Vertebral compression exacerbates osteoporotic pain in an ovariectomy-induced osteoporosis rat model

Characterization of neuropathic component of back pain in patients with osteoporotic vertebral fractures

BACKGROUND:

Osteoporotic vertebral fractures (OVFs) are often followed by chronic back pain which may have a nociceptive, neuropathic, or mixed component. However, literature on this topic is lacking.

OBJECTIVE:

The objective of this cross-sectional study is to characterize the neuropathic component of chronic back pain in patients with OVFs.

METHODS:

Spine fractures were detected by morphometric examination. Pain severity and its impact on activities of daily living (ADL) were evaluated through the Brief Pain Inventory (BPI). Neuropathic pain was investigated through the Italian versions of the Leeds Assessment of Neuropathic Symptoms and Signs pain scale (LANSS) and the painDETECT questionnaire (PD-Q).

RESULTS:

We included 72 patients, mainly women (88.8%), with mean age of 69.2 years. The 70.8% of patients had multiple OVFs, of which 47% located at the thoracic spine, 43.1% at the thoracic and at lumbar spine, and 9.8% at the lumbar spine. The BPI showed moderate back pain in 23.6% of cases and severe in 8.3% of cases, with high interference with ADL in 38.9% of patients. The PD-Q revealed the presence of neuropathic pain in 5.5% of cases, while the LANSS in 23.6% of cases.

CONCLUSIONS:

In our study, the prevalence of neuropathic component of chronic back pain ranged from 5.5% to 23.6%, according to PD-Q and LANSS respectively, in patients with OVFs. Further studies should investigate if the characterization of chronic back pain might contribute to appropriateness of interventions for this population.

A Multicenter, Randomized, Double-Blind, Placebo-Controlled Clinical Study of Jianyao Migu Granules in the Treatment of Osteopenic Low Back Pain

Purpose

This randomized controlled trial aimed to evaluate the clinical efficacy of Jianyao Migu granules (JYMGG) in the treatment of primary osteopenic low back pain (LBP).

Patients and Methods

A total of 108 patients with primary osteopenic LBP were randomly divided into the JYMGG group and placebo group. Both groups took 600 mg of oral Caltrate D daily; in addition, the JYMGG group was given oral JYMGG, while the placebo group was given placebo granules. The treatment period was 6 months for both groups. The pre- to post-treatment changes in the bone mineral density (BMD), visual analogue scale (VAS) score, Oswestry disability index (ODI), and bone turnover markers were compared between the two groups.

Results

The post-treatment VAS score and ODI were significantly lower than baseline in both groups (P<0.05). In the JYMGG group, the lumbar BMD increased from 0.88±0.07 g/cm2 to 0.90±0.13 g/cm2 and the hip BMD increased from 0.77±0.08 g/cm2 to 0.78±0.10 g/cm2, giving increases of 2.70% and 1.96% respectively, but the differences were not statistically significant. The post-treatment levels of ALP, osteocalcin, P1NP, and β-CTX were increased compared with baseline in both groups, but the differences were not statistically significant. The thyrotropin level was significantly increased after treatment in the placebo group (P<0.05). There were no abnormalities detected in routine blood and kidney function tests performed during the observation period. Some patients showed elevated liver enzymes and gastrointestinal reactions.

Conclusion

JYMGG effectively relieved the bone pain, and improved the quality of life of patients with primary osteopenic LBP.

Painful intervertebral disc degeneration and inflammation: from laboratory evidence to clinical interventions

Low back pain (LBP), as a leading cause of disability, is a common musculoskeletal disorder that results in major social and economic burdens. Recent research has identified inflammation and related signaling pathways as important factors in the onset and progression of disc degeneration, a significant contributor to LBP. Inflammatory mediators also play an indispensable role in discogenic LBP. The suppression of LBP is a primary goal of clinical practice but has not received enough attention in disc research studies. Here, an overview of the advances in inflammation-related pain in disc degeneration is provided, with a discussion on the role of inflammation in IVD degeneration and pain induction. Puncture models, mechanical models, and spontaneous models as the main animal models to study painful disc degeneration are discussed, and the underlying signaling pathways are summarized. Furthermore, potential drug candidates, either under laboratory investigation or undergoing clinical trials, to suppress discogenic LBP by eliminating inflammation are explored. We hope to attract more research interest to address inflammation and pain in IDD and contribute to promoting more translational research.

Percutaneously-quantified advanced glycation end-products (AGEs) accumulation associates with low back pain and lower extremity symptoms in middle-aged low back pain patients

Advanced glycation end-products (AGEs) have been reported as a possible biomarker of ageing and metabolic diseases; however, its role in the clinical progression of these diseases remains unclear. We aimed to evaluate how AGEs are associated with clinical symptoms and comorbidities in lower back pain (LBP) patients. This prospective cohort study enrolled 636 LBP patients. They were subjected to quantified AGE (qAGE) analysis using skin autofluorescence, and their clinical symptoms and comorbidities, such as diabetes, renal failure with haemodialysis treatment, and osteoporosis, were measured. LBP, lower extremity pain, and numbness were evaluated using a visual analogue scale (VAS). The measured qAGE was significantly higher in subjects with any comorbidity. Age also showed a strong positive correlation with qAGE. qAGE and VAS for leg numbness were positively correlated. Furthermore, in LBP patients under 50-years-old, qAGE was positively correlated with VAS for LBP, lower extremity pain, and numbness. In conclusion, qAGE, as measured by skin autofluorescence measurement, was significantly higher in LBP patients with diabetes and dialysis, as well as in osteoporosis patients. Furthermore, qAGE showed potential as a biomarker for LBP, lower extremity pain, and numbness in patients under 50-years-old. If accumulated AGEs are identified at a young age, researchers should be vigilant for the development of osteoporosis and LBP-related clinical symptoms later in life.

Tramadol enhances PGF2α-stimulated osteoprotegerin synthesis in osteoblasts

Osteoprotegerin (OPG) synthesized by osteoblasts is currently considered a crucial regulator to suppress the formation and function of osteoclasts. We previously showed that the synthesis of OPG is stimulated by prostaglandin F_2α (PGF_2α) in the involvement of p38 mitogen-activated protein kinase (MAPK), stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) and p44/p42 MAPK in osteoblast-like MC3T3-E1 cells. We also found that Rho-kinase is involved in the signaling of PGF_2α upstream of p38 MAPK in these cells. Tramadol is widely used to treat chronic pain, such as low back pain associated with osteoporosis. We investigated whether or not tramadol affects the OPG release induced by PGF_2α in osteoblast-like MC3T3-E1 cells. The levels of OPG in the conditioned medium were measured by an enzyme-linked immunosorbent assay. The mRNA expression of OPG was determined with real-time reverse transcription polymerase chain reaction. The phosphorylation of target protein was determined with a Western blot analysis. PGF_2α induced the release and the mRNA expression of OPG, which tramadol significantly enhanced. Morphine, a selective μ-opioid receptor (MOR) agonist, also enhanced the PGF_2α-induced OPG release. In addition, naloxone, a MOR antagonist, suppressed the enhancement by tramadol or morphine of the PGF_2α-induced OPG synthesis. Tramadol upregulated the phosphorylation of SAPK/JNK and p38 MAPK stimulated by PGF_2α but not that of p44/p42 MAPK or myosin phosphatase targeting protein (MYPT), a substrate of Rho-kinase. The inhibitors of both p38 MAPK and SAPK/JNK, SB203580 and SP600125, respectively, reduced the tramadol amplification of OPG release stimulated by PGF_2α. The present results strongly suggest that tramadol enhances the synthesis of OPG stimulated by PGF_2α through MOR in osteoblasts, and that the amplifying effect is exerted at upstream of p38 MAPK and SAPK/JNK but downstream of Rho-kinase.

A perspective from experimental studies of burning mouth syndrome

Burning mouth syndrome (BMS) is one of the most frequently seen idiopathic pain conditions in a dental setting. Peri- and postmenopausal women are most frequently affected, and patients who experience BMS complain of persistent burning pain mainly at the tip and the bilateral border of the tongue. Recent studies have assessed whether BMS is a neuropathic pain condition, based on morphologic changes in biopsied tongue specimens, and whether there are abnormal pain responses in patients with this disease. Somatosensory studies have reported some abnormal findings in sensory and pain detection thresholds with inconsistency; however, the most distinct finding was exaggerated responses to painful stimuli. Imaging and electrophysiologic studies have suggested the possibility of dysregulation of the pain-modulating system in the central nervous system, which may explain the enhanced pain responses despite the lack of typical responses toward quantitative sensory tests. Basic studies have suggested the possible involvement of neuroprotective steroids, although the underlying mechanisms of this condition have not been elucidated. Experimental studies are looking for preferable supportive therapies for BMS patients despite the obscure pathogenesis.

Anti-nerve growth factor therapy attenuates cutaneous hypersensitivity and musculoskeletal discomfort in mice with osteoporosis

Introduction

The prevalence of osteoporosis is increasing with the aging population and is associated with increased risk of fracture and chronic pain. Osteoporosis is currently treated with bisphosphonate therapy to attenuate bone loss. We previously reported that improvement in bone mineral density is not sufficient to reduce osteoporosis-related pain in an ovariectomy (OVX)-induced mouse model of osteoporosis, highlighting the need for new treatments. Targeting of nerve growth factor (NGF) with sequestering antibodies is a promising new direction for the treatment of musculoskeletal pain including back pain and arthritis. Its efficacy is currently unknown for osteoporotic pain.

Objective

To investigate the efficacy of anti-NGF antibody therapy on osteoporotic pain in an OVX-induced mouse model.

Methods

Ovariectomy- and sham-operated mice were injected with an anti-NGF antibody (10 mg/kg, intraperitoneally, administered 2×, 14 days apart), and the effect on behavioural indices of osteoporosis-related pain and on sensory neuron plasticity was evaluated.

Results

Treatment with anti-NGF antibodies attenuated OVX-induced hypersensitivity to mechanical, cold, and heat stimuli on the plantar surface of the hind paw. The OVX-induced impairment in grip force strength, used here as a measure of axial discomfort, was partially reversed by anti-NGF therapy. No changes were observed in the rotarod or open-field tests for overall motor function and activity. Finally, anti-NGF treatment attenuated the increase in calcitonin gene-related peptide-immunoreactive dorsal root ganglia neurons observed in OVX mice.

Conclusion

Taken together, these data suggest that anti-NGF antibodies may be useful in the treatment of prefracture hypersensitivity that is reported in 10% of patients with osteoporosis.

Osteoporotic Pain is Associated with Increased Transient Receptor Vanilloid 4 Expression in the Dorsal Root Ganglia of Ovariectomized Osteoporotic Rats: A Pilot Basic Study

INTRODUCTION

Osteoporosis can produce a persistent state of pain known as osteoporotic pain. One proposed mechanism of this pathology is increased calcitonin gene-related peptide (CGRP; a marker related to inflammatory pain) expression in the dorsal root ganglia (DRG) innervating osteoporotic vertebrae. Alternatively, a previous study revealed that axial loading caused osteoporotic pain in a rodent model of coccygeal vertebrae compression. Because this compression model is associated with trauma, additional mechanistic studies of osteoporotic pain in the absence of trauma are required. The current study aimedto evaluate the expression and relative distribution of transient receptor potential vanilloid 4 (TRPV4), a pain-related mechanoreceptor, in ovariectomized (OVX) osteoporotic rats.

METHODS

CGRP-immunoreactive (-ir) and TRPV4-ir DRG neurons innervating the L3 vertebrae of Sprague-Dawley rats were labeled with a neurotracer, FluoroGold. Intravertebral pH was also measured during the neurotracer procedure. TRPV4-ir/CGRP-ir FluoroGold-positive DRG neurons were quantified in sham control and OVX rats (n = 10, ea). The threshold for statistical significance was set at P < 0.05.

RESULTS

There was no statistical difference in the number of FluoroGold-positive DRG neurons between groups; however, there were significantly more CGRP-ir/TRPV4-ir FluoroGold-positive DRG neurons in the OVX group compared with the sham control group (P < 0.05) as well as the significantly increased molecular production of each peptide. Intravertebral pH was also lower in the OVX group compared with the sham control group (P < 0.05).

CONCLUSION

Sensory neurons innervating osteoporotic vertebrae exhibited increased expression of co-localized CGRP and TRPV4 in OVX osteoporotic rats. Additionally, intravertebral pH was low in the vicinity osteoporotic vertebrae. Considering that TRPV4 is a mechanosensitive nociceptor that is activated in acidic environments, its upregulation may be associated with the pathology of osteoporotic pain derived from microinflammation involved in osteoporosis.

Pathomechanisms and management of osteoporotic pain with no traumatic evidence

Introduction

Osteoporosis is a pathological state with an unbalanced bone metabolism mainly caused by accelerated osteoporotic osteoclast activity due to a postmenopausal estrogen deficiency, and it causes some kinds of pain, which can be divided into two types: traumatic pain due to a fragility fracture from impaired rigidity, and pain derived from an osteoporotic pathology without evidence of fracture. We aimed to review the concepts of osteoporosis-related pain and its management.

Methods

We reviewed clinical and basic articles on osteoporosis-related pain, especially with a focus on the mechanism of pain derived from an osteoporotic pathology (i.e., osteoporotic pain) and its pharmacological treatment.

Results

Osteoporosis-related pain tends to be robust and acute if it is due to fracture or collapse, whereas pathology-related osteoporotic pain is vague and dull. Non-traumatic osteoporotic pain can originate from an undetectable microfracture or structural change such as muscle fatigue in kyphotic patients. Furthermore, basic studies have shown that the osteoporotic state itself is related to pain or hyperalgesia with increased pain-related neuropeptide expression or acid-sensing channels in the local tissue and nervous system. Traditional treatment for osteoporotic pain potentially prevents possible fracture-induced pain by increasing bone mineral density and affecting related mediators such as osteoclasts and osteoblasts. The most common agent for osteoporotic pain management is a bisphosphonate. Other non-osteoporotic analgesic agents such as celecoxib have also been reported to have a suppressive effect on osteoporotic pain.

Conclusions

Osteoporotic pain has traumatic and non-traumatic factors. Anti-osteoporotic treatments are effective for osteoporotic pain, as they improve bone structure and the condition of the pain-related sensory nervous system. Physicians should always consider these matters when choosing a treatment strategy that would best benefit patients with osteoporotic pain.

The nature of osteoporotic low back pain without acute vertebral fracture: A prospective multicenter study on the analgesic effect of monthly minodronic acid hydrate

BACKGROUND

Patients with osteoporosis but no evidence of fracture can sometimes report low back pain. However, few studies have evaluated the nature of osteoporotic low back pain in a clinical situation. Therefore, the aim of this study was to examine the nature of osteoporotic low back pain without fracture, and the analgesic effect of minodronic acid hydrate on such pain.

METHODS

The current study examined 136 patients with osteoporotic low back pain and no lower extremity symptoms. The following factors were evaluated before and after minodronic acid hydrate administration: the nature of osteoporotic low back pain was evaluated using the painDETECT questionnaire, numeric rating scale (NRS) score for low back pain at rest and in motion, bone mineral density (BMD) of the lumbar spine, and the serum concentration of tartrate-resistant acid phosphatase 5b (TRACP-5b) as a bone metabolism marker.

RESULTS

A total of 113 patients were enrolled. The painDETECT questionnaire revealed the percentage of patients with nociceptive pain and neuropathic or mixed pain was approximately 85% and 15%, respectively. the average NRS scores for low back pain at rest decreased significantly 2 months after treatment (p = 0.01), while those in motion decreased significantly 1 month after treatment (p = 0.04). The average lumbar spine BMD tended to increase after treatment, but not significantly. On the other hand, the changes in the average serum concentration of TRACP-5b did significantly decrease 1 month after treatment. There was a significant positive correlation between the rate of NRS score improvement for low back pain at rest, and the rate of improvement in serum concentration of TRACP-5b (p < 0.05).

CONCLUSIONS

Osteoporotic low back pain consisted of 85% nociceptive pain and 15% neuropathic or mixed pain. The pain is strongly related to pain at rest rather than that in motion.

Behavioral signs of pain and functional impairment in a mouse model of osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a congenital disorder caused most often by dominant mutations in the COL1A1 or COL1A2 genes that encode the alpha chains of type I collagen. Severe forms of OI are associated with skeletal deformities and frequent fractures. Skeletal pain can occur acutely after fracture, but also arises chronically without preceding fractures. In this study we assessed OI-associated pain in the Col1a1Jrt/+ mouse, a recently developed model of severe dominant OI. Similar to severe OI in humans, this mouse has significant skeletal abnormalities and develops spontaneous fractures, joint dislocations and vertebral deformities. In this model, we investigated behavioral measures of pain and functional impairment. Significant hypersensitivity to mechanical, heat and cold stimuli, assessed by von Frey filaments, radiant heat paw withdrawal and the acetone tests, respectively, were observed in OI compared to control wildtype littermates. OI mice also displayed reduced motor activity in the running wheel and open field assays. Immunocytochemical analysis revealed no changes between OI and WT mice in innervation of the glabrous skin of the hindpaw or in expression of the pain-related neuropeptide calcitonin gene-related protein in sensory neurons. In contrast, increased sensitivity to mechanical and cold stimulation strongly correlated with the extent of skeletal deformities in OI mice. Thus, we demonstrated that the Col1a1Jrt/+ mouse model of severe OI has hypersensitivity to mechanical and thermal stimuli, consistent with a state of chronic pain.

Increase of TRPV1-immunoreactivity in dorsal root ganglia neurons innervating the femur in a rat model of osteoporosis

PURPOSE

Transient receptor potential vanilloid 1 (TRPV1) is a ligand-gated nonselective cation channel, which can be activated by capsaicin and other noxious stimuli. Recently, an association between bone pain and TRPV1 has been reported. However, the influence of osteoporosis on TRPV1 in the sensory system innervating the femur has not been reported.

MATERIALS AND METHODS

TRPV1-immunoreactive (ir) in dorsal root ganglia (DRG) neurons labeled with neurotracer [Fluoro-Gold (FG)] innervating the femurs of Sprague Dawley rats were examined in control, sham, and ovariectomized (OVX) rats. We evaluated osteoporosis in the femurs and compared the proportion of TRPV1-ir DRG neurons innervating femur between the 3 groups of rats.

RESULTS

OVX rats showed osteoporotic cancellous bone in the femur. FG labeled neurons were distributed from L1 to L6 DRG, but there was no significant difference in the proportion of labeled neurons between the 3 groups (p>0.05). The proportions of FG labeled TRPV1-ir DRG neurons were 1.7%, 1.7%, and 2.8% of DRG neurons innervating the femur, in control, sham-operated, and OVX rats, respectively. The proportion of TRPV1-ir neurons in DRG innervating the femur in OVX rats was significantly higher than that in control and sham-operated rats (p<0.05).

CONCLUSION

Under physiological conditions, DRG neurons innervating femurs in rats contain TRPV1. Osteoporosis increases the numbers of TRPV1-ir neurons in DRG innervating osteoporotic femurs in rats. These findings suggest that TRPV1 may have a role in sensory perception of osteoporotic femurs.

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.