Biochimica et Biophysica Acta, 473 (1978)149-186 © E l s e v i e r / N o r t h - H o l l a n d Biochemical Press B B A 87039
THE
METABOLISM
RELATIONSHIP
OF
POLYCYCLIC
HYDROCARBONS
AND
ITS
TO CANCER
J O S E P H W. D e P I E R R E a n d L A R S E R N S T E R
Department of Biochemistry, Arrhenius Laboratory, University of Stockholm, Fack, S-106 91 Stoekholm (Sweden) (Received M a y 23rd, 1977)
CONTENTS I.
Introduction
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
149
II.
Characterization o f the m e t a b o l i s m o f polycyclic h y d r o c a r b o n s in rat liver a n d lung A. P r o d u c t s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. T h e e n z y m e s involved . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Aryl h y d r o c a r b o n m o n o o x y g e n a s e . . . . . . . . . . . . . . . . . . . . . a. Relation to the m i c r o s o m a l mixed function oxidase . . . . . . . . . . . . b. A s s a y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . c. Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . d. Subcellular localization . . . . . . . . . . . . . . . . . . . . . . . . . e. I n d u c t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . f. Purification a n d reconstitution . . . . . . . . . . . . . . . . . . . . . . 2. Epoxide hydrase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . a. A s s a y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . b. Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . c. Various properties . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. G l u t a t h i o n e S-epoxide transferase . . . . . . . . . . . . . . . . . . . . . a. A s s a y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . b. Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . c. Various properties . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Studies with isolated intact cells a n d perfused organs . . . . . . . . . . . . . . D. Studies on the m a n n e r in which reactive metabolites of polycyclic h y d r o c a r b o n s travel f r o m the site o f generation to the "target site" . . . . . . . . . . . . . .
IlL Characterization o f the m e t a b o l i s m o f polycyclic h y d r o c a r b o n s by h u m a n lung, skin, a n d other tissues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV. Relationship to cancer . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
150 150 154 154 154 155 156 157 158 159 16l 16l 162 164 164 164 164 166 167 168 169 171
Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
176
References
176
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I. I N T R O D U C T I O N Polycyclic A number
hydrocarbons
may
be a major
of studies have demonstrated
cause
of cancer
the carcinogenic
in human
properties
beings.
of these com-
150 pounds in different species, including man, and in different tissues, including the lung and skin [1-13]. In addition, polycyclic hydrocarbons have been observed to cause malignant transformations and mutagenesis when applied to cells in culture (e.g. refs. 14-17). Benzpyrene seems to be either the most active carcinogenic agent or at least the best indicator of the carcinogenicity of the complex residues resulting from the incomplete combustion of organic fuels [11 ]. Some early studies by Campbell [18,19] are illustrative: mice exposed to dust from the highways develop lung cancer. The stepwise removal of benzpyrene from this dust results in a stepwise decrease in its carcinogenicity. Benzpyrene is found in urban air [20] and in cigarette smoke (e.g. refs. 21 and 22). The major pathways for metabolism of benzpyrene and other polycyclic hydrocarbons in mammalian tissues involve the aryl hydrocarbon monooxygenase system, epoxide hydrase, and glutathione S-epoxide transferase (see ref. 23,24). There is much evidence in support of the hypothesis that epoxide intermediates formed by aryl hydrocarbon monooxygenase activity react non-enzymatically with DNA and are the immediate carcinogens. Such expoxides can also rearrange in water to form phenols, be hydrated to dihydrodiols, or be conjugated with glutathione; all of these products seems to be considerably less carcinogenic than the epoxides themselves. Thus, it appears that a very important factor in carcinogenesis caused by polycyclic hydrocarbons is the relative rates of synthesis and breakdown of the carcinogenic intermediates, i.e. the steady state level of the arene oxides. This steady state level would be expected to be different in various tissues because of differences in the relative activities of the enzymes involved in polycyclic hydrocarbon metabolism. In addition, diet, various physiological states, and exposure to xenobiotics do not affect these enzymes in the same manner.
I[. CHARACTERIZATIONOF THE METABOLISM OF POLYCYCLICHYDROCARBONS IN RAT LIVERAND LUNG In attempts to determine how polycyclic hydrocarbons cause cancer in mammalian tissues, valuable clues may be obtained by comparing the metabolism of these substances and the binding of their metabolites to DNA in different organs with different susceptibilities to their carcinogenicity. Thus, rat lung, which develops cancers relatively easily in response to polycyclic hydrocarbons, should be compared to rat liver, where these compounds are relatively non-carcinogenic. In addition, time has often been saved by first developing a method with liver and then applying it to lung tissue. IIA. Products
In discussing the metabolic products of benz(a)pyrene, it is best to have the structure and numbering of the carbon atoms in this compound fresh in mind
151
12 1 111~~2
7
6
5
Fig. i. Benz(a)pyrene.
I further r~etabolisrn
OH •
b
0
t further
°Hso
~.+,
THE
METABOLISM
RELATIONSHIP
OF
POLYCYCLIC
HYDROCARBONS
AND
ITS
TO CANCER
J O S E P H W. D e P I E R R E a n d L A R S E R N S T E R
Department of Biochemistry, Arrhenius Laboratory, University of Stockholm, Fack, S-106 91 Stoekholm (Sweden) (Received M a y 23rd, 1977)
CONTENTS I.
Introduction
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
149
II.
Characterization o f the m e t a b o l i s m o f polycyclic h y d r o c a r b o n s in rat liver a n d lung A. P r o d u c t s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. T h e e n z y m e s involved . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Aryl h y d r o c a r b o n m o n o o x y g e n a s e . . . . . . . . . . . . . . . . . . . . . a. Relation to the m i c r o s o m a l mixed function oxidase . . . . . . . . . . . . b. A s s a y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . c. Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . d. Subcellular localization . . . . . . . . . . . . . . . . . . . . . . . . . e. I n d u c t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . f. Purification a n d reconstitution . . . . . . . . . . . . . . . . . . . . . . 2. Epoxide hydrase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . a. A s s a y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . b. Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . c. Various properties . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. G l u t a t h i o n e S-epoxide transferase . . . . . . . . . . . . . . . . . . . . . a. A s s a y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . b. Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . c. Various properties . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Studies with isolated intact cells a n d perfused organs . . . . . . . . . . . . . . D. Studies on the m a n n e r in which reactive metabolites of polycyclic h y d r o c a r b o n s travel f r o m the site o f generation to the "target site" . . . . . . . . . . . . . .
IlL Characterization o f the m e t a b o l i s m o f polycyclic h y d r o c a r b o n s by h u m a n lung, skin, a n d other tissues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV. Relationship to cancer . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
150 150 154 154 154 155 156 157 158 159 16l 16l 162 164 164 164 164 166 167 168 169 171
Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
176
References
176
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I. I N T R O D U C T I O N Polycyclic A number
hydrocarbons
may
be a major
of studies have demonstrated
cause
of cancer
the carcinogenic
in human
properties
beings.
of these com-
150 pounds in different species, including man, and in different tissues, including the lung and skin [1-13]. In addition, polycyclic hydrocarbons have been observed to cause malignant transformations and mutagenesis when applied to cells in culture (e.g. refs. 14-17). Benzpyrene seems to be either the most active carcinogenic agent or at least the best indicator of the carcinogenicity of the complex residues resulting from the incomplete combustion of organic fuels [11 ]. Some early studies by Campbell [18,19] are illustrative: mice exposed to dust from the highways develop lung cancer. The stepwise removal of benzpyrene from this dust results in a stepwise decrease in its carcinogenicity. Benzpyrene is found in urban air [20] and in cigarette smoke (e.g. refs. 21 and 22). The major pathways for metabolism of benzpyrene and other polycyclic hydrocarbons in mammalian tissues involve the aryl hydrocarbon monooxygenase system, epoxide hydrase, and glutathione S-epoxide transferase (see ref. 23,24). There is much evidence in support of the hypothesis that epoxide intermediates formed by aryl hydrocarbon monooxygenase activity react non-enzymatically with DNA and are the immediate carcinogens. Such expoxides can also rearrange in water to form phenols, be hydrated to dihydrodiols, or be conjugated with glutathione; all of these products seems to be considerably less carcinogenic than the epoxides themselves. Thus, it appears that a very important factor in carcinogenesis caused by polycyclic hydrocarbons is the relative rates of synthesis and breakdown of the carcinogenic intermediates, i.e. the steady state level of the arene oxides. This steady state level would be expected to be different in various tissues because of differences in the relative activities of the enzymes involved in polycyclic hydrocarbon metabolism. In addition, diet, various physiological states, and exposure to xenobiotics do not affect these enzymes in the same manner.
I[. CHARACTERIZATIONOF THE METABOLISM OF POLYCYCLICHYDROCARBONS IN RAT LIVERAND LUNG In attempts to determine how polycyclic hydrocarbons cause cancer in mammalian tissues, valuable clues may be obtained by comparing the metabolism of these substances and the binding of their metabolites to DNA in different organs with different susceptibilities to their carcinogenicity. Thus, rat lung, which develops cancers relatively easily in response to polycyclic hydrocarbons, should be compared to rat liver, where these compounds are relatively non-carcinogenic. In addition, time has often been saved by first developing a method with liver and then applying it to lung tissue. IIA. Products
In discussing the metabolic products of benz(a)pyrene, it is best to have the structure and numbering of the carbon atoms in this compound fresh in mind
151
12 1 111~~2
7
6
5
Fig. i. Benz(a)pyrene.
I further r~etabolisrn
OH •
b
0
t further
°Hso
~.+,
