Vesa Oikonen

Publications (111) View all

• Article: Validation of [(18)F]fluorodeoxyglucose and positron emission tomography (PET) for the measurement of intestinal metabolism in pigs, and evidence of intestinal insulin resistance in patients with morbid obesity.

  H Honka, J Mäkinen, J C Hannukainen, M Tarkia, V Oikonen, M Teräs, V Fagerholm, T Ishizu, A Saraste, C Stark, T Vähäsilta, P Salminen, A Kirjavainen, M Soinio, A Gastaldelli, J Knuuti, P Iozzo, P Nuutila
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  ABSTRACT: AIMS/HYPOTHESIS: The role of the intestine in the pathogenesis of metabolic diseases is gaining much attention. We therefore sought to validate, using an animal model, the use of positron emission tomography (PET) in the estimation of intestinal glucose uptake (GU), and thereafter to test whether intestinal insulin-stimulated GU is altered in morbidly obese compared with healthy human participants. METHODS: In the validation study, pigs were imaged using [(18)F]fluorodeoxyglucose ([(18)F]FDG) and the image-derived data were compared with corresponding ex vivo measurements in tissue samples and with arterial-venous differences in glucose and [(18)F]FDG levels. In the clinical study, GU was measured in different regions of the intestine in lean (n = 8) and morbidly obese (n = 8) humans at baseline and during euglycaemic hyperinsulinaemia. RESULTS: PET- and ex vivo-derived intestinal values were strongly correlated and most of the fluorine-18-derived radioactivity was accumulated in the mucosal layer of the gut wall. In the gut wall of pigs, insulin promoted GU as determined by PET, the arterial-venous balance or autoradiography. In lean human participants, insulin increased GU from the circulation in the duodenum (from 1.3 ± 0.6 to 3.1 ± 1.1 μmol [100 g](-1) min(-1), p < 0.05) and in the jejunum (from 1.1 ± 0.7 to 3.0 ± 1.5 μmol [100 g](-1) min(-1), p < 0.05). Obese participants failed to show any increase in insulin-stimulated GU compared with fasting values (NS). CONCLUSIONS/INTERPRETATION: Intestinal GU can be quantified in vivo by [(18)F]FDG PET. Intestinal insulin resistance occurs in obesity before the deterioration of systemic glucose tolerance.
  Diabetologia 01/2013; · 6.81 Impact Factor
• Article: Cholinergic dysfunction after traumatic brain injury: preliminary findings from a PET study.

  A Östberg, J Virta, J O Rinne, V Oikonen, P Luoto, K Någren, E Arponen, O Tenovuo
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  ABSTRACT: There is evidence that the cholinergic system is frequently involved in the cognitive consequences of traumatic brain injury (TBI). We studied whether the brain cholinergic function is altered after TBI in vivo using PET. Cholinergic function was assessed with [methyl-(11)C]N-methylpiperidyl-4-acetate, which reflects the acetylcholinesterase (AChE) activity, in 17 subjects more than 1 year after a TBI and in 12 healthy controls. All subjects had been without any centrally acting drugs for at least 4 weeks. The AChE activity was significantly lower in subjects with TBI compared to controls in several areas of the neocortex (-5.9% to -10.8%, p=0.053 to 0.004). Patients with chronic cognitive symptoms after TBI show widely lowered AChE activity across the neocortex.
  Neurology 03/2011; 76(12):1046-50. · 8.31 Impact Factor
• Source

  Available from: Anne Roivainen

  Dataset: Roivainen 10.1007 s00259-012-2282-x

  Anne Roivainen, Sannamari Hautaniemi, Timo Möttönen, Pirjo Nuutila, Vesa Oikonen, Riitta Parkkola, Luminita Pricop, Rudyard Ress, Nicholas Seneca, Marko Seppänen, Timo Yli-Kerttula
• Article: Different metabolic responses of human brown adipose tissue to activation by cold and insulin.

  Janne Orava, Pirjo Nuutila, Martin E Lidell, Vesa Oikonen, Tommi Noponen, Tapio Viljanen, Mika Scheinin, Markku Taittonen, Tarja Niemi, Sven Enerbäck, Kirsi A Virtanen
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  ABSTRACT: We investigated the metabolism of human brown adipose tissue (BAT) in healthy subjects by determining its cold-induced and insulin-stimulated glucose uptake and blood flow (perfusion) using positron emission tomography (PET) combined with computed tomography (CT). Second, we assessed gene expression in human BAT and white adipose tissue (WAT). Glucose uptake was induced 12-fold in BAT by cold, accompanied by doubling of perfusion. We found a positive association between whole-body energy expenditure and BAT perfusion. Insulin enhanced glucose uptake 5-fold in BAT independently of its perfusion, while the effect on WAT was weaker. The gene expression level of insulin-sensitive glucose transporter GLUT4 was also higher in BAT as compared to WAT. In conclusion, BAT appears to be differently activated by insulin and cold; in response to insulin, BAT displays high glucose uptake without increased perfusion, but when activated by cold, it dissipates energy in a perfusion-dependent manner.
  Cell metabolism 08/2011; 14(2):272-9. · 17.35 Impact Factor
• Source

  Available from: Anne Roivainen

  Article: Cross-validation of input functions obtained by H₂ ¹⁵O PET imaging of rat heart and a blood flow-through detector.

  Nobuyuki Kudomi, Hannu Sipilä, Anu Autio, Vesa Oikonen, Heidi Liljenbäck, Miikka Tarkia, Jarno Laivola, Jarkko Johansson, Mika Teräs, Anne Roivainen
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  ABSTRACT: Positron emission tomography (PET) with ¹⁵O-labeled water (H₂ ¹⁵O) facilitates the visualization and quantification of blood flow in clinical investigations and also in small animals. The quantification of blood flow requires an input function, which is generally obtained by measuring radioactivity in arterial blood withdrawn during PET scanning. However, this approach is not always feasible, because abundant blood sampling may affect the physiological process being measured. The purpose of the present study was to develop and cross-validate two methods, namely, a blood- and an image-based method for obtaining the input function for blood flow studies from rat H₂ ¹⁵O PET. The study material consisted of two separate groups of rats. Group 1 rats were imaged twice by a high-resolution research tomograph PET camera at resting condition for a test-retest study (n = 4), and group 2 rats were imaged with and without adenosine infusion for a rest-stress study (n = 4). In group 1, radioactivity concentration in arterial blood was measured with a new flow-through detector during imaging and a blood-based input function was obtained. The image-based input function was estimated using time-activity curves from the left ventricle and myocardial regions. To validate the two input function methods, myocardial blood flow (MBF) and cerebral blood flow (CBF) were computed, and the methods were tested for reproducibility (test-retest study) and changes (rest-stress study). The blood- and image-based input functions were similar, and the corresponding CBF values differed only by -6.9 ± 8.1%. In the test-retest study, both MBF and CBF showed good reproducibility, and in the rest-stress study, adenosine significantly increased both MBF (P = 0.035) and CBF (P = 0.029), compared with the resting condition. It is possible both to measure the input function from rat arteria femoralis during H₂ ¹⁵O PET imaging and to estimate the input function from rat H₂ ¹⁵O PET images, thereby facilitating the assessment of blood flow in organs visible in PET images.
  Molecular imaging and biology: MIB: the official publication of the Academy of Molecular Imaging 08/2011; 14(4):509-16. · 2.47 Impact Factor