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Omega-3 and Macular Pigment Accumulation
C H A P T E R
26
Omega-3 and Macular Pigment Accumulation: Results from the Pimavosa Study Marie-Noëlle Delyfer1,2,3, Benjamin Buaud4, Jean-François Korobelnik1,2,3, Marie-Bénédicte Rougier3, Carole Vaysse4, Nicole Combe4, Cécile Delcourt1,2 1Universite
de Bordeaux, Bordeaux, France, 2Inserm, ISPED, Centre INSERM U897-Epidemiologie-Biostatistique, Bordeaux, France, 3Service d’Ophtalmologie, CHU de Bordeaux, Bordeaux, France, 4ITERG – Equipe Nutrition Métabolisme & Santé, Bordeaux, France
The characterization of macular pigment (MP) has taken more than 200 years. Yet, its precise pathophysiologic properties remain elusive. The existence of a macular central yellow spot was first observed on postmortem histologic sections by Buzzi in 1782.1 Decades later, in vivo observation of the macular area using Hermann von Helmholtz’s ophthalmoscope (1851) enabled scientists to determine that this yellow spot was due to the presence of a macular yellow pigment. In 1945, Wald demonstrated that MP absorbs wavelengths between 430 and 490 nm, with a maximum absorption at 465 nm, and that MP contains carotenoids belonging to the xanthophyll family.2,3 Xanthophylls are a class of oxygen-containing carotenoid pigments,4 responsible for the color of many of the yellow, orange, and red hues of flowers, fruits, vegetables (corn, pepper, etc.), egg yolks, and feathers, shells, or flesh of many animal species (flamingo, canary, shrimp, lobster, chicken, or salmonids).5 In plants, they are involved in photosynthesis with chlorophyll and are responsible for the red, yellow, and/or brown colors of autumn foliage as the chlorophyll levels decline. Approximately 600 different carotenoids have been characterized to date.6 However, in 1985, Bone demonstrated that, in the retina, macular xanthophylls that compose MP are specifically restricted to two – lutein (L) and its structural isomer zeaxanthin (Z).7 Anatomically, L and Z are concentrated in the Henle fiber layer of the macular area8 and display a particular spatial distribution, Z being clearly dominant in the center of the fovea with a Z:L ratio decreasing peripherally.7
Handbook of Nutrition, Diet, and the Eye http://dx.doi.org/10.1016/B978-0-12-401717-7.00026-5
In humans, L and Z exclusively derive from dietary intake.9,10 They are lipid-soluble and their metabolism is, therefore, strongly interlinked with lipids.11,12 High dietary intake of L and Z, or their oral supplementation, is known to result in an increase of their plasma concentrations and, consequently, in their specific accumulation within the macula, in which they form the MP.13–16 The precise mechanism of MP accumulation remains to be determined. It is suspected that it is based on a regulated active transport mechanism, thus explaining a 10,000fold higher concentration in the macula than in the blood. As proposed recently, it may rely on specific carotenoidbinding proteins.17,18 The macular over-concentration of L and Z further implies organ-specific biologic roles. The two main biologic properties suggested include, first, a distinctive blue light-absorbing capability due to the presence of the long chromophore of conjugated double bonds (polyene chain) and, second, an antioxidant capability through reactive oxygen species scavenging (e.g., superoxide anion and hydroxyl radical).11 This last role underpins the growing interest for MP in aging macular diseases, especially in age-related macular degeneration (AMD). Indeed, AMD is the leading cause of blindness in developed countries and represents an increasing burden for public health systems.19–21 AMD is a multifactorial disease that results from the combination of nonmodifiable factors (i.e., genetics, sex, age) and identified modifiable factors (i.e., nutritional and/or smoking status).22 Controlling these modifiable factors may therefore be a way of preventing a significant percentage
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26. OMEGA-3 AND MACULAR PIGMENT ACCUMULATION: RESULTS FROM THE PIMAVOSA STUDY
of AMD cases. Evidence from both epidemiologic and laboratory studies has demonstrated an inverse associ ation between dietary intake of xanthophyll carotenoids –L and Z – and risk of advanced AMD.22–24 In contrast, long-chain polyunsaturated fatty acids (omega-3 LC-PUFAs) – notably docosahexaenoic acid (DHA) – are abundant in the human retina, in which they exert some identified structural, functional, and neuroprotective roles.26,27 DHA reaches its highest concentration in the membranes of photoreceptors and is important in photoreceptor differentiation and survival, as well as in retinal function.26 Omega-3 LC-PUFAs furthermore exhibit anti-inflammatory properties,26 which are of particular interest in AMD, since inflammation appears to play a pivotal role in the pathogenesis of the disease.28 The neuroprotective role of omega-3 LC-PUFAs in AMD has been demonstrated by a number of epidemiologic studies that observed a decreased risk for AMD in subjects with high intakes of omega-3 LC-PUFAs.26,27,29–31 Among other potential mechanisms supporting neuroprotection, it has been suggested that dietary intake of omega-3 LC-PUFAs may favor the retinal accumulation of L and Z and thereby increase MP density.12,13 The PIMAVOSA (PIgment MAculaire chez le VOlontaire SAin, i.e., MP in the healthy volunteer) study is an observational study that was hence initiated to evaluate the inter-relations between MP, plasma L and Z, and plasma omega-3 LC-PUFAs (as well as other fatty acids) in a homogeneous population of healthy volunteers.32 The characteristics of the studied population are detailed in Table 26.1. All of the recruited participants were healthy adults ages 20–60 years and born in a restricted geographic area (i.e., the southwest of France) in order to optimize the homogeneity of nutritional habits. None had any previous ocular history (all being phakic with a visual acuity of 20/24 or greater, without chronic diseases with significant ocular consequences or myopia exceeding 4 diopters). The use of vitamins and/or supplements was systematically checked and recorded (only seven subjects out of the 107 recruited were supplemented). Participants underwent bilateral eye exam including measurement of best-corrected visual acuity, refraction, retinal photographs after pupil dilation, fundus autofluorescence imaging, macular pigment optical density (MPOD) measurements, and fasting blood tests on the same day.32 The choice of the technique to be used for our MPOD measurements was difficult since several techniques can measure MP in vivo. We wanted a method that would be the most i) objective, ii) reproducible, and iii) easy to perform both for participants and technicians. Heterochromatic flicker photometry is classically considered as the ‘gold standard’; however, although rather easy to perform and reliable, it requires cooperation from the subject. Raman spectroscopy is also highly reproducible
but again requires active participation of the subject for the initial setting up of the device. In contrast, imaging techniques offer a means of measuring the spatial distribution of MPOD objectively and easily and require less subject compliance.33,34 They are based on retinal excitation by an incident light and the analysis of the reflected signal obtained (Fig. 26.1). However, absence of nuclear opacities seems important to avoid any bias.35 This was the technique we finally chose for our MPOD measurements, first because it appeared to be the most objective and, second, because MPOD mapping offered the possibility of studying the correlations between MPOD at different degrees of eccentricity from the center of the fovea and our other variables. Quantification of our nutritional variables (i.e., L, Z, and fatty acids) could either have been estimated from food intakes or directly measured from plasma samples. Because of the multiple difficulties of dietary assessment (including memory bias, difficulties in taking into account high complexity and day-to-day variability of the human diet, imprecisions in estimations of quantities of ingested foods and of nutrient content of foods, etc.) and of interindividual variability in nutrient absorption, we deemed it more objective – and potentially more effective – to use plasma measurements. Plasma L and Z measurements were determined by reversed-phase high-performance liquid chromatography. Plasma phospholipid fatty acid measurements not only focused on omega-3 (alfa-linolenic acid and omega-3 LC-PUFAs) but also on omega-6 (linoleic acid (LA) and omega-6 LCPUFAs), monounsaturated, and saturated fatty acids. The first step of our work was a type of ‘internal validation test’ of our measurements in the studied population. Relationships between MP and xanthophylls, indeed, are now well established. MP is composed of two xanthophyll carotenoids, L and Z. Supplementation or high dietary intake of L and Z increase L and Z plasma levels and, in turn, MP density.13–16 We hence checked the association of plasma L and Z with MPOD in our sample. This was confirmed within 1° of eccentricity and beyond, plasma L and Z being considered separately and/or together (Table 26.2, Fig. 26.2A).32 The result was not affected by the exclusion of the seven subjects declaring use of dietary supplements (data not shown). However, MPOD within 0.5° was not found to be significantly correlated with plasma macular xanthophylls. Interindividual variations in the spatial distribution of MPOD at the very center of the macula may explain – at least in part – this lack of correlation.34,36 The identification of the mechanisms underlying the specific macular accumulation of xanthophylls represents a key step toward a better understanding of macular physiology and disease. Among the different determinants of MP concentration under focus, omega-3 LC-PUFAs have been proposed as key factors.12,13
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TABLE 26.1 Characteristics of the Studied Population Total (n = 107) Age (years) Gender (men) Best corrected visual acuity (LogMAR units) MPOD (within 6° of eccentricity, optical density units)
20–39 Years (n = 53)
38.9 ± 12.1 43
28.2 ± 5.9 23
–0.10 ± 0.1 0.2 ± 0.1
40–60 Years (n = 54) 49.3 ± 5.5 20
–0.10 ± 0.09 0.2 ± 0.0
P Value < 0.0001 0.50
–0.09 ± 0.1
0.48
0.2 ± 0.1
0.11
PLASMA PHOSPHOLIPID OMEGA-3 PUFAs (% OF TOTAL FATTY ACIDS) Total
6.9 ± 1.9
6.5 ± 1.8
7.2 ± 1.9
0.05
ALA
0.2 ± 0.1
0.2 ± 0.1
0.2 ± 0.1
0.96
Total
6.7 ± 1.9
6.3 ± 1.8
7.0 ± 1.9
0.05
EPA
1.2 ± 0.7
1.1 ± 0.7
1.4 ± 0.7
0.02
DPA
0.9 ± 0.2
0.9 ± 0.3
1.0 ± 0.2
0.08
DHA
4.5 ± 1.2
4.3 ± 1.3
4.7 ± 1.2
0.18
Omega-3 LC-PUFAs
PLASMA PHOSPHOLIPID OMEGA-6 PUFAs (% OF TOTAL FATTY ACIDS) Total
34.8 ± 2.4
34.9 ± 2.2
34.7 ± 2.5
0.60
Linoleic acid
18.7 ± 2.4
18.5 ± 2.6
18.9 ± 2.2
0.40
15.3 ± 2.1
15.6 ± 1.9
15.0 ± 2.2
0.19
Eicosadienoic acid
0.3 ± 0.1
0.3 ± 0.1
0.3 ± 0.1
0.47
Dihomo-γ-linolenic acid
3.0 ± 0.7
3.1 ± 0.7
2.9 ± 0.7
0.11
Arachidonic acid
12.0 ± 2.0
12.1 ± 2.0
11.8 ± 2.0
0.43
Plasma phospholipid saturated fatty acids (% of total fatty acids)
44.4 ± 1.2
44.3 ± 1.3
44.5 ± 1.1
0.35
Plasma phospholipid monounsaturated fatty acids (% of total fatty acids)
13.0 ± 1.4
13.4 ± 1.3
12.7 ± 1.4
0.01
150.1 ± 58.9
137.8 ± 48.4
161.8 ± 65.8
0.04
Plasma zeaxanthin* (μg/L)
40.9 ± 20.2
40.4 ± 17.5
41.3 ± 22.6
0.83
Plasma lutein + zeaxanthin* (μg/L)
191.1 ± 75.4
178.2 ± 62.4
203.1 ± 84.8
0.10
Omega-6 LC-PUFAs Total
PLASMA XANTHOPHYLLS* Plasma lutein* (μg/L)
Data are the mean ± standard deviation; n = 107 unless specified otherwise. ALA: alfa-linolenic acid; DHA: docosahexaenoic acid; DPA: docosapentaenoic acid; EPA: eicosapentaenoic acid; LC-PUFA: long-chain polyunsaturated fatty acid; MPOD: macular pigment optical density; PUFA: polyunsaturated fatty acid; * = due to technical failure, L and Z plasma measurements were available only in 99 subjects. Reprinted from Delyfer et al., Invest Ophthalmol Vis Sci. 53:1204–1210, with permission.
Omega-3 PUFAs include a precursor (ALA) and three long-chain derivatives (eicosapentaenoic acid (EPA, 20:5 omega-3), docosapentaenoic acid (DPA; 22:5 omega-3), and DHA (22:6 omega-3)]. ALA is an essential nutrient, since humans cannot synthesize it de novo and, therefore, rely on diet as its sole source (mainly from vegetables and vegetable oils). Synthesis of the long-chain derivatives is very limited in humans,37 who must, therefore, also rely
on their dietary supply, mainly through fish and seafood. In the PIMAVOSA study, the analysis of the fatty acid composition of total plasma phospholipids was used as a valid biomarker of LC-PUFA dietary intakes.38 As shown in Table 26.3, high plasma levels of total omega-3 PUFAs were associated with high MPOD (Table 26.3).32 This was even more marked when considering total omega-3 LC-PUFAs only (Table 26.3, Fig. 26.2B). The mechanisms
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26. OMEGA-3 AND MACULAR PIGMENT ACCUMULATION: RESULTS FROM THE PIMAVOSA STUDY
(A)
(B)
(C)
(D)
FIGURE 26.1 Macular pigment optical density (MPOD) measurements with the modified confocal scanning laser ophthalmoscope (mpHRA; Heidelberg Engineering, Heidelberg, Germany) using autofluorescence images obtained at two wavelengths: 488 nm (A) and 514 nm (B), with a high-pass filter transmitting at a wavelength greater than 530 nm. MPOD was quantified by calculating a MPOD map (C) and comparing foveal and parafoveal autofluorescence at 488 nm and 514 nm. Density maps were processed to estimate MPOD within a circle centered on the fovea at different degrees of eccentricities (0.5°, 1°, 2°, and 6°), using the software provided by the manufacturer of the device (D).
TABLE 26.2 Correlation of Macular Pigment Optical Density (MPOD) with Plasma Lutein and Zeaxanthin Levels (n = 99) MPOD within 0.5°
MPOD within 1°
MPOD within 2°
MPOD within 6°
Lutein + zeaxanthin
0.16 (0.1)
0.26 (0.01)*
0.33 (0.001)*
0.36 (0.0005)*
Lutein
0.16 (0.1)
0.24 (0.01)*
0.32 (0.001)*
0.35 (0.0006)*
Zeaxanthin
0.15 (0.1)
0.24 (0.02)*
0.29 (0.005)*
0.30 (0.003)*
Results are expressed as ‘r (p)’, r being the correlation coefficient and p the P value. *indicates significance. MPOD: macular pigment optical density. Reprinted from Delyfer et al., Invest Ophthalmol Vis Sci. 53:1204–10, with permission.
through which omega-3 LC-PUFAs correlate with MPOD remain to be determined. A first hypothesis could be that omega-3 LC-PUFAs may act as a modulator of L and Z gastrointestinal uptake. However, such a mechanism would have implied a correlation between plasma levels of omega-3 LC-PUFAs and xanthophyll carotenoids, which was not observed (Table 26.4).32 A second hypothesis could be that omega-3 LC-PUFAs influence L and Z carriage by lipoproteins.39 An increase of high-density lipoprotein (HDL) and low-density lipoprotein (LDL) subfractions has indeed been observed after omega-3
LC-PUFA supplementation.40–42 Finally, omega-3 LCPUFAs may favor L and Z concentration within the macular area through an influence on xanthophyll-binding proteins.17 When the different omega-3 LC-PUFAs were detailed, we observed that EPA and DPA both correlated significantly with MPOD, while, surprisingly, DHA did not (Table 26.3).32 DHA is the major LC-PUFA in structural lipids of the human retina, accounting for about 30% of total retinal fatty acids. DHA is an essential structural component of retinal membranes and exhibits several
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OMEGA-3 AND MACULAR PIGMENT ACCUMULATION: RESULTS FROM THE PIMAVOSA STUDY
(B)
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
MPOD
MPOD
(A)
(µg/L) 0
100
200
300
400
500
600
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
(% of total fatty acids) 2
0
4
L+Z
MPOD
MPOD (% of total fatty acids) 0
0.5
1
1.5
2
2.5
3
3.5
4
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
(% of total fatty acids) 0.2
0
0.4
0.5
0.8
1
1.2
1.4
1.6
DPA
(F)
MPOD
(E)
MPOD
14
(D)
EPA
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
12
Total omega-3 LC-PUFAs
(C) 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
10
8
6
(% of total fatty acids) 0
0.1
0.2
0.3
0.4
0.5
0.6
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
(% of total fatty acids) 0
0.5
eicosadienoic acid
1
1.5
2
2.5
3
3.5
4
4.5
5
DGLA
FIGURE 26.2 Scatter plots depicting the correlations between macular pigment optical density (MPOD) at 1° of eccentricity with (A) lutein and zeaxanthin (L + Z); with (B) total omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs); with (C) EPA (eicosapentaenoic acid); with (D) DPA (docosapentaenoic acid); with (E) eicosadienoic acid; and with (F) DGLA (dihomo-γ-linolenic acid). Note that the associations are not driven by isolated cases. Reprinted from Delyfer et al., Invest Ophthalmol Vis Sci. 53:1204–10, with permission.32
essential neuroprotective properties.26 The lack of correlation we observed between plasma DHA level and MPOD is not sufficient to assess the importance of DHA in MP accumulation. Nevertheless, the absence of correlation between DHA and MPOD seems corroborated by a previous study showing that DHA supplementation did not induce a significant increase of total MPOD values,12 although it may influence MPOD distribution. EPA, the other major dietary omega-3 LC-PUFA present in plasma, is poorly accreted to the retina, as it is quickly converted to DHA or eicosanoid biosynthesis. EPA undergoes oxidative metabolism by cyclooxygenases and lipoxygenases to produce eicosanoids
with vasoregulatory and anti-inflammatory properties.26 Contrary to DHA, a significant positive relationship was observed between plasma EPA level and MPOD (Table 26.3, Fig. 26.2C).32 The positive correlation was even more significant with DPA (Table 26.3, Fig. 26.2D).32 DPA is a metabolic intermediary between EPA and DHA and the second most abundant omega-3 LC-PUFA found within the retina after DHA, its endogenous level being around one-tenth that of DHA in the retinal lipids.43 The precise functions of DPA have not been identified yet. DPA appears to be the precursor of omega-3 very long-chain polyunsaturated fatty acids (VLC-PUFAs) not found in normal human diet, and
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TABLE 26.3 Correlation of Macular Pigment Optical Density (MPOD) with Plasma Phospholipid Omega-3 PUFA Levels and Other Plasma Phospholipid Fatty Acids (n = 107) MPOD within 0.5°
MPOD within 1°
MPOD within 2°
MPOD within 6°
0.19 (0.04)* 0.0035 (0.97)
0.21 (0.03)* -0.0011 (0.99)
0.20 (0.04)* -0.00074 (0.99)
0.22 (0.02)* 0.0016 (0.98)
Total
0.20 (0.04)*
0.22 (0.02)*
0.20 (0.04)*
0.22 (0.02)*
EPA
0.18 (0.06)
0.21 (0.04)*
0.20 (0.04)*
0.21 (0.03)*
DPA
0.33 (0.0006)*
0.32 (0.0007)*
0.30 (0.002)*
0.31 (0.001)*
DHA
0.13 (0.18)
0.14 (0.16)
0.12 (0.23)
0.14 (0.14)
Saturated fatty acids
–0.15 (0.1)
–0.11 (0.2)
–0.11 (0.3)
–0.12 (0.2)
Monounsaturated fatty acids
–0.04 (0.7)
–0.09 (0.3)
–0.08 (0.4)
–0.06 (0.5)
Total
–0.07 (0.5)
–0.064 (0.5)
–0.076 (0.5)
–0.092 (0.3)
Linoleic acid
0.02 (0.8)
0.014 (0.9)
0.0088 (0.9)
–0.027 (0.8)
Total
–0.07 (0.5)
–0.064 (0.5)
–0.076 (0.5)
–0.092 (0.3)
Eicosadienoic acid
–0.30 (0.001)*
–0.24 (0.008)*
–0.22 (0.02)*
–0.21 (0.03)*
Dihomo-γ-linolenic acid
–0.21 (0.03)*
–0.20 (0.04)*
–0.19 (0.05)*
–0.19 (0.05)*
Arachidonic acid
0.02 (0.8)
0.022 (0.8)
0.0083 (0.9)
0.0075 (0.9)
OMEGA-3 PUFAs Total ALA OMEGA-3 LC-PUFAs
OTHER FATTY ACIDS
OMEGA-6 PUFAs
Omega-6 LC-PUFAs
Results are expressed as ‘r (p)’, r being the correlation coefficient and p the P value. *Indicates significance. ALA: alfa-linolenic acid; DHA: docosahexaenoic acid; DPA: docosapentaenoic acid; EPA: eicosapentaenoic acid; LC-PUFAs: long-chain polyunsaturated fatty acids; PUFA: polyunsaturated fatty acid. Reprinted from Delyfer et al., Invest Ophthalmol Vis Sci. 53:1204–10, with permission.
especially of 24:5 omega-3, the most abundant omega-3 VLC-PUFA in the retina.43 These omega-3 VLC-PUFAs are present in restricted mammalian organs, that is, retina, brain, testes, and thymus. Although identified early, their precise role has not been elucidated due to their great length and minor abundance, which makes them very difficult to analyze. The synthesis of 24:5 omega-3 VLC-PUFA, however, is an important metabolic step in the retina because 24:5 omega-3 plays a central role as a metabolic precursor in the synthesis of other omega-3 VLC-PUFAs and is an obligatory intermediate in the synthesis of DHA.44 Moreover, alterations in omega-3 VLC-PUFA biosynthesis have been shown to result in macular alteration. In particular, defect in the elongation of the very long-chain fatty acids 4 (ELOVL4) gene is associated with dominant Stargardt macular dystrophy.45 Recently, a decrease of DPA, DHA, and some omega-3 VLC-PUFAs (notably 24:5 omega-3) was observed in early and intermediate AMD retinas as compared with age-matched controls,43 suggesting a retinal vulnerability associated with a decreased level of omega-3 LC-PUFAs and VLC-PUFAs.
Analysis of correlations between MPOD and fatty acids was further continued with plasma phospholipid monounsaturated, saturated, and omega-6 fatty acids (Table 26.3).32 Neither saturated nor monounsaturated fatty acids were found to be associated with MPOD. Interest in omega-6 fatty acids has increased, since imbalance between omega-6 and omega-3 LC-PUFAs has emerged as a potential risk factor of AMD.43,46 Our results concerning omega-6 were heterogeneous. Total plasma phospholipid omega-6 LC-PUFAs did not display any association with MPOD measurements (Table 26.3). However, when the different omega-6 were detailed, we observed that two minor omega-6 LC-PUFAs (i.e., eicosadienoic acid (20:2 omega-6) and dihomo-γ-linolenic acid (DGLA; 20:3 omega-6)), exhibited a negative relationship with MPOD (Table 26.3, Fig. 26.2E and 2F). In plasma, DGLA is almost exclusively localized in phospholipids and represents about 20% of omega-6 LC-PUFAs. In the retina, DGLA accounts for less than 2.5% of total retinal fatty acids. DGLA has been reported to have notable anti-inflammatory properties.47 Regarding eicosadienoic acid (20:2
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References
TABLE 26.4 Correlation of Plasma Carotenoids with Plasma Phospholipid Omega-3 PUFAs (n = 99) Lutein + Zeaxanthin
Lutein
Zeaxanthin
Total omega-3 PUFAs
0.14 (0.2)
0.15 (0.1)
0.07 (0.5)
ALA
0.03 (0.8)
0.008 (0.9)
0.05 (0.6)
OMEGA-3 LC-PUFAS Total
0.14 (0.2)
0.15 (0.1)
0.06 (0.5)
EPA
0.15 (0.1)
0.16 (0.1)
0.09 (0.4)
DPA
0.08 (0.4)
0.12 (0.2)
-0.06 (0.6)
DHA
0.08 (0.4)
0.09 (0.4)
0.02 (0.8)
Results are expressed as ‘r (p)’, r being the correlation coefficient and p the P value. ALA: alfa-linolenic acid; DHA: docosahexaenoic acid; DPA: docosapentaenoic acid; EPA: eicosapentaenoic acid; LC-PUFA: long-chain polyunsaturated fatty acid; PUFA: polyunsaturated fatty acids. Reprinted from Delyfer et al., Invest Ophthalmol Vis Sci. 53:1204–10, with permission.
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• A mong the different omega-3 PUFAs, DPA has the highest correlation with MPOD, while correlation with EPA is moderate and did not reach statistical significance for DHA. • In contrast, MPOD is not significantly associated with plasma saturated fatty acids or monounsaturated fatty acids or total omega-6 PUFAs. However, MPOD exhibits a negative relationship with two minor omega-6 PUFAs: eicosadienoic acid and dihomo-γ-linolenic acid.
Acknowledgment This study received financial support from Laboratoires Théa (Clermont-Ferrand, France). This sponsor participated in the design of the study but not in the collection, management, statistical analysis, and interpretation of the data, neither in the preparation, review, and approval of the present manuscript. This study received a grant from the Institut Carnot Lisa (Lipids for Industry and Health).
References mega-6), its physiologic role remains unknown. It is a o relatively minor metabolite of LA (18:2 omega-6) found in human plasma and erythrocytes.48 Lately, eicosadienoic acid has been shown to modulate the inflammatory response in vitro.49 Since inflammation is postulated to be involved in AMD pathogenesis, the negative relationship of both plasma DGLA and eicosadienoic acid with MPOD we observed may suggest a reduced risk of AMD by a metabolic utilization of these anti-inflammatory omega-6 LC-PUFAs. The PIMAVOSA study hence demonstrates that MP density is associated not only with plasma L and Z but also with plasma phospholipid omega-3 LC-PUFAs, and more particularly with DPA and EPA.32 MP is further correlated – but negatively – with two omega-6 LC-PUFAs, which may have anti-inflammatory properties. The mechanisms underlying the associations of omega-3 or omega-6 LC-PUFAs with MP remain to be determined. Still, our results suggest that macular xanthophylls and omega-3 LC-PUFAs may act synergistically in the constitution of MP, thereby providing a rationale for combined supplementation in patients at high risk for AMD.
TAKE-HOME MESSAGES • M POD correlates with plasma levels of L and Z. • MPOD is associated positively with total plasma omega-3 polyunsaturated fatty acids (PUFAs). • These results suggest that xanthophylls and omega-3 PUFAs may act synergistically in the constitution of MP.
1. Buzzi F. Nuove sperienze fatte sull’ occhio umano. Opuscoli Scetti Sulle Scienze e Arti 1782;5:87. 2. Wald G. Human vision and the spectrum. Science 1945;101:653–8. 3. Brown PK, Wald G. Visual pigments in human and monkey retinas. Nature 1963;200:37–43. 4. Goodwin TW. The Biochemistry of the Carotenoids. London: Chapman & Hall; 1980. 5. Mangels AR, Holden JM, Beecher GR, Forman MR, Lanza E. Carotenoid content of fruits and vegetables: an evaluation of analytic data. J Am Diet Assoc 1993;93:284–96. 6. Pfander H. Key to Carotenoids. Basel: Birkhauser; 1987. 7. Bone RA, Landrum JT, Tarsis SL. Preliminary identification of the human macular pigment. Vision Res 1985;24:1531–5. 8. Snodderly DM, Auran JD, Delori FC. The macular pigment, II: spatial distribution in primate retinas. Invest Ophthalmol Vis Sci 1984;24:674–85. 9. Snodderly DM, Brown PK, Delori FC, Auran JD. The macular pigment. I. Absorbance spectra, localization, and discrimination from other yellow pigments in primate retinas. Invest Ophthalmol Vis Sci 1984;24:660–73. 10. Bernstein PS, Khachik F, Carvalho LS, Muir GJ, Zhao DY, Katz NB. Identification and quantitation of carotenoids and their metabolites in the tissues of the human eye. Exp Eye Res 2001;72:215–23. 11. Whitehead AJ, Mares JA, Danis RP. Macular pigment: a review of current knowledge. Arch Ophthalmol 2006;124:1038–45. 12. Johnson EJ, Chung HY, Caldarella SM, Snodderly DM. The influence of supplemental lutein and docosahexaenoic acid on serum, lipoproteins, and macular pigmentation. Am J Clin Nutr 2008;87:1521–9. 13. Mares JA, LaRowe TL, Snodderly DM, Moeller SM, Gruber MJ, Klein ML, et al. Predictors of optical density of lutein and zeaxanthin in retinas of older women in the Carotenoids in Age-Related Eye Disease Study, an ancillary study of the Women’s Health Initiative. Am J Clin Nutr 2006;84:1107–22. 14. Kvansakul J, Rodriguez-Carmona M, Edgar DF, Barker FM, Köpcke W, Schalch W, et al. Supplementation with the carotenoids lutein or zeaxanthin improves human visual performance. Ophthalmic Physiol Opt 2006;26:362–71. 15. Richer S, Devenport J, LAST II Lang JC. Differential temporal responses of macular pigment optical density in patients with atrophic
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age-related macular degeneration to dietary supplementation with xanthophylls. Optometry 2007;78:213–9. 16. Trieschmann M, Beatty S, Nolan JM, Hense HW, Heimes B, Austermann U, et al. Changes in macular pigment optical density and serum concentrations of its constituent carotenoids following supplemental lutein and zeaxanthin: the LUNA study. Exp Eye Res 2007;84:718–28. 17. Li B, Vachali P, Bernstein PS. Human ocular carotenoid-binding proteins. Photochem Photobiol Sci 2010;9:1418–24. 18. Li B, Vachali P, Frederick JM, Bernstein PS. Identification of StARD3 as a lutein-binding protein in the macula of the primate retina. Biochemistry 2011;50:2441–9. 19. Klein R, Klein BE, Linton KL. Prevalence of age-related maculopathy: the Beaver Dam Eye Study. Ophthalmology 1992;99:933–43. 20. Mitchell P, Smith W, Attebo K, Wang JJ. Prevalence of age-related maculopathy in Australia: the Blue Mountains Eye Study. Ophthalmology 1995;102:1450–60. 21. Vingerling JR, Dielemans I, Hofman A, Grobbee DE, Hijmering M, Kramer CF, et al. The prevalence of age-related maculopathy in the Rotterdam Study. Ophthalmology 1995;102:205–10. 22. Jager RD, Mieler WF, Miller JW. Age-related macular degeneration. N Engl J Med 2008;358:2606–17. 23. Eye Disease Case-Control Study Group. Antioxidant status and neovascular age-related macular degeneration. Arch Ophthalmol 1993;111:104–9. 24. SanGiovanni JP, Chew EY, Clemons TE, Ferris 3rd FL, Gensler G, Lindblad AS, et al. The relationship of dietary carotenoid and vitamin A, E, and C intake with age-related macular degeneration in a case-control study: AREDS Report No. 22. Arch Ophthalmol 2007;124:1224–32. 25. Mares-Perlman JA, Fisher AI, Klein R, Palta M, Block G, Millen AE, et al. Lutein and zeaxanthin in the diet and serum and their relation to age-related maculopathy in the third national health and nutrition examination survey. Am J Epidemiol 2001;153:424–32. 26. SanGiovanni JP, Chew EY. The role of omega-3 long-chain polyunsaturated fatty acids in health and disease of the retina. Prog Retin Eye Res 2005;24:87–138. 27. Kishan AU, Modjtahedi BS, Martins EN, Modjtahedi SP, Morse LS. Lipids and age-related macular degeneration. Surv Ophthalmol 2011;56:195–213. 28. Donoso LA, Kim D, Frost A, Callahan A, Hageman G. The role of inflammation in the pathogenesis of age-related macular degeneration. Surv Ophthalmol 2006;51:137–52. 29. SanGiovanni JP, Chew EY, Agrón E, Clemons TE, Ferris 3rd FL, Gensler G, et al. The relationship of dietary omega-3 long-chain polyunsaturated fatty acid intake with incident age-related macular degeneration: AREDS report no. 23. Arch Ophthalmol 2008;126:1274–9. 30. Swenor BK, Bressler S, Caulfield L, West SK. The impact of fish and shellfish consumption on age-related macular degeneration. Ophthalmology 2010;117:2395–401. 31. Merle B, Delyfer MN, Korobelnik JF, Rougier MB, Colin J, Malet F, et al. Dietary omega3 fatty acids and the risk for age-related maculopathy: the Alienor Study. Invest Ophthalmol Vis Sci 2011;52:6004–11. 32. Delyfer MN, Buaud B, Korobelnik JF, Rougier MB, Schalch W, Etheve S, et al. Association of macular pigment density with
plasma ω-3 fatty acids: the PIMAVOSA study. Invest Ophthalmol Vis Sci 2012;53:1204–10. 33. Delori FC, Goger DG, Hammond BR, Snodderly DM, Burns SA. Macular pigment density measured by autofluorescence spectrometry: comparison with reflectometry and heterochromatic flicker photometry. J Opt Soc Am 2001;18:1212–30. 34. Wolf-Schnurrbusch UE, Röösli N, Weyermann E, Heldner MR, Höhne K, Wolf S. Ethnic differences in macular pigment density and distribution. Invest Ophthalmol Vis Sci 2007;48:3783–7. 35. Sasamoto Y, Gomi F, Sawa M, Sakaguchi H, Tsujikawa M, Nishida K. Effect of cataract in evaluation of macular pigment optical density by autofluorescence spectrometry. Invest Ophthalmol Vis Sci 2011;52:927–32. 36. Davies NP, Morland AB. Macular pigments: their characteristics and putative role. Prog Retin Eye Res 2004;23:533–59. 37. Arterburn LM, Hall EB, Oken H. Distribution, interconversion, and dose response of n-3 fatty acids in humans. Am J Clin Nutr 2006;83:1467S–76S. 38. Hodson L, Murray Skeaff C, Fielding BA. Fatty acid composition of adipose tissue and blood in humans and its use as a biomarker of dietary intake. Prog Lipid Res 2008;47:348–80. 39. Parker RS. Absorption, metabolism, and transport of carotenoids. FASEB J 1996;10:542–51. 40. Nelson GJ, Schmidt PC, Bartolini GL, Kelley DS, Kyle D. The effect of dietary docosahexaenoic acid on plasma lipoproteins and tissue fatty acid composition in humans. Lipids 1997;32:1137–46. 41. Foulon T, Richard MJ, Payen N, Bourrain JL, Beani JC, Laporte F, et al. Effects of fish oil fatty acids on plasma lipids and lipoproteins and oxidant-antioxidant imbalance in healthy subject. Scand J Clin Lab Invest 1999;59:239–48. 42. Thomas TR, Smith BK, Donahue OM, Altena TS, James-Kracke M, Sun GY. Effects of omega-3 fatty acid supplementation and exercise on low-density lipoprotein and high-density lipoprotein subfractions. Metabolism 2004;53:749–54. 43. Liu A, Chang J, Lin Y, Shen Z, Bernstein PS. Long-chain and very long-chain polyunsaturated fatty acids in ocular aging and agerelated macular degeneration. J Lipid Res 2010;51:3217–29. 44. Rotstein NP, Pennacchiotti GL, Sprecher H, Aveldanno MI. Active synthesis of C24:5 n-3 fatty acid in retina. Biochem J 1996;316:859–64. 45. Zhang K, Kniazeva M, Han M, Li W, Yu Z, Yang Z, et al. A 5-bp deletion in ELOVL4 is associated with two related forms of autosomal dominant macular dystrophy. Nat Genet 2001;27:89–93. 46. Seddon JM, Cote J, Rosner B. Progression of age-related macular degeneration: association with dietary fat, transunsaturated fat, nuts, and fish intake. Arch Ophthalmol 2003;121:1728–37. 47. Umeda-Sawada R, Fujiwara Y, Ushiyama I, Sagawa S, Morimitsu Y, Kawashima H, et al. Distribution and metabolism of dihomoγ-linolenic acid (DGLA, 20:3n-6) by oral supplementation in rats. Biosci Biotechnol Biochem 2006;70:2121–30. 48. Park WJ, Kothapalli KSD, Lawrence P, Tyburczy C, Brenna JT. An alternate pathway to long-chain polyunsaturates: the FADS2 gene product D8-desaturates 20:2n-6 and 20:3n-3. J Lipid Res 2009;50:1195–202. 49. Huang YS, Huang WC, Li CW, Chuang LT. Eicosadienoic acid differentially modulates production of pro-inflammatory modulators in murine macrophages. Mol Cell Biochem 2011;358:85–94.
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Omega-3 and Macular Pigment Accumulation: Results from the Pimavosa Study Marie-Noëlle Delyfer1,2,3, Benjamin Buaud4, Jean-François Korobelnik1,2,3, Marie-Bénédicte Rougier3, Carole Vaysse4, Nicole Combe4, Cécile Delcourt1,2 1Universite
de Bordeaux, Bordeaux, France, 2Inserm, ISPED, Centre INSERM U897-Epidemiologie-Biostatistique, Bordeaux, France, 3Service d’Ophtalmologie, CHU de Bordeaux, Bordeaux, France, 4ITERG – Equipe Nutrition Métabolisme & Santé, Bordeaux, France
The characterization of macular pigment (MP) has taken more than 200 years. Yet, its precise pathophysiologic properties remain elusive. The existence of a macular central yellow spot was first observed on postmortem histologic sections by Buzzi in 1782.1 Decades later, in vivo observation of the macular area using Hermann von Helmholtz’s ophthalmoscope (1851) enabled scientists to determine that this yellow spot was due to the presence of a macular yellow pigment. In 1945, Wald demonstrated that MP absorbs wavelengths between 430 and 490 nm, with a maximum absorption at 465 nm, and that MP contains carotenoids belonging to the xanthophyll family.2,3 Xanthophylls are a class of oxygen-containing carotenoid pigments,4 responsible for the color of many of the yellow, orange, and red hues of flowers, fruits, vegetables (corn, pepper, etc.), egg yolks, and feathers, shells, or flesh of many animal species (flamingo, canary, shrimp, lobster, chicken, or salmonids).5 In plants, they are involved in photosynthesis with chlorophyll and are responsible for the red, yellow, and/or brown colors of autumn foliage as the chlorophyll levels decline. Approximately 600 different carotenoids have been characterized to date.6 However, in 1985, Bone demonstrated that, in the retina, macular xanthophylls that compose MP are specifically restricted to two – lutein (L) and its structural isomer zeaxanthin (Z).7 Anatomically, L and Z are concentrated in the Henle fiber layer of the macular area8 and display a particular spatial distribution, Z being clearly dominant in the center of the fovea with a Z:L ratio decreasing peripherally.7
Handbook of Nutrition, Diet, and the Eye http://dx.doi.org/10.1016/B978-0-12-401717-7.00026-5
In humans, L and Z exclusively derive from dietary intake.9,10 They are lipid-soluble and their metabolism is, therefore, strongly interlinked with lipids.11,12 High dietary intake of L and Z, or their oral supplementation, is known to result in an increase of their plasma concentrations and, consequently, in their specific accumulation within the macula, in which they form the MP.13–16 The precise mechanism of MP accumulation remains to be determined. It is suspected that it is based on a regulated active transport mechanism, thus explaining a 10,000fold higher concentration in the macula than in the blood. As proposed recently, it may rely on specific carotenoidbinding proteins.17,18 The macular over-concentration of L and Z further implies organ-specific biologic roles. The two main biologic properties suggested include, first, a distinctive blue light-absorbing capability due to the presence of the long chromophore of conjugated double bonds (polyene chain) and, second, an antioxidant capability through reactive oxygen species scavenging (e.g., superoxide anion and hydroxyl radical).11 This last role underpins the growing interest for MP in aging macular diseases, especially in age-related macular degeneration (AMD). Indeed, AMD is the leading cause of blindness in developed countries and represents an increasing burden for public health systems.19–21 AMD is a multifactorial disease that results from the combination of nonmodifiable factors (i.e., genetics, sex, age) and identified modifiable factors (i.e., nutritional and/or smoking status).22 Controlling these modifiable factors may therefore be a way of preventing a significant percentage
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of AMD cases. Evidence from both epidemiologic and laboratory studies has demonstrated an inverse associ ation between dietary intake of xanthophyll carotenoids –L and Z – and risk of advanced AMD.22–24 In contrast, long-chain polyunsaturated fatty acids (omega-3 LC-PUFAs) – notably docosahexaenoic acid (DHA) – are abundant in the human retina, in which they exert some identified structural, functional, and neuroprotective roles.26,27 DHA reaches its highest concentration in the membranes of photoreceptors and is important in photoreceptor differentiation and survival, as well as in retinal function.26 Omega-3 LC-PUFAs furthermore exhibit anti-inflammatory properties,26 which are of particular interest in AMD, since inflammation appears to play a pivotal role in the pathogenesis of the disease.28 The neuroprotective role of omega-3 LC-PUFAs in AMD has been demonstrated by a number of epidemiologic studies that observed a decreased risk for AMD in subjects with high intakes of omega-3 LC-PUFAs.26,27,29–31 Among other potential mechanisms supporting neuroprotection, it has been suggested that dietary intake of omega-3 LC-PUFAs may favor the retinal accumulation of L and Z and thereby increase MP density.12,13 The PIMAVOSA (PIgment MAculaire chez le VOlontaire SAin, i.e., MP in the healthy volunteer) study is an observational study that was hence initiated to evaluate the inter-relations between MP, plasma L and Z, and plasma omega-3 LC-PUFAs (as well as other fatty acids) in a homogeneous population of healthy volunteers.32 The characteristics of the studied population are detailed in Table 26.1. All of the recruited participants were healthy adults ages 20–60 years and born in a restricted geographic area (i.e., the southwest of France) in order to optimize the homogeneity of nutritional habits. None had any previous ocular history (all being phakic with a visual acuity of 20/24 or greater, without chronic diseases with significant ocular consequences or myopia exceeding 4 diopters). The use of vitamins and/or supplements was systematically checked and recorded (only seven subjects out of the 107 recruited were supplemented). Participants underwent bilateral eye exam including measurement of best-corrected visual acuity, refraction, retinal photographs after pupil dilation, fundus autofluorescence imaging, macular pigment optical density (MPOD) measurements, and fasting blood tests on the same day.32 The choice of the technique to be used for our MPOD measurements was difficult since several techniques can measure MP in vivo. We wanted a method that would be the most i) objective, ii) reproducible, and iii) easy to perform both for participants and technicians. Heterochromatic flicker photometry is classically considered as the ‘gold standard’; however, although rather easy to perform and reliable, it requires cooperation from the subject. Raman spectroscopy is also highly reproducible
but again requires active participation of the subject for the initial setting up of the device. In contrast, imaging techniques offer a means of measuring the spatial distribution of MPOD objectively and easily and require less subject compliance.33,34 They are based on retinal excitation by an incident light and the analysis of the reflected signal obtained (Fig. 26.1). However, absence of nuclear opacities seems important to avoid any bias.35 This was the technique we finally chose for our MPOD measurements, first because it appeared to be the most objective and, second, because MPOD mapping offered the possibility of studying the correlations between MPOD at different degrees of eccentricity from the center of the fovea and our other variables. Quantification of our nutritional variables (i.e., L, Z, and fatty acids) could either have been estimated from food intakes or directly measured from plasma samples. Because of the multiple difficulties of dietary assessment (including memory bias, difficulties in taking into account high complexity and day-to-day variability of the human diet, imprecisions in estimations of quantities of ingested foods and of nutrient content of foods, etc.) and of interindividual variability in nutrient absorption, we deemed it more objective – and potentially more effective – to use plasma measurements. Plasma L and Z measurements were determined by reversed-phase high-performance liquid chromatography. Plasma phospholipid fatty acid measurements not only focused on omega-3 (alfa-linolenic acid and omega-3 LC-PUFAs) but also on omega-6 (linoleic acid (LA) and omega-6 LCPUFAs), monounsaturated, and saturated fatty acids. The first step of our work was a type of ‘internal validation test’ of our measurements in the studied population. Relationships between MP and xanthophylls, indeed, are now well established. MP is composed of two xanthophyll carotenoids, L and Z. Supplementation or high dietary intake of L and Z increase L and Z plasma levels and, in turn, MP density.13–16 We hence checked the association of plasma L and Z with MPOD in our sample. This was confirmed within 1° of eccentricity and beyond, plasma L and Z being considered separately and/or together (Table 26.2, Fig. 26.2A).32 The result was not affected by the exclusion of the seven subjects declaring use of dietary supplements (data not shown). However, MPOD within 0.5° was not found to be significantly correlated with plasma macular xanthophylls. Interindividual variations in the spatial distribution of MPOD at the very center of the macula may explain – at least in part – this lack of correlation.34,36 The identification of the mechanisms underlying the specific macular accumulation of xanthophylls represents a key step toward a better understanding of macular physiology and disease. Among the different determinants of MP concentration under focus, omega-3 LC-PUFAs have been proposed as key factors.12,13
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TABLE 26.1 Characteristics of the Studied Population Total (n = 107) Age (years) Gender (men) Best corrected visual acuity (LogMAR units) MPOD (within 6° of eccentricity, optical density units)
20–39 Years (n = 53)
38.9 ± 12.1 43
28.2 ± 5.9 23
–0.10 ± 0.1 0.2 ± 0.1
40–60 Years (n = 54) 49.3 ± 5.5 20
–0.10 ± 0.09 0.2 ± 0.0
P Value < 0.0001 0.50
–0.09 ± 0.1
0.48
0.2 ± 0.1
0.11
PLASMA PHOSPHOLIPID OMEGA-3 PUFAs (% OF TOTAL FATTY ACIDS) Total
6.9 ± 1.9
6.5 ± 1.8
7.2 ± 1.9
0.05
ALA
0.2 ± 0.1
0.2 ± 0.1
0.2 ± 0.1
0.96
Total
6.7 ± 1.9
6.3 ± 1.8
7.0 ± 1.9
0.05
EPA
1.2 ± 0.7
1.1 ± 0.7
1.4 ± 0.7
0.02
DPA
0.9 ± 0.2
0.9 ± 0.3
1.0 ± 0.2
0.08
DHA
4.5 ± 1.2
4.3 ± 1.3
4.7 ± 1.2
0.18
Omega-3 LC-PUFAs
PLASMA PHOSPHOLIPID OMEGA-6 PUFAs (% OF TOTAL FATTY ACIDS) Total
34.8 ± 2.4
34.9 ± 2.2
34.7 ± 2.5
0.60
Linoleic acid
18.7 ± 2.4
18.5 ± 2.6
18.9 ± 2.2
0.40
15.3 ± 2.1
15.6 ± 1.9
15.0 ± 2.2
0.19
Eicosadienoic acid
0.3 ± 0.1
0.3 ± 0.1
0.3 ± 0.1
0.47
Dihomo-γ-linolenic acid
3.0 ± 0.7
3.1 ± 0.7
2.9 ± 0.7
0.11
Arachidonic acid
12.0 ± 2.0
12.1 ± 2.0
11.8 ± 2.0
0.43
Plasma phospholipid saturated fatty acids (% of total fatty acids)
44.4 ± 1.2
44.3 ± 1.3
44.5 ± 1.1
0.35
Plasma phospholipid monounsaturated fatty acids (% of total fatty acids)
13.0 ± 1.4
13.4 ± 1.3
12.7 ± 1.4
0.01
150.1 ± 58.9
137.8 ± 48.4
161.8 ± 65.8
0.04
Plasma zeaxanthin* (μg/L)
40.9 ± 20.2
40.4 ± 17.5
41.3 ± 22.6
0.83
Plasma lutein + zeaxanthin* (μg/L)
191.1 ± 75.4
178.2 ± 62.4
203.1 ± 84.8
0.10
Omega-6 LC-PUFAs Total
PLASMA XANTHOPHYLLS* Plasma lutein* (μg/L)
Data are the mean ± standard deviation; n = 107 unless specified otherwise. ALA: alfa-linolenic acid; DHA: docosahexaenoic acid; DPA: docosapentaenoic acid; EPA: eicosapentaenoic acid; LC-PUFA: long-chain polyunsaturated fatty acid; MPOD: macular pigment optical density; PUFA: polyunsaturated fatty acid; * = due to technical failure, L and Z plasma measurements were available only in 99 subjects. Reprinted from Delyfer et al., Invest Ophthalmol Vis Sci. 53:1204–1210, with permission.
Omega-3 PUFAs include a precursor (ALA) and three long-chain derivatives (eicosapentaenoic acid (EPA, 20:5 omega-3), docosapentaenoic acid (DPA; 22:5 omega-3), and DHA (22:6 omega-3)]. ALA is an essential nutrient, since humans cannot synthesize it de novo and, therefore, rely on diet as its sole source (mainly from vegetables and vegetable oils). Synthesis of the long-chain derivatives is very limited in humans,37 who must, therefore, also rely
on their dietary supply, mainly through fish and seafood. In the PIMAVOSA study, the analysis of the fatty acid composition of total plasma phospholipids was used as a valid biomarker of LC-PUFA dietary intakes.38 As shown in Table 26.3, high plasma levels of total omega-3 PUFAs were associated with high MPOD (Table 26.3).32 This was even more marked when considering total omega-3 LC-PUFAs only (Table 26.3, Fig. 26.2B). The mechanisms
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26. OMEGA-3 AND MACULAR PIGMENT ACCUMULATION: RESULTS FROM THE PIMAVOSA STUDY
(A)
(B)
(C)
(D)
FIGURE 26.1 Macular pigment optical density (MPOD) measurements with the modified confocal scanning laser ophthalmoscope (mpHRA; Heidelberg Engineering, Heidelberg, Germany) using autofluorescence images obtained at two wavelengths: 488 nm (A) and 514 nm (B), with a high-pass filter transmitting at a wavelength greater than 530 nm. MPOD was quantified by calculating a MPOD map (C) and comparing foveal and parafoveal autofluorescence at 488 nm and 514 nm. Density maps were processed to estimate MPOD within a circle centered on the fovea at different degrees of eccentricities (0.5°, 1°, 2°, and 6°), using the software provided by the manufacturer of the device (D).
TABLE 26.2 Correlation of Macular Pigment Optical Density (MPOD) with Plasma Lutein and Zeaxanthin Levels (n = 99) MPOD within 0.5°
MPOD within 1°
MPOD within 2°
MPOD within 6°
Lutein + zeaxanthin
0.16 (0.1)
0.26 (0.01)*
0.33 (0.001)*
0.36 (0.0005)*
Lutein
0.16 (0.1)
0.24 (0.01)*
0.32 (0.001)*
0.35 (0.0006)*
Zeaxanthin
0.15 (0.1)
0.24 (0.02)*
0.29 (0.005)*
0.30 (0.003)*
Results are expressed as ‘r (p)’, r being the correlation coefficient and p the P value. *indicates significance. MPOD: macular pigment optical density. Reprinted from Delyfer et al., Invest Ophthalmol Vis Sci. 53:1204–10, with permission.
through which omega-3 LC-PUFAs correlate with MPOD remain to be determined. A first hypothesis could be that omega-3 LC-PUFAs may act as a modulator of L and Z gastrointestinal uptake. However, such a mechanism would have implied a correlation between plasma levels of omega-3 LC-PUFAs and xanthophyll carotenoids, which was not observed (Table 26.4).32 A second hypothesis could be that omega-3 LC-PUFAs influence L and Z carriage by lipoproteins.39 An increase of high-density lipoprotein (HDL) and low-density lipoprotein (LDL) subfractions has indeed been observed after omega-3
LC-PUFA supplementation.40–42 Finally, omega-3 LCPUFAs may favor L and Z concentration within the macular area through an influence on xanthophyll-binding proteins.17 When the different omega-3 LC-PUFAs were detailed, we observed that EPA and DPA both correlated significantly with MPOD, while, surprisingly, DHA did not (Table 26.3).32 DHA is the major LC-PUFA in structural lipids of the human retina, accounting for about 30% of total retinal fatty acids. DHA is an essential structural component of retinal membranes and exhibits several
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(B)
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
MPOD
MPOD
(A)
(µg/L) 0
100
200
300
400
500
600
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
(% of total fatty acids) 2
0
4
L+Z
MPOD
MPOD (% of total fatty acids) 0
0.5
1
1.5
2
2.5
3
3.5
4
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
(% of total fatty acids) 0.2
0
0.4
0.5
0.8
1
1.2
1.4
1.6
DPA
(F)
MPOD
(E)
MPOD
14
(D)
EPA
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
12
Total omega-3 LC-PUFAs
(C) 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
10
8
6
(% of total fatty acids) 0
0.1
0.2
0.3
0.4
0.5
0.6
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
(% of total fatty acids) 0
0.5
eicosadienoic acid
1
1.5
2
2.5
3
3.5
4
4.5
5
DGLA
FIGURE 26.2 Scatter plots depicting the correlations between macular pigment optical density (MPOD) at 1° of eccentricity with (A) lutein and zeaxanthin (L + Z); with (B) total omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs); with (C) EPA (eicosapentaenoic acid); with (D) DPA (docosapentaenoic acid); with (E) eicosadienoic acid; and with (F) DGLA (dihomo-γ-linolenic acid). Note that the associations are not driven by isolated cases. Reprinted from Delyfer et al., Invest Ophthalmol Vis Sci. 53:1204–10, with permission.32
essential neuroprotective properties.26 The lack of correlation we observed between plasma DHA level and MPOD is not sufficient to assess the importance of DHA in MP accumulation. Nevertheless, the absence of correlation between DHA and MPOD seems corroborated by a previous study showing that DHA supplementation did not induce a significant increase of total MPOD values,12 although it may influence MPOD distribution. EPA, the other major dietary omega-3 LC-PUFA present in plasma, is poorly accreted to the retina, as it is quickly converted to DHA or eicosanoid biosynthesis. EPA undergoes oxidative metabolism by cyclooxygenases and lipoxygenases to produce eicosanoids
with vasoregulatory and anti-inflammatory properties.26 Contrary to DHA, a significant positive relationship was observed between plasma EPA level and MPOD (Table 26.3, Fig. 26.2C).32 The positive correlation was even more significant with DPA (Table 26.3, Fig. 26.2D).32 DPA is a metabolic intermediary between EPA and DHA and the second most abundant omega-3 LC-PUFA found within the retina after DHA, its endogenous level being around one-tenth that of DHA in the retinal lipids.43 The precise functions of DPA have not been identified yet. DPA appears to be the precursor of omega-3 very long-chain polyunsaturated fatty acids (VLC-PUFAs) not found in normal human diet, and
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26. OMEGA-3 AND MACULAR PIGMENT ACCUMULATION: RESULTS FROM THE PIMAVOSA STUDY
TABLE 26.3 Correlation of Macular Pigment Optical Density (MPOD) with Plasma Phospholipid Omega-3 PUFA Levels and Other Plasma Phospholipid Fatty Acids (n = 107) MPOD within 0.5°
MPOD within 1°
MPOD within 2°
MPOD within 6°
0.19 (0.04)* 0.0035 (0.97)
0.21 (0.03)* -0.0011 (0.99)
0.20 (0.04)* -0.00074 (0.99)
0.22 (0.02)* 0.0016 (0.98)
Total
0.20 (0.04)*
0.22 (0.02)*
0.20 (0.04)*
0.22 (0.02)*
EPA
0.18 (0.06)
0.21 (0.04)*
0.20 (0.04)*
0.21 (0.03)*
DPA
0.33 (0.0006)*
0.32 (0.0007)*
0.30 (0.002)*
0.31 (0.001)*
DHA
0.13 (0.18)
0.14 (0.16)
0.12 (0.23)
0.14 (0.14)
Saturated fatty acids
–0.15 (0.1)
–0.11 (0.2)
–0.11 (0.3)
–0.12 (0.2)
Monounsaturated fatty acids
–0.04 (0.7)
–0.09 (0.3)
–0.08 (0.4)
–0.06 (0.5)
Total
–0.07 (0.5)
–0.064 (0.5)
–0.076 (0.5)
–0.092 (0.3)
Linoleic acid
0.02 (0.8)
0.014 (0.9)
0.0088 (0.9)
–0.027 (0.8)
Total
–0.07 (0.5)
–0.064 (0.5)
–0.076 (0.5)
–0.092 (0.3)
Eicosadienoic acid
–0.30 (0.001)*
–0.24 (0.008)*
–0.22 (0.02)*
–0.21 (0.03)*
Dihomo-γ-linolenic acid
–0.21 (0.03)*
–0.20 (0.04)*
–0.19 (0.05)*
–0.19 (0.05)*
Arachidonic acid
0.02 (0.8)
0.022 (0.8)
0.0083 (0.9)
0.0075 (0.9)
OMEGA-3 PUFAs Total ALA OMEGA-3 LC-PUFAs
OTHER FATTY ACIDS
OMEGA-6 PUFAs
Omega-6 LC-PUFAs
Results are expressed as ‘r (p)’, r being the correlation coefficient and p the P value. *Indicates significance. ALA: alfa-linolenic acid; DHA: docosahexaenoic acid; DPA: docosapentaenoic acid; EPA: eicosapentaenoic acid; LC-PUFAs: long-chain polyunsaturated fatty acids; PUFA: polyunsaturated fatty acid. Reprinted from Delyfer et al., Invest Ophthalmol Vis Sci. 53:1204–10, with permission.
especially of 24:5 omega-3, the most abundant omega-3 VLC-PUFA in the retina.43 These omega-3 VLC-PUFAs are present in restricted mammalian organs, that is, retina, brain, testes, and thymus. Although identified early, their precise role has not been elucidated due to their great length and minor abundance, which makes them very difficult to analyze. The synthesis of 24:5 omega-3 VLC-PUFA, however, is an important metabolic step in the retina because 24:5 omega-3 plays a central role as a metabolic precursor in the synthesis of other omega-3 VLC-PUFAs and is an obligatory intermediate in the synthesis of DHA.44 Moreover, alterations in omega-3 VLC-PUFA biosynthesis have been shown to result in macular alteration. In particular, defect in the elongation of the very long-chain fatty acids 4 (ELOVL4) gene is associated with dominant Stargardt macular dystrophy.45 Recently, a decrease of DPA, DHA, and some omega-3 VLC-PUFAs (notably 24:5 omega-3) was observed in early and intermediate AMD retinas as compared with age-matched controls,43 suggesting a retinal vulnerability associated with a decreased level of omega-3 LC-PUFAs and VLC-PUFAs.
Analysis of correlations between MPOD and fatty acids was further continued with plasma phospholipid monounsaturated, saturated, and omega-6 fatty acids (Table 26.3).32 Neither saturated nor monounsaturated fatty acids were found to be associated with MPOD. Interest in omega-6 fatty acids has increased, since imbalance between omega-6 and omega-3 LC-PUFAs has emerged as a potential risk factor of AMD.43,46 Our results concerning omega-6 were heterogeneous. Total plasma phospholipid omega-6 LC-PUFAs did not display any association with MPOD measurements (Table 26.3). However, when the different omega-6 were detailed, we observed that two minor omega-6 LC-PUFAs (i.e., eicosadienoic acid (20:2 omega-6) and dihomo-γ-linolenic acid (DGLA; 20:3 omega-6)), exhibited a negative relationship with MPOD (Table 26.3, Fig. 26.2E and 2F). In plasma, DGLA is almost exclusively localized in phospholipids and represents about 20% of omega-6 LC-PUFAs. In the retina, DGLA accounts for less than 2.5% of total retinal fatty acids. DGLA has been reported to have notable anti-inflammatory properties.47 Regarding eicosadienoic acid (20:2
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References
TABLE 26.4 Correlation of Plasma Carotenoids with Plasma Phospholipid Omega-3 PUFAs (n = 99) Lutein + Zeaxanthin
Lutein
Zeaxanthin
Total omega-3 PUFAs
0.14 (0.2)
0.15 (0.1)
0.07 (0.5)
ALA
0.03 (0.8)
0.008 (0.9)
0.05 (0.6)
OMEGA-3 LC-PUFAS Total
0.14 (0.2)
0.15 (0.1)
0.06 (0.5)
EPA
0.15 (0.1)
0.16 (0.1)
0.09 (0.4)
DPA
0.08 (0.4)
0.12 (0.2)
-0.06 (0.6)
DHA
0.08 (0.4)
0.09 (0.4)
0.02 (0.8)
Results are expressed as ‘r (p)’, r being the correlation coefficient and p the P value. ALA: alfa-linolenic acid; DHA: docosahexaenoic acid; DPA: docosapentaenoic acid; EPA: eicosapentaenoic acid; LC-PUFA: long-chain polyunsaturated fatty acid; PUFA: polyunsaturated fatty acids. Reprinted from Delyfer et al., Invest Ophthalmol Vis Sci. 53:1204–10, with permission.
269
• A mong the different omega-3 PUFAs, DPA has the highest correlation with MPOD, while correlation with EPA is moderate and did not reach statistical significance for DHA. • In contrast, MPOD is not significantly associated with plasma saturated fatty acids or monounsaturated fatty acids or total omega-6 PUFAs. However, MPOD exhibits a negative relationship with two minor omega-6 PUFAs: eicosadienoic acid and dihomo-γ-linolenic acid.
Acknowledgment This study received financial support from Laboratoires Théa (Clermont-Ferrand, France). This sponsor participated in the design of the study but not in the collection, management, statistical analysis, and interpretation of the data, neither in the preparation, review, and approval of the present manuscript. This study received a grant from the Institut Carnot Lisa (Lipids for Industry and Health).
References mega-6), its physiologic role remains unknown. It is a o relatively minor metabolite of LA (18:2 omega-6) found in human plasma and erythrocytes.48 Lately, eicosadienoic acid has been shown to modulate the inflammatory response in vitro.49 Since inflammation is postulated to be involved in AMD pathogenesis, the negative relationship of both plasma DGLA and eicosadienoic acid with MPOD we observed may suggest a reduced risk of AMD by a metabolic utilization of these anti-inflammatory omega-6 LC-PUFAs. The PIMAVOSA study hence demonstrates that MP density is associated not only with plasma L and Z but also with plasma phospholipid omega-3 LC-PUFAs, and more particularly with DPA and EPA.32 MP is further correlated – but negatively – with two omega-6 LC-PUFAs, which may have anti-inflammatory properties. The mechanisms underlying the associations of omega-3 or omega-6 LC-PUFAs with MP remain to be determined. Still, our results suggest that macular xanthophylls and omega-3 LC-PUFAs may act synergistically in the constitution of MP, thereby providing a rationale for combined supplementation in patients at high risk for AMD.
TAKE-HOME MESSAGES • M POD correlates with plasma levels of L and Z. • MPOD is associated positively with total plasma omega-3 polyunsaturated fatty acids (PUFAs). • These results suggest that xanthophylls and omega-3 PUFAs may act synergistically in the constitution of MP.
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