Utility of 99mTc-Sestamibi Heart/Liver Uptake Ratio in Screening Nonalcoholic Fatty Liver Disease During Myocardial Perfusion Imaging

Purpose: Nonalcoholic fatty liver disease (NAFLD) is the most common chronic hepatic disease worldwide, with functional impairment of the mitochondria occurring from early stages. Technetium-99m methoxy-isobutyl-isonitrile (99mTc-MIBI) is a lipophilic agent trapped in the mitochondria. This study aims to evaluate the utility of 99mTc-MIBI heart/liver uptake ratio in screening for NAFLD during myocardial perfusion imaging (MPI). Methods: Seventy eligible patients underwent a 2-d rest/stress 99mTc-MIBI scan with a 2-min planar image acquired in rest phase, at 30, 60, and 120 min postradiotracer administration. Heart/liver uptake ratio was calculated by placing identical regions of interest on the heart and liver dome. All patients underwent liver ultrasound and were allocated into groups A, having NAFLD; and B, healthy individuals without NAFLD. Results: Mean count per pixel heart/liver ratios gradually increased over time in either group; nonetheless the values were significantly higher in group A, regardless of acquisition timing; with the p-value equal to 0.007, 0.014, and 0.010 at 30, 60, and 120 min, respectively. Conclusion: Determining 99mTc-MIBI heart/liver uptake ratio during rest phase in patients undergoing MPI may be a useful, noninvasive screening method for NAFLD; with no additional cost, radiation burden, or adverse effects in these patients. Trial registration number: IR.SBMU.MSP.REC.1398.308.

Comparison of accuracy in calculation of absorbed dose to the kidneys following radioligand therapy with 177Lu-DKFZ-PSMA-617 by two different background correction methods

Background:

To improve the accuracy of activity image quality, scatter correction is a critical method. The aim of this study is to compare the accuracy in calculation of absorbed dose to patients following radioligand therapy (RLT) with ¹⁷⁷Lu-DKFZ-PSMA-617 by two different methods of background correction in the conjugate view method.

Materials and Methods:

This study involved 10 patients. The individualized patient dosimetry calculations were based on whole-body planar scintigraphy images acquired in 10 patients with a mean age of 71.4 ± 6.07 years (range 63–85 years) at approximately 0–2 h, 4–6 h, 18–24 h, and 36–48 h after administration of the mean 6253 ± 826.4 MBq (range 5500–7400 MBq) of ¹⁷⁷Lu-DKFZ-PSMA-617. Organ activities were calculated using the conjugate view method by Buijs and conventional background correction. Eventually, the absorbed dose of radiation was calculated using Medical Internal Radiation Dose formalism.

Results:

The dose per unit of injected activity (mGy/MBq) ± standard deviation for kidney using Buijs and conventional methods was 1.05 ± 0.11 and 0.63 ± 0.14, respectively.

Conclusion:

The Buijs background correction method was more accurate than the conventional method.

Radiation Dose to Medical Staff in 177Lu-PSMA-DKFZ-617 therapy And Estimation of Annual Dose

Radioligand therapy applications for metastatic castration-resistant prostate cancer have been continuously rising in most nuclear medicine departments in Iran, but to our knowledge, no one has studied the doses of staff who perform treatment procedures. The current study aimed to determine the external radiation dose received by the staff of patients treated with ¹⁷⁷Lu- prostate-specific membrane antigen therapy with and without a lead shield. This study used a dose ionization chamber to measure dose rates to the staff at various distances from patients and determined the average time spent by staff at these distances using an ionization chamber. Deep-dose equivalent to staff was obtained. The measured deep-dose equivalent to staff per patient was whitening the range of 1.8 to 5.2 mSv using a lead shield and 3.3 to 8.1 mSv without a lead shield. This study showed that a 2-mm lead shield markedly reduced the external dose to staff.It was indicated that the skill, accuracy, and speed of action of staff can directly affect their received dose.

Patient-Specific Dosimetry in Radioligand Therapy (RLT) for Metastatic Prostate Cancer Using 177Lu-DKFZ-PSMA-617

Purpose

¹⁷⁷Lu-DKFZ-PSMA-617 is a promising treatment for patients with metastatic prostate cancer. Specific dosimetry for each patient is an important factor in planning the patient's treatment process. This study aimed to perform an image-based absorbed dose calculation for the treatment of metastatic prostate cancer with ¹⁷⁷Lu-DKFZ-PSMA-617.

Methods

The individualized patient dosimetry calculations were based on whole-body planar scintigraphy images acquired in 10 patients with a mean age of 71.4 ± 6.07 years (range 63-85 years) at approximately 0-2 h, 4-6 h, 18-24 h, and 36-48 h after administration of the mean 6253 ± 826.4 MBq (range 5500-7400 MBq) of ¹⁷⁷Lu-DKFZ-PSMA-617. Time-activity curves were generated for various organs. For count conversion to activities, calibration factors were calculated. Finally, the absorbed dose for an individual cycle was calculated using IDIAC-DOSE 2.1 software.

Results

On average, the calculated absorbed dose for the kidneys and salivary glands were 0.46 ± 0.09 mGy/MBq and 0.62 ± 0.07 mGy/MBq, respectively.

Conclusions

Based on the results, the¹⁷⁷Lu-PSMA-617 therapy is a safe method for the treatment of castration-resistant prostate cancer patients. Large inter-individual variations in organ dose were found, demonstrating the need for patient-specific dosimetry and treatment planning.

Somatostatin-receptor avidity of pancreatic neuroendocrine tumor thrombus in porto-caval venous systems on 99mTc-Octreotide and posttherapeutic 177Lu-DOTA-TATE scans

A 62-year-old woman with a history of abdominal pain presented with multiple hepatic lesions and dilatation of portal, splenic and superior mesenteric veins on the magnetic resonance imaging referred for a ^99mTc-octreotide scan. Accordingly, similar octreotide-avid lesions were found as well as an uptake in the epigastric region conforming to the anatomy of the portocaval venous system, compatible with a tumor thrombosis. Then, the patient underwent two cycles of therapy with ¹⁷⁷Lu-DOTA-TATE, on that the same appearance was observed. The uptake in the tumor thrombus remained somewhat unchanged, but clinically, a significant improvement of the intractable ascites was achieved.

Assessing the prevalence and predicting factors of an abnormal gated myocardial perfusion SPECT in asymptomatic patients with type 2 diabetes

Considering the significant prevalence of silent myocardial ischemia and its related morbidity and mortality in asymptomatic type 2 diabetic patients, it is not well known whether early screening with MPI is cost-effective and predicting factors are not well elucidated. This was a cross-sectional study including 63 asymptomatic patients with type 2 diabetes mellitus (T2DM), with normal ECG and ejection fraction. Patients with any history of documented valvular, congestive or ischemic heart disease, renal or hepatic failure were excluded. At first all patients were interviewed and checked for risk factors and then patients underwent a two-day rest/stress 99mTc-MIBI gated MPI SPECT. Data was assessed by QPS/QGS and 4DM software and evaluated by a nuclear medicine specialist with summed stress score (SSS) of more than 4 defined as CAD. There were 42 females (67%) and 21 males (33%), with a mean age of 61.33 ± 6.98 years and 7.97 ± 4.86 years history of T2DM. CAD was detected in 26 (41.3%) patients and was significantly associated with male gender, smoking and requiring insulin therapy (P-value = 0.019, 0.046, 0.05, respectively). A significant association was found between the duration of diabetes, especially when > 15 years, and the probability of having CAD. Multivariable logistic regression revealed that smoking; male gender and diabetes duration were the strongest independent predictors of abnormal MPI results. We found a high (46%) prevalence of abnormal stress MPI SPECT in patients with type 2 diabetes mellitus, despite being asymptomatic. Asymptomatic patients with a history of smoking, long duration of diabetes, being under insulin treatment and male gender might benefit from MPI for early detection of silent ischemia.

Efficacy and safety of 177Lutetium-prostate-specific membrane antigen therapy in metastatic castration-resistant prostate cancer patients: First experience in West Asia - A prospective study

Prostate-specific membrane antigen (PSMA) is a transmembrane protein that is highly expressed on the surface of prostate cancer (PC) cells, making it an excellent radiotracer for both therapeutic and diagnostic purposes. In this prospective study, we investigated the efficacy and toxicity of ¹⁷⁷Lutetium (Lu)-PSMA in metastatic castration-resistant PC (mCRPC) patients for the establishment and approval of this therapy in Iran. Fourteen mCRPC patients (mean age 70.57 ± 7.3 years) were treated with a single dose of ¹⁷⁷Lu-PSMA. Complete blood count, liver function tests (aspartate aminotransferase and alanine aminotransferase), alkaline phosphatase levels, renal function tests (urea and creatinine), and prostate-specific antigen (PSA) levels were obtained for the patients at baseline and every 2 weeks. A majority of the patients (11 patients, 64.2%) experienced a decline in their PSA levels; in 5 (45.4%) of these patients, the PSA levels declined > 50%.The severity of pain decreased in 8 (57.1%) patients, and performance status was improved in 5 (45.4%) patients. The treatment was well tolerated, and no severe hematological or nonhematological side effects were observed. Our findings show that ¹⁷⁷Lu-PSMA had a high efficacy and a low toxicity in an Iranian population and is a promising treatment option for PC patients.

An update on radiation absorbed dose to patients from diagnostic nuclear medicine procedures in Tehran: A study on four academic centers

Purpose:

Use of radiopharmaceuticals for diagnostic nuclear medicine procedures is one of the main sources of radiation exposure. We performed this study with respect to the rapid growth in nuclear medicine in Iran and lack of updated statistics.

Materials and Methods:

The data were obtained for all active Nuclear Medicine Centers affiliated to Shahid Beheshti University of Medical Sciences during 2009 and 2010.

Results:

The most frequently performed procedures were bone (30.16%), cardiac (28.96%), renal (17.97%), and thyroid (7.93%) scans. There was a significant decrease in the number of thyroid scintigraphies with ¹³¹I and ^99mTc-sulfur colloid liver/spleen scans and tremendous increase in the frequencies of cardiac and bone scintigraphies compared to one decade ago.

Conclusion:

Compared to previous studies, there were striking changes in trends of diagnostic nuclear medicine procedures in Tehran. This field is still evolving in the country, and this trend will further change with the introduction of positron emission tomography scanners in future.

Uptake Difference by Somatostatin Receptors in a Patient with Neuroendocrine Tumor: 99mTc-Octreotide Uptake in the Lung without Uptake in Liver Lesions

The diagnostic value of somatostatin receptor scintigraphy (SRS) in detecting tumors has been assessed in a number of studies. We present a 30-year-old female with a history of eight months cough and left shoulder pain. Radiologic evaluation showed pulmonary mass and hepatic lesions, which were pathologically diagnosed as neuroendocrine carcinoma. 99mTc-octreotide scan demonstrated that the pulmonary lesion was positive for somatostatin receptor (SSTR), while the liver metastases were SSTR negative. The present case highlights the significance of a differential uptake pattern by somatostatin receptors in SRS in patients with neuroendocrine tumors.

Diagnostic Efficacy of UBI Scan in Musculoskeletal Infections

BACKGROUND

Limited recent studies have demonstrated that 99mTc-UBI scan can be a helpful method in precise diagnosis of infection. In the current study, we aimed to investigate the diagnostic efficacy of 99mTc-UBI scan in detection of musculoskeletal infections.

METHODS

Fifty patients with suspected musculoskeletal infections (painful THA, TKA, implant and nonunion) were enrolled in this study. After injection of 99mTc-Ubiquicidin 29-41, up to 30 minutes, dynamic imaging was performed every 1 minute. Whole body anterior and posterior images were acquired at 60 and 120 min (5 min/frame). A polygonal region of interest (ROI) was drawn manually around the area of increased accumulation of tracer (lesion) and anatomically similar area on the contralateral side (background) and the lesion to background ratio (LBR) was calculated. Then, patients underwent surgical procedures to assess infection by tissue sampling and histopathologic studies as gold standard. The receiver operating characteristics (ROC) analysis was performed to find a cut-off value for LBR and determining the diagnostic efficacy of UBI scan in musculoskeletal infections.

RESULTS

Histopathologic studies revealed infection in 38 patients. The mean LBR was significantly higher in infected patients (2.05 ± 0.41 vs. 1.52 ± 0.22; P < 0.001). ROC analysis showed that a cut-off point of 1.74 for LBR will have 94.7% sensitivity, 83.3% specificity and 92% accuracy for diagnosis of musculoskeletal infections.

CONCLUSION

UBI scan is a useful diagnostic tool for evaluation of patients with suspected musculoskeletal infection. However, UBI imaging has some limitations which result in some incorrect diagnoses. It is important to interpret the results of the scan with regard to the clinical findings.

Abnormal focal 99mTc-DMSA uptake in the lung--report of two cases

Extrarenal uptake of 99mTc-DMSA is a rare finding, which has been described in some unusual conditions as bone metastasis, aortic aneurysm and hemangioma. The purpose of this report is to present two cases of abnormal 99mTc-DMSA uptake in the lungs, which remained unexplained even after radiologic assessment.

Value of sentinel lymph node biopsy in breast cancer surgery with simple pathology facilities--an Iranian local experience with a review of potential causes of false negative results

INTRODUCTION

Sentinel lymph node biopsy (SLNB) is a precise procedure for lymphatic staging in early breast cancer. In a valid SLNB procedure, axillary lymph node dissection (ALND) can be omitted in node- negative cases without compromising patient safety. In this study, detection rate, accuracy and false negative rate of SLNB for breast cancer was evaluated in a setting with simple modified conventional pathology facilities without any serial sectioning or immunohistochemistry.

MATERIAL AND METHOD

Patients with confirmed breast cancer were enrolled in the study. SLNB and ALND were performed in all cases. Lymph node metastasis was evaluated in SLN and in nodes removed by ALND to determine the false negative rate. Pathologic assessment was carried out only by modified conventional technique with only 3 sections. Detection rate was determined either by lymphoscintigraphy or during surgery.

RESULTS

78 patients with 79 breast units were evaluated. SLN was detected in 75 of 79 cases (95%) in lymphoscintigraphy and 76 of 79 cases (96%) during surgery. SLN metastases was detected in 30 of 75 (40%) cases either in SLNB and ALND groups. Accuracy of SLNB method for detecting LN metastases was 92%. False negative rate was 3 of 30 of positive cases: 10%. In 7 of 10 cases with axillary lymphadenopathy, LN metastastates was detected.

CONCLUSION

SLNB is recommended for patients with various tumor sizes without palpable lymph nodes. In modified conventional pathologic examination of SLNs, at least macrometastases and some micrometastases could be detected similar to ALND. Consequently, ALND could be omitted in node-negative cases with removal of all palpable LNs. We conclude that SLNB, as one of the most important developments in breast cancer surgery, could be expanded even in areas without sophisticated pathology facilities.

Short-term effectiveness of radiochemoembolization for selected hepatic metastases with a combination protocol

AIM: To introduce the combination method of radiochemoembolization for the treatment of selected hepatic metastases.

METHODS: Twenty patients with biopsy proven hepatic metastases were selected from those who underwent transarterial radiochemoembolization, a novel combination protocol, between January 2009 and July 2010. Patients had different sources of liver metastasis. The treatment included transarterial administration of three chemotherapeutic drugs (mitomycin, doxorubicin and cisplatin), followed by embolization with large (50-150 μm) radioisotope particles of chromic 32P. Multiphasic computer tomography or computer tomography studies, with and without contrast medium injections, were performed for all patients for a short-term period before and after the treatment sessions. The short-term effectiveness of this procedure was evaluated by modified response evaluation criteria in solid tumors (mRECIST), which also takes necrosis into account. The subjective percentage of necrosis was also assessed. The response evaluation methods were based on the changes in size, number, and the enhancement patterns of the lesions between the pre- and post-treatment imaging studies.

RESULTS: Patients had liver metastasis from colorectal carcinomas, breast cancer, lung cancer and carcinoid tumors. The response rate based on the mRECIST criteria was 5% for complete response, 60% for partial response, 10% for stable disease, and 25% for progressive disease. Regarding the subjective necrosis percentage, 5% of patients had complete response, 50% had partial response, 25% had stable disease, and 20% had progressive disease. Based on traditional RECIST criteria, 3 patients (15%) had partial response, 13 patients (65%) had stable disease, and 4 patients (20%) had disease progression. In most patients, colorectal carcinoma was the source of metastasis (13 patients). Based on the mRECIST criteria, 8 out of these 13 patients had partial responses, while one remained stable, and 5 showed progressive disease. We also had 5 cases of breast cancer metastasis which mostly remained stable (4 cases), with only one partial response after the procedure. Six patients had bilobar involvement; three of them received two courses of radiochemoembolization. The follow up imaging study of these patients was performed after the second session. In the studied patients there was no evidence of extrahepatic occurrence, including pulmonary radioactive deposition, which was proven by Bremsstrahlung scintigraphy performed after the treatment sessions. For the short-term follow-ups for the 2 mo after the therapy, no treatment related death was reported. The mostly common side effect was post-embolization syndrome, presented as vomiting, abdominal pain, and fever. Nineteen (95%) patients experienced this syndrome in different severities. Two patient had ascites (with pleural effusion in one patient) not related to hepatic failure. Moreover, no cases of acute liver failure, hepatic infarction, hepatic abscess, biliary necrosis, tumor rupture, surgical cholecystitis, or non-targeted gut embolization were reported. Systemic toxicities such as alopecia, marrow suppression, renal toxicity, or cardiac failure did not occur in our study group.

CONCLUSION: Radiochemoembolization is safe and effective for selected hepatic metastases in a short-term follow-up. Further studies are required to show the long-term effects and possible complications of this approach.

Automatic left ventricle segmentation in volumetric SPECT data set by variational level set

INTRODUCTION

Left ventricle (LV) quantification in nuclear medicine images is a challenging task for myocardial perfusion scintigraphy. A hybrid method for left ventricle myocardial border extraction in SPECT datasets was developed and tested to automate LV ventriculography.

METHODS

Automatic segmentation of the LV in volumetric SPECT data was implemented using a variational level set algorithm. The method consists of two steps: (1) initialization and (2) segmentation. Initially, we estimate the initial closed curves in SPECT images using adaptive thresholding and morphological operations. Next, we employ the initial closed curves to estimate the final contour by variational level set. The performance of the proposed approach was evaluated by comparing manually obtained boundaries with automated segmentation contours in 10 SPECT data sets obtained from adult patients. Segmented images by proposed methods were visually compared with manually outlined contours and the performance was evaluated using ROC analysis.

RESULTS

The proposed method and a traditional level set method were compared by computing the sensitivity and specificity of ventricular outlines as well as ROC analysis. The results show that the proposed method can effectively segment LV regions with a sensitivity and specificity of 88.9 and 96.8%, respectively. Experimental results demonstrate the effectiveness and reasonable robustness of the automatic method.

CONCLUSION

A new variational level set technique was able to automatically trace the LV contour in cardiac SPECT data sets, based on the characteristics of the overall region of LV images. Smooth and accurate LV contours were extracted using this new method, reducing the influence of nearby interfering structures including a hypertrophied right ventricle, hepatic or intestinal activity, and pulmonary or intramammary activity.

Differential phosphorylation of IRS-1 by insulin and insulin-like growth factor I receptors in Chinese hamster ovary cells

Insulin receptor (IR) and insulin-like growth factor I receptor (IGF-IR) are closely related receptor tyrosine kinases. Despite their high degree of homology, recent evidence suggests that the two receptors have distinct biological roles. In several recent studies, the cytoplasmic tyrosine kinase domains of the two receptors have been shown to possess different signalling specificities. In this study, we examine the hypothesis that differential phosphorylation of insulin receptor substrate 1 (IRS-1) may contribute to these differences in signalling between the two receptors. Using Chinese hamster ovary (CHO) cells stably expressing human IR or IGF-IR and activated by their respective ligands, we show that there are differences between the two receptors with regard to the complement of SH2-containing proteins recruited to IRS-1. In particular, IGF-IR appears to couple IRS-1 preferentially to Grb2 whereas, in contrast, IR appears to couple IRS-1 preferentially to the p85 subunit of phosphatidyl inositol 3-kinase (PI3-kinase) and to Nck. The two receptors couple IRS-1 equally to the tyrosine phosphatase SHP2. We have also generated phosphospecific antibodies to three important tyrosine phosphorylation sites on IRS-1 (pY608, pY895 and pY1172). We used these antibodies to probe the phosphorylation status of these sites in intact CHO/IR and CHO/IGF-IR cells. In the case of pY608, these results also show evidence for differential phosphorylation of IRS-1 by the two receptors. Taken together, the results presented here support the notion that the cytoplasmic domains of IR and IGF-IR have differences in their intrinsic signalling potentials.

Dach1 mutant mice bear no gross abnormalities in eye, limb, and brain development and exhibit postnatal lethality

Drosophila dachshund is necessary and sufficient for compound eye development and is required for normal leg and brain development. A mouse homologue of dachshund, Dach1, is expressed in the developing retina and limbs, suggesting functional conservation of this gene. We have generated a loss-of-function mutation in Dach1 that results in the abrogation of the wild-type RNA and protein expression pattern in embryos. Homozygous mutants survive to birth but exhibit postnatal lethality associated with a failure to suckle, cyanosis, and respiratory distress. The heart, lungs, kidneys, liver, and skeleton were examined to identify factors involved in postnatal lethality, but these organs appeared to be normal. In addition, blood chemistry tests failed to reveal differences that might explain the lethal phenotype. Gross examination and histological analyses of newborn eyes, limbs, and brains revealed no detectable abnormalities. Since Dach1 mutants die shortly after birth, it remains possible that Dach1 is required for postnatal development of these structures. Alternatively, an additional Dach homologue may functionally compensate for Dach1 loss of function.

The substrate specificity of the catalytic domain of Abl plays an important role in directing phosphorylation of the adaptor protein Crk

c-Abl preferentially phosphorylates peptide substrates that contain proline at the P+3 site (relative to the phosphorylated tyrosine). We previously described a mutant form of the Abl catalytic domain (Y569W) with altered substrate specificity at the P+3 position, as measured using synthetic peptides. In this study, we examine the phosphorylation of Crk, a protein substrate of Abl that is phosphorylated in the sequence Tyr221-Ala-Gln-Pro. In vitro, phosphorylation of Crk by Y569W Abl is greatly reduced relative to wild-type Abl. Overexpression of Y569W mutant Abl in 293T kidney cells produces a similar overall pattern of tyrosine phosphorylation as wild-type Abl, indicating that not all cellular proteins depend on Pro at P+3 for Abl recognition. However, phosphorylation of Crk by Y569W Abl in these cells is markedly reduced relative to wild-type Abl. A truncated form of Abl lacking the C-terminal polyproline region is not able to phosphorylate Crk in these assay conditions. Thus, proper phosphorylation of Crk by Abl depends not only on the interaction of the Crk SH3 domain with the Abl polyproline region, but also on the recognition of amino acids surrounding tyrosine by the Abl catalytic domain.

Improving SH3 domain ligand selectivity using a non-natural scaffold

BACKGROUND

Src homology 3 (SH3) domains bind sequences bearing the consensus motif PxxP (where P is proline and x is any amino acid), wherein domain specificity is mediated largely by sequences flanking the PxxP core. This specificity is limited, however, as most SH3 domains show high ligand cross-reactivity. We have recently shown that diverse N-substituted residues (peptoids) can replace the prolines in the PxxP motif, yielding a new source of ligand specificity.

RESULTS

We have tested the effects of combining multiple peptoid substitutions with specific flanking sequences on ligand affinity and specificity. We show that by varying these different elements, a ligand can be selectively tuned to target a single SH3 domain in a test set. In addition, we show that by making multiple peptoid substitutions, high-affinity ligands can be generated that completely lack the canonical PxxP motif. The resulting ligands can potently disrupt natural SH3-mediated interactions.

CONCLUSIONS

Peptide-peptoid hybrid scaffolds yield SH3 ligands with markedly improved domain selectivity, overcoming one of the principal challenges in designing inhibitors against these domains. These compounds represent important leads in the search for orthogonal inhibitors of SH3 domains, and can serve as tools for the dissection of complex signaling pathways.

Dachshund and eyes absent proteins form a complex and function synergistically to induce ectopic eye development in Drosophila

The eyeless, dachshund, and eyes absent genes encode conserved, nuclear proteins that are essential for eye development in Drosophila. Misexpression of eyeless or dachshund is also sufficient to induce the formation of ectopic compound eyes. Here we show that the dachshund and eyes absent genes act synergistically to induce ectopic retinal development and positively regulate the expression of each other. Moreover, we show that the Dachshund and Eyes Absent proteins can physically interact through conserved domains, suggesting a molecular basis for the genetic synergy observed and that a similar complex may function in mammals. We propose that a conserved regulatory network, rather than a linear hierarchy, controls retinal specification and involves multiple protein complexes that function during distinct steps of eye development.

Src family-selective tyrosine kinase inhibitor, PP1, inhibits both Fc epsilonRI- and Thy-1-mediated activation of rat basophilic leukemia cells

Cross-linking of the surface receptor with high affinity for IgE (Fc epsilonRI) by multivalent antigen/immunoglobulin E complexes, as well as aggregation of Thy-1 glycoprotein by monoclonal antibodies lead in rat basophilic leukemia cells, clone RBL-2H3, to tyrosine phosphorylation of several cellular proteins, followed by a release of secretory components. To investigate the molecular mechanisms of Fc epsilonRI- and Thy-1-mediated transmembrane signaling and to map a step at which they converge into a common secretory pathway, we used a novel Src family-selective tyrosine kinase inhibitor, 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP1), and analyzed its inhibitory activity on cell activation. Here we show that in RBL-2H3 cells PP1 demonstrates substrate specificity for a Src family kinase Lyn. In immunocomplex kinase assays in vitro, PP1 inhibited the Lyn kinase activity at nanomolar levels without any effect on Syk kinase activity. However, in RBL cells activated via aggregation of Fc epsilonRI, phosphorylation of both Syk and Lyn kinases was inhibited. Fc epsilonRI- and Thy-1-mediated early (protein-tyrosine phosphorylation) and late (release of beta-hexosaminidase) activation events were similarly affected by PP1. The inhibition was specific for membrane receptor-mediated signaling and was not observed in cells activated by an exposure to pervanadate. The combined data suggest that activation of Lyn is the early activation step at which the Fc epsilonRI- and Thy-1-mediated activation pathways of mast cells and basophils may converge.

Direct interaction of Syk and Lyn protein tyrosine kinases in rat basophilic leukemia cells activated via type I Fc epsilon receptors

Activation of rat mast cells through the receptor with high affinity for IgE (Fc epsilonRI) requires a complex set of interactions involving transmembrane subunits of the Fc epsilonRI and two classes of nonreceptor protein tyrosine kinase (PTK). the Src family PTK p53/p56(lyn) (Lyn) and the Syk/ZAP-family PTK p72(syk) (Syk). Early activation events involve increased activity of Lyn and Syk kinases and their translocation into membrane domains containing aggregated Fc epsilonRI, but the molecular mechanisms responsible for these changes have remained largely unclear. To determine the role of Fc epsilonRI subunits in this process, we have analyzed Syk- and Lyn-associated proteins in activated rat basophilic leukemia (RBL) cells and their variants deficient in the expression of Fc epsilonRI beta or gamma subunits. Sepharose 4B gel chromatography of postnuclear supernatants from Nonidet-P40-solubilized antigen (Ag)- or pervanadate-activated RBL cells revealed extensive changes in the size of complexes formed by Lyn and Syk kinases and other cellular components. A fusion protein containing Src homology 2 (SH2) and SH3 domains of Lyn bound Syk from lysates of nonactivated RBL cells; an increased binding was observed when lysates from Ag- or pervanadate-activated cells were used. A similar amount of Syk was bound when lysates from pervanadate-activated variant cells deficient in the expression of Fc epsilonRI beta or gamma subunits were used, suggesting that Fc epsilonRI does not function as the only intermediate in the formation of the Syk-Lyn complexes. Further experiments have indicated that Syk-Lyn interactions occur in Ag-activated RBL cells under in vivo conditions and that these interactions could involve direct binding of the Lyn SH2 domain with phosphorylated tyrosine of Syk. The physical association of Lyn and Syk during mast-like cell activation supports the recently proposed functional cooperation of these two tyrosine kinases in Fc epsilonRI signaling.

The functional expression of sodium-dependent bile acid transport in Madin-Darby canine kidney cells transfected with the cDNA for microsomal epoxide hydrolase

Previous studies have suggested that the enzyme microsomal epoxide hydrolase (mEH) is able to mediate sodium-dependent transport of bile acids such as taurocholate into hepatocytes (von Dippe, P., Amoui, M., Alves, C., and Levy, D.(1993) Am. J. Physiol. 264, G528-G534). In order to characterize directly the putative transport properties of the enzyme, a pCB6 vector containing the cDNA for this protein (pCB6-mEH) was transfected into Madin-Darby canine kidney (MDCK) cells, and stable transformants were isolated that could express mEH at levels comparable with the levels expressed in hepatocytes. Sodium-dependent transport of taurocholate was shown to be dependent on the expression of mEH and to be inhibited by the bile acid transport inhibitor 4,4'-diisothiocyanostilbene-2,2'disulfonic acid (DIDS), as well as by other bile acids. Kinetic analysis of this system indicated a Km of 26.3 microM and a Vmax of 117 pmol/mg protein/min. The Km value is essentially the same as that observed in intact hepatocytes. The transfected MDCK cells also exhibited sodium-dependent transport of cholate at levels 150% of taurocholate in contrast to hepatocytes where cholate transport is only 30% of taurocholate levels, suggesting that total hepatocyte bile acid transport is a function of multiple transport systems with different substrate specificities, where mEH preferentially transports cholate. This hypothesis is further supported by the observation that a monoclonal antibody that partially protects (26%) taurocholate transport from inhibition by DIDS in hepatocytes provides almost complete protection (88%) from DIDS inhibition of hepatocyte cholate transport, suggesting that taurocholate is also taken up by an alternative system not recognized by this antibody. Additional support for this concept is provided by the observation that the taurocholate transport system is almost completely protected (92%) from DIDS inhibition by this antibody in MDCK cells that express mEH as the only bile acid transporter. These results demonstrate that mEH is expressed on the surface of hepatocytes as well as on transfected MDCK cells and is able to mediate sodium-dependent transport of taurocholate and cholate.

Thy-1-mediated activation of rat mast cells: the role of Thy-1 membrane microdomains

The glycosyl-phosphatidylinositol (GPI)-anchored glycoprotein Thy-1 is one of the most abundant molecules expressed on the surface of rat mast cells and rat basophilic leukemia (RBL) cells. The finding that Thy-1 from detergent-solubilized RBL-2H3 cells forms complexes with src-related protein-tyrosine kinase p56/p53lyn suggested that this kinase may play a key role in Thy-1-mediated mast-cell activation. The molecular mechanism of this activation is, however, unknown. Here we show that in RBL-2H3-derived cells extracted by the standard procedure with several non-ionic detergents, the majority of Thy-1 and p56/p53lyn were not released into postnuclear supernatant but remained associated with the detergent-resistant cytoskeletal/nuclear fraction. Pretreatment of the cells with the cholesterol-complexing agents, saponin or digitonin, resulted in complete solubilization of Thy-1 and p56/p53lyn in non-ionic detergents and dissociation of the complexes; this implies that cholesterol plays a crucial role in stabilization of the complexes. This conclusion was supported by double immunofluorescence colocalization experiments which also allowed us to estimate the size of the insoluble complexes to be about 0.1 micron. Sequential treatment with saponin and Nonidet P-40 was used to fractionate tyrosine-phosphorylated proteins during Thy-1-mediated activation of RBL-2H3 cells. Among the soluble cytoplasmic proteins the most dramatic change in tyrosine phosphorylation was found in pp72, whereas pp40 and pp33 were found mainly in the membrane fraction. Our data suggest that surface aggregation of GPI-anchored Thy-1 molecules leads to aggregation of p56/p53lyn kinase located in the same membrane microdomain, followed by transphosphorylation of both soluble and membrane-bound substrates.

Bile acid transport into hepatocyte smooth endoplasmic reticulum vesicles is mediated by microsomal epoxide hydrolase, a membrane protein exhibiting two distinct topological orientations

Bile acids, such as taurocholate, have been shown to be transported into hepatocyte smooth endoplasmic reticulum (SER) vesicles. This process is Na(+)-independent, electrogenic, inhibitable by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid and taurochenodeoxycholate, with a Km of 352 microM and a Vmax of 29.6 nmol/mg protein/min. The observed transport is mediated by the bifunctional protein, microsomal epoxide hydrolase (mEH) which can also mediate bile acid transport into hepatocytes across the sinusoidal plasma membrane (von Dippe, P., Amoui, M., Alves, C., and Levy, D. (1993) Am. J. Physiol. 264, G528-G534). mEH was isolated from SER membranes by immunoprecipitation with monoclonal antibody (mAb) 25D-1 which recognizes this protein on the surface of intact hepatocytes. The SER-derived protein exhibited an apparent molecular weight, isoelectric point, N-terminal amino acid sequence, and mEH-specific activity that were indistinguishable from the plasma membrane form of the enzyme. Proteoliposome reconstitution of the SER taurocholate transport system indicated that mEH was absolutely required for the expression of transport capacity. The interaction of mAb 25D-1 with mEH on intact right-side-out SER vesicles demonstrated that the epitope found on the surface of hepatocytes was also found on the cytoplasmic surface of these vesicles (80%) and in the lumen (20%) suggesting the presence of two forms of this protein in the SER, the latter from being sorted to the cell surface. The existence of two orientations of this protein in the SER was confirmed by the sensitivity to tryptic digestion, where 75% of the mAb epitope was accessible to the enzyme. The loss of the 25D-1 epitope correlated with loss of taurocholate transport capacity. The role of mEH in the transport process and the orientation of the transporting isoform was further established by demonstrating that mAb 25A-3, which also reacts with mEH on the hepatocyte surface, was able to directly inhibit taurocholate transport in the SER vesicle system. These and previous results thus establish that isoforms of mEH can mediate taurocholate transport at the sinusoidal plasma membrane and in SER vesicles and that this bifunctional protein can exist in two orientations in the SER membrane. The association of bile acids with the SER suggests a possible role of intracellular vesicles in the transhepatocellular movement of bile acids from the sinusoidal to the canalicular compartment.

Na(+)-dependent bile acid transport by hepatocytes is mediated by a protein similar to microsomal epoxide hydrolase

A protein mediating hepatocyte sodium-dependent bile acid transport across the sinusoidal plasma membrane has been purified by immunoprecipitation with monoclonal antibody (MAb) 25D-1, which specifically recognizes this protein on the surface of intact hepatocytes (Ananthanarayanan et al. J. Biol. Chem. 263: 8338-8343, 1988). The function of this protein was further established by proteoliposome reconstitution (von Dippe et al. J. Biol. Chem. 265: 14812-14816, 1990). NH2-terminal amino acid sequence analysis and amino acid composition revealed this protein to be closely related to the enzyme microsomal epoxide hydrolase (mEH). Both proteins exhibited the same elution times on a reverse-phase high-pressure liquid chromatography column, comigrated with an apparent molecular weight of 49,000 as measured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and possessed identical isoelectric points of 8.2. The MAb was capable of immunoprecipitating chromatographically purified mEH, as well as a protein derived from the sinusoidal plasma membrane that exhibited mEH activity comparable to that of the protein isolated from the endoplasmic reticulum. The subtilisin fragmentation patterns derived from chromatographically purified mEH and the MAb-precipitated plasma membrane protein were also identical. Hydropathy profile analysis of the amino acid sequence of mEH suggested the presence of four transmembrane domains. The results of these studies indicate that a protein that is involved in mediating sodium-dependent bile acid transport is closely related to mEH.