See editorial on page 824.
While most COVID-19 patients clear the infection, some develop severe disease with organ failure. Based on patterns associated with severe COVID-19, underlying mechanisms, we propose a simple, low risk supportive intervention.
Unsaturated fat intake is associated with increased mortality from COVID-19. Unsaturated fatty acids cause injury, organ failure resembling COVID-19. Early albumin and calcium can bind unsaturated fatty acids, reduce injury.
We do not have a clinical trial to support that “keeping a normal serum calcium and albumin all through COVID-19” improved mortality. Such a trial may be helpful in the future.
Although most coronavirus disease 2019 (COVID-19) infections are self-limited, some develop into sepsis and multisystem organ failure (MSOF),1 resembling lipotoxic acute pancreatitis.2, 3 Understanding underlying mechanisms may guide supportive care while clinical trials are ongoing. Unsaturated fatty acids (UFAs) generated by adipose lipolysis2, 3 cause MSOF, including acute lung injury.2 Severe acute pancreatitis and severe COVID-19 share obesity as a risk factor,4 along with lipase elevation,5 hypoalbuminemia,1 and hypocalcemia.6 The latter 2 may progress undetected because calcium-albumin correction calculations (eg, https://www.mdcalc.com/calcium-correction-hypoalbuminemia) can pseudonormalize calcium values (eg, uncorrected calcium of 5.9 mg/dL and albumin of 0.1 g/dL to corrected calcium of 9.0 mg/dL). Notably, calcium ameliorates MSOF,7 and UFAs cause nonendocrine hypocalcemia.7
The ACE2 receptor resides on adipocytes8 containing triglycerides and adipocyte triglyceride lipase (ATGL) and on pancreatic acini expressing pancreatic triglyceride lipase (PNLIP).2 Both oleic acid (C18:1) administration and adipose lipolysis3 by PNLIP can cause acute lung injury and MSOF. These, and previous data showing that UFAs depolarize mitochondria,2 inhibit complexes I and V,3 decrease adenosine triphosphate, release intracellular calcium,3 and increase inflammatory mediators,3 made us explore lipotoxicity during severe COVID-19. This approach, culminating in clinical advice to keep calcium and albumin levels normal from early on in the disease, is summarized in Figure 1A and explained diagrammatically in supplementary figure 1.
Seven of 15 hospitalized patients were discharged home by 3. 4 ±1.6 days. One died of hypoxemic failure after declining intubation. Seven patients with severe disease required intensive care (mean, 3.9 ± 2 days after admission). Although otherwise similar to those with mild disease, severely ill patients had higher blood urea nitrogen (BUN) level; lower platelets and lymphocytes (Supplementary Figure 2); early, steady progressive hypocalcemia and hypoalbuminemia; and lower oxygen saturation nadirs (Figure 1B ). Mice administered linoleic acid (LA) (C18:2) (Supplementary Figure 3A ) but not the saturated fatty acid C16:0 developed hypoalbuminemia. Because albumin and calcium bind fatty acids and reduce toxicity,7 we graphed serum unbound fatty acids in patients in the intensive care unit (Figure 1C) vs their P/F ratio (ie, the arterial partial pressure of oxygen/percentage of oxygen). Lower P/F ratios (0.97 ± 0.1) were associated with higher unbound fatty acid levels (15.5 ± 7.7 μmol/L vs 4.2 ± 2.3 μmol/L; P < .002), and vice versa (2.36 ± 0.4; P < .003).
C18:1, C18:2, and C16:0 make up 10%–50% of dietary fat and adipose triglycerides in humans. Mice given C18:1 (not shown) or C18:2, but not C16:0, (Figure 1D ) developed leucopenia, lymphopenia,1 lymphocytic injury, relative thrombocytopenia,1 hypercytokinemia,1 elevated alanine aminotransferase levels,1 hypoalbuminemia1, hypocalcemia6, shock,1 and renal failure resembling lethal COVID-19.
Because adipose triglyceride composition corresponds to dietary fat composition, we compared dietary fat patterns to other risk factors for COVID-19 mortality from countries with >1000 COVID-19 cases reported between March 25, 2020, and April 8, 2020 (61 countries; 1,476,418 patients).
We first did a univariate analysis using the linear mixed model, accounting for daily reported percent mortality vs dietary and other factors (Figure 1E). Because of skewness, log-transformed mortality was used in the model. Only saturated fat intake (kg/capita/y) was negatively associated (P = .05), and percent UFA intake was positively associated (P < .001) with mortality (Figure 1F and G). The rate ratio indicates the relative change in mortality for each parameter; for example, a rate ratio of 0.97 for saturated fat intake indicates that for a 1-unit increase in saturated fat, there is a 3% reduction in mortality: (1 – 0.97) × 100% = 3%. Multivariate analysis showed only percent UFA as significantly associated with mortality (P < .0001).
Interestingly, per capita GDP consistently and positively correlated with tests/million (not shown), and COVID-19 cases/million (Supplementary Figure 3B), with the infliction point noted above US$10,000. Thus, COVID-19 may be undiagnosed in low-income countries.
We next studied how dietary and adipose triglyceride saturation could protect from severe COVID-19.
Because it is not known which lipase is active in COVID-19, we examined how saturation affects triglyceride interaction with ATGL. On unbiased in silico docking simulation, the linoleic acid triglyceride trilinolein (LLL) docked to the ATGL homology model with a GlideScore of –6.71 kcal/mol and 7.02 Å between the catalytic Ser47 hydroxyl and the carbonyl C atom of the glycerol backbone (Figure 1H ). Substituting palmitate at Sn-3, 1,2-dilinoleoyl-3-palmitoyl-racglycerol (LLP) docked with a GlideScore of –3.34 kcal/mol and 8.49 Å from the catalytic serine (Figure 1I). Thus, saturation reduces lipolysis by making the complex less energetically and structurally favorable.
Exposure of an established human umbilical vein endothelial cell (HUV-EC-C) cell monolayer to UFAs decreased transendothelial resistance and increased dextran permeability and apoptotic peripheral blood mononuclear cells (Figure 1J–L ). LA increased the baseline and frequency of cytosolic calcium elevation in spontaneously beating cardiomyocytes (Figure 1M). Thus, UFAs may cause vascular (albumin) leak, inflammatory injury, and arrhythmia during severe COVID-19.
On isothermal titration calorimetry, albumin-bound LA strongly (stoichiometry ≈ 6:1; enthalpy, –230 KJ/mol) (Figure 1N ). However, adding albumin 30 minutes after LA to macrophages did not reduce necrosis. Although preincubating HEK293 cells with albumin and calcium (Figure 1O and P ) completely prevented necrosis, delayed addition of albumin only partially blocked or reversed LA-induced mitochondrial depolarization2 (Figure 1Q and R ). Therefore, early neutralization of UFAs may prevent mitochondrial dysfunction and injury resulting in MSOF.3 In vivo, prophylactic calcium and albumin prevented LA-induced MSOF (not shown). Thus, early supplementation with albumin and calcium may be better than correcting deficiencies later during severe COVID-19 infection or sepsis, which may be too little, too late.
Calcium binds C18:2 more weakly7 (–20 kJ/mol) than albumin. However, calcium’s total concentration (2.25–2.75 mmol/L) is 3–5 times higher, and it ameliorates MSOF.7 Thus, supplementing calcium (eg, oral calcium carbonate) and albumin to normal values early during COVID-196 could reduce lipotoxic MSOF without violating the calcium-albumin correction. Despite COVID-19 being underdiagnosed in lower-income countries, mortality in diagnosed COVID-19 is likely from the infection and, thus, supports our conclusions. Additionally, while we did incorporate the number of ventilators per country, the numbers quoted are in some cases more than 8 years old, and therefore may not be reliable. Similarly, the number of ICU beds available may not reflect the exact number in each country. Although our clinical study is small and retrospective and experimental studies are correlative, their congruence to severe COVID-19 is supported by larger published studies1, 6 and can be validated by future interventional studies. Thus, keeping calcium and albumin levels normal through COVID-19 is a low-cost, low-risk strategy to improve outcomes.
Lipotoxicity in COVID-19 Study Group contributors: Bara El-Kurdi, Biswajit Khatua, Christopher Rood, Christine Snozek, Sergiy Kostenko, Shubham Trivedi, Clifford Folmes, Katherine Minter Dykhouse, Sumbal Babar, Yu-Hui Chang, Rahul Pannala, Rodrigo Cartin-Ceba, and Vijay P. Singh.
We are extremely thankful to Jill Lauritsen, Sheila Sandolo, and the staff at the Mayo Clinic Arizona Biospecimen repository and accession core for their help. We acknowledge the websites worldometers.info/coronavirus, the Johns Hopkins University Coronavirus resource center (https://coronavirus.jhu.edu/), Wikipedia.com, the World Bank website (https://data.worldbank.org/) and World Health Organization website (https://apps.who.int/gho/data/view.main.HS07v) and data publicly provided by www.ourworldindata.org/.
Bara El-Kurdi, MD (Data curation: Equal; Investigation: Equal; Methodology: Equal; Writing – original draft: Equal); Biswajit Khatua, PhD (Data curation: Equal; Investigation: Equal; Methodology: Equal); Christopher Rood, BS (Data curation: Equal; Formal analysis: Equal; Methodology: Equal); Christine Snozek, PhD (Data acquisition -Equal, Methodology: Equal, Writing – subsequent draft: Equal); Rodrigo Cartin-Ceba, MD (Data curation: Equal; Funding acquisition: Equal; Investigation: Equal; Methodology: Equal; Project administration: Equal; Supervision: Equal; Writing – original draft: Supporting); Vijay P. Singh, M.D. (Conceptualization: Lead; Data curation: Lead; Formal analysis: Lead; Funding acquisition: Lead; Investigation: Lead; Methodology: Lead; Project administration: Lead; Resources: Lead; Supervision: Lead; Validation: Lead; Visualization: Lead; Writing – original draft: Lead); The Lipotoxicity in COVID-19 Study Group (Data curation: Equal; Formal analysis: Equal; Investigation).