Is quantitative sensory testing helpful in the management of oxaliplatin neuropathy? a two-year clinical study.

PURPOSE: To better understand how quantitative sensory testing could help the clinician in the management of oxaliplatin-induced peripheral neuropathy in terms of earlier and more reliable detection, we conducted a two-year prospective study. METHODS: Thermal sensory assessment, tactile sensory assessment, neuropathic pain assessment and adverse events gradation (NCI-CTC) were performed during treatment and 6 months after treatment completion. RESULTS: 35 patients were enrolled and followed-up during one year. Cold and Warm Detection Thresholds were higher 6 months after treatment completion than at enrollment. Mechanical detection thresholds didn't change significantly. Neurotoxicity was mostly grade-1, only 18% grade-2 and no grade-3. Grade-2 patients received lower oxaliplatin cumulative dose than grade-1, which reveals effective dose adaptation and grade-2 patients were more likely to develop painful neuropathy. CONCLUSION: Thermal thresholds impairment emerges too late to help the clinician in the prophylaxis of neuropathy. Management of OXA-treatment based on NCI-CTC, as currently recommended, remains the best way to detect neuropathy and ensure treatment adaptation.

Antinociceptive activity of the new triple reuptake inhibitor NS18283 in a mouse model of chemotherapy-induced neuropathic pain.

BACKGROUND: Chronic neuropathic pain can lead to anxiety and depression. Drugs that block reuptake of serotonin, norepinephrine and/or dopamine are widely used to treat depression, and have emerged as useful drugs in the treatment of neuropathic pain. This study compared the acute antinociceptive effects of NS18283, a novel triple monoamine reuptake inhibitor (MRI) with indatraline, venlafaxine and escitalopram in a mouse model of neuropathic pain. METHOD: Neuropathic pain-like behaviours were induced in mice by repeated injections of oxaliplatin (OXA), and assessed using the von Frey hair test, the cold plate test and the thermal preference plate test. Anxio/depressive phenotype and antidepressant-like properties of compounds were assessed by the novelty suppressed feeding test and the tail suspension test, respectively. RESULTS: In vivo microdialysis experiments showed that each MRI increased extracellular serotonin, norepinephrine and/or dopamine levels in the cingulate cortex, in agreement with their in vitro reuptake inhibitory properties. Indatraline (3 mg/kg) reversed the full repertoire of OXA-induced neuropathic hypersensitivity. NS18283 (10 mg/kg) reversed OXA-induced mechano-hypersensitivity and cold allodynia. Venlafaxine (16 mg/kg) and escitalopram (4 mg/kg) only reversed cold allodynia and mechano-hypersensitivity, respectively. All MRIs produced antidepressant-like activity in anxio/depressive phenotype of OXA mice. CONCLUSIONS: Acute administration of drugs that enhance the activity of serotonin, norepinephrine and dopamine neurotransmission within nociceptive pathways may provide a broader spectrum of antinociception than dual or selective reuptake inhibitors in animal models of neuropathic pain. Whether similar observations would occur after repeated administration of such compounds in an attempt to simulate dosing in humans, or be compromised by dopaminergic-mediated adverse effects warrants further investigation.

Behavioral and serotonergic consequences of decreasing or increasing hippocampus brain-derived neurotrophic factor protein levels in mice.

Antidepressants such as Selective Serotonin Reuptake Inhibitors (SSRI) act as indirect agonists of serotonin (5-HT) receptors. Although these drugs produce a rapid blockade of serotonin transporters (SERTs) in vitro, several weeks of treatment are necessary to observe clinical benefits. This paradox has not been solved yet. Recent studies have identified modifications of intracellular signaling proteins and target genes that could contribute to antidepressant-like activity of SSRI (e.g., increases in neurogenesis and BDNF protein levels), and may explain, at least in part, their long delay of action. Although these data suggest a positive regulation of 5-HT on the expression of the gene coding for BDNF, the reciprocal effects of BDNF on brain 5-HT neurotransmission remains poorly documented. To study the impact of BDNF on serotonergic activity, a dual experimental strategy was used to analyze neurochemical and behavioral consequences of its decrease (strategy 1) or increase (strategy 2) in the brain of adult male mice. (1) In heterozygous BDNF+/- mice in which brain BDNF protein levels were decreased by half, an enhancement of basal extracellular 5-HT levels (5-HText) that induced a down-regulation of SERT, i.e., a decrease in its capacity to reuptake 5-HT, was found in the hippocampus. In addition, the SSRI, paroxetine, failed to increase hippocampal 5-HText in BDNF+/- mice, while it produces robust effects in wild-type littermates. Thus, BDNF+/- mice can be viewed as an animal model of genetic resistance to serotonergic antidepressant drugs. (2) In wild-type BDNF+/+ mice, the effects of intra-hippocampal (vHi) injection of BDNF (100 ng) in combination with a SSRI was examined by using intracerebral microdialysis and behavioral paradigms that predict an antidepressant- and anxiolytic-like activity of a molecule [the forced swim test (FST) and the open field paradigm (OF) respectively]. BDNF induced a rapid and transient increase in paroxetine response on 5-HText in the adult hippocampus, which was correlated with a potentiation of its antidepressant-like activity in the FST. The effects of BDNF were selectively blocked by K252a, an antagonist of its high-affinity TrkB receptor. Such a correlation between neurochemical and behavioral effects of [BDNF+SSRI] co-administration suggests that its antidepressant-like activity is linked to the activation of 5-HT neurotransmission in the adult hippocampus. BDNF also had a facilitatory effect on anxiety-like behavior in the OF test, and paroxetine prevented this anxiogenesis. What was the mechanism by which BDNF exerted these latter effects? Surprisingly, by using zero net flux method of quantitative microdialysis in vivo, we found that an intra-hippocampal BDNF injection in wild-type mice decreased the functional activity of SERT as observed in BDNF+/- mice. However, the decreased capacity of SERT to reuptake 5-HT was not associated to an increase in basal 5-HText in the hippocampus of WT mice. Interestingly, using in situ hybridization experiments indicated that TrkB receptor mRNA was expressed in the hippocampus and dorsal raphe nucleus in adult mice suggesting that the neurochemical and behavioral effects of intra-hippocampal BDNF injection can mobilize both pre- and post-synaptic elements of the brain 5-HT neurotransmission. Taken together, these set of experiments unveiled a relative opposition of neurochemical and behavioral responses following either a decrease (in BDNF+/- mutant mice) or an increase in brain BDNF levels (bilateral intra-hippocampal injection) in adult mice. In view of developing new antidepressant drug strategy, a poly-therapy combining BDNF with a chronic SSRI treatment could thus improve the efficacy of current medications.

Behavioural assessment of dimethylsulfoxide neurotoxicity in rats.

Dimethylsulfoxide (DMSO) is a solvent used to dissolve hydrophobic drugs. Recent studies have demonstrated that repeated administration of DMSO induces significant disorders of the peripheral nervous system. To address this issue, we have studied the behavioural effects of repeated intraperitoneal injections of various concentrations of DMSO (1.8-3.6-7.2%) in male Sprague-Dawley rats. Behavioural effects were assessed with a commonly used battery of sensory and motor tests. The motor tests used were actimeter and grip strength test. Sensory test used noxious and non-noxious mechanical (paw pressure test and von Frey hairs test) and thermal (plantar test and tail immersion test) stimuli. Clinical status of the animals was good throughout the experiment and no motor deficits were observed. Nevertheless, sensory assessment displayed a mechanical allodynia of short duration.

Assessment of neurotoxicity following repeated cremophor/ethanol injections in rats.

As the mixture cremophor/ethanol is known to have side-effects affecting the peripheral nervous system, we have assessed its behavioural and morphological neurotoxicity after repeated intraperitoneal injections in male Sprague Dawley rats. Clinical status of the animals was good throughout the experiment and no motor deficits were observed. Nevertheless, sensory testing demonstrated an hyperalgesia and an allodynia to mechanical stimuli, associated to peripheral axon degeneration.

[Pathophysiology of pain]. / Physiopathologie de la douleur.

Progress in the knowledge of the pathophysiology of pain allow to associate clinical symptoms of painful syndroms to physiological, morphological and neurobiochemical changes observed both at peripheral and central sites. Thus, nociceptive pains involve both a sensitisation of nociceptors and a secondary central sensitisation. Numerous mediators are involved in these phenomena which reflect neuroplasticity. Peripherally, they come from plasma, immune cells and afferent fibres involved in neurogenic inflammation. Their number explains how the peripheral mechanisms of pain are complex and how it is difficult to pharmacologically suppress the activity of nociceptors. Other mediators are involved in the dorsal horn of the spinal cord. Excitatory amino acids are particularly involved by acting on NMDA receptors; substance P seems to work as a facilitatory neuromodulator rather than as a neurotransmitter. The mechanisms of neuropathic pains are different because both small and large diameter afferent fibers are involved. Ectopic discharges from lesional sites of C fibers, sprouting and abnormal neuronal connections have been described. Up regulation of ionic, especially sodic, channels has been demonstrated and could explain spontaneous discharges. Here again, central sensitisation is also observed but present knowledge does not allow to distinguish specific mechanisms. These progress in the knowledge of pathophysiology of pain allow to improve the understanding of the mechanism of action of analgesic drugs. They also give basis to the discovery of novel drugs with original mechanisms.

Assessment of allodynia and hyperalgesia after cisplatin administration to rats.

This work describes the behavioural responses of Sprague-Dawley rats to mechanical or thermal stimuli during and after administration of ten intraperitoneal injections of, alternatively, 1 and 2 mg/kg cisplatin every three days (cumulative dose: 15 mg/kg). Nociceptive signs including mechanical allodynia and hyperalgesia appeared after 3 and 6 cisplatin injections, respectively, and were maintained until 15 days after the last injection. The conservation of a good clinical status and fast appearance of symptoms are favourable criteria for using this animal model to understand the pathophysiological mechanisms implicated in the cisplatin-induced sensory peripheral neuropathy.

Cyclophosphamide-induced cystitis in freely-moving conscious rats: behavioral approach to a new model of visceral pain.

PURPOSE: To develop a model of visceral pain in rats using a behavioral approach. Cyclophosphamide (CP), an antitumoral agent known to produce toxic effects on the bladder wall through its main toxic metabolite acrolein, was used to induce cystitis. MATERIALS AND METHODS: CP was administered at doses of 50, 100 and 200 mg./kg. i.p. to male rats, and their behavior observed and scored. The effects of morphine (0.5 to 4 mg./kg. i.v.) on CP-induced behavioral modifications were tested administered alone and after naloxone (1 mg./kg. s.c.). In addition, 90 minutes after CP injection, that is, at the time of administration of morphine, the bladder was removed in some rats for histological examination. Finally, to show that the bladder is essential for the CP-induced behavioral modifications, female rats also received CP at doses of 200 mg./kg. i.p. and of 20 mg. by the intravesical route, and acrolein at doses of 0.5 mg. by the intravesical route and of 5 mg./kg. i.v. RESULTS: CP dose-relatedly induced marked behavioral modifications in male rats: breathing rate decrease, closing of the eyes and occurrence of specific postures. Morphine dose-dependently reversed these behavioral disorders. A dose of 0.5 mg./kg. produced a reduction of almost 50% of the behavioral score induced by CP 200 mg./kg. This effect was completely prevented by pretreatment with naloxone. At the time of administration of morphine, histological modifications of the bladder wall, such as chorionic and muscle layer edema, were observed. In female rats, CP 200 mg./kg. i.p. produced the same marked behavioral modifications as those observed in male rats. Administered at the dose of 20 mg. intravesically, CP did not produce any behavioral effects, whereas acrolein at 0.5 mg. intravesically induced behavioral modifications identical to those under CP 200 mg./kg. i.p., with the same maximal levels. Conversely, acrolein 5 mg./kg. i.v. did not produce any behavioral effects at all. CONCLUSIONS: Overall, these results indicate that this experimental model of CP-induced cystitis may be an interesting new behavioral model of inflammatory visceral pain, allowing a better understanding of these painful syndromes and thus a better therapeutic approach to them.

Description of a short-term Taxol-induced nociceptive neuropathy in rats.

This work describes a new animal model of neuropathic pain produced by the single intraperitoneal administration of Taxol (32 mg/kg) to male Sprague-Dawley rats. During the course of the experiment, the clinical status of the rats remained satisfactory and motor function was not altered. A number of classical behavioural tests of nociception as well as histological and electrophysiological investigations were performed. Taxol administration produced an important and rapidly developing mechanical hyperalgesia, a thermal hypoalgesia but no mechanical or thermal allodynia. Degenerative changes were observed in the sciatic nerve, the nerve fibres in the paw subcutaneous tissue and in the lumbar spinal cord. When Taxol or vehicle (a mix of Cremophor and ethanol) were repeatedly injected once a week for 5 weeks, similar nociceptive disorders were observed in addition to a decrease in peripheral nerve conduction velocity. The selective dysfunction of high-diameter myelinated fibres observed after one single administration of Taxol (32 mg/kg) may be attributable to paclitaxel-induced neuropathy, however other mechanisms causing neurochemical dysfunction must also be involved.

Another use of silica gel and aqueous eluent for HPLC analysis of clozapine and desmethylclozapine.

A procedure that involves a high-performance liquid chromatographic system with silica-bonded columns and reversed-phase eluents was fitted from a previously described method to measure clozapine and desmethylclozapine plasma levels. Clozapine and its demethylated metabolite were extracted from alkalinized serum by a liquid-liquid extraction, separated in 10 min, then quantitated at 254 nm at a minimum concentration of 20 ng/mL. The standard curves were linear over the range of 50-3000 ng/mL (r > 0.99) both for clozapine and desmethylclozapine and the assay had good sensitivity and recovery. Intra- and interday coefficients of variation for 200 and 800 ng/mL controls were less than 11.5% for clozapine and desmethylclozapine. This simple and efficient assay was used to monitor clozapine and desmethylclozapine levels from some treatment-refractory schizophrenic patients.

Pain related behaviour during vincristine-induced neuropathy in rats.

The development of suitable animal models of neuropathic pain is essential to understand the pathophysiological mechanisms responsible for this condition. This study presents the alterations in nociception observed in rats suffering from a peripheral neuropathy induced by 10 daily repeated intravenous injections of vincristine at doses of 50 or 75 microg/kg (total dose 500 or 750 microg/ kg). The rats present both mechanical hyperalgesia, allodynia and a loss of sensitivity (thermal hypoalgesia). Conservation of good health, the fast appearance of symptoms which correspond well with human responses and the easy induction of nociceptive symptoms are favourable criteria for using this model at 50 microg/kg vincristine dose in the future.

Hyperkalemia risks in hemodialysed patients consuming fluoride-rich water.

In order to observe the consequences of chronic ingestion of high fluoride-rich water on plasma potassium levels of hemodialysed subjects, we have conducted a retrospective study on 25 patients with chronic renal failure, treated with a substitute method, six of whom (consumers group, group C) were drinkers of a bicarbonate (about 4500 mg/l) and fluoride-rich (9 mg/l) mineral water, the Vichy Saint-Yorre water. With respect to sodium polystyrene sulfonate consumption (n = 17), there was no significant difference between group C and NC (non-consumers group). A significant correlation between plasma fluoride and potassium levels was observed only before dialysis (P < 1 x 10(-7)) but not after dialysis. A group by group analysis revealed that this correlation was linked to group C (P < 5 x 10(-6)), in which kalemia before dialysis was higher than that observed in group NC (P < 0.005). Moreover, it appeared that the higher fluoride levels were, the higher the kalemia was inclined to be. Thus, the risks of hyperkalemia in dialysed patients, who also drink Vichy St-Yorre water or other fluoride-rich waters, are more important, while not forgetting the risk of fluorosis. The mechanisms by which chronically administered fluoride could increase kalemia are also discussed.

High-performance liquid chromatographic determination of paclitaxel in rat serum: application to a toxicokinetic study.

A simple and sensitive high-performance liquid chromatographic method is described for the determination of paclitaxel (Taxol) at 230 nm using a Nucleosil C18 (5 microm) column and a methanol-water (70:30, v/v) mobile phase following a single-step extraction from serum with dichloromethane. The assay was validated against the classical criteria and was applied to a toxicokinetic study in rats after one or five, one per week) intraperitoneal administrations of 16 mg/kg Taxol.

Investigation of fluoride elimination during a dialysis session.

We have conducted a study of the elimination kinetics of fluoride ions by a log linear regression analysis of plasma levels obtained during a bicarbonate hemodialysis session, with a dialyzer in polymercaprin for six patients with chronic renal failure. Using plasma fluoride levels of 35 patients studied for 20 months, we have validated these kinetics for hemodialysis with sodium bicarbonate, acetate-free biofiltration, hemodiafiltration with low flow rate and other dialyzers. Our results show that the decrease in plasma fluoride levels is statistically significant only after the first hour, and the fall reaches approximately 30% after a 4 h dialysis session. We propose that post-dialysis measurements of plasma fluoride are now not necessary if levels before dialysis are known.

Is the reduced efficacy of morphine in diabetic rats caused by alterations of opiate receptors or of morphine pharmacokinetics?

Because it generally is admitted that neuropathic pain is resistant to opioid analgesia, we investigated the effect of morphine on hyperalgesia in streptozocin-induced diabetes in rats. The antinociceptive effect of morphine (0.5-4 mg/kg i.v.) on mechanical (paw pressure test), thermal (tail immersion test) and chemical (formalin test) hyperalgesia was reduced. To clarify the mechanisms involved in the alteration of morphine analgesia, the binding characteristics of mu and delta receptor agonists and the pharmacokinetics of morphine and its glucuronide metabolites morphine 3-glucuronide and morphine 6-glucuronide were determined. KD and Bmax values for [3H][D-Ala2,(Me)Phe4, Gly(ol)5]enkephalin and [3H][D-Pen2,D-Pen5]enkephalin to cerebral mu and delta opiate receptors were not altered by diabetes. Likewise, the plasma maximal concentration of morphine and metabolites, as well as the area under the curve, did not differ between diabetic and normal rats. Only the total clearance and the apparent volume of distribution of morphine were increased in diabetic rats, which suggests that the diabetes-induced glycosylation of proteins might increase the distribution of morphine in the aqueous compartment. These data indicate that the reduced analgesic effect of morphine caused by diabetes cannot be explained by a decrease in opiate-receptor affinity or density but rather by kinetic alteration of morphine (increase of total clearance and of volume of distribution in comparison with healthy animals).

DNA repair activity in protein extracts from rat tissues.

Among DNA repair pathways, nucleotide excision repair (NER) is able to recognize and process a wide variety of DNA lesions. The NER mechanism can be summarized in two stages: incision/excision of the lesion and DNA repair synthesis. Here, we have assessed the repair synthesis activity of protein extracts from different rat tissues by an in vitro biochemical assay that reproduces the entire NER reaction. The protein extraction procedure was adapted to rat tissues and the biochemical parameters of the assay (high salt concentration, addition of EGTA) in order to minimize non-specific nuclease activity which allows the measurement of repair activity. Using this repair assay we detected a small increase in the extent of repair synthesis in liver compared to brain and lung tissue protein extracts. Similar results were obtained using a derivative assay that allows the measurement of the incision activity of tissue protein extracts with lower incision activity in lung tissue extract.

Effect of tolcapone on plasma and striatal apomorphine disposition in rats.

The influence of tolcapone, an inhibitor of catechol-O-methyl transferase, was evaluated on the disposition of apomorphine, a dopamine agonist used to treat Parkinson's disease, to explain a previously observed increase of duration of the effect of apomorphine associated with tolcapone. Sampling was performed in rats before and at different times after administration of apomorphine and following that of tolcapone or saline. Both in plasma and striatum, times to reach maximal-concentration and maximal concentrations did not significantly differ between the two groups but the elimination half-life times and areas under the curve were significantly greater following tolcapone treatment than in the saline group. These results show that tolcapone can increase plasma apomorphine bioavailability by modifying its liver catabolism.

Comparison of amitriptyline metabolism in hepatocytes from streptozocin-induced diabetic rats and from non-diabetic rats.

Biotransformation of amitriptyline (AMI) was studied at different intervals in freshly isolated hepatocytes from healthy or streptozocin-induced diabetic rats in order to investigate the influence of the diabetic state. Levels of free and conjugated AMI, demethylated and hydroxylated metabolites, were assessed by HPLC analysis. In hepatocytes isolated from diabetic rats, AMI was less completely metabolized and the demethylation reaction became more important than in non-diabetic rat hepatocytes. Although the proportions of hydroxylated metabolites decreased in diabetic rats, it always remained predominant. Furthermore, glucuronidation of metabolites was greater, especially for (Z)-10-hydroxynortriptyline in diabetic animals.