FGF23, klotho and vitamin D interactions: What have we learned from in vivo mouse genetics studies?

Association between serum soluble α-klotho and bone mineral density (BMD) in middle-aged and older adults in the United States: a population-based cross-sectional study

BACKGROUND

Osteoporosis is a degenerative disease defined by low bone mineral density, has a high prevalence, and causes fractures at multiple sites throughout the body, greatly affecting the quality of patients. α-Klotho is an endocrine factor involved in the regulation of various metabolic processes in humans, and its role in bone metabolism has attracted widespread attention. The relationship between α-klotho and bone mineral density has not been uniformly recognized, and no large-scale correlation analysis has been conducted in the middle-aged and elderly population.

OBJECTIVE

To determine the relationship between α-klotho and bone mineral density in middle-aged and elderly people.

METHODS

Population data of 3120 individuals aged 40-79 years were obtained from the NHANES database for the period 2011-2016. Regression analysis was performed using a general linear model with serum α-klotho as the independent variable and total bone mineral density, thoracic bone mineral density, lumbar bone mineral density, pelvic bone mineral density, and trunk bone mineral density as the dependent variables, respectively. The generalized additive model was also used for smoothing curve fitting and threshold effect analysis.

RESULTS

Serum α-klotho was positively correlated with total bone mineral density at lg (Klotho) < 2.97 and with thoracic bone mineral density at lg (Klotho) > 2.69 (β = 0.05, p = 0.0006), and negatively correlated (β = -0.27, p = 0.0341) with lumbar bone mineral density at lg (Klotho) < 2.69. It also positively correlated with trunk bone mineral density (β = 0.027, p = 0.03657) and had no segmental effect but did not correlate with pelvic bone mineral density. The positive association of serum α-klotho with those aged 40-49 years, female, non-Hispanic White, and without hypertension was clearer. In the population with diabetes, a significantly positive association between total (β = 0.15, p = 0.01), thoracic (β = 0.23, p = 0.0404), and lumbar (β = 0.22, p = 0.0424) bone mineral density and α-klotho was observed.

CONCLUSIONS

α-Klotho has different relationships with total, thoracic, lumbar, and trunk bone mineral density. Among them, the positive correlation between α-klotho and trunk bone mineral density is more valuable for predicting osteoporosis. The significant effect of α-klotho on bone mineral density in diabetes patients suggests its potential as a predictive marker of diabetes progression.

Inverse J-Shaped Relationship of Dietary Carbohydrate Intake with Serum Klotho in NHANES 2007-2016

BACKGROUND

The relationship between dietary carbohydrate intake and serum Klotho levels, an aging biomarker, remains uncertain.

OBJECTIVE

This study aimed to investigate the association between dietary carbohydrate intake and serum Klotho levels among American adults aged 40-79.

METHODS

We analyzed data from 10,669 adults aged 40-79 years who participated in the National Health and Nutrition Examination Survey (NHANES) from 2007 to 2016. Trained interviewers assessed dietary carbohydrate intake using a 24 h dietary recall. Serum Klotho concentrations were measured using commercially available ELISA kits provided by IBL International, Japan, which served as the study outcome. Generalized linear models were used to assess the relationship between the carbohydrate energy percentage and serum Klotho concentration, and restricted cubic spline (RCS) analysis was employed to explore any nonlinear associations.

RESULTS

After adjusting for multiple variables, we observed a nonlinear inverse J-shaped relationship (p for non-linearity < 0.001) between the carbohydrate energy percentage and serum Klotho levels. Specifically, the highest serum Klotho levels were associated with a total carbohydrate energy percentage ranging from 48.92% to 56.20% (third quartile). When the carbohydrate energy percentage was evaluated in quartiles, serum Klotho levels decreased by 5.37% (95% CI: -7.43%, -3.26%), 2.70% (95% CI: -4.51%, -0.86%), and 2.76% (95% CI: -4.86%, -0.62%) in the first quartile (<41.46%), second quartile (41.46% to 48.92%), and fourth quartile (≥56.20%), respectively, compared to the third quartile. This relationship was more pronounced in male, non-obese and non-diabetic participants under 60 years of age.

CONCLUSION

A non-linear inverse J-shaped relationship exists among the general U.S. middle-aged and older population between the carbohydrate energy percentage and serum Klotho levels, with the highest levels observed at 48.92% to 56.20% carbohydrate intake.

COVID-19: Focusing on the Link between Inflammation, Vitamin D, MAPK Pathway and Oxidative Stress Genetics

An uncontrolled inflammatory response during SARS-CoV-2 infection has been highlighted in several studies. This seems to be due to pro-inflammatory cytokines whose production could be regulated by vitamin D, ROS production or mitogen-activated protein kinase (MAPK). Several genetic studies are present in the literature concerning genetic influences on COVID-19 characteristics, but there are few data on oxidative stress, vitamin D, MAPK and inflammation-related factors, considering gender and age. Therefore, the aim of this study was to evaluate the role of single nucleotide polymorphisms in these pathways, clarifying their impact in affecting COVID-19-related clinical features. Genetic polymorphisms were evaluated through real-time PCR. We prospectively enrolled 160 individuals: 139 patients were positive for SARS-CoV-2 detection. We detected different genetic variants able to affect the symptoms and oxygenation. Furthermore, two sub-analyses were performed considering gender and age, showing a different impact of polymorphisms according to these characteristics. This is the first study highlighting a possible contribution of genetic variants of these pathways in affecting COVID-19 clinical features. This may be relevant in order to clarify the COVID-19 etiopathogenesis and to understand the possible genetic contribution for further SARS infections.

Benefits of Vitamin D Supplementation on Pregnancy of Rats with Pregestational Diabetes and Their Offspring

Studies on vitamin D supplementation have been performed in experimental and clinical investigations considering gestational diabetes and/or vitamin D deficiency in pregnancy. However, the results are controversial and few present the effects and mechanisms of this micronutrient on pregestational diabetes. The objective of this study was to evaluate the effect of vitamin D on the pregnancy of rats with pre-existing diabetes and their fetuses. Pregestational diabetes was induced in Sprague-Dawley rats at birth. The adult diabetic and nondiabetic rats were orally administered with vitamin D (cholecalciferol) throughout the pregnancy. The diabetes status was monitored during pregnancy by an oral glucose tolerance test (OGTT). At the end of the pregnancy, pancreas and blood samples were collected for morphological analyses and lipid peroxidation measurements, respectively. The influence of vitamin D treatment on reproductive outcomes, fetal growth, and development were compared to those of untreated diabetic and nondiabetic pregnant rats. P < 0.05 was considered a significant statistical limit. The diabetic rats given vitamin D had a greater number of insulin-positive cells, contributing to reduced blood glucose levels and thiobarbituric acid reactive substance concentrations (TBARS-an indicator of membrane lipid peroxidation), and increased reduced thiol group levels, contributing to suitable intrauterine conditions for better fetal development, which was confirmed by higher fetal viability rates. Thus, this study shows the effects and mechanisms of vitamin D supplementation on pre-existing diabetes in pregnant rats, confirming its beneficial effects on maternal redox status and glycemic control, and the decline of adverse maternal-fetal repercussions.

Vitamin D and Chronic Kidney Disease Association with Mineral and Bone Disorder: An Appraisal of Tangled Guidelines

Chronic kidney disease (CKD) is a highly prevalent condition worldwide in which the kidneys lose many abilities, such as the regulation of vitamin D (VD) metabolism. Moreover, people with CKD are at a higher risk of multifactorial VD deficiency, which has been extensively associated with poor outcomes, including bone disease, cardiovascular disease, and higher mortality. Evidence is abundant in terms of the association of negative outcomes with low levels of VD, but recent studies have lowered previous high expectations regarding the beneficial effects of VD supplementation in the general population. Although controversies still exist, the diagnosis and treatment of VD have not been excluded from nephrology guidelines, and much data still supports VD supplementation in CKD patients. In this narrative review, we briefly summarize evolving controversies and useful clinical approaches, underscoring that the adverse effects of VD derivatives must be balanced against the need for effective prevention of progressive and severe secondary hyperparathyroidism. Guidelines vary, but there seems to be general agreement that VD deficiency should be avoided in CKD patients, and it is likely that one should not wait until severe SHPT is present before cautiously starting VD derivatives. Furthermore, it is emphasized that the goal should not be the complete normalization of parathyroid hormone (PTH) levels. New developments may help us to better define optimal VD and PTH at different CKD stages, but large trials are still needed to confirm that VD and precise control of these and other CKD-MBD biomarkers are unequivocally related to improved hard outcomes in this population.

Effects of the Vitamin D3 on Alleviating the Oxidative Stress Induced by Diquat in Wenchang Chickens

Vitamin D₃ (VD₃) is an indispensable micronutrient in livestock and poultry feed. Its function in antioxidant stress has been reported. We investigate whether the addition of different concentrations of VD₃ to the diet affects the production performance, slaughter performance, meat quality, organ index, and gut injury on the diquat (DQ)-induced model of oxidative stress in Wenchang chickens. Four hundred and eighty one-day-old chickens were randomly divided into six groups: control (basal diet), 4000 VD (basal diet + VD₃ 4000 IU per kg feed intake), 1000 VD+DI (DQ, basal diet + VD₃ 1000 IU per kg feed intake), 2000 VD+DI (DQ, basal diet + VD₃ 2000 IU per kg feed intake), and 4000 VD+DI (DQ, basal diet + VD₃ 4000 IU per kg feed intake). The results showed that the addition of VD₃ to the diet promoted DQ-induced weight loss and reduced ADFI, slaughter rate, splenic index, and pH after 1 h and 24 h in the leg muscles. VD₃ decreased the increase in content of interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) among proinflammatory cytokines (p < 0.05) and increased the reduction in anti-inflammatory cytokines content of interleukin-10 (IL-10) (p < 0.05) induced by DQ. In addition, liver and kidney injury biomarkers and the intestinal permeability index in serum were disordered after treatment with DQ (p < 0.05). VD₃ perfected the increase of D-lactic acid (D-LA), diamine oxidase (DAO), total cholesterol (T-CHO), creatinine (CR), blood urea nitrogen (BUN), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C) content, aspartate transaminase (AST), alanine transaminase (ALT), and lactate dehydrogenase (LDH) activity (p < 0.05); it increased the decrease of albumin (ALB) content (p < 0.05). Meanwhile, VD₃ regulated the intestinal morphology and intestinal barrier. Moreover, DQ induced a decrease in total antioxidant capacity and antioxidant enzyme activity in the serum, liver, and jejunum (p < 0.05), and an increase in malonaldehyde (MDA) content (p < 0.05). However, the addition of different levels of VD₃ could alleviate the above phenomenon of oxidative stress in Wenchang chickens to different degrees. Thus, this research suggested that the addition of VD₃ can relieve the DQ-induced oxidative stress of Wenchang chickens, and the level of VD₃ acquisition is positively correlated with the remission effect.

The Role of Alterations in Alpha-Klotho and FGF-23 in Kidney Transplantation and Kidney Donation

Cardiovascular disease and mineral bone disorders are major contributors to morbidity and mortality among patients with chronic kidney disease and often persist after renal transplantation. Ongoing hormonal imbalances after kidney transplant (KT) are associated with loss of graft function and poor outcomes. Fibroblast growth factor 23 (FGF-23) and its co-receptor, α-Klotho, are key factors in the underlying mechanisms that integrate accelerated atherosclerosis, vascular calcification, mineral disorders, and osteodystrophy. On the other hand, kidney donation is also associated with endocrine and metabolic adaptations that include transient increases in circulating FGF-23 and decreases in α-Klotho levels. However, the long-term impact of these alterations and their clinical relevance have not yet been determined. This manuscript aims to review and summarize current data on the role of FGF-23 and α-Klotho in the endocrine response to KT and living kidney donation, and importantly, underscore specific areas of research that may enhance diagnostics and therapeutics in the growing population of KT recipients and kidney donors.

Vitamin D, Chronic Migraine, and Extracranial Pain: Is There a Link? Data From an Observational Study

Several studies focused on the role of vitamin D (vitD) in pain chronification. This study focused on vitD level and pain chronification and extension in headache disorders. Eighty patients with primary headache underwent neurological examination, laboratory exams, including serum calcifediol 25(OH)D, and headache features assessment along with three questionnaires investigating depression, anxiety, and allodynia. The 86.8% of the population had migraine (48% episodic and 52% chronic). The 44.1% of patients had extracranial pain, and 47.6% suffered from allodynia. A vitD deficit, namely a serum 25(OH)D level <20 ng/ml, was detectable in 46.1% of the patients, and it occurred more frequently (p = 0.009) in patients suffering from chronic migraine (CM)–medication overuse migraine (MOH) (62.9%) than in episodic migraine (EM, 25.7%) or tension-type headache (TTH, 11.4%). The occurrence of extracranial pain and allodynia was higher in the CM-MOH than in the EM and in the TTH groups but was not related to the co-occurrence of vitD deficiency (Fisher's exact test p = 0.11 and p = 0.32, respectively). Our findings show that 25(OH)D deficit is also related to chronic headache, probably because of vitD anti-inflammatory and tolerogenic properties, reinforcing the idea of a neuroinflammatory mechanism underpinning migraine chronification.

Oxidative Stress and Low-Grade Inflammation in Polycystic Ovary Syndrome: Controversies and New Insights

The pathophysiology of Polycystic Ovary Syndrome (PCOS) is quite complex and different mechanisms could contribute to hyperandrogenism and anovulation, which are the main features of the syndrome. Obesity and insulin-resistance are claimed as the principal factors contributing to the clinical presentation; in normal weight PCOS either, increased visceral adipose tissue has been described. However, their role is still debated, as debated are the biochemical markers linked to obesity per se. Oxidative stress (OS) and low-grade inflammation (LGI) have recently been a matter of researcher attention; they can influence each other in a reciprocal vicious cycle. In this review, we summarize the main mechanism of radical generation and the link with LGI. Furthermore, we discuss papers in favor or against the role of obesity as the first pathogenetic factor, and show how OS itself, on the contrary, can induce obesity and insulin resistance; in particular, the role of GH-IGF-1 axis is highlighted. Finally, the possible consequences on vitamin D synthesis and activation on the immune system are briefly discussed. This review intends to underline the key role of oxidative stress and low-grade inflammation in the physiopathology of PCOS, they can cause or worsen obesity, insulin-resistance, vitamin D deficiency, and immune dyscrasia, suggesting an inverse interaction to what is usually considered.

No significant association of serum klotho concentration with blood pressure and pulse wave velocity in a Chinese population

Klotho, an important anti-aging protein, may be related to elevated blood pressure (BP) and arterial stiffness. We aimed to investigate associations between the serum klotho concentration and peripheral/central BP and arterial stiffness based on the carotid–femoral pulse wave velocity (cfPWV) in a Chinese population. We invited all inhabitants aged ≥ 18 years in two Dali communities for participation. The SphygmoCor system was used to record radial arterial waveforms. Aortic waveforms were derived using a generalized transfer function. The central BP was assessed by calibrating the brachial BP, which was measured using an oscillometric device. The serum klotho concentration was measured using an enzyme-linked immunosorbent assay and logarithmically transformed. Of the 716 participants (mean age: 51.9 ± 12.6 years), 467 (65.2%) were women. The median serum klotho concentration was 381.8 pg/mL. The serum klotho concentration did not significantly differ between patients with and without hypertension (P > 0.05) and between those with and without arterial stiffness (cfPWV ≥ 10 m/s) (P > 0.05). After adjusting for confounders, the serum klotho concentration was not significantly associated with the peripheral or central BP (P > 0.05) and cfPWV (P > 0.05). Our data indicated that the serum klotho concentration was not associated with BP or cfPWV in the general Chinese population.

Protective Role of Vitamin D in Renal Tubulopathies

Vitamin D is tightly linked with renal tubular homeostasis: the mitochondria of proximal convoluted tubule cells are the production site of 1α,25-dihydroxyvitamin D3. Patients with renal impairment or tubular injury often suffer from chronic inflammation. This alteration comes from oxidative stress, acidosis, decreased clearance of inflammatory cytokines and stimulation of inflammatory factors. The challenge is to find the right formula for each patient to correctly modulate the landscape of treatment and preserve the essential functions of the organism without perturbating its homeostasis. The complexity of the counter-regulation mechanisms and the different axis involved in the Vitamin D equilibrium pose a major issue on Vitamin D as a potential effective anti-inflammatory drug. The therapeutic use of this compound should be able to inhibit the development of inflammation without interfering with normal homeostasis. Megalin-Cubilin-Amnionless and the FGF23-Klotho axis represent two Vitamin D-linked mechanisms that could modulate and ameliorate the damage response at the renal tubular level, balancing Vitamin D therapy with an effect potent enough to contrast the inflammatory cascades, but which avoids potential severe side effects.

Fibroblast Growth Factor 23 and Klotho in AKI

Acute kidney injury (AKI) is associated with many of the same mineral metabolite abnormalities that are observed in chronic kidney disease. These include increased circulating levels of the osteocyte-derived, vitamin D-regulating hormone, fibroblast growth factor 23 (FGF23), and decreased renal expression of klotho, the co-receptor for FGF23. Recent data have indicated that increased FGF23 and decreased klotho levels in the blood and urine could serve as novel predictive biomarkers of incident AKI, or as novel prognostic biomarkers of adverse outcomes in patients with established AKI. In addition, because FGF23 and klotho exert numerous classic as well as off-target effects on a variety of organ systems, targeting their dysregulation in AKI may represent a unique opportunity for therapeutic intervention. We review the pathophysiology, kinetics, and regulation of FGF23 and klotho in animal and human studies of AKI, and we discuss the challenges and opportunities involved in targeting FGF23 and klotho therapeutically.

Re-evaluation of phosphoric acid-phosphates - di-, tri- and polyphosphates (E 338-341, E 343, E 450-452) as food additives and the safety of proposed extension of use

The Panel on Food Additives and Flavourings added to Food (FAF) provided a scientific opinion re-evaluating the safety of phosphates (E 338-341, E 343, E 450-452) as food additives. The Panel considered that adequate exposure and toxicity data were available. Phosphates are authorised food additives in the EU in accordance with Annex II and III to Regulation (EC) No 1333/2008. Exposure to phosphates from the whole diet was estimated using mainly analytical data. The values ranged from 251 mg P/person per day in infants to 1,625 mg P/person per day for adults, and the high exposure (95th percentile) from 331 mg P/person per day in infants to 2,728 mg P/person per day for adults. Phosphate is essential for all living organisms, is absorbed at 80-90% as free orthophosphate excreted via the kidney. The Panel considered phosphates to be of low acute oral toxicity and there is no concern with respect to genotoxicity and carcinogenicity. No effects were reported in developmental toxicity studies. The Panel derived a group acceptable daily intake (ADI) for phosphates expressed as phosphorus of 40 mg/kg body weight (bw) per day and concluded that this ADI is protective for the human population. The Panel noted that in the estimated exposure scenario based on analytical data exposure estimates exceeded the proposed ADI for infants, toddlers and other children at the mean level, and for infants, toddlers, children and adolescents at the 95th percentile. The Panel also noted that phosphates exposure by food supplements exceeds the proposed ADI. The Panel concluded that the available data did not give rise to safety concerns in infants below 16 weeks of age consuming formula and food for medical purposes.

Vitamin D Deficiency: Effects on Oxidative Stress, Epigenetics, Gene Regulation, and Aging

Recent advances in vitamin D research indicate that this vitamin, a secosteroid hormone, has beneficial effects on several body systems other than the musculoskeletal system. Both 25 dihydroxy vitamin D [25(OH)₂D] and its active hormonal form, 1,25-dihydroxyvitamin D [1,25(OH)₂D] are essential for human physiological functions, including damping down inflammation and the excessive intracellular oxidative stresses. Vitamin D is one of the key controllers of systemic inflammation, oxidative stress and mitochondrial respiratory function, and thus, the aging process in humans. In turn, molecular and cellular actions form 1,25(OH)₂D slow down oxidative stress, cell and tissue damage, and the aging process. On the other hand, hypovitaminosis D impairs mitochondrial functions, and enhances oxidative stress and systemic inflammation. The interaction of 1,25(OH)₂D with its intracellular receptors modulates vitamin D–dependent gene transcription and activation of vitamin D-responsive elements, which triggers multiple second messenger systems. Thus, it is not surprising that hypovitaminosis D increases the incidence and severity of several age-related common diseases, such as metabolic disorders that are linked to oxidative stress. These include obesity, insulin resistance, type 2 diabetes, hypertension, pregnancy complications, memory disorders, osteoporosis, autoimmune diseases, certain cancers, and systemic inflammatory diseases. Vitamin D adequacy leads to less oxidative stress and improves mitochondrial and endocrine functions, reducing the risks of disorders, such as autoimmunity, infections, metabolic derangements, and impairment of DNA repair; all of this aids a healthy, graceful aging process. Vitamin D is also a potent anti-oxidant that facilitates balanced mitochondrial activities, preventing oxidative stress-related protein oxidation, lipid peroxidation, and DNA damage. New understandings of vitamin D-related advances in metabolomics, transcriptomics, epigenetics, in relation to its ability to control oxidative stress in conjunction with micronutrients, vitamins, and antioxidants, following normalization of serum 25(OH)D and tissue 1,25(OH)₂D concentrations, likely to promise cost-effective better clinical outcomes in humans.

Thymic Epithelial Cell Support of Thymopoiesis Does Not Require Klotho

Age-related thymic involution is characterized by a decrease in thymic epithelial cell (TEC) number and function parallel to a disruption in their spatial organization, resulting in defective thymocyte development and proliferation as well as peripheral T cell dysfunction. Deficiency of Klotho, an antiaging gene and modifier of fibroblast growth factor signaling, causes premature aging. To investigate the role of Klotho in accelerated age-dependent thymic involution, we conducted a comprehensive analysis of thymopoiesis and peripheral T cell homeostasis using Klotho-deficient (Kl/Kl) mice. At 8 wk of age, Kl/Kl mice displayed a severe reduction in the number of thymocytes (10-100-fold reduction), especially CD4 and CD8 double-positive cells, and a reduction of both cortical and medullary TECs. To address a cell-autonomous role for Klotho in TEC biology, we implanted neonatal thymi from Klotho-deficient and -sufficient mice into athymic hosts. Kl/Kl thymus grafts supported thymopoiesis equivalently to Klotho-sufficient thymus transplants, indicating that Klotho is not intrinsically essential for TEC support of thymopoiesis. Moreover, lethally irradiated hosts given Kl/Kl or wild-type bone marrow had normal thymocyte development and comparably reconstituted T cells, indicating that Klotho is not inherently essential for peripheral T cell reconstitution. Because Kl/Kl mice have higher levels of serum phosphorus, calcium, and vitamin D, we evaluated thymus function in Kl/Kl mice fed with a vitamin D-deprived diet. We observed that a vitamin D-deprived diet abrogated thymic involution and T cell lymphopenia in 8-wk-old Kl/Kl mice. Taken together, our data suggest that Klotho deficiency causes thymic involution via systemic effects that include high active vitamin D levels.

Role of αKlotho and FGF23 in regulation of type II Na-dependent phosphate co-transporters

Alpha-Klotho is a member of the Klotho family consisting of two other single-pass transmembrane proteins: βKlotho and γKlotho; αKlotho has been shown to circulate in the blood. Fibroblast growth factor (FGF)23 is a member of the FGF superfamily of 22 genes/proteins. αKlotho serves as a co-receptor with FGF receptors (FGFRs) to provide a receptacle for physiological FGF23 signaling including regulation of phosphate metabolism. The extracellular domain of transmembrane αKlotho is shed by secretases and released into blood circulation (soluble αKlotho). Soluble αKlotho has both FGF23-independent and FGF23-dependent roles in phosphate homeostasis by modulating intestinal phosphate absorption, urinary phosphate excretion, and phosphate distribution into bone in concerted interaction with other calciophosphotropic hormones such as PTH and 1,25-(OH)₂D. The direct role of αKlotho and FGF23 in the maintenance of phosphate homeostasis is partly mediated by modulation of type II Na⁺-dependent phosphate co-transporters in target organs. αKlotho and FGF23 are principal phosphotropic hormones, and the manipulation of the αKlotho-FGF23 axis is a novel therapeutic strategy for genetic and acquired phosphate disorders and for conditions with FGF23 excess and αKlotho deficiency such as chronic kidney disease.

Periodontal diseases and adverse pregnancy outcomes: Is there a role for vitamin D?

Studies have shown a relationship between maternal periodontal diseases (PDs) and premature delivery. PDs are commonly encountered oral diseases which cause progressive damage to the periodontal ligament and alveolar bones, leading to loss of teeth and oral disabilities. PDs also adversely affect general health by worsening of cardiovascular and metabolic diseases. Moreover, maternal PDs are thought to be related to increasing the frequency of preterm-birth with low birth weight (PBLBW) in new-borns. Prematurity and immaturity are the leading causes of prenatal and infant mortality and is a major public health problem around the world. Inflamed periodontal tissues generate significantly high levels of proinflammatory cytokines that may have systemic effects on the host mother and the fetus. In addition, the bacteria that cause PDs produce endotoxins which can harm the fetus. Furthermore, studies have shown that microorganisms causing PDs can get access to the bloodstream, invading uterine tissues, to induce PBLBW. Another likely mechanism that connects PDs with adverse pregnancy outcome is maternal vitamin D status. A role of inadequate vitamin D status in the genesis of PDs has been reported. Administration of vitamin D supplementation during pregnancy could reduce the risk of maternal infections and adverse pregnancy outcomes. As maternal PDs are significant risk factors for adverse pregnancy outcome, preventive antenatal care for pregnant women in collaboration with the obstetric and dental professions are required.

Changes in vitamin D endocrinology during aging in adults

Worldwide, vitamin D deficiency is a common finding. Within individuals 25-hydroxyvitamin D (25OH)D) concentrations remain fairly stable over time although large differences in individual longitudinal changes exist. During aging vitamin D metabolism and activity changes in several different ways. Intestinal resistance to 1,25(OH)2D develops which hampers intestinal calcium uptake. Vitamin D receptor number decreases with aging in several organs involved in calcium metabolism and 1alpha-hydroxylase activity decreases mainly due to a decrease in renal function reducing vitamin D activation. Effects of 1,25(OH)2D on cell proliferation and differentiation may influence potential anti-cancer effects whereas regulation of telomere length may result in longevity. In older individuals, vitamin D supplementation has positive effects on fracture risk, number of falls and physical function. Supplementation in older populations warrants specific attention. Effects on "non-classical" outcomes may be revealed by ongoing large randomized clinical trials with high doses of vitamin D.

Vitamin D Impacts the Expression of Runx2 Target Genes and Modulates Inflammation, Oxidative Stress and Membrane Vesicle Biogenesis Gene Networks in 143B Osteosarcoma Cells

Osteosarcoma (OS) is an aggressive malignancy of bone affecting children, adolescents and young adults. Understanding vitamin D metabolism and vitamin D regulated genes in OS is an important aspect of vitamin D/cancer paradigm, and in evaluating vitamin D as adjuvant therapy for human OS. Vitamin D treatment of 143B OS cells induced significant and novel changes in the expression of genes that regulate: (a) inflammation and immunity; (b) formation of reactive oxygen species, metabolism of cyclic nucleotides, sterols, vitamins and mineral (calcium), quantity of gap junctions and skeletogenesis; (c) bone mineral density; and (d) cell viability of skeletal cells, aggregation of bone cancer cells and exocytosis of secretory vesicles. Ingenuity pathway analysis revealed significant reduction in Runx2 target genes such as fibroblast growth factor -1, -12 (FGF1 and FGF12), bone morphogenetic factor-1 (BMP1), SWI/SNF related, matrix associated actin dependent regulator of chromatin subfamily a, member 4 (SMARCA4), Matrix extracellular phosphoglycoprotein (MEPE), Integrin, β4 (ITGBP4), Matrix Metalloproteinase -1, -28 (MMP1 and MMP28), and signal transducer and activator of transcription-4 (STAT4) in vitamin D treated 143B OS cells. These genes interact with the inflammation, oxidative stress and membrane vesicle biogenesis gene networks. Vitamin D not only inhibited the expression of Runx2 target genes MMP1, MMP28 and kallikrein related peptidase-7 (KLK7), but also migration and invasion of 143B OS cells. Vitamin D regulated Runx2 target genes or their products represent potential therapeutic targets and laboratory biomarkers for applications in translational oncology.

αKlotho and Chronic Kidney Disease

Alpha-Klotho (αKlotho) protein is encoded by the gene, Klotho, and functions as a coreceptor for endocrine fibroblast growth factor-23. The extracellular domain of αKlotho is cleaved by secretases and released into the circulation where it is called soluble αKlotho. Soluble αKlotho in the circulation starts to decline in chronic kidney disease (CKD) stage 2 and urinary αKlotho in even earlier CKD stage 1. Therefore soluble αKlotho is an early and sensitive marker of decline in kidney function. Preclinical data from numerous animal experiments support αKlotho deficiency as a pathogenic factor for CKD progression and extrarenal CKD complications including cardiac and vascular disease, hyperparathyroidism, and disturbed mineral metabolism. αKlotho deficiency induces cell senescence and renders cells susceptible to apoptosis induced by a variety of cellular insults including oxidative stress. αKlotho deficiency also leads to defective autophagy and angiogenesis and promotes fibrosis in the kidney and heart. Most importantly, prevention of αKlotho decline, upregulation of endogenous αKlotho production, or direct supplementation of soluble αKlotho are all associated with attenuation of renal fibrosis, retardation of CKD progression, improvement of mineral metabolism, amelioration of cardiac function and morphometry, and alleviation of vascular calcification in CKD. Therefore in rodents, αKlotho is not only a diagnostic and prognostic marker for CKD but the enhancement of endogenous or supplement of exogenous αKlotho are promising therapeutic strategies to prevent, retard, and decrease the comorbidity burden of CKD.

Angiotensin II blockade: how its molecular targets may signal to mitochondria and slow aging. Coincidences with calorie restriction and mTOR inhibition

Caloric restriction (CR), renin angiotensin system blockade (RAS-bl), and rapamycin-mediated mechanistic target of rapamycin (mTOR) inhibition increase survival and retard aging across species. Previously, we have summarized CR and RAS-bl's converging effects, and the mitochondrial function changes associated with their physiological benefits. mTOR inhibition and enhanced sirtuin and KLOTHO signaling contribute to the benefits of CR in aging. mTORC1/mTORC2 complexes contribute to cell growth and metabolic regulation. Prolonged mTORC1 activation may lead to age-related disease progression; thus, rapamycin-mediated mTOR inhibition and CR may extend lifespan and retard aging through mTORC1 interference. Sirtuins by deacetylating histone and transcription-related proteins modulate signaling and survival pathways and mitochondrial functioning. CR regulates several mammalian sirtuins favoring their role in aging regulation. KLOTHO/fibroblast growth factor 23 (FGF23) contribute to control Ca(2+), phosphate, and vitamin D metabolism, and their dysregulation may participate in age-related disease. Here we review how mTOR inhibition extends lifespan, how KLOTHO functions as an aging suppressor, how sirtuins mediate longevity, how vitamin D loss may contribute to age-related disease, and how they relate to mitochondrial function. Also, we discuss how RAS-bl downregulates mTOR and upregulates KLOTHO, sirtuin, and vitamin D receptor expression, suggesting that at least some of RAS-bl benefits in aging are mediated through the modulation of mTOR, KLOTHO, and sirtuin expression and vitamin D signaling, paralleling CR actions in age retardation. Concluding, the available evidence endorses the idea that RAS-bl is among the interventions that may turn out to provide relief to the spreading issue of age-associated chronic disease.

Fibroblast growth factor 23 and Klotho serum levels in healthy children

Data for fibroblast growth factor 23 (FGF23) and particularly for Klotho in healthy children are limited. We aimed to investigate the relationship between FGF23 and Klotho with age and TmP/GFR and to evaluate parameters that might affect FGF23 and Klotho. In 159 healthy children (82 boys) with a mean±SD age of 8.78±3.47years we measured FGF23 (intact FGF23/iFGF23 and C-terminal FGF23/cFGF23) and soluble aKlotho serum levels by ELISA. Mean±SD value for cFGF23, was 51.14±12.79 RU/ml whereas median (range) values for iFGF23 and Klotho were 35 (8.8, 120) pg/ml and 1945 (372, 5866) pg/ml respectively. Neither FGF23 nor Klotho were significantly associated with age. Pubertal children had higher Klotho than prepubertal (p<0.05), and girls had higher levels of cFGF23 (p<0.05) and Klotho (p<0.001) than boys. Serum phosphate and TmP/GFR were positively associated with cFGF23 (p<0.01 and p<0.001), iFGF23 (p<0.05 and p<0.001) and Klotho (p<0.05 and p<0.01). Klotho was positively correlated with IGF-I (p<0.0001) and 1,25 (OH)2 vitamin D (p<0.05). In this study we provide data on cFGF23, iFGF23, and Klotho measured simultaneously in healthy children. The positive association of serum phosphate and TmP/GFR with FGF23 and Klotho suggests that they have a counterregulatory effect on phosphate homeostasis. The strong association of Klotho with IGF-I could indicate a role of Klotho in linear growth through phosphate regulation, but further studies are required.

Effect of carbon monoxide donor CORM-2 on vitamin D3 metabolism

BACKGROUND/AIMS

Carbon monoxide (CO) interferes with cytochrome-dependent cellular functions and acts as gaseous transmitter. CO is released from CO-releasing molecules (CORM) including tricarbonyl-dichlororuthenium (II) dimer (CORM-2), molecules considered for the treatment of several disorders including vascular dysfunction, inflammation, tissue ischemia and organ rejection. Cytochrome P450-sensitive function include formation of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) by renal 25-hydroxyvitamin D3 1-alpha-hydroxylase (Cyp27b1). The enzyme is regulated by PTH, FGF23 and klotho. 1,25(OH)2D3 regulates Ca(2+) and phosphate transport as well as klotho expression. The present study explored, whether CORM-2 influences 1,25(OH)2D3 formation and klotho expression.

METHODS

Mice were treated with intravenous CORM-2 (20 mg/kg body weight). Plasma 1,25(OH)2D3 and FGF23 concentrations were determined by ELISA, phosphate, calcium and creatinine concentrations by colorimetric methods, transcript levels by quantitative RT-PCR and protein expression by western blotting. Fgf23 mRNA transcript levels were further determined in rat osteosarcoma UMR106 cells without or with prior treatment for 24 hours with 20 µM CORM-2.

RESULTS

CORM-2 injection within 24 hours significantly increased FGF23 plasma levels and decreased 1,25(OH)2D3 plasma levels, renal Cyp27b1 gene expression as well as renal klotho protein abundance and transcript levels. Moreover, treatment of UMR106 cells with CORM-2 significantly increased Fgf23 transcript levels.

CONCLUSION

CO-releasing molecule CORM-2 enhances FGF23 expression and release and decreases klotho expression and 1,25(OH)2D3 synthesis. © 2013 S. Karger AG, Basel.

Infection and smoking are associated with decreased plasma concentration of the anti-aging protein, α-klotho

OBJECTIVE

The objective of this study was to determine whether maternal plasma concentrations of soluble α-klotho are different between women with microbial invasion of the intra-amniotic cavity (MIAC) and those without MIAC among preterm labor and intact membranes (PTL) or preterm prelabor rupture of membranes (pPROM).

METHODS

A cross-sectional study was conducted to include women in the following groups: i) PTL with MIAC (n=14); ii) PTL without MIAC (n=79); iii) pPROM with MIAC (n=30); and iv) pPROM without MIAC (n=33). MIAC was defined as a positive amniotic fluid culture for microorganisms (aerobic/anaerobic bacteria or genital mycoplasmas). Amniotic fluid samples were obtained within 48 h of maternal blood collection. Plasma concentration of soluble α-klotho was determined by ELISA.

RESULTS

i) The median plasma concentration (pg/mL) of soluble α-klotho was significantly lower in patients with MIAC than in those without MIAC (787.0 vs. 1117.8; P<0.001). ii) Among patients with PTL, those with MIAC had a lower median plasma concentration (pg/mL) of soluble α-klotho than those without MIAC (787.0 vs. 1138.9; P=0.007). iii) Among patients with pPROM, those with MIAC had a lower median plasma concentration (pg/mL) of soluble α-klotho than those without MIAC (766.4 vs. 1001.6; P=0.045). iv) There was no significant difference in the median plasma concentration of soluble α-klotho between PPROM without MIAC and PTL without MIAC (1001.6 pg/mL vs. 1138.9 pg/mL, respectively; P=0.5). v) After adjustment for potential confounders (maternal age, tobacco use, gestational age at venipuncture), soluble α-klotho remained significantly associated with MIAC (P=0.02); and vi) Among patients without MIAC, smoking was significantly associated with a lower median plasma concentration soluble α-klotho than in non-smokers (794.2 pg/mL vs. 1382.0 pg/mL, respectively; P<0.001); however, this difference was not observed in patients with MIAC.

CONCLUSIONS

Intra-amniotic infection occurring at preterm gestations (regardless of membrane status) was associated with a decrease in maternal plasma concentrations of soluble α-klotho. Moreover, among patients without infection, the plasma concentration of α-klotho was lower in smokers.

High vitamin D3 diet administered during active colitis negatively affects bone metabolism in an adoptive T cell transfer model

Decreased bone mineral density (BMD) represents an extraintestinal complication of inflammatory bowel disease (IBD). Vitamin D₃ has been considered a viable adjunctive therapy in IBD. However, vitamin D₃ plays a pleiotropic role in bone modeling and regulates the bone formation-resorption balance, depending on the physiological environment, and supplementation during active IBD may have unintended consequences. We evaluated the effects of vitamin D₃ supplementation during the active phase of disease on colonic inflammation, BMD, and bone metabolism in an adoptive IL-10-/- CD4⁺ T cell transfer model of chronic colitis. High-dose vitamin D₃ supplementation for 12 days during established disease had negligible effects on mucosal inflammation. Plasma vitamin D₃ metabolites correlated with diet, but not disease, status. Colitis significantly reduced BMD. High-dose vitamin D₃ supplementation did not affect cortical bone but led to a further deterioration of trabecular bone morphology. In mice fed a high vitamin D₃ diet, colitis more severely impacted bone formation markers (osteocalcin and bone alkaline phosphatase) and increased bone resorption markers, ratio of receptor activator of NF-κB ligand to osteoprotegrin transcript, plasma osteoprotegrin level, and the osteoclast activation marker tartrate-resistant acid phosphatase (ACp5). Bone vitamin D receptor expression was increased in mice with chronic colitis, especially in the high vitamin D₃ group. Our data suggest that vitamin D₃, at a dose that does not improve inflammation, has no beneficial effects on bone metabolism and density during active colitis or may adversely affect BMD and bone turnover. These observations should be taken into consideration in the planning of further clinical studies with high-dose vitamin D₃ supplementation in patients with active IBD.

Unraveling the effects of 1,25OH2D3 on global gene expression in pancreatic islets

INTRODUCTION

Vitamin D deficiency has been linked to type 1 and 2 diabetes, whereas supplementation may prevent both diseases. However, the extent of the effects of vitamin D or its metabolites directly on pancreatic islets is still largely unknown. The aim of the present study was to investigate how active vitamin D, 1,25(OH)2D3, affects beta cells directly by establishing its effects on global gene expression in healthy murine islets.

MATERIALS AND METHODS

Pancreatic islets were isolated from 2 to 3 week old C57BL/6 mice and cultured in vitro with 1,25(OH)2D3 or vehicle for 6 and 24h. Total RNA was extracted from the islets and the effects on global gene expression were analyzed using Affymetrix microarrays.

RESULTS AND DISCUSSION

Exposure to 1,25(OH)2D3 compared to vehicle resulted in 306 and 151 differentially expressed genes after 6 and 24h, respectively (n=4, >1.3-fold, p<0.02). Of these 220 were up-regulated, whereas 86 displayed a decreased expression after 6h. Furthermore, expression levels were increased for 124 and decreased for 27 genes following 24h of exposure. Formation of intercellular junctions, cytoskeletal organization, and intracellular trafficking as well as lipid metabolism and ion transport were among the most affected gene classes. Effects on several genes already identified as being part of vitamin D signaling in other cell types were observed along with genes known to affect insulin release, although with our assay we were not able to detect any effects of 1,25(OH)2D3 on glucose-stimulated insulin release from healthy pancreatic islets.

CONCLUSION

The effects of 1,25(OH)2D3 on the expression of cytoskeletal and intracellular trafficking genes along with genes involved in ion transport may influence insulin exocytosis. However, an effect of 1,25(OH)2D3 on insulin release could not be detected for healthy islets in contrast to islets subjected to pathological conditions such as cytokine exposure and vitamin D deficiency as suggested by other studies. Thus, in addition to previously identified tolerogenic effects on the immune system, 1,25(OH)2D3 may affect basic functions of pancreatic beta cells, with the potential to render them more resistant to the detrimental conditions encountered during type 1 and 2 diabetes. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

The kidney sodium-phosphate co-transporter alters bone quality in an age and gender specific manner

Mutations in the kidney NaPiIIa co-transporter are clinically associated with hypophosphatemia, hyperphosphaturia (phosphate wasting), hypercalcemia, nephrolithiasis and bone demineralization. The mouse lacking this co-transporter system was reported to recover its skeletal defects with age, but the "quality" of the bones was not considered. To assess changes in bone quality we examined both male and female NaPiIIa knockout (KO) mice at 1 and 7months of age using micro-computed tomography (micro-CT) and Fourier transform infrared imaging (FTIRI). KO cancellous bones at both ages had greater bone volume fraction, trabecular thickness and lesser structure model index based on micro-CT values relative to age- and sex-matched wildtype animals. There was a sexual-dimorphism in the micro-CT parameters, with differences at 7months seen principally in males. Cortical bone at 1month showed an increase in bone volume fraction, but this was not seen at 7months. Cortical thickness which was elevated in the male and female KO at 1month was lower in the male KO at 7months. FTIRI showed a reduced mineral and acid phosphate content in the male and female KO's bones at 1month with no change in acid phosphate content at 7months. Collagen maturity was reduced in KO cancellous bone at 1month. The observed sexual dimorphism in the micro-CT data may be related to altered phosphate homeostasis, differences in animal growth rates and other factors. These data indicate that the bone quality of the KO mice at both ages differs from the normal and suggests that these bone quality differences may contribute to skeletal phenotype in humans with mutations in this co-transporter.

Phosphate is a vascular toxin

Elevated phosphate (P) levels are seen in advanced renal failure and, together with dysregulated calcium, parathyroid hormone and vitamin D levels, contribute to the complex of chronic kidney disease-mineral and bone disease (CKD-MBD). Converging evidence from in vitro, clinical and epidemiological studies suggest that increased P is associated with vascular calcification and mortality. When vessels are exposed to high P conditions in vitro, they develop apoptosis, convert to bone-like cells and develop extensive calcification. Clinical studies in children on dialysis show that high P is associated with increased vessel wall thickness, arterial stiffness and coronary calcification. Epidemiological studies in adult dialysis patients demonstrate a significant and independent association between raised P and mortality. Importantly, raised P is associated with cardiovascular changes even in pre-dialysis CKD, and also in subjects with normal renal function but high P. All P binders can effectively reduce serum P, and this decrease is linked to improved survival. Raised serum P triggers the release of fibroblast growth factor 23 (FGF-23), which has the beneficial effect of increasing P excretion in early CKD, but is increased several 1,000-fold in dialysis, and may be an independent cardiovascular risk factor. Both FGF-23 and its co-receptor Klotho may have direct effects on the vasculature leading to calcification. Fascinatingly, disturbances in FGF-23-Klotho and raised P have also been associated with premature aging. These data suggest that high P levels have adverse vascular effects and that maintaining the serum P levels in the normal range reduces cardiovascular risk and mortality.

FGF23 associated bone diseases

Recently, fibroblast growth factor 23 (FGF23) has sparked widespread interest because of its potential role in regulating phosphate and vitamin D metabolism. In this review, we summarized the FGF superfamily, the mechanism of FGF23 on phosphate and vitamin D metabolism, and the FGF23 related bone disease.