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Behavioral and pharmacological characteristics of bortezomib-induced peripheral neuropathy in rats
Shota Yamamoto a, Takehiro Kawashiri b, Hitomi Higuchi a, Kuniaki Tsutsumi a, Soichiro Ushio a, Takanori Kaname b, Masafumi Shirahama b, Nobuaki Egashira a'b' *
a Department of Clinical Pharmacology and Biopharmaceutics, Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
b Department of Pharmacy, Kyushu University Hospital, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
ARTICLE INFO
Article history: Received 8 May 2015 Received in revised form 3 August 2015 Accepted 19 August 2015 Available online 29 August 2015
Keywords: Allodynia
Bortezomib-induced
neuropathy
Duloxetine
Pregabalin
Tramadol
ABSTRACT
Bortezomib, an effective anticancer drug for multiple myeloma, often causes peripheral neuropathy which is mainly characterized by numbness and painful paresthesia. Nevertheless, there is no effective strategy to escape or treat bortezomib-induced peripheral neuropathy (BIPN), because we have understood few mechanism of this side effect. In this study, we evaluated behavioral and pathological characteristics of BIPN, and investigated pharmacological efficacy of various analgesic drugs and adjuvants on mechanical allodynia induced by bortezomib treatment in rats. The repeated administration of borte-zomib induced mechanical and cold allodynia. There was axonal degeneration of sciatic nerve behind these neuropathic symptoms. Furthermore, the exposure to bortezomib shortened neurite length in PC12 cells. Finally, the result of evaluation of anti-allodynic potency, oral administration of tramadol (10 mg/ kg), pregabalin (3 mg/kg), duloxetine (30 mg/kg) or mexiletine (100 mg/kg), but not amitriptyline or diclofenac, transiently relieved the mechanical allodynia induced by bortezomib. These results suggest that axonal degeneration of the sciatic nerve is involved in BIPN and that some analgesic drugs and adjuvants are effective in the relief of painful neuropathy.
© 2015 Japanese Pharmacological Society. Production and hosting by Elsevier B.V. on behalf of Japanese Pharmacological Society. This is an open access article under the CC BY-NC-ND license (http://
creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction
Bortezomib is a proteasome inhibitor widely used in chemotherapy to treat multiple myeloma. A side effect of bortezomib is that it often causes severe peripheral neuropathy and is therefore dose limiting. Bortezomib-induced peripheral neuropathy (BIPN) occurs in 35—52% of patients (grade >3 in 8—14% of patients) and is mainly characterized by hypoesthesia and painful paresthesia (1—3). At present, the mechanism of BIPN is not well understood and there is no established method to treat it. Thus, the development of peripheral neuropathy is an important issue in bortezomib chemotherapy.
We previously reported that other anticancer drugs such as paclitaxel and oxaliplatin induce pain symptoms that are characteristic of neuropathy including mechanical allodynia associated
* Corresponding author. Department of Pharmacy, Kyushu University Hospital, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan. Tel.: +81 92 642 5920; fax: +81 92 642 5937.
E-mail address: n-egashi@pharm.med.kyushu-u.ac.jp (N. Egashira). Peer review under responsibility of Japanese Pharmacological Society.
with axonal degeneration of the sciatic nerve in rats (4,5). These anticancer drugs also inhibited neurite outgrowth in cultured rat pheochromocytoma 12 (PC12) and rat dorsal root ganglion (DRG) cells. Furthermore, we reported that neurotropin, which attenuated the inhibition of neurite outgrowth in these cultured cells, ameliorated neuropathy induced by these anticancer drugs (4,5). Our findings indicate that axonal degeneration in the sciatic nerve is involved in mechanical allodynia induced by paclitaxel and oxaliplatin, and that the effect on neurite outgrowth has the potential to affect axonal degeneration in sciatic nerve.
It has been reported that administration of bortezomib induces mechanical and cold allodynia and pathological changes in sciatic nerve and DRG in rodents (6—9). Recently, it has been revealed a part of mechanisms of BIPN such as changes the expression of tumor necrosis factor-a (TNF-a), transient receptor potential vanilloid 1 (TRPV1), calcitonin gene-related peptide (CGRP), and substance P in DRG neurons, and the contributions of peroxynitrite, and altered discharges of spinal neurons (10—14). Furthermore, bortezomib-induced mechanical allodynia is inhibited by gabapentin in mice (15). However, the effects of various analgesic drugs or adjuvants,
http://dx.doi.org/10.1016/j.jphs.2015.08.006
1347-8613/© 2015 Japanese Pharmacological Society. Production and hosting by Elsevier B.V. on behalf of Japanese Pharmacological Society. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
which approved for use in clinical practice, on pain behaviors in animal models of BIPN have been not well studied.
In this study, we developed an animal model of BIPN, and consequently characterized pain behaviors and pathological changes. In addition, we investigated the effect of bortezomib on neurite length in cultured PC12 cells for adequacy evaluation of bortezomib-induced neurotoxicity. Finally, we evaluated the pharmacological efficacy of various analgesic drugs and adjuvants on painful neuropathy.
2. Materials and methods
2.1. Animals
Male Sprague—Dawley rats weighing 200—250 g (Kyudo Co., Tosu) were housed in groups of four to five per cage, with lights on from 7:00 to 19:00 h. Animals had free access to food and water in their home cages. All experiments were approved by the Experimental Animal Care and Use Committee of Kyushu University according to the National Institutes of Health guidelines, and we followed the International Association for the Study of Pain Committee for Research and Ethical Issues guidelines for animal research (16).
2.2. Drugs
Bortezomib was purchased from LC Laboratories (Woburn, MA, USA). Tramadol hydrochloride and mexiletine hydrochloride were purchased from Sigma—Aldrich, Inc. (St. Louis, MO, USA). Pre-gabalin, duloxetine hydrochloride, amitriptyline, and diclofenac sodium were obtained from Pfizer Inc. (New York, NY, USA), Tokyo Chemical Industry Co., Ltd. (Tokyo), LKT Laboratories, Inc. (St. Paul, MN, USA), and Novartis International AG (St. Johann, Basel, Switzerland), respectively. Bortezomib was dissolved in 5% dimethyl sulfoxide (DMSO, Sigma—Aldrich, Inc.) solution. Bortezomib (0.05, 0.1, or 0.2 mg/kg) or vehicle (5% DMSO solution) was administered intraperitoneally (i.p.) twice a week for 2 weeks (on days 1, 4, 8, and 11). The administration schedule and doses of bortezomib were determined based on clinical treatment (1.3 mg/ m2 of bortezomib on days 1, 4, 8, and 11). Tramadol, amitriptyline, and mexiletine were dissolved in sterile water. Pregabalin, dulox-etine, and diclofenac were suspended in 0.25% sodium carboxy-methylcellulose (CMC-Na) solution. The volume of vehicle or drug solution injected was 1 mL/kg.
2.3. Behavioral studies
2.3.1. Rota-rod test
Rota-rod test was performed to investigate the change in motor coordination. Rats were placed on a rotating rod (Mur-omachi Kikai Co., Ltd., Tokyo) and the latency to falling was measured for up to 2 min according to the method described previously (17). The test was performed three times, and the rotating speed was 10 rpm.
2.3.2. von Frey test
Mechanical allodynia was assessed by the von Frey test. Each rat was placed in a clear plastic box with a wire mesh floor and allowed to habituate for 30 min prior to testing. von Frey filaments (The Touch Test Sensory Evaluator Set; Linton Instrumentation, Diss, Norfolk, UK) with a range of 1—15 g bending force were applied to the mid-plantar skin of each hind paw six times, with each application held for 6 s. The paw withdrawal threshold was determined by a modified up-down method (4).
2.3.3. Acetone test
Cold allodynia was assessed by the acetone test. Each rat was placed in a clear plastic box and allowed to habituate for 30 min prior to testing. Fifty microliters of acetone (Wako Pure Chemical Industries, Ltd., Osaka) was sprayed onto the plantar skin of each hind paw, and the number of withdrawal responses was counted for 40 s from the start of the acetone spray according to the method described previously (18). The test was performed six times (three times per hind limb).
2.3.4. Hot-plate test
Thermal hyperalgesia was assessed using a hot-plate test. Each rat was placed on a hot/cold-plate apparatus (Ugo Basile Biological Research Apparatus, Gemonio, Varese, Italy), and the latency to licking their hind paw was measured for up to 60 s. The temperature of the hot-plate was kept at 52.5 °C (19). The test was performed three times.
2.4. Drug evaluation
Mechanical allodynia was confirmed on days 12—15 and drug evaluation was carried out the next day. Tramadol, pregabalin, duloxetine, amitriptyline, mexiletine, and diclofenac were administered orally through a stainless steel gavage tube. Control rats were injected with the drug vehicle. For tramadol and diclofenac,
(A) Body weight
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- Bortezomib 0.20 mg/kg
1 8 Bortezomib ft t T
15 Day
(B) Rota-rod test
Vehicle
0.20 mg/kg
Bortezomib
Fig. 1. Effects of bortezomib on body weight (A) and motor coordination (B) in rats. Bortezomib (0.05, 0.1, or 0.2 mg/kg) was administered i.p. twice a week for 2 weeks. Body weight was measured on days 1—5, 8—12,15—19, and 22—25. The rota-rod test was performed on day 15. Results are expressed as mean ± SEM of 10 rats.
(A) von Frey test (mechanical allodynia)
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the von Frey test was performed every 30 min after drug administration. For pregabalin, duloxetine, amitriptyline and mexiletine, the von Frey test was performed every 60 min after drug administration. Each evaluation was continued until the effects disappeared. The doses and measurement times of these drugs were chosen based on previous reports (20—24).
2.5. Toluidine blue staining for sciatic nerves
On day 15, sciatic nerves were harvested from rats anesthetized with isoflurane (Mylan, Inc., Canonsburg, PA, USA). Nerves were immersed in a fixative containing 2% glutaraldehyde at 4 °C for 4 h followed by washing with 0.1 M phosphate buffer. After 8% sucrose-substitution, samples were embedded in Epon and sliced, and then stained with toluidine blue. Sample sections were evaluated by light microscopy (BX51; Olympus, Tokyo), and analyzed using ImageJ software version 1.36 (Wayne Rasband, National Institutes of Health, Bethesda, MD, USA). The g-ratio, myelin sheath thickness and axonal diameter were analyzed in three fields of each sample section from three animals of both groups. The area and circularity were analyzed in six fields of each sample section from three animals of both groups.
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2.6. Cell culture
PC12 cells were obtained from RIKEN (Saitama). The cells were grown in Dulbecco's modified Eagle's medium (MP Biomedicals, Inc., Santa Ana, CA, USA) supplemented with 100 unit/mL penicillin, 100 mg/mL streptomycin, 2 mM L-glutamine, 10% horse serum, and 10% fetal bovine serum (GIBCO BRL, Grand Island, NY, USA). The cells were cultured at 37 °C in air supplemented with 5% CO2 under humidified conditions.
2.7. WST-8 assay
Cell viability was assessed by mitochondrial activity measured by the reduction of 2-(2-methoxy-4-nitrophenyl)-3-(4-nitro phenyl)-5-(2, 4-disulfophenyl)-2H-tetrazolium monosodium salt (WST-8) to formazan. Twenty-four hours prior to bortezomib treatment, PC12 cells were seeded onto 24-well plates with 50 ng/ mL recombinant rat b-nerve growth factor (NGF, R&D Systems, Inc., Minneapolis, MN, USA). The cells were treated with borte-zomib, and then washed with phosphate buffer saline (PBS) and incubated with 210 mL serum-free medium and 10 mL WST-8 assay solution (Cell Counting Kit-8; Dojindo, Kumamoto) for 2 h at 37 °C in humidified air supplemented with 5% CO2. The incubation medium was carefully removed and transferred to 96-well plates. The amount of formazan formed was measured from the absorbance at 450 nm with a reference wavelength of 620 nm using a microplate reader (Immuno-Mini NJ-2300; Inter Medical, Tokyo).
2.8. Assay of PC12 neurite length
PC12 cells were seeded onto 96-well plates with 50 ng/mL NGF 72—96 h prior to bortezomib treatment. The cells were treated with bortezomib, and then washed with PBS and fixed with 4% para-formaldehyde for 15 min at room temperature. Cells were blocked in PBS containing 5% bovine serum albumin (BSA, Sigma—Aldrich, Inc.) for 30 min at room temperature. Acti-stain 488 phalloidin
Fig. 2. Effects of bortezomib on mechanical allodynia (A), cold allodynia (B), and thermal hyperalgesia (C) in rats. Bortezomib (0.05, 0.1, or 0.2 mg/kg) was administered i.p. twice a week for 2 weeks. The von Frey, acetone, and hot-plate (52.5 °C) tests
were performed before the first drug administration and on days 4,8,11,15,18, and 25. Results are expressed as mean ± SEM of 10—15 rats. *P < 0.05, **P < 0.01 compared with vehicle.
(Cytoskeleton, Inc., Denver, CO, USA), which binds to F-actin, was diluted (1:1000) with PBS containing 5% BSA and 0.1% Triton X-100 and placed on the cells overnight at 4 °C. After washing with PBS, cells were mounted in 80% glycerol. The nucleus was stained with 4',6-Diamidino-2-phenylindole dihydrochloride (DAPI; Dojindo). F-actin and nuclear staining were visualized using ImageXpress Micro XL (Molecular Devices, LLC, Sunnyvale, CA, USA), and neurite length was measured by analysis software (MetaXpress; Molecular Devices, LLC).
2.9. Statistical analysis
Data are expressed as the mean ± SEM. Data were analyzed using the Student's t-test or one-way analysis of variance followed by the Dunnett's post hoc test to determine differences between the groups. A probability level of P < 0.05 was accepted as statistically significant.
3. Results
3.1. Effects of bortezomib on body weight and motor coordination in rats
all groups in any of the von Frey, acetone, or hot-plate tests (Fig. 2). Bortezomib at a dose of 0.2 mg/kg significantly decreased the withdrawal threshold on days 11 and 15 (P < 0.05; Fig. 2A) and increased the number of withdrawal responses on days 11 and 15 (day 11: P < 0.01, day 15: P < 0.05; Fig. 2B) compared with the vehicle group in the von Frey and acetone tests. Conversely, bor-tezomib did not affect the latency to licking at any time in the hotplate test (Fig. 2C).
3.3. Histopathology of the sciatic nerve in vehicle and bortezomib-treated rats
No histological abnormalities in the sciatic nerve were observed in vehicle-treated rats (Fig. 3A). However, bortezomib (0.2 mg/kg, i.p.) induced the degeneration of myelinated fibers in the rat sciatic nerve (Fig. 3B). The circularity of fibers, a quantitative index of degeneration, was significantly decreased in bortezomib-treated rats compared with vehicle-treated rats (P < 0.05; Table 1). There were no significant differences in axonal area, axonal diameter, myelin sheath thickness, and g-ratio (the ratio of axon diameter to total fiber diameter) (Fig. 3C).
Treatment with bortezomib showed no observable change and no rats died during the course of the experiment. Compared with the vehicle group, no significant difference in body weight and motor coordination was observed at any time in the bortezomib-treated groups (Fig. 1).
3.2. Effects of bortezomib on mechanical allodynia, cold allodynia, and thermal hyperalgesia in rats
Prior to the first bortezomib injection, there were no significant differences in reactivity to mechanical, cold, and thermal stimuli in
3.4. Effects of bortezomib on cell viability and neurite length in PC12 cells
No histological abnormalities were observed in vehicle-treated PC12 cells (Fig. 4A). The exposure to bortezomib (30 and 300 nM) for 6,12, or 24 h time dependently shortened the length of neurites in cultured PC12 cells (6 h: P < 0.05,12 and 24 h: P < 0.01; Fig. 4B and D). Moreover, the exposure to bortezomib (30 and 300 nM) for 12 or 24 h significantly decreased the cell viability of cultured PC12 cells (30 nM, 12 h: P < 0.05, 24 h: P < 0.01, 300 nM, 12 and 24 h: P < 0.01; Fig. 4C).
Fig. 3. Histopathology of sciatic nerve in rats treated with vehicle (A) and bortezomib (B). (A, B) Bortezomib (0.2 mg/kg) was administered i.p. twice a week for 2 weeks. On day 15, sciatic nerve was harvested, and samples were stained with toluidine blue. Photographs were originally magnified 1200 x. Scale bar, 25 mm. (C) Each diameter and axonal perimeter were measured for calculating g-ratio and circularity. Other parameters were measured as follows. Area; axonal area, axonal diameter; average of d1 and d2, myelin sheath thickness; half of (average of (Di and D2) minus axonal diameter).
Table 1
Histopathology of sciatic nerve in rats treated with vehicle and bortezomib.
Vehicle Bortezomib 0.2 mg/kg
Area (mm2) 11.5 z t 0.17 9.14 t 1.26
Axonal diameter (mm) 4.81 z t 0.26 4.18 t 0.23
Circularity 0.74 z 0.01 0.64 t 0.03*
Myelin sheath thickness (mm) 1.07 z 0.06 1.04 0.01
G-ratio 0.69 z 0.01 0.67 0.01
*P < 0.05 compared with vehicle.
3.5. Effects of tramadol, pregabalin, duloxetine, amitriptyline, mexiletine, and diclofenac on bortezomib-induced mechanical allodynia
Bortezomib (0.2 mg/kg, i.p.) significantly reduced the paw withdrawal threshold in the von Frey test compared with vehicle (P < 0.01; Fig. 5). Tramadol (10 mg/kg, per os (p.o.)), duloxetine (30 mg/kg, p.o.), and mexiletine (100 mg/kg, p.o.) significantly reversed the reduction of paw withdrawal threshold by bortezomib at 60 min after administration in the von Frey test (P < 0.01; Fig. 5A, C, and E). These effects disappeared 120—240 min after bortezomib administration. Similarly, pregabalin (3 mg/kg, p.o.) significantly reversed the reduction of paw withdrawal threshold by bortezomib
at 120 and 180 min after administration in the von Frey test (120 min: P < 0.05: P < 0.01; Fig. 5B). At 300 min after administration this effect of pregabalin had disappeared. Conversely, amitriptyline and diclofenac did not affect the reduction of paw withdrawal threshold by bortezomib in the von Frey test (Fig. 5D and F).
4. Discussion
In the present study, we observed mechanical and cold allody-nia, but not thermal hyperalgesia after bortezomib administration, which is consistent with previous reports (7,9), and there was no deterioration in general status. In addition, there was no difference in change of body weight or motor coordination among the four groups. It is unlikely that bortezomib-induced mechanical and cold allodynia are due to changes in body weight, impairment of motor coordination, or deterioration in general status and the present model is characterized by both sensory neuropathies (mechanical and cold allodynia).
In this study, we observed bortezomib (0.2 mg/kg, i.p.) induced degeneration of myelinated fibers in the rat sciatic nerve. In fact, there was a significant decrease of circularity in the sciatic nerve in bortezomib-treated rats, indicating that bortezomib induced
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* Bortezomib 3 nM ■— Bortezomib 30 nM 120 |- —■— Bortezomib 300 nM
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Fig. 4. Effects of bortezomib on cell viability and neurite outgrowth in PC12 cells. Control (0.2% DMSO) (A) or bortezomib (300 nM) (B) was exposed to PC12 cells for 24 h. The nucleus was stained with DAPI. F-actin and nucleus were visualized by ImageXpress Micro XL. Photographs were originally magnified 600 x. Scale bar, 50 mm. The cell viabilities (C) were measured using WST-8 assay. The neurite lengths (D) were measured by analysis software (MetaXpress). PC12 cells were incubated with bortezomib (3, 30 or 300 nM) for 3—24 h. Results are expressed as mean ± SEM of four experiments. *P < 0.05, **P < 0.01 compared with control.
(A) von Frey test / Tramadol (В) von Frey test / Preqabalin
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Fig. 5. Effects of tramadol (A), pregabalin (B), duloxetine (C), amitriptyline (D), mexiletine (E) and diclofenac (F) on bortezomib-induced mechanical allodynia. Rats were treated with bortezomib (0.2 mg/kg, i.p.) twice a week for 2 weeks. We confirmed the incidence of mechanical allodynia on days 12—15. Tramadol, pregabalin, duloxetine, amitriptyline, mexiletine, and diclofenac were administered orally. Results are expresses as mean ± SEM of 6—10 rats. **P < 0.01 compared with vehicle, yP < 0.05, ||P < 0.01 compared with control.
axonal degeneration. There were no significant differences in axonal area, axonal diameter, myelin sheath thickness, and g-ratio. Moreover, we did not observe a change in the number of activating transcription factor 3 (ATF-3) positive neurons in DRG neurons (data not shown). Because ATF-3 is a standard marker of neuronal injury (25), our animal model simulates a neuropathy model that induces axonal degeneration but not neuronal injury. Some studies have reported pathological changes in myelinated and
unmyelinated axons, mitochondria and endoplasmic reticulum in Schwann cells in the sciatic nerve of bortezomib-induced neuropathy models, and axonal transport dysfunction in primary cultured DRG cells (6,7,26—29). Additionally, a recent study showed that bortezomib induced upregulation of ATF-3 in the nuclei of DRG neurons (8). These studies indicate neuronal injury induced by bortezomib and these differences may be attributed to the administration schedule of bortezomib, which was short term in
the model used in the present study. Moreover, we found that exposure to bortezomib shortened neurite length before decreasing cell viability in cultured PC12 cells. Therefore, bortezomib may induce axonal degeneration in the sciatic nerve before inducing neuronal injury in the long term. In general, axonal degeneration is known to be responsible for symptoms of neuropathy including allodynia and hyperalgesia (5,30). Taken together, our results suggest axonal degeneration is involved in the bortezomib-induced neuropathy in early phase, and that bortezomib induces axonal degeneration prior to neuronal injury.
Our data indicated single administration of tramadol (10 mg/kg) and duloxetine (30 mg/kg) had anti-allodynic effects on bortezomib-induced mechanical allodynia. Similarly, these agents have been reported to exert analgesic effects in animal models of neuropathy induced by oxaliplatin, paclitaxel, or chronic constriction injury (CCI) of the sciatic nerve (21,31—33). Tramadol, duloxetine and amitriptyline inhibit serotonin and noradrenaline reuptake, besides, tramadol stimulates m opioid receptors. The anti-allodynic effects of these agents may be due to their known actions in activating the descending pain inhibitory system. However, although amitriptyline also has same action, a single administration of amitriptyline had no effect on bortezomib-induced mechanical allodynia. Moreover, we found that repeated administration of amitriptyline had no analgesic effect on the bortezomib-induced pain behavior after the development of neuropathy (data not shown). Therefore, it is possible that mechanisms other than the descending pain inhibitory systems are involved in analgesic effect of duloxetine.
In our study, single administration of pregabalin (3 mg/kg) and mexiletine (100 mg/kg) exerted anti-allodynic effects on bortezomib-induced mechanical allodynia. Anti-allodynic effects of these agents have been reported in animal models of neuropathy induced by oxaliplatin, paclitaxel or spinal nerve ligation (20,31,33). Pregabalin and mexiletine have inhibitory effects on Ca2+ channels and Na+ channels, respectively. It is well known that Na+ and Ca2+ channels regulate the release of pain-related neurotransmitters, including glutamate and substance P. Therefore, the anti-allodynic effects of these agents are thought to be due to the inhibition of Na+ and Ca2+ channels. It has been reported that intra-cerebroventricular injection of pregabalin reduces peripheral nerve injury-induced painful neuropathy and increases spinal noradrena-line turnover in mice, indicating that pregabalin produces analgesic effects that involve the descending noradrenergic system (34). Moreover, anti-allodynic effect of gabapentin on bortezomib-induced mechanical allodynia is suppressed by noradrenaline, but not serotonin, depletion in the spinal cord (15). This descending pain inhibitory system may also be involved in the relieving effect that pregabalin has on bortezomib-induced neuropathic pain.
The cyclooxygenase-2 (COX-2) inhibitor diclofenac did not affect bortezomib-induced mechanical allodynia. It has previously been shown that paclitaxel-induced mechanical allodynia is not affected by the COX-2 inhibitors diclofenac, indomethacin, or celecoxib (33). Thus, COX-2 inhibitors do not appear to improve BIPN.
In conclusion, the present study has characterized pain behaviors and pathological changes in the rat model of peripheral neuropathy induced by bortezomib. It indicates that axonal degeneration of the sciatic nerve is involved in BIPN. Moreover, our data reveal that some analgesic drugs and adjuvants are effective in the relief of painful neuropathy induced by bortezomib, and that these drugs may improve the welfare of patients with multiple myeloma who are experiencing the adverse neurological effects of bortezomib chemotherapy.
Conflict of interest
The authors declare that there are no conflicts of interest.
Acknowledgments
Part of this study was supported by Japan Society for the Promotion of Science KAKENHI Grant Numbers 25460335, 25870496, and 25929029. We appreciate the technical support from the Research Support Center, Graduate School of Medical Sciences, Kyushu University.
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