Impact of lipid emulsions in parenteral nutrition on platelets: a literature review

Lipid emulsions are essential components of parenteral nutrition solutions that provide energy and essential fatty acids. The complexity of the formulations of lipid emulsions may lead to adverse outcomes such as platelet reactivity and changes in platelet aggregation and related coagulation. Platelets are responsible for haemostasis; they activate and demonstrate morphological changes upon extracellular factors to maintain blood fluidity and vascular integrity. Although parenteral nutrition lipid emulsions are generally found safe with regard to modulation of platelet activity, studies are still accumulating. Thus, this review aims to investigate platelet-related changes by parenteral nutrition lipid emulsions in human studies. Studies have pointed out patients at risk of bleeding and increased platelet aggregation responses due to the administration of lipid emulsions. Lipid emulsions may further benefit patients at high risk of thrombosis due to anti-thrombotic effects and should be cautiously used in patients with thrombocytopenia. The reported platelet-related changes might be associated with the fatty acid change in the plasma membranes of platelets following changes in platelet synthesis and plasma levels of eicosanoids. In conclusion, studies investigating platelets and parenteral nutrition should be supported to minimize the adverse effects and to benefit from the potential protective effects of parenteral nutrition lipid emulsions.

Commercially available lipid emulsions contain primarily long-chain triglycerides (LCT) along with mixes, including medium-chain triglycerides (MCT), which are referred to as MCT/LCT (5) .Soybean oil-based emulsions contain 44-62% of linoleic acid (LA) (Table 1) (2,11) and may have pro-inflammatory effects via eicosanoids synthesized from n-6 PUFA arachidonic acid (AA) (11) .Olive oil is reported to be more advantageous than SO because of its higher MUFA and lower n-6 PUFA content (Table 1) (11) .Similarly, FO lipid emulsions are used for their proposed anti-inflammatory and immunomodulatory effects (2,3,6,7,12) .These lipid emulsions may be used in combination with other lipid sources (SO, MCT, OO, and FO-containing lipid emulsions) to lower the amount of SO.Furthermore, they contain higher n-3 PUFA, α-tocopherol, and low amounts of plant phytosterols than SO-based lipid emulsions (Table 1) (11) .
Parenteral nutrition may influence haemorheological parameters and platelet function (13) , and it is now well established that these complications may result from the lipid source of PN solutions.Lipid emulsions will likely affect platelet function due -Not detected or not reported (in either situation, there is little or none present).
a Data provided is from the manufacturer data sheets or (7,12) .b MCT lipid sources may be coconut, palm kernel or other tropical nut oils.c Data taken from (96) .
to the many biological functions (inflammatory and immune responses, coagulation, cell signalling) (2,(14)(15)(16) .Platelets, the most abundant cells in the blood, are the vital cells responsible for haemostasis (17,18) .The functional changes of platelets (adhesion, activation, spreading, secretion, aggregation, pro-coagulant activity, microparticle formation, clot retraction) followed by tissue damage or other pathophysiological conditions (atherosclerotic lesion, inflammation) exist to maintain haemostasis (19,20) .Impaired platelet function and abnormal platelet number may result in bleeding or thrombus formation (19,20) .A group of agonists activates platelets in physiological haemostasis and pathological bleeding or thrombosis, and a cascade of reactions occurs.It is important to note that increased responsiveness of platelets to agonists in conditions like endothelial damage or pro-inflammatory state over-activates platelets in favour of a thrombotic state (21) (Fig. 1).
Platelet function tests to monitor the risk of bleeding or predict thrombosis are essential in the hospital (19,20) .Traditional tests such as bleeding time and aggregometry are widely used (19,20) .Partial thromboplastin time (PTT) and prothrombin time (PT) are basic clotting tests used to exclude coagulation defects (19,20,22) .As the gold standard of platelet function (20) aggregometry tests that give responses to a panel of agonists (19,20) are still used; however, these tests are proposed not to define responses to weak agonists on a clinical basis (19,20) .Platelet function tests such as flow cytometry can explore the assessment of signalling processes and activation properties (19,20,23) .Flow cytometry and cell morphology under the microscope can measure platelet activation, such as integrin activation, secretion of granule contents, and phosphatidylserine (PS) exposure (23) .Platelet glycoproteins, activation markers, and platelet function are investigated (19,20) .Moreover, studies also investigate the phospholipid composition of platelet plasma membranes that is tightly regulated for haemostasis (24) and can also signify platelet activation; for example, PS is exposed highly on the surface before coagulation (24) (Fig. 1).
Thrombocytopenia, platelet dysfunction, hypercoagulation, and bleeding were reported in patients when lipid emulsions were introduced in PN solutions.Thromboembolic events, including thrombosis, thromboembolism (25)(26)(27)(28)(29) , major bleeding (30) , vena cava syndrome, thrombocytopenia, and heparin complications (31) , are seen in many patients due to PN.During hospital stays, patients are prone to thromboembolic events due to reduced physical activity (32) .PN might affect haemostasis and could potentially increase the risk of bleeding or postoperative thrombosis.Also, PN is used in patients (critically ill, patients on chemotherapy, bone marrow transplantation) who are likely to develop thrombocytopenia (30) .Intravenous (IV) fat emulsion infusions have been associated with bleeding complications, thrombocytopenia, effects on cholesterol, triglyceride, glucose, insulin and blood pressure (33) .
On the other hand, lipid emulsion infusion may be used for the benefit of patients to prevent preoperative infarction, postoperative occlusion of coronary arteries (34) , and severe hypercoagulability cases (35) .Potentially, some lipid emulsions may have anti-atherogenic properties (36,37) , and these effects should be defined to be used in patients with accelerated atherosclerosis as the inhibition of platelet aggregation could lead to arrest or regression of atherosclerotic process (36) .
The influence of PN lipid emulsions on platelet function and coagulation is a controversial issue (32) .Although ESPEN defines lipid emulsions as generally safe concerning platelet activity (38,39) , there needs to be more knowledge on the effects of PN solution contents on normal platelet functions, as well as in bleeding and thrombotic disease processes.Platelet activation plays a central role in the pathogenesis of thromboembolic incidents (32) , and platelet dysfunction is a significant cause of excessive bleeding (34) .Therefore, the PN treatment should not lead to platelet aggregation, which might lead to atherosclerotic lesions and acute thrombosis (32) , or platelet dysfunction and bleeding (34) .In this review, we gathered and summarized studies investigating parenteral nutrition lipid emulsions and their effects on platelets in order to provide clinically-relevant updates on parenteral nutrition and haemostasis.

Methods
This review gathered human studies investigating parenteral nutrition lipid emulsions and their effects on platelets.PubMed, Science Direct, Google Scholar, and Scopus databases were used with the keywords 'lipid emulsion/parenteral nutrition and platelets'.Due to limited research, all studies (1971-2022) conducted on human subjects (n = 51) were included, and studies on experimental animals were excluded.

Soybean oil-based lipid emulsion
Impact on platelet function.The most studied lipid emulsion in the literature in the context of platelets is soybean oil-based lipid emulsion (100% LCT) (Fig. 2).To start with, no change was reported in platelet aggregation in infants (40) and adult patients (30,41,42) with SO (100% LCT) lipid emulsion administration.Interestingly, it is known that SO lipid emulsions contain the precursor (linoleic acid) of arachidonic acid, which, even in low concentrations, might activate and induce platelets to undergo a release reaction and aggregate (30) .Despite this, there was no clinical evidence of bleeding or thrombotic tendency in these patients receiving SO lipid emulsion (41) .Further, the lipid emulsions may also lead to increased plasma levels of nonesterified fatty acids (NEFA), associated with platelet aggregation (40,41) .In contrast, decreased platelet aggregation was reported in familial hypercholesterolaemia patients receiving SO (100% LCT) infusion (36) .Since enhanced platelet aggregation is seen in patients with accelerated atherosclerosis thus, inhibition of platelet aggregation points to potential anti-journals.cambridge.org/jnsatherosclerotic effects of SO (100% LCT) and may be due to specific diseases and patients (36,37) (Table 2).
Studies investigating healthy subjects have shown different results.Decreased platelet aggregation responses to agonists were also shown in healthy male donors (37,43) due to SO (100% LCT) lipid infusion.These studies also indicated antiatherogenic properties of SO (100% LCT) lipid emulsion due to reduced free cholesterol in mononuclear cells (43) and platelets (37) , which might decrease platelet aggregation.The liposomes and triglyceride-phospholipid particles in SO (100% LCT) were held responsible for the change in platelet cholesterol content and in vitro platelet aggregation (37) as they can lead to the depletion of cholesterol in cells and blood vessel endothelium (43) .Additionally, reduced platelet adhesion by SO (100% LCT) lipid emulsion infusion to healthy donors (35) was shown; however platelet adhesion increased ex vivo.This study concludes that a humoral factor can reduce platelet adhesion.
The slight decrease in platelet adhesion concluded that this lipid emulsion should not be infused in cases with severe hypercoagulability.In general, this lipid emulsion is safe to use without a risk of hypercoagulability (35) (Table 2).
Other studies on healthy volunteers receiving SO (100% LCT) lipid infusion showed no change in platelet aggregation (33,44) .However, some subjects tended towards an increase in threshold values of platelet aggregation of some agonists, and there was a release of platelet-specific peptides such as βTG (beta-thromboglobulin), PF4 (platelet-activating factor 4), and 5-HT (5-hydroxytryptamine).The release of platelet products in the plasma and no sign of platelet activation under the electron microscope indicate different platelet subpopulations.Although normal platelet morphology was seen under the electron microscope, the lipid infusion showed internalized small lipid particles on the surface of platelets.These findings suggests that platelets are in close contact with lipid emulsion particles, which Fig. 1. a. Signalling mechanisms during platelet activation.A resting platelet owns a discoid shape with α and δ granules, and an activated platelet becomes round and forms pseudopods.Strongly activated platelets have high cytosolic Ca 2þ .Collagen is exposed from the damaged endothelium and binds to GPVI and GPIb-IX-V with another ligand vWF.Fibrinogen activates the platelet through the integrin α IIb β 3 (GPIIb/IIIa).Integrin activation leads to platelet aggregation.Agonists ADP and thrombin take roles through receptors P 2 Y 1 , P 2 Y 12 , and PAR.Activated platelets express PS on their surface.An adhesive molecule, P-selectin, is expressed on an activated platelet.b.Scheme of the coagulation cascade.Steps into the coagulation cascade: fibrinogen produces fibrin through thrombin.Fibrin is responsible for forming a tight thrombus.c.Scheme of the produced lipid mediators via the platelet plasma membrane.Lipid mediators form through the release of platelet membrane phospholipid fatty acids, which may affect platelet activation/aggregation. 12-HETE may increase or decrease platelet activation.TXA 2 and TXB 2 are pro-coagulants and increase platelet activation.TXA 3 reduced platelet activation, whereas endothelial cell-derived PGI 2 inhibits platelet activation.DHA is known to inhibit AA formation in human platelets.AA, arachidonic acid; ADP, adenosine diphosphate; COX, cyclooxygenase; DHA, docosahexaenoic acid; EPA, eicosapentaenoic acid; LOX: lipoxygenase; PG, prostaglandin; PS, phosphatidylserine; TX, thromboxane; vWF, von Willebrand factor; 12-HETE, 12-hydroxyeicosatetraenoic acid.journals.cambridge.org/jns may induce changes in platelet surface properties, leading to electrochemical charge and rapid clearance of platelets from the circulation (44) .Additionally, mitochondrial inhibitors used in one study have led to limited ATP production eventually, leading to reduced platelet aggregation because platelets do not have enough energy to undergo shape change and granule release.However, these inhibitors were less effective postinfusion of SO (100% LCT), which may indicate promotion of aggregation at some point.Thus, SO (100% LCT) lipid emulsion might increase platelet aggregation when mitochondria function is inhibited and can affect the transcript profile of platelets with up-or down-regulation of genes associated with cell motility, adhesion, cell cycle progression, and metabolism.Continuous exposure would significantly solidify these changes and negatively impact haemostasis by increasing the risk for thrombosis (33) (Table 2).
Accordingly, studies investigated the effects of PN lipid emulsions on platelet plasma membrane phospholipids.For instance, SO (100% LCT) lipid emulsion increased platelet LA and AA levels (45,46) and conversely decreased oleic acid, caprylic acid, and docosahexaenoic acid (DHA) levels (45) .However, lauric acid and myristic acids were not detected in platelet phospholipids (46) .These fatty acid changes in platelet membranes may be due to lipid emulsions' exogenous fatty acid source (41) .Additionally, the platelet fatty acid profile may change following differences in the plasma fatty acids.After SO (100% LCT) lipid emulsion administration, increased plasma of AA (41) , LA, palmitoleic, and palmitic acid levels, and decreased oleic acid levels were reported (46) (Table 2).
Impact on platelet count and coagulation.Platelet count is a common blood test used in many studies investigating PN (Fig. 2a).Decreased platelet count, defined as thrombocytopenia, may increase risk of bleeding (20) .Thrombocytopenia was reported in patients (including children) receiving SO (100% LCT) along with morphologically abnormal large platelets (50) , decreased platelet survival (51) , and cholestatic liver disease (52) .Decreased platelet counts over time, and a higher risk of bleeding were reported to be associated with children with intestinal failure-associated liver disease (IFALD) that received SO (100% LCT) (53) .
In other studies, SO (100% LCT) administration did not cause thrombocytopenia (33,35,(54)(55)(56) in adult patients (55) , healthy donors (35) , and term and preterm newborns (56) .It is important to note that this may be due to phytosterols in lipid emulsions, which correlate with high plasma phytosterol levels.Also, reducing lipid infusion improved platelet count and liver function tests in some patients (52) .Further, high serum lipid levels may lead to fat overload syndrome with haematologic symptoms such as prolonged bleeding time and decreased platelet survival (40) .Interestingly, SO (100% LCT) administration may stimulate thrombocytopenia with more extended study duration periods (56) (Table 3).
Coagulation tests are frequently used clinical tests to assess blood clotting function in patients (57) .The steps in the coagulation cascade are measured by prothrombin time (PT), partial thromboplastin time (PTT), and thrombin time (TT).They can be used to provide information about blood clotting and thrombosis; however, they cannot predict the occurrence of bleeding (57) .A study conducted with paediatric patients reported that administration of SO (100% LCT) PN significantly increased PT and PTT after 1 year follow-up.Nevertheless, coagulation factor V and fibrinogen remained in their usual range, which was attributed to vitamin K journals.cambridge.org/jnsdeficiency (58) .A case study reported prolonged bleeding time (PT, PTT) and haematemesis in a patient that received SO (100% LCT) PN, which was due to the developed fat overload syndrome of the high lipid dose; however, the exact aetiology of platelet dysfunction is not known (59) .
Platelet engraftment is defined as 'the independence from platelet infusion for at least seven days, during which the platelet count is regularly measured' (more than 20 × 10 9 /L) (60) and is known to be crucial for the success of transplantation (61) .Platelet engraftment timing is a valid predictor of possible complications in transplantation patients (61) , and PN is used to quicken engraftment in these patients (62,63) .Studies have shown that individualized PN compared to conventional PN (63) and SO (100% LCT) total PN compared to partial PN in patients with delayed platelet engraftment (62) .These results suggest that SO (100% LCT) may protect against thrombocytopenia in transplant patients; however, this may be related to thrombopoiesis.
To conclude, many studies report that SO (100% LCT) lipid emulsion administration is safe (13,33,35,40,41,54,64) .Studies demonstrate the potential for increased platelet aggregation (33,44) , and this effect may be attributed to the modified fatty acid composition of Healthy male volunteers (n = 8) = ex vivo platelet aggregation = platelet morphology Internalization of small lipid particles in circulating platelets. ( Healthy male donors (n = 10) infusion over 4 h after overnight fasting ↓ post-infusion in vitro platelet aggregation in response to ADP, the peak rate by 31%, and the 1 min.rate by 21%.The rates increased again, reaching the pre-infusion levels 20 hours later. ( Healthy donors (n = 20) infusion 5 h after overnight fasting ↑ (slightly) post-infusion platelet aggregation in the presence of TRAP and collagen; however, NS ≤ TRAP and collagen-induced platelet aggregation pre-infusion but to a lesser degree post-infusion (mitochondrial inhibitors) Healthy male donors (n = 5) 6 h infusion after overnight fasting ≤ in vitro platelet aggregation induced by collagen or ADP ≤ platelet-free cholesterol content during the infusion period 18 h after the end of the infusion, platelet aggregation and cholesterol content returned to pre-infusion levels.7 days ↑ PF4 (platelet-activating factor 4) and βTG (beta-thromboglobulin) continued to be elevated at 4-7 days of PN (42)   Healthy male volunteers (n = 8) ↑ plasma βTG (beta-thromboglobulin), PF4 (platelet factor 4), serotonin (5-HT).
(  Continued journals.cambridge.org/jns the platelet plasma membrane (41,45,46) .On the other hand, in other studies, it has been reported that SO (100% LCT) may reduce platelet aggregation (36,37,43) , which is associated with reduced levels of free cholesterol in platelets (37) .The phytosterols in SO (100% LCT) were found to be potentially responsible for thrombocytopenia, leading to bleeding.However, it is essential to note that the observed bleeding was primarily associated with other factors, including PN-related liver disease (52,53) , developed fat overload syndrome reported in a case study (59) .Moreover, the SO (100% LCT) lipid emulsion should be applied carefully in paediatric patients at risk of bleeding (53) .In conclusion, the variability of in vitro methods used to test platelet activation (30) , as well as differences in the amounts and durations of the lipid emulsions applied (33,40) , makes it hard to compare all studies.Accordingly, given that exact aetiology of platelet dysfunction remains unknown, sensitive platelet function tests should be used to investigate SO (100% LCT) lipid emulsions.

Soybean oil/medium-chain triglycerides-based lipid emulsion
Impact on platelet function.Soybean oil/MCT-based lipid emulsions are frequently studied to compare their effects with SO (100% LCT) lipid emulsions (Fig. 2).A small number of studies have demonstrated that platelet aggregation did not change in patients receiving MCT/LCT (50%/50%) emulsions compared to LCT (SO (100% LCT)) (30,42) .Because the lipid emulsion may lead to changes in the cell membrane fatty acid composition of platelets due to the different fatty acid composition, MCT/LCT (50%/50%) is theoretically proposed to affect platelets differently compared to LCT (SO (100% LCT)) (30,42) .However, the length of the study might be an essential factor for the modification of platelet membranes, and short study periods might be associated with similar aggregation responses (42) .Additionally, the platelet function analyser system (PFA-100) is a new standard to detect platelet dysfunction.It reports a closure time of an easily measured and formed platelet plug under high shear flow conditions (65) .A study in healthy male volunteers showed no difference in platelet function via the PFA-100 system due to the lipid emulsion MCT/LCT (50%/50%), indicating it is safe to use (65) (Table 4).Flow cytometry is used as a sensitive tool for platelet function (66) ; however, studies regarding the effects of parenteral lipid emulsions on platelet aggregation and expression of GPIb, GPIIb/IIIa, and P-selectin are limited.The upregulation of platelet membrane glycoproteins may be associated with coagulopathy induced by PN (64) .In vivo studies have shown that MCT/LCT (50%/50%) administration did not show any difference in the expression of platelet receptors GPIIb/
Platelet-related mediators were analysed in patients treated with lipid emulsions MCT/LCT (50%/50%).A study reported that the release of prostacyclin (measured by stable metabolite 6-keto-PGF 1α ) decreased in patients receiving MCT/LCT (50%/50%), although the difference was not statistically significant (42) .Additionally, the administration of MCT/LCT (50%/50%) to patients resulted in a continuous elevation of PF4 and βTG in activated platelets at 4-7 days of PN treatment; however, no significant difference was observed when compared to the lipid emulsion SO (100% LCT) (42) .These activation markers may be affected by the oxygen radicals in critical patients and thus showed no alterations in platelet function (42) (Table 4).
Conversely, a study on children receiving long-term PN with either MCT/LCT (50%/50%) or SO (100% LCT) lipid emulsions reported a reduction in platelet count.Interestingly, normalization of platelet count occurred in some cases within the first month after suspension of lipid infusions.As a result, this study could not report a protective effect of MCT/LCT (50%/ 50%) emulsions against hepatic injury and cholestasis, which may develop with the long-term infusion of lipid emulsions even within lipid infusion rate limits (69) .While lipid emulsion-induced thrombocytopenia may be an adverse effect in paediatric patients, a case study involving an adult patient showed thrombocytopenia following lipid emulsion MCT/LCT (50%/50%) administration, which may be because of the pre-existing malnutrition of the patient (70) .On the other hand, both healthy donors and patients who received the lipid emulsion MCT/LCT (50%/50%) showed no change in the coagulation tests, including PT, PTT, fibrinogen, TT (64) .Furthermore, the comparison of MCT/LCT (50%/50%) and SO (100% LCT) lipid emulsions did not differ in coagulation parameters, including PT, PTT, and fibrinogen levels (71) (Table 3).
Similarly, the lipid emulsion MCT/LCT (50%/50%) did not differ in platelet engraftment in patients with various haematologic malignancies who underwent a haematopoietic peripheral blood stem cell transplantation (71) .Thus, MCT/LCT (50%/50%) may protect against thrombocytopenia.However, it is also proposed that engraftment duration is shorter in well-nourished patients; therefore, PN instead of the lipid emulsion type may be therapeutic in the context of platelet engraftment (63) (Table 3).
In conclusion, MCT/LCT (50%/50%) lipid emulsion showed no risk of bleeding in patients (30,64,71) .Low platelet count was reported in children receiving long-term PN (69) .Additionally, increased platelet GPIIb/IIIa (32) and P-selectin (32,64) expression and decreased GPIb expression (32) were shown.However, platelet aggregation (30,42) was not affected by the lipid emulsion MCT/LCT (50%/50%).The increased platelet activation may be due to ex vivo results (32) or patient status (64) , as platelet reactivity did not change in other studies (65,67) .The change in platelet membrane fatty acids as in reduced AA (45,46) ; however, increased SFAs percentage (46) and increased LA (68) may be a mechanism leading to platelet activation, however, the following production of platelet lipid mediators did not show any change in studies.Moreover, the stable proportion of n-3 and n-6 fatty acids in platelets (72) may represent the underlying mechanism for the protective effects of MCT/LCT (50%/50%) during platelet activation.To conclude, although MCT/LCT (50%/50%) lipid emulsion was reported safe to use towards the risk of thrombosis and bleeding, its protective effects compared to SO (100% LCT) lipid emulsion are not clearly shown in studies.

Fish oil-based lipid emulsion
Impact on platelet function.Pure fish oil-based lipid emulsions were also investigated in the context of platelets (Fig. 2).It has been reported that PN consisting of FO (100%) lipid emulsion decreased the aggregation response of platelets in surgical patients (34) .This result was particularly pronounced with collagen aggregation, and there was no risk of bleeding in these patients.Therefore, FO (100%) lipid emulsions may be used to inhibit platelet aggregation, providing a cardioprotective effect in patients undergoing open heart surgery.However, the risk of bleeding should be considered carefully.Moreover, a remarkable reduction in aggregation was reported in healthy subjects following administration of FO (100%) lipid emulsion (73) .Following the 24-hour administration of FO (100%) infusion to healthy subjects, collagen-induced aggregation of platelets increased even higher than the starting value, whereas ADP-induced aggregation (20% reduction) remained the same (73) .Thus, FO (100%) infusion may have potential use in patients with high thrombosis risk (73) .In contrast, IV or oral administration of FO (100%) lipid emulsion to healthy subjects showed no change in platelet function as in platelet adhesion and aggregation tested via a PFA-100 system, which may be due to the short-term study period (15 days) (74) (Table 5).
The potential of lipid mediators has yet to be fully understood; moreover, their role in platelets in health and disease states encourage new lipidomic methodologies to scan and image lipid mediators (82) .In a case study, the administration of IV FO (100%) resulted in an increase in the TXB 3 /TXB 2 ratio in stimulated platelets during infusion (75) .Various studies involving patients or healthy subjects have demonstrated decreased blood TX and TXB 2 levels and increased blood and platelet-generated TXA 3 levels (49,73) .Moreover, an increase in platelet TXB 3 generation (80) and elevated TXA 3 /TXA 2 ratio have been observed (49) , while prostaglandin levels remained stable (73) .Also, FO (100%) administration increased plateletactivating factors synthesis over time (49) .Together, these findings may indicate the influence of the alternative lipid precursor on central lipoxygenase and cyclooxygenase pathways.These findings suggest that some EPA-containing journals.cambridge.org/jnsmembrane lipid pool(s), providing precursor fatty acids to the metabolic pathways of eicosanoid formation, may be rapidly regulated in exchange with plasma EPA (80) (Table 5).
Impact on platelet count and coagulation.Fish oil-based lipid emulsions have been investigated concerning the risk of bleeding (Fig. 2a) and have been reported safe to use, with no evidence suggesting an increased risk of coagulopathy or bleeding abnormalities (8) .However, it is essential to recall that the studies are limited.Patients receiving PN formulations with FO (100%) þ SO (100% LCT) or SO (100% LCT) were investigated, and no differences were observed in terms of platelet counts or platelet function (measured by RTG-p-time) between groups (83) .Alternatively, bleeding was reported in a patient with intestinal failure after 26 days of sole FO (100%) lipid emulsion administration, following a regimen of FO (100%) þ SO (100% LCT) lipid emulsion.Besides, there was no evidence of clot formation, PTT was normal, and haemorrhage resolved on day 3 with clot formation at bleeding sites (84) .It has been reported that preoperative IV FO (100%) did not induce a change in PTT among surgical patients (34) .Given this data, it was suggested that the potential for bleeding complications from sole FO-based therapy in high-risk infants with liver disease should be reconsidered (84) (Table 3).
In contrast, a study showed that FO (100%) lipid emulsion had a lower risk of bleeding in children with IFALD compared to SO (100% LCT) lipid emulsion, which was associated with bleeding.In theory, FO-based lipid emulsions have an increased risk of bleeding due to their inhibitory effects in platelet adhesion and platelet-stimulated thrombin generation.However, this might be a weak effect due to this study.Nevertheless, due to the lack of data, there should be caution Cardiac surgery patients (n = 28) 3 times as 2 h infusions ↑ platelet EPA and DHA ↑ atrial tissue EPA concentrations (77)   Healthy male subjects (n = 16) 0. Pre-op IV = post-op platelet aggregation by ADP, AA, TRAP ↓ post-op platelet aggregation by collagen = surgical blood loss (34)   Healthy male subjects (n = 13) IV injection >60 min ↓ platelet aggregation induced by collagen and ADP in 60 min, till 6 hours.
journals.cambridge.org/jnswhen using FO-based lipid emulsions, especially in paediatric patients at risk of bleeding (53) In conclusion, the demonstrated anti-inflammatory effects of fish oil endorse the FO-based lipid emulsions as advantageous components in PN (2,3,6,7,12,85) .The proposed reduction in platelet aggregation (73) after FO (100%) administration may result from two possible mechanisms.Firstly, the inhibition of cyclooxygenase by n-3 PUFAs, leading to decreased synthesis of TXA 2 from AA in platelets (34,84) .Secondly, it could be a result from the synthesis of TXA 3 from EPA or a general reduction in total TX synthesis (49,73) .In the end, leading to elevated levels of TXB 3 (80) and TXA 3 (73) , thus elevated ratios of TXB 3 /TXB 2 (75)   and TXA 3 /TXA 2 (49) .In addition, this may be supported by the changes in platelet membrane structure, characterized by an increase in EPA and DHA (75,76,79,81) along with decreased AA in membrane phospholipids.Moreover, an increase in n-3 PUFA/ AA membrane ratios in the platelet membrane was reported (75) .Alternatively, a very low AA source may potentially result in AA inhibition that has been found to block platelet shape change and granule secretion, thus decreasing platelet aggregation (84) .However, there might be a temporary inhibition of platelet aggregation due to FO (100%) lipid emulsion; hence, it may be favourable in high thrombosis risk patients (73) .However, the acute effects of n-3 PUFAs might not be mediated by platelet plasma membrane incorporation since there was no change in platelet function via the PFA-100 system (74) , and other alternative lipid precursor pools are pointed out (80) .Additionally, the reported anti-platelet effects were not shown to cause bleeding risk in many studies (8,53) , except a case report (84) indicating that this lipid emulsion should be carefully used in paediatric patients (53) .Although n-3 fatty acids may likely affect haemostasis (86) , The American Society for Parenteral and Enteral Nutrition states that there is no evidence to support that fish oil-containing lipid emulsions increase the risk of coagulopathy or bleeding abnormalities (8) .
Olive oil/soybean oil-based lipid emulsion Impact on platelet function.The evidence in the literature on the effects of OO/SO (80%/20%) lipid emulsion is limited, with only one ex vivo study related to the topic found (Fig. 2).Flow cytometry, a sensitive tool for platelet function (66) , was used to examine the effects of OO/SO (80%/20%) lipid emulsion on platelet function.Previous research indicated that the stimulation of platelets of healthy donors by OO/SO (80%/20%) incubation did not influence GPIIb/IIIa, P-selectin, and GPIb receptor expression independent of lipid concentration and stimulation of ADP and TRAP-6 (32) .A study suggests that olive oil-based lipid emulsion OO/SO (80%/20%) has superior anti-inflammatory effects when compared to the blend lipid emulsion MCT/OO/ FO (30%/25%/15%) (87) .Therefore, its effects on platelets should be further investigated, including whether it may be used in patients with high thrombosis or bleeding risk (Table 6).

Medium-chain triglycerides/fish oil-based lipid emulsion
Impact on platelet function.Studies investigating the lipid emulsion MCT/FO (50%/10%) are also limited in the literature (Fig. 2).In PN solutions, including MCT/FO (20%/4%) that were added to healthy subjects' plasma in different concentrations of volume (4, 10, 25%), platelet aggregation was decreased at a concentration of 4%, and the pore closure time was prolonged, indicating platelet function inhibition (13) .Compared to the lipid emulsion MCT/LCT (50%/50%) in healthy male volunteers, both emulsions showed no difference in platelet function via the PFA-100 system.Although the overall closure time was lower than basal values by MCT/FO (80%/20%) and MCT/LCT (50%/50%), it is indicated that both lipid emulsions are safe to use in the context of platelet adhesion and aggregation (65) (Table 5).
The platelet function after MCT/FO (80%/20%) lipid emulsion administration was further assessed using flow cytometry.Since MCT is a substrate for lipoprotein lipase hydrolysis, the MCT/FO (80%/20%) lipid emulsion is proposed to serve as a rapid source of released MCT and n-3 fatty acids from emulsion particles, which subsequently incorporate into platelet cell membranes (65,67) .The n-3 fatty acid availability may be associated with decreased platelet aggregation and increased bleeding risk, which raises safety concerns regarding using MCT/ FO (80%/20%) lipid emulsion (65) .A previous report indicated that MCT/FO (80%/20%) administration to healthy subjects resulted in a lower P-selectin expression on day two by collagen (65) .Nevertheless, after a bolus IV injection of MCT/ FO (80%/20%) to healthy subjects, no significant changes in the expression of platelet receptors GPIIb/IIIa (65,67) , P-selectin (65,67) , fibrinogen (65,67) , and GPIb (65,67) were observed in response to agonists ADP, collagen, and TRAP-6 (67) .These bolus IV studies have concluded that MCT/FO (80%/20%) lipid emulsions are safe to use and may show cardioprotective effects.An ex vivo study using the MCT/FO (50%/10%) (0.6 mg/ml) lipid emulsion on healthy subjects increased the expression of GPIIb/IIIa and P-selectin and, by contrast, decreased the expression of GPIb, indicating platelet activation (32) .However, these results indicate that in vivo outcomes may differ (Table 7).
Soybean oil/medium-chain triglycerides/olive oil/fish oil-based lipid emulsion Impact on platelet function.The lipid emulsion MCT/OO/ FO (30%/25%/15%) is discussed in the literature due to its varying lipid sources and different fatty acids (Fig. 2).However, there is a limited number of studies related to its effects on platelets.When compared to SO (100% LCT), the journals.cambridge.org/jnsMCT/OO/FO (30%/25%/15%) lipid emulsion increased total n-3 PUFA, DHA levels, n-3/n-6 PUFA and EPA/ AA ratios, decreased total n-6 PUFA, and did not change AA in plasma phospholipids in patients receiving PN for over five days.This change in plasma fatty acids was also reported as similar to changes in platelet phospholipid composition (90) .These findings may be attributed to its n-6:n-3 PUFA ratio, 2.5:1 (10) (Table 1).The plasma lipid mediator profile after PN, including MCT/OO/FO (30%/25%/15%), showed increased leukotriene B 5 and not significantly decreased leukotriene B 4 with increased plasma leukotriene B 5 /B 4 ratio in the plasma, suggesting favourable anti-inflammatory effects.However, platelet responses to this environment were not investigated (90) .Thus, the proposed anti-inflammatory environment due to MCT/OO/FO (30%/25%/ 15%) lipid emulsion should be investigated in platelets and thrombus formation.
Impact of blend lipid emulsions on platelet count and coagulation.The blend lipid emulsion MCT/OO/FO (30%/ 25%/15%) has been investigated in the literature and is shown that it may have benefits over the first-generation lipid emulsion SO (100% LCT) (91,92) ; however, platelet-related studies are limited (Fig. 2a).According to a case report, thrombocytopenia was observed in a paediatric patient, with short bowel syndrome and IFALD, receiving a very rapid infusion of PN including MCT/OO/FO (30%/25%/15%) lipid emulsion (93) (Table 3).It was reported that the lipid composition is also essential as fish oilbased lipid emulsions may not lead to the fat overload syndrome due to an n-6:n-3 PUFA ratio of approximately 2.5:1 in contrast to soybean oil lipid emulsions, which has a ratio of 7:1 (Table 1).Thus, this case study confirms the infusion rate's importance before the solution's lipid composition (93) .On the other hand, the lipid emulsion MCT/OO/FO (30%/25%/15%) did not increase the risk of thrombocytopenia in long-term patients (94,95)   journals.cambridge.org/jns and did not change PT and PTT (95) ; thus, was reported without increased coagulation risk and bleeding (94,95) (Table 3).Moreover, the lipid emulsion MCT/FO (20%/4%) administered to healthy subjects at different concentrations of plasma did not change PT and PTT (13) (Table 3), and OO/SO (80%/20%) lipid emulsion was not investigated in the literature on platelet count and coagulation (Fig. 2).
Furthermore, the literature lacks data about blend parenteral nutrition lipid emulsions OO/SO (80%/20%) and MCT/OO/ FO (30%/25%/15%) on platelets.The lipid emulsion OO/SO (80%/20%) demonstrated no change in platelet activation assessed by flow cytometry and was reported as a safe formula to use (32) .Moreover, MCT/OO/FO (30%/25%/15%) lipid emulsion was also reported safe to use without increased coagulation risk and bleeding (94,95) ; however, platelet activation and aggregation along with changes in platelet lipids and the potentially synthesized lipid mediators were not investigated.According to the limited literature, both fish oil blend lipid emulsions may be advantageous in patients who have a high risk of bleeding (13,95) , yet this subject should be further investigated.The proposed anti-inflammatory effects of these blend lipid emulsions should be further investigated in platelets to define their protocol in patients with high thrombosis or bleeding risk (Table 6).

Conclusions and future directions
According to guidelines, lipid emulsions that are essential macronutrient components of parenteral nutrition solutions, are generally found safe to use in bleeding and thrombotic disease processes.Potentially, lipid emulsions may be responsible for platelet-related changes by altering the plasma and cell membrane fatty acid composition and further eicosanoid synthesis.This may lead to changes in the platelet plasma membrane cholesterol/phospholipid ratio, which is an important determinant of membrane fluidity.Altered membrane fluidity might change the permeability and behaviour of membrane-bound enzymes and the receptor activity of platelets.The cell membrane structure is reported to be modified by PN with lipid emulsions.
Further, the plasma levels of NEFA may, in turn, activate platelets directly, leading to bleeding or thrombotic tendency.
The lipid emulsions may also contain fatty acids (arachidonic acid), which might activate platelets directly.Additionally, the development of fat accumulation as the fat overload syndrome with high serum lipid levels may result in haematologic symptoms such as prolonged bleeding time and decreased platelet survival.
The reviewed papers on parenteral nutrition lipid emulsions and their effects on platelets pointed out patients at risk of bleeding and platelet aggregation.A limited number of studies have mentioned that some lipid emulsions (SO (100% LCT), FO (100%)) were reported to lead to bleeding in patients, which may be associated with other parenteral nutrition or patient-related factors.However, these lipid emulsions should be used cautiously, especially in paediatric patients with parenteral nutrition-related liver disease.In this context, due to the risk of decreased platelet aggregation response by FO (100%) lipid emulsion, FO blend lipid emulsions may be advantageous.However, there is only a limited number of studies investigating their effects on platelets.The inconsistency of studies is principally due to the methodological differences of the studies (platelet function tests, in vivo/ex vivo study design), patient characteristics (adult/paediatric, age, comorbidities), etc.
Furthermore, the results from patients and healthy subjects exclude the status of critically ill patients and their affected haemostasis due to other pathological factors.However, the investigated studies enhance the assumption that lipid emulsions affect platelets differently.Studies investigating platelets and parenteral nutrition should be supported to minimize the adverse effects and to benefit from the potential protective effects of parenteral nutrition lipid emulsions on platelets.
To conclude, it is now well known that the membranes of platelets that provide substrates for enzymatic conversion, can change in health and disease states and are responsive to the diet.Additionally, dietary intake of lipids and fatty acids is an evolving area of research in many diseases and health.Thus, the in vivo nature of parenteral nutrition therapy benefits future studies to investigate the effects of dietary lipids and fatty acids on diseases, health, and human metabolism.

Fig. 2 .
Fig. 2. Heat map of studies investigating parenteral nutrition lipid emulsion on platelets distributed to a. platelet function tests b. type of research.FO, fish oil; LCT, longchain triglycerides; MCT, medium-chain triglycerides; OO, olive oil; PN, parenteral nutrition; SO, soybean oil.

Table 3 .
Summary of the studies measuring the effect of different lipid emulsions on platelet count and coagulation

Table 6 .
Summary of the studies measuring the effect of olive oil/soybean oil-based lipid emulsions on platelet function