The effect of pre-infection omega-3 fatty acid status on anaemia of infection and morbidity in tuberculosis infected mice

Abstract

Background: Tuberculosis (TB) is currently a major health problem worldwide, and despite improvement, mortality rates are not ideal. Since the immune response, underlying protection against TB is incompletely understood, long durations of treatment time and poor health outcomes remain a problem. Therefore, host directed non-pharmaceutical interventions, supporting TB treatment, may be a promising approach to improve outcomes. Previous studies have found anti-inflammatory treatment to improve TB outcomes and the anti-inflammatory and pro-resolving properties of omega-3 (n-3) polyunsaturated fatty acids (PUFAs) treatment have been proven beneficial in other inflammatory diseases. Due to the fact that TB is known to be a disease of non-resolving inflammation leading to host tissue damage and poor clinical outcomes, the main aim of this study was to investigate whether sufficient and deficient n-3 PUFA status, after TB infection, had an influence on markers of morbidity, disease progression and anaemia of infection (AI). Methods: Eighteen 8 to 12-week-old C3HeB/FeJ mice were infected with TB via the intranasal route (high dose acute infection), and 12 mice via the aerosol route (low dose chronic infection) after conditioning for six weeks on an n-3 PUFA sufficient (FAS) or deficient (FAD) diet. Red blood cell (RBC) fatty acid status, whole blood haemoglobin (Hb), and body weight were determined the day before infection and markers of AI (Hb, plasma ferritin, transferrin receptor (TfR) and hepcidin), morbidity (appearance, respiratory rate, and body weight) and disease progression and clinical outcomes (lung bacillary load, organ indexes, and lung cytokine concentrations) were analyzed and compared between the two different groups 35 days after infection upon euthanization. Results: At euthanasia, intranasal and aerosol groups showed differences in PUFA composition with regards to all n-6 PUFA (all p < 0.001) and n-3 PUFAs (all p < 0.001, except docosahexaenoic acid (DHA) in aerosol subgroup p = 0.003) in RBC. Mice from the aerosol FAD subgroup had lower Hb concentrations prior to infection (p = 0.003), and a lower bacterial load (p = 0.008) and spleen-body-weight-index (p = 0.006) at 35 days post infection. In contrast, in the aerosol infected mice, the decrease in Hb in the n-3 FAS subgroup were more than in the n-3 FAD subgroup during the five weeks of TB infection (p = 0.027). No effects were found post-infection in other markers of AI. Inflammatory marker profiles showed a trend (p=0.061) towards lower pro-inflammatory cytokine IL-12 in the aerosol n-3 FAD subgroup. Conclusion: The lower-dose aerosol infection model was generally more sensitive to effects of n-3 PUFA sufficiency and deficiency. Without infection, n-3 PUFA sufficiency may contribute to improved Hb concentrations compared to n-3 PUFA deficiency. However, n-3 PUFA sufficiency may give rise to a bigger decrease in Hb concentrations after infection. Furthermore, contradicting to what was expected n-3 PUFA deficiency caused slower disease progression compared to an n-3 PUFA sufficient status. Future research should investigate whether an additional n-3 PUFA supplement together with TB medication (rather than only providing sufficient n-3 PUFA intake) may improve markers of AI and whether morbidity may be affected positively or even worsened in this case.