Susan Jim

Stable carbon isotopic evidence for differences in the dietary origin of bone cholesterol, collagen and apatite: implications for their use in palaeodietary reconstruction

the narrow range of variation observed in apatite-to-cholesterol spacings ( 13 Capat-bchol) suggests that cholesterol 13 C values can potentially also be used as an independent test for the isotopic integrity of apatite 13 C values. These insights into bone cholesterol, collagen and apatite dietary signals, diet-to-bone fraction ations and bone component-to-bone component spacings provide the basis for more accurate interpretations of the dietary behaviour of archaeological populations and food webs when the 13 C analysis of bone is employed. Copyright

Quantifying dietary macronutrient sources of carbon for bone collagen biosynthesis using natural abundance stable carbon isotope analysis

The diets of laboratory rats were isotopically and nutritionally manipulated using purified C3 and/or C4 macronutrients to investigate the routing of dietary carbon to bone collagen biosynthesis. Diets were formulated with purified proteins, carbohydrates and lipids of defined composition and natural abundance stable isotope ratios. Bulk protein and constituent amino acid delta(13)C values determined for whole diet and bone collagen provided the basis for assessing isotopic fractionation and estimating the degree of routing versus synthesis de novo of essential, non-essential and conditionally indispensable amino acids. Essential and conditionally indispensable amino acids were shown to be routed from diet to collagen with little isotopic fractionation whereas non-essential amino acids differed by up to 20 per thousand. Mathematical modelling of the relationships between macronutrient and tissue delta(13)C values provided qualitative and quantitative insights into the metabolic and energetic controls on bone collagen biosynthesis. Essential amino acids comprise 21.7 % of the carbon in collagen, defining the minimum amount of dietary carbon routing. Estimates of 42 and 28 % routing were shown for the non-essential amino acids, glycine and aspartate, respectively. In total, the routing of non-essential and conditionally indispensable amino acids was estimated to equal 29.6 % of the carbon in collagen. When the contribution of carbon from the essential amino acids is also considered, we arrive at an overall minimum estimate of 51.3 % routing of dietary amino acid carbon into bone collagen.

Natural abundance stable carbon isotope evidence for the routing and de novo synthesis of bone FA and cholesterol.

This research reported in this paper investigated the relationship between diet and bone FA and cholesterol in rats raised on a variety of isotopically controlled diets comprising 20% C3 or C4 protein (casein) and C3 and/or C4 nonprotein or energy (sucrose, starch, and oil) macronutrients. Compoundspecific stable carbon isotope analysis (δ13C) was performed on the FA (16∶0, 18∶0, 18∶1, and 18∶2) and cholesterol isolated from the diet (n=4) and bone (n=8) of these animals. The dietary signals reflected by the bone lipids were investigated using linear regression analysis. δ13C values of bone cholesterol and stearic (18∶0) acid were shown to reflect whole-diet δ13C values. whereas the δ13C values of bone palmitic (16∶0), oleic (18∶1), and linoleic (18∶2) acids reflected dietary FA δ13C values. Dietary signal differences are a result of the balance between direct incorporation (or routing) and de novo synthesis of each of these bone lipids. Estimates of the degree of routing of these bone lipids gleaned from correlations between Δ13Cdlipid-wdiet (δ13Cdiet lipid-δ13Cwhole diet) spacings and Δ13Cblipid-wdiet (δ13Cbone lipid-δ13Cwhole diet fractionations demonstrated that the extent of routing, where 18∶2>16∶0>18∶1>18∶0>cholesterol, reflected the relative abundances of these lipids in the diet. These findings provide the basis for more accurate insights into diet when the δ13C analysis of bone fatty FA or cholesterol is employed.