Association of circulating serum free bioavailable and total vitamin D with cathelicidin levels among active TB patients and household contacts

Abstract

The free hormone hypothesis postulates that the estimation of free circulating 25 (OH)D may be a better marker of vitamin D status and is of clinical importance compared to total vitamin D fraction. The unbound fraction is involved in biological activities since it is able to penetrate into the cell. Studies have shown that cathelicidin/LL-37 inhibits the growth of Mycobacterium tuberculosis in a vitamin D-dependent manner and therefore adequate vitamin D is required for its expression. The study aimed to determine the association between serum bioavailable and total vitamin D with LL-37 levels in ATB patients, LTBI, and individuals with no TB infection. This was a cross-sectional study in which bioavailable vitamin D and LL-37 levels were measured using competitive ELISA kits and total vitamin D was measured using electrochemilumiscence and consequently determined their association. The mean (SD) bioavailable vitamin D levels of the study participants were 3.8 ng/mL (2.6) and the median (IQR) of LL-37 levels were 320 ng/mL (160, 550 ng/mL). The mean (SD) of total vitamin D levels was 19.0 ng/mL (8.3) ng/mL. Similar weak correlations were observed between the bioavailable and total vitamin D with LL-37 levels, therefore, deviating from our hypothesis.

Figure 1

Correlation of bioavailable total vitamin D levels in ATB, LTBI, and individuals with no TB infection.

Figure 2

Comparison of serum LL-37 levels among ATB patients, LTBI individuals, and individuals with no TB infection. Median serum concentrations were significantly higher among the ATB patients compared to the LTBI and those with no TB infection.

Figure 3

Shows the correlation of LL-37 with Bioavailable vitamin D levels among ATB patients, LTBI, and individuals with no TB infection.

Figure 4

Correlation of LL-37 with total vitamin D levels in ATB, LTBI, and individuals with no TB infection.