Cytoplasmic
sulfate for sulfation reactions may be derived either from extracellular fluids or from catabolism of
sulfur-containing
amino acids and other
thiols. In vitro studies have pointed out the potential relevance of
sulfur-containing
amino acids as sources for sulfation when extracellular
sulfate concentration is low or when its transport is impaired such as in DTDST [DTD (
diastrophic dysplasia)
sulfate transporter] chondrodysplasias. In the present study, we have considered the contribution of
cysteine and
cysteine derivatives to in vivo macromolecular sulfation of cartilage by using the mouse model of DTD we have recently generated [Forlino, Piazza, Tiveron, Della Torre, Tatangelo, Bonafe, Gualeni, Romano, Pecora, Superti-Furga et al. (2005) Hum. Mol. Genet. 14, 859-871]. By
intraperitoneal injection of [35S]
cysteine in wild-type and mutant mice and determination of the specific activity of the
chondroitin 4-sulfated
disaccharide in cartilage, we demonstrated that the pathway by which
sulfate is recruited from the intracellular oxidation of
thiols is active in vivo. To check whether
cysteine derivatives play a role, sulfation of cartilage
proteoglycans was measured
after treatment for 1 week of newborn mutant and wild-type mice with hypodermic NAC (
N-acetyl-L-cysteine). The relative amount of sulfated
disaccharides increased in mutant mice treated with NAC compared with the placebo group, indicating an increase in
proteoglycan sulfation due to NAC catabolism, although pharmacokinetic studies demonstrated that the
drug was rapidly removed from the bloodstream. In conclusion,
cysteine contribution to cartilage
proteoglycan sulfation in vivo is minimal under physiological conditions even if extracellular
sulfate availability is low; however, the contribution of
thiols to sulfation becomes significant by increasing their plasma concentration.