Alterations of chondroitin sulfate synthesized by chick embryo cartilage cultured in the presence of 6-aminonicotinamide.

Treatment of day-4 chick embryos with 6-aminonicotinamide (6-AN) impairs limbs chondrogenesis and produces micromelia. Interference with limb cartilage development may be related to decreased NAD-dependent synthesis of ATP due to the fact that chondrogenesis is dependent upon anaerobic metabolism. To better understand the effect of 6-AN on chondrogenesis, isolated cartilage epiphyses from day-11 chick embryos were treated in vitro. Sulfate incorporation into total glycosaminoglycans of treated epiphyses was 30% of control. Incorporation of [3H]glucosamine was normal. Fractionation by gel chromatography showed that 40% of the glycosaminoglycans synthesized by treated cells had a molecular weight of less than 15000 compared with 5% of that of the control. A decrease in amount of chondroitin 6-sulfate, an increase of chondroitin 4-sulfate and no change in amount of unsulfated polysaccharide were observed. These results suggest that, upon exposure to 6-AN, chondrocytes produce shorter than normal chondroitin sulfate chains that are preferentially sulfated in the 4 position. Since endochondral bone formation plays an integral role in growth and development of the limb, a defect in production of chondroitin sulfate, a major constituent of cartilage matrix, appears to be involved in 6-AN-induced micromelia.