Collagen Hydrolysate Corrects Anemia in Chronic Kidney Disease via Anti-Inflammatory Renoprotection and HIF-2α-Dependent Erythropoietin and Hepcidin Regulation

Collagen Peptides as a Hypoxia-Inducible Factor-2α-Stabilizing Prolyl Hydroxylase Inhibitor to Stimulate Intestinal Iron Absorption by Upregulating Iron Transport Proteins

Iron intervention is not always safe and effective to correct iron deficiency. Host iron absorption stimulation is emerging as a promising adjunctive/alternative treatment. Here, porcine collagen hydrolysate (CH) and collagen-derived dipeptide prolyl-hydroxyproline, rather than collagen amino acids, namely, glycine, proline, and hydroxyproline, were found to increase cellular iron reduction, absorption, and transportation, to upregulate duodenal cytochrome b (Dcytb), divalent metal transporter 1 (DMT1), ferroportin (FPN), and hephaestin, and to nongenomically activate hypoxia-inducible factor-2α signaling in polarized Caco-2 cells. Prolyl-hydroxyproline showed both competitive and uncompetitive inhibition of recombinant human prolyl hydroxylase-3 activity with EC₅₀ and K_i values of 10.62 and 6.73 μM, respectively. Docking simulations revealed collagen peptides as iron chelators and/or steric hindrances for prolyl hydroxylase-3. CH and prolyl-hydroxyproline acutely increased duodenal hypoxia-inducible factor-2α stability and Dcytb, DMT1, FPN, and hephaestin transcription in rats. Overall, collagen peptides act as a hypoxia-inducible factor-2α-stabilizing prolyl hydroxylase inhibitor to stimulate intestinal iron absorption.

Exogenous Bioactive Peptides Have a Potential Therapeutic Role in Delaying Aging in Rodent Models

In recent years, some exogenous bioactive peptides have been shown to have promising anti-aging effects. These exogenous peptides may have a mechanism similar to endogenous peptides, and some can even regulate the release of endogenous active peptides and play a synergistic role with endogenous active peptides. Most aging studies use rodents that are easy to maintain in the laboratory and have relatively homogenous genotypes. Moreover, many of the anti-aging studies using bioactive peptides in rodent models only focus on the activity of single endogenous or exogenous active peptides, while the regulatory effects of exogenous active peptides on endogenous active peptides remain largely under-investigated. Furthermore, the anti-aging activity studies only focus on the effects of these bioactive peptides in individual organs or systems. However, the pathological changes of one organ can usually lead to multi-organ complications. Some anti-aging bioactive peptides could be used for rescuing the multi-organ damage associated with aging. In this paper, we review recent reports on the anti-aging effects of bioactive peptides in rodents and summarize the mechanism of action for these peptides, as well as discuss the regulation of exogenous active peptides on endogenous active peptides.

Contribution of Oxidative Stress to HIF-1-Mediated Profibrotic Changes during the Kidney Damage

Hypoxia and oxidative stress are the common causes of various types of kidney injury. During recent years, the studies on hypoxia inducible factor- (HIF-) 1 attract more and more attention, which can not only mediate hypoxia adaptation but also contribute to profibrotic changes. Through analyzing related literatures, we found that oxidative stress can regulate the expression and activity of HIF-1α through some signaling molecules, such as prolyl hydroxylase domain-containing protein (PHD), PI-3K, and microRNA. And oxidative stress can take part in inflammation, epithelial-mesenchymal transition, and extracellular matrix deposition mediated by HIF-1 via interacting with classical NF-κB and TGF-β signaling pathways. Therefore, based on previous literatures, this review summarizes the contribution of oxidative stress to HIF-1-mediated profibrotic changes during the kidney damage, in order to further understand the role of oxidative stress in renal fibrosis.