A new publication from Africa Health Research Institute (AHRI) scientists reveals how an instrument called the extracellular flux analyzer (XF96) can be used to measure and track disease in order to assess the effectiveness of potential new host-directed drugs and vaccines.

The paper, published in eLIFE, was led by AHRI Faculty Member, Prof Adrie Steyn. It shows how the XF96 can accurately measure the effects of Mycobacterium tuberculosis (Mtb) infection on the energy metabolism of macrophages. This instrument measures, in real-time, the oxygen consumed by the cells in addition to the acidification of the immediate external environment of the cell due to by-products of metabolism secreted by the cell. Up until now, how Mtb rewires macrophage energy metabolism to facilitate survival was poorly understood.

“Scientists at AHRI have the distinct advantage of having the XF96 in a BSL3 laboratory, which enabled the team to measure the effects of pathogenic, live Mtb on the energy metabolism of human macrophages in real-time,” said first author, Dr Bridgette Cumming.

Their findings demonstrate that an energy pathway that is associated with pro-inflammatory responses in macrophages necessary to control bacterial infections (glycolysis) is downregulated in macrophages infected with Mtb. This decreases the rate at which the Mtb-infected macrophages can produce ATP, the energy currency of the cell, and will subsequently affect the functioning of the macrophage. Mtb also induces the macrophage to switch from a preference for glucose to fatty acids as its source of nourishment. These findings were compared to an infection of human macrophages with a vaccine strain, M. bovis BCG, which distinctly increased glycolysis in the macrophages, thus generating the appropriate pro-inflammatory response needed to bring the infection under control.

AHRI has recently purchased a new model of this instrument (XF96e), which opens up the exciting possibility of analyzing 3-D cultures, which are better models of diseased tissue. This new feature will enable scientists to gain a deeper understanding of metabolic energy changes occurring in infected tissue.

(Top photo: First author, Dr Bridgette Cumming, in the lab at AHRI)