Circulating immunoreactive substance P in man

The Role of Substance P Within Traumatic Brain Injury and Implications for Therapy

This review examines the role of the neuropeptide substance P within the neuroinflammation that follows traumatic brain injury. It examines it in reference to its preferential receptor, the neurokinin-1 receptor, and explores the evidence for antagonism of this receptor in traumatic brain injury with therapeutic intent. Expression of substance P increases following traumatic brain injury. Subsequent binding to the neurokinin-1 receptor results in neurogenic inflammation, a cause of deleterious secondary effects that include an increased intracranial pressure and poor clinical outcome. In several animal models of TBI, neurokinin-1 receptor antagonism has been shown to reduce brain edema and the resultant rise in intracranial pressure. A brief overview of the history of substance P is presented, alongside an exploration into the chemistry of the neuropeptide with a relevance to its functions within the central nervous system. This review summarizes the scientific and clinical rationale for substance P antagonism as a promising therapy for human TBI.

Inhibitors of endopeptidase and angiotensin-converting enzyme lead to an amplification of the morphological changes and an upregulation of the substance P system in a muscle overuse model

Background

We have previously observed, in studies on an experimental overuse model, that the tachykinin system may be involved in the processes of muscle inflammation (myositis) and other muscle tissue alterations. To further evaluate the significance of tachykinins in these processes, we have used inhibitors of neutral endopeptidase (NEP) and angiotensin-converting enzyme (ACE), substances which are known to terminate the activity of various endogenously produced substances, including tachykinins.

Methods

Injections of inhibitors of NEP and ACE, as well as the tachykinin substance P (SP), were given locally outside the tendon of the triceps surae muscle of rabbits subjected to marked overuse of this muscle. A control group was given NaCl injections. Evaluations were made at 1 week, a timepoint of overuse when only mild inflammation and limited changes in the muscle structure are noted in animals not treated with inhibitors. Both the soleus and gastrocnemius muscles were examined morphologically and with immunohistochemistry and enzyme immunoassay (EIA).

Results

A pronounced inflammation (myositis) and changes in the muscle fiber morphology, including muscle fiber necrosis, occurred in the overused muscles of animals given NEP and ACE inhibitors. The morphological changes were clearly more prominent than for animals subjected to overuse and NaCl injections (NaCl group). A marked SP-like expression, as well as a marked expression of the neurokinin-1 receptor (NK-1R) was found in the affected muscle tissue in response to injections of NEP and ACE inhibitors. The concentration of SP in the muscles was also higher than that for the NaCl group.

Conclusions

The observations show that the local injections of NEP and ACE inhibitors led to marked SP-like and NK-1R immunoreactions, increased SP concentrations, and an amplification of the morphological changes in the tissue. The injections of the inhibitors thus led to a more marked myositis process and an upregulation of the SP system. Endogenously produced substances, out of which the tachykinins conform to one substance family, may play a role in mediating effects in the tissue in a muscle that is subjected to pronounced overuse.

Growth-promoting effects of substance P on endothelial cells in vitro. Synergism with calcitonin gene-related peptide, insulin, and plasma factors

The purpose of this study was to determine the effects of the vasoactive perivascular neuropeptide substance P (SP) on the growth and function of vascular endothelial cells in serum-free culture conditions with cells quiescent in the G0-G1 phase of the cell cycle and to characterize the response. In addition, interactions between SP and other growth factors and neuropeptides including insulin, platelet factors, neurokinin A, neurokinin B, and calcitonin gene-related peptide (CGRP) were studied on endothelial cell growth and compared. Growth effects were determined by stimulation of tritiated thymidine incorporation into DNA and cell proliferation. SP exhibited differential effects on cell growth that were a function of concentration, incubation time, interaction with other growth factors, and cell culture conditions. DNA synthesis in response to SP showed a bell-shaped distribution with a maximal effect that was 10.5-fold over control at 500 micrograms/mL of SP after 48 hours of incubation. The effect showed marked synergism with insulin (10 micrograms/mL) and with CGRP (0.01 to 10 micrograms/mL), which is colocalized with SP in vivo. Insulin and CGRP alone had no significant effect on endothelial cell growth. Furthermore, no synergism was observed between SP and platelet-derived growth factor or platelet-derived endothelial cell growth factor. Endothelial cell proliferation increased in response to SP to 2.6-fold over control at 48 hours, was maximal at 10 micrograms/mL SP, and also demonstrated synergism with insulin (10 micrograms/mL). Our studies indicate that neuropeptides play a significant role in regulating endothelial cell growth and proliferation.(ABSTRACT TRUNCATED AT 250 WORDS)

Substance P-induced fibrinolysis in the forearm of healthy humans

Physiological saline with or without substance P (50 ng/ml) was infused into the humeral artery in 6 healthy males. Indices of fibrinolytic activity (whole blood diluted lysis time, euglobulin lysis time, lysis areas in non-heated fibrin plates produced by plasma or euglobulin precipitate, plasminogen plasma levels, alpha 2-macroglobulin, C1-inhibitor, and alpha 2-antiplasmin) were evaluated in the homolateral antecubital vein before and after 5 min of substance P or saline infusion. After substance P the fibrinolytic activity increased, as can be seen from the shortening of lysis times (p < 0.01) and enlargement of the lysis areas (p < 0.01). A reduction of plasminogen plasma levels (p < 0.01), associated with a decrease in alpha 2-antiplasmin (p < 0.01), was also found. Alpha 2-macroglobulin and C1-inhibitor were instead unaltered by the peptide. The saline infusion, on the other hand, was unable to modify any of the examined indices. We concluded that exogenous substance P given intra-arterially increases fibrinolytic activity in locally-sampled venous blood through a mechanism which remains to be elucidated.

The binding of endogenous and exogenous substance-P in human plasma

High levels of substance-P are present in the plasma of patients with carcinoid tumours and some thyrotoxic conditions. The majority of the substance-P in the blood plasma was shown, by immunoassay, to be associated with high molecular-weight material in a complex that could be dissociated by repeated gel-filtration. Smaller amounts of an intermediate molecular-weight (about 65,000 Da) complex were also detected. Chemical crosslinking with glutaraldehyde was used to show that the radioactively-labelled derivative [125I]Tyr-8-substance-P was able to bind to the high-Mr fraction of human plasma and also to human serum albumin. Binding to serum albumin was also demonstrated by equilibrium gel-filtration. Substance-P added to human plasma from a thyrotoxic subject, which contained high endogenous levels of the tachykinin (980 pg/mL), was rapidly degraded during incubation at 37 degrees, whereas the endogenous substance-P was considerably more stable. These results suggest that the binding of substance-P to blood plasma components may play an important role in protecting it against degradation. Furthermore, immunoassay techniques involving prior extraction, which fail to detect the bound substance-P, will give inaccurate measurements of the levels of this peptide in plasma.

Substance P enhances interferon-gamma production by human peripheral blood mononuclear cells

Substance P (SP), a neuropeptide widely distributed in the organism, has been shown to stimulate lymphocyte proliferation and immunoglobulin synthesis. However, the effect of SP on specific lymphokines is unknown. Therefore we investigated the influence of SP on mitogen-induced interferon-gamma (IFN-gamma) production in vitro. Peripheral blood mononuclear cells (PBMC) of healthy donors were isolated by density gradient centrifugation and cultured in supplemented RPMI 1640 medium with phytohemagglutinin (PHA) or pokeweed mitogen (PWM), 0.125 and 0.25 mg/liter each, and varying concentrations of SP (10(-12) to 10(-6) M). After 24 and 48 h, IFN-gamma was measured in the supernatant using radioimmunoassay. Results were expressed as percent change of controls. SP alone had no relevant IFN-gamma inducing properties. It enhanced the IFN-gamma production of PWM-stimulated cells significantly up to 18%. The maximal effect was observed at 10(-8) M. PHA-stimulated cells also increased their IFN-gamma production after addition of SP. However, due to great interindividual variations this effect did not attain statistical significance. Stimulation of IFN-gamma production by SP might be of physiological importance, since the effect was seen at concentrations comparable to those found in the body. Our data lend further support to the immunoregulatory functions of SP.

Bronchoconstrictor and hypotensive effects in relation to pharmacokinetics of tachykinins in the guinea-pig--evidence for extraneuronal cleavage of neuropeptide K to neurokinin A

1. The biological effects of the tachykinins substance P (SP), neurokinin A (NKA) and neuropeptide K (NPK) were studied in relation to their pharmacokinetic properties in the guinea-pig in vivo. 2. NKA and NPK exerted a considerably larger bronchoconstrictor effect than SP. The effect of NPK was slow in onset and had a long duration. The three tachykinins showed similar hypotensive effects although NPK had a longer duration of action than SP and NKA. 3. The disappearance of NPK-like immunoreactivity (-LI) from plasma after i.v. infusion of synthetic NPK was biphasic with apparent half-lives of 0.9 min and 6 min. The plasma half-life of NKA-LI was less than 2 min, while plasma SP-LI was degraded before biochemical analysis could be performed. 4. In guinea-pig plasma at 37 degrees C in vitro, NKA- and NPK-LI were stable for 10 min, while SP-LI disappeared with a half-life of 10 s. 5. Reversed phase HPLC analysis of plasma collected after an i.v. infusion of NPK for 25 min, indicated a partial cleavage of NPK into NKA. 6. It is concluded that potency of the biological effects of SP, NKA and NPK in the guinea-pig in vivo, may not only be attributed to activation of multiple tachykinin receptors but must also be related to the marked differences in pharmacokinetical properties between the tachykinins. Furthermore, whereas SP is rapidly degraded in plasma, NKA and NPK seem to be metabolized in other compartments.

Flushing and plasma substance P concentration during infusion of synthetic substance P in normal man

Six normal subjects received synthetic substance P intravenously in successively increasing doses of 0.5, 1.0, 2.0, 4.0, and 8.0 pmol X kg-1 X min-1. Each dose was given for 20 min. Concentrations of substance P in plasma and infusions were measured radioimmunochemically. The incremental plasma concentration of substance P correlated linearly to the dose infused. Metabolic clearance rate was 0.361 X kg-1 X min-1, and the half-life of exogenous substance P 1.6 min. Lacrimation and sustained flushing were elicited at plasma concentrations above normal range. Transient flushing in spite of continued infusion was seen at 'physiological' levels. Pulse rate and blood pressure did not change significantly.

Do substance P and vasoactive intestinal polypeptide (VIP) play a role in the acute occlusive or chronic ischaemic vasodilation in man?

The concentrations of substance P (SP) and vasoactive intestinal polypeptide (VIP) were determined in plasma in normal volunteers during acute occlusive ischaemia (n=5) and in patients with chronic ischaemia (n=5) due to obliterative arterial disease in the lower limbs. Venous SP, but not VIP, increased significantly in the early post-occlusive period in normal volunteers (P less than 0.02). In the patients no significant veno-arterial difference in plasma concentration of SP or VIP could be detected across normal or chronic ischaemic areas. The results may suggest a role for SP in the acute post-occlusive vasodilation and/or in the post-occlusive heat-pain sensation. A role for SP in chronic ischaemia could not be defined. Plasma VIP was unchanged in both acute and chronic ischaemia.

Does liver-intestine significantly degrade circulating endogenous substance P in man?

Elevated concentrations of circulating substance P in patients with liver insufficiency have been ascribed to decreased hepatic degradation. To establish a possible biodegradation of the peptide in liver-intestine and kidneys, the concentration of endogenous immunoreactive substance P was determined in various vascular beds during a right-sided catheterization in 13 subjects without liver insufficiency. All subjects had normal values of circulating substance P, and no significant difference was found between systemic plasma and hepatic venous or renal venous concentrations of substance P. The results indicate that degradation of circulating endogenous substance P in man is not confined to liver-intestine or kidney but may take place in many tissues.

Substance P-like immunoreactivity in plasma of psychotic patients and effects of neuroleptics and electroconvulsive therapy

Radioimmunoassay of substance P (SP)-like reactivity, using N alpha-tyrosyl-SP, was performed in plasma of psychotic patients. Schizophrenic patients under neuroleptic medication over 1 year, and those patients with organic brain disease showed a significant increase in immunoreactivity. The immunoreactivity in unmedicated schizophrenic patients just before treatment and in depressed patients, both bipolar and major, did not differ significantly from that of controls. The immunoreactivity in unmedicated schizophrenics was followed after medication for a maximum of 5 months. The reactivity decreased in five cases, and increased in three cases. No definite pattern could be discerned between changes in the immunoreactivity, the type of medication administered, and the resultant response to the therapy. Chlorpromazine injection caused no definite acute effect on the plasma level of SP-like immunoreactivity for 120 minutes. Electroconvulsive therapy increased the plasma level of SP-like immunoreactivity for 90 minutes in a male schizophrenic patient.

Substance P: its distribution, pharmacological actions and possible physiological role in sensory neurons

The undecapeptide substance P (SP) is a normal constituent of most tissues, particularly the central and peripheral nervous system. SP-immunoreactive cell bodies and terminal networks are distributed in most areas of the brain. Particular interest has been focused on the presence and function of SP in the primary sensory neuron. SP is released from both the central and peripheral part of the sensory neuron following stimulation of the dorsal roots and peripheral sensory nerves. Evidence is given for a transmitter role of SP in the sensory neurons and for the hypothesis that SP is involved in the vascular effects induced by sensory stimulation, referred to as the axon reflex. SP is present in large amounts in the gastro-intestinal tract. By immunohistochemistry SP is demonstrated within nerve cell bodies and terminals of the intramular plexuses but also in extrinsic neurons. It is released both from intrinsic sensory neurons of the gut and from the gastro-intestinal lumen in response to vagal stimulation. SP stimulates motor activity and is ascribed a regulatory role for both the intestinal motility and blood flow. SP has numerous pharmacological effects, the most obvious being excitation of spinal motoneurons, vasodilation and stimulation of salivary and pancreatic secretion. It is a normal constituent of blood plasma but there is no evidence that SP acts as a circulating hormone.

Plasma substance P levels in normotensive and hypertensive subjects

Since substance P is a potent natriuretic, diuretic, and vasodilatory peptide, a radioimmunoassay for substance P was developed, and its levels measured in the plasma of normal subjects and patients with essential hypertension. The plasma substance P levels were 186+/-14 pg/ml in normal subjects and 164+/-3 pg/ml in hypertensive patients. When the sodium content of their diet was reduced to 10 mEq/day, substance P levels failed to change, but plasma renin activity and urinary kallikrein increased. An acute saline infusion also failed to alter plasma substance P levels. Assuming an upright posture increased plasma renin activity, but not substance P, in both groups of subjects. Thus, it appears that substance P is not involved in the control of blood pressure, kallikrein excretion or renin release in man.

Substance P in ovarian carcinoid

A high content of substance P (124 ng/g wet tissue) was demonstrated by radioimmunoassay in lymph node metastases in a patient with bilateral ovarian carcinoid tumours. The plasma substance P level was elevated but urinary 5-hydroxyindoleacetic acid (5-HIAA) was low. It is suggested that, in some carcinoid patients, an elevated plasma substance P level may help diagnosis and follow-up when urinary 5-HIAA is normal.

Substance P in medullary carcinoma of the thyroid

High levels of substance P-like immunoreactivity were demonstrated by radioimmunoassay in the plasma and tumour of a patient with a medullary carcinoma of the thyroid.

The intestine as source of immunoreactive substance P in plasma of the cat

1. Substance P (SP) was measured in acid acetone extracted plasma of cats using a sensitive radioimmunoassay. The immunoreactive material was submitted to ion exchange chromatography and at least 90% of immunoreactivity co-chromatographed with synthetic SP. 2. The level of immunoreactive SP (I-SP) in extracted plasma of the cat was 69.3 +/- 9.8 fmol/ml with values ranging from 2.5 to 165 fmol/ml. Evisceration of the cats caused a decrease of I-SP levels from 70.8 +/- 30.8 fmol/ml to 20.8 +/- 9.9 15 min and to 26.8 +/- 19.7 fmol/ml 60 min after the operation. 3. Ligation of intestinal blood vessels led to a fall in I-SP levels from 58.7 +/- 11.5 to 25.9 +/- 4.1 fmol/ml within 15 min. 4. No difference between I-SP values in portal (71.8 +/- 11.2 fmol/ml) and peripheral plasma (68.3 +/- 12.1 fmol/ml) was found under the conditions in which these experiments were performed. 5. It is concluded that a major part of circulating immunoreactive SP originates from the intestine.

Substance P in rat brain synaptosomes

1. Rat brain synaptosomes were incubated under different conditions to study the release of substance P (SP). 2. Potassium ions and electrical field stimulation induced a loss of SP from synaptosomes. The release of SP by potassium in high concentrations (23.8 mM) was shown to be calcium dependent. 3. Substance P was retained in synaptosomes during incubation in 0.32 M sucrose at +4 degrees C up to 120 min. During incubation at 30 degrees C the SP content fell initially (30 min) but was gradually restored (120 min). 4. If these pre-incubated synaptosomes were reincubated for 45 min at 30 degrees C in potassium free Krebs-Ringer-phosphate buffer a further rise in their SP content occurred which was taken as indication that SP is being synthesized in synaptosomes. 5. The newly synthesized SP is presumably stored by binding to phosphatidyl serine until a sudden release is initiated by depolarization.