Effect of vitamin C depletion on UVR-B induced cataract in SMP30/GNL knockout mice

Oxidative Stress and Cataract Formation: Evaluating the Efficacy of Antioxidant Therapies

This comprehensive review investigates the pivotal role of reactive oxygen species (ROS) in cataract formation and evaluates the potential of antioxidant therapies in mitigating this ocular condition. By elucidating the mechanisms of oxidative stress, the article examines how ROS contribute to the deterioration of lens proteins and lipids, leading to the characteristic aggregation, cross-linking, and light scattering observed in cataracts. The review provides a thorough assessment of various antioxidant strategies aimed at preventing and managing cataracts, such as dietary antioxidants (i.e., vitamins C and E, lutein, and zeaxanthin), as well as pharmacological agents with antioxidative properties. Furthermore, the article explores innovative therapeutic approaches, including gene therapy and nanotechnology-based delivery systems, designed to bolster antioxidant defenses in ocular tissues. Concluding with a critical analysis of current research, the review offers evidence-based recommendations for optimizing antioxidant therapies. The current literature on the use of antioxidant therapies to prevent cataract formation is sparse. There is a lack of evidence-based conclusions; further clinical studies are needed to endorse the use of antioxidant strategies in patients to prevent cataractogenesis. However, personalized treatment plans considering individual patient factors and disease stages can be applied. This article serves as a valuable resource, providing insights into the potential of antioxidants to alleviate the burden of cataracts.

The evidence to date: implications of l-ascorbic acid in the pathophysiology of aging

L-Ascorbic acid, commonly known as vitamin C, has been used not only for disease prevention and in complementary and alternative medicine, but also for anti-aging purposes. However, the scientific evidence is not yet sufficient. Here, we review the physiological functions of vitamin C and its relationship with various pathological conditions, including our previous findings, and discuss the prospects of its application in healthy longevity. In summary, vitamin C levels are associated with lifespan in several animal models. Furthermore, clinical studies have shown that the blood vitamin C levels are lower in middle-aged and older adults than in younger adults. Lower blood vitamin C levels have also been observed in various pathological conditions such as chronic kidney disease and chronic obstructive pulmonary disease in the elderly. These observations suggest the implications of vitamin C in age-related pathological mechanisms owing to its physiological functions.

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.

Ultraviolet B radiation induces oxidative stress and apoptosis in human lens epithelium cells by activating NF-κB signaling to down-regulate sodium vitamin C transporter 2 (SVCT2) expression

Ultraviolet B (UVB) exposure is reported to cause cataract formation by inducing excessive reactive oxygen species (ROS) and apoptosis in human lens epithelial cells (HLECs). Sodium-dependent Vitamin C transports-2 (SVCT2) is a ascorbic acid (AsA) transporter for that can protect cells and tissues from oxidative stress. Here, we focus on the functional characterization and mechanism analysis of SVCT2 in UVB-treated HLECs. The results showed a significant reduction of SVCT2 expression in HLECs treated with UVB. SVCT2 abated apoptosis and Bax expression and increased Bcl-2 expression. Moreover, SVCT2 decreased ROS accumulation and MDA level, but increased the activities of antioxidant enzymes (SOD and GSH-PX). NF-κB inhibitor (PDTC) alleviated ROS production and apoptosis, and promoted SVCT2 expression in UVB-treated HLECs. Additionally, ROS inhibitor (NAC) suppressed oxidative stress, apoptosis, and induced SVCT2 expression in UVB-treated HLECs, while these effects were significantly abated due to the activation of NF-κB signaling. Furthermore, SVCT2 facilitated 14C-AsA absorption in UVB-treated HLECs. Together, our findings demonstrated that UVB exposure-induced ROS generation, which further activated NF-κB signaling to down-regulate SVCT2 expression in HLECs. Then, downregulated SVCT2 promoted ROS accumulation and induced apoptosis by decreasing AsA uptake. Our data reveal a novel NF-κB/SVCT2/AsA regulatory pathway and suggest the therapeutic potential of SVCT2 in UVB-induced cataract.

Functional pleiotropy of calcium binding protein Regucalcin in signaling and diseases

Regucalcin (Mr ∼ 33.38 kDa) is a calcium binding protein, discovered in rat liver. In humans, gene for regucalcin is located on chromosome-11 (p11.3-q11.2) consisting of seven exons and six introns. The protein differs from other calcium binding protein in the way that it lacks EF-hand motif of calcium binding domain. It is also called as Senescence Marker Protein-30 (SMP-30) as previously its weight assumes to be 30 kDa and expression of this protein decreases with aging in androgen independent manner. Among vertebrates, it is a highly conserved protein showing gene homology in Drosophila, Xenopus, fireflies and others too. It is primarily expressed in liver and kidney in addition to brain, lungs, and skeletal muscles. Regucalcin acts as a Ca²⁺ regulatory protein and controls various cellular functions in liver and other organs. It suppresses protein phosphatase, protein kinase, DNA and RNA synthesis. Published evidences suggest regucalcin to be a reliable biomarker in various disorders of liver, kidney, brain and ocular. In over expressed state, it subdues apoptosis in cloned rat hepatoma cells and also induces hyperlipidemia and osteoblastogenesis by regulating various factors. Owing to the multi-functionality of regucalcin this review is presented to elaborate its importance in order to understand its involvement in cellular signaling during various pathologies.

Oxidative Stress in the Anterior Ocular Diseases: Diagnostic and Treatment

The eye is a metabolically active structure, constantly exposed to solar radiations making its structure vulnerable to the high burden of reactive oxygen species (ROS), presenting many molecular interactions. The biomolecular cascade modification is caused especially in diseases of the ocular surface, cornea, conjunctiva, uvea, and lens. In fact, the injury in the anterior segment of the eye takes its origin from the perturbation of the pro-oxidant/antioxidant balance and leads to increased oxidative damage, especially when the first line of antioxidant defence weakens with age. Furthermore, oxidative stress is related to mitochondrial dysfunction, DNA damage, lipid peroxidation, protein modification, apoptosis, and inflammation, which are involved in anterior ocular disease progression such as dry eye, keratoconus, uveitis, and cataract. The different pathologies are interconnected through various mechanisms such as inflammation, oxidative stress making the diagnostics more relevant in early stages. The end point of the molecular pathway is the release of different antioxidant biomarkers offering the potential of predictive diagnostics of the pathology. In this review, we have analysed the oxidative stress and inflammatory processes in the front of the eye to provide a better understanding of the pathomechanism, the importance of biomarkers for the diagnosis of eye diseases, and the recent treatment of anterior ocular diseases.

Nutraceuticals: A Promising Therapeutic Approach in Ophthalmology

Oxidative stress represents one of the main factors driving the pathophysiology of multiple ophthalmic conditions including presbyopia, cataracts, dry eye disease (DED), glaucoma, age-related macular degeneration (AMD) and diabetic retinopathy (DR). Currently, different studies have demonstrated the role of orally administered nutraceuticals in these diseases. For instance, they have demonstrated to improve lens accommodation in presbyopia, reduce protein aggregation in cataracts, ameliorate tear film stability, break up time, and tear production in dry eye, and participate in the avoidance of retinal neuronal damage and a decrease in intraocular pressure in glaucoma, contribute to the delayed progression of AMD, or in the prevention or treatment of neuronal death in diabetic retinopathy. In this review, we summarized the nutraceuticals which have presented a positive impact in ocular disorders, emphasizing the clinical assays. The characteristics of the different types of nutraceuticals are specified along with the nutraceutical concentration used to achieve a therapeutic outcome in ocular diseases.

Ascorbate Is a Primary Antioxidant in Mammals

Ascorbate (vitamin C in primates) functions as a cofactor for a number of enzymatic reactions represented by prolyl hydroxylases and as an antioxidant due to its ability to donate electrons, which is mostly accomplished through non-enzymatic reaction in mammals. Ascorbate directly reacts with radical species and is converted to ascorbyl radical followed by dehydroascorbate. Ambiguities in physiological relevance of ascorbate observed during in vivo situations could be attributed in part to presence of other redox systems and the pro-oxidant properties of ascorbate. Most mammals are able to synthesize ascorbate from glucose, which is also considered to be an obstacle to verify its action. In addition to animals with natural deficiency in the ascorbate synthesis, such as guinea pigs and ODS rats, three strains of mice with genetic removal of the responsive genes (GULO, RGN, or AKR1A) for the ascorbate synthesis have been established and are being used to investigate the physiological roles of ascorbate. Studies using these mice, along with ascorbate transporter (SVCT)-deficient mice, largely support its ability in protection against oxidative insults. While combined actions of ascorbate in regulating epigenetics and antioxidation appear to effectively prevent cancer development, pharmacological doses of ascorbate and dehydroascorbate may exert tumoricidal activity through redox-dependent mechanisms.

The Pathomechanism, Antioxidant Biomarkers, and Treatment of Oxidative Stress-Related Eye Diseases

Oxidative stress is an important pathomechanism found in numerous ocular degenerative diseases. To provide a better understanding of the mechanism and treatment of oxidant/antioxidant imbalance-induced ocular diseases, this article summarizes and provides updates on the relevant research. We review the oxidative damage (e.g., lipid peroxidation, DNA lesions, autophagy, and apoptosis) that occurs in different areas of the eye (e.g., cornea, anterior chamber, lens, retina, and optic nerve). We then introduce the antioxidant mechanisms present in the eye, as well as the ocular diseases that occur as a result of antioxidant imbalances (e.g., keratoconus, cataracts, age-related macular degeneration, and glaucoma), the relevant antioxidant biomarkers, and the potential of predictive diagnostics. Finally, we discuss natural antioxidant therapies for oxidative stress-related ocular diseases.

Vitamin C and the Lens: New Insights into Delaying the Onset of Cataract

Cataracts or clouding of the lens is the leading cause of blindness in the world. Age and diabetes are major risk factors, and with an increasing aging and diabetic population, the burden of cataracts will grow. Cataract surgery is an effective way to restore vision; however, alternatives to cataract surgery are required to reduce the looming cataract epidemic. Since it is well established that oxidative damage plays a major role in the etiology of cataracts, antioxidants have been promoted as therapies to delay and/or prevent cataracts. However, many antioxidant interventions including vitamin C have produced mixed results as anti-cataract therapies. Progress has been made towards our understanding of lens physiology and the mechanisms involved in the delivery and uptake of antioxidants to the lens which may guide future studies aimed at addressing some of the inconsistencies seen in previous animal and human studies. Of interest is the potential for vitamin C based supplements in delaying the onset of cataracts post vitrectomy which occurs in up to 80% of patients within two years. These targeted approaches are required to reduce the burden of cataract on hospitals and improve the quality of life of our aging and diabetic population.

Topical administration of a ROCK inhibitor prevents anterior subcapsular cataract induced by UV-B irradiation

The deposition of extracellular matrix (ECM)-which is mainly composed of type I collagen-in anterior subcapsular cataracts (ASCs) during epithelial-to-mesenchymal transition (EMT) of lens epithelial cells (LECs) decreases visual function. Transforming growth factor (TGF)-β is a key factor in the induction of EMT in LECs. Although Rho kinase (ROCK) plays an important role in EMT induced by TGF-β, it is unknown whether ROCK inhibition affects type I collagen expression in TGF-β-stimulated LECs and ASC formation. This was investigated in the present study both in vitro using human lens epithelium (HLE)-B3 cells and in vivo using mice with ultraviolet radiation (UVR)-B-induced cataracts. We found that TGF-β2 increased type I collagen mRNA expression in HLE-B3 cells; this was inhibited in a dose-dependent manner by treatment with the ROCK inhibitor Y-27632. UVR-B exposure caused ASC formation in mice. A histopathological examination revealed that LECs in the anterior subcapsular area were flattened and multi-layered, and had a spindle shape in cross section. Immunohistochemical analysis revealed the presence of α-smooth muscle actin and type I collagen around these flattened LECs; these opacities were reduced by topical instillation of Y-27632. These findings suggest that suppression of TGF-β signaling in LECs by topical application of a ROCK inhibitor can prevent the formation of ASCs.

Effect of senescence marker protein 30 on the proliferation and apoptosis of human lens epithelial cells SRA01/04

AIM

To study the effect of senescence marker protein 30 (SMP30) on the proliferation and apoptosis of human lens epithelial cell (HLEC) SRA01/04.

METHODS

SMP30 overexpression (OE) and knock down (KD) type cell lines were cultivated by using two groups regucalcin (RGN; SMP30) lentiviral vectors (LV-RGN, LV-RGN-RNAi) and the respective negative control virus infect SRA01/04 cells. Western blot and real-time quantitative polymerase chain reaction (q-PCR) analysis were used to determine RGN overexpression and knock down efficiency. We use cell counting kit-8 (CCK8) assay to measure cell viability and 5-bromodeoxyuridine (BrdU) assay to test cell proliferation. Cell cycle was measured by PI FACS assay and cell apoptosis was tested by Annexin V-APC assay through flow cytometry. We use Western blot to measure the content of caspase-3 in SRA01/04.

RESULTS

We used PCR and Western blot techniques to determine the successful transfection of SMP30 OE and KD SRA01/04 cell lines. By CCK8, Brdu and PI FACS cell cycle assay, it was found that the SMP30 OE group promoted cell proliferation (P<0.05) compared with the control group, and the KD group inhibited cell proliferation (P<0.05). The results of Annexin V-APC signal staining detection indicated that compared with respective control group, the cell apoptosis rate was higher in KD group (P<0.05) but lower in OE group (P<0.01). The expression of caspase-3 was down-regulated in OE group through Western blot assay and up-regulated in KD group compared with respective control group.

CONCLUSION

Proliferation of SRA01/04 was promoted by SMP30 OE and apoptosis was suppressed. Increasing the expression of SMP30 may protect HLEC SRA01/04 against apoptosis in cataract.

Drug delivery to the lens for the management of cataracts

Cataracts are one of the most prevalent diseases of the lens, affecting its transparency and are the leading cause of reversible blindness in the world. The clarity of the lens is essential for its normal physiological function of refracting light onto the retina. Currently there is no pharmaceutical treatment for prevention or cure of cataracts and surgery to replace the affected lens remains the gold standard in the management of cataracts. Pharmacological treatment for prevention of cataracts is hindered by many physiological barriers that must be overcome by a therapeutic agent to reach the avascular lens. Various therapeutic agents and formulation strategies are currently being investigated to prevent cataract formation as access to surgery is limited. This review provides a summary of recent research in the field of drug delivery to the lens for the management of cataracts including models used to study cataract treatments and discusses the future perspectives in the field.

Downregulation of SMP30 in senescent human lens epithelial cells

Senescence marker protein 30 (SMP30) has been reported to serve antiapoptotic and antioxidant roles, as well as roles in Ca²⁺ regulation, and may be involved in the occurrence and development of cataract. The present study aimed to investigate the expression of SMP30 in senescent human lens epithelial cells (HLECs) and explored the relationship between SMP30 and aging. SRA01/04 cells, a HLEC line, were treated with H₂O₂ to mimic aging, and cell morphological changes were observed by microscopy and cell activity was examined by MTT assay, senescence-associated-β-galactosidase (SA-β-Gal) staining and cell cycle analysis. The expression of SMP30 mRNA and protein was measured by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blotting. Following prolonged low-dose H₂O₂ exposure, cells exhibited senescence-related morphological changes, reduced growth activity, increased SA-β-Gal positive staining and cell cycle arrest in the S and G2/M phases. SMP30 mRNA expression levels were significantly downregulated following exposure to 75 and 100 µM H₂O₂, and the protein expression levels in the same groups were decreased by >6-fold compared with the control untreated cells. However, no significant change was observed in SMP30 expression in the 25 and 50 µM H₂O₂ exposure groups. These results suggest that, in the early stage of senescence induced by H₂O₂-mediated chronic oxidative stress, there may be no significant change in SMP30 expression, but when the oxidative stress increases and senescence is aggravated, SMP30 may be significantly downregulated in the senescent HLECs. The present study indicates that SMP30 may be an important factor involved in the aging process of HLECs and the development of cataract.

Involvement of senescence marker protein-30 in glucose metabolism disorder and non-alcoholic fatty liver disease

Senescence marker protein-30 (SMP30) was found to decrease in the liver, kidneys and lungs of mice during aging. SMP30 is a pleiotropic protein that acts to protect cells from apoptosis by enhancing plasma membrane Ca(2+) -pump activity and is bona fide gluconolactonase (EC 3.1.1.17) that participates in the penultimate step of the vitamin C biosynthetic pathway. For the past several years, we have obtained strong evidence showing the close relationship between SMP30, glucose metabolism disorder and non-alchoholic fatty liver disease in experiments with SMP30 knockout mice. Emerging proof links the following abnormalities: (i) the reduction of SMP30 by aging and/or excessive dietary fat or genetic deficiency causes a loss of Ca(2+) pumping activity, which impairs acute insulin release in pancreatic β-cells, initiates inflammatory responses with oxidative stress and endoplasmic reticulum stress in non-alchoholic steatohepatitis, exacerbates renal tubule damage, and introduces tubulointerstitial inflammation and fibrosis in diabetic nephropathy; (ii) vitamin C insufficiency also impairs acute insulin secretion in pancreatic β-cells by a mechanism distinct from that of the SMP30 deficiency; and (iii) the increased oxidative stress by concomitant deficiencies of SMP30, superoxide dismutase 1 and vitamin C similarly causes hepatic steatosis. Here, we review recent advances in our understanding of SMP30 in glucose metabolism disorder and non-alchoholic fatty liver disease.

Bone Degeneration and Its Recovery in SMP30/GNL-Knockout Mice

Senescence marker protein-30 (SMP30) decreases androgen-independently with aging and is a lactone-hydrolyzing enzyme gluconolactonase (GNL) that is involved in vitamin C biosynthesis. In the present study, bone properties of SMP30/GNL knockout (KO) mice with deficiency in vitamin C synthesis were investigated to reveal the effects of SMP30/GNL and exogenous vitamin C supplementation on bone formation. Mineral content (BMC) and mineral density (BMD) of the mandible and femur of SMP30/GNL KO and wild-type mice at 2 and 3 months of age with or without vitamin C supplementation were measured by dual-energy X-ray absorptiometry. Body and bone weight of both age groups decreased and became significantly lower than those of wild-type mice. The bones of SMP30/GNL KO mice were rough and porous, with BMC and BMD significantly below wild-type. Oral supplementation with vitamin C eliminated differences in body weight, bone weight, BMC, and BMD between SMP30/GNL KO and wild-type mice at each age. These results indicate that bone degeneration in SMP30/GNL KO mice was caused by lack of vitamin C, and that this mouse strain is an appropriate model for bone metabolism in humans, which have no ability to synthesize vitamin C.

Solar ultraviolet radiation cataract

Despite being a treatable disease, cataract is still the leading cause for blindness in the world. Solar ultraviolet radiation is epidemiologically linked to cataract development, while animal and in vitro studies prove a causal relationship. However, the pathogenetic pathways for the disease are not fully understood and there is still no perfect model for human age related cataract. This non-comprehensive overview focus on recent developments regarding effects of solar UV radiation wavebands on the lens. A smaller number of fundamental papers are also included to provide a backdrop for the overview. Future studies are expected to further clarify the cellular and subcellular mechanisms for UV radiation-induced cataract and especially the isolated or combined temporal and spatial effects of UVA and UVB in the pathogenesis of human cataract. Regardless of the cause for cataract, there is a need for advances in pharmaceutical or other treatment modalities that do not require surgical replacement of the lens.

Association between serum 25-hydroxyvitamin D levels and age-related cataracts

PURPOSE

To investigate associations between serum 25-hydroxyvitamin D levels and age-related cataracts.

SETTING

Department of Ophthalmology, College of Medicine, Catholic University of Korea, South Korea.

DESIGN

Observational cross-sectional study.

METHODS

Participants aged 40 years or older in the fourth (2008 to 2009) and fifth (2010 to 2012) Korea National Health and Nutrition Examination Survey (KNHANES) had evaluation of their serum 25-hydroxyvitamin D levels and ophthalmic slitlamp examinations to identify cataract. An age-related cataract was defined as the presence of a cortical, nuclear, anterior subcapsular, posterior subcapsular, or mixed cataract or a history of cataract surgery.

RESULTS

The study evaluated eyes of 18 804 patients. The mean levels of serum 25-hydroxyvitamin D were 20.0 ng/mL in men and 17.5 ng/mL in women. In men, but not in women, the odds ratio (OR) for age-related cataracts decreased statistically significantly when the serum 25-hydroxyvitamin D levels were in the highest quintile than when they were in the lowest quintile (OR, 0.76; 95% confidence interval, 0.59-0.99) after adjusting for potentially confounding factors including age, sex, smoking status, diabetes, hypertension, and sunlight exposure. However, trend analysis did not show a significant declining trend in the cataract risk associated with higher serum 25-hydroxyvitamin D quintiles (P = .084). In women, serum 25-hydroxyvitamin D levels were not associated with age-related cataracts.

CONCLUSIONS

The age-related cataract risk decreased in men with higher serum 25-hydroxyvitamin D levels than in those with lower serum 25-hydroxyvitamin D levels after adjusting for potential confounding factors. In light of previous research indicating an antioxidative effect of vitamin D, the connection between vitamin D and age-related cataract warrants further study.

FINANCIAL DISCLOSURE

Neither author has a financial or proprietary interest in any material or method mentioned.

Effects of ELL-associated factor 2 on ultraviolet radiation-induced cataract formation in mice

ELL-associated factor 2 (Eaf2) has an important role in crystalline lens development and maturation; however, its role in ultraviolet radiation (UV)-induced cataract formation has remained elusive. The present study compared UV-induced cell apoptosis, activation of caspase-3 and caspase-9 and changes in protein expression levels of B-cell lymphoma 2 (bcl-2), bcl-2-associated X protein (bax) and phosphorylated extracellular signal-regulated kinase in wild-type and Eaf2-knockout mice. The results showed that Eaf2 knockout can reduce UV-induced apoptosis in crystalline lenses and mitigate the formation of cataracts. Further functional studies indicated that Eaf2 can induce the activation of caspase-3 and caspase-9, increase the protein expression of the pro-apoptotic protein bax and inhibit the expression of the anti-apoptotic protein bcl-2; thereby, Eaf2 promotes cell apoptosis and is implicated in the formation and development of cataracts. The present study laid a theoretical foundation for the development of drugs for cataract treatment.

The consequences for human health of stratospheric ozone depletion in association with other environmental factors

Ozone depletion, climate and human health.

Anti-inflammatory activity of SMP30 modulates NF-κB through protein tyrosine kinase/phosphatase balance

Recent studies on senescence marker protein-30 (SMP30) have shown that it has an important functional role in the aging process, but its precise participation in cellular works has not been fully determined. We hypothesize that SMP30 plays crucial roles in signaling processes by modulating the balance of protein tyrosine kinase (PTK)/protein tyrosine phosphatase (PTP) and in activating proinflammatory NF-κB. An experimental paradigm of gain and loss of SMP30 function was established using SMP30-overexpressed YPEN-1 cells (herein referred to as "SMP30(+) cells") and SMP30 (Y/-) knockout mouse kidneys. The resulting data show that SMP30 expression suppressed oxidative stress-induced PTK/PTP dysregulation and PP1/2A inactivation in SMP30(+) cells, leading to the suppression of NF-κB activation. In the kidneys of SMP30 (Y/-) mice, SMP30 deficiency was found to induce NF-κB activation via the upstream signaling of NIK/IKK and MAPKs and to upregulate downstream NF-κB-responsive gene expression. In this study, we also demonstrate for the first time that SMP30 deficiency induced PTK activity in SMP30 (Y/-) kidneys, thereby significantly increasing the tyrosine phosphorylation of a catalytic subunit of PP2A (PP2Ac-Tyr307). Based on these findings, we propose that SMP30 involves NF-κB regulation through the PTK/PTP balance and that the age-related decrease of SMP30 causes NF-κB activation, which contributes to an exacerbation of the inflammatory process during aging.

KEY MESSAGES

SMP30-deficient mice induced a shorter lifespan and redox changes. Overexpression of SMP30 prevented oxidative stress insults. The depletion of SMP30 increased redox-related PTK/PTP imbalance and PP1/PP2A inactivation. The depletion of SMP30 caused an elevation of NF-κB-responsive inflammatory markers. SMP30 may be a potent inhibitory protein against oxidative stress and chronic inflammation.

Effects of ascorbic acid deficiency on protein and lipid oxidation in livers from SMP30/GNL knockout mice

Ascorbic acid (AA) functions as an electron donor and scavenges reactive oxygen species such as superoxide, singlet oxygen, and hydroxyl radicals in vitro. However, little is known about the effect of an AA deficiency on protein and lipid oxidation levels in the liver. Therefore, we measured the levels of protein carbonyl and thiobarbituric acid reactive substances (TBARS) in livers from senescence marker protein-30 (SMP30)/gluconolactonase (GNL) knockout (KO) mice. These mice are deficient in AA, because they lack the SMP30/GNL gene, which is essential for the biosynthesis of AA in vivo. To track the effect of an AA deficiency, at 30 d of age, mice were divided into the following four groups: AA (-) SMP30/GNL KO, AA (+) SMP30/GNL KO, AA (-) wild type (WT), and AA (+) WT. The AA (+) groups were given water containing 1.5 g/L AA, whereas the AA (-) groups received water without AA for 57 d. All mice were fed an AA-free diet. Subsequently, protein carbonyl levels in livers from AA (-) SMP30/GNL KO mice were significantly higher than those from the other three groups; however, TBARS levels were not significantly different among the four groups. Therefore, AA must act as an anti-oxidant for proteins but might not directly protect lipid oxidation in the liver.

Senescence marker protein-30/superoxide dismutase 1 double knockout mice exhibit increased oxidative stress and hepatic steatosis

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We generated SMP30/SOD1-double knockout (DKO) mice for oxidative stress research.

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SMP30/SOD1-DKO mice showed low levels of ascorbic acid and premature death.

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SMP30/SOD1-DKO mice exhibited high levels of oxidative stress and liver injury.

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SMP30/SOD1-DKO mice manifest hepatic steatosis due to decreased levels of Apolipoprotein B.

Superoxide dismutase 1 (SOD1) is an antioxidant enzyme that converts superoxide anion radicals into hydrogen peroxide and molecular oxygen. The senescence marker protein-30 (SMP30) is a gluconolactonase that functions as an antioxidant protein in mammals due to its involvement in ascorbic acid (AA) biosynthesis. SMP30 also participates in Ca²⁺ efflux by activating the calmodulin-dependent Ca²⁺-pump. To reveal the role of oxidative stress in lipid metabolism defects occurring in non-alcoholic fatty liver disease pathogenesis, we generated SMP30/SOD1-double knockout (SMP30/SOD1-DKO) mice and investigated their survival curves, plasma and hepatic lipid profiles, amounts of hepatic oxidative stress, and hepatic protein levels expressed by genes related to lipid metabolism. While SMP30/SOD1-DKO pups had no growth retardation by 14 days of age, they did have low plasma and hepatic AA levels. Thereafter, 39% and 53% of male and female pups died by 15–24 and 89 days of age, respectively. Compared to wild type, SMP30-KO and SOD1-KO mice, by 14 days SMP30/SOD1-DKO mice exhibited: (1) higher plasma levels of triglyceride and aspartate aminotransferase; (2) severe accumulation of hepatic triglyceride and total cholesterol; (3) higher levels of superoxide anion radicals and thiobarbituric acid reactive substances in livers; and (4) decreased mRNA and protein levels of Apolipoprotein B (ApoB) in livers – ApoB is an essential component of VLDL secretion. These results suggest that high levels of oxidative stress due to concomitant deficiency of SMP30 and/or AA, and SOD1 cause abnormal plasma lipid metabolism, hepatic lipid accumulation and premature death resulting from impaired VLDL secretion.

Senescence-induced increases in intracellular oxidative stress and enhancement of the need for ascorbic acid in human fibroblasts

Many studies have suggested that there is a close correlation among declines in internal ascorbic acid (AsA) levels, various disorders, and senescence. To clarify the relationships between age-associated changes in intracellular AsA levels and the effects of AsA administration on intracellular reactive oxygen species (ROS) levels, we investigated aging-related changes in AsA uptake, ROS levels, and the effects of AsA administration on intracellular ROS levels in young and old (senescent) human fibroblasts. Our results demonstrated that AsA uptake was increased in old cells compared with young cells, although mRNA and protein expression of sodium-dependent vitamin C transporter 2 was barely altered between the young and old cells. We also demonstrated that the intracellular superoxide anion level was higher in young cells, whereas the level of intracellular peroxides was significantly increased in old cells under both normal and oxidative stress conditions. Moreover, AsA administration markedly decreased the augmentation of intracellular peroxides in old cells, whereas there was no effect of AsA treatment in young cells under both normal and oxidative stress conditions. Therefore, our results also indicate that AsA could play an important role in regulating the intracellular ROS levels in senescent cells and that the need for AsA is enhanced by cellular senescence.

Antioxidants and cataract

The major causes for cataract formation are free radicals, and these free radicals are neutralized by the presence of endogenous antioxidants in the eye. Using xenobiotics, it has been confirmed that free radicals mediate the formation of cataract. Two cataract model-selenite model and the diabetic cataract model-have been developed to study the pathophysiology of cataract formation due to free radicals and the role of antioxidants during the process of cataractogenesis. This review focuses on natural compounds with antioxidant properties that could actually be applied as an interventional strategy on a large scale and are also relatively inexpensive. A brief overview of plants with antioxidant properties that in addition possess potential anti-cataract properties has been discussed. In addition to plants, three natural compounds (curcumin, vitamin C and vitamin E), on which a lot of data exist showing anti-cataract and antioxidant activities, have also been discussed. These antioxidants can be supplemented in the diet for a better defence against free radicals. Studies on vitamin C and vitamin E have proved that they are capable of preventing lipid peroxidation, thereby preventing the generation of free radicals, but their efficacy as anti-cataract agent is questionable. Unlike vitamins C and E, curcumin is well established as an anti-cataract agent, but the issue of curcumin bioavailability is yet to be addressed. Nanotechnology proves to be a promising area in increasing the curcumin bioavailability, but still a lot more research needs to be done before the use of curcumin as an effective anti-cataract agent for humans.

Recent applications of engineered animal antioxidant deficiency models in human nutrition and chronic disease

Dietary antioxidants are essential nutrients that inhibit the oxidation of biologically important molecules and suppress the toxicity of reactive oxygen or nitrogen species. When the total antioxidant capacity is insufficient to quench these reactive species, oxidative damage occurs and contributes to the onset and progression of chronic diseases, such as neurodegenerative diseases, cardiovascular diseases, and cancer. However, epidemiological studies that examine the relationship between antioxidants and disease outcome can only identify correlative associations. Additionally, many antioxidants also have prooxidant effects. Thus, clinically relevant animal models of antioxidant function are essential for improving our understanding of the role of antioxidants in the pathogenesis of complex diseases as well as evaluating the therapeutic potential and risks of their supplementation. Recent progress in gene knockout mice and virus-based gene expression has potentiated these areas of study. Here, we review the current genetically modified animal models of dietary antioxidant function and their clinical relevance in chronic diseases. This review focuses on the 3 major antioxidants in the human body: vitamin C, vitamin E, and uric acid. We examine genetic models of vitamin C synthesis (guinea pig, Osteogenic Disorder Shionogi rat, Gulo(-/-) and SMP30(-/-) mouse mutants) and transport (Slc23a1(-/-) and Slc23a2(-/-) mouse mutants), vitamin E transport (Ttpa(-/-) mouse mutant), and uric acid synthesis (Uox(-/-) mouse mutant). The application of these models to current research goals is also discussed.