The diagnosis of many neurologic diseases benefits from the ability to quantitatively assess iron in the brain. Paramagnetic iron modifies the magnetic susceptibility causing magnetic field inhomogeneity in MRI. The local field can be mapped using the MR signal phase, which is discarded in a typical image reconstruction. The calculation of the susceptibility from the measured magnetic field is an ill-posed inverse problem. In this work, a bayesian regularization approach that adds spatial priors from the MR magnitude image is formulated for susceptibility imaging. Priors include background regions of known zero susceptibility and edge information from the magnitude image. There is a growing scientific and clinical interest in quantitatively mapping magnetic biomaterials by measuring their susceptibilities using MRI. Quantifying endogenous paramagnetic iron would be useful for assessing blood oxygenation (1-3) and iron overloading in organs such as the liver (4) and the heart (5). The diagnosis and monitoring of vascular and neurodegenerative diseases in the brain would benefit directly from iron quantification (6). Susceptibility quantification may allow exploiting the strong diamagnetism of calciumbased structures to characterize osteoporosis (7,8) or calcifications in the breast and brain. Furthermore, quantitative susceptibility mapping (QSM) would allow robust quantification of paramagnetic and superparamagnetic contrast agents essential to molecular and cellular imaging (9-11) and also be valuable to the characterization of cardiovascular function (12)(13)(14). Recently, an MR reporter gene enabling iron accumulation within the cell was demonstrated (15), and quantifying the induced iron would be very important for investigating in vivo molecular biology.Quantifying the susceptibility from the magnetic field is an inverse problem similar to magnetoencephalography, in which magnetic sources inside the brain must be located and quantified from limited measurements of the field outside the head (16). While quantification based on geometrical models has long been used for specific applications (1,2,4,8,14,(17)(18)(19)(20), the reconstruction of susceptibility maps in which each voxel has an unknown susceptibility is a much more complex problem. While some approaches have been theoretically proposed (6,21,22), the ill-posedness due to limited measurements was dealt with recently by using regularization approaches (8,23) or acquisition strategies (24). Here, a bayesian regularized approach is presented that introduces priors derived from the MR magnitude image. It is shown that imposing values at given locations together with seeking a solution that shares edges with the MR magnitude image is more robust that the previously proposed methods (23). The technique is validated using simulations and phantom experiments. Additionally, in vivo brain susceptibility maps are obtained, introducing a new quantitative contrast that is directly linked to the amount of iron in the brain. MATERIALS AND METHODS Susceptibility an...

To examine the mechanism by which metformin lowers endogenous glucose production in type 2 diabetic patients, we studied seven type 2 diabetic subjects, with fasting hyperglycemia (15.5 ± 1.3 mmol/l), before and after 3 months of metformin treatment. Seven healthy subjects, matched for sex, age, and BMI, served as control subjects. Rates of net hepatic glycogenolysis, estimated by 13 C nuclear magnetic resonance spectroscopy, were combined with estimates of contributions to glucose production of gluconeogenesis and glycogenolysis, measured by labeling of blood glucose by 2 H from ingested 2 H 2 O. Glucose production was measured using [6,6-2 H 2 ]glucose. The rate of glucose production was twice as high in the diabetic subjects as in control subjects (0.70 ± 0.05 vs. 0.36 ± 0.03 mmol · m -2 · min -1 , P < 0.0001). Metformin reduced that rate by 24% (to 0.53 ± 0.03 mmol · m -2 · min -1 , P = 0.0009) and fasting plasma glucose concentration by 30% (to 10.8 ± 0.9 mmol/l, P = 0.0002). The rate of gluconeogenesis was three times higher in the diabetic subjects than in the control subjects (0.59 ± 0.03 vs. 0.18 ± 0.03 mmol · m -2 · min -1 ) and metformin reduced that rate by 36% (to 0.38 ± 0.03 mmol · m -2 · min -1 , P = 0.01). By the 2 H 2 O method, there was a twofold increase in rates of gluconeogenesis in diabetic subjects (0.42 ± 0.04 mmol · m -2 · min -1 ), which decreased by 33% after metformin treatment (0.28 ± 0.03 mmol · m -2 · min -1 , P = 0.0002). There was no glycogen cycling in the control subjects, but in the diabetic subjects, glycogen cycling contributed to 25% of glucose production and explains the differences between the two methods used. In conclusion, patients with poorly controlled type 2 diabetes have increased rates of endogenous glucose production, which can be attributed to increased rates of gluconeogenesis. Metformin lowered the rate of glucose production in these patients through a reduction in gluconeogenesis. A lthough it is generally agreed that metformin reduces fasting plasma glucose concentrations by reducing rates of hepatic glucose production (1,2), its effect on the relative contributions of hepatic glycogenolysis and gluconeogenesis remains controversial. Some studies conclude that metformin works mostly by reducing rates of gluconeogenesis (3); others, that it works by reducing rates of hepatic glycogenolysis (4,5).Because of limitations of the methods used in the previous studies to assess gluconeogenesis and glycogenolysis, we used two independent and complementary methods to assess these processes in patients with poorly controlled type 2 diabetes before and after 3 months of metformin therapy. 13C nuclear magnetic resonance (NMR) spectroscopy was used to directly measure rates of net hepatic glycogenolysis, in combination with [6,6-2 H 2 ]glucose administration, to calculate the rates of endogenous glucose production (6). Rates of gluconeogenesis were estimated by subtracting the rates of net hepatic glycogenolysis from the rates of endogenous glucose production. In addition...

We examined the effect of three months of rosiglitazone treatment (4 mg b.i.d.) on whole-body insulin sensitivity and in vivo peripheral adipocyte insulin sensitivity as assessed by glycerol release in microdialysis from subcutaneous fat during a two-step (20 and 120 mU ⅐ m ؊2 ⅐ min ؊1 ) hyperinsulinemic-euglycemic clamp in nine type 2 diabetic subjects. In addition, the effects of rosiglitazone on liver and muscle triglyceride content were assessed by 1 H-nuclear magnetic resonance spectroscopy. Rosiglitazone treatment resulted in a 68% (P < 0.002) and a 20% (P < 0.016) improvement in insulinstimulated glucose metabolism during the low-and highdosage؊insulin clamps, respectively, which was associated with ϳ40% reductions in plasma fatty acid concentration (P < 0.05) and hepatic triglyceride content (P < 0.05). These changes were associated with a 39% increase in extramyocellular lipid content (P < 0.05) and a 52% increase in the sensitivity of peripheral adipocytes to the inhibitory effects of insulin on lipolysis (P ‫؍‬ 0.04). In conclusion, these results support the hypothesis that thiazolidinediones enhance insulin sensitivity in patients with type 2 diabetes by promoting increased insulin sensitivity in peripheral adipocytes, which results in lower plasma fatty acid concentrations and a redistribution of intracellular lipid from insulin responsive organs into peripheral adipocytes. Diabetes 51: 797-802, 2002

Increasing evidence supports a crucial role for glial metabolism in maintaining proper synaptic function and in the etiology of neurological disease. However, the study of glial metabolism in humans has been hampered by the lack of noninvasive methods. To specifically measure the contribution of astroglia to brain energy metabolism in humans, we used a novel noninvasive nuclear magnetic resonance spectroscopic approach. We measured carbon 13 incorporation into brain glutamate and glutamine in eight volunteers during an intravenous infusion of [2-13C] acetate, which has been shown in animal models to be metabolized specifically in astroglia. Mathematical modeling of the three established pathways for neurotransmitter glutamate repletion indicates that the glutamate/glutamine neurotransmitter cycle between astroglia and neurons (0.32 +/- 0.07 micromol x gm(-1) x min(-1)) is the major pathway for neuronal glutamate repletion and that the astroglial TCA cycle flux (0.14 +/- 0.06 micromol x gm(-1) x min(-1)) accounts for approximately 14% of brain oxygen consumption. Up to 30% of the glutamine transferred to the neurons by the cycle may derive from replacement of oxidized glutamate by anaplerosis. The further application of this approach could potentially enlighten the role of astroglia in supporting brain glutamatergic activity and in neurological and psychiatric disease.

The metabolism and composition of skeletal muscle tissue is of special interest because it is a primary site of insulin action and plays a key role in the pathogenesis of insulin resistance. Intramyocellular (IMCL) triglyceride stores are an accessible form of energy that may decrease skeletal muscle glucose utilization, thereby contributing to impaired glucose metabolism. Because of the invasive nature of muscle biopsies, there is limited, if any, information about intramuscular lipid stores in children. The development of 1 H nuclear magnetic resonance (NMR) spectroscopy provides a unique noninvasive alternative method that differentiates intracellular fat from intercellular fat in muscle tissue. The present study was performed to determine whether IMCL and extramyocellular (EMCL) lipid contents are increased early in the development of juvenile obesity and to explore the relationships between IMCL and EMCL to in vivo insulin sensitivity, independently of total body fat and central adiposity in obese and nonobese adolescents. Eight nonobese (BMI 21 kg/m 2 , age 11-16 years) and 14 obese (BMI 35 ؎ 1.5 kg/m 2 , age 11-15 years) adolescents underwent 1) 1 H-NMR spectroscopy to noninvasively quantify IMCL and EMCL triglyceride content of the soleus muscle, 2) a 2-h euglycemic-hyperinsulinemic clamp (40 mU ⅐ m ؊2 ⅐ min ؊1 ) to assess insulin sensitivity, 3) a dual-energy X-ray absorptiometry scan to measure total percent body fat, and 4) magnetic resonance imaging to measure abdominal fat distribution. Both the IMCL and EMCL content of the soleus muscle were significantly greater in the obese adolescents than in the lean control subjects. A strong inverse correlation was found between IMCL and insulin sensitivity, which persisted and became even stronger after controlling for percent total body fat and abdominal subcutaneous fat mass (partial correlation r ‫؍‬ ؊0.73, P < 0.01) but not when adjusting for visceral fat (r ‫؍‬ ؊0.54, P < 0.08). In obese adolescents, increase in total body fat and central adiposity were accompanied by higher IMCL and EMCL lipid stores. The striking relationships between both IMCL and EMCL with insulin sensitivity in childhood suggest that these findings are not a consequence of aging but occur early in the natural course of obesity. Diabetes

Astrocytes and microglia become reactive under most brain pathological conditions, making this neuroinflammation process a surrogate marker of neuronal dysfunction. Neuroinflammation is associated with increased levels of translocator protein 18 kDa (TSPO) and binding sites for TSPO ligands. Positron emission tomography (PET) imaging of TSPO is thus commonly used to monitor neuroinflammation in preclinical and clinical studies. It is widely considered that TSPO PET signal reveals reactive microglia, although a few studies suggested a potential contribution of reactive astrocytes. Because astrocytes and microglia play very different roles, it is crucial to determine whether reactive astrocytes can also overexpress TSPO and yield to a detectable TSPO PET signal in vivo. We used a model of selective astrocyte activation through lentiviral gene transfer of the cytokine ciliary neurotrophic factor (CNTF) into the rat striatum, in the absence of neurodegeneration. CNTF induced an extensive activation of astrocytes, which overexpressed GFAP and become hypertrophic, whereas microglia displayed minimal increaseinreactivemarkers.TwoTSPOradioligands,[ TSPO mRNA levels were significantly increased, and TSPO protein was overexpressed by CNTF-activated astrocytes. We show that reactive astrocytes overexpress TSPO, yielding to a significant and selective binding of TSPO radioligands. Therefore, caution must be used when interpreting TSPO PET imaging in animals or patients because reactive astrocytes can contribute to the signal in addition to reactive microglia.

Mutations in SQSTM1 encoding the sequestosome 1/p62 protein have recently been identified in familial and sporadic cases of amyotrophic lateral sclerosis (ALS). p62 is a component of the ubiquitin inclusions detected in degenerating neurons in ALS patients. We sequenced SQSTM1 in 90 French patients with familial ALS (FALS) and 74 autopsied ALS cases with sporadic ALS (SALS). We identified, at the heterozygote state, one missense c.1175C>T, p.Pro392Leu (exon 8) in one of our FALS and one substitution in intron 7 (the c.1165+1G>A, previously called IVS7+1 G-A, A390X) affecting the exon 7 splicing site in one SALS. These mutations that are located in the ubiquitin-associated domain (UBA domain) of the p62 protein have already been described in Paget's disease and ALS patients carrying these mutations had both concomitant Paget's disease. However, we also identified two novel missense mutations in two SALS: the c.259A>G, p.Met87Val in exon 2 and the c.304A>G, p.Lys102Glu in exon 3. These mutations that were not detected in 360 control subjects are possibly pathogenic. Neuropathology analysis of three patients carrying SQSTM1 variants revealed the presence of large round p62 inclusions in motor neurons, and immunoblot analysis showed an increased p62 and TDP-43 protein levels in the spinal cord. Our results confirm that SQSTM1 gene mutations could be the cause or genetic susceptibility factor of ALS in some patients.

We hypothesized that increased capacity for brain utilization of nonglucose substrates (monocarboxylic acids [MCAs]) by upregulation of the MCA transporters may contribute metabolic substrates during hypoglycemia. To test this hypothesis, we assessed brain acetate metabolism in five well-controlled type 1 diabetic subjects and six nondiabetic control subjects using 13 C magnetic resonance spectroscopy during infusions of [2-13 C]acetate during hypoglycemia (ϳ55 mg/dl). Acetate is transported into the brain through MCA transporters that are also used for lactate and ketones. Brain acetate concentrations were over twofold higher in the subjects with diabetes than the control subjects (P ‫؍‬ 0.01). The fraction of oxidative metabolism from acetate (P ‫؍‬ 0.015) and the rate of MCA transport (P ‫؍‬ 0.01) were also approximately twofold higher in the diabetic subjects. We conclude that during hypoglycemia MCA transport in the brain was increased by appoximately twofold in patients with well-controlled type 1 diabetes, as reflected by higher brain acetate concentrations and rates of acetate oxidation. This upregulation would potentially allow a similar twofold increase in the transport of other MCAs, including lactate, during insulininduced hypoglycemia. These data are consistent with the hypothesis that upregulation of MCA transport may contribute to the maintenance of brain energetics during hypoglycemia in patients with type 1 diabetes. Diabetes 55: 929 -934, 2006 U nder normal, nonfasting conditions, oxidation of glucose is the main source of energy for brain function (1). In intensively treated subjects with type 1 diabetes, there is often a loss of both the counterregulatory response and the mild cognitive symptoms before severe cognitive dysfunction (2,3). Both of these adaptations are believed to significantly contribute to hypoglycemic unawareness, which increases the risk of severe hypoglycemia, which may result in seizure or coma (4). The loss of cognitive symptoms is believed to be, at least in part, secondary to adaptations that allow brain energy metabolism to be maintained during moderate hypoglycemia (5). Several studies have found that intensively treated patients with type 1 diabetes have cortical metabolic adaptations during hypoglycemia. Positron emission tomography (PET) and arterio-venous difference studies have found that in contrast to control subjects who show a 20 -30% decrease in glucose uptake during moderate hypoglycemia (ϳ2.8 mmol/l), subjects with intensively treated type 1 diabetes show minimal reduction in glucose uptake (5-8).Several hypotheses have been proposed to explain this metabolic adaption, particularly increased brain glucose transport, based on studies in rat models that showed an increase in glucose transporter activity in rats exposed to prolonged hypoglycemia (rev. in 9), but this concept is controversial. Studies of humans with diabetes have generally not been able to establish a change in transport parameters in poorly controlled and well-controlled patients. The study ...