(200d) Peptoid JPT1A Reduces RAGE Expression and Attenuates Inflammatory Response: A Potential AD Therapeutic

Introduction: For
several decades, amyloid‑b (Ab) has been a key therapeutic target for Alzheimer’s disease (AD)‑related
therapies, but more recent studies have recast Ab as one of several
participants in the disease rather than its sole etiology. AD therapies that
aim to inhibit Ab production and/or aggregate formation alone have yielded
little success in clinical trials.  At the same time, Phase II clinical
trials that target AD-associated inflammation using an antagonist for the
receptor for advanced glycation end products (RAGE) demonstrate improved
outcomes in patients with mild‑to‑moderate AD. We envision that a therapeutic
capable of affecting both of these targets would exhibit enhanced efficacy. 

A peptoid mimic of Ab’s
KLVFF hydrophobic core, JPT1a, was designed as a potential peptoid therapeutic
for AD, with prospective capabilities to both antagonize RAGE via ligand‑mimicking
sequences and inhibit aggregation of Abvia self-recognition. Peptoids
are peptidomimetics that attain invulnerability to proteolytic degradation
through repositioning of the side‑chain from the a‑carbon
to the amide nitrogen.  This invulnerability to proteases, as well as
other qualities such as diminished immunogenicity, enhanced cellular
permeability, and capacity for intranasal administration, make peptoids
immensely attractive as neurotherapeutic agents. We previously demonstrated
that JPT1a has the capacity to modulate Ab aggregation
as well as alter the morphology of Ab aggregates.  In the
current study, we examine JPT1a for protection against inflammatory responses
associated with RAGE signaling. 

Materials and Methods: THP-1
monocytes were differentiated into macrophages through exposure to phorbol
12-myristate 13-acetate (PMA) for three days prior to experimentation; THP-1
monocytes differentiated in this manner closely resemble the behavior and
phenotype of primary human monocyte-derived macrophages. To assess the capacity
of peptoid JPT1a to modulate RAGE expression, differentiated cells were
incubated (3 days) with 0 -50 Î¼M
JPT1a in the presence of low-dose LPS (2 ng/mL) or Ab_1–42 oligomers
(0.01 mM).
The capacity of peptoid JPT1a to reverse RAGE expression was assessed in THP‑1
macrophages following chronic (48-h) exposure to low‑dose LPS (2 ng/mL) or
Ab_1–42 oligomers
(0.01 mM) , at which time media was
removed and replaced with media containing 25, 5, 1, or 0 mM
JPT1a (24-h incubation).  Following each treatment, supernatant was
harvested for cytokine analysis via ELISA and cells were stained for
quantitative image analysis of RAGE expression. 

Results and Discussion: Co‑incubation
of the peptoid JPT1a with a chronic pro‑inflammatory stimulus (LPS or Ab oligomers)
significantly reduces RAGE upregulation in a dose‑dependent manner within this
model that utilizes THP‑1 macrophages (Figure 1A ). Upon ligand-binding, RAGE can activate multiple signaling
pathways to influence the magnitude and character of the immune response, as
well as initiate a positive feedback cycle that upregulates its own
transmembrane expression.  Membrane-bound RAGE expression is altered as
part of a feed-forward mechanism for environmental stress or exposure;
therefore RAGE is a means through which cells anticipate and interpret their
local environment, and RAGE may also be a source of dysfunction in chronic
inflammation. In parallel, JPT1a also reduces the production of
pro-inflammatory cytokines IL‑1b, IL‑6, and IL‑8 within this model (Figure 1B – D).  Addition of JPT1a to THP‑1
macrophages pre‑treated with chronic pro-inflammatory stimulus (LPS or Ab 
oligomer) also significantly reduces RAGE expression but does not significantly
impact the generation of pro‑inflammatory cytokines.  

Conclusions: When
paralleled by the ability of JPT1a to reverse RAGE expression, these results
demonstrate the potential of JPT1a as a dual-target therapy in AD, modulating
both inflammation and Ab aggregation. Moreover, as RAGE has also shown promise as a
therapeutic target in several pathologies, a RAGE inhibitor such as JPT1a may
yield a new therapeutic option to a wide array of illnesses.