Erythrocyte Nucleotides in Children—Increased Blood Lead and Cytidine Triphosphate

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Abstract
Summary: The erythrocyte nucleotides of 25 children, 1–5 years old, with normal and increased blood leads, were assayed by anion-exchange high-performance liquid chromatography. Red blood cells of the 12 children with blood lead (PbB) below 30 μ/dl (20.3 ± 6 μ/dl, X ± S.D.) had normal levels of activity of pyrimidine 5‘-nucleotidase (P5N) and their erythrocytes were virtually free of pyrimidine nucleotides except for small amounts of UMP and UDP. The purine nucleotides, predominantly ATP and GTP, were present at values similar to adults. In the 13 children with PbB 30–72 μ/dl (45.3 ± 14.3 μ/dl), total cytidine phosphates (CMP, CDP, CTP) were significantly (P < 0.001) increased from trace values to 8.31 ± 6.21 nmoles/1010 erythrocytes. The purine nucleotides were unchanged. P5N activity was 143.3 ± 22.0 units/g hemoglobin in children with PbB < 30 μ/dl and 75.4 ± 24.2 units (P < 0.001) in the high lead subjects. There was a logarithmic correlation of erythrocyte cytidine phosphates with PbB (r = 0.89, P < 0.001) and an inverse correlation of cytidine phosphates with ln P5N activity (r = 0.59, P < 0.001), of ln P5N with PbB (r = 0.64, P < 0.001) and of ln P5N with ln erythrocyte zinc protoporphyrin (Protoporphyrin IX) (r = 0.57, P < 0.001). Speculation: The accumulation of small amounts of erythrocyte CTP in children with increased lead exposure but with blood concentrations of leads as low as 30 μg/dl supports a lower threshold for the consequences of lead induced inhibition of pyrimidine 5′-nucleotidase (P5N) than indicated by earlier, less sensitive assays of nucleotides in adults with lead poisoning. The presence of CTP as the predominant pyrimidine nucleotide is similar to the profile in congenital deficiency of P5N but the nucleotides accumulate with less suppression of P5N than found in congenital deficiency. The significance of increased red cell cytidine phosphates at low levels of lead exposure is unknown but it appears to relate to suppression of P5N activity early in red cell maturation, and thus provides an index of antecedant lead exposure that correlates with erythrocyte zinc protoporphyrin.