(250d) Viscosity Measurements of High Concentration DNA Solutions Over a Wide Temperature Range

Cystic Fibrosis (CF) is an autosomal recessive disease. It affects exocrine glands throughout the body and is mainly characterized by chronic respiratory infection that is acquired during childhood and persists through the patient's life. CF airway surface liquids contain high concentrations of extracellular DNA. The resulting sputum exhibits changes in elasticity, adhesivity, and rheological properties, which impair cough clearance and mucosillary transport. The extracellular DNA from immune cells and dead bacteria may also induce antibiotic resistance and support biofilm growth. Understanding the rheological properties of high concentration DNA solutions and screening for possible therapeutics to modify the solution properties could lead to better CF management.

As a model for sputum, the viscosity of DNA solutions, and its susceptibility to condensing agents, was examined in this work. DNA was dissolved in water in concentrations of 2 mg/ml, 4 mg/ml, and 6 mg/ml. The DNA was uncut genomic from calf-thymus, highly polymerized, with high molecular weight (tens of thousands of base pairs.) Because the temperature dependence of viscosity is as important as the viscosity itself, the viscosity of the DNA solutions was measured at 25.00 ˚C, 37.78 ˚C, and 50.00 ˚C. Initial measurements at these temperatures indicated a viscosity increase toward 50 ˚C. This phenomenon was resolved by extended measurements from 10 ˚C to 90 ˚C, which revealed concentration dependent viscosity maxima in the range from 50 ˚C to 65 ˚C. The associated viscosity increases up to 400 % may be indicative of DNA melting. This work is possibly the first characterization of this phenomenon at high DNA concentrations by viscometry rather than differential scanning calorimetry or spectroscopic methods. Once the DNA solutions had been characterized, the polycations spermine and poly-L-lysine were added to DNA solutions to test the resulting mixtures for viscosity changes. The polycations, decreased the viscosity of 2 mg/ml DNA solutions, but increased viscosity in the 6 mg/ml DNA solutions. Also, in some cases adding the polycations altered the temperature dependence of viscosity in DNA solutions.

The compact viscometer that was mainly used in this work offers high throughput for screening of potential therapeutic agents. The self-contained compact design of the instrument makes bench-top use in medical practices and clinical laboratories possible. Thus, viscometery may become a rapid diagnostic technique for determining rheological markers for overall disease progression. With these perspectives and methods our work is an interdisciplinary convergence of metrology and bioscience for healthcare.