Gene expression of glutamate metabolizing enzymes in the hippocampal formation in human temporal lobe epilepsy

PURPOSE

Increased interictal concentrations of extracellular hippocampal glutamate have been implicated in the pathophysiology of temporal lobe epilepsy (TLE). Recent studies suggest that perturbations of the glutamate metabolizing enzymes glutamine synthetase (GS) and phosphate activated glutaminase (PAG) may underlie the glutamate excess in TLE. However, the molecular mechanism of the enzyme perturbations remains unclear. A better understanding of the regulatory mechanisms of GS and PAG could facilitate the discovery of novel therapeutics for TLE.

METHODS

We used in situ hybridization on histologic sections to assess the distribution and quantity of messenger RNA (mRNA) for GS and PAG in subfields of hippocampal formations from the following: (1) patients with TLE and concomitant hippocampal sclerosis, (2) patients with TLE and no hippocampal sclerosis, and (3) nonepilepsy autopsy subjects.

KEY FINDINGS

GS mRNA was increased by ~50% in the CA3 in TLE patients without hippocampal sclerosis versus in TLE patients with sclerosis and in nonepilepsy subjects. PAG mRNA was increased by >100% in the subiculum in both TLE patient categories versus in nonepilepsy subjects. PAG mRNA was also increased in the CA1, CA2, CA3, and dentate hilus in TLE without hippocampal sclerosis versus in TLE with sclerosis. Finally, PAG mRNA was increased in the dentate gyrus in TLE with sclerosis versus in nonepilepsy subjects, and also increased in the hilus in TLE without sclerosis versus in TLE with sclerosis.

SIGNIFICANCE

These findings demonstrate complex changes in the expression of mRNAs for GS and PAG in the hippocampal formation in TLE, and raise the possibility that both transcriptional and posttranscriptional mechanisms may underlie the regulation of GS and PAG proteins in the epileptic brain.

[Correlation between four-hour creatinine clearance and 51Cr-EDTA test]

BACKGROUND

Creatinine clearance as a measure of glomerular filtration rate has several sources of error such as tubular creatinine secretion or faulty urine collections. On the other hand 51Cr-EDTA test is reliable and accurate, except in patients with edema, in whom the radioisotope equilibrium is retarded after injection.

AIM

To validate a 4-hours creatinine clearance correlating it with 51Cr-EDTA test.

METHODS

In 59 non insulin dependent diabetic patients without diabetic nephropathy, glomerular filtration rate was measured using one 50 microCi injection of 51Cr-EDTA and collecting blood samples for radioactivity measurement at 10, 30, 120 and 240 min. Simultaneously, creatinine clearance was measured using a 4 hours urine collection.

RESULTS

The general correlation coefficient between both methods was 0.85 (p < 0.001). For glomerular filtration rates below 95 ml/min, the correlation coefficient was 0.8 (p < 0.001), for values between 95 and 127 ml/min, the correlation was 0.51 (p < 0.001) and for values over 127 ml/min the correlation was 0.8 (p < 0.001). The regression equation obtained was y = 1,2x + 13 where y was the glomerular filtration rate measured with 51Cr-EDTA and x the same value measured with creatinine clearance.

CONCLUSIONS

The four hours creatinine clearance is a reliable method to estimate glomerular filtration rate.