Serum lipids as biomarkers for therapeutic monitoring of latent tuberculosis infection

To the Editor: The World Health Organization has estimated that more than two billion persons in the world carry latent tuberculosis infection (LTBI). The diagnosis and treatment of LTBI could have an important impact in preventing the development of active tuberculosis (TB), a disease that causes 1.4 million deaths annually [1]. The current standard treatment of LTBI is nine months of isoniazid (INH) [2]. To improve adherence, a shorter regimen of 4 months rifampicin (RIF) is being evaluated in a multicentre randomised trial (CIHR MCT-94831, registered at www.controlled-trials.com/ISRCTN05675547). This ongoing trial offers an opportunity to study potential biomarkers as surrogates of successful prevention of active disease [3]. Several changes in lipid metabolism could potentially be utilised as biomarkers of effectiveness of LTBI treatment with RIF or INH. RIF is an important stimulator of the pregnane X receptor (PXR), which has been hypothesised to increase the blood levels of high density lipoprotein cholesterol (HDLC) and its protein component apolipoprotein A-1 (apoA) [4, 5]. This hypothesis was supported by observational studies that demonstrated an increased plasma level of HDLC among epileptic patients who were taking anticonvulsant medications which activate the PXR [6]. By contrast, treatment with INH was associated with lower cholesterol blood levels in one small study [7]. ApoA and apolipoprotein B (apoB), a protein component of low density lipoprotein cholesterol (LDLC), have stable serum blood levels without post-prandial changes and low within-individual variability [8]. Total cholesterol and HDLC are inexpensive to measure, reliably …