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Int. J. Cancer: 39, 560-564 (1987)
0 1987 Alan R. Liss, Inc.
Publication of the International Union Against Cancer
Publication de I’Union lnternationale Contre le Cancer
BENZO(a)PYRENE METABOLISM BY LYMPHOCYTES FROM NORMAL
INDIVIDUALS AND INDIVIDUALS CARRYING THE MEDITERRANEAN VARIANT
OF GLUCOSE-6-PHOSPHATE DEHYDROGENASE
F. FEO’, M.E. RUGGIU,L. LENZEFSNI,
R. GARCEA,L. DAINO, S. FRASSETTO,
V. ADDIS,L. GASPAand R. PASCALE
Istituto di Patologia generale dell ’Universitb di Sassari, Via P. Manzella 4 , 07100, Sassari, Italy.
In vitro growing human lymphocytes (HL) and fibroblasts,
isolated from glucose-6-phosphate dehydrogenase (G6PD).de.
ficient subjects (Mediterranean variant), show a sharp decrease in this enzymatic activity and in NADPH:NADP+ ratio.
These cells are less able than controls to hydroxylate
benzo(a)pyrene (BaP) when tested in the absence of an exogenous NADPH-generating system. They exhibit great resistance to the toxic effect of BaP. G6PD-deficient fibroblasts
are less prone than controls to in vitro transformation by BaP.
To investigate whether this depends on a decreased production of active BaP metabolites and 6aP:DNA adducts by
G6PD-deficient cells, BaP metabolism was studied in G6PDdeficient H L cultured in vitro in the presence of mitogens and
treated with BaP for 24 hr. HPLC profiles of organo- and
water-soluble metabolites revealed that both types of
benzo(a)anthracene (6aA)-induced HL produced: 4,5-, 7.8-,
9,IO-diols. l,3-, 3,6-quinones, 3-, 9-hydroxy and 2 peaks of more
polar metabolites. There was a 25-76% decrease of organoand water-soluble metabolites in the G6PD-deficient cells.
When H L were incubated with 7,8-diol, the formation of metabolites mutagenic for Salmonella typhimurium (His-) was
very low in G6PD-deficient cells. 6aP:deoxyadenosine (dAde)
and BaPdeoxyaguanosine (dGua) adducts were identified after
incubation of both types of H L with BaP. There was a 31.79%
fall in adduct formation by G6PD-deficient cells. Our results
indicate that G6PD-deficient human lymphocytes are less able
to metabolize BaP than normal lymphocytes. We suggest that
the NADPH pool is inadequate, in deficient cells, for active
BaP metabolism.
Most carcinogens are activated by one or more NADPHdependent reactions catalyzed by the mixed function monooxygenase system (Gelboin, 1967). G6PD activity plays an
essential role as a regulator of the hexose monophosphate
shunt (HMS) (Horecker, 1967). The latter is the major source
of cellular NADPH.
Previous work (Feo et al., 1981, 1982, 1984a,b; Pirisi et
al., 1982) has shown that human skin fibroblasts and HL
carrying the Mediterranean variant of G6PD exhibit a great
decrease in HMS as well as in the NADPH/NADP+ ratio.
G6PD deficiency protects in vitro growing fibroblasts and HL
from the toxic effect of BaP. G6PD-deficient human skin
fibroblasts are less prone than normal cells to in vitro transformation by BaP (Feo et al., 1984a,b). NADPH-cytochrome C
reductase and aryl-hydrocarbon hydroxylase (AHH) activities
are lower in homogenates of G6PD-deficient HL, when tested
in the absence of an exogenous NADPH-generating system
(Feo et al., 1984b). G6PD-deficient cells also produce lower
amounts of water-soluble and mutagenic metabolites than controls after incubation with BaP (Feo et al., 1984a,b). Watersoluble metabolites, formed during detoxification reactions,
may arise from proximate carcinogens, such as BaP epoxides
and diols, as well as from phenols (Gelboin, 1980). Consequently, the determination of these metabolites does not represent a substantial evaluation of the ultimate BaP metabolite
production. Further, the mutagenicity of genotoxic compounds
does not always correspond to their carcinogenicity (DeFlora,
1984; Saffiotti et al., 1984). Therefore, a better knowledge of
the effect of G6PD deficiency on the transformation process
could be obtained by evaluation of the ability of G6PD-deficient cells to produce BaP metabolites which form adducts
with DNA. In the current report, the BaP metabolite pattern
and the production of BaP:DNA adducts during incubation of
G6PD-deficient HL with the carcinogen are studied. Preliminary results have been reported elsewhere (Pirisi et al., 1987).
MATERIAL AND METHODS
Medium and chemicals
Eagle’s minimum essential medium (GIBCO, Mascia Brunelli, Milan, Italy) was supplemented with 24 mM sodium
bicarbonate, heparin (60 U/ml), antibiotics (100 IU penicillin/
ml, 100 pg streptomycin/ml and 25 IU nystatiniml) and 10%
heat-inactivated fetal bovine serum (Flow, Milan). Phytohemagglutinin and pokeweed mitogen (GIBCO) were added to the
culture medium at a final concentration of 1% each. BaP,
BaA, DNase (Type II), and snake venom phosphodiesterase
(Type IV) were supplied by Sigma (St. Louis, MO). dAde and
dGua, alkaline phosphatase (Grade I, lyophilized), RNase A
and proteinase K were obtained from Boehringer (Mannheim,
FRG). [3H]BaP (52.6 Ci/mmol) was obtained from New England Nuclear (NEN, Dreieichenhain, FRG). BaP and BaA
were purified (Van Cantfort et al., 1977) prior to use and
added to the medium at a final concentration of 0.01 mM and
0.009 mM, respectively. Some BaP standards: 9,lO-, 4 3 - and
7,8-diols, 7,8-diol-9,1O-epoxide (BaPDE), 1,3 and 3,6-quinones, 9- and 3-hydroxy, were obtained from the Chemical
Repository, NCI (Bethesda, MD) and some were a generous
gift from Dr. H.V. Gelboin (NCI). [1’,2’-3H]dGua (35 Ci/
mmol) was obtained from Amersham (Little Chalfont, UK)
and [8-I4C]dAde (54.9 mCi/mmol) from NEN. They were
diluted with the unlabelled nucleosides before use. [1-I4C]glucose (7 mCi/mmol) was purchased from NEN. All other
chemicals were of purest grade available. Radioactivity measurements were performed in an LS 1800 liquid scintillation
system (Beckman, Geneva, Switzerland) with a Beckman MP
solvent.
Cell isolation and culture methods
Blood samples were obtained from normal males or from
males carrying the Mediterranean variant of G6PD. Donors,
aged between 20 and 50, were healthy and not undergoing any
therapy when samples were collected (between 8 and 9 A.M.).
These samples were kept at 0°C for no more than 6 hr before
HL isolation. Sixty-six donors for each G6PD activity group
were examined for G6PD, HMS, and AHH activities. Two
28-individual subgroups were used for analysis of BaP metabolite pattern and adduct formation, respectively. Total BaP
metabolites were determined in both subgroups (56 donors).
In order to avoid bias in selecting the subgroups of 28 from
the total group studied, donors were chosen each week for one
of the two types of analysis (metabolite pattern or adduct
formation), alternatively. HL were isolated (Feo et al., 1984b),
suspended at 600,000/ml of medium and cultured in 25-cm2
‘To whom reprint requests should be sent.
Received: September 3, 1986 and in revised form November 26, 1986.
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BaP METABOLISM AND G6PD DEFICIENCY
56 1
covalently bound to BaP metabolites were isolated from free
nucleosides by elution of a Sephadex LH 20 column with water
and then with methanol (Baird and Diamond, 1976). The
material eluting with methanol was separated into individual
derivatized nucleosides by HPLC using a C18 column maintained at room temperature, with a 1 ml/min constant flow
rate. The column was eluted with a 20-min gradient of 5599% methanol. Effluent was monitored at 254 nm and fractions were collected every 20 sec. For the preparation of the
( + )anti-BaPDE-dGua or ( +)anti-BaPDE-dAde markers,
BaPDE (3.3 pmol) was dissolved in 1 ml of methanol and 0.5
Assays
ml of labelled nucleoside (1.6 pmol; 10 mCi/mmol) in 100 mM
G6PD was determined by following NADP+ reduction at TrisCl buffer (PH 7.4) were added. After 16 hr incubation at
340 nm, at 37°C (Feo et al., 1984u), and HMS activity was 37 “ C , the hydrocarbon-deoxynucleosideadducts were isolated
determined (Feo et al., 1984a) by measuring the release of (Ashurst and Cohen, 1981).
14C02 from [1-14C] glucose. AHH activity was determined by
the radioactive assay developed by Van Cantfort et al. (1977), Mutagenicity experiments
Mutagenicity experiments were performed by using His- S.
using HL suspensions (lo8 cells/ml).
typhimurium TA-100 (Ames et al., 1960). Bacteria were grown
Determination of BaP metabolites
overnight in Oxoid Nutrient Broth 2, centrifuged for 10 min at
HL suspended in culture medium were extracted into 3 2,000 g and resuspended in Hanks’ medium free of C a + + and
volumes of ethyl acetate/acetone (2: 1 by vol) containing Mg++ to a titer of 3.5 X 107/ml. The incubations with intact
0.001 % butylated hydroxy-toluene. Additional extractions with HL (4 X 106/ml) or liver S9 fraction (2 mg protein), (Ames et
3 vols of ethyl-acetate were performed until no further radio- al., 1960) were performed for 3 hr at 37°C in the dark, in the
active material was released (generally 2 extractions were presence of the indicated amounts of BaP-7,8-diol and 50 pl of
sufficient). The organic phases were combined and evaporated bacterial suspension, in a final volume of 1 ml. When BaPDE
under vacuum. The residue was dissolved in a small volume was substituted for BaP-7,8-diol, HL and S9 fraction were
of methanol and subjected to HPLC analysis. The radioactivity omitted. At the end of incubation the bacterial suspensions
of total organo-soluble metabolites was determined in the ex- were plated and the His+ revertant colonies were counted
tracts after removal of unreacted BaP by TLC (Selkirk et al., (Feo et al., 1984b). Controls incubated without BaP metabo1975). For determination of water-soluble metabolites, HL lites, HL and S9 fraction were used to calculate the spontasuspensions were homogenized using a Polytron PT-10 ho- neous reversed mutation.
mogenizer at full speed (3 bursts of 5 sec each). Homogenates
Proteins were determined as previously published (Feo et
were combined with 0.2 vols of 1 M acetate buffer (PH 5.5) al., 1984~).
and incubated for 30 min at 37°C with 0.5 IU/ml of 0glucuronidase and 0.5 IU/ml of aryl-sulfatase. The reaction
RESULTS
was stopped by adding 2 vols of ice-cold ethyl acetate:acetone
(2: 1) and extracting as above. HPLC profiles of organo-solu- BaP metabolism
ble metabolites from untreated samples were subtracted from
The G6PD activity of freshly isolated normal and G6PDthose of enzyme-treated samples. The radioactivity of the deficient HL was respectively 26.7 f 4.96 and 0.88 k 0.06
material remaining after extraction of glucuronide and sulfate nmol of NADPH produced per min/mg of protein (n=66 for
conjugates as well as of organo-soluble metabolites was taken each type of HL, SD). The HMS activity was respectively 823
as the amount of other conjugated metabolites (for instance,
36 and 242 rt 21 dpm of 14C02 released/min/lO6 cells (n
glutathione conjugates). The BaP metabolites were separated = 66 for each type of HL, SD). G6PD and HMS activities did
on HPLC (Perkin Elmer Series 10) with an 84-S UV detector not change significantly during 48 hr of culture in the presence
and a Perkin Elmer Analytical C18 column (25 X 0.46 cm, of mitogens and BaA.
i.d.), and eluted with a 15-min gradient of 50-75% methanol
The 2 HL populations used in this study exhibited the same
followed by 75% methanol for 15 min and then a 15-min
gradient of 75-99% methanol (flow rate: 1 ml/min). Effluent range of AHH activities (1.5-9.0 pmol of BaP hydroxylated/
was monitored at 254 nm and fractions were collected every min/mg of protein, for BaA-induced AHH and 0.63-3.7 pmol/
min/mg protein for non-induced AHH). No differences in
20 sec and used to determine radioactivity.
AHH activity were found between the 2 28-individual
Isolation and adduct analysis of DNA
subgroups (see “Material and Methods”) of both control and
In order to isolate DNA from harvested cells, HL were experimental HL, used for analysis of metabolite pattern and
suspended in a solution containing 10 mM TrisCl (PH 7), 10 adduct formation.
Organo-soluble and water-soluble metabolites produced by
mM EDTA and 0.5% sodium dodecylsulfate, incubated for 15
min at 37°C and then for 12 hr with proteinase K (750 pglml). both types of HL were: 9.10-, 4 3 - and 7,8-diols, 1,3- and
DNA was extracted once with phenol/chloroform/isoamyl al- 3,6-quinones, 9- and 3-hydroxy (Table I). Two peaks that
cohol (25:24: l, by vol), and twice with chloroform/isoamyl eluted before diols, referred to as more polar, are probably
alcohol (24:l). It was then precipitated from the collected mixtures of triols and tetrols (Yang et al., 1977). It cannot be
organic phases with 0.1 vol of 2 M NaCl and 2 vol of ethanol. excluded, however, that small amounts of ethyl-acetate-exDNA from lo7 cells was dissolved in 1 ml of a solution tractable, sulfate-conjugated metabolites belong to this fraccontaining 10 mM TrisCl (PH 8) and 10 mM EDTA, incubated tion. Total organo-soluble metabolites represented 61-71 % in
for 1 hr at 37°C with 1 U / d of heat-inactivated RNase, for 2 both normal and G6PD-deficient HL. Total organo-soluble and
hr with proteinase K (350 pg/ml) and then extracted and water-soluble metabolites were about twice as low in the defiprecipitated as above. Purified DNA was dissolved in 10 mM cient cells as in controls. The data in Table I do not take into
TrisCl buffer (PH 7.2) and digested to the constituent nucleo- account the fraction of water-soluble metabolites not extractasides with DNase, snake venom phosphodiesterase, and alka- ble with ethyl acetate after digestion with 0-glucuronidase and
line phosphatase (Baird and Cohen, 1981). Nucleosides aryl sufatase (see “Material and Methods”). This fraction
flasks at 37°C in a humidified atmosphere of 5% COz, in the
presence of mitogens and BaA. After 24 hr, HL were harvested by centrifugation (10 min at 320 g) and suspended at
1.2 X lo7 cells per ml in fresh medium containing labelled
BaP. Twenty-four hours later the cultures (medium plus cells)
were used to extract BaP metabolites. Alternatively, the cells
were harvested by centrifugation in phosphate-buffered saline
and suspended at 5-7 x lo6 cellslml. The suspensions of
washed cells were used for the determination of enzymatic
activities and BaP:DNA adducts.
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562
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FEO ET AL.
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TABLE 1 - FORMATION OF BENZO(a)PYRENE METABOLITES lN,CULTURES OF NORMAL AND G6PDDEFICIENT LYMPHOCYTES
pmoli5 x 10’ cells’
Metabolites
Normal
Total
Organo-soluble
Water-soluble
Organo-soluble
More Polar I
More Polar I1
9,lO-Diol
4,5-Diol
7,8-Diol
1,6-Quinone
3,6-Quinone
9-Hydroxy
3-H ydroxy
Water-soluble
More Polar I
More Polar I1
9,IO-Diol
4.5-Diol
7,8-Diol
1,6-Quinone
3.6-Quinone
9-Hyhroxy
3-Hydroxy
Variant’
1,456k293
984 172 (67.4)
476k225 (32.6)
721 2244
498k115 (68.0)
234k101 (32.0)
128.2k22.7 (12.9)
63.9k18.6 (6.4)
107.4f20.5 (10.8)
31.2+7.9 (3.1)
77.6k8.6 (7.8)
155.3f26.8 (15.7)
1I5 .O 24.5 (1 I . 6)
88.1 q16.9 (8.9) ’
233.2k44.7 (22.5)
54.3+ 17.2 (10.6)
23.6+12.7 (4.6)
34.8k 10.6 (6.8)
20.4+9.5 (4.0)
38.4k15.1 (5.5)
62.6 + 3 1.7 (14.2)
90.2+31.8 (17.6)
66.5z28.5 (13.0)
120.5+25.7 (23.6)
112.O k25.3 (25.4)
45.2c26.3 (10.2)
7.2k2.9 (1.6)
29.0+8.1 (6.6)
28.776.7 ( 6 s j
58.7+14.7 (13.3)
112.6& 65.4 (25.5)
15.4k5.2 (3.5)
32.4+ 10.6 (7.3)
34.3k9.8 (15.6)
31.0k6.4 (14.1)
1.4k0.7 (0.6)
7.0+2.6 (3.2)
7.0+2.1 (3.2)
43.3k7.3 (19.48)
68.4k13.6 (31.2)
7.4k1.1 (3.4)
19.5k9.0 (8.9)
+
+
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‘Cultures of HL in MEM containing 10%inactivated FBS, mitogens and 2 pg of BaAiml, were exposed to 0.01
SD of 56
determinations, for total metabolites, and of 28 determinations for the metabolite pattern of each type of HL. In
parentheses, percentages of total metabolites or percentages of the total organo- and water-soluble metabolites.
-”‘t”-test: variant vs. normal, significant for at least p < 0.05 for total, organo-soluble and water-soluble.
mM BaP for 24 hr and the metabolites were isolated as described in “Material and Methcds”.-2Means k
TABLE 11 - BENZO(a)PYRENE-DNAADDUCTS FORMED IN CYLTURES OF
NORMAL AND G6PD-DEFICIENT LYMPHOCYTES
Adducts
Overall binding
I
I1
~~
I11
IV
V
pmolI5
lo7 cells’
Variant’
Normil
7.8- D 10 L9.10 - E PO X ID E
W
+
7.8-OIOL
7,8 - D IOL
1 2 1
1
~2
L
3000
LYMPHOCYTES
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15.23k0.99
1.56+0.15
6.63 1.31
4.2971.71
2.73 k 1.26
1.05 f0.08
+
X
LOO
6.31+1.51
1.08k0.27
3.34 0.54
0.90 0.06
1.18k0.24
+
+
4
a
300
WITHOUT
S9 W I T H S9
G6PD*
G6PD-
[L
W
a
ln
g
20(
2
E
‘HL were grown for 24 hr in MEM supplemented with 10% inactivated FBS,
W
>
mitogens and 2 pgiml of BaA. The cultures then received 0.01 miv BaP and 24 hr
W
later DNA was isolated, purified and hydrolyzed to hydrocarbon-deoxyribonucleo- .x
side adducts separated by HPLC.-*Means f S D of 28 determinations with lymphocytes of each type-3“r”-test: Variant vs. normal, significant for at leastp < 0.01
for overall binding and adducts.
lo(
t
FIGURE
1 - Induction of reversed mutation of S. iyphimurium TA100 (His-) by benzo(a)pyrene metabolites. 7,8-dihydrodiol-9,1O-epoxide was present at a final concentration of 2 p g l m l of reaction meamounted to 22.13
3.27 and 17.95 2.95 pmols of BaP dium. 7,8-diol was present at concentrations of 1 , 2 and 4 pg/rnl in the
metabolite per 5 x lo7 cells (n = 28 for each type of HL, experiments with fraction S9 and at a concentration of 4 pg/ml in those
SD) for normal and deficient HL, respectively, which corre- with lymphocytes. After incubation the bacteria were plated and the
sponds to 1.5% and 2.3% of total metabolites produced by number of revertant colonies was counted after 72 hr at 37°C. The
normal and deficient cells. It may be calculated from the data mutagenic activity of BaPDE was tested in the absence of fraction S9
in Table I that the percent distribution of organo- and water- and lymphocytes. Data are means of 2 triplicate determinations or
means + SD of 5 triplicate determinations. The number of revertants
soluble metabolites did not exhibit any major difference be- per
plate for the BaPDE-treated bacteria is indicated on the appropritween the 2 types of HL. However, there was a lower percent- ate column.
Abbreviations: G6PD+, normal lymphocytes; G6PD-,
age of 9,lO-diol among organo-soluble metabolites in the G6PD-deficient lymphocytes.
G6PD-deficient HL. A lower percentage of more polar fraction I and diols was also found for water-soluble metabolites.
Comparison of the relative amounts of each metabolite showed
a 25-67% decrease for organo-soluble metabolites and a 27- Mutagenesis experiments
76 % decrease for the water-soluble ones in the G6PD-deficient
The ability of HL to transform the proximate carcinogen
HL as compared to controls.
7,8-diol to a mutagenic compound was studied by the Ames
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563
BaP METABOLISM AND G6PD DEFICIENCY
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test. As expected (Fig. I), BaPDE was highly mutagenic for
S. typhimurium TA-100 (His-) without preliminary activation
by the rat liver S9 fraction. In contrast, this activation was
necessary to render the BaP-7,8-diol mutagenic. When intact
HL were used as a source of the activating enzyme system, a
significant reversed mutation was only observed with normal
HL .
Adduct formation
The DNA adducts formed in normal and G6PD-deficient
HL are shown in Table 11. It appears that 5 adducts were found
with normal HL. Peaks I1 and 111 co-chromatographed with
standards derived from ( +)-antiBaPDE and tritium-labelled
dGua, while peak IV co-chromatographed with standards derived from ( +)-antiBaPDE and carbonium-labelled dAdE. The
other peaks were not identified. Only 4 adducts were formed
with G6PD-deficient HL, which corresponded to the first 4
peaks obtained with control cells. Peaks I1 and 111 made up, in
both types of HL, about 70% of total organo-soluble adducts,
while peak IV constituted 18-19%, for normal and deficient
HL. A comparison between normal and G6PD-deficient HL,
as concerns the amount of BaP:DNA adducts formed after
incubation with BaP, shows that overall adduct formation
decreased about 60% in G6PD-deficient HL in relation to
controls. Decreases of 31 % , 50%, 79% and 57 % were recorded for peaks I,II,III and IV, respectively, in the deficient
cells.
DISCUSSION
Our results show that the relative percentages of the different organo-soluble and water-soluble metabolites are similar
for normal and G6PD-deficient HL, and correspond roughly
to those found in normal human HL by Selkirk et al. (1975).
This might indicate that no variations of the BaP metabolic
patterns take place as a consequence of G6PD deficiency.
Further, the decrease in organo-soluble metabolite production
by G6PD-deficient cells incubated with BaP does not appear
to depend on variations of the ability of these cells to conjugate
BaP metabolites. We suggest that the decreased production by
G6PD-deficient HL of both organo- and water-soluble metabolites depends on a reduced capacity of these cells to metabolize BaP. This appears to be confirmed by the low ability of
the deficient HL to activate BaP-7,8-diol to a compound mutagenic for S. typhimurium TA-100 (His-). This compound is
presumably BaPDE, a carcinogen that does not need further
activation to give rise to S. typhimurium (His-) reversed mutation (Gelboin, 1980; see also Fig. 1).
The decrease of G6PD activity in HL carrying the Mediterranean enzyme variant is coupled with that of the NADPH/
NADP+ ratio and of HMS activity (Feo et al., 1984~).G6PD
and HMS, and then presumably also the NADPH level, are
apparently not influenced by the stimulation of the monooxygenase system by BaA. This system is involved in different
steps of BaP metabolism (Gelboin, 1980). The decrease of the
NADPH pool, in G6PD-deficient HL, could explain the great
reduction of BaP metabolism in these cells compared to normal
HL. In agreement with this interpretation it has recently been
observed that ethanol infusion into rats, which causes liver
NADPH oxidation (Reinke et al., 1980) strongly inhibits
phenol production by BaP (Reinke et al., 1982). In addition,
recent evidence, obtained from a permeabilized whole-cell
system, suggests that NADPH is rate-limiting in the mixed
function oxidation of BaP (Sadowski et al., 1985).
The major adduct detected in BaP-treated rodent (see Phillips, 1983) and human (Autrup et al., 1985; Stampfer et al.,
1981) cell cultures is the (+)anti-BaPDE:dGua adduct. This
represents about 70% of total adducts produced by both G6PDdeficient and normal HL. The other adduct identified was
( +)anti-BaPDE:dAde adduct. Although a correlation between
the amount of DNA adducts and the individual carcinogen
metabolite yields has not always been observed (Bartley and
Stampfer, 1985), it may be that the pattern of carcinogen
metabolism is of value in predicting the extent of DNA damage
(Jones et al., 1983). In HL carrying the Mediterranean G6PD
variant, a decrease of about 50%in organo-soluble BaP metabolite production is associated with a 60% decrease in DNA
adduct formation. Many factors may influence the extent of
DNA adduct formation, such as the extent of conjugation, the
production of 7,8-diol and its subsequent epoxidation and DNA
repair. As already noted, metabolite conjugation presumably
does not undergo major changes in G6PD-deficient cells as
compared to controls, while 7,8-diol production and its subsequent epoxidation appear to be considerably reduced in the
deficient cells. However, the influence of DNA repair on the
observed phenomena in the 2 types of HL is not known.
The decrease in BaP metabolism and DNA adduct formation
in G6PD-deficient cells could explain the resistance of these
cells to the BaP toxic effect in vitro (Feo et al., 1984b) as well
as that of in vitro growing human fibroblasts to BaP toxicity
and transforming activity (Feo et al., 1981, 1982, 1984~).In
vitro experiments do not completely reproduce in vivo conditions. However, some epidemiological evidence of a decreased
tumor incidence in G6PD-deficient subjects has been described (Beaconfield et al., 1965; Naik and Anderson, 1971;
Sulis, 1972; Mbensa et al., 1978). In addition, long-term per
os treatment with dehydroepiandrosterone, a strong G6PD
inhibitor (Lopez and Rene, 1973) which mimics many of the
effects of genetically transmitted G6PD deficiency as concerns
resistance to carcinogens (Schwartz and Perantoni, 1975; Feo
et al., 1981, 1982, 1984a), inhibits the formation of spontaneous (Schwartz, 1979) as well as chemically induced
(Schwartz and Tannen, 1981; Nyce et al., 1984) tumors in
mice.
ACKNOWLEDGEMENTS
This investigation was supported by grants from the “Progetto Finalizzato Ingegneria Genetica e Basi Molecolari delle
Malattie Ereditarie del CNR” , the “Minister0 Pubblica Istruzione” (programs 40% and 60%) and the “Regione Autonoma
Sardegna”.
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BARTLEY,
J.C., and STAMPFER,
M . R . , Factors influencing benzo(a)pyrene
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L., and JEPSEN, sis, 6, 1017-1022 (1985).
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