Pulmonary cavitation, a hallmark of tuberculosis (TB), is the site of high mycobacterial burden leading to disease transmission. The cause of tissue destruction leading to cavitation in TB is primarily due to the host inflammatory response. A matrix degrading phenotype develops in TB, in which the activity of host proteolytic enzymes, specifically matrix metalloproteinases (MMPs) is unopposed by their specific Tissue Inhibitors of Metalloproteinases (TIMPs), thus driving tissue destruction and cavitation in TB. This tissue destruction causes morbidity and mortality. MMP inhibition with doxycycline has shown to improve lung function in patients with chronic lung diseases but its use in TB is unclear.

We hypothesise that the MMP inhibitor doxycycline will reduce tissue destruction in human pulmonary tuberculosis.

Specific aims:

• To investigate the MMP and TIMP secretion and gene expression in M. tuberculosis (M.tb) - infected primary neutrophils and monocytes from healthy volunteers taking doxycycline.
• To investigate the intracellular signaling pathways modulated by doxycycline
• To investigate the effects doxycycline has on biological markers of tissue destruction in TB patients
• To assess the tolerability and side effects of doxycycline with concurrent standard TB therapy

All TB patients are to keep to their standard anti-tuberculous treatment. A standardized questionnaire of symptoms, side-effects and weight shall be recorded. Induced sputum and plasma samples from all TB patients shall be analysed for MMPs and TIMPs before and after the administration of doxycycline for two weeks. In addition, neutrophils and mononuclear cells from TB patients and these shall be stimulated with live, virulent M. tuberculosis in a Biosafety Level 3 laboratory. The supernatants from these cells shall be analysed for MMPs and TIMPs.

Healthy volunteers shall be recruited and administered doxycycline for 2 weeks. Neutrophils and mononuclear cells will be isolated from blood prior to treatment, at weeks 2 and 8 and infected with M.tb. Cell culture supernatants and nucleic acids will be harvested. MMP and TIMP expression will be analysed using luminex array and real-time polymerase chain reaction. Intracellular signaling pathways will be examined with a human phospho-kinase array. Matrix destruction will be assessed using collagen quantitative fluorescent assays.

Healthy Volunteers 10 volunteers will be recruited comprising 5 females and 5 males.

Inclusion criteria:

1. No known medical conditions
2. Aged 21 years to less than 70.

Exclusion criteria:

1. Unable to give informed consent
2. Prisoners
3. Pregnancy or nursing
4. On medication or oral contraceptives
5. Any concurrent illness, such as influenza

TB patients

Inclusion criteria: Patients should meet all criteria

1. Patients receiving ≤ 7 days of TB treatment or about to start standard combination TB treatment
2. Confirmed pulmonary TB with positive acid-fast bacilli smear and/or positive TB GeneXpert test and/or culture results
3. Chest radiograph demonstrating pulmonary involvement
4. Aged 21 years to less than 70

Exclusion criteria:

1. HIV co-infection
2. Previous pulmonary TB
3. Severe, pre-existing lung disease such as pulmonary fibrosis, bronchiectasis, Chronic obstructive pulmonary disease and lung cancer
4. Pregnant or breast feeding
5. Allergies to tetracyclines
6. Patients on retinoic acid, neuromuscular blocking agents and pimozide which may increase risk of drug toxicity
7. Autoimmune disease and/or on systemic immunosuppressants
8. Unable to provide informed consent
9. Haemoglobin < 8 g/dl
10. Creatinine 2 times upper limit of normal (ULN)
11. Alanine transaminase >3 times ULN
12. Use of any investigational or non-registered drug, vaccine or medical device other than the study drug within 182 days preceding dosing of study drug, or planned use during the study period
13. Enrolment in any other clinical trial involving a systemic drug or intervention involving the lung
14. Evidence of severe depression, schizophrenia or mania
15. Principal investigator assessment of lack of willingness to participate and comply with all requirements of the protocol, or identification of any factor felt to significantly increase the participant's risk of suffering an adverse outcome