Oral Calcitriol Use, Vertebral Fractures, and Vitamin K in Hemodialysis Patients: A Cross-Sectional Study

Fractures and vascular calcifications (VCs) are common in patients with chronic kidney disease (CKD). They are related to abnormalities in vitamin D metabolism, calcium, phosphorus, parathyroid hormone, and fibroblast growth factor 23 (FGF23)/Klotho that occur with CKD. Impaired vitamin D metabolism and abnormal levels of calcium, phosphate, parathyroid hormone (PTH), and FGF23/Klotho drive bone and vascular changes in CKD. It is unclear if oral calcitriol safely mitigates fracture risk without increasing the burden of calcifications. Therefore, we investigated whether treatment with calcitriol affected the prevalence of fractures and VC progression in hemodialysis (HD) patients. This report is a secondary analysis of the Vitamin K Italian (VIKI) study, a cross-sectional study involving 387 HD patients. We assessed vitamin 25(OH)D, alkaline phosphatase, PTH, calcium, phosphate, osteocalcin or bone Gla protein, matrix Gla protein, and vitamin K levels. Vertebral fractures (VFs) and VCs were determined by spine radiograph. A reduction of >20% of vertebral body height was considered a VF. VCs were quantified by the length of calcific lesions along the arteries. The patients treated with oral calcitriol were 177 of 387 patients (45.7%). The prevalence of VF was lower in patients receiving oral calcitriol than in those untreated (48.6% versus 61.0%, p = 0.015), whereas the presence of aortic and iliac calcifications was similar (aortic: 81.9% versus 79.5%, respectively, p = 0.552; iliac: 52.0% and 59.5%, respectively, p = 0.167). In multivariable logistic regression analysis, oral calcitriol was associated with a 40.2% reduced odds of fracture (OR 0.598; 95% confidence interval [CI], 0.363-0.985; p = 0.043). In conclusion, we found a significant association between oral calcitriol and lower VF in HD patients without an increase in the burden of VC. Further prospective and interventional studies are needed to confirm these findings. © 2021 American Society for Bone and Mineral Research (ASBMR).

Sevelamer Use, Vitamin K Levels, Vascular Calcifications, and Vertebral Fractures in Hemodialysis Patients: Results from the VIKI Study

Hyperphosphatemia is a risk factor for vascular calcifications (VCs), which are part of the chronic kidney disease-mineral and bone disorders (CKD-MBD). Vitamin K-dependent proteins such as matrix Gla protein (MGP) and bone Gla proteins (BGP, or osteocalcin) can inhibit VCs and regulate bone mineralization. In this analysis of the Vitamin K Italian (VIKI) study, the relationship between vitamin K status, vertebral fractures (VFs) and VCs in 387 hemodialysis (HD) patients with (N = 163; 42.1%) or without N = 224; 57.9%) sevelamer was evaluated. Levels of vitamin K vitamers K1 and K2 or menaquinones (MK; MK4-7), total and undercarboxylated (uc) forms for both BGP and MGP were determined. Although no differences in clinical characteristics were noted, lower levels of MK4 (0.45 versus 0.6 ng/mL, p = .01) and a greater MK4 deficiency was observed in sevelamer-treated patients (13.5% versus 5.4%, p = .005). Multivariate logistic regression revealed that MK4 deficiency was associated with sevelamer use (odds ratio [OR] = 2.64, 95% confidence interval [CI] 1.25-5.58, p = .011) and aortic calcification (OR = 8.04, 95% CI 1.07-60.26, p = .04). In the same logistic model, sevelamer amplified the effect of total BGP levels on the odds of VFs in patients with total BGP <150 μg/L compared with those with total BGP ≥150 μg/L (OR = 3.15, 95% CI 1.46-6.76, p = .003). In contrast, there was no such effect in those untreated (total BGP <150 μg/L versus total BGP ≥150 μg/L: OR = 1.21, 95% CI 0.66-2.23, p = .54]; p = .049 for effect modification by sevelamer). Sevelamer may interfere with MK4 levels in HD patients and interact with low BGP levels to increase bone fractures in CKD patients. © 2020 American Society for Bone and Mineral Research (ASBMR).

Osteoblast-Specific γ-Glutamyl Carboxylase-Deficient Mice Display Enhanced Bone Formation With Aberrant Mineralization

Vitamin K is a fat-soluble vitamin that is necessary for blood coagulation. In addition, it has bone-protective effects. Vitamin K functions as a cofactor of γ-glutamyl carboxylase (GGCX), which activates its substrates by carboxylation. These substrates are found throughout the body and examples include hepatic blood coagulation factors. Furthermore, vitamin K functions as a ligand of the nuclear receptor known as steroid and xenobiotic receptor (SXR) and its murine ortholog, pregnane X receptor (PXR). We have previously reported on the bone-protective role of SXR/PXR signaling by demonstrating that systemic Pxr-knockout mice displayed osteopenia. Because systemic Ggcx-knockout mice die shortly after birth from severe hemorrhage, the GGCX-mediated effect of vitamin K on bone metabolism has been difficult to evaluate. In this work, we utilized Ggcx-floxed mice to generate osteoblast-specific GGCX-deficient (Ggcx(Δobl/Δobl)) mice by crossing them with Col1-Cre mice. The bone mineral density (BMD) of Ggcx(Δobl/Δobl) mice was significantly higher than that of control Col1-Cre (Ggcx(+/+)) mice. Histomorphometrical analysis of trabecular bones in the proximal tibia showed increased osteoid volume and a higher rate of bone formation in Ggcx(Δobl/Δobl) mice. Histomorphometrical analysis of cortical bones revealed a thicker cortical width and a higher rate of bone formation in Ggcx(Δobl/Δobl) mice. Electron microscopic examination revealed disassembly of mineralized nodules and aberrant calcification of collagen fibers in Ggcx(Δobl/Δobl) mice. The mechanical properties of bones from Ggcx(Δobl/Δobl) mice tended to be stronger than those from control Ggcx(+/+) mice. These results suggest that GGCX in osteoblasts functions to prevent abnormal mineralization in bone formation, although this function may not be a prerequisite for the bone-protective effect of vitamin K.

FORMATE--PYRUVATE EXCHANGE REACTION IN STREPTOCOCCUS FAECALIS. II. REACTION CONDITIONS FOR CELL EXTRACTS

Oster, M. O. (A. & M. College of Texas, College Station), and N. P. Wood. Formate-pyruvate exchange reaction in Streptococcus faecalis. II. Reaction conditions for cell extracts. J. Bacteriol. 87:104-113. 1964.-In contrast to intact cells of Streptococcus faecalis, no stimulation of the formate-pyruvate exchange reaction was observed in cell extracts when yeast extract was added to the reaction mixture. A heated extract of Micrococcus lactilyticus, vitamin K(5), ferrous sulfate, and ferrous ammonium sulfate stimulated an active exchange by protecting the system from oxygen. Tetrahydrofolate, 2,3-dimercaptopropanol, and sodium sulfide provided partial protection, whereas ascorbate, glutathione, sodium hydrosulfite, ammonium sulfide, and sodium bisulfite gave insufficient protection or were inhibitory. Oxidation-reduction (O-R) indicators were not inhibitory and were used to estimate the O-R potentials of reaction mixtures. A potential at least as negative as -125 mv was estimated to be necessary to preserve or initiate formate-pyruvate exchange activity. The reaction operated over a narrow pH range when strict anaerobic conditions were not maintained but, when the system was suitably poised, the pH range was broader. The influence of high phosphate concentrations was less under strictly anaerobic conditions, and orthophosphate could be replaced by small amounts of pyrophosphate. Effect of temperature, time, and amount of extract is presented. Addition of reduced benzyl viologen and hydrogen-saturated palladium in the buffer during 8 hr of dialysis prevented inactivation of extracts. Recovery of activity could be obtained after ammonium sulfate treatment when a combination of palladium chloride, neutral red, and hydrogen bubbling were used.

INDUCED PROTECTION OF ADRENAL CORTEX AGAINST 7,12-DIMETHYLBENZ(ALPHA)ANTHRACENE. INFLUENCE OF ETHIONINE. INDUCTION OF MENADIONE REDUCTASE. INCORPORATION OF THYMIDINE-H3

7,12-Dimethylbenz[a]anthracene (7,12-DMBA) exerts adrenocorticolytic effects which set it apart from all other polynuclear aromatic hydrocarbons and aromatic amines which have been investigated. Adrenal damage by this compound appears to be due to its steric and electronic properties together with its unusually high solubility in lipides. Many compounds given prior to 7,12-DMBA induced protection of adrenal. The most efficient inducers of protection are flat condensed aromatics possessing 4 or 5 rings; very small doses of these compounds were required to induce protection. Other compounds devoid of these properties induced protection but large or repeated doses were necessary. All inducers of protection had to be given prior to 7,12-DMBA to prevent adrenal necrosis; when given simultaneously with, or later than, this compound adrenal apoplexy resulted. Protective aromatics and 7,12-DMBA as well induced synthesis of menadione reductase in liver. 3-Methylcholanthrene (3-MC) induced this enzyme in many normal organs including liver, lung, adrenal, and in mammary cancer as well. dl-Ethionine under appropriate conditions of time and dosage eliminated the adrenal protection induced by aromatics and also delayed the induction of menadione reductase while depressing the amount of this enzyme which was synthesized. 7,12-DMBA caused a greatly reduced incorporation of tritium from thymidine-H³ into washed acid-insoluble residue of adrenal. 3-MC given in advance mitigated the drastic effect of 7,12-DMBA on DNA synthesis and increased considerably the amount of tritium which was incorporated. The specific damage to adrenal by 7,12-DMBA is a direct effect on cells. Protection of adrenal is a secondary effect which requires induction of protein synthesis and it results in improvement in synthesis of DNA.

THE EFFECT OF MENADIONE AND PHENAZINE METHOSULFATE ON THE TETRAZOLIUM REDUCTION SYSTEM UNDER HISTOCHEMICAL CONDITIONS

The influence of phenazine methosulfate and menadione on the activity of DPNH- and TPNH-tetrazolium reductase, succinic, lactic, and triphosphopyridine nucleotide-linked isocitric dehydrogenase were studied with reference to applied histochemistry. Fresh frozen sections of various tissues were employed in conjunction with nitro blue tetrazolium as the hydrogen acceptor.

Phenazine methosulfate was found to produce a variable effect upon staining, enhancing it or suppressing it according to incubation conditions. Suppression was most pronounced with higher concentrations. Menadione had no suppressive influence and was useful in increasing tetrazolium reduction. Its usefulness is, however, limited unless a soluble factor, possibly DT-(DPNH-TPNH)-diaphorase, can be prevented from diffusing into the medium, and "nothing dehydrogenase" is selectively inactivated.

AROMATIC-INDUCED PREVENTION OF FETAL TOXICITY OF 7,12-DIMETHYLBENZ(ALPHA)ANTHRACENE

Large doses of 7,12-dimethylbenz[a]anthracene (7,12-DMBA) caused the death of rats within 1 day. A small amount of any of 5 polynuclear aromatic hydrocarbons or of an aromatic amine given before the highly toxic dose of 7,12-DMBA resulted in survival for more than 2 months and the specific atrophy of testis which follows 7,12-DMBA was largely prevented. Among the protective aromatics is 7,12-DMBA itself; a small dose of 7,12-DMBA given in advance induced protection of life against an otherwise lethal dose of 7,12-DMBA but only in a proportion of the animals, and testis was not protected from injury. The highly efficient inducers of protection were condensed aromatics composed of 4 or 5 rings. Protection of life against toxicity of big doses of 7,12-DMBA by pretreatment with small doses of aromatics required time (ca. 5 to 8 hours) for its induction. Ethionine given a few minutes after a highly efficient inducer of protection, 3-methylcholanthrene (3-MC), abolished induction of protection; ethionine given 8 hours after 3-MC exerted no influence on its protective effect. A lethal dose of 7,12-DMBA resulted in a considerable reduction in incorporation of tritium in DNA from tritiated thymidine while at the same time synthesis of menadione reductase was induced in liver. A small dose of 3-MC given prior to 7,12-DMBA was advantageous in partially protecting DNA synthesis.

CHYLOTHORAX IN INFANCY AND CHILDHOOD

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