Blood levels of kinins in experimental allergic encephalomyelitis

Pathophysiology of the kallikrein-kinin system in mammalian nervous tissue

The nervous system and peripheral tissues in mammals contain a large number of biologically active peptides and proteases that function as neurotransmitters or neuromodulators in the nervous system, as hormones or cellular mediators in peripheral tissue, and play a role in human neurological diseases. The existence and possible functional relevance of bradykinin and kallidin (the peptides), kallikreins (the proteolytic enzymes), and kininases (the peptidases) in neurophysiology and neuropathological states are discussed in this review. Tissue kallikrein, the major cellular kinin-generating enzyme, has been localised in various areas of the mammalian brain. Functionally, it may assist also in the normal turnover of brain proteins and the processing of peptide-hormones, neurotransmitters, and some of the nerve growth factors that are essential for normal neuronal function and synaptic transmission. A specific class of kininases, peptidases responsible for the rapid degradation of kinins, is considered to be identical to enkephalinase A. Additionally, kinins are known to mediate inflammation, a cardinal feature of which is pain, and the clearest evidence for a primary neuronal role exists so far in the activation by kinins of peripherally located nociceptive receptors on C-fibre terminals that transmit and modulate pain perception. Kinins are also important in vascular homeostasis, the release of excitatory amino acid neurotransmitters, and the modulation of cerebral cellular immunity. The two kinin receptors, B2 and B1, that modulate the cellular actions of kinins have been demonstrated in animal neural tissue, neural cells in culture, and various areas of the human brain. Their localisation in glial tissue and neural centres, important in the regulation of cardiovascular homeostasis and nociception, suggests that the kinin system may play a functional role in the nervous system.

Kinin B1 receptors: a review

The kinin B1 receptor has been initially defined as the one mediating the contractile effect of bradykinin (BK)-related peptides in the isolated rabbit aorta. The B1 receptor is selectively sensitive to kinin metabolites without the C-terminal arginine residue, e.g. des-Arg9-BK and Lys-des-Arg9-BK; it is apparently rapidly up-regulated in immunopathology under the influence of cytokines and is further regulated by growth factors. Progress in the understanding of this pharmacologic entity is reviewed, including the development of B1 receptor agonists and antagonists, binding assays, physiopathological applications and the recent cloning and sequencing of the receptor cDNA.

Kinins and kinin receptors in the nervous system

Kinins, including bradykinin and kallidin, are peptides that are produced and act at the site of tissue injury or inflammation. They induce a variety of effects via the activation of specific B1 or B2 receptors that are coupled to a number of biochemical transduction mechanisms. In the periphery the actions of kinins include vasodilatation, increased vascular permeability and the stimulation of immune cells and peptide-containing sensory neurones to induce pain and a number of neuropeptide-induced reflexes. Mechanisms for kinin synthesis are also present in the CNS where kinins are likely to initiate a similar cascade of events, including an increase in blood flow and plasma leakage. Kinins are potent stimulators of neural and neuroglial tissues to induce the synthesis and release of other pro-inflammatory mediators such as prostanoids and cytotoxins (cytokines, free radicals, nitric oxide). These events lead to neural tissue damage as well as long lasting disturbances in blood-brain barrier function. Animal models for CNS trauma and ischaemia show that increases in kinin activity can be reversed either by kinin receptor antagonists or by the inhibition of kinin production. A number of other central actions have been attributed to kinins including an effect on pain signalling, both within the brain (which may be related to vascular headache) and within the spinal dorsal horn where primary afferent nociceptors can be stimulated. Kinins also appear to play a role in cardiovascular regulation especially during chronic spontaneous hypertension. Presently, however, direct evidence is lacking for the release of kinins in pathophysiological conditions of the CNS and it is not known whether spinal or central neurones, other than afferent nerve terminals, are sensitive to kinins. A more detailed examination of the effects of kinins and their central pharmacology is necessary. It is also important to determine whether the inhibition of kinin activity will alleviate CNS inflammation and whether kinin receptor antagonists are useful in pathological conditions of the CNS.

A radioimmunoassay for bradykinin based on monoclonal antibodies

We describe two monoclonal antibodies with recognise the peptides bradykinin and kallidin. These antibodies were used in a study to assess the feasibility of using monoclonal antibodies in place of conventional sera for radioimmunoassay. Antibody SBK1 recognises bradykinin with a Kd of 0.67 +/- 0.17 nM. It fails to recognise bradykinin from which any carboxyl terminal amino acid has been removed. Antibody SBK2 recognises bradykinin with a Kd of 58.11 +/- 7.55 nM; it recognises 1-8 and 1-7 bradykinin about 30% as effectively as the full-length sequence, and shorter carboxyl terminal truncated sequences with a progressively declining efficiency. In this model system, bradykinin concentrations of 0.2 nM could be reliably measured, and carboxyl truncated versions of the peptide could be distinguished from the parent molecule. The feasibility of using monoclonal antibodies to assay bradykinin and other small peptides is discussed in the light of these results.

Experimental allergic encephalomyelitis: a neurourological study

To assess the neurourological disturbances produced by the perivascular inflammatory process in the acute phase of experimental allergic encephalomyelitis, we carried out a controlled study. Forty-six New Zealand male rabbits were inoculated with an encephalitogenic preparation. Twenty-seven of them developed neurological deficits in an average of 9.3 days postinoculation. A sample of 19 subjects was used as a control. The subjects were studied within 2 days after the manifestation of the first sign of encephalomyelitis. An average of eight successive cystosphincterograms were recorded. Their entire central nervous system was removed intact and suspended in 10% neutral buffered Formalin solution for 2 weeks, then cut into segments, embedded in paraffin, and finally stained with hematoxylin-eosin and Luxol Fast Blue. The results demonstrated a significant reduction of mean vesical capacity, maximum urethral pressure, and mean urethral pressure in the group with encephalomyelitis. Furthermore, we found a significant negative correlation between the average number of cellular perivascular infiltrates in the spinal sacral segment and urethral pressures. The results showed a significant negative correlation between supreamesencephalic inflammation and mean vesical capacity.

Increased blood concentration of des-Arg9-bradykinin in experimental allergic encephalomyelitis

Experimental allergic encephalomyelitis (EAE) is a delayed cell-mediated autoimmune reaction to myelin basic protein. The neuropathology of this acute inflammatory process is characterized by cellular infiltration of the perivascular nervous parenchyma which increases the blood-brain barrier permeability. There is good evidence for an activation of the kallikrein-kinin system during inflammation. In order to assess blood concentrations of kinins in a group of 21 New Zealand rabbits in the acute phase of EAE and a group of 12 normal controls, we performed a sensitive and specific radioimmunoassay. All subjects in the encephalomyelitic group were inoculated with 0.05 ml of an antigenic preparation. They all developed neurological deficits on average 30 days later and within 4 days 10 ml of arterial blood were withdrawn for radioimmunoassay of kinins. On the same days their central nervous system was dissected and prepared for staining and histological study. We demonstrated a significant difference in bradykinin blood concentration between the encephalomyelitic (170.6 pg/ml) and the control (245.8 pg/ml) groups. There is also a significant difference in des-Arg9-bradykinin blood concentration between the encephalomyelitic (168.0 pg/ml) and the control (96.1 pg/ml) groups. These results suggest an activation of circulating carboxypeptidases involved in the transformation of bradykinin into des-Arg9-bradykinin during EAE.