Jenny Harvey

The effect of mild heat stress on postprandial high fat meal microvascular endothelial function

Introduction

Definition Mechanisms for dysfunction Sauna bathing

What is microvascular endothelial dysfunction?

“state of enhanced vasoconstriction and reduced vasodilation”

Microvascular Endothelial Function

Unclear how high fat meals (HFM) and hypertriglyceridemia (HTG) affect microvascular endothelial function TPR and glucose uptake occur at microvascular level Microvascular endothelial dysfunction precedes

macrovascular dysfunction Important to determine how HFM affect human

microvascular endothelial function and determine the mechanism for dysfunction

Mechanisms for Microvascular Endothelial Dysfunction

Chronic low-grade inflammation Hypertriglyceridemia Oxidative stress

High fat diet and chronic low-grade inflammation

Postprandial lipid accumulation triggers oxidative stress and an inflammatory response

Link between increased adiposity from high fat diet and chronic low-grade inflammation Relationship to cardiometabolic diseases and microvascular

endothelial function is significant (Brandauer et al., Physiol Rep, 2013; Calder et al., Br J Nutr, 2011)

Hypertriglyceridemia established as a risk factor of cardiovascular disease

Oxidative Stress

Oxidative stress is worsened over postprandial period as free fatty acids accumulate post high fat meal (Wang et al., Am J Physiol Heart Circ Physiol, 2011)

May inhibit endothelial nitric oxide synthase (eNOS) phosphorylation Important precursor for NO production Activated by physiological mechanisms such as

shear stress, estrogens, and insulin

Nitric Oxide (NO)

Reduction in NO bioavailability seems to be a central mechanism for impaired endothelial function

Vital molecule for cardiovascular health as it regulates platelet aggregation and vasodilation within endothelium

NO deficiency creates a vascular environment conducive to inflammation and vasoconstriction

Consumption of a high fat diet

Enhanced vasoconstriction and reduced vasodilation

Chronic oxidative stress and inflammation leading to reduced NO bioavailability

Impaired microvascular endothelial function and increased risk for atherosclerosis

Sauna Therapy

Minimally invasive therapeutic modality that closely mimics the outcomes of exercise potential to reduce negative effects of HFM on endothelial

function curb development of atherosclerosis

Individuals who are unable to exercise because of aging, injury, disease, or organ dysfunction may benefit from sauna treatment

Potential hemodynamic modifications for the healthy population that lasts up to two hours

Heat Therapy as a Mediator of Endothelial Function

Induce vasodilation of systemic arteries

Stimulus for greater NO bioavailability

Shear stress upregulates eNOS phosphorylation

Elevated blood flow on surface of body

Research Questions

Does a HFM affect NO-dependent vasodilation? Can mild heat stress mitigate the potential decrease in

NO-dependent vasodilation?

Hypothesis

Consumption of a high fat meal will blunt microvascular endothelial function

ANDMild heat stress will minimize the

detrimental effects of a high fat meal on microvascular endothelial function

Methods

Participant Recruitment and Screening Participant Instrumentation Protocols Statistical Analysis

Recruitment and Screening

Free of any known cardiovascular or metabolic disease, skin allergy/disease, history of adverse reaction to heat stress, smoking in last 6 months

Not taking any medication for corresponding conditions

4 male and 4 female participants Age 18 - 32

Participant Instrumentation

Blood samples analyzed via Cholestech LDX (Alere, USA) To ensure stable core temperature and to clamp skin

temperature, each participant wore a suit consistently perfused with 33-34°C water

3-lead ECG Blood pressure cuff on right arm

Wireless Telemetry Relatively new technology Subject swallows small, ingestible

“thermometer” pill Pill transmits signal to recording

unit Measures temperature in

digestive tract Measurement depends on

where pill is located (time given to subject)

Can “slip” with changes in posture

Lowered with ingestion of fluids

High Fat Meal Calculation

Fat consumption for each participant was calculated on a basis of 1g fat per kilogram of body weight (Ade et al., EJAP, 2014)

Blue Bell ice cream (chocolate or vanilla) Serving size: 74-88 g Total fat: 9-11g 672.43 ± 53.70 g of ice cream

Participants allotted ~20 minutes to consume the ice cream.

Experimental Protocols

Local heating protocol High fat meal High fat meal + mild heat stress

Local Heating Protocol

10 minutes of baseline Skin heaters increased from 33°C to 39°C at a rate of

0.1°C/second to evoke submaximal vasodilation Plateau of local heating response is ~80% of NO-dependent

(Choi et al., JAP, 2014)

Once participant reaches plateau in RBC flux (~30 min), skin heaters increased to 43°C to elicit maximal vasodilation (Wong et al., JAP, 2006)

(Choi, JAP, 2014)

L-NAME inhibits NO-induced endothelial

vasodilation

(Choi, JAP, 2014)

Experimental Protocol 1: High Fat Meal

Baseline fasting blood sample + 10 min of baseline 33°C water pumped through water perfused suit for 30

min Participants consumed ice cream in ~20 min Additional 60 min of thermoneutral water heating

before turned off Blood samples via finger stick were then measured

every 30 minutes until the 120th min post-HFM

Experimental Protocol 2: High Fat Meal + Mild Heat Stress

Same as protocol 1 + mild heat stress during the HFM Mild heat stress performed by pumping 50°C water

through the water perfused suit for 90 min 30 min prior to ice cream consumption, 60 min post

Aiming for a ~0.2- 0.3°C increase in core temperature above baseline Point at which there is a significant increase in blood flow

without skin reaching the point of maximal vasodilation, so as to leave room for NO-dependent vasodilation to take effect during local heating protocol

Data Analysis

Outcome Measures Statistics

Outcome Measures

Cutaneous Vascular Conductance Control vs. High Fat Meal vs. High Fat Meal + Whole Body

Heat % CVC max = RBC flux ÷ mean arterial pressure (mV/mmHg)

Blood Analysis [Triglycerides] vs. time

Statistical Analysis

SPSS 22 (IBM Corporation)

Mean ± standard error of the mean (SEM) 95% confidence intervals with P-values of < 0.05

considered significant Paired t-tests and one- and two-way repeated

measures analysis of variance with a Bonferroni correction factor was used where appropriate

Results

Blood Pressure Core Temperature %CVCmax

Triglycerides vs. Time

 Systolic Blood

Pressure (mmHg)Diastolic Blood

Pressure (mmHg)

Mean Arterial Blood Pressure

(mmHg)

Control 116 ± 5 76 ± 5 89 ± 5

HFM 120 ± 5 77 ± 5 91 ± 5

HFM + WBH 118 ± 6 75 ± 4 90 ± 4

Blood Pressure Data

 Average core temp ± SE (°C )

Control 37.31 ± 0.11

HFM 37.27 ± 0.10

HFM + WBH 37.68 ± 0.18 *

Core Temperature

Based on these numbers, the heat stress was sufficient to significantly raise core temperature to the goal of ~0.2-0.3°C

above baseline (P = .042)

Control HFM HFM-WBH0

20

40

60

80

100

Cuta

neou

s Vas

cula

r Con

duct

ance

(% M

ax-

imal

)

*

#

Figure 1. Cutaneous vascular conductance responses

*, P < 0.05 vs. Control; #, P < 0.05 vs. HFM.

0 30 60 90 12050

70

90

110

130

150

170

190

210

230

250HFM TRG HFM-WBH TRG Baseline

Time (Minutes)

Trig

lyce

rides

(mg/

dl)

** * *

*

#

Figure 2. Blood triglyceride response

*, P < 0.05 vs. time 0 within a trial; #, P < 0.05 vs. HFM at same time point

Discussion

Explanation of Results Clinical Implications Limitations

Cutaneous Vascular Conductance

Acute HFM and consequent elevated blood triglycerides negatively affect microvascular endothelial function Potentially by interrupting

NO production

Control HFM HFM-WBH0

20

40

60

80

100

Cuta

neou

s Va

scul

ar C

ondu

ctan

ce (%

M

axim

al)

*

#

Mild heat stress prior to, and during, consumption of HFM attenuates peak triglycerides and restores microvascular endothelial function

Local heating and NO production

Local heating protocol resulted in submaximal cutaneous vasodilation that is largely NO dependent (Choi, JAP, 2014)

Cutaneous vasodilation is a good measure of microvascular endothelial function

Reduction in cutaneous hyperemic response due to reduced NO and impaired microvascular endothelial function

Triglycerides vs. Time

Blood [TG] continued to significantly rise every thirty minutes for 2 hours post HFM

Mild heat stress prior to consumption of high fat meal significantly reduced triglyceride response at minute 60 and attenuated peak triglyceride

0 30 60 90 120507090

110130150170190210230250

HFM TRG HFM-WBH TRG

Baseline

Time (Minutes)

Trig

lyce

rides

(mg/

dl)

** * *

*#

Postprandial High Fat Meal Microvascular Endothelial Function

The majority of the data suggests there is attenuated endothelial-dependent vasodilation two hours post high fat meal even in apparently healthy individuals

Serum triglyceride levels also increase in otherwise healthy individuals following a high fat meal, which further suggests the negative effects of a high fat meal on endothelial function are mediated, in part by, hypertriglyceridemia (Bae et al., Athersclerosis, 2001)

Consumption of a high fat diet

Enhanced vasoconstriction and reduced vasodilation

Chronic oxidative stress and inflammation leading to reduced NO bioavailability

Impaired microvascular endothelial function and increased risk for atherosclerosis

Why sauna therapy?

skin blood flow is a direct result of thermal therapy or heat

Shear stress from blood flow acts as stimulus in the cutaneous microvasculature for NO bioavailability

Indeed, whole body mild heat stress attenuated the rise in triglycerides and improved CVC (%maximal) presumably from additional NO

Clinical Implications: Disease Populations

Well tolerated form of therapy in several disease states (Akasaki et al., Circ J, 2006; Gayda et al., J Clin Hypertens, 2012)

Ability for vascular smooth muscle to respond more adequately as endothelial function improves via sauna therapy Improve exercise tolerance in chronic heart failure

Mild heat stress may stimulate NO-induced vasodilation and HSPs to the point of beneficial and improved blood flow

Delayed onset of pain for peripheral artery disease Improved exercise tolerance

Sauna therapy for healthy populations

Hemodynamic modifications from sauna can last up to two hours (Imamura et al., JACC, 2001)

Cardiac output increases peripheral blood flow and shear stress NO production

Upregulation of NO-driven endothelial vasodilation decreases total peripheral resistance

Limitations and Delimitations

Protocol based on previously established and tested heating protocols We did not specifically inhibit NO and cannot therefore be certain

our results reflect changes in NO-dependent endothelial vasodilation

Use L-NAME via microdialysis to directly assess effect of high fat meal and hypertriglyceridemia on NO-dependent endothelial vasodilation

Conclusion

A single high fat meal attenuates cutaneous vascular conductance

AND

Mild heat stress prior to, and during, the consumption of a high fat meal can restore cutaneous vascular conductance

SUGGESTING

A high fat meal negatively affects microvascular endothelial function and mild heat stress may mitigate these

deleterious affects

Acknowledgements

Thesis Advisor: Dr. Brett Wong

Committee Members: Dr. Jeff Otis Dr.

Benjamin Goerger

External Collaborator: Dr. Bruno Roseguini

Heat Shock Proteins

HSPs help maintain cellular integrity Upregulated both independently and in conjuction

with eNOS (Miyauchi et al., Circ J, 2012)

Increase in number of HSPs following exercise and elevated core temperature

Mechanism for cardioprotection (Milne et al., JAP, 2012)

reduce inflammatory pathways and blunt oxidative stress

0 30 60 90 12050

60

70

80

90

100

110

120

130

140

150

HFM GLU HFM-WBH GLU Baseline

Time (Minutes)

Gluc

ose

(mg/

dl)

*

*

Figure 3. Blood glucose responses

Blood Glucose vs. Time

Possible that blood glucose is having an effect on reduced blood flow response

Seems unlikely WBH + HFM restored CVC

and attenuated peak TG whereas it had no effect on glucose

0 30 60 90 12050

60

70

80

90

100

110

120

130

140

150 HFM GLU HFM-WBH GLUBaseline

Time (Minutes)Gl

ucos

e (m

g/dl

)

*

*

*

Why %CVCmax?

Perimed Instruments, Sweden, 2015

We do not know how many blood vessels each dopplar is sampling

Standardize to maximum so that everything is normalized