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Month: August 2018 (page 1 of 2)

08.31.2018

the persistent myth of the super sperm

sperm egg fertilization

Fertilization occurs when a sperm cell fuses with an egg.

Over at Aeon, Robert D Martin debunks a persistent myth of biology. Many people, including scientists, believe that during fertilization, sperm are in competition, racing to be the first to fertilize an egg. Because sperm competition is observed in chimpanzees and other mammals closely related to humans, people think that the same holds true for men. But Robert points out all the evidence against this theory.

First, human sperm contains a higher proportion of deformed or abnormal sperm compared to chimpanzees. If sperm were in competition to fertilize an egg, you would expect for there to be fewer nonmotile sperm than are observed. Chimpanzees, have relatively few abnormalities in their sperm cells.

Secondly, much of the sperm’s transport to the ovary is achieved passively. Through the womb and oviducts, a wafting and pumping motions propel sperm through the female tract. And in fact much of the selection of intact sperm is happens because of  environment in the woman’s vagina and cervix.

Many sperm do not even make it into the neck of the womb (cervix). Acid conditions in the vagina are hostile and sperm do not survive there for long. Passing through the cervix, many sperm that escape the vagina become ensnared in mucus. Any with physical deformities are trapped. Moreover, hundreds of thousands of sperm migrate into side-channels, called crypts, where they can be stored for several days. Relatively few sperm travel directly though the womb cavity, and numbers are further reduced during entry into the oviduct. Once in the oviduct, sperm are temporarily bound to the inner surface, and only some are released and allowed to approach the egg.

Robert continues from there, explaining what happens when too many sperm reach an egg and how cervical mucus can contain and release viable intact sperm for up to 5-10 day. The essay is quite interesting and well worth a read, so I won’t spoil it all. It’s an interesting counterargument to the manly notion that the best sperm gets the egg.

08.30.2018

the problem with cancer cells

HeLa cells cancer research

HeLa cells, cancer cells originally isolated from Henerietta Lacks, are among the most widely used cell lines for scientific research

Cell lines are frequently used in cancer research studies. They are pretty easy to maintain and they grow fast. The cell lines give us insight into some of the cellular pathways involved in tumor biology. They are often used as early-stage screens for potential cancer therapeutics, even though scientists know that they do not exactly share the same biology as an actual tumor. Cancer cells grow rapidly and they generate many mutations in the process. In a few cycles, the cells that you have in culture are different genomically than the cells that you started with. But still, having some information on what cells maybe doing in a tumor is better than no information at all.

Now Derek Lowe calls attention to a new study in Nature, which points out a potential problem with these cell lines in culture. In this new paper, the researchers found that not only are cancer cells different from the tumor that they started from, but there can be many differences within a strains of any given cell line.  When they observed 27 strains of the MCF7 breast cancer line, the discovered rapid genetic diversification. They then looked at 13 additional cell lines and saw similar results. The genetic differences changed activation of gene expression, cell morphology and cell proliferation.

Derek Lowe sums up what this means for compound screening in cancer cell lines:

At least 75% of the compounds that showed strong inhibition of one MCF7 line were totally inactive against others. That’s going to confound experiments big-time, and this paper is a loud warning for people to be aware of this problem and to do something about it.

08.28.2018

is there really no safe level of drinking?

drink more than one per day

Researchers insist that results of a recent meta-analysis show that there is no safe level of drinking, but he scientific community remains unconvinced.

Last week, the Lancet published a study that concluded “the level of consumption that minimises health loss is zero.” The researchers state that there is no level of alcohol consumption that does not put your health at some increased risk. This of course was picked up by major news networks like CBS and splashed as a leading headline.

But there has been some pushback on these claims and many members of the scientific community are not convinced.

First off there are methodological issues.  There was no way for the researchers to remove or control for confounding variables. Their methods could only control for age, sex and location. If there were other variables like exercise, smoking, or socio-economic status, they could not be controlled for in this study. Without controlling for these variables, the researchers could be leaping to causal conclusion that is not supported by the data. As Aaron Caroll in the NY Times writes:

But when we compile observational study on top of observational study, we become more likely to achieve statistical significance without improving clinical significance. In other words, very small differences are real, but that doesn’t mean those differences are critical.

–Aaron E. Carroll

Secondly, the risk increase that they observed from having one drink per day was an increase of  alcohol-related health problems to 918 per 100,000 people from 914 per 100,000. Only 4 out of 100,000 people or (0.004% of people) who have one drink a day may have a alcohol-related health problem. At two drinks per day the rate increased to 977 per 100,000 persons. 63 out of 100,000 people had alcohol-related issues, which is only a slight increase in risk. The vast majority of drinkers according to their results had no deleterious effect to their health.

There are  other criticisms. But, for those of us who imbibe,  David Spiegelhalter offers this comparison to demonstrate how unconvincing the data are as a support for recommending abstinence:

The paper argues that their conclusions should lead public health bodies “to consider recommendations for abstention”.

But claiming there is no ‘safe’ level does not seem an argument for abstention. There is no safe level of driving, but government do not recommend that people avoid driving.

Come to think of it, there is no safe level of living, but nobody would recommend abstention.

Many studies continue to show that the having one or two drinks per day is not harmful and could have potential health benefits for heart disease. So until more convincing evidence get published… CHEERS!

 

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