GPR55 and GPR119 Receptors Contribute to the Processing of Neuropathic Pain in Rats.

Orphan G-protein-coupled receptors (GPCR) comprise a large number of receptors which are widely distributed in the nervous system and represent an opportunity to identify new molecular targets in pain medicine. GPR55 and GPR119 are two orphan GPCR receptors whose physiological function is unclear. The aim was to explore the participation of spinal GPR55 and GPR119 in the processing of neuropathic pain in rats. Mechanical allodynia was evaluated using von Frey filaments. Protein localization and modulation were measured by immunohistochemistry and western blotting, respectively. Intrathecal administration of CID16020046 (selective GPR55 antagonist) or AS1269574 (selective GPR119 agonist) produced a dose-dependent antiallodynic effect, whereas O1062 (GPR55 agonist) and G-protein antagonist peptide dose-dependently prevented the antiallodynic effect of CID16020046 and AS1269574, respectively. Both GPR55 and GPR119 receptors were expressed in spinal cord, dorsal root ganglia and sciatic nerve, but only GPR119 was downregulated after 14 days of spinal nerve ligation. Data suggest that GPR55 and GPR119 participate in the processing of neuropathic pain and could be useful targets to manage neuropathic pain disorders.

Anorectic interaction and safety of 5-hydroxytryptophan/carbidopa plus phentermine or diethylpropion in rat.

Drug combinations are being studied as potential therapies to increase the efficacy or improve the safety profile of weight loss medications. This study was designed to determine the anorectic interaction and safety profile of 5-hydroxytryptophan (5-HTP)/carbidopa + diethylpropion and 5-HTP/carbidopa + phentermine combinations in rats. The anorectic effect of individual drugs or in combination was evaluated by the sweetened milk test. Isobologram and interaction index were employed to determine the anorectic interaction between 5-HTP/carbidopa and diethylpropion or phentermine. Plasma serotonin (5-HT) was measured by ELISA. Safety of repeated doses of both combinations in rats was evaluated using the tail sphygmomanometer, cardiac ultrasound, hematic biometry and blood chemistry. A single oral 5-HTP, diethylpropion or phentermine dose increased the anorectic effect, in a dose-dependent fashion, in 12 h-fasted rats. A dose of carbidopa at 30 mg/kg reduced the 5-HTP-induced plasmatic serotonin concentration and augmented the 5-HTP-induced anorectic effect. Isobologram and interaction index indicated a potentiation interaction between 5-HTP/30 mg/kg carbidopa + diethylpropion and 5-HTP/30 mg/kg carbidopa + phentermine. Chronic administration of experimental ED40 of 5-HTP/30 mg/kg carbidopa + phentermine, but not 5-HTP/30 mg/kg carbidopa + diethylpropion, increased the mitral valve leaflets area. Moreover, there were no other significant changes in cardiovascular, hematic or blood parameters. Both combinations induced around 20% body weight loss after 3 months of oral administration. Results suggest that 5-HTP/30 mg/kg carbidopa potentiates the anorectic effect of diethylpropion and phentermine with an acceptable safety profile, but further clinical studies are necessary to establish their therapeutic potential in the obesity treatment.

Efficacy and safety of the metformin-mazindol anorectic combination in rat.

The current study investigates the anorectic interaction and safety of the mazindol-metformin combination in rats. Isobologram and interaction index were used to determine anorectic interaction between mazindol and metformin in the sweetened milk model. The safety profile of the mazindol-metformin combination was determined by measuring anxiety, blood pressure, hematic biometry and blood chemistry. An acute dose of mazindol and metformin administered per os, individually or as a mixture, has reduced the milk consumption in rats in a dose-dependent manner. Theoretical effective dose 40 (ED40t) did not differ from the experimental effective dose 40 (ED40e) obtained with the mazindol-metformin mixture in the anorexia experiments, by Student's t-test. In addition, the interaction index confirmed the additive anorectic effect between both drugs. A single oral dose of ED40e mazindol-metformin mixture induced anxiolysis in the elevated plus-maze test. Moreover, oral administration of mazindol-metformin combination for 3 months significantly decreased glycemia, but not blood pressure nor other parameters of hematic biometry and blood chemistry. Results suggest that mazindol-metformin combination exerts an additive anorectic effect, as well as anxiolytic and hypoglycemic properties. Mazindol-metformin combination might be useful in obese patients with anxiety disorders or diabetes risk factors.

Possible involvement of peripheral TRP channels in the hydrogen sulfide-induced hyperalgesia in diabetic rats.

BACKGROUND: Peripheral diabetic neuropathy can be painful and its symptoms include hyperalgesia, allodynia and spontaneous pain. Hydrogen sulfide (H2S) is involved in diabetes-induced hyperalgesia and allodynia. However, the molecular target through which H2S induces hyperalgesia in diabetic animals is unclear. The aim of this study was to determine the possible involvement of transient receptor potential (TRP) channels in H2S-induced hyperalgesia in diabetic rats. RESULTS: Streptozotocin (STZ) injection produced hyperglycemia in rats. Intraplantar injection of NaHS (an exogenous donor of H2S, 3-100 µg/paw) induced hyperalgesia, in a time-dependent manner, in formalin-treated diabetic rats. NaHS-induced hyperalgesia was partially prevented by local intraplantar injection of capsazepine (0.3-3 µg/paw), HC-030031 (100-316 µg/paw) and SKF-96365 (10-30 µg/paw) blockers, at 21 days post-STZ injection. At the doses used, these blockers did not modify formalin-induced nociception. Moreover, capsazepine (0.3-30 µg/paw), HC-030031 (100-1000 µg/paw) and SKF-96365 (10-100 µg/paw) reduced formalin-induced nociception in diabetic rats. Contralateral injection of the highest doses used did not modify formalin-induced flinching behavior. Hyperglycemia, at 21 days, also increased protein expression of cystathionine-ß-synthase enzyme (CBS) and TRPC6, but not TRPA1 nor TRPV1, channels in dorsal root ganglia (DRG). Repeated injection of NaHS enhanced CBS and TRPC6 expression, but hydroxylamine (HA) prevented the STZ-induced increase of CBS protein. In addition, daily administration of SKF-96365 diminished TRPC6 protein expression, whereas NaHS partially prevented the decrease of SKF-96365-induced TRPC6 expression. Concordantly, daily intraplantar injection of NaHS enhanced, and HA prevented STZ-induced intraepidermal fiber loss, respectively. CBS was expressed in small- and medium-sized cells of DRG and co-localized with TRPV1, TRPA1 and TRPC6 in IB4-positive neurons. CONCLUSIONS: Our data suggest that H2S leads to hyperalgesia in diabetic rats through activation of TRPV1, TRPA1 and TRPC channels and, subsequent intraepidermal fibers loss. CBS enzyme inhibitors or TRP-channel blockers could be useful for treatment of painful diabetic neuropathy.

Antiallodynic interaction and motor performance of the pregabalin/thioctic acid and pregabalin/α-tocopherol combinations in neonatal streptozotocin-induced diabetic rats.

Painful peripheral neuropathy can be associated with nerve damage caused by diabetes mellitus. Although pregabalin is the first-line therapy for peripheral neuropathy, it shows substantial discontinuation rates, mainly because of nervous system side effects as motor incoordination. Multimodal therapy may improve the motor side effect profile of pregabalin. The aim of this study was to evaluate the interaction of pregabalin + thioctic acid or pregabalin + α-tocopherol on allodynia and motor performance in neonatal streptozotocin-induced diabetic rats. Efficacy of drugs separately or in combination was tested by tactile allodynia using von Frey filaments. Isobolographic and interaction index analysis were used to determine the antiallodynic interaction between pregabalin and either thioctic acid or α-tocopherol. Motor performance was measured using a rotarod test. Pregabalin, thioctic acid, and α-tocopherol reduced, in a dose-dependent fashion, tactile allodynia. Pregabalin + thioctic acid and pregabalin + α-tocopherol combinations also dose-dependently reduced allodynic behavior in diabetic rats. Isobolographic analysis revealed an additive interaction for both combinations. Consistently, the interaction indices confirmed the additive effect between pregabalin + thioctic acid and pregabalin + α-tocopherol. In addition, the administration of either combination improved motor incoordination induced by pregabalin. Data suggests that thioctic acid or α-tocopherol could positively impact the therapeutic profile of pregabalin, because they might be useful for reducing motor incoordination associated to pregabalin in patients with peripheral neuropathy.

Anorectic efficacy and safety of the diethylpropion-topiramate combination in rats.

Preclinical Research & Development Current drugs for obesity treatment have limited efficacy and considerable adverse effects. Combination of drugs with complementary mechanisms of action at lower doses may produce a greater efficacy with a better safety profile. This study was designed to assess the anorectic effect and safety of a diethylpropion + topiramate mixture in rats. The anorectic effect of drugs was measured using a sweetened milk consumption model, and the corresponding interaction was determined by isobolographic analysis, interaction index and confidence intervals. Additionally, blood pressure was measured using a sphygmomanometer in the rat tail. Diethylpropion and topiramate alone or in combination increased the anorectic effect in a dose-dependent fashion in either nondeprived or 12 hr food-deprived rats. All theoretical ED30 values of diethylpropion + topiramate combinations at 1:1, 1:3, and 3:1 dose ratios were significantly higher than experimental ED30 values. In addition, interaction indices and confidence intervals confirmed the potentiation between both drugs. Theoretical ED30 of diethylpropion + topiramate combination did not affect the blood pressure. Data suggests that low doses of the diethylpropion + topiramate combination can potentiate the anorectic effect of individual drugs with a better safety profile, which deserves further investigation in clinical trials.

Combination of diacerhein and antiepileptic drugs after local peripheral, and oral administration in the rat formalin test.

Preclinical Research The present study was designed to evaluate the possible antinociceptive interaction between diacerhein and some antiepileptic drugs (carbamazepine, topiramate and gabapentin) on formalin-induced nociception. Diacerhein, each of the antiepileptics or a fixed dose-ratio combination of these drugs was assessed after local peripheral and oral administration in rats. lsobolographic analyses were used to define the interaction between drugs. Diacerhein, antiepileptic drugs (carbamazepine, topiramate and gabapentin) or their combinations yielded a dose-dependent antinociceptive effect when administered by both routes. Theoretical ED30 values for the combination estimated from the isobolograms were obtained as follows: diacerhein-carbamazepine (85.99 ± 7.07 µg/paw; 56.53 ± 4.56 mg/kg po), diacerhein-topiramate (197.97 ± 22.90 µg/paw; 13.06 ± 2.44 mg/kg po) and diacerhein-gabapentin (96.87 ± 17.73 µg/paw; 17.90 ± 4.70 mg/kg p.o.) for the local peripheral and oral administration routes, respectively. These values were significantly higher than the experimentally obtained ED30 values: diacerhein-carbamazepine (49.33 ± 3.37 µg/paw; 35.49 ± 7.91 mg/kg po), diacerhein-topiramate (133.00 ± 39.10 µg/paw; 8.87 ± 1.46 mg/kg po) and diacerhein-gabapentin (70.98 ± 14.73 µg/paw; 10.95 ± 3.23 mg/kg po). The combinations produced their antinociceptive effects without motor impairment in the rotarod test indicating synergistic interactions with a good side effect profile.