Biochemistry and Clinical Role of Human Cystatin C

Impact of renal function or folate status on altered plasma homocysteine levels in hypothyroidism

Hyperhomocysteinemia is an independent risk factor for coronary, peripheral and cerebrovascular diseases. Moderately elevated total homocysteine (tHcy) levels have been reported in patients with overt hypothyroidism. Plasma tHcy concentration is affected by several physiological factors and is elevated under conditions of impaired folate and cobalamin status and in renal failure. The aim of this study was to assess plasma tHcy concentrations and to evaluate the role of potential determinants of plasma tHcy levels in hypothyroid patients. Fasting plasma tHcy, serum homocysteine-related vitamins folate and vitamin B(12), serum cystatin C (CysC) and creatinine, were determined in 22 hypothyroid patients and compared with 25 healthy control subjects. Creatinine clearance (CCr) was calculated using the Cockroft-Gault formula. Plasma tHcy levels were determined by HPLC with fluorescence detection and serum CysC by automated particle enhanced immunoturbidimetry. Plasma tHcy, creatinine levels were significantly higher, and serum CysC levels, and creatinine clearance values were lower in hypothyroid patients than in control subjects. Folate levels were lower in hypothyroidic group compared to the control group. There were no differences in vitamin B(12) levels between hypothyroid and control groups. Positive correlation was noted between tHcy and creatinine levels in hypothyroid patients (r = 0.596); however, an inverse correlation was found between tHcy and folate levels (r = -0.705) in hypothyroid patients. In conclusion, tHcy was increased in hypothyroidism, and this increase was more strongly associated with changes in serum folate than in serum creatinine and CysC, suggesting an altered folate status.

Genotype (cystatin C) and EEG phenotype in Alzheimer disease and mild cognitive impairment: A multicentric study

Previous findings demonstrated that haplotype B of CST3, the gene coding for cystatin C, is a recessive risk factor for late-onset Alzheimer's disease (AD; Finckh, U., von der Kammer, H., Velden, J., Michel, T., Andresen, B., Deng, A., Zhang, J., Muller-Thomsen, T., Zuchowski, K., Menzer, G., Mann, U., Papassotiropoulos, A., Heun, R., Zurdel, J., Holst, F., Benussi, L., Stoppe, G., Reiss, J., Miserez, A.R., Staehelin, H.B., Rebeck, G.W., Hyman, B.T., Binetti, G., Hock, C., Growdon, J.H., Nitsch, R.M., 2000. Genetic association of the cystatin C gene with late-onset Alzheimer disease. Arch. Neurol. 57, 1579-1583). In the present multicentric electroencephalographic (EEG) study, we analyzed the effects of CST3 haplotypes on resting cortical rhythmicity in subjects with AD and mild cognitive impairment (MCI) with the hypothesis that sources of resting EEG rhythms are more impaired in carriers of the CST3 B haplotype than non-carriers. We enrolled a population of 84 MCI subjects (42% with the B haplotype) and 65 AD patients (40% with the B haplotype). Resting eyes-closed EEG data were recorded in all subjects. EEG rhythms of interest were delta (2-4 Hz), theta (4-8 Hz), alpha 1 (8-10.5 Hz), alpha 2 (10.5-13 Hz), beta 1 (13-20 Hz), and beta 2 (20-30 Hz). EEG cortical sources were estimated by low-resolution brain electromagnetic tomography (LORETA). Results showed that the amplitude of alpha 1 (parietal, occipital, temporal areas) and alpha 2 (occipital area) was statistically lower in CST3 B carriers than non-carriers (P < 0.01). Whereas there was a trend towards statistical significance that amplitude of occipital delta sources was stronger in CST3 B carriers than in non-carriers. This was true for both MCI and AD subjects. The present findings represent the first demonstration of relationships between the AD genetic risk factor CST3 B and global neurophysiological phenotype (i.e., cortical delta and alpha rhythmicity) in MCI and AD subjects, prompting future genotype-EEG phenotype studies for the early prediction of AD conversion in individual MCI subjects.