Exploring the Impact of Glyoxal Glycation on β-Amyloid Peptide (Aβ) Aggregation in Alzheimer's Disease

Investigation of the factors influencing the selectivity and response times of glyoxal-selective probes

In this work, four o-phenylenediamine-conjugated fluorescent probes 1-4 with different substituents on the amino group have been designed and prepared to investigate the factors influencing the selectivity and response times of the probes toward glyoxal (GO). The introduced substituted groups, including n-propyl, iso-propyl, tert-butyl, and phenyl, 1-4 displayed sufficient selectivity toward GO. Due to the fact that GO normally exists in a hydrated state in aqueous media, the reaction rates between 1-4 and GO exhibited significant deviation from the steric hindrance effects of most organic reactions. Compounds 3 and 4 with bulky substituted groups presented faster reaction rates with GO than those of compounds 1-2. To further elucidate the properties of these compounds, we selected compound 3 as the representative compound, because of its best selectivity and fast response time, for detailed investigation of the recognition behaviors both in aqueous solution and in living cells. Probe 3 exhibited high selectivity and high sensitivity toward GO with a large Stokes shift (>100 nm), making it highly suitable for in vivo imaging research.

Peptide-Bound Glycative, AGE and Oxidative Modifications as Biomarkers for the Diagnosis of Alzheimer's Disease-A Feasibility Study

Background: The diagnosis of Alzheimer's disease (AD) relies on core cerebrospinal fluid (CSF) biomarkers, amyloid beta (Aβ) and tau. As the brain is then already damaged, researchers still strive to discover earlier biomarkers of disease onset and the progression of AD. Glycation, advanced glycation end products (AGEs) and oxidative modifications on proteins in CSF mirror the underlying biological mechanisms that contribute to early AD pathology. However, analyzing free AGEs in the body fluids of AD patients has led to controversial results. Thus, this pilot study aimed to test the feasibility of detecting, identifying and quantifying differentially glycated, AGE or oxidatively modified peptides in CSF proteins of AD patients (n = 5) compared to a control group (n = 5). Methods: To this end, we utilized a data-dependent (DDA) nano liquid chromatography (LC) linear ion trap-Orbitrap tandem mass spectrometry (MS/MS) ) approach and database search that included over 30 glycative and oxidative modifications in four search nodes to analyze endogenous modifications on individual peptides. Furthermore, we quantified candidate peptide abundance using LC Quan. Results: We identified 299 sites of early and advanced glycation and 53 sites of oxidatively modified tryptophan. From those, we identified 17 promising candidates as putative biomarkers (receiver operating curve-area under the curve (ROC-AUC) > 0.8), albeit without statistical significance. Conclusions: The potential candidates with higher discrimination power showed correlations with established diagnostic markers, thus hinting toward the potential of those peptides as biomarkers.

Stability of Protein Pharmaceuticals: Recent Advances

There have been significant advances in the formulation and stabilization of proteins in the liquid state over the past years since our previous review. Our mechanistic understanding of protein-excipient interactions has increased, allowing one to develop formulations in a more rational fashion. The field has moved towards more complex and challenging formulations, such as high concentration formulations to allow for subcutaneous administration and co-formulation. While much of the published work has focused on mAbs, the principles appear to apply to any therapeutic protein, although mAbs clearly have some distinctive features. In this review, we first discuss chemical degradation reactions. This is followed by a section on physical instability issues. Then, more specific topics are addressed: instability induced by interactions with interfaces, predictive methods for physical stability and interplay between chemical and physical instability. The final parts are devoted to discussions how all the above impacts (co-)formulation strategies, in particular for high protein concentration solutions.'

Communal interaction of glycation and gut microbes in diabetes mellitus, Alzheimer's disease, and Parkinson's disease pathogenesis

Diabetes and its complications, Alzheimer's disease (AD), and Parkinson's disease (PD) are increasing gradually, reflecting a global threat vis-à-vis expressing the essentiality of a substantial paradigm shift in research and remedial actions. Protein glycation is influenced by several factors, like time, temperature, pH, metal ions, and the half-life of the protein. Surprisingly, most proteins associated with metabolic and neurodegenerative disorders are generally long-lived and hence susceptible to glycation. Remarkably, proteins linked with diabetes, AD, and PD share this characteristic. This modulates protein's structure, aggregation tendency, and toxicity, highlighting renovated attention. Gut microbes and microbial metabolites marked their importance in human health and diseases. Though many scientific shreds of evidence are proposed for possible change and dysbiosis in gut flora in these diseases, very little is known about the mechanisms. Screening and unfolding their functionality in metabolic and neurodegenerative disorders is essential in hunting the gut treasure. Therefore, it is imperative to evaluate the role of glycation as a common link in diabetes and neurodegenerative diseases, which helps to clarify if modulation of nonenzymatic glycation may act as a beneficial therapeutic strategy and gut microbes/metabolites may answer some of the crucial questions. This review briefly emphasizes the common functional attributes of glycation and gut microbes, the possible linkages, and discusses current treatment options and therapeutic challenges.

Glycation modulates superoxide dismutase 1 aggregation and toxicity in models of sporadic amyotrophic lateral sclerosis

Different SOD1 proteoforms are implicated## in both familial and sporadic cases of Amyotrophic Lateral Sclerosis (ALS), an aging-associated disease that affects motor neurons. SOD1 is crucial to neuronal metabolism and health, regulating the oxidative stress response and the shift between oxidative-fermentative metabolism, which is important for astrocyte-neuron metabolic cooperation. Neurons have a limited capacity to metabolize methylglyoxal (MGO), a potentially toxic side product of glycolysis. MGO is highly reactive and can readily posttranslationally modify proteins, in a reaction known as glycation, impacting their normal biology. Here, we aimed to investigate the effect of glycation on the aggregation and toxicity of human SOD1WT (hSOD1WT). Cells with deficiency in MGO metabolism showed increased levels of hSOD1WT inclusions, displaying also reduced hSOD1WT activity and viability. Strikingly, we also found that the presence of hSOD1WT in stress granules increased upon MGO treatment. The treatment of recombinant hSOD1WT with MGO resulted in the formation of SDS-stable oligomers, specially trimers, and thioflavin-T positive aggregates, which can promote cell toxicity and TDP-43 pathology. Together, our results suggest that glycation may play a still underappreciated role on hSOD1WT and TDP-43 pathologies in sporadic ALS, which could open novel perspectives for therapeutic intervention.

Oxymatrine-mediated prevention of amyloid β-peptide-induced apoptosis on Alzheimer's model PC12 cells: in vitro cell culture studies and in vivo cognitive assessment in rats

Alzheimer's disease (AD) is a major neurological disease affecting elderly individuals worldwide. Existing drugs only reduce the symptoms of the disease without addressing the underlying causes. Commonly, Aβ25-35 peptide aggregation is the main reason for AD development. Recently, the discovery of multiple protein-targeting molecules has provided a new strategy for treating AD. This study demonstrates the neuroprotective potential of oxymatrine against multiple mechanisms, such as acetylcholinesterase, mitochondrial damage, and β-amyloid-induced cell toxicity. The in vitro cell culture studies showed that oxymatrine possesses significant potential to inhibit acetylcholine esterase and promotes antioxidant, antiapoptotic effects while preventing Aβ25-35 peptide aggregation in PC12 cells. Furthermore, oxymatrine protects PC12 cells against Aβ25-35-induced cytotoxicity and down-regulates the reactive oxygen species generation. The in vivo acute toxicological studies confirm the safety of oxymatrine without causing organ damage or death in animals. Overall, this study provided evidence that oxymatrine is an efficient neuroprotective agent, with a potential to be a multifunctional drug for Alzheimer's disease treatment. These findings present a reliable and synergistic approach for treating AD.

The inhibitory effects of natural antioxidants on protein glycation as well as aggregation induced by methylglyoxal and underlying mechanisms

The non-enzymatic glycation of protein can result in the formation of advanced glycation end-products (AGEs), leading to the deposition of amyloid proteins, and it's essential for the pathogenesis of diabetes complications and amyloid diseases. Reactive dicarbonyl compounds, such as methylglyoxal (MGO), are one of the most reactive glycating agents. Therefore, it's crucially necessary to inhibit protein glycation and aggregation induced by MGO. In the present study, we aimed to systemically investigate the anti-glycation and anti-fibrillization activities of eight natural antioxidants, including apigenin, quercetin (Que), catechin, resveratrol (Res), and gallic acid (GA), L-ascorbic acid (L-AA), limonene, and β-carotene, during MGO-induced protein glycation and aggregation. Furthermore, the underlying mechanisms were clarified. The formation of AGEs and the degree of protein aggregation were characterized by optical detection, flow cytometry, and so on. The results demonstrated that eight selected natural antioxidants could inhibit glycation and protein aggregation induced by MGO via the synergy of scavenging free radicals, capturing MGO, and interacting with proteins, among which GA (300 μM) and Res (15 μM) had higher inhibition rates on both argpyrimidine (specific fluorescent AGEs, 17% and 22%, respectively) and protein amyloid aggregation (42% and 29%, respectively). These findings suggested that antioxidants could act as potential inhibitors of AGEs and glycation-induced protein aggregation, which were expected to become a new strategy for the prevention and treatment of diabetes and amyloid diseases. Besides, these inhibition mechanisms provided valuable insights into the design and development of candidate drugs for the prevention and treatment of AGEs and protein aggregation-related diseases.