Colon-targeting potential and metabolic effects of sodium butyrate-loaded CPC microspheres in type 2 diabetic mice

Background Oral sodium butyrate (SB) is rapidly absorbed in the proximal small intestine, limiting its colonic availability and local metabolic effects. We evaluated the in vitro release characteristics of chitosan-protocatechualdehyde/calcium alginate microspheres loaded with SB (CPC/SB), together with metabolic and microbial outcomes in mice with high-fat diet/streptozotocin-induced diabetes. Methods CPC/SB release was measured in separate simulated gastric, intestinal, and colonic fluids. Thirty-five male C57BL/6J mice were assigned to seven groups: normal control and six diabetic groups receiving vehicle, unloaded CPC, free SB, CPC/SB, metformin, or metformin plus CPC/SB for 4 weeks (34 completed). Endpoints included gastrointestinal and fecal butyrate; blood glucose, homeostasis model assessment of insulin resistance (HOMA-IR), low-density lipoprotein cholesterol (LDL-C), and interleukin-6 (IL-6); and fecal microbiota assessed by 16S rRNA gene sequencing and PICRUSt2. Results Relative butyrate release was 0.91%, 8.53%, and 94.17% in simulated gastric, intestinal, and colonic fluids, respectively. After CPC/SB administration, colonic butyrate exceeded gastric and small-intestinal levels, and fecal butyrate increased versus the model group (0.0523 ± 0.0121 vs. 0.0180 ± 0.0068 μg/mg; p < 0.0001). Random blood glucose decreased to 18.64 mmol/L at week 4 ( p < 0.0001 vs. baseline and model). CPC/SB also reduced HOMA-IR (3.14 ± 0.43 vs. 4.81 ± 1.30; p = 0.046) and serum IL-6 (85.82 ± 1.90 vs. 93.55 ± 4.10 pg./mL; p = 0.008); LDL-C and α-diversity were unchanged. Exploratory 16S analyses suggested taxonomic and predicted pathway differences, but none survived Benjamini-Hochberg correction. Conclusion At the tested dose, CPC/SB increased fecal butyrate, improved glycemic indices, and reduced serum IL-6 relative to the diabetic model group. SB, carrier, and delivery-related effects could not be separated, and in vivo targeting efficiency was not demonstrated.