Motor control system in Parkinson’s disease: a modeling approach

Parkinson’s disease is a neurodegenerative disorder due to the death of the dopaminergic neurons of the substantia nigra of the basal ganglia. The process that leads to these neural alterations is still unknown. Parkinson’s disease affects most of all the motor sphere, with a wide array of impairment such as bradykinesia, akinesia, tremor, postural instability and singular phenomena such as freezing of gait. Moreover, in the last few years the fact that the degeneration in the basal ganglia circuitry induces not only motor but also cognitive alterations, not necessarily implicating dementia, and that dopamine loss induces also further implications due to dopamine-driven synaptic plasticity got more attention. At the present moment, no neuroprotective treatment is available, and even if dopamine-replacement therapies as well as electrical deep brain stimulation are able to improve the life conditions of the patients, they often present side effects on the long term, and cannot recover the neural loss, which instead continues to advance. In the present thesis both motor and cognitive aspects of Parkinson’s disease and basal ganglia circuitry were investigated, at first focusing on Parkinson’s disease sensory and balance issues by means of a new instrumented method based on inertial sensor to provide further information about postural control and postural strategies used to attain balance, then applying this newly developed approach to assess balance control in mild and severe patients, both ON and OFF levodopa replacement. Given the inability of levodopa to recover balance issues and the new physiological findings than underline the importance in Parkinson’s disease of non-dopaminergic neurotransmitters, it was therefore developed an original computational model focusing on acetylcholine, the most promising neurotransmitter according to physiology, and its role in synaptic plasticity. The rationale of this thesis is that a multidisciplinary approach could gain insight into Parkinson’s disease features still unresolved.

Rehabilitation Engineering in Parkinson's disease

Impairment of postural control is a common consequence of Parkinson's disease (PD) that becomes more and more critical with the progression of the disease, in spite of the available medications. Postural instability is one of the most disabling features of PD and induces difficulties with postural transitions, initiation of movements, gait disorders, inability to live independently at home, and is the major cause of falls. Falls are frequent (with over 38% falling each year) and may induce adverse consequences like soft tissue injuries, hip fractures, and immobility due to fear of falling. As the disease progresses, both postural instability and fear of falling worsen, which leads patients with PD to become increasingly immobilized. The main aims of this dissertation are to: 1) detect and assess, in a quantitative way, impairments of postural control in PD subjects, investigate the central mechanisms that control such motor performance, and how these mechanism are affected by levodopa; 2) develop and validate a protocol, using wearable inertial sensors, to measure postural sway and postural transitions prior to step initiation; 3) find quantitative measures sensitive to impairments of postural control in early stages of PD and quantitative biomarkers of disease progression; and 4) test the feasibility and effects of a recently-developed audio-biofeedback system in maintaining balance in subjects with PD. In the first set of studies, we showed how PD reduces functional limits of stability as well as the magnitude and velocity of postural preparation during voluntary, forward and backward leaning while standing. Levodopa improves the limits of stability but not the postural strategies used to achieve the leaning. Further, we found a strong relationship between backward voluntary limits of stability and size of automatic postural response to backward perturbations in control subjects and in PD subjects ON medication. Such relation might suggest that the central nervous system presets postural response parameters based on perceived maximum limits and this presetting is absent in PD patients OFF medication but restored with levodopa replacement. Furthermore, we investigated how the size of preparatory postural adjustments (APAs) prior to step initiation depend on initial stance width. We found that patients with PD did not scale up the size of their APA with stance width as much as control subjects so they had much more difficulty initiating a step from a wide stance than from a narrow stance. This results supports the hypothesis that subjects with PD maintain a narrow stance as a compensation for their inability to sufficiently increase the size of their lateral APA to allow speedy step initiation in wide stance. In the second set of studies, we demonstrated that it is possible to use wearable accelerometers to quantify postural performance during quiet stance and step initiation balance tasks in healthy subjects. We used a model to predict center of pressure displacements associated with accelerations at the upper and lower back and thigh. This approach allows the measurement of balance control without the use of a force platform outside the laboratory environment. We used wearable accelerometers on a population of early, untreated PD patients, and found that postural control in stance and postural preparation prior to a step are impaired early in the disease when the typical balance and gait intiation symptoms are not yet clearly manifested. These novel results suggest that technological measures of postural control can be more sensitive than clinical measures. Furthermore, we assessed spontaneous sway and step initiation longitudinally across 1 year in patients with early, untreated PD. We found that changes in trunk sway, and especially movement smoothness, measured as Jerk, could be used as an objective measure of PD and its progression. In the third set of studies, we studied the feasibility of adapting an existing audio-biofeedback device to improve balance control in patients with PD. Preliminary results showed that PD subjects found the system easy-to-use and helpful, and they were able to correctly follow the audio information when available. Audiobiofeedback improved the properties of trunk sway during quiet stance. Our results have many implications for i) the understanding the central mechanisms that control postural motor performance, and how these mechanisms are affected by levodopa; ii) the design of innovative protocols for measuring and remote monitoring of motor performance in the elderly or subjects with PD; and iii) the development of technologies for improving balance, mobility, and consequently quality of life in patients with balance disorders, such as PD patients with augmented biofeedback paradigms.

Ottimizzazione di un protocollo di anticoagulazione regionale con citrato in CRRT

Ottimizzazione di un protocollo di anticoagulazione regionale con citrato in CRRT Introduzione: La necessità di un'anticoagulazione continua e l'ipofosforemia in corso di trattamento sono problemi costranti in corso di CRRT. Il nostro studio ha cercato di dimostrare l'efficacia e la sicurezza dell'anticoagulazione regionale con citrato in CVVH basato sull'utilizzo di una soluzione di citrato (18 mmol/L) associata ad una soluzione di reinfusione contenente fosfato, recentemente disponibile in commercio, al fine di ridurre l'ipofosfatemia in corso di CRRT. Metodi: Abbiamo utilizzato il nostro protocollo basato sull'utilizzo di una concentrazione di citrato contenente 18 mmol/l associata ad una soluzione di reinfusione contenente fosfato in un piccolo gruppo di pazienti ricoverati in terapia intensiva post-cardiochirurgica, sottoposti a CRRT per insufficienza renale acuta. Risultati: Il nostro protocollo ha garantito un'adeguata durata del circuito ed un ottimo controllo dell'equilibrio acido-base in ogni paziente. E' stata necessaria solo una minima supplementazione di fosforo in alcuni dei pazienti trattati. Conclusioni: Il nostro protocollo basato sull' utilizzo di una soluzione a concentrazione di citrato maggiore (18 mmol/l), permette un miglior controllo dell'equilibrio acido-base rispetto all'utilizzo della soluzione a più bassa concentrazione di citrato. L'uso di una minore dose di citrato ed il mantenimento di un target maggiore di calcio ionizzato all'interno del circuito sono comunque associati ad un'adeguata durata del circuito. I livelli di fosforemia sono rimasti sostanzialmente stabili nella maggior parte dei pazienti trattati, grazie alla presenza di fosfato nella soluzione utilizzata come reinfusione in post-diluizione.

Nutritional strategies to control mycotoxin damages in swine

Mycotoxins are contaminants of agricultural products both in the field and during storage and can enter the food chain through contaminated cereals and foods (milk, meat, and eggs) obtained from animals fed mycotoxin contaminated feeds. Mycotoxins are genotoxic carcinogens that cause health and economic problems. Ochratoxin A and fumonisin B1 have been classified by the International Agency for Research on Cancer in 1993, as “possibly carcinogenic to humans” (class 2B). To control mycotoxins induced damages, different strategies have been developed to reduce the growth of mycotoxigenic fungi as well as to decontaminate and/or detoxify mycotoxin contaminated foods and animal feeds. Critical points, target for these strategies, are: prevention of mycotoxin contamination, detoxification of mycotoxins already present in food and feed, inhibition of mycotoxin absorption in the gastrointestinal tract, reduce mycotoxin induced damages when absorption occurs. Decontamination processes, as indicate by FAO, needs the following requisites to reduce toxic and economic impact of mycotoxins: it must destroy, inactivate, or remove mycotoxins; it must not produce or leave toxic and/or carcinogenic/mutagenic residues in the final products or in food products obtained from animals fed decontaminated feed; it must be capable of destroying fungal spores and mycelium in order to avoiding mycotoxin formation under favorable conditions; it should not adversely affect desirable physical and sensory properties of the feedstuff; it has to be technically and economically feasible. One important approach to the prevention of mycotoxicosis in livestock is the addition in the diets of the non-nutritionally adsorbents that bind mycotoxins preventing the absorption in the gastrointestinal tract. Activated carbons, hydrated sodium calcium aluminosilicate (HSCAS), zeolites, bentonites, and certain clays, are the most studied adsorbent and they possess a high affinity for mycotoxins. In recent years, there has been increasing interest on the hypothesis that the absorption in consumed food can be inhibited by microorganisms in the gastrointestinal tract. Numerous investigators showed that some dairy strains of LAB and bifidobacteria were able to bind aflatoxins effectively. There is a strong need for prevention of the mycotoxin-induced damages once the toxin is ingested. Nutritional approaches, such as supplementation of nutrients, food components, or additives with protective effects against mycotoxin toxicity are assuming increasing interest. Since mycotoxins have been known to produce damages by increasing oxidative stress, the protective properties of antioxidant substances have been extensively investigated. Purpose of the present study was to investigate in vitro and in vivo, strategies to counteract mycotoxin threat particularly in swine husbandry. The Ussing chambers technique was applied in the present study that for the first time to investigate in vitro the permeability of OTA and FB1 through rat intestinal mucosa. Results showed that OTA and FB1 were not absorbed from rat small intestine mucosa. Since in vivo absorption of both mycotoxins normally occurs, it is evident that in these experimental conditions Ussing diffusion chambers were not able to assess the intestinal permeability of OTA and FB1. A large number of LAB strains isolated from feces and different gastrointestinal tract regions of pigs and poultry were screened for their ability to remove OTA, FB1, and DON from bacterial medium. Results of this in vitro study showed low efficacy of isolated LAB strains to reduce OTA, FB1, and DON from bacterial medium. An in vivo trial in rats was performed to evaluate the effects of in-feed supplementation of a LAB strain, Pediococcus pentosaceus FBB61, to counteract the toxic effects induced by exposure to OTA contaminated diets. The study allows to conclude that feed supplementation with P. pentosaceus FBB61 ameliorates the oxidative status in liver, and lowers OTA induced oxidative damage in liver and kidney if diet was contaminated by OTA. This P. pentosaceus FBB61 feature joined to its bactericidal activity against Gram positive bacteria and its ability to modulate gut microflora balance in pigs, encourage additional in vivo experiments in order to better understand the potential role of P. pentosaceus FBB61 as probiotic for farm animals and humans. In the present study, in vivo trial on weaned piglets fed FB1 allow to conclude that feeding of 7.32 ppm of FB1 for 6 weeks did not impair growth performance. Deoxynivalenol contamination of feeds was evaluated in an in vivo trial on weaned piglets. The comparison between growth parameters of piglets fed DON contaminated diet and contaminated diet supplemented with the commercial product did not reach the significance level but piglet growth performances were numerically improved when the commercial product was added to DON contaminated diet. Further studies are needed to improve knowledge on mycotoxins intestinal absorption, mechanism for their detoxification in feeds and foods, and nutritional strategies to reduce mycotoxins induced damages in animals and humans. The multifactorial approach acting on each of the various steps could be a promising strategy to counteract mycotoxins damages.

The role of bifidobacteria in newborn health and the intestinal microbial balance

Gut microbial acquisition during the early stage of life is an extremely important event since it affects the health status of the host. In this contest the healthy properties of the genus Bifidobacterium have a central function in newborns. The aim of this thesis was to explore the dynamics of the gut microbial colonization in newborns and to suggest possible strategies to maintain or restore a correct balance of gut bacterial population in infants. The first step of this work was to review the most recent studies on the use of probiotics and prebiotics in infants. Secondly, in order to prevent or treat intestinal disorders that may affect newborns, the capability of selected Bifidobacterium strains to reduce the amount of Enterobacteriaceae and against the infant pathogen Streptococcus agalactiae was evaluated in vitro. Furthermore, the ability of several commercial fibers to stimulate selectively the growth of bifidobacterial strains was checked. Finally, the gut microbial composition in the early stage of life in response to the intrapartum antibiotic prophylaxis (IAP) against group B Streptococcus was studied using q-PCR, DGGE and next generation sequencing. The results globally showed that Bifidobacterium breve B632 strain is the best candidate for the use in a synbiotic product coupled to a mixture of two selected prebiotic fibers (galactooligosaccharides and fructooligosaccharides) for gastrointestinal disorders in infants. Moreover, the early gut microbial composition was affected by IAP treatment with infants showing lower counts of Bifidobacterium spp. and Bacteroides spp. coupled to a decrement of biodiversity of bacteria, compared to control infants. These studies have shown that IAP could affect the early intestinal balance in infants and they have paved the way to the definition of new strategies alternative to antibiotic treatment to control GBS infection in pregnant women.

Influence of optic flow on postural control

The study of optic flow on postural control may explain how self-motion perception contributes to postural stability in young males and females and how such function changes in the old falls risk population. Study I: The aim was to examine the optic flow effect on postural control in young people (n=24), using stabilometry and surface-electromyography. Subjects viewed expansion and contraction optic flow stimuli which were presented full field, in the foveral or in the peripheral visual field. Results showed that optic flow stimulation causes an asymmetry in postural balance and a different lateralization of postural control in men and women. Gender differences evoked by optic flow were found both in the muscle activity and in the prevalent direction of oscillation. The COP spatial variability was reduced during the view of peripheral stimuli which evoked a clustered prevalent direction of oscillation, while foveal and random stimuli induced non-distributed directions. Study II was aimed at investigating the age-related mechanisms of postural stability during the view of optic flow stimuli in young (n=17) and old (n=19) people, using stabilometry and kinematic. Results showed that old people showed a greater effort to maintain posture during the view of optic flow stimuli than the young. Elderly seems to use the head stabilization on trunk strategy. Visual stimuli evoke an excitatory input on postural muscles, but the stimulus structure produces different postural effects. Peripheral optic flow stabilizes postural sway, while random and foveal stimuli provoke larger sway variability similar to those evoked in baseline. Postural control uses different mechanisms within each leg to produce the appropriate postural response to interact with extrapersonal environment. Ageing reduce the effortlessness to stabilize posture during optic flow, suggesting a neuronal processing decline associated with difficulty integrating multi-sensory information of self-motion perception and increasing risk of falls.