[Antioxidant micronutrients and cataract. Review and comparison of the AREDS and REACT cataract studies]. / Antioxidative Mikronährstoffe und Katarakt. Ein Uberblick und ein Vergleich der Kataraktstudien "AREDS" und "REACT"

Age-related cataract remains the major cause of preventable blindness throughout the world. It has long been realized that one of the important etiological factors for this disease is oxidative and in particular photooxidative damage to the lens. Therefore, the antioxidant micronutrients, vitamins C and E and the carotenoids, in particular beta-carotene, have been discussed as factors that could reduce the risk for this disease. The present article reviews what is known about the transport of these substances to the lens, their accumulation, and their concentrations in the lens. Furthermore, the available epidemiological literature is briefly mentioned, but more emphasis has been placed on a description and discussion of major clinical intervention studies. Finally, the design and results of two of those trials using antioxidant micronutrients, the Age-Related Eye Disease Study (AREDS) and the Roche European American Cataract Trial (REACT), are compared. The AREDS trial did show a positive effect only for age-related macular degeneration but not for cataract, while the REACT trial demonstrated a small but statistically significant deceleration of cataract progression. The techniques for following the course of a cataract in the REACT study were more sensitive to subtle changes than those used in the AREDS study, and this may have been one important factor accounting for the differences. The authors' detailed comparison of these studies, however, suggests that even more important may have been the fact that in the REACT study intervention started earlier in the disease process,with higher doses of vitamins C and E and beta-carotene and consequently with larger plasma concentrations of these antioxidant micronutrients. The REACT trial results support the early complementation of a diversified diet with supplements containing vitamins C and E and beta-carotene as well as other carotenoids. The authors also believe that it is reasonable to include these micronutrients in the therapeutic armamentarium of general ophthalmological practice.

Fat-soluble nutrient concentrations in different layers of human cataractous lens.

PURPOSE: Recent epidemiologic studies suggest that differential risk for cataract in different areas of the lens may be related to intake of carotenoids, retinol, and tocopherol. Nevertheless, there is little information about differential localization of these nutrients in the lens. To determine the spatial distribution of fat-soluble nutrients within the lens, we determined levels of these nutrients in the epithelium/ outer cortex vs. inner cortex/nucleus. METHODS: Concentrations of carotenoids, retinol, and tocopherol were determined in the epithelial/cortical (younger, more metabolically active tissue) and nuclear (older, less metabolically active) layers of human cataractous lenses (n = 7, 64-75 yr) by reverse-phase high-performance liquid chromatography (HPLC). RESULTS: Lutein/zeaxanthin was the only carotenoid, which was detected, in human lens. Consistent with prior reports, no beta-carotene or lycopene were detected. Concentrations of lutein/zeaxanthin, tocopherol, and retinol in epithelium/cortex tissue were approximately 3-, 1.8-, and 1.3-fold higher than in the older lens tissue. Specifically, the epithelial/cortical lens layer, comprising about half of the tissue, contains 74% of lutein/zeaxanthin (44 ng/g wet wt), 65% of alpha-tocopherol (2227 ng/g wet wt), and 60% of retinol (30 ng/g wet wt). CONCLUSIONS: The data suggest that upon development and aging, there is differential localization of these nutrients. The data are also consistent with a protective role of these nutrients against oxidative damage in the epithelium and cortex of the human lens.

Vitamin C and human health--a review of recent data relevant to human requirements.

The recent scientific literature indicates that beyond merely protecting against scurvy vitamin C contributes to many aspects of human health. The main areas of research reviewed include: 1. Vitamin C requirements of smokers. The data indicate that the vitamin C requirement of smokers is higher by at least 60 mg per day (up to 140 mg per day) than that of nonsmokers. 2. Important functions of the body, such as immune response, pulmonary function, and iron absorption are related to vitamin C intakes. Daily vitamin C intake of at least 150-200 mg per day enhance these functions. 3. Vitamin C may play critical roles in the prevention of CHD, cancer and cataract. Based on the available data, vitamin C intakes of at least 80-120 mg per day are associated with lowering the risk of these chronic diseases. 4. The literature documents that these and much higher intake levels of vitamin C are safe.

Validation of methods for the assessment of cataract progression in the Roche European-American Anticataract Trial (REACT)

The Roche European-American Anticataract Trial (REACT) will assess the effect of antioxidants on progression of cataract in humans. This report evaluates the methods used in REACT. Seventy three subjects (139 eyes) with cortical (C), posterior subcapsular (P), nuclear (N) or mixed cataract were seen twice within two weeks for eye examinations, assessments of visual function, lens photographs and CCD images. The degree of cataract and nuclear color (NC) were assessed with subjective (LOCS III) and objective (computerized, CASE 2000 CCD) methods. Repeat visit values were used to calculate intraclass correlation coefficients (r1) and 95% tolerance limits (TL). A clinically significant change (CSC) was defined as one step in LOCS III. The relative power of each method to detect cataract change and sample sizes needed to achieve statistically significant results were calculated. The r1 values for visual function tests ranged from 0.76 to 0.88; if these tests of visual function were used to detect a clinically significant change in cataract severity, sample sizes of 840 to 2707 per group would be needed. The r1 values for LOCS III were 0.88 to 0.97, and sample sizes ranged from 50 to 135 per group. The r1 values for the CCD were 0.93 to 0.98, and sample sizes ranged from 1 to 42 with poorer values relating to measurement of P. We conclude that the methods used in REACT are reproducible. The analytical algorithms in the image analysis programs did not permit differentiation between C and P opacification; therefore, P cataract is best measured with LOCS III. REACT sample sizes are adequate to detect a difference of 0.2 LOCS III units/year between the mean rates of cataract progression in two groups.

Dietary carotenoids protect human cells from damage.

A physical chemistry technique based on singlet oxygen luminescence at about 1270 nm and a biological cell membrane technique were used to study the quenching of singlet oxygen by four carotenoids bound to the surface of lymphoid cells. All the carotenoids studied showed a beneficial effect in cell protection, but there were subtle differences between them.

Cellular bound beta-carotene quenches singlet oxygen in man.

It is often postulated that a major role of carotenoids in biology and medicine involves their ability to quench a toxic form of oxygen, known as singlet oxygen, although direct observations of such mechanisms do not exist. Using beta-carotene, bound to lymphocytes taken from human blood, we have used a direct, pulsed laser, physical chemical technique and, separately, a biological method to show a particularly efficient quenching reaction of singlet oxygen by carotene in a cellular environment.

Carotene-oxygen radical interactions.

All-trans beta-carotene radical anion efficiently transfers an electron to oxygen but the reverse reaction is not observed and, instead we suggest the formation of a beta-carotene-superoxide radical addition complex. On the other hand, all-trans lycopene undergoes a reversible electron transfer with the superoxide radical. This distinctive behaviour may be related to the anti-cancer properties of these molecules.

Carotenoids in the retina--a review of their possible role in preventing or limiting damage caused by light and oxygen.

Two of the circa 600 naturally occurring carotenoids, zeaxanthin and lutein, the major carotenoids of maize and melon respectively, are the constituents of the macula lutea, the yellow spot in the macula, the central part of the retina in primates and humans. Of the circa ten carotenoids found in the blood these two are specifically concentrated in this area, which is responsible for sharp and detailed vision. This paper reviews the ideas that this concentration of dietary carotenoids in the macula is not accidental, but that their presence may prevent or limit damage due to their physicochemical properties and their capability to quench oxygen free radicals and singlet oxygen, which are generated in the retina as a consequence of the simultaneous presence of light and oxygen. Additionally, in vitro and in vivo animal experiments are reviewed as well as observational and epidemiological data in humans. These show that there is enough circumstantial evidence for a protective role of carotenoids in the retina to justify further research. Some emphasis will be put on age-related macular degeneration (AMD), a multifactorial degenerative retinal disease for which the exposure to light and thus photochemical damage has been suggested as one of the etiological factors. Recent attempts at nutritional intervention in this condition will also be reviewed.

The singlet oxygen and carotenoid interaction.

Second-order rate constants kQ for the quenching of O2(1 delta g) by carotenoids were determined at room temperature in benzene and toluene using the technique of time-resolved luminescence. Of the C40 pigments studied, lycopene was found to be the most efficient quencher, but the increased efficiency compared with all-trans beta-carotene was less than previously reported. The efficiency of quenching of O2(1 delta g) was extended to a number of solvents with varying viscosities. kQ was found to be inversely proportional to solvent viscosity, although the relationship is not simply linear. The results suggest the involvement of thermodynamic factors. The efficiency of deactivation of O2(1 delta g) was found to increase with the number of conjugated carbon-carbon double bonds, i.e. kQ(C60) greater than kQ(C50) greater than kQ(C40). A number of xanthophylls were included in this study; it would appear that an epoxide group rather than carbonyl or hydroxyl substituents increase the reactivity of the carotenoid with respect to O2(1 delta g).

Effects of antioxidant supplementation on platelet function: a randomized pair-matched, placebo-controlled, double-blind trial in men with low antioxidant status.

We investigated the effect on platelet function of supplementing men with low antioxidant status with 600 mg ascorbic acid, 300 mg alpha-tocopherol, 27 mg beta-carotene, and 75 micrograms selenium in yeast daily. Eighty men were randomly assigned in pairs (matched for smoking, baseline antioxidant status, and time and day of entry) by use of a double-blind design to receive supplement or placebo for 5 mo. Compared with 39 control subjects, 39 antioxidant-supplemented men experienced the following net reductions during the double-blind period: 20% (P = 0.012) in serum lipid peroxides, 24% (P = 0.035) in ADP-induced platelet aggregation, 42% (P = 0.040) in the rate of ATP release during aggregation, 51% (P = 0.018) in serum (platelet-produced) thromboxane B2, and 29% (P = 0.024) in plasma beta-thromboglobulin concentration. The data support our hypothesis that antioxidant supplementation of men with low antioxidant status and high fat intake reduces lipid peroxidation, the capacity of platelets to aggregate and to produce thromboxane A2, and in vivo platelet activation.

Vitamin nutritional status and immunocompetence of elderly in Perugia (Italy): an epidemiological approach.

The influence of the vitamin nutritional status on the immunocompetence of a group of elderly people in the city of Perugia has been investigated. The impairment of some immunological (humoral as well as innate and acquired cell-mediated) functions seemed to be mostly related to age. Statistically significant correlations between the complement component C4 and plasma levels of retinol as well as alpha-tocopherol and an inverse correlation between titers of IgG and plasma retinol have been observed (significance level alpha = 5%).

Gastric delivery system for iron supplementation.

A gastric delivery system (GDS) for iron supplementation was evaluated. Radioisotopic studies in 9 volunteers demonstrated a three-fold higher absorption of GDS iron compared with ferrous sulphate elixir. A double-blind placebo controlled trial was done in 200 women to compare the gastrointestinal side-effects associated with 50 mg iron daily given either as GDS or conventional ferrous sulphate. The conventional preparation was associated with a significantly higher frequency of nausea and anorexia, whereas there were no significant differences in reported side-effects between subjects receiving GDS or placebo. A single GDS capsule daily provides the same amount of absorbed iron as conventional ferrous sulphate given three times daily, and does not produce gastrointestinal side-effects.

Effects of pyridoxine and riboflavin supplementation on physical fitness in young adolescents.

The effects of pyridoxine and riboflavin supplementation on physical fitness was studied in a group of children with higher prevalence of subclinical, biochemically defined pyridoxine and riboflavin deficiencies. One hundred and thirteen children aged 12-14 years were allocated to three groups to receive daily (except Sundays) for two months either a placebo or a supplement of pyridoxine or riboflavin. The supplementation resulted in marked improvement of pyridoxine and riboflavin nutrition status and was followed by disappearance of respective biochemical deficiencies. The improvement in pyridoxine biochemical status was also accompanied by a slight and statistically significant increase in physical fitness (p less than 0.05) assessed by bicycle ergometer technique. The increase in physical fitness in the riboflavin supplemented group was statistically non-significant (p greater than 0.05). In both supplemented groups there was a significant increase in physical fitness in subjects with initially deficient biochemical vitamin status whereas supplementation had no effect on physical fitness in subjects with initially high biochemical values.

Distinct functions of monoclonal IgG antibody depend on antigen-site specificities.

Intraveneous hyperimmunization of selectivity bred rabbits with streptococcal group A-variant vaccines elicits antibody responses of restricted heterogeneity at high antibody levels. All antisera contain two functionally distinct antibody populations, which can be isolated in single-band purity upon analytical isoelectric focusing. Typical examples of these two kinds of single-band antibodies were investigated in great detail for several parameters by a variety of methods. 85--99% of the streptococcal group A-variant polysaccharide (Av-CHO)-specific antibody in the antisera does not precipitate the isolated 5,000 daltons poly-L-rhamnose antigen, neither agglutinates nor lyses in the presence of complement Av-CHO-coated sheep erythrocytes (SRBC), binds the radio-labeled Av-CHO with an association constant in the ragne of 10(5)--10(6) M-1, and is of terminal specificity (nonreducing end) for the linear Av-CHO. In contrast, the minor fraction of Av-CHO-specific antibody (1--15%) does precipitate the linear Av-CHO, both agglutinates and lyses Av-CHO-coated SRBC in the presence of complement, has an affinity range of 10(8)--10(9) M-1, and is of internal specificity for the Av-CHO. The antigenic determinants of the Av-CHO for the antibodies are nonoverlapping, only one Fab of the low affinity antibody can be bound whereas four Fab of the high affinity antibody are accommodated. Hence, the determinant specificity explains the functional differences observed, for there is no indication of subclass differences. A mechanistic model of the A-variant carbohydrate presentation on the vaccine appears to account best for the unbalanced levels of low and high affinity antibody.

Clonal dominance of low-affinity antibodies in rabbit hyperimmune anti-streptococcal group A-variant polysaccharide antisera.

Intraveneous hyperimmunization of selectively bred rabbits with streptococcal group A-variant vaccines elicits antibody responses of restricted heterogeneity at high antibody levels. In these antisera, IgG with dissociation constants Kd = 10(-6) M constitutes 90% and IgG with Kp = 10(-9) M accounts for only 10% of the group A-variant polysaccharide-specific antibodies. The low affinity antibody fraction represents the dominant clonotypes. Preparative isoelectric focusing in granulated (Ultrodex G-75) gels was used to successfully purify single-band material belonging to dominant spectrotypes. Affinity studies with these antibody fractions with the highest reported degree of purity yielded Kd = 10(-6) M values, thus confirming that clonal dominance is exclusively associated with low-affinity antibodies. Since it is known from previous work (M. Cramer and D. G. Braun, Scand. J. Immunol. 1975. 4:63) and from the rabbit antisera used here that clonal dominance of this sort is long-lived, this work fails to support the argument of immune maturation. The data more logically relate to antibodies that emerge with different subspecificities -- recognized in the antigen as a function of time in immunization procedures -- rather than to an inherent property of the immune system.