Impact of rubidium imaging availability on management of patients with acute chest pain

OBJECTIVE

Evaluate the impact of 82-Rubidium positron emission tomography (PET) myocardial perfusion imaging (MPI) availability on patient management presenting at the emergency department (ED) with chest pain (CP).

METHODS

This is a single-center retrospective study of clinical databases. Patients presenting with CP with a non-definitive suspicion of acute coronary syndrome (ACS) at the ED between April 2016 and February 2020 were divided into 2 groups based on PET availability. The proportion of invasive coronary angiography (ICA) without significant coronary artery disease (CAD), length of stay (LoS), and additional downstream testing were evaluated.

RESULTS

There were 21,242 ED visits for CP without definitive ACS: 5,492 when PET is not available and 15,750 when PET is available. When PET is available, proportion of patients undergoing a MPI study was greater (20.7% vs 17.6%, P<0.0001), proportion of ICA without significant CAD was similar (18.5% vs 21.4%, P=0.24), and median ED LoS was shorter (16.6 vs 18.1 hours, P=0.03). Patients undergoing SPECT MPI had significantly more downstream testing (8.9% vs 6.4%, P=0.003) and a higher rate of coronary angiogram without significant CAD (21.2% vs 14.2%, P=0.09) compared to those who underwent PET MPI.

CONCLUSION

Availability of PET MPI was associated with an increased number of MPI referral from the ED, similar rates of ICA without significant CAD, decreased LoS, and fewer downstream testing.

Comparison of 18F-sodium fluoride positron emission tomography imaging and 99mTc-pyrophosphate in cardiac amyloidosis

BACKGROUND

Pyrophosphate (PYP) scintigraphy provides high diagnostic accuracy for the detection of transthyretin (ATTR) cardiac amyloidosis (CA). There has recently been emerging interest in using 18F-sodium fluoride (NaF) for this application, yet its sensitivity has never been directly compared to that of PYP, the current molecular gold standard METHODS: Twelve subjects with ATTR-CA and 5 controls referred for PYP-SPECT were prospectively enrolled. 18F-NaF PET/CT scans were performed at 1 and 3 hours. Qualitative and quantitative analyses of the images were performed, and the sensitivity of 18F-NaF PET/CT and PYP-SPECT were compared RESULTS: Visual interpretation of NaF PET/CT yielded a sensitivity of 0.25 (95% CI 0.089 to 0.53) for the detection of ATTR-CA, which is significantly inferior to that of PYP-SPECT/CT (100%, P = .016). Visual interpretation at 3 hours yielded a similar sensitivity of 0.30 (95% CI 0.11 to 0.60, P  = 1.00). There were no false-positive NaF PET studies. Mean target-to-background ratio (TBRmean) at 1h did not differ significantly (P = .21) in ATTR-CA subjects (0.83 ± 0.15) compared to controls (0.72 ± 0.15). Receiver operating characteristic (ROC) analysis yielded an area under the curve (AUC) of 0.69 ± 0.16 (95% CI 0.37 to 1.00, P = .23).

CONCLUSION

With qualitative and quantitative analyses, sensitivity of NaF PET/CT is significantly inferior to that of PYP-SPECT for the diagnosis of ATTR-CA.

[18F]FDG-PET CT for the evaluation of native valve endocarditis

BACKGROUND

We examined the use of [18F]FDG-PET/CT for the diagnosis of native valve endocarditis (NVE).

METHODS

PET/CT images in patients with suspected NVE were retrospectively reviewed independently by two experienced physicians blinded to all clinical information. The gold standard consisted of surgical findings, when available, or the modified Duke criteria.

RESULTS

Fifty four subjects were included, 31 (57%) with a diagnosis of NVE. [18F]FDG-PET/CT correctly identified 21/31 (67.7%) subjects, yielding a sensitivity and specificity of 68% (95% CI 49-83%) and 100% (95% CI 85-100%), respectively. The sensitivity and specificity of the modified Duke criteria were 48% and 74%, respectively. Positive and negative predictive values of PET were 100% (95% CI 84-100%) and 70% (95% CI 51-84%), respectively. Modifying the Duke criteria to include [18F]FDG-PET positivity as a major criterion increased sensitivity to 77% without affecting specificity and led to the correct reclassification of 8/18 (44.4%) subjects from Possible IE to Definite IE.

CONCLUSION

The addition of a positive [18F]FDG-PET/CT as a major criterion in the modified Duke Criteria improved performance of the criteria for the diagnosis of NVE, particularly in those subjects with Possible IE.

Site qualification and clinical interpretation standards for 99mTc-SPECT perfusion imaging in a multi-center study of MITNEC (Medical Imaging Trials Network of Canada)

BACKGROUND

Qualification and interpretation standards are essential for establishing 99mTc-SPECT MPI accuracy vs. alternative modalities.

METHODS

Rest-stress 99mTc-SPECT phantom scans were acquired on 35 cameras. LV defects were quantified with summed stress (SSS) and difference scores (SDS) at 2 core labs. SDS ≥ 2 in the right coronary artery (RCA) was the qualifying standard. Twenty rest (R)-stress (S) patient images were acquired on qualified cameras and interpreted by core labs. Global scoring differences > 3 between labs or discordant clinical interpretations underwent review. Scoring, interpretation, image quality, and diagnostic parameter agreement were assessed.

RESULTS

Phantom scans: visual scoring confirmed RCA-ischemia on all cameras. Regional SSS, SDS agreement was moderate to very good: ICC-r = 0.57, 0.84. Patient scans: 90% of global SSS, 85% of SDS differences were ≤ 3. Regional SSS, SDS agreement: ICC-r = 0.87, 0.86, and global abnormal (SSS ≥ 4) and ischemic (SDS ≥ 2) interpretation: ICC-r = 0.90 were excellent. Clinical interpretation agreement was 100% following review. Image quality agreement was 70%. Automated metrics also agreed: ischemic total perfusion deficit ICC-r = 0.75, reversible perfusion defect, transient ischemic dilation, and S-R LV ejection fraction ICC-r ≥ 0.90.

CONCLUSION

Quantitative scoring and interpretation of scans were highly repeatable with site qualification and clinical interpretation standardization, indicating that dual-core lab interpretation is appropriate to determine 99mTc-SPECT MPI accuracy.

SPECT imaging of pulmonary vascular disease in bleomycin-induced lung fibrosis using a vascular endothelium tracer

Background

Pulmonary hypertension (PH) complicating idiopathic pulmonary fibrosis (IPF) is associated to worse outcome. There is a great need for a non-invasive diagnostic modality to detect and evaluate the severity of pulmonary vascular disease (PVD). ^99mTc-PulmoBind is a novel imaging agent that binds to the adrenomedullin (AM) receptor on the pulmonary microvascular endothelium. SPECT imaging employing the endothelial cell tracer ^99mTc-PulmoBind was used to assess PVD associated with lung fibrosis.

Methods

Rats with selective right lung bleomycin-induced fibrosis were compared to control rats. SPECT imaging was performed after three weeks with ^99mTc-PulmoBind and ^99mTc-macroaggregates of albumin (MAA). PH and right ventricular (RV) function were assessed by echocardiography. Lung perfusion was evaluated by fluorescent microangiography. Lung AM receptor expression was measured by qPCR and by immunohistology. Relevance to human IPF was explored by measuring AM receptor expression in lung biopsies from IPF patients and healthy controls.

Results

The bleomycin group developed preferential right lung fibrosis with remodeling and reduced perfusion as assessed with fluorescent microangiography. These rats developed PH with RV hypertrophy and dysfunction. ^99mTc-PulmoBind uptake was selectively reduced by 50% in the right lung and associated with reduced AM receptor expression, PH and RV hypertrophy. AM receptor was co-expressed with the endothelial cell protein CD31 in alveolar capillaries, and markedly reduced after bleomycin. Quantitative dynamic analysis of ^99mTc-PulmoBind uptake in comparison to ^99mTc-MAA revealed that the latter distributed only according to flow, with about 60% increased left lung uptake while left lung uptake of ^99mTc-PulmoBind was not affected. Lung from human IPF patients showed important reduction in AM receptor expression closely associated with CD31.

Conclusions

SPECT imaging with ^99mTc-PulmoBind detects PVD and its severity in bleomycin-induced lung fibrosis. Reduced AM receptor expression in human IPF supports further clinical development of this imaging approach.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-021-01836-3.

Examining the sensitivity of 18F-NaF PET for the imaging of cardiac amyloidosis

BACKGROUND

Conventional nuclear imaging with bone-seeking radiopharmaceuticals has been shown to be a sensitive test for the detection of transthyretin cardiac amyloidosis (ATTR); however, to date, few data exist on the utility of 18F-sodium fluoride (NaF) positron emission tomography (PET) in subjects with cardiac amyloidosis (CA).

METHODS

Myocardial perfusion imaging and cardiac 18F-NaF PET/CT of 7 subjects with ATTR, four with light-chain CA (AL), and four controls were retrospectively reviewed. Qualitative interpretation and quantitative analyses with average left ventricular standardized uptake values (SUVmean) and target-to-background ratios (TBRmean) were performed.

RESULTS

Average TBRmean was significantly increased in subjects with ATTR (0.98 ± 0.09) compared to AL (0.85 ± 0.08, P = .026) and CTL (0.82 ± 0.07, P = .020), while SUVmean was not (P = .14). Receiver-operator characteristic (ROC) analysis yielded an area under the curve (AUC) of 0.91, with a sensitivity/specificity of 75%/100% for TBRmean using a cutoff value of 0.89 for the diagnosis of ATTR. Qualitative interpretation resulted in a sensitivity/specificity of 57%/100% for ATTR.

CONCLUSIONS

While 18F-NaF PET/CT demonstrates good diagnostic accuracy for ATTR, particularly when using quantitative analysis, the low TBRmean values observed in ATTR indicate poor myocardial signal. 18F-NaF PET/CT is not yet ready for clinical use in CA until further comparison studies are performed with 99mTc-DPD/PYP.

Comparison of two dipyridamole infusion protocols for myocardial perfusion imaging in subjects with low likelihood of significant obstructive coronary artery disease

BACKGROUND

Myocardial perfusion imaging (MPI) with positron emission tomography allows accurate measurements of myocardial blood flow (MBF). Stress MBF thresholds have been proposed to provide diagnostic and prognostic information in different pathology. Most studies relying on dipyridamole use a 5-minute infusion protocol, while current guidelines recommend a 4-minute infusion. The purpose of this study is to compare the effects of different dipyridamole infusion times on stress MBF.

METHODS

The charts of 2,207 patients who underwent rubidium-82 MPI were retrospectively reviewed and 147 subjects with low likelihood of significant coronary artery disease (CAD) defined as calcium score = 0, body mass index < 45 kg·m-2, and summed stress score ≤ 3 were included. Of those, 65 were imaged with a 4-minute dipyridamole infusion (0.56 mg·kg-1) protocol and 82 with a 5-minute protocol (0.70 mg·kg-1).

RESULTS

Stress MBF (3.23±0.76 vs 3.02±0.71 mL·min-1·g-1, P = 0.09), myocardial flow reserve (2.70±0.67 vs 2.85±0.74, P = 0.20), and coronary vascular resistance index (30±10 vs 31±9 mmHg × g × min·mL-1, P = 0.38) were not significantly different between the two protocols. The 5-minute protocol was associated with higher prevalence of symptoms (92.7% vs 81.5%, P = 0.04) and greater decrease in systolic blood pressure (- 9 vs - 6 mmHg, P = 0.03).

CONCLUSIONS

The 4-minute and 5-minute dipyridamole infusion protocols produce comparable myocardial flow response, hemodynamic changes, and symptoms, in subjects with low likelihood of significant obstructive CAD.

Assessment of left ventricular ejection fraction with cardiofocal collimators: Comparison between IQ-SPECT, planar equilibrium radionuclide angiography, and cardiac magnetic resonance

BACKGROUND

IQ-SPECT has been shown to significantly reduce acquisition time and administered dose while preserving image quality in myocardial perfusion imaging. Whether IQ-SPECT provides accurate left ventricular ejection fractions (LVEF) with gated blood pool SPECT (GBPS) remains unknown.

METHODS

Sixty patients underwent IQ-SPECT GBPS and planar imaging. Among those patients, 11 underwent both cMRI and GBPS. GBPS LVEF, LVEDV, and LVESV were calculated using 2 validated software; QBS (Cedars-Sinai Medical Center, Los Angeles, USA) and MHI (Montreal Heart Institute, Montreal, Canada). LVEF, LVEDV, and LVESV obtained with the different modalities were compared.

RESULTS

Average planar LVEF was 48 ± 11% (mean ± SD), average LVEDV was 177 ± 59 mL (range 63 to 342 mL), and average LVESV was 96 ± 46 mL (range 16 to 234 mL). GBPS LVEF and their correlation coefficient with planar LVEF were 40 ± 12% (r = 0.70) and 44 ± 12% (r = 0.83) with QBS and MHI, respectively. Correlation coefficient between cMRI and planar LVEF was 0.65 and were 0.69 and 0.52 between cMRI and GBPS using QBS and MHI, respectively.

CONCLUSIONS

LVEF calculated with GBPS using IQ-SPECT correlates with planar measurements. Correlation is best using the MHI method and variation is independent of LVEDV.

SPECT and PET imaging of adrenomedullin receptors: a promising strategy for studying pulmonary vascular diseases

Circulating adrenomedullin (AM) levels are elevated in several cardiovascular diseases, including pulmonary vascular diseases causing pulmonary hypertension. To date the perfusion agent ^99mTc-albumin macroaggregates (MAA) is the only approved radiopharmaceutical used for imaging of pulmonary circulation. Unlike ^99mTc-MAA, imaging the AM receptors involves a molecular process dependent on the density of the receptors and the affinity of specific radioligands. The AM receptors are abundantly distributed in lung capillaries and its integrity provides protection in the development of pulmonary vascular diseases. This review summarizes the development and characterization of radioligands for in vivo imaging of AM receptors as an early predictor of the onset of a pulmonary vascular disease.

Utility of FDG-PET/CT for the Detection and Characterization of Sternal Wound Infection Following Sternotomy

Purpose

FDG-PET/CT has the potential to play an important role in the diagnosis of sternal wound infections (SWI). The purpose of this study was to analyze the diagnostic accuracy of FDG-PET/CT for SWI in patients following sternotomy.

Methods

We performed a single-center, retrospective analysis of patients who had undergone median sternotomy and FDG-PET/CT imaging. The gold standard consisted of positive bacterial culture and/or the presence of purulent material at surgery. Qualitative patterns of sternal FDG uptake, SUV_max, and associated CT findings were determined, and an imaging scoring system was developed. The diagnostic performances were studied in both the recent (≤ 6 months between sternotomy and imaging) and remote surgery phase (> 6 months).

Results

A total of 40 subjects were identified with 11 confirmed SWI cases. Consensus interpretation was associated with a sensitivity of 91% and specificity of 97%. Combination of uptake patterns yielded an AUC of 0.96 while use of SUVmax yielded an AUC of 0.82.

Conclusions

Results suggest that FDG-PET/CT may be useful for the diagnosis of SWI with optimal diagnostic accuracy achieved by identifying specific patterns of uptake. SUV_max can be helpful in assessing subjects with remote surgery, but its use is limited in the context of recent surgery. Further studies are required to confirm these results.

Al[18F]F-complexation of DFH17, a NOTA-conjugated adrenomedullin analog, for PET imaging of pulmonary circulation

INTRODUCTION

Adrenomedullin receptors are highly expressed in human alveolar capillaries and provide a molecular target for imaging the integrity of pulmonary microcirculation. In this work, we aimed to develop a NOTA-derivatized adrenomedullin analog (DFH17), radiolabeled with [¹⁸F]AlF, for PET imaging of pulmonary microcirculation.

METHODS

Highly concentrated [¹⁸F](AlF)²⁺ (15 μL) was produced from purified fluorine-18 in NaCl 0.9%. Various complexation experiments were carried out at Al-to-NOTA molar ratios ranging from 1:1 to 1:40 to assess optimal radiolabeling conditions before using the peptide. DFH17 peptide (2 mM, pH 4) was radiolabeled with [¹⁸F](AlF)²⁺ for 15 min at 100 °C in a total volume of 60 μL. As part of the radiolabeling process, parameters such as fluorine-18 activity (~37 and 1480 MBq), concentration of AlCl₃ (0.75, 2, 3, 6 or 10 mM) and the effects of hydrophilic organic solvent (aqueous vs ethanol 50%) were studied. The final formulation was tested for purity, identity and stability in saline. Initial in vivo evaluation of [¹⁸F]AlF-DFH17 was performed in normal rats by PET/CT.

RESULTS

The scaled-up production of [¹⁸F]AlF-DFH17 was performed in high radiochemical and chemical purities in an overall radiochemical yield of 22-38% (at end-of-synthesis) within 60 min. The final formulation was stable in saline at different radioactive concentrations for 8 h. PET evaluation in rats revealed high lung-to-background ratios and no defluorination in vivo up to 1 h post-injection.

CONCLUSION

The novel radioconjugate [¹⁸F]AlF-DFH17 appears to be a promising PET ligand for pulmonary microcirculation imaging.

Cardiopulmonary, biomarkers, and vascular responses to acute hypoxia following cardiac transplantation

Previous studies have suggested good adaptation of cardiac transplant (CTx) recipients to exposure to a high altitude. No studies have investigated the cardiopulmonary and biomarker responses to acute hypoxic challenges following CTx. Thirty-six CTx recipients and 17 age-matched healthy controls (HC) were recruited. Sixteen (16) patients (42%) had cardiac allograft vasculopathy (CAV). Cardiopulmonary responses to maximal and submaximal exercise at 21% O₂ , 20-minutes hypoxia (11.5% O₂ ), and following a 10-minute exposure to 11.5% O₂ using 30% of peak power output were completed. Vascular endothelial growth factor (VEGF), interleukin-6 (IL-6), suppression of tumorigenicity 2 (ST2) were measured at baseline and at peak stress. Endothelial peripheral function was assessed using near-infrared spectroscopy. Compared with HC, CTx presented a lesser O₂ desaturation both at rest (-19.4 ± 6.8 [CTx] vs -24.2 ± 6.0% O₂ [HC], P < 0.05) and following exercise (-23.2 ± 4.9 [CTx] vs -26.2 ± 4.7% O₂ [HC], P < 0.05). CTx patients exhibited a significant decrease in peak oxygen uptake. IL-6 and VEGF levels were significantly higher in CTx recipients in basal conditions but did not change in response to acute stress. CTx patients exhibit a favorable ventilatory and overall response to hypoxic stress. These data provide further insights on the good adaptability of CTx to exposure to high altitude.

Molecular imaging of the human pulmonary vascular endothelium in pulmonary hypertension: a phase II safety and proof of principle trial

PURPOSE

The adrenomedullin receptor is densely expressed in the pulmonary vascular endothelium. PulmoBind, an adrenomedullin receptor ligand, was developed for molecular diagnosis of pulmonary vascular disease. We evaluated the safety of PulmoBind SPECT imaging and its capacity to detect pulmonary vascular disease associated with pulmonary hypertension (PH) in a human phase II study.

METHODS

Thirty patients with pulmonary arterial hypertension (PAH, n = 23) or chronic thromboembolic PH (CTEPH, n = 7) in WHO functional class II (n = 26) or III (n = 4) were compared to 15 healthy controls. Lung SPECT was performed after injection of 15 mCi ^99mTc-PulmoBind in supine position. Qualitative and semi-quantitative analyses of lung uptake were performed. Reproducibility of repeated testing was evaluated in controls after 1 month.

RESULTS

PulmoBind injection was well tolerated without any serious adverse event. Imaging was markedly abnormal in PH with ∼50% of subjects showing moderate to severe heterogeneity of moderate to severe extent. The abnormalities were unevenly distributed between the right and left lungs as well as within each lung. Segmental defects compatible with pulmonary embolism were present in 7/7 subjects with CTEPH and in 2/23 subjects with PAH. There were no segmental defects in controls. The PulmoBind activity distribution index, a parameter indicative of heterogeneity, was elevated in PH (65% ± 28%) vs. controls (41% ± 13%, p = 0.0003). In the only subject with vasodilator-responsive idiopathic PAH, PulmoBind lung SPECT was completely normal. Repeated testing 1 month later in healthy controls was well tolerated and showed no significant variability of PulmoBind distribution.

CONCLUSIONS

In this phase II study, molecular SPECT imaging of the pulmonary vascular endothelium using ^99mTc-PulmoBind was safe. PulmoBind showed potential to detect both pulmonary embolism and abnormalities indicative of pulmonary vascular disease in PAH. Phase III studies with this novel tracer and direct comparisons to lung perfusion agents such as labeled macro-aggregates of albumin are needed.

CLINICAL TRIAL

ClinicalTrials.gov, NCT02216279.

Phase analysis of gated blood pool SPECT for multiple stress testing assessments of ventricular mechanical dyssynchrony in a tachycardia-induced dilated cardiomyopathy canine model

BACKGROUND

Stress-induced dyssynchrony has been shown to be independently correlated with clinical outcomes in patients with dilated cardiomyopathy (DCM) and narrow QRS complexes. However, the extent to which stress levels affect inter- and intraventricular dyssynchrony parameters remains unknown.

METHODS

Ten large dogs were submitted to tachycardia-induced DCM by pacing the right ventricular apex for 3-4 weeks to reach a target ejection fraction (EF) of 35% or less. Stress was then induced in DCM dogs by administering intravenous dobutamine up to a maximum of 20 μg·kg-1·min-1. Hemodynamic and ventricular dyssynchrony data were analyzed by left ventricular (LV) pressure measurements and gated blood pool SPECT (GBPS) imaging. In order to assess mechanical dyssynchrony in DCM subjects and compare it with that of 8 normal counterparts, we extracted the following data: count-based indices of LV contraction homogeneity index (CHI), entropy and phase standard deviation, and interventricular dyssynchrony index.

RESULTS

A significant LV intraventricular dyssynchrony (CHI: 96.4 ± 1.3% in control vs 78.6% ± 10.9% in DCM subjects) resulted in an intense LV dysfunction in DCM subjects (EF: 49.5% ± 8.4% in control vs 22.6% ± 6.0% in DCM), compared to control subjects. However, interventricular dyssynchrony did not vary significantly between the two groups. Under stress, DCM subjects showed a significant improvement in ventricular functional parameters at each level (EF: 22.6% ± 6.0% at rest vs 48.1% ± 5.8% at maximum stress). All intraventricular dyssynchrony indices showed a significant increase in magnitude of synchrony from baseline to stress levels of greater than or equal to 5 μg·kg-1·min-1 dobutamine. There were individual differences in the magnitude and pattern of change in interventricular dyssynchrony during the various levels of stress.

CONCLUSIONS

Based on GBPS analyses, different levels of functional stress, even in close intervals, can have a significant impact on hemodynamic and intraventricular dyssynchrony parameters in a DCM model with narrow QRS complex.

Evaluation of pulmonary perfusion by SPECT imaging using an endothelial cell tracer in supine humans and dogs

Background

Pulmonary perfusion is not spatially homogeneously distributed, and its variations could be of diagnostic value in lung vascular disease. PulmoBind is a ligand of the adrenomedullin receptor densely expressed in endothelial cells of lung capillaries. The aim of this study was to evaluate spatial distribution of human lung perfusion by using this novel molecular tracer of the pulmonary vascular endothelium.

Methods

Normal humans (n = 19) enrolled into the PulmoBind phase I trial were studied (Clinicaltrials.gov.NCT01539889). They were injected with ^99mTc-PulmoBind for SPECT imaging. Results were compared with ^99mTc-PulmoBind in quadruped mammals (dogs, n = 5). Imaging was performed in the supine position and distribution of activity was determined as a function of cumulative voxels along the different anatomical planes.

Results

PulmoBind uptake in humans was 58 ± 1 % (mean ± SEM) of the injected dose. Dorsal activity was 18.1 ± 2.1 % greater than ventral, and caudal activity was 25.7 ± 1.6 % greater than cranial. Lateral activity was only mildly higher than medial by 7.0 ± 1.0 %. In supine dogs, similar but higher PulmoBind gradients were present: dorsal 28.6 ± 2.5 %, caudal 34.1 ± 5.0 % and lateral 18.1 ± 2.0 %.

Conclusions

The perfused pulmonary circulation of supine humans, assessed by an adrenomedullin receptor ligand, is not homogeneously distributed with more prominent distribution in dorsal and caudal regions. It is qualitatively similar to a supine quadruped mammal confirming the presence of a microcirculatory gravitational perfusion gradient detectable with this tracer. Future studies are needed to determine if this novel endothelial cell tracer could be used to detect physiologic and pathologic variations of lung perfusion such as in pulmonary hypertension.

Clinical trial

ClinicalTrial.gov, NCT01539889

Molecular imaging of the human pulmonary vascular endothelium using an adrenomedullin receptor ligand

This phase I study (NCT01539889) evaluated the safety, efficacy, and dosing of PulmoBind for molecular imaging of pulmonary circulation. PulmoBind is a ligand of the adrenomedullin receptor abundantly distributed in lung capillaries. Labeled with 99mTc, it allows single-photon emission computed tomographic (SPECT) imaging of lung perfusion. In preclinical studies, PulmoBind scans enabled detection of lung perfusion defects and quantification of microcirculatory occlusion caused by pulmonary hypertension. Healthy humans (N  =  20) were included into escalating groups of 5 mCi (n  =  5), 10 mCi (n  =  5), or 15 mCi (n  =  10) 99mTc-PulmoBind. SPECT imaging was serially performed, and 99mTc-PulmoBind dosimetric analysis was accomplished. The radiochemical purity of 99mTc-PulmoBind was greater than 95%. There were no safety concerns at the three dosages studied. Imaging revealed predominant and prolonged lung uptake with a mean peak extraction of 58% ± 7%. PulmoBind was well tolerated, with no clinically significant adverse event related to the study drug. The highest dose of 15 mCi provided a favorable dosimetric profile and excellent imaging. The postural lung perfusion gradient was detectable. 99mTc-PulmoBind is safe and provides good quality lung perfusion imaging. The safety/efficacy of this agent can be tested in disorders of pulmonary circulation such as pulmonary arterial hypertension.

The effects of dobutamine stress on cardiac mechanical synchrony determined by phase analysis of gated SPECT myocardial perfusion imaging in a canine model

BACKGROUND

Precise identification of left ventricular (LV) systolic mechanical dyssynchrony may be useful in optimizing the response to cardiac resynchronization therapy in heart failure (HF) patients. However, LV dyssynchrony is mostly measured at rest; patients often suffer from the HF symptoms during exercise.

OBJECTIVES

Our objective was to examine the impacts of stress on LV synchronism with phase analysis of gated SPECT myocardial perfusion imaging (GMPS) within a normal animal cohort.

METHODS

Stress was induced with different levels of dobutamine infusion in six healthy canine subjects. Hemodynamic properties were assessed by LV pressure measurements. Also, LV mechanical synchronism (coordination of LV septal and lateral wall at the time of contraction) was determined by phase analysis of GMPS using commercially available QGS software and in-house MHI4MPI software, with the thickening- and displacement-based method. Synchrony indexes in MHI4MPI included the septal-to-lateral delay and homogeneity index, derived from each of the two methods. Also, bandwidth, SD, and entropy (synchrony indexes) of the QGS software were assessed.

RESULTS

LVEF increased from 36.7% ± 8.7% at rest to 53.67% ± 12.34% at 20 μg · kg(-1) · minute(-1) (P < .001). Also, cardiac output increased from 3.67 ± 1.0 L · minute(-1) at rest to 8.4 ± 2.6 L · minute(-1) at 10 μg · kg(-1) · minute(-1) (P < .001). The same trend was observed for dP/dt max which increased from 1,247 ± 382.7 at rest to 5,062 ± 1,800 mm Hg · s(-1) at 10 μg · kg(-1) · minute(-1) (P < .01). Entropy decreased from 55.2% ± 8% at baseline to 43.5% ± 8.5% at 5 and 43.0% ± 3.7% at 10 μg · kg(-1) · minute(-1) dobutamine (P < .01). Thickening homogeneity index showed a difference from 91.7% ± 5.53% at rest to 98.2% ± 0.75% at 20 μg · kg(-1) · minute(-1) (P < .05).

CONCLUSIONS

Dobutamine stimulation could amplify the ventricular synchronism, and the thickening-based approach is more accurate than wall displacement for assessment of mechanical dyssynchrony in GMPS.

Effects of dobutamine stress on cardiac contraction synchronism in a canine model

In cardiac resynchronization therapy, many devices need to be optimized to take into account the magnitude and characteristics of patients' ventricular mechanical dyssynchrony. The optimization process is mostly performed at rest; however, mechanical resynchronization might be more important under stress, while patients need to improve their cardiac efficiency. The objective of this study was to observe if levels of cardiac stress could modify the ventricular contraction synchronism. Cardiac stress was induced with dobutamine infusion in eight healthy canine subjects. Hemodynamic and ventricular synchronism assessments were performed by left ventricular pressure measurements and radionuclide tomographic-gated blood pools. Cardiac output increased from 2.8 ± 1.0 at rest to 5.7 ± 2.2 L min(-1) at 20 µg kg(-1) min(-1), while the ventricular performance (dP/dtmax) increased from 1588 ± 374 to 8004 ± 710 mmHg s(-1). At baseline, the interventricular delay (in degrees) was -6.3 ± 2.6°, the left ventricle contraction preceding the right. The delay significantly increased to -21.6 ± 3.1° with dobutamine stress (p < 0.0001). On assessment of the left intraventricular synchrony, septal-to-lateral delay was -6.9 ± 5.1° at baseline which revealed a preceded contraction of the left lateral wall from the septum. Cardiac stress produced a significant modulation (p = 0.01), with an inversion of the contraction pattern, the septum contraction preceding the lateral wall contraction by 15.5 ± 5.6° at maximum dobutamine infusion; a significant linear trend (p < 0.001) was found between cardiac stress levels and septal-to-lateral delays. Cardiac activity levels modified the ventricular synchronism supporting the fact that optimizations of cardiac resynchronization devices could be improved by taking cardiac stress into account.

Post-Translational Modification as a Potential Explanation of High Levels of Enzyme Polymorphism: Xanthine Dehydrogenase and Aldehyde Oxidase in DROSOPHILA MELANOGASTER

Xanthine dehydrogenase (XDH) and aldehyde oxidase (AO) in Drosophila melanogaster require for their activity the action of another unlinked locus, maroon-like (mal). While the XDH and AO loci are on chromosome 3, mal maps to the X chromosome. Although functional mal gene product is required for XDH and AO activity, it is possible to examine the effects of mutant mal alleles in those cases when pairs of mutants complement to produce a partial restoration of activity. To test whether mal mediates a post-translational modification of the XDH and AO proteins, we constructed several mal heteroallelic complementing stocks of Drosophila in which the third chromosomes were co-isogenic. Since all lines were co-isogenic for the XDH and AO structural genes, any variation in these enzymes seen when comparing these stocks must have been produced by post-translational modification by mal. We examined the XDH and AO proteins in these stocks by gel-sieving electrophoresis, a procedure that permits independent characterization of a protein's charge and shape, and is capable of discriminating many variants not detected in routine electrophoresis. In every mal heteroallelic combination, there is a significant alteration in protein shape, when compared to wild type. The magnitude of differences in shape of XDH and AO is correlated both with differences in their enzyme activities and with differences in their thermal stabilities. As the body of this variation appears heritable, any functional differences resulting from these variants are of real genetic and evolutionary interest. A similar post-translational modification of XDH and AO by yet another locus, lxd, was subsequently documented in an analogous manner. The pattern of electrophoretic differences produced by mal and lxd modification is similar to that reported for electrophoretic "alleles" of XDH in natural populations. The implication is that heritable variation in electrophoretic mobility at these two enzyme loci, and potentially at other loci, is not necessarily allelic to the structural gene loci.

Gated blood-pool SPECT versus cardiac magnetic resonance imaging for the assessment of left ventricular volumes and ejection fraction

BACKGROUND

We evaluated the accuracy of planar radionuclide angiography and different count-based and space-based electrocardiogram (ECG)-gated blood-pool single-photon emission computed tomography (GBPS) algorithms for assessment of left ventricular end-diastolic volume (LVEDV), end-systolic volume (LVESV), and ejection fraction (LVEF) compared with the gold standard of cardiac magnetic resonance imaging (cMRI). The goal is to assess the accuracy of a recently developed GBPS algorithm.

METHODS AND RESULTS

Subjects had planar, GBPS, and cMRI sequentially. Datasets were processed by QBS software (Cedar-Sinai) and by MHI software (Montreal Heart Institute). Space-based approaches were used to compute LVEDV, LVESV, and LVEF. Count-based techniques were also used to assess LVEF. All results were compared to cMRI. Fifty-five patients (85% male; mean age 63 +/- 9 years) completed the study. LVEFs and their correlations to cMRI values were 43 +/- 12% (r = .82), 39 +/- 14% (r = .82), and 39 +/- 13% for MHI(space), QBS(space), and cMRI methodologies, respectively. LVEF by count-based methods also demonstrated good correlation to LVEF provided by cMRI (42 +/- 13%, r = .88 for MHI(count) and 46 +/- 15%, r = .84 for QBS(count)). Strong correlations were obtained for LVEDV (r = .96 for MHI and r = .92 for QBS) and for LVESV (.97 for MHI and r = .94 for QBS).

CONCLUSIONS

All Gated blood-pool SPECT algorithms had significant variation in estimating LVEF. Nevertheless our software provides good estimates of LV volumes and LVEF. Such software may, therefore, be applied to assess LV morphology and function.

Comparison of left ventricular contraction homogeneity index using SPECT gated blood pool imaging and planar phase analysis

BACKGROUND

There is growing interest in developing a practical technique to accurately assess ventricular synchrony. We describe a novel 3-dimensional (3D) gated blood pool single photon emission computed tomography (SPECT) approach, from which a contraction homogeneity index (CHI) is derived and compared with planar phase analyses.

METHODS AND RESULTS

Subjects underwent planar and SPECT blood pool acquisition. Planar images were processed for left ventricular ejection fraction computation and phase values. SPECT images were processed by our novel algorithm, with which CHI was computed. Overall, 235 patients (79% male; mean age, 62 +/- 11 years) completed the study. Left ventricular ejection fractions were similar by planar (33.5% +/- 13.5%) and 3D (34.7% +/- 12.7%) methods (r = 0.83, P < .0001). Mean phase angles for planar and tomographic methods were 126.3 degrees +/- 29.6 degrees and 124.4 degrees +/- 28.7 degrees , respectively (r = 0.53, P < .0001). Phase and amplitude signals were incorporated in the CHI, which was non-normally distributed with a median of 73.8% (interquartile range, 58.7%-84.9%). This index minimized the negative impact of dyskinetic wall segments with limited regional motion. The planar heterogeneity index (SDPhi) was 28.2 degrees (interquartile range, 17.5 degrees -46.8 degrees ) and correlated inversely with CHI (r = -0.61, P < .0001).

CONCLUSION

The novel 3D dispersion index CHI accounts for both phase delay of a dyssynchronous segment and its magnitude of contraction and is moderately correlated with planar phase analyses. Its potential in cardiac resynchronization therapy remains to be exploited.

Mobile detection system to evaluate reactive hyperemia using radionuclide plethysmography

We validated a novel mobile detection system to evaluate reactive hyperemia using the radionuclide plethysmography technique. Twenty-six subjects underwent simultaneously radionuclide plethysmography with strain gauge plethysmography. Strain gauge and radionuclide methods showed excellent reproducibility with intraclass correlation coefficients of 0.96 and 0.89 respectively. There was also a good correlation of flows between the two methods during reactive hyperemia (r = 0.87). We conclude that radionuclide plethysmography using this mobile detection system is a non-invasive alternative to assess forearm blood flow and its dynamic variations during reactive hyperemia.

SPECT versus planar gated blood pool imaging for left ventricular evaluation

BACKGROUND

We developed a new segmentation algorithm based on the invariance of the Laplacian (IL) to compute volumes and ejection fractions and compared these results with planar analysis and gradients by use of a standard algorithm (QBS).

METHODS AND RESULTS

Planar and single photon emission computed tomography blood pool acquisition was performed in 202 patients. Planar left ventricular ejection fraction (LVEF) was used as the gold standard, and single photon emission computed tomography images were processed by both 3-dimensional (3D) methods. Correlations between each 3D algorithm and planar methodology were as follows: r = 0.77 for QBS and r = 0.84 for IL. Mean LVEFs were 32.72% +/- 13.05% for the planar method, 32.32% +/- 15.98% for QBS, and 31.93% +/- 13.44% for IL (P = .16). Bland-Altman analysis closely demonstrated negligible systematic bias for both 3D methods. Standard errors of bias were comparable between methods (9.36% for QBS and 7.44% for IL, P = .48). Linear regression of the Bland-Altman bias revealed a slope significantly different from 0 for the QBS method (0.22 +/- 0.048, P < .0001) but not for IL (-0.032 +/- 0.0044, P = .47).

CONCLUSION

The new segmentation algorithm provides comparable results to QBS and planar analysis. However, with QBS, the difference in LVEF was correlated with the magnitude of LVEF, which was not found with the new algorithm.

Comparison of the sequences of the Aspergillus nidulans hxB and Drosophila melanogaster ma-l genes with nifS from Azotobacter vinelandii suggests a mechanism for the insertion of the terminal sulphur atom in the molybdopterin cofactor

The molybdopterin cofactor (MoCF) is required for the activity of a variety of oxidoreductases. The xanthine oxidase class of molybdoenzymes requires the MoCF to have a terminal, cyanolysable sulphur ligand. In the sulphite oxidase/nitrate reductase class, an oxygen is present in the same position. Mutations in both the ma-l gene of Drosophila melanogaster and the hxB gene of Aspergillus nidulans result in loss of activities of all molybdoenzymes that necessitate a cyanolysable sulphur in the active centre. The ma-l and hxB genes encode highly similar proteins containing domains common to pyridoxal phosphate-dependent cysteine transulphurases, including the cofactor binding site and a conserved cysteine, which is the putative sulphur donor. Key similarities were found with NifS, the enzyme involved in the generation of the iron-sulphur centres in nitrogenase. These similarities suggest an analogous mechanism for the generation of the terminal molybdenum-bound sulphur ligand. We have identified putative homologues of these genes in a variety of organisms, including humans. The human homologue is located in chromosome 18.q12.

The Drosophila cinnamon gene is functionally homologous to Arabidopsis cnx1 and has a similar expression pattern to the mammalian gephyrin gene

Molybdoenzymes are involved in a variety of essential pathways including nitrate assimilation, sulfur and/or purine metabolism and abscisic acid biosynthesis. Most organisms produce several such enzymes requiring a molybdopterin cofactor for catalytic function. Mutations that result in a lack of the molybdopterin cofactor display a pleiotropic loss of molybdoenzyme activities, and this phenotype has been used to identify genes involved in cofactor biosynthesis or utilization. Although several cofactor genes have been analyzed in prokaryotes, much less is known concerning eukaryotic molybdenum cofactor (MoCF) genes. This work is focused on the Drosophila MoCF gene cinnamon (cin) which encodes a multidomain protein, CIN, that shows significant similarity to three proteins encoded by separate prokaryotic MoCF genes. These domains are also present in the product of cnx1, an Arabidopsis MoCF gene, and in GEPHYRIN, a rat protein thought to organize the glycine receptor, GlyR, within the postsynaptic membrane. Since this apparent consolidation of separate prokaryotic genes into a single eukaryotic gene is a feature of other conserved metabolic pathways, we wished to determine whether the protein's function is also conserved. This report shows that the plant gene cnx1 can rescue both enzymatic and physiological defects of Drosophila carrying cin mutations, indicating that the two genes serve similar or identical functions. In addition, we have investigated the relationship between CINNAMON and GEPHYRIN, using immunohistochemical methods to localize the CIN protein in Drosophila embryos. Most of the CIN protein, like GEPHYRIN in the rat CNS, is localized to the cell borders and shows a tissue-specific pattern of expression. In a parallel study, antibody to GEPHYRIN revealed the same tissue-specific expression pattern in fly embryos. Both antibodies show altered staining patterns in cin mutants. Taken together, these results suggest that GEPHYRIN may also carry out a MoCF-related function.

Eye pigments in wild-type and eye-color mutant strains of the African malaria vector Anopheles gambiae

Chromatographic analysis of pigments extracted from wild-type eyes of the mosquito Anopheles gambiae reveals the presence of the ommatin precursor 3-hydroxykynurenine, its transamination derivative xanthurenic acid, and a dark, red-brown pigment spot that probably is composed of two or more low mobility xanthommatins. No colored or fluorescent pteridines are evident. Mosquitoes homozygous for an autosomal recessive mutation at the red-eye (r) locus have a brick-red eye color in larvae, pupae, and young adults, in contrast to the almost black color of the wild eye. Mosquitoes homozygous for this mutant allele have levels of ommochrome precursors that are indistinguishable from the wild-type, but the low-mobility xanthommatin spot is ochre-brown in color rather than red-brown as in the wild-type. Mosquitoes with two different mutant alleles at the X-linked pink-eye locus (p, which confers a pink eye color, and pw, which confers a white eye phenotype in homozygotes or hemizygous males) have normal levels of ommochrome precursors but no detectable xanthommatins. Mosquitoes homozygous for both the r and p mutant alleles have apricot-colored eyes and show no detectable xanthommatins. Both the pink-eye and red-eye mutations appear to involve defects in the transport into or assembly of pigments in the membrane-bound pigment granules rather then defects in ommochrome synthesis.

The Drosophila molybdenum cofactor gene cinnamon is homologous to three Escherichia coli cofactor proteins and to the rat protein gephyrin

Essentially all organisms depend upon molybdenum oxidoreductases which require a molybdopterin cofactor for catalytic activity. Mutations resulting in a lack of the cofactor show a pleiotropic loss of molybdoenzyme activities and thereby define genes involved in cofactor biosynthesis or utilization. In prokaryotes, two operons are directly associated with biosynthesis of the pterin moiety and its side chain while additional loci play a role in the acquisition of molybdenum and/or activation of the cofactor. Here we report the cloning of cinnamon, a Drosophila molybdenum cofactor gene encoding a protein with sequence similarity to three of the prokaryotic cofactor proteins. In addition, the Drosophila cinnamon protein is homologous to gephyrin, a protein isolated from the rat central nervous system. Our results suggest that some portions of the prokaryotic cofactor biosynthetic pathway composed of monofunctional proteins have evolved into a multifunctional protein in higher eukaryotes.

Transient expression of DNA in Drosophila via electroporation

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Comparison of DNA probe and cytogenetic methods for identifying field collected Anopheles gambiae complex mosquitoes

A recently developed DNA probe method was compared with the standard cytogenetic method for identifying the species of individual mosquitoes in the Anopheles gambiae complex. The complex consists of 6 morphologically indistinguishable sibling species that include the major African malaria vectors. Half-gravid, field collected mosquitoes were split into 2 portions: the abdomen was preserved for ovarian nurse cell cytotaxonomy and the head/thorax portion was desiccated for DNA extraction. Cytogenetic examination of the Kenya specimens showed 88 An. gambiae and 108 An. arabiensis. The Zimbabwe specimens consisted of 6 An. gambiae and 55 An. Quadriannulatus. All samples of the 3 species were polymorphic for the major chromosomal inversions previously recorded in field specimens from eastern and southern Africa, indicating that the collections reflected natural levels of intraspecific variation in the field populations sampled. Approximately 97% of the cytologically identified mosquitoes were also identified to species by the DNA probe method, and in every case the DNA probe and cytogenetic methods of species identification produced concordant results.

Ribosomal DNA-probes differentiate five cryptic species in the Anopheles gambiae complex

This study describes the use of ribosomal DNA probes to identify the species of individual mosquitoes in the Anopheles gambiae complex, a group of six morphologically identical mosquito species among which are two of the principal vectors of malaria in Africa. The DNA probes are sequences of DNA derived from the ribosomal genes of An. gambiae. Each probe reveals a different sized restriction enzyme fragment specific to each of the five species in the complex that were examined in this study: An. gambiae, An. arabiensis, An. quadriannulatus, An. melas and An. merus. The probes detect highly repeated sequences of DNA, thus the method is sufficiently sensitive to be applied to a small portion of a mosquito. Furthermore, because the DNA can be extracted from desiccated or alcohol preserved specimens, the test is compatible with other mosquito assays performed on dried specimens such as blood meal and malaria sporozoite antigen ELISAs. Determination of the nucleotide sequences that underlie the species-specific restriction enzyme site differences detected by these probes will lead to the development of synthetic DNA probes that can be used to identify an individual mosquito to species on the basis of a simple dot-blot or squash-blot.

A ribosomal RNA gene probe differentiates member species of the Anopheles gambiae complex

A 0.59 kilobase DNA fragment cloned from an rDNA cistron of the mosquito Anopheles gambiae can be used as a probe to differentiate between A. gambiae, A. arabiensis, and A. melas, three morphologically identical sibling species in the A. gambiae complex which otherwise can be reliably distinguished only by polytene chromosome banding patterns. Although all are important (and often sympatric) African malaria vectors, their relative roles in malaria transmission have thus far been difficult to assess. The probe, an EcoRI-SalI fragment from the 3' end of the 28S beta coding region of the cistron, is present in all three species, but the species differ uniquely with respect to the location of an EcoRI site in the nontranscribed spacer (NTS) downstream of the fragment. We have routinely used the probe to identify A. gambiae complex mosquitoes to species on the basis of genomic DNA extracted from individual air dried specimens. A single mosquito abdomen provides more than sufficient DNA for the assay, and neither eggs nor a bloodmeal in the abdomen interfere with DNA yield. Moreover, the DNA extraction procedure does not degrade the bloodmeal IgG, so the residual protein pellet can be used to identify the mosquito bloodmeal source. Since the rDNA cistron organization as detected by the probe does not differ between male and female mosquitoes, the probe can be used for either sex. Preliminary experiments show that the probe is equally useful for mosquito larvae and pupae.

Molybdenum hydroxylases in Drosophila. III. Further characterization of the low xanthine dehydrogenase gene

The biochemical effects of several newly induced low xanthine dehydrogenase (lxd) mutations in Drosophila melanogaster were investigated. When homozygous, all lxd alleles simultaneously interrupt each of the molybdoenzyme activities to approximately the same levels: xanthine dehydrogenase, 25%; aldehyde oxidase, 12%; pyridoxal oxidase, 0%; and sulfite oxidase, 2% as compared to the wild type. In order to evaluate potentially small complementation or dosage effects, mutant stains were made coisogenic for 3R. These enzymes require a molybdenum cofactor, and lxd cofactor levels are also reduced to less than 10% of the wild type. These low levels of molybdoenzyme activities and cofactor activity are maintained throughout development from late larval to adult stages. The lxd alleles exhibit a dosage-dependent effect on molybdoenzyme activities, indicating that these mutants are leaky for wild-type function. In addition, cofactor activity is dependent upon the number of lxd+ genes present. The lxd mutation results in the production of more thermolabile XDH and AO enzyme activities, but this thermolability is not transferred with the cofactor to a reconstituted Neurospora molybdoenzyme. The lxd gene is localized to salivary region 68A4-9, 0.1 map unit distal to the superoxide dismutase (Sod) gene.

A genetic variant of beta-glucuronidase in Drosophila melanogaster

The beta-glucuronidase activity of Drosophila melanogaster exists as two chromatographically separable forms, both of which are glycoproteins. Form I is membrane-bound in vivo, has a pI of 8.0-8.5, and can be irreversibly inactivated either by incubation at 55 degrees C for 20 min or by incubation at 37 degrees C in the presence of 6 M urea. Form II exists both membrane-bound as well as membrane-free, has a pI of 4.5, and is resistant to the conditions which inactivate form I. The two forms are similar in Km and Vmax for the artificial substrate 4-methylumbelliferyl-beta-D-glucuronide and both forms are precipitated by antibody to form II. A natural genetic variant, beta-GluL1, completely lacks from I beta-glucuronidase. This variant behaves in a co-dominant fashion for the determination of the presence of form I and has been localized to the extreme distal portion of chromosome 3R. Other data indicate that at least one genetic determinant for the amount of form II is also localized to this portion of chromosome 3R.

Drosophila melanogaster ma-l mutants are defective in the sulfuration of desulfo Mo hydroxylases

Xanthine dehydrogenase was purified more than 1500-fold from crude extracts of wild type Drosophila melanogaster. Like the bovine milk and chicken liver enzymes, the purified Drosophila enzyme was inactivated by cyanide, and the cyanide-inactivated desulfo enzyme was reactivated by anaerobic incubation with 1 mM sulfide and 1 mM dithionite. Application of the resulfuration procedure to crude extracts of Drosophila ma-l flies which slow pleiotropic deficiencies of xanthine dehydrogenase, aldehyde oxidase, and pyridoxal oxidase led to the emergence of xanthine dehydrogenase and aldehyde oxidase activities. Representatives of all the five known complementation groups of ma-l mutants were amenable to activation; 59-95% of wild type xanthine dehydrogenase activity and 1-7% of wild type aldehyde oxidase activity were reconstituted. Evidence for the identity of in vitro reconstituted xanthine dehydrogenase from ma-l mutants with wild type enzyme is presented. Since the inactive xanthine dehydrogenase and aldehyde oxidase proteins present in ma-l mutants are identical with the catalytically inactive desulfo forms obtained by cyanide treatment of active enzymes, these data constitute evidence for genetic control of the incorporation of the cyanolyzable sulfur of Mo hydroxylases.

Molybdenum hydroxylases in Drosophila. II. Molybdenum cofactor in xanthine dehydrogenase, aldehyde oxidase and pyridoxal oxidase

The molybdenum hydroxylases are a ubiquitous class of enzymes which contain molybdenum in association with a low molecular weight cofactor. Genetic evidence suggests that the Drosophila loci, ma--1, cin and lxd are concerned with this cofactor because mutants for any one of these loci simultaneously interrupt activity for two molybdenum hydroxylases, XDH and A0. A third enzyme activity, P0, is also absent in each of the three mutants but evidence classifying P0 as a molybdoenzyme has been lacking. This study utilizes the known tungsten sensitivity of molybdoenzymes to demonstrate directly that pyridoxal oxidase is also molybdoenzyme. The low molecular weight molybdenum cofactor is found to be severely reduced in extracts of the 1xd and cin mutants but ma--1 mutants have high levels of cofactor. A partially purified preparation of XDH crossreacting material from ma--1 was also shown to contain the molybdenum cofactor. These results, considered with data from other workers are taken to indicate that the functions of all three of the loci examined could be concerned with some aspect of cofactor biosynthesis.

Post-translation modification of xanthine dehydrogenase in a natural population of Drosophila melanogaster

Second chromosomes of D. melanogaster were isolated from a single natural population, and 40 were analyzed by gel-sieving electrophoresis for the presence of polymorphic loci on chromosome 2 that act to modify xanthine dehydrogenase and/or aldehyde oxidase, whose structural genes map to chromosome 3. Clear evidence of polymorphism for one or more xanthine dehydrogenase modifier loci was obtained.

Gene expression in Drosophila: post-translational modification of aldehyde oxidase and xanthine dehydrogenase

Maroon-like homozygotes are completely deficient for xanthine dehydrogenase (XDH) and aldehyde oxidase (AO), however, ma-l is not a structural locus for either enzyme. Quantitative immunoelectrophoresis of ma-l and wild type extracts suggests that the ma-l function must be post-translational. To determine whether the ma-l function involves some direct physical changes in XDH and/or AO the enzymes were characterized with respect to temperature sensitivity and behavior in gel sieving electrophoresis. Since the XDH and AO from complementary ma-l heterozygotes is more thermolabile and different in shape from wild type XDH and AO, we conclude that ma-l is involved in a post-translational modification of these enzymes.