Long-term exposure to PM_2.5 compositions and O₃ and their interactive effects on DNA methylation of peripheral brain-derived neurotrophic factor promoter

Figures & data

Table 1. Baseline characteristics of 101 participants in this study.

Characteristic	Female (n = 64)	Male (n = 37)	Total (n = 101)	P^b
Age (years); mean (SD)	67.4 (4.8)	72.3 (4.8)	69.2 (5.4)	<0.0001
Education; n (%)				0.6133
Illiterate	3 (4.7)	1 (2.7)	4 (4.0)
Primary school	17 (26.6)	11 (29.7)	28 (27.7)
Junior high school	31 (48.4)	13 (35.1)	44 (43.6)
High school/Junior college	8 (12.5)	8 (21.6)	16 (15.8)
College and above	5 (7.8)	4 (10.8)	9 (8.9)
Smoking status; n (%)				<0.0001
Never	60 (93.8)	16 (43.2)	76 (75.2)
Former	0 (0.0)	14 (37.8)	14 (13.9)
Current	4 (6.2)	7 (18.9)	11 (10.9)
Occupation before retirement; n (%)				0.1047
Production worker	25 (39.1)	13 (35.1)	38 (37.6)
Government worker	9 (14.1)	9 (24.3)	18 (17.8)
Technician	14 (21.9)	12 (32.4)	26 (25.7)
Others	16 (25.0)	3 (8.1)	19 (18.8)
Physical activity^b (MET-min/week); median (IQR)	2205 (0.0)	2205 (1470.0)	2205 (1170.0)	0.0150
Cardiovascular disease; n (%)				0.8231
No	19 (29.7)	10 (27.0)	29 (28.7)
Yes	45 (70.3)	27 (73.0)	72 (71.3)
Diabetes; n (%)				0.1172
No	59 (92.2)	30 (81.1)	89 (88.1)
Yes	5 (7.8)	7 (18.9)	12 (11.9)
Respiratory disease; n (%)				0.5407
No	57 (89.1)	31 (83.8)	88 (87.1)
Yes	7 (10.9)	6 (16.2)	13 (12.9)

^aPhysical activity is represented by metabolic equivalent (MET) -min/week.

^bP for t test or chi-square test, referring to the significance of the difference between females and males.

Table 2. Summary statistics of PM_2.5 compositions, O₃ and BDNF promoter methylation levels in this panel study.

		Baseline (in 2011)		Follow-up (in 2015)		P ^c
		Mean (SD)^a	Median (IQR)^b	Mean (SD) ^a	Median (IQR) ^b
Air pollutants (μg/m^3)	PM2.5	96.44 (2.70)	96.38 (1.33)	100.36 (2.72)	99.93 (0.19)	<0.0001
	SO4^2-	15.63 (0.41)	15.59 (0.03)	15.88 (0.42)	15.78 (0.06)	<0.0001
	NO3^−	15.28 (0.64)	15.05 (0.06)	16.97 (0.61)	16.74 (0.15)	<0.0001
	NH4^+	10.35 (0.37)	10.23 (0.03)	11.05 (0.33)	10.94 (0.05)	<0.0001
	OM	24.57 (0.99)	24.29 (0.13)	26.16 (1.05)	25.84 (0.13)	<0.0001
	BC	4.92 (0.14)	4.92 (0.11)	4.92 (0.14)	4.91 (0.04)	0.0021
	O3	97.75 (1.11)	97.20 (0.67)	98.07 (1.49)	97.43 (0.40)	<0.0001
BDNF promoter methylation	lnCpG1^d	−3.21 (4.13)	−6.91 (7.65)	−4.42 (4.06)	−6.91 (7.67)	0.1000
	lnCpG2	1.31 (2.39)	1.64 (0.98)	2.01 (1.03)	1.95 (0.61)	0.0001
	lnCpG3	−2.63 (4.09)	−0.19 (8.04)	−4.24 (4.14)	−6.91 (8.27)	0.0572
	lnCpG4	−0.35 (3.32)	1.03 (0.87)	−2.68 (4.09)	0.11 (8.08)	<0.0001
	lnCpG5	−0.27 (3.38)	1.08 (1.03)	−0.98 (3.56)	0.57 (8.22)	0.0046
	lnCpG6	0.88 (2.78)	1.63 (0.67)	0.79 (2.74)	1.49 (0.70)	0.1747
	lnCpG7	−3.40 (4.04)	−6.91 (7.83)	−3.20 (4.03)	−6.91 (8.03)	0.7598

^aMean (SD) represents the mean levels and standard deviations of levels of exposure to air pollutants during the three years before 2011 (or 2015), or those of participants’ methylation levels in 2011 (or 2015).

^bMedian (IQR) represents the median levels and interquartile ranges of levels of exposure to air pollutants during the three years before 2011 (or 2015), or those of participants’ methylation levels in 2011 (or 2015).

^cP for rank-sum test, referring to the significance of the difference in air pollutant exposure or methylation levels during the two time periods.

^dlnCpG represents the logarithmically transformed methylation levels of the corresponding sites.

Table 3. The percent changes of BDNF promoter methylation levels associated with each interquartile range increase of PM_2.5 compositions and O_3..

Air pollutants (per IQR increase; μg/m^3)	% Change (95%CI)
PM2.5
CpG2	35 (6, 64)
CpG4	-92 (−153, −31)
CpG5	−52 (−107, 3)
SO4^2-
CpG2	63 (31, 95)
CpG4	-125 (−194, −55)
CpG5	−5 (−67, 58)
NO3^−
CpG2	48 (5, 90)
CpG4	-181 (−270, −93)
CpG5	-99 (−178, −19)
NH4^+
CpG2	37 (−1, 75)
CpG4	-153 (−232, −74)
CpG5	-90 (−161, −19)
OM
CpG2	29 (−3, 61)
CpG4	-103 (−171, −36)
CpG5	-62 (−123, −2)
BC
CpG2	4 (−8, 16)
CpG4	−4 (−29, 21)
CpG5	−7 (−30, 15)
O3
CpG2	−2 (−29, 24)
CpG4	−17 (−73, 40)
CpG5	−47 (−96, 2)

Bold indicates that the estimates are statistically significant. Models were adjusted for sex, age, education, physical, occupation, smoking, cardiovascular disease, respiratory diseases, and diabetes.

Abbreviations: SO₄^2-, sulfate; NO₃⁻, nitrate; NH₄⁺, ammonium; OM, organic matter; BC, black carbon; PM_2.5, particulate matter ≤2.5 μm in diameter; O₃, ozone; CI, confidence interval; BDNF, Brain-derived neurotrophic factor.

Figure 1. The joint and individual effects of PM_2.5 compositions and O₃ on BDNF promoter methylation using BKMR models.

(a) The joint effects (percent change, 95% CI) of air pollution mixtures on BDNF promoter methylation using the BKMR model. This plot shows the percent change in each CpG methylation level when all pollutants are fixed at a certain percentile compared to their lowest level. (b) Individual pollutant effects (percent change, 95% CI) on BDNF promoter methylation when other pollutants are fixed at a specific quantile (25th, 50th, 75th). Models were adjusted for sex, age, education, physical, occupation, smoking, cardiovascular disease, respiratory diseases, and diabetes.

Abbreviations: SO42-, sulfate; NO3-, nitrate; NH4+, ammonium; OM, organic matter; BC, black carbon; PM2.5, particulate matter ≤2.5 μm in diameter; O3, ozone; CI, confidence interval; BDNF, Brain-derived neurotrophic factor.

Figure 2. The percent changes of BDNF promoter methylation levels (CpG2) associated with each interquartile range increase of PM_2.5 compositions (μg/m³) in different O₃ exposure levels.

* P-interaction <0.1. ** P-interaction <0.05. Models were adjusted for sex, age, education, physical, occupation, smoking, cardiovascular disease, respiratory diseases, and diabetes.

Abbreviations: SO42-, sulfate; NO3-, nitrate; NH4+, ammonium; OM, organic matter; BC, black carbon; PM2.5, particulate matter ≤2.5 μm in diameter; O3, ozone; CI, confidence interval; BDNF, Brain-derived neurotrophic factor.