Blocking IL-12 and IL-23 in APPPS1 Mouse Model Shows Promise as an Experimental Therapeutic Approach to Alzheimer’s Disease

blocking IL-12
Blocking IL-12 and IL-23 – Alzheimer’s Disease

A recent study, published in Nature Medicine is perhaps the first one to suggest a putative interleukin (IL)-23 involvement in Alzheimer’s disease, and that blocking IL-12 and IL-23 shows promise as an experimental therapeutic approach.

New epidemiologic data suggest a key role of neuroinflammation in the pathogenesis of Alzheimer’s. The pathology of Alzheimer’s disease has an inflammatory component that is characterized by upregulation of proinflammatory cytokines. Upregulation of proinflammatory cytokines such as IL 1β and tumor necrosis factor α (TNF α), reactive oxygen species and other hallmarks of inflammation have been described as a local cellular response.

In 1996 Chou, working under the mentorship of Robert Spengler PhD, along with Tracey Ignatowski, at SUNY Buffalo, published research illuminating brain effects of TNF. In 2003 Kaj Blennow MD and colleagues in Sweden reported an association between elevated levels of TNF in the cerebrospinal fluid and progression of mild cognitive impairment to AD.

In 2006 Edward Tobinick MD and colleagues in the U.S. were the first to publish clinical trial data providing evidence of the therapeutic activity of etanercept against Alzheimer’s disease, using a novel method of etanercept administration, perispinal delivery. Other neuroscientists, including Sue Griffin, Nigel Grieg, Ian Clark have provided additional scientific rationale for targeting excess TNF and neuroinflammation in AD.

Despite some descriptive evidence for differential expression of inflammatory mediators in Alzheimer’s disease, studies on the expression patterns of proinflammatory cytokines are sparse. Glial cells, especially microglia, which typically associate closely with Aβ plaques, are reported to be a major source of proinflammatory cytokines in many CNS diseases, including Alzheimer’s disease and its corresponding mouse models.

IL 12 and IL 23 share a common subunit (p40), as well as thesignaling chain of their respective receptors (IL 12Rβ1). Although the number of different leukocyte cell types that are known to be able to respond to IL 12 and IL 23 is growing, the role of IL 12/IL 23 signaling in the context of amyloid induced neurodegeneration has not yet been established.

In the Nature Medicine study Johannes vom Berg and colleagues, as part of a joint Swiss and German research team, found that the microglial cells in the brains of the mouse model of Alzheimer’s disease expressed high levels of IL-12 and IL-23, including during the formation of amyloid plaques.

As IL-12 and IL-23 share a common subunit (p40), blocking p40 signaling in APPPS1 mice by peripheral (intraperitoneal), or central (intracerebroventricular) injection with the neutralizing p40-specific antibody reduced amyloid beta deposits in the brain and improved cognitive deficits in aged APPPS1 mice.

Notably, checking the translational significance in humans, the authors found that the concentrations of p40 were increased in the cerebrospinal fluid of Alzheimer’s disease patients, and individuals with higher levels of p40 had lower cognitive performance.

The authors discuss that the IL-12 and IL-23 signal­ing might be “crucially involved in regulating not only the amount of a central component of Alzheimer’s disease pathology, namely, Aβ plaques, but also cognitive impairment”.

As p40-neutralizing antibodies and the IL-12/23inhibitors (ustekinumab) are approved in the United States, Canada and Europe to treat moderate to severe plaque psoriasis, the authors also suggest that treatment trials in subjects with mild cognitive impairment or Alzheimer’s disease may be warranted.

An Update

More recent research seems to substantiate and support the 2012 vom Berg’s study showing increased serum levels of IL-23, and the presence of IL-12A, IL-12B and IL-23R polymorphisms in patients with Alzheimer’s disease.

Besides neurodegeneration, the disease-accelerating role of neuroinflammation has become a focus of research in AD. Also, the central role of IL-23 in neuroinflammation, especially in multiple sclerosis (MS), and the role of IL-23 in the development of MS is now well established. Thus, IL-23 is increased in serum, cerebrospinal fluid (CSF), and lesional tissue of MS patients.

Since then, several interesting studies about AD and IL-23 have been published. Thus, single nucleotide polymorphisms in the IL-12/23 subunit p40 (rs3212227) and IL-23 receptor polymorphisms are associated with AD in a northern Han Chinese population.

AD patients show higher peripheral levels of IL-23. Thus, serum concentrations of IL-23, IL-17 and IL-18, are significantly higher in AD patients than controls. Of note, the serum level of IL-23 was observed to be significantly higher in female AD patients than male AD patients.

A plasma multianalyte profiling study of patients with mild cognitive impairment and AD demonstrated an association of plasma p40 levels with abnormal cognitive performance.

Although the actions of IL-23 in other neuroinflammatory processes like MS are mediated via Th17 cells, in AD, IL-23 and IL-12/23 p40 might act through novel mechanisms independent from T cells.

Further data are needed to elucidate if neuroinflammation in AD is driven by IL-12/23 p40, IL-23 or even partly by IL-12.

Source: Nat Med, 2012, 12:1812-9. doi: 10.1038/nm.2965. Epub 2012 Nov 25.
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