Alpha1-antitrypsin Review Robert A. Stockley, MD, DSc,FRCP KEYWORDS (cid:1)Alpha1-antitrypsin deficiency (cid:1) Neutrophils (cid:1) Genetics (cid:1) Emphysema(cid:1) Therapy KEY POINTS (cid:1) Alpha1-antitrypsindeficiencyremainsthecommonestgeneticcauseofemphysema. (cid:1) Theclinicalpenetranceisvariablebutisamplifiedbycigarettesmoking. (cid:1) Thepathophysiologyreflectsexcessivetissuedamagebyneutrophilserineproteinases. (cid:1) Augmentation therapy with plasma-derived alpha1-antitrypsin is widely (but not uniformly) accepted,butefficacyhasbeendifficulttoprovebyconventionallyacceptedoutcomes. (cid:1) Understandingthegeneticdefectsresponsibleandthemechanismsofdeficiencyprovidespros- pectsforfuturetreatmentstrategies,includinggenetherapy. The first description of alpha1-antitrypsin (AAT) pathologicchangesofemphysema.Thisconcept deficiency (AATD)identifiedbypaperelectropho- has continued to dominate research into the resis was published in 1963 by Laurel and Eriks- pathophysiologyofemphysema,exploringseveral son.1 As part of their publication they reported potential mechanisms, namely deficiency of pro- the first 5 individuals who had been identified, 3 tective inhibitors, poor function of defective in- ofwhomhadrecurrentchestproblemsandsignif- hibitors, modulation of the function of inhibitors icant evidence of emphysema, the eldest being by oxidation or proteolytic cleavage, and over- 42 yearsofage and1ofwhom alsohad afamily whelmingoftheinhibitorsbyexcessiveinflamma- historyofemphysema.Becauseofthishighprev- tory cell recruitment and/or activation releasing alenceofemphysema,particularlyatayoungage, sufficient enzyme to exceed any protective subsequent studies of the family of these index inhibitors. cases identified nonindex cases with the defi- ciencyandalsopulmonaryemphysema,confirm- PREVALENCE ingtheinheritednatureofthecondition. Because AAT was known to be an inhibitor of AATofthePiZphenotypeisthoughttohaveorig- proteolytic enzymes, subsequent research was inated some 2000 years ago in the Baltic region, basedonthehypothesisthatanenzymenormally thereafter becoming spread by Viking migration. inhibitedbyAATplayedacentralroleinthedevel- Theprevalencefollowsthismigrationinadilutional opment of emphysema. Senior and colleagues2 mannerandtheincidencecanvaryfrom1in1600 subsequently showed in an animal model that insomeoftheBalticcountriestoapproximately1 neutrophil elastase was able to reproduce these in5000intheUnitedStates. features of emphysema, as can proteinase 3,3 AAT is a 52-kDa single-chain glycoprotein with another serine proteinase from the neutrophil. asequenceof394aminoacidsthatissynthesized Theseobservationsledtotheproteinase/antipro- predominantlyintheliverandfunctionsasaserine teinase theory of the mechanism of emphysema, proteinase inhibitor or serpin. The protein is en- inwhichproteolyticdestructionofthelungintersti- coded on the serpin a-1 gene and consists of 7 tium(andparticularlylungelastin)resultedinstruc- exons on the long arm of chromosome 14. Since m turalchangesinthealveolarregion,leadingtothe the original discovery there have been more than o c s. c i n i l c ADAPT Project, Lung Function & Sleep Department, Queen Elizabeth Hospital Birmingham, Ground Floor, e h Out-patientsArea3,MindelsohnWay,Edgbaston,BirminghamB152WB,UK t E-mailaddress:[email protected] d. e m ClinChestMed35(2014)39–50 st http://dx.doi.org/10.1016/j.ccm.2013.10.001 e h 0272-5231/14/$–seefrontmatter(cid:1)2014ElsevierInc.Allrightsreserved. c 40 Stockley 500 single-nucleotide polymorphisms reported at However, in recent years testing has become this gene locus, although many are associated more widespread and the variability of the age with normal gene transcription, translation, and of presentation has become more apparent as protein function. However, several mechanisms well as variations in the clinical phenotype. Pa- are recognized as being related to deficiency, tients may present with bronchiectasis and no including total absence of the gene, frame shift emphysema,10 upper zone and centrilobular mutations that lead to premature stop codons, emphysema,11 as well as the classic lower zone aswellaspointmutationsthatmayleadtonopro- panacinar emphysema. There may be evidence duction or production of abnormal AAT pheno- ofairwayspredominancewithlittleemphysema,12 types.4 The function of the protein depends on a whichcanbereflectedinphysiologicdiscordance methionine amino acid at position 358 that gives with some patients having reduced gas transfer the protein its specificity for interlocking with the alone, and others reduced spirometry alone,13 catalytic triad of serine proteinases and in partic- whichatleastpartlyreflectstheemphysemadistri- ular neutrophil elastase.5 This interlocking results bution.However,inmostcases,bothphysiologic in inactivation of both proteins and the formation measures are impaired. This discordance can of a stable complex. In the commonest severe Z alsobeseenwithinsiblings,inwhomthereseems type of AATD, the gene is normally transcribed tobenoconcordancewithspirometrybutclearer and translated although a single point mutation concordance with both gas transfer and upper leads to an amino acid change at position 342 zoneratherthanlowerzoneemphysemaasdeter- (glu-lys). This change affects the mobility of the mined by lung densitometry.14 This finding raises reactive center loop and produces a gap in beta thepossibilitythattheemphysemaandgastrans- sheet A. The reactive loop of one molecule can fer abnormalities are more closely linked to the then insert itself into this gap, causing the so- AATD and that airways disease may reflect other calledloopsheetpolymerization6leadingtoaccu- modifying or epigenetic phenomena (discussed mulationofAATinthehepatocytes,areductionin later). secretionofAAT,andaretainedtendencytoform Smokingplaysakeyroleintheclinicalimpactof spontaneous polymers both in the serum and AATD. Patients who present earlier are nearly al- tissues (especially the lung). The most common wayssmokersandsmokingcessationcanlargely phenotypeofAATisthenormalMform.Affected stabilizethedisease.Inaddition,recurrentexacer- individualshave2genesandtheseareusuallyex- bations also influence spirometric decline as well pressedinacodominantform,thusheterozygotes as gas transfer decline,15 and reversibility of air- are common (1%–3% of affected populations) ways obstruction is associated with more rapid such that MZ heterozygotes have partially spirometric decline.16 Recent studies have not reduced levels (approximately 60% of normal shown a significant reduction in life expectancy MM homozygotes) and SZ heterozygotes have in never smokers17 and such patients often pre- levels approximately 40% of the normal MM ho- sentatalaterage.8 mozygotes. The level of AAT may be key to the However, even in smoking individuals, the pro- susceptibility to develop pulmonary emphysema gression of lung disease can be widely variable. (discussedlater). Recentstudieshavesuggestedthatspirometryin individuals identified at birth remains normal until their 30s despite an increased prevalence of CLINICAL IMPACT breathlessness.18 Studies of never smokers have TheclassicpresentationforindividualswithAATD indicated that deterioration in gas transfer and is early-onset basal panacinar emphysema lung densitometry can be identified even in this (comparedwiththeusuallateronsetapicalcentri- good-prognosis group in the early to late 20s, lobularemphysemaofchronicobstructivepulmo- whereasspirometricchangestartstooccurinthe nary disease [COPD]). For these reasons, initially 50s and 60s.19 In addition, in cross-sectional testing for AAT was confined to such patients, data,thegreatestrateofdeclineofforcedexpira- leading to an acquisition bias that continued to toryvolumein1second(FEV )occursintherange 1 support theclinical phenotype. Oncethese index of 35% to 60% predicted, whereas the greatest individuals had been identified, family screening change in gas transfer occurs when the FEV is 1 identified further deficient subjects as nonindex lower.16Lungdensitometry(whichisamoredirect patients and, in general, these individuals have measure of the emphysema process) seems to much less severe disease.7 Subsequent testing showsteadyprogression throughout allstagesof also confirmed that never smokers also had less thedisease,20suggestingthatthedisjunctionwith clinicalevidenceoflungdisease8andmoreoften spirometryorgastransferchangereflectstheparts presentedlaterinlife.9 of the lungs that are undergoing emphysematous Alpha1-antitrypsinDeficiency 41 change.Nevertheless,thesefeaturessuggestthat Studies of airway secretions from patients with all individuals with AATD should be monitored on AATD confirmed that LTB4 was the major recog- aregularbasistodeterminethenatureanddegree nized chemoattractant that influenced neutrophil ofprogressioninorderthatprognosisandthepo- migration.29 tentialeffectsoftherapycanbepredictedandeval- In an elegant series of experiments Campbell uated(discussedlater). andcolleagues30 describedtheprocessofquan- MostpatientswithAATDaretreatedasforusual tumproteolysis, wherebyneutrophils migratingin COPD with long-acting bronchodilators and thepresenceofconnectingtissuereleaseconcen- inhaledcorticosteroids.ManypatientswithAATD trations of serine proteinases in excess of the haveadegreeofreversibility(Fig.1)andrecurrent concentration of AAT even in individuals without exacerbations,21althoughnoformaltrialsofusual deficiency. It was thought that this process was inhaledtherapieshavebeenperformedindeficient necessarytoallowneutrophilstomigratethrough patients. However, at least one small study has theinterstitiumofthelungbydestroyingthecon- indicated that inhaled corticosteroids have some nective tissue in close proximity to the cell. This benefit.22 processshowedlittlerelationshiptotheAATcon- The continuous progression and young age in centration until it decreased to less than 11 mM someindividualsleadstolungtransplantationbe- (Pi Z antitrypsin deficiency has an approximate inga viableoption toward theendofthedisease concentrationof5mM).Atthispointtherewasan process. Survivaldata(especially overtheperiod exponential increase in the degree of damage of 2–9 years after transplantation) suggests that seen in the presence of a migrating neutrophil. this is improved23 and is associated with an This concept has major implications concerning improvement in lung function and health status, the risk ofheterozygotes suchas theMZ and SZ although longer term survival is not necessarily phenotypes,becauseingeneralthesephenotypes betterwhenpatientsarecloselymatchedforphys- have AAT plasma levels that are more than the iologicimpairmentatbaseline.24 critical 11 mM threshold (discussed later). More Lungvolumereductionsurgeryisrarelyindicated recently it has been recognized that polymers of becausemostpatientshavebasalemphysema,25 AATcanbechemoattractantsintheirownright,31 although studies are ongoing of nonsurgical lung although they are also proinflammatory.32 It has volumereduction. beensuggestedthatthesepropertiesofthepoly- mersmaybemoreimportantindrivingtheneutro- philic infiltration into the lung than the effect of PATHOPHYSIOLOGY uninhibited elastase on LTB4. Whether this is Theneutrophil,whichisthemainsourceofserine true remains unresolved. However, AAT enters proteinases thought to cause the pathologic the lung mainly by diffusion from plasma and the changes, is present in large numbers both in the interstitial concentration should be about 80% of airways26 and the interstitium of patients with that in plasma.33 Larger proteins (including poly- AATD.27 Early studies suggested that failure to mers)wouldberestrictedinthisdiffusion,leading controlelastasewithintheairwaysledtothestim- toareversedplasma/lunggradientthatwouldthus ulation of the neutrophil chemoattractant leuko- not act as a conventional chemoattractant. In triene B4 (LTB4) by alveolar macrophages.28 addition, polymer formation is concentration Fig. 1. The change in FEV as a per- 1 centageofpredictedfollowinginha- lation of 400 mg of salbutamol expressed as the proportion of the populationshowingeachchange. 42 Stockley dependent and hence should not increase in the ThenullvariantshaveundetectablelevelsofAAT interstitiumtomorethanthatinplasma.However, and hence no circulating polymers, suggesting there are potential caveats to this concept. First, thatthelevelismorecriticalthanpolymersinthe lung cells have the potential to produce some pathophysiology of AATD lung disease. This AATlocally34andhenceincreasepolymerforma- findingisconsistentwiththequantumproteolysis tioninsitu,establishingagradient.Asanalterna- processdescribedbyCampbellandcolleagues.30 tive, the proinflammatory nature of polymers With this last concept in mind, the in vitro may increase local chemoattractant production, studies of Campbell and colleagues41 indicated providing an alternative gradient. Nevertheless, that a prevailing plasma AAT concentration also polymers of AAT are in the interstitium of the showed this critical threshold for more extensive lung and this chemoattractant property may be tissuedamageinthepresenceofadegranulating the reason that some neutrophils colocalize with neutrophil. For this reason the common MZ het- thepolymers28and,ifso,arelikelytocauseeven erozygotecarriersshouldnotbeatgreaterriskof morelocalconnectivetissuedestructionbyretain- developingemphysemathanthenormalMMindi- ing them (and their proteolytic activity) in situ. viduals because their AAT levels are invariably TheseconceptsaresummarizedinFig.2. morethanthisthreshold.However,thereissome Thereareotherfactorsthatmaycomplicatethe controversyintheliteraturebecauseMZsubjects developmentofemphysema,includingtheroleof have been reported as having evidence of uninhibited proteinases on cell apoptosis (which increased elastase activity in 1 study,42 are more has also been implicated in the emphysema pro- likely to have slightly lower lung function as a cess)35 and activation of other proteinases in the group43 and more severe COPD than MM sub- inflammationcascadeandinactivationofcognate jects,44aswellasgreaterhospitalizationandmor- inhibitors.36 In addition, MMP-9 (matrix metallo tality.45 Although these data do not indicate the proteinase)37andIREB2(ironresponsiveelement MZ as a susceptibility factor, they do suggest bindingprotein)38havebeenimplicatedasfurther that, if a patient is going to develop COPD and genetic modifiers in AATD, and, more recently, also has the MZ phenotype, the disease may polymorphism of the tumor necrosis factor alpha becomemoreofaproblem.However,thesedata gene has also been shown to amplify the inflam- mainly relate to known patients with COPD or mation and progression of lung function decline subjects tested or detected as part of family aswellasinfluencingtheclinicalphenotype.39 screening, and as such represent a selection bias. The most robust data from epidemiologic studies suggested that, at worst, MZ subjects Susceptibility of Other Phenotypes have a minimal decrease in FEV compared with 1 Most information concerning AATD relates to MM subjects.46 Thus, in general, the MZ pheno- studiesofthePiZphenotype(usuallyPiZZgeno- typealoneisnotconsideredariskfactor. type) because this is the most common severe The SZ phenotype is approximately 3 times as variant presenting with disease. There is limited common as the Z phenotype, especially around literature on the null variants of AAT, although in theMediterranean.TheaverageAATlevelinthese a small series the patients seem (if anything) to individualsisabout14,althoughaproportionhas have worse lung function than Pi Z subjects.40 levels less than the 11 mM threshold, suggesting Fig. 2. Airway neutrophils release elastase (1) which remains active becauseofAATdeficiency.Thisstimu- latesmacrophagesandepithelialcells to release chemoattractants (2), which leads to neutrophil recruit- ment(3)andretentionintheintersti- tium adjacent to polymers (4) enhancing tissue destruction. IL8, interleukin8. Alpha1-antitrypsinDeficiency 43 atheoreticsusceptibilityinsomeindividuals.Meta 5 years was greater in individuals who had never analysis of published data provides credence to received such therapy. In addition, the decline in this possibility,47 although again selection bias is FEV between the values of 35% and 60% pre- 1 likelytohaveinfluencedtheresults.However,pa- dicted was also greater in individuals who had tients with the SZ phenotype are more likely to never received augmentation therapy.54 This last haveemphysemawiththeusualapicaldistribution observation has led to a general belief that of usual nondeficient COPD,48 which is therefore augmentation therapy is only effective within this nottypicaloftheAATDphenotype. physiologicrange,andinsomecountriesaugmen- Furthermore, despite the greater prevalence, tationisstoppedoncetheFEV decreasestoless 1 few patients with COPD and the SZ phenotype than 30% predicted. However, there are some have been identified (approximately one-fifth as problems with the interpretation of these data. manyaspatientswiththeZphenotype49).Never- First, in the health care systems in the United theless, in some countries the SZ phenotype is States,theleastprivilegedindividualsareunlikely consideredappropriateforaugmentationtherapy. to receive therapy and individuals of low social Even less information is available for other classhavepooreroutcomesforallhealthcareis- partial deficiencies including the IZ, PZ, and FZ sues.Thistrendisconsistentwiththeobservation phenotypes.AlthoughtheFZphenotypehascom- that patients who had always or only partially parable plasma AAT with the MZ phenotype, it is received augmentation therapy seemed to have lessfunctional.50TheFvarianthasareducedas- a similar outcome. Second, in all clinical trials it sociation rate constant for neutrophil elastase iseasiertodetectabenefitontheoutcomemea- and binds it more slowly once the enzyme is sure if the outcome measure is highly prevalent released. This property could provide a mecha- and changing most rapidly. As indicated earlier, nism to increase local elastase-induced tissue the FEV decline in AATD is most rapid in the 1 damage. However, few such subjects have been 35% to60% predicted range, whichmay explain identified and studied to provide more certainty thepositivedataonlyinthisrange.Otherobserva- abouttheroleoftheFvariant. tional studies have also shown some benefit on FEV decline, namely comparing countries where 1 augmentation therapy is available with those AUGMENTATION where it is not.55 Sequential studies of decline in Becauseoftheproteinase/antiproteinasehypoth- FEV beforeandaftertherapy,56althoughitshould 1 esis it became accepted that augmentation of benotedthatFEV declineisnotlinearandslows 1 theAATlevelwouldprovebeneficialinprotecting down later in the disease process,16 which could thelungfromprogressivedamage.Studiesinthe explain the sequential change. In addition, meta- 1980sshowedthatpurifiedAATgivenbytheintra- analysis fromreported data on decline in FEV in 1 venousrouteincreasedandmaintainedAATlevels treated and untreated cohorts also suggests an intheblood(beyondthatofSZheterozygotesand overall benefit in terms of spirometric decline if thusthoughttoremovetheincreasedrisk)andin augmentationwasgiven.57 the airways of deficient individuals, where it re- In recent years it has become accepted that mainedfunctional51andwassubsequentlyshown FEV is generally a poor surrogate of the emphy- 1 to reduce inflammation, in particular the major sema process. Because emphysema is thought neutrophil chemoattractant LTB4.52 Although to be central to the pathophysiology of COPD in biochemicalefficacywasthereforeshown,clinical AATD,lungdensitometryhasbecometheoutcome efficacy has been difficult to show. In the early measureofchoice.Datashowthatlungdensitom- days the FEV was the gold standard outcome etryprogresses inalinear fashionthroughoutthe 1 measureforstudiesinCOPD.Powercalculations diseaseprocess.20Itisthesensitiveparameterto indicated that it would be impossible to recruit change58andthuspowercalculationsforinterven- anddeliveraclinicaltrialofaugmentationtherapy tionalstudieswithdensitometryasanoutcomeare with FEV as the primary outcome.53 For this morefavorableforthisrarediseasegroup.Aninitial 1 reason no such trial was deemed feasible or has study between Denmark and Holland confirmed been undertaken. Evidence for efficacy therefore that augmentation therapy had no benefit on has come predominantly from indirect observa- spirometry but did show a trend (P 5 .07) for tionalstudies. preservation of lung density and, by implication, TheUS National Institutes of Health developed stabilization of the emphysema process.59 The an AATD register and eventually analyzed out- subsequent Exacerbations and Computed To- comesinindividualswhohadreceivedaugmenta- mography as Lung Endpoints (EXACTLE) study tiontherapy(atleastfor6months)andthosewho wasperformedusingmoresophisticatedscanning had never received augmentation. Mortality over techniques with densitometry as a primary 44 Stockley outcome.Again,thedeclineinlungdensitometryin exacerbations.AbouthalfthepatientswithAATD patientsreceivingaugmentationwaslessthanon do not have a history of exacerbations but, in placebo using the same analysis as the Danish/ thosewhodo,mosthave1or2peryear(Fig.3). Dutchstudy,althoughagainitfailedtoachievesta- These episodes usually include all 3 of the major tisticalsignificance(P5.07),buttherewasasignif- symptomsofsuchepisodesandoccurthroughout icant reduction in severe exacerbations requiring theyearwithsomepreponderanceintheautumn hospitalization.60Furtheranalysisofthedatafrom and winter months (Fig. 4) Exacerbations in theEXACTLEtrialdidshowasignificantreduction AATD are more inflammatory than those in usual in densitometry progression at the bases of the COPD, with higher elastase activity,66 and tend lung where the characteristic emphysema oc- to last longer.67 These episodes are related to curs,61andcombiningthedataofthesetwotrials the progressive reduction in FEV .15 AAT by the 1 inwhichdensitometrywasmeasured,evenwhen inhaledrouteispredictedtoresultinamorerapid biasing the data in favor of the earlier and hence reduction in the local proteinase burden of these less sophisticated trial, led to a highly significant larger airways events and may therefore reduce difference between treatment and placebo, indi- the proteinase-generated inflammation and fre- catingpreservationoflungdensity.62 quency,severity,andperhapslengthofexacerba- Augmentation therapy is currently licensed in tions.Suchatrialiscurrentlyunderway68andthe many countries as a weekly infusion, although results will be informative in terms of the fre- othertherapeuticregimenshavebeenused;how- quency,severity,andpathophysiologicprocesses ever,itisexpensive63andthisraisesthepossibility involved. At worst, the treatment may change of providing augmentation through the inhaled episodesrequiringtreatmenttolesssevere/symp- route. However, deposition studies have shown tomaticonesnotrequiringintervention(Fig.5). that the inhaled route does not target the most Itwouldalsobepossibletogiveintravenousbo- affected emphysematous areas64 and deposition lusesofAATatthestartofanexacerbation,which is unlikely to occur in the alveolar region (as with mayhavethesame(althoughlessefficient)effect most nebulized drug delivery). Even if such a of increasing airways AAT by diffusion from deposition could be achieved, the integrity of the plasma. However, this would require an ability to epithelial surface wouldrestrict anymovementof predict early whether the episode would be mild AAT into the interstitium65 where the destruction or severe; perhaps limiting to episodes at admis- is occurring. One possible caveat to this physio- siontohospitalmayprovemostbeneficialiflength logic problem is that, if the chemoattractant ofstayormortality weretobeinfluenced. Never- (LTB4) is generated on the airway side of the theless, at present, even if the overall efficacy of lung, augmentation of the elastase inhibitory ca- augmentationtherapyisaccepted,itislargelyun- pacity at this site would lead to a reduction in known whether all patients should receive such free elastase activity and hence LTB4 production therapyorwhetheritispossibletoidentifyasub- by local macrophages, and this in turn would set for whom it would be important and hence in leadtoreductioninneutrophilmigrationandhence whomthereislikelytobeagreatercost/benefit. neutrophil-dependentconnectivetissuedamage. At best, effective augmentation therapy slows Nevertheless,theinhaledroutemaybeofmore downtheprogressionofemphysemaanditsphys- benefit for individuals having recurrent iologic markers. Thus, ideally all patients with Fig.3. Thefeaturesandfrequencyof exacerbationsisshownasapercent- ageofpatientsexperiencingatleast 1episodeperyear. Alpha1-antitrypsinDeficiency 45 Month of Exacerbations (%) Fig. 4. Distribution of exacerbations throughout the year for patients withAATD. Breathlessness (n = 219) Cough (n = 274) 18 Phlegm (n = 254) 16 14 12 10 8 6 4 2 0 Jan Mar May Jul Sep Nov Month AATD who are identified should be monitored thelinesofthisapproachmaybecomecriticalfor so that the natural history in the absence of the prescription and funding of augmentation augmentation can be determined. For smokers therapy.69 this should be done after smoking cessation and ForPiZindividualswithoutrespiratorydisease, in many such patients lung function stabilizes. In less information is available of the benefits of others there is a continual progression that may augmentationtherapy.Acutenecrotizingpannicu- bewithinorgreaterthanthenormalagingdecline. litis can respond dramatically70 but it is unknown It seems logical therefore that, for individuals in whether the vasculitis would also benefit from whomthedeclineineitherspirometryorgastrans- augmentation therapy, although this is also a fer exceeds that expected as part of the normal proteinase-dependent process in some sub- aging process, augmentation therapy would be jects.71 The cirrhosis caused by liver damage indicated and that the younger the individual the fromAATretentionisnotexpectedtorespondto more important this would be to either stabilize or require augmentation therapy because the diseaseorprolongthephaseuntiltransplantation endogenous polymerization will still continue. becomes the only remaining option. In never Methods to silence gene transcription may prove smokers, the physiologic measurements at pre- protective to the liver but potentially amplify the sentationrelatedtotheagewouldalreadyprovide lung damage. Mechanisms to enhance liver AAT good evidence of the rate of progression even secretion by preventing polymerization treat the thoughlifeexpectancyinsuchindividualsremains liver and protect the lung if AAT function can be normal. In times of austerity, rationalization along retained(discussedlater). Total daily scores Fig. 5. Daily diary card score reflect- 35 ing severity and duration of symp- tomsforexacerbationsinAATDthat did or did not require intervention (dataarederivedfromRef.68). Treated Untreated ores 30 n sc a Me 25 20 Days 46 Stockley NEW TREATMENTS of gene-modifying agents into the hepatocytes beforetrialscanbeundertaken. There are many strategies that can potentially A further strategy is to deliver the gene to the overcometheproblemsofAATD. lunginawaythatminimizesanyimmuneresponse to the vector and provides significant and sus- Recombinant A1AT tainedAATproduction.Thisstrategywouldmake Becauseofthecostandlimitedsupplyofplasma- repeated treatments less frequent and immune derived AAT, recombinant forms of protein have activationtothevectorlesslikely.Suchastrategy been generated. Initial studies produced nongly- introducing the vector into the pleural space cosylatedproteinsthatresultinmorerapidclear- seems to fulfill these criteria in animal models.83 ance,72 and potential problems with structural Further studies including long-term safety in hu- stability and exposure of immunogenic epitopes mansneedtobeundertaken. normallyhidden.Aglycosylatedtransgenicsheep Inaddition,transfectionand/orastemcellstrat- proteininducedimmuneresponsesbecauseofim- egytodelivernormalhepatocytestothediseased purities73 that were impractical to remove. More liver84 may provide further long-term solutions, recently a sialyzed version has been produced in althoughagainsafetymaybeamajorissue. a human neuronal cell line74 and it remains to be Drugs seenwhetherthisbecomesaviablesource. SpecificinhibitorsofNeutrophilElastase(NE)have Secretion Strategies been developed, although they have not been Because at least the Z form of AAT is translated tested in AATD. Most have failed at the phase 2 normally, strategies to prevent retention in the development stage because of failure to improve hepatocytes would have 2 potential benefits. lung function in usual COPD (an outcome that is Release of AAT would reduce the endoplasmic improbable in phase 2 studies for such agents). stress in the hepatocytes and thus (potentially) Because AAT inhibits other serine proteinases preventthedevelopmentofcirrhosisandliverfail- released at thesametime asNE (Pr3and CatG) ure. At the same time, the increased secretion havingmanysimilareffectsonthelungandbeing wouldraisetheplasmaconcentrationandpoten- increasedinAATD,85itispossiblethatahighlyse- tially protect the lung from proteolytic damage. lective NE inhibitormay notprovide significantor Chemicalchaperonesintendedtostabilizethein- total protection against serine proteolytic attack termediateformsofZAATonthefoldingpathway to the lung. However, in the absence of such a were shown to work in animal studies75 but have study,thedirectroleofelastaseand,inparticular, provedtobetoxicandineffectiveinhumans.76 the contribution of other serine proteinases re- Small peptides can prevent intrahepatic poly- mainsspeculative. merization in vitro,77 although there is currently In addition, alveolar repair could potentially no identified method of delivering these com- progress ahead of alveolar damage. Retinoic poundstotheendoplasmicreticulum(ER)ofhepa- acidreceptor(RAR)gammaagonistsareeffective tocytes. In addition, they inactivate the AAT,78 inanimalmodelsofemphysema.86However,this which produces a null phenotype. This process strategyprovedineffectiveina1-yearstudyofpa- wouldbeexpectedtoworsenthelungdiseasein tientswithAATD87andfurtherdevelopmentison suchnaturallyoccurringindividuals.40 hold. Inhibitorsofchemotaxis(CXCR1and2antago- Gene Therapies nistsorparticularlyonLTB4receptorantagonists) may have a potential role. These inhibitors would Avarietyofgenetherapieshavebeenexplored.In reduce neutrophil reflux and hence proteinase general,theseresultinminimalandonlytransient release in the lung. However, these agents have expressionandhenceproductionofA1AT.79This notbeenstudiedinAATD. approachwouldfailtoinfluencetheliverdisease. ThehepatocyteERstresscouldbeabrogatedby BIOMARKERS the use of a silencing strategy using Si RNA.80 This strategy would lead to a null phenotype but Biomarkersofdiseaseactivityandhencedetermi- potentially can be combined with a transgenic nantsoffutureprogressionremainillusiveinAATD approach leading to normal AAT production to as in usual COPD. However, the mechanism that protectthelungaswell.81Analternativeistocor- leads to the development of emphysema has rect the gene defect using small DNA fragment been accepted as destruction of lung connective technology.82 However all these methods still tissue and specifically elastin by serine protein- depend on the development of effective transfer ases and most likely elastase. For this reason Alpha1-antitrypsinDeficiency 47 elastindegradationproductshavebeenproposed 2. SeniorRM,TegnerH,KuhnC,etal.Theinduction and extensively studied as appropriate markers. of pulmonary emphysema with human leukocyte However, elastin is a widespread connective tis- elastase.AmRevRespirDis1977;116(3):469–75. sue and little is know about systemic turnover, 3. KaoRC,WehnerNG,SkubitzKM,etal.Proteinase although in the healthy lung it is minimal.88 Thus 3. A distinct human polymorphonuclear leukocyte systemic or secreted elastin peptides or cross- proteinasethatproducesemphysemainhamsters. linking amino acids may reflect changes in other JClinInvest1988;82(6):1963–73. tissues orevendiet.Nevertheless,recent studies 4. Dickens JA, Lomas DA. Why has it been so diffi- havesuggestedthatreassessmentoftheseelastin cult to prove the efficacy of alpha-1-antitrypsin products may still be useful as an indicator of replacement therapy? Insights from the study of emphysemaprogressionandtheeffectivenessof disease pathogenesis. Drug Des Devel Ther specific,protectiveinterventions.89 2011;5:391–405. An alternative is to measure elastase directly, 5. Matheson NR, Gibson HL, Hallewell RA, et al. although, because of the presence of inhibitors Recombinant DNA-derived forms of human alpha bothintheplasmaandtheairways,enzymeactiv- 1-proteinase inhibitor. Studies on the alanine 358 ityisoftenlargelyinhibitedbythetimesamplesare and cysteine 358 substituted mutants. J Biol collected and analyzed. Such data do not inform Chem1986;261(22):10404–9. abouttheactivityatthepointofrelease(ie,where 6. LomasDA,EvansDL,FinchJT,etal.Themecha- thedamageoccurs).Forthisreasonafootprintof nism of Z alpha 1-antitrypsin accumulation in the the local activity would serve all potential needs. liver.Nature1992;357(6379):605–7. Recent studies of a specific cleavage product of 7. SeersholmN,Kok-JensenA,DirksenA.Survivalof fibrinogen may serve this purpose. The peptide patientswithseverealpha1-antitrypsindeficiency is increased in AATD and correlates with physio- withspecialreferencetonon-indexcases.Thorax logic impairment. In addition, it increases during 1994;49(7):695–8. exacerbations, which are known to influence 8. 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