Uremic Toxins and Ciprofloxacin Affect Human Tenocytes In Vitro

Tendinopathy is a rare but serious complication of quinolone therapy. Risk factors associated with quinolone-induced tendon disorders include chronic kidney disease accompanied by the accumulation of uremic toxins. Hence, the present study explored the effects of the representative uremic toxins phenylacetic acid (PAA) and quinolinic acid (QA), both alone and in combination with ciprofloxacin (CPX), on human tenocytes in vitro. Tenocytes incubated with uremic toxins +/- CPX were investigated for metabolic activity, vitality, expression of the dominant extracellular tendon matrix (ECM) protein type I collagen, cell-matrix receptor β1-integrin, proinflammatory interleukin (IL)-1β, and the ECM-degrading enzyme matrix metalloproteinase (MMP)-1. CPX, when administered at high concentrations (100 mM), suppressed tenocyte metabolism after 8 h exposure and at therapeutic concentrations after 72 h exposure. PAA reduced tenocyte metabolism only after 72 h exposure to very high doses and when combined with CPX. QA, when administered alone, led to scarcely any cytotoxic effect. Combinations of CPX with PAA or QA did not cause greater cytotoxicity than incubation with CPX alone. Gene expression of the pro-inflammatory cytokine IL-1β was reduced by CPX but up-regulated by PAA and QA. Protein levels of type I collagen decreased in response to high CPX doses, whereas PAA and QA did not affect its synthesis significantly. MMP-1 mRNA levels were increased by CPX. This effect became more pronounced in the form of a synergism following exposure to a combination of CPX and PAA. CPX was more tenotoxic than the uremic toxins PAA and QA, which showed only distinct suppressive effects.

L-dopa response pattern in a rat model of mild striatonigral degeneration

Background

Unresponsiveness to dopaminergic therapies is a key feature in the diagnosis of multiple system atrophy (MSA) and a major unmet need in the treatment of MSA patients caused by combined striatonigral degeneration (SND). Transgenic, alpha-synuclein animal models do not recapitulate this lack of levodopa responsiveness. In order to preclinically study interventions including striatal cell grafts, models that feature SND are required. Most of the previous studies focused on extensive nigral and striatal lesions corresponding to advanced MSA-P/SND. The aim of the current study was to replicate mild stage MSA-P/SND with L-dopa failure.

Methods and results

Two different striatal quinolinic acid (QA) lesions following a striatal 6-OHDA lesion replicating mild and severe MSA-P/SND, respectively, were investigated and compared to 6-OHDA lesioned animals. After the initial 6-OHDA lesion there was a significant improvement of motor performance after dopaminergic stimulation in the cylinder and stepping test (p<0.001). Response to L-dopa treatment declined in both MSA-P/SND groups reflecting striatal damage of lateral motor areas in contrast to the 6-OHDA only lesioned animals (p<0.01). The remaining striatal volume correlated strongly with contralateral apomorphine induced rotation behaviour and contralateral paw use during L-dopa treatment in cylinder and stepping test (p<0.001).

Conclusion

Our novel L-dopa response data suggest that L-dopa failure can be induced by restricted lateral striatal lesions combined with dopaminergic denervation. We propose that this sequential striatal double-lesion model replicates a mild stage of MSA-P/SND and is suitable to address neuro-regenerative therapies aimed at restoring dopaminergic responsiveness.

Time course of oxidative events in the hippocampus following intracerebroventricular infusion of quinolinic acid in mice

The excitotoxicity induced by QA has been related to its ability to increase free radical content and oxidative stress. In order to investigate the time course of toxicity and oxidative profile in the mice hippocampus following seizures induced by QA infusion (36.8 nM, i.c.v.), we evaluated the cellular damage (PI uptake assay), content of ROS formation (DCF assay) and the total radical antioxidant potential (TRAP) and reactivity (TAR) levels. The present results showed that a cellular damage occurred as early as 4 h after QA infusion coincident with an increase in the ROS contents, which returned to control levels after 24 h, while the cellular damage persisted for 72 h. There was a marked increased in the total antioxidant capacity at 8 h after QA infusion in both reactivity and potential levels. By 72 h post-treatment, the TRAP levels decreased, but the TAR levels remained augmented. Therefore, the delayed and persistent increase in the antioxidant capacity after QA insult may be a cellular adaptative response, probably contributing to decrease the ROS levels in order to prevent the spreading of the cellular damage. Therefore, the increase in the QA level in the brain ventricle may induce oxidative stress, which is followed by a persistent response in the antioxidant system in the hippocampus. The present study may, therefore, contribute to elucidate the mechanism of the brain dysfunction in patients with several neurological disorders involving elevation of QA in the CSF.

Brain mitochondrial defects amplify intracellular [Ca2+] rise and neurodegeneration but not Ca2+entry during NMDA receptor activation

According to the "indirect" excitotoxicity hypothesis, mitochondrial defects increase Ca2+ entry into neurons by rendering NMDA-R hypersensitive to glutamate. We tested this hypothesis by investigating in the rat striatum and cultured striatal cells how partial mitochondrial complex II inhibition produced by 3-nitropropionic acid (3NP) modifies the toxicity of the NMDA-R agonist quinolinate (QA). We showed that nontoxic 3NP treatment, leading to partial inhibition of complex II activity, greatly exacerbated striatal degeneration produced by slightly toxic QA treatment through an "all-or-nothing" process. The potentiation of QA-induced cell death by 3NP was associated with increased calpain activity and massive calpain-mediated cleavage of several postsynaptic proteins, suggesting major neuronal Ca2+ deregulation in the striatum. However, Ca2+ anomalies probably do not result from NMDA-R hypersensitivity. Indeed, brain imaging experiments using [(18)F]fluorodeoxyglucose indirectly showed that 3NP did not increase QA-induced ionic perturbations at the striatal glutamatergic synapses in vivo. Consistent with this, the exacerbation of QA toxicity by 3NP was not related to an increase in the QA-induced entry of 45Ca2+ into striatal neurons. The present results demonstrate that the potentiation of NMDA-R-mediated excitotoxicity by mitochondrial defects involves primarily intracellular Ca2+ deregulation, in the absence of NMDA-R hypersensitivity.

Deficits induced by quinolinic acid lesion to the striatum in a position discrimination and reversal task are ameliorated by permanent and temporary lesion to the globus pallidus: a potential novel treatment in a rat model of Huntington's disease

Symptoms in the early stages of Huntington's disease (HD) are assumed to reflect basal ganglia circuit dysfunction secondary to degeneration of striatal projections to the external segment of the globus pallidus (GPe). The hypothesis that GPe lesion would ameliorate HD symptoms by "normalizing" the circuit's functioning was tested in a rat model of this disease. The performance of rats sustaining quinolinic acid lesion to the striatum (a rat model of HD) in a position discrimination and reversal task was compared with the performance of rats sustaining in addition a bilateral excitotoxic lesion to the globus pallidus (GP) carried out simultaneously with the striatal lesion (Experiment 1) or 1 month after the striatal lesion (Experiment 2), as well as a unilateral temporary lesion of the GP (Experiment 3). The striatal lesion-induced deficit in the task was effectively reversed by a bilateral excitotoxic GP lesion carried out simultaneously or 1 month after the striatal lesion, as well as by a temporary unilateral GP inactivation. Given that a similar dysfunction of basal ganglia circuitry is thought to subserve the behavioral alterations seen in quinolinic acid lesioned rats and some of the symptoms in HD, these results raise the possibility that lesion or inactivation of the GPe may alleviate some of HD symptoms.

Role of the medial and lateral caudate-putamen in mediating an auditory conditional response association

Rats with quinolinic acid lesions of the medial or lateral caudate-putamen (CPu) and controls were tested for performance of a previously learned auditory conditional response association task. The task involved the selection of two possible responses when presented with one of two different tones. Results indicated that lesions of either the medial or the lateral CPu produced a sustained deficit in the auditory conditional response association task. Only the lateral CPu lesioned rats exhibited transient motor problems immediately following surgery, but these problems did not interfere with the execution of the appropriate responses. It is suggested that both the medial and the lateral CPu are involved in response selection and response separation within egocentric space.

[Behavior characterization of a model of Huntington's disease in rats, induced by quinolinic acid]

INTRODUCTION

Huntington's disease (HD) is a progressive neurodegenerative disorder, characterized by severe degeneration of basal ganglia neurons. Behavioral symptoms of HD include abnormal, uncontrollable and constant choreiform movements, impaired cognitive function and emotional disturbance.

OBJECTIVE

In order to explore the changes of cognitive and motor functions induced by quinolinate lesion we realized this experiment.

MATERIALS AND METHODS

We studied the behavior of rats with unilateral quinolinate induced lesions of the medial striatum. Intact 3 months old male rats (n = 23) were trained in the Morris Water Maze during three consecutive days, eight trials/day (acquisition), and before surgery they were randomly assigned either to intact or lesion groups. Fifteen days after the lesion the rats were tested using retention test (one day/four trials, with the escape platform in the same position as in acquisition test), on the next three days the rats were tested in the transfer test (three days/eight trials-day, with the platform in the new position). The Paw reaching test and the asymmetrical rotational behavior test in respond to amphetamine were also tested in these rats.

RESULTS

Lesioned animals exhibited deficient retrieval of stored memories of visuospatial skills and impaired transfer of learning. In relation with motor activity the lesioned rats showed a profound impairment in the skill of the left forelimb for reaching food compared with its right forelimb as well as with the forelimb abilities of intact rats. The lesioned animals showed significant rotational behavior induced by amphetamine agonist, ipsilateral to the lesioned striatum.

CONCLUSIONS

These results are consistent with the notion that the striatal degeneration could sufficiently account for the cognitive abnormalities associated with HD, and with the key role played by basal ganglia in enabling voluntary and postural adjustment of the movements.

Changes in limbic dopamine metabolism following quinolinic acid lesions of the left entorhinal cortex in rats

To examine the effects of lesions of the entorhinal cortex on limbic dopamine (DA) metabolism, DA and its metabolites were assayed in five brain regions (the medial prefrontal cortex, anterior cingulate cortex, caudate-putamen, accumbens nucleus, and lateral amygdala), 14 and 28 days after quinolinic acid or sham lesions of the left entorhinal cortex in rats. Concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC) on day 14 in the medial prefrontal cortex, accumbens nucleus, and lateral amygdala of the entorhinal cortex lesioned animals were significantly decreased compared with the controls, but they returned to control levels on day 28. The concentration of DA in the lateral amygdala and spontaneous locomotion to a novel environment were significantly increased on day 28 after the lesion. These results suggest that entorhinal cortex lesions alter mesolimbic dopamine metabolism, particularly in the amygdala.

Time-course analysis and comparison of acute and chronic intrastriatal quinolinic acid administration on forelimb reaching deficits in the rat

Rats were trained to use a single forelimb for a food pellet retrieval task. During baseline testing all rats exhibited > 90% use of a preferred limb for the task. Following baseline, rats were subjected to chronic administration (18 day) or acute injection of quinolinic acid (QUIN) or vehicle to the striatum contralateral to the preferred limb. Rats were tested 48 h after insertion of chronic delivery probes or after acute injection and retested every 48 h over an 18-day period. Compared to vehicle, rats receiving chronic QUIN (7.6 nmol/h) exhibited an increase in the number of reach attempts required to meet task criteria. Chronic QUIN did not produce a significant change in latency to initiate the task or an increase in latency to complete the task. No rats exposed to chronic QUIN exhibited a switch in limb preference for the task. Unlike animals exposed to chronic QUIN, a significant number of animals receiving acute QUIN injections switched to exclusive use of the ipsilateral (nonpreferred) limb for the task. Quantitative histological analysis revealed no significant difference in lesion volume between acute and chronic lesion animals. These findings suggest that behavioral manifestations of histopathologically similar lesions may be vastly different depending on the methods used to produce these lesions. More specifically, the acute injection model resulted primarily in forelimb disuse, whereas the chronic model resulted in continued abnormal use of the affected limb. Understanding adaptive strategies used in these models may be particularly important when testing newly developed transgenic models of neurodegenerative diseases and the therapeutic potential of newly developed neuroprotectants.

Effects of severity of host striatal damage on the morphological development of intrastriatal transplants in a rodent model of Huntington's disease: implications for timing of surgical intervention

OBJECT

The goal of this study was to investigate the effect of the severity of host neural damage on the morphological development of intrastriatal transplants in a rodent model of Huntington's disease.

METHODS

Sprague-Dawley rats were subjected to unilateral striatal lesioning induced by administration of quinolinic acid (20 nM, 40 nM, or 90 nM). Seven days postlesioning, intrastriatal cell suspension grafts were placed in the right striatum in some of these animals. Grafts were also placed in the right striatum of additional animals that had not been subjected to lesioning. The rats were killed and processed for morphological analysis 8 weeks after grafting. The results indicate that striatal grafts survive and grow much better when implanted into a lesioned striatum rather than into an intact striatum, as measured both by the volume and the numbers of medium-sized spiny neurons within the graft. Only a small or modest lesion is necessary to produce this effect. By some measures (such as graft volume) grafts survive less well when the lesion is more extensive. The presence of a graft reduced the extent of striatal atrophy induced by the lesions, but this effect was not caused by differences in the numbers of surviving neurons per se.

CONCLUSIONS

These results have significant implications for the timing of surgical intervention and patient selection with respect to current and future clinical trials of striatal transplantation in the treatment of Huntington's disease.

Histological and behavioral protection by (-)-nicotine against quinolinic acid-induced neurodegeneration in the hippocampus

Injections of quinolinic acid (60, 180, and 600 nmol) in the dorsal hippocampus induced significant neurotoxicity that was evident 1 day after the injection. By day 3, pyramidal as well as granular cells were affected even at the lowest dose of quinolinic acid, an effect that persisted up to 20 days. Consistent with the histological findings, animals with bilateral injections in the dorsal hippocampus were cognitively impaired during acquisition and retention of spatial information in the water maze. A subacute treatment with (-)-nicotine (62 micromol/kg/day) delivered by subcutaneous minipumps prevented the histological and cognitive deficits induced by the bilateral quinolinic acid (60 nmol) injections. These data indicate that quinolinic acid can induce degeneration of both pyramidal as well as granule cells in the hippocampus, leading to cognitive impairments in the rat, and that activation of neuronal nicotinic acetylcholine receptors can prevent the neurodegenerative process induced by quinolinic acid.

Metabotropic receptors in excitotoxicity: (S)-4-carboxy-3-hydroxyphenylglycine ((S)-4C3HPG) protects against rat striatal quinolinic acid lesions

Striatal quinolinate lesions mimic many of the neuropathological characteristics of Huntington's disease. This excitotoxicity is mediated by combined activity of N-methyl-D-aspartate and metabotropic glutamate receptors (mGluRs). Using recently developed phenylglycine derivatives, (S)-4-carboxy-3-hydroxyphenylglycine ((S)-4C3HPG) and (+)-alpha-methyl-4-carboxyphenylglycine ((+)-MCPG), we investigated the role of the different sub-classes of mGluRs in the in vivo excitotoxic process. (S)-4C3HPG (500 and 1000 nmol), co-injected with quinolinic acid, significantly reduced lesion volumes by 52 and 89%, respectively, whereas the same doses of (+)-MCPG had no effect on lesion size. The differential actions of these two drugs at Group 1 and Group 2 metabotropic receptors may explain their differential effects. These observations confirm the important role of mGluRs in excitotoxicity and identify them as promising targets for intervention.

Both apoptosis and necrosis occur following intrastriatal administration of excitotoxins

To learn about the mechanisms of excitotoxic cell death in vivo, three different excitatory amino acid receptor agonists (kainic acid, quinolinic acid or quisqualic acid) were injected in the left striatum of adult rats. Brains were examined at 24 and 48 h after injection. Morphological and biochemical studies were performed using conventional stains, histochemistry, in situ labelling of nuclear DNA fragmentation, and agarose gel electrophoresis of extracted DNA. Large numbers of cells with cytoplasmic shrinkage and nuclear condensation or granular degeneration of the chromatin, and fewer cells with apoptotic morphology were distributed at random in the injured areas of the three groups of treated animals but not in rats injected with vehicle alone. A ladder pattern, typical of internucleosomal DNA fragmentation, was observed 24 h after treatment. This was replaced by a smear pattern, consistent with random DNA breakdown, at 48 h. These morphological and biochemical results suggest that prevailing necrosis together with apoptosis occur following intrastriatal injection of different excitotoxins.

Sensorineural hearing loss from quinolinic acid: a neurotoxin in middle ear effusions

Quinolinic acid (QUIN) is an endogenous metabolite that exerts a neurotoxic effect by binding to specific neuronal receptors. Studies involving a broad spectrum of infectious and inflammatory central nervous system diseases have suggested a role for QUIN in causing neuronal injury. Since there is evidence for presence of the QUIN receptor in mammalian cochleas, QUIN was measured in middle ear effusions (MEEs). Gas chromatography/mass spectrometry detected QUIN in each of 65 diluted human MEEs, with a mean of 482 +/- 75 (SEM) nmol/L and a range from 15 to 2667 nmol/L. QUIN was also detected in each of 197 chinchilla MEEs from five different models of otitis media, with a mean of 10.6 +/- 1.3 (SEM) mumol/L and a range from 0.23 to 146.0 mumol/L (corrected for dilution). To determine whether QUIN causes sensorineural hearing loss (SNHL), QUIN solutions were placed on round window membranes (RWM) for 20 to 240 minutes, in 20 chinchillas. SNHL was detected by electrocochleography in QUIN-exposed animals, but not in saline controls. We conclude that QUIN is present in MEEs and that QUIN in the middle ear has the potential to cross the RWM and cause sensorineural hearing loss, possibly by binding to specific neuronal receptors in mammalian cochleas.