Ovariectomy-induced hyperalgesia and antinociceptive effect of elcatonin, a synthetic eel calcitonin

Estrogenic impregnation alters pain expression: analysis through functional neuropeptidomics in a surgical rat model of osteoarthritis

PURPOSE

Several observational studies suggest that estrogens could bias pain perception. To evaluate the influence of estrogenic impregnation on pain expression, a prospective, randomized, controlled, blinded study was conducted in a Sprague-Dawley rat model of surgically induced osteoarthritis (OA).

METHODS

Female rats were ovariectomized and pre-emptive 17β-estradiol (0.025 mg, 90-day release time) or placebo pellets were installed subcutaneously during the OVX procedures. Thirty-five days after, OA was surgically induced on both 17β-estradiol (OA-E) and placebo (OA-P) groups. Mechanical hypersensitivity was assessed by static weight-bearing (SWB) and paw withdrawal threshold (PWT) tests. Mass spectrometry coupled with high-performance liquid chromatography (HPLC-MS) was performed to quantify the spinal pronociceptive neuropeptides substance P (SP), calcitonin gene-related peptide (CGRP), bradykinin (BK), somatostatin (SST), and dynorphin-A (Dyn-A).

RESULTS

Compared to control, ovariectomized rats presented higher SP (P = 0.009) and CGRP (P = 0.017) concentrations. OA induction increased the spinal level of SP (+ 33%, P < 0.020) and decreased the release of BK (- 20%, (P < 0.037)). The OA-E rats at functional assessment put more % body weight on the affected hind limb than OA-P rats at D7 (P = 0.027) and D56 (P = 0.033), and showed higher PWT at D56 (P = 0.009), suggesting an analgesic and anti-allodynic effect of 17β-estradiol. Interestingly, the 17β-estradiol treatment counteracted the increase of spinal concentration of Dyn-A (P < 0.016) and CGRP (P < 0.018).

CONCLUSION

These results clearly indicate that 17β-estradiol interfers with the development of central sensitization and confirm that gender dimorphism should be considered when looking at pain evaluation.

The Effect of Lactobacillus gasseri BNR17 on Postmenopausal Symptoms in Ovariectomized Rats

Clinical and preclinical studies have reported that Lactobacillus gasseri BNR17, a probiotic bacterial strain isolated from human breast milk, reduces body weight and white adipose tissue volume. In order to further explore the actions of L. gasseri BNR17, we investigated the anti-menopausal effects of L. gasseri BNR17 in an ovariectomized (OVX) rat model. The serum alanine aminotransferase levels of the rats in the OVX-BNR17 group were lower than those of the rats in the OVX-vehicle only (OVX-Veh) group. Upon administration of L. gasseri BNR17 after ovariectomy, calcitonin and Serotonin 2A levels increased significantly, whereas serum osteocalcin levels showed a decreasing tendency. Compared to the rats in the OVX-Veh group, those in the OVX-BNR17 group showed lower urine deoxypyridinoline levels, lower pain sensitivity, and improved vaginal cornification. Furthermore, L. gasseri BNR17 administration increased bone mineral density in the rats with OVX-induced femoral bone loss. These results suggest that L. gasseri BNR17 administration could alleviate menopausal symptoms, indicating that this bacterium could be a good functional probiotic for managing the health of older women.

Teriparatide relieves ovariectomy-induced hyperalgesia in rats, suggesting the involvement of functional regulation in primary sensory neurons by PTH-mediated signaling

Clinical studies have reported that teriparatide (TPTD), a human parathyroid hormone analog, reduces back pain in osteoporotic patients. However, the mechanistic insights of this pharmacological action remain elusive. This study investigated the antinociceptive effect of TPTD mainly on primary sensory neurons in ovariectomized (OVX) rats. The plantar test showed thermal hyperalgesia in the OVX rats, which was significantly, but not fully, recovered immediately after the initial TPTD administration. The von Frey test also demonstrated reduced withdrawal threshold in the OVX rats. This was partially recovered by TPTD. Consistently, the number and size of spinal microglial cells were significantly increased in the OVX rats, while TPTD treatment significantly reduced the number but not size of these cells. RNA sequencing-based bioinformatics of the dorsal root ganglia (DRG) demonstrated that changes in neuro-protective and inflammatory genes were involved in the pharmacological effect of TPTD. Most neurons in the DRG expressed substantial levels of parathyroid hormone 1 receptor. TPTD treatment of the cultured DRG-derived neuronal cells reduced the cAMP level and augmented the intracellular calcium level as the concentration increased. These findings suggest that TPTD targets neuronal cells as well as bone cells to exert its pharmacological action.

Efficacy and safety of elcatonin in postmenopausal women with osteoporosis: a systematic review with network meta-analysis of randomized clinical trials

The present systematic review aimed to evaluate bone mineral density (BMD) change and complication rates of elcatonin on treating postmenopausal osteoporosis. The result confirmed efficacy of elcatonin and safety in combination therapies of elcatonin (C-E).

INTRODUCTION

Postmenopausal osteoporosis is an important issue in global aging trends. One treatment of osteoporosis is elcatonin, a kind of calcitonin. However, it has been challenged for long time because of safety. Many trials investigated on this topic, but they were designed differently. Those designs can be categorized in monotherapy of elcatonin (M-E) and C-E. Unfortunately, no synthesized evidence dealt this topic.

METHODS

This study systematically identified target trials from six important databases and only included randomized controlled trial for synthesis. Two investigators assessed quality of eligible trials using the Cochrane Risk of Bias Tool, and they independently extracted data. Network meta-analysis performed Peto odds ratio (POR, used for dealing with zero cell) or weighted mean difference (WMD, for continuous data) with 95% confidence intervals (CI) and consistency H.

RESULTS

Sixteen trials recruiting 2754 women with postmenopausal osteoporosis were included in our study. Elcatonin therapies and non-elcatonin medications had comparable fracture rates and bone mineral density change. Yet, C-E (WMD, - 18.93; 95% CI, - 23.97 to - 13.89) and M-E (WMD, - 13.72; 95% CI, - 19.51 to - 7.94) had significantly lower pain score than non-elcatonin medications. However, M-E (POR = 8.413, 95% CI, 2.031 to 34.859) and non-elcatonin medication (Peto OR, 7.450; 95% CI, 1.479 to 37.530) had significantly higher complication rates than placebo. No evidence detected inconsistency and small study effect in this network model.

CONCLUSIONS

Based on current evidence, C-E may be considered for treating postmenopausal osteoporosis because it benefits on pain relief and complications. Moreover, it shows comparable fracture rate and bone mineral density change as compared with anti-osteoporosis and calcium supplements. Nevertheless, further trials are needed to investigate formula and dosages of elcatonin.

A randomized, double-blind, placebo-controlled study of once weekly elcatonin in primary postmenopausal osteoporosis

OBJECTIVE

Very few reports have described changes in bone mineral density (BMD) with long-term, once weekly administration of elcatonin, and its effects in reducing incident fractures remain unverified. Therefore, the efficacy and safety of once weekly elcatonin were examined over a 3 year period.

METHODS

This was a multicenter, double-blinded, randomized, placebo-controlled study. Postmenopausal women with primary osteoporosis received either 20 units of elcatonin (EL group, n = 433) or placebo (P group, n = 436) once a week for 144 weeks (3 years) intramuscularly. The primary endpoint was the incidence of new vertebral fractures at 24, 48, 72, 96, 120, and 144 weeks after the start. Secondary endpoints were the incidence of non-vertebral fractures, changes in lumbar, hip total and femoral neck BMD, and the incidence of adverse drug reactions (ADRs).

RESULTS

No significant reduction in the incidence of new vertebral fractures was found in the EL group. The percentage increase in lumbar BMD was significantly higher in the EL group from 24 weeks to the last administration. Although the EL group showed tendencies toward smaller decreased hip total and femoral neck BMD, no significant differences were observed between groups. The incidence of ADRs was significantly greater in the EL group, although these have all been previously reported and no new safety concerns were identified.

CONCLUSIONS

Once weekly injection of 20 units of elcatonin significantly increased lumbar BMD over a 3 year period and did not cause any safety problems, but no significant reduction in the incidence of vertebral or non-vertebral fractures was demonstrated.

Analgesic effects of calcitonin on radicular pain in male rats

Purpose

Radicular pain is a frequently observed symptom of lumbar disk herniation or lumbar spinal canal stenosis. Achieving radicular pain relief is difficult. This type of pain may progress to chronic neuropathic pain. Calcitonin (elcatonin [eCT]) has been used mainly for hypercalcemia and pain associated with osteoporosis. The purpose of this study was to investigate analgesic effects of repeated eCT administration on radicular pain in male rats and changes in mRNA-expression levels of voltage-dependent sodium channels in the dorsal root ganglion (DRG).

Methods

Seventy male Sprague-Dawley rats were used. A right L5 hemilaminectomy and an L5-L6 partial facetectomy were performed to expose the right L5 nerve root. Under a microscope, the right L5 spinal nerve root was tightly ligated extradurally with 8-0 nylon suture proximally to the DRG to cause radicular pain in rats. Mechanical hyperalgesia, thermal hyperalgesia, and analgesic effects of eCT were compared among rats with radicular pain that received eCT, those that received the vehicle, and sham rats that received the vehicle. Real-time reverse-transcription PCR was performed to measure mRNA-expression levels of tetrodotoxin-sensitive (Na_V1.3 and Na_V1.6) and tetrodotoxin-resistant (Na_V1.8 and Na_V1.9) sodium channels in the DRG.

Results

Mechanical and thermal hyperalgesic reactions occurring in rats with radicular pain significantly improved on days 5 and 9 of eCT administration, respectively. In rats with radicular pain, mRNA-expression levels of Na_V1.3, Na_V1.8, and Na_V1.9 increased. After repeated eCT administration, mRNA-expression levels of these sodium channels in rats with radicular pain improved to the same levels as in sham rats.

Conclusion

The present study demonstrated that repeated systemic eCT administration was effective for radicular pain. No serious side effects of eCT have been reported thus far. Therefore, calcitonin may be a preferred therapeutic option for patients with radicular pain or for those requiring long-term treatment.

Mechanisms of the analgesic effect of calcitonin on chronic pain by alteration of receptor or channel expression

The polypeptide hormone calcitonin is well known clinically for its ability to relieve osteoporotic back pain and neuropathic pain such as spinal canal stenosis, diabetic neuropathy, chemotherapy-induced neuropathy, and complex regional pain syndrome. Because the analgesic effects of calcitonin have a broad range, the underlying mechanisms of pain relief by calcitonin are largely unknown. However, recent studies using several types of chronic pain models combined with various methods have been gradually clarifying the mechanism. Here, we review the mechanisms of the analgesic action of calcitonin on ovariectomy-induced osteoporotic and neuropathic pain. The analgesic action of calcitonin may be mediated by restoration of serotonin receptors that control selective glutamate release from C-afferent fibers in ovariectomized rats and by normalization of sodium channel expression in damaged peripheral nerves. Serotonin receptors are reduced or eliminated by the relatively rapid reduction in estrogen during the postmenopausal period, and damaged nerves exhibit hyperexcitability due to abnormal expression of Na⁺ channel subtypes. In addition, in chemotherapy-induced peripheral neuropathy, inhibition of signals related to transient receptor potential ankyrin-1 and melastatin-8 is proposed to participate in the anti-allodynic action of calcitonin. Further, an unknown calcitonin-dependent signal appears to be present in peripheral nervous tissues and may be activated by nerve injury, resulting in regulation of the excitability of primary afferents by control of sodium channel transcription in dorsal root ganglion neurons. The calcitonin signal in normal conditions may be non-functional because no target is present, and ovariectomy or nerve injury may induce a target. Moreover, it has been reported that calcitonin reduces serotonin transporter but increases serotonin receptor expression in the thalamus in ovariectomized rats. These data suggest that calcitonin could alleviate lower back pain in patients with osteoporosis or neuropathic pain by the alteration in receptor or channel expression.

Sarcopenia in elderly patients with chronic low back pain

Objectives

The prevalence of chronic low back pain (CLBP) increases with age and several mechanisms are involved in the development of CLBP, including osteoporosis; however, no associations with sarcopenia have yet been identified.

Methods

In total, 100 patients with CLBP and 560 patients without CLBP (nCLBP) aged over 65 years were studied. Skeletal muscle mass index (SMI) and percentage of body fat were evaluated using whole-body dual-energy X-ray absorptiometry. Sarcopenia was diagnosed when the relative SMI was more than 2 standard deviations below the mean in young adults. Thus, the cutoff value for sarcopenia was defined according to Sanada's Japanese population data. Paraspinal muscle cross-sectional areas of the lumbar multifidus and the erector spinae muscles were calculated using magnetic resonance imaging.

Results

Forty patients (40.0%) from the CLBP group and 149 (26.6%) from the nCLBP group met the criteria of sarcopenia. SMI was significantly lower and the body fat ratio was significantly higher in the CLBP group compared with the nCLBP group. Sarcopenic obesity was significantly observed in the CLBP group. Lumbar multifidus and the erector spinae muscle cross sectional area were significantly lower in the CLBP group.

Conclusions

Elderly patients with CLBP have significantly lower skeletal muscle mass, and age-related mechanisms in sarcopenia are considered to be associated with chronic pain. Therapeutic procedures that are used to treat elderly aging muscle, including muscle strengthening and performance training, can possibly be a treatment for or used to prevent elderly CLBP.

Effect of elcatonin versus nonsteroidal anti-inflammatory medications for acute back pain in patients with osteoporotic vertebral fracture: a multiclinic randomized controlled trial

The aim of this study was to compare the efficacy of elcatonin injections and oral nonsteroidal anti-inflammatory drugs (NSAIDs) for patients with osteoporosis who have acute lumbar pain after experiencing new vertebral compression fractures. Two hundred twenty-eight Japanese female patients (mean age 77.3 years) with acute lumbar pain from osteoporotic vertebral fractures were randomly divided into two groups. Patients in one group were given an NSAID (NSAIDs group) and patients in the other group were given weekly intramuscular injections of 20 units of elcatonin (elcatonin group). All patients underwent follow-up examinations up to 6 weeks from the start of the trial. Outcome measures were the level of functional impairment according to the Japan Questionnaire for Osteoporotic Pain (JQ22), the Roland-Morris Disability Questionnaire (RDQ), and a visual analog scale (VAS) of pain intensity. Statistical analyses focused on (1) the time course of pain and functional level using linear mixed effects models to analyze the longitudinal data and (2) the effectiveness of elcatonin injection with mean difference values and 95 % confidence intervals. Significant differences were seen over time between the initial values and the postintervention values (4 and 6 weeks) in JQ22, RDQ, and VAS scores (effect size d > 0.4) in each group. The mean differences between the elcatonin group and the NSAIDs group in each measure at 4 and 6 weeks were -4.8 and -8.3 for the JQ22, -1.3 and -2.6 for the RDQ, and -11.3 and -11.5 for the VAS, shifted to elcatonin. Once weekly elcatonin injection was more effective than NSAIDs for treating acute lumbar pain and improving mobility in Japanese women with osteoporotic vertebral fractures.

Chronic Osteoporotic Pain in Mice: Cutaneous and Deep Musculoskeletal Pain Are Partially Independent of Bone Resorption and Differentially Sensitive to Pharmacological Interventions

Although the pathological changes in osteoporotic bones are well established, the characterization of the osteoporotic pain and its appropriate treatment are not fully elucidated. We investigated the behavioral signs of cutaneous and deep musculoskeletal pain and physical function; time-dependent changes in bone mineral density (BMD) and the emergence of the behavioral phenotype; and the effects of pharmacological interventions having different mechanisms of action (chronic intraperitoneal administration of pamidronate [0.25 mg/kg, 5x/week for 5 weeks] versus acute treatment with intraperitoneal morphine [10 mg/kg] and pregabalin [100 mg/kg]) in a mouse model of ovariectomized or sham-operated mice 6 months following surgery. We observed reduced BMD associated with weight gain, referred cutaneous hypersensitivity, and deep musculoskeletal pain that persisted for 6 months. Chronic bisphosphonate treatment, 6 months after ovariectomy, reversed bone loss and hypersensitivity to cold, but other behavioral indices of osteoporotic pain were unchanged. While the efficacy of acute morphine on cutaneous pain was weak, pregabalin was highly effective; deep musculoskeletal pain was intractable. In conclusion, the reversal of bone loss alone is insufficient to manage pain in chronic osteoporosis. Additional treatments, both pharmacological and nonpharmacological, should be implemented to improve quality of life for osteoporosis patients.

Vasodilator Effects of Elcatonin, a Synthetic Eel Calcitonin, on Retinal Blood Vessels in Rats

The aim of this study was to examine the effects of elcatonin, a synthetic derivative of eel calcitonin, on rat retinal blood vessels, and to determine how diabetes affects the retinal vascular responses. Ocular fundus images were captured with an original high-resolution digital fundus camera in vivo. The retinal vascular responses were evaluated by measuring the diameter of retinal blood vessels contained in the digital images. Both systemic blood pressure and heart rate were continuously recorded. Elcatonin increased the diameter of retinal blood vessels but decreased mean blood pressure in a dose-dependent manner, whereas it had no significant effect on heart rate. A diminished retinal vasodilator response and significant pressor response to elcatonin were observed in rats injected intravenously with N(G)-nitro-L-arginine methyl ester, a nitric oxide (NO) synthase inhibitor. Intravitreal injection of indomethacin, a non-selective cyclooxygenase (COX) inhibitor, and SQ22536, an adenylyl cyclase inhibitor, markedly attenuated the vasodilator effects of elcatonin on retinal blood vessels. The retinal vasodilator responses to elcatonin were unaffected 2 weeks after the induction of diabetes by a combination of streptozotocin treatment and D-glucose feeding. These results suggest that elcatonin dilates rat retinal blood vessels via NO- and COX-dependent mechanisms and that the adenylyl cyclase-adenosine 3',5'-cyclic monophosphate system plays a major role in the vasodilator mechanisms. The retinal vasodilatory effects of elcatonin seem to be preserved at early stages of diabetes.

Calcitonin attenuates cartilage degeneration and nociception in an experimental rat model of osteoarthritis: role of TGF-β in chondrocytes

We investigated the role of the calcitonin (Miacalcin) in the progression of osteoarthritis (OA) and in nociceptive behavior in an experimental rat model of OA and osteoporosis. OA was induced by anterior cruciate ligament transection (ACLT) of the right knee and by bilateral ovariectomy (OVX) in Wistar rats. Nociceptive behaviors (secondary mechanical allodynia and weight-bearing distribution of the hind paws) were analyzed prior to surgery and every week, beginning at 12 weeks after surgery, up to 20 weeks. At 20 weeks, histopathological studies were performed on the cartilage of the knee joints. Immunohistochemical analysis was performed to examine the effect of calcitonin on transforming growth factor (TGF)-β1 expression in articular cartilage chondrocytes. Rats subjected to ACLT + OVX surgery showed obvious OA changes in the joints. Animals subjected to ACLT + OVX and treated with calcitonin showed significantly less cartilage degeneration and improved nociceptive tests compared with animals subjected to ACLT + OVX surgeries alone. Moreover, calcitonin increased TGF-β1 expression in chondrocytes in ACLT + OVX-affected cartilage. Subcutaneous injection of calcitonin (1) attenuated the development of OA, (2) concomitantly reduced nociception, and (3) modulated chondrocyte metabolism, possibly by increasing cellular TGF-β1 expression.

Elcatonin prevents bone loss caused by skeletal unloading by inhibiting preosteoclast fusion through the unloading-induced high expression of calcitonin receptors in bone marrow cells

This study aimed to clarify whether elcatonin (EL) has a preventive action on bone dynamics in skeletal unloading. Seven-week-old male C57BL/6J mice with either ground control (GC) or tail suspension (TS) were administered EL 20U/kg or a vehicle (veh) three times per week and assigned to one of the following four groups: GCEL, GCveh, TSEL, and TSveh. Blood samples and bilateral femurs and tibias of the mice were obtained for analysis. After 7days of unloading, the trabecular bone mineral density in the distal femur obtained via peripheral quantitative computed tomography and the trabecular bone volume were significantly higher in the TSEL group than in the TSveh group. The bone resorption histomorphometric parameters, such as the osteoclast surface and osteoclast number, were significantly suppressed in the TSEL mice, whereas the number of preosteoclasts was significantly increased. The plasma level of tartrate-resistant acid phosphatase-5b (TRACP-5b) was significantly lower in the TSEL group than in all other groups. In the bone marrow cell culture, the number of TRACP-positive (TRACP(+)) multinucleated cells was significantly lower in the TSEL mice than in the TSveh mice, whereas the number of TRACP(+) mononucleated cells was higher in the TSEL mice. On day 4, the expression of nuclear factor of activated T-cells, cytoplasmic, calcineurin-dependent 1 (NFATc1), cathepsin K and d2 isoform of vacuolar ATPase V0 domain (ATP6V0D2) mRNA in the bone marrow cells in the TSEL mice was suppressed, and the expression of calcitonin receptor (Calcr) mRNA on day 1 and Calcr antigen on day 4 were significantly higher in the TSveh mice than in the GCveh mice. EL prevented the unloading-induced bone loss associated with the high expression of Calcr in the bone marrow cells of mouse hindlimbs after tail suspension, and it suppressed osteoclast development from preosteoclasts to mature osteoclasts through bone-resorbing activity. This study of EL-treated unloaded mice provides the first in vivo evidence of a physiological role of EL in the inhibition of the differentiation process from preosteoclasts to osteoclasts.

Management of chronic pain in osteoporosis: challenges and solutions

Osteoporosis (OP) is a pathological condition that manifests clinically as pain, fractures, and physical disability, resulting in the loss of independence and the need for long-term care. Chronic pain is a multidimensional experience with sensory, affective, and cognitive aspects. Age can affect each of these dimensions and the pain that is experienced. In OP, chronic pain appears to have sensory characteristics and properties of nociceptive and neuropathic pain. Its evaluation and treatment thus require a holistic approach that focuses on the specific characteristics of this population. Pain management must therefore include pharmacological approaches, physiotherapy interventions, educational measures, and, in rare cases, surgical treatment. Most rehabilitative treatments in the management of patients with OP do not evaluate pain or physical function, and there is no consensus on the effects of rehabilitation therapy on back pain or quality of life in women with OP. Pharmacological treatment of pain in patients with OP is usually insufficient. The management of chronic pain in patients with OP is complicated with regard to its diagnosis, the search for reversible secondary causes, the efficacy and duration of oral bisphosphonates, and the function of calcium and vitamin D. The aim of this review is to discuss the most appropriate solutions in the management of chronic pain in OP.

Bone mineral density is not associated with musculoskeletal pain in postmenopausal Korean women aged ≥50 years

Although many studies reported improvement of back pain after osteoporosis treatment, there is insufficient evidence to determine whether osteoporosis is painful. We investigated whether bone mineral density correlated with musculoskeletal pain in postmenopausal Korean women aged ≥50 years. Data for postmenopausal women aged ≥50 years were obtained from the fifth Korea National Health and Nutrition Examination Survey database. Demographics, Kellgren-Lawrence grade, and numeric rating scale for pain in the hip and knee joints, presence of back pain, and activity level were analyzed. Only subjects with dual-energy X-ray absorptiometry scans and hip and knee radiographs were included. Those with malignancy, pain medication use, or a history of fragility fractures were excluded. After univariate analysis, multiple linear regression analysis was performed to examine the significant factors correlated with the degree of hip and knee pain. Binary logistic regression analysis was performed to identify factors significantly associated with the presence of back pain. In total, 387 women were included in the data analysis. Age (p = 0.005) was the only significant factor correlated with the intensity of hip pain, while Kellgren-Lawrence grade (p < 0.001) was the only significant factor correlated with knee pain intensity in multiple regression analysis. Binary logistic regression analysis showed that age (p = 0.002) was the only significant factor associated with the presence of back pain. Musculoskeletal pain was not affected by or associated with the bone mineral density (BMD) of the affected body part in postmenopausal Korean women aged ≥50 years after adjusting for the degree of osteoarthritis.

Effect of synthetic eel calcitonin, elcatonin, on cold and mechanical allodynia induced by oxaliplatin and paclitaxel in rats

Oxaliplatin and paclitaxel are commonly used anti-cancer drugs, but they frequently cause peripheral neuropathic pain. In this study, we investigated the effect of elcatonin, a synthetic eel calcitonin, on oxaliplatin- and paclitaxel-induced neuropathy in rats. The rats were treated with a single dose of oxaliplatin (6 mg/kg, i.p.) or repeated doses of paclitaxel (2 mg/kg, i.p.) on 4 alternate days. Both treatments resulted in cold and mechanical allodynia. We assessed the anti-allodynic effects of subcutaneously administered elcatonin (20 U/kg/day) by using a newly developed method to provide cold stimulation (8°C) directly to the hind paw of the rats and by using the von Frey test. Elcatonin almost completely reversed the effects of both cold and mechanical allodynia. To determine the mechanism of this anti-allodynic effect, we examined the effect of elcatonin on neuropathy induced by intraplantar injection of two organic compounds: allyl isothiocyanate (1 nmol/paw), which activates transient receptor potential ankyrin-1 channels, and menthol (1.28 μmol/paw), which activates transient receptor potential ankyrin-1 and melastatin-8. Pre-administration of elcatonin almost completely prevented cold and mechanical allodynia from being induced by both compounds. These results suggest that elcatonin attenuates oxaliplatin- and paclitaxel-induced neuropathic pain by inhibiting the cellular signaling related to transient receptor potential ankyrin-1 and melastatin-8. Thus, we conclude that administration of elcatonin may improve the quality of life of cancer patients receiving chemotherapy.

Anti-hyperalgesic effects of calcitonin on neuropathic pain interacting with its peripheral receptors

Background

The polypeptide hormone calcitonin is clinically well known for its ability to relieve neuropathic pain such as spinal canal stenosis, diabetic neuropathy and complex regional pain syndrome. Mechanisms for its analgesic effect, however, remain unclear. Here we investigated the mechanism of anti-hyperalgesic action of calcitonin in a neuropathic pain model in rats.

Results

Subcutaneous injection of elcatonin, a synthetic derivative of eel calcitonin, relieved hyperalgesia induced by chronic constriction injury (CCI). Real-time reverse transcriptase-polymerase chain reaction analysis revealed that the CCI provoked the upregulation of tetrodotoxin (TTX)-sensitive Nav.1.3 mRNA and downregulation of TTX-resistant Nav1.8 and Nav1.9 mRNA on the ipsilateral dorsal root ganglion (DRG), which would consequently increase the excitability of peripheral nerves. These changes were reversed by elcatonin. In addition, the gene expression of the calcitonin receptor and binding site of ¹²⁵I-calcitonin was increased at the constricted peripheral nerve tissue but not at the DRG. The anti-hyperalgesic effect and normalization of sodium channel mRNA by elcatonin was parallel to the change of the calcitonin receptor expression. Elcatonin, however, did not affect the sensitivity of nociception or gene expression of sodium channel, while it suppressed calcitonin receptor mRNA under normal conditions.

Conclusions

These results suggest that the anti-hyperalgesic action of calcitonin on CCI rats could be attributable to the normalization of the sodium channel expression, which might be exerted by an unknown signal produced at the peripheral nerve tissue but not by DRG neurons through the activation of the calcitonin receptor. Calcitonin signals were silent in the normal condition and nerve injury may be one of triggers for conversion of a silent to an active signal.

Alendronate is more effective than elcatonin in improving pain and quality of life in postmenopausal women with osteoporosis

A randomized controlled trial was performed to compare the short-term effects of alendronate (ALN) and ECT on pain and quality of life (QOL) in postmenopausal women with osteoporosis. Back pain and QOL [Short-Form Health Survey (SF-8)] significantly improved at 1, 3, and 6 months in both groups, with greater improvements in the ALN group than in the ECT group. These results suggested that ALN reduced back pain and improved QOL more markedly than ECT in postmenopausal osteoporotic women with back pain.

INTRODUCTION

Intramuscular ECT is known to reduce pain via the central nervous system. A multicenter randomized controlled trial was performed to compare the short-term effects of ALN and ECT on pain and QOL in postmenopausal women with osteoporosis.

METHODS

One hundred and 94 postmenopausal osteoporotic women with back pain (mean age 79.8 years, range 60-96 years) were randomly divided into two groups: the ALN group (35 mg weekly) and the ECT group (intramuscular 20 units a week). The duration of the study was 6 months. The trial was completed in 97 (100%) women of the ALN group and 96 (99.0%) women of the ECT group. Urinary levels of cross-linked N-terminal telopeptide of type I collagen (NTX), serum alkaline phosphatase (ALP), face scale score (FSS, back pain), and SF-8 (QOL) were monitored.

RESULTS

Urinary NTX levels significantly decreased at 3 months in the ALN group, but not in the ECT group. Serum ALP levels significantly decreased at 6 months in the both groups, with a greater reduction in the ALN group. The FSS and SF-8 significantly improved at 1, 3, and 6 months in both groups, with greater improvements in the ALN group than in the ECT group.

CONCLUSIONS

ALN suppressed bone turnover, reduced back pain, and improved QOL more markedly than ECT in postmenopausal osteoporotic women with back pain.

Blocking TNF-α with infliximab alleviates ovariectomy induced mechanical and thermal hyperalgesia in rats

Studies have proved an increased expression of tumor necrosis factor alpha (TNF-α) in estrogen deficiency animals, and TNF-α also plays a role in inflammation and neuropathic pain. This study aimed to explore the relationship between TNF-α and ovariectomy induced hyperalgesia. 36 female Sparague-Dawley were included, estrogen depletion models were established by ovariectomy. Then infliximab (a TNF-α blocker) was administrated to the ovariectomized rats for 8 weeks. Pain behavioral tests were performed once a week. The bone mineral density (BMD), serum estradiol and TNF-α level were determined at the 8th week after ovariectomy. The expression of TNF-α in lumbar 5 dorsal root ganglions (L5 DRGs) was examined by immunofluorescence method. Significant hyperalgesia to mechanical and thermal stimuli in groups Ovx-1 and Ovx-2 was observed 1 week after the operation. After treated with infliximab, the pain threshold of Ovx-2 was partially restored, although still lower than the Sham group. The serum TNF-α level of Ovx-1 was significantly higher than Sham and Ovx-2. TNF-α immunofluorescence indicated a significant increase in the expression of TNF-α at L5 DRGs in group Ovx-1 when compared with groups Sham and Ovx-2. The BMD of group Ovx-2 was significantly higher than group Ovx-1 and lower than group Sham. In conclusion, TNF-α plays an important role in estrogen deficiency induced mechanical and thermal hyperalgesia, and DRG may be one site on which TNF-α acts to cause hyperalgesia. Blocking the effect of TNF-α could partially alleviate the estrogen deficiency induced hyperalgesia in rats. Thus, TNF-α may contribute to chronic pain in postmenopausal women.

Effects of short-term combined treatment with alendronate and elcatonin on bone mineral density and bone turnover in postmenopausal women with osteoporosis

The antiresorptive drug elcatonin (ECT) is known to relieve pain in postmenopausal women with osteoporosis. A prospective open-labeled trial was conducted to compare the effects of short-term combined treatment with alendronate (ALN) and ECT on bone mineral density (BMD) and bone turnover with those of single treatment with ALN in postmenopausal women with osteoporosis. Two hundred and five postmenopausal osteoporotic women (mean age: 70 years) were recruited in our outpatient clinic. Forty-six women with back pain were treated with ALN and ECT (intramuscular, 20 units a week), and 159 women without obvious back pain were treated with ALN alone. The lumbar BMD, urinary levels of cross-linked N-terminal telopeptides of type I collagen (NTX), and serum levels of alkaline phosphatase (ALP) were measured during the six-month treatment period. The baseline characteristics, except for age, body weight and number of patients with prevalent vertebral fractures, were not significantly different between the two groups. The mean increase rate in the lumbar BMD at six months was similar in the ALN (+4.41%) and ALN+ECT (+5.15%) groups, following similar reduction rates in urinary NTX levels (-40.2% and -43.0%, respectively, at three months) and serum ALP levels (-19.0% and -19.7%, respectively, at six months). These results were consistent even after adjustments for age, body weight, and number of patients with prevalent vertebral fractures. The present study in postmenopausal osteoporotic women confirmed that the effects of short-term combined treatment with ALN and ECT on lumbar BMD and bone turnover in patients with back pain appeared to be comparable to those of single treatment with ALN in patients without obvious back pain.

Estrogen-dependent changes in visceral afferent sensitivity

Many forms of chronic pain are more prevalent in women and this is interpreted as the consequence of a direct role of estrogens in the modulation of pain perception. Some functional pain states, i.e. those without a clear and demonstrable pathology, are also more prevalent in women and the pain in these conditions is also modulated by hormonal variations during the menstrual cycle. Increased pain sensitivity is commonly interpreted as the consequence of peripheral or central hyperexcitability of nociceptive pathways. Therefore a role has been suggested for estrogen in the modulation of the excitability of nociceptive afferents and central neurons. The literature on the sign of this modulation is not uniform, with reports pointing to estrogen as either pro- or anti-nociceptive. In our hands, a permanent reduction in the levels of estrogen, such as that induced by surgical ovariectomy (OVX) generates a hyperalgesic state of slow onset and long duration that can be prevented or reversed by exogenous administration of estrogen. The hyperalgesia is characterized by mechanical and thermal hyperalgesia in the abdominal and pelvic regions as well as by visceral hypersensitivity. The possible role of estrogen in the prevention of chronic painful states is discussed.

An immunohistochemical study of the antinociceptive effect of calcitonin in ovariectomized rats

BACKGROUND

Calcitonin is used as a treatment to reduce the blood calcium concentration in hypercalcemia and to improve bone mass in osteoporosis. An analgesic effect of calcitonin has been observed and reported in clinical situations. Ovariectomized (OVX) rats exhibit the same hormonal changes as observed in humans with osteoporosis and are an animal model of postmenopausal osteoporosis. The aim of this study to investigate antinociceptive effect of calcitonin in OVX rats using the immunohistochemical study.

METHODS

We assessed the antinociceptive effects of calcitonin in an ovariectomized (OVX) rat model, which exhibit osteoporosis and hyperalgesia, using the immunohistochemical method. Fifteen rats were ovariectomized bilaterally, and ten rats were received the same surgery expected for ovariectomy as a sham model. We used five groups: the OVX-CT (n = 5), the sham-CT (n = 5), and the OVX-CT-pcpa (n = 5) groups received calcitonin (CT: 4 U/kg/day), while OVX-vehi (n = 5) and the sham-vehi (n = 5) groups received vehicle subcutaneously 5 times a week for 4 weeks. The OVX-CT-pcpa-group was given traperitoneal injection of p-chlorophenylalanine (pcpa; an inhibitor of serotonin biosynthesis) (100 mg/kg/day) in the last 3 days of calcitonin injection. Two hours after 5% formalin (0.05 ml) subcutaneously into the hind paw, the L5 spinal cord were removed and the number of Fos-immunoreactive (ir) neurons were evaluated using the Mann-Whitney-U test.

RESULTS

The numbers of Fos-ir neurons in the OVX-CT and sham-CT groups were significantly less than in the OVX-vehi and sham-vehi groups, respectively (p = 0.0090, p = 0.0090). The number of Fos-ir neurons in the OVX-CT-pcpa-group was significantly more than that of the OVX-CT-group (p = 0.0283), which means pcpa inhibits calcitonin induced reduction of c-Fos production.

CONCLUSION

The results in this study demonstrated that 1) the increase of c-Fos might be related to hyperalgesia in OVX-rats. 2) Calcitonin has an antinociceptive effect in both OVX and sham rats. 3) The central serotonergic system is involved in the antinociceptive properties of calcitonin.

Efficacy and safety of alendronate and risedronate for postmenopausal osteoporosis

INTRODUCTION

This paper discusses the efficacy and safety of alendronate and risedronate in the treatment of postmenopausal osteoporosis.

METHODS

The literature was searched with the PubMed from 1996 to the present, with respect to strictly conducted systematic reviews with homogeneity, meta-analyses with homogeneity, and randomized controlled trials (RCTs) with narrow Confidence Interval.

RESULTS

According to the results of large randomized controlled trials (RCTs), bisphosphonates (alendronate, risedronate, and ibandronate), raloxifene, calcitonin, parathyroid hormone (PTH), and strontium ranelate effectively prevent vertebral fractures in postmenopausal women with osteoporosis. Because raloxifene has been shown to be effective in preventing the initial vertebral fracture in postmenopausal osteoporotic women without prevalent vertebral fractures, it is considered in the treatment of postmenopausal women with mild osteoporosis or osteopenia with some risk factors for fractures. RCTs have also demonstrated that alendronate, risedronate, PTH, and strontium are useful to prevent non-vertebral fractures and that alendronate and risedronate prevent hip fractures, thus alendronate or risedronate are primarily considered as the first-line drugs in the treatment of elderly women with osteoporosis having some risk factors for falls. While it has been suggested that PTH may be considered in patients with severe osteoporosis, the use of PTH in the treatment for osteoporosis is limited to 2 years or less, and it may be appropriate to use other anti-resorptive drugs after the completion of PTH treatment to maintain the skeletal effects gained during the treatment. RCTs have demonstrated that the incidence of gastrointestinal tract adverse events in postmenopausal osteoporotic women treated with bisphosphonates and placebo are similar, and also the long-term efficacy and safety of alendronate and risedronate.

CONCLUSION

The evidence derived from the literature, based on strict evidence-based medicine guidelines, suggests that there is long-term efficacy and safety with alendronate and risedronate in the treatment of osteoporosis in postmenopausal women.

Estrogen-dependent abdominal hyperalgesia induced by ovariectomy in adult mice: A model of functional abdominal pain

Some abdominal pain syndromes are characterized by persistent pain without demonstrable pathology. Many of them are prevalent in women and it is known that sex hormones are associated with differences in pain perception between males and females. To model a process of functional abdominal pain in females we studied the time course and estrogen dependency of a hyperalgesic state induced by ovariectomy in adult mice. Three groups of C57/BL6 mice were used: virgin mice, proven breeders (2 or 3 successful pregnancies) and retired breeders (more than three successful pregnancies). Within each group, a third of the mice were ovariectomized (OVX), a third received sham surgery and a third were controls. OVX mice, but not sham or controls, developed a robust mechanical hyperalgesia and allodynia in the abdomen, hindlimbs and proximal tail, but not in the forelimbs, that was established 4 weeks after OVX and lasted for the 7 weeks of the experiment. Increases in visceral sensitivity were also observed in OVX mice. Thermal pain thresholds (hot plate) remained unchanged. The reproductive history of the animals had no influence on the hyperalgesia. In another series of experiments a slow release pellet containing 17beta-estradiol was implanted in half of the OVX mice and a similar pellet without the hormone in the other half. Hormone replacement prevented the development of hyperalgesia in OVX animals but did not stop the involution of the internal reproductive organs. We conclude that OVX in mice provides a useful model for a hormonally dependent hyperalgesic state resembling functional pain.

Administration of estrogen shortly after ovariectomy mimics the anti-nociceptive action and change in 5-HT1A-like receptor expression induced by calcitonin in ovariectomized rats

Although many clinical reviews are consistent with the view that hormone replacement therapy should be recommended for increasing bone mass of osteoporotic patients, calcitonin administration is preferable to hormone replacement therapy for the alleviation of pain accompanying osteoporosis, despite the fact that osteoporosis and the accompanying pain are accelerated by the reduction in estrogen levels. Distinct from the clinical view, animal studies have shown that estrogen treatment reduces ovariectomy-induced hyperalgesia, although the mechanism of this phenomenon is unknown. The discrepancy in clinical and animal study outcomes may be due to the timing of administration of estrogen after depletion of the hormone. To address this possibility, the anti-nociceptive effect of estrogen was compared with calcitonin using the tail withdrawal test in rats injected with estrogen or calcitonin at 3 weeks (short term) or 15 weeks (long term) after ovariectomy. Furthermore, we analyzed the change in [3H]8-OH-DPAT binding in the spinal cord, addressing whether estrogen exerts its anti-nociceptive effect by the expression of 5-HT receptors attributable to calcitonin-induced analgesia, as has been reported in our previous animal studies. The present study demonstrates that the administration of estrogen injected in the short term, but not long term, after ovariectomy mimicked the effects of calcitonin-induced anti-nociception and prevention of ovariectomy-induced decrease in 5-HT receptor expression in the spinal cord, although the effects of calcitonin were observed regardless of the timing of calcitonin injection. These results suggest that the estrogen receptor is downregulated gradually after ovariectomy. Disappearance of the estrogen receptor may be one of the reasons that estrogen is not recommended for the treatment for chronic pain associated with osteoporosis.

Mechanisms for ovariectomy-induced hyperalgesia and its relief by calcitonin: participation of 5-HT1A-like receptor on C-afferent terminals in substantia gelatinosa of the rat spinal cord

Chronic treatment with calcitonin in osteoporotic patients alleviates the pain associated with this condition by an unknown mechanism. In ovariectomized rats that develop osteoporosis and hyperalgesia, we examined whether a functional change in serotonergic systems in the spinal dorsal horn was involved, using whole-cell recordings from substantia gelatinosa neurons in spinal cord slices and [(3)H]8-hydroxy-2(di-n-propylamino)tetralin ([(3)H]8-OH-DPAT) binding. Hyperalgesia could be attributed to the elimination of presynaptic inhibition by 5-HT of glutamatergic primary C-afferent terminals and an associated decrease in the density of [(3)H]8-OH-DPAT binding sites whose receptors are neither 5-HT(1A)- nor 5-HT(7)-subtype. These changes in serotonergic systems were restored after chronic treatment with calcitonin. Reversal of 5-HT receptor changes by calcitonin treatment may provide an explanation for its analgesic actions in patients.