The rapid recognition of intravenously injected colloidal carriers, such as liposomes and polymeric nanospheres from the blood by Kupffer cells, has initiated a surge of development for "Kupffer cell-evading" or long-circulating particles. Such carriers have applications in vascular drug delivery and release, site-specific targeting (passive as well as active targeting), as well as transfusion medicine. In this article we have critically reviewed and assessed the rational approaches in the design as well as the biological performance of such constructs. For engineering and design of long-circulating carriers, we have taken a lead from nature. Here, we have explored the surface mechanisms, which affords red blood cells long-circulatory lives and the ability of specific microorganisms to evade macrophage recognition. Our analysis is then centered where such strategies have been translated and fabricated to design a wide range of particulate carriers (e.g., nanospheres, liposomes, micelles, oil-in-water emulsions) with prolonged circulation and/or target specificity. With regard to the targeting issues, attention is particularly focused on the importance of physiological barriers and disease states.

Long-Circulating and Target-Specific Nanoparticles: Theory to Practice

In this study, the authors show that oligodendrocyte differentiation and remyelination after a CNS lesion coincides with a switch in microglial/macrophage polarization from a pro-inflammatory, M1, phenotype to an anti-inflammatory, M2, phenotype. This M2-dependant effect was in part mediated by secretion of the TGFβ family member, Activin-A.

M2 microglia and macrophages drive oligodendrocyte differentiation during CNS remyelination

https://www.cell.com/cell/pdf/S0092-8674(05)00394-6.pdf

IKKβ Couples Hepatocyte Death to Cytokine-Driven Compensatory Proliferation that Promotes Chemical Hepatocarcinogenesis

This review encompasses the most important advances in liver functions and hepatotoxicity and analyzes which mechanisms can be studied in vitro. In a complex architecture of nested, zonated lobules, the liver consists of approximately 80 % hepatocytes and 20 % non-parenchymal cells, the latter being involved in a secondary phase that may dramatically aggravate the initial damage. Hepatotoxicity, as well as hepatic metabolism, is controlled by a set of nuclear receptors (including PXR, CAR, HNF-4α, FXR, LXR, SHP, VDR and PPAR) and signaling pathways. When isolating liver cells, some pathways are activated, e.g., the RAS/MEK/ERK pathway, whereas others are silenced (e.g. HNF-4α), resulting in up- and downregulation of hundreds of genes. An understanding of these changes is crucial for a correct interpretation of in vitro data. The possibilities and limitations of the most useful liver in vitro systems are summarized, including three-dimensional culture techniques, co-cultures with non-parenchymal cells, hepatospheres, precision cut liver slices and the isolated perfused liver. Also discussed is how closely hepatoma, stem cell and iPS cell-derived hepatocyte-like-cells resemble real hepatocytes. Finally, a summary is given of the state of the art of liver in vitro and mathematical modeling systems that are currently used in the pharmaceutical industry with an emphasis on drug metabolism, prediction of clearance, drug interaction, transporter studies and hepatotoxicity. One key message is that despite our enthusiasm for in vitro systems, we must never lose sight of the in vivo situation. Although hepatocytes have been isolated for decades, the hunt for relevant alternative systems has only just begun.

/pdf/recent-advances-in-2d-and-3d-in-vitro-systems-using-primary-46n7hrqknx.pdf

Recent advances in 2D and 3D in vitro systems using primary hepatocytes, alternative hepatocyte sources and non-parenchymal liver cells and their use in investigating mechanisms of hepatotoxicity, cell signaling and ADME.

Nanoparticle-liver interactions: Cellular uptake and hepatobiliary elimination

Blockade of phagocytosis and selective elimination of macrophages (m phi s) are generally accepted procedures for gaining knowledge about the function of m phi s in vivo. This study demonstrates that intravenous injection of gadolinium chloride (GdCl3) not only blocks phagocytosis by rat liver m phi s (Kupffer cells) but also selectively eliminates the large m phi s situated in the periportal zone of the liver acinus. Repopulation of m phi s starts at 4 days after injection. During repopulation, m phi s are less vulnerable to GdCl3. When repopulation is complete, the new m phi s show the same vulnerability as the original ones. Splenic m phi s are less vulnerable to GdCl3 because only some of the red pulp m phi s transiently disappear. The white pulp m phi s are not affected. Repopulation occurs sooner than in liver. These results indicate that administration of GdCl3 is a suitable approach to studying the in vivo function of large Kupffer cells.

Heterogeneity of rat liver and spleen macrophages in gadolinium chloride-induced elimination and repopulation.

To compare histochemical and biochemical determinations of enzyme activities, enzymehistochemical procedures are applied to sections of pellets of subcellular fractions. These investigations are of value to determine the subcellular localization of histochemically demonstrable enzyme activities and to test the homogeneity of an isolated fraction. In homogenating duckling liver a great part of the endothelial cells is not destructed and consequently is found in the nuclear fraction. Kupffer cell lysosomes land in the heavy mitochondrial fraction, whereas hepatocyte lysosomes are chiefly found in the light mitochondrial fraction. β-Glucuronidase activity shows a preferentially microsomal localization. Application of enzymehistochemical staining reactions to discontinuous gradients and comparison with biochemical data provides additional information about the validity of an enzymehistochemical reaction. In rat liver the tetrazolium reductases show a distinctly dual localization: activity in the mitochondrial band and in microsomal bands. As to their localization in different bands of the gradients non-specific esterases demonstrate a clear pH-dependency.

Application of enzyme-histochemical methods to isolated subcellular-fractions and to sucrose-ficoll density gradients - contribution to comparison of histochemical and biochemical data

1. Pretreatment of frozen cryostat sections with formaldehyde or calcium ions inhibits diffusion of the plasma membrane enzymes 5′-nucleotidase, ATP-ase and alkaline phosphatase during incubation. 2. Treatment of fixed sections with different kinds of buffer at 37°C induces diffusion of enzyme activity from the plasma membrane to other sites of the section and into the incubation medium. This buffer influence depends on temperature: at 4°C only a slight diffusion occurs. Addition of phospholipase C, digitonin or taurocholate to the buffer opposes the buffer effect. 3. Pretreatment of frozen cryostat sections with a mixture of equal parts of chloroform and acetone gives a good fixation of the plasma membrane enzymes 5′-nucleotidase, ATP-ase, alkaline phosphatase and leucyl-β-naphthylamidase. During this treatment the different kinds of lipids present in the membrane are extracted equally. After this fixation buffer treatment does not cause a visible diffusion of enzyme activity in the section. Only a slight diffusion (1 till 7 percent) into the buffer solution takes place. 4. The mentioned treatments open up possibilities to get insight into the membrane anchorage of plasma membrane enzymes.

F. W. J. Dijkhuis

Papers

Heterogeneity of rat liver and spleen macrophages in gadolinium chloride-induced elimination and repopulation.

Application of enzyme-histochemical methods to isolated subcellular-fractions and to sucrose-ficoll density gradients - contribution to comparison of histochemical and biochemical data

Influence of fixation and buffer treatment on the release of enzymes from the plasma membrane.