Directed differentiation of embryonic stem cells using a bead-based combinatorial screening method

We have developed a rapid, bead-based combinatorial screening method to determine optimal combinations of variables that direct stem cell differentiation to produce known or novel cell types having pre-determined characteristics. Here we describe three experiments comprising stepwise exposure of mouse or human embryonic cells to 10,000 combinations of serum-free differentiation media, through which we discovered multiple novel, efficient and robust protocols to generate a number of specific hematopoietic and neural lineages. We further demonstrate that the technology can be used to optimize existing protocols in order to substitute costly growth factors with bioactive small molecules and/or increase cell yield, and to identify in vitro conditions for the production of rare developmental intermediates such as an embryonic lymphoid progenitor cell that has not previously been reported

Residual aortic valve regurgitation after aortic root remodeling without a direct annuloplasty

Background. Aortic insufficiency secondary to degenerative aneurysms of the ascending aorta can be surgically treated with replacement of the valve or with remodeling of the aortic root. Methods. In 15 patients who underwent aortic root remodeling from January 1994 to December 1996, we evaluated the postoperative aortic regurgitation and correlated it with several anatomic and functional variables. Operative success was defined as a residual aortic regurgitation less than or equal to 1 on a scale of 0 to 4. Results. Root dimensions and aortic incompetence decreased significantly after the operation (p < 0.0001). The difference between preoperative and postoperative root diameters (p = 0.0006) and the presence of Marfan's syndrome (p < 0.0001) were independently predictive of persisting significant aortic insufficiency. Operative success was obtained in patients with a difference between preoperative and postoperative root diameters smaller than 30 mm. Conclusions. Aortic root remodeling is effective in reducing aortic regurgitation. Severe aortic root dilatation may result in excessive geometric alteration, leading to suboptimal results. The choice of a larger graft contributes to avoiding excessive geometric constraint of a profoundly diseased aortic root. Indication to undergo root remodeling should be evaluated cautiously in patients with Marfan's syndrome. (Ann Thorac Surg 1998;66:1269-72

Regression of left ventricular hypertrophy after aortic valve replacement for aortic stenosis with different valve substitutes

Objective: Stentless biologic aortic valves are less obstructive than stented biologic or mechanical valves. Their superior hemodynamic performances are expected to reflect in better regression of left ventricular hypertrophy. We compared the regression of left ventricular hypertrophy in 3 groups of patients undergoing aortic valve replacement for severe aortic stenosis. Group I (10 patients) received stentless biologic aortic valves, group II (10 patients) received stented biologic aortic valves, and group III (10 patients received bileaflet mechanical aortic valves. Methods: Echocardiographic evaluations were performed before the operation and after I Seal; and the results were compared with those of a control group. Left ventricular diameters and function, left ventricular mall thickness, and left ventricular mass were assessed by echocardiography. Results: Group I patients had a significantly lower maximum and mean transprosthetic gl adient than the other valve groups (P =.001), One year after operation there was a significant reduction in left. ventricular mass for all patient groups (P<.01), hut mass did not reach normal values (P =.05). Although the rate of regression in the interventricular septum and posterior wall thickness differed slightly among groups, their values at follow-up were comparable and still higher than control values (P =.002), The ratio between interventricular septum and posterior wall and the ratio between wall thickness and chamber radius did not change significantly at follow-up, Conclusions: Because the number of patients was relatively small, we could not use Left ventricular mass regression after 1 Scar to distinguish among patients undergoing aortic valve replacement for aortic stenosis by means of valve prostheses with different hemodynamic performances