title: Microscopic images of intraspheroidal pH by 1H magnetic resonance chemical shift imaging of pH sensitive indicators.
abstract: OBJECTIVE
  We investigate microscopic pH heterogeneity within tumor spheroids using a novel 1H NMR methodology that provides high resolution measurements of intraspheroidal pH.
  
  
  METHODS
  High resolution microscopic images of intraspheroidal pH were obtained by 1H NMR using chemical shift selective excitation of the H2 resonance of imidazole added to the incubation medium. Imidazole accumulated in the intraspheroidal space in a pH dependent manner. Maps of intraspheroidal pH could be obtained by transforming pixel by pixel (32 x 32 micro) the regional variation of imidazole H2 intensity into a relative pH scale.
  
  
  RESULTS
  Our analysis revealed drastic intraspheroidal pH alterations depending on the size of the spheroid, ca. 0.6 pH units more acidic in the necrotic core than in the periphery, for spheroids of 600 mum diameter. The presence of concentric regions having similar intraspheroidal pH was consistently observed. The thickness of these regions decreased from pH 7.2 to pH 6.8 and increased below the latter pH value.
  
  
  CONCLUSIONS
  Our observations are compatible with the general model of spheroid growth where the more external layers of cells are in active growth and depict more alkaline pH values while the inner layers remain quiescent or evolve to a necrotic core, depicting more acidic pH values.
authors.affiliation: Laboratory for Imaging and Spectroscopy by Magnetic Resonance LISMAR, Instituto de Investigaciones Biomédicas Alberto Sols C.S.I.C./UAM, c/Arturo Duperier 4, Madrid, 28029, Spain.
authors.forename: Jose
authors.initials: J
authors.lastname: Alvarez-Pérez
authors.forename: Paloma
authors.initials: P
authors.lastname: Ballesteros
authors.forename: Sebastián
authors.initials: S
authors.lastname: Cerdán
mesh_terms: D000818:Animals; D005910:Glioma / Q000473:pathology; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D006859:Hydrogen / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D021621:Imaging, Three-Dimensional / Q000379:methods*; D007093:Imidazoles / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D018613:Microscopy, Confocal / Q000379:methods*; D009369:Neoplasms / Q000188:drug therapy / Q000378:metabolism; D011522:Protons; D018874:Spheroids, Cellular / Q000473:pathology; D014407:Tumor Cells, Cultured
chemical_list: D007093:Imidazoles; D011522:Protons; C029899:imidazole; D006859:Hydrogen