Excretion and metabolism of [14C]-pyridostigmine in the rat

Development of KVO treatment strategies for chronic pain in a rat model of Gulf War Illness

We examined whether combinations of K_v7 channel openers could be effective modifiers of deep tissue nociceptor activity; and whether such combinations could then be optimized for use as safe analgesics for pain-like signs that developed in a rat model of GWI (Gulf War Illness) pain. Voltage clamp experiments were performed on subclassified nociceptors isolated from rat DRG (dorsal root ganglion). A stepped voltage protocol was applied (-55 to -40 mV; V_h = -60 mV; 1500 ms) and K_v7 evoked currents were subsequently isolated by linopirdine subtraction. Directly activated and voltage activated K⁺ currents were characterized in the presence and absence of Retigabine (5-100 μM) and/or Diclofenac (50-140 μM). Retigabine produced substantial voltage dependent effects and a maximal sustained current of 1.14 pA/pF ± 0.15 (ED₅₀: 62.7 ± 3.18 μM). Diclofenac produced weak voltage dependent effects but a similar maximum sustained current of 1.01 ± 0.26 pA/pF (ED₅₀: 93.2 ± 8.99 μM). Combinations of Retigabine and Diclofenac substantially amplified resting currents but had little effect on voltage dependence. Using a cholinergic challenge test (Oxotremorine, 10 μM) associated with our GWI rat model, combinations of Retigabine (5 uM) and Diclofenac (2.5, 20 and 50 μM) substantially reduced or totally abrogated action potential discharge to the cholinergic challenge. When combinations of Retigabine and Diclofenac were used to relieve pain-signs in our rat model of GWI, only those combinations associated with serious subacute side effects could relieve pain-like behaviors.

Determination of Pyridostigmine Bromide in Presence of its Related Impurities by Four Modified Classical Least Square Based Models: A Comparative Study

Introduction:

Novel manipulations of the well-known classical least squares multivariate calibration model were explained in detail as a comparative analytical study in this research work. In addition to the application of plain classical least squares model, two preprocessing steps were tried, where prior to modeling with classical least squares, first derivatization and orthogonal projection to latent structures were applied to produce two novel manipulations of the classical least square-based model. Moreover, spectral residual augmented classical least squares model is included in the present comparative study.

Methods:

3 factor 4 level design was implemented constructing a training set of 16 mixtures with different concentrations of the studied components. To investigate the predictive ability of the studied models; a test set consisting of 9 mixtures was constructed.

Results:

The key performance indicator of this comparative study was the root mean square error of prediction for the independent test set mixtures, where it was found 1.367 when classical least squares applied with no preprocessing method, 1.352 when first derivative data was implemented, 0.2100 when orthogonal projection to latent structures preprocessing method was applied and 0.2747 when spectral residual augmented classical least squares was performed.

Conclusion:

Coupling of classical least squares model with orthogonal projection to latent structures preprocessing method produced significant improvement of the predictive ability of it.

Orthogonal projection to latent structures and first derivative for manipulation of PLSR and SVR chemometric models' prediction: A case study

Novel manipulations of the well-established multivariate calibration models namely; partial least square regression (PLSR) and support vector regression (SVR) are introduced in the presented comparative study. Two preprocessing methods comprising first derivatization and orthogonal projection to latent structures (OPLS) are implemented prior to modeling with PLSR and SVR. Quantitative determination of pyridostigmine bromide (PR) in existence of its two associated substances; impurity a (IMP A) and impurity b (IMP B); was utilized as a case study for achieving comparison. A series consisting of 16 mixtures with numerous percentages of the studied compounds was applied for implementation of a 3 factor 4 level experimental design. Additionally, a series consisting of 9 mixtures was employed in an independent test to verify the predictive power of the suggested models. Significant improvement of predictive abilities of the two studied chemometric models was attained via implementation of OPLS processing method. The root mean square error of prediction RMSEP for the test set mixtures was employed as a key comparison tool. About PLSR model, RMSEP was found 0.5283 without preprocessing method, 1.1750 when first derivative data was used and 0.2890 when OPLS preprocessing method was applied. With regard to SVR model, RMSEP was found 0.2173 without preprocessing method, 0.3516 when first derivative data was used and 0.1819 when OPLS preprocessing method was applied.

Novel manipulations of ratio spectra as powerful tools for resolution and quantitative determination of Pyridostigmine bromide and its' related substances; A comparative study

Resolution and quantitative determination of ternary mixture with severely overlapped spectra without any preliminary separation steps represents a big challenge for any analyst. Smart and novel spectrophotometric methods are continuously innovated for achieving the above mentioned target. Novel applications of ratio difference spectrophotometric technique utilizing ratio spectra and derivative ratio spectra are applied in presented work. The proposed methods included derivative ratio difference (DRD) and ratio subtraction ratio difference (RSRD) methods. Comparative study was achieved between the proposed methods and the recently developed induced ratio difference (IRD) method. The developed methods were assessed through the analysis of ternary mixtures with different ratios of Pyridostigmine bromide (PR) and its related substances; impurity a (IMP A) and impurity b (IMP B). Analysis of PR in a pharmaceutical dosage form without any interference from other inactive ingredients was also a successful application of the proposed methods. As per ICH guidelines, the proposed methods were validated ensuring their accuracy, precision and specificity. Statistical comparison between the developed methods and the reference method was done, where calculated F and t values were less than the theoretical ones in regards to accuracy and precision.

Behavioral, cellular and molecular maladaptations covary with exposure to pyridostigmine bromide in a rat model of gulf war illness pain

Many veterans of Operation Desert Storm (ODS) struggle with the chronic pain of Gulf War Illness (GWI). Exposure to insecticides and pyridostigmine bromide (PB) have been implicated in the etiology of this multisymptom disease. We examined the influence of 3 (DEET (N,N-diethyl-meta-toluamide), permethrin, chlorpyrifos) or 4 GW agents (DEET, permethrin, chlorpyrifos, pyridostigmine bromide (PB)) on the post-exposure ambulatory and resting behaviors of rats. In three independent studies, rats that were exposed to all 4 agents consistently developed both immediate and delayed ambulatory deficits that persisted at least 16 weeks after exposures had ceased. Rats exposed to a 3 agent protocol (PB excluded) did not develop any ambulatory deficits. Cellular and molecular studies on nociceptors harvested from 16WP (weeks post-exposure) rats indicated that vascular nociceptor Na_v1.9 mediated currents were chronically potentiated following the 4 agent protocol but not following the 3 agent protocol. Muscarinic linkages to muscle nociceptor TRPA1 were also potentiated in the 4 agent but not the 3 agent, PB excluded, protocol. Although K_v7 activity changes diverged from the behavioral data, a K_v7 opener, retigabine, transiently reversed ambulation deficits. We concluded that PB played a critical role in the development of pain-like signs in a GWI rat model and that shifts in Na_v1.9 and TRPA1 activity were critical to the expression of these pain behaviors.

DEET potentiates the development and persistence of anticholinesterase dependent chronic pain signs in a rat model of Gulf War Illness pain

Exposure to DEET (N,N-diethyl-meta-toluamide) may have influenced the pattern of symptoms observed in soldiers with GWI (Gulf War Illness; Haley and Kurt, 1997). We examined how the addition of DEET (400mg/kg; 50% topical) to an exposure protocol of permethrin (2.6mg/kg; topical), chlorpyrifos (CP; 120mg/kg), and pyridostigmine bromide (PB;13mg/kg) altered the emergence and pattern of pain signs in an animal model of GWI pain (Nutter et al., 2015). Rats underwent behavioral testing before, during and after a 4week exposure: 1) hindlimb pressure withdrawal threshold; 2) ambulation (movement distance and rate); and 3) resting duration. Additional studies were conducted to assess the influence of acute DEET (10-100μM) on muscle and vascular nociceptor K_v7, K_DR, Na_v1.8 and Na_v1.9. We report that a 50% concentration of DEET enhanced the development and persistence of pain-signs. Rats exposed to all 4 compounds exhibited ambulation deficits that appeared 5-12weeks post-exposure and persisted through weeks 21-24. Rats exposed to only three agents (CP or PB excluded), did not fully develop ambulation deficits. When PB was excluded, rats also developed rest duration pain signs, in addition to ambulation deficits. There was no evidence that physiological doses of DEET acutely modified nociceptor K_v7, K_DR, Na_v1.8 or Na_v1.9 activities. Nevertheless, DEET augmented protocols decreased the conductance of K_v7 expressed in vascular nociceptors harvested from chronically exposed rats. We concluded that DEET enhanced the development and persistence of pain behaviors, but the anticholinesterases CP and PB played a determinant role.

Pharmacodynamic analysis of contractile potentiation by cholinesterase inhibitors in rats

Pharmacological profiles of four cholinesterase (ChE) inhibitors: edrophonium, pyridostigmine, neostigmine, and ambenonium after to administration to rats were analyzed. A pharmacodynamic model was developed by considering acetylcholinesterase (AChE) inhibition, direct antagonism to the nicotinic receptor, and desensitization of the nicotinic receptor. Pharmacokinetics of these drugs are dose-independent and have similar volumes of distribution at steady state (0.4-0.6 L/kg various doses). The t1/2 increases in the order of neostigmine, edrophonium, pyridostigmine, and ambenonium. Inhibitory constants of ChE inhibitors to bovine erythrocyte AChE determined in vitro were 2019, 276, 26, and 3.7 nM for edrophonium, pyridostigmine, neostigmine, and ambenonium, respectively. The effect of ChE inhibitor was monitored as the increase of developed tension of triceps muscle induced by sciatic nerve stimulation. The maximum value of contractile tension after i.v. administration decreased at high doses of each drug and the dose-response curves were biphasic. Time courses of plasma concentration and contractile muscle tension were modeled to estimate the association/dissociation rate constants to AChE and the nicotinic receptor, desensitization rate constant of receptor and the dissociation constant of acetylcholine (ACh) to nicotinic receptor/basal acetylcholine level ratio (Kd/ACh0). The estimated Kd/ACh0 values were not dependent on the drug. A significant correlation between inhibitory constants of ChE inhibitors to AChE estimated by in vivo pharmacodynamic analysis and those determined by an in vitro enzyme kinetic study was shown, while the relationship between dissociation constants to nicotinic receptor estimated by in vivo pharmacodynamic analysis and those measured by an in vitro binding study was not clear. Other process such as desensitisization induced by endogenous ACh diffusion rate of drugs into the synaptic cleft, action of presynaptic receptors, etc., might contribute to the dose-effect relationship of ChE inhibitors.

Ligated renal pedicles and duration of action of neostigmine and pyridostigmine

1. The duration of neostigmine or pyridostigmine antagonism of a (+)-tubocurarine (Tc) neuromuscular blockade was determined in the cat anterior tibialis-peroneal nerve preparation with and without ligated renal pedicles. 2. The infusion rate of Tc required to maintain a 90% depression of twitch tension was reduced from 8.8 +/- 1.4 (s.e.) to 3.4 +/- 0.6 mugkg-1 min-1 by renal pedicle ligation. 3. Renal pedicle ligation resulted in an increased duration of antagonism of Tc by both neostigmine and pyridostigmine.

The pharmacokinetics of pyridostigmine and 3-hydroxy-N-methylpyridinium in the rat: dose-dependent effects after portal vein administration

1 The elimination kinectis of [14C]-pyridostigmine iodine and [14-C-methyl]-3-hydroxypyridinium bromide (3-OH NMP) have been studied in the rat. 2 For pyridostigmine, at a given dose level, the fraction of the dose eliminated unchanged was reduced and the metabolite fraction was increased after portal vein administration when compared to jugular vein administration. This indicates that pyridostigmine is subject to metabolism during the first passage through the liver. 3 When doses of pyridostigmine 1.25 mumol/kg and higher were injected via the portal vein, the proportion excreted in urine as unchanged drug remained constant; in contrast, the percentage of the dose eliminated as the metabolite was significantly reduced. This indicates that a dose-dependent process is involved in the urinary excretion of 3-OH NMP. 4 This conclusion was supported by studies involving the portal and systemic venous injection of 3-OH NMP at different dose levels. After 4 h, approximately85% of the lowest dose was eliminated unchanged in ug this period. The proportion of the dose eliminated in urine was not related to the route of administration. 5 After the injection of pyridostigmine into the jugular vein, the initial rate of drug excretion fell rapidly for approximately 10 min; in contrast, after injection into the portal vein, the rate of excretion of the drug rose to a maximum at 30 minutes. This suggests that the hepatoportal system behaves as a distinct region during the distribution of this drug.

The excretion and metabolism of oral 14C-pyridostigmine in the rat

1. Pyridostigmine labelled with carbon-14 in the methyl group of the quaternary nitrogen has been used to investigate the excretion and metabolism of the drug after administration of single doses (500 mug) to the rat by stomach tube.2. Pyridostigmine is slowly excreted in the urine; the maximum excretion occurs between 1-3 hr after administration. In 24 hr 42% of the dose is excreted in urine and 38.4% is present in faeces and intestinal contents.3. The peak concentration of radioactivity in liver and blood occurs about 2 hr after administration.4. About 75% of the radioactivity in urine is present as unchanged pyridostigmine, the remainder as metabolite.5. The results are compared with those previously obtained after oral administration of neostigmine.6. It is concluded that after oral administration the absorption of pyridostigmine is greater and the metabolism substantially less than that of neostigmine.