Zinc is an essential trace element required for normal cell growth, development, and differentiation. It is involved in DNA synthesis, RNA transcription, and cell division and activation. It is a critical component in many zinc protein/ enzymes, including critical zinc transcription factors. Zinc deficiency/altered metabolism is observed in many types of liver disease, including alcoholic liver disease (ALD) and viral liver disease. Some of the mechanisms for zinc deficiency/ altered metabolism include decreased dietary intake, increased urinary excretion, activation of certain zinc transporters, and induction of hepatic metallothionein. Zinc deficiency may manifest itself in many ways in liver disease, including skin lesions, poor wound healing/liver regeneration, altered mental status, or altered immune function. Zinc supplementation has been documented to block/attenuate experimental ALD through multiple processes, including stabilization of gut-barrier function, decreasing endotoxemia, decreasing proinflammatory cytokine production, decreasing oxidative stress, and attenuating apoptotic hepatocyte death. Clinical trials in human liver disease are limited in size and quality, but it is clear that zinc supplementation reverses clinical signs of zinc deficiency in patients with liver disease. Some studies suggest improvement in liver function in both ALD and hepatitis C following zinc supplementation, and 1 study suggested improved fibrosis markers in hepatitis C patients. The dose of zinc used for treatment of liver disease is usually 50 mg of elemental zinc taken with a meal to decrease the potential side effect of nausea.

BackgroundImmunotherapy using checkpoint inhibitors, especially PD-1/PD-L1 inhibitors, has now evolved into the most promising therapy for cancer patients. However, most of these inhibitors are monoclonal antibodies, and their large size may limit their tumor penetration, leading to suboptimal efficacy. As a result, there has been a growing interest in developing low-molecular-weight checkpoint inhibitors.MethodsWe developed a novel biopanning strategy to discover small peptide-based anti-PD-L1 inhibitors. The affinity and specificity of the peptides to PD-L1 were examined using various assays. Three-dimensional (3D) spheroid penetration study was performed to determine the tumor penetration capability of the peptides. Anti-tumor activity of the peptides was evaluated in mice bearing CT26 tumor cells.ResultsWe discover several anti-PD-L1 peptide inhibitors to block PD-1/PD-L1 interaction. The peptides exhibit high affinity and specificity to human PD-L1 protein as well as PD-L1-overexpressing human cancer cells MDA-MB-231 and DU-145. Molecular docking studies indicate that the peptide CLP002 specifically binds to PD-L1 at the residues where PD-L1 interacts with PD-1. The peptide also blocks the CD80/PD-L1 interaction, which may further enhance the immune response of tumor-infiltrating T cells. Compared to antibody, the peptide CLP002 exhibits better tumor penetration in a 3D tumor spheroid model. The peptide CLP002 restores proliferation and prevents apoptosis of T cells that are co-cultured with cancer cells. The peptide CLP002 also inhibits tumor growth and increases survival of CT26 tumor-bearing mice.ConclusionsThis study demonstrated the feasibility of using phage display to discover small peptide-based checkpoint inhibitors. Our results also suggested that the anti-PD-L1 peptide represents a promising low-molecular-weight checkpoint inhibitor for cancer immunotherapy.Electronic supplementary materialThe online version of this article (10.1186/s40425-019-0705-y) contains supplementary material, which is available to authorized users.

Protein-based drug delivery carrier has been one of the most employed modalities in biopharmaceuticals. In this study, we have compared avidin and its two analogues, neutravidin and streptavidin, as nanocarriers for the delivery of biotin-labeled siRNA with the help of biotinylated cholesterol (targeting ligand) and protamine (condensing agent). These proteins have similar binding affinity to biotin but substantial difference in their physical and chemical characteristics. Here, we have shown how these characteristics affect the size, cellular uptake, and activity of the avidin-based siRNA nanocomplex. In contrast to avidin and streptavidin nanocomplexes, neutravidin-based nanocomplex shows very low endosome entrapment and high cytoplasmic localization at extended times. High amount of the siRNA released in the cytoplasm by neutravidin-based nanocomplex at extended times (24 h) results in extensive and sustained PCBP2 gene silencing activity in HSC-T6 rat hepatic stellate cells. Neutravidin-based nanocomplex shows significantly low exocytosis in comparison to the streptavidin-based nanocomplex. Avidin-, neutravidin-, and streptavidin-based nanocomplexes are similar in size and had no significant cytotoxicity in transfected HSC-T6 cells or inflammatory cytokine induction in a whole blood assay. Compared to free siRNA, the neutravidin-based siRNA nanocomplex exhibits higher accumulation at 2 h in the liver of the rats with CCl-induced liver fibrosis. Neutravidin has therefore been shown to be the most promising avidin analogue for the delivery of siRNA.

Malnutrition, both protein energy malnutrition (PEM) and deficiencies in individual nutrients, is a frequent complication of alcoholic liver disease (ALD). Severity of malnutrition correlates with severity of ALD. Malnutrition also occurs in patients with cirrhosis due to etiologies other than alcohol. The mechanisms for malnutrition are multifactorial, and malnutrition frequently worsens in the hospital due to fasting for procedures and metabolic complications of liver disease, such as hepatic encephalopathy. Aggressive nutritional support is indicated in inpatients with ALD, and patients often need to be fed through an enteral feeding tube to achieve protein and calorie goals. Enteral nutritional support clearly improves nutrition status and may improve clinical outcome. Moreover, late-night snacks in outpatient cirrhotics improve nutritional status and lean body mass. Thus, with no FDA-approved therapy for ALD, careful nutritional intervention should be considered as frontline therapy.