Kyotorphin derived peptides in the relationship between analgesia and alzheimer’s disease

Tese de doutoramento, Ciências Biomédicas (Bioquímica Médica), Universidade de Lisboa, Faculdade de Medicina, 2014

The increased lifespan has brought about an increase in the incidence of diseases related to the aging process. Among these, there are the neurodegenerative diseases, including Alzheimer's disease (AD) and other entities associated with the phenomena of chronic pain. The possible correlation between two entities - pain and Alzheimer's disease - with such a large epidemiological burden is of enormous importance. Nowadays pain is considered the fifth vital sign and is highly prevalent, still largely under-treated. New drugs acting on different targets with a smaller range of adverse effects are needed. Moreover, Alzheimer's disease is widely spread in our population, primarily affecting the elderly but also a younger population. The ignorance of the complexity of the biochemical and physiological processes involved and progressive cognitive impairment of patients still result in ineffective treatment. The increase in scientific knowledge about the disease at various levels is mandatory in order to ensure an improvement in the provision of appropriate health care and the chance of intervening in the early stages of the disease, including at the level of prevention and diagnosis. The consequences of diagnosis and evolution of this pathology are well known: change in family / emotional environment of the patient and burden on caregivers. Therefore, a strategy for the correlation between these two entities and possible common therapeutic targets involving a single pharmacological agent is promising. As already mentioned, this project focuses on two issues of utmost clinical importance and strong social impact: Pain and Alzheimer's disease. The most innovative aspect relates to the hypothesis that both problems can be related and may, therefore, be addressed in a single therapeutic approach. This hypothesis is supported by previous experimental work in vitro, evolving now to another phase, with animal experimentation in disease models and clinical research. This thesis intended to evaluate a molecule, kyotorphin, as a molecular link in the mechanisms involved in both cases. Kyotorphin (KTP), discovered in 1979, was described as an endogenous analgesic dipeptide actuating in the brain. With na analgesic activity about 4 times higher than other endogenous peptides such as met-enkephalin, this dipeptide has very interesting features and is thought to act via opioid mechanisms. Analgesic derived molecules of kyotorphin had previously been tested for their analgesic effect in vivo in animal models and for in vitro neuroprotective effects after peripheral administration. This project brings these results to clinical research and its main objectives were: 1) to understand if there is a correlation between Alzheimer's disease and pain, 2) if analgesic peptides derived from kyotorphin are capable of neuromodulation and 3) evaluate kyotorphin as a potential molecular marker in Alzheimer's disease. To achieve these objectives, clinical and basic research were combined using diverse techniques such as questionnaires and pain scales, sophisticated analytical techniques of mass spectrometry and animal experimentation. In a first stage we assessed pain perception in Alzheimer patients and their caregivers, using validated pain scales. This study concluded that, in line with the findings in the literature, pain in Alzheimer patients is often under-evaluated and therefore undertreated. This phenomenon probably occurs because these patients are unable to value and/or express their suffering, even in moderate stages of the disease. Clinical research involved another component: the collection of cerebrospinal fluid samples of patients with AD for determination of Kyotorphin levels and its comparison with individuals without known neurodegenerative diseases; it was found that the levels of kyotorphin , a neuropeptide endogenous per se, decreases with the progression of Alzheimer's disease. This finding opens new possibilities, including the use of kyotorphin as a possible marker of neurodegenerescence and that this neuropeptide has neuromodulatory actions. Subsequently, we studied the effect of neuropeptide kyotorphin derivatives capable of crossing the blood brain barrier - IbKTP-NH2 e KTP-NH2 – in animal models with two objectives: realize if these drugs showed significant side effects compared to reference opioids used in clinical practice, and what were their effects in an animal model of neurodegenerescence. These amidated derivatives IbKTP-NH2 e KTP-NH2, unlike morphine and tramadol (two largely used drugs in clinical practice), caused no major side effects associated with opioids, which is a further indication that the mechanism of action of these peptides and opioids not fully coincide. On the other hand, the neurodegeneration animal model to which these compounds were chronically administered revealed an improvement in the behavioral pattern in comparison with animals with neurological lesions to which none of the compounds had been administered. Overall, our results indicate kyotorphin as a possible biomarker for Alzheimer's disease, and its derivatives IbKTP-NH2 and KTP-NH2 capable of neuromodulation/neuroprotection, in addition to effective analgesic molecules with reduced side effects.

Fundação para a Ciência e a Tecnologia (FCT)