A composite protein enriched with threonine, lysine, and tryptophan improves osteoporosis by modulating the composition and metabolism of the gut microbiota

Abstract

A composite protein enriched with threonine, lysine, and tryptophan improves osteoporosis by modulating the composition and metabolism of the gut microbiota Abstract：Osteoporosis is a metabolic bone disorder characterized by therapeutic challenges and considerable adverse effects. Amino acids serve as essential structural and nutritional constituents of bone tissue, and threonine, lysine, and tryptophan play pivotal roles in maintaining bone health. However, single protein sources often display imbalanced amino acid compositions. Composite proteins combine multiple protein sources to achieve complementary amino acid profiles. Moreover, maintaining a balanced amino acid profile is essential for optimal nutrient absorption and physiological utilization in humans. Therefore, according to the essential amino acid standards established by the Food and Agriculture Organization and the World Health Organization (FAO/WHO), we selected soy, whey, and yeast proteins. Using grey relational analysis to optimize the formulation, we developed a composite protein (MPH) fortified with threonine, lysine, and tryptophan. We evaluated its efficacy in a retinoic acid-induced osteoporosis rat model and explored the underlying mechanisms via gut microbiota 16S rRNA sequencing, PICRUSt-based functional prediction, and metabolomic analysis. Results demonstrated that MPH increased body weight and serum calcium/phosphorus levels; upregulated type I procollagen N-terminal propeptide (PINP), osteocalcin (OC), and alkaline phosphatase (ALP); downregulated type I collagen carboxy-terminal cross-linked telopeptide (CTX-1); and improved femoral and tibial length, bone mass, trabecular architecture, and bone mineral density, thereby effectively alleviating osteoporotic symptoms. Additionally, MPH modulated the gut microbiota-enhancing the relative abundance of Lactobacillus, Akkermansia, and Ruminococcus-and promoted the production of key metabolites such as β-hydroxybutyrate (β-HB), lipoxin A4 (LXA4), indolepropionic acid (IPA), and butyrate. These findings indicate that the developed composite protein exerts significant ameliorative effects on osteoporosis.