The aim of this study is to investigate the physicochemical properties, biosafety, and biocompatibility of the collagen extract from the skin of Nile tilapia, and evaluate its use as a potential material for biomedical applications. Two extraction methods were used to obtain acid-soluble collagen (ASC) and pepsin-soluble collagen (PSC) from tilapia skin. Amino acid composition, FTIR, and SDS-PAGE results showed that ASC and PSC were type I collagen. The molecular form of ASC and PSC is (α₁)₂α₂. The FTIR spectra of ASC and PSC were similar, and the characteristic peaks corresponding to amide A, amide B, amide I, amide II, and amide III were 3323 cm⁻¹, 2931 cm⁻¹, 1677 cm⁻¹, 1546 cm⁻¹, and 1242 cm⁻¹, respectively. Denaturation temperatures (Td) were 36.1 °C and 34.4 °C, respectively. SEM images showed the loose and porous structure of collagen, indicting its physical foundation for use in applications of biomedical materials. Negative results were obtained in an endotoxin test. Proliferation rates of osteoblastic (MC3T3E1) cells and fibroblast (L929) cells from mouse and human umbilical vein endothelial cells (HUVEC) were increased in the collagen-treated group compared with the controls. Furthermore, the acute systemic toxicity test showed no acute systemic toxicity of the ASC and PSC collagen sponges. These findings indicated that the collagen from Nile tilapia skin is highly biocompatible in nature and could be used as a suitable biomedical material.

Calcium binding peptides from Pacific cod (Gadus macrocephalus) bone have attracted attention due to their potential effects on bone health. In this study, calcium binding peptides (CBP) were prepared from Pacific cod bone by trypsin and neutral protease. Ultraviolet spectra, circular dichroism (CD), and Fourier transform infrared spectroscopy (FTIR) revealed that carboxyl and amino groups in CBP could bind to Ca²⁺, and form the peptide-calcium complex (CBP-Ca). Single-pass intestinal perfusion (SPIP) experiments indicated that the intestinal calcium absorption was significantly enhanced (p < 0.01) in CBP-Ca treated Wistar rats. The anti-osteoporosis activity of CBP-Ca was investigated in the ovariectomized (OVX) Wistar rat model. The administration of CBP-Ca significantly (p < 0.01) improved the calcium bioavailability, trabecular bone structure, bone biomechanical properties, bone mineral density, and bone mineralization degree. CBP-Ca notably (p < 0.01) increased serum calcium, however, it remarkably (p < 0.01) reduced the levels of osteocalcin (OCN), bone alkaline phosphatase (BALP), tartrate-resistant acid phosphatase isoform 5b (TRAP5b), and C-telopeptide of type I collagen (CTX-1) in serum. Results suggested that the cod bone derived CBP could bind with calcium, improve the intestinal calcium absorption, calcium bioavailability, and serum calcium, then reduce the bone turnover rate, and thus ameliorate osteoporosis.

Dysfunction of the intestinal barrier plays a key role in the pathogenesis of inflammatory bowel disease (IBD) and multiple organ failure. The effect of Alaska pollock skin-derived collagen and its 3 tryptic hydrolytic fractions, HCP (6 kDa retentate), MCP (3 kDa retentate) and LCP (3 kDa permeate) on TNF-α induced barrier dysfunction was investigated in Caco-2 cell monolayers. TNF-α induced barrier dysfunction was significantly attenuated by the collagen and its peptide fractions, especially LCP, compared to TNF-α treated controls (P < 0.05). Compared to a negative control, 24 h pre-incubation with 2 mg mL⁻¹ LCP significantly alleviated the TNF-α induced breakdown of the tight junction protein ZO-1 and occludin and inhibited MLC phosphorylation and MLCK expression. The activation of NFκB and Elk-1 was suppressed by LCP. Thus, collagen peptides may attenuate TNF-α induced barrier dysfunction of Caco-2 cells by inhibiting the NFκB and ERK1/2-mediated MLCK pathway with associated decreases in ZO-1 and occludin protein expression.