillatory behavior compared to the case when a topological defect is not considered.

A deep neural network for parametric image reconstruction on a large axial field-of-view PET

PURPOSE

The PET scanners with long axial field of view (AFOV) having ~ 20 times higher sensitivity than conventional scanners provide new opportunities for enhanced parametric imaging but suffer from the dramatically increased volume and complexity of dynamic data. This study reconstructed a high-quality direct Patlak Ki image from five-frame sinograms without input function by a deep learning framework based on DeepPET to explore the potential of artificial intelligence reducing the acquisition time and the dependence of input function in parametric imaging.

METHODS

This study was implemented on a large AFOV PET/CT scanner (Biograph Vision Quadra) and twenty patients were recruited with ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) dynamic scans. During training and testing of the proposed deep learning framework, the last five-frame (25 min, 40-65 min post-injection) sinograms were set as input and the reconstructed Patlak Ki images by a nested EM algorithm on the vendor were set as ground truth. To evaluate the image quality of predicted Ki images, mean square error (MSE), peak signal-to-noise ratio (PSNR), and structural similarity index measure (SSIM) were calculated. Meanwhile, a linear regression process was applied between predicted and true Ki means on avid malignant lesions and tumor volume of interests (VOIs).

RESULTS

In the testing phase, the proposed method achieved excellent MSE of less than 0.03%, high SSIM, and PSNR of ~ 0.98 and ~ 38 dB, respectively. Moreover, there was a high correlation (DeepPET: [Formula: see text]= 0.73, self-attention DeepPET: [Formula: see text]=0.82) between predicted Ki and traditionally reconstructed Patlak Ki means over eleven lesions.

CONCLUSIONS

The results show that the deep learning-based method produced high-quality parametric images from small frames of projection data without input function. It has much potential to address the dilemma of the long scan time and dependency on input function that still hamper the clinical translation of dynamic PET.

Comparison of preoperative anxiety, bruxism, and postoperative pain among patients undergoing surgery for septoplasty, endoscopic sinus surgery, and tympanoplasty

BACKGROUND

Septoplasty, endoscopic sinus surgery, and tympanoplasty are the most commonly performed elective functional ear-nose-throat surgeries. Aim: This study investigated the relationship between preoperative anxiety, bruxism, and postoperative pain in inpatient groups undergoing three different functional otorhinolaryngologic surgeries. Patients and.

METHODS

This study was conducted in a single center of a tertiary referral hospital. The patients (n = 90) who had undergone septoplasty (group A), endoscopic sinus surgery (group B), and tympanoplasty (group C) were included. The State-Trait Anxiety Inventory (STAI) questionnaire and the Amsterdam Preoperative Anxiety Information Scale (APAIS) were administered. To evaluate bruxism, a self-questionnaire was administered, and for the evaluation of pain, the visual analogue scale (VAS) was administered.

RESULTS

In group C, preoperative STAI and APAIS and early and late pain values were higher than in the other groups. When patients were divided into two groups according to the presence of bruxism. A significant difference was found between the preoperative STAI and immediate and late VAS values (P < 0.001). A strong correlation was observed between APAIS and early and late VAS values in group C (P < 0.001).

CONCLUSION

Patients who will undergo tympanoplasty should be aware of the preoperative anxiety level and pain follow-up. Bruxism can be considered a vital follow-up parameter that manifests due to high preoperative anxiety. It may also be useful to examine preoperative bruxism and take appropriate measures due to its pain-increasing effect in patients.

The level of anxiety in pregnant women in COVID-19 pandemic: a cross-sectional study

OBJECTIVE

We aimed to determine the COVID-19 anxiety level in pregnant women who presented to an outpatient clinic during the COVID-19 pandemic.

PATIENTS AND METHODS

This is a descriptive cross-sectional study including 203 of 310 pregnant women who presented to the outpatient clinic of a training and research hospital of the Ministry of Health between 29 September-1 October, 2020. The level of anxiety was assessed with the COVID-19 Anxiety Inventory (CAS) using a face-to-face survey method.

RESULTS

The mean age of the patients was 28.15±5.95 years. In the study, while 6.2% of women over 30 years old was identified to have psychological problems, 0.7% of those under 30 years old had such problems. The rate of diagnosis of COVID-19 in the family/acquaintances of those with an educational level of high school or higher was 56.9%, and those who had an educational level under high school had a corresponding rate of 39.5%. The rate of COVID-19 diagnosis in the family/acquaintances of those with an educational level of high school or higher was significantly higher (p<0.05). The mean COVID-19 anxiety scale score was 0.18±0.47; COVID-19 anxiety was not observed in pregnant women.

CONCLUSIONS

This study detected no anxiety in pregnant women. Therefore, it can be said that pregnant women do not need immediate psycho-social support.

A novel technique in septal perforation: Fascia lata and costal cartilage sandwich graft

Background

Nasal septum perforation (NSP) is an anatomical defect of the mucosa, cartilage/bone of nasal septum and septoplasty is the most common cause of it. A perforated septum rarely heals on its own, it is more likely to get worse. The success for large perforations is approximately 78%, it is harder to be successful in vertically larger perforations. We introduce a new technique to close large perforations by the fascia lata and costal cartilage sandwich graft (FLSG). The main advantage of this technique is that the fascia lata eliminates the opening between the septal mucosal flaps in case the septal mucosal flaps may not meet each other.

Patients and Methods

16 cases presenting with nasal septum perforation were repaired with the FLSG technique. Grafts were harvested, the perforation was accessed through open rhinoplasty approach, FLSG is inserted and sutured.

Results

16 cases consisting of 9 males (56.25%) and 7 females (43.75%) were operated. The age range was between 20 and 43 years (mean 32.6 ± 6.94). 3 cases (18.75%) had medium and 13 cases (81.25%) had large NSP. 8 cases (50%) were smokers. Nine month postoperatively, all medium NSP were closed. During this period, 14 NSP (87.5%) medium size NSP achieved complete closure, while the remaining two NSP that were yet to close had large defects (>2 cm) and smokers.

Conclusion

FLSG is an effective, easy, and novel technique in NSP repair and the postoperative controls have proven a high success rate even in large NSP.

Optical characterization of laser-driven double Morse quantum wells

In this study, the first-order linear, third-order nonlinear, and total absorption coefficients for the intersubband transition between the two lower-lying electronic levels in both symmetric and asymmetric double Morse quantum wells under the non-resonant high-frequency intense laser field are investigated. The study takes into account the effects of the structure parameters. The results show that the electronic and also accordingly optical properties of the structures which we focus on can be adjustable to obtain a convenient response to certain studies or purposes by changing the applied external field and optical intensity as well as structure parameters.

Sertraline inhibits the transport of PAT1 substrates in vivo and in vitro

BACKGROUND AND PURPOSE

Intestinal nutrient transporters may mediate the uptake of drugs. The aim of this study was to investigate whether sertraline interacts with the intestinal proton-coupled amino acid transporter 1 PAT1 (SLC36A1).

EXPERIMENTAL APPROACH

In vitro investigations of interactions between sertraline and human (h)PAT1, hSGLT1 (sodium-glucose linked transporter 1) and hPepT1 (proton-coupled di-/tri-peptide transporter 1) were conducted in Caco-2 cells using radiolabelled substrates. In vivo pharmacokinetic investigations were conducted in male Sprague-Dawley rats using gaboxadol (10 mg·kg(-1), p.o.) as a PAT1 substrate and sertraline (0-30.6 mg·kg(-1)). Gaboxadol was quantified by hydrophilic interaction chromatography followed by MS/MS detection.

KEY RESULTS

Sertraline inhibited hPAT1-mediated L-[(3)H]-Pro uptake in Caco-2 cells. This interaction between sertraline and PAT1 appeared to be non-competitive. The uptake of the hSGLT1 substrate [(14)C]-α-methyl-D-glycopyranoside and the hPepT1 substrate [(14)C]-Gly-Sar in Caco-2 cells was also decreased in the presence of 0.3 mM sertraline. In rats, the administration of sertraline (0.1-10 mM, corresponding to 0.3-30.6 mg·kg(-1), p.o.) significantly reduced the maximal gaboxadol plasma concentration and AUC after its administration p.o.

CONCLUSIONS AND IMPLICATIONS

Sertraline is an apparent non-competitive inhibitor of hPAT1-mediated transport in vitro. This inhibitory effect of sertraline is not specific to hPAT1 as substrate transport via hPepT1 and hSGLT1 was also reduced in the presence of sertraline. In vivo, sertraline reduced the amount of gaboxadol absorbed, suggesting that the inhibitory effect of sertraline on PAT1 occurs both in vitro and in vivo. Hence, sertraline could alter the bioavailability of drugs absorbed via PAT1.

Active myofascial trigger points might be more frequent in patients with cervical radiculopathy

BACKGROUND

Myofascial trigger points (MTrPs) are commonly observed in the neck, parascapular region, and upper back muscles of patients with cervical pathology.

AIM

To assess the frequency of latent and active myofascial trigger point (aMTrP) in the neck and upper back muscles in patients with cervical radiculopathy and healthy subjects.

DESIGN

Controlled clinical trials.

SETTING

Outpatients and controls.

POPULATION

Two hundred and forty four patients and 122 controls

METHODS

The patients clinically diagnosed as cervical radiculopathy with positive Spurling's test and confirmed by MRI, were enrolled in this study. All subjects were examined for active and latent MTrP. In patients with cervical radiculopathy, an aMTrP was distinguished from a latent one when the referred pain elicited by exploration of the MTrP is recognized as familiar.

RESULTS

The patients comprised of 128 female (52.5%) and 116 male (47.5%) patients. Mean age was 44.58(20-65 years). In 125 (51.2%) of patients with cervical radiculopathy were found an aMTrP at least one muscle from upper trapezius, multifidus, splenius capitis, levator scapulae, rhomboid major, minor and deep paraspinal muscles. Number and distribution of MTrPs in patients with 244 cervical radiculopathy and in healthy controls. aMTrPs were detected most common in levator scapula (16.3%), splenius capitis (14.7%), rhomboid minor (14.3%), upper part of trapezius (13.5%), rhomboid major (10.2%) and multifidus (8.6%) muscles. Patients with cervical radiculopathy showed latent MTrP in levator scapula (27%), splenius capitis (16.8%), rhomboid minor (24.6%), upper part of trapezius (33.2%), rhomboid major (9%) and multifidus (8.2%) muscles. There was significant difference in terms of distribution of active and latent MTrPs in patients with cervical radiculopathy (P=0.019). Number of latent MTrPs in upper trapezius muscles in patients with cervical radiculopathy was more than the expected distribution. None of the subjects of control group had aMTrP. However, healthy controls showed latent MTrP in levator scapula (33.6%), splenius capitis (16.4%), rhomboid minor (21.3%), upper part of trapezius (40.2%), rhomboid major (6.5%) and multifidus (17.2%) muscles. There was no significant difference in terms of distribution of latent MTrPs between cervical radiculopathy and control groups (P=0.249). The frequency of aMTrP was found to be significantly higher in CDH with median localization as compared to posterolateral herniations (P=0.041). After conservative treatment for two weeks, number of patients with active MTrP in cervical radiculopathy were decreased about 50%.

CONCLUSION

Cervical root compression would be considered as the starting or maintaining factor of aMTrP.

CLINICAL REHABILITATION IMPACT

The treatment of cervical radiculopathy might be facilitated the improving in aMTrPs located in aforementioned muscles.

Electrical properties of a novel 1,3-bis-(p-iminobenzoic acid) indane Langmuir-Blodgett films containing ZnS nanoparticles

ZnS nanoparticles have been formed in a newly synthesized 1,3-bis-(p-iminobenzoic acid) indane (IBI) by exposing Zn2+ doped multilayered Langmuir-Blodgett (LB) film to H2S gas after the growth. The formation of ZnS nanoparticles in the LB film structure was verified by measuring UV-Visible absorption spectra. DC electrical measurements were carried out for thin films of IBI prepared in a metal/LB films/metal sandwich structure with and without ZnS nanoparticles. It was observed that ZnS nanoparticles in the LB films cause a blue-shift in the absorption spectra as well as a decrease in both capacitance and conductivity values. By analysing I-V curves and assuming a Schottky conduction mechanism the barrier height was found to be about 1.13 eV and 1.21 eV for IBI LB films without and with ZnS nanoparticles, respectively. It is thought that the presence of ZnS nanoparticles influences the barrier height at the metal-organic film interface and causes a change in electrical conduction properties of LB films.

Breathing noise elimination in through-water speech communication between divers

Breathing noise and bubble noise are the main factors affecting the subjective quality of through-water speech signals in communications between divers wearing full-face masks or aural-nasal masks. Only breathing noise is considered here, which can be gated out by applying a combination of zero-crossing detection and energy measurements to noisy speech signals above predetermined threshold values. The signals are picked up by a microphone placed close to the diver's mouth in the air cavity of the mask. Results were obtained during diving trials with four different types of masks.

Sex determination from the ribs of contemporary Turks

There have been several in-depth studies showing that the sternal extremity of the fourth rib can be used in estimating age as well as in determining sex, as illustrated in North American whites and blacks. Yet biological differences between populations may preclude the cross-application of standards. To test this hypothesis and develop a sex determination standard for the Turkish population, a sample of the sternal ends of the fourth rib was collected from 294 individuals autopsied in Istanbul, Turkey. Dimensions from the superior edge to the inferior one (SI) and the anterior edge to its posterior edge (AP) were measured with a caliper. The sample was divided into three age groups, "young," "old," and "total." Using discriminant function analysis, three formulae were developed, one for each group. The results indicated that SI height is the most dimorphic dimension and that both dimensions together can given an accuracy of 86% to 90%. To reach such an accuracy, the age of the unknown should be estimated, at least whether it is phase 4 or above or below, using the age standards for ribs developed by Işcan and associates. When cross-validation tests are carried out, incorrect formulae reduce accuracy by as much as 20%. Furthermore, it was observed that North American based white sex determination formulae assign many Turkish males into a female category. In conclusion, it is important to note that population and age specificity are essential in determining sex from the rib. Yet its accuracy is as good as, if not better than, many bones of the postcranial skeleton.

Analysis of plasma lipids by NMR spectroscopy: application to modifications induced by malignant tumors

Lipid extracts of plasma were studied by 31P and 1H NMR spectroscopy at 9.4 T. Signals recorded on lipid mixtures were assigned to different lipid classes using a data base built with two-dimensional 1H COSY spectra of seven standard lipids. Signals unique to glycerophospholipids, sphingolipids, and triacylglycerols were identified. 31P and 1H NMR spectroscopy was used to study qualitative and quantitative modifications induced in plasma by malignant tumors. The results show a significant increase in triglyceride/phospholipid ratio and a concomitant decrease of total phospholipids in patients with cancer. In order to check for the possible presence of particular lipids such as glycolipids in these patients, 1H COSY spectra were recorded on the intact plasma and on extracts of plasma lipids in patients with cancer and in healthy subjects. Only in one case of ovarian cancer, a cross-peak at 1.35 and 4.15 ppm, corresponding to fucose residue in glycolipids, was detected.

Lumbar spinal stenosis: clinical/radiologic therapeutic evaluation in 145 patients. Conservative treatment or surgical intervention?

In this prospective study, 145 patients with lumbar spinal stenosis were evaluated for clinical signs and radiologic findings and conservative treatment results. Clinical parameters such as pain on motion, lumbar range of motion, straight leg raising test, deep tendon reflexes, dermatomal sensations, motor functions and neurogenic claudication distances were assessed at admission and were compared after a conservative treatment program was completed. A conservative treatment program consisted of physical therapy (infrared heating, ultrasonic diathermy and active lumbar exercises) and salmon calcitonin. Pain on motion (100%), restriction of extension (77%), limited straight leg raising test (23%), neurogenic claudication (100%), dermatomal sensory impairment (47%), motor deficit (29%), and reflex deficit (40%) were observed in the patients. All aforementioned disturbances except reflex deficits improved by the conservative treatment and results were statistically significant. The authors conclude that this conservative treatment should be the treatment of choice in elderly patients and in those patients without clinical surgical indications.

Differences in lipid characteristics of undifferentiated and enterocytic-differentiated HT29 human colonic cells

In this paper we compared several lipid characteristics of the homogenate and the corresponding plasma membrane in undifferentiated and differentiated HT29 human colon cancer cells, using normal human colonic cells as a reference. Electron microscopy showed that HT29 cells were morphologically undifferentiated when cultured in the presence of either glucose or inosine without glucose at early confluency. On the contrary, HT29 cells cultured at late confluency in a glucose-free medium containing inosine or grown in nude mice exhibited an enterocytic differentiation with the presence of tight junctions and an apical brush border. The cell homogenate and the plasma membrane were prepared from each cell type. The study of specific marker enzymes showed the same degree of purity in all plasma membranes, with a highly marked increase of brush border-associated hydrolases (N-aminopeptidase and alkaline phosphatase) only in the organelles isolated from differentiated HT29 and colonic cells. Respective similar increases in the amount of free cholesterol and phospholipid and in the free cholesterol:phospholipid molar ratio were found in the plasma membrane as compared with the homogenate in all HT29 cell types. This ratio, due to an increased phospholipid content in both homogenate and plasma membrane, was lowered in colonic cells. No differences in the phospholipid profile were found between the homogenates of all cell types and the plasma membrane of undifferentiated HT29 cells, with the exception of a decrease of cardiolipin in this organelle. On the contrary, the plasma membrane phospholipid composition was different from that of the corresponding homogenate in differentiated HT29 and colonic cells. The most striking changes were a highly increased sphingomyelin amount and concomitant decreases in phosphatidylethanolamine, phosphatidylserine, and cardiolipin. Moreover, differences in the percentage of phosphatidylcholine plus sphingomyelin as well as in phosphatidylcholine:sphingomyelin, phosphatidylethanolamine, and/or phosphatidylcholine molar ratios were also found. The monounsaturated:polyunsaturated fatty acid ratio in phosphatidylethanolamine was similar in differentiated HT29 and colonic cells and lower than in undifferentiated HT29 cells. A decrease in this latter ratio in phosphatidylcholine was also observed in colonic cells and HT29 cells grown in nude mice. These changes were essentially due to opposite variations in the percentage of palmitoleic acid and those of linoleic and/or arachidonic acids in both phospholipids. Thus, these data indicate that undifferentiated HT29 cells were characterized by the absence of a specific phospholipid composition in their plasma membrane, which is suggested to be related to altered phospholipid sorting. The plasma membrane phospholipid profile reversed essentially to the normal pattern when HT29 cells recovered the ability to differentiate.

Computed tomographic investigation of the effect of traction on lumbar disc herniations

The aim of this study was to evaluate the effect of static horizontal traction on disc herniations by computed tomographic investigation. Changes occurring under the effect of a traction load of 45 kg have been evaluated in 30 patients with lumbar disc herniation. The herniated nuclear material (HNM) has retracted in 11 (78.5%) of median, six (66.6%) of posterolateral, and four (57.1%) of lateral herniations. Clinical response of these cases to conservative treatment varied with the amount and location of HNM, the retraction of HNM, and calcification of protruded disc. Static lumbar traction showed variable effects on lumbar disc herniations, especially in relation with the amount and location of HNM.

Differences in lipid characteristics of autologous human melanoma cell lines with distinct biological properties

Significant differences in lipid composition were found when six established human melanoma cell lines were compared. A pair of cell lines was initiated from a superficial spreading melanoma and the lymph node of the same patient; four others were also autologous, three of which originated from the same nodular melanoma and the other from its metastasis. Cell lines varied in pigmentation level and ability to grow in nude mice. Cell lines contained similar amounts of total cholesterol, glycerides, and phospholipids but different amounts of free cholesterol and cholesterol esters. In particular, the molar ratio of free cholesterol to phospholipid was increased in highly tumorigenic cell lines. No changes in phospholipid profiles were noted among cell lines, except an increase in sphingomyelin with a concomitant decrease in phosphatidylcholine in one cell line compared to the profiles of its counterpart cell line. The saturated-to-unsaturated fatty acid ratios in phosphatidylcholine and phosphatidylethanolamine were similar in all cell lines, but the monounsaturated-to-polyunsaturated fatty acid ratio in phosphatidylcholine was increased in highly tumorigenic cell lines. A significant variation in the latter ratio in phosphatidylethanolamine was also observed in the pair of autologous cell lines. These changes were unrelated to a depletion in linoleic acid in culture medium. Results obtained by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene were consistent with the differences in lipid composition between two autologous cell lines. The present results indicate that two lipid characteristics were significantly changed in highly tumorigenic cell lines as compared to cell lines with low tumorigenicity, but no correlation was found between either pigmentation level or origin (primary or metastatic) and lipid composition.

Modification of HT 29 cell response to the vasoactive intestinal peptide (VIP) by membrane fluidization

We used liposomes made with phospholipids of fatty acid chain length ranging from C12:0 to C16:0 to modify the cAMP dependent protein kinase (PK) activity of HT 29 cells induced by VIP or forskolin. Both VIP and forskolin effects were inhibited in dilauroylphosphatidylcholine (DLPC) treated cells. PK activity was slightly lowered when cells were treated by dimyristoylphosphatidylcholine (DMPC) liposomes. However neither VIP nor forskolin-induced PK activities were affected with dipalmitoylphosphatidylcholine (DPPC) liposomes. Furthermore, the binding of [125I]VIP to DLPC treated cells was drastically lowered whereas no change was observed when cells were incubated with DMPC or DPPC liposomes. On the other hand, the interaction of HT 29 cells with DLPC vesicles provoked a decrease in membrane cholesterol content with subsequent increase in membrane fluidity. These findings provide evidence that, in HT 29 cells, the mechanisms of VIP-receptor interaction and of adenylate cyclase activation is lipid dependent and is regulated by membrane fluidity.

[Effect of the addition of hog pancreatic colipase on the permeability to glucose and the phase transition of phosphatidyl choline liposomes]

An interaction between porcine pancreatic coli-pase and lecithin liposomes is demonstrated by gel filtration assays. The extent of the colipase penetration into the phospholipid bilayer was assessed by permeability and calorimetry studies carried out on the liposome colipase complex. The addition of colipase to liposomes induces a three fold increase in the permeability to [6-H3] glucose. This result reflects a perturbation in the bilayer which may be the consequence of the colipase interaction. The phase transition temperature is not modified by the added colipase. This observation suggests that the perturbation brought by the protein does not affect the acyl chain packing of the bulk lipid. On the other hand the enthalpy of transition (delta H) is decreased from 8.9 to 7.8 kcal/mole by the addition of colipase to the lipid. This could be explained by the interaction of the colipase with neighbouring acyl chains which do not participate in the cooperative melting of the bulk lipid. In agreement with previous spectrophotometric observations, the present results are indicative of hydrophobic interactions between colipase and bilayer hydrocarbon chains.

Inhibition of pancreatic lipase by mixed micelles of diethyl p-nitrophenyl phosphate and bile salts

Solubility and Sephadex filtration assays have shown that dissolved diethyl p-nitrophenyl phosphate can be included into bile salt micelles with a partition coefficient of 32 : 1. This inclusion is probably a prerequisite for the organophosphate to inhibit lipase. The essential role played by colipase confirms that the primary step in the inhibition is an interaction of lipase with bile salt containing micelles. Therefore, it appears that the requirements of lipase towards specific substrates and inhibitors are very similar. The inhibition rate strongly depends on the total bile salt concentration and on the micellar concentration of the organophosphate. This effect may be explained, at least qualitatively, by a competition between simple and mixed micelles for the binding of colipase and lipase.

On the formation of a ternary complex between lipase, colipase and micelles of amphipathic compounds

Pancreatic lipase, colipase and 1-glyceryl octyl ether or lysolecithin micelles were shown to form a ternary complex probably resulting from the fixation of the enzyme to the binary colipase-micelle association already well documented in the case of bile salt micelles. Kinetic assays show that the colipase favours the lipase activity on tributyrin emulsions in presence of 1-glyceryl octyl ether. The UV spectrum of a derivative of lipase in which two 2-hydroxy 5-nitrobenzyl groups are attached to tryptophan, is distinctly modified by addition of 1-glyceryl octyl ether micelles in the presence of colipase.

Interactions of colipase with bile salt micelles. 2. Study by dialysis and spectrophotometry

The finding reported in the preceding paper that colipase is able to bind one sodium taurodeoxycholate micelle per molecule was confirmed by dialysis and spectrophotometry. Dialysis in the presence of labelled sodium taurodeoxycholate provided a direct qualitative proof of taurodeoxycholate binding to colipase. This binding was found to occur only above the critical micelle concentration. But, dialysis did not give any information about the composition of the associations, because equilibrium was not attained at the end of the assays. Addition of sodium taurodeoxycholate above the critical micelle concentration was also observed to induce a strong perturbation of the ultraviolet spectrum of one or several of the three tyrosines of colipase. The variation of the perturbation as a function of sodium taurodeoxycholate concentration was consistent with the binding of a single micelle to colipase. The dissociation constant calculated in "micelle molarity" was approximately 1 X 10(-4) M. The colipase-bile salt micelle association can fix one molecule of lipase to form a ternary complex which represents an interesting model of a protein-protein interaction mediated by an organized lipid structure. The ternary complex is probably also a model for lipase-substrate interactions in the presence of an amphipath.