Global DNA hypomethylation is associated with in utero exposure to cotinine and perfluorinated alkyl compounds

Figures & data

Figure 1 Global DNA methylation index in cord blood serum DNA of 11 newborns exposed in utero to tobacco smoke constituents from maternal smoking, 11 newborns whose mothers were passive smokers and eight newborns whose mothers were nonsmokers. (Box plots).

Figure 2 (A) Linear relationship between the natural log of cotinine in cord blood serum and the global DNA methylation index in 30 newborns with high (11), low (11) and very low (8) cotinine serum levels. (B) Linear relationship between the natural log of PFOA in cord blood serum and the global DNA methylation index in 30 newborns. (C) Linear relationship between the natural log of PFOS in cord blood serum and the global DNA methylation index in 30 newborns.

Table 1 Characteristics of infants selected for epigenetics study compared with all eligible infants, Baltimore THREE study

		Epigenetics study	Eligible births (not included)
		n = 30	n = 83
	n (%)	n (%)	p value*
Male infant	15 (50%)	47 (57%)	0.49
African American	27 (90%)	61 (74%)	0.54
Mother <18 yr	4 (13%)	7 (9%)	0.45
Mother >30 yr	7 (23%)	23 (28%)	0.80
Baltimore residence	25 (83%)	60 (72%)	0.22
Parity: first birth	11 (37%)	48 (58%)	0.65
Prenatal care first 4 months	23 (77%)	72 (88%)	0.15
Smoking by history	8 (27%)	9 (11%)	0.04
	Mean (SD)	Mean (SD)	p value**
Serum cotinine (ng/ml)
Very Low (VL) (<1 ng/ml)	0.06 (0.04)	0.16 (0.22)	0.20
Low (L) (1–10 ng/ml)	2.0 (1.3)	2.5 (2.1)	0.59
High (H) (>10 ng/ml)	135.6 (94.3)	121.8 (87.7)	0.79
Serum cotinine (ng/ml) by smoking history
No	11.8 (34.2)	0.16 (0.23)	0.004
Yes	140.1 (106.4)	68.5† (88.5)	0.15
Serum cotinine (ng/ml) by smoking history and cotinine levels
Nonsmokers (No & cot-VL)	0.06 (0.02)	0.16 (0.03)	0.20
Passive smokers (No & cot-L)	2.0 (1.2)	§	N/A
Smokers (Yes &/or cot-H)	135.6‡ (94.3)	68.5† (88.5)	0.13
PFOA (ng/ml)	1.8 (0.89)	1.8 (1.09)	0.84
PFOS (ng/ml)	5.8 (3.12)	6.1 (3.55)	0.72
Birth weight (g)	3408 (378)	3336 (506)	0.48
Length (cm)	50.7 (1.8)	50.4 (2.5)	0.52
Ponderal index	2.61 (0.043)	2.60 (0.033)	0.88
Head circumference (cm)	33.9 (1.3)	33.9 (1.6)	0.84
Gestational age (days)	278.3 (6.9)	274.8 (7.6)	0.03
Paternal age (years)	27.4 (7.4)	28.0 (7.6)	0.74
Maternal prepregnancy BMI	27.8 (8.0)	26.2 (6.1)	0.30
DNA methylation (%5-mC)	21.0 (10.3)	-	N/A

* Chi-square.

** t-test.

§ All eligible passive smokers were included in this study.

† Two with no smoking history had cotinines in the active smoking range, 117 and 118 ng/mL respectively and are classified as smokers.

‡ One with a smoking history had cotinine below the active smoking range, 4 ng/mL.

Table 2 Results of linear models (pearson's correlations and slope beta values) for cotinine, PFOA and PFOS concentrations (log-transformed) and other selected study variables on %5-mC (n = 30), Baltimore THREE study

			Crude		Model 2§		Model 3§§
		r	beta	p value	beta	p value	beta	p value
Cotinine (ng/ml)
		-0.39	-0.048	0.04	-0.054	0.05	-0.043	0.06
Ln (Cotinine)
		-0.62	-1.99	<0.001	-2.11	<0.001	-1.91	0.001
Smoking status
	None (comparison)
	Passive	*	-8.07	0.051	-9.48	0.03	-8.17	0.06
	Active	*	-14.5	0.002	-15.3	0.001	-13.7	0.004
	PFOA (ng/ml)	-0.32	-3.74	0.08	-3.39	0.11	-3.20	0.15
	Ln (PFOA)	-0.35	-7.59	0.06	-7.00	0.07	-6.61	0.11
	PFOS (ng/ml)	-0.21	-0.71	0.26	-0.367	0.58	-0.52	0.42
	Ln (PFOS)	-0.28	-5.36	0.13	-3.45	0.37	-4.46	0.22
Maternal age (years)
	<20	*	-5.96	0.18
	20–29		(comparison)
	30+	*	-7.60	0.12
Maternal age (years)
		-0.138	-0.236	0.46
Gestational age (days)
		0.245	0.366	0.19
	Sex (male)	*	0.16	0.97
Prepregnancy BMI
		0.016	0.022	0.93
Birthweight (100 gm)
		-0.17	-0.46	0.37
Length (cm)
		-0.18	-1.03	0.33
Head circumference (cm)
		0.02	0.88	0.56
Ponderal index
		0.03	1.28	0.88

* N/A.

§ Adjusted for maternal age.

§§ Adjusted for gestational age.

Table 3 Quantification of serum Y chromosome human DNA (ng/ul) and serum total human DNA (ng/ul) obtained from umbilical cord blood of seven male infants, Baltimore THREE study

	Quantifiler Y human DNA (ng/µl)		Quantifiler human DNA (ng/µl)		Y human DNA/human DNA
Sample	Levels	Mean	Levels	Mean	Ratio
1	4.38	4.32	2.75	2.71
	4.26		2.66		1.6
2	0.18	0.16	0.08	0.09
	0.15		0.10		1.8
3	0.20	0.21	0.02	0.02
	0.22		0.02		8.7
4	3.93	4.08	2.94	2.80
	4.23		2.66		1.5
5	0.08	0.08	0.01	0.01
	0.08		0.01		15.5
6	0.46	0.44	0.05	0.03
	0.42		0.01		14.3
7	0.11	0.12	0.04	0.04
	0.14		0.04		3.4