Morphological abnormalities in vitamin B6 deficient tarsometatarsal chick cartilage.

The aim of this study was to test the hypothesis that deficiency of vitamin B6 would produce morphological characteristics of osteochondral lathyrism. To accomplish this goal, morphological characteristics of chick cartilage in which lathyrism was produced by two separate dietary regimens was compared to morphological changes encountered in vitamin B6 deficiency. Vitamin B6 deficiency should reduce activity of lysyloxidase needed for producing intermolecular cross-links. The question to be addressed was: would this latter deficiency impair collagen morphological features and secondarily other structures indirectly by reducing collagen molecular assembly? Failure of cross-linking of collagen in the positive controls was related to a lack of functional aldehyde cross-link intermediates which are blocked by homocysteine and aminoacetonitrile. Day-old-male Lohmann chicks were fed adequate (6 mg/kg) or vitamin B6-deficient diets. Cross-link defects were induced by homocysteine-rich diets (0.6% w/w) or a diet containing aminoacetonitrile (0.1% w/w). Animals were sacrificed at 6 weeks of age and Ossa tarsalia articular cartilage specimens, as well as the proximal end of tarsometatarsus were dissected from the tibial metatarsal joint, a major weight-bearing site. Light microscopic observations revealed reduction of subarticular trabecular bone formation, concurrent with overexpansion of the hypertrophic cell zone. Ultrastructural electron microscopy observation of articular fibro-cartilage indicated significant thickening of collagen fibers in vitamin B6 deficient birds, as well as the positive controls in comparison to that of cage-matched control birds. It was concluded that vitamin B6 deficient cross-linking may be responsible for the observed delay in bone development and aforementioned cartilage histological alterations.