Ovine proinflammatory cytokines cross the murine blood-brain barrier by a common saturable transport mechanism.

OBJECTIVES: The cytokines interleukin (IL)-1beta and IL-6 are modulators of the neuroimmune axis and have been implicated in neuronal cell death cascades after ischemia or infection. Previous work has shown that some cross-species conservation exists between human and rodent blood-brain barrier (BBB) transport systems. To further assess cross-species conservation of cytokine transport across the BBB, the current studies investigated permeability and inhibition of ovine IL-1beta and IL-6 in the mouse. METHODS: IL-1beta or IL-6 was radioactively labeled with (131)I and injected into the jugular vein at time zero. A subset of mice received 1 or 3 microg/mouse of an unlabeled ovine or murine cytokine (IL-1beta or IL-6) to assess self- and/or cross-inhibition of transport. Permeability was assessed using multiple-regression analysis. RESULTS: There was a significant linear relationship for both ovine (131)I-IL-1beta and (131)I-IL-6 between brain/serum ratios and exposure time, indicating BBB permeability. Inclusion of 3 microg/mouse unlabeled ovine IL-1beta or IL-6 significantly reduced the transport of ovine (131)I-IL-1beta or (131)I-IL-6, respectively, across the BBB. Transport of both ovine (131)I-IL-1beta and (131)I-IL-6 was significantly inhibited by 1 microg/mouse of murine IL-1beta or IL-6, respectively. In contrast, 1 microg/mouse of unlabeled ovine IL-1beta or IL-6 did not inhibit the transport of murine (131)I-IL-1beta or (131)I-IL-6. CONCLUSIONS: Ovine IL-1beta and IL-6 cross the mouse BBB by saturable transport. Inhibition of transport by murine homologs indicates that both species use the same transport mechanisms. Conversely, an inability of ovine cytokines to significantly inhibit the transport of murine cytokines indicates that mouse BBB has a lower affinity for ovine than murine cytokines. Knowledge of species-conserved BBB transport mechanisms may facilitate the development of novel animal models of central nervous system pathogenesis.

Peripheral administration of antisense oligonucleotides targeting the amyloid-ß protein precursor reverses AßPP and LRP-1 overexpression in the aged SAMP8 mouse brain.

The senescence accelerated mouse-prone 8 (SAMP8) mouse model of Alzheimer's disease has a natural mutation leading to age-related increases in the amyloid-ß protein precursor (AßPP) and amyloid-ß (Aß) in the brain, memory impairment, and deficits in Aß removal from the brain. Previous studies show that centrally administered antisense oligonucleotide directed against AßPP can decrease AßPP expression and Aß production in the brains of aged SAMP8 mice, and improve memory. The same antisense crosses the blood-brain barrier and reverses memory deficits when injected intravenously. Here, we give 6 µg of AßPP or control antisense 3 times over 2 week intervals to 12 month old SAMP8 mice. Object recognition test was done 48 hours later, followed by removal of whole brains for immunoblot analysis of AßPP, low-density lipoprotein-related protein-1 (LRP-1), p-glycoprotein (Pgp), receptor for advanced glycation endproducts (RAGE), or ELISA of soluble Aß(40). Our results show that AßPP antisense completely reverses a 30% age-associated increase in AßPP signal (p < 0.05 versus untreated 4 month old SAMP8). Soluble Aß(40) increased with age, but was not reversed by antisense. LRP-1 large and small subunits increased significantly with age (147.7%, p < 0.01 and 123.7%, p < 0.05 respectively), and AßPP antisense completely reversed these increases (p < 0.05). Pgp and RAGE were not significantly altered with age or antisense. Antisense also caused improvements in memory (p < 0.001). Together, these data support the therapeutic potential of AßPP antisense and show a unique association between AßPP and LRP-1 expression in the SAMP8 mouse.

Insulin detemir is not transported across the blood-brain barrier.

Insulin detemir has a different profile of action on the central nervous system (CNS) than human insulin. It has been hypothesized that this is caused by an altered ability of insulin detemir to cross the blood-brain barrier (BBB). Here, we measured the permeability of the BBB to insulin detemir. We labeled insulin detemir with radioactive iodine (I-Det) and examined its ability to cross the BBB of the mouse. Permeation was assessed after intravenous injection and by brain perfusion in the presence or absence of excess insulin detemir. The ability of insulin detemir to inhibit human insulin transport across the BBB was also assessed. I-Det did not cross the BBB either after intravenous injection or when studied by brain perfusion, a method which removes or reduces the influence of circulating proteins. Unlabeled detemir was about 10 times less potent than human insulin at inhibiting the transport of radioactive human insulin across the BBB. The altered CNS profile of insulin detemir may be caused by its poor access to CNS receptors and by a block of human insulin from crossing the BBB.