To investigate the levels of the triglyceride-glucose (TyG) index and sex hormone-binding globulin (SHBG) in patients with type 2 diabetes mellitus (T2DM) with diabetic retinopathy (DR), and to explore their correlations with biochemical parameters and the homeostasis model assessment of insulin resistance (HOMA-IR) in DR patients.

Patients with T2DM and healthy individuals were enrolled. Age and body mass index (BMI) of the participants were collected, TyG of the subjects was calculated using the formula, SHBG level of the subjects was detected, and blood biochemical indexes were measured at the same time. The changes of each index among the groups were statistically analyzed, and the relationship between TyG, SHBG, DR and each index was analyzed.

A total of 150 patients with T2DM and 64 healthy individuals as normal controls (NC, 28 males and 36 females, mean age 54.49±10.10y) were enrolled following ophthalmic evaluation. Patients were categorized into non-DR group (42 males and 36 females, mean age 56.68±8.02y) and DR group (35 males and 37 females, mean age, 53.83±11.10y). TyG levels were significantly elevated in both non-DR (7.25±0.62) and DR groups (8.02±0.82) compared to controls (6.85±0.48), with the DR group demonstrating higher TyG values than the non-DR group (P<0.05). The level of SHBG (nmol/L) in DR group (25.05±14.06) was lower than that in control group (41.90±22.6) and non-DR group (36.27±20.00; P<0.05). TyG exhibited significant inverse correlations with SHBG (r=-0.455) and high density lipoprotein (HDL; r=-0.430) levels (P<0.05). It was positively correlated with BMI, fasting blood glucose (FBG), 2h postprandial blood glucose (PBG), fasting C-peptide (FCP), glycated hemoglobin A1c (HbA1c), HOMA-IR, total cholesterol (TC) and triglycerides (TG) (r=0.406, 0.768, 0.386, 0.393, 0.475, 0.250, 0.242, 0.888, respectively, P<0.05). SHBG was negatively correlated with BMI, FBG, FCP, HbA1c and TyG (r=-0.440, -0.304, -0.407, -0.209, -0.455, respectively, P<0.05), and positively correlated with age, TG and HDL (r=0.238, 0.034, 0.227, respectively, P<0.05). Further multiple regression analysis showed that SHBG was negatively correlated with TyG (P=0.006).

Elevated TyG index, reduces SHBG levels, and their negative correlation in the DR group suggest potential roles of TyG and SHBG in the pathogenesis and progression of DR. Combined assessment of SHBG and TyG may provide valuable insights for DR prediction and diagnosis.

To observe the effect of ghrelin, a growth hormone-releasing peptide, on retinal angiogenesis in vitro under high glucose (HG) stress and to explore the possible mechanism of autophagy.

Human retinal microvascular endothelial cells (HRMECs) were treated with high concentration of glucose alone or in combination with ghrelin. The cell migration, tube formation and the expression of the autophagy-related proteins LC3-Ⅱ/Ⅰ, Beclin-1, p62, phosphorylated AKT (p-AKT)/AKT and phosphorylated mammalian target of rapamycin (p-mTOR)/mTOR were detected. Then, to clarify the correlation between ghrelin effect and autophagy, AKT inhibitor Ⅷ was adopted to treat HRMECs, and cell migration, tube formation as well as the protein expressions of LC3-Ⅱ/Ⅰ, Beclin-1 and p62 were observed.

Under HG stress, ghrelin inhibited migration and tube formation of HRMECs. Ghrelin inhibited the increases in the protein levels of LC3-Ⅱ/Ⅰ, Beclin-1 and the decreases in the protein levels of p62, p-AKT/AKT and p-mTOR/mTOR induced by HG stress. Moreover, under the action of AKT/mTOR pathway inhibitors, the effects of ghrelin on migration and tube formation were both reduced. In addition, the expression of LC3-Ⅱ/Ⅰ and Beclin-1 were significantly up-regulated and the expression of p62 was down-regulated.

Retinal angiogenesis under in vitro HG stress can be inhibited by ghrelin through activating AKT/mTOR pathway to inhibit autophagy.

To investigate the protective role of ghrelin against diabetic retinopathy (DR), focusing on its anti-ferroptotic mechanism in high glucose-induced retinal endothelial injury.

First, small interfering RNA (siRNA)-mediated interference was conducted to knockdown nuclear factor erythroid 2-related factor 2 (Nrf2). Using reverse transcription-polymerase chain reaction (RT-PCR), the expression level of Nrf2 was determined from human retinal microvascular endothelial cells (HRMECs) transfected with either si-NC or si-Nrf2. After that, cells were treated with 10 nmol/L ghrelin and then cultured in a high glucose (30 mmol/L) environment. EdU assay was utilized to assess cell proliferation, while transmission electron microscopy was employed to observe mitochondrial morphology. Flow cytometry was used to measure the level of intracellular reactive oxygen species (ROS), and biochemical assays were conducted to detect malondialdehyde (MDA), glutathione (GSH), superoxide dismutase (SOD), and ferrous iron (Fe²⁺). Western blotting was used to identify the presence of ferroptosis-related proteins such as glutathione peroxidase 4 (GPX4), solute carrier family 7 member 11 (SLC7A11), Nrf2, and haem oxygenase-1 (HO-1).

Under a high glucose environment, ghrelin could significantly promote the proliferation of HRMECs and mitochondrial status, remarkably decrease the levels of intracellular ROS and MDA, and up-regulate the level of GSH and SOD. Besides, ghrelin greatly reduced Fe²⁺ level in the cells while increased protein levels of GPX4 and SLC7A11. Subsequently, we found that high glucose induced inactivation of Nrf2/HO-1 axis and the protein expression profile were significantly promoted by ghrelin. Moreover, silencing of Nrf2 by siRNA delivery markedly diminished the changes induced by ghrelin in high glucose-induced HRMECs, shown as reduced cell proliferation and increased mitochondrial malformation, up-regulated ROS, MDA, Fe²⁺, GPX4 and SLC7A11, as well as down-regulated GSH, SOD, Nrf2 and HO-1.

Ghrelin attenuates high glucose-induced injury of retinal endothelial cells via inhibiting ferroptosis, and activation of Nrf2/HO-1 pathway may be one of the mechanisms involved in this effect of ghrelin.