# Analysis of Correlation between Serum Inflammatory Factors and Cognitive Function, Language, and Memory in Alzheimer’s Disease and Its Clinical Significance

Authors: Yan Lu; Jie Li; Tingjun Hu
Journal: Computational and Mathematical Methods in Medicine
 (2022)

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## Abstract

Objective. A case-control study was conducted to explore the correlation between serum inflammatory factor monitoring and cognitive function, language, and memory ability of Alzheimer’s disease (AD) and its clinical significance. Methods. Thirty-six patients with AD treated from April 2019 to August 2021 in our hospital were enrolled as the study subjects (AD group), and 30 healthy volunteers from the physical examination center and the AD group with the same sex, age, education, and no complaints of memory loss were enrolled as the control group. Montreal Cognitive Assessment (MoCA) and AD Rating Scale-Cognitive (ADAS-cog) were employed to assess the cognitive function of AD and the control group. The Chinese Standard aphasia Test of China Rehabilitation Research Center (CRRCAE) was employed to assess the language function of AD and NC population. The World Health Organization-University of California, Los Angeles Auditory Word Learning Test (WHO-UCLAAV-LT) scale was employed to evaluate the memory function of AD group and control group. The levels of inflammatory factors in serum of the AD group and control group were detected by enzyme-linked immunosorbent assay (ELISA). The serum inflammatory factors levels were compared between the AD group and the control group, and the correlation between the level of serum inflammatory factors and cognitive function, language, and memory ability in the AD group was analyzed. Results. In terms of the demographic data of the two groups, there exhibited no significant difference in gender, age, education level, and other general data (P>0.05). In terms of cognitive function, MoCA scores were remarkably lower compared to the AD group. In the comparison of memory ability, the scores of long-term delayed recognition, delayed memory, and instantaneous memory in the AD group were remarkably lower (P<0.05). In the comparison of language ability, the scores of listening comprehension, reading, and naming in the AD group exhibited remarkably lower (P<0.05). With regard to the levels of serum inflammatory factors, the levels of serum interleukin-4 (IL-4), interleukin-6 (IL-6), interleukin-10 (IL-10), tumor necrosis factor-alpha (TNF-α), and CCL-12 in AD group were remarkably higher, while the level of TNF-β in the AD group was lower compared to the control group. Furthermore, there exhibited no significant correlation between the levels of serum IL-4, IL-6, IL-10, TNF-α, CCL-2, and the total scores, MoCA, and ADAS-cog, but there exhibited a positive relationship between the level of serum TNF-β and the score of MoCA scale. The correlations between IL-4, IL-6, IL-10, TNF-α, TNF-β, CCL-2, and the scores of long-term delayed recognition, delayed memory, and instantaneous memory were analyzed in the AD group. The serum levels of IL-4, IL-6, IL-10, TNF-α, CCL-2, and TNF-β were not remarkably correlated with the scores of long-term delayed recognition, delayed memory, and instantaneous memory. The correlations between IL-4, IL-6, IL-10, TNF-α, TNF-β, CCL-2, and the scores of listening comprehension, reading, and naming were analyzed in the AD group, but with no significant correlation between the serum levels of IL-4, IL-6, IL-10, CCL-2, TNF-α, and TNF-β and the scores of listening comprehension, reading, and naming. Conclusion. Compared with the control group, the levels of serum IL-4, IL-6, IL-10, TNF-α, and CCL-2 in patients with AD exhibited remarkably higher, while the level of serum TNF-β exhibited remarkably lower. The level of serum TNF-β was remarkably correlated with cognitive function in patients with AD, which may reflect the severity of cognitive impairment in patients with AD.


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## Body

## 1. Introduction

Alzheimer’s disease (AD) is an acquired, persistent, and progressive intelligence decline syndrome with memory loss as the main manifestation in the early stage, which is accompanied by other cognitive impairment [1]. At the end of the disease, the patient’s ability of daily living may even be completely lost. Its pathological mechanism mainly includes neurofibrillary tangles (NFTs) formed by intracellular Tau protein hyperphosphorylation and senile plaque (SP) formed by extracellular β-amyloid protein (Aβ) deposition [2]. Aβ deposition can promote inflammation and neurotoxicity, while Tau protein can cause nerve cell atrophy and apoptosis [3]. In addition, pathological mechanisms such as genetic variation inflammatory response and oxidative stress have been reported to be involved in the pathological process of AD, while extensive and in-depth study of the pathological mechanism of AD is an important way to predict the occurrence and development of the disease and explore potential targets for treatment [4].The inflammatory process is usually considered to be part of the pathological changes of the brain in AD [5]. Reducing protein aggregation, limiting oxidative stress and cytotoxicity, and controlling inflammation are the main concerns of academic circles on the treatment of AD in recent years. There is growing evidence that persistent inflammation may be related to the pathogenesis of AD [6, 7]. In AD, Aβ activating resident glial cells may lead to the production of neurotoxic mediators and cytokines (such as IL-6, TNF-α), which are considered to contribute to the formation of plaques in nerve cells and ultimately damage local neurons [8]. Understanding the biochemical reaction between inflammatory reactions in the pathogenesis of AD is very important to understand the occurrence and development of the disease. However, due to the complexity of the pathological mechanism of AD and related inflammatory reactions, the current academic research is limited [9].In previous reports, the most popular serum inflammatory factors are interleukin (IL) and tumor necrosis factor-α (TNF-α), which belong to cytokines, and play a very important role in regulating immune response [9]. In the state of inflammation, IL and TNF-α are highly expressed in the central nervous system. Meanwhile, in the fields of genetics and bioinformatics, inflammation has also been reported to participate in the pathological process of AD and accompany the occurrence and development of AD [9, 10]. In their research, Julian et al. found that the occurrence of inflammatory reaction is driven by activated microglia, and the expression of inflammatory cytokines will also be affected by this change [10]. In addition, it has been reported that special macrophages and activated microglia in the brain have been found in AD patients and animal models [11]. More researches have confirmed that inflammation can occur and lead to the continuous increase of Aβ deposition in the early stage of AD [12]. However, inflammation is common in degenerative diseases of the central nervous system, such as multiple sclerosis and Parkinson’s disease (PD), and is not specific for AD [13]. Therefore, studies of further clinic needed to explain the pathogenesis of sporadic AD and to predict and evaluate inflammatory response as a specific pathological marker of AD. On this basis, our study enrolled 36 cases with AD treated from April 2019 to August 2021 in our hospital, which are indicated as follows.


## 2. Patients and Methods

### 2.1. Patients’ Clinical Information

Thirty-six patients with AD treated from April 2019 to August 2021 were enrolled in our hospital as the study subjects (AD group), and about 30 healthy volunteers from the physical examination center and the AD group with the same sex, age, education, and no complaints of memory loss were enrolled as the control group. In the control group, the age was 55-80 years old, with an average of (69.83±8.47) years, containing 15 males and 21 females, while in the study group, the age was 56-81 years old, with an average of (70.52±6.63) years, containing 16 males and 14 females. And there exhibited no significance in the general data of the two groups. This study was permitted by the Medical Ethics Association of our hospital, and all patients signed informed consent.Inclusion criteria were as follows: (1) patients are of no gender, male or female, and their eyesight, hearing, and physical health are required; (2) they can cooperate with scale evaluation and skull MRI examination; (3) they meet the criteria of NINCDS-ADRDA for the diagnosis of “probable AD dementia”; and (4) the imaging findings of skull MRI examination are consistent with the diagnosis of AD.Exclusion criteria were as follows: (1) various types of dementia leading to cognitive decline; (2) patients with depression, anxiety, schizophrenia, and other mental disorders before AD; (3) mental disorders caused by other organic diseases or psychoactive substances; (4) accompanied by other organic diseases that may cause memory loss; and (5) history of infection or use of anti-inflammatory drugs in recent 3 months.


### 2.2. Treatment Methods

#### 2.2.1. General Demographic Data Collection

The age, sex, course of disease, education, family history, left and right handedness, nationality, smoking, and drinking history of the subjects in the two groups were recorded in detail, and the general somatic diseases, such as hypertension, diabetes, coronary heart disease, hyperlipidemia, and whether there is a history of severe brain trauma, were recorded in detail.


#### 2.2.2. Neuropsychological Assessment

All subjects completed the following scale tests by psychological evaluators: MoCA, Chinese Standard Aphasia Test of Chinese Rehabilitation Research Center (CRRCAE), ADAS-cog, and WHO-UCLAAV-LT scale.


#### 2.2.3. Determination of Serum Inflammatory Factors

All the subjects collected venous blood samples (5 ml) on an empty stomach. Within 1 hour, the specimens were centrifuged, 3000 r/min and centrifuged 10 min, and the serum was separated. After subpackaging, it was stored at-20°C. IL-4, IL-6, IL-10, TNF-α, TNF-β, CCL-2, and enzyme-linked antibody adsorption test (ELASIA) kits were employed in Shanghai Langton Biotechnology Co., Ltd., and all samples were examined by ELASIA kit after collection.


### 2.3. Observation Index

#### 2.3.1. Montreal Cognitive Assessment Scale (MoCA)

MoCA was developed and applied by Nasreddine in 2004. It can be used as a simple screening tool for MCI and mild AD. MoCA can be divided into seven parts: (1) visual space/execution, (2) naming, (3) memory, (4) attention, (5) language, (6) abstraction, and (7) direction. The total score was 30, thescore≥26 was normal, and the score was positively correlated with the state of cognitive function.


#### 2.3.2. AD Assessment Scale-Cognitive (ADAS-cog)

ADAS-cog covers the cognitive areas mentioned by DSM-IV and NINCDS-ADRDA about the diagnostic criteria of AD. The scale is sensitive for evaluating cognitive and noncognitive impairment in patients with AD. ADAS-cog can be divided into four cognitive subareas, namely, memory, language, operational ability, and attention (see schedule 3 for details). The deficiency of the scale lies in the higher requirements for the subjects’ reading and writing ability; so, it is not suitable for illiteracy. The score of the scale is between 0 and 70, and the higher the score is, the more serious the cognitive impairment is.


#### 2.3.3. Language Ability

The Chinese Standard Aphasia Test (CRRCAE) of China Rehabilitation Research Center was used to evaluate their listening comprehension, reading ability, and naming ability. The higher the score, the more prominent the patient’s related ability.


#### 2.3.4. Memory Ability Assessment

Through the WHO-UCLAAV-LT scale, three parts of delayed recognition, delayed memory, and instantaneous memory of the two groups were investigated on the day of admission and 180 days after intervention: (1) instantaneous memory: it includes two lists A and B, with a total of 30 words in the list, which can be presented in a random but fixed way [14]. List A is rendered five times and then converted to list B. The score of the average correct number of 5 free memories in list A is instantaneous recall, <18 as instantaneous memory abnormality; (2) delayed memory: it mainly investigates long-term delayed memory and short-term delayed memory. Short-term delayed memory of list B presentation leads to patients to recall list A, score as the correct number obtained by free recall, less than 6 points as abnormal. Long-term delayed memory refers to the need for patients to recall the A list after 30 min, with a score of the correct number of free recall, less than 6 as abnormal; (3) recognition: after the completion of delayed memory, patients need to recognize 15 interfering words and 15 target words marked with A list and less than 6 points as abnormal.


### 2.4. Statistical Analysis

SPSS23.0 statistical software was employed to measure the data. Independent samplet-test was employed to analyze and compare the serum inflammatory factors levels between AD and control groups. Linear regression was employed for further analysis and comparison. Chi-square (x2) test was employed for gender. Measurement data were presented by normal distribution and variance homogeneity test. In this study, Pearson correlation analysis was employed to detect the continuous data in accordance with normal distribution, P<0.05. The difference exhibited statistically significant.


## 2.1. Patients’ Clinical Information

Thirty-six patients with AD treated from April 2019 to August 2021 were enrolled in our hospital as the study subjects (AD group), and about 30 healthy volunteers from the physical examination center and the AD group with the same sex, age, education, and no complaints of memory loss were enrolled as the control group. In the control group, the age was 55-80 years old, with an average of (69.83±8.47) years, containing 15 males and 21 females, while in the study group, the age was 56-81 years old, with an average of (70.52±6.63) years, containing 16 males and 14 females. And there exhibited no significance in the general data of the two groups. This study was permitted by the Medical Ethics Association of our hospital, and all patients signed informed consent.Inclusion criteria were as follows: (1) patients are of no gender, male or female, and their eyesight, hearing, and physical health are required; (2) they can cooperate with scale evaluation and skull MRI examination; (3) they meet the criteria of NINCDS-ADRDA for the diagnosis of “probable AD dementia”; and (4) the imaging findings of skull MRI examination are consistent with the diagnosis of AD.Exclusion criteria were as follows: (1) various types of dementia leading to cognitive decline; (2) patients with depression, anxiety, schizophrenia, and other mental disorders before AD; (3) mental disorders caused by other organic diseases or psychoactive substances; (4) accompanied by other organic diseases that may cause memory loss; and (5) history of infection or use of anti-inflammatory drugs in recent 3 months.


## 2.2. Treatment Methods

### 2.2.1. General Demographic Data Collection

The age, sex, course of disease, education, family history, left and right handedness, nationality, smoking, and drinking history of the subjects in the two groups were recorded in detail, and the general somatic diseases, such as hypertension, diabetes, coronary heart disease, hyperlipidemia, and whether there is a history of severe brain trauma, were recorded in detail.


### 2.2.2. Neuropsychological Assessment

All subjects completed the following scale tests by psychological evaluators: MoCA, Chinese Standard Aphasia Test of Chinese Rehabilitation Research Center (CRRCAE), ADAS-cog, and WHO-UCLAAV-LT scale.


### 2.2.3. Determination of Serum Inflammatory Factors

All the subjects collected venous blood samples (5 ml) on an empty stomach. Within 1 hour, the specimens were centrifuged, 3000 r/min and centrifuged 10 min, and the serum was separated. After subpackaging, it was stored at-20°C. IL-4, IL-6, IL-10, TNF-α, TNF-β, CCL-2, and enzyme-linked antibody adsorption test (ELASIA) kits were employed in Shanghai Langton Biotechnology Co., Ltd., and all samples were examined by ELASIA kit after collection.


## 2.2.1. General Demographic Data Collection

The age, sex, course of disease, education, family history, left and right handedness, nationality, smoking, and drinking history of the subjects in the two groups were recorded in detail, and the general somatic diseases, such as hypertension, diabetes, coronary heart disease, hyperlipidemia, and whether there is a history of severe brain trauma, were recorded in detail.


## 2.2.2. Neuropsychological Assessment

All subjects completed the following scale tests by psychological evaluators: MoCA, Chinese Standard Aphasia Test of Chinese Rehabilitation Research Center (CRRCAE), ADAS-cog, and WHO-UCLAAV-LT scale.


## 2.2.3. Determination of Serum Inflammatory Factors

All the subjects collected venous blood samples (5 ml) on an empty stomach. Within 1 hour, the specimens were centrifuged, 3000 r/min and centrifuged 10 min, and the serum was separated. After subpackaging, it was stored at-20°C. IL-4, IL-6, IL-10, TNF-α, TNF-β, CCL-2, and enzyme-linked antibody adsorption test (ELASIA) kits were employed in Shanghai Langton Biotechnology Co., Ltd., and all samples were examined by ELASIA kit after collection.


## 2.3. Observation Index

### 2.3.1. Montreal Cognitive Assessment Scale (MoCA)

MoCA was developed and applied by Nasreddine in 2004. It can be used as a simple screening tool for MCI and mild AD. MoCA can be divided into seven parts: (1) visual space/execution, (2) naming, (3) memory, (4) attention, (5) language, (6) abstraction, and (7) direction. The total score was 30, thescore≥26 was normal, and the score was positively correlated with the state of cognitive function.


### 2.3.2. AD Assessment Scale-Cognitive (ADAS-cog)

ADAS-cog covers the cognitive areas mentioned by DSM-IV and NINCDS-ADRDA about the diagnostic criteria of AD. The scale is sensitive for evaluating cognitive and noncognitive impairment in patients with AD. ADAS-cog can be divided into four cognitive subareas, namely, memory, language, operational ability, and attention (see schedule 3 for details). The deficiency of the scale lies in the higher requirements for the subjects’ reading and writing ability; so, it is not suitable for illiteracy. The score of the scale is between 0 and 70, and the higher the score is, the more serious the cognitive impairment is.


### 2.3.3. Language Ability

The Chinese Standard Aphasia Test (CRRCAE) of China Rehabilitation Research Center was used to evaluate their listening comprehension, reading ability, and naming ability. The higher the score, the more prominent the patient’s related ability.


### 2.3.4. Memory Ability Assessment

Through the WHO-UCLAAV-LT scale, three parts of delayed recognition, delayed memory, and instantaneous memory of the two groups were investigated on the day of admission and 180 days after intervention: (1) instantaneous memory: it includes two lists A and B, with a total of 30 words in the list, which can be presented in a random but fixed way [14]. List A is rendered five times and then converted to list B. The score of the average correct number of 5 free memories in list A is instantaneous recall, <18 as instantaneous memory abnormality; (2) delayed memory: it mainly investigates long-term delayed memory and short-term delayed memory. Short-term delayed memory of list B presentation leads to patients to recall list A, score as the correct number obtained by free recall, less than 6 points as abnormal. Long-term delayed memory refers to the need for patients to recall the A list after 30 min, with a score of the correct number of free recall, less than 6 as abnormal; (3) recognition: after the completion of delayed memory, patients need to recognize 15 interfering words and 15 target words marked with A list and less than 6 points as abnormal.


## 2.3.1. Montreal Cognitive Assessment Scale (MoCA)

MoCA was developed and applied by Nasreddine in 2004. It can be used as a simple screening tool for MCI and mild AD. MoCA can be divided into seven parts: (1) visual space/execution, (2) naming, (3) memory, (4) attention, (5) language, (6) abstraction, and (7) direction. The total score was 30, thescore≥26 was normal, and the score was positively correlated with the state of cognitive function.


## 2.3.2. AD Assessment Scale-Cognitive (ADAS-cog)

ADAS-cog covers the cognitive areas mentioned by DSM-IV and NINCDS-ADRDA about the diagnostic criteria of AD. The scale is sensitive for evaluating cognitive and noncognitive impairment in patients with AD. ADAS-cog can be divided into four cognitive subareas, namely, memory, language, operational ability, and attention (see schedule 3 for details). The deficiency of the scale lies in the higher requirements for the subjects’ reading and writing ability; so, it is not suitable for illiteracy. The score of the scale is between 0 and 70, and the higher the score is, the more serious the cognitive impairment is.


## 2.3.3. Language Ability

The Chinese Standard Aphasia Test (CRRCAE) of China Rehabilitation Research Center was used to evaluate their listening comprehension, reading ability, and naming ability. The higher the score, the more prominent the patient’s related ability.


## 2.3.4. Memory Ability Assessment

Through the WHO-UCLAAV-LT scale, three parts of delayed recognition, delayed memory, and instantaneous memory of the two groups were investigated on the day of admission and 180 days after intervention: (1) instantaneous memory: it includes two lists A and B, with a total of 30 words in the list, which can be presented in a random but fixed way [14]. List A is rendered five times and then converted to list B. The score of the average correct number of 5 free memories in list A is instantaneous recall, <18 as instantaneous memory abnormality; (2) delayed memory: it mainly investigates long-term delayed memory and short-term delayed memory. Short-term delayed memory of list B presentation leads to patients to recall list A, score as the correct number obtained by free recall, less than 6 points as abnormal. Long-term delayed memory refers to the need for patients to recall the A list after 30 min, with a score of the correct number of free recall, less than 6 as abnormal; (3) recognition: after the completion of delayed memory, patients need to recognize 15 interfering words and 15 target words marked with A list and less than 6 points as abnormal.


## 2.4. Statistical Analysis

SPSS23.0 statistical software was employed to measure the data. Independent samplet-test was employed to analyze and compare the serum inflammatory factors levels between AD and control groups. Linear regression was employed for further analysis and comparison. Chi-square (x2) test was employed for gender. Measurement data were presented by normal distribution and variance homogeneity test. In this study, Pearson correlation analysis was employed to detect the continuous data in accordance with normal distribution, P<0.05. The difference exhibited statistically significant.


## 3. Results

### 3.1. Comparison of Demographic Data and Clinical Data

First of all, we compared the demographic data, but with no significant difference in gender, age, education level, and other general data. We compared the cognitive function of the two groups, and the scores of MoCA in the AD group exhibited remarkably lower (P<0.05). All the data results are indicated in Table 1.Table 1
Comparison of demographic data and clinical data.
GroupAD (n=36)Control (n=30)t/χ2PGender (male/female)15/2116/140.9840.344Age (Y)69.83±8.4770.52±6.630.3630.718Education level (Y)6.61±3.767.66±2.581.2960.200Time of illness (M)75.76±45.34NA——MOCA13.08±5.4227.88±0.7314.826<0.001ADAS-cog24.15±9.03NA——


### 3.2. Comparison of Memory Ability and Language Ability Score

The scores of long-term delayed recognition, delayed memory and instantaneous memory in the AD group exhibited remarkably lower (P<0.05), and the scores of listening comprehension, reading, and naming in the AD group exhibited remarkably lower (P<0.05). The scores of long-term delayed recognition, delayed memory, and instantaneous memory exhibited remarkably lower in the AD group. All the data results are indicated in Table 2.Table 2
Comparison of memory ability and language ability score.
ItemAD (n=36)Control (n=30)t/χ2PMemory abilityLong delay recognition6.03±1.248.78±1.567.979<0.001Delayed memory3.22±0.566.14±0.7218.529<0.001Instantaneous memory5.08±0.738.24±1.1713.387<0.001Language abilityListening comprehension44.23±16.1758.46±22.213.007<0.001Reading42.38±12.1372.46±21.357.182<0.001Naming26.43±8.4842.34±3.379.651<0.001


### 3.3. Comparison of Serum Inflammatory Factors

We compared the levels of serum inflammatory factors, the serum levels of IL-4, IL-6, IL-10, TNF-α, and CCL-12 in the AD group were remarkably higher, and the serum TNF-β level in the AD group exhibited remarkably lower. All the data results are indicated in Figures 1 and 2.Figure 1
Comparison of IL-4, IL-6, and IL-10 levels between two groups.Figure 2
Comparison of TNF-α, TNF-β, and CCL-2 levels between two groups.


### 3.4. Analysis of Correlation between Serum Inflammatory Factors and Cognitive Function Score in Patients with AD

We analyzed the correlation between the scores of IL-4, IL-6, IL-10, TNF-α, TNF-β, CCL-2, and the scores of MoCA and ADAS-cog in the AD group. There exhibited no significant correlation between the levels of serum IL-4, IL-6, IL-10, TNF-α, CCL-2, and the total scores of MoCA and ADAS-cog cognitive assessment scale, but there exhibited a positive correlation between the level of serum TNF-β and the score of MoCA scale. All the data results are indicated in Table 3.Table 3
Analysis of correlation between cognitive function score and serum inflammatory factors in patients with AD.
GroupMoCAADAS-cogrPrPIL-4-0.2560.1770.2930.116IL-6-0.2960.113-0.0410.831IL-10-0.1130.5560.0140.932TNF-α-0.1250.5230.1460.459TNF-β0.2750.034-0.0380.769CCL-12-0.0760.5330.1240.386


### 3.5. Analysis of Correlation between Cognitive Function Score and Serum Inflammatory Factors in Patients with AD

We analyzed the correlation between IL-4, IL-6, IL-10, TNF-α, TNF-β, CCL-2, and the scores of long-term delayed recognition, delayed memory, and instantaneous memory in the AD group. The serum levels of IL-4, IL-6, IL-10, TNF-α, CCL-2, and TNF-β were not remarkably correlated with the scores of long-term delayed recognition, delayed memory, and instantaneous memory. All the data results are indicated in Table 4.Table 4
Analysis of correlation between cognitive function score and serum inflammatory factors in patients with AD.
GroupLong delay recognitionDelayed memoryInstantaneous memoryrPrPrPIL-4-0.0870.189-0.0570.583-0.2050.109IL-6-0.0740.192-0.0490.568-0.2070.112IL-10-0.0830.214-0.0670.592-0.2130.121TNF-α-0.1370.253-0.0240.832-0.2310.056TNF-β0.4130.1730.3640.1240.0430.712CCL-12-0.0370.778-0.0670.5140.1260.376


### 3.6. Analysis of the Relationship between the Score of Language Function and the Level of Serum Inflammatory Factors in Patients with AD

We analyzed the correlation between IL-4, IL-6, IL-10, TNF-α, TNF-β, CCL-2, and the scores of listening comprehension, reading, and naming in the AD group. The levels of serum IL-4, IL-6, IL-10, TNF-α, CCL-2, and TNF-β were not remarkably correlated with the scores of listening comprehension, reading, and naming. All the data results are indicated in Table 5.Table 5
Analysis of the relationship between the score of language function and the level of serum inflammatory factors in patients with AD.
GroupListening comprehensionReadingNamingrPrPrPIL-4-0.3740.233-0.0450.703-0.0790.484IL-6(-0.2370.056-0.0430.711-0.0680.432IL-10-0.3520.108-0.6940.191-0.5180.143TNF-α-0.0950.442-0.1230.336-0.1610.179TNF-β0.0740.5330.1470.2630.0620.667CCL-12-0.0340.751-0.0030.992-0.2040.095


## 3.1. Comparison of Demographic Data and Clinical Data

First of all, we compared the demographic data, but with no significant difference in gender, age, education level, and other general data. We compared the cognitive function of the two groups, and the scores of MoCA in the AD group exhibited remarkably lower (P<0.05). All the data results are indicated in Table 1.Table 1
Comparison of demographic data and clinical data.
GroupAD (n=36)Control (n=30)t/χ2PGender (male/female)15/2116/140.9840.344Age (Y)69.83±8.4770.52±6.630.3630.718Education level (Y)6.61±3.767.66±2.581.2960.200Time of illness (M)75.76±45.34NA——MOCA13.08±5.4227.88±0.7314.826<0.001ADAS-cog24.15±9.03NA——


## 3.2. Comparison of Memory Ability and Language Ability Score

The scores of long-term delayed recognition, delayed memory and instantaneous memory in the AD group exhibited remarkably lower (P<0.05), and the scores of listening comprehension, reading, and naming in the AD group exhibited remarkably lower (P<0.05). The scores of long-term delayed recognition, delayed memory, and instantaneous memory exhibited remarkably lower in the AD group. All the data results are indicated in Table 2.Table 2
Comparison of memory ability and language ability score.
ItemAD (n=36)Control (n=30)t/χ2PMemory abilityLong delay recognition6.03±1.248.78±1.567.979<0.001Delayed memory3.22±0.566.14±0.7218.529<0.001Instantaneous memory5.08±0.738.24±1.1713.387<0.001Language abilityListening comprehension44.23±16.1758.46±22.213.007<0.001Reading42.38±12.1372.46±21.357.182<0.001Naming26.43±8.4842.34±3.379.651<0.001


## 3.3. Comparison of Serum Inflammatory Factors

We compared the levels of serum inflammatory factors, the serum levels of IL-4, IL-6, IL-10, TNF-α, and CCL-12 in the AD group were remarkably higher, and the serum TNF-β level in the AD group exhibited remarkably lower. All the data results are indicated in Figures 1 and 2.Figure 1
Comparison of IL-4, IL-6, and IL-10 levels between two groups.Figure 2
Comparison of TNF-α, TNF-β, and CCL-2 levels between two groups.


## 3.4. Analysis of Correlation between Serum Inflammatory Factors and Cognitive Function Score in Patients with AD

We analyzed the correlation between the scores of IL-4, IL-6, IL-10, TNF-α, TNF-β, CCL-2, and the scores of MoCA and ADAS-cog in the AD group. There exhibited no significant correlation between the levels of serum IL-4, IL-6, IL-10, TNF-α, CCL-2, and the total scores of MoCA and ADAS-cog cognitive assessment scale, but there exhibited a positive correlation between the level of serum TNF-β and the score of MoCA scale. All the data results are indicated in Table 3.Table 3
Analysis of correlation between cognitive function score and serum inflammatory factors in patients with AD.
GroupMoCAADAS-cogrPrPIL-4-0.2560.1770.2930.116IL-6-0.2960.113-0.0410.831IL-10-0.1130.5560.0140.932TNF-α-0.1250.5230.1460.459TNF-β0.2750.034-0.0380.769CCL-12-0.0760.5330.1240.386


## 3.5. Analysis of Correlation between Cognitive Function Score and Serum Inflammatory Factors in Patients with AD

We analyzed the correlation between IL-4, IL-6, IL-10, TNF-α, TNF-β, CCL-2, and the scores of long-term delayed recognition, delayed memory, and instantaneous memory in the AD group. The serum levels of IL-4, IL-6, IL-10, TNF-α, CCL-2, and TNF-β were not remarkably correlated with the scores of long-term delayed recognition, delayed memory, and instantaneous memory. All the data results are indicated in Table 4.Table 4
Analysis of correlation between cognitive function score and serum inflammatory factors in patients with AD.
GroupLong delay recognitionDelayed memoryInstantaneous memoryrPrPrPIL-4-0.0870.189-0.0570.583-0.2050.109IL-6-0.0740.192-0.0490.568-0.2070.112IL-10-0.0830.214-0.0670.592-0.2130.121TNF-α-0.1370.253-0.0240.832-0.2310.056TNF-β0.4130.1730.3640.1240.0430.712CCL-12-0.0370.778-0.0670.5140.1260.376


## 3.6. Analysis of the Relationship between the Score of Language Function and the Level of Serum Inflammatory Factors in Patients with AD

We analyzed the correlation between IL-4, IL-6, IL-10, TNF-α, TNF-β, CCL-2, and the scores of listening comprehension, reading, and naming in the AD group. The levels of serum IL-4, IL-6, IL-10, TNF-α, CCL-2, and TNF-β were not remarkably correlated with the scores of listening comprehension, reading, and naming. All the data results are indicated in Table 5.Table 5
Analysis of the relationship between the score of language function and the level of serum inflammatory factors in patients with AD.
GroupListening comprehensionReadingNamingrPrPrPIL-4-0.3740.233-0.0450.703-0.0790.484IL-6(-0.2370.056-0.0430.711-0.0680.432IL-10-0.3520.108-0.6940.191-0.5180.143TNF-α-0.0950.442-0.1230.336-0.1610.179TNF-β0.0740.5330.1470.2630.0620.667CCL-12-0.0340.751-0.0030.992-0.2040.095


## 4. Discussion

AD is a degenerative disease of the central nervous system, with the passage of time, accompanied by diffuse cognitive degradation and loss of independence, as well as the existence of mental and behavioral disorders, showing general memory loss [15]. AD is the most common type of dementia, accounting for 50% to 70% of all dementia cases. It is reported that the number of AD patients in the all over the world achieved 50 million in 2018 and is expected to achieve 152 million by 2050. The global cost of AD treatment and care achieved US $1 trillion in 2018 and is expected to reach US $2 trillion in 2030 [15, 16]. At present, it is considered that the incidence of AD is a dynamic process. In 2011, the National Institute of Aging and the Alzheimer’s Association (NIA-AA) issued guidelines to divide the course of AD into three stages, namely, the preclinical stage of AD, AD-derived MCI stage, and AD dementia stage, which emphasizes the importance of early diagnosis and early treatment of AD [16]. Due to the lack of effective treatment, early intervention is very important to delay the disease progression and strength the prognosis of patients with AD. However, the early diagnosis of AD is still a difficult problem. At present, it mainly depends on the patient’s own chief complaint and neuropsychological measurement to evaluate the cognitive function of the patient, and the diagnosis depends on the pathological examination of brain tissue. Although biomarkers such as Aβ and tau protein are also included in the clinical diagnostic criteria of AD, they are rarely used in clinical practice because of their poor sensitivity and specificity.There is more evidence that neuroimmune inflammation may occur earlier than the clinical symptoms of AD, and studies have also found that abnormal regulation of cytokines can be seen in many patients with AD [17]. Cytokines are a kind of small molecule proteins with a wide range of biological activities, which play an important role in the process of inflammation and the regulation of the immune system [18]. At present, there are many studies on the level of inflammatory cytokines in peripheral blood of patients with AD, trying to find inflammatory cytokines related to the course of disease as diagnostic markers, but the sample size is small, and the results are not uniform. In current study, serum IL-4, IL-6, IL-10, TNF-α, TNF-β, and CCL-2 were enrolled as observation indexes to compare the levels of serum inflammatory cytokines between patients with AD and normal controls and to evaluate the correlation between peripheral blood inflammatory cytokines and cognitive function, in order to offer basis to the diagnosis of AD.TNF-α is a cytokine produced by mononuclear macrophages, which has a wide range of biological effects and participates in normal inflammatory and immune responses [19]. TNF-α plays a nonspecific but powerful role in the development of many neuropsychiatric diseases such as depression and dementia. TNF-α can be produced by activated microglia due to Aβ deposition or oxidative stress. Excessive expression of TNF-α can be found around Aβ plaques in AD patients [20]. In the meanwhile, TNF-α can also upregulate the expression of Aβ1-42 chemotactic receptor in microglia and enhance the chemotactic effect of microglia to Aβ [19]. Some studies have also indicated that when severe AD patients are exposed to inflammatory stimulation, the level of TNF-α released by blood cells is remarkably lower compared to normal controls [20]. The mechanism of AD neurotoxicity mediated by TNF-α may be to induce the activation of astrocytes and microglia in the brain, resulting in chronic inflammation of the central nervous system and the formation of Aβ plaques. In most studies, the increase of TNF-α is mainly seen in patients with severe AD, which may be due to the fact that the inflammatory factor appears in the early stage of AD, and then increases slowly with the progress of the disease [21]. Consistently, the level of serum TNF-α in the AD group exhibited remarkably higher compared to the control group.By determining the relationship between serum IL-4 factor levels and hippocampal volume among healthy controls, patients with AD, and patients with MCI, it was found that serum IL-4 factor had a potential neuroprotective effect on areas of the brain that are more prone to aging and neurodegeneration [21]. The relationship between serum IL-4 and pathophysiology of AD is still controversial. Magalhães et al. found that IL-6 gene is present in primary astrocytes and microglia, and IL-6 gene signal increases in the central nervous system of patients with late-onset AD in an IL-6 receptor-dependent manner [22]. It has been reported that the level of serum IL-10 factor in dementia patients is higher compared to healthy controls [23], but another study found that there is no difference in serum IL-10 factor levels among AD patients, vascular dementia patients, PD patients, and healthy controls [21]; so, the relationship between IL-10 and the pathological mechanism of AD patient needs to be further studied.TNF-α is produced by macrophages, adipocytes, and astrocytes, previous studies have indicated that TNF-α mediates inflammation in many neurological diseases, and its function is regulated by the activation of transcription factor NF-KB [22]. Studies have pointed out that the increase of TNF-α in the body will increase the level of glutamate receptor, and the imbalance of glutamate level may lead to the accumulation of neurotransmitters, thus affecting the function of neurons, leading to the occurrence and development of AD [24]. In a meta-analysis, compared with the control group, the peripheral blood TNF-α level of the subjects with different severity of AD was not remarkably higher, which is contrary to the previous research on the development and occurrence of AD by participating in inflammatory response, which may need further research to explain scientifically [25]. In the present study, we compared the serum inflammatory factors and found that there exhibited significant differences in serum IL-4, IL-6, IL-10, TNF-α, TNF-β, CCL-2, and other factors. Next, it was demonstrated that the level of serum TNF-β in patients with AD was positively correlated with the score of MoCA scale, while there exhibited no significant correlation between serum inflammatory factors such as IL-4, IL-6, IL-10, TNF-α, CCL-2, MoCA, and ADAS-cog, which was consistent with previous studies [23]. TGF-β is a kind of cytokine with immunomodulatory effect, which is committed to regulating cell differentiation and proliferation and promoting the formation of cell stroma [26]. In this study, the level of serum TGF-β in the AD group exhibited remarkably lower compared to the control group. The level of serum TGF-β in the AD group was positively correlated with the total score of MoCA scale, suggesting that the level of serum TGF-β may be employed as a screening index to assist the early diagnosis of AD.In addition, with regard to the correlation between the level of serum inflammatory factors and the ability of language and memory in patients with AD, the results of this study indicated that there exhibited no significant correlation between the levels of serum IL-4, IL-6, IL-10, TNF-α, CCL-2, and TNF-β and the scores of long-term delayed recognition, delayed memory, and instantaneous memory in the AD group [25]. There exhibited no significant connection between the levels of serum IL-4, IL-6, IL-10, TNF-α, CCL-2, and TNF-β and the scores of listening comprehension, reading, and naming in the AD group. To some extent, this indicates that there exhibits no significant connection between the level of serum inflammatory factors and language and memory ability in patients with AD, but the error caused by small sample data cannot be excluded. In the past, there are few studies on the relationship between serum inflammatory factors and language and memory ability of AD patients. This study is a small sample study. In the future, we still need to conduct statistical analysis based on larger sample data to further study whether there exhibits a connection between the level of serum inflammatory factors and language and memory ability of AD patients, in order to explore the potential effect of inflammatory reaction on language and memory ability of AD patients.The limitations of this study are as follows: first of all, the number of cases in the experimental group and the control group included in our study is relatively small, and the experimental group is only diagnosed with AD, but not yet included in MCI; so, our experimental results may not necessarily be applicable to all stages of AD, and in this study, we have not facilitated the full cognitive function evaluation of subjects in the control group [26]. In the future, we will further strengthen the clinical data of the subjects in order to get more scientific experimental results. Secondly, our results did not show significant differences between gender and age, but we could not completely rule out a confounding effect of these two factors on the conclusions In future studies, we will expand the sample size to more deep study the connection between inflammatory factors and AD and mild cognitive impairment.Conclusively, we expanded the study on the relationship between cognitive function and serum inflammatory factors. The results showed that the increase of some serum inflammatory factors was related to the decrease of cognitive function. Among them, the level of TNF-β indicated that the level of serum TGF-β might reflect the severity of cognitive impairment in patients with AD. In the meantime, our results show that there is no significant correlation between language and memory ability and serum levels of inflammatory factors in patients with AD. Therefore, based on the correlation between the levels of some serum inflammatory factors and the cognitive function of AD, it may be instructive to further explore the blood biomarkers of AD and is very significant for the early identification of AD disease and better clinical intervention in the future.



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