S-Homocysteinylation effects on transthyretin: worsening of cardiomyopathy onset

Plasma homocysteine levels and risk of congestive heart failure or cardiomyopathy: A Mendelian randomization study

Background

Although observational studies have demonstrated associations between elevated plasma homocysteine levels and the risk of cardiovascular diseases, controversy remains.

Objective

This study investigated the causal association of plasma homocysteine levels with congestive heart failure and cardiomyopathy risk.

Methods

We performed a two-sample Mendelian randomization (MR) study of congestive heart failure (n = 218,792), cardiomyopathy (n = 159,811), and non-ischemic cardiomyopathy (n = 187,152). Genetic summary data on the association of single-nucleotide polymorphisms with homocysteine were extracted from the most extensive genome-wide association study of 44,147 individuals. MR analyses, including the random-effect inverse variance-weighted (IVW) meta-analysis, weighted median, simple median, maximum likelihood, penalized weighted median, MR-PRESSO, and MR-Egger regression, were used to estimate the associations between the selected single-nucleotide polymorphisms and congestive heart failure or cardiomyopathy.

Results

The MR analyses revealed no causal role of higher genetically predicted plasma homocysteine levels with congestive heart failure risk (random-effect IVW, odds ratio [OR] per standard deviation (SD) increase in homocysteine levels = 1.753, 95% confidence interval [CI] = 0.674-4.562, P = 0.250), cardiomyopathy (random-effect IVW, OR per SD increase in homocysteine levels = 0.805, 95% CI = 0.583 to 1.020, P = 0.189), or non-ischemic cardiomyopathy (random-effect IVW, OR per SD increase in homocysteine levels = 1.064, 95% CI = 0.927-1.222, P = 0.379). The results were consistent with other analytical methods and sensitivity analyses.

Conclusion

Genetically predicted homocysteine level was not associated with congestive heart failure or cardiomyopathy risk. It is unlikely that homocysteine-lowering therapy decreases the incidence or improves the outcomes of congestive heart failure and cardiomyopathy.

Multidisciplinary amyloidosis care in the era of personalized medicine

Amyloidosis refers to a group of conditions where abnormal protein-or amyloid-deposits in tissues or organs, often leading to organ malfunction. Amyloidosis affects nearly any organ system, but especially the heart, kidneys, liver, peripheral nervous system, and gastrointestinal tract. Neuromuscular deficits comprise some of its ubiquitous manifestations. Amyloidosis can be quite challenging to diagnose given its clinical heterogeneity and multi-system nature. Early diagnosis with accurate genetic and serologic subtyping is key for effective management and prevention of organ decline. In this review, we highlight the value of a multidisciplinary comprehensive amyloidosis clinic. While such a model exists at numerous clinical and research centers across the globe, the lack of more widespread adoption of such a model remains a major hindrance to the timely diagnosis of amyloidosis. Such a multidisciplinary care model allows for the timely and effective diagnosis of amyloidosis, be it acquired amyloid light amyloidosis (AL), hereditary transthyretin amyloidosis (hATTR), or wild type amyloidosis (TTR-wt), especially in the current era of personalized genomic medicine. A multidisciplinary clinic optimizes the delivery of singular or combinatorial drug therapies, depending on amyloid type, fibril deposition location, and disease progression. Such an arrangement also helps advance research in the field. We present our experience at The Ohio State University, as one example out of many, to highlight the centrality of a multi-disciplinary clinic in amyloidosis care.

Aggregation-Prone Structural Ensembles of Transthyretin Collected With Regression Analysis for NMR Chemical Shift

Monomer dissociation and subsequent misfolding of the transthyretin (TTR) is one of the most critical causative factors of TTR amyloidosis. TTR amyloidosis causes several human diseases, such as senile systemic amyloidosis and familial amyloid cardiomyopathy/polyneuropathy; therefore, it is important to understand the molecular details of the structural deformation and aggregation mechanisms of TTR. However, such molecular characteristics are still elusive because of the complicated structural heterogeneity of TTR and its highly sensitive nature to various environmental factors. Several nuclear magnetic resonance (NMR) spectroscopy and molecular dynamics (MD) studies of TTR variants have recently reported evidence of transient aggregation-prone structural states of TTR. According to these studies, the stability of the DAGH β-sheet, one of the two main β-sheets in TTR, is a crucial determinant of the TTR amyloidosis mechanism. In addition, its conformational perturbation and possible involvement of nearby structural motifs facilitates TTR aggregation. This study proposes aggregation-prone structural ensembles of TTR obtained by MD simulation with enhanced sampling and a multiple linear regression approach. This method provides plausible structural models that are composed of ensemble structures consistent with NMR chemical shift data. This study validated the ensemble models with experimental data obtained from circular dichroism (CD) spectroscopy and NMR order parameter analysis. In addition, our results suggest that the structural deformation of the DAGH β-sheet and the AB loop regions may correlate with the manifestation of the aggregation-prone conformational states of TTR. In summary, our method employing MD techniques to extend the structural ensembles from NMR experimental data analysis may provide new opportunities to investigate various transient yet important structural states of amyloidogenic proteins.

Transthyretin and retinol-binding protein as discriminators of diabetic retinopathy in type 1 diabetes mellitus

PURPOSE

Diabetic retinopathy (DR) is one of the most common complications of diabetes mellitus (DM), which is still a major reason for blindness. Transthyretin (TTR) and retinol-binding protein (RBP) are thought to be related to the pathogenesis both in T2DM and T1DM. We aimed to investigate the association between serum levels of TTR, RBP, RBP/TTR ratio, and DR.

METHODS

This retrospective study involved 188 T1DM inpatients divided into two groups: patients with DR (n = 95) and patients without DR (n = 93). Data of serum levels on lipids and inflammation were collected. Multiple logistic regression analysis was performed to research the association between TTR, RBP, RBP/TTR, and diabetic retinopathy in T1DM.

RESULTS

Compared with patients without DR, those with DR have a higher level of TTR (207 versus 195 mg/L, p = 0.034) and RBP4 (36.85 versus 25.68 mg/L, p < 0.001). Significant differences were also observed between two groups with respect to body mass index (BMI), blood pressure (BP), total cholesterol (TC), triglycerides (TG), low-density lipoprotein (LDL), homocysteine, apolipoprotein B (APOB), leucocyte, monocyte, neutrophil, and uric acid (p < 0.05 for all). TTR, RBP, and RBP/TTR were positively correlated with BP, BMI, TG, LDL, homocysteine, APOB, and uric acid. A multivariate logistic regression model revealed individuals with RBP4 level in the highest quartile had 58.95 times higher risk of developing diabetic retinopathy than those in the lowest quartile.

CONCLUSIONS

In conclusion, TTR, RBP, and RBP/TTR ratio are risk factors of DR in T1DM. They are potential markers and targets for diagnosis and treatment of DR.

Transthyretin as a target of alkylation and a potential biomarker for sulfur mustard poisoning: Electrophoretic and mass spectrometric identification and characterization

For the verification of exposure to the banned blister agent sulfur mustard (SM) and the better understanding of its pathophysiology, protein adducts formed with endogenous proteins represent an important field of toxicological research. SM and its analogue 2-chloroethyl ethyl sulfide (CEES) are well known to alkylate nucleophilic amino acid side chains, for example, free-thiol groups of cysteine residues. The specific two-dimensional thiol difference gel electrophoresis (2D-thiol-DIGE) technique making use of maleimide dyes allows the staining of free cysteine residues in proteins. As a consequence of alkylation by, for example, SM or CEES, this staining intensity is reduced. 2D-thiol-DIGE analysis of human plasma incubated with CEES and subsequent matrix-assisted laser desorption/ionization time-of-flight (tandem) mass-spectrometry, MALDI-TOF MS(/MS), revealed transthyretin (TTR) as a target of alkylating agents. TTR was extracted from SM-treated plasma by immunomagnetic separation (IMS) and analyzed after tryptic cleavage by microbore liquid chromatography-electrospray ionization high-resolution tandem-mass spectrometry (μLC-ESI MS/HR MS). It was found that the Cys¹⁰ -residue of TTR present in the hexapeptide C(-HETE)PLMVK was alkylated by the hydroxyethylthioethyl (HETE)-moiety, which is characteristic for SM exposure. It was shown that alkylated TTR is stable in plasma in vitro at 37°C for at least 14 days. In addition, C(-HETE)PLMVK can be selectively detected, is stable in the autosampler over 24 h, and shows linearity in a broad concentration range from 15.63 μM to 2 mM SM in plasma in vitro. Accordingly, TTR might represent a complementary protein marker molecule for the verification of SM exposure.