Principles of strategic drug delivery to the brain (SDDB): development of anorectic and orexigenic analogs of leptin

Nose-to-brain delivery of nanotherapeutics: Transport mechanisms and applications

The blood-brain barrier presents a key limitation to the administration of therapeutic molecules for the treatment of brain disease. While drugs administered orally or intravenously must cross this barrier to reach brain targets, the unique anatomical structure of the olfactory system provides a route to deliver drugs directly to the brain. Entering the brain via receptor, carrier, and adsorption-mediated transcytosis in the nasal olfactory and trigeminal regions has the potential to increase drug delivery. In this review, we introduce the physiological and anatomical structures of the nasal cavity, and summarize the possible modes of transport and the relevant receptors and carriers in the nose-to-brain pathway. Additionally, we provide examples of nanotherapeutics developed for intranasal drug delivery to the brain. Further development of nanoparticles that can be applied to intranasal delivery systems promises to improve drug efficacy and reduce drug resistance and adverse effects by increasing molecular access to the brain. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease.

COVID-19 Severity in Obesity: Leptin and Inflammatory Cytokine Interplay in the Link Between High Morbidity and Mortality

Obesity is one of the foremost risk factors in coronavirus infection resulting in severe illness and mortality as the pandemic progresses. Obesity is a well-known predisposed chronic inflammatory condition. The dynamics of obesity and its impacts on immunity may change the disease severity of pneumonia, especially in acute respiratory distress syndrome, a primary cause of death from SARS-CoV-2 infection. The adipocytes of adipose tissue secret leptin in proportion to individuals’ body fat mass. An increase in circulating plasma leptin is a typical characteristic of obesity and correlates with a leptin-resistant state. Leptin is considered a pleiotropic molecule regulating appetite and immunity. In immunity, leptin functions as a cytokine and coordinates the host’s innate and adaptive responses by promoting the Th1 type of immune response. Leptin induced the proliferation and functions of antigen-presenting cells, monocytes, and T helper cells, subsequently influencing the pro-inflammatory cytokine secretion by these cells, such as TNF-α, IL-2, or IL-6. Leptin scarcity or resistance is linked with dysregulation of cytokine secretion leading to autoimmune disorders, inflammatory responses, and increased susceptibility towards infectious diseases. Therefore, leptin activity by leptin long-lasting super active antagonist’s dysregulation in patients with obesity might contribute to high mortality rates in these patients during SARS-CoV-2 infection. This review systematically discusses the interplay mechanism between leptin and inflammatory cytokines and their contribution to the fatal outcomes in COVID-19 patients with obesity.

Preparation and characterization of PEGylated liposomal Doxorubicin targeted with leptin-derived peptide and evaluation of their anti-tumor effects, in vitro and in vivo in mice bearing C26 colon carcinoma

Employing targeting ligands on the surface of liposomes has the great potential to improve therapeutic efficacy and decreases off-target effects of liposomal formulations. In the present study, a leptin-derived peptide (Lp31) was evaluated to optimize the therapeutic efficacy of PEGylated liposomal Doxorubicin (PLD, Caelyx®). Leptin is an appetite regulatory hormone that is secreted into the blood circulation by the adipose tissue and it functions via its over expressed receptors (Ob-R) in a wide variety of cancers. Lp31, as targeting ligand, was conjugated to Maleimide-PEG2000-DSPE and then post-inserted into Caelyx. The anti-tumor activity and therapeutic efficacy of leptin modified Caelyx were evaluated and compared with Caelyx. The in vitro experiments demonstrated enhanced cytotoxicity and cellular uptake of Lp31-targeted Caelyx in C26 cell line compared to Caelyx. In BALB/c mice bearing C-26 murine carcinoma, Lp31 modified Caelyx groups exhibited significantly higher doxorubicin concentration at tumor tissue. Furthermore, Lp31 modified Caelyx at the dose of 10 mg/kg resulted in significant tumor growth inhibition and enhanced survival time compared to Caelyx. According to these results, the novel Lp31-liposomal doxorubicin offers great promise for the treatment of colon cancer and merits further investigation.

Treating brain diseases using systemic parenterally-administered protein therapeutics: Dysfunction of the brain barriers and potential strategies

The parenteral administration of protein therapeutics is increasingly gaining importance for the treatment of human diseases. However, the presence of practically impermeable blood-brain barriers greatly restricts access of such pharmaceutics to the brain. Treating brain disorders with proteins thus remains a great challenge, and the slow clinical translation of these therapeutics may be largely ascribed to the lack of appropriate brain delivery system. Exploring new approaches to deliver proteins to the brain by circumventing physiological barriers is thus of great interest. Moreover, parallel advances in the molecular neurosciences are important for better characterizing blood-brain interfaces, particularly under different pathological conditions (e.g., stroke, multiple sclerosis, Parkinson's disease, and Alzheimer's disease). This review presents the current state of knowledge of the structure and the function of the main physiological barriers of the brain, the mechanisms of transport across these interfaces, as well as alterations to these concomitant with brain disorders. Further, the different strategies to promote protein delivery into the brain are presented, including the use of molecular Trojan horses, the formulation of nanosystems conjugated/loaded with proteins, protein-engineering technologies, the conjugation of proteins to polymers, and the modulation of intercellular junctions. Additionally, therapeutic approaches for brain diseases that do not involve targeting to the brain are presented (i.e., sink and scavenging mechanisms).

Governing Transport Principles for Nanotherapeutic Application in the Brain

Neurological diseases account for a significant portion of the global disease burden. While research efforts have identified potential drugs or drug targets for neurological diseases, most therapeutic platforms are still ineffective at reaching the target location selectively and with high yield. Restricted transport, including passage across the blood-brain barrier, through the brain parenchyma, and into specific cells, is a major cause of ineffective therapeutic delivery. However, nanotechnology is a promising, tailorable platform for overcoming these transport barriers and improving therapeutic delivery to the brain. We provide a transport-oriented analysis of nanotechnology's ability to navigate these transport barriers in the brain. We also provide an opinion on the need for technology development for increasing our capacity to characterize and quantify nanoparticle passage through each transport barrier. Finally, we highlight the importance of incorporating the effect of disease, metabolic state, and regional dependencies to better understand transport of nanotherapeutics in the brain.

The role of IL-6 in exercise-induced anorexia in normal-weight boys

Our previous study showed that interleukin-6 (IL-6) is associated with suppression of appetite after high-intensity exercise (HIEX), but an independent role in food intake (FI) was not defined. We hypothesized that IL-6 suppresses appetite and FI, independently of appetite hormones, after HIEX in normal-weight (NW) boys. We investigated the effect of HIEX, with and without the inflammation inhibitor ibuprofen (IBU), on IL-6, other biomarkers of inflammation and appetite, FI, and ratings of appetite in NW boys. Fifteen NW boys (aged 13–18 years) were randomly assigned in a crossover design to 4 sessions: (i) water and rest, (ii) IBU and rest, (iii) water and HIEX, and (iv) IBU and HIEX. HIEX consisted of three 10-min bouts of exercise at 75% of maximal oxygen uptake with 90 s of active rest between bouts. IBU (300 mg) was given as a liquid suspension. FI, ratings of appetite, and plasma biomarkers of appetite, inflammation, stress, and glucose control were measured. FI was not affected by HIEX or IBU. Appetite increased over time (p = 0.002) but was lower after HIEX (p < 0.001) and not affected by IBU. HIEX, but not IBU, resulted in higher levels of IL-6 (p < 0.001) and cortisol (p < 0.001) and lower active ghrelin (p < 0.001). IL-6 correlated with active ghrelin (r = 0.37; p = 0.036) and cortisol (r = 0.26; p = 0.049). An independent role for IL-6 in appetite suppression was not supported. However, IL-6 was correlated with active ghrelin and cortisol, thus potentially mediating appetite via these interactions.

Development of inhibitors of receptor protein tyrosine phosphatase β/ζ (PTPRZ1) as candidates for CNS disorders

A new series of blood-brain barrier permeable molecules designed to mimic the activity of Pleiotrophin in the CNS has been designed and synthesized. These compounds exert their action by interacting with the intracellular domain PD1 of the Protein Tyrosine-Phosphatase Receptor Z1 (PTPRZ1), and inhibiting its tyrosine phosphatase activity. The most potent compounds 10a and 12b (IC₅₀ = 0,1 μM) significantly increase the phosphorylation of key tyrosine residues of PTPRZ1 substrates involved in neuronal survival and differentiation, and display protective effects against amphetamine-induced toxicity. Docking and molecular dynamics experiments have been used to analyze the binding mode and to explain the observed selectivity against PTP1B. An In vivo experiment has demonstrated that 10a can cross the BBB, thus promoting the possibility of moving forward these candidates for the development of drugs for the treatment of CNS disorders, such as drug addiction and neurodegenerative diseases.

Blood-Brain Barriers in Obesity

After decades of rapid increase, the rate of obesity in adults in the USA is beginning to slow and the rate of childhood obesity is stabilizing. Despite these improvements, the obesity epidemic continues to be a major health and financial burden. Obesity is associated with serious negative health outcomes such as cardiovascular disease, type II diabetes, and, more recently, cognitive decline and various neurodegenerative dementias such as Alzheimer's disease. In the past decade, major advancements have contributed to the understanding of the role of the central nervous system (CNS) in the development of obesity and how peripheral hormonal signals modulate CNS regulation of energy homeostasis. In this article, we address how obesity affects the structure and function of the blood-brain barrier (BBB), the impact of obesity on Alzheimer's disease, the effects of obesity on circulating proteins and their transport into the brain, and how these changes can potentially be reversed by weight loss.

Pathways and progress in improving drug delivery through the intestinal mucosa and blood-brain barriers

One of the major hurdles in developing therapeutic agents is the difficulty in delivering drugs through the intestinal mucosa and blood-brain barriers (BBB). The goal here is to describe the general structures of the biological barriers and the strategies to enhance drug delivery across these barriers. Prodrug methods used to improve drug penetration via the transcellular pathway have been successfully developed, and some prodrugs have been used to treat patients. The use of transporters to improve absorption of some drugs (e.g., antiviral agents) has also been successful in treating patients. Other methods, including blocking the efflux pumps to improve transcellular delivery, and modulation of cell-cell adhesion in the intercellular junctions to improve paracellular delivery across biological barriers, are still in the investigational stage.

PASylation of Murine Leptin Leads to Extended Plasma Half-Life and Enhanced in Vivo Efficacy

Leptin plays a central role in the control of energy homeostasis and appetite and, thus, has attracted attention for therapeutic approaches in spite of its limited pharmacological activity owing to the very short circulation in the body. To improve drug delivery and prolong plasma half-life, we have fused murine leptin with Pro/Ala/Ser (PAS) polypeptides of up to 600 residues, which adopt random coil conformation with expanded hydrodynamic volume in solution and, consequently, retard kidney filtration in a similar manner as polyethylene glycol (PEG). Relative to unmodified leptin, size exclusion chromatography and dynamic light scattering revealed an approximately 21-fold increase in apparent size and a much larger molecular diameter of around 18 nm for PAS(600)-leptin. High receptor-binding activity for all PASylated leptin versions was confirmed in BIAcore measurements and cell-based dual-luciferase assays. Pharmacokinetic studies in mice revealed a much extended plasma half-life after ip injection, from 26 min for the unmodified leptin to 19.6 h for the PAS(600) fusion. In vivo activity was investigated after single ip injection of equimolar doses of each leptin version. Strongly increased and prolonged hypothalamic STAT3 phosphorylation was detected for PAS(600)-leptin. Also, a reduction in daily food intake by up to 60% as well as loss in body weight of >10% lasting for >5 days was observed, whereas unmodified leptin was merely effective for 1 day. Notably, application of a PASylated superactive mouse leptin antagonist (SMLA) led to the opposite effects. Thus, PASylated leptin not only provides a promising reagent to study its physiological role in vivo but also may offer a superior drug candidate for clinical therapy.

Cell penetrating peptides: efficient vectors for delivery of nanoparticles, nanocarriers, therapeutic and diagnostic molecules

Efficient delivery of therapeutic and diagnostic molecules to the cells and tissues is a difficult challenge. The cellular membrane is very effective in its role as a selectively permeable barrier. While it is essential for cell survival and function, also presents a major barrier for intracellular delivery of cargo such as therapeutic and diagnostic agents. In recent years, cell-penetrating peptides (CPPs), that are relatively short cationic and/or amphipathic peptides, received great attention as efficient cellular delivery vectors due to their intrinsic ability to enter cells and mediate uptake of a wide range of macromolecular cargo such as plasmid DNA (pDNA), small interfering RNA (siRNAs), drugs, and nanoparticulate pharmaceutical carriers. This review discusses the various uptake mechanisms of these peptides. Furthermore, we discuss recent advances in the use of CPP for the efficient delivery of nanoparticles, nanocarriers, DNA, siRNA, and anticancer drugs to the cells. In addition, we have been highlighting new results for improving endosomal escape of CPP-cargo molecules. Finally, pH-responsive and activable CPPs for tumor-targeting therapy have been described.

Agile delivery of protein therapeutics to CNS

A variety of therapeutic proteins have shown potential to treat central nervous system (CNS) disorders. Challenge to deliver these protein molecules to the brain is well known. Proteins administered through parenteral routes are often excluded from the brain because of their poor bioavailability and the existence of the blood-brain barrier (BBB). Barriers also exist to proteins administered through non-parenteral routes that bypass the BBB. Several strategies have shown promise in delivering proteins to the brain. This review, first, describes the physiology and pathology of the BBB that underscore the rationale and needs of each strategy to be applied. Second, major classes of protein therapeutics along with some key factors that affect their delivery outcomes are presented. Third, different routes of protein administration (parenteral, central intracerebroventricular and intraparenchymal, intranasal and intrathecal) are discussed along with key barriers to CNS delivery associated with each route. Finally, current delivery strategies involving chemical modification of proteins and use of particle-based carriers are overviewed using examples from literature and our own work. Whereas most of these studies are in the early stage, some provide proof of mechanism of increased protein delivery to the brain in relevant models of CNS diseases, while in few cases proof of concept had been attained in clinical studies. This review will be useful to broad audience of students, academicians and industry professionals who consider critical issues of protein delivery to the brain and aim developing and studying effective brain delivery systems for protein therapeutics.

Advances in understanding the interrelations between leptin resistance and obesity

Obesity, which has developed into a global epidemic, is a risk factor in most chronic diseases and some forms of malignancy. The discovery of leptin in 1994 has opened a new field in obesity research. Currently, we know that leptin is the primary signal from energy stores and exerts negative feedback effects on energy intake. However, most individuals with diet-induced obesity (DIO) develop leptin resistance, which is characterized by elevated circulating leptin levels and decreased leptin sensitivity. To date, though various mechanisms have been proposed to explain leptin resistance, the exact mechanisms of leptin resistance in obesity are poorly understood. Consequently, it's an important issue worth discussing regarding what the exact interrelations between leptin resistance and obesity are. Here, we review the latest advancements in the molecular mechanisms of leptin resistance and the exact interrelations between leptin resistance, obesity, and obesity-related diseases, in order to supply new ideas for the study of obesity.

Targeting midkine and pleiotrophin signalling pathways in addiction and neurodegenerative disorders: recent progress and perspectives

Midkine (MK) and pleiotrophin (PTN) are two neurotrophic factors that are highly up-regulated in different brain regions after the administration of various drugs of abuse and in degenerative areas of the brain. A deficiency in both MK and PTN has been suggested to be an important genetic factor, which confers vulnerability to the development of the neurodegenerative disorders associated with drugs of abuse in humans. In this review, evidence demonstrating that MK and PTN limit the rewarding effects of drugs of abuse and, potentially, prevent drug relapse is compiled. There is also convincing evidence that MK and PTN have neuroprotective effects against the neurotoxicity and development of neurodegenerative disorders induced by drugs of abuse. Exogenous administration of MK and/or PTN into the CNS by means of non-invasive methods is proposed as a novel therapeutic strategy for addictive and neurodegenerative diseases. Identification of new molecular targets downstream of the MK and PTN signalling pathways or pharmacological modulation of those already known may also provide a more traditional, but probably effective, therapeutic strategy for treating addictive and neurodegenerative disorders.

LINKED ARTICLES

This article is part of a themed section on Midkine. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-4.

Conjugates of superoxide dismutase 1 with amphiphilic poly(2-oxazoline) block copolymers for enhanced brain delivery: synthesis, characterization and evaluation in vitro and in vivo

Superoxide dismutase 1 (SOD1) efficiently catalyzes dismutation of superoxide, but its poor delivery to the target sites in the body, such as brain, hinders its use as a therapeutic agent for superoxide-associated disorders. Here to enhance the delivery of SOD1 across the blood-brain barrier (BBB) and in neurons the enzyme was conjugated with poly(2-oxazoline) (POx) block copolymers, P(MeOx-b-BuOx) or P(EtOx-b-BuOx), composed of (1) hydrophilic 2-methyl-2-oxazoline (MeOx) or 2-ethyl-2-oxazoline (EtOx) and (2) hydrophobic 2-butyl-2-oxazoline (BuOx) repeating units. The conjugates contained from 2 to 3 POx chains joining the protein amino groups via cleavable -(ss)- or noncleavable -(cc)- linkers at the BuOx block terminus. They retained 30% to 50% of initial SOD1 activity, were conformationally and thermally stable, and assembled in 8 or 20 nm aggregates in aqueous solution. They had little if any toxicity to CATH.a neurons and displayed enhanced uptake in these neurons as compared to native or PEGylated SOD1. Of the two conjugates, SOD1-(cc)-P(MeOx-b-BuOx) and SOD1-(cc)-P(EtOx-b-BuOx), compared, the latter was entering cells 4 to 7 times faster and at 6 h colocalized predominantly with endoplasmic reticulum (41 ± 3%) and mitochondria (21 ± 2%). Colocalization with endocytosis markers and pathway inhibition assays suggested that it was internalized through lipid raft/caveolae, also employed by the P(EtOx-b-BuOx) copolymer. The SOD activity in cell lysates and ability to attenuate angiotensin II (Ang II)-induced superoxide in live cells were increased for this conjugate compared to SOD1 and PEG-SOD1. Studies in mice showed that SOD1-POx had ca. 1.75 times longer half-life in blood than native SOD1 (28.4 vs 15.9 min) and after iv administration penetrated the BBB significantly faster than albumin to accumulate in brain parenchyma. The conjugate maintained high stability both in serum and in brain (77% vs 84% at 1 h postinjection). Its amount taken up by the brain reached a maximum value of 0.08% ID/g (percent of the injected dose taken up per gram of brain) 4 h postinjection. The entry of SOD1-(cc)-P(EtOx-b-BuOx) to the brain was mediated by a nonsaturable mechanism. Altogether, SOD1-POx conjugates are promising candidates as macromolecular antioxidant therapies for superoxide-associated diseases such as Ang II-induced neurocardiovascular diseases.