Is copper imbalance an environmental factor influencing keratoconus development?

Vitamin D Supplementation Impacts Systemic Biomarkers of Collagen Degradation and Copper Metabolism in Patients With Keratoconus

Purpose

To evaluate the impact of vitamin D (Vit D) supplementation on systemic biomarkers of collagen degradation, inflammation, oxidative stress, and copper metabolism in adolescent patients with keratoconus (KC).

Methods

This was a prospective observational pilot study. Twenty patients (age range, 16-19 years) presenting KC and Vit D insufficiency (<30 ng/mL) were included. Vit D supplementation was prescribed by their general practitioner as per the standard of care. Patients were followed up for 12 months. At each visit, best spectacle-corrected visual acuity (BSCVA), maximal keratometry (Kmax), and thinnest corneal thickness (TCT) were evaluated. The primary outcome of the study was the proportion of patients with Kmax progression of less than 1 D throughout the 12-month follow-up time. Blood samples were collected at different time points to evaluate Vit D levels and systemic markers of collagen degradation, inflammation, oxidative stress, and copper metabolism by ELISA or RT-PCR.

Results

Lower Vit D levels in the plasma were correlated with higher levels of systemic biomarkers of collagen degradation. Vit D supplementation increased the cell availability of copper. Moreover, stabilization of KC progression was found in 60% of patients (72% of eyes) after 12 months with Vit D supplementation. BSCVA, Kmax, and TCT rates remained stable during the observation period.

Conclusions

Our findings support that Vit D administration could affect ocular and systemic biomarkers in KC and illuminate a possible mechanism that can be used to develop new treatment alternatives.

Translational Relevance

Although KC therapy currently relies exclusively on surgical procedures, Vit D supplementation may offer a non-invasive and inexpensive alternative with minimal associated side effects.

Assessment of serum catalase, reduced glutathione, and superoxide dismutase activities and malondialdehyde levels in keratoconus patients

BACKGROUND

The aim of this study was to investigate the relationship between keratoconus disease and the antioxidant activities of catalase (CAT), reduced glutathione (GSH) and superoxide dismutase (SOD) and the level of the oxidative stress marker malondialdehyde (MDA) in serum.

METHODS

The study included 50 patients diagnosed with keratoconus and 53 healthy age- and sex-matched control subjects. The keratoconus patients were grouped according to the four keratoconus stages based on the modified Krumeich keratoconus classification system. The CAT, GSH and SOD activities and MDA levels in the serum samples collected from the patient and control groups were compared.

RESULTS

The mean serum CAT, GSH, SOD and MDA levels in the keratoconus group were determined to be 0.075 (0.074-0.078)U/L, 0.002 (0.001-0.006) mmol/ml, 1.56 (1.51-1.62)U/L and 1.69 (1.65-1.99) mmol/L, respectively, and those in the control group were determined to be 0.024 (0.013-0.037)U/L, 0.029 (0.018-0.049) mmol/ml, 4.13 (4.01-4.17) U/L and 0.74 (0.65-0.82) mmol/L. The serum GSH levels and SOD activity were significantly lower in the keratoconus group (p < 0.001 for both) than in the control group while the CAT activity and MDA levels were significantly higher (p < 0.001 for both).

CONCLUSION

The low serum GSH levels and SOD activity and the high CAT activity and MDA levels observed in this study suggest the presence of oxidative stress and inadequate antioxidant defence mechanisms in keratoconus patients. The studied parameters may offer auxiliary markers for use in the diagnosis and treatment of the keratoconus disease and in its potential therapeutic targets in the future.

Association of keratoconus with serum levels of 25-hydroxyvitamin D and antioxidant trace elements: A systematic review and meta-analysis

The aim of this systematic review and meta-analysis was to summarize and compare the available evidence on the level of vitamin D and antioxidant trace elements between the keratoconus (KC) patients and healthy controls. Seven case-control studies with 830 subjects were found eligible with a systematic search using PubMed, SCOPUS, Web of Science, and EMBASE till November 21, 2021. Data were synthesized with a DerSimonian and Laird random-effects method of meta-analysis. The mean serum vitamin D level was significantly lower in the patients with KC [standardized mean difference (SMD): -0.71; P < 0.001] as compared with the control group. The mean serum vitamin D level decreased more in the progressive patients (SMD: -0.80; P = 0.016) than in the stable patients (SMD: -0.66; P < 0.001) when compared with the control group. The mean serum zinc level was found significantly lower in the patients with KC compared with the control group (SMD: -1.98; P = 0.005). Pooled analysis based on the two studies showed significantly lower mean selenium levels in the KC patients (SMD: -0.34; P = 0.003). Regular evaluation of serum vitamin D, zinc, and selenium levels among the patients with KC at disease onset and future follow-ups could be promising in predicting the progressive disease and disease severity.

Nutritional and Metabolic Imbalance in Keratoconus

Keratoconus (KC) is a progressive corneal degeneration characterized by structural changes consisting of progressive thinning and steepening of the cornea. These alterations result in biomechanical weakening and, clinically, in vision loss. While the etiology of KC has been the object of study for over a century, no single agent has been found. Recent reviews suggest that KC is a multifactorial disease that is associated with a wide variety of genetic and environmental factors. While KC is typically considered a disease of the cornea, associations with systemic conditions have been well described over the years. In particular, nutritional and metabolic imbalance, such as the redox status, hormones, metabolites, and micronutrients (vitamins and metal ions), can deeply influence KC initiation and progression. In this paper, we comprehensively review the different nutritional (vitamins and minerals) and metabolic (hormones and metabolites) factors that are altered in KC, discussing their possible implication in the pathophysiology of the disease.

Serum 25-Hydroxyvitamin D, Selenium, Zinc and Copper in Patients with Keratoconus

PURPOSE

To assess the possible association between keratoconus (KC) and serum levels of 25-hydroxyvitamin D (25OHD), Selenium (Se), Zinc (Zn), and Copper (Cu) and to compare it with age-matched healthy subjects.

METHODS

One hundred patients with KC and 100 normal subjects were included. The two groups were compared for serum 25OHD and serum levels of three trace elements: Se, Zn, and Cu. These factors were also compared between groups with different KC stages.

RESULTS

Serum levels of vitamin D, Zn, Cu, and Se were significantly different between the KC and normal groups (P = 0.006, P = 0.015, P = 0.004, and P = 0.038, respectively). Although a lower level of 25OHD was found in severe stages of KC, it was not significantly different among different KC groups (P = 0.441). KC stage groups were not significantly different for mean serum Zn, Cu, and Se (P = 0.130, P = 0.98, P = 0.113, respectively). Although the Cu/Zn ratio was higher in cases than in controls, there was no significant difference between the two groups and between KC stages (P = 0.168, P = 0.143, respectively).

CONCLUSION

Lower serum 25OHD, Cu, Zn, and Se were found in the KC group compared to the control group. The results of this study suggest that a lower antioxidative activity may be involved in the possible etiology of KC.

Evaluation of Serum Superoxide Dismutase Activity, Malondialdehyde, and Zinc and Copper Levels in Patients With Keratoconus

PURPOSE

The aim of this study was to evaluate the relationship between antioxidant superoxide dismutase (SOD) enzyme activity, malondialdehyde (MDA) as a lipid peroxidation marker, and some trace elements such as zinc (Zn) and copper (Cu) levels in patients with keratoconus.

METHODS

A total of 58 patients with keratoconus and 53 control subjects with similar age and sex were evaluated in this study. The modified Krumeich keratoconus classification was used to divide the patients into 4 stages. Serum SOD activity, MDA, and zinc and copper levels were compared between the patient and control groups.

RESULTS

The median serum SOD activity, MDA, and Zn and Cu levels were 27.2 (42.4-13.7) U/mL, 10.2 (11.9-8.5) nmol/mL, 87.9 (104.6-76.5) μmol/L, and 103.2 (117.9-90.3) μmol/L in the keratoconus group and 26.2 (32.5-14.4) U/mL, 8.8 (11.4-7.1) nmol/mL, 100.5 (121.1-81.8) μmol/L, and 98.4 (120.3-83.4) μmol/L in the control group, respectively. There was a statistically significant difference between the MDA and Zn levels of the keratoconus group and control subjects but not between the respective SOD activities or Cu levels (P = 0.016, P = 0.031, P = 0.440, and P = 0.376, respectively). We found no significant difference between the keratoconus group stages for serum SOD activity, serum MDA, and Zn and Cu levels (P > 0.05), and there was also no significant correlation between the keratoconus group stages and serum SOD activity, serum MDA, and Zn and Cu levels (P > 0.05).

CONCLUSIONS

There is imbalance in the systemic oxidant/antioxidant status where Zn deficiency also plays a role in patients with keratoconus.