Distribution of aluminum in hair of Brazilian infants and correlation to aluminum-adjuvanted vaccine exposure
Introduction
The sensitivity of the developing central nervous system (CNS) makes infants and fetuses highly vulnerable to toxic metals, which can cause both transient and lasting damage to the system. Young children have immature or highly diminished detoxification pathways that may impair Al metabolism as compared to adults and older children [1]. Additionally, in neonates, renal function is not fully developed, making Al an important toxic challenge for pediatric patients [2]. Depending on the severity of exposure, it may result in psychomotor and mental effects.
Exposure to aluminum during infancy is linked to maternal Al in breastfed babies and to Al in infants immunized with aluminum-adjuvanted vaccines (AAVs) [3]. Maternal dietary sources of aluminum can increase bio-accessibility of elemental Al to young animals [4]. We have shown that exposure to an acute dose of adjuvant-Al in newborns and in infants is greater than Al exposure through breastfeeding [3]; the high acute doses of injected adjuvant-Al (250 to 1500 μg) during recommended schedules contrasted with estimated Al available after absorption from breastfeeding [3]. In exclusively breastfed infants, estimates of Al intake vary depending on maternal dietary Al exposure; however, non-breastfed infants can be exposed to even higher levels of the metal, depending on its concentration in formulas. Zeager et al. [5] summarized estimates of dietary intake for children aged 6 to 11 months (0.7 mgAl/day) and for 2-y-olds (4.6 mgAl/day) [5], [6] on formulas and infant foods respectively.
At young ages, starting with hepatitis B vaccine (at birth) and subsequently through the first year, immunization with AAVs elicits acute parenteral Al exposure [3], [7]. The toxicity of acute exposure to low doses of adjuvanted-Al has only recently received attention. Intra-peritoneal injection of AAVs (diphtheria-tetanus, and diphtheria-tetanus-pertussis vaccine adjuvanted with aluminum hydroxide) into four-week-old female mice caused a transient rise of aluminum in brain tissue which peaked between the second and third day post-injection [8].
The studies of toxicokinetics (TK) and toxicodynamics (TD) of aluminum during early life have to rely on characteristics that help to trace its bioavailability and mobility in organ, tissues, or body compartments. Information regarding adjuvant-Al levels in hair after exposure to AAVs is scarce. Studies have shown that medical products containing Al can be detected in adult hair as a result of Al-containing medication [2], but so far there have been no attempts to determine Al in infant hair after acute exposure to AAVs. The aim of the study is to evaluate a standard analytical method for aluminum determination in hair samples of young children who received AAVs as recommended by the Brazilian immunization scheme.
Section snippets
Materials and methods
The hair samples in this study were part of a large ongoing project with riverine communities along the Madeira river basin. A detailed description of the study has appeared in a previous publication dealing with Hg exposure [9]; the protocol was approved by the Ethics Committee for Studies in Humans of the Federal University of Rondonia (Of. 001-07/CEP/NUSAU). Parental written consent was always obtained for hair sampling. The hair samples represent material that was saved after hair analysis
Results
The analytical results for infants' hair are summarized in Table 2. All hair samples could be measured with precision and reliability. The median Al concentration was 47.7 μg/g while the median age of children was 205 days, thus suggesting that Al may reflect the heavy exposure of the immunization schedule (0.63 to 6.88 mg Al). However, the range of hair-Al concentration (12.2 to 221.9 μg/g) represents both enteral (Al in diet) and parenteral adjuvant-Al sources. There was a wide range of
Discussion
This is the first attempt to trace residual Al in hair of young children after AAVs. The work shows that it is feasible to use infants' hair to monitor Al exposure allowing insight into a) the minimum hair mass that can produce useful results, and b) the detection windows likely to capture hair-Al during peak exposure to AAVs. Our results showed a normal distribution of hair-Al concentrations, but did not show any significant correlation with vaccine parameters (adjuvant-Al taken, and time
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