Medium-chain Fatty Acids as Metabolic Therapy in Cardiac Disease

ACETYL-COA PRODUCTION BY OCTANOIC ACID ALLEVIATES ACUTE COMPARTMENT SYNDROME-INDUCED SKELETAL MUSCLE INJURY THROUGH REGULATING MITOPHAGY

ABSTRACT

Background: Treatment of acute compartment syndrome (ACS)-induced skeletal muscle injury remains a challenge. Previous studies have shown that octanoic acid is a promising treatment for ACS owing to its potential ability to regulate metabolic/epigenetic pathways in ischemic injury. The present study was designed to investigate the efficacy and underlying mechanism of octanoic acid in ACS-induced skeletal muscle injury. Methods: In this study, we established a saline infusion ACS rat model. Subsequently, we assessed the protective effects of sodium octanoate (NaO, sodium salt of octanoic acid) on ACS-induced skeletal muscle injury. Afterward, the level of acetyl-coenzyme A and histone acetylation in the skeletal muscle tissue were quantified. Moreover, we investigated the activation of the AMP-activated protein kinas pathway and the occurrence of mitophagy in the skeletal muscle tissue. Lastly, we scrutinized the expression of proteins associated with mitochondrial dynamics in the skeletal muscle tissue. Results: The administration of NaO attenuated muscle inflammation, alleviating oxidative stress and muscle edema. Moreover, NaO treatment enhanced muscle blood perfusion, leading to the inhibition of apoptosis-related skeletal muscle cell death after ACS. In addition, NaO demonstrated the ability to halt skeletal muscle fibrosis and enhance the functional recovery of muscle post-ACS. Further analysis indicates that NaO treatment increases the acetyl-CoA level in muscle and the process of histone acetylation by acetyl-CoA. Lastly, we found NaO treatment exerts a stimulatory impact on the activation of the AMPK pathway, thus promoting mitophagy and improving mitochondrial dynamics. Conclusion: Our findings indicate that octanoic acid may ameliorate skeletal muscle injury induced by ACS. Its protective effects may be attributed to the promotion of acetyl-CoA synthesis and histone acetylation within the muscular tissue, as well as its activation of the AMPK-related mitophagy pathway.

Systemic primary carnitine deficiency induces severe arrhythmia due to shortening of QT interval

BACKGROUND

Systemic primary carnitine deficiency (PCD) is characterized by cardiomyopathy and arrhythmia. Without carnitine supplementation, progression is usually towards fatal cardiac decompensation. While the cardiomyopathy is most likely secondary to energy deficiency, the mechanism of arrhythmia is unclear, and may be related to a short QT interval.

OBJECTIVE

We aim to describe rhythmic manifestations at diagnosis and with carnitine supplementation.

METHODS

French patients diagnosed for PCD were retrospectively included. Clinical and para clinical data at diagnosis and during follow-up were collected. Electrocardiograms with QT interval measurements were blinded reviewed by two paediatric cardiologists.

RESULTS

Nineteen patients (median age at diagnosis 2.3 years (extremes 0.3-28.9)) followed in 8 French centres were included. At diagnosis, 21% of patients (4/19) had arrhythmia (2 ventricular fibrillations, 1 ventricular tachycardia and 1 sudden death), and 84% (16/19) had cardiomyopathy. Six electrocardiograms before treatment out of 11 available displayed a short QT (QTc < 340 ms). Median corrected QTc after carnitine supplementation was 404 ms (extremes 341-447) versus 350 ms (extremes 282-421) before treatment (p < 0.001). The whole QTc was prolonged, and no patient reached the criterion of short QT syndrome with carnitine supplementation. Three patients died, probably from rhythmic cause without carnitine supplementation (two extra-hospital sudden deaths and one non-recoverable rhythmic storm before carnitine supplementation), whereas no rhythmic complication occurred in patients with carnitine supplementation.

CONCLUSION

PCD is associated with shortening of the QT interval inducing severe arrhythmia. A potential explanation would be a toxic effect of accumulated fatty acid and metabolites on ionic channels embedded in the cell membrane. Carnitine supplementation normalizes the QTc and prevents arrhythmia. Newborn screening of primary carnitine deficiency would prevent avoidable deaths.

Remodeling of lipid landscape in high fat fed very-long chain acyl-CoA dehydrogenase null mice favors pro-arrhythmic polyunsaturated fatty acids and their downstream metabolites

Very-long chain acyl-CoA dehydrogenase (VLCAD) catalyzes the initial step of mitochondrial long chain (LC) fatty acid β-oxidation (FAO). Inherited VLCAD deficiency (VLCADD) predisposes to neonatal arrhythmias whose pathophysiology is still not understood. We hypothesized that VLCADD results in global disruption of cardiac complex lipid homeostasis, which may set conditions predisposing to arrhythmia. To test this, we assessed the cardiac lipidome and related molecular markers in seven-month-old VLCAD-/- mice, which mimic to some extent the human cardiac phenotype. Mice were sacrificed in the fed or fasted state after receiving for two weeks a chow or a high-fat diet (HFD), the latter condition being known to worsen symptoms in human VLCADD. Compared to their littermate counterparts, HFD/fasted VLCAD-/- mouse hearts displayed the following lipid alterations: (1) Lower LC, but higher VLC-acylcarnitines accumulation, (2) higher levels of arachidonic acid (AA) and lower docosahexaenoic acid (DHA) contents in glycerophospholipids (GPLs), as well as (3) corresponding changes in pro-arrhythmogenic AA-derived isoprostanes and thromboxane B2 (higher), and anti-arrythmogenic DHA-derived neuroprostanes (lower). These changes were associated with remodeling in the expression of gene or protein markers of (1) GPLs remodeling: higher calcium-dependent phospholipase A2 and lysophosphatidylcholine-acyltransferase 2, (2) calcium handling perturbations, and (3) endoplasmic reticulum stress. Altogether, these results highlight global lipid dyshomeostasis beyond FAO in VLCAD-/- mouse hearts, which may set conditions predisposing the hearts to calcium mishandling and endoplasmic reticulum stress and thereby may contribute to the pathogenesis of arrhythmias in VLCADD in mice as well as in humans.

Microbial metabolites in chronic heart failure and its common comorbidities

This study aimed to identify microbial signatures that contribute to the shared etiologies between chronic heart failure (CHF), type 2 diabetes, and chronic kidney disease. The serum levels of 151 microbial metabolites were measured in 260 individuals from the Risk Evaluation and Management of heart failure cohort, and it was found that those metabolites varied by an order of 10⁵ fold. Out of 96 metabolites associated with the three cardiometabolic diseases, most were validated in two geographically independent cohorts. In all three cohorts, 16 metabolites including imidazole propionate (ImP) consistently showed significant differences. Notably, baseline ImP levels were three times higher in the Chinese compared with the Swedish cohorts and increased by 1.1-1.6 fold with each additional CHF comorbidity in the Chinese population. Cellular experiments further supported a causal link between ImP and distinct CHF relevant phenotypes. Additionally, key microbial metabolite-based risk scores were superior in CHF prognosis than the traditional Framingham or Get with the Guidelines-Heart Failure risk scores. Interactive visualization of these specific metabolite-disease links is available on our omics data server (https://omicsdata.org/Apps/REM-HF/).

Associations between dairy fat intake, milk-derived free fatty acids, and cardiometabolic risk in Dutch adults

PURPOSE

Milk-derived free fatty acids (FFAs) may act as both biomarkers of intake and metabolic effect. In this study we explored associations between different types of dairy consumption, a selection of milk-derived free fatty acids, and cardiometabolic disease (CMD) risk factors.

METHODS

Sixty-seven FFAs were quantified in the plasma of 131 free-living Dutch adults (median 60 years) using gas chromatography-flame ionization detector. Intakes of different dairy foods and groups were assessed using a food frequency questionnaire. Twelve different CMD risk factors were analyzed. Multiple linear regressions were used to evaluate the associations under study.

RESULTS

Based on the fully adjusted models, 5 long-chain unsaturated FFAs (C18:1 t13 + c6 + c7 + u, C18:2 c9t11 + u, C20:1 c11, C20:3 c8c11c14, and C20:4 c5c8c11c14), 2 medium-chain saturated FFAs (C15, C15 iso), and a trans FFA (C16:1 t9) were positively associated with at least one variable of dairy intake, as well as plasma total and LDL cholesterol, blood pressure, and SCORE (p ≤ 0.05). A long-chain PUFA associated with high-fat fermented dairy intake (C18:2 t9t12), was negatively associated with serum triglyceride levels, and a long-chain saturated FFA associated with cheese intake (C18:1 u1) was negatively associated with plasma LDL cholesterol and serum triglyceride levels. No clear associations were observed between dairy intake and CMD risk factors.

CONCLUSION

Milk-derived FFAs could act as sensitive biomarkers for dairy intake and metabolism, allowing the association between dairy and CMD risk to be more precisely evaluated.

Nutritional Profiles, Phytochemical Analysis, Antioxidant Activity and DNA Damage Protection of Makapuno Derived from Thai Aromatic Coconut

Makapuno is a natural mutant coconut cultivar with jelly-like endosperm. Here, we investigated the nutritional compositions, active ingredients, and antioxidant activities of Makapuno meat and water. The contents of macronutrients, sugars, vitamins, amino acids, and fatty acids were reported. We found that Makapuno meat has higher dietary fiber with lower protein and fat content compared to normal coconut meat. Medium-chain fatty acids were the major fat component of Makapuno meat and water. Phytochemical analysis revealed that while flavonoid content was lower, the total phenolic, alkaloid, and tannin contents of Makapuno meat were comparable with those of mature coconut. However, Makapuno water contained higher alkaloid content when compared to mature and young coconuts. The antioxidant activities, as examined by DPPH, FRAP, and ABTS assays, showed that Makapuno meat and water had antioxidant activities, and Makapuno water exhibited protective activity against DNA damage. Hence, this research provides the nutraceutical importance of Makapuno, which could be used in the food industry.

Key nutrients important in the management of canine myxomatous mitral valve disease and heart failure

The most common cause of heart failure in dogs is myxomatous mitral valve disease (MMVD), which accounts for approximately 75% of canine heart disease cases and is especially common in smaller dogs. Although low-sodium diets have been recommended for humans with heart diseases for decades, there is little evidence to support this practice in dogs. In recent years, however, it has become clear that other nutrients are important to heart health. Dogs with heart disease secondary to MMVD experience patterns of metabolic changes that include decreased mitochondrial energy metabolism and ATP availability, with increased oxidative stress and inflammation. These changes occur early in disease and progress with worsening heart disease. Key nutrients that may support normal function and address these changes include omega-3 fatty acids, medium-chain triglycerides, magnesium, antioxidants including vitamin E and taurine, and the amino acids methionine and lysine. The long-chain omega-3 fatty acids provide anti-inflammatory, antithrombotic, and other benefits. Medium-chain fatty acids and ketones derived from medium-chain triglycerides provide an alternative energy source for cardiac mitochondria and help reduce free radical production. Magnesium supports mitochondrial function, normal cardiac rhythm, and provides other benefits. Both vitamin E and taurine counter oxidative stress, and taurine also has direct cardiac benefits. Dogs with MMVD have reduced plasma methionine. Methionine and lysine are important for carnitine production as well as other functions. This article reviews the evidence supporting the functions and benefits of these and other nutrients in MMVD and other cardiac conditions.

Placental OLAH Levels Are Altered in Fetal Growth Restriction, Preeclampsia and Models of Placental Dysfunction

Previously, we identified elevated transcripts for the gene Oleoyl-ACP Hydrolase (OLAH) in the maternal circulation of pregnancies complicated by preterm fetal growth restriction. As placental dysfunction is central to the pathogenesis of both fetal growth restriction and preeclampsia, we aimed to investigate OLAH levels and function in the human placenta. We assessed OLAH mRNA expression (qPCR) throughout pregnancy, finding placental expression increased as gestation progressed. OLAH mRNA and protein levels (Western blot) were elevated in placental tissue from cases of preterm preeclampsia, while OLAH protein levels in placenta from growth-restricted pregnancies were comparatively reduced in the preeclamptic cohort. OLAH expression was also elevated in placental explant tissue, but not isolated primary cytotrophoblast cultured under hypoxic conditions (as models of placental dysfunction). Further, we discovered that silencing cytotrophoblast OLAH reduced the expression of pro- and anti-apoptosis genes, BAX and BCL2, placental growth gene, IGF2, and oxidative stress gene, NOX4. Collectively, these findings suggest OLAH could play a role in placental dysfunction and may be a therapeutic target for mitigating diseases associated with this vital organ. Further research is required to establish the role of OLAH in the placenta, and whether these changes may be a maternal adaptation or consequence of disease.

Applications of Medium-Chain Triglycerides in Foods

In the 1950s, the production of processed fats and oils from coconut oil was popular in the United States. It became necessary to find uses for the medium-chain fatty acids (MCFAs) that were byproducts of the process, and a production method for medium-chain triglycerides (MCTs) was established. At the time of this development, its use as a non-fattening fat was being studied. In the early days MCFAs included fatty acids ranging from hexanoic acid (C6:0) to dodecanoic acid (C12:0), but today their compositions vary among manufacturers and there seems to be no clear definition. MCFAs are more polar than long-chain fatty acids (LCFAs) because of their shorter chain length, and their hydrolysis and absorption properties differ greatly. These differences in physical properties have led, since the 1960s, to the use of MCTs to improve various lipid absorption disorders and malnutrition. More than half a century has passed since MCTs were first used in the medical field. It has been reported that they not only have properties as an energy source, but also have various physiological effects, such as effects on fat and protein metabolism. The enhancement of fat oxidation through ingestion of MCTs has led to interest in the study of body fat reduction and improvement of endurance during exercise. Recently, MCTs have also been shown to promote protein anabolism and inhibit catabolism, and applied research has been conducted into the prevention of frailty in the elderly. In addition, a relatively large ingestion of MCTs can be partially converted into ketone bodies, which can be used as a component of "ketone diets" in the dietary treatment of patients with intractable epilepsy, or in the nutritional support of terminally ill cancer patients. The possibility of improving cognitive function in dementia patients and mild cognitive impairment is also being studied. Obesity due to over-nutrition and lack of exercise, and frailty due to under-nutrition and aging, are major health issues in today's society. MCTs have been studied in relation to these concerns. In this paper we will introduce the results of applied research into the use of MCTs by healthy subjects.

Golden Syrian hamster as a model to study cardiovascular complications associated with SARS-CoV-2 infection

Severe acute respiratory syndrome coronavirus (SARS-CoV)-2 infection in the Golden Syrian hamster causes lung pathology that resembles human coronavirus disease (COVID-19). However, extra-pulmonary pathologies associated with SARS-CoV-2 infection and post COVID sequelae remain to be understood. Here we show, using a hamster model, that the early phase of SARS-CoV-2 infection leads to an acute inflammatory response and lung pathologies, while the late phase of infection causes cardiovascular complications (CVC) characterized by ventricular wall thickening associated with increased ventricular mass/ body mass ratio and interstitial coronary fibrosis. Molecular profiling further substantiated our findings of CVC, as SARS-CoV-2-infected hamsters showed elevated levels of serum cardiac Troponin-I (cTnI), cholesterol, low-density lipoprotein and long-chain fatty acid triglycerides. Serum metabolomics profiling of SARS-CoV-2-infected hamsters identified N-acetylneuraminate, a functional metabolite found to be associated with CVC, as a metabolic marker was found to be common between SARS-CoV-2-infected hamsters and COVID-19 patients. Together, we propose hamsters as a suitable animal model to study post-COVID sequelae associated with CVC which could be extended to therapeutic interventions.

Circulating short and medium chain fatty acids are associated with normoalbuminuria in type 1 diabetes of long duration

A substantial number of subjects with Type 1 Diabetes (T1D) of long duration never develop albuminuria or renal function impairment, yet the underlying protective mechanisms remain unknown. Therefore, our study included 308 Joslin Kidney Study subjects who had T1D of long duration (median: 24 years), maintained normal renal function and had either normoalbuminuria or a broad range of albuminuria within the 2 years preceding the metabolomic determinations. Serum samples were subjected to global metabolomic profiling. 352 metabolites were detected in at least 80% of the study population. In the logistic analyses adjusted for multiple testing (Bonferroni corrected α = 0.000028), we identified 38 metabolites associated with persistent normoalbuminuria independently from clinical covariates. Protective metabolites were enriched in Medium Chain Fatty Acids (MCFAs) and in Short Chain Fatty Acids (SCFAs) and particularly involved odd-numbered and dicarboxylate Fatty Acids. One quartile change of nonanoate, the top protective MCFA, was associated with high odds of having persistent normoalbuminuria (OR (95% CI) 0.14 (0.09, 0.23); p < 10-12). Multivariable Random Forest analysis concordantly indicated to MCFAs as effective classifiers. Associations of the relevant Fatty Acids with albuminuria seemed to parallel associations with tubular biomarkers. Our findings suggest that MCFAs and SCFAs contribute to the metabolic processes underlying protection against albuminuria development in T1D that are independent from mechanisms associated with changes in renal function.

Effect of dietary supplementation of Emblica officinalis fruit pomace on methane emission, ruminal fermentation, nutrient utilization, and milk production performance in buffaloes

Effects of dietary supplementation of Emblica officinalis fruit (Indian gooseberry) pomace (EFP), a waste from fruit processing plants and rich in polyphenolic compounds, were investigated for ruminal fermentation, nutrient utilization, methane production, and milk production performance in buffaloes. An in vitro experiment was conducted using 0 to 50 g/kg of EFP (six treatments) to select an optimum dose for feeding of buffaloes. Organic matter (OM) degradability, total volatile fatty acid concentration, and acetate proportion decreased, but propionate proportion increased at the higher doses (> 30 g/kg). Methane production also decreased at the higher doses (≥ 20 g/kg). In the in vivo study, ten lactating buffaloes were randomly allotted into control and EFP groups (n = 5/group). The control group was fed a total mixed ration, whereas the EFP group was fed the control ration along with EFP at 20 g/kg of dry matter (DM) intake for 120 days. Feeding of EFP to buffaloes improved milk yield (P < 0.01) and milk production efficiency (P < 0.01). Concentration of milk protein tended (P = 0.071) to increase and that of solid not fat increased (P = 0.032) due to the EFP feeding. Yields (kg/day) of milk fat (P = 0.026), solid not fat (P = 0.011), and protein (P = 0.002) were greater in the EFP group than the control group. Somatic cell count in milk decreased (P = 0.032) due to EFP feeding. Digestibility of ether extract (P < 0.001) increased and OM (P = 0.051) tended to increase by EFP feeding. Methane production (g/d), yield (g/kg DM intake or g/kg digestible organic matter intake), and intensity (g/kg milk, g/kg milk fat, or g/kg milk protein), and methane conversion rate (percentage of gross energy intake) were lower (P < 0.01) in the EFP group than the control group. For milk fatty acid (FA) profiles, total saturated FA proportion tended to be greater (P = 0.057) in the EFP group than the control group, which was due to increased (P = 0.045) proportion of total short- and medium-chain FA (C4 to C14). Feed intake, digestibility of crude protein and fiber, and total n-6, n-3, mono-unsaturated FA, poly-unsaturated FA, and long-chain FA (C18 to C24) proportions were similar between the groups. This study suggests that feeding of EFP at 20 g/kg DM intake increases milk production and decreases methane production and intensity without impacting health of buffaloes and FA profiles of milk. This is a win-win situation for sustainable and cleaner buffalo production by improving milk production and decreasing environmental burdens of greenhouse gas emission and EFP residue disposal problems.

Serum untargeted metabolomic changes in response to diet intervention in dogs with preclinical myxomatous mitral valve disease

Myocardial energy deprivation plays a causal role in the development of heart failure. A cardiac protection blend (CPB) of nutrients including medium chain triglycerides, fish oil and other key nutrients was developed to slow the progression of canine myxomatous mitral valve disease (MMVD). A six-month dietary intervention demonstrated efficacy of CPB in slowing MMVD progression. Untargeted metabolomic analysis of serum from these dogs identified 102 differential metabolites (adjusted P < 0.05). The ratios of omega-6 to omega-3 fatty acid (FA) changed from 2.41 and 1.46 in control and CPB groups at baseline to 4.30 and 0.46 at 6 months respectively. A 2.7-fold increase of α-aminobutyrate, a myocardial modulator of glutathione homeostasis, was found in CPB dogs compared to 1.3-fold increase in control dogs. Arginine and citrulline, precursors of nitric oxide biosynthesis, were both increased 2-fold; caprate, a medium chain FA, was increased 3-fold; and deoxycarnitine, precursor of carnitine biosynthesis, was increased 2.5-fold in CPB dogs. Margarate and methylpalmitate decreased in response to CPB, a potential benefit in MMVD dogs as positive correlations were found between changes in both these FAs and left atrial diameter (r = 0.69, r = 0.87 respectively, adjusted P < 0.05). Sphingomyelins with very long chain saturated FAs associated with decreased risk of heart failure in humans were increased in MMVD dogs fed the CPB diet. Our data supports the hypothesis that CPB improves FA utilization and energetics, reduces oxidative stress and inflammation in MMVD dogs. More studies are needed to understand the roles of specific metabolites in MMVD.

Metabolic environment in vivo as a blueprint for differentiation and maturation of human stem cell-derived cardiomyocytes

Patient-derived human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) are increasingly being used for disease modeling, drug screening and regenerative medicine. However, to date, an immature, fetal-like, phenotype of hPSC-CMs restrains their full potential. Increasing evidence suggests that the metabolic state, particularly important for provision of sufficient energy in highly active contractile CMs and anabolic and regulatory processes, plays an important role in CM maturation, which affects crucial functional aspects of CMs, such as contractility and electrophysiology. During embryonic development the heart is subjected to metabolite concentrations that differ substantially from that of hPSC-derived cardiac cell cultures. A deeper understanding of the environmental and metabolic cues during embryonic heart development and how these change postnatally, will provide a framework for optimizing cell culture conditions and maturation of hPSC-CMs. Maturation of hPSC-CMs will improve the predictability of disease modeling, drug screening and drug safety assessment and broadens their applicability for personalized and regenerative medicine.

Detection of myocardial medium-chain fatty acid oxidation and tricarboxylic acid cycle activity with hyperpolarized [1-13 C]octanoate

Under normal conditions, the heart mainly relies on fatty acid oxidation to meet its energy needs. Changes in myocardial fuel preference are noted in the diseased and failing heart. The magnetic resonance signal enhancement provided by spin hyperpolarization allows the metabolism of substrates labeled with carbon-13 to be followed in real time in vivo. Although the low water solubility of long-chain fatty acids abrogates their hyperpolarization by dissolution dynamic nuclear polarization, medium-chain fatty acids have sufficient solubility to be efficiently polarized and dissolved. In this study, we investigated the applicability of hyperpolarized [1-¹³ C]octanoate to measure myocardial medium-chain fatty acid metabolism in vivo. Scanning rats infused with a bolus of hyperpolarized [1-¹³ C]octanoate, the primary metabolite observed in the heart was identified as [1-¹³ C]acetylcarnitine. Additionally, [5-¹³ C]glutamate and [5-¹³ C]citrate could be respectively resolved in seven and five of 31 experiments, demonstrating the incorporation of oxidation products of octanoate into the tricarboxylic acid cycle. A variable drop in blood pressure was observed immediately following the bolus injection, and this drop correlated with a decrease in normalized acetylcarnitine signal (acetylcarnitine/octanoate). Increasing the delay before infusion moderated the decrease in blood pressure, which was attributed to the presence of residual gas bubbles in the octanoate solution. No significant difference in normalized acetylcarnitine signal was apparent between fed and 12-hour fasted rats. Compared with a solution in buffer, the longitudinal relaxation of [1-¹³ C]octanoate was accelerated ~3-fold in blood and by the addition of serum albumin. These results demonstrate the potential of hyperpolarized [1-¹³ C]octanoate to probe myocardial medium-chain fatty acid metabolism as well as some of the limitations that may accompany its use.

Cardiac ketone body metabolism

The ketone bodies, d-β-hydroxybutyrate and acetoacetate, are soluble 4-carbon compounds derived principally from fatty acids, that can be metabolised by many oxidative tissues, including heart, in carbohydrate-depleted conditions as glucose-sparing energy substrates. They also have important signalling functions, acting through G-protein coupled receptors and histone deacetylases to regulate metabolism and gene expression including that associated with anti-oxidant activity. Their concentration, and hence availability, increases in diabetes mellitus and heart failure. Whilst known to be substrates for ATP production, especially in starvation, their role(s) in the heart, and in heart disease, is uncertain. Recent evidence, reviewed here, indicates that increased ketone body metabolism is a feature of heart failure, and is accompanied by other changes in substrate selection. Whether the change in myocardial ketone body metabolism is adaptive or maladaptive is unknown, but it offers the possibility of using exogenous ketones to treat the failing heart.

The Diagnostic Criteria 2020 for Triglyceride Deposit Cardiomyovasculopathy

Triglyceride deposit cardiomyovasculopathy (TGCV) is a newly identified disease that was discovered in individuals who required cardiac transplantation in Japan in 2008. Defective intracellular lipolysis causes triglyceride (TG) accumulation in the myocardium and coronary artery vascular smooth muscle cells, which results in severe heart failure and coronary artery disease with poor prognosis. A known cause of TGCV is a genetic deficiency of adipose triglyceride lipase (ATGL), a rate-limiting enzyme in the intracellular hydrolysis of TG. TGCV is classified into primary TGCV with ATGL mutations and idiopathic TGCV without ATGL mutations. Since its discovery, the Japan TGCV Study Group has attempted to elucidate its pathophysiology, develop diagnostic procedures, and specific treatment. Myocardial scintigraphy with iodine-123-β-methyl iodophenyl-pentadecanoic acid (¹²³I-BMIPP) is a unique imaging modality for evaluating myocardial lipolysis in vivo. The washout rate of ¹²³I-BMIPP is an essential indicator for the diagnosis of TGCV. Along with our efforts to provide awareness of and insights into this disease concept, we found that the cumulative number of clinically diagnosed patients has reached >200 and the cases are distributed throughout Japan. In addition, we successfully completed three investigator-initiated clinical trials of a potential therapeutic agent (CNT-01) for TGCV, which was assigned by the Ministry of Health, Labour, and Welfare, Japan, under the SAKIGAKE Designation System in June 2020. Here, we provide the Diagnostic Criteria 2020 for TGCV in order to further promote this "rare and intractable disease" project.

Dietary intervention reduces left atrial enlargement in dogs with early preclinical myxomatous mitral valve disease: a blinded randomized controlled study in 36 dogs

Background

Myxomatous mitral valve disease (MMVD), the most common naturally-occurring heart disease in dogs, is associated with alterations in energy metabolism, oxidative stress and inflammation. Energy deprivation plays a causal role in the development of heart failure. This study was designed to determine if a cardiac protection blend (CPB) of nutrients containing medium-chain triglycerides as an alternative energy source, fish oil to reduce inflammation, antioxidants, and other key nutrients important to cardiac health and function could slow or prevent MMVD progression. Nineteen dogs with early stage MMVD and 17 breed-, age-, and sex-matched healthy dogs were enrolled for a 6-month blinded, placebo-controlled study. Dogs in each cardiac health group were randomly assigned to either control diet (CON) or CPB-supplemented diet. Echocardiography was performed at baseline, 3 months and 6 months.

Results

No changes were found in healthy dogs. While MMVD-CON dogs had an average 10% increase over baseline in left atrial diameter (LAD) and left atrial to aortic root ratio (LA/Ao) at 6 months, MMVD-CPB dogs showed 3% decreases, resulting significant diet by time interactions (P = 0.037, P = 0.005, respectively). More MMVD-CON dogs progressed from stage B1 to B2 during the study. A positive correlation was found between 6-month changes in LAD and blood pressures in MMVD-CPB dogs (systolic: P = 0.050, diastolic: P = 0.035) but not MMVD-CON dogs.

Conclusions

Our results demonstrated efficacy of CPB-based dietary intervention in reducing LA size and mitral regurgitation, and in slowing or preventing the progression of early MMVD in dogs.

Cholesterol lowering attenuates pressure overload-induced heart failure in mice with mild hypercholesterolemia

Epidemiological studies support a strong association between non-high-density lipoprotein cholesterol levels and heart failure incidence. The objective of the current study was to evaluate the effect of selective cholesterol lowering adeno-associated viral serotype 8 (AAV8)-mediated low-density lipoprotein receptor (LDLr) gene transfer on cardiac remodelling and myocardial oxidative stress following transverse aortic constriction (TAC) in female C57BL/6 LDLr^-/- mice with mild hypercholesterolemia. Cholesterol lowering gene transfer resulted in a 65.9% (p<0.0001) reduction of plasma cholesterol levels (51.2 ± 2.2 mg/dl) compared to controls (150 ± 7 mg/dl). Left ventricular wall area was 11.2% (p<0.05) lower in AAV8-LDLr TAC mice than in control TAC mice. In agreement, pro-hypertrophic myocardial proteins were potently decreased in AAV8-LDLr TAC mice. The degree of interstitial fibrosis and perivascular fibrosis was 31.0% (p<0.001) and 29.8% (p<0.001) lower, respectively, in AAV8-LDLr TAC mice compared to control TAC mice. These structural differences were associated with improved systolic and diastolic function and decreased lung congestion in AAV8-LDLr TAC mice compared to control TAC mice. Cholesterol lowering gene therapy counteracted myocardial oxidative stress and preserved the potential for myocardial fatty acid oxidation in TAC mice. In conclusion, cholesterol lowering gene therapy attenuates pressure overload-induced heart failure in mice with mild hypercholesterolemia.

Intake of medium-chain fatty acids induces myocardial oxidative stress and atrophy

Background

Oral intake of medium-chain fatty acids (MCFAs) reportedly suppresses the accumulation of visceral fat and has antitumor effects in tumor-bearing animals. MCFAs penetrate the mitochondrial membrane in a carnitine shuttle-independent manner and are metabolized more quickly than long-chain fatty acids. Based on these characteristics, MCFAs may have pronounced effects in mitochondria-rich tissues, such as the myocardium. We examined the effect of oral intake of MCFAs on the heart.

Methods

We fed BALB/c mice with a control diet supplemented with 0%, 2%, 5%, or 10% lauric acid (LAA; a 12-carbon saturated MCFA). After euthanasia, the hearts, both sides of quadriceps femoris muscle (QFM) and epididymal fat pad (EFP) were excised and weighed. Then myocardial tissue morphology, oxidative stress accumulation, and mitochondrial volume were observed by histological analysis. The expression levels of myosin light chain 1 were measured by ELISA.

Results

There were no differences among the groups in food and calorie intake, but the intake of LAA increased with the dietary proportion. The 10%-LAA-fed mice experienced significant weight loss and became moribund on day 6. The body, cardiac and EFP weights of the mice fed 5% and 10% LAA were lower than those of the control group. And 10% LAA fed group showed significant decrease of the QFM weights. Protein analysis of the excised hearts revealed higher expression of myosin light chain 1 in the 5% group than in the control group. Histological examination of the hearts revealed myocardial atrophy and accumulation of oxidative stress in the 10% group. Fewer mitochondria were observed with increased LAA intake.

Conclusions

Excessive LAA consumption may damage the myocardium and the damage might result from oxidative stress accumulation and cellular atrophy.

Uncoupling protein 3 deficiency impairs myocardial fatty acid oxidation and contractile recovery following ischemia/reperfusion

Patients with insulin resistance and type 2 diabetes have poor cardiac outcomes following myocardial infarction (MI). The mitochondrial uncoupling protein 3 (UCP3) is down-regulated in the heart with insulin resistance. We hypothesized that decreased UCP3 levels contribute to poor cardiac recovery following ischemia/reperfusion (I/R). After confirming that myocardial UCP3 levels were systematically decreased by 20-49% in animal models of insulin resistance and type 2 diabetes, we genetically engineered Sprague-Dawley rats with partial loss of UCP3 (ucp3^+/-). Wild-type littermates (ucp3^+/+) were used as controls. Isolated working hearts from ucp3^+/- rats were characterized by impaired recovery of cardiac power and decreased long-chain fatty acid (LCFA) oxidation following I/R. Mitochondria isolated from ucp3^+/- hearts subjected to I/R in vivo displayed increased reactive oxygen species (ROS) generation and decreased respiratory complex I activity. Supplying ucp3^+/- cardiac mitochondria with the medium-chain fatty acid (MCFA) octanoate slowed electron transport through the respiratory chain and reduced ROS generation. This was accompanied by improvement of cardiac LCFA oxidation and recovery of contractile function post ischemia. In conclusion, we demonstrated that normal cardiac UCP3 levels are essential to recovery of LCFA oxidation, mitochondrial respiratory capacity, and contractile function following I/R. These results reveal a potential mechanism for the poor prognosis of type 2 diabetic patients following MI and expose MCFA supplementation as a feasible metabolic intervention to improve recovery of these patients at reperfusion.

Acute Respiratory Infection Unveiling CPT II Deficiency

Carnitine Palmitoyl transferase 2 (CPT II) is involved in long-chain fatty-acid mitochondrial transport. Three clinical phenotypes of CPT II deficiency have been described: Lethal neonatal onset, infantile severe form, and the late onset more common muscular form. The muscular form of CPT II deficiency is characterized by pain crises and rhabdomyolysis triggered by energy-dependent factors. This form has been described as a benign condition; however, the acute crises are insidious and thus, pose a risk of death. We report a 3-year-old female child with an acute pulmonary infection and a concomitant rhabdomyolysis. The acylcarnitine profile was consistent with CPT II deficiency and a molecular study allowed the identification of the common missense variant (NM_000098.2: c.338C>T – p. Ser113Leu) at the homozygous state. The striking difference between the initial cause and the decompensation severity prompted us to consider other diagnoses. Deciphering the symptoms linked to CPT II deficiency among those of the initial decompensation results in initiating a timely a targeted therapy.

Myocardial fatty acid uptake through CD36 is indispensable for sufficient bioenergetic metabolism to prevent progression of pressure overload-induced heart failure

The energy metabolism of the failing heart is characterized by reduced fatty acid (FA) oxidation and an increase in glucose utilization. However, little is known about how energy metabolism-function relationship is relevant to pathophysiology of heart failure. Recent study showed that the genetic deletion of CD36 (CD36KO), which causes reduction in FA use with an increased reliance on glucose, accelerates the progression from compensated hypertrophy to heart failure. Here, we show the mechanisms by which CD36 deletion accelerates heart failure in response to pressure overload. CD36KO mice exhibited contractile dysfunction and death from heart failure with enhanced cardiac hypertrophy and interstitial fibrosis when they were subjected to transverse aortic constriction (TAC). The pool size in the TCA cycle and levels of high-energy phosphate were significantly reduced in CD36KO-TAC hearts despite an increase in glycolytic flux. De novo synthesis of non-essential amino acids was facilitated in CD36KO-TAC hearts, which could cause a further decline of the pool size. The ingestion of a diet enriched in medium-chain FA improved cardiac dysfunction in CD36KO-TAC hearts. These findings suggest that myocardial FA uptake through CD36 is indispensable for sufficient ATP production and for preventing an increased glycolytic flux-mediated structural remodeling during pressure overload-induced hypertrophy.

Metabolic Response of the Immature Right Ventricle to Acute Pressure Overloading

BACKGROUND

Surgical palliation or repair of complex congenital heart disease in early infancy can produce right ventricular (RV) pressure overload, often leading to acute hemodynamic decompensation. The mechanisms causing this acute RV dysfunction remain unclear. We tested the hypothesis that the immature right ventricle lacks the ability to modify substrate metabolism in order to meet increased energy demands induced by acute pressure overloading.

METHODS AND RESULTS

Twenty-two infant male mixed breed Yorkshire piglets were randomized to a sham operation (Control) or pulmonary artery banding yielding >2-fold elevation over baseline RV systolic pressure. We used carbon 13 (¹³C)-labeled substrates and proton nuclear magnetic resonance to assess RV energy metabolism. [Phosphocreatine]/[ATP] was significantly lower after pulmonary artery banding. [Phosphocreatine]/[ATP] inversely correlated with energy demand indexed by maximal sustained RV systolic pressure/left ventricular systolic pressure. Fractional contributions of fatty acids to citric acid cycle were significantly lower in the pulmonary artery banding group than in the Control group (medium-chain fatty acids; 14.5±1.6 versus 8.2±1.0%, long-chain fatty acids; 9.3±1.5 versus 5.1±1.1%). ¹³C-flux analysis showed that flux via pyruvate decarboxylation did not increase during RV pressure overloading.

CONCLUSIONS

Acute RV pressure overload yielded a decrease in [phosphocreatine]/[ATP] ratio, implying that ATP production did not balance the increasing ATP requirement. Relative fatty acids oxidation decreased without a reciprocal increase in pyruvate decarboxylation. The data imply that RV inability to adjust substrate oxidation contributes to energy imbalance, and potentially to contractile failure. The data suggest that interventions directed at increasing RV pyruvate decarboxylation flux could ameliorate contractile dysfunction associated with acute pressure overloading.

Similarities and differences between the responses induced in human phagocytes through activation of the medium chain fatty acid receptor GPR84 and the short chain fatty acid receptor FFA2R

GPR84 is a recently de-orphanized member of the G-protein coupled receptor (GPCR) family recognizing medium chain fatty acids, and has been suggested to play important roles in inflammation. Due to the lack of potent and selective GPR84 ligands, the basic knowledge related to GPR84 functions is very limited. In this study, we have characterized the GPR84 activation profile and regulation mechanism in human phagocytes, using two recently developed small molecules that specifically target GPR84 agonistically (ZQ16) and antagonistically (GLPG1205), respectively. Compared to our earlier characterization of the short chain fatty acid receptor FFA2R which is functionally expressed in neutrophils but not in monocytes, GPR84 is expressed in both cell types and in monocyte-derived macrophages. In neutrophils, the GPR84 agonist had an activation profile very similar to that of FFA2R. The GPR84-mediated superoxide release was low in naïve cells, but the response could be significantly primed by TNFα and by the actin cytoskeleton disrupting agent Latrunculin A. Similar to that of FFA2R, a desensitization mechanism bypassing the actin cytoskeleton was utilized by GPR84. All ZQ16-mediated cellular responses were sensitive to GLPG1205, confirming the GPR84-dependency. Finally, our data of in vivo transmigrated tissue neutrophils indicate that both GPR84 and FFA2R are involved in neutrophil recruitment processes in vivo. In summary, we show functional similarities but also some important differences between GPR84 and FFA2R in human phagocytes, thus providing some mechanistic insights into GPR84 regulation in blood neutrophils and cells recruited to an aseptic inflammatory site in vivo.

Difference in Binding of Long- and Medium-Chain Fatty Acids with Serum Albumin: The Role of Macromolecular Crowding Effect

Fatty acids (FAs) are transported by serum albumin in plasma. Studies have been undertaken to address the binding of MCFAs or LCFAs to human plasma albumin (HPA) and bovine serum albumin (BSA) by characterizing the binding affinities. Previous research on FA binding to serum albumin was usually performed in dilute solutions that are not sufficiently concentrated for the interpretation of the significance of the results under normal physiological conditions. How macromolecular crowded media affect fatty acids and bovine serum albumin (BSA) binding remains unknown. In this article, we investigated the mechanism of FA-BSA binding in a polyethylene glycol crowding environment by using thermodynamic and spectroscopic methods. Molecular crowding increased the binding constant for saturated medium-chain fatty acids (MCFAs) but significantly decreased the binding constant for unsaturated long-chain FAs. The binding sites tended to increase in all the cases. Further investigation revealed that crowding media might loosen the structure of BSA, facilitating MCFA-BSA binding. This research is useful for understanding the transportation of FAs by BSA under physiological conditions and may also help to control digestion by the eventual incorporation of macromolecular crowding agents into food formulations.

Coconut Oil Aggravates Pressure Overload-Induced Cardiomyopathy without Inducing Obesity, Systemic Insulin Resistance, or Cardiac Steatosis

Studies evaluating the effects of high-saturated fat diets on cardiac function are most often confounded by diet-induced obesity and by systemic insulin resistance. We evaluated whether coconut oil, containing C12:0 and C14:0 as main fatty acids, aggravates pressure overload-induced cardiomyopathy induced by transverse aortic constriction (TAC) in C57BL/6 mice. Mortality rate after TAC was higher (p < 0.05) in 0.2% cholesterol 10% coconut oil diet-fed mice than in standard chow-fed mice (hazard ratio 2.32, 95% confidence interval 1.16 to 4.64) during eight weeks of follow-up. The effects of coconut oil on cardiac remodeling occurred in the absence of weight gain and of systemic insulin resistance. Wet lung weight was 1.76-fold (p < 0.01) higher in coconut oil mice than in standard chow mice. Myocardial capillary density (p < 0.001) was decreased, interstitial fibrosis was 1.88-fold (p < 0.001) higher, and systolic and diastolic function was worse in coconut oil mice than in standard chow mice. Myocardial glucose uptake was 1.86-fold (p < 0.001) higher in coconut oil mice and was accompanied by higher myocardial pyruvate dehydrogenase levels and higher acetyl-CoA carboxylase levels. The coconut oil diet increased oxidative stress. Myocardial triglycerides and free fatty acids were lower (p < 0.05) in coconut oil mice. In conclusion, coconut oil aggravates pressure overload-induced cardiomyopathy.

Pharmacological inhibition of carnitine palmitoyltransferase 1 restores mitochondrial oxidative phosphorylation in human trifunctional protein deficient fibroblasts

BACKGROUND

Mitochondrial Trifunctional Protein deficiency (TFPD) is a severe genetic disease characterized by altered energy metabolism and accumulation of long-chain (LC) acylcarnitines in blood and tissues. This accumulation could impair the mitochondrial oxidative phosphorylation (OxPhos), contributing to the non-optimal outcome despite conventional diet therapy with medium-chain triglycerides (MCT).

METHOD

Acylcarnitine and OxPhos parameters were measured in TFPD-fibroblasts obtained from 8 children and cultured in medium mimicking fasting (LCFA) or conventional treatment (MCT), with or without Etomoxir (ETX) an inhibitor of carnitine palmitoyltransferase 1 (CPT1) activity, and were compared to results obtained with fibroblasts from 5 healthy-control children. The effects of various acylcarnitines were also tested on control fibroblasts.

RESULTS

In the LCFA-condition, TFPD-fibroblasts demonstrated a large accumulation of LC-acylcarnitines associated with decreased O₂-consumption (63±3% of control, P<0.001) and ATP production (67±5%, P<0.001) without modification of coupling efficiency. A dose-dependent decrease in O₂-consumption was reproduced in control fibroblasts by addition of increasing dose of LC-acylcarnitines, while it was almost preserved with MC-acylcarnitines. The MCT-condition reduced LC-acylcarnitine accumulation and partially improved O₂-consumption (80±3%, P<0.01) in TFPD-fibroblasts. The addition of ETX in both LCFA- and MCT-conditions normalized acylcarnitine profiles and restored O₂-consumption and ATP production at the same levels than control.

CONCLUSION

Accumulation of LC-acylcarnitines plays a major role in the pathophysiology of TFPD, reducing OxPhos capacities. These deleterious effects could be partially prevented by MCT-therapy and totally corrected by ETX. Inhibition of CPT1 may be view as a new therapeutic target for patients with a severe form of TFPD.

Right ventricular metabolism during venoarterial extracorporeal membrane oxygenation in immature swine heart in vivo

Venoarterial extracorporeal membrane oxygenation (VA-ECMO) provides hemodynamic rescue for patients encountering right or left ventricular (RV or LV) decompensation, particularly after surgery for congenital heart defects. ECMO, supported metabolically by parenteral nutrition, provides reductions in myocardial work and energy demand and, therefore, enhances functional recovery. The RV must often assume systemic ventricular pressures and function on weaning from VA-ECMO. However the substrate utilization responses of the RV to VA-ECMO or stimulation are unknown. We determined RV and LV substrate utilization response to VA-ECMO in immature swine heart. Mixed-breed male Yorkshire pigs (33-49 days old) underwent normal pressure volume loading (control, n = 5) or were unloaded by VA-ECMO (ECMO, n = 10) for 8 h. Five pigs with ECMO received intravenous thyroid hormone [triiodothyronine (T₃)] to alter substrate utilization. Carbon 13 (¹³C)-labeled substrates (lactate and medium-chain and long-chain fatty acids) were systemically infused as metabolic tracers. Analyses by nuclear magnetic resonance showed that both ventricles have similar trends of fractional ¹³C-labeled substrate contributions to the citric acid cycle under control conditions. VA-ECMO produced higher long-chain fatty acids and lower lactate contribution to the citric acid cycle via inhibition of pyruvate dehydrogenase, whereas T₃ promoted lactate metabolism in both ventricles. However, these metabolic shifts were smaller in RV, and RV fatty acid contributions showed minimal response to perturbations. Furthermore, VA-ECMO and T₃ also achieved high [phosphocreatine]/[ATP] and low [NADH]/[NAD⁺] in LV but not in RV. These data suggest that the RV shows decreased ability to modify substrate utilization and achieve improvements in energy supply/demand during VA-ECMO.NEW & NOTEWORTHY We showed that the right ventricle unloaded by venoarterial extracorporeal membrane oxygenation (VA-ECMO) has diminished capacity to alter substrate utilization compared with the left ventricle. This decrease in metabolic flexibility contributes to the inability to increase high-energy phosphate reserves during myocardial rest by VA-ECMO.

Medium-chain fatty acids modulate myocardial function via a cardiac odorant receptor

Several studies have demonstrated the expression of odorant receptors (OR) in various human tissues and their involvement in different physiological and pathophysiological processes. However, the functional role of ORs in the human heart is still unclear. Here, we firstly report the functional characterization of an OR in the human heart. Initial next-generation sequencing analysis revealed the OR expression pattern in the adult and fetal human heart and identified the fatty acid-sensing OR51E1 as the most highly expressed OR in both cardiac development stages. An extensive characterization of the OR51E1 ligand profile by luciferase reporter gene activation assay identified 2-ethylhexanoic acid as a receptor antagonist and various structurally related fatty acids as novel OR51E1 ligands, some of which were detected at receptor-activating concentrations in plasma and epicardial adipose tissue. Functional investigation of the endogenous receptor was carried out by Ca²⁺ imaging of human stem cell-derived cardiomyocytes. Application of OR51E1 ligands induced negative chronotropic effects that depended on activation of the OR. OR51E1 activation also provoked a negative inotropic action in cardiac trabeculae and slice preparations of human explanted ventricles. These findings indicate that OR51E1 may play a role as metabolic regulator of cardiac function.

The effects of proteins and medium-chain fatty acids from milk on body composition, insulin sensitivity and blood pressure in abdominally obese adults

BACKGROUND/OBJECTIVES

To investigate whether intake of whey protein and butter naturally enriched in medium-chain fatty acids (MC-SFAs) (C6-C12) affected body composition, insulin sensitivity, blood pressure (BP) and plasma cholesterol concentrations.

SUBJECTS/METHODS

A 12-week randomised, double-blinded, intervention study was completed in 52 abdominally obese adults. Subjects were assigned to one of four dietary supplementations: 63 g per day of milk fat with either high- (8.5 g per day) or low-MC-SFA (6.9 g per day) content combined with 60 g per day of whey or casein.We examined changes in the body composition by dual-energy X-ray absorption scan, insulin sensitivity using homoeostatic model assessment of insulin resistance (HOMA-IR) and Matsuda index, and diurnal BP and plasma cholesterol concentrations. Two-factor analysis of variance was used to examine the impact of MC-SFA content and protein type.

RESULTS

We observed that lean body mass increased by 981 g (95% confidence interval (CI): 248-1713; P=0.010) after high-MC-SFA compared with low-MC-SFA supplementation. Concomitantly, total body-fat percentage increased by 0.70 percentage points (95% CI: 0.10-1.31; P=0.024) after intake of low-MC-SFA butter compared with intake of high-MC-SFA butter. Both changes were independent of protein type (P=0.96 and P=0.99, respectively). We found no difference in HOMA-IR, Matsuda index, diurnal BP or plasma cholesterol concentrations related to MC-SFA content or protein type.

CONCLUSIONS

Enhanced intake of MC-SFA increased the lean body mass and caused a significantly lower total body-fat percentage compared with lower intake of MC-SFA. Consequently, the composition of dairy fat should be considered when evaluating the impact of dairy products on body composition.

Short- and medium-chain fatty acids in energy metabolism: the cellular perspective

Short- and medium-chain fatty acids (SCFAs and MCFAs), independently of their cellular signaling functions, are important substrates of the energy metabolism and anabolic processes in mammals. SCFAs are mostly generated by colonic bacteria and are predominantly metabolized by enterocytes and liver, whereas MCFAs arise mostly from dietary triglycerides, among them milk and dairy products. A common feature of SCFAs and MCFAs is their carnitine-independent uptake and intramitochondrial activation to acyl-CoA thioesters. Contrary to long-chain fatty acids, the cellular metabolism of SCFAs and MCFAs depends to a lesser extent on fatty acid-binding proteins. SCFAs and MCFAs modulate tissue metabolism of carbohydrates and lipids, as manifested by a mostly inhibitory effect on glycolysis and stimulation of lipogenesis or gluconeogenesis. SCFAs and MCFAs exert no or only weak protonophoric and lytic activities in mitochondria and do not significantly impair the electron transport in the respiratory chain. SCFAs and MCFAs modulate mitochondrial energy production by two mechanisms: they provide reducing equivalents to the respiratory chain and partly decrease efficacy of oxidative ATP synthesis.

Revisiting the metabolism and physiological functions of caprylic acid (C8:0) with special focus on ghrelin octanoylation

Caprylic acid (octanoic acid, C8:0) belongs to the class of medium-chain saturated fatty acids (MCFAs). Dairy products and specific oils like coconut oil are natural sources of dietary C8:0 but higher intakes of this fatty acid can be provided with MCT (Medium-Chain Triglycerides) oil that consists in 75% of C8:0. MCFAs have physical and metabolic properties that are distinct from those of long-chain saturated fatty acids (LCFAs ≥ 12 carbons). Beneficial physiological effects of dietary C8:0 have been studied for a long time and MCT oil has been used as a special energy source for patients suffering from pancreatic insufficiency, impaired lymphatic chylomicron transport and fat malabsorption. More recently, caprylic acid was also shown to acylate ghrelin, the only known peptide hormone with an orexigenic effect. Through its covalent binding to the ghrelin peptide, caprylic acid exhibits an emerging and specific role in modulating physiological functions themselves regulated by octanoylated ghrelin. Dietary caprylic acid is therefore now suspected to provide the ghrelin O-acyltransferase (GOAT) enzyme with octanoyl-CoA co-substrates necessary for the acyl modification of ghrelin. This review tries to highlight the discrepancy between the formerly described beneficial effects of dietary MCFAs on body weight loss and the C8:0 newly reported effect on appetite stimulation via ghrelin octanoylation. The subsequent aim of this review is to demonstrate the relevance of carrying out further studies to better understand the physiological functions of this particular fatty acid.

Differential effects of octanoate and heptanoate on myocardial metabolism during extracorporeal membrane oxygenation in an infant swine model

Nutritional energy support during extracorporeal membrane oxygenation (ECMO) should promote successful myocardial adaptation and eventual weaning from the ECMO circuit. Fatty acids (FAs) are a major myocardial energy source, and medium-chain FAs (MCFAs) are easily taken up by cell and mitochondria without membrane transporters. Odd-numbered MCFAs supply carbons to the citric acid cycle (CAC) via anaplerotic propionyl-CoA as well as acetyl-CoA, the predominant β-oxidation product for even-numbered MCFA. Theoretically, this anaplerotic pathway enhances carbon entry into the CAC, and provides superior energy state and preservation of protein synthesis. We tested this hypothesis in an immature swine model undergoing ECMO. Fifteen male Yorkshire pigs (26-45 days old) with 8-h ECMO received either normal saline, heptanoate (odd-numbered MCFA), or octanoate (even-numbered MCFA) at 2.3 μmol·kg body wt(-1)·min(-1) as MCFAs systemically during ECMO (n = 5/group). The 13-carbon ((13)C)-labeled substrates ([2-(13)C]lactate, [5,6,7-(13)C3]heptanoate, and [U-(13)C6]leucine) were systemically infused as metabolic markers for the final 60 min before left ventricular tissue extraction. Extracted tissues were analyzed for the (13)C-labeled and absolute concentrations of metabolites by nuclear magnetic resonance and gas chromatography-mass spectrometry. Octanoate produced markedly higher myocardial citrate concentration, and led to a higher [ATP]-to-[ADP] ratio compared with other groups. Unexpectedly, octanoate and heptanoate increased the flux of propionyl-CoA relative to acetyl-CoA into the CAC compared with control. MCFAs promoted increases in leucine oxidation, but were not associated with a difference in protein synthesis rate. In conclusion, octanoate provides energetic advantages to the heart over heptanoate.

Triheptanoin Alleviates Ventricular Hypertrophy and Improves Myocardial Glucose Oxidation in Rats With Pressure Overload

OBJECTIVE

Cardiac hypertrophy is characterized by changes in substrate utilization and activity of the Krebs cycle. We assessed the effects of triheptanoin, an odd-chain fat that might support the Krebs cycle, on cardiac metabolism and function in a model of cardiac hypertrophy.

METHODS AND RESULTS

Rats were subjected to aortic banding (AoB) to induce pressure overload (PO). Starting at 1 week after AoB, rats were blindly fed a control diet or a special diet containing triheptanoin at 7% (T7 group) or 30% (T30 group) of total energy value. Six weeks after AoB, echocardiography revealed attenuated hypertrophy and improved diastolic function of the left ventricle. Isolated working heart perfusion showed similar cardiac power, fatty acid oxidation, substrate preference, and insulin response among groups. However, cardiac glucose oxidation (GO) was increased in the T30 group compared with the T7 and control groups. Blood levels of the odd-chain ketone body beta-hydroxypentanoate confirmed adequate bioavailability of triheptanoin. Importantly, they were directly proportional to cardiac GO.

CONCLUSIONS

Treatment with triheptanoin-enriched diet reduces ventricular hypertrophy and improves diastolic function in rats with PO, which is associated with enhanced cardiac GO. The results suggest targeting supplementation of the Krebs cycle to approach ventricular and metabolic remodeling in cardiac hypertrophy.

Ligand specific variation in cardiac response to stimulation of peroxisome proliferator-activated receptor-alpha in spontaneously hypertensive rat

Left ventricular hypertrophy (LVH) is an independent risk factor for cardiac failure. Reduction of LVH has beneficial effects on the heart. LVH is associated with shift in energy substrate preference from fatty acid to glucose, mediated by down regulation of peroxisome proliferator-activated receptor-alpha (PPAR-α). As long-term dependence on glucose can promote adverse cardiac remodeling, it was hypothesized that, prevention of metabolic shift by averting down regulation of PPAR-α can reduce cardiac remodeling in spontaneously hypertensive rat (SHR). Cardiac response to stimulation of PPAR-α presumably depends on the type of ligand used. Therefore, the study was carried out in SHR, using two different PPAR-α ligands. SHR were treated with either fenofibrate (100 mg/kg/day) or medium-chain triglyceride (MCT) Tricaprylin (5% of diet) for 4 months. Expression of PPAR-α and medium-chain acylCoA dehydrogenase served as markers, for stimulation of PPAR-α. Both ligands stimulated PPAR-α. Decrease of blood pressure was observed only with fenofibrate. LVH was assessed from heart-weight/body weight ratio, histology and brain natriuretic peptide expression. As oxidative stress is linked with hypertrophy, serum and cardiac malondialdehyde and cardiac 3-nitrotyrosine levels were determined. Compared to untreated SHR, LVH and oxidative stress were lower on supplementation with MCT, but higher on treatment with fenofibrate. The observations indicate that reduction of blood pressure is not essentially accompanied by reduction of LVH, and that, progressive cardiac remodeling can be prevented with decrease in oxidative stress. Contrary to the notion that reactivation of PPAR-α is detrimental; the study substantiates that cardiac response to stimulation of PPAR-α is ligand specific.

Emerging nutrition science on fatty acids and cardiovascular disease: nutritionists' perspectives

Recent dietary guidance for heart health recommends a reduction (by ∼50%) in saturated fatty acid (SFA) intake to reduce LDL cholesterol and to decrease risk of cardiovascular disease (CVD). The 2010 Dietary Guidelines for Americans recommends substituting unsaturated fat [both polyunsaturated and monounsaturated fatty acids (PUFAs and MUFAs, respectively)] for SFAs. There are many dietary options that can be implemented to replace SFAs, given the different sources of unsaturated fats in the food supply. Compelling evidence exists for the cardioprotective benefits of n-3 (ω-3) PUFAs, both marine- and plant-derived. In addition, the evidence of cardioprotective benefits of n-6 (ω-6) PUFAs is strong, whereas that for MUFAs is mixed, although there is emerging evidence of benefits. Quantitatively, lowering SFAs by 50% will require, in part, substituting food sources of n-6 and n-3 PUFAs and MUFAs for food sources of SFAs. The use of n-3 PUFAs as a replacement for SFAs will result in a shortfall in reaching the SFA goal because of the relatively low amounts that can be incorporated in the diet, even with very high n-3 PUFA substitution. SFAs also can be replaced with dietary carbohydrate and/or protein. Replacing SFAs with carbohydrate, specifically refined sources, however, has little impact on reducing CVD risk. There is evidence about the health benefits of dietary protein on CVD risk, which merits study. Dietary guidelines have advanced considerably with the "replacement of SFA with unsaturated fat message" instead of recommending decreasing SFAs alone. A key question that remains is what is the optimal mix of macronutrients to maximally reduce CVD risk.

A review of odd-chain fatty acid metabolism and the role of pentadecanoic Acid (c15:0) and heptadecanoic Acid (c17:0) in health and disease

The role of C17:0 and C15:0 in human health has recently been reinforced following a number of important biological and nutritional observations. Historically, odd chain saturated fatty acids (OCS-FAs) were used as internal standards in GC-MS methods of total fatty acids and LC-MS methods of intact lipids, as it was thought their concentrations were insignificant in humans. However, it has been thought that increased consumption of dairy products has an association with an increase in blood plasma OCS-FAs. However, there is currently no direct evidence but rather a casual association through epidemiology studies. Furthermore, a number of studies on cardiometabolic diseases have shown that plasma concentrations of OCS-FAs are associated with lower disease risk, although the mechanism responsible for this is debated. One possible mechanism for the endogenous production of OCS-FAs is α-oxidation, involving the activation, then hydroxylation of the α-carbon, followed by the removal of the terminal carboxyl group. Differentiation human adipocytes showed a distinct increase in the concentration of OCS-FAs, which was possibly caused through α-oxidation. Further evidence for an endogenous pathway, is in human plasma, where the ratio of C15:0 to C17:0 is approximately 1:2 which is contradictory to the expected levels of C15:0 to C17:0 roughly 2:1 as detected in dairy fat. We review the literature on the dietary consumption of OCS-FAs and their potential endogenous metabolism.

Plasma capric acid concentrations in healthy subjects determined by high-performance liquid chromatography

BACKGROUND

Capric acid (FA10:0, decanoic acid) is a medium-chain fatty acid abundant in tropical oils such as coconut oil, whereas small amounts are present in milk of goat, cow, and human. Orally ingested FA10:0 is transported to the liver and quickly burnt within it. Only few reports are available for FA10:0 concentrations in human plasma.

METHODS

Fasting (n = 5, male/female = 3/2, age 31 ± 9.3 years old) and non-fasting (n = 106, male/female = 44/62, age 21.9 ± 3.2 years old) blood samples were collected from apparently healthy Japanese volunteers. The total FA10:0 in the plasma were measured by high-performance liquid chromatography after derivatization with 2-nitrophenylhydrazine followed by UV detection.

RESULTS

Inter and intra-assay coefficient of variation of FA10:0 assay at three different concentrations ranged in 1.7-3.9 and 1.3-5.4%, respectively, with an analytical recovery of 95.2-104.0%. FA10:0 concentration was below detection limit (0.1 µmol/L) in each fasting human plasma. FA10:0 was not detected in 50 (47.2%) of 106 non-fasting blood samples, while 29 (27.4%) plasma samples contained FA10:0 less than or equal to 0.5 µmol/L (0.4 ± 0.1), and 27 (25.5%) contained it at more than 0.5 µmol/L (0.9 ± 0.3).

CONCLUSION

A half of the non-fasting plasma samples contained detectable FA10:0. This simple, precise, and accurate high-performance liquid chromatography method might be useful for monitoring plasma FA10:0 during medium-chain triglycerides therapy.

Extracorporeal membrane oxygenation promotes long chain fatty acid oxidation in the immature swine heart in vivo

Extracorporeal membrane oxygenation (ECMO) supports infants and children with severe cardiopulmonary compromise. Nutritional support for these children includes provision of medium- and long-chain fatty acids (FAs). However, ECMO induces a stress response, which could limit the capacity for FA oxidation. Metabolic impairment could induce new or exacerbate existing myocardial dysfunction. Using a clinically relevant piglet model, we tested the hypothesis that ECMO maintains the myocardial capacity for FA oxidation and preserves myocardial energy state. Provision of 13-Carbon labeled medium-chain FA (octanoate), long-chain free FAs (LCFAs), and lactate into systemic circulation showed that ECMO promoted relative increases in myocardial LCFA oxidation while inhibiting lactate oxidation. Loading of these labeled substrates at high dose into the left coronary artery demonstrated metabolic flexibility as the heart preferentially oxidized octanoate. ECMO preserved this octanoate metabolic response, but also promoted LCFA oxidation and inhibited lactate utilization. Rapid upregulation of pyruvate dehydrogenase kinase-4 (PDK4) protein appeared to participate in this metabolic shift during ECMO. ECMO also increased relative flux from lactate to alanine further supporting the role for pyruvate dehydrogenase inhibition by PDK4. High dose substrate loading during ECMO also elevated the myocardial energy state indexed by phosphocreatine to ATP ratio. ECMO promotes LCFA oxidation in immature hearts, while maintaining myocardial energy state. These data support the appropriateness of FA provision during ECMO support for the immature heart.

Ketone body metabolism and cardiovascular disease

Ketone bodies are metabolized through evolutionarily conserved pathways that support bioenergetic homeostasis, particularly in brain, heart, and skeletal muscle when carbohydrates are in short supply. The metabolism of ketone bodies interfaces with the tricarboxylic acid cycle, β-oxidation of fatty acids, de novo lipogenesis, sterol biosynthesis, glucose metabolism, the mitochondrial electron transport chain, hormonal signaling, intracellular signal transduction pathways, and the microbiome. Here we review the mechanisms through which ketone bodies are metabolized and how their signals are transmitted. We focus on the roles this metabolic pathway may play in cardiovascular disease states, the bioenergetic benefits of myocardial ketone body oxidation, and prospective interactions among ketone body metabolism, obesity, metabolic syndrome, and atherosclerosis. Ketone body metabolism is noninvasively quantifiable in humans and is responsive to nutritional interventions. Therefore, further investigation of this pathway in disease models and in humans may ultimately yield tailored diagnostic strategies and therapies for specific pathological states.

High-fat diet alters prostanoid balance and perfusion in ischemic myocardium of naproxen-treated swine

BACKGROUND

The effect of nonsteroidal anti-inflammatory drugs (NSAIDs) on the cardiovascular system remains controversial, especially in patients with cardiovascular comorbidities. We used a swine model of chronic myocardial ischemia to investigate whether hypercholesterolemia alters the cardiovascular effects of the nonselective NSAID naproxen.

METHODS

Yorkshire swine were fed normal chow (NAP; n = 7) or a high-fat diet (HF-NAP; n = 8). Chronic myocardial ischemia was created in all animals by left circumflex ameroid constrictor placement. All swine were started on oral naproxen (440 mg/day) at the time of ameroid placement. After 7 weeks, myocardial perfusion and microvessel reactivity in the ischemic territory were assessed. Tissue levels of prostanoid metabolites 11-dehydrothromboxane B2 (11-d-TXB₂) and 6-keto-prostaglandin F1-α (6-k-PGF(1α)) were measured. Tissue was analyzed for capillary density and protein expression.

RESULTS

Myocardial perfusion was significantly decreased in the HF-NAP group both at rest and during ventricular pacing. Microvessel relaxation responses to sodium nitroprusside and adenosine 5'-diphosphate were similar between groups. Tissue 11-d-TXB₂ levels were similar between groups, but tissue 6-k-PGF(1α) was significantly decreased in the HF-NAP group (P = .001). Expression of thromboxane synthase was significantly higher in the HF-NAP group (P = .02), while prostacyclin synthase expression was significantly decreased in the HF-NAP group (P = .04). Capillary density was higher in the HF-NAP group (P = .005). Proangiogenic vascular endothelial growth factor (VEGF; P = .0002) and Akt (P = .01) were downregulated in the HF-NAP group.

CONCLUSION

A high-fat diet impairs tissue perfusion in ischemic myocardium of naproxen-treated swine by shifting the prostanoid balance to favor production of thromboxane over prostacyclin. Dietary modification may improve myocardial blood flow and alter the safety profile in chronically ischemic cardiac patients taking naproxen.