Transport across the blood-brain barrier of pluronic leptin

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

The blood-brain barrier (BBB) presents a tremendous challenge for the delivery of drugs to the central nervous system (CNS). This includes drugs that target brain receptors for the treatment of obesity and anorexia. Strategic drug delivery to brain (SDDB) is an approach that considers in depth the relations among the BBB, the candidate therapeutic, the CNS target, and the disease state to be treated. Here, we illustrate principles of SDDB with two different approaches to developing drugs based on leptin. In normal body weight humans and in non-obese rodents, leptin is readily transported across the BBB and into the CNS where it inhibits feeding and enhances thermogenesis. However, in obesity, the transport of leptin across the BBB is impaired, resulting in a resistance to leptin. As a result, it is difficult to treat obesity with leptin or its analogs that depend on the leptin transporter for access to the CNS. To treat obesity, we developed a leptin agonist modified by the addition of pluronic block copolymers (P85-leptin). P85-leptin retains biological activity and is capable of crossing the BBB by a mechanism that is not dependent on the leptin transporter. As such, P85-leptin is able to cross the BBB of obese mice at a rate similar to that of native leptin in lean mice. To treat anorexia, we developed a leptin antagonist modified by pegylation (PEG-MLA) that acts primarily by blocking the BBB transporter for endogenous, circulating leptin. This prevents blood-borne, endogenous leptin from entering the CNS, essentially mimicking the leptin resistance seen in obesity, and resulting in a significant increase in adiposity. These examples illustrate two strategies in which an understanding of the interactions among the BBB, CNS targets, and candidate therapeutics under physiologic and diseased conditions can be used to develop drugs effective for the treatment of brain disease.

Oral fatty acid signaling and intestinal lipid processing: support and supposition

There is increasing recognition that specialized processes once thought to be relatively isolated to the oral cavity (e.g., taste) and intestine (e.g., nutrient absorption) are better characterized as common and continuous. This is exemplified by accumulating evidence linking oral detection of dietary fats to their intestinal processing. This review first summarizes this literature focusing on purported gustatory signaling by free fatty acid stimulation and enterocyte lipid storage and mobilization in humans. It then willfully speculates on the possible functions of this integrated system. It is proposed that it may aid absorption of fat soluble nutrients, enhance acute energy intake, sustain intestinal function during long inter-meal intervals, modulate appetite and/or detoxify ingested compounds including free fatty acids.

Protein modification with amphiphilic block copoly(2-oxazoline)s as a new platform for enhanced cellular delivery

Several homopolymers, random copolymers and block copolymers based on poly(2-oxazoline)s (POx) were synthesized and conjugated to horseradish peroxidase (HRP) using biodegradable and nonbiodegradable linkers. These conjugates were characterized by amino group titration, polyacrylamide gel electrophoresis (PAGE), isoelectric focusing, enzymatic activity assay and conformation analysis. The conjugates contained on average from about one to two polymer chains per enzyme. From 70% to 90% of enzymatic activity was retained in most cases. Circular dichroism (CD) analysis revealed that HRP modification affected the secondary structure of the apoprotein but did not affect the tertiary structure and heme environment. Enhanced cellular uptake was found in the conjugates of two block copolymers using both MDCK cells and Caco-2 cells, but not in the conjugates of random copolymer and homopolymer. Conjugation with a block copolymer of 2-methyl-2-oxazoline and 2-butyl-2-oxazoline led to the highest cellular uptake as compared to other conjugates. Our data indicates that modification with amphiphilic POx has the potential to modulate and enhance cellular delivery of proteins.

In vivo methods to study uptake of nanoparticles into the brain

Several in vivo techniques have been developed to study and measure the uptake of CNS compounds into the brain. With these techniques, various parameters can be determined after drug administration, including the blood-to-brain influx constant (K_in), the permeability-surface area (PS) product, and the brain uptake index (BUI). These techniques have been mostly used for drugs that are expected to enter the brain via transmembrane diffusion or by carrier-mediated transcytosis. Drugs that have limitations in entering the brain via such pathways have been encapsulated in nanoparticles (based on lipids or synthetic polymers) to enhance brain uptake. Nanoparticles are different from CNS compounds in size, composition and uptake mechanisms. This has led to different methods and approaches to study brain uptake in vivo. Here we discuss the techniques generally used to measure nanoparticle uptake in addition to the techniques used for CNS compounds. Techniques include visualization methods, behavioral tests, and quantitative methods.

Pluronic-modified superoxide dismutase 1 attenuates angiotensin II-induced increase in intracellular superoxide in neurons

Overexpressing superoxide dismutase 1 (SOD1; also called Cu/ZnSOD), an intracellular superoxide (O(2)(*-))-scavenging enzyme, in central neurons inhibits angiotensin II (AngII) intraneuronal signaling and normalizes cardiovascular dysfunction in diseases associated with enhanced AngII signaling in the brain, including hypertension and heart failure. However, the blood-brain barrier and neuronal cell membranes impose a tremendous impediment for the delivery of SOD1 to central neurons, which hinders the potential therapeutic impact of SOD1 treatment on these diseases. To address this, we developed conjugates of SOD1 with poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer (Pluronic) (SOD1-P85 and SOD1-L81), which retained significant SOD1 enzymatic activity. The modified SOD1 effectively scavenged xanthine oxidase/hypoxanthine-derived O(2)(*-), as determined by HPLC and the measurement of 2-hydroxyethidium. Using catecholaminergic neurons, we observed an increase in neuronal uptake of SOD1-Pluronic after 1, 6, or 24h, compared to neurons treated with pure SOD1 or PEG-SOD1. Importantly, without inducing neuronal toxicity, SOD1-Pluronic conjugates significantly inhibited AngII-induced increases in intraneuronal O(2)(*-) levels. These data indicate that SOD1-Pluronic conjugates penetrate neuronal cell membranes, which results in elevated intracellular levels of functional SOD1. Pluronic conjugation may be a new delivery system for SOD1 into central neurons and therapeutically beneficial for AngII-related cardiovascular diseases.