Kupffer Cell Isolation for Nanoparticle Toxicity Testing

Summary

Liver macrophages, named Kupffer cells, are responsible for the capture of circulating nanoparticles. We describe here a method, of high cell purity and yield, for Kupffer cell isolation. The modified LDH assay is used here to measure the toxicity induced by carbon nanotubes in Kupffer cells.

Abstract

The large majority of in vitro nanotoxicological studies have used immortalized cell lines for their practicality. However, results from nanoparticle toxicity testing in immortalized cell lines or primary cells have shown discrepancies, highlighting the need to extend the use of primary cells for in vitro assays. This protocol describes the isolation of mouse liver macrophages, named Kupffer cells, and their use to study nanoparticle toxicity. Kupffer cells are the most abundant macrophage population in the body and constitute part of the reticulo-endothelial system (RES), responsible for the capture of circulating nanoparticles. The Kupffer cell isolation method reported here is based on a 2-step perfusion method followed by purification on density gradient. The method, based on collagenase digestion and density centrifugation, is adapted from the original protocol developed by Smedsrød et al. designed for rat liver cell isolation and provides high yield (up to 14 x 10⁶ cells per mouse) and high purity (>95%) of Kupffer cells. This isolation method does not require sophisticated or expensive equipment and therefore represents an ideal compromise between complexity and cell yield. The use of heavier mice (35-45 g) improves the yield of the isolation method but also facilitates remarkably the procedure of portal vein cannulation. The toxicity of functionalized carbon nanotubes f-CNTs was measured in this model by the modified LDH assay. This method assesses cell viability by measuring the lack of structural integrity of Kupffer cell membrane after incubation with f-CNTs. Toxicity induced by f-CNTs can be measured consistently using this assay, highlighting that isolated Kupffer cells are useful for nanoparticle toxicity testing. The overall understanding of nanotoxicology could benefit from such models, making the nanoparticle selection for clinical translation more efficient.

Introduction

The field of nanotoxicology research aims to characterize the biological effect of nanoparticles. Toxicological studies based on in vivo investigations remain the most accurate methods. However, their use is limited by their cost, labor and time requirements¹. As alternatives, in vitro assays have been used because of their simplicity and the possibility of developing high-throughput in vitro testing platforms² - so extending the number of conditions tested. Most nanotoxicological studies are performed using in vitro assays with immortalized cell lines. However, there are concerns regarding the extrapolation of....

Protocol

All animal experiments were executed in compliance with all relevant guidelines, regulations and regulatory agencies. The protocol being demonstrated was performed under the guidance and approval of the UK Home office regulation

1. Perfusion and Cell Collection (Figure 1)

Figure 1: Liver Perfusion. After anaesthesia of the mouse, the digestive tract is laterally moved to the left.......

Discussion

The following steps are critical to achieve high yield and high viability of Kupffer cells. Aseptic conditions should be used to limit the risk of bacterial and fungal contamination. All instruments need to be sterilized before use. Reagents should be freshly prepared before carrying out the isolation procedure.

The choice of collagenase IV, with low tryptic activity, is crucial. Different lots from the same supplier have different enzymatic activity and they may need to be compared initially .......

Materials

Name	Company	Catalog Number	Comments
Euthatal (pentobarbital sodium)	Merial
CD1 mice	Charles River	-	Mouse weight should vary from 35 to 45 g. We advise the use of male CD1 mice as their weight increase rapidly (e.g. a male CD1 mouse of 7 weeks old exceeds 35 g in weight). It is also advised to contact the animal supplier in advance to arrange for the delivery of older animals. Alternatively animals can be in-house to reach the desired weight.
HBSS (Ca2+ and Mg2+ free, with bicarbonate)	Life Technologies	14175-053	HBSS must be  Ca2+ free.
Ethylene Glycol Tetraacetic Acid (EGTA) tetrasodium salt	Sigma-Aldrich	E8145	EDTA can also be used but EGTA has the advantage of chelating Ca2+ selectively.
HEPES (1M)	Life Technologies	15630-056	100 ml
Collagenase type IV	Worthington	CSL-4	It is advised to test different batches of collagenase or at least mention to the supplier the product has to be suitable for liver cell isolation
Low glucose DMEM	Sigma-Aldrich	D5523	500 ml
RPMI (with sodium pyruvate and Glutamax®)	Life Technologies	12633-012	500 ml
Penicillin/Steptomycin	Life Technologies	15140-122	100 ml
Fetal Bovine Serum	First-Link	60-00-850	500 ml
Trypan blue solution	Sigma-Aldrich	T8154	100 ml
Coated silica particle solution (Percoll®)	GE Healtcare	17-0891-02	Percoll® is very stable and can be kept for several years
1x Phosphate Buffered Saline	Life Technologies	10010-023	500 ml
10x Phosphate Buffered Saline	Life Technologies	70011-036	500 ml
Dimethyl sulfoxide	Fisher	D/4120/PB08	500 ml
LDH kit (CytoTox 96®)	Promega	G1781	Keep protected from light
DMEM phenol red free	Life Technologies	31053-028	500 ml
F4/80 antibody (Alexa 488)	AbD Serotec	MCA497A488	Do not dilute, used neat for flow cytometry
Fluorescent beads	Sigma	L2778	Latex beads, amine-modified polystyrene, fluorescent red. 1 ml
Name of the Material	Company	Catalog number	Comments/Description
Butterfly blood collection set (23G/305mm long tubing)	BD	367288
Syringe Filters (0.22 μm Blue Rim)	Minisart	16534-K
Centrifuge Tubes (50 ml Blue Cap)	BD Biosciences, Falcon	35 2070
Petri dish (90 x 15 mm)	Thermo Fisher Scientific	BSN 101VR20
100 μm cell strainer	BD	352360
Peristaltic pump	Watson Marlow	SciQ 300	Rinse tubing before and after each usage with sterile PBS and 70% ethanol.
24-well plates	Corning	3526
96-well plates	Corning	3595
Centrifuge	Eppendorf	5810R
Plate reader	BMG Labtech	FLUOstar Omega
Serrefine forceps	Hammacher GmbH	Art. Nr. HSE 004-35 / Cat. Nr. 221-0051	The serrefine forceps allow to clamp the vessel cannulated with the 23G needle without the need of holding the forceps during the perfusion procedure. URL: (http://www.hammacher.de/Laboratory-Products/Clamps-forceps/Serrefines/HSE-004-35-Serrefine::25126.html)
Flow cytometry tubes	BD Biosciences, Falcon	352052
Microcentrifuge tubes (1.5 ml)	Elkay	000-MICR-150
Cell scraper	BD Biosciences, Falcon	353086	Cut blade extremities with a pair of scissors to scrape cells in 24-well plates.
Name of the Reagent	Company	Catalog number	Comments/Description
EGTA (Ethylene Glycol Tetraacetic Acid)/HBSS (Hank's Balanced Salt Solution) Solution			HBSS containing 0.5 mM EGTA and 25 mM HEPES. Adjust pH to 7.4. Prepare 50 ml for each liver to perfuse.
Collagenase Solution			DMEM low glucose containing collagenase type IV at 100 UI/ml, 15 mM HEPES and 1% Penicllin/Streptamycin (v/v). Adjust pH to 7.4. Prepare 100 ml for each liver to perfuse. After adding the collagenase, it is advised to warm up the solution for 30 min before use. This allows the collagenase activity to be optimum.
Kupffer Cell Isolation Medium			RPMI containing, 1% Non-Essential Amino-Acids (v/v),1% glutamax® (v/v) and 1% Penicllin/Streptomycin (v/v). Prepare at least 100 ml for 1-3 livers.
Kupffer Cell Culture Medium			RPMI containing 10% Fetal Bovine Serum, 1% Non-Essential Amino-Acids (v/v),1% Glutamax® (v/v) and 1% Penicllin/Streptamycin (v/v). Prepare at least 100 ml for 1-3 livers.
SIP (solution of isotonic coated silica particles)			Mix 1.7 ml of 10x Phosphate Buffered Saline  with 15.3 ml of Percoll® to obtain 17mL of SIP.
25% SIP solution			Mix 5 ml of SIP with 15 ml of 1x Phosphate Buffered Saline
50% SIP solution			Mix 10 ml of SIP with 10 ml of 1x Phosphate Buffered Saline
Lysis Buffer			DMEM media with 0.9% Triton X-100
PBS/BSA Solution			Prepare fresh Phosphate Buffered Saline pH 7.4 with 1% Bovine Serum Albumin.