Natural helix 9 mutants of PPARγ differently affect its transcriptional activity.

OBJECTIVE: The nuclear receptor PPARγ is the master regulator of adipocyte differentiation, distribution, and function. In addition, PPARγ induces terminal differentiation of several epithelial cell lineages, including colon epithelia. Loss-of-function mutations in PPARG result in familial partial lipodystrophy subtype 3 (FPDL3), a rare condition characterized by aberrant adipose tissue distribution and severe metabolic complications, including diabetes. Mutations in PPARG have also been reported in sporadic colorectal cancers, but the significance of these mutations is unclear. Studying these natural PPARG mutations provides valuable insights into structure-function relationships in the PPARγ protein. We functionally characterized a novel FPLD3-associated PPARγ L451P mutation in helix 9 of the ligand binding domain (LBD). Interestingly, substitution of the adjacent amino acid K450 was previously reported in a human colon carcinoma cell line. METHODS: We performed a detailed side-by-side functional comparison of these two PPARγ mutants. RESULTS: PPARγ L451P shows multiple intermolecular defects, including impaired cofactor binding and reduced RXRα heterodimerisation and subsequent DNA binding, but not in DBD-LBD interdomain communication. The K450Q mutant displays none of these functional defects. Other colon cancer-associated PPARγ mutants displayed diverse phenotypes, ranging from complete loss of activity to wildtype activity. CONCLUSIONS: Amino acid changes in helix 9 can differently affect LBD integrity and function. In addition, FPLD3-associated PPARγ mutations consistently cause intra- and/or intermolecular defects; colon cancer-associated PPARγ mutations on the other hand may play a role in colon cancer onset and progression, but this is not due to their effects on the most well-studied functional characteristics of PPARγ.

[Pancytopenia associated with thioguanine use]. / Pancytopenie bij tioguaninegebruik.

Thiopurine drugs, such as thioguanine, mercaptopurine and azathioprine, are used for treating inflammatory bowel disease, such as ulcerative colitis. One must be aware of the serious side effects these drugs can have (e.g. bone marrow depression). A 56-year-old man with ulcerative colitis was treated with mercaptopurine. He developed leukopenia as a result. Thioguanine was started ten months later, resulting in life-threatening pancytopenia. Thiopurine methyltransferase (TPMT) genotyping proved that the patient was a poor metaboliser of thioguanine (TPMT3A*/3A*). Dose reduction is recommended for patients with reduced or absent TPMT activity. This life-threatening side effect could have been prevented by taking a number of relatively simple precautions.

A randomized controlled trial of orbital radiotherapy versus sham irradiation in patients with mild Graves' ophthalmopathy.

Radiotherapy is often used in Graves' ophthalmopathy, but its efficacy has been doubted. We compared its efficacy with sham irradiation in mild ophthalmopathy. In a double-blind randomized trial, 44 patients received orbital irradiation, and 44 were sham-irradiated. The primary outcome was assessed using major and minor criteria. As secondary outcome, we used a disease-specific quality of life questionnaire (the GO-QoL) and compared cost-effectiveness and need for follow-up treatment. The primary outcome was successful in 23 of 44 (52%) irradiated patients vs. 12 of 44 (27%) sham-irradiated patients at 12 months after treatment (relative risk, 1.9; 95% confidence interval, 1.1-3.4; P = 0.02). Radiotherapy was effective in improving eye muscle motility and decreasing the severity of diplopia. However, quality of life improved similarly in both groups. In the radiotherapy group there was less need for follow-up treatment; 66% vs. 84% of the patients needed further treatment (P = 0.049). Retrobulbar irradiation did not prevent worsening of ophthalmopathy, which occurred in 14% of the irradiated and 16% of the sham-irradiated patients. Radiotherapy is an effective treatment in mild ophthalmopathy. However, the improvement upon irradiation may not be associated with an increase in quality of life or a reduction in treatment costs.

Strategies to detect abnormal glucose metabolism in people at high risk of cardiovascular disease from the ORIGIN (Outcome Reduction with Initial Glargine Intervention) trial population.

BACKGROUND: To investigate whether the combination of HbA1c and fasting plasma glucose (FPG) can be used for the diagnosis of diabetes and impaired glucose tolerance (IGT) in people at high risk of cardiovascular disease (CVD). METHODS: A cross-sectional study was performed on 2907 people at high risk of cardiovascular events but without a previous diagnosis of diabetes. Optimal cut-off points and the diagnostic potential of FPG, HbA1c, and their combination were determined. RESULTS: The sensitivity of the usually applied FPG cut-off point of 7.0 mmol/L to diagnose diabetes mellitus was low (59.0%). Receiver operating characteristic (ROC) curve analysis indicated that the optimal cut-off points for the diagnosis of diabetes using FPG and HbA1c were 6.4 mmol/L (sensitivity 75.7%; specificity 77.5%; likelihood ratio 3.37) and 5.9% (41 mmol/mol; sensitivity 68.7%; specificity 67.1%; likelihood ratio 2.09), respectively. To diagnose IGT, the optimal cut-off points for FPG and HbA1c were 6.1 mmol/L (sensitivity 57.1%; specificity 57.9%) and 5.7% (39 mmol/mol; sensitivity 63.8%; specificity 60.3%), respectively. For diabetes, combining cut-off points for FPG and HbA1c identified four categories with likelihood ratios ranging from 5.59 to 0.21, and post-test probabilities between 69.3% and 7.8%. For IGT, likelihood ratios varied between 2.05 and 0.56, whereas post-test probabilities ranged from 84.0% to 58.8%. CONCLUSIONS: Using FPG alone results in the underdiagnosis of glucometabolic abnormalities in people at high risk of CVD. Using an algorithm with both HbA1c and FPG improves the detection of diabetes, but not IGT, and could be easily implemented in patient care.