Pharmacokinetics and metabolism of the reactive oxygen scavenger alpha-phenyl-N-tert-butylnitrone in the male Sprague-Dawley rat

Intraganglionic reactive oxygen species mediate inflammatory pain and hyperalgesia through TRPA1 in the rat

Reactive oxygen species (ROS) are generated in nociceptive pathways in response to inflammation and injury. ROS are accumulated within the sensory ganglia following peripheral inflammation, but the functional role of intraganlionic ROS in inflammatory pain is not clearly understood. The aims of this study were to investigate whether peripheral inflammation leads to prolonged ROS accumulation within the trigeminal ganglia (TG), whether intraganglionic ROS mediate pain hypersensitivity via activation of TRPA1, and whether TRPA1 expression is upregulated in TG during inflammatory conditions by ROS. We demonstrated that peripheral inflammation causes excess ROS production within TG during the period when inflammatory mechanical hyperalgesia is most prominent. Additionally, scavenging intraganglionic ROS attenuated inflammatory mechanical hyperalgesia and a pharmacological blockade of TRPA1 localized within TG also mitigated inflammatory mechanical hyperalgesia. Interestingly, exogenous administration of ROS into TG elicited mechanical hyperalgesia and spontaneous pain-like responses via TRPA1, and intraganglionic ROS induced TRPA1 upregulation in TG. These results collectively suggest that ROS accumulation in TG during peripheral inflammation contributes to pain and hyperalgesia in a TRPA1 dependent manner, and that ROS further exacerbate pathological pain responses by upregulating TRPA1 expression. Therefore, any conditions that exacerbate ROS accumulation within somatic sensory ganglia can aggravate pain responses and treatments reducing ganglionic ROS may help alleviate inflammatory pain.

Induction of the cell survival kinase Sgk1: A possible novel mechanism for α-phenyl-N-tert-butyl nitrone in experimental stroke

Nitrones (e.g. α-phenyl-N-tert-butyl nitrone; PBN) are cerebroprotective in experimental stroke. Free radical trapping is their proposed mechanism. As PBN has low radical trapping potency, we tested Sgk1 induction as another possible mechanism. PBN was injected (100 mg/kg, i.p.) into adult male rats and mice. Sgk1 was quantified in cerebral tissue by microarray, quantitative RT-PCR and western analyses. Sgk1+/+ and Sgk1-/- mice were randomized to receive PBN or saline immediately following transient (60 min) occlusion of the middle cerebral artery. Neurological deficit was measured at 24 h and 48 h and infarct volume at 48 h post-occlusion. Following systemic PBN administration, rapid induction of Sgk1 was detected by microarray (at 4 h) and confirmed by RT-PCR and phosphorylation of the Sgk1-specific substrate NDRG1 (at 6 h). PBN-treated Sgk1+/+ mice had lower neurological deficit ( p < 0.01) and infarct volume ( p < 0.01) than saline-treated Sgk1+/+ mice. PBN-treated Sgk1-/- mice did not differ from saline-treated Sgk1-/- mice. Saline-treated Sgk1-/- and Sgk1+/+ mice did not differ. Brain Sgk3:Sgk1 mRNA ratio was 1.0:10.6 in Sgk1+/+ mice. Sgk3 was not augmented in Sgk1-/- mice. We conclude that acute systemic treatment with PBN induces Sgk1 in brain tissue. Sgk1 may play a part in PBN-dependent actions in acute brain ischemia.

Therapeutic effects of orally administrated antioxidant drugs on acute noise-induced hearing loss

OBJECTIVE

The objective of this study was to investigate the dose-dependent therapeutic effect of the orally administrated antioxidant drugs [4-hydroxy alpha-phenyl-tert-butylnitrone (4-OHPBN) and N-acetyl-L-cysteine (NAC)] on acute noise-induced hearing loss because oral administration is the most commonly used method of drug administration due to its convenience, safety, and economical efficiency.

METHODS

Thirty chinchilla were exposed to a 105 dB octave band noise centered at 4 kHz for 6 h and randomly assigned to a control group (saline only) and three experimental groups [4-OHPBN (10 mg/kg) plus NAC (20 mg/kg), 4-OHPBN (20 mg/kg) plus NAC (50 mg/kg), and 4-OHPBN (50 mg/kg) plus NAC (100 mg/kg)]. The drugs were orally administrated beginning 4 h after noise exposure and then administered twice daily for the next 2 days. Permanent auditory brainstem response threshold shifts, distortion product otoacoustic emission threshold shifts, and the percentage of missing outer hair cell were determined.

RESULTS

The oral administration significantly reduced permanent hearing threshold shift, distortion product otoacoustic emission threshold shift, and the percentage of missing outer hair cell in a dose-dependent manner.

DISCUSSION

This result demonstrates that orally administered drugs can treat acute noise-induced hearing loss in a dose-dependent manner. This suggests that oral administration was effective in treating acute noise-induced hearing loss as in intraperitoneal administration.

Improvement of pharmacokinetics behavior of apocynin by nitrone derivatization: comparative pharmacokinetics of nitrone-apocynin and its parent apocynin in rats

Apocynin, a potent inhibitor of NADPH-oxidase, was widely studied for activities in diseases such as inflammation-mediated disorders, asthma and cardiovascular diseases. In our recent study, a novel nitrone derivative of apocynin, AN-1, demonstrated potent inhibition to oxidative injury and to high expression of gp91^phox subunit of NADPH-oxidase induced by tert-butyl hydroperoxide (t-BHP) in RAW 264.7 macrophage cells, and displayed promising preclinical protective effect against lipopolysaccharide (LPS)-induced acute lung injury in rats. In this work, the pharmacokinetic behaviors of AN-1 in Sprague-Dawley rats with single intravenous and intragastric doses were investigated for further development. Furthermore, apocynin’s pharmacokinetics remain lacking, even though its pharmacological action has been extensively evaluated. The pharmacokinetics of parent apocynin were also comparatively characterized. A simple HPLC method was developed and validated to determine both AN-1 and apocynin in rat plasma. The chromatographic separation was achieved on an Agilent HC-C18 column (250 mm×4.6 mm, 5 µm) at an isocratic flow rate of 1.0 mL/min, with the mobile phase of methanol and water (53∶47, v/v) and the UV detection set at 279 nm. Good linearity was established over the concentration range of 0.1–500 µg/mL for AN-1 and 0.2–100 µg/mL for apocynin. The absolute recovery, precision and accuracy were satisfactory. Compared with the parent compound apocynin, AN-1 yielded a much longer T_1/2 (AN-1 179.8 min, apocynin 6.1 min) and higher AUC_0–t (AN-1 61.89 mmol/L·min, apocynin 2.49 mmol/L·min) after equimolar intravenous dosing (0.302 mmol/kg). The absolute bioavailability of oral AN-1 was 78%, but that of apocynin was only 2.8%. The significant improvement of pharmacokinetic behavior might be accounted for the effective pharmacodynamic results we documented for the novel nitrone derivative AN-1.

Moderate correlations of in vitro versus in vivo pharmacokinetics questioning the need of early microsomal stability testing

BACKGROUND/AIMS

Putative in vitro-in vivo correlations of pharmacokinetic (PK) parameters are regarded as a prerequisite to filter hits derived from high-throughput screening (HTS) approaches for subsequent murine in vivo PK studies.

METHODS

In this study, we assessed stabilities in rat and human microsomes of 121 compounds from an early, academic drug discovery programme targeting the (pro)renin receptor and correlated the respective data with single-dose, in vivo PK parameters of 22 hits administered intravenously in rats.

RESULTS

After transformation of in vitro half-lives to predicted in vivo hepatic clearances, r(2) regarding in vitro-in vivo clearance correlations were 0.31 and 0.27 for the rat and human species, respectively.

CONCLUSIONS

Our data concerning structurally diverse real-world compounds indicate that microsomal stability testing is not a tool to triage early compounds for in vivo PK testing.

In vitro evaluation of hepatic and extra-hepatic metabolism of coumarins using rat subcellular fractions: correlation of in vitro clearance with in vivo data

7-Ethoxycoumarin (7-EC) and 7-hydroxycoumarin (7-HC) were chosen as model compounds to study hepatic and extra-hepatic metabolism in rat tissue subcellular (microsomal and S9) fractions and to scale the observed in vitro clearance to in vivo plasma clearance. 7-EC and 7-HC showed significant metabolic degradation in liver subcellular fractions as compared to subcellular fractions obtained from intestine, kidney, lung and brain. The total in vitro metabolic clearance for 7-EC and 7-HC was determined by adding the individual in vitro organ clearance values obtained in hepatic and extra-hepatic microsomes or S9 fractions. The predicted in vivo clearance for 7-HC was 63.6 and 81.6 ml/min/kg by in vitro scaling from microsomes and S9 fractions, respectively. For 7-EC, the values were 78.5 and 76.8 ml/min/kg, respectively. The predicted clearance was found to be reasonably accurate with slight over- and underprediction. Interestingly, the relative contribution of hepatic and extra-hepatic metabolism to the total clearance of 7-EC and 7-HC was remarkably high, ranging from 62-77% and 22-38%, respectively, of the total metabolic clearance. It is concluded that the model of multi-organ subcellular fractions is a useful in vitro tool for the prediction of in vivo metabolic clearance, as it can provide information about the relative contribution of extra-hepatic and hepatic metabolism to total metabolic clearance.

New therapeutic targets in atrophic age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness in developed countries. There is no effective treatment for the most prevalent atrophic (dry) form of AMD. Atrophic AMD is triggered by abnormalities in the retinal pigment epithelium (RPE) that lies beneath the photoreceptor cells and normally provides critical metabolic support to these light-sensing cells. Secondary to RPE dysfunction, macular rods and cones degenerate leading to the irreversible loss of vision. Oxidative stress, formation of drusen, accumulation of lipofuscin, local inflammation and reactive gliosis represent the pathologic processes implicated in pathogenesis of atrophic AMD. This review discusses potential target areas for small-molecule and biologic intervention, which may lead to development of new therapeutic treatments for atrophic AMD.

Levels of mitochondrial reactive oxygen species increase in rat neuropathic spinal dorsal horn neurons

Reactive oxygen species (ROS) are toxic agents that may be involved in various neurodegenerative diseases. Recent studies indicate that ROS are also involved in persistent pain through a spinal mechanism. Since the major source of ROS in neurons is mitochondria, mitochondrial ROS generation was examined in dorsal horn neurons of neuropathic rats. Neuropathic rats were produced by L5 spinal nerve ligation and mitochondrial ROS was detected by the mitochondrial marker, Mitotracker Red CM-H(2)XRos (MT-Red). Neurons were identified immunohistochemically for the neuronal marker NeuN. The number of MT-Red positive cells was increased 60-100% in the neuropathic dorsal horn. Approximately 75-85% of MT-Red positive cells were neurons. These data suggest that increased mitochondrial ROS in dorsal horn neurons may contribute to central sensitization in neuropathic rats.

Enhanced efficacy of single-dose versus multi-dose azithromycin regimens in preclinical infection models

OBJECTIVES

As a result of the prolonged half-life and unique pharmacokinetic and pharmacodynamic (PK-PD) characteristics of azithromycin, shorter dosing regimens are being evaluated for the treatment of community-acquired infections. To provide further support for a shorter dosing regimen, the efficacy of azithromycin was determined in preclinical infection models comparing single- versus multi-dose regimens.

METHODS

The efficacy of single versus multi-dose regimens of azithromycin was compared in mouse pneumonia, acute peritonitis, and neutropenic thigh infection models and in a gerbil model of Haemophilus influenzae acute otitis media. Azithromycin was administered as a single oral dose on the first treatment day, or as two divided doses over 2 treatment days, or as three divided doses over 3 treatment days. The pharmacokinetics of azithromycin was profiled following single and multi-dose regimens with the single dose data fit to an Emax model to characterize the PK-PD of azithromycin.

RESULTS

In the mouse efficacy models, administration of single-dose azithromycin produced superior rates of survival and bacterial clearance compared with the same total dose divided over 2 or 3 days. In the gerbil model, a single dose sterilized the middle ear and more rapidly cleared H. influenzae. The pharmacokinetic evaluation confirmed similar total exposure (AUC) in serum and pulmonary tissue for the three regimens. Correlation of PK-PD parameters and antimicrobial efficacy confirmed a concentration-dependent and dosing-independent relationship for azithromycin.

CONCLUSIONS

These data are consistent with data reported from clinical studies and indicate that a single-dose regimen would be at least as effective as the same dose administered over several days.

Stilbazulenyl nitrone, a second-generation azulenyl nitrone antioxidant, confers enduring neuroprotection in experimental focal cerebral ischemia in the rat: neurobehavior, histopathology, and pharmacokinetics

Stilbazulenyl nitrone (STAZN) is a potent lipophilic second-generation azulenyl nitrone antioxidant, which is highly neuroprotective in rodent models of cerebral ischemia and trauma. This study was conducted to establish whether the neuroprotection induced by STAZN persists with chronic survival and to characterize STAZN's pharmacokinetics. Physiologically regulated rats received a 2-h middle cerebral artery occlusion by intraluminal suture and were treated with either STAZN [four 0.6 mg/kg doses i.p. administered at 2 (i.e., onset of recirculation), 4, 24, and 48 h; n = 16] or dimethyl sulfoxide vehicle (n = 11). They received sequential neurobehavioral examinations followed by quantitative neuropathology at 30 days. STAZN improved neurological deficits compared with vehicle controls, beginning within <2 h of the first dose and persisting throughout a 30-day survival. Large cystic necrotic infarcts were common in vehicle-treated rats but infrequent in STAZN-treated rats, and noninfarcted forebrain tissue was increased on average by 15%. In normal rats administered 5 mg/kg STAZN i.v. in Solutol HS 15/ethanol/saline vehicle, STAZN blood levels exhibited a biexponential decline, with an initial half-life of 28 min and a subsequent slow decay with half-life of approximately 7 h. STAZN tissue levels at 2 to 3 h were, on average, 2.5% of blood levels in forebrain, 56% in myocardium, and 41% in kidney. STAZN was concentrated in liver with initial concentrations averaging 5.2-fold above blood levels and a subsequent linear decline of 40% between 24 and 72 h. These results establish that STAZN confers enduring ischemic neuroprotection, has a long circulating half-life, and penetrates well into brain and other organs-characteristics favoring its potential therapeutic utility.

Nitrone-related therapeutics: potential of NXY-059 for the treatment of acute ischaemic stroke

At present, none of the neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease and stroke are treatable with compounds that slow or halt neuronal cell death. However, the prototype nitrone radical trap alpha-phenyl-tert-butylnitrone (PBN) has been shown to be an effective neuroprotective agent in various models of neurodegeneration. Some of these data are briefly reviewed as an introduction to an examination of the effect of the novel nitrone radical trapping agent disodium 2,4-disulfophenyl-N-tert-butylnitrone (NXY-059) in various animal models of stroke. NXY-059 has been shown to be an effective neuroprotective agent in both transient (reperfusion) and permanent focal ischaemia models in rats. In both types of model, NXY-059 has a large window of opportunity, providing effective neuroprotection when given up to 5 hours after the start of the occlusion in transient ischaemia and 4 hours after the start of permanent ischaemia. The compound is also effective in a marmoset permanent ischaemia model when administered up to 4 hours after the start of the occlusion. In this model it has been found to attenuate the problem of spatial neglect and maintain function to the paretic arm. NXY-059 administration also improves motor function in a rat haemorrhagic stroke model and has a neuroprotective effect in a rabbit thromboembolic stroke model. The compound is also well tolerated in stroke patients at plasma levels shown to provide a maximum neuroprotective effect in animal models of stroke.NXY-059, like PBN, is a nitrone with free radical trapping properties and this may be the basis of its neuroprotective action. However, experiments with PBN and NXY-059 suggest the possibility of other mechanisms being involved and these are also reviewed. Further experiments are required to fully elucidate the mechanism of action of these very effective neuroprotective agents.

Reactive oxygen species (ROS) play an important role in a rat model of neuropathic pain

Reactive oxygen species (ROS) are free radicals produced in biological systems that are involved in various degenerative brain diseases. The present study tests the hypothesis that ROS also play an important role in neuropathic pain. In the rat spinal nerve ligation (SNL) model of neuropathic pain, mechanical allodynia develops fully 3 days after nerve ligation and persists for many weeks. Systemic injection of a ROS scavenger, phenyl-N-tert-butylnitrone (PBN), relieves SNL-induced mechanical allodynia in a dose-dependent manner. Repeated injections cause no development of tolerance or no loss of potency. Preemptive treatment with PBN is also effective in preventing full development of neuropathic pain behavior. Systemic injection was mimicked by intrathecal injection with a little less efficacy, while intracerebroventricular administration produced a much smaller effect. These data suggest that PBN exerts its anti-allodynic action mainly by spinal mechanisms. Systemic treatment with other spin-trap reagents, 5,5-dimethylpyrroline-N-oxide and nitrosobenzene, showed similar analgesic effects, suggesting that ROS are critically involved in the development and maintenance of neuropathic pain. Thus this study suggests that systemic administration of non-toxic doses of free radical scavengers could be useful for treatment of neuropathic pain.

Intravenous Pharmacokinetics and Metabolism of the Reactive Oxygen Scavenger α-Phenyl-N-Tert-Butyl Nitrone (PBN) in the Cynomolgus Monkey

The pharmacokinetics and metabolism of the antioxidant and reactive oxygen scavenger alpha-phenyl-N-tert-butyl nitrone (PBN) was examined in the male cynomolgus monkey after intravenous administration. Following an i.v. bolus dose of 5 mg/kg, plasma concentrations of PBN declined in a bi-exponential fashion. PBN demonstrated a moderate plasma clearance (CL(p) = 27.02 +/- 6.46 ml/min/kg) and a moderate volume of distribution at steady state (Vd(ss) = 1.70 +/- 0.23 l/kg), resulting in a terminal elimination half-life of 0.76 +/- 0.25 h. The corresponding area under the curve (AUC(0-infinity)) was 3.20 +/- 0.77 microg-h/ml. Scale-up of the in vitro microsomal intrinsic clearance data for PBN afforded a blood clearance (CLb) value of 22 ml/min/kg, which was in reasonable agreement with the observed in vivo CLb. Monkey liver microsomes catalyzed the NADPH-dependent monohydroxylation of PBN to the corresponding alpha-4-hydroxyphenyl-N-tert-butylnitrone (4-HOPBN) metabolite. The formation of 4-HOPBN and its corresponding O-glucuronide was also discernible upon qualitative analysis of pooled (0-24 h) monkey plasma and urine samples. Less than 5% of the administered dose was excreted as unchanged PBN in the urine, suggesting that P450-catalyzed metabolism constituted the major route of PBN clearance in the primate. In conclusion, the pharmacokinetic attributes and the clearance mechanism of PBN in the cynomolgus monkey is similar to that observed in the Sprague-Dawley rat.

Acrylonitrile potentiates noise-induced hearing loss in rat

Acrylonitrile, one of the 50 most commonly produced industrial chemicals, has recently been identified as a promoter of noise-induced hearing loss (NIHL). This agent has the potential to produce oxidative stress through multiple pathways. We hypothesize that acrylonitrile potentiates NIHL as a consequence of oxidative stress. The objectives of this study were to characterize acrylonitrile exposure conditions that promote permanent NIHL in rats and determine the ability of this nitrile to produce auditory dysfunction by itself. Additionally, we sought to determine whether a spin-trap agent that can form adducts with ROS would protect against the effects of acrylonitrile. Acrylonitrile administration produced significant elevation in NIHL detected as a loss in compound action potential sensitivity. The effect was particularly robust for high-frequency tones and particularly when acrylonitrile and noise were given on repeated occasions. Acrylonitrile by itself did not disrupt threshold sensitivity. Administration of the spin-trap agent phenyl- N- tert-butylnitrone (PBN), given to rats prior to acrylonitrile and noise, did block the elevation of NIHL by acrylonitrile. However, PBN at the dose and time interval given was ineffective in protecting auditory function in subjects exposed to noise alone. The results suggest that oxidative stress may play a role in the promotion of NIHL by acrylonitrile.