## 3 Metabolic Profiling of Urine: Recent Trends
### MEPS and SPME Advantages for the Metabolic Profile of Urine  
In the previous section, a large number of selected applications showed the potentialities of the metabolic profile of urine in unveiling many diseases processes and pointing to new directions and their treatments. In most cases, however, instead of specific metabolites, we have information about up- or down-regulated pathways, but this information is too complex to be used in the clinical disease diagnostics. Furthermore, to make this information biochemically relevant, it would require long and complex analysis. Therefore, these metabolic profiles should instead provide biomarkers able to be readily used in disease biomarker. In this sense, SPME and MEPS are suitable for fulfilling this objective of breaking urine metabolomic complexity. Different high throughput solutions are nowadays available to easily process a large amount of samples, speeding up metabolomic research. Several applications in different fields of research have been reviewed [9; 61; 62], but here, we will focus in more detail on specific applications to the most prevalent human diseases, Cardiovascular (CVDs), oncologic (ODs) and neurodegenerative diseases (NDDs). Early Diagnosis of Highly Prevalent Diseases, Such As Cardiovascular, Oncologic and Neurodegenerative Ones  
CVDs, ODs and NDDs are the three main causes of mortality worldwide. Moreover, the morbidity burden associated with these diseases is also very high, presenting an increasing trend that is proportional to the rise in life expectancy. The main cause of this scenario is the late diagnosis of these diseases, which, moreover, is usually performed in invasive and expensive formats, when the diseases already have reached the medium to late stages. Therefore, there is a great potential to unveil using urine as a tool to achieve an early and potentially inexpensive disease diagnose. Although these diseases develop slowly and progress in a relative asymptomatic way till they reach an advanced stage development, there are certainly causes and modifications that can be assessed in order to obtain an early diagnosis, particularly specific metabolites, whose levels are necessarily different from the healthy status. Oxidative damage to the cell components (particularly lipids of the membrane layer, proteins and nucleic acids) caused by reactive oxygen and nitrogen species (ROS and RNS, respectively) is nowadays recognized as a hallmark in these diseases. In fact, several reports point to oxidative damage as a triggering event in different ODs, NDDs and CVDs [63; 64; 65; 66]. CVD progression, for instance, is characterized by an increase in lipid peroxidation that causes vascular lesions, inflammation events and, finally, atherosclerosis [67; 68]. Therefore, there should be different metabolites that reflect these events, these being potentially suitable biomarkers for the early diagnosis of CVD progression. The success of this approach depends, however, on powerful analytical methodologies able to reliably characterize metabolites in vestigial concentrations. In the last few years, improvements in liquid chromatography (LC), gas chromatography (GC) and mass spectrometry (MS) have allowed an unprecedented analytical performance, able to go deeper into the characterization on new disease biomarkers. If properly conjugated with microextraction techniques (METs), namely MEPS and SPME, the limit of the single molecule quantification is increasingly closer. This fulfills the metabolomic characterization of the main human diseases that is necessary to find the best biomarkers for an early diagnosis. Additionally, the powerful analytical performance that can be obtained by using high throughputplatforms conjugating METs with LC, GC and MS is being successfully used in the characterization of a vast number of drugs and drugs metabolites used against diseases (reviewed in [13, 61, 62]).