Synthetic Peptide VKGFY and Its Cyclic Analog Stimulate Macrophage Bactericidal Activity through Non-Opioid beta-Endorphin Receptors

E. V. Navolotskaya^1*, A. A. Kolobov², E. A. Kampe-Nemm², T. A. Zargarova¹, N. V. Malkova¹, S. B. Krasnova¹, Yu. A. Kovalitskaya¹, V. P. Zav'yalov³, and V. M. Lipkin¹

¹Branch of Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Pushchino, Moscow Region, 142290 Russia; fax: (0967) 79-0527; E-mail: navolots@fibkh.serpukhov.su

²State Research Institute for Highly Pure Biopreparations, Ministry of Health of the Russian Federation, ul. Pudozhskaya 7, St. Petersburg, 197110 Russia; fax: (812) 235-5504

³Center for Immunological Engineering “Biokad”, Lyubuchany, Moscow Region, 142380 Russia; fax: (095) 797-5689

^* To whom correspondence should be addressed.

Received July 18, 2002

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We synthesized linear and cyclic pentapeptides corresponding to the sequence 369-373 of human immunoglobulin G heavy chain--VKGFY (referred to as pentarphin and cyclopentarphin, respectively). The effect of pentarphin and cyclopentarphin on phagocytosis of Salmonella typhimurium virulent 415 strainbacteria by mouse peritoneal macrophages in vitro was studied. Control experiments showed that macrophages actively captured these bacteria, but did not digest them: the captured microbes were viable and continued to proliferate inside the phagocytes; within 12 h all macrophage monolayer was destroyed (incomplete phagocytosis). If 1 nM pentarphin or cyclopentarphin was added to the cultivation medium, macrophage bactericidal activity was significantly increased and they digested all captured microorganisms within 6 h (complete phagocytosis). To study the receptor binding properties of pentarphin and cyclopentarphin we prepared ¹²⁵I-labeled pentarphin (179 Ci/mmol specific activity). The binding of ¹²⁵I-labeled pentarphin to mouse peritoneal macrophages was high-affinity (K_d = 3.6 ± 0.3 nM) and saturable. Studies on binding specificity revealed that this binding was insensitive to naloxone and [Met⁵]enkephalin, but completely inhibited by unlabeled cyclopentarphin (K_i = 2.6 ± 0.3 nM), immunorphin (K_i = 3.2 ± 0.3 nM), and beta-endorphin (K_i = 2.8 ± 0.2 nM). Thus, the effects of pentarphin and cyclopentarphin on macrophages are mediated by naloxone-insensitive receptors common for pentarphin, cyclopentarphin, immunorphin, and beta-endorphin.

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KEY WORDS: phagocytosis, macrophage, beta-endorphin, tuftsin, naloxone, immunoglobulin G, peptides, receptors, immune system

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