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<article xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:mml="http://www.w3.org/1998/Math/MathML" dtd-version="3.0" article-type="research-article" xml:lang="pt">
  <front>
    <journal-meta>
      <journal-id journal-id-type="nlm-ta">Arq. Bras. Cardiol.</journal-id>
      <journal-title-group>
        <journal-title>Arquivos Brasileiros de Cardiologia</journal-title>
        <abbrev-journal-title abbrev-type="publisher">Arq. Bras. Cardiol.</abbrev-journal-title>
      </journal-title-group>
      <issn pub-type="ppub">0066-782X</issn>
      <issn pub-type="epub">1678-4170</issn>
      <publisher>
        <publisher-name>Sociedade Brasileira de Cardiologia</publisher-name>
      </publisher>
    </journal-meta>
    <article-meta>
      <article-id pub-id-type="publisher-id" specific-use="scielo-v3">VWGYmdts4nfhJrvJNPmGMfk</article-id>
      <article-id pub-id-type="publisher-id" specific-use="scielo-v2">S0066-782X2014000100019</article-id>
      <article-id pub-id-type="other">0019</article-id>
      <article-id pub-id-type="doi">10.5935/abc.20130248</article-id>
      <article-categories>
        <subj-group subj-group-type="heading">
          <subject>Ponto De Vista</subject>
        </subj-group>
      </article-categories>
      <title-group>
        <article-title xml:lang="pt">De Volta ao B&#225;sico: PCSK9 como um Novo Alvo para o Receptor
               LDL</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <name>
            <surname>Corral</surname>
            <given-names>Pablo</given-names>
          </name>
          <xref ref-type="corresp" rid="c01"/>
        </contrib>
        <aff>
          <institution content-type="orgname">Internal Medicine Institute</institution>
          <institution content-type="orgdiv1">Lipid Section</institution>
          <addr-line>
            <named-content content-type="city">Mar del Plata</named-content>
          </addr-line>
          <country>Argentina</country>
          <institution content-type="original">Lipid Section, Internal Medicine Institute, Mar
                  del Plata, Argentina</institution>
        </aff>
      </contrib-group>
      <author-notes>
        <corresp id="c01"><bold>Correspond&#234;ncia: Pablo Corral</bold>, Rawson 1006, Playa Grande. C&#243;digo Postal
               7600, Mar Del Plata, Buenos Aires. E-mail: <email>drpablocorral@gmail.com</email>
				</corresp>
        <fn fn-type="conflict">
          <p>
            <bold>Potencial Conflito de Interesses</bold>
          </p>
          <p>Declaro n&#227;o haver conflito de interesses pertinentes.</p>
        </fn>
      </author-notes>
      <pub-date pub-type="epub-ppub">
        <month>1</month>
        <year>2014</year>
      </pub-date>
      <volume>102</volume>
      <issue>1</issue>
      <elocation-id>e5</elocation-id>
      <history>
        <date date-type="received">
          <day>26</day>
          <month>04</month>
          <year>2013</year>
        </date>
        <date date-type="rev-recd">
          <day>05</day>
          <month>08</month>
          <year>2013</year>
        </date>
        <date date-type="accepted">
          <day>05</day>
          <month>08</month>
          <year>2013</year>
        </date>
      </history>
      <permissions>
        <license license-type="open-access" xlink:href="http://creativecommons.org/licenses/by-nc/3.0/">
          <license-p>This is an Open Access article distributed under the terms of the Creative
                  Commons Attribution Non-Commercial License which permits unrestricted
                  non-commercial use, distribution, and reproduction in any medium, provided the
                  original work is properly cited. </license-p>
        </license>
      </permissions>
      <kwd-group xml:lang="pt">
        <kwd>PCSK9 Prote&#237;na humana</kwd>
        <kwd>Polimorfismo gen&#233;tico</kwd>
        <kwd>Tend&#234;ncias</kwd>
        <kwd>Aterosclerose</kwd>
      </kwd-group>
      <counts>
        <fig-count count="1"/>
        <table-count count="1"/>
        <equation-count count="0"/>
        <ref-count count="10"/>
        <page-count count="4"/>
      </counts>
    </article-meta>
  </front>
  <body>
    <sec sec-type="intro">
      <title>Introdu&#231;&#227;o</title>
      <p>Quarenta anos ap&#243;s a descoberta de Goldstein e Brown do receptor de lipoprote&#237;na de
            baixa densidade (LDLR)<xref ref-type="bibr" rid="B01">1</xref>e 25 anos ap&#243;s a
            introdu&#231;&#227;o das estatinas<xref ref-type="bibr" rid="B02">2</xref>, um marco do
            gerenciamento da aterosclerose, os olhos da comunidade cient&#237;fica se voltam novamente
            para o LDLR, por meio do mecanismo de a&#231;&#227;o da pr&#243;-prote&#237;na convertase subtilisina/ kexin
            tipo 9 (PCSK9)<xref ref-type="bibr" rid="B03">3</xref>.</p>
      <p>A avalia&#231;&#227;o do polimorfismo gen&#233;tico com resultados inesperados em grandes estudos
            trouxe novamente &#224; vida a hip&#243;tese sobre o importante papel do colesterol de
            lipoprote&#237;na de alta densidade (HDL-C) no metabolismo da lipoprote&#237;na<xref ref-type="bibr" rid="B04">4</xref>; o debate aparentemente eterno sobre a
            contribui&#231;&#227;o de triglic&#233;rides (TG) e seus remanescentes para o fen&#244;meno da
               aterosclerose<xref ref-type="bibr" rid="B05">5</xref>. Tais avan&#231;os levaram &#224; nova
            prioriza&#231;&#227;o do gerenciamento do LDL como o objetivo central e prim&#225;rio em rela&#231;&#227;o &#224;
            preven&#231;&#227;o da principal causa da morbidade e mortalidade no ocidente, a
            aterosclerose.</p>
      <p>Mais uma vez, retornamos &#224; descoberta que levou Goldstein e Brown ao Pr&#234;mio Nobel em
            1985, o LDLR<xref ref-type="bibr" rid="B01">1</xref>; agora buscando evitar sua
            degrada&#231;&#227;o pelo do conhecimento e compreens&#227;o do mecanismo de a&#231;&#227;o da PCSK9.</p>
      <sec>
        <title>Bases bioqu&#237;micas e moleculares</title>
        <p>A PCSK9, tamb&#233;m chamada de convertase 1 regulada por apoptose neuronal (NARC-1), &#233;
               uma prote&#237;na serina, caracterizada por uma estrutura de tr&#234;s dom&#237;nios e um trio
               catal&#237;tico; ela &#233; o novo membro da fam&#237;lia de convertase das pr&#243;-prote&#237;nas<xref ref-type="bibr" rid="B03">3</xref>.</p>
        <p>O gene PCSK9 est&#225; localizado no cromossomo 1p32.3 e apresenta 22-kb de comprimento,
               englobando 12 exons codificando 692 amino&#225;cidos da glicoprote&#237;na. Esta convertase &#233;
               altamente expressa no f&#237;gado, intestino e rins<xref ref-type="bibr" rid="B06">6</xref>.</p>
        <p>A PCSK9 &#233; sintetizada como um zimog&#234;nio sol&#250;vel 74 kDa (proPCSK9) que ap&#243;s um
               processo auto-catal&#237;tico dentro do ret&#237;culo endoplasm&#225;tico, libera o pr&#243;-pept&#237;deo
               (14kDa)-N terminal, resultando em uma enzima 60-kDa. Este processo autom&#225;tico de
               clivagem &#233; necess&#225;rio para a sua ativa&#231;&#227;o e libera&#231;&#227;o do ret&#237;culo endoplasm&#225;tico<xref ref-type="bibr" rid="B03">3</xref>.</p>
        <p>O processo auto-catal&#237;tico permite a progress&#227;o por meio do caminho de secre&#231;&#227;o e
               assim, interage diretamente com o LDLR. &#201; importante mencionar que a atividade
               catal&#237;tica n&#227;o parece ser exigida para a degrada&#231;&#227;o de LDLR, mas somente para a
               ativa&#231;&#227;o da secre&#231;&#227;o de PCSK9<xref ref-type="bibr" rid="B06">6</xref>.</p>
        <p>Esta protease serina lida o fator dominante de crescimento epid&#233;rmico A (EGF-A) no
               LDLR, no qual PCSK9 e LDLR s&#227;o internalizados pelo hepat&#243;cito para que sejam
               finalmente degradados dentro do lisossomo (<xref ref-type="fig" rid="f01">Figura
                  1</xref>)<xref ref-type="bibr" rid="B06">6</xref>.</p>
        <fig id="f01" fig-type="other">
          <label>Figura 1</label>
          <caption>
            <title>PCSK9 regula a rota&#231;&#227;o de LDLR por meio da degrada&#231;&#227;o intracelular
                     elevada.</title>
          </caption>
          <graphic xlink:href="1678-4170-abc-102-01-00e5-30248-gf01.jpg"/></fig>
      </sec>
      <sec>
        <title>Passado, presente e futuro da PCSK9 </title>
        <p>H&#225; dez anos a Abifadel e cols. relatou 3 fam&#237;lias na Fran&#231;a com hipercolesterolemia
               familiar relacionada &#224; funcionalidade e express&#227;o elevadas de PCSK9, sem altera&#231;&#227;o no
               receptor de LDL ou estrutura apo B<xref ref-type="bibr" rid="B07">7</xref>.</p>
        <p>Em 2005, dois anos mais tarde, Cohen e cols. por meio do programa/estudo Risco de
               Aterosclerose em Comunidades (ARIC) descreveram a perda da fun&#231;&#227;o de PCSK9 em
               indiv&#237;duos afro-americanos e caucasianos. No passado, eles relataram uma preval&#234;ncia
               de 2,6% no d&#233;ficit da fun&#231;&#227;o, concomitantemente, com n&#237;veis s&#233;ricos reduzidos de
               colesterol de lipoprot&#237;na de baixa densidade LDL-C (28% inferior) e eventos CV, tais
               como infarto do mioc&#225;rdio, necessidade de cirurgia para bypass card&#237;aco e mortes
               coron&#225;rias (88%). O &#250;ltimo, por sua vez, exibiu uma diminui&#231;&#227;o na express&#227;o de PCSK9
               de 3,2%, com redu&#231;&#227;o m&#233;dia de LDL-C de 15% vs. grupos de controle e redu&#231;&#227;o de 47%
               nos eventos cardiovasculares exigindo cirurgia card&#237;aca, bem como a mortalidade
               relacionada a esta causa. De forma interessante, no estudo ARIC, 50% dos pacientes
               apresentavam hipertens&#227;o, 30% eram fumante e 20% apresentavam diabetes<xref ref-type="bibr" rid="B08">8</xref>.</p>
        <p>A inevit&#225;vel compara&#231;&#227;o entre a redu&#231;&#227;o do risco observada entre os indiv&#237;duos com um
               d&#233;ficit da express&#227;o/fun&#231;&#227;o de PCSK9 e os indiv&#237;duos avaliados com estatinas por 5
               anos (diminui&#231;&#227;o similar do LDL-C entre os dois grupos com risco reduzido marcado nos
               pacientes com a altera&#231;&#227;o gen&#233;tica) levou ao desenvolvimento de diferentes
               estrat&#233;gias para silenciar a protease serina e, assim, elevar os n&#237;veis de LDLR no
               f&#237;gado, com uma consequente diminui&#231;&#227;o dos n&#237;veis circulantes de LDL-C.</p>
        <p>A interven&#231;&#227;o precoce pode magnificar a efic&#225;cia cl&#237;nica da terapia redutora do
               colesterol, por meio da atenua&#231;&#227;o do desenvolvimento e progress&#227;o da
               aterosclerose.</p>
        <p>Os grupos terap&#234;uticos primariamente envolvidos nesta estrat&#233;gia seriam aqueles com
               hipercolesterolemia familiar, intoler&#226;ncia &#224; estatina e, talvez, pacientes com um
               risco cardiovascular muito elevado com falha para atingir os alvos por meio do
               armament&#225;rio farmacol&#243;gico existente.</p>
        <p>Tamb&#233;m &#233; necess&#225;rio determinar se a PCSK9 afeta somente os n&#237;veis de LDL-C, ou se
               tamb&#233;m pode exercer uma a&#231;&#227;o direta sobre a vasculatura e outras estruturas. Sua
               intera&#231;&#227;o/a&#231;&#227;o rec&#237;proca com a prote&#237;na de transfer&#234;ncia do colesterol esterificado
               (CETP) e com o efluxo de colesterol mediado por HDL-C ainda tem de ser
               determinada.</p>
        <p>Apesar de um mecanismo de a&#231;&#227;o indubitavelmente interessante, diversas quest&#245;es
               permanecem: a seguran&#231;a da combina&#231;&#227;o da PCSK9 com estatinas, a resposta imune dos
               anticorpos de PCSK9 ap&#243;s um tratamento prolongado, o valor real dos efeitos
               pleitr&#243;picos que a estatina exibe e, finalmente, as potenciais intera&#231;&#245;es com outras
               enzimas e proteases.</p>
      </sec>
      <sec>
        <title>Estrat&#233;gias terap&#234;uticas e a PCSK9 </title>
        <p>Considerando o que foi anteriormente descrito, diversas linhas de pesquisa est&#227;o
               focando atualmente no desenvolvimento de moduladores/inibidores da PCSK9, em um
               esfor&#231;o para reduzir o LDL-C mediado por um aumento no n&#250;mero de LDLRs hep&#225;ticos.</p>
        <p>Diferentes estrat&#233;gias farmacol&#243;gicas est&#227;o em diferentes etapas de desenvolvimento;
               da fase 3 a etapas pr&#233;-cl&#237;nicas (<xref ref-type="table" rid="t01">Tabela
                  1</xref>)<xref ref-type="bibr" rid="B09">9</xref>.</p>
        <table-wrap id="t01">
          <label>Tabela 1</label>
          <caption>
            <title>PCSK9, terapias em desenvolvimento</title>
          </caption>
          <table frame="hsides" rules="rows">
            <thead>
              <tr>
                <th align="left">
                  <bold>Alvo/Mecanismos de A&#231;&#227;o</bold>
                </th>
                <th align="center">
                  <bold>Medicamento/Agente</bold>
                </th>
                <th align="center">
                  <bold>Fase</bold>
                </th>
              </tr>
            </thead>
            <tbody>
              <tr>
                <td>Anticorpos Monoclonais</td>
                <td align="center">SAR236553/REGN727</td>
                <td align="center">3</td>
              </tr>
              <tr>
                <td>Anticorpos Monoclonais</td>
                <td align="center">AMG-145</td>
                <td align="center">2</td>
              </tr>
              <tr>
                <td>Anticorpos Monoclonais</td>
                <td align="center">RN3169A/RG7652</td>
                <td align="center">2</td>
              </tr>
              <tr>
                <td>Anticorpos Monoclonais</td>
                <td align="center">MPSK3169A/RG7652</td>
                <td align="center">2</td>
              </tr>
              <tr>
                <td>Anticorpos Monoclonais</td>
                <td align="center">LGT209</td>
                <td align="center">2</td>
              </tr>
              <tr>
                <td>Oligonucleot&#237;deo siRNA</td>
                <td align="center">ALN-PCS02</td>
                <td align="center">1</td>
              </tr>
              <tr>
                <td>Oligonucleot&#237;deo antisense</td>
                <td align="center">TBD</td>
                <td align="center">Pr&#233;-cl&#237;nico</td>
              </tr>
              <tr>
                <td>Prote&#237;na de fus&#227;o utilizando Adectin</td>
                <td align="center">BMS-962476</td>
                <td align="center">Pr&#233;-cl&#237;nico</td>
              </tr>
              <tr>
                <td>Mim&#233;tico de pequeno pept&#237;deo</td>
                <td align="center">SX-PCSK9</td>
                <td align="center">Pr&#233;-cl&#237;nico</td>
              </tr>
              <tr>
                <td>Modulador pequeno de PCSKP</td>
                <td align="center">TBD</td>
                <td align="center">Pr&#233;-cl&#237;nico</td>
              </tr>
            </tbody>
          </table>
        </table-wrap>
        <p>Atualmente na fase 3, os anticorpos monoclonais definem a dire&#231;&#227;o para esta
               estrat&#233;gia terap&#234;utica, com resultados demonstrados com rela&#231;&#227;o &#224; seguran&#231;a e
               efic&#225;cia; da mesma forma os pept&#237;deos, inibidores de pequenas mol&#233;culas e tentativas
               de silenciar os genes s&#227;o algumas das diferen&#231;as estrat&#233;gias e condutas sendo
               seguidas atualmente<xref ref-type="bibr" rid="B09">9</xref>.</p>
        <p>Os potenciais resultados das diferentes estrat&#233;gias farmacol&#243;gicas, juntamente com a
               hip&#243;tese atrativa sobre o potencial efeito sinerg&#237;stico quando administrada com
               estatinas, torna a modula&#231;&#227;o da PCSK9 a terapia futura mais promissora para evitar e
               prevenir o processo da aterosclerose em indiv&#237;duos com LDLR funcional.</p>
      </sec>
    </sec>
    <sec sec-type="discussion">
      <title>Discuss&#227;o</title>
      <p>A descoberta da PCSK9 h&#225; dez anos, juntamente com os recentes resultados de estudos
            sobre interven&#231;&#227;o e polimorfismo gen&#233;tico acerca de diferentes fra&#231;&#245;es de lipoprote&#237;nas,
            abrem um futuro campo terap&#234;utico promissor. Os efeitos adversos de altas doses de
            estatinas e afirma&#231;&#227;o l&#243;gica e racional da necessidade de alternativas no gerenciamento
            desta fra&#231;&#227;o de lipoprote&#237;na para valores &lt; 70 ou 50 mg/dL LDL-C<xref ref-type="bibr" rid="B10">10</xref>, geram a necessidade de alternativas no gerenciamento desta
            fra&#231;&#227;o de lipoprote&#237;na, central para o processo ateroscler&#243;tico.</p>
      <p>Resultados inesperados e falhas em diversos estudos cl&#237;nicos com diferentes mol&#233;culas
            (ezetimibe, niacina, fibratos, &#244;mega 3, inibidores de prote&#237;nas de transfer&#234;ncia do
            colesterol esterificado -iCETP-) de forma oposta &#224; clara demonstra&#231;&#227;o dos efeitos
            ben&#233;ficos das estatinas em diferentes cen&#225;rios e popula&#231;&#245;es, destacou a import&#226;ncia de
            n&#227;o somente diminuir os n&#237;veis de LDL-C, mas tamb&#233;m o mecanismo pelo qual o processo
            ocorre.</p>
      <p>N&#227;o podemos ignorar a atual controv&#233;rsia sobre a fun&#231;&#227;o que o HDL-C desempenha no
            processo da aterosclerose; os resultados claros dos estudos de popula&#231;&#245;es com forte
            evid&#234;ncia epidemiol&#243;gica s&#227;o contrastados com as recentes an&#225;lises gen&#233;ticas do
            polimorfismo e regress&#227;o de Mendelian, juntamente com as falhas recentes dos estudos de
            interven&#231;&#227;o. Pendente dos resultados de diferentes estudos (IMPROVE IT com ezetimibe e
            DEFINE com anacetrapibe), a fun&#231;&#227;o atual do HDL-C (fator marcador versus fator de risco)
            redefine o foco sobre o LDL-C, bem como aos mecanismos ao redor de sua modula&#231;&#227;o.</p>
      <p>As estatinas comprovaram ser compostos insuper&#225;veis em seu efeito preventivo e
            terap&#234;utico sobre as doen&#231;as cardiovasculares e cerebrovasculares. Contudo, 60% a 70%
            dos pacientes com eventos cardiovasculares cl&#237;nicos mantiveram, persistentemente, altos
            n&#237;veis de LDL-C, mesmo ap&#243;s atingir as doses m&#225;ximas recomendadas. Isto leva claramente
            &#224; necessidade de novas condutas em rela&#231;&#227;o &#224; redu&#231;&#227;o do risco residual de eventos
            cardiovasculares. Relatos recentes e revis&#245;es sistem&#225;ticas dos efeitos das estatinas
            sobre os perfis glic&#234;micos e novos casos de diabetes associado &#224; dimens&#227;o renal, bem
            como a import&#226;ncia de outros efeitos adversos, tais como a miopatia induzida por
            estatina, acrescentam mais raz&#245;es para buscar terapias adicionais visando combater &#224;
            aterosclerose.</p>
      <p>O cen&#225;rio descrito acima aumenta, direta e indiretamente, a import&#226;ncia e enfatiza a
            PCSK9, sua evid&#234;ncia gen&#233;tica e epidemiol&#243;gica e o potencial efeito terap&#234;utico neste
            campo.</p>
      <p>A determina&#231;&#227;o de um subgrupo de pessoas com uma muta&#231;&#227;o da codifica&#231;&#227;o gen&#233;tica da
            PCSK9, baixos n&#237;veis de LDL-C desde uma idade precoce e risco cardiovascular
            extremamente baixo sugere n&#227;o somente a possibilidade de uma nova estrat&#233;gia
            terap&#234;utica, mas tamb&#233;m a necessidade de gerenciar e manter o LDL-C em n&#237;veis
            consistentemente baixos e a partir de uma idade precoce. Esta &#250;ltima talvez seja a maior
            base a partir das estrat&#233;gias atuais de preven&#231;&#227;o, aplic&#225;vel hoje desde as d&#233;cadas de
            40, 50 e 60.</p>
      <p>Em conclus&#227;o, podemos dizer que estamos encarando uma nova classe terap&#234;utica em
            potencial, com um mecanismo de a&#231;&#227;o no qual o receptor de LDL est&#225; localizado no centro
            do processo, 40 anos ap&#243;s sua descoberta, atingindo um marco na hist&#243;ria da
            aterosclerose que deve se tornar um ponto crucial no progn&#243;stico e terapia desta doen&#231;a,
            atualmente posicionada como uma indubit&#225;vel prioridade da sa&#250;de p&#250;blica.</p>
    </sec>
    <sec>
      <title>Contribui&#231;&#227;o dos autores</title>
      <p>Concep&#231;&#227;o e desenho da pesquisa, Obten&#231;&#227;o de dados, An&#225;lise e interpreta&#231;&#227;o dos dados,
            An&#225;lise estat&#237;stica, Reda&#231;&#227;o do manuscrito, Revis&#227;o cr&#237;tica do manuscrito quanto ao
            conte&#250;do intelectual: Corral P.</p>
    </sec>
  </body>
  <back>
    <ref-list>
      <title>Refer&#234;ncias </title>
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    <fn-group>
      <fn fn-type="other">
        <p>
          <bold>Vincula&#231;&#227;o Acad&#234;mica</bold>
        </p>
        <p>N&#227;o h&#225; vincula&#231;&#227;o deste estudo a programas de p&#243;s-gradua&#231;&#227;o.</p>
      </fn>
      <fn fn-type="financial-disclosure">
        <p>
          <bold>Fontes de Financiamento</bold>
        </p>
        <p>O presente estudo n&#227;o teve fontes de financiamento externas.</p>
      </fn>
    </fn-group>
  </back>
  <sub-article id="SA1" article-type="translation" xml:lang="en">
    <front-stub>
      <article-categories>
        <subj-group subj-group-type="heading">
          <subject>Viewpoint</subject>
        </subj-group>
      </article-categories>
      <title-group>
        <article-title xml:lang="en">Back to Basics: PCSK9 as a New Target for the LDL
               Receptor</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <name>
            <surname>Corral</surname>
            <given-names>Pablo</given-names>
          </name>
          <xref ref-type="corresp" rid="c02"/>
        </contrib>
        <aff>
          <institution content-type="orgname">Internal Medicine Institute</institution>
          <institution content-type="orgdiv1">Lipid Section</institution>
          <addr-line>
            <named-content content-type="city">Mar del Plata</named-content>
          </addr-line>
          <country>Argentina</country>
          <institution content-type="original">Lipid Section, Internal Medicine Institute, Mar
                  del Plata, Argentina</institution>
        </aff>
      </contrib-group>
      <author-notes>
        <corresp id="c02"><bold>Mailing Address: Pablo Corral</bold>, Rawson 1006, Playa Grande. Postal Code
               7600, Mar Del Plata, Buenos Aires. E-mail: <email>drpablocorral@gmail.com</email></corresp>
        <fn fn-type="conflict">
          <p>
            <bold>Potential Conflict of Interest</bold>
          </p>
          <p>No potential conflict of interest relevant to this article was reported.</p>
        </fn>
      </author-notes>
      <kwd-group xml:lang="en">
        <kwd>Receptors, LDL</kwd>
        <kwd>PCSK9 Protein, human</kwd>
        <kwd>Polymorphism, genetic</kwd>
        <kwd>Trends</kwd>
        <kwd>Atherosclerosis</kwd>
      </kwd-group>
      <counts>
        <fig-count count="1"/>
        <table-count count="1"/>
        <equation-count count="0"/>
        <ref-count count="10"/>
        <page-count count="7"/>
      </counts>
    </front-stub>
    <body>
      <sec sec-type="intro">
        <title>Introduction</title>
        <p>Forty years after Goldstein and Brown's discovery of the low density lipoprotein
               receptor (LDLR)<xref ref-type="bibr" rid="B01">1</xref> and 25 years after the
               introduction of the statins<xref ref-type="bibr" rid="B02">2</xref>, a cornerstone of
               the atherosclerotic disease management, the view of the scientific community studying
               the process of atherosclerosis turns once again to the LDLR through the action
               mechanism of proprotein convertase subtilisin/kexin type 9 (PCSK9)<xref ref-type="bibr" rid="B03">3</xref>.</p>
        <p>The assessment of genetic polymorphism with unexpected results in large studies
               revived the hypothesis about the important role of high density lipoprotein
               cholesterol (HDL-C) in lipoprotein metabolism<xref ref-type="bibr" rid="B04">4</xref>; the apparent eternal debate about the contribution of triglycerides (TG)
               and their remnants to the phenomenon of atherogenesis<xref ref-type="bibr" rid="B05">5</xref>. Such advances have lead to the re-prioritization of LDL management as a
               central and primary objective towards the prevention of the morbidity and mortality
               main cause in the Western world, atherosclerosis.</p>
        <p>Once again, we return to the discovery that led Goldstein and Brown to a Nobel Prize
               in 1985, the LDLR<xref ref-type="bibr" rid="B01">1</xref>; now seeking to avoid its
               degradation through the knowledge and understanding of PCSK9 action mechanism.</p>
        <sec>
          <title>Biochemical and molecular bases</title>
          <p>PCSK9, also called neural-apoptosis-regulated convertase 1 (NARC-1), is a serine
                  protease, characterized by a three domain structure and a catalytic triad; it is
                  the ninth member of the pro-protein convertase family<xref ref-type="bibr" rid="B03">3</xref>.</p>
          <p>The PCSK9 gene is located on chromosome 1p32.3 and is 22-kb in length, comprising
                  12 exons encoding a 692 amino acid glycoprotein. This convertase is highly
                  expressed in liver, intestine and kidneys<xref ref-type="bibr" rid="B06">6</xref>.</p>
          <p>PCSK9 is synthesized as 74 kDa soluble zymogen (proPCSK9) which after an
                  autocatalytic process within the endoplasmic reticulum, releases the pro-peptide
                  (14kDa)-N terminal, resulting in a 60-kDa enzyme. This autoclivage process is
                  necessary both towards its activation and release from the endoplasmic
                     reticulum<xref ref-type="bibr" rid="B03">3</xref>.</p>
          <p>The autocatalytic process allows the progression through the secretory pathway and
                  thus directly interacts with the LDLR. It is important to mention, that the
                  catalytic activity, does not seems to be required for LDLR degradation, but only
                  for the activation and secretion of PCSK9 <xref ref-type="bibr" rid="B06">6</xref>.</p>
          <p>This serine protease binds the epidermal growth factor domain A (EGF-A) on the
                  LDLR, upon which both PCSK9 and LDLR are internalized by the hepatocyte to be
                  finally degraded within the lysosome (<xref ref-type="fig" rid="f02">Figure
                     1</xref>)<xref ref-type="bibr" rid="B06">6</xref>.</p>
          <fig id="f02" fig-type="other">
            <label>Figure 1</label>
            <caption>
              <title>PCSK9 regulates LDLR turnover through increased intracellular
                        degradation.</title>
            </caption>
            <graphic xlink:href="1678-4170-abc-102-01-00e5-30248-gf01-en.jpg"/></fig>
        </sec>
        <sec>
          <title>Past, present and future of PCSK9</title>
          <p>Ten years ago, Abifadel et al. have reported 3 families in France with familial
                  hypercholesterolemia associated with increased functionality and expression of
                  PCSK9, with no alteration in the LDL receptor or apo B structure<xref ref-type="bibr" rid="B07">7</xref>.</p>
          <p>In 2005, two years later, Cohen et al. through the program/study Atherosclerosis
                  Risk in Communities (ARIC) described the loss of PCSK9 function in African
                  American and Caucasian individuals. In the past, they reported a prevalence of
                  2.6% in deficit of function, with concomitantly reduced serum levels of low
                  density lipoprotein cholesterol LDL-C (28% lower) and CV events, such as
                  myocardial infarction, need for cardiac bypass surgery and coronary deaths (88%).
                  The latter, in turn, showed a decrease in PCSK9 expression of 3.2%, with an
                  average LDL-C reduction of 15% vs. control groups and reduction of 47% in CV
                  events requiring cardiac surgery and mortality related to this cause.
                  Interestingly, in the ARIC study, 50% of subjects had hypertension, 30% were
                  smokers and 20% had diabetes<xref ref-type="bibr" rid="B08">8</xref>.</p>
          <p>The inevitable comparison between the reduction on risk observed among individuals
                  with a deficit of PCSK9 expression/function and the individuals evaluated in large
                  studies with statins for 5 years (similar LDL-C decrease between the two groups
                  with marked lower risk in patients with the genetic alteration), has led to the
                  development of different strategies to silence this serin protease and thus,
                  increase LDLR levels in the liver, with a consequent decrease of circulating LDL-C
                  levels.</p>
          <p>The early intervention might magnify the clinical efficacy of cholesterol-lowering
                  therapy by attenuating the development and progression of atherosclerosis.</p>
          <p>Therapeutic groups primarily involved in this strategy, would be those with
                  familial hypercholesterolemia, statin-intolerance and perhaps patients with a very
                  high cardiovascular risk with failure to meet the targets through the existing
                  pharmacological armamentarium.</p>
          <p>It also necessary to determine whether PCSK9 affects only LDL-C levels, or whether
                  it may also exert a direct action on the vasculature and other structures. Its
                  interaction/interplay with cholesterol ester transfer protein (CETP) and with the
                  cholesterol efflux mediated by HDL-C is also yet to be determined.</p>
          <p>Despite an undoubtedly interesting mechanism of action, several questions remain:
                  the safety of PCSK9 combination with statins, the immune response to PCSK9
                  antibodies after a prolonged treatment, the real value of the pleiotropic effects
                  that statins show and finally, the potential interactions with others enzymes and
                  proteases.</p>
        </sec>
        <sec>
          <title>Therapeutic strategies and PCSK9</title>
          <p>Considering what was previously described, several lines of research are currently
                  focused on PCSK9 modulators/inhibitors development in an effort to lower LDL-C
                  mediated by an increase in the number of hepatic LDLRs.</p>
          <p>Different pharmacological strategies are at different stages of development; from
                  phase 3 to preclinical stages (<xref ref-type="table" rid="t02">Table
                     1</xref>)<xref ref-type="bibr" rid="B09">9</xref>.</p>
          <table-wrap id="t02">
            <label>Table 1</label>
            <caption>
              <title>PCSK9, therapies in development</title>
            </caption>
            <table frame="hsides" rules="rows">
              <thead>
                <tr>
                  <th align="left">
                    <bold>Target/Mechanism of Action</bold>
                  </th>
                  <th align="center">
                    <bold>Drug/Agent</bold>
                  </th>
                  <th align="center">
                    <bold>Phase</bold>
                  </th>
                </tr>
              </thead>
              <tbody>
                <tr>
                  <td>Monoclonal antibodies</td>
                  <td align="center">SAR236553/REGN727</td>
                  <td align="center">3</td>
                </tr>
                <tr>
                  <td>Monoclonal antibodies</td>
                  <td align="center">AMG-145</td>
                  <td align="center">2</td>
                </tr>
                <tr>
                  <td>Monoclonal antibodies</td>
                  <td align="center">RN3169A/RG7652</td>
                  <td align="center">2</td>
                </tr>
                <tr>
                  <td>Monoclonal antibodies</td>
                  <td align="center">MPSK3169A/RG7652</td>
                  <td align="center">2</td>
                </tr>
                <tr>
                  <td>Monoclonal antibodies</td>
                  <td align="center">LGT209</td>
                  <td align="center">2</td>
                </tr>
                <tr>
                  <td>siRNA Oligonucleotide</td>
                  <td align="center">ALN-PCS02</td>
                  <td align="center">1</td>
                </tr>
                <tr>
                  <td>Antisense Oligonucleotide</td>
                  <td align="center">TBD</td>
                  <td align="center">PRE-CLINICAL</td>
                </tr>
                <tr>
                  <td>Fusion protein using Adectin</td>
                  <td align="center">BMS-962476</td>
                  <td align="center">PRE-CLINICAL</td>
                </tr>
                <tr>
                  <td>Small peptide mimetic</td>
                  <td align="center">SX-PCSK9</td>
                  <td align="center">PRE-CLINICAL</td>
                </tr>
                <tr>
                  <td>Small PCSK9 modulator</td>
                  <td align="center">TBD</td>
                  <td align="center">PRE-CLINICAL</td>
                </tr>
              </tbody>
            </table>
          </table-wrap>
          <p>Currently in phase 3, monoclonal antibodies define the direction for this
                  therapeutic strategy, with demonstrated outcomes of safety and efficacy; peptide
                  mimetics, small molecule inhibitors and attempts to gene silencing are some of the
                  different strategies and approaches currently being pursued<xref ref-type="bibr" rid="B09">9</xref>.</p>
          <p>The potential results of different pharmacological strategies, alongside the
                  attractive hypothesis about the potential synergistic effect when administered
                  with statins, make the PCSK9 modulation the most promising future therapy to avoid
                  and prevent atherosclerosis process in those with functional LDLR.</p>
        </sec>
      </sec>
      <sec sec-type="discussion">
        <title>Discussion</title>
        <p>The PCSK9 discovery ten years ago, along with the recent results of studies in both
               intervention and genetic polymorphism around different lipoprotein fractions, open a
               promising future therapeutic field. The adverse effects of high doses of statins, and
               the logical and rational posing of the need to descend to values &lt; 70 or 50 mg/dL
                  LDL-C<xref ref-type="bibr" rid="B10">10</xref>, raised the need for alternatives
               in the management of this lipoprotein fraction, central to the atherosclerotic
               process.</p>
        <p>Unexpected results and failures in different trials with different molecules
               (ezetimibe, niacin, fibrates, omega 3, protein inhibitors of cholesterol ester
               transfer-iCETP-) in a opposite way to the clear demonstration of statins beneficial
               effects in different scenarios and populations , highlighted the importance of not
               only decreasing LDL-C levels but also the mechanism by which this process occurs.</p>
        <p>We cannot ignore the current controversy about the role that HDL-C plays in the
               atherosclerosis process; the clear results of population's studies with strong
               epidemiological evidence are contrasted with recent genetic analysis of polymorphism
               and Mendelian regression, along with the recent failures of intervention studies.
               Pending the results of different studies (IMPROVE IT with ezetimibe and DEFINE with
               anacetrapib) the current role of the HDL-C (marker factor versus risk factor) resets,
               once again, the focus on LDL-C, as well as the mechanisms towards its modulation.</p>
        <p>Statins have proven to be insurmountable compounds in their preventive and
               therapeutic effect on cardiovascular and cerebrovascular disease. However, 60% to 70%
               of patients with clinical cardiovascular events maintain persistently high LDLC
               levels, even after reaching the maximum recommended doses. This clearly leads to the
               need of new approaches towards reducing the residual risk of cardiovascular events.
               Recent reports and systematic reviews of the statins effects on glycemic profiles and
               new cases of diabetes associated with the real dimension and importance of other
               adverse effects, such as statin-induced myopathy, adds more reasons to seek
               alternative therapies to combat atherosclerosis.</p>
        <p>The scenario described above, directly and indirectly enhances the importance and
               emphasizes the PCSK9, its genetic and epidemiological evidence and potential
               therapeutic effect in this field.</p>
        <p>The determination of a people's subgroup with a mutation in the gene encoding the
               PCSK9, low levels of LDL-C since an early age, and extremely low atherosclerotic
               cardiovascular risk, suggests not only the possibility of a new therapeutic strategy,
               but also the need to manage and maintain LDL-C at consistently lower levels and from
               an early age. The latter is perhaps the biggest basis from current prevention
               strategies, applicable today since the years 40', 50' and 60'.</p>
        <p>In conclusion, we can say that we are facing a new potential therapeutic class, with
               an action mechanism in which the LDL receptor is located at the center of the process
               40 years after its discovery, reaching a milestone in the history of atherosclerosis
               that meant to be a turning point in the prognosis and therapy of this disease,
               currently positioned as an undoubted public health priority.</p>
      </sec>
      <sec>
        <title>Author contributions</title>
        <p>Conception and design of the research, Acquisition of data, Analysis and
               interpretation of the data, Statistical analysis, Writing of the manuscript, Critical
               revision of the manuscript for intellectual content: Corral P.</p>
      </sec>
    </body>
    <back>
      <fn-group>
        <fn fn-type="other">
          <p>
            <bold>Study Association</bold>
          </p>
          <p>This study is not associated with any post-graduation program.</p>
        </fn>
        <fn fn-type="financial-disclosure">
          <p>
            <bold>Sources of Funding</bold>
          </p>
          <p>There were no external funding sources for this study.</p>
        </fn>
      </fn-group>
    </back>
  </sub-article>
</article>
