ACE2 gene polymorphisms do not affect outcome of severe acute respiratory syndrome

IL-12 RB1 genetic variants contribute to human susceptibility to severe acute respiratory syndrome infection among Chinese

Background

Cytokines play important roles in antiviral action. We examined whether polymorphisms of interleukin (IL)-12 receptor B1 (IL-12RB1) affect the susceptibility to and outcome of severe acute respiratory syndrome (SARS).

Methods

A case-control study was carried out in Chinese SARS patients and healthy controls. The genotypes of 4SNPs on IL-12 RB1 gene, +705A/G,+1158T/C, +1196G/C and +1664 C/T, were determined by PCR-RFLP. Haplotypes were estimated from the genotype data using the expectation-maximisation algorithm.

Results

Comparison between patients and close contacts showed that individuals with the +1664 C/T (CT and TT) genotype had a 2.09-fold (95% confidence interval [CI], 1.90–7.16) and 2.34-fold (95% CI, 1.79–13.37) increased risk of developing SARS, respectively. For any of the other three polymorphisms, however, no significant difference can be detected in allele or genotype frequencies between patients and controls. Additionally, estimation of the frequencies of multiple-locus haplotypes revealed potential risk haplotypes (GCCT) for SARS infection.

Conclusions

Our data indicate that genetic variants of IL12RB1confer genetic susceptibility to SARS infection, but not necessary associated with the progression of the disease in Chinese population.

Quantitative temporal-spatial distribution of severe acute respiratory syndrome-associated coronavirus (SARS-CoV) in post-mortem tissues

Few post-mortem studies have been performed on patients who have died from severe acute respiratory syndrome (SARS). No studies have examined how the SARS-associated coronavirus (SARS-CoV) loads in different organs with respect to time, post-mortem. The aim of this study was to determine the quantitative temporal-spatial distribution of SARS-CoV in the post-mortem tissue samples of seven patients. Quantitation of a house-keeping gene, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was undertaken to standardize the amount of tissue tested. SARS-CoV viral load and SARS-CoV/GAPDH RNA ratio for each organ type were related to four time durations: onset of illness to death, death to post-mortem tissue sampling, and total durations of treatment with ribavirin and hydrocortisone. The SARS-CoV/GAPDH RNA ratio remained relatively stable in most organ tissue types for all these time durations. The ratio reached the highest value of equal to or greater than one for lung and small bowel, whereas those for heart, liver, spleen, and kidney were always less than one. It is concluded that SARS-CoV viral loads in these organs remain relatively stable, post-mortem. This quantitative assessment further supports SARS-CoV has a specific tropism for the human respiratory and gastrointestinal tracts, which may be related to the density of SARS-CoV receptors.

The emerging role of ACE2 in physiology and disease

The renin–angiotensin–aldosterone system (RAAS) is a key regulator of systemic blood pressure and renal function and a key player in renal and cardiovascular disease. However, its (patho)physiological roles and its architecture are more complex than initially anticipated. Novel RAAS components that may add to our understanding have been discovered in recent years. In particular, the human homologue of ACE (ACE2) has added a higher level of complexity to the RAAS. In a short period of time, ACE2 has been cloned, purified, knocked‐out, knocked‐in; inhibitors have been developed; its 3D structure determined; and new functions have been identified. ACE2 is now implicated in cardiovascular and renal (patho)physiology, diabetes, pregnancy, lung disease and, remarkably, ACE2 serves as a receptor for SARS and NL63 coronaviruses. This review covers available information on the genetic, structural and functional properties of ACE2. Its role in a variety of (patho)physiological conditions and therapeutic options of modulation are discussed. Copyright © 2007 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

The Immunobiology of SARS*

Severe acute respiratory syndrome (SARS) presented as an atypical pneumonia that progressed to acute respiratory distress syndrome in approximately 20% of cases and was associated with a mortality of about 10%. The etiological agent was a novel coronavirus (CoV). Angiotensin-converting enzyme 2 is the functional receptor for SARS-CoV; DC-SIGN and CD209L (L-SIGN) can enhance viral entry. Although the virus infects the lungs, gastrointestinal tract, liver, and kidneys, the disease is limited to the lungs, where diffuse alveolar damage is accompanied by a disproportionately sparse inflammatory infiltrate. Pro-inflammatory cytokines and chemokines, particularly IP-10, IL-8, and MCP-1, are elevated in the lungs and peripheral blood, but there is an unusual lack of an antiviral interferon (IFN) response. The virus is susceptible to exogenous type I IFN but suppresses the induction of IFN. Innate immunity is important for viral clearance in the mouse model. Virus-specific neutralizing antibodies that develop during convalescence prevent reinfection in animal models.

Association of ICAM3 genetic variant with severe acute respiratory syndrome

Genetic polymorphisms have been demonstrated to be associated with vulnerability to human infection. ICAM3, an intercellular adhesion molecule important for T cell activation, and FCER2 (CD23), an immune response gene, both located on chromosome 19p13.3 were investigated for host genetic susceptibility and association with clinical outcome. A case-control study based on 817 patients with confirmed severe acute respiratory syndrome (SARS), 307 health care worker control subjects, 290 outpatient control subjects, and 309 household control subjects unaffected by SARS from Hong Kong was conducted to test for genetic association. No significant association to susceptibility to SARS-CoV infection was found for the FCER2 and the ICAM3 single nucleotide polymorphisms. However, patients with SARS homozygous for ICAM3 Gly143 showed significant association with higher lactate dehydrogenase levels (P=.0067; odds ratio [OR], 4.31 [95% confidence interval [CI], 1.37–13.56]) and lower total white blood cell counts (P=.022; OR, 0.30 [95% CI, 0.10–0.89]) on admission. These findings support the role of ICAM3 in the immunopathogenesis of SARS.

Polymorphisms of ACE2 gene are associated with essential hypertension and antihypertensive effects of Captopril in women

ACE2 appears to counterbalance the vasopressor effect of angiotensin I converting enzyme (ACE) in the reninangiotensin system. We hypothesized that ACE2 polymorphisms could confer a high risk of hypertension and have an impact on the antihypertensive response to ACE inhibitors. The hypothesis was tested in two casecontrol studies and a clinical trial of 3,408 untreated hypertensive patients randomized to Atenolol, Hydrochlorothiazide, Captopril, or Nifedipine treatments for 4 weeks. ACE2 rs2106809 T allele was found to confer a 1.6-fold risk for hypertension in women (95% confidence interval (CI), 1.132.06), whereas when combined with the effect of the ACE DD genotype, the risk was 2.34-fold (95% CI, 1.754.85) in two independent samples. The adjusted diastolic blood pressure response to Captopril was 3.3 mm Hg lower in ACE2 T allele carriers than in CC genotype carriers (P=0.019) in women. We conclude that the ACE2 T allele confers a high risk for hypertension and reduced antihypertensive response to ACE inhibitors.

Association study of ACE2 (angiotensin I-converting enzyme 2) gene polymorphisms with coronary heart disease and myocardial infarction in a Chinese Han population

Results are accumulating that ACE2 (angiotensin I-converting enzyme 2) might act as a protective protein for cardiovascular diseases; however, only a few studies in human populations have been carried out. This prompted us to perform a case-control study to investigate the relationship of ACE2 polymorphisms with CHD (coronary heart disease) and MI (myocardial infarction). Three single nucleotide polymorphisms in the ACE2 gene (1075A/G, 8790A/G and 16854G/C) were genotyped by PCR-RFLP (restriction-fragment-length polymorphism) in 811 patients with CHD (of which 508 were patients with MI) and 905 normal controls in a Chinese population. The polymorphisms were in linkage disequilibrium (r(2)=0.854-0.973). Analyses were conducted by gender, because the ACE2 gene is on the X chromosome. In females, an association was detected with MI for 1075A/G (P=0.026; odds ratio=1.98) and 16854G/C (P=0.028; odds ratio=1.97) in recessive models after adjusting for covariates. In male subjects, two haplotypes (AAG and GGC) were common in frequency. In male subjects not consuming alcohol, the haplotype GGC was associated with a 1.76-fold risk of CHD [95% CI (confidence interval), 1.15-2.69; P=0.007] and a 1.77-fold risk of MI (95% CI, 1.12-2.81; P=0.015) with environmental factors adjusted, when compared with the most common haplotype AAG. In conclusion, the results of the present study indicate that common genetic variants in the ACE2 gene might impact on MI in females, and may possibly interact with alcohol consumption to affect the risk of CHD and MI in Chinese males.

Association of angiotensin-converting enzyme 2 gene A/G polymorphism and elevated blood pressure in Chinese patients with metabolic syndrome

To establish whether angiotensin-converting enzyme 2 (ACE2) gene A/G single nucleotide polymorphism is associated with hypertension in Chinese patients with metabolic syndrome. The study was conducted in 353 patients with metabolic syndrome. The alleles of the ACE2 A/G polymorphism, which is located on the X chromosome, were detected using polymerase chain reaction and subsequent cleavage by Alu I restriction endonuclease. G allele frequencies in patients with metabolic syndrome were 36.6% in female subjects and 43.4% in male subjects, respectively. Female patients with metabolic syndrome who carry the GG genotype had a significantly higher diastolic blood pressure compared with other genotypes. Multivariate logistic regression showed that female gender (P = 0.019) and carrying only the G allele (odds ratio 2.83 [95% CI 1.36 to 5.91]; P = 0.005) were significantly associated with increased diastolic blood pressure. It is concluded that the ACE2 A/G polymorphism is associated with hypertension in patients with metabolic syndrome.

How the SARS coronavirus causes disease: host or organism?

The previous epidemic of severe acute respiratory syndrome (SARS) has ended. However, many questions concerning how the aetiological agent, the novel SARS coronavirus (CoV), causes illness in humans remain unanswered. The pathology of fatal cases of SARS is dominated by diffuse alveolar damage. Specific histological changes are not detected in other organs. These contrast remarkably with the clinical picture, in which there are apparent manifestations in multiple organs. Both pathogen and host factors are important in the pathogenesis of SARS. The choice of specific receptors and the unique genome of the SARS‐CoV are important elements in understanding the biology of the pathogen. For the host cells, the outcome of SARS‐CoV infection, whether there are cytopathic effects or not, depends on the cell types that are infected. At the whole‐body level, immune‐mediated damage, due to activation of cytokines and/or chemokines and, perhaps, autoimmunity, may play key roles in the clinical and pathological features of SARS. Continued research is still required to determine the pathogenetic mechanisms involved and to combat this new emerging human infectious disease. Copyright © 2006 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Treatment of severe acute respiratory syndrome

The best treatment strategy for severe acute respiratory syndrome (SARS) is still unknown. Ribavirin and corticosteroids were used extensively during the SARS outbreak. Ribavirin has been criticized for its lack of efficacy. Corticosteroids are effective in lowering the fever and reversing changes in the chest radiograph but have the caveat of encouraging viral replication. The effectiveness of corticosteroids has only been suggested by uncontrolled observations, and the role of these agents in therapy remains to be established by randomized controlled studies. Both ribavirin and corticosteroids have very significant side effects. The lopinavir/ritonavir combination has been shown to reduce the intubation rate and the incidence of adverse clinical outcomes when used with ribavirin. When patients deteriorate clinically despite treatment with ribavirin and corticosteroids, rescue treatment with convalescent plasma and immunoglobulin may be beneficial. Noninvasive positive pressure ventilation is a sound treatment for SARS patients with respiratory failure if administered with due precaution in the correct environment. Interferons and other novel agents may hold promise as useful anti-SARS therapies in the future. The experience with traditional Chinese medicine is encouraging, and its use as an adjuvant should be further investigated.

Identification of an alternative 5'-untranslated exon and new polymorphisms of angiotensin-converting enzyme 2 gene: lack of association with SARS in the Vietnamese population

We analyzed genetic variations of angiotensin‐converting enzyme 2 (ACE2), considering that it might influence patients' susceptibility to severe acute respiratory syndrome‐associated coronavirus (SARS‐CoV) or development of SARS as a functional receptor. By cloning of the full‐length cDNA of the ACE2 gene in the lung, where replication occurs on SARS‐CoV, it was shown that there are different splicing sites. All exons including the new alternative exon, exon‐intron boundaries, and the corresponding 5′‐flanking region of the gene were investigated and 19 single nucleotide polymorphisms (SNPs) were found. Out of these, 13 SNPs including one non‐synonymous substitution and three 3′‐UTR polymorphisms were newly identified. A case control study involving 44 SARS cases, 16 anti‐SARS‐CoV antibody‐positive contacts, 87 antibody‐negative contacts, and 50 non‐contacts in Vietnam, failed to obtain any evidence that the ACE2 gene polymorphisms are involved in the disease process in the population. Nevertheless, identification of new 5′‐untranslated exon and new SNPs is considered helpful in investigating regulation of ACE2 gene expression in the future. © 2005 Wiley‐Liss, Inc.

Pathogenesis of severe acute respiratory syndrome

Severe acute respiratory syndrome (SARS) is a zoonotic infectious disease caused by a novel coronavirus (CoV). The tissue tropism of SARS-CoV includes not only the lung, but also the gastrointestinal tract, kidney and liver. Angiotensin-converting enzyme 2 (ACE2), the C-type lectin CD209L (also known L-SIGN), and DC-SIGN bind SARS-CoV, but ACE2 appears to be the key functional receptor for the virus. There is a prominent innate immune response to SARS-CoV infection, including acute-phase proteins, chemokines, inflammatory cytokines and C-type lectins such as mannose-binding lectin, which plays a protective role against SARS. By contrast there may be a lack of type 1 interferon response. Moreover, lymphopenia with decreased numbers of CD4+ and CD8+ T cells is common during the acute phase. Convalescent patients have IgG-class neutralizing antibodies that recognize amino acids 441-700 of the spike protein (S protein) as the major epitope.

Absence of association between angiotensin converting enzyme polymorphism and development of adult respiratory distress syndrome in patients with severe acute respiratory syndrome: a case control study

BACKGROUND

It has been postulated that genetic predisposition may influence the susceptibility to SARS-coronavirus infection and disease outcomes. A recent study has suggested that the deletion allele (D allele) of the angiotensin converting enzyme (ACE) gene is associated with hypoxemia in SARS patients. Moreover, the ACE D allele has been shown to be more prevalent in patients suffering from adult respiratory distress syndrome (ARDS) in a previous study. Thus, we have investigated the association between ACE insertion/deletion (I/D) polymorphism and the progression to ARDS or requirement of intensive care in SARS patients.

METHOD

One hundred and forty genetically unrelated Chinese SARS patients and 326 healthy volunteers were recruited. The ACE I/D genotypes were determined by polymerase chain reaction and agarose gel electrophoresis.

RESULTS

There is no significant difference in the genotypic distributions and the allelic frequencies of the ACE I/D polymorphism between the SARS patients and the healthy control subjects. Moreover, there is also no evidence that ACE I/D polymorphism is associated with the progression to ARDS or the requirement of intensive care in the SARS patients. In multivariate logistic analysis, age is the only factor associated with the development of ARDS while age and male sex are independent factors associated with the requirement of intensive care.

CONCLUSION

The ACE I/D polymorphism is not directly related to increased susceptibility to SARS-coronavirus infection and is not associated with poor outcomes after SARS-coronavirus infection.