Recombinant versus natural human 111In-beta2-microglobulin for scintigraphic detection of Abeta2m amyloid in dialysis patients

Positron Emission Tomography Can Support the Diagnosis of Dialysis-Related Amyloidosis

BACKGROUND

The improvements in dialysis have not eliminated long-term problems, including dialysis-related amyloidosis (DRA), caused by Beta-2 microglobulin deposition. Several types of scintigraphy have been tested to detect DRA, none entered the clinical practice. Aim of the study was to assess the potential of PET-FDG scan in the diagnosis of DRA.

METHODS

Forty-six dialysis patients with at least one PET scan (72 scans) were selected out 162 patients treated in 2016-2018. Subjective global assessment (SGA), malnutrition inflammation score (A), Charlson Comorbidity Index (CCI), were assessed at time of scan; 218 age-matched cases with normal kidney function were selected as controls. PET scans were read in duplicate. Carpal tunnel syndrome was considered a proxy for DRA. A composite "amyloid score" score considered each dialysis year = 1 point; carpal tunnel-DRA = 5 points per site. Logistic regression, ROC curves and a prediction model were built.

RESULTS

The prevalence of positive PET was 43.5% in dialysis, 5% in controls (p < 0.0001). PET was positive in 14/15 (93.3%) scans in patients with carpal tunnel. PET sensitivity for detecting DRA was 95% (specificity 64%). Carpal tunnel was related to dialysis vintage and MIS. A positive PET scan was significantly associated with dialysis vintage, MIS and amyloid score. A prediction model to explain PET positivity combined clinical score and MIS, allowing for an AUC of 0.906 (CI: 0.813-0.962; p < 0.001).

CONCLUSIONS

PET-FDG may identify DRA, and may be useful in detecting cases in which inflammation favours B2M deposition. This finding, needing large-scale confirmation, could open new perspectives in the study of DRA.

A new era for understanding amyloid structures and disease

The aggregation of proteins into amyloid fibrils and their deposition into plaques and intracellular inclusions is the hallmark of amyloid disease. The accumulation and deposition of amyloid fibrils, collectively known as amyloidosis, is associated with many pathological conditions that can be associated with ageing, such as Alzheimer disease, Parkinson disease, type II diabetes and dialysis-related amyloidosis. However, elucidation of the atomic structure of amyloid fibrils formed from their intact protein precursors and how fibril formation relates to disease has remained elusive. Recent advances in structural biology techniques, including cryo-electron microscopy and solid-state NMR spectroscopy, have finally broken this impasse. The first near-atomic-resolution structures of amyloid fibrils formed in vitro, seeded from plaque material and analysed directly ex vivo are now available. The results reveal cross-β structures that are far more intricate than anticipated. Here, we describe these structures, highlighting their similarities and differences, and the basis for their toxicity. We discuss how amyloid structure may affect the ability of fibrils to spread to different sites in the cell and between organisms in a prion-like manner, along with their roles in disease. These molecular insights will aid in understanding the development and spread of amyloid diseases and are inspiring new strategies for therapeutic intervention.

Nuclear imaging of amyloidosis

Summary Amyloidosis is a clinical condition caused by deposition of various protein fibrills in extracellular space. The presented symptoms depend on the type of deposits and the organ or organs involved. The correct diagnosis is often difficult, due to lack of nonivasive imaging techniques and insufficiency of morphological imaging procedures delievered by radiology. We presented a list of potential radiopharmaceuticals that can be used in detecting various types of amyloidoses. (123)I-SAP proved to have high sensitivity in imaging of AA and AL amyloidosis in visceral organs. (99m)Tc-Aprotinin was found to be useful in detecting cardiac amyloidosis. A couple of classical radiotracers, such as (201)Tl, (123)I-mIBG, together with (111)In-antimyosin were also tested for accuracy in cardiac imaging, however the main problem was low specificity. Potential applicability was also found in case of some bone-seeking agents and other radiotracers, e.g. (67)Ga-citrate and (99m)Tc-penta-DMSA. High sensitivity and specificity was achieved with β2-microglobulin labeled with (131)I or (111)In. Among PET tracers, (11)C-PIB deserves more attention, because it may have an important role in diagnosing of AD in the near future. Further clinical studies are expected to take place, because noninvasive diagnosing and monitoring of amyloidosis is still a challenge.

Clinical, radiological, and biochemical features of a bilateral buttock amyloidoma emerging after 27 years of hemodialysis

Deposition of amyloid in the buttock is a rare complication of dialysis related amyloidosis (DRA), but this localization is even rarer in other types of amyloidoses. We report here the clinical, radiological, and biochemical features of a patient who incurred into this complication after 27 years of hemodialysis. Imaging of the amyloid deposition by magnetic resonance imaging (MRI) documents the amyloid infiltration in the muscles of the buttock region and highlights a peculiar feature of amyloid fibrils deposition in the subcutaneous fat. The amyloid deposition is confirmed by biochemical and microscopic analysis of fibrils extracted from a biopsy specimen. Review of literature and the features of this case lead to speculation that the peculiar involvement of the buttock region including muscles and subcutaneous fat in DRA might derive from the propagation of amyloid initially deposited in the hip joint.

Radiopharmaceuticals for renal positron emission tomography imaging

Radiopharmaceuticals for functional renal imaging, including renal blood flow, renal blood volume, glomerular excretion, and metabolism have been available for some time. This review outlines radiopharmaceuticals for functional renal imaging as well as those that target pertinent molecular constituents of renal injury and repair. The angiotensin and endothelin receptors are particularly appealing molecular targets for renal imaging because of their association with renal physiology and pathology. Other targets such as the vascular endothelial growth factor (VEGF) receptor, integrin, or phosphatidylserine have been investigated at length for cancer imaging, but they are just as important constituents of the renal injury/repair process. Various diseases can involve identical mechanisms, such as angiogenesis and apoptosis, and radiopharmaceuticals developed for these processes in other organs can also be used for renal imaging. The sensitivity and spatial resolution of positron emission tomography makes it an ideal tool for molecular and functional kidney imaging. Radiopharmaceutical development for the kidneys must focus on achieving high target selectivity and binding affinity, stability and slow metabolism in vivo, and minimal nonspecific accumulation and urinary excretion.

Production and characterization of RNA aptamers specific for amyloid fibril epitopes

One of the most fascinating features of amyloid fibrils is their generic cross-beta architecture that can be formed from many different and completely unrelated proteins. Nonetheless, amyloid fibrils with diverse structural and phenotypic properties can form, both in vivo and in vitro, from the same protein sequence. Here, we have exploited the power of RNA selection techniques to isolate small, structured, single-stranded RNA molecules known as aptamers that were targeted specifically to amyloid-like fibrils formed in vitro from beta(2)-microglobulin (beta(2)m), the amyloid fibril protein associated with dialysis-related amyloidosis. The aptamers bind with high affinity (apparent K(D) approximately nm) to beta(2)m fibrils with diverse morphologies generated under different conditions in vitro, as well as to amyloid fibrils isolated from tissues of dialysis-related amyloidosis patients, demonstrating that they can detect conserved epitopes between different fibrillar species of beta(2)m. Interestingly, the aptamers also recognize some other, but not all, amyloid fibrils generated in vitro or isolated from ex vivo sources. Based on these observations, we have shown that although amyloid fibrils share many common structural properties, they also have features that are unique to individual fibril types.

An improved 99mTc-aprotinin kit formulation: quality control analysis of radiotracer stability and cold kit shelf life

(99m)Tc-aprotinin scintigraphy has been demonstrated to be a useful noninvasive imaging technique for amyloid deposits located in extraabdominal regions of patients. The aim of this study was to develop an improved aprotinin cold kit formulation, to validate the kit for long-term stability, as well as to assess the radiotracer stability by novel quality control methods. The aprotinin cold kit formulation of Trasylol, pyrophosphate (PYP)-chelated stannous reductant and an alkaline buffer, was dispensed into nitrogen-filled vials and aliquots frozen at -20 degrees C. After 0, 1, 2, 3 and 6 months of storage, three samples were reconstituted with 750-850 MBq of (99m)Tc-pertechnetate, followed by quality control analyses by paper chromatography methods at 25, 85 and 265 min postreconstitution (pr). Cation-exchange cartridge quality control methods were also investigated. The cold kits proved to be stable to long-term storage for up to 6 months, and the radiotracer was stable for at least 4 h pr. (99m)Tc-aprotinin was formed at greater than 95% efficiency at all time points tested with (99m)TcO2 present as the major impurity (1-4%) and (99m)Tc-pertechnetate and (99m)Tc-PYP present in trace amounts. An alternative, rapid, safe and reliable method was found in Oasis MCX-BSA-treated cartridges using saline as the eluting solution to assay for (99m)Tc-aprotinin.

Pharmacokinetics and normal scintigraphic appearance of 99mTc aprotinin

OBJECTIVE

To confirm the pharmacokinetics and biodistribution of 99mTc aprotinin in normal volunteers and to determine the optimum time for scanning post-injection, prior to further investigations of 99mTc aprotinin as an imaging agent for amyloidosis.

METHODS

Five patients (three men and two women, average age 49 years, age range 38-66 years) without a history of amyloidosis or any of the associated diseases, were included in this prospective study. Blood and urine were collected and images were performed of the whole body and wrists.

CONCLUSIONS

Normal biodistribution of 99mTc aprotinin includes early cardiac and lung activity in the blood pool phase with subsequent hepatic activity and renal excretion with variable splenic activity. There is variable bowel uptake on later images. The best quality images were obtained 90 min post-intravenous administration, and this is likely to be the optimum time for clinical imaging.

Imaging in dialysis spondyloarthropathy

Destructive spondyloarthropathy has recently been described in patients who undergo maintenance hemodialysis for chronic renal disease. The condition most frequently involves the lower segment of the cervical spine, although the craniocervical junction also may be affected. Although the pathogenesis of destructive spondyloarthropathy remains unclear, the disorder is thought to relate to a hemodialysis-associated amyloidosis. It appears that the disease correlates with the duration of hemodialysis, although it has been reported in patients with chronic renal insufficiency not associated with hemodialysis. Radiographic features simulate those of an infectious process, encompassing a range of abnormalities from superficial erosions to large bony defects. Computed tomography (CT) images reveal osteolytic areas, with bone sclerosis of adjacent vertebral endplates, and minimal osteophytosis. The intervertebral spaces appear narrow or obliterated. On magnetic resonance imaging (MRI), the disorder may show the imaging characteristics of spondylodiskitis. The absence of high signal intensity on T2-weighted images generally helps to eliminate the diagnosis of an infection. With progression of the disease, collapse of a vertebral body and spinal instability may occur. Severe complications of destructive spondyloarthropathy in long-term dialysis patients may include spinal cord compromise, necessitating surgical decompression, with or without spinal stabilization.

Beta(2)-microglobulin and its deamidated variant, N17D form amyloid fibrils with a range of morphologies in vitro

Amyloid fibrils formed by incubation of recombinant wild-type human beta(2)-microglobulin (beta(2)M) ab initio in vitro at low pH and high ionic strength are short and highly curved. By contrast, fibrils extracted from patients suffering from haemodialysis-related amyloidosis and those formed by seeding growth of the wild-type protein in vitro with fibrils ex vivo are longer and straighter than those previously produced ab initio in vitro. Here we explore the effect of growth conditions on morphology of beta(2)M fibrils formed ab initio in vitro from the wild-type protein, as well as a variant form of beta(2)M in which Asn17 is deamidated to Asp (N17D). We show that deamidation results in significant destabilisation of beta(2)M at neutral pH. Despite this, acidification is still necessary to form amyloid from the mutant protein in vitro. Interestingly, at low pH and low ionic strength long, straight fibrils of recombinant beta(2)M are formed in vitro. The fibrils comprise three distinct morphological types when examined using electron microscopy (EM) and atomic force microscopy (AFM) that vary in periodicity and the number of constituent protofibrils. Using kinetic experiments we suggest that the immature fibrils observed previously do not represent intermediates in the assembly of fully mature amyloid, at least under the conditions studied here.

Imaging techniques in the diagnosis of dialysis-related amyloidosis

beta(2)-microglobulin amyloidosis (A beta(2)M) is a major determinant of morbidity in patients on dialysis treatment. Symptoms of A beta(2)M amyloid are mainly related to (peri-)articular amyloid deposition. Imaging techniques [i.e., joint ultrasonography, X-ray, computed tomography (CT), or magnetic resonance imaging (MRI) findings], as well as conventional bone scans, are helpful in the screening of local lesions but are relatively nonspecific and/or not sensitive enough. Scintigraphic techniques using radiolabeled serum amyloid P component (SAP) or the radiolabeled A beta(2)M precursor protein, beta(2)M, generate more specific results. A beta(2)M deposits have been visualized in several long-term hemodialysis patients by using (123)I-labeled SAP. However, this scan did not show tracer accumulation in some frequently involved sites such as hips or shoulders, and frequently labeled the spleen, which is usually spared from A beta(2)M deposits. Improvements in technical sensitivity and specificity could be achieved by scanning with (131)I-labeled beta(2)M: this technique detected tracer accumulations corresponding to the typical distribution pattern of A beta(2)M. Further, both the radiation exposure and the optical resolution of this latter scan have been refined by substituting (111)In for (131)I. In a final step we generated recombinant human beta(2)M (rh beta(2)M). While (111)In rh beta(2)M again failed to show significant tracer accumulation over joint regions in patients on short-term hemodialysis without evidence of A beta(2)M, local tracer accumulations similar to those observed with natural, (111)In-labeled beta(2)M could be demonstrated in long-term hemodialysis patients with evidence of A beta(2)M. In conclusion, scintigraphy for A beta(2)M with (111)In-labeled rh beta(2)M provides a homogeneous and safe recombinant protein source and represents a suitable detection method of beta(2)M amyloid deposits in dialysis patients.

Production of recombinant human beta2-microglobulin for scintigraphic diagnosis of amyloidosis in uremia and hemodialysis

Amyloid of beta2-microglobulin (beta2m) origin can be diagnosed using 131I-radiolabelled-beta2m scintigraphy in patients with uremia and hemodialysis treatment. As the tracer beta2m is isolated from another patient, it carries the common risks, including viral infections such as Hepatitis B, C and HIV, which are associated with human plasma products. In order to exclude these risks we have produced recombinant human beta2m (rhbeta2m) in Escherichia coli. The expression vector pASK40DeltaLbeta2m(His)5 contains a C-terminal (His)5-tag for purification via immobilized metal ion affinity chromatography (IMAC). Size exclusion chromatography on a Superose 12 column represents the second step of purification. The isolated rhbeta2mH5 reacted in an immunochemically identical manner to native human beta2m, and showed a single band of approximately 11.8 kDa in Western blot analysis and revealed a single spot in two-dimensional gel electrophoresis. Mass spectrometry analysis revealed a single peak at the expected molecular mass of 12 415.8 Da. Uniformity was further proven by crystallization and N-terminal amino-acid sequence analysis. The rhbeta2mH5 protein was then produced under conditions that allow the intravenous use in humans. Intraveneously applied indium-111-labelled rhbeta2mH5 was monitored in hemodialysed patients with and without known beta2m-amyloidosis. The tracer was localized specifically to particular areas known to contain amyloid. Thus, this rhbeta2mH5 preparation is suitable for detecting amyloid-containing organs of the beta2m-class in vivo and fulfils the requirements of a tracer for common use. Finally, the use of indium-111 instead of iodine-131 has reduced the radioactive load and resulted in higher resolution.