Effect of local injection of cysteamine and cystamine on somatostatin and neuropeptide Y levels in the rat striatum

Somatostatin and neuropeptide Y neurons undergo different plasticity in parahippocampal regions in kainic acid-induced epilepsy

Parahippocampal brain areas including the subiculum, presubiculum and parasubiculum, and entorhinal cortex give rise to major input and output neurons of the hippocampus and exert increased excitability in animal models and human temporal lobe epilepsy. Using immunohistochemistry and in situ hybridization for somatostatin and neuropeptide Y, we investigated plastic morphologic and neurochemical changes in parahippocampal neurons in the kainic acid (KA) model of temporal lobe epilepsy. Although constitutively contained in similar subclasses of γ-aminobutyric acid (GABA)-ergic neurons, both neuropeptide systems undergo distinctly different changes in their expression. Somatostatin messenger RNA (mRNA) is rapidly but transiently expressed de novo in pyramidal neurons of the subiculum and entorhinal cortex 24 hours after KA. Surviving somatostatin interneurons display increased mRNA levels at late intervals (3 months) after KA and increased labeling of their terminals in the outer molecular layer of the subiculum; the labeling correlates with the number of spontaneous seizures, suggesting that the seizures may trigger somatostatin expression. In contrast, neuropeptide Y mRNA is consistently expressed in principal neurons of the proximal subiculum and the lateral entorhinal cortex and labeling for the peptide persistently increased in virtually all major excitatory pathways of the hippocampal formation. The pronounced plastic changes differentially involving both neuropeptide systems indicate marked rearrangement of parahippocampal areas, presumably aiming at endogenous seizure protection. Their receptors may be targets for anticonvulsive drug therapy.

Treatment of YAC128 mice and their wild-type littermates with cystamine does not lead to its accumulation in plasma or brain: implications for the treatment of Huntington disease

Cystamine is beneficial to Huntington disease (HD) transgenic mice. To elucidate the mechanism, cystamine metabolites were determined in brain and plasma of cystamine-treated mice. A major route for cystamine metabolism is thought to be: cystamine --> cysteamine --> hypotaurine --> taurine. Here we describe an HPLC system with coulometric detection that can rapidly measure underivatized cystamine, cysteamine and hypotaurine, as well as cysteine and glutathione in the same deproteinized tissue sample. A method is also described for the coulometric estimation of taurine as its isoindole-sulfonate derivative. Using this new methodology we showed that cystamine and cysteamine are undetectable (< or = 0.2 nmol/100 mg protein) in the brains of 3-month-old HD transgenic (YAC128) mice (or their wild-type littermates) treated daily for 2 weeks with cystamine (225 mg/kg) in their drinking water. No significant changes were observed in brain glutathione and taurine but significant increases were observed in brain cysteine. Cystamine and cysteamine were not detected in the plasma of YAC128 mice treated daily with cystamine between the ages of 4 and 12 or 7 and 12 months. These findings suggest that cystamine is not directly involved in mitigating HD but that increased brain cysteine or uncharacterized sulfur metabolites may be responsible.

Modulation of inflammatory paw oedema by cysteamine in the rat

Cysteamine, a potent somatostatin depletor, was used in the present study to investigate the role of endogenous somatostatin in acute peripheral inflammation. The acute inflammation was induced by intraplantar injection of carrageenan (1%), histamine (5 micromol), or formalin (2.5%) in the rat hind paw. The induced inflammation and the formation of oedema were determined by measurement of the paw thickness. Given subcutaneously (s.c.) 1 h before carrageenan, cysteamine caused significant, dose-dependent and long-lasting inhibition of rat paw oedema induced by carrageenan. At doses of 12.5, 25, 50 or 100 mg kg (-1), cysteamine significantly inhibited the carrageenan-induced paw oedema at 4 h by 52.3, 40, 40.7 or 26.3%. Cysteamine given at 300 mg kg (-1), a dose well known to deplete tissue somatostatin, reduced oedema by only 16.2% vs control values. Significant inhibition of the carrageenan-induced rat paw oedema was still evident 24 h post-injection at cysteamine doses of 12.5, 25, 50 or 100 mg kg (-1). Given s.c. at 300 mg kg (-1), 4 h prior to carrageenan, cysteamine decreased rat paw oedema at 4 h by 14.9%. Cysteamine (300 mg kg (-1)), 4 h beforehand, had little modulatory effect on the oedema induced by formalin (2.5%) but reduced that caused by intraplantar histamine (5 micromol). The anti-oedematogenic effect of indomethacin, but not that of the selective COX-2 inhibitor celecoxib, was less marked in rats pre-treated with cysteamine at 300 mg kg (-1). Cysteamine (0.3 microg- 0.3 mg paw (-1)) co-administered with carrageenan was devoid of anti-inflammatory effect and even promoted inflammation at low concentrations. Cysteamine given locally alone induced slight paw oedema. These data indicate that systemic cysteamine possesses potent and long-lasting anti-inflammatory effects and modulates the anti-inflammatory effect of cyclooxygenase inhibitors in a model of peripheral inflammation in the rat. The effect of cysteamine is likely to be mediated via central action.

Effects induced by cysteamine on chemically-induced nociception in mice

The effects were investigated of cysteamine--a well known somatostatin depletor--on the pain induced by chemical stimuli in mice. Cysteamine injected intraperitoneally 4 h before the test at doses of 50 and 100 mg/kg reduced the second phase of the licking response which was induced by formalin injected into the hind paw. Furthermore, cysteamine administered at the doses of 10, 50 and 100 mg/kg reduced the writhing induced by acetic acid. Naloxone, yohimbine and CGP 35348 administered in cysteamine-pretreated animals were not able to change the cysteamine antinociceptive effects in the formalin test. Intrathecally injected somatostatin was able to revert the cysteamine antinociceptive effects in the second phase of the formalin test and in the writhing test, whereas intracerebroventricularly injected somatostatin reduced the antinociceptive effects induced by cysteamine in the second phase of the formalin test. Intrathecally injected cyclo(7-aminoheptanoyl-Phe-D-Trp-Lys-Thr[Bzl])--a reported somatostatin antagonist--increased cysteamine antinociceptive effects in the second phase of the formalin test and in the writhing test. These results suggest that somatostatin is involved in the effects of cysteamine on the nociceptive threshold.

Preclinical and clinical studies with cysteamine and pantethine related to the central nervous system

1. Cysteamine is formed by degradation of coenzyme A (CoA) and causes somatostatin (SS), prolactin and noradrenaline depletion in the brain and peripheral tissues. 2. Cysteamine influences several behavioral processes, like active and passive avoidance behavior, open-field activity, kindled seizures, pain perception and SS-induced barrel rotation. 3. Cysteamine has several established (cystinosis, radioprotection, acetaminophen poisoning) and theoretical (Huntington's disease, prolactin-secreting adenomas) indications in clinical practice. 4. Pantethine is a naturally occurring compound which is metabolized to cysteamine. 5. Pantethine depletes SS, prolactin and noradrenaline with lower efficacy compared to that of cysteamine. 6. Pantethine is well tolerated by patients and has been suggested to treatment of atherosclerosis. The other possible clinical indications (alcoholism, Parkinson's disease, instead of cysteamine) are discussed.

Local injection of cysteamine into the rat striatum decreases number and intensity of staining of neurons by indirect NADPH diaphorase reaction

Cysteamine (100 micrograms) markedly reduces the number (by about 60%) and intensity of staining of NADPH diaphorase-reactive neurons 6 h after local injection into the striatum. This effect was reversible (after 24 h) and was only observed when the indirect staining procedure was applied in which NADPH formed by endogenous malate dehydrogenase is used. However, no direct effect of cysteamine on the malate dehydrogenase reaction was found. The decrease in NADPH diaphorase activity parallels the previously reported cysteamine induced decrease in somatostatin contained in the same neurons and may point to a biochemical interrelation of somatostatin and NADPH diaphorase in these neurons.