Acute pharmacodynamic responses to exenatide: Drug-induced increases in insulin secretion and glucose effectiveness.

AIM: Glucagon-like peptide-1 receptor agonists provide multiple benefits to patients with type 2 diabetes, including improved glycaemic control, weight loss and decreased risk of major adverse cardiovascular events. Because drug responses vary among individuals, we initiated investigations to identify genetic variants associated with the magnitude of drug responses. METHODS: Exenatide (5 µg, subcutaneously) or saline (0.2 ml, subcutaneously) was administered to 62 healthy volunteers. Frequently sampled intravenous glucose tolerance tests were conducted to assess the impact of exenatide on insulin secretion and insulin action. This pilot study was a crossover design in which participants received exenatide and saline in random order. RESULTS: Exenatide increased first phase insulin secretion 1.9-fold (p = 1.9 × 10-9 ) and accelerated the rate of glucose disappearance 2.4-fold (p = 2 × 10-10 ). Minimal model analysis showed that exenatide increased glucose effectiveness (Sg ) by 32% (p = .0008) but did not significantly affect insulin sensitivity (Si ). The exenatide-induced increase in insulin secretion made the largest contribution to interindividual variation in exenatide-induced acceleration of glucose disappearance while interindividual variation in the drug effect on Sg contributed to a lesser extent (ß = 0.58 or 0.27, respectively). CONCLUSIONS: This pilot study provides validation for the value of a frequently sampled intravenous glucose tolerance test (including minimal model analysis) to provide primary data for our ongoing pharmacogenomic study of pharmacodynamic effects of semaglutide (NCT05071898). Three endpoints provide quantitative assessments of the effects of glucagon-like peptide-1 receptor agonists on glucose metabolism: first phase insulin secretion, glucose disappearance rates and glucose effectiveness.

Genome-wide association study in 79,366 European-ancestry individuals informs the genetic architecture of 25-hydroxyvitamin D levels.

Vitamin D is a steroid hormone precursor that is associated with a range of human traits and diseases. Previous GWAS of serum 25-hydroxyvitamin D concentrations have identified four genome-wide significant loci (GC, NADSYN1/DHCR7, CYP2R1, CYP24A1). In this study, we expand the previous SUNLIGHT Consortium GWAS discovery sample size from 16,125 to 79,366 (all European descent). This larger GWAS yields two additional loci harboring genome-wide significant variants (P = 4.7×10-9 at rs8018720 in SEC23A, and P = 1.9×10-14 at rs10745742 in AMDHD1). The overall estimate of heritability of 25-hydroxyvitamin D serum concentrations attributable to GWAS common SNPs is 7.5%, with statistically significant loci explaining 38% of this total. Further investigation identifies signal enrichment in immune and hematopoietic tissues, and clustering with autoimmune diseases in cell-type-specific analysis. Larger studies are required to identify additional common SNPs, and to explore the role of rare or structural variants and gene-gene interactions in the heritability of circulating 25-hydroxyvitamin D levels.

Multistage genome-wide association meta-analyses identified two new loci for bone mineral density.

Aiming to identify novel genetic variants and to confirm previously identified genetic variants associated with bone mineral density (BMD), we conducted a three-stage genome-wide association (GWA) meta-analysis in 27 061 study subjects. Stage 1 meta-analyzed seven GWA samples and 11 140 subjects for BMDs at the lumbar spine, hip and femoral neck, followed by a Stage 2 in silico replication of 33 SNPs in 9258 subjects, and by a Stage 3 de novo validation of three SNPs in 6663 subjects. Combining evidence from all the stages, we have identified two novel loci that have not been reported previously at the genome-wide significance (GWS; 5.0 × 10(-8)) level: 14q24.2 (rs227425, P-value 3.98 × 10(-13), SMOC1) in the combined sample of males and females and 21q22.13 (rs170183, P-value 4.15 × 10(-9), CLDN14) in the female-specific sample. The two newly identified SNPs were also significant in the GEnetic Factors for OSteoporosis consortium (GEFOS, n = 32 960) summary results. We have also independently confirmed 13 previously reported loci at the GWS level: 1p36.12 (ZBTB40), 1p31.3 (GPR177), 4p16.3 (FGFRL1), 4q22.1 (MEPE), 5q14.3 (MEF2C), 6q25.1 (C6orf97, ESR1), 7q21.3 (FLJ42280, SHFM1), 7q31.31 (FAM3C, WNT16), 8q24.12 (TNFRSF11B), 11p15.3 (SOX6), 11q13.4 (LRP5), 13q14.11 (AKAP11) and 16q24 (FOXL1). Gene expression analysis in osteogenic cells implied potential functional association of the two candidate genes (SMOC1 and CLDN14) in bone metabolism. Our findings independently confirm previously identified biological pathways underlying bone metabolism and contribute to the discovery of novel pathways, thus providing valuable insights into the intervention and treatment of osteoporosis.

Decreased bone mineral density in subjects carrying familial defective apolipoprotein B-100.

CONTEXT: Although numerous epidemiologic studies have documented associations between osteoporosis and cardiovascular disease, the mechanisms underlying this association remain to be clarified. One hypothesis is that hyperlipidemia may be a common predisposing factor to both atherosclerotic heart disease and bone fragility. OBJECTIVE: To evaluate this, we compared bone mineral density (BMD) between subjects with and without the R3500Q APOB mutation, the cause of familial defective apolipoprotein B-100, which has been previously shown to markedly increase low-density lipoprotein cholesterol (LDL-C). We hypothesized that R3500Q carriers would have lower BMD due to lifetime, elevated LDL-C. DESIGN: This was a a cross-sectional study in the Old Order Amish (OOA) population. PARTICIPANTS: The R3500Q APOB mutation is present at a high frequency (∼6% vs <0.5%) in the OOA population due to a founder effect. Therefore, we conducted analysis on 1097 Amish individuals of whom 125 were R3500Q carriers. MAIN OUTCOME MEASURE: BMD was measured by dual-energy x-ray absorptiometry. RESULTS: After adjusting for age, age(2), sex, body mass index, and family structure, carriers for the Q risk allele had significantly lower BMD than noncarriers at the femoral neck (P = .037), lumbar spine (P = .035) and whole body (P = .016). Adjusting for LDL-C attenuated the association between R3500Q genotype and BMD but did not completely explain the relationship. Subgroup analyses showed no significant interactions with sex, age, or presence of metabolic syndrome. CONCLUSION: These results use the unique genetic architecture of the OOA population to provide a novel line of evidence supporting a causal role for elevated LDL-C in lowering BMD.

A functional haplotype in EIF2AK3, an ER stress sensor, is associated with lower bone mineral density.

EIF2AK3 is a type I transmembrane protein that functions as an endoplasmic reticulum (ER) stress sensor to regulate global protein synthesis. Rare mutations in EIF2AK3 cause Wolcott-Rallison syndrome (OMIM 226980), an autosomal recessive disorder characterized by diabetes, epiphyseal dysplasia, osteoporosis, and growth retardation. To investigate the role of common genetic variation in EIF2AK3 as a determinant of bone mineral density (BMD) and osteoporosis, we sequenced all exons and flanking regions, then genotyped six potentially functional single nucleotide polymorphisms (SNPs) in this gene in 997 Amish subjects for association analysis, and attempted replication in 887 Mexican Americans. We found that the minor allele of a nonsynonymous SNP rs13045 had borderline associations with decreased forearm BMD in both discovery and replication cohorts (unadjusted p = 0.036 and ß = -0.007 for the Amish; unadjusted p = 0.031 and ß = -0.008 for Mexican Americans). A meta-analysis indicated this association achieved statistical significance in the combined sample (unadjusted p = 0.003; Bonferroni corrected p = 0.009). Rs13045 and three other potentially functional SNPs, a promoter SNP (rs6547787) and two nonsynonymous SNPs (rs867529 and rs1805165), formed two haplotypes: a low-BMD associated haplotype, denoted haplotype B [minor allele frequency (MAF) = 0.311] and a common haplotype A (MAF = 0.676). There were no differences in mRNA expression in lymphoblastoid cell lines between the two haplotypes. However, after treating lymphoblastoid cell lines with thapsigargin to induce ER stress, cell lines with haplotype B showed increased sensitivity to ER stress (p = 0.014) compared with cell lines with haplotype A. Taken together, our results suggest that common nonsynonymous sequence variants in EIF2AK3 have a modest effect on ER stress response and may contribute to the risk for low BMD through this mechanism.

Vitamin D: a potential role in reducing suicide risk?

Suicide attempts are known to peak in the spring, overlapping with the time of year when 25-hydroxyvitamin D [25(OH)D] levels are at their nadir in the northern hemisphere because of negligible skin production of vitamin D owing to low levels of ultraviolet B radiation. Low levels of 25(OH)D, the vitamin D metabolite used to diagnose vitamin D deficiency, have been associated with certain pro-suicidal factors such as exacerbation of depression, anxiety, psychosis, and certain medical conditions. Therefore, we hypothesize that vitamin D deficiency could also be associated with increased risk of completed suicides. Here, we briefly review the literature on vitamin D, its deficiency, and its reported association with certain risk factors for suicide.

Association of the vitamin D metabolism gene CYP24A1 with coronary artery calcification.

OBJECTIVE: The vitamin D endocrine system is essential for calcium homeostasis, and low levels of vitamin D metabolites have been associated with cardiovascular disease risk. We hypothesized that DNA sequence variation in genes regulating vitamin D metabolism and signaling pathways might influence variation in coronary artery calcification (CAC). METHODS AND RESULTS: We genotyped single-nucleotide polymorphisms (SNPs) in GC, CYP27B1, CYP24A1, and VDR and tested their association with CAC quantity, as measured by electron beam computed tomography. Initial association studies were carried out in a discovery sample comprising 697 Amish subjects, and SNPs nominally associated with CAC quantity (4 SNPs in CYP24A1, P=0.008 to 0.00003) were then tested for association with CAC quantity in 2 independent cohorts of subjects of white European ancestry (Genetic Epidemiology Network of Arteriopathy study [n=916] and the Penn Coronary Artery Calcification sample [n=2061]). One of the 4 SNPs, rs2762939, was associated with CAC quantity in both the Genetic Epidemiology Network of Arteriopathy (P=0.007) and Penn Coronary Artery Calcification (P=0.01) studies. In all 3 populations, the rs2762939 C allele was associated with lower CAC quantity. Metaanalysis for the association of this SNP with CAC quantity across all 3 studies yielded a P value of 2.9×10(-6). CONCLUSIONS: A common SNP in the CYP24A1 gene was associated with CAC quantity in 3 independent populations. This result suggests a role for vitamin D metabolism in the development of CAC quantity.

Serum 25-hydroxyvitamin d levels are not associated with subclinical vascular disease or C-reactive protein in the old order amish.

The relationship between vitamin D metabolites and subclinical vascular disease is controversial. Because low serum levels of 25-hydroxyvitamin D (25(OH)D) have been associated with many cardiovascular disease (CVD) risk factors, we hypothesized that serum 25(OH)D levels would be inversely associated with inflammation as measured by C-reactive protein (CRP) and with subclinical vascular disease as measured by carotid intimal medial thickness (cIMT) and coronary artery calcification (CAC). We measured 25(OH)D levels in 650 Amish participants. CAC was measured by computed tomography and cIMT by ultrasound. The associations of 25(OH)D levels with natural log(CAC + 1), cIMT, and natural log(CRP) levels were estimated after adjustment for age, sex, family structure, and season of examination. Additional analyses were carried out adjusting for body mass index (BMI) and other CVD risk factors. 25(OH)D deficiency (<20 ng/ml) and insufficiency (21-30 ng/ml) were common among the Amish (38.2% and 47.7%, respectively). 25(OH)D levels were associated with season, age, BMI, and parathyroid hormone levels. In neither the minimally or fully adjusted analyses were significant correlations observed between 25(OH)D levels and CAC, cIMT, or CRP (R (2) < 0.01 for all). Contrary to our hypothesis, this study failed to detect a cross-sectional association between serum 25(OH)D levels and CAC, cIMT, or CRP. Either there is no causal relationship between 25(OH)D and CVD risk, or if there is, it may be mediated through mechanisms other than subclinical vascular disease severity.

Osteoporosis-pseudoglioma syndrome: description of 9 new cases and beneficial response to bisphosphonates.

Osteoporosis-pseudoglioma syndrome (OPPG) is a rare autosomal recessive disorder of severe juvenile osteoporosis and congenital blindness, due to mutations in the low-density lipoprotein receptor-related protein 5 (LRP5) gene. Approximately fifty cases of OPPG have been reported. We report 9 new cases of OPPG, in three related nuclear families of Conservative Mennonites in Pennsylvania. All 9 children with OPPG were blind and had osteoporosis. Four of six parents had low bone mineral density (BMD) or osteoporosis; 2 were normal. Sequence analysis from genomic DNA revealed homozygosity for a nonsense mutation of exon 6 of LRP5 (W425X) in four OPPG cases tested in families A and C. In family B, OPPG cases were compound heterozygotes for the exon 6 W425X LRP5 mutation and a second exon 6 mutation (T409A); bone phenotype was milder than in family A. Neither of these mutations was present in an unrelated normal. The four treated OPPG patients all responded to bisphosphonates (duration 1.5-6.5 years) with improvement in Z-scores. One patient had a negligible response to teriparatide. In summary, we report 9 new cases of OPPG due to two novel LRP5 mutations, note a milder bone phenotype but similar ocular phenotype in LRP5 W425X/T409A compound heterozygotes than in W425X homozygotes and describe positive response to bisphosphonate treatment in four cases.

Coronary artery calcification in patients with primary hyperparathyroidism in comparison with control subjects from the multi-ethnic study of atherosclerosis.

OBJECTIVE: To determine whether coronary artery calcification (CAC) is increased in patients with primary hyperparathyroidism (pHPT) because of the presence of hypercalcemia, which has been shown in vitro to promote vascular calcification. METHODS: Electron beam computed tomography of the coronary arteries was performed on 20 patients with pHPT referred to our endocrinology clinic for evaluation of hypercalcemia. All patients were nonsmokers, with normal renal function, no history of diabetes, and no history of coronary artery disease. CAC in the patients with pHPT was compared with that in population-based control subjects from the Multi-Ethnic Study of Atherosclerosis (MESA). Two methods of analysis were used: (1) calculation of the odds ratio of CAC and (2) a nested case-control (1:4) study. RESULTS: One patient with pHPT had a history of nephrolithiasis; the other 19 patients were asymptomatic. The mean age (+/- SD) of the patients with pHPT was 57.3 +/- 9.1 years, the mean serum calcium concentration was 2.68 +/- 0.18 mmol/L, and the mean intact parathyroid hormone level was 119 +/- 76.5 pg/mL. Of the 20 patients, 14 had CAC scores of zero. The odds ratio for measurable CAC in the presence of pHPT in comparison with that in the MESA control subjects was 0.17, which was not significant. In the matched analysis, the CAC scores for the patients with pHPT did not differ significantly from those for the MESA control subjects (P = 0.25 with use of the Wilcoxon test). CONCLUSION: We found no evidence for a difference in CAC in patients with pHPT in comparison with the population-based control subjects in this small pilot study.

The inpatient consultation approach to osteoporosis treatment in patients with a fracture. Is automatic consultation needed?

BACKGROUND: Osteoporosis has been described as a "silent epidemic." We describe an osteoporosis consultation program to facilitate the evaluation and treatment of inpatients with fragility fractures. METHODS: The inpatient orthopaedic team voluntarily requested an osteoporosis consultation on all patients with a fragility fracture. The osteoporosis consultant evaluated patients for secondary causes and started treatment with calcium, vitamin D, and bisphosphonates unless contraindicated. From November 2001 to December 2003, fifty-three osteoporosis consultations were performed. A retrospective review of the charts of all patients with a hip fracture treated during this twenty-six-month period revealed that only 47% were actually seen by the osteoporosis consultants, creating an unintentional "nonintervention" cohort of thirty-one patients with a hip fracture. Treatment for osteoporosis was assessed by a review of the inpatient charts and by a telephone interview after discharge. RESULTS: The study group consisted of eighty-four patients, which included fifty-three in the intervention cohort (twenty-eight hip and twenty-five other fractures) and thirty-one in the nonintervention cohort (all patients with a hip fracture). In the intervention cohort, most patients were vitamin-D deficient. Calcium and vitamin-D treatment was recommended for all fifty-three patients, and bisphosphonates were recommended for forty-one of the fifty-three patients in the intervention cohort. In the nonintervention cohort, two patients received calcium and vitamin D and one received a bisphosphonate; the difference between the cohorts was significant (p < 0.0001). In the intervention cohort, twenty-seven of the thirty-four patients who were available for a telephone interview after discharge (at a mean of eighteen months) remained on calcium and vitamin D; twenty-two of the thirty-four patients remained on bisphosphonates. In the nonintervention cohort, only one of the twelve patients who were available for follow-up (at a mean of thirty-nine months) was receiving calcium and vitamin D and none were on bisphosphonate treatment. CONCLUSIONS: This consultation program cannot be considered an outright success since only half of all patients with a hip fracture actually received a consultation. However, osteoporosis consultation, when provided, facilitated the recognition of secondary causes and the generic treatment of osteoporosis, and inpatients started on treatment generally continued the medication after discharge. The results of this study strongly support the need for a mechanism of automatic osteoporosis consultation for inpatients with a fragility fracture and suggest that, if consultation is reliably obtained, this approach can be effective in improving patient care. LEVEL OF EVIDENCE: Therapeutic Level III.

Localisation of mesenchymal tumours by somatostatin receptor imaging.

Oncogenic osteomalacia, an acquired hypophosphataemic syndrome associated with mesenchymal tumours, is characterised by hypophosphataemia secondary to inappropriate phosphaturia, reduced concentrations of serum calcitriol, and defective bone mineralisation. Removal of these tumours results in complete reversal of these biochemical defects. However, because these tumours are small, slow-growing, and frequently situated in unusual anatomical sites, conventional imaging techniques often fail to detect them. Since mesenchymal tumours express somatostatin receptors, we postulated that somatostatin analogues would be able to detect these tumours. We did Indium-111 labeled pentetreotide imaging in seven patients with oncogenic osteomalacia. In five patients, we identified a mesenchymal tumour, and clinical improvement occurred after tumour resection. Our findings suggest that 111In-pentetreotide imaging effectively detects occult mesenchymal tumours and facilitates surgical treatment of oncogenic osteomalacia.