Fatty Liver Disease

ReportRepeat

ReviseNAFLD (Non-Alcoholic Fatty Liver Disease)
A Brief Scientific Literature Review- December 2012by Matthew Ricci, Ph.D., VP, Science Director- Research Diets, Inc.

40LoCSLoCD

As with many human diseases, fatty liver in rodents is also
diet-inducible. Here we briefly summarize three such dietary
protocols for inducing fatty liver: a methionine and cholinedeficient (MCD) diet, a choline-deficient diet (CD) or a high-fat
diet (HFD). These terms do not define a specific diet formula andof course there is overlap in these diet types. Different dietary
approaches produce different severities of disease along the NAFLD
spectrum and likely work by unique mechanisms. Therefore it isimportant for the researcher to choose the diet that best suits theneeds of their study.

MCD diets
Of the dietary approaches discussed here, MCD diets produce themost severe phenotype in the shortest timeframe. Used for over 40years, MCD diets will quickly induce measurable hepatic steatosis(mainly macrovesicular) in rodents by 2-4 weeks and this progresses
to inflammation and fibrosis shortly thereafter (22, 26). Fat levels in
MCD diets can vary, though typically they contain about 20% fat
by energy. The mechanism for steatosis includes impaired VLDL
secretion due to lack of phosphatidyl choline synthesis (11). MCD
diet-induced NASH is reversible in rats by switching to a diet with
sufficient methionine and choline (15).
Importantly, unlike human or other diet-induced rodent modelsof NAFLD, rodents fed MCD diets lose weight (due to a vastly
lower caloric intake) and do not become insulin resistant (9, 19).
Since most humans with NASH are obese and insulin resistant,this represents an important difference in how MCD diets model
human NASH.
Within the context of an MCD diet, other dietary components
affect the NASH phenotype. Sucrose is an important componentof the MCD diet, since replacing it with corn starch greatly reduces
liver fat accumulation, inflammation and injury, likely through

HiCS
gram

NAFLD encompasses a spectrum of disease states, from steatosis(fatty liver) to non-alcoholic steatohepatitis (also called NASH;
steatosis with inflammatory changes) followed by progression tofibrosis and cirrhosis and hepatocellular carcinoma (27). Excess liver
fat is believed to be a manifestation of the metabolic syndrome (14)and not surprisingly NASH is associated with obesity, insulin
resistance, dyslipidemia and type II diabetes in humans (2).
Most obese adults have hepatic steatosis and at least one-third ofthese individuals will eventually develop worsening NAFLD (1, 3).
Therefore, the prevalence of NAFLD will likely rise with obesity
rates.

HiCD30CS or CD diet
Hi or Lo fat diet
200102030405060

days
Effects of high-fat diet and CDD on body weight. Twelve animals were fed a low-fat
diet D12450B(10% calories as fat; Lo), and 12 were fed a high-fat diet D12451(45% calories as fat; Hi) for 8 weeks. During the last 4 weeks, one-half of the animals
in each group (n = 6) received a CDD (CD), whereas the other one-half (n = 6)
continued on a diet supplemented with choline (CS). Data are expressed as means ±SE. Total weight change was compared by two-way ANOVA with post hoc Tukey’s
test. Animals on a high-fat diet gained significantly more weight than those on a
low-fat diet (HiCS vs. LoCS, P = 0.001). A CDD (CD) had no effect on weight gain.
Graphic representation - for details see reference (15).

reductions in sucrose-induced de novo lipogenesis and triglyceride
synthesis (17). In a follow-up study, Pickens et al. showed that
despite inducing the same overall level of hepatic fat accumulation,
fructose was more effective than glucose at inducing hepatocellular
injury in mice fed MCD diets for 21 days (16). Not surprisingly,
the source of dietary fat can also alter the phenotype. For example,relative to saturated fat, polyunsaturated fats increase liver fat
oxidation, and induce expression of proinflammatory genes leading
to inflammation though this does not necessarily correlate withincreased liver damage (12). Also, relative to butter fat, olive oil
reduced liver triglyceride accumulation while fish oil reduced livercholesterol levels (8).

CD diets
Like MCD diets, CD diets also tend to contain higher levels of fat,though it is often difficult to know the specifics since unfortunately
authors rarely publish the details of the diets. CD diets induce
steatosis, inflammation and fibrosis over 10 weeks without any
difference in body weight compared to the control group (6).
This lack of weight loss makes CD diets more appealing to someresearchers. When both CD and MCD diets were fed to rats for 7weeks, the MCD diet group had higher scores of liver inflammationand steatosis than the CD group. However, the CD fed rats gained
weight, were insulin resistant and had higher plasma lipids than theMCD group (25).

Fatty Liver Disease
The mechanisms involved with liver fat accumulation on CD diets
may be different from those at work during MCD diet feeding (11).
Interestingly, choline deficiency in the context of a lard-based HFD(45% of calories) was shown to improve glucose tolerance comparedto the choline sufficient group in mice (18).

High-fat diets (HFD)
HFD are well-known to increase body weight, body fat and induce
insulin resistance in rodent models. HFD can also increase liver fat
levels quite rapidly (within days) as well as hepatic insulin resistance
before significant increases in peripheral fat deposition occur (23).
Chronically, HFD-induced liver fat accumulation may not follow alinear progression and liver fat levels may actually decrease, thenincrease again during prolonged HFD feeding (7). When fed for equal
lengths of time, HFD feeding results in 10-fold lower liver fat levels
compared to what accumulates on an MCD diet (20). In general,
HFD feeding does not produce liver fibrosis and only mild steatosis
as compared to MCD diets (2), thus highlighting an importantdifference between these dietary regimes. It is important to rememberthat the term ‘HFD’ encompasses a wide variety of diet formulas anddiets of different composition can be expected to alter the liver
phenotype in various ways.
Cong et al. (5) took an interesting approach by modifying a very HFD(60% of calories) to simultaneously contain low levels (but not zero)of methionine and choline. C57BL/6 mice were fed the diet for 23
weeks and developed obesity, insulin resistance, dyslipidemia as wellas liver steatosis, inflammation and fibrosis. While the study design isweakened by the lack of a high fat, choline and methionine replete
control group, it seems plausible that longer-term feeding of HFDs
containing lower than normal levels of methionine and choline allow
for the development of NASH without the issues of weight loss.
This idea of modifying so-called ‘standard’ HFDs is powerful since itallows the researcher to ‘fine-tune’ the phenotype to meet their needs.
Along these lines, in the LDLR (-/-) mouse, adding cholesterol to a
HFD increases liver fat levels, signs of liver damage and produces
macro- and microvesicular steatosis similar to that seen in humanNASH, compared to HFD alone (24). Vitamin D deficiency within
a HFD worsened NAFLD versus HFD alone in Sprague Dawley
rats (21). When medium chain triglycerides replaced long chain
triglycerides in a 35 kcal% fat diet, steatosis was prevented in rats (13).
In C57BL/6 mice, animals consuming both HFD andfructose/sucrose enriched drinking water developed hepatic fibrosis
while a group consuming HFD alone did not (10).
As with other diet diseases, it appears possible to influence liverdisease using a HFD while mice are still in utero. Bruce et al. foundthat feeding a HFD to dams during gestation and lactation madeoffspring more susceptible to developing NASH when fed a HFDfrom weaning (4).

Where NutriPhenomics Begins

References
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Fatty Liver Disease
References

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Miles MV, Balistreri WF, Woods SC, Seeley RJ. High-fructose, medium chain transfat diet induces liver fibrosis and elevates plasma coenzyme Q9 in a novel murine
model of obesity and nonalcoholic steatohepatitis. Hepatology (Baltimore, Md.)
52: 934-44, 2010.
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hepatocellular injury. Journal of Lipid Research 48: 1885-96, 2007.
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Beneficial effects versus toxicity of medium-chain triacylglycerols in rats with NASH.
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liver but attenuates IR and glucose intolerance in mice fed a high-fat diet.
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NASH in Wistar rats. Nutrition & Metabolism 4: 4, 2007.
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