High incidence of microsatellite instability in colorectal cancer from African Americans.

PURPOSE: Colorectal carcinoma (CRC) is the second most common cause of cancer death in the United States, and the rate of CRC is nearly 1.5 times higher in African-Americans (AA) than in Caucasians. Microsatellite instability (MSI) is observed in sporadic CRC reflecting promoter hypermethylation of the DNA mismatch repair gene hMLH1, and anecdotal evidence suggests an increased incidence of MSI among AAs. Additionally, p16 can be inactivated by hypermethylation of the promoter region, abrogating its ability to regulate cell proliferation. The objective of this study is to determine the frequency of MSI and p16 gene methylation in CRC from AA patients. EXPERIMENTAL DESIGN: Experiments were conducted on serially collected archival samples of colon cancer and adjacent normal tissue (n = 22). Five microsatellite markers were used to measure MSI in tumors with direct comparison to normal tissue from the same patient. p16 promoter methylation status was determined by methylation-specific PCR. RESULTS: Ten cancers (45%) demonstrated high MSI (MSI-H), 1 demonstrated low MSI, and the remaining 11 tumors were microsatellite stable. Most of the MSI-H tumors were proximal, well differentiated, and showed high levels of mucin production. Most patients in the MSI-H group were female (70%), whereas most of the microsatellite-stable group (81%) were male. Five of the 22 tumors (22%) had methylation of the p16 promoter. CONCLUSION: Data provided here demonstrated that the incidence of MSI-H tumors was 3-fold higher in our study group of AA patients compared with data reported in nonracially selected but serially collected studies. Odds ratio analysis indicates that the chance of female patients having MSI-H was 11.7 times more than male patients (P < 0.03). The reason for this gender difference is unknown. These findings might reflect dietary differences or genetic polymorphisms that may be common in the AA population. Additional investigation in a larger patient population is needed before strong conclusion can be drawn.     

Low cobalamin levels in African Americans with and without sickle cell disease

About 7% of the adult population has subclinical cobalamin (B12) deficiency. Subjects with sickle cell disease (SCD) may be at higher risk of cobalamin deficiency because of increased demand, inadequate supply, coexisting folate deficiency or malabsorption. We compared the clinical and laboratory characteristics of low serum cobalamin levels in patients with SCD with those patients without this hemoglobinopathy (non-SCD). Between 1993 and 2003, 105 SCD patients and 112 non-SCD patients who had serum cobalamin measurements were identified at our institution. The mean cobalamin level in SCD patients was significantly lower (496 +/- 352 pg/ml) than that in patients without SCD (869 +/- 660 pg/ml, p<0.0001). The frequency of low cobalamin levels, defined by a serum cobalamin level of <200 pg/ml, was 18.1% (19/105) and 9.8% (11/112) in SCD and non-SCD patients, respectively (chi2=3.11, nonsignificant). The mean age of the low-cobalamin SCD and non-SCD patients was 28.1 and 62.9, respectively, and their male:female ratios were 11:8 in SCD patients and 2:9 in non-SCD patients. None of the SCD patients had neurological manifestations, but nine of the 11 non-SCD low-cobalamin level patients did. The proportion of SCD patients with unexplained low cobalamin levels (13/19) was higher than that in non-SCD patients (4/11, chi2=2.92, nonsignificant) Our data suggest that cobalamin levels are lower in SCD patients than in subjects without SCD, and low-cobalamin SCD patients are younger and more likely to be males.     

Platelet senescence and phosphatidylserine exposure

BACKGROUND: The exposure of phosphatidylserine occurs during platelet (PLT) activation and during in vitro storage. Phosphatidylserine exposure also occurs during apoptosis after the release of mitochondrial cytochrome c. We have examined the role of cytochrome c release, mitochondrial membrane potential (ΔΨm), and cyclophilin D (CypD) in phosphatidylserine exposure due to activation and storage. STUDY DESIGN AND METHODS: The exposure of phosphatidylserine and the loss of ΔΨm were determined in a flow cytometer using fluorescein isothiocyanate–lactadherin and JC‐1, a lipophilic cationic reporter dye. The role of CypD was determined with cyclosporin A and CypD‐deficient murine PLTs. Cytochrome c‐induced caspase‐3 and Rho‐associated kinase I (ROCK1) activation were determined by immunoblotting and using their inhibitors. RESULTS: Collagen‐ and thrombin‐induced exposure of phosphatidylserine was accompanied by a decrease in ΔΨm. Cyclosporin A inhibited the phosphatidylserine exposure and the loss of ΔΨm. CypD^?/? mice had decreased loss of ΔΨm and impaired phosphatidylserine exposure. Collagen and thrombin did not induce the release of cytochrome c nor the activation of caspase‐3 and ROCK1. In contrast, in PLTs stored for more than 5 days, the phosphatidylserine exposure was associated with cytochrome c–induced caspase‐3 and ROCK1 activation. ABT737, a BH3 mimetic that induces mitochondrial pathway of apoptosis, induced cytochrome c release and activation of caspase‐3 and ROCK1 and phosphatidylserine exposure independent of CypD. CONCLUSION: These results show that in stored PLTs cytochrome c release and the subsequent activation of caspase‐3 and ROCK1 mediate phosphatidylserine exposure and it is distinct from activation‐induced phosphatidylserine exposure.