Reversing cortical porosity: Cortical pore infilling in preclinical models of chronic kidney disease.

PURPOSE: Chronic kidney disease (CKD) patients have a high incidence of fracture due in part to cortical porosity. The goal of this study was to study cortical pore infilling utilizing two rodent models of progressive CKD. METHODS: Exp 1: Female C57Bl/6J mice (16-week-old) were given dietary adenine (0.2%) to induce CKD for 10 weeks after which calcium water supplementation (Ca-H2O; 1.5% and 3%) was given to suppress PTH for another 4 weeks. Exp 2: Male Cy/+ rats were aged to ~30 weeks with baseline porosity assessed using in vivo µCT. A second in vivo scan followed 5-weeks of Ca-H2O (3%) supplementation. RESULTS: Exp 1: Untreated adenine mice had elevated blood urea nitrogen (BUN), parathyroid hormone (PTH), and cortical porosity (~2.6% porosity) while Ca-H2O lowered PTH and cortical porosity (0.5-0.8% porosity). Exp 2: Male Cy/+ rats at baseline had variable porosity (0.5%-10%), but after PTH suppression via Ca-H2O, cortical porosity in all rats was lower than 0.5%. Individual pore dynamics measured via a custom MATLAB code demonstrated that 85% of pores infilled while 12% contracted in size. CONCLUSION: Ca-H2O supplementation causes net cortical pore infilling over time and imparted mechanical benefits. While calcium supplementation is not a viable clinical treatment for CKD, these data demonstrate pore infilling is possible and further research is required to examine clinically relevant therapeutics that may cause net pore infilling in CKD.

Skeletal levels of bisphosphonate in the setting of chronic kidney disease are independent of remodeling rate and lower with fractionated dosing.

BACKGROUND: Chronic kidney disease (CKD) results in a dramatic increase in skeletal fracture risk. Bisphosphates (BP) are an effective treatment for reducing fracture risk but they are not recommended in advanced CKD. We have recently shown higher acute skeletal accumulation of fluorescently-tagged zoledronate (ZOL) in the setting of CKD but how this accumulation is retained/lost over time is unclear. Furthermore, it is unknown if alternative dosing approaches can modulate accumulation in the setting of CKD. METHODS: To address these two questions normal (NL) and Cy/+ (CKD) rats were divided into control groups (no dosing), a single dose of a fluorescent-tagged ZOL (FAM-ZOL), a single dose of non-labelled zoledronate (ZOL) or ten weekly doses of FAM-ZOL each at 1/10th the dose of the single dose group. Half of the CKD animals in each group were provided water with 3% calcium in drinking water (CKD + Ca) to suppress PTH and remodeling. At 30 or 35 weeks of age, serum, tibia, ulna, radius, vertebra, femora, and mandible were collected and subjected to assessment methods including biochemistry, dynamic histomorphometry and multi-spectral fluorescence levels (using IVIS SpectrumCT). RESULTS: FAM-ZOL did not significantly reduce bone remodeling in either NL or CKD animals while Ca supplementation in CKD produced remodeling levels comparable to NL. At five- and ten-weeks post-dosing, both CKD and CKD + Ca groups had higher levels of FAM-ZOL in most, but not all, skeletal sites compared to NL with no difference between the two CKD groups suggesting that the rate of remodeling did not affect skeletal retention of FAM-ZOL. Fractionating the FAM-ZOL into ten weekly doses led to 20-32% less (p < 0.05) accumulation/retention of compound in the vertebra, radius, and ulna compared to administration as a single dose. CONCLUSIONS: The rate of bone turnover does not have significant effects on levels of FAM-ZOL accumulation/retention in animals with CKD. A lower dose/more frequent administration paradigm results in lower levels of accumulation/retention over time. These data provide information that could better inform the use of bisphosphonates in the setting of CKD in order to combat the dramatic increase in fracture risk.

Differential effects of Epigallocatechin-3-gallate containing supplements on correcting skeletal defects in a Down syndrome mouse model.

SCOPE: Down syndrome (DS), caused by trisomy of human chromosome 21 (Hsa21), is characterized by a spectrum of phenotypes including skeletal abnormalities. The Ts65Dn DS mouse model exhibits similar skeletal phenotypes as humans with DS. DYRK1A, a kinase encoded on Hsa21, has been linked to deficiencies in bone homeostasis in DS mice and individuals with DS. Treatment with Epigallocatechin-3-gallate (EGCG), a known inhibitor of Dyrk1a, improves some skeletal abnormalities associated with DS in mice. EGCG supplements are widely available but the effectiveness of different EGCG-containing supplements has not been well studied. METHODS AND RESULTS: Six commercially available supplements containing EGCG were analyzed, and two of these supplements were compared with pure EGCG for their impact on skeletal deficits in a DS mouse model. The results demonstrate differential effects of commercial supplements on correcting skeletal abnormalities in Ts65Dn mice. Different EGCG-containing supplements display differences in degradation, polyphenol content, and effects on trisomic bone. CONCLUSION: This work suggests that the dose of EGCG and composition of EGCG-containing supplements may be important in correcting skeletal deficits associated with DS. Careful analyses of these parameters may lead to a better understanding of how to improve skeletal and other deficits that impair individuals with DS.

Physical weight loading induces expression of tryptophan hydroxylase 2 in the brain stem.

Sustaining brain serotonin is essential in mental health. Physical activities can attenuate mental problems by enhancing serotonin signaling. However, such activity is not always possible in disabled individuals or patients with dementia. Knee loading, a form of physical activity, has been found to mimic effects of voluntary exercise. Focusing on serotonergic signaling, we addressed a question: Does local mechanical loading to the skeleton elevate expression of tryptophan hydroxylase 2 (tph2) that is a rate-limiting enzyme for brain serotonin? A 5 min knee loading was applied to mice using 1 N force at 5 Hz for 1,500 cycles. A 5-min treadmill running was used as an exercise (positive) control, and a 90-min tail suspension was used as a stress (negative) control. Expression of tph2 was determined 30 min - 2 h in three brain regions --frontal cortex (FC), ventromedial hypothalamus (VMH), and brain stem (BS). We demonstrated for the first time that knee loading and treadmill exercise upregulated the mRNA level of tph2 in the BS, while tail suspension downregulated it. The protein level of tph2 in the BS was also upregulated by knee loading and downregulated by tail suspension. Furthermore, the downregulation of tph2 mRNA by tail suspension can be partially suppressed by pre-application of knee loading. The expression of tph2 in the FC and VMH was not significantly altered with knee loading. In this study we provided evidence that peripheral mechanical loading can activate central tph2 expression, suggesting that physical cues may mediate tph2-cathalyzed serotonergic signaling in the brain.