Trabecular meshwork bradykinin receptors: mRNA levels, immunohistochemical visualization, signaling processes pharmacology, and linkage to IOP reduction.
OBJECTIVE
To localize mRNA and protein of bradykinin (BK) receptors, BK precursor polypeptide (kininogen) mRNA, and to study functional biochemical pharmacology of the signal transduction processes mediated by B2-receptors in isolated human trabecular meshwork (h-TM) cells. Intraocular pressure (IOP) lowering effects of 2 kinins were also investigated.


METHODS
Previously documented procedures were utilized throughout these studies.


RESULTS
Kinninogen mRNA was most abundant in TM, ciliary body (CB), and optic nerve head and appeared elevated in glaucomatous h-TM tissue. High levels of B2-receptor mRNA were found in the sclera, iris, TM, and CB. B2-receptor subtype protein was localized in cells of the monkey and h-TM, and the treatment of isolated h-TM cells with transforming growth factor-β2 (5 ng/mL) caused significant (P<0.04) downregulation of B2-receptor mRNA. In isolated primary h-TM cells, BK (EC50=0.8±0.2 nM; n=19) and Met-Lys-BK (EC50=6.5±1.5 nM) mobilized intracellular Ca(2+) and induced the release of prostaglandins (PGs) that was blocked by 2 B2-receptor antagonists [HOE-140; (S)-WIN-64338]. The cyclooxygenase inhibitor, bromfenac, abolished BK-induced PGs production. BK concentration dependently increased cell impedance, and it significantly (P<0.05) decreased h-TM cell volume in vitro. Intravitreal (ivt) administration of BK (50 μg), but not a B1-agonist (Sar-[D-Phe(9)]-Des-Arg(9)-BK; also at 50 μg), efficaciously lowered IOP (22.9% to 37% from baseline) of Dutch-Belted rabbits that naturally have high IOPs (27-28 mmHg).


CONCLUSIONS
BK activates multiple signal transduction pathways in h-TM cells via B2-receptors that also mediate IOP reduction as observed in rabbits following ivt administration of BK. These ocular hypotensive effects of BK may be physiologically important and suggest a novel therapeutic potential of BK-related B2-agonists.
1 Pharmaceutical Research , Alcon Research, Ltd. (A Novartis Company), Fort Worth, Texas.
Najam A
NA
Sharif
Parvaneh
P
Katoli
Curtis R
CR
Kelly
Linya
L
Li
Shouxi
S
Xu
Yu
Y
Wang
Laura
L
Klekar
David
D
Earnest
Shenouda
S
Yacoub
Gwenette
G
Hamilton
Nasreen
N
Jacobson
Allan R
AR
Shepard
Dorette
D
Ellis
D000368:Aged; D000818:Animals; D001577:Benzophenones / Q000494:pharmacology; D001920:Bradykinin / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D065094:Bradykinin B2 Receptor Antagonists; D001969:Bromobenzenes / Q000494:pharmacology; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007429:Intraocular Pressure / Q000187:drug effects / Q000502:physiology*; D007704:Kininogens / Q000235:genetics / Q000378:metabolism*; D008252:Macaca fascicularis; D008297:Male; D009281:Naphthalenes / Q000494:pharmacology; D009943:Organophosphorus Compounds / Q000494:pharmacology; D011453:Prostaglandins / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D011817:Rabbits; D043782:Receptor, Bradykinin B2 / Q000235:genetics / Q000378:metabolism; D018002:Receptors, Bradykinin / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D014129:Trabecular Meshwork / Q000166:cytology / Q000378:metabolism
D001577:Benzophenones; D065094:Bradykinin B2 Receptor Antagonists; D001969:Bromobenzenes; D007704:Kininogens; D009281:Naphthalenes; D009943:Organophosphorus Compounds; D011453:Prostaglandins; D012333:RNA, Messenger; D043782:Receptor, Bradykinin B2; D018002:Receptors, Bradykinin; C087374:WIN 64338; C065679:icatibant; C053083:bromfenac; D001920:Bradykinin