Table 2 Milk protein-derived bioactive peptides with osteoprotective effects

Casein phosphopeptides [31, 33]

Tryptic digest of milk casein or Commercial CPP mixtures

1. Supplementation of CPPs in diets prevented the decline of BMD in OVX rats [31]

2. CPP treatments increased serum Ca and OC levels, femur index, and femoral Ca content and decreased serum ALP and PTH levels in normal rats [33]

RELEELNVPGEIVESLSSSEESITR [32]

β-CN (16–40)

Phosphorylation at Ser-30 and Ser-32–34

1. β-CN (16–40) treatment increased Ca²⁺ transport and TRPV6 expression in Caco-2 cells

2. β-CN (16–40) supplementation increased serum Ca level, femur length, and femoral Ca content and decreased serum ALP level and urinary pyridinoline content in normal rats

IPP, VPP [36,37,38]

Synthetic tripeptides or the peptide solutions (< 1 kD) prepared from L. helveticus-fermented whey

1. IPP and VPP increased the bone mineralization during BMMSC-based osteoblast differentiation but caused no effects on BMM-based osteoclast differentiation [36]

2. IPP increased bone mineralization in BMMSCs due to enhanced cell survival and matrix formation, and also reduced the RANKL/OPG ratio [37]

3. Microarray analysis indicated that IPP holds the promise to enhance in vitro osteoblast growth, differentiation, and signaling [38]

EDVPSER (PEP1)

NAVPITPTL (PEP2)

VLPVPQK (PEP3)

HPHPHLSF (PEP4)

[39,40,41,42,43]

α_S1-CN (99‒105)

α_S2-CN (130‒138)

β-CN (185‒191)

κ-CN (119‒126)

1. These peptides were shown to stimulate the proliferation of preosteoblasts and increase the expression of ALP, OC, and collagen I genes, ALP activity, OC secretion, and bone mineralization during in vitro osteoblast differentiation

2. PEP2 was shown to induce in vitro osteoblast differentiation by the PI3K/Akt signal cascade [39]

YVEEL (P2)

YLLF (P3)

WLAHK (P6)

[44, 45]

β-LG (58‒62)

β-LG (118‒121)

α-LA (123‒127)

1. These peptides were shown to increase the proliferation of preosteoblasts, ALP activity, and bone mineralization with a trend of P2 > P6 > P3

2. These peptides upregulated the expression of ALP, type I collagen, OC, and RUNX2 during in vitro osteoblastic differentiation [44]

3. P2 and P3 administrations reduced serum ALP, RANKL, and OC levels and prevented bone loss in OVX rats; they also decreased serum TNF-α while elevating TGF-β and IFN-γ levels [45]

4. The antioxidative peptide (P2) shows a greater ability to protect bones compared to the ACE-inhibitory peptide (P3) by reducing inflammation and enhancing bone formation markers [45]

TEVPAINTIASAEPTVH (KFP-1) [49]

κ-CN (138‒154)

1. KFP-1 promoted intestinal Ca²⁺ absorption in mice

2. KFP-1 inhibited in vitro RANKL-induced osteoclast differentiation and bone resorption

3. KFP-1 enhanced in vitro osteoblast differentiation and bone mineralization

4. KFP-1 administration prevented bone loss in AKR1A1-KO mice with vitamin C deficiency