3.1 Clinical characteristics and cognitive function of patients with SLE and HCs
The demographic features of 121 patients with SLE and 65 HCs in the study are summarized in Table 1. The mean age of patients and HCs was 33.88 ± 11.77 and 36.69 ± 13.88 years, respectively. The mean level of education was 11.95 ± 3.05 years in the patient group, which was significantly lower than that in the HC group (P < 0.01).
Table 1. Demographic features of the 121 SLE patients and 65 healthy controls in the study.
Variables
|
SLE (n=121)
|
HC (n=65)
|
P Value
|
Age, (years)
|
33.88 (±11.77)
|
36.69 (±13.88)
|
0.150
|
Females, n (%)
|
106 (87.60%)
|
50 (76.92%)
|
0.093
|
Education, (years)
|
11.95 (±3.05)
|
13.28 (±4.58)
|
< 0.05*
|
SLEDAI
|
10 (0-47)
|
NA
|
/
|
Data are expressed as median (minimum - maximum, number (percentage), or mean ± standard deviation (SD) values. P values are based on independent sample t-test and Chi-square test for normally distributed variables. *P < 0.05, **P < 0.01, *** P < 0.005, vs. Low RBANS Score. The Graph Pad Prism 7.0 and SPSS Statistics 16.0 software were used for statistical analysis.
Afterward, an RBANS was performed on 121 patients and 65 HCs. Significant differences were found in List Learning (P < 0.0001) between patients with SLE and HCs, while Immediate Story Recall, Picture Naming, Coding, List Recall, List Recognition Test, and Delayed Story Recall (all P < 0.01), as well as Judgment of Line Orientation, Digit Span, and Figure Recall (all P < 0.05), were lower in patients with SLE. However, Figure Copy and Semantic Fluency showed no differences (Table 2). These tests corresponded to five cognitive domains: immediate memory, visuospatial/construction, attention, language, and delayed memory. After categorizing the aforementioned cognitive function tests according to these five cognitive domains, the difference between patients and normal volunteers was analyzed. The results showed that levels of immediate memory, visuospatial/construction, attention, and delayed memory were significantly lower in patients than in HCs, while language features showed no obvious difference (Fig. 1).
Table 2. The data of commonly cognitive assessment.
RBANS score
|
SLE (n =121)
|
HC (n = 65)
|
P Value
|
Immediate memory
|
|
|
|
List Learning, median (range)
|
24 (5-39)
|
29 (15-36)
|
< 0.005***
|
Immediate Story Memory, median (range)
|
13 (1-22)
|
16 (1-21)
|
< 0.01**
|
Visuospatial/constructional
|
|
|
|
Figure Copy, median (range)
|
20 (14-20)
|
20 (17-20)
|
0.2963
|
Line Orientation, median (range)
|
17 (8-20)
|
18 (9-20)
|
< 0.05*
|
Language
|
|
|
|
Picture Naming, median (range)
|
9 (7-10)
|
9 (8-10)
|
< 0.01**
|
Semantic Fluency, median (range)
|
21 (7-33)
|
23 (11-35)
|
0.0873
|
Attention
|
|
|
|
Digit Span, median (range)
|
13 (6-16)
|
14 (8-16)
|
< 0.05*
|
Coding, median (range)
|
46 (4-70)
|
54 (13-74)
|
< 0.01**
|
Delayed memory
|
|
|
|
List Recall, median (range)
|
5 (0-10)
|
7 (2-10)
|
< 0.01**
|
List Recognition, median (range)
|
20 (16-20)
|
20 (17-20)
|
< 0.01**
|
Delay Story Recall, median (range)
|
7 (0-12)
|
9 (0-12)
|
< 0.01**
|
Figure Recall, median (range)
|
15 (5-20)
|
16 (7-20)
|
< 0.05*
|
Data are expressed as mean ± standard deviation (SD) values. P values are based on independent sample t-test for normally distributed variables. *P < 0.05, **P < 0.01, *** P < 0.005, vs. Low RBANS Score. The Graph Pad Prism 7.0 software were used for statistical analysis.
3.2 Demographic features, clinical manifestations, and treatment of patients
Based on the RBANS score, 81 patients were divided into high-cognition group (n = 33) and low-cognition group (n = 48). As shown in Table 3, no statistically significant differences in age and sex were found between the two groups. The mean level of education was 10.77 ± 3.64 years in the low-cognition group, which was lower than that in the high-cognition group (P < 0.01). The levels of SLEDAI (13.91 ± 11.79 vs 9.38 ± 5.79) significantly increased in patients with low cognition compared with those in high cognition (all P < 0.05).
Table 3. Demographic features, clinical manifestations, and treatment of SLE patients.
SLE characteristics
|
Low Cognition (n=48)
|
High Cognition (n=33)
|
P Value
|
Demographic
|
|
|
|
Age, (years)
|
34.67 (±12.03)
|
32.23 (±10.98)
|
0.3530
|
Females, n (%)
|
40 (83.33%)
|
30 (90.90%)
|
0.763
|
Education, (years)
|
10.77 (±3.64)
|
13.26 (±3.21)
|
< 0.01**
|
SLEDAI, mean ± (SD)
|
13.91 (±11.79)
|
9.38 (±5.79)
|
< 0.05*
|
Clinical chart review (%)
|
|
|
|
Rash, (%)
|
10 (21.28%)
|
6 (18.18%)
|
0.768
|
Mucosal ulcers, (%)
|
2 (4.26%)
|
1 (3.03%)
|
1.000
|
Hematuria, (%)
|
22 (46.81%)
|
13 (39.33%)
|
0.510
|
Proteinuria, (%)
|
22 (46.81%)
|
13 (39.33%)
|
0.510
|
Pyuria, (%)
|
14 (39.79%)
|
11 (33.33%)
|
0.736
|
Arthritis, (%)
|
8 (17.02%)
|
5 (15.15%)
|
0.823
|
Vasculitis, (%)
|
4 (8.51%)
|
0 (0%)
|
0.231
|
Pleurisy, (%)
|
1 (2.13%)
|
1 (3.03%)
|
1.00
|
Pericarditis, (%)
|
1 (2.13%)
|
0 (%)
|
1.00
|
Low complement, (%)
|
36 (76.60%)
|
27 (81.82%)
|
0.574
|
Anemia, (%)
|
11 (23.40%)
|
1 (3.03%)
|
< 0.05*
|
Thrombocytopenia, (%)
|
11 (23.40%)
|
4 (12.12
|
0.203
|
Leukopenia, (%)
|
11 (23.40%)
|
7 (21.21%)
|
0.817
|
Lupus nephritis, (%)
|
19 (40.43%
|
20 (60.61%)
|
0.075
|
Neurological disorder, (%)
|
6 (12.77%)
|
5 (15.15%)
|
1.00
|
Current medication (%)
|
|
|
|
Prednisone (%)
|
31 (64.58%)
|
18 (54.54%)
|
0.425
|
Hydroxychloroquine (%)
|
29 (61.70%)
|
19 (57.58%)
|
0.711
|
Cyclophosphamide (%)
|
5 (10.64%)
|
3 (9.09%)
|
1.000
|
Azathioprine (%)
|
1 (2.13%)
|
1 (3.03%)
|
1.000
|
Methotrexate (%)
|
2 (4.26%)
|
2 (6.06%)
|
1.000
|
Cyclosporine (%)
|
0 (0%)
|
2 (6.06%)
|
0.326
|
Data are expressed as number (percentage). P values are based on Chi-square test for normally distributed variables. *P < 0.05, **P < 0.01, *** P < 0.005, vs. Low RBANS Score. The SPSS Statistics 16.0 software were used for statistical analysis.
Patients with low cognition had more frequent anemia (23.4% vs 3.03%) compared with patients with high cognition (P < 0.05). Meanwhile, the prevalence of rash, mucosal ulcers, hematuria, proteinuria, pyuria, arthritis, vasculitis, pleurisy, pericarditis, low complement, thrombocytopenia, leukopenia, lupus nephritis, and neurological disorder showed no difference between the two groups. In addition, the treatment with prednisone, hydroxychloroquine, cyclophosphamide, azathioprine, methotrexate, and cyclosporine was not different between the two groups (Table 3).
3.3 Comparison of clinical and laboratory characteristics of patients
The study investigated the laboratory parameters of patients enrolled in this study (Table 4). Patients with low cognition had substantially lower albumin (31.76 ± 5.79 mg/dL vs 34.91 ± 4.13 mg/dL; P < 0.01), T3 (3.20 ± 1.03 ng/dL vs 3.71 ± 1.06 ng/dL; P < 0.05), and T4 levels (12.51 ± 3.43 μg/dL vs 14.97 ± 2.14 μg/dL; P < 0.05). The levels of anti-dsDNA antibody (P < 0.05) and IgM (P < 0.01) and the number of B cells (P < 0.05) were higher and the D-dimer levels were considerably higher in patients with low cognition (P < 0.001). The incidence of other clinical indexes, including globulin, 24-h urine protein (24-h UP), C3, C4, C-reactive protein, and creatinine (Cr), displayed no difference between the two groups.
In addition, the difference in the proportion of various blood cells in the peripheral blood between the two groups was detected. The results showed that the number of B cells was higher in the low-cognition group (0.15 ± 0.16 % vs 0.10 ± 0.13 %; P < 0.05), but no difference was found in the numbers of erythrocytes, WBCs, CD3+ cells, CD3+CD4+ cells, CD3+CD8+ cells, and natural killer cells between the groups (Table 4). As shown in Table 4, the serum levels of anti-dsDNA antibodies (P < 0.05) and IgM (P < 0.01) were both higher in patients with low cognition. However, no statistically significant differences in positive rates of anti-Sm antibodies, anti-RNP antibodies, anti-SSA antibodies, anti-SSB antibodies, anti-Rib P antibodies, and anti-β2GPI antibodies, as well as the levels of IgG, IgA, and IgE, were found between the two groups.
Table 4. Comparison of clinical and laboratory characteristics of SLE patients.
SLE characteristics
|
Low Cognition (n=48)
|
High Cognition (n=33)
|
P Value
|
Clinical characteristics
|
|
|
|
Globulin, mg/dL
|
28.18 (±7.97)
|
27.94 (±6.59)
|
0.764
|
Albumin, mg/dL
|
31.76 (±5.79)
|
34.91 (±4.13)
|
< 0.01**
|
24-h urine protein, (g/24 h)
|
1.97 (±2.59)
|
1.88 (±3.11)
|
0.433
|
C3 Levels, mg/dL
|
0.66 (±0.32)
|
0.77 (±0.29)
|
0.143
|
C4 Levels, mg/dL
|
0.12 (±0.08)
|
0.14 (±0.06)
|
0.323
|
CRP (mg/dL)
|
12.36 (±14.00)
|
11.95 (±16.98)
|
0.869
|
D-dimer (mg/dL)
|
1.74 (±1.28)
|
0.75 (±0.82)
|
< 0.001***
|
Cr (µmol/L)
|
86.95 (±80.42)
|
66.07 (±36.13)
|
0.200
|
BUN (mmol/L)
|
8.04 (±5.66)
|
7.07 (±4.69)
|
0.491
|
UA (µmol/L)
|
362.20 (±129.73)
|
339.38 (±142.41)
|
0.523
|
GFR (mL/min/1.73 m2)
|
117.37 (±56.97)
|
140.31 (±83.36)
|
0.223
|
ESR (mm/hour)
|
50.53 (±32.03)
|
42.59 (±28.74)
|
0.271
|
PLT (109/L)
|
149.32 (±79.69)
|
176.09 (±90.84)
|
0.099
|
TSH (mIU/L)
|
2.78 (±2.31)
|
2.69 (±2.21)
|
0.830
|
T3 Levels (ng/dL)
|
3.20 (±1.03)
|
3.71 (±1.06)
|
< 0.05*
|
T4 Levels (μg/dL)
|
12.51 (±3.43)
|
14.97 (±2.14)
|
< 0.05*
|
Blood Cells
|
|
|
|
Erythrocyte, (%)
|
68.66 (±118.01)
|
40.23 (±66.60)
|
0.419
|
WBC, (109/L)
|
4.73 (±2.42)
|
5.43 (±3.62)
|
0.255
|
CD3+ cells, (%)
|
0.73 (±0.50)
|
0.67 (±0.40)
|
0.605
|
CD3+CD4+ cells, (%)
|
0.33 (±0.22)
|
0.30 (±0.23)
|
0.591
|
CD3+CD8+ cells, (%)
|
0.39 (±0.29)
|
0.36 (±0.19)
|
0.563
|
B cells, (%)
|
0.15 (±0.16)
|
0.10 (±0.13)
|
<0.05*
|
NK cells, (%)
|
0.06 (±0.06)
|
0.06 (±0.04)
|
0.929
|
Autoantibodies
|
|
|
|
Anti-dsDNA antibodies, U/mL
|
746.12 (±441.82)
|
314.56 (±223.99)
|
<0.05*
|
Anti-Sm antibodies, n (%)
|
10 (21.28%)
|
8 (24.24%)
|
0.754
|
Anti-RNP antibodies, n (%)
|
16 (34.04%)
|
13 (39.39%)
|
0.624
|
Anti-SSA antibodies, n (%)
|
19 (40.43%)
|
14 (42.42%)
|
0.858
|
Anti-SSB antibodies, n (%)
|
4 (8.51%)
|
2 (6.06%)
|
1.000
|
Anti-Rib-P, n (%)
|
10 (21.28%)
|
11 (33.33%)
|
0.228
|
Anti-β2-GPI, n (%)
|
1 (2.13%)
|
0 (0%)
|
1.000
|
IgM (mg/dL)
|
1.13 (±0.72)
|
0.76 (±0.41)
|
<0.01**
|
IgG (mg/dL)
|
14.52 (±6.79)
|
12.56 (±5.34)
|
0.172
|
IgA (mg/dL)
|
2.49 (±1.60)
|
2.56 (±1.19)
|
0.857
|
IgE (mg/dL)
|
0.26 (±0.44)
|
0.23 (±0.41)
|
0.620
|
Data are expressed as number (percentage), or mean ± standard deviation (SD) values. P values are based on independent sample t-test and Chi-square test for normally distributed variables. *P < 0.05, **P < 0.01, *** P < 0.005, vs. Low RBANS Score. The Graph Pad Prism 7.0 and SPSS Statistics 16.0 software were used for statistical analysis.
3.4 Correlation analysis between cognitive function and IgG, IgM dsDNA, and albumin levels
The characteristics of SLE are high levels of autoantibodies and damages to multiple organs [41]. The serum anti-dsDNA antibodies are considered a diagnostic marker and one of the classification criteria for SLE [42-44]. Moreover, abnormal immunoglobulin levels were observed in many of the patients. The results showed that the IgG level was inversely associated with neuropsychological tests of immediate memory (List Learning: r = –0.344, P < 0.01; Immediate Story Recall: r = –0.264, P < 0.05; Fig. 2A and 2B). Besides, attention (Digit Span: r = –0.288, P < 0.01; Coding: r = –0.294, P < 0.05; Fig. 2C and 2D) and delayed memory (Delayed Story Recall: r = –0.289, P < 0.01; Figure Recall: r = –0.275, P < 0.05; Fig. 2E and 2F) showed a similar correlation, while no significant correlation was found with the other six cognitive functions (Supplementary Fig. 1). The serum IgM level showed a significant negative correlation with Immediate Story Recall (r = –0.267, P < 0.05; Fig. 2G), Picture Naming (r = –0.299, P < 0.01; Fig. 2H), Digit Span (r = –0.243, P < 0.05; Fig. 2I), Delayed Story Recall (r = –0.299, P < 0.01; Fig. 2J), and Figure Recall (r = –0.254, P < 0.05; Fig. 2K). Nevertheless, no correlation was found with other cognitive functions (Supplementary Fig. 2). However, dsDNA did not have a significant correlation with any cognitive function (Supplementary Fig. 3).
The cerebrospinal fluid (CSF)/serum quotient of albumin, known as quotient albumin (Q albumin), is widely accepted as a biomarker for estimating blood–brain barrier (BBB) function [45]; BBB plays a critical role in the pathogenesis of NPSLE [46]. The potential relationship between the serum albumin levels in SLE and cognitive dysfunction was analyzed. The results showed that the albumin levels correlated positively with List Learning, Immediate Story Recall, and Figure Copy (all P < 0.05; Fig. 2L, M, and 2N), as well as List Recognition Test and Delayed Story Recall (both P < 0.01; Fig. 2O and 2P), but had no relationship with other cognitions (Supplementary Fig. 4).
3.5 Correlation analysis between cognitive function and C3, C4, and lipoprotein levels
Studies indicated that a significant higher prevalence of thyroid autoantibodies was observed in patients with SLE compared with HCs [47-48]. Many studies tried to associate thyroid abnormalities with clinical findings of SLE, but with no unified conclusion [49-51]. This study explored the relationship between the serum T3 and T4 levels and cognitive functions in patients with SLE. A regression analysis revealed that the serum T3 levels positively correlated with Immediate Memory, including List Learning (r = 0.293, P < 0.05; Fig. 3A) and Immediate Story Recall (r = 0.269, P < 0.05; Fig. 3B). Moreover, Figure Copy (r = 0.321, P < 0.05; Fig. 3C), Digit Span (r = 0.285, P < 0.05; Fig. 3D), List Recall (r = 0.187, P < 0.05; Fig. 3E), List Recognition test (r = 0.245, P < 0.01; Fig. 3F), and Delayed Story Recall (r = 0.258, P < 0.05; Fig. 3G) also correlated positively with the T3 level. The serum T4 level positively correlated with up to nine items (0.275 ≤ r ≤ 0.417; all P < 0.05; Fig. 3H–3P), including List Learning, Immediate Story Recall, Figure Copy, Digit Span, Coding, List Recall, List Recognition test, Delayed Story Recall, and Figure Recall.
The results indicated that T3 and T4 levels positively correlated with most cognitive functions. Increasing evidence shows that thyroid hormones (mainly T3 and T4) were involved in all aspects of lipid metabolism [52-54]. The relationship between thyroid hormones and lipid metabolism is evident in patients with thyroid dysfunction [55-56]. Moreover, lipid metabolism was markedly altered in patients with SLE [57]. The serum of 81 patients was collected for ELISA, and the expression of four lipoproteins (APOE, APOA1, IGF-1, and IGFBP7) was analyzed to explore any correlation between lipid metabolism and cognitive dysfunction in patients with SLE. The results showed no significant difference in the expression of these four proteins between the two groups (Fig. 4A, 4B, 4C, and 4D). Then, the correlations between the levels of these four lipoproteins and cognitive function were analyzed. The serum APOE levels significantly negatively correlated with Line Orientation (r = –0.206, P <0.05; Fig. 4E), and IGFBP7 and Figure Recall (r = –0.223, P < 0.05; Fig. 4F), whereas APOA1 showed a positive correlation with Coding (r = –0.207, P < 0.05; Fig. 4G). Apart from this, no other correlations were found.