Insulin, but Not Metformin, Supports Wound Healing Process in Rats with Streptozotocin-Induced Diabetes.

PURPOSE: Optimal glycemic control is crucial for proper wound healing in patients with diabetes. However, it is not clear whether other antidiabetic drugs support wound healing in mechanisms different from the normalization of blood glucose control. We assessed the effect of insulin and metformin administration on the wound healing process in rats with streptozotocin-induced diabetes. METHODS: The study was conducted on 200 male Wistar rats with streptozotocin-induced diabetes. In the last phase of the study, 45 rats, with the most stable glucose levels in the range of 350-500 mg/dL, were divided into three groups: group I received human non-protamine insulin subcutaneously (5 IU/kg body mass) once a day, group II received metformin intragastrically (500 mg/kg b.m.), and group III (control) was given saline subcutaneously. After 14 days of antidiabetic treatment, a 2 cm × 2 cm thin layer of skin was cut from each rat's dorsum and a 4 cm disk with a hole in its center was sewn in to stabilize the skin and standardize the healing process. The wound healing process was followed up for 9 days, with assessment every 3 days. Biopsy samples were subjected to hematoxylin and eosin staining and immunohistochemical assays. RESULTS: Analysis of variance revealed significant influence of treatment type (insulin, control, or metformin) on the relative change in wound surface area. The wound healing process in rats treated with insulin was more effective than in the metformin and control groups. Wound tissue samples taken from the insulin-treated animals presented significantly lower levels of inflammatory infiltration. Immunohistochemical assessment showed the greatest density of centers of proliferation Ki-67 in insulin-treated animals. CONCLUSION: These results suggest that an insulin-based treatment is more beneficial than metformin, in terms of accelerating the wound healing process in an animal model of streptozocin-induced diabetes.

Inhibitory effect of Ligustrum vulgare leaf extract on the development of neuropathic pain in a streptozotocin-induced rat model of diabetes.

BACKGROUND: Chronic hyperalgesia and allodynia associated with progressive damage of peripheral neurons are the most prevalent complications of diabetes mellitus. Plants belonging to the family of Oleaceae were traditionally used in folk medicine for the management of diabetes. HYPOTHESIS/PURPOSE: The aim of this study was to investigate whether an aqueous extract from the leaves of Ligustrum vulgare (common privet) could be useful to target neuropathic pain in a rat streptozotocin (STZ) model of diabetes. METHODS: The chemical composition of the aqueous extract from privet leaf was characterized with the UHPLC-DAD-MS method and the analytical quantification of its constituents was performed with HPLC-DAD. Mechanical hyperalgesia and allodynia were evaluated with the Randall-Selitto and von Frey tests. RESULTS: Our investigation revealed the presence of secoiridoids: oleacein (23.48 ±â€¯0.87 mg/g), oleocanthal (8.44 ±â€¯0.08 mg/g), oleuropein (1.50 ±â€¯0.01 mg/g), as well as phenylpropanoids: echinacoside (6.46 ±â€¯0.07 mg/g), verbascoside (4.03 ± 0.04 mg/g) and p-coumaroyl glucarates in the dried aqueous extract of privet leaves. Behavioral data indicated that chronic intraperitoneal administration of the extract (50-200 mg/kg) for 21 days resulted in a decrease in diabetes-induced hyperalgesia and allodynia. Blood glucose levels remained unaltered, while body weight and water intake decreased significantly. CONCLUSION: The aqueous privet leaf extract could serve useful in facilitating treatment of painful diabetic neuropathy. Additionally, the study showed that the antihyperalgesic activity of Ligustrum vulgare leaf extract is not likely related to its antihyperglycemic properties.

Esculetin reduces leukotriene B4 level in plasma of rats with adjuvant-induced arthritis.

OBJECTIVES: Esculetin (6,7-dihydroxycoumarin) is a natural coumarin with anti-oxidant, anti-inflammatory and anti-nociceptive activity. It acts as a potent inhibitor of lipoxygenases (5-LOX and 12-LOX) and decreases the production of matrix metalloproteinases (MMP-1, MMP-3 and MMP-9). Because both inhibition of lipoxygenases and inhibition of matrix metalloproteinases are effective strategies in the treatment of rheumatoid arthritis, we investigated whether esculetin may be effective in adjuvant-induced arthritis in rats. MATERIAL AND METHODS: The study was performed on male Lewis rats, in the adjuvant-induced arthritis model. Rats were divided into two groups: control (treated with 1% methylcellulose) and experimental (treated with esculetin - 10 mg/kg ip.). The tested compound was administered for 5 consecutive days starting on the 21st day after induction of arthritis. Each group consisted of 7 animals. After 5 days of treatment, rats were anesthetized. The concentration of leukotriene B4 (LTB4) in plasma was determined by a competitive enzyme immunoassay. RESULTS: The LTB4 level in plasma of rats with adjuvant-induced arthritis is increased in comparison to rats without inflammation (362 ±34 vs. 274 ±15 pg/ml, p < 0.01, respectively). Five-day treatment with esculetin in adjuvant-induced arthritis rats decreases the LTB4 level to a level comparable with rats without inflammation (284 ±23 pg/ml, p < 0.01). CONCLUSIONS: LTB4 is the most potent chemotactic agent influencing neutrophil migration into the joint. It is known that its level in serum of patients with active rheumatoid arthritis is increased and correlates with disease severity. Some other lipoxygenase inhibitors have already been tested as potential drug candidates in clinical and preclinical trials for rheumatoid arthritis (Zileuton, PF-4191834). Because esculetin decreases the LTB4 level in plasma of rats in adjuvant-induced arthritis, it may also be considered as an attractive drug candidate for patients with rheumatoid arthritis.

Micronized Organic Magnesium Salts Enhance Opioid Analgesia in Rats.

PURPOSE: As previously reported, magnesium sulphate administered parenterally significantly increased an opioid antinociception in different kinds of pain. Since the typical form of magnesium salts are poorly and slowly absorbed from the gastrointestinal tract we examined whether their micronized form could increase opioids induced antinociception. METHODS: In behavioural studies on rats morphine, tramadol and oxycodone together with magnesium (lactate dihydrate, hydroaspartate, chloride) in micronized (particles of size D90 < 50 µm) and conventional forms were used. Changes in pain thresholds were determined using mechanical stimuli. The intestinal absorption of two forms of magnesium lactate dihydrate (at the doses of 7.5 or 15 mg ions) in the porcine gut sac model were also compared. RESULTS: Micronized form of magnesium lactate dihydrate or hydroaspartate but not chloride (15 mg of magnesium ions kg-1) enhanced the analgesic activity of orally administered opioids, significantly faster and more effective in comparison to the conventional form of magnesium salts (about 40% for oxycodone administered together with a micronized form of magnesium hydroaspartate). Moreover, in vitro studies of transport across porcine intestines of magnesium ions showed that magnesium salts administered in micronized form were absorbed from the intestines to a greater extent than the normal form of magnesium salts. CONCLUSIONS: The co-administration of micronized magnesium organic salts with opioids increased their synergetic analgesic effect. This may suggest an innovative approach to the treatment of pain in clinical practice.

Antinociceptive properties of esculetin in non-inflammatory and inflammatory models of pain in rats.

Some studies suggest that 5-lipoxygenase (5-LOX) inhibition or leukotriene receptor antagonism may effectively attenuate different kinds of pain. In the present study, we investigated whether esculetin (which, among other actions, potently inhibits 5-LOX) possesses analgesic activity in acute non-inflammatory pain and acute inflammatory pain models in rats. We also examined the effects of zileuton, a selective 5-LOX inhibitor, on esculetin activity. Plasma concentrations of leukotriene B4 (LTB4 ) after administration of esculetin were also determined. Esculetin (1.25-20 mg/kg, i.p.) dose-dependently alleviated hyperalgesia and exhibited antinociceptive effects in both experimental models. The greatest effect of esculetin was observed with a dose of 20 mg/kg. In carrageenan-induced inflammatory pain in rats, 20 mg/kg esculetin reversed or mitigated hyperalgesia, increasing the threshold to mechanical stimuli from a control value of -23.8 ± 1.8% to 15.2 ± 2.2% (P < 0.01) and that to thermal stimuli from -52.5 ± 6.1% to -9.5 ± 3.9% (P < 0.01). In non-inflammatory pain, after esculetin (20 mg/kg) administration the threshold values to mechanical and thermal stimuli increased to 75.9 ± 4.2% and 59.2 ± 4.3%, respectively (P < 0.01 for both). Zileuton (30 mg/kg, p.o.) alone slightly but significantly increased the pain threshold in the non-inflammatory and inflammatory acute pain models. Pretreatment with 30 mg/kg, p.o., zileuton significantly enhanced the analgesic activity of 5 mg/kg, i.p., esculetin in both pain models. Moreover, esculetin (10 mg/kg, i.p.) decreased LTB4 concentrations in the blood from 244 ± 29 pg/mL in the control group to 185 ± 11 pg/mL (P < 0.005). The results of the present study suggest the involvement of the 5-LOX pathway in esculetin analgesia.

Tapentadol and nitric oxide synthase systems.

Tapentadol, a new analgesic drug with a dual mechanism of action (µ-opioid receptor agonism and norepinephrine reuptake inhibition), is indicated for the treatment of moderate to severe acute and chronic pain. In this paper, the possible additional involvement of the nitric oxide synthase (NOS) system in the antinociceptive activity of tapentadol was investigated using an unspecific inhibitor of NOS, L-NOArg, a relatively specific inhibitor of neuronal NOS, 7-NI, a relatively selective inhibitor of inducible NOS, L-NIL, and a potent inhibitor of endothelial NOS, L-NIO. Tapentadol (1-10 mg/kg, intraperitoneal) increased the threshold for mechanical (Randall-Selitto test) and thermal (tail-flick test) nociceptive stimuli in a dose-dependent manner. All four NOS inhibitors, administered intraperitoneally in the dose range 0.1-10 mg/kg, potentiated the analgesic action of tapentadol at a low dose of 2 mg/kg in both models of pain. We conclude that NOS systems participate in tapentadol analgesia.

Enhancement of antinociceptive effect of morphine by antidepressants in diabetic neuropathic pain model.

BACKGROUND: Recent studies have shown that influence of antidepressants on analgesic action of opioids is heterogeneous. The aim of this study was to investigate the effect of acute and repeated (21 days) antidepressant (amitriptyline, moclobemide and reboxetine) treatment on the antinociceptive action of morphine, an opioid agonist, in streptozotocin (STZ)-induced neuropathic pain model. METHODS: The studies were performed on the male Wistar rats. The changes in nociceptive thresholds were determined by using mechanical stimuli (the Randall-Selitto and the von Frey tests). Diabetes was induced by intramuscular administration of STZ. RESULTS: In this work we report that acute as well as repeated per os administration of antidepressants (amitriptyline, moclobemide and reboxetine) significantly potentiated the antihyperalgesic effect of morphine in STZ-induced neuropathic pain model. CONCLUSION: Combination therapy, such as classical antidepressants (amitriptyline, moclobemide) with opioids, or agents with noradrenaline reuptake inhibition and µ-opioid receptor activation could be a new target for research into treatment of painful diabetic neuropathy.

Dose-depending effect of intracerebroventricularly administered bradykinin on nociception in rats.

BACKGROUND: The effect of small and high doses of intracerebroventricularly (icv) applied bradykinin (BK) on nociception produced by mechanical stimuli and the participation of B1 and B2 receptors in this nociception were investigated in rats. RESULTS: BK at the lowest dose (0.06 µg) produced hyperalgesia whereas at the higher doses (6 and 12 µg) antinociception. This effect was abolished by B1 or B2 receptor antagonists, des-Arg(10)-HOE140 and HOE140 (1 pmol icv), respectively. CONCLUSION: Depending on the dose used, BK produces pro- or anti-nociceptive action. Both B1 and B2 receptors are involved in the action of icv applied BK.

Venlafaxine and neuropathic pain.

The possible mechanisms involved in the antinociceptive effect of venlafaxine (VFX), a selective serotonin and noradrenaline reuptake inhibitor, after a single administration and chronic treatment were investigated in a diabetic neuropathic pain (DNP) model. VFX produced a significant antihyperalgesic effect after a single and repeated administration. This effect was reversed by pretreatment with yohimbine (a relatively selective α(2)-adrenergic antagonist) and p-chloroamphetamine (a neurotoxin which destroys serotonergic neurons). Conversely, naloxone (a nonselective opioid antagonist) did not reverse the effect of VFX in a DNP model. It is concluded that both noradrenergic and serotonergic mechanisms participate in the antinociceptive effect of VFX in the DNP model. However, the noradrenergic mechanism probably plays a more important role.

Influence of acute and subchronic oral administration of dehydroepiandrosterone (DHEA) on nociceptive threshold in rats.

BACKGROUND: Dehydroepiandrosterone (DHEA), a neurosteroid, is known to be the most abundant hormone in the human body. Its role in the central nervous system has not been well defined. Previous studies indicate that DHEA is synthesized in the spinal cord and plays an important role in pain modulation. In the present study, we investigated the effect of DHEA on pain threshold in rats after both acute and subchronic treatment. METHOD: Rats were orally administered with DHEA at a dose of 10 mg/kg once daily and the pain threshold was measured with mechanical and thermal stimuli. RESULTS: After acute treatment, DHEA exhibited pronociceptive effects which lasted up to 150 min. After subchronic administration, DHEA showed an opposite effect by elevating the pain threshold. CONCLUSION: The results suggest that DHEA could be indicated as a drug to improve treatment of chronic pain disorders.