Evidence for a Direct Effect of the NAD+ Precursor Acipimox on Muscle Mitochondrial Function in Humans

Recent preclinical studies showed the potential of nicotinamide adenine dinucleotide (NAD⁺) precursors to increase oxidative phosphorylation and improve metabolic health, but human data are lacking. We hypothesize that the nicotinic acid derivative acipimox, an NAD⁺ precursor, would directly affect mitochondrial function independent of reductions in nonesterified fatty acid (NEFA) concentrations. In a multicenter randomized crossover trial, 21 patients with type 2 diabetes (age 57.7 ± 1.1 years, BMI 33.4 ± 0.8 kg/m²) received either placebo or acipimox 250 mg three times daily dosage for 2 weeks. Acipimox treatment increased plasma NEFA levels (759 ± 44 vs. 1,135 ± 97 μmol/L for placebo vs. acipimox, P < 0.01) owing to a previously described rebound effect. As a result, skeletal muscle lipid content increased and insulin sensitivity decreased. Despite the elevated plasma NEFA levels, ex vivo mitochondrial respiration in skeletal muscle increased. Subsequently, we showed that acipimox treatment resulted in a robust elevation in expression of nuclear-encoded mitochondrial gene sets and a mitonuclear protein imbalance, which may indicate activation of the mitochondrial unfolded protein response. Further studies in C2C12 myotubes confirmed a direct effect of acipimox on NAD⁺ levels, mitonuclear protein imbalance, and mitochondrial oxidative capacity. To the best of our knowledge, this study is the first to demonstrate that NAD⁺ boosters can also directly affect skeletal muscle mitochondrial function in humans.     

Blood loss and replacement in total hip arthroplasty: a multicenter study. The Preoperative Autologous Blood Donation Study Group

To determine blood loss, the number of transfusions, and the hemoglobin levels achieved in patients via transfusion in the course of total hip arthroplasty, 324 patient records from 1987 through 1989 were reviewed at three university and three community hospitals. Calculated blood loss was 3.2 +/- 1.3 units in primary procedures and 4.0 +/- 2.1 units in revision procedures (mean +/- SD). Of 777 red cell units transfused, 455 (59%) were autologous units. Transfused patients received 2.0 +/- 1.8 units for primary procedures and 2.9 +/- 2.3 units for revision procedures (mean +/- SD). The maximum number of units given to 95 percent of the transfused patients was 4 for primary procedures and 6 for revision procedures. The mean postoperative hemoglobin level after all transfusions was 103 to 110 g per L, regardless of patient age group of physical status, autologous donor status, or hospital. No difference in length of hospital stay was observed for patients less than 65 years old with hemoglobin concentrations of 80 to 139 g per L at discharge.     

Angiotensin II formation in the intact human heart. Predominance of the angiotensin-converting enzyme pathway.

It has been proposed that the contribution of myocardial tissue angiotensin converting enzyme (ACE) to angiotensin II (Ang II) formation in the human heart is low compared with non-ACE pathways. However, little is known about the actual in vivo contribution of these pathways to Ang II formation in the human heart. To examine angiotensin II formation in the intact human heart, we administered intracoronary 123I-labeled angiotensin I (Ang I) with and without intracoronary enalaprilat to orthotopic heart transplant recipients. The fractional conversion of Ang I to Ang II, calculated after separation of angiotensin peptides by HPLC, was 0.415 +/- 0.104 (n = 5, mean +/- SD). Enalaprilat reduced fractional conversion by 89%, to a value of 0.044 +/- 0.053 (n = 4, P = 0.002). In a separate study of explanted hearts, a newly developed in vitro Ang II-forming assay was used to examine cardiac tissue ACE activity independent of circulating components. ACE activity in solubilized left ventricular membrane preparations from failing hearts was 49.6 +/- 5.3 fmol 125I-Ang II formed per minute per milligram of protein (n = 8, +/- SE), and 35.9 +/- 4.8 fmol/min/mg from nonfailing human hearts (n = 7, P = 0.08). In the presence of 1 microM enalaprilat, ACE activity was reduced by 85%, to 7.3 +/- 1.4 fmol/min/mg in the failing group and to 4.6 +/- 1.3 fmol/min/mg in the nonfailing group (P < 0.001). We conclude that the predominant pathway for angiotensin II formation in the human heart is through ACE.     

Blood group A immunodeterminants on human red cells differ in biologic activity and sensitivity to alpha-N-acetylgalactosaminidase

BACKGROUND: Epitopes of blood group A antigen can be enzymatically cleaved from red cells (RBCs), but the extent of cleavage required for normal survival in allogeneic blood transfusion recipients is unknown. Therefore, the cleavage rates were studied for A antigen epitope binding of 1) complement-activating anti-A, 2) Dolichos biflorus anti- A, lectin, and 3) hemagglutinating anti-A during incubation with a purified alpha-N-acetylgalactosaminidase, E.C. 3.2.1.49 (alpha- GalNAc'ase). STUDY DESIGN AND METHODS: Suspensions of group A RBCs were incubated with alpha-GalNAc'ase. Cells were removed at intervals, washed, and tested for loss of binding by monoclonal, polyclonal, and complement-activating anti-A, D. biflorus anti-A1 lectin, and Ulex europaeus anti-H lectin. RESULTS: A epitopes binding D. biflorus lectin were highly susceptible to alpha-GalNAc'ase; simultaneously with their loss, binding with U. europaeus lectin emerged. Loss of complement- mediated hemolysis was slower. A epitopes binding hemagglutinating anti- A were most resistant. Cleavage of A epitopes from membrane glycosphingolipids with short oligosaccharide chains was similarly resistant. Rates of cleavage from A1 and A2 RBCs were similar. CONCLUSION: RBC epitopes of blood group A differ in susceptibility to cleavage and biologic reactivity, which suggests that subsets mediating important biologic functions exist on functionally and topographically distinct membrane glycoconjugates.     

Comparative in vitro electrophysiology of quinidine, its major metabolites and dihydroquinidine

Although metabolites of quinidine are active in animal models and can accumulate to plasma levels similar to those of quinidine during chronic therapy, their effects on cardiac transmembrane action potentials have not been reported. We therefore examined the effects of quinidine, its major metabolites, 3-hydroxyquinidine, quinidine-N-oxide, O-desmethylquinidine, and 2'-oxoquinidinone, and a common commercial impurity, dihydroquinidine, on action potentials from canine Purkinje fibers. Using standard microelectrode techniques, measurements at stimulation basic cycle lengths (BCLs) of 300 to 8000 msec were made at base line and repeated after a 1 hr of superfusion with a 10 microM concentration of drug or vehicle controls. Vehicle controls (n = 5) produced no change in maximum phase 0 upstoke slope of the action potential (Vmax) or action potential duration at 90% repolarization (APD90). Vmax depression when present was greatest at short BCL with statistically significant changes seen at BCL = 300 msec with all compounds tested except quinidine-N-oxide. The time constants for the onset of and recovery from frequency-dependent Vmax depression were similar to those of quinidine. In contrast, changes in APD90 were greatest at long BCL, with significant prolongation seen with all drugs at BCL = 4000 msec. In addition, the agents prolonging repolarization to the greatest extent, quinidine, dihydroquinidine, 3-hydroxyquinidine and O-desmethylquinidine, caused early afterdepolarizations at long BCL. We conclude that these metabolites and dihydroquinidine may contribute to the antiarrhythmic and/or arrhythmogenic effects of quinidine therapy.     

Prognostic significance of ventricular premature depolarizations measured 1 year after myocardial infarction in patients with early postinfarction asymptomatic ventricular arrhythmia.

OBJECTIVES. The objective of this study was to examine the relation between death and the frequency of premature ventricular depolarizations measured approximately 1 year after myocardial infarction. BACKGROUND. The reported association between premature ventricular depolarizations and death in the weeks after myocardial infarction is in part the basis for the use of antiarrhythmic drugs. Such an association has not been reported on for observations obtained at a much greater interval after myocardial infarction. METHODS. We examined the association between mortality and premature ventricular depolarization rates measured 1 year after myocardial infarction in patients with asymptomatic ventricular arrhythmia early (between 6 and 90 days, median 28) after infarction, as measured by 24-h ambulatory electrocardiographic recording. The study group consisted of 502 patients enrolled in the Cardiac Arrhythmia Pilot Study during 1983 to 1985. They were followed up during the course of the study and subsequently by a National Death Index search (average follow-up interval 1,080 days). RESULTS. Death was recorded for 87 patients through 1987. Because patients were admitted to the Cardiac Arrhythmia Pilot Study only if they had greater than or equal to 10 ventricular premature depolarizations/h, the arrhythmia rate measured at baseline (that is, early after infarction) was not expected to, and did not, predict mortality. In 360 patients ventricular premature depolarization rates were measured approximately 1 year from their index myocardial infarction while they were not receiving antiarrhythmic therapy. In these patients, who had survived 1 year after the index infarction, the rate of ventricular premature depolarizations/h measured 1 year after infarction was highly predictive of subsequent death (p less than 0.001). Recent heart failure and a history of diabetes mellitus were also strongly predictive of death. CONCLUSION. The prognostic value of ventricular premature depolarizations observed 1 year after a myocardial infarction may be significant even in a sample selected for frequent ventricular premature depolarizations observed early after the event.