Serum amyloid P component scintigraphy and turnover studies for diagnosis and quantitative monitoring of AA amyloidosis in juvenile rheumatoid arthritis

Repeat doses of antibody to serum amyloid P component clear amyloid deposits in patients with systemic amyloidosis

Systemic amyloidosis is a fatal disorder caused by pathological extracellular deposits of amyloid fibrils that are always coated with the normal plasma protein, serum amyloid P component (SAP). The small-molecule drug, miridesap, [(R)-1-[6-[(R)-2-carboxy-pyrrolidin-1-yl]-6-oxo-hexanoyl]pyrrolidine-2-carboxylic acid (CPHPC)] depletes circulating SAP but leaves some SAP in amyloid deposits. This residual SAP is a specific target for dezamizumab, a fully humanized monoclonal IgG1 anti-SAP antibody that triggers immunotherapeutic clearance of amyloid. We report the safety, pharmacokinetics, and dose-response effects of up to three cycles of miridesap followed by dezamizumab in 23 adult subjects with systemic amyloidosis (ClinicalTrials.gov identifier: NCT01777243). Amyloid load was measured scintigraphically by amyloid-specific radioligand binding of ¹²³I-labeled SAP or of ^99mTc-3,3-diphosphono-1,2-propanodicarboxylic acid. Organ extracellular volume was measured by equilibrium magnetic resonance imaging and liver stiffness by transient elastography. The treatment was well tolerated with the main adverse event being self-limiting early onset rashes after higher antibody doses related to whole body amyloid load. Progressive dose-related clearance of hepatic amyloid was associated with improved liver function tests. ¹²³I-SAP scintigraphy confirmed amyloid removal from the spleen and kidneys. No adverse cardiac events attributable to the intervention occurred in the six subjects with cardiac amyloidosis. Amyloid load reduction by miridesap treatment followed by dezamizumab has the potential to improve management and outcome in systemic amyloidosis.

Laryngeal amyloidosis: diagnosis, pathophysiology and management

Background:

Laryngeal amyloidosis represents approximately 1 per cent of all benign laryngeal lesions, and can cause variable symptoms depending on anatomical location and size. Treatment ranges from observation through to endoscopic microsurgery, laser excision and laryngectomy.

Objectives:

To highlight the diversity of presentations, increase awareness of paediatric amyloidosis and update the reader on current management.

Case series:

Five cases are illustrated. Four adult patients were female, and the one child, the second youngest in the literature, was male. Amyloid deposits were identified in all laryngeal areas, including the supraglottis, glottis and subglottis. Treatment consisted of balloon dilatation, endoscopic excision, laser cruciate incision, and resection with carbon dioxide laser, a microdebrider and coblation wands.

Conclusion:

Laryngeal amyloidosis remains a rare and clinically challenging condition. Diagnosis should be considered for unusual appearing submucosal laryngeal lesions. Treatment of this disease needs to be evaluated on a case-by-case basis and managed within an appropriate multidisciplinary team.

AA amyloidosis: pathogenesis and targeted therapy

The understanding of why and how proteins misfold and aggregate into amyloid fibrils has increased considerably during recent years. Central to amyloid formation is an increase in the frequency of the β-sheet structure, leading to hydrogen bonding between misfolded monomers and creating a fibril that is comparably resistant to degradation. Generation of amyloid fibrils is nucleation dependent, and once formed, fibrils recruit and catalyze the conversion of native molecules. In AA amyloidosis, the expression of cytokines, particularly interleukin 6, leads to overproduction of serum amyloid A (SAA) by the liver. A chronically high plasma concentration of SAA results in the aggregation of amyloid into cross-β-sheet fibrillar deposits by mechanisms not fully understood. Therefore, AA amyloidosis can be thought of as a consequence of long-standing inflammatory disease. This review summarizes current knowledge about AA amyloidosis. The systemic amyloidoses have been regarded as intractable conditions, but improvements in the understanding of fibril composition and pathogenesis over the past decade have led to the development of a number of different therapeutic approaches with promising results.

In vivo visualization of amyloid deposits in the heart with 11C-PIB and PET

Cardiac amyloidosis is a differential diagnosis in heart failure and is associated with high mortality. There is currently no noninvasive imaging test available for specific diagnosis. N-[methyl-(11)C]2-(4'-methylamino-phenyl)-6-hydroxybenzothiazole ((11)C-PIB) PET is used in the evaluation of brain amyloidosis. We evaluated the potential use of (11)C-PIB PET in systemic amyloidosis affecting the heart.

METHODS

Patients (n = 10) diagnosed with systemic amyloidosis-including heart involvement of either monoclonal immunoglobulin light-chain (AL) or transthyretin (ATTR) type-and healthy volunteers (n = 5) were investigated with PET/CT using (11)C-PIB to study cardiac amyloid deposits and with (11)C-acetate to measure myocardial blood flow to study the impact of global and regional perfusion on PIB retention.

RESULTS

Myocardial (11)C-PIB uptake was visually evident in all patients 15-25 min after injection and was not seen in any volunteer. A significant difference in (11)C-PIB retention in the heart between patients and healthy controls was found. The data indicate that myocardial amyloid deposits in patients diagnosed with systemic amyloidosis could be visualized with (11)C-PIB. No correlation between (11)C-PIB retention index and myocardial blood flow as measured with (11)C-acetate was found on the global level, whereas a positive correlation on the segmental level was seen in a single patient.

CONCLUSION

(11)C-PIB and PET could be a method to study systemic amyloidosis of type AL and ATTR affecting the heart and should be investigated further both as a diagnostic tool and as a noninvasive method for treatment follow-up.

Isolation and characterization of pharmaceutical grade human pentraxins, serum amyloid P component and C-reactive protein, for clinical use

The human pentraxin proteins, serum amyloid P component (SAP) and C‐reactive protein (CRP) are important in routine clinical diagnosis, SAP for systemic amyloidosis and CRP for monitoring the non‐specific acute phase response. They are also targets for novel therapies currently in development but their roles in health and disease are controversial. Thus, both for clinical use and to rigorously elucidate their functions, structurally and functionally intact, pharmaceutical grade preparations of the natural, authentic proteins are required. We report here the production from normal human donor plasma and the characterization of the first such preparations. Importantly, we demonstrate that, contrary to reports using recombinant proteins and less well characterized preparations, neither CRP nor SAP stimulate the release by human peripheral blood mononuclear cells in vitro of any TNFα, IL‐6 or IL‐8, nor does SAP cause release of IL‐1β or IL‐10. Furthermore neither of our preparations was pro‐inflammatory in mice in vivo.

Amyloid features and neuronal toxicity of mature prion fibrils are highly sensitive to high pressure

Prion proteins (PrP) can aggregate into toxic and possibly infectious amyloid fibrils. This particular macrostructure confers on them an extreme and still unexplained stability. To provide mechanistic insights into this self-assembly process, we used high pressure as a thermodynamic tool for perturbing the structure of mature amyloid fibrils that were prepared from recombinant full-length mouse PrP. Application of high pressure led to irreversible loss of several specific amyloid features, such as thioflavin T and 8-anilino-1-naphthalene sulfonate binding, alteration of the characteristic proteinase K digestion pattern, and a significant decrease in the β-sheet structure and cytotoxicity of amyloid fibrils. Partial disaggregation of the mature fibrils into monomeric soluble PrP was observed. The remaining amyloid fibrils underwent a change in secondary structure that led to morphologically different fibrils composed of a reduced number of proto-filaments. The kinetics of these reactions was studied by recording the pressure-induced dissociation of thioflavin T from the amyloid fibrils. Analysis of the pressure and temperature dependence of the relaxation rates revealed partly unstructured and hydrated kinetic transition states and highlighted the importance of collapsing and hydrating inter- and intramolecular cavities to overcome the high free energy barrier that stabilizes amyloid fibrils.

Molecular mechanisms of fibrillogenesis and the protective role of amyloid P component: two possible avenues for therapy

Amyloid deposits regress when the supply of fibril precursor proteins is sufficiently reduced, indicating that amyloid fibrils are degradable in vivo. Serum amyloid P component (SAP), a universal constituent of amyloid deposits, efficiently protects amyloid fibrils from proteolysis in vitro, and may contribute to persistence of amyloid in vivo. Drugs that prevent binding of SAP to amyloid fibrils in vivo should therefore promote regression of amyloid and we are actively seeking such agents. A complementary strategy is identification of critical molecular processes in fibrillogenesis as targets for pharmacological intervention. All amyloidogenic variants of apolipoprotein AI contain an additional positive charge in the N-terminal fibrillogenic region of the protein. This is unlikely to be a coincidence and should be informative about amyloidogenesis by this protein. The two amyloidogenic variants of human lysozyme, caused by the first natural mutations found in its gene, provide a particularly powerful model system because both the crystal structure and folding pathways of wild-type lysozyme are so well characterized. The amyloidogenic variant lysozymes have similar 3D crystal structures to the wild type, but are notably less thermostable. They unfold on heating, lose enzymic activity, and aggregate to form amyloid fibrils in vitro.

Drug Insight: emerging therapies for amyloidosis

Amyloidosis is a clinical disorder caused by extracellular deposition of proteins that are normally soluble as insoluble, abnormal fibrils that impair organ function. More than 20 unrelated proteins can form amyloid fibrils in vivo. All fibrils share cross-beta core structure and pathognomonic red-green birefringence when viewed under cross-polarized light after staining with Congo red. Amyloidosis can be acquired or hereditary, localized or systemic, and is classified according to the fibril precursor protein. Local amyloid deposition occurs in the brain in Alzheimer's disease and in the pancreas in maturity-onset diabetes, but a direct role in the pathogenesis of these diseases remains unproven. Systemic amyloidosis, with amyloid deposits in the viscera, blood vessel walls and connective tissues, is usually fatal and is the cause of about one death per thousand in developed countries. Recent elucidation of fundamental aspects of the pathogenesis of amyloidosis, and developments in diagnosis and monitoring of this disorder have greatly improved outcome for patients. Several exciting novel therapeutic strategies, reviewed in this article, are in development. These include interference with different stages of fibrillogenesis and enhancement of clearance of amyloid deposits.

Diagnostic performance of 123I-labeled serum amyloid P component scintigraphy in patients with amyloidosis

PURPOSE

To assess the diagnostic accuracy and additional information provided by 123I-labeled serum amyloid P component (SAP) scintigraphy in patients with systemic and localized amyloidosis.

SUBJECTS AND METHODS

123I-labeled human SAP was injected intravenously into 20 controls and 189 consecutive patients with histologically proven amyloidosis: of AA type in 60 cases, AL type in 80, hereditary ATTR type in 27, and localized amyloidosis in 22 cases. SAP scintigrams were obtained 24 hours after tracer injection and were analyzed for abnormal patterns of uptake. Sensitivity and specificity were determined, and scintigraphic findings were compared with clinical data.

RESULTS

Diagnostic sensitivity of SAP scintigraphy for systemic AA, AL, and ATTR amyloidosis was 90%, 90%, and 48% respectively, and specificity was 93%. The distribution of amyloid was less diverse in AA than in AL type. Myocardial uptake was not visualized in any patient. Splenic amyloid was very frequent (80%) in AA and AL type but rarely detected clinically (14%). Abnormal tracer uptake in the liver and kidneys correlated with disturbed liver function and proteinuria, respectively. Bone marrow uptake was specific for AL (21%) and was more frequent in AL kappa than AL lambda. Localized amyloid deposits were not imaged.

CONCLUSION

SAP scintigraphy is diagnostic of amyloid in most patients with AA and AL type but fewer with hereditary ATTR type, relating to differing distributions and burdens of amyloid in these disorders. It usually reveals more widespread organ involvement than is identified clinically, and certain distributions of amyloid are characteristic of particular fibril types.

Renal amyloidosis: an uncommon complication of juvenile idiopathic arthritis

A 9-year-old girl presented with systemic-onset juvenile idiopathic arthritis, diagnosed at 3.5 of age and which was difficult to control despite several therapeutic trials. Five years after diagnosis of juvenile idiopathic arthritis, nephrotic proteinuria was noticed. Renal biopsy confirmed the diagnosis of amyloidosis, and chlorambucil was initiated, with general improvement of the disease and reduction of proteinuria.

Serum amyloid A production by chicken fibroblast-like synoviocytes

In brown chicken with chronic inflammatory processes of the joints amyloid arthropathy easily develops. The amyloid has been shown to be of the AA type which is derived from serum amyloid A (SAA). The aim of the present study was to investigate whether fibroblast-like synoviocytes (FLS) originating from brown chicken and other chicken breeds express SAA mRNA and produce SAA protein. FLS were isolated from the knee joint synovium of healthy brown chickens, white chickens, and broilers. The absence of macrophages in FLS cultures was confirmed by assessment of the phagocytic capability and by immunohistochemistry. Additionally, cultured cells were identified by electron microscopy and immunohistochemical staining. Expression of SAA mRNA in normal and lipopolysaccharide (LPS)-stimulated cells was assessed by in situ hybridization, Northern blot analysis, reverse transcriptase-polymerase chain reaction (RT-PCR), Southern blot analysis and real-time quantitative PCR. SAA protein production was analyzed by Western blotting and ELISA. SAA mRNA was detected in unstimulated FLS isolated from the three different chicken breeds and more abundantly in those stimulated with LPS. However, SAA protein production was only detected in culture medium and cell lysate of LPS-stimulated FLS. Furthermore, FLS produced SAA in a concentration-dependent manner after stimulation with different amounts of LPS. The data suggest that during infection and inflammation chicken FLS may act as a source of articular SAA. This process may enhance development of amyloid from SAA in the joint.

The effects of vitamin A, pentoxyfylline and methylprednisolone on experimentally induced amyloid arthropathy in brown layer chicks

The effects of vitamin A, pentoxyfylline and methylprednisolone on experimentally induced amyloid arthropathy were investigated. In this study, 175 1-day-old brown layer chicks were used. Throughout the study Group II (vitamin A) received high doses of vitamin A (75,000 IU/kg), whereas Group I (negative control), Group III (positive control), Group IV (pentoxyfylline) and Group V (methylprednisolone) received normal levels of vitamin A in the diet. At the fifth week, the experimental Groups II, III, IV and V were injected with Freund's adjuvant intra-articularly to induce amyloid arthropathy. Group IV received pentoxyfylline and Group V received methylprednisolone (10 mg/kg, intramuscularly) once. Joint and blood samples were examined 13 weeks after the injections. The values in Groups I, II, III, IV and V, respectively, were as follows: amyloid arthropathy formation (%), 0, 100, 87, 76, 66; serum amyloid A (ng/ml), 166+/-17, 607+/-40, 423+/-39, 342+/-27, 293+/-22; serum retinol (microg/dl): 59.75+/-3.8, 42.72+/-3, 59.24+/-3.6, 102+/-9.1, 101.3+/-12.3; heterophil/lymphocyte ratio: 0.504, 0.75, 0.75, 0.087, 0.44. In conclusion, it was observed that vitamin A enhanced the development of amyloid arthropathy and there were positive associations between amyloidosis, increased levels of serum amyloid A and increased numbers of tissue infiltrating macrophages. Methylprednisolone had a more successful inhibitory effect on amyloid arthropathy than pentoxyfylline.

Reduced intensity allogeneic stem cell transplantation for systemic primary amyloidosis refractory to high-dose melphalan

Complete elimination of the plasma cell dyscrasia is a rational therapeutic goal, as intercepting supply of precursor protein is a necessary condition for a major regression of amyloid deposits. High-dose melphalan with autologous stem cell transplantation has shown the ability to induce complete hematological response (HR) along with recovery of organ dysfunction. However, the rate of HR with this treatment rarely exceeds 40%. We describe here the first known case of successful reduced intensity allogeneic stem cell transplantation (RIST) for a patient with primary amyloidosis complicated with nephrotic syndrome but without cardiac disease, who had obtained only partial HR by high-dose melphalan with autologous stem cell transplantation. RIST may be feasible and be capable of achieving complete HR along with recovery from nephrotic syndrome with acceptable toxicity.

Amyloidosis

Amyloidosis is not a single disease but a series of diseases in which there is extracellular deposition of a protein which, although it may be derived from different and unrelated sources, folds into a beta pleated sheet. There have recently been significant advances in elucidating the pathogenesis and in the treatment of this group of disorders. By identifying the source of precursor protein, treatment is aimed at eliminating or reducing the extent of deposition and is tailored for each patient. Early diagnosis is required for the optimal effect of treatment on patient survival and quality of life. An increased awareness among physicians of the spectrum of the disease and tools to aid its diagnosis is of increasing importance.

Secondary amyloidosis as a life-ending event in multifocal motor neuropathy

Multifocal motor neuropathy (MMN) is a disorder of peripheral nerve often associated with a high monosialoganglioside (GM1) antibody and multifocal conduction block. It has a chronic, indolent course with involvement of predominantly peripheral motor nerves, usually in an asymmetric fashion. There have been few reported cases of progression to frank quadriplegia. Secondary amyloidosis refers to the deposition of amyloid in various tissues due to an underlying chronic inflammatory state. We report the first case, to our knowledge, of a patient with MMN associated with high titer of GM1 antibody who developed acute paraplegia with both cranial nerve and worsening sensory involvement associated with multiorgan compromise due to a secondary amyloidosis involving the myocardium.

Prognostic factors in juvenile idiopathic arthritis

Prognostic factors in juvenile arthritis are related to many variables that must be evaluated according to the different subtypes. The International League of Associations of Rheumatologists (ILAR) recently proposed six different categories referred to as the Durban criteria, under the eponym of juvenile idiopathic arthritis (JIA). The aim of this classification was to define homogeneous groups according to their clinical and biologic features. The prognostic factors were classified into the different categories of JIA. A poor outcome in the systemic form correlated with markers of disease activity, such as fever and polyarticular involvement, within the first 6 months. The risk of joint destruction in oligoarthritis correlated with the severity of arthritis within the first 2 years. Polyarthritis with positive rheumatoid factor is associated with marked disability in adulthood. In a group of psoriatic patients, the risk of developing sacroiliitis is higher in male and HLA-B27-positive patients. Patients with enthesitis-related arthritis with lower limb, knee, and tarsal involvement also are at greater risk of developing sacroiliitis. Chronic uveitis is a complication of JIA observed mainly in patients with oligoarthritis associated with positive antinuclear antibodies in serum. Secondary amyloidosis is observed mainly in children with systemic JIA. The long-term outcome must be discussed according to the various therapies. Corticosteroids contribute to growth retardation and osteoporosis, for which the use of human recombinant growth hormone and biphosphonates may be an option. Newer encouraging therapies such as anticytokines have been proposed for children with active disease. Autologous stem cell transplantation is being evaluated in some centers with promising results; however, it has a high rate of mortality. Further discussion regarding which patients should undergo autologous stem cell transplantation is needed, as is further discussion regarding the technical adaptations necessary.

Amyloid load and clinical outcome in AA amyloidosis in relation to circulating concentration of serum amyloid A protein

BACKGROUND

Reactive systemic (AA, secondary) amyloidosis occurs in chronic inflammatory diseases, and most patients present with nephropathy. The amyloid fibrils are derived from the circulating acute-phase reactant serum amyloid A protein (SAA), but the relation between production of fibril precursor protein, amyloid load, and clinical outcome in AA and other types of amyloidosis is unclear.

METHODS

We studied amyloidotic organ function and survival prospectively for 12-117 months in 80 patients with systemic AA amyloidosis in whom serum SAA concentration was measured monthly and visceral amyloid deposits were assessed annually by serum amyloid P component scintigraphy. Underlying inflammatory diseases were treated as vigorously as possible.

FINDINGS

Amyloid deposits regressed in 25 of 42 patients whose median SAA values were within the reference range (<10 mg/L) throughout follow-up, and amyloidotic organ function stabilised or improved in 39 of these cases. Outcome varied substantially among patients whose median SAA concentration exceeded 10 mg/L, but amyloid load increased and organ function deteriorated in most of those whose SAA was persistently above 50 mg/L. Estimated survival at 10 years was 90% in patients whose median SAA was under 10 mg/L, and 40% among those whose median SAA exceeded this value (p=0.0009).

INTERPRETATION

Although isolated amyloid fibrils are stable in vitro, AA amyloid deposits exist in a state of dynamic turnover, and outcome is favourable in AA amyloidosis when the SAA concentration is maintained below 10 mg/L. The potential for amyloid to regress and for the function of amyloidotic organs to recover support therapeutic strategies to decrease the supply of amyloid fibril precursor proteins in amyloidosis generally.

CLINICAL AND BIOCHEMICAL OUTCOME OF HEPATORENAL TRANSPLANTATION FOR HEREDITARY SYSTEMIC AMYLOIDOSIS ASSOCIATED WITH APOLIPOPROTEIN AI Gly26Arg1

BACKGROUND

Treatment of systemic amyloidosis comprises measures to support failing organ function coupled with attempts to reduce the supply of the respective amyloid fibril precursor protein. Orthotopic hepatic transplantation is effective in familial amyloid polyneuropathy associated with variant transthyretin, because this protein is produced almost exclusively in the liver. Hepatic transplantation has not been performed in hereditary apolipoprotein AI (apoAI) amyloidosis, and the liver's contribution to plasma apoAI levels has not been determined in vivo.

METHODS

A 57-year-old Irish man with hereditary systemic amyloidosis associated with apoAI Gly26Arg, which had led to end-stage renal failure and progressive liver dysfunction, underwent hepatorenal transplantation. His outcome was followed clinically and his amyloid deposits were monitored with serum amyloid P component scintigraphy. The proportion of variant apoAI in the plasma was estimated by quantitative isoelectric focusing before and after liver transplantation.

RESULTS

Plasma levels of variant apoAI decreased by 50% after liver transplantation, and the patient was asymptomatic 2 years after surgery. Subclinical amyloid deposits that were present in his spleen and heart preoperatively have regressed and stabilized respectively.

CONCLUSIONS

Orthotopic liver transplantation substantially reduces the supply of the amyloid fibril precursor protein in hereditary apoAI amyloidosis, and the excellent outcome in this patient probably reflects the balance between deposition and turnover of amyloid having been altered in favor of the latter. These findings support the use of liver transplantation in patients with hereditary apoAI amyloidosis who develop hepatic dysfunction.

Pathogenesis, diagnosis and treatment of systemic amyloidosis

Amyloidosis is a disorder of protein folding in which normally soluble proteins are deposited as abnormal, insoluble fibrils that disrupt tissue structure and cause disease. Although about 20 different unrelated proteins can form amyloid fibrils in vivo, all such fibrils share a common cross-beta core structure. Some natural wild-type proteins are inherently amyloidogenic, form fibrils and cause amyloidosis in old age or if present for long periods at abnormally high concentration. Other amyloidogenic proteins are acquired or inherited variants, containing amino-acid substitutions that render them unstable so that they populate partly unfolded states under physiological conditions, and these intermediates then aggregate in the stable amyloid fold. In addition to the fibrils, amyloid deposits always contain the non-fibrillar pentraxin plasma protein, serum amyloid P component (SAP), because it undergoes specific calcium-dependent binding to amyloid fibrils. SAP contributes to amyloidogenesis, probably by stabilizing amyloid fibrils and retarding their clearance. Radiolabelled SAP is an extremely useful, safe, specific, non-invasive, quantitative tracer for scintigraphic imaging of systemic amyloid deposits. Its use has demonstrated that elimination of the supply of amyloid fibril precursor proteins leads to regression of amyloid deposits with clinical benefit. Current treatment of amyloidosis comprises careful maintenance of impaired organ function, replacement of end-stage organ failure by dialysis or transplantation, and vigorous efforts to control underlying conditions responsible for production of fibril precursors. New approaches under development include drugs for stabilization of the native fold of precursor proteins, inhibition of fibrillogenesis, reversion of the amyloid to the native fold, and dissociation of SAP to accelerate amyloid fibril clearance in vivo.

Human neurons generate C-reactive protein and amyloid P: upregulation in Alzheimer's disease

C-reactive protein (CRP) and amyloid P (AP) are pentraxins which are associated with many pathological lesions, including the amyloid deposits and neurofibrillary tangles (NFTs) of Alzheimer disease (AD). It has always been assumed that they are generated by liver and delivered to their sites of action by serum. Here we report by in situ hydridization, reverse transcriptase-polymerase chain reaction analysis, Western blotting and immunohistochemistry that the mRNAs and proteins of both CRP and AP are concentrated in pyramidal neurons and are upregulated in affected areas of AD brain. Controlling pentraxin production at the tissue level may be important in reducing inflammatory damage in AD.

Localization of injected anti-serum amyloid A antibody to the lesions in murine reactive amyloidosis

Abstract This paper examines whether an antibody to serum amyloid A (SAA) protein is incorporated into amyloid deposits in vivo in murine reactive amyloidosis. First, monoclonal anti-SAA antibody was injected into amyloid-laden mice, and localization of the antibody was immunohistochemically assessed. Following the injection, plasma clearance of the antibody was analyzed. The antibody was detected in the amyloid deposits in spleen, liver, and kidney from mice killed on days 0-3 postinjection. The injected antibody disappeared more rapidly from the circulation of amyloidotic animals than from nonamyloidotic animals. The anti-SAA antibody can associate with amyloid deposits in vivo. Further applications, particularly amyloid imaging, should be investigated.

Renal transplantation for amyloid end-stage renal failure-insights from serial serum amyloid P component scintigraphy

Although end-stage renal failure (ESRF) is common in systemic amyloidosis, few such patients receive renal transplants. Serum amyloid P component (SAP) scintigraphy is a specific method for the imaging and quantification of amyloid deposits in vivo, which has not previously been used to evaluate the outcome of renal transplantation in patients with amyloidosis. Evidence of renal graft amyloid was sought by SAP scintigraphy in 15 patients with systemic amyloidosis who had undergone renal transplantation 42-216 months (median, 73 months) previously. Prospective serial scans were obtained annually in eight cases. Renal grafts studied shortly after transplantation gave blood-pool images. The grafts remained normal in all patients whose underlying amyloidogenic disorder had remitted, whereas there was abnormal uptake of labelled SAP, indicating graft amyloidosis, in four out of 10 patients whose amyloid fibril precursor protein supply had not diminished. Graft amyloidosis was corroborated by renal dysfunction in each case, and by histology in one patient. SAP scintigraphy enables renal transplant grafts to be monitored noninvasively for involvement by amyloid. The lack of graft amyloidosis in all patients in whom the amyloidogenic underlying disorder had remitted, and in more than half of those in whom it had not, supports the use of renal transplantation for ESRF in systemic amyloidosis.

[Diagnostic strategy in amyloidosis]

INTRODUCTION

The diagnosis of amyloidosis is a four-step strategy requiring: 1) a high degree of suspicion, as the clinical presentation of the disease is very polymorphous; 2) the biochemical nature of the disease; 3) the evaluation of the disease spread and 4) how it evolves.

EXEGESIS

Simple and noninvasive biopsies usually make it possible to diagnose amyloidosis. Available treatments of generalized amyloidosis require an exact characterization of the nature of amyloid deposits, which is based on the clinical context, immunohistochemical analysis of amyloid deposits, and genetic testing.

CONCLUSION

Management of amyloidosis should be improved by better characterization of amyloid deposits. This would result in epidemiological data which are currently lacking.

[Treatments for amyloidosis beyond symptomatic care]

INTRODUCTION

Amyloid syndromes are pathogenetically different, each of the various amyloid diseases requiring specific treatment. Unfortunately, those treatments are often preventive and symptomatic, some efficient therapies being limited to particular types of amyloidosis.

CURRENT KNOWLEDGE AND KEY POINTS

Colchicine is effective in the prevention of amyloidosis due to familial Mediterranean fever but is less or not effective in other situations. Cytotoxic agents are useful in the treatment of AL amyloidosis with or without hemopoietic stem cell transplantation. Liver transplantation is indicated for familial polyneuropathy and kidney transplantation for dialysis-related beta 2 microglobulin amyloidosis.

FUTURE PROSPECTS AND PROJECTS

In vivo binding of serum amyloid P (SAP) (component shared by all amyloid deposits) to amyloid fibril, is a new avenue in the therapeutic approach. Development of radiolabeled SAP scintigraphy allows assessment of the disease outcome and evaluation of treatment-related effects. The various treatments that were assessed until now with the objective of curing the disease are reviewed.

A quantitative method for detecting deposits of amyloid A protein in aspirated fat tissue of patients with arthritis

OBJECTIVE

To describe a new, quantitative, and reproducible method for detecting deposits of amyloid A protein in aspirated fat tissue and to compare it with smears stained with Congo red.

METHODS

After extraction of at least 30 mg of abdominal fat tissue in guanidine, the amyloid A protein concentration was measured by a monoclonal antibody-based sandwich ELISA.

RESULTS

The concentrations in 24 patients with arthritis and AA amyloidosis (median 236, range 1.1-8530 ng/mg tissue) were higher (p < 0.001) than in non-arthritic controls, uncomplicated rheumatoid arthritis, and other types of systemic amyloidosis (median 1.1, range 1.1-11.6 ng/mg tissue). Patients with extensive deposits, according to Congo red staining, had higher concentrations than patients with minute deposits.

CONCLUSION

This is a new, quantitative, and reproducible method for detecting deposits of amyloid A protein in aspirated fat tissue of patients with arthritis, even when minute deposits are present as detected in smears stained with Congo red.

SAA1 alleles as risk factors in reactive systemic AA amyloidosis

SAA1 is the predominant isoform of acute phase human SAA deposited as AA amyloid fibrils in reactive systemic amyloidosis. It has recently been reported that in the Japanese population, in whom the SAA1 gamma allele occurs with a frequency of 37%, possession of, and especially, homozygosity for this allele is a significant risk factor for AA amyloidosis in adult patients with rheumatoid arthritis (RA). In contrast we report here that in a control sample of 95 healthy adult male Caucasians the SAA1 gamma allele occurs at the much lower frequency of 5.3% and that, among 41 patients with juvenile chronic arthritis (JCA) and AA amyloidosis, there was a highly significantly increased frequency of the SAA1 alpha allele (90.2%), and particularly homozygosity for this allele (80.5%), compared both to the healthy controls (75.8% and 57.9% respectively) and to 8 JCA cases without amyloid (56.3% and 12.5%). A similar trend with respect to frequency of the SAA1 alpha allele and homozygosity for it was observed among 26 adult Caucasian RA patients with AA amyloid and 26 such cases without amyloid, although it did not reach statistical significance. These results suggest that there is probably differential amyloidogenicity amongst the different SAA1 isoforms and indicate that homozygosity for SAA1 alpha and SAA1 gamma in the different populations is a significant risk factor for development of AA amyloidosis. In Caucasian patients with JCA, the presence of the homozygous SAA1 alpha genotype indicates high risk of amyloidosis and should encourage early and aggressive anti-inflammatory therapy to keep circulating SAA levels as low as possible.

Progressive cardiac amyloidosis following liver transplantation for familial amyloid polyneuropathy: implications for amyloid fibrillogenesis

BACKGROUND

Circulating transthyretin (TTR) is derived from the liver, and orthotopic liver transplantation (OLT) is widely performed for variant TTR-associated familial amyloid polyneuropathy (FAP). The effect of OLT on FAP-related cardiac amyloid is of particular interest because wild-type TTR can itself be deposited as senile cardiac amyloid.

METHODS

Serial echocardiography was performed in 20 FAP patients, 14 of whom underwent OLT, and 10 other liver transplant patients. Follow-up included serum amyloid P component scintigraphy and measurement of plasma TTR before and after OLT.

RESULTS

Cardiac amyloidosis progressed rapidly in three FAP patients (TTR Pro52 and Thr84 mutations) after OLT, even though the deposits elsewhere had stabilized or regressed. Results of echocardiography improved in three transplant patients with TTR Met30 and remained normal in seven other patients. Plasma TTR levels were altered substantially after OLT, but they did not reflect the cardiac findings.

CONCLUSIONS

Although amyloid deposition in FAP is generally inhibited after OLT, cardiac amyloidosis can be exacerbated, probably due to enhanced deposition of wild-type TTR on a template of amyloid derived from variant TTR. The phenomenon may be mutation-dependent. These findings suggest that amyloid formation de novo and its subsequent accumulation can be promoted by different factors, which may be organ-specific.

The first international standard for serum amyloid A protein (SAA). Evaluation in an international collaborative study

An ampouled preparation of acute phase serum rich in serum amyloid A protein (SAA) was evaluated in seven laboratories in six countries for its suitability to serve as the international standard for immunoassay of SAA. A variety of different immunoassays were used. On the basis of the results reported here and with the authorization of the Expert Committee on Biological Standardization of the World Health Organization (WHO) this preparation (coded 92/680) was established as the first international standard of SAA.

Amyloid deposition is delayed in mice with targeted deletion of the serum amyloid P component gene

The tissue amyloid deposits that characterize systemic amyloidosis, Alzheimer's disease and the transmissible spongiform encephalopathies always contain serum amyloid P component (SAP) bound to the amyloid fibrils. We have previously proposed that this normal plasma protein may contribute to amyloidogenesis by stabilizing the deposits. Here we show that the induction of reactive amyloidosis is retarded in mice with targeted deletion of the SAP gene. This first demonstration of the participation of SAP in pathogenesis of amyloidosis in vivo confirms that inhibition of SAP binding to amyloid fibrils is an attractive therapeutic target in a range of serious human diseases.

Long term effect of renal transplantation on dialysis-related amyloid deposits and symptomatology

We report the five year outcome of nine patients with dialysis-related amyloid (DRA) who underwent successful renal transplantation (RT) and six patients who remained on hemodialysis (HD). Amyloid bone cysts, a radiologic feature of DRA, and scintigraphy with 123I-labeled serum amyloid P component (SAP), a specific technique for evaluating amyloid deposits in vivo, were monitored and compared with clinical features. In all HD patients there was clinical, scintigraphic and/or radiologic evidence that DRA progressed. In contrast, eight of the RT patients experienced profound early relief of DRA symptoms following transplantation that persisted throughout follow-up, despite the reduction or withdrawal of corticosteroids. Amyloid bone cysts improved in four patients and SAP scans demonstrated regression of articular amyloid in eight out of nine cases. The modest radiographic improvement suggests that amyloid is mobilized more slowly in bone cysts than elsewhere or that cystic bone is remodeled poorly. This is the first objective evidence that DRA regresses following renal transplantation, and suggests that this may contribute to the long-term relief of DRA symptoms in transplant recipients who discontinue corticosteroids.

Prospective and serial study of primary amyloidosis with serum amyloid P component scintigraphy: from diagnosis to prognosis

OBJECTIVE

The purpose of this study was to assess the value of the serum amyloid P (SAP) component scintigraphy in patients with primary amyloidosis (AL).

MATERIAL AND METHODS

Pure human SAP labeled with iodine-123 (123I-SAP) was given intravenously to 24 patients with biopsy-proven systemic amyloidosis (15 without multiple myeloma = group 1, and 9 with multiple myeloma = group 2) and to 6 patients with multiple myeloma without any clinical or biological signs of amyloidosis (group 3). Whole-body images as well as regional views and tissue retention levels were obtained after 24 hours. Our study was approved by the institutional review committee and all individuals gave informed consent and were prospectively studied (median 13 months, range 1 to 47 from the date of the scintigraphy to May 1995).

RESULTS

Organ localization of 123I-SAP, indicating the presence of substantial visceral amyloid deposits, was observed in all patients in group 1 and 2. The organ uptake of 123I-SAP included the spleen (1 patient was splenectomized) in 20 of 23 cases (87%), the liver in 15 of 24 (60%), and the kidneys in 6 of 24 (25%). Myocardial 123I-SAP was never seen although 13 out of the 24 patients had clinical or echographic data for amyloidosis. Twenty-four hour tissue retention was significantly elevated in all patients (group 1 and group 2): 55.66% +/- 19.16% in group 1 and 34.37% +/- 24.92% in group 2, as compared with normal levels < 24%. The sensitivity of the technique was 79% when only organ uptake was considered but reached 100% when tissue retention was also considered. The 24-hour tissue retention might be correlated with the severity of the amyloidosis: mean survival in patients with tissue retention greater than 50% was 11.3 months versus 24.5 months in patients with levels less or equal to 50%. Five of the 6 patients with multiple myeloma without evidence of amyloidosis had abnormal 123I-SAP imaging and 24-hour tissue retention levels. In 2 of them, amyloidosis was secondly detected. In the 9 patients who had two scintigraphies, variations in 24-hour tissue retention values were in accordance with the clinical evaluation.

CONCLUSIONS

Spleen and liver distribution of amyloidosis is mostly revealed by 123I-SAP scintigraphy in patients with AL amyloidosis. The uptake of 123I-SAP appeared in proportion to the quantity of amyloidosis present in different tissues, and the relative quantity of amyloid deposits in the myocardium, carpal tunnel, digestive tract, and kidneys was often small and seldom visualized by 123I-SAP scintigraphy. In contrast 24-hour tissue retention levels were abnormal in all cases of known AL amyloidosis. This may be a positive argument for the diagnosis of amyloidosis when histopathological tests are normal. Tissue retention levels appear important as they may be correlated with survival.

Cardiac and pleuropulmonary AL amyloid imaging with technetium-99m labelled aprotinin

Antiproteases are known to be present in amyloid deposits. We evaluated the possibility of using an anti-serine protease (aprotinin) labelled with technetium-99m (TcA), usually employed as a cortical renal tracer, for the imaging of amyloid deposits. Because of the known high uptake of TcA by the kidneys, we limited our analysis to extra-abdominal amyloid localizations. We report the scintigraphic findings observed in 24 patients with light chain amyloidosis (AL) and one with a hereditary form who were known or suspected to have extra-abdominal involvement. Planar scans obtained 100min after i.v. TcA administration showed myocardial accumulation in 11 patients, pleuropulmonary accumulation in nine, pericardial accumulation in two and localization in the neck region (thyroid, salivary glands and tongue) in eight. TcA scintigraphy was negative in five patients without clinical or laboratory evidence of extra-abdominal involvement, as well as in 12 control group patients with cardiac and renal diseases. These preliminary results indicate TcA to be a low-cost, readily available radiopharmaceutical for imaging of extra-abdominal involvement in AL type amyloidosis.

Treatment of amyloidosis

Amyloidosis is the extracellular deposition of normally soluble autologous protein in a characteristic abnormal fibrillar form. Systemic amyloidosis and some local forms are progressive, cause major morbidity, and are often fatal. No treatment specifically causes the resolution of amyloid deposits, but therapy that reduces the supply of amyloid fibril precursor proteins can improve survival and preserve organ function. Major regression of amyloid occurs in at least a proportion of such cases, suggesting that the clinical improvement reflects mobilization of amyloid. The clearest evidence for regression of amyloid has been obtained in juvenile rheumatoid arthritis patients with AA amyloidosis treated with chlorambucil. This drug suppresses the acute phase production of serum amyloid A protein, the precursor of AA amyloid fibrils, and is associated with remission of proteinuria and greatly improved survival. In many such patients, scintigraphy with serum amyloid P component shows major regression of amyloid over 12 to 36 months and frequently reveals a discrepancy between the local amyloid load and organ dysfunction. Measurement of target organ function is therefore not an adequate method for monitoring treatment aimed at promoting the resolution of amyloid. In monoclonal immunoglobulin light chain (AL) amyloidosis the aim of treatment is to suppress the underlying B-cell clone and, therefore, production of the amyloid fibril precursor protein. This can be difficult to achieve or sustain and, since the prognosis is so poor, many patients die before benefits of therapy are realized. A recent development has been the introduction of liver transplantation as treatment for familial amyloid polyneuropathy caused by transthyretin gene mutations. This leads to the disappearance of variant transthyretin from the plasma and halts progression of the neurologic disease. Features of autonomic neuropathy frequently ameliorate, and improvement in peripheral motor nerve function has been recently reported. Serum amyloid P component scans show regression of associated visceral amyloidosis. This surgical form of gene therapy holds much promise for patients with familial amyloid polyneuropathy and has been widely adopted. The only other form of amyloidosis in which the supply of the fibril precursor protein can be sharply reduced is beta 2M amyloidosis in long-term hemodialysis patients. Renal transplantation lowers the plasma concentration of beta 2M to normal levels and is associated with rapid improvement of the osteoarticular symptoms. Preliminary observations suggest that the beta 2M amyloid deposits also can regress in some patients.(ABSTRACT TRUNCATED AT 400 WORDS)

Amyloidosis

Amyloidosis is the generic term for a heterogeneous group of disorders characterised by the common finding of amyloid deposition. The various acquired and hereditary syndromes are classified according to the identity of the respective amyloid fibril sub-unit protein. Systemic amyloidosis and some local forms are progressive diseases that are frequently fatal. The diagnosis of systemic amyloidosis is only occasionally suspected on clinical grounds alone, and is more often considered when an associated disorder such as a chronic inflammatory disease or monoclonal gammopathy is present. No blood test is diagnostic of amyloidosis but routine haematological and biochemical investigations have important roles in defining the underlying metabolic disturbance and evaluating function of affected organs. The diagnosis can only be confirmed by demonstrating the presence of tissue amyloid deposits. Traditionally this required histology but the recent introduction of labelled serum amyloid P component scintigraphy is a specific alternative that provides a quantitative macroscopic whole body survey of amyloid deposits. No treatment specifically causes the resolution of amyloid but therapy which reduces the supply of amyloid fibril precursor proteins can improve survival and preserve organ function. Major regression of amyloid occurs in at least a proportion of such cases suggesting that clinical improvement reflects mobilisation of amyloid.

In vitro degradation of serum amyloid A by cathepsin D and other acid proteases: possible protection against amyloid fibril formation

The effects of acid proteases on degradation of serum amyloid A protein (SAA) were investigated in vitro. Human recombinant SAA1 (rSAA1), when incubated with human spleen extracts at pH 3.2, was degraded in the amino-terminal portion of the molecule. This reaction was inhibited by an acid protease inhibitor, pepstatin. The degraded SAA molecules lacking nine or more amino-terminal residues, when exposed to in vitro fibril-forming conditions, failed to form Congo red positive precipitates and did not show amyloid fibril-like structure by electron microscopy. This suggests that the amino-terminal portion of SAA is essential for fibril formation. Cathepsin D, one of the lysosomal enzymes, also initiated degradation of rSAA1 at the amino-terminus. Cathepsin D immunoreactivity was detected in marginal areas of amyloid deposits in spleens from patients with reactive amyloidosis. These findings suggest that cathepsin D or similar acid proteases may be involved in SAA catabolism and may protect against amyloid formation.

Serum amyloid P component prevents proteolysis of the amyloid fibrils of Alzheimer disease and systemic amyloidosis

Extracellular deposition of amyloid fibrils is responsible for the pathology in the systemic amyloidoses and probably also in Alzheimer disease [Haass, C. & Selkoe, D. J. (1993) Cell 75, 1039-1042] and type II diabetes mellitus [Lorenzo, A., Razzaboni, B., Weir, G. C. & Yankner, B. A. (1994) Nature (London) 368, 756-760]. The fibrils themselves are relatively resistant to proteolysis in vitro but amyloid deposits do regress in vivo, usually with clinical benefit, if new amyloid fibril formation can be halted. Serum amyloid P component (SAP) binds to all types of amyloid fibrils and is a universal constituent of amyloid deposits, including the plaques, amorphous amyloid beta protein deposits and neurofibrillary tangles of Alzheimer disease [Coria, F., Castano, E., Prelli, F., Larrondo-Lillo, M., van Duinen, S., Shelanski, M. L. & Frangione, B. (1988) Lab. Invest. 58, 454-458; Duong, T., Pommier, E. C. & Scheibel, A. B. (1989) Acta Neuropathol. 78, 429-437]. Here we show that SAP prevents proteolysis of the amyloid fibrils of Alzheimer disease, of systemic amyloid A amyloidosis and of systemic monoclonal light chain amyloidosis and may thereby contribute to their persistence in vivo. SAP is not an enzyme inhibitor and is protective only when bound to the fibrils. Interference with binding of SAP to amyloid fibrils in vivo is thus an attractive therapeutic objective, achievement of which should promote regression of the deposits.

A novel variant of transthyretin, 59Thr-->Lys, associated with autosomal dominant cardiac amyloidosis in an Italian family

BACKGROUND

Amyloidosis is a disorder of protein metabolism characterized by extracellular accumulation of abnormal protein fibrils. Different proteins form the fibrils in different forms of the disease, and the condition can be acquired or hereditary. Involvement of the heart is quite common, producing a serious and usually fatal cardiomyopathy. Cardiac amyloidosis is often diagnosed late, and cardiac biopsy together with proper histological examination is essential. Contrary to previous perceptions, there is much recent evidence of effective treatment for several different types of systemic and cardiac amyloidosis, including the most common hereditary form caused by mutations in the transthyretin gene. Chemical and genetic typing of amyloid is therefore of considerable clinical importance.

METHODS AND RESULTS

Seven members in two generations of an Italian family presented with cardiac disease inherited as an autosomal dominant and were found to have systemic amyloidosis. Angina pectoris-like pain, an unusual feature in cardiac amyloidosis, was a prominent symptom, possibly related to partial obliteration of the distal coronary arteries by amyloid infiltration. There were also cases of sudden cardiac death. Peripheral and autonomic neuropathy, which are the usual features of hereditary amyloidosis, were present in only two cases, and a diagnosis of acquired, immunoglobulin light chain (AL type) amyloidosis was suspected in the index case before the family history emerged. In fact, the amyloid fibrils were composed of transthyretin, and the two affected individuals from whom DNA was available were both heterozygotes for a single base change in exon 3 of the transthyretin gene, encoding substitution of Lys for the wild-type Thr residue at position 59 in the mature protein. This mutation has not previously been reported.

CONCLUSIONS

We have identified a novel mutation in the transthyretin gene encoding 59Thr-->Lys associated with autosomal dominant hereditary systemic amyloidosis in an Italian kindred in whom cardiac involvement was the major feature. This family illustrates the difficulty in diagnosis of cardiac amyloid, the variable clinical phenotype in hereditary amyloidosis even within a family, and the importance of precise fibril typing for correct management in this condition.

Structure and function of the pentraxins

Over the past two years, the three-dimensional structure of the serum amyloid P component was defined by X-ray diffraction, the first such visualization of a pentraxin. Binding sites for calcium, ligands and complement were identified. New fusion proteins with amino acid sequence homology to the pentraxins were described, and new insights were gained into pentraxin phylogeny, biosynthesis, ligands, complement activation, leukocyte reactivity and biological functions in vivo.

Amyloidosis

Amyloidosis is a heterogeneous group of disorders characterized by extracellular deposition of abnormal protein fibrils which are derived from different proteins in different forms of the disease. Asymptomatic amyloid deposition in a variety of tissues is a universal accompaniment of ageing, and clinical amyloidosis is not rare. Intracerebral and cerebrovascular beta-protein amyloid deposits are a hallmark of the pathology of both sporadic and familial Alzheimer's disease, beta 2-microglobulin-derived amyloid is a common complication of long term haemodialysis, and islet amyloid polypeptide is the fibril protein in the universal islet amyloidosis of type II diabetes mellitus. New fibril proteins have lately been identified in hereditary amyloidosis, including variants of gelsolin, apolipoprotein AI, lysozyme and fibrinogen. The development of radiolabelled serum amyloid P component (SAP) scintigraphy has allowed amyloid to be diagnosed non-invasively in vivo for the first time, provided unique insight into the distribution and size of amyloid deposits, and yielded novel information on the natural history and the effects of treatment. Amyloid deposits are in a state of dynamic turnover and can regress if new fibril formation is halted. The recent elucidation of the three dimensional structure of human SAP may enable the design of specific therapeutic agents.

Amyloidosis: prognosis and treatment

The objective of this study was to review (1) the factors that have been linked to prediction of clinical outcome and survival in amyloidosis and (2) the available studies on the therapy for localized and systemic forms of amyloidosis. We made a retrospective review of the relevant literature on treatment and prognosis in localized and systemic amyloidosis dating back to 1975. The most important prognostic factors in amyloidosis are the presence of congestive heart failure, beta 2-microglobulin, and whether peripheral neuropathy dominates the presentation. The presence of a monoclonal light chain in serum or urine, multiple myeloma, and hepatic involvement are also important adverse factors. Colchicine is beneficial in treating familial Mediterranean fever and may play a role in managing secondary amyloidosis in inflammatory bowel disease. Chlorambucil is particularly useful in juvenile rheumatoid arthritis with amyloidosis. Dimethyl sulfoxide provides benefit in bladder and lichen amyloidosis. A trial of alkylating agent-based chemotherapy is reasonable in symptomatic primary systemic amyloidosis. Advances have been made in the treatment of amyloidosis and include chemotherapy, dialysis, transplantation, and improved supportive care. Definite disease regressions with long-term survival (> 10 years) are seen. Unfortunately, alternatives still need to be developed: Of 859 patients with primary systemic amyloidosis seen at the Mayo Clinic from 1982 to 1992, the median survival was 2.1 years.

The pentraxins, C-reactive protein and serum amyloid P component, are cleared and catabolized by hepatocytes in vivo

The cellular sites of clearance and degradation of the pentraxin plasma proteins, C-reactive protein, the classical acute phase reactant, and serum amyloid P component (SAP), a universal constituent of amyloid deposits, were sought using the ligand 125I-tyramine cellobiose (TC) which is substantially retained within the cells in which catabolism takes place. Pentraxins labeled with 125I-TC showed the same in vitro and in vivo ligand binding and the same in vivo plasma t1/2 as the directly iodinated proteins and the native unlabeled pentraxins, indicating that their mode of clearance was likely to be physiological. After intravenous injection into mice and rabbits of human C-reactive protein, human SAP, and mouse SAP, each labeled with 125I-TC, most of the radioactivity remaining in the body at 24 h was located in hepatocytes. None was detected in other liver cells, and only traces were present in other viscera; the rest was in the carcass, representing intact pentraxins in the blood and extravascular compartment, and escaped label which had not yet been excreted. Hepatocytes are thus the single major site of pentraxin clearance and catabolism in vivo. This is consistent with the observation that SAP that has localized to amyloid deposits persists there and is not degraded.