A study has found that curcumin in nanoparticle form has the potential to enhance the efficacy of the BCG vaccine so that it confers protection against adult pulmonary tuberculosis (TB). The researchers working on mice models found that injecting curcumin nanoparticles soon after vaccinating the mice with BCG produced an appreciable enhancement of immune memory cells (T central memory cells) responsible for long-term protection against TB infection. This was reported in September 2019.
BCG vaccine is effective against disseminated and meningeal TB in young children. But the protection does not last for long as the host-protective immune responses that the vaccine induces diminishes over time. In other words, the vaccine is not protective in adults.
The results were published in the journal Infection and Immunity.
What it involves
The team led by Gobardhan Das and Anand Ranganathan from the Special Centre for Molecular Medicine at the Jawaharlal Nehru University (JNU), in collaboration with KIIT University, Bhubaneswar, demonstrated that, in mice models, curcumin nanoparticles enhance vaccine efficacy in two important ways.
In children, the vaccine is known to induce two types of immune cells — effector memory T cells and central memory T cells. The effector memory T cells have a vital role in mounting an immediate immune response against virulent TB bacteria and killing them, while the central memory T cells are for long-term protection in children from childhood TB. But the latter cells ultimately diminish. So, the protection does not last into adulthood and people become vulnerable to TB infection despite having had BCG vaccination when they were children.
To improve the efficacy of the BCG vaccine, the attempt was to increase the number of central memory cells so that they last longer and confer protection for a longer time. There is a dynamic balance between the two types of immune T cells in the body — central memory cells and effector memory cells. However, altering the ratio to increase the number of central memory cells is now seen as a way of enhancing the efficacy of the BCG vaccine. The ratio of these two cell types was enhanced in the experiment performed on mice using curcumin nanoparticles.
The number of central memory cells was increased with respect to the effector memory cells through a simple process. The potassium ion channel (Kv1.3) is required for the differentiation of central memory cells into effector memory T cells. In mice, nanocurcumin was injected to block this channel and as a result the conversion of central memory cells into effector memory cells reduced. So the number of central memory cells showed an increase leading to better vaccine efficacy.
Curcumin helps in the activation of innate immune cells— macrophages and dendritic cells. TB bacteria grow inside the macrophages. When activated by curcumin nanoparticles, the macrophages and dendritic cells clear the bacteria and improve the level of TB-specific acquired immune cells, called Th1 and Th17 cells. Curcumin nanoparticles also simultaneously reduce the level of certain other cells (Th2 and Tregs), which may contribute to the efficacy of the BCG vaccine. After TB infection, the levels of Th2 and Tregs cells increase and they inhibit the host-protective effect of Th1 and Th17 responses. So blocking or reducing the level of Th2 and Tregs cells is seen as a way of enhancing the vaccine efficacy.
Following vaccination, the mice were treated with curcumin nanoparticles and then infected with TB bacteria. Researchers measured the bacterial burden in the lungs and spleen several times and observed that mice treated with curcumin nanoparticles had much less bacterial load.
About Turmeric and Curcumin
Turmeric is a flowering plant, Curcuma longa of the ginger family, Zingiberaceae. The roots of the turmeric plant are used in cooking to give food a yellow colour. Though pure turmeric in small amounts is considered safe and even beneficial for most people, turmeric powders that are prepared and sold can be mixed with wheat starch and food colorants such as metanil yellow (largely used in India) which can cause cancer and neurological damage in high amounts. The prepared turmeric powders readily available may even contain lead.
Turmeric contains many plant substances but curcuminoids in it have the largest health promoting effects. It has 3 major curcuminoids: curcumin, the key active ingredient which is most beneficial; demethoxycurcumin; and bisdemethoxycurcumin. A typical turmeric root contains about 2 to 5 per cent of curcumin. Turmeric is used as a spice and the curcumin extract is used in medicine.