909
appears after islet transplantation.8 Nevertheless, there are still hopes that islet transplantation may prevent the onset and progress of secondary complications of diabetes, since glomerular lesions in diabetic rats regressed after islet transplantation. 10 The encouraging results with animals have led some workers to attempt isolation of pancreatic islets from the human pancreas. So far, however, these efforts have been hampered not only by the high fibrous content of the human pancreas compared with that of laboratory animals but also by the scarcity of suitable organs. Some success has been reported with the less fibrous glands of fetuses" or the very young.2 12 The few reports on isolation of adult human islets13-15 disclose great variations in purity and specific functional capacity. That freshly isolated human islets showed signs of reduced viability is not surprising, since they were often ischaemic for many hours before being processed. More extensive investigations have been done on islets isolated from the pancreas of kidney donors and subsequently maintained in tissue-culture. Such islets survived for a week or even longer with well-preserved ultrastructure and normal regulation by glucose of insulin and gluca-
isation
Islet-cell Transplantation DESPITE insulin, oral hypoglycaemic agents,
and intensive research over many decades the diabetic patient is still prone to crippling long-term complications. In Western countries, diabetes is one of the main causes of blindness and of renal, cerebral, and cardiovascular diseases. Since the primary cause of the disorder is unknown, and since existing treatment is unsatisfactory, attempts to cure diabetes by pancreatic transplantation are of much interest. Adequate endocrine function has been obtained in transplants, but transplantation of the vascularised1 "whole organ" has met with very little success. The main problem has been immune rejection of the graft, but many of the other complications, such as fistula formation, are associated with the exocrine part of the gland. So far, only a few pancreatic transplants have functioned for more than six months. Techniques for whole-pancreas transplantation may well improve, but the alternative approach of transplanting only endocrine tissue should obviate complications associated with the exocrine gland. Such experiments have been done in animals with chemically induced diabetes, and lasting amelio-3 ration of the diabetic state has been reported.2 These encouraging results were obtained by transplanting isolated pancreatic islets into the peritoneal cavity,2 or by injecting islets into the portal vein’ so that they lodged in the liver. Morphologically the transplanted islets remained intact4 and, when they were transplanted within a highly inbred strain of rats (isografts), function was preserved. By contrast allograft islet transplantation did not lessen hyperglycaemia.6-* This last finding banishes the hope that isolated pancreatic islets, like other endocrine organs such as the parathyroid, may be only weakly antigenic:9 and sensit1. Goetz, F. C. Metabolism, 1974, 9, 875. 2. Ballinger, W. F., Lacy, P. E. Surgery, 1972, 72, 175. 3. Kemp, C. B., Knight, M. J., Scharp, D. W., Lacy, P. E., Ballinger, W. F. Nature, 1973, 244, 447. 4. Griffith, R. C., Scharp, D. W., Ballinger, W. F., Lacy, P. E. Diabetes, 1975, 24, suppl. 2, p. 419. 5. Charles, A., Imagawa, W., Grodsky, G. ibid. p. 419. 6 Kramp, R. C., Congdon, C. C., Smith, L. H. Europ. J. clin. Invest. 1975,
5, 249. 7. Reckard, C. R., Barker, C. F.
Transplantation Proc. 1973, 5, 761.
to test
skin-grafts
gon secretion. 15 16 The qualitative aspect of human islet isolation
have been tackled successfully, but quantitatively there are still great difficulties. One of the most crucial questions is the number of islets that will be needed to restore normal glucose homoeostasis to a diabetic patient. The islet population in the normal human pancreas is reckoned at about 2 millions, with a total wet weight of about 1 g.17 The greater part of the endocrine pancreas consists of medium-sized islets with a diameter of 100-200 µm; 17 probably these are the islets which can be isolated most easily from the human pancreas, and the average dry-weight of such islets is about 0.8µg.15 If, say, 90% of the pancreas can be removed from a healthy person without causing overt diabetes, the total islet-cell mass required for transplantation should correspond to 30 mg dry weight or about 50 000 medium-sized islets-a yield difficult to obtain from a single human pancreas with current isolation procedures. To make possible successive collection of islets from several donors, some kind of tissue bank will therefore be needed. Cryopreservation of islets, storage at low
thus
seems to
8. Reckard, C. R., Ziegler, M. M., Barker, C. F. Surgery, 1973, 74, 91. 9. Russel, P. S., Gittes, R. F. J. exp. Med. 1959, 109, 571. 10. Mauer, S. M., Steffes, M. W., Sutherland, D. E. R., Najarian, J. S., Michael, A. F., Brown, D. M. Diabetes, 1975, 24, 280. 11. Espinosa, A., Driscoll, S. G., Steinke, J. Science, 1970, 168, 111. 12. Ashcroft, S. J. H., Bassett, J. M., Randle, P. J. Lancet, 1971, i, 888. 13. Sutherland, D. E. R., Steffes, M. W., Bauer, G. E., McManus, D., Noe, B. D., Najarian, J. S. J. Surg. Res. 1974, 16, 102. 14. Lawson, R. K., Poutala, S. D. Surg. Forum, 1974, 25, 377. 15. Hellerström, C., Andersson, A., Groth, C. G., Gunnarsson, R., Lundgren, G., Westman, J., Ostman, J. Diabetologia, 1975, 11, 348. 16. Andersson, A. Acta endocr., Copenh. (in the press). 17. Hellman, B., Hellerström, C. in Handbook of Diabetes Mellitus (edited by E. F. Pfeiffer); vol. i, p. 89. Munich, 1969.
910
temperatures,18 19 or storage in tissue-culture’a-’6 are possibilities. So far, functional preservation of human islets has been reported only after tissueculture.15 16 These systems have the advantage that islet function can be tested before transplantation; and, in addition, there is still the possibility that organ culture may reduce the immunogenicity of the transplanted tissue.20-22 Before attempts to transplant islets into diabetic patients, further experimental work must be done on animals. We need to be more sure that correction of carbohydrate metabolism in the recipient will prevent the secondary complications of diabetes. Furthermore, the yield of human pancreaticislet isolation will have to be increased, and this may
require completely
new
techniques. Probably
this part of the project will be the most difficult. Thereafter, there seems no reason to suppose that rejection and immunosuppressive therapy will be harder to manage with transplanted islet cells than with other transplanted tissues. But a note of caution is due. The process responsible for islet-cell deterioration in diabetes, possibly an autoimmune reaction,23 may also affect newly transplanted islets. In other words, a technically adequate islet transplant might not benefit the diabetic recipient.
Lactase
Deficiency
THE disaccharide lactose is found naturally only in mammalian milk. In young mammals lactase is found in the brush border of the enterocyte; this enzyme releases the monosaccharides glucose and galactose which are then actively transported into the epithelial cell. Trace amounts of lactose may pass the mucosal barrier but there is no hydrolysis elsewhere in the body and the sugar is lost in the urine. A few mammals, such as the Californian sealion, have no lactase at birth; their mother’s milk contains no lactose.24 Human infants, with the rare exception of those with primary alactasia, have high lactase levels at birth. Concentrations fall quite rapidly in the first 4 or 5 years and in many populations reach very low levels by adolescence. In three major ethnic groups lactase usually persists into adult life. The Northern Europeans and their descendants all over the world form the most familiar group. In Africa several Hamitic tribes in Uganda, Kenya, and Ruanda show persistence,,25as do the Hausa and Fulani in Nigeria;26these people Knight, M. J., Scharp, D. W., Kemp, C. B., Ballinger, W. F., Lacy, P. E. Cryobiology, 1973, 10, 89. 19. Frankel, B. J., Gylfe, E., Hellman, B., Idahl, L.-A, J. clin. Invest. (in the press). 20. Raaf, J. H., Farr, H. W., Meyers, W. P. L., Good, R. A. Am. J. Surg. 1974, 18.
128, 478. Lafferty, K. J., Cooley, M. A., Woolnough, J., Walker, K. Z. Science, 1975, 188, 259. 22. Boyles, R. R., Seltzer, H. S. Diabetes, 1975, 24, suppl. 2, p. 420. 23. MacCuish. A. C., Irvine, W. J. Clins, Endocr. Metab. 1975, 4, 435. 24. Sunshine, P., Kretchmer, N. Science, 1964, 144, 850. 25. Cook, G. C., Kajubi, S. K. Lancet, 1966, i, 725. 21.
the Bantu. In the Middle East the Bedouin, Saudi, and Yemeni Arabs show enzyme persistence while Eastern Mediterranean people do not 27 Milk and lactose feeding in man does not increase enzyme levels and there is now good evidence that a recessive autosomal gene determines persistence?* The adaptive changes in milk-fed rats are small compared with the tenfold difference in human adults with and without deficiency. The age at which deficiency becomes evident shows geographical differences-between 1 and 4 years in Thailand and between 5 and 20 years in Finland. Both genetic and environmental factors may be responsible. When the enterocyte is damaged lactase levels are depressed more than other disaccharides and low levels may continue for several months after the primary disease is relieved. Conditions causing low levels include acute gastroenteritis, protein-energy malnutrition, tropical sprue, coeliac disease, cystic fibrosis, ulcerative colitis, and gastrointestinal surgery in infants. Several hypotheses have been proposed to explain enzyme persistence in certain populations. In animals, dietary lactose enhances the absorption of calcium as effectively as vitamin D, and FLATZ and ROTTHAUWE29 have proposed that milk-drinking would have an antirachitic effect in populations exposed to little sunlight. Thus lactose persistence, like a depigmented skin, would have survival value in Northern Europe; this hypothesis does not account for the other ethnic groups. The milking of domestic sheep and goats began between five thousand and eight thousand years ago in South-West Asia, where cattle and camels were used not long after. Man may be presumed to have been originally lactase deficient, but mutants with the enzyme would be able to adopt the milk-drinking habit more easily and so gain in biological fitness. It has been calculated that in 400 generations a biological fitness 1% greater than average would decrease the prevalence of deficiency from 90% to 16%.30 All the present populations with enzyme persistence seem to have originated in South-West Asia; the African groups are all cattle pastoralists and the Arabian groups still use camel milk. COOK" has suggested that since water absorption is coupled to that of monosaccharides, so adults with high lactase levels could better withstand epidemics of cholera. Low enzyme levels have been overcome by several cultural adaptations. Thus, bacterial fermentation destroys the lactose in cheese, ghee, and yoghurt; while the addition of lime-juice in Mexico, or baobab juice in Africa, precipitates the protein curd. are
unrelated
to
26. Kretchmer,
N., Ransome-Kuti, O., Hurwitz, R., Dungy, C., Alakija, W ibid 1971, ii 392. 27. Cook, G. C., Al-Torki, M. T. Br. med. J. 1975, iii. 135. 28. Sahi, T., Isokoski, M., Jussila, J., Launiala, K., Pyöväla, K. Lancet, 1973. ii, 823. 29. Flatz, G., Rotthauwe, H. W. ibid p.76. 30. Bayless, T. M.
Gastroenterology, 1972, 63, 524.
appears after islet transplantation.8 Nevertheless, there are still hopes that islet transplantation may prevent the onset and progress of secondary complications of diabetes, since glomerular lesions in diabetic rats regressed after islet transplantation. 10 The encouraging results with animals have led some workers to attempt isolation of pancreatic islets from the human pancreas. So far, however, these efforts have been hampered not only by the high fibrous content of the human pancreas compared with that of laboratory animals but also by the scarcity of suitable organs. Some success has been reported with the less fibrous glands of fetuses" or the very young.2 12 The few reports on isolation of adult human islets13-15 disclose great variations in purity and specific functional capacity. That freshly isolated human islets showed signs of reduced viability is not surprising, since they were often ischaemic for many hours before being processed. More extensive investigations have been done on islets isolated from the pancreas of kidney donors and subsequently maintained in tissue-culture. Such islets survived for a week or even longer with well-preserved ultrastructure and normal regulation by glucose of insulin and gluca-
isation
Islet-cell Transplantation DESPITE insulin, oral hypoglycaemic agents,
and intensive research over many decades the diabetic patient is still prone to crippling long-term complications. In Western countries, diabetes is one of the main causes of blindness and of renal, cerebral, and cardiovascular diseases. Since the primary cause of the disorder is unknown, and since existing treatment is unsatisfactory, attempts to cure diabetes by pancreatic transplantation are of much interest. Adequate endocrine function has been obtained in transplants, but transplantation of the vascularised1 "whole organ" has met with very little success. The main problem has been immune rejection of the graft, but many of the other complications, such as fistula formation, are associated with the exocrine part of the gland. So far, only a few pancreatic transplants have functioned for more than six months. Techniques for whole-pancreas transplantation may well improve, but the alternative approach of transplanting only endocrine tissue should obviate complications associated with the exocrine gland. Such experiments have been done in animals with chemically induced diabetes, and lasting amelio-3 ration of the diabetic state has been reported.2 These encouraging results were obtained by transplanting isolated pancreatic islets into the peritoneal cavity,2 or by injecting islets into the portal vein’ so that they lodged in the liver. Morphologically the transplanted islets remained intact4 and, when they were transplanted within a highly inbred strain of rats (isografts), function was preserved. By contrast allograft islet transplantation did not lessen hyperglycaemia.6-* This last finding banishes the hope that isolated pancreatic islets, like other endocrine organs such as the parathyroid, may be only weakly antigenic:9 and sensit1. Goetz, F. C. Metabolism, 1974, 9, 875. 2. Ballinger, W. F., Lacy, P. E. Surgery, 1972, 72, 175. 3. Kemp, C. B., Knight, M. J., Scharp, D. W., Lacy, P. E., Ballinger, W. F. Nature, 1973, 244, 447. 4. Griffith, R. C., Scharp, D. W., Ballinger, W. F., Lacy, P. E. Diabetes, 1975, 24, suppl. 2, p. 419. 5. Charles, A., Imagawa, W., Grodsky, G. ibid. p. 419. 6 Kramp, R. C., Congdon, C. C., Smith, L. H. Europ. J. clin. Invest. 1975,
5, 249. 7. Reckard, C. R., Barker, C. F.
Transplantation Proc. 1973, 5, 761.
to test
skin-grafts
gon secretion. 15 16 The qualitative aspect of human islet isolation
have been tackled successfully, but quantitatively there are still great difficulties. One of the most crucial questions is the number of islets that will be needed to restore normal glucose homoeostasis to a diabetic patient. The islet population in the normal human pancreas is reckoned at about 2 millions, with a total wet weight of about 1 g.17 The greater part of the endocrine pancreas consists of medium-sized islets with a diameter of 100-200 µm; 17 probably these are the islets which can be isolated most easily from the human pancreas, and the average dry-weight of such islets is about 0.8µg.15 If, say, 90% of the pancreas can be removed from a healthy person without causing overt diabetes, the total islet-cell mass required for transplantation should correspond to 30 mg dry weight or about 50 000 medium-sized islets-a yield difficult to obtain from a single human pancreas with current isolation procedures. To make possible successive collection of islets from several donors, some kind of tissue bank will therefore be needed. Cryopreservation of islets, storage at low
thus
seems to
8. Reckard, C. R., Ziegler, M. M., Barker, C. F. Surgery, 1973, 74, 91. 9. Russel, P. S., Gittes, R. F. J. exp. Med. 1959, 109, 571. 10. Mauer, S. M., Steffes, M. W., Sutherland, D. E. R., Najarian, J. S., Michael, A. F., Brown, D. M. Diabetes, 1975, 24, 280. 11. Espinosa, A., Driscoll, S. G., Steinke, J. Science, 1970, 168, 111. 12. Ashcroft, S. J. H., Bassett, J. M., Randle, P. J. Lancet, 1971, i, 888. 13. Sutherland, D. E. R., Steffes, M. W., Bauer, G. E., McManus, D., Noe, B. D., Najarian, J. S. J. Surg. Res. 1974, 16, 102. 14. Lawson, R. K., Poutala, S. D. Surg. Forum, 1974, 25, 377. 15. Hellerström, C., Andersson, A., Groth, C. G., Gunnarsson, R., Lundgren, G., Westman, J., Ostman, J. Diabetologia, 1975, 11, 348. 16. Andersson, A. Acta endocr., Copenh. (in the press). 17. Hellman, B., Hellerström, C. in Handbook of Diabetes Mellitus (edited by E. F. Pfeiffer); vol. i, p. 89. Munich, 1969.
910
temperatures,18 19 or storage in tissue-culture’a-’6 are possibilities. So far, functional preservation of human islets has been reported only after tissueculture.15 16 These systems have the advantage that islet function can be tested before transplantation; and, in addition, there is still the possibility that organ culture may reduce the immunogenicity of the transplanted tissue.20-22 Before attempts to transplant islets into diabetic patients, further experimental work must be done on animals. We need to be more sure that correction of carbohydrate metabolism in the recipient will prevent the secondary complications of diabetes. Furthermore, the yield of human pancreaticislet isolation will have to be increased, and this may
require completely
new
techniques. Probably
this part of the project will be the most difficult. Thereafter, there seems no reason to suppose that rejection and immunosuppressive therapy will be harder to manage with transplanted islet cells than with other transplanted tissues. But a note of caution is due. The process responsible for islet-cell deterioration in diabetes, possibly an autoimmune reaction,23 may also affect newly transplanted islets. In other words, a technically adequate islet transplant might not benefit the diabetic recipient.
Lactase
Deficiency
THE disaccharide lactose is found naturally only in mammalian milk. In young mammals lactase is found in the brush border of the enterocyte; this enzyme releases the monosaccharides glucose and galactose which are then actively transported into the epithelial cell. Trace amounts of lactose may pass the mucosal barrier but there is no hydrolysis elsewhere in the body and the sugar is lost in the urine. A few mammals, such as the Californian sealion, have no lactase at birth; their mother’s milk contains no lactose.24 Human infants, with the rare exception of those with primary alactasia, have high lactase levels at birth. Concentrations fall quite rapidly in the first 4 or 5 years and in many populations reach very low levels by adolescence. In three major ethnic groups lactase usually persists into adult life. The Northern Europeans and their descendants all over the world form the most familiar group. In Africa several Hamitic tribes in Uganda, Kenya, and Ruanda show persistence,,25as do the Hausa and Fulani in Nigeria;26these people Knight, M. J., Scharp, D. W., Kemp, C. B., Ballinger, W. F., Lacy, P. E. Cryobiology, 1973, 10, 89. 19. Frankel, B. J., Gylfe, E., Hellman, B., Idahl, L.-A, J. clin. Invest. (in the press). 20. Raaf, J. H., Farr, H. W., Meyers, W. P. L., Good, R. A. Am. J. Surg. 1974, 18.
128, 478. Lafferty, K. J., Cooley, M. A., Woolnough, J., Walker, K. Z. Science, 1975, 188, 259. 22. Boyles, R. R., Seltzer, H. S. Diabetes, 1975, 24, suppl. 2, p. 420. 23. MacCuish. A. C., Irvine, W. J. Clins, Endocr. Metab. 1975, 4, 435. 24. Sunshine, P., Kretchmer, N. Science, 1964, 144, 850. 25. Cook, G. C., Kajubi, S. K. Lancet, 1966, i, 725. 21.
the Bantu. In the Middle East the Bedouin, Saudi, and Yemeni Arabs show enzyme persistence while Eastern Mediterranean people do not 27 Milk and lactose feeding in man does not increase enzyme levels and there is now good evidence that a recessive autosomal gene determines persistence?* The adaptive changes in milk-fed rats are small compared with the tenfold difference in human adults with and without deficiency. The age at which deficiency becomes evident shows geographical differences-between 1 and 4 years in Thailand and between 5 and 20 years in Finland. Both genetic and environmental factors may be responsible. When the enterocyte is damaged lactase levels are depressed more than other disaccharides and low levels may continue for several months after the primary disease is relieved. Conditions causing low levels include acute gastroenteritis, protein-energy malnutrition, tropical sprue, coeliac disease, cystic fibrosis, ulcerative colitis, and gastrointestinal surgery in infants. Several hypotheses have been proposed to explain enzyme persistence in certain populations. In animals, dietary lactose enhances the absorption of calcium as effectively as vitamin D, and FLATZ and ROTTHAUWE29 have proposed that milk-drinking would have an antirachitic effect in populations exposed to little sunlight. Thus lactose persistence, like a depigmented skin, would have survival value in Northern Europe; this hypothesis does not account for the other ethnic groups. The milking of domestic sheep and goats began between five thousand and eight thousand years ago in South-West Asia, where cattle and camels were used not long after. Man may be presumed to have been originally lactase deficient, but mutants with the enzyme would be able to adopt the milk-drinking habit more easily and so gain in biological fitness. It has been calculated that in 400 generations a biological fitness 1% greater than average would decrease the prevalence of deficiency from 90% to 16%.30 All the present populations with enzyme persistence seem to have originated in South-West Asia; the African groups are all cattle pastoralists and the Arabian groups still use camel milk. COOK" has suggested that since water absorption is coupled to that of monosaccharides, so adults with high lactase levels could better withstand epidemics of cholera. Low enzyme levels have been overcome by several cultural adaptations. Thus, bacterial fermentation destroys the lactose in cheese, ghee, and yoghurt; while the addition of lime-juice in Mexico, or baobab juice in Africa, precipitates the protein curd. are
unrelated
to
26. Kretchmer,
N., Ransome-Kuti, O., Hurwitz, R., Dungy, C., Alakija, W ibid 1971, ii 392. 27. Cook, G. C., Al-Torki, M. T. Br. med. J. 1975, iii. 135. 28. Sahi, T., Isokoski, M., Jussila, J., Launiala, K., Pyöväla, K. Lancet, 1973. ii, 823. 29. Flatz, G., Rotthauwe, H. W. ibid p.76. 30. Bayless, T. M.
Gastroenterology, 1972, 63, 524.
