Background/Purpose:

Kinins are a group of peptides formed in plasma and tissues in response to infection, tissue trauma or inflammation (inflamm) whose actions are mediated by activation of B1 and B2 receptors (B1R and B2R). B1R are normally sparsely expressed, but can be induced by inflammatory stimuli. The current study explored the time dependence of oedema and B1 messenger ribonucleic acid (mRNA) expression in different tissues following intraplantar (ipl) carrageenan (carra) injection as well as the action of dexamethasone (dex).  In a separate study, the importance of B1 mRNA induction to carra-induced oedema and hyperalgesia were explored using a novel selective bradykin B1 receptor antagonist, BI-113823.

Methods:

Male rats were dosed orally with water (n=110) or dex (1 mg per kg, n=20).  1 h later at T=0, rats were given ipl injections of carra (100 µL x 1% in saline, n=60) or saline (n=70). Of the dex treated rats, half received carra. Paw volumes were measured 0, 1, 2, 4, 8 and 24 h after ipl injections.  Corresponding liver, lung and paw pad samples were also collected at each timepoint (10 carra and 10 saline rats per time point) and frozen. All dex treated rats were culled after the 2 h time point.

Tissues and blood were lysed and tissues homogenised on ice. Total RNA was extracted using a MagMAX^TM-96 Total or Blood RNA isolation procedure and quality (260:280 ratios) and quantity assessed by spectrophotometer. Reverse transcription was performed using a high capacity RNA-to-copy deoxyribonucleic acid (cDNA) kit and 96 well Thermal Quantitative polymerase chain reaction (PCR) analysis was performed on the resultant cDNA, using  TaqMan^® gene expression assay kit for the target gene B1R and endogenous control (β-actin). Samples were then analysed using a real time PCR machine.

In thermal hyperalgesia and oedema studies, rats were habituated to the test room on day 1. On day 2, basal paw volumes were measured prior to compound administration.  At T=-0.75 h vehicle or dex (1 mg/kg po) or B113823 (30 or 100 mg/kg po) were administered.  Carra (100 μL x 1%) or saline was then injected into the right paw at T=0. Paw volume was measured at T=0, 3, 4, 6 and 24 h post-carra injection while thermal sensitivity of left and right paws was assessed at T=0, 1 and 3 h using an incident light beam.

Results:

Ipl injection of carra elicited paw oedema persisting over 24h. Ipl injection of carra also induced B1R mRNA expression in paw pads which peaked between 2 and 4 hour after ipl injection but remained significant 24h later.  Both oedema and B1R mRNA expression were attenuated by pretreatment with dex (1 mg per kg) when assessed 1 and or 2 h post carra.  B1R mRNA in lung tissue was not increased by carra, although lowered by dex treatment.  No B1R mRNA was found in either liver or blood samples.  Dex also reduced thermal hyperalgesia, but BI-113823 had no effect on either oedema or thermal hyperalgesia.

Conclusion:

The onset of ipl carra-induced hindpaw pad B1 mRNA induction parallels that of oedema development and both are attenuated by dex.  However, the selective B1R antagonist, B113823 had no effect on oedema or thermal hyperalgesia challenging the hypothesis that the B1R might have a key role in the onset and maintenance of carra-induced inflamm and pain.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/studies-on-the-relationship-between-intraplantar-carrageenan-induced-bradykin-b1-receptor-messenger-ribonucleic-acid-expression-and-oedema-and-hyperalgesia-in-rats-effects-of-dexamethasone-and-a-b1-r/