Solution properties and in vitro anti-tumor activities of polysaccharides from longan pulp

Abstract

The solution properties of four fractions (LPI-IV) from crude longan pulp polysaccharides (LP3) were analyzed by size-exclusion chromatography combined with laser light scattering, viscometry, complex formation with Congo red, and atomic force microscopy. Their radii of gyration <S²>(z)(½) were 43.3, 62.6, 43.2 and 77.3 nm, exponents of <S²>(z)(½) = k M(w)(v) were 0.04, 0.50, 0.52 and 0.02, and intrinsic viscosities ([η]) were 9.945, 25.38, 308.2 and 452.1 mL/g, respectively. Moreover, the dependence of [η] on M(w) was established to be [η] = 5.3 × 10⁻²M(w)⁰·⁶¹ (mL/g). LPI had both a sphere-like conformation and a triple-helix structure, and LPII-IV existed as flexible chains. LP3, LPI, LPII and LPIII all exhibited direct inhibitory effects on A549, HeLa and HepG2 cells in a positive dose-dependent manner in the range of 50-400 µg/mL. The activities of LPIII, especially the inhibition of HepG2 cell proliferation, were stronger than those of others, which may be partly related to its flexible conformation. The present results support the cancer therapeutic potential of longan polysaccharides.

Figure 1

The size-exclusion chromatograms of longan polysaccharide fractions LPI–IV detected by a refractive index detector in water at 25 °C.

Figure 2

The double logarithmic plots of 2>_z^1/2 vs. M_w of longan polysaccharide fractions LPI–IV.

Figure 3

Huggins’ plot of longan polysaccharide fractions LPI–IV in water at 25 °C.

Figure 4

The maximum absorption wavelengths of longan polysaccharide-Congo red complexes at the NaOH concentration range of 0–0.5 mol/L; * represents the data obtained from our previous work [36].

Figure 5

The atomic force microscope images (500 × 500 nm) of longan polysaccharide LPI–IV. 5 μL of sample (1 × 10⁻³ mg/mL) was air dried onto mica and imaged. The phase diagrams and corresponding three-dimension graphics were shown. The images of LPI were obtained from our previous work [36].

Figure 6

Inhibitory effects of longan polysaccharides on tumor cells in vitro. LPI–III were the fractions isolated from LP3. The cell proliferation was detected using a modified methylene blue method. Column expressed values were significantly different if marked with different letters (p < 0.05). At 400 µg/mL, the experimental value which showed significant difference from that of LP3 treated group was marked with * (p < 0.05) or ** (p < 0.01).