Inhibition of Leishmania Major Parasite Growth by Blocking Inflammation Signaling Pathway in Infected Macrophages
Mosigisi, Albert Nyaberi
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Human leishmaniasis is a spectrum of diseases caused by protozoan parasites of the genus Leishmania transmitted by female Phlebotomous sand flies. Amphotericin B, Pentamidine and pentavalent antimony compounds are the current drugs being used for treatment of leishmaniasis. However, they are expensive and have shown elevated toxicity, persistent side effects and parasites have developed resistance against them. Leishmania regulates nuclear factor- kappa beta (NF-KB) signalling pathway, which has been shown to be important in immunity against the parasite. Activation ofNF-KB is by inducing the cleavage and activation ofNF-KB p65 RelA subunit that translocates to the nucleus. This induces the expression of Th2 cytokines blocking the induction of nitric oxide synthase, lNF -a and interleukin 1p thus subverting the host defense response and promoting the survival and development of the parasite inside the macrophages. Glucocorticoids namely dexamethasone and hydrocortisone have been demonstrated to repress the NF-KB signalling pathway. The current study aimed at determining the effects of dexamethasone and hydrocortisone on Leishmania major parasite growth in macrophages. The current study was a laboratory based, done at KEMRI, Leishmania laboratory. Macrophages were treated separately with dexamethasone, hydrocortisone and Lipopolysaccharide (LPS), for eight hours after which they were infected with Leishmania promastigotes. Evaluation of expression of genes downstream NF-KB promoter site in the nucleus was done by using quantitative real time peR. Parasite development in macrophages was then evaluated by counting the number of amastigotes in treated and untreated macrophages (negative control). Macrophages treated with LPS (positive control). Data was obtained in form of parasite counts and relative expression values and were analyzed using student's t test. Results indicated that interleukin-I p gene was repressed in macrophages treated with dexamethasone and hydrocortisone with 1.3 fold and 16 fold respectively and down expressed in LPS treated macrophage with 3.25 fold. lNF-a gene was repressed in macrophages treated with dexamethasone and hydrocortisone drugs. There was significantly low expression of inducible nitric oxide synthase (iNOS) gene in macrophages treated with dexamethasone and hydrocortisone as compared to LPS treated macrophages. The study also demonstrated that dexamethasone and LPS had significantly higher reduction of parasite growth (p<0.05) compared to untreated macrophages, respectively. Of importance is that dexamethasone showed reduction of infection rates in macrophages (34%) as compared to hydrocortisone (47%), untreated macrophages (63%) and LPS treated macrophages (47%). The study also found out that dexamethasone and hydrocortisone drugs did not stimulate macrophages to produce Nitric oxide (NO) (all produced less than optical density of 0.05). Since this experiments were conducted in vitro, there is need to confirm the validity of results obtained in in vivo experiments. Furthermore, this study suggests that by inhibition of NF-KB pathway in macrophages, dexamethasone can be developed as drug for treatment regimen of leishmaniasis.
- MST-Zoological Sciences