FattyLiver in Cows

Some of the information in the post may be new to the average dairy farmer. Our featured image, adapted from sirtuins for human health, is a good introduction to what this post is about. The dairy farmer may have heard that drinking resveratrol rich red wine is a good way to get the same benefits of caloric restriction as they both activate the longevity enzyme called sirtuin 1, or Sirt1 for short. Why is negative energy balance so bad for cows? Maybe it is not so bad if the cow has the right nutrition. We will argue that the rumen protected niacin and copper supplements you’ve been giving your cows have some interesting science behind them.

When cows restrict their food calories

According to the MSD Vet Manual fatty liver disease in cattle occurs during a time of negative energy balance, i.e. when the cow is tapping into triglyceride fat stores to make up for a deficit of food calories.  Calving and going off feed are times when a cow can experience a negative energy balance. 

When a cow is burning more calories than she consumes, she taps into her fat stores by releasing the fatty acids from triglycerides.  The liver takes these fatty acids, puts them back onto glycerol backbones, and then packs them into low density lipoprotein particles to be released into her blood stream.  Sometimes the cow’s liver just cannot keep up.  Cows eating too much does not cause fatty liver disease, but not eating does according to msdvetmanual.com. While some humans might restrict their calorie intake to tap into fat reserves, this is not a common practice of lactating humans. We will discuss what happens in cows when they are supplemented with rumen protected niacin.

Niacin in fatty liver disease

In a previous post we reviewed a study showing the ability of Cu(I)NA₂ to mitigate fatty liver disease in a rat model. We neglected the potential niacin contribution to the story. Nassir and Ibadh have a nice review on the role of “longevity” enzymes called sirtuins in human fatty liver disease. [1] We have modified a summary figure from this review to illustrate the deacetylation reaction and the players.

the players

Niacin, vitamin B3, is the other two thirds of Cu(I)NA₂. It is also a component of nicotinamide adenine dinucleotide NADH/NAD⁺. We have covered reduction of TCA cycle generated NADH to NAD⁺ in a post in a introducing sirtuins and other NAD⁺ dependent enzymes.

The reaction, for the sake of our discussion, is simply the removal of acetyl groups from lysine side chains of proteins. These proteins may be histones, the spools on which chromatin DNA is wound. The acetyl group abrogates the positive charge of the of the lysine group. Make careful note of the role of NAD⁺ dependent sirtuins in shuttling fats in and out of the liver but also activation of genes involved in anti-oxidant response. [1] Make careful note that human Sirt1 is reduced by high fat diets (HFD) and increased by exercise and caloric restriction. [1] Some Chinese investigators asked,

“What happens to Sirt1 in peripartum dairy cows with mild fatty liver?”

Dairy cows were classified based on their hepatic triglyceride content. The fatty liver cows’ triglyceride content was about 2% of the liver weight whereas the control cow’s were slightly under 1%. [2] Let’s simplify this discussion of a very complicated paper by looking at a few panels of Figure 3 at a time. These data are enzyme activities. We are about to learn that enzyme activity of anti oxidant enzymes also takes a hit. From the description in reference [2] liver samples were homogenized. Enzymes from soluble fractions were capture with antibodies in ELISA plates and analyzed for their respective activities.

Enzymes that control gene tanscription

Sirt1 gets placed in this category because histone acetylation influences gene trancription.

peroxisome proliferator-activated receptor γ coactivator-1 alpha (PGC-1α),in simple terms binds fatty acids and helps regulate gene transcription. Sterol regulatory element binding proteins (SREBP) are also transcription factors that bind to the regulatory elements of genes. SREBP gets its start in membranes as bHLH-Zip. When cleaved, bHLH-Zip/SREBP reports back to the nucleus to regulate cholesterol related gene transcription.

Anti-oxidant enzymes

Catalase is an iron containing enzyme that catalyzes the decomposition of hydrogen peroxideH₂O₂ to water H₂O and molecular oxygen, O₂. Superoxide dismutases catalyze the dismutation of super oxide to O₂ and H₂O₂. In Cu/Zn SOD the Zn is only structural. Cu²⁺-SOD + O^–₂ → Cu⁺-SOD + O₂ followed by Cu⁺-SOD + O⁻₂ + 2H⁺ → Cu²⁺-SOD + H₂O₂ . Manganese cofactor SOD is found in the mitochondria

Four electrons participate in a double bound between the two oxygen molecules in molecular oxygen, O₂. Super has only a single bond between the two oxygens. An additional electron completes the eight electron valence shell of one oxygen leaving the other oxygen with an unpaired electron. This unpaired electron makes super oxide a reactive oxygen species. Note the remarkable decrease in Cu/Zn SOD and the break in the Y-axis of panel E needed to document the >10x decrease in Cu/Zn SOD activity in bovine fatty liver disease.

Thiol redox balance and reactive oxygen species

Glutathione peroxidases are a family of selenocysteine containing enzymes serve the same function of catalase: conversion of H₂O₂ to H₂O. They also convert lipid peroxides to their corresponding alcohols.

These authors saw a significant, but not so large, decrease in Sirt1 activity in cows with mild fatty liver disease. They did see large decreases in the Sirt protein and mRNA (not shown in this post). These authors saw decreases in the following transcripts in fatty livers:

• Mn SOD, ~20x
• catalase, ~5x
• glutathione peroxidase, ~10x
• Cu/Zn SOD, ~ 3x

Unlike Cu/Zn SOD activity, the changes in Cu/Zn SOD transcripts did not reach the threshold of significance at p<0.05. This publication was far more focused on changes in transcripts of genes involved in fatty acid metabolismi. Whether the fatty liver condition interfered with Cu/Zn SOD being loaded with metal cofactor was not part of the objectives. [2] A follow up to this study looked at which proteins were acetylated in fatty liver disease in cattle. [3] These authors identified many mitochondrial enzymes involved in fatty acid metabolism. Electron transport enzymes and anti oxidant enzymes were not prominent or even present in this “acetylome.” [3]

Back to the basics, making milk

Modifying protein function by placing acetate tags on protein lysines is trendy in biological science.

This whole discussion of the longevity sirtuin enzymes, them getting enough NAD⁺ cofactor to deacetylate proteins that somehow get acetylated in the peripartum fatty cow liver seems to be missing the point of making milk! How milk production is responsive to the cow’s energy status will probably continue to keep scientists busy.

RPN increases dry matter intake and milk yield

Rumen protected niacin (RPN) has become a popular dietary supplement for milk cows. Chinese dairy farmers observed that cows on RPN simply ate more. [4] Chinese scientists conducted a bovine “clinical” trial of 12 multiparous Holstein dairy cows. The cows were divided into two groups with diet supplemented with either 0 (CON) or 20 g/day RPN (RPN). [4] Each group contained three 3^rd parity and three 4^th parity cows. Milk production, milk composition, and dry matter intake were the “tried and true” outcome measures in this mini trial. [4] 21^st Century outcome measures were appetite stimulating homores neuropeptide Y (NPY), orexin A (OXA), non-esterified fatty acids (NEFA), β-hydroxy butyric acid (BHBA), and rumen bacteria counts.

eating more and making more milk

The neurotransmitter revolt?

How calorie restricted were these cows? When cows are niacin supplemented, peptide Deeurotransmitters that increase appetite are relased. Going back to the Wikipedia links, orexin and neuropeptide Y secreting neurons depolarize in response to lowered blood glucose. Depolarization translates into increased firing and neuro transmitter release. NPY secreting neurons are inhibited by glucose and leptin, a peptide secreted by fat cells.

• 

“Brain food” from fatty acids requires NADH

Non-esterized fatty acids (NEFA) have been covered. Free fatty acids are taken apart two carbons at a time in a process called beta-oxidation. Acetyl-CoA feeds into the TCA cycle that generates NADH to be used by the electron transport chain. Alternatively, two acetyl-CoA may condense to form acetoacylCoA. This compound is further reduced by NADH to form beta-hydroxy butyric acid. BHBA can be used as a fuel for the brain when the cow in a state of negative energy balance.

The authors stated that none of their cows reached the threshold of NEFA and BHBA seen in fatty liver disease. Small increases in NEFA and the corresponding BHBA may be a good thing if it keeps the cow’s brain going until it can produce more NPY and/or orexin to stimulate her appetite. If she eats more, her rumen will produce more propionic acid that her liver will use to make glucose, proper brain food and a precursor for lactose for her milk.

Supplementing cows with copper because our soils are soils are depleted

Dairy farmers can probably teach us more than a few things about this problem. We have addressed our copper depleted soils on the Copper Electron Thesis page. We have visited company websites that sell copper supplements to rancher. Copper is needed for proper flow of electrons through the electron transport chain to ATP. Remember that these cows go through a spat of eating less so there is less propionate to make glucose. Anaerobic glycolysis is not a favorable option. Their mitochondria may be generating more superoxide than usual. Cow’s need Cu/Zn and Mn SOD to clean up the mess.

A milk cow supplement containing copper and niacin?

What are your thoughts on rumen protected copper? Would you be interested in supplementing your cows with rumen protected copper and niacin? Among many other things, copper is needed for proper flow of electrons.

References

1. Nassir F, Ibdah JA. (2016) Sirtuins and nonalcoholic fatty liver disease. World J Gastroenterol. 2016 Dec 14;22(46):10084-10092 PMC free article
2. Li Y, Zou S, Ding H, Hao N, Huang Y, Tang J, Cheng J, Feng S, Li J, Wang X, et al. Low expression of sirtuin 1 in the dairy cows with mild fatty liver alters hepatic lipid metabolism. Animals (Basel) 2020;10(4):560. PMC free article
3. Le-Tian, Z., Cheng-Zhang, H., Xuan, Z., Zhang, Q., Zhen-Gui, Y., Qing-Qing, W., Sheng-Xuan, W., Zhong-Jin, X., Ran-Ran, L., Ting-Jun, L., Zhong-Qu, S., Zhong-Hua, W., & Ke-Rong, S. (2020). Protein acetylation in mitochondria plays critical functions in the pathogenesis of fatty liver disease. BMC genomics, 21(1), 435. PMC free article
4. Gaowa, N., Zhang, X., Li, H., Wang, Y., Zhang, J., Hao, Y., Cao, Z., & Li, S. (2021). Effects of Rumen-Protected Niacin on Dry Matter Intake, Milk Production, Apparent Total Tract Digestibility, and Faecal Bacterial Community in Multiparous Holstein Dairy Cow during the Postpartum Period. Animals : an open access journal from MDPI, 11(3), 617.   PMC  free article