Feeding Behavior Modifies the Circadian Variation in RR and QT intervals by Distinct Mechanisms in Mice

Rhythmic feeding behavior is critical for regulating phase and amplitude in the »24-hour variation of heart rate (RR intervals), ventricular repolarization (QT intervals), and core body temperature in mice. We hypothesized changes in cardiac electrophysiology associated with feeding behavior were secondary to changes in core body temperature. Telemetry was used to record electrocardiograms and core body temperature in mice during ad libitum-fed conditions and after inverting normal feeding behavior by restricting food access to the light cycle. Light cycle-restricted feeding modified the phase and amplitude of 24-hour rhythms in RR and QT intervals, and core body temperature to realign with the new feeding time. Changes in core body temperature alone could not account for changes in phase and amplitude in the »24-hour variation of the RR intervals. Heart rate variability analysis and inhibiting β-adrenergic and muscarinic receptors suggested that changes in the phase and amplitude of 24-hour rhythms in RR intervals were secondary to changes in autonomic signaling. In contrast, changes in QT intervals closely mirrored changes in core body temperature. Studies at thermoneutrality confirmed that the daily variation in QT interval, but not RR interval, primarily reflected daily changes in core body temperature (even in ad libitum-fed conditions). Correcting the QT interval for differences in core body temperature helped unmask QT interval prolongation after starting light cycle-restricted feeding and in a mouse model of long QT syndrome. We conclude feeding behavior alters autonomic signaling and core body temperature to regulate phase and amplitude in RR and QT intervals, respectively.

Feeding Behavior Modifies the Circadian Variation in RR and QT intervals by Distinct Mechanisms in Mice

Rhythmic feeding behavior is critical for regulating the phase and amplitude in the ≍24-hour variation of the heart rate (RR intervals), ventricular repolarization (QT intervals), and core body temperature in mice. We hypothesized the changes in cardiac electrophysiology associated with feeding behavior were secondary to changes in core body temperature. Telemetry was used to record electrocardiograms and core body temperature in mice during ad libitum-fed conditions and after inverting normal feeding behavior by restricting food access to the light cycle. Light cycle-restricted feeding quickly modified the phase and amplitude of the 24-hour rhythms in RR intervals, QT intervals, and core body temperature to realign with the new feeding time. Heart rate variability analysis and inhibiting β-adrenergic and muscarinic receptors suggested that the changes in the phase and amplitude of the 24-hour rhythms in RR intervals were secondary to changes in autonomic signaling. In contrast, the changes in the QT intervals closely mirrored changes in core body temperature. Studies at thermoneutrality confirmed the daily variation in the QT interval, but not the RR interval, and reflected daily changes in core body temperature (even in ad libitum-fed conditions). Correcting the QT interval for differences in core body temperature helped to unmask QT interval prolongation after starting light cycle-restricted feeding and in a mouse model of long QT syndrome. We conclude feeding behavior alters autonomic signaling and core body temperature to regulate the phase and amplitude in RR and QT intervals, respectively.

Circadian Regulation of Cardiac Arrhythmias and Electrophysiology

Circadian rhythms in physiology and behavior are ≈24-hour biological cycles regulated by internal biological clocks (ie, circadian clocks) that optimize organismal homeostasis in response to predictable environmental changes. These clocks are present in virtually all cells in the body, including cardiomyocytes. Many decades ago, clinicians and researchers became interested in studying daily patterns of triggers for sudden cardiac death, the incidence of sudden cardiac death, and cardiac arrhythmias. This review highlights historical and contemporary studies examining the role of day/night rhythms in the timing of cardiovascular events, delves into changes in the timing of these events over the last few decades, and discusses cardiovascular disease-specific differences in the timing of cardiovascular events. The current understanding of the environmental, behavioral, and circadian mechanisms that regulate cardiac electrophysiology is examined with a focus on the circadian regulation of cardiac ion channels and ion channel regulatory genes. Understanding the contribution of environmental, behavioral, and circadian rhythms on arrhythmia susceptibility and the incidence of sudden cardiac death will be essential in developing future chronotherapies.

Mutation-Specific Differences in Kv7.1 (KCNQ1) and Kv11.1 (KCNH2) Channel Dysfunction and Long QT Syndrome Phenotypes

The electrocardiogram (ECG) empowered clinician scientists to measure the electrical activity of the heart noninvasively to identify arrhythmias and heart disease. Shortly after the standardization of the 12-lead ECG for the diagnosis of heart disease, several families with autosomal recessive (Jervell and Lange-Nielsen Syndrome) and dominant (Romano-Ward Syndrome) forms of long QT syndrome (LQTS) were identified. An abnormally long heart rate-corrected QT-interval was established as a biomarker for the risk of sudden cardiac death. Since then, the International LQTS Registry was established; a phenotypic scoring system to identify LQTS patients was developed; the major genes that associate with typical forms of LQTS were identified; and guidelines for the successful management of patients advanced. In this review, we discuss the molecular and cellular mechanisms for LQTS associated with missense variants in KCNQ1 (LQT1) and KCNH2 (LQT2). We move beyond the "benign" to a "pathogenic" binary classification scheme for different KCNQ1 and KCNH2 missense variants and discuss gene- and mutation-specific differences in K+ channel dysfunction, which can predispose people to distinct clinical phenotypes (e.g., concealed, pleiotropic, severe, etc.). We conclude by discussing the emerging computational structural modeling strategies that will distinguish between dysfunctional subtypes of KCNQ1 and KCNH2 variants, with the goal of realizing a layered precision medicine approach focused on individuals.

The role of the cardiomyocyte circadian clocks in ion channel regulation and cardiac electrophysiology

Daily variations in cardiac electrophysiology and the incidence for different types of arrhythmias reflect ≈24 h changes in the environment, behaviour and internal circadian rhythms. This article focuses on studies that use animal models to separate the impact that circadian rhythms, as well as changes in the environment and behaviour, have on 24 h rhythms in heart rate and ventricular repolarization. Circadian rhythms are initiated at the cellular level by circadian clocks, transcription-translation feedback loops that cycle with a periodicity of 24 h. Several studies now show that the circadian clock in cardiomyocytes regulates the expression of cardiac ion channels by multiple mechanisms; underlies time-of-day changes in sinoatrial node excitability/intrinsic heart rate; and limits the duration of the ventricular action potential waveform. However, the 24 h rhythms in heart rate and ventricular repolarization are primarily driven by autonomic signalling. A functional role for the cardiomyocyte circadian clock appears to buffer the heart against perturbations. For example, the cardiomyocyte circadian clock limits QT-interval prolongation (especially at slower heart rates), and it may facilitate the realignment of the 24 h rhythm in heart rate to abrupt changes in the light cycle. Additional studies show that modifying rhythmic behaviours (including feeding behaviour) can dramatically impact the 24 h rhythms in heart rate and ventricular repolarization. If these mechanisms are conserved, these studies suggest that targeting endogenous circadian mechanisms in the heart, as well as modifying the timing of certain rhythmic behaviours, could emerge as therapeutic strategies to support heart function against perturbations and regulate 24 h rhythms in cardiac electrophysiology.

Timing of food intake in mice unmasks a role for the cardiomyocyte circadian clock mechanism in limiting QT-interval prolongation

Cardiac electrophysiological studies demonstrate that restricting the feeding of mice to the light cycle (time restricted feeding or TRF) causes a pronounced change in heart rate and ventricular repolarization as measured by the RR- and QT-interval, respectively. TRF slows heart rate and shifts the peak (acrophase) of the day/night rhythms in the RR- and QT-intervals from the light to the dark cycle. This study tested the hypothesis that these changes in cardiac electrophysiology are driven by the cardiomyocyte circadian clock mechanism. We determined the impact that TRF had on RR- and QT-intervals in control mice or mice that had the cardiomyocyte circadian clock mechanism disrupted by inducing the deletion of Bmal1 in adult cardiomyocytes (iCSΔBmal1^-/- mice). In control and iCSΔBmal1^-/- mice, TRF increased the RR-intervals measured during the dark cycle and shifted the acrophase of the day/night rhythm in the RR-interval from the light to the dark cycle. Compared to control mice, TRF caused a larger prolongation of the QT-interval measured from iCSΔBmal1^-/- mice during the dark cycle. The larger QT-interval prolongation in the iCSΔBmal1^-/- mice caused an increased mean and amplitude in the day/night rhythm of the QT-interval. There was not a difference in the TRF-induced shift in the day/night rhythm of the QT-interval measured from control or iCSΔBmal1^-/- mice. We conclude that the cardiomyocyte circadian clock does not drive the changes in heart rate or ventricular repolarization with TRF. However, TRF unmasks an important role for the cardiomyocyte circadian clock to prevent excessive QT-interval prolongation, especially at slow heart rates.

Cardiomyocyte Deletion of Bmal1 Exacerbates QT- and RR-Interval Prolongation in Scn5a +/ΔKPQ Mice

Circadian rhythms are generated by cell autonomous circadian clocks that perform a ubiquitous cellular time-keeping function and cell type-specific functions important for normal physiology. Studies show inducing the deletion of the core circadian clock transcription factor Bmal1 in adult mouse cardiomyocytes disrupts cardiac circadian clock function, cardiac ion channel expression, slows heart rate, and prolongs the QT-interval at slow heart rates. This study determined how inducing the deletion of Bmal1 in adult cardiomyocytes impacted the in vivo electrophysiological phenotype of a knock-in mouse model for the arrhythmogenic long QT syndrome (Scn5a^+/ΔKPQ). Electrocardiographic telemetry showed inducing the deletion of Bmal1 in the cardiomyocytes of mice with or without the ΔKPQ-Scn5a mutation increased the QT-interval at RR-intervals that were ≥130 ms. Inducing the deletion of Bmal1 in the cardiomyocytes of mice with or without the ΔKPQ-Scn5a mutation also increased the day/night rhythm-adjusted mean in the RR-interval, but it did not change the period, phase or amplitude. Compared to mice without the ΔKPQ-Scn5a mutation, mice with the ΔKPQ-Scn5a mutation had reduced heart rate variability (HRV) during the peak of the day/night rhythm in the RR-interval. Inducing the deletion of Bmal1 in cardiomyocytes did not affect HRV in mice without the ΔKPQ-Scn5a mutation, but it did increase HRV in mice with the ΔKPQ-Scn5a mutation. The data demonstrate that deleting Bmal1 in cardiomyocytes exacerbates QT- and RR-interval prolongation in mice with the ΔKPQ-Scn5a mutation.

Long QT Syndrome Type 2: Emerging Strategies for Correcting Class 2 KCNH2 (hERG) Mutations and Identifying New Patients

Significant advances in our understanding of the molecular mechanisms that cause congenital long QT syndrome (LQTS) have been made. A wide variety of experimental approaches, including heterologous expression of mutant ion channel proteins and the use of inducible pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) from LQTS patients offer insights into etiology and new therapeutic strategies. This review briefly discusses the major molecular mechanisms underlying LQTS type 2 (LQT2), which is caused by loss-of-function (LOF) mutations in the KCNH2 gene (also known as the human ether-à-go-go-related gene or hERG). Almost half of suspected LQT2-causing mutations are missense mutations, and functional studies suggest that about 90% of these mutations disrupt the intracellular transport, or trafficking, of the KCNH2-encoded Kv11.1 channel protein to the cell surface membrane. In this review, we discuss emerging strategies that improve the trafficking and functional expression of trafficking-deficient LQT2 Kv11.1 channel proteins to the cell surface membrane and how new insights into the structure of the Kv11.1 channel protein will lead to computational approaches that identify which KCNH2 missense variants confer a high-risk for LQT2.

Functional Invalidation of Putative Sudden Infant Death Syndrome-Associated Variants in the KCNH2-Encoded Kv11.1 Channel

BACKGROUND

Heterologous functional validation studies of putative long-QT syndrome subtype 2-associated variants clarify their pathological potential and identify disease mechanism(s) for most variants studied. The purpose of this study is to clarify the pathological potential for rare nonsynonymous KCNH2 variants seemingly associated with sudden infant death syndrome.

METHODS

Genetic testing of 292 sudden infant death syndrome cases identified 9 KCNH2 variants: E90K, R181Q, A190T, G294V, R791W, P967L, R1005W, R1047L, and Q1068R. Previous studies show R181Q-, P967L-, and R1047L-Kv11.1 channels function similar to wild-type Kv11.1 channels, whereas Q1068R-Kv11.1 channels accelerate inactivation gating. We studied the biochemical and biophysical properties for E90K-, G294V-, R791W-, and R1005W-Kv11.1 channels expressed in human embryonic kidney 293 cells; examined the electronic health records of patients who were genotype positive for the sudden infant death syndrome-linked KCNH2 variants; and simulated their functional impact using computational models of the human ventricular action potential.

RESULTS

Western blot and voltage-clamping analyses of cells expressing E90K-, G294V-, R791W-, and R1005W-Kv11.1 channels demonstrated these variants express and generate peak Kv11.1 current levels similar to cells expressing wild-type-Kv11.1 channels, but R791W- and R1005W-Kv11.1 channels accelerated deactivation and activation gating, respectively. Electronic health records of patients with the sudden infant death syndrome-linked KCNH2 variants showed that the patients had median heart rate-corrected QT intervals <480 ms and none had been diagnosed with long-QT syndrome or experienced cardiac arrest. Simulating the impact of dysfunctional gating variants predicted that they have little impact on ventricular action potential duration.

CONCLUSIONS

We conclude that these rare Kv11.1 missense variants are not long-QT syndrome subtype 2-causative variants and therefore do not represent the pathogenic substrate for sudden infant death syndrome in the variant-positive infants.

Molecular pathogenesis of long QT syndrome type 2

The molecular mechanisms underlying congenital long QT syndrome (LQTS) are now beginning to be understood. New insights into the etiology and therapeutic strategies are emerging from heterologous expression studies of LQTS-linked mutant proteins, as well as inducible pluripotent stem cell derived cardiomyocytes (iPSC-CMs) from LQTS patients. This review focuses on the major molecular mechanism that underlies LQTS type 2 (LQT2). LQT2 is caused by loss of function (LOF) mutations in KCNH2 (also known as the human Ether-à-go-go-Related Gene or hERG). Most LQT2-linked mutations are missense mutations and functional studies suggest that ~90% of them disrupt the intracellular transport (trafficking) of KCNH2-encoded Kv11.1 proteins to the cell membrane. Trafficking deficient LQT2 mutations disrupt Kv11.1 protein folding and misfolded Kv11.1 proteins are retained in the endoplasmic reticulum (ER) until they are degraded in the ER associated degradation pathway (ERAD). This review focuses on the quality control mechanisms in the ER that contribute to the folding and ERAD of Kv11.1 proteins; the mechanism for ER export of Kv11.1 proteins in the secretory pathway; different subclasses of trafficking deficient LQT2 mutations; and strategies being developed to mitigate or correct trafficking deficient LQT2-related phenotypes.

The cardiomyocyte molecular clock regulates the circadian expression of Kcnh2 and contributes to ventricular repolarization

BACKGROUND

Sudden cardiac death (SCD) follows a diurnal variation. Data suggest the timing of SCD is influenced by circadian (~24-hour) changes in neurohumoral and cardiomyocyte-specific regulation of the heart's electrical properties. The basic helix-loop-helix transcription factors brain muscle arnt-like1 (BMAL1) and circadian locomotor output control kaput (CLOCK) coordinate the circadian expression of select genes.

OBJECTIVE

We sought to test whether Bmal1 expression in cardiomyocytes contributes to K(+) channel expression and diurnal changes in ventricular repolarization.

METHODS

We used transgenic mice that allow for the inducible cardiomyocyte-specific deletion of Bmal1 (iCSΔBmal1(-/-)). We used quantitative polymerase chain reaction, voltage clamping, promoter-reporter bioluminescence assays, and electrocardiographic telemetry.

RESULTS

Although several K(+) channel gene transcripts were downregulated in iCSΔBmal1(-/-)mouse hearts, only Kcnh2 exhibited a robust circadian pattern of expression that was disrupted in iCSΔBmal1(-/-) hearts. Kcnh2 underlies the rapidly activating delayed-rectifier K(+) current, and the rapidly activating delayed-rectifier K(+) current recorded from iCSΔBmal1(-/-) ventricular cardiomyocytes was ~50% smaller than control ventricular myocytes. Promoter-reporter assays demonstrated that the human Kcnh2 promoter is transactivated by the coexpression of BMAL1 and CLOCK. Electrocardiographic analysis showed that iCSΔBmal1(-/-) mice developed a prolongation in the heart rate-corrected QT interval during the light (resting) phase. This was secondary to an augmented circadian rhythm in the uncorrected QT interval without a corresponding change in the RR interval.

CONCLUSION

The molecular clock in the heart regulates the circadian expression of Kcnh2, modifies K(+) channel gene expression, and is important for normal ventricular repolarization. Disruption of the cardiomyocyte circadian clock mechanism likely unmasks diurnal changes in ventricular repolarization that could contribute to an increased risk of cardiac arrhythmias/SCD.

Light phase-restricted feeding slows basal heart rate to exaggerate the type-3 long QT syndrome phenotype in mice

Long QT syndrome type 3 (LQT3) is caused by mutations in the SCN5A-encoded Nav1.5 channel. LQT3 patients exhibit time of day-associated abnormal increases in their heart rate-corrected QT (QTc) intervals and risk for life-threatening episodes. This study determines the effects of uncoupling environmental time cues that entrain circadian rhythms (time of light and time of feeding) on heart rate and ventricular repolarization in wild-type (WT) or transgenic LQT3 mice (Scn5a(+/ΔKPQ)). We used an established light phase-restricted feeding paradigm that disrupts the alignment among the circadian rhythms in the central pacemaker of the suprachiasmatic nucleus and peripheral tissues including heart. Circadian analysis of the RR and QT intervals showed the Scn5a(+/ΔKPQ) mice had QT rhythms with larger amplitudes and 24-h midline means and a more pronounced slowing of the heart rate. For both WT and Scn5a(+/ΔKPQ) mice, light phase-restricted feeding shifted the RR and QT rhythms ~12 h, increased their amplitudes greater than twofold, and raised the 24-h midline mean by ~10%. In contrast to WT mice, the QTc interval in Scn5a(+/ΔKPQ) mice exhibited time-of-day prolongation that was flipped after light phase-restricted feeding. The time-of-day changes in the QTc intervals of Scn5a(+/ΔKPQ) mice were secondary to a steeper power relation between their QT and RR intervals. We conclude that uncoupling time of feeding from normal light cues can dramatically slow heart rate to unmask genotype-specific differences in the QT intervals and aggravate the LQT3-related phenotype.

A KCNQ1 mutation contributes to the concealed type 1 long QT phenotype by limiting the Kv7.1 channel conformational changes associated with protein kinase A phosphorylation

BACKGROUND

Type 1 long QT syndrome (LQT1) is caused by loss-of-function mutations in the KCNQ1-encoded Kv7.1 channel that conducts the slowly activating component of the delayed rectifier K(+) current (IKs). Clinically, the diagnosis of LQT1 is complicated by variable phenotypic expressivity, whereby approximately 25% of genotype-positive individuals present with concealed LQT1 (resting corrected QT [QTc] interval ≤460 ms).

OBJECTIVE

To determine whether a specific molecular mechanism contributes to concealed LQT1.

METHODS

We identified a multigenerational LQT1 family whereby 79% of the patients genotype-positive for p.Ile235Asn-KCNQ1 (I235N-Kv7.1) have concealed LQT1. We assessed the effect I235N-Kv7.1 has on IKs and the ventricular action potential (AP) by using in vitro analysis and computational simulations.

RESULTS

Clinical data showed that all 10 patients with I235N-Kv7.1 have normal resting QTc intervals but abnormal QTc interval prolongation during the recovery phase of an electrocardiographic treadmill stress test. Voltage-clamping HEK293 cells coexpressing wild-type Kv7.1 and I235N-Kv7.1 (to mimic the patients' genotypes) showed that I235N-Kv7.1 generated relatively normal functioning Kv7.1 channels but were insensitive to protein kinase A (PKA) activation. Phosphomimetic and quinidine sensitivity studies suggest that I235N-Kv7.1 limits the conformational changes in Kv7.1 channels, which are necessary to upregulate IKs after PKA phosphorylation. Computational ventricular AP simulations predicted that the PKA insensitivity of I235N-Kv7.1 is primarily responsible for prolonging the AP with β-adrenergic stimulation, especially at slower cycle lengths.

CONCLUSIONS

KCNQ1 mutations that generate relatively normal Kv7.1 channels, but limit the upregulation of IKs by PKA activation, likely contribute to concealed LQT1.

A KCNQ1 mutation causes a high penetrance for familial atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is the most common cardiac arrhythmia, and its incidence is expected to grow. A genetic predisposition for AF has long been recognized, but its manifestation in these patients likely involves a combination of rare and common genetic variants. Identifying genetic variants that associate with a high penetrance for AF would represent a significant breakthrough for understanding the mechanisms that associate with disease.

METHOD AND RESULTS

Candidate gene sequencing in 5 unrelated families with familial AF identified the KCNQ1 missense mutation p.Arg231His (R231H). In addition to AF, several of the family members have abnormal QTc intervals, syncope or experienced sudden cardiac arrest or death. KCNQ1 encodes the voltage-gated K(+) channel that conducts the slowly activating delayed rectifier K(+) current in the heart. Functional and computational analyses suggested that R231H increases KCNQ1 current (I(KCNQ1)) to shorten the atrial action potential (AP) duration. R231H is predicted to minimally affect ventricular excitability, but it prevented the increase in I(KCNQ1) following PKA activation. The unique properties of R231H appeared to be caused by a loss in voltage-dependent gating.

CONCLUSIONS

The R231H variant causes a high penetrance for interfamilial early-onset AF. Our study indicates R231H likely shortens atrial refractoriness to promote a substrate for reentry. Additionally, R231H might cause abnormal ventricular repolarization by disrupting PKA activation of IKCNQ1 . We conclude genetic variants, which increase IKs during the atrial AP, decrease the atrial AP duration, and/or shorten atrial refractoriness, present a high risk for interfamilial AF.

High-risk long QT syndrome mutations in the Kv7.1 (KCNQ1) pore disrupt the molecular basis for rapid K(+) permeation

Type 1 long QT syndrome (LQT1) is caused by loss-of-function mutations in the KCNQ1 gene, which encodes the K(+) channel (Kv7.1) that underlies the slowly activating delayed rectifier K(+) current in the heart. Intragenic risk stratification suggests LQT1 mutations that disrupt conserved amino acid residues in the pore are an independent risk factor for LQT1-related cardiac events. The purpose of this study is to determine possible molecular mechanisms that underlie the loss of function for these high-risk mutations. Extensive genotype-phenotype analyses of LQT1 patients showed that T322M-, T322A-, or G325R-Kv7.1 confers a high risk for LQT1-related cardiac events. Heterologous expression of these mutations with KCNE1 revealed they generated nonfunctional channels and caused dominant negative suppression of WT-Kv7.1 current. Molecular dynamics simulations of analogous mutations in KcsA (T85M-, T85A-, and G88R-KcsA) demonstrated that they disrupted the symmetrical distribution of the carbonyl oxygen atoms in the selectivity filter, which upset the balance between the strong attractive and K(+)-K(+) repulsive forces required for rapid K(+) permeation. We conclude high-risk LQT1 mutations in the pore likely disrupt the architectural and physical properties of the K(+) channel selectivity filter.

Extended longitudinal analysis of arterial pressure and heart rate control in unanesthetized rats with type 1 diabetes

We recorded arterial pressure (BP) and heart rate (HR) in type-1 diabetic rats vs. controls for >6 months. Diabetic rats (DIAB) were maintained on insulin from the day glucose >250 mg/dl ("Day 0"). Weight was similar between groups until ~3 weeks before Day 0 when the weight in DIAB transiently lagged the controls (CONT); this difference was maintained throughout the study, but both groups otherwise gained weight in parallel. Plasma glucose attained 371 ± 109 (SD) mg/dl by day 1 in DIAB. Mean BP was similar across groups, and declined through the initial 4-6 months in both the CONT (at -0.06 ± 0.04 mmHg/day) and in the DIAB (at -0.14 ± 0.21 mmHg/day; NS vs. CONT). HR in the CONT (Month 1: 341 ± 13 bpm) exceeded DIAB (325 ± 25 bpm) through ~6 months after Day 0, and also decreased progressively over this period in CONT (-0.19 ± 0.14 bpm/day) and DIAB (-0.29 ± 0.23 bpm/day; NS vs. CONT) before leveling. The BP power within 0.35-0.45 Hz changed during the 90 min before vs. after the transition from dark to light, and light to dark; there were no between group differences. The slope of the log-log linear portion of the BP power spectrum between 1.0/h and 1/min was similar across groups, and increased in both from month 1 to month 6. Regulatory mechanisms maintain similar profiles in BP and HR in diabetic vs. control animals through the initial half year of the disease.

Longitudinal analysis of arterial blood pressure and heart rate response to acute behavioral stress in rats with type 1 diabetes mellitus and in age-matched controls

We recorded via telemetry the arterial blood pressure (BP) and heart rate (HR) response to classical conditioning following the spontaneous onset of autoimmune diabetes in BBDP/Wor rats vs. age-matched, diabetes-resistant control (BBDR/Wor) rats. Our purpose was to evaluate the autonomic regulatory responses to an acute stress in a diabetic state of up to 12 months duration. The stress was a 15-s pulsed tone (CS+) followed by a 0.5-s tail shock. The initial, transient increase in BP (i.e., the "first component," or C(1)), known to be derived from an orienting response and produced by a sympathetic increase in peripheral resistance, was similar in diabetic and control rats through ∼9 months of diabetes; it was smaller in diabetic rats 10 months after diabetes onset. Weakening of the C(1) BP increase in rats that were diabetic for >10 months is consistent with the effects of sympathetic neuropathy. A longer-latency, smaller, but sustained "second component" (C(2)) conditional increase in BP, that is acquired as a rat learns the association between CS+ and the shock, and which results from an increase in cardiac output, was smaller in the diabetic vs. control rats starting from the first month of diabetes. A concomitant HR slowing was also smaller in diabetic rats. The difference in the C(2) BP increase, as observed already during the first month of diabetes, is probably secondary to the effects of hyperglycemia upon myocardial metabolism and contractile function, but it may also result from effects on cognition. The small HR slowing concomitant with the C(2) pressor event is probably secondary to differences in baroreflex activation or function, though parasympathetic dysfunction may contribute later in the duration of diabetes. The nearly immediate deficit after disease onset in the C(2) response indicates that diabetes alters BP and HR responses to external challenges prior to the development of structural changes in the vasculature or autonomic nerves.

In vitro development and antigen analysis of Sarcocystis

During the past year considerable progress has been made in developing an in vitro system for growing large numbers of merozoites (the disease-causing stages) of Sarcocystis species that infect livestock. This system provides researchers with a means to study mechanisms of immunity and pathogenesis; and may eventually be used to develop effective diagnostic tests and vaccines against these economically important parasites. In this article, Carl Speer and Don Burgess discuss their in vitro system and show how preliminary antigen analysis has helped to deduce a possible mechanism for the vascular damage commonly observed in Sarcocystis infections.

Blood pressure power within frequency range ∼0.4 Hz in rat conforms to self-similar scaling following spinal cord transection

This study quantified the effect of interrupting the descending input to the sympathetic preganglionic neurons on the dynamic behavior of arterial blood pressure (BP) in the unanesthetized rat. BP was recorded for ∼4-h intervals in six rats in the neurally intact state and in the same animals after complete spinal cord transection (SCT) between T4 and T5. In the intact state, power within the frequency range of 0.35–0.45 Hz was 1.53 ± 0.38 mmHg2/Hz (mean ± SD by fast Fourier transform). One week after SCT, power within this range decreased significantly ( P < 0.05) to 0.43 ± 0.62 mmHg2/Hz. To test for self-similarity before and after SCT, we analyzed data using a wavelet (i.e., functionally, a digital bandpass filter) tuned to be maximally sensitive to fluctuations with periods of ∼2, 4, 8, 16, 32, or 64 s. In the control state, all fluctuations with periods of ≥4 s conformed to a “self-similar” (i.e., fractal) distribution. In marked contrast, the oscillations with a period of ∼2 s (i.e., ∼0.4 Hz) were significantly set apart from those at lower frequencies. One day and seven days after the complete SCT, however, the BP fluctuations at ∼0.4 Hz now also conformed to the same self-similar behavior characteristic of the lower frequencies. We conclude that 1) an intact sympathetic nervous system endows that portion of the power spectrum centered around ∼0.4 Hz with properties (e.g., a periodicity) that differ significantly from the self-similar behavior that characterizes the lower frequencies and 2) even within the relatively high frequency range at 0.4 Hz self-similarity is the “default” condition after sympathetic influences have been eliminated.

Divergent action potential morphologies reveal nonequilibrium properties of human cardiac Na channels

OBJECTIVE

Fast inward Na current (I(Na)) carried by the voltage-gated Na channel (Na(V)1.5) is critical for action potential (AP) propagation and the rapid upstroke of the cardiac AP. In addition, a small fraction of Na(V)1.5 channels remains open throughout the plateau of the AP, and this current is termed as late I(Na). In patients with mutant Na(V)1.5-based congenital long Q-T (LQT) syndrome, mutant channels pass more late I(Na) compared to wild-type channels in unaffected patients. Although LQT mutant Na(V)1.5 channels are well studied, there is no careful evaluation of the effects of cardiac APs on early and late current. This is important with the recent documentation of nonequilibrium I(Na).

METHODS

We measured AP-stimulated I(Na) through Na(V)1.5 wild-type and two LQT mutant channels (DeltaKPQ and N1325S). Three distinct AP morphologies were used: human embryonic stem cell-derived cardiac myocyte (hES-CM) APs with a relatively slow upstroke and canine endocardial and epicardial ventricular myocytes with rapid upstrokes.

RESULTS

All three APs elicited both early and late I(Na). For wild-type Na(V)1.5, the hES-CM AP elicits more early and late I(Na) than either the endocardial or epicardial AP. The mechanism for this difference is that the hES-CM has a relative slow dV/dt(max) that causes a maximal open channel probability. Slower upstroke stimulation also allows greater Na flux through wild-type and N1325S channels, but not the DeltaKPQ mutant.

CONCLUSIONS

The inherent gating properties of Na(V)1.5 provide natural tuning of optimal I(Na) density. Slower upstroke velocities can yield more I(Na) and Na flux in some Na(V)1.5 variants.

Coupling of sympathetic nerve traffic and BP at very low frequencies is mediated by large-amplitude events

This study explores the functional association between renal sympathetic nerve traffic (NT) and arterial blood pressure (BP) in the very-low-frequency range (i.e., <0.1 Hz). NT and BP (n = 6) or BP alone (n = 17) was recorded in unanesthetized rats (n = 6). Data were collected for 2-5 h, and wavelet transforms were calculated from data epochs of up to 1 h. From these transforms, we obtained probability distributions for fluctuation amplitudes over a range of time scales. We also computed the cross-wavelet power spectrum between NT and BP to detect the occurrence in time of large-amplitude transient events that may be important in the autonomic regulation of BP. Finally, we computed a time sequence of cross correlations between NT and BP to follow the relationship between NT and BP in time. We found that NT and BP follow comparable self-similar scaling relationships (i.e., NT and BP fluctuations exhibit a certain type of power law behavior). Scaling of this nature 1) points to underlying dynamics over a wide range of scales and 2) is related to large-amplitude events that contribute to the very-low-frequency variability of NT and BP. There is a strong correlation between NT and BP during many of these transient events. These strong correlations and the uniformity in scaling imply a functional connection between these two signals at frequencies where we previously found no connection using spectral coherence.

Heart rate-arterial blood pressure relationship in conscious rat before vs. after spinal cord transection

This experiment quantified the initial disruption and subsequent adaptation of the blood pressure (BP)-heart rate (HR) relationship after spinal cord transection (SCT). BP and HR were recorded for 4 h via an implanted catheter in neurally intact, unanesthetized rats. The animals were then anesthetized, and their spinal cords were severed at T(1)-T(2) (n = 5) or T(4)-T(5) (n = 6) or sham lesioned (n = 4). BP was recorded for 4 h daily over the ensuing 6 days. The neurally intact rat showed a positive cross correlation, with HR leading BP at the peak by 1.8 +/- 0.8 (SD) s. The cross correlation in unanesthetized rats (n = 2) under neuromuscular blockade was also positive, with HR leading. After SCT at T(1)-T(2), the cross correlation became negative, with BP leading HR, and did not change during the next 6 days. The cross correlation also became negative 1-3 days after SCT at T(4)-T(5), but in four rats by day 6 and thereafter the cross correlation progressively reverted to a positive value. We propose that the positive cross correlation with HR leading BP in the intact rat results from an open-loop control that depends on intact supraspinal input to sympathetic preganglionic neurons in the spinal cord. After descending sympathetic pathways were severed at T(1)-T(2), the intact vagal pathway to the sinoatrial node dominated BP regulation via the baroreflex. We suggest that reestablishment of the positive correlation after SCT at T(4)-T(5) was attributable to the surviving sympathetic outflow to the heart and upper vasculature reasserting some effective function, perhaps in association with decreased spinal sympathetic hyperreflexia. The HR-BP cross correlation may index progression of sympathetic dysfunction in pathological processes.

Mechanism of inactivation gating of human T-type (low-voltage activated) calcium channels

Recovery from inactivation of T-type Ca channels is slow and saturates at moderate hyperpolarizing voltage steps compared with Na channels. To explore this unique kinetic pattern we measured gating and ionic currents in two closely related isoforms of T-type Ca channels. Gating current recovers from inactivation much faster than ionic current, and recovery from inactivation is much more voltage dependent for gating current than for ionic current. There is a lag in the onset of gating current recovery at -80 mV, but no lag is discernible at -120 mV. The delay in recovery from inactivation of ionic current is much more evident at all voltages. The time constant for the decay of off gating current is very similar to the time constant of deactivation of open channels (ionic tail current), and both are strongly voltage dependent over a wide voltage range. Apparently, the development of inactivation has little influence on the initial deactivation step. These results suggest that movement of gating charge occurs for inactivated states very quickly. In contrast, the transitions from inactivated to available states are orders of magnitude slower, not voltage dependent, and are rate limiting for ionic recovery. These findings support a deactivation-first path for T-type Ca channel recovery from inactivation. We have integrated these concepts into an eight-state kinetic model, which can account for the major characteristics of T-type Ca channel inactivation.

Low prevalence of Epstein-Barr virus in incident gastric adenocarcinomas from the United Kingdom

Epstein-Barr virus has been associated with a proportion of typical gastric adenocarcinomas. Here we report that the prevalence of Epstein-Barr virus in gastric adenocarcinomas from the United Kingdom is one of the lowest in the World. Gastric adenocarcinoma is another tumour whose association with Epstein-Barr virus varies with the population studied.

Antibody responses of cattle immunized with the Tf190 adhesin of Tritrichomonas foetus

The antibody response patterns of cattle after subcutaneous and intranasal immunizations with adhesin Tf190 of Tritrichomonas foetus were investigated. Reactions of antibody from cattle parenterally immunized with Tf190 revealed antigen specificity and Tf190 sensitization in the majority of the animals, as determined by Western blotting. The results also demonstrated strong preimmune immunoglobulin G2 (IgG2) binding to T. foetus antigens not seen in IgG1 profiles. Subcutaneous injections of Tf190 resulted in significant (P < 0.05) increases in serum IgG1 and IgG2 titers over time, as determined by parasite specific enzyme-linked immunosorbent assay. Immune sera also significantly inhibited parasite adhesion to mammalian cell lines compared to the level of inhibition obtained with preimmune sera (P < 0.05). Intranasal immunization with Tf190 failed to produce measurable parasite-specific antibody in serum; however, this immunization route did result in significant (P < 0.05) increases in parasite-specific IgA titers in cervical mucus secretions from immunized animals that were more resistant to intravaginal challenge with T. foetus than controls. These results suggest that systemic immunization with Tf190 results in serum antibody production and antiparasitic adhesin antibodies. Additionally, the results of challenge experiments with intranasally immunized animals suggests that Tf190 primes protective immune responses that lead to lower rates of infection among these animals.

Antigen-specific T-cell responses in cattle immunized with antigens of Tritrichomonas foetus

The cellular immune responses of cattle immunized with antigens of Tritrichomonas foetus were investigated. Subcutaneous injections of antigen preparations primed bovine peripheral blood mononuclear cells (PBMC) by 30 days of immunization as demonstrated by antigen-specific proliferation and by cytokine production upon antigen challenge of PBMC. Antigen-specific T-cells derived from PBMC responded by production of interferon (IFN)-gamma message detected by reverse transcriptase polymerase chain reaction, secreted IFN-gamma detected by enzyme-linked immunosorbent assay, and intracellular IFN-gamma detected by flow cytometry. Phenotypic analysis of PBMC responding in vitro to parasite antigen demonstrated a shift from a mixed CD4+, CD8+, gammadelta+, to predominantly CD4+, CD8-, gammadelta- phenotype in the Tf190-primed PBMC. In conclusion, systemic immunization of cattle with parasite antigen results in priming of bovine T-cells that are antigen specific and can produce an anamnestic IFN-gamma response to subsequent stimulation with antigens of T. foetus.

Evaluation of ewe and lamb immune response when ewes were supplemented with vitamin E

Fifty-two Targhee twin-bearing ewes were used in a factorial arrangement of treatments to investigate the role of supplemental vitamin E (vit E); 0 (NE) vs 400 IU of vit E x ewe x (-1)d(-1) (E) and parainfluenza type 3 (PI3) vaccination; none (NP) vs PI3 vaccination (P) in immune function. Parainfluenza type 3 vaccination was used to evoke an immune response. Ewes receiving PI3 were vaccinated at 49 and 21 d before the expected lambing date. Ewes receiving vit E were orally dosed daily, 32 to 0 d before lambing. Blood was collected from ewes at the time of the initial PI3 vaccination and 4 h postpartum. Blood was collected from lambs (n = 104) at 3 d postpartum. Ewe and lamb sera were analyzed for anti-PI3 antibody titers, immunoglobulin G (IgG) titers, and vit E concentrations. Colostrum was collected 4 h postpartum and analyzed for IgG. The model for ewe and lamb analysis included the main effects of vit E and PI3, sex (lambs model only), and their interactions. No interactions were detected (P > 0.20) for any ewe or lamb variables. Serum anti-PI3 titers were greater (P < 0.01) in P ewes and their lambs than NP ewes and their lambs. Serum vit E concentrations were greater (P < 0.01) in E ewes and their lambs than NE ewes and their lambs. Colostral IgG titers and serum anti-PI3 titers did not differ (P > 0.20) between E and NE ewes. Serum IgG titers in E ewes and their lambs did not differ (P > 0.15) from IgG titers in NE ewes and their lambs. Lamb anti-PI3 titers did not differ (P = 0.76) between lambs reared by E and NE ewes. These results indicate that, although supplemental vit E to the ewe increased lamb serum vit E concentration, it had no effect on measures used in this study to assess humoral immunity in the ewe or passive immunity to the lamb.

Renal SNA as the primary mediator of slow oscillations in blood pressure during hemorrhage

Blood pressure contains a distinct low-frequency oscillation often termed the Mayer wave. This oscillation is caused by the action of the sympathetic nervous system on the vasculature and results from time delays in the baroreflex feedback loop for the control of sympathetic nerve activity (SNA) in response to changes in blood pressure. In this study, we used bilateral renal denervation to test the hypothesis that it is SNA to the kidney that contributes a large portion of the vascular resistance associated with changes in the strength of the slow oscillation in blood pressure. In conscious rabbits, SNA and blood pressure were measured during hemorrhage (blood withdrawal at 1.35 ml. min(-1). kg(-1) for 20 min). Spectral analysis identified a strong increase in power at 0.3 Hz in SNA and blood pressure in the initial compensatory phase of hemorrhage before blood pressure started to fall. However, in a separate group of renal denervated rabbits, although the power of the 0.3-Hz oscillation under control conditions in blood pressure was similar, it was not altered during hemorrhage. Wavelet analysis revealed the development of low-frequency oscillations at 0.1 Hz in both intact and denervated animals. In conclusion, we propose that changes in the strength of the oscillation at 0.3 Hz in arterial pressure during hemorrhage are primarily mediated by sympathetic activity directed to the kidney.

Demonstration of Tritrichomonas foetus in the external genitalia and of specific antibodies in preputial secretions of naturally infected bulls

Portions of penis and prepuce were collected from 24 bulls with current or recent Tritrichomonas foetus infection. Epididymides were collected from seven of the bulls, and seminal vesicles and prostate were collected from four. Following immunohistochemical staining with two monoclonal antibodies (34.7C4.4 and TF1.15) prepared against T. foetus surface antigens, trichomonads were identified in sections from 15 of the bulls. Organisms were most often located in penile crypts in the midshaft and caudal regions and less often in preputial crypts. Trichomonads were not observed in sections from other genitalia or in subepithelial tissue. T. foetus antigen, however, was present in the cytoplasm of some epithelial cells and the cytoplasm of some mononuclear cells in subepithelial lymphoid aggregates and follicles. Preputial smegma was collected from 16 T. foetus-infected bulls and from 16 control bulls with negative T. foetus cultures. Preputial antibody levels to TF1.17, a surface antigen of T. foetus, were determined by an enzyme-linked immunosorbent assay. Preputial secretions from infected bulls contained specific antibody of each isotype and subisotype tested. IgG1 responses were the greatest, IgM and IgA responses were approximately equal, and IgG2 responses were low. Each isotype and subisotype response in infected bulls was significantly greater than that in the controls. These results confirm previous speculation concerning anatomical sites of infection and suggest that parasite antigen can be taken up and processed locally, resulting in deposition of specific IgG1, IgG2, IgA, and IgM antibodies in the preputial cavity.

Low-frequency renal sympathetic nerve activity, arterial BP, stationary "1/f noise," and the baroreflex

The object of this study is to quantify the very low frequency (i.e., <0.1 Hz) interactions between renal sympathetic nerve activity (SNA) and arterial blood pressure (ABP). Six rats were instrumented for chronic recordings of SNA and ABP. Data were collected 24 h after surgery at 10 kHz for 2-5 h and subsequently compressed to a 1-kHz signal. The power spectra and ordinary coherence were calculated from data epochs up to 1 h in length. The very low frequency spectra for both variables were fitted to a constant times f (-beta). The peak magnitude squared of the coherence near 0.4 Hz was 0.82 +/- 0.08, but the apparent linear coherence fell off quickly at lower frequencies so that it was close to zero for frequencies <0.1 Hz. Moreover, at these low frequencies beta, as computed by a coarse grain spectral analysis, was significantly (P < 0.01) different for SNA (0.66 +/- 0.12) and ABP (1.12 +/- 0.14). Assuming that SNA and ABP are stationary time series, the results of our classical spectral analysis would indicate that SNA and ABP are not linearly correlated at frequencies with a period more than approximately 10 s. Accordingly, we tested for stationarity by computing the spectral coherence and found that SNA and ABP are not stationary "1/f noise" within the frequency range from 0.02 to 2.0 Hz. Rather the SNA exerts control over the cardiovascular system through intermittent bursts of activity. Such intermittent behavior can be modeled by nonlinear dynamics.

Purification and expression of the Tf190 adhesin in Tritrichomonas foetus

Bovine trichomoniasis is a sexually transmitted disease caused by Tritrichomonas foetus and characterized by early embryo loss. The mechanism of this loss is not known, although the parasite is known to cause inflammation and to have the ability to kill host cells by a contact-dependent cytotoxic mechanism. Antibody specific for a 190,000-Da surface complex (Tf190) was previously shown to inhibit this adhesion. In this study we used immunoaffinity chromatography to purify Tf190 from T. foetus in order to analyze its composition and examine its expression. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of purified Tf190 followed by silver staining revealed three components of Tf190. Western blotting and antibody-binding experiments showed that the 140- and 60-kDa bands were immunogenic. By using a battery of monoclonal antibodies (MAbs) periodate-sensitive epitopes were identified on Tf190, suggesting that these epitopes contained carbohydrate structures. Analyses of affinity-purified Tf190 by high-performance liquid chromatography and gas-liquid chromatography demonstrated the presence of the monosaccharides and lipids known to be prominent constituents of the lipophosphoglycan (LPG) of T. foetus. Flow cytometry experiments on several isolates of T. foetus with Tf190-specific antibodies revealed that Tf190 was present on subpopulations of all isolates but that not all epitopes were present on every isolate. This pattern of reactivities on the different parasite isolates was confirmed by Western blots of whole-parasite extracts probed with MAbs and antiserum. These results suggest that although variation in the expression of epitopes of Tf190 occurs in different strains of T. foetus, the Tf190 adhesion complex is widespread in different populations of the parasite. The data further suggest that immunogenic structures, important in the adhesion of T. foetus to mammalian cells, are located in the LPG-like component of Tf190.

First-order differential-delay equation for the baroreflex predicts the 0.4-Hz blood pressure rhythm in rats

We have described a 0.4-Hz rhythm in renal sympathetic nerve activity (SNA) that is tightly coupled to 0.4-Hz oscillations in blood pressure in the unanesthetized rat. In previous work, the relationship between SNA and fluctuations in mean arterial blood pressure (MAP) was described by a set of two first-order differential equations. We have now modified our earlier model to test the feasibility that the 0.4-Hz rhythm can be explained by the baroreflex without requiring a neural oscillator. In this baroreflex model, a linear feedback term replaces the sympathetic drive to the cardiovascular system. The time delay in the feedback loop is set equal to the time delay on the efferent side, approximately 0.5 s (as determined in the initial model), plus a time delay of 0.2 s on the afferent side for a total time delay of approximately 0.7 s. A stability analysis of this new model yields feedback resonant frequencies close to 0.4 Hz. Because of the time delay in the feedback loop, the proportional gain may not exceed a value on the order of 10 to maintain stability. The addition of a derivative feedback term increases the system's stability for a positive range of derivative gains. We conclude that the known physiological time delay for the sympathetic portion of the baroreflex can account for the observed 0.4-Hz rhythm in rat MAP and that the sensitivity of the baroreceptors to the rate of change in blood pressure, as well as average blood pressure, would enhance the natural stability of the baroreflex.

Multifiber renal SNA recordings predict mean arterial blood pressure in unanesthetized rat

The goal of this analysis was to quantify the relationship between renal sympathetic nerve activity (SNA) and mean arterial blood pressure (MAP). We previously recorded renal SNA and MAP in conscious rats during a stressful behavioral stimulus and during a nonstressful stimulus. We then formulated a set of two linear, first-order differential equations that uses our SNA recordings after a time delay (the input) to predict fluctuations in MAP (the output). Our model has four parameters: 1) the cardiovascular time constant T that characterizes the frequency response function between the effector elements controlled by the sympathetic nerves and the cardiovascular system (1-5 s); 2) the effector time constant Te determined by the coupling between the sympathetic nervous system and the effectors (0.0-0.6 s); 3) the efferent time delay tau e between a change in SNA and a change in MAP (0.4-0.6 s); and 4) a proportionality constant C between fluctuations in SNA and fluctuations in MAP (0.3-3.4 mmHg/nV). The parameters of the model were determined that minimize the residual error between the simulated time series and the actual data time series for a stressful stimulus. Then we tested the ability of the transfer function to predict the MAP response to a nonstressful stimulus. In five of seven rats tested, the model's predictions were good, with mean cross-correlation coefficients for the predicted trials between 0.62 and 0.83. We show that multifiber renal SNA recordings can reliably predict changes in MAP in the unanesthetized rat. Thus the overall sympathetic drive to the cardiovascular system is indexed by renal SNA, although the vasomotor effectors driven by renal SNA control only approximately 20% of the blood cow.

Immunohistochemical detection of Tritrichomonas foetus in formalin-fixed, paraffin-embedded sections of bovine placenta and fetal lung

An immunohistochemical technique using a monoclonal antibody was evaluated as a diagnostic tool to specifically label Tritrichomonas foetus in formalin-fixed, paraffin-embedded sections of placenta and fetal lung from bovine abortions. Trichomonads were demonstrated in tissues from each of 12 abortions due to T. foetus and none of 15 abortions due to other or unidentified causes. Moderate to marked background staining occurred only in severely autolyzed tissues from T. foetus-infected fetuses. The antibody faintly labeled 1 of 3 other species of trichomonads (Trichomonas gallinae) but did not label other protozoa, bacteria, or fungi tested.

Genograms: a psychosocial assessment tool for hospice

Genograms are a valuable and non-threatening evaluation tool for hospice patients and families. The genogram provides basic information about the family including the role of each member and the family dynamics. As the diagram is drawn, family life cycle issues and relationships between family members become evident. The genogram may go beyond the household to include supportive neighbors, friends, and community resources. Religious and spiritual support is also noted. The information is used to assess family needs and to provide interventions both before the death and during bereavement.

Analysis of adhesion and cytotoxicity of Tritrichomonas foetus to mammalian cells by use of monoclonal antibodies

The relationship of Tritrichomonas foetus adhesion to mammalian cells and cytotoxicity to these targets was investigated. High-adherence and low-adherence lines of T. foetus, derived by repeated adhesion to HeLa cells, showed high and low cytotoxicity, respectively, to HeLa cells. When parasites were separated from targets by membranes (0.4-microns pore size), no cytotoxicity was detectable. Monoclonal antibodies elicited against T. foetus that lowered adhesion also lowered parasite-mediated cytotoxicity. Flow cytometry experiments revealed that the levels of an adhesion- and cytotoxicity-blocking antibody bound to the surface of high-adherence clones of T. foetus were higher than those in low-adherence clones. Western blots of parasite extracts separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis were probed with an anti-T. foetus antibody. A molecule with a molecular weight of approximately 190,000 composed of subunits with molecular weights of approximately 140,000 to 150,000 and approximately 65,000 was identified. Immunoprecipitation experiments with metabolically labeled T. foetus and the same antibody confirmed that similar subunits were synthesized by the parasite. These results indicate that adhesion of T. foetus to mammalian cells is an important step in cytotoxic damage of these targets and that a surface adhesin on the parasite is involved in the adhesion mechanism.

Cytotoxic and hemolytic effects of Tritrichomonas foetus on mammalian cells

Geographically distinct lines of Tritrichomonas foetus were assayed for their ability to cause cytotoxicity in nucleated mammalian cells and lysis of bovine erythrocytes. T. foetus was highly cytotoxic toward a human cervical cell line (HeLa) and early bovine lymphosarcoma (BL-3) but displayed low levels of cytotoxicity against African green monkey kidney (Vero) cells. In addition to variation in the extent of cytotoxicity toward different targets, differences in the levels of cytotoxicity in the same nucleated target occurred with different parasite lines. Whole T. foetus, unfractionated whole-cell extracts, and parasite-conditioned medium (RPMI 1640 without serum) all caused lysis of bovine erythrocytes. Lytic activity in the conditioned medium was substantially reduced by repeated freezing and thawing or heating to 90 degrees C for 30 min. Damage of mammalian target cells by live T. foetus could be reduced by the presence of protease inhibitors; however, such inhibitors did not diminish the lytic effects of conditioned medium. These results suggested that proteolytic enzymes were necessary for the lytic mechanism of the live parasites but were not required once lytic factors were released into the parasite-conditioned medium. They further suggested that the lytic molecules were either proteins or had proteinaceous components.

Identification of Tritrichomonas foetus in sections of bovine placental tissue with monoclonal antibodies

Sections of bovine placenta from cases of bovine trichomoniasis were examined for the presence of Tritrichomonas foetus by standard histological methods using phase-contrast microscopy and by indirect immunofluorescence assay (IFA) employing monoclonal antibodies (mAbs) specific for T. foetus. Parasites were identified readily in deparaffinized tissue up to 4 yr old by IFA with 2 mAbs previously shown to bind to the surface of living T. foetus. These results indicated that the IFA provided a rapid and specific method of identifying T. foetus in tissue sections as compared to standard histological methods.

Inhibition of penetration of cultured cells by Eimeria bovis sporozoites by monoclonal immunoglobulin G antibodies against the parasite surface protein P20

Five monoclonal antibodies (MAbs) were partially characterized and tested for their ability to inhibit penetration of Madin-Darby bovine kidney (MDBK) cells by sporozoites of Eimeria bovis. By indirect fluorescent-antibody assays, all MAbs reacted with acetone-fixed sporozoites, but only two MAbs, EbS9 (immunoglobulin G1) and EbS11 (immunoglobulin G2a), localized specifically on the plasmalemma of live sporozoites. Two of the five MAbs also reacted with acetone-fixed first-generation merozoites of E. bovis; however, none of the MAbs reacted with live merozoites. Treatment of live sporozoites with EbS9 or EbS11 resulted in 79 and 73% decreases, respectively, in sporozoite penetration of MDBK cells. No significant differences in cell penetration occurred in MDBK cells inoculated with sporozoites that had been treated with the other three MAbs. Both EbS9 and EbS11 reacted in Western blots (immunoblots) of sporozoites with the same 20,000-relative-molecular-weight protein. The antigens against which these neutralizing MAbs react might be useful in immunizing against bovine coccidiosis.

Identification of antigens of Sarcocystis cruzi sporozoites, merozoites, and bradyzoites with monoclonal antibodies

Sporozoites and culture-derived merozoites of Sarcocystis cruzi were used to elicit monoclonal antibodies (MAb's) in mice. Some of these antibodies reacted with the surface of live sporozoites and merozoites as determined by immunofluorescence. An array of similar antigens was identified in Western blots of sporozoites by both anti-merozoite MAb's and an anti-sporozoite MAb. At least 1 antigen in blots of bradyzoites was identified by anti-merozoite MAb's and a cluster of antigens was identified by an anti-sporozoite antibody. These results indicate that several surface epitopes of sporozoites and merozoites are shared with molecules of bradyzoites and that antigen patterns of molecules bearing these epitopes in 3 stages of Sarcocystis may be either distinct or similar.

Clonal and geographic distribution of a surface antigen of Tritrichomonas foetus

Geographically diverse strains and clones of Tritrichomonas foetus have been examined with respect to their expression of a major surface antigen of approximately 150,000 relative molecular weight (Mr), designated the 150 Ag. Radioiodination and 35S-methionine labeling of T. foetus followed by immunoprecipitation with monoclonal antibodies (MAbs), separation of polypeptides by SDS-PAGE, and autoradiography or fluorography confirmed the parasite origin of the 150 Ag. The results of flow cytometry analysis employing a panel of MAbs against live T. foetus parasites revealed that from 5 to 84% of individuals in a given population of T. foetus expressed a particular epitope of the 150 Ag. All strains and clones were positive for surface expression of epitopes of this antigen. These results show that the 150 Ag is widely distributed in populations of T. foetus, confirm the surface location of this antigen, and suggest its importance as a target for protective immune responses.

Tritrichomonas foetus: preparation of monoclonal antibodies with effector function

Monoclonal antibodies were prepared against Tritrichomonas foetus and characterized with regard to binding and immune effector activities. Nine of 27 monoclonal antibodies which reacted with T. foetus appeared to bind to the surface of live parasites. Immunoelectron microscopy confirmed the surface binding of two of these. At least six of these surface reactive monoclonal antibodies facilitated complement mediated lysis of T. foetus and one acted as an opsonin for phagocytosis by peripheral blood bovine monocytes. Five surface reactive monoclonal antibodies identified a molecule of approximately 150,000 relative molecular weight on Western blots of whole parasite preparations. These results collectively suggest the 150,000 relative molecular weight molecule may be an important target antigen for the immune response to T. foetus.

Molecular identity and location of invariant antigens on Trypanosoma brucei rhodesiense defined with monoclonal antibodies reactive with sera from trypanosomiasis patients

Monoclonal antibodies (MAbs) which are reactive with several antigenically distinct variable antigen types were prepared by immunization with Trypanosoma brucei rhodesiense. Certain MAbs were shown to be specific for members of the genus Trypanosoma and not reactive with Leishmania spp. or Plasmodium falciparum by the indirect immunofluorescence assay. These genus-specific MAbs were used to identify the molecular location of these invariant antigen determinants in whole T. brucei rhodesiense antigen preparations. Two monoclonals reacted with a low-molecular-weight doublet of approximately 22,000 relative molecular weight on Western blots of whole trypanosome antigen preparations separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These determinants did not appear to be on the variable surface glycoprotein molecule and were destroyed by trypsin digestion. Binding studies in which live, DEAE-purified, bloodstream trypanosomes were exposed to invariant antigen-specific MAbs suggested these determinants were accessible on living trypanosomes. Genus-specific MAbs also reacted with determinants present in sera from African trypanosomiasis patients in a dot immunobinding assay but not sera from patients with malaria or leishmaniasis. These results suggest that certain invariant molecules of African trypanosomes are immunogenic, possibly accessible on the trypanosome surface, and may be present as circulating invariant antigen in trypanosomiasis patients.