Prevent Tolerance Development Research Articles

Long-lasting antiseizure effects of chronic intrasubthalamic convection-enhanced delivery of valproate

Intracerebral drug delivery is an experimental approach for the treatment of drug-resistant epilepsies that allows for pharmacological intervention in targeted brain regions. Previous studies have shown that targeted pharmacological inhibition of the subthalamic nucleus (STN) via modulators of the GABAergic system produces antiseizure effects. However, with chronic treatment, antiseizure effects are lost as tolerance develops. Here, we report that chronic intrasubthalamic microinfusion of valproate (VPA), an antiseizure medication known for its wide range of mechanisms of action, can produce long-lasting antiseizure effects over three weeks in rats. In the intravenous pentylenetetrazole seizure-threshold test, seizure thresholds were determined before and during chronic VPA application (480 μg/d, 720 μg/d, 960 μg/d) to the bilateral STN. Results indicate a dose-dependent variation in VPA-induced antiseizure effects with mean increases in seizure threshold of up to 33%, and individual increases of up to 150%. The lowest VPA dose showed a complete lack of tolerance development with long-lasting antiseizure effects. Behavioral testing with all doses revealed few, acceptable adverse effects. VPA concentrations were high in STN and low in plasma and liver. In vitro electrophysiology with bath applied VPA revealed a reduction in spontaneous firing rate, increased background membrane potential, decreased input resistance and a significant reduction in peak NMDA, but not AMPA, receptor currents in STN neurons. Our results suggest an advantage of VPA over purely GABAergic modulators in preventing tolerance development with chronic intrasubthalamic drug delivery and provide first mechanistic insights in intracerebral pharmacotherapy targeting the STN.

Rapid tolerance to behavioral effects of ethanol in rats: Prevention by R-(−)-ketamine

R-(−)-ketamine has emerged as a potentially improved medication over that of the (S)-isomer (marketed as Spravato for depression). Recent data have suggested (R)-ketamine could have value in the treatment of substance use disorder. The present set of experiments was undertaken to examine whether (R)-ketamine might prevent tolerance development. Rapid ethanol (ETOH) tolerance was studied since racemic ketamine had previously been shown to block this tolerance development in rats. In the present study, male Sprague-Dawley rats were given two large doses of ETOH on Day 1 (2.3 + 1.7 g/kg) and 2.3 g/kg ETOH on Day 2. Animals were tested for effects of 2.3 g/kg ETOH on grip strength, inclined screen performance and rotarod performance on Day 1 with or without (R)-ketamine as a pretreatment. (R)-ketamine alone was tested at the highest dose studied (10 mg/kg) and did not significantly influence any dependent measure. (R)-ketamine (1–10 mg/kg) did not alter the acute effects of ETOH except for enhancing the effects of ETOH on the inclined screen test at 3 mg/kg. Between-subjects analysis documented that tolerance developed to the effects of ETOH only on the measure of grip strength. (R)-ketamine (3 mg/kg) given prior to ETOH on Day 1 exhibited a strong trend toward preventing tolerance development (p = 0.062). The present results extend prior findings on the potential value of (R)-ketamine in substance abuse disorder therapeutics and add to the literature on NMDA receptor blockade as a tolerance-regulating mechanism.

Effect of captopril, an angiotensin-converting enzyme inhibitor, on morphine analgesia and tolerance in rats, and elucidating the inflammation and endoplasmic reticulum stress pathway in this effect

The purpose of current study was to examine the possible involvement of captopril, an angiotensin-converting enzyme inhibitor, on nociception, morphine analgesia and morphine tolerance development involving inflammation and ER-stress pathways in rats. In this study, thirty-six male Wistar rats were used. Animals were divided into six groups: Saline, 50 mg/kg captopril, 5 mg/kg morphine, morphine + captopril, morphine tolerance and morphine tolerance + captopril. The resulting analgesic effect was measured with hot plate and tail flick analgesia tests. The dorsal root ganglions (DRG) tissues were collected for inflammation parameters, endoplasmic reticulum (ER) stress and apoptosis proteins by using ELISA. Captopril showed anti-nociceptive effect when given alone (p < 0.05 to p < 0.01). In addition, captopril increased the analgesic effect of morphine (p < 0.05 to p < 0.001) and also decreased the tolerance to morphine at a significant level (p < 0.05 to p < 0.001). However, it decreased inflammation and ER-stress when applied with single-dose morphine and tolerance induction (p < 0.001). Moreover, captopril decreased apoptosis proteins after tolerance development (p < 0.001). In conclusion, captopril has antinociceptive properties, increasing analgesic effect of morphine, and preventing tolerance development. These effects may occur by suppressing inflammation and ER-stress pathways.

Characterization of the antinociceptive effects of the individual isomers of methadone after acute and chronic administrations

Methadone is a long-acting opioid used in the treatment of various pain states and substitution therapy in heroin addiction. Extensive behavioral characterization has been carried out using the racemate, but limited investigation has been performed with the individual isomers. The L-isomer is a potent opioid agonist, whereas the D-isomer has weak µ-opioid activity and has also been shown to possess N-methyl-D-aspartate antagonist properties in vitro. The acute antinociceptive effects of the isomers were evaluated in rats using a warm-water, tail-withdrawal procedure at two stimulus intensities (50° and 55°C). Increasing dose ratios of D-methadone to L-methadone were administered chronically to determine the ability of the D-isomer to modulate antinociceptive tolerance to the L-isomer. Acutely, both L-methadone (0.1-5.6 mg/kg, subcutaneously) and D-methadone (3.0-56.0 mg/kg, subcutaneously) produced antinociception, although the efficacy of the D-isomer was limited at 55°C. These effects were dose dependently blocked by naltrexone (0.01-1.0 mg/kg, subcutaneously). Administered chronically, D-methadone (1.7-10 mg/kg, subcutaneously) dose dependently blocked tolerance development to the L-isomer (1.7 mg/kg, subcutaneously). These findings support the antinociceptive effects of the isomers being opioid receptor mediated with the L-isomer functioning as a full-efficacy agonist, whereas the D-isomer seems to have lower efficacy. The ability of nonracemic doses of the D-isomer to prevent tolerance development to the L-isomer may be attributed to partial µ-agonist activity; however, N-methyl-D-aspartate antagonist activity cannot be discounted.

193 Hyoscine- n-butyl bromide failed to prevent tolerance development to the antinociceptive effect of pilocarpine

193 Hyoscine- n-butyl bromide failed to prevent tolerance development to the antinociceptive effect of pilocarpine

Possible usefulness of apocynin, an NADPH oxidase inhibitor, for nitrate tolerance: prevention of NO donor-induced endothelial cell abnormalities

The long-term benefits of nitroglycerin therapy are limited by tolerance development. Understanding the precise nature of mechanisms underlying nitroglycerin-induced endothelial cell dysfunction may provide new strategies to prevent tolerance development. In this line, we tested interventions to prevent endothelial dysfunction in the setting of nitrate tolerance. When bovine aortic endothelial cells (BAECs) were continuously treated with nitric oxide (NO) donors, including nitroglycerin, over 2-3 days, basal production of nitrite and nitrate (NO(x)) was diminished. The diminished basal NO(x) levels were mitigated by intermittent treatment allowing an 8-h daily nitrate-free interval during the 2- to 3-day treatment period. Addition of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor apocynin restored the basal levels of NO(x) that were decreased by continuous nitroglycerin treatment of BAECs. Apocynin caused significant improvement of increased mRNA and protein levels of endothelial nitric oxide synthase (eNOS) in BAECs given nitroglycerin continuously over the treatment period. Apocynin also reduced endothelial production of reactive oxygen species (ROS) after continuous nitroglycerin treatment. These results showed an essential similarity to the effects of a nitrate-free interval. Application of the NOS inhibitor N(omega)-nitro- l-arginine methyl ester caused a recovery effect on basal NO(x) and eNOS expression but was without effect on ROS levels in continuously NO donor-treated BAECs. In conclusion, the present study characterized abnormal features and functions of endothelial cells following continuous NO donor application. We suggest that inhibition of NADPH oxidase, by preventing NO donor-induced endothelial dysfunction, may represent a potential therapeutic strategy that confers protection from nitrate tolerance development.

In VivoActivation of a Mutant μ-Opioid Receptor by Naltrexone Produces a Potent Analgesic Effect But No Tolerance: Role of μ-Receptor Activation and δ-Receptor Blockade in Morphine Tolerance

Opioid analgesics are the standard therapeutic agents for the treatment of pain, but their prolonged use is limited because of the development of tolerance and dependence. Recently, we reported the development of a mu-opioid receptor knock-in (KI) mouse in which the mu-opioid receptor was replaced by a mutant receptor (S196A) using a homologous recombination gene-targeting strategy. In these animals, the opioid antagonist naltrexone elicited antinociceptive effects similar to those of partial agonists acting in wild-type (WT) mice; however, development of tolerance and physical dependence were greatly reduced. In this study, we test the hypothesis that the failure of naltrexone to produce tolerance in these KI mice is attributable to its simultaneous inhibition of delta-opioid receptors and activation of mu-opioid receptors. Simultaneous implantation of a morphine pellet and continuous infusion of the delta-opioid receptor antagonist naltrindole prevented tolerance development to morphine in both WT and KI animals. Moreover, administration of SNC-80 [(+)-4-[(alphaR)-alpha-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide], a delta agonist, in the naltrexone-pelleted KI animals resulted in a dose-dependent induction in tolerance development to both morphine- and naltrexone-induced analgesia. We conclude that although simultaneous activation of both mu- and delta-opioid receptors results in tolerance development, mu-opioid receptor activation in conjunction with delta-opioid receptor blockade significantly attenuates the development of tolerance.

Involvement of the cyclic AMP system in the switch from tolerance into supersensitivity to the antinociceptive effect of the opioid sufentanil.

1. We have previously demonstrated that chronic and simultaneous treatment of rats with the mu-opioid receptor agonist sufentanil and the Ca(2+) channel blocker nimodipine, not only prevented tolerance development, but the animals became supersensitive to the antinociceptive effect of the opioid. The focus of the present work was to determine the possible involvement of cross interactions between the adenylyl cyclase pathway and L-type voltage-sensitive Ca(2+)-channels, in modulating the switch from opioid tolerance into supersensitivity. 2. The modulatory effect of sufentanil on adenylyl cyclase activity was determined by measuring cyclic AMP production in slices from the cortex of rats rendered tolerant or supersensitive to the antinociceptive effect of the opioid. Tolerance was induced by chronic infusion of sufentanil, at a rate of 2 microg h(-1), for 7 days. Supersensitivity was induced by concurrent infusion of sufentanil (2 microg h(-1)) and nimodipine (1 microg h(-1)) for 7 days. Antinociception was evaluated by the tail-flick test. 3. Tolerance to the analgesic effect of sufentanil was associated with a significant reduction in the response of adenylyl cyclase to forskolin. Furthermore, the effect of the opioid on forskolin-induced cyclic AMP accumulation was abolished. On the other hand, supersensitivity to the analgesic effect of the opioid was associated with an increase in both, the adenylyl cyclase response to forskolin, and the opioid inhibition of cyclic AMP production. 4. We suggest that sustained L-type Ca(2+) channel blockade may result in changes in the adenylyl cyclase effector system triggered by mu-opioid receptor activation, leading to the switch from opioid tolerance into supersensitivity.

Different role of carboxylesterases in toxicity and tolerance to paraoxon and DFP

The contribution of carboxylesterase (CarbE) to toxicity and tolerance to the organophosphorus anticholinesterases (OP-antiChE) paraoxon (diethyl p-nitrophenyl phosphate) and DFP (diisopropylphosphorofluoridate) was investigated in rats. Daily injections (20 days) of paraoxon (0.33 μmol/kg) or DFP (2.72 μmol/kg) reduced AChE activity in brain to 29 or 16% and in diaphragm to 58 or 54%, respectively. The animals tolerated an accumulated 6-fold LD50 dose and survived an LD90 dose of carbachol, indicating tolerance to this cholinergic agonist. A single dose of paraoxon or DFP significantly reduced CarbE activity of plasma, lung and liver. After paraoxon, rapid recovery was seen of plasma and liver CarbE while recovery after DFP was much slower. Daily pretreatment with the CarbE inhibitors CBDP (2-[o-cresyl]-4H-1,2,3-benzodioxa- phosphorin-2-oxide) (7.22 μmol/kg, s.c.) or iso-OMPA (tetraisopropylpyrophosphoramide) (8.76 μmol/kg, i.p.), followed by paraoxon (0.33 μmol/kg, s.c.) 30 min later, prevented the development of tolerance to paraoxon and potentiated its toxicity. Rats died on day four of the combined treatment. The CarbE inhibitors neither potentiated the DFP toxicity, nor prevented tolerance development to DFP. We conclude that rat plasma CarbE provides a significant protection against paraoxon toxicity because its rapid reactivation can reduce the toxicity of repeated paraoxon applications and thus contribute to tolerance development. This same mechanism does not apply to DFP toxicity, as inhibition of CarbE of plasma, liver and lung neither potentiated its toxicity, nor prevented tolerance development. These findings confirm previous observations that CarbE detoxification is of greater importance for highly toxic OP-antiChEs such as nerve agents and paraoxon than for less toxic ones such as DFP.

Nitrate therapy and the development of tolerance

The efficacy of organic nitrates in the treatment of acute episodes of angina pectoris is unquestioned. However, long-term use of these agents is associated with the development of tolerance or of reduced efficacy over time when given in doses or formulations that maintain therapeutic blood levels for 24-hour periods. Thus, the role of long-term use of nitrates in prophylactic treatment of stable angina has been questioned. The purpose of this brief review is to evaluate nitrate tolerance, a key issue in the prophylactic use of nitrates, as well as to review what is known about clinical rebound. These issues are discussed, and ways of preventing tolerance development are explored. Intermittent therapy involving a dose-free interval during each 24-hour period helps prevent tolerance.

Hemodynamic tolerance and pharmacokinetics of nicorandil in experimental heart failure.

We tested whether nicorandil (NCR), a nitrovasodilator which also possesses K+ channel action, will produce in vivo hemodynamic tolerance commonly observed with other nitrovasodilators such as nitroglycerin (NTG). NCR was infused at 50 micrograms/kg/min for 10 h through a femoral cannula into conscious rats (n = 5) with congestive heart failure (CHF). Left ventricular end-diastolic pressure (LVEDP), LV peak-systolic pressure (LVPSP), and heart rate (HR) were measured periodically through an implanted catheter. Under these conditions, NCR produced a 40% reduction (p < 0.05) in LVEDP from baseline at 40 min after the start of the infusion. This reduction lasted approximately 6 h, followed by a slow return to baseline between 6 and 10 h. LVPSP was reduced (p < 0.05) from 2 h and leveled at approximately 8 h. HR increased by 12% from baseline at 40 min (p < 0.05). Plasma NCR concentrations were identical at 5 h (pretolerant state) and at 10 h (tolerant state) in these animals, suggesting that plasma pharmacokinetics were unrelated to NCR pharmacodynamics. NCR kinetics were not changed by the presence of CHF. Thus, in this animal model, tolerance to NCR developed in LVEDP but not LVPSP, and the K+ channel action of NCR apparently could not prevent tolerance development to venodilation arising from nitrate action.

Mechanisms of nitrate-induced vasodilatation and tolerance

Nitrovasodilators have been found to relax vascular smooth muscle by stimulating soluble guanylate cyclase and thus by increasing the formation of cyclic GMP (cGMP). This nucleotide is responsible for relaxation, most likely by decreasing cytosolic free Ca2+ by one or several mechanisms. Repeated administration of organic nitrates causes tolerance development characterized by a diminished relaxing effect and an attenuated rise in cGMP. Experiments in isolated circular strips from bovine coronary arteries were performed in order to study the mechanism of tolerance development. It was found that after nitroglycerin (NG) pretreatment the response of the coronary strips to NG was less sensitive with respect to relaxation and increases in cGMP. These strips were also cross-tolerant against isosorbide-5-mononitrate, which by itself caused only little tolerance. With NG, the degree of tolerance development depended on the time and the concentration of NG pre-exposure. NG was found to stimulate guanylate cyclase (GC) in coronary supernatant provided that cysteine was added to the incubation medium. As in the intact strips, activation of GC by NG was attenuated when supernatants were preincubated with NG. It was found that addition of cysteine during incubation lessened the degree of desensitization but did not prevent it completely. Similarly, in coronary strips, tolerance development was lower when N-acetylcysteine was present during pre-exposure of the strips with NG. Considerably more effective in preventing tolerance development by about 50% was L-2-oxothiazolidine-4-carboxylate (OTC), a substance that easily penetrates into the cell and is transformed into cysteine by 5-oxo-prolinase.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitrates: Why and how should they be used today?

Nitrates are highly effective both in terminating acute attacks of angina pectoris and in the prophylaxis of symptomatic and asymptomatic myocardial ischemia. Preload reduction by venodilatation is the prevailing mechanism of nitrates in patients with chronic stable angina and is the unique feature distinguishing them from beta and calcium-channel blockers. Nitrates dilate coronary arteries not only in pre- and poststenotic vessels, but also in eccentric lesions. In patients with endothelial dysfunction, nitrates seem to be the physiological substitute for endothelium-derived relaxing factor. During the past decade, however, there has been substantial evidence of a clinically relevant loss of the anti-ischemic effects ("nitrate tolerance"). Many studies with oral dosing of isosorbide dinitrate or isosorbide-5-mononitrate at least three times daily have proven nitrate tolerance in patients with coronary artery disease and/or congestive heart failure. Complete loss of anti-ischemic effects after repetitive, continuous patch attachments has also been found. As we first showed in 1983, intermittent therapy with once-daily ingestion of high-dose sustained-release isosorbide dinitrate was successful in preventing the development of tolerance. Similarly, tolerance to isosorbide-5-mononitrate also does not develop when it is ingested once daily. It is now generally accepted that a daily low-nitrate interval is required to prevent tolerance development. Although the minimal patch-free interval required to prevent tolerance needs further investigation, a 12-h patch-free interval should prevent tolerance in most patients. The prolonged duration of action of once-daily high-dosage administration of sustained-release formulations, the improved patient compliance with a single daily administration, and the increased likelihood of maximal anti-ischemic effects are important reasons for recommending high single daily doses of isosorbide dinitrate or isosorbide-5-mononitrate.

Sustained effect of and lack of development of tolerance to controlled-release isosorbide-5-mononitrate in chronic stable angina

Tolerance has been shown to develop when nitrate preparations are used in such a manner as to produce plasma levels within the therapeutic range continuously over a 24-hour period. However, a period of reduced or low nitrate plasma levels of a few hours per day may limit or completely prevent tolerance development. In 18 patients with chronic stable angina pectoris, a single 60-mg daily dose of a controlled-release preparation of isosorbide-5-mononitrate (ISMN) was compared with the administration of 30 mg, 4 times daily, of immediate-release isosorbide dinitrate (ISDN) in a double-blind, randomized, placebo-controlled, crossover study. The comparisons were carried out on the first day of therapy and after 11 to 14 days of continuous therapy to assess the duration of effectiveness and the development of tolerance. On short-term therapy, both drugs produced a significant improvement in treadmill walking times to moderate angina in comparison with placebo. The values for ISMN were 87 ± 99 seconds (23%) at 12:30 P.M., 72 ± 91 seconds (19%) at 5 p.m. and 51 ± 81 seconds (13%) at 8:30 P.M. For ISDN, the respective values were 71 ± 83 seconds (19%), 89 ± 98 seconds (24%) and 79 ± 87 seconds (21%). There were no significant differences between drugs. Plasma nitrate levels for each drug paralleled the improvements in exercise performance. After 11 to 14 days of sustained therapy, only ISMN retained any significant beneficial effects (61 ± 71 seconds [21%] at 12:30 p.m. and 42 ± 60 seconds [14%] at 5 P.M.), but no significant effect at 8:30 p.m., with plasma levels slightly higher than those achieved on short-term therapy. ISDN produced no effect at any time point. This loss of effectiveness for ISDN occurred despite a slight increase in serum nitrate levels in comparison with short-term dosing, at all time points. Thus, the use of controlled-release ISMN minimized the development of tolerance, presumably because the nitrate plasma levels decreased into the subtherapeutic range during the inactive hours of the late evening and night. ISMN provided significant antianginal effects both with short-term and sustained therapy for at least 8.5 hours after a single morning dose.

Prevention by naltrexone of tolerance to the rate-decreasing effects of morphine on schedule-controlled responding in the pigeon.

Key-pecking in the pigeon was maintained under 10-min fixed-interval and 30-response fixed-ratio schedules of food presentation. Naltrexone alone (0.003–17 mg/kg) had no systematic effect on responding at any dose studied, and 10 and 17 mg/kg morphine practically eliminated responding. When naltrexone regularly preceded daily injections of morphine, tolerance was prevented for some dose combinations but not for others. If the daily dose of morphine was 17 mg/kg, tolerance was prevented by 1.0 mg/kg naltrexone but not by 0.3 mg/kg naltrexone. If the dose of naltrexone was 0.56 mg/kg, tolerance was prevented for 10 mg/kg morphine but not for 17 mg/kg morphine. Thus naltrexone prevented the development of tolerance to the rate-decreasing effects of morphine, although there were doses of naltrexone which completely antagonized the acute effects of morphine but which did not prevent tolerance development. The relative doses of naltrexone and morphine, not the absolute doses, determined whether or not development of tolerance was prevented. When combinations of naltrexone (0.3 or 1.0 mg/kg) and morphine (17 mg/kg) preceded experimental sessions by 6 h, the effects of the combination with 0.3 mg/kg naltrexone were more like those of 17 mg/kg morphine alone, whereas the effects of the combination with 1.0 mg/kg naltrexone were almost indistinguishable from those of saline. Differences in prevention of tolerance by doses of naltrexone that antagonized the acute effects of morphine were probably due to differences in duration of effect.

On the interaction of drugs with the cholinergic nervous system—III: Tolerance to phencyclidine derivatives: In vivo and in vitro studies

A possible contribution of metabolic processes to the tolerance to cyclohexamine (l-(l-phenylcyclohexyl) ethylamine) was investigated by determining the kinetics of brain and liver uptake of the labeled drug. A similar time course was found for both naive and tolerant mice. In addition, the amount of the drug uptaken by the brain was found to be linearly dependent on the dose injected in both groups. The possibility of adaptive changes in brain enzymes was investigated using mouse brain acetylcholinesterase (AcChE, E.C.3.1.1.7) as a model of a putative enzyme, affected by phencyclidine derivatives. Although brain AcChE is believed to be chronically affected by these drugs in vivo, no measurable changes could be observed in the amount, the affinity towards diverse ligands or the kinetic properties of this enzyme, between naive, cyclohexamine-tolerant and physostigmine tolerant mice. Possible changes in receptors as the mechanism of tolerance induction were tested by determining the amount of the central muscarinic receptor and its affinity towards a highly specific antimuscarinic ligand in vitro. When comparing naive animals to mice tolerant to cyclohexamine, physostigmine and oxotremorine, no measurable differences could be found in any of these parameters. Repeated injections of cyclohexamine together with scopolamine prevented tolerance development to the former. The possibility of homeostatic events as tolerance mechanism is presented and discussed.

On the interaction of drugs with the cholinergic nervous system—IV: Tolerance to oxotremorine in mice: In vivo and in vitro studies

A new procedure was used to follow continuously and simultaneously four systemic effects induced by oxotremorine in mice: salivation, tremor, hypothermia and those measured in the rotarod test. Using an equipotent dose of methoxotremorine, it was found that apart from salivation, the other systemic effects are centrally originated. By comparing the complete dose-response curves for these systemic effects in naive and tolerant mice, it was found that: (1) Salivation is the most sensitive effect in naive mice; (2) All curves shift in parallel to the right on continuous exposure to oxotremorine, in a manner that seems to be dose-dependent; (3) the tolerance to oxotremorine is reversible. Since oxotremorine-tolerant mice were found to be cross-tolerant to various tertiary anti-cholinesterase agents and cholinergic agonists, the involvement of the muscarinic receptor in the tolerance to oxotremorine was investigated, using two different approaches. (1) Continuous blockade of the receptor by scopolamine in vivo prevented tolerance development to oxotremorine; this effect was found to depend on the time of scopolamine administration relative to oxotremorine injection, and on the systemic effect measured. (2) The amount of receptor and its affinity towards a specific ligand were determined in vitro; no significant differences were found between naive and oxotremorine-tolerant animals. The significance of these results in the elucidation of possible tolerance mechanisms is discussed.