Prostanoid synthesis in peripheral nerve

Schwann cells express IP prostanoid receptors coupled to an elevation in intracellular cyclic AMP

We have shown previously that prostaglandin E(2) (PGE(2)) and prostaglandin I(2) (PGI(2)) are each produced in an explant model of peripheral nerve injury. We report that IP prostanoid receptor mRNA and protein are present in primary rat Schwann cells. IP prostanoid receptor stimulation using prostacyclin produced an elevation in intracellular cyclic AMP concentration ([cAMP](i)) in primary Schwann cells. Peak [cAMP](i) was observed between 5-15 min of stimulation followed by a gradual recovery toward basal level. Phosphorylation of cyclic AMP-response element binding protein (CREB) on Ser(133) was also detected after IP prostanoid receptor stimulation and CREB phosphorylation was inhibited completely by the protein kinase A inhibitor, H-89. Intracellular calcium levels were not affected by IP prostanoid receptor stimulation. Unlike forskolin, IP prostanoid receptor stimulation did not significantly augment Schwann cell proliferation in response to growth factor treatment. However, IP prostanoid receptor stimulation increased the number of Schwann cells that were able to generate a calcium transient in response to P2 purinergic receptor activation. These findings suggest that signaling via the IP prostanoid receptor may by relevant to Schwann cell biology in vivo.

Prostaglandin E(2) and 6-keto-prostaglandin F(1alpha) production is elevated following traumatic injury to sciatic nerve

Sciatic nerve explants cultured either alone or in the presence of peritoneal macrophages were used to study prostaglandin E(2) (PGE(2)) and 6-keto-PGF(1alpha) production following traumatic peripheral nerve injury. Although barely detectable at early time points (1-3 h in vitro), the production of PGE(2) and 6-keto-PGF(1alpha) by sciatic nerve explants increased significantly after 18 h and remained elevated for up to 96 h. The cyclooxygenase-2 (COX-2) selective inhibitor, NS-398, inhibited PGE(2) and 6-keto-PGF(1alpha) production by injured sciatic nerve in a dose-dependent manner. Consistent with the observed effect of NS-398, peripheral nerve explants, as well as Schwann cells and perineural fibroblasts cultured from neonatal sciatic nerve, each contained COX-2 immunoreactivity after 24 h in vitro. Both Schwann cells and perineural fibroblasts produced significant amounts of PGE(2) and 6-keto-PGF(1alpha); but only in the presence of arachidonic acid. As observed for injured sciatic nerve, the production of PGE(2) and 6-keto-PGF(1alpha) by primary Schwann cells and perineural fibroblasts was completely inhibited by NS-398. Compared to macrophages cultured alone, macrophages cultured in the presence of sciatic nerve explants produced large amounts of PGE(2), whereas the level of 6-keto-PGF(1alpha) was unchanged. In contrast, macrophages treated with adult sciatic nerve homogenate did not produce significant amounts of either PGE(2) or 6-keto-PGF(1alpha) during the entire course of treatment. We conclude that injured sciatic nerves produce PGE(2) and 6-keto-PGF(1alpha) by a mechanism involving COX-2 activity and that macrophages produce large amounts of PGE(2) in response to soluble factors produced by injured nerve but not during the phagocytosis of peripheral nerve debris.

Eicosanoid and amino acid metabolism in transient acute psychoses with psychedelic symptoms

It has been hypothesized that a disturbance of glutathione (GSH) metabolism might be a common factor in many psychiatric disorders. The aim of the present study was to test this hypothesis in transient acute psychotic patients with distorted perceptions. Since the metabolism of GSH is related to that of thromboxane B2 (TXB2), prostaglandin E (PGE) and some amino acids, we determined these substances in the plasma of 15 patients and 17 normal controls. Plasma concentrations of TXB2 were significantly higher and concentrations of serine and tryptophan were significantly lower in patients than in controls. Large variation was observed in plasma PGE levels in patients, although mean values did not differ significantly from controls. These results are consistent with the hypothesis that the metabolism of GSH is impaired in transient psychotic states.

Arachidonic fatty acid in red blood cell membranes, lymphocytes, and cultured skin fibroblasts of dominant Charcot-Marie-Tooth syndrome

Altered proportions of long-chain unsaturated n - 6 fatty acids (FA) in plasma and myelin of the heredodegenerative peripheral neuropathy, Charcot-Marie-Tooth syndrome (CMT), may implicate FA metabolism in the pathogenesis of CMT demyelination. A significant relationship between low plasma values of the polyunsaturated n - 6 FA, arachidonic acid, and an increased amount of prostaglandin-mediated immune responses had suggested the possibility of immune system metabolic usage of these n - 6 FA rather than an inherited FA enzyme defect. This relationship between peripheral immunostimulation and altered FA was documented repeatedly in CMT patients. Increased and cyclic lymphocyte activation expressions were measured at the same time as low amounts of plasma arachidonic acid, which is the FA precursor of prostaglandin immunoregulatory agents. An autoimmune process with possible enhanced formation of the n - 6 immune prostenoid agents in CMT had also been suggested by increased class II antigen expression on CMT sural nerves. Here, normal proportions of total FA in cultured CMT skin fibroblasts diminishes a notion of hereditary defects in CMT fatty acid metabolism. In addition, a significant depletion of the key arachidonic acid in lipid stores of CMT red blood cell membranes with elevated values of this FA in functional CMT lymphocytes, compared to controls, support the concept in CMT patients of a metabolic diversion of n - 6 FA, particularly arachidonic acid, from tissue stores for immunoregulatory prostenoid agent formation.

Sensory neuropeptide release by bradykinin: mechanisms and pathophysiological implications

Bradykinin (BK) and related kinins excite primary sensory neurons, thus leading to the activation of sensory impulses. More recently, both functional and neurochemical evidence have been accumulated that BK evokes release of neuropeptides, including calcitonin gene-related peptide and the tachykinins substance P and neurokinin A, from peripheral terminals of capsaicin-sensitive primary afferents. The present article will review the mechanisms and the pathophysiological implications of the ability of BK to release sensory neuropeptides at the peripheral level. An account of the clinical studies performed on this subject will be also given.

Preferential synthesis of prostaglandin D2 by neurons and prostaglandin E2 by fibroblasts and nonneuronal cells in chick dorsal root ganglia

To determine the type and the relative amount of prostaglandins (PGs) synthesized by various neural tissues, homogenates of meninges, dorsal root ganglia (DRG) capsules, decapsulated DRG, and unsheathed sciatic nerves were incubated with [1-14C]arachidonic acid. Homogenates of cultured cells (meningeal cells, fibroblasts, and nonneuronal or neuronal DRG cells) were used to specify the cells producing particular PGs. The highest synthetic capacity was found in fibroblast-rich tissues (meninges and DRG capsules) and in cultures of meningeal cells or fibroblasts. Two major cyclooxygenase products were formed: [14C]PGE2 and an unusual 14C-labeled compound, Y. The accumulation of compound Y, corresponding probably to 15-hydroperoxy PGE2, was completely impaired by addition of exogenous GSH, which conversely enhanced the synthesis of [14C]PGE2 and promoted the formation of [14C]PGD2. In contrast, decapsulated DRG or unsheathed sciatic nerves displayed a 10-20 times lower capacity to synthesize PGs than fibroblast-rich tissues and produced mainly [14C]PGE2 and [14C]PGD2. In this case, [14C]PGE2 or [14C]PGD2 synthesis was neither enhanced nor promoted by addition of exogenous GSH. Neuron-enriched DRG cell cultures allowed us to specify that [14C]PGD2 is the major prostanoid produced by primary sensory neurons as compared with nonneuronal DRG cells. Because PGD2 synthesis in DRG and more specifically in DRG neurons does not depend on exogenous GSH and differs from PGD2 synthesis in fibroblast-rich tissues, it is concluded that at least two distinct enzymatic processes contribute to PGD2 formation in the nervous system.(ABSTRACT TRUNCATED AT 250 WORDS)

Biosynthesis of prostaglandins D2 and E2 in chick dorsal root ganglion during development

Newly formed prostaglandins (PGs), which are assumed to act as modulators of afferent sensory messages, were studied in chick dorsal root ganglia (DRG) during development. [1-14C]Arachidonic acid was converted by DRG homogenates from 1-week-old chickens into two major 14C-PGs: PGE2 and PGD2. The enzymatic conversion of arachidonic acid was characterized as follows: (a) Boiled preparations were inactivated; (b) synthesis of PGs was inhibited by pretreatment with aspirin or indomethacin and enhanced by esculetin, a protector of cyclooxygenase; and (c) [14C]PGE2 and [14C]PGD2 accumulation was a protein dose-dependent process. Further fractionation of crude homogenates indicated that PG endoperoxide synthetase (EC 1.14.99.1) and PGE2 synthetase (EC 5.3.99.3) were membrane-bound enzymes, whereas PGD2 synthetase (EC 5.3.99.2) was recovered in the cytosol. During development, from embryonic day 10 to day 14 after hatching, PGD2 synthetase activity remained constant; in contrast, a sharp rise in [14C]PGE2 synthesis was observed from embryonic day 14 to 18. The time curves of PGD2 and PGE2 synthetase specific activity may be related to changes taking place in the cell population of developing DRG. It is therefore suggested that arachidonic acid would be enzymatically converted early into PGD2 by maturing ganglion cells and then later into PGE2 by proliferating fibroblasts.

Severe Guillain-Barré syndrome: an association with IgA anti-cardiolipin antibody in a series of 92 patients

To determine whether anti-cardiolipin antibodies (ACA) are associated with acute Guillain-Barré syndrome (GBS), we studied sera from 92 patients with GBS, 82 age- and sex-matched hospital controls and 24 patients with uncomplicated cytomegalovirus or Campylobacter jejuni infection, using an isotype-specific ACA enzyme-linked immunosorbent assay (ELISA). IgA ACA titres (but not IgG ACA or IgM ACA) were significantly elevated (P = 0.002) in GBS patients compared to controls, and associated with peak disease severity (P = 0.01), but not initial or residual disability, nor duration of neuropathy. Abnormal IgG ACA may cause or result from myelin damage in GBS.