Gianfranco Natale

Parkinson’s disease and the gut: a well known clinical association in need of an effective cure and explanation

Abstract  Parkinson’s disease (PD) is a neurodegenerative disorder which leads to severe movement impairment; however, Parkinsonian patients frequently suffer from gastrointestinal (GI) problems which at present are poorly understood, scarcely investigated, and lack an effective cure. Traditionally, PD is attributed to the loss of mesencephalic dopamine‐containing neurons; nonetheless, additional nuclei, such as the dorsal motor nucleus of the vagus nerve and specific central noradrenergic nuclei, are now identified as targets of PD. While the effects of PD on the somatic motor systems are well characterized, the influence on the digestive system still needs to be clarified. Recent findings demonstrate the occurrence of pathological alterations within peripheral neuronal networks in the GI tract of Parkinsonian patients. However, it remains unclear whether a real cell loss occurs, and whether this happens specifically for a subclass of autonomic neurons or if it reflects the sole loss of autonomic nerves. This review summarizes the neurochemical and morphological changes which might be responsible for impaired GI motility. Moreover, we focus on the experimental models to reproduce the altered digestive system of Parkinsonian patients since an experimental model able to mimic such features of PD is required. In the last part of the manuscript, we suggest potential therapeutic targets.

Occurrence of neuronal inclusions combined with increased nigral expression of α-synuclein within dopaminergic neurons following treatment with amphetamine derivatives in mice

In recent years several clinical and research findings have demonstrated the involvement of the presynaptic protein alpha-synuclein in a variety of neurodegenerative disorders which are known as synucleinopathies. Although the function of this protein in the physiology of the cell remains unknown, it is evident that both genetic alterations or a mere overexpression of the native molecule produces a degeneration of nigral dopamine-containing neurons leading to movement disorders, as demonstrated in inherited Parkinsons disease. In the present study, we investigated whether widely abused drugs such as methamphetamine and methylenedioxymethamphetamine (ecstasy), which are known to damage the nigrostriatal dopamine pathway of mice, increase the expression of alpha-synuclein within dopamine neurons of the substantia nigra pars compacta. The results of this study demonstrate that nigrostriatal dopamine denervation and occurrence of intracellular inclusions in nigral neurons produced by amphetamine derivatives are related to increased expression of alpha-synuclein within dopamine neurons of the substantia nigra. This lends substance to the hypothesis that increased amounts of native alpha-synuclein may be per se a detrimental factor for the dopamine neurons.

MPTP-induced parkinsonism extends to a subclass of TH-positive neurons in the gut

Gastrointestinal (GI) dysfunction occurs frequently in early Parkinsons disease (PD) and it is supposed to anticipate motor symptoms. About 80% of PD patients suffer from constipation before the onset of movement disorders. Despite such a high prevalence of gut impairment in PD, the molecular mechanisms remain poorly investigated. This is also due to the scarcity of experimental studies. In the present work, we tried to reproduce digestive abnormalities observed in PD patients by administering the parkinsonism-inducing neurotoxin 1-methyl-4-phenyl-1,2,3,6,-tetrahydropyridine (MPTP) to C57BL mice. We show that in these mice, MPTP (20mg/kg × 3) while producing the classic striatal dopamine (DA) denervation, persistently delays colonic motility, produces constipation, and reduces the number of enteric TH-positive neurons. The loss of TH-positive cells in the gut is selectively due to the disappearance of DA neurons within both myenteric and mostly submucosal plexus in the intestine, while no change is detected in the esophagus and stomach. In contrast, norepinephrine (NE) neurons are not affected. These data were confirmed by immunohistochemistry and by HPLC showing the significant loss of DA levels while NE and 5-HT content was not affected. Dopamine cell loss was associated with increased α-synuclein levels. These functional, biochemical, and morphological findings extend the PD-mimicking effects of MPTP to GI dysfunctions and provide a useful experimental model to understand gut dysfunction in PD and to find effective treatments for digestive symptoms.

Acid-Independent Gastroprotective Effects of Lansoprazole in Experimental Mucosal Injury

The protective effects of the proton pumpinhibitor lansoprazole on gastric mucosal damage inducedby ethanol-HCl or hemorrhagic shock were investigated inthe present study. The morphometric analysis of gastric histological sections revealed thatlansoprazole dosedependently reduced mucosal injuryevoked by ethanol-HCl (ED50 = 24.3μmol/kg) or hemorrhagic shock (ED50 = 38.9μmol/kg), these effects being associated with markedincrements of Alcian blue recovery from gastric boundmucus (ED50 = 31.4 μmol/kg and 27.6μmol/kg, respectively). In addition, lansoprazoleinhibited gastric acid secretion from pylorusligated rats(ED50 = 9.8 μmol/kg). Further experiments,performed on rats with ethanol-HCl-induced gastricinjury, indicated that the protective effects of lansoprazole were not modified by L-365,260,suramin, NG-nitro-L-arginine, or systemicablation of capsaicin-sensitive sensory nerves, whereasthey were partly blocked by indomethacin and fullyprevented by N-ethyl-maleimide. In addition, lansoprazoledid not modify somatostatin concentrations in gastricmucosa. The present results provide evidence thatlansoprazole prevents the necrotic damage of gastric mucosa induced by ethanol-HCl or hemorrhagicshock. According to the rank order of ED50values, these effects appear to depend mainly on theenhancement of the gastric mucus barrier rather than on the reduction of acid secretion. It is alsoproposed that an increased production of prostaglandins,as well as an increased availability of sulfhydrylcompounds at level of gastric mucosa may account for the gastroprotective effects oflansoprazole.

Parallel manifestations of neuropathologies in the enteric and central nervous systems

Background  Neurodegenerative diseases may extend outside the central nervous system (CNS) and involve the gastrointestinal (GI) tract. The gut would appear to be a pathological marker for neurodegeneration, as well as a site for studying the pathophysiology of neurodegeneration. In fact, both in the ENS and CNS, misfolded proteins are likely to initiate a process of neurodegeneration. For example, the very same protein aggregates can be detected both in the ENS and CNS. In both systems, misfolded proteins are likely to share common cell‐to‐cell diffusion mechanisms, which may occur through a parallel prion‐like diffusion process. Independently from the enteric or central origin, misfolded proteins may proceed along the following steps, they: (i) form aggregates; (ii) are expressed on plasma membrane; (iii) are secreted extracellularly; (iv) are glycated to form advanced glycation end‐products (AGEs); (v) are internalized through specific receptors placed on neighboring cells (RAGEs); (vi) are cleared by autophagy; and (vii) are neurotoxic. These features are common for a‐synuclein (in Parkinsons disease and other synucleinopathies), β‐amyloid and tau (in degenerative dementia), SOD‐1 and TDP43 (in amyotrophic lateral sclerosis), and PrPsc (in prion diseases). While in some diseases these features are common to both ENS and CNS, in others this remains a working hypothesis.

The Blockade of Adenosine Deaminase Ameliorates Chronic Experimental Colitis through the Recruitment of Adenosine A2A and A3 Receptors

Adenosine modulates immune/inflammatory reactions. This study investigates the expression of adenosine deaminase in the inflamed colon, the effects of adenosine deaminase inhibitors on established colitis, and the recruitment of adenosine receptors by endogenous adenosine after adenosine deaminase blockade. Adenosine deaminase expression was determined by Western blot. The effects of 4-amino-2-(2-hydroxy-1-decyl)pyrazole[3,4-d]pyrimidine (APP; a novel adenosine deaminase inhibitor), erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA; a reference adenosine deaminase inhibitor), dexamethasone, and selective adenosine receptor antagonists were tested in rats with 2,4-dinitrobenzenesulfonic acid-induced colitis. Systemic (food intake, body and spleen weight) and colonic [macroscopic/microscopic damage, tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and malondialdehyde (MDA)] inflammatory parameters were assessed. Test drugs were administered intraperitoneally for 6 days, starting at day 5 from colitis induction. Adenosine deaminase was detected in normal colon, and its expression was increased in inflamed tissues. Colitis was associated with decreased food intake and body weight, augmented spleen weight, and increased levels of colonic TNF-α, IL-6, and MDA. APP or EHNA, but not dexamethasone, improved food intake and body weight. APP, EHNA, and dexamethasone counteracted the increments of spleen weight, ameliorated macroscopic and microscopic indexes of inflammation, and reduced TNF-α, IL-6, and MDA levels. The beneficial effects of APP and EHNA on inflammatory parameters were prevented by the pharmacological blockade of A2A or A3 receptors, but not A1 or A2B. The present results show that: 1) bowel inflammation is associated with an enhanced adenosine deaminase expression; and 2) the anti-inflammatory actions of adenosine deaminase inhibitors against chronic established colitis depend on the sparing of endogenous adenosine, leading to enhanced A2A and A3 receptor activation.

Morphological evidence that xenon neuroprotects against N-methyl-DL-aspartic acid-induced damage in the rat arcuate nucleus: a time-dependent study.

Abstract:  The hyperactivation of glutamate receptors, especially those of the N‐methyl‐d‐aspartate subtype (NMDA), can induce excess calcium entry into cells, leading to neuronal death. Since the anesthetic gas xenon behaves as an NMDA antagonist, the present article investigated, by distinct morphological approaches and after different times, the possible neuroprotectant effects of this gas in a model of neuronal damage induced by N‐methyl‐dl‐aspartic acid (NMA) on rat arcuate nucleus. Rats were assigned to the following groups: controls; xenon exposure; NMA treatment; or xenon exposure + NMA treatment. Animals were placed in an experimental cage and after 10 min a mixture of xenon (or nitrogen) 70% and oxygen 30% was delivered. After 3 h, 1, 2, 5, or 7 days from gas exposure, rats were euthanized and the whole brain was removed and processed for either transmission electron microscopy or light microscopy. In the arcuate nucleus from NMA‐treated animals only 40–60% of cell population survived in all times with several degenerating neurons giving the typical appearance of a “bulls eye.” At ultrastructural level, chromatin margination, nuclear shrinkage, mitochondria with matrix dilution, dilated endoplasmic cisternae, and electrondense cytoplasm were detected. Xenon alone did not induce changes, but reduced of about 50% NMA‐induced cell loss as well as degenerating neurons, with the maximal neuroprotection at 7 days. These results confirm that in the rat arcuate nucleus NMA can induce a severe neuronal damage that is already marked after 3 h. Xenon significantly reduced the neuronal damage at all times and can be then regarded as a promising neuroprotectant agent.

Characterization of α2-adrenoceptor subtypes involved in the modulation of gastric acid secretion

Abstract The effects of several α 2 -adrenoceptor agonists and antagonists were examined on gastric acid secretion from reserpinized rats undergoing electrical stimulation of the left vagus nerve. Both detomidine and oxymetazoline inhibited vagal acid hypersecretion, their effects being fully prevented by idazoxan, 7,8-(methylenedioxy)-14-α-hydroxyalloberbane (CH 38083), or 2-(2-methoxy-1,4-benzodioxan-2-yl)-2-imidazoline (RX 821002), and partly antagonized by yohimbine or rauwolscine. 2-(2,4-( O -methoxy-phenyl)-piperazin-1-yl)-ethyl-4,4-dimethyl-1,3-(2 H ,4 H )-isoquinolindione (ARC 239) did not affect the antisecretory action of the two agonists, while prazosin at the highest dose was partly effective only against detomidine. Atropine markedly reduced vagally evoked acid output. It is suggested that acid secretion induced by vagal cholinergic stimulation is modulated by α 2A -like adrenoceptor subtypes.

NSAID-Induced Enteropathy: Are the Currently Available Selective COX-2 Inhibitors All the Same?

Nonsteroidal anti-inflammatory drugs (NSAIDs) can induce intestinal mucosal damage, but the underlying mechanisms remain poorly understood. The present study investigated the effects of celecoxib, etoricoxib, indomethacin, and diclofenac on small bowel integrity in rats. Male rats were treated orally with test drugs for 14 days. Animals were processed for assessment of blood hemoglobin levels and hepatic mitochondrial functions, microscopic evaluation of small intestinal damage, Western blot analysis of cyclooxygenase-1 and -2 (COX-1, COX-2) expression, and assay of malondialdehyde (MDA), myeloperoxidase (MPO), and prostaglandin E2 (PGE2) levels in small intestine. Indomethacin and diclofenac decreased blood hemoglobin levels, whereas etoricoxib and celecoxib were without effects. Celecoxib caused a lower degree of intestinal damage in comparison with the other test drugs. Indomethacin and diclofenac, but not etoricoxib or celecoxib, reduced intestinal PGE2 levels. Test drugs did not modify intestinal COX-1 expression, although they enhanced COX-2, with the exception of celecoxib, which downregulated COX-2. Indomethacin, diclofenac, and etoricoxib altered mitochondrial respiratory parameters, although celecoxib was without effects. Indomethacin or diclofenac increased MDA and MPO levels in both jejunum and ileum. In the jejunum, etoricoxib or celecoxib did not modify such parameters, whereas in the ileum, etoricoxib, but not celecoxib, increased both MDA and MPO levels. These findings suggest that nonselective NSAIDs and etoricoxib can induce enteropathy through a topic action, whereas celecoxib lacks relevant detrimental actions. The selectivity profile of COX-1/COX-2 inhibition by test drugs and the related effects on prostaglandin production do not appear to play a major role in the pathogenesis of enteropathy.

Mechanisms of protection by omeprazole against experimental gastric mucosal damage in rats

In the present study, the protective effect of omeprazole on gastric mucosa injury induced by ethanol.HCl in rats and the putative mechanisms involved in this action were investigated. Misoprostol and ranitidine were used as reference drugs. The morphometric analysis of histological sections showed that omeprazole caused a significant reduction of mucosal necrotic damage, this effect being associated with a marked increase in Alcian blue recovery from gastric bound mucus. In addition, omeprazole elicited a significant inhibition of gastric acid secretion from pylorus-ligated rats. Misoprostol exerted similar effects to those obtained with omeprazole, even if the Alcian blue recovery and the acid output were affected to a lesser extent. By contrast, ranitidine failed to influence both the mucosal damage and the Alcian blue recovery, while it exerted a marked inhibition on acid secretion. The present results indicate that omeprazole is effective in protecting gastric mucosa from necrotic damage induced by ethanol.HCl and suggest that an enhancement of gastric mucus barrier may account for this protective action.