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  Clinical Abstracts

 

 

 

 

May 2010

Editor:
Michael Bissell, MD, PhD, MPH

Homozygous DNA deletions and cancer Homozygous DNA deletions and cancer

A major obstacle to drug-based therapies of human diseases that are efficacious and substantially free of side effects is the massive interconnectedness and redun-dancy of molecular circuits in living cells. With cancer, the problem is exacerbated by the genomic instability of many, if not most, cancers. This property in-creases the heterogeneity of malignant cells in tumor progression or anticancer treatment and is one reason why most drug-based cancer therapies fail. A few relatively rare cancers, such as testicular carcinoma, Wilm’s kidney tumor, and some leukemias in children, often can be cured through chemotherapy but require cytotoxic treatments of a kind that cause severe side effects and are carcinogenic. Several recent advances, including the use of antiangiogenic compounds and inhibitors of specific kinases, may produce efficacious, curative therapies. The authors suggested an approach to cancer therapy that involves homozygous deletions (HDs). Recent studies have demonstrated that many human cancers, including major cancers, contain a significant number of scattered homozygous deletions. A salient property of an HD that involves DNA sequences not present elsewhere in the genome is that HD cannot revert. For this and other reasons, HDs may prove to be an appropriate target for therapy. The difficulty is that HD is an “absence,” and therefore it cannot be a conventional molecular target. Nevertheless, an HD-specific anticancer regimen is feasible through a strategy termed deletion-specific targeting (DST), which employs homozygous deletions as negative targets of cancer therapy. The DST strategy is implemented through molecular circuits that combine ex-isting and new methodologies. One such method is the ubiquitin (Ub) fusion technique. In addition, an essential part of the DST strategy is based on helper-dependent split-protein devices, introduced with the split-Ub assay and thereafter extended to other split-protein constructs, including dihydrofolate reductase, GFP, and β-lact-a-mase. Split-protein domains coupled to DNA-recognizing proteins are also a component of the DST strategy. Another part of DST is conditional destruction of DST vectors by (reconstituted) split-restriction nucleases and a time delay in activating a vector’s payload. The logic of DST makes possible an incremental and essentially unlimited increase in the selectivity of therapy. If the DST strategy can be implemented in a clinical setting, it may prove to be curative and substantially free of side effects.

Varshavsky A. Targeting the absence: Homozygous DNA deletions as immutable signposts for cancer therapy. Proc Natl Acad Sci USA. 2007;104:14935–14940.

Correspondence: Alexander Varshavsky at avarsh@caltech.edu

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A new SLE marker for atherosclerosis risk A new SLE marker for atherosclerosis risk

Nitric oxide released from endothelial cells is a strong vasodilator that regulates vascular tone. Decreased bioavailability of nitric oxide results in endothelial dysfunction, one of the earliest steps in the process of atherosclerosis. Nitric oxide regulates tissue blood flow and inhibits platelet aggregation and leukocyte ad-hesion on the endothelial surface. It is synthesized by stereospecific oxidation of the terminal guanidinonitrogen of the amino acid 1-arginine by a family of nitric oxide synthases. Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide synthase inhibitor. After posttranslational methylation from proteins involved in RNA processing and transcriptional control, ADMA is released by endothelial cells. High ADMA concentrations are seen in chronic heart failure, diabetes mellitus, and hypertension. In a study of healthy Japanese people, ADMA was associated with age, hypertension, and carotid artery intima-media thickness. ADMA and C-reactive protein (CRP) levels emerged as the sole independent predictors of progression of carotid intimal lesions during a followup period of one year. In a prospective, nested case-control study of middle-aged, nonsmoking men in Finland, plasma levels of ADMA in the highest quartile were associated with a 3.9-fold increase in risk for acute coronary events. In the CARDIAC study, an ADMA concen-tration of more than 1.75 µm/L led to a six- to seven-fold increase in cardiovascular disease. In a study of 107 patients with systemic lupus erythematosus (SLE), mean plasma ADMA levels were higher in those with cardiovascular events, including coronary artery disease, ischemic cerebrovascular events, and peripheral artery disease. Multivariate analysis showed that high SLE Disease Activity Index activity scores, high Systemic Lupus International Collaborating Clinics/American College of Rheumatology damage index, high antidsDNA titers, and low serum high-density lipoprotein (HDL) were also significantly associated with high plasma ADMA levels. ADMA has not been previously studied in subclinical atherosclerosis in SLE. The authors conducted a study involving 200 patients with SLE to determine the association of ADMA with clinical features, laboratory tests, treatment, cardiovascular risk factors, and subclinical artherosclerosis in patients with SLE. Serum ADMA concentrations were determined by enzyme-linked immunosorbent assay using purified ADMA as a standard. Coronary calcium was measured by helical computerized tomography. Patients were a mean age of 44.3±11.4 years. The study make-up was 92 percent female, 61 percent Cauca-sian, 34 percent African-American, two percent Asian, and two percent Hispanic; 18 percent had elevated ADMA levels. The mean ADMA was 0.31. Significantly higher ADMA levels were found in African-Americans (P<.001) and were correlated with anti-dsDNA (P<.001), anti-Sm (P=.005), anti-ribonucleoprotein (P=.002), low C4 (P=.004), and high erythrocyte sedi-mentation rate (P<.001). ADMA was negatively associated with total cholesterol (P=.004). Elevated ADMA was associated with coronary calcium (P=.02). The authors concluded that elevated ADMA is strongly associated with African-American ethnicity, anti-dsDNA, low complement, and prednisone use, all markers of poor prognosis in SLE. It is negatively associated with hyperlipidemia and positively associated with coronary calcium. Therefore, elevated ADMA identifies a subset of SLE patients with normal lipid levels who are at risk for developing atherosclerosis.

Kiani AN, Mahoney JA, Petri M. Asymmetric dimethylarginine is a marker of poor prognosis and coronary calcium in systemic lupus erythematosus. J Rheumatol. 2007;34:1502–1505.

Correspondence: Dr. M. Petri at mpetri@ihmi.edu

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Salivary proteomic and genomic biomarkers in Sjogren syndrome Salivary proteomic and genomic biomarkers in Sjogren syndrome

Sjogren syndrome, which was first described in 1933 by the Swedish physician Henrik Sjogren, is a chronic autoimmune disorder clinically characterized by a dry mouth and dry eyes. The disease affects more women than men (ratio, 9:1). While Sjogren syndrome (SS) affects up to 4 million Americans, about half the cases are primary SS, which occurs alone. Secondary SS is present in connection with another autoimmune disease, such as rheumatoid arthritis or systemic lupus erythematosus. There is evidence of B-cell activation with autoantibody production and an increase in B-cell malignancy. SS patients exhibit a 40-fold increased risk of developing lymphoma. SS is a complex disease that can go undiagnosed for several months or years. Although the underlying immune-mediated glandular destruction is thought to develop slowly over several years, a long delay from start of symptoms to final diagnosis has been frequently reported. SS presumably involves the interplay of genetic and environmental factors. To date, few of these factors are well under-stood. As a result, there is a lack of early diagnostic markers, and diagnosis usually lags symptom onset by years. It is widely believed that developing molecular biomarkers for the early diagnosis of primary SS will improve the application of systematic therapies and the establishment of criteria with which to monitor therapies and assess prognosis. Saliva is the product of three pairs of major salivary glands—the parotid, submandibular, and sublingual glands—and multiple minor salivary glands that lie beneath the oral mucosa. Human saliva contains many informative proteins that can be used to detect diseases. Therefore, it is crucial to use emerging proteome- and genome-wide approaches to discover a wide spectrum of informative and discriminatory biomarkers that can be combined to improve the sensitivity and specificity for detecting primary SS. The authors conducted a study in which they used mass spectrometry and expression microar-ray profiling to identify candidate protein and mRNA biomarkers of primary SS in human whole saliva (WS) samples. Validation of the discovered mRNA and protein biomarkers was also demonstrated using real-time quantitative polymerase chain reaction and immunoblotting techniques. The authors found that 16 WS pro-teins were downregulated and 25 WS proteins were upregulated in primary SS patients compared with matched healthy control subjects. These proteins reflected the damage of glandular cells and inflammation of the oral cavity system in patients with primary SS. In addition, 16 WS peptides (10 upregulated and six downregulated in primary SS) were found at significantly different levels (P<.05) in primary SS patients and controls. Using stringent criteria (three-fold change; P<.0005), 27 mRNA in saliva samples were found to be significantly upregulated in primary SS patients. Strikingly, 19 of 27 genes that were found to be overex-pressed were interferon-inducible or related to lymphocyte filtration and antigen presentation known to be involved in the pathogenesis of primary SS. The study indicated that WS from patients with primary SS contains molecular signatures that reflect damaged glandular cells and an activated immune response in this autoimmune disease. These candidate proteomic and genomic biomarkers may improve the clinical detection of primary SS once they have been validated further. WS contains more informative proteins, peptides, and mRNA than gland-specific saliva and can be used to generate candidate biomarkers for detecting primary SS.

Hu S, Wang J, Meijer J, et al. Salivary proteomic and genomic biomarkers for primary Sjogren’s syndrome. Arthritis Rheum. 2007;56:3588–3600.

Correspondence: Dr. David T. Wong at dtww@ucla.edu

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Isolated transaminase elevations in children Isolated transaminase elevations in children

A plethora of literature addresses cholestasis in infants and children. In medical literature about adults, much attention is devoted to evaluating asymptomatic patients with abnormal liver enzymes. On the other hand, few, if any, studies have involved asymptomatic infants or children with isolated elevation of serum aminotransferases. In most cases, increased enzyme levels resolve within a few weeks, so no further evaluation is needed. However, some apparently healthy subjects continue to exhibit high enzyme levels for several months. Therefore, the authors conducted a study to assess the clinical significance and prognosis of isolated elevation of serum aminotransferases without cholestasis in infants and young children and to establish a protocol for their investigation and followup. The study was a combined prospective-retrospective analysis of apparently healthy babies and young children with isolated elevation of serum amino-transferases of at least 1.5 times above the norm for age that persisted for at least three months. The study involved 72 children (47 males and 25 females). The subjects’ creatine phosphokinase (CK), gamma glutamyltransferase (GGT), alkaline phosphatase, and bilirubin levels remained normal throughout the study. The children underwent abdominal ultrasound and infectious, metabolic, and/or immunological investigation, depending on the duration of the abnormality. Six children were eliminated following the finding of positive cytomegalovirus (CMV) antigen in the urine. Elevated serum amino-transferases endured for three to 36 months (average, 12.4 months; median, 11.5 months). The initial, maximal, and final alanine amino-transferase values were 85.5, 140.5, and 39.8 IU/L, respectively. Of seven children who had liver biopsies performed, three (42.8 percent) were suspected of having a glycogen storage disease, which was not confirmed enzymatically. Four biopsies revealed nonspecific histological changes. The authors concluded that isolated elevation of serum aminotransferases in healthy looking young children is mostly a benign condition that usually resolves within a year. If no pathology is found during routine investigation, these children can be followed conservatively. Liver biopsy does not contribute significantly to the diagnosis and is probably unnecessary.

Bugeac N, Pacht A, Mandel H, et al. The significance of isolated elevation of serum aminotransferases in infants and young children. Arch Dis Child. 2007;92:1109–1112.

Correspondence: Dr. Ron Shaoul at shaoul_r@012.net.il

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Clinical pathology abstracts editor: Michael Bissell, MD, PhD, MPH, professor, Department of Pathology, Ohio State University, Columbus.