Optimal dietary zinc inclusion improved growth performance, serum antioxidant capacity, immune status, and liver lipid and glucose metabolism of largemouth bass (Micropterus salmoides).

This study was conducted to ascertain the effect of dietary Zn on growth and health status of juvenile largemouth bass (Micropterus salmoides). Six experimental diets with Zn level of 50.17, 56.74, 73.34, 86.03, 123.94, and 209.20 mg/kg, respectively were compounded using complex amino acid-chelated zinc, and were fed to juvenile fish (5.50 ± 0.10 g) for 70 d. The specific growth rate (SGR) varied with dietary Zn level in a quadratic model and peaked at the 73.34 mg/kg group, while the feeding rate exhibited an opposite trend (P < 0.05). The condition factor, hepatosomatic index and mesenteric fat index all exhibited a tendency similar with SGR (P < 0.05). Dietary Zn level affected serum total proteins, urea, triglycerides, and glucose (P < 0.05). Serum Zn and copper levels linearly increased with dietary Zn level, while serum iron and manganese showed the opposite trend. Serum superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) increased with dietary Zn level and reached a plateau at 86.03 mg/kg. Serum complement component 3 (C3), IgM, and lysozyme also were enhanced by 73.34 mg/kg Zn. Body protein content increased with zinc level up to 73.34 mg/kg, and then remained steadily. As dietary Zn level increased, hepatic lipid level increased and then reached a plateau at 86.03 mg/kg group, while glycogen increased linearly. Moreover, gene expression related to lipid and glycogen metabolism from liver transcriptome further explained the liver lipid and glycogen variations. To conclude, a dietary Zn requirement of 76.99 mg/kg was suggested for juvenile largemouth bass to improve growth, antioxidant capacity, and immune status.

Evaluation of dietary zinc on antioxidant-related gene expression, antioxidant capability and immunity of soft-shelled turtles Pelodiscussinensis.

Zinc (Zn) plays a role in the antioxidant capacity and immunity of aquatic animals. A twelve-week feeding experiment was performed to estimate the impact of dietary zinc on antioxidant enzyme-related gene expression, antioxidant enzyme activity and non-specific immune functions of soft-shelled turtles, Pelodiscus sinensis. Six fishmeal-based experimental diets with 32.45% protein were formulated, which contained 35.43, 46.23, 55.38, 66.74, 75.06 and 85.24 mg/kg Zn, respectively. Catalase (CAT), glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) levels improved with an elevation in dietary Zn from 35.43 to 55.38 mg/kg and then reduced when dietary Zn was further elevated. The expression levels of Nrf2 and antioxidant-related genes CuZnSOD, MnSOD, CAT, GPX1, GPX2, GPX3 and GPX4 escalated with elevating Zn concentration up to 55.38 mg/kg in diets and then reduced as dietary Zn elevated. The expression levels of Kelch-like ECH-associating protein 1 (keap1) showed a reverse trend with that of Nrf2. The contents of malondialdehyde (MDA) in the 55.38 and 66.74 mg/kg Zn diet-fed groups were the lowest. Alkaline phosphatase activity (AKP), superoxide anion (O2-), lysozyme activity and total antioxidant capacity (T-AOC) improved with an escalation in dietary Zn concentration up to 66.74 mg/kg. Optimal dietary Zn improved antioxidant capability, immunity, and antioxidant enzyme-related gene expression. The dietary Zn demand for soft-shelled turtles were 60.93 and 61.63 mg/kg, based on second regression analysis of SOD and T-AOC activity, respectively.

Calcium-enhanced phosphorus toxicity in calcifuge and soil-indifferent Proteaceae along the Jurien Bay chronosequence.

Many Proteaceae are highly phosphorus (P)-sensitive and occur exclusively on old nutrient-impoverished acidic soils (calcifuge), whilst a few also occur on young calcareous soils (soil-indifferent) that are higher in available calcium (Ca) and P. Calcium increases the severity of P-toxicity symptoms, but its underlying mechanisms are unknown. We propose that Ca-enhanced P toxicity explains the calcifuge habit of most Proteaceae. Four calcifuge and four soil-indifferent Proteaceae from South-Western Australia were grown in hydroponics, at a range of P and Ca concentrations. Calcium increased the severity of P-toxicity symptoms in all species. Calcifuge Proteaceae were more sensitive to Ca-enhanced P toxicity than soil-indifferent ones. Calcifuges shared these traits: low leaf zinc concentration ([Zn]), low Zn allocation to leaves, low leaf [Zn]:[P], low root : shoot ratio, and high seed P content, compared with soil-indifferent species. This is the first demonstration of Ca-enhanced P toxicity across multiple species. Calcium-enhanced P toxicity provides an explanation for the calcifuge habit of most Proteaceae and is critical for the management of this iconic Australian family. This study represents a major advance towards an understanding of the physiological mechanisms of P toxicity and its role in the distribution of Proteaceae.

Zinc absorption from biofortified maize meets the requirements of young rural Zambian children.

BACKGROUND: The zinc content of maize, a major global food staple, is generally insufficient alone to meet the requirements of young children. OBJECTIVES: The primary objective of this study was to determine whether substitution of biofortified maize (34 µg zinc/g grain) for control maize (21 µg zinc/g) was adequate to meet zinc physiologic requirements in young children for whom maize was the major food staple. A secondary objective was to compare total daily zinc absorption when maize flour was fortified with zinc oxide to a total concentration of 60 µg zinc/g. METHODS: Participants included 60 rural Zambian children with a mean age of 29 mo who were randomly assigned to receive 1 of 3 maize types (control, biofortified, or fortified) all of which were readily consumed (>100 g on 1 d). Total daily zinc intake (from maize and low-zinc relish) was determined from duplicate diet collections. Multiplication by fractional absorption of zinc, measured by a dual isotope ratio technique, determined the total daily zinc absorption on the day the test meals were given. RESULTS: The mean ± SD total daily zinc intake (milligrams per day) from the biofortified maize (5.0 ± 2.2) was higher (P < 0.0001) than for the control maize (2.3 ± 0.9). Intake of zinc from the fortified maize (6.3 ± 2.6) did not differ from the biofortified maize. Fractional absorption of zinc from control maize (0.28 ± 0.10) did not differ from the biofortified maize (0.22 ± 0.06). Total daily absorption of zinc (milligrams per day) from the biofortified maize (1.1 ± 0.5) was higher (P = 0.0001) than for the control maize (0.6 ± 0.2), but did not differ from the fortified maize (1.2 ± 0.4). CONCLUSIONS: These results indicate that feeding biofortified maize can meet zinc requirements and provide an effective dietary alternative to regular maize for this vulnerable population. This trial was registered at clinicaltrials.gov as NCT02208635.

Zinc and its importance for human health: An integrative review.

Since its first discovery in an Iranian male in 1961, zinc deficiency in humans is now known to be an important malnutrition problem world-wide. It is more prevalent in areas of high cereal and low animal food consumption. The diet may not necessarily be low in zinc, but its bio-availability plays a major role in its absorption. Phytic acid is the main known inhibitor of zinc. Compared to adults, infants, children, adolescents, pregnant, and lactating women have increased requirements for zinc and thus, are at increased risk of zinc depletion. Zinc deficiency during growth periods results in growth failure. Epidermal, gastrointestinal, central nervous, immune, skeletal, and reproductive systems are the organs most affected clinically by zinc deficiency. Clinical diagnosis of marginal Zn deficiency in humans remains problematic. So far, blood plasma/serum zinc concentration, dietary intake, and stunting prevalence are the best known indicators of zinc deficiency. Four main intervention strategies for combating zinc deficiency include dietary modification/diversification, supplementation, fortification, and bio-fortification. The choice of each method depends on the availability of resources, technical feasibility, target group, and social acceptance. In this paper, we provide a review on zinc biochemical and physiological functions, metabolism including, absorption, excretion, and homeostasis, zinc bio-availability (inhibitors and enhancers), human requirement, groups at high-risk, consequences and causes of zinc deficiency, evaluation of zinc status, and prevention strategies of zinc deficiency.