Joseph J. Bahl

Principles of drug therapy for the elderly patient.

Physicians will treat larger numbers of elderly patients as the US population ages. Being treated simultaneously for more than 1 condition with multiple prescription drugs is only 1 reason why elderly patients are at greater risk of experiencing adverse drug reactions. The need for physicians to minimize the incidence of these reactions has become incumbent on both physicians and administrators. We review the underlying reasons why the elderly population is at risk of adverse drug reactions and summarize the principles of drug-drug interaction, metabolism, and distribution, which can help elderly patients receive proper pharmacological treatment.

Clinical and experimental studies on the use of 3,5-diiodothyropropionic acid, a thyroid hormone analogue, in heart failure

Thyroid hormone has unique actions that make it a novel and possibly useful agent for treatment of heart failure. Because of potential adverse effects of thyroid hormone, however, there has been interest in developing analogues with fewer undesirable side effects. Screening of compounds structurally related to levothyroxine identified 3,5-diiodothyropropionic acid (DITPA) as an analogue with inotropic selectivity and low metabolic activity in hypothyroid rats. When DITPA was administered alone or in combination with captopril in rat and rabbit postinfarction models of heart failure, cardiac output was increased and left ventricular end-diastolic pressure (LV EDP) was decreased without increasing heart rate. A pilot clinical study was undertaken to evaluate the safety and efficacy of DITPA. In a dose-ranging study in 7 normal volunteers the drug was well tolerated. A double-blind comparison then was made of DITPA versus placebo in a group of 19 patients with moderately severe heart failure. Patients were randomly assigned to receive either 1.875 mg/kg of DITPA or placebo daily. After 2 weeks the drug was increased to 3.75 mg/kg daily for an additional 2 weeks. In heart failure patients receiving the drug for 4 weeks, cardiac index was increased (p = 0.04) and systemic vascular resistance index was decreased (p = 0.02). Total serum cholesterol (p = 0.013) and triglycerides (p = 0.005) also were decreased significantly. These results indicate that DITPA is well tolerated and could represent a useful new agent for treatment of congestive heart failure.

In vitro and in vivo suppression of gluconeogenesis by inhibition of pyruvate carboxylase

The mechanism of inhibition of gluconeogenesis by phenylalkanoic acids was studied in vitro and in vivo. In vitro production of 14CO2 from labeled glucose or palmitate was not inhibited at 4 mM, a concentration of phenylacetic acid that inhibited gluconeogenesis from lactate/pyruvate. In vitro studies with isolated mitochondria showed that the CoA ester of phenylacetic acid was formed. The parent phenylalkanoic acid had no effect on purified pyruvate carboxylase activity, but phenylacetyl CoA ester decreased pyruvate carboxylation in a concentration-dependent manner. Phenylacetic acid inhibited gluconeogenesis in isolated rat liver cells from 10 mM lactate/1 mM pyruvate (decreased 39%, P < 0.05), but not 10 mM L-glutamine or [14C]aspartate, showing that the inhibition of gluconeogenesis occurred at the level of pyruvate carboxylase. A 20 mg bolus with infusion of 1 mg/min of phenylpropionic acid decreased blood glucose levels of normal [110 +/- 12 to 66 +/- 11 mg/dL, N = 7, P < 0.05 (unpaired Students t-test vs control)] and streptozocin diabetic rats [295 +/- 14 to 225 +/- 12 mg/dL, N = 7, P < 0.01 (paired t-test vs basal)]. Hepatic glucose production in control and diabetic rats was suppressed under conditions where liver glycogen was depleted, indicating that gluconeogenesis had been inhibited in vivo. The results suggest the possibility that the inappropriate overproduction of glucose can be controlled by inhibitors of pyruvate carboxylase. This class of inhibitors may be useful in the treatment of non-insulin-dependent diabetes mellitus.

Expression of α and β integrins during terminal differentiation of cardiomyocytes

Background: In the myocardium, myocyte cell division is irreversibly blocked shortly after birth. The signal that initiates cell cycle withdrawal is unknown. The purpose of this study was to relate changes in expression of β1 integrin and its associated α subunits to cardiomyocyte cell cycle progression during the fetal-to-neonatal developmental transition in rat. Methods and results: The developmental expression pattern and function of β1 integrin and several of its associated α subunits were examined using reverse transcription (RT) polymerase chain reaction (PCR) and β1 blocking antibodies. During the fetal to neonatal transition, a dramatic shift occurred in the levels of β1 and α isoforms. At the 17-day fetal stage only β1A was present, which remained relatively constant until immediately after birth then decreased by 30% at the adult stage. By contrast, β1D appeared at fetal day 18, increased at neonatal day 2, and afterwards remained constant. This resulted in a ratio of β1A to β1D of about 1:1 in the adult heart. The integrin β1-associated subunits, α3, α6, and α7, were expressed at extremely low levels in 17-day fetal cardiomyocytes. After birth α3 and α6 transiently increased at the 2-day neonatal stage, while α7 isoforms B, C, and X2 progressively increased to the adult stage. Unlike skeletal muscle cells, fluorescence-activated cell sorting analysis (FACS) showed no down regulation of the α5β1 fibronectin receptor during cell cycle withdrawal. Treatment of cultured cardiomyocytes with β1 blocking antibody inhibited the cell cycle in fetal but not in neonatal cells. Conclusion: These results suggest that progression through the cardiomyocyte cell cycle may be dependent upon cell attachment via integrin β1 and correlate with changes that occur in β1 spliced variants and their respective α isoforms.

Tolerance to physiological calcium by isolated myocytes from the adult rat heart; An improved cellular preparation

Abstract The preparation of isolated adult rat heart myocytes able to tolerate physiological calcium concentrations is described. The use of tissue culture medium as the buffer for the enzymic perfusion and digestion of the heart and, subsequently, not exposing isolated myocytes to temperatures below room temperature, proved necessary for the preparation of isolated myocytes able to maintain integrity in the presence of 2 mM calcium. After 60 minutes, 85 percent of the myocytes incubated at 37° with 2 mM calcium exclude the dye trypan blue. Levels of ATP and related compounds, although depressed, were maintained for an extended period. Oxidation of glucose and pyruvate was greater and succinate oxidation lower in calcium-resistant mycoytes compared to myocytes not resistant to calcium. The two types of myocytes were equally rapid in converting succinate to malate. Oxygen utilization increased following the addition of calcium. Myocytes demonstrated both Pasteur and Randle effects and responded to plasma levels of insulin by increasing glucose oxidation. This is the first report of isolated adult rat heart myocytes able to tolerate millimolar calcium concentrations in physiologic medium.

Pilot studies on the use of 3,5-diiodothyropropionic acid, a thyroid hormone analog, in the treatment of congestive heart failure.

After an initial safety study in 7 normal volunteers, a randomized double-blind comparison was made between 3,5-diiodothyropropionic acid (DITPA) and placebo in 19 patients with moderately severe congestive failure. In heart failure patients receiving the drug for 4 weeks, cardiac index was increased (p = 0.04) and systemic vascular resistance index was decreased (p = 0.02). Systolic cardiac function was unchanged but isovolumetric relaxation time was decreased significantly, suggesting improvement in diastolic function. Total serum cholesterol (p = 0.005) and triglycerides (p = 0.01) also were decreased significantly. DITPA could represent a useful new agent for treatment of congestive heart failure.

Oxidative stress and apoptosis in cardiomyocyte induced by high-dose alcohol

Binge drinking of alcohol causes cardiac dysfunction in some people. The mechanism remains unclear. This study was designed to investigate high doses of alcohol-induced oxidative stress and apoptosis in cardiomyocytes and protective effects of antioxidants. Cardiomyocytes isolated from 1- to 2-day-old Sprague-Dawley rats were treated with ethanol at doses of 0 mM, 50 mM, 100 mM, and 200 mM for 24 hours. Vitamin E (1 mM) and vitamin C (0.2 mM) were added to medium 1 hour before addition of ethanol. Results showed typical apoptosis: chromatin condensation, membrane blebbing, shrinkage, and cytoplasm condensation. Apoptosis is concentration-dependent in the range of 0 to 100 mM ethanol (apoptosis rates were respectively 0.68%, 2.03%, and 9.66% at ethanol concentration of 0 mM, 50 mM, and 100 mM). Necrotic cells became greatly increased in the 200 mM ethanol-treated group. Intracellular production of reactive oxygen intermediates increased as mitochondrial membrane potential decreased after ethanol treatment. Cytochrome c was found to be greater in the cytosol of the ethanol-treated groups. Activity of caspase-3 was higher in ethanol-treated groups (P < 0.05). Both vitamin E and vitamin C inhibited oxidative stress and myocyte apoptosis in ethanol-treated groups (P < 0.05). In conclusion, our data indicated that acute high-dose ethanol treatment primarily induces cardiomyocyte apoptosis at concentration up to 100 mM while necrosis is predominate at 200 mM. The underlying mechanism appears to involve mitochondrial damage via an increase in oxidative stress and releasing cytochrome c, which activates caspases that initiate chromatin fragmentation and apoptosis. Antioxidants, to a large extent, inhibit oxidative stress and apoptosis induced by ethanol.

Carnitine transport in isolated adult rat heart myocytes and the effect of 7,8-diOH chlorpromazine.

We studied the carnitine transport system in isolated adult rat heart myocytes able to tolerate physiological concentrations of calcium. Carnitine uptake occurred against a concentration gradient and was inhibited by 2,4-dinitrophenol (2,4-DNP). The transport system had a Kra of 60 fiM and a Vraai of 110 pmol/mg protein per hour. The carnitine precursor deoxycarnitine, acetylcarnitine, and both the D and L isomers were effective inhibitors of uptake. The transport of carnitine was not dependent on sodium ions, but was stimulated by decreasing concentrations of calcium ions. Decreased uptake was observed in the presence of β-adrenergic agonists and antagonists, dibutyrl cyclic AMP, local anesthetics, and ouabain. No significant alteration of uptake was effected by atropine, carbachol or a variety of tricyclic agents. The auto-oxidation product of 7,8-dihydroxychlorpromazine (7,8-diOH CPZ) decreased carnitine efflux from myocytes, which were highly permeable to low molecular weight compounds. We found that this effect was not substrate specific, and is discussed as possibly resulting from a change in the arrangement or state of polymerization of subcellular structural components. Circ Res 48: 378-385, 1981

In vitro osmoregulation of taurine in fetal mouse hearts.

Regulation of taurine transport and accumulation in explanted fetal mouse hearts is shown to be under osmotic control. All osmotic agents studied, both ionic (NaCl, LiCl, choline Cl) and nonionic (sucrose, glucose) stimulated [3H]-taurine transport during an incubation of 19 h. Hyperosmotic stimulation of transport achieved statistical significance by 3 h in the presence of sucrose (P less than 0.05). After 1 h, 40 mM NaCl engendered a 56% increase in [3H]-taurine transport (P less than 0.01). The NaCl stimulation at 1 h may relate more to the transport systems absolute sodium ion requirement than hyperosmotic stimulation. Incremental addition of NaCl or sucrose linearly stimulates [3H]-taurine transport in an incubation of 19 h. Total taurine, measured by HPLC, increased 25% with addition of either 40 mM NaCl or 80 mM sucrose. Hyperosmotic stimulation of transport was not blocked with propranolol but was additive to beta-adrenergic stimulation of transport. Osmotic stimulation occurred with a large increase in Vmax (0.41----0.81 nmol/mg tissue/h) but only a small change in Km (0.51----0.43 mM). After 1 h preincubation with a hyperosmotic addition phenylalanine transport was measured, but was not different from control. Phenylalanine accumulation measured during 19 h incubation similarly was not altered. Streptozotocin induced diabetic rats had elevated plasma osmolarities (295 +/- 2.1----322 +/- 1.3 mosmol) and cardiac taurine (24.3 +/- 1.2----36 +/- 1.0 mumol/g wet wt.). The data presented demonstrates that mammalian cardiac taurine is regulated by the osmotic environment of the heart, suggesting an osmoregulatory function for intracellular taurine and physiological relevance in disease states such as diabetes.

Prevention of the metabolic effects of 2-tetradecylglycidate by octanoic acid in the genetically diabetic mouse (db/db)

2-Tetradecylglycidate is a specific inhibitor of the enzyme carnitine palmitoyl transferase, the rate-limiting step in long chain fatty acid oxidation. We previously showed that chronic administration of TDGA to genetically diabetic mice caused a dose-dependent decrease in blood glucose, retarded the development of renal immunopathologic lesions, and resulted in significant cardiomegaly. The present study was designed to evaluate whether all the observed consequences of chronic TDGA administration resulted from inhibition of long chain fatty acid oxidation or whether the drug exerted other nonspecific effects. To circumvent the effects of LCFAO inhibition, diabetic mice were dosed with TDGA and given a diet containing 9% octanoic acid. Octanoic acid is a medium chain fatty acid, whose oxidation is not dependent on the carnitine transferase system and is not inhibited by TDGA. Administration of the octanoate diet to diabetics receiving TDGA abrogated all the drug effects, including lowering of blood glucose and prevention of renal immunopathology. Cardiomegaly, a consequence of increased protein accretion associated with TDGA dosing, did not occur in the octanoate-fed animals. These results indicate that all the actions of TDGA are mediated via its inhibitory effects on long chain fatty acid oxidation. The cardiac changes resulting from chronic TDGA administration suggest that long chain fatty acid oxidation and its relationship with myocardial energetics may exert a regulatory role on protein synthesis in the myocardium.