Effect of (R)L-sulforaphane on 5-aminolevulinic
acid-mediated photodynamic therapy
PATRYCJA MIKOLAJEWSKA, ASTA JUZENIENE, and JOHAN MOAN
Topical photodynamic therapy (PDT) with 5-aminolevulinic acid (ALA), or so-called
ALA-PDT, is a standard procedure in the clinical practice. For optimal treatment of
nonmelanoma skin cancer, actinic keratoses and other dermatoses improvements
are required because of adverse side effects, which include pruritus, erythema,
edema, and pain. (R)L-sulforaphane (SF) is a compound that protects against
erythema, but it can also induce DNA fragmentation that leads to cell death by
apoptosis. The aim of our study was to investigate whether SF has any impact on
protoporphyrin IX (PpIX) production and on PDT effectiveness. We have investigated
some relevant properties of SF: its photostability in dimethyl sulfoxide (DMSO), its
effect on ALA-induced production of PpIX in A431 human squamous carcinoma
cells and in human skin, its effect on the photoinactivation of PpIX sensitized cells,
and its effect on the rate of photobleaching of PpIX. SF had no influence on PpIX
photodegradation, neither in solution nor in A431 cells. The synthesis of PpIX was
increased by SF in human skin, but not in A431 cells. The average increase in PpIX
fluorescence in human skin was 18% ? 6% and 43% ? 10% for ALA combined with
80 nmol/L SF and 120 nmol/L SF, respectively. Pretreatment with (R)L-sulforaphane
before topical ALA-PDT may improve penetration of ALA through the stratum cor-
neum, and, subsequently, increase PpIX synthesis. (Translational Research 2008;
Abbreviations: ALA ? aminolevulinic acid; DMSO ? dimethyl sulfoxide; FBS ? fetal bovine
serum; FST ? Fitzpatrick skin type; PBS ? phosphate-buffered saline; PDT ? photodynamic
therapy; PpIX ? photosensitizer protoporphyrin IX; SF ? (R)L-sulforaphane
applied for the treatment of nonmalignant skin cancers,
actinic keratoses, acne vulgaris, and other dermatoses.1–3
opical photodynamic therapy (PDT) with 5-amin-
olevulinic acid (ALA) is a standard procedure that
is widely used in clinical practice. ALA-PDT is
Topical application of ALA leads to overproduction of the
endogenous photosensitizer protoporphyrin IX (PpIX).4–6
ALA-PDT is based on selective accumulation of PpIX
in neoplastic tissue, which is followed by exposure to
visible light of wavelengths within the absorption spec-
trum of PpIX. Upon light activation, the PpIX molecule
transfers energy to molecular oxygen. This transfer
leads to production of the highly reactive product sin-
glet oxygen, which can cause oxidative damage to
biomolecules and tissues close to the site of its gener-
ation.7,8 ALA-PDT is a noninvasive, selective treat-
ment that offers high cure rates as well as good-to-
excellent cosmetic outcome.4 However, temporary side
effects often occur during and after topical PDT, such
as pain, pruritus, erythema, and edema.4,9–21 The pain,
which is described as burning, stinging, and prickling
sensations, develops within a few seconds to a minute
after the start of the light exposure. Erythema is max-
From the Department of Radiation Biology, Institute for Cancer
Research, Rikshospitalet-Radiumhospitalet Medical Center, Monte-
bello, Oslo, Norway, and the Institute of Physics, University of Oslo,
Blindern, Oslo, Norway.
Supported by Helse-Sør, Norway.
Submitted for publication May 5, 2008; revision submitted July 9,
2008; accepted July 17, 2008.
Reprint requests: Patrycja Mikolajewska, Department of Radiation
Biology, The Norwegian Radium Hospital, N-0310 Oslo, Norway;
1931-5244/$ – see front matter
© 2008 Mosby, Inc. All rights reserved.
imal within 1–2 h after light exposure and can persist
for up to 6 days.22
(R)L-sulforaphane (SF) is a naturally occurring iso-
thiocyanate found in high concentrations in broccoli.
(R)L-sulforaphane is the biologically active isomer (Fig
1, A and B). In this article, the abbreviation SF will be
given to (R)L-sulforaphane, unless specifically stated.
SF is known to induce phase II detoxifying enzymes,
enhance detoxification of carcinogens, and block initi-
ation of chemically induced carcinogenesis in animal
models.23–26Cell culture and xenograft studies suggest
additional roles of SF, which include inhibition of
growth of tumors, arrest of the cell cycle progression,
and enhancement of apoptosis.27At high concentra-
tions (30–100 ?mol/L), SF is an effective inducer of
apoptosis.28It can also be useful for protection against
erythema caused by ultraviolet radiation.29The aim of
our study was to investigate whether SF will influence
ALA-induced synthesis of PpIX, PDT effectiveness,
and PDT-related side effects.
MATERIALS AND METHODS
Chemicals. 5-ALA, PpIX, phosphate-buffered saline
(PBS), dimethyl sulfoxide (DMSO), Dulbecco’s mod-
ified Eagle’s medium, (R)L-SF, penicillin/streptomycin
solution, L-glutamine, and trypsin/ethylenediamine tet-
raacetic acid solution were obtained from Sigma-Al-
drich Norway AS (Oslo, Norway). Fetal bovine serum
(FBS) was obtained from GIBCO BRL, Life Technol-
ogies (Roskilde, Denmark). All chemicals were of the
highest purity commercially available. The stock solu-
tions of the compounds were prepared in DMSO (4
mmol/L SF stock solution, 1.15 mmol/L PpIX stock
solution) or in serum-free medium (10 mmol/L ALA
stock solution) immediately before being used in the
experiments. In the study that involved volunteers, the
SF-DMSO solution was diluted in cream base (Un-
guentum M; Almirall Hermal GmbH, Reinbek, Ger-
many). The concentrations of DMSO were 0.002% and
0.003% for 80 nmol/L and 120 nmol/L final SF con-
centrations in cream, respectively.
Cell cultivation. Experiments were carried out on hu-
man squamous carcinoma A431 cell line. The cells
were cultured in DMEM medium that contained 2
mmol/L L-glutamine, 10% FBS, 100 U/mL penicillin,
and 100 ?g/mL streptomycin. Cells were incubated at
37°C in a humidified atmosphere that contained 5% CO2.
Light exposure. An in-house built lamp with 4 fluo-
rescent tubes (Philips TLK 40 W/03, the Netherlands),
which emit light in the region 400–460 nm and with a
peak at 420 nm, was used in the experiments. The
fluence rate at the position of the sample was 10 ? 0.5
mW/cm2, as measured with a photodiode (NewPort,
Model 1815-C, Irvine, Calif). For studies that involved
volunteers, a light-emitting diode lamp (Photocure
ASA, Oslo, Norway) was used. The lamp emits in the
spectral range 580–670 nm, and it has a peak at 632
nm. The fluence rate at the surface of the skin was 90 ?
4 mW/cm2. Similar fluence rates are continually being
used in clinical PDT.
The influence of SF on PpIX fluorescence. Solutions of
0.28 ?mol/L PpIX with 0–100 ?mol/L SF were pre-
pared in DMSO. Fluorescence spectra of the samples
were recorded in cuvettes placed directly in the stan-
dard cuvette holder of a luminescence spectrometer
(Perkin Elmer LS45 Norwalk, Conn). The background
fluorescence (autofluorescence) of the solvent without
PpIX was recorded and subtracted. The 407-nm exci-
tation light from the luminescence spectrometer was of
low intensity (less than 1 mW/cm2) and did not induce
any significant photobleaching of PpIX. The excitation
and emission slits were both set at 10 nm.
PpIX photobleaching in DMSO. In all, 0.28 ?mol/L
PpIX solutions, with or without 10 or 20 ?mol/L SF,
were prepared in DMSO and exposed to blue light (420
nm). PpIX fluorescence was recorded before and after
light exposure as described previously.
Dark cytotoxicity of SF. A431 cells were subcultured
into 25-cm2flasks with filters (NUN, Denmark) at
densities of 500 cells/flask and were incubated for 48 h
for proper attachment to the substratum. Afterward, the
AT A GLANCE COMMENTARY
We have investigated (R)L-sulforaphane (SF),
which is known to trigger many reactions in the
cells. Lately, it was found to reduce erythema in
human skin. Next to pain, erythema is the most
adverse side effect of topical photodynamic ther-
apy (PDT). Therefore, SF could be possibly used
to reduce erythema after PDT. No data were found
regarding the influence of SF on PDT effective-
ness and outcome. Our goal was to investigate the
influence of SF on protoporphyrin IX (PpIX) pro-
duction and photobleaching in solutions, A431
cells, and human skin. We found that SF enhances
PpIX production in human skin.
Our obtained data will be very interesting for
clinicians who would like to use SF as a means to
reduce erythema after topical PDT and would be
concerned with the effect SF can have on PDT
Volume 152, Number 3Mikolajewska et al
cells were washed with fresh serum-free medium, and
0–100 ?mol/L SF was added for the next 24 h. Cell
survival was determined by means of colony assay.
Photobleaching of PpIX in cells. A431 cells were ex-
posed to 10 ?mol/L or 20 ?mol/L SF in culture me-
dium with serum for 20 h. Then, the medium was
removed, the cells were washed with serum-free me-
dium, and 1 mmol/L ALA in culture medium without
serum was added for 4 h to allow buildup of intracel-
lular PpIX. Subsequently, the treated cells were washed
3 times with ice-cold PBS and scraped into 1 mL PBS.
The cell suspensions were exposed to blue light. PpIX
fluorescence was measured before and after light expo-
sure as described previously.
The influence of SF on ALA-PDT. A431 cells were ex-
posed to 10 ?mol/L SF for 20 h. Afterward, the cells
were washed with serum-free medium and incubated
with 1 mmol/L ALA in serum-free medium for the next
4 h. Light exposure was carried out immediately after
the incubation (blue light). After the treatment, the cells
were washed with fresh medium and kept for 8 days at
37oC in serum-containing culture medium.
The influence of SF on PpIX production and erythema
after ALA-PDT. The work that involved healthy human
volunteers was approved by the Regional Committee
for medical and health research (Regional komité for
medisinsk og helsefaglig forskningsetikk Helseregion
Sør avdeling B, REK Sør B; ref. nr. S-07434b). The
study was performed on 10 healthy volunteers (2 vol-
unteers with Fitzpatrick skin type (FST) II, 5 volunteers
with FST III, 2 with FST IV, and 1 with FST V). Four
spots (1.5 cm2each) were selected and marked on the
forearm of each volunteer. Then, 0.1 g of creams that
contained 80 nmol/L or 120 nmol/L of SF was applied
on the first and second spot, respectively. After 20 h,
creams that contained SF were removed, and creams
that contained 10% ALA were applied to the first,
second, and fourth spot. Cream base was applied to the
third spot as a control. After 4 h, the creams were
removed and the erythema baseline was determined by
narrow-band reflectance measurements at 568 nm
(green) and 655 nm (red) (DermaSpectrometer; Cortex
Technology, Hadsund, Denmark). The fluorescence of
the produced ALA-PpIX was measured in all spots
before and after light exposure by means of a fiber-
optic probe coupled to a fluorescence spectrometer
(LS50B; PerkinElmer, Norwalk, Conn). The exposure
time was set to 2 min to avoid pain for the volunteers
(CureLight; Photocure ASA, Oslo, Norway).
Statistics. Data are presented as means ? standard
error. Experiments in solutions and in cells are shown
as means from at least 3 independent experiments,
which were all performed in triplicates. The Student’s
t-test was used to compare the significance between
data points. Values of P ? 0.05 were considered as
indicating significant differences.
The fluorescence of PpIX was unchanged in the
presence of SF at concentrations up to 10 ?mol/L in
Fig 1. A, The chemical structure of SF. B, The absorbance spectrum of SF in 100% DMSO. C, Changes in PpIX
fluorescence in the presence of different concentrations of SF in 100% DMSO. D, Photobleaching kinetics of
PpIX in 100% DMSO in the absence and presence of SF.
Mikolajewska et al
solution (Fig 1, C). Higher concentrations of SF led to
a slight increase of the PpIX fluorescence. Concentra-
tions of 10 ?mol/L and 20 ?mol/L SF were chosen for
additional experiments. SF had no influence on the
PpIX degradation rate in DMSO (Fig 1, D).
SF gradually changed the attachment of the A431
cells to the surface of the flasks, and at concentrations
higher than 80 ?mol/L, the cells detached completely
(Fig 2, A). For additional investigations, we decided to
use 10 ?mol/L SF, which killed less than 50% of the
cells. SF did not influence the photobleaching rates of
ALA-PpIX in cells (Fig 2, B). Neither did we find any
difference between cell survival after ALA-PDT and
ALA-PDT combined with SF (Fig 2, C). The cell-
survival curves for both cells pretreated and not pre-
treated with SF showed a parallel pattern.
SF enhanced PpIX production (Fig 3, A) in the skin
of healthy human volunteers but not in A431 cells (Fig
2, D). Neither had it induced PpIX synthesis by itself
(Fig 2, D). SF in concentrations that are believed to
have a significant impact on erythema (6 ?mol/L and 4
?mol/L)29tended to induce skin irritation, probably
due to the DMSO content in the cream. For the skin
studies, we chose 120 nmol/L and 80 nmol/L of SF.
The most common way of pretreating human skin with
SF is application 3 times with 24 h intervals be-
tween.29,30However, this procedure would be long and
inconvenient for our volunteers. Therefore, we decided
on 1 application of SF 20 h before application of the
ALA-containing cream. This decision is supported by
the observation that 1-time application of SF gives
lesser, but still significant, effects compared with the
3-time application mode.30A significant increase in
PpIX production in the presence of SF was found in all
participants (P ? 0.01). The difference in the amount of
PpIX produced from 10% ALA in the presence of 80
nmol/L SF varied from 3% to 45% compared with
PpIX produced by 10% ALA without SF. Pretreatment
with 120 nmol/L SF increased the PpIX fluorescence
from 4% to 85% in comparison with ALA applied
alone (Fig 3, A).
Multiple biologic mechanisms are activated by SF, in-
cluding suppression of cytochrome P450 enzymes, induc-
tion of apoptotic pathways, and suppression of cell-cycle
progression. A major mechanism is Nrf2-mediated induc-
tion of phase 2 detoxification enzymes that increase cell
defense against oxidative damage and promote the re-
moval of carcinogens.23,24,26,27,29–34Inducible heme ox-
ygenase-1 is one of the phase 2 enzymes induced by SF.
The heme oxygenase enzyme system catalyzes the rate-
limiting step in heme degradation, which produces
equimolar quantities of biliverdin, iron, and carbon
monoxide.35CO stimulates mitochondrial generation
of free radicals and can poison heme proteins.36The
iron liberated during heme degradation can catalyze
ALA-PpIX in A431 cells incubated alone or in the presence of 10 ?mol/L or 20 ?mol/L SF. C, SF influence
on ALA-PDT outcome in A431 cells. D, The influence of 10 ?mol/L or 20 ?mol/L SF alone or in combination
with 1 mmol/L ALA on PpIX production in A431 cells.
A, The dark toxicity of SF in A431 cells after 24 h of incubation. B, Photobleaching kinetics of
Volume 152, Number 3Mikolajewska et al
The slight increase in PpIX fluorescence in solution
in the presence of SF may be caused by PpIX mono-
merization. We did not observe any influence of SF on
PpIX photobleaching in DMSO solution (Fig 1, D).
SF reduced the attachment of A431 cells to the
surface of the flask. The killing effect could have been
a result of SF-induced DNA damage, which led to
apoptosis.34No difference between cells pretreated
with SF and control cells was found with regard to the
ALA-PDT effect on cell survival and PpIX photo-
We observed an SF-induced increase of ALA-PpIX
fluorescence in the skin of the healthy volunteers but
not in A431 cells. Our initial hypothesis for this was
that SF may induce heme degradation that can lead to
activation of heme biosynthesis feedback-control sys-
tem activation and resulted in increased production of
PpIX. However, this hypothesis turned to be incorrect
since we did not observe any PpIX fluorescence in
spots treated with SF only. We also did not observe
PpIX production in cells treated only with SF. DMSO
is a well-known penetration enhancer,38and we con-
sidered the possibility of an influence of DMSO on the
skin permeability in the spots where SF was applied.
According to Notman et al,38DMSO exerts its perme-
ability enhancement effect on the stratum corneum to a
significant extent only at high concentrations (?0.26%).
The concentration of DMSO in our cream that contained
SF was very low (?0.01%); therefore, the effect is likely
to be negligible. Nevertheless, another factor turned out to
have an impact on the skin permeability. The cream base
that contained SF was kept on the skin for 20 h prior to
application of the ALA-containing cream. Such a long
incubation time with the cream on the skin resulted in
a softening of the stratum corneum, which might allow
ALA to penetrate deeper into the skin. We found that
PpIX fluorescence was slightly greater in the spots that
were pretreated with cream base only prior to ALA
application. However, this increase was not significant
(P ? 0.46) compared with what was observed in the
areas treated with ALA and SF. The mechanism behind
the observed increase in PpIX production in the pres-
ence of SF remains unidentified.
We did not observe any effect of SF on ALA-PpIX
photobleaching in human skin (Fig 3, B). In some
volunteers, SF gave some PpIX protection (volunteer
3), whereas in others, it gave an opposite effect (vol-
unteers 7, 8, 9, and 10). Such variations in photobleach-
ing may depend on the melanin content in the skin, the
PpIX concentration, and the yield of singlet oxygen
generation. Thus, melanin seemed to protect PpIX from
bleaching in volunteers with a dark skin type (volun-
teers 1, 3, and 5). Application of SF before topical
ALA-PDT increases the PpIX synthesis and, therefore,
also the effectiveness of ALA-PDT.
We also appreciate the inspiration for this work from our colleague
Håvar A. Sollund.
1. Angell-Petersen E, Sorensen R, Warloe T, et al. Porphyrin for-
mation in actinic keratosis and basal cell carcinoma after topical
application of methyl 5-aminolevulinate. J Invest Dermatol
2. Cairnduff F, Stringer MR, Hudson EJ, Ash DV, Brown SB.
Superficial photodynamic therapy with topical 5-aminolaevulinic
acid for superficial primary and secondary skin cancer. Br J
3. Chen HM, Chen CT, Yang H, et al. Successful treatment of oral
verrucous hyperplasia with topical 5-aminolevulinic acid-
mediated photodynamic therapy. Oral Oncol 2004;40:630–7.
4. Braathen LR, Szeimies RM, Basset-Seguin N, et al. Guidelines
on the use of photodynamic therapy for nonmelanoma skin
cancer: an international consensus. J Am Acad Dermatol 2007;
5. Kennedy JC, Pottier RH. Endogenous protoporphyrin IX, a clin-
ically useful photosensitizer for photodynamic therapy. J Photo-
chem Photobiol B 1992;14:275–92.
6. Marcus SL, Sobel RS, Golub AL, Carroll RL, Lundahl S, Shulman
DG. Photodynamic therapy (PDT) and photodiagnosis (PD) using
endogenous photosensitization induced by 5-aminolevulinic acid
Fig 3. A, ALA- PpIX fluorescence in human skin before exposure to
light (peak at 631 nm) in the presence of 80 nmol/L or 120 nmol/L
SF in comparison with the fluorescence of ALA-PpIX alone. B,
Percentage of ALA-PpIX fluorescence photobleached during light
exposure in the presence of 80 nmol/L SF or 120 nmol/L SF.
Mikolajewska et al
(ALA): current clinical and development status. J Clin Laser Med Download full-text
7. Juzeniene A, Nielsen KP, Moan J. Biophysical aspects of photody-
namic therapy. J Environ Pathol Toxicol Oncol 2006;25:7–28.
8. Triesscheijn M, Baas P, Schellens JH, Stewart FA. Photody-
namic therapy in oncology. Oncologist 2006;11:1034–44.
9. Borelli C, Herzinger T, Merk K, et al. Effect of subcutaneous
infiltration anesthesia on pain in photodynamic therapy: a con-
trolled open pilot trial. Dermatol Surg 2007;33:314–8.
10. Brown SB, Shillcock M, Jones P. Equilibrium and kinetic studies
of the aggregation of porphyrins in aqueous solution. Biochem J
11. Ericson MB, Sandberg C, Stenquist B, et al. Photodynamic
therapy of actinic keratosis at varying fluence rates: assessment
of photobleaching, pain and primary clinical outcome. Br J
12. Grapengiesser S, Ericson M, Gudmundsson F, Larko O, Rosen
A, Wennberg AM. Pain caused by photodynamic therapy of skin
cancer. Clin Exp Dermatol 2002;27:493–7.
13. Holmes MV, Dawe RS, Ferguson J, Ibbotson SH. A randomized,
double-blind, placebo-controlled study of the efficacy of tetra-
caine gel (Ametop) for pain relief during topical photodynamic
therapy. Br J Dermatol 2004;150:337–40.
14. Kasche A, Luderschmidt S, Ring J, Hein R. Photodynamic
therapy induces less pain in patients treated with methyl amin-
olevulinate compared to aminolevulinic acid. J Drugs Dermatol
15. Misra A, Maybury K, Eltigani T. Late erythema after photody-
namic therapy to the face. Plast Reconst Surg 2006;117:2522–3.
16. Radakovic-Fijan S, Blecha-Thalhammer U, Kittler H, Honigsmann
H, Tanew A. Efficacy of 3 different light doses in the treatment
of actinic keratosis with 5-aminolevulinic acid photodynamic
therapy: a randomized, observer-blinded, intrapatient, compari-
son study. J Am Acad Dermatol 2005;53:823–7.
17. Sandberg C, Stenquist B, Rosdahl I, et al. Important factors for
pain during photodynamic therapy for actinic keratosis. Acta
Derm Venereol 2006;86:404–8.
18. Skiveren J, Haedersdal M, Philipsen PA, Wiegell SR, Wulf HC.
Morphine gel 0.3% does not relieve pain during topical photody-
namic therapy: a randomized, double-blind, placebo-controlled
study. Acta Derm Venereol 2006;86:409–11.
19. van Oosten EJ, Kuijpers DIM, Thissen MRTM. Different pain
sensations in photodynamic therapy of nodular basal cell carci-
noma: results from a prospective trial and a review of the
literature. Photodiagn Photodyn Ther 2006;3:61–8.
20. Wennberg AM. Pain, pain relief and other practical issues in
photodynamic therapy. Australas J Dermatol 2005;46:S3–4.
21. Wiegell SR, Stender IM, Na R, Wulf HC. Pain associated with
photodynamic therapy using 5-aminolevulinic acid or 5-
aminolevulinic acid methylester on tape-stripped normal skin.
Arch Dermatol 2003;139:1173–7.
22. Clark C, Dawe RS, Moseley H, Ferguson J, Ibbotson SH. The
characteristics of erythema induced by topical 5-aminoleavulinic
acid photodynamic therapy. Photodermatol Photoimmunol Pho-
23. Fahey JW, Zhang Y, Talalay P. Broccoli sprouts: an exception-
ally rich source of inducers of enzymes that protect against
chemical carcinogens. Proc Natl Acad Sci U S A 1997;
24. Fahey JW, Talalay P. Antioxidant functions of sulforaphane: a
potent inducer of Phase II detoxication enzymes. Food Chem
25. Zhang Y, Talalay P, Cho CG, Posner GH. A major inducer of
anticarcinogenic protective enzymes from broccoli: isolation and
elucidation of structure. Proc Natl Acad Sci U S A 1992;89:
26. Zhang Y, Talalay P. Anticarcinogenic activities of organic iso-
thiocyanates: chemistry and mechanisms. Cancer Res 1994;54:
27. Gills JJ, Jeffery EH, Matusheski NV, Moon RC, Lantvit DD,
Pezzuto JM. Sulforaphane prevents mouse skin tumorigenesis
during the stage of promotion. Cancer Lett 2006;236:72–9.
28. Yeh CT, Yen GC. Effect of sulforaphane on metallothionein
expression and induction of apoptosis in human hepatoma
HepG2 cells. Carcinogenesis 2005;26:2138–48.
29. Talalay P, Fahey JW, Healy ZR, et al. Sulforaphane mobilizes
cellular defenses that protect skin against damage by UV radia-
tion. Proc Natl Acad Sci U S A 2007;104:17500–5.
30. Dinkova-Kostova AT, Fahey JW, Wade KL, et al. Induction of
the phase 2 response in mouse and human skin by sylforaphane-
containing broccoli sprout extracts. Cancer Epidemiol Biomark-
ers Prev 2007;16.
31. Gao X, nkova-Kostova AT, Talalay P. Powerful and prolonged
protection of human retinal pigment epithelial cells, keratino-
cytes, and mouse leukemia cells against oxidative damage: the
indirect antioxidant effects of sulforaphane. Proc Natl Acad Sci
U S A 2001;98:15221–6.
32. Talalay P, Fahey JW, Holtzclaw WD, Prestera T, Zhang Y.
Chemoprotection against cancer by phase 2 enzyme induction.
Toxicol Lett 1995;82–83:173–9.
33. Choi WY, Choi BT, Lee WH, Choi YH. Sulforaphane generates
reactive oxygen species leading to mitochondrial perturbation for
apoptosis in human leukemia U937 cells. Biomed Pharmacother
34. Yeh CT, Yen GC. Effect of sulforaphane on metallothionein
expression and induction of apoptosis in human hepatoma
HepG2 cells. Carcinogenesis 2005;26:2138–48.
35. Sikorski EM, Hock T, Hill-Kapturczak N, Agarwal A. The story
so far: molecular regulation of the heme oxygenase-1 gene in
renal injury. Am J Physiol Renal Physiol 2004;286:F425–41.
36. Zhang J, Piantadosi CA. Mitochondrial oxidative stress after
carbon monoxide hypoxia in the rat brain. J Clin Invest 1992;
37. Dennery PA, Seidman DS, Stevenson DK. Neonatal hyperbiliru-
binemia. N Engl J Med 2001;344:581–90.
38. Notman R, den Otter WK, Noro MG, Briels WJ, Anwar J. The
permeability enhancing mechanism of DMSO in ceramide bilayers
simulated by molecular dynamics. Biophys J 2007;93:2056–68.
Volume 152, Number 3Mikolajewska et al