Editor's note: Science Scan is a roundup of recently published biotechnology-relevant research.
Prions have hit the top of the news charts this month with the unexpected spread of chronic wasting disease (CWD) among herds of deer (family cervus) and elk (Cervus canadensis) in the Rocky Mountain states of the U.S. Until now, CWD was confined to the state of Wisconsin, 1,000 miles away from its present alarming threat.
The alarm is due to the apparent jump of prion infection from bovine to cervine animals. Bovine spongiform encephalopathy (BSE) is better known as mad cow disease. The British epizootic passes its inevitably fatal prion infection to humans, in the form of Creutzfeldt-Jakob disease (CJD). By latest count, the death toll from CJD in Britain, Ireland and France is at 114, and still rising. (See BioWorld Today, March 21, 2002, p.1.)
Prions are submicroscopic protein particles that consist of amino acids, but contain neither DNA nor RNA, so presumably lack immune defenses. Besides BSE, CWD and CJD, infectious prions cause scrapie, a slow-growing infection in sheep and goats, so-named for their frenzied scraping of itchy necks on fences and trees. Researchers have created scrapie-infected mice as a new animal model of this caprine and ovine scourge.
CJD contagion from mad cows is presumed inflicted on victims who consumed beef from prion-infected cattle. However, medical personnel, such as neurosurgeons, pathologists, nurses, morticians, histology technicians and laboratory workers, are at special risk of accidentally contracting CJD.
Authors of a fast-track research letter in The Lancet dated July 20, 2002, report a therapeutic treatment that increases the survival time of scrapie-infected mice. This finding suggests a new approach to treating CJD in human patients. The paper is titled "Postexposure prophylaxis against prion disease with a stimulator of innate immunity." Its authors are German neuropathologists at two universities in Munich.
They inoculated 24 healthy mice intraperitoneally with brain homogenates from mice terminally infected with scrapie-prion. The authors followed this challenge with a specific nucleotide arrangement called oligodeoxynucleotides. These molecules had previously been shown to strongly stimulate the innate immune system's arsenal of macrophages, monocytes and dendritic cells.
Mice in the first two treatment groups, which received the treatment immediately or seven hours after scrapie challenge, survived for 38 percent longer than control cohorts. They showed no clinical disease 330 days after inoculation plus repeated therapy, compared with 180 days without treatment.
An accompanying commentary by George Carlson at the McLaughlin Research Institute in Great Falls, Mont., finds the German scientists' hypothesis "reasonable," and concludes: "Development of improved diagnostics and postexposure prophylaxis are urgently needed, given the unknown prevalence of subclinical prion infection associated with the BSE outbreak."
Lilly Goes Its Own Recombinant Human Insulin One Better For Enhancement Of Glucose Control
It's biotech folklore that on Oct. 14, 1980, Genentech launched the industry's first IPO by going public at $35 a share. An hour later, that stock was selling at $89. Investors had their eye on Genentech's first commercial venture, recombinant insulin, which it had cloned in 1978. In 1980, the company promptly sold its insulin interest to Eli Lilly and Co. Two years later, the FDA approved Lilly's sale of recombinant human insulin, trademarked Humulin. In 1998, it chalked up sales of more than $700 million.
Recombinant human insulin spared diabetics the drug reactions of bovine and porcine insulin. But even today Humulin shots fall short of assuring the tight regulation of blood glucose levels that aim to avoid the life-threatening, long-term complications of diabetes mellitus. Now, in the August 2002 issue of Nature Biotechnology, Lilly researchers report how they generated novel crystalline insulin, for longer and smoother control of blood glucose. Their article is titled "Hybrid insulin cocrystals for controlled release delivery."
Interestingly, controlled-release insulin was developed in the early 1930s. That followed the summer of 1921, when two Canadian physiologists gave the first pancreatic islets of Langerhans to a diabetic dog near death from the disease. As the islets released their insulin into its bloodstream, the canine animal model sat up and wagged its tail. The rest is history.
Today, current insulin injections comprise a suspension of the hormone's crystals, which form when insulin molecules combine with zinc and protamine. The Lilly authors doped human insulin with a less-soluble version, also mixed with zinc and protamine. By juggling the solubility ratio of these ingredients they built a stable cocrystal that releases insulin at a slower rate than standard formulations. In beagle dogs with experimental diabetes, a single cocrystal injection provided sustained control of blood glucose levels for 24 hours, without the usual early fluctuations.
Mirus Corp. Unveils High Pressure' Method To Inhibit Gene Expression In Adult Mouse Organs
A "Brief Communication" in Nature Genetics, published online July 29, 2002, bears a title that sums up its findings: "Efficient delivery of siRNA for inhibition of gene expression in postnatal mice." Its authors are key personnel at Mirus Corp. in Madison, Wis., and the University of Wisconsin. Their technique involves rapidly injecting a large volume of physiological solution into the tail veins of postnatal mice.
This "high pressure" approach delivered short interfering RNA (siRNA) double-stranded molecules in vivo to organs of adult mice, and inhibited transgenic expression of luciferase reporter genes in a variety of organs. These included spleen, lung, kidney, pancreas and, in particular, liver. This blockage resulted in the induction of a newly discovered genetic inhibitory pathway named RNA interference (RNAi). It operates by degrading a target messenger RNA through the action of a ribonucleoprotein complex containing the siRNA and cellular proteins.
Until recently, the authors point out, the use of RNAi has been limited to plants and lower eukaryotic organisms because the long, double-stranded RNA molecules used to induce RNAi in those targets also induced the nonspecific interferon response in mammalian cells. The discovery that synthetic RNAs themselves could induce RNAi and bypass the interferon pathway, the Nature Genetics paper concludes, "opens the door for exploring the use of siRNA in humans to treat disease."