Role of L-type Ca2+ channels in attenuated morphine antinociception in streptozotocin-diabetic rats

Teneligliptin Co-Infusion Alleviates Morphine Tolerance by Inhibition of Spinal Microglial Cell Activation in Streptozotocin-Induced Diabetic Rats

Morphine (MOR) is a commonly prescribed drug for the treatment of moderate to severe diabetic neuropathic pain (DNP). However, long-term MOR treatment is limited by morphine analgesic tolerance (MAT). The activation of microglial cells and the release of glia-derived proinflammatory cytokines are known to play an important role in the development of MAT. In this study, we aimed to investigate the effects of the dipeptidyl peptidase-4 inhibitor (DPP-4i) teneligliptin (TEN) on MOR-induced microglial cell activation and MAT in DNP rats. DNP was induced in four groups of male Wistar rats through a single intraperitoneal injection of streptozotocin (STZ) (50 mg/kg, freshly dissolved in 5 mmol/L citrate buffer, pH 4.5). Sham rats were administered with the vehicle. Seven days after STZ injection, all rats were implanted with an intrathecal (i.t) catheter connected to a mini-osmotic pump, divided into five groups, and infused with the following combinations: sham + saline (1 µL/h, i.t), DNP + saline (1 µL/h, i.t), DNP + MOR (15 µg/h, i.t), DNP + TEN (2 µg/h, i.t), and DNP + MOR (15 µg/h, i.t) + TEN (2 µg/h, i.t) for 7 days at a rate of 1 μL/h. The MAT was confirmed through the measurement of mechanical paw withdrawal threshold and tail-flick tests. The mRNA expression of neuroprotective proteins nuclear factor erythroid 2-related factor (Nrf2) and heme oxygenase-1 (HO-1) in the dorsal horn was evaluated by quantitative PCR (qPCR). Microglial cell activation and mononucleate cell infiltration in the spinal cord dorsal horn were assessed by immunofluorescence assay (IFA) and Western blotting (WB). The results showed that co-infusion of TEN with MOR significantly attenuated MAT in DNP rats through the restoration of neuroprotective proteins Nrf2 and HO-1 and suppression of microglial cell activation in the dorsal horn. Though TEN at a dose of 2 μg has mild antinociceptive effects, it is highly effective in limiting MAT.

Metformin prevents morphine-induced apoptosis in rats with diabetic neuropathy: a possible mechanism for attenuating morphine tolerance

Morphine is a drug of choice for the treatment of severe and chronic pain, but tolerance to the antinociceptive effect limits its use. The development of tolerance to morphine has recently been associated with neuronal apoptosis. In this study, our aim was to investigate the effects of metformin on morphine-induced neuronal apoptosis and antinociceptive tolerance in diabetic rats. Three days of cumulative dosing were administered to establish morphine tolerance in rats. The antinociceptive effects of metformin (50 mg/kg) and test dose of morphine (5 mg/kg) were considered at 30-min intervals by thermal antinociceptive tests. To induce diabetic neuropathy, streptozotocin (STZ, 65 mg/kg) was injected intraperitoneally. ELISA kits were used to measure caspase-3, bax, and bcl-2 levels from dorsal root ganglion (DRG) tissue. Semi-quantitative scoring system was used to evaluate apoptotic cells with the the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) method. The findings suggest that co-administration of metformin with morphine to diabetic rats showed a significant increase in antinociceptive effect compared to morphine alone. The antinociceptive tests indicated that metformin significantly attenuated morphine antinociceptive tolerance in diabetic rats. In addition, metformin decreased the levels of apoptotic proteins caspase 3 and Bax in DRG neurons, while significantly increased the levels of antiapoptotic Bcl-2. Semi-quantitative scoring showed that metformin provided a significant reduction in apoptotic cell counts in diabetic rats. These data revealed that metformin demonstrated antiapoptotic activity in diabetic rat DRG neurons and attenuated morphine tolerance. The antiapoptotic activity of metformin probably plays a significant role in reducing morphine tolerance.

The Relationship Between Pre-Operative Glycosylated Haemoglobin and Opioid Consumption After Caesarean Section in Women With Gestational Diabetes Mellitus

INTRODUCTION

Women with Gestational diabetes mellitus (GDM) had a higher need and consumption of analgesics than women without GDM. The preoperative level of HbA1c was associated with the postoperative consumption for analgesics in diabetic patients. This prospective observational study go further to investigate the relationship between the pre-operative HbA1c and the post-operative consumption for analgesics in women with GDM.

METHODS

Women with GDM and a singleton pregnancy undergoing elective cesarean section under combined spinal-epidural anaesthesia were divided into two groups based on pre-operative HbA1c: group HbA1c < 6% and group HbA1c ≥ 6%. Analgesics consumption, number of patient-controlled analgesia (PCA) compression, and pain scores in 6 hours and 24 hours post-operation were compared between the two groups. Then Pearson's correlation coefficient and a stepwise multivariate linear regression were performed to investigate possible independentpredictors of post-operative 24-hour sufentanil consumption.

RESULTS

Analgesics consumption was significantly lower (18.8 ± 0.4 vs 23.2 ± 4.3; 82.7 ± 2.4 vs 115.8 ± 17.4, P < 0.001), and number of PCA compressions was significantly less frequent (1 [1-2] vs 3 [1-5]; 5 [3-7] vs 7 [3-15], P < 0.001), and in group HbA1c < 6% than in group HbA1c ≥ 6% in 6 hours and 24 hours post-operation.The univariate analysis showed that sufentanil consumption at 24 hours post-operation was significantly related to pre-operative HbA1c (r = 0.338, P < 0.001) and parity (r = 0.184, P = 0.03) and was related to blood glucose management methods (r = 0.172, P = 0.043). Multivariate linear regression analysis showed that HbA1c was the independent factor related to post-operative 24-hour sufentanil consumption (adjusted r2 = 0.246, P < 0.001).

CONCLUSIONS

This study demonstrated that in pregnant women with GDM, the pre-operative HbA1c is independently related to the need for and consumption of analgesics in 24 hours after CS.

The effect of gestational diabetes mellitus on sufentanil consumption after cesarean section: a prospective cohort study

Background

Previous studies have shown that patients with long-term diabetes require more opioids after surgery than patients without diabetes. Gestational diabetes mellitus (GDM) normally only lasts for a brief period; nevertheless, its effect on sufentanil consumption after cesarean section is unknown.

Methods

This prospective cohort study included two groups: a GDM group (n = 32) and a matched non-GDM (NGDM) group (n = 32). All patients underwent routine combined spinal-epidural anesthesia for cesarean delivery. Sufentanil consumption through an intravenous patient-controlled analgesia (PCA) pump, the frequency of PCA requests, and visual analog scale (VAS) scores 6 and 24 h after surgery were compared between groups.

Results

Sufentanil consumption (μg) 6 h after surgery was higher in the GDM group than in the NGDM group (24.0 ± 6.6 vs 20.1 ± 5.7, P = 0.023). PCA was used more frequently 6 and 24 h after surgery by the GDM group than by the NGDM group (1[0–2] vs 0[0–1], P = 0.001; 6 [1–5] vs 3 [1, 2, 6–8], P = 0.001, respectively). The VAS score during activity 24 h after surgery was higher in the GDM group than in the NGDM group (5 [2, 3] vs 5 [1, 2], respectively, P = 0.03).

Conclusion

Pregnant women with GDM require more opioids during the immediate postoperative period after cesarean section than those without GDM.

Clinical trials registration

No. ChiCTR1800016014, ChenYang, May 6th 2018.

Orofacial sensory changes after streptozotocin-induced diabetes in rats

Peripheral neuropathy is a common complication of diabetes and is often accompanied by episodes of pain. There is evidence that diabetic neuropathy may affect the trigeminal nerve, altering the transmission of orofacial sensory information. Structural changes in the trigeminal ganglia may be involved in the development of these sensory alterations. Herein, we evaluate the development of orofacial sensory changes after streptozotocin-induced diabetes in rats, and their sensitivity to pregabalin and morphine treatments. Furthermore, stereological analysis of the trigeminal ganglia was performed. Diabetic rats showed similar responses to 1% formalin applied into the upper lip compared to normoglycemic rats on weeks 1, 2 and 4 after streptozotocin. Additionally, there was no difference in the facial mechanical threshold of normoglycemic and diabetic rats, on weeks 1 up to 5 after streptozotocin, while the paw mechanical threshold of diabetic rats was significantly reduced. In contrast, diabetic rats developed long-lasting orofacial heat and cold hyperalgesia. Moreover, stereological analyses revealed significant neuronal loss in the trigeminal ganglia of diabetic compared to normoglycemic rats. Pregabalin treatment (30mg/kg, p.o.) of diabetic rats resulted in marked and prolonged (up to 6h) reduction of heat and cold orofacial hyperalgesia. Likewise, morphine treatment (2.5mg/kg, s.c.) abolished orofacial heat and cold hyperalgesia, but its effect was significant only up to 1h after the administration. In conclusion, the results of the present study demonstrated that streptozotocin-treated rats developed long-lasting orofacial heat and cold hyperalgesia, which is more amenable to reduction by pregabalin than morphine.

Chronic treatment of silymarin improves hyperalgesia and motor nerve conduction velocity in diabetic neuropathic rat

The effect of chronic silymarin (SM) treatment on hyperalgesia, sciatic motor nerve conduction velocity (MNCV) and oxidative stress in streptozotocin (STZ)-diabetic neuropathic rat was evaluated. Rats were divided into control, diabetic, SM-treated control and diabetic, and sodium salisylate (SS)-treated control and diabetic. SM was administered daily at a dose of 100 mg/kg for two months. Finally, hyperalgesia and sciatic MNCV and oxidative stress markers were assessed. Diabetic rats showed a significant deficit in MNCV and markedly exhibited chemical and thermal hyperalgesia, indicating development of diabetic neuropathy. Antioxidant enzyme superoxide dismutase (SOD) level significantly reduced and malondialdehyde (MDA) level significantly increased in diabetic rats compared to control rats; SM treatment significantly ameliorated the alteration in MNCV, hyperalgesia, MDA level and antioxidant enzyme SOD in diabetic rats. These results clearly suggest the potential effect of SM in prevention and treatment of diabetic neuropathy.

Changes in the gene expression of specific G-protein subunits correlate with morphine insensitivity in streptozotocin-induced diabetic rats

Several animal and human studies have shown a decreased analgesic potency of morphine in diabetic subjects. Since G-protein subunits have an important role in morphine effects at the cellular level and the exact mechanism(s) of diabetes-induced morphine insensitivity has not been fully clarified yet, the present study was designed to determine the changes in the levels of G(alphai), G(alphas), G(beta) mRNAs and proteins involved in this phenomenon. All experiments were carried out on male Wistar rats. The tail-flick test was used to assess the nociceptive threshold. Diabetes was induced by injection of 50 mg/kg (i.p.) streptozotocin. Four weeks after diabetes induction, the dorsal half of the lumbar spinal cord was assayed for the expression of G-protein subunits using semiquantitative RT-PCR and immunoblotting. The antinociceptive effect of intrathecal morphine (5, 10 and 15 microg i.t.) was significantly reduced in diabetic rats and these effects were reversed with insulin replacement. In diabetic animals, a significant increase in the mRNA levels of G(alphai) (23.5%) was observed in the dorsal portion of the lumbar spinal cord. The mRNA level of G(alphas) and G(beta) did not change. Following diabetes a significant decrease in the protein levels of G(alphai) was induced. In contrast, no significant changes were observed in the protein level of G(alphas) and G(beta). In diabetic animals that received insulin, levels of G(alphai) mRNA and protein were close to those in control rats. In conclusion, our results demonstrate that the expression pattern of the cellular components involved in morphine analgesia changes in diabetic animals. This may be, at least partly, responsible for diabetes-induced morphine insensitivity.

The role of nitric oxide in diabetes-induced changes of morphine tolerance in rats

Several neuroendocrine complications including diabetes change the morphine antinociception and the development of tolerance to the drug. Morphine antinociception was reduced significantly in morphine tolerant diabetic rats compared to the non-diabetic animals. The exact mechanism of this effect is not known. This study was performed to determine the role of nitric oxide (NO) on morphine tolerance in diabetic state. Nociceptive responses in alloxan-induced diabetic morphine tolerated rats were measured by the hot-plate test. The urinary nitric oxide level was measured spectrophotometrically with Griess reagent. For the conversion of nitrate to nitrite, vanadium chloride was used. The results showed that experimental diabetes increased morphine analgesia. Conversely, degree of tolerance to morphine was diminished in diabetic state. The urinary nitrite content in diabetic morphine tolerated rats was higher than non-diabetic groups. L-arginine significantly increased the NO production in diabetic morphine tolerated animals, whereas aminoguanidine decreased it. Appropriately, L-arginine increased the latency time of reaction to noxious stimuli in diabetic compared to non-diabetic rats. L-arginine-treated animals also showed more tolerance to morphine analgesia. As expected, aminoguanidine deducted the level of morphine tolerance in diabetic animals. It is suggested that NO has a modulatory role in the effects of diabetes on morphine analgesia and tolerance.

Perioperative Nimodipine and Postoperative Analgesia

There is experimental evidence that nimodipine, an L-type dihydropiridine calcium channel blocker with relatively high blood-brain barrier penetration, enhances the antinociceptive properties of morphine. We tested the hypothesis that oral nimodipine taken preoperatively and 6 hourly for 48 h postoperatively would reduce visual analog scale pain scores and morphine consumption in morphine-naive patients with acute postoperative pain. Forty patients undergoing total knee replacement surgery (age 70 +/- 7 yr, 28 male) were randomized by computer-generated numbers to receive capsules containing either nimodipine 30 mg or placebo in a double-blind study design. All patients received 3 capsules (nimodipine 90 mg or placebo) 1-2 h before induction of anesthesia followed by oral nimodipine 30 mg or placebo 6 hourly for 48 hours postoperatively. Spinal anesthesia was induced with hyperbaric bupivacaine 0.5% (2.4-3.0 mL) and fluids and ephedrine were given at the discretion of the anesthesiologist. Morphine patient-controlled analgesia (PCA, bolus 1 mg, lockout 5 min) was given for postoperative analgesia. Primary outcome measures were visual analog pain scores at rest and on moving (sitting forward) and PCA morphine consumption. Morphine consumption was significantly larger in nimodipine patients at 12 h (39 +/- 18 versus 29 +/- 15; P = 0.04), 24 h (62 +/- 23 versus 45 +/- 24; P = 0.02), and 48 h (88 +/- 34 versus 61 +/- 27; P = 0.01). There were no significant differences in pain scores at rest or moving or in time to first use of morphine analgesia. This study has demonstrated increased morphine consumption after 12 h in postoperative patients receiving nimodipine, suggesting that, in patients undergoing knee replacement surgery, it has no adjunctive analgesic effect and may actually inhibit the analgesic effect of morphine.

Antinociceptive effect of Teucrium polium leaf extract in the diabetic rat formalin test

This study was designed to evaluate the analgesic effect of Teucrium polium leaf extract in the diabetic rat formalin test. For this purpose, streptozotocin (STZ)-diabetic rats received intraperitoneal injection of this extract (100 and 200 mg/kg per day) for a period of 2 weeks. It was found out that Teucrium polium-treated diabetic rats exhibited a lower nociceptive score as compared to untreated diabetics. The results may suggest therapeutic potential of Teucrium polium extract for the treatment of diabetic hyperalgesia.

The analgesic effect of morphine on postoperative pain in diabetic patients

BACKGROUND

Many clinical and experimental studies have suggested that diabetes or hyperglycemia alter opioid responsiveness. However, little information is available on the effects of diabetes mellitus on opioid requirements in the postoperative period.

METHODS

Sixty-four patients scheduled for elective, total abdominal hysterectomy were included into this prospective study to evaluate the effect of diabetes mellitus on morphine requirement in the postoperative period. A loading dose of morphine (50 micro g kg(-1)) was administered in the perioperative period. Postoperative analgesia consisted of intravenous morphine-PCA. No analgesic other than morphine was allowed during the study. In cases of inadequate analgesia intravenous 1 mg of morphine was given as a rescue analgesic. Cumulative morphine consumption, pain scores and morphine-related adverse effects were recorded.

RESULTS

A total of 60 patients were evaluated: Group D, 30; and Group ND, 30. Patients in Group D received more morphine than those in Group ND (54.12 +/- 25.09 and 42.66 +/- 20.67, respectively). The difference in cumulative morphine consumption was higher in the first hour (P = 0.037) in diabetic patients and they required significantly more morphine in the last 24 h (P = 0.015). Postoperative pain scores were higher in the diabetic group. More patients in the diabetic group required rescue medication (26 vs. 19) and felt nauseous (25 vs. 14; P = 0.003).

CONCLUSION

The findings of the study appear to support experimental and clinical impressions that the analgesic effect of morphine is attenuated in hyperglycemic conditions. Therefore, larger doses of morphine may be administered to diabetic patients for effective postoperative analgesia.

Reduction in [D-Ala2, NMePhe4, Gly-ol5]enkephalin-induced peripheral antinociception in diabetic rats: the role of the L-arginine/nitric oxide/cyclic guanosine monophosphate pathway

To test our hypothesis that the abnormally small efficacy of mu-opioid agonists in diabetic rats may be due to functional changes in the L-arginine/nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) pathway, we evaluated the effects of N-iminoethyl-L-ornithine, methylene blue, and 3-morpholino-sydnonimine on [D-Ala(2), NMePhe(4), Gly-ol(5)]enkephalin (DAMGO)-induced antinociception in both streptozotocin (STZ)-diabetic and nondiabetic rats. Animals were rendered diabetic by an injection of STZ (60 mg/kg intraperitoneally). Antinociception was evaluated by the formalin test. The mu-opioid receptor agonist DAMGO (1 microg per paw) suppressed the agitation response in the second phase. The antinociceptive effect of DAMGO in STZ-diabetic rats was significantly less than in nondiabetic rats. N-Iminoethyl-L-ornithine (100 microg per paw), an NO synthase inhibitor, or methylene blue (500 microg per paw), a guanylyl cyclase inhibitor, significantly decreased DAMGO-induced antinociception in both diabetic and nondiabetic rats. Furthermore, 3-morpholino-sydnonimine (200 microg per paw), an NO donor, enhanced the antinociceptive effect of DAMGO in nondiabetic rats but did not change in diabetic rats. These results suggest that the peripheral antinociceptive effect of DAMGO may result from activation of the L-arginine/NO/cGMP pathway and dysfunction of this pathway; also, events that are followed by cGMP activation may have contributed to the demonstrated poor antinociceptive response of diabetic rats to mu-opioid agonists.

IMPLICATIONS

This is the first study on the role of the nitric oxide (NO)/cyclic guanosine monophosphate pathway on [D-Ala(2), NMePhe(4), Gly-ol(5)]enkephalin (DAMGO)-induced peripheral antinociception and the effect of diabetes on this pathway. The study suggests a possible role of DAMGO as a peripherally-acting analgesic drug.

Regulation of dihydropyridine-sensitive Ca2+ channels during naloxone-induced opioid supersensitivity in rats

The Ca(2+) channel blocker, nimodipine, increases the chronic naltrexone-induced supersensitivity to morphine analgesia in mice without affecting the density of up-regulated mu-opioid receptors. In the present study, the change in dihydropyridine-sensitive Ca(2+) channels associated with chronic naloxone-induced supersensitivity to morphine analgesia was studied in rat whole-brain membranes using a radiolabeled Ca(2+) channel blocker, [3H]PN200-110 [isopropyl 4-(2,1,3-benzoxadiazol-4-yl)-1,4-dihydro-2,6-dimethyl-5-methoxycarbonylpyridine-3-carboxylate] (0.02-1.0 nmol/l). Rats were chronically treated with naloxone (1 mg/kg, i.p.), nimodipine (1 mg/kg, i.p.) or their respective vehicles twice daily for 10 days. On the 11th day, 16 h after the last injection of either nimodipine or naloxone, morphine (2 mg/kg, i.p.)-induced tail-flick analgesia was determined or rats were killed for the binding study. Chronic naloxone significantly potentiated (+84%) the morphine-induced analgesia. Chronic nimodipine also potentiated (+76%) morphine analgesia. In rats treated with nimodipine and naloxone, there was an additive increase (206%) in morphine analgesia. In binding studies, chronic naloxone resulted in a significant decrease (-39%) in the density (B(max)) of [3H]PN200-110 binding with no change in K(d) value when compared to the effect of chronic vehicle. Chronic nimodipine resulted in a slight but significant (+14.5%) increase in the B(max) of [3H]PN200-110. However, when nimodipine was co-administered with naloxone, it not only reversed the down-regulation but actually up-regulated (+25%) [3H]PN200-110 binding with no change in K(d) value. Our results show significant down-regulation of [3H]PN200-110 binding in association with naloxone-induced analgesic supersensitivity to morphine. The supersensitivity was also observed following chronic blockade of up-regulated Ca(2+) channels by nimodipine. These results indicate an important role of L-type Ca(2+) channel regulation in naloxone-induced analgesic supersensitivity to morphine.