Palaeopathology and amino acid δ13C analysis: Investigating pre-Columbian individuals with tuberculosis at Pica 8, northern Chile (1050-500 BP)

Bulk δ15N and δ13C values of proteinaceous tissues are being increasingly used in bioarchaeological studies to elucidate the physio-pathological status of ancient individuals. This method has not always been successful. The present study aims to explore the novel use of single amino acid carbon isotope analysis in palaeopathology by investigating the effect of a serious infectious disease, tuberculosis (TB), on the isotope composition of two collagenous tissues (tendon, rib). This is achieved by comparing the bulk and amino acid stable isotope compositions of collagenous tissues collected from human remains with and without TB-like bone lesions. The sample set comprises twelve adult individuals (males = 6, females = 6), who were buried at Pica 8, an inland oasis situated on the mid-elevation plains of northern Chile (Late Intermediate Period, ~1050-500 BP). Similarity and consistency in the diet of these individuals are explored using amino acid carbon isotope analysis of 1-cm hair segments longitudinally cut along a single hair fibre. The results show that there is a difference between collagen δ13C serine values measured in the rib collagen of five individuals presenting TB-like bone lesions (3 males and 2 females) and in those five without lesions (3 males and 2 females; control individuals). The rib collagen δ13C serine values of pathological individuals are lower (more negative) than those of the control individuals. Within the group of pathological individuals, lower δ13C serine values in rib collagen are correlated with higher (more positive) δ15N values. Since only individuals (N = 10) with similar dietary intakes were included in the statistical analyses, it appears that the δ13C serine values could be linked to altered carbon metabolism, rather than induced by dietary factors. Serine accounts for less than 3% of the total carbon in bone collagen, and thus an altered serine metabolism would be masked within the averaged bulk carbon isotope value. In future studies, it is advised to undertake stable carbon isotope analysis of non-essential amino acids as a means of characterising pathologically altered body tissues.