Stability of human salivary lactate dehydrogenase in the present of ethylenediaminetetraacetic acid, glycerol and polyethylene glycol at various temperatures: preliminary study

Abstract

This study aims to determine the best storage condition for salivary lactate dehydrogenase due to decreased in native enzyme’s activity after seven days of storage. Saliva samples were collected from five healthy and good oral hygiene patients. The specific enzyme activities were measured after 0 (control), 1 and 2 weeks of storage treated with 2.5 mM ethylenediaminetetraacetic acid, 10% (v/v) glycerol or 15% (w/v) polyethylene glycol at three different temperatures, i.e., room temperature, 4 and -20°C. Enzyme activity (unit mL-1) was based on the rate of Nicotinamide Adenine Dinucleotide oxidations standardized at 30°C. The rate of oxidation directly proportional to enzyme’s activity was measured at 340 nm. The specific activity (unit mg-1) was determined through estimated protein content using Bradford analysis. The data were statistically analyzed with paired t-test based on average percentage of enzyme activities from three independent experiments. After two weeks, saliva sample in the presence of polyethylene glycol showed no significant different (p>0.01) at all three temperatures compared to Lactate dehydrogenase basal activity. Lactate dehydrogenase activity of sample in the presence of ethylenediaminetetraacetic acid remained stable (p>0.01) only after a week at room temperature. On the other hand, glycerol managed to stabilize salivary lactate dehydrogenase activity for two weeks at 4 and -20°C. As conclusion, polyethylene glycol showed as the best additive for salivary lactate dehydrogenase storage whereas, ethylenediaminetetraacetic acid suitable only at room temperature for a week. In addition, glycerol was suitable only in cooler conditions.