Circulating DNA and DNase Activity in Human Blood

Effects of the incorporation of a hydrophobic middle block into a PEG-polycation diblock copolymer on the physicochemical and cell interaction properties of the polymer-DNA complexes

One-component homopolymers of cationic monomers (polycations) and diblock copolymers comprising poly(ethylene glycol) (PEG) and a polycation block have been the most widely used types of polymers for the formulation of polymer-based gene delivery systems. In this study, we incorporate a hydrophobic middle block into the conventional PEG-polycation architecture and investigate the effects of this hydrophobic modification on the physicochemical and cell-level biological properties of the polymer-DNA complexes that are relevant to gene delivery applications. The ABC-type triblock copolymer used in this study consists of (A) PEG, (B) hydrophobic poly( n-butyl acrylate) (PnBA), and (C) cationic poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) component polymers. The properties of the triblock copolymer/DNA complexes are compared with those of two other more conventional DNA carriers derived, respectively, using a PDMAEMA homopolymer and a PEG-PDMAEMA diblock copolymer that had comparable molecular weights for individual blocks. In aqueous solution, the PEG-PnBA-PDMAEMA polymer forms positively charged spherical micelles. The electrostatic complexation of these micelles with plasmid DNA molecules results in the formation of stable small-sized DNA particles that are coated with a micelle monolayer, as confirmed by agarose gel electrophoresis, dynamic light scattering (DLS), and cryogenic transmission electron microscopy (cryo-TEM). Proton nuclear magnetic resonance ( (1)H NMR) spectroscopy measurements indicate that the whole micelle-DNA assembly (named "micelleplex" for convenience) is shielded predominantly by the PEG chains. DLS and optical microscopy imaging measurements indicate that compared with PDMAEMA-DNA polyplexes, the micelleplexes have a significantly lower tendency to aggregate under physiological salt concentrations and show reduced interactions with negatively charged components in serum such as albumin and erythrocytes. While the micelleplexes are comparable to the PEG-PDMAEMA-based DNA polyplexes in terms of their stability against aggregation under high salt concentrations and in the presence of the albumin protein, they have a slightly higher tendency to interact with erythrocytes than the diblock copolymer polyplexes. Agarose gel electrophoresis measurements indicate that relative to the PEG-PDMAEMA polyplexes, the micelleplexes provide better protection of the encapsulated DNA from enzymatic degradation and also exhibit greater stability against disintegration induced by polyanionic additives; in these respects, the PDMAEMA homopolymer-based polyplexes show the best performance. In vitro studies in HeLa cells indicate that the PDMAEMA polyplexes show the highest gene transfection efficiency among the three different gene delivery systems. Between the micelleplexes and the PEG-PDMAEMA polyplexes, a higher gene transfection efficiency is observed with the latter system. All three formulations show comparable levels of cytotoxicity in HeLa cells.

Circulating DNA. Its origin and fluctuation

Circulating DNA is present in the blood of all individuals, but it has been found that cancer patients and patients with a variety of other conditions have increased amounts of these circulating DNA fragments in their blood. Even though more than 30 years of research have been done on this subject, the origin of these nucleic acid molecules is still not clear. We present evidence that does not support the general notion that apoptosis or necrosis is the major source of circulating free DNA. Active release of free circulating DNA by living cells may be a plausible mechanism. Disturbance of the equilibrium between the release of DNA by living cells and the mechanisms used for clearing this DNA may play the main role in the appearance of increased amounts of circulating DNA in the blood of individuals with different ailments. Elucidating the origin and the mechanism that cells use to release free circulating DNA into the blood may enhance the diagnostic and prognostic value of these nucleic acid molecules.

Comparison of serum VEGF and its soluble receptor sVEGFR1 with serum cell-free DNA in patients with breast tumor

BACKGROUND

The observed elevated levels of vascular endothelial growth factor (VEGF), its soluble receptor (sVEGFR1) and cell-free DNA (cfDNA) in the serum of patients with various cancers have attracted much attention to the possibility of using these agents as biomarkers for cancers. We wanted to find out whether VEGF, VEGFR1 or cfDNA is a biomarker for breast cancer.

METHODS

In this study, we used enzyme-linked immunosorbent assay (ELISA) to examine the levels of serum VEGF and VEGFR1 in 23 patients with benign tumors, 19 patients with breast cancer and 32 age-matched healthy females. The levels of circulating cell-free DNA were measured using TaqMan real-time PCR analysis for the glyceraldehydes 3 phosphate dehydrogenase gene (GAPDH), We compared the serum levels of VEGF and its soluble receptors with those of the cell-free serum DNA.

RESULTS

In terms of serum levels of either VEGF or its soluble receptors VEGFR1, we found no significant difference between healthy individuals and women with benign breast tumors and breast cancer. However, there was a significant increase in circulating cell-free DNA in women with both benign and malignant breast tumors when compared with the corresponding healthy control group. We also found a significant negative correlation between VEGF and its soluble receptor VEGFR1 (r=-0.328 and p=0.004), and a significant positive correlation between VEGF and cell-free serum DNA (r=0.241 and p=0.033).

CONCLUSIONS

We can conclude that quantitative analysis of circulating cell-free DNA in serum may provide molecular biological understanding of breast tumors in women. It would also suggest that serum levels of VEGF and VEGFR1 have less significance.

Immunochemical assay for deoxyribonuclease activity in body fluids

We have developed two microtiter plate assays to quantify the deoxyribonuclease activity in biological fluids. Both assays are based on hydrolysis of biotinylated and fluorescein-labeled DNA substrates, with subsequent immunochemical detection of non-digested DNA. The assay based on hydrolysis of 974 bp PCR product labeled with biotinylated forward and fluorescein-labeled reverse primers is more sensitive (0.05 U/ml) and convenient for quantifying the DNase activity in biological fluids than the assay based on hydrolysis of double-labeled 20 bp oligonucleotide. The DNase activity in urine and blood plasma of healthy donors was measured using the PCR product-based assay. Urine samples revealed greater activity, 1.49+/-1.41 U/ml; blood plasma DNase I-like activity was 0.36+/-0.20 U/ml. DNase II-like activity was not detected in the plasma samples. The data obtained confirm that DNase I-like enzymes are responsible for the majority of deoxyribonuclease activity in blood plasma.

Cell-free and cell-bound circulating DNA in breast tumours: DNA quantification and analysis of tumour-related gene methylation

Tumour development is characterised by the increased circulating DNA (cirDNA) concentration and by tumour-related changes in blood plasma DNA. Concentration of cirDNA and methylation of RARβ2, RASSF1A and HIC-1 gene promoters were investigated in cell-free and cell-surface-bound fractions from healthy donors, patients with breast cancer, and patients with breast fibroadenoma. Tumour development was shown to lead to significant changes in the distribution of cirDNA between cell-free and cell-surface-bound fractions. Analysis of RARβ2 and RASSF1A methylation in the total cirDNA provides 95% diagnostic coverage in breast cancer patients, 60% in patients with benign lesions, and is without false-positive results in healthy women. Results of the study indicate that methylation-specific PCR of RARβ2 and RASSF1A genes based on the total cirDNA combined with the quantitative analysis of cirDNA distribution between cell-bound and cell-free fractions in blood provide the sensitive and accurate detection and discrimination of malignant and benign breast tumours.