Architecture of polyglutamine-containing fibrils from time-resolved fluorescence decay.

The disease risk and age of onset of Huntington disease (HD) and nine other repeat disorders strongly depend on the expansion of CAG repeats encoding consecutive polyglutamines (polyQ) in the corresponding disease protein. PolyQ length-dependent misfolding and aggregation are the hallmarks of CAG pathologies. Despite intense effort, the overall structure of these aggregates remains poorly understood. Here, we used sensitive time-dependent fluorescent decay measurements to assess the architecture of mature fibrils of huntingtin (Htt) exon 1 implicated in HD pathology. Varying the position of the fluorescent labels in the Htt monomer with expanded 51Q (Htt51Q) and using structural models of putative fibril structures, we generated distance distributions between donors and acceptors covering all possible distances between the monomers or monomer dimensions within the polyQ amyloid fibril. Using Monte Carlo simulations, we systematically scanned all possible monomer conformations that fit the experimentally measured decay times. Monomers with four-stranded 51Q stretches organized into five-layered ß-sheets with alternating N termini of the monomers perpendicular to the fibril axis gave the best fit to our data. Alternatively, the core structure of the polyQ fibrils might also be a zipper layer with antiparallel four-stranded stretches as this structure showed the next best fit. All other remaining arrangements are clearly excluded by the data. Furthermore, the assessed dimensions of the polyQ stretch of each monomer provide structural evidence for the observed polyQ length threshold in HD pathology. Our approach can be used to validate the effect of pharmacological substances that inhibit or alter amyloid growth and structure.

Natural osmolytes remodel the aggregation pathway of mutant huntingtin exon 1.

In response to stress small organic compounds termed osmolytes are ubiquitously accumulated in all cell types to regulate the intracellular solvent quality and to counteract the deleterious effect on the stability and function of cellular proteins. Given the evidence that destabilization of the native state of a protein either by mutation or by environmental changes triggers the aggregation in the neurodegenerative pathologies, the modulation of the intracellular solute composition with osmolytes is an attractive strategy to stabilize an aggregating protein. Here we report the effect of three natural osmolytes on the in vivo and in vitro aggregation landscape of huntingtin exon 1 implicated in the Huntington's disease. Trimethylamine N-oxide (TMAO) and proline redirect amyloid fibrillogenesis of the pathological huntingtin exon 1 to nonamyloidogenic amorphous assemblies via two dissimilar molecular mechanisms. TMAO causes a rapid formation of bulky amorphous aggregates with minimally exposed surface area, whereas proline solubilizes the monomer and suppresses the accumulation of early transient aggregates. Conversely, glycine-betaine enhances fibrillization in a fashion reminiscent of the genesis of functional amyloids. Strikingly, none of the natural osmolytes can completely abrogate the aggregate formation; however, they redirect the amyloidogenesis into alternative, nontoxic aggregate species. Our study reveals new insights into the complex interactions of osmoprotectants with polyQ aggregates.

N-Nitrosodimethylamine-Contaminated Valsartan and the Risk of Cancer­A Longitudinal Cohort Study Based on German Health Insurance Data.

BACKGROUND: N-Nitrosodimethylamine (NDMA), classified as a probable human carcinogen, has been found as a contaminant in the antihypertensive drug valsartan. Potentially carcinogenic effects associated with the consumption of NDMAcontaminated valsartan have not yet been analyzed in large-scale cohort studies. We therefore carried out the study reported here to explore the association between NDMA-contaminated valsartan and the risk of cancer. METHODS: This cohort study was based on longitudinal routine data obtained from a large German statutory health insurance provider serving approximately 25 million insurees. The cohort comprised patients who had filled a prescription for valsartan in the period 2012-2017. The endpoint was an incident diagnosis of cancer. Hazard ratios (HR) for cancer in general and for certain specific types of cancer were calculated by means of Cox regression models with time-dependent variables and adjustment for potential confounders. RESULTS: A total of 780 871 persons who had filled a prescription for valsartan between 2012 and 2017 were included in the study. There was no association between exposure to NDMA-contaminated valsartan and the overall risk of cancer. A statistically significant association was found, however, between exposure to NDMA-contaminated valsartan and hepatic cancer (adjusted HR 1.16; 95% confidence interval [1.03; 1.31]). CONCLUSION: These findings suggest that the consumption of NDMA-contaminated valsartan is associated with a slightly increased risk of hepatic cancer; no association was found with the risk of cancer overall. Close observation of the potential long-term effects of NDMA-contaminated valsartan seems advisable.