PROLONGED MILD HYPOHYDRATION ABOLISHES INCREASES IN CREATININE CLEARANCE DURING ORAL PROTEIN LOADING

S.C. Brazelton, C.L. Chapman, S.M. Holt, K. Wiedenfeld Needham, C.T. O’Connell, H.N. Medved, W.A.B. Howells, E.L. Reed, J.R. Halliwill, FACSM, C.T. Minson, FACSM University of Oregon, Eugene, OR Oral protein loading increases glomerular filtration rate (GFR) via nephron recruitment and/or glomerular hyperfiltration. This response reflects renal functional reserve where filtration capacity is increased to maintain GFR at basal levels or increase GFR when stressed. Passive heating induced mild hypohydration (3% reduction in body mass) attenuates oral protein induced increases in creatinine clearance (CCr). It is not known whether mild hypohydration, independent of heat stress, also attenuates increases in CCr during oral protein loading. PURPOSE: To test the hypothesis that increases in CCr following oral protein loading are attenuated during prolonged mild hypohydration compared to euhydration. METHODS: In a block-randomized crossover design, twenty healthy adults [(9 females (F) and 11 males (M); age: 21 (3) years] completed 24 hours of fluid deprivation (HYPO) and 24 hours of normal fluid consumption (EUHY). The protocols were separated by ³72 hours. After the 24-hour protocols, participants underwent oral protein loading by ingesting a whey protein shake (1.0 g protein and 10 ml water per kg body mass) within 10 minutes. Body fluid loss was estimated via the percent change in body mass (∆BM) over the 24-hour protocol. Blood and urine samples were collected at baseline and 150-min post-protein consumption (POST) to calculate CCr. Data are presented as mean with 95% confidence intervals. RESULTS: ∆BM was reduced in HYPO vs. EUHY [-2.6% (-3.0, -2.2) vs. 0.1% (-0.3, 0.4), P\u3c0.0001]. Baseline CCr was elevated in HYPO vs. EUHY [261 ml/min (218, 303) vs. 143 ml/min (118, 168), P\u3c0.0001]. There were no differences in CCr between conditions at POST [HYPO: 246 ml/min (212, 280); EUHY: 231 ml/min (196, 265), P=0.2691]. At POST, CCr was elevated from baseline in EUHY (P\u3c0.0001) but not HYPO (P=0.2941). CONCLUSION: These findings suggest that CCr is not altered with oral protein loading during prolonged mild hypohydration. Whether our findings suggest that a ceiling effect was reached in the HYPO condition (i.e., maximum CCr was already achieved at baseline) or are influenced by increased tubular creatinine secretion during hypohydration requires further investigation. Supported by NIH R01HL144128 and F32HL164021

MILD PROLONGED HYPOHYDRATION ATTENUATES RENAL HEMODYNAMIC RESPONSE TO EXERCISE PRESSOR REFLEX ACTIVATION

C.T. O’Connell, C.L. Chapman, S.M. Holt, S.C. Brazelton, H.N. Medved, W.A.B. Howells, K. Wiedenfeld Needham, E.L. Reed, J.R. Halliwill, FACSM, C.T. Minson, FACSM University of Oregon, Eugene, OR Renal vasoconstriction supports the regulation of arterial pressure. Passive heat stress induced hypohydration abates both renal vasoconstriction and increases in blood pressure during sympathetic activation. However, it is not known if this effect is due to hypohydration independent of heat stress. PURPOSE: To test the hypothesis that prolonged mild hypohydration attenuates reductions in renal artery blood velocity (RBV) and increases in renal artery vascular resistance (RVR) during exercise pressor reflex activation compared to a hydrated state (euhydration). METHODS: In a block-randomized crossover design, twenty-two healthy adults (11 females, 11 males; age: 21(3) years) completed 24 hours of fluid deprivation (HYPO) or 24 hours of normal fluid consumption (EUHY). Protocols were separated by ³72 hours. Body fluid losses were estimated via the percent change in body mass (∆BM) over 24 hours. Baseline RBV (Doppler ultrasound) and brachial artery blood pressure (electrosphygmomanometer) were measured. Participants completed 2 min static handgrip exercise (HG) followed by 2 min arterial occlusion (OCC) to activate the exercise pressor reflex. RVR was calculated as mean arterial pressure divided by RBV. Data are presented as the change from baseline (∆) with mean and 95% confidence intervals. RESULTS: Body mass was reduced in HYPO vs. EUHY [-2.5% (-2.9, -2.1) vs. 0.0% (-0.4, 0.4), P\u3c0.0001]. Increases in mean arterial pressure during HG and OCC did not differ between conditions (P=0.8790). Reductions in RBV were attenuated in HYPO compared to EUHY at the end of HG [-0.8 cm/s (-2.5, 0.9) vs. -5.9 cm/s (-8.2, 3.7), P\u3c0.0001] and OCC [0.7 cm/s (-0.6, 2.1) vs. -2.4 cm/s (-4.2, -0.6), P=0.0109]. Increases in RVR were also attenuated in HYPO compared to EUHY at the end of HG [0.5 mmHg/cm/s (0.4, 0.7) vs. 0.8 mmHg/cm/s (0.6, 1.1), P=0.0012] and OCC [0.2 mmHg/cm/s (0.1, 0.3) vs. 0.4 mmHg/cm/s (0.3, 0.6), P=0.0418]. CONCLUSION: Mild prolonged hypohydration attenuates both reductions in RBV and increases in RVR during exercise pressor reflex activation. Thus, these data suggest that the blunted renal vasoconstriction to sympathetic activation during passive heat stress induced hypohydration is only partially explained by hypohydration. Supported by NIH R01HL144128 and F32HL164021

PROLONGED MILD HYPOHYDRATION INCREASES ACUTE KIDNEY INJURY BIOMARKERS IN HEALTHY YOUNG MALES AND FEMALES

S.M. Holt, C.L. Chapman, W.A.B. Howells, C.T. O’Connell, S.C. Brazelton, H.N. Medved, E.L. Reed, K. Wiedenfeld Needham, J.R. Halliwill, FACSM, C.T. Minson, FACSM University of Oregon, Eugene, OR (Award Winner) The top causes of hospitalizations during extreme heat events are fluid and/or electrolyte disorders, and acute kidney injury (AKI) secondary to hypohydration. Prior to extreme heat exposure, people are likely mildly hypohydrated (approximate 2% body mass loss) during normal daily living due to inadequate fluid intake. In this context, an important knowledge gap exists as to whether mild hypohydration independent of heat stress increases AKI biomarkers that are suggestive of increased AKI risk. PURPOSE: To test the hypothesis that urinary AKI biomarkers are elevated in humans following prolonged mild hypohydration compared to euhydration. METHODS: In a block-randomized crossover design, twenty-two healthy adults [11 females, 11 males; 21(3) years; body mass index: 23(3) kg/m2] completed 24 hours of fluid deprivation (HYPO) or 24 hours normal fluid consumption (EUHY). Protocols were separated by ³72 hours. Body fluid losses were estimated via the percent change in nude body mass over the 24-hour protocol. Spot urine samples were collected from participants immediately following the 24-hour protocol. Urinary AKI biomarkers insulin-like growth factor binding-protein 7 (IGFBP7), tissue inhibitor of metalloproteinase-2 (TIMP-2), kidney injury molecule-1 (KIM-1), and neutrophil gelatinase associated lipocalin (NGAL) were measured with enzyme-linked immunosorbent assays. The primary dependent variable was the U.S. Food and Drug Administration approved biomarker urinary ([IGFBP7∙TIMP-2]). Data are presented as mean with 95% confidence intervals. RESULTS: Body mass loss was greater in HYPO vs. EUHY [-2.5% (-2.9, -2.1) vs. 0.0% (-0.4, 0.4), P2/1000 (1.0, 2.8) vs. 0.2 (ng/ml)2/1000 (0.1, 0.3), P=0.0011] and KIM-1 [1.0 ng/ml (0.8, 1.3) vs. 0.3 ng/ml (0.2, 0.4) P Supported by NIH R01HL144128 and F32HL164021, and the Knight Campus Undergraduate Scholars Program

PROLONGED MILD HYPOHYDRATION REDUCES ORAL PROTEIN LOADING INDUCED RENAL HYPEREMIA

W.A.B. Howells, C.L. Chapman, S.M. Holt, C.T. O’Connell, S.C. Brazelton, H.M. Medved, E.L. Reed, K. Wiedenfeld Needham, J.R. Halliwill, FACSM, C.T. Minson, FACSM University of Oregon, Eugene, OR Oral protein consumption increases circulating amino acids that increase renal perfusion. Prolonged water deprivation evokes marked reductions in renal blood flow. Reduced renal perfusion during hypohydration is the primary mechanism of acute kidney injury of pre-renal etiology. It is not known whether the renal hemodynamic response to oral protein consumption is modified during prolonged hypohydration. This knowledge gap has implications for oral rehydration strategies following prolonged hypohydration. PURPOSE: To test the hypothesis that increases in segmental artery blood velocity following oral protein loading are attenuated during prolonged mild hypohydration compared to when euhydrated. METHODS: In a block-randomized crossover design, twenty-two healthy adults [11 males, 11 females; age: 21(3) years] completed 24 hours of fluid deprivation to induce hypohydration (HYPO) or 24 hours normal fluid consumption (EUHY). Protocols were separated by ³72 hours. Baseline measurements were obtained at the end of each 24-hour protocol. Participants then ingested a whey protein shake (1.0 g protein and 10 ml water per kg of body mass). Body fluid losses were estimated via the change in body mass over 24 hours (∆BM). Blood pressure (electrosphygmomanometer) and segmental artery blood velocity in the right kidney (Doppler ultrasound) were measured at baseline and 150-minutes post-protein. Segmental artery vascular conductance was calculated as blood velocity divided by mean arterial pressure. Data are presented as the change from baseline (∆) as mean with 95% confidence intervals. RESULTS: Reductions in ∆BM were greater in HYPO vs. EUHY [-2.5% (-2.9, -2.1) vs. 0.0% (-0.4, 0.4), P Supported by NIH R01HL144128 and F32HL164021

PROLONGED MILD HYPOHYDRATION ABOLISHES DIFFERENTIAL BLOOD PRESSURE RESPONSE TO EXERCISE PRESSOR REFLEX BETWEEN SEXES

H.N. Medved, C.L. Chapman, S.M. Holt, C.T. O’Connell, S.C. Brazelton, W.A.B. Howells, E.L. Reed, K. Wiedenfeld Needham, J.R. Halliwill, FACSM, C.T. Minson, FACSM University of Oregon, Eugene, OR Females have attenuated increases in blood pressure to the exercise pressor reflex (EPR) compared to males. Mild hypohydration (~2% body mass loss) alters blood pressure regulation but increases in blood pressure to EPR are not modified by very mild hypohydration (~0.5% body mass loss). It is unknown whether mild hypohydration modulates the differential blood pressure responses to EPR. PURPOSE: To test the hypothesis that increases in blood pressure during EPR remain attenuated in females compared to males during mild hypohydration. METHODS: In a block-randomized crossover design, twenty-two healthy adults [11 females (F), 11 males (M); 21 (3) years] completed 24 hours of fluid deprivation (HYPO) or 24 hours of normal fluid consumption (EUHY). Participants underwent 2 min static handgrip exercise at 30% of maximum voluntary isometric contraction (HG) and 2 min arterial occlusion of the right arm (OCC). Body fluid losses were estimated by the change in body mass (∆BM) over 24 hours. Blood pressure was measured via finger photoplethysmography corrected to brachial artery blood pressure at baseline (electrosphygmomanometer). Data are presented as the change from baseline (∆) as mean with 95% confidence intervals. RESULTS: ∆BM was not different between sexes (P=0.5393) during HYPO [F: -2.2% (-2.9, -1.6); M: -2.8% (-3.4, -2.3)] or EUHY [F: -0.1% (-0.8, 0.5); M: 0.1% (-0.3, 0.6)]. At end HG and OCC, increases in systolic [HG, F: 14 mmHg (6, 21), M: 26 mmHg (16, 36); OCC, F: 7 mmHg (-1, 15), M: 23 mmHg (13, 33), P≤0.0500] and diastolic [HG, F: 14 mmHg (9, 19), M: 23 mmHg (16, 30); OCC, F: 6 mmHg (1, 10), M: 16 mmHg (10, 22), P≤0.0371] blood pressure were attenuated in females during EUHY compared to males. There were no differences between sexes at end HG and OCC in systolic [HG, F: 18 mmHg (12, 24), M: 25 mmHg (15, 35); OCC, F: 12 mmHg (4, 19), M: 16 mmHg (10, 22), P³0.2029] and diastolic [HG, F: 16 mmHg (10, 22), M: 22 mmHg (16, 28); OCC, F: 16 mmHg (10, 22), M: 22 mmHg (16, 28), P³0.1223] blood pressure. CONCLUSION: These findings indicate that mildly hypohydrated females do not retain the attenuated increases in blood pressure during EPR compared to males that is observed in euhydration. Supported by NIH R01HL144128 and F32HL164021, and the UO Summer Program for Undergraduate Research

PROLONGED MILD HYPOHYDRATION DIFFERENTIALLY ALTERS HANDGRIP STRENGTH IN HEALTHY YOUNG FEMALES AND MALES

A.D. Wayne, C.L. Chapman, S.M. Holt, S.C. Brazelton, C.T. O’Connell, H.N. Medved, W.A.B. Howells, E.L. Reed, K. Wiedenfeld Needham, J.R. Halliwill, FACSM, C.T. Minson, FACSM University of Oregon, Eugene, OR An overwhelming majority of the scientific literature investigating the effects of hypohydration on muscular strength has been performed in male participants. One study recently reported that passive heat-stress induced hypohydration reduces upper body muscular strength in females. To our knowledge, there are no data on whether prolonged mild hypohydration, in the absence of heat stress, similarly reduces upper body strength in females. This knowledge gap has implications for female athletes and workers in physically demanding occupations. PURPOSE: To test the hypothesis that maximum voluntary isometric handgrip strength is reduced in females following prolonged mild hypohydration compared to a hydrated state (i.e., euhydrated) and to investigate whether this response differs between males and females. METHODS: In a block-randomized crossover design, twenty-two healthy adults [11 females (F), 11 males (M); 21 (3) years] completed 24 hours of fluid deprivation (HYPO) or 24 hours of normal fluid consumption (EUHY). Protocols were separated by ³72 hours. Body fluid losses were estimated via the percent change in body mass (∆BM) over 24 hours. Participants performed three maximal voluntary isometric handgrip strength on a hand dynamometer with one minute rest between sets. Data are presented as mean with 95% confidence intervals. RESULTS: ∆BM was not different between sexes (P=0.5393) during HYPO [F: -2.2% (-2.9, -1.6); M: -2.8% (-3.4, -2.3)] or EUHY [F: -0.1% (-0.8, 0.5); M: 0.1% (-0.3, 0.6)]. Maximal handgrip strength was reduced in HYPO vs. EUHY in males [48 kg (43, 54) vs. 51 kg (45, 57), P=0.0468)] but there were no differences between conditions in females [27 kg (24, 30) vs. 28 kg (25, 32), P=0.3166)]. During HYPO, there was a trend toward greater reductions in handgrip strength between the first to third attempts in females vs. males during HYPO [-2.7 kg (-5.2, -0.2) vs. 0.8 kg (-1.6, 3.3), P=0.0762]. CONCLUSION: These findings suggest that prolonged hypohydration caused by fluid deprivation causes modest reductions in maximum handgrip strength in males but not females. However, unlike males, our data suggest that females are not able to reproduce initial handgrip strength on subsequent attempts when mildly hypohydrated. Supported by NIH R01HL144128 and F32HL164021

DIAGNOSTIC ACCURACY OF URINE COLOR IN PREDICTING ACUTE KIDNEY INJURY RISK SCORE DURING PROLONGED HYPOHYDRATION

M.R. Gradow, C.L. Chapman, S.M. Holt, H.N. Medved, J.A. Yep, W.A.B. Howells, S.C. Brazelton, C.T. O’Connell, E.L. Reed, K. Wiedenfeld Needham, J.R. Halliwill, FACSM, C.T. Minson, FACSM University of Oregon, Eugene, OR, USA (Award Winner) Hypohydration increases hospitalizations for acute kidney injury (AKI) during extreme heat events. A barrier to accurate self-monitoring of hydration status includes the impracticality of invasive methods. The 8-point urine color scale is a non-invasive assessment with potential use as a low-cost screening tool for elevated AKI risk during prolonged hypohydration. The AKI risk score (AKIrisk) has a U.S. Food and Drug Administration approved indication to screen for the risk of developing moderate-to-severe AKI. AKIrisk is calculated from the product of urinary insulin-like growth factor binding protein 7 and tissue inhibitor of metalloproteinase-2 ([IGFBP7∙TIMP-2]). PURPOSE: To determine the diagnostic accuracy of the 8-point urine color scale in assessing AKIrisk in healthy young males and females during prolonged mild hypohydration. METHODS: In a block-randomized crossover design, twenty-two healthy adults [11 females, 11 males; 21(3) years] completed 24 hours of fluid deprivation to induce hypohydration or 24 hours normal fluid consumption to remain euhydrated. Protocols were separated by ³72 hours. Spot morning urine samples were collected immediately following each 24-hour protocol. Urine color was assessed using a validated 8-point visual scale by three independent investigators. AKIrisk was determined by urinary [IGFBP7∙TIMP-2] \u3e0.3 (ng∙ml-1)2∙1000-1 via enzyme-linked immunosorbent assay. Contingency analyses were performed to calculate positive and negative predictive values for urine color ≥3, ≥4, and ≥5 a.u. in predicting AKIrisk. Data are presented as mean with 95% confidence intervals. RESULTS: Fisher’s exact test revealed an association between AKIrisk \u3e0.3 (ng∙ml-1)2∙1000-1 and urine color ≥3 (P\u3c0.0001), but no association with urine color ≥4 or ≥5 a.u. (P≥0.1327). The positive predictive value and negative predictive value for urine color ≥3 a.u. in predicting AKIrisk \u3e0.3 (ng∙ml-1)2∙1000-1 were 0.91 (0.72, 0.98) and 0.73 (0.52, 0.87). CONCLUSION: These data indicate that values of three or greater on the 8-point urine color scale have excellent positive predictive value for AKIrisk and lend preliminary support for the utility of the color scale as a rudimentary screening tool during prolonged mild hypohydration. Supported by NIH R01HL144128 and F32HL164021

URINE CONCENTRATING ABILITY DURING PROLONGED MILD HYPOHYDRATION IS NOT ENHANCED BY ORAL PROTEIN LOADING

J.A. Yep, C.L. Chapman, S.M. Holt, S.C. Brazelton, C.T. O’Connell, H.N. Medved, W.A.B. Howells, M.R. Gradow, A.D. Wayne, E.L. Reed, K. Wiedenfeld Needham, J.R. Halliwill, FACSM, C.T. Minson, FACSM University of Oregon, Eugene, OR Oral protein consumption in a hydrated state (i.e., euhydration) stimulates urine concentrating mechanisms, reducing free water clearance (CH2O) and conserving water. This response may be abated during a hyperhydrated state as evidenced by blunted post-prandial changes in renal hemodynamics with oral protein consumption. On the other end of the hydration spectrum, it remains unknown whether urine concentrating ability is altered when oral protein is consumed during mild hypohydration, a physiological state associated with negative CH2O. PURPOSE: To test the hypothesis that oral protein loading during mild hypohydration attenuates reductions in CH2O compared to during euhydration. METHODS: In a block-randomized crossover design, twenty healthy adults [9 females, 11 males; age: 21 (3) years] completed 24 hours fluid deprivation (HYPO) and 24 hours normal fluid consumption (EUHY). Protocols were separated by ³72 hours. Participants ingested a whey protein shake (1.0 g protein and 10 ml water per kg body mass) within 10 minutes. Body fluid loss was estimated via the percent change in body mass (∆BM) over 24 hours. Blood and urine samples collected at pre- (baseline) and 150-min post-protein consumption (POST) were analyzed osmolality for the calculation of CH2O. Data are presented as mean with 95% confidence intervals. RESULTS: ∆BM was reduced in HYPO vs. EUHY [-2.6% (-3.0, -2.2) vs. 0.1% (-0.3, 0.4), P\u3c0.0001]. Baseline CH2O was lower in HYPO vs. EUHY [-1.6 ml/min (-1.8, -1.4) vs. 4.8 ml/min (3.5, 6.1), P\u3c0.0001]. There were no differences in CH2O between conditions at POST [HYPO: -2.4 ml/min (-2.7, -2.1); EUHY: -2.1 ml/min (-2.4, -2.1), P=0.0758]. Compared to baseline, CH2O at POST was reduced in EUHY (P\u3c0.0001) but was not different in HYPO (P=0.1464). CONCLUSION: These findings indicate oral protein loading does not enhance urine concentrating ability during prolonged mild hypohydration. It is unclear whether the lack of further reductions in CH2O during HYPO, as opposed to EUHY, reflect a “ceiling effect” of having reached the physiological maximal ability to concentrate urine whereby the already negative CH2O is not able to be further reduced with oral protein loading. Supported by NIH R01HL144128 and F32HL164021

Generation of long-lived charges in organic semiconductor heterojunction nanoparticles for efficient photocatalytic hydrogen evolution

Organic semiconductor photocatalysts for the production of solar fuels are attractive as they can be synthetically tuned to absorb visible light while simultaneously retaining suitable energy levels to drive a range of processes. However, a greater understanding of the photophysics that determines the function of organic semiconductor heterojunction nanoparticles is needed to optimize performance. Here, we show that such materials can intrinsically generate remarkably long-lived reactive charges, enabling them to efficiently drive sacrificial hydrogen evolution. Our optimized hetereojunction photocatalysts comprise the conjugated polymer PM6 matched with Y6 or PCBM electron acceptors, and achieve external quantum efficiencies of 1.0% to 5.0% at 400 to 900 nm and 8.7% to 2.6% at 400 to 700 nm, respectively. Employing transient and operando spectroscopies, we find that the heterojunction structure in these nanoparticles greatly enhances the generation of long-lived charges (millisecond to second timescale) even in the absence of electron/hole scavengers or Pt. Such long-lived reactive charges open potential applications in water-splitting Z-schemes and in driving kinetically slow and technologically desirable oxidations

Enhanced photocatalytic hydrogen evolution from organic semiconductor heterojunction nanoparticles

Photocatalysts formed from a single organic semiconductor typically suffer from inefficient intrinsic charge generation, which leads to low photocatalytic activities. We demonstrate that incorporating a heterojunction between a donor polymer (PTB7-Th) and non-fullerene acceptor (EH-IDTBR) in organic nanoparticles (NPs) can result in hydrogen evolution photocatalysts with greatly enhanced photocatalytic activity. Control of the nanomorphology of these NPs was achieved by varying the stabilizing surfactant employed during NP fabrication, converting it from a core–shell structure to an intermixed donor/acceptor blend and increasing H2 evolution by an order of magnitude. The resulting photocatalysts display an unprecedentedly high H2 evolution rate of over 60,000 µmol h−1 g−1 under 350 to 800 nm illumination, and external quantum efficiencies over 6% in the region of maximum solar photon flux