Plasma amino acid concentrations in healthy and cognitively impaired oldest-old individuals: associations with anthropometric parameters of body composition and functional disability

NMR analysis seeking for cognitive decline and dementia metabolic markers in plasma from aged individuals

BACKGROUND

Blood biomarkers can improve the ability to diagnose dementia, providing new information to better understand the pathophysiology and causes of the disease. Some studies with patients have already shown changes in metabolic profiles among patients with pathological cognitive decline or Alzheimer's disease, when compared to individuals with normal cognition.

METHODS

To search for new metabolic biomarkers of dementia, we analyzed serum levels of several metabolites, measured by nuclear magnetic resonance spectroscopy, in elderly individuals, a group with normal cognitive decline (control), and three other groups with cognitive decline. pathological (low, moderate, and severe).

RESULTS

Decreased plasma levels of tyrosine, glutamate, valine, leucine, and isoleucine are associated with worsening of pathological cognitive decline. However, the area under analysis of receptor operating characteristics suggests that tyrosine and glutamate have low specificity and sensitivity. Valine, leucine, and isoleucine are influenced by blood glucose or diabetes, but these conditions do not seem to be of great influence in the differences observed. Isobutyrate, histidine, acetone and unknown-1 metabolite also decrease their plasma levels with increasing CD. Isobutyrate ad histidine could have neuroprotective and antioxidant actions, respectively. To elucidate the role of decreased unknown metabolite-1 as a CD biomarker, it will be necessary to previously investigate its identity. To define and elucidate the role of acetone in pathological CD, additional laboratory and clinical studies must be performed. All these metabolites together may constitute a set of biomarkers with capability to identify pathological CD or dementia.

SIGNIFICANCE AND NOVELTY

Decrease of glutamate, tyrosine, valine, leucine, isoleucine, histidine, isobutyrate, acetone and unknown-1 metabolite together are a set of biomarkers able to identify pathological CD or dementia. Histidine, isobutyrate, acetone and unknown-1 metabolite are more specific biomarkers of CD.

Maternal Factors Are Associated with the Expression of Placental Genes Involved in Amino Acid Metabolism and Transport

Introduction

Maternal environment and lifestyle factors may modify placental function to match the mother’s capacity to support the demands of fetal growth. Much remains to be understood about maternal influences on placental metabolic and amino acid transporter gene expression. We investigated the influences of maternal lifestyle and body composition (e.g. fat and muscle content) on a selection of metabolic and amino acid transporter genes and their associations with fetal growth.

Methods

RNA was extracted from 102 term Southampton Women’s Survey placental samples. Expression of nine metabolic, seven exchange, eight accumulative and three facilitated transporter genes was analyzed using quantitative real-time PCR.

Results

Increased placental LAT2 (p = 0.01), y⁺LAT2 (p = 0.03), aspartate aminotransferase 2 (p = 0.02) and decreased aspartate aminotransferase 1 (p = 0.04) mRNA expression associated with pre-pregnancy maternal smoking. Placental mRNA expression of TAT1 (p = 0.01), ASCT1 (p = 0.03), mitochondrial branched chain aminotransferase (p = 0.02) and glutamine synthetase (p = 0.05) was positively associated with maternal strenuous exercise. Increased glutamine synthetase mRNA expression (r = 0.20, p = 0.05) associated with higher maternal diet quality (prudent dietary pattern) pre-pregnancy. Lower LAT4 (r = -0.25, p = 0.05) and aspartate aminotransferase 2 mRNA expression (r = -0.28, p = 0.01) associated with higher early pregnancy diet quality. Lower placental ASCT1 mRNA expression associated with measures of increased maternal fat mass, including pre-pregnancy BMI (r = -0.26, p = 0.01). Lower placental mRNA expression of alanine aminotransferase 2 associated with greater neonatal adiposity, for example neonatal subscapular skinfold thickness (r = -0.33, p = 0.001).

Conclusion

A number of maternal influences have been linked with outcomes in childhood, independently of neonatal size; our finding of associations between placental expression of transporter and metabolic genes and maternal smoking, physical activity and diet raises the possibility that their effects are mediated in part through alterations in placental function. The observed changes in placental gene expression in relation to modifiable maternal factors are important as they could form part of interventions aimed at maintaining a healthy lifestyle for the mother and for optimal fetal development.

Investigation of the Material Basis Underlying the Correlation between Presbycusis and Kidney Deficiency in Traditional Chinese Medicine via GC/MS Metabolomics

Objective. To investigate the correlation between presbycusis and kidney deficiency as defined by traditional Chinese medicine (TCM) and its material basis from the perspective of metabolism. Methods. Pure-tone audiometry was used to test auditory function. A kidney deficiency symptom scoring table was used to measure the kidney deficiency accumulated scores of the research subjects. Gas chromatography/mass spectrometry (GC/MS) was used to measure the metabolites in the urine samples from 11 presbycusis patients and 9 elderly people with normal hearing. Results. Hearing loss in the elderly was positively correlated with kidney deficiency score in TCM. There were significant differences in urine metabolite profile between the presbycusis patients and the controls. A total of 23 differentially expressed metabolites were found. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that these metabolites were related to glutathione metabolism, amino acid metabolism, glucose metabolism, the N-methyl-D-aspartic acid (NMDA) receptor pathway, and the γ -aminobutyric acid (GABA) receptor pathway. Conclusion. Glutathione metabolism, amino acid metabolism, glucose metabolism, NMDA receptors, and GABA receptors may be related to the pathogenesis of presbycusis and may be the material basis underlying the correlation between presbycusis and kidney deficiency in TCM.

Changes in kinetics of amino acid uptake at the ageing ovine blood-cerebrospinal fluid barrier

Amino acids (AA) in brain are precisely controlled by blood-brain barriers, which undergo a host of changes in both morphology and function during ageing. The effect of these age-related changes on AA homeostasis in brain is not well described. This study investigated the kinetics of four AA (Leu, Phe, Ala and Lys) uptakes at young and old ovine choroid plexus (CP), the blood-cerebrospinal fluid (CSF) barrier (BCB), and measured AA concentrations in CSF and plasma samples. In old sheep, the weight of lateral CP increased, so did the ratio of CP/brain. The expansion of the CP is consistent with clinical observation of thicker leptomeninges in old age. AA concentrations in old CSF, plasma and their ratio were different from the young. Both V(max) and K(m) of Phe and Lys were significant higher compared to the young, indicating higher trans-stimulation in old BCB. Cross-competition and kinetic inhibition studies found the sensitivity and specificity of these transporters were impaired in old BCB. These changes may be the first signs of a compromised barrier system in ageing brain leading increased AA influx into the brain causing neurotoxicity.

Mercaptopyruvate Inhibits Tissue-Nonspecific Alkaline Phosphatase and Calcium Pyrophosphate Dihydrate Crystal Dissolution

Objective.

The enzymatic activities of tissue-nonspecific alkaline phosphatase (TNAP) including capacity to inhibit calcium pyrophosphate dihydrate (CPPD) crystal dissolution are known to be inhibited by endogenous amino acids, notably cysteine. As cysteine is recognized as a strong TNAP inhibitor, we investigated whether cysteine-related metabolites such as mercaptopyruvate (MPA) could show similar enzyme inhibition effects and, if so, whether these effects might be synergistic with cysteine at approximate physiologic concentrations of the amino acids.

Methods.

We studied the inhibitory effects of MPA as well as MPA and cysteine combined in equimolar concentrations on TNAP’s phosphatase, inorganic pyrophosphatase, and CPPD crystal dissolution activities. Kinetic parameters Vmax, KM, concentration for 50% inhibition (I50), inhibitor constant (KI), and specific activities calculated from initial velocity, Eadie-Hofstee, Simple, Dixon, and secondary plots were used to assess enzyme inhibition.

Results.

MPA significantly inhibited TNAP’s phosphatase and pyrophosphatase activities at 10× and 100× physiological concentrations. In the presence of calcium [Ca2+] and [Mg2+] = 1 mM, MPA inhibited uncompetitively TNAP’s phosphatase activity and inhibited noncompetitively its pyrophosphatase activity. CPPD crystal dissolution activity was also inhibited. Cysteine and MPA together in equimolar concentrations inhibited TNAP enzyme activities and CPPD crystal dissolution much more effectively than MPA or cysteine alone, reducing CPPD dissolution to 38% of controls at approximate physiologic inhibitor concentrations.

Conclusion.

Endogenous amino acids like cysteine and its derivative MPA have the capacity to inhibit TNAP activities at physiologic concentrations. Downregulation of their inhibiting concentration in the cartilage interstitial fluid environment may provide a therapeutic avenue to controlled dissolution of CPPD crystal deposition in tissues.

Conversion of mild cognitive impairment to dementia: predictive role of mild cognitive impairment subtypes and vascular risk factors

Mild cognitive impairment (MCI) is regarded as a precursor to dementia, but not all patients with MCI develop dementia. We followed up 165 elderly outpatients with MCI for a mean of 3 years. The aims were (1) to investigate the risk of conversion to dementia for different MCI subtypes diagnosed according to standardized criteria (amnestic; impairment of memory plus other cognitive domains; nonamnestic); (2) to assess whether the risk of conversion was affected by several established and emerging vascular risk factors. Forty-eight subjects (29%) converted to dementia, and the risk of conversion was doubled for amnestic MCI with respect to the other subtypes. Independently of MCI subtype, risk of conversion was associated with atrial fibrillation and low serum folate levels. Our results show that current diagnostic criteria for MCI define heterogeneous populations, but some potentially treatable vascular risk factors may be of help in predicting conversion to dementia.

Nutritional factors, cognitive decline, and dementia

Nutritional factors and nutritional deficiencies have been repeatedly associated with cognitive impairment. Most of the evidence is based on cross-sectional studies, which cannot prove whether a nutritional deficit is the cause or the consequence of an impaired cognitive status. In fact, cognitive impairment, in turn, can determine changes in dietary habits and consequent nutritional deficiencies. We reviewed clinical and epidemiological studies from January 1983 to June 2004. Several cross-sectional and fewer prospective studies reported an association between dietary or supplemental intake of antioxidants and protection from cognitive decline and dementia. There are negative reports as well and some methodological biases might have affected the consistencies across studies. Deficiencies of several B vitamins have been associated with cognitive dysfunction in many observational studies. More recently, deficiencies of folate (B9) and cobalamine (B12) have been studied in relation to hyperhomocysteinemia as potential determinants of cognitive impairment, dementia, and Alzheimer's disease (AD). A small number of studies assessed the association between intake of macronutrients and cognitive function or dementia. Among the others, the intake of fatty acids and cholesterol has received particular attention. Although the results are not always consistent, most studies have reported a protective role of dietary intakes of poly- and mono-unsaturated fatty acids against cognitive decline and AD. We point out that well designed intervention studies are warranted in order to establish specific levels of micro- and macronutrient deficiencies and to set general recommendations for the population.

A longitudinal study on the nutritional state of elderly women at a nursing home in Japan

OBJECTIVE

Elderly people at nursing homes often suffer from malnutrition, which is characterized by a loss of muscle mass and hypoalbuminemia. This malnourished state is closely associated with an impaired activity of daily living (ADL). We analyzed the nutritional state of such elderly individuals longitudinally over 3 years by anthropometry, serum albumin, and muscle and fat volume as estimated by MRI.

PATIENTS AND METHODS

The subjects consisted of 16 elderly women aged 83 +/- 7 (mean +/- SD) years who resided at a nursing home in an urban area of central Japan. We determined their ADL levels using the Barthel Index (BI) at entry. Seven women belonged to group A (BI; 65-100), thus implying either a mild or no decline in ADL, while the other 9 were in group B (BI; 0-60) and they demonstrated a severe decline in ADL. We measured the following parameters every year from 2000 to 2003; anthropometry including height, body weight, arm circumference (AC), and arm muscle circumference (AMC), thigh muscle and fat volume as estimated by MRI [thigh muscle volume (TMV) and thigh fat volume (TFV)], serum albumin, and plasma amino acid levels by blood biochemistry. The anthropometric values were converted into percentages of the age- and sex-matched reference values for Japanese.

RESULTS

In all subjects, the TMV, %AMC, and serum albumin level decreased significantly during the three-year period (p<0.05, respectively). The change in TMV correlated significantly with those in the %AC and %AMC (p<0.05, respectively). Group B showed significantly larger decreases in the %AMC and serum albumin level than group A.

CONCLUSION

Both the muscular and visceral protein levels were found to decrease with aging in the subjects at the nursing home. This decrease depends partly on the ADL level of each subject.

Occurrence of cognitive impairment after age 90: MCI and other broadly used concepts

BACKGROUND

Few data are available on the impact of applying different concepts to define cognitive impairment among nonagenarians and centenarians. This study explored the occurrence of four broadly used concepts in an over 90-year-old population.

DESIGN/METHODS

We examined a community-based cohort of 34 people with a mean age (+/- S.D.) of 96.4 (+/- 3.9) years, living in Bologna (Italy). We calculated the proportion of subjects that was given a diagnosis of cognitive impairment according to the following four commonly used concepts: Mild Cognitive Impairment (MCI), Age-Associated Memory Impairment (AAMI), Cognitive Impairment, No Dementia (CIND), and Questionable Dementia stage of the Clinical Dementia Rating (CDR 0.5).

RESULTS

The proportion of subjects with cognitive impairment varied from 5.9%, according to CIND, to 32.4%, according to MCI. The four concepts identified different groups of subjects as having cognitive impairment, and no subject was given a diagnosis of cognitive impairment according to all four concepts.

CONCLUSION

Commonly used criteria for diagnosis of cognitive impairment can differ by a factor of five in the number of subjects they classified as impaired. Such disagreement has serious implications for prevention, as people with a mild cognitive impairment may be a suitable target group for interventions before the development of dementia.

Plasma amino acid concentrations in patients with amnestic mild cognitive impairment or Alzheimer disease

BACKGROUND

Plasma concentrations of several amino acids may affect the availability of important neurotransmitter precursors in the brain. Abnormalities in the plasma amino acid profile have been reported in elderly persons with cognitive impairment, but no data exist for the prodromal phase of Alzheimer disease (AD), which is characterized by amnestic mild cognitive impairment (aMCI).

OBJECTIVE

The objective was to investigate whether the plasma amino acid profiles of elderly patients with aMCI or AD are abnormal.

DESIGN

The plasma amino acid profile was assessed in 29 cognitively normal control subjects (age: 86.7 +/- 5.9 y), 21 patients with aMCI (age: 84.9 +/- 7.0 y), and 51 patients with AD (age: 86.7 +/- 5.4 y). The participants were from the University of Bologna Research Center for Physiopathology of Aging, Italy.

RESULTS

Higher plasma concentrations of the aromatic amino acid phenylalanine were found in the aMCI (68 micromol/L; 95% CI: 63, 73) and AD (62 micromol/L; 95% CI: 59, 65) patients than in the control subjects (54 micromol/L; 95% CI: 48, 61; P < 0.05). The ratio of arginine to other basic amino acids was also higher in the aMCI (0.31 +/- 0.04) and AD (0.27 +/- 0.08) patients than in the control subjects (0.21 +/- 0.05; P < 0.05). Adjustment for differences in body composition, serum vitamin B-12 concentrations, and serum folate concentrations did not significantly affect the results.

CONCLUSIONS

The plasma amino acid profiles of elderly patients with aMCI or AD show abnormalities in aromatic and basic amino acids that potentially affect neurotransmitter biosynthesis.

Different classification systems yield different dementia occurrence among nonagenarians and centenarians

Literature data consistently show different prevalence estimates of dementia when different classification systems are used in the same population. Very few data are available for the oldest old of the elderly. We investigated the occurrence of dementia among 34 nonagenarians and centenarians according to four classification systems: the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders, third edition revised (DSM-III-R) and fourth edition (DSM-IV), the World Health Organization's International Classification of Diseases, 10th revision (ICD-10), and the Cambridge Examination for Mental Disorders of the Elderly (CAMDEX). Cognitive functioning, work, social function and independence in activities of daily living were evaluated by using an extensive neuropsychological examination. The prevalence (95% CI) of dementia was the following: 47.1% (95% CI 30.3-63.8) with the DSM-III-R criteria, 41.2% (95% CI 24.6-57.7) with the DSM-IV criteria, 29.4% (95% CI 14.1-44.7) with the ICD-10 criteria and 38.2% (95% CI 21.9-54.6) with the CAMDEX. The factors that best predicted disagreement between DSM-III-R and DSM-IV were calculation impairment and the presence or absence of personality changes. DSM-III-R and ICD-10 were differentiated by the weight given to executive functions that all have to be impaired according to ICD-10, whereas progressive deterioration differentiated CAMDEX from DSM-III-R. It should be noted that although the DSM-III-R diagnoses differ by a factor of 1.6 times from the ICD-10 and 1.2 times from the CAMDEX diagnoses, we are speaking about dementia, which is very frequent in nonagenarians and centenarians. Moreover, with regard to public health, an estimation of the number of subjects who will lose their autonomy is rather more useful and informative than simple prevalence figures of dementia by itself. In this light, classification systems, such as the ICD-10, that do not include impairment of social function as a criterion for assessing dementia become less adequate.