Association between vitamin D status and physical function in the severely obese

CONTEXT

Mortality is 85% higher in severely obese subjects (body mass index [BMI] > 40 kg/m(2)) than in subjects with a healthy BMI; poor physical function may be contributory. Hypovitaminosis D is common in obese subjects and is associated with physical dysfunction in the elderly.

OBJECTIVE

We determined the relationship between vitamin D status and physical function in severely obese subjects.

DESIGN, SETTING, AND PATIENTS

We conducted a clinic-based, cross-sectional study of severely obese subjects. Participants were stratified into three groups according to the Institute of Medicine (IOM) vitamin D status categorization.

MAIN OUTCOME MEASURES

We compared levels of self-reported activity and times taken to walk 500 m and to ascend and descend a 17-cm step 50 times.

RESULTS

We recruited 252 subjects (age, 43.7 ± 11.2 y; BMI, 50.7 ± 9.7 kg/m(2)); 25-hydroxyvitamin D (25OHD) concentrations were less than 30 nmol/L in 109 participants. Participants with a 25OHD > 50 nmol/L, compared to those with a 25OHD < 30 nmol/L, had the highest activity levels (3.1 ± 3.4 h/wk versus 1.5 ± 2.5 h/wk; P = .015) and the shortest 500-m walk times (6.2 ± 1.1 min versus 7.4 ± 1.5 min; P = .003). Serum 25OHD concentrations had a weakly positive association with activity level (r = 0.19; P = .008) and a moderately negative association with 500-m walk time (r = -0.343; P < .001).

CONCLUSIONS

Vitamin D status had a significant relationship with physical activity and physical function in this cohort of severely obese subjects. Low activity levels are likely to perpetuate the problem of hypovitaminosis D due to less time spent outdoors. Studies exploring the effects of vitamin D supplementation in this population are warranted.

The double-edged sword of vitamin D in Ireland: the need for public health awareness about too much as well as too little

INTRODUCTION

The Institute of Medicine (IOM) 2011 on dietary references intakes for calcium and vitamin D specified that a 25-hydroxyvitamin D (25OHD) level below 30 nmol/L indicated risk of deficiency and that a level above 125 nmol/L indicated risk of harm.

METHODS

We noted a high prevalence of hypovitaminosis D (23.9 %) and a substantive prevalence of hypervitaminosis D (4.8 %) in a retrospective audit of clinical samples (n = 10,181) obtained over 10 months in 2013.

CONCLUSION

Hypovitaminosis D should be corrected by low dose supplementation (5 µg or 200 IU daily) with some at-risk groups needing higher doses (10 µg or 400 IU daily) based on 25OHD levels. Whereas, those taking high-dose vitamin D supplements based on mistaken beliefs about recently authorised claims of benefit for muscle function and misleading unauthorised claims need to be alerted to the potential harms of excessive supplementation.

Clinician approach to diagnosis of stress fractures including bisphosphonate-associated fractures

Stress fractures are repetitive strain injuries that occur in normal bones and in abnormal bones. Stress fractures share many features in common but differences depend on the status of the underlying bone. This review article for clinicians addresses aspects about stress fractures with particular respect to fatigue fractures, Looser zones of osteomalacia, atypical Looser zones, atypical femoral fractures associated with bisphosphonate therapy and stress fractures in Paget's disease of bone.

Sarcoplasmic reticulum Ca2+ uptake and leak properties, and SERCA isoform expression, in type I and type II fibres of human skeletal muscle

The Ca(2+) uptake properties of the sarcoplasmic reticulum (SR) were compared between type I and type II fibres of vastus lateralis muscle of young healthy adults. Individual mechanically skinned muscle fibres were exposed to solutions with the free [Ca(2+)] heavily buffered in the pCa range (-log10[Ca(2+)]) 7.3-6.0 for set times and the amount of net SR Ca(2+) accumulation determined from the force response elicited upon emptying the SR of all Ca(2+). Western blotting was used to determine fibre type and the sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) isoform present in every fibre examined. Type I fibres contained only SERCA2 and displayed half-maximal Ca(2+) uptake rate at ∼pCa 6.8, whereas type II fibres contained only SERCA1 and displayed half-maximal Ca(2+) uptake rate at ∼pCa 6.6. Maximal Ca(2+) uptake rate was ∼0.18 and ∼0.21 mmol Ca(2+) (l fibre)(-1) s(-1) in type I and type II fibres, respectively, in good accord with previously measured SR ATPase activity. Increasing free [Mg(2+)] from 1 to 3 mM had no significant effect on the net Ca(2+) uptake rate at pCa 6.0, indicating that there was little or no calcium-induced calcium release occurring through the Ca(2+) release channels during uptake in either fibre type. Ca(2+) leakage from the SR at pCa 8.5, which is thought to occur at least in part through the SERCA, was ∼2-fold lower in type II fibres than in type I fibres, and was little affected by the presence of ADP, in marked contrast to the larger SR Ca(2+) leak observed in rat muscle fibres under the same conditions. The higher affinity of Ca(2+) uptake in the type I human fibres can account for the higher relative level of SR Ca(2+) loading observed in type I compared to type II fibres, and the SR Ca(2+) leakage characteristics of the human fibres suggest that the SERCAs are regulated differently from those in rat and contribute comparatively less to resting metabolic rate.

Effects of type 1 diabetes, sprint training and sex on skeletal muscle sarcoplasmic reticulum Ca2+ uptake and Ca2+-ATPase activity

Calcium cycling is integral to muscle performance during the rapid muscle contraction and relaxation of high-intensity exercise. Ca(2+) handling is altered by diabetes mellitus, but has not previously been investigated in human skeletal muscle. We investigated effects of high-intensity exercise and sprint training on skeletal muscle Ca(2+) regulation among men and women with type 1 diabetes (T1D, n = 8, 3F, 5M) and matched non-diabetic controls (CON, n = 8, 3F, 5M). Secondarily, we examined sex differences in Ca(2+) regulation. Subjects undertook 7 weeks of three times-weekly cycle sprint training. Before and after training, performance was measured, and blood and muscle were sampled at rest and after high-intensity exercise. In T1D, higher Ca(2+)-ATPase activity (+28%) and Ca(2+) uptake (+21%) than in CON were evident across both times and days (P < 0.05), but performance was similar. In T1D, resting Ca(2+)-ATPase activity correlated with work performed until exhaustion (r = 0.7, P < 0.01). Ca(2+)-ATPase activity, but not Ca(2+) uptake, was lower (-24%, P < 0.05) among the women across both times and days. Intense exercise did not alter Ca(2+)-ATPase activity in T1D or CON. However, sex differences were evident: Ca(2+)-ATPase was reduced with exercise among men but increased among women across both days (time × sex interaction, P < 0.05). Sprint training reduced Ca(2+)-ATPase (-8%, P < 0.05), but not Ca(2+) uptake, in T1D and CON. In summary, skeletal muscle Ca(2+) resequestration capacity was increased in T1D, but performance was not greater than CON. Sprint training reduced Ca(2+)-ATPase in T1D and CON. Sex differences in Ca(2+)-ATPase activity were evident and may be linked with fibre type proportion differences.

Endogenous and maximal sarcoplasmic reticulum calcium content and calsequestrin expression in type I and type II human skeletal muscle fibres

The relationship between sarcoplasmic reticulum (SR) Ca(2+) content and calsequestrin (CSQ) isoforms was investigated in human skeletal muscle. A fibre-lysing assay was used to quantify the endogenous Ca(2+) content and maximal Ca(2+) capacity of the SR in skinned segments of type I and type II fibres from vastus lateralis muscles of young healthy adults. Western blotting of individual fibres showed the great majority contained either all fast or all slow isoforms of myosin heavy chain (MHC), troponins C and I, tropomyosin and SERCA, and that the strontium sensitivity of the force response was closely indicative of the troponin C isoform present. The endogenous SR Ca(2+) content was slightly lower in type I compared to type II fibres (0.76 ± 0.03 and 0.85 ± 0.02 mmol Ca(2+) per litre of fibre, respectively), with virtually all of this Ca(2+) evidently being in the SR, as it could be rapidly released with a caffeine-low [Mg(2+)] solution (only 0.08 ± 0.01 and <0.07 mmol l(-1), respectively, remaining). The maximal Ca(2+) content that could be reached with SR Ca(2+) loading was 1.45 ± 0.04 and 1.79 ± 0.03 mmol l(-1) in type I and type II fibres, respectively (P < 0.05). In non-lysed skinned fibres, where the SR remained functional, repeated cycles of caffeine-induced Ca(2+) release and subsequent Ca(2+) reloading similarly indicated that (i) maximal SR Ca(2+) content was lower in type I fibres than in type II fibres (P < 0.05), and (ii) the endogenous Ca(2+) content represented a greater percentage of maximal content in type I fibres compared to type II fibres (∼59% and 41%, respectively, P < 0.05). Type II fibres were found on average to contain ∼3-fold more CSQ1 and ∼5-fold less CSQ2 than type I fibres (P < 0.001). The findings are consistent with the SR Ca(2+) content characteristics in human type II fibres being primarily determined by the CSQ1 abundance, and in type I fibres by the combined amounts of both CSQ1 and CSQ2.

Limited utility of tartrate-resistant acid phosphatase isoform 5b in assessing response to therapy in osteoporosis

BACKGROUND

Tartrate-resistant acid phosphatase isoform 5b (TRACP5b) is a serum bone resorption marker. Our aim was to investigate its utility in monitoring metabolic bone disease.

METHODS

Serum TRACP5b, C-terminal cross-linking telopeptide of type I collagen, urine N-terminal cross-linking telopeptide of type I collagen and free deoxypyridinoline were measured pre- and post-treatment with a parathyroid hormone analogue [PTH (1-34)] (n = 14) or a bisphosphonate (N-BP) (n = 8). TRACP5b, bone alkaline phosphatase (bone ALP), 25-hydroxyvitamin D (25OHD) and parathyroid hormone (PTH) were measured in 100 osteoporosis patients on prolonged bisphosphonate therapy.

RESULTS

Changes in TRACP5b were smaller in magnitude but mimicked those of other bone resorption markers. Absolute changes in TRACP5b and the other resorption markers correlated significantly (p < 0.001). In patients on long-term bisphosphonates, TRACP5b and bone ALP levels were not suppressed. Vitamin D status was consistent with the level of supplementation.

CONCLUSION

TRACP5b has limited utility as a single marker of metabolic bone disease treatment.

Geographic and taxonomic disparities in species diversity: dispersal and diversification rates across Wallace's line

Broad-scale patterns of species diversity have received much attention in the literature, yet the mechanisms behind their formation may not explain species richness disparities across small spatial scales. Few taxa display high species diversity on either side of Wallace's Line and our understanding of the processes causing this biogeographical pattern remains limited, particularly in plant lineages. To understand the evolution of this biogeographical pattern, a time-calibrated molecular phylogeny of Livistoninae palms (Arecaceae) was used to infer the colonization history of the Sahul tectonic plate region and to test for disparities in diversification rates across taxa and across each side of Wallace's Line. Our analyses allowed us to examine how timing, migration history, and shifts in diversification rates have contributed to shape the biogeographical pattern observed in Livistoninae. We inferred that each of the three genera found in Sahul crossed Wallace's Line only once and relatively recently. In addition, at least two of the three dispersing genera underwent an elevation in their diversification rate leading to high species richness on each side of Wallacea. The correspondence of our results with Southeast Asian geologic and climatic history show how palms emerge as excellent models for understanding the historical formation of fine-scale biogeographic patterns in a phylogenetic framework.

Immunomodulators for multiple sclerosis may ameliorate spinal bone loss

BACKGROUND

The effect of immunomodulator therapy (IMT) for multiple sclerosis (MS) on bone turnover is unknown.

AIM

The aim of this study was to assess bone turnover in MS patients on IMT.

METHODS

MS patients (n = 29) on maintenance IMT had repeat measurement of bone mineral density (BMD) after a 4.0 ± 0.4 years; bone turnover markers (BTM) were measured at the time of repeat BMD.

RESULTS

BMD was unchanged at the spine but declined at the hip. BTMs, both resorption and formation, were reduced compared to normative range that may indicate an anti-resorptive action of IMT. Significant negative correlations were noted between BTMs and changes in BMD at spine but not hip.

CONCLUSION

These observations suggest that IMT may have a beneficial effect on spinal bone by an antiresorptive action. A prospective study of the effect of IMT on BMD and bone turnover is warranted.

Infusion with the antioxidant N-acetylcysteine attenuates early adaptive responses to exercise in human skeletal muscle

AIM

Production of reactive oxygen species (ROS) in skeletal muscle is markedly increased during exercise and may be essential for exercise adaptation. We, therefore, investigated the effects of infusion with the antioxidant N-acetylcysteine (NAC) on exercise-induced activation of signalling pathways and genes involved in exercise adaptation in human skeletal muscle.

METHODS

Subjects completed two exercise tests, 7 days apart, with saline (control, CON) or NAC infusion before and during exercise. Exercise tests comprised of cycling at 71% VO(2peak) for 45 min, and then 92% VO(2peak) to fatigue, with vastus lateralis biopsies at pre-infusion, after 45-min cycling and at fatigue.

RESULTS

Analysis was conducted on the mitogen-activated protein kinase signalling pathways, demonstrating that NAC infusion blocked the exercise-induced increase in JNK phosphorylation, but not ERK1/2, or p38 MAPK. Nuclear factor-κB p65 phosphorylation was unaffected by exercise; however, it was reduced in NAC at fatigue by 14% (P < 0.05) compared with pre-infusion. Analysis of exercise and/or ROS-sensitive genes demonstrated that exercise-induced mRNA expression is ROS dependent of MnSOD, but not PGC-1α, interleukin-6, monocyte chemotactic protein-1, or heat-shock protein 70.

CONCLUSION

These results suggest that inhibition of ROS attenuates some skeletal muscle cell signalling pathways and gene expression involved in adaptations to exercise.

Evaluating multiple criteria for species delimitation: an empirical example using Hawaiian palms (Arecaceae: Pritchardia)

BACKGROUND

Robust species delimitations are fundamental for conservation, evolutionary, and systematic studies, but they can be difficult to estimate, particularly in rapid and recent radiations. The consensus that species concepts aim to identify evolutionarily distinct lineages is clear, but the criteria used to distinguish evolutionary lineages differ based on the perceived importance of the various characteristics of evolving populations. We examined three different species-delimitation criteria (monophyly, absence of genetic intermediates, and diagnosability) to determine whether currently recognized species of Hawaiian Pritchardia are distinct lineages.

RESULTS

Data from plastid and nuclear genes, microsatellite loci, and morphological characters resulted in various levels of lineage subdivision that were likely caused by differing evolutionary rates between data sources. Additionally, taxonomic entities may be confounded because of the effects of incomplete lineage sorting and/or gene flow. A coalescent species tree was largely congruent with the simultaneous analysis, consistent with the idea that incomplete lineage sorting did not mislead our results. Furthermore, gene flow among populations of sympatric lineages likely explains the admixture and lack of resolution between those groups.

CONCLUSIONS

Delimiting Hawaiian Pritchardia species remains difficult but the ability to understand the influence of the evolutionary processes of incomplete lineage sorting and hybridization allow for mechanisms driving species diversity to be inferred. These processes likely extend to speciation in other Hawaiian angiosperm groups and the biota in general and must be explicitly accounted for in species delimitation.

S-glutathionylation of troponin I (fast) increases contractile apparatus Ca2+ sensitivity in fast-twitch muscle fibres of rats and humans

Oxidation can decrease or increase the Ca2+ sensitivity of the contractile apparatus in rodent fast-twitch (type II) skeletal muscle fibres, but the reactions and molecular targets involved are unknown. This study examined whether increased Ca2+ sensitivity is due to S-glutathionylation of particular cysteine residues. Skinned muscle fibres were directly activated in heavily buffered Ca2+ solutions to assess contractile apparatus Ca2+ sensitivity. Rat type II fibres were subjected to S-glutathionylation by successive treatments with 2,2′-dithiodipyridine (DTDP) and glutathione (GSH), and displayed a maximal increase in pCa50 (−log10 [Ca2+] at half-maximal force) of ∼0.24 pCa units, with little or no effect on maximum force or Hill coefficient. Partial similar effect was produced by exposure to oxidized gluthathione (GSSG, 10 mM) for 10 min at pH 7.1, and near-maximal effect by GSSG treatment at pH 8.5. None of these treatments significantly altered Ca2+ sensitivity in rat type I fibres. Western blotting showed that both the DTDP–GSH and GSSG–pH 8.5 treatments caused marked S-glutathionylation of the fast troponin I isoform (TnI(f)) present in type II fibres, but not of troponin C (TnC) or myosin light chain 2. Both the increased Ca2+ sensitivity and glutathionylation of TnI(f) were blocked by N-ethylmaleimide (NEM). S-nitrosoglutathione (GSNO) also increased Ca2+ sensitivity, but only in conditions where it caused S-glutathionylation of TnI(f). In human type II fibres from vastus lateralis muscle, DTDP–GSH treatment also caused similar increased Ca2+ sensitivity and S-glutathionylation of TnI(f). When the slow isoform of TnI in type I fibres of rat was partially substituted (∼30%) with TnI(f), DTDP–GSH treatment caused a significant increase in Ca2+ sensitivity (∼0.08 pCa units). TnIf in type II fibres from toad and chicken muscle lack Cys133 present in mammalian TnIf, and such fibres showed no change in Ca2+ sensitivity with DTDP–GSH nor any S-glutathionylation of TnI(f) (latter examined only in toad). Following 40 min of cycling exercise in human subjects (at ∼60% peak oxygen consumption), TnI(f) in vastus lateralis muscle displayed a marked increase in S-glutathionylation (∼4-fold). These findings show that S-glutathionylation of TnI(f), most probably at Cys133, increases the Ca2+ sensitivity of the contractile apparatus, and that this occurs in exercising humans, with likely beneficial effects on performance.

Phylogeny of Celastraceae tribe Euonymeae inferred from morphological characters and nuclear and plastid genes

The phylogeny of Celastraceae tribe Euonymeae (≈ 230 species in eight genera in both the Old and New Worlds) was inferred using morphological characters together with plastid (matK, trnL-F) and nuclear (ITS and 26S rDNA) genes. Tribe Euonymeae has been defined as those genera of Celastraceae with generally opposite leaves, isomerous carpels, loculicidally dehiscent capsules, and arillate seeds (except Microtropis). Euonymus is the most diverse (129 species) and widely cultivated genus in the tribe. We infer that tribe Euonymeae consists of at least six separate lineages within Celastraceae and that a revised natural classification of the family is needed. Microtropis and Quetzalia are inferred to be distinct sister groups that together are sister to Zinowiewia. The endangered Monimopetalum chinense is an isolated and early derived lineage of Celastraceae that represents an important component of phylogenetic diversity within the family. Hedraianthera is sister to Brassiantha, and we describe a second species (Brassiantha hedraiantheroides A.J. Ford) that represents the first reported occurrence of this genus in Australia. Euonymus globularis, from eastern Australia, is sister to Menepetalum, which is endemic to New Caledonia, and we erect a new genus (Dinghoua R.H. Archer) for it. The Madagascan species of Euonymus are sister to Pleurostylia and recognized as a distinct genus (Astrocassine ined.). Glyptopetalum, Torralbasia, and Xylonymus are all closely related to Euonymus sensu stricto and are questionably distinct from it. Current intrageneric classifications of Euonymus are not completely natural and require revision.

High bone turnover in Irish professional jockeys

SUMMARY

Professional jockeys are routinely exposed to high impact trauma and sustain fractures frequently. We found that jockeys restrict their caloric intake in order to maintain regulation weights, and that bone turnover is high. There are significant health and safety implications for the racing industry.

INTRODUCTION

Professional jockeys routinely sustain fractures from high impact falls. Jockeys maintain a low percentage body fat and a low body mass index (BMI) to achieve low weight targets in order to race. We evaluated dietary habits and bone metabolism in jockeys.

METHODS

Bone mineral density (BMD) was measured in 27 male jockeys of the 144 jockeys licensed in Ireland. Fourteen (52%) had BMD T score below -1.0, of whom 12 consented to clinical review, nutritional survey, endocrine studies, and bone turnover markers (BTM). BTM were compared to age- and sex-matched controls (n = 16).

RESULTS

BMI was 20.6 +/- 1.7 kg/m(2); previous fracture frequency was 3.2 +/- 2.0 per rider. All had normal endocrine axes. The jockeys' diet as determined by a 7-day dietary recall was deficient in energy, calcium, and vitamin D intake. Compared with the control group, the jockey group had evidence of increased bone turnover.

CONCLUSIONS

A substantial proportion of the professional jockeys in Ireland have low-normal BMD, low BMI, and high bone turnover that may result from weight and dietary restrictions. These factors seem to have a deleterious effect on their bone health and predispose the jockeys to a high fracture risk that should be remediated.

Weight changes in type 2 diabetes and the impact of gender

AIMS

Many studies suggest that weight gain occurs during treatment of type 2 diabetes, irrespective of the treatment type. The aim of this study was to address the questions (i) whether weight gain is inevitable in patients treated for type 2 diabetes, and (ii) whether treatment escalation is prompted by a rise in glycaemic control [haemoglobin A 1c (HbA 1c)] or weight gain.

METHODS

A diabetes database was used to identify all patients with type 2 diabetes attending our clinic between 1 January 1990 and 31 December 2000. To facilitate further analysis, independent anonymized database resources were established. Data collected included height, weight, gender, HbA(1c), age and diabetes treatment at each visit.

RESULTS

One thousand and eighty-four patients were included; after 6 months of treatment, patients' average weight had reduced by 1.0 kg (s.d. 4.6) (p < 0.001). Sixty per cent of the patients had either a decrease or no change in weight, while 40% demonstrated a weight gain. Women demonstrated more weight loss than men. After a mean follow-up of 50 months (s.d. 25.7), 439 patients (40%) who received treatment with diet alone, diet followed by metformin or metformin alone demonstrated a maintained weight reduction in addition to improved glycaemic control. A rise in HbA(1c) rather than weight gain prompted treatment change.

CONCLUSIONS

This study provides evidence that weight gain is not a necessary consequence of the treatment of type 2 diabetes. Women were more successful than men in losing weight, and diet, with or without the addition of metformin, was the treatment type most usually associated with weight loss.

Muscle Na+-K+-ATPase activity and isoform adaptations to intense interval exercise and training in well-trained athletes

The Na+-K+-ATPase enzyme is vital in skeletal muscle function. We investigated the effects of acute high-intensity interval exercise, before and following high-intensity training (HIT), on muscle Na+-K+-ATPase maximal activity, content, and isoform mRNA expression and protein abundance. Twelve endurance-trained athletes were tested at baseline, pretrain, and after 3 wk of HIT (posttrain), which comprised seven sessions of 8 × 5-min interval cycling at 80% peak power output. Vastus lateralis muscle was biopsied at rest (baseline) and both at rest and immediately postexercise during the first (pretrain) and seventh (posttrain) training sessions. Muscle was analyzed for Na+-K+-ATPase maximal activity (3- O-MFPase), content ([3H]ouabain binding), isoform mRNA expression (RT-PCR), and protein abundance (Western blotting). All baseline-to-pretrain measures were stable. Pretrain, acute exercise decreased 3- O-MFPase activity [12.7% (SD 5.1), P < 0.05], increased α1, α2, and α3 mRNA expression (1.4-, 2.8-, and 3.4-fold, respectively, P < 0.05) with unchanged β-isoform mRNA or protein abundance of any isoform. In resting muscle, HIT increased ( P < 0.05) 3- O-MFPase activity by 5.5% (SD 2.9), and α3 and β3 mRNA expression by 3.0- and 0.5-fold, respectively, with unchanged Na+-K+-ATPase content or isoform protein abundance. Posttrain, the acute exercise induced decline in 3- O-MFPase activity and increase in α1 and α3 mRNA each persisted ( P < 0.05); the postexercise 3- O-MFPase activity was also higher after HIT ( P < 0.05). Thus HIT augmented Na+-K+-ATPase maximal activity despite unchanged total content and isoform protein abundance. Elevated Na+-K+-ATPase activity postexercise may contribute to reduced fatigue after training. The Na+-K+-ATPase mRNA response to interval exercise of increased α- but not β-mRNA was largely preserved posttrain, suggesting a functional role of α mRNA upregulation.

Single-nucleotide polymorphisms in the COL1A1 regulatory regions are associated with otosclerosis

Otosclerosis (MIM 166800) has a prevalence of 0.2-1% among white adults, making it the single most common cause of hearing impairment in this ethnic group. Although measles virus, hormones, human leukocyte antigen alleles and genetic factors have been implicated in the development of otosclerosis, its etiology remains unknown. In a focused effort to identify genetic factors in otosclerosis, we have mapped four disease loci (MIM 166800/605727/608244/608787); however, cloning the disease-causing genes in these intervals has not been successful. Here, we used a case-control study design to investigate the association between collagen type I genes and otosclerosis. We identified susceptibility and protective haplotypes in COL1A1 that are significantly associated with otosclerosis in the Caucasian population. These haplotypes alter reporter gene activity in an osteoblast cell line by affecting binding of transcription factors to cis-acting elements. Our data suggest that increased amounts of collagen alpha1(I) homotrimers are causally related to the development of otosclerosis. Consistent with this hypothesis, mouse mutants homozygous for a Col1a2 frameshift mutation on a C57BL/6J background that deposit only homotrimeric type I collagen have hearing loss.

Effects of endurance training status and sex differences on Na+,K+-pump mRNA expression, content and maximal activity in human skeletal muscle

AIM

This study investigated the effects of endurance training status and sex differences on skeletal muscle Na+,K+-pump mRNA expression, content and activity.

METHODS

Forty-five endurance-trained males (ETM), 11 recreationally active males (RAM), and nine recreationally active females (RAF) underwent a vastus lateralis muscle biopsy. Muscle was analysed for Na+,K+-pump alpha1, alpha2, alpha3, beta1, beta2 and beta3 isoform mRNA expression (real-time reverse transcription-polymerase chain reaction), content ([3H]-ouabain-binding site) and maximal activity (3-O-methylfluorescein phosphatase, 3-O-MFPase).

RESULTS

ETM demonstrated lower alpha1, alpha3, beta2 and beta3 mRNA expression by 74%, 62%, 70% and 82%, respectively, than RAM (P<0.04). In contrast, [3H]-ouabain binding and 3-O-MFPase activity were each higher in ETM than in RAM, by 16% (P<0.03). RAM demonstrated a 230% and 364% higher alpha3 and beta3 mRNA expression than RAF, respectively (P<0.05), but no significant sex differences were found for alpha1, alpha2, beta1 or beta2 mRNA, [3H]-ouabain binding or 3-O-MFPase activity. No significant correlation was found between years of endurance training and either [3H]-ouabain binding or 3-O-MFPase activity. Significant but weak correlations were found between the number of training hours per week and 3-O-MFPase activity (r=0.31, P<0.02) and between incremental exercise VO2(peak)) and both [3H]-ouabain binding (r=0.33, P<0.01) and 3-O-MFPase activity (r=0.28, P<0.03).

CONCLUSIONS

Isoform-specific differences in Na+,K+-pump mRNA expression were found with both training status and sex differences, but only training status influenced Na+,K+-pump content and maximal activity in human skeletal muscle.

Dermatitis herpetiformis: no evidence of bone disease despite evidence of enteropathy

The majority of patients with dermatitis herpetiformis (DH) have small intestinal enteropathy that may result in bone loss. The objective of this study was to evaluate bone mineral density (BMD) in DH and to examine whether dietary treatment or degree of the small intestinal lesion correlate with BMD. Twenty-five patients with DH (18 men) were investigated. Detailed dietary assessment and duodenal biopsies were performed on all patients before entry into the study. BMD at lumbar spine and femur was determined by DXA scan. Bone biomarkers, vitamin D, and parathyroid status were assessed. Twenty patients had enteropathy. None of the patients had hypovitaminosis D or secondary hyperparathyroidism. Resorption and formation markers were within normal limits. BMD Z-scores were not significantly different from expected (-0.38; CI, -0.84 to 0.07) and femur (0.46; CI, -0.06 to 0.97). There was no relationship between BMD Z-scores and the severity of the degree of enteropathy. We conclude that enteropathy of differing severity is present in 80% of patients with DH, but this is not associated with bone disease.

Interspersed normoxia during live high, train low interventions reverses an early reduction in muscle Na+, K +ATPase activity in well-trained athletes

Hypoxia and exercise each modulate muscle Na(+), K(+)ATPase activity. We investigated the effects on muscle Na(+), K(+)ATPase activity of only 5 nights of live high, train low hypoxia (LHTL), 20 nights consecutive (LHTLc) versus intermittent LHTL (LHTLi), and acute sprint exercise. Thirty-three athletes were assigned to control (CON, n = 11), 20-nights LHTLc (n = 12) or 20-nights LHTLi (4 x 5-nights LHTL interspersed with 2-nights CON, n = 10) groups. LHTLc and LHTLi slept at a simulated altitude of 2,650 m (F(I)O(2) 0.1627) and lived and trained by day under normoxic conditions; CON lived, trained, and slept in normoxia. A quadriceps muscle biopsy was taken at rest and immediately after standardised sprint exercise, before (Pre) and after 5-nights (d5) and 20-nights (Post) LHTL interventions and analysed for Na(+), K(+)ATPase maximal activity (3-O-MFPase) and content ([(3)H]-ouabain binding). After only 5-nights LHTLc, muscle 3-O-MFPase activity declined by 2% (P < 0.05). In LHTLc, 3-O-MFPase activity remained below Pre after 20 nights. In contrast, in LHTLi, this small initial decrease was reversed after 20 nights, with restoration of 3-O-MFPase activity to Pre-intervention levels. Plasma [K(+)] was unaltered by any LHTL. After acute sprint exercise 3-O-MFPase activity was reduced (12.9 +/- 4.0%, P < 0.05), but [(3)H]-ouabain binding was unchanged. In conclusion, maximal Na(+), K(+)ATPase activity declined after only 5-nights LHTL, but the inclusion of additional interspersed normoxic nights reversed this effect, despite athletes receiving the same amount of hypoxic exposure. There were no effects of consecutive or intermittent nightly LHTL on the acute decrease in Na(+), K(+)ATPase activity with sprint exercise effects or on plasma [K(+)] during exercise.

Ionic mechanisms of excitation-induced regulation of Na+-K+-ATPase mRNA expression in isolated rat EDL muscle

This study investigated the effects of electrical stimulation on Na+-K+-ATPase isoform mRNA, with the aim to identify factors modulating Na+-K+-ATPase mRNA in isolated rat extensor digitorum longus (EDL) muscle. Interventions designed to mimic exercise-induced increases in intracellular Na+and Ca2+contents and membrane depolarization were examined. Muscles were mounted on force transducers and stimulated with 60-Hz 10-s pulse trains producing tetanic contractions three times at 10-min intervals. Ouabain (1.0 mM, 120 min), veratridine (0.1 mM, 30 min), and monensin (0.1 mM, 30 min) were used to increase intracellular Na+content. High extracellular K+(13 mM, 60 min) and the Ca2+ionophore A-23187 (0.02 mM, 30 min) were used to induce membrane depolarization and elevated intracellular Ca2+content, respectively. Muscles were analyzed for Na+-K+-ATPase α1–α3and β1–β3mRNA (real-time RT-PCR). Electrical stimulation had no immediate effect on Na+-K+-ATPase mRNA; however at 3 h after stimulation, it increased α1, α2, and α3mRNA by 223, 621, and 892%, respectively ( P = 0.010), without changing β mRNA. Ouabain, veratridine, and monensin increased intracellular Na+content by 769, 724, and 598%, respectively ( P = 0.001) but did not increase mRNA of any isoform. High intracellular K+concentration elevated α1mRNA by 160% ( P = 0.021), whereas A-23187 elevated α3mRNA by 123% ( P = 0.035) but reduced β1mRNA by 76% ( P = 0.001). In conclusion, electrical stimulation induced subunit-specific increases in Na+-K+-ATPase mRNA in isolated rat EDL muscle. Furthermore, Na+-K+-ATPase mRNA appears to be regulated by different stimuli, including cellular changes associated with membrane depolarization and increased intracellular Ca2+content but not increased intracellular Na+content.

Cystic fibrosis-related diabetes in adults

We aimed to examine the differences between patients with cystic fibrosis-related diabetes (CFRD), and those with normal glucose handling in adults with cystic fibrosis (CF) in Ireland. We conducted a retrospective analysis of patients who attend the national referral centre for adult CF. Patients were diagnosed as having CFRD by the American Cystic Fibrosis Foundation criteria for diagnosis of CFRD. Of 259 patients, 150 were classifiable and 81 (54%) were classified as having CFRD. The groups with and without CFRD were not significantly different with regard to age (median 28.4 vs 26.0 years), sex (males 56% vs 55%) or BMI (median 20.9 vs 21.3 kg/m2). The group with CFRD had poorer lung function (mean % predicted FEV1 49.9 vs 66.4, P < 0.001), poorer bone mineral density (T-scores at the lumbar spine -1.95 vs -1.44, P < 0.05 and femur -1.19 vs -0.57, P < 0.01) and a greater proportion of PSEUDOMONAS AERUGINOSA positive sputum cultures (82.5% vs 64.2%, P < 0.05). No patients with CFRD carried the R1 17H mutation whilst 19% of the group without CFRD were heterozygous for this defect (P < 0.001). In conclusion, CFRD was highly prevalent in adults. The presence of CFRD was associated with poorer lung function, poorer bone mineral density and an increased prevalence of PSEUDOMONAS AERUGINOSA in sputum. The R1 17H mutation may be protective for CFRD.

Prolonged submaximal exercise induces isoform-specific Na+-K+-ATPase mRNA and protein responses in human skeletal muscle

This study investigated effects of prolonged submaximal exercise on Na+-K+-ATPase mRNA and protein expression, maximal activity, and content in human skeletal muscle. We also investigated the effects on mRNA expression of the transcription initiator gene, RNA polymerase II (RNAP II), and key genes involved in protein translation, eukaryotic initiation factor-4E (eIF-4E) and 4E-binding protein 1 (4E-BP1). Eleven subjects (6 men, 5 women) cycled at 75.5% (SD 4.8%) peak O2uptake and continued until fatigue. A vastus lateralis muscle biopsy was taken at rest, fatigue, and 3 and 24 h postexercise. We analyzed muscle for Na+-K+-ATPase α1, α2, α3, β1, β2, and β3, as well for RNAP II, eIF-4E, and 4E-BP1 mRNA expression by real-time RT-PCR and Na+-K+-ATPase isoform protein abundance using immunoblotting. Muscle homogenate maximal Na+-K+-ATPase activity was determined by 3 -O-methylfluorescein phosphatase activity and Na+-K+-ATPase content by [3H]ouabain binding. Cycling to fatigue [54.5 (SD 20.6) min] immediately increased α3( P = 0.044) and β2mRNA ( P = 0.042) by 2.2- and 1.9-fold, respectively, whereas α1mRNA was elevated by 2.0-fold at 24 h postexercise ( P = 0.036). A significant time main effect was found for α3protein abundance ( P = 0.046). Exercise transiently depressed maximal Na+-K+-ATPase activity ( P = 0.004), but Na+-K+-ATPase content was unaltered throughout recovery. Exercise immediately increased RNAP II mRNA by 2.6-fold ( P = 0.011) but had no effect on eIF-4E and 4E-BP1 mRNA. Thus a single bout of prolonged submaximal exercise induced isoform-specific Na+-K+-ATPase responses, increasing α1, α3, and β2mRNA but only α3protein expression. Exercise also increased mRNA expression of RNAP II, a gene initiating transcription, but not of eIF-4E and 4E-BP1, key genes initiating protein translation.

Oral bisphosphonates improve Bone Mineral Density in adults with cystic fibrosis

In adults with Cystic Fibrosis (CF) we sought to establish the effect of oral bisphosphonate therapy. Bone densitometry measured by dual energy X-ray absorptiometry (DXA), and clinical patient data, were reviewed retrospectively. Eighty-one patients (median age 27 years) had baseline and follow-up DXA, with an interval of 19.2 +/- 7.1 months. Thirty-six patients were treated with bisphosphonates (alendronate=23 and risedronate=13). Median follow-up Bone Mineral Density in the bisphosphonate group was 3.7% greater at the lumbar spine (95%CI 1.9 to 5.7%, P<0.0005) and 2.4% greater at the femur (95%CI 0.8 to 3.9%, P<0.005) than the group not treated with bisphosphonates. Oral bisphosphonate therapy had a beneficial effect on BMD in adults with CF.