Fatty acids, C5-10, esters with pentaerythritol

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics, other

Remarks:

written assessment based upon read across

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Justification for type of information:

see the attached justification in section 13 for details.

Cross-reference

Cross-reference 1

Reason / purpose for cross-reference:

read-across source

Reference

Endpoint:

basic toxicokinetics

Type of information:

other: review article

Adequacy of study:

other information

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

other: only secondary data

Reason / purpose for cross-reference:

reference to same study

Lipids are not only structural building blocks of cells and tissues but at the same time suppliers of C atoms for a number of biosynthetic pathways as well as carriers of essential fatty acids and fat-soluble vitamins. In addition, fatty acids are precursors of prostaglandins and other eicosanoids and therefore have important metabolic functions.

Fatty acids can be divided into three groups, saturated, monounsaturated, and polyunsaturated fatty acids.

Each class of fatty acids has a preferential specific role.

- Saturated fatty acids (medium or long-chain) are more devoted to energy supply, but one should not forget their specific structural role.

- The polyunsaturated fatty acids of the n–3 and n–6 families have very important structural and functional roles and ideally should not be utilized for energy purposes.

 

Table 1:

Role of different classes of fatty acids

Fatty acids	Energy	Structure	Function
Medium-chain saturated fatty acids	+++	0	0
Long-chain fatty acids
Saturated	++	++	(+)
Monounsaturated	++	++	(+)
Polyunsaturated
Linoleic or n-6 family	0	+++	+++
Linolenic or n-3 family	0	+++	+++

 0, +, ++, +++ : Emphasis of contribution, increasing in rank order

Cross-reference 2

Reason / purpose for cross-reference:

read-across source

Reference

Endpoint:

basic toxicokinetics

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

other information

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

other: Only secondary data Short review on metabolism from previous publications.

Objective of study:

metabolism

The metabolism of Medium chain triglycerides in the canine is a process whereby lipases from the buccal cavity and pancreas release the fatty acids in the gastrointestinal tract where they are absorbed. Unlike long chain triglycerides (LCT), where long chain fatty acids (LCFA) form micelles and are absorbed via the thoracic lymph duct, MCFA are most often transported directly to the liver through the portal vein and do not necessarily form micelles. Also, MCFA do not re-esterify into MCT across the intestinal mucosa. MCFA are transported into the hepatocytes through a carnitine-independent mechanism, and are metabolized into carbon dioxide, acetate, and ketones through b-oxidation and the citric acid cycle.

Cross-reference 3

Reason / purpose for cross-reference:

read-across source

Reference

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

other information

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Acceptable, well-documented publication meeting basic scientific principles.

Objective of study:

absorption

Principles of method if other than guideline:

The absorbability of the fatty acid moiety of the complete, oleate esters of alcohols containing from one to six hydroxyl groups was determined by the fat balance technique in adult rats. Similarly, the absorbability of sucrose octaoleate and sucrose monooleate was determined.

GLP compliance:

no

Radiolabelling:

no

Species:

rat

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS

- Source: no data
- Age at study initiation: young adult
- Weight at study initiation: approx. 200 g
- Housing: Individually in cages with raised screen bottoms
- Diet (e.g. ad libitum): ad libitum

Route of administration:

oral: feed

Duration and frequency of treatment / exposure:

10 Days, diet ad libitum

Remarks:

Doses / Concentrations:
10% and 25 % of dietary fat

Details on absorption:

The fatty acids of the compounds containing less than four ester groups, methyl oleate, ethylene glycol dioleate, glycerol trioleate, and sucrose monooleate, were almost completely absorbed. As the number of ester groups was increased - erythritol and pentaerythritol tetraoleate and xylitol pentaoleate - the absorbability decreased. The fatty acids of sorbitol hexaoleate and sucrose octaoleate were not absorbed. These differences in absorbability are related to the activity and specificity of the lipolytic enzymes in the lumen of the intestinal tract.

Test fat	Percentage of dietary fat	Absorbability [%]
Methyl Oleate	10	100
	25	96
Ethylen Glycol Oleate	10	100
	25	92
Glycerol Trioleate	100	(100)
Erythritol Tetraoleate	10	-
	25	72
Pentaerythritol Tetraoleate	10	90
	25	64
Xylol Pentaoleate	10	50
	25	24
Sorbitol hexaoleate	10	0
	25	0
Sucrose Octaoleate	5	0
	10	0
	15	0
Sucrose Monooleate	5	100
	10	100
	15	100

Conclusions:

Absorption rates were between 0 an 100 %, depending on the amount of ester groups present in the substance fed. Pentaerythritole tetraoleate had an absorption rate of 90% (10% of dietary fat) and 64% (25% of dietary fat), respectively. Erythritole tetraoleate had an absorption rate of 72% (25% of dietary fat).

Cross-reference 4

Reason / purpose for cross-reference:

read-across source

Reference

Endpoint:

basic toxicokinetics in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

other information

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Acceptable, well-documented publication meeting basic scientific principles

Objective of study:

metabolism

Principles of method if other than guideline:

The lipolytic activity of human gastric and duodenal juice against medium chain and long chain triglycerides was compared.

GLP compliance:

no

Radiolabelling:

yes

Remarks:

Glyceryl trioctanoate-1-14C

Species:

human

Route of administration:

other: in vitro testing

Enzymatic Lipolysis by Gastric and Duodenal Juice:

All samples of gastric juice showed lipolytic activity against trioctanoin and triolein. Hydrolysis of emulsified trioctanoin was greater than of emulsified triolein. Hydrolysis of unemulsified trioctanoin was less and more variable.

Duodenal juice was more active, even against unemulsified trioctanoin and triolein. Duodenal juice was more active against unemulsified substrate than gastric juice against emulsified substrate.

Table 1: Hydrolysis of trioctanoin and triolein*

	Substrate and form (μmoles)	Hydrolysis (%)
		Trioctanoin	Triolein
Gastric juice	30, unemulsified	21	1
	60, emulsified	33	16
Duodenal juice	30, unemulsified	40	34
	45, emulsified	42	35
	105, emulsified	45	36

*Gastric or duodenal juice (1 mL) was incubated (1 hour, continuous shaking, 37ºC) with 1 mL of buffer and unemulsified substrate or 1 mL of substrate emulsified in 10 mM sodium taurodeoxycholate, pH6.

pH Optimum

In the presence of bile acids, gastric lipolytic activity against trioctanoin had a broad pH optimum, between 4 and 7. The lipolytic activity of duodenal juice had a sharper pH optimum, between 6 and 8. The pH optimum was lower for short chain triglycerides, indicating that pH optimum values for lipases must be defined for a particular substrate.

Chain Length Specificity

Lipolysis rates increased with decreasing chain lengths for pure triglycerides.

Tributyrin was cleaved more rapidly than trihexanoin which in turn was cleaved more rapidly than trioctanoin (ratio of rates, 100:69:53). Because the pH optimum of gastric lipase is lower for short chain triglycerides than for MCT, trihexanoin and tributyrin were cleaved much more rapidly than, for example, trioctanoin at pH5.

Esterification and Fatty Acid Acceptors by Gastric and Duodenal Lipases

Gastric and duodenal lipases did not induce esterification of the fatty acid acceptor, glyceryl 2 -monooleyl ester, by octanoic acid over the pH range of 2 to 6. However, it was esterified by oleic acid in the presence of gastric juice, duodenal juice, or pancreatic fistula juice when bile acids were added. Esterification, calculated by disappearance of titratable fatty acid, was confirmed by TLC which showed the formation of compounds having the mobilities of a monoether monoester and a monoether diester. Control incubations without enzyme showed no loss of oleic acid or appearance of new lipids by TLC. To determine the amount of disubstituted and trisubstituted glyceryl derivatives which were formed, 14C-labeled glyceryl 2 -monooleyl ether was used and the products of the reaction were examined by zonal scanning. The glyceryl 2 -monooleyl ether was not cleaved during the incubation procedure. The amounts of ester bonds formed estimated by titration and by zonal scanning were in good agreement.

Products of Lipolysis and Positional Specificity

The specificity of pancreatic lipase for the 1 -ester bond in LCT has been demonstrated previously by establishing the formation of 2 -monoglycerides and fatty acid as end products of lipolysis. This procedure cannot be used for MCT because medium chain 2 -monoglycerides are either cleaved by pancreatic lipase or rapidly isomerized to the 1 -isomer which is rapidly hydrolyzed or both. Indeed, chromatographic examination of the products of hydrolysis of trioctanoin-14C showed only a small fraction of monoglyceride present.

Table 2: Products of hydrolysis of trioctanoin by gastric juice*

	Radioactivity distribution** (%)				Lipolysis (%)
	Monoglyceride	Diglyceride	Fatty acid	Triglyceride
Buffer (control)	0	0	0	100	0
Gastric juice 1 mL	3	26	26	44	34
	3	28	24	43	33
	4	28	25	43	36
	4	28	25	43	36
Duodenal juice
0.4 mL	4	9	15	72	26
0.5 mL	4	14	20	62	40

*Glyceryl trioctanoate-1-¹⁴C was added to 1 mL of emulsified trioctanoin (60 μmoles) and incubated for 1 hour at 37ºC with buffer (blank) or gastric or duodenal juice. The reaction mixture was extracted and a 50 μL aliquot was analyzed by TLC and zonal scanning. A 3 mL aliquot was titrated to quantify fatty acids liberated.

Discussion:

The work confirmed extensive literature showing that gastric juice contains lipolytic activity, that ingested triglyceride is hydrolyzed in the stomach, even after pancreatic diversion, that lipase may be demonstrated histochemically in gastric mucosa, and that gastric mucosal homogenates have lipolytic activity. Pancreatic lipase has some activity at the pH of gastric content, which is between pH6 and pH3 in normal subjects.

Cross-reference 5

Reason / purpose for cross-reference:

read-across source

Reference

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

other information

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Study well documented, meets generally accepted scientific principles, acceptable for assessment

Objective of study:

absorption

Principles of method if other than guideline:

The mechanism of the intestinal fat absorption has been studied with 14C labeled fat in rats with the intestinal lymph duct cannulated.

GLP compliance:

no

Radiolabelling:

yes

Remarks:

14C labeled fat

Species:

rat

Strain:

not specified

Sex:

not specified

Route of administration:

oral: gavage

Duration and frequency of treatment / exposure:

single oral exposure
(at least 18 hours after surgery)

Remarks:

Doses / Concentrations:
A) 0.5 mL corn oil + 2.5 mg active palmitic acid-1-14C
B) 0.5 mL corn oil transesterified with 2.5 mg active palmitic acid-1-14C
C) 0.5 mL hydrolysed corn oil + 2.5 mg active palmitic acid-1-14C

No. of animals per sex per dose / concentration:

5-6

Control animals:

no

Details on absorption:

24 hours after administration of the different fats the mean recovered activities in lymph were as following:
A) 0.5 mL corn oil + 2.5 mg active palmitic acid-1-14C: 57.0 %
B) 0.5 mL corn oil transesterified with 2.5 mg active palmitic acid-1-14C: 61.7 %
C) 0.5 mL hydrolysed corn oil + 2.5 mg active palmitic acid-1-14C: 62.3 %

In all three groups of experiments maximum recoveries were found after 24 hours, i.e. 80.9, 85.0 and 87.5 % of the activity given.
Free fatty acids administered alone or together with glycerides appear in the lymph in glycerides and phospholipids.
No free fatty acids or soaps appear in the lymph.
The intestinal wall supplies a quantitatively important part of phospholipids to the blood during fat absorption.
The recoveries in the lymph of the fat fed varied widely. Diarrhea occured in some animals especially after feeding hydrolysed corn oil.

Details on distribution in tissues:

Absorbed fat is mainly transported via lymphatic channels to the systemic circulation whether fed as glycerides or as fatty acids.

Details on metabolites:

A complete hydrolysis of the fat in the intestinal lumen might occur in the rat.

The proportions of neutral fat and phospholipids in the lymph were in all three cases about the same. 90% of the fatty acids were present in the neutral fat and the remaining 10 % in phospholipids. The neutral fat consisted chiefly of triglycerides; cholesterol and cholesterol esters representing only a minor part of this fraction. No free fatty acids or soaps appeared in the lymph.

The results indicated that glycerides might be completely hydrolysed in the intestinal lumen of the rat and then resynthesized in the intestinal wall.

Conclusions:

Mean absorption rate of corn oil combined with palmitic acid was between 57 - 62 %.

Materials and methods

Test material

Test material information

1

Reference substance name:

Fatty acids, C5-10, esters with pentaerythritol

EC Number:

270-291-9

EC Name:

Fatty acids, C5-10, esters with pentaerythritol

Cas Number:

68424-31-7

Molecular formula:

not applicable (UVCB)

IUPAC Name:

Esterification products of pentaerythritol and dipentaerythritol and pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid and decanoic acid

Test material form:

liquid

Applicant's summary and conclusion

Executive summary:

Basic toxicokinetics

There are no studies available in which the toxicokinetic behaviour ofPentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acidshas been investigated.

Therefore, in accordance with Annex VIII, Column 1, Item 8.8 of Regulation (EC) 1907/2006 and with Guidance on information requirements and chemical safety assessment Chapter R.7c: Endpoint specific guidance (ECHA, 2012), assessment of the toxicokinetic behavior of the substancePentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acidswas conducted based on the relevant available information. This comprises a qualitative assessment of the available substance-specific data on physico-chemical and toxicological properties according to ‚Guidance on information requirements and chemical safety assessment Chapter R.7c: Endpoint specific guidance‘ (ECHA, 2012) and taking into account further available information on the polyol esters category from which data was used for read-across to cover data gaps.

The UVCB substancePentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acidsis an organic liquid. It is poorly water soluble (< 1 mg/L, Lumsden, 1999) with a molecular weight of 472.62 – 753.14 g/mol, a log Pow of 6.74 - > 10 (Müller, 2013) and a vapour pressure of < 0.0001 Pa at 20 °C (Dr. Knoell, 2009).

Absorption

Absorption is a function of the potential for a substance to diffuse across biological membranes. The most useful parameters providing information on this potential are the molecular weight, the octanol/water partition coefficient (log Pow) value and the water solubility. The log Pow value provides information on the relative solubility of the substance in water and lipids (ECHA, 2012).

Oral

The smaller the molecule, the more easily it will be taken up. In general, molecular weights below 500 g/mol are favorable for oral absorption (ECHA, 2012). As the molecular weight ofPentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acidsis 472.62 – 753.14 g/mol, absorption of the molecule in the gastrointestinal tract is unlikely.

Absorption after oral administration is also unexpected when the “Lipinski Rule of Five” (Lipinski et al. (2001), Ghose et al. (1999)) is applied to the substance Pentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acids as the log Pow value of 6.74 - > 10 is above the given range of ‑0.4 to 5.6.

The log Pow of 6.74 - > 10 of the substance Pentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acids is favourable for absorption by micellar solubilisation, as this mechanism is of importance for highly lipophilic substances (log Pow > 4), which are poorly soluble in water (1 mg/L or less).

In the gastrointestinal (GI) tract, metabolism prior to absorption via enzymes of the microflora may occur. In fact, after oral ingestion, fatty acid esters with glycerol (glycerides) are rapidly hydrolysed by ubiquitously expressed esterases and the cleavage products are almost completely absorbed (Mattson and Volpenhein, 1972a). On the contrary, lower rate of enzymatic hydrolysis in the GI tract was observed for compounds with more than three ester groups (Mattson and Volpenhein, 1972a,b). In vitro hydrolysis rate of pentaerythritol ester was about 2000 times slower in comparison to glycerol esters (Mattson and Volpenhein, 1972a,b).

Moreover in vivo studies in rats demonstrated the incomplete absorption of the compounds containing more than three ester groups. This decrease became more pronounced as the number of ester groups increased, probably the results of different rates of hydrolysis in the intestinal lumen (Mattson and Volpenhein, 1972c).

The available data on oral toxicity of the structurally related substances Fatty acids, C5-10, esters with pentraerythritol (CAS 68424-31-7), Fatty acids, C16-18 (even numbered), esters with pentaerythritol (CAS 85116-93-4), and Fatty acids, C5-9 tetraesters with pentaerythritol (CAS 67762-53-2) are also considered for assessment of oral absorption. Acute oral toxicity studies were conducted at concentrations of 2000 and 15000 mg/kg bw in rats where no signs of systemic toxicity were seen (Robinson, 1991; Potokar, 1983; Zolyniene, 1999; D’Aleo, 1984). No systemic effects were observed in a 28-day repeated dose toxicity study with the structurally related substance Fatty acids, C5-10, esters with pentraerythritol (CAS 68424-31-7) up to and including the highest dose level of 1450 mg/kg bw/day for male rats and 1613 mg/kg bw/day for female rats (Brammer, 1993). Moreover, the structurally related substance Pentaerythritol ester of pentanoic acids , mixed esters with pentaerythritol, isopentanoic and isononanoic acid (CAS No. 146289-36-3) showed no systemic effects up the high-dose group (1000 mg/kg bw/day) in a 90-day repeated dose toxicity study (NOAEL ≥ 1000mg/kg bw/day; Müller, 1998). Therefore, if absorption of the intact parental compound or the respective metabolites occurred, this will result in a low order of systemic toxicity. These results suggest that Pentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acids is of low systemic toxicity, either due to low toxicity potency or by a low absorption in combination with a low systemic toxicity.

In general, after oral ingestion, aliphatic esters of polyhydroxy alcohol (Polyol) and 1 – 6 fatty acids will undergo chemical changes in the gastro-intestinal fluids as a result of slow enzymatic hydrolysis. Pentaerythritol (PE, parental polyol) as well as the fatty acids will be formed, even if according to the available literature hydrolysis is not assumed to be rapid for pentaerythriol- and dipentaerythritol-ester and in general for polyol esters with more than three ester groups (multiple linked polyol esters) probably due to steric hindrance. The in-vitro hydrolysis rate of Pentaerythritol tetraoleate when compared with the hydrolysis rate of the triglyceride Glycerol trioleate was very slow (Mattson and Volpenhein, 1972). The physico-chemical characteristics of the cleavage products (e.g. physical form, water solubility, molecular weight, log Pow, vapour pressure, etc.) will be different from those of the parent substance before absorption into the blood takes place, and hence the predictions based upon the physico-chemical characteristics of the parent substance do no longer apply (ECHA, 2012). However, also for both cleavage products, it is anticipated that they will be absorbed in the gastro-intestinal tract.

The highly lipophilic fatty acids will be absorbed by micellar solubilisation (Ramirez et al., 2001). A study by Mattson and Nolen (1972) determined the absorbability of the fatty acid moiety of the complete oleate esters of alcohols containing from one to six hydroxyl groups. The fatty acids of the compounds containing less than four ester groups were almost completely absorbed. As the number of ester groups was increased (erythritol and pentaerythritol tetraoleate and xylitol pentaoleate) the absorbability of the fatty acids decreased but was still present.

The pentaerythritol, having a low molecular weight (136.15 g/mol) and being a highly water-soluble substance (25 g/L, OECD SIDS, 1998), will readily dissolve into the gastrointestinal fluids. After oral administration of 10 mg/kg C14-labled PE to mice, almost half of the administered dose was absorbed from the gastrointestinal tract within 15 minutes (DiCarlo et al., 1965).

In summary, the above discussed physical-chemical properties of Pentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acids and relevant data from available literature on fatty acid esters with more than three ester bonds do not indicate rapid hydrolysis before absorption of Pentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acids to the respective fatty acids and the polyol pentaerythritol.

On the basis of the above mentioned data, a low absorption of the parent substance is anticipated.

Dermal

The smaller the molecule, the more easily it may be taken up. In general, a molecular weight below 100 g/mol favors dermal absorption, above 500 g/mol the molecule may be too large (ECHA, 2012). As the molecular weight of Pentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acids is 472.62 – 753.14 g/mol, a dermal absorption of the molecule is not likely.

If the substance is a skin irritant or corrosive, damage to the skin surface may enhance penetration (ECHA, 2012). As Pentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acids was not tested for skin irritation, read-across from Fatty acids, C5-10, esters with pentaerythritol (CAS 68424-31-7) (Robinson, 1991) was applied. As the read –across substance is not considered skin irritating in humans an enhanced penetration of the substance due to local skin damage can be excluded.

For substances with a log Pow above 4, the rate of dermal penetration is limited by the rate of transfer between the stratum corneum and the epidermis, but uptake into the stratum corneum will be high. For substances with a log Pow above 6, the rate of transfer between the stratum corneum and the epidermis will be slow and will limit absorption across the skin, and the uptake into the stratum corneum itself is also slow. The substance must be sufficiently soluble in water to partition from the stratum corneum into the epidermis (ECHA, 2012). As the water solubility ofPentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acidsis less than 1 mg/L and log Pow is 6.74 - > 10, dermal uptake is likely to be very low.

The available data on dermal toxicity of the structurally related substances Decanoic acid, mixed esters with heptanoic acid, octanoic acid, pentaerythritol and valeric acid (CAS 71010-76-9) and Fatty acids, C5-9, tetraesters with pentaerythritol (CAS 67762-53-2) are also considered for assessment of dermal absorption.

An acute dermal toxicity study was available for Decanoic acid, mixed esters with heptanoic acid, octanoic acid, pentaerythritol and valeric acid (CAS 71010-76-9). At a concentration of 2000 mg/kg bw in rats no signs of systemic toxicity were seen (Mallory, 2006).

In the 90-day repeated dose toxicity study performed with the Fatty acids, C5-9, tetraesters with pentaerythritol (CAS 67762-53 -2), no toxicologically relevant effects were noted up to and including the highest dose level of 2000 mg/kg bw/day in male and female rats (Cruzan, 1988).

Overall, the calculated low dermal absorption potential, the low water solubility, the high molecular weight (> 100), the high log Pow values and the fact that the substance is not irritating to skin implies that dermal uptake of Pentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acids in humans is considered to be very low.

Inhalation

Pentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acids has a low vapour pressure of less than 0.0001 Pa at 20°C, thus being of low volatility. Therefore, under normal use and handling conditions, inhalation exposure and thus availability for respiratory absorption of the substance in the form of vapours, gases, or mists is not expected to be significant.

However, the substance may be available for respiratory absorption in the lung after inhalation of aerosols, if the substance is sprayed. In humans, particles with aerodynamic diameters below 100 μm have the potential to be inhaled. Particles with aerodynamic diameters below 50 μm may reach the thoracic region and those below 15 μm the alveolar region of the respiratory tract (ECHA, 2012).

Lipophilic compounds with a log Pow > 4, that are poorly soluble in water (1 mg/L or less) like Pentaerythritol tetraoleate can be taken up by micellar solubilisation. Esterases present in the lung lining fluid may also hydrolyse the substance, hence making the resulting alcohol and fatty acid available for respiratory absorption. Due to the high molecular weight of the substance, absorption is driven by enzymatic hydrolysis of the ester to the respective metabolites and subsequent absorption. However, as discussed above, hydrolysis of fatty acid esters with more than three ester bonds is considered to be slow (Mattson und Volpenhein, 1968, 1972a) and the possibility the test substance to be hydrolysed enzymatically to the respective metabolites and its relative absorption is considered to be low as well.

The available data on inhalation toxicity of the structurally related substances Fatty acids, C5-10, esters with pentraerythritol (CAS 68424-31-7) and Fatty acids, C5-9, tetraesters with pentaerythritol (CAS 67762-53-2) are also considered for assessment of inhalation absorption. An acute inhalation toxicity read-across study conducted with Fatty acids, C5-9, esters with pentaerythritol (CAS 68424-31-7; Parr-Dobrzansk, 1994) in rats show no effects of systemic toxicity. In the 90-day repeated dose toxicity study performed with the Fatty acids, C5-9, tetraesters with pentaerythritol (CAS 67762-53-2), no toxicologically relevant effects were noted up to and including the highest dose level of 0.5 mg/L in male and female rats (Dulbey, 1992).

Therefore, respiratory absorption of Pentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acids is considered not to be higher than absorption through the intestinal epithelium.

Overall, a systemic bioavailability of Pentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acids in humans is considered possible after inhalation but is not expected to be higher than following oral exposure.

Accumulation

Generally highly lipophilic substances tend to concentrate in adipose tissue, and depending on the conditions of exposure may accumulate. Although there is no direct correlation between the lipophilicity of a substance and its biological half-life, it is generally the case that substances with high log Pow values have long biological half-lives. The high log Pow of 6.74 - > 10 implies that Pentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acids may have the potential to accumulate in adipose tissue (ECHA, 2012).

However, as absorption of Pentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acids is considered to be very low, the potential of bioaccumulation is very low as well.

Nevertheless, as further described in the section metabolism below, Pentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acids will undergo to slow esterase-catalyzed hydrolysis, leading to the cleavage products pentaerythritol and fatty acids.

The log Pow of the first cleavage product pentaerythritol is < 0.3 and it is highly soluble in water (25 g/L) (OECD SIDS, 1998). Consequently, there is no potential for pentaerythritol to accumulate in adipose tissue. The other cleavage products, the fatty acids, can be stored as triglycerides in adipose tissue depots or be incorporated into cell membranes. At the same time, fatty acids are also required as a source of energy. Thus, stored fatty acids underlie a continuous turnover as they are permanently metabolized and excreted. Bioaccumulation of fatty acids only takes place, if their intake exceeds the caloric requirements of the organism.

Overall, the available information indicates that no significant bioaccumulation in adipose tissue of the parent substance and cleavage products is anticipated.

Distribution

Distribution within the body through the circulatory system depends on the molecular weight, the lipophilic character and water solubility of a substance. In general, the smaller the molecule, the wider is the distribution. If the molecule is lipophilic, it is likely to distribute into cells and the intracellular concentration may be higher than extracellular concentration particularly in fatty tissues (ECHA, 2012)

Furthermore, the concentration of a substance in blood or plasma and subsequently its distribution is dependent on the rates of absorption.

As discussed above, absorption ofPentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acidsis considered very low based on its physicochemical characterisation as poor water solubility and high molecular weight.

Nevertheless, esters of pentaerythritol and fatty acids will undergo chemical changes as a result of slow enzymatic hydrolysis, leading to the cleavage products pentaerythritol and the different fatty acids.

The fatty acids are also distributed in the organism and can be taken up by different tissues. They can be stored as triglycerides in adipose tissue depots or they can be incorporated into cell membranes (Masoro, 1977).

Overall, the available information indicates that the cleavage products, pentaerythritol and fatty acids can be distributed in the organism.

Metabolism

On the basis of the properties of the test substance a very low absorption of Pentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acids is anticipated.

As discussed above, hydrolysis of an esterified alcohol with more than three ester groups is assumed to be slow. In in-vivo studies in rats, a decrease in absorption was observed with an increasing esterification grade. For example, for pentaerythritol tetraoleate an absorption rate of 64% and 90% was observed, when ingested at 25% and 10% of dietary fat, respectively, while an absorption rate of 100% was observed for glycerol trioleate when ingested at 100% of dietary fat (Mattson and Nolen, 1972). In addition, it has been shown in-vitro that the hydrolysis rate of pentaerythritol tetraoleate was about 2000 times lower when compared with the hydrolysis rate of the triglyceride Glycerol trioleate (Mattson and Volpenhein, 1972a).

Esters of fatty acids are hydrolysed to the corresponding alcohol and fatty acid by esterases (Fukami and Yokoi, 2012). Depending on the route of exposure, esterase-catalysed hydrolysis takes place at different places in the organism: after oral ingestion, esters of alcohols and fatty acids undergo enzymatic hydrolysis already in the gastro-intestinal fluids. In contrast, substances which are absorbed through the pulmonary alveolar membrane or through the skin enter the systemic circulation unchanged before entering the liver where hydrolysis will basically take place. Pentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acids will be hydrolysed to pentaerythritol and fatty acids, even though it was shown in-vitro that the hydrolysis rate of PE esters was lower when compared with the hydrolysis rate of the triglyceride Glycerol trioleate (Mattson and Volpenhein, 1972a).

The first cleavage products, Fatty acids, are stepwise metabolized by beta-oxidation, following the same pattern as other odd carbon number, straight-chain, aliphatic acids (Bingham et al 2001; HSDB, 2013). The metabolism of the uneven fatty acids results in carbon dioxide and an activated C3-unit, which undergoes a conversion into succinyl-CoA before entering the citric acid cycle (Stryer, 1996). The second cleavage product, pentaerythritol, is absorbed rapidly but excreted unchanged. DiCarlo et al. (1965) reported that C14-labeled PE, orally administered at 10 mg/kg to mice, was absorbed to 50% from the gastrointestinal tract within 15 minutes. 68% of the dose appeared as unchanged PE in the urine and faeces after 4 hours.

Excretion

On the basis of the low absorption of the test substance Pentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acids is expected to be excreted via faeces.

However based on the hydrolysis described above, fatty acids and pentaerythritol as breakdown products will occur in the body. The fatty acid components will be metabolized for energy generation, stored as lipids in adipose tissue or used for further physiological properties e.g. incorporation into cell membranes (Lehninger, 1970; Stryer, 1996). Therefore, the fatty acid components are not expected to be excreted to a significant degree via the urine or faeces but excreted via exhaled air as CO2 or stored. The other cleavage product, pentaerythritol is not metabolized but excreted unchanged via urine. 10 mg/kg C14-labled PE orally administered to mice was absorbed from the gastrointestinal tract to almost 50% within 15 minutes. 68% of the dose was excreted via urine and faeces after 4 hours (DiCarlo et al., 1965). The amount found in faeces was assumed to arise from contamination with urine due to the setup of the metabolic cages. Additionally, Kutscher (1948) found 85-87% of unaltered PE in the urine of humans ingesting a radiolabeled PE.

A detailed reference list is provided in the technical dossier (see IUCLID, section 13) and within CSR.