Biocompatibility characteristics of the metal organic framework ZIF-8 for therapeutical applications

TLDR: A clear understanding is established of the interaction of ZIF-8 and its constituents with various cell lines and highlights the important biocompatibility factors that must be considered for future in vivo testing.

About: This article is published in Applied Materials Today.The article was published on 2018-06-01 and is currently open access. It has received 162 citations till now. The article focuses on the topics: Drug delivery & Biocompatibility.

Figures

Fig. 4 – LIVE / DEAD assay of MG – 631 cells after three days of incubation with different concentrations of ZIF-8: BF – Brightfield image; SYTO 9 – live cells; PI – dead cells; SYTO 9 / PI – merged channel of live / dead cells.

Fig. A.3 – Fluorescence activated cell sorting analysis for MG-63 cells after three days incubation with (a) 0 µg/mL, (b) 30 µg/mL, and (c) 100 µg/mL of ZIF-8.

Fig. A.1 – MTT cell viability of Raw 264.7 and 3T3 cells after 5 days exposure to various amounts of 2-MIM.

Fig. A.2 – Fluorescence images detecting ROS production in MG-63 cells at different ZIF-8 concentrations.

Fig. 5 – (a) Schematic representation of the one-pot synthesis method for the incorporation of insulin into ZIF-8 followed by a theoretical calculation of the release of insulin from 37.84 µg/mL of In@ZIF-8 (37.84 µg/mL of In@ZIF-8 imply the release of 30 µg/mL of Zn2+, which has been determined as a cytotoxic threshold value). For details concerning the calculation please refer to the supporting information. (b) Initial insulin stock solutions and the resulting insulin (wt%) encapsulated into the In@ZIF-8 biocomposite.

Table 1: Overview of cell lines used in this study and their origin.

Frequently asked questions

Q1. What is the effect of the increased levels of ROS on the cell cycle?

Augmented intracellular levels of ROS cause the arrest of the cell cycle at the G2/M checkpoint, a necessary step for DNA repair mechanism.[53] 

Q2. How did the encapsulation of insulin affect cell viability?

only ZIF-8 concentrations above 30 µg/mL or Zn2+ concentrations above 4 µg/mL induced a significant reduction in cell viability. 

Q3. What is the role of Zn2+ in the human body?

43]Zn2+ ions are one of the essential trace elements responsible for multiple catalytic,structural, and regulatory functions in the human body. 

Q4. How did the authors exclude the results from the cell cultures treated with 75 and 100 g/?

During all ROS experiments, the authors excluded the results from the cell cultures treated with 75 and 100 µg/mL, since the resulting cell density was too low to obtain a significant signal for comparison. 

Q5. What is the key aspect associated with biocompatibility?

The key aspect associated with biocompatibility is the nature of the interaction between the material and human cells, and its resulting effects. 

Q6. What is the effect of increased intracellular Zn2+ concentrations on mitochondria?

increased intracellular Zn2+ concentrations have been shown to inhibit the Krebs cycle associated with enzymes (e.g. glycerol-3-phosphate dehydrogenase), induce permeability transition of the mitochondrial membrane, and inhibit the mitochondrial bc1 cytochrome complex, leading to an augmented production and accumulation of reactive oxygen species (ROS).[46-49] 

Q7. What is the effect of ZIF-8 on cell viability?

An increase in ZIF-8 up to 50 µg/mL resulted in a 50 to 80 % increase of ROS in the cells compared to the untreated cell culture. 

Q8. How do the authors determine the biocompatibility of ZIF-8?

Future therapeutic in vivo trials using ZIF-8 as a drug carrier should focus on a critical concentration value significantly below 30 µg/mL. 

Q9. How much is the amount of Zn2+ released in the blood?

at a concentration of 30 µg/mL of ZIF-8 crystals, the amount of Zn2+ released was found to be around 3-5 µg/mL, a value that corresponds to the average homeostatic Zn2+ concentration reported in the literature, i.e. 3 - 6.4 µg/mL in the human blood. 

Q10. What is the IC50 of the ZIF-8 crystals?

At this stage the authors can conclude that ZIF-8 crystals show a concentration dependent inhibition of cellular metabolism and proliferation above a critical concentration of around 30 µg/mL of pure ZIF-8 for non-cancerous cell lines. 

Q11. How did the results show that the zinc ions released and present in the cell media did not?

Low ZIF-8 concentrations (below 30 µg/mL), showed biocompatible results, since the zinc ions released and present in the cell media did not exceed homeostatic conditions. 

Q12. What is the effect of the increased ROS levels on DNA repair?

If ROS levels are above a certain threshold, DNA repair is no longer possible, and cellular apoptosis pathways are eventually induced.[54] 

Q13. How did the authors determine the release of Zn2+ in cells?

To assess the stability of ZIF-8 crystals in cell media at physiological conditions (pH 7.4), the authors incubated different concentrations of ZIF-8 for 5 days and determined the release of Zn2+ by atomic absorption spectroscopy (AAS). 

Q14. What is the effect of the concentration of ZIF-8 on cell viability?

the amount of crystal formation (determined by absorbance spectroscopy) corresponds to the viability of the present cell culture. 

Q15. What is the sensitivity of the cell line to low ZIF-8 concentrations?

The results show that 3T3, RAW 264.7, and MG-63 cell lines show the highest sensitivity towards low ZIF-8 concentrations, with a 20% cell viability reduction at only 20-25 µg/mL. 

Q16. What is the IC50 of the MB-231 cells?

In contrast, MB-231 cancer cells displayed the highest resistance towards ZIF-8 crystals, where more than 50 µg/mL was necessary to reduce the cell viability by 20%. 

Q17. What is the effect of ZIF-8 on the cell membrane?

From the overlay images (live/dead) it is clearly visible that an increment of ZIF-8 crystals leads to an increased amount of dead (red) cells.