Electrophysiological Abnormalities in VLCAD Deficient hiPSC-Cardiomyocytes Do not Improve with Carnitine Supplementation

Patients with a deficiency in very long-chain acyl-CoA dehydrogenase (VLCAD), an enzyme that is involved in the mitochondrial beta-oxidation of long-chain fatty acids, are at risk for developing cardiac arrhythmias. In human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs), VLCAD deficiency (VLCADD) results in a series of abnormalities, including: 1) accumulation of long-chain acylcarnitines, 2) action potential shortening, 3) higher systolic and diastolic intracellular Ca²⁺ concentrations, and 4) development of delayed afterdepolarizations. In the fatty acid oxidation process, carnitine is required for bidirectional transport of acyl groups across the mitochondrial membrane. Supplementation has been suggested as potential therapeutic approach in VLCADD, but its benefits are debated. Here, we studied the effects of carnitine supplementation on the long-chain acylcarnitine levels and performed electrophysiological analyses in VLCADD patient-derived hiPSC-CMs with a ACADVL gene mutation (p.Val283Ala/p.Glu381del). Under standard culture conditions, VLCADD hiPSC-CMs showed high concentrations of long-chain acylcarnitines, short action potentials, and high delayed afterdepolarizations occurrence. Incubation of the hiPSC-CMs with 400 µM L-carnitine for 48 h led to increased long-chain acylcarnitine levels both in medium and cells. In addition, carnitine supplementation neither restored abnormal action potential parameters nor the increased occurrence of delayed afterdepolarizations in VLCADD hiPSC-CMs. We conclude that long-chain acylcarnitine accumulation and electrophysiological abnormalities in VLCADD hiPSC-CMs are not normalized by carnitine supplementation, indicating that this treatment is unlikely to be beneficial against cardiac arrhythmias in VLCADD patients.

ArrhythmoGenoPharmacoTherapy

This review is focusing on the understanding of various factors and components governing and controlling the occurrence of ventricular arrhythmias including (i) the role of various ion channel-related changes in the action potential (AP), (ii) electrocardiograms (ECGs), (iii) some important arrhythmogenic mediators of reperfusion, and pharmacological approaches to their attenuation. The transmembrane potential in myocardial cells is depending on the cellular concentrations of several ions including sodium, calcium, and potassium on both sides of the cell membrane and active or inactive stages of ion channels. The movements of Na+, K+, and Ca2+ via cell membranes produce various currents that provoke AP, determining the cardiac cycle and heart function. A specific channel has its own type of gate, and it is opening and closing under specific transmembrane voltage, ionic, or metabolic conditions. APs of sinoatrial (SA) node, atrioventricular (AV) node, and Purkinje cells determine the pacemaker activity (depolarization phase 4) of the heart, leading to the surface manifestation, registration, and evaluation of ECG waves in both animal models and humans. AP and ECG changes are key factors in arrhythmogenesis, and the analysis of these changes serve for the clarification of the mechanisms of antiarrhythmic drugs. The classification of antiarrhythmic drugs may be based on their electrophysiological properties emphasizing the connection between basic electrophysiological activities and antiarrhythmic properties. The review also summarizes some important mechanisms of ventricular arrhythmias in the ischemic/reperfused myocardium and permits an assessment of antiarrhythmic potential of drugs used for pharmacotherapy under experimental and clinical conditions.

Survival of a dog with accidental colchicine overdose

OBJECTIVE

To describe the treatment and clinical course of a dog accidentally prescribed 10 times the recommended dose of colchicine (0.3 mg/kg/d instead of 0.03 mg/kg/d).

CASE SUMMARY

After glaucoma surgery, a 1-year-old male neutered Pomeranian weighing 6.8 kg was prescribed 1,000 μg colchicine twice a day per os. The dog presented to the emergency department after the first dose with vomiting and was treated as an outpatient. Two colchicine doses later, the dog represented with vomiting, ocular pain, and increased intraocular pressure. The dog's vital signs were normal, and the dog was admitted for rehydration, analgesia, and revision glaucoma surgery the next day. Two hours after revision surgery, the dog developed vomiting and diarrhea. Postoperatively, the dog was hypothermic (36.3°C), persistently hypertensive (227 mm Hg), and bradycardic (60/min). Biochemistry revealed metabolic acidosis and increased hepatic enzyme activities. Mannitol was administered for presumed cerebral edema. Later, the dog developed bradycardia due to second-degree atrioventricular heart block, which responded to atropine. Total hospitalization was 9 days. Treatment included IV fluids, IV lipid emulsion, N-acetylcysteine, activated charcoal, gastroprotectants, antiemetics, opioids, antimicrobials, and barrier nursing due to transient neutropenia.

NEW OR UNIQUE INFORMATION PROVIDED

This is the first report to describe the successful treatment of a dog with colchicine overdose. The systemic effects were presumed to be secondary to colchicine toxicosis rather than diet, infection, or other drug reaction, and may have been compounded by a second anesthetic episode. Gastrointestinal signs, symptoms of cerebral edema, cardiac arrhythmias, and neutropenia were documented. One other report of colchicine overdose in a dog exists, and that patient was euthanized. This report demonstrates that complete recovery with intensive care is possible; however, the prognosis remains guarded.