Response to Bernstein et al

Abstract

Sir, Response to Bernstein et alWe welcome the letter by Bernstein et al 1 in response to our publication 'What is meso-zeaxanthin, and where does it come from?' in Eye 2013. 2 In their letter, Bernstein and colleagues argue that our review article contains 'several critical errors that need to be considered. ' Bernstein and colleagues endeavour to make their points under the following headings:1. Quantitation of xanthophylls using reverse-and normal-phase HPLC. 2. The role of saponification in the quantitation of xanthophylls in food and supplements. 3. Meso-zeaxanthin in lutein supplements.4. Additional evidence supporting lutein as the precursor of meso-zeaxanthin.In our letter below, we reply directly to these points in normal font. Statements made by Bernstein and colleagues are presented in bold font for clarity.1. Quantitation of xanthophylls using reverse-and normal-phase HPLC. 'Nolan et al argue that the two-step HPLC method used for MZ quantitation by Johnson et al is limited because of the labor involved in the manual collection of the total Z þ MZ fraction in the first step. The authors suggest that this process is prone to human error, that only a portion of the Z þ MZ fraction would be collected, and that this fraction typically is contaminated with L carryover. ' We thank Bernstein et al for summarising the two-step method in their correspondence, commonly used for quantifying MZ. We are very familiar with this method, as we have used it in several of our recently published studies. [3][4][5][6] In our review article, we point out the limitations of the standard 'two-step method' commonly used by many laboratories to quantify MZ. These limitations include the following: its labour intensive nature due to manual collection; operator dependency and potential for human error; and a very long sample run time, rendering it difficult to perform bulk analysis (eg, for clinical trials). Our concerns with respect to the traditional 'two-step method' remain, and we believe that it is important to recognise these limitations when discussing published methodology and findings from papers, and that is why we included these points in our review.Bernstein et al premise their defence of the methodology of carotenoid quantification in the paper by Johnson et al 7 on the basis that:'The fact that L, MZ and Z appear on the subsequent normal-phase, chiral column chromatogram verifies that the desired peaks were collected, and this was also confirmed by absorption spectra.'Bernstein et al attempt to address our concerns with respect to the unknown peak that was found to co-elute with the Z fractions of retinal samples in the report by Johnson et al 7 by stating that 'ythe peak also appeared in the reverse phase HPLC of retinal samples from the carotenoid-free monkeys. ' We agree that identifying the peaks and confirming their presence by assessing their absorbance spectra are important. However, it is clear from the Johnson et al 7 paper that the already challenging method used to analyse MZ was made more diffic...

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“…There have been several attempts to identify Mz in human food sources but little consensus has been reached [18][19][20][21][22][23]. Currently the balance of evidence suggests that Mz is present in the skin of a handful of marine species, though the quantities of Mz present in these sources is under dispute.…”

Recent Insights Into Health Benefits of Carotenoids

“…The carotenoids in the macula are primarily lutein and zeaxanthin (present as two stereoisomers, (3R,3′R)-zeaxanthin and (3R,3′S)-zeaxanthin, also called meso-zeaxanthin) (Bone et al, 1997). Although still debated, meso-zeaxanthin is not thought to be normally found in the diet (nor is it found in the blood stream) and hypothesized to be a metabolite of lutein (Johnson et al, 2005;Nolan et al, 2014Nolan et al, , 2013. There is a higher ratio of total zeaxanthin:lutein (and higher meso-zeaxanthin) in the carotenoid-rich center of the macula and a higher ratio of lutein:zeaxanthin toward the less carotenoid-rich periphery, additionally suggesting that meso-zeaxanthin is derived from lutein (Bone et al, 1997).…”