#ExpBio - Oh, K!

(by whizbang) Apr 25 2017

I live tweeted this lecture, so the post is my Storify. Got a bit lost during the talk in a string of critical phosphorylations midway through. If you want to know that much about the topic, go read Welling's work!

 

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#ExpBio - Short Term Diet Restrictions for Obesity

(by whizbang) Apr 24 2017

Obesity and its complications raise major challenges for US healthcare, so better understanding its pathophysiology may help a great many people. Traditional caloric restriction has poor long-term outcomes because very few people can stick to dietary limitations forever. Other approaches have similar problems.

Click for image source

This group from the University of Wisconsin took a new tactic with short-term restriction of a single nutrient. Methionine is an amino acid that has high levels in beans, nuts, beef, turkey, pork, fish, eggs, and dairy. The study started with 6-week-old mice fed a high-fat western diet for ten weeks to induce obesity, hepatosteatosis, and hyperglycemia. Some mice continued on this diet, while others received an isocaloric high fat diet without methionine for 5 weeks.

 

At the end of that time, mice with methionine restriction showed decreased body weight, decreased body fat, less fat in the liver, and improved blood sugars. They looked more like mice on standard chow than high-fat fed mice. Remarkable, considering they were still getting a high-fat diet!

Would this work in people? I don't know if I could do a stringent methionine restriction for a month; look at that food list in the second paragraph! Other strategies might be in order, like swearing off this amino acid one or two days each week or month.

As always, only more research will tell us what might work!

Abstract here.

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#ExpBio - Why Do We Eat THAT?

(by whizbang) Apr 24 2017

Continue Reading »

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#ExpBio - More Medulla Please

(by whizbang) Apr 24 2017

Structure of Metformin

Newly diagnosed patients with type 2 diabetes generally start the drug metformin. Through a number of metabolic effects, this medication improves hyperglycemia. Over time, most drugs prove to have effects other than those initially identified. Metformin seems beneficial to the kidney, but how does that happen?

Once again we will ponder medullary hypoxia. In yesterday's post, the hypoxia occurred acutely, during heart surgery; now, we will address chronic hypoxia due to diabetes.

In this study, rats were made diabetic with streptozotocin. Some were treated with metformin. After approximately 1 month, kidney function and oxygenation in the cortex and medulla were measured under anesthesia. Cortical and medullary tissue were studied for mitochondrial function.

Metformin did not prevent elevation of glomerular filtration rate, a known phenomenon of diabetes. While oxygenation, measured as the partial pressure of O2, was lowered in both the cortex and medulla of control animals, metformin improved oxygenation in the medulla of diabetic animals.

Diabetes also promotes oxidative stress in the kidney. As a defense against this, the mitochondria become less efficient. An uncoupling protein (UCP2) allows respiration to continue but without ATP formation. In the present study, uncoupled respiration doubled in the medulla in diabetic animals, while metformin treatment returned this parameter to normal.

Metformin increases medullary oxygenation in animals, perhaps via inhibiting UCP2. More study is needed to characterize this effect and what it means for diabetic kidney disease. It also points out our ignorance of the medulla on the clinical side of things. When we biopsy a kidney, we examine the cortex. Our attention has been so focused on the glomeruli and the tubules surrounding them that we may be missing the real action.

ABSTRACT

Metformin†Normalises†Medullary†Hypoxia†in†The†Diabetic†Rat†Kidney

Michael Christensen1, Tomas Schiffer2, Rikke Nørregaard1, Fredrik Palm2. 1Aarhus University, Aarhus N, Denmark, 2Uppsala University, Uppsala, Sweden

Background

Metformin is the first choice treatment of type 2 diabetes where it can lower the level of blood glucose by inhibiting hepatic gluconeogenesis and increase cellular glucose uptake. Besides the effect on blood glucose metformin has also shown protective effects in several renal diseases including diabetic nephropathy. The development of hypoxia in the kidney is suggested to be an important driving force for the development of diabetic nephropathy and we therefore wanted to investigate how metformin affects the oxygenation levels and mitochondrial function in the diabetic kidney.

Methods

Sprague Dawley rats were injected with streptozotocin (STZ) (50 mg/kg) and when rats were diabetic, metformin (250 mg/kg) was administrated in the drinking water. Rats were prepared for In†Vivo†measurements 25-30 days after STZ injection. Rats were anesthetized, placed on a heating pad, tracheotomized and a catheter was placed in the left femoral vein for infusion of Ringer solution containing H-inulin and Paraaminohippurate. The left femoral artery was catheterized for blood pressure measurements and blood sampling. The left kidney was exposed by a subcostal flank incision, immobilized in a plastic cup and catheters were placed in the left ureter as well as bladder for collection of urine. Intrarenal pO2 was measured in kidney cortex and medulla by oxygen microsensors. To assess mitochondrial function, mitochondria were isolated from kidney cortex and medulla and analyzed by highresolution respirometry (Oroboros, O2K)

Important findings

Diabetic rats showed increased glomerular filtration rate (GFR), which was not affected by metformin treatment. PO2 was lower both in the outer medulla as well as cortex in the diabetic animals. Metformin treatment elevated PO2 in the outer medulla both in the control animals as well as in the diabetic animals. Isolated mitochondria from the outer medulla of diabetic rats showed a significantly higher GDP dependent respiration which was normalized by metformin treatment indicating inhibition of uncoupling protein 2 (UCP2) activity.

Conclusion

Metformin increases PO2 in the outer medulla both in control and diabetic animals, this could in part be mediated by inhibition of UCP2.

 

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#ExpBio - Urine Oxygen and Acute Kidney Injury

(by whizbang) Apr 24 2017

Original source: ajprenal.physiology.org/content/284/3/F433

All nephrologists know that acute kidney injury (AKI) commonly complicates heart surgery, especially if patients require cardiopulmonary bypass (CPB). AKI increases morbidity and mortality in this setting, so heading it off could improve patient outcomes.

AKI in this setting usually occurs due to acute tubular necrosis, when low oxygen in the outer medulla of the kidney (see image at right) damages proximal tubular cells. Patients often require support with dialysis until these cells can repopulate in a few weeks.

At present, detecting medullary hypoxia is a guessing game. Did the patient get hypoxia? Did the blood pressure drop? How long were they on CPB?

Probe sits just above catheter tip

Experimental evidence from animals showed that the pressure of oxygen in the urine (UO2) correlates with medullary hypoxia. A surgical group wondered if UO2 during operations might predict AKI in heart surgery patients requiring CPB. UO2 can be measured with a fiber-optic probe inside the urinary catheter all of these patients have placed before the cutting begins (see diagram).

Their study included 35 adult patients, with 14 developing AKI (defined as rise in creatinine). The lowest intra-operative UO2 was 50% lower in patients who developed AKI than those who did not (p=0.02). Worse levels of UO2 had even greater predictive value for AKI. However, no level of UO2 completely eliminated AKI risk.

Continuous monitoring of UO2 can be done and may provide additional information about renal risk during heart surgery with CPB. As a pediatric nephrologist, I wonder about it's use in other conditions with high risk for AKI.

ABSTRACT

IntraOperative Urinary Hypoxia During Cardiac Surgery on Cardiopulmonary Bypass Predicts Later Development of Acute Kidney Injury

Roger G. Evans1, Michael Z. Zhu1,2, Julian A. Smith2, Gerard K. Harrop1, Amanda G. Thrift3, Andrew D. Cochrane2. 1Cardiovascular Disease Program, Biosciences Discovery Institute and Department of Physiology, Monash University, Melbourne, Australia, 2Department of Surgery (School of Clinical Sciences), Monash University and Department of Cardiothoracic Surgery, Monash Health, Clayton, Australia, 3Department of Medicine (School of Clinical Sciences) at Monash Health, Monash University, Clayton, Australia

Renal medullary hypoxia may be a common pathway in the development of acute kidney injury (AKI). There are no validated methods to detect medullary hypoxia in patients. However, experimental findings indicate that changes in urinary oxygen tension (UPO2) reflect changes in medullary PO2. Therefore, we evaluated the relationship between intraoperative UPO2 and the development of AKI after cardiac surgery requiring cardiopulmonary bypass (CPB). From January 2015 to July 2016, thirty-five adult patients undergoing onpump cardiac surgery were prospectively enrolled. UPO2 was continuously recorded intraoperatively via a fiberoptic probe deployed through the lumen of the urinary catheter, with the end of the probe at the catheter tip, where it was in contact with bladder urine. UPO2 fell during surgery, particularly during CPB. The lowest (nadir) UPO2 was most frequently observed during the rewarming phase of CPB, or shortly after weaning from CPB (n=25, 71%). Fourteen patients (40%) developed AKI as defined by an increase in serum creatinine from baseline of either > 26.5 μmol/L (0.3 mg/dL) within 48 hours or > 50% within 5 days. Nadir intraoperative UPO2 was lower in patients who later developed AKI (8.5 ± 1.6 mmHg, mean ± SE) than in those who did not (16.5 ± 4.2 mmHg, P†= 0.02). UPO2 below 10 mmHg at any time during surgery was associated with a 4.5fold [95% confidence limits 1.6 19.1] greater risk of AKI (P†= 0.03). Furthermore, urinary PO2 below 15 mmHg for longer than the median time for all patients (5.6 min per hour of surgery) was associated with a 7.3fold [1.8 35.1] greater risk of AKI (P†= 0.01) and an area under the receiver operator curve of 0.73 [0.56 0.90] (P†= 0.03). We conclude that low UPO2 during cardiac surgery requiring CPB is strongly associated with later development of AKI. Continuous intraoperative monitoring of UPO2 is simple and relatively noninvasive. It may provide a realtime biomarker of risk of AKI. Early detection of risk of AKI may in turn provide a window of opportunity to intervene and thus avoid development of AKI in patients undergoing cardiac surgery.

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#ExpBio - Safer Is Not Safe; Just Don't Vape

(by whizbang) Apr 23 2017

Electronic cigarettes, or vaping, has been advertised as a safer alternative to smoking tobacco. It provides the addictive ingredient in tobacco (nicotine) in a liquid base that gets heated and delivers it in an inhaled form. Nicotine patches and gum may provide levels of the chemical, but they do not satisfy the ritual of smoking. Vape liquid can contain high amounts of nicotine, often in a flavored liquid base. Heating elements in the devices can release other chemicals into the mix as well.

Tobacco has systemic effects well beyond the lungs. These include cardiovascular disease and kidney dysfunction.

In this study, mice were exposed to vapor generated by a commercial vaping device and then collected and piped into mice. Mice breathed the vapor for 1 hr each day, 5 days each week. In the first experiment, the default laboratory mice (C57Bl6) vaped for 3 months. Findings included a 20% reduction in glomerular filtration rate and an 87% increase in kidney scarring. Changes in heart rate and blood pressure suggested cardiovascular damage as well.

An outbred mouse strain (CD1) received the same exposure for 6 months. This genetically heterogeneous strain might have more resistance to adverse exposures. However, it showed a 64% increase in kidney scarring over control animals. Cardiac scarring increased 2.75-fold over controls. Multiple pro-fibrotic factors studied in each tissue were elevated with exposure to vaping. These patterns of damage were similar to those seen with tobacco smoke exposure in animals from a separate but parallel study (data not included; noted during discussion at poster).

Vaping may not carry the cancer risk of tobacco use, but this animal study strongly suggests it still promotes cardiovascular and kidney disease.

ABSTRACT

Chronic Electronic Cigarette Vapor Inhalation Induces Renal Injury and Functional Decline in Female Mice

Christopher Drummond1, Laura E Crotty Alexander2,3, Jiang Tian1. 1Medicine, University of Toledo, Toledo, OH, 2Pulmonary, Critical Care and Sleep Medicine, University of California San Diego, La Jolla, CA, 3Pulmonary Critical Care, Veterans Affairs San Diego Health System, La Jolla, CA

Clinical studies indicate that combustible cigarette smoke increases renal and cardiac tissue injury progression and functional decline in the setting of chronic kidney disease (CKD). Novel nicotine delivery devices like electronic (e)cigarettes are used by over 10% of the population and produce vapor which may also induce renal injury. To establish whether ecigarette vapor inhalation induced renal injury in the form of fibrosis and decreased renal injury our current study utilized a noseonly

inhalation exposure system to induce 8 weekold female mice to inhale ecigarette vapor containing 24mg/mL of nicotine suspended in a solution of 50% propylene glycol and 50% vegetable glycerin using the following parameters: 12 seconds of vapor exposure every 60 seconds for 60 minutes five days per week for 1, 3 and 6months. Following ecigarette exposure, assessment of renal fibrosis, glomerular filtration rate, and expression of the antifibrotic microRNA miR29b3p were evaluated. Mice exposed to ecigarette vapor suffered a 31% decline in renal tissue expression of miR29b3p vs airexposed

controls (p<0.05). Additionally, mRNA targets of miR29b3p that regulate fibrosis formation or are part of fibrosis were also significantly increased in the kidneys of ecigarette exposed mice versus air controls, i.e., Collagen 1A1 (increased 98%; p<0.05); Collagen 3A1 (129% increase; p<0.05); Collagen 4a1 (72%

increase; p<0.05); Integrin beta 1 (58% increase; p<0.05); and Fibrillin 1 (100% increase; p<0.05). Additionally, we observed a significant increase in renal fibrosis at the 3and 6month

time points as assessed by Trichrome staining in these animals. Lastly, following 3months of

exposure to ecigarette vapor renal function was significantly reduced by 21% versus air exposed controls (p=0.017). These data are the first to indicate that ecigarettes induce renal fibrosis and functional decline. In addition, these data suggest a novel miR29b3p mediated mechanism linking ecigarette vapor exposure and renal injury and functional decline.

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#ExpBio - Cannon Lecture

(by whizbang) Apr 23 2017

The most prestigious award of the American Physiological Society is named for Walter Cannon, who developed the concept of homeostasis. This year’s award goes to Michael Welsh, a professor of medicine and physiology at the University of Iowa. He presented his life’s research into the pathogenesis of the lung disease of CF.

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Facebook Bummer

(by whizbang) Apr 22 2017

The badge on my Facebook app called this morning. Someone had tagged me! But then, the top of my feed provided a Facebook memory from 1 year ago - Jim ringing the bell after completing his initial course of radiation for the glioblastoma multiforme.

That radiation and chemo produced great effects. He was pretty normal over the summer and fall, and we had some great times. Now, of course, that bastard tumor has returned. Chemo and radiation have returned as well.

A year ago, that radiation gave us hope. Today, we must acknowledge that this tumor generally wins the war. Therapy buys us time, and not as much as we would like.

My spouse has insisted that I take my current trip to blog at Experimental Biology. You will see a lot more activity at WhizBang for the next 5 days, and it will be real science blogging.

What a pleasant break from the realities of our life.

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The Problem with Podcasts

(by whizbang) Apr 04 2017

Yesterday I received notice of a podcast. The topic sounded interesting, and they gave a teaser summary that had me considering listening. They even gave a table of contents for it, with the time point where various topics within the recording would be addressed.

The stuff I really wanted to know started 45 minutes into the piece, but I likely needed to listen to the earlier stuff to get the gist. Did I really want to spend an hour of my life taking notes on a podcast?

I don’t think podcasts should be forbidden. I listen to NPR discussions and interviews most of my day, and many podcasts present similar audio adventures. However, I really learn best when I read something, not when I hear it. Listening to Serial as entertainment is fine; if I really want to retain something, I need to read it.

I beg those of you who aim to provide information and skills to the public to remember that not all of us can benefit fully from listening. Please provide a transcript of each and every podcast for those of us who want or need it. That includes those of us who learn better with the written word, as well as the hearing impaired.

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My Mantra

(by whizbang) Mar 24 2017

Today I will be repeating the following:

  1. I am a bitch
  2. Bitches get stuff done
  3. I can handle this because I have resources, I can find help, and I am a bitch.

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