Macrophage-targeted versus free calcitriol as host-directed adjunct therapy against Mycobacterium tuberculosis infection in mice is bacteriostatic and mitigates tissue pathology

Host-directed therapy (HDT) with vitamin D in tuberculosis (TB) is beneficial only if the subject is deficient in vitamin D. We investigated pulmonary delivery of 1,25-dihydroxy vitamin D3 (calcitriol) in mice infected with Mycobacterium tuberculosis (Mtb). We made two kinds of dry powder inhalations (DPI)— soluble particles or poly(lactide) (PLA) particles. We compared treatment outcomes when infected mice were dosed with a DPI alone or as an adjunct to standard oral anti-TB therapy (ATT). Mice infected on Day 0 were treated between Days 28–56 and followed up on Days 57, 71, and 85. Neither DPI significantly reduced Mtb colony forming units (CFU) in the lungs. Combining DPI with ATT did not significantly augment bactericidal activity in the lungs, but CFU were 2-log lower in the spleen. CFU showed a rising trend on stopping treatment, sharper in groups that did not receive calcitriol. Lung morphology and histology improved markedly in animals that received PLA DPI; with or without concomitant ATT. Groups receiving soluble DPI had high mortality. DPI elicited cathelicidin, interleukin (IL)-1 and induced autophagy on days 57, 71, and 85. Macrophage-targeted calcitriol is therefore bacteriostatic, evokes innate microbicidal mechanisms, and mitigates pathology arising from the host response to Mtb. [Display omitted] •Calcitriol, the ‘active metabolite’ of Vitamin D can be targeted to lung macrophages by inhaling a powder.•Targeted calcitriol is less efficacious in inducing host responses, but much better tolerated than free calcitriol.•In mice with M.tuberculosis infection, inhaled, targeted calcitriol does not ‘kill the bug’ but ‘heals the host.