Fluorescence Lifetime Measurements and Analyses: Protocols Using Flow Cytometry and High-Throughput Microscopy

This chapter focuses on applications and protocols that involve the measurement of the fluorescence lifetime as an informative cytometric parameter. The timing of fluorescence decay has been well-studied for cell counting, sorting, and imaging. Therefore, provided herein is an overview of the techniques used, how they enhance cytometry protocols, and the modern techniques used for lifetime analysis. The background and theory behind fluorescence decay kinetic measurements in cells is first discussed followed by the history of the development of time-resolved flow cytometry. These sections are followed by a review of applications that benefit from the quantitative nature of fluorescence lifetimes as a photophysical trait. Lastly, perspectives on the modern ways in which the fluorescence lifetime is scanned at high throughputs which include high-speed microscopy and machine learning are provided.

A Review of New High-Throughput Methods Designed for Fluorescence Lifetime Sensing From Cells and Tissues

Though much of the interest in fluorescence in the past has been on measuring spectral qualities such as wavelength and intensity, there are two other highly useful intrinsic properties of fluorescence: lifetime (or decay) and anisotropy (or polarization). Each has its own set of unique advantages, limitations, and challenges in detection when it comes to use in biological studies. This review will focus on the property of fluorescence lifetime, providing a brief background on instrumentation and theory, and examine the recent advancements and applications of measuring lifetime in the fields of high-throughput fluorescence lifetime imaging microscopy (HT-FLIM) and time-resolved flow cytometry (TRFC). In addition, the crossover of these two methods and their outlooks will be discussed.

120 MATERNAL EXPOSURE TO DIESEL ENGINE EXHAUST DURING PREGNANCY AFFECTS EARLY EMBRYO DEVELOPMENT IN A RABBIT MODEL

Airborne pollution has been associated with various adverse effects on human reproductive health, especially intrauterine growth retardation and early pregnancy loss. However, few studies have analysed its effect on early development. Diesel exhaust particles (DEP) have been shown to alter blastocyst formation when diluted in embryo culture medium (2010 Toxicol Sci. 117, 200–208), but no data are available concerning the effect of maternal inhalation of diesel exhaust on early embryo development. Our study has been designed to answer this question using rabbit as a model and DEP doses mimicking daily exposure to traffic in large European cities. New Zealand female rabbits were superovulated by means of 5 subcutaneous administration of pFSH for 3 days before mating, followed 10 to 12 h later by an intravenous administration of 30 IU of hCG at the time of mating (natural mating). Dams were exposed to a representative air pollution mixture; that is, diluted diesel engine exhaust (1 mg m–3; N = 14) or clean air (N = 12), for 1 h every morning and afternoon, from Day 3 to Day 6 post-coitum (dpc). At 6 dpc, in vivo-developed embryos were collected from uteri perfused with PBS and counted; their diameter was measured on pictures using ImageJ software (NIH, Bethesda, MD, USA). Another group of female rabbits was exposed to the same inhalation conditions from 3 to 27 dpc without superovulation treatment. Measures by ultrasound were performed on these dams at 7 dpc. Data were analysed by Mann-Whitney test and ANOVA, including dams as cofactor. At 6 dpc, number of embryos per dams was higher in exposed group compared with control (P < 0.05). In contrast, embryo diameter was significantly lower in the DEP exposed group compared with the clean air exposed group (P < 0.01). Gene expression analysis is being performed in these embryos. At 7 dpc, ultrasound measurements evidenced a decrease in embryo diameter, perimeter, and volume in the exposed group compared with control (P < 0.01, P < 0.01, and P < 0.01, respectively). These data indicate that repeated exposure to airborne pollution even for daily short periods affects early development. Consequences of maternal DEP exposure on feto-placental development are under investigation.

73 INTRAUTERINE GROWTH RESTRICTION AFTER BETWEEN-BREED EMBRYO TRANSFER IS ASSOCIATED WITH STRONG ALTERATIONS IN PLACENTAL STRUCTURE AND FUNCTION IN HORSES

In equids, placentation is diffuse and the nutrient supply to the fetus is determined by uterine size, which is correlated with maternal size. The size of the mare affects fetal development as shown by embryo transfer (ET) between Ponies and Thoroughbreds. In turn, insulin sensitivity in the newborn foal and subsequent postnatal growth rate are affected. We enhanced or restricted fetal growth through ET using Pony (P), Saddlebred (S), and Draft (D) horses and investigated placental morphology, structure, and function at term. Control pregnancies of P-P (n = 21), S-S (n = 28), and D-D (n = 8) were obtained by AI. Enhanced and restricted pregnancies were obtained by transferring P (P-D, n = 6) and S embryos (S-D, n = 8) into D mares or S embryos into P mares (S-P, n = 6), respectively. Placental weight and surface were recorded at delivery. Samples were collected for stereology and RT-qPCR analysis of expression of genes involved in placental growth, vascularization, and nutrient transport. Housekeeping genes were RPL32, SCAMP3, and B2M. Data were analysed by Kruskal-Wallis followed by Dunn's post hoc test. Placental weight and surface were increased in S-S and in D-D compared with P-P, whereas S-S and D-D were not different. No histological changes were observed among controls, but most genes had their expression decreased in P-P compared with S-S and D-D. The P-D foals had a 57% increased birthweight with heavier and larger placentas than P-P foals. The S-D foals were similar to both S-S and D-D in terms of birthweight and placental weight and surface. No major modifications in placental histology or transcript levels were observed in both enhanced groups. In contrast, S-P foals had a 37% decreased birthweight with lighter and smaller placentas compared with S-S and S-D foals. There was no gross histological difference between S-P and S-S but the microcotyledonary surface density was higher in S-P compared with S-D. Moreover, the expression of IGF2, IGF2R, SLC2A1, and eNOS was decreased in S-P compared with S-S. There was no difference in gene expression between S-P and P-P. In conclusion, intrauterine growth restriction led to marked changes in placental morphology, histology, and gene expression. The increased microcotyledonary surface density suggests a lengthening of villi, which could increase feto-maternal contact surface as a compensatory mechanism for the restricted uterine capacity. Surprisingly, placental adaptation to the restricted intrauterine environment in S-P induced gene profiles resembling that of control P, whereas no difference was observed in enhanced pregnancies.

Early nocturnal blood pressure changes in diabetic autonomic neuropathy assessed by Fourier series

The 24 h periodic pattern of blood pressure was studied in 44 patients with diabetes mellitus (14 type 1, 30 type 2; mean duration of disease 6.5 +/- 1.8 years) in good metabolic control but with abnormal cardiovascular reflex responses; of these 21 were normotensive and 23 hypertensive. All had abnormal responses to at least two out of four tests: deep breathing, lying to standing, Valsalva manoeuvre and postural hypotension. Two sex- and age-matched groups, consisting of 20 normotensive and 20 hypertensive diabetic patients without dysautonomia, were studied as controls. Each patient underwent ambulatory blood pressure monitoring for at least 24 h, using an auscultatory automatic device. Data were analysed using the sum of three periodic functions (Fourier partial sum). In the diabetic normotensive groups, the absolute blood pressure fell to its night-time minimum more rapidly, and increased to its morning maximum more slowly, in those with abnormal cardiovascular reflexes than in the controls (nightly blood pressure decrease -5.8/-4.7 vs. -3.8/-4.0 mmHg/h; increase 4.7/3.6 vs. 5.9/6.1 mmHg/h). The same behaviour was found in both hypertensive groups but the amplitude of the differences was more marked (blood pressure nocturnal decrease -7.7/-7.1 vs. -4.3/-3.9 mmHg/h; increase 3.2/2.1 vs. 5.8/4.3 mmHg/h). This analysis of 24 h ambulatory blood pressure data may be of value in diagnosis and evaluation of autonomic deficits.

[A validation of the data obtained with the simultaneous recording of blood pressure and the 24-hour electrocardiogram]

Aim of this study was to evaluate the blood pressure (BP) measurement reliability of a light weight ambulatory BP and ECG recorder. Micro AM is a new 300 g portable apparatus that combines in one device both the ambulatory BP and solid state ECG recording. The dimensions of the Micro AM are 75 x 140 x 29 mm. The monitor measures BP using Korotkoff phase 1 for systolic and phase 5 for diastolic BP, and concurrently measures oscillometric BP, one method validating the other. In addition, the manual and programmed BP measurement modes can be supplemented by an "intelligent" mode in which the ECG triggers an ambulatory BP reading during an abnormal ST segment change. A standard mercury manometer was connected with the cuff of the Micro AM with a Y-shaped part, and 12 BP measurements were simultaneously taken at 5 min intervals by the automatic device in auscultatory mode and by a trained technician in 86 normotensive volunteers (aged from 18 to 44 years, 37 males and 49 females). The algebraic differences, the frequency distribution and the difference distribution of systolic and diastolic data between the 2 methods were calculated. The results show that the automatic method gives values for systolic BP that are lower than conventional ones (average differences -0.643 mmHg), whereas for diastolic BP, the values are higher (average differences +0.229 mmHg). Then, Student's paired t-test was used to evaluate statistically significant differences. The test relative to systolic BP was significant to the critical level of 0.1%, but the differences being 3 times smaller than the instrumental tolerance. On the contrary, diastolic BP differences were non significant. In conclusion, we found a good agreement between BP recorded automatically and by sphygmomanometer.

Plasma atrial natriuretic peptide in young normotensive subjects with a family history of hypertension and in young hypertensive patients

Plasma atrial natriuretic peptide (ANP) behavior was evaluated in 26 untreated essential hypertensives, 21 normotensives, and 20 normotensives with hypertensive heredity under normal sodium intake (120 mEq of Na+/day). All subjects were men, mean age 22.1 +/- 1.9 years. Plasma ANP was evaluated by radioimmunoassay on samples collected in supine position upon waking and again after 1 h of orthostatism. Resulting data showed that ANP in hypertensives (supine = 44.5 +/- 19.4 pg/mL, orthostatism = 24.1 +/- 11.6 pg/mL) was at higher levels than in controls (supine = 38.3 +/- 19.4 pg/mL, orthostatism = 19.9 +/- 10.6 pg/mL) or in normotensives with hypertensive heredity (supine = 42.1 +/- 16.8 pg/mL, orthostatism = 23.2 +/- 10.8 pg/mL). Mean ANP level was higher in the latter group than in the control group (supine = +9%; orthostatism = +14.2%). In conclusion, plasma ANP is raised in young essential hypertensives, resulting in slightly elevated levels in normotensives with hypertensive heredity.

[Relation of atrial natriuretic peptide and endogenous digoxin-like activity in the plasma of young hypertensive patients]

The relationships between plasma digoxin-like immunoreactivity (DLS) and atrial natriuretic peptide (ANP) were investigated in 10 young essential hypertensives (mean age 22 +/- 2 years) and in 10 normotensives. In young hypertensives, plasma DLS and ANP were at an average level of 31.2 +/- 8 pg/ml and 56.7 +/- 20 pg/ml respectively, showing a significant correlation (r = 0.66; p less than 0.05). In normal subjects plasma DLS and ANP were at an average level of 19.1 +/- 8 pg/ml and 37.6 +/- 16.7 pg/ml respectively (n.s.). Plasma DLS and ANP were higher in hypertensives than in normotensives (p less than 0.01). In conclusion, DLS and ANP appear to have a similar behaviour, possibly due to their modulation by common stimuli.

[Effects of active orthostatism on blood levels of atrial natriuretic peptide in the healthy subject]

The effects of active changes in posture, from recumbency to upright position (60 minutes), on the circulating levels of atrial natriuretic peptide (ANP) in healthy human subjects were studied by using a radioimmunoassay method. In supine position, plasma ANP levels ranged from 12 pg/ml to 51.5 pg/ml, with an average level of 35.3 +/- 11.5 pg/ml. After 1 hour of orthostatic position, plasma ANP levels varied from 10 pg/ml to 35 pg/ml, with an average level of 21 +/- 11.5 pg/ml. These results suggest that ANP is involved in the hemodynamic modifications following postural stimuli. Thus, postural changes can be taken in to account for evaluating plasma ANP behaviour properly.