Home • AltMed Home • Search

Liu et al  found that when the aqueous extracts of nine Chinese herbs were screened for inhibition of HIV-1 binding to cell, all exhibited an inhibitory effect.  In particular, 1) extracts from Prunella vulgaris and Rhizoma cibotte showed very efficacious anti-HIV-1 activity.  In addition, 2) Liu et al study further analyzed the anti-HIV component in these extracts, and the data suggests it is a tannin.

The details of the study:

1) extracts from Prunella vulgaris and Rhizoma cibotte showed very efficacious anti-HIV-1 activity

• HIV entry into a target cell requires several steps: one of these steps is a conformation change in the subunit gp41: the C- and N-terminus of the polypeptide must interact to form the six-helix bundle.
• The sequences of both the C- and N- terminus are known, and identical sequences can be derived from them and used in a lab for experimentation.
• It has been previously shown, through both laboratory and clinical research that analogs of the C-terminus can inhibit the formation of the six-helical bundle and thus prevent HIV entry into the target cell.  So-called "fusion-inhibitors."
• These analogs, unfortunately, are not useful as drugs (a great example of how a drug can show promise in a lab but not in a clinical study--see the original paper for more details, in reference section).
• However, this experiment gave the researchers the idea to search for similar compounds using the laboratory methods they had already developed to verify the fusion-inhibitory activity of the C-terminus analogs.  These lab methods include...
• Using both polyclonal and monoclonal antibodies which have specificity for the six-helix bundle of the HIV-cell membrane fusion complex, investigators developed an sandwich enzyme-linked immunosorbent assay (ELISA) for screening fusion-inhibitors.
• Using this method, researchers screened extracts from nine Chinese herbs, using a pre-identified fusion-inhibitor as a control.
• extracts from Prunella vulgaris (PV) and Rhizoma cibotte (RC) showed the highest fusion-inhibition.
• it should be noted that the Chinese herb aqueous extracts were prepared for this experiment  in a way similar to that the pharmaceutists in China have used to prepare the traditional Chinese herb medicines for thousands of years.₅
• the concentrations of Chinese herbs that demonstrated fusion-inhibitory activity were 50 ug/ml
•     details of material and method
• 
   

  

  Fig. 1. The specificity of the mAb NC-1. A) As measured by the sandwich ELISA, NC-1 specifically bound to the gp41 six-helix bundle formed by mixing of N36 and C34, but did not bind to the isolated N36 or C34. B) ADS-J1 specifically inhibited the six-helix bundle formation, but did not block the binding of NC-1 to the pre-formed gp41 core formed by N36 and C34. Other HIV-1 entry inhibitors had no effect on the six-helix bundle formation.

  
   

  

  Fig. 4. Correlation between the concentrations of polyphenols in herb extracts and their inhibitory activity. A) Measurement of the concentrations of polyphenols in the aqueous extracts of nine Chinese medicinal herbs. B) The inhibitory activity of herb extracts on six-helix bundle formation is correlated with the concentrations of polyphenols in these herb extracts.

2) their study suggests that the anti-HIV component in these extracts is a tannin (a polyphenol).

• To determine whether the active components in PV and RC were proteins or other organic compounds, the extracts were boiled, then retested.  They retained their activity, suggesting that the component is not a protein.
• the fusion-inhibitory effects of the herb extracts is correlated with the concentrations of the polyphenols
• the active components, like tannin, could be removed from the herb extracts by passing the extracts through polyamide resin mini-column.
• the elutes from this column contain the active components
• tannins purchases commercially inhibited the six-helix bundle in a dose-dependant manner, with IC50 on the range of ug/ml.

Study conclusion: The aqueous extracts of PV and RC contain inhibitor of the HIV-1 six-helix bundle.  The active component in these extracts is likely a polyphenol, probably tannin.

Critique of Liu et al.

On to the next laboratory study