The immunomodulatory effects of Sutherlandia frutescens extracts in human normal peripheral blood mononuclear cells

Abstract

Sutherlandia frutescens (SF) is one of the medicinal plants used as an immune booster in the treatment of chronic ailments such as HIV/AIDS and cancer. Limited data suggest that its efficacy is based on its regulatory effect on cytokines, the critical components of the immune response. In this study, we investigated the in vitro immunomodulatory effects of SF extracts on normal human peripheral blood mononuclear cells (PBMCs). An ELISA-based assay was used to assess the levels of expression of 12 cytokines in treated cells. An adenosine triphosphate (ATP) assay was used to assess cell viability in relation to cytokine secretion. SF ethanol extracts induced changes in cytokine secretion relative to the dose of the extract. Generally cytokine expression and secretion was low in concentration because were not stimulated with any endotoxin. The high SFE dose (2.5 mg/ml) significantly (p<0.001) decreased some cytokines including TNF-α and IL 1β. Low doses of this extract (0.5 mg/ml) did not change TNF-α and IL 1β secretion from the baseline (untreated cells). Changes in cytokine secretion of SFE treated cells tracked changes in ATP levels (cell viability). The SFW extract-induced changes in cytokine secretion were independent of cell viability. TNF-α was decreased (p<0.001) by the high dose of SFW extract while IL 1β and IFNγ were increased (p<0.01) by the same dose. High doses decreased cell viability which was reflected in cytokine secretion. It is evident, from these results, that SF extracts can modulate cytokine secretion in unstimulated normal PBMCs in vitro. Further studies in animal models are recommended to advance understanding of this immunomodulatory activity.

Keywords: ELISA; Sutherlandia frutescens; cell viability; cytokines; immune response.

Figure 1

Graphical illustration of changes in secretion of interleukins 1α, 1β, 2 and 4 in controls and Sutherlandia frutescens extracts treated samples. An ELISA-based kit was used to measure secretion of cytokines in cell supernatants and the results were obtained by measuring absorbance at 450 nm using a plate reader. The SFW doses increased the secretion of IL 1α & 1β while the high dose of SFE decreased both cytokines. A high dose of SFW also increased IL 4 secretion. In contrast, the secretion of all 4 cytokines was decreased in CPT treated cells, while PHA either showed no change or increased levels of all 4 cytokines.

Figure 2

Changes in secretion of IL 6, IL 8, IL 10, and IL 12 in controls and Sutherlandia frutescens extract dilutions treated samples. SF extracts decreased levels of IL 6 in all treated samples while similarly increasing the secretion of IL 8. A high dose of the SFE extract (2.5 mg/ml) significantly decreased IL 10 & 12 secretion. Both SFW doses showed a decrease in IL 10 secretion. All cytokines were significantly decreased in the CPT treated samples while PHA did not change levels of any of these cytokine.

Figure 3

Changes in the secretion of IL 17α, IFNγ, TNF-α, and GM-CSF in controls and Sutherlandia frutescens extract dilutions treated samples. CPT treated samples significantly decreased all cytokines while PHA samples showed an increase in all cytokines. High dose of SFE (2.5 mg/ml) significantly decreased all cytokines but also caused increased cytotoxicity in PBMCs. SFW extracts decreased TNF-α secretion without the excessive cytotoxicity shown by the ethanol extract of SF. The SFW extract doses also increased secretion of IFN-γ, an important cytokine in fighting viral infections.

Figure 4

Changes in cell viability of PBMCs treated with various doses of Sutherlandia frutescens extracts (SFE and SFW) over 24 hours. Conversion of the luminescence readings into a percentage cell viability change against the negative control showed that the high doses (2.5 mg/ml) of the SFE & SFW extracts induced a very significant decrease in cell viability. A low dose (0.5 mg/ml) of SFE induced a slightly significant decrease in ATP while the same SFW dose was not significant. It was also shown that the actions of the SFE extract doses were independent of ethanol (70% ethanol). PHA induced a significant increase in ATP levels while CPT decreased ATP levels significantly (p< 0.001).