Demographic and clinical characteristics of the study population
A total of 90 idiopathic PD patients and their healthy spouses from the same household were enrolled in this study. Demographic and clinical characteristics of the study population are shown in Table 1. No significant difference in mean age was observed between the patients with PD and the control groups (65.76 ± 9.90 vs control: 64.23 ± 9.14, P = 0.285); however, there were more male patients in the PD group than in control group (53 male /37 female vs 37 male/53 female, P = 0.017). Among the subjects, 44 patients with PD and their spouses were from the urban area in Shanghai City, whereas the others were recruited from the rural area of Tonglu County in Hangzhou City. There were no differences in the age and sex distribution between PD patients and controls in these two subgroups.
Table 1
Demographic and clinical characteristics of the participants
|
Total (n = 180)
|
Urban area (n = 88)
|
Rural area (n = 92)
|
|
PD (n = 90)
|
Con (n = 90)
|
P value
|
PD (n = 44)
|
Con (n = 44)
|
P value
|
PD (n = 46)
|
Con (n = 46)
|
P value
|
Age (years)
|
65.76 ± 9.90
|
64.23 ± 9.14
|
0.285
|
64.59 ± 8.72
|
63.09 ± 9.25
|
0.436
|
66.87 ± 10.88
|
65.33 ± 9.00
|
0.460
|
Sex
|
|
|
0.017*
|
|
|
0.088
|
|
|
0.095
|
Male
|
53 (58.9%)
|
37 (41.1%)
|
|
26 (59.1%)
|
18(40.9%)
|
|
27 (58.7%)
|
19 (41.3%)
|
|
Female
|
37 (41.1%)
|
53 (58.9%)
|
|
18 (40.9%)
|
26(59.1%)
|
|
19 (41.3%)
|
27 (58.7%)
|
|
Age of onset (years)
|
59.83 ± 10.43
|
NA
|
|
59.39 ± 8.83
|
NA
|
|
60.26 ± 11.84
|
NA
|
|
Disease duration (years)
|
5.60 ± 4.48
|
NA
|
|
4.18 ± 3.72
|
NA
|
|
6.96 ± 4.76
|
NA
|
|
H&Y stage
|
2.29 ± 0.99
|
NA
|
|
1.93 ± 0.78
|
NA
|
|
2.59 ± 1.12
|
NA
|
|
UPDRS Part Ⅰ
|
4.32 ± 3.03
|
NA
|
|
3.11 ± 2.36
|
NA
|
|
5.48 ± 3.17
|
NA
|
|
UPDRS Part Ⅱ
|
14.00 ± 11.53
|
NA
|
|
10.84 ± 11.27
|
NA
|
|
17.02 ± 11.07
|
NA
|
|
UPDRS Part Ⅲ
|
28.97 ± 18.51
|
NA
|
|
21.20 ± 13.89
|
NA
|
|
36.39 ± 19.45
|
NA
|
|
UPDRS Part Ⅳ
|
2.79 ± 3.14
|
NA
|
|
1.59 ± 2.14
|
NA
|
|
3.93 ± 3.52
|
NA
|
|
UPDRS total
|
49.53 ± 31.97
|
NA
|
|
35.64 ± 20.92
|
NA
|
|
62.83 ± 35.12
|
NA
|
|
NMS
|
7.74 ± 4.80
|
NA
|
|
6.30 ± 3.83
|
NA
|
|
9.13 ± 5.26
|
NA
|
|
HAMD
|
7.77 ± 8.37
|
NA
|
|
5.61 ± 7.09
|
NA
|
|
9.83 ± 9.03
|
NA
|
|
HAMA
|
9.33 ± 8.63
|
NA
|
|
7.14 ± 8.17
|
NA
|
|
11.43 ± 8.61
|
NA
|
|
MMSE
|
25.96 ± 4.75
|
NA
|
|
27.66 ± 4.63
|
NA
|
|
24.33 ± 4.31
|
NA
|
|
MoCA
|
22.17 ± 5.49
|
NA
|
|
24.48 ± 4.53
|
NA
|
|
19.96 ± 5.45
|
NA
|
|
Data were shown as mean ± SD |
Abbreviations: PD, Parkinson’s disease; Con, control; H&Y stage, Hoehn and Yahr stage; UPDRS, Unified Parkinson’s Disease Rating Scale; NMS, Non-Motor Symptoms; |
HAMD, Hamilton Depression Scale; HAMA, Hamilton Anxiety Scale; MMSE, Mini Mental State Examination; MoCA, Montreal Cognitive Assessment; SD, standard deviation. |
UPDRS scores were obtained during the on-phase at the outpatient clinic. *: P < 0.05. |
Detected pesticides in PD patients and controls
All the examined pesticides were present in any of the samples (Table 2). In all subjects, α-HCH (51.1% vs 34.4%, P = 0.024), β-HCH (77.8% vs 63.3%, P = 0.034), aldrin (96.7% vs 88.9%, P = 0.044) and p,p’-DDE (95.6% vs 84.4%, P = 0.013) were more detectable in PD patients compared with controls. While there was no difference in serum pesticide levels between the two groups from the urban area (P > 0.05), in those from the rural area, heptachlor (60.9% vs 28.3%, P = 0.002) and p,p’-DDE (97.8% vs 80.4%, P = 0.007) were more often detectable in patients with PD than controls.
Table 2
Detected pesticides in PD patients and controls
Pesticides
|
Total (n = 180)
|
Urban area (n = 88)
|
Rural area (n = 92)
|
PD (n = 90)
|
Con (n = 90)
|
P value
|
PD (n = 44)
|
Con (n = 44)
|
P value
|
PD (n = 46)
|
Con (n = 46)
|
P value
|
α-HCH
|
46 (51.1%)
|
31 (34.4%)
|
0.024*
|
21 (47.7%)
|
15 (34.1%)
|
0.193
|
25 (54.3%)
|
16 (34.8%)
|
0.059
|
β-HCH
|
70 (77.8%)
|
57 (63.3%)
|
0.034*
|
31 (70.5%)
|
24 (54.5%)
|
0.123
|
39 (84.8%)
|
33 (71.7%)
|
0.129
|
γ-HCH
|
58 (64.4%)
|
50 (55.6%)
|
0.224
|
26 (59.1%)
|
24 (54.5%)
|
0.667
|
32 (69.6%)
|
26 (56.5%)
|
0.195
|
δ-HCH
|
68 (75.6%)
|
57 (63.3%)
|
0.075
|
35 (79.5%)
|
33 (75.0%)
|
0.611
|
33 (71.7%)
|
24 (52.2%)
|
0.053
|
Propanil
|
88 (97.8%)
|
87 (96.7%)
|
0.650
|
42 (95.5%)
|
42 (95.5%)
|
1.000
|
46 (100%)
|
45 (97.8%)
|
0.315
|
Vinclozolin
|
86 (95.6%)
|
89 (98.9%)
|
0.174
|
42 (95.5%)
|
43 (97.7%)
|
0.557
|
44 (95.7%)
|
46 (100%)
|
0.153
|
Heptachlor
|
42 (46.7%)
|
31 (34.4%)
|
0.095
|
14 (31.8%)
|
18 (40.9%)
|
0.375
|
28 (60.9%)
|
13 (28.3%)
|
0.002**
|
Aldrin
|
87 (96.7%)
|
80 (88.9%)
|
0.044*
|
41 (93.2%)
|
37 (84.1%)
|
0.179
|
46 (100%)
|
43 (93.5%)
|
0.078
|
Dieldrin
|
86 (95.6%)
|
85 (94.4%)
|
0.732
|
41 (93.2%)
|
40 (90.9%)
|
0.694
|
45 (97.8%)
|
45 (97.8%)
|
1.000
|
Endosulfan
|
83 (92.2%)
|
78 (86.7%)
|
0.225
|
40 (90.9%)
|
38 (86.4%)
|
0.502
|
43 (93.5%)
|
40 (87.0%)
|
0.292
|
Hexachlorobenzene
|
55 (61.1%)
|
52 (57.8%)
|
0.649
|
17 (38.6%)
|
22 (50.0%)
|
0.283
|
38 (82.6%)
|
30 (65.2%)
|
0.058
|
Quintozene
|
69 (76.7%)
|
64 (71.1%)
|
0.396
|
29 (65.9%)
|
31 (70.5%)
|
0.647
|
40 (87.0%)
|
33 (71.7%)
|
0.071
|
p,p’-DDE
|
86 (95.6%)
|
76 (84.4%)
|
0.013*
|
41 (93.2%)
|
39 (88.6%)
|
0.458
|
45 (97.8%)
|
37 (80.4%)
|
0.007**
|
p,p’-DDD
|
81 (90.0%)
|
76 (84.4%)
|
0.264
|
41 (93.2%)
|
35 (79.5%)
|
0.062
|
40 (87.0%)
|
41 (89.1%)
|
0.748
|
o,p’-DDT
|
85 (94.4%)
|
81 (90.0%)
|
0.266
|
41 (93.2%)
|
39 (88.6%)
|
0.458
|
44 (95.7%)
|
42 (91.3%)
|
0.398
|
p,p’-DDT
|
79 (87.8%)
|
74 (82.2%)
|
0.297
|
37 (84.1%)
|
37 (84.1%)
|
1.000
|
42 (91.3%)
|
37 (80.4%)
|
0.135
|
Parathion-methyl
|
47 (52.2%)
|
41 (45.6%)
|
0.371
|
24 (54.5%)
|
23 (52.3%)
|
0.831
|
23 (50.0%)
|
18 (39.1%)
|
0.294
|
Methidathion
|
43 (47.8%)
|
36 (40.0%)
|
0.293
|
19 (43.2%)
|
17 (38.6%)
|
0.665
|
24 (52.2%)
|
19 (41.3%)
|
0.296
|
Phosalone
|
48 (53.3%)
|
50 (55.6%)
|
0.765
|
26 (59.1%)
|
23 (52.3%)
|
0.520
|
22 (47.8%)
|
27 (58.7%)
|
0.296
|
Abbreviations: PD, Parkinson’s disease; Con, control; α-HCH, α-hexachlorocyclohexane; β-HCH, β-hexachlorocyclohexane; γ-HCH, γ-hexachlorocyclohexane; δ-HCH, δ-hexachlorocyclohexane; p,p’-DDE, p,p’-dichloro-diphenyldichloroethylene; p,p’-DDD, p,p’-Dichlorodiphenyldichloroethane; o,p’-DDT, o,p’-dichloro-diphenyl-trichloroethane, p,p’-DDT, p,p’-dichloro-diphenyl-trichloroethane. *: P < 0.05, **: P < 0.01. |
Serum levels of pesticides in PD patients and controls
Serum concentration of pesticides are shown in Table 3. In previous studies, nondetects were designated at half of the LOD [17, 20]. In the overall population, mean levels of α-HCH (80.19 ± 51.54 vs 1.79 ± 0.29, P < 0.001), β-HCH (1126.40 ± 255.69 vs 349.88 ± 90.63, P = 0.012), γ-HCH (583.30 ± 189.10 vs 39.62 ± 17.16, P = 0.031), δ-HCH (12.09 ± 2.12 vs 5.82 ± 1.33, P = 0.002), propanil (29.48 ± 4.12 vs 18.06 ± 3.02, P < 0.001), heptachlor (45.00 ± 11.81 vs 1.50 ± 0.15, P < 0.001), dieldrin (14.18 ± 1.18 vs 10.29 ± 1.11, P = 0.003), hexachlorobenzene (375.39 ± 95.87 vs 65.46 ± 12.79, P = 0.018), p,p’-DDE (149.52 ± 29.28 vs 53.30 ± 11.68, P = 0.001) and o,p’-DDT (10.35 ± 1.15 vs 6.85 ± 0.91, P = 0.009) were significantly higher in PD group than in control group. In the urban cohort, the levels of propanil, dieldrin and o,p’-DDT were higher in PD patients than in control subjects (22.61 ± 6.58 vs 14.07 ± 3.99, P = 0.012; 14.44 ± 1.57 vs 7.13 ± 1.16, P < 0.001; 10.70 ± 1.87 vs 5.60 ± 0.78, P = 0.042). Whereas in the rural cohort, higher levels of α-HCH (71.80 ± 64.23 vs 1.98 ± 0.49, P < 0.001), β-HCH (1589.62 ± 364.09 vs 357.02 ± 132.45, P = 0.002), γ-HCH (1133.57 ± 353.00 vs 69.24 ± 33.11, P = 0.012), δ-HCH (7.04 ± 1.78 vs 3.40 ± 0.95, P = 0.004), propanil (36.04 ± 4.9 vs 21.88 ± 4.48, P = 0.003), heptachlor (62.26 ± 16.02 vs 1.48 ± 0.21, P < 0.001), hexachlorobenzene (712.56 ± 174.25 vs 106.14 ± 23.01, P < 0.001), quintozene (816.91 ± 188.11 vs 319.31 ± 125.02, P = 0.002), p,p’-DDE (272.42 ± 51.05 vs 95.39 ± 21.12, P = 0.001) and methidathion (3.52 ± 0.56 vs 3.04 ± 0.66, P = 0.039) were observed in PD patients compared to healthy subjects.
Table 3
Serum levels of pesticides in PD patients and controls (ng/g lipid)
Pesticides
|
Total (n = 180)
|
|
Urban area (n = 88)
|
Rural area (n = 92)
|
PD (n = 90)
|
Con (n = 90)
|
P value
|
PD (n = 44)
|
Con (n = 44)
|
P value
|
PD (n = 46)
|
Con (n = 46)
|
P value
|
α-HCH
|
80.19 ± 51.54
|
1.79 ± 0.29
|
< 0.001***
|
88.95 ± 82.04
|
1.58 ± 0.31
|
0.059
|
71.80 ± 64.23
|
1.98 ± 0.49
|
< 0.001***
|
β-HCH
|
1126.40 ± 255.69
|
349.88 ± 90.63
|
0.012*
|
642.12 ± 347.95
|
342.4 ± 124.80
|
0.399
|
1589.62 ± 364.09
|
357.02 ± 132.45
|
0.002**
|
γ-HCH
|
583.30 ± 189.10
|
39.62 ± 17.16
|
0.031*
|
8.02 ± 1.92
|
8.64 ± 2.07
|
0.51
|
1133.57 ± 353.00
|
69.24 ± 33.11
|
0.012*
|
δ-HCH
|
12.09 ± 2.12
|
5.82 ± 1.33
|
0.002**
|
17.36 ± 3.79
|
8.36 ± 2.50
|
0.07
|
7.04 ± 1.78
|
3.40 ± 0.95
|
0.004**
|
Propanil
|
29.48 ± 4.12
|
18.06 ± 3.02
|
< 0.001***
|
22.61 ± 6.58
|
14.07 ± 3.99
|
0.012*
|
36.04 ± 4.91
|
21.88 ± 4.48
|
0.003**
|
Vinclozolin
|
21.76 ± 9.10
|
9.49 ± 0.98
|
0.267
|
16.29 ± 5.37
|
9.53 ± 1.26
|
0.664
|
27.00 ± 17.11
|
9.46 ± 1.5
|
0.226
|
Heptachlor
|
45.00 ± 11.81
|
1.50 ± 0.15
|
< 0.001***
|
26.94 ± 17.18
|
1.52 ± 0.20
|
0.617
|
62.26 ± 16.02
|
1.48 ± 0.21
|
< 0.001***
|
Aldrin
|
33.90 ± 4.35
|
31.73 ± 4.62
|
0.122
|
30.52 ± 6.16
|
35.75 ± 7.57
|
0.713
|
37.14 ± 6.18
|
27.89 ± 5.42
|
0.062
|
Endosulfan
|
26.89 ± 7.20
|
15.27 ± 2.92
|
0.114
|
31.44 ± 13.60
|
15.34 ± 3.95
|
0.499
|
22.54 ± 5.54
|
15.19 ± 4.32
|
0.144
|
Dieldrin
|
14.18 ± 1.18
|
10.29 ± 1.11
|
0.003**
|
14.44 ± 1.57
|
7.13 ± 1.16
|
< 0.001***
|
13.93 ± 1.75
|
13.31 ± 1.77
|
0.645
|
Hexachlorobenzene
|
375.39 ± 95.87
|
65.46 ± 12.79
|
0.018*
|
22.88 ± 5.74
|
22.93 ± 5.53
|
0.815
|
712.56 ± 174.25
|
106.14 ± 23.01
|
< 0.001***
|
Quintozene
|
661.71 ± 151.37
|
349.35 ± 95.94
|
0.066
|
499.46 ± 238.93
|
380.74 ± 147.72
|
0.77
|
816.91 ± 188.11
|
319.31 ± 125.02
|
0.002**
|
p,p’-DDE
|
149.52 ± 29.28
|
53.30 ± 11.68
|
0.001**
|
21.03 ± 4.94
|
9.30 ± 1.282
|
0.08
|
272.42 ± 51.05
|
95.39 ± 21.12
|
0.001**
|
p,p’-DDD
|
14.89 ± 2.28
|
11.99 ± 1.82
|
0.267
|
15.55 ± 3.72
|
10.25 ± 1.93
|
0.468
|
14.26 ± 2.74
|
13.66 ± 3.05
|
0.369
|
o,p’-DDT
|
10.35 ± 1.15
|
6.85 ± 0.91
|
0.009**
|
10.70 ± 1.87
|
5.60 ± 0.78
|
0.042*
|
10.01 ± 1.38
|
8.05 ± 1.61
|
0.132
|
p,p’-DDT
|
42.94 ± 7.20
|
36.29 ± 5.35
|
0.413
|
42.84 ± 12.22
|
38.07 ± 7.40
|
0.98
|
43.04 ± 8.03
|
34.60 ± 7.76
|
0.115
|
Parathion-methyl
|
6.72 ± 1.01
|
9.81 ± 3.78
|
0.07
|
6.88 ± 1.27
|
14.14 ± 7.58
|
0.404
|
6.57 ± 1.59
|
5.68 ± 1.44
|
0.057
|
Methidathion
|
3.31 ± 0.49
|
3.07 ± 0.50
|
0.056
|
3.10 ± 0.79
|
3.10 ± 0.77
|
0.428
|
3.52 ± 0.56
|
3.04 ± 0.66
|
0.039*
|
Phosalone
|
12.35 ± 1.6
|
12.21 ± 1.79
|
0.602
|
13.86 ± 2.53
|
10.37 ± 1.60
|
0.413
|
10.91 ± 2.11
|
13.96 ± 3.14
|
0.975
|
Abbreviations: PD, Parkinson’s disease; Con, control; α-HCH, α-hexachlorocyclohexane; β-HCH, β-hexachlorocyclohexane; γ-HCH, γ-hexachlorocyclohexane; δ-HCH, δ-hexachlorocyclohexane; p,p’-DDE, p,p’-dichloro-diphenyldichloroethylene; p,p’-DDD, p,p’-Dichlorodiphenyldichloroethane; o,p’-DDT, o,p’-dichloro-diphenyl-trichloroethane, p,p’-DDT, p,p’-dichloro-diphenyl-trichloroethane. *: P < 0.05, **: P < 0.01, ***: P < 0.001 |
Association between serum levels of pesticides and PD risk
To investigate the association between concentrations of pesticides and risk of PD, α-HCH, β-HCH, γ-HCH, δ-HCH, propanil, heptachlor, dieldrin, hexachlorobenzene, p,p’-DDE and o,p’-DDT levels were divided into tertiles as indicated by the distribution of concentrations of pesticides in controls [17, 21]. Nondetects were designated at half of the LOD, and the OR was estimated using logistic regression analysis.
As shown in Table 4, after adjusting for sex, age and region, the risk of PD increased with α-HCH level (P = 0.002), the adjusted OR was 3.635 (95% CI: 1.507–8.769) and 4.518 (95% CI: 1.903–10.725) in Tertile 2 and 3 groups; the risk of PD was also increased with β-HCH level (P = 0.044), and the adjusted OR was 2.701 (95% CI: 1.236-5.90) in Tertile 3 group; the risk of PD was increased with δ-HCH (P = 0.023), and the adjusted OR was 3.017 (95% CI: 1.371–6.636) in Tertile 3 group; the risk of PD was increased with propanil concentration (P < 0.001), and the adjusted OR was 3.327 (1.561–7.089) in Tertile 3 group (Table 4). Moreover, the concentration of heptachlor was positively associated with the risk of PD (P = 0.010), and this association was significant in the Tertile 2 and 3 groups (OR: 2.774, 95% CI: 1.197–6.431; OR: 3.517, 95% CI: 1.542–8.023); the concentration of dieldrin was associated with PD risk (P = 0.015), and this association was significant in Tertile 2 (OR: 2.516, 95% CI: 1.099–5.761) and Tertile 3 group (OR: 3.270, 95% CI: 1.455–7.350); Hexachlorobenzene concentration was associated with the risk of PD (P = 0.028), however, this association was not significant in Tertile 2 or Tertile 3 compared with Tertile 1 group. The concentration of p,p’-DDE and o,p’-DDT was also positively associated with the risk of PD (P = 0.017 and 0.025, respectively), and this association was significant in the Tertile 3 group (OR: 2.652, 95% CI: 1.252–5.614 and OR: 2.967, 95% CI: 1.354-6.500).
Table 4
Association of the serum levels of pesticides and risk of PD
Categorical levels of pesticides
|
PD (n = 90)
|
Con (n = 90)
|
OR (95% CI)
|
P value a
|
OR (95% CI)
|
P value b
|
α-HCH
|
|
|
|
0.002**
|
|
0.013*
|
Tertile 1
|
30(33.3%)
|
10(11.1%)
|
1[Reference]
|
|
|
|
Tertile 2
|
30(33.3%)
|
35(38.9%)
|
3.635[1.507–8.769]
|
0.004**
|
2.814[1.130–7.009]
|
0.026*
|
Tertile 3
|
30(33.3%)
|
45(50.0%)
|
4.518[1.903–10.725]
|
0.001**
|
3.874[1.573–9.541]
|
0.003**
|
β-HCH
|
|
|
|
0.044*
|
|
|
Tertile 1
|
30(33.3%)
|
17(18.9%)
|
1[Reference]
|
|
|
|
Tertile 2
|
30(33.3%)
|
32(35.6%)
|
1.904[0.863–4.199]
|
0.111
|
|
|
Tertile 3
|
30(33.3%)
|
41(45.6%)
|
2.701[1.236–5.901]
|
0.013*
|
|
|
γ-HCH
|
|
|
|
0.208
|
|
|
Tertile 1
|
30(33.3%)
|
19(21.1%)
|
1[Reference]
|
|
|
|
Tertile 2
|
30(33.3%)
|
36(37.8%)
|
NA
|
0.682
|
|
|
Tertile 3
|
30(33.3%)
|
37(41.1%)
|
NA
|
0.238
|
|
|
δ-HCH
|
|
|
|
0.023*
|
|
|
Tertile 1
|
30(33.3%)
|
15(16.7%)
|
1[Reference]
|
|
|
|
Tertile 2
|
30(33.3%)
|
31(34.4%)
|
2.087[0.925–1.095]
|
0.075
|
|
|
Tertile 3
|
30(33.3%)
|
44(48.9%)
|
3.017[1.371–6.636]
|
0.006**
|
|
|
Propanil
|
|
|
|
< 0.001***
|
|
0.002**
|
Tertile 1
|
30(33.3%)
|
17(18.9%)
|
1[Reference]
|
|
|
|
Tertile 2
|
30(33.3%)
|
16(17.8%)
|
0.819[0.342–1.962]
|
0.655
|
1.009[0.407-2.500]
|
0.984
|
Tertile 3
|
30(33.3%)
|
57(63.3%)
|
3.327[1.561–7.089]
|
0.002**
|
3.298[1.505–7.227]
|
< 0.001***
|
Heptachlor
|
|
|
|
0.010*
|
|
|
Tertile 1
|
30(33.3%)
|
12(13.3%)
|
1[Reference]
|
|
|
|
Tertile 2
|
30(33.3%)
|
34(37.8%)
|
2.774[1.197–6.431]
|
0.017*
|
|
|
Tertile 3
|
30(33.3%)
|
44(48.9%)
|
3.517 [1.542–8.023]
|
0.003**
|
|
|
Dieldrin
|
|
|
|
0.015*
|
|
|
Tertile 1
|
30(33.3%)
|
13(14.4%)
|
1[Reference]
|
|
|
|
Tertile 2
|
30(33.3%)
|
33(36.7%)
|
2.516[1.099–5.761]
|
0.029*
|
|
|
Tertile 3
|
30(33.3%)
|
44(48.9%)
|
3.270[1.455–7.350]
|
0.004**
|
|
|
Hexachlorobenzene
|
|
|
|
0.028*
|
|
|
Tertile 1
|
30(33.3%)
|
25(27.8%)
|
1[Reference]
|
|
|
|
Tertile 2
|
30(33.3%)
|
18(20.0%)
|
0.707[0.317–1.578]
|
0.328
|
|
|
Tertile 3
|
30(33.3%)
|
47(52.2%)
|
1.899[0.970–3.875]
|
0.078
|
|
|
p,p’-DDE
|
|
|
|
0.017*
|
|
|
Tertile 1
|
30(33.3%)
|
19(21.1%)
|
1[Reference]
|
|
|
|
Tertile 2
|
30(33.3%)
|
23(25.6%)
|
1.164[0.520–2.606]
|
0.712
|
|
|
Tertile 3
|
30(33.3%)
|
48(53.3%)
|
2.652[1.252–5.614]
|
0.011*
|
|
|
o,p’-DDT
|
|
|
|
0.025*
|
|
|
Tertile 1
|
30(33.3%)
|
15(16.7%)
|
1[Reference]
|
|
|
|
Tertile 2
|
30(33.3%)
|
30(33.3%)
|
1.915[0.850–4.315]
|
0.117
|
|
|
Tertile 3
|
30(33.3%)
|
45(50.0%)
|
2.967[1.354-6.500]
|
0.007**
|
|
|
Abbreviations: PD, Parkinson’s disease; Con, control; NA, not available; α-HCH, α-hexachlorocyclohexane; β-HCH, β-hexachlorocyclohexane; γ-HCH, γ-hexachlorocyclohexane, δ-HCH, δ-hexachlorocyclohexane; p,p’-DDE, p,p’-dichloro-diphenyldichloroethylene, o,p’-DDT, o,p’-dichloro-diphenyl-trichloroethane; OR: Odds Ratio; CI: confidence interval; LOD: the limit of detection. |
a: Adjusted by age, gender and region; b: Adjusted by age, gender, region and pesticides. *: P < 0.05, **: P < 0.01, ***: P < 0.001; |
After adjusting for sex, age, region and pesticides levels, α-HCH and propanil concentrations were positively associated with risk of PD (P = 0.013; P = 0.002), and this association was significant in the Tertile 2 and 3 groups for α-HCH (OR: 2.814, 95% CI: 1.130–7.009; OR: 3.874, 95% CI: 1.573–9.541, respectively) and in the highest Tertile 3 group for propanil (OR: 3.298, 95% CI: 1.505–7.227) compared with the reference category.
Correlation between pesticides and clinical features of PD patients
We compared the difference in clinical characteristics of PD patients with different serum levels of pesticides. Although some of the clinical characteristics of PD patients varied among Tertile 1, 2 and 3 groups for a-HCH, β-HCH, hexachlorobenzene and o,p’-DDT, there was no significant association between these characteristics and serum levels of four pesticides (data not shown). HAMD, HAMA and MoCA scores also differed among the Tertile 1, 2 and 3 groups for dieldrin (HAMD: 2.69 ± 0.77, 5.70 ± 1.11, 10.82 ± 1.44, P = 0.005; HAMA: 5.69 ± 1.32, 7.30 ± 1.41, 11.93 ± 1.39, P = 0.015; MoCA: 26.00 ± 3.49, 21.97 ± 0.92, 21.18 ± 0.86, P = 0.018). A multiple comparison test revealed that the HAMD score was significantly higher in the Tertile 3 group compared to Tertile1 and 2 groups (P = 0.004 and 0.017, respectively), while the MoCA score was lower in the Tertile 3 group than Tertile 1 group (P = 0.015). Meanwhile, multiple comparison test showed no differences between groups in terms of HAMA score. After controlling for age and sex, serum level of dieldrin was positively associated with HAMD score and negatively associated with MoCA score in PD patients (P < 0.001, P = 0.042).
Genotype and allele distributions of candidate SNPs in PD patients and controls
We analyzed the genotype and allele distributions of candidate SNPs located in PD-related genes and genes related to pesticides transportation and metabolism. All the observed genotype or allele frequencies did not differ from the expected frequencies according to Hardy-Weinberg equilibrium. There were no significant differences in the genotype or allele distributions of the 10 candidate SNPs between PD patients and controls (Table e-2 in Additional file 1).
Effect of interaction between genotype and pesticides on the PD risk
The potential interaction between serum levels of pesticides and the genotype of the candidate SNPs on PD risk was evaluated with an unconditional logistic regression model. After controlling for confounding factors such as sex, age and region, statistically significant interactions were found between rs11931074 polymorphism in the SNCA gene and α-HCH (OR: 2.08; 95% CI: 1.131–3.826; P = 0.018), between rs11931074 in SNCA gene and β-HCH (OR: 2.08; 95% CI: 1.003–3.218; P = 0.049), and between rs16940758 in MAPT and δ-HCH (OR: 2.48; 95% CI: 1.049–5.880 P = 0.039), causing an increased risk for PD.
Effect of α-HCH and propanil on oxidative injury and α-synuclein aggregation in neuronal cells
Given that α-HCH and propanil levels were associated with increased risk of PD, we investigated the molecular basis for this observation using SH-SY5Y cells. We found that cell viability was decreased in a dose-dependent manner upon α-HCH or propanil stimulation. The effective concentration to induce about 25% and 50% decrease in cell viability was about 700 and 1000 µM for α-HCH (Fig. A) and 100 and 200 µM for propanil (Fig. B), respectively. We found here that α-HCH and propanil increased the production of ROS (Fig. C, D) while decreasing the ΔΨm in neuronal cells (Fig. E, F).
We further investigated whether α-HCH or propanil had an effect on α-synuclein levels. Results showed that α-synuclein aggregation was unaffected by α-HCH in SH-SY5Y cells, but was induced in a dose-dependent manner by propanil (Figure G, H).