Amyloid formation in rat transthyretin: effect of oxidative stress

Alteration of Transthyretin Microheterogeneity in Serum of Multiple Trauma Patients

Transthyretin (TTR) which exists in various isoforms, is a valid marker for acute phase response and subclinical malnutrition. The aim of the study was to investigate the relationship between inflammation, oxidative stress and the occurrence of changes in microheterogeneity of TTR.

A prospective, observational study at a level-I trauma center of a large urban medical university was performed. Patients were severely injured (n = 18; injury severity score (ISS): 34–66), and were observed within the first 24 hours of admittance and over the following days until day 20 after injury. 20 healthy subjects, matched by age and sex, were used as controls.

TTR was enriched by immunoprecipitation. Microheterogeneity of TTR was determined by linear matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS). Four major mass signals were observed for TTR representing native, S-cysteinylated, S-cysteinglycinylated and S-glutathionylated TTR. In the course of their ICU stay, 14 of the 18 patients showed a transient change in microheterogeneity in favour of the S-cysteinglycinylated form of TTR (p < 0.05 vs. controls). The occurrence of this variant was not associated with the severity of trauma or the intensity of the acute-phase response, but was associated with oxidative stress as evidenced by Trolox.

Our results demonstrate that changes in microheterogeneity of TTR occur in a substantial number of ICU trauma patients. The diagnostic values of these changes remains to be elucidated. It is speculated that TTR modification may well be the mechanism underlying the morphological manifestation of amyloidose or Alzheimer's diseases in patients surviving multiple trauma.

Emerging treatments for amyloidosis

Amyloidosis results from protein misfolding, and ongoing amyloid deposition can ultimately lead to organ failure and death. Historically, this is a group of diseases with limited treatment options and frequently poor prognosis. However, there are now 'targeted' therapeutics emerging in the form of stabilizers of the precursor protein, inhibitors of fibrillogenesis, fibril disruptors, and blockers of protein translation, transcription, and immunotherapy. We review many of these approaches that are currently being assessed in clinical trials.

Discovery and verification of amyotrophic lateral sclerosis biomarkers by proteomics

Recent studies using mass spectrometry have discovered candidate biomarkers for amyotrophic lateral sclerosis (ALS). However, those studies utilized small numbers of ALS and control subjects. Additional studies using larger subject cohorts are required to verify these candidate biomarkers. Cerebrospinal fluid (CSF) samples from 100 patients with ALS, 100 disease control, and 41 healthy control subjects were examined by mass spectrometry. Sixty-one mass spectral peaks exhibited altered levels between ALS and controls. Mass peaks for cystatin C and transthyretin were reduced in ALS, whereas mass peaks for posttranslational modified transthyretin and C-reactive protein (CRP) were increased. CRP levels were 5.84 +/- 1.01 ng/ml for controls and 11.24 +/- 1.52 ng/ml for ALS subjects, as determined by enzyme-linked immunoassay. This study verified prior mass spectrometry results for cystatin C and transthyretin in ALS. CRP levels were increased in the CSF of ALS patients, and cystatin C level correlated with survival in patients with limb-onset disease. Our biomarker panel predicted ALS with an overall accuracy of 82%.

Amyloidogenic potential of transthyretin variants: insights from structural and computational analyses

Human transthyretin (TTR) is an amyloidogenic protein whose mild amyloidogenicity is enhanced by many point mutations affecting considerably the amyloid disease phenotype. To ascertain whether the high amyloidogenic potential of TTR variants may be explained on the basis of the conformational change hypothesis, an aim of this work was to determine structural alterations for five amyloidogenic TTR variants crystallized under native and/or destabilizing (moderately acidic pH) conditions. While at acidic pH structural changes may be more significant because of a higher local protein flexibility, only limited alterations, possibly representing early events associated with protein destabilization, are generally induced by mutations. This study was also aimed at establishing to what extent wild-type TTR and its amyloidogenic variants are intrinsically prone to beta-aggregation. We report the results of a computational analysis predicting that wild-type TTR possesses a very high intrinsic beta-aggregation propensity which is on average not enhanced by amyloidogenic mutations. However, when located in beta-strands, most of these mutations are predicted to destabilize the native beta-structure. The analysis also shows that rat and murine TTR have a lower intrinsic beta-aggregation propensity and a similar native beta-structure stability compared with human TTR. This result is consistent with the lack of in vitro amyloidogenicity found for both murine and rat TTR. Collectively, the results of this study support the notion that the high amyloidogenic potential of human pathogenic TTR variants is determined by the destabilization of their native structures, rather than by a higher intrinsic beta-aggregation propensity.

Stability and fibril formation properties of human and fish transthyretin, and of the Escherichia coli transthyretin-related protein

Human transthyretin (hTTR) is one of several proteins known to cause amyloid disease. Conformational changes in its native structure result in aggregation of the protein, leading to insoluble amyloid fibrils. The transthyretin (TTR)-related proteins comprise a protein family of 5-hydroxyisourate hydrolases with structural similarity to TTR. In this study, we tested the amyloidogenic properties, if any, of sea bream TTR (sbTTR) and Escherichia coli transthyretin-related protein (ecTRP), which share 52% and 30% sequence identity, respectively, with hTTR. We obtained filamentous structures from all three proteins under various conditions, but, interestingly, different structures displayed different tinctorial properties. hTTR and sbTTR formed thin, curved fibrils at low pH (pH 2-3) that bound thioflavin-T (thioflavin-T-positive) but did not stain with Congo Red (CR) (CR-negative). Aggregates formed at the slightly higher pH of 4.0-5.5 had different morphology, displaying predominantly amorphous structures. CR-positive material of hTTR was found in this material, in agreement with previous results. ecTRP remained soluble at pH 2-12 at ambient temperatures. By raising of the temperature, fibril formation could be induced at neutral pH in all three proteins. Most of these temperature-induced fibrils were thicker and straighter than the in vitro fibrils seen at low pH. In other words, the temperature-induced fibrils were more similar to fibrils seen in vivo. The melting temperature of ecTRP was 66.7 degrees C. This is approximately 30 degrees C lower than the melting temperatures of sbTTR and hTTR. Information from the crystal structures was used to identify possible explanations for the reduced thermostability of ecTRP.

The effect of storage on the accumulation of oxidative biomarkers in donated packed red blood cells

BACKGROUND

Transfusion-related acute lung injury (TRALI) is a life-threatening condition characterized by oxidative stress. Longer storage times of packed red blood cells (PRBC) and other blood products have been implicated with an increased risk in developing TRALI in transfused patients.

METHODS

A total of 10 units of blood containing PRBC stored in citrate-phosphate-dextrose buffer at 4 degrees C were included in the study. At Bonfils Blood Center (Denver, CO), samples were collected on storage day 1 and day 42. Samples were immediately centrifuged, and the supernatants were collected and stored at -80 degrees C until further analysis. Oxidation-reduction potential and protein oxidation were measured in both the day 1 and day 42 samples.

RESULTS

Oxidation-reduction potential significantly increased (p < 0.05) in the day 42 sample (98.1 mV +/- 21.9 SD) versus the day 1 sample (62.6 mV +/- 21.5 SD). The oxidation of human serum albumin increased by 63.6% during the storage time. Other serum proteins such as apolipoprotein A1 and transthyretin demonstrated similar increases in oxidation. Also, proteins with a cleaved C-terminal amino acid were observed indicating the presence of carboxypeptidase activity, a marker of inflammation.

CONCLUSIONS

The presence of an oxidative environment in transfused PRBC increases with storage time. This could partially explain the increased risk of developing TRALI related to the transfusion of older blood products.

Structural modifications of serum transthyretin in rats during protein-energy malnutrition

Transthyretin (TTR) is a sensitive marker of protein-energy malnutrition and changes in serum and expression levels during protein and energy deficiency are well described. However, little is known about structural modifications of TTR during protein and/or energy deprivation. Therefore, the aim of this study was to determine the effects of protein inadequacies on post-translational modifications of TTR. For this purpose, male Wistar rats were fed a diet with either casein or gelatine as sole protein source subsequent to a protein wash-out period. Changes in TTR serum levels as well as other markers of nutritional status as body weight, food consumption, total serum protein and serum RBP4 levels as well as antioxidative capacity were determined. Post-translational modifications of TTR were examined by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS) analysis. The rats from the gelatine group revealed a marked change in the post-translational modification pattern of TTR which was reflected by a significant elevation of sulfonated TTR and which was inversely correlated to the antioxidative capacity. Additionally, the elevation of sulfonated TTR was accompanied by a decrease in body weight and food consumption, low antioxidative capacity as well as a deprivation of serum TTR, RBP4 and total serum protein levels in the animals of the gelatine group. Protein-energy malnutrition leads therefore next to changes in TTR serum concentration, also to changes in the post-translational modification pattern of TTR. Such changes are probably induced by protein-energy malnutrition-driven oxidative stress and might be linked to alterations in protein function and stability.

Nutritional Proteomics: Methods and Concepts for Research in Nutritional Science

Nutritional proteomics or nutriproteomics is the application of proteomics methodology to nutrition-related research but also represents the interaction of bioactive food ingredients with proteins, whereby the interaction with proteins occurs in two basically specific ways. Firstly, the effect of nutrients on protein expression, which can be monitored by protein mapping, and secondly, the interaction of nutrients with proteins by post-translational modifications or small-molecule protein interactions. These interactions result in changes to the three-dimensional structure of such effected proteins. As a consequence, their original functions are modulated, resulting for example in reduced activity in the case of enzymes or changes in ability of recognition between molecules such as protein-protein interactions and ligand-receptor interactions. The characterization of such modifications together with functional data from established biochemical and physiological methods will result in a better understanding of the interplay between bioactive dietary components and diet-related diseases such as cancer, diabetes or neurodegenerative diseases. The occurrence of such modifications can possibly be additionally used as biomarkers in the diagnosis and therapy of these diseases as well as biomarkers for the efficacy or safety of selected nutrients.

A transgenic rat with the human ATTR V30M: a novel tool for analyses of ATTR metabolisms

Amyloidogenic transthyretin (ATTR) is the pathogenic protein of familial amyloidotic polyneuropathy (FAP). To establish a tool for analyses of ATTR metabolisms including after liver transplantations, we developed a transgenic rat model expressing human ATTR V30M and confirmed expressions of human ATTR V30M in various tissues. Mass spectrometry for purified TTR revealed that rat intrinsic TTR and human ATTR V30M formed tetramers. Congo red staining and immunohistochemistry revealed that nonfibrillar deposits of human ATTR V30M, but not amyloid deposits, were detected in the gastrointestinal tracts of the transgenic rats. At 24h after liver transplantation, serum human ATTR V30M levels in transgenic rats that received livers from normal rats became lower than detectable levels. These results thus suggest that this transgenic rat may be a useful animal model which analyzes the metabolism of human ATTR V30M including liver transplantation studies.

Effect of tacrolimus and partial hepatectomy on transthyretin metabolism in rats

Liver transplantation, which serves as treatment of familial amyloidotic polyneuropathy (FAP), and domino liver transplantation, which utilizes resected livers from patients with FAP for treatment of liver diseases, may induce changes in transthyretin (TTR), a pathogenic FAP-related protein. To evaluate this possibility, we performed a 70% hepatectomy or administered tacrolimus to Dark Agouti (DA) rats for 7 days and then measured changes in liver TTR mRNA levels and changes in serum TTR concentrations. After hepatectomy, TTR mRNA levels decreased by 77%; at day 3, they returned to preoperative levels. Except for slightly elevated serum TTR concentrations 12 h after operation, serum TTR levels remained unchanged. Thus, partial hepatectomy did not influence serum TTR concentrations. After tacrolimus administration, TTR mRNA declined by 56% 12 h after the experiment started; however, after day 3, a rebound phenomenon occurred until day 7. Tacrolimus may facilitate serum TTR degradation, although production of TTR in the liver also increased. This finding -- that TTR, the source of FAP-inducing amyloid, did not increase after transplantation -- may help post-transplantation treatment of patients who have FAP and other liver diseases.

Cys-10 mixed disulfide modifications exacerbate transthyretin familial variant amyloidogenicity: a likely explanation for variable clinical expression of amyloidosis and the lack of pathology in C10S/V30M transgenic mice?

The marked variation in clinical expression and age of familial amyloid disease onset is not well understood. One possibility is that metabolite modification(s) of a disease-associated mutant protein can change the energetics and propensity for misfolding, influencing the disease course. Each subunit of the transthyretin (TTR) tetramer has a single Cys residue that can exist in the SH form or as a mixed disulfide with the amino acid Cys or the peptide glutathione or fragments of the latter. The stability and amyloidogenicity of the clinically most important TTR variants (V30M and V122I) in their SH oxidation state were compared with those of their mixed disulfide adducts. All the Cys-10 mixed disulfide conjugates exhibited substantially decreased protein stability (urea, pH 7) and a higher rate and extent of amyloidogenesis (slightly acidic conditions). We also investigated the amyloidogenicity and stability of a C10S/V30M TTR double mutant which lacks the ability to make mixed disulfides, but retains the disease-associated V30M mutation. Unlike V30M TTR, this double mutant is nonamyloidogenic in transgenic mice. Our in vitro data reveal that the C10S/V30M and V30M TTR homotetramers have identical amyloidogenicity and stability, implying that Cys-10 mixed disulfide formation enhances amyloidogenesis in V30M transgenic mice. Given the high proportion of TTR subunits having mixed disulfide modifications in human plasma ( approximately 50%), and the data within demonstrating their increased amyloidogenicity, we submit that disulfide metabolite modifications have the potential to influence the course of amyloidoses, including TTR amyloidoses caused by mutations.

Transthyretin amyloidosis presenting with multifocal demyelinating mononeuropathies

We describe a patient with transthyretin amyloidosis who presented with multifocal mononeuropathies with features of demyelination on nerve conduction studies, a constellation of findings not previously described in amyloid polyneuropathy. Genetic testing revealed a valine122isoleucine mutation in the coding region of the transthyretin gene, a mutation that generally presents with late-onset cardiac amyloidosis. Our patient was also unusual in that she was 34 years old at the time of presentation and had no cardiac involvement.

Identification of S-sulfonation and S-thiolation of a novel transthyretin Phe33Cys variant from a patient diagnosed with familial transthyretin amyloidosis

Familial transthyretin amyloidosis (ATTR) is an autosomal dominant disorder associated with a variant form of the plasma carrier protein transthyretin (TTR). Amyloid fibrils consisting of variant TTR, wild-type TTR, and TTR fragments deposit in tissues and organs. The diagnosis of ATTR relies on the identification of pathologic TTR variants in plasma of symptomatic individuals who have biopsy proven amyloid disease. Previously, we have developed a mass spectrometry-based approach, in combination with direct DNA sequence analysis, to fully identify TTR variants. Our methodology uses immunoprecipitation to isolate TTR from serum, and electrospray ionization and matrix-assisted laser desorption/ionization mass spectrometry (MS) peptide mapping to identify TTR variants and posttranslational modifications. Unambiguous identification of the amino acid substitution is performed using tandem MS (MS/MS) analysis and confirmed by direct DNA sequence analysis. The MS and MS/MS analyses also yield information about posttranslational modifications. Using this approach, we have recently identified a novel pathologic TTR variant. This variant has an amino acid substitution (Phe --> Cys) at position 33. In addition, like the Cys10 present in the wild type and in this variant, the Cys33 residue was both S-sulfonated and S-thiolated (conjugated to cysteine, cysteinylglycine, and glutathione). These adducts may play a role in the TTR fibrillogenesis.