Abstract
Natural protein-derived peptides are gaining attention for their potential in promoting health, particularly in nutraceutical formulations. In this study, calcium-binding peptides from lotus seed were produced and characterized using UV, FT-IR, Raman, and EDS, and SEM. The calcium-peptide (LSPIH-Ca) complex was subjected to its osteogenic effect in murine bone marrow-derived mesenchymal stem cells (D1 MSCs). Peptides from 4 % Alcalase® showed the highest calcium-binding capacity (49.14 μg/mg). Spectroscopy indicated calcium bound to LSPIH via amide (1537 cm−1 to 1553 cm−1), carboxyl, carbonyl, and carboxylate groups. Moreover, the LSPIH-Ca complex enhanced osteoblast differentiation, as evidenced by increased alkaline phosphatase activity and mineralization (123.29 % at 100 μg/mL). Underlying mechanism investigation revealed that the LSPIH-Ca complex stimulated osteogenesis by activating MAPK pathways and upregulating key osteogenic marker such as BMP-2/4, Runx2, ALP activity, COLI, and promoting mineralization. Furthermore, the LSPIH-Ca complex improved calcium transport than Ca2+ alone in Caco-2 cells (30.0 ± 2.01 μg/well within 120 min). Finally, this study was conducted to purify and identify calcium-binding peptides and the identified calcium-binding peptides composed of pentapeptide to nonapeptide. The findings of this study establish a theoretical foundation for the creation of innovative calcium nutraceutical additives aimed at enhancing calcium bioavailability and supporting health benefit.
Graphical abstract
Introduction
Calcium deficiency, continues to be a prevalent concern, particularly among older adults and postmenopausal women. A lack of calcium can result in several diseases, such as rickets in children and osteoporosis in older adults [1]. This deficit is generally attributed to inadequate calcium consumption and limited bioavailability. Therefore, creating dependable calcium supplements is essential to mitigate and avert future shortages. Various calcium supplements, such as amino acid chelates, organic acids, and inorganic forms have been widely studied for addressing calcium deficiency [2]. Inorganic types like CaCl? and CaCO? have low bioavailability due to intestinal precipitation [3], while organic forms such as calcium lactate are better absorbed but have lower calcium content and require adequate vitamin D. Though generally well-tolerated, supplements like calcium carbonate can cause digestive side effects [4]. Conversely, amino acid-chelated calcium improves absorption but is costly and prone to oxidation [5]. These limitations emphasize the need for cost-effective, stable alternatives like calcium-binding peptides.
Recently, bioactive peptides derived from natural dietary proteins have attracted significant attention as efficient calcium-binding agents due to their biological compatibility, including enhanced bioavailability and improved intestinal absorption [6]. Alongside these findings, recent studies have also explored innovative strategies for improving bone regeneration such as using bioactive materials and immunomodulatory scaffolds that synergize with the body's natural repair mechanisms [7]. While calcium-binding peptides derived from dietary proteins exhibited considerable promise in enhancing bone health by stimulating osteogenesis, the formation of new bone tissue, mineralization, and aiding the transport of calcium through the intestinal epithelium in both in vitro and in vivo studies. The majority of research on calcium-binding peptides has concentrated on animal or specific plant sources, including antarctic krill protein, bovine bone collagen, and peanut [6,8,9]. This has prompted researchers to investigate more animal and plant-derived sources for calcium-binding peptides, in accordance with the increasing demand for sustainable solutions in supplements and functional meals.
Lotus (N. nucifera G.) is also known as water lily and Kamala. It is a freshwater annual flower belonging to the genus Nelumbo, which includes the species N. nucifera [10]. As a significant economic crop in China, it produces 45,000 tons of lotus seeds and 9 million metric tons of freshly harvested rhizomes [11]. The scientific community has demonstrated a growing interest in the sacred lotus due to its importance in gardening, medicinal use, and botanical phylogeny [10]. Recently, bone health-benefits of lotus ingredients such as polysaccharides and alkaloids have been reported [[12], [13], [14]]. Although plant-derived calcium-binding peptides are known, the specific capacity of lotus seed protein to form bioactive calcium-peptide complexes, and their combined osteogenic and bioavailability benefits, have not been characterized. The objective of this study is to isolate lotus seed protein and generate calcium-binding peptides by enzymatic hydrolysis. Structural characterization of lotus seed calcium-peptide (LSPIH-Ca) complex was performed. Further, this study investigated osteogenic effect of LSPIH-Ca in mesenchymal stem cells and bioavailability by the Caco-2 calcium transport assay. Finally, the sequences of calcium-binding peptides were identified.
Section snippets
Materials
Lotus seeds were procured from a nearby market. Cell culture media and certain components were obtained from Gibco-BRL (Gaithersburg, MD, USA). Primary antibodies for extracellular signal-regulated kinase (ERK), p-38, c-Jun N-terminal kinase (JNK), Osteocalcin, collagen type I alpha 1 chain (COL1A1), distal-less homeobox 5 (Dlx5), phosphorylated-ERK (p-ERK), phosphorylated-p38 (p-p38), osterix, runt-related transcription factor 2 (Runx2), phosphorylated-JNK (p-JNK), b-actin, and p-p38 were
Protein isolates of lotus seed
Alkaline extraction is a well-established and effective technique commonly employed for obtaining high-quality protein isolates. In this study, lotus seed protein isolate (LSPI) was obtained with a purity of 83.80 %. Additionally, SDS-PAGE analysis revealed distinct protein bands, reflecting the presence of proteins with varying molecular weights (Fig. S1). A light band at 140 kDa suggested a low amount of high-molecular-weight protein. Moderate amounts were found in the 35–50 kDa range, but
Conclusion
Alcalase hydrolysis effectively produced calcium-binding peptides from lotus seed and facilitated LSPIH-Ca complex formation. Spectroscopic study revealed that calcium reacted with LSPIH to generate LSPIH-Ca complex via amide, carboxyl, carbonyl groups, and carboxylate oxygen atoms. Furthermore, the structural alterations from LSPIH to LSPIH-Ca complex, as evidenced by SEM and EDS, were attributed to interactions between peptides and calcium ions. Subsequent findings shown that LSPIH-Ca complex
CRediT authorship contribution statement
Jasmadi: Writing – original draft, Methodology, Investigation, Data curation, Conceptualization. Jae-Young Je: Writing – review & editing, Methodology, Investigation, Funding acquisition, Conceptualization.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This research was supported by grants (RS-2021-NR065989) of the Basic Science Research Program through the National Research Foundation (NRF) funded by the Ministry of Education, Republic of Korea.
References (56)
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