New Ophiobolins from the Deep-Sea Derived Fungus Aspergillus sp. WHU0154 and Their Anti-Inflammatory Effects

Abstract

Deep-sea fungi have become a new arsenal for the discovery of leading compounds. Here five new ophiobolins 1-5, together with six known analogues 6-11, obtained from a deep-sea derived fungus WHU0154. Their structures were determined by analyses of IR, HR-ESI-MS, and NMR spectra, along with experimental and calculated electronic circular dichroism (ECD) analysis. Pharmacological studies showed that compounds 4 and 6 exhibited obvious inhibitory effects on nitric oxide (NO) production induced by lipopolysaccharide (LPS) in murine macrophage RAW264.7 cells. Mechanical study revealed that compound 6 could inhibit the inducible nitric oxide synthase (iNOS) level in LPS-stimulated RAW264.7 cells. In addition, compounds 6, 9, and 10 could significantly inhibit the expression of cyclooxygenase 2 (COX 2) in LPS-induced RAW264.7 cells. Preliminary structure-activity relationship (SAR) analyses revealed that the aldehyde group at C-21 and the α, β-unsaturated ketone functionality at A ring in ophiobolins were vital for their anti-inflammatory effects. Together, the results demonstrated that ophiobolins, especially for compound 6, exhibited strong anti-inflammatory effects and shed light on the discovery of ophiobolins as new anti-inflammatory agents.

Keywords: anti-inflammatory effect; deep-sea derived fungus; ophiobolin; secondary metabolites.

Figure 1

Structures of ophiobolins 1–11 from the fungus strain WHU0154.

Figure 2

Key ¹H-¹H COSY and HMBC correlations of new compounds 1–5.

Figure 3

Key ROESY correlations of new compounds 1–5.

Figure 4

Experimental and calculated electronic circular dichroism (ECD) spectra of compounds 1–5.

Figure 5

Effects of ophiobolins 2–11 on NO production induced by LPS (A) and their cytotoxicity (B) in murine macrophage RAW 264.7 cells. Cells were pretreated with LPS (500 ng/mL) and then treated with compounds or curcumin at a concentration of 10 µM for 24 h. The data was presented as means ± SEM of three independent experiments. ^## p < 0.01 vs. control group; ** p < 0.01 vs. LPS group.

Figure 6

Effect of ophiobolins 1–11 on COX 2 and iNOS protein levels in LPS-stimulated murine macrophage RAW 264.7 cells. Cells were pretreated with LPS (100 ng/mL) and then treated with compounds (10 µM) or curcumin (20 µM) for 24 h. The total protein levels were analyzed by western blot. (A) The expression of COX 2 and iNOS protein levels. (B) The quantification histogram of COX 2 and iNOS (C). ^### p < 0.001 vs. control group; * p < 0.05 vs.LPS group.