Fluorescence spectroscopy to diagnose hepatic steatosis in a rat model of fatty liver

Point-of-care device for the noninvasive assessment of hepatic macrosteatosis in liver donors

BACKGROUND

Quantification of macrosteatosis (MS) in the liver is important given that it has shown to directly correlate with adverse post-liver transplant (LT) outcomes. With advances in medical technology and an implicit understanding of pathology, noninvasive methods of quantitatively assessing MS are in various stages of development. Each of these methods is based on the physical principles of differences between a fat-laden hepatocyte and a normal one.

METHODS

In this regard, after a proof-of-concept study on a prototype for a simple, real-time, handheld device using the principle of diffuse reflectance spectroscopy, this study presents an upgraded point-of-care (POC) device for the noninvasive assessment of hepatic MS in liver donors.

RESULTS

The device was validated on cohort of donor livers and showed a sensitivity (0.0021 V/% fat) and highly correlated (r = 0.9868, P < .0001) with gold-standard liver biopsy. Results showed that this upgraded POC device provides a reliable method for the noninvasive assessment of hepatic MS, which is crucial for selecting suitable donor livers for LT.

CONCLUSION

The device has the potential to be an invaluable apparatus at the hands of the organ-retrieving surgeon. It is noninvasive, portable (handheld), and economic; provides real-time readings of the percentage of MS; and can be efficaciously handled by any member of the organ-retrieving team.

Combined methods of optical spectroscopy and artificial intelligence in the assessment of experimentally induced non-alcoholic fatty liver

BACKGROUND AND OBJECTIVE

Due to the existing prevalence of nonalcoholic fatty liver disease (NAFLD) and its relation to the epidemic of obesity in the general population, it is imperative to develop detection and evaluation methods of the early stages of the disease with improved efficacy over the current diagnostic approaches. We aimed to obtain an improved diagnosis, combining methods of optical spectroscopy -diffuse reflectance and fluorescence- with statistical data analysis applied to detect early stages of NAFLD.

METHODS

Statistical analysis scheme based on quadratic discriminant analysis followed by canonical discriminant analysis were applied to the diffuse reflectance data combined with endogenous fluorescence spectral data excited at one of these wavelengths: 330, 365, 385, 405 or 415 nm. The statistical scheme was also applied to the combinations of fluorescence spectrum (405 nm) with each one of the other fluorescence spectra. Details of the developed software, including the application of machine learning algorithms to the combination of spectral data followed by classification statistical schemes, are discussed.

RESULTS

Steatosis progression was differentiated with little classification error (≤1.3%) by using diffuse reflectance and endogenous fluorescence at different wavelengths. Similar results were obtained using fluorescence at 405 nm and one of the other fluorescence spectra (classification error ≤1.0%). Adding the corresponding areas under the curves to the above combinations of spectra diminished errors to 0.6% and 0.3% or less, respectively. The best results for the compounded reflectance-plus-fluorescence spectra were obtained with fluorescence spectra excited at 415 nm with a total classification error of 0.2%; for the combination of the 405nm-excited fluorescence spectrum with another fluorescence spectrum, the best results were achieved for 385 nm, for which total relative classification error amounted 0.4%. The consideration of the area under the spectral curves further improved both classifiers, reducing the error to 0.0% in both cases.

CONCLUSION

Spectrometric techniques combined with statistical processing are a promising tool to improve steatosis classification through a label free approach. However, statistical schemes here applied, might result complex for the everyday medical practice, the designed software including machine learning algorithms is able to render automatic classification of samples according to their steatosis grade with low error.

Study of Methionine Choline Deficient Diet-Induced Steatosis in Mice Using Endogenous Fluorescence Spectroscopy

Non-alcoholic fatty liver disease is a highly prevalent condition worldwide that increases the risk to develop liver fibrosis, cirrhosis, and hepatocellular carcinoma. Thus, it is imperative to develop novel diagnostic tools that together with liver biopsy help to differentiate mild and advanced degrees of steatosis. Ex-vivo liver samples were collected from mice fed a methionine-choline deficient diet for two or eight weeks, and from a control group. The degree of hepatic steatosis was histologically evaluated, and fat content was assessed by Oil-Red O staining. On the other hand, fluorescence spectroscopy was used for the assessment of the steatosis progression. Fluorescence spectra were recorded at excitation wavelengths of 330, 365, 385, 405, and 415 nm by establishing surface contact of the fiber optic probe with the liver specimens. A multi-variate statistical approach based on principal component analysis followed by quadratic discriminant analysis was applied to spectral data to obtain classifiers able to distinguish mild and moderate stages of steatosis at the different excitation wavelengths. Receiver Operating Characteristic (ROC) curves were computed to compare classifier’s performances for each one of the five excitation wavelengths and steatosis stages. Optimal sensitivity and specificity were calculated from the corresponding ROC curves using the Youden index. Intensity in the endogenous fluorescence spectra at the given wavelengths progressively increased according to the time of exposure to diet. The area under the curve of the spectra was able to discriminate control liver samples from those with steatosis and differentiate among the time of exposure to the diet for most of the used excitation wavelengths. High specificities and sensitivities were obtained for every case; however, fluorescence spectra obtained by exciting with 405 nm yielded the best results distinguishing between the mentioned classes with a total classification error of 1.5% and optimal sensitivities and specificities better than 98.6% and 99.3%, respectively.

A new formula as a predictive score of post-liver transplantation outcome: postoperative MELD-lactate

INTRODUCTION

Liver transplantation (OLT) involves a 5% to 10% 30-day mortality rate. Multiple scores have been used as predictors of early postoperative mortality, such as the original Model for End-stage Liver Disease (MELD) and MELD sodium. Investigations have been conducted over the last 5 years to find new predictors of early post-OLT mortality.

OBJECTIVE

The aim of this study was to develop a new mathematical model to predict the individual chance of 30-day mortality after OLT.

METHODS

The study was conducted on 58 patients submitted to OLT at the University Hospital, between October 2008 and March 2012. The 29 latest survivor and 29 latest nonsurvivor cases were selected. Arterial blood sodium, lactate, international normalized ratio, total bilirubin, and creatinine values were determined 1 hour after the end of surgery. The MELD original equation, MELD sodium, and new MELD lactate were also elaborated. The results were analyzed by the Mann-Whitney and Wilcoxon tests. The level of significance was set at .05.

RESULTS

The new formula elaborated was as follows: MELD lactate = 5.68 × loge (lactate) + 0.64 × (Original MELD) + 2.68. The MELD lactate values were significantly higher than the MELD sodium and original MELD values (P < .05). The area under the receiver operating characteristic curve of MELD lactate in predicting the outcome of patients submitted to OLT was 0.80, as opposed to 0.71 for the original MELD and 0.72 for MELD sodium (P < .05).

CONCLUSION

The postoperative MELD lactate score proved to be more specific and sensitive than the original MELD and MELD sodium as a predictive model of the outcome of patients submitted to OLT.

Bilirubin: an autofluorescence bile biomarker for liver functionality monitoring

Excitation at 366-465 nm of bilirubin in aqueous solution with solubilizing agents results in emission spectra composed by two main bands. The variation of their relative contributions as shown by changes in the spectral shape are consistent with the bilirubin bichromophore nature. This latter accounts for an exciton-coupling phenomenon, intramolecular interchromophore energy transfer efficiency being affected by microenvironment. Excitation at 366 nm, despite the poor absorption of bilirubin, gives rise to appreciable emission signals from both pure compounds and bile - collected from functionally altered rat livers - favouring the spectral shape response to environment and molecular conformation changes. As compared to the merely bile flow estimation, real-time detection of fluorescence, revealing composition variations, improves near-UV optical-biopsy diagnostic potential in hepatology.

Integrated autofluorescence characterization of a modified-diet liver model with accumulation of lipids and oxidative stress

Oxidative stress in fatty livers is mainly generated by impaired mitochondrial β-oxidation, inducing tissue damages and disease progression. Under suitable excitation, light liver endogenous fluorophores can give rise to autofluorescence (AF) emission, the properties of which depend on the organ morphofunctional state. In this work, we characterized the AF properties of a rat liver model of lipid accumulation and oxidative stress, induced by a 1–9-week hypercaloric methionine-choline deficient (MCD) diet administration. The AF analysis (excitation at 366 nm) was performed in vivo, via fiber optic probe, or ex vivo. The contribution of endogenous fluorophores involved in redox reactions and in tissue organization was estimated through spectral curve fitting analysis, and AF results were validated by means of different histochemical and biochemical assays (lipids, collagen, vitamin A, ROS, peroxidised proteins, and lipid peroxidation -TBARS-, GSH, and ATP). In comparison with the control, AF spectra changes found already at 1 week of MCD diet reflect alterations both in tissue composition and organization (proteins, lipopigments, and vitamin A) and in oxidoreductive pathway engagement (NAD(P)H, flavins), with a subsequent attempt to recover redox homeostasis. These data confirm the AF analysis potential to provide a comprehensive diagnostic information on negative effects of oxidative metabolism alteration.

Multi-excitation fluorescence spectroscopy for analysis of non-alcoholic fatty liver disease

BACKGROUND AND OBJECTIVES

The increasing incidence of non-alcoholic fatty liver diseases (NAFLD) and the consequent progression to cirrhosis is expected to become a major cause of liver transplantation. This will exacerbate the organ donor shortage and mean that 'marginal' fatty liver grafts are more frequently used. Autofluorescence spectroscopy is a fast, objective, and non-destructive method to detect change in the endogenous fluorophores distribution and could prove to be a valuable tool for NAFLD diagnosis and transplant graft assessment.

MATERIALS AND METHODS

A system was constructed consisting of a fibre probe with two laser diodes that provided excitation light at 375 and 405 nm, and an imaging spectrograph system. This was used to distinguish fluorescence spectra acquired from the harvested livers from mice with NAFLD of differing severity (healthy, mild steatotic and steatohepatitic). The fluorescence data were entered into a sparse multiclass probabilistic algorithm for disease classification. Histopathology, thiobarbituric acid reactive substances (TBARS) and alanine transaminase (ALT) assays were conducted in addition to the fluorescence measurements

RESULTS

TBARS and ALT assays enabled differentiation of the steatohepatitic group from the mild steatosis and control groups (P ≤ 0.028) but failed to separate the mild steatotic group from the control group. The three groups were all clearly differentiated from each other using fluorescence spectroscopy, and classification accuracy was found to be 95%.

CONCLUSION

Fluorescence spectroscopy appears to be a promising approach for the analysis of diseased liver tissue.

Human liver autofluorescence: an intrinsic tissue parameter discriminating normal and diseased conditions

BACKGROUND AND OBJECTIVE

Autofluorescence (AF) emission is an intrinsic parameter that can provide real-time information on morpho-functional properties of biological tissue, being strictly related with their biochemical composition and structural organization. The diagnostic potentials of AF-based techniques have been investigated on normal, fibrotic, and steatotic liver tissues, in reference to histological features as evidenced by specific histochemical stainings.

MATERIALS AND METHODS

AF emission under excitation at 366 nm has been examined on cryostatic tissue sections obtained from biopsies collected during surgical operation, by means of fluorescence imaging and microspectrofluorometric techniques.

RESULTS

NAD(P)H, collagen, and vitamin A were found to be the endogenous fluorophores characterizing normal, fibrotic, and steatotic liver tissue AF, respectively. The differences of their photo-physical properties, in terms of emission amplitude, spectral shape, and response to irradiation, give rise to modifications of overall AF signal collected from tissues that allow the liver conditions to be distinguished.

CONCLUSION

The study provides a valid premise for a development of AF-based optical biopsy techniques for a real-time discrimination of liver anatomo-pathological patterns.