Resonance Raman spectroscopy and the preterm infant carotenoid status

Carotenoids are fat-soluble, extensively conjugated polyene pigments synthesized exclusively by plants and microorganisms. Adults and children obtain carotenoids from the diet, especially from fruits and vegetables. Newborn infants, however, obtain their carotenoids via the placenta prenatally and then from mother’s milk or commercial formula. There are >600 known carotenoids, but only about 15 are routinely detected in human tissues, serum, and milk (1). The major carotenoids in human serum include β-carotene, lycopene, lutein, α-carotene, β-cryptoxanthin, and zeaxanthin. The various carotenoids are deposited with widely varying concentrations and distributions in many tissues of the body including retina, skin, liver, and fat. Carotenoids have a variety of functions that may be of importance to human health and development. In adults, they appear to be physiologically important nutrients in preventing breast and lung cancer, heart disease, stroke, arteriosclerosis, and macular degeneration (2). In infants, carotenoids may function as antioxidants and anti-inflammatory mediators (3). They may also play important roles in preventing oxidative stress in chronic lung disorder, necrotizing enterocolitis, sepsis, intraventricularhemorrhage, and retinopathy of prematurity (4). In eye development, carotenoids lutein and zeaxanthin are postnatally concentrated in the macula of the eye and may be protective against harmful short-wave blue light (5) and be important in maturation of the visual system (6). The standard method to measure an individual’s carotenoid status is to determine the blood levels. This method requires blood sampling, solvent extraction, and then quantitative analysis by high-performance liquid chromatography (HPLC). Resonance Raman spectroscopy (RRS) has been developed tomeasure the total carotenoid levels noninvasively in accessible tissues such as skin and the macula of the eye. The skin method is particularly attractive in infants and children because drawing sufficient blood for analysis may be a challenge. Raman spectroscopy is a laser spectroscopic technique that detects the characteristic vibrational energy of carotenoids in the tissue of interest. The carotenoid’s carbon-carbon single bonds and carbon double bonds each generate a spectrally sharp, resonantly enhanced, Raman scattered intensity when excited in any of the carotenoid’s vibronic absorption transitions in the visible wavelength region. The RRS measured the combined concentration of all or total carotenoids. The method cannot distinguish individual carotenoids that HPLC can. When blue laser light is used, the extremely large resonance enhancement readily permits total carotenoid (sum of lutein, carotene, lycopene, and so on) quantitation even in complex biological tissues. In the present study, all the infants were white; however, skin pigmentation may interfere with the Raman method. To date, the skin resonance Raman method has been used mainly in adults (7,8) and preschool age children (9) where it has been found to be a valid biomarker of fruit and vegetable consumption (8,9) but it has had limited use in neonates. The purpose of the study is to validate the Raman spectroscopy method in infants in comparison with the HPLC method and to evaluate the carotenoid status in preterm infants fed with mother’s milk or formula.