Date of Award

2010-01-01

Degree Name

Master of Science

Department

Public Health

Advisor(s)

Rodrigo X. Armijos

Abstract

Background. Leishmaniasis is a parasitic disease caused by an intracellular parasite belonging to the genus Leishmania. The cutaneous form of the disease causes often significant disfigurement, accelerates progression to clinical AIDS and tuberculosis, and is associated with a number of adverse economic, psychosocial, and nutritional consequences. An estimated 350 million persons are at risk for this globally distributed disease and 1.5-2 million new cases occur annually. Leishmaniasis is endemic in 88 countries on five continents. It is distributed throughout most of the Americas ranging from southern Texas to northern Argentina. It is also regarded as a threat to the readiness of U.S armed forces and civilian contractors deployed in Afghanistan, Iraq, and Kuwait. The sole first-line drug available for treating leishmaniasis is based on a heavy metal, antimony. It is associated with toxic side effects, is difficult to administer, is costly, and drug resistance is becoming increasingly common. The few available second-line drugs also are costly and have adverse side effects. In addition, there is no intervention available which can prevent the often extensive tissue destruction in patients caused by oxygen radicals generated during the immune response. The WHO has designated the development of new therapeutic alternatives for leishmaniasis as an important priority. Emerging evidence suggests that plant polyphenols such as those found in green tea may have beneficial health effects. Green tea contains a group of antioxidant scavengers (polyphenols) which have the ability to eliminate oxygenfree radicals that originate during inflammatory events. Green tea also is rich in ethylamine, which is recognized directly by γδ T lymphocytes and confers important γδ T-cell protective immune response during the early stage of certain infections (e.g., malaria, TB, herpes).

Objectives and Hypothesis. The major objective of the experimental study was to examine the potential beneficial effect of green tea caused by Leishmania mexicana. The a priori working hypothesis was that the use of green tea for the treatment of cutaneous leishmaniasis may provide some degree of protection from the deleterious effects of oxygen radicals originating during hagocytosis and thus improve clinical response during the early stage of infection.

Methods. 72 Leishmania-susceptible BALB/c mice were randomized to one of two groups. The experimental group (EG) with 36 mice drank green tea (1-1.2 mg/ml concentration) ad libitum and the control group (CG) of 36 mice drank tap water ad libitum for 14 weeks. During treatment week 4, mice were challenged by footpad injections of 1x106 L. mexicana promastigotes. Infection progression was followed-up by measuring weekly footpad thickness. Every two weeks, 5 mice from each group were euthanized and their tissues harvested for immunological and parasitological studies. Peritoneal macrophage cultures were infected with Leishmania promastigotes to assess their

microbicidal activity. Spleen lymphocytes were stimulated with Leishamia antigen to determine stimulation index, a cellular immune response indicator. Inflammatory cytokines were quantified by QRT-PCR. In addition, γδ T lymphocyte subpopulations in spleen leukocytes were assessed using flow cytometry.

Results. The average intake of green tea or water was estimated at ~9.17 ml/mice/day. The results indicated that the EG mice had reduced lesion size compared to CG mice ( = 0.027 mm ± 0.198 vs.0.09 mm ± 0.278). This pattern was evident by post-challenge week 8. However, by week 11, lesion size was similar in both groups. The In vitro analysis of infected peritoneal macrophages indicated that EG mice had fewer Leishmania parasites than CG mice when exposed to 5 ul ( =17,877.33 ± 5578.16 vs. 20,466 ± 4029.95) or 2.5μl ( =18,744 ± 11,092.58 vs. 22,179 ± 14,287.41) green teaconcentrations. The higher microbicidal activity also was evident even without any green tea ( =16405.88 ± 3705.21 vs. 25,757 ± 12,103.23). The lymphocyte proliferation assay results indicated that spleen lymphocytes from EG mice had a higher stimulation index when compared with those from CG mice ( =5.73 vs 0.94).

Conclusions. Green tea increased cellular immune response and microbicidal macrophage activity. It resulted in a significant deceleration of infection progression until the week 8th post challenge. The results suggest that green tea has possible potential as an antileishmaniasis adjunctive therapy. Further studies are needed to identify specific compounds in green tea that possess apparent anti-Leishmania activity.

Language

en

Provenance

Received from ProQuest

File Size

45 pages

File Format

application/pdf

Rights Holder

Alejandra Avila

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