Microspectroscopy (μFTIR) reveals co-localization of lipid oxidation and amyloid plaques in human Alzheimer disease brains

Exhaled breath is feasible for mild cognitive impairment detection: A diagnostic study with portable micro-gas chromatography

BACKGROUND

Mild cognitive impairment (MCI) is an important prodromal stage of Alzheimer's disease (AD), affecting 69 million individuals worldwide. At present, there is a lack of a community-applicable tool for MCI screening. Exhaled breath volatile organic compounds (VOCs) have been used to distinguish MCI from cognitively normal (CN) individuals only in small sample size studies and the efficacy has not been compared with blood biomarkers.

OBJECTIVE

This diagnostic study aimed to assess the feasibility of using exhaled breath VOCs detection by a portable micro-gas chromatography (μGC) device as a screening tool to discriminate MCI from CN individuals in a community population.

METHODS

A detection model was developed and optimized from five distinct machine learning algorithms based on the differential VOCs between 240 MCI and 241 CN individuals. Among these 481 participants, five plasma biomarkers were measured in 397 individuals (166 MCI and 231 CN).

RESULTS

The final model (481 individuals) incorporating eight differential VOCs showed good performance with an area under the receiver-operating characteristic curve (AUC) of 0.84 (95% confidence interval (95% CI): 0.83-0.85). The AUC of the VOC model (0.80, 95% CI: 0.69-0.90) was higher than that of the plasma model (0.77, 95% CI: 0.65-0.88) (397 individuals).

CONCLUSIONS

The detection of exhaled breath VOCs by a portable μGC device is feasible for MCI screening in community populations, potentially facilitating early detection and intervention strategies for individuals at high risk.

Subventricular Accumulation of Cu in the Aging Mouse Brain Does Not Associate with Anticipated Increases in Markers of Oxidative Stress

Natural aging is associated with mild memory loss and cognitive decline, and age is the greatest risk factor for neurodegenerative diseases, such as Alzheimer's disease. There is substantial evidence that oxidative stress is a major contributor to both natural aging and neurodegenerative disease, and coincidently, levels of redox active metals such as Fe and Cu are known to be elevated later in life. Recently, a pronounced age-related increase in Cu content has been reported to occur in mice and rats around a vital regulatory brain region, the subventricular zone of lateral ventricles. In our study herein, we have characterized lateral ventricle Cu content in a unique murine model of accelerated aging, senescence accelerated mouse-prone 8 (SAMP8) mice. Our results confirm an age-related increase in ventricle Cu content, consistent with the studies by others in wild-type mice and rats. Specifically, we observed Cu content to increase over the time frame 1 to 5 months and 5 to 9 months, but interestingly, no significant increase occurred between 9 and 12 months (although brain Cu content at 12 months was significantly elevated relative to 1 and 5 month-old animals). Despite the magnitude of Cu increase observed within the cells that comprise the subventricular zone of lateral ventricles (average 3 mM Cu, with isolated subcellular concentrations of 17 mM), we did not detect spectroscopic markers of thiol oxidation, protein aggregation, or lipid oxidation. The lack of evidence for oxidative stress in ex vivo animal tissue is in contrast to in vitro studies demonstrating that thiol, protein, and lipid oxidation is pronounced at these Cu concentrations. We suggest that our findings most likely indicate that the Cu ions in this brain region are sequestered in an unreactive form, possibly extended chains of Cu-thiolate complexes, which do not readily redox cycle in the aqueous cytosol. These results also appear to partially challenge the long-held view that age-related increases in brain metal content drive oxidative stress as we did not observe a concomitant association between age-related Cu increase and markers of oxidative stress, nor did we observe a net increase in Cu content between mice aged 9 and 12 months.

Selegiline Improves Cognitive Impairment in the Rat Model of Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurological disorder characterized by cognitive decline. This study was undertaken to evaluate the effects of selegiline (SEL) against AD-induced cognitive deficits and explore the possible involved mechanisms. AD was induced by unilateral intracerebroventricular (U-ICV) injection of 5 μg of amyloid beta1-42 (Aβ1-42), and oral administration of SEL (0.5 mg/kg/day) was performed for 30 consecutive days. Aβ injection resulted in spatial cognitive decline, as demonstrated by a decrease in the time spent in the target zone on the probe day (P < 0.01) in the Barnes maze test (BMT). This spatial cognitive decline was associated with disrupted synaptic plasticity, as indicated by reductions in both components of hippocampal long-term potentiation (LTP), namely population spike amplitude (P < 0.001) and field excitatory postsynaptic potential (P < 0.001). On the other hand, the injection of Aβ resulted in oxidative stress by decreasing total thiol group (TTG) content and increasing malondialdehyde (MDA) levels in the rat plasma (P < 0.001). Additionally, the number of healthy cells in the hippocampal dentate gyrus (DG) and CA1 regions was reduced in AD rats (P < 0.001). However, oral administration of SEL improved spatial cognitive decline in the Aβ-induced AD rats. The results suggest that improvement of neuroplasticity deficiency, regulation of oxidant/antioxidant status, and suppression of neuronal loss by SEL may be the mechanisms underlying its beneficial effect against AD-related spatial cognitive impairment.

An overview of the genes and biomarkers in Alzheimer's disease

Alzheimer's disease (AD) is the most common type of dementia and neurodegenerative disease characterized by neurofibrillary tangles (NFTs) and amyloid plaque. Familial AD is caused by mutations in the APP, PSEN1, and PSEN2 genes and these mutations result in the early onset of the disease. Sporadic AD usually affects older adults over the age of 65 years and is, therefore classified as late-onset AD (LOAD). Several risk factors associated with LOAD including the APOE gene have been identified. Moreover, GWAS studies have identified a wide array of genes and polymorphisms that are associated with LOAD risk. Currently, the diagnosis of AD involves the evaluation of memory and personality changes, cognitive impairment, and medical and family history to rule out other diseases. Laboratory tests to assess the biomarkers in the body fluids as well as MRI, CT, and PET scans to analyze the presence of plaques and NFTs are also included in the diagnosis of AD. It is important to diagnose AD before the onset of clinical symptoms, i.e. during the preclinical stage, to delay the progression and for better management of the disease. Research has been conducted to identify biomarkers of AD in the CSF, serum, saliva, and urine during the preclinical stage. Current research has identified several biomarkers and potential biomarkers in the body fluids that enhance diagnostic accuracy. Aside from genetics, other factors such as diet, physical activity, and lifestyle factors may influence the risk of developing AD. Clinical trials are underway to find potential biomarkers, diagnostic measures, and treatments for AD mainly in the preclinical stage. This review provides an overview of the genes and biomarkers of AD.

Unsaturated Fatty Acids Are Decreased in Aβ Plaques in Alzheimer's Disease

Alzheimer's disease (AD) is characterized by the accumulation of amyloid-beta (Aβ) plaques in the brain, contributing to neurodegeneration. This study investigates lipid alterations within these plaques using a novel, label-free, multimodal approach. Combining infrared (IR) imaging, machine learning, laser microdissection (LMD), and flow injection analysis mass spectrometry (FIA-MS), we provide the first comprehensive lipidomic analysis of chemically unaltered Aβ plaques in post-mortem human AD brain tissue. IR imaging revealed decreased lipid unsaturation within plaques, evidenced by a reduction in the alkene (=C-H) stretching vibration band. The high spatial resolution of IR imaging, coupled with machine learning-based plaque detection, enabled precise and label-free extraction of plaques via LMD. Subsequent FIA-MS analysis confirmed a significant increase in short-chain saturated lipids and a concomitant decrease in long-chain unsaturated lipids within plaques compared to the surrounding tissue. These findings highlight a substantial depletion of unsaturated fatty acids (UFAs) in Aβ plaques, suggesting a pivotal role for lipid dysregulation and oxidative stress in AD pathology. This study advances our understanding of the molecular landscape of Aβ plaques and underscores the potential of lipid-based therapeutic strategies in AD.

Exploring fatty acid metabolism in Alzheimer's disease: the key role of CPT1A

Alzheimer's disease (AD) is a severe neurodegenerative disease, and the most common type of dementia, with symptoms of progressive cognitive dysfunction and behavioral impairment. Studying the pathogenesis of AD and exploring new targets for the prevention and treatment of AD is a very worthwhile challenge. Accumulating evidence has highlighted the effects of fatty acid metabolism on AD. In this study, fatty acid metabolism was used as an entry point to understand the pathogenesis of AD and identify new targets. After identifying differentially expressed genes, multiple machine learning algorithms, carnitine palmitoyltransferase 1 A (CPT1A) was identified as the key gene for fatty acid metabolism in AD. Further single nucleus RNA sequencing analysis were performed, and the GSEA results showed that the fatty acid β-oxidation pathway was enriched only in astrocytes, and the fatty acid β-oxidation pathway was down-regulated in the AD astrocytes compared to the CN astrocytes, while CPT1A was specifically downregulated in astrocytes of AD, which was confirmed in vitro experiment subsequently, and decreased expression level of CPT1A would lead to abnormal lipid metabolism, which shapes astrocyte reactivity and injury, neuroinflammatory, and thus affects AD pathogenesis. Our findings report the involvement of CPT1A in AD. We confirm that the primary role of astrocytes for fatty acid β-oxidation, and CPT1A is localized in astrocytes. Downregulated CPT1A could be a novel potential target for the prevention and treatment of AD. Our study provides strong evidence for the involvement of fatty acid metabolism in the pathogenesis of AD.

Structural diversity of Alzheimer-related protein aggregations revealed using photothermal ratio-metric micro-spectroscopy

The crucial link between pathological protein aggregations and lipids in Alzheimer's disease pathogenesis is increasingly recognized, yet its spatial dynamics remain challenging for labeling-based microscopy. Here, we demonstrate photothermal ratio-metric infrared spectro-microscopy (PRISM) to investigate the in situ structural and molecular compositions of pathological features in brain tissues at submicron resolution. By identifying the vibrational spectroscopic signatures of protein secondary structures and lipids, PRISM tracks the structural dynamics of pathological proteins, including amyloid and hyperphosphorylated Tau (pTau). Amyloid-associated lipid features in major brain regions were observed, notably the enrichment of lipid-dissociated plaques in the hippocampus. Spectroscopic profiling of pTau revealed significant heterogeneity in phosphorylation levels and a distinct lipid-pTau relationship that contrasts with the anticipated lipid-plaque correlation. Beyond in vitro studies, our findings provide direct visualization evidence of aggregate-lipid interactions across the brain, offering new insights into mechanistic and therapeutic research of neurodegenerative diseases.

Identification of tauopathy-associated lipid signatures in Alzheimer's disease mouse brain using label-free chemical imaging

There is cumulative evidence that lipid metabolism plays a key role in the pathogenesis of various neurodegenerative disorders including Alzheimer's disease (AD). Visualising lipid content in a non-destructive label-free manner can aid in elucidating the AD phenotypes towards a better understanding of the disease. In this study, we combined multiple optical molecular-specific methods, Fourier transform infrared (FTIR) spectroscopic imaging, synchrotron radiation-infrared (SR-IR) microscopy, Raman and stimulated Raman scattering (SRS) microscopy, and optical-photothermal infrared (O-PTIR) microscopy with multivariate data analysis, to investigate the biochemistry of brain hippocampus in situ using a mouse model of tauopathy (rTg4510). We observed a significant difference in the morphology and lipid content between transgenic (TG) and wild type (WT) samples. Immunohistochemical staining revealed some degree of microglia co-localisation with elevated lipids in the brain. These results provide new evidence of tauopathy-related dysfunction in a preclinical study at a subcellular level.

Identification and classification of proteins by FTIR microspectroscopy. A proof of concept

FTIR spectroscopy is well known for its molecule fingerprinting capability but is also able to differentiate classes in complex biological systems. This includes strain typing and species level identification of bacterial, yeast or fungal cells, as well as distinguishing between cell layers in eukaryotic tissues. However, its use for the identification of macromolecules such as proteins remains underexplored and rarely used in practice. Here we demonstrate the efficacy of FTIR microspectroscopy coupled with machine learning methods for rapid and accurate identification of proteins in their dry state within minutes, from very small quantities of material, if they are obtained in a pure aqueous solution. FTIR microspectroscopy can provide additional information beside identification: it can detect small differences among different purification batches potentially originating from post-translational modifications or distinct folding states. Moreover, it distinguishes glycoproteins and evaluate glycosylation while detecting contaminants. This methodology presents itself as a valuable quality control tool in protein purification processes or any process requiring the utilization of precisely identified, pure proteins.

Relationship between Plasma Lipid Profile and Cognitive Status in Early Alzheimer Disease

Alzheimer disease (AD) is a heterogeneous and complex disease in which different pathophysiological mechanisms are involved. This heterogenicity can be reflected in different atrophy patterns or clinical manifestations. Regarding biochemical pathways involved in early AD, lipid metabolism plays an important role; therefore, lipid levels have been evaluated as potential AD diagnosis biomarkers, and their levels could be related to different AD clinical manifestations. Therefore, the aim of this work is to study AD lipid profiles from early AD patients and evaluate their clinical significance. For this purpose, untargeted plasma lipidomic analysis was carried out in early AD patients (n = 31) diagnosed with cerebrospinal fluid (CSF) biomarkers. Cluster analysis was carried out to define early AD subgroups according to the lipid levels. Then, the clinical significance of each lipid profile subgroup was studied, analyzing differences for other variables (cognitive status, CSF biomarkers, medication, comorbidities, age, and gender). The cluster analysis revealed two different groups of AD patients. Cluster 1 showed higher levels of plasma lipids and better cognitive status than Cluster 2. However, no differences were found for the other variables (age, gender, medication, comorbidities, cholesterol, and triglycerides levels) between both groups. Plasma lipid levels could differentiate two early AD subgroups, which showed different cognitive statuses. However, further research with a large cohort and longitudinal study evaluating the clinical evolution of these patients is required. In general, it would involve a relevant advance in the knowledge of AD pathological mechanisms, potential treatments, and precision medicine.

Caenorhabditis elegans endorse bacterial nanocellulose fibers as functional dietary Fiber reducing lipid markers

Bacterial nanocellulose (BNC) is a promising dietary fiber with potential as a functional food additive. We evaluated BNC fibers (BNCf) in the Caenorhabditis elegans model to obtain insight into the BNCf's biointeraction with its gastrointestinal tract while reducing the variables of higher complex animals. BNCf were uptaken and excreted by worms without crossing the intestinal barrier, confirming its biosafety regarding survival rate, reproduction, and aging for concentrations up to 34 μg/ml BNCf. However, a slight decrease in the worms' length was detected. A possible nutrient shortage or stress produced by BNCf was discarded by measuring stress and chemotactic response pathways. Besides, we detected a lipid-lowering effect of BNCf in N2 C. elegans in normal and high-caloric diets. Oxidative damage was computed in N2 worms and Rac1/ced-10 mutants. The GTPase Rac1 is involved in neurological diseases, where its dysregulation enhances ROS production and neuronal damage. BNCf reduced the lipid oxidative markers produced by ROS species in this worm strain. Finally, we detected that BNCf activated the genetic expression of the immunological response and lipid catabolic process. These results strengthen the use of BNCf as a functional dietary fiber and encourage the potential treatment of neurological disease by modulating diet.

Biochemical analysis of Hyalomma dromedarii salivary glands and gut tissues using SR-FTIR micro-spectroscopy

Ticks are obligatory voracious blood feeders infesting diverse vertebrate hosts, that have a crucial role in the transmission of diverse pathogens that threaten human and animal health. The continuous emergence of tick-borne diseases due to combined worldwide climatic changes, human activities, and acaricide-resistant tick strains, necessitates the development of novel ameliorative tick control strategies such as vaccines. The synchrotron-based Fourier transform infrared micro-spectroscopy (SR-FTIR) is a bioanalytical microprobe capable of exploring the molecular chemistry within microstructures at a cellular or subcellular level and is considered as a nondestructive analytical approach for biological specimens. In this study, SR-FTIR analysis was able to explore a qualitative and semi-quantitative biochemical composition of gut and salivary glands of Hyalomma dromedarii (H. dromedarii) tick detecting differences in the biochemical composition of both tissues. A notable observation regarding Amide I secondary structure protein profile was the higher ratio of aggregated strands in salivary gland and beta turns in gut tissues. Regarding the lipid profile, there was a higher intensity of lipid regions in gut tissue when compared to salivary glands. This detailed information on the biochemical compositions of tick tissues could assist in selecting vaccine and/or control candidates. Altogether, these findings confirmed SR-FTIR spectroscopy as a tool for detecting differences in the biochemical composition of H. dromedarii salivary glands and gut tissues. This approach could potentially be extended to the analysis of other ticks that are vectors of important diseases such as babesiosis and theileriosis.

Caenorhabditis elegans RAC1/ced-10 mutants as a new animal model to study very early stages of Parkinson's disease

Patients with Parkinson's disease (PD) display non-motor symptoms arising prior to the appearance of motor signs and before a clear diagnosis. Motor and non-motor symptoms correlate with progressive deposition of the protein alpha-synuclein (Asyn) both within and outside of the central nervous system, and its accumulation parallels neurodegeneration. The genome of Caenorhabditis elegans does not encode a homolog of Asyn, thus rendering this nematode an invaluable system with which to investigate PD-related mechanisms in the absence of interference from endogenous Asyn aggregation. CED-10 is the nematode homolog of human RAC1, a small GTPase needed to maintain the function and survival of dopaminergic neurons against human Asyn-induced toxicity in C. elegans. Here, we introduce C. elegans RAC1/ced-10 mutants as a predictive tool to investigate early PD symptoms before neurodegeneration occurs. Deep phenotyping of these animals reveals that, early in development, they displayed altered defecation cycles, GABAergic abnormalities and an increased oxidation index. Moreover, they exhibited altered lipid metabolism evidenced by the accumulation of lipid droplets. Lipidomic fingerprinting indicates that phosphatidylcholine and sphingomyelin, but not phosphatidylethanolamine or phosphatidylserine, were elevated in RAC1/ced-10 mutant nematodes. These collective characteristics reflect the non-motor dysfunction, GABAergic neurotransmission defects, upregulation of stress response mechanisms, and metabolic changes associated with early-onset PD. Thus, we put forward an easy-to-manipulate preclinical animal model to deepen our understanding of early-stage PD and accelerate the translational path for therapeutic target discovery.

Orthosiphon aristatus (Blume) Miq. Extracts attenuate Alzheimer-like pathology through anti-inflammatory, anti-oxidative, and β-amyloid inhibitory activities

ETHNOPHARMACOLOGICAL RELEVANCE

Orthosiphon aristatus (Blume) Miq. (OA) is a traditional folk-herb, which is usually used to treat acute and chronic nephritis, epilepsy, cystitis, and other diseases. Phenols and flavonoids are the main active compound compounds of OA, with proven anti-inflammatory and antioxidant activities.

AIMS OF THIS STUDY

Based on evidenced therapeutic activities, we aimed to investigate the impact of OA on Alzheimer's disease (AD) which is the most common age-related neurodegenerative disease, and the pathological features include accumulation of beta-amyloid (Aβ) and neurofibrillary tangles (NFT).

MATERIALS AND METHODS

OA was extracted with water, methanol, chloroform, and ethyl acetate, and determined its total flavonoid and phenolic contents. Initially, Aβ1-42 based cytotoxicity was induced in BV2 cells and C6 cells to investigate the therapeutic impact of OA therapy by MTT, RT-PCR, Western blot, and ELISA. Further, Aβ1-42 Oligomer (400 pmol)-induced AD mice model was established to evaluate the impact of OA extract on improving learning and memory impairment.

RESULTS

The results showed that the extract of OA could increase cell survival, inhibit the expression of TNF-α, IL-6, IL-1β, COX-2, and iNOS, and increase BDNF levels. We infer that the OA extract may attenuate Aβ-induced cytotoxicity by retarding the production of inflammatory-related factors. In the animal behavior test, the number of mice entering darkroom and the time of arriving at the platform were significantly reduced, indicating the learning and memory-improving ability of OA extract.

CONCLUSIONS

These findings imply that the OA ethanolic extract demonstrated an improving effect on memory and hence could serve as a potential therapeutic target for the treatment of neurodegenerative diseases like AD.

Lipid metabolism and oxidative stress in patients with Alzheimer's disease and amnestic mild cognitive impairment

Lipid metabolism and oxidative stress are key mechanisms in Alzheimer's disease (AD). The link between plasma lipid metabolites and oxidative stress in AD patients is poorly understood. This study was to identify markers that distinguish AD and amnestic mild cognitive impairment (aMCI) from NC, and to reveal potential links between lipid metabolites and oxidative stress. We performed non-targeted lipid metabolism analysis of plasma from patients with AD, aMCI, and NC using LC-MS/MS. The plasma malondialdehyde (MDA), glutathione peroxidase (GSH-Px), and superoxide dismutase (SOD) levels were assessed. We found significant differences in lipid metabolism between patients with AD and aMCI compared to those in NC. AD severity is associated with lipid metabolites, especially TG (18:0_16:0_18:0) + NH4, TG (18:0_16:0_16:0) + NH4, LPC(16:1e)-CH3, and PE (20:0_20:4)-H. SPH (d16:0) + H, SPH (d18:1) + H, and SPH (d18:0) + H were high-performance markers to distinguish AD and aMCI from NC. The AUC of three SPHs combined to predict AD was 0.990, with specificity and sensitivity as 0.949 and 1, respectively; the AUC of three SPHs combined to predict aMCI was 0.934, with specificity and sensitivity as 0.900, 0.981, respectively. Plasma MDA concentrations were higher in the AD group than in the NC group (p = 0.003), whereas plasma SOD levels were lower in the AD (p < 0.001) and aMCI (p = 0.045) groups than in NC, and GSH-Px activity were higher in the AD group than in the aMCI group (p = 0.007). In addition, lipid metabolites and oxidative stress are widely associated. In conclusion, this study distinguished serum lipid metabolism in AD, aMCI, and NC subjects, highlighting that the three SPHs can distinguish AD and aMCI from NC. Additionally, AD patients showed elevated oxidative stress, and there are complex interactions between lipid metabolites and oxidative stress.

Molecular mechanism and potential therapeutic targets of necroptosis and ferroptosis in Alzheimer's disease

Alzheimer's disease (AD), a neurodegenerative condition, is defined by neurofibrillary tangles, amyloid plaques, and gradual cognitive decline. Regardless of the advances in understanding AD's pathogenesis and progression, its causes are still contested, and there are currently no efficient therapies for the illness. The post-mortem analyses revealed widespread neuronal loss in multiple brain regions in AD, evidenced by a decrease in neuronal density and correlated with the disease's progression and cognitive deterioration. AD's neurodegeneration is complicated, and different types of neuronal cell death, alone or in combination, play crucial roles in this process. Recently, the involvement of non-apoptotic programmed cell death in the neurodegenerative mechanisms of AD has received a lot of attention. Aberrant activation of necroptosis and ferroptosis, two newly discovered forms of regulated non-apoptotic cell death, is thought to contribute to neuronal cell death in AD. In this review, we first address the main features of necroptosis and ferroptosis, cellular signaling cascades, and the mechanisms involved in AD pathology. Then, we discuss the latest therapies targeting necroptosis and ferroptosis in AD animal/cell models and human research to provide vital information for AD treatment.

Iron and Targeted Iron Therapy in Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disease worldwide. β-amyloid plaque (Aβ) deposition and hyperphosphorylated tau, as well as dysregulated energy metabolism in the brain, are key factors in the progression of AD. Many studies have observed abnormal iron accumulation in different regions of the AD brain, which is closely correlated with the clinical symptoms of AD; therefore, understanding the role of brain iron accumulation in the major pathological aspects of AD is critical for its treatment. This review discusses the main mechanisms and recent advances in the involvement of iron in the above pathological processes, including in iron-induced oxidative stress-dependent and non-dependent directions, summarizes the hypothesis that the iron-induced dysregulation of energy metabolism may be an initiating factor for AD, based on the available evidence, and further discusses the therapeutic perspectives of targeting iron.

Label-Free High-Resolution Photothermal Optical Infrared Spectroscopy for Spatiotemporal Chemical Analysis in Fresh, Hydrated Living Tissues and Embryos

Label-free chemical imaging of living and functioning systems is the holy grail of biochemical research. However, existing techniques often require extensive sample preparation to remove interfering molecules such as water, rendering many molecular imaging techniques unsuitable for in situ structural studies. Here, we examined freshly extracted tissue biopsies and living small vertebrates at submicrometer resolution using optical photothermal infrared (O-PTIR) microspectroscopy and demonstrated the following major advances: (1) O-PTIR can be used for submicrometer structural analysis of unprocessed, fully hydrated tissue biopsies extracted from diverse organs, including living brain and lung tissues. (2) O-PTIR imaging can be performed on living organisms, such as salamander embryos, without compromising their further development. (3) Using O-PTIR, we tracked the structural changes of amyloids in functioning brain tissues over time, observing the appearance of newly formed amyloids for the first time. (4) Amyloid structures appeared altered following standard fixation and dehydration procedures. Thus, we demonstrate that O-PTIR enables time-resolved submicrometer in situ investigation of chemical and structural changes in diverse biomolecules in their native conditions, representing a technological breakthrough for in situ molecular imaging of biological samples.

Early-stage mapping of macromolecular content in APPNL-F mouse model of Alzheimer's disease using nuclear Overhauser effect MRI

Non-invasive methods of detecting early-stage Alzheimer's disease (AD) can provide valuable insight into disease pathology, improving the diagnosis and treatment of AD. Nuclear Overhauser enhancement (NOE) MRI is a technique that provides image contrast sensitive to lipid and protein content in the brain. These macromolecules have been shown to be altered in Alzheimer's pathology, with early disruptions in cell membrane integrity and signaling pathways leading to the buildup of amyloid-beta plaques and neurofibrillary tangles. We used template-based analyzes of NOE MRI data and the characteristic Z-spectrum, with parameters optimized for increase specificity to NOE, to detect changes in lipids and proteins in an AD mouse model that recapitulates features of human AD. We find changes in NOE contrast in the hippocampus, hypothalamus, entorhinal cortex, and fimbria, with these changes likely attributed to disruptions in the phospholipid bilayer of cell membranes in both gray and white matter regions. This study suggests that NOE MRI may be a useful tool for monitoring early-stage changes in lipid-mediated metabolism in AD and other disorders with high spatial resolution.

Arrhythmic Effects Evaluated on Caenorhabditis elegans: The Case of Polypyrrole Nanoparticles

Experimental studies and clinical trials of nanoparticles for treating diseases are increasing continuously. However, the reach to the market does not correlate with these efforts due to the enormous cost, several years of development, and off-target effects like cardiotoxicity. Multicellular organisms such as the Caenorhabditis elegans (C. elegans) can bridge the gap between in vitro and vertebrate testing as they can provide extensive information on systemic toxicity and specific harmful effects through facile experimentation following 3R EU directives on animal use. Since the nematodes' pharynx shares similarities with the human heart, we assessed the general and pharyngeal effects of drugs and polypyrrole nanoparticles (Ppy NPs) using C. elegans. The evaluation of FDA-approved drugs, such as Propranolol and Racepinephrine reproduced the arrhythmic behavior reported in humans and supported the use of this small animal model. Consequently, Ppy NPs were evaluated due to their research interest in cardiac arrhythmia treatments. The NPs' biocompatibility was confirmed by assessing survival, growth and development, reproduction, and transgenerational toxicity in C. elegans. Interestingly, the NPs increased the pharyngeal pumping rate of C. elegans in two slow-pumping mutant strains, JD21 and DA464. Moreover, the NPs increased the pumping rate over time, which sustained up to a day post-excretion. By measuring pharyngeal calcium levels, we found that the impact of Ppy NPs on the pumping rate could be mediated through calcium signaling. Thus, evaluating arrhythmic effects in C. elegans offers a simple system to test drugs and nanoparticles, as elucidated through Ppy NPs.

Biomolecular alterations detected in multiple sclerosis skin fibroblasts using Fourier transform infrared spectroscopy

Multiple sclerosis (MS) is the leading cause of non-traumatic disability in young adults. New avenues are needed to help predict individuals at risk for developing MS and aid in diagnosis, prognosis, and outcome of therapeutic treatments. Previously, we showed that skin fibroblasts derived from patients with MS have altered signatures of cell stress and bioenergetics, which likely reflects changes in their protein, lipid, and biochemical profiles. Here, we used Fourier transform infrared (FTIR) spectroscopy to determine if the biochemical landscape of MS skin fibroblasts were altered when compared to age- and sex-matched controls (CTRL). More so, we sought to determine if FTIR spectroscopic signatures detected in MS skin fibroblasts are disease specific by comparing them to amyotrophic lateral sclerosis (ALS) skin fibroblasts. Spectral profiling of skin fibroblasts from MS individuals suggests significant alterations in lipid and protein organization and homeostasis, which may be affecting metabolic processes, cellular organization, and oxidation status. Sparse partial least squares-discriminant analysis of spectral profiles show that CTRL skin fibroblasts segregate well from diseased cells and that changes in MS and ALS may be unique. Differential changes in the spectral profile of CTRL, MS, and ALS cells support the development of FTIR spectroscopy to detect biomolecular modifications in patient-derived skin fibroblasts, which may eventually help establish novel peripheral biomarkers.

Mid-infrared chemical imaging of intracellular tau fibrils using fluorescence-guided computational photothermal microscopy

Amyloid proteins are associated with a broad spectrum of neurodegenerative diseases. However, it remains a grand challenge to extract molecular structure information from intracellular amyloid proteins in their native cellular environment. To address this challenge, we developed a computational chemical microscope integrating 3D mid-infrared photothermal imaging with fluorescence imaging, termed Fluorescence-guided Bond-Selective Intensity Diffraction Tomography (FBS-IDT). Based on a low-cost and simple optical design, FBS-IDT enables chemical-specific volumetric imaging and 3D site-specific mid-IR fingerprint spectroscopic analysis of tau fibrils, an important type of amyloid protein aggregates, in their intracellular environment. Label-free volumetric chemical imaging of human cells with/without seeded tau fibrils is demonstrated to show the potential correlation between lipid accumulation and tau aggregate formation. Depth-resolved mid-infrared fingerprint spectroscopy is performed to reveal the protein secondary structure of the intracellular tau fibrils. 3D visualization of the β-sheet for tau fibril structure is achieved.

Lipid metabolism and Alzheimer's disease: clinical evidence, mechanistic link and therapeutic promise

Alzheimer's disease (AD) is an age-associated neurodegenerative disorder with multifactorial etiology, intersecting genetic and environmental risk factors, and a lack of disease-modifying therapeutics. While the abnormal accumulation of lipids was described in the very first report of AD neuropathology, it was not until recent decades that lipid dyshomeostasis became a focus of AD research. Clinically, lipidomic and metabolomic studies have consistently shown alterations in the levels of various lipid classes emerging in early stages of AD brains. Mechanistically, decades of discovery research have revealed multifaceted interactions between lipid metabolism and key AD pathogenic mechanisms including amyloidogenesis, bioenergetic deficit, oxidative stress, neuroinflammation, and myelin degeneration. In the present review, converging evidence defining lipid dyshomeostasis in AD is summarized, followed by discussions on mechanisms by which lipid metabolism contributes to pathogenesis and modifies disease risk. Furthermore, lipid-targeting therapeutic strategies, and the modification of their efficacy by disease stage, ApoE status, and metabolic and vascular profiles, are reviewed.

Correlative imaging to resolve molecular structures in individual cells: Substrate validation study for super-resolution infrared microspectroscopy

Light microscopy has been a favorite tool of biological studies for almost a century, recently producing detailed images with exquisite molecular specificity achieving spatial resolution at nanoscale. However, light microscopy is insufficient to provide chemical information as a standalone technique. An increasing amount of evidence demonstrates that optical photothermal infrared microspectroscopy (O-PTIR) is a valuable imaging tool that can extract chemical information to locate molecular structures at submicron resolution. To further investigate the applicability of sub-micron infrared microspectroscopy for biomedical applications, we analyzed the contribution of substrate chemistry to the infrared spectra acquired from individual neurons grown on various imaging substrates. To provide an example of correlative immunofluorescence/O-PTIR imaging, we used immunofluorescence to locate specific organelles for O-PTIR measurement, thus capturing molecular structures at the sub-cellular level directly in cells, which is not possible using traditional infrared microspectroscopy or immunofluorescence microscopy alone.

Biomolecular characterization of placental tissues in gestational diabetes mellitus using Fourier transform infrared microspectroscopy

Gestational diabetes mellitus (GDM) is a common complication during pregnancy. It could cause severe side-effect on the mother's and newborn's heath in the short- and long-term. Prevalence has been increasing over time, likely due to increases in mean maternal age and body weight. However, how GDM affects the placenta structure and function are still unclear. Fourier transform infrared microspectroscopy is well suited to study biological samples, such as tissues and cells. Biomolecules of human tissues have characteristic absorptions in mid-infrared range. In this study, Fourier transform infrared microspectroscopy was used to measure unfixed placental tissue sections from women with GDM and matched controls. The molecular composition of different type of placental tissue sections were further analyzed with principle component analysis (PCA) and orthogonal partial least squares-discriminant analysis (OPLS-DA). The major spectral characteristic of biomolecules in GDM placental tissue and control group were compared. The conformational change of lipid chains and higher level of lipid oxidation were found for placental tissues from GDM pregnancies. The increase of proteins β-sheet structures relative to the α-helix structures in the GDM placental tissues were also found. The fingerprint region showed the variances of carbohydrates, nucleic acids and phospholipids between GDM and control group placental tissues. These findings are helpful for understanding how GDM affects placenta's biochemical composition and how GDM causes maternal and fetal metabolism changes. This study also provides a new approach to investigating biomolecular composition of samples from GDM pregnancy through spectroscopic method.

Identification of Ferroptosis-Related Genes in Alzheimer’s Disease Based on Bioinformatic Analysis

Introduction

Alzheimer’s disease (AD) is the most prevalent cause of dementia, and emerging evidence suggests that ferroptosis is involved in the pathological process of AD.

Materials and Methods

Three microarray datasets (GSE122063, GSE37263, and GSE140829) about AD were collected from the GEO database. AD-related module genes were identified through a weighted gene co-expression network analysis (WGCNA). The ferroptosis-related genes were extracted from FerrDb. The apoptosis-related genes were downloaded from UniProt as a control to show the specificity of ferroptosis. The overlap was performed to obtain the module genes associated with ferroptosis and apoptosis. Then the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses and the protein-protein interaction (PPI) were conducted. Cytoscape with CytoHubba was used to identify the hub genes, and the Logistic regression was performed to distinguish the AD patients from controls.

Results

53 ferroptosis-related module genes were obtained. The GO analysis revealed that response to oxidative stress and starvation, and multicellular organismal homeostasis were the most highly enriched terms. The KEGG analysis showed that these overlapped genes were enriched not only in renal cell carcinoma pathways and central carbon metabolism in cancer, but also in autophagy-related pathways and ferroptosis. Ferroptosis-related hub genes in AD (JUN, SLC2A1, TFRC, ALB, and NFE2L2) were finally identified, which could distinguish AD patients from controls (P &lt; 0.05). The area under the ROC curve (AUC) was 0.643. Apoptosis-related hub genes in AD (STAT1, MCL1, and BCL2L11) were also identified and also could distinguish AD patients from controls (P &lt; 0.05). The AUC was 0.608, which was less than the former AUC value, suggesting that ferroptosis was more special than apoptosis in AD.

Conclusion

We identified five hub genes (JUN, SLC2A1, TFRC, ALB, and NFE2L2) that are closely associated with ferroptosis in AD and can differentiate AD patients from controls. Three hub genes of apoptosis-related genes in AD (STAT1, MCL1, and BCL2L11) were also identified as a control to show the specificity of ferroptosis. JUN, SLC2A1, TFRC, ALB, and NFE2L2 are thus potential ferroptosis-related biomarkers for disease diagnosis and therapeutic monitoring.

Oral Cancer Discrimination and Novel Oral Epithelial Dysplasia Stratification Using FTIR Imaging and Machine Learning

The Fourier transform infrared (FTIR) imaging technique was used in a transmission model for the evaluation of twelve oral hyperkeratosis (HK), eleven oral epithelial dysplasia (OED), and eleven oral squamous cell carcinoma (OSCC) biopsy samples in the fingerprint region of 1800–950 cm⁻¹. A series of 100 µm × 100 µm FTIR imaging areas were defined in each sample section in reference to the hematoxylin and eosin staining image of an adjacent section of the same sample. After outlier removal, signal preprocessing, and cluster analysis, a representative spectrum was generated for only the epithelial tissue in each area. Two representative spectra were selected from each sample to reflect intra-sample heterogeneity, which resulted in a total of 68 representative spectra from 34 samples for further analysis. Exploratory analyses using Principal component analysis and hierarchical cluster analysis showed good separation between the HK and OSCC spectra and overlaps of OED spectra with either HK or OSCC spectra. Three machine learning discriminant models based on partial least squares discriminant analysis (PLSDA), support vector machines discriminant analysis (SVMDA), and extreme gradient boosting discriminant analysis (XGBDA) were trained using 46 representative spectra from 12 HK and 11 OSCC samples. The PLSDA model achieved 100% sensitivity and 100% specificity, while both SVM and XGBDA models generated 95% sensitivity and 96% specificity, respectively. The PLSDA discriminant model was further used to classify the 11 OED samples into HK-grade (6), OSCC-grade (4), or borderline case (1) based on their FTIR spectral similarity to either HK or OSCC cases, providing a potential risk stratification strategy for the precancerous OED samples. The results of the current study support the application of the FTIR-machine learning technique in early oral cancer detection.

Label-Free Infrared Spectroscopic Imaging Reveals Heterogeneity of β-Sheet Aggregates in Alzheimer's Disease

The aggregation of the amyloid beta (Aβ) protein into plaques is a pathological feature of Alzheimer's disease (AD). While amyloid aggregates have been extensively studied in vitro, their structural aspects and associated chemistry in the brain are not fully understood. In this report, we demonstrate, using infrared spectroscopic imaging, that Aβ plaques exhibit significant heterogeneities in terms of their secondary structure and phospholipid content. We show that the capabilities of discrete frequency infrared imaging (DFIR) are ideally suited for characterization of amyloid deposits in brain tissues and employ DFIR to identify nonplaque β-sheet aggregates distributed throughout brain tissues. We further demonstrate that phospholipid-rich β-sheet deposits exist outside of plaques in all diseased tissues, indicating their potential clinical significance. This is the very first application of DFIR toward a characterization of protein aggregates in an AD brain and provides a rapid, label-free approach that allows us to uncover β-sheet heterogeneities in the AD, which may be significant for targeted therapeutic strategies in the future.

Loss of presenilin function enhances tau phosphorylation and aggregation in mice

Mutations in the presenilin (PS/PSEN) genes encoding the catalytic components of γ-secretase accelerate amyloid-β (Aβ) and tau pathologies in familial Alzheimer’s disease (AD). Although the mechanisms by which these mutations affect Aβ are well defined, the precise role PS/γ-secretase on tau pathology in neurodegeneration independently of Aβ is largely unclear. Here we report that neuronal PS deficiency in conditional knockout (cKO) mice results in age-dependent brain atrophy, inflammatory responses and accumulation of pathological tau in neurons and glial cells. Interestingly, genetic inactivation of presenilin 1 (PS1) or both PS genes in mutant human Tau transgenic mice exacerbates memory deficits by accelerating phosphorylation and aggregation of tau in excitatory neurons of vulnerable AD brain regions (e.g., hippocampus, cortex and amygdala). Remarkably, neurofilament (NF) light chain (NF-L) and phosphorylated NF are abnormally accumulated in the brain of Tau mice lacking PS. Synchrotron infrared microspectroscopy revealed aggregated and oligomeric β-sheet structures in amyloid plaque-free PS-deficient Tau mice. Hippocampal-dependent memory deficits are associated with synaptic tau accumulation and reduction of pre- and post-synaptic proteins in Tau mice. Thus, partial loss of PS/γ-secretase in neurons results in temporal- and spatial-dependent tau aggregation associated with memory deficits and neurodegeneration. Our findings show that tau phosphorylation and aggregation are key pathological processes that may underlie neurodegeneration caused by familial AD-linked PSEN mutations.

Micro-Raman spectroscopy of lipid halo and dense-core amyloid plaques: aging process characterization in the Alzheimer's disease APPswePS1ΔE9 mouse model

The deposition of amyloid plaques is considered one of the main microscopic features of Alzheimer's disease (AD). Since plaque formation can precede extensive neurodegeneration and it is the main clinical manifestation of AD, it constitutes a relevant target for new treatment and diagnostic approaches. Micro-Raman spectroscopy, a label-free technique, is an accurate method for amyloid plaque identification and characterization. Here, we present a high spatial resolution micro-Raman hyperspectral study in transgenic APPswePS1ΔE9 mouse brains, showing details of AD tissue biochemical and histological changes without staining. First we used stimulated micro-Raman scattering to identify the lipid-rich halo surrounding the amyloid plaque, and then proceeded with spontaneous (conventional) micro-Raman spectral mapping, which shows a cholesterol and sphingomyelin lipid-rich halo structure around dense-core amyloid plaques. The detailed images of this lipid halo relate morphologically well with dystrophic neurites surrounding plaques. Principal Component Analysis (PCA) of the micro-Raman hyperspectral data indicates the feasibility of the optical biomarkers of AD progression with the potential for discriminating transgenic groups of young adult mice (6-month-old) from older ones (12-month-old). Frequency-specific PCA suggests that plaque-related neurodegeneration is the predominant change captured by Raman spectroscopy, and the main differences are highlighted by vibrational modes associated with cholesterol located majorly in the lipid halo.

Synthesis of human amyloid restricted to liver results in an Alzheimer disease-like neurodegenerative phenotype

Several lines of study suggest that peripheral metabolism of amyloid beta (Aß) is associated with risk for Alzheimer disease (AD). In blood, greater than 90% of Aß is complexed as an apolipoprotein, raising the possibility of a lipoprotein-mediated axis for AD risk. In this study, we report that genetic modification of C57BL/6J mice engineered to synthesise human Aß only in liver (hepatocyte-specific human amyloid (HSHA) strain) has marked neurodegeneration concomitant with capillary dysfunction, parenchymal extravasation of lipoprotein-Aß, and neurovascular inflammation. Moreover, the HSHA mice showed impaired performance in the passive avoidance test, suggesting impairment in hippocampal-dependent learning. Transmission electron microscopy shows marked neurovascular disruption in HSHA mice. This study provides causal evidence of a lipoprotein-Aß /capillary axis for onset and progression of a neurodegenerative process.

It has been suggested that peripheral metabolism of amyloid-beta is associated with risk for Alzheimer’s disease. This study reveals that the expression of human amyloid exclusively in the liver induces Alzheimer’s disease-like pathologies in mice, potentially indicating a completely novel pathway of Alzheimer’s disease aetiology and therapies.

In situ identification and G4-PPI-His-Mal-dendrimer-induced reduction of early-stage amyloid aggregates in Alzheimer's disease transgenic mice using synchrotron-based infrared imaging

Amyloid plaques composed of Aβ amyloid peptides and neurofibrillary tangles are a pathological hallmark of Alzheimer Disease. In situ identification of early-stage amyloid aggregates in Alzheimer's disease is relevant for their importance as potential targets for effective drugs. Synchrotron-based infrared imaging is here used to identify early-stage oligomeric/granular aggregated amyloid species in situ in the brain of APP/PS1 transgenic mice for the first time. Also, APP/PS1 mice show fibrillary aggregates at 6 and 12 months. A significant decreased burden of early-stage aggregates and fibrillary aggregates is obtained following treatment with poly(propylene imine) dendrimers with histidine-maltose shell (a neurodegenerative protector) in 6-month-old APP/PS1 mice, thus demonstrating their putative therapeutic properties of in AD models. Identification, localization, and characterization using infrared imaging of these non-fibrillary species in the cerebral cortex at early stages of AD progression in transgenic mice point to their relevance as putative pharmacological targets. No less important, early detection of these structures may be useful in the search for markers for non-invasive diagnostic techniques.

Ferroptosis, a Potential Therapeutic Target in Alzheimer's Disease

Cell death is a common phenomenon in the progression of Alzheimer’s disease (AD). However, the mechanism of triggering the death of neuronal cells remains unclear. Ferroptosis is an iron-dependent lipid peroxidation-driven cell death and emerging evidences have demonstrated the involvement of ferroptosis in the pathological process of AD. Moreover, several hallmarks of AD pathogenesis were consistent with the characteristics of ferroptosis, such as excess iron accumulation, elevated lipid peroxides, and reactive oxygen species (ROS), reduced glutathione (GSH), and glutathione peroxidase 4 (GPX4) levels. Besides, some ferroptosis inhibitors can relieve AD-related pathological symptoms in AD mice and exhibit potential clinical benefits in AD patients. Therefore, ferroptosis is gradually being considered as a distinct cell death mechanism in the pathogenesis of AD. However, direct evidence is still lacking. In this review, we summarize the features of ferroptosis in AD, its underlying mechanisms in AD pathology, and review the application of ferroptosis inhibitors in both AD clinical trials and mice/cell models, to provide valuable information for future treatment and prevention of this devastating disease.

Cytotoxic Effects of 5-Azacytidine on Primary Tumour Cells and Cancer Stem Cells from Oral Squamous Cell Carcinoma: An In Vitro FTIRM Analysis

In the present study, the cytotoxic effects of 5-azacytidine on primary Oral Squamous Cell Carcinoma cells (OSCCs) from human biopsies, and on Cancer Stem Cells (CSCs) from the same samples, were investigated by an in vitro Fourier Transform InfraRed Microscospectroscopy (FTIRM) approach coupled with multivariate analysis. OSCC is an aggressive tumoral lesion of the epithelium, accounting for ~90% of all oral cancers. It is usually diagnosed in advanced stages, and this causes a poor prognosis with low success rates of surgical, as well as radiation and chemotherapy treatments. OSCC is frequently characterised by recurrence after chemotherapy and by the development of a refractoriness to some employed drugs, which is probably ascribable to the presence of CSCs niches, responsible for cancer growth, chemoresistance and metastasis. The spectral information from FTIRM was correlated with the outcomes of cytotoxicity tests and image-based cytometry, and specific spectral signatures attributable to 5-azacytidine treatment were identified, allowing us to hypothesise the demethylation of DNA and, hence, an increase in the transcriptional activity, together with a conformational transition of DNA, and a triggering of cell death by an apoptosis mechanism. Moreover, a different mechanism of action between OSSC and CSC cells was highlighted, probably due to possible differences between OSCCs and CSCs response.

Correlative optical photothermal infrared and X-ray fluorescence for chemical imaging of trace elements and relevant molecular structures directly in neurons

Alzheimer's disease (AD) is the most common cause of dementia, costing about 1% of the global economy. Failures of clinical trials targeting amyloid-β protein (Aβ), a key trigger of AD, have been explained by drug inefficiency regardless of the mechanisms of amyloid neurotoxicity, which are very difficult to address by available technologies. Here, we combine two imaging modalities that stand at opposite ends of the electromagnetic spectrum, and therefore, can be used as complementary tools to assess structural and chemical information directly in a single neuron. Combining label-free super-resolution microspectroscopy for sub-cellular imaging based on novel optical photothermal infrared (O-PTIR) and synchrotron-based X-ray fluorescence (S-XRF) nano-imaging techniques, we capture elemental distribution and fibrillary forms of amyloid-β proteins in the same neurons at an unprecedented resolution. Our results reveal that in primary AD-like neurons, iron clusters co-localize with elevated amyloid β-sheet structures and oxidized lipids. Overall, our O-PTIR/S-XRF results motivate using high-resolution multimodal microspectroscopic approaches to understand the role of molecular structures and trace elements within a single neuronal cell.

The Progress of Label-Free Optical Imaging in Alzheimer's Disease Screening and Diagnosis

As the major neurodegenerative disease of dementia, Alzheimer's disease (AD) has caused an enormous social and economic burden on society. Currently, AD has neither clear pathogenesis nor effective treatments. Positron emission tomography (PET) and magnetic resonance imaging (MRI) have been verified as potential tools for diagnosing and monitoring Alzheimer's disease. However, the high costs, low spatial resolution, and long acquisition time limit their broad clinical utilization. The gold standard of AD diagnosis routinely used in research is imaging AD biomarkers with dyes or other reagents, which are unsuitable for in vivo studies owing to their potential toxicity and prolonged and costly process of the U.S. Food and Drug Administration (FDA) approval for human use. Furthermore, these exogenous reagents might bring unwarranted interference to mechanistic studies, causing unreliable results. Several label-free optical imaging techniques, such as infrared spectroscopic imaging (IRSI), Raman spectroscopic imaging (RSI), optical coherence tomography (OCT), autofluorescence imaging (AFI), optical harmonic generation imaging (OHGI), etc., have been developed to circumvent this issue and made it possible to offer an accurate and detailed analysis of AD biomarkers. In this review, we present the emerging label-free optical imaging techniques and their applications in AD, along with their potential and challenges in AD diagnosis.

Synchrotron X-ray Fluorescence and FTIR Signatures for Amyloid Fibrillary and Nonfibrillary Plaques

Amyloid plaques are one of the principal hallmarks of Alzheimer's disease and are mainly composed of Aβ amyloid peptides together with other components such as lipids, cations, or glycosaminoglycans. The structure of amyloid peptide's aggregates is related to the peptide toxicity and highly depends on the aggregation conditions and the presence of cofactors. While fibrillary aggregates are nowadays considered nontoxic, oligomeric/granular (nonfibrillary) aggregates have been found to be toxic. In this work we have characterized in situ two different types of amyloid deposits analyzing sections of the cortex of patients in advanced stages of Alzheimer disease. By combining SR-μFTIR for the study of the secondary structure of the peptide and ThS fluorescence as an indicator of fibrillary structures, we found two types of plaques: ThS positive plaques with a clear infrared band at 1630 cm^-1 that would correspond to fibrillary plaques and ThS negative plaques showing a mixture of nonfibrillar β-sheet and unordered aggregated structures that would correspond to the nonfibrillary plaques (plaques with increased unordered structure). The analysis of the FTIR spectra has allowed correlation of lipid oxidation with the presence of nonfibrillary plaques. The metal composition of the two types of plaques has been analyzed using SR-nano-XRF and XANES. The results have shown higher accumulation of iron (mainly Fe²⁺) in fibrillary plaques than in nonfibrillary ones. However, in nonfibrillary plaques Fe³⁺ has been found to predominate over Fe²⁺. The identification of different types of aggregated forms and the different composition of metals found in the different types of plaques could be of paramount importance for the understanding of the development of Alzheimer disease.

Amyloid Structural Changes Studied by Infrared Microspectroscopy in Bigenic Cellular Models of Alzheimer's Disease

Alzheimer's disease affects millions of lives worldwide. This terminal disease is characterized by the formation of amyloid aggregates, so-called amyloid oligomers. These oligomers are composed of β-sheet structures, which are believed to be neurotoxic. However, the actual secondary structure that contributes most to neurotoxicity remains unknown. This lack of knowledge is due to the challenging nature of characterizing the secondary structure of amyloids in cells. To overcome this and investigate the molecular changes in proteins directly in cells, we used synchrotron-based infrared microspectroscopy, a label-free and non-destructive technique available for in situ molecular imaging, to detect structural changes in proteins and lipids. Specifically, we evaluated the formation of β-sheet structures in different monogenic and bigenic cellular models of Alzheimer's disease that we generated for this study. We report on the possibility to discern different amyloid signatures directly in cells using infrared microspectroscopy and demonstrate that bigenic (amyloid-β, α-synuclein) and (amyloid-β, Tau) neuron-like cells display changes in β-sheet load. Altogether, our findings support the notion that different molecular mechanisms of amyloid aggregation, as opposed to a common mechanism, are triggered by the specific cellular environment and, therefore, that various mechanisms lead to the development of Alzheimer's disease.

Fourier Transform Infrared Spectroscopy in Oral Cancer Diagnosis

Oral cancer is one of the most common cancers worldwide. Despite easy access to the oral cavity and significant advances in treatment, the morbidity and mortality rates for oral cancer patients are still very high, mainly due to late-stage diagnosis when treatment is less successful. Oral cancer has also been found to be the most expensive cancer to treat in the United States. Early diagnosis of oral cancer can significantly improve patient survival rate and reduce medical costs. There is an urgent unmet need for an accurate and sensitive molecular-based diagnostic tool for early oral cancer detection. Fourier transform infrared spectroscopy has gained increasing attention in cancer research due to its ability to elucidate qualitative and quantitative information of biochemical content and molecular-level structural changes in complex biological systems. The diagnosis of a disease is based on biochemical changes underlying the disease pathology rather than morphological changes of the tissue. It is a versatile method that can work with tissues, cells, or body fluids. In this review article, we aim to summarize the studies of infrared spectroscopy in oral cancer research and detection. It provides early evidence to support the potential application of infrared spectroscopy as a diagnostic tool for oral potentially malignant and malignant lesions. The challenges and opportunities in clinical translation are also discussed.

A matter of concern - Trace element dyshomeostasis and genomic stability in neurons

Neurons are post-mitotic cells in the brain and their integrity is of central importance to avoid neurodegeneration. Yet, the inability of self-replenishment of post-mitotic cells results in the need to withstand challenges from numerous stressors during life. Neurons are exposed to oxidative stress due to high oxygen consumption during metabolic activity in the brain. Accordingly, DNA damage can occur and accumulate, resulting in genome instability. In this context, imbalances in brain trace element homeostasis are a matter of concern, especially regarding iron, copper, manganese, zinc, and selenium. Although trace elements are essential for brain physiology, excess and deficient conditions are considered to impair neuronal maintenance. Besides increasing oxidative stress, DNA damage response and repair of oxidative DNA damage are affected by trace elements. Hence, a balanced trace element homeostasis is of particular importance to safeguard neuronal genome integrity and prevent neuronal loss. This review summarises the current state of knowledge on the impact of deficient, as well as excessive iron, copper, manganese, zinc, and selenium levels on neuronal genome stability.

•

Post-mitotic neurons show an increased vulnerability to oxidative stress.

•

Trace element dyshomeostasis impairs neuronal genome maintenance, affecting DNA damage response as well as DNA repair.

•

The review summarises the effects of excessive and deficient trace element levels neuronal genome stability maintenance.

Label-free vibrational imaging of different Aβ plaque types in Alzheimer's disease reveals sequential events in plaque development

The neuropathology of Alzheimer’s disease (AD) is characterized by hyperphosphorylated tau neurofibrillary tangles (NFTs) and amyloid-beta (Aβ) plaques. Aβ plaques are hypothesized to follow a development sequence starting with diffuse plaques, which evolve into more compact plaques and finally mature into the classic cored plaque type. A better molecular understanding of Aβ pathology is crucial, as the role of Aβ plaques in AD pathogenesis is under debate. Here, we studied the deposition and fibrillation of Aβ in different plaque types with label-free infrared and Raman imaging. Fourier-transform infrared (FTIR) and Raman imaging was performed on native snap-frozen brain tissue sections from AD cases and non-demented control cases. Subsequently, the scanned tissue was stained against Aβ and annotated for the different plaque types by an AD neuropathology expert. In total, 160 plaques (68 diffuse, 32 compact, and 60 classic cored plaques) were imaged with FTIR and the results of selected plaques were verified with Raman imaging. In diffuse plaques, we detect evidence of short antiparallel β-sheets, suggesting the presence of Aβ oligomers. Aβ fibrillation significantly increases alongside the proposed plaque development sequence. In classic cored plaques, we spatially resolve cores containing predominantly large parallel β-sheets, indicating Aβ fibrils. Combining label-free vibrational imaging and immunohistochemistry on brain tissue samples of AD and non-demented cases provides novel insight into the spatial distribution of the Aβ conformations in different plaque types. This way, we reconstruct the development process of Aβ plaques in human brain tissue, provide insight into Aβ fibrillation in the brain, and support the plaque development hypothesis.

Calcium oxalate kidney stones, where is the organic matter?: A synchrotron based infrared microspectroscopy study

Kidney stones are collections of microcrystals formed inside the kidneys, which affect 6% to 12% of the population worldwide, with an increasing recurrence (50%-72%) after the first episode. The most abundant type is calcium oxalate (66%), described as monohydrated (COM) and dihydrated (COD). An issue in their chemistry is the transformation process of the metastable specie (COD) into the stable one, which is chemically, and in appearance, monohydrated. Since the origin of these species is different, it is important to differentiate between the transformation stage (and what stabilize COD) to understand the physiopathology and prevent the patients' recurrence. This work focuses on the organic matter distribution along these nephroliths by synchrotron radiation-based infrared microspectroscopy. Differences in the asymmetric stretching of the aliphatic hydrocarbons suggest that lipids may participate in the stabilization of COD and as inhibitors of COM formation/development; however, the presence of proteins in the nucleus could indicate a promoting role.

Detection of presymptomatic Alzheimer's disease through breath biomarkers

Introduction

Novel sensors were developed to detect exhaled volatile organic compounds to aid in the diagnosis of mild cognitive impairment associated with early stage Alzheimer's disease (AD). The sensors were sensitive to a rat model that combined the human apolipoprotein E (APOE)4 gene with aging and the Western diet.

Methods

Gas sensors fabricated from molecularly imprinted polymer-graphene were engineered to react with alkanes and small fatty acids associated with lipid peroxidation. With a detection sensitivity in parts per trillion the sensors were tested against the breath of wild-type and APOE4 male rats. Resting state BOLD functional connectivity was used to assess hippocampal function.

Results

Only APOE4 rats, and not wild-type controls, tested positive to several small hydrocarbons and presented with reduced functional coupling in hippocampal circuitry.

Discussion

These results are proof-of-concept toward the development of sensors that can be used as breath detectors in the diagnosis, prognosis, and treatment of presymptomatic AD.

Biochemical assay and spectroscopic analysis of oxidative/antioxidative parameters in the blood and serum of substance use disorders patients. A methodological comparison study

Substance abuse such as opioids, cannabis, and alcohol causes activation on the immune system and the release of reactive oxygen species (ROS) into the blood and serum. These substances cause an effect on oxidant and antioxidant status in patients with substance abuse. Mainly, wide-open to the ROS are lipids and proteins included blood, which suffers peroxidation. In this study, for the first-time differentiation of the effects of cannabis, alcohol and other synthetic substances on blood and serum samples, were performed. For this purpose, the level of the malondialdehyde (MDA) and glutathione (GSH) in serum and red blood cells, was measured using biochemical assay methods and Fourier Transform InfraRed spectroscopy (FTIR). The results showed, that peroxidation which is dignified as the production of MDA was increased for substance use disorder (SUD) patients (18.01 ± 2.97) compared to the control group (10.75 ± 2.28) (p < 0.001) and for antioxidant capacity, GSH level were significantly increased for SUD patients (p < 0.001). For the discrimination of protein and lipid region obtained from FTIR spectroscopy, we extracted features by principal component analyze (PCA) of protein (1800 cm^-1 to 900 cm^-1) and lipid (3200 cm^-1 to 2800 cm^-1) regions for blood and serum samples collected from patients with different types of SUD and healthy control (HC) participants. For the consideration of lipid oxidation, lipid saturation, lipid desaturation and protein aggregation the peak heights at 1740 cm^-1 to 2960 cm^-1, 2920 cm^-1 to 2960 cm^-1, 3012 cm^-1 to 2960 cm^-1, and 1630 cm^-1 to 1650 cm^-1 regions were studied for SUD and HC. Moreover, more visible changes were noticed for proteins region, than for lipids. The most notice structural changes were observed in amide II in serum spectra. Then we classified protein and lipid region's PCA results of blood and serum by Linear discriminant analysis (LDA) and Support vector machine (SVM). Confidence of the specificity, sensitivity and accuracy of blood and serum were obtained as 100%, 100% and 100% individually. This is the first comparative study on the spectrochemical tool and biochemical assay on SUD. Our results presented 100% discrimination of disorder region compared to healthy subjects.

From Mouse to Human: Comparative Analysis between Grey and White Matter by Synchrotron-Fourier Transformed Infrared Microspectroscopy

Fourier Transform Infrared microspectroscopy (μFTIR) is a very useful method to analyze the biochemical properties of biological samples in situ. Many diseases affecting the central nervous system (CNS) have been studied using this method, to elucidate alterations in lipid oxidation or protein aggregation, among others. In this work, we describe in detail the characteristics between grey matter (GM) and white matter (WM) areas of the human brain by μFTIR, and we compare them with the mouse brain (strain C57BL/6), the most used animal model in neurological disorders. Our results show a clear different infrared profile between brain areas in the lipid region of both species. After applying a second derivative in the data, we established a 1.5 threshold value for the lipid/protein ratio to discriminate between GM and WM areas in non-pathological conditions. Furthermore, we demonstrated intrinsic differences of lipids and proteins by cerebral area. Lipids from GM present higher C=CH, C=O and CH₃ functional groups compared to WM in humans and mice. Regarding proteins, GM present lower Amide II amounts and higher intramolecular β-sheet structure amounts with respect to WM in both species. However, the presence of intermolecular β-sheet structures, which is related to β-aggregation, was only observed in the GM of some human individuals. The present study defines the relevant biochemical properties of non-pathological human and mouse brains by μFTIR as a benchmark for future studies involving CNS pathological samples.

Clinical Utility of Plasma Lipid Peroxidation Biomarkers in Alzheimer's Disease Differential Diagnosis

BACKGROUND

Differential diagnosis of Alzheimer's disease (AD) is a complex task due to the clinical similarity among neurodegenerative diseases. Previous studies showed the role of lipid peroxidation in early AD development. However, the clinical validation of potential specific biomarkers in minimally invasive samples constitutes a great challenge in early AD diagnosis.

METHODS

Plasma samples from participants classified into AD (n = 138), non-AD (including MCI and other dementias not due to AD) (n = 70) and healthy (n = 50) were analysed. Lipid peroxidation compounds (isoprostanes, isofurans, neuroprostanes, neurofurans) were determined by ultra-performance liquid chromatography coupled with tandem mass spectrometry. Statistical analysis for biomarkers' clinical validation was based on Elastic Net.

RESULTS

A two-step diagnosis model was developed from plasma lipid peroxidation products to diagnose early AD specifically, and a bootstrap validated AUC of 0.74 was obtained.

CONCLUSION

A promising AD differential diagnosis model was developed. It was clinically validated as a screening test. However, further external validation is required before clinical application.

CMS121, a fatty acid synthase inhibitor, protects against excess lipid peroxidation and inflammation and alleviates cognitive loss in a transgenic mouse model of Alzheimer's disease

The oxidative degradation of lipids has been shown to be implicated in the progression of several neurodegenerative diseases and modulating lipid peroxidation may be efficacious for treating Alzheimer’s disease (AD). This hypothesis is strengthened by recent findings suggesting that oxytosis/ferroptosis, a cell death process characterized by increased lipid peroxidation, plays an important role in AD-related toxicities. CMS121 is a small molecule developed against these aspects of neurodegeneration. Here we show that CMS121 alleviates cognitive loss, modulates lipid metabolism and reduces inflammation and lipid peroxidation in the brains of transgenic AD mice. We identify fatty acid synthase (FASN) as a molecular target of CMS121 and demonstrate that modulating lipid metabolism through the inhibition of FASN protects against several AD-related toxicities. These results support the involvement of lipid peroxidation and perturbed lipid metabolism in AD pathophysiology and propose FASN as a target in AD-associated toxicities.

•

CMS121, a fisetin-derivative, alleviates memory decline in a double transgenic AD mouse model.

•

CMS121 is able to reduce lipid peroxidation and neuroinflammation, both in vitro and in vivo.

•

We identify fatty acid synthase (FASN), which shows increased protein levels in human AD patients, as a target of CMS121.

•

Our results confirm the involvement of lipid peroxidation and perturbed lipid metabolism in AD pathophysiology.

•

Decreasing lipid levels through FASN inhibition can be effective against excess lipid peroxidation.

In situ structural characterization of early amyloid aggregates in Alzheimer's disease transgenic mice and Octodon degus

Amyloid plaques composed of Aβ amyloid peptides and neurofibrillary tangles are a pathological hallmark of Alzheimer’s disease. In situ identification of early-stage amyloid aggregates in Alzheimer’s disease is relevant for their importance as potential targets for effective drugs. Synchrotron-based infrared imaging is here used to identify early-stage oligomeric/granular aggregated amyloid species in situ in the brain of APP/PS1 transgenic mice and Octodon degus for the first time. Also, APP/PS1 mice show fibrillary aggregates at 6 and 12 months whereas very little formation of fibrils is found in aged Octodon degus. Finally, significant decreased burden of early-stage aggregates and fibrillary aggregates is obtained following treatment with G4-His-Mal dendrimers (a neurodegenerative protector) in 6-month-old APP/PS1 mice, thus demonstrating putative therapeutic properties of G4-His-Mal dendrimers in AD models. Identification, localization, and characterization using infrared imaging of these non-fibrillary species in the cerebral cortex at early stages of AD progression in transgenic mice point to their relevance as putative pharmacological targets. No less important, early detection of these structures may be useful in the search for markers for non-invasive diagnostic techniques.

Lipids and Alzheimer's Disease

Lipids, as the basic component of cell membranes, play an important role in human health as well as brain function. The brain is highly enriched in lipids, and disruption of lipid homeostasis is related to neurologic disorders as well as neurodegenerative diseases such as Alzheimer’s disease (AD). Aging is associated with changes in lipid composition. Alterations of fatty acids at the level of lipid rafts and cerebral lipid peroxidation were found in the early stage of AD. Genetic and environmental factors such as apolipoprotein and lipid transporter carrying status and dietary lipid content are associated with AD. Insight into the connection between lipids and AD is crucial to unraveling the metabolic aspects of this puzzling disease. Recent advances in lipid analytical methodology have led us to gain an in-depth understanding on lipids. As a result, lipidomics have becoming a hot topic of investigation in AD, in order to find biomarkers for disease prediction, diagnosis, and prevention, with the ultimate goal of discovering novel therapeutics.

Antioxidant effect of phenolic compounds (PC) at different concentrations in IEC-6 cells: A spectroscopic analysis

Phenolic compounds (PC) have been proposed as natural antioxidant agents that protect cells against oxidative stress-related diseases. Nonetheless, their low bioavailability forecasts controversy about mechanisms on their in vivo scavenging activity against reactive oxygen species (ROS). It has been proposed that PC reduce directly ROS concentration. An alternative or complementary action of PC could be the activation of the cell's antioxidant pathway, involving the regulation of gene expression, like that initiated by the Nrf2 transcription factor. To date there is not enough experimental data to support or discard this possibility. In the present study, we evaluated the use of several PC to prevent peroxidation of macromolecules and to elicit the activation of the Nrf2 transcription factor in H₂O₂-stresed IEC-6 enterocytic cell line. Synchrotron microspectroscopy demonstrated that PC compounds protected proteins, lipids and nucleic acids against oxidation induced by H₂O₂. Immunofluorescence results showed that treatment with quercetin (Qc), catechin (Cat) and capsaicin (Cap) induced the translocation of Nrf2 into the nucleus, at the same level as did H₂O₂ treatment, thus mimicking the action of the endogenous cell response to peroxidation. Even though the detailed mechanism still needs to be elucidated, we demonstrated the activation of Nrf2 by PCs in response to oxidative stress.