Expression of the dietary isotope signal in the compound-specific δ13 values of pig bone lipids and amino acids

Pigs were raised on six isotopically controlled diets to examine the dietary macronutrients used in the synthesis of bulk bone isochemical components (apatite, collagen and lipids) and individual compounds (bone fatty acids, cholesterol and amino acids from collagen). delta C-13 values of apatite and bulk bone lipids reflected those of the whole diet, with Delta C-13(apatite-whole diet)=10.2 +/-1.3% and Delta C-13(bone lipids-whole diet)=-2.4 +/-0.7%. A wide variation observed in the Delta C-13(collagen-whole diet) values (0.5 to 6.1%) was hypothesized to reflect the relative importance of (i) the direct incorporation of essential amino acids, and (ii) the balance between direct incorporation and de novo synthesis of non-essential amino acids. Linear regression (n=6) was used to assess the relationship between the delta C-13 values of whole diet and bulk bone components and individual compounds. Whole diet delta C-13 values showed a strong correlation with those of bone cholesterol (R-2=0.85) and glutamate (R-2=0.96) in collagen. The essential amino acids leucine (Delta (13)C(collagen leu diet leu)0.5 +/-1.2%) and phenylalanine (Delta C-13(collagen phe-diet phe)=-0.6 +/-0.6%) showed little isotopic fractionation between diet and bone collagen.