Lactoferrin Conjugated with 40-kDa Branched Poly(ethylene Glycol) Has an Improved Circulating Half-Life

The Art of PEGylation: From Simple Polymer to Sophisticated Drug Delivery System

The development of effective drug delivery systems (DDSs) is important for cancer and infectious disease treatment to overcome low bioavailability, rapid clearance and the toxicity of the therapeutic towards non-targeted healthy tissues. This review discusses how PEGylation, the attachment of poly(ethylene glycol) (PEG) molecules to nanoparticles (NPs), enhances drug pharmacokinetics by creating a "stealth effect". We provide the synthesis methods for several PEG derivatives, their conjugation with NPs, proteins and characterization using modern analytical tools. This paper focuses particularly on covalent conjugation and self-assembly strategies for successful PEGylation and discusses the influence of PEG chain length, density and conformation on drug delivery efficiency. Despite the PEGylation benefits, there are several challenges associated with it, including immunogenicity and reduced therapeutic efficacy due to accelerated blood clearance. Therefore, the balance between PEGylation benefits and its immunogenic risks remains a critical area of investigation.

Digestive Profiles of Human Milk, Recombinant Human and Bovine Lactoferrin: Comparing the Retained Intact Protein and Peptide Release

Lactoferrin (LF) is a major component of human milk. LF supplementation (currently bovine) supports the immune system and helps maintain iron homeostasis in adults. No recombinant human lactoferrin (rhLF) is available for commercial food use. To determine the extent to which rhLF (Effera™) produced by Komagataella phaffii digests similarly to hmLF, a validated in vitro digestion protocol was carried out. Bovine LF (bLF) was used as an additional control, as it is approved for use in various food categories. This study compared the extent of intact protein retention and the profile of peptides released in hmLF, bLF and rhLF (each with low and high iron saturation) across simulated adult gastric and intestinal digestion using gel electrophoresis, ELISA and LC-MS. Intact LF retention across digestion was similar across LF types, but the highest iron-saturated hmLF had greater retention in the simulated gastric fluid than all other sample types. Peptides identified in digested hmLF samples strongly correlated with digested rhLF samples (0.86 < r < 0.92 in the gastric phase and 0.63 < r < 0.70 in the intestinal phase), whereas digested bLF samples were significantly different. These findings support the potential for rhLF as a food ingredient for human consumption.

Research progress on the PEGylation of therapeutic proteins and peptides (TPPs)

With the rapid advancement of genetic and protein engineering, proteins and peptides have emerged as promising drug molecules for therapeutic applications. Consequently, there has been a growing interest in the field of chemical modification technology to address challenges associated with their clinical use, including rapid clearance from circulation, immunogenicity, physical and chemical instabilities (such as aggregation, adsorption, deamination, clipping, oxidation, etc.), and enzymatic degradation. Polyethylene glycol (PEG) modification offers an effective solution to these issues due to its favorable properties. This review presents recent progress in the development and application of PEGylated therapeutic proteins and peptides (TPPs). For this purpose, firstly, the physical and chemical properties as well as classification of PEG and its derivatives are described. Subsequently, a detailed summary is provided on the main sites of PEGylated TPPs and the factors that influence their PEGylation. Furthermore, notable instances of PEG-modified TPPs (including antimicrobial peptides (AMPs), interferon, asparaginase and antibodies) are highlighted. Finally, we propose the chemical modification of TPPs with PEG, followed by an analysis of the current development status and future prospects of PEGylated TPPs. This work provides a comprehensive literature review in this promising field while facilitating researchers in utilizing PEG polymers to modify TPPs for disease treatment.

Nanoparticular and other carriers to deliver lactoferrin for antimicrobial, antibiofilm and bone-regenerating effects: a review

Bone and joint infections are a rare but serious problem worldwide. Lactoferrin’s antimicrobial and antibiofilm activity coupled with its bone-regenerating effects may make it suitable for improving bone and joint infection treatment. However, free lactoferrin (LF) has highly variable oral bioavailability in humans due to potential for degradation in the stomach and small intestine. It also has a short half-life in blood plasma. Therefore, encapsulating LF in nanocarriers may slow degradation in the gastrointestinal tract and enhance LF absorption, stability, permeability and oral bioavailability. This review will summarize the literature on the encapsulation of LF into liposomes, solid lipid nanoparticles, nanostructured lipid carriers, polymeric micro and nanoparticles and hydroxyapatite nanocrystals. The fabrication, characterization, advantages, disadvantages and applications of each system will be discussed and compared.

Milk protein-shelled gold nanoparticles with gastrointestinally active absorption for aurotherapy to brain tumor

Orally absorbable gold nanoparticles (AuNP) having cancer ablation therapy is strongly demanded to treat glioblastoma multiforme (GBM) for patients with its highest incidence rate. Here, we develop a milk protein lactoferrin-conjugated AuNP for its oral absorption and targeting to the GBM through the interaction between lactoferrin (Lf) and lactoferrin receptor (LfR) that is highly expressed in the intestine, blood-brain barrier and GBM. For stability and long circulation of AuNP, glutathione and polyethylene glycol (PEG) is introduced, which is called to Lf-PEG-AuNP. When Lf-PEG-AuNP are orally administered to orthotopic GBM-bearing mice, 11-fold and 8-fold higher concentrations of AuNP are measured in bloodstreams and GBM in the brain, respectively, compared with unconjugated-AuNP. Therefore, orally administered Lf-PEG-AuNP exhibit an outstanding temperature rise in GBM by irradiating laser and significantly reduce tumor volume. Collectively, we suggest that the Lf-PEG-AuNP can fundamentally target GBM in the brain through oral absorption, and that its efficient photothermal therapy is possible.

Kidney protective potential of lactoferrin: pharmacological insights and therapeutic advances

Kidney disease is becoming a global public health issue. Acute kidney injury (AKI) and chronic kidney disease (CKD) have serious adverse health outcomes. However, there is no effective therapy to treat these diseases. Lactoferrin (LF), a multi-functional glycoprotein, is protective against various pathophysiological conditions in various disease models. LF shows protective effects against AKI and CKD. LF reduces markers related to inflammation, oxidative stress, apoptosis, and kidney fibrosis, and induces autophagy and mitochondrial biogenesis in the kidney. Although there are no clinical trials of LF to treat kidney disease, several clinical trials and studies on LF-based drug development are ongoing. In this review, we discussed the possible kidney protective mechanisms of LF, as well as the pharmacological and therapeutic advances. The evidence suggests that LF may become a potent pharmacological agent to treat kidney diseases.

Allyl group-containing polyvinylphosphonates as a flexible platform for the selective introduction of functional groups via polymer-analogous transformations

Polyvinylphosphonates are highly promising candidates for (bio)medical applications as they exhibit a tunable lower critical solution temperature, high biocompatibility of homo- and copolymers, and a broad foundation for post-synthetic modifications. In this work we explored polymer-analogous transformations with statistical polyvinylphosphonates comprising diethyl vinylphosphonate (DEVP) and diallyl vinylphosphonate (DAlVP). The C[double bond, length as m-dash]C double bonds were used as a starting point for a cascade of organic transformations. Initially, the reactive moieties were successfully introduced via bromination, epoxidations with OXONE and mCPBA, or thiol-ene click chemistry with methyl thioglycolate (6). The obtained substrates were then employed in a variety of consecutive reactions depending on the introduced functional motif: (1) the brominated substrates were converted with sodium azide to enable the copper-mediated alkyne-azide coupling with phenylacetylene (1). (2) The epoxides were reacted with sodium azide for an alkyne-azide click coupling with 1 as well as small nucleophilic compounds (phenol (2), benzylamine (3), and 4-amino-2,1,3-benzothiadiazol (4)). Afterwards the non-converted allyl groups were reacted with thiochloesterol (5) to form complex polymer conjugates. (3) An acid-labile hydrazone-linked conjugate was formed in a two-step approach. The polymeric substrates were characterized by NMR, FTIR, and UV/Vis spectroscopy as well as elemental analysis and gel permeation chromatography to monitor the structural changes of the polymeric substrates and to prove the success of these modification approaches.

Development of X-ray contrast agents using single nanometer-sized gold nanoparticles and lactoferrin complex and their application in vascular imaging

The technology to accurately image the morphology of tumor vessels with X-ray contrast agents is important to clarify mechanisms underlying tumor progression and evaluate the efficacy of chemotherapy. However, in clinical practice, iodine-based contrast agents present problems such as short blood retention owing to a high clearance ability and insufficient X-ray absorption capacity when compared with other high atomic number elements. To resolve these issues, gold nanoparticles (AuNPs), with a high atomic number, have attracted a great deal of attention as contrast agents for angiography, and have been employed in small animal models. Herein, we developed novel contrast agents using AuNPs and captured changes in tumor vessel morphology with time using X-ray computed tomography (CT). First, glutathione-supported single nanometer-sized AuNPs (sAu/GSH) (diameter, 2.2 nm) were fabricated using tetrakis(hydroxymethyl)phosphonium chloride as a reducing agent. The sAu/GSH particles were intravenously injected into mice, remained in vessels for a few minutes, and were then excreted by the kidneys after 24 h, similar to the commercial contrast agent iopamidol. Next, the Au/GSH and lactoferrin (sAu/GSH-LF) (long axis size, 17.3 nm) complex was produced by adding lactoferrin to the sAu/GSH solution under the influence of a condensing agent. On intravenously administering sAu/GSH-LF to mice, the blood retention time was 1-3 h, which was considerably longer than that observed with iopamidol and sAu/GSH. Moreover, we succeeded in imaging morphological changes in identical tumor vessels for several days using X-ray CT with sAu/GSH-LF.

Oral fate and stabilization technologies of lactoferrin: a systematic review

Lactoferrin (Lf), a bioactive protein initially found in many biological secretions including milk, is regarded as the nutritional supplement or therapeutic ligand due to its multiple functions. Research on its mode of action reveals that intact Lf or its active peptide (i.e., lactoferricin) shows an important multifunctional performance. Oral delivery is considered as the most convenient administration route for this bioactive protein. Unfortunately, Lf is sensitive to the gastrointestinal (GI) physicochemical stresses and lactoferricin is undetectable in GI digesta. This review introduces the functionality of Lf at the molecular level and its degradation behavior in GI tract is discussed in detail. Subsequently, the absorption and transport of Lf from intestine into the blood circulation, which is pivotal to its health promoting effects in various tissues, and some assisting labeling methods are discussed. Stabilization technologies aiming at preserving the structural integrity and functional properties of orally administrated Lf are summarized and compared. Altogether, this work comprehensively reviews the structure-function relationship of Lf, its oral fate and the development of stabilization technologies for the enhancement of the oral bioavailability of Lf. The existing limitations and scope for future research are also discussed.

Albumin fusion at the N-terminus or C-terminus of human lactoferrin leads to improved pharmacokinetics and anti-proliferative effects on cancer cell lines

Human lactoferrin (hLF), a soluble factor of the innate immune system, exhibits various biological functions and therefore has potential as a therapeutic protein. However, the clinical applications of hLF are limited by its low stability in blood. We therefore attempted to resolve this by producing recombinant hLF fused to human serum albumin (HSA). Two HSA-fused hLFs with different fusion orientations (hLF-HSA and HSA-hLF) were produced in Chinese hamster ovary (CHO) DG44 cells. hLF-HSA revealed higher thermal stability, resistance to peptic degradation, and stability during the process of cellular uptake and release in an intestinal enterocyte model (Caco-2 cells) than HSA-hLF. The lower stability of HSA-hLF is presumably due to the steric hindrance imposed by HSA fusion to the N-terminus of hLF. Both HSA fusion proteins, especially HSA-hLF, displayed improved pharmacokinetic properties despite the lower protein stability of HSA-hLF. hLF-HSA and HSA-hLF exhibited approximately 3.3- and 20.7-fold longer half-lives (64.0 and 403.6 min), respectively, than holo-rhLF (19.5 min). Both HSA fusion proteins were found to exert enhanced growth inhibition effects on cancer cells in vitro, but not normal cells. Their enhanced growth inhibitory activities were considered to be due to the synergetic effects of hLF and HSA because hLF alone or HSA alone failed to exert such an effect. Altogether, Fusion of HSA to hLF yielded superior pharmacokinetics and anti-proliferative activities against cancer cells. HSA-fused hLF is a novel candidate for further application of hLF as biopharmaceuticals for intravenous administration.

Lactoferrin, a multi-functional glycoprotein: Active therapeutic, drug nanocarrier & targeting ligand

Recent progress in protein-based nanomedicine, inspired by the success of Abraxane® albumin-paclitaxel nanoparticles, have resulted in novel therapeutics used for treatment of challenging diseases like cancer and viral infections. However, absence of specific drug targeting, poor pharmacokinetics, premature drug release, and off-target toxicity are still formidable challenges in the clinic. Therefore, alternative protein-based nanomedicines were developed to overcome those challenges. In this regard, lactoferrin (Lf), a glycoprotein of transferrin family, offers a promising biodegradable well tolerated material that could be exploited both as an active therapeutic and drug nanocarrier. This review highlights the major pharmacological actions of Lf including anti-cancer, antiviral, and immunomodulatory actions. Delivery technologies of Lf to improve its pries and enhance its efficacy were also reviewed. Moreover, different nano-engineering strategies used for fabrication of drug-loaded Lf nanocarriers were discussed. In addition, the use of Lf for functionalization of drug nanocarriers with emphasis on tumor-targeted drug delivery was illustrated. Besides its wide application in oncology nano-therapeutics, we discussed the recent advances of Lf-based nanocarriers as efficient platforms for delivery of anti-parkinsonian, anti-Alzheimer, anti-viral drugs, immunomodulatory and bone engineering applications.

Nanoconjugation and Encapsulation Strategies for Improving Drug Delivery and Therapeutic Efficacy of Poorly Water-Soluble Drugs

Nanoconjugations have been demonstrated to be a dominant strategy for drug delivery and biomedical applications. In this review, we intend to describe several strategies for drug formulation, especially to improve the bioavailability of poorly water-soluble molecules for future application in the therapy of numerous diseases. The context of current studies will give readers an overview of the conjugation strategies for fabricating nanoparticles, which have expanded from conjugated materials to the surface conjugation of nanovehicles. Moreover, nanoconjugates for theranostics are also discussed and highlighted. Overall, these state-of-the-art conjugation methods and these techniques and applications for nanoparticulate systems of poorly water-soluble drugs will inspire scientists to explore and discover more productive techniques and methodologies for drug development.

Glucagon-Like Peptide-1 Receptor Agonists and Strategies To Improve Their Efficiency

Type 2 diabetes mellitus (T2DM) is increasing in global prevalence and is associated with serious health problems (e.g., cardiovascular disease). Various treatment options are available for T2DM, including the incretin hormone glucagon-like peptide-1 (GLP-1). GLP-1 is a therapeutic peptide secreted from the intestines following food intake, which stimulates the secretion of insulin from the pancreas. The native GLP-1 has a very short plasma half-life, owning to renal clearance and degradation by the enzyme dipeptidyl peptidase-4. To overcome this issue, various GLP-1 agonists with increased resistance to proteolytic degradation and reduced renal clearance have been developed, with several currently marketed. Strategies, such as controlled release delivery systems, methods to reduce renal clearance (e.g., PEGylation and conjugation to antibodies), and methods to improve proteolytic stability (e.g., stapling, cyclization, and glycosylation) provide means to further improve the ability of GLP-1 analogs. These will be discussed in this literature review.

Lactoferrin promotes hair growth in mice and increases dermal papilla cell proliferation through Erk/Akt and Wnt signaling pathways

Hair loss affects men and women of all ages. Dermal papilla (DP) plays a crucial role in regulating the growth and cycling of hair follicles. Lactoferrin (LF) exhibits a wide range of biological functions, including antimicrobial activity and growth regulation. However, its effect on DP and its role in hair growth remain unknown. In this study, we found that bovine LF (bLF) promoted the proliferation of DP cells and enhanced the phosphorylation of Erk and Akt. The bLF-mediated proliferation was significantly blocked by the Erk phosphorylation inhibitor PD98059 or the Akt phosphorylation inhibitor LY294002. Moreover, biotin-labeled bLF could bind to DP cells, and the binding was independent of lipoprotein receptor-related protein 1, a known LF receptor. Importantly, bLF stimulated hair growth in both young and aged mice. Moreover, we also found that bLF significantly induced the expression of Wnt signaling-related proteins, including Wnt3a, Wnt7a, Lef1, and β-catenin. The bLF-mediated DP cell proliferation could be significantly reversed by the Wnt pathway inhibitor XAV939. Our findings suggest that bLF promotes hair growth in mice and stimulates proliferation of DP cells through Erk/Akt and Wnt signaling pathways. This study highlights a great potential of the use of bLF in developing drugs to treat hair loss.

Hypothesis: apo-lactoferrin-Galantamine Proteo-alkaloid Conjugate for Alzheimer's disease Intervention

Alzheimer's disease (AD) is known to be caused by the accumulation of deformed beta amyloid and hyperphosphorylated tau proteins resulting into formation and aggregation of senile plaques and neurofibrillary tangles in the brain. Additionally, AD is associated with the accumulation of iron or metal ions in the brain which causes oxidative stress. Galantamine (Gal) is one of the therapeutic agents that has been approved for the treatment of AD, but still saddled with numerous side effects and could not address the issue of iron accumulation in the brain. The use of metal chelators to address the iron accumulation has not been successful due to toxicity and inability to address the aggregation of the plaques. We therefore hypothesize a combinatorial antioxidant-metal-chelator approach by formulating a single dosage form that has the ability to prevent the formation of free radicals, plaques and accumulation of iron in the brain. This can be achieved by conjugating Gal with apo-lactoferrin (ApoLf), a natural compound that has high binding affinity for iron, to form an apo-lactoferrin-galantamine proteo-alkaloid conjugate (ApoLf-Gal) as a single dosage form for AD management. The conjugation is achieved through self-assembly of ApoLf which results in encapsulation of Gal. ApoLf changes its conformational structure in the presence of iron; therefore, ApoLf-Gal is proposed to deliver Gal and pick up excess iron when in contact with iron. This strategy has the potential to proffer a dual neuroprotection and neurotherapeutic interventions for the management of AD.

Raloxifene-/raloxifene-poly(ethylene glycol) conjugate-loaded microspheres: A novel strategy for drug delivery to bone forming cells

Raloxifene (Ral)- or Ral-poly(ethylene glycol) (PEG) conjugate-loaded microspheres were prepared with poly(ε-caprolactone) (PCL) alone or with the blend of PCL and poly(D,L-lactide-co-glycolide) (PLGA) to provide controlled and sustained Ral release systems. Benefits of these formulations were evaluated on bone regeneration. Ral-loaded PCL microspheres had the highest encapsulation efficiency (70.7±5.0%) among all groups owing to high hydrophobic natures of both Ral and PCL. Cumulative amount of Ral released from Ral-PEG (1:2) conjugate-loaded PCL:PLGA (1:1) microspheres (26.9±8.8%) after 60days was significantly higher relative to other microsphere groups. This finding can be ascribed to two factors: i) Ral-PEG conjugation, resulting in increased water-solubility of Ral and increased degradation rates of PCL and PLGA with enhanced water penetration into the polymer matrix, and ii) usage of PLGA besides PCL in the carrier composition to benefit from less hydrophobic and faster degradable nature of PLGA in comparison to PCL. In vitro cytotoxicity studies performed using adipose-derived mesenchymal stem cells (ASCs) demonstrated that all microspheres were non-toxic. Evaluation of intensities of Alizarin red S staining conducted after 7 and 14days of incubation of ASCs in the release media of the different microsphere groups was performed with Image J analysis software. At day 7, it was observed that the matrix deposited by the cells cultivated in the release medium of Ral-PEG (1:2) conjugate-loaded PCL:PLGA (1:1) microspheres had significantly higher mineral content (26.78±6.23%) than that of the matrix deposited by the cells cultivated in the release media of the other microsphere groups except Ral-loaded PCL:PLGA (1:1) microsphere group. At day 14, Ral release from Ral-PEG (1:2) conjugate-loaded PCL:PLGA (1:1) microsphere group resulted with significantly higher mineralization of the matrix (32.31±1.85%) deposited by ASCs in comparison to all other microsphere groups. Alizarin red S staining results eventuated in parallel with the release results. Thus, it can be suggested that Ral-PEG (1:2) conjugate-loaded PCL:PLGA (1:1) microsphere formulation has a potential as an effective controlled drug delivery system for bone regeneration.

Design of Self-Assembling Protein-Polymer Conjugates

Protein-polymer conjugates are of particular interest for nanobiotechnology applications because of the various and complementary roles that each component may play in composite hybrid-materials. This chapter focuses on the design principles and applications of self-assembling protein-polymer conjugate materials. We address the general design methodology, from both synthetic and genetic perspective, conjugation strategies, protein vs. polymer driven self-assembly and finally, emerging applications for conjugate materials. By marrying proteins and polymers into conjugated bio-hybrid materials, materials scientists, chemists, and biologists alike, have at their fingertips a vast toolkit for material design. These inherently hierarchical structures give rise to useful patterning, mechanical and transport properties that may help realize new, more efficient materials for energy generation, catalysis, nanorobots, etc.

Potential Use of Biological Proteins for Liver Failure Therapy

Biological proteins have unlimited potential for use as pharmaceutical products due to their various biological activities, which include non-toxicity, biocompatibility, and biodegradability. Recent scientific advances allow for the development of novel innovative protein-based products that draw on the quality of their innate biological activities. Some of them hold promising potential for novel therapeutic agents/devices for addressing hepatic diseases such as hepatitis, fibrosis, and hepatocarcinomas. This review attempts to provide an overview of the development of protein-based products that take advantage of their biological activity for medication, and discusses possibilities for the therapeutic potential of protein-based products produced through different approaches to specifically target the liver (or hepatic cells: hepatocytes, hepatic stellate cells, liver sinusoidal endothelial cells, and Kupffer cells) in the treatment of hepatic diseases.

Vaginal lactoferrin administration before genetic amniocentesis decreases amniotic interleukin-6 levels

AIM

To verify the eventual efficacy of lactoferrin (LF), an iron-binding glycoprotein, to decrease the amniotic concentration of interleukin-6 (IL-6).

METHODS

We prospectively enrolled 60 Caucasian patients at the 16th week of their singleton physiological gestation. A vaginal compound containing 300 mg of LF was administered randomly 4 or 12 h prior to amniocentesis, as to obtain 3 groups: A, 20 untreated patients; B, 20 treated 4 h before amniocentesis; C, 20 treated 12 h before amniocentesis.

RESULTS

A normal karyotype was registered in all cases. The comparison of the distribution of IL-6 among the 3 groups showed a highly significant difference (p = 0.001). The difference between mean values of group B and both groups C and A was shown to be highly significant (p = 0.006 and p = 0.03, respectively). In contrast, there was no significant difference between mean values of groups A and C.

CONCLUSION

Vaginal LF administration decreases amniotic IL-6 concentration. We therefore suggest that the glycoprotein may exert a protective role against ominous pregnancy complications linked to an increased level of the cytokine, such as abortion secondary to amniocentesis.

Site-specific PEGylation of therapeutic proteins via optimization of both accessible reactive amino acid residues and PEG derivatives

Modification of accessible amino acid residues with poly(ethylene glycol) [PEG] is a widely used technique for formulating therapeutic proteins. In practice, site-specific PEGylation of all selected/engineered accessible nonessential reactive residues of therapeutic proteins with common activated PEG derivatives is a promising strategy to concomitantly improve pharmacokinetics, allow retention of activity, alleviate immunogenicity, and avoid modification isomers. Specifically, through molecular engineering of a therapeutic protein, accessible essential residues reactive to an activated PEG derivative are substituted with unreactive residues provided that protein activity is retained, and a limited number of accessible nonessential reactive residues with optimized distributions are selected/introduced. Subsequently, all accessible nonessential reactive residues are completely PEGylated with the activated PEG derivative in great excess. Branched PEG derivatives containing new PEG chains with negligible metabolic toxicity are more desirable for site-specific PEGylation. Accordingly, for the successful formulation of therapeutic proteins, optimization of the number and distributions of accessible nonessential reactive residues via molecular engineering can be integrated with the design of large-sized PEG derivatives to achieve site-specific PEGylation of all selected/engineered accessible reactive residues.

Polymeric conjugates for drug delivery

The field of polymer therapeutics has evolved over the past decade and has resulted in the development of polymer-drug conjugates with a wide variety of architectures and chemical properties. Whereas traditional non-degradable polymeric carriers such as poly(ethylene glycol) (PEG) and N-(2-hydroxypropyl methacrylamide) (HPMA) copolymers have been translated to use in the clinic, functionalized polymer-drug conjugates are increasingly being utilized to obtain biodegradable, stimuli-sensitive, and targeted systems in an attempt to further enhance localized drug delivery and ease of elimination. In addition, the study of conjugates bearing both therapeutic and diagnostic agents has resulted in multifunctional carriers with the potential to both "see and treat" patients. In this paper, the rational design of polymer-drug conjugates will be discussed followed by a review of different classes of conjugates currently under investigation. The design and chemistry used for the synthesis of various conjugates will be presented with additional comments on their potential applications and current developmental status.

Lactoferrin delivery systems: approaches for its more effective use

INTRODUCTION

Recently, pharmacotherapy has advanced extensively, but there are still many refractory diseases which cannot be solved fully by existing therapeutic agents. Therefore, alternative medicine and health foods are now attracting much attention, for example, lactoferrin (LF): a multifunctional glycoprotein. As LF is non-toxic and low-cost, its application in healthcare and therapeutics is expected to be widespread.

AREAS COVERED

In this review, LF's general basic features are described. The interaction of LF with its receptors activates the immune system, including cytokine production and balance. In particular, the immune activation of orally administered LF is considered as a new strategy for the treatment of refractory diseases, such as inflammatory bowel disease, virus infection and tumor metastasis. Also mentioned are the problems associated with the use of LF. As LF is degraded rapidly in the body due to enzymatic hydrolysis, high amounts or frequent dosing is required; an appropriate delivery system may improve these problems and increase its efficiency.

EXPERT OPINION

Chemical modifications, such as PEGylation, can enhance the stability of LF in the body, resulting in increased efficacy. Also, liposomes and enteric or microparticulate formulations can promote the function of LF in oral administration due to target site delivery and protection of LF from enzymatic hydrolysis. These delivery systems are expected to improve the utility of LF.

Comparison of tissue distribution of a PEGylated Radix Ophiopogonis polysaccharide in mice with normal and ischemic myocardium

PEGylation was found to be a promising approach to improve the anti-myocardial ischemic activity of Radix Ophiopogonis polysaccharide (ROP) by prolonging its retention in plasma. To fully evaluate the effectiveness and safety of this strategy, the tissue distribution of PEGylated ROP was investigated in this study. A long-circulating and bioactive PEGylated ROP with 1.04 mol 20-kDa mPEG per mol ROP ((1.04)P(20k)-R) was prepared by a moderate coupling reaction between the hydroxyl-activated ROP and the amino-terminated mPEG. Its tissue distribution in mice with normal and ischemic myocardium was studied and compared with ROP. The results show that the descending order of tissue distribution of (1.04)P(20k)-R ranked by AUC was kidney, lung, heart, liver, and brain in normal mice and kidney ≈ lung ≈ heart, liver and brain in mice with myocardial ischemia. With the exception of the heart, myocardial ischemia did not cause obvious changes in the distribution of (1.04)P(20k)-R in the other tissues studied. Owing to the enhanced permeability and retention effect caused by ischemia, the AUC of (1.04)P(20k)-R in ischemic hearts was approximately 1.6-fold greater than in normal hearts. Compared with ROP in rats, the distribution tendency of (1.04)P(20k)-R in mouse kidney, brain, and lung was reduced by approximately 42, 1.6, and 1.3 times, respectively, whereas it was increased by approximately 1.3-fold in the liver. The results of this study are highly instructive for the further pharmaceutical development of PEGylated ROP.

PEGylated lactoferrin enhances its hepatoprotective effects on acute liver injury induced by D-galactosamine and lipopolysaccharide in rats

Polyethylene glycol (PEG) is attached to proteins in order to increase their half-life in circulation and reduce their immunogenicity in vivo. The present study was conducted to examine whether two different sizes of PEGylated bovine lactoferrin (40k- and 20k-PEG-bLf) would enhance the protective effect of native bLf on liver injury induced by D-galactosamine (GalN) and lipopolysaccharide (LPS) in rats. The treatment of PEGylated bLf more remarkably prevented the elevation of serum levels of hepatic enzyme markers and inhibited inflammatory and hemorrhagic changes and hepatic apoptosis induced by GalN/LPS than native bLf. The treatment of PEGylated bLf more significantly inhibited the increased concentration of proinflammatory cytokines (TNF-alpha and IL-6) in serum caused by GaIN/LPS, and enhanced anti-inflammatory cytokine (IL-10) production more than native bLf. PEGylated bLf decreased serum levels of nitric oxide (NO) more than native bLf. These results indicate that PEGylated bLf inhibits more significantly the induction of inflammatory mediators such as cytokines and NO than native bLf, resulting in the enhancement of its prevention of fulminant liver failure induced by GalN/LPS in rats. The present study provided evidence that PEGylated bLf may offer a novel alternative therapy for the prevention of acute hepatic failure through its anti-inflammatory and immunomodulatory properties.