Gestational diabetes mellitus (GDM) affects a substantial proportion of pregnancies and is driven in large part by insulin resistance. Both the active form of vitamin D, 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃), and astragalus polysaccharide (APS) have individually been reported to attenuate insulin resistance. The combined effects and underlying molecular mechanisms of these agents in GDM models, however, remain incompletely defined. This study investigated whether combined 1,25(OH)₂D₃ and APS therapy improves metabolic outcomes in a rat model of GDM and explored potential pathways involved, including VDR signaling, oxidative stress markers, and the PI3K/AKT/FOXO1 axis.
Sprague-Dawley rats were used to establish GDM by feeding a high-fat diet and administering low-dose streptozotocin. After diabetes induction, animals received treatment with 1,25(OH)₂D₃, APS, or the combination of both agents for two weeks. The report specifies the model induction method and the two-week treatment duration. Details such as exact doses, timing relative to gestation, and individual group sizes were reported in the original article but are not reproduced here.
Following treatment, the investigators measured a panel of systemic metabolic and liver function markers. Outcomes included serum glucose and insulin (used to calculate HOMA-IR), lipid parameters (free fatty acids, triglycerides, apolipoprotein B), and liver enzymes—alanine aminotransferase (ALT) and aspartate aminotransferase (AST). These measures assessed systemic glycemic control, insulin resistance, dyslipidemia, and hepatocellular injury associated with GDM and intervention effects.
Liver tissue was analyzed for oxidative stress and antioxidant status. The study measured reactive oxygen species (ROS) and malondialdehyde (MDA) as markers of oxidative damage, and superoxide dismutase (SOD) activity as an index of antioxidant defense. Changes in these parameters were used to evaluate whether interventions modified hepatic oxidative stress linked to insulin resistance.
Molecular investigations in liver tissue included measurement of mRNA and protein expression relevant to vitamin D metabolism and insulin/glucose homeostasis. Reported targets included VDR and cytochrome P450 2R1 (CYP2R1) mRNA, and protein levels of VDR, insulin receptor, insulin receptor substrate 1 (IRS1), glucose transporter 2 (GLUT2), PI3K, AKT, phosphorylated AKT (pAKT), FOXO1, PEPCK, G6pase, SREBP1C and PPARγ. These markers probe the insulin signaling cascade, gluconeogenic enzymes, and lipid metabolism regulators.
To explore protein–protein interactions relevant to signaling, co-immunoprecipitation assays were performed on liver tissue to examine a putative interaction between VDR and the PI3K regulatory subunit p85. The assay provided evidence consistent with a potential VDR–PI3K p85 association in the liver.
Combination therapy with 1,25(OH)₂D₃ and APS produced multiple favorable changes compared with untreated GDM rats. Specifically, the combination significantly reduced serum glucose, AST, ALT, free fatty acids, triglycerides, apolipoprotein B, and HOMA-IR (p < 0.05). In the liver, combination treatment decreased ROS and MDA levels and increased SOD activity, indicating reduced oxidative stress and enhanced antioxidant response.
At the molecular level, the combined intervention upregulated VDR and CYP2R1 mRNA and increased protein expression of VDR, insulin receptor, IRS1, GLUT2, PI3K, AKT, and pAKT, with an increased pAKT/AKT ratio (p < 0.05). Concomitantly, it suppressed proteins associated with gluconeogenesis and lipogenesis—FOXO1, PEPCK, G6pase and SREBP1C—and increased PPARγ levels (p < 0.05). Co-immunoprecipitation supported a potential interaction between VDR and PI3K p85 in hepatic tissue.
The authors interpret these findings to indicate that combined 1,25(OH)₂D₃ and APS therapy alleviates insulin resistance and related metabolic disturbances in this GDM rat model. The proposed mechanistic contributors are: upregulation of VDR, attenuation of hepatic oxidative stress, and modulation of the PI3K/AKT/FOXO1 signaling pathway leading to reduced gluconeogenic enzyme expression and improved insulin signaling. The observed VDR–PI3K p85 association provides a potential molecular link between vitamin D receptor activity and insulin-responsive PI3K signaling.
The animal experiment was conducted under Institutional Animal Care and Use Committee (IACUC) oversight of the School of Public Health, Jilin University, and complied with Chinese guidelines cited in the original report. The authors declared no competing interests.
In this preclinical GDM model, a two-week combined regimen of 1,25(OH)₂D₃ and APS improved systemic glucose and lipid parameters, reduced hepatic oxidative stress, and favorably altered expression of key regulators of insulin signaling, gluconeogenesis, and lipid metabolism. The data support a plausible mechanism involving VDR upregulation and PI3K/AKT/FOXO1 pathway modulation. Further work would be required to confirm dosing details, safety, and translatability to human pregnancy; such translational details were not reported in the abstract.