By David N. Leff
Editor¿s note: Science Scan is a roundup of recently published biotechnology-relevant research.
Israeli scientists have conned human embryonic stem cells into generating beating human heart-muscle cells. The Journal of Clinical Investigation for August 2001 reports their feat under the title: ¿Human embryonic stem cells can differentiate into myocytes with structural and functional properties of cardiomyocytes.¿
The paper¿s 10 co-authors are cardiovascular, obstetrical and anatomy researchers at the Technion-Israel Institute of Technology in Haifa.
They make a preliminary point: ¿Given that human fetal tissue cannot be obtained in sufficient quantities in the clinical setting, a new source of human cardiomyocytes is sorely needed. In this report we describe the use of human ES [embryonic stem] cells as a reproducible differentiation system for human cardiomyocytes. Using this system,¿ they continued, ¿spontaneously contracting foci were, for the first time to our knowledge, demonstrated to have ultrastructural and functional properties consistent with a cardiomyocyte phenotype.¿
For starters, the team dispersed small clumps of three to 20 ES cells, seeded colonies of half a million cells into Petri dishes, then cultured them in suspension for seven to 10 days. During this incubation, the cells aggregated to form embryoid bodies (EB). They plated 1,884 of these EBs onto gelatin-coated dishes, and monitored them by electron microscopy for the emergence of cardiac-like contractions.
¿Rhythmically contracting areas,¿ their paper recounted, ¿appeared at 4 to 22 days, in 153 (8.1 percent) of the 1,884 EBs studied. Their diameter ranged from 0.2 to 2 millimeters, and they continued to beat vigorously for up to 5 weeks (the longest period studied). The average spontaneous pulsation rate was 94 plus/minus 33 beats per minute.¿
The team assessed the expression of several cardiac-specific genes in the human ES cell-derived muscle cells by PCR analysis. Myocytes from the contracting EBs expressed cardiac transcription factors and cardiac-specific genes, notably atrial and ventricular myosin light and heavy chains.
¿In the normal human embryo,¿ the paper noted, ¿heart formation begins with the initiation of differentiation by myocardial and endocardial precursors, and leads up to the formation of the cardiac valves. These events cover the first 35 days in the life of a human embryo.¿
Their findings, the co-authors observe, suggest an ¿attractive application of these cells in cell replacement therapy.¿ This prospect contrasts embryonic with adult stem cells: ¿Adult cardiomyocytes,¿ they point out, ¿withdraw permanently from the cell cycle during differentiation; hence, any significant loss of cardiomyocytes (as occurs, for example, during myocardial infarction) is irreversible and leads to diminished cardiac function and progressive heart failure.¿ A novel potential approach for this situation, they propose, ¿may be the implantation of myogenic cells within the infarcted tissue.¿
¿Nevertheless,¿ they conclude, ¿several obstacles must be overcome in order to achieve this goal, including the generation of enriched and relatively pure cardiomyocyte cultures and the establishment of different strategies to counter immune rejection.¿
In a one-page commentary accompanying this nine-page article, a distinguished pioneer in stem cell research, J. Hescheler, at the University of Cologne in Germany, opened up by stating: ¿This Commentary is written by rather disappointed German scientists who are not allowed to establish human embryonic stem cells, and have been publicly blamed for using them, [while] other countries, Israel among them, are actively supporting basic research on this interesting topic.
¿Their study,¿ he added, ¿provides the first compelling evidence that human embryonic stem cells can be differentiated into cardiomyocytes.¿ Hescheler sees as ¿the most interesting aspect¿ of the Israeli article ¿the possibility of using human embryonic stem cells as a source for cell replacement or growing organ tissue, such as structures in vitro for transplantation purposes after heart injury, and testing pharmacological agents onto cardiomyocytes in vitro. Furthermore,¿ he concluded, ¿it provides scientists with a formidable tool to compare the therapeutic efficiency of embryonic versus adult stem cells.¿
Subbing For Mice, Humans Accepted Severe Pain To Identify Cerebral, Subjective Responses
Does it hurt, or do you only think it hurts?
This quixotic question reflects the fact that pain perception plays out in the head. It recalls the classic story of a battlefield machine gunner whose leg gets carried away by a cannonball. He keeps right on firing, oblivious to the painful and stressful loss of the limb.
Laboratory rats and mice are the perennial in vivo models of mammalian reaction to pain. Of late, the advent of MRI (magnetic resonance imaging) and PET (positron emission tomography) have made it feasible to scrutinize in real time the human brain¿s response to real pain. A report in Science dated July 13, 2001, reports such a high-tech, high-hurt experiment in 20 willing volunteers. Its title: ¿Regional Mu opioid receptor regulation of sensory and affective dimensions of pain.¿ The paper¿s authors are at the University of Michigan, Ann Arbor.
The endogenous opioid system in the brain was acclaimed, when first discovered in the 1970s, as ¿the brain¿s own morphine.¿ To this day, morphine remains the pain-killing drug of choice for intractable pain, such as suffered by late-stage cancer patients.
The paper¿s co-authors ¿examined the function of the endogenous opioid system and m-opioid receptors during the experience of sustained pain in healthy human subjects.¿ They explained, ¿The m-opioid receptors are implicated in antinociception, in stress-induced analgesia and in the actions of exogenously administered opiate drugs.¿ (In neurospeak, pain perception is nociception.¿)
The team enlisted 13 men and seven women, ages 20 to 30, and tortured their unilateral masseter muscles (which shut the jaw) with severe, prolonged pain. PET and MRI imaging pinpointed their nociception to particularly responsive regions of the brain, while daily questionnaires produced by the participating subjects disclosed the subjective aspects of their pain perception. Among other findings, the results revealed that these responses can vary from one person to another.