A Study On The Association Between Peripheral Blood Leukocyte Telomere Length And Severity Of Disease And Prognosis On Patients With Critical Illness

Objective:Telomeres are nuclear protein structures that protect the ends of chromosomes from degradation.Telomere length decreases with cell division senescence and exposure to genotoxicity.When telomeres are severely shortened,the Shelterin complex,a protective protein cap,is damaged,exposing a blunt end of the telomeres that activates the deoxyribonucleic acid(DNA)damage response,leading to senescence or cell death and apoptosis.Telomere length can be measured using a variety of methods,including southern blots,flow fluorescence in situ hybridization(Flow-FISH),or quantitative polymerase chain reaction(qPCR).These methods of quantify the average telomere length of the population of cells being analyzed.The longer the average telomere length,the less likely the cells in the population are to have very short telomeres.Therefore,the average telomere length in tissues can be used as a surrogate marker for of telomere length in other tissues within the same individual.A large number of studies have confirmed peripheral blood leukocytes(PBL)telomere length(TL)is associated with various chronic diseases.For example,shorter PBL-TLs are associated with mental illness disease,atherosclerosis,cardiovascular disease,idiopathic pulmonary fibrosis(IPF),chronic allergic alveolitis(CHP),and other lung diseases,associated with poor prognosis.Short PBL-TL is associated with worse survival of IPF patients,and telomere dysfunction is increasingly recognized as a molecular driver of the disease.Patients with IPF may suffer from acute exacerbation of the underlying disease,which is characterized by diffuse alveolar injury(DAD).In addition,damage to alveolar epithelial cells in mice with telomere dysfunction was observed in animal experiments,increasing the susceptibility of mice to influenza infection.Telomere dysfunction also caused pulmonary edema in mice.On the basis of the human studies of telomere dysfunction and histopathological studies in mice,and acute IPF exacerbation and acute lung injury,this project analyzed the association between PBL-TL and clinically relevant outcomes in critically ill patients.Methods:This study is a prospective observational cohort study.Enrolled subjects were hospitalized patients in the Intensive care unit(ICU)of Vanderbilt medical university medical center(VUMC)in the United States.All experimental samples are from 2112patients in the VALID(verified acute lung injury for the diagnosis of biomarker)cohort.Agarose gel electrophoresis was used to evaluate whether the DNA of the patients was degraded,and the degraded samples were removed.The final analysis included DNA data from 937 critically ill patients at VUMC.Telomere length of DNA samples isolated from human peripheral blood was measured using qPCR.The results were converted into base pairs and then analyzed by statistical method.Findings were validated in an independent cohort of 394 critically ill patients with sepsis admitted to the University of California,San Francisco(UCSF).Results:The VUMC cohort included 937 critically ill patients admitted to the ICU.The mean age was 53±17 years,and 60%(563/937)were male.18%(172/937)were non-white.The mean body mass index(BMI)was 29±8.3 kg/m~2.23%(212/937)were former smokers and 33%(307/937)were current smokers.Upon admission to the ICU,23%(216/937)of patients had sepsis,11%(105/937)had pneumonia,and 30%(275/937)had severe trauma.The mean oxygenation index was 219±123 mmHg.The average Acute Physiology and Chronic Health Evaluation(APACHE)II score was 25.7±8.06.At admission to the ICU,63.1%(591/937)of patients had circulatory failure and 38.2%(358/937)of patients were treated with vasoconstrictors.The average telomere length of the VUMC cohort was 6.95±0.79 kilobase-pair(kb).Shorter PBL-TL was associated with worse 90-day survival(unadjusted Hazard Ratio(HR)1.6 per 1 kb TL decrease,95%confidence interval(CI)1.3–1.8,p<0.0001;adjusted HR 1.3 per 1 kb TL decrease,95%CI 1.1–1.6,p=0.004);in subgroup analyses,shorter PBL-TL was associated with worse 90-day survival for patients with sepsis(aHR 1.5 per 1 kb TL decrease,95%CI 1.2–2.0,p=0.001),but not trauma.Although not associated with development of acute respiratory distress syndrome(ARDS),among ARDS subjects,shorter PBL-TL was associated with more severe ARDS(Odds ratio(OR)1.7 per 1 kb TL decrease,95%CI 1.2–2.5,p=0.006).UCSF sepsis validation cohort:the mean age of the UCSF sepsis cohort was 66±16years,with 56%(221/394)of males and 49%(193/394)of non-whites.The mean BMI was28±23 kg/m~2.33.8%(133/394)were former smokers and 12%(47/394)were current smokers.At ICU admission,35%(123/394)of patients had ARDS,55.8%(220/394)had sepsis,and 36%(140/394)had pneumonia.The mean oxygenation index was209±131mmHg.The APACHE II score averaged 24.6±10,significantly lower than that of the VUMC subgroup of sepsis(p<0.001).When admitted to the ICU,78.2%(308/394)of patients had organ failure.Circulatory failure was present in 61.5%(241/394)of patients,significantly lower than that in the subgroup of sepsis in the VUMC cohort(p=0.001).The mean telomere length was 6.19±0.62kb,significantly shorter than the mean telomere length of the sepsis subgroup in the VUMC cohort(p<0.001).The associations of PBL-TL with 60-day survival(unadjusted HR 1.5 per 1 kb TL decrease,95%CI 1.2–2.0,p=0.001;adjusted HR 1.6 per 1 kb TL decrease,95%CI 1.2–2.1,p=0.003)and risk for developing severe ARDS(OR 2.5 per 1 kb TL decrease,95%CI 1.1–6.3,p=0.044)were validated in the UCSF cohort.Conclusion:Short PBL-TL is strongly associated with worse survival and more severe ARDS in critically ill patients,especially patients with sepsis.These findings suggest that telomere dysfunction may contribute to outcomes from critical illness.