Decreased bone mineral density and reduced bone quality in H⁺/K⁺ATPase beta‐subunit deficient mice

Abstract

Proton pump inhibitors (PPIs) are widely used against gastroesophageal reflux disease. Recent epidemiological studies suggest that PPI users have an increased risk of fractures, but a causal relationship has been questioned. We have therefore investigated the skeletal phenotype in H(+) /K(+) ATPase beta-subunit knockout (KO) female mice. Skeletal parameters were determined in 6- and 20-month-old KO mice and in wild-type controls (WT). Whole body bone mineral density (BMD) and bone mineral content (BMC) were measured by dual energy X-ray absorptiometry (DXA). Femurs were examined with µCT analyses and break force were examined by a three-point bending test. Plasma levels of gastrin, RANKL, OPG, osteocalcin, leptin, and PTH were analyzed. KO mice had lower whole body BMC at 6 months (0.53 vs. 0.59 g, P = 0.035) and at 20 months (0.49 vs. 0.74 g, P < 0.01) compared to WT as well as lower BMD at 6 months (0.068 vs. 0.072 g/cm(2) , P = 0.026) and 20 months (0.067 vs. 0.077 g/cm(2) , P < 0.01). Mechanical strength was lower in KO mice at the age of 20 months (6.7 vs. 17.9 N, P < 0.01). Cortical thickness at 20 months and trabecular bone volume% at 6 months were significantly reduced in KO mice. Plasma OPG/RANKL ratio and PTH was increased in KO mice compared to controls. H(+) /K(+) ATPase beta subunit KO mice had decreased BMC and BMD, reduced cortical thickness and inferior mechanical bone strength. Whereas the mechanism is uncertain, these findings suggest a causal relationship between long-term PPI use and an increased risk of fractures.

Skeletal effects of a gastrin receptor antagonist in H+/K+ATPase beta subunit KO mice

“…Gastric anacidity has been suggested to affect bone metabolism through malabsorption of calcium, giving rise to secondary hyperparathyroidism. This is in accordance with our previous study on H + /K + ATPase beta subunit KO mice, showing higher plasma PTH in KO mice at 6 months of age (Fossmark et al 2012). A study by Schinke and coworkers revealed that CCK2-deficient mice also had an osteoporotic phenotype (Schinke et al 2009).…”

“…A number of large studies have reported increased risk of fractures in long-term users of PPIs (Vestergaard et al 2006, Yang et al 2006, Targownik et al 2008 Corley et al 2010, Gray et al 2010, Khalili et al 2012 and patients with chronic atrophic gastritis (Goerss et al 1992, Merriman et al 2010). Histing and coworkers demonstrated delayed fracture healing in mice given the PPI pantoprazole (Histing et al 2012), and our group has previously found reduced BMC, BMD and mechanical bone strength in H + /K + ATPase beta subunit KO mice (Fossmark et al 2012). Gastric hypoacidity and secondary hypergastrinemia are common features of PPI users, patients with chronic atrophic gastritis and the H + /K + ATPase beta subunit KO mice.…”

“…H + /K + ATPase beta subunit knockout (KO) mice display gastric anacidity and hypergastrinemia (Scarff et al 1999). We have previously shown that these mice exhibit lower bone mineral content (BMC) and BMD, impaired microarchitecture, as well as reduced mechanical bone strength, compared with wild-type mice (Fossmark et al 2012). In this study, we wanted to explore whether long-term administration of a gastrin/CCK2 receptor antagonist could prevent the development of an osteoporotic phenotype in H + /K + ATPase beta subunit KO mice.…”

Polyphosphate: A Morphogenetically Active Implant Material Serving as Metabolic Fuel for Bone Regeneration

“…It could be well established that absence of leptin signaling results in a high bone mass in spite of a hypogonadism situation, underscoring the critical function of this hormone. Leptin, a powerful inhibitor of bone formation in vivo, is expressed in bone cells and involved in regulation of osteoblast differentiation and mineralization and is assumed to act on the ATP exchange in those cells via the H + /K + ATPase …”

Gastric secretion

“…It consists of an a subunit that contains the catalytic site and a b subunit that is necessary for targeting of the enzyme to the apical membrane. H þ K þ -ATPase b-subunit knockout female mice have gastric hypoacidity along with lower bone mineral content, bone mineral density, and bone quality compared to wild-type mice [39]. The findings support the proposed causal relationship between the use of PPIs and increased fracture risk in patients but cannot differentiate between a direct effect of the PPI and an indirect effect mediated by hypoacidity.…”