Nicotinamide, a SIRT1 inhibitor, inhibits differentiation and facilitates expansion of hematopoietic progenitor cells with enhanced bone marrow homing and engraftment

Strategies that increase homing to the bone marrow and engraftment efficacy of ex?vivo expended CD34(+) cells are expected to enhance their clinical utility. Here we report that nicotinamide (NAM), a form of vitamin B-3, delayed differentiation and increased engraftment efficacy of cord blood-derived human CD34(+) cells cultured with cytokines. In the presence of NAM, the fraction of CD34(+)CD38(-) cells increased and the fraction of differentiated cells (CD14(+), CD11b(+), and CD11c(+)) decreased. CD34(+) cells cultured with NAM displayed increased migration toward stromal cell derived factor-1 and homed to the bone marrow with higher efficacy, thus contributing to their increased engraftment efficacy, which was maintained in competitive transplants with noncultured competitor cells. NAM is a known potent inhibitor of several classes of ribosylase enzymes that require NAD for their activity, as well as sirtuin (SIRT1), class III NAD(+)-dependent-histone-deacetylase. We demonstrated that EX-527, a specific inhibitor of SIRT1 catalytic activity, inhibited differentiation of CD34(+) cells similar to NAM, while specific inhibitors of NAD-ribosylase enzymes did not?inhibit differentiation, suggesting that the NAM effect is SIRT1-specific. Our findings suggest?a critical function of SIRT1 in the regulation of hematopoietic stem cell activity and imply the?clinical utility of NAM for ex?vivo expansion of functional CD34(+) cells.     

NKCC1 does not accumulate chloride in developing retinal neurons

GABA excites immature neurons due to their relatively high intracellular chloride concentration. This initial high concentration is commonly attributed to the ubiquitous chloride cotransporter NKCC1, which uses a sodium gradient to accumulate chloride. Here we tested this hypothesis in immature retinal amacrine and ganglion cells. Western blotting detected NKCC1 at birth and its expression first increased, then decreased to the adult level. Immunocytochemistry confirmed this early expression of NKCC1 and localized it to all nuclear layers. In the ganglion cell layer, staining peaked at P4 and then decreased with age, becoming undetectable in adult. In comparison, KCC2, the chloride extruder, steadily increased with age localizing primarily to the synaptic layers. For functional tests, we used calcium imaging with fura-2 and chloride imaging with 6-methoxy-N-ethylquinolinium iodide. If NKCC1 accumulates chloride in ganglion and amacrine cells, deleting or blocking it should abolish the GABA-evoked calcium rise. However, at P0-5 GABA consistently evoked a calcium rise that was not abolished in the NKCC1-null retinas, nor by applying high concentrations of bumetanide (NKCC blocker) for long periods. Furthermore, intracellular chloride concentration in amacrine and ganglion cells of the NKCC1-null retinas was approximately 30 mM, same as in wild type at this age. This concentration was not lowered by applying bumetanide or by decreasing extracellular sodium concentration. Costaining for NKCC1 and cellular markers suggested that at P3, NKCC1 is restricted to Müller cells. We conclude that NKCC1 does not serve to accumulate chloride in immature retinal neurons, but it may enable Müller cells to buffer extracellular chloride.     

Assessment of metabolic changes within normal appearing gray and white matter in children with growth hormone deficiency: Magnetic resonance spectroscopy and hormonal correlation

Objective: The pathogenesis of idiopathic growth hormone deficiency (GHD) in children, including possible cerebral metabolic alterations, remains unclear. The aim of the study was to evaluate metabolic changes within the normal appearing brain in children with GHD using MR spectroscopy (MRS) and to correlate MRS measurements with hormonal concentrations and with pituitary gland size. Methods: Seventy children with GHD (mean age 7.8 yrs) and 11 healthy controls (mean age 8.4 yrs) were enrolled in the study. The MRS examinations were performed on a 1.5T scanner. Voxels were located in the posterior cingulate gyrus (PCG) and the left parietal white matter (PWM). The NAA/Cr, Cho/Cr and mI/Cr ratios were analyzed. The metabolite ratios, pituitary gland size and hormonal concentrations: growth hormone (GH) in two stimulation tests and GH during the night, as well as IGF-1 (insulin-like growth factor) and IGFBP3 (insulin-like growth factor-binding protein) levels were also correlated. Results: There was a significant (p < 0.05) decrease of the NAA/Cr ratios in PCG and PWM in children with GHD compared to the normal subjects. Other metabolite ratios showed no significant differences. We also found significant positive correlations between NAA/Cr ratio in PWM and IGFBP3 level, as well as with GH concentration in a stimulation test with glucagon. Conclusions: The reduction of NAA/Cr ratios may suggest loss of neuronal activity within normal appearing gray and white matters in children with GHD. MRS could be a sensitive marker of cerebral metabolic disturbances associated with GHD and maybe used as an additional indicator for therapy with recombinant GH.     

Spontaneous rupture of liver hemangioma: Risk factors for rupture

We report a case of spontaneous rupture of a giant cavernous hemangioma of the liver arising from the caudate lobe, with extrahepatic growth, in a 67-year-old man. At emergency laparotomy, partial resection of the caudate lobe was performed and the hemangioma was found to measure 13 ×12×8 cm. The patient had a 10-year history of severe asthma requiring steroid therapy. To investigate the risk factors for spontaneous rupture of hepatic hemangioma, we compared the characteristics of patients with ruptured and non-ruptured lesions showing extrahepatic growth reported in the Japanese literature. Lesions with a diameter ≥4 cm located on the surface of the liver or showing extrahepatic growth appear to have a high risk of spontaneous rupture if the patient receives steroid therapy for a coexisting disorder. Even in patients who have not received steroid therapy, hemangiomas≥7–8 cm in diameter located in the left lobe with extrahepatic growth may also have a high risk of rupture. The treatment of hepatic hemangioma should be decided on the basis of the size and the location, and on the requirement for steroid therapy.     

Structural basis for cooperative interactions of substituted 2-aminopyrimidines with the acetylcholine binding protein

The nicotinic acetylcholine receptor (nAChR) and the acetylcholine binding protein (AChBP) are pentameric oligomers in which binding sites for nicotinic agonists and competitive antagonists are found at selected subunit interfaces. The nAChR spontaneously exists in multiple conformations associated with its activation and desensitization steps, and conformations are selectively stabilized by binding of agonists and antagonists. In the nAChR, agonist binding and the associated conformational changes accompanying activation and desensitization are cooperative. AChBP, which lacks the transmembrane spanning and cytoplasmic domains, serves as a homology model of the extracellular domain of the nAChRs. We identified unique cooperative binding behavior of a number of 4,6-disubstituted 2-aminopyrimidines to Lymnaea AChBP, with different molecular variants exhibiting positive, n_H > 1.0, and negative cooperativity, n_H < 1.0. Therefore, for a distinctive set of ligands, the extracellular domain of a nAChR surrogate suffices to accommodate cooperative interactions. X-ray crystal structures of AChBP complexes with examples of each allowed the identification of structural features in the ligands that confer differences in cooperative behavior. Both sets of molecules bind at the agonist-antagonist site, as expected from their competition with epibatidine. An analysis of AChBP quaternary structure shows that cooperative ligand binding is associated with a blooming or flare conformation, a structural change not observed with the classical, noncooperative, nicotinic ligands. Positively and negatively cooperative ligands exhibited unique features in the detailed binding determinants and poses of the complexes.Nicotinic acetylcholine receptors (nAChRs) function as allosteric pentamers of identical or homologous transmembrane spanning subunits. Ligand binding at two or more of the five intersubunit sites, located radially in the extracellular domain, drives a conformational change that results in the opening of a centrosymmetric transmembrane channel, internally constructed among the five subunits (SI Appendix, Fig. S2A) (1–4). Up to five potential agonist-competitive antagonist sites on the pentamer are found at the outer perimeter of the subunit interfaces. Amino acid side-chain determinants on both subunit interfaces dictate selectivity among the many subtypes of nAChRs. The interconversion between resting, active, and desensitized states occurs in the absence of ligands, and partial occupation of the binding sites suffices for agonist activation of the receptor and its antagonism (5–7). Cooperativity of agonist association and its coupling to channel gating likely play important roles in the dynamics of nicotinic responses and in sharpening the concentration and temporal windows for activation.As revealed in functional studies, most nAChRs are hetero-oligomeric, where the sites of ligand occupation are not identical (1–4). This arrangement arises when a common α-subunit pairs with one or more nonidentical subunit partners, termed non–α-subunits (7, 8). Nonidentity of the subunit interface complementary to the α-subunit may also give rise to heterogeneity in binding constants typically seen for antagonists and mask partially the degree of agonist cooperativity. An exception to this is the α7-neuronal nAChR composed of five identical subunits and exhibiting a high degree of cooperativity for agonist activation (9). Recently, sequence alignments identified genes coding for pentameric ligand-gated ion channels in prokaryotes led to the resolution of the first structure by X-ray crystallography on 3D crystals of a pentameric receptor protein from Erminia chrysanthemi (ELIC) (10) and Gloeobacter violaceus (GLIC) (11, 12) and provided high-resolution structures of the two end point states of the cooperative gating mechanism in the same pentameric ligand-gated ion channel (GLIC) (13). Recently, the first structure of a eukaryotic member of the family, the anionic glutamate receptor from Caenorhabditis elegans (GluCl), was solved at atomic resolution (14), revealing remarkable identity of 3D structure with GLIC.The acetylcholine binding protein (AChBP) was characterized from mollusks (15–17) and consists of only a homologous extracellular domain of the nAChR. Assembled as a homomeric pentamer, AChBP exhibits a similar profile of ligand selectivity toward the classical nicotinic agonists and antagonists of quaternary amine, tertiary and secondary amine (alkaloid), imine, and peptide origin that bind nicotinic receptors (18–25). If looked at solely on the basis of ligand-binding capacities, AChBP could be considered as a distinct subtype of nAChR. Although its homomeric composition and ligand selectivity best resemble the α7-subtype of nAChR, when the concentration dependence of ligand occupation has been examined, no evidence of cooperativity emerged (21). Accordingly the cooperative behavior for both activation and desensitization of receptors, seen for the classical nicotinic agonists with nAChRs, might arise from a cooperative torsional motion driven by the transmembrane spanning domain of the receptor (26).We demonstrate here a set of ligands that bind to the AChBP in a cooperative fashion, whereby binding to a single subunit affects the binding energy at identical interfaces in the pentamer. Hence, interactions within the extracellular domain of this family of homologous pentameric proteins establish a circumferential linkage between subunit interfaces which results in cooperative behavior.     

Spine radiosurgery for spinal metastases: indications,technique and outcome

Abstract

Early diagnosis, better imaging, and advanced treatment of cancer patients extend survival and increase the incidence of symptomatic spine metastases. The treatment algorithm for spine metastases has shifted to a more aggressive approach in recent years. Spine stereotactic radiosurgery (SRS) is a relatively new tool utilizing advanced imaging systems, planning software, image-guided localization, and intensity-modulated dose delivery. Radiosurgery of spine metastases yields high rates of pain- and tumor control, and offers both the patients and the treating physicians an effective noninvasive alternative. This review presents the indications and outcomes for SRS and describes current techniques.