High fat feeding in mice is insufficient to induce cardiac dysfunction and does not exacerbate heart failure

Preclinical studies of animals with risk factors, and how those risk factors contribute to the development of cardiovascular disease and cardiac dysfunction, are clearly needed. One such approach is to feed mice a diet rich in fat (i.e. 60%). Here, we determined whether a high fat diet was sufficient to induce cardiac dysfunction in mice. We subjected mice to two different high fat diets (lard or milk as fat source) and followed them for over six months and found no significant decrement in cardiac function (via echocardiography), despite robust adiposity and impaired glucose disposal. We next determined whether antecedent and concomitant exposure to high fat diet (lard) altered the murine heart's response to infarct-induced heart failure; high fat feeding during, or before and during, heart failure did not significantly exacerbate cardiac dysfunction. Given the lack of a robust effect on cardiac dysfunction with high fat feeding, we then examined a commonly used mouse model of overt diabetes, hyperglycemia, and obesity (db/db mice). db/db mice (or STZ treated wild-type mice) subjected to pressure overload exhibited no significant exacerbation of cardiac dysfunction; however, ischemia-reperfusion injury significantly depressed cardiac function in db/db mice compared to their non-diabetic littermates. Thus, we were able to document a negative influence of a risk factor in a relevant cardiovascular disease model; however, this did not involve exposure to a high fat diet. High fat diet, obesity, or hyperglycemia does not necessarily induce cardiac dysfunction in mice. Although many investigators use such diabetes/obesity models to understand cardiac defects related to risk factors, this study, along with those from several other groups, serves as a cautionary note regarding the use of murine models of diabetes and obesity in the context of heart failure.

A comparison of skeletal maturation in patients with tooth agenesis and unaffected controls assessed by the cervical vertebral maturation (CVM) index

OBJECTIVE

The aims of this study were to (1) investigate if there is a difference in skeletal maturation between tooth agenesis and control patients and (2) whether skeletal maturation is affected by the severity of tooth agenesis. The cervical vertebral maturation (CVM) index can be used to assess skeletal maturation.

DESIGN

A retrospective cross-sectional study.

SETTING

Eastman Dental Hospital, London, UK.

METHODS AND MATERIALS

A total of 360 cephalograms of patients aged 9-17 years (164 males and 196 females) allocated to four subgroups (mild, moderate and severe tooth agenesis patients, and controls) were assessed retrospectively. There were 90 patients in each of the four subgroups. The skeletal maturation of each subject was assessed both quantitatively and qualitatively using the CVM index. All patients in the study were either currently receiving treatment or had been discharged from the hospital.

RESULTS

There was no statistically significant relationship between skeletal maturation and the presence of tooth agenesis. Furthermore, there was no statistically significant relationship between the skeletal maturity of patients and different severities of tooth agenesis.

CONCLUSIONS

The data obtained from this group of patients and using this measurement tool alone does not supply sufficient reason to reject the null hypothesis. However, it suggests that it is possible that no difference exists between the groups.

O-GlcNAc and the cardiovascular system

The cardiovascular system is capable of robust changes in response to physiologic and pathologic stimuli through intricate signaling mechanisms. The area of metabolism has witnessed a veritable renaissance in the cardiovascular system. In particular, the post-translational β-O-linkage of N-acetylglucosamine (O-GlcNAc) to cellular proteins represents one such signaling pathway that has been implicated in the pathophysiology of cardiovascular disease. This highly dynamic protein modification may induce functional changes in proteins and regulate key cellular processes including translation, transcription, and cell death. In addition, its potential interplay with phosphorylation provides an additional layer of complexity to post-translational regulation. The hexosamine biosynthetic pathway generally requires glucose to form the nucleotide sugar, UDP-GlcNAc. Accordingly, O-GlcNAcylation may be altered in response to nutrient availability and cellular stress. Recent literature supports O-GlcNAcylation as an autoprotective response in models of acute stress (hypoxia, ischemia, oxidative stress). Models of sustained stress, such as pressure overload hypertrophy, and infarct-induced heart failure, may also require protein O-GlcNAcylation as a partial compensatory mechanism. Yet, in models of Type II diabetes, O-GlcNAcylation has been implicated in the subsequent development of vascular, and even cardiac, dysfunction. This review will address this apparent paradox and discuss the potential mechanisms of O-GlcNAc-mediated cardioprotection and cardiovascular dysfunction. This discussion will also address potential targets for pharmacologic interventions and the unique considerations related to such targets.

Cardiomyocyte Ogt is essential for postnatal viability

The singly coded gene O-linked-β-N-acetylglucosamine (O-GlcNAc) transferase (Ogt) resides on the X chromosome and is necessary for embryonic stem cell viability during embryogenesis. In mature cells, this enzyme catalyzes the posttranslational modification known as O-GlcNAc to various cellular proteins. Several groups, including our own, have shown that acute increases in protein O-GlcNAcylation are cardioprotective both in vitro and in vivo. Yet, little is known about how OGT affects cardiac function because total body knockout (KO) animals are not viable. Presently, we sought to establish the potential involvement of cardiomyocyte Ogt in cardiac maturation. Initially, we characterized a constitutive cardiomyocyte-specific (cm)OGT KO (c-cmOGT KO) mouse and found that only 12% of the c-cmOGT KO mice survived to weaning age (4 wk old); the surviving animals were smaller than their wild-type littermates, had dilated hearts, and showed overt signs of heart failure. Dysfunctional c-cmOGT KO hearts were more fibrotic, apoptotic, and hypertrophic. Several glycolytic genes were also upregulated; however, there were no gross changes in mitochondrial O2 consumption. Histopathology of the KO hearts indicated the potential involvement of endoplasmic reticulum stress, directing us to evaluate expression of 78-kDa glucose-regulated protein and protein disulfide isomerase, which were elevated. Additional groups of mice were subjected to inducible deletion of cmOGT, which did not produce overt dysfunction within the first couple of weeks of deletion. Yet, long-term loss (via inducible deletion) of cmOGT produced gradual and progressive cardiomyopathy. Thus, cardiomyocyte Ogt is necessary for maturation of the mammalian heart, and inducible deletion of cmOGT in the adult mouse produces progressive ventricular dysfunction.

Protein O-GlcNAcylation is a novel cytoprotective signal in cardiac stem cells

Clinical trials demonstrate the regenerative potential of cardiac stem cell (CSC) therapy in the postinfarcted heart. Despite these encouraging preliminary clinical findings, the basic biology of these cells remains largely unexplored. The principal requirement for cell transplantation is to effectively prime them for survival within the unfavorable environment of the infarcted myocardium. In the adult mammalian heart, the β-O-linkage of N-acetylglucosamine (i.e., O-GlcNAc) to proteins is a unique post-translational modification that confers cardioprotection from various otherwise lethal stressors. It is not known whether this signaling system exists in CSCs. In this study, we demonstrate that protein O-GlcNAcylation is an inducible stress response in adult murine Sca-1(+) /lin(-) CSCs and exerts an essential prosurvival role. Posthypoxic CSCs responded by time-dependently increasing protein O-GlcNAcylation upon reoxygenation. We used pharmacological interventions for loss- and gain-of-function, that is, enzymatic inhibition of O-GlcNAc transferase (OGT) (adds the O-GlcNAc modification to proteins) by TT04, or inhibition of OGA (removes O-GlcNAc) by thiamet-G (ThG). Reduction in the O-GlcNAc signal (via TT04, or OGT gene deletion using Cre-mediated recombination) significantly sensitized CSCs to posthypoxic injury, whereas augmenting O-GlcNAc levels (via ThG) enhanced cell survival. Diminished O-GlcNAc levels render CSCs more susceptible to the onset of posthypoxic apoptotic processes via elevated poly(ADP-ribose) polymerase cleavage due to enhanced caspase-3/7 activation, whereas promoting O-GlcNAcylation can serve as a pre-emptive antiapoptotic signal regulating the survival of CSCs. Thus, we report the primary demonstration of protein O-GlcNAcylation as an important prosurvival signal in CSCs, which could enhance CSC survival prior to in vivo autologous transfer.

PDGF-mediated autophagy regulates vascular smooth muscle cell phenotype and resistance to oxidative stress

Vascular injury and chronic arterial diseases result in exposure of VSMCs (vascular smooth muscle cells) to increased concentrations of growth factors. The mechanisms by which growth factors trigger VSMC phenotype transitions remain unclear. Because cellular reprogramming initiated by growth factors requires not only the induction of genes involved in cell proliferation, but also the removal of contractile proteins, we hypothesized that autophagy is an essential modulator of VSMC phenotype. Treatment of VSMCs with PDGF (platelet-derived growth factor)-BB resulted in decreased expression of the contractile phenotype markers calponin and α-smooth muscle actin and up-regulation of the synthetic phenotype markers osteopontin and vimentin. Autophagy, as assessed by LC3 (microtubule-associated protein light chain 3 α; also known as MAP1LC3A)-II abundance, LC3 puncta formation and electron microscopy, was activated by PDGF exposure. Inhibition of autophagy with 3-methyladenine, spautin-1 or bafilomycin stabilized the contractile phenotype. In particular, spautin-1 stabilized α-smooth muscle cell actin and calponin in PDGF-treated cells and prevented actin filament disorganization, diminished production of extracellular matrix, and abrogated VSMC hyperproliferation and migration. Treatment of cells with PDGF prevented protein damage and cell death caused by exposure to the lipid peroxidation product 4-hydroxynonenal. The results of the present study demonstrate a distinct form of autophagy induced by PDGF that is essential for attaining the synthetic phenotype and for survival under the conditions of high oxidative stress found to occur in vascular lesions.

O-GlcNAc signaling entrains the circadian clock by inhibiting BMAL1/CLOCK ubiquitination

Circadian clocks are coupled to metabolic oscillations through nutrient-sensing pathways. Nutrient flux into the hexosamine biosynthesis pathway triggers covalent protein modification by O-linked β-D-N-acetylglucosamine (O-GlcNAc). Here we show that the hexosamine/O-GlcNAc pathway modulates peripheral clock oscillation. O-GlcNAc transferase (OGT) promotes expression of BMAL1/CLOCK target genes and affects circadian oscillation of clock genes in vitro and in vivo. Both BMAL1 and CLOCK are rhythmically O-GlcNAcylated, and this protein modification stabilizes BMAL1 and CLOCK by inhibiting their ubiquitination. In vivo analysis of genetically modified mice with perturbed hepatic OGT expression shows aberrant circadian rhythms of glucose homeostasis. These results establish the counteraction between O-GlcNAcylation and ubiquitination as a key mechanism that regulates the circadian clock and suggest a crucial role for O-GlcNAc signaling in transducing nutritional signals to the core circadian timing machinery.

Reduced cardiac fructose 2,6 bisphosphate increases hypertrophy and decreases glycolysis following aortic constriction

This study was designed to test whether reduced levels of cardiac fructose-2,6-bisphosphate (F-2,6-P₂) exacerbates cardiac damage in response to pressure overload. F-2,6-P₂ is a positive regulator of the glycolytic enzyme phosphofructokinase. Normal and Mb transgenic mice were subject to transverse aortic constriction (TAC) or sham surgery. Mb transgenic mice have reduced F-2,6-P₂ levels, due to cardiac expression of a transgene for a mutant, kinase deficient form of the enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2) which controls the level of F-2,6-P₂. Thirteen weeks following TAC surgery, glycolysis was elevated in FVB, but not in Mb, hearts. Mb hearts were markedly more sensitive to TAC induced damage. Echocardiography revealed lower fractional shortening in Mb-TAC mice as well as larger left ventricular end diastolic and end systolic diameters. Cardiac hypertrophy and pulmonary congestion were more severe in Mb-TAC mice as indicated by the ratios of heart and lung weight to tibia length. Expression of α-MHC RNA was reduced more in Mb-TAC hearts than in FVB-TAC hearts. TAC produced a much greater increase in fibrosis of Mb hearts and this was accompanied by 5-fold more collagen 1 RNA expression in Mb-TAC versus FVB-TAC hearts. Mb-TAC hearts had the lowest phosphocreatine to ATP ratio and the most oxidative stress as indicated by higher cardiac content of 4-hydroxynonenal protein adducts. These results indicate that the heart’s capacity to increase F-2,6-P₂ during pressure overload elevates glycolysis which is beneficial for reducing pressure overload induced cardiac hypertrophy, dysfunction and fibrosis.

Standardized bioenergetic profiling of adult mouse cardiomyocytes

Mitochondria are at the crux of life and death and as such have become ideal targets of intervention in cardiovascular disease. Generally, current methods to measure mitochondrial dysfunction rely on working with the isolated organelle and fail to incorporate mitochondrial function in a cellular context. Extracellular flux methodology has been particularly advantageous in this respect; however, certain primary cell types, such as adult cardiac myocytes, have been difficult to standardize with this technology. Here, we describe methods for using extracellular flux (XF) analysis to measure mitochondrial bioenergetics in isolated, intact, adult mouse cardiomyocytes (ACMs). Following isolation, ACMs were seeded overnight onto laminin-coated (20 μg/ml) microplates, which resulted in high attachment efficiency. After establishing seeding density, we found that a commonly used assay medium (containing a supraphysiological concentration of pyruvate at 1 mmol/l) produced a maximal bioenergetic response. After performing a pyruvate dose-response, we determined that pyruvate titrated to 0.1 mmol/l was optimal for examining alternative substrate oxidation. Methods for measuring fatty acid oxidation were established. These methods lay the framework using XF analysis to profile metabolism of ACMs and will likely augment our ability to understand mitochondrial dysfunction in heart failure and acute myocardial ischemia. This platform could easily be extended to models of diabetes or other metabolic defects.

The COX-2/PGI2 receptor axis plays an obligatory role in mediating the cardioprotection conferred by the late phase of ischemic preconditioning

Background

Pharmacologic studies with cyclooxygenase-2 (COX-2) inhibitors suggest that the late phase of ischemic preconditioning (PC) is mediated by COX-2. However, nonspecific effects of COX-2 inhibitors cannot be ruled out, and the selectivity of these inhibitors for COX-2 vs. COX-1 is only relative. Furthermore, the specific prostaglandin (PG) receptors responsible for the salubrious actions of COX-2-derived prostanoids remain unclear.

Objective

To determine the role of COX-2 and prostacyclin receptor (IP) in late PC by gene deletion.

Methods

COX-2 knockout (KO) mice (COX-2^−/−), prostacyclin receptor KO (IP^−/−) mice, and respective wildtype (WT, COX-2^+/+ and IP^+/+) mice underwent sham surgery or PC with six 4-min coronary occlusion (O)/4-min R cycles 24 h before a 30-min O/24 h R.

Results

There were no significant differences in infarct size (IS) between non-preconditioned (non-PC) COX-2^+/+, COX-2^−/−, IP^+/+, and IP^−/− mice, indicating that neither COX-2 nor IP modulates IS in the absence of PC. When COX-2^−/− or IP^−/− mice were preconditioned, IS was not reduced, indicating that the protection of late PC was completely abrogated by deletion of either the COX-2 or the IP gene. Administration of the IP selective antagonist, RO3244794 to C57BL6/J (B6) mice 30 min prior to the 30-min O had no effect on IS. When B6 mice were preconditioned 24 h prior to the 30-min O, IS was markedly reduced; however, the protection of late PC was completely abrogated by pretreatment of RO3244794.

Conclusions

This is the first study to demonstrate that targeted disruption of the COX-2 gene completely abrogates the infarct-sparing effect of late PC, and that the IP, downstream of the COX-2/prostanoid pathway, is a key mediator of the late PC. These results provide unequivocal molecular genetic evidence for an essential role of the COX-2/PGI2 receptor axis in the cardioprotection afforded by the late PC.

O-GlcNAc signaling is essential for NFAT-mediated transcriptional reprogramming during cardiomyocyte hypertrophy

The regulation of cardiomyocyte hypertrophy is a complex interplay among many known and unknown processes. One specific pathway involves the phosphatase calcineurin, which regulates nuclear translocation of the essential cardiac hypertrophy transcription factor, nuclear factor of activated T-cells (NFAT). Although metabolic dysregulation is frequently described during cardiac hypertrophy, limited insights exist regarding various accessory pathways. One metabolically derived signal, beta-O-linked N-acetylglucosamine (O-GlcNAc), has emerged as a highly dynamic posttranslational modification of serine and threonine residues regulating physiological and stress processes. Given the metabolic dysregulation during hypertrophy, we hypothesized that NFAT activation is dependent on O-GlcNAc signaling. Pressure overload-induced hypertrophy (via transverse aortic constriction) in mice or treatment of neonatal rat cardiac myocytes with phenylephrine significantly enhanced global O-GlcNAc signaling. NFAT-luciferase reporter activity revealed O-GlcNAc-dependent NFAT activation during hypertrophy. Reversal of enhanced O-GlcNAc signaling blunted cardiomyocyte NFAT-induced changes during hypertrophy. Taken together, these results demonstrate a critical role of O-GlcNAc signaling in NFAT activation during hypertrophy and provide evidence that O-GlcNAc signaling is coordinated with the onset and progression of cardiac hypertrophy. This represents a potentially significant and novel mechanism of cardiac hypertrophy, which may be of particular interest in future in vivo studies of hypertrophy.

Abstract P137: Metabolomic Analysis of the Early and Late Hypertrophic Heart

The metabolic adaptations to acute myocardial pressure overload are characterized by alterations in metabolism that drive the hypertrophic response and that balance workload with energy demand. Under conditions of chronic pressure overload, it is known that substrate utilization becomes less flexible and that the heart shifts energy preference from fatty acids to glucose. Nevertheless, the metabolic changes that underlie the progression of compensated hypertrophy to heart failure are incompletely understood and attempts to correct the known metabolic defects to delay decompensation have been largely unsuccessful. To identify key changes in metabolic phenotype that could underlie progression to heart failure, we measured metabolites in a transverse aortic constriction (TAC) mouse model using an unbiased metabolomic approach. Hearts were harvested 1 d, 1 wk and 8 wks after sham or TAC operation, and metabolites were extracted from the hearts and analyzed via GC/MS and LC/MS/MS. The signal intensities of 288 named metabolites were re-scaled to median values. Welch’s t-test and two-way ANOVA were used to identify metabolites that changed significantly with pressure overload and progression to heart failure. Echocardiographic measurements showed a significant decrease in ejection fraction after 1 d (65±2% vs. 49±5%) and 8 wks (61±2% vs. 34±8%) of TAC; 1 wk of TAC showed a compensated phenotype characterized by a largely preserved ejection fraction. One day after TAC, only 1.7% of the metabolites changed significantly; however, nearly all amino acids measured were increased by 1 wk. By 8 wks, amino acids returned to near sham levels and a significant and robust decrease in phospholipid, carnitine, inositol, sterol, and fatty acid metabolites occurred. These findings demonstrate that the temporal changes in metabolic phenotype are more complex than previously thought. The preservation of pathways involved in lipid and amino acid metabolism may be important for maintaining myocardial energetics and preventing pump failure under conditions of chronic pressure overload.

The effects of lubrication on the static frictional resistance of orthodontic brackets

BACKGROUND

Difficulties are experienced with the collection and storage of freshly harvested human saliva to use as a lubricant for the laboratory testing of the frictional resistance of orthodontic brackets. In order to overcome these difficulties, researchers have suggested the use of saliva substitutes due to their ease of storage and consistency of properties throughout testing. Others have criticized the use of artificial saliva and prefer the dry state. The present study aimed to compare the effects of human saliva and an artificial saliva (Saliva Orthana) with the dry state for the static frictional resistance testing of orthodontic brackets.

METHODS

The static frictional resistance and the lubrication effect of human saliva, Saliva Orthana and the dry state were investigated using upper central incisor stainless steel brackets and 0.019 x 0.025 inch stainless steel wires in an Instron Universal Testing Machine. Static frictional resistance was measured 100 times for each lubrication state. The 'wettability' of each lubricant was determined by measuring the contact angle against a stainless steel surface using the CAM 200 Optical Contact Angle Meter. Distilled water acted as a control. The viscosity of each lubricant and their Newtonian or non-Newtonian fluid behaviour under stress was measured using a Brookfield Digital Rheometer Model DV-III+.

RESULTS

The differences in static frictional resistance between the three lubricants when examined as a group did not reach statistical significance (p = 0.059). The difference between human saliva and Saliva Orthana was considered to be of weak statistical significance and clinical relevance (Means: 0.917 N; 0.819 N: p = 0.053). Human saliva and the dry state revealed very similar mean frictional values (Means: 0.917 N; 0.875 N: p = 0.932). The contact angle tests indicated a statistically significant difference between the lubricants with Saliva Orthana having the smallest angle and therefore the highest 'wettability'. Human saliva had the highest initial viscosity and behaved as a non-Newtonian fluid, contrasting with Saliva Orthana and distilled water, both of which behaved as Newtonian fluids.

CONCLUSION

The current results indicate that artificial saliva is not an ideal alternative to human saliva for friction testing in the laboratory The results therefore support the proposal that, when human saliva is not available, it may be preferable to test orthodontic frictional resistance in the dry state.

The relationship between base dimensions, force to failure, and shear bond strengths of bondable molar tubes

OBJECTIVES

To compare forces versus failure and shear bond strengths, and to explore their association with the base dimensions of four currently available bondable molar tubes.

MATERIALS AND METHODS

Tubes were bonded to hydroxyapatite discs using a conventional light-cured adhesive and were tested to shear failure with the Instron Universal testing machine. Results were analyzed using the Kruskal-Wallis test and regression and survival analyses.

RESULTS

No statistical difference was observed between the four groups globally in terms of force to failure (P  =  .059) and bond strength (P  =  .179). However, regression analysis showed that each 1 mm(2) increase in base surface area required an additional force of 3.11 N to debond the tube. Survival analysis showed that the tube with the greatest base dimensions had the best survival with increasing force to failure.

CONCLUSIONS

Although a relationship was demonstrated between force to failure and base surface area, it was not a simple one. No statistically significant relationship was found between bond strength and base surface area.

Cardiac overexpression of 8-oxoguanine DNA glycosylase 1 protects mitochondrial DNA and reduces cardiac fibrosis following transaortic constriction

Cardiac failure is associated with increased levels of oxidized DNA, especially mitochondrial (mtDNA). It is not known if oxidized mtDNA contributes to cardiac dysfunction. To test if protection of mtDNA can reduce cardiac injury, we produced transgenic mice with cardiomyocyte-specific overexpression of the DNA repair enzyme 8-oxoguanine DNA glycosylase 1 (OGG1) isoform 2a. In one line of mice, the transgene increased OGG1 activity by 115% in mitochondria and by 28% in nuclei. OGG1 transgenic mice demonstrated significantly lower cardiac mitochondrial levels of the DNA guanine oxidation product 7,8-dihydro-8-oxoguanine (8-oxo-dG) under basal conditions, after doxorubicin administration, or after transaortic constriction (TAC), but the transgene produced no detectable reduction in nuclear 8-oxo-dG content. OGG1 mice were tested for protection from the cardiac effects of TAC 13 wk after surgery. Compared with FVB-TAC mice, hearts from OGG1-TAC mice had lower levels of β-myosin heavy chain mRNA but they did not display significant differences in the ratio of heart weight to tibia length or protection of cardiac function measured by echocardiography. The principle benefit of OGG1 overexpression was a significant decrease in TAC-induced cardiac fibrosis. This protection was indicated by reduced Sirius red staining on OGG1 cardiac sections and by significantly decreased induction of collagen 1 and 3 mRNA expression in OGG1 hearts after TAC surgery. These results provide a new model to assess the damaging cardiac effects of 8-oxo-dG formation and suggest that increased repair of 8-oxo-dG in mtDNA decreases cardiac pathology.

Augmented O-GlcNAc signaling attenuates oxidative stress and calcium overload in cardiomyocytes

O-linked β-N-acetylglucosamine (O-GlcNAc) is an inducible, dynamically cycling and reversible post-translational modification of Ser/Thr residues of nucleocytoplasmic and mitochondrial proteins. We recently discovered that O-GlcNAcylation confers cytoprotection in the heart via attenuating the formation of mitochondrial permeability transition pore (mPTP) and the subsequent loss of mitochondrial membrane potential. Because Ca(2+) overload and reactive oxygen species (ROS) generation are prominent features of post-ischemic injury and favor mPTP formation, we ascertained whether O-GlcNAcylation mitigates mPTP formation via its effects on Ca(2+) overload and ROS generation. Subjecting neonatal rat cardiac myocytes (NRCMs, n ≥ 6 per group) to hypoxia, or mice (n ≥ 4 per group) to myocardial ischemia reduced O-GlcNAcylation, which later increased during reoxygenation/reperfusion. NRCMs (n ≥ 4 per group) infected with an adenovirus carrying nothing (control), adenoviral O-GlcNAc transferase (adds O-GlcNAc to proteins, AdOGT), adenoviral O-GlcNAcase (removes O-GlcNAc to proteins, AdOGA), vehicle or PUGNAc (blocks OGA; increases O-GlcNAc levels) were subjected to hypoxia-reoxygenation or H(2)O(2), and changes in Ca(2+) levels (via Fluo-4AM and Rhod-2AM), ROS (via DCF) and mPTP formation (via calcein-MitoTracker Red colocalization) were assessed using time-lapse fluorescence microscopy. Both OGT and OGA overexpression did not significantly (P > 0.05) alter baseline Ca(2+) or ROS levels. However, AdOGT significantly (P < 0.05) attenuated both hypoxia and oxidative stress-induced Ca(2+) overload and ROS generation. Additionally, OGA inhibition mitigated both H(2)O(2)-induced Ca(2+) overload and ROS generation. Although AdOGA exacerbated both hypoxia and H(2)O(2)-induced ROS generation, it had no effect on H(2)O(2)-induced Ca(2+) overload. We conclude that inhibition of Ca(2+) overload and ROS generation (inducers of mPTP) might be one mechanism through which O-GlcNAcylation reduces ischemia/hypoxia-mediated mPTP formation.

Bioenergetic function in cardiovascular cells: the importance of the reserve capacity and its biological regulation

The ability of the cell to generate sufficient energy through oxidative phosphorylation and to maintain healthy pools of mitochondria are critical for survival and maintenance of normal biological function, especially during periods of increased oxidative stress. Mitochondria in most cardiovascular cells function at a basal level that only draws upon a small fraction of the total bioenergetic capability of the organelle; the apparent respiratory state of mitochondria in these cells is often close to state 4. The difference between the basal and maximal activity, equivalent to state 3, of the respiratory chain is called the reserve capacity. We hypothesize that the reserve capacity serves the increased energy demands for maintenance of organ function and cellular repair. However, the factors that determine the volume of the reserve capacity and its relevance to biology are not well understood. In this study, we first examined whether responses to 4-hydroxynonenal (HNE), a lipid peroxidation product found in atherosclerotic lesions and the diseased heart, differ between vascular smooth muscle cells, adult mouse cardiomyocytes, and rat neonatal cardiomyocytes. In both types of cardiomyocytes, oxygen consumption increased after HNE treatment, while oxygen consumption in smooth muscle cells decreased. The increase in oxygen consumption in cardiomyocytes decreased the reserve capacity and shifted the apparent respiratory state closer to state 3. Neonatal rat cardiomyocytes respiring on pyruvate alone had a fourfold higher reserve capacity than cells with glucose as the sole substrate, and these cells were more resistant to mitochondrial dysfunction induced by 4-HNE. The integration of the concepts of reserve capacity and state-apparent are discussed along with the proposal of two potential models by which mitochondria respond to stress.

Initial and fatigue bond strengths of chromatic and light-cured adhesives

AIM

To compare the initial and fatigue shear bond strengths of a chromatic adhesive with a light-cured adhesive in an ex vivo laboratory study.

METHODS

Hydroxyapatite discs were used as the bonding substrate. They were produced by cold uni-axial compression at 20 tons, sintered at 1300 degrees C and embedded in epoxy resin before grinding and polishing. One hundred and fifty upper left central incisor brackets were bonded to the discs with Transbond PLUS Color Change (3M Unitek, Monrovia, CA, USA) while another 150 similar brackets were bonded with Transbond XT (3M Unitek, Monrovia, CA, USA). Seventy-five brackets from each group were subjected to cyclic loading (5000 cycles at 2 Hz) at 50 per cent of the mean bond strength in a Dartec Series HC 10 Testing Machine. Initial (unfatigued) and fatigued bond strengths were determined by applying a shear force at the bracket-substrate interface using a custom-made metal jig in an Instron Universal Testing Machine. One-way ANOVA with Bonferroni post-hoc correction and two-way ANOVA were used to analyse the differences between the initial and fatigue mean shear bond strengths of the adhesives. The survival and bond reliability of both adhesives were evaluated with the Kaplan-Meier and Cox regression analyses.

RESULTS

The initial mean shear bond strength for Transbond PLUS Color Change (16.72 MPa) was higher than Transbond XT (15.11 MPa), but this was not statistically significant (p = 0.109). The fatigue mean shear bond strength for Transbond XT (15.87 MPa) was similar to that of Transbond PLUS Color Change (15.33 MPa), and the difference was not statistically significant (p > 0.999). There were no significant differences when the effects of the material (p = 0.264) or fatiguing (p = 0.512) were considered separately, but in combination, the effect on bond strength was statistically significant (p = 0.026). The survival analysis showed that both adhesives demonstrated similar survival patterns in the unfatigued and fatigued states. Analysis of the material type and fatiguing showed no effect on the survival pattern for both adhesives (p = 0.098).

CONCLUSIONS

There were no statistically significant differences between the mean initial (unfatigued) and fatigue bond strengths of Transbond XT and Transbond PLUS Color Change under laboratory conditions. A survival analysis for both resins with and without fatigue loading exhibited similar behaviour with respect to their survival patterns. Although this may imply that under clinical conditions the two adhesives could behave similarly, the clinical extrapolation of these results should be interpreted with caution.

A cephalometric study to investigate the skeletal relationships in patients with increasing severity of hypodontia

OBJECTIVES

To determine the skeletal relationships in patients with hypodontia and analyze the effects of severity and pattern.

MATERIALS AND METHODS

Pretreatment lateral cephalograms from 277 patients with hypodontia, categorized by the number of missing teeth as mild (1-2), moderate (3-5), or severe (> or =6), were digitized recording angular measurements and ratios and compared with published norms matched for age and gender. Pattern was determined as mandibular, maxillary, bimaxillary, bilateral, anterior, posterior, and anteroposterior. Linear regression models assessed relationships between number of missing teeth and cephalometric parameters, controlling for the pattern of hypodontia.

RESULTS

For every additional missing tooth, SNA, SNB, and ANB decreased 0.3 degrees , 0.1 degrees , and 0.2 degrees , respectively; this was clinically significant for >4, >10, and >5 missing teeth, respectively. Mandibular to cranial base ratio decreased 0.3% for every additional missing tooth; this was clinically significant for >10 missing teeth. The MMPA decreased 0.3 degrees for every additional missing tooth; this was clinically significant for >7 missing teeth. Percentage LAFH decreased 0.2% for every additional missing tooth; this was significant for >7 missing teeth. Jarabak ratio increased 0.2% for each additional missing tooth; this was clinically significant for >10 missing teeth. Anterior hypodontia significantly decreased most cephalometric parameters.

CONCLUSIONS

Patients with hypodontia demonstrated a tendency toward a Class III relationship, caused by decreased maxillary and mandibular angular prognathism and MnCB ratio, though the effect was greater on the maxilla than the mandible. Clinical significance was only associated with severe hypodontia. Vertically, there was a tendency toward decreased MMPA and %LAFH; this was clinically relevant only with severe hypodontia. Anterior hypodontia had a significant effect on skeletal relationship.