81
23. Komuro I, Kurihara H, Sugiyama T, et al. Endothelin stimulates c-fos and c-myc expression and proliferation of vascular smooth muscle cell. FEBS Lett 1988; 238: 249-52. 24. de Nucci G, Thomas GR, D’Orleans-Juste P, et al. Pressor effects of circulating endothelin are limited by its removal in the pulmonary
circulation and by the release of prostacyclin and endothelium-derived relaxing factor. Proc Natl Acad Sci USA 1988; 85: 9797-800. 25. Goetz KL, Wang BC, Madwed JB, et al. Cardiovascular, renal and endocrine responses to intravenous endothelin in conscious dogs. Am J Physiol 1988; 255: R1064-68. 26. Randall MD, Douglas SA, Hiley CR. Vascular activities of endothelin-1 and some alanyl substituted analogues in resistance beds of the rat. Br J Pharmacol 1989; 98: 685-99. 27. Arai H, Hori S, Aramori I, Ohkubo H, Nakanishi S. Cloning and expression of a cDNA encoding an endothelin receptor. Nature 1990; 348: 730-32. 28. Sakurai T, Yanagisawa M, Takuwa Y, et al. Cloning ofa cDNA encoding a non-isopeptide-selective subtype of the endothelin receptor. Nature
1990; 348: 732-35. 29. Lee M-E, De La Monte SM, Ng S-C, et al. Expression of the potent vasoconstrictor endothelin in the human central nervous system. J Clin Invest 1990; 86: 141-47. 30. Jones CR, Hiley CR, Pelton JT, Mohr M. Autoradiographic localisation of the binding sites for [125] endothelin in the rat and human brain. Neurosci Lett 1989; 97: 276-79. 31. Crawford MLA, Hiley CR, Young JM. Characteristics of endothelin-1 and endothelin-3 stimulation of phosphoinositide breakdown differ between regions of guinea-pig and rat brain. N S Arch Pharmacol 1990; 341: 268-71. 32. Hoffman A, Keiser HR, Grossman E, Goldstein DS, Gold PW, Kling M. Endothelin concentrations in cerebrospinal fluid in depressive patients. Lancet 1989; ii: 1519.
A carrot
a
day keeps cancer at bay?
The desire to offset a dreaded event, the wrath of gods, or the occurrence of disease by rigid adherence to a certain dietary regimen seems to be as old as mankind. In the animal kingdom at large, there must be evolutionary advantage in inheriting the behavioural trait to avoid toxic foods and to search diligently for those that contain substances in which the organism is temporarily deficient. Such an inborn trait might underlie much of our present-day speculation on the preventive effect of a group of about 2000 natural and synthetic substances1 collectively known as "vitamin A" on the onset of cancer.2.3 Within the vitamin A family, it is important to distinguish two classes: biological precursors or provitamins, often designated as carotenoids; and analogues or derivatives, called retinoids. The roots of our fancy with carrots differ somewhat according to the discipline involved--clinical medicine, epidemiology, and basic science. In dermatology, the interest is with synthetic retinoids; this started with the use of etretinate in the treatment of dyskeratotic skin disorders, mainly psoriasis, and with acne therapy, first with tretinoin topically and later with isotretinoin systemically.44 Initial
therapeutic enthusiasm, coupled to rudimentary insight into the role of these molecules in epithelial differentiation, led to their use in other skin diseases, including malignant tumours.s Isotretinoin has now acquired a fair pedigree of successful clinical trials in the prevention of secondary and some primary skin membrane tumours.33 For renal transplant patients, who have an extremely high burden of wart-like skin growths and ensuing and
mucous
squamous and basal cell skin cancer,etretinate, which held early promise,4,7 is now being tested in further trials. Other family members, of carotenoid stock, seem devoid of these dermatological actions. 3.8 In epidemiology, interest seems to have followed some bold speculation from Doll and Peto,9 who forwarded the hypothesis that about a third of human malignancies might be explained by variation in nutrition;9 one of the likely culprits was beta-carotene, a carotenoid The ensuing flurry of observational studies, either long-term follow-up investigations linking serum "banks" to cancer incidence, or nutritional questionnaires in case-control research, has yielded variable results concerning very different types of "epithelial" cancer, from the lung to the uterine cervix. The carotenoids remain the most promising compounds.2,11.12 Some epidemiologists have already felt confident enough to begin randomised controlled trials in the population, as the final acid test for primary cancer prevention (site largely unspecified).3 The results of megatrials involving hundreds of thousands of person-years of users and non-users of one or another retinoid or carotenoid are eagerly awaited. One smaller careful trial on the effect of beta-carotene on the evolution of cervical dysplasia was negative.13 Meanwhile, basic scientists happily purr in pursuit of their own real agenda-the study of cellular differentiation. They tend to hide under the fashionable aegis of research in oncogene expression, as modulated by retinoids and carotenoids, and receive generous support from cancer foundations, who can now reassure public and politicians that money is spent well. Basic research is finally directed at the real concerns of the people-the wickedness or miracles contained in their daily food. It is not certain that these lines of research will easily Whilst the broad hypotheses of converge. epidemiology lend further credence to the popular notion that there must be something in nutrition, epidemiological methods might be too crude to come close to identification of the causal substance. Only a handful of mostly synthetic substances, whose mode of action was at least partly understood from the laboratory, have shown proven efficacy for specific dermatological indications, and these often in doses close to the toxic; so many a large trial on the effects of another lower dosed and naturally occurring member of the vitamin A family to prevent other types of malignant disease, as seemed warranted by observational research, may have been started in vain. Once, during a heated debate on funding priorities of a
national cancer society, a toxicologist was overheard to exclaim passionately that "... nutrition must be important, there are tens of thousands of chemical substances in our food...". Whereupon a molecular biologist drily quipped: "Yes, tens of thousands, that is why we do not study it...". The difference between research generated by specific hypotheses (Medawar’s
82
"art of the soluble"14) and the more or less hypothesisgenerating studies of nutritional epidemiologists, who are at best looking for very weak associations,l5 could not have been stated more succinctly. The outcome of the debate will determine whether we will stick to the cautious general admonition to vary our food intake so that we regularly eat vegetables of all colours, or whether the 21 st century will see us all swallowing preventive pills containing the winning competitor from industry. 1. Kraemer
KH, DiGiovanna JJ, Moshell AN, et al. Prevention of skin in xeroderma pigmentosum and the use of oral isotretinoin. N Engl J Med 1988; 318: 1633-37. 2. Hennekens Ch H, Mayrent SL, Willet W. Vitamin A, carotenoids and retinoids. Cancer 1986; 58: 1837-41. 3. Meyskens FL Jr. Coming of age—the chemoprevention of cancer. N Engl J Med 1990; 323: 825-26. 4. Editorial. Retinoids and control of cutaneous malignancy. Lancet 1988; ii: 545-46. 5. Peck GL, Yoder FW, Olsen TG, et al. Treatment of Darrier’s disease, lammelar ichthyosis, pityriasis rubra piloris, cystic acne and basal cell carcinoma with oral 13-cis-retinoic add. Dermatologica 1978; 157 cancer
(suppl 11): 1-12. 6. Hartvelt AM, Bouwes Bavinck JN, Kootte AMM, et al. Incidence of skin cancer after renal transplantation in the Netherlands. Transplantation
1990; 49: 506-09. 7. Shuttleworth D, Marks R, Griffin PJA, et al. Treatment of cutaneous neoplasia with etretinate in renal transplant patients. Q J Med 1988; 68: 717-24. 8. Greenberg RE, Baron JA, Stukel Th, et al. Clinical trial of beta carotene to prevent basal-cell and squamous-cell cancer of the skin. N Engl J Med 1990; 323: 789-95. 9. Doll R, Peto R. The causes of cancer. Oxford: Oxford University Press, 1981. 10. Peto R, Doll R, Buckley JD, et al. Can dietary beta carotene materially reduce human cancer rates? Nature 1981; 290: 201-08. 11. Wald N. Retinol, beta-carotene and cancer. Cancer Surv 1987; 6: 635-51. 12. Knekt P, Aromaa AA, Maatela J, et al. Serum vitamin A and subsequent risk of cancer: cancer incidence and follow-up of the Finnish mobile clinic health examination survey. Am J Epidemiol 1990; 132: 857-70. 13. de Vet HCW, Knipschild PG, Willebrand D, et al. The effect of beta-carotene on the regression and progression of cervical dysplasia: a clinical experiment. J Clin Epidemiol (in press). 14. Medawar P. Advice to a young scientist. London: Harper and Row, 1979. 15. Rothman KJ, Poole CH. A strengthening program for weak associations. Int J Epidemiol 1988; 17 (suppl): 955-59.
Bronchial inflammation and asthma treatment The realisation that fibreoptic bronchoscopy can be carried out safely in patients with asthma has encouraged researchers to look for inflammatory cells in bronchoalveolar lavage fluid (BAL) and, more recently, in mucosal biopsy specimens from such subjects. The salient findings to emerge from these studies are that the eosinophil-rich bronchial inflammation and epithelial desquamation, features previously documented in material obtained at necropsy from patients who had died in status asthmaticus, occur during life in some individuals with asthma.3,4 The emphasis on cellular appearances of the bronchial mucosa partly reflects the difficulties of interpreting findings in BAL, since the anatomical source of the cells and the denominator for the expression of concentrations in BAL have not been
clearly defined. In an early study, Laitinen and colleagues3 found damaged bronchial epithelial cells in asthmatic subjects but did not detect eosinophilic infiltration of the epithelium. Mast cell degranulation and pronounced mucosal infiltration by eosinophils were subsequently reported by other investigators in some subjects whose disease severity ranged from almost subclinical to mild, but there was no correlation between inflammatory cell numbers and bronchial hyperreactivity or severity of asthma. More detailed immunohistochemical studies have similarly failed to yield significant correlations with symptom 5 scores or bronchial responsiveness. Studies of peripheral blood lymphocytes have provided evidence of an immunological basis for some severe asthmatic attacks, but not in every case; surprisingly, patients with atopic asthma had the least indication of T-cell activation.66 Immunohistochemical analysis of bronchial mucosal T cells in stable asthma has not consistently shown features of inflammation in all
patients.7 Although measurements of inflammatory cell population have become increasingly complex, all studies that attempt to relate inflammation to asthma are hampered by the difficulties of quantifying the disease. The clinical significance of bronchial provocation tests is a separate issue, but both these and spirometry are measurements of the state of the airway, changes in which may differ in time course from those of inflammatory cell infiltration. Moreover, a biopsy done at one point in time may not reflect the patterns of disease found in patients. To relate disease severity to inflammation, Bousquet et al8 have used a cumulative clinical scoring system and eosinophil enumeration in BAL and biopsy specimens. Although they report significant correlations between BAL and intraepithelial eosinophil counts, many of their subjects with more severe disease did not have any bronchial eosinophils. Another cautionary note comes from studies that have shown similar sputum or biopsy features in patients with cough9 and in atopic subjects,lO,l1 none of whom had bronchial asthma. The demonstration of inflammatory cells in BAL and bronchial biopsy specimens from at least some subjects with asthma has led both physicians 12,13 and the pharmaceutical industry to identify suppression of inflammation as a therapeutic aim in the management of patients with asthma. Treatment of bronchial inflammation is based on the premise that such inflammation affects the clinical condition of most patients with asthma. However, a preliminary study has indicated that hyperreactivity and symptoms can persist in steroid-treated patients with intrinsic asthma despite biopsy evidence of suppression of inflammation. 14 Moreover, in an editorial last month (Dec 8, p 1411), we highlighted the controversy surrounding the anti-inflammatory actions of longacting inhaled (3Z agonists.
23. Komuro I, Kurihara H, Sugiyama T, et al. Endothelin stimulates c-fos and c-myc expression and proliferation of vascular smooth muscle cell. FEBS Lett 1988; 238: 249-52. 24. de Nucci G, Thomas GR, D’Orleans-Juste P, et al. Pressor effects of circulating endothelin are limited by its removal in the pulmonary
circulation and by the release of prostacyclin and endothelium-derived relaxing factor. Proc Natl Acad Sci USA 1988; 85: 9797-800. 25. Goetz KL, Wang BC, Madwed JB, et al. Cardiovascular, renal and endocrine responses to intravenous endothelin in conscious dogs. Am J Physiol 1988; 255: R1064-68. 26. Randall MD, Douglas SA, Hiley CR. Vascular activities of endothelin-1 and some alanyl substituted analogues in resistance beds of the rat. Br J Pharmacol 1989; 98: 685-99. 27. Arai H, Hori S, Aramori I, Ohkubo H, Nakanishi S. Cloning and expression of a cDNA encoding an endothelin receptor. Nature 1990; 348: 730-32. 28. Sakurai T, Yanagisawa M, Takuwa Y, et al. Cloning ofa cDNA encoding a non-isopeptide-selective subtype of the endothelin receptor. Nature
1990; 348: 732-35. 29. Lee M-E, De La Monte SM, Ng S-C, et al. Expression of the potent vasoconstrictor endothelin in the human central nervous system. J Clin Invest 1990; 86: 141-47. 30. Jones CR, Hiley CR, Pelton JT, Mohr M. Autoradiographic localisation of the binding sites for [125] endothelin in the rat and human brain. Neurosci Lett 1989; 97: 276-79. 31. Crawford MLA, Hiley CR, Young JM. Characteristics of endothelin-1 and endothelin-3 stimulation of phosphoinositide breakdown differ between regions of guinea-pig and rat brain. N S Arch Pharmacol 1990; 341: 268-71. 32. Hoffman A, Keiser HR, Grossman E, Goldstein DS, Gold PW, Kling M. Endothelin concentrations in cerebrospinal fluid in depressive patients. Lancet 1989; ii: 1519.
A carrot
a
day keeps cancer at bay?
The desire to offset a dreaded event, the wrath of gods, or the occurrence of disease by rigid adherence to a certain dietary regimen seems to be as old as mankind. In the animal kingdom at large, there must be evolutionary advantage in inheriting the behavioural trait to avoid toxic foods and to search diligently for those that contain substances in which the organism is temporarily deficient. Such an inborn trait might underlie much of our present-day speculation on the preventive effect of a group of about 2000 natural and synthetic substances1 collectively known as "vitamin A" on the onset of cancer.2.3 Within the vitamin A family, it is important to distinguish two classes: biological precursors or provitamins, often designated as carotenoids; and analogues or derivatives, called retinoids. The roots of our fancy with carrots differ somewhat according to the discipline involved--clinical medicine, epidemiology, and basic science. In dermatology, the interest is with synthetic retinoids; this started with the use of etretinate in the treatment of dyskeratotic skin disorders, mainly psoriasis, and with acne therapy, first with tretinoin topically and later with isotretinoin systemically.44 Initial
therapeutic enthusiasm, coupled to rudimentary insight into the role of these molecules in epithelial differentiation, led to their use in other skin diseases, including malignant tumours.s Isotretinoin has now acquired a fair pedigree of successful clinical trials in the prevention of secondary and some primary skin membrane tumours.33 For renal transplant patients, who have an extremely high burden of wart-like skin growths and ensuing and
mucous
squamous and basal cell skin cancer,etretinate, which held early promise,4,7 is now being tested in further trials. Other family members, of carotenoid stock, seem devoid of these dermatological actions. 3.8 In epidemiology, interest seems to have followed some bold speculation from Doll and Peto,9 who forwarded the hypothesis that about a third of human malignancies might be explained by variation in nutrition;9 one of the likely culprits was beta-carotene, a carotenoid The ensuing flurry of observational studies, either long-term follow-up investigations linking serum "banks" to cancer incidence, or nutritional questionnaires in case-control research, has yielded variable results concerning very different types of "epithelial" cancer, from the lung to the uterine cervix. The carotenoids remain the most promising compounds.2,11.12 Some epidemiologists have already felt confident enough to begin randomised controlled trials in the population, as the final acid test for primary cancer prevention (site largely unspecified).3 The results of megatrials involving hundreds of thousands of person-years of users and non-users of one or another retinoid or carotenoid are eagerly awaited. One smaller careful trial on the effect of beta-carotene on the evolution of cervical dysplasia was negative.13 Meanwhile, basic scientists happily purr in pursuit of their own real agenda-the study of cellular differentiation. They tend to hide under the fashionable aegis of research in oncogene expression, as modulated by retinoids and carotenoids, and receive generous support from cancer foundations, who can now reassure public and politicians that money is spent well. Basic research is finally directed at the real concerns of the people-the wickedness or miracles contained in their daily food. It is not certain that these lines of research will easily Whilst the broad hypotheses of converge. epidemiology lend further credence to the popular notion that there must be something in nutrition, epidemiological methods might be too crude to come close to identification of the causal substance. Only a handful of mostly synthetic substances, whose mode of action was at least partly understood from the laboratory, have shown proven efficacy for specific dermatological indications, and these often in doses close to the toxic; so many a large trial on the effects of another lower dosed and naturally occurring member of the vitamin A family to prevent other types of malignant disease, as seemed warranted by observational research, may have been started in vain. Once, during a heated debate on funding priorities of a
national cancer society, a toxicologist was overheard to exclaim passionately that "... nutrition must be important, there are tens of thousands of chemical substances in our food...". Whereupon a molecular biologist drily quipped: "Yes, tens of thousands, that is why we do not study it...". The difference between research generated by specific hypotheses (Medawar’s
82
"art of the soluble"14) and the more or less hypothesisgenerating studies of nutritional epidemiologists, who are at best looking for very weak associations,l5 could not have been stated more succinctly. The outcome of the debate will determine whether we will stick to the cautious general admonition to vary our food intake so that we regularly eat vegetables of all colours, or whether the 21 st century will see us all swallowing preventive pills containing the winning competitor from industry. 1. Kraemer
KH, DiGiovanna JJ, Moshell AN, et al. Prevention of skin in xeroderma pigmentosum and the use of oral isotretinoin. N Engl J Med 1988; 318: 1633-37. 2. Hennekens Ch H, Mayrent SL, Willet W. Vitamin A, carotenoids and retinoids. Cancer 1986; 58: 1837-41. 3. Meyskens FL Jr. Coming of age—the chemoprevention of cancer. N Engl J Med 1990; 323: 825-26. 4. Editorial. Retinoids and control of cutaneous malignancy. Lancet 1988; ii: 545-46. 5. Peck GL, Yoder FW, Olsen TG, et al. Treatment of Darrier’s disease, lammelar ichthyosis, pityriasis rubra piloris, cystic acne and basal cell carcinoma with oral 13-cis-retinoic add. Dermatologica 1978; 157 cancer
(suppl 11): 1-12. 6. Hartvelt AM, Bouwes Bavinck JN, Kootte AMM, et al. Incidence of skin cancer after renal transplantation in the Netherlands. Transplantation
1990; 49: 506-09. 7. Shuttleworth D, Marks R, Griffin PJA, et al. Treatment of cutaneous neoplasia with etretinate in renal transplant patients. Q J Med 1988; 68: 717-24. 8. Greenberg RE, Baron JA, Stukel Th, et al. Clinical trial of beta carotene to prevent basal-cell and squamous-cell cancer of the skin. N Engl J Med 1990; 323: 789-95. 9. Doll R, Peto R. The causes of cancer. Oxford: Oxford University Press, 1981. 10. Peto R, Doll R, Buckley JD, et al. Can dietary beta carotene materially reduce human cancer rates? Nature 1981; 290: 201-08. 11. Wald N. Retinol, beta-carotene and cancer. Cancer Surv 1987; 6: 635-51. 12. Knekt P, Aromaa AA, Maatela J, et al. Serum vitamin A and subsequent risk of cancer: cancer incidence and follow-up of the Finnish mobile clinic health examination survey. Am J Epidemiol 1990; 132: 857-70. 13. de Vet HCW, Knipschild PG, Willebrand D, et al. The effect of beta-carotene on the regression and progression of cervical dysplasia: a clinical experiment. J Clin Epidemiol (in press). 14. Medawar P. Advice to a young scientist. London: Harper and Row, 1979. 15. Rothman KJ, Poole CH. A strengthening program for weak associations. Int J Epidemiol 1988; 17 (suppl): 955-59.
Bronchial inflammation and asthma treatment The realisation that fibreoptic bronchoscopy can be carried out safely in patients with asthma has encouraged researchers to look for inflammatory cells in bronchoalveolar lavage fluid (BAL) and, more recently, in mucosal biopsy specimens from such subjects. The salient findings to emerge from these studies are that the eosinophil-rich bronchial inflammation and epithelial desquamation, features previously documented in material obtained at necropsy from patients who had died in status asthmaticus, occur during life in some individuals with asthma.3,4 The emphasis on cellular appearances of the bronchial mucosa partly reflects the difficulties of interpreting findings in BAL, since the anatomical source of the cells and the denominator for the expression of concentrations in BAL have not been
clearly defined. In an early study, Laitinen and colleagues3 found damaged bronchial epithelial cells in asthmatic subjects but did not detect eosinophilic infiltration of the epithelium. Mast cell degranulation and pronounced mucosal infiltration by eosinophils were subsequently reported by other investigators in some subjects whose disease severity ranged from almost subclinical to mild, but there was no correlation between inflammatory cell numbers and bronchial hyperreactivity or severity of asthma. More detailed immunohistochemical studies have similarly failed to yield significant correlations with symptom 5 scores or bronchial responsiveness. Studies of peripheral blood lymphocytes have provided evidence of an immunological basis for some severe asthmatic attacks, but not in every case; surprisingly, patients with atopic asthma had the least indication of T-cell activation.66 Immunohistochemical analysis of bronchial mucosal T cells in stable asthma has not consistently shown features of inflammation in all
patients.7 Although measurements of inflammatory cell population have become increasingly complex, all studies that attempt to relate inflammation to asthma are hampered by the difficulties of quantifying the disease. The clinical significance of bronchial provocation tests is a separate issue, but both these and spirometry are measurements of the state of the airway, changes in which may differ in time course from those of inflammatory cell infiltration. Moreover, a biopsy done at one point in time may not reflect the patterns of disease found in patients. To relate disease severity to inflammation, Bousquet et al8 have used a cumulative clinical scoring system and eosinophil enumeration in BAL and biopsy specimens. Although they report significant correlations between BAL and intraepithelial eosinophil counts, many of their subjects with more severe disease did not have any bronchial eosinophils. Another cautionary note comes from studies that have shown similar sputum or biopsy features in patients with cough9 and in atopic subjects,lO,l1 none of whom had bronchial asthma. The demonstration of inflammatory cells in BAL and bronchial biopsy specimens from at least some subjects with asthma has led both physicians 12,13 and the pharmaceutical industry to identify suppression of inflammation as a therapeutic aim in the management of patients with asthma. Treatment of bronchial inflammation is based on the premise that such inflammation affects the clinical condition of most patients with asthma. However, a preliminary study has indicated that hyperreactivity and symptoms can persist in steroid-treated patients with intrinsic asthma despite biopsy evidence of suppression of inflammation. 14 Moreover, in an editorial last month (Dec 8, p 1411), we highlighted the controversy surrounding the anti-inflammatory actions of longacting inhaled (3Z agonists.
