Milestones in the History of Research on Cardiac Energy Metabolism

Lessons for Cardiovascular Clinical Investigators: The Tumultuous 2,500-Year Journey of Physicians Who Ignited Our Fire

Whereas medical practice stems from Hippocrates, cardiovascular science originates with Aristotle. The Hippocratic philosophy was championed by Galen (129-216 CE), whose advocacy of a tripartite soul found favor in the early Christian Church. In contrast, Aristotle's works were banned as heresy by ecclesiastical authority, only to survive and prosper in the Islamic Golden Age (775-1258 CE). Galen theorized that the circulation consisted of separate venous and arterial systems. Blood was produced in the liver and traveled centrifugally through veins. When arriving in the right ventricle, venous blood passed through tiny pores in the ventricular septum into the left ventricle, where it became aerated by air passing from the lungs through the pulmonary veins to the left side of the heart. Following arrival at distal sites, arterial blood disappeared, being consumed by the tissues, requiring that the liver needed to continually synthesize new blood. The heart was viewed as a sucking organ, and the peripheral pulse was deemed to result from changes in arterial tone, rather than cardiac systole. Galen's framework remained undisputed and dominated medical thought for 1,300 years, but the reintroduction of Aristotelian principles from the Islamic world into Europe (through the efforts of the Toledo School of Translators) were nurtured by the academic freedom and iconoclastic environment uniquely cultivated at the University of Padua, made possible by Venetian rebellion against papal authority. At Padua, the work of Andreas Vesalius, Realdo Colombo, Hieronymus Fabricius ab Acquapendente, and William Harvey (1543-1628) methodically destroyed Galen's model, leading to the modern concept of a closed-ended circulation. Yet, due to political forces, Harvey was ridiculed, as was James Lind, who performed the first prospective controlled trial, involving citrus fruits for scurvy (1747); it took nearly 50 years for his work to be accepted. Even the work of William Withering (1785), the father of cardiovascular pharmacology, was tarnished by professional jealously and the marketing campaign of a pharmaceutical company. Today's cardiovascular investigators should understand that major advances are routinely derided by the medical establishment for political or personal reasons; and it may take decades or centuries for important work to be accepted.

Current status and emerging trends of cardiac metabolism from the past 20 years: A bibliometric study

Background

Abnormal cardiac metabolism is a key factor in the development of cardiovascular diseases. Consequently, there has been considerable emphasis on researching and developing drugs that regulate metabolism. This study employed bibliometric methods to comprehensively and objectively analyze the relevant literature, offering insights into the knowledge dynamics in this field.

Methods

The data source for this study was the Web of Science Core Collection (WoSCC), from which the collected data were imported into bibliometric software for analysis.

Results

The United States was the leading contributor, accounting for 38.33 % of publications. The University of Washington and Damian J. Tyler were the most active institution and author, respectively. The American Journal of Physiology-Heart and Circulatory Physiology, Journal of Molecular and Cellular Cardiology, Cardiovascular Research, Circulation Research, and American Journal of Physiology-Endocrinology and Metabolism were highly influential journals that published numerous high-quality articles on cardiac metabolism. Common keywords in this research area included heart failure, insulin resistance, skeletal muscle, mitochondria, as well as topic words such as cardiac metabolism, fatty acid oxidation, glucose metabolism, and myocardial metabolism. Co-citation analysis has shown that research on heart failure and in vitro modeling of cardiovascular disease has gained prominence in recent years and making it a research hotspot.

Conclusion

Research on cardiac metabolism is steadily growing, with a specific focus on heart failure and the interplay between mitochondrial dysfunction, insulin resistance, and cardiac metabolism. An emerging trend in this field involves the enhancement of maturation in human induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) through the manipulation of cardiac metabolism.

Lactate and Myocadiac Energy Metabolism

The myocardium is capable of utilizing different energy substrates, which is referred to as “metabolic flexibility.” This process assures ATP production from fatty acids, glucose, lactate, amino acids, and ketones, in the face of varying metabolic contexts. In the normal physiological state, the oxidation of fatty acids contributes to approximately 60% of energy required, and the oxidation of other substrates provides the rest. The accumulation of lactate in ischemic and hypoxic tissues has traditionally be considered as a by-product, and of little utility. However, recent evidence suggests that lactate may represent an important fuel for the myocardium during exercise or myocadiac stress. This new paradigm drives increasing interest in understanding its role in cardiac metabolism under both physiological and pathological conditions. In recent years, blood lactate has been regarded as a signal of stress in cardiac disease, linking to prognosis in patients with myocardial ischemia or heart failure. In this review, we discuss the importance of lactate as an energy source and its relevance to the progression and management of heart diseases.

Lipid partitioning during cardiac stress

It is well documented that fatty acids serve as the primary fuel substrate for the contracting myocardium. However, extensive research has identified significant changes in the myocardial oxidation of fatty acids during acute or chronic cardiac stress. As a result, the redistribution or partitioning of fatty acids due to metabolic derangements could have biological implications. Fatty acids can be stored as triacylglycerols, serve as critical components for biosynthesis of phospholipid membranes, and form the potent signaling molecules, diacylglycerol and ceramides. Therefore, the contribution of lipid metabolism to health and disease is more intricate than a balance of uptake and oxidation. In this review, the available data regarding alterations that occur in endogenous cardiac lipid pathways during the pathological stressors of ischemia-reperfusion and pathological hypertrophy/heart failure are highlighted. In addition, changes in endogenous lipids observed in exercise training models are presented for comparison. This article is part of a Special Issue entitled: Heart Lipid Metabolism edited by G.D. Lopaschuk.