A protein extracted from St John’s wort can inhibit HIV replication

A protein extracted from St John’s wort can inhibit HIV replication, according to a study published in the October 27th edition of Gene Therapy. The study authors, from Temple University in Philadelphia, found in laboratory studies that the protein, p27SJ, inhibited HIV gene expression and the replication of cells infected with HIV. 

The investigators are urging, however, that their findings should be treated with caution. “We don’t yet know how to deliver the protein to cells infected with HIV”, said lead author Prof. Kamel Khalili. He also cautioned HIV-positive individuals against taking St John’s wort to treat HIV, “even if the protein were available in [St John’s wort] tablets, we don’t know how much might be present and whether the protein would be effective when ingested.” 

St John’s wort, which is a popular treatment for depression and is usually bought over the counter without medical advice, has been shown to interfere with the way the body metabolises the protease inhibitor indinavir (Crixivan). This interaction can lead to low blood levels of indinavir, increasing the chance that HIV resistant to indinavir and other protease inhibitors will emerge. It is also thought that St John’s wort will similarly interfere with the metabolising of other protease inhibitors with the same risks of resistance. 

Investigators at Temple University were conducting test tube studies to see if extract from St John’s wort had any effect on cell growth or the behaviour of brain cells. This led the investigators to examine if extracts from St John’s wort had any anti-viral activity. Prof. Khalili explained, “we soon discovered that the plant extract inhibited HIV gene expression and replication in infected cells.” 

They then identified the protein responsible for the anti-viral effect. The gene of this protein was cloned and the investigators realised that it was previously unreported. They named the protein p27SJ. 

“Our studies indicate that p27SJ has the capacity to inhibit expression of the HIV gene by interacting with both cellular proteins and viral proteins”, said Prof. Khalili. He added, “since HIV gene expression relies heavily on these factors, p27SJ can block viral replication by interfering with proteins recruited by HIV to increase viral gene expression.” 

Caution is, however, being urged by the investigators who point out that St John’s wort’s anti-HIV effects have only been demonstrated in early laboratory studies. “Remember, it is a plant protein”, Prof. Khalili emphasised, “so far, to my knowledge, there is no similar protein to that in mammalian calls.” 

Khalili K et al. p27SJ, a novel protein in St John’s wort, that suppresses expression of HIV-1 genome. Gene Therapy 12 (online edition), 2005.