page_title: Isothermal microcalorimetry
section_title: Toxicology
hierarchical_section_title: Isothermal microcalorimetry / Applications / Examples of applications / Biology and medicine / Toxicology
caption_attribution_description: The fibroblast suspension was in a stirred IMC ampoule maintained at 37C. The IMC heat flow curve shows the heat flow from the living fibroblasts, a heat flow spike due to injection of SDS and a return of heat flow to baseline (zero) do to lysis of the fibroblasts by SDS.
context_page_description: Isothermal microcalorimetry is a laboratory method for real-time monitoring and dynamic analysis of chemical, physical and biological processes. Over a period of hours or days, IMC determines the onset, rate, extent and energetics of such processes for specimens in small ampoules at a constant set temperature.
  IMC accomplishes this dynamic analysis by measuring and recording vs. elapsed time the net rate of heat flow to or from the specimen ampoule, and the cumulative amount of heat consumed or produced.
  IMC is a powerful and versatile analytical tool for four closely related reasons:
  All chemical and physical processes are either exothermic or endothermic—produce or consume heat.
  The rate of heat flow is proportional to the rate of the process taking place.
  IMC is sensitive enough to detect and follow either slow processes in a few grams of material, or processes which generate minuscule amounts of heat.
  IMC instruments generally have a huge dynamic range—heat flows as low as ca. 1 μW and as high as ca. 50,000 μW can be measured by the same instrument.
  The IMC method of studying rates of processes is thus broadly applicable, provides real-time continuous data, and is sensitive.
context_section_description: As of 2012, IMC has not become widely used in cultured cell toxicology even though it has been used periodically and successfully since the 1980s. IMC is advantageous in toxicology when it is desirable to observe cultured cell metabolism in real time and to quantify the rate of metabolic decline as a function of the concentration of a possibly toxic agent. One of the earliest reports (Ankerst et al. 1986) of IMC use in toxicology was a study of antibody-dependent cellular toxicity (ADCC) against human melanoma cells of various combinations of antiserum, monoclonal antibodies and also peripheral blood lymphocytes as effector cells. Kinetics of melanoma cell metabolic heat flow vs. time in closed ampoules were measured for 20 hours. The authors concluded that 
  "...microcalorimetry is a sensitive and particularly suitable method for the analysis of cytotoxicity kinetics."
  IMC is also being used in environmental toxicology. In an early study (Thorén 1992) toxicity against monolayers of alveolar macrophages of particles of MnO₂, TiO₂ and SiO₂ (silica) were evaluated. IMC results were in accord with results obtained by fluorescein ester staining and microscopic image analysis—except that IMC showed toxic effects of quartz not discernable by image analysis. This latter observation—in accord with known alveolar effects—indicated to the authors that IMC was a more sensitive technique.
  Much more recently (Liu et al. 2007), IMC has been shown to provide dynamic metabolic data which assess toxicity against fibroblasts of Cr(VI) from potassium chromate. Fig. 5 shows baseline results determining the metabolic heat flow from cultured fibroblasts prior to assessing the effects of Cr(VI). The authors concluded that 
   "Microcalorimetry appears to be a convenient and easy technique for measuring metabolic processes...in...living cells. As opposed to standard bioassay procedures, this technique allows continuous measurements of the metabolism of living cells. We have thus shown that Cr(VI) impairs metabolic pathways of human fibroblasts and particularly glucose utilization."
  Simple closed ampoule IMC has also been used and advocated for assessing the cultured cell toxicity of candidate surgical implant materials—and thus serve as a biocompatibility screening method. In one study (Xie et al. 2000) porcine renal tubular cells in culture were exposed to both polymers and titanium metal in the form of "microplates" having known surface areas of a few cm². The authors concluded that IMC
   "...is a rapid method, convenient to operate and with good reproducibility. The present method can in most cases replace more time-consuming light and electron microscopic investigations for quantitating of adhered cells."
  In another implant materials study (Doostmohammadi et al. 2011) both a rapidly growing yeast culture and a human chondrocyte culture were exposed to particles (diam.< 50 μm) of calcium hydroxyapatite (HA) and bioactive (calcium-containing) silica glass. The glass particles slowed or curtailed yeast growth as a function of increasing particle concentration. The HA particles had much less effect and never entirely curtailed yeast growth at the same concentrations. The effects of both particle types on chondrocyte growth were minimal at the concentration employed. The authors concluded that
  "The cytotoxicity of particulate materials such as bioactive glass and hydroxyapatite particles can be evaluated using the microcalorimetry method. This is a modern method for in vitro study of biomaterials biocompatibility and cytotoxicity which can be used alongside the old conventional assays."
caption: Heat flow vs. time for the treatment of fibroblasts in culture in a stirred stainless steel ampoule. A = introduction of the ampoule into the measurement position, with metabolic heat flow then reaching an equilibrium level. B = injection of sodium dodecyl sulfate (SDS) which produced sharp heat flow peaks related to exothermic diluton of the SDS and lysis of the fibroblasts. After lysis, the heat flow rate returned near zero since fibroblast metabolism had ceased. dQ/dt = the metabolic heat flow of the fibroblasts in culture (from Liu, et al. 2007 with publisher permission). Fig. 5
exif: {}