Letno poročilo 2005

Laboratorij za biotehnologijo
Laboratory of Biotechnology
uporabljene tudi preventivno za terapijo gramnegativne
sepse«, pravi Sunil David iz Univerze
v Kansasu v ZDA.
»Za naravni antibioti~ni lipopeptid polimiksin B
je `e dolgo znano, da nevtralizira bakterijski
endotoksin, vendar njegova toksi~nost prepre-
~uje uporabo kot sistemski antibiotik«, pravi
Jerala. »Za lipopoliamine vemo, da nevtralizirajo
endotoksin, ne da bi bili toksi~ni za sesalske
celice, vendar doslej znane spojine niso imele
antimikrobnega delovanja«. Njegova skupina
raziskuje sinteti~ne lipopeptide, med katerimi
posku{ajo pripraviti tak{ne, ki bi posnemali
polimiksin B, ob tem pa bi se izognili njegovi
toksi~nosti za gostiteljske celice.
»Pri na{ih raziskavah smo ob izvajanju kontrol
opazili, da ima ena od izhodnih sestavin -
oleilamin, ne pa tudi sorodne spojine, antimikrobno
delovanje, kar nas je navedlo, da
razi{~emo strukturne zahteve za to aktivnost«,
pravi Jerala. »Lipid A, neobhoden del strukture
endotoksina, je zelo ohranjen med bakterijami.
Z analizo njegove strukture smo ugotovili, da
bi morala imeti spojina, ki bi nevtralizirala
endotoksin, hidrofobno povr{ino ter par
kationskih mest na ustrezni razdalji, tako da bi
se vezali na dve fosfatni skupini lipida A«.
Z upo{tevanjem teh zahtev so raziskovalci
sintetizirali skupino spojin in testirali njihovo
delovanje na bakterije. Pokazalo se je, da je
dejansko mo`no kombinirati tako antimikrobno
aktivnost kot tudi nevtralizacijo endotoksina,
dodatno pa spojine za razliko od polimiksina B
presenetljivo dobro delujejo tudi proti grampozitivnim
bakterijam.
»Predvidevamo, da bodo bakterije te`ko razvile
odpornost proti oleoilaminom«, pravi Jerala.
»Verjetno bodo te spojine imele podobno
delovanje kot naravni kationski antimikrobni
peptidi, proti katerim je odpornost dokaj redka,
saj je bistvena sprememba lastnosti membrane
za bakterije neugodna. Bakterije, ki so odporne
proti kationskim peptidom, imajo obi~ajno
nizko virulenco in jih organizem tudi la`je
inaktivira s fagocitozo«.
150
the therapy of gram-negative sepsis,” says Sunil
A. David, of the University of Kansas, Lawrence.
A lipopeptide compound called polymyxin B
“has long been known to neutralize bacterial
endotoxin, but its toxicity prevents its use as a
systemic drug,” says Jerala. Lipopolyamines had
been known to neutralize endotoxin (AKA lipopolysaccharide
¢LPS¥ without toxicity to
eukaryotic cells, says Jerala, but they lacked
antibiotic activity. His group had been experimenting
with synthetic lipopeptides, trying to
find one that one mimic polymyxin B’s LPS-neutralizing
without killing eukaryotic cells. “We
noticed that oleylamine but not other saturated
alkylamines had antimicrobial activity, which
prompted us to investigate the structural requirements
for the activity,” says Jerala. Part of
the structure of the “lipid A” section of LPS is
highly conserved across the bacteria. The details
of this structure suggested that an LPS
neutralizing agent should have a water-repelling
surface, and a pair of “cationic interaction
sites” that would be spaced such that they could
interact with the two phosphate groups of lipid
A. The researchers then synthesized novel
oleoylamines incorporating these properties,
and then tested them against bacteria. The results
“showed that it is indeed possible to combine
both antimicrobial activity and neutralization
of LPS and that surprisingly, the compounds
showed also comparable activity against grampositive
bacteria. Bacteria would probably have
trouble developing resistance to oleoylamine
antibiotics, says Jerala. “I believe that oleylamines
probably would behave like cationic antimicrobial
peptides, where resistance is quite
rare since it is expensive for the bacteria to
modify the properties of their membrane,” he
says. “Bacteria resistance to cationic antimicrobial
peptides usually have attenuated virulence
and are more efficiently inactivated by
phagocytes.”