Lipid compounds of human Wharton's jelly and their alterations in preeclampsia

Abstract

Wharton's jelly is a myxomatous substance which surrounds the umbilical cord vessels protecting them against extension, bending, twisting and compression. Very low number of cells in this tissue produce high amounts of extracellular matrix; collagen, hyaluronate and proteoglycans which bind large quantities of peptide growth factors (PGFs). Preeclampsia (the most common pregnancy-associated syndrome) is accompanied by a significant reduction in hyaluronate and a concomitant increase in sulphated glycosaminoglycans/proteoglycans content in Wharton's jelly. Such a phenomenon corresponds to an ‘early ageing’ of this tissue. We have evaluated the lipid composition of Wharton's jelly and its alteration in preeclampsia. Thin layer chromatography and high-performance liquid chromatography were employed. It was found that Wharton's jelly contains free fatty acids (FFA), mono-, di- and triacylglycerols, free cholesterol and its esters. The characteristic feature is the presence of relatively high amounts of unsaturated fatty acids, including those (C18:2 and C18:3) which are nutritionally essential. Preeclampsia is associated with a slight increase in the total fatty acid content in Wharton's jelly and with marked changes in the proportional relationships between various lipids. A distinct decrease in the amounts of FFA was observed with a concomitant increase in monoacylglycerols and cholesterol esters. At least in some cases the effects exerted by PGFs are mediated by the lipid second messengers. Thus it is possible that alterations in lipid compounds of Wharton's jelly may participate in the deregulation of various cell functions, including overproduction of sulphated glycosaminoglycans or down-regulation of enzymes which participate in their degradation.

The umbilical cord forms a connection between the placenta and foetus. It contains one vein and two arteries surrounded by myxomatous substance called Wharton's jelly, consisting of very low number of cells and high amounts of extracellular matrix (ECM) components; mainly collagen, hyaluronate and several sulphated proteoglycans (Sobolewski et al. 1997; Franc et al. 1998). The large amount of hyaluronate makes this tissue highly hydrated, whereas the abundant content of collagen makes it resistant to extension, bending, twisting and compression evoked by foetal movements and uterine contractions. Furthermore, the ECM of Wharton's jelly is an abundant reservoir of numerous peptide growth factors (Sobolewski et al. 2005).

Rapid and localized changes in the activity of these factors can be induced by their release from matrix storage and/or by activation of latent forms. These growth factors, in turn, control cell proliferation, differentiation and synthesis and remodelling of the extracellular matrix. This suggests that ECM plays a major role in the control of growth factor signalling (Tajpale & Keski-Oja 1997).

As Wharton's jelly contains a low number of cells and very high amounts of extracellular matrix components, it may be concluded that the cells are strongly stimulated to produce large amounts of collagen, hyaluronate and sulphated proteoglycans. It is well known that biosynthesis of extracellular matrix components is enhanced by several peptide growth factors (PGF), mainly insulin-like growth factor (Edmondson et al. 2003), fibroblast growth factor (Yu et al. 2003) and transforming growth factor β (Shalitin et al. 2003). These growth factors may accumulate within Wharton's jelly to promote the synthesis of large amounts of ECM. Furthermore, Mitchell et al. (2003) found that stromal cells of Wharton's jelly have properties of potentially multipotent stem cells. Treatment with basic fibroblast growth factor induces these cells to express a neural phenotype.

Some products of lipid metabolism may be engaged in this process. The fatty acids serve as a source of energy for a number of cells; many are substrates for synthesis of regulatory molecules: prostaglandins, thromboxanes and leucotrienes (Tapiero et al. 2002). Several lipids are constituents of biological membranes, which separate the cells from the surrounding hydrophilic environment and contribute to organelle structures. Some are substrates for the production of second messengers (e.g. diacylglycerol, inositol-1,4,5-tris-phosphate, ceramides), which participate in intracellular signal transduction induced by hormones and PGFs bound to membrane receptors. Thus it is possible that alterations in lipid compounds of Wharton's jelly may participate in the deregulation of various cell functions, including overproduction of sulphated glycosaminoglycans or the down-regulation of enzymes, which participate in their degradation.

Lipids constitute about 50% of the mass of most animal plasma membranes and intracellular membranes, nearly all of the remainder being protein. The most abundant membrane lipids are the phospholipids with polar head group and two hydrophobic tails – both saturated and unsaturated fatty acids of different length. Four major phospholipids predominate in the plasma membrane of many mammalian cells: phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine and sphingomyelin. Together they constitute more than half the mass of lipids in most membranes. Other phospholipids, such as the inositol phospholipids, are present in smaller quantities but are functionally very important having a crucial role in cell signalling (Alberts et al. 2002).

The vascular system of the umbilical cord and placenta plays an important role in the intrauterine development of the foetus. Preeclampsia is the most common pregnancy-associated pathological syndrome (Niswander 1982). It is accompanied by significant morphological and functional alterations in the arterial walls of the uterus and placenta (Bańkowski 1999) and impairs foetus development (Gonzalez et al. 2007).

Our previous studies showed that preeclampsia is accompanied by an extensive remodelling of the extracellular matrix of the umbilical cord (Bańkowski et al. 1993, 2000a,b; Romanowicz et al. 1994; Pawlicka et al. 1999), including that of Wharton's jelly (Sobolewski et al. 1997; Bańkowski 1999). It is associated with a significant reduction in hyaluronic acid and simultaneous increase in sulphated glycosaminoglycans contents. Such a phenomenon corresponds to an ‘early ageing’ of the investigated tissue.

Wharton's jelly is a highly hydrophilic tissue. The main structures which may contain hydrophobic lipids are cell membranes. Plasma membranes of eukaryotic cells contain large amounts of cholesterol. Its molecules orient themselves in the bilayer with their hydroxyl groups close to the polar heads of the phospholipids. Cholesterol rigid, plate-like steroid rings interact with hydrophobic fatty acids closest to the polar heads of phospholipids and partly immobilize them. In this way cholesterol makes the lipid bilayer less deformable in this region and thereby decreases the permeability of the bilayer to small water-soluble molecules. It tends to make the lipid bilayer less fluid (Crane & Tamm 2004).

The non-polar lipids such as acylglycerols and cholesterol esters can be found inside the cell in a form of lipid droplets. Monoacylglycerols (MAG) and diacylglycerols are the products of triacylglycerols (TAG) breakdown. The free fatty acids may be both the products of lipolysis and lipogenesis.

The specificity of the Wharton's jelly lipid compounds was not investigated till now. It was decided to evaluate the lipid components of this tissue in healthy newborns and those delivered by mothers with preeclampsia.

Materials and methods

The study protocol was approved by the Bioethical Committee of the Medical University of Bialystok.

Tissue material

Studies were performed on the umbilical cord (UC), taken from 20 newborns. Some clinical data of mothers and newborns are shown in Table 1. The babies were born between 36 and 41 weeks of gestation. In all the cases, 20 cm long sections of each UC were excised beginning from their placental end and Wharton's jelly was carefully separated from the UC vessels.

Table 1.

Some clinical data of healthy (control) mothers (n = 10) and those with preeclampsia (n = 10) and their newborns

	Control	Preeclampsia
Maternal age (years)	26.1 ± 3.1	31.0 ± 5.3*
Body mass index	22.6 ± 1.5	25.0 ± 3.4*
Pregnancy weight gain	13.3 ± 1.0	17.9 ± 3.5***
Gestational age (weeks)	39.4 ± 0.8	38.8 ± 1.4
Parity	2.1 ± 1.2	2.0 ± 1.0
Number of physiologicaldeliveries	10	6
Number of Caesareansections	None	4
Blood pressure before20 week of gestation(mmHg)	Systolic 114 ± 4	Systolic 122 ± 7*
	Diastolic 66 ± 7	Diastolic 78 ± 8
Blood pressure atterm (mmHg)	Systolic 119 ± 4	Systolic 169 ± 14***
	Diastolic 70 ± 8	Diastolic 106 ± 7***
Proteinuria (mg/100 ml)	None	131 ± 128
Oedema (after bed rest)	None	10
Neonatal weight (g)	3.540 ± 453	3.245 ± 606

Values given are mean ± SD.

^*P < 0.05,

^***P < 0.001.

The control material was taken from 10 newborns delivered by healthy mothers aged 20–30 with normal blood pressure (systolic 110–135 mmHg, diastolic 60–86 mmHg). The mothers presented no symptoms of oedema or renal failure. The mean body weight of the newborns was 3.540 ± 453 g.

The preeclamptic material was taken from 10 newborns delivered by mothers aged 21–38 with preeclampsia, diagnosed according to the criteria accepted by the Organisation Gestosis (Rippmann 1971). All patients demonstrated an elevation of blood pressure (systolic >140 mmHg, diastolic >90 mmHg) and proteinuria (greater than trace). All cases of patients with cardio-vascular, renal and metabolic diseases were excluded. The mean body weight of these newborns was equal to 3.245 ± 606 g. The mean percentage of foetal growth restriction was equal to 8.3%.

Analytical procedures

Lipids (free fatty acids, acylglycerols, free cholesterol, cholesterol esters) were isolated and submitted to quantitative analysis as described in our recent papers (Romanowicz & Bańkowski, 2009a,b;). They were extracted from the investigated tissue with chloroform/methanol mixture. Thin layer chromatography was used for separation of individual lipid fraction. Fatty acids released by basic hydrolysis from each of them were separated and determined by reversed-phase high-performance liquid chromatography. Free cholesterol was determined in whole lipid extract according to BioMerieux protocol without cholesterol esterase in the reagent.

Statistical analysis

Mean values from 10 assays ± standard deviations (SD) were calculated. Individual fatty acid content in each class of lipid was expressed in nmol/g of fresh tissue. The results were submitted to statistical analysis with the use of Student's t-test, accepting P < 0.05 as significant.

Results

Free fatty acids

Figure 1a shows that Wharton's jelly of normal UC contained about 21 μmol of free fatty acids (free FA) per gram of fresh tissue. Both saturated free fatty acids (SAFA), monounsaturated free fatty acids (MUFA) as well as polyunsaturated free fatty acids (PUFA) were found. The SAFA comprised about 38%, whereas MUFA and PUFA made up about 24% and 38% of this lipid fraction respectively.

Figure 1.

Total, saturated, monounsaturated and polyunsaturated fatty acid contents in lipid fractions of control (n = 10) and preeclamptic (n = 10) samples of Wharton's jelly. (a) free fatty acids, (b) monoacylglycerols, (c) 1,2-diacylglycerols, (d) 1,3-diacylglycerols, (e) triacylglycerols and (f) cholesterol esters. (SAFA, saturated fatty acids; MUFA, monounsaturated fatty acids; PUFA, polyunsaturated fatty acids; □– control, – preeclampsia, *P < 0.05, **P < 0.01, ***P < 0.001).

In contrast to controls, the preeclamptic Wharton's jelly contained distinctly lower amounts of these lipids. About 8 μmol free FA per gram of fresh tissue were found. The proportional relationship between them also changed. The SAFA comprised about 43%, whereas MUFA and PUFA made up about 26% and 30% of total free FA respectively (Figure 1a).

Table 2 presents the individual free FA contents in Wharton's jelly tissue. It was apparent from the Table that palmitate (C16:0) was the most abundant component of free SAFA. It constituted about 42% of this fraction. The contents of other SAFA were distinctly lower. Altogether they constituted about 58% of this lipid fraction.

Table 2.

Individual fatty acid content in different lipid fraction of control (n = 10) and preeclamptic (n = 10) samples of Wharton's jelly (nmol/g tissue)

	Free fatty acids		Monoacylglycerols		1,2-diacylglycerols		1,3-diacylglycerols		Triacylglycerols
Fatty acid	Control	Preeclamptic	Control	Preeclamptic	Control	Preeclamptic	Control	Preeclamptic	Control	Preeclamptic
SAFA
C 12:0	1759.7 ± 36.2	152.5 ± 35.9***	32.7 ± 13.4	195.7 ± 17.6***	190.9 ± 32.1	300.7 ± 34.2***	178.9 ± 27.2	132.4 ± 26.3***	266.3 ± 27.8	302.0 ± 28.9 **
C 14:0	242.4 ± 14.4	42.6 ± 10.8***	6.9 ± 1.4	Undetectable	623.2 ± 120.5	Undetectable	318.3 ± 57.2	439.1 ± 59.1***	595.2 ± 29.4	236.2 ± 28.6***
C 16:0	3407.4 ± 259.1	1150.3 ± 248.7***	74.0 ± 14.3	835.5 ± 15.8***	1223.2 ± 236.0	2020.6 ± 245.3***	511.4 ± 100.7	758.7 ± 104.3***	1996.6 ± 374.8	2885.9 ± 388.9***
C 18:0	1859.9 ± 368.3	1652.5 ± 363.2	169.0 ± 35.2	2340.6 ± 39.3***	7402.5 ± 384.6	2827.4 ± 376.5***	660.2 ± 128.9	1339.9 ± 135.7***	4196.0 ± 738.2	5318.5 ± 744.4**
C 20:0	849.1 ± 64.7	331.9 ± 62.3***	Undetectable	435.9 ± 89.1	1591.2 ± 52.4	295.9 ± 49.7***	281.8 ± 22.3	182.9 ± 18.6***	534.8 ± 94.3	628.8 ± 99.6*
C 22:0	Undetectable	67.0 ± 13.1	Undetectable	Undetectable	Undetectable	Undetectable	Undetectable	Undetectable	38.6 ± 7.3	48.2 ± 8.4**
MUFA
C 14:1	2797.7 ± 97.8	415.9 ± 89.5***	37.2 ± 14.7	386.5 ± 16.8***	471.3 ± 86.5	1079.1 ± 92.8***	260.9 ± 36.2	262.3 ± 38.3	956.5 ± 109.9	638.6 ± 104.5***
C 16:1	684.6 ± 112.3	639.7 ± 111.2	80.9 ± 17.4	552.2 ± 18.5***	Undetectable	887.7 ± 154.1	Undetectable	147.9 ± 26.4	721.4 ± 68.4	319.5 ± 67.2***
C 18:1	1643.4 ± 215.5	1008.4 ± 212.6***	13.8 ± 4.9	1974.2 ± 7.2***	1516.9 ± 371.2	2526.0 ± 386.6***	567.2 ± 109.4	837.0 ± 113.7***	3791.5 ± 531.6	3348.4 ± 549.3*
C 24:1	Undetectable	12.2 ± 2.5	Undetectable	Undetectable	Undetectable	Undetectable	Undetectable	Undetectable	Undetectable	9.4 ± 2.3
PUFA
C 18:2	1475.2 ± 74.9	361.2 ± 72.1***	33.7 ± 7.3	745.9 ± 8.6***	1705.2 ± 221.0	1497.5 ± 213.2*	149.3 ± 28.5	352.1 ± 31.8***	1281.1 ± 257.3	1259.6 ± 261.0
C 18:3	241.3 ± 22.6	96.9 ± 19.2***	Undetectable	125.8 ± 25.7***	38.7 ± 5.1	21.0 ± 4.6***	30.1 ± 7.2	32.7 ± 8.1	35.3 ± 7.8	254.4 ± 8.4***
C 20:4	1622.2 ± 41.7	215.5 ± 39.6***	Undetectable	Undetectable	86.6 ± 20.3	233.5 ± 23.6***	659.1 ± 49.0	394.3 ± 42.7***	515.8 ± 102.4	751.0 ± 108.7***
C 20:5	3848.3 ± 252.3	1442.5 ± 249.8***	127.6 ± 26.6	691.8 ± 28.0***	704.8 ± 138.6	2214.5 ± 143.9***	147.9 ± 23.9	846.6 ± 25.3***	2486.6 ± 361.1	3655.0 ± 369.9***
C 22:6	841.2 ± 52.8	276.0 ± 49.2***	Undetectable	359.4 ± 66.3	107.0 ± 20.4	319.5 ± 23.8***	18.3 ± 3.8	105.7 ± 4.5***	560.6 ± 63.5	504.9 ± 62.8*

^*P < 0.05,

^**P < 0.01,

^***P < 0.001.

Preeclampsia was accompanied with a marked decrease in almost all free SAFA, except C18:0 (Table 2).

Control Wharton's jelly contained a large amount of myristoleate (C14:1) which comprised more than 54% of free MUFA. Furthermore, some amounts of C16:1 and C18:1 were found (Table 2).

A marked reduction in the amounts of C14:1 and C18:1 were found in preeclamptic material, although the amount of C16:1 did not change (Table 2).

Table 2 shows the control Wharton's jelly containing large amounts of free PUFA. The eicosapentaenate (C20:5) was the main component of this fraction amounting to about 48%.

Preeclampsia was accompanied by a marked decrease in all of free PUFA with an eight fold reduction on C20:4 observed (Table 2).

Monoacylglycerols

Figure 1b shows that normal Wharton's jelly contained only 0.6 μmol of MAG per gram of fresh tissue. About half of them contained SAFA, whereas the rest were unsaturated fatty acids, MUFA- and PUFA-containing MAG, 23% and 28% respectively.

By contrast, the preeclamptic Wharton's jelly contained a distinctly higher amount of MAG; about 9 μmol of MAG per gram of fresh tissue were found. The proportional relationship between them also changed. Despite SAFA was still the most abundant fraction (44%), the proportional amount of MUFA (34%) increased whereas that of PUFA (22%) decreased (Figure 1b).

Table 2 presents the individual MAG-fractions in Wharton's jelly. It is apparent from the Table that the SAFA-containing MAG contained mainly C18:0, about 60% of total MAG. Low amounts of others were found. The most common unsaturated fatty acids occurring in MAG, were C20:5 and C16:1.

Preeclampsia is accompanied with a marked increase in most MAG, except those which contained C14:0 (Table 2).

1,2-diacylglycerols

Figure 1c shows that the normal Wharton's jelly contained above 15 μmol of 1,2-diacylglycerols (1,2-DAG) per gram of fresh tissue. Both saturated and unsaturated FA were found. More than 70% of them constituted SAFA, then PUFA and low amounts of MUFA.

No significant difference between control and preeclamptic Wharton's jelly was observed. The preeclamptic Wharton's jelly contained about 14 μmol of 1,2-DAG per gram of fresh tissue. The proportional relationship between various FA changed. Significant decrease in proportional amount of SAFA (38%) with simultaneous increase in MUFA (32%) and PUFA (30%) were observed (Figure 1c).

Table 2 presents the individual 1,2-DAG fractions in Wharton's jelly tissue. It is apparent that C18:0 was the dominating FA in this fraction.

Preeclampsia is accompanied by a reduction of 1,2-DAG containing C18:0 with simultaneous increase of most PUFA, especially C20:5 (Table 2).

1,3-diacylglycerols

The amount of 1,3-diacylglycerols (1,3-DAG) in normal Wharton's jelly was lower than that of 1,2-DAG. About 4 μmol of these lipids per gram of fresh tissue were found. More than half of FA contained in this fraction were SAFA, the rest constituted MUFA and PUFA in similar amounts (Figure 1d).

Preeclampsia is accompanied by a slight increase in 1,3-DAG in Wharton's jelly tissue. Almost 6 μmol of fatty acids per gram were found. No significant changes in proportional amounts of SAFA, MUFA and PUFA were observed (Figure 1d).

Table 2 presents the individual 1,3-DAG fractions in Wharton's jelly tissue. The C18:0, C16:0, C18:1 and C20:4 predominated.

Preeclampsia is accompanied by a marked increase in C18:0 and most PUFA (especially C18:2, C20:5 and C22:6) contents (Table 2).

Triacylglycerols

Figure 1e shows that the amount of TAG in normal Wharton's jelly is comparable with that of 1,2-DAG, about 18 μmol/g of fresh tissue. They contained about 42% of SAFA, 30% of MUFA and 27% of PUFA.

In contrast to other acylglycerols the amount of TAG in preeclamptic Wharton's jelly did not change much. A slight increase in SAFA and PUFA was accompanied by a decrease in MUFA content (Figure 1e).

Table 2 presents the individual TAG fractions in Wharton's jelly tissue. As in all other acylglycerols, stearate (C18:0) was the main FA. It is of interest that this acylglycerols fraction contains large amounts of unsaturated FA, especially C18:1 and C20:5. Even C22:6 in significant amount was found.

Preeclampsia is accompanied by an increase in almost all saturated FA (except C14:0) and most PUFA (C18:3, C20:4 and C20:5) with simultaneous slight reduction of all MUFA contents (Table 2).

Cholesterol (Ch) and its esters (ChE)

Figure 1f shows the amounts of cholesterol esters in Wharton's jelly tissue. The normal Wharton's jelly contained more than 4 μmol of ChE per gram of fresh tissue. Almost half comprised SAFA and the rest of ChE contained MUFA (35%) and PUFA (18%).

It is of interest that preeclampsia is associated with a 3-fold increase of ChE content in Wharton's jelly tissue. The proportional amount of SAFA in these esters is similar like in control material, proportional amount of MUFA distinctly decreased, whereas that of PUFA slightly increased (Figure 1f).

A variety of fatty acids were detected in ChE of Wharton's jelly tissue (Table 3). It is of interest that unsaturated FA constituted more than half of total FA contained in cholesterol esters. The main SAFA were C20:0 and C18:0, large amount of C18:1 was found in MUFA, whereas the dominating FA in PUFA was C18:2.

Table 3.

Individual fatty acid content in cholesterol esters of control (n = 10) and preeclamptic (n = 10) samples of Wharton's jelly

Fatty acid	Control (nmol/g tissue)	Preeclamptic (nmol/g tissue)
SAFA
C 12:0	88.4 ± 15.4	1353.3 ± 18.3***
C 14:0	54.3 ± 10.5	285.9 ± 11.4***
C 16:0	463.2 ± 96.1	699.9 ± 106.2***
C 18:0	626.1 ± 108.8	1374.5 ± 110.7***
C 20:0	703.6 ± 109.7	1888.8 ± 112.3***
C 22:0	Undetectable	17.7 ± 4.5
MUFA
C 14:1	455.9 ± 92.8	2204.3 ± 97.2***
C 16:1	71.6 ± 14.6	55.4 ± 13.4***
C 18:1	924.4 ± 129.3	1282.7 ± 130.8***
C 24:1	Undetectable	4.2 ± 1.3
PUFA
C 18:2	308.4 ± 35.5	522.0 ± 37.2***
C 18:3	27.3 ± 9.7	462.5 ± 11.2***
C 20:4	252.1 ± 32.9	217.3 ± 30.3**
C 20:5	56.7 ± 14.8	983.7 ± 15.5***
C 22:6	100.2 ± 22.4	715.9 ± 26.8***

^**P < 0.01,

^***P < 0.001.

It is of interest that preeclampsia is accompanied by a distinct increase in almost all FA in cholesterol esters. Many fold increase in C12:0, C14:0, C14:1, C18:3, C20:5 and C22:6 contents were found. In some cases (C12:0, C18:3 and C20:5), the increase was higher than 10 times (Table 3).

As can be seen from Figure 2a, the normal Wharton's jelly contains very low amount of free cholesterol, about 1 μmol, whereas the preeclamptic material contains slightly less (0.8 μmol of this sterol per gram of fresh tissue. Distinctly more esterified cholesterol has been found. Control Wharton's jelly contained about 4 μmol, whereas the preeclamptic material contained about 12 μmol of ChE per gram of fresh tissue (Figure 2a). It is of interest that preeclampsia is accompanied by an increase in ChE:Ch ratio, from 4 (in control) to 14 (in preeclamptic Warton's jelly) (Figure 2b).

Figure 2.

(a) Free cholesterol (Ch) and cholesterol ester (ChE) contents and (b) ChE: Ch quantitative ratio in control (n = 10) and preeclamptic (n = 10) samples of Wharton's jelly. (□– control, – preeclampsia, *P < 0.05, ***P < 0.001).

Total lipids

Table 4 shows the comparison of total lipid contents in the control and preeclamptic samples of Wharton's jelly. Molar amounts of free FA, acylglycerols, free cholesterol and cholesterol esters are presented. It is apparent that in control tissue the free FA are dominating fraction, next are DAG, TAG and ChE whereas the amount of MAG and free cholesterol is very low. Preeclampsia is accompanied by a deep (threefold) reduction in free FA with a distinct increase in MAG and ChE. Cholesterol ester became a dominant lipid fraction in preeclamptic tissue. The amounts of DAG and TAG did not change much.

Table 4.

Lipid fraction content in control (n = 10) and preeclamptic (n = 10) samples of Wharton's jelly

Lipid fraction	Control (μmol/g tissue)	Preeclamptic (μmol/g tissue)
Free fatty acids	21.2725 ± 1.743	7.865 ± 1.628***
Monoacylglycerols	0.576 ± 0.185	8.643 ± 0.227***
Diacylglycerols	9.723 ± 1.769	10.028 ± 1.893
Triacylglycerols	5.992 ± 0.899	6.720 ± 0.934
Cholesterol esters	4.132 ± 0.835	12.068 ± 0.908***
Total fatty acids	63.402 ± 6.284	68.793 ± 6.327*
Free cholesterol	1.019 ± 0.143	0.864 ± 0.129*

^*P < 0.05,

^***P < 0.001.

Discussion

Lipids play an important role in human physiology. The fatty acids serve as a source of energy for a number of cells; many are substrates for synthesis of regulatory molecules such as prostaglandins, thromboxanes and leucotrienes (Tapiero et al. 2002). Several lipids are constituents of biological membranes, which separate the cells from the surrounding hydrophilic environment and contribute to organelle structures. Some others are substrates for the production of second messengers (e.g. diacylglycerol, inositol-1,4,5-tris-phosphate, ceramides), which participate in intracellular signal transduction induced by hormones and peptide growth factors bound to membrane receptors.

Here we have evaluated the lipid composition of normal and preeclamptic Wharton's jelly. This, as with most human tissues, contains free fatty acids, mono-, di- and triacylglycerols, free cholesterol and its esters. The characteristic feature is the presence of high amounts of free (mainly unsaturated) fatty acids, which are the dominating lipid fraction of normal Wharton's jelly. Total amounts of DAG, TAG and especially MAG were markedly lower. It is of interest that Wharton's jelly contains relatively large amounts of cholesterol esters, whereas the quantity of free cholesterol was low.

Wharton's jelly contains a low number of cells which are scattered within the amorphic, gelatinous, highly hydrated tissue. Our previous paper (Sobolewski et al. 2005) has reported distinctly lower (about six times) cell numbers per gram of tissue in comparison with those of the umbilical cord arterial wall. Although the amounts of lipid in this tissue are lower in comparison with those detected in the umbilical cord artery (Romanowicz & Bańkowski 2008) and vein (Romanowicz & Bańkowski 2009), our findings suggest that the total amount of lipids per cell in Wharton's jelly must be higher in comparison with other parts of the umbilical cord. Thus we conclude that lipids may be important for the function of the cells scattered within Wharton's jelly.

Some lipids of Wharton's jelly may participate in the formation of plasma membranes, which separate the cells from the highly hydrated extracellular matrix and intracellular membranes, which divide the cell interior into numerous compartments. The membrane fluidity may be regulated by varying in lipid composition. The high amount of cholesterol in relation to cell number makes the membranes less fluid and more rigid (van Meer et al. 2008). Cholesterol has a concentration-dependent effect on membrane organization. It is able to control the membrane permeability by inducing conformational ordering of the lipid chains. An increase in cholesterol content in experimental lipid membrane results in increased hydrophobicity and formation of effective barriers for the permeation of polar substances (Raffy & Teissie 1999).

Wharton's jelly contains relatively high amount of long chain polyunsaturated fatty acids, including eicosapentaenoic acid (C20:5) and docosahexaenoic acid (C22:6), which are rather minor lipid components of most human tissues. They were found both in a free form and in a form of acylglycerols and cholesterol esters.

Preeclampsia is associated with only a slight increase in the total FA content per gram of Wharton's jelly. On the other hand a great change in proportional relationship between various lipid fractions has been observed. Preeclampsia is accompanied by threefold decrease in the amount of free fatty acids with simultaneous 16-fold increase in MAG and threefold increase in cholesterol esters. The shortage of free fatty acids may impair energetic metabolism of Wharton's jelly.

It is of interest that Wharton's jelly contains a high amount of unsaturated FA. Some of them: palmitoleate (C16:1), oleate (C18:1), linolenate (C18:3), eicosapentaenate (C20:5) and docosahexaenate (C22:6) even increase in preeclamptic tissue.

Foetal tissues are unable to synthesize sufficient amounts of unsaturated fatty acids and the maternal tissues mobilize membrane PUFA to meet the high foetal requirement for these nutrients. These are actively transported via the foetal blood through the placenta (Haggarty et al. 1999). However, Wharton's jelly does not contain its own blood vessels and therefore it cannot be supplied with nutrients by foetal circulation. Moreover, the amniotic fluid also cannot deliver fatty acids because of their insolubility in aqueous medium. For these reasons, the only source of FA in Wharton's jelly may be de novo synthesis in the sparse cellular distribution of this tissue. Glucose and hydrocarbon skeletons of some amino acids may serve as a source of acetyl-CoA; a substrate for the synthesis of fatty acids. However, the formation of some polyunsaturated fatty acids remains uncertain.

It is known that human tissues are unable to synthesize linoleate (C18:2) and linolenate (C18:3), these being nutritionally essential (Meisenberg & Simmons 2006). As they are neither supplied by the umbilical cord blood nor by the amniotic fluid, we suppose that the poorly differentiated cells of Wharton's jelly may be able to perform desaturation of C18:0 and C18:1.

It is possible that alterations in lipid compounds of preeclamptic compared with normal Wharton's jelly may participate in the deregulation of various cell functions, including the overproduction of sulphated glycosaminoglycans or the down-regulation of enzymes which participate in their degradation. Such phenomena may correspond to an “early ageing” of that tissue.