Is erythrocyte alkaline phosphatase activity a marker of zinc status in humans?

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

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.

Zinc nutritional status during pregnancy: a longitudinal study

During a controlled zinc depletion-repletion study, fifteen men aged 25.3 (SD 3.3) years were fed on a low-Zn diet with high phytate:Zn and phytate x calcium:Zn molar ratios for 7 weeks, followed by a 2 week repletion period when 30 mg supplemental Zn/d was given. Changes in plasma, urine, and hair Zn concentrations, taste acuity, and cellular immune response confirmed the development of mild Zn deficiency. Zn concentrations in neutrophils, platelets, erythrocytes and erythrocyte membranes, mean platelet volume, and activities of alkaline phosphatase (EC 3.1.3.1) and alpha-D-mannosidase (EC 3.2.1.24) in neutrophils did not respond to changes in Zn status. In contrast, alkaline phosphatase activity in erythrocyte membranes showed a significant decline which was consistent in all subjects (nmol product formed/min per mg protein; baseline v. 7-week Zn depletion, 0.656 (SD 0.279) v. 0.506 (SD 0.230), at 7 weeks; P < 0.05); neutral phosphatase activity remained unchanged. Alkaline phosphatase activity in erythrocyte membranes may be a potential index of Zn status in humans.

A longitudinal assessment of maternal zinc status in normal pregnant women

Zinc deficiency and IL-6 −174G/C polymorphism in old people from different European countries: Effect of zinc supplementation. ZINCAGE study

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.

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 causes and degree of zinc (Zn) deficiency in uraemia are still controversial. The effect of different treatment modalities are still unsettled. Plasma Zn represents only a small part of the total body Zn (about 0.5%). Thus determination of intracellular Zn in the peripheral blood cells might be more reliable. The present study was designed to assess the actual Zn status in uraemia and to find whether the treatment modalities of CRF (conservative and dialytic) could influence Zn status. Also to determine the elfeet of single dialysis session, type of dialysis and dialysate buffer on the Zn status. This study included ten healthy controls and fourty CRF patients divided in three subgroups on different treatment modalities (10 conservative treatment, 15 on intermittent perioneal dialysis ((IPD) and 15 on haemedialysis (HD). Zinc was measured by atomic absorption spectrophotometry in plasma and platelets. Statistically significant decrease of plasma Zn and significant increase of platelet Zn were found in CRF patients on different treatment modalities as compared to controls (P<0.01), but there was no significant difference in this respect hetween the three uraemic subgroups. There was no difference as regard serum protein and albunun levels in uraemic subgroups compared to controls. Moreover plasma Zn was significantly increased (still less than control) and platelet Zn was significantly decreased (P<0.01) after a single dialysis session in both IPD and HD subgroups, but the changes of both parameters (before and after dialysis) were insignificant in IPD patients compared to HD patients. Significant negative correlation was found between platelet Zn and creatinine clearance in the three uraemic subgroups (r = -0.81 P<0.01 in conservative patients, r= -0.72 P<0.01 in IPD and r= -0.76 P<0.01 in HD) while no correlation could be detected between the duration of dialysis and each of platelet & plasma Zn and between plasma Zn and each of platelet Zn, serum creatinine and clearance. Plasma Zn showed transient significant rise in HD patients using bicarbonate (11.6 ± 1.1 umol/L) as compared to those using acetate buffer (9.1 ± 1.3 umol/L), P<0.01. We can conclude that intracellular measurements of Zn (platelet) is of value in diagnosis and monitoring of Zn status in uraemics. Different treatment modalities does not influence Zn haernostasis. with no superiority of particular type of dialysis in this respect. The effect of a single dialysis session and the use of bicarbonate versus acetate buffer was just a transient rise of plasma Zn due to haemoconcentration and better correction of acidosis during dialysis.

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

The DRI assumes FZA to be constant when estimating dietary Zn needs, regardless of Zn intake or status. We assessed the independent effects of Zn intake and status on FZA in adult men. Nine men (aged 28–50 yrs, BMI 21–26, usual dietary Zn intake >11 mg/d) were studied 3 times: 1) at baseline; 2) after 1 wk on a liquid diet of 0.6 mg Zn/d and 5 wks on a low Zn diet (LoZ, 4 mg Zn/d); and 3) after 4 wks on an adequate zinc diet (AdZ, 11 mg Zn/d) with supplemental Zn (20 mg/d) given for the first 7d. At the end of each period, subjects consumed a day of 3 AdZ test meals with oral tracers of 67Zn (total 1.1 mg 67Zn/d) followed by a day of 3 LoZ test meals with oral tracers of 70Zn (total 0.4 mg 70Zn/d) or vice versa, depending on diet period. Five days after oral dosing, 0.5 mg 70Zn was given IV. Urine collected d 3–5 and d 8–10 after oral dosing was analyzed by ICPMS for 67:66 and 70:66 Zn ratios. FZA was estimated using a modified dual isotope tracer ratio method. Mean FZA was greater from LoZ meals than from AdZ meals (61 ± 14 % vs 36 ± 9 %, p<0.0001), regardless of diet period. Mean combined FZA of test meals decreased from the LoZ to the final AdZ period (53 ± 20 % vs 44 8 ± 16 %, p= 0.04). Plasma Zn concentration did not change by diet period. In summary, current Zn intake markedly affects FZA and is independent of smaller changes in FZA due to chronic zinc intake. Supported by NCBA and GCRC at SFGH, NCRR, NIH (grant MO1-RR00083-43).

Zinc (Zn) plays an essential role in many biological processes including immune response. Impaired Zn status promotes immune dysfunction, and it has been associated with enhanced chronic inflammation during aging. It has been suggested that the measurement of circulating Zn by itself could not reflect the real Zn status of an individual. It is therefore necessary to identify other determinants associated with plasma Zn to better understanding how physiopathological conditions during aging may affect the concentration of this metal. We have investigated the association between Zn levels and some biomarkers in 1090 healthy elderly from five European countries to increase the accuracy in the assessment of the Zn status. Stepwise multivariate linear regression models were used to analyze the influence of factors such as age, dietary intake, inflammatory mediators, laboratory parameters and polymorphisms previously associated with Zn homeostasis. Plasma Zn decrement was most strongly predicted by age, while positive correlations were found with albumin, RANTES and Zn intake after adjustment for multiple confounders. HSP70 +1267 AA genotype was an independent factor associated with Zn plasma concentrations. Cu/Zn ratio was positively associated with markers of systemic inflammation and age and negatively associated with albumin serum levels. Our findings show the most important independent determinants of plasma Zn concentration and Cu/Zn ratio variability in elderly population and suggest that the decline with age of Zn circulating levels is more dependent on physiopathological changes occurring with aging rather than to its nutritional intake.

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.

Following pulmonary infection with Francisella tularensis, we observed an unexpected but significant reduction of alkaline phosphatase, an enzyme normally up-regulated following inflammation. However, no reduction was observed in mice infected with a closely related gram-negative pneumonic organism (Klebsiella pneumoniae) suggesting the inhibition may be Francisella-specific. In similar fashion to in vivo observations, addition of Francisella lysate to exogenous alkaline phosphatase (tissue-nonspecific isozyme) was inhibitory. Partial purification and subsequent proteomic analysis indicated the inhibitory factor to be the heat shock protein DnaK. Incubation with increasing amounts of anti-DnaK antibody reduced the inhibitory effect in a dose-dependent manner. Furthermore, DnaK contains an adenosine triphosphate binding domain at its N terminus, and addition of adenosine triphosphate enhances dissociation of DnaK with its target protein, e.g. alkaline phosphatase. Addition of adenosine triphosphate resulted in decreased DnaK co-immunoprecipitated with alkaline phosphatase as well as reduction of Francisella-mediated alkaline phosphatase inhibition further supporting the binding of Francisella DnaK to alkaline phosphatase. Release of DnaK via secretion and/or bacterial cell lysis into the extracellular milieu and inhibition of plasma alkaline phosphatase could promote an orchestrated, inflammatory response advantageous to Francisella.

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