Following femoral artery removal in the rabbit, the time course of angiogenesis and arteriogenesis were clearly distinct. Tissue ischemia and/or VEGF may stimulate capillary sprouting, but this response does not translate to a significant improvement in collateral flow. The growth and development of the larger collateral vessels was correlated with a large functional improvement in collateral flow, and occurred at a time when VEGF levels were undetectable.

The accumulation of amyloid ␤ (A␤) in Alzheimer's disease is caused by an imbalance of production and clearance, which leads to increased soluble A␤ species and extracellular plaque formation in the brain. Multiple A␤-lowering therapies are currently in development: an important goal is to characterize the molecular mechanisms of action and effects on physiological processing of A␤, as well as other amyloid precursor protein (APP) metabolites, in models which approximate human A␤ physiology. To this end, we report the translation of the human in vivo stable-isotope-labeling kinetics (SILK) method to a rhesus monkey cisterna magna ported (CMP) nonhuman primate model, and use the model to test the mechanisms of action of a ␥-secretase inhibitor (GSI). A major concern of inhibiting the enzymes which produce A␤ (␤-and ␥-secretase) is that precursors of A␤ may accumulate and cause a rapid increase in A␤ production when enzyme inhibition discontinues. In this study, the GSI MK-0752 was administered to conscious CMP rhesus monkeys in conjunction with in vivo stable-isotope-labeling, and dose-dependently reduced newly generated CNS A␤. In contrast to systemic A␤ metabolism, CNS A␤ production was not increased after the GSI was cleared. These results indicate that most of the CNS APP was metabolized to products other than A␤, including C-terminal truncated forms of A␤: 1-14, 1-15 and 1-16; this demonstrates an alternative degradation pathway for CNS amyloid precursor protein during ␥-secretase inhibition.

BACE, a ␤-secretase, is an attractive potential disease-modifying therapeutic strategy for Alzheimer's disease (AD) as it results directly in the decrease of amyloid precursor protein (APP) processing through the ␤-secretase pathway and a lowering of CNS amyloid-␤ (A␤) levels. The interaction of the ␤-secretase and ␣-secretase pathway-mediated processing of APP in the rhesus monkey (nonhuman primate; NHP) CNS is not understood. We hypothesized that CNS inhibition of BACE would result in decreased newly generated A␤ and soluble APP␤ (sAPP␤), with increased newly generated sAPP␣.A stable isotope labeling kinetics experiment in NHPs was performed with a 13 C 6 -leucine infusion protocol to evaluate effects of BACE inhibition on CNS APP processing by measuring the kinetics of sAPP␣, sAPP␤, and A␤ in CSF. Each NHP received a low, medium, or high dose of MBI-5 (BACE inhibitor) or vehicle in a four-way crossover design. CSF sAPP␣, sAPP␤, and A␤ were measured by ELISA and newly incorporated label following immunoprecipitation and liquid chromatography-mass spectrometry. Concentrations, kinetics, and amount of newly generated APP fragments were calculated. sAPP␤ and sAPP␣ kinetics were similar, but both significantly slower than A␤. BACE inhibition resulted in decreased labeled sAPP␤ and A␤ in CSF, without observable changes in labeled CSF sAPP␣. ELISA concentrations of sAPP␤ and A␤ both decreased and sAPP␣ increased. sAPP␣ increased by ELISA, with no difference by labeled sAPP␣ kinetics indicating increases in product may be due to APP shunting from the ␤-secretase to the ␣-secretase pathway. These results provide a quantitative understanding of pharmacodynamic effects of BACE inhibition on NHP CNS, which can inform about target development.

This study was designed to test the ability of adenovirus-delivered vascular endothelial growth factor (Ad-VEGF) to stimulate angiogenesis and arteriogenesis in the rabbit hindlimb following the induction of ischemia and to evaluate the functional changes in the collateral circulation. Ten days after the surgical induction of hindlimb ischemia, either a control virus (1 x 10(9) pfu) or an adenovirus containing the gene for VEGF(165) (1 x 10(6), 1 x 10(7), 1 x 10(8), or 1 x 10(9) pfu) was administered intramuscularly into the ischemic limb. Thirty days after administration of the adenoviral vectors, skeletal muscle capillary density was assessed and angiography was performed as markers of angiogenesis and arteriogenesis, respectively. Hindlimb blood flow was directly measured and hyperemic tests were performed to evaluate the functional improvements in collateral blood flow. Animals treated with Ad-VEGF at 1 x 10(8) and 1 x 10(9) pfu showed elevated levels of circulating VEGF and dose-dependent hindlimb edema. These doses also led to a robust angiogenic response (i.e., increase in capillary density), but failed to improve collateral blood flow. Consistent with the lack of a functional response, there was no angiographic evidence of enhanced arteriogenesis with any dose of Ad-VEGF. Following the induction of hindlimb ischemia, administration of Ad-VEGF stimulated capillary sprouting (i.e., angiogenesis), but did not increase the growth and development of larger conduit vessels (i.e., arteriogenesis) or improve collateral blood flow. These results support the concept that VEGF may not be expected to have therapeutic utility for the treatment of peripheral or myocardial ischemia.

The present findings suggest that selective blockade of I(Ks) may be a potentially useful intervention for the prevention of malignant ischemic ventricular arrhythmias.