Neuropathology of substance use disorders

Addictions to licit and illicit drugs are chronic relapsing brain disorders that affect circuits that regulate reward, motivation, memory, and decision-making. Drug-induced pathological changes in these brain regions are associated with characteristic enduring behaviors that continue despite adverse biopsychosocial consequences. Repeated exposure to these substances leads to egocentric behaviors that focus on obtaining the drug by any means and on taking the drug under adverse psychosocial and medical conditions. Addiction also includes craving for the substances and, in some cases, involvement in risky behaviors that can cause death. These patterns of behaviors are associated with specific cognitive disturbances and neuroimaging evidence for brain dysfunctions in a diverse population of drug addicts. Postmortem studies have also revealed significant biochemical and/or structural abnormalities in some addicted individuals. The present review provides a summary of the evidence that has accumulated over the past few years to implicate brain dysfunctions in the varied manifestations of drug addiction. We thus review data on cerebrovascular alterations, brain structural abnormalities, and postmortem studies of patients who abuse cannabis, cocaine, amphetamines, heroin, and “bath salts”. We also discuss potential molecular, biochemical, and cellular bases for the varied clinical presentations of these patients. Elucidation of the biological bases of addiction will help to develop better therapeutic approaches to these patient populations.     

When Genetic Load Does Not Correlate with Phenotypic Spectrum: Lessons from the GnRH Receptor (GNRHR)

Context: A broad spectrum of GnRH-deficient phenotypes has been identified in individuals with both mono- and biallelic GNRHR mutations. Objective: The objective of the study was to determine the correlation between the severity of the reproductive phenotype(s) and the number and functional severity of rare sequence variants in GNRHR. Subjects: Eight hundred sixty-three probands with different forms of GnRH deficiency, 46 family members and 422 controls were screened for GNRHR mutations. The 70 subjects (32 patients and 38 family members) harboring mutations were divided into four groups (G1-G4) based on the functional severity of the mutations (complete or partial loss of function) and the number of affected alleles (monoallelic or biallelic) with mutations, and these classes were mapped on their clinical phenotypes. Results: The prevalence of heterozygous rare sequence variants in GNRHR was significantly higher in probands vs. controls (P < 0.01). Among the G1-G3 groups (homozygous subjects with successively decreasing severity and number of mutations), the hypogonadotropic phenotype related to their genetic load. In contrast, subjects in G4, with only monoallelic mutations, demonstrated a greater diversity of clinical phenotypes. Conclusions: In patients with GnRH deficiency and biallelic mutations in GNRHR, genetic burden defined by severity and dose is associated with clinical phenotype. In contrast, for patients with monoallelic GNRHR mutations this correlation does not hold. Taken together, these data indicate that as-yet-unidentified genetic and/or environmental factors may combine with singly mutated GNRHR alleles to produce reproductive phenotypes.     

Tcl1 protein functions as an inhibitor of de novo DNA methylation in B-cell chronic lymphocytic leukemia (CLL)

B-cell chronic lymphocytic leukemia (CLL) is the most common human leukemia. Deregulation of the T-cell leukemia/lymphoma 1 oncogene (TCL1) in mouse B cells causes a CD5(+) leukemia similar to aggressive human CLL. To examine the mechanisms by which Tcl1 protein exerts its oncogenic activity in B cells, we performed proteomics experiments to identify its interacting partners. We found that Tcl1 physically interacts with de novo DNA methylthansferases Dnmt3A and Dnmt3B. We further investigated the effects of Tcl1 up-regulation on the enzymatic activity of Dnmt3A and found that Tcl1 overexpression drastically inhibits Dnmt3A function. In addition, B cells from TCL1 transgenic mice showed a significant decrease in DNA methylation compared with WT controls. Similarly, CLL samples with high Tcl1 expression showed a decrease in DNA methylation compared with CLL samples with low Tcl1 expression. Given the previous reports of inactivating mutations of DNMT3A in acute myelogenous leukemia and myelodysplastic syndrome, our results suggest that inhibition of de novo DNA methylation may be a common oncogenic mechanism in leukemogenesis.     

Thieving rodents as substitute dispersers of megafaunal seeds

The Neotropics have many plant species that seem to be adapted for seed dispersal by megafauna that went extinct in the late Pleistocene. Given the crucial importance of seed dispersal for plant persistence, it remains a mystery how these plants have survived more than 10,000 y without their mutualist dispersers. Here we present support for the hypothesis that secondary seed dispersal by scatter-hoarding rodents has facilitated the persistence of these large-seeded species. We used miniature radio transmitters to track the dispersal of reputedly megafaunal seeds by Central American agoutis, which scatter-hoard seeds in shallow caches in the soil throughout the forest. We found that seeds were initially cached at mostly short distances and then quickly dug up again. However, rather than eating the recovered seeds, agoutis continued to move and recache the seeds, up to 36 times. Agoutis dispersed an estimated 35% of seeds for >100 m. An estimated 14% of the cached seeds survived to the next year, when a new fruit crop became available to the rodents. Serial video-monitoring of cached seeds revealed that the stepwise dispersal was caused by agoutis repeatedly stealing and recaching each other's buried seeds. Although previous studies suggest that rodents are poor dispersers, we demonstrate that communities of rodents can in fact provide highly effective long-distance seed dispersal. Our findings suggest that thieving scatter-hoarding rodents could substitute for extinct megafaunal seed dispersers of tropical large-seeded trees.     

In situ observation of peptide bond formation at the water–air interface

We report unambiguous spectroscopic evidence of peptide bond formation at the air–water interface, yielding a possible mechanism providing insight into the formation of modern ribosomal peptide bonds, and a means for the emergence of peptides on early Earth. Protein synthesis in aqueous environments, facilitated by sequential amino acid condensation forming peptides, is a ubiquitous process in modern biology, and a fundamental reaction necessary in prebiotic chemistry. Such reactions, however, are condensation reactions, requiring the elimination of a water molecule for every peptide bond formed, and are thus unfavorable in aqueous environments both from a thermodynamic and kinetic point of view. We use the hydrophobic environment of the air–water interface as a favorable venue for peptide bond synthesis, and demonstrate the occurrence of this chemistry with in situ techniques using Langmuir-trough methods and infrared reflection absorption spectroscopy. Leucine ethyl ester (a small amino acid ester) first partitions to the water surface, then coordinates with Cu²⁺ ions at the interface, and subsequently undergoes a condensation reaction selectively forming peptide bonds at the air–water interface.Protein synthesis (condensation of amino acids through sequential peptide bond formation) is a fundamental and ubiquitous reaction in biology. Aqueous media are the required environments in which this chemistry takes place; however, protein synthesis is unfavorable in aqueous solution. In modern biology, the condensation reactions necessary in the formation of peptide bonds are facilitated catalytically by the large subunit of the ribosome. The mechanism of this catalyzed reaction originally proposed by Nissen et al. in 2000 (1) involved favorable orientation of peptide precursors, acid-base catalysis and transition-state stabilization, and the altered pK_a of the functional groups of the precursors caused by the reaction environment provided by the active site; such pK_a shifts had previously been seen in the active sites of other proteins (2). Since then, the original mechanism has been contested (3, 4). The acknowledged mechanistic function of the ribosome’s active site is its ability to bring the precursors in close proximity and orient them for reaction, with further mechanistic details remaining unresolved (4). Studies of peptide bond formation in the absence of modern biological machinery can give insight into the mechanism employed by the ribosome’s active site, as well as yield important information in the prebiotic route to the first peptides in the origin of life. The formation of a peptide bond (reaction R1 shown below) is a condensation reaction, eliminating a water molecule for each peptide bond formed, and thus faces both thermodynamic and kinetic constraints in bulk aqueous solution (5).5, 6). Amino acid monomers have the added kinetic disadvantage of existing primarily as zwitterions at environmentally and physiologically relevant pH values in bulk aqueous solution (5, 7). Insightful experiments have been performed, yielding peptide bonds in anhydrous solvents with amino acid ester starting materials and copper(II) ion catalysis (8, 9). Transition metal ions are thought to have been components of the early ocean (10), with one source being the heavy meteoritic and cometary bombardment experienced by the early Earth, but the anhydrous solvents used in these studies are neither physiologically relevant nor likely to have been present on early Earth. The same mechanism was attempted in aqueous solution, but no peptide formation was detected (9). Polymer formation in aqueous environments would most likely have been necessary on early Earth because the liquid ocean would have been the reservoir of amino acid precursors needed for protein synthesis. In this work, the air–water interface is utilized as the auspicious environment for peptide bond formation, coupling the water surface with the bulk water reservoir of monomers. In situ surface-sensitive techniques are used here to observe the condensation reaction of a model system composed of a small, water-soluble amino acid ester (leucine ethyl ester) through Cu²⁺ coordination.Air–water interfaces are found now, as on prebiotic Earth, at the surfaces of lakes, oceans, and atmospheric aerosols. The air–water interface (atmospheric aerosols in particular) has previously been proposed to be important in prebiotic chemistry (11–14) because it provides a unique environment for chemistry through its ability to concentrate and align biochemical precursors and to alter the state of ionization of surface species (15–19). Contemporary marine aerosols have been found to contain the amino acid precursors necessary for peptide bond chemistry (20), enabling the possibility for their use in such reactions. Further, the fluctuating conditions experienced by aerosols throughout their atmospheric lifetime, including evaporation of water, coagulation, and possibly reentry into the ocean, would naturally provide the compression of the surface layer shown in this work to be necessary for Cu²⁺ coordination leading to peptide bond chemistry (12).In addition, the unfavorable equilibrium constant for peptide bond formation in bulk aqueous solution is shifted when the molecules experience a water-restricted reaction environment at the water surface. Although the exact surface pH of water is debated (21–23), the surface is known to alter the pK_a of surface-active molecules toward their neutral form (24, 25), which aids in the promotion of peptide bond chemistry at the interface by reducing zwitterion formation and alleviating the kinetic constraint on peptide bond synthesis. The air–water interface has been reported in the literature to have a catalytic role in peptide bond formation (26–29) using synthetic long-chain amino acid esters that are anchored to the surface by the polar groups attached to their 18-carbon-long hydrocarbon tails, thus forced to reside solely at the surface of the water. Reaction amongst the surface monomers was promoted in these studies (27–29) through surface compression, and supported by subsequent collection, drying, and analysis of the surface products. In the work presented here, infrared reflection absorption spectroscopy (IRRAS) and Langmuir trough methods were used to observe, in situ, complex formation with a metal cation followed by condensation chemistry leading to peptide bond formation occurring at the air–water interface. The observation of such condensation reactions in situ at the interface and with such a small activation group (an ethyl ester) on the starting amino acid precursor in an aqueous environment is unique.     

Addition of iron to erythropoiesis-stimulating agents in cancer patients: a meta-analysis of randomized trials

Background  

Iron supplementation could improve the hematopoietic response of erythropoiesis-stimulating agents (ESAs) used for chemotherapy-induced anemia.