Cystic fibrosis: lysosomal and mitochondrial enzyme activities of lymphoid cell lines.

Extract: Seven lysosomal enzymes and three mitochondrial enzymes were studied in cultured lymphoid cells from four patients with cystic fibrosis, three heterozygotes, one borderline patient, and six healthy controls. The lysosomes and mitochondria were isolated by differential and density gradient centrifugation. The activity of α-glucosidase, which is a lysosomal enzyme degrading glycogen, showed a marked increase in activity in the lysosomes of cultured lymphoid cells obtained from patients with cystic fibrosis as compared with the healthy controls. Two substrates were used for measuring the activity of this enzyme, the synthetic p-nitrophenyl-α-glucoside (p-NP-α-glucoside), and the physiologic substrate glycogen. The values obtained withp-NP-α-glucoside were 32.6 (SD ± 8.6) and 13.8 (SD ± 12.2) μmoles/g lysosomal protein/hr and with glycogen 543.5 (SD ± 163.3) and 188.6 (SD ± 156.3) μmoles/g lysosomal protein/hr for patients with cystic fibrosis and controls, respectively. The values of α-glucosidase in the heterozygotes were also elevated, 17.2 (sD ± 5.5), controls 13.8 (SD ± 12.2) usingp-NP-α-glucoside as substrate. When glycogen was used as substrate, the values were 226.7 (SD ± 85.3) in the heterozygote and 188.6 (SD plusmn; 156.3) μmoles/g lysosomal protein/hr in the control. The activities of the other six lysosomal enzymes—β-Dglucosidase, ‡-galactosidase, ‡-glucuronidase, N-acetyl-‡-glucosaminidase, aryl-sulfatase, and acid phosphatase—were the same in patients with cystic fibrosis as in the controls. The three mitochondrial enzymes assayed, succinic dehydrogenase, glutamic dehydrogenase, and malic dehydrogenase, showed the same activity in all subjects tested. Speculation: This study indicated that the metabolism of lymphoid cells obtained from patients with cystic fibrosis (CF) and maintained in culture for prolonged periods differs from that of cells of healthy controls. The abnormal elevated activity for α-glucosidase inlymphoid cells derived from patients with cystic fibrosis in noted when measured with synthetic substrate as well as with a physiologic substrate, glycogen. To date no defect n glycogen metabolism has been noted in cystic fibrosis although Pallvicini et al. did observe an increase in the glycogen content of cultured fibroblasts obtained from patients with cystic fibrosis. Bartman et al. found and increase in size of lysosomes in cultured fibroblasts from patients with CF by electron microscopy. These and our observations suggest the possibility of and impaired cellular metabolism in CF indicating that we may be dealing with a lysosomal disorder. Of some importance is the observation that the activity of a-glucosidase is also elevated in the heterozygote, but not to the same extent as in the homozygote. Perhaps this could offer a means of detecting the heterozygote, a possibility which should appeal to the genetic counsellor. Although numerous techniques and reports have suggested methods of identifying the heterozygote, none is practical or reliable. To be of value the test would have to take less time than required in the technique used here. For this purpose we are in the process of studying the activity of the a-glucosidase from cells derived from the patient rather than from cells grown in continuous culture. It is quite possible that patients suffering from malignant disorders or those receiving radiation or drugs may also show abnormal levels of lysosomal enzymes but may not have the same specificity; i.e., many of the lysosomal enzymes may be elevated rather than an isolated one.