Vitamins, Sunshine and Cannibalism: New Partners in the Fight to Stop Tuberculosis

17 Feb 2010
by Working Group

Can Vitamin-D from sunshine help TB treatment?
Can Vitamin-D from sunshine help TB treatment?(photo: Jon Sullivan, courtesy of Public Domain Photos)

One of the characteristics making M. tuberculosis such an insidious killer is its uncanny ability to thwart many of our best defenses. Whether through hiding itself in our lungs for years or escaping our efforts at treatment through multi-drug resistance, this bug often acts as an exceptional escape artist.

One such form of evasion occurs in the very cells which are designed to be part of our bodies’ first line of defense against potential invaders. Upon arrival in the host lung, M. tuberculosis infect the macrophage, a white blood cell capable of engulfing foreign material it views as hostile. This process occurs, as expected, when the macrophage encounters the TB pathogen.

The macrophage comes across a roadblock, however, when attempting to fuse the TB-containing compartment (the phagosome) with a separate compartment containing bactericidal chemical species and peptides (the lysosome). The bacterium has demonstrated several mechanisms which prevent this fusion process by constructing barriers to normal host cellular function.

Why Self-Eating may be Useful for Finding New Tuberculosis Treatments

All is not lost, however. One possible mechanism for bypassing this obstruction is the normal cellular process of autophagy. As may be inferred from the name, autophagy is essentially “self-eating,” in which the cell recycles organelles and proteins by digesting them into components suitable for reuse. It has been observed in several studies that, when TB are captured in autophagy compartments (the autophagosome) instead of in normal phagosomes, the bacteria can no longer prevent fusion with the lysosome, and subsequent bactericidal activity.

In a recent study by Yuk, et al. it was reported that, not only does autophagy kill bacteria, but it is induced by a chemical we all get after a day at the beach: vitamin D. Yuk and colleagues demonstrated that, after treatment with the active form of vitamin D, TB are effectively targeted into autophagosomes, and the autophagy process is kick started through a cascade of protein activators and transcription factors. Notably among them is the antimicrobial peptide cathelicidin, which appears to be instrumental in shifting bacteria into the autophagy hopper. Vitamin D has previously been implicated in antimicrobial activity in other studies, and this work provides one potential mechanism.

What Does this Mean for the Treatment for TB?

So should we all grab our goggles and Glamour, and head off to the tanning salon as the next hot new treatment for TB? Probably not, considering the warnings of our friendly neighborhood dermatologist. But these studies certainly warrant a closer look at the utility of supplemental vitamin D therapy in the context of TB treatment, as well as exploring other potential ways to capture bacteria through cellular “self-eating.”

What do you think about vitamin D therapy and cellular “self-eating”? Is it worth a look as we search for new treatments for TB?

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