Background Alzheimer’s disease (AD) is the most common form of dementia with remarkable impact on the patients, caregivers and society. AD is one of the main leading cause of death in the world; nevertheless, the etiopathogenesis of this neurodegenerative disorder is still not completely understood. A wealth of in vitro and animal data suggest a role of oxidative stress (OxS), a condition characterized by a detrimental derangement redox homeostasis, in the pathological process. Furthermore, some epidemiological studies found an association between AD and systemic and neuronal dysregulation of metabolism of energetic substrates, in particular lipids. Owing these findings, it is reasonable to hypothesize that all factors able to affect the lipid and/or Redox homeostasis can play a role in AD development. Notably, AD risk factors such as aging, in both sexes, and menopausal oestrogen decline, in women, appears to be associated with a worsening of lipid and oxidative profile. Nevertheless, a definitive appreciation of these possible interconnections and how these can contribute to AD onset and progression have been seldom investigated in humans. Aims Based on these considerations, the aims of our study were: I. to investigate the possible association between systemic markers of OxS and dementia; II. to evaluate a possible alteration on lipid metabolism in healthy women and rat models during perimenopause transition. Material and methods Part I: The patients enrolled (n=698 subjects) were divided in: late onset Alzheimer disease (LOAD), vascular dementia (VaD), mild cognitive impairment (MCI), and healthy controls. The serum subjects of two subgroups were evaluated for markers of: 1) biomolecular oxidative damage such as hydroperoxides, advance oxidation protein products; 2) enzymatic antioxidant such as arylesterase/paraoxonase activities of HDL-bound PON-1, ferroxidase I/II activities and 3) non-enzymatic antioxidants as residual antioxidant power, protein thiols and uric acid. Furthermore, 141 MCI patients were followed-up for an average of 2 years (2.0 ± 0.6 years) and their clinical progression was related to the levels of biochemical markers assessed at baseline. Part II: Gene and protein expression involved in lipoprotein transport and cholesterol metabolism were evaluated in rat brain cortex. Moreover, serum lipid profile (HDL, LDL, triglycerides and total cholesterol) was compared with data from 231 women divided in different groups according to menopausal status (reproductive age, peri- and postmenopause). Results: Part I: Multivariate analysis (covariates: age, gender, smoking and comorbidities) of our data showed a significant increase (p<0.05) of hydroperoxides in LOAD patients, and a less pronounced elevation in vascular dementia (VaD) respect to controls. Moreover, residual antioxidant power emerged as significantly lower in MCI, LOAD and VaD patients, compared to controls (p<0.01 for all). Multivariate logistic regression analysis showed that, compared with controls, high levels (over median value) of serum hydroperoxides were independently associated with an increase in the likelihood of having MCI (Odd Ratio: 2.59, 95% Confidence Interval: 1.08–6.21) or LOAD (OR: 4.09, 95% CI: 1.36–11.81). Moreover, low levels of residual antioxidant power were associated with increased risk of having MCI (OR: 3.97, 95% CI: 1.62–9.72), but not LOAD (OR: 2.31, 95% CI: 0.83–6.63). The trend towards a worse oxidative balance in demented patients was further confirmed by the results obtained with the assessment of arylesterase activity, which was independently associated with the likelihood of having MCI (OR: 2.3, 95% CI: 1.3–3.8), LOAD (OR: 2.8, 95% CI: 1.5–5.0) or VAD (O.R.: 2.7; 95% CI: 1.3–3.8). In longitudinal data, no differences in hydroperoxides or residual antioxidant power were found by comparing MCI patients who converted or not converted to LOAD. However low levels of paraoxonase activity were significantly associated with an increased likelihood of converting to VAD (MCI/VAD vs. MCI/MCI, OR: 3.74, 95% CI: 1.37–10.25) but not LOAD. Likewise, low levels of arylesterase were associated with the risk of conversion to VAD (MCI/ VAD vs. MCI/MCI, OR: 3.16, 95% CI: 1.17–8.56), but not LOAD. Part II: Cholesterol and lipid gene’s expression analysis in rat cortex indicated two distinct aging programs: chronological and endocrine. Chronological aging showed an activation of genes involved in cholesterol synthesis, transport and efflux mainly before perimenopause. Conversely, endocrine aging presented a down regulation of the same pathway and a contemporary reduction of proteins involved in cholesterol efflux (ABCA1 regular cycle vs acyclic ANOVA p<0.01), and amyloid beta clearance (LRP1 and Cyp46; regular cycle vs acyclic ANOVA p<0.05 and p<0.01 respectively). Similarly, serum lipid profile analysis showed an age–dependent increase of total cholesterol and LDL levels (regular vs irregular cycle ANOVA p< 0.05 for both), but endocrine effects were not correlated to modification of the same markers. Serum cholesterol profile data in human, shown a similar trend compared to animal models, but not significant, probably caused by low sample size and similar abdominal fat distribution. Conclusion: Our data indicate that significant derangement in systemic redox balance appears to be an early event in dementia pathogenesis. Increasing OxS may, in turn, influence HDL–bound PON–1, thereby leading to an alteration in the function of this lipoprotein, and, most likely, of the systemic cholesterol metabolism. It is well known that the in AD patients’ homeostasis of this lipid is deranged at both systemic and brain level. Our data from perimenopause animal model, consistent with the human population with high risk for dementia, suggest an early deregulation of cholesterol pathway along with worsen beta amyloid clearance in female brain.

Introduzione La malattia di Alzheimer (AD) è la più comune forma di demenza e ha un importante impatto sui pazienti, sui famigliari e sulla società. Nonostante AD sia una delle principali cause di morte nel mondo, la sua eziopatogenesi non è ancora stata completamente compresa. Numerosi studi in vitro e sul modello animale hanno suggerito un ruolo dello stress ossidativo (OxS), condizione caratterizzata da un pericoloso squilibrio dell’omeostasi redox nel processo patologico. Inoltre, alcuni studi epidemiologici hanno evidenziato un’associazione tra AD e disregolazione del metabolismo energetico, specialmente a carico dei lipidi, sia a livello cerebrale che a livello sistemico. Sulla base di queste evidenze, è possibile ipotizzare che i fattori che influenzano l’omeostasi redox e/o lipidica possano essere coinvolti anche nello sviluppo dell’AD. Tra questi possibili fattori, quelli maggiormente degni di nota sono l’invecchiamento, in entrambi i sessi, e il declino estrogenico legato alla transizione menopausale, nelle donne, poichè ambedue rappresentano processi fisiologici fortemente associati al rischio di AD. Obiettivi Alla luce delle premesse evidenziate, gli obiettivi del nostro studio sono state: I. Valutare la possibile associazione tra marker dello stress ossidativo sistemico e la demenza; II. Valutare la possibile alterazione del metabolismo lipidico in donne sane e nel modello animale (ratti), durante la transizione menopausale. Metodi Parte I: I pazienti arruolati (n=698) per lo studio sono stati suddivisi in quattro gruppi in base alla diagnosi: controlli sani, Alzheimer (AD), demenza vascolare (VaD) e deterioramento cognitivo lieve (MCI). Il siero dei pazienti è stato utilizzato per misurare diversi marcatori di: 1) danno ossidativo come gli idroperossidi e i prodotti di ossidazione delle proteine (AOPP); 2) antiossidanti ad azione enzimatica come attività paraoxonasica/arilesterasica della PON-1 e attività ferrosidasica I/II; 3) antiossidanti ad azione non enzimatica come il potere antiossidante residuo, l’acido urico e i tioli. Tra i pazienti MCI, un sottogruppo di 141 soggetti, sono stati seguiti per un “follow-up” di circa 2 anni (2.0 ± 0.6 anni) e lo stato clinico è stato comparato con i valori del marcatori ottenuti al tempo zero. Parte II: L’espressione di alcuni geni e proteine coinvolti nel metabolismo lipidico sono sati valutati in tessuto corticale di ratti (femmine) con diverse età e stato endocrino. Il profilo lipidico sierico (HDL, LDL, trigliceridi e colesterolo totale) dei ratti sono stati comparate con i risultati ottenuti in 231 donne divise in diversi gruppi in base all’ età e allo stato menopausale (età fertile, peri- e post- menopausa). Risultati Parte I: L’analisi multivariata (covariate: età, sesso, fumo e comorbidità) dei dati evidenzia un significativo aumento (p<0.05) dei livelli di idroperossidi nei AD, mentre un meno marcato aumento si evidenza nei pazienti affetti da demenza vascolare (VaD) rispetto ai controlli. Inoltre, il potere antiossidante residuo risulta significativamente ridotto in MCI, AD e VaD rispetto ai controlli (per tutti p< 0.01). Dalla regressione logistica, inoltre, emerge che elevati livelli di idroperossidi sono associati con un aumento della probabilità di essere affetti da MCI, (Odd Ratio: 2.59, 95% intervallo di confidenza (IC): 1.08-6.21) o AD (OR: 4.09, 95%IC: 1.36-11.81). Bassi livelli di potere antiossidante residuo si associano ad un incremento della probabilità di sviluppare MCI (OR: 3.97, 95% IC: 1.62-9.72), ma non AD (OR: 2.31, 95% IC: 0.83-6.63). Questo trend di peggioramento del bilancio redox nei pazienti con demenza, è stato confermato anche dai risultati ottenuti con la valutazione dell’attività della PON-1. Infatti la riduzione dell’attività arilesterasica si associa ad una aumentata probabilità di sviluppare MCI (OR: 2.3; 95% IC: 1.3-3.8), AD (O.R.: 2.8; 95% IC: 1.5 – 5.0) o VaD (O.R.: 2.7; 95% IC: 1.3 – 3.8). Dai dati longitudinali, non emergono differenze nei livelli basali di idroperossidi o del potere antiossidante residuo comparando MCI che non convertono e quelli che convertono a AD. Al contrario, bassi livelli di attività paroxonasica sono risultati significativamente associati con un incremento della probabilità di convertire in VaD (MCI/VAD vs. MCI/MCI, OR: 3.74, 95% IC: 1.37–10.25) ma non AD. Allo stesso modo bassi livelli di attività arilesterasica si associano ad un aumentato rischio di convertire a VaD (MCI/VaD vs. MCI/MCI, OR: 3.16, 95% IC: 1.17–8.56), ma non AD. Parte II: Analizzando il modello animale, l’espressione dei geni legati al metabolismo del colesterolo e dei lipidi, indicano la presenza di due distinti programmi: invecchiamento e transizione endocrina. Il classico processo di invecchiamento durante la fase fertile, è accompagnato da un’attivazione dei geni coinvolti nella sintesi, trasporto ed efflusso del colesterolo. Invece, la transizione endocrina evidenzia una down-regolazione degli stessi processi, oltre che ad una riduzione di alcune proteine coinvolte nell’efflusso del colesterolo (ABCA1, fertili vs aciclici ANOVA p<0.01) e della clearance del beta amiloide. (LRP1 e Cyp46; fertili vs aciclici, rispettivamente ANOVA p<0.05 e p<0.01). In modo simile, anche il profilo lipidico sierico, evidenzia un incremento del colesterolo totale, LDL con l’invecchiamento (fertili vs aciclici; ANOVA p< 0.05 per entrambi) I risultati ottenuti nelle donne durante la transizione menopausale, presentano un trend simile al modello animale, senza tuttavia differenze significative tra i diversi gruppi, probabilmente dovuto alla similarità della distribuzione del grasso addominale. Conclusioni I dati ottenuti suggeriscono che OxS è già presente nella forma presintomatica della demenza. L’instaurarsi di questa forma di stress biochimico a sua volta può influenzare l’attività dell’enzima PON-1,legato alle HDL, causando una alterazione nella funzionalità di queste lipoproteine e probabilmente del metabolismo del colesterolo a livello sistemico. Una mancata regolazione del metabolismo lipidico a livello sia sistemico che cerebrale è stata già evidenziata nei pazienti con AD conclamato. I nostri dati ottenuti da ratti suggeriscono che la disregolazione dei pathway in cui è coinvolto il colesterolo, oltre che il peggioramento della clearance del beta amiloide, è un evento precoce associato con la transizione menopausale nel cervello femminile.

Disturbance of redox and lipid homeostasis in Alzheimer’s disease pathogenesis

ROMANI, Arianna
2016

Abstract

Background Alzheimer’s disease (AD) is the most common form of dementia with remarkable impact on the patients, caregivers and society. AD is one of the main leading cause of death in the world; nevertheless, the etiopathogenesis of this neurodegenerative disorder is still not completely understood. A wealth of in vitro and animal data suggest a role of oxidative stress (OxS), a condition characterized by a detrimental derangement redox homeostasis, in the pathological process. Furthermore, some epidemiological studies found an association between AD and systemic and neuronal dysregulation of metabolism of energetic substrates, in particular lipids. Owing these findings, it is reasonable to hypothesize that all factors able to affect the lipid and/or Redox homeostasis can play a role in AD development. Notably, AD risk factors such as aging, in both sexes, and menopausal oestrogen decline, in women, appears to be associated with a worsening of lipid and oxidative profile. Nevertheless, a definitive appreciation of these possible interconnections and how these can contribute to AD onset and progression have been seldom investigated in humans. Aims Based on these considerations, the aims of our study were: I. to investigate the possible association between systemic markers of OxS and dementia; II. to evaluate a possible alteration on lipid metabolism in healthy women and rat models during perimenopause transition. Material and methods Part I: The patients enrolled (n=698 subjects) were divided in: late onset Alzheimer disease (LOAD), vascular dementia (VaD), mild cognitive impairment (MCI), and healthy controls. The serum subjects of two subgroups were evaluated for markers of: 1) biomolecular oxidative damage such as hydroperoxides, advance oxidation protein products; 2) enzymatic antioxidant such as arylesterase/paraoxonase activities of HDL-bound PON-1, ferroxidase I/II activities and 3) non-enzymatic antioxidants as residual antioxidant power, protein thiols and uric acid. Furthermore, 141 MCI patients were followed-up for an average of 2 years (2.0 ± 0.6 years) and their clinical progression was related to the levels of biochemical markers assessed at baseline. Part II: Gene and protein expression involved in lipoprotein transport and cholesterol metabolism were evaluated in rat brain cortex. Moreover, serum lipid profile (HDL, LDL, triglycerides and total cholesterol) was compared with data from 231 women divided in different groups according to menopausal status (reproductive age, peri- and postmenopause). Results: Part I: Multivariate analysis (covariates: age, gender, smoking and comorbidities) of our data showed a significant increase (p<0.05) of hydroperoxides in LOAD patients, and a less pronounced elevation in vascular dementia (VaD) respect to controls. Moreover, residual antioxidant power emerged as significantly lower in MCI, LOAD and VaD patients, compared to controls (p<0.01 for all). Multivariate logistic regression analysis showed that, compared with controls, high levels (over median value) of serum hydroperoxides were independently associated with an increase in the likelihood of having MCI (Odd Ratio: 2.59, 95% Confidence Interval: 1.08–6.21) or LOAD (OR: 4.09, 95% CI: 1.36–11.81). Moreover, low levels of residual antioxidant power were associated with increased risk of having MCI (OR: 3.97, 95% CI: 1.62–9.72), but not LOAD (OR: 2.31, 95% CI: 0.83–6.63). The trend towards a worse oxidative balance in demented patients was further confirmed by the results obtained with the assessment of arylesterase activity, which was independently associated with the likelihood of having MCI (OR: 2.3, 95% CI: 1.3–3.8), LOAD (OR: 2.8, 95% CI: 1.5–5.0) or VAD (O.R.: 2.7; 95% CI: 1.3–3.8). In longitudinal data, no differences in hydroperoxides or residual antioxidant power were found by comparing MCI patients who converted or not converted to LOAD. However low levels of paraoxonase activity were significantly associated with an increased likelihood of converting to VAD (MCI/VAD vs. MCI/MCI, OR: 3.74, 95% CI: 1.37–10.25) but not LOAD. Likewise, low levels of arylesterase were associated with the risk of conversion to VAD (MCI/ VAD vs. MCI/MCI, OR: 3.16, 95% CI: 1.17–8.56), but not LOAD. Part II: Cholesterol and lipid gene’s expression analysis in rat cortex indicated two distinct aging programs: chronological and endocrine. Chronological aging showed an activation of genes involved in cholesterol synthesis, transport and efflux mainly before perimenopause. Conversely, endocrine aging presented a down regulation of the same pathway and a contemporary reduction of proteins involved in cholesterol efflux (ABCA1 regular cycle vs acyclic ANOVA p<0.01), and amyloid beta clearance (LRP1 and Cyp46; regular cycle vs acyclic ANOVA p<0.05 and p<0.01 respectively). Similarly, serum lipid profile analysis showed an age–dependent increase of total cholesterol and LDL levels (regular vs irregular cycle ANOVA p< 0.05 for both), but endocrine effects were not correlated to modification of the same markers. Serum cholesterol profile data in human, shown a similar trend compared to animal models, but not significant, probably caused by low sample size and similar abdominal fat distribution. Conclusion: Our data indicate that significant derangement in systemic redox balance appears to be an early event in dementia pathogenesis. Increasing OxS may, in turn, influence HDL–bound PON–1, thereby leading to an alteration in the function of this lipoprotein, and, most likely, of the systemic cholesterol metabolism. It is well known that the in AD patients’ homeostasis of this lipid is deranged at both systemic and brain level. Our data from perimenopause animal model, consistent with the human population with high risk for dementia, suggest an early deregulation of cholesterol pathway along with worsen beta amyloid clearance in female brain.
BELLINI, Tiziana
CERVELLATI, Carlo
BERNARDI, Francesco
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/2403377
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