Papers of the Month
By Sanya Mehta, Victoria Placentra, Saniya Rattan, Nancy Urbano, Qing Xu
Hydroxyurea tolerability and toxicokinetics in rats
Researchers in the Division of the National Toxicology Program (DNTP) examined the long-term use of hydroxyurea (HU) therapy, the most effective strategy for managing sickle cell anemia, a genetic disorder of the blood. HU effectively increases healthy fetal hemoglobin production, but through a mechanism that is harmful to cells. The use of HU and its adverse side-effects are well-managed in adults. However, the U.S. Food and Drug Administration only recently approved HU for use in children and data is limited for understanding the impact the drug may have on child development.
The scientists conducted critical preliminary studies to identify appropriate doses for evaluating long-term effects. They assessed HU kinetics, or the movement of the chemical in the body, during critical periods of rodent development. HU was administered to pregnant rats from late gestation through lactation and to their offspring for 34 days after birth. Decreased body weight and adverse clinical observations, such as hair loss, appeared in offspring receiving at least 75 milligrams per kilogram per day. Data revealed gestational transfer of HU, but minimal lactational transfer. There was no difference in the half-life of HU between age and sex, but systemic exposure decreased with increasing age. (SM)
Citation: Huang MC, Turner KJ, Vallant M, Robinson VG, Lu Y, Price CJ, Fennell TR, Silinski MA, Waidyanatha S, Ryan KR, Black SR, Fernando RA, McIntyre BS. 2020. Tolerability and age-dependent toxicokinetics following perinatal hydroxyurea treatment in Sprague Dawley rats. J Appl Toxicol; doi:10.1002/jat.4087 [Online 25 November 2020].
Ancestry affects reprogramming of fibroblasts to iPSCs
Individual heterogeneity, or genetic variability, can substantially affect reprogramming of somatic cells into induced pluripotent stem cells (iPSCs), according to NIEHS scientists and their collaborators. iPSCs are stem cells that are derived from differentiated cells, such as fibroblasts, and they can both self-renew and are pluripotent, meaning they can be differentiated into other cell-types. In a previous publication, the research team obtained fibroblasts — tissue cells — from healthy, diverse donors and observed that each person’s fibroblasts had consistent differences in the ability to be reprogrammed to iPSCs. Ancestry was identified as a large contributing factor. In this publication, the research team identified genes and pathways that may be responsible for the observed differences.
Using 72 dermal fibroblast-iPSCs from self-identified African Americans and white Americans, the researchers found ancestry-dependent and ancestry-independent genes associated with reprogramming efficiency. These include genes involved in intracellular transport regulation, protein localization, and cytoskeletal organization, as well as dynamic biological processes like cancer and wound healing. The findings suggest that the heterogeneity of an individual can influence iPSC reprogramming, and the scientists suggested that these genes will provide insights into ancestry-dependent regulation of cell fate and reprogramming. (NU)
Citation: Bisogno LS, Yang J, Bennett BD, Ward JM, Mackey LC, Annab LA, Bushel PR, Singhal S, Schurman SH, Byun JS, Napoles AM, Perez-Stable EJ, Fargo DC, Gardner K, Archer TK. 2020. Ancestry-dependent gene expression correlates with reprogramming to pluripotency and multiple dynamic biological processes. Sci Adv 6(47):eabc3851.
New method to deliver polyphosphate molecules into cultured cells
NIEHS researchers and their collaborators have developed tools to deliver diphosphoinositol polyphosphates (PP-InsPs) into cultured cells to study their actions. The PP-InsPs are multipurpose cell signaling molecules that regulate diverse biological processes. The few tools that exist to study PP-InsP activities in living cells require hours-long procedures and are plagued by the possibility of off-target effects, thereby compromising short-term studies.
Because the PP-InsPs are highly charged, they cannot enter cells. Therefore, the researchers masked the charge by encapsulating the PP-InsPs inside liposomes. These are minute spherical sacs of phospholipid molecules are similar to those found in cell membranes, except that the researchers used phospholipids that melt at 40 degrees Celsius (i.e., fractionally above body temperature). The liposomes also contain a dye that warms when exposed to biologically harmless red light. These liposomes are readily accumulated by the cells. Finally, the cells are briefly placed under red light for two to five minutes, causing the liposomes to heat, melt, and release their PP-InsP cargo.
To validate this new delivery method, the scientists developed a fluorescent PP-InsP analogue and monitored its release into cells. This new intracellular PP-InsP delivery method is adjustable and applicable to all PP-InsPs and analogs. (SR)
Citation: Wang Z, Jork N, Bittner T, Wang H, Jessen HJ, Shears SB. 2020. Rapid stimulation of cellular Pi uptake by the inositol pyrophosphate InsP8 induced by its photothermal release from lipid nanocarriers using a near infra-red light-emitting diode. Chem Sci 11:10265–10278.
Prenatal vitamin D supplement and maternal absorption of toxic metals
In a study of pregnant women in Bangladesh, taking vitamin D supplements was associated with nonsignificant increases in lead levels, but significant increases in cord blood levels of lead and cadmium, according to NIEHS researchers and their collaborators. Vitamin D is important for building healthy bones, but animal studies indicate it increases the absorption of toxic metals a body is exposed to, such as lead, cadmium, manganese, and mercury. The study was the first to examine the effect of prenatal vitamin D supplementation and blood metal levels in a randomized clinical trial.
In the study, 1,300 pregnant women were randomized into groups that received a placebo or weekly doses of either 4,200, 16,800, or 28,000 international units (IU) of vitamin D3.
Randomization occurred in the second trimester and supplementation or placebo were continued throughout pregnancy. At delivery, maternal blood and umbilical cord blood samples were collected, and researchers measured their cadmium, lead, mercury, and manganese levels using a technique called inductively coupled plasma mass spectrometry. The pregnant women who received vitamin D supplementation showed no significant increase in blood metal concentrations compared to the placebo group. However, they were more likely to have infants with higher cord blood lead levels and with detectable cadmium. The authors say further investigation is needed since there is no safe level of toxic metals for infants. (VP)
Citation: Jukic AMZ, Zuchniak A, Qamar H, Ahmed T, Mahmud AA, Roth DE. 2020. Vitamin D treatment during pregnancy and maternal and neonatal cord blood metal concentrations at delivery: Results of a randomized controlled trial in Bangladesh. Environ Health Perspect 128(11):117007.
Stress and genetic variation contribute to end of menstruation
NIEHS researchers and their collaborators have revealed that genetic factors contribute to development of hypothalamic amenorrhea (HA), a condition in which menstruation stops in women of reproductive age. The finding provides new insight into the development of HA and women’s reproductive health.
Studies have shown that HA is more prevalent in women with excessive exercise, food restriction, or psychological stress. Both physical and emotional stressors could cause altered secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus in the brain. GnRH deficiency, in turn, impairs the synthesis of gonadotropins that are essential for reproduction and fertility and leads to hypogonadotropic hypogonadism (HH). Several rare, pathogenic sequence variants in genes that control the development or function of GnRH have been identified in individuals with a rare syndrome called isolated hypogonadotropic hypogonadism (IHH), an inherited form of HH. Due to the varied menstrual and hormonal response to similar stressors, this study investigated whether genetic variation influenced individual susceptibility to known risk factors for HA.
The researchers sequenced all the protein-coding regions of genes in women with HA and women in the control group. After comparing the frequency of rare variants in more than 50 IHH-associated genes, they found HA patients had a greater burden of variants than the control heathy women, confirming the genetic impact on the development of HA. (QX)
Citation: Delaney A, Burkholder AB, Lavender CA, Plummer L, Mericq V, Merino PM, Quinton R, Lewis KL, Meader BN, Albano A, Shaw ND, Welt CK, Martin KA, Seminara SB, Biesecker LG, Bailey-Wilson JE, Hall JE. 2020. Increased burden of rare sequence variants in GnRH-associated genes in women with hypothalamic amenorrhea. J Clin Endocrinol Metab; doi: 10.1210/clinem/dgaa609 [Online 1 September 2020].
(Sanya Mehta is an Intramural Research Training Award [IRTA] postbaccalaureate fellow in the NIEHS Matrix Biology Group. Victoria Placentra is an IRTA postbaccalaureate fellow in the NIEHS Mutagenesis and DNA Repair Regulation Group. Saniya Rattan, Ph.D., is an IRTA fellow in the NIEHS Reproductive Developmental Biology Group. Nancy Urbano is an IRTA postbaccalaureate fellow in the DNTP Predictive Toxicology and Screening Group. Qing Xu is a biologist in the NIEHS Metabolism, Genes, and Environment Group.)