APC stops apoptosis in ischaemic stroke

For personal use. Only reproduce with permission from The Lancet Publishing Group.

THE LANCET Neurology Vol 2 April 2003 http://neurology.thelancet.com 203

Newsdesk

Interleukin-23 is the essential cytokinein the development of autoimmuneinflammation of the brain, notinterleukin-12 as has been thought forthe past decade, report US researchers.“Interleukin-23 has a broader role than interleukin-12”, says JonathanSedgwick (DNAX Research Inc, PaloAlto, CA, USA), “and given our results,I think we have to add interleukin-23 tothe list of possible targets for thetreatment of inflammatory disease”.

Interleukin-12 is important in theactivation of T-helper type 1 (Th1)lymphocytes, which are involved ininflammatory responses. However,despite early indications thatinterleukin-12 was central to theinflammation seen in experimentalautoimmune encephalomyelitis (EAE; amouse model of multiple sclerosis)researchers, such as AbdolmohammadRostami of Thomas JeffersonUniversity, Philadelphia, PA, USA, haverecently reported discordant results(J Immunol 2002; 169: 7104–10).“Interleukin-12 consists of two sub-units, p40 and p35, and when wetreated mice with EAE with antibodiesto p40, the disease was suppressed”,Rostami explains. Similarly, EAE couldnot be induced in p40 knockout mice.However, p35 knockout mice weresusceptible to EAE, even though, likethe p40 knockouts, they made nointerleukin-12. “This result reallysurprised us”, says Rostami, “and wehad no explanation for it”.

Now the DNAX team has providedan answer. The discordant results arosebecause interleukin-23 shares the p40subunit with interleukin-12, explainsSedgwick. In interleukin-23, however,the p35 subunit is replaced by p19.“We couldn’t induce EAE in p19 nullmice”, explains lead author DanielCua, “even though they expressedinterleukin-12”. In other words,interleukin-23 not interleukin-12 is thecritical cytokine for EAE development,although interleukin-12 is probablyinvolved in the pathogenesis of EAE insome way.

Further experiments indicate that alack of interleukin-23 does not preventthe development of Th1 lymphocytesor their entry into the CNS but that

Wrong cytokine backed in multiple-sclerosis model

Researchers in the USA have foundthat activated protein C (APC), asystemic anti-inflammatory and anti-coagulatory agent, might also protectbrain endothelial cells in patients withischaemic stroke by preventingapoptosis (Nat Med 2003; 9: 338–42).

APC is best known for its use in thetreatment of severe infections, butevidence from animal models suggestsit can also reduce ischaemic injury—including brain damage caused bystroke. However, no-one knew whetherthis was the result of anti-inflammatoryor anticoagulatory actions, or whetherAPC had a direct protective effect oncells. This new work suggests that APCstops hypoxic brain endothelial cellsfrom undergoing apoptosis byinhibition of the production of p53,thus tipping the Bax/Bcl-2 ratio infavour of cell survival and stoppingcaspase 3 signalling. “Many brainendothelial cells that become hypoxicbecause of an ischaemic stroke startmoving towards apoptosis”, explainsBerislav Zlokovic (University ofRochester Medical Center, Rochester,NY, USA), “but APC seems able to stopthem from going over the brink. Ifgiven early enough, it might prevent alot of the brain cell death we see instroke patients.”

The researchers induced hypoxiain human brain endothelial cells invitro and showed that apoptosis—as assessed by standard lactatedehydrogenase spillage and terminaldeoxynucleotide transferase-mediateddUTP nick-end labelling (TUNEL)

techniques—was reduced by 60–70%in the presence of APC. “The amountof p53 being made in these cells wasaround 78% down compared to non-treated cells”, explains coauthor TongCheng. “Further, not only was Baxproduction down some 67%compared to controls, APC actuallyincreased Bcl-2 levels, giving a clear‘no-apoptosis’ signal to the cell. Thisall translated into a 60% fall in thenumber of cells producing caspase 3,hamstringing apoptosis.”

Further experiments in miceshowed that although low tomoderate doses of APC clearlyreduced the damage caused byischaemia, the drug had no effect onpostischaemic cerebral blood flow,fibrin concentration or neutrophildeposition. “The neuroprotectiveproperties of APC are therefore due toits antiapoptotic action rather than itsother properties”, explains Zlokovic.

APC might have a bright future asa neuroprotective agent in stroketreatment since the only currentlyapproved drug, alteplase, can actuallydamage nerve cells. APC might also beused to prevent ischaemic injury toother organs. “One wonders whetherit could be useful in other situationswhere apoptosis caused by hypoxiacould be a problem”, remarks JuliaBuján, Department of MorphologicalSciences and Surgery, AlcaláUniversity, Alcalá de Henares, Spain,“such as in transplants or even inautologous grafting”.Adrian Burton

APC stops apoptosis in ischaemic stroke

interleukin-23 is essential for late-stageinflammation in EAE (Nature 2003;421: 744–48). “We don’t know exactlyhow interleukin-23 induces late-stageinflammation but it seems to affectmemory T cells, inflammatory macro-phages, and various myeloid cells”,explains Cua.

“These data are very convincing and encouraging because macrophageactivation is an important new target for drug development”, says Richard Ransohoff (Cleveland Clinic

Foundation, OH, USA). “The challengewill be to develop reagents that canaccess the CNS and selectively impairsignalling to the interleukin-23 receptoron macrophages and microglia.”However, both he and Sedgwick warnthat several therapies that lookedpromising in EAE have failed inmultiple sclerosis. Ultimately, con-cludes Sedgwick, “only clinical trials canprove the value of any given therapeutictarget”.Jane Bradbury