The acute antinociceptive effect of HBO₂ is mediated by a NO-cyclic GMP-PKG-KATP channel pathway in mice

Effect of hyperbaric oxygen on chemotherapy-induced neuropathy in male and female rats

Chemotherapeutic agents can cause peripheral neuropathy, a deleterious side effect of cancer treatment. Hyperbaric oxygen (HBO2) treatment has shown great potential for decreasing pain in numerous clinical pain conditions and in preclinical studies. This study was designed to test whether HBO2 might also be useful for treating chemotherapy-induced peripheral neuropathy. Male and female Sprague-Dawley rats were injected with 1 mg/kg paclitaxel or vehicle every other day for 7 days to induce allodynia, followed by either one single, or four daily 60-min exposures to HBO2 or room air. Mechanical and cold allodynia as well as locomotor behavior and body weight were assessed intermittently for several weeks. Estrous cycling was also tracked in female rats. Paclitaxel caused pronounced mechanical allodynia in both sexes that was completely reversed by either one or four treatments of HBO2. Females in all treatment groups showed greater cold acetone scores than males, and acetone scores were not reliably reduced by HBO2 treatment. Neither paclitaxel nor HBO2 treatment altered locomotor behavior or estrous cycling. We conclude that HBO2 treatment was highly effective at reducing mechanical allodynia in paclitaxel-treated rats without affecting weight gain, locomotion, or estrous cycling, suggesting that HBO2 may be effective for treating chemotherapy-induced neuropathic pain without producing significant side effects.

Hydrogen sulfide attenuates diabetic neuropathic pain through NO/cGMP/PKG pathway and μ-opioid receptor

IMPACT STATEMENT

There are currently approximately 425 million diabetic patients worldwide, of which approximately 90% of patients with diabetes suffer from neuropathy. Diabetic neuropathic pain (DNP) is a common complication of diabetic neuropathy. Nearly half of the patients hospitalized with diabetes have pain symptoms or symptoms related to neurological injury, and the incidence increases with age and diabetic duration. Anti-DNP analgesics have either limited therapeutic effects or serious side effects or lack of clinical trials, which has limited their application. Physiopathological mechanisms and treatment of DNP remain a significant challenge. The present confirmed that inhalation of H₂S may attenuate the diabetic neuropathic pain through NO/cGMP/PKG pathway and μ-opioid receptor. It provides us the animal study foundation for the application of H₂S on the treatment of DNP and clarifies some target molecules in the pain modulation of DNP.

Role of spinal GABA receptors in the acute antinociceptive response of mice to hyperbaric oxygen

New pain treatments are in demand due to the pervasive nature of pain conditions. Hyperbaric oxygen (HBO₂) has shown potential in treating pain in both clinical and preclinical settings, although the mechanism of this effect is still unknown. The aim of this study was to investigate whether the major inhibitory neurotransmitter γ-aminobutyric acid (GABA) is involved in HBO₂-induced antinociception in the central nervous system (CNS). To accomplish this goal, pharmacological interactions between GABA drugs and HBO₂ were investigated using the behavioral acetic acid abdominal constriction test. Western blotting was used to quantify protein changes that might occur as a result of the interactions. GABA_A but not GABA_B receptor antagonists dose-dependently reduced HBO₂ antinociception, while antagonism of the GABA reuptake transporter enhanced this effect. Western blot results showed an interaction between the pain stimulus and HBO₂ on expression of the phosphorylated β3 subunit of the GABA_A receptor at S408/409 in homogenates of the lumbar but not thoracic spinal cord. A significant interaction was also found in neuronal nitric oxide synthase (nNOS) expression in the lumbar but not thoracic spinal cord. These findings support the notion that GABA may be involved in HBO₂-induced antinociception at the GABA_A receptor but indicate that more study will be needed to understand the intricacies of this interaction.

The NO-cGMP-PKG signal transduction pathway is involved in the analgesic effect of early hyperbaric oxygen treatment of neuropathic pain

Background

Hyperbaric oxygen (HBO) has the potential to relieve neuropathic pain. The purpose of this study was to determine whether the NO-cGMP-PKG signaling pathway is involved in the analgesic effects of early hyperbaric oxygen treatment of neuropathic pain in rats.

Methods

Rats were randomly grouped for establishment of chronic constriction injury (CCI) models. Intrathecal catheters were inserted and 2.5ATA HBO therapy was administered from day 1 post-surgery for 60 minutes daily, continuously for 5 days; menstruum NS, DMSO, NO synthase(NOS) nonspecific inhibitor (L-NAME), soluble guanylyl cyclase(sGC) inhibitor (ODQ) and protein kinase G(PKG) inhibitor (KT5823) were administered intrathecally 30 minutes prior to HBO therapy. Pain-related behaviors in rats were observed at specific time points. Western blot and real-time RT-PCR were used to observe the expressions of PKG1 mRNA and protein in the spinal dorsal horn.

Results

Compared with the CCI group, HBO could significantly relieve mechanical and thermal hyperalgesia in rats. After intrathecal administration of L-NAME, ODQ and KT5823, effects of HBO on relieving hyperalgesia in rats were reversed (P < 0.05 vs. HBO), and expression of PKG1 mRNA and protein decreased in the spinal dorsal horn of the animals (P < 0.05 vs. HBO).

Conclusions

Early HBO therapy could significantly improve symptoms of hyperalgesia of neuropathic pain in rats, possibly via activation of the NO-cGMP-PKG signaling transduction pathway.

Roles of ATP sensitive potassium channel in modulating gastric tone and accommodation in dogs

OBJECTIVE

The ATP sensitive potassium (K_ATP) channel plays an important role in the regulation of resting membrane potential and membrane excitability. The role of the K_ATP channel in modulating gastric motility is unclear. The aim of this study was to investigate the role and mechanism of the K_ATP channel in modulating gastric tone and accommodation in dogs.

MATERIALS AND METHODS

Gastric volume under a constant pressure reflecting gastric tone was measured using a barostat device in dogs equipped with a gastric cannula. Gastric accommodation was evaluated by the difference in gastric volume before and after a liquid meal. The roles of cholinergic and nitrergic pathways in the inhibitory effect of pinacidil (a K_ATP opener) were assessed.

RESULTS

1) Pinacidil dose-dependently decreased gastric tone at a dosage of 30 (p = 0.628), 100 (p = 0.013) and 300 μg kg^-1 (p < 0.001). 2) Glibenclamide, a K_ATP blocker, completely blocked the inhibitory effect of pinacidil on gastric tone. 3) Atropine did not block the inhibitory effect of pinacidil on gastric tone but N_ω-Nitro-L-arginine methyl ester markedly attenuated the inhibitory effect of pinacidil (p = 0.004). 4) Glibenclamide significantly reduced gastric accommodation (p < 0.001) while pinacidil had no effects on gastric accommodation. 5) Glibenclamide significantly reduced nitric oxide donor sodium nitroprusside-induced gastric relaxation.

CONCLUSIONS

These findings indicate that the K_ATP channel plays an important role in modulating gastric tone and accommodation in dogs. The inhibitory effect of pinacidil on gastric tone was through the nitrergic pathway as well as acting directly on smooth muscle cells.

Successful Treatment of Lower Limb Complex Regional Pain Syndrome following Three Weeks of Hyperbaric Oxygen Therapy

Hyperbaric oxygen therapy (HBOT) is a treatment that delivers 100% oxygen at increased atmospheric pressures. The efficacy of HBOT for treating pain has been described in various animal pain models and may have clinical efficacy in the treatment of human chronic pain syndromes. We present our experience with posttraumatic Complex Regional Pain Syndrome (CRPS) type 2 in a patient who underwent 15 sessions of HBOT. A 41-year-old male with one-year history of CRPS of left foot followed by left ankle fracture demonstrated less pain, decreased swelling, less allodynia, and improvement in skin color and range of motion of the lower limb after 3 weeks of HBOT. Patient was back to work for the first time in over a year. HBOT may be considered as a valuable therapeutic tool in the treatment of long-standing CRPS.

Hyperbaric Oxygen Therapy: A New Treatment for Chronic Pain?

BACKGROUND AND OBJECTIVE

Hyperbaric oxygen therapy (HBOT) is a treatment providing 100% oxygen at a pressure greater than that at sea level. HBOT is becoming increasingly recognized as a potential treatment modality for a broad range of ailments, including chronic pain. In this narrative review, we discuss the current understanding of pathophysiology of nociceptive, inflammatory and neuropathic pain, and the body of animal studies addressing mechanisms by which HBOT may ameliorate these different types of pain. Finally, we review clinical studies suggesting that HBOT may be useful in treating chronic pain syndromes, including chronic headache, fibromyalgia, complex regional pain syndrome, and trigeminal neuralgia.

DATABASE AND DATA TREATMENT

A comprehensive search through MEDLINE, EMBASE, Scopus, and Web of Science for studies relating to HBOT and pain was performed using the following keywords: hyperbaric oxygen therapy or hyperbaric oxygen treatment (HBOT), nociceptive pain, inflammatory pain, neuropathic pain, HBOT AND pain, HBOT AND headache, HBOT AND fibromyalgia, HBOT AND complex regional pain syndrome, and HBOT AND trigeminal neuralgia.

RESULTS

Twenty-five studies examining the role of HBOT in animal models of pain and human clinical trials were found and reviewed for this narrative review.

CONCLUSIONS

HBOT has been shown to reduce pain using animal models. Early clinical research indicates HBOT may also be useful in modulating human pain; however, further studies are required to determine whether HBOT is a safe and efficacious treatment modality for chronic pain conditions.

The acute antinociceptive effect of hyperbaric oxygen is not accompanied by an increase in markers of oxidative stress

AIMS

Exposure to hyperbaric oxygen (HBO2) causes an antinociceptive response in mice. However, breathing oxygen (O2) at an elevated pressure can potentially cause oxygen toxicity. The aim of this study was to identify the determinants of HBO2 antinociception and the toxicity profile of HBO2.

MAIN METHODS

Male NIH Swiss mice were assessed for acute antinociceptive responsiveness under room air or 100% O2 at 1.0 or 3.5 atmospheres absolute (ATA), using the acetic acid-induced abdominal constriction test. For the oxygen toxicity test, mice were exposed to 3.5 ATA oxygen for 11min, 60min, and 60min daily for 2days (120min) or 60min daily for 4days (240min), then assessed by analyzing the levels of two oxidative stress markers, MDA (malondialdehyde) and protein carbonyl in brain, spinal cord and lung.

KEY FINDINGS

Only the combination of 100% O2 and 3.5 ATA caused significant antinociception. The antinociceptive effect of 100% O2 was pressure-dependent up to 3.5 ATA. In the oxygen toxicity test, mice exposed to HBO2 for different time intervals had levels of brain, spinal cord and lung MDA and protein carbonyl that were comparable to that of control animals exposed to room air.

SIGNIFICANCE

Treatment with 100% O2 evokes a pressure-dependent antinociceptive effect. Since there was no significant increase in levels of the oxidative stress markers in the tested tissues, it is concluded that HBO2 at 3.5 ATA produces antinociception in the absence of oxidative stress in mice.

Involvement of spinal cord opioid mechanisms in the acute antinociceptive effect of hyperbaric oxygen in mice

Earlier research has demonstrated that treatment with hyperbaric oxygen (HBO2) can elicit an antinociceptive response in models of acute pain. We have demonstrated that this antinociceptive effect is centrally-mediated and is dependent on opioid receptors. The purpose of the present study was to examine the role of endogenous opioid peptides and opioid receptors specifically in the spinal cord in the acute antinociceptive effect of HBO2 in mice. Male NIH Swiss mice were exposed to HBO2 (100% oxygen at 3.5atm absolute) for 11min and their antinociceptive responsiveness was determined using the glacial acetic acid-induced abdominal constriction test. HBO2-induced antinociception was sensitive to antagonism by intrathecal (i.t.) pretreatment with the κ- and μ-selective opioid antagonists norbinaltorphimine and β-funaltrexamine, respectively, but not the δ-selective antagonist naltrindole. The antinociceptive effect of HBO2 was also significantly attenuated by i.t. pretreatment with a rabbit antiserum against rat dynorphin1-13 but not antisera against β-endorphin or methionine-enkephalin. Based on these experimental findings, the acute antinociceptive effect of HBO2 appears to involve neuronal release of dynorphin and activation of κ- and μ-opioid receptors in the spinal cord.

Involvement of brain opioid receptors in the anti-allodynic effect of hyperbaric oxygen in rats with sciatic nerve crush-induced neuropathic pain

Earlier research has demonstrated that hyperbaric oxygen (HBO2) can produce an antinociceptive effect in models of acute pain. Recent studies have revealed that HBO2 can produce pain relief in animal models of chronic pain as well. The purpose of the present investigation was to ascertain whether HBO2 treatment might suppress allodynia in rats with neuropathic pain and whether this effect might be blocked by the opioid antagonist naltrexone (NTX). Male Sprague Dawley rats were subjected to a sciatic nerve crush under anesthesia and mechanical thresholds were assessed using an electronic von Frey anesthesiometer. The time course of the HBO2-induced anti-allodynic effect in different treatment groups was plotted, and the area-under-the-curve (AUC) was determined for each group. Seven days after the nerve crush procedure, rats were treated with HBO2 at 3.5 atm absolute (ATA) for 60 min and exhibited an anti-allodynic effect, compared to nerve crush-only control rats. Twenty-four hours before HBO2 treatment, another group of rats was implanted with Alzet(®) osmotic minipumps that continuously released NTX into the lateral cerebral ventricle for 7 days. These NTX-infused, HBO2-treated rats exhibited an allodynic response comparable to that exhibited by rats receiving nerve crush only. Analysis of the AUC data showed that HBO2 significantly reduced the nerve crush-induced allodynia; this anti-allodynic effect of HBO2 was reversed by NTX. These results implicate opioid receptors in the pain relief induced by HBO2.

An anxiolytic-like effect of hyperbaric oxygen in the mouse light/dark exploration test

AIMS

We studied whether hyperbaric oxygen (HBO(2)) treatment, which is known to increase production of nitric oxide (NO) in the brain, might also produce an NO-dependent anxiolytic-like behavioral response.

MAIN METHODS

Male NIH Swiss mice (20-25g) were subjected to a 60-min HBO(2) treatment at different absolute atmospheres, and anxiety was assessed using the light/dark exploration test at different time intervals following the cessation of HBO(2) treatment. To ascertain the underlying mechanism of action, other groups of mice were pretreated with the NO synthase inhibitor N(G)-monomethyl-l-arginine acetate, the NO scavenger 2-(4-carboxyphenyl)-4,5-dihydro-4,4,5,5-tetramethyl-1H-imidazolyl-1-oxy-3-oxide (carboxy-PTIO), the soluble guanylyl cyclase-inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) or the benzodiazepine antagonist flumazenil to determine their influence on the HBO(2)-induced anxiolytic-like effect.

KEY FINDINGS

A 60-min HBO(2) treatment at 3.0 absolute atmospheres increased the time spent by mice in the light compartment that lasted up to 90 min following the end of HBO(2) treatment. This anxiolytic effect of HBO(2) was significantly reduced by pretreatment with L-NMMA, carboxy-PTIO, ODQ and flumazenil.

SIGNIFICANCE

Based on these findings, we conclude that a 60-min HBO(2) treatment is capable of inducing an anxiolytic effect that possibly involves NO, cyclic GMP and the benzodiazepine binding site.