A proposed site of action for zinc in DNA synthesis

Effects of increasing supplemental zinc to non-implanted and implanted finishing steers

The effects of supplemental Zn within steroidal implant strategy on performance, carcass characteristics, trace mineral status, and muscle gene expression were tested in a 59-d study using 128 Angus-crossbred steers (492 ± 29 kg) in a 2 × 4 complete randomized design. Implant strategies included no implant (NoIMP) or Component TE-200 (TE200; Elanco, Greenfield, IN) administered on day 0. Zinc was supplemented at 0, 30, 100, or 150 mg Zn/kg dry matter (Zn0, Zn30, Zn100, Zn150, respectively) from ZnSO4. Steers were stratified by body weight (BW) to pens (n = 5 or 6 steers/pen) equipped with GrowSafe bunks (GrowSafe Systems Ltd., Airdrie, AB, Canada) and assigned treatments (n = 15, 16, or 17 steers/treatment). Cattle were weighed on days -1, 0, 18, and 59 with blood collected on days -1, 18, 40, and 59. Muscle samples were collected from the longissimus thoracis on day 11 and liver samples were collected on day 55 or 56. Data were analyzed using the Mixed Procedure of SAS via contrast statements testing the linear and quadratic response to Zn supplementation within implant treatment and NoIMP vs. TE200 for performance, carcass, blood, and liver parameters. Specific contrast statements were formed for the analysis of gene expression in muscle including: Zn0 vs. Zn150 within NoIMP and TE200, NoIMP vs. TE200 (Zn0 and Zn150 only), and the linear effect of supplementing Zn0, Zn100, and Zn150 within TE200. Steer was the experimental unit. Day 18 BW and days 0 to 18 average daily gain (ADG) were linearly increased due to Zn supplementation within TE200 (P ≤ 0.002) in conjunction with a linear increase from Zn in day 11 muscle epidermal growth factor receptor, matrix metalloproteinase 2, and phosphodiesterase 4B gene expression of TE200 steers (P ≤ 0.05). Plasma Zn on days 18 and 40 linearly increased with increasing Zn supplementation regardless of implant treatment (P ≤ 0.03) and was lesser for TE200 than NoIMP steers on day 18 (P = 0.001). Day 59 BW and hot carcass weight (HCW) were greater for TE200 vs. NoIMP (P ≤ 0.002) and HCW of implanted steers tended to linearly increase with increasing Zn supplementation (P = 0.09). No effects of Zn supplementation were observed in NoIMP for HCW, BW, or ADG (P ≥ 0.17). Yield grade and 12th rib fat tended to quadratically decrease within NoIMP (P ≤ 0.09), with Zn100 being the most lean. These data indicate increasing supplemental Zn influences steroidal implant signaling machinery while increasing the Zn status and implant-induced growth of feedlot cattle.

Effects of increasing supplemental zinc in beef feedlot steers administered a steroidal implant and beta agonist

Ninety-two Angus-crossbred steers (424 ± 28.3 kg initial body weight) were used in a 98-d study to assess the effects of increasing Zn supplementation on cattle performance, liver and plasma trace mineral concentrations, blood metabolites, and carcass characteristics. All steers were implanted with a Component TE-200 (200 mg trenbolone acetate + 20 mg estradiol; Elanco Animal Health, Greenfield, IN) on d 0 and fed 300 mg‧steer⁻¹‧d⁻¹ of ractopamine hydrochloride (Zoetis, Parsippany, NJ) from d 70 to 98. Cattle were fed via GrowSafe bunks (GrowSafe Systems Ltd., Airdrie, AB, Canada), and steer served as the experimental unit (n = 22 or 23 steers/treatment). Supplemental Zn was administered through the diet at 0, 100, 150, or 180 mg Zn/kg on a dry matter basis from ZnSO₄ (Zn0, Zn100, Zn150, or Zn180, respectively). Cattle were weighed on d −1, 0, 9/10, 20, 41, 59, 69, 70, 78/79, 97, and 98. Blood was collected on d 0, 9/10, 69, 78/79, and 97, and liver biopsies on d 9/10 and 78/79 (n = 12 steers/treatment). Data were analyzed as a complete randomized design. Contrast statements were formed to test the linear, quadratic, and cubic effects of Zn supplementation and test Zn0 vs. Zn supplementation. Day 10 and 70 body weight (BW) and d 0 to 10 and 0 to 70 average daily gain were linearly increased with Zn supplementation (P ≤ 0.05), and greater for Zn supplemented steers (P ≤ 0.03). No effects of Zn supplementation were observed on final BW, dressing percentage, ribeye area, 12th rib fat, or marbling (P ≥ 0.11). Hot carcass weight tended to be 7 kg greater for Zn supplemented steers than Zn0 (P = 0.07), and yield grade linearly increased with increasing Zn supplementation (P = 0.02). Day 10 liver Mn concentrations tended to quadratically decrease (P = 0.08) with increasing Zn supplementation, though d 79 liver Mn concentrations and arginase activity were not influenced by Zn (P ≥ 0.28). Day 10 liver arginase activity tended to be (r = 0.27; P = 0.07) and d 10 serum urea nitrogen was correlated with d 10 liver Mn (r = 0.55; P < 0.0001). Zinc supplementation linearly increased d 10 liver Zn and d 10, 69, 79, and 97 plasma Zn concentrations (P ≤ 0.05). A cubic effect of Zn was observed on d 79 liver Zn (P = 0.01) with lesser liver Zn in Zn0 and Zn150 steers. These data suggest increasing dietary Zn improves growth directly following the administration of a steroidal implant and that steroidal implants and beta agonists differ in their effects on protein metabolism.

Biological activities of polypyridyl-type ligands: implications for bioinorganic chemistry and light-activated metal complexes

Polypyridyl coordinating ligands are common in metal complexes used in medicinal inorganic chemistry. These ligands possess intrinsic cytotoxicity, but detailed data on this phenomenon are sparse, and cytotoxicity values vary widely and are often irreproducible. To provide new insights into the biological effects of bipyridyl-type ligands and structurally related metal-binding systems, reports of free ligand cytotoxicity were reviewed. The cytotoxicity of 25 derivatives of 2,2'-bipyridine and 1,10-phenanthroline demonstrates that there is no correlation between IC₅₀ values and ligand properties such as pKa, log D, polarizability volume, and electron density, as indicated by NMR shifts. As a result of these observations, as well as the various reported mechanisms of action of polypyridyl ligands, we offer the hypothesis that biological effects are governed by the availability of and affinity for specific metal ions within the experimental model.

Intestinal cellular proliferation and protein synthesis in zinc-deficient rats

Immature male Wistar rats were given a low-zinc semi-synthetic diet (2 mg Zn/kg) for 28 d. Control groups received a similar diet supplemented with 58 mg Zn/kg either ad lib. or in amounts matched to the consumption of the Zn-deficient group. Rates of growth, food consumption and small intestinal length were significantly reduced in the Zn-depleted rats. Zn deficiency in the rat was associated with a reduction in the ratio, crypt: villus and a lower rate of crypt cell division in the jejunum. This resulted in a substantial decrease in the net influx of new cells into the villi of the Zn-deficient animals compared with controls. The fractional rates of protein synthesis in jejunal mucosa were measured by a technique based on the determination of L-[4-3H]phenylalanine incorporation. There was no evidence of a decline in the protein synthetic rate in total mucosa from Zn-deficient rats. It is suggested that a reduction in cell influx into the villi may be responsible for the morphological and functional changes observed in the small intestine of rats fed on a low-Zn diet.

Placental transport and embryonic utilization of essential metabolites in the rat at the teratogenic dose of cadmium

Administration of Cd2+ to the 12-day pregnant rat caused a dose-dependent inhibition of placental 65Zn2+ transport. At 4 h after the injection of the teratogenic dose (1.25 mg Cd2+ per kg body weight), transport of 65Zn2+ to the embryo was inhibited by 75%. This inhibition decreased with time and at 48 h was no longer statistically significant. In contrast with Zn2+, the administration of Cd2+ did not affect the transport of sugar, amino acids and nucleic acid precursors from the maternal circulation to the embryo at any time. The incorporation of [14C]thymidine into embryonic DNA, however, was inhibited by about 50% at 4 h and by 75% at 20 h. By 48 h it returned to control levels. Incorporation of [14C]formate into DNA also was reduced. Inhibition of the incorporation of L-[14C]leucine into protein was apparent at 20 h, but not at 4 h, after the administration of Cd2+. Inhibition of DNA synthesis, which led to a significant reduction in embryonic DNA concentration at 20 h, was associated with a marked decrease in the activity in embryonic thymidine kinase. In extracts of embryos from Cd2+-treated dams, the activity of this enzyme was restored to the control level by the addition of 7.7 microM zinc acetate to the assay system. In vivo, the simultaneous injection of Zn2+ at a 2:1 atomic ratio with Cd2+ prevented the inhibition of thymidine incorporation into DNA. At the teratogenic dose, only about 16 ng Cd2+ per g wet weight is incorporated into the embryo. The inhibition of placental transport, particularly of Zn2+, therefore, may be of prime importance in the teratogenic response.

Incorporation of(3)H-thymidine into DNA and the activity of alkaline phosphatase in zinc-deficient fetal rat brains

The incorporation of(3)H-thymidine into DNA in the brains of the 17-day and 20-day old rat fetuses was significantly reduced by maternal zinc restriction during pregnancy. The activity of the enzyme thymidine kinase (EC 2.7.1.21) was similarly reduced in the zine-deprived fetal brains on days 14 and 20 of gestation, but not on day 17. Fetal brain alkaline phosphatase (EC 3.1.3.1) was significantly depressed by maternal zinc deprivation on days 17 and 20 of pregnancy.The data suggest an association between thymidine kinase and the reduced incorporation of(3)H-thymidine into DNA in the brains of 20-day old fetuses but not in animals on day 17. Alkaline phosphatase was however depressed at this stage.The suggestion is made that because of the complexity of brain development, future biochemical studies in this area should concern specific structures in the brain at particular critical stages during neurogenesis.

Lysosomal stability, superoxide dismutase and zinc deficiency in regenerating rat liver

1. Lysosomal stability was slightly increased in regenerating livers from rats receiving a zinc-deficient (less than 0.5 mg/kg) diet for 10 d before surgery. 2. The activity of superoxide dismutase (EC 1.15.1.1) was significantly reduced in the same tissues. 3. The results do not support the view that increased lysosomal fragility represents a major biochemical consequence of nutritional Zn deficiency in animals.