Metabolic and chemical regulation of tRNA modification associated with taurine deficiency and human disease.

Modified uridine containing taurine, 5-taurinomethyluridine (τm5U), is found at the anticodon first position of mitochondrial (mt-)transfer RNAs (tRNAs). Previously, we reported that τm5U is absent in mt-tRNAs with pathogenic mutations associated with mitochondrial diseases. However, biogenesis and physiological role of τm5U remained elusive. Here, we elucidated τm5U biogenesis by confirming that 5,10-methylene-tetrahydrofolate and taurine are metabolic substrates for τm5U formation catalyzed by MTO1 and GTPBP3. GTPBP3-knockout cells exhibited respiratory defects and reduced mitochondrial translation. Very little τm5U34 was detected in patient's cells with the GTPBP3 mutation, demonstrating that lack of τm5U results in pathological consequences. Taurine starvation resulted in downregulation of τm5U frequency in cultured cells and animal tissues (cat liver and flatfish). Strikingly, 5-carboxymethylaminomethyluridine (cmnm5U), in which the taurine moiety of τm5U is replaced with glycine, was detected in mt-tRNAs from taurine-depleted cells. These results indicate that tRNA modifications are dynamically regulated via sensing of intracellular metabolites under physiological condition.

Overexpression of heart-specific small subunit of myosin light chain phosphatase results in heart failure and conduction disturbance.

Mutations in genes encoding components of the sarcomere cause cardiomyopathy, which is often associated with abnormal Ca2+ sensitivity of muscle contraction. We have previously shown that a heart-specific myosin light chain phosphatase small subunit (hHS-M21) increases the Ca2+ sensitivity of muscle contraction. The aim of the present study was to investigate the function of hHS-M21 in vivo and the causative role of abnormal Ca2+ sensitivity in cardiomyopathy. We generated transgenic mice with cardiac-specific overexpression of hHS-M21. We confirmed that hHS-M21 increased the Ca2+ sensitivity of cardiac muscle contraction in vivo, which was not followed by an increased phosphorylation of myosin light chain 2 isoforms. hHS-M21 transgenic mice developed severe systolic dysfunction with myocardial fibrosis and degeneration of cardiomyocytes in association with sinus bradycardia and atrioventricular conduction defect. The contractile dysfunction and cardiac fibrosis were improved by treatment with the Rho kinase inhibitor fasudil. Our findings suggested that the overexpression of hHS-M21 results in cardiac dysfunction and conduction disturbance via non-myosin light chain 2 phosphorylation-dependent regulation. NEW & NOTEWORTHY The present study is the first to develop mice with transgenic overexpression of a heart-specific myosin light chain phosphatase small subunit (hHS-M21) and to examine the effects of hHS-M21 on cardiac function. Elevation of hHS-M21 induced heart failure with myocardial fibrosis and degeneration of cardiomyocytes accompanied by supraventricular arrhythmias.

Cephalic and saphenous venous blood collected by continuous heating of the paws compared with arterial blood for measurement of blood gas values in well-perfused dogs.

BACKGROUND: "Arterialization" of the dorsal hand vein is well-established in human medicine, but not in veterinary medicine. OBJECTIVES: To compare cephalic and saphenous venous blood collected by continuously heating the paws to 37°C ("arterialization"), with arterial blood (AB) for measurement of blood gas variables in well-perfused dogs. ANIMALS: Eight healthy dogs. METHODS: Experimental study. Fore and hind paws were continuously heated to 37°C to "arterialize" cephalic and saphenous venous blood. AB and "arterialized" cephalic and saphenous venous blood (ACV and ASV, respectively) were simultaneously collected from lightly anesthetized dogs with induced metabolic and respiratory acid-base disorders. The pH, partial pressures of carbon dioxide (PCO2 ) and oxygen (PO2 ), bicarbonate concentration [HCO3 - ], and base excess (BE) were measured once in each state. Systolic blood pressure was maintained above 100 mm Hg. The AB, ACV, and ASV values were compared. RESULTS: The pH, [HCO3 - ], and BE values had no significant difference and good agreement, the PCO2 values had a strong correlation (correlation coefficient of .91-1.00), and the PO2 values had a significant difference (P < .01) and poor agreement between AB and ACV, and between AB and ASV. The PCO2 values of ASV overestimated those of AB by ~3.0 mm Hg, which was considered within clinically allowable limits, while those of ACV were not within clinically allowable limits. CONCLUSIONS AND CLINICAL IMPORTANCE: Under experimental conditions, the ASV samples were more identical to the AB samples than the ACV samples for pH, PCO2 , [HCO3 - ], and BE values in well-perfused dogs. The saphenous vein is suitable for "arterialization."

Effects of enfonidipine hydrochloride in dogs with experimental supraventricular tachyarrhythmia.

It is required not to increase the ventricular rate and to preserve the ventricular systolic function in treating supraventricular tachyarrhythmia (SVTA). The objective of this study is to investigate whether or not Efonidipine hydrochloride (EH), a T and L dual type Ca(2+) channel blocker, suppresses the increasing ventricular rate without reducing the ventricular systolic function using canine SVTA models by rapid atrial pacing (RAP) method. Clinically healthy fourteen beagles were used. The 14 dogs were randomly assigned to the EH-administered group (EH group, n=7) and non-EH-administered group (control group, n=7). The EH group was orally-administered EH at 5 mg/kg SID during RAP. On the other hand, the control group was applied RAP without oral administration of EH. Duration of RAP was for 3 weeks for both groups. The ventricular rate for the EH group was significantly lower than that for the control group. The left ventricular- fractional shortening for the control group declined significantly compared to baseline. Those for the EH group did not show any changes over time and were significantly higher than the control group. The ratio between pre-ejection period and ejection for the EH group were significantly lower than those of the control group. In conclusion, the study demonstrated that EH suppresses the increasing ventricular rate without reducing the ventricular systolic function in canine SVTA model. Therefore, EH is expected to become a new treatment for canine SVTA.

Purulent pericarditis in a dog administered immune-suppressing drugs.

A 5-year-old castrated mongrel dog was brought to our hospital with anorexia and vomiting. Laboratory testing revealed immune-mediated hemolytic anemia (IMHA), and so treatment was initiated with multiple immune-suppressing drugs, achieving partial remission from IMHA. However, cardiac tamponade due to purulent pericarditis was identified as a secondary disease. Culture of pericardial fluid yielded numerous Candida albicans and multidrug-resistant Acinetobacter sp. Pericardiocentesis was performed, and the condition of the dog improved. However, the dog died the next day.

Successful surgical correction of supravalvular pulmonary stenosis under beating heart using a cardiopulmonary bypass system in a dog.

A male Pomeranian dog aged 1 year and 8 months was presented for evaluation of severe systolic ejection, cardiac murmur and syncope on excitation. Supravalvular pulmonary stenosis was diagnosed. An echocardiogram showed a supravalvular membranous stricture and a severely increased pulmonary arterial velocity in the stricture (6.49 m/s, pressure gradient of 169 mmHg). The supravalvular stricture was surgically removed by pulmonary arteriotomy with the heart beating using a cardiopulmonary bypass system. The postoperative pulmonary arterial velocity at the narrow area decreased to 3.80 m/s, and the pressure gradient decreased to 57.7 mmHg. Six months after the operation, there were no signs of restenosis, and the dog was in good condition without syncope. Surgical correction of pulmonary stenosis with the heart beating using a cardiopulmonary bypass system is useful because of the improvement it brings in safety and reliability.

Histological study of right ventricle-pulmonary artery valved conduit implantation (RPVC) in dogs with pulmonic stenosis.

We examined whether right ventricle-pulmonary artery valved conduit (RPVC) implantation can overcome the disadvantages of current procedures for pulmonic stenosis (PS). We histologically evaluated the feasibility of RPVC using a homograft in PS model dogs. Eight dogs underwent pulmonary artery banding (PAB) and then 12 weeks later were assigned to PAB (n=4) or PAB+RPVC (n=4) groups. Dogs in the PAB group received no treatment throughout the experimental period, whereas the PAB+RPVC group underwent RPVC. At 1 year after PAB, hearts and conduits were explanted from euthanized dogs and histologically evaluated. The ratios (%) of myocardial fibrosis on right ventricle (RV) epicardial, median and endocardial layers were significantly lower in the PAB+RPVC, than in the PAB group. The ratio of myocardial fibrosis on left ventricular (LV) epicardial and endocardial layers were significantly lower in the PAB+RPVC, than in the PAB group. Neo-intimal thickness in the anastomosis areas of the Denacol and PAB+RPVC groups was 42.77 +/- 30.19 and 88.30 +/- 27.24 microm, respectively, with no significant differences between the groups. Calcification and neo- intima hypertrophy were not obvious in the valve area. Immunohistological staining showed that the internal surface of the anastomosis and intermediate areas were positive for endothelial cells. We concluded that RPVC using a bioprosthetic graft can apparently overcome the disadvantages of current procedures for pulmonic stenosis.

Cardiovascular effects of right ventricle-pulmonary artery valved conduit implantation in experimental pulmonic stenosis.

Right ventricle (RV)-pulmonary artery (PA) valved conduit (RPVC) implantation decreases RV systolic pressure in pulmonic stenosis (PS) by forming a bypass route between the RV and the PA. The present study evaluates valved conduits derived from canine aortae in a canine model of PS produced by pulmonary artery banding (PAB). Pulmonary stenosis was elicited using PAB in 10 conditioned beagles aged 8 months. Twelve weeks after PAB, the dogs were assigned to one group that did not undergo surgical intervention and another that underwent RPVC using denacol-treated canine aortic valved grafts (PAB+RPVC). Twelve weeks later, the rate of change in the RV-PA systolic pressure gradient was significantly decreased in the PAB+RPVC, compared with the PAB group (60.5 +/- 16.7% vs. 108.9 +/- 22.9%; p<0.01). In addition, the end-diastolic RV free wall thickness (RVFWd) was significantly reduced in the PAB+RPVC, compared with the PAB group (8.2 +/- 0.2 vs. 9.4 +/- 0.7 mm; p<0.05). Thereafter, regurgitation was not evident beyond the conduit valve and the decrease in RV pressure overload induced by RPVC was confirmed. The present results indicate that RPVC can be performed under a beating heart without cardiopulmonary bypass and adapted to dogs with various types of PS, including "supra valvular" PS or PS accompanied by dysplasia of the pulmonary valve. Therefore, we consider that this method is useful for treating PS in small animals.

Long-term clinical evaluation of mitral valve replacement with porcine bioprosthetic valves in dogs.

This study evaluated the long-term clinical performance of newly developed porcine bioprosthetic valves cross-linked with glutaraldehyde and polyepoxy compound for mitral valve replacement (MVR) in dogs. Five beagle dogs underwent MVR using the porcine bioprosthetic valves during cardiopulmonary bypass. Antithrombotic drugs were administered only for one month after MVR. Six months after MVR, transvalvular regurgitation was not observed in all dogs, paravalvular leakage was seen only in one dog. Twelve months after MVR, mild transvalvular regurgitations were observed in two dogs. Although diastolic atrioventricular pressure gradient was increased gradually, no significant differences were observed. Pressure half-time and valve area were within normal ranges as the bioprosthetic value. There was no clinical symptom of the thrombosis and the thrombogenesis was not observed in the porcine bioprosthetic valve and the annulus in all dogs for twelve months after MVR. The clinical findings suggest that antithrombogenicity of the valves were maintained, though the duability might not be enough in the long-term period.

Effects of beta-blocker on left ventricular remodeling in rats with volume overload cardiac failure.

The beneficial effects of beta-blockers on left ventricular (LV) remodeling have been reported in association with several conditions that cause heart failure, but their effects on the volume overloaded heart failure have not been well defined. Fifty Wistar rats that survived aortocaval (AC) shunt creation were randomly allotted into the following two groups: untreated animals (ACS; n=26) and animals treated with 100 mg/kg/day metoprolol (MP; ACS+MP; n=24). The effects of MP were evaluated at 1, 4 and 12 weeks post-surgery through echocardiographic, hemodynamic and pathologic studies. At 12 weeks post-surgery, LV wall thinning associated with chamber dilatation was observed in ACS but not in ACS+MP. LV end-diastolic pressure and diastolic wall stress were lower in ACS+MP than in ACS. The increase in LV weight was similar in both ACS and ACS+MP at 1 and 4 weeks post-surgery, but at 12 weeks post-surgery, it was significantly greater in ACS+MP than in ACS. At the cellular level, although the cardiac myocyte length progressively increased to a similar extent in both groups, the mean cross-sectional diameter of these cells in ACS+MP was greater than in ACS. In conclusion, MP did not prevent early eccentric hypertrophy in response to volume overload. However, in the late phase of volume overload-induced heart failure, MP appears to allow for myocyte cross-sectional growth and thus prevents LV wall thinning, resulting in a net increase in LV mass. In this manner, MP might contribute to reduction of diastolic wall stress and thereby delay progression of heart failure.