Opioid peptides: the heroin within?

Screen Shot 2014-11-07 at 10.36.51 PMBy: Emily Brown PhD

If you were to hear the words ‘opioid peptides’, they might not trigger much within your brain, other than that the former sounds a bit like opium and together they sound quite scientific. Opium (also known as poppy tears) is a dried substance or latex that originates, as the alternative name suggests, from the opium poppy. Beautifully intricate pipes of bamboo, ivory, silver, jade and porcelain have been carved over the centuries and used to vaporise and inhale the latex traditionally obtained by scratching immature poppy seed pods by hand. Numerous Empires including the Egyptian, Greek, Roman, Persian and Arab made widespread use of the drug, which was then the most potent form of pain relief available. This analgesic property is conferred by morphine, which constitutes approximately twelve per cent of opium and is chemically processed to produce heroin. Commonly known by the street names H, smack, horse and brown, among others, the effects of heroin will be well known by any ‘Trainspotting’ fans. What writer Irvine Welsh did not reveal, however, is that opiates such as heroin mimic the effects of naturally occurring molecules that can be generated inside our own bodies.

Opioid peptides are small molecules that are produced in the central nervous system (the brain and spinal cord) and in various glands throughout the body such as the pituitary and adrenal glands. These peptides can be divided into three categories (enkephalins, endorphins, and dynorphins), depending on the type of larger precursor molecule from which they are derived. Opioid peptides function both as hormones and as neuromodulators; the former are secreted in the blood system by glands and are delivered to a variety of target tissues where they induce a response, while the later are produced and secreted by nerve cells (or neurons) and act in the central nervous system to modulate the actions of other neurotransmitters.

Neurons are electrically excitable cells that process and transmit information through electrical and chemical signals that travel via synapses, specialised connections with other cells. These signals are transmitted across a synapse from one neuron to another by neurotransmitters. By altering the electrical properties of their target neurons and making them difficult to excite, opioid peptides can influence the release of various neurotransmitters.

Through these two different mechanisms, opioid peptides can produce many effects including pain relief, euphoria and altered behaviour such as food and alcohol consumption. The apparent connection between exercise and happiness has been explained at least somewhat by the release of endorphins, for example. Exercise is commonly recommended as a strategy for stress-relief and mood improvement, but less widely accepted forms of therapy might also be connected to opioid peptides. Evidence suggests that pain relief induced by acupuncture results from stimulation of opioid peptides – these peptides act through receptors on their target neurons, and chemicals that inhibit opioid receptor function have been found to reverse acupuncture-induced analgesia. Painful, stressful or traumatic events or stimuli can induce the release of opioid peptides, with the resulting euphoria and pain relief making the sufferer less sensitive to noxious events. Opioid peptides have been reported to affect the release of specific neurotransmitters such as dopamine and serotonin, but the response of the neurons that receive opioid-peptide stimulation depends on their excitatory versus inhibitory nature, making the outcome difficult to predict.

The words ‘opioid peptides’ may not have left a dazzling feeling of recognition within your memory upon first encounter, but these peptides act within the brain and wider body to influence a number of important functions. Although it is not easy to predict the effect of neuromodulators that alter the release of other neurotransmitters, there is little question that opioid systems play a critical role in modulating a large number of sensory, motivational, emotional and cognitive functions. Alterations in opioid peptide systems may contribute to a variety of clinical conditions, including alcoholism, obesity, depression, diabetes and epilepsy. Many questions still remain, particularly those concerning the exact role of opioid peptides produced within the body in relation to addictive and emotional behaviour and psychiatric disorders. Since these disorders are typically of a complex nature, seeking the answers to these questions is not a simple feat. Advances in genetics and genomics research that aim to explain function by studying our DNA are helping to pave the way. But perhaps if there is one thing that can help motivate our talented scientists to reach their challenging goals, a healthy dose of opioid peptide might be just the thing.

Emily Brown PhD

Bacterial heroes and viral villains – snipping the way to the future

spider man By: Emily Brown, PhD

The most recent Spider-Man film grossed nearly $800 million worldwide, and cinemas are set to unleash a new and improved Spider-Man 2 this May. Whilst the great charm and beauty of actors Tobey Maguire and Kirsten Dunst most likely helped fuel the initial success of the film series, our fascination with the part-man-part-beast concept has spanned far beyond the glitter of Hollywood. Peter Parker’s DNA may have flashed before our eyes as his body assimilated superhuman powers, but the idea of genetic modification existed in both the fantasy and real worlds long before the advent of such impressive computer generated images. Wikipedia, arguably the source of all valuable knowledge, lists 85 characters, comics or films that involve some form of genetic engineering. Ranging from the less suspecting (Tracy Strauss, Madelyn Pryor, Julian Bashir) to the more ridiculous (Shaggy Man, Venus Bluegenes, The DNAgents), these characters share in common a possession of extraordinary powers, and sometimes the adoption of highly colourful and figure-hugging body suits.

But how exactly is the acquisition of such power explained by the respective literary proponents? Peter Parker’s body-wide changes are initiated by radioactive mutagenic enzymes present in the venom of the lethally irradiated spider un(fortunate) enough to bite him. Not long after this bite does Parker start to display spider-like characteristics -superhuman strength (the jumping spider can for example hold 170 times its own body weight), reflexes, balance, a subconscious sense of danger (the so-called ‘spider-sense’) and the ability to cling to any surface. No doubt all highly desirable traits. But as unlikely as this might sound, the suggestion that enzymes can alter DNA is not such a wild idea. Genetic modification, the direct manipulation of an organism’s DNA, requires the DNA to first be cut so that it can then be joined or spliced together with DNA from another source. A restriction enzyme is an enzyme that cuts DNA at or near specific recognition nucleotide sequences, known as restriction sites. These ‘molecular scissors’ are routinely used for DNA modification in laboratories and are a vital tool in molecular cloning.

Over 3000 restriction enzymes have been studied in detail, and more than 600 are available commercially. Whilst the idea of an irradiated spider might seem far-fetched, restriction enzymes are naturally found in bacteria and archaea (a group of single-celled microorganisms). Here they provide a defence mechanism against invading viruses; the foreign viral DNA is cut up by the restriction enzymes, while the host DNA is protected by an enzyme that modifies the DNA and blocks cleavage. The term restriction enzyme originates in fact from the studies of phage l (a virus that infects the bacteria Escherichia coli, better known as E. coli). In the early 1950s, in the laboratories of Italian scientists Salvador Luria and Giuseppe Bertani, it was discovered that a phage could grow well in one strain of bacteria, yet fare significantly worse in another. In the latter case, the bacterial host cell was evidently capable of reducing the biological activity of the virus (in a process known as restriction), although the exact mechanism remained unclear. This mystery was solved in the 1960s, this time in the laboratories of Werner Arber and Matthew Meselson, where it was shown that the restriction is caused by enzymatic cleavage of the phage DNA. Unsurprisingly, the enzyme involved was termed a restriction enzyme.

The restriction enzymes studied by Arber and Meselson were type I restriction enzymes that recognise a restriction site, but cleave the DNA at a non-specific point located some distance away. Another decade later, in 1970, Hamilton O. Smith, Thomas Kelly and Kent Welcox isolated and characterised the first type II restriction enzyme, HindII, found in the bacteria Haemophilus influenzae. This type of restriction enzyme differs in that it cleaves DNA at the restriction site, and in doing so serves to be much more useful in the laboratory. Cohesive end cutter type II restriction enzymes cut the two DNA strands (most DNA molecules are double-stranded helices) at different points within the restriction site. The result is a staggered cut that generates a short single-stranded sequence or overhang, known as the sticky or cohesive end. These overhangs become very useful in genetic engineering, since the unpaired nucleotides that make up the sticky end can pair with other overhangs made using the same restriction enzyme. If DNA from two different sources are cut with the same enzyme, it is highly probable that the two DNA fragments will splice together because of the complementary overhang. The product is a recombinant DNA molecule, composed of DNA from two different origins, created by DNA technology.

Since the first discovery of restriction in the 1950s, the use of recombinant DNA technology has become commonplace, as new products from genetically altered plants, animals and microbes have become available. In 1997, Dolly the sheep dominated the headlines as the world’s first animal to be cloned from an adult cell. Whilst her early death may have left some scientist ‘wooly’ on the cloning issue (thanks to Jim Giles and Jonathan Knight for this clever pun), the technology has since gone on to bring advances to various areas of life, from treatments for cancer to transgenic insect-resistant crops. As far as is known however, we are yet to see the technology confer super-human strength and power. Thankfully we are not currently at risk of encountering deadly villains and their counterpart heroes on a daily basis, sporting their ridiculous costumes and egos. Instead, we are surrounded by the unseen heroes, the special enzyme molecules that battle to fight invading viral villains, and the scientific geniuses that brought them to light. Mr Muscle may argue that bacteria are best destroyed, but we should also thank these microorganisms for opening a whole new realm of our world, whatever that world may hold.

Emily Brown, PhD

Naked mole rats are living long cancer-free lives, and now we know why

moleBy: Chloe Nevitt
It’s not surprising to hear the word rat associated with scientific research. Of course, most people immediately imagine the red-eyed furry white lab rat that runs through mazes. However, recent cancer research has focused the microscope on its’ furless cousin, the naked mole rat.
These sausage-like creatures live in huge underground colonies, centered on a queen, similar to ants. Some of the moles are responsible for foraging for food for the colony, while others tend to the queen. While blind mole rats do possess eyes, they are located beneath the skin and fur, and instead they rely on sensitive hairs found on the ends of their snouts to find their way.
The naked mole rat also has an astonishingly long life span, upward of 30 years, and is apparently cancer-resistant. Not a single incidence in cancer in the African rodent has been found, ever. Compared to their lab rat cousins, whose life spans hover around four years and are extraordinarily cancer prone – a 47% cancer rate, these curious observations make the naked mole rat a novel model for new cancer-fighting methods.
Scientists went searching for the answer. A team at the University of Rochester attempted to trigger cancer in naked mole rats by infecting them with viruses known to commonly cause cancers in mice and rats. Dr. Gorbunova and Dr. Seluanov, a husband-and-wife team of biologists at Rochester, then tried growing the cells in culture mediums. Here, they began to uncover the naked mole rats’ secret.
The naked mole rats cells stopped growing at a third of the density that mouse cells do. They also noticed that the nutritional medium they were in, after a few days, turned into syrup. “We need to find out what this goo is,” said Dr. Gorbunova. Their postdoctoral researcher, Christopher Hine, discovered that the goo was composed of a large polymer called Hyaluronan.
The team at the University of Rochester found, simultaneously as scientists at the University of Haifa, was the Hyaluronan in naked mole rats was five times as large as human Hyaluronan. This sugar was called high-molecular-mass Hyaluronan (HMM-HA). HMM-HA is a form of Hyaluronan, a polysaccharide found in the extracellular matrix and soft connective tissue. Commonly found in humans, it is responsible for signaling and elasticity.
HMM-HA secretion by naked mole rat cells has been shown to prevent overcrowding and the formation of tumours. “Experiments showed that when HMM-HA was removed from naked mole rat cells, they became susceptible to tumours and lost their contact inhibition.” Explains Prof. Eviatar Nevo, from the Institute of Evolution at the University of Haifa.
Contact inhibition when observed in normal cells is the arrest of growth when two cells’ plasma membranes touch. Cancer cells, on the other hand, will continue to grow until overtaking the other cells, ultimately creating a tumour.
HMM-HA in naked mole rats also accumulates in abundant amounts, owing to decreased enzymatic degradation and increased synthesis by a protein called HAS2. On a genetic level, theHas2 naked mole rat gene differs in sequence by only two amino acids, this substitution perhaps the reason for its’ high output levels.
When the scientists shut down this gene in naked mole rats and then inserted a cancer-causing virus, the hyaluronan-free cells multiplied uncontrollably. The researchers moved these cells into mice and watched as tumours developed. The new cells were just as cancer susceptible as the mouse, or human cells.
Researchers owe the increased HMM-HA as necessary for subterranean life. “If you grab an animal, it feels like you’re removing their skin,” Dr. Seluanov said. Stretchy skin is necessary for moving around in underground tunnels. And HA provides this elasticity.
While the questions of how exactly HA fights cancer and how increased levels of HA will react in human and mice cells have yet to be answered, we are perhaps on our way for new types of cancer prevention.

Epigenetics – Could the central dogma be in danger?

DNA moleculeIn 1859, Charles Darwin set out his theory of evolution by natural selection, a theory that consists of three vital components – variation, inheritance and differential reproductive success. We are not all as beautiful as Angelina Jolie, for example (number one on the Official Top 30 World’s Most Beautiful Women of 2013), but her biological children likely will be, and no doubt many a man would be willing to father those children. Parents and offspring can share more than looks, however, and we can only hope that Angelina’s biological daughters are not also at risk of developing breast cancer. Without inheritance, adaptations (such as good looks), and maladaptations (for example heritable cancer risk) alike, could not be passed on from one generation to the next.  A century’s worth of work aimed at understanding this process of inheritance, including experiments with peas and bacteria viruses, finally culminated in 1953, when James Watson and Francis Crick revealed the structure and properties of DNA, the molecule that carries genetic information from generation to generation.

Eight years later in 1961, a young biochemist Marshall Nirenberg made a breakthrough discovery that allowed the genetic code – ‘the blueprint for life’ – to be deciphered. According to the code, the great diversity of life on our planet is generated in a remarkably simple manner – a 5-letter alphabet (the bases or nucleotides A, C, G, T and U), written to form 64 three-letter words (codons, such as AGG), codes for twenty amino acids that serve as the building blocks of proteins, and in turn the building blocks of life. Discovering the genetic code allowed us to understand how the variation essential for Darwin’s theory of natural selection could arise. Mutations that cause a change of a base from an A to a C, for example, can cause a different amino acid to be produced and a different protein to be built. This might sound trivial, but such minor changes in the genetic code can have dramatic impacts on an organism – how it appears physically, how it behaves, how likely it is to develop cancer.  Who we are as humans and our uniqueness relative to others appeared to be controlled quite tangibly and inflexibly by what is written in our DNA.

It almost seems foolish to have believed it so simple. The burgeoning field of epigenetics has more recently forced us to see the DNA world in a completely different light. Epigenetics (‘epi’ = ‘on top of’ or ‘above’) is the study of changes in gene activity that are not caused by changes in the DNA sequence. You can see the dilemma here – modification of gene function without change in the nucleotide sequence surely breaks the previously accepted rules. If DNA is the blueprint for life, how can we explain changes to ‘life’ that are not prewritten in the code? The term ‘epigenetics’ was first coined in 1942 by Conrad Hal Waddington, a man interested in bridging the gap between genetics and embryology (the science of the development of an embryo). Waddington considered development to be an ‘epigenetic process’ – a phenotype (such as Angelina’s looks) results not only from genetic processes but also from interactions with the external environment (such as diet or stress). Whilst Waddington’s work expanded the classical genetic vision on the phenotype, his concepts were accused of being ‘rather fuzzy at the edges’.

The definition of epigenetics has since been refined, and we now know that although epigenetic modifications can arise through various different mechanisms, they usually involve chemical changes that affect gene expression (gene expression is the process by which the information contained within a gene is translated into a functional gene product). The most studied epigenetic modification is DNA methylation. Along the human genome there are millions of sites (known as CpG sites) where methyl groups (a carbon atom bonded with three hydrogen atoms) can attach and affect the expression of nearby genes. These methyl groups act as tags on the DNA, controlling how strongly the genes are switched on. This methylation process forms an integral part of our development as human beings. When sperm and egg collide, the process of cell division and specialisation begins through the activation of certain genes and the inhibited expression of others. In this sense, epigenetics can be seen as the study of the chemical reactions that switch on and off certain parts of the genome at strategic times, and the factors that influence these reactions.

Epigenetic changes may last through cell divisions for the duration of a cell’s life. For cell specialisation to occur, as during development, any previous epigenetic tags added to the cell’s DNA need to be erased through a process of ‘reprogramming’, returning the cell to a genetically ‘blank state’.  It is possible, however, for some of these tags to escape reprogramming and pass unchanged from parent to child. Recent debate over the definition of epigenetics has in fact related to whether or not epigenetic modifications are heritable, and whether they are required to be so. If epigenetic modifications were to occur in sperm, for example, these could potentially be transmitted from father to offspring. A recent study published by researchers at McGill University has shown that a male mouse’s diet can affect the methylation in sperm of genes implicated in the development of chronic diseases such as cancer and diabetes. Although only two of these differentially methylated genes were differentially expressed in the placenta of the male’s offspring, the study nevertheless highlights the importance of understanding the potential mechanisms underlying inter-generational disease transmission.

If parents are able to pass environmental information, in the form of epigenetic modifications, on to their offspring as well as their genetic code, epigenetic inheritance adds a whole new dimension to the modern picture of evolution. For over a hundred years we have accepted that the genetic code changes slowly, through the processes of random mutation and natural selection. Epigenetics creates the possibility for a much more rapid response to signals from the environment. It requires a completely different concept of information transfer – experiences had generations ago, such as a famine during your grandmothers time, could influence the way that your body develops, even in today’s more plentiful western world. Having said this, the epigenome (the combination of DNA plus epigenetic tags) has the potential to remain flexible as your environment continues to change, and may allow continual adjustment of gene expression accordingly. All this could happen without a single change in the DNA code. Could nurture have finally gained a place over nature? Perhaps there is hope for those on the quest for world-renowned beauty after all.

Emily Brown PhD

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