A recent study published in the Virology Journal has highlighted the importance of high-density lipoprotein (HDL) in the pathogenesis and outcome of coronavirus disease 2019 (COVID-19). A very low serum HDL level has been observed in most patients with COVID-19.
Study: High-density lipoproteins may play a crucial role in COVID-19. Image credit: piccreative/Shutterstock
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Lipoproteins are complex molecules comprising a central core of cholesterol esters and triglycerides surrounded by free cholesterol, phospholipids and apolipoproteins. Lipoproteins play a vital role in the transport of water-insoluble cholesterol and triglycerides. They are divided into seven classes, including low-density lipoprotein (LDL), very-low-density lipoprotein (VLDL), HDL, chylomicrons, chylomicron remnants, intermediate-density lipoprotein (IDL), and lipoprotein a (Lpa).
Of all the lipoproteins, only HDL has antiatherogenic activity. HDL facilitates the transport of excess cholesterol to the liver and prevents its accumulation in the arteries. This process is called reverse cholesterol transport. In addition, HDL prevents free radical-induced oxidation of LDL and the subsequent accumulation of oxidation products in the arterial wall. Because of these beneficial effects, HDL is considered “good cholesterol.”
Lipids are vital structural components of cells and play a crucial role in the induction of host antiviral immune responses. Changes in plasma lipid levels have been observed in many viral infections, including human immunodeficiency virus (HIV), hepatitis C, and dengue infections. Viruses can modulate host lipid metabolism to support their life cycle.
A significant reduction in plasma HDL level has been observed in many viral infections. Apolipoprotein AI and apolipoprotein M are vital components of HDL with antiviral properties. They prevent viral host cell entry and replication, respectively. In patients with COVID-19, reductions in cholesterol, HDL, LDL, and triglycerides have been found to correlate with disease severity.
In the current study, the scientists compared the lipid profiles of patients with COVID-19 and healthy individuals to assess the role of lipoproteins in the pathogenesis and prognosis of COVID-19.
Study design
The study was conducted on the Indian population. Blood samples were collected from 75 patients with COVID-19 and 10 healthy individuals without a history of COVID-19. The samples were subjected to lipid profile tests, which included triglycerides, HDL cholesterol, total cholesterol, VLDL cholesterol, LDL cholesterol, total cholesterol/HDL ratio, and LDL/HDL cholesterol ratio.
The prevalence of dyslipidemia (imbalance of lipids in the blood) in India was determined by screening and analyzing available studies demonstrating the percentages of different lipoproteins in the Indian population. The final analysis included a total of 15 studies that were published between 2006 and 2021.
Lipid profiles in the Indian population
Analysis of the available literature indicated that the prevalence of moderate to severe HDL deficiency is approximately 72% in the Indian population. In contrast, about 12% and 14% of Indians had high levels of LDL and total cholesterol, respectively. The most common dyslipidemia found in the selected studies was low HDL.
Lipid profiles in patients with COVID-19
Of all enrolled COVID-19 patients, about 65% had severely low HDL levels and 35% had moderately low HDL levels. None of the patients had normal levels of HDL in their blood. Most male patients had very low HDL levels.
Regarding total cholesterol, the majority of enrolled patients (96%) had normal levels, with only 3% showing high levels. A low total cholesterol level was detected in only one patient. Regarding gender variation, all women had normal total cholesterol levels, while 5% of men had low or high levels.
Like total cholesterol, no significant changes were observed in LDL levels in patients with COVID-19. Although most patients had normal LDL levels, only 2% had very high LDL levels.
Variation in triglyceride and VLDL levels was observed among patients with COVID-19. About 43% and 57% of patients had high and normal triglyceride levels, respectively. Similarly, about 51%, 41%, and 8% of patients had normal, high, and low VLDL levels, respectively.
All healthy individuals enrolled in the study had normal total cholesterol and moderately low HDL levels. Unlike the patients with COVID-19, none of the healthy individuals showed severely low HDL levels. About 80% of healthy individuals had normal triglyceride and LDL levels.
Study the importance
The study indicates that a low level of HDL in the blood could be associated with the pathogenesis and prognosis of COVID-19. Although the level of LDL is not primarily affected by the disease, the majority of patients with COVID-19 (65%) have very low levels of HDL.
Given these observations, scientists suggest that HDL could play a vital role in increasing the risk of contracting COVID-19 or modulating the severity of the disease. A low level of HDL may also increase the risk of cardiovascular disease in patients with COVID-19.