Serum Irisin levels as a predictor of presence of diabetic retinopathy: A case-control study

Introduction

Diabetes Mellitus (DM) is a group of metabolic diseases characterized by disturbances in glucose metabolism that lead to chronic hyperglycemia due to impaired insulin secretion, insulin resistance, or both [1] . Long-term diabetes causes a number of complications, including microvascular and macrovascular [2] . Diabetic retinopathy (DR) is the most prevalent microvascular complication of diabetes [3] . Characterized by damage to the retina's tiny blood vessels caused by chronic hyperglycemia [4] . This can result in irreversible visual loss and blindness [5] . Therefore, early detection and treatment are critical to preventing vision loss from DR in patients with diabetes [6] . According to recent epidemic estimates for 2030, DR prevalence rates are expected to rise in low-to middle-income regions such as the Middle East, North Africa, and Africa, from 20.6% to 47.2%, significantly higher than in high-income regions such as Europe and North America [7] . Therefore, DR will become one of the world's most critical health issues [8] . Novel markers could help us understand the pathogenesis of DR. In 2012, Boström et al. discovered irisin, a novel myokine produced by skeletal muscle in response to physical activity [9] . This activity increases peroxisome-proliferator-activated receptor gamma coactivator 1-alpha (PGC1-α), which stimulates expression of the fibronectin type III International Journal of Advanced Biochemistry Research https://www.biochemjournal.com Domain-containing protein 5 (FNDC5) gene, thereby increasing FNDC5, a membrane cell protein that when cleaved, generates irisin [10] . Irisin plays an important role in converting white to brown adipose tissue, thereby reducing lipid accumulation [11] , regulates blood glucose by improving insulin sensitivity and reducing insulin resistance [12] , reduces oxidative stress effects induced by diabetes mellitus [13] , and reduces pro-inflammatory cytokines and increases the release of anti-inflammatory cytokines. This helps protect tissues from chronic inflammation [14] .

Materials and Methods

This case-control study was conducted from January to December 2025 at Basrah

Anthropometric measurements

Anthropometric measurements were taken of all study participants, including their height, weight, systolic blood pressure (SBP), and diastolic blood pressure (DBP). BMI is calculated by dividing weight in kilograms by height in meters squared (kg/m²).

Collection and processing of samples

Blood samples were collected from all participants. A part of each obtained blood sample was placed in an anticoagulant tube for HbA1c testing. The remaining blood was deposited in sterile gel test tubes, left at room temperature for 30 minutes, and then centrifuged at 3000 rpm for 5 minutes to obtain serum. The divided serum parts were used for biochemical testing, including FBS and lipid profiling. The remaining portion is stored at -20°C for subsequent ELISA analysis of irisin levels.

Statistical analysis

Normality of continuous variables was assessed with the Shapiro-Wilk test. Normally distributed variables are presented as mean ± SD and compared using ANOVA; nonnormal variables are summarized as median (IQR) and compared using the Kruskal-Wallis test. Multivariable logistic regression was used to assess the independent association between serum irisin and the presence of diabetic retinopathy, after adjustment for potential confounders. p<0.05 was considered statistically significant.

Results

Table 1:

The data for groups of patients with DR, patients without DR, and the control group were distributed by demographic characteristics, including age, sex, and BMI. There were no significant differences between study groups (p>0.05). In contrast, there are significant differences between patients with DR, patients without DR, and controls in SBP and DBP (p<0.001). The results indicate that FBS and HbA1c in patients with DR were higher than in both patients without DR and controls (p<0.001). Additionally, the study found highly significant differences between study groups in TC, TG, VLDL, and LDL levels (p<0.001). For HDL levels, a significant difference was observed (P = 0.02).

Regarding irisin, the study found that the mean serum irisin level was lower in patients with DR (69.68 ± 19.77 ng/ml) compared to patients without DR and controls (82.17 ± 9.24 ng/ml) and (120.66 ± 24.07 ng/ml), respectively, with a highly significant difference (p<0.001). Table 3: presents the data for the clinical stages of diabetic retinopathy. The study found no significant differences in FBS, TC, and HDL levels among the mild, moderate, severe NPDR, and PDR stages of diabetic retinopathy (p>0.05). Regarding HbA1c and irisin, the study revealed highly Significant differences (p<0.001), with a gradual decrease in irisin levels across the stages of diabetic retinopathy, with the lowest levels observed in the advanced stage (PDR). Additionally, TG and VLDL were significantly different (p<0.01) across the stages of DR. The study found that irisin correlates negatively and significantly with disease duration, HbA1c, TG, and VLDL. At the same time, a negative but non-significant correlation was observed between irisin and FBS (p>0.05). Table 5: A multivariable logistic regression analysis was performed to evaluate the independent association between serum irisin levels and DR. After adjusting for age, sex, BMI, FBG, HbA1c, lipid profile, duration of DM, SBP, and DBP, serum irisin remained a significant independent predictor of DR. Lower irisin levels were significantly associated with higher odds of DR (adjusted OR = 0.94, 95% CI: 0.91-0.97, p<0.001). All lipid profile parameters (TC, LDL, HDL, TG, and VLDL), FBG, HbA1c, and duration of DM were independently associated with diabetic retinopathy, whereas age, sex, BMI, SBP, and DBP were not statistically significant in the adjusted model.

Discussion

The results of the study demonstrated that patients with DR had significantly lower serum irisin levels than patients without DR or the control group. Our findings are supported by previous studies by Hou et al. [15] and Hu et al. [16] , which examined the relationship between irisin concentrations and DR and found that patients with PDR had lower irisin concentrations than patients without PDR or the control group. Despite being focused on PDR, these findings confirmed our finding that irisin levels decline with occurrence and progression of disease.

This decrease in serum irisin levels in patients with DR could be attributed to the negative effects of T2DM on blood components, in which increased glycated molecules lead to increased oxidative stress across a variety of organs, including skeletal muscle [17] . Skeletal muscle is the primary source of irisin. Impaired skeletal muscle function inhibits PGC-1α activation in muscle tissue. This reduces FNDC5 gene expression, thereby decreasing irisin production [18] . The study's additional subgroup analysis of the DR group reveals that serum irisin levels gradually decrease across the clinical stages of DR, with the lowest levels observed in the advanced stage (PDR). This finding is consistent with a previous study by Abu-Yaghi et al. [19] . Inflammation plays a significant role in the pathogenesis of DR [20] . Irisin modulates inflammation by promoting anti-inflammatory cytokines, such as IL-10, and inhibiting the release of proinflammatory cytokines, such as TNF-α [21] . This may indirectly contribute to the progression of DR [16] . This supports the hypothesis that low irisin levels indicate a loss of protective effects against retinal inflammation, leading to retinal damage and increased disease severity.

Regarding the lipid profile, the study found that TC, TG, LDL, and VLDL levels were elevated in patients with DR. In contrast, HDL levels were lower in patients with DR compared to patients without DR and the control group. Furthermore, a significant negative correlation was found between irisin and both TG and VLDL. These results align with the findings of Abu Tarboush et al. [17] , who reported a significant negative correlation between irisin and TG levels. No significant correlation were observed in our study between irisin and TC, HDL, and LDL. Furthermore, lipid profiles across clinical stages of DR differ significantly in TG, VLDL, and LDL levels. At the same time, TC and HDL showed no significant differences across clinical stages. These results were consistent with the findings of a previous study by Alattas et al. [22] . According to these results, patients with DR have increased lipid levels. This may damage the retinal microvasculature by forming lipid particles within capillaries. Additionally, dyslipidemia damages mitochondria, which may accelerate retinal neuronal apoptosis and retinal destruction [23] . Irisin is involved in regulating lipid metabolism. Irisin activates the expression of uncoupling protein-1 (UCP-1), thereby accelerating the conversion of white adipose tissue to brown adipose tissue and enhancing lipid utilization [24] . Therefore, decreased irisin levels may impair lipid control, leading to elevated blood lipid levels, which contribute to retinal damage and the progression of diabetic retinopathy.

In the correlation analysis, irisin was negatively correlated with FBG; however, this association was not statistically significant in our study. While the correlation of HbA1c was negative and statistically significant. These findings are in line with Wang et al. [25] , who observed increased irisin levels associated with decreased FBG and HbA1c levels. Supporting the role of irisin in maintaining glucose homeostasis by enhancing insulin sensitivity, facilitating glucose uptake in skeletal muscles, and improving hepatic glucose metabolism [26] . Furthermore, a significant negative correlation between irisin levels and the duration of DM was observed in patients with DR. This finding is consistent with a previous study by Ali et al. [27] , which suggested that prolonged hyperglycemia may further suppress irisin secretion.

In logistic regression analysis, irisin is an independent predictor of diabetic retinopathy, remaining significant even after adjustment for major confounders. These findings suggest that irisin may have a beneficial effect on the retina and that lower irisin levels may be associated with increased severity of diabetic retinopathy. In summary, our study found that circulating irisin levels were significantly reduced in diabetic retinopathy and decreased progressively across clinical disease stages. Irisin showed a significant association with disease presence and may act as an independent predictor of disease presence and progression.

Conclusions

This study discovered that patients with DR had significantly lower irisin levels than patients without DR or the control group. It also demonstrated that irisin levels decreased throughout the clinical stages of DR. Lower irisin levels are associated with the presence and severity of diabetic retinopathy in our study groups.

Study Limitations

This study has some limitations. It was conducted at a single center with a moderate sample size; therefore, the findings may not be generalizable outside Basrah. Variability in ELISA kits and serum storage time could also affect measurements. Further studies with multi-center recruitment and larger samples are needed to confirm these findings. In addition, future studies are required to investigate the potential therapeutic effects of irisin in diabetic retinopathy.

List of Abbreviations

Acknowledgement

AcknowledgementWe extend our heartfelt thanks to the College of Medicine at the University of Basrah for their ongoing support and cooperation. We gratefully acknowledge all participants who contributed to the completion of this study. Their cooperation and assistance were invaluable to the success of the research.

References

1. Goyal S, Rani J, Bhat MA, Vanita V. Genetics of diabetes. World Journal of Diabetes. 2023;14(6):656.
2. Farrugia F, Aquilina A, Vassallo J, Pace NP. Bisphenol A and type 2 diabetes mellitus: a review of epidemiologic, functional, and early life factors. International Journal of Environmental Research and Public Health. 2021;18(2):716.
3. Gelcho GN, Gari FS. Time to diabetic retinopathy and its risk factors among diabetes mellitus patients in Jimma University Medical Center, Jimma, Southwest Ethiopia. Ethiopian Journal of Health Sciences. 2022;32(5):937-946.
4. Bhatwadekar AD, Shughoury A, Belamkar A, Ciulla TA. Genetics of diabetic retinopathy, a leading cause of irreversible blindness in the industrialized world. Genes. 2021;12(8):1200.
5. Wan C, Chen Y, Li H, Zheng B, Chen N, Yang W, et al. EAD-net: A novel lesion segmentation method in diabetic retinopathy using neural networks. Disease Markers. 2021;2021(1):6482665.
6. Zhu S, Xiong C, Zhong Q, Yao Y. Diabetic retinopathy classification with deep learning via fundus images: A short survey. IEEE Access. 2024;12:20540-20558.
7. Wong TY, Tan TE. The diabetic retinopathy "pandemic" and evolving global strategies: the 2023 Friedenwald lecture. Investigative Ophthalmology and Visual Science. 2023;64(15):47.
8. Gong T, Wang D, Wang J, Huang Q, Zhang H, Liu C, et al. Study on the mechanism of plant metabolites to intervene oxidative stress in diabetic retinopathy. Frontiers in Pharmacology. 2025;16:1517964.
9. Boström P, Wu J, Jedrychowski MP, Korde A, Ye L, Lo JC, et al. A PGC1-α-dependent myokine that drives brown-fat-like development of white fat and thermogenesis. Nature. 2012;481(7382):463-468.
10. Han C, Zhou Z, Kong L, Lu J, Li X. Association between irisin level and cognitive function: a systematic review and meta-analysis. Brain and Behavior. 2025;15(7):e70662.
11. Minuti A, Raffaele I, Scuruchi M, Lui M, Muscarà C, Calabrò M. Role and functions of irisin: a perspective on recent developments and neurodegenerative diseases. Antioxidants. 2025;14(5):554.
12. Barbagallo F, Cannarella R, Garofalo V, Marino M, La Vignera S, Condorelli RA, et al. The role of irisin throughout women's life span. Biomedicines. 2023;11(12):3260.
13. Imran M, Ahsin S, Saeed GN, Ashraf H. Adipomyokine Irisin, a promising antioxidant against nicotine induced oxidative stress in BALB/c mice. Pakistan Journal of Medical Sciences. 2024;40(1 Pt 1):115.
14. Berberoğlu H, Hacışevki A. An overview of the effects of irisin on metabolic disorders. Gazi Sağlık Bilimleri Dergisi. 2021;6(2):33-41.
15. Hou Q, Song R, Zhao X, Yang C, Feng Y. Lower circulating irisin levels in type 2 diabetes mellitus patients with chronic complications: a meta-analysis. Heliyon. 2023;9(11).
16. Hu W, Wang R, Li J, Zhang J, Wang W. Association of irisin concentrations with the presence of diabetic nephropathy and retinopathy. Annals of Clinical Biochemistry. 2016;53(1):67-74.
17. Tarboush NA, Abu-Yaghi NE, Al Ejeilat LH, Wahed RK, Jeris IN. Association of irisin circulating level with diabetic retinopathy: a case-control study. Experimental and Clinical Endocrinology and Diabetes. 2021;129(1):36-42.
18. Aminov E, Folan P, Pisconti A. Are circulating levels of the myokine irisin linked to type 2 diabetes? A systematic review and meta-analysis. bioRxiv. 2024:2024-06.
19. Abu-Yaghi NE, Abu Tarboush NM, Abojaradeh AM, Al-Akily AS, Abdo EA, Emoush LO. Relationship between serum vascular endothelial growth factor levels and stages of diabetic retinopathy and other biomarkers. Journal of Ophthalmology. 2020;2020(1):8480193.
20. Tang L, Xu GT, Zhang JF. Inflammation in diabetic retinopathy: possible roles in pathogenesis and potential implications for therapy. Neural Regeneration Research. 2023;18(5):976-982.
21. Slate-Romano JJ, Yano N, Zhao TC. Irisin reduces inflammatory signaling pathways in inflammationmediated metabolic syndrome. Molecular and Cellular Endocrinology. 2022;552:111676.
22. Alattas K, Alsulami DW, Alem RH, Alotaibi FS, Alghamdi BA, Baeesa LS. Relation between lipid profile, blood pressure and retinopathy in diabetic patients in King Abdulaziz University hospital: a retrospective record review study. International Journal of Retina and Vitreous. 2022;8(1):20.
23. Rao H, Jalali JA, Johnston TP, Koulen P. Emerging roles of dyslipidemia and hyperglycemia in diabetic retinopathy: molecular mechanisms and clinical perspectives. Frontiers in Endocrinology. 2021;12:620045.
24. Paoletti I, Coccurello R. Irisin: A multifaceted hormone bridging exercise and disease pathophysiology. International Journal of Molecular Sciences. 2024;25(24):13480.
25. Wang Q, Ma L, Zhang Y, Zhang L, An Y, Liu J, et al. Effect of sitagliptin on serum irisin levels in patients with newly diagnosed type 2 diabetes mellitus. Diabetes Therapy. 2021;12(4):1029-1039.
26. Arhire LI, Mihalache L, Covasa M. Irisin: a hope in understanding and managing obesity and metabolic syndrome. Frontiers in Endocrinology. 2019;10:524.
27. Ali EY, Hegazy GA, Hashem EM. Evaluation of irisin, retinol-binding protein 4, and leptin serum levels as biomarkers of macrovascular complications involvement in Saudi type 2 diabetes mellitus: a casecontrol study. Saudi Medical Journal. 2020;41(12):1369.