Polyamine synthesis and levels during the growth and replication of Leishmania tropica minor and Leishmania aethiopica

Abstract

1. Introduction The polyamines putrescine, spermidine and spermine, which occur widely in nature [l-5], are involved in cellular growth processes [6]. At physiol- ogical levels, they stimulate DNA [7], RNA [8] and protein ]9,10] synthesis, and reach their peak levels during periods of maximal growth [I]. They are required for optimal growth in bacteria, where their limitation leads to reduced cellular growth [ 111 and their concentration is markedly increased in rapidly growing mammalian cells [l], with this growth being arrested on inhibition of polyamine synthesis [ 121. It was shown that polyamines also occur in various trypanosomatid protozoa, where they are at their maximal levels during the logarithmic phase of growth [13-l 61. We have demonstrated that some antileishmanial drugs and polyamine analogues, i.e., pentamidine isethionate, ethidium bromide and methyglyoxal-bis (guanyl hydrazone) (MGBG), impair leishmanial growth by interfering with polyamine biosynthesis [ 161. In order to demonstrate the causal relationship between leishmanial growth and polyamine biosynthesis, a correlation between growth rate and putrescine to spermidine ratio must be established. In this study we demonstrate such a correlation. 2. Materials and methods The two strains studied were obtained from the 202 culture collection of the World Health Organisation’s International Reference Centre for Leishmaniasis (WHO-LRC), housed in the Department of Protozoology of the Hebrew University-Hadassah Medical School, Jerusalem. Their origins and some of their intrinsic taxonomic characters are given in table 1. These strains were maintained at 28°C by biweekly passage on semisolid Locke-blood-agar [ 191 or NNN diphasic medium [20]. For experimental studies, the strains were grown in a fully-liquid, Panmede (Paines and Byrne Ltd., Greenford, Middlesex, England) based medium, containing 7.5% normal rabbit blood