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BLOOD RNA CONCENTRATION IN ALZHEIMER DISEASE AND VASCULAR DEMENTIA

Associate Professor Stephen A Margolis MBBS MFM
School of Medicine
University of Queensland
Australia

Professor Kate D. Hammond BSc (Hons) PhD
and
Mr M M Qureshi
Department of Biochemistry
UAE University
United Arab Emirates

Keywords: blood, RNA, Alzheimer disease, vascular dementia.
Sources of Support: The authors gratefully acknowledge the support of the Office of Research Affairs, UAE University and the financial support given to this project (grant number 01-09-8-11/03).


ABSTRACT

Background: To determine if blood RNA concentrations are altered in people with Alzheimer disease [AD] or vascular dementia [VaD]. Methods: Venous blood samples were collected from a population sample of 31 people aged 60+ years, living in an aged care residential centre, with AD or VaD, 20 randomly selected aged controls, living in the community, with normal cognition and no history of cerebrovascular disease and a convenience sample of 20 healthy young controls. Results: Total RNA was successfully extracted from the blood with the PAXGENE RNA system. There was a statistically significant difference in the blood RNA concentration between those with AD [n = 15, mean = 3.0 +/- 0.9], VaD [n = 15, mean = 3.7 +/- 1.4], young controls [n = 18, mean = 4.5 +/- 1.4] and aged controls [n = 19. mean = 5.0 +/- 1.1] [F= 9.05; p<0.0001], including when controlled for age [F=7.09, p<0.0001]. The RNA concentration in AD was statistically significantly lower than the aged controls [p<0.0001] and young controls [p=0.003]. RNA in VaD was statistically significantly lower than the aged controls [p=0.02]. Conclusion: As total blood RNA concentrations were lower in those with AD or VAD in this population based sample, further studies may be needed to ascertain the significance of this preliminary finding.

INTRODUCTION

Dementia is the name of a progressive syndrome characterized by a persistent loss of memory and at least one other type of cognitive deficit. ⁽¹⁾ Alzheimer disease (AD) is the most common cause of dementia (7 - 8% of all people aged 65+ years), while the second most common type is vascular dementia (VaD).

At present there is no reliable indicator in the peripheral venous blood of the presence of AD or VaD. Decreased activity of ribosomal RNA genes has been reported in AD; the study by Payão et al demonstrated that the rRNA 28S/18S ratio in older people with AD and healthy aged people was lower than in younger controls, with AD having the lowest results. ⁽²⁾ A later study demonstrated a statistically significantly lower level of mature rRNA 28S/18S RNA in AD when compared with old and young controls. ⁽³⁾ However, it is not yet known whether the concentration of RNA changes with age and in dementia.

The aim of this preliminary study was to determine if the RNA concentration in whole blood was significantly different in subjects with AD or VaD as compared with both older and younger healthy controls.

METHODS

Study Design

Cross-sectional Survey

Study Population

This study was conducted in the United Arab Emirates (UAE). Of the seven aged care residential centres present in country, six agreed to participate. All Gulf Arabs aged 60+ years living in long term institutionalized care with a clinical diagnosis of either AD or VaD were included. The diagnosis of AD was established by the NINCDS-ADRDA criteria ⁽⁴⁾, while VaD was established by the NINDS-AIREN criteria.⁽⁵⁾ Relatives of those with dementia were contacted to provide written consent to participate.

Control Groups

Old: Twenty UAE citizens from the general population without cognitive impairment or cerebrovascular disease and aged 60+ years chosen by stratified random sampling by sex from a previously identified random sample of the total older population and who provided informed consent.⁽⁶⁾
Young: A convenience sample of twenty ostensibly healthy UAE medical students who provided informed consent.

Isolation of RNA

Venous blood was collected directly into PAXgene RNA tubes and RNA isolated using the PAXgene blood RNA system.⁽⁷⁾ The procedure involves centrifugation to pellet nucleic acids, treatment of the pellet with Proteinase K to digest proteins and application of the sample to a spin column. RNA is eluted from the column with an optimized buffer. Concentration of RNA was determined, in duplicate, by measuring absorbance at 260nm in 10mM Tris-Cl buffer, pH 7.5. The purity of the RNA sample was confirmed by measuring the ratio of the absorbance readings at 260nm and 280nm. Integrity of RNA was checked by denaturing agarose gel electrophoresis and ethidium bromide staining. These methods were as described in the PAXgene handbook. ⁽⁷⁾

Ethical Approval

Ethics approval was obtained from the Research Ethics Committee of the Faculty of Medicine and Health Sciences, UAE University.

RESULTS

Of the total of 70 Gulf Arab residents living in long term aged care residential centres aged 60+ years in the six participating institutions, only 59 residents were diagnosed with either AD or VAD. Table 1 details the sex and age of all residents and details of those included and excluded from analysis.

There was a statistically significant difference in the RNA concentration for each of the 4 groups, Alzheimer disease, vascular dementia, young controls and aged controls [F= 9.05; p<0.0001]. See Table 2. The statistical significance remained unchanged when analysed by the General Linear Model: Univariate analysis controlling for age [F=7.09, p<0.0001].

A post hoc analysis of the RNA levels analyzing multiple comparisons with Tukey HSD is detailed in Table 3 .The RNA value in AD was statistically significantly lower than in the aged controls [p<0.0001] and young controls [p=0.003]. The RNA in VaD was statistically significantly lower than the aged controls [p=0.02].

DISCUSSION

This preliminary study has demonstrated a statistically significant difference between cognitively intact older people without cerebrovascular disease and those with AD or VAD, in a population sample. In particular, the most marked difference was between aged controls and those with AD.

Previous studies of AD looked at rRNA gene expression levels but did not correlate these with RNA concentration and they were done on convenience samples of patients. ^{(2) (3)} The use of a population based sample in this study suggests that these finding may be generalized to similar population samples elsewhere, especially as the UAE population has a multiplicity of ethnic origins, varying from those of Bedouin ancestry, through those from Asian subcontinent, to northern Africa.

Blood RNA is mostly derived from mononuclear cells, although there may be some leakage from other tissues via the intercellular fluid; generally rRNA constitutes more than 80% and mRNA up to 5% of the total. A problem with the analysis of RNA is its instability in vitro. The PAXgene system used in the present study enables the collection, stabilization and transportation of whole blood samples and provides a rapid and efficient procedure for isolation of intact RNA.

The use of peripheral tissues has the potential to identify diagnostic markers that could be used for selecting treatment or monitoring therapeutic effectiveness. ⁽⁸⁾ The lower concentrations of blood total RNA reported here may be a reflection of decreased rate of production and/or increased degradation in AD or VAD patients. Apoptosis, a complex process that removes aging or injured cells from the body, has been implicated in neurodegenerative processes; inappropriate activation of apoptotic pathways may contribute to dementia. ^{(9) (10)} The possibility therefore arises that the changes in RNA seen in AD or VAD may be associated with altered apoptotic mechanisms. Apoptosis involves activation of DNA-degrading enzymes, transcriptional impairment and modification of proteins involved in RNA biogenesis. ^{(10) (11)} Certain 28S rRNA sites are specifically cleaved in cells undergoing apoptosis and mRNA degradation seems to be an early apoptotic event. ^{(12) (13)}

As measurement of total blood RNA is a relatively straightforward procedure, further studies appear indicated to determine the importance and generalisability of this preliminary finding.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the support of the Office of Research Affairs, UAE University and the financial support given to this project (grant number 01-09-8-11/03).

LITERATURE REFERENCES

November 2004
Volume 1,
Issue 2

Table of Contents

Home

Editorial Ageing

Meet the team

Blood RNA concentration in Alzheimer disease and vascular dementia

Serum Zinc and Copper Concentration in Human-Age related cataract

The likelihood of being helped versus being harmed: useful in geriatric treatment dilemma's

Feasibility of the Divided Attention Steering Simulator (DASS) for the Assessment of Vigilance in Stroke Patients

The European Nursing Academy for Care of Older persons (ENACO)

Middle-East Academy for Medicine of Ageing, third session of the first course

Urogenital atrophy in climacteric women: Menopause or Geripause?

The diagnosis and management of dementia

The length of hospital stay of Home Health Care patients at King Khalid National Guard Hospital, Jeddah, 1999

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