Dr Juliette Hughes & Dr Brendan Norman.
Department of Musculoskeletal and Ageing Science, University of Liverpool.
October 2025.
About us
Brendan and Juliette completed their PhD studies at the University of Liverpool, beginning in 2015 and 2016 respectively under the supervision of Prof Ranganath and Prof Jim Gallagher. They now lead their own research projects at the University of Liverpool, working together with other lab members in the Liverpool AKU Research Group. Juliette and Brendan both research AKU with complimentary expertise. Brendan has vast expertise in the metabolic side of AKU, and Juliette has focussed mainly on the mouse model and musculoskeletal areas.
Bone and Joint Action Week
Bone and Joint Health National Action week (12th – 20th October) is a global initiative that promotes awareness, prevention, and treatment of musculoskeletal conditions. These affect millions of individuals worldwide. When AKU is not treated, the cartilage of joints, and other tissues such as tendons and ligaments become damaged. AKU is therefore a rare form of osteoarthritis (OA). Many people around the world carry out research into OA, each studying different components of the joint and various biological processes that occur. Unfortunately, common OA in the general population has no cure or effective treatment. Similarly to untreated AKU, this leads to painful joints and the need to have joint replacements.
AKU, nitisinone and joint damage
In AKU, a research collaboration between patients, clinicians and scientists has led to the successful testing and approval of Nitisinone to treat AKU. Nitisinone is a drug that prevents the liver from forming homogentisic acid (HGA), the molecule responsible for causing tissue pigmentation and joint damage.
Although Nitisinone is a huge breakthrough in the treatment of AKU, it will be most effective when given in early adulthood to prevent pigmentation of joints at a younger age. Studies in AKU mice at the University of Liverpool have previously shown that Nitisinone prevents pigmentation, and when given mid-life, can halt pigmentation. In more advanced AKU, we know that Nitisinone will prevent further attack of tissues by lowering HGA in the body. However, it cannot take away the pigment that is already there in cartilage and other tissues, nor reverse severe damage. There is still therefore a need to study and understand the process of tissue pigmentation and joint damage.
Many questions must still be answered, such as:
- What does HGA/pigment bind to in tissues?
- How does HGA/pigment affect cartilage and accelerate degeneration?
- Can pigment be blocked or reversed?
- Do other small molecules speed up cartilage degeneration, but without a visible pigment, in non-AKU OA?
We currently use a variety of methods in our research to study AKU cartilage disease here in Liverpool. These include:
- Harriet Willett, a fourth year PhD student, is studying the reaction leading to the formation of pigment from HGA utilising a variety of chemistry techniques.
- Daisy Quinn, a second year PhD student, is studying the effect of HGA on cartilage cells in a dish, using a technique that she learnt from the Royal Veterinary College (London) in February 2025 (supported by an AKU Society Travel Bursary).
- Studying AKU mice, which have high HGA in the blood and early stage AKU in their joints. These mice were critical in showing that nitisinone could prevent pigmentation. They also allow us to study early-stage disease, interventions and disease processes.
- Examination of tissues and samples from people with AKU. This includes tissues donated at surgery.
Left: synthetic HGA, right: 7-day old synthetic pigment
Some members of the Liverpool AKU Research Group (August 2025).
These methods each have advantages and disadvantages, which is why we use a combination of them in our research to answer different questions. The access to joint tissue from people with AKU is an invaluable resource that we hope to continue to use in the future.
What have we learnt from donated AKU joints so far? Here at the University of Liverpool, under Prof Ranganath and Prof Gallagher’s lead, we have ethical permission to collect and use tissue from AKU patients for research. Over the past 18 years, 84 surgical samples have been collected from 51 people, both from people with AKU and OA.
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Authors
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Title
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Major findings
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Taylor et al,
2010.
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Ultrastructural examination of tissue in a
patient with alkaptonuric arthropathy
reveals a distinct pattern of binding of
ochronotic pigment.
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Showed the association of pigment with a
protein called collagen, using the joint capsule
from an AKU hip joint. Pigment was observed
inside cells and outside of them.
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Taylor et al,
2011.
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The role of calcified cartilage and
subchondral bone in the initiation and
progression of ochronotic arthropathy in
alkaptonuria.
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Used AKU and OA joints to show that black AKU
cartilage was stiff compared to both white AKU
cartilage and OA cartilage.
Studying a range of AKU joints demonstrated
that pigmentation started in the deepest part of
the cartilage (next to the bone) and spread
towards the cartilage surface, causing
degeneration.
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Boyde et al,
2014.
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On fragmenting, densely mineralised
acellular protrusions into articular
cartilage and their possible role in
osteoarthritis.
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Found extremely hard mineralised “spikes” deep
within the cartilage of an AKU hip joint which are
called high density mineralised protrusions.
These were then found in OA and non-OA joints.
These are thought to speed up joint destruction.
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Taylor et al,
2017.
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Cartilage biomarkers in the
osteoarthropathy of alkaptonuria reveal
low turnover and accelerated ageing.
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Hip and knee cartilage obtained from AKU, OA
and non-OA people was studied, and showed
that AKU cartilage had an altered composition
when looking at key cartilage proteins. It
suggested that AKU cartilage was older and
more damaged with low renewal, and had
reduced cushioning ability.
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Taylor et al,
2019.
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Raman spectroscopy identifies
differences in ochronotic and non-
ochronotic cartilage; a potential novel
technique for monitoring ochronosis.
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Showed some insight into the chemical
differences between AKU and non-AKU cartilage,
using ear and hip joint samples.
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B Norman,
2019. PhD
thesis.
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Biochemical Investigations in the Rare
Disease Alkaptonuria: Studies on the
Metabolome and the Nature of
Ochronotic Pigment.
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Studying both synthetic pigment, and pigment
from AKU and non-AKU cartilage, Dr Norman
provides evidence that pigment is unlikely to be
a polymer (a long chain of HGA molecules joined
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together). The HGA molecule was also shown to
undergo structural changes when it forms
pigment in the lab, and that pigment formation
is very complex.
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Chow et al,
2020.
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Pigmentation chemistry and radical-
based collagen degradation in
alkaptonuria and osteoarthritic
cartilage.
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Pigmented AKU cartilage and non-pigmented OA
cartilage were studied. A technique called NMR
was applied. This uses powerful magnets to
analyse chemical structures. It identified that the
structure of the protein collagen was disrupted
in pigmented cartilage. A complementary
technique called EPR was used to specifically
look for reactive molecules called radicals, and
the signal was positive.
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Hughes et
al, 2024
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An anatomical investigation of
alkaptonuria: Novel insights into
ochronosis of cartilage and bone.
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Several bone and cartilage tissues from an AKU
person were studied, revealing that pigment was
widespread highlighting that most cartilage is
susceptible. It also highlighted that cartilage in
different locations was affected at different
rates.
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Future research
How such a small, seemingly harmless molecule such as HGA, can cause such severe and accelerated osteoarthritis is astonishing. In the next few years, Juliette and Brendan’s lab will continue to study the effect of HGA on musculoskeletal tissues, including cartilage, tendons and ligaments. They plan to investigate the effect that HGA has as a “reactive” radical molecule on cells and tissues, and the wider role of oxidative stress. Multiple approaches and techniques, using lab-made pigment, mouse models and human samples, will be combined to understand the mechanism of joint degeneration. This will be furthered through collaborations with other researchers. For example, Dr Mariusz Kujawa from Gdansk in Poland visited the University of Liverpool in March 2024, in order to collaborate with Juliette using medical imaging scans to study the impact of AKU on the musculoskeletal system.
Dr Mariusz Kujawa (right) visiting Dr Juliette Hughes’ (left) lab at the University of Liverpool.
We aim to help not only AKU joint disease, but also general OA joints. Studying joint degeneration in AKU may also help us to
understand how cartilage is affected by other similar small molecules in OA and may uncover hidden mechanisms that have not yet been discovered.
Joint donation in AKU
Even though AKU is rare, an impressive number of AKU joint tissues have been donated over the past 18 years, and they have been crucial to research. The University of Liverpool hope to continue to receive these tissues from any AKU patients in the UK undergoing surgery. The AKU Society can support this process for anyone wishing to donate. Research always generates new questions to answer. Evolving methods and technologies give rise to new opportunities in research to answer these questions that could not previously be investigated.