Surface Tension and Intrinsic Amyloid Fluorescence of Serum and Cerebrospinal Fluid Samples in Alzheimer´S Disease

Figures & data

Table 1. Characteristics of patients providing serum or cerebrospinal fluid samples.

Group	n (M/F)	Age (years)
Serum
Young controls	33 (12/21)	42.1 ± 11.9
Aged controls	11 (5/6)	71.6 ± 6.9*
AD	22 (9/13)	75.8 ± 9.4*
Total	66 (26/40)	ANOVA: F (2, 63) = 79.98, p < 0.001
CSF
Young controls	22 (11/11)	54.6 ± 10.1
Aged controls	24 (17/7)	74.9 ± 7.7*
MCI-AD	12 (7/5)	75.3 ± 5.8*
AD	36 (13/23)	74.8 ± 8.5*
Total	94 (48/46)	ANOVA: F (3, 90) = 32.49, p < 0.001

Data are presented as the mean ± standard deviation.

Statistical significance (Student´s t-test) was calculated with respect to young controls.

AD: Alzheimer´s disease; ANOVA: Analysis of variance; CSF: Cerebrospinal fluid; F: Females; IAF: Intrinsic amyloid fluorescence; M: Males; MCI-AD: Mild cognitive impairment due to Alzheimer's disease; NF: Native fluorescence; ST: Surface tension; ThTF: Thioflavin T-based fluorescence.

*p < 0.001.

Table 2. Results of surface tension and fluorescence measurements obtained from serum and cerebrospinal fluid samples.

Groups	ST	NF	ThTF	IAF
Serum
Young controls	58.6 ± 2.3	4266 ± 1272	51 588 ± 20,505	17 100 ± 3679
Aged controls	57.2 ± 3.4	4912 ± 1631	59 018 ± 22,854	18 033 ± 4862
AD	56.1 ± 3.0*	4897 ± 2006	55 925 ± 20,374	19 350 ± 4334
ANOVA	F (2, 63) = 5.69  p = 0.005	F (2, 63) = 1.29  p = 0.282	F (2, 63) = 0.63  p = 0.537	F (2, 63) = 1.98  p = 0.147
CSF
Young controls	68.9 ± 2.1	324 ± 164	3548 ± 1230	2650 ± 2353
Aged controls	67.8 ± 2.4**	410 ± 172	4095 ± 1432	2368 ± 1650
MCI-AD	68.2 ± 0.7	305 ± 95	5044 ± 1358*	1226 ± 721**
AD	68.4 ± 1.2	334 ± 177	4619 ± 1724**	1551 ± 1306**
ANOVA	F(3, 90) = 1.57  p = 0.202	F(3, 90) = 1.64  p = 0.185	F(3, 90) = 3.50  p = 0.019	F(3, 90) = 3.30  p = 0.024

Data are presented as the mean ± standard deviation.

Statistical significance (Student´s t-test) was calculated with respect to young controls.

AD: Alzheimer´s disease; ANOVA: Analysis of variance; CSF: Cerebrospinal fluid; IAF: Intrinsic amyloid fluorescence; MCI-AD: Mild cognitive impairment due to Alzheimer's disease; NF: Native fluorescence; ST: Surface tension; ThTF: Thioflavin T-based fluorescence.

*p < 0.010, **p < 0.05.

Table 3. Correlation analysis performed on data from surface tension and fluorescence measurements.

Correlation	Young controls R p	Aged controls R p Z-test (p) vs. young controls	AD R p Z-test (p) vs. aged controls
Serum	n = 33	n = 11	n =  22
Age vs. ST vs. NF vs. ThTF vs. IAF	-0.581 < 0.001 -0.009 0.960 +0.391 0.025 +0.074 0.683	-0.138 0.686 0.187 +0.661 0.027 0.043* -0.360 0.277 0.047* +0.562 0.072 0.158	+0.416 0.054 0.168 -0.736 < 0.001 < 0.001** +0.357 0.103 0.075 -0.297 0.180 0.025*
ST vs. NF vs ThTF vs IAF	+0.087 0.630 -0.554 < 0.001 -0.230 0.198	-0.640 0.034 0.034* +0.333 0.317 0.015* -0.629 0.038 0.204	-0.498 0.018 0.616 +0.198 0.377 0.730 -0.411 0.058 0.472
NF vs. ThTF vs. IAF	-0.023 0.897 +0.345 0.049	-0.168 0.621 0.713 +0.543 0.085 0.532	-0.433 0.044 0.485 +0.558 0.007 0.959
ThTF vs. IAF	+0.110 0.543	-0.687 0.020 0.017*	-0.487 0.022 0.462
CSF	n = 22	n = 24	n = 36
Age vs. ST vs. NF vs. ThTF vs. IAF	-0.311 0.159 -0.245 0.271 +0.432 0.045 -0.428 0.047	-0.122 0.569 0.529 +0.180 0.400 0.174 -0.054 0.801 0.103 -0.067 0.755 0.219	-0.163 0.343 0.881 +0.332 0.048 0.562 +0.349 0.037 0.134 +0.272 0.108 0.215
ST vs. NF vs. ThTF vs. IAF	-0.073 0.747 -0.555 0.007 -0.116 0.607	-0.488 0.015 0.147 -0.535 0.007 0.928 -0.273 0.196 0.603	-0.368 0.027 0.734 -0.725 < 0.001 0.205 +0.376 0.024 0.016*
NF vs. ThTF vs. IAF	+0.113 0.617 +0.381 0.080	+0.452 0.027 0.238 +0.085 0.694 0.317	+0.654 < 0.001 0.289 +0.593 < 0.001 0.032*
ThTF vs. IAF	+0.005 0.983	+0.116 0.589 0.726	+0.092 0.593 0.928

Correlation coefficients (Rs) were compared by a test based on the Fisher´s Z-transformation (Z-test). Statistical significance was calculated with respect to young or aged controls.

AD: Alzheimer's disease; CSF: Cerebrospinal fluid; IAF: Intrinsic amyloid fluorescence; NF: Native fluorescence; ST: Surface tension; ThTF: Thioflavin T-based fluorescence.

*p < 0.050, **p < 0.001.

Table 4. Ratios of surface tension values to intrinsic amyloid fluorescence signals in serum and thioflavin T-based fluorescence to intrinsic amyloid fluorescence signals in cerebrospinal fluid.

Group	Serum (ST/IAF) x 10^3	CSF ThTF/IAF
Young controls	3.6 ± 0.8	2.8 ± 2.6
Aged controls	3.4 ± 1.1	2.5 ± 1.5
AD	3.1 ± 0.8*	4.3 ± 2.1*++
ANOVA	F(2, 63) = 2.85,  p = 0.065	F(2, 79) = 6.45, p = 0.003

Data are presented as the mean ± standard deviation.

Statistical significance (student´s t-test) was calculated with respect to young (*p < 0.05) or aged (**p < 0.010) controls.

AD: Alzheimer's disease; ANOVA: Analysis of variance; CSF: Cerebrospinal fluid; IAF: Intrinsic amyloid fluorescence; ST: Surface tension; ThTF: Thioflavin T-based fluorescence.

*p < 0.010; **p < 0.010.

Figure 1. The ratio of thioflavin T-based fluorescence to intrinsic amyloid fluorescence signals in cerebrospinal fluid.

Individual plots showing part of the data presented in Table 4. Fluorescence signals were estimated from cerebrospinal fluid samples of aged controls (n = 24) and AD patients (n = 36). Statistical significance (Student´s t-test) was calculated with respect to aged controls.

AD: Alzheimer's disease; IAF: Intrinsic amyloid fluorescence; ThTF: ThioflavinT-based fluorescence.

*p < 0.010.

Table 5. Levels of Aβ 1–42, τ and phosphorylated τ in cerebrospinal fluid.

Group	n	Aβ 1–42 (pg/ml)	Total τ (pg/ml)	Phosphorylated τ (pg/ml)
Aged controls	24	777.1 ± 347.0	281.6 ± 145.4	38.4 ± 15.8
MCI-AD	12	387.3 ± 165.8*	522.3 ± 261.1**	67.8 ± 33.6***
AD	36	426.5 ± 215.5*	718.8 ± 400.8*	66.7 ± 33.8*
ANOVA		F(2, 69) = 15.37, p < 0.001	F(2, 69) = 13.87, p < 0.001	F(2, 69) = 7.78, p < 0.001

Data are presented as the mean ± standard deviation.

Statistical significance (Student´s t-test) was calculated with respect to aged controls.

AD: Alzheimer´s disease; ANOVA: Analysis of variance; MCI-AD: Mild cognitive impairment due to Alzheimer´s disease.

*p < 0.010, **p < 0.001, ***p < 0.050