Cytotoxic Effects of Sarcophyton sp. Soft Corals-Is There a Correlation to Their NMR Fingerprints?

Abstract

Sarcophyton sp. soft corals are rich in cembranoid diterpenes, which represent the main chemical defense of corals against their natural predators in addition to their myriad biological effects in humans. Quantitative NMR (qNMR) was applied for assessing the diterpene variation in 16 soft coral specimens in the context of their genotype, origin, and growing habitat. qNMR revealed high diterpene levels in Sarcophyton sp. compared to Sinularia and Lobophyton, with (ent)sarcophines as major components (17-100 µg/mg) of the coral tissues. Multivariate data analysis was employed to classify samples based on the quantified level of diterpenes, and compared to the untargeted NMR approach. Results revealed that qNMR provided a stronger classification model of Sarcophyton sp. than untargeted NMR fingerprinting. Additionally, cytotoxicity of soft coral crude extracts was assessed against androgen-dependent prostate cancer cell lines (PC3) and androgen-independent colon cancer cell lines (HT-29), with IC₅₀ values ranging from 10-60 µg/mL. No obvious correlation between the extracts' IC₅₀ values and their diterpene levels was found using either Spearman or Pearson correlations. This suggests that this type of bioactivity may not be easily predicted by NMR metabolomics in soft corals, or is not strongly correlated to measured diterpene levels.

Keywords: Sarcophyton; cembranoids; metabolomics; quantitative nuclear magnetic resonance (qNMR); terpenoids.

Figure 1

Structures of the major C15- and C20-terpenoids and a sterol quantified in Sarcophyton extracts using qNMR, and discussed in the manuscript. Note that the same carbon numbering system is used for each compound throughout the manuscript for NMR assignment and thus is based on analogy rather than the International Union of Pure and Applied Chemistry (IUPAC) rules. Signals highlighted in red represent those used for qNMR.

Figure 2

Representative ¹H-NMR spectrum (0–6.5 ppm) of S. convolutum (SC1). For complete assignment of quantifiable NMR signals refer to Suppl. Table S2. Signals used in quantification are marked in blue boxes.

Figure 3

Stacked column graph showing N1–N6 metabolite levels in soft coral species. Values are expressed as mean (µg/mg) ± SE. (n = 3). For complete information on sample codes refer to Suppl. Table S1.

Figure 4

(a) Targeted ¹H-NMR signal biplot principal component analysis (PCA) (b) and hierarchical cluster analysis (HCA) of soft coral species showing two clear clusters of soft coral species described by two principal component vectors accounting for 84.6% of the total variance. For complete information on sample codes refer to Suppl. Table S1.

Figure 5

Cytotoxicity data of soft coral species against PC3 and HT29 cell lines. Results are expressed as mean IC₅₀ (µg/mL, lower values = higher activity) ± SE. (n = 3). For complete information on sample codes refer to Suppl. Table S1.