Increased oxidative modification of albumin when illuminated in vitro in the presence of a common sunscreen ingredient: protection by nitroxide radicals

We previously reported on the ability of dibenzoylmethane (DBM) and a relative, Parsol 1789, used as a ultraviolet A (UVA)-absorbing sunscreen, to generate free radicals upon illumination, and as a consequence, to inflict strand breaks in plasmid DNA in vitro. This study has now been extended to determine the effects of Parsol 1789 and DBM on proteins, under UVA illumination, with the sole purpose of gaining more knowledge on the photobiological effects of sunscreen chemicals. Parsol 1789 (100 microM) caused a 2-fold increase in protein carbonyl formation (an index of oxidative damage) in bovine serum albumin (BSA) when exposed to illumination, and this damage was both concentration- and time-dependent. The degree of protein damage was markedly reduced by the presence of free radical scavengers, namely piperidinic and indolinonic nitroxide radicals, in accordance with our previous study. Vitamin E had no effect under the conditions used. The results obtained corroborate the fact that Parsol 1789 generates free radicals upon illumination and that these are, most probably, responsible for the protein damage observed under the conditions used in our system. However, at present, we cannot extrapolate from these results the relevance to human use of sunscreens; therefore, further studies should be necessary to determine the efficacy at the molecular and cellular level of this UVA-absorber in order to ascertain protection against photocarcinogenic risk.     

In vitro synthesis of nitroxide free radicals by hog liver microsomes

The in vitro biooxidation of 4-hydroxy-2,2,6,6-tetramethylpiperidine (TEMP), 4-hydroxy-2,2,4,4-tetramethyl-1,3-oxazolidine (TEMO) and diphenylamine (DPA) by hog liver microsomes to their respective nitroxide free radicals, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), 2,2,4,4-tetramethyl-1,3-oxazolidine-1-oxyl (TEMOO), and diphenylnitroxide (DPNO) has been investigated. For extending the life span of the liver microsomes, a calcium alginate immobilization procedure was used. The biooxidation rates of the above amines to their respective nitroxide metabolites were measured by means of oxygen uptake at 37 degrees C and pH 7.4. N-octylamine was found to be an activator in the biooxidation of the amines. The formation of the nitroxide radicals was identified by E.S.R. spectroscopy.     

Electrochemistry of norcocaine nitroxide and related compounds: implications for cocaine hepatotoxicity

Norcocaine nitroxide, a free radical metabolite of cocaine, displays a reversible one-electron cyclic voltammogram which is abolished by the addition of reduced glutathione. The corresponding nitrosonium ion was synthesized. It showed the same electrochemical characteristics as the nitroxide. The spin label 4-hydroxy-2,2,6,6-tetramethyl piperidine-1-oxyl (TEMPOL) and its nitrosonium ion behaved like morcocaine nitroxide and its nitrosonium ion. The nitrosonium ion of TEMPOL caused hemolysis of red blood cells, but TEMPOL did not. These observations suggest that the highly reactive nitrosonium ion may be involved in the production of cocaine-induced hepatic necrosis in mice.     

Singlet oxygen production in thylakoid membranes during photoinhibition as detected by EPR spectroscopy

Exposure of isolated spinach thylakoids to high intensity illumination (photoinhibition) results in the well-characterized impairment of Photosystem II electron transport, followed by degradation of the D1 reaction centre protein. In the present study we demonstrate that this process is accompanied by singlet oxygen production. Singlet oxygen was detected by EPR spectroscopy, following the formation of stable nitroxide radicals from the trapping of singlet oxygen with a sterically hindered amine TEMP (2,2,6,6-tetramethylpiperidine). There was no detectable singlet oxygen production during anaerob photoinhibition or in the presence of sodium-azide. Comparing the kinetics of the loss of PS II function and D1 protein with that of singlet oxygen trapping suggests that singlet oxygen itself or its radical product initiates the degradation of D1.Abbreviations HEPES 4-(2-hydroxyethyl)-1-piperazine ethanesulphonle acid - PS Photosystem - TEMP 2,2,6,6-tetramethylpiperidine - TEMPO 2,2,6,6-tetramethylpiperidine-1-oxyl     

Interaction of dipyridamole with micelles of lysophosphatidylcholine and with bovine serum albumin: fluorescence studies.

The interaction of the coronary vasodilator dipyridamole with biological systems, protein and membranes has been studied through optical absorption and fluorescence spectroscopies. Using the analysis of the spectra and fluorescence intensity of dipyridamole (DIP) in solution, the interaction of this compound with the transport protein albumin (BSA) and with a model of cell membranes, namely micelles of lysophosphatidylcholine (L-PC), was investigated. Measurements were performed at pH 5.0 and pH 7.0 where the molecule of DIP is fully protonated and partially protonated, respectively. The quenching of fluorescence with nitroxide-stable radicals 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) as well as with acrylamide and iodide allowed the localization of the drug in the polar interface of micelles. Quenching by acrylamide and iodide in L-PC micelles demonstrated the effect of micelle protonation which increased the accessibility of iodide to the chromophore. An effective association constant was obtained both at pH 7.0 (7.5 x 10(3) M-1) and pH 5.0 (2.5 x 10(3) M-1) and a very good agreement with the proposed binding model was observed. The quantum yields of fluorescence data agree very well with the fluorescence lifetimes. The measurement of lifetimes was important to understand the kinetic data obtained from Stern-Volmer plots both of radical, acrylamide and iodide quenching of fluorescence. It was observed that, in the presence of micelles, the kq value increased for TEMPO while decreased for TEMPOL. This result, together with the vanishing solubility of DIP in saturated hydrocarbons and the preferential partition of TEMPO in micelles, suggested the localization of DIP in the polar micellar interface. This is also supported by the enhanced iodide quenching at pH 5.0, constancy of acrylamide quenching in the range of pH 7.0-5.0 and the partition of TEMPO and TEMPOL in SDS micelles. The association constant of DIP to BSA was also estimated both at pH 7.0 (2 x 10(4) M-1) and pH 5.0 (4 x 10(3) M-1). Quenching studies with nitroxide radicals, acrylamide and iodide also suggested the binding of the drug to a hydrophobic region of the protein. At pH 5.0, the protein undergo a conformational change which leads to a loosening of the overall structure so that the accessibility of the nitroxide radicals for DIP is increased at this pH. The differences in kq values at pH 7.0 and pH 5.0 suggested that at pH 7.0 the chromophore is protected in the protein site.(ABSTRACT TRUNCATED AT 400 WORDS)     

γ-Irradiation Damage to Liposomes Differing in Composition and Their Protection by Nitroxides

The present study aims to determine the effect of bilayer composition on oxidative damage and the protection against it in lipid multicomponent membranes. Irradiation damage in 200-nm liposomes and the protection provided by the nitroxide radicals, 2,2,6,6-tetramethylpiperidine-1-oxyl (Tempo) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol) were assessed by monitoring several chemical and physical parameters. Liposomes were prepared in four different lipid compositions (mole ratios), DPPC:DPPG 10:1; DPPC:DPPG:cholesterol 10:1:4; EPC:EPG 10:1; and EPC:EPG:cholesterol 10:1:4, and γ-irradiated with a dose of 32 kGy. Lipid degradation was determined by HPLC and GC analyses, whereas size and differential scanning calorimetry measurements were used to monitor physical changes in the liposomal dispersions. The results indicate that: (1) addition of 5 mM Tempo or Tempol, or freezing of the sample inhibited radiation-induced lipid degradation; (2) Tempo and Tempol caused neither physical nor chemical changes in the liposomal dispersions; and (3) both nitroxides prevented or reduced some of the radiation-induced changes in thermotropic characteristics of the liposomes, preventing a shift in the temperature of the maximum of the main phase transition (T_m).     

Effect of thiol reagents and ionizing radiation on the permeability of erythrocyte membrane for spin-labeled non-electrolytes

Four different thiol reagents: p-chloromercuribenzoic acid (pCMB), mercuric chloride (HgCl2), N-ethylmaleimide (NEM), and 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) were employed as agents modifying the transport of a hydrophilic and hydrophobic non-electrolyte spin labels: 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) into bovine erythrocytes. Gamma-irradiation of erythrocytes amplified the effects of pCMB, HgCl2 and NEM of inhibition of TEMPOL transport and attenuated them in the case of TEMPO transport. These results suggest that the transport of TEMPOL across the erythrocyte membrane is controlled by both superficially and more deeply located membrane -SH groups while only superficial -SH groups control the transport of TEMPO. The lower extent of inhibition of TEMPO transport indicates a higher contribution of diffusion through the lipid phase to the transport of TEMPO across the erythrocyte membrane as compared with TEMPOL.     

Identification by an EPR technique of decreased mitochondrial reducing activity in puromycin aminonucleoside-induced nephrosis

The temporal changes in the electron paramagnetic resonance (EPR) signal intensities of a nitroxide radical, 4-hydroxy 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL), in the kidney in rat puromycin aminonucleoside (PAN) nephrosis were investigated in vivo and in vitro. The rats of the PAN nephrosis group received intraperitoneal injections of PAN at 75 mg/kg body weight while those of control group received saline. The in vivo renal half-lives of TEMPOL were calculated from the decay curve of EPR signal intensities after the intravenous injection of the TEMPOL solution. The mitochondrial half-lives were obtained from the decay curve of the EPR signals after mixing the mitochondrial fraction of the kidney and TEMPOL solution. The in vivo half-lives of TEMPOL of the kidney from 7 to 14 d after PAN administration were significantly longer than those of the controls. The mitochondrial half-lives of TEMPOL on the 9th day after the PAN administration prolonged remarkably compared to the controls (378 +/- 69 vs. 676 +/- 183 s, p <.01). These findings indicate that the in vivo and mitochondrial reducing activity in PAN treated rats decreased markedly, because the half-life of TEMPOL in the kidney reflects the renal reducing activity.     

Nitroxides prevent exacerbation of indomethacin-induced gastric damage in adjuvant arthritis rats

Nonsteroidal anti-inflammatory drugs are the drugs of choice in the treatment of rheumatoid arthritis (RA) because of their rapid analgesic effect. However, they induce severe gastric damage in RA patients and animals by a process mediated by reactive oxygen species (ROS). Nitroxides (nitroxyl radicals) are widely used as imaging agents and antioxidants to explore the role of ROS generation in the pathogenesis of disease. In this study, the effectiveness of the newly synthesized nitroxides 8-aza-7,7,9,9-tetramethyl-1,4-dioxaspiro[4.5]undecan-8-oxyl (compound 1) and 4-oxo-2,2,6,6-tetraethylpiperidine-1-oxyl (compound 2) in the prevention of gastric ulcers in adjuvant arthritis rats treated with indomethacin was evaluated by monitoring the reaction of reactive oxygen species in gastric tissue with Overhauser-enhanced magnetic resonance imaging (OMRI). Pretreatment with all tested nitroxides suppressed the ulcers induced by indomethacin treatment in arthritic rats. OMRI using compounds 1 and 2 as well as 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) demonstrated a redox imbalance in the stomach of these rats. Lipid peroxide and interleukin (IL)-1β levels in the gastric mucosa were significantly suppressed by compound 1 and TEMPOL, whereas CINC/gro, a member of the IL-8 family, was significantly suppressed by compound 1 only. These results suggest that the preventive effects of nitroxides on gastric ulcers may operate by different mechanisms.     

The effects of nitroxide radicals on oxidative DNA damage

The indolinonic and quinolinic aromatic nitroxides synthesized by us are a novel class of biological antioxidants, which afford a good degree of protection against free radical-induced oxidation in different lipid and protein systems. To further our understanding of their antioxidant behavior, we thought it essential to have more information on their effects on DNA exposed to free radicals. Here, we report on the results obtained after exposure of plasmid DNA and calf thymus DNA to peroxyl radicals generated by the water-soluble radical initiator, 2,2'-azobis(2-amidinopropane)dihydrochloride (AAPH), and the protective effects of the aromatic nitroxides and their hydroxylamines, using a simple in vitro assay for DNA damage. In addition, we also tested for the potential of these nitroxides to inhibit hydroxyl radical-mediated DNA damage inflicted by Fenton-type reactions using copper and iron ions. The commercial aliphatic nitroxides 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL), and bis(2,2, 6,6-tetramethyl-1-oxyl-piperidin-4-yl)sebacate (TINUVIN 770) were included for comparison. The results show that the majority of compounds tested protect: (i) both plasmid DNA and calf thymus DNA against AAPH-mediated oxidative damage in a concentration-dependent fashion (1-0.1 mM), (ii) both Fe(II) and Cu(I) induced DNA oxidative damage. However, all compounds failed to protect DNA against damage inflicted by the presence of the transition metals in combination with H(2)O(2). The differences in protection between the compounds are discussed in relation to their molecular structure and chemical reactivity.     

The effects of manganese doping on UVA absorption and free radical generation of micronised titanium dioxide and its consequences for the photostability of UVA absorbing organic sunscreen components.

The effect of manganese doping on the free radical generation rate, free radical scavenging and UVA absorption properties of micronised sunscreen grade titania has been studied with respect to enhancement of the UVA photostability of test sunscreen formulations containing the organic UVA absorber Parsol 1789. Manganese doping has been shown to increase the UVA:UVB absorption ratio of titania, reduce free radical generation rates by over 90%, and provide free radical scavenging behaviour. Adding manganese-doped titania to a test formulation incorporating Parsol 1789 shows that manganese doping increases UVA attenuation stability by up to 3 times the amount achieved by comparable commercial undoped titania materials. HPLC data shows this to be related to an improved stabilisation of the organic sunscreen components. Manganese doped titania shows improved efficacy over undoped titania in sunscreen formulations containing organic UV absorbers.     

Effect of proline on the production of singlet oxygen

Molecular oxygen in electronic singlet state is a very powerful oxidant. Its damaging action in a variety of biological processes has been well recognized. Here we report the singlet oxygen quenching action of proline. Singlet oxygen (1O2) was produced photochemically by irradiating a solution of sensitiser and detected by following the formation of stable nitroxide radical yielded in the reaction of 1O2 with the sterically hindered amine (2,2,6,6-tetramethylpiperidine, TEMP). Illumination of a sensitiser, toluidine blue led to a time dependent increase in singlet oxygen production as detected by the formation of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) by EPR spectrometry. Interestingly, the production of TEMPO was completely abolished by the presence of proline at concentration as low as 20mM. These results show that proline is a very effective singlet oxygen quencher. Other singlet oxygen generating photosensitizer like hematopophyrin and fluorescein also produced identical results with proline. Since proline is one of the important solutes which accumulate in many organisms when they are exposed to environmental stresses, it is likely that proline accumulation is related to the protection of these organisms against singlet oxygen production during stress conditions. A possible mechanism of singlet oxygen quenching by proline is discussed.     

High-performance liquid chromatographic assay for common sunscreening agents in cosmetic products,bovine serum albumin solution and human plasma

This paper reports the development of a reversed-phase high-performance liquid chromatographic assay for quantifying five of the most common sunscreen agents, namely 2-ethylhexyl-p-dimethyl aminobenzoate (Escalol 507), 2-ethylhexyl-p-methoxycinnamate (Parsol MCX); 4-tert.-butyl-4′-methoxydibenzoylmethane (Parsol 1789), 2-hydroxy-4-methoxybenzophenone-3 (oxybenzone) and 2-ethylhexyl-salicylate (octylsalicylate). The assay permits analysis of the sunscreen agents in formulations and in biological fluids, including bovine serum albumin (BSA) solution, a common additive to in vitro skin diffusion cell receptor fluids, as well as human plasma. Separation was achieved using an ODS C₁₈ column with a methanol-water (88:12) mobile phase. The analytes were detected by ultraviolet light absorption at a wavelength of 315 nm. The assay was linear with minimum detectable limits, calculated as greater than 3-times the baseline noise level: for oxybenzone and Escalol 507, 0.05 μg/ml; for Parsol 1789 and Parsol MCX, 0.1 μg/ml; for octylsalicylate, 1 μg/ml. Recoveries from both plasma and 2% BSA were within the range 89–107%. The inter- and intra-day coefficients of variation for the five agents were not more than 4% at the upper end of the linear range and not more than 10% at the lower end. Preliminary stability studies of the sunscreen agents in a commercial product and in two diffusion cell receptor fluids were also conducted.     

Inhibition of Photosystem II by the singlet oxygen sensor compounds TEMP and TEMPD

2,2,6,6-tetramethylpiperidine (TEMP) and 2,2,6,6-tetramethyl-4-piperidinone (TEMPD) have earlier been used to quantify singlet oxygen produced by plant material. Both compounds were found to cause severe side effects on Photosystem II. Addition of TEMP or TEMPD to thylakoids immediately stabilized the reduced state of the Q(A) electron acceptor and destabilized the reduced state of the Q(B) acceptor, causing decrease in the driving force of forward electron transfer. Oxygen evolution, thermoluminescence and fluorescence measurements indicated that the number of functional PSII units decreased during incubation of thylakoids with TEMP or TEMPD. Singlet oxygen determinations in photosynthetic systems with piperidine derivatives should be interpreted with care.     

Evaluation of adriamycin nephropathy by an in vivo electron paramagnetic resonance

A rat model for human minimal change nephropathy was obtained by the intravenous injection of adriamycin (ADR) at 5 mg/kg. By using an in vivo electron paramagnetic resonance (EPR) spectrometer operating at 700 MHz, the temporal changes in signal intensities of a nitroxide radical, 4-hydroxyl-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL), in the kidneys of rats with ADR nephropathy were investigated. The decay rate of the EPR signal intensity obtained in the kidney is indicative of the renal reducing ability. It was found that the reducing ability in the kidney declined on the 7th day after ADR administration and recovered after the 14th day. Impairment of the reducing ability occurred before the appearance of continuous urinary protein. The in vitro EPR study showed that this impairment of in vivo renal reducing ability is related to impairment of the reducing ability in the mitochondria.     

The synthesis of deuterium-substituted, spin-labeled analogues of AMP and NAD+ and their use in ESR studies of lactate dehydrogenase

Two spin-labeled analogues of AMP and NAD+ were synthesized, in which a perdeuterated nitroxide radical (4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl, TEMPAMINE) was attached to C-6 or C-8 position of the adenine ring. The ESR spectra of these derivatives exhibit a 4-fold increase in sensitivity and a concomitant decrease in line-width as compared to the corresponding protonated analogues. The improved resolution of composite spectra consisting of freely tumbling and immobilized components is demonstrated in ternary complexes of the spin-labeled NAD+ derivatives with lactate dehydrogenase (L-lactate:NAD+ oxidoreductase, EC 1.1.1.27) and oxalate.     

Polynitroxyl hemoglobin: a pharmacokinetic study of covalently bound nitroxides to hemoglobin platforms

Adding antioxidant activities to hemoglobin-based oxygen carriers (HBOCs) represents a means of reducing cell-free hemoglobin-mediated oxidative cascades. We have covalently bound nitroxides, a class of antioxidant enzyme mimetics, to HBOCs. The objectives of this study were (1) to evaluate the pharmacokinetic (PK) effects of administering nitroxide covalently bound to HBOCs compared to those of free nitroxide coadministered with HBOCs and (2) to elucidate the effects of differing molecular weight HBOCs on the PK of bound nitroxide in a conscious guinea pig model of 25% blood exchange transfusion. Two HBOC platforms were used, intramolecular cross-linked hemoglobin (XLHb) and dextran polymerized/conjugated XLHb (PolyHb). Polynitroxylation was achieved by reacting 4-(2-bromoacetamido)-2,2,6,6,-tetramethylpiperidine-1-oxyl with XLHb or PolyHb to form polynitroxylated XLHb and polynitroxylated PolyHb, respectively, whereas a physical mixture of XLHb or PolyHb with 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl was prepared to reflect a molar equivalence to HBOC-bound nitroxide. Plasma concentrations of two redox states, nitroxide and hydroxylamine, were determined by electron paramagnetic resonance spectroscopy. Results are presented to illustrate the influence of covalent labeling and HBOC molecular weight on nitroxide PK. The therapeutic potential of polynitroxylation of HBOCs as it relates to observations from the current and previously reported studies is discussed.     

Antioxidant effects of water- and lipid-soluble nitroxide radicals in liposomes

Liposomes are today useful tools in different fields of science and technology. A lack of stability due to lipid peroxidation is the main problem in the extension of the use of these formulations. Recent investigative works have reported the protective effects of stable nitroxide radicals against oxidative processes in different media and under different stress conditions. Our group has focused its attention on the natural aging of liposomes and the protection provided by the water- and lipid-soluble nitroxide radicals 2,2,6,6-tetramethylpiperdine-1-oxyl (TEMPO) and doxylstearic acids (5-DSA, 12-DSA, and 16-DSA), respectively. Unilamellar liposomes were incubated under air atmosphere at 37°C, both in the absence and in the presence of these radicals. Conjugated dienes, lipid hydroperoxides, TBARS, membrane fluidity, and nitroxide ESR signal intensity were followed as a function of time. Our results demonstrated that doxylstearic acids were more efficient than TEMPO in retarding lipid peroxidation at all the concentrations tested. The inhibition percentages, depending on the total nitroxide concentration, were not proportional to the lipid–water partition coefficient. Furthermore, time-course ESR signals showed a slower decrease for doxylstearic acids than for TEMPO. No significant differences were found among 5-DSA, 12-DSA, and 16-DSA. We concluded that the nitroxide radical efficiency as antioxidant directly depends on both nitroxide concentration and lipophilicity.     

Inhibiting properties of stable nitroxyl radicals in reactions of linoleic acid and linoleyl alcohol oxidation catalyzed by 5-lipoxygenase

The inhibiting effects of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and its 4-substituted derivatives in reactions of linoleyl acid or linoleyl alcohol oxidation catalyzed by potato tuber 5-lipoxygenase were investigated. Inhibiting properties of stable nitroxyl radicals in presence of lubrol and SDS were reduced at the transition from TEMPO to 4-hydroxy-TEMPO or 4-amino-TEMPO and increased at use of adamantane-1-carboxylic or 3-methyladamantane-1-carboxylic acid 1-oxyl-2,2,6,6-tetramethylpiperidine-4-yl esters. Enzyme activity at saturating concentrations of inhibitor was not suppressed completely, and decreased up to the certain level determined by the substrate nature. The dependence of partial inhibition efficiency on rotational correlation time of stable nitroxides in model micellar systems were analysed. It was supposed that 5-lipoxygenase inhibition includes the interaction of hydrophobic nitroxide with radical intermediate formed in enzymatic process.     

Synthesis and application of a novel sunscreen-antioxidant

Background information on the inefficacy of sunscreens to provide free radical protection in skin, despite their usefulness in preventing sunburn/erythema, prompted us to synthesize a compound which would display in the same molecule both UV-absorbing and antioxidant capacities. For this purpose, the UVB absorber, 2-ethylhexyl-4-methoxycinnamate (OMC) was combined with the piperidine nitroxide TEMPOL, which has antioxidant properties. The spectral properties of the new nitroxide-based sunscreen (MC-NO) as well as its efficacy to prevent photo-oxidative damage to lipids induced by UVA, natural sunlight and 4-tert-butyl-4-methoxydibenzoylmethane (BMDBM), a photo-unstable sunscreen which generates free radicals upon UV radiation, was studied. The results obtained demonstrate that MC-NO: (a) absorbs in the UVB region even after UVA irradiation; (b) acts as free radical scavenger as demonstrated by EPR experiments; (c) strongly reduces both UVA-, sunlight- and BMDBM-induced lipid peroxidation in liposomes, measured as reduced TBARS levels; and (d) has comparable antioxidant activity to that of commonly used vitamin E and BHT in skin care formulations. These results suggest that the use of the novel sunscreen-antioxidant or of other nitroxide-based sunscreens in formulations aimed at reducing photoinduced skin damage may be envisaged.