The pre-clinical drug development process frequently uses in vitro and in vivo animal models to try and predict the safety and efficacy of drugs in humans. The selection of animal species can have a pronounced influence on the outcome and potential fate of the test drug. When penicillin was discovered, researchers firstly chose to test it in mice and the encouraging results led to its use in humans. Had the researchers chosen hamsters or guinea pigs instead as their research model, penicillin would likely have been discarded, as it is lethal to both species. Conversely, many drugs have been extensively scrutinised in preclinical animal tests only to be withdrawn after causing unpredictable and unacceptable side effects in human trials.
Biopta’s ability to perform comparative in vitro studies in multiple preclinical species, including human tissue, highlights potential species differences early in the drug development process. This has become especially important for translation of preclinical safety studies to patients and to improve the prediction of efficacy by using phenotypically-relevant fresh diseased human tissue.
For example, the 5-hydroxytryptamine (5-HT, serotonin) pathway is more prominent in the coronary artery function of human than in dogs, a standard preclinical safety species and pig, a favoured cardiac model species.
Figure 1 shows that in coronary arteries there are significant differences in the potency of 5-HT (5-hydroxytryptamine, serotonin) in human, dog and pig coronary arteries.
In subcutaneous resistance arteries, human and non-human primate species differ significantly (10-fold) to rodent in their sensitivity to the vasorelaxant acetylcholine (Ach), which reflects species differences in the expression of nitric oxide synthase enzymes (NOS enzymes).
Figure 2. In this test of eNOS activity, we elicited vasodilatation of isolated small arteries by adding ACh, which released NO from the endothelium and caused roughly 80% relaxation in human arteries and the response was found to be similar in arteries from non-human primates. Arteries isolated from rats however showed a less sensitive response to Ach.
Although animal models have a vital part to play in the testing of potential new drug therapies, early cross-species comparisons with fresh functional human tissues would increase confidence that the selected animal models are a relevant model and display similar responses to that observed in humans.
Biopta has been providing contract research services to the pharmaceutical industry since 2002 and has established itself as the world leader in the use of fresh human and animal tissues to better predict drug activity prior to clinical trials. The clear commercial benefits of reducing risk by generating early human data on safety, efficacy and absorption are making human tissue research a routine part of drug development. Biopta’s expertise in all areas of human tissues research including sourcing, handling and experimenting on human tissue allows us to act as your “Human Tissue Research Department”.
 Yale J Biol Med. 1974 September; 47(3): 166–181.
The use of fresh human native tissues and cell lines are essential to research advancements. Both have their unique benefits. Cell lines are easy to grow and maintain, amend for genetic manipulation and generally are uniform in their responses in assay systems. These benefits have made them invaluable for drug screening programs, allowing numerous compounds to be tested in the search for drug candidates. Cell lines are, however, a contrived experimental system and one should be cognizant of the risks in extrapolating the properties of a compound in these systems relative to that in the native human setting. This is particularly true for receptor agonists where the potency of a molecule is the product of the compounds property and that of the tissue in which it is tested. Clearly, native intact human tissue would be advantageous in this situation; however, for most experimentalists, human tissue availability is limited and comes with viability concerns. Biopta, through its extensive network of quality tissue suppliers and highly committed staff, (10 years’ expertise in the logistics of accessing human tissue, and highly specialised scientists on-hand 24/7) have solved these issues and for the past decade have led the way in human tissue research.
By using human fresh tissue, both healthy and diseased, Biopta have de-risked the drug discovery programs of numerous companies. Furthermore, by embracing the inherent intrinsic variation between patient responses, we can now advance the utility of human fresh tissue in providing functionality (phenotyope) linked to genotype, a key step in the development of personalized medicines. The decision to use either cell lines or native fresh tissue should ideally depend upon the question one is trying to answer. If the question centres on intrinsic functionality of a single protein, potential binding partners or specific defined signalling pathways, cell lines have been the standard choice; however, if one wishes to look at drug compounds in a complex system representative of the clinical physiology, then fresh human tissue research is a must.
Why should is fresh human so important when translating drug responses to the clinic?
Having a drug target in its native setting allows the following:
- The target is in its natural environment, coupled to its pathways as it would be in a clinical setting.
- The potency of an agonist is dependent on receptor number/efficiency of the resultant coupled system. The potency value for an agonist in this system is more akin to the potency in humans and is more accurate for defining the dose required for clinical efficacy. High expression cloned systems will report higher potency values.
- The inaccuracies of cell lines will be compounded if disease tissue shows different coupling from healthy tissue; something that Biopta can often compare.
- Few compound/target interactions are neutral in effect. Antagonists can show internalization properties (act as agonists for switching receptors off) and so pathway coupling holds true for these antagonists as well as conventional agonists.
In tissue, targets exist in a complex cellular system that encompasses interactions from many cell types. Therefore, even while co-culture experiments may tell us nicely of the changing biology between cell interactions between differing cell types, the correct ratio of cell types and often the need for appropriate extracellular matrix can affect the outcome of these experiments.
Cell lines demonstrate what can happen whereas native tissue shows what does happen.
There is no arguing that cell lines are a stable system when defined in particular terms. However, events such as genetic variation occurs when cells are cultured such that gene and protein expression patterns vary with passage number, causing diversion, not only from native physiology, but also between the cell lines themselves. Even when using primary cells, de-differentiation and changes in morphology and pharmacology can occur in a matter of days or even hours and, still, important interactions between various cell types which exist in tissue are lost. Nevertheless, the ability of cell lines to grow continuously with an unlimited lifespan makes them a cost effective and relatively uniform system with which to test drug compounds and cofactor interactions. They are also highly susceptible to transient gene transfer (transfection), allowing researchers to better understand specific protein/gene function.
Native human tissue, however, represents the most physiological experimental system available short of clinical trials. It allows direct investigation into human tissue functionality and pharmacology, thus giving the most accurate data regarding drug efficacy or mechanism of function not just on an individual, but throughout a population. Only in human tissue is it possible to measure drug effects in vitro on systemic processes such as muscle tone modulation and true multicellular inflammatory processes. As not all individuals respond similarly to drug treatments, having tissue that characterizes this inter-patient variance best demonstrates how a drug will affect the general populace overall. Through use of diseased tissues, researchers also get the most accurate representation of varying human pathologies allowing for treatment identification. As tissue has a limited lifespan, experiments must be done promptly or on preserved tissue.
At Biopta, we only use fresh, not frozen, tissue, to create the most physiologically relevant drug-testing systems available to the pharmaceutical industry.
The drugs don’t work (sometimes)
Leukotriene antagonists are extremely successful drugs for the treatment of asthma. By successful, I mean that they work in most patients; in fact, a significant proportion of patients (perhaps as many as one-third) fail to respond sufficiently to gain a clear clinical benefit (such patients are often termed “non-responders”)1, 2.
Bronchodilatation to salmeterol in human isolated airways shows clear inter-individual differences, perhaps explaining the lack of effect of beta agonists in many patients.
It turns out the same is true for many other drugs used to treat asthma. It’s also true of drugs used to treat most conditions. For many patients, drug treatment is simply ineffective, and this only becomes apparent after a period of unsuccessful drug therapy. Wasn’t personalised medicine supposed to change all this?
The problem with pharmacogenomics: too much genomics, not enough pharmacology
It has been 12 years since the term “personalised medicine” was coined following the mapping of the human genome; however, the expected flow of personalised drugs has not yet materialised. For some drugs, where a single mutation predicts “response” or “no response”, then pharmacogenomics follows a clearly defined path. Benefits arise for both the pharmaceutical company (by providing evidence of a clinical benefit and potentially allowing the design of less expensive clinical trials that exclude non-responders) and patients (greater certainty that the drug will effectively treat their condition)- but what about the vast majority of conditions where a single gene fails to predict drug responses?
For this type of drug, multiple genes, or more likely, one or more “continuous” biomarkers (e.g. serum levels of a hormone rather than a yes/no genetic test), are required to predict who will turn out to be a responder to the drug. It is interesting to consider how the development process might be altered to gain an early understanding of efficacy in such a target patient population. What if the efficacy of a drug in different patients could be tested before clinical trials and could run in tandem with the development/validation of biomarkers?
Predicting clinical endpoints using fresh, functional human tissues
Functional demonstrations of human efficacy can be made using fresh, intact human tissues obtained from patients with the relevant clinical condition, in other words, a mini clinical trial can be conducted in a lab before the actual clinical trial. The predictive value of fresh tissues is maintained by 1) using the tissue as rapidly as possible 2) minimising any changes to the tissue (thereby retaining its predictive value of the actual patient responses) and 3) by measuring end-points that translate to the clinical goals of the drug.
For example, the end-points for a drug to treat asthma might be bronchodilatation (relaxation of isolated human airways) and anti-inflammatory activity (reduction in cytokine production from cultured sections of intact human airways). The inter-individual responses of patients to the test drug can be further examined in relation to the production of biomarkers by the tissue or presence of biomarkers in blood from the same patient that the tissue was obtained from. By freezing the tissues and measuring biomarkers or gene expression in tissues from the same patients, the missing link between biomarkers, genomics and clinical efficacy is filled.
Why this matters: cost savings and added commercial value
Two key benefits emerge from this approach. Firstly, improved clinical trial designs (smaller patient numbers) and secondly, an increased chance of demonstrating efficacy during phase II trials.
In most clinical trials, it is the average safety and efficacy of a drug that is measured (an “all-comers” approach). Testing in a subpopulation of patients who have a greater likelihood of response to the drug changes the economics of the clinical development process. Even though the ultimate market size may be reduced (by only treating responders and not all-comers), the savings from a smaller clinical trial (fewer patients needed to demonstrate benefit above placebo), together with the concomitant reduction in risk of failure at phase II and III (greater certainty of clinical efficacy) means that the net present value prior to entering development may in fact be increased. Clearly, the decision to embrace a stratified approach is dependent on the level of confidence in predictive biomarkers. Fresh human tissues form part of a platform of evidence of the likely clinical effectiveness of the drug.
Paul et al.3 calculated that based on an average cost to market for a NCE of $1.78bn, a reduction in phase II attrition from 66% to 50% would reduce the cost to around $1.28bn. Three factors are particularly important in driving economic value for stratified medicines4:
-Relative therapeutic performance of the drug (measure in vitro efficacy in fresh human tissue)
-The prevalence of the biomarker (measure release of the biomarker from the tissue or in the matched blood)
-Clinical performance of the biomarker (compare the release of the biomarker to the in vitro measure of efficacy)
Assays in fresh, functional human tissues provide:
- Increased evidence of clinical efficacy at an early stage
- Input into stratified medicine approaches
- Increase net present value of compounds by increased ability to predict clinical success
1. Wenzel SE. Antileukotriene drugs in the management of asthma. JAMA 1998; 280:2068–9.
2. Drazen JM, Israel E, O’Byrne PM. Treatment of asthma with drugs modifying the leukotriene pathway. N Engl J Med 1999; 340:197–206.
3. Paul, S.M. et al. How to improve R&D productivity: the pharmaceutical industry’s grand challenge. Nature Reviews Drug Discovery 2008, 8, 203-214.
4. Trusheim, M.R. et al. Quantifying factors for the success of stratified medicine. Nature Reviews Drug Discovery 2011; 10, 817-833.
A successful Pharmaceutical industry, as a whole, is required if we are to improve the health and well being of our population. We can debate at length which new working models are best to achieve these lofty goals but one thing I do believe; that with such goals, this is a fulfilling and good career to be involved in. So when people ask me about whether I am comfortable with my recent move from Big Pharma (nearly 20 years with AstraZeneca in its various guises) to Biopta, a small, vibrant CRO, expert at delivering fresh human tissue programs it is easy for me to say… yes.
The basic elements of high scientific standards and the generation of decision-making data aligned to defined business needs, is common. What really attracted me to Biopta was that this alignment was evident immediately. When visiting I found the labs were professional and purposeful, stocked with well-maintained, pristine equipment, and populated with informed, energetic scientists- all evidence that scientific quality was high. On talking further, I found a real sense of purpose to the discussions. The science had to be value adding, whether for the internal R&D of Biopta, generating new tissue models, or for the operational delivery of data for contracted programs.
From a personal point of view the specialist area that Biopta operates so successfully in, the provision of fresh human tissue studies, is an attractive prospect. It is a well-defined area to delve into the scientific detail yet its application fits across the whole discovery and early development pipeline; from early target validation, through lead identification and optimisation phases and of course into development. It covers aspects of efficacy, drug pharmacokinetics and safety pharmacology. Since I have experience with all aspects of these phases I could see the value I could bring. This is important to me. I have been struck immediately by one difference in working in a smaller company, the impact that you have on the business is more transparent.
The use of fresh human tissue studies for both early target validation and confirmation of compound activity has been a common factor in every Discovery project I have worked upon; quite a number in the near 20 years I spent in large Pharma. So much so that I virtually take it for granted that human tissue data is a prerequisite if a compound is to progress into the early Development phases. What I never took for granted is the challenge this was to achieve, both in terms of sourcing the human tissue and the quality and the dedication of the scientists needed to work with an innately more variable tissue. The very nature of its source means that human tissue delivery to the laboratories is usually during unsociable hours, and this is when the day starts for tissue preparation and experimentation. Tissue dissection and manipulation needs technical expertise not easy to source for bespoke studies especially in an age where screening in clonal cell lines is the norm.
All of these challenges are offset against the power of that one graph in your slide pack showing your compound has the desired activity against the relevant tissue using a relevant end-point; Compound X blocks contraction of human COPD bronchus for >24 hours after washout, compound Y inhibits etc.
And why is that so powerful to your audience? Possibly because many of them have witnessed what I have seen; across numerous target classes and disease areas, the expression of your target can differ between animals and humans, not just in relative expression levels but also in which cells types they are expressed. This knowledge should at the very least guide your choice of animal model to mimic human mechanistic concepts; a strong argument for gaining that relevant human tissue data prior to choice animal models, if not indeed to replace it altogether.
Even within human target studies, access to an intracellular compartment required for efficacy can vary between cell lines and native tissue, presumably because of transporter expression. So profound can this difference be on a compound activity, especially in relationship to time, that it can or should change your dosing regimen for early pharmacodynamic readouts in Phase I and II clinical trials.
We can go further and talk about allosteric modulation and the concept of pathway selection by receptors depending upon the agonist. There are known examples of synthetic compounds that differentially stimulate or inhibit some cellular pathways, leaving others intact; biased agonism or antagonism. Such complexity, the balance of pathway activation/inhibition and the effect of background cell type, shows itself as altered compound activity in different models. Native human tissue, and possibly even disease tissue, would recapitulate this complexity in a clinically relevant manner and so should be the assay of choice for confirmation of compound activity. Indeed, I predict that the relevance of this argument will become greater as more high-throughput screening systems move towards label-free technologies. In this instance, the deliberate choice not to measure a distinct second messenger pathway to define a compound activity, but more to identify direct compound/target interaction, will lead to a greater need for deconvolution of the mechanism of action. Data from the use of native human tissue must be high in the pecking order for defining which compound/pathway interaction will be ultimately efficacious, or even more attractive, efficacious and differentiated from competitor molecules.
Of course these, and many other related concepts fall under the broad umbrella of translational science/medicine. Such a focus on the issues of translatability of preclinical data to the clinical setting is only correct given the attrition the Pharma industry experiences in phase II and III clinical trials. The use of native human tissue is a powerful tool in strengthening the predictive nature of preclinical data and I can only see its use increasing. Biopta has just opened new laboratories in Maryland, USA to meet this challenge and so it is exciting times indeed. I am looking forward to bringing together the expertise of Biopta with the needs of the Pharma/Biotechnology industry.
In modern society we don’t like to talk much about the inner workings of our bowels, it’s still a taboo in polite society, but here at Biopta we talk about it almost every day. That’s because an understanding of gastrointestinal behaviour is so important to the successful development of a new drug, from its oral delivery and absorption to GI metabolism and the potential for drug-drug interactions.
Thanks to Hans Ussing, who invented the Ussing Chamber in the 1950’s, and its recent miniaturisation for use with small sections of GI mucosa we now have the ability to assess new compounds in the most relevant and predictive model available – fresh human tissue.
Such tests allow assessment of drug permeability to try and predict clinical absorption, monitor drug effects on ion channel function or to look at different transport systems and possible interactions with other compounds.
Hans Ussing: a short hop from frogs to humans
Ussing’s invention came from the observation that frogs can absorb water into their body without actually drinking it. He surmised that they must somehow absorb the water through their skin and this led him to design the Ussing chamber to test his hypothesis. He set up a system with some frog skin placed between two fluid-filled glass chambers. In each chamber were electrodes able to measure the voltage on either side of the skin. Ussing established that frogs absorb sodium ions through their skin, thereby drawing water through the skin by osmosis. Ussing achieved this by measuring the potential difference (voltage) across the membrane while simultaneously injecting current into the system; by determining the amount of current required to cancel out the voltage, he could effectively measure the net flow of ions across the membrane.
His work gave scientists the means to study almost any polarised membrane and the movement of ions across tissue. The human GI shares some similarities to frog skin, for example, we absorb sodium ions and the electrochemical gradient leads to water absorption. The GI tract can also secrete chloride ions, which causes water to be secreted. This process of sodium absorption and chloride secretion is very important and any interruption can have very dramatic and potentially fatal results. For example, infection by cholera bacteria and subsequent release of the toxin puts the chloride channels into a “hyper” secretive state, resulting in a large volume of water and salts being secreted into the intestine causing dysentery for the patient, which if untreated can be fatal. The Ussing chamber affords a sensitive measurement of current flow; compounds to treat hyper-secretion can be readily assessed.
GI Adverse Effects: A Major Problem for Clinical Development
A major reason for clinical problems is poor patient compliance due to GI side-effects1; for example, many commonly used drugs such as metformin, cancer therapies, Alzheimer’s treatments and NSAIDs cause GI effects that to the patient often lead to them abandoning treatment or failing to comply with a clinically effective dosing regimen. For example, 56% of patients receiving the molecular therapy erlatinib had diarrhea, compared with only 19% of the placebo group 2. The Ussing chamber, when used with fresh human small intestine or colon tissues, is a sensitive way to predict such GI disturbances.
Permeability and transporters
A further cause of drug failure is poor bioavailability. Using fresh human tissue in the Ussing system allows us to study a compound’s permeability across the gut mucosa and can give a prediction of the clinical fraction absorbed. Bioavailability of course involves a number of other factors such as drug solubility and first-pass metabolism, but the key factor in oral absorption is permeability across the GI mucosa. Fresh human small intestine (which is the target for absorption of most drugs) has the relevant expression of transporters, which is lacking in animal models or in human cell line systems such as the CaCo2 cell line, which is a colon cancer cell type. The Ussing chamber method therefore allows us to investigate whether a compound is a substrate of an efflux transporter such as Pgp and whether any drug-drug interactions are likely.
Perhaps there is something true about having to kiss a few frogs to find a prince; OK, so Hans Ussing didn’t need to kiss any frogs (as far as we know) but he did create a technique that is now showing its true value as a means to truly predict the behaviour of drugs in human tissues.
- Medscape Education Article. http://www.medscape.org/viewarticle/571554_2. Gastrointestinal and Hepatic Adverse Effects of Molecular-Targeted Agents: Diarrhea
- Shepherd FA et al. (2005) Erlotinib in previously treated non-small-cell lung cancer. N Engl J Med 353: 123-132
As a number of the big Pharma companies move out of the respiratory and allergy fields, you’d perhaps think that the interest in this market is starting to dwindle. In our experience it’s pretty much the opposite. More and more we’re being asked to develop new and innovative human tissue-based tests for our clients to assess the immunological or functional aspects of human airways and pulmonary blood vessels, for diseases as common as asthma, to the rarer conditions such as primary pulmonary hypertension that affects only 1 in 10,000 women each year. So how do we do it?
Obtaining Fresh Tissues for Research
First of all we need to obtain the fresh lung samples. We could spend the rest of this blog on the complexities of tissue access, but it all really boils down to the creation of effective partnerships with clinical teams. We have frequent access to lung tissue from a variety of patient sub-sets including those with asthma and COPD. At Biopta, our work really starts once a sample has been donated. Often the hardest part is identifying and dissecting the airways or blood vessels within a tissue sample as there can be a lot of variation in the location and size of the sample, which depends on the pathology of the tissue (e.g. the type of surgery it is retrieved from), and also the hospital which is retrieving the sample (transplant obviously yields a greater volume of tissue as opposed to surgical operations, where the smallest section possible is removed).
Next, we have to maintain the tissue quality; this means getting the tissue sample to our labs as quickly as possible so that all normal functions are still intact. This is extremely important when examining the immunological response of a tissue sample as this is the first point of degradation, and often means a night shift for our lab staff (of which I am familiar!). Other functional aspects of the tissue samples are maintained longer, such as responses of airways to known bronchoconstrictors or dilators, however our aim is always to use a sample as soon as possible so that it is fresh and therefore any intervention in our experiments reflects as much as possible the usual response that would take place in the human body.
Investigations in Human Lung
Currently we use organ culture and organ bath systems, which are two methods that allow a wide range of end-points to be measured. As each client study is tailor-made, we build each protocol around the specific drug-induced effects we wish to detect.
Organ culture or organoculture (the term is really a bit of a misnomer as it is intact tissues that are being cultured) is a technique we commonly use to assess inflammation within a tissue and the method can be flexibly applied to a number of different organs/tissues including lung. Cytokines released by airways during inflammation are critical parts of the pathophysiology of disorders such as asthma and COPD. The aim of our assays is often to up-regulate these inflammatory mediators and then assess whether or not they can they be dampened by anti-inflammatory drugs. We culture these tissues over hours or days in order to see the long-term effects of the compounds.
In our organ bath systems, currently the most popular assay is one that reflects duration of action of asthma drugs. Today’s target for pharma companies is to create long-lasting compounds that dissociate from their binding site very slowly. For the patient this can mean a once a day dose, which can greatly improve patient compliance. To test these compounds we first incubate the airway segment with the compound; this allows the drug to bind to its target receptors. We then repeatedly challenge the airway with a bronchoconstrictor over a defined time period, washing the fluid surrounding the airway between each challenge. As the drug compound slowly dissociates from the receptor, the response to the bronchoconstrictor increases and thus those that keep the constrictor response at bay for a longer time have a longer duration of action and are potentially the more worthy compounds.
Another popular assay type is to assess bronchodilatory responses. Test and/or reference compounds are added cumulatively to bronchial rings following pre-constriction with a bronchoconstrictor such as carbachol. For example, see the figure below where the phosphodiesterase inhibitor theophylline (3 mM) was added at the end of each cumulative concentration response curve to induce full relaxation. All reference compound responses shown as % of maximum response to theophylline.
In addition to this we are able to monitor airway bronchoconstriction to antibodies, vascular dilators to relieve pulmonary hypertension, transportation of drugs across the airway epithelium…who knew you could get so much information from one lung sample?!
And on to the next step the compounds proceed. Fingers crossed they pass the next pre-clinical challenge!
Click here to find out more information on Biopta’s respiratory models, or contact one of our experts at +44 (0141) 330 3831 or here.
In the last few years there has been a steadily increasing interest in the possible importance of perivascular fat. Like the endothelium (pre 1980’s), the perivascular adipocytes were previously thought to be unimportant and were discarded prior to investigation of the physiology and pharmacology of isolated vascular segments. With the benefit of hindsight, that might have been a bad idea. This short commentary provides a quick introduction to the possible importance of perivascular adipocytes.
Vessel structure: The blood vessel wall is comprised of three main tunics separated by two elastic sheets. The inner layer of cells, the tunica intima, comprises a single layer of endothelial cells which are in contact with blood on their luminal surface and are attached to the internal elastic lamina (IEL) on their abluminal surface. The IEL has holes (fenestrae) which permit the formation of myo-endothelial connections between the endothelial cells and smooth muscle cells of the tunica media. The medial smooth muscle is separated from the tunica adventitia by the external elastic lamina (EEL). The EEL is a loose weave of elastin and so there is ample opportunity for adventitial cells to make contact with the medial smooth muscle. However, such connections are not widely recognised. In fact the overall structure and function of the vascular adventitia is poorly understood and has only recently attracted the attention of investigators. Virtually nothing is known about the adipocytes that surround the blood vessels, although recent reports have indicated an extremely important modulatory role in vascular reactivity and general vascular health.
Obesity: A report published by the Association of Public Health Observatories identified the UK as having the highest levels of obesity in Europe. The increased risk of hypertension and diabetes, among the obese population, has been comprehensively reviewed and reported on in the popular press. The main focus of these reports has tended to be on visceral fat and body mass index (BMI). The fact that obese elderly people are rarely seen perhaps speak volumes. What has been overlooked is the, possibly devastating, direct effect that fat may have on the normal functions of the vasculature.
Adipokines: Body fat (adipocytes) can now be regarded as an important part of the endocrine system and may even represent an endocrine organ in itself. Numerous factors (adipokines) are released from adipocytes and these can be either anti-atherogenic or pro-atherogenic. The list of adipokines includes, but is not limited to; tumor necrosis factor (TNF-α), adiponectin, plasminogen activator inhibitor-1 (PAI-1), resistin, Heparin-binding epidermal-growth-factor-like growth factor (HBEGF), interleukin 1 (IL-1) and leptin. Two particularly important adipokines related to obesity and cardiovascular disease are adiponectin (anti-atherogenic) and IL-1 (pro-atherogenic). Unfortunately in cases of obesity, levels of the protective adiponectin are reduced whilst those of IL-1 are increased.
Vascular adipocytes: In addition to the wide array of adipokines, the vascular adipocytes also express a host of receptors including; alpha1a- & alpha1b-adrenoceptors, beta1- & beta3-adrenoceptors, P1, P2x & P2y purinoceptors, cannabinoid receptors (GPR55, CB1 & CB2), substance-p (NK1). Therefore, the circumstantial evidence suggests a possible interaction between the sympathetic neurotransmitters noradrenalin and ATP, the sensory transmitter Substance-P and the endocannabinoids. A picture is now emerging that supports a model of adventitial nerves activating perivascular adipocytes which then release factors that have direct effects on all vascular cell types.
Vascular modulation: Simple experiments in which the perivascular fat is removed from segments of blood vessels prior to in-vitro experimentation are providing surprising results. In most cases the responses to the catecholamines, noradrenalin and adrenalin, are inhibited when fat is present. Therefore, published reports may have overestimated the physiological role of these catecholamines since most in-vitro experiments are performed following ‘careful removal of perivascular fat’. One surprising observation is that the responses to some agonists are actually increased in the presence of fat thus demonstrating that the presence of fat per se does not just simply block access of the exogenously applied drugs.
So, when we are performing experiments on isolated vascular segments should we keep the fat on or remove it? We generally ask the same question of the endothelium and adjust our experiments accordingly. I believe we have now reached a point where we must treat the perivascular fat with the same degree of respect that is given to the endothelium. Most of the work that has been published on perivascular fat has been on experimental animals. Given that obesity and cardiovascular disease are seriously debilitating (and costly) human disorders it will be interesting to examine a range of arteries and veins taken from patient biopsies.
Overall, the study of perivascular fat could hold the key to new cardiovascular therapies.
Craig J Daly
Fresh, functional human tissues have long been considered the closest possible model of human in vivo function and can be used to measure a wide range of pharmacological responses. Despite this, relatively little drug development is conducted using fresh human tissue because of the logistical and ethical difficulties surrounding the availability of tissue and practicalities of experimental work. Most tests of drug activity require a living test system comprising cells, tissues or whole organisms. In some instances, ‘‘living’’ (fresh) human tissues have the potential to reduce or replace animal tests through superior prediction of drug safety and efficacy.
Before functional human tissue tests become a routine part of drug development, two factors must co-exist, namely, the evidence that fresh human tissue assays are a powerful way to predict drug activity and sufficient access to the fresh human tissues.
Biopta’s new article in volume 12 of Cell and Tissue Banking discusses both of these factors and looks to the future of human tissue research.
For further information on human tissue research, complete our Ask an Expert form to contact one of Biopta’s human tissue scientists.
Blood vessel myography is a valuable in vitro technique for the sensitive measurement of constriction and relaxation of blood vessels in response to test drugs.
Why would you use isolated blood vessels as opposed to testing in animals?
Assessing drug responses in human blood vessels gives us a much more accurate prediction of how the compound will perform in the clinic, compared to studying the responses in animals (see figure below showing differences between canine and human arteries exposed to serotonin (5-HT)).
How is myography performed?
There are two main types of myography that are routinely performed in laboratories today. Isometric myography (constant length myography), typically conducted via wire myography, and isobaric myography (constant pressure) typically conducted via pressure myography.
What’s the difference between isometric and isobaric myography?
In isometric experiments, the tissue is held at a constant initial stretch. Changes in contraction/relexation are indicated by measurements of force from sensitive isometric force transducers. Isometric myography is a higher throughput technique than isobaric myography, and is therefore often the method of choice. The advantages of this technique are that vessels remain viable showing consistent contractility and relaxatory responses. Perivascular nerves and endothelium function also remain functional. Unfortunately with this technique the vessels acquire a flattened rather than cylindrical shape and the wires exert pressure on the end walls of the vessel rather than distributing it evenly along the wall length. There is also a risk of the endothelium being damaged by the wires in the mounting procedure. However as many vessels can be run in parallel, this potential effect can be tested for at the start of the experiment, and that specific blood vessel ring removed if necessary.
Isobaric myography allows tubular sections of vessels to be mounted on cannulae inserted into either end of the vessel. Fluid is pumped into the vessel to create a desired intraluminal pressure and the diameter of the vessel is measured using an optical video dimension analyser. As the vessel constricts the vessel diameter decreases and this can be recorded using charting software. Using this technique the vessels maintain a much more physiologically round shape and there is less potential for endothelial damage. It is also possible to mimic in vivo conditions such as blood flow and blood pressure and to apply drugs of interest to the inside of the vessel, instead of the outer wall. However it is a very challenging technique and only allows a 2-3 vessels to be run at a time, therefore it is mainly used to study specific components of vascular control, such as flow mediated dilatation or vascular compliance (pressure-diameter relationships).
Why are these techniques useful to the pharmaceutical industry?
Myography is an important tool in the pharmaceutical industry for assessing the effects of potential new drugs on the vasculature. This gives the pharmaceutical companies invaluable early data on the safety and/or efficacy of their drugs in the human cardiovascular system. Both of these techniques have helped to increase the knowledge of normal function and responses of small vessels, however there is still much to learn about vascular biology and many academic laboratories employ this method in their research as they strive to learn more about the control of blood vessel function.
Does Biopta offer myography?
Biopta has over 75 years combined experience in myography and has run countless client studies using isolated human blood vessels to assess both the safety and efficacy of drugs. We also have four specially developed pressure myographs (PM-1 instrument) which allow us to investigate the effects of drugs on flow-mediated relaxation, vascular compliance and permeability in human blood vessels.
Running several vessels in parallel allows us to assess a variety of parameters at once, and the frequency with which we receive human blood vessels allows us to offer a rapid turnaround on our client studies.
The majority of our client studies are tailor made, so whether the drug company is looking to assess safety and/or efficacy, we design each study to meet the client’s individual requirements.
To find out how Biopta can help you, please call us on +44 (0) 141 330 3831 or contact one of our experts here.
We were physically blown into the Edinburgh International Conference Centre last Thursday after a day of gales in Edinburgh. The Scottish Enterprise Life Sciences Awards Dinner is always an occasion to look forward to, and this years didn’t disappoint.
Attended by over 750 people in the Scottish life sciences community, it provides a fitting celebration of Scotland’s resilience in the current economic climate and ability to develop and grow over the last 12 months; we live in one of the four UK key clusters of life sciences start-ups and Scotland also has the highest rate of life science start-ups per capita in the UK (1).
With a glass of fizz to set the mood, off I set to network with old, existing and new contacts before the main event; speeches followed by dinner, awards and some late-night catching up.
Scottish funny man Fred MacAulay once again hosted this year’s awards and along with Nicola Sturgeon, Deputy First Minister, provided an interesting distraction from our rumbling stomachs. The keynote address was from Hugh Griffith, CEO of NuCana BioMed and Alida Capital International, who provided a very personal and moving insight into one wee girl’s life changing experience of vaccine trials and a realistic reflection on the state of the UK investment climate. Hugh reminded us of the dramatic impact life sciences research can have with the story of an 8 year-old girl with leukaemia, given four weeks to live by clinicians, who went into complete remission after receiving their novel drug.
After a hefty three course dinner brilliantly catered for by Leith’s (duck as the main course for 700 people- very brave!), the awards began with an introduction from Lena Wilson, Chief Exec of Scottish Enterprise. Our fingers were crossed for Biopta’s very own Chairman, Kevin Moore, who was up for the Lifetime achievement award, aka Outstanding contribution to the growth of Scottish Life Sciences. Few people have done so much to commercialise Scottish life sciences and chemical science innovations, but Kevin lost out to Professor Sir Ian Wilmut, MRC Centre for Regenerative Medicine, Edinburgh. Anyone with a Sir in their title, as well as being creator of one of the world’s most famous science icons, Dolly the sheep, is going to provide stiff competition.
Other award winners included CarieScan Ltd for Best New Life Sciences company in Scotland, the Innovation Award went to Lynn Garrett, NHS Argyll & Bute as part of NHS Highland, Dave Tudor of GSK Montrose won the Life Science Business Leadership award, and the SHIL award for best innovation originating in NHS Scotland went to NHS Greater Glasgow and Clyde for its Epaware product.
Us Scots are often reluctant to celebrate successes, but the dinner was a welcome reminder that Scotland punches well above its weight and is continuing its long tradition of scientific innovation.
(1) UK Life Science Start Up Report, Mobius Life Sciences 2010