APPRAISAL OF METHODS FOR THE DETERMINATION OF L-ASCORBIC ACID

Ascorbate regulation of collagen biosynthesis in Ehlers-Danlos syndrome, type VI

We studied two unrelated individuals with Ehlers-Danlos syndrome type VI, which is characterized by congenital hypotonia, lax joints, severe kyphoscoliosis, friable skin, and hemorrhagic hypotrophic scars. The diagnosis was confirmed by decreased hydroxylysine residues in dermal collagen and decreased collagen lysyl hydroxylase activities in their cultured skin fibroblasts. Despite the diminished hydroxylysine residues in dermal collagen from the probands, we found no differences in hydroxylysyl residues of collagen synthesized by fibroblasts in culture. When patient 1 was given oral sodium ascorbate (5 g/d) for 3 weeks, ascorbate concentrations increased two-fold in plasma and 300-fold in urine. Urinary excretion of hydroxylysine and hydroxyproline increased during ascorbate administration. After a 1-year interval, bleeding time, wound healing, and muscle strength improved. Ascorbate supplementation (50 micrograms/mL) to confluent fibroblasts cultured from the two patients and controls increased hydroxyprolyl and hydroxylysyl residues of fibroblasts four to seven and three to four-fold respectively. Total protein associated with the cell layer increased 14% to 32% without concomitant change in cellular DNA. Total soluble collagenous material recovered from culture media increased 61% to 103% with ascorbate supplementation. These studies demonstrate that ascorbate improves the clinical status of patients with impaired collagen lysyl hydroxylase activity by enhancing lysyl and prolyl hydroxylation and total collagen production.

Inherited human collagen lysyl hydroxylase deficiency: ascorbic acid response

A patient is described with congenital hypotonia, lax joints, friable skin, hemorrhagic scars, high-arched palate, and borderline microcornea. Acid hydrolyzed whole skin collagen had a reduced hydroxylysine content of 0.5 residues per 1,000 as compared to 5.1 +/- 0.7 in control skin. Collagen lysyl hydroxylase in dialyzed subcellular fractions of cultured skin fibroblasts required L-ascorbate as a principal cofactor. Activity of this enzyme in cultured skin fibroblasts derived from this patient, his father, and mother were 17%, 66%, and 39% of control values, respectively. Collagen prolyl hydroxylase activity was normal. Pharmacologic amounts of oral vitamin C (4 gm/day) produced an increase and withdrawal resulted in abrupt diminution of urinary excretion of hydroxylysine. Over a two-year period the patient's wound healing and muscle strength improved and corneal diameter increased. Hydroxylysine content of the skin did not increase.

Human requirements and needs. Vitamin C status: methods and findings

Although vitamin C nutritional status in man may be determined on the basis of dietary intake findings and on clinical signs of a dietary deprivation, biochemical measurements represent the most objective approach. Without the availability of a functional biochemical procedure that relates to vitamin C status, information concerning inadequacies in this nutrient has been derived mainly from measuring ascorbate levels in serum (plasma), leukocytes, blood, and urine. The measurement of serum levels of ascorbic acid is the most commonly used and practical procedure for determining vitamin C nutritional status in individuals or population groups. Although leukocyte ascorbate levels provide information concerning the body stores of the vitamin, the measurement is technically more difficult to perform, and, hence, its use is largely confined to clinical situations as an aid in the diagnosis of scurvy. The clinical diagnosis of scurvy can be aided also by information on the urinary levels of ascorbic acid and the use of vitamin C loading or saturation tests. With recognized limitations, ascorbic acid can be measured in biological samples with the use of automated or manual colorimetric and fluorometric procedures. Nutrition surveys conducted in Canada and the United States have indicated vitamin C deficits among certain population groups.