Polyamines Impair Immunity to Helicobacter pylori by Inhibiting L-Arginine Uptake Required for Nitric Oxide Production.
OBJECTIVE
Helicobacter pylori-induced immune responses fail to eradicate the bacterium. Nitric oxide (NO) can kill H pylori. However, translation of inducible NO synthase (iNOS) and NO generation by H pylori-stimulated macrophages is inhibited by the polyamine spermine derived from ornithine decarboxylase (ODC), and is dependent on availability of the iNOS substrate L-arginine (L-Arg). We determined if spermine inhibits iNOS-mediated immunity by reducing L-Arg uptake into macrophages.


METHODS
Levels of the inducible cationic amino acid transporter (CAT)2, ODC, and iNOS were measured in macrophages and H pylori gastritis tissues. L-Arg uptake, iNOS expression, and NO levels were assessed in cells with small interfering RNA knockdown of CAT2 or ODC, and in gastric macrophages. The ODC inhibitor, α-difluoromethylornithine, was administered to H pylori-infected mice for 4 months after inoculation.


RESULTS
H pylori induced CAT2 and uptake of L-Arg in RAW 264.7 or primary macrophages. Addition of spermine or knockdown of CAT2 inhibited L-Arg uptake, NO production, and iNOS protein levels, whereas knockdown of ODC had the opposite effect. CAT2 and ODC were increased in mouse and human H pylori gastritis tissues and localized to macrophages. Gastric macrophages from H pylori-infected mice showed increased ODC expression, and attenuated iNOS and NO levels upon ex vivo H pylori stimulation versus cells from uninfected mice. α-Difluoromethylornithine treatment of infected mice restored L-Arg uptake, iNOS protein expression, and NO production in gastric macrophages, and significantly reduced both H pylori colonization levels and gastritis severity.


CONCLUSIONS
Up-regulation of ODC in gastric macrophages impairs host defense against H pylori by suppressing iNOS-derived NO production.
Chaturvedi
Rupesh
R
Division of Gastroenterology, Hepatology, and Nutrition, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
Asim
Mohammad
M
Hoge
Svea
S
Lewis
Nuruddeen D
ND
Singh
Kshipra
K
Barry
Daniel P
DP
de Sablet
Thibaut
T
Piazuelo
M Blanca
MB
Sarvaria
Aditya R
AR
Cheng
Yulan
Y
Closs
Ellen I
EI
Casero
Robert A
RA
Gobert
Alain P
AP
Wilson
Keith T
KT
D000818:Animals; D001120:Arginine / Q000037:antagonists & inhibitors* / Q000378:metabolism; D027202:Cationic Amino Acid Transporter 2 / Q000096:biosynthesis / Q000235:genetics; D002478:Cells, Cultured; D004195:Disease Models, Animal; D005753:Gastric Mucosa / Q000378:metabolism* / Q000382:microbiology; D005756:Gastritis / Q000378:metabolism / Q000382:microbiology / Q000473:pathology; D005786:Gene Expression Regulation; D016481:Helicobacter Infections / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology; D016480:Helicobacter pylori / Q000276:immunology / Q000472:pathogenicity*; D006801:Humans; D007111:Immunity, Cellular / Q000502:physiology*; D008264:Macrophages / Q000276:immunology / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009569:Nitric Oxide / Q000096:biosynthesis*; D052247:Nitric Oxide Synthase Type II / Q000096:biosynthesis / Q000235:genetics; D009955:Ornithine Decarboxylase / Q000096:biosynthesis / Q000235:genetics; D011073:Polyamines / Q000494:pharmacology; D012313:RNA / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013096:Spermine / Q000494:pharmacology*
D027202:Cationic Amino Acid Transporter 2; D011073:Polyamines; D013096:Spermine; D009569:Nitric Oxide; D012313:RNA; D001120:Arginine; D052247:Nitric Oxide Synthase Type II; D009955:Ornithine Decarboxylase