Tryptophan and Non-Tryptophan Fluorescence of the Eye Lens Proteins Provides Diagnostics of Cataract at the Molecular Level

Thin Film Formation of HSA in the Presence of CTAB-Capped Gold Nanorods through Phase Separation

Phase behavior in protein-nanoparticle systems in light of protein corona formation has been investigated. We report the formation of HSA thin films following the addition of a solid protein to a solution of CTAB-capped gold nanorods (AuNRs) via phase separation. The phase separation behavior was observed through UV-vis spectroscopy, turbidity assays, and DLS studies. UV-vis spectra for the protein-AuNR solution indicated a possible self-assembly formation by CTAB-HSA complexes and AuNR-HSA conjugates. The turbidity was found to increase linearly up to 30-50% v/v for each component. The growth phase slope is proportional to the concentration of the components, AuNRs, and HSA, with no lag phase. Dynamic light scattering (DLS) shows the formation of larger aggregates with time, implying a segregated phase of AuNR-HSA and a CTAB-HSA-AuNR network. ζ-potential values confirm surface modification, implying protein corona formation on nanorods. The thin films were also characterized using SEM, AFM, SAXS, XPS, FTIR, and TGA studies. SEM images show a smooth surface with a reduced number of pores, indicating the compactness of the deposited structure. AFM shows two different structural pattern formations with the deposition, indicating possible self-assembly of the protein-conjugated nanoparticles. FTIR studies indicate a change in the hydrogen bonding network and confirm the CTAB-HSA-AuNR complex network formation. The XPS studies indicate Au-S bond formation, along with Au-S-S-Au interactions. SAXS studies indicate the formation of aggregates (oligomers), as well as the presence of dominant attractive intermolecular interactions in the thin films.

Label-Free Assessment of Key Biological Autofluorophores: Material Characteristics and Opportunities for Clinical Applications

Autofluorophores are endogenous fluorescent compounds that naturally occur in the intra and extracellular spaces of all tissues and organs. Most have vital biological functions - like the metabolic cofactors NAD(P)H and FAD+, as well as the structural protein collagen. Others are considered to be waste products - like lipofuscin and advanced glycation end products - which accumulate with age and are associated with cellular dysfunction. Due to their natural fluorescence, these materials have great utility for enabling non-invasive, label-free assays with direct ties to biological function. Numerous technologies, with different advantages and drawbacks, are applied to their assessment, including fluorescence lifetime imaging microscopy, hyperspectral microscopy, and flow cytometry. Here, the applications of label-free autofluorophore assessment are reviewed for clinical and health-research applications, with specific attention to biomaterials, disease detection, surgical guidance, treatment monitoring, and tissue assessment - fields that greatly benefit from non-invasive methodologies capable of continuous, in vivo characterization.

The role of tryptophan derivatives as anti-kinetoplastid agents

Kinetoplastids are the causative agents for a spectrum of vector-borne diseases including Leishmaniasis, Chagas disease and Trypanosomiasis that affect millions of people worldwide. In the absence of safe and effective vaccines, chemotherapy, in conjunction with vector control, remain the most significant control approach for kinetoplastid diseases. However, commercially available treatment for these neglected tropical diseases frequently ends up with toxic side effects and increasing resistance. To meet the rising need for innovative medications, alternative chemotherapeutic agents are required. Moreover, insights into target-based mode of action of chemotherapeutic agents are required if novel drugs that may outwit resistance to commercially available drugs are to be developed. Tryptophan has been implicated in a variety of diseases and disorders due to its fundamental role as a precursor to several bioactive metabolites, as well as its importance in the improvement of health and nutrition, diagnostics, and therapeutics. The regulation of tryptophan metabolism plays a fundamental role in the growth of kinetoplastids. Moreover, the levels of tryptophan may serve as a biomarker to distinguish between the stages of kinetoplastids making it an important amino acid to explore for drug targets. The main aim of this review is thus to provide a comprehensive literature synthesis of tryptophan derivatives to explore as potential anti-kinetoplastids. Here we highlight the role of tryptophan derivatives as chemotherapeutic agents against kinetoplastids. The reviewed compounds provide insights into potential new drug interventions that may combat the increasing problem of anti-kinetoplastid resistance.

Oxidative stress in the eye and its role in the pathophysiology of ocular diseases

Oxidative stress occurs through an imbalance between the generation of reactive oxygen species (ROS) and the antioxidant defense mechanisms of cells. The eye is particularly exposed to oxidative stress because of its permanent exposure to light and due to several structures having high metabolic activities. The anterior part of the eye is highly exposed to ultraviolet (UV) radiation and possesses a complex antioxidant defense system to protect the retina from UV radiation. The posterior part of the eye exhibits high metabolic rates and oxygen consumption leading subsequently to a high production rate of ROS. Furthermore, inflammation, aging, genetic factors, and environmental pollution, are all elements promoting ROS generation and impairing antioxidant defense mechanisms and thereby representing risk factors leading to oxidative stress. An abnormal redox status was shown to be involved in the pathophysiology of various ocular diseases in the anterior and posterior segment of the eye. In this review, we aim to summarize the mechanisms of oxidative stress in ocular diseases to provide an updated understanding on the pathogenesis of common diseases affecting the ocular surface, the lens, the retina, and the optic nerve. Moreover, we discuss potential therapeutic approaches aimed at reducing oxidative stress in this context.

Multifarious analytical capabilities of the UV/Vis protein fluorescence in blood plasma

Autofluorescence of blood plasma has been broadly considered as a prospective disease screening method. However, the assessment of such intrinsic fluorescence is mostly phenomenological, and its origin is still not fully understood, complicating its use in the clinical practice. Here we present the detailed evaluation of analytical capabilities, variability, and formation of blood plasma protein fluorescence based on the open dataset of excitation-emission matrices measured for ∼300 patients with suspected colorectal cancer, and our supporting model experiments. Using high-resolution size-exclusion chromatography coupled with comprehensive spectral analysis, we demonstrate, for the first time, the dominant role of HSA in the formation of blood plasma fluorescence in the visible spectral range (excitation wavelength >350 nm), presumably caused by its oxidative modifications. Furthermore, the diagnostic value of the tryptophan emission, as well as of the tyrosine fluorescence and visible fluorescence of proteins is shown by building a tree-based classification model that uses a small subset of physically interpretable fluorescence features for distinguishing between the control group and cancer patients with >80% accuracy. The obtained results extend current understanding and approaches used for the analysis of blood plasma fluorescence and pave the way for novel autofluorescence-based disease screening methods.

Role of Oxidative Stress in Ocular Diseases: A Balancing Act

Redox homeostasis is a delicate balancing act of maintaining appropriate levels of antioxidant defense mechanisms and reactive oxidizing oxygen and nitrogen species. Any disruption of this balance leads to oxidative stress, which is a key pathogenic factor in several ocular diseases. In this review, we present the current evidence for oxidative stress and mitochondrial dysfunction in conditions affecting both the anterior segment (e.g., dry eye disease, keratoconus, cataract) and posterior segment (age-related macular degeneration, proliferative vitreoretinopathy, diabetic retinopathy, glaucoma) of the human eye. We posit that further development of therapeutic interventions to promote pro-regenerative responses and maintenance of the redox balance may delay or prevent the progression of these major ocular pathologies. Continued efforts in this field will not only yield a better understanding of the molecular mechanisms underlying the pathogenesis of ocular diseases but also enable the identification of novel druggable redox targets and antioxidant therapies.

Impact of the Aging Lens and Posterior Capsular Opacification on Quantitative Autofluorescence Imaging in Age-Related Macular Degeneration

Purpose

The purpose of this study was to investigate quantitative autofluorescence (qAF8) in patients with and without early or intermediate age-related macular degeneration (AMD); to determine the impact of the aged crystalline lens and posterior capsular opacification (PCO).

Methods

In phakic and pseudophakic eyes ≥60 years, AMD status was determined by the Beckman system. PCO presence and severity was extracted from clinical records. qAF8 was calculated using custom FIJI plugins. Differences in qAF8, stratified by lens status, PCO severity, and AMD status, were analyzed using generalized estimating equations.

Results

In 210 eyes of 115 individuals (mean age = 75.7 ± 6.6 years), qAF8 was lower in intermediate AMD compared to early AMD (P = 0.05). qAF8 did not differ between phakic and pseudophakic eyes (P = 0.8909). In phakic (n = 83) and pseudophakic (n = 127) eyes considered separately, qAF8 did not differ by AMD status (P = 0.0936 and 0.3494, respectively). Qualitative review of qAF images in phakic eyes illustrated high variability. In pseudophakic eyes, qAF8 did not differ with PCO present versus absent (54.5% vs. 45.5%). Review of implanted intraocular lenses (IOLs) revealed that 43.9% were blue-filter IOLs.

Conclusions

qAF8 was not associated with AMD status, up to intermediate AMD, considering only pseudophakic eyes to avoid noisy images in phakic eyes. In pseudophakic eyes, qAF8 was not affected by PCO. Because blue-filter IOLs may reduce levels of exciting light for qAF8, future studies investigating qAF in eyes with different IOL types are needed.

Translational Relevance

To reduce variability in observational studies and clinical trials requiring qAF8, pseudophakic participants without blue-filter IOLs or advanced PCO should be preferentially enrolled.

Modifying Anthocyanins Biosynthesis in Tomato Hairy Roots: A Test Bed for Plant Resistance to Ionizing Radiation and Antioxidant Properties in Space

Gene expression manipulation of specific metabolic pathways can be used to obtain bioaccumulation of valuable molecules and desired quality traits in plants. A single-gene approach to impact different traits would be greatly desirable in agrospace applications, where several aspects of plant physiology can be affected, influencing growth. In this work, MicroTom hairy root cultures expressing a MYB-like transcription factor that regulates the biosynthesis of anthocyanins in Petunia hybrida (PhAN4), were considered as a testbed for bio-fortified tomato whole plants aimed at agrospace applications. Ectopic expression of PhAN4 promoted biosynthesis of anthocyanins, allowing to profile 5 major derivatives of delphinidin and petunidin together with pelargonidin and malvidin-based anthocyanins, unusual in tomato. Consistent with PhAN4 features, transcriptomic profiling indicated upregulation of genes correlated to anthocyanin biosynthesis. Interestingly, a transcriptome reprogramming oriented to positive regulation of cell response to biotic, abiotic, and redox stimuli was evidenced. PhAN4 hairy root cultures showed the significant capability to counteract reactive oxygen species (ROS) accumulation and protein misfolding upon high-dose gamma irradiation, which is among the most potent pro-oxidant stress that can be encountered in space. These results may have significance in the engineering of whole tomato plants that can benefit space agriculture.

Relationship between the Structure and Chaperone Activity of Human αA-Crystallin after Its Modification with Diabetes-Associated Oxidative Agents and Protective Role of Antioxidant Compounds

The study was aimed to evaluate the impact of peroxynitrite (PON, oxidative stress agent in diabetes), methylglyoxal (MGO, diabetes-associated reactive carbonyl compound), and their simultaneous application on the structural and functional features of human αA-crystallin (αA-Cry) using various spectroscopy techniques. Additionally, the surface tension and oligomer size distribution of the treated and untreated protein were tested using tensiometric analysis and dynamic light scattering, respectively. Our results indicated that the reaction of PON and MGO with human αA-Cry leads to the formation of new chromophores, alterations in the secondary to quaternary protein structure, reduction in the size of protein oligomers, and significant enhancement in the chaperone activity of αA-Cry. To reverse the effects of the tested compounds, ascorbic acid and glutathione (main components of lens antioxidant defense system) were applied. As expected, the two antioxidant compounds significantly prevented formation of high molecular weight aggregates of αA-Cry (according to SDS-PAGE). Our results suggest that the lens antioxidant defense system, in particular, glutathione, may provide a strong protection against rapid incidence and progression of diabetic cataract by preventing the destructive reactions of highly reactive DM-associated metabolites.

Cataract Development by Exposure to Ultraviolet and Blue Visible Light in Porcine Lenses

Background and Objectives: Cataract is still the leading cause of blindness. Its development is well researched for UV radiation. Modern light sources like LEDs and displays tend to emit blue light. The effect of blue light on the retina is called blue light hazard and is studied extensively. However, its impact on the lens is not investigated so far. Aim: Investigation of the impact of the blue visible light in porcine lens compared to UVA and UVB radiation. Materials and Methods: In this ex-vivo experiment, porcine lenses are irradiated with a dosage of 6 kJ/cm2 at wavelengths of 311 nm (UVB), 370 nm (UVA), and 460 nm (blue light). Lens transmission measurements before and after irradiation give insight into the impact of the radiation. Furthermore, dark field images are taken from every lens before and after irradiation. Cataract development is illustrated by histogram linearization as well as faults coloring of recorded dark field images. By segmenting the lens in the background's original image, the lens condition before and after irradiation could be compared. Results: All lenses irradiated with a 6 kJ/cm2 reveal cataract development for radiation with 311 nm, 370 nm, and 460 nm. Both evaluations reveal that the 460 nm irradiation causes the most cataract. Conclusion: All investigated irradiation sources cause cataracts in porcine lenses-even blue visible light.

Fluorescence lifetime imaging ophthalmoscopy: autofluorescence imaging and beyond

Fluorescence lifetime imaging ophthalmoscopy, FLIO, has gained large interest in the scientific community in the recent years. It is a noninvasive imaging modality that has been shown to provide additional information to conventional imaging modalities. The FLIO device is based on a Heidelberg Engineering Spectralis system. Autofluorescence lifetimes are excited at 473 nm and recorded in two spectral wavelength channels, a short spectral channel (SSC, 498-560 nm) and a long spectral channel (LSC, 560-720 nm). Typically, mean autofluorescence lifetimes in a 30° retinal field are investigated. FLIO shows a clear benefit for imaging different retinal diseases. For example, in age-related macular degeneration (AMD), ring patterns of prolonged FLIO lifetimes 1.5-3.0 mm from the fovea can be appreciated. Macular telangiectasia type 2 (MacTel) shows a different pattern, with prolonged FLIO lifetimes within the typical MacTel zone. In Stargardt disease, retinal flecks can be appreciated even before they are visible with other imaging modalities. Early hydroxychloroquine toxicity appears to be detectable with FLIO. This technique has more potential that has yet to be discovered. This review article focuses on current knowledge as well as pitfalls of this technology. It highlights clinical benefits of FLIO imaging in different ophthalmic and systemic diseases, and provides an outlook with perspectives from the authors.

Glycation-mediated protein crosslinking and stiffening in mouse lenses are inhibited by carboxitin in vitro

Proteins in the eye lens have negligible turnover and therefore progressively accumulate chemical modifications during aging. Carbonyls and oxidative stresses, which are intricately linked to one another, predominantly drive such modifications. Oxidative stress leads to the loss of glutathione (GSH) and ascorbate degradation; this in turn leads to the formation of highly reactive dicarbonyl compounds that react with proteins to form advanced glycation end products (AGEs). The formation of AGEs leads to the crosslinking and aggregation of proteins contributing to lens aging and cataract formation. To inhibit AGE formation, we developed a disulfide compound linking GSH diester and mercaptoethylguanidine, and we named it carboxitin. Bovine lens organ cultured with carboxitin showed higher levels of GSH and mercaptoethylguanidine in the lens nucleus. Carboxitin inhibited erythrulose-mediated mouse lens protein crosslinking, AGE formation and the formation of 3-deoxythreosone, a major ascorbate-derived AGE precursor in the human lens. Carboxitin inhibited the glycation-mediated increase in stiffness in organ-cultured mouse lenses measured using compressive mechanical strain. Delivery of carboxitin into the lens increases GSH levels, traps dicarbonyl compounds and inhibits AGE formation. These properties of carboxitin could be exploited to develop a therapy against the formation of AGEs and the increase in stiffness that causes presbyopia in aging lenses.

Stress-dependent conformational changes of artemin: Effects of heat and oxidant

Artemin is an abundant thermostable protein in Artemia embryos and it is considered as a highly efficient molecular chaperone against extreme environmental stress conditions. The conformational dynamics of artemin have been suggested to play a critical role in its biological functions. In this study, we have investigated the conformational and functional changes of artemin under heat and oxidative stresses to identify the relationship between its structure and function. The tertiary and quaternary structures of artemin were evaluated by fluorescence measurements, protein cross-linking analysis, and dynamic light scattering. Based on the structural analysis, artemin showed irreversible substantial conformational lability in responses to heat and oxidant, which was mainly mediated through the hydrophobic interactions and dimerization of the chaperone. In addition, the chaperone-like activity of heated and oxidized artemin was examined using lysozyme refolding assay and the results showed that although both factors, i.e. heat and oxidant, at specific levels improved artemin potency, simultaneous incubation with both stressors significantly triggered the chaperone activation. Moreover, the heat-induced dimerization of artemin was found to be the most critical factor for its activation. It was suggested that oxidation presumably acts through stabilizing the dimer structures of artemin through formation of disulfide bridges between the subunits and strengthens its chaperoning efficacy. Accordingly, it is proposed that artemin probably exists in a monomer–oligomer equilibrium in Artemia cysts and environmental stresses and intracellular portion of protein substrates may shift the equilibrium towards the active dimer forms of the chaperone.

Fluorescence Quantum Yields in Complex Environments from QM-MM TDDFT Simulations: The Case of Indole in Different Solvents

Fluorescence is commonly exploited to probe microscopic properties. An important example is tryptophan in protein environments, where variations in fluorescence quantum yield, and in absorption and emission maxima, are used as indicators of changes in the environment. Modeling the fluorescence quantum yield requires the determination of both radiative and nonradiative decay constants, both on the potential energy surface of the excited fluorophore. Furthermore, the inclusion of complex environments implies their accurate representation as well as extensive configurational sampling. In this work, we present and test various methodologies based on time-dependent density functional theory (TDDFT) and quantum mechanics/molecular mechanics (QM/MM) dynamics that take all of these requirements into account to provide a quantitative prediction of the effect of the environment on the fluorescence quantum yield of indole, a tryptophan fluorophore. This investigation paves the way for applications to the realistic spectroscopic characterization of the local protein environment of tryptophan from computer simulations.

Probing heat and oxidation induced conformational changes of molecular chaperone artemin by excitation-emission fluorescence spectroscopy

Artemin is a potent molecular chaperone, which protects Artemia embryos undergoing encystment against extreme environmental stresses. In the present work, we have examined the structural changes of artemin from A. urmiana upon exposure to oxidant and heat, by using CD measurements as well as excitation-emission fluorescence spectroscopy as a powerful tool for monitoring the conformational transitions and molecular interactions in proteins. We have also provided here the first document on reporting the three dimensional fluorescence spectra of a protein using ANS. Totally, the fluorescence results indicated that the microenvironments of tyrosine and tryptophan residues and the hydrophobic pockets as well as the polypeptide backbone or secondary structure of the chaperone were influenced in responses to heat and H₂O₂ in different degrees. Moreover, the native state of artemin did not induce a considerable exposure of the internal non-polar groups to the solvent. Besides, the excitation-emission spectra of heated artemin by ANS revealed new emission peaks at 430-450 nm when it was excited at 330 nm, which suggests probable exposure of new binding sites for hydrophobic or electrostatic interactions of the protein with ANS. The protein also showed a greater conformational sensitivity to the temperature fluctuations compared to oxidation. Here, we presented some evidence in support of the relation between artemin and its stress dependent activation in vitro and in vivo. This study can expect that the EEM fluorescence spectroscopy could provide a promising tool to study conformational transitions of proteins.

Influence of Lens Fluorescence on Fluorescence Lifetime Imaging Ophthalmoscopy (FLIO) Fundus Imaging and Strategies for Its Compensation

Purpose

To explore the contribution of crystalline lens fluorescence to fluorescence lifetimes measured with fluorescence lifetime imaging ophthalmoscopy (FLIO) and to propose a computational model to reduce the lens influence.

Methods

FLIO, which detects autofluorescence decay over time in a short-wavelength spectral channel (SSC, 498–560 nm) and a long-wavelength spectral channel (LSC, 560–720 nm), was performed on 32 patients before and after cataract extraction. The mean autofluorescence lifetime (τ_m) of the fundus was determined from a three-exponential fit of the postoperative fluorescence decays. The preoperative measurements were fit with series of exponential functions in which one fluorescence component was time-shifted in order to represent lens fluorescence.

Results

Postoperatively, τ_m was 185 ± 22 ps in the SSC and 209 ± 34 ps in the LSC at the posterior pole. These values were best reproduced by fitting the postoperative measurements with a three-exponential model with a time-shifted third fluorescence component (SSC, 203 ± 45 ps; LSC, 215 ± 29 ps), whereas disregarding time-shifted lens fluorescence resulted in significantly (P < 0.001) longer τ_m values (SSC, 474 ± 206 ps; LSC, 215 ± 29 ps). The fluorescence of the cataract lens contributed to the total fluorescence by 54.2 ± 10.6% (SSC) and 29.5 ± 9.9% (LSC).

Conclusions

Cataract lens fluorescence greatly alters fluorescence lifetimes measured at the fundus by FLIO, resulting in an overestimation of the lifetimes; however, this may be compensated for considerably by taking lens influence into account in the fitting model.

Translational Relevance

This study investigates cataract fluorescence in FLIO and a mathematical model for compensation of this influence.

Glycation-mediated inter-protein cross-linking is promoted by chaperone-client complexes of α-crystallin: Implications for lens aging and presbyopia

Lens proteins become increasingly cross-linked through nondisulfide linkages during aging and cataract formation. One mechanism that has been implicated in this cross-linking is glycation through formation of advanced glycation end products (AGEs). Here, we found an age-associated increase in stiffness in human lenses that was directly correlated with levels of protein-cross-linking AGEs. α-Crystallin in the lens binds to other proteins and prevents their denaturation and aggregation through its chaperone-like activity. Using a FRET-based assay, we examined the stability of the αA-crystallin-γD-crystallin complex for up to 12 days and observed that this complex is stable in PBS and upon incubation with human lens-epithelial cell lysate or lens homogenate. Addition of 2 mm ATP to the lysate or homogenate did not decrease the stability of the complex. We also generated complexes of human αA-crystallin or αB-crystallin with alcohol dehydrogenase or citrate synthase by applying thermal stress. Upon glycation under physiological conditions, the chaperone-client complexes underwent greater extents of cross-linking than did uncomplexed protein mixtures. LC-MS/MS analyses revealed that the levels of cross-linking AGEs were significantly higher in the glycated chaperone-client complexes than in glycated but uncomplexed protein mixtures. Mouse lenses subjected to thermal stress followed by glycation lost resilience more extensively than lenses subjected to thermal stress or glycation alone, and this loss was accompanied by higher protein cross-linking and higher cross-linking AGE levels. These results uncover a protein cross-linking mechanism in the lens and suggest that AGE-mediated cross-linking of α-crystallin-client complexes could contribute to lens aging and presbyopia.

Anomalous fluorescence of white hair compared to other unpigmented keratin fibres

OBJECTIVE

To demonstrate that the tryptophan (Trp) fluorescence of natural white hair is much weaker than other unpigmented keratin fibres such as wool, cashmere, rabbit hair and mink fur, and to explore possible reasons for this behaviour. The origin of the blue visible fluorescence (~450 nm) excited by UVA radiation in the range 360-380 nm, often associated with Trp degradation products, is also discussed and compared to other fibrous and globular proteins.

METHODS

As the fluorescence spectrum of keratin fibres usually contains at least two major features, a visual comparison is more effectively demonstrated by creating a 3D contour plot of excitation versus emission wavelength, which is sometimes referred to as an excitation emission matrix (EEM).

RESULTS

The Trp fluorescence from white hair is very much weaker than for wool, cashmere, rabbit hair and mink fur, but its visible fluorescence emission is stronger. Oxidation and reduction have little effect on the Trp intensity, which suggests quenching by cystine is not a major factor. Decuticulation of hair fibres had no effect on the Trp intensity showing that the increased number of cuticle scales surrounding the fibre cortex is not responsible. Trp fluorescence is very sensitive to exposure to UVB wavelengths, so possibly its low intensity in hair is due to greater levels of environmental exposure to sunlight than the other fibres examined.

CONCLUSION

Trp fluorescence from natural white hair is either extremely weak or completely absent, in contrast to the four other keratin fibres examined. It is possible that environmental exposure to UV wavelengths presents in sunlight contributes to a reduction in the Trp fluorescence intensity of white hair. However, another explanation is that Trp is quenched, by either an unknown substance introduced into hair during keratinization or as a result of regular exposure to personal care products, which may interact with Trp or tyrosine residues and disrupt the energy transfer process involved in keratin fluorescence. Further studies will be required to definitively determine the cause.

3-Hydroxykynurenine bound to eye lens proteins induces oxidative modifications in crystalline proteins through a type I photosensitizing mechanism

Photosensitized reactions mediated by endogenous chromophores have been associated with the etiology of age-related cataract disease. Endogenous chromophores such as 3-hydroxykynurenine (3OHKN) can be found in both free form, and bound to crystallin proteins. However, their efficiency in generating photo-induced oxidative modifications on eye lens proteins is not completely understood. In this work, the efficiency and photodynamic activity of 3OHKN bound to both lysine (3OHKN-Lys) and bovine lens proteins (3OHKN-BLP) was assessed and compared with the photosensitizing activity of the major chromophore arising from glucose degradation (GDC). The photosensitizing activity of 3OHKN-Lys, 3OHKN-BLP and GDC was characterized by measurement of singlet oxygen quantum yields, O₂ consumption, SDS-PAGE and amino acid analysis of the photo-oxidized proteins. Singlet oxygen quantum yields under 20% O₂ atmosphere were 0.02, 0.01, and 0.27 for 3OHKN-Lys, 3OHKN-BLP and GDC, respectively. O₂ consumption by photosensitized reactions was more efficient for 3OHKN-BLP, with the extent of O₂ consumption being ∼28% higher than for 3OHKN-Lys and GDC under both 5 and 20% O₂. SDS-PAGE showed that protein crosslinking is dependent on the O₂ concentration, and more extensive at 5 than 20% O₂. GDC and 3OHKN-Lys were the most efficient crosslinkers at 20 and 5% O₂, respectively. Amino acid analysis of the irradiated proteins showed consumption of Trp, His, Tyr and Phe, and formation of kynurenine (from Trp), methionine sulfoxide (from Met) and DOPA (from Tyr). Kynurenine formation was dependent on the O₂ concentration with higher amounts detected at 5 than 20% O₂ for 3OHKN-BLP and 3OHKN-Lys, with 3OHKN-BLP the most efficient sensitizer. Our results suggest that 3OHKN-BLP can elicit photo-oxidative damage mainly by a type I photosensitizing mechanism, with this likely to be the most prevalent pathway at the low physiologic O₂ concentrations in the eye lens.

Phototoxicity of environmental radiations in human lens: revisiting the pathogenesis of UV-induced cataract

The magnitude of cataract pathology is indeed significant as it is the principal cause of blindness worldwide. Also, the prominence of this concept escalates with the current aging population. The burden of the disease is more tangible in developing countries than developed ones. Regarding this concern, there is a gap in classifying the pathogenesis of the ultraviolet (UV) radiation-induced cataracts and explaining the possible cellular and subcellular pathways. In this review, we aim to revisit the effect of UV radiation on cataracts categorizing the cellular pathways involved. This may help for better pharmaceutical treatment alternatives and their wide-reaching availability. Also, in the last section, we provide an overview of the protecting agents utilized as UV shields. Further studies are required to enlighten new treatment modalities for UV radiation-induced pathologies in human lens.

Analysis, Nutrition, and Health Benefits of Tryptophan

Tryptophan is an essential plant-derived amino acid that is needed for the in vivo biosynthesis of proteins. After consumption, it is metabolically transformed to bioactive metabolites, including serotonin, melatonin, kynurenine, and the vitamin niacin (nicotinamide). This brief integrated overview surveys and interprets our current knowledge of the reported multiple analytical methods for free and protein-bound tryptophan in pure proteins, protein-containing foods, and in human fluids and tissues, the nutritional significance of l-tryptophan and its isomer d-tryptophan in fortified infant foods and corn tortillas as well the possible function of tryptophan in the diagnosis and mitigation of multiple human diseases. Analytical methods include the use of acid ninhydrin, near-infrared reflectance spectroscopy, colorimetry, basic hydrolysis; acid hydrolysis of S-pyridylethylated proteins, and high-performance liquid and gas chromatography-mass spectrometry. Also covered are the nutritional values of tryptophan-fortified infant formulas and corn-based tortillas, safety of tryptophan for human consumption and the analysis of maize (corn), rice, and soybean plants that have been successfully genetically engineered to produce increasing tryptophan. Dietary tryptophan and its metabolites seem to have the potential to contribute to the therapy of autism, cardiovascular disease, cognitive function, chronic kidney disease, depression, inflammatory bowel disease, multiple sclerosis, sleep, social function, and microbial infections. Tryptophan can also facilitate the diagnosis of certain conditions such as human cataracts, colon neoplasms, renal cell carcinoma, and the prognosis of diabetic nephropathy. The described findings are not only of fundamental scientific interest but also have practical implications for agriculture, food processing, food safety, nutrition, and animal and human health. The collated information and suggested research need will hopefully facilitate and guide further studies needed to optimize the use of free and protein-bound tryptophan and metabolites to help improve animal and human nutrition and health.

Imaging Lenticular Autofluorescence in Older Subjects

Purpose

To evaluate whether a practical method of imaging lenticular autofluorescence (AF) can provide an individualized measure correlated with age-related lens yellowing in older subjects undergoing tests involving shorter wavelength lights.

Methods

Lenticular AF was imaged with 488-nm excitation using a confocal scanning laser ophthalmoscope (cSLO) routinely used for retinal AF imaging. There were 75 older subjects (ages 47–87) at two sites; a small cohort of younger subjects served as controls. At one site, the cSLO was equipped with an internal reference to allow quantitative AF measurements; at the other site, reduced-illuminance AF imaging (RAFI) was used. In a subset of subjects, lens density index was independently estimated from dark-adapted spectral sensitivities performed psychophysically.

Results

Lenticular AF intensity was significantly higher in the older eyes than the younger cohort when measured with the internal reference (59.2 ± 15.4 vs. 134.4 ± 31.7 gray levels; P < 0.05) as well as when recorded with RAFI without the internal reference (10.9 ± 1.5 vs. 26.1 ± 5.7 gray levels; P < 0.05). Lenticular AF was positively correlated with age; however, there could also be large differences between individuals of similar age. Lenticular AF intensity correlated well with lens density indices estimated from psychophysical measures.

Conclusions

Lenticular AF measured with a retinal cSLO can provide a practical and individualized measure of lens yellowing, and may be a good candidate to distinguish between preretinal and retinal deficits involving short-wavelength lights in older eyes.