Clonidine reduces hypersensitivity and alters the balance of pro- and anti-inflammatory leukocytes after local injection at the site of inflammatory neuritis.

Perineural alpha2-adrenoceptor activation relieves hypersensitivity induced by peripheral nerve injury or sciatic inflammatory neuritis. This effect is associated with a reduction in pro-inflammatory cytokines, as well as a reduction in local leukocyte number and their capacity to produce pro-inflammatory cytokines. Curiously, clonidine's antinociceptive effect appears with a 2-3-day delay after injection. Previous observations have shown that alpha-adrenoceptor activation induces apoptosis in leukocytes, which would reduce leukocyte number. Additionally, macrophage scavenging of apoptotic cells results in a shift to an anti-inflammatory phenotype, with expression of transforming growth factor (TGF)-beta1. We therefore examined the effects of perineural clonidine 24 h and 3 days after its injection on apoptosis, TGF-beta1 expression and lymphocyte and macrophage phenotype in acute sciatic inflammatory neuritis. Perineural clonidine reduced ipsilateral neuritis-induced hypersensitivity in a delayed manner (3 days after treatment), along with a reduction at this time in lymphocyte number and an increase in caspase-3 and TGF-beta1 expressing cells and macrophages co-expressing TGF-beta1 in the sciatic nerve. One day after injection clonidine treatment was associated with a reduction in lymphocytes and pro-inflammatory Th-1 cells as well as increased numbers of caspase-3 and TGF-beta1 expressing cells and macrophages co-expressing TGF-beta1 in sciatic nerve. Clonidine's effects were prevented by co-administration of an alpha2-adrenoceptor antagonist. These data suggest that alpha2-adrenoceptor activation in sciatic inflammatory neuritis increases local apoptosis and anti-inflammatory products early after treatment. This early effect likely underlies the delayed anti-inflammatory and anti-hypersensitivity effects of perineural clonidine in this setting.

Production and characterization of an iminoimidazolidine specific monoclonal antibody using para-aminoclonidine as antigen.

Para-aminoclonidine coupled to hemocyanin was used to produce mouse monoclonal antibodies directed against clonidine. The properties of one of these, called mFE7, secreted by a clone of hybrid myeloma, are described. This antibody displayed total crossreactivity with imidazolidines and no crossreactivity at all with catecholamines or other known naturally occurring substances tested. A liquid phase radioimmunoassay permitted the detection of immunoreactivity in human brain extracts. The mFE7 antibody could be useful for immunopurifying the endogenous ligand of Imidazolines Preferring Receptors (IPR) which are catecholamines insensitive.

Production and characterization of anti-clonidine antibodies not cross-reacting with catecholamines.

Polyclonal antibodies against clonidine were developed, with para-aminoclonidine coupled to bovine serumalbumin or hemocyanine with glutaraldehyde used as antigens. The selected antibody (from rabbits) cross-reacted with high specificity with clonidine and its structurally closely related analogues but it recognized neither catecholamines nor various endogenous imidazole molecules such as histamine, purine, adenine, and adenosine, thus appearing to be specific for the aminoimidazoline structure. An interesting cross-reactivity was observed with the bovine clonidine displacing substance, the probable endogenous ligand for receptors involved in the hypotensive effect of clonidine-type substances. This suggested that this molecule should contain an aminoimidazoline or guanidine moiety.