The Logistical Backbone of Photoreceptor Cell Function: Complementary Mechanisms of Dietary Vitamin A Receptors and Rhodopsin Transporters.

In this review, we outline our current understanding of the mechanisms involved in the absorption, storage, and transport of dietary vitamin A to the eye, and the trafficking of rhodopsin protein to the photoreceptor outer segments, which encompasses the logistical backbone required for photoreceptor cell function. Two key mechanisms of this process are emphasized in this manuscript: ocular and systemic vitamin A membrane transporters, and rhodopsin transporters. Understanding the complementary mechanisms responsible for the generation and proper transport of the retinylidene protein to the photoreceptor outer segment will eventually shed light on the importance of genes encoded by these proteins, and their relationship on normal visual function and in the pathophysiology of retinal degenerative diseases.

In Silico Prediction of MYO1C-Rhodopsin Interactions and Its Significance in Protein Localization and Visual Function.

Rods and cones are photoreceptor neurons in the retina that are required for visual sensation in vertebrates, where proper protein localization and compartmentalization are critical for phototransduction and visual function. In human retinal diseases, improper protein transport to the outer segment (OS) or mislocalization of proteins to the inner segment (IS) could lead to impaired visual responses and photoreceptor cell degeneration, causing a loss of visual function. We showed involvement of an unconventional motor protein, MYO1C, in the proper localization of rhodopsin to the OS, where loss of MYO1C in a mammalian model caused mislocalization of rhodopsin to IS and cell bodies, leading to progressively severe retinal phenotypes. In this study, using modeling and docking analysis, we aimed to identify the protein-protein interaction sites between MYO1C and Rhodopsin to establish a hypothesis that a physical interaction between these proteins is necessary for the proper trafficking of rhodopsin and visual function.

Quantitative fundus autofluorescence in smokers compared to non-smokers.

Increased fundus autofluorescence is directly related to increased RPE lipofuscin deposition in the retina and has been observed in eyes with age-related macular degeneration (AMD). Smoking is the most significant modifiable risk factor for the development and progression of AMD, in which one of the main mechanisms is oxidative damage from smoking leading to RPE cell toxicity. The relationship between smoking and autofluorescence is not established and could provide insight into pathogenic mechanism of AMD. Therefore, our objective was to compare quantitative fundus autofluorescence (qAF) in the retinae of healthy non-smokers to smokers. We conducted a cross-sectional study at the 2016 Minnesota State Fair. Participants self-reported past medical and ocular history and underwent eye examination as well as qAF imaging with Spectralis confocal scanning laser ophthalmoscope (cSLO) equipped with an internal fluorescent reference. Two sets of images were obtained per eye. Stepwise multiple mixed effects regression model was used to examine the relationship between mean qAF values and smoking status. We enrolled 105 individuals (54 smokers, 61 females, mean age 41 years with range 18-78 years old). Fundus autofluorescence images were analyzable for 85 of 105 individuals contributing 161 eyes (80 right, 81 left). The repeatability coefficients between the first set and second set of images were ±21% of their mean qAF values. Older age and female gender were independently associated with higher qAF. Positive smoking history tended to result in higher qAF values after adjusting for age and gender but was not statistically significant (0.118, 95%CI -0.003, 0.240, P = 0.056). Among smokers, the number of pack-years smoked was not significantly associated with higher qAF. Our study's results are consistent with existing literature in which older age is predictive of intensified autofluorescence, while smoking history does not have as important of an impact on autofluorescence as hypothesized. Several large epidemiological studies have shown that smoking is significantly associated with AMD, and qAF is likely not the appropriate modality to clinically assess smoking's impact on retinae.

Chronic retinal necrosis: cytomegalovirus necrotizing retinitis associated with panretinal vasculopathy in non-HIV patients.

PURPOSE: To characterize a unique cytomegalovirus (CMV)-associated retinopathy in patients with limited immune dysfunction. METHODS: Retrospective observational case series. CMV was confirmed as the pathogenic agent via polymerase chain reaction analysis of aqueous or vitreous humor samples or via immunohistochemical analysis of retinal biopsy specimens. RESULTS: Five non-HIV patients with granular necrotizing retinitis, vitritis, and severe occlusive vasculopathy were identified. Patient histories all suggested a basis for limited immune dysfunction including advanced age (n = 4), diabetes mellitus (n = 4), and noncytotoxic immunotherapy (n = 3). Diagnosis of CMV retinitis was delayed in all cases and patients received either no antiviral therapy (n = 2) or incorrect antiviral therapy (n = 3) for presumed herpes simplex/varicella zoster-related acute retinal necrosis. Retinitis subsequently regressed in all cases with introduction of systemic ganciclovir/valganciclovir (n = 5) and/or intravitreal foscarnet (n = 2). Four of five patients developed neovascularization because of extensive retinal ischemia. CONCLUSION: The clinical expression of CMV-associated retinopathy is strongly related to immune status. In patients with limited immune dysfunction, a mixed clinical picture of intraocular inflammation with panretinal occlusive vasculopathy, more characteristic of acute retinal necrosis, and peripheral slowly progressive granular retinitis, more characteristic of classic CMV retinitis, is observed. Recognition of this atypical clinical presentation, which the authors term chronic retinal necrosis, should prompt molecular testing for CMV to determine the appropriate antiviral therapy. Consideration should also be given to prophylactic panretinal photocoagulation in such eyes, given the high risk of neovascular complications.

Adverse COVID-19 outcomes in American Veterans with age-related macular degeneration: a case-control study.

OBJECTIVES: Prior studies suggest that patients with age-related macular degeneration (AMD) have poorer COVID-19 outcomes. This study aims to evaluate whether AMD is associated with adverse COVID-19 outcomes in a large clinical database. DESIGN: Case-control study. SETTING: We obtained demographic and clinical data from a national US Veterans Affairs (VA) database for all Veterans aged 50 years or older with positive COVID-19 testing prior to 2 May 2021. PRIMARY AND SECONDARY OUTCOME MEASURES: The primary outcome measure was hospitalisation. Secondary outcome measures were intensive care unit admission, mechanical ventilation and death. Potential associations between AMD and outcome measures occurring within 60 days of COVID-19 diagnosis were evaluated using multiple logistic regression analyses. RESULTS: Of the 171 325 patients in the study cohort, 7913 (5%) had AMD and 2152 (1%) had severe AMD, defined as advanced atrophic or exudative AMD disease coding. Multiple logistic regression adjusting for age, Charlson Comorbidity Index, sex, race, ethnicity and COVID-19 timing showed that an AMD diagnosis did not significantly increase the odds of hospitalisation (p=0.11). Using a Bonferroni-adjusted significance level of 0.006, AMD and severe AMD also were not significant predictors for the secondary outcomes, except for AMD being modestly protective for death (p=0.002). CONCLUSIONS: After adjusting for other variables, neither AMD nor severe AMD was a risk factor for adverse COVID-19 outcomes in the VA healthcare system. These findings indicate that an AMD diagnosis alone should not alter recommended ophthalmic management based on COVID-19 adverse outcome risk.

The role of motor proteins in photoreceptor protein transport and visual function.

BACKGROUND: Rods and cones are photoreceptor neurons in the retina that are required for visual sensation in vertebrates, wherein the perception of vision is initiated when these neurons respond to photons in the light stimuli. The photoreceptor cell is structurally studied as outer segments (OS) and inner segments (IS) where proper protein sorting, localization, and compartmentalization are critical for phototransduction, visual function, and survival. In human retinal diseases, improper protein transport to the OS or mislocalization of proteins to the IS and other cellular compartments could lead to impaired visual responses and photoreceptor cell degeneration that ultimately cause loss of visual function. RESULTS: Therefore, studying and identifying mechanisms involved in facilitating and maintaining proper protein transport in photoreceptor cells would help our understanding of pathologies involving retinal cell degeneration in inherited retinal dystrophies, age-related macular degeneration, and Usher Syndrome. CONCLUSIONS: Our mini-review will discuss mechanisms of protein transport within photoreceptors and introduce a novel role for an unconventional motor protein, MYO1C, in actin-based motor transport of the visual chromophore Rhodopsin to the OS, in support of phototransduction and visual function.

Short term visual and structural outcomes of anti-vascular endothelial growth factor (anti-VEGF) treatment delay during the first COVID-19 wave: A pilot study.

Regularly scheduled intravitreal anti-vascular endothelial growth factor (anti-VEGF) injections are essential to maintaining and/or improving many ocular conditions including: neovascular age-related macular degeneration (nAMD), diabetic retinopathy, and retinal vein occlusions with macular edema (RVO). This study aims to assess the effect of unintended delays in anti-VEGF treatment during the first wave of the COVID-19 pandemic. This retrospective case series identified patients receiving regularly scheduled anti-VEGF intravitreal injections based on current procedural terminology (CPT) code at two practices in Minnesota. Diagnoses were limited to nAMD, diabetic macular edema (DME), proliferative diabetic retinopathy, and RVO. Patients were divided into two groups based on whether they maintained or delayed their follow-up visit by more than two weeks beyond the recommended treatment interval during the COVID-19 lockdown. The 'COVID-19 lockdown' was defined as the period after March, 28th, 2020, when a lockdown was declared in Minnesota. We then compared the visual acuity and structural changes to the retina using ocular coherence tomography (OCT) to assess whether delayed treatment resulted in worse visual outcomes. A total of 167 eyes from 117 patients met criteria for inclusion in this study. In the delayed group, the average BCVA at the pre- and post-lockdown visits were 0.614 and 0.715 (logMAR) respectively (p = 0.007). Central subfield thickness (CST) increased from 341 to 447 in the DME delayed group (p = 0.03) while the CST increased from 301 to 314 (p = 0.4) in the nAMD delayed group. The results of this pilot study suggests that treatment delays may have a negative impact on the visual and anatomic outcomes of patients with nAMD and DME. Future studies with larger sample sizes are required for further investigation.

Comparing fundus autofluorescence and infrared imaging findings of peripheral retinoschisis, schisis detachment, and retinal detachment.

PURPOSE: The primary goal of this study was to identify characteristic features of peripheral degenerative retinoschisis (RS), schisis detachment (SD) and retinal detachment (RD) on both fundus autofluorescence (FAF) and infrared (IR) imaging, using spectral domain optical coherence tomography (SD-OCT) imaging of the peripheral retina as the confirmatory imaging tool. METHODS: This is a descriptive case series study. A total of 27 eyes of 22 patients were included. Thirteen eyes of 10 patients diagnosed with RS, 4 eyes of 3 patients diagnosed with SD, and 10 eyes of 9 patients diagnosed with RD were included. Patients with images of poor quality were excluded. Heidelberg Spectralis HRA + OCT machine (Heidelberg Engineering, Heidelberg, Germany) were used to acquire the images. RESULTS: All conditions appeared as areas of hypo-AF on FAF and hypo-reflectance on IR imaging. Accentuated vasculature of the lesion was noted with IR imaging due to elevation of the RS and RD, which was less frequently observed with FAF. On FAF, a hyper-AF leading edge around the RS lesion indicated the presence of intraretinal or subretinal fluid and an extension of the RS. Retinal breaks/holes were best visualized with IR imaging. SD-OCT confirmed the diagnosis in all performed cases. CONCLUSIONS: We were unable to differentiate between RS and RD based solely on findings from FAF and IR imaging. However, the combination of them with SD-OCT can assist in the diagnosis of RS from RD and in the evaluation of RS progression. OCT remains the main modality imaging to differentiate these conditions.

Cadmium-induced apoptotic death of human retinal pigment epithelial cells is mediated by MAPK pathway.

Cadmium (Cd), released from cigarette smoke and metal industrial activities, is known to accumulate in human body organs including retina and is particularly higher in retinal tissues of age-related macular degeneration (AMD) eyes compared to non-AMD eyes. We have determined the cytotoxic effects of Cd on human retinal pigment epithelial (RPE) cells. Upon Cd treatment, there was a dose- and time-dependent decline in ARPE-19 cell viability as well as early apoptotic changes such as altered mitochondrial membrane potential (MMP) and Cytochrome C release in cytosol. Depletion of GSH by buthionine-[S,R]-sulfoximine (BSO) resulted in increased Cd toxicity in ARPE-19 cells. Cadmium also caused reactive oxygen species (ROS) generation and activation of mitogen-activated protein kinases (MAPKs) pathway including c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase 1/2 (Erk1/2), and p38 in ARPE-19 cells. Antioxidants such as N-acetylcysteine (NAC) significantly reduced Cd-induced toxicity. These results indicate that elevated ROS-induced activation of the MAPK signaling pathway could be associated with Cd-induced RPE cell apoptosis, one of the major contributing factors in AMD. The toxic effects of Cd on ARPE-19 cells indicate that environmental heavy metals such as Cd could be important potential factors in RPE cells death associated retinal diseases particularly related to smoking.

Beneficial Effects of Spatial Remapping for Reading With Simulated Central Field Loss.

Purpose: People with central field loss (CFL) lose information in the scotomatous region. Remapping is a method to modify images to present the missing information outside the scotoma. This study tested the hypothesis that remapping improves reading performance for subjects with simulated CFL. Methods: Circular central scotomas, with diameters ranging from 4° to 16°, were simulated in normally sighted subjects using an eye tracker on either a head-mounted display (HMD) (experiments 1, 2) or a traditional monitor (experiment 3). In the three experiments, reading speed was measured for groups of 7, 11, and 13 subjects with and without remapping of text. Results: Remapping increased reading speed in all three experiments. On the traditional monitor, it increased reading speed by 34% (8°), 38% (12°), and 35% (16°). In the two HMD experiments, remapping increased reading speed only for the largest scotoma size, possibly due to latency of updating of the simulated scotoma. Conclusions: Remapping significantly increased reading speed in simulated CFL subjects. Additional testing should examine the efficacy of remapping for reading and other visual tasks for patients with advanced CFL.

Enhanced Detection of Sub-Retinal Pigment Epithelial Cell Layer Deposits in Human and Murine Tissue: Imaging Zinc as a Biomarker for Age-Related Macular Degeneration (An American Ophthalmological Society Thesis).

PURPOSE: Understanding the apparent paradoxical role of zinc in the pathogenesis and prevention of age-related macular degeneration (AMD) has been limited by the lack of animal models for its detection in sub-retinal epithelial deposits (drusen), a definitive early hallmark of AMD. In-vitro studies using Zinpyr-1 showed drusen contained high levels of zinc, but the probe was not suitable for in-vivo studies. This study compares Zinpyr-1 to ZPP1, a new fluorescein-based probe for zinc, to assess the potential of ZPP1 for in-vivo detection of zinc in drusen. METHODS: Flat mounts of human sub-RPE tissue using the probes were analyzed by fluorescence and confocal microscopy. Flat mounts of sub-RPE tissue from mice deficient in superoxide dismutase isoform-1 (CuZn-SOD-KO) or isoform-2 (Mn-SOD-RPE-KO) were analyzed with sub-RPE deposits confirmed by histology. RESULTS: Drusen are detected in greater numbers and intensity with ZPP1 compared to Zinpyr-1. Using ZPP1, drusen was detected in a sample from a 46-year old human donor without ocular history, suggesting that ZPP1 might be sensitive enough to detect drusen at an early stage. With CuZn-SOD KO mice, ZPP1 detected sub-RPE deposits at 10 months of age, whereas Zinpyr-1 required 14 months. CONCLUSION: Detection of sub-RPE deposits by ZPP1 was greatly enhanced compared to Zinpyr-1. This enhanced sensitivity will allow for more insightful analysis of zinc in AMD using human specimens and mouse models. This could result in the development of a sensitive in-vivo probe to enhance research on the role zinc in drusen formation and the early clinical diagnosis of AMD.

Ultra Wide-Field Indocyanine Green Angiogram Highlights Choroidal Perfusion Delay Secondary to Giant Cell Arteritis.

Vision loss in giant cell arteritis (GCA) often presents as anterior ischemic optic neuropathy and central retinal artery occlusion. Previous studies have established an acute delay in choroidal perfusion on fluorescein angiography (FA) as a classic sign of GCA. The authors present a unique imaging case report of GCA where ultra wide-field (UWF) indocyanine green angiography (ICGA) offers improved characterization of delayed choroidal perfusion compared to FA. Routine use of ICGA, particularly UWF imaging, in patients with suspected GCA should be studied in a larger cohort to determine whether it may improve detection of choroidal perfusion delay. [Ophthalmic Surg Lasers Imaging Retina. 2016;47:471-473.].

Implantation of the Argus II Retinal Prosthesis in an Eye With Short Axial Length.

The authors describe the implantation of the Argus II Retinal Prosthesis System (Argus II) (Second Sight Medical Products, Sylmar, CA) into a short axial length (AL) eye. The authors' main modification is the use of endocyclophotocoagulation (endo-CPC) to the ciliary processes in the area that the cable enters through the sclerotomy. This case describes the surgical technique necessary for successful implantation of the Argus II into a short AL eye. The use of endo-PC prevents chafing to the ciliary processes, does not affect postoperative intraocular pressure, and facilitates direct visualization of the structures during the surgery, preventing damage during implantation.

The Effect of Scleral Buckling Surgery on Choroidal Thickness Measured by Enhanced Depth Optical Coherence Tomography: A Cross-Sectional Study.

INTRODUCTION: To assess the anatomical changes taking place in the choroid after a scleral buckle (SB) procedure for retinal detachment repair. METHODS: This cross-sectional study looked at 23 adults with a history of unilateral retinal detachment repaired with a SB or other encircling element. The subjects underwent bilateral Enhanced Depth Spectral Domain Optical Coherence Tomography to image the choroid. The choroidal thickness (CT) was measured, and the non-operative eye was used as an internal control. RESULTS: CT was measured to be 170.8 ± 60.9 µm (mean ± SD) in eyes with SBs compared to 175.1 ± 61.9 µm in non-operative eyes. There was no statistically significant difference between the two groups (mean 4.3 µm, 95% CI -8.7, 17.3, p value 0.4973, paired t test). CONCLUSION: Placement of an SB as part of a surgery to repair retinal detachment did not significantly alter CT at the macula.

Strategies for Improving Patient Comfort During Intravitreal Injections: Results from a Survey-Based Study.

INTRODUCTION: Many ocular diseases require intravitreal injections of pharmacological agents. Optimizing patients' experiences during injections is important to ensure compliance and maintenance of quality of life. The objective of this study was to identify strategies to help alleviate discomfort during intravitreal injections. METHODS: A cross-sectional study surveying 128 patients during clinic visits between 2014 and 2015 in two outpatient Retina Clinics (one academic and one private). Patients receiving an intravitreal injection(s) for any retinal disorder were given a questionnaire with 10-yes/no responses for various potential strategies. Responses were stratified by sex, age (<30 years, 30-60 years, and >60 years) and total number of prior injections (0-9 injections, 10-20 injections and >20 injections). RESULTS: A total of 128 patients were surveyed: 59 males, 41 females and 28 with no sex specified. Our results identified four favorable strategies as those receiving more than 50% "yes" votes. These included the presence of technician/staff during the procedure, the use of a neck pillow, a verbal warning before the injection and performing injections in both eyes on the same day. Other specific strategies were identified for females, younger patients and those with greatest experience. These included: females preferred having their hand held during injections (P = 0.001) and using a stress ball (P = 0.000) when compared to males. Stratifying by age, patients 30-60 years old preferred having their hand held (P = 0.008) and background music (P = 0.007). Stratifying by prior injections, patients with >20 prior injections preferred having their hand held (P = 0.001), using a stress ball (P = 0.021) and, if necessary, having bilateral injections performed the same day to improve comfort (P = 0.037). CONCLUSIONS: Having an extra staff member present during the injection, having a neck pillow, having a verbal warning prior to injection and having both eyes injected on the same day were indicated as favorable strategies by over half of those surveyed. Further, specific strategies were identified for females, younger patients (30-60 years old) and those with greatest experience (>20 injections).

Electrospray tandem mass spectrometric analysis of zeaxanthin and its oxidation products.

Carotenoids have been implicated in protection of the eye from light-mediated photo-toxicity caused by free radicals. Under conditions of normal oxidative stress the carotenoids serve as protective antioxidants; however, when the oxidative stress exceeds the antioxidant capacity, carotenoids can be oxidized into numerous cleavage products. The determination and identification of oxidized carotenoids in biological samples remains a major challenge due to the small sample size and low stability of these compounds. We investigated the reaction of various zeaxanthin cleavage products with O-ethyl hydroxylamine to evaluate their levels in a biological sample. For this, a sensitive and specific electrospray tandem mass spectrometry (ESI-MS/MS) was developed, avoiding the classical lower sensitive and specific HPLC-UV and fluorescence absorption methods. Protonated molecules [M + H](+) of carotenoids upon collision-induced dissociation produced a number of structurally characteristic product ions. A series of complicated clusters of product ions differing in 14 (CH(2))and 26 (C(2)H(2))Da was characteristic of the polyene chain of intact carotenoids. All carotenoid ethyl oximes of zeaxanthin cleavage products were characterized by the losses of 60 and 61 Da in their MS/MS spectra. Through the application of the LC/MS/MS method, we identified two oxime derivatives of 3-hydroxy-beta-ionone and 3-hydroxy-14'-apocarotenal with protonated molecules at m/z 252 and m/z 370 respectively, in a human eye sample.

Association of Disorganization of Retinal Inner Layers With Vision After Resolution of Center-Involved Diabetic Macular Edema.

IMPORTANCE: Macular edema (ME) prognosis and treatment response vary according to the underlying abnormalities. Biomarkers of visual acuity (VA) improvement could influence management decisions in different types of ME. OBJECTIVE: To investigate whether disorganization of retinal inner layers (DRIL) and other spectral-domain optical coherence tomography (SD-OCT)-derived variables are associated with subsequent VA after ME resolution in both nondiabetic and diabetic ME. DESIGN, SETTING, AND PARTICIPANTS: A retrospective, longitudinal cohort study in which Snellen VA testing and SD-OCT macular imaging were performed, was conducted at a tertiary referral eye center for retinal diseases. The medical records of all patients with ME from December 1, 2010, to December 31, 2012, were reviewed. The date of the last follow-up was June 1, 2013. Participants included 55 patients (70 eyes) with center-involved ME that had resolved during an 8-month period. Patients were grouped based on the source of ME (diabetic vs nondiabetic). Exclusion criteria included significant media opacity interfering with good-quality SD-OCT image acquisition. Masked graders analyzed the central 1500-µm macular region for changes, including cysts, DRIL length and extent, and outer retinal layers disruption. Intragrader and intergrader agreement Spearman rank correlation coefficients ranged from 0.70 to 0.93 for quantitative measurement, and κ values ranged from 0.88 to 1.00 for qualitative grading. MAIN OUTCOMES AND MEASURES: Visual acuity and morphologic changes measured on SD-OCT. RESULTS: In both groups, VA after ME resolution correlated with baseline VA. In diabetic ME involving a multivariable model including baseline VA and DRIL, total length was associated with subsequent VA as determined by a parameter estimate (PE) of 0.0003 (95% CI, 0-0.0006) (P = .03). The VA change during the 8-month period, after adjusting for baseline VA, was best associated with DRIL change (PE, 0.0002 [95% CI, 0-0.0003]; P = .04). Participants whose DRIL resolved, both early and late, showed improvement in their VA deficit at 8 months (least squares mean [SE], 41.3 [28.5] and 40.9 [37.5], respectively) compared with nonresolvers, whether inconsistent or persistent, whose VA worsened. After adjustment for baseline VA, eyes with persistent DRIL showed the largest difference in VA deficit compared with those with no baseline DRIL (-89.6 [27.2] vs 49.7 [19.6], respectively; P = .006). CONCLUSIONS AND RELEVANCE: The presence of DRIL at baseline and its resolution pattern may be associated with subsequent VA after resolution of center-involved diabetic ME.

Macular pigment density and distribution: comparison of fundus autofluorescence with minimum motion photometry.

Macular pigment (MP) distribution profiles were measured for 18 subjects using a Moreland anomaloscope modified for motion photometry. The total amount of MP within the central 7 degrees was estimated from the distribution profile by numerical integration. Fundus autofluorescence images were obtained for eight of these subjects using a scanning laser ophthalmoscope. Peak optical density of MP increased with the total amount present, but the correlation was weakened by inter-subject differences in MP distribution. The mean MP distribution derived from mean grey-scale profiles of fundus autofluorescence images correlated closely with that obtained psychophysically (r=0.96). Autofluorescence imaging provides a fast non-invasive method for assessing MP in vivo.

Oxidation of carotenoids by heat and tobacco smoke.

The stability to autoxidation of the polar carotenoids, lutein and zeaxanthin, was compared to that of the less polar carotenoids, beta-carotene and lycopene at physiologically or pathophysiologically relevant concentrations of 2 and 6 microM, after exposure to heat or cigarette smoke. Three methodological approaches were used: 1) Carotenoids dissolved in solvents with different polarities were incubated at 37 and 80 degrees C for different times. 2) Human plasma samples were subjected to the same temperature conditions. 3) Methanolic carotenoid solutions and plasma were also exposed to whole tobacco smoke from 1-5 unfiltered cigarettes. The concentrations of individual carotenoids in different solvents were determined spectrophotometrically. Carotenoids from plasma were extracted and analyzed using high performance liquid chromatography. Carotenoids were generally more stable at 37 than at 80 degrees C. In methanol and dichloromethane the thermal degradation of beta-carotene and lycopene was faster than that of lutein and zeaxanthin. However, in tetrahydrofuran beta-carotene and zeaxanthin degraded faster than lycopene and lutein. Plasma carotenoid levels at 37 degrees C did not change, but decreased at 80 degrees C. The decrease of beta-carotene and lycopene levels was higher than those for lutein and zeaxanthin. Also in the tobacco smoke experiments the highest autoxidation rates were found for beta-carotene and lycopene at 2 microM, but at 6 microM lutein and zeaxanthin depleted to the same extent as beta-carotene. These data support our previous studies suggesting that oxidative stress degrade beta-carotene and lycopene faster than lutein and zeaxanthin. The only exception was the thermal degradation of carotenoids solubilized in tetrahydrofuran, which favors faster breakdown of beta-carotene and zeaxanthin.