Structural Characterization and Cytotoxic Activity Evaluation of Ulvan Polysaccharides Extracted from the Green Algae Ulva papenfussii

Abstract

Ulvan, a sulfated heteropolysaccharide with structural and functional properties of interest for various uses, was extracted from the green seaweed Ulva papenfussii. U. papenfussii is an unexplored Ulva species found in the South China Sea along the central coast of Vietnam. Based on dry weight, the ulvan yield was ~15% (w/w) and the ulvan had a sulfate content of 13.4 wt%. The compositional constitution encompassed L-Rhamnose (Rhap), D-Xylose (Xylp), D-Glucuronic acid (GlcAp), L-Iduronic acid (IdoAp), D-Galactose (Galp), and D-Glucose (Glcp) with a molar ratio of 1:0.19:0.35:0.52:0.05:0.11, respectively. The structure of ulvan was determined using High-Performance Liquid Chromatography (HPLC), Fourier Transform Infrared Spectroscopy (FT-IR), and Nuclear Magnetic Resonance spectroscopy (NMR) methods. The results showed that the extracted ulvan comprised a mixture of two different structural forms, namely ("A3s") with the repeating disaccharide [→4)-β-D-GlcAp-(1→4)-α-L-Rhap 3S-(1→]n, and ("B3s") with the repeating disaccharide [→4)-α-L-IdoAp-(1→4)-α-L-Rhap 3S(1→]n. The relative abundance of A3s, and B3s was 1:1.5, respectively. The potential anticarcinogenic attributes of ulvan were evaluated against a trilogy of human cancer cell lineages. Concomitantly, Quantitative Structure-Activity Relationship (QSAR) modeling was also conducted to predict potential adverse reactions stemming from pharmacological interactions. The ulvan showed significant antitumor growth activity against hepatocellular carcinoma (IC₅₀ ≈ 90 µg/mL), human breast cancer cells (IC₅₀ ≈ 85 µg/mL), and cervical cancer cells (IC₅₀ ≈ 67 µg/mL). The QSAR models demonstrated acceptable predictive power, and seven toxicity indications confirmed the safety of ulvan, warranting its candidacy for further in vivo testing and applications as a biologically active pharmaceutical source for human disease treatment.

Keywords: QSAR modeling; Ulva papenfussii; anti-tumorigenic; structural determination; ulvan.

Figure 1

FT-IR spectrum for ulvan extracted from U. papenfussii. The U. pen present in FT-IR of the ulvan isolated from U. papenfussii and the %T is represented in the % Transmittance.

Figure 2

¹H NMR spectrum of ulvan from U. papenfussii.

Figure 3

¹³C NMR spectrum of ulvan extracted from U. papenfussii.

Figure 4

NMR spectra of ulvan extracted from U. papenfussii (a) ¹H-¹H COSY, A1/2 indicated the cross-peak between H-1 and H-2 of residue A, etc.; (b) ¹H-¹³C HSQC, in the COSY and HSQC spectra of ulvan, cross-peaks were observed, enabling the assignment of signals to residues A, B, B’, C and D each exhibiting distinct structures as detailed in (Table 2).

Figure 5

¹H-¹³C HMBC spectrum of ulvan extracted from U. papenfussii. The HMBC spectra of the ulvan featured interactions, from which the signals could be assigned to A, B, B’, C and D residues with different structures (Table 2).

Figure 6

Structural characterization of ulvans extracted from U. papenfussii.