Angiotensin 1-7 as means to prevent the metabolic syndrome: lessons from the fructose-fed rat model.

We studied the effects of chronic angiotensin 1-7 (Ang 1-7) treatment in an experimental model of the metabolic syndrome, i.e., rats given high-fructose/low-magnesium diet (HFrD). Rats were fed on HFrD for 24 weeks with and without Ang 1-7 (576 µg/kg/day, s.c., Alzet pumps). After 6 months, Ang 1-7-treated animals had lower body weight (-9.5%), total fat mass (detected by magnetic resonance imaging), and serum triglycerides (-51%), improved glucose tolerance, and better insulin sensitivity. Similar metabolic effects were also evident, albeit in the absence of weight loss, in rats first exposed to HFrD for 5 months and then subjected to short-term (4 weeks) treatment with Ang 1-7. Six months of Ang 1-7 treatment were associated with lower plasma renin activity (-40%) and serum aldosterone (-48%), less hepatosteatatitis, and a reduction in epididymal adipocyte volume. The marked attenuation of macrophage infiltration in white adipose tissue (WAT) was associated with reduced levels of the pP65 protein in the epididymal fat tissue, suggesting less activation of the nuclear factor-κB (NFκB) pathway in Ang 1-7-treated rats. WAT from Ang 1-7-treated rats showed reduced NADPH-stimulated superoxide production. In single muscle fibers (myofibers) harvested and grown ex vivo for 10 days, myofibers from HFrD rats gave rise to 20% less myogenic cells than the Ang 1-7-treated rats. Fully developed adipocytes were present in most HFrD myofiber cultures but entirely absent in cultures from Ang 1-7-treated rats. In summary, Ang 1-7 had an ameliorating effect on insulin resistance, hypertriglyceridemia, fatty liver, obesity, adipositis, and myogenic and adipogenic differentiation in muscle tissue in the HFrD rats.

Delivery of neuropeptides from the periphery to the brain: studies with enkephalin.

Many peptides with the potential of therapeutic action for brain disorders are not in clinical use because they are unable to cross the blood-brain barrier (BBB) following peripheral administration. We have developed two potential strategies for the delivery of peptides to the brain and demonstrated their feasibility with enkephalins. In the first approach, designated induced reversible lipophilization, Leu/Met Enkephalins were converted to 9-fluorenylmethoxycarbonyl (Fmoc) derived lipophilic prodrug analogues, which undergo slow, spontaneous hydrolysis under physiological conditions, generating the native agonists. In contrast to Enkephalin, Fmoc-Met-Enkephalin was found to facilitate an analgesic effect following intraperitoneal administration in mice. Fmoc-Leu-Enkephalin was not analgesic. In the second approach, Enkephalin was linked to BBB transport vectors through an Fmoc based linker spacer, forming conjugates that slowly release Enkephalin under physiological conditions. A pronounced antinociceptive response was thus obtained following intraperitoneal administration of either cationized-human serum albumin-Fmoc-Enkephalin or polyethylene glycol(5)-Fmoc-Enkephalin. Derivatives of Enkephalin covalently linked to the same BBB-transport vectors through a stable (nonreversible) chemical bond were not analgesic. In summary, we have demonstrated that lipophilicity can be conferred to hydrophilic peptides to a degree permitting the permeation of the BBB by passive diffusion, without the drawback of agonist inactivation, which is often caused by irreversible derivatization. Similarly, in the second strategy, the conjugation to BBB-permeable vectors overcomes the obstacle of peptide inactivation by releasing the active form in the central nervous system.