3. Results
Study population . The study population included 134
pregnant women (age 33 ± 4 years). BMI was 22.6 ± 4.2
kg/m2. Pregnancy associated endocrine factors, such as
placental growth factor (PLGF) and pregnancy associated plasma protein A
(PAPP-A), were in the normal range, as was hCG (Table 1). Signs of
diabetes and dyslipidemias were not found. Specifically, median glucose
was 86.6 ± 14.8 mg/dL. LDL-C, non-high-density lipoprotein cholesterol
(non-HDL-C), HDL-C, and triglycerides (TG) were also within the normal
range (97.4 ± 22.1 mg/dL, 117.2 ± 25 mg/dL, 65.5 mg/dL and 99 ± 38.3
mg/dL, respectively). Levels of Lp(a) were 13.7 ± 19 mg/dL (Table 1).
Circulating levels of plasma PCSK9 were normally distributed, with a
mean of 193.7 ± 54.2 ng/mL (Figure 1). These levels were lower than
those previously described by us for non-pregnant women recruited in the
same geographical area (27). None of
these healthy women were on any drug treatment. The estimated level of
exposure to PM10, PM2.5, and
NO2, from the first week before the visit (week 0–1)
and 12 weeks previously (week 0–12), are depicted in Figure 2. The
similarities in pollutant concentrations across the weeks of exposure
were clearly observed. Mean PM10 and NO2concentrations remained beneath the annual regional air-quality
standards of 40 μg/m3. Mean PM2.5concentrations were slightly higher than annual limits, which are set at
25 micrograms per μg/m3.
Mean fetal crown-rump length at the time of exposure assessment was
62.4±5.2 mm. Nuchal translucency thickness, which is an ultrasound
marker for chromosomal and structural abnormalities, was within the
normal range in all cases, as well as fetal heart rate and ductus
venosus blood flow (Table 1). All pregnancies ended with the live birth
of a phenotypically normal neonate, at a mean gestational age of 38.7
1.4 weeks. Neonatal biometric parameters are presented in Table 1.
Univariate data analysis. None of the three air pollutants was
associated to circulating PCSK9 levels in the univariate analysis
(Supplemental Table 1). As expected, the main lipid parameters related
to CV risk, LDL-C (β = 0.605, SE = 0.235, p = 0.011) and non-HDL-C (β =
0.425, SE = 0.210, p = 0.045) were positively associated with PCSK9.
Inflammatory markers, which are linked to the initiation and progression
of atherosclerosis, were also evaluated. PCSK9 levels were positively
associated with the IL-6 (β = 3.447, SE = 1.711, p = 0.046) and
fibrinogen (β = 0.170, SE = 0.083, p = 0.043) levels. No relationship
was obtained with the high-sensitivity C-reactive protein and with the
adhesion molecules, ICAM and VCAM. Newborn features, e.g.,crown-rump length, fetal heart rate, and cranial circumference were not
associated with PCSK9 levels (Supplemental Table 1).
Multivariable data analyses. To define the exposure window to air
pollutants that was most effective in modifying PCSK9, we investigated
how different time lags were associated with PCSK9 levels.
We observed a positive significant effect of PM10exposure for all time lags. The effect on PCSK9 levels was maximal, as
we considered the mean of the entire gestational period, i.e.,0–12 weeks (Table 2). In particular, for each 1-µg/m3increase in PM10 concentration, we observed a
significant increase in PCSK9 levels (β = 1.903, SE = 0.733, p = 0.011).
This effect was also confirmed for NO2 exposure, as
every unit increase in NO2 led to a 2.265 ng/mL rise in
PCSK9 levels (β = 2.265, SE = 1.002, p = 0.026). For
PM2.5 exposure, a significant positive association was
only detected with the 0–6 and 0–10-week time lags.
Association of PCSK9 concentrations with gestational age for
different levels of exposure to pollutants. No association was found
between PCSK9 measured at the first trimester of pregnancy and features
of newborns at birth, such as weight and length at birth, cranial
circumference at birth, and APGAR score (Supplemental table 1).
Nevertheless, when the interaction between PCSK9 concentrations and
gestational age at birth was taken into account, we observed a strong
modifying effect of air pollutants, particularly PM2.5.
For different PM2.5 levels (15 mg/m3,
24 mg/m3, 42 mg/m3, and 55
mg/m3, respectively; 25°, 50°, 75°, and 95°
percentile), the association was significant at the highest
PM2.5 concentrations (i.e., those in the
75th and 95th percentiles; Figure
3). For example, at a PM2.5 concentrations of 42
mg/m3, we observed an advance in delivery date of
approximately 1 week every 100 ng/mL rise in circulating levels of PCSK9
(β = -0.810, SE = 0.332, p = 0.0164). The steepness of the association
was more evident when the highest quartile of PM2.5 was
considered (i.e., delivery advanced by 1.28 weeks for every 100
ng/mL change in PCSK9 levels; β = -1.282, SE = 0.498, p = 0.012).
Overall, at fixed PM2.5 concentrations of 42
mg/m3 and 55 mg/m3, for every 100
ng/mL increment in PCSK9, the gestational age decreased by 2.3% to
3.7% weeks. This finding was also supported by the observation that the
odds ratio (OR) of urgent cesarean delivery associated with a 100 mg/dL
rise in PCSK9 was 2.99 (95% CI 1.22–6.57). A similar trend was found
when PM10 and NO2 were considered
(Supplemental table 3).