Uptake of cystine by cystine-depleted fibroblasts from patients with cystinosis

Cystine accumulation in cystinotic fibroblasts from free and protein-linked cystine but not cysteine

“…Incorporation of label into the GSH and , 1981), and may also be due to dilution of the difference in total amount of cystine accumulated in specific radioactivity of intracellular [35Slcystine by the two experiments is the result of variability in the unlabelled cystine released from protein catabolism. rate of cystine accumulation, which has been The contribution of pinocytosed cystine to total previously described States et cell (lysosomal) cystine accumulation was de- horseradish peroxidase and cystine in the culture medium as shown in Fig. 6. ing the intracellular cystine content (Figs.…”

Human Renal Fanconi Syndrome – Then and Now

“…States et al [5] showed that such cells take up cystine more rapidly than normal fibroblasts, although the possibility that this was simply related to exchange diffusion with the large intracellular pool of cystine in cystinotic fibroblasts could not be excluded. Later studies employing cystinotic fibroblasts depleted of intracellular cystine by preincubation with cysteamine supported these findings suggesting that the biochemical basis of the cystine storage could be related, in part, to increased uptake [6], Reduction of cystine to cysteine appeared to be unimpaired in cystinotics [7], These cultured fibroblasts have been useful in demon strating the effectiveness of various reducing agents in depleting the raised intracellular cystine pool including dithiothreitol, ascorbic acid, and cysteamine [8]. This led to an unsuccessful trial of ascorbic acid treatment [9] and the successful use of oral cysteamine therapy in some patients with cystinosis [10,II], These agents presumably exert their effect by reducing cystine to cysteine or by forming the mixed disulfide of cysteine-cysteamine: both of which can easily exit from the cell.…”

“…Transported solute is then either used by the cell or returned to the blood across the basolateral membrane. The Fan coni syndrome could arise because of a defect of influx [I], leakage back into the lumen after influx [2], decreased flux out of the cell across the basolateral membrane [3], increased flux into the cell from the blood [4], a defect in energy generation or transduction to the plasma membrane [5], or, finally, an increase in backflux across the tight junctions between the cells [6]. BBM = Brushborder mem brane; BLM= basolateral membrane; TBM = tubular basement membrane.…”

Altered Leukotriene Generation in Leukocytes from Cystinotic Children

“…The association of increased uptake (24) and reduction rates of cystine (25) as well as increased y-glutamyl transpeptidase activity and accelerated GSH turnover (15,16) are considered to be secondary findings. Also, an increase in GSH synthetase activity has been shown in lag and early growth phases of cystinotic cells, and it was not reflected in increased GSH content (26).…”