The role of mesotherapy in the management of spinal pain. A randomized controlled study.

Background: Mesotherapy is a technique through which active ingredients are administered into the thickness of the skin in order to increase the local analgesic effect. Methods: 141 patients with spinal pain not responding to systemic therapy with NSAIDs were randomized to receive one or more intra-cutaneous drugs on a weekly basis. Results: All patients achieved a pain reduction of at least 50% compared to baseline, and all tolerated the therapy without having to resort to systemic drug dose increases. Conclusions: The data from our study show that the active ingredients infiltrated into the skin induce a mesodermal modulation between the infiltrated liquid and the cutaneous nervous and cellular structures from which the typical drug-saving effect of mesotherapy arises. Although further studies are needed to establish how to integrate mesotherapy in various clinical settings, it appears to be a useful technique available to the practicing physician. This research is also useful in guiding future clinical research.

Should we be concerned when COVID-19-positive patients take opioids to control their pain? Insights from a pharmacological point of view.

OBJECTIVE: The purpose of this narrative review is to discuss the available information regarding the currently utilized COVID-19 therapies (and the evidence level supporting them) and opioids for chronic pain with a focus on warnings of potential interactions between these two therapeutic approaches. MATERIALS AND METHODS: Papers were retrieved from a PubMed search, using different combinations of keywords [e.g., pain treatment AND COVID-19 AND drug-drug interaction (DDI)], without limitations in terms of publication date and language. RESULTS: Remdesivir is an inhibitor of CYP3A4 and may increase the plasma concentration of CYP3A4 substrates (e.g., fentanyl). Dexamethasone is an inducer of CYP3A4 and glycoprotein P, thus coadministration with drugs metabolized by this isoform will lead to their increased clearance. Dexamethasone may cause hypokalemia, thus potentiating the risk of ventricular arrhythmias if it is given with opioids able to prolong the QT interval, such as oxycodone and methadone. Finally, the existing differences among opioids with regard to their impact on immune responses should also be taken into account with only tapentadol and hydromorphone appearing neutral on both cytokine production and immune parameters. CONCLUSIONS: Clinicians should keep in mind the frequent DDIs with drugs extensively metabolized by the CYP450 system and prefer opioids undergoing a limited hepatic metabolism. Identification and management of DDIs and dissemination of the related knowledge should be a major goal in the delivery of chronic care to ensure optimized patient outcomes and facilitate updating recommendations for COVID-19 therapy in frail populations, namely comorbid, poly-medicated patients or individuals suffering from substance use disorder.

Kynurenine hydroxylase inhibitors reduce ischemic brain damage: studies with (m-nitrobenzoyl)-alanine (mNBA) and 3,4-dimethoxy-[-N-4-(nitrophenyl)thiazol-2yl]-benzenesulfonamide (Ro 61-8048) in models of focal or global brain ischemia.

Two kynurenine hydroxylase inhibitors, (m-nitrobenzoyl)-alanine (mNBA) and 3,4-dimethoxy-[-N-4-(nitrophenyl)thiazol-2yl]-benzenesulfona mide (Ro 61-8048), have been tested as neuroprotective agents on brain lesions induced by bilateral carotid occlusion in gerbils or by middle cerebral artery occlusion in rats. The percentage of lesioned pyramidal neurones found in the hippocampal CA1 region of gerbils subjected to bilateral carotid occlusion for 5 minutes decreased from 92+/-10% in vehicle-treated animals to 7+/-6% after mNBA (400 mg/kg intraperitoneally, three times at 1, 30, and 180 minutes after occlusion) or to 10+/-11% after Ro 61-8048 (40 mg/kg intraperitoneally, three times). A significant reduction in infarct volumes also was found when the kynurenine hydroxylase inhibitors were given to rats after permanent middle cerebral artery occlusion (from 207+/-111 mm3 in vehicle-treated rats to 82+/-18 and to 62+/-57 mm3 in rats treated with mNBA, 400 mg/kg intraperitoneally, or with Ro 61-8048, 40 mg/kg intraperitoneally, respectively). The administration of mNBA (400 mg/kg intraperitoneally) or Ro 61-8048 (40 mg/kg intraperitoneally) to gerbils with a dialysis probe in their dorsal hippocampus or to rats with a dialysis probe in their parietal cortex significantly increased kynurenic acid concentration in the dialysates. The data suggest that inhibition of kynurenine hydroxylase could be a new avenue to reduce neuronal loss in brain ischemia.

Modulation of the kynurenine pathway in search for new neuroprotective agents. Synthesis and preliminary evaluation of (m-nitrobenzoyl)alanine, a potent inhibitor of kynurenine-3-hydroxylase.

The synthesis of (o-nitrobenzoyl)-, (m-nitrobenzoyl)-, and (p-nitrobenzoyl)alanine (o-, m-, and p-NBA), three new kynurenine analogues, and their evaluation as inhibitors of kynureninase and kynurenine-3-hydroxylase are reported. The most potent of these compounds, m-NBA, has an IC50 of 0.9 +/- 0.1 microM as an inhibitor of kynurenine-3-hydroxylase and of 100 +/- 12 microM as an inhibitor of kynureninase. When administered to rats, m-NBA significantly increases the concentration of kynurenine and kynurenic acid in the brain as well as in blood and in the liver. m-NBA has also been shown to increase the concentration of kynurenic acid in hippocampal extracellular fluid. This increase is associated with sedative and anticonvulsant activities, thus confirming the possibility of antagonizing L-glutamate-mediated effects by modulating the kynurenine pathway of L-tryptophan metabolism.

Inhibitors of kynurenine hydroxylase and kynureninase increase cerebral formation of kynurenate and have sedative and anticonvulsant activities.

Kynurenate is an endogenous antagonist of the ionotropic glutamate receptors. It is synthesized from kynurenine, a tryptophan metabolite, and a significant increase in its brain concentration could be useful in pathological situations. We attempted to increase its neosynthesis by modifying kynurenine catabolism. Several kynurenine analogues were synthesized and tested as inhibitors of kynurenine hydroxylase (E.C.1.14.13.9) and of kynureninase (E.C.3.7.1.3), the two enzymes which catalyse the conversion of kynurenine to excitotoxin quinolinate. Among these analogues we observed that nicotinylalanine, a compound whose pharmacological properties have previously been reported, had an IC50 of 900 +/- 180 microM as inhibitor of kynurenine hydroxylase and of 800 +/- 120 microM as inhibitor of kynureninase. In the search for more potent molecules we noticed that meta-nitrobenzoylalanine had an IC50 of 0.9 +/- 0.1 microM as inhibitor of kynurenine hydroxylase and of 100 +/- 12 microM as inhibitor of kynureninase. When administered to rats meta-nitrobenzoylalanine (400 mg/kg) significantly increased the concentration of kynurenine (up to 10 times) and kynurenate (up to five times) in the brain. Similar results were obtained in the blood and in the liver. Furthermore meta-nitrobenzoylalanine increased in a dose dependent, long lasting (up to 13 times and up to 4 h) manner the concentration of kynurenate in the hippocampal extracellular fluid, as evaluated with a microdialysis technique. This increase was associated with a decrease in the locomotor activity and with protection from maximal electroshock-induced seizures in rats or from audiogenic seizures in DBA/2 mice. The conclusions drawn from the present study are: (i) meta-nitrobenzoylalanine is a potent inhibitor of kynurenine hydroxylase also affecting kynureninase; (ii) the inhibition of these enzymes causes a significant increase in the brain extracellular concentration of kynurenate; (iii) this increase is associated with sedative and anticonvulsant actions, suggesting a functional antagonism of the excitatory amino acid receptors.

Electrophysiological studies on oxindole, a neurodepressant tryptophan metabolite.

1. The aim of the present work was to investigate the electrophysiological effects of oxindole, a tryptophan metabolite present in rat blood and brain, and recently proposed as a contributing factor in the pathogenesis of hepatic encephalopathy. 2. Using rat hippocampal slices in vitro and extra- or intracellular recordings, we evaluated oxindole effects on the neurotransmission of the CA1 region following orthodromic stimulation of the Schaffer collaterals. 3. Oxindole (0.3-3 mM) decreased the amplitude of population spikes extracellularly recorded at the somatic level and of the fEPSPs recorded at the dendritic level. In intracellular recordings, oxindole (0.1-3 mM) did not affect the resting membrane potential or the neuronal input resistance, but reduced the probability of firing action potentials upon either synaptic or direct activation of the pyramidal cells. 4. Oxindole (0.3-3 mM) increased the threshold and the latency of firing action potentials elicited by depolarizing steps without changing the duration or the peak amplitude of the spikes. It also significantly increased the spike frequency adaptation induced by long lasting (400 ms) depolarizing stimuli. 5. In separate experiments, performed by measuring AMPA or NMDA-induced responses in cortical slices, oxindole (1-3 mM) did not modify glutamate receptor agonist responses. 6. Our results show that concentrations of oxindole which may be reached in pathological conditions, significantly decrease neuronal excitability by modifying the threshold of action potential generation.

Set-up and validation of an adsorptive stripping voltammetric method for kynurenic acid determination in human urine.

Validation of an adsorptive stripping voltammetric method for kynurenic acid determination in urine, was presented. The selection of appropriate validation parameters, the design consideration for evaluation and the problem of endogenous metabolites were discussed. The considered fundamental criteria for assessing the reliability and overall performance of the method in the urine matrix were selectivity, linearity and range, limit of quantitation, accuracy, precision and analyte stability. The intermediate precision was also evaluated by means of a full factorial design. An HPLC method with fluorimetric detection was used as a reference method to assess the accuracy. The analysis in urine required a pH control as pointed out by robustness testing and the found kynurenic acid concentration in daily urine ranged from 5 to 40 microM.

Neuroprotective effects of kynurenine-3-hydroxylase inhibitors in models of brain ischemia.

The neuroprotective effects of two kynurenine hydroxylase inhibitors, (m-nitrobenzoyl)-alanine (mNBA) and 3,4-dimethoxy-[-N-4-(nitrophenyl)thiazol-2yl]-benzenesulfona mide (Ro 61-8048), were studied in vitro and in vivo. In organotypic hippocampal slice cultures deprived of oxygen and glucose, these inhibitors significantly reduced neuronal damage. In gerbils subjected to bilateral carotid occlusion for 5 min, the administration of mNBA (400 mg/kg i.p., 3 times) or Ro 61-8048 (40 mg/kg i.p., 3 times) dramatically decreased the percentage of damaged pyramidal neurones in the hippocampal CA1 region. Finally, in rats with permanent occlusion of the middle cerebral artery, mNBA (200-400 mg/kg i.p.) and Ro 61-8048 (40 mg/kg i.p.) administration reduced the infarct volume. Our results demonstrate that ischemic neuronal damage may be significantly decreased by inhibiting kynurenine hydroxylase.

Tryptophan metabolism and hepatic encephalopathy. Studies on the sedative properties of oxindole.

Oxindole administration (1-100 mg/kg i.p.) to mammals decreases locomotor activity, reduces muscular tone and blood pressure and at larger doses causes coma and death. Utilizing both HPLC and GC/MS, we showed that oxindole is present in the blood, brain and other organs of several animal species, including humans. We demonstrated that oxindole is a tryptophan metabolite able to significantly decrease neuronal excitability by modifying the function of voltage-operated sodium channels. Its synthesis requires the availability of indole, which is formed in the gut. When liver function is impaired, a sufficient amount of indole reaches systemic circulation and is oxidized into oxindole, which seems to be one of the responsible agents for the neurological symptoms found in the course of liver impairment.

Gabapentin and pregabalin for the acute post-operative pain management. A systematic-narrative review of the recent clinical evidences.

BACKGROUND: Gabapentin and pregabalin inhibit Ca(2+) currents via high-voltage-activated channels containing the alpha2delta-1 subunit, reducing neurotransmitter release and attenuating the postsynaptic excitability. They are antiepileptic drugs successfully used also for the chronic pain treatment. A large number of clinical trials indicate that gabapentin and pregabalin could be effective as postoperative analgesics. This systematic-narrative review aims to analyse the most recent evidences regarding the effect of gabapentinoids on postoperative pain treatment. METHODS: Medline, The Cochrane Library, EMBASE and CINHAL were searched for recent (2006-2009) randomized clinical trials (RCTs) of gabapentin-pregabalin for postoperative pain relief in adults. Quality of RCTs was evaluated according to Jadad method. Visual analogue scale (VAS), opioid consumption and side-effects (nausea, vomiting, dizziness and sedation) were considered the most important outcomes. RESULTS: An overall of 22 gabapentin (1640 patients), 8 pregabalin (707 patients) RCTs and seven meta-analysis were involved in this review. Gabapentin provided better post-operative analgesia and rescue analgesics sparing than placebo in 6 of the 10 RCTs that administered only pre-emptive analgesia. Fourteen RCTs suggested that gabapentin did not reduce PONV when compared with placebo, clonidine or lornoxicam. Pregabalin provided better post-operative analgesia and rescue analgesics sparing than placebo in two of the three RCTs that evaluated the effects of pregabalin alone vs placebo. Four studies reported no pregabalin effects on preventing the PONV. CONCLUSION: Gabapentin and pregabalin reduce pain and opioid consumption after surgery in confront with placebo, but comparisons with other standard post-operative regimens are not sufficient. Gabapentin and pregabalin seem not to have any influence on the prevention of PONV.

Oxindole, a sedative tryptophan metabolite, accumulates in blood and brain of rats with acute hepatic failure.

Rats treated with oxindole (10-100 mg/kg i.p.), a putative tryptophan metabolite, showed decreased spontaneous locomotor activity, loss of the righting reflex, hypotension, and reversible coma. Brain oxindole levels were 0.05 +/- 0.01 nmol/g in controls and increased to 8.1 +/- 1.7 or 103 +/- 15 nmol/g after its administration at doses of 10 or 100 mg/kg i.p., respectively. To study the role that oxindole plays in the neurological symptoms associated with acute liver failure, we measured the changes of its concentration in the brain after massive liver damage, and we investigated the possible metabolic pathways leading to its synthesis. Rats treated with either thioacetamide (0.2 and 0.4 g/kg i.p., twice) or galactosamine (1 and 2 g/kg i.p.) showed acute liver failure and a large increase in blood or brain oxindole concentrations (from 0.05 +/- 0.01 nmol/g in brains of controls to 1.8 +/- 0.3 nmol/g in brains of thioacetamide-treated animals). Administration of tryptophan (300-1,000 mg/kg p.o.) caused a twofold increase, whereas administration of indole (10-100 mg/kg p.o.) caused a 200-fold increase, of oxindole content in liver, blood, and brain, thus suggesting that indole formation from tryptophan is a limiting step in oxindole synthesis. Oral administration of neomycin, a broad-spectrum, locally acting antibiotic agent able to reduce intestinal flora, significantly decreased brain oxindole content. Taken together, our data show that oxindole is a neurodepressant tryptophan metabolite and suggest that it may play a significant role in the neurological symptoms associated with acute liver impairment.

Kynurenine disposition in blood and brain of mice: effects of selective inhibitors of kynurenine hydroxylase and of kynureninase.

To study the regulation of the synthesis of quinolinic and kynurenic acids in vivo, we evaluated (a) the metabolism of administered kynurenine by measuring the content of its main metabolites 3-hydroxykynurenine, anthranilic acid, and 3-hydroxyanthranilic acid in blood and brain of mice; (b) the effects of (m-nitrobenzoyl)alanine, a selective inhibitor of kynurenine hydroxylase and of (o-methoxybenzoyl) alanine, a selective inhibitor of kynureninase, on this metabolism; and (c) the effects of (o-methoxybenzoyl)alanine on liver kynureninase and 3-hydroxykynureninase activity. The conclusions drawn from these experiments are (a) the disposition of administered kynurenine preferentially occurs through hydroxylation in brain and through hydrolysis in peripheral tissues; (b) (m-nitrobenzoyl)alanine, the inhibitor of kynurenine hydroxylase, causes the expected changes in brain kynurenine metabolism, such as a decrease of 3-hydroxykynurenine, and an increase of kynurenic acid; and (c) (o-methoxybenzoyl)alanine, the kynureninase inhibitor, increases brain concentration of the cytotoxic compound 3-hydroxykynurenine, and unexpectedly does not reduce brain concentration of 3-hydroxyanthranilic acid, the direct precursor of quinolinic acid. Taken together, the experiments suggest that the systemic administration of a kynurenine hydroxylase inhibitor is a rational approach to increase the brain content of kynurenate and to decrease that of cytotoxic kynurenine metabolites, such as 3-hydroxykynurenine and quinolinic acid.

Identification and measurement of oxindole (2-indolinone) in the mammalian brain and other rat organs.

Oxindole, a putative tryptophan metabolite able to cause profound sedation when administered in relatively low doses to mammals, has been identified and measured in the brains of mice, rats, and guinea pigs using HPLC and GC/MS with a quadrupole ion trap and a collision-induced dissociation mass spectrometer. The identification and measurement of the compound required a protein precipitation step with HClO4, extraction into chloroform, an HPLC separation on a reverse-phase column, and detection by UV or coulometry. The definitive identification of the oxindole peak was obtained with a Saturn 4D GC/MS quadrupole ion trap operated under GC/MS, GC/MS/MS, and GC/MS/MS/MS modes. The HPLC methods we used had a low interassay variability, easily allowing the identification and measurement of the compound in 1 g of tissue. The oxindole concentrations in rat brain, blood, liver, and kidney were each approximately 100 pmol/g wt. Interestingly, the content of oxindole in the guinea pig brain was found to be significantly lower than that in the mouse and rat brains, possibly reflecting a lower dietary intake of tryptophan in the guinea pigs.

Comparison of the neurochemical and behavioral effects resulting from the inhibition of kynurenine hydroxylase and/or kynureninase.

Several kynurenine analogues were synthesized and tested as inhibitors of the enzymes kynurenine hydroxylase and/or kynureninase with the aim of identifying new compounds able to inhibit the synthesis of quinolinic acid (an endogenous excitotoxin) and to increase that of kynurenic acid, an endogenous antagonist of ionotropic glutamate receptors. Among these analogues, we selected m-nitrobenzoylalanine (mNBA) as an inhibitor of kynurenine hydroxylase and o-methoxybenzoylalanine (oMBA) as an inhibitor of kynureninase. When administered to rats, mNBA was more potent than oMBA in increasing the content of kynurenine and of kynurenic acid in the brain, blood, liver, and kidney. This confirms that hydroxylation is the main pathway of kynurenine metabolism. Both mNBA and oMBA (50-400 mg/kg i.p.) increased the concentration of kynurenate in hippocampal extracellular spaces (as measured with a microdialysis technique) and, when simultaneously injected, their effects were additive. This biochemical effect was associated with a decrease in locomotor activity in rats and with a protection of audiogenic convulsions in DBA/2 mice. In conclusion, the results of the present experiments indicate the possibility of increasing the neosynthesis of kynurenic acid by inhibiting the enzymes that metabolize kynurenine to 3-hydroxykynurenine or to anthranilic acid. The increased synthesis of kynurenate is associated with behavioral effects such as sedation and protection from seizures, which suggests a functional antagonism of the excitatory amino acid receptors.

Synthesis and structure-activity relationships of 1-aminophthalazinium bromides as GABAA receptor ligands.

The synthesis and the GABAA binding activity of a series of 1-amino-2-alkylphthalazinium bromides (series A) and 1-amino-3-alkylphthalazinium bromides (series B) bearing different substituents at position-4 are reported. Some compounds of series A, bearing a lipophilic substituent at position-4, showed a good binding activity as well as in vivo convulsant activity.

Presynaptic kynurenate-sensitive receptors inhibit glutamate release.

Kynurenic acid is a tryptophan metabolite provided with antagonist activity on ionotropic glutamate and alpha7 nicotinic acetylcholine receptors. We noticed that in rats with a dialysis probe placed in the head of their caudate nuclei, local administration of kynurenic acid (30-100 nM) significantly reduced glutamate output. Qualitatively and quantitatively similar effects were observed after systemic administration of kynurenine hydroxylase inhibitors, a procedure able to increase brain kynurenate concentrations. Interestingly, in microdialysis studies, methyllycaconitine (0.3-10 nM), a selective alpha7 nicotinic receptor antagonist, also reduced glutamate output. In isolated superfused striatal synaptosomes, kynurenic acid (100 nM), but not methyllycaconitine, inhibited the depolarization (KCl 12.5 mM)-induced release of transmitter or previously taken-up [3H]-D-aspartate. This inhibition was not modified by glycine, N-methyl-D-aspartate or subtype-selective kainate receptor agents, while CNQX or DNQX (10 microM), two AMPA and kainate receptor antagonists, reduced kynurenic acid effects. Low concentrations of kynurenic acid, however, did not modify [3H]-kainate (high and low affinity) or [3H]-AMPA binding to rat brain membranes. Finally, because metabotropic glutamate (mGlu) receptors modulate transmitter release in striatal preparations, we evaluated, with negative results, kynurenic acid (1-100 nM) effects in cells transfected with mGlu1, mGlu2, mGlu4 or mGlu5 receptors. In conclusion, our data show that kynurenate-induced inhibition of glutamate release is not mediated by glutamate receptors. Nicotinic acetylcholine receptors, however, may contribute to the inhibitory effects of kynurenate found in microdialysis studies, but not in those found in isolated synaptosomes.

Plasma and brain levels of oxindole in experimental chronic hepatic encephalopathy: effects of systemic ammonium acetate and L-tryptophan.

It has previously been shown that the neurodepressant L-tryptophan metabolite oxindole is increased in the blood and brain of rats with fulminant hepatic failure and in the blood of cirrhotic patients affected by chronic hepatic encephalopathy. In the present investigation, we found that oxindole levels were significantly increased in the blood and brain of portacaval-shunted rats, an animal model of chronic hepatic encephalopathy, compared with sham-operated controls. A further increase in plasma and brain oxindole content was found after oral administration of L-tryptophan (300 mg/kg) to both portacaval-shunted or sham-operated animals, while intraperitoneal injection of the amino acid did not modify oxindole content either in brain or blood. Ammonium acetate administration (4.0 mmol/kg, intraperitoneal) reversibly deteriorated the neurological status of portacaval-shunted animals, but did not modify, in a directly related manner, plasma and brain oxindole content. The present findings are in line with the possibility that oxindole may be an additional L-tryptophan-related candidate in the pathogenesis of chronic hepatic encephalopathy.