Oxidative stress and antioxidants in cataract development

Crosstalk between signaling pathways (Rho/ROCK, TGF-β and Wnt/β-Catenin Pathways/ PI3K-AKT-mTOR) in Cataract: A Mechanistic Exploration and therapeutic strategy

Cataract are a leading cause of visual impairment that is characterized by clouding or lens opacification of the healthy clear lens of the eye or its capsule. It can be classified based on their etiology and clinical presentation such as congenital, age-related, and secondary cataracts. Clinically, it may be further classified as a cortical or nuclear cataract. Cortical cataracts are responsible for opacification of the lens cortex, while nuclear cataracts cause age-related degeneration of the lens nucleus. This review aims to explore the molecular mechanism associated with various signaling pathways underlying cataract formation. Additionally, explore the potential therapeutic strategies for the management of cataracts. A comprehensive literature search was performed utilizing different keywords such as cataract, pathogenesis, signaling pathways, therapeutic approaches, RNA therapeutics, and surgery. Electronic databases such as PubMed, Google Scholar, Springer Link, and Web of Science were used for the literature search. The cataract formation is responsible for protein aggregation, primarily of γ-crystallin, and causes disruptions in signaling pathways. Key pathways include Rho/ROCK, TGF-β, Wnt/β-catenin, NF-κB, and PI3K-AKT-mTOR. Signaling pathways governing lens epithelial cell differentiation and epithelial-to-mesenchymal transition (EMT) are essential for maintaining lens transparency. Disruptions in these pathways, often caused by genetic mutations in genes like MIP, TDRD7, PAX6, FOXE3, HSF4, MAF, and PITX3 lead to cataract formation. While surgical intervention remains the primary treatment, pharmacological therapies and emerging RNA-based strategies offer promising strategies for the prevention and management of cataracts. A deeper understanding of the underlying molecular mechanisms is essential to develop innovative therapeutic strategies and improve the quality of life for individuals affected by cataracts.

Oxysterols, age-related-diseases and nutritherapy: Focus on 7-ketocholesterol and 7β-hydroxycholesterol

Age-related diseases are often associated with a disruption of RedOx balance that can lead to lipid peroxidation with the formation of oxysterols, especially those oxidized on carbon-7: 7-ketocholesterol (also known as 7-oxo-cholesterol) and 7β-hydroxycholesterol. Like cholesterol, these oxysterols have 27 carbons, they are composed of a sterane nucleus and have a hydroxyl function in position 3. The oxysterols 7-ketocholesterol and 7β-hydroxycholesterol are mainly formed by cholesterol autoxidation and are biomarkers of oxidative stress. These two oxysterols are frequently found at increased levels in the biological fluids (plasma, cerebrospinal fluid), tissues and/or organs (arterial wall, retina, brain) of patients with age-related diseases, especially cardiovascular diseases, neurodegenerative diseases (mainly Alzheimer's disease), ocular diseases (cataract, age-related macular degeneration), and sarcopenia. Depending on the cell type considered, 7-ketocholesterol and 7β-hydroxycholesterol induce either caspase- dependent or -independent types of cell death associated with mitochondrial and peroxisomal dysfunctions, autophagy and oxidative stress. The caspase dependent type of cell death associated with oxidative stress and autophagy is defined as oxiapoptophagy. These two oxysterols are also inducers of inflammation. These biological features associated with the toxicity of 7-ketocholesterol, and 7β-hydroxycholesterol are often observed in patients with age-related diseases, suggesting an involvement of these oxysterols in the pathophysiology of these disorders. The cytotoxic effects of 7-ketocholesterol and 7β-hydroxycholesterol are counteracted on different cell models by representative nutrients of the Mediterranean diet: ω3 and ω9 fatty acids, polyphenols, and tocopherols. There are also evidences, mainly in cardiovascular diseases, of the benefits of α-tocopherol and phenolic compounds. These in vitro and in vivo observations on 7-ketocholesterol and 7β-hydroxycholesterol, which are frequently increased in age-related diseases, reinforce the interest of nutritherapeutic treatments to prevent and/or cure age-related diseases currently without effective therapies.

METTL14-mediated depression of NEIL1 aggravates oxidative damage and mitochondrial dysfunction of lens epithelial cells through regulating KEAP1/NRF2 pathways

Abnormal base excision repair (BER) pathway and N6-methyladenosine (m6A) of RNA have been proved to be significantly related to age-related cataract (ARC) pathogenesis. However, the relationship between the Nei Endonuclease VIII-Like1 (NEIL1) gene (a representative DNA glycosylase of BER pathway) and its m6A modification remains unclear. Here, we showed that the expression of NEIL1 was decreased in the ARC anterior lens capsules and H2O2-stimulated SRA01/04 cells. Our findings demonstrated that ectopic expression of NEIL1 alleviated DNA oxidative damage, apoptosis and mitochondrial dysfunction through disturbing KEAP1/NRF2 interaction. Furthermore, silencing NEIL1 aggravated H2O2-induced lens opacity, whereas ML334 could mitigate lens cloudy ex vitro in rat lenses. Besides, intravitreal injection of AAV2-NEIL1 alleviated lens opacity in Emory mice in vivo. Mechanistically, the N(6)-Methyladenosine (m6A) methyltransferase-like 14 (METTL14) was identified as a factor in promoting m6A modification of NEIL1, which resulted in the recruitment of YTHDF2 to recognize and impair NEIL1 RNA stability. Collectively, these findings highlight the critical role of the m6A modification in NEIL1 on regulating oxidative stress and mitochondrial homeostasis through KEAP1/NRF2 pathways, providing a new way to explore the pathogenesis of ARC.

The role of potential oxidative biomarkers in the prognosis of intracerebral hemorrhage and the exploration antioxidants as possible preventive and treatment options

Intracerebral hemorrhage (ICH) is a non traumatic hemorrhage that occurs in a certain part of the brain. It usually leads to brain cell damage. According to a large number of experimental research, oxidative stress is an important pathophysiological processes of cerebral hemorrhage. In this paper, we aim to determine how changes in oxidative stress biomarkers indicate the damage degree of cerebral hemorrhage, and to explore and summarize potential treatments or interventions. We found that patients with cerebral hemorrhage are characterized by increased levels of oxidative stress markers, such as total malondialdehyde (MDA), F2 isoprostaglandin, hydroxynonenal, myeloperoxidase and protein hydroxyl. Therefore, the changes of oxidative stress caused by ICH on these markers can be used to evaluate and diagnose ICH, predict its prognosis, and guide preventive treatment to turn to antioxidant based treatment as a new treatment alternative.

A biomarker framework for auditory system aging: the Aging Biomarker Consortium consensus statement

Hearing is one of the most vital sensory functions in human beings and a crucial means of perceiving and acquiring information from the natural environment. The advancement of human society is closely linked to the development of language, with hearing serving as the foundation for verbal communication. As individuals age, the deterioration of the auditory system becomes a significant factor contributing to sensory impairments in the elderly. In addition to hearing loss, the aging of the auditory system is also associated with cognitive decline and psychosocial disorders, which severely impact the quality of life for older adults. Currently, there are no effective treatments or interventions available for addressing the aging of the auditory system. Therefore, identifying biomarkers of the auditory system aging is of great significance. The Aging Biomarker Consortium of China has conducted a comprehensive evaluation of aging biomarkers in the auditory system, focusing on three dimensions: morphological, functional, and humoral biomarkers. This initiative aims to establish a foundation for assessing the degree of aging in the auditory system and to promote the management of auditory health in an aging society, ultimately enhancing the auditory health of the elderly population both in China and globally.

2-Ethylhexyl diphenyl phosphate induces lung oxidative stress and pyroptosis in chicks

2-Ethylhexyl diphenyl phosphate (EHDPHP) is a widely used organophosphorus flame retardant and plasticizer easily released into the environment. Its biological toxicity is of great concern. The lung is considered a possible target organ for EHDPHP, but currently, there are limited studies on the biotoxicity of EHDPHP in poultry lungs. Therefore, the lungs were selected as the target organ to study the toxic effects of EHDPHP on chicks and their mechanisms of action. In this study, 7-day-old chicks were gavaged with different concentrations of EHDPHP, and lung samples were collected at 14, 28, and 42 days after intragastric administration. Lung histopathological and ultrapathological changes were examined by paraffin section-HE staining and transmission electron microscopy. The levels of lung damage markers (LDH) and oxidative stress markers (GSH-Px, SOD, and MDA) were detected by applying the kit. In contrast, lung cell pyroptosis-related factors (NLRP3, ASC, NF-κB, Pro-Caspase-1, IL-18, and IL-1β) and inflammatory factors (IL-6 and TNF-α) were assessed by using the qRT-PCR, Western blot and ELISA techniques. The results showed that EHDPHP induced pathological morphological changes and elevated LDH content in chick lungs, decreased lung antioxidant enzymes (GSH-Px and SOD) activities, increased peroxidation product MDA content and up-regulated the expression levels of cellular pyroptosis factors (NLRP3, ASC, NF-κB, Pro-Caspase-1, IL-18, and IL-1β), and the synthesis and secretion of inflammatory factors (IL-6 and TNF-α) were promoted. The above changes were EHDPHP dose-dependent. The results indicated that EHDPHP induced oxidative stress in chick lungs, resulting in oxidative damage to the lungs, and, intriguingly, the cellular pyroptosis pathway was activated, which was also involved in the process of EHDPHP-induced inflammatory damage in chick lungs. The results of this study revealed for the first time the damaging effects and mechanisms of EHDPHP on chick lungs. Also, they provided a scientific basis for further exploring the mechanisms of toxicity damage, safe use, and pollution control of EHDPHP.

Klotho relieves H2O2-induced lens epithelial cell damage via suppression of NOX4

BACKGROUND

Age-related cataract (ARC) is a common eye disease and represents a common contributing factor to visual damage and loss. Klotho is a longevity gene and has been reported to participate in aging-related disorders. This work aims to investigate the potential role of klotho in ARC.

METHODS

In human lens epithelial cells (HLECs) induced by varying concentrations of hydrogen peroxide (H2O2), CCK-8 assay was used to detect cell viability. DCFH-DA probe was used to detect reactive oxygen species (ROS) level. Western blot was used to detect klotho expression. JC-1 fluorochrome assay was used to detect mitochondrial membrane potential (MMP). The concentrations of oxidative stress markers malondialdehyde (MDA) and superoxide dismutase (SOD) were detected by related assay kits. Flow cytometry analysis, immunofluorescence staining and western blot were used to detect cell apoptosis. SA-β-gal staining and western blot were used to detect cell senescence.

RESULTS

Klotho expression was decreased in HLECs induced by increasing concentrations of H2O2. Overexpression of klotho significantly inhibited ROS generation, decreased MDA content, increased SOD content, promoted cell viability and suppressed cell apoptosis and senescence in H2O2-induced HLECs. Furthermore, klotho down-regulated NOX4 expression and NOX4 elevation partially reversed the effects of klotho on H2O2-induced HLECs.

CONCLUSIONS

To sum up, klotho may down-regulate NOX4 to protect against H2O2-induced HLECs damage. This finding suggested the potential therapeutic use of klotho in ARC, which needs further investigation.

Protective effect of apelin-13 in lens epithelial cells via inhibiting oxidative stress-induced apoptosis

BACKGROUND

It is widely accepted that glaucoma-induced oxidative stress expedites cataracts' process. Therefore, we examined the effects of apelin-13 against oxidative stress-induced damage in human lens epithelial cells (HLECs) and investigated the potential pathogenic mechanism of acute primary angle-closure glaucoma.

METHODS

This experiment included five groups: control, H2O2, apelin-13 + H2O2, ML221 + H2O2, and apelin-13 + ML221 + H2O2. ML221 was employed in rescue experiments as an APJ antagonist. HLECs were pretreated with or without apelin-13 and subsequently exposed to H2O2. HLECs' viability was assessed by CCK8. Cell apoptosis was determined using Annexin V-FITC/PI staining. The mitochondrial membrane potential was assessed by fluorescent probe JC-1. Intracellular G6PD activity, NADPH/NADP+, and GSH/GSSG ratios were detected to assess the cells' oxidative damage.

RESULT

Apelin-13 reversed the H2O2-induced decrease in cell viability. The increased expression of G6PD and GLTU1, the G6PD, GSH/GSSG and NADPH/NADP + levels showed that apelin-13 can mitigate the H2O2-induced inhibition of the pentose phosphate pathway and dysregulation of cell redox status in the apelin-13 + H2O2 group compared with the H2O2 group. In H2O2-treated HLECs, apelin-13 can mitigate cell apoptosis, promote Bcl-2 expression, and suppress the Bax and Caspase-3 expression. In addition, H2O2 substantially reduced the mitochondrial membrane potential in HLECs, which was reversed by apelin-13. Notably, the inhibition of APJ intensified oxidative damage in H2O2-induced HLECs, demonstrating that the effects of apelin-13 were hindered by ML221.

CONCLUTIONS

Apelin-13 reduced oxidative damage and apoptosis in HLECs through APJ. These results demonstrate that apelin-13 can be employed as a potential drug for glaucoma with cataracts to delay the progression of cataracts.

Oxidative Stress in Genetic Cataract Formation

BACKGROUND

Cataracts are the leading cause of blindness worldwide, and age-related cataracts are the result of environmental insults that largely lead to oxidative stress imposed on a genetic background that determines susceptibility to these stresses.

METHODS

A comprehensive literature review was performed to identify GWAS, targeted association studies, and TWAS that identified genes associated with age-related cataract. Additional genes associated with age-related cataracts were identified through the CAT-MAP online database. Pathway analysis was performed using Qiagen Ingenuity Pathway Analysis and pathways related to oxidative stress were analyzed using the same program.

RESULTS

A large number of genes have been identified as causes of both Mendelian and complex cataracts. Of these, 10 genes related to oxidative stress were identified, and all were associated with age-related cataracts. These genes fall into seven canonical pathways primarily related to glutathione metabolism and other pathways related to detoxifying reactive oxygen species.

CONCLUSIONS

While a relatively small number of antioxidant related genes were identified as being associated with cataracts, they allow the identification of redox pathways important for lens metabolism and homeostasis. These are largely related to glutathione and its metabolism, other pathways for detoxification of reactive oxygen species, and the transcriptional systems that control their expression.

Oxidative Stress in Cataract Formation: Is There a Treatment Approach on the Horizon?

Cataracts, a leading cause of blindness worldwide, are closely linked to oxidative stress-induced damage to lens epithelial cells (LECs). Key factors contributing to cataract formation include aging, arterial hypertension, and diabetes mellitus. Given the high global prevalence of cataracts, the burden of cataract-related visual impairment is substantial, highlighting the need for pharmacological strategies to supplement surgical interventions. Understanding the molecular pathways involved in oxidative stress during cataract development may offer valuable insights for designing novel therapeutic approaches. This review explores the role of oxidative stress in cataract formation, focusing on critical mechanisms, such as mitochondrial dysfunction, endoplasmic reticulum stress, loss of gap junctions, and various cell death pathways in LECs. Additionally, we discuss emerging therapeutic strategies and potential targeting options, including antioxidant-based treatments.

Mangiferin Ameliorates CCl4-Triggered Acute Liver Injury by Inhibiting Inflammatory Response and Oxidative Stress: Involving the Nrf2-ARE Pathway

Purpose

Acute liver injury (ALI) is characterized by inflammation and oxidative stress (OS). Although mangiferin (MGF) has antioxidant and anti-inflammatory effects, its role in ALI remains unclear. Accordingly, we investigated the MGF molecular mechanism in carbon tetrachloride (CCl4)-induced ALI in vivo and in vitro.

Materials and Methods

The CCl4 was utilized to induce ALI in mice. In vivo, the therapeutic effects of MGF on CCl4-induced liver injury were evaluated through biochemical assays and histomorphological analysis. Additionally, immunohistochemistry, immunofluorescence, ELISA and Western blotting were further applied to explore the mechanism. In vitro, The CCK-8 assay and flow cytometry were employed to investigate the protective effects of MGF against CCl4-induced toxicity in HepG2 cells, while mitochondrial reactive oxygen species levels and Western blotting were used to explore the biological effects and molecular mechanisms.

Results

MGF treatment resulted in a reduction in serum levels of AST and ALT, diminished concentrations of TNF-α, IL-6, and IL-1β in liver tissue, and concurrently decreased cellular apoptosis. Furthermore, MGF pretreatment enhanced the activity of SOD and GSH while concurrently diminishing the MDA production. This study further demonstrated the upregulation of Nrf2, NQO1, and HO-1 protein expression levels, as well as the downregulation of p-p65 protein expression levels. In vitro investigations revealed that the mitigation of CCl4-induced inflammation and OS by MGF was mediated via the Nrf2- antioxidant response element (ARE) pathway, which was disrupted by ML385 in HepG2 cells.

Conclusion

CCl4 can induce liver injury, while treatment with MGF mitigates ALI by inhibiting oxidative stress, inflammation, and apoptosis. The protective mechanism of MGF is mediated by the Nrf2-ARE pathway activation.

Minimizing Oxidative Stress in the Lens: Alternative Measures for Elevating Glutathione in the Lens to Protect against Cataract

Oxidative stress plays a major role in the formation of the cataract that is the result of advancing age, diabetes or which follows vitrectomy surgery. Glutathione (GSH) is the principal antioxidant in the lens, and so supplementation with GSH would seem like an intuitive strategy to counteract oxidative stress there. However, the delivery of glutathione to the lens is fraught with difficulties, including the limited bioavailability of GSH caused by its rapid degradation, anatomical barriers of the anterior eye that result in insufficient delivery of GSH to the lens, and intracellular barriers within the lens that limit delivery of GSH to its different regions. Hence, more attention should be focused on alternative methods by which to enhance GSH levels in the lens. In this review, we focus on the following three strategies, which utilize the natural molecular machinery of the lens to enhance GSH and/or antioxidant potential in its different regions: the NRF2 pathway, which regulates the transcription of genes involved in GSH homeostasis; the use of lipid permeable cysteine-based analogues to increase the availability of cysteine for GSH synthesis; and the upregulation of the lens's internal microcirculation system, which is a circulating current of Na+ ions that drives water transport in the lens and with it the potential delivery of cysteine or GSH. The first two strategies have the potential to restore GSH levels in the epithelium and cortex, while the ability to harness the lens's internal microcirculation system offers the exciting potential to deliver and elevate antioxidant levels in its nucleus. This is an important distinction, as the damage phenotypes for age-related (nuclear) and diabetic (cortical) cataract indicate that antioxidant delivery must be targeted to different regions of the lens in order to alleviate oxidative stress. Given our increasing aging and diabetic populations it has become increasingly important to consider how the natural machinery of the lens can be utilized to restore GSH levels in its different regions and to afford protection from cataract.

Ferroptosis: a new perspective on the pathogenesis of radiation-induced cataracts

Ionizing radiation is a significant risk factor for cataracts, but the pathogenesis of radiation-induced cataracts remains incompletely understood. Ferroptosis, an iron-dependent form of programmed cell death discovered in recent years, has gained increasing attention for its role in various diseases. This article systematically reviews research progress on ionizing radiation, ferroptosis, age-related cataracts, and radiation-induced cataracts. It proposes the "ferroptosis hypothesis" for the pathogenesis of radiation-induced cataracts. Through ionization and oxidative stress effects, ionizing radiation leads to elevated free iron levels and exacerbated lipid peroxidation in lens cells, activating the ferroptosis pathway and resulting in lens opacity. The involvement of ferroptosis in the development of age-related cataracts suggests that it may also be an important pathogenic mechanism of radiation-induced cataracts. Targeting the ferroptosis pathway may be a novel strategy for preventing and treating radiation-induced cataracts. Furthermore, developing new ferroptosis-specific inhibitors with improved targeting and pharmacokinetic properties is also an essential direction for research on preventing and treating radiation-induced cataracts. The study of ferroptosis provides new insights into the mechanism and management of radiation-induced cataracts, potentially transforming radiation-induced cataracts from "inevitable" to "preventable and treatable."

Effect of hydrogen peroxide on lens transparency, intracellular pH, gap junction coupling, hydrostatic pressure and membrane water permeability

Clouding of the eye lens or cataract is an age-related anomaly that affects middle-aged humans. Exploration of the etiology points to a great extent to oxidative stress due to different forms of reactive oxygen species/metabolites such as Hydrogen peroxide (H2O2) that are generated due to intracellular metabolism and environmental factors like radiation. If accumulated and left unchecked, the imbalance between the production and degradation of H2O2 in the lens could lead to cataracts. Our objective was to explore ex vivo the effects of H2O2 on lens physiology. We investigated transparency, intracellular pH (pHi), intercellular gap junction coupling (GJC), hydrostatic pressure (HP) and membrane water permeability after subjecting two-month-old C57 wild-type (WT) mouse lenses for 3 h or 8 h in lens saline containing 50 μM H2O2; the results were compared with control lenses incubated in the saline without H2O2. There was a significant decrease in lens transparency in H2O2-treated lenses. In control lenses, pHi decreases from ∼7.34 in the surface fiber cells to 6.64 in the center. Experimental lenses exposed to H2O2 for 8 h showed a significant decrease in surface pH (from 7.34 to 6.86) and central pH (from 6.64 to 6.56), compared to the controls. There was a significant increase in GJC resistance in the differentiating (12-fold) and mature (1.4-fold) fiber cells compared to the control. Experimental lenses also showed a significant increase in HP which was ∼2-fold higher at the junction between the differentiating and mature fiber cells and ∼1.5-fold higher at the center compared to these locations in control lenses; HP at the surface was 0 mm Hg in either type lens. Fiber cell membrane water permeability significantly increased in H2O2-exposed lenses compared to controls. Our data demonstrate that elevated levels of lens intracellular H2O2 caused a decrease in intracellular pH and led to acidosis which most likely uncoupled GJs, and increased AQP0-dependent membrane water permeability causing a consequent rise in HP. We infer that an abnormal increase in intracellular H2O2 could induce acidosis, cause oxidative stress, alter lens microcirculation, and lead to the development of accelerated lens opacity and age-related cataracts.

Famine exposure in early life increases risk of cataracts in elderly stage

BACKGROUND

Epidemiological studies have shown that early-life nutritional deficiencies are associated with an increased risk of diseases later in life. This study aimed to explore the correlation between famine exposure during the early stages of life and cataracts.

METHODS

We included 5,931 participants from the Chinese Longitudinal Healthy Longevity Survey (CLHLS) 2018 cross-sectional data in our study. Subjects were categorized into three groups by their age during the famine: adulthood group, school age famine exposure group, and teenage famine exposure group. Utilizing binary logistic regression models, we investigated the relationship between early-life famine exposure and cataracts.

RESULTS

Compared to the adulthood group, both the school age exposure group (OR = 2.49, 95%CI = 1.89-3.27) and teenage exposure group (OR = 1.45, 95%CI = 1.20-1.76) had a heightened risk of developing cataracts in elderly stage. And the sex differences in the impact of famine during early years on elderly cataract risk were observed, particularly indicating a higher risk among women who experienced childhood famine compared to men with similar exposure.

CONCLUSION

Famine exposure during the early stages of life is associated with a heightened risk of developing cataracts in old age. To prevent cataracts in elderly individuals, particularly in females, measures should be taken to address nutritional deficiencies in these specific periods.

A bibliometric and visualized analysis of the pathogenesis of cataracts from 1999 to 2023

Research on the pathogenesis of cataracts is ongoing and the number of publications on this topic is increasing annually. This study offers an overview of the research status, popular topics, and scholarly tendencies in the field of cataract pathogenesis over recent decades，which helps to guide future research directions, and optimize resource allocation. In the present study, we performed a bibliometric analysis of cataract pathogenesis. Publications from January 1, 1999, to December 20, 2023, were collected from the Web of Science Core Collection (WoSCC), and the extracted data were quantified and analyzed. We analyzed and presented the data using Microsoft Excel, VOSviewer, CiteSpace, and Python. In all, 4006 articles were evaluated based on various characteristics, including publication year, authors, countries, institutions, journals, citations, and keywords. This study utilized VOSviewer to conduct visualized analysis, including co-authorship, co-citation, co-occurrence, and network visualization. The CiteSpace software was used to identify keywords with significant bursts of activity. The number of annual global publications climbed from 76 to 277 between 1999 and 2023, a 264.47% rise. Experimental Eye Research published the most manuscripts (178 publications), whereas Investigative Ophthalmology & Visual Science received the most citations (6675 citations). The most influential and productive country, institution, and author were the United States (1244 publications, 54,456 citations), University of California system (136 publications, 5401 citations), and Yao Ke (49 publications, 838 citations), respectively. The top 100 ranked keywords are divided into four clusters through co-occurrence analysis: (1) secondary cataracts, (2) oxidative stress, (3) gene mutations and protein abnormalities, and (4) alteration of biological processes in lens epithelial cells. Further discussions on the four subtopics outline the research topics and trends. In conclusion, the specific mechanism of cataract formation remains a popular topic for future research and should be explored in greater depth.