Whales, lifespan, phospholipids, and cataracts

Abstract

This study addresses the question: why do rats get cataracts at 2 years, dogs at 8 years, and whales do not develop cataracts for 200 years? Whale lens lipid phase transitions were compared with the phase transitions of other species that were recalculated. The major phospholipids of the whale lens were sphingolipids, mostly dihydrosphingomyelins with an average molar cholesterol/phospholipid ratio of 10. There was a linear correlation between the percentage of lens sphingolipid and lens lipid hydrocarbon chain order until about 60% sphingolipid. The percentage of lens sphingolipid correlated with the lens lipid phase transition temperature. The lifespan of the bowhead whale was the longest of the species measured and the percentage of whale lens sphingolipid fit well in the correlation between the percentage of lens sphingolipid and lifespan for many species. In conclusion, bowhead whale lens membranes have a high sphingolipid content that confers resistance to oxidation, allowing these lenses to stay clear relatively longer than many other species. The strong correlation between sphingolipid and lifespan may form a basis for future studies, which are needed because correlations do not infer cause. One could hope that if human lenses could be made to have a lipid composition similar to whales, like the bowhead, humans would not develop age-related cataracts for over 100 years.

Keywords: Balaena mysticetus; Cetacean; bowhead whale; lens; lipids.

Fig. 1.

³¹P-NMR spectra of phospholipids extracted from bowhead whale lenses. Spectra were used to quantify the phospholipid composition in Table 1. Pool (i), whale C (ii), whale A plus SM standard (iii), whale A (iv), Whale B (v). DHSM, dihydrosphpningomyelin; PEe, phosphatidylethanolamine ether; PSe, phosphatidylserine ether; PCe, PC ether.

Fig. 2.

¹H-NMR spectra of lipids extracted from bowhead whale lenses. The spectra were used to quantify the molar cholesterol/phospholipid ratios of the extracts. Phospholipid was quantified from the amide NH resonances near 6.81 and 6.22 ppm (B) assigned to hydrated and partially hydrated sphingolipid, respectively, and the resonance near 3.48 ppm (A) assigned to the choline head group N-CH₂ moiety. Cholesterol was quantified from the CH₃ resonance near 0.67 ppm (C) assigned to carbon 18 and the CH resonance near 1.83 ppm (D) assigned to carbons 1, 2, and 16 of the cholesterol molecule.

Fig. 3.

Fourier transform infrared spectra of: bowhead whale lens lipid extract (i), bovine brain SM (ii), and cholesterol (iii). A: CH₂, OH, and amide A stretching region. B: Fingerprint region.

Fig. 4.

Lipid phase transition of aqueous suspensions of bowhead whale lens lipids. Whale A (black circle), whale B (gray square), whale C (gray triangle), curve fit of all data to a four parameter sigmoidal curve (solid black line). Data from the fit are presented in Table 3. An increase in the stretching frequency is associated with an increase in hydrocarbon chain trans rotomers, disorder, and fluidity.

Fig. 5.

A, B: Lipid phase transition parameters from Tables 3 and 4 and phospholipid composition data from (35) and the current study. C, D: Lifespan versus lipid phase transition parameters from Tables 3 and 4 and (35). Curve fitting (solid black line): hyperbola, single rectangular, two parameter (A); line (B); and four parameter logistic curve (C, D).

Fig. 6.

Relationship between bowhead whale lens dihydrosphingomyelin content and estimated age. From Table 1. Linear curve fit, 3rd order (r = 1) (solid black line).

Fig. 7.

External eye anatomy of the bowhead whale showing a small palpebral fissure, thick and fleshy palpebra with a thick overlaying epidermis that protects the bowhead whales’ eyes from the extreme arctic environmental conditions allowing them to maintain vision for their long, up to 200 year life. (Photo credit: North Slope Borough, Department of Wildlife Management, Utqiagvik, AK).