您现在的位置: VOA美国之音 >> VOA双语新闻 >> 双语新闻 >> 正文


更新时间:2020-3-26 8:13:40 来源:本站原创 作者:佚名 浏览:

One Day, Growing Spare Parts Inside the Body

LOS ANGELES — Dr. Tracy Grikscheit held a length of intestine in her gloved hands, examining it inch by inch as if she were checking a bicycle tube for leaks.

洛杉矶——特蕾西·格里克施特医生(Tracy Gritscht)戴手套的手中持有一段小肠,她一段一段地仔细检查,如同在检查一个漏气的自行车轮胎一样。

The intestine was still attached, at one end, to Mark Barfknecht, a 1-year-old whose pink cheeks belied the reason he was lying on an operating table at Children’s Hospital Los Angeles. Born three months premature, Mark had developed a disorder that affects up to 10 percent of babies who weigh about 3 pounds or less at birth, causing some of their intestinal tissue to die. Mark’s case was so severe that most of his intestines had been removed.

这段小肠的一端仍连接在一岁小男孩马克·巴夫克内施特(Mark Barfknecht)的体内。他的小脸红扑扑的,这掩盖了他正躺在洛杉矶儿童医院的手术台上的原因。马克早产三个月,在出生时体重不足3磅(合1.36公斤)的婴儿中,有多达10%的婴儿会罹患一种疾病,导致部分患儿的肠组织坏死,马克就遇到了这种情况。他的病情很严重,大部分的小肠都已被切除。

Now Dr. Grikscheit, a surgeon, was trying to determine how much of the rest she could save.


Dr. Grikscheit is renowned for her skill in treating infants like Mark, whose only way to survive may be as what she calls a “short gut kid” — left with too little intestine to absorb food normally and forced to get nutrition through a needle into the bloodstream.


But devoted as she is to saving children in the operating room, Dr. Grikscheit is equally determined to find a better solution than the intravenous feeding, possibly for life, that such patients face. Much of her time is spent in her laboratory across the street, at the hospital’s Saban Research Institute, where she is working with her research team to find a way to make replacement intestines for infants like Mark, using the body itself to nourish and push the engineered tissue to grow.

格里克施特医生一面在手术室努力拯救患儿,一面还在决意找到一种比静脉营养更好的解决方法,否则这类患者有可能终身离不开静脉滴注营养液。大部分时间,她都泡在医院对面的沙班研究中心(Saban Research Institute)实验室里,和她的研究团队一起为像马克这样的患儿寻找构建替代小肠的方法,他们要通过利用机体本身去为组织提供营养,并促进其生长。

Dr. Grikscheit’s work is at the forefront of efforts in laboratories around the world to build replacement organs and tissues. Although the long-sought goal of creating complex organs like hearts and livers to ease transplant shortages remains a long way off, researchers are having success making simpler structures like bladders and windpipes, thanks to advances in understanding stem cells — basic cells that can be transformed into other types within the body — and to the development of innovative techniques.


So far Dr. Grikscheit has concentrated on growing rat, mouse and pig intestinal tissue in laboratory animals. But she has recently had success in growing human intestinal tissue, using donor cells, and is beginning to study how to develop the technique for human patients. There are many hurdles, and human testing is still years away, but she has a surgeon’s confidence that the technique will work.


“We have a huge problem that if we solve it, it will change the future for a lot of children,” she said.


In her lab, her team is currently working with mice. They first remove good intestine from the animals, cut it up and treat it with enzymes and other compounds to form clusters of mixed cells, including stem cells that are found in the absorptive lining of the intestine and others that make up the tougher connective tissue.


The clusters are then placed on a piece of porous biodegradable plastic, about the size and shape of the eraser on a pencil. The plastic serves as a scaffold, supporting the cells and orienting them, which has the effect of making the lining grow inward while the connective tissue grows on the outside.


This kind of seeding of scaffolds with cells is a common approach in the field of regenerative medicine, also known as tissue engineering. But in most cases, the goal is to swap the bad organ — a windpipe, for example — with the engineered replacement, where it can grow into its permanent position in the body.


Dr. Grikscheit has had success in the lab with a different method, using another part of the body to nourish the replacement as it grows.


She and her team sew the bundle of cells into the mouse’s omentum, a membranous fold inside the abdomen. There, the bundle is surrounded by blood vessels that supply nutrients, helping it to grow. The plastic eventually dissolves as the bundle grows into a hollow ball of tissue. A few weeks later, Dr. Grikscheit and her researchers remove the ball from the omentum — for study, to better understand how the regenerative growth occurs. The tissue has all the components of intestines, including the lining, muscles, nerves and blood vessels.


In earlier studies in rats, Dr. Grikscheit went a step further, splicing the tissue into the digestive tract of animals that had had much of their intestines removed. Rats with the engineered intestine recovered more quickly than those without it.


By combining this kind of lab work with her surgical practice, Dr. Grikscheit is doing what she has always thought surgeons should do. “You move medicine ahead,” she said.


Dr. Grikscheit, 40, who is intense and energetic and easy to spot in the hospital in her strawberry-print surgical cap, says she always knew she was going to be a surgeon — she told her great-grandmother as much when she was 6, growing up outside Salt Lake City. During her training she gravitated toward pediatric surgery. Compared with adults, children were works in progress — sometimes imperfect ones.


“The really fascinating thing is how to put something together that came out wrong and make it as right as possible,” she said.


She envisions a day when her approach moves beyond the lab to the operating room. Future operations to remove dead intestine from a baby — or from other patients with severe intestinal damage — would include an additional step: a little bit of good intestine would be sent to a table nearby, where technicians would quickly prepare a bundle for immediate implantation in the patient’s omentum.


The patient might have to be on intravenous nutrition for a month or so while the intestine grows, but eventually could be weaned off it after the new tissue was harvested and sewn in.


Not much new intestine would be required. “You only need to engineer an organ up to the point where you fix the missing function,” Dr. Grikscheit said. Even a couple of inches might be enough. “That will tip them back over into having enough absorptive function to get off of I.V. nutrition and live a full life.”


Such a remedy is still too far off for Mark Barfknecht.


Back in the operating room on that day earlier this year, Dr. Grikscheit and a fellow surgeon, Dr. Demetri Merianos, continued to examine Mark’s intestines. Without the ability — yet — to regenerate the child’s intestinal tissue, they were focused on keeping as much of the damaged organ as possible.

让我们再回到今年早些时候的那一天,在手术室,格里克施特医生和手术助理迪米特利·梅里亚诺斯(Demitri Merianos)医生继续检查马克的小肠。那时还没有再生小儿小肠组织的技术,他们集中精力保留尽可能多的损坏的器官。

“This is coming down to something narrow,” Dr. Grikscheit said as she felt the tissue, which she and Dr. Merianos had spent the better part of two hours delicately freeing from Mark’s abdominal cavity, smoke rising from the cauterizing blade as they cut through places where it had adhered to the liver after an earlier surgery.


To ensure that they could properly reconnect Mark’s digestive tract at the end of the four-hour procedure, they tagged the open ends of the intestines with surgical thread and clamps of different kinds, and jotted notes on the paper surgical drapes about which end went where.


“I don’t care for this,” Dr. Grikscheit said, frowning. She and Dr. Merianos agreed that a 3-inch length of intestine would probably have to be cut out.


For a baby who had about only 15 inches of small intestine remaining, that was not good news.


But Mark, his mother says, is a survivor.


“Oh yeah, he’s been through it,” Karen Barfknecht said a few hours before the surgery, after his father, Michael, had detailed all the procedures their son had endured. “He has a cry that just makes you feel so bad,” Ms. Barfknecht said. “You’ll do absolutely anything for him.”


No one knows precisely what triggers the disorder, but prematurity plays a role.


Called necrotizing enterocolitis, the disorder can crop up suddenly in the weeks after birth. In about a quarter of cases, the death of intestinal tissue ultimately proves fatal. For many of the rest, emergency surgery to resect, or remove, dead tissue creates new problems.


“When I look at their intestine, I already know that to save their life I’m going to resect more than they can manage,” Dr. Grikscheit said. If the amount of dead tissue exceeds 75 percent of the total, the child will almost certainly be forced to get nutrition intravenously, which over the long term can damage the liver. Other operations, up to and including an intestinal transplant, may be needed, which bring other risks.


Mark is near that 75 percent threshold, so doctors at another hospital closer to his home in Indio, Calif., had put him on the special intravenous feeding, called total parenteral nutrition, or T.P.N., months before; now his liver is starting to suffer.

马克很靠近75%的阈值,因此在这次手术几周前,他被送去一家离加州印第奥市他的家较近的另外一家医院,医生让他接受特殊静脉营养,也称作全肠外营养(total parental nutrition, 简称TPN)。现在他的肝脏已经开始受到损伤。

He has required such a high level of care that Mr. Barfknecht quit his job as a mechanic. Still, Mark has been in either a hospital or a convalescent facility almost all his short life; his big sister has hardly spent any time with him.


“We want him home,” his mother said. “We just want him home.”


That is Dr. Grikscheit’s goal, too. But before she and Dr. Merianos could determine whether Mark had enough good intestine to be weaned off the intravenous feeding eventually, they had to assess the narrow, diseased section they had found earlier. They looked at it again, weighing the options. They checked and rechecked their notes scribbled on the drapes.


“Unfortunately, sayonara,” she said, directing Dr. Merianos to begin cutting.


But that was the last piece of bad news for Mark. As the doctors continued to look at the remaining intestine, they grew increasingly optimistic that he would have enough. If so, they would stitch the remaining pieces together and reconnect everything from the stomach to the colon. Mark will have to continue the intravenous nutrition for some time, but eventually he should be able to eat normally.


“I think we’ll make it off T.P.N. and get him home,” Dr. Grikscheit said.


It is the infants who are not so fortunate — for whom surgery could not do enough — who motivate Dr. Grikscheit to keep working on a way to make new tissue.


“You keep finding these kids, in my case, who die,” she said. “I think it would be very frustrating to keep beating your head on the same problem and saying, ‘Well, that’s too bad.’ ”