Hepatic stellate cells uptake of retinol associated with retinol-binding protein or with bovine serum albumin

Understanding Nanomaterial-Liver Interactions to Facilitate the Development of Safer Nanoapplications

Nanomaterials (NMs) are widely used in commercial and medical products, such as cosmetics, vaccines, and drug carriers. Exposure to NMs via various routes such as dermal, inhalation, and ingestion has been shown to gain access to the systemic circulation, resulting in the accumulation of NMs in the liver. The unique organ structures and blood flow features facilitate the liver sequestration of NMs, which may cause adverse effects in the liver. Currently, most in vivo studies are focused on NMs accumulation at the organ level and evaluation of the gross changes in liver structure and functions, however, cell-type-specific uptake and responses, as well as the molecular mechanisms at cellular levels leading to effects at organ levels are lagging. Herein, the authors systematically review diverse interactions of NMs with the liver, specifically on major liver cell types including Kupffer cells (KCs), liver sinusoidal endothelial cells (LSECs), hepatic stellate cells (HSCs), and hepatocytes as well as the detailed molecular mechanisms involved. In addition, the knowledge gained on nano-liver interactions that can facilitate the development of safer nanoproducts and nanomedicine is also reviewed.

Hepatic Retinyl Ester Hydrolases and the Mobilization of Retinyl Ester Stores

For mammals, vitamin A (retinol and metabolites) is an essential micronutrient that is required for the maintenance of life. Mammals cannot synthesize vitamin A but have to obtain it from their diet. Resorbed dietary vitamin A is stored in large quantities in the form of retinyl esters (REs) in cytosolic lipid droplets of cells to ensure a constant supply of the body. The largest quantities of REs are stored in the liver, comprising around 80% of the body’s total vitamin A content. These hepatic vitamin A stores are known to be mobilized under times of insufficient dietary vitamin A intake but also under pathological conditions such as chronic alcohol consumption and different forms of liver diseases. The mobilization of REs requires the activity of RE hydrolases. It is astounding that despite their physiological significance little is known about their identities as well as about factors or stimuli which lead to their activation and consequently to the mobilization of hepatic RE stores. In this review, we focus on the recent advances for the understanding of hepatic RE hydrolases and discuss pathological conditions which lead to the mobilization of hepatic RE stores.

ATGL and CGI-58 are lipid droplet proteins of the hepatic stellate cell line HSC-T6

Lipid droplets (LDs) of hepatic stellate cells (HSCs) contain large amounts of vitamin A [in the form of retinyl esters (REs)] as well as other neutral lipids such as TGs. During times of insufficient vitamin A availability, RE stores are mobilized to ensure a constant supply to the body. To date, little is known about the enzymes responsible for the hydrolysis of neutral lipid esters, in particular of REs, in HSCs. In this study, we aimed to identify LD-associated neutral lipid hydrolases by a proteomic approach using the rat stellate cell line HSC-T6. First, we loaded cells with retinol and FAs to promote lipid synthesis and deposition within LDs. Then, LDs were isolated and lipid composition and the LD proteome were analyzed. Among other proteins, we found perilipin 2, adipose TG lipase (ATGL), and comparative gene identification-58 (CGI-58), known and established LD proteins. Bioinformatic search of the LD proteome for α/β-hydrolase fold-containing proteins revealed no yet uncharacterized neutral lipid hydrolases. In in vitro activity assays, we show that rat (r)ATGL, coactivated by rat (r)CGI-58, efficiently hydrolyzes TGs and REs. These findings suggest that rATGL and rCGI-58 are LD-resident proteins in HSCs and participate in the mobilization of both REs and TGs.

Bovine immunoglobulin/protein isolate binds pro-inflammatory bacterial compounds and prevents immune activation in an intestinal co-culture model

Intestinal barrier dysfunction is associated with chronic gastrointestinal tract inflammation and diseases such as IBD and IBS. Serum-derived bovine immunoglobulin/protein isolate (SBI) is a specially formulated protein preparation (>90%) for oral administration. The composition of SBI is greater than 60% immunoglobulin including contributions from IgG, IgA, and IgM. Immunoglobulin within the lumen of the gut has been recognized to have anti-inflammatory properties and is involved in maintaining gut homeostasis. The binding of common intestinal antigens (LPS and Lipid A) and the ligand Pam3CSK4, by IgG, IgA, and IgM in SBI was shown using a modified ELISA technique. Each of these antigens stimulated IL-8 and TNF-α cytokine production by THP-1 monocytes. Immune exclusion occurred as SBI (≤50 mg/mL) bound free antigen in a dose dependent manner that inhibited cytokine production by THP-1 monocytes in response to 10 ng/mL LPS or 200 ng/mL Lipid A. Conversely, Pam3CSK4 stimulation of THP-1 monocytes was unaffected by SBI/antigen binding. A co-culture model of the intestinal epithelium consisted of a C2BBe1 monolayer separating an apical compartment from a basal compartment containing THP-1 monocytes. The C2BBe1 monolayer was permeabilized with dimethyl palmitoyl ammonio propanesulfonate (PPS) to simulate a damaged epithelial barrier. Results indicate that Pam3CSK4 was able to translocate across the PPS-damaged C2BBe1 monolayer. However, binding of Pam3CSK4 by immunoglobulins in SBI prevented Pam3CSK4 translocation across the damaged C2BBe1 barrier. These results demonstrated steric exclusion of antigen by SBI which prevented apical to basal translocation of antigen due to changes in the physical properties of Pam3CSK4, most likely as a result of immunoglobulin binding. This study demonstrates that immunoglobulins in SBI can reduce antigen-associated inflammation through immune and steric exclusion mechanisms and furthers the mechanistic understanding of how SBI might improve immune status and reduce inflammation in various intestinal disease states.

Corona-directed nucleic acid delivery into hepatic stellate cells for liver fibrosis therapy

Strategies to modify nanoparticles with biological ligands for targeted drug delivery in vivo have been widely studied but met with limited clinical success. A possible reason is that, in the blood circulation, serum proteins could rapidly form a layer of protein "corona" on the vehicle surface, which might block the modified ligands and hamper their targeting functions. We speculate that strategies for drug delivery can be designed based upon elegant control of the corona formation on the vehicle surfaces. In this study, we demonstrate a retinol-conjugated polyetherimine (RcP) nanoparticle system that selectively recruited the retinol binding protein 4 (RBP) in its corona components. RBP was found to bind retinol, and direct the antisense oligonucleotide (ASO)-laden RcP carrier to hepatic stellate cells (HSC), which play essential roles in the progression of hepatic fibrosis. In both mouse fibrosis models, induced by carbon tetrachloride (CCl4) and bile duct ligation (BDL), respectively, the ASO-laden RcP particles effectively suppressed the expression of type I collagen (collagen I), and consequently ameliorated hepatic fibrosis. Such findings suggest that this delivery system, designed to exploit the power of corona proteins, can serve as a promising tool for targeted delivery of therapeutic agents for the treatment of hepatic fibrosis.

Interaction of zinc, ascorbic acid, and folic acid in glycation with albumin as protein model

Using albumin as model, we conducted series of in vitro glycation experiments to examine role of zinc in glycation using glucose at 4-100 mg/ml, incubations at 37°C or 60°C, duration of 2 or 4 weeks and in presence of zinc or ascorbic acid (AA) or folic acid (FA). Modifications of bovine serum albumin (BSA) were examined by using fluorescence of advanced glycation end products (AGEs) and dityrosine, UV, and Fourier transformed infrared spectroscopy. Adding zinc (0 to 768.5 μmol/l) resulted in significant inhibition of albumin glycation by glucose with a linear fit, y = -0·0895x + 230·99(R² = 0·7676, p = 0·013). The glycation by fructose was greater than that of glucose with stronger inhibitory effect by zinc in fructose-glycation (t= -5.8, p=0.002). Addition of zinc significantly decreased fluorescence as seen in Zn + FA or Zn + AA sets as compared to sets of FA alone (p=0.00056) or AA alone (p=0.037). The fluorescence for dityrosine and AGE had a correlation of 0.897 (p<0.01). The data from fluorescence, UV, and FTIR spectra collectively suggested inhibitory effect of zinc in BSA glycation alone or in presence of FA and AA, showing new dimension for the protective action of zinc in hyperglycemic conditions.

Aflatoxin B1 albumin adducts in plasma and aflatoxin M1 in urine are associated with plasma concentrations of vitamins A and E

BACKGROUND

Although aflatoxin exposure has been associated with micronutrient deficiency in animals, there are few investigations on the effects of aflatoxin exposure on micronutrient metabolism in humans.

OBJECTIVE

To examine the relationship between aflatoxin B1 (AFB1) albumin adducts (AF-ALB) in plasma and the aflatoxin M1 (AFM1) metabolite in urine and plasma concentrations of retinol (vitamin A) and alpha-tocopherol (vitamin E) in Ghanaians.

METHODS

A cross-sectional study of 147 adult participants was conducted. Blood and urine samples were tested for aflatoxin and vitamins A and E levels.

RESULTS

Multivariable analysis showed that participants with high AF-ALB (>or=0.80 pmol/mg albumin) had increased odds of having vitamin A deficiency compared to those with lower AF-ALB [Odds Ratio (OR)=2.61; CI=1.03-6.58; p=0.04]. Participants with high AF-ALB also showed increased odds of having vitamin E deficiency but this was not statistically significant (OR=2.4; CI=0.96-6.05; p=0.06). Conversely, those with higher AFM1 values had a statistically nonsignificant reduced odds of having vitamin A deficiency (OR=0.31; CI=0.09-1.02; p=0.05) and a statistically significant reduced odds of having vitamin E deficiency (OR=0.31; CI=0.10-0.97; p=0.04). Participants with high AF-ALB or high AFM1 (>or=437.95 pg/dL creatinine) were almost 6 times more likely to be hepatitis B virus surface antigen (HBsAg)-positive (OR=5.88; CI=1.71-20.14; p=0.005) and (OR=5.84; CI=1.15-29.54; p=0.03) respectively.

CONCLUSIONS

These data indicate that aflatoxin may modify plasma micronutrient status. Thus, preventing aflatoxin exposure may reduce vitamin A and E deficiencies.

Targeted delivery of drugs for liver fibrosis

Liver fibrosis and its end stage disease cirrhosis are a major cause of mortality and morbidity around the world. There is no effective pharmaceutical intervention for liver fibrosis at present. Many drugs that show potent antifibrotic activities in vitro often show only minor effects in vivo because of insufficient concentrations of drugs accumulating around the target cell and their adverse effects as a result of affecting other non-target cells. Hepatic stellate cells (HSC) play a critical role in the fibrogenesis of liver, so they are the target cells of antifibrotic therapy. Several kinds of targeted delivery system that could target the receptors expressed on HSC have been designed, and have shown an attractive targeted potential in vivo. After being carried by these delivery systems, many agents showed a powerful antifibrotic effect in animal models of liver fibrosis. These targeted delivery systems provide a new pathway for the therapy of liver fibrosis. The characteristics of theses targeted carriers are reviewed in this paper.

Lycopene isomerisation and storage in an in vitro model of murine hepatic stellate cells

BACKGROUND

Lycopene is a carotenoid whose biological activities and protective effect on prostate and breast cancer have been described, but little is known on its extra-intestinal metabolism and storage. While most alimentary lycopene is in all-trans configuration, in animal and human tissues approximately half of the lycopene is in cis isoforms.

AIM OF STUDY

Our object was to monitor the capacity of storage, isomerisation, and intracellular localization of all-trans and cis lycopene in hepatic stellate cells, which are the major sites of metabolism and storage of retinoids and carotenoids in the body.

METHODS

We used the GRX cell line representative of murine hepatic stellate cells, incubated with 1-30 muM lycopene in culture medium. Analysis was done by high-performance liquid chromatography.

RESULTS

Lycopene was able to induce expression of the lipocyte phenotype and it was internalized into GRX cells. Its cellular release only occurred in presence of albumin with a rapid initial decrease of intracellular lycopene. A corresponding increase in the culture medium was observed at 24 h. All-trans, 13-cis and 9-cis lycopene isoforms were identified in all the cell compartments. The membrane fraction contained the major part of lycopene, followed by the cytoplasmic fraction, lipid droplets and nuclei. The ratio between all-trans and cis isomers was approximately 2/1 in the majority parts of cell compartments.

CONCLUSIONS

This study identified a novel hepatic cell type able to store and isomerise lycopene. Liver can contribute to the serum and tissue equilibrium of cis/trans isomers of lycopene, and to participate in storage of lycopene under high extracellular concentration such as observed after the alimentary input.

Resolution of liver cirrhosis using vitamin A-coupled liposomes to deliver siRNA against a collagen-specific chaperone

There are currently no approved antifibrotic therapies for liver cirrhosis. We used vitamin A-coupled liposomes to deliver small interfering RNA (siRNA) against gp46, the rat homolog of human heat shock protein 47, to hepatic stellate cells. Our approach exploits the key roles of these cells in both fibrogenesis as well as uptake and storage of vitamin A. Five treatments with the siRNA-bearing vitamin A-coupled liposomes almost completely resolved liver fibrosis and prolonged survival in rats with otherwise lethal dimethylnitrosamine-induced liver cirrhosis in a dose- and duration-dependent manner. Rescue was not related to off-target effects or associated with recruitment of innate immunity. Receptor-specific siRNA delivery was similarly effective in suppressing collagen secretion and treating fibrosis induced by CCl(4) or bile duct ligation. The efficacy of the approach using both acute and chronic models of liver fibrosis suggests its therapeutic potential for reversing human liver cirrhosis.

Changes in expression of extracellular matrix genes, fibrogenic factors, and actin cytoskeletal organization in retinol treated and untreated vocal fold stellate cells

The regulation of extracellular matrix (ECM) constituency is critical in maintaining vocal cord biomechanical viscoelasticity required for phonation. Recently our laboratory successfully isolated and cultured a novel cell called a vocal fold stellate cell (VFSC), thought to play a central role in laryngeal ECM metabolism, aging, scarring and cancer. Our laboratory has shown that these cells undergo transdifferentiation that is partially reversed by exposure to all-trans retinol (ATROH). Here we make the first report on the expression of various ECM components, MMPs, TIMPs, pro-fibrogenic cytokines, and other ECM modulators in transdifferentiated and deactivated VFSCs. We show that VFSCs maintain an ECM expression pattern similar to laryngeal cancer and scars but distinct from tracheal fibroblasts. Exposure to ATROH differentially affects the VFSC expression of ECM components, matrix-regulating enzymes, and fibrogenic factors suggesting that the inhibitory effects of this synthetic cofactor should be studied further in laryngeal fibrosis and scarring. We also show that increased exposure to retinol induces sequential reorganization of the actin cytoskeleton in activated VFSCs. Our findings demonstrate that VFSCs are capable of regulating vocal fold ECM constituency important throughout normal laryngeal development. Furthermore, our results implicate VFSC activation in ECM misregulation which is a hallmark of several laryngeal pathologies.

Transdifferentiation of vocal-fold stellate cells and all-trans retinol-induced deactivation

The maculae flavae of the human vocal folds include dense extracellular matrices and compacted cells with a stellate morphology. These vocal-fold stellate cells are thought to participate in the metabolism of extracellular matrices essential in maintaining vocal-fold viscoelasticity required for phonation. We have isolated and cultured these new cells and have tested the hypothesis that they maintain a distinct cellular and biochemical phenotype. We have compared proliferation rates, changes on immunophenotype, and intracellular lipid and vitamin A storage. Vocal-fold stellate cells undergo culture-induced transdifferentiation to a myofibroblast-like phenotype with an altered phenotype resembling, but not identical to, activated hepatic and pancreatic stellate cells. Our results reveal that these cells are capable of responding to exogenous all-trans retinol in culture. Exposure to this synthetic co-factor causes deactivation characterized by decreased proliferation, loss of the activated stellate cell marker, alpha-smooth muscle actin, and restoration of intracellular lipid and vitamin A metabolite storage. These data establish a new and distinct cellular target for future investigations of the viscoelastic properties of the vocal-fold mucosa during normal phonation, aging, vocal-fold scarring, laryngeal fibrosis, and myofibroblastoma.

Study of factors affecting binding of zinc with albumin at physiological zinc concentrations

Albumin has very high affinity for many organic and inorganic compounds that may influence albumin bound Zn (ABZn). To get insight of these molecular interactions, the effect of riboflavin, nicotinic acid, thiamine, folic acid, pyruvic acid and glucose on ABZn were studied. The ABZn was separated from the unbound zinc using equilibrium dialysis and estimated using atomic absorption spectrometer. At therapeutic zinc concentrations, folic acid and thiamine significantly enhanced the ABZn (p < 0.010), while nicotinic acid inhibited zinc binding to albumin. Folic acid was found to enhance the ABZn also at lower zinc concentrations representing physiological levels of plasma zinc (138-150 micromoles) (p < 0.05).

?-Carotene storage, conversion to retinoic acid, and induction of the lipocyte phenotype in hepatic stellate cells

Hepatic stellate cells (HSCs) are the major site of retinol (ROH) metabolism and storage. GRX is a permanent murine myofibroblastic cell line, derived from HSCs, which can be induced to display the fat-storing phenotype by treatment with retinoids. Little is known about hepatic or serum homeostasis of beta-carotene and retinoic acid (RA), although the direct biogenesis of RA from beta-carotene has been described in enterocytes. The aim of this study was to identify the uptake, metabolism, storage, and release of beta-carotene in HSCs. GRX cells were plated in 25 cm(2) tissue culture flasks, treated during 10 days with 3 micromol/L beta-carotene and subsequently transferred into the standard culture medium. beta-Carotene induced a full cell conversion into the fat-storing phenotype after 10 days. The total cell extracts, cell fractions, and culture medium were analyzed by reverse phase high-performance liquid chromatography for beta-carotene and retinoids. Cells accumulated 27.48 +/- 6.5 pmol/L beta-carotene/10(6) cells, but could not convert it to ROH nor produced retinyl esters (RE). beta-Carotene was directly converted to RA, which was found in total cell extracts and in the nuclear fraction (10.15 +/- 1.23 pmol/L/10(6) cells), promoting the phenotype conversion. After 24-h chase, cells contained 20.15 +/- 1.12 pmol/L beta-carotene/10(6) cells and steadily released beta-carotene into the medium (6.69 +/- 1.75 pmol/ml). We conclude that HSC are the site of the liver beta-carotene storage and release, which can be used for RA production as well as for maintenance of the homeostasis of circulating carotenoids in periods of low dietary uptake.