Date of Award:

8-2012

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biological and Irrigation Engineering

Advisor/Chair:

Dr. Charles D. Miller

Abstract

Due to the essential demands for novel anti-tuberculosis treatments for global tuberculosis control, this research investigated the antimycobacterial activity of Hypericum perforatum herb (commonly known as St. John’s wort, SJW), including a SJW methanol extract, purified major bioactive constituents of SJW: hypericin (Hpn), pseudohypericin (Phn) and hyperforin (Hfn). The SJW acidified methanol extract showed bactericidal activity against Mycobacterium JLS at 0.05 mg/ml culture. Purified compounds were tested at similar concentrations contained in the SJW methanol extract treatment. Among three purified bioactive compounds, only Hfn was bactericidal at 12 μg/ml. The other two compounds Phn and Hpn were not inhibitory or bactericidal at concentrations corresponding to the SJW methanol extract treatments.

The Polysorbate surfactant Tween 80, which is commonly added to the mycobacterial cultures to prevent cell clumping, was found to have inhibitory effects on the antimycobacterial activities of SJW extract and hyperforin. The addition of Tween 80 (0.05% v/v) increased the minimum bactericidal concentration (MIC) of SJW methanol extract from 0.05 to 0.33mg /ml and from 12 to 80 μg/ml for Hfn. This inhibitory effect of Tween 80 on SJW is opposite to the effect of Tween 80 on the antimycobacterial activity of rifampin and isoniazid. These observations are also in conflict with the existing permeability barrier hypothesis. A hypothesis that hyperforin molecules were sequestered in the core of Tween 80 micelles was given out to explain the repression effect of Tween 80 on hyperforin activity. The effectiveness of Tween 60, Tween 40 and Tween 20 on SJW activity was also tested. Tween 60 and Tween 40 showed the similar dose-dependent inhibitory effect on SJW extract activity with Tween 80, while the inhibitory effect of Tween 20 is much weaker.

A preliminary test was performed to detect the activity of SJW acidified MeOH extract and hyperforin on M. tuberculosis H37Rv strain. Results showed the MIC was 0.67mg SJW extract/ml and 200 μg Hfn /ml. In all, M. tuberculosis H37Rv stain is not that sensitive to SJW and hyperforin as other non-pathogenic strains tested in the present and previous studies.

Comments

This work made publicly available electronically on September 20, 2012.

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