Cataract formation in a strain of rats selected for high oxidative stress
The primary purpose of this study was to define the clinical and morphological features of cataractogenesis in the OXYS strain of rats that generate excess reactive oxygen species. Rats were sequentially examined from birth to the development of mature cataracts with slit lamp biomicroscopy. Morphology of selected stages of cataract development was studied using light and transmission electron microscopy (TEM), immunohistochemical localization of the lipid peroxidation product 4-hydroxynonenal (HNE) and fluorescent antibody labeling for DNA oxidation products. Lenses from age-matched normal rats were used as controls. OXYS rats developed cataracts as young as two weeks of age with progression to maturity by 1 year. Clinically, cataracts appeared initially either as nuclear or sub-capsular cortical changes and progressed to pronounced nuclear cataracts within months. TEM confirmed the light microscopic impression of region-specific alterations in both fiber cell cytoplasmic protein matrix and membrane structure. The outer adult nuclear region showed extensive cellular damage similar to osmotic cataracts, which is consistent with the postulated high uptake of glucose in the OXYS strain. The adult and outer fetal nuclear cells displayed several types of focal damage. The inner fetal and embryonic nuclear cells demonstrated textured cytoplasm, suggesting protein degradation or redistribution. Staining for HNE was increased in epithelium, cortex and nucleus compared to control lenses. Fluorescent antibody probes demonstrated increased levels of DNA oxidation products in OXYS rat lenses compared to age-matched controls. Fourier analysis of nuclear cytoplasm revealed significant components with corresponding sizes greater than 100 nm and, using a new theoretical approach, the texturing of the cytoplasm was shown to be sufficient to cause opacification of the nucleus. The OXYS rat appears to be an ideal model for oxidative stress cataractogenesis. The potential oxidative damage observed is extensive and characteristic of the developmental region. The source of oxidative damage may in part be a response to elevated levels of glucose. Because oxidative stress is thought to be a major factor in cataract formation in both diabetic and non-diabetic aging humans, this animal model may be a useful tool in assessing efficacy of antioxidant treatments that may slow or prevent cataract formation.
Cataracts refers to a clouding of the lens of the eye, which affect vision and remain a major cause of blindness in the world (1,2). According to the World Health Organization (WHO), cataracts account for approximately 51% of global blindness. Therefore, cataracts are a critical public health and social problem worldwide. At present, it is impossible to entirely prevent cataract formation, and cataract surgery remains the most common method of treatment. In order to decrease the burden of surgery in older adults, it is of great interest to establish alternative therapies to delay or prevent the development of cataracts.
Lenses that are chronically exposed to ultraviolet (UV) radiations generate reactive oxygen species (ROS) and oxidative modifications (3) and have high levels of reduced glutathione (GSH) and ascorbic acid (AsA) to maintain a constant redox state, protecting against oxidative stress and preserving lens transparency. Consequently, the levels of these compounds in the lens are frequently used as markers of cataract formation or development in both human and animal models (4–7). The lens also uses chaperone activity to maintain its transparency. α-Crystallin, which constitutes up to 30% of total water-soluble proteins in the lens, acts as a molecular chaperone. Molecular chaperone activity plays an important role in in vivo due to the longevity and negligible turnover of lens proteins. Furthermore, it is well-known that lens proteins in cataracts have weaker chaperone activity than those in the non-disease state. Therefore, we measured the effect of hesperetin and hesperetin derivatives on the changes in chaperone activity in lenses with cataracts.
We have previously reported that hesperetin, one of the natural flavonoids in orange rinds, could delay cataract onset as assessed by observing cataract grade and measuring lens GSH and AsA levels. We also showed that treatment with hesperetin prevented down-regulation of chaperone activity in the lens (8,9). In the current study, we assessed the therapeutic ability of hesperetin derivatives to produce strong-acting anti-cataract activity using an Se-induced cataract model, a well-established rodent model used for screening potential anti-cataract molecules.
In this study, we determined whether anti-cataract properties of these derivatives could be altered by linking fatty acids. Either hesperetin or hesperetin derivatives were administered to rats with Se-induced cataracts in order to assess the anti-cataract effect of these compounds.
Materials and methods
Sodium selenite (Na2SeO3: Se), hesperetin, isoflurane, GSH, dithionitrobenzene (DTNB), AsA, metaphosphoric acid, and 2-vinylpyridine were purchased from Wako Pure Chemical Industries, Ltd. (Osaka, Japan). Stearic acid and oleic acid were purchased from Tokyo Chemical Industry Co., Ltd. (Tokyo, Japan). Trichloroacetic acid was purchased from Nacalai Tesque Inc. (Kyoto, Japan). 2,6-Dichlorophenol-indophenol (DCPIP) was purchased from Merck KGaA, (Darmstadt, Germany). Sprague Dawley (SD) rats were obtained from Sankyo Labo Service Corporation (Tokyo, Japan).
From hesperetin (Hes, Fig. 1A), we synthesized hesperetin stearic acid ester (Hes-S, Fig. 1B) and oleic acid ester (Hes-O, Fig. 1C) according to a previously reported procedure (10), and purified materials were used for the anti-cataract experiments.
SD rats were housed in temperature-controlled (25°C ± 5°C) and light-controlled rooms (12 h cycle of light and dark). Animals were fed balanced rat chow (CE-2; Clea Japan, Inc., Tokyo, Japan) and provided water ad libitum. Keio University Animal Research Committee (Tokyo, Japan) approved all of the animal procedures that were performed in the present study [11014-(4)]. Rats were euthanized with isoflurane (5%, inhalation). Blood samples were immediately collected form the vena cava; as much blood as possible was obtained from each rat for subsequent measurements. All of the animals in this work were treated according to the National Institutes of Health (NIH) guide for the care and use of laboratory animals.
Se-induced cataracts and hesperetin treatment
A total of 168 female rats that were 13 days old were randomized into 12 groups: Group 1, Control group (G1); Group 2, Treatment with hesperetin (G2); Group 3, Treatment with stearic acid (G3); Group 4, Treatment with oleic acid (G4); Group 5, Treatment with Hes-S (G5); Group 6, Treatment with Hes-O (G6); Group 7, Treatment with Se (G7); Group 8, Treatment with hesperetin and Se (G8); Group 9, Treatment with stearic acid and Se (G9); Group 10, Treatment with oleic acid and Se (G10); Group 11, Treatment with Hes-S and Se (G11); and Group 12, Treatment with Hes-O and Se (G12). (Table I; n=6 or 8 per group in each experiment).
Experimental groups used in the present study.
Experimental groups used in the present study.
|Group||Challenge||Test compound||Administration route|
|Group 3||PBS||Stealic acid||S.C.|
|Group 4||PBS||Oleic acid||S.C.|
|Group 9||Se||Stealic acid||S.C.|
|Group 10||Se||Oleic acid||S.C.|
Either test compound or vehicle was administered to each group of rats as described in Table I. Rats in groups G1-G6 were subcutaneously injected with phosphate-buffered saline (PBS) and those in G7-G12 were subcutaneously injected with Se at 20 µmol/kg body weight. PBS or Se was injected into 13-day-old rats (day 0) 4 h after administration of test compound. Hes, stearic acid, oleic acid, Hes-S, or Hes-O was dissolved in 7% ethanol and 93% olive oil solution and administered on Days 0, 1 and 2 subcutaneously at 10 nmol/kg body weight per day. The doses of hesperetin and its derivatives were decided according to our previous reports (8,9). On day 6, when the rats were 19 days old, following euthanization, enucleated eyes were analyzed for levels of GSH and AsA, and lens chaperone activities were determined. Plasma samples were separated by centrifugation of whole blood with heparin; plasma was stored at −80°C before analysis.
Cataract classifications were defined as previously described (11). Briefly, cataract stage 1 was defined as <5% opacity in the lens, stage 2 was defined as 5–20% opacity, stage 3 was defined as 20–40% opacity, stage 4 was defined as 40–60% opacity, stage 5 was defined as 60–80% opacity, and stage 6 was defined as >80% opacity. Following lens observation, rats were euthanized by isoflurane inhalation and lenses were recovered for further analyses.
Measurement of GSH
The level of lens GSH was determined according to a method previously described by Sedlak & Lindsay, with minor modifications (12). Briefly, lenses were homogenized in 0.1 M sodium phosphate buffer (pH 8.0) and centrifuged. The water-soluble fraction was deproteinized using trichloroacetic acid and centrifuged to remove the proteins. The supernatant was diluted with sodium phosphate buffer according to the wet lens weight (1 mg lens weight/ml). The sample was divided into two tubes: one tube contained 10 mM 2-vinylpyridine to sequester GSH for measuring oxidative GSH, and the other tube contained the same volume of sodium phosphate buffer to measure the total GSH content. Both tubes were incubated for 1 h at room temperature in a fume hood. After incubation, the excess 2-vinylpyridine was neutralized with triethanolamine. DTNB was then added to both tubes, and the mixture was incubated for 30 min at room temperature. Absorbance at 412 nm was then measured in an Infinite M200PRO microplate reader (Tecan Ltd., Männedorf, Switzerland). The levels of lens GSH were calculated by subtracting total GSH concentration from two times the concentration of oxidative GSH.
Measurement of AsA
Levels of AsA were determined using DCPIP as described previously (6). Lenses were homogenized in 0.1 M PBS (pH 7.4) and de-proteinized by using metaphosphoric acid. The lens homogenate was centrifuged to remove the proteins. The supernatant was titrated with DCPIP. Absorbance at 540 nm was measured in a microplate reader, Infinite M1000 (Tecan Ltd.).
Chaperone activity measurement
Chaperone activity was measured according to methods described previously, with minor modifications (13). Briefly, water-soluble lens proteins were mixed with aldehyde dehydrogenase (ALDH) in 50 mM sodium phosphate buffer containing 100 mM NaCl (pH 7.0). ALDH aggregation was induced with 1,10-phenanthroline at 42°C. Protein aggregation was monitored by measurement of light scattering at 360 nm using an Infinite M200PRO microplate reader (Tecan Ltd.).
All data are reported as means ± standard error. Statistical analysis of data was performed using one-way analysis of variance with a post-hoc Tukey's multiple comparison test. SPSS version 24 software (IBM Corp., Armonk, NY, USA) was used for analysis. P<0.05 was considered to indicate a statistically significant difference.
Thirteen-day-old SD rats were randomized into two groups and injected with either PBS (control groups: G1-G6) or Se (cataract groups: G7-G12), and each group was divided into five subgroups to further examine the effects of Hes, Hes-S, and Hes-O (Table I). Hes-S and Hes-O were synthesized as previously reported (10), and administered 4 h prior to injecting the rats with either PBS or Se, and then once daily for two days (total of three days). Six days after the PBS or Se injection, cataract classifications were determined as previously described (11). Fig. 2A-F show nuclear cataracts in rats from groups 7 to 12, respectively (Fig. 2A-F). More than 80% of lenses from G7 (Se-treatment only) had mature grade 6 nuclear cataracts, with grade 5 cataracts present in the lenses of the remaining rats in that group (Fig. 2G). All lenses from control groups were transparent, and all had grade 1 cataracts (data not shown). The lenses of rats in G8, G11, and G12 (Se-Hes, Se-Hes-S, or Se-Hes-O co-treatment, respectively) lacked central opacity and/or had lower-grade cataracts compared to those of rats in groups G7, G9, or G10 (Se treatment only, Se-stearic acid, or Se-oleic acid co-treatment, respectively). In G8, 8, 8, 33, 33, and 17% of rat lenses had cataract grades 5, 4, 3, 2, and 1, respectively. In contrast, 8, 8, 42, 25, and 17% of rat lenses from G11 had cataract grades 5, 4, 3, 2, and 1, and 17, 58, 17%, and 8 lenses in G12 had cataract grades 4, 3, 2, and 1, respectively (Fig. 2G). These data suggest that treatment of the lens with hesperetin or hesperetin-derived compounds can delay Se-induced onset of cataracts.
Anti-cataract effects of hesperetin and hesperetin derivatives. (A-F) Lenses from rats with selenite-induced cataracts: Lenses from a rat from (A) the Se-treated group (group 7: Cataract grade 6), (B) Se-Hes treatment group (group 8: Cataract grade 2), (C) Se-oleic acid treatment group (group 9: Cataract grade 5), (D) Se-stearic acid treatment group (group 10: Cataract grade 6), (E) Se-Hes-S treatment group (group 11: Cataract grade 2) or (F) Se-Hes-O treatment group (group 12: Cataract grade 2). (G) Cataract grade was determined for lenses from rats in the groups of rats that were treated with either hesperetin or hesperetin derivatives (n=6 or 8 per group). G1, control group; G7-12, groups 7–12; Se, selenite; Hes, hesperetin; Hes-S, hesperetin stearic acid ester; Hes-O, hesperetin oleic acid ester.
GSH and AsA levels in the lens and plasma of Se-treated rats
The GSH and AsA levels in the lens and plasma were determined to evaluate the effects of hesperetin derivatives on the levels of antioxidant compounds in the lens. In the control groups (G1-G6), GSH levels in the lens showed no change either with or without treatment with hesperetin-derived compounds. In the G7 lenses, GSH levels were significantly decreased compared to the levels observed in control G1 lenses (1.40 µmol/wet weight vs. 0.41 µmol/wet weight) (Fig. 3A). Hesperetin treatment of rats with Se-induced cataracts rats prevented a reduction in GSH levels. The concentration of GSH in the lenses of rats in G8 lens was 0.98 µmol/wet weight. Interestingly, the lens GSH levels in G11 or G12 rats were higher than those in G8. GSH concentrations in the lenses of rats in G11 were 1.04 µmol/wet weight and in G12 were 1.2 µmol/wet weight (Fig. 3A). Next, we measured the AsA concentrations in the lenses of rats with selenite-induced cataracts. In the control groups, AsA levels did not change regardless of treatment (G1-6). In the lenses of rats with Se-induced cataracts (G7), AsA levels were significantly lower than those in the lenses of rats in the control group. The concentrations were 13.70 µg/lens wet weight in G7, and 32.53 µg/wet weight in G1 (Fig. 3B). Co-treatment of lenses with Hes and Se (G8) prevented the reduction in AsA levels (24.12 µg/wet weight). AsA concentrations were higher in G11 and G12, those observed in in G7 rat lenses. AsA levels in G11 were 27.20 µg/wet weight and 27.55 µg/wet weight in G12.
Subsequently, we quantified the levels of plasma antioxidant compounds in the lenses. We did not observe any changes in the levels of GSH or AsA concentrations in the plasma following treatment with Hes-S or Hes-O, regardless of whether the lenses had cataracts or not (were transparent) (Fig. 4A and B). These results suggest that Hes-S and Hes-O prevent the reduction of antioxidants exclusively in the cataract lens, with no effect on systemic antioxidant levels.
Lens chaperone activity in cataract rats
The lens possesses chaperoning ability that helps to prevent protein aggregation and cataract formation. Cataract lenses are known to have weaker chaperone activity than normal, transparent lenses. Therefore, we measured the effect of both hesperetin and hesperetin-derived compounds on chaperone activity in cataract lenses. Chaperone activity was evaluated by the measurement of the time course of aldehyde dehydrogenase (ALDH) light scattering using 1,10-phenanthroline at 360 nm (Fig. 5A). The sample in ALDH alone did not show any light scattering (Fig. 5A, curve 9) and a mixture of ALDH and 1,10-phenanthroline in the absence of lens proteins demonstrated the largest amount of light scattering (Fig. 5A, curve 1). Lens proteins from mature cataracts in G7 were not able to suppress light scattering (Fig. 5A, curve 7). However, the lens proteins from Se-induced cataracts in rats treated with either Hes, Hes-S, or Hes-O showed reduced ALDH light scattering (Fig. 5A, curve 5, 11, or 12, respectively). A mixture of ALDH, 1,10-phenanthroline, and lens proteins from transparent, normal lenses from G1 rats showed the lowest amount of ALDH light scattering (Fig. 5A, curve 8).
Effect of hesperetin and hesperetin derivatives on lens chaperone activity. (A) The time course of light scattering of ALDH at 360 nm. Curve 1 represents the light scattering of the ALDH and 1,10-phenanthroline mixture without lens proteins. Curves 2–8 represent the light scattering of a mixture of ALDH and lens proteins from each group (from G7, G10, G9, G8, G11, G12 and G1, respectively). Curve 10 is that of ALDH alone. (B) Relative chaperone activity of cataract lens proteins with antioxidants was calculated using ALDH light scattering at 180 min following the addition of 1,10-phenanthroline. The change of light scattering of ALDH in the absence of water-soluble lens proteins was defined as 100%. Bars represent the mean ± standard error (n=6 or 8 per group). *P<0.05, as indicated. G, group; ALDH, aldehyde dehydrogenase.
Light scattering in the absence of lens proteins was defined as 100% scattering. Suppression of ALDH light scattering was represented as relative ΔA360, as indicated in the bar graph in Fig. 5B. The lens proteins from G1 suppressed ALDH light scattering, and those from G7 did not affect ALDH light scattering (Fig. 5B). The lens proteins from G8 protected against an increase in ALDH light scatter. However, light scattering suppression ability in G11 or G12 lens proteins was significantly stronger than that of G8 lens proteins. Light scattering reflected ALDH protein aggregation and the suppression of this aggregation was assumed to be dependent upon chaperone activity.
As age-related cataract progression in humans is very slow and therapeutics must be applied for a long period of time to effectively ameliorate or prevent the development of cataracts, it is vital to study the long-term safety of pharmacological therapies for cataracts. Furthermore, identifying and developing effective anti-cataract agents in the human diet that can be consumed daily would provide significant health economic benefits.
In this study, we used an Se-induced cataract model that is well-characterized for screening potential anti-cataract agents. The selenite-induced cataract animal model can be efficiently induced by the administration of sodium selenite to rat pups younger than 16 days old. Cataracts appear within 3–5 days following sodium selenite administration. We previously reported that a 3 day course of administration of antioxidant compounds can ameliorate selenite-induced cataracts (11,13). Manikandan et al (14) previously reported that curcumin injected 24 h before the administration of selenite could prevent the onset of cataract. Furthermore, Aydemir et al (15) reported that the administration of ebselen for 4 days inhibited oxidative stress in the lens and prevented selenite-induced cataract development in rats.
Hesperetin, a natural flavonoid isolated from orange rinds, has a flavanone backbone structure and is known to have strong antioxidant activity (16). As humans are unable to synthesize hesperetin, it is usually acquired from oranges and other orange-colored fruits. Hesperetin exhibits antioxidant activity by regulating the expression of antioxidant enzymes such as catalase, GSH peroxides, and GSH reductase (17,18). Consumption of antioxidant compounds and maintaining a constant redox state in the lens are currently the recommended methods for preserving lens transparency, as cataracts are mainly caused by oxidative stress. We synthesized two hesperetin derivatives, Hes-S and Hes-O, that have a fatty acid linked to the 7-hydroxy position of hesperetin, to evaluate the effect of hesperetin derivatives on cataract onset by measuring cataract development, antioxidant levels, and lens chaperone activity.
In this report, we show that fatty acid-linked hesperetins have greater anti-cataract effects compared to that of the original chemical compound, hesperetin, especially for lens chaperone activity. We hypothesize that hesperetin fatty acid ester compounds may improve hesperetin pharmacokinetics due to the following effects: i) Improvement of uptake from subcutaneous areas into the bloodstream and systemically; ii) greater permeability across the blood-aqueous barrier; iii) hydrolysis of Hes-S or Hes-O into hesperetin by esterase(s) localized in the lens; and iv) trapping of hesperetin within the lens due to poor water solubility. Firstly, cellular uptake of Hes-S or Hes-O is thought to be enhanced by improving the lipophilicity of hesperetin which was achieved by linking it to either stearic acid or oleic acid. It is well known that drugs are generally absorbed by passive diffusion into the systemic circulation and that improving the lipophilicity of the drug can increase absorption rate. Furthermore, the absorption of lipophilic compounds is thought to be mediated primarily by membrane diffusion, whereas hydrophilic compounds appear to be absorbed via passive diffusion through intercellular junction pores (19,20).
In this current study, we were unable to detect any differences in cataract classification or levels of antioxidant compounds in the between the hesperetin treatment and hesperetin derivative treatment groups. Indeed, neither hesperetin nor its derived compounds could be detected in the serum or lens by HPLC 4 h after injection (data not shown). However, we did observe significant differences in the retention of chaperone activity, we hypothesized that tiny amounts of hesperetin or its derivatives could reach the lens. It will be necessary to use a detector and/or HPLC system with a greater sensitivity to detect the presence of these compounds, and further studies will be needed to decipher how hesperetin and its derivatives reach the lens and/or interact with α-crystallin at a molecular level to maintain lens chaperone activity.
The results of the current study indicate that hesperetin and hesperetin-derived compounds may delay or prevent cataract onset by preserving chaperone activity in lens proteins, and fatty acid-linked hesperetins had greater chaperone activity than that of the original compound (hesperetin). We previously reported that hesperetin treatment could prevent chaperone activity decreasing in the lens by preventing oxidative modification of α-crystallin and retaining water solubility (9). Generally, α-crystallin purified from the lens is used to measure chaperone activity. However, the water solubility of this protein and its concentration in the water-soluble fraction was changed after cataract onset. Therefore, we used measurements of total water-soluble protein to determine the lens chaperone activity.
Hes-O-treated rats displayed lower cataract grades, higher lens GSH levels, and stronger chaperone activity than Hes-S-treated rats. Although the carbon number of stearic acid is the same as that of oleic acid, but oleic acid has a cis-double bond in its structure. This double bond structure may affect the membrane permeability and pharmacokinetics of the hesperetin esters. Interestingly, cataract stages and markers of cataract development were improved in the animals treated with fatty acid (groups G9 and G10). We hypothesize that this improvement may be due to enhanced lens membrane stability. Further in-depth investigation is required to assess the pharmacokinetics of these compounds. In addition, further studies are needed to determine how Hes-S and Hes-O interact with lens proteins and prevent cataract onset at the molecular level, and how they affect the molecular disposition of antioxidants in vivo.
In addition to the anti-cataract effect, hesperetin has several general health benefits, such as anti-inflammatory properties, antihypertensive effects, and the improvement of very low-density lipoprotein (VLDL) metabolic abnormalities (21–23). We speculate that these health benefits may be more pronounced in Hes-S or His-O compared to that in the original compound (hesperetin).
As age-related cataract progression in humans is very slow and treatments must be applied for long periods of time to delay or prevent the development of cataracts, it is vital to study the long-term safety of pharmacological therapies. As anti-cataract pharmaceutical therapies require long-term treatment, identifying affordable anti-cataract compounds that can be found ubiquitously in the human diet and that have no adverse effects is of paramount importance.
MP would like to thank the Graduate School of SIGMA Clermont, France, for the opportunity to be a visiting research student (2017) under an agreement between SIGMA Clermont and Keio University.
The present study was supported by grants from the Japan Society for the Promotion of Science KAKENHI (grant no. 16K18957), and from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT)-supported program for Strategic Research Foundation at Private Universities (grant no. S1101003).
Availability of data and materials
The analyzed datasets generated during the study are available from the corresponding author on reasonable request.
YN and HT conceived and designed the present study. YN, MFT, TS and HT designed the methods. YN, MP, KF and NN performed the laboratory experiments. YN, NN and HT analyzed and interpreted the data. YN was major contributor in the writing of the manuscript.
Ethics approval and consent to participate
Keio University Animal Research Committee (Tokyo, Japan) approved all of the animal procedures that were performed in the present study [11014-(4)].
Consent for publication
The authors declare that they have no competing interests.
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Normal mouse and rat strains as models for age-related cataract and the effect of caloric restriction on its development
The purpose of this study was to determine: (1) which of the commonly used strains of laboratory rats and mice provide good models for human age-related cataract, and (2) whether long term caloric restriction, a regimen that prolongs both median and maximum life span in rodents, would also delay the time of appearance of this age-related pathology. Three strains of mice and two rat strains commonly used in laboratory work and maintained on either ad libitum (AL) or calorically restricted (CR) diets in the National Institutes of Aging and Diet Restriction colony were examined by slit lamp for age-related cataracts at four or more time points during their life spans. These strains were Brown Norway and Fischer 344 rats, and C57BL/6, (C57BL6 x DBA/2)F1 and (C57BL/6 x C3H)F1 mice. None of these strains develop congenital cataracts. Various stages of cataract were found in the great majority of these animals in old age. In both rat strains and one mouse strain the cataracts occurred after mid-life, were most advanced late in life, and were similar in locations and appearance to those in humans. In the two mouse strains in which some cataracts appeared as early as 10-14 months of age, previously identified genetic defects affecting the eye were probably involved in the early appearances. CR extended life spain in all five rat and mouse strains and also delayed both the time of first appearances and the subsequent increase in cataract severity over time in the four dark-eyed strains. CR did not delay cataract formation in the single albino rat strain studied. In summation: (1) commonly used strains of laboratory rats and mice that are free of congenital or early appearing cataracts due to genetic defects would appear to serve as appropriate models for human age-related cataract, (2) caloric restriction (CR) provides a protective effect, delaying development of cataracts in the dark-eyed mouse and rat strains, while also extending their life spans, (3) CR did not delay the development of lens damage in the nonpigmented eye of the single albino strain studied, although it extended life span.
A degenerative opacity of the lens that leads to loss of vision.
May observe the following:
- Initially the start of a cataract will be seen as a white dot behind pupil.
- The progression of a gray or milky white discoloration of the lens.
Cataracts, a white/gray cloudy discoloration of the otherwise normally clear lens of the eye, can occur due to trauma, inflammation, systemic disease, congenital or genetic disorders (e.g., inherited retinal dystrophy in the rat, a recessive genetic inherited disorder1), and aging. They can begin as a small partial clouding of the lens and progress so that it covers the entire lens leading to blindness. Cataracts are typically bilateral, but may progress more in one eye than the other depending upon the cause.
A transient form of cataracts has been known to happen frequently in rodents when they are placed under anesthesia. It is believed to be due to the changing composition and temperature of
the aqueous humor of the eye while open and unblinking. This does resolve once the animal recovers.2 It is recommended that veterinary surgeons protect the rat’s eyes from drying out, while under anesthesia, by using an ophthalmic ointment. Also when surgical scrub solutions are used it is important to protect the rat’s eyes from being contaminated.3
Cataracts occurring with age may be due to changes as seen in protein destruction and clumping, accumulation of water and edema, and the disruption of normal fibers in the lens.
Additional causes and factors that can contribute to the early formation of cataracts are long term use of corticosteroids or phenothiazines, hypertension, diseases such as diabetes, and microphthalmia.
Case Histories of Cataract Formation
- Fig. 1: Cataracts in male rat (Boomer)
- Fig. 2: Cataracts in hairless rat
- Fig. 3: Cataract in 20-month-old Siamese rat
- Fig. 4: Cataracts in aging male rat (Jerry)
- Cataracts Visit Lisa Jenny’s page for photo of rat showing initial cataracts
Visualized by ophthalmoscopy
Rats, having poor vision to start with, adapt well. Treatment should be directed at correcting underlying conditions if possible.
- Provide for safe environment. Reduce chances of falls from heights by keeping cage levels to a minimum.
- Allow the rat to become familiar with cage surroundings. Prevent redesigning or moving interior cage accessories around.
- Keep water bottles and food dishes in same familiar area of cage.
- Underlying conditions corrected
- No advancement of condition noted
- Early treatment of conditions or illnesses associated with the formation of cataracts may prevent or delay their onset.
- LaVail, M., Sidman, R., & Gerhardt, C. (1975). Congenic strains of RCS rats with inherited retinal dystrophy. J Hered., 66(4), 242-4. Retrieved February 7, 2012, from http://www.oxfordjournals.org/our_journals/jhered/freepdf/66-242.pdf
- Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery. (1997). Philadelphia: W.B. Saunders Company.
- Guidelines for the Use of Anesthetics, Analgesics and Tranquilizers in Laboratory Animals. (n.d.). Research Animal Resources. Retrieved February 7, 2012, from www.ahc.umn.edu/rar/anesthesia.html
In rats cataracts
.CatARact Simulating Cataracts in Augmented Reality
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