Determining fetal manganese exposure from mantle dentine of deciduous teeth

Abstract

Studies addressing health effects of manganese (Mn) excess or deficiency during prenatal development are hampered by a lack of biomarkers that can reconstruct fetal exposure. We propose a method using the neonatal line, a histological feature in deciduous teeth, to identify regions of mantle dentine formed at different prenatal periods. Micromeasurements of Mn in these regions may be used to reconstruct exposure at specific times in fetal development. To test our hypothesis, we recruited pregnant women before 20 weeks gestation from a cohort of farmworkers exposed to Mn-containing pesticides. We collected house floor dust samples and mother's blood during the second trimester; umbilical cord blood at birth; and shed deciduous incisors when the child was ∼7 years of age. Mn levels in mantle dentine formed during the second trimester (as (55)Mn:(43)Ca area under curve) were significantly associated with floor dust Mn loading (r(spearman) = 0.40; p = 0.0005; n = 72). Furthermore, (55)Mn:(43)Ca in sampling points immediately adjacent the neonatal line were significantly associated to Mn concentrations in cord blood (r(spearman) = 0.70; p = 0.003; n = 16). Our results support that Mn levels in mantle dentine are useful in discerning perinatal Mn exposure, offering a potentially important biomarker for the study of health effects due to environmental Mn exposure.

Figure 1

Tooth analysis methodology. (a) Schematic of human primary central incisor showing the neonatal line (blue line), enamel (En), dentine (D), enamel-dentine junction (EDJ) and sampling points in dentine adjacent to the EDJ. Similar points were also sampled in enamel. (b) Light micrograph of NL in enamel. Sampling points in dentine are indicated by arrowheads. (c) Estimating the location of dentine formed during the second trimester. A line (indicated in red) is drawn parallel to the NL at a distance determined by formulae on incremental formation of enamel (see Methods). Intersection of this line with the EDJ indicates the boundary between dentine formed in the second and third trimesters. Dashed red lines indicate 95% confidence limits of this estimate; black circles indicate location of sampling points in mantle dentine. (d) Mantle (MD) is demarcated from circumpulpal dentine in polarized light. Laser ablation spots are visible in MD adjacent to the EDJ. Scale bar 50 μm. (e) Area highlighted in white box in Panel d. Laser ablation spot and few branched dentinal tubules in mantle dentine are visible. Scale bar 10 μm.

Figure 2

The relationship of Mn levels (⁵⁵Mn:⁴³Ca x 10⁴) in pre-and postnatally formed dentine with Mn loading in house dust and Mn concentrations in cord blood. (a-c) Association of Mn loading in house dust (μg Mn/m² floor area) with area under curve (AUC) of Mn levels in sampling points in dentine formed during the second trimester (a), third trimester (b) and postnatally (c). (d) No significant association between cord blood Mn (μg/L) and AUC of Mn levels in all sampling points in prenatal dentine. (e) ⁵⁵Mn:⁴³Ca in sampling points in prenatal mantle dentine immediately adjacent to the neonatal line (NL) showed a significant association with cord blood Mn.

Figure 3

The relationship of Mn levels (⁵⁵Mn:⁴³Ca x 10⁴) in pre-and postnatally formed enamel with Mn loading in house dust and Mn concentrations in cord blood. (a-c) Association of Mn loading in house dust (μg Mn/m² floor area) with area under curve (AUC) of Mn levels in sampling points in enamel formed during the second trimester (a), third trimester (b) and postnatally (c). (d) No significant association between cord blood Mn (μg/L) and AUC of Mn levels in all sampling points in prenatal enamel. (e) ⁵⁵Mn:⁴³Ca in sampling points in prenatal enamel immediately adjacent to the neonatal line (NL) did not show a significant association with cord blood Mn.