2,6,10,15,19,23-hexamethyltetracosa-2,6,10,14,18,22-hexaene

Endpoint summary

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Additional information

Animal studies indicate that Squalane is slowly absorbed through the skin, while both compounds squalane and squalene, are poorly absorbed from the gastrointestinal tract. Squalene is a metabolic precursor of cholesterol and other steroids

Tritiated Squalane was tested for percutaneous absorption on normal and denuded skin of mice. Over a period of 60 minutes, the average

quantity absorbed through the normal skin of 12 mice was 0.12 nmol/cm2/min (3.05 ug/cm2) with a standard error of the mean of 0.94 ug/cm2. Over 120 minutes, the average quantity absorbed through the normal skin of five mice was 0.103 nmol/cm2/min (5.25 ) with a standard error of the mean of 1.65 ug/cm2. On the denuded skin of nine mice, the average rate of absorption was 0.148 nmol/cm2/min (3.75 ug/cm2) over 60 minutes with a

standard error of the mean of 1.2 ug/cm2 . To account for the slight percutaneous absorption, the authors concluded that the main barrier to

penetration of Squalane resulted from failure to be removed from the dermis via circulation. ^[1]

Using an autoradiographic technique, Wepierre^[2] showed that tritiated Squalene is able to penetrate mouse skin and migrate via hair follicles into the sebaceous glands. It was found that the compound is not systemically absorbed even when the epidermal barrier is removed

When it was orally administered in bulk as a solution in corn oil, or fed as a mixture with the standard diet wafer, Squalane was not absorbed from the gastrointestinal tract of rats. Ninety-six to 100% of the Squalane administered to both fed and fasted animals was recovered in the feces collected over a four-day period. Squalane was not detected in the 72-hour urine of 400 g rats given 85 mg doses by stomach tube. Bile collected for eight hours and lymph collected for five hours after administration contained no detectable amounts of Squalane. Seventy-two hours after administration of Squalane, only 120 +/-10 ug (14% of the dose) was recovered from extracts of the gastrointestinal tract^{[3][4 ]}

Two male subjects were given 1 g Squalene per day for 14 days, while a third male subject received similar doses of cholesterol. Each test substance was mixed with 5 g of butter and eaten with bread. Sebum from the three subjects' backs was then collected and its Squalene content was determined. The Squalene content of sebum did not change significantly upon the ingestion of either Squalene or cholesterol. The mean values (with standard deviations) for the percent of Squalene in sebum were 7.8 +/-0.9 and 8.0 +/- 1.1, respectively, for the periods before and during administration of cholesterol. The corresponding percentage for the two subjects who ingested Squalene were 7.4 +/- 1.5 before and 8.1 +/- 6 during Squalene administration for one subject; and 7.4 +/- 1.9 before and 7.2 +/- 1.4 during Squalene administration for the second subject. Both subjects receiving Squalene showed a marked fall in the Squalene content of sebum, just before the first test dose; however, according to the authors, this may have been after applying Squalene that contained 1 .O% 3-methylcholanthracene or 1 .O% menthyl anthranilate to the shaved backs of rats, biopsies of the skin were taken at intervals, fixed, frozen, and sectioned. Subsequent fluorescent microscopy gave no evidence that the materials were absorbed.^[5]

Oral ingestion of Squalene by rats failed to potentiate adrenocorticotropin because the material was poorly absorbed from the gut ^[6][7]

Four drops of 30% Squalene in acetone were applied daily for five or 14 days, or three times weekly for three weeks to the backs of mice less than 50 days old; this caused an increase in the concentration of both D7-cholestenol and cholesterol in the epidermis. The relative increase of D'-cholestenol in the skin was 18.4% for control of mice and 36.9% for treated mice. Application of Squalene to mice aged 50 days or more caused no consistent change in the concentration of D'-cholestenol, although in some instances the concentration of cholesterol appeared to increase.[8]

(The hair cycle of mice was not considered. The latter is known to influence appreciably the absorption of chemicals.) Mice were fed a purified ration containing 1 % Squalene for one or two days. In addition, rats were either fasted for one day and then fed the 1% Squalene ratio for two days, or fed 1% Squalene for one day without having been fasted. This dietary Squalene caused no increase in the concentration of D7-cholestenol in the livers of the tested rats and mice.^{[8 ]}

Rats fed Squalene in amounts equivalent to 1 % of the diet for 21 days showed a 50% increase in liver sterols and a 33% increase in fecal sterols, though there was no change in the carcass sterols. The sum of liver and fecal sterol increases equalled approximately one-eighth of the Squalene that had been administered.^[9]

Vitamin A deficient rats fed beta-carotene with either 10 or 50 mg of Squalene for 12-14 days showed a marked reduction in the vitamin A content of the liver and kidneys. When vitamin A instead of beta-carotene was fed with Squalene, the vitamin A content of the organs was unaffected; thus Squalene does not interfere with the utilization of vitamin A, but rather with that of beta-carotene, the vitamin A percursor. ^{[10 ]}

Matschner et al.^[11] reported that dietary Squalene inhibits vitamin K absorption in the rat. A vitamin K-deficient diet of the following composition (given in percentages) was fed for two weeks to individually caged adult male rats: casein, 21; corn starch, 43; glucose monohydrate, 27; corn oil, 5; and a supplement of vitamins and minerals. Other rats were fed a diet that was the same as this one, except that added to it was either (a) 0.5% Squalene; (b) Squalene (0.5%) plus vitamin K (0.25 ug/g of diet); or (c) vitamin K (0.25 ug/g of diet). Feces were collected daily and assayed for vitamin K. As shown in Table 4, rats fed the basal diet alone for two weeks excreted 141 5 ug of vitamin K. Rats fed the diet containing 0.5% Squalene had a fecal vitamin K content of 1095 ug. When both vitamin K and Squalane were added to the diet, the rats excreted 560 ug of the 700 ug ingested, When a similar amount (600 ug) was fed in the diet to which vitamin K alone had been added, only 155 ug of the vitamin was recovered. According to the authors, “These data support a mechanism of interrupted absorption and possible diminished bacterial synthesis of vitamin K for the action of dietary Squalene.”

It is known that Squalene, a normal constituent of the liver of most higher animals, is synthesized by animal tissues from acetate, and that it can serve as a direct precursor of cholesterol both in vivo and in vitro. In the biogenesis of cholesterol, acetate is converted to mevalonic acid, mevalonic acid is converted to Squalene, Squalene is cyclized to lanosterol, which, in turn, is converted to

cholesterol

Hamsters fed a gallstone-producing diet with 1 % added Squalene for 42-44 days showed complete protection against the formation of gallstones. The authors suggested this may have been due to the inhibition of biosynthesis of cholesterol in the liver.^[12] This does not appear to be consistent with the work of Bloch,^[13] according to which it is “virtually certain that Squalene is an obligatory intermediate in sterol biogenesis.”

McGuire and Lipsky ,^[14] confirmed Bloch’s earlier findings that both Squalene and cholesterol inhibited the bioconversion of acetate to cholesterol, postulate the following explanation for this paradox. “Squalene, by causing a ’piling up’ of hepatic cholesterol may therefore evoke a homeostatic reduction in cholesterol synthesis from all sources” (feedback inhibition).

Evidence for the in-vivo metabolic conversion of Squalene to glucocorticoids was developed in hypophysectomized male rats given suboptimal injections of ACTH. The resulting increases in adrenal weight and decreases in thymus weight were enhanced when Squalene was injected subcutaneously as little as 24 hours prior to ACTH injection. Squalene alone did not produce statistically significant changes in the organ weights. Orally administered Squalene was not effective. According to the author, these data are consistent with the idea that exogenous Squalene could serve as a ready precursor of glucocorticoids in vivo, and that it may be a potential intermediate in steroid biogenesis.^[15][16] cholesterol.

Rabbits were injected subcutaneously with Squalene twice a day for up to 12 days. In the body of animals, the test material was oxidized to succinic and laevulinic acids. Urine samples showed succinic acid, along with small amounts of benzoic and hippuric acids. In animals sacrificed either four hours or 90 days after the last injection, there were considerable amounts of stored Squalene in liver, muscle, and skin ^[17]

In a study with human subjects, a direct relationship was found between plasma levels of Squalene and triglycerides, but not between the levels of Squalene and cholesterol. Levels of Squalene in plasma rose with increased dietary Squalene and varied directly with the cholesterol synthesis rate. That large amounts of Squalene excreted in skin surface lipids was thought to reflect de novo synthesis in the skin rather than transference from the plasma. Small amounts were excreted in the urine and feces. ^[18]

If ingested, approximately 20% of squalene is cyclized into sterols and ejected back into the gut without being effectively taken up into systemic circulation.^[19][20]Despite this, approximately 60-85% of orally ingested squalene is distributed to body tissues.^[21][22]

References

[1]WEPIERRE, I., COHEN, Y., and VALETTE,G. (1968).Percutaneous absorption and removal by the body fluids of¹⁴C p-cymene. Eur. J. Pharmacol.3(1), 47-51.

[2]WEPIERRE, J.(1967).Impermeability of mouse skin to tritiated perhydrosqualene. Ann. Pharm. Fr.25(7-8), 515-21 

[3]ALBRO, P.W. and FISHBEIN, L.(1970).Absorption of aliphatic hydrocarbons by rats. Biochem. Biophys. Acta219, 437-46 

[4]ALBRO, P.W. and THOMAS, R.(1974).Intestinal absorption of hexachlorobenzene and hexachlorocyclohexane isomers in rats. Bull. Environ. Contam. Toxicol.12(3), 289-94 

[5]BOUGHTON, B., HODGSON-JONES, 1.5, MACKENNA, R.M.B., WHEATLEY, V.R., and WORMALL, A.(1955).Some observations on the nature, origin, and possible function of the squalene and other hydrocarbons of human sebum. J. Invest. Dermatol.24(3), 179-89 

[6]KLINE, I.T.(1957).Potentiation by squalene of adrenal and thymic responses to corticotropin. Endocrinology61, 85-92 

[7]KLINE, I.T.(1958).Studies on squalene potentiation of thymic response to corticotropin. Endocrinology63, 335-44. 

[8]KANDUTSCH, A.A. and BAUMANN, C.A.(1955).Skin sterols. IX. Effect of squaleneonthe sterols of mouse skin. Arch. Biochem. Biophys.56(2), 356-62 

[9]CANNON, H.J. and TRISTRAM, G.R.(1937).XCVIII. The effect of the administration of squalene and other hydrocarbons on cholesterol metabolism in the rat. Biochem. J.31, 738-47. 

[10]HIGH, E.G. and DAY, H.G.(1951).Effects of different amounts of lutein, squalene, phytol, and related substances on the utilization of carotene and vitamin A for storage and growth in the rat. J. Nutr.43(2), 245-260 

[11]MATSCHINER, J.T., AMELOTTI, J.M., and DOISY, JR., E.A.(1967).Mechanism of the effect of retinoic acid and squalene on vitamin K deficiency in the rat. J. Nutr.91(Pt.11,303-6. 

[12]SONDERGAARD, E., PRANCE, I., and DAM, H.(1974).Alimentary production of gallstones in hamsters.28.Influence of isornerized squalene of gallstone production. Z. Ernaechrungswiss13(4), 237-41 

[13]BLOCH, K.(1959).Biogenesis and transformation of squalene. Ciba Found. Symp., Biosynthesis of Terpenes and Sterols1958, 4-19 

[14]MCGUIRE, JR., J.S. and LIPSKY, S.R.(1955).The effects of squalene on the incorporation of acetate into plasma cholesterol in man.J.Clin. Invest.34(5), 704-10 

[15]BUTCHER, E.O.(1953).The penetration of fat and fatty acids into the skin of the rat. J. Invest. Dermatol.21, 43-8 

[16]KLINE, I.T.(1958).Studies on squalene potentiation of thymic response to corticotropin. Endocrinology63, 335-44. 

[17]YAMASAKI,S. (1950).On the fate of squalene in the animal body. J. Biochem.37(1),99-10 

[18] LIU, G.C.K., AHRENS, JR., E.H., SCREIBMAN, P.H., and CROUSE, J.R. (1976). Measurement of squalene in human tissues and plasma: validation and application. J. Lipid Res. 17(1), 38 -45

[19]Tilvis RS, Miettinen TA.Absorption and metabolic fate of dietary 3H-squalene in the rat.Lipids. (1983)

[20]Strandberg TE.Sterol synthesis from biliary squalene in the jejunal mucosa of the rat in vivo.Lipids. (1983)

[21]Serum concentration and metabolism of cholesterol during rapeseed oil and squalene feeding

[22]Gylling H, Miettinen TA.Postabsorptive metabolism of dietary squalene.Atherosclerosis. (1994)