Capture of a dimeric intermediate during transthyretin amyloid formation. (1/93)

Point mutations in the human plasma protein transthyretin are associated with the neurological disorder familial amyloidosis with polyneuropathy type 1. The disease is characterized by amyloid fibril deposits causing damage at the site of deposition. Substitution of two amino acids in the hydrophobic core of transthyretin lead to a mutant that was very prone to form amyloid. In addition, this mutant has also been shown to induce a toxic response on a neuroblastoma cell line. Renaturation of the transthyretin mutant at low temperature facilitated the isolation of an amyloid-forming intermediate state having the apparent size of a dimer. Increasing the temperature effectively enhanced the rate of interconversion from a partly denatured protein to mature amyloid. Using circular dichroism the beta-sheet content of the formed mature fibrils was significantly lower than that of the native fold of transthyretin. Morphology studies using electron microscopy also indicated a temperature-dependent transformation from amorphous aggregates toward mature amyloid fibrils. In addition, 1-anilino-8-naphtalenesulfonate fluorescence studies suggested the loss of the thyroxin-binding channel within both the isolated intermediate and the mature fibrils.  (+info)

Deposition of transthyretin in early stages of familial amyloidotic polyneuropathy: evidence for toxicity of nonfibrillar aggregates. (2/93)

Familial amyloidotic polyneuropathy (FAP) is a neurodegenerative disorder characterized by extracellular deposition of transthyretin (TTR) amyloid fibrils, particularly in the peripheral nervous system. No systematic immunohistochemical data exists relating TTR deposition with FAP progression. We assessed nerves from FAP patients in different stages of disease progression (FAP 0 to FAP 3) for TTR deposition by immunohistochemistry, and for the presence of amyloid fibrils by Congo Red staining. The nature of the deposited material was further studied by electron microscopy. We observed that early in FAP (FAP 0), TTR is already deposited in an aggregated nonfibrillar form, negative by Congo Red staining. This suggested that in vivo, preamyloidogenic forms of TTR exist in the nerve, in a stage before fibril formation. Cytotoxicity of nonfibrillar TTR was assessed in nerves of different FAP stages by immunohistochemistry for macrophage colony-stimulating factor. FAP 0 patients already presented increased axonal expression of macrophage colony-stimulating factor that was maintained in all other stages, in sites related to TTR deposition. Toxicity of synthetic TTR fibrils formed in vitro at physiological pH was studied on a Schwannoma cell line by caspase-3 activation assays and showed that early aggregates but not mature fibrils are toxic to cells. Taken together, these results show that nonfibrillar cytotoxic deposits occur in early stages of FAP.  (+info)

Myocardial muscarinic receptor upregulation and normal response to isoproterenol in denervated hearts by familial amyloid polyneuropathy. (3/93)

BACKGROUND: Patients with familial amyloid polyneuropathy, a rare hereditary form of amyloidosis, have progressive autonomic neuropathy. The disease usually does not induce heart failure but is associated with sudden death, conduction disturbances, and an increased risk of complications during anesthesia. Although cardiac sympathetic denervation has been clearly demonstrated, the postsynaptic status of the cardiac autonomic nervous system remains unelucidated. METHODS AND RESULTS: Twenty-one patients were studied (age, 39+/-11 years; normal coronary arteries; left ventricular ejection fraction 68+/-9%). To evaluate the density and affinity constants of myocardial muscarinic receptors, PET with (11)C-MQNB (methylquinuclidinyl benzilate), a specific hydrophilic antagonist, was used. Cardiac beta-receptor functional efficiency was studied by the heart rate (HR) response to intravenous infusion of isoproterenol (5 minutes after 2 mg of atropine, 5, 10, and 15 ng/kg per minute during 5 minutes per step). The mean muscarinic receptor density was higher in patients than in control subjects (B'(max), 35.5+/-8.9 versus 26.1+/-6.7 pmol/mL, P=0.003), without change in receptor affinity. The increase in HR after injection of atropine as well as of MQNB was lower in patients compared with control subjects despite a similar basal HR (DeltaHR after atropine, 11+/-21% versus 62+/-17%; P<0.001), consistent with parasympathetic denervation. Incremental infusion of isoproterenol induced a similar increase in HR in patients and control subjects. CONCLUSIONS: Cardiac autonomic denervation in familial amyloid polyneuropathy results in an upregulation of myocardial muscarinic receptors but without change in cardiac beta-receptor responsiveness to catecholamines.  (+info)

Results of liver transplantation for familial amyloid polyneuropathy type I in Brazil. (4/93)

Familial amyloid polyneuropathy type I (FAP-I) is an inherited amyloidosis secondary to systemic deposition of amyloid fibrils containing mutant transthyretin (TTR) variants. The disease has a progressive clinical course and is usually fatal 10 years after its onset. TTR is mainly produced in hepatocytes, and liver transplantation (LT) has been proposed as an effective treatment for FAP-I. The aim of this study is to evaluate the results of LT for FAP-I in Brazil and analyze prognostic factors associated with survival after surgery. Twenty-four patients (median age, 36 years; range, 25 to 52 years) who underwent LT with the diagnosis of FAP-I were evaluated. Surgery was uneventful in all but six patients who died of complications of primary liver nonfunction (n = 1), cardiogenic shock (n = 1), sepsis (n = 3), and hepatic artery thrombosis (n = 3). Overall 1- and 5-year survival rates were 70% and 58%, respectively. Most patients had stabilization or improvement of symptoms after a median follow-up of 36 months (range, 14 to 82 months). Survivors had a shorter disease duration before LT (median, 6 years; range, 2 to 17 years v 9 years; range, 7 to 12 years; P =.02), greater albumin levels (median, 4 g/dL; range, 3 to 4.7 g/dL v 3.6 g/dL; range, 2.6 to 4.1 g/dL; P =.03), and greater modified body mass index scores (median, 735; range, 502 to 1,432 v 659; range, 411 to 803; P =.04) compared with nonsurvivors. However, only disease duration and albumin levels were independently associated with survival in multivariate analysis. In conclusion, LT is an effective therapy for FAP-I. Mortality after surgery is associated with poor nutritional status and long-standing disease before LT. Thus, LT should be performed as early as possible after the onset of FAP-I symptoms to avoid major disability and improve survival.  (+info)

Long-term follow-up of survival of liver transplant recipients with familial amyloid polyneuropathy (Portuguese type). (5/93)

Portuguese type familial amyloid polyneuropathy is a dominantly inherited neuropathic amyloidosis caused by a mutant transthyretin (TTR). Because TTR is produced mainly by the liver, liver transplantation (LT) abolishes production of the amyloidogenic variant TTR. To date, the procedure appears to halt the progress of the disease. However, long-term outcome is unknown. The aim of the present study is to evaluate the survival of our initial group of unselected liver transplant recipients with FAP. Seventy patients, 51 transplant recipients and a control group of 19 nontransplantation patients, with disease onset before the age of 55 years were included on the study. Transplant recipients were divided into two categories: (1) early series, with patients followed up for 5 years or longer, and (2) new series, with patients followed up for 1 to 5 years. Nonparametric statistical methods were used. Binary regression analyses were performed by stepwise logistic regression and Cox proportional hazard regression. Survival analysis was performed using Kaplan-Meier analysis, the Cox-Mantel test. Survival analyses and Cox proportional hazard regression analysis were performed from disease onset, not from LT. Significantly decreased survival was noted for transplant recipients with a modified body mass index (mBMI) less than 600 compared with the control group (P < .05). A significant difference in survival also was observed between transplant recipients with an mBMI greater than 600 at the time of LT compared with those with an mBMI less than 600 (P < .02). mBMI and age at LT had a significant impact on survival; whereas late deaths were related to age at LT, early deaths were related to mBMI. The cumulative 10-year survival rate after disease onset was 94% in the new series, with one early death (< 6 months) after LT, compared with a 78% survival rate and eight early deaths in the early series (P = .1).  (+info)

Effect of the intestinal flora on amyloid deposition in a transgenic mouse model of familial amyloidotic polyneuropathy. (6/93)

Familial amyloidotic polyneuropathy (FAP) is a hereditary disease characterized by the systemic accumulation of amyloid fibrils. A mutant transthyretin (TTR) gene is mainly responsible for the disease. However, the variable age of onset and low penetrance might be due to environmental factors, one of which is the intestinal flora. Three types of intestinal flora were introduced into a transgenic (Tg) mouse FAP model, 6.0-hMet30. The CV1 and CV2 group transgenic mice were transferred with the intestinal flora from two different mouse facilities housed under conventional conditions, and the SPF group transgenic mice were kept under specific pathogen free conditions in our facility. All the mice were maintained under controlled temperature, humidity and bacterial conditions. Over a period of 28 months, amyloid was not deposited in the SPF and CV1 groups. In contrast, amyloid was deposited in the esophagus and small intestine of two of the three CV2 mice at 18 months. Many neutrophils infiltrated the lesions. The numbers of tissue neutrophils were higher in the CV2 group than in the SPF and CV1 groups at 18 months. The CV2 flora included fewer gram-positive anaerobic cocci as well as higher proportions of yeasts, staphylococci and enterobacteriaceae compared with the SPF and CV1 flora. These findings suggest that the intestinal flora plays an important role in amyloid deposition.  (+info)

Evidence for early cytotoxic aggregates in transgenic mice for human transthyretin Leu55Pro. (7/93)

Familial amyloidotic polyneuropathy (FAP) is a lethal autosomal dominant disorder characterized by systemic extracellular deposition of transthyretin (TTR) amyloid fibrils. Several groups have generated transgenic mice carrying human TTR Val30Met, the most common mutation in FAP. To study amyloidogenicity and cytotoxicity of different TTRs, we produced transgenic mice expressing human TTR Leu55Pro, one of the most aggressive FAP-related mutations. TTR deposition and presence of amyloid fibrils was investigated and compared to animals carrying the human TTR Val30Met gene kept under the same conditions. Deposition in a C57BL/6J background (TTR-Leu55Pro mice) and in a TTR-null background [TTR-Leu55Pro X TTR-knockout (KO) mice] was compared. Animals in a C57BL/6J background presented early (1 to 3 months) nonfibrillar TTR deposition but amyloid was absent. In a TTR-null background, presence of amyloid fibrils was detected starting at 4 to 8 months with a particular involvement of the gastrointestinal tract and skin. This data suggested that TTR homotetramers are more prone to fibril formation than TTR murine wild-type/human mutant heterotetramers. The nature of the deposited material was further investigated by immunocytochemistry. Both amorphous aggregates and small TTR fibrils were present in TTR-Leu55Pro X TTR-KO transgenics. We observed that these TTR deposits mimic the toxic effect of TTR deposits in FAP: animals with TTR deposition, present approximately twofold increased levels of nitrotyrosine in sites related to deposition. The TTR-Leu55Pro X TTR-KO mice here described are an important tool for the dual purpose of investigating factors involved in amyloidogenesis and in cytotoxicity of deposited TTR.  (+info)

Familial ATTR amyloidosis: microalbuminuria as a predictor of symptomatic disease and clinical nephropathy. (8/93)

BACKGROUND: Portuguese type familial amyloid polyneuropathy (FAP) is a neuropathic amyloidosis caused by a mutant transthyretin (TTR). Varying degrees of renal involvement have been reported. Our aim was to assess the value of microalbuminuria (MA) for predicting clinical neurological disease and overt nephropathy in TTR-related amyloidosis. METHODS: All subjects had the TTR Val30Met mutation, and were recruited between 1993 and 1999. We have prospectively evaluated 22 asymptomatic gene carriers (7 male, 15 female; mean age 41.6+/-9.6 years) and 32 patients with neuropathy (14 male, 18 female; 36.8+/-8.8 years, on average, 33.0+/-9.3 years at the onset of neuropathy). We measured urinary albumin excretion every year, if asymptomatic, or every 6 months if already affected. Kidney biopsies were performed in patients with normal urinary albumin excretion, MA, and overt nephropathy, respectively. RESULTS: In asymptomatic carriers, persistent MA was detected in eight (36%) subjects. The presence of MA in asymptomatic gene carriers, compared with those having normal urinary albumin excretion, conferred a 4.8-fold risk of developing neuropathy, usually within the subsequent 3 years. Once neurological signs appeared, nephropathy, manifested as MA, progressed to overt nephropathy in one-half of subjects. In patients with neuropathy, 24 (75%) had MA during follow-up: evolution towards clinical renal disease occurred in 14 (58%) and renal failure occurred in five (21%), always after a course of MA. Proteinuria or renal failure without prior persistent MA were never observed in the present patient cohort. Histopathological evaluation did not reveal glomerular lesions other than amyloid deposits to explain abnormal urinary albumin excretion. The amount of mesangial and vascular-pole amyloid deposits was correlated with the degree of albuminuria. CONCLUSIONS: Microalbuminuria represents the first stage of clinical TTR amyloid nephropathy and is premonitory of neuropathy. Its presence identifies a subgroup of patients who are more prone to develop overt nephropathy. Screening of MA may be important to assess disease onset and to recommend liver transplantation in individuals at risk.  (+info)

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