Protein energy malnutrition increases arginase activity in monocytes and macrophages.

BACKGROUND: Protein energy malnutrition is commonly associated with immune dysfunctions and is a major factor in susceptibility to infectious diseases. METHODS: In this study, we evaluated the impact of protein energy malnutrition on the capacity of monocytes and macrophages to upregulate arginase, an enzyme associated with immunosuppression and increased pathogen replication. RESULTS: Our results show that monocytes and macrophages are significantly increased in the bone marrow and blood of mice fed on a protein low diet. No alteration in the capacity of bone marrow derived macrophages isolated from malnourished mice to phagocytose particles, to produce the microbicidal molecule nitric oxide and to kill intracellular Leishmania parasites was detected. However, macrophages and monocytes from malnourished mice express significantly more arginase both in vitro and in vivo. Using an experimental model of visceral leishmaniasis, we show that following protein energy malnutrition, the increased parasite burden measured in the spleen of these mice coincided with increased arginase activity and that macrophages provide a more permissive environment for parasite growth. CONCLUSIONS: Taken together, these results identify a novel mechanism in protein energy malnutrition that might contributes to increased susceptibility to infectious diseases by upregulating arginase activity in myeloid cells.

Arginase activity - a marker of disease status in patients with visceral leishmaniasis in ethiopia.

The underlying mechanisms resulting in the profound immune suppression characteristic of human visceral leishmaniasis (VL) are not fully understood. Here, we tested the hypothesis that arginase, an enzyme associated with immunosuppression, is higher in patients with VL and contributes to impaired T cell responses. We recruited patients with VL before and after treatment and healthy controls and measured the arginase metabolism in the blood of these individuals. Our results show that arginase activity is significantly higher in the blood of patients with active VL as compared to controls. These high levels of arginase decline considerably once the patients are successfully treated. We identified the phenotype of arginase-expressing cells among PBMCs as neutrophils and show that their frequency was increased in PBMCs of patients before treatment; this coincides with reduced levels of L-arginine in the plasma and decreased expression levels of CD3ζ in T cells.

Local increase of arginase activity in lesions of patients with cutaneous leishmaniasis in Ethiopia.

BACKGROUND: Cutaneous leishmaniasis is a vector-borne disease that is in Ethiopia mainly caused by the parasite Leishmania aethiopica. This neglected tropical disease is common in rural areas and causes serious morbidity. Persistent nonhealing cutaneous leishmaniasis has been associated with poor T cell mediated responses; however, the underlying mechanisms are not well understood. METHODOLOGY/PRINCIPAL FINDINGS: We have recently shown in an experimental model of cutaneous leishmaniasis that arginase-induced L-arginine metabolism suppresses antigen-specific T cell responses at the site of pathology, but not in the periphery. To test whether these results translate to human disease, we recruited patients presenting with localized lesions of cutaneous leishmaniasis and assessed the levels of arginase activity in cells isolated from peripheral blood and from skin biopsies. Arginase activity was similar in peripheral blood mononuclear cells (PBMCs) from patients and healthy controls. In sharp contrast, arginase activity was significantly increased in lesion biopsies of patients with localized cutaneous leishmaniasis as compared with controls. Furthermore, we found that the expression levels of CD3ζ, CD4 and CD8 molecules were considerably lower at the site of pathology as compared to those observed in paired PBMCs. CONCLUSION: Our results suggest that increased arginase in lesions of patients with cutaneous leishmaniasis might play a role in the pathogenesis of the disease by impairing T cell effector functions.

Accelerated healing of cutaneous leishmaniasis in non-healing BALB/c mice using water soluble amphotericin B-polymethacrylic acid.

Cutaneous leishmaniasis (CL) is a neglected tropical disease that causes prominent skin scaring. No water soluble, non-toxic, short course and low cost treatment exists. We developed a new water soluble amphotericin B-polymethacrylic acid (AmB-PMA) using established and scalable chemistries. AmB-PMA was stable for 9 months during storage. In vitro, it was effective against Leishmania spp. promastigotes and amastigote infected macrophages. It was also less toxic and more effective than deoxycholate-AmB, and similar to liposomal AmB. Its in vivo activity was determined in both early and established CL lesion models of Leishmania major infection in genetically susceptible non-healing BALB/c mice. Intradermal AmB-PMA at a total dose of 18 mg of AmB/kg body weight led to rapid parasite killing and lesion healing. No toxicity was seen. No parasite relapse occurred after 80 days follow-up. Histological studies confirmed rapid parasite clearance from macrophages followed by accelerated fibroblast mediated tissue repair, regeneration and cure of the infection. Quantitative mRNA studies of the CL lesions showed that accelerated healing was associated with increased Tumour Necrosis Factor-α and Interferon-γ, and reduced Interleukin-10. These results suggest that a cost-effective AmB-PMA could be used to pharmacologically treat and immuno-therapeutically accelerate the healing of CL lesions.

An amphotericin B-based drug for treating experimental Leishmania major infection.

There is an urgent need for a non-toxic and low-cost treatment for cutaneous leishmaniasis. We synthesised and tested in vivo an amphotericin B-poly(methacrylic acid) drug (AmB-PMA) that had previously shown in-vitro activity against Leishmania major and L. donovani parasites. Efficacy was determined using L. major footpad infection in 30 non-healing BALB/c mice. Three subcutaneous injections of AmB-PMA at days 7, 14 and 21 post-infection resulted in a reduction of ∼80% in lesion size by day 35 post-infection in 18 treated mice compared with six untreated controls, and complete healing of lesions by day 50 with no lesion relapse seen at day 80 post-infection in six treated mice. Healing was associated with decreased IL-10 (P=0.002) and increased IFN-γ (P=0.005) in the footpad.

Leishmania infantum proteophosphoglycans regurgitated by the bite of its natural sand fly vector, Lutzomyia longipalpis, promote parasite establishment in mouse skin and skin-distant tissues.

We demonstrate that a proteophosphoglycan-rich gel secreted by Leishmania infantum inside the midgut of Lutzomyia longipalpis sand flies (promastigote secretory gel) is regurgitated along with an average dose of 500 L. infantum metacyclic promastigotes per infected bite. Using both low (10³) and high (105) doses of parasites in the ears of BALB/c mice we show that the infections benefit from the presence of vector saliva and parasite gel in the skin. However, chronic infection of the spleen was only enhanced in high dose co-infections with gel. These results provide the framework for a more natural experimental model of visceral leishmaniasis.