Intracranial injection of Gammagard, a human IVIg, modulates the inflammatory response of the brain and lowers Aß in APP/PS1 mice along a different time course than anti-Aß antibodies.

Gammagard IVIg is a therapeutic approach to treat Alzheimer's disease currently in phase 3 clinical trials. Despite the reported efficacy of the approach the mechanism of action is poorly understood. We have previously shown that intracranial injection of anti-Aß antibodies into the frontal cortex and hippocampus reveals important information regarding the time course of events once the agent is in the brain. In the current study we compared IVIg, mouse-pooled IgG, and the anti-Aß antibody 6E10 injected intracranially into the frontal cortex and hippocampus of 7-month-old APP/PS1 mice. We established a time course of events ranging from 1 to 21 d postinjection. IVIg and pooled mouse IgG both significantly reduced Aß deposition to the same degree as the 6E10 anti-Aß antibody; however, the clearance was much slower to occur, happening between the 3 and 7 d time points. In contrast, as we have previously shown, Aß reductions were apparent with the 6E10 anti-Aß group at the 1 d time point. Also, neuroinflammatory profiles were significantly altered by the antibody treatments. APP/PS1 transgenic mice at 7 months of age typically exhibit an M2a inflammatory phenotype. All antibody treatments stimulated an M2b response, yet anti-Aß antibody was a more rapid change. Because the neuroinflammatory switch occurs before the detectable reductions in amyloid deposition, we hypothesize that the IVIg and pooled mouse IgG act as immune modulators and this immune modulation is responsible for the reductions in amyloid pathology.

Transition from an M1 to a mixed neuroinflammatory phenotype increases amyloid deposition in APP/PS1 transgenic mice.

BACKGROUND: The polarization to different neuroinflammatory phenotypes has been described in early Alzheimer's disease, yet the impact of these phenotypes on amyloid-beta (Aß) pathology remains unknown. Short-term studies show that induction of an M1 neuroinflammatory phenotype reduces Aß, but long-term studies have not been performed that track the neuroinflammatory phenotype. METHODS: Wild-type and APP/PS1 transgenic mice aged 3 to 4 months received a bilateral intracranial injection of adeno-associated viral (AAV) vectors expressing IFNγ or green fluorescent protein in the frontal cortex and hippocampus. Mice were sacrificed 4 or 6 months post-injection. ELISA measurements were used for IFNγ protein levels and biochemical levels of Aß. The neuroinflammatory phenotype was determined through quantitative PCR. Microglia, astrocytes, and Aß levels were assessed with immunohistochemistry. RESULTS: AAV expressing IFNγ induced an M1 neuroinflammatory phenotype at 4 months and a mixed phenotype along with an increase in Aß at 6 months. Microglial staining was increased at 6 months and astrocyte staining was decreased at 4 and 6 months in mice receiving AAV expressing IFNγ. CONCLUSIONS: Expression of IFNγ through AAV successfully induced an M1 phenotype at 4 months that transitioned to a mixed phenotype by 6 months. This transition also appeared with an increase in amyloid burden suggesting that a mixed phenotype, or enhanced expression of M2a and M2c markers, could contribute to increasing amyloid burden and disease progression.

Carriage of Methicillin-resistant Staphylococcus aureus in a Colony of Rhesus (Macaca mulatta) and Cynomolgus (Macaca fascicularis) Macaques.

Methicillin-resistant Staphylococcus aureus (MRSA) carriage and infection are well documented in the human and veterinary literature; however only limited information is available regarding MRSA carriage and infection in laboratory NHP populations. The objective of this study was to characterize MRSA carriage in a representative research colony of rhesus and cynomolgus macaques through a cross-sectional analysis of 300 animals. MRSA carriage was determined by using nasal culture. Demographic characteristics of carriers and noncarriers were compared to determine factors linked to increased risk of carriage, and MRSA isolates were analyzed to determine antimicrobial susceptibility patterns, staphylococcal chromosome cassette mec (SCCmec) type, and multilocus sequence type (ST). Culture results demonstrated MRSA carriage in 6.3% of the study population. Animals with greater numbers of veterinary or experimental interventions including antibiotic administration, steroid administration, dental procedures, and surgery were more likely to carry MRSA. Susceptibility results indicated that MRSA isolates were resistant to ß-lactams, and all isolates were resistant to between 1 and 4 non ß-lactam antibiotics. In addition, 73.7% of MRSA isolates were identified as ST188-SCCmec IV, an isolate previously observed in an unrelated population of macaques and 15.8% were ST3268-SCCmec V, which has only been described in macaques. A single isolate had a novel sequence type, ST3478, and carried SCCmec V. These results suggest that NHP-adapted strains of MRSA exist and highlight the emergence of antimicrobial resistance in laboratory NHP populations.

Hepatocyte-specific, PPARγ-regulated mechanisms to promote steatosis in adult mice.

Peroxisome proliferator-activated receptor γ (PPARγ) is the target for thiazolidinones (TZDs), drugs that improve insulin sensitivity and fatty liver in humans and rodent models, related to a reduction in hepatic de novo lipogenesis (DNL). The systemic effects of TZDs are in contrast to reports suggesting hepatocyte-specific activation of PPARγ promotes DNL, triacylglycerol (TAG) uptake and fatty acid (FA) esterification. As these hepatocyte-specific effects of PPARγ could counterbalance the positive therapeutic actions of systemic delivery of TZDs, the current study used a mouse model of adult-onset, liver (hepatocyte)-specific PPARγ knockdown (aLivPPARγkd). This model has advantages over existing congenital knockout models, by avoiding compensatory changes related to embryonic knockdown, thus better modeling the impact of altering PPARγ on adult physiology, where metabolic diseases most frequently develop. The impact of aLivPPARγkd on hepatic gene expression and endpoints in lipid metabolism was examined after 1 or 18 weeks (Chow-fed) or after 14 weeks of low- or high-fat (HF) diet. aLivPPARγkd reduced hepatic TAG content but did not impact endpoints in DNL or TAG uptake. However, aLivPPARγkd reduced the expression of the FA translocase (Cd36), in 18-week Chow- and HF-fed mice, associated with increased NEFA after HF feeding. Also, aLivPPARγkd dramatically reduced Mogat1 expression, that was reflected by an increase in hepatic monoacylglycerol (MAG) levels, indicative of reduced MOGAT activity. These results, coupled with previous reports, suggest that Cd36-mediated FA uptake and MAG pathway-mediated FA esterification are major targets of hepatocyte PPARγ, where loss of this control explains in part the protection against steatosis observed after aLivPPARγkd.

Induction of hyperhomocysteinemia models vascular dementia by induction of cerebral microhemorrhages and neuroinflammation.

Vascular dementia (VaD) is the second leading cause of dementia behind Alzheimer's disease (AD) and is a frequent comorbidity with AD, estimated to occur in as many as 40% of AD patients. The causes of VaD are varied and include chronic cerebral hypoperfusion, microhemorrhages, hemorrhagic infarcts, or ischemic infarcts. We have developed a model of VaD by inducing hyperhomocysteinemia (HHcy) in wild-type mice. By placing wild-type mice on a diet deficient in folate, B6, and B12 and supplemented with excess methionine, we induced a moderate HHcy (plasma level homocysteine 82.93 ± 3.561 µmol). After 11 weeks on the diet, the hyperhomocysteinemic mice showed a spatial memory deficit as assessed by the 2-day radial-arm water maze. Also, magnetic resonance imaging and subsequent histology revealed significant microhemorrhage occurrence. We found neuroinflammation induced in the hyperhomocysteinemic mice as determined by elevated interleukin (IL)-1ß, tumor necrosis factor (TNF)α, and IL-6 in brain tissue. Finally, we found increased expression and increased activity of the matrix metalloproteinase 2 (MMP2) and MMP9 systems that are heavily implicated in the pathogenesis of cerebral hemorrhage. Overall, we have developed a dietary model of VaD that will be valuable for studying the pathophysiology of VaD and also for studying the comorbidity of VaD with other dementias and other neurodegenerative disorders.