Non-alcoholic fatty liver disease (NAFLD) and steatohepatitis (NASH) have become the world's most common liver diseases, placing a growing strain on healthcare systems worldwide. Nonetheless, no effective pharmacological treatment has been approved. The naturally occurring compound cyclo histidine-proline (His-Pro) (CHP) is an interesting candidate for NAFLD management, given its safety profile and anti-inflammatory effects. Two different mouse models of liver disease were used to evaluate protective effects of CHP on disease progression towards fibrosis: a model of dietary NAFLD/NASH, achieved by thermoneutral housing (TN) in combination with feeding a western diet (WD), and liver fibrosis caused by repeated injections with carbon tetrachloride (CCl₄). Treatment with CHP limited overall lipid accumulation, lowered systemic inflammation, and prevented hyperglycaemia. Histopathology and liver transcriptomics highlighted reduced steatosis and demonstrated remarkable protection from the development of inflammation and fibrosis, features which herald the progression of NAFLD. We identified the extracellular signal-regulated kinase (ERK) pathway as an early mediator of the cellular response to CHP. CHP was active in both the preventive and therapeutic setting, reducing liver steatosis, fibrosis, and inflammation and improving several markers of liver disease. Considering the incidence and the lack of approved treatments, it is urgent to identify new strategies that prevent and manage NAFLD. CHP was effective in attenuating NAFLD progression in two animal models of the disease. Overall, our work points to CHP as a novel and effective strategy for the management of NAFLD, fuelling optimism for potential clinical studies.

Persistent damage to liver cells leads to liver fibrosis, which is characterized by the accumulation of scar tissue in the liver, ultimately leading to cirrhosis and serious complications. Because it is difficult to reverse cirrhosis once it has progressed, the primary focus has been on preventing the progression of liver fibrosis. However, studies on therapeutic agents for liver fibrosis are still lacking. Here, we investigated that the natural dipeptide cyclic histidine-proline (CHP, also known as diketopiperazine) shows promising potential as a therapeutic agent in models of liver injury by inhibiting the progression of fibrosis through activation of the Nrf2 pathway. To elucidate the underlying biological mechanism of CHP, we used the Cellular Thermal Shift Assay (CETSA)-LC-MS/MS, a label-free compound-based target identification platform. Chloride intracellular channel protein 1 (CLIC1) was identified as a target whose thermal stability is increased by CHP treatment. We analyzed the direct interaction of CHP with CLIC1 which revealed a potential interaction between CHP and the E228 residue of CLIC1. Biological validation experiments showed that knockdown of CLIC1 mimicked the antioxidant effect of CHP. Further investigation using a mouse model of CCl₄-induced liver fibrosis in wild-type and CLIC1 KO mice revealed the critical involvement of CLIC1 in mediating the effects of CHP. Taken together, our results provide evidence that CHP exerts its anti-fibrotic effects through specific binding to CLIC1. These insights into the mechanism of action of CHP may pave the way for the development of novel therapeutic strategies for fibrosis-related diseases.

Background: CycloZ, a combination of cyclo-His-Pro and zinc, has anti-diabetic activity. However, its exact mode of action remains to be elucidated.Methods: KK-Ay mice, a type 2 diabetes mellitus (T2DM) model, were administered CycloZ either as a preventive intervention, or as a therapy. Glycemic control was evaluated using the oral glucose tolerance test (OGTT), and glycosylated hemoglobin (HbA1c) levels. Liver and visceral adipose tissues (VATs) were used for histological evaluation, gene expression analysis, and protein expression analysis.Results: CycloZ administration improved glycemic control in KK-Ay mice in both prophylactic and therapeutic studies. Lysine acetylation of peroxisome proliferator-activated receptor gamma coactivator 1-alpha, liver kinase B1, and nuclear factor-κB p65 was decreased in the liver and VATs in CycloZ-treated mice. In addition, CycloZ treatment improved mitochondrial function, lipid oxidation, and inflammation in the liver and VATs of mice. CycloZ treatment also increased the level of β-nicotinamide adenine dinucleotide (NAD+), which affected the activity of deacetylases, such as sirtuin 1 (Sirt1).Conclusion: Our findings suggest that the beneficial effects of CycloZ on diabetes and obesity occur through increased NAD+ synthesis, which modulates Sirt1 deacetylase activity in the liver and VATs. Given that the mode of action of an NAD+ booster or Sirt1 deacetylase activator is different from that of traditional T2DM drugs, CycloZ would be considered a novel therapeutic option for the treatment of T2DM.

Asthma is a chronic lung disease characterized by airway inflammation, hyperresponsiveness, and narrowing, with a risk of life-threatening attacks. Most current treatments primarily consist of inhalable steroids, which are not without adverse effects. Recently, there has been growing interest in alternative approaches to asthma management. In this study, we investigated the anti-asthmatic effects of the non-steroidal compound CycloZ using acute and chronic mouse models of asthma. Allergic reactions were induced with house dust mite (HDM) extract, and CycloZ or fluticasone propionate (FP) was administered orally or intranasally, respectively. CycloZ significantly ameliorated the HDM-induced robust expression of Th2 cytokines in both models. CycloZ also decreased immune cell infiltration into the lungs and reduced IL-4 and IL-13 cytokine levels in bronchoalveolar lavage fluid (BALF). Moreover, CycloZ greatly attenuated the activation of the TLR-4 pathway, which is involved in HDM recognition and signaling. The beneficial effects of CycloZ were comparable to or even superior to the current steroid treatment, FP, suggesting that CycloZ could be a promising new option for asthma therapy.

Amino acids are key regulators of metabolism, their coordinated effects on skeletal muscle signaling and metabolic remodeling under physiological conditions remain incompletely understood. Here, we investigated whether 14 weeks of combined histidine and proline supplementation (HISPRO; 700 mg/kg) enhances skeletal muscle function through metabolic reprogramming in normal ICR mice. HISPRO significantly improved muscle performance compared with the control group, including grip strength, rota-rod, and treadmill. Histological and biochemical analyses revealed a shift toward oxidative muscle phenotype compared with the control group, with larger muscle fibers and succinate dehydrogenase-positive fibers. Consistently, HISPRO promoted mitochondrial biogenesis and oxidative metabolism compared with the control group, as evidenced by upregulation of mitochondrial regulatory genes, mitochondrial DNA copy number, citrate synthase activity, and oxidative phosphorylation (OXPHOS) complex levels in skeletal muscles. Mechanistically, HISPRO was associated with activation of the SIRT1-PGC1α-AMPK signaling axis compared with the control group, as evidenced by increased Nampt and Nmnat1 expression, an elevated NAD⁺/NADH ratio, and enhanced AMPK phosphorylation. SIRT1 inhibition markedly attenuated HISPRO-induced increases in mitochondrial biogenesis markers but did not fully suppress OXPHOS protein expression, suggesting the involvement of both SIRT1-dependent and -independent mechanisms. Notably, HISPRO also improved muscle function in dexamethasone-induced muscle atrophy model. It restored mitochondrial biogenesis and function, and suppressed atrophy-related markers compared with the dexamethasone-treated group. HISPRO may contribute to improving muscle quality through coordinated metabolic regulation and could represent a complementary nutritional for supporting muscle metabolic health.

Idiopathic pulmonary fibrosis (IPF) is a progressive, fatal lung disease with limited treatment options, while approved antifibrotics provide modest benefit, particularly in elderly patients. We investigated the oral small‑molecule combination CycloZ in bleomycin (BLM)‑induced pulmonary fibrosis. Pulmonary fibrosis was induced by intravenous or intratracheal BLM in young ICR/C57BL/6 and 18‑month‑old C57BL/6 mice, and CycloZ (15 mg/kg/day, oral) was administered immediately after BLM (preventive) or from day 7 (therapeutic), and its effects were compared with pirfenidone or nintedanib. Lung mechanics (flexiVent®), micro‑CT Hounsfield unit analysis, histology (Ashcroft score, Masson’s trichrome) and hydroxyproline content were used to assess functional and structural changes, while bronchoalveolar lavage fluid and lung tissue levels of TGFβ, IL‑6 and extracellular matrix markers were measured. Across preventive and therapeutic regimens, including aged mice, CycloZ significantly improved BLM‑induced reductions in lung compliance and increases in total and tissue elastance, restored aerated lung volumes on micro‑CT, and reduced Ashcroft scores, collagen deposition and hydroxyproline levels, with equal or greater efficacy than pirfenidone and nintedanib. Pro‑inflammatory cytokines and extracellular matrix markers were consistently decreased in bronchoalveolar lavage fluid and lung tissue. CycloZ therefore provides robust functional and structural protection in diverse BLM‑induced pulmonary fibrosis settings and represents a promising oral candidate for further clinical development in IPF.