Photosensitivity associated with the Smith-Lemli-Opitz syndrome

Diplomats' Mystery Illness and Pulsed Radiofrequency/Microwave Radiation

Importance: A mystery illness striking U.S. and Canadian diplomats to Cuba (and now China) "has confounded the FBI, the State Department and US intelligence agencies" (Lederman, Weissenstein, & Lee, 2017). Sonic explanations for the so-called health attacks have long dominated media reports, propelled by peculiar sounds heard and auditory symptoms experienced. Sonic mediation was justly rejected by experts. We assessed whether pulsed radiofrequency/microwave radiation (RF/MW) exposure can accommodate reported facts in diplomats, including unusual ones. Observations: (1) Noises: Many diplomats heard chirping, ringing or grinding noises at night during episodes reportedly triggering health problems. Some reported that noises were localized with laser-like precision or said the sounds seemed to follow them (within the territory in which they were perceived). Pulsed RF/MW engenders just these apparent "sounds" via the Frey effect. Perceived "sounds" differ by head dimensions and pulse characteristics and can be perceived as located behind in or above the head. Ability to hear the "sounds" depends on high-frequency hearing and low ambient noise. (2) Signs/symptoms: Hearing loss and tinnitus are prominent in affected diplomats and in RF/MW-affected individuals. Each of the protean symptoms that diplomats report also affect persons reporting symptoms from RF/MW: sleep problems, headaches, and cognitive problems dominate in both groups. Sensations of pressure or vibration figure in each. Both encompass vision, balance, and speech problems and nosebleeds. Brain injury and brain swelling are reported in both. (3) Mechanisms: Oxidative stress provides a documented mechanism of RF/MW injury compatible with reported signs and symptoms; sequelae of endothelial dysfunction (yielding blood flow compromise), membrane damage, blood-brain barrier disruption, mitochondrial injury, apoptosis, and autoimmune triggering afford downstream mechanisms, of varying persistence, that merit investigation. (4) Of note, microwaving of the U.S. embassy in Moscow is historically documented. Conclusions and relevance: Reported facts appear consistent with pulsed RF/MW as the source of injury in affected diplomats. Nondiplomats citing symptoms from RF/MW, often with an inciting pulsed-RF/MW exposure, report compatible health conditions. Under the RF/MW hypothesis, lessons learned for diplomats and for RF/MW-affected civilians may each aid the other.

Photosensitization of TRPA1 and TRPV1 by 7-dehydrocholesterol: implications for the Smith-Lemli-Opitz syndrome

Loss-of-function mutations in the enzyme 7-dehydrocholesterol reductase are responsible for the Smith-Lemli-Opitz syndrome, in which 7-dehydrocholesterol (7-DHC) levels are markedly increased in the plasma and tissues of patients. This increase in 7-DHC is probably associated with the painful and itchy photosensitivity reported by the majority of patients with Smith-Lemli-Opitz syndrome. To identify the molecular targets involved in the activation and photosensitization of primary afferents by 7-DHC, we focused on TRPA1 and TRPV1, two ion channels expressed in nociceptive nerve endings and previously shown to respond to ultraviolet and visible light under pathophysiological circumstances. Recombinant human TRPA1 is activated and photosensitized in the presence of 7-DHC. Prolonged preexposure to 7-DHC causes more pronounced photosensitization, and while TRPV1 contributes less to the acute effect, it too becomes highly photosensitive upon preincubation with 7-DHC for 1 to 15 hours. Dorsal root ganglion neurons in primary culture display acute sensitivity to 7-DHC in the dark and also light-evoked responses in the presence of 7-DHC, which are exclusively dependent on TRPA1 and TRPV1. Similarly, prolonged exposure of mouse dorsal root ganglion neurons to 7-DHC renders these cells photosensitive in a largely TRPA1- and TRPV1-dependent manner. Single-fiber recordings in mouse skin-nerve preparations demonstrate violet light-evoked activation and a sensitization to 7-DHC exposure. Vice versa, 7-DHC pretreatment of the isolated trachea leads to a TRPA1- and TRPV1-dependent increase of the light-induced calcitonin gene-related peptide release. Taken together, our results implicate TRPA1 and TRPV1 channels as potential pharmacological targets to address the 7-DHC-induced hypersensitivity to light in patients.

Vitamin D levels in Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive congenital malformation syndrome caused by mutations in the 7-dehydrocholesterol reductase gene. This inborn error of cholesterol synthesis leads to elevated concentrations of 7-dehydrocholesterol (7-DHC). 7-DHC also serves as the precursor for vitamin D synthesis. Limited data is available on vitamin D levels in individuals with SLOS. Due to elevated concentrations of 7-DHC, we hypothesized that vitamin D status would be abnormal and possibly reach toxic levels in patients with SLOS. Through a retrospective analysis of medical records between 1998 and 2006, we assessed markers of vitamin D and calcium metabolism from 53 pediatric SLOS patients and 867 pediatric patients who were admitted to the NIH Clinical Center (NIHCC) during the same time period. SLOS patients had significantly higher levels of 25(OH)D (48.06 ± 19.53 ng/ml, p < 0.01) across all seasons in comparison to the NIHCC pediatric patients (30.51 ± 16.14 ng/ml). Controlling for season and age of blood draw, 25(OH)D levels were, on average, 15.96 ng/ml (95%CI 13.95-17.90) higher in SLOS patients. Although, mean calcium values for both patient cohorts never exceeded the normal clinical reference range (8.6-10.2 mg/dl), the levels were higher in the SLOS cohort (9.49 ± 0.56 mg/dl, p < 0.01) compared to the NIHCC patients (9.25 ± 0.68 mg/dl). Overall, in comparison to the control cohort, individuals with SLOS have significantly higher concentrations of 25(OH)D that may be explained by elevated concentrations of serum 7-DHC. Despite the elevated vitamin D levels, there was no laboratory or clinical evidence of vitamin D toxicity.

Enhanced sensitivity of Neil1-/- mice to chronic UVB exposure

Oxidative stress and reactive oxygen species (ROS)-induced DNA base damage are thought to be central mediators of UV-induced carcinogenesis and skin aging. However, increased steady-state levels of ROS-induced DNA base damage have not been reported after chronic UV exposure. Accumulation of ROS-induced DNA base damage is governed by rates of lesion formation and repair. Repair is generally performed by Base Excision Repair (BER), which is initiated by DNA glycosylases, such as 8-oxoguanine glycosylase and Nei-Endonuclease VIII-Like 1 (NEIL1). In the current study, UV light (UVB) was used to elicit protracted low-level ROS challenge in wild-type (WT) and Neil1^-/- mouse skin. Relative to WT controls, Neil1^-/- mice showed an increased sensitivity to tissue destruction from the chronic UVB exposure, and corresponding enhanced chronic inflammatory responses as measured by cytokine message levels and profiling, as well as neutrophil infiltration. Additionally, levels of several ROS-induced DNA lesions were measured including 4,6-diamino-5-formamidopyrimidine (FapyGua), 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyAde), 8-hydroxyguanine (8-OH-Gua), 5,6-dihydroxyuracil (5,6-diOH-Ura) and thymine glycol (ThyGly). In WT mice, chronic UVB exposure led to increased steady-state levels of FapyGua, FapyAde, and ThyGly with no significant increases in 8-OH-Gua or 5,6-diOH-Ura. Interestingly, the lesions that accumulated were all substrates of NEIL1. Collectively, these data suggest that NEIL1-initiated repair of a subset of ROS-induced DNA base lesions may be insufficient to prevent the initiation of inflammatory pathways during chronic UV exposure in mouse skin.

Free radical oxidation of cholesterol and its precursors: Implications in cholesterol biosynthesis disorders

Free radical oxidation of cholesterol and its precursors contribute significantly to the pathophysiology of a number of human diseases. This review intends to summarize recent developments and provide a perspective on the reactivities of sterols toward free radical oxidation, the free radical reaction mechanism, and the biological consequences of oxysterols derived from the highly oxidizable cholesterol precursor, 7-dehydrocholesterol. We propose that the rigid structures, additional substituents on the double bonds, and the well-aligned reactive C-H bonds in sterols make them more prone to free radical oxidation than their acyclic analogs found in unsaturated fatty acids. The mechanism of sterol peroxidation follows some well-established reaction pathways found in the free radical peroxidation of polyunsaturated fatty acids, but sterols also undergo some reactions that are unique to these compounds. Peroxidation of 7-dehydrocholesterol gives arguably the most diverse set of oxysterol products that have been observed to date. The metabolism of these oxysterols in cells and the biological consequences of their formation will be discussed in the context of the pathophysiology of the human disease Smith-Lemli-Opitz syndrome. Considering the high reactivity of sterols, we propose that a number of other cholesterol biosynthesis disorders may be associated with oxidative stress.

Evaluation of cytotoxic effects of 7-dehydrocholesterol on melanoma cells

Ultraviolet radiation is the main cause of skin cancers, and melanoma is the most serious form of tumor. There is no therapy for advanced-stage melanoma and its metastasis because of their high resistance to various anticancer therapies. Human skin is an important metabolic organ in which occurs photoinduced synthesis of vitamin D3 from 7-dehydrocholesterol (7-DHC). 7-DHC, the precursor of cholesterol biosynthesis, is highly reactive and easily modifiable to produce 7-DHC-derived compounds. The intracellular levels of 7-DHC or its derivatives can have deleterious effects on cellular functionality and viability. In this study we evaluated the effects on melanoma cell lines of 7-DHC as such and for this aim we used much care to minimize 7-DHC modifications. We found that from 12 to 72 h of treatment 82-86% of 7-DHC entered the cells, and the levels of 7-DHC-derived compounds were not significant. Simultaneously, reactive oxygen species production was significantly increased already after 2h. After 24 h and up to 72 h, 7-DHC-treated melanoma cells showed a reduction in cell growth and viability. The cytotoxic effect of 7-DHC was associated with an increase in Bax levels, decrease in Bcl-2/Bax ratio, reduction of mitochondrial membrane potential, increase in apoptosis-inducing factor levels, unchanged caspase-3 activity, and absence of cleavage of PARP-1. These findings could explain the mechanism through which 7-DHC exerts its cytotoxic effects. This is the first report in which the biological effects found in melanoma cells are mainly attributable to 7-DHC as such.

Metabolism of oxysterols derived from nonenzymatic oxidation of 7-dehydrocholesterol in cells

Recent studies suggest that 7-dehydrocholesterol (7-DHC)-derived oxysterols play important roles in the pathophysiology of Smith-Lemli-Opitz syndrome (SLOS), a metabolic disorder that is caused by defective 3β-hydroxysterol-Δ(7)-reductase (DHCR7). Although 14 oxysterols have been identified as the primary products of 7-DHC autoxidation in organic solution, the metabolic fate of these oxysterols in a biological environment has not yet been elucidated. Therefore, we incubated these primary 7-DHC oxysterols in control Neuro2a and control human fibroblast cells and identified metabolites of these oxysterols by HPLC-MS. We also incubated Dhcr7-deficient Neuro2a cells and fibroblasts from SLOS patients with isotopically labeled 7-DHC (d(7)-7-DHC). The observation of matching d(0)- and d(7) peaks in HPLC-MS confirmed the presence of true metabolites of 7-DHC after excluding the possibility of ex vivo oxidation. The metabolites of primary 7-DHC oxysterols were found to contribute to the majority of the metabolic profile of 7-DHC in cells. Furthermore, based on this new data, we identified three new 7-DHC-derived metabolites in the brain of Dhcr7-KO mice. Our studies suggest that 7-DHC peroxidation is a major source of oxysterols observed in cells and in vivo and that the stable metabolites of primary 7-DHC oxysterols can be used as markers of 7-DHC peroxidation in these biological systems.

Lipid biomarkers of oxidative stress in a genetic mouse model of Smith-Lemli-Opitz syndrome

7-Dehydrocholesterol (7-DHC) accumulates in tissues and fluids of patients with Smith-Lemli-Opitz syndrome (SLOS), which is caused by mutations in the gene encoding 3β-hydroxysterol-Δ(7)-reductase (DHCR7). We recently reported that 7-DHC is the most reactive lipid molecule toward free radical oxidation (lipid peroxidation) and 14 oxysterols have been identified as products of oxidation of 7-DHC in solution. As the high oxidizability of 7-DHC may lead to systemic oxidative stress in SLOS patients, we report here lipid biomarkers of oxidative stress in a Dhcr7-KO mouse model of SLOS, including oxysterols, isoprostanes (IsoPs), and neuroprostanes (NeuroPs) that are formed from the oxidation of 7-DHC, arachidonic acid and docosahexaenoic acid, respectively. In addition to a previously described oxysterol, 3β,5α-dihydroxycholest-7-en-6-one (DHCEO), we provide evidence for the chemical structures of three new oxysterols in the brain and/or liver tissue of Dhcr7-KO mice, two of which were quantified. We find that levels of IsoPs and NeuroPs are also elevated in brain and/or liver tissues of Dhcr7-KO mice relative to matching WT mice. While IsoPs and NeuroPs have been established as a reliable measurement of lipid peroxidation and oxidative stress in vivo, we show that in this genetic SLOS mouse model, 7-DHC-derived oxysterols are present at much higher levels than IsoPs and NeuroPs and thus are better markers of lipid oxidation and related oxidative stress.

A review of UVA-mediated photosensitivity disorders

A number of skin conditions are characterised by photosensitivity to UVA. Some of these are exclusively UVA-mediated conditions, while others include UVA in the action spectrum which also include UVB and/or visible light. This review aims to describe this diverse range of conditions for non-dermatologist scientists with an interest in this topic. As such, clinical details, including treatments, are brief and succinct. Recent advances in understanding the pathogenesis of these conditions is highlighted.

Novel oxysterols observed in tissues and fluids of AY9944-treated rats: a model for Smith-Lemli-Opitz syndrome

Treatment of Sprague-Dawley rats with AY9944, an inhibitor of 3β-hydroxysterol-Δ(7)-reductase (Dhcr7), leads to elevated levels of 7-dehydrocholesterol (7-DHC) and reduced levels of cholesterol in all biological tissues, mimicking the key biochemical hallmark of Smith-Lemli-Opitz syndrome (SLOS). Fourteen 7-DHC-derived oxysterols previously have been identified as products of free radical oxidation in vitro; one of these oxysterols, 3β,5α-dihydroxycholest-7-en-6-one (DHCEO), was recently identified in Dhcr7-deficient cells and in brain tissues of Dhcr7-null mouse. We report here the isolation and characterization of three novel 7-DHC-derived oxysterols (4α- and 4β-hydroxy-7-DHC and 24-hydroxy-7-DHC) in addition to DHCEO and 7-ketocholesterol (7-kChol) from the brain tissues of AY9944-treated rats. The identities of these five oxysterols were elucidated by HPLC-ultraviolet (UV), HPLC-MS, and 1D- and 2D-NMR. Quantification of 4α- and 4β-hydroxy-7-DHC, DHCEO, and 7-kChol in rat brain, liver, and serum were carried out by HPLC-MS using d(7)-DHCEO as an internal standard. With the exception of 7-kChol, these oxysterols were present only in tissues of AY9944-treated, but not control rats, and 7-kChol levels were markedly (>10-fold) higher in treated versus control rats. These findings are discussed in the context of the potential involvement of 7-DHC-derived oxysterols in the pathogenesis of SLOS.

Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive, multiple congenital malformation and intellectual disability syndrome, with clinical characteristics that encompass a wide spectrum and great variability. Elucidation of the biochemical and genetic basis for SLOS, specifically understanding SLOS as a cholesterol deficiency syndrome caused by mutation in DHCR7, opened up enormous possibilities for therapeutic intervention. When cholesterol was discovered to be the activator of sonic hedgehog, cholesterol deficiency with inactivation of this developmental patterning gene was thought to be the cause of SLOS malformations, yet this explanation is overly simplistic. Despite these important research breakthroughs, there is no proven treatment for SLOS. Better animal models are needed to allow potential treatment testing and the study of disease pathophysiology, which is incompletely understood. Creation of human cellular models, especially models of brain cells, would be useful, and in vivo human studies are also essential. Biomarker development will be crucial in facilitating clinical trials in this rare condition, because the clinical phenotype can change over many years. Additional research in these and other areas is critical if we are to make headway towards ameliorating the effects of this devastating condition.

Malformation syndromes caused by disorders of cholesterol synthesis

Cholesterol homeostasis is critical for normal growth and development. In addition to being a major membrane lipid, cholesterol has multiple biological functions. These roles include being a precursor molecule for the synthesis of steroid hormones, neuroactive steroids, oxysterols, and bile acids. Cholesterol is also essential for the proper maturation and signaling of hedgehog proteins, and thus cholesterol is critical for embryonic development. After birth, most tissues can obtain cholesterol from either endogenous synthesis or exogenous dietary sources, but prior to birth, the human fetal tissues are dependent on endogenous synthesis. Due to the blood-brain barrier, brain tissue cannot utilize dietary or peripherally produced cholesterol. Generally, inborn errors of cholesterol synthesis lead to both a deficiency of cholesterol and increased levels of potentially bioactive or toxic precursor sterols. Over the past couple of decades, a number of human malformation syndromes have been shown to be due to inborn errors of cholesterol synthesis. Herein, we will review clinical and basic science aspects of Smith-Lemli-Opitz syndrome, desmosterolosis, lathosterolosis, HEM dysplasia, X-linked dominant chondrodysplasia punctata, Congenital Hemidysplasia with Ichthyosiform erythroderma and Limb Defects Syndrome, sterol-C-4 methyloxidase-like deficiency, and Antley-Bixler syndrome.

Photosensitivity in Smith-Lemli-Opitz syndrome: a flux balance analysis of altered metabolism

Ultraviolet A photosensitivity is a debilitating symptom associated with the metabolic disorder Smith-Lemli-Opitz syndrome (SLOS). SLOS is a manifestation of the deficiency of 7-dehydrocholesterol reductase, an enzyme involved in the cholesterol biosynthesis. As a result several abnormal intermediary compounds are formed among which Cholesta 5, 7, 9(11)-trien-3beta-ol is the most likely cause of photosensitivity. The effect of various drugs acting on cholesterol biosynthetic pathway on SLOS is not clear as clinical trials are not available for this rare disorder. A Flux Balance Analysis (FBA) has been carried out using the software CellNetAnalyzer or FluxAnalyzer to gain insight into the probable effects of various drugs acting on cholesterol biosynthetic pathway on photosensitivity in SLOS. The model consisted of 44 metabolites and 40 reactions. The formation flux of Cholesta 5, 7, 9(11)-trien-3beta-ol increased in SLOS and remained unchanged on simulation of the effect of miconazole and SR31747. However zaragozic acid can potentially reduce the flux through the entire pathway. FBA predicts zaragozic acid along with cholesterol supplementation as an effective treatment for photosensitivity in SLOS.

Nox1-based NADPH oxidase is the major source of UVA-induced reactive oxygen species in human keratinocytes

UVA radiation is a major environmental stress on skin, causing acute and chronic photodamage. These responses are mediated by reactive oxygen species (ROS), although the cellular source of these ROS is unknown. We tested the hypotheses that UVA-induced activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is required for ROS generation in human keratinocytes (HK) and that these ROS initiate rapid prostaglandin E2 (PGE2) synthesis. Treatment of HK with a non-toxic dose of UVA rapidly increased NADPH oxidase activity and intracellular ROS, which were partially blocked by an inhibitor of NADPH oxidase and by a mitochondria-selective antioxidant. Depleting the Nox1 isoform of the catalytic subunit of NADPH oxidase using small interfering RNA (siRNA) blocked the UVA-induced ROS increase, indicating that ROS produced by mitochondria or other sources are downstream from Nox1. Nox1 siRNA also blocked UVA-initiated PGE2 synthesis. The mechanism for activation of Nox1 is mediated by an increase in intracellular calcium. Ceramide, which has been proposed to mediate responses to UVA in HK, also activated NADPH oxidase. These results indicate that UVA activates Nox1-based NADPH oxidase to produce ROS that stimulate PGE2 synthesis, and that Nox1 may be an appropriate target for agents designed to block UVA-induced skin injury.

7-Dehydrocholesterol enhances ultraviolet A-induced oxidative stress in keratinocytes: roles of NADPH oxidase, mitochondria, and lipid rafts

Long wavelength solar UVA radiation stimulates formation of reactive oxygen species (ROS) and prostaglandin E(2) (PGE(2)), which are involved in skin photosensitivity and tumor promotion. High levels of 7-dehydrocholesterol (7-DHC), the precursor to cholesterol, cause exaggerated photosensitivity to UVA in patients with Smith-Lemli-Opitz syndrome (SLOS). Partially replacing cholesterol with 7-DHC in keratinocytes rapidly (<5 min) increased UVA-induced ROS, intracellular calcium, phospholipase A(2) activity, PGE(2), and NADPH oxidase activity. UVA-induced ROS and PGE(2) production were inhibited in these cells by depleting the Nox1 subunit of NADPH oxidase using siRNA or using a mitochondrial radical quencher, MitoQ. Partial replacement of cholesterol with 7-DHC also disrupted membrane lipid raft domains, although depletion of cholesterol, which also disrupts lipid rafts, did not affect UVA-induced increases in ROS and PGE(2). Phospholipid liposomes containing 7-DHC were more rapidly oxidized by a free radical mechanism than those containing cholesterol. These results indicate that 7-DHC enhances rapid UVA-induced ROS and PGE(2) formation by enhancing free radical-mediated membrane lipid oxidation and suggests that this mechanism might underlie the UVA photosensitivity in SLOS.

School in photodermatology: Smith-Lemli-Opitz syndrome

The Smith-Lemli-Opitz syndrome has only recently been added to the small number of congenital disorders characterized by photosensitivity. The clinical features of this disorder are distinct from other photosensitivity syndromes. Details on the patho-mechanism of photosensitivity in the Smith-Lemli-Opitz syndrome have yet to be fully determined. However, preliminary evidence points to the deranged cholesterol metabolism that characterizes the syndrome as causal in this UVA-mediated photosensitivity disorder.

Ultraviolet A sensitivity in Smith-Lemli-Opitz syndrome: Possible involvement of cholesta-5,7,9(11)-trien-3 beta-ol

Smith-Lemli-Opitz syndrome (SLOS) is a severe developmental disorder caused by mutations in the DHCR7 gene coding for 7-dehydrocholesterol (7-DHC) reductase, the enzyme involved in the last step of cholesterol biosynthesis. SLOS homozygotes exhibit marked deficiency of cholesterol in plasma and tissues with concomitant increase in 7-DHC. Ultraviolet A (UVA) photosensitivity has been recognized as part of SLOS with maximal response occurring at 350 nm. 7-DHC itself has no UVA absorption and so cannot be the direct cause of SLOS photosensitivity. However, cholesta-5,7,9(11)-trien-3beta-ol (9-DDHC), a metabolite of 7-DHC, has been detected in plasma from SLOS patients. Because 9-DDHC has strong absorption in the UVA range (approximately 15,000 @ 324 nm), we have examined its photobiology to determine whether it could be involved in SLOS photosensitivity. High levels of 7-DHC (0.65 mg/100 g wet weight) and measurable amounts of 9-DDHC (0.042 mg/100 g wet weight) were found in skin lipids extracted from CD-1 mice treated with AY9944 (trans-1,4-bis(2-chlorobenzylaminomethyl)cyclohexane dihydrochloride), an inhibitor of 7-DHC reductase. Human HaCaT keratinocytes treated with 9-DDHC (10 microM) and then immediately exposed to UVA (15 J/cm2) exhibited an 88% decrease in viability (compared to dark controls). No damage was observed in cells exposed to 7-DHC/UVA or UVA alone. However, HaCaT keratinocytes treated with 7-DHC (5 microM) for 15 h and then exposed to UVA (30 J/cm2) were damaged. 9-DDHC was detected in keratinocytes incubated with 7-DHC. Reactive oxygen species were detected in 9-DDHC/UVA-exposed cells using the fluorescent probe 5-(and 6-)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate acetyl ester. Singlet oxygen was generated when 9-DDHC was UVA irradiated in CCl4. UVA irradiation of 9-DDHC in acetonitrile generated superoxide and carbon-centered and alkoxyl radicals which were trapped by 5,5-dimethyl-1-pyrroline N-oxide. These findings suggest that reactive oxygen species generated by 9-DDHC may play a role in the UVA skin photosensitivity of SLOS patients. Furthermore, several statin drugs inhibit 7-DHC reductase, in addition to hydroxymethylglutaryl-CoenzymeA reductase, so that 9-DDHC may also be responsible for statin-derived photosensitivity, dermatoses, and cataract formation. Finally, we have previously detected 9-DDHC in skin lipids from normal subjects, so this sterol may also be the skin chromophore responsible for skin photoaging and UV-induced skin cancer.

Ultraviolet A induces apoptosis via reactive oxygen species in a model for Smith-Lemli-Opitz syndrome

Solar ultraviolet A (UVA) radiation induces many responses in skin including oxidative stress, DNA damage, inflammation, and skin cancer. Smith-Lemli-Opitz syndrome (SLO-S) patients show dramatically enhanced immediate (5 min) and extended (24-48 h) skin inflammation in response to low UVA doses compared to normal skin. Mutations in Delta7-dehydrocholesterol reductase, which converts 7-dehydrocholesterol to cholesterol, produces high levels of 7-dehydrocholesterol in SLO-S patient's serum. Since 7-dehydrocholesterol is more rapidly oxidized than cholesterol, we hypothesized that 7-dehydrocholesterol enhances UVA-induced oxidative stress leading to keratinocyte death and inflammation. When keratinocytes containing high 7-dehydrocholesterol and low cholesterol were exposed to UVA (10 J/cm2), eightfold greater reactive oxygen species (ROS) were produced than in normal keratinocytes after 15 min. UVA induced 7-dehydrocholesterol concentration-dependent cell death at 24 h. These responses were inhibited by antioxidants, reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor (diphenyleneiodonium) and a mitochondria-specific radical quencher. Cell death was characterized by activation of caspases-3, -8, and -9 and by phosphatidylserine translocation. Studies using antioxidants and specific caspase inhibitors indicated that activation of caspase-8, but not caspase-9, mediates ROS-dependent caspase-3 activation and suggested that ROS from NADPH oxidase activate caspase-8. These results support a ROS-mediated apoptotic mechanism for the enhanced UVA-induced inflammation in SLO-S patients.

Light-induced exacerbation of retinal degeneration in a rat model of Smith-Lemli-Opitz syndrome

Potentiation of retinal degeneration by intense light exposure, and its amelioration by an antioxidant, were studied in a rat model of Smith-Lemli-Opitz syndrome (SLOS), in comparison with normal (control) Sprague-Dawley rats. The SLOS model is created by treating rats with AY9944, a selective inhibitor of cholesterol synthesis at the level of 3beta-hydroxysterol-Delta7-reductase. A subset of rats was treated with dimethylthiourea (DMTU), a synthetic antioxidant, 24 and 1 hr prior to light exposure. Half of the animals (+/-DMTU) were exposed to intense, constant, green light (24hr, 1700lx, 490-580 nm), while the others were maintained in darkness. Subsequently all animals were returned to dim cyclic light (20-40 lx, 12 hr light-12 hr dark) for 2 weeks, after which electroretinograms were recorded. One eye from each rat was taken for histological and quantitative morphometric analyses; sterol analysis was performed on retinas from contralateral eyes. HPLC analysis confirmed the accumulation of 7-dehydrocholesterol (7DHC) in retinas of AY9944-treated rats; cholesterol represented >99% of the sterol in control retinas. Histology of retinas from unexposed, AY9944-treated rats (6-week-old) was normal. In contrast, age-matched, light-exposed rats exhibited massive photoreceptor cell loss in both the superior and inferior hemispheres, and concomitant rod and cone dysfunction. The severity and geographic extent of the damage was far greater than that observed in normal albino rats exposed to the same conditions. DMTU pre-treatment largely prevented these degenerative changes. These findings indicate that the AY9944-induced rat SLOS model is hypersensitive to intense light-induced retinal damage, relative to normal rats. DMTU protection against light-induced damage implicates free radical-based oxidation in the retinal degeneration process. Furthermore, the use of green light (corresponding to the absorption maxima of rhodopsin) implicates rhodopsin in the initiation of the pathobiological mechanism. We propose that generation of cytotoxic oxysterols (by-products of 7DHC oxidation) is an integral part of retinal cell death in the SLOS rat model, which is exacerbated by intense light. Furthermore, the results predict light-dependent potentiation of retinal degeneration in SLOS patients, and the possible ameliorative effects of antioxidant therapy.

Photomedicine: lessons from the Smith-Lemli-Opitz syndrome

The Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive disorder caused by a discrete block in the cholesterol biosynthetic pathway. Recognition of the metabolic basis of this condition has bought into focus knowledge from fields as diverse as clinical genetics, sterol biochemistry, foetal nutrition, and experimental teratology, resulting in a rush of new insights in these fields. Unfortunately, late recognition of photosensitivity as part of this syndrome has largely excluded photodermatologists and photobiologists from the recent frenzy of research in this disorder. However, clinical features of this new inherited photosensitivity syndrome have now been established, and monochromator light testing has confirmed it to be a UVA-mediated condition. Current knowledge concerning photosensitivity in SLOS is reviewed and future research into the pathogenesis of this disorder is discussed.

Cholesterol supplementation objectively reduces photosensitivity in the Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz (SLO) affected children have multiple congenital physical and mental abnormalities; photosensitivity to ultraviolet A (UVA) has recently become a recognized feature. We present a patient with SLO and prominent photosensitivity in whom detailed phototesting has been performed at baseline and following 6 months of cholesterol supplementation. There was significant improvement in the symptoms of photosensitivity, confirmed objectively by phototesting and accompanied by partial correction of the biochemical abnormalities seen in SLO. This case report is the first to show that cholesterol supplementation in SLO can lead to an objective improvement in the associated photosensitivity.

Characterization of photosensitivity in the Smith-Lemli-Opitz syndrome: a new congenital photosensitivity syndrome

Photosensitivity has recently been reported as a feature of the Smith-Lemli-Opitz syndrome (SLO). The aim of this study was to establish the photobiological features of this disorder and to examine the hypothesis that the photosensitivity is caused by the high levels of 7-dehydrocholesterol found in SLO. All known cases of SLO in the U.K. were reviewed and clinical details of photosensitivity were recorded in detail. The action spectrum of the photosensitive eruption was defined by monochromator light testing. Thirteen of the 23 subjects (57%) had severe photosensitivity, and in 10 there was no photosensitivity. No correlation was identified between levels of 7-dehydrocholesterol and severity of photosensitivity, suggesting that the photosensitivity in SLO is not caused by a direct phototoxic effect mediated by 7-dehydrocholesterol. A novel pattern of photosensitivity was observed, with onset of a sunburn-like erythema on sun-exposed skin within minutes of sun exposure, which persisted in most cases for up to 24-48 h before fading. Monochromator light testing in three subjects showed an ultraviolet (UV) A-mediated photosensitivity eruption with greatest photosensitivity at 350 nm. Photosensitivity is a common and prominent feature of SLO and appears to be UVA-mediated. Elucidation of its biochemical basis may provide insight into normal cutaneous protective mechanisms against UVA-induced photodamage, and also sun sensitivity in general.

Photosensitivity in the Smith-Lemli-Opitz syndrome: the US experience of a new congenital photosensitivity syndrome

Photosensitivity has been briefly mentioned in several publications on the Smith-Lemli-Opitz (SLO) syndrome, an autosomal recessive mental retardation syndrome. We conducted a questionnaire-based survey to determine the incidence and main features of photosensitivity in SLO. We confirmed a high incidence, and initial evidence suggests that SLO may be the first example of an inherited photosensitivity disorder in which sensitivity to UVA is common.