PYRIDOXINE-DEFICIENCY AFFECTS BIOMECHANICAL PROPERTIES OF CHICK TIBIAL BONE

The mechanical integrity of bone is dependent on the bone matrix, whic h is believed to account for the plastic deformation of the tissue, an d the mineral, which is believed to account for the elastic deformatio n. The validity of this model is shown in this study based on analysis of the bones of vitamin B-6-deficient and vitamin B-6-replete chick b ones. In this model, when B-6-deficient and control animals are compar ed, vitamin B-6 deficiency has no effect on the mineral content or com position of cortical bone as measured by ash weight (63 +/- 6 vs, 58 /- 3); mineral to matrix ratio of the FTIR spectra (4.2 +/- 0.6 vs, 4. 5 +/- 0.2), line-broadening analyses of the X-ray diffraction 002 peak (beta(002) = 0.50 +/- 0.1 vs. 0.49 +/- 0.01), or other features of th e infrared spectra, In contrast, collagen was significantly more extra ctable from vitamin B-6-deficient chick bones (20 +/- 2% of total hydr oxyproline extracted vs. 10 +/- 3% p less than or equal to 0.001). The B-6-deficient bones also contained an increased amount of the reducib le cross-links DHLNL, dehydro-dihydroxylysinonorleucine, (1.03 +/- 0.0 7 vs. 0.84 +/- 0.13 p less than or equal to 0.001); and a nonsignifica nt increase in HLNL, dehydro-hydroxylysinonorleucine, (0.51 +/- 0.03 v s, 0.43 +/- 0.03, p less than or equal to 0.10). There were no signifi cant changes in bone length, bone diameter, or area moment of inertia, In four-point bending, no significant changes in elastic modulus, sti ffness, offset yield deflection, or fracture deflection were detected, However, fracture load in the B-6-deficient animals was decreased fro m 203 +/- 35 MPa to 151 +/- 23 MPa, p less than or equal to 0.01, and offset yield load was decreased from 165 +/- 9 MPa to 125 +/- 14 MPa, p less than or equal to 0.05. Since earlier histomorphometric studies had demonstrated that the B-6-deficient bones were osteopenic, these d ata suggest that although proper cortical bone mineralization occurred , the alterations of the collagen resulted in changes to bone mechanic al performance.