Effects of temperature on intracellular sodium, pH and cellular energy status in RIF‐1 tumor cells

Self Cite

The acute effects of hyperthermia on intracellular Na+ (Nai+), bioenergetic status and intracellular pH (pHi) were investigated in superfused Radiation Induced Fibrosarcoma-1 (RIF-1) tumour cells using shift-reagent-aided 23Na and 31P nuclear magnetic resonance (NMR) spectroscopy. Hyperthermia at 45 degrees C for 30 min produced a 50% increase in Na, a 0.42 unit decrease in pHi and a 40-45% decrease in NTP/P(i). During post-hyperthermia superfusion at 37 degrees C, pHi and NTP/P(i) recovered to the baseline value, but Na initially decreased and then increased to the hyperthermic level 60 min after heating. Hyperthermia at 42 degrees C caused only a 15-20% increase in Nai+. In the presence of 3 microM 5-(N-ethyl-N-isopropyl)amiloride (EIPA), an inhibitor of the Na+/H+ exchanger, the increase in Nai+ during 45 degrees C hyperthermia was attenuated, suggesting that the heat-induced increase in Nai+ was mainly due to an increase in Na+/H+ anti-porter activity. EIPA did not prevent hyperthermia-induced acidification. This suggests that pHi is controlled by other ion exchange mechanisms in addition to the Na+/H+ exchanger. EIPA increased the thermo-sensitivity of the RIF-1 tumour cells only slightly as measured by cell viability and clonogenic assays. The hyperthermia-induced irreversible increase in Nai+ suggests that changes in transmembrane ion gradients play an important role in cell damage induced by hyperthermia.

Section: Superfusion Preparation For Nmr Experimentsmentioning

confidence: 99%

Heat-induced changes in intracellular Na⁺, pH and bioenergetic status in superfused RIF-1 tumour cells determined by²³Na and³¹P magnetic resonance spectroscopy

Babsky

Hekmatyar

Gorski

et al. 2005

Self Cite

“…Active transport systems create and maintain ionic gradients. Thus, heat can produce significant alterations in trans-membrane sodium and pH gradients [8,9,14,15]. These ion gradients can also be affected by disruption of cellular energy metabolism during HT treatment [9,12].…”

Section: Discussionmentioning

confidence: 98%

“…The effects of HT on plasma membrane permeability and ionic exchange processes have been suggested to play a key role in cellular damage and death from the treatment [8][9][10][11]. A trans-membrane sodium concentration (Na þ ) gradient that is essential in maintaining cellular ion homeostasis for cell survival could be disrupted when heat is applied, therefore the effects of HT on total tissue ðNa þ t Þ and intra-cellular sodium ðNa þ i Þ may be useful for monitoring therapy response.…”

Section: Introductionmentioning

confidence: 99%

Controlled radio-frequency hyperthermia using an MR scanner and simultaneous monitoring of temperature and therapy response by¹H,²³Na and³¹P magnetic resonance spectroscopy in subcutaneously implanted 9L-gliosarcoma

James

Gao

Soon

et al. 2010

Self Cite

A magnetic resonance (MR) technique is developed to produce controlled radio-frequency (RF) hyperthermia (HT) in subcutaneously-implanted 9L-gliosarcoma in Fisher rats using an MR scanner and its components; the scanner is also simultaneously used to monitor the tumour temperature and the metabolic response of the tumour to the therapy. The method uses the (1)H chemical shift of thulium 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetra-acetic acid (TmDOTA(-)) to monitor temperature. The desired HT temperature is achieved and maintained using a feedback loop mechanism that uses a proportional-integral-derivative controller. The RF HT technique was able to heat the tumour from 33 degrees to 45 degrees C in approximately 10 min and was able to maintain the tumour temperature within +/-0.2 degrees C of the target temperature (45 degrees C). Simultaneous monitoring of the metabolic changes with RF HT showed increases in total tissue and intracellular Na(+) as measured by single-quantum and triple-quantum filtered (23)Na MR spectroscopy (MRS), respectively, and decreases in intra- and extracellular pH and cellular bioenergetics as measured by (31)P MRS. Monitoring of metabolic response in addition to the tumour temperature measurements may serve as a more reliable and early indicator of therapy response. In addition, such measurements during HT treatment will enhance our understanding of the tumour response mechanisms during HT, which may prove valuable in designing methods to improve therapeutic efficiency.

“…In all of the animal experiments performed, the tumour temperature calculated from the chemical shift of methyl resonance from TmDOTMA À was always lower than the rectal temperature measured using a fibre-optic probe. The temperature of sc-implanted tumours is usually lower than the body temperature because of impaired thermoregulation, poor perfusion resulting from aberrant blood vessels and increased conductive heat loss compared to deep-seated tissue [14]. TmDOTMA À was well tolerated by the animal, with no adverse effects being observed [30].…”

Section: Tmdota àmentioning

confidence: 98%

“…Thirdly, water proton T 1 , diffusion coefficient and resonance frequency are sensitive to metabolic and physiological changes in tissue microenvironment during HT [13]. For example, changes in pH and other ion concentrations during HT [14] can modify the screening effect of bonded electrons and alter water chemical shift. Fourthly, absolute temperature measurements are not possible using water relaxation rates and molecular diffusion rates and are difficult using water frequency shift because another much less sensitive signal (such as N-acetylaspartate in brain) is needed for reference [15].…”

Section: Mr Thermometrymentioning

confidence: 98%

Noninvasive thermometry using hyperfine-shifted MR signals from paramagnetic lanthanide complexes

Hekmatyar

Kerkhoff

Pakin

et al. 2005

Self Cite

MR thermometry techniques based on the strong water 1H signal provide high spatial and temporal resolution and have shown promise for applications such as laser surgery and RF ablation. However, these techniques have low temperature sensitivity for hyperthermia applications and are greatly influenced by local motion and susceptibility variations. 1H NMR signals from paramagnetic lanthanide complexes of Pr3+, Yb3+ and Tm3+ show up to 300-fold stronger temperature dependence compared to the water 1H signal. In addition, 1H chemical shifts of many of these complexes are insensitive to other factors such as the concentration of the paramagnetic complex, pH, [Ca2+], and the presence of plasma macro-molecules and ions. Applications of lanthanide complexes for temperature measurement in intact animals and the feasibility of mapping temperatures in phantoms have been demonstrated. Among all the lanthanide complexes examined so far, thulium 1, 4, 7, 10-tetramethyl-1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetraacetate (TmDOTMA-) appears to be the most attractive for in vivo MR thermometry. The 1H signal from the methyl groups on this complex is relatively intense because of 12 equivalent protons and provides high temperature sensitivity because of the large paramagnetic shifts induced by thulium. The possibility of imaging TmDOTMA2--in intact animals at physiologically safe concentrations has recently been demonstrated. Overall, MR thermometry methods based on hyperfine-shifted MR signals from paramagnetic lanthanide complexes appear promising for animal applications, but further studies relating to acceptable dose and signal-to-noise ratio are necessary before clinical use.