Journal of Alzheimer’s Disease 24 (2011) 327–333DOI 10.3233/JAD-2010-101872IOS Press327Plasma Fetuin-A is Associated withthe Severity of Cognitive Impairmentin Mild-to-Moderate Alzheimer’s DiseaseEdward R. Smitha,*, Ramin Nilforooshanb, Gary Weavingaand Naji Tabetb,caDepartment of Clinical Biochemistry and Immunology, Royal Sussex County Hospital, Brighton, UKbCognitive Treatment and Research Unit, Sussex Partnership NHS Foundation Trust, Uckfield, East Sussex, UKcInstitute of Postgraduate Medicine, Brighton & Sussex Medical School, University of Brighton, Falmer,Brighton, UKAccepted 8 December 2010Abstract. The significance of vascular risk factors in the development and progression of Alzheimer’s disease (AD) is nowwidely recognized. Fetuin-A is an abundant plasma protein that predicts vascular risk in a variety of clinical settings. In thecontext of cerebral ischemia, fetuin-A appears to be anti-inflammatory. Given the apparent importance of neuroinflammation incognitive decline, we analyzed fetuin-A concentrations and pro-inflammatory cytokine levels in a cohort of 34 patients with mild-to-moderate AD, and compared these to age-matched controls. Further, we analyzed the relationship between plasma fetuin-Aconcentration and a measure of cognitive impairment using multivariate regression modeling. Plasma fetuin-A concentrationswere lower in the patient group (p= 0.006) compared with controls and were significantly correlated with Mini-Mental StateExamination (MMSE) score (r= 0.504,p= 0.002). Fetuin-A concentration was also significantly and inversely correlated withplasma TNF-concentration (r=-0.496,p= 0.003). The association between MMSE performance and fetuin-A was maintainedeven after multivariate adjustment for other risk factors including TNF-(adjustedR2total = 0.371). Using this model, plasmafetuin-A concentration explained 21% of the variance in MMSE scores. Further studies are needed to evaluate whether fetuin-Ais related to the progression and pathogenesis of AD.Keywords: Alpha2HS glycoprotein, Alzheimer’s disease, inflammation, tumor necrosis factor-alphaINTRODUCTIONCompelling evidence supports the view that vascularrisk factors significantly contribute to the developmentof Alzheimer’s disease (AD). Progressive dysregula-tion and compromise of the cerebral vasculature resultsin a state of increased oxidative stress, inducing aneuroinflammatory response [1]. Furthermore, animalmodels have indicated that pro-inflammatory cytokineproduction (e.g., tumor necrosis factor, TNF-) may*Correspondence to: Edward R. Smith, Department of ClinicalBiochemistry and Immunology, Royal Sussex County Hospital,Eastern Road, Brighton, BN2 5BE, UK. Tel.: +44 1273 696955;Fax: +44 1273 664828; E-mail:
[email protected] augment amyloid-(A) plaque deposition andneurofibrillary tangle (NFT) formation—the classicalhistopathological hallmarks of AD [2, 3]. Thus, acrossthe spectrum dementia-related disorders, vascular andneurodegenerative processes generally co-exist and areinter-related.Human fetuin-A (or2-Heremans-Schmidt glyco-protein; AHSG) is an abundant plasma glycoproteinsecreted by the liver, and is a member of thecystatin-superfamily of cysteine protease inhibitors[4]. Fetuin-A is a multi-functional protein with seem-ingly disparate physiological roles. Fetuin-A acts asmineral chaperone inhibiting ectopic calcification [5]and a transforming growth factor (TGF)-antagonistISSN 1387-2877/11/$27.50 © 2011 – IOS Press and the authors. All rights reserved
328E.R. Smith et al. / Fetuin-A and Alzheimer’s Disease[6] regulating bone growth, fibrotic and tumoro-genic pathways. Fetuin-A is also purported to inhibitinsulin-stimulated insulin receptor autophosphoryla-tion, thereby acting as an endogenous mediator ofinsulin resistance [7]. In clinical studies, low plasmaconcentrations have been associated with increasedaortic stiffness, dystrophic calcification, and mortal-ity in patients with chronic kidney disease [8, 9], whilehigh levels have predicted increased risk of diabetesmellitus [10], stroke [11], and myocardial infarction[12].Depending on the setting, fetuin-A also exhibitsdivergent effects on the inflammatory and immuneresponse. Fetuin-A is a negative acute phase reac-tant [13], with levels of hepatic synthesis beingdown-regulated by increased concentrations of inter-leukin (IL)-1and IL-6 resulting from a switch inCCAAT-enhancer-binding protein (C/EBP) isoforms[14]. Fetuin-A has also been shown to induce TNF-and IL-6 expression in differentiated adipocytes, whiledown-regulating production of a key insulin sensitizer,adiponectin [15]. Thus, in the context of the metabolicsyndrome, prevalent in those suffering with AD,fetuin-A is considered pro-inflammatory. However,fetuin-A appears to play an important role incounter-regulating macrophage/monocyte activationby facilitating the uptake of anti-inflammatoryfactors, like spermine [16]. At much higher, supra-physiological concentrations, fetuin-A itself appearsto be anti-inflammatory, abolishing the response ofmacrophage to bacterial lipopolysaccharide [17] andattenuating the innate inflammatory response to car-rageenan in rats [18]. Interestingly, in a recent studyby Wang and colleagues [19], peripheral administra-tion of bovine fetuin-A was found to significantlyattenuate the inflammatory response in a rat model offocal cerebral ischemia. Here, fetuin-A was found toreduce activation of centrally and peripherally derivedmacrophage/monocytes and suppress TNF produc-tion in ischemic brain tissue. The potential role ofendogenous fetuin-A as an anti-inflammatory and neu-roprotective factor may therefore be of particularrelevance in the setting of AD.Proteomic analysis of cerebrospinal fluid (CSF)from a small number of AD sufferers, demonstratedlower concentrations of fetuin-A compared to con-trols [20]. While, in a relatively large Italian cohort,individuals homozygous for the AHSG 1×1 geno-type (previously associated with significantly higherserum fetuin-A levels) were found to be at almost four-times the risk for the development of late-onset AD[21]. However, to date no study has investigated theassociation between plasma fetuin-A concentration,pro-inflammatory cytokine concentrations and esti-mates of cognitive impairment in a cohort of patientswith AD. In the present study we compared the con-centrations of plasma fetuin-A and pro-inflammatorycytokines in patient and control groups and assessedtheir relationship to an established measure of cogni-tive impairment, the Mini-Mental State Examination(MMSE).MATERIALS AND METHODSStudy participants and clinical evaluationPatients taking part in the study were 65 years ofage or older and were recruited through the memoryclinic service in East Sussex, United Kingdom. Allpatients included were diagnosed with mild to mod-erate AD according to the National Institute of Neu-rological and Communicative Disorders and Strokeand the Alzheimer’s Disease and Related DisordersAssociation (NINCDS-ADRDA) criteria [22]. Patientsand controls underwent clinical evaluation at recruit-ment which included medical history and MMSE[23]. Patients were considered to be hypertensive ifreceiving anti-hypertensive therapy and dyslipidemicif receiving lipid-lowering therapy. Individuals witha history of myocardial infarction, stroke, transientischemic attack, heart failure, or angina were definedas having significant previous cardiovascular (CV)comorbidity. Individuals that reported current or pasthistory of smoking were considered smokers. Con-trols were partners of recruited patients who hadno diagnosis of dementia and had normal MMSEscores (=29). The study was approved by the LocalEthics and Research and Development Committees(Ref: 07/Q1911/3) and all participants provided writ-ten informed consent. The study was conducted inaccordance with the Declaration of Helsinki.Sample collection & biochemical analysisLithium-heparin plasma samples were taken atrecruitment, centrifuged at 3,000gfor 10 minutes andaliquots stored in cryogenic vials at-80?C untilanalysis. All assays were performed blinded to thecase identity. Creatinine concentration was determinedusing standard chemical analysis on a routine auto-mated analyzer (Roche Modular, Haywards Heath,UK). Human fetuin-A was measured using a commer-cially available ELISA kit obtained from Biovendor