29
Mutation Research, 39 (1976) 29--74 © Elsevier/North-Holland Biomedical Press
MOLECULAR
AND GENETIC BASIS OF FUROCOUMARIN
REACTIONS
BARRY R. SCOTT 1, MADHU A. PATHAK 2 and GEORGES R. MOHN s 1 National Institute o f Environmental Health Sciences, P.O. Box 12233, Research Triangle Park, North Carolina 2 7709; 2Department o f Dermatology, Harvard Medical School, Massachusetts General Hospital, Boston, Massachusetts 02114 (U.S.A.) and SZentrallaboratorium fiir Mutagenitfftspriifung, 78 Freiburg 1, Br, Breisacher Strasse 33 (West Germany) (Received May 4th, 1976) (Accepted June 24th, 1976)
Contents Introduction ................................................ Occurrence and nomenclature .................................. Furocoumarins and radiant energy ............................... Non-ionizing radiation ...................................... General considerations .................................... Some factors that affect furocoumarin photosensitization ......... Absorption spectra ..................................... Relationship between structure and photosensitivity ........... Dose and concentration of photosensitizer ................... Temperature .......................................... Hydrogen ion concentration (pH) ......................... A c t i v i t y is o x y g e n i n d e p e n d e n t ........................... Radiation variables ..................................... Erythemal threshold of human subjects ..................... Vitiligo ................................................ 8-Methoxypsoralen sensitization by ionizing radiation .............. Biochemical effects .......................................... Pharmacological action and metabolic alteration .................. Inhibition of DNA synthesis -- psoriasis treatment ................. Inhibition of template activity ................................ Inactivation and toxicity ...................................... Carcinogenicity ............................................. Teratogenicity .............................................. Mutagenicity ............................................... Repair of damage ............................................ Proposed mechanism of action ..................................
30 31 35 35 35 36 36 37 38 39 40 40 40 41 42 43 44 44 46 48 49 52 54 54 59 60
30 Molecular complexing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Photobinding of furocoumarin to DNA and bases . . . . . . . . . . . . . . . . . Cross-linking between opposite strands of DNA . . . . . . . . . . . . . . . . . . . Genetic hazards to man . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
60 61 62 63 65
Introduction Ancient Hindus, Turks, Egyptians and other orientals have known about some of the biological effects of furocoumarins for more than 3000 years [99]. In particular, the Indian sacred book, "Atharva Veda" [32] and the old Buddhist Bower manuscript [125] both mentioned treatment of leukoderma using a poultice application of material from a plant that is now classified as Psoralea corylifolia. Another important plant, A m m i majus (Umbelliferae), a weed found in the Nile Valley, has also been employed for centuries as a " c u r e " for leukoderma (vitiligo). In the 13th century, Ibn E1 Bitar gave a description of the usefulness of this plant for leukoderma in his famous book, "Mofradat E1 A d w i y a " [130]. Deleterious effects of the furocoumarins were also mentioned in a German Fairy tale of the 18th century [120]. In this tale, the central character, " L i t t l e Muck", suffers from photodermatitis after ingesting figs and exposing himself to sunlight. However, it was not until 1834, that the first furocoumarins, 5-methoxypsoralen, was isolated by Kalbrunner from bergamot oil [101]. Seventy-seven years later the most c o m m o n l y used medicinal furocoumarin today, 8-methoxypsoralen, was isolated by Thoms [265]. Finally in 1933, Sp~ith and Holzen [254] established its chemical structure and reported on its successful synthesis. Only in 1972 was the crystal and molecular structure of 8-methoxypsoralen established [260]. Another important information-stone in the history of the furocoumarins was made available when in 1931, Phyladelphy [225] recognized the importance of sunlight in reactions of these compounds with biological materials. Kuske [157] then established the relationship between the chemical components of certain plant tissues and the development of phytophotodermatitis (phyto = plant, photo = light). By studying the time factor, the causative agent, and the nature of photoreaction produced by fig extracts (Ficus carica), Pastinice sativa, Angelica officinalis, Ruta graveolens and Heracleurn mantegazzianum with his associate Mickelmann, he succeeded in presenting evidence that the photosensitizing substances responsible for p h y t o p h o t o d e r m a t i t i s were furocoumarins. At about the same time, Jensen and Hansen [138] were able to establish the wavelengths (320--400 nm) responsible for phytophotodermatitis. This lead to the development of an artifical UV light source by Kuske in 1940 [157,158] and its use in bio-assay for detecting other photosensitizing agents [184]. Finally, a Woods-Horn Filter was added to the artifical UV light source to filter out the shorter wavelengths of light (less than 3200 •) in the 1950's [216]. Interestingly, even though these compounds have been used in folk-medicine for a long time, it was only in the first half of this century that the pharmokinetic properties of these compounds were clinically studied. One of the first
31 clinical trials using substances isolated by Fahmy and Abu-Shady [1,93], from the grey-green powder used b y Egyptian herb doctors was conducted by E1 M o f t y [87] in 1948. As a result of these trials it became apparent that furocoumarins might possibly be developed as drugs to increase the melanin production and hence, increase the tolerance of human skin to sunlight. Because of the important basic and clinical implications of this hypothesis, a fairly extensive research effort was begun in the 1950's into the botanical sources of furocoumarihs, their mechanism of action, their toxicity in animals and man, the development of high intensity monochromatic UV light source and the effect of furocoumarins on the incidence of solar or UV light-induced skin cancer in man and mice. Besides accomplishing many of these objectives, it was also determined that these c o m p o u n d s were very useful in the treatment of pigmentary disorders such as vitiligo (leukoderma), psoriasis and to increase the tolerance of skin to solar radiation in people who easily sunburn. Several aspects of the biological and chemical properties of furocoumarins have already been reviewed individually (historical [97], new clinical uses [126], photochemistry [48,70,185,221], photosensitization [174,182,187, 189,191,192,207,221], occurrence and uses [223,244], isolation and identification [233], biological action [243], and genetic effects [290]). Thus, the purpose of the present review is to give a summerized general overview, with particular emphasis on the genetic toxicology of these compounds. Occurrence and nomencalture Furocoumarins are distributed both in the natural environment and the synthetic environment (see Table I). In nature the source of these compounds have world-wide distribution and belong to a b o u t eight families of plants.Whereas, in the synthetic environment, many natural and synthetic furocoumarins have been made in the laboratory. The furocoumarins, certain isomers of which are called psoralens, belong to a group of heterocyclic compounds that are considered to be derivatives of coumarin (benz-a-pyrone or 1,2-benzopyrone). The fusion of a pyrone ring with a benzene nucleus can give rise to a class of heterocyclic c o m p o u n d s known as benzopyrones (Fig. 1). The two distinct types of benzopyrones that are c o m m o n l y recognized are the coumarins (benzo
Mutation Research, 39 (1976) 29--74 © Elsevier/North-Holland Biomedical Press
MOLECULAR
AND GENETIC BASIS OF FUROCOUMARIN
REACTIONS
BARRY R. SCOTT 1, MADHU A. PATHAK 2 and GEORGES R. MOHN s 1 National Institute o f Environmental Health Sciences, P.O. Box 12233, Research Triangle Park, North Carolina 2 7709; 2Department o f Dermatology, Harvard Medical School, Massachusetts General Hospital, Boston, Massachusetts 02114 (U.S.A.) and SZentrallaboratorium fiir Mutagenitfftspriifung, 78 Freiburg 1, Br, Breisacher Strasse 33 (West Germany) (Received May 4th, 1976) (Accepted June 24th, 1976)
Contents Introduction ................................................ Occurrence and nomenclature .................................. Furocoumarins and radiant energy ............................... Non-ionizing radiation ...................................... General considerations .................................... Some factors that affect furocoumarin photosensitization ......... Absorption spectra ..................................... Relationship between structure and photosensitivity ........... Dose and concentration of photosensitizer ................... Temperature .......................................... Hydrogen ion concentration (pH) ......................... A c t i v i t y is o x y g e n i n d e p e n d e n t ........................... Radiation variables ..................................... Erythemal threshold of human subjects ..................... Vitiligo ................................................ 8-Methoxypsoralen sensitization by ionizing radiation .............. Biochemical effects .......................................... Pharmacological action and metabolic alteration .................. Inhibition of DNA synthesis -- psoriasis treatment ................. Inhibition of template activity ................................ Inactivation and toxicity ...................................... Carcinogenicity ............................................. Teratogenicity .............................................. Mutagenicity ............................................... Repair of damage ............................................ Proposed mechanism of action ..................................
30 31 35 35 35 36 36 37 38 39 40 40 40 41 42 43 44 44 46 48 49 52 54 54 59 60
30 Molecular complexing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Photobinding of furocoumarin to DNA and bases . . . . . . . . . . . . . . . . . Cross-linking between opposite strands of DNA . . . . . . . . . . . . . . . . . . . Genetic hazards to man . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
60 61 62 63 65
Introduction Ancient Hindus, Turks, Egyptians and other orientals have known about some of the biological effects of furocoumarins for more than 3000 years [99]. In particular, the Indian sacred book, "Atharva Veda" [32] and the old Buddhist Bower manuscript [125] both mentioned treatment of leukoderma using a poultice application of material from a plant that is now classified as Psoralea corylifolia. Another important plant, A m m i majus (Umbelliferae), a weed found in the Nile Valley, has also been employed for centuries as a " c u r e " for leukoderma (vitiligo). In the 13th century, Ibn E1 Bitar gave a description of the usefulness of this plant for leukoderma in his famous book, "Mofradat E1 A d w i y a " [130]. Deleterious effects of the furocoumarins were also mentioned in a German Fairy tale of the 18th century [120]. In this tale, the central character, " L i t t l e Muck", suffers from photodermatitis after ingesting figs and exposing himself to sunlight. However, it was not until 1834, that the first furocoumarins, 5-methoxypsoralen, was isolated by Kalbrunner from bergamot oil [101]. Seventy-seven years later the most c o m m o n l y used medicinal furocoumarin today, 8-methoxypsoralen, was isolated by Thoms [265]. Finally in 1933, Sp~ith and Holzen [254] established its chemical structure and reported on its successful synthesis. Only in 1972 was the crystal and molecular structure of 8-methoxypsoralen established [260]. Another important information-stone in the history of the furocoumarins was made available when in 1931, Phyladelphy [225] recognized the importance of sunlight in reactions of these compounds with biological materials. Kuske [157] then established the relationship between the chemical components of certain plant tissues and the development of phytophotodermatitis (phyto = plant, photo = light). By studying the time factor, the causative agent, and the nature of photoreaction produced by fig extracts (Ficus carica), Pastinice sativa, Angelica officinalis, Ruta graveolens and Heracleurn mantegazzianum with his associate Mickelmann, he succeeded in presenting evidence that the photosensitizing substances responsible for p h y t o p h o t o d e r m a t i t i s were furocoumarins. At about the same time, Jensen and Hansen [138] were able to establish the wavelengths (320--400 nm) responsible for phytophotodermatitis. This lead to the development of an artifical UV light source by Kuske in 1940 [157,158] and its use in bio-assay for detecting other photosensitizing agents [184]. Finally, a Woods-Horn Filter was added to the artifical UV light source to filter out the shorter wavelengths of light (less than 3200 •) in the 1950's [216]. Interestingly, even though these compounds have been used in folk-medicine for a long time, it was only in the first half of this century that the pharmokinetic properties of these compounds were clinically studied. One of the first
31 clinical trials using substances isolated by Fahmy and Abu-Shady [1,93], from the grey-green powder used b y Egyptian herb doctors was conducted by E1 M o f t y [87] in 1948. As a result of these trials it became apparent that furocoumarins might possibly be developed as drugs to increase the melanin production and hence, increase the tolerance of human skin to sunlight. Because of the important basic and clinical implications of this hypothesis, a fairly extensive research effort was begun in the 1950's into the botanical sources of furocoumarihs, their mechanism of action, their toxicity in animals and man, the development of high intensity monochromatic UV light source and the effect of furocoumarins on the incidence of solar or UV light-induced skin cancer in man and mice. Besides accomplishing many of these objectives, it was also determined that these c o m p o u n d s were very useful in the treatment of pigmentary disorders such as vitiligo (leukoderma), psoriasis and to increase the tolerance of skin to solar radiation in people who easily sunburn. Several aspects of the biological and chemical properties of furocoumarins have already been reviewed individually (historical [97], new clinical uses [126], photochemistry [48,70,185,221], photosensitization [174,182,187, 189,191,192,207,221], occurrence and uses [223,244], isolation and identification [233], biological action [243], and genetic effects [290]). Thus, the purpose of the present review is to give a summerized general overview, with particular emphasis on the genetic toxicology of these compounds. Occurrence and nomencalture Furocoumarins are distributed both in the natural environment and the synthetic environment (see Table I). In nature the source of these compounds have world-wide distribution and belong to a b o u t eight families of plants.Whereas, in the synthetic environment, many natural and synthetic furocoumarins have been made in the laboratory. The furocoumarins, certain isomers of which are called psoralens, belong to a group of heterocyclic compounds that are considered to be derivatives of coumarin (benz-a-pyrone or 1,2-benzopyrone). The fusion of a pyrone ring with a benzene nucleus can give rise to a class of heterocyclic c o m p o u n d s known as benzopyrones (Fig. 1). The two distinct types of benzopyrones that are c o m m o n l y recognized are the coumarins (benzo
