JOURNAL OF OCULAR PHARMACOLOGY AND THERAPEUTICS
Volume 33, Number 3, 2017
ª Mary Ann Liebert, Inc.
DOI: 10.1089/jop.2016.0053
In Vitro Evaluation of the Ophthalmic Toxicity Profile
of Chlorhexidine and Propamidine Isethionate Eye Drops
Anxo Fernández-Ferreiro,1–3 Marı́a Santiago-Varela,4 Marı́a Gil-Martı́nez,4,5 Miguel González-Barcia,2,3
Andrea Luaces-Rodrı́guez,1 Victoria Dı́az-Tome,1 Marı́a Pardo,6 José Blanco Méndez,1 Antonio Piñeiro-Ces,4
Marı́a Teresa Rodrı́guez-Ares,4 Maria Jesus Lamas,2,3 and Francisco J. Otero-Espinar1
Abstract
Purpose: Acanthamoeba keratitis causes frequent epithelial lesions that fully expose the corneal stroma. The
aim of this study was to determine the toxic profile of chlorhexidine and propamidine eye drops.
Methods: We used primary human keratocytes in cell culture in combination with a novel technology that
evaluates dynamic real-time cytotoxicity through impedance analysis. Additional studies such as a classic cell
viability test (WST-1Ò), a bovine corneal opacity and permeability assay, and an irritation eye study (Hen’s Egg
Test [HET]) have been made.
Results: Both eye drop formulations showed a time- and concentration-dependent toxicity profile, in which long
periods and high concentrations were more detrimental to cells. In prolonged times of exposure, propamidine is
more harmful to cells than chlorhexidine. On the contrary, no irritation has been detected in using the HETchorioallantoic membrane test and no alterations in the corneal transparency nor permeability was produced by
the treatment with both eye drops.
Conclusions: In culture assay, chlorhexidine eye drops have proven to be less cytotoxic than BroleneÒ for a
long contact period of time, but no signs of irritation or alterations in transparency or permeability have been
observed in the cornea after both treatments.
N
Y
O
I
L
T
N
U
O
B
I
W ISTR
E
I
V
D ON
E
R
R
R
I
O
T
F
O
C
F
D
U
E
D
D
O
N
R
E
P
T
E
N
I
R
T
R
O
O
N
F
Keywords: Acanthamoeba, chlorhexidine, cornea, eye drops, keratitis, propamidine, toxicology
Introduction
ree-living amoeba of the Acanthamoeba spp. genus is
the causal agent of Acanthamoeba keratitis, an ocular
infection that poses a risk to corneal integrity. The number
of reported cases worldwide is increasing yearly, especially
among contact lens users, and the rate of successful treatment is low despite advances in antimicrobial chemotherapy
and supportive care.1
Currently, no universal protocols exist for therapeutic
treatment of this pathology. The most common protocol is an
initial intensive treatment that combines a diamidine and a
biguanide, which produces a rapid lysis of trophozoites to
prevent them from reverting into more resistant cystic forms.
After an initial intensive treatment, the number of instillations
is reduced due to the frequent incidence of toxic phenomena.
In certain cases, it is even necessary to continue with
monotherapy using only one of the medications. Therapeutic
treatment with topical ophthalmic pharmacologic agents is
prolonged, with a minimum duration of 4 weeks, and some
authors recommend therapy for at least 6 or 12 months.2
The low investment in research and development for
low-incidence pathologies hinders the development and
commercialization of effective medications by the pharmaceutical industry.3 Currently, no ophthalmic topical treatment for Acanthamoeba keratitis is commercially available
1
Department Pharmacy and Pharmaceutical Technology, Faculty of Pharmacy, University of Santiago de Compostela (USC), Santiago
de Compostela, Spain.
2
Department of Pharmacy, Xerencia de Xestión Integrada de Santiago de Compostela (SERGAS), Santiago de Compostela, Spain.
3
Clinical Pharmacology Group, Health Research Institute of Santiago de Compostela (IDIS-ISCIII), Santiago de Compostela, Spain.
4
Department of Ophthalmology, Hospital de Conxo, Xerencia de Xestión Integrada de Santiago de Compostela (SERGAS), Santiago de
Compostela, Spain.
5
Instituto Oftalmológico Gómez-Ulla, Santiago de Compostela, Spain.
6
Obesidomic Group, Health Research Institute of Santiago de Compostela (IDIS-ISCIII), Santiago de Compostela, Spain.
202
OPHTHALMIC TOXICITY PROFILE OF CHLORHEXIDINE AND ISETHIONATE EYE DROPS
in Spain. Thus, hospital pharmacies are responsible for the
foreign acquisition and transaction involved in importing
diamidines, such as propamidine isethionate 0.1% (BroleneÒ
or Golden EyeÒ), and for developing biguanides through
compounded formulation of chlorhexidine 0.02% eye drops.4
Typically, compounded ophthalmic formulations made at
hospital pharmacies use commercially available medications
intended for use via the parenteral route. The medications
are dissolved or diluted in tamponades that are compatible
with the ocular route. However, these medications are not
designed or adapted for that route; therefore, they may have
side effects at the ophthalmic level.5 Conversely, only ocular toxicity and dose–response studies are available for the
pharmaceutical drugs used, which is why the concentrations
used are adapted and used based on results and clinical
experience gained over time. Furthermore, poor adaptation
to the ocular route and the tendency to use very simple
formulations generate systems that lack effectiveness because they have a very low retention time on the ocular
surface due to high precorneal clearance.6
Dosage intervals based on frequent instillations of eye
drops with high drug concentrations and for long periods of
time are prescribed with the goal of maintaining therapeutic
concentrations. This practice leads to increased patient discomfort, resulting in reduced treatment adherence and, thus,
reduced therapeutic effectiveness.7 Furthermore, toxic ocular effects are frequent and are caused by commercial
medications such as nonsteroidal anti-inflammatory drugs
and antiglaucomatous prostaglandins. These medications,
despite being tightly controlled by regulatory agencies,
sometimes present unacceptable toxicities.8
One essential aspect in the development of new ophthalmic
drugs is the evaluation of the local tolerance. The effects of
the eye drops on the ocular structures are usually studied
using in vitro cellular studies, ex vivo assays, or in vivo animal models such as mice, rabbits, or rats. The in vivo standard
model proposed to study ocular irritation is the Draize test,9
however, the use of vertebrates to evaluate the safety has
been widely criticized based on scientific and ethical reasons.
The concept of the 3Rs (refinement, replacement, and reduction) stimulates the development of alternative methods
such as in vitro methods, ex vivo methods, or the use of
‘‘lower’’ organisms as models (invertebrates, plants, and
microorganisms).10 According to different articles, the Hen’s
Egg Test–chorioallantoic membrane (HET-CAM) method,
bovine corneal opacity and permeability assay, or the in vitro
cellular studies are a good alternative to the use of animal
model in toxicity eye studies.11–13
Cellular models of detection of toxicity, including cytotoxicity assays, based on the observation of changes on
morphology, viability, metabolism, or cell adhesion can be a
good alternative to determine the behavior that the cells adopt
in vivo. The most commonly used cytotoxicity assays are
the neutral red dye, MTTÒ, WST-1Ò or AlamarBlueÒ. In
addition, novel detection systems in real time without cell
markings as xCELLigence real-time cell analyzer system
impedance analysis (RTCA) are increasingly used.14 RTCA is
a novel methodology with several advantages over the classical methods because it does not require the use of labels, is
noninvasive, it does not interfere with dyes, and allows to
make continuous measurement in time. Also, previous articles
have demonstrated a good correlation between RTCA and
classical cytotoxicity assays.15,16
203
It is of interest to guarantee that the preparations are
suitable for their intended use and pose no threat to the
patient. To achieve this, the toxic potential of these formulations must be established to develop estimations of the
benefits and risks that the formulations can have in complicated clinical situations where the integrity of the cornea
is compromised. This study aims to evaluate the toxicity
profile of anti-Acanthamoeba eye drops.
Methods
This is an in vitro experimental study developed to determine the toxicity of the compounded ophthalmic formulation made in hospital pharmacies, 0.22 mM chlorhexidine
eye drops and 0.17 mM propamidine isethionate eye drops
(Brolene). Table 1 shows the composition of the evaluated
eye drops.
Cell culture assays
Isolation of the stromal keratocyte primary culture. Keratocyte primary cultures were obtained from human
cornea fragments remaining from those used for corneal
transplant in a manner consistent with institutional ethical
standards and the Declaration of Helsinki. Cells were incubated for 10 min in trypsin at 37°C based on the modified
Ramke method, followed by mechanical elimination of the
endothelium and epithelium. The corneal stroma was cut
into 2-mm sections that were submerged in Dulbecco’s
modified Eagle’s medium/Ham F-12 supplemented with
10% fetal bovine serum, 2 mM L-glutamine, and antibiotics
(100 IU penicillin, 100 mg/mL streptomycin, and 50 mg/mL
gentamycin).
N
Y
O
I
L
T
N
U
O
B
I
W ISTR
E
I
V
D ON
E
R
R
R
I
O
T
F
O
C
F
D
U
E
D
D
O
N
R
E
P
T
E
N
I
R
T
R
O
NO
Cytotoxicity assay. Cell assays were performed using
a cellular bioimpedance biosensor system (xCELLigence
Real-Time System Cell Analyzer; RTCA).17 This system
uses electronic microchips that measure changes in the
impedance between the electrodes and the solution. When
the cell adheres to the well (16-well E-plate; ACEA Biosciences), the resistance increases, which increases the impedance. The impedance values are transformed into a
parameter known as the cellular index (CI)14 using an algorithm. A low CI indicates a lower number of cells adhering to the microelectrode, and an increase in the CI
indicates an increase in the number of cells18; therefore, all
Table 1. Composition of the Evaluated
Anti-Acanthamoeba Eye Drops
0.22 mM Chlorhexidine eye
drops
Propamidine isethionate
eye drops (BroleneÒ)
Bohmclorh chlorhexidine
0.5%
Water for injection
Compounded formulation
made at pharmacy hospitals
under sterile conditions
established by the Guide
for Good Practices in the
Preparation of Medicinal
Products in Healthcare
Establishments.10
Ammonium chloride
Benzalkonium chloride
Sodium chloride
Sodium hydroxide
Water for injection
204
FERNÁNDEZ-FERREIRO ET AL.
changes are detected in a continuous manner in real time. To
evaluate cytotoxicity, CI values are expressed as the normalized CI (NCI), where CIi(t) is the CI at a given time, and
CIi(t of dose) is the CI at the moment at which the medications
are added to the culture medium. The results were graphed
to show the dynamic changes for each of the assayed concentrations, and NCI is represented over time starting with
the addition of the compounds. The concentrations of
compounds that reduced the CI by 50% were calculated by
interpolation from the graphs that showed the normalized
response (%), and this parameter was called the CI50.19
Cytotoxicity assays. Cytotoxicity was evaluated using
an RTCA. Previous studies have shown that the optimal
number of cells is 3,000 per well.8 On reaching a CI of
*1.0, eye drops were added to the culture at different
concentrations. After adding the medications, the cell behavior, measured as the CI, was recorded continuously and
automatically every 15 min for 20 h. All assays were performed using cells between passages 4 and 10.
In addition, the colorimetric reaction assays WST-1 (Cell
Proliferation Reagent WST-1 from Roche Applied Science),
which are based on cell viability in relation to mitochondrial
enzymes,20 were performed. Both methods determined
keratocyte viability after 30 min, 75 min, 8 h, and 24 h of
incubation with these eye drops.
the light between the light source (Olympus Highlight 200
pipe light in Brightness position 3) and the light probe,
which detects the transmitted light measured by an illuminance meter (Gossen 5032C USB). An initial baseline
opacity measurement (%Tinitial, difference of light intensity
without and with cornea) is performed for all the corneas in
contact with BSS. The initial opacity reading is representative of a normal, untreated cornea. After the initial opacity
reading, each cornea was placed in Franz cells with the
epithelium oriented to the receptor chamber that contains
500 mL of the tested products (chlorhexidine 0.02% and
Brolene eye drops and BSSÒ as negative control). After
10 min of contact, the corneas were removed and the
transparency was measured again (%T10min). For permeability assay, the treated corneas were fixed in the Franz
cell, fluorescein is added to the anterior chamber and PBS in
the receptor chamber and incubated for 90 min. After this
time, the receptor medium is transferred to a quartz cuvette
and the optical density at 490 nm is determined using a
spectrophotometer (Agilent 8453). Each product was tested
in duplicate and the corneal surface in contact with the
products was 0.785 cm2.
N
Y
O
I
L
T
N
U
O
B
I
W ISTR
E
I
V
D ON
E
R
R
R
I
O
T
F
O
C
F
D
U
E
D
D
O
N
R
E
P
T
E
N
I
R
T
R
O
NO
The Hen’s Egg Test–chorioallantoic membrane
The HET-CAM test was used to determine the potential
irritancy of the anti-Acanthamoeba eye drops. The method
used was similar to that described in previous studies.21
Briefly, freshly fertilized white leghorn eggs, weighing 50–
60 g, were incubated at 37.5°C with a relative humidity of
*65% for 9 days in an incubator with an automatic rotating
device. After removing the eggshell covering their air cell
with an electric drill and cutting through the inner egg
membranes, the test substance (0.3 mL) was applied onto the
vasculated CAM of at least three eggs. The CAM was observed over time (300 s) under a stereomicroscope (Olympus
SZ-STN) with an integrated standalone digital camera with
full live HD video output (Leica IC80 HD) and scored for
the following effects: hemorrhage, vascular lysis, and coagulation. Sodium hydroxide (0.1 N) served as the positive
control, and sodium chloride 0.9% served as the negative
control. These anti-Acanthamoebas were placed in the CAM
to determine the irritation score (IS) by the classic methodology described in Protocol No. 96 de INVITTOX.
Statistical analysis
The statistical analysis used to compare the results of
cellular assays was a two-way analysis of variance using the
Tukey test as multiple comparison test. Analyses were developed using GraphPad Prism 6.0 software.
Results
Cell culture assays
Adding anti-Acanthamoeba eye drops to the standard
culture medium of keratocytes at confluence (Fig. 1) led to a
marked decrease in cell viability, which can be observed in
Figs. 2 and 3.
Figure 2A reveals that the highest propamidine isethionate concentrations caused a pronounced decrease in cell
viability, leading to null NCIs when testing the highest eye
drop concentrations. In addition, the highest concentrations
Bovine corneal opacity and permeability assay
The procedure used was a variation of the method described by Parekh et al.22 The bovine whole eye balls were
obtained from a local slaughter house and collected immediately after the cows were slaughtered. They were transported to the laboratory in balanced salt solution (BSS) in
cold condition (4°C). Corneas were excised along with 1–
2 mm of surrounding scleral tissues and were placed in
warm BSS for 50 min. The corneas were placed between
two cylindrical supporting black holders (fabricated with
polylactic acid filaments using a 3D print, Witbox BQ) that
have a special shape adapted to the cornea curvature and a
hole (diameter = 11.5 mm), which allows the transmission of
FIG. 1. Immunostaining in cell cultures of keratocytes
(10X). The cells presented cytoplasmic fibrillar immunoreactivity for vimentin.
OPHTHALMIC TOXICITY PROFILE OF CHLORHEXIDINE AND ISETHIONATE EYE DROPS
205
N
Y
O
I
L
T
N
U
O
B
I
W ISTR
E
I
V
D ON
E
R
R
R
I
O
T
F
O
C
F
D
U
E
D
D
O
N
R
E
P
T
E
N
I
R
T
R
O
NO
FIG. 2. Toxicokinetic profile of BroleneÒ eye drops 20 h
after exposure to different concentrations of the drug. (A)
Changes in normalized cell index over time. (B) Changes in
CI50 over time. CI, cellular index.
FIG. 3. Toxicokinetic profile of chlorhexidine eye drops
20 h after exposure to keratinocytes using different drug
concentrations. (A) Changes in normalized cell index over
time. (B) Changes in CI50 over time. CI, cellular index.
of eye drops led to an earlier decrease in the NCI, with a
sharp reduction in viability during the initial period of exposure. These effects are shown in Fig. 2B, which demonstrates an increase in compound toxicity as the cell exposure
time increases. Table 2 shows that the original eye drop
concentrations (OEDC) used for therapy were several fold
greater than the CI50 toxicity parameter. On increasing the
time of exposure, the CI50 decreases from the initial value
of 110 microM (which is 1.5-fold lower than the OEDC
typically used for therapy) to 4 microM (the OEDC is 42
times greater than the CI50 after 20 h).
Figure 3A, as in the previous case, shows that chlorhexidine exhibits a concentration-dependent toxic effect, with a
correlation between the most pronounced reductions in viability and the highest concentrations. In the case of chlorhexidine, the reductions in viability are less pronounced
than those of propamidine because full loss of the total
keratocyte population does not occur with any of the assayed concentrations. Meanwhile, as seen in the previous
case, the highest eye drop concentrations led to earlier decreases in the NCI. The effects of chlorhexidine eye drop
toxicity can be observed quantitatively in Fig. 3B. The data
show a progressive decrease in the CI50 over time, from an
initial value of 94 microM to 20 microM at 20 h, and the
OEDC surpasses these values by 2.3- and 10-fold, respectively (see Table 2).
We performed a complementary assay of cell viability
based on the measurement of the mitochondrial activity of
the keratocytes in the presence of the anti-Acanthamoeba
eye drops (WST-1 assay). The results obtained with this
method are showed in Fig. 4. Two-way analysis of variance
shows that both the time of contact (a<0.01) and the different treatments and concentrations (a<0.01) have significant influence on percentage of cellular viability. Cell death
increases as the exposition time increases and also with
ChlorhexidineÒ or Brolene concentration. No significant
differences were observed between both drugs for similar
concentrations, but there is a tendency to present higher cell
viability of chlorhexidine. These results are in accordance
with those obtained using RTCA.
Hen’s Egg Test–chorioallantoic membrane
In Fig. 5, no damage to the blood vessels on the CAM surface after a period of 5 min of contact with the antiAcanthamoeba eye drops was observed. A null IS for both eye
drops was observed; thus, these can be classified as nonirritants.
Bovine corneal opacity and permeability assay
Results shown in Table 3 indicate that no alterations in
transparency nor permeability were produced in the cornea
206
FERNÁNDEZ-FERREIRO ET AL.
Table 2.
CI50 Evolution and Fold Change of the Original Eye Drop Concentration
and the CI50 Over Time
BroleneÒ eye drops
(foreign commercial product)
Exposure time
20 min
1h
8h
10 h
20 h
ChlorhexidineÒ eye drops
(compounded formulation)
CI50 (mM)
Number of times
OEDC surpasses CI50
CI50 (mM)
Number of times
OEDC surpasses CI50
110
94
12
10
4
1.5
1.8
14.2
17
42.5
94
40
32
29
22
2.3
5.5
6.9
7.6
10
CI, cellular index; OEDC, original eye drop concentration.
by the treatment with chlorhexidine 0.02% and Brolene. The
values of percentage of transparency and the OD were
similar in the formulations compared with BSSÒ.
Discussion
contact between keratocytes and the assayed substances,
which provides significant dynamic information about
toxicity.26 Keratitis exhibits an initial phase of dendritiform epithelial defects, anterior stromal infiltrates, and
radial keratoneuritis, such that the stroma becomes partially exposed to the prescribed pharmaceutical drugs.
Therefore, detection of the toxicity of these products on
stromal keratocytes is of interest. The present study is the
first published in vitro study of the toxicity of these products on this cell line using the novel technique of cellular
bioimpedance.
We have observed that despite having initial CI50 values
similar to propamidine, chlorhexidine is more toxic because the OEDC surpasses the CI50 by 2.3-fold, while
propamidine surpasses its respective OEDC by 1.5-fold.
N
Y
O
I
L
T
N
U
O
B
I
W ISTR
E
I
V
D ON
E
R
R
R
I
O
T
F
O
C
F
D
U
E
D
D
O
N
R
E
P
T
E
N
I
R
T
R
O
NO
Previous evidence has shown corneal toxicity due to the
use of propamidine isethionate23,24 and chlorhexidine25 eye
drops; however, their mechanism of action has not been
determined. In this study, a new in vitro cellular method
based on the use of a cellular impedance biosensor system
in primary cultures of human keratocytes was used. The
method, unlike classical techniques such as MTT or alamarBlue, allows for direct and continuous evaluation of
changes in cell viability over time as a consequence of
FIG. 4. Cell viability in the presence of anti-Acanthamoeba eye
drops obtained using WST-1Ò assay.
OPHTHALMIC TOXICITY PROFILE OF CHLORHEXIDINE AND ISETHIONATE EYE DROPS
FIG. 5. Images of chorioallantoic membrane after a contact time of 5 min with anti-Acanthamoeba eye drops.
However, at prolonged times of exposure to cells, the value
is inverted, with propamidine (with an OEDC 42 times
larger than the CI50) becoming more harmful to cells than
chlorhexidine (with an OEDC 10 times greater than the
CI50). Classical WST-1 assay confirms the toxicity of both
eye drops and their high dependence of contact time and
drug concentration. Despite the formulation showing significant cytotoxicity, neither acute irritation nor alteration
on permeability or transparency was observed. This behavior can produce an absence of discomfort and observable apparent injuries after their administration, so patients
using these eye drops have to be carefully surveilled to
avoid ocular adverse reactions.
Extrapolating data from in vitro to in vivo settings are
complicated and should be performed with caution. The results here show that the currently used concentrations greatly
surpass the in vitro toxicological margin of safety.27 The use
of high concentrations occurs, in part, due to the significant
precorneal clearance that occurs in ocular physiology, which
makes it difficult to achieve efficient medication concentrations for prolonged periods of time on the ocular surface.
This strategy is likely inadequate because it favors periods
of contact between the cornea or conjunctiva and high
concentrations of the medication, leading to adverse effects.
Instead, strategies should be promoted to determine alternative formulations that aim to increase the residence time
of the medication on the ocular surface through adequate
design of formulations for the ophthalmic route. Hydrogels
are an example of a substance with the capacity for in situ
207
gelification.16 These substances are used because of their
ability to change consistency and structure when exposed to
specific stimuli. The ocular surface provides conditions that
can facilitate the formation of gels with certain polymers
that are sensitive to stimuli. In the absence of stimuli, these
gels behave similar to fluid systems and are easy to administer. Once administered, the formulations transform
into a bioadhesive hydrogel film that remains adhered over
the ocular surface for prolonged periods of time while delivering the active compound.28
Meanwhile, it must be mentioned that often, issues of
ophthalmic toxicity are related to the excipients used to
produce the eye drops and those that coexist with the active
compound. In many cases, these excipients or their combination with the active compounds are the main causes of
ocular toxicity. It should be noted that in this study, the full
eye drop formulation was used, and Brolene includes preservatives such as benzalkonium chloride, which must be
considered when evaluating toxicity. Some authors have
described that excipients commonly used in ophthalmologic
treatments, such as benzalkonium chloride,29 etilendiaminotetraacetic acid,30 or cyclodextrins,31 are responsible for
the toxicity of some ophthalmic products. Thus, the increased cytotoxicity exhibited by propamidine isethionate
eye drops relative to chlorhexidine could be due to the
presence of a preservative, while chlorhexidine also has
shown antibacterial therapeutic efficiency.32
Therefore, future research should be performed to evaluate the safety of excipients used in the production of eye
drops. This will provide the information needed to select
and optimize the composition of the formulations used in
ophthalmologic treatments and promote the use of multidose
administration systems with no preservatives, such as HylabakÒ,33 because preservatives often cause irritation or
toxic effects. Currently, several research lines are focusing
on determining new pharmacological targets to treat Acanthamoeba keratitis. Pharmaceutical drugs such as statins34
and miltefosine35 are being studied, and strategies based on
crosslinking are being developed.36 However, these strategies have not been adopted in clinical treatment guides
because most studies only show in vitro results or are case
studies. To avoid the development of ocular toxicity episodes, it is crucial to determine the safety of the medications
that are currently used as the first line of topical ophthalmic
treatments for Acanthamoeba keratitis. In this study, both
eye drops chlorhexidine and Brolene have proven to have
a favorable cytotoxicity profile from ex vivo corneal transparence, permeability, and acute irritation point of view, but
the cell culture assays shows that chlorhexidine eye drops
N
Y
O
I
L
T
N
U
O
B
I
W ISTR
E
I
V
D ON
E
R
R
R
I
O
T
F
O
C
F
D
U
E
D
D
O
N
R
E
P
T
E
N
I
R
T
R
O
NO
Table 3.
Bovine Corneal Opacity and Permeability Results
Transparency
% Tinitial
BSS (negative control)
Chlorhexidine 0.02% eye drops
BroleneÒ (propamidine isethionate 0.1%)
Permeability
% T10min
ODForm-ODBBS
Mean
SD
Mean
SD
Mean
SD
88
86
92
0.01
0.01
0.07
88
89
90
0.01
0.01
0.01
0
0.0026
-0.0001
0
0.0080
0.0106
BSS, balanced salt solution; OD, optical density; SD, standard deviation; T, transparency.
208
FERNÁNDEZ-FERREIRO ET AL.
are the less toxic current alternative. The use and efficiency
of chlorhexidine eye drops have been supported by recently
published studies.37,38
Acknowledgments
A.F-F. acknowledges the support of Instituto de Salud
Carlos III (Rio Hortega research grant CM15/00188). The
authors also acknowledge the support of Fundación Mutua
Madrileña and Fundación Española Farmacia Hospitalaria
(AISEFH).
Author Disclosure Statement
No competing financial interests exist.
References
1. Lorenzo-Morales, J., Martı́n-Navarro, C.M., López-Arencibia,
A., Arnalich-Montiel, F., Piñero, J.E., and Valladares, B.
Acanthamoeba keratitis: an emerging disease gathering importance worldwide? Trends Parasitol. 29:181–187, 2013.
2. Lorenzo-Morales, J., Khan, N.A., and Walochnik, J. An
update on Acanthamoeba keratitis: diagnosis, pathogenesis
and treatment. Parasite. 22:1–20, 2015.
3. Pammolli, F., Magazzini, L., and Riccaboni, M. The productivity crisis in pharmaceutical R&D. Nat. Rev. Drug
Discov. 10:428–438, 2011.
4. Lim, N., Goh, D., Bunce, C., et al. Comparison of polyhexamethylene biguanide and chlorhexidine as monotherapy agents in the treatment of Acanthamoeba keratitis.
Am. J. Ophthalmol. 145:130–135, 2008.
5. Herreros, J.M.A. Preparación de medicamentos y formulación magistral para oftalmologı́a. Madrid, España:
Ediciones Dı́az de Santos; 2003.
6. Gaudana, R., Ananthula, H.K., Parenky, A., and Mitra,
A.K. Ocular drug delivery. AAPS J. 12:348–360, 2010.
7. Tatham, A.J., Sarodia, U., Gatrad, F., and Awan, A. Eye
drop instillation technique in patients with glaucoma. Eye.
27:1293–1298, 2013.
8. Fernández-Ferreiro, A., Santiago-Varela, M., Gil-Martı́nez,
M., et al. Ocular safety comparison of non-steroidal antiinflammatory eye drops used in pseudophakic cystoid macular edema prevention. Int. J. Pharm. 495:680–691, 2015.
9. Draize, J.H., Woodard, G., and Calvery, H.O. Methods for
the study of irritation and toxicity of substances applied
topically to the skin and mucous membranes. J. Pharmacol.
Exp. Ther. 82:377–390, 1944.
10. York, M., and Steiling, W. A critical review of the assessment of eye irritation potential using the Draize rabbit
eye test. J. Appl. Toxicol. 18:233–240, 1998.
11. Zuang, V., Schäffer, M., et al. EURL ECVAM progress
report on the development, validation and regulatory acceptance of alternative methods (2010–2013). JRC Scientific and Policy reports.
12. OECD 405 (October 2012) Acute Eye Irritation/Corrosion,
OECD Guidlines for the Testing of Chemicals. Available at
www.oecd.org/env/ehs/testing/TG%20List%20EN%20Aug
%202012.pdf (accessed February 15, 2016).
13. Luepke, N.P. Hen’s egg chorioallantoic membrane test for
irritation potential. Food Chem. Toxicol. 23:287–291, 1985.
14. Atienza, J.M., Zhu, J., Wang, X., Xu, X., and Abassi, Y.
Dynamic monitoring of cell adhesion and spreading on microelectronic sensor arrays. J. Biomol. Screen. 10:795–805,
2005.
15. Quereda, J.J., Martı́nez-Alarcón, L., Mendoça, L., et al.
Validation of xCELLigence real-time cell analyzer to assess compatibility in xenotransplantation with pig-tobaboon model. Transplant. Proc. 42:3239–3243, 2010.
16. Fernández-Ferreiro, A., González Barcia, M., Gil-Martı́nez,
M., et al. In vitro and in vivo ocular safety and eye surface
permanence determination by direct and Magnetic Resonance Imaging of ion-sensitive hydrogels based on gellan
gum and kappa-carrageenan. Eur. J. Pharm. Biopharm. 94:
342–351, 2015.
17. Boyd, J.M., Huang, L., Xie, L., Moe, B., Gabos, S., and Li,
X.-F. A cell-microelectronic sensing technique for profiling
cytotoxicity of chemicals. Anal. Chim. Acta. 615:80–87, 2008.
18. Halle, W. The registry of cytotoxicity: toxicity testing in
cell cultures to predict acute toxicity (LD50) and to reduce
testing in animals. Altern. Lab. Anim. 31:89–198, 2003.
19. Otero-González, L., Sierra-Alvarez, R., Boitano, S., and
Field, J.A. Application and validation of an impedancebased real time cell analyzer to measure the toxicity of
nanoparticles impacting human bronchial epithelial cells.
Environ. Sci. Technol. 46:10271–10278, 2012.
20. Peskin, A.V., and Winterbourn, C.C. A microtiter plate
assay for superoxide dismutase using a water-soluble tetrazolium salt (WST-1). Clin. Chim. Acta. 293:157–166,
2000.
21. Fernández-Ferreiro, A., González Barcia, M., Gil Martı́nez,
M., Blanco Mendez, J., Lamas Dı́az, M.J., and Otero
Espinar, F.J. Analysis of ocular toxicity of fluconazole and
voriconazole eyedrops using HET-CAM. Farm. Hosp. 38:
300–304, 2014.
22. Parekh, M., Ferrari, S., Ruzza, A., Pugliese, M., Ponzin, D.,
and Salvalaio, G. A portable device for measuring donor
corneal transparency in eye banks. Cell. Tissue. Bank. 15:
7–13, 2014.
23. Johns, K.J., Head, W.S., and O’Day, D.M. Corneal toxicity
of propamidine. Arch. Ophthalmol. 106:68–69, 1988.
24. Alizadeh, H., Silvany, R.E., Meyer, D.R., Dougherty, J.M.,
and McCulley, J.P. In vitro amoebicidal activity of propamidine and pentamidine isethionate against Acanthamoeba
species and toxicity to corneal tissues. Cornea. 16:94–100,
1997.
25. Fraunfelder, F.T., Fraunfelder, F.W., Jr., and Chambers,
W.A. Drug-Induced Ocular Side Effects: Clinical Ocular
Toxicology. Elsevier Health Sciences; 2014.
26. Meindl, C., Absenger, M., Roblegg, E., and Frohlich, E.
Suitability of cell-based label-free detection for cytotoxicity screening of carbon nanotubes. BioMed. Res. Int. 2013:
1–13, 2013.
27. Yoon, M., Campbell, J.L., Andersen, M.E., and Clewell,
H.J. Quantitative in vitro to in vivo extrapolation of cellbased toxicity assay results. Crit. Rev. Toxicol. 42:633–652,
2012.
28. Geethalakshmi, A., Karki, R., Jha, S.K., Venkatesh, D.P.,
and Nikunj, B. Sustained ocular delivery of brimonidine
tartrate using ion activated in situ gelling system. Curr.
Drug. Deliv. 9:197–204, 2012.
29. Mencucci, R., Paladini, I., Pellegrini-Giampietro, D.E.,
Menchini, U., and Scartabelli, T. In vitro comparison of the
cytotoxic effects of clinically available ophthalmic solutions of fluoroquinolones on human keratocytes. Can. J.
Ophthalmol. 46:513–520, 2011.
30. Epstein, S.P., Ahdoot, M., Marcus, E., and Asbell, P.A.
Comparative toxicity of preservatives on immortalized
corneal and conjunctival epithelial cells. J. Ocul. Pharmacol. Ther. 25:113–119, 2009.
N
Y
O
I
L
T
N
U
O
B
I
W ISTR
E
I
V
D ON
E
R
R
R
I
O
T
F
O
C
F
D
U
E
D
D
O
N
R
E
P
T
E
N
I
R
T
R
O
NO
OPHTHALMIC TOXICITY PROFILE OF CHLORHEXIDINE AND ISETHIONATE EYE DROPS
31. Fernández-Ferreiro, A., Fernández Bargiela, N., Varela,
M.S., et al. Cyclodextrin-polysaccharide-based, in situgelled system for ocular antifungal delivery. Beilstein. J.
Org. Chem. 10:2903–2911, 2014.
32. Tu, E.Y., Shoff, M.E., Gao, W., and Joslin, C.E. Effect of
low concentrations of benzalkonium chloride on acanthamoebal survival and its potential impact on empirical
therapy of infectious keratitis. J. Am. Med. Assoc. Ophthalmol. 131:595–600, 2013.
33. Brjesky, V.V., Maychuk, Y.F., Petrayevsky, A.V., and Nagorsky, P.G. Use of preservative-free hyaluronic acid (HylabakÒ) for a range of patients with dry eye syndrome:
experience in Russia. Clin. Ophthalmol. Auckl. NZ. 8:1169–
1177, 2014.
34. Martı́n-Navarro, C.M., Lorenzo-Morales, J., Machin, R.P.,
et al. Inhibition of 3-hydroxy-3-methylglutaryl-coenzyme
A reductase and application of statins as a novel effective
therapeutic approach against Acanthamoeba infections.
Antimicrob. Agents Chemother. 57:375–381, 2013.
35. Barisani-Asenbauer, T., Walochnik, J., Mejdoubi, L., and
Binder, S. Successful management of recurrent Acanthamoeba keratitis using topical and systemic miltefosine.
Acta. Ophthalmol. (Copenh.). 90, 2012.
36. Khan, Y.A., Kashiwabuchi, R.T., Martins, S.A., et al. Riboflavin and ultraviolet light a therapy as an adjuvant
209
treatment for medically refractive Acanthamoeba keratitis:
report of 3 cases. Ophthalmology. 118:324–331, 2011.
37. Mafra, C.S.P., Carrijo-Carvalho, L.C., Chudzinski-Tavassi,
A.M., et al. Antimicrobial action of biguanides on the viability of Acanthamoeba cysts and assessment of cell toxicity. Invest. Ophthalmol. Vis. Sci. 54:6363–6372, 2013.
38. Rahimi, F., Hashemian, S.M.N., Tafti, M.F., et al. Chlorhexidine monotherapy with adjunctive topical corticosteroids for Acanthamoeba keratitis. J. Ophthalmic. Vis. Res.
10:106–111, 2015.
Received: May 10, 2016
Accepted: December 23, 2016
Address correspondence to:
Prof. Francisco J. Otero-Espinar
Department of Pharmacy and Pharmaceutical Technology
Faculty of Pharmacy
University of Santiago de Compostela
Campus Vida s/n
Santiago de Compostela 15782
Spain
N
Y
O
I
L
T
N
U
O
B
I
W ISTR
E
I
V
D ON
E
R
R
R
I
O
T
F
O
C
F
D
U
E
D
D
O
N
R
E
P
T
E
N
I
R
T
R
O
NO
E-mail: francisco.otero@usc.es