افزایش وابسته به سن در گلوتامات گانگلیون بازال با TNF همراه است، انگیزش کاهش یافته و سرعت روانی حرکتی کاهش یافته در طول درمان IFN-آلفا: یافته های اولیه

Inflammation-induced alterations in central nervous system (CNS) metabolism have focused on glutamate. At excessive concentrations, glutamate is toxic to glia and neurons, and inflammatory cytokines have been shown to influence glutamate turnover by blocking glutamate reuptake and increasing glutamate release. Increased glutamate has also been found in depression, a disorder associated with increased inflammation. Data by our group have shown increased glutamate as measured by magnetic resonance spectroscopy (MRS) in basal ganglia and dorsal anterior cingulate cortex of patients administered the inflammatory cytokine interferon (IFN)-alpha. Given data that increasing age is associated with an exaggerated CNS inflammatory response, we examined whether older age (>55 years) would be associated with a greater IFN-alpha-induced increase in CNS glutamate. Using a longitudinal design, 31 patients with hepatitis C virus (HCV) underwent MRS, blood sampling for inflammatory markers, and behavioral assessments before (Visit 1) and after 4 weeks (Visit 2) of either IFN-alpha (n = 17) or no treatment (n = 14). Older patients treated with IFN-alpha exhibited a significantly greater increase in glutamate from Visit 1 to Visit 2 as reflected by the glutamate/creatine ratio (Glu/Cr) in left basal ganglia compared to older controls and younger IFN-alpha-treated and untreated subjects. In addition, increased Glu/Cr in older but not younger IFN-alpha-treated and untreated patients was associated with increased tumor necrosis factor, reduced motivation as measured by the Multidimensional Fatigue Inventory and increased choice movement time on the Cambridge Neuropsychological Test Automated Battery. Taken together, these preliminary data support the notion that older age may interact with inflammation to exaggerate the effects of inflammatory stimuli on CNS glutamate and behavior.

Patients exposed to the inflammatory cytokine interferon (IFN)-alpha were found to exhibit increased glutamate in left basal ganglia and dorsal anterior cingulate cortex (dACC) as determined by single voxel magnetic resonance spectroscopy (MRS) (Haroon et al., 2014). Increased glutamate was in turn correlated with depressive symptoms. These data are consistent with increased CNS glutamate in bipolar and some unipolar depression (Yuksel and Ongur, 2010), both of which exhibit increased inflammatory markers (Miller et al., 2009). Regarding mechanisms by which inflammation may increase CNS glutamate, inflammatory cytokines can decrease expression of glutamate transporters on astrocytes, resulting in decreased glutamate reuptake (Tilleux and Hermans, 2007), and stimulate astrocytic glutamate release (Malarkey and Parpura, 2008). Moreover, inflammatory cytokines can activate indoleamine 2,3 dioxygenase (IDO), an enzyme which catabolizes tryptophan into kynurenine that in turn can be converted into quinolinic acid (Miller et al., 2009). Quinolinic acid is an agonist at glutamate receptors and can also stimulate glutamate release while inhibiting astrocytic glutamate reuptake (Miller et al., 2009, Savitz et al., 2014 and Tavares et al., 2002). At high concentrations, extracellular glutamate is toxic to both neurons and glia. However, it should be noted that current MRS methodology is limited in discriminating extra- versus intra-cellular glutamate, making it difficult to determine whether increases in CNS glutamate as determined by MRS represent increased extracellular glutamate concentrations or increased intracellular pools (Haroon et al., 2014). One process that may interact with depression and the impact of inflammatory stimuli on CNS glutamate is aging. Advancing age is associated with chronic, low-grade central and peripheral inflammatory responses (Franceschi and Campisi, 2014 and Norden and Godbout, 2013). As a consequence of aging, microglia have been shown in laboratory animals to exhibit a “primed” phenotype that is associated with an exaggerated and prolonged inflammatory response that correlates with increased depressive-like behavior and cognitive deficits (Norden and Godbout, 2013 and Salminen et al., 2011). In addition, aging is associated with increased inflammation-induced CNS IDO activity in mice (Godbout et al., 2008). Moreover, expression of glutamate transporters appears to decline with age (Sheldon and Robinson, 2007). Finally, as indicated above, CNS glutamate is abnormally regulated in patients with mood disorders including those with late-life depression (Binesh et al., 2004). These data suggest that the intersection of aging, inflammation and depression in older patients may represent a “perfect storm” of glutamate pathology. We therefore explored effects of aging on the glutamate response to IFN-alpha in patients with hepatitis C virus (HCV) and determined whether these effects were associated with alterations in inflammatory markers and behaviors previously shown to be altered in IFN-alpha-treated patients including tumor necrosis factor (TNF) and its soluble receptor sTNFR2, motivation, and motor activity (Capuron et al., 2012, Majer et al., 2008 and Raison et al., 2010).

3. Results 3.1. Sample Thirty-one subjects (17 IFN-alpha-treated patients and 14 HCV controls) met inclusion and exclusion criteria and were enrolled (Table 1). The younger IFN-alpha-treated group exhibited higher BMI than the other three groups (p = 0.03). There was also a significant main effect of age on education (F(3,27) = 5.8, p < 0.003) with the two older groups exhibiting higher education levels than the two younger groups (all p < 0.05). These variables (BMI and education) along with sex were therefore included in all statistical models. 3.2. Glutamate metabolites As we have previously reported, there was a significant treatment by visit interaction for both the left basal ganglia and the dACC (F[1,22] = 4.76, p = 0.04, d = 0.48, power = 0.68 and F[1,23] = 9.68, p = 0.005, d = 0.65, power = 0.94, respectively) ( Haroon et al., 2014) with IFN-alpha-treated subjects exhibiting significantly greater increases from Visit 1 to Visit 2 in the Glu/Cr ratio in the left basal ganglia and dACC (p < 0.05). Regarding the focus of the current study on age, no significant main effects of age or visit were found for any of the brain regions examined (all p > 0.40). Nevertheless, there was a significant age by treatment by visit interaction for the left basal ganglia (F[1,22] = 10.4, p = 0.004, d = 0.68, power = 0.96) with older IFN-alpha-treated patients exhibiting significantly greater increases in left basal Glu/Cr from Visit 1 to Visit 2 than older controls and both younger IFN-alpha-treated and control individuals (all p < 0.05) ( Table 2). No age by treatment by visit interactions were found for the right basal ganglia or the dACC. 3.3. Main effects, associations and interactions involving left basal ganglia glutamate, inflammatory markers, and behavioral and cognitive measures There was a significant treatment by visit interaction for TNF and sTNFR2 (F[1,25] = 7.7, p < 0.02, d = 0.56, power = 0.83 and F[1,24] = 13.8, p = 0.001, d = 0.75, power = 0.99, respectively) with IFN-alpha-treated patients exhibiting significantly greater increases in plasma concentrations of TNF and sTNFR2 from Visit 1 to Visit 2 than controls ( Table 2). There was also a significant interaction between age and visit for sTNFR2 (F[1,24] = 6.6, p = 0.02, d = 0.53, power = 0.76), with older patients exhibiting significantly higher plasma concentrations of sTNFR2 than younger patients. No treatment by age by visit interactions for TNF or sTNFR2 were found. Regarding reduced motivation and choice movement time, a significant age by treatment by visit interaction was found for both variables (F[1,24] = 4.67, p = 0.04, d = 0.44, power = 0.58 and F[1,18]=6.9, p = 0.02, d = 0.62, power = 0.91, respectively) with older IFN-alpha-treated patients exhibiting significantly greater increases in reduced motivation and choice movement time from Visit 1 to Visit 2 than older controls and both younger IFN-alpha-treated and control individuals (all p < 0.05) ( Table 2). As shown in Fig. 1A, delta (Visit 2–Visit 1) log left basal ganglia glutamate was higher in older IFN-alpha-treated patients than all other groups (all p < 0.05). Linear regression analyses of the relationship between delta log left basal ganglia Glu/Cr and delta log inflammatory markers (log TNF and log sTNFR2) revealed a significant association between delta log TNF and delta log left basal ganglia Glu/Cr in older IFN-alpha-treated and control patients with sex, BMI and education included in the model (β = 0.61, p = 0.026) ( Fig. 1B). A significant association was also found between delta log left basal ganglia Glu/Cr and delta reduced motivation in older IFN-alpha-treated and control subjects including other MFI-subscales and the HAM-D-17 in the model as well as sex, BMI and education (β = 0.66, p = 0.014) ( Fig. 1C). Finally, delta log left basal ganglia Glu/Cr was significantly associated with increased delta choice movement time in older IFN-alpha-treated and control subjects including delta values of other reaction and movement time measures as well as sex, BMI and education in the model (β = 0.56, p = 0.027) ( Fig. 1D). Of note, similar associations with delta log left basal ganglia Glu/Cr as noted above were found in older IFN-alpha-treated subjects alone (delta log TNF: r = 0.62; delta reduced motivation: r = 0.47 and delta choice movement time: r = 0.97) controlling for sex, BMI and education. Nevertheless, due to the small sample size, these correlations did not reach statistical significance (all p > 0.15). Correlations in older control patients were either in the opposite direction (log TNF: r = −0.67) or lower than in older IFN-alpha-treated patients (delta reduced motivation: r = 0.33 and delta choice movement time: r = 0.25, both p > 0.34). No significant associations between the indicated delta variables and delta Glu/Cr were found in younger IFN-alpha-treated and control subjects using linear regression analyses or partial correlations. Full-size image (47 K) Fig. 1. Increased left basal ganglia glutamate in older IFN-alpha-treated subjects and correlation of left basal ganglia glutamate with TNF, reduced motivation and motor slowing in older hepatitis C subjects. (A) Delta (Visit 2–Visit 1) log left basal ganglia glutamate (Glu/Cr) was higher in older (>55 years) interferon (IFN)-alpha-treated patients than older controls and younger (<55 years) IFN-alpha-treated and untreated subjects. (B) Increased delta log TNF correlated with increased delta log left basal ganglia Glu/Cr in older IFN-alpha-treated and control subjects (B = 0.61, p = 0.026). (C) Increased delta log left basal Glu/Cr correlated with increased delta reduced motivation in older IFN-alpha-treated and untreated subjects (B = 0.67, p = 0.014). (D) Increased delta log left basal ganglia Glu/Cr correlated with increased delta choice movement time in older IFN-alpha-treated and untreated subjects (B = 0.61, p = 0.04). Of note, one subject did not complete the CANTAB reaction time task. ∗p < 0.05, ∗∗∗p < 0.001; open circles: IFN-alpha; closed circles: controls. Figure options 3.4. Other MRS metabolites An analysis of the spectral peaks of other brain metabolites showed a significant treatment by visit interaction for choline (Cho/Cr) in the dACC (F[1,24] = 4.63, p = 0.04, d = 0.44, power = 0.57) (see Supplementary Data) with older and younger IFN-alpha-treated subjects exhibiting significantly decreased choline from Visit 1 to Visit 2. No main effects or interactions were found for the other MRS metabolites.