Emerging scientific research is leading to breakthroughs in the understanding of albumin, the most abundant serum protein. This research links together many of albumin’s diverse roles in human physiology and disease states. This includes albumin’s critical roles in: redox and antioxidant biology, acute inflammation, hemostasis, osmotic fluid regulation, and cellular energy metabolism. This article is an exploration into the various functions and clinical implications of albumin, its involvement in numerous pathological situations, as well as implications for integrative and functional medicine therapeutics.
Human Serum Albumin: Characteristics & Functions
Human Serum Albumin (HSA) is the most abundant protein in human blood, comprising 60% of total proteins. Albumin functions as a protein transport for a wide variety of endogenous and exogenous molecules, including: fatty acids, hormones, cholesterol, amino acids, minerals, bile acids, lysophosphatidylcholines, bilirubin and drugs. Importantly, the presence of Albumin’s sole free cysteine residue, Cys34, bestows Albumin as the most abundant thiol in human serum, comprising roughly 80% of the total thiol pool. As such, albumin accounts for 80% of the sulfhydryl antioxidant capacity of blood. Albumin exists in 2 states: Oxidized Albumin (human non-mercaptal Albumin, or HNA), and Reduced Albumin (human mercaptal Albumin, or HMA). Because of the effect of the thiol pool in the maintenance of redox homeostasis in serum, the ratio of Reduced to Oxidized Albumin has been recognized as a significant factor in acute and chronic diseases. Due to Albumin’s central role in the binding and transport of numerous cargo, including free fatty acids, coupled with its proclivity to undergo oxidation, albumin has emerged as one of the most significant therapeutic targets in human physiology.
Of the total body pool of albumin, 40% is located in whole blood, and 60% in extravascular fluids. Albumin is a large protein, consisting of 585 amino acids. Albumin contains 17 disulfide bridges, and all but one of its cysteines are bound in disulfide bridges. That leaves a single cysteine, Cys34, to freely undergo redox reactions. Cys34 accounts for 80% of the total thiol pool in human plasma. In healthy subjects, the amount of oxidized albumin (oxidized Cys34) is approximately 35%. During oxidative stress, or in chronic disease, oxidized albumin has been observed as high as 70% (8).
Albumin synthesis begins in liver hepatocytes as preproalbumin, followed by conversion into proalbumin within the endoplasmic reticulum. This is followed by furin cleavage of an N-terminal oligopeptide within the trans-Golgi network, leading to mature albumin formation. Dietary protein has long been known as critical in the biosynthesis of albumin. Several amino acids are necessary in these regards, especially the essential amino acids L-Tryptophan, and the branch chain amino acids (BCAA’s), leucine, isoleucine and valine. Albumin has a life in circulation of approximately 20 days, under normal conditions, and it is believed that albumin’s 17 disulfide bridges contributes to its longevity (53).
Albumin & Fatty Acids
Free fatty acids (FFA’s), also referred to as non-esterified fatty acids or NEFA’s serve as a primary source of energy for cells. In addition to this, FFA’s are centrally involved in immunological signaling, in the inflammatory response, and in human pathology.
In the blood, fatty acids are transported via chylomicrons, triglycerides (bound to lipoproteins), or as free fatty acids (FFA’s) bound to albumin. Because of the very low solubility of fatty acids in aqueous solutions, albumin serves as a crucial transport of fatty acids.
Remarkably, 99% of the fatty acids in plasma are transported by albumin. When fatty acids are delivered to cells, they arrive as albumin-fatty acid complexes (1, 2). Cell surface CD36 receptors are then activated, which take up free fatty acids for cellular utilization. As a carrier protein, albumin also facilitates the transport of fatty acids between blood, tissues and lipoproteins.
Under normal physiological conditions, albumin binds 0.3-1 fatty acid per albumin protein, although the protein is capable of carrying 5-7 fatty acids per protein molecule. Under stress conditions, such as adrenal catecholamine activation, exercise, or various pathologies, the amount of fatty acids per albumin protein can increase to as many as 4-6. The increased load of FFA’s that are bound to albumin can significantly alter the protein’s structure and function, as well as affect its oxidation state (26, 27).
The type of fatty acids that bind albumin vary, and are typically found between 10-20 carbons in length: Oleic (18:1), Palmitic (16:0), Linoleic (18:2), Arachidonic (20:4) (5). The fact that both linoleic and arachidonic acids (both polyunsaturated omega 6’s) can bind albumin has significance for a wide variety of inflammatory conditions. Both linoleic acid and arachidonic acid have a high proclivity to generate reactive oxidative species.
Free and unbound FFA’s are a primary source of energy for cells, and are delivered to mitochondria via intracellular transport, including the carnitine shuttle. However, FFA’s are also major drivers of pathology, particularly if unbound to albumin, or when bound to albumin in excess. Elevations in FFA’s have been observed and studied in several diseases, including: Type 2 diabetes, preeclampsia, obesity, sepsis, cardiovascular disease, cancer, kidney disease, ME/CFS, steatosis, NAFLD (non-alcoholic fatty liver disease), fibrosis, platelet activation, and thrombosis.
Diseases that involve mitochondrial dysfunction, or involve states of mitochondrial conservation often feature high serum FFA’s. This is likely because reduced mitochondrial consumption of fatty acids will increase their prevalence in blood. FFA’s induce reactive oxygen species (ROS), and are associated with physiological stress and inflammation. For example, patients with NAFLD (non-alcoholic fatty liver disease) and NASH (non-alcoholic steatohepatitis) feature high levels of FFA’s, mitochondrial dysfunction, insulin resistance, increased malondialdehyde (a lipid peroxidation marker), lower SOD levels (superoxide dismutase), as well as elevated inflammatory cytokines. Ex vivo research using hepatocytes of NASH cattle has found significantly increased levels of ROS when cells were infused with FFA’s (33). In type 2 diabetes research, infusion of FFA’s in diabetic subjects induces hypertension (3). Additionally, injections of FFA preparations induces insulin resistance to occur, and this effect can be partly abrogated by the amino acid L-Taurine (34).
Experimental research has long demonstrated the toxic effects of FFA’s. FFA infusion was administered intravenously with heparin in a cohort of healthy subjects. The inflammatory effects induced by FFA’s were studied over several hours, as reflected in increases in the nuclear transcription of the NFkappaß signaling pathways in mononuclear cells and polymorphonuclear lymphocytes. Sustained released of ROS was observed along with impaired arterial vasodilation (46).
Albumin: Inflammation, Oxidation & Free Fatty Acids
Albumin is a negative acute phase protein. That is, during certain states of acute inflammation, it’s appearance in the blood decreases. While the reason for this has not been definitively elucidated, an inflammatory milieu involves a local and/or organismic shift from constructive metabolic processes to inflammatory processes. Inflammation is driven in large part by the reaction of FFA’s (54). Given albumin’s role as a primary free fatty acid transport, the decrease of albumin during inflammation may be an evolutionarily conserved mechanism that enables longer chain free fatty acids to react with molecules, pathogens and tissues, enabling inflammatory, processes to ensue. Under prolonged pathological conditions, however, a low albumin level is strongly correlative with disturbances in osmotic pressure, increased hemostasis, reduced ligand binding affinities, and increased morbidity.
During inflammatory processes, redox activity is altered, and in the early phases of inflammation, conditions will tend to favor an increase in ROS generation from the reaction of oxygen with cell membrane lipids. Albumin’s single, free sulfhydryl group, Cys34 bestows albumin as a redox protein, and as a major regulator of antioxidant activities. Cys34 undergoes oxidation. Too much oxidized albumin signals problems.
There are 2 forms of oxidized albumin:
- Reversibly oxidized albumin: comprised of sulfenic acids and mixed disulfides, as well as S-nitrosylated species
- Non-reversibly oxidized albumin: comprised of sulfonic and sulfinic acids
Reversible and irreversible are what the names imply; the ability or inability to be reduced and regenerated by electron donation. The antioxidant effect bestowed to Cys34 induces the formation of reversibly oxidized albumin, and the formation of sulfenic acids. Under certain inflammatory states, this reaction can lead to the cysteinylation of albumin’s mixed disulfides. Cysteinylated albumin forms irreversibly oxidized sulfur molecules, such as sulfonic and sulfinic acids. As a consequence, too much irreversibly oxidized sulfur species accumulates, and cannot be reduced back.
The increase of cysteinylated Cys34 is present in excess in numerous pathological and oxidative conditions (9). A critical finding is that the albumin sulfhydryl group, Cys34 is more oxidizable in the presence of free fatty acids (FFA’s). This effect has been demonstrated both in vitro and in vivo (27, 61). The implications are that as the FFA/albumin ratio increases, the oxidation of albumin increases.
Under conditions where more sulfenic acid is present per albumin protein (sulfenic being ‘reversibly oxidized’), the albumin sulfhydryl reacts 3-fold faster when fatty acids are bound, and this reactivity is believed to lead to greater amounts of irreversible, oxidized forms, sulfonic and sulfinic (27). Under oxidative stress conditions, where more free fatty acids are present and bound to albumin, there are conformational changes in both the structure and function of albumin. This includes increased oxidation and the higher oxidation states (sulfonic and sulfinic). These intricate mechanisms between FFA’s and albumin’s thiol and sulfur groups play out in numerous critical care situations, and in various disease processes.
For example, in decompensated cirrhosis, a condition that features high levels of FFA’s and elevations of oxidized albumin, increased oxidized albumin-1 (HNA1, which comprises the ‘reversibly oxidizable’ form), is strongly associated with increased inflammatory cytokines, IL1ß, IL6, IL8 and TNFa. Furthermore, ex vivo studies using HNA1 albumin from decompensated cirrhosis patients found an up-regulation of oxidized, fatty acid-derived eicosanoids, prostaglandins: PGE2, PGF2α, thromboxane TXB2 and Leukotriene LTB4 (10). In chronic kidney disease, the accumulation of FFA’s in the proximal tubule was identified long ago to play a central role in disease progression. In CKD, both forms of oxidized albumin, HNA1 and HNA2 increase with the corresponding progression of the disease (32).
Albumin, Platelet Activation & Diabetes
Albumin plays an important role in controlling platelet activation. When the free fatty acid, arachidonic acid is activated, this effect is capable of generating noxious inflammatory signals. Free arachidonic acid (AA) is a primary fatty acid-activator of platelet mediated prostaglandins: arachidonate 12-lipoxygenase (ALOX12) and thromboxane A2 (TXA2). It has been observed that when the Arachidonic acid/Albumin molar ratio is 2 or less, platelet activation does not occur. However, when the AA/albumin ratio doubles to 4 or greater, platelet activation reaches a maximum (58). Moreover, albumin inhibits platelet-activated thromboxane B2 through the sequestration of free arachidonic acid in the extracellular space. In conditions of severe hypoalbuminemia, this effect is abolished (60).
Aside from arachidonic acid, histone H4 has been shown to also activate platelets. Following cellular damage, cellular debris is released, including DNA and histones. When albumin levels decrease in plasma, free histones are able to activate platelets. However, if albumin levels remain within normal range, this effect is blocked (59).
In insulin resistance and diabetes mellitus, albumin can become glycated. The accumulation of glycated albumin leads to the activation of inflammatory signaling, and to hepatic-related complications, reduced proteolytic enzyme function and impaired enzyme activities. Glycated albumin induces glycoxidation, reduced binding of FFA’s to albumin, the subsequent increase in the oxidation of Cys34, and platelet aggregation. The in vitro effect of glyoxylated or glycated albumin was shown to reduce FFA binding of albumin by 32%, and albumin’s ability to block platelet aggregation by 50% (4). Hence, hyperglycermia and diabetes mellitus have major effects on albumin; an increase in the protein’s oxidation state, and reactions between free fatty acids and platelets.
Free Fatty Acid (FFA) to Albumin Molar Ratio: Aging, CVD and Others
Aging is associated with a progressive elevation of the FFA to albumin ratio. However, this progression is markedly increased in cardiovascular disease (15). The elevation of the FFA/Albumin ratio is also seen in: Hemolysis, pre-eclampsia, acute pancreatitis, kidney disease, and conditions featuring increased fibrinogen (16, 17). The greater the FFA/albumin molar ratio, the lower the binding coefficient between albumin and FFA’s. This effect results in an increase in unbound FFA’s, activation of Hageman Factor (coagulation factor XII), increases in fibrinogen, including to levels that are seen in thrombosis, stroke, plaques and atheroma (20).
The tight binding of FFA’s to albumin protects platelets from activation, while their dissociation from albumin causes their activation (49). Additionally, experimental research done in vivo and in vitro demonstrated that unbound FFA’s are capable of suppressing lymphocytic T-cell function (6).
A form of albumin known as ‘Ischemia Modified Albumin’ or IMA is elevated among patients with myocardial ischemia, sepsis and diabetes mellitus. This form of albumin is characterized by low cobalt and zinc binding affinity, and the presence of high amounts of FFA’s. IMA research has elucidated that albumin carrying an excess of FFA’s reduces binding of metals at albumin’s A and B sites. Under these circumstances, increased FFA binding to albumin reduces binding of both zinc and cobalt (44). It is reasonable to speculate that under IMA conditions caused by elevated FFA’s bound to albumin that zinc and Vitamin B-12 may be in short supply or deficient.
Which Biomarkers Are Associated with the FFA/Albumin Ratio?
In a small study performed on stable geriatric patients, the FFA/albumin ratio was strongly and positively associated with: the reticulocyte count, LDH (lactate dehydrogenase), and haptoglobin (18).
Research in COVID-19 patients suggests an inverse relationship between Albumin and D-dimer (evidence of intravascular clot formation). This research supports existing evidence that hypoalbuminemia is associated with thrombosis, hypercoagulation and death (40).
Albumin: Hemostasis, Clot Formation: Implications for Thromboembolism
Ex vivo research using whole blood from 25 volunteers was induced to feature low, normal and high albumin. Compared to physiologically normal albumin, the low albumin preparations featured: increased primary hemostasis, increased ATP release, and increased clot formation. Compared to the physiologically normal albumin group, the high albumin group featured impaired clot formation (36). The findings corroborate the literature that hypoalbuminemia levels may be the cause of venous thromboembolism in cancer patients, inflammatory bowel disease, and in critical illness (37, 38, 39).
Linoleic Acid, Albumin & Cardiovascular Disease
Linoleic acid is a type of omega 6, polyunsaturated fatty acid found in large quantities in vegetable oils. Linoleic acid has emerged through a chain of literature as strongly associated with cardiovascular disease. This theory is now referred to as the ‘Oxidized Linoleic Acid Hypothesis’. This hypothesis largely centers around the fact that linoleic acid consumption has drastically risen over the past hundred years, and is linearly associated with the rise of heart disease. Linoleic acid’s oxidized metabolites, 9-HODE and 13-HODE induce insulin resistance, cell adhesion, endothelial toxicity, are present in systemic Lupus (a condition which can lead to cardiovascular disease), are present abundantly in endothelial plaque, and in liver injury (47). Early albumin literature identified that a significant amount of linoleic acid can be bound to albumin (5). While the fate of albumin-bound linoleic acid is not presently known, I propose that under oxidizing conditions, such as the increased oxidation of Cys34, 9 and 13-HODE may form or accumulate in greater quantities.
Linoleic acid-derived 13-HODE’s, along with arachidonic-derived 15(S)-HpETE form the atherogenic, 4-hydroxynonenal lipids (HNE’s). Increased generation of these unsaturated, lipid peroxidative cabonyl species are pro-atherogenic, and are studied as etiological in cardiovascular, metabolic and neurological diseases. HNE’s induce insulin resistance, damage ß-islet cells of the pancreas, modify lipoproteins, damage metabolic enzymes, as well as disrupt neurotransmitter signaling (48). HNE’s have been proposed as centrally involved in atherogenesis, due to their ability to recruit macrophage foam cells, and smooth muscle cell activation, two characteristic cell types involved in fibrinogenic processes (49, 50). HNE’s along with malondialdehydes, and acrolein (unsaturated aldehyde) are capable of altering nuclear transcription factors, and converting LDL to pro-atherogenic forms, via carbonyl adduct formation with apolipoprotein B (50).
While reactive HNE’s can be efficiently detoxified in tissues via glutathione, phase 1 cytochromes, as well as lactate dehydrogenases, it is significant to point out that research from Aldini, Vistoli, et al identified that reactive carbonyl species are formed primarily from the fatty acids within circulating lipoproteins in plasma. Importantly, proteomics research from this same research team identified albumin’s Cys34 residue as primarily involved in the clearance of HNE’s from plasma. HNE trapping by albumin was found to be 1 order of magnitude greater than glutathione (50). The implications for this are significant because it links the oxidized/reduced albumin ratio (as determined by the redox state of Cys34) to cardiovascular disease, due to the increased demand of reduced albumin to scavenge HNE’s and carbonyl species from circulation. It is known from studies of bovine serum albumin (BSA) that PUFA-derived malondialdehyde alters both the reactivity of Cys34 and albumin’s esterase activity (51). Linoleic acid’s carbonyl species are known to form adducts with proteins, and albumin can become a central target. These adducts lead to conformational changes in both the structure and function of human serum albumin.
While dietary debate over saturated versus polyunsaturated fatty acids carries onward, it is clear from mining the literature that polyunsaturated omega 6 fatty acids (namely linoleic and arachidonic), which are abundant in vegetable oils, are far more atherogenic, due to their ability to form reactive carbonyl species, malondialdehydes, 13-HODE, 15(S)-HpETE, HNE’s, LTB4 leukotrienes, reactive alkenes, protein adducts, and other reactive metabolites and processes.
Importantly, albumin plays a central role in the regulation of plasma redox, cargo and fatty acid transport, trapping inflammatory HNE’s from plasma, as well as a mediator of cholesterol efflux. The role albumin plays in trapping and scavenging HNE’s, is an under-appreciated mechanism that places this critical protein, front-row-center of heart disease. Albumin’s effect on cholesterol efflux is yet another under-appreciated and not well studied action, which invariably will play out in vascular disease (52).
Albumin & Cholesterol Efflux
Serum albumin mediates the efflux of cholesterol, and significantly mediates the transfer of cholesterol between cells and lipoproteins. An early study from 1982 found that removal of albumin from blood plasma reduced the efflux of cholesterol from fibroblasts by more than 50% (41). Research from 1996 (Zhao, Marcel) confirmed that albumin, like HDL promotes a multi-directional transfer of cholesterol between cells and lipo-proteins, making its effect on par with that of Apolipoprotein A1. The authors also noted that albumin fractions containing more fatty acids were capable of slightly more cholesterol efflux, compared to fatty acid-free albumin (42). In rats, 24% of non-esterified cholesterol (free, unbound cholesterol) is bound to albumin. While the subject of esterified versus non-esterified cholesterol is beyond the subject of this paper, it should be pointed out that non-esterified lipids (both fatty acids and cholesterol) are capable of undergoing modifications, and are the primary lipid types associated with pathology. When bound to esters, cholesterol and fatty acids are not pathological. As a point of reference, consider that in cardiovascular disease, non-esterified cholesterol is atherogenic, whereas esterified cholesterol is not (43).
Nitric Oxide, S-Nitrosylated Albumin & Nitrosylated Fatty Acids
Nitric oxide (NO) is a critical signaling molecule with diverse functions. NO can be classified into 3 categories: 1) those involving cGMP mediated vasodilation, 2) those involved in post-translational effects and signal transduction, 3) as an immunological killing weapon of immune cells. S-nitrosylation is the addition of nitric oxide to a cysteine residue. S-nitrosylation is a post-translational protein modification that attenuates redox signaling, and as such is emerging as a significant therapeutic target for a wide range of conditions.
S-nitrosylation leads to the formation of S-nitrosothiols. There are 2 classes of S-nitrosothiols: 1) low molecular weight (such as nitrosoglutathione, nitrosohomocysteine, nitrosocysteine), and 2) higher molecular weight (nitrosoalbumin). Over 100 S-nitrosylated proteins have been identified. Many of these are associated with pathologies such as Parkinson’s, stroke, Alzheimer’s disease, heart failure, asthma, among others. Of the 100 or so proteins that can undergo S-nitrosylation, 2 primary nitric oxide-producing proteins also are affected: iNOS (inducible nitric oxide synthase) and eNOS (endogenous nitric oxide synthase). iNOS is primarily utilized by immune cells as a killing weapon, whereas eNOS is the endothelial vasodilator. (28). In conditions where nitric oxide is overproduced (such as in chronic immune stimulation from iNOS), sustained S-nitrosylation occurs, and this leads to conformational changes in protein structure and functions of NOS’s, suppressing their functions. Reportedly, in insulin resistance, S-nitrosylation of the insulin receptor inhibits insulin effect and signaling. Thioredoxin (Trx), a regulatory seleno-protein, is responsible for the effect of de-nitrosylation. On the other hand, when nitric oxide is in short supply (such as in genetic knockout of eNOS), S-nitrosylation is reduced in tissues (28). S-nitrosylation has been shown to exhibit both anti-proliferative and anti-bacterial properties (29). S-nitrosylation of glutathione (nitrosoglutathione) is protective against ischemia, traumatic brain injury, and autoimmune encephalomyelitis (30, 31).
Serum albumin serves as the transport vessel for S-nitrosylated proteins to the cells and tissues. Albumin’s Cys34 is reversibly oxidized into sulfinic acids, as well as S-nitrosyl species. This effect makes albumin a reservoir of nitric oxide. S-nitrosylated albumin is a potent anti-cancer weapon, and numerous research studies have been underway to elucidate these actions. Therapeutically, investigations have been underway to discover which ligands increase S-nitrosylation when bound to albumin. Fatty acids, such as Oleic acid are significant in these regards (23).
Oleic acid (omega 9 fatty acid most notably found in olive oil) has been the subject of nitrosylation research. Nitrosylated fatty acids are formed from the reaction between nitrogen species (namely nitric oxide) and unsaturated fatty acids. Several potentially inflammatory fatty acids (such as arachidonic and linoleic) are converted to an anti-inflammatory profile through nitrosylation. Nitro fatty acids are effectively called Nitroalkenes. Nitro oleic acid is mainly found bound to cysteine or thiol groups in blood, not in the free form in tissues. The effects induced by nitro fatty acids are pleitropic, antioxidative and anti-inflammatory. Nitro oleic acid inhibits xanthine oxidase (which generates uric acid), as well as 5-lipooxygenase (which generates leukotrienes). In addition, nitro oleic acid binds to the angiotensin I receptor (which regulates blood pressure), and modulates KEAP1, which directly controls NRF2 and ARE (antioxidant response element) signaling (24).
Nitro oleic acid has great therapeutic potential for a wide range of conditions including: cancer, fibrosis, cardiovascular disease, and classical inflammatory diseases (25). Because nitro oleic acid (and other nitro fatty acids) are transported by albumin, the qualitative state of albumin likely influences the binding potential and effects of these important nitro lipids.
Summary of Clinical Implications for Low Serum Albumin
Healthy people typically exhibit a serum albumin level greater than 4.0 mg/dl, or 40 g/l, and less than 5.0 mg/dl, or 50 g/l. Serum albumin levels maintained in this range is inversely related to the mortality rate, including mortality from cardiovascular diseases and cancer (16).
Magnitude & Degree of Hypoalbuminemia
When albumin levels decrease, the magnitude of that decrease can range clinically from mild or acute inflammation, to severe disturbances in osmotic pressure, increased clot formation, activation of fibrinogen, and hemolysis of erythrocytes.
- Acute inflammation – During the acute phase, it is common that the albumin level drops below 4.0mg/dl or 40 g/l
- Liver distress – Since more than 90% of albumin is produced by hepatocytes, a decrease in albumin may also be associated with liver distress. Hepatic enzymes will typically rise.
- Reduced antioxidant capacity of the serum – Because albumin’s free cysteine, Cys34 accounts for 80% of the sulfhydryl antioxidant capacity of the blood, the acute phase induces changes in albumin levels, which invariably causes an increased oxidation of Cys34.
- Alteration of the osmotic pressure – Albumin regulates osmotic pressure, and severe hypoalbuminemia may cause edema and tissue fluid disturbances.
- Increased blood clot formation – As the albumin level drops precipitously, this increases the FFA/albumin ratio. When this molar ratio exceeds 1.2, Factor XII is activated, and fibrinogen levels increase to the levels seen in thrombotic stroke.
- Red blood cell hemolysis – It has been confirmed through in vitro experiments that under condition of severe hypoalbuminemia, when the FFA/albumin ratio exceeds 8, hemolysis occurs (16). Clinically, the association between severe hypoalbuminemia and a low RBC is well established.
An increase in the FFA/albumin ratio is associated with:
- Activation of Factor 12, and increased Fibrinogen
- Intravascular inflammation
- Stroke & Ischemia
- Formation of a type of albumin known as ‘Ischemia Modified Albumin’, characterized by decreased zinc and cobalt binding
- Because albumin is also a major transport protein, hypoalbuminemia and an elevated FFA/ratio is known to reduce the binding affinities for a number of compounds, including drugs.
FFA’s, Albumin & Inflammation: Brief Summary of 4 States
While there are several possible scenarios by which non-esterified, free fatty acids can become toxic and induce pathological conditions, I believe these can be discussed as caused by the following 4 etiological factors:
- Mitochondrial Dysfunction or Mitochondrial Conservation – Mitochondrial oxidative metabolism is the primary sink for free fatty acids. It is now understood that mitochondria are centrally involved in coordinating cellular danger signaling, through altering mitochondrial and cellular energy metabolism (Naviaux, 2016, 2019). During danger signaling, mitochondria conserve oxidative phosphorylation in favor of glycolytic pathways. In such cases (which are referred to as CDR1, CDR2, CDR3), it would be anticipated FFA levels to be higher because mitochondrial energy metabolism has been conserved. Many of the diseases associated with CDR1, CDR2 and CDR3 show high levels of FFA’s in adjacent research studies.
- Acute Inflammatory Process – Cellular damage or necrosis causes membrane injury, and the release of membrane fatty acids. Fatty acid ester bonds are broken by esterases and there are more FFA’s that react to form peroxidative products such as MDA. Remarkably, albumin possesses esterase activity, but these functions during the acute phase are still poorly characterized.
- Catecholamine & Cortisol Release – The stress response induces the release of FFA’s. This is observed during exercise, as well as when cortisol is infused intravenously into subjects, and during periods of prolonged stress. Cortisol increases FFA’s, which is partly due to cortisol’s effect on increasing gluconeogenesis. Cortisol also acts to increase lipolysis, that is the hydrolysis of triglycerides into constituent free fatty acids and glycerol (45).
- Iatrogenic or Drug-Induced – A wide range of drugs can increase FFA/NEFA’s, or can lower albumin levels, which affect the FFA/albumin ratio.
Albumin & Fatty Acid Therapeutics
NAC (n-acetyl cysteine) Has been found to break the cysteinylated disulfide bond of albumin’s Cys34, and restore or improve the sulfhydryl antioxidative capacity of plasma. These effects indicate that NAC does not only act as a precursor to intracellular glutathione, but also acts extracellularly, by regulating the redox state of Cys34 (63).
Branch chain amino acids (BCAA’s: leucine, isoleucine, valine) have been shown to improve the reduced/oxidized albumin ratio. In liver cirrhosis, increased albumin oxidation causes a decreased binding of tryptophan and bilirubin, as well as warfarin and diazepam. BCAA supplementation significantly restored the albumin oxidized/reduced ratio, and significantly improved the binding of these endogenous and exogenous compounds (12, 22). Additionally, BCAA supplementation prevents sarcopenia, reduces fat accumulation in skeletal muscle of hypoalbuminemic cirrhosis patients (46). One mechanism of how BCAA benefits hypoalbuminemia is through the increase in mTOR signaling via leucine. Importantly, animal studies have identified that the BCAA isoleucine increases the metabolic oxidation of free fatty acids, via up-regulation of the CD36 receptor and activation of PPARalpha (47).
Cystine is a reversibly oxidized form of cysteine. A study found that cystine supplementation is important to maintain mercaptoalbumin levels in low protein diet-fed rats (13). A follow-up to that study showed that cystine is more effective at restoring mercaptoalbumin in low-protein diet fed rats, than methionine (14).
Non-esterified, free fatty acids (FFA’s) directly bind to magnesium (Mg2+), thereby causing an ionized magnesium deficiency. Additionally, there is an inverse relationship between triglycerides and magnesium. The implications are that in metabolic syndrome, diabetes mellitus, and other conditions involving elevated triglycerides and FFA’s, ionized magnesium is likely deficient (21).
Alpha Lipoic acid given at 600mg/day for 1 year reduces FFA plasma levels on average 8-10% in metabolic syndrome subjects (61).
Acipimox, a drug that is structurally similar to nicotinic acid (Vitamin B-3), which is a precursor of NAD+. Acipimox significantly reduces NEFA levels by 45% in 7 days (46). However additional reports indicate that this drug results in a “rebound effect” of NEFA’s. This rebound effect does not occur with Nicotinamide Riboside (NR), and NR effect suppresses plasma NEFA levels in subjects given an insulin/glucose challenge (47).
Nicotinic Acid, an analogue of Vitamin B-3 reduces FFA’s by way of inhibiting lipolysis in adipose tissue (62).
L-Carnitine & Propionyl L-Carnitine – Both of these forms of the amino acid carnitine have studies demonstrating their ability to improve fatty acid oxidation. Carnitine mediates the Acyl Carnitine transport of free fatty acids across the mitochondrial membrane. This is particularly true of longer chain fatty acids. Intravenous administration of L-carnitine in dialysis patients resulted in significantly lower levels of arachidonic acid, as well as lower levels of saturated fatty acids, compared to untreated dialysis patients (45). In vitro research demonstrates L-Carnitine inhibits arachidonic acid incorporation into blood platelets, inhibits both phospholipase A2 activation, and AA-induced thromboxane A2 (46). Further research indicates that L-carnitine significantly lowers both CRP and Fibrinogen levels among dialysis patients (47). While the mechanism of action was not elucidated in the referenced study, remember research from Pilgeram demonstrates increases in the FFA/Albumin molar ratio, to levels of 1.2 and higher, leads to levels of fibrinogen that are concurrent in patients with thrombotic stroke. Given that L-carnitine mediates transport of free fatty acids, it would appear evident that carnitine’s fibrinogen-lowering effect is due to its ability to convert free fatty acids into metabolic fuel via mitochondria.
Taurine is a ß-amino acid, derived from sulfonic acid. Taurine is considered a non-essential amino acid, that can be biosynthesized from cysteine under normal conditions. However, taurine may become conditionally essential during acute conditions. Taurine was shown to prevent FFA-induced malondialdehyde formation, and subsequent insulin resistance (35). Taurine is a notable osmolyte, it can mediate osmotic pressure, and thus may be suitable for hypoalbuminemic conditions that feature edema. To date, however, no human trials have been conducted using taurine for edema. 4 decades of animal studies have revealed Taurine benefits kidney disease by several mechanisms, including improving proteinuria. Proteinuria is characterized by a loss of proteins through the kidneys, most notably, albumin. Proteinuria can cause or exacerbate hypoalbuminemia, and thus be a factor in edema. Although numerous animal study models have clearly shown taurine can reduce proteinuria, no human trials have been conducted to date.
Melatonin – Studies in rats demonstrate that melatonin administration improves free fatty acid oxidation in both brown adipose tissue, as well as in muscle cell mitochondria (55). One mechanism of melatonin’s action on FFA’s is through increasing oxidative phosphorylation in mitochondria. Melatonin has also shown the ability to reduce proteinuria in animal studies, but like Taurine, no such studies have been performed in humans (56, 57). Meta-analysis of RCT’s in humans demonstrates melatonin significantly lowers triglyceride levels (58).
Carnosine – Is a beta amino acid, that has been the subject of research for scavenging 4-hydroxyneonal lipids and other unsaturated aldehydes derived from Linoleic and arachidonic acid.
Chyrisin & Luteolin – Are common dietary polyphenols (found in broccoli, honey, celery, rosemary, peppers) that can reduce glycated albumin (64)
Garlic – Sulfur groups can reduce glycated albumin (65)