An initial evaluation of newly proposed biomarker of zinc status in humans - linoleic acid: dihomo-γ-linolenic acid (LA:DGLA) ratio

The prevalence of obesity and dyslipidemia has increased worldwide. The role of trace elements in the pathogenesis of these conditions is not well understood. This study examines the relationship between dietary zinc (Zn) intake and plasma concentrations of Zn, copper (Cu) and iron (Fe) with lipid profile indicators, fatty acid composition in plasma phospholipids and desaturase enzyme activities in a dyslipidemic population. The role of the newly proposed biomarker of Zn status, the linoleic:dihomo-gama-linolenic acid (LA:DGLA) ratio, in predicting Zn status of dyslipidemic subjects has been explored. The study included 27 dyslipidemic adults, 39–72 years old. Trace elements were determined using atomic absorption spectrometry and fatty acid composition by a liquid gas chromatography. Desaturase activities were calculated from product-precursor fatty acid ratios. Dietary data were obtained using 24 h recall questionnaires. Insufficient dietary intake of Zn, low plasma Zn concentrations and an altered Cu:Zn ratio is related to modified fatty acid profile in subjects with dyslipidemia. Plasma Zn status was associated with obesity. There was no correlation between dietary Zn intake and plasma Zn status. The LA:DGLA ratio was inversely linked to dietary Zn intake. Cu, in addition to Zn, may directly or indirectly, affect the activity of desaturase enzymes.

Despite enormous research efforts, a sufficiently sensitive and reliable biomarker for the assessment of zinc (Zn) status has not been identified to date. Zn affects fatty acid metabolism and alters the activity of certain desaturases; thus, desaturase activity has been proposed as a potential new biomarker of Zn status. This systematic review complied and assessed studies that examined changes in fatty acid desaturase 1 (FADS1) and fatty acid desaturase 2 (FADS2) activities in relation to modifications in dietary Zn intake. A systematic search was performed in PubMed, Web of Science, Scopus, Web of Knowledge, and Central with strictly defined search, inclusion, and exclusion criteria. Twenty-one studies were included, 8 animal and 13 human trials (5 randomized controlled trials, two non-randomized controlled trials, and 6 cross-sectional studies). This systematic review was performed using PRISMA guidelines and where feasible a random-effects meta-analysis was conducted. No significant correlation was seen between the delta 6 desaturase and Zn status (-0.0958, 95% CIs (-0.2912; 0.1074), p = 0.2928). Delta 6 desaturase seems to respond in a greater magnitude than Zn status to Zn-containing interventions (the standardized mean difference for delta 6 desaturase was −0.6052, 95% CIs (-2.7162; 1.5058), p = 0.4289, while for plasma/serum Zn it was 0.0319, 95% CIs (-0.9133; 0.9770), p = 0.9213). Finally, two separate meta-analyses on same studies that assessed the correlations between LA:DGLA and Zn intake and Zn status and Zn intake revealed that the magnitude of correlations was only slightly different (the pooled correlation coefficient between the LA:DGLA ratio and Zn intake had a value of −0.1050, 95% CIs (-0.5356; 0.3690), p = 0.454, while between plasma Zn and Zn intake had a value of −0.0647, 95% CIs (-0.4224; 0.3106), p = 0.5453). According to the descriptive analysis, the magnitude of variation in desaturase activities in response to Zn intake was not consistent among studies, FADS1 and FADS2 activity corresponded to dietary Zn manipulations, both in animals and humans. A plausible explanation for this observation might be the difference between the studies in study populations, types of dietary interventions, study durations, etc. In addition, several potential confounders and covariates are identified from the qualitative synthesis, such as gender, age, the type of fat provided within the dietary intervention, the size of Zn particles, among others. Further high-quality studies are needed to additionally clarify the suggested associations and applicability of utilizing fatty acid desaturase activities as Zn status biomarkers.

Updates on the Linoleic Acid: Dihomo-γ-Linolenic Acid Ratio (LA: DGLA)- as an Emerging Biomarker of Zinc Status (P24-019-19)

Background Sensitive biomarkers are needed to assess Zn status. A useful nutritional status biomarker should ideally reflect habitual dietary intake and the amount of absorbed nutrient. Measurement of EZP, which requires isotope methodology and thus is not “field friendly”, has been proposed as a “gold standard” against which to measure new markers. Objective and Methods Using stable isotope methods, we measured EZP size at 9–10 mo of age in healthy breastfed infants (n=37) who had a wide range of habitual dietary Zn resulting from random assignment at ~ 6 mo of age to 1 of 3 complementary feeding groups: infant cereal, with and without Zn fortification, or meats. Diet Zn, daily absorbed Zn, and plasma Zn were also measured. Results Mean EZP size was marginally significantly higher in infants who received Zn fortified cereal, compared to unfortified cereal (p = 0.06). EZP was significantly correlated with dietary Zn intake (r = 0.42, P = 0.02) and daily absorbed Zn (r = 0.54; P < 0.001). Plasma Zn was not different among groups and was not correlated with diet Zn, absorbed Zn, or EZP. Conclusion EZP appeared to reflect host Zn status better than plasma Zn. Evaluation of EZP in relation to functional outcomes is required to confirm its utility as a sensitive biomarker of Zn status. Support: The Beef Checkoff, NCBA and NIH K24DK083772.

The identification of an enzyme activity that responds to changes in Zn intake may serve as a useful biomarker for Zn status. Alkaline phosphatase (ALP) is a dimeric protein with each subunit containing two Zn atoms. The activity of ALP in erythrocytes (E) decreases as a result of a low Zn diet, which suggests that this enzyme may be a marker of Zn status. To investigate this further, we determined the response of E-ALP in six healthy subjects following supplementation with 50 mg Zn (4.2 x RDI) daily for 4 wk. A small but significant increase in plasma Zn was observed with supplementation (p < 0.05), whereas there was no significant change in E-Zn over the same period. Plasma and E-Cu showed no change. Conversely, the activity of E-ALP increased in all subjects from 1.7 +/- 0.5 to 5.9 +/- 0.7 U/g protein (mean +/- SE) (p < 0.0001). The small change observed in plasma Zn is not biologically significant in view of the many documented factors that influence its concentration. Our data support the hypothesis that E-ALP is a marker of Zn status in humans.

Kinetic Parameters and Plasma Zinc Concentration Correlate Well with Net Loss and Gain of Zinc from Men

Plasma zinc status, growth, and maturation in children with sickle cell disease

Zinc nutritional status during pregnancy: a longitudinal study

Investigation of Lymphocyte Gene Expression for Use as Biomarkers for Zinc Status in Humans

Zinc and copper status of adolescent females

BackgroundBreast milk is the gold standard of infant feeding especially during the first 6 months of life. Nutritional status and dietary intake of lactating women may affect breast milk concentration of iron (Fe) and zinc (Zn).ObjectiveTo assess the status of Fe and Zn as well as their concentrations in breast milk of lactating women during the first 6 months of lactation, and to determine factors associated with Fe and Zn status in breast milk of lactating women.DesignThis was a longitudinal study over a 6‐month period. Lactating women were enrolled when visiting a well child clinic at Faculty of Medicine Ramathibodi Hospital. Maternal intakes of dietary Fe and Zn, anthropometry, and breast milk Fe and Zn concentrations were determined at 2, 4 and 6 months of lactation. Complete blood count, Fe status using serum ferritin, and plasma Zn levels of the women were analyzed at 6 months of lactation.ResultsThere were 63 lactating women. The prevalence of Fe depletion (serum ferritin &lt;12 ug/dL), Fe deficiency anemia (Hb &lt;110 g/L) and Zn deficiency (plasma Zn &lt;10.7 umol/L) were 4.8%, 3.2%, and 17.5%, respectively. The medians of dietary Fe and Zn intakes at 6 months were 8.67 and 5.04 mg, respectively. At 2, 4, and 6 months of lactation, the median levels of Fe in breast milk were 0.16, 0.13, and 0.13 mcg/L, while Zn levels were 1.1, 0.72, and 0.54 mcg/L, respectively. Breast milk Fe and Zn levels were significantly different between each period of lactation. At 6 months, Fe status was positively correlated with dietary Fe intake (b=0.515, p=0.018) and Fe levels in breast milk were inversely correlated with plasma Zn levels (b=−0.101, p=0.01).ConclusionThere were deficiencies of Fe and Zn during the first 6 months of lactation.Breast milk Fe and Zn concentrations were decreased during the lactation period. Nutrients in breast milk were affected by maternal nutritional status. Appropriate dietary intakes of lactating mothers should be advised and monitored.

The EZP is the pool of rapidly exchanging, metabolically active zinc (Zn) in the human body. Its size is measured routinely in stable isotope tracer studies of Zn absorption, and it has been given consideration as a potential biomarker of Zn status. Linear regression models were used to investigate relationships of EZP to body size, age, gender, plasma Zn concentration, dietary Zn intake and absorbed Zn in data from studies of healthy adults. EZP size measurements ranged from 75 to 280 mg in subjects between 18 and 83 yrs of age. Age, body weight (or surface area), gender and plasma Zn (in decreasing order of importance) were all significant predictors of EZP in multiple regression models of data from 100 subjects having adequate Zn intake (>7 mg/d) and absorption (> 2.8 mg/d). The models showed EZP size to increase with body weight and plasma Zn, and to decrease with age. The gender difference was largest in young adults (EZP in males was 50 mg larger at 20 yrs of age) and decreased to equality at 80 yrs. Younger subjects with Zn intakes-absorption lower than the ranges mentioned above had smaller EZP sizes on average than model predictions when controlling for age, body weight and gender. No such difference was evident in elderly subjects having lower intakes-absorption. EZP sizes in subjects experiencing severe Zn depletion were consistently lower than the model's 95% prediction intervals. The models have descriptive and predictive utility: contributing to an understanding of the physiological characteristics of the EZP, establishing normal values and ranges for healthy subjects and evaluating the suitability of EZP size as a biomarker of Zn status.

Zn is an essential nutrient for humans; however, a sensitive biomarker to assess Zn status has not been identified. The objective of this study was to determine the reliability and sensitivity of Zn transporter and metallothionein (MT) genes in peripheral blood mononuclear cells (PBMCs) to Zn exposure ex vivo and to habitual Zn intake in human subjects. In study 1, human PBMCs were cultured for 24 h with 0-50 µm ZnSO4 with or without 5 µm N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN), and mRNA expression of SLC30A1-10, SLC39A1-14, MT1 subtypes (A, B, E, F, G, H, L, M and X), MT2A, MT3 and MT4 mRNA was determined. In study 2, fifty-four healthy male and female volunteers (31·9 (sd 13·8) years, BMI 25·7 (sd 2·9) kg/m2) completed a FFQ, blood was collected, PBMCs were isolated and mRNA expression of selected Zn transporters and MT isoforms was determined. Study 1: MT1E, MT1F, MT1G, MT1H, MT1L, MT1M, MT1X, MT2A and SLC30A1 increased with increasing concentrations of Zn and declined with the addition of TPEN. Study 2: Average daily Zn intake was 16·0 (sd 5·3) mg/d (range: 9-31 mg/d), and plasma Zn concentrations were 15·5 (SD 2·8) μmol/l (range 11-23 μmol/l). PBMC MT2A was positively correlated with dietary Zn intake (r 0·306, P = 0·03) and total Zn intake (r 0·382, P < 0·01), whereas plasma Zn was not (P > 0·05 for both). Findings suggest that MT2A mRNA in PBMCs reflects dietary Zn intake in healthy adults and may be a component in determining Zn status.

The Linoleic Acid: Dihomo-γ-Linolenic Acid Ratio (LA: DGLA)- an Emerging Biomarker of Zinc Status

Zinc (Zn) is an essential micronutrient, and Zn deficiency remains a major global public health challenge. Recognised biomarkers of population Zn status include blood plasma or serum Zn concentration and proxy data such as dietary Zn intake and prevalence of stunting. Urine Zn concentration is rarely used to assess population Zn status. This study assessed the value of urine Zn concentration as a biomarker of population Zn status using a nationally representative sample of non-pregnant women of reproductive age (WRA) and school-aged children (SAC) in Malawi. Spot (casual) urine samples were collected from 741 WRA and 665 SAC. Urine Zn concentration was measured by inductively coupled plasma mass spectrometry with specific gravity adjustment for hydration status. Data were analysed using a linear mixed model with a spatially correlated random effect for between-cluster variation. The effect of time of sample collection (morning or afternoon), and gender (for SAC), on urine Zn concentration were examined. There was spatial dependence in urine Zn concentration between clusters among SAC but not WRA, which indicates that food system or environmental factors can influence urine Zn concentration. Mapping urine Zn concentration could potentially identify areas where the prevalence of Zn deficiency is greater and thus where further sampling or interventions might be targeted. There was no evidence for differences in urine Zn concentration between gender (P = 0.69) or time of sample collection (P = 0.85) in SAC. Urine Zn concentration was greater in afternoon samples for WRA (P = 0.003). Relationships between urine Zn concentration, serum Zn concentration, dietary Zn intake, and potential food systems covariates warrant further study.