Adjuvant properties of selected medicinal plants for tuberculosis treatment

Abstract

Introduction

Tuberculosis is a disease caused by Mycobacterium tuberculosis (M.tb). Many plant extracts with antimycobacterial activity have been identified in recent years. The current study investigated seventeen (17) ethanolic plant extracts for their antimycobacterial, antioxidant, cytotoxicity, hepatoprotective and immunomodulatory properties.

Methods

The ethanolic extracts were tested for their antimycobacterial activity against Mycobacterium tuberculosis H37Rv, and their cytotoxicity on both the human leukemic monocyte lymphoma (U937) and human liver hepatocellular carcinoma cell lines (HepG2). Furthermore, their antioxidant activity was determined by measuring the radical scavenging potential against 2, 2-diphenyl-1-picrylhydrazyl (DPPH). Additionally, selected samples were tested for their hepatoprotective activity through acetaminophen induced toxicity of HepG2 cells. A cytokine analysis of the selected extracts was investigated in U937 cells.

Results

Heteromorpha arborescens, Sutherlandia frutescens, Eucalyptus deglupta, and Plectranthus neochilus showed the most effective antimycobacterial activity, exhibiting a minimum inhibitory concentration (MIC) of 250 µg/ml. Heteromorpha arborescens showed cytotoxicity on both cell lines with a fifty percent inhibitory concentration (IC₅₀) of 40 ± 4.30 µg/ml and 72.40 ± 1.50 µg/ml in U937 and HepG2 cells, respectively. Eucalyptus deglupta and Melianthus major had the most effective antioxidant capacity with IC₅₀ values of 1.33 ± 0.50 µg/ml and 1.32 ± 0.70 µg/ml, respectively. Searsia lancea (¼ IC₅₀) showed significant hepatoprotection protection (56.28 ± 5.95). Increased concentrations of interleukin- 12 (IL-12) in U937 cells were observed when the cells were exposed to varied concentrations of both Eucalyptus deglupta and Sutherlandia frutescens.

Conclusion

Eucalyptus deglupta, Searsia lancea and Sutherlandia frutescens showed good antimycobacterial, antioxidant, hepatoprotective and immunomodulatory activity. These plants may be considered for their potential to be used as adjuvants for tuberculosis treatment in preclinical and clinical studies.