Two Weeks of Continuous Opioid Treatment in an Adenine-Induced Mouse Model of Chronic Kidney Disease Exacerbates the Bone Inflammatory State and Increases Osteoclasts

Abstract

Patients with chronic kidney disease (CKD) report high pain levels, but reduced renal clearance eliminates many analgesic options; therefore, 30-50% of CKD patients have chronic opioid prescriptions. Opioid use in CKD is associated with higher fracture rates. Opioids may directly alter bone turnover directly through effects on bone cells and indirectly via increasing inflammation. We hypothesized that continuous opioid exposure would exacerbate the high bone turnover state of CKD and be associated with elevated measures of inflammation. Male C57Bl/6J mice after 8 weeks of adenine-induced CKD (AD) and non-AD controls (CON) had 14-day osmotic pumps (0.25-µL/hr release) containing either saline or 50-mg/mL oxycodone (OXY) surgically implanted in the subscapular region. After 2 weeks, all AD mice had elevated blood urea nitrogen, parathyroid hormone, and serum markers of bone turnover compared to controls with no effect of OXY. Immunohistochemical staining of the distal femur showed increased numbers of osteocytes positive for the mu opioid and for toll-like receptor 4 (TLR4) due to OXY. Osteocyte protein expression of tumor necrosis factor-α (TNF-α) and RANKL were higher due to both AD and OXY so that AD + OXY mice had the highest values. Trabecular osteoclast-covered surfaces were also significantly higher due to both AD and OXY, resulting in AD + OXY mice having 4.5-fold higher osteoclast-covered surfaces than untreated CON. These data demonstrate that opioids are associated with a pro-inflammatory state in osteocytes which increases the pro-resorptive state of CKD.

Keywords: Chronic kidney disease; Inflammation; Opioids; Osteoclasts; Oxycodone.

Fig. 1

Timeline of study and body weight and food intake at study endpoint. A Schematic of study timeline. Figure created with BioRender. B Control mice weighed more than adenine mice with no effect of oxycodone treatment. C Food intake was lower in adenine mice compared to control mice regardless of oxycodone treatment. Bars not sharing the same letter are statistically different (p < 0.05)

Fig. 2

Serum markers of kidney disease and bone turnover. A Serum BUN was higher on both AD groups compared to CON groups. B Serum PTH was elevated in AD groups compared to CON groups. C Serum P1NP was higher in AD vs. CON groups. D Serum TRAcP 5b was elevated in both AD groups vs. CON groups. Bars not sharing the same letter are statistically different (p < 0.05)

Fig. 3

Femoral microarchitecture parameters. A Trabecular bone volume in AD + OXY mice was lower than both CON groups. B Cortical bone area was lower in both AD groups vs. both CON groups. C Cortical thickness was lower in AD vs. CON regardless of treatment. D Cortical porosity was higher in both AD groups compared to both CON groups. Bars not sharing the same letter are statistically different (p < 0.05)

Fig. 4

Immunohistochemical analyses on trabecular and cortical bone of the distal femur. A Mu receptor-positive osteocytes were elevated due to both adenine and oxycodone treatment with AD + OXY having the highest levels of all groups. B TLR4-positive osteocytes were higher in both cortical and trabecular bone due to oxycodone treatment with no elevation due to adenine. C TNF-α-positive osteocytes were higher in AD + SAL mice vs. both CON groups with AD + OXY being higher than AD + SAL. D RANKL-positive osteocytes were elevated due to both adenine and oxycodone with AD + OXY having the highest value of all groups. Bars not sharing the same letter are statistically different (p < 0.05)

Fig. 5

Histological assessment of osteoclasts and osteoid in trabecular bone of the distal femur. A Osteoclast-covered trabecular surfaces (Oc.S/BS) were lowest in CON + SAL with increases due to both oxycodone and adenine with AD + OXY having the highest group value. B Osteoclast numbers (Oc.N/B.Pm) were lower in CON + SAL vs. all other groups. C Osteoid-covered trabecular surfaces (OS/BS) were higher in both adenine groups compared to both control groups. D Osteoid width was elevated in both adenine groups compared to control groups with no effect of oxycodone treatment. Bars not sharing the same letter are statistically different (p < 0.05)