Biomedical subjects

M B Pepys

Publications and source records attributed to M B Pepys.

At least 73 records · Page 4Linked to original sources

PubMed1997

Common core structure of amyloid fibrils by synchrotron X-ray diffraction.

Tissue deposition of normally soluble proteins as insoluble amyloid fibrils is associated with serious diseases including the systemic amyloidoses, maturity onset diabetes, Alzheimer's disease and transmissible spongiform encephalopathy. Although the precursor proteins in different diseases do not share sequence homology or related native structure, the morphology and properties of all amyloid fibrils are remarkably similar. Using intense synchrotron sources we observed that six different ex vivo amyloid fibrils and two synthetic fibril preparations all gave similar high-resolution X-ray fibre diffraction patterns, consistent with a helical array of beta-sheets parallel to the fibre long axis, with the strands perpendicular to this axis. This confirms that amyloid fibrils comprise a structural superfamily and share a common protofilament substructure, irrespective of the nature of their precursor proteins.

Amyloid↗

PubMed1997

Echocardiographic assessment of cardiac involvement in systemic AL amyloidosis in relation to whole body amyloid load measured by serum amyloid P component (SAP) clearance.

The severity of cardiac infiltration in AL amyloidosis is unrelated to whole body amyloid load as measured by serum amyloid P (SAP) tracer studies. Radiolabeled SAP and echocardiography permit identification of patients with severe cardiac disease with a low whole body load who may be the best candidates for transplantation.

Adult↗

PubMed1997

Pentameric and decameric structures in solution of serum amyloid P component by X-ray and neutron scattering and molecular modelling analyses.

Human serum amyloid P component (SAP) is a normal plasma glycoprotein and the precursor of amyloid P component which is a universal constituent of the abnormal tissue deposits in amyloidosis. X-ray and neutron scattering data showed that pentameric or decameric ring structures for SAP in solution are readily distinguished. Further neutron data collection showed that SAP pentamers were reproducibly obtained in the presence of Ca2+ at pH 5.5 or in the presence of methyl 4,6-O-(1-carboxyethylidene)-beta-d-galactopyranoside (MObetaDG) and Ca2+ at pH 6.0 to 8.0, while SAP decamers were obtained in the presence of EDTA between pH 5.5 and 8.0. SAP pentamers have a mean X-ray RG of 3.99(+/-0.11) nm and a mean neutron RG of 3.69(+/-0.12) nm in 100% 2H2O. SAP decamers have a mean X-ray RG of 4.23(+/-0.12) nm and a mean neutron RG of 4.09(+/-0.14) nm in 100% 2H2O. The absorption coefficients of SAP pentamers and decamers differ by 10%. If we infer that the two alpha-helical A-faces are in contact with each other in the SAP decamer, the lack of structural change of the decamer with pH may be explained by the absence of His residues from the A-face of the SAP pentamer, and the change in absorption coefficients is compatible with the presence of Trp residues at this A-face. The rigid ring structure of pentameric SAP provided a test of scattering curves calculated from crystal structures. The only structural unknown is the orientation of the five chemically homogeneous oligosaccharide chains relative to the protein, but extended oligosaccharide structures were found to account for its scattering curve. X-ray scattering curves were best calculated using a hydrated structure, while neutron scattering curves were best calculated using an unhydrated structure. The outcome of these analyses was used to model the structure of decameric SAP. The evaluation of 640 structures for two SAP pentamers brought face-to-face to form SAP decamers gave better curve fits for structures in which the two A-faces were in contact with each other, in which it is likely that the two pentamers were out of alignment by a rotation of 36 degrees and the oligosaccharide chains were extended.

Carbohydrate Conformation↗

PubMed1997

Crystal structure of a decameric complex of human serum amyloid P component with bound dAMP.

Serum amyloid P component (SAP) is a glycoprotein that binds in a calcium-dependent fashion to a variety of ligands including other proteins, glycosaminoglycans and DNA. SAP is universally associated with the amyloid deposits in all forms of amyloidoses including Alzheimer's disease. Small-molecule ligands that displace SAP from amyloid fibrils and thereby expose the fibrils to proteolytic clearance mechanisms hold potential as drugs for the prevention and treatment of amyloidosis. We have carried out a screen for novel SAP ligands and have identified 2'-deoxyadenosine-5'-monophosphate (dAMP) as a ligand. The crystal structure of the SAP-dAMP complex determined at 2.8 A resolution (R = 0.232, R(free) = 0.252) reveals a decamer in which all interactions between SAP pentamers are mediated by the ligand. The stability of the decamer in solution has been demonstrated by gel filtration chromatography. The two calcium ions of SAP are bridged by the dAMP phosphate group and five hydrogen bonds are formed between the protein and the ligand, including specific interactions made by the adenine base. This mode of dAMP binding is not compatible with the nucleotide being part of double-helical DNA. The SAP-dAMP decamer is stabilized mainly by base-stacking of adjacent ligand molecules and possibly by electrostatic interactions involving the dAMP phosphate groups; decamerization buries 1000 A2 (2.6%) of the pentamer solvent-accessible surface. Ligand-induced decamerization of SAP, which utilizes the high cooperativity of a multiple-site interaction, may be a strategy to overcome the problems for drug design associated with the rather modest affinities of SAP for small-molecule ligands.

Computer Graphics↗

PubMed1997

Instability, unfolding and aggregation of human lysozyme variants underlying amyloid fibrillogenesis.

Tissue deposition of soluble proteins as amyloid fibrils underlies a range of fatal diseases. The two naturally occurring human lysozyme variants are both amyloidogenic, and are shown here to be unstable. They aggregate to form amyloid fibrils with transformation of the mainly helical native fold, observed in crystal structures, to the amyloid fibril cross-beta fold. Biophysical studies suggest that partly folded intermediates are involved in fibrillogenesis, and this may be relevant to amyloidosis generally.

Amyloid↗

PubMed1997

Production of C-reactive protein and risk of coronary events in stable and unstable angina. European Concerted Action on Thrombosis and Disabilities Angina Pectoris Study Group.

BACKGROUND: Inflammation is an important feature of atherosclerotic lesions, and increased production of the acute-phase reactant. C-reactive protein (CRF), is associated with a poor prognosis in severe unstable angina. We have investigated the existence and possible significance of the acute-phase responses of CRP and another sensitive reactant, serum amyloid A protein (SAA), in patients with unstable or stable angina. METHODS: We used new ultrasensitive immunoassays to measure CRP and SAA concentrations in plasma from 2121 outpatients with angina (1030 unstable, 743 stable, the rest atypical) enrolled in the European Concerted Action on Thrombosis and Disabilities (ECAT) Angina Pectoris Study. All patients underwent coronary angiography and extensive clinical and laboratory assessment at study entry, and were then followed up for 2 years. All suspected coronary events during follow-up were reviewed by an independent endpoint committee. FINDINGS: 75 individuals (41 with unstable, 29 with stable, and 5 with atypical angina) had a coronary event during follow-up. Concentrations of CRP at study entry were associated with coronary events in patients with stable or unstable angina: there was about a two-fold increase in the risk of a coronary event in patients whose CRP concentration was in the fifth quintile (> 3.6 mg/L), compared with the first four quintiles. A third of the events occurred among patients who had a CRP concentration of more than 3.6 mg/L. CRP concentrations were positively correlated with age, smoking, body-mass index, triglycerides, extent of coronary stenosis, history of myocardial infarction, and lower ejection fraction. By contrast, concentrations of SAA were not associated with risk of a coronary event. INTERPRETATION: We found that raised circulating concentrations of CRP are predictors of coronary events in patients with stable or unstable angina. The modest acute-phase responses of CRP were probably not the result of myocardial necrosis. Whatever the underlying mechanisms, the sensitive measurement of CRP as a prognostic marker may be useful in the management of coronary heart disease.

Angina Pectoris↗

PubMed1997

Low-level increases in serum C-reactive protein are present in early osteoarthritis of the knee and predict progressive disease.

OBJECTIVE: To examine the role of low-grade inflammation in the etiology and progression of early osteoarthritis (OA) of the knee. METHODS: We used a new, high-sensitivity, automated monoclonal antibody immunoassay for the classic acute-phase protein, C-reactive protein (CRP), in serum. Anteroposterior radiographs of the knee with weight bearing were obtained on 845 women (ages 44-67) on entry into a population-based study of OA in Chingford, North London. In those defined radiologically as "cases," the knee radiographs were repeated after 4 years. RESULTS: Levels of CRP were higher in 105 women with knee OA defined radiologically as Kellgren-Lawrence grade 2+ (median 2.4 mg/liter, interquartile range [IQR] 1.0-5.1), compared with 740 women without OA (median 0.7 mg/liter, IQR 0.3-1.8) (P < 0.001). Median levels of CRP were higher in the 31 women whose disease progressed at least 1 Kellgren-Lawrence grade (median 2.6 mg/liter, IQR 1.9-4.6), compared with the 39 whose disease did not (median 1.3 mg/liter, IQR 0.6-2.4) (P = 0.006) . The significance of these differences persisted after adjustment for age, weight, height, smoking, knee pain, or injury. Classifying disease by the presence of joint space narrowing or osteophytes alone produced similar results. CONCLUSION: CRP levels are modestly but significantly increased in women with early knee OA, and higher levels predict those whose disease will progress over 4 years, suggesting that low-grade inflammation may be a significant aspect of early OA and may be amenable to therapeutic intervention and secondary prevention.

Adult↗

PubMed1997

Long-term survival in systemic amyloid A amyloidosis complicating Crohn's disease.

Systemic AA amyloidosis is a serious and potentially fatal complication of Crohn's disease. Proteinuria is the most common presentation, but the diagnosis can only be confirmed by showing amyloid in the tissues and is often delayed. Recently, scintigraphy has been developed using 123I-serum amyloid P component (SAP) as a noninvasive and quantitative alternative to histology in which this nuclear medicine tracer specifically targets amyloid deposits in vivo. This study investigates 4 patients with Crohn's disease who, despite having only low-grade clinical activity, developed progressive AA amyloidosis and renal failure. One patient died while receiving hemodialysis, but in the other 3 cases, renal transplantation and standard antirejection therapy were associated with remission of inflammatory activity. Serial SAP scintigraphy showed regression of amyloid in 2 of these patients and absence of progression in the other. These case studies show the dynamic but variable behavior of AA deposits in different patients and show the use of radiolabeled SAP for diagnosis and monitoring of amyloidosis in Crohn's disease.

Adolescent↗

PubMed1997

The MHC class II-restricted T cell response of C57BL/6 mice to human C-reactive protein: homology to self and the selection of T cell epitopes and T cell receptors.

The T cell response of C57BL/6 mice to human C-reactive protein (hCRP), an inducible acute phase protein, was analysed. Two I-A(b)-restricted epitopes at positions 79 95 (epitope A) and 87-102 (epitope B) were identified using a panel of CD4+ T cell clones. Human C-reactive protein shares considerable homology with mouse C-reactive protein and mouse serum amyloid P component. Interestingly, the two epitopes map to the region of lowest homology between human CRP and its mouse homologues. Human CRP-specific T cell clones express a restricted T cell receptor (TCR) repertoire, both with regard to usage of TCR germline gene segments (V alpha, J alpha, V beta, J beta) and certain TCR alpha beta combinations. Therefore, epitope-A specific clones preferentially use TCR V beta8.3 and V alpha3 J alpha15 V beta8.3-J beta2.3 and epitope-B specific clones use V beta2 and V alpha1-J alpha24/30-V beta2. This bias is even more pronounced when TCR usage is correlated with epitope fine specificity. A role for homology of hCRP to self components in selecting these particular T cell epitopes and TCR is discussed.

Amino Acid Sequence↗

PubMed1997

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.

Amyloid↗

PubMed1997

Amyloidosis: a review of recent diagnostic and therapeutic developments.

Amyloid deposition is associated with a diverse range of disorders that includes Alzheimer's disease, type II diabetes mellitus and dialysis arthropathy. Although less common, systemic AA and AL amyloidosis remain important because effective treatments have increasingly become available. The pathology in all forms of amyloidosis involves the extracellular deposition of protein as characteristic fibrillar aggregates which interfere with tissue structure and function. Amyloid fibrils are derived from different unrelated proteins in the different forms of the disease but share many common properties, including the capacity to bind the normal plasma protein serum amyloid P component (SAP). This is the basis for our development of radiolabelled SAP as a nuclear medicine tracer for the diagnosis and quantitative monitoring of amyloid. Serial studies have shown that the deposits are far from inert but are actually turned over quite rapidly in many patients. The treatment of amyloidosis involves supportive measures whilst every effort is made to reduce the supply of the respective fibril precursor protein. Under favourable circumstances further amyloid deposition will be prevented. existing deposits will regress and improvement of organ function will occur. Since this strategy is not always possible or may fail, new approaches to inhibit fibril formation and promote regression of amyloid are being pursued.

Amyloid↗

PubMed1997

Acute phase proteins, C-reactive protein and serum amyloid A protein, as prognostic markers in the elderly inpatient.

AIM: to study the clinical significance and potential utility of measuring serum amyloid A protein (SAA) compared with the classical acute phase protein, C-reactive protein (CRP). METHOD: a 3 month prospective study on 66 women, mean age 83 years (range 69-106) and 33 men, mean age 84 years (range 69-95), admitted to the geriatric medicine unit at Hammersmith Hospital. CRP and SAA were determined on admission and at intervals throughout hospital stay; outcome end-points were death during the study, detection of infection, duration of admission and early re-admission to hospital after discharge. RESULTS: CRP and SAA responses were highly correlated (r = 0.75, P = 0.0001). However, the SAA response was greater than that of CRP in most individuals, with a median ratio of initial SAA to CRP of 2.2 in patients with infective pathology and 1.6 in those with inflammatory pathology. Median (range) SAA on admission was 98 (0.1-940) mg/ml in patients with infection and was twice that observed in patients with other causes of inflammation, median value 50 (0.6-699) mg/l. There was no difference between median CRP on admission in patients with infection or inflammation, median value 53 (0.1-235) and 51.5 (5-246) mg/l respectively. Initial and peak levels of CRP, but not of SAA, were significantly greater in patients who subsequently died, whereas high levels of both proteins predicted length of admission and early re-admission. CONCLUSION: major elevations of the serum concentrations of CRP and SAA indicated serious disease and predicted poor outcome. Measurement of SAA as well as CRP enhanced the clinical utility of monitoring the acute phase response in 7% of patients with a diagnosis of infection.

Acute-Phase Proteins↗

PubMed1997

Serum amyloid A protein is a clinically useful indicator of acute renal allograft rejection.

BACKGROUND: Early diagnosis of acute rejection after renal transplantation is important. There is evidence that measurement of the acute phase proteins, C-reactive protein (CRP) and serum amyloid A protein (SAA) is helpful. METHODS: In 64 consecutive patients, CRP was measured in a routine clinical system (Technicon RA1000, Bayer) and SAA in a new sensitive automated immunoassay on the Abbott IMx instrument, daily or on alternate days for 30 days after renal transplantation. RESULTS: Patients all received triple immunosuppression with cyclosporin, azathioprine, and prednisolone and all mounted a post-surgical acute phase response of SAA, but the CRP response was reduced or absent. Serum creatinine rose significantly in 36 patients, leading to treatment for first rejection. Thirty of these episodes were confirmed rejection, three were definitely not and three were uncertain. SAA. normally < 10 mg/l, rose to more than 100 mg/l in all episodes except when rejection was definitely absent. In six cases SAA rose above 100 mg/l 1-3 days before the rise in creatinine leading to antirejection therapy, and only twice did creatinine rise 1 day before SAA. In contrast, CRP responses to rejection were modest or absent. In four patients there were SAA and CRP responses unrelated to rejection, three associated with intercurrent infection and one with administration of antilymphocyte globulin. There were also two unexplained isolated spikes of SAA. CONCLUSIONS: SAA is a sensitive marker of acute renal allograft rejection. It is not specific, but the differential behaviour of CRP in patients receiving cyclosporin helps to distinguish infection from rejection. Availability of rapid assays for these analytes should facilitate management of renal allograft recipients.

Acute Disease↗

PubMed1997

Individual relationship between progression of radiological damage and the acute phase response in early rheumatoid arthritis. Towards development of a decision support system.

OBJECTIVE: Evaluation of the individual relationship between C-reactive protein (CRP) production or erythrocyte sedimentation rate (ESR) and progression of radiologic damage in early rheumatoid arthritis (RA), to improve the predictive value of monitoring the acute phase response. METHODS: The relationship was modeled mathematically using adjustments for discontinuity in the radiographic scoring system and for clustering in the occurrence of score points in the initial phase. The model was evaluated in a prospective study of 149 patients with early RA, monthly CRP assays, and 6-monthly Sharp scores of radiographs of the hands and feet. RESULTS: Time integrated CRP values correlated closely with radiologic progression in each patient, but there was considerable variation between individuals with similar radiographic scores. The theoretical model accommodated these results, and based on CRP measurements and radiographic scores over 6 months, it provided a k value for each patient that reflected the individual relationship between CRP and radiologic damage. Using this k value combined with actual CRP levels over 3 and 6 years, the model accurately predicted the extent of radiologic progression that was actually observed at these times. Best results were obtained using estimation of the k value from 6 or 12 month observational data. The model has been incorporated into a software program for routine clinical use that indicates the levels to which CRP should fall to prevent further joint damage. Similar results were obtained for ESR. CONCLUSION: A model has been established defining the individual relationship between time integrated CRP and ESR values, reflecting rheumatoid disease activity, and progression of radiologic damage. It accurately prediets outcome from 6 months after presentation and can be used as a practical decision support system.

Acute Disease↗

PubMed1996

Plasma protein acute-phase response in unstable angina is not induced by ischemic injury.

BACKGROUND: Elevated levels of C-reactive protein (CRP) are associated with an unfavorable clinical outcome in patients with unstable angina. To determine whether ischemia-reperfusion injury causes this acute-phase response, we studied the temporal relation between plasma levels of CRP and ischemic episodes in 48 patients with unstable angina and 20 control patients with active variant angina, in which severe myocardial ischemia is caused by occlusive coronary artery spasm. METHODS AND RESULTS: Blood samples were taken on admission and subsequently at 24, 48, 72, and 96 hours. All patients underwent Holter monitoring for the first 24 hours and remained in the coronary care unit under ECG monitoring until completion of the study. On admission, CRP was significantly higher in unstable angina than in variant angina patients (P < .001). In unstable angina, 70 ischemic episodes (1.5 +/- 2 per patient) and in variant angina 192 ischemic episodes (9.6 +/- 10.7 per patient) were observed during Holter monitoring (P < .001), for a total ischemic burden of 14.8 +/- 30.2 and 44.4 +/- 57.2 minutes per patient, respectively (P < .001). The plasma concentration of CRP did not increase in either group during the 96 hours of study, even in patients who had episodes of ischemia lasting > 10 minutes. CONCLUSIONS: The normal levels of CRP in variant angina, despite a significantly larger number of ischemic episodes and greater total ischemic burden, and the failure of CRP values to increase in unstable angina indicate that transient myocardial ischemia, within the range of duration observed, does not itself stimulate an appreciable acute-phase response.

Acute-Phase Reaction↗

PubMed1996

Hereditary hepatic and systemic amyloidosis caused by a new deletion/insertion mutation in the apolipoprotein AI gene.

We report a Spanish family with autosomal-dominant non-neuropathic hereditary amyloidosis with a unique hepatic presentation and death from liver failure, usually by the sixth decade. The disease is caused by a previously unreported deletion/insertion mutation in exon 4 of the apolipoprotein AI (apoAI) gene encoding loss of residues 60-71 of normal mature apoAI and insertion at that position of two new residues, ValThr. Affected individuals are heterozygous for this mutation and have both normal apoAI and variant molecules bearing one extra positive charge, as predicted from the DNA sequence. The amyloid fibrils are composed exclusively of NH2-terminal fragments of the variant, ending mainly at positions corresponding to residues 83 and 92 in the mature wild-type sequence. Amyloid fibrils derived from the other three known amyloidogenic apoAI variants are also composed of similar NH2-terminal fragments. All known amyloidogenic apoAI variants carry one extra positive charge in this region, suggesting that it may be responsible for their enhanced amyloidogenicity. In addition to causing a new phenotype, this is the first deletion mutation to be described in association with hereditary amyloidosis and it significantly extends the value of the apoAI model for investigation of molecular mechanisms of amyloid fibrillogenesis.

Adult↗

PubMed1996

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.

Amyloid↗

PubMed1996

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.

Adult↗