Quercetin attenuates thermal hyperalgesia and cold allodynia in STZ-induced diabetic rats

Neuropathic pain is one of the important microvascular complications of diabetes. Oxidative stress and superoxide play a critical role in the development of neurovascular complications in diabetes. Aim of the present study was to evaluate the effect of quercetin, a bioflavonoid on thermal nociceptive responses in streptozotocin (STZ)-induced diabetic rats assessed by tail-immersion and hot plate methods. After 4-weeks of a single intravenous STZ injection (45 mg/kg body weight), diabetic rats exhibited a significant thermal hyperalgesia and cold allodynia along with increased plasma glucose and decreased body weights as compared with control rats. Chronic treatment with quercetin (10 mg/kg body weight; p.o) for 4-weeks starting from the 4th week of STZ-injection significantly attenuated the cold allodynia as well as hyperalgesia. Results indicate that quercetin, a natural antioxidant, may be helpful in diabetic neuropathy.     

Resveratrol, a polyphenolic phytoalexin attenuates thermal hyperalgesia and cold allodynia in STZ-induced diabetic rats

The effects of resveratrol, a polyphenolic phytoalexin present in red wine have been investigated on hyperalgesia and cold allodynia in streptozotocin (STZ) induced diabetic rats. Diabetes was induced by a single intraperitoneal injection of streptozotocin (65mg/kg). After 4-weeks of STZ injection, diabetic rats exhibited a significant thermal hyperalgesia and cold allodynia along with increased plasma glucose and decreased body weights as compared with controls rats. Chronic treatment with resveratrol (10mg/kg orally) from week 4 to week 6 significantly attenuated the cold allodynia and thermal hyperalgesia. The results emphasize the role of oxidative stress in development of hyperalgesia and cold allodynia in diabetic animals and point towards the potential of resveratrol as an adjuvant therapy for the prevention and treatment of diabetic neuropathy.     

Detection of cold pain, cold allodynia and cold hyperalgesia in freely behaving rats

In mammals, somatosensory input activates feedback and feed-forward inhibitory circuits within the spinal cord dorsal horn to modulate sensory processing and thereby affecting sensory perception by the brain. Conventionally, feedback and feed-forward inhibitory activity evoked by somatosensory input to the dorsal horn is believed to be driven by glutamate, the principle excitatory neurotransmitter in primary afferent fibers. Substance P (SP), the prototypic neuropeptide released from primary afferent fibers to the dorsal horn, is regarded as a pain substance in the mammalian somatosensory system due to its action on nociceptive projection neurons. Here we report that endogenous SP drives a novel form of feed-forward inhibitory activity in the dorsal horn. The SP-driven feed-forward inhibitory activity is long-lasting and has a temporal phase distinct from glutamate-driven feed-forward inhibitory activity. Compromising SP-driven feed-forward inhibitory activity results in behavioral sensitization. Our findings reveal a fundamental role of SP in recruiting inhibitory activity for sensory processing, which may have important therapeutic implications in treating pathological pain conditions using SP receptors as targets.     

Transplantation of bone marrow-derived mononuclear cells improves mechanical hyperalgesia, cold allodynia and nerve function in diabetic neuropathy

Relief from painful diabetic neuropathy is an important clinical issue. We have previously shown that the transplantation of cultured endothelial progenitor cells or mesenchymal stem cells ameliorated diabetic neuropathy in rats. In this study, we investigated whether transplantation of freshly isolated bone marrow-derived mononuclear cells (BM-MNCs) alleviates neuropathic pain in the early stage of streptozotocin-induced diabetic rats. Two weeks after STZ injection, BM-MNCs or vehicle saline were injected into the unilateral hind limb muscles. Mechanical hyperalgesia and cold allodynia in SD rats were measured as the number of foot withdrawals to von Frey hair stimulation and acetone application, respectively. Two weeks after the BM-MNC transplantation, sciatic motor nerve conduction velocity (MNCV), sensory nerve conduction velocity (SNCV), sciatic nerve blood flow (SNBF), mRNA expressions and histology were assessed. The BM-MNC transplantation significantly ameliorated mechanical hyperalgesia and cold allodynia in the BM-MNC-injected side. Furthermore, the slowed MNCV/SNCV and decreased SNBF in diabetic rats were improved in the BM-MNC-injected side. BM-MNC transplantation improved the decreased mRNA expression of NT-3 and number of microvessels in the hind limb muscles. There was no distinct effect of BM-MNC transplantation on the intraepidermal nerve fiber density. These results suggest that autologous transplantation of BM-MNCs could be a novel strategy for the treatment of painful diabetic neuropathy.     

General administration of cyclohexenonic long-chain fatty alcohol ameliorates hyperreactivity of STZ-induced diabetic rat aorta

Diabetic neuropathy, a major complication of diabetes mellitus, is associated with the development of vascular dysfunction and autonomic neuropathy. We studied the effects of cyclohexenonic long-chain fatty alcohol (FA) on streptozotocin-diabetic hyperreactivity in the rat aorta smooth muscle. The rats were divided randomly into four groups and were maintained for 4 weeks: age-matched control rats, diabetic rats without treatment with FA, and diabetic rats treated with FA (2 and 8 mg/kg, i.p. everyday). The serum glucose and insulin levels were determined, and the contractile responses of the aorta induced by a thromboxane A2 agonist, U46619 and KCl were investigated. Treatment with FA did not alter rats' diabetic status, i.e., body weight, thickness of the aorta, serum glucose levels, and serum insulin levels, but significantly improved the diabetic-induced hyperreactivity of the rat aorta in a dose-dependent manner. Removal of endothelium did not change contractile force between groups. In histological examinations, thinning of smooth muscle bundle in the wall of aorta was observed in the diabetic rat, which was not significantly improved by treatment with FA. Our data indicate that FA can prevent hyperreactivity in the diabetic aorta.     

Inhibition of soluble epoxide hydrolase reduces LPS-induced thermal hyperalgesia and mechanical allodynia in a rat model of inflammatory pain

Soluble epoxide hydrolases catalyze the hydrolysis of epoxides in acyclic systems. In man this enzyme is the product of a single copy gene (EPXH-2) present on chromosome 8. The human sEH is of interest due to emerging roles of its endogenous substrates, epoxygenated fatty acids, in inflammation and hypertension. One of the consequences of inhibiting sEH in rodent inflammation models is a profound decrease in the production of pro-inflammatory and proalgesic lipid metabolites including prostaglandins. This prompted us to hypothesize that sEH inhibitors may have antinociceptive properties. Here we tested if sEH inhibitors can reduce inflammatory pain. Hyperalgesia was induced by intraplantar LPS injection and sEH inhibitors were delivered topically. We found that two structurally dissimilar but equally potent sEH inhibitors can be delivered through the transdermal route and that sEH inhibitors effectively attenuate thermal hyperalgesia and mechanical allodynia in rats treated with LPS. In addition we show that epoxydized arachidonic acid metabolites, EETs, are also effective in attenuating thermal hyperalgesia in this model. In parallel with the observed biological activity metabolic analysis of oxylipids showed that inhibition of sEH resulted with a decrease in PGD2 levels and sEH generated degradation products of linoleic and arachidonic acid metabolites with a concomitant increase in epoxides of linoleic acid. These data show that inhibition of sEH may become a viable therapeutic strategy to attain analgesia.     

Mechanical and cold allodynia in a rat spinal cord contusion model

This study examined the time course of mechanical and cold allodynia in rat hindpaw after spinal cord contusion. Hindpaw withdrawal threshold to graded von Frey hair stimulation and withdrawal frequency to acetone application were measured in rats subjected to contusions of varying severity, produced by a MASCIS impactor device with a 10?g weight dropped from 6.25, 12.5, or 25?mm. Mechanical and cold allodynia developed following the injury, and differences in the incidence of allodynia and in withdrawal threshold were significant among these groups. The least severe injury (6.25?mm) most consistently caused a decreased hindpaw threshold to mechanical stimulation and an increased withdrawal frequency to cold.     

Mechanical and cold allodynia in a rat spinal cord contusion model

This study examined the time course of mechanical and cold allodynia in rat hindpaw after spinal cord contusion. Hindpaw withdrawal threshold to graded von Frey hair stimulation and withdrawal frequency to acetone application were measured in rats subjected to contusions of varying severity, produced by a MASCIS impactor device with a 10 g weight dropped from 6.25, 12.5, or 25 mm. Mechanical and cold allodynia developed following the injury, and differences in the incidence of allodynia and in withdrawal threshold were significant among these groups. The least severe injury (6.25 mm) most consistently caused a decreased hindpaw threshold to mechanical stimulation and an increased withdrawal frequency to cold.     

Supraspinal injection of Substance P attenuates allodynia and hyperalgesia in a rat model of inflammatory pain

The neuropeptide Substance P (SP), that has a high affinity for the neurokinin 1 (NK1) receptor, is involved in modulation of pain transmission. Although SP is thought to have excitatory actions and promote nociception in the spinal cord, the peptide induces analgesia at the supraspinal level. The aim of this study was to evaluate the role of supraspinal SP and the NK1 receptor in inflammatory pain induced by injection of carrageenan in the hind paw of the rat. There are two nociceptive behavioral responses associated with this pain state: mechanical allodynia and heat hyperalgesia. Because the NK1 receptor colocalizes with the MOP receptor in supraspinal sites involved in pain modulation, we also decided to study the possible involvement of the opioid system on SP-induced analgesia. We found that treatment with SP, at doses of 3.5, 5 and 7 μg/5 μl/rat i.c.v., clearly showed inhibition of allodynia and hyperalgesia. Pretreatment with the selective NK1 antagonist L-733,060 (10mg/kg i.p.) blocked the SP-induced analgesia, suggesting the involvement of the NK1 receptor. This SP-induced analgesia was significantly reduced by administration of the opioid antagonist naloxone (3mg/kg s.c.). This reduction occurred when SP was administered either before or after the carrageenan injection. These results suggest a significant antinociceptive role for SP and the NK1 receptor in inflammatory pain at the supraspinal level, possibly through the release of endogenous opioids.     

Gastrodin inhibits allodynia and hyperalgesia in painful diabetic neuropathy rats by decreasing excitability of nociceptive primary sensory neurons

Painful diabetic neuropathy (PDN) is a common complication of diabetes mellitus and adversely affects the patients' quality of life. Evidence has accumulated that PDN is associated with hyperexcitability of peripheral nociceptive primary sensory neurons. However, the precise cellular mechanism underlying PDN remains elusive. This may result in the lacking of effective therapies for the treatment of PDN. The phenolic glucoside, gastrodin, which is a main constituent of the Chinese herbal medicine Gastrodia elata Blume, has been widely used as an anticonvulsant, sedative, and analgesic since ancient times. However, the cellular mechanisms underlying its analgesic actions are not well understood. By utilizing a combination of behavioral surveys and electrophysiological recordings, the present study investigated the role of gastrodin in an experimental rat model of STZ-induced PDN and to further explore the underlying cellular mechanisms. Intraperitoneal administration of gastrodin effectively attenuated both the mechanical allodynia and thermal hyperalgesia induced by STZ injection. Whole-cell patch clamp recordings were obtained from nociceptive, capsaicin-sensitive small diameter neurons of the intact dorsal root ganglion (DRG). Recordings from diabetic rats revealed that the abnormal hyperexcitability of neurons was greatly abolished by application of GAS. To determine which currents were involved in the antinociceptive action of gastrodin, we examined the effects of gastrodin on transient sodium currents (I(NaT)) and potassium currents in diabetic small DRG neurons. Diabetes caused a prominent enhancement of I(NaT) and a decrease of potassium currents, especially slowly inactivating potassium currents (I(AS)); these effects were completely reversed by GAS in a dose-dependent manner. Furthermore, changes in activation and inactivation kinetics of I(NaT) and total potassium current as well as I(AS) currents induced by STZ were normalized by GAS. This study provides a clear cellular basis for the peripheral analgesic action of gastrodin for the treatment of chronic pain, including PDN.     

Endothelin antagonism normalizes VEGF signaling and cardiac function in STZ-induced diabetic rat hearts

Abnormal alterations in cardiac expression of vascular endothelial growth factor (VEGF) as well as its receptors and impairment in the development of coronary collaterals have recently been reported in diabetic subjects. However, the presence of pharmacological intervention on these defects in diabetes remains unsettled. Here, we studied the effect of endothelin (ET) receptor blockade on cardiac VEGF signaling pathways and cardiac function in Sprague-Dawley rats 5 wk after induction of type I diabetes with streptozotocin (65 mg/kg ip) in comparison with age-matched control rats. After streptozotocin (1 wk), some diabetic rats were treated with the ET receptor antagonist SB-209670 (1 mg/day) for 4 wk. VEGF, its receptors, and its angiogenic signaling molecules [phosphorylated Akt and endothelial nitric-oxide synthase (eNOS)] were analyzed by Western blot, ELISA, real-time PCR, and immunohistochemistry, and cardiac function was evaluated by echocardiography. Coronary capillary morphology was assessed by lectin and enzymatic double staining. We found significant decreases in cardiac expression of VEGF, its receptors, phosphorylation of Akt and eNOS, and coronary capillary density in diabetic rats compared with controls. Treatment of diabetic rats with SB-209670 reversed these alterations to the control levels and ameliorated impairment of cardiac function. From a molecular point of view, the present study is the first to indicate the potential usefulness of an ET receptor antagonist in the treatment of cardiac dysfunction in type I diabetes.     

Morin attenuates STZ-induced diabetic retinopathy in experimental animals

Diabetic retinopathy (DR) occurs in untreated diabetic patients due to the strong influence of oxidative stress. Bioflavonoids are well known for their antioxidant property. Morin, a bioflavonoid, has been demonstrated for its antioxidant as well as antidiabetic activity. Thus, this research work intended to determine the ameliorative impact of morin in DR rats using STZ-induced type 1 diabetic model. To induce type 1 diabetic in rats STZ (60 mg/kg) was administered intraperitoneally. Grouping of animals was done as described below (n = 6), where, group I – normal control, group II – diabetic control, group III – morin (25 mg/kg), group IV – morin (50 mg/kg), and group V – metformin (350 mg/kg) were used. All the animals underwent treatment for 60 days as given above. It was observed that supplementation of morin (25 and 50 mg/kg) showed a noteworthy decline in elevated serum glucose level. Moreover, decrease in the level of LPO and improved activity of endogenous antioxidants (GPx, CAT, and SOD) was observed in morin treated groups. It also notably drops the concentration of TNF-α, IL-1β, and VEGF in the tissue homogenate of the retina. Furthermore, it increased the retinal thickness and cell count in the ganglion cell layer of the retina in diabetic animals. Hence, we can conclude that morin encumbers the progression of DR in diabetic animals, which may be via antioxidant property and suppression of TNF-α, IL-1β, and VEGF.     

鞘内注射γ-氨基丁酸转运体抑制剂NO-711抑制坐骨神经慢性挤压伤大鼠神经病理性痛觉过敏

为研究γ-氨基丁酸转运体在神经病理性痛中的作用,实验用坐骨神经慢性挤压伤致神经病理性痛模型大鼠,以清醒大鼠分别对辐射热刺激和机械性触觉刺激的缩腿潜伏期和机械阈值为指标,分为NS组、N5组、N10组、N20组、N40组5组,分别在坐骨神经结扎前和结扎后第三天鞘内给予生理盐水或不同剂量的γ-氨基丁酸转运体特异性抑制剂NO-711(5、10、20、40μg),观察鞘内注射NO-711对大鼠热痛敏和触诱发痛的影响.结果表明,NO-711可显著抑制神经病理性痛大鼠的热痛觉过敏和触诱发痛(P＜0.05,P＜0.01),其抑制作用持续时间最长分别可达2 h(N40组)和4 h(N20组),其抗热痛敏作用呈剂量依赖性.坐骨神经结扎前鞘内给予不同剂量的NO-711可不同程度地延迟坐骨神经结扎所致的热痛觉过敏的发生,但不能延迟结扎所致的触诱发痛的发生.结果表明γ-氨基丁酸转运体抑制剂在神经病理性痛大鼠具有抗热痛敏和抗触诱发痛的作用.     

3,5-Diiodo-l-thyronine ameliorates diabetic nephropathy in streptozotocin-induced diabetic rats

3, 5-Diiodothyronine (T2), a natural metabolite of triiodothyronine (T3) from deiodination pathway, can mimic biologic effects of T3 without inducing thyrotoxic effects. Recent studies revealed T3 acted as a protective factor against diabetic nephropathy (DN). Nevertheless, little is known about the effect of T2 on DN. This study was designed to investigate whether and how T2 affects experimental models of DN in vivo and in vitro. Administration of T2 was found to prevent significant decrease in SIRT1 protein expression and activity as well as increases in blood glucose, urine albumin excretion, matrix expansion, transforming growth factor-β1 expression, fibronectin and type IV collagen deposition in the diabetic kidney. Concordantly, similar effects of T2 were exhibited in the cultured rat mesangial cells (RMC) exposed to high glucose and that could be abolished by a known SIRT1 inhibitor, sirtinol. Moreover, enhanced NF-κB acetylation and JNK phosphorylation present in both diabetic rats and high glucose-treated RMC were distinctly dampened by T2. Collectively, these results suggested that T2 was a protective agent against renal damage in diabetic nephropathy, whose action involved regulation of SIRT1.     

Esophageal stress softening recovery is altered in STZ-induced diabetic rats

This study investigated stress softening recovery in intact, separated muscle and mucosa-submucosa esophageal tubes in streptozotocin-induced diabetic rats. Fifteen Wistar rats were made diabetic (DM group) by intraperitoneal injection of 50 mg kg⁻¹ streptozotocin and another 11 rats served as Sham group by injection of saline. All rats survived for 8-weeks. Three series of inflation-deflation loadings at luminal pressure levels of 0.5, 1.0 and 2.0 kPa were carried out on different esophageal tubes. Five distension cycles on each pressure level were done in Ca⁺⁺-free Krebs solution before and after KCl activation in Ca⁺⁺-containing Krebs solution. The wall stiffness and stored energy recovery were compared between two groups. The stiffness was biggest in the DM group for the intact tube at pressure 0.5 kPa (P < 0.01) and for the muscle tube at all pressure levels (P < 0.05). Energy recovery induced by stress softening and stiffness loss recovery were significantly smaller in the DM group than in the Sham group for the intact esophagus and separated tubes at all pressure levels (P < 0.05, P < 0.01). In conclusion, the reversible stress softening and passive stiffness recovery were altered in STZ-induced diabetic rats. This study fills a gap in the knowledge about diabetes-induced esophageal remodeling.     

The effects of aminoguanidine on retinopathy in STZ-induced diabetic rats

BackgroundThe accumulation of advanced glycated end products (AGEs) in retinal blood vessels is one of the major etiological factors contributing to diabetic retinopathy. Aminoguanidine (AG) is one of the most extensively used inhibitors of AGEs formation. The aim of this study was to investigate whether AG could protect the development of diabetic retinopathy through inhibition of AGEs.MethodsRat diabetes was induced by intraperitoneal injection with streptozotocin (STZ). AG was given to rats in drinking water. Retina was extracted 3 and 6 months following STZ and AG administration. Immunochemistry and transmission electron microscope were used to detect the expression of AGEs and retina morphology.ResultsExtensive staining of AGEs was detected in retinal blood vessels of 3- and 6-month diabetic rats, while no significant staining was found in the control non-diabetic retina or AG treated groups. Pericyte loss, endothelial cell proliferation, increased ratio of endothelial cells/pericytes, acellular capillaries and capillary occlusion were observed in the retina of 6-month diabetic rats. The increased electron density of retinal capillary basement membrane, mitochondrial swelling in pericytes and endothelial cells were also found in 6-month diabetic rats. The 3-month diabetic rats and the AG-treated rats did not have similar morphological changes compared to control group. The AGEs staining in AG-treated rats was still weakly positive.ConclusionsAGEs plays pivotal roles in diabetic retinopathy. AGE deposition occurs prior to retinal microvasculature changes. AG could prevent the onset and development of diabetic retinopathy through inhibition of AGEs.     

Carvacrol partially reverses symptoms of diabetes in STZ-induced diabetic rats

Little is known about the protective effects of carvacrol on the symptoms of streptozotocin induced diabetes in rats. Hence, this present study was designed to evaluate the protective effect of the strong antioxidant, carvacrol, on the symptoms of streptozotocin induced diabetes in rats. Carvacrol at the doses of 25 and 50 mg/kg body weight were orally administered to diabetic rats for a period of 7 days after the onset of diabetes. Food-water intake and body weight changes were daily recorded. Biochemical parameters such as serum glucose, insulin, total cholesterol, alanine aminotransferase, aspartate aminotransferase and lactate dehydrogenase were measured. Although treatment of diabetic rats with oral administration of carvacrol resulted in a slight reduction in serum glucose level and significant reduction in serum total cholesterol, alanine aminotransferase, aspartate aminotransferase and lactate dehydrogenase in comparison with diabetic control rats, there were no significant differences in serum insulin levels, food-water intake values and body weight changes. Despite the inadequacy of carvacrol on diabetes treatments, it was determined to have at least a partially protective role on liver enzymes.     

Repetitive intradermal capsaicin: differential effect on pain and areas of allodynia and punctate hyperalgesia

This study examined the effect of repeated intradermal capsaicin injections on capsaicin pain intensity and areas of allodynia and punctate hyperalgesia. Seventeen healthy volunteers participated in four sessions separated by at least 5 days. Each session included four intradermal injections of 10 microg of capsaicin. In one session injections were given with 0.5 cm and 6 min intervals, in a second with 0.5 cm and 15 min intervals, in a third with 0.5 cm and 24 min intervals, and in a fourth session with 4 cm and 15 min intervals. Following each injection capsaicin pain intensity was measured in the first 5 min, the area of allodynia at 5 min and area of punctate hyperalgesia at 10 min. With 6 min and 0.5 cm between repeated injections, capsaicin pain intensity decreased significantly whereas areas of allodynia and punctate hyperalgesia increased. In contrast, both capsaicin pain intensity and areas of allodynia and punctate hyperalgesia increased when the interval between injections was 24 min and 0.5 cm or 15 min and 4 cm. With 15 min and 0.5 cm between injections, capsaicin pain intensity did not change, whereas areas of allodynia and punctate hyperalgesia increased. There were no significant relations between capsaicin pain intensity and areas of allodynia and punctate hyperalgesia after first injections. The findings indicate that the response to intradermal injection of capsaicin is dependent on the time and distance between injections. The lack of significant relation between capsaicin pain intensity and area of allodynia and punctate hyperalgesia suggests that the two phenomena are mediated by different central mechanisms.